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Integrated optical polarizers based on novel 2D materials

April 2024

April 2024

DOI:10.1364/opticaopen.25556337.v1

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Optical polarizers are essential components for the selection and manipulation of light polarization states in optical systems. Over the past decade, the rapid advancement of photonic technologies and devices has led to the development of a range of novel optical polarizers, opening avenues for many breakthroughs and expanding applications across diverse fields. Particularly, two-dimensional (2D) materials, known for their atomic thin film structures and unique optical properties, have become attractive for implementing optical polarizers with high performance and new features that were not achievable before. This paper reviews recent progress in 2D-material-based optical polarizers. First, an overview of key properties of various 2D materials for realizing optical polarizers is provided. Next, the state-of-the-art optical polarizers based on 2D materials, which are categorized into spatial-light devices, fiber devices, and integrated waveguide devices, are reviewed and compared. Finally, we discuss the current challenges of this field as well as the exciting opportunities for future technological advances.

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Integrated optical polarizers based on novel 2D materials

David Moss

Optical Sciences Centre Swinburne University of Technology Hawthorn, VIC 3122, Australia

Abstract

Optical polarizers are essential components for the selection and manipulation of light

polarization states in optical systems. Over the past decade, the rapid advancement of photonic

technologies and devices has led to the development of a range of novel optical polarizers,

opening avenues for many breakthroughs and expanding applications across diverse fields.

Particularly, two-dimensional (2D) materials, known for their atomic thin film structures and

unique optical properties, have become attractive for implementing optical polarizers with high

performance and new features that were not achievable before. This paper reviews recent

progress in 2D-material-based optical polarizers. First, an overview of key properties of

various 2D materials for realizing optical polarizers is provided. Next, the state-of-the-art

optical polarizers based on 2D materials, which are categorized into spatial-light devices, fiber

devices, and integrated waveguide devices, are reviewed and compared. Finally, we discuss

the current challenges of this field as well as the exciting opportunities for future technological

advances.

Keywords: Optical polarizers, 2D materials.

Introduction

The control of light polarization plays a critical role in advanced optical technologies,

underpinning the functionality and efficiency of modern optical systems [1, 2]. Optical

polarizers, which selectively transmit light with a specific polarization orientation and block

light with the orthogonal polarization, are crucial components to realize light polarization

control for a diverse range of applications as illustrated in Fig. 1. The applications in Fig. 1

are divided into four main categories, including optical sensing, imaging and display, optical

analysis, and optical communications. For optical sensing applications such as navigation,

astronomical detection, and atmosphere detection [3, 4], optical polarizers enhance the

sensitivity and accuracy by selecting the desired polarization state of incident light. The use of

optical polarizers for imaging and display includes applications such as glasses, liquid crystal

display, and photography [5, 6], where optical polarizers help reduce glare, enhance contrast,

and improve the color reproduction in displays, contributing significantly to image quality and

visibility. For optical analysis such as spectroscopy, biomedical measurements, and materials

analysis [7, 8], optical polarizers have been employed in various analytical techniques to

extract valuable information from measured optical signals. In optical communication systems,

optical polarizers have been widely used for implementing laser systems, reducing

polarization-mode dispersion, and realizing polarization-division multiplexing [9, 10], thereby

maintaining signal integrity and achieving efficient data transmission.

The rapid progress of the photonics industry urgently requires high-performance optical

polarizers on different device platforms and at extended wavelengths, which has posed

significant challenges for conventional optical polarizers based on bulk materials [11]. Since

the first experimental isolation of graphene in 2004 [12], the family of two-dimensional (2D)

materials has been growing rapidly and become a hotbed of scientific inquiry. Many 2D

materials, contrasted with their bulk counterparts, are renowned for their extraordinary

material properties. Amongst them, the attractive optical properties of 2D materials, such as

layer-dependent optical bandgaps, strong quantum confinement effects, tunable light

emissions, high optical nonlinearity, and significant material anisotropy [13-16], have been the

cornerstone of extensive research interests for their utilization in implementing functional

optical devices.

In recent years, owing to their highly anisotropic light absorption and broad response

bandwidths, the use of 2D materials to manipulate light polarization states has come into the

spotlight [17-22]. This opens new avenues for the implementation of optical polarizers,

enabling high device performance and new features previously unattainable with conventional

bulk materials. In addition, the fast progress in fabrication technologies enables the

incorporation of 2D materials into different device platforms. This facilitates the development

of a series of advanced optical polarizers based on spatial light devices, fiber devices, and

integrated waveguide devices, significantly enhancing the range of application scenarios.

Fig. 1. Typical applications of optical polarizers.

Here, we provide a systematic review of 2D-material-based optical polarizers,

highlighting the significant progress achieved in this field and offering performance analysis

of devices in different platforms. This paper is organized as follows: First, the distinctive

material properties of 2D materials are introduced within the context of their applications to

optical polarizers. Subsequently, different types of 2D-material-based optical polarizers are

reviewed and compared, which are classified into spatial-light devices, fiber devices, and

integrated waveguide devices. Finally, we discuss the present challenges faced by this field,

alongside the promising prospects that pave the way for future technological breakthroughs.

Properties of 2D materials for optical polarizers

2D materials with atomically thin film thickness exhibit anisotropic absorption for light in

different polarization states, which forms the basis for their applications to optical polarizers

[13]. As illustrated in Fig. 2a, 2D materials typically show higher absorption for in-plane

polarized light (i.e., with its optical field E parallel to the surface of 2D material) that enables

stronger light-matter interaction, as compared to light in the out-of-plane polarization (i.e.,

with its optical field E perpendicular to the surface of 2D material). For 2D-material-based

optical polarizers, the difference in absorption for light with different polarization states

determines the polarization extinction ratio (PER, defined as the ratio of transmitted power for

the desired polarization over the undesired one), and the capability to maintain such anisotropy

in broad optical bandwidths influences their operational bandwidths (OBW). In addition, some

other properties of 2D materials play important roles in enhancing device functionality. For

instance, low optical absorption of 2D materials in the high-transmittance polarization state is

desired for minimizing the additional insertion loss (IL) induced by them, and the ability to

alter material properties through gate voltage or light power enables the realization of devices

with dynamic tunability. In this section, we provide an overview of distinctive properties of

typical 2D materials illustrated in Fig. 2b, highlighting those that are particularly relevant and

advantageous for implementing high performance optical polarizers.

Graphene

Graphene consists of single-layered carbon atoms arranged in a hexagonal lattice, where the

linearly dispersive conduction and valence bands meet at the Dirac point of the Brillouin zone,

resulting in a gapless and semi-metallic band structure [23, 24]. This unique structure endows

graphene with the capability to interact with light waves in different directions and across

ultrabroad optical bandwidths. Despite its ultra-low film thickness of ~0.35 nm, monolayer

graphene can absorb ~2.3% of light power incident perpendicularly [25]. Such absorption

could introduce additional insertion loss for graphene-based optical polarizers. Due to

intraband transition and its property related to surface plasmon resonance, graphene can also

strongly interact with terahertz (THz) light waves, making it promising for optical polarizers

operating at this spectral range [26, 27]. In addition, the zero bandgap in graphene can be

further tuned by applying external electric fields or through chemical doping, enabling the

flexible changing of its properties to enhance the device performance [28-30].

Fig. 2. (a) Anisotropic absorption for light propagating along 2D materials. (b) Typical 2D materials

for optical polarizer applications. (c) 2D-material-based optical polarizers based on different device

platforms. GO: graphene oxide. TMDCs: transition metal dichalcogenides. BP: black phosphorus.

Graphene oxide

Graphene oxide (GO), as a common derivative of graphene, consists of a basal plane of carbon

atoms decorated with a series of oxygen-containing functional groups (OCFGs) such as

hydroxyl, carboxyl and carbonyl groups [31]. Due to the existence of the OCFGs, a monolayer

GO film, with a typical thickness of ~1 nm, has a higher thickness than monolayer graphene

[32]. The OCFGs also result in a highly heterogenous atomic structure for GO, which allows

it to exhibit strong anisotropic absorption for light with in-plane and out-of-plane polarizations

[33]. It is also observed that such anisotropic light absorption diminishes progressively with

the augmentation of film thickness [34]. The large optical bandgap of GO, typically ranging

from ~2.1 to ~3.6 eV, can be altered through a variety of reduction and doping treatments [35],

allowing for the engineering of optical absorption across various spectral bands. The large

bandgap of GO also results in much lower optical absorption as compared to graphene that has

a zero bandgap, particularly at infrared wavelengths [36, 37]. These material properties of GO,

combined with its facile solution-based synthesis processes and the ability to be directly grown

on diverse dielectric substrates, contribute to the attractiveness of GO for the implementation

of optical polarizers [38-40].

Transition metal dichalcogenides

Transition metal dichalcogenides (TMDCs) are characterized by the general formula MX2,

where ‘M’ stands for a transition metal and ‘X’ for a chalcogen element. TMDC layers, such

as molybdenum disulfide (MoS2), tungsten disulfide (WS2), molybdenum diselenide (MoSe2),

and tungsten diselenide (WSe2), have a typical sandwich-like configuration, where a plane of

metal atoms is flanked by two hexagonal planes of chalcogen atoms. This distinct structure

allows TMDCs to exhibit varied bandgap (e.g., from ~1 to ~2.5 eV [41, 42]) as well as indirect-

to-direct bandgap transition when the material thickness decreases from multilayer to

monolayer (e.g., MoS2 with a typical thickness of ~0.72 nm) [43]. TMDCs also show

significant anisotropy in light absorption (>10% per layer) that covers from the visible to the

infrared wavelength regions [44, 45]. In addition, monolayer TMDCs exhibit unique valley-

dependent properties, where light with a particular polarization state can excite electron

transitions in specific valleys [41, 46]. For example, it is observed that right-handed and left-

handed circularly polarized light can effectively excite electrons at the K and K’ points (i.e.,

the two non-equivalent corners of the Brillouin zone in a hexagonal lattice system),

respectively, thereby allowing for sensitive control over the polarization states of light in these

materials [47]. Recently, noble metal-based TMDCs including rhenium disulfide (ReS2),

palladium diselenide (PdSe2), platinum diselenide (PtSe2), and palladium ditelluride (PdTe2)

have also be utilized for polarization-sensitive devices due to their exceptional ability for

anisotropic light absorption [48-50].

Black phosphorus

Black phosphorus (BP), commonly referred to as black phosphorene in its monolayer form,

has a layered atomic structure with phosphorus atoms arranged in a puckered honeycomb

lattice. In contrast to in-plane centrosymmetry observed for graphene and TMDCs, the

distinctive puckered configuration of BP breaks the in-plane centrosymmetry, which gives rise

to anisotropic in-plane optical conductivity [51-53]. As a result, the optical absorption in BP

exhibits anisotropy for in-plane light waves that travel in different directions, and it is

influenced by several factors such as film thickness and doping levels [54, 55]. Besides, BP

features a layer-dependent bandgap, ranging from ~0.3 eV in its bulk form to ~2.0 eV for a

monolayer film with a typical thickness of ~0.50 nm, effectively covering the visible to near-

infrared wavelengths [53, 56, 57]. This versatility enables the design of optical polarizers

targeted for specific wavelength bands. Due to chemical degradation caused by the oxygen

and moisture in ambient conditions, BP experiences instability upon exposure to air, posing

potential challenges for its practical implementation [58]. To address such limitation, several

methods have been employed, including organic functionalization, inorganic coatings, and

synthesis through liquid phase exfoliation [59, 60].

MXene

MXenes are a novel class of 2D materials composed of transition metal carbides, nitrides, or

carbonitrides. The general formula of MXenes is Mn+1XnTx, where M represents a transition

metal, X stands for C and/or N element, T denotes surface terminations such as -OH, =O, and

-F, and n = 1, 2, or 3 [61]. These surface terminations enhance the water affinity of MXenes,

making them easily dispersible in aqueous and other polar solvents, leading to stable colloidal

solutions. The hydrophilic nature of MXenes facilitates their deposition on a variety of

substrates, showing the potential for simple device fabrication [62, 63]. Depending on the

composition of chemical elements, the typical thickness of monolayer MXene films varies

from ~1 to ~3 nm [64]. With their unique metallic conductivity attributed to the free electrons

in the transition metal carbide or nitride backbone, MXenes present a compelling electronic

structure. This, combined with their surface terminations, leads to strong anisotropy in optical

absorption covering broad bandwidths from the visible to the mid-infrared (MIR) regions [65].

Similar to the intraband transition in graphene, the strong optical absorption of MXenes in the

THz range makes them appealing for advanced THz optical polarizers [66]. In addition, the

properties of MXenes are enriched by the ability to adjust their surface functionalization,

which allows for the modulation of their bandgaps within a wide range spanning from ~0.05

to ~2.87 eV [67, 68].

Perovskites

2D perovskites are characterized by layered structures, comprising single (or multiple)

inorganic sheets sandwiched between organic spacers held together by Coulombic forces. They

have a general formula R2An−1BnX3n+1, where R is an additional bulky organic cation such as

aliphatic or aromatic that functions as a spacer between the inorganic sheets, n defines the

number of inorganic layers held together and determines the thickness of the perovskite film,

A is an organic cation, B is a metal cation, and X represents a halide (Cl−, Br− or I−) [69]. Due

to the existence of interleaved inorganic and organic sheets, perovskite materials possess a

tunable bandgap that can be modified by changing their composition. For example, the

bandgap of PEA2MAn−1PbnI3n+1 decreases from ~2.36 eV (n = 1) to ~1.94 eV (n = ∞) as the

number of inorganic layers increases [69, 70]. Due to their high photovoltaic efficiency and

strong light absorption across the solar spectrum, perovskites have been extensively utilized

in solar cell applications [71, 72]. In addition, the intrinsic non-centrosymmetry of the crystal

structures endow perovskites with strong optical anisotropy for the detection or emission of

polarized light [73, 74], which forms their applications to polarization selective devices.

Moreover, perovskite materials demonstrate environmental stability since the organic

components can provide hydrophobicity and mechanical flexibility, while the inorganic parts

offer structural robustness and chemical resistance [75].

Van der Waals heterostructures

Exploring beyond the use of a single material, the assembly of different 2D materials into Van

der Waals (vdW) heterostructures introduces many new features and possibilities for photonic

and electronic devices, and these also include optical polarizers. Compared with conventional

bulk heterostructures that suffer from lattice mismatch and defects at the interface when

combining materials with different lattice constants, vdW heterostructures can address these

challenges due to the inherent propensity of 2D materials to adhered through van der Waals

(vdW) force [76, 77]. Furthermore, the interface can be atomically sharp, and the thickness

can be as thin as a few atomic layers. By combining the distinct properties of various 2D

materials such as anisotropic conductivity, direct bandgaps, and strong light-matter

interactions, the vdW heterostructures can overcome the drawbacks of a specific 2D material.

For example, 2D materials such as black phosphorus are prone to environmental degradation

or possess inadequate mechanical properties. By integrating them into vdW heterostructures,

the stability and durability of the composite structure can be significantly improved, as the

more resilient materials afford protection to those that are more susceptible. The vdW

heterostructures also enable more efficient manipulation of light polarization states. For

example, an optical polarizer based on graphene/MoS2 heterostructure exhibited ~1.75 times

enhancement of light absorption than a comparable graphene-based optical polarizer [78]. In

addition, the flexibility in designing the vdW heterostructures enables customization for the

optical responses and operational wavelength ranges. This allows for tailoring of the polarizer

performance parameters and the broadening of their potential applications.

2D-material-based optical polarizers in different device platforms

The dangling-bond free surfaces of 2D materials allow them to be readily incorporated

into different device platforms without stress or restrictions due to lattice mismatch. To

implement optical polarizers based on 2D materials, various devices based on different

platforms have been proposed and demonstrated [17, 20, 21], each presenting unique

advantages and constraints. In this section, we review and compare the performance of these

optical polarizers, which are categorized into spatial-light devices, fiber devices, and integrated

waveguide devices according to the device platforms illustrated in Fig. 2c.

Spatial-light devices

Spatial-light optical polarizers allow for the selection of light polarization states in free-space

environments. They are featured by high polarization selectivity across a specific wavelength

range and robust environmental stability. Spatial-light optical polarizers can be realized based

on various schemes with different device configurations. For instance, wire-grid polarizers

utilize finely spaced metallic wires to selectively absorb light in one polarization while

allowing the transmission of the other [79]. For sheet polarizers, polarization selection is

achieved by absorbing one polarization state more efficiently than the other [80]. In prism

polarizers, birefringent materials are employed to refract and separate light in different

polarization states [81]. Brewster-Angle polarizers operate by reflecting light at a specific

angle to isolate a particular polarization state [82]. As compared to conventional spatial-light

optical polarizers based on bulk materials, the incorporation of 2D materials in spatial-light

optical polarizers could yield broader OBWs and flexible polarization selection through

thermal or electrical tuning methods. In addition, 2D materials have a high mechanical

flexibility to maintain their functionality when subject to bending, twisting, or compression.

In Fig. 3, we summarize typical spatial-light optical polarizers incorporating 2D materials.

As mentioned in the previous section, graphene can effectively interact with light at THz

wavelengths. This has motivated many studies on THz graphene optical polarizers. In 2012,

Bludov et al. first proposed a THz graphene spatial-light optical polarizer and theoretically

analyzed its performance. In such device, a graphene layer was sandwiched between two

dielectric media and a prism was placed on top of them (Fig. 3a) [83]. Polarization selection

was realized by leveraging the resonant coupling between transverse magnetic (TM)-polarized

light waves and graphene surface plasmons, where TM-polarized waves were absorbed at

resonance, and transverse electric (TE)-polarized waves were reflected. By adjusting the

voltage applied to graphene, it was possible to modulate the degree of polarization change and

achieve 100% reflection of the TE-polarized waves. This could also enable the transition

between circular and linear polarizations.

Metasurfaces consisting of 2D arrays of elements have been widely used for manipulating

anisotropic propagation of light waves [84-86]. By incorporating graphene layers into metallic

metasurfaces [20, 26] or utilizing purely graphene-based metasurfaces [27, 87, 88], tunable

THz polarizers have been realized.

In 2017, Kim et al. experimentally demonstrated effective polarization manipulation of

THz waves by incorporating a graphene layer into chiral metasurfaces composed of

subwavelength metallic building blocks (Fig. 3b) [20]. In such a device, the gate voltage

applied to graphene selectively adjusted the transmission of right-handed circularly polarized

light without impacting the transmission of left-handed circularly polarized light, allowing for

large-intensity modulation depths (> 99%) at a low gate voltage of ~2 V. In contrast to the

device in Fig. 3b where the graphene sheet spanned the entire area of metallic metasurface,

Meng et al. experimentally demonstrated a tunable THz spatial-light optical polarizer based

on a graphene-metal metasurface with graphene wire grids positioned over a metallic

metasurface (Fig. 3c) [26]. Metal patterns were first fabricated to deposit Ti/Au layers,

followed by transferring graphene onto the metal arrays via a wet transfer process and etching

to form the wire-grid structure via oxygen plasma etching. The device with interleaved

graphene and metal elements enhanced the THz wave-plasmon resonant coupling, enabling

tunable PER from ~3.7 to ~10.3 dB by adjusting the gate voltage.

Although the light-graphene interaction can be enhanced by using metallic metastructures,

they also face limitations, such as complicated fabrications and high costs. To address this

issue, some THz optical polarizers based on pure graphene metasurfaces were investigated. A

THz optical polarizer was proposed by placing an array of rectangular or L-shaped graphene

patches on top of a dielectric layer to form metasurfaces (Fig. 3d) [87]. Owing to the strong

plasmonic behavior of graphene, the rectangular graphene patches facilitated the conversion

of linearly polarized waves into circular or elliptical polarization during transmission, while

the L-shaped graphene patches enabled the conversion of linearly polarized waves into their

cross-polarized counterparts during reflection. In addition, a tunable THz optical polarizer with

adjustable operating frequency within 1.81-3.81 THz was theoretically investigated (Fig. 3e)

[27], where a graphene ribbon array on silicon substrate passed TM-polarized light and

blocked the TE polarization due to the surface plasmon resonance of graphene. By employing

a double-stage graphene layered structure in such a device, an optimized PER up to ~30 dB

was achieved. Similarly, a THz graphene wire-grid optical polarizer was proposed by utilizing

the surface plasmon resonance in graphene ribbons to select TM-polarized light [88].

Simulation results showed that an average PER of ~30 dB and a low IL of ~2 dB over a broad

frequency range of 0.8–2.5 THz was achieved.

Apart from graphene, other 2D materials have also been employed in spatial-light optical

polarizers. A mid-infrared (MIR) spatial-light optical polarizer formed by periodic GO ribbons

was demonstrated (Fig. 3f) [89], achieving a high PER (~20 dB) as well as adjustable

operational wavelengths in the MIR region. The device was designed based on the guided-

mode resonance theory to allow more efficient coupling between TE-polarized light and the

GO film as compared to TM-polarized light. In addition, Ti3C2Tz MXene films with

anisotropic optical conductivity were used in a wire-grid configuration to effectively

manipulate the polarization of THz radiation (Fig. 3g) [66]. The devices were made by

spinning a water-based mixture of Ti3C2Tz nanosheets onto a photolithographically patterned

THz-transparent base before soaking in acetone. Experimental results showed that the

polarizer achieved a PER of ~6 dB over the spectral range from ~0.3 to ~2.0 THz.

An optical polarizer based on 2D perovskites was also demonstrated, which enabled the

conversion of deep ultraviolet incident light into polarized photoluminescence of the 2D

perovskite at visible wavelengths (Fig. 3h) [75]. The polarizer was consisted of a periodic sub-

30-nm 2D BA2MA2Pb3Br10 perovskite line pattern, which was fabricated by nanoimprinting a

precursor film of the 2D perovskite via spin coating on a silicon substrate with a

topographically prepatterned hard PDMS mold. A thin aluminum metal layer was deposited

on the perovskite nanopattern to enhance the transmission of linearly polarized light

perpendicular to the line direction. The patterned 2D perovskite films with the narrow pitch

size of 30 nm significantly improved the optical anisotropy, where the maximum PER was

~1.5 times higher than the pitch size of 100 nm over the spectral range of 200 ‒ 600 nm. In

addition, a BP reflective optical polarizer was demonstrated (Fig. 3i) based on mode

interference in a multilayered system [90]. The polarizer consisted of an anisotropic BP layer

atop a multilayer SiO2/Si substrate, where the BP layer and the bottom substrate form a Fabry-

Perot (FP) cavity. By adjusting the thickness of the BP layer with a high optical anisotropy, a

PER of ~9 dB was achieved at visible wavelengths.

Fig. 3. Schematic illustrations of spatial-light optical polarizers based on 2D materials. a. A THz

optical polarizer based on a graphene layer sandwiched between two dielectric media and with a prism

on top of them. b. A tunable THz optical polarizer based on graphene incorporated into chiral

metasurfaces. c. A tunable THz optical polarizer based on graphene-metal metasurfaces. d. A THz

optical polarizer based on metasurfaces formed by L-shaped graphene patches. e. A tunable THz optical

polarizer based on a graphene nanoribbon array on a silicon substrate. f. A mid-infrared graphene oxide

(GO) optical polarizer. g. A THz MXene wire-grid optical polarizer. h. A perovskite optical polarizer

working at visible wavelengths. i. A black phosphorus (BP) optical polarizer working at visible

Fiber devices

Fiber optical polarizers provide in-line polarization control and find direct applications in

fiber-optic systems. Fiber devices are highly effective in applications like sensing and optical

communications, where maintaining the integrity of the polarized light over long distances is

crucial. Conventional fiber optical polarizers achieve the selection of light polarization states

by incorporating birefringent crystals or metals that show polarization-selective coupling with

the evanescent fiber optical field [91-93]. Due to inherent limitations of these materials (e.g.,

polarization mode dispersion and high insertion loss [94]) and structural constraints in fiber

optical polarizers, these devices face challenges in terms of fabrication, bandwidth, and

tunability. In contrast, the incorporation of 2D materials with highly anisotropic light

absorption over broad bands can enhance the efficiency for polarization selection and improve

the OBW for fiber optical polarizers. In Fig. 4, we summarize typical fiber optical polarizers

incorporating 2D materials.

In 2011, Bao et al. first demonstrate a graphene optical polarizer in a single-mode fiber,

achieving a high PER of ~27 dB and an IL of ~5 dB (Fig. 4a) [17]. To enhance the interaction

between graphene and the evanescent optical field, the fiber was polished into the core with a

depth of ~1 μm. Owing to the broadband light absorption of graphene, the polarizer operated

from visible to NIR wavelengths. Compared to conventional metal-clad polarizers, the

graphene fiber optical polarizer also provided advantages of simpler fabrication and lower cost.

Subsequently, there were many related studies aiming to improve the performance of graphene

fiber optical polarizers by using various methods to enhance the light-graphene interaction.

These include engineering fiber core geometry (Fig. 4b) [95], optimizing fiber core or

graphene film position (Figs. 4c and 4d) [96, 97], and introducing auxiliar materials like

polymethyl methacrylate (PMMA) (Fig. 4e) [98] and polyvinyl butyral (PVB) (Fig. 4f) [99].

In addition to graphene, fiber optical polarizers incorporating other 2D materials were

also investigated. By using the drop-casting method to coat GO on a non-adiabatic microfiber,

a TM-pass optical polarizer was demonstrated (Fig. 4g) [100]. A high PER of ~37 dB at 1480

nm was achieved for a device with a ~24-μm-thick GO film at a length of ~12 mm. An optical

polarizer consisting of a 2D ReS2 film transferred onto a D-shaped fiber was demonstrated

(Fig. 4h) [101]. Due to the periodical change of linear absorption with the polarization angle,

the ReS2-covered fiber exhibited different responses for TE and TM polarizations, which was

exploited to achieved polarization selection from the visible to MIR regions.

Recently, some fiber optical polarizers incorporating vdW heterostructures were also

reported. A fiber optical polarizer consisting of MoS2/graphene/Au film was demonstrated,

achieving a high PER of ~19 dB (Fig. 4i) [78]. The polarizer was fabricated by wet transferring

a graphene/MoS2/PMMA hybrid film onto a side-polished fiber, followed by employing a

mask to pattern interdigitated Au electrodes atop the graphene surface. In such a device, the

MoS2 film and the Au finger electrode significantly enhanced TM mode absorption by ~1.75

and ~24.8 times than a comparable device with only graphene, respectively. Another fiber

optical polarizer based on graphene/ hexagonal boron nitride (hBN) heterostructure was also

proposed (Fig. 4j) [102], where the graphene and hBN material were sequentially deposited

on the surface of a silicon-core microfiber. Compared to the device with only graphene, more

power was coupled into the graphene film to enhance the light-graphene interaction.

Depending on the input wavelength and the diameter of the silicon-core, the device had the

capability to function as either a TM or TE mode polarizer.

Except for using side-polished fibers in the above studies, other fiber platforms and

structures were also investigated. For example, a graphene helical microfiber polarizer was

structure enabled ultralong light-graphene interaction, yielding a high PER ~16 dB and a broad

OBW from ~1200 nm to ~1650 nm. In addition, a graphene-coupled microfiber polarizer was

demonstrated by attaching an optical microfiber onto a polydimethylsiloxane (PDMS)

substrate coated with a graphene monolayer (Fig. 4l) [103]. Experimental results showed that

a high PER of ~31 dB was achieved for a microfiber with an optimized diameter of ~3.9 µm.

Fig. 4. Schematic illustrations of fiber optical polarizers based on 2D materials. a. A graphene

optical polarizer with a graphene film coated on a side-polished optical fiber. b‒c. Graphene optical

fiber polarizers with engineered fiber core geometry and optimized fiber core position to enhance the

light-graphene interaction. d. A graphene optical polarizer with graphene films coated on four sides of

a microfiber surface. e‒f. Graphene optical polarizers with auxiliar materials polymethyl methacrylate

(PMMA) and polyvinyl butyral to enhance the light-graphene interaction. g. A graphene oxide (GO)

optical polarizer with a GO film coated on a microfiber. h. A rhenium disulfide (ReS2) optical polarizer

with a ReS2 film coated on a side-polished optical fiber. i. A vdW heterostructure optical polarizer with

MoS2/graphene/Au film coated on a side-polished optical fiber. j. A 2D heterostructure optical polarizer

with graphene/hBN film coated on the surface of a silicon-core microfiber. k. A graphene optical

polarizer with a graphene film coated on a rod wrapped by a microfiber. l. A graphene optical polarizer

with a graphene film coated on a polydimethylsiloxane (PDMS) substrate attached with a microfiber.

Integrated waveguide devices

Integrated waveguide devices with compact footprint, low power consumption, and high

compatibility with photonic integrated circuits offer great benefits to achieve efficient

polarization management in on-chip optical networks and photonic processing systems.

Conventional metal-clad optical waveguides have been extensively used as integrated

waveguide optical polarizers [104, 105]. Although they can provide high PERs, this advantage

comes at the expense of a considerable IL and the demand for intricate buffer layers to facilitate

a large OBW. On-chip integration of 2D materials can enhance the ability of polarizers to

manipulate light with high precision and responsivity, leading to improved performance in

terms of PER and OBW [18, 21, 22, 106]. Fig. 5 shows typical integrated waveguide optical

polarizers incorporating 2D materials.

Similar to spatial-light and fiber devices, graphene has been the choice for many

integrated waveguide polarizers incorporating 2D materials. In 2012, a graphene waveguide

polarizer was first demonstrated (Fig. 5a) [18]. By positioning a graphene strip supporting TE-

mode surface waves on a SiO2 waveguide core with an air cladding (Fig. 5a, left panel), the

hybrid waveguide served as a TE-pass polarizer with a PER ~10 dB. By doping the graphene

strip via UV-curable perfluorinated acrylate polymer resin and make it support TM-mode

waves, a TM-pass polarizer was realized with a PER ~19 dB (Fig. 5a, right panel). In addition,

a graphene/glass waveguide polarizer assisted by a ploy(methyl methacrylate) (PMMA) film

was demonstrated (Fig. 5b) [106]. The PMMA film was used to decrease the doping level of

graphene to a lower Femi level, in contrast to the use of UV-curable polymer in Fig. 5a to

obtain a higher Femi level. By engineering the difference between the attenuation constants of

the TE and TM modes in the hybrid waveguide, a high PER of ~27 dB was achieved.

In contrast the above graphene waveguide optical polarizers with the graphene layer

positioned outside the waveguide cores, a graphene waveguide optical polarizer featured with

a graphene film sandwiched between two chalcogenide layers was demonstrated (Fig. 5c) [21].

Owing to the significantly enhanced light-graphene interaction in such a device configuration,

a high PER of over 20 dB extending from ~940 nm to ~1600 nm was achieved. The excess

propagation losses induced by graphene for the TE and TM modes were ~590 dB/cm and ~20

dB/cm, respectively. The fabrication of the polarizer involved depositing a chalcogenide layer

on a silicon wafer substrate before graphene was transferred by wet transferring method. After

that, electron-beam lithography and oxygen plasma etching were employed to pattern graphene,

followed by the deposition of another chalcogenide glass layer via thermal evaporation.

To simplify polarization manipulation and achieve flexible adjustment of PER in practical

operation, tunable graphene waveguide optical polarizers assisted by the micro-opto-

mechanical systems (MOMS) technology were demonstrated (Fig. 5d) [22]. In such devices,

graphene layers with different thicknesses were coated on the polymer waveguide core, which

were mechanically pushed to suppress the undesired polarization state. Experimental results

showed that the device with a few-layer graphene film selectively attenuated TE mode and

enabled the device to pass TM polarization (Fig. 5d, left panel), whereas the device with a

thicker graphene film reduced the TM mode intensity, thus transforming the device to pass TE

polarization (Fig. 5d, right panel). The PERs of the devices were dynamically tuned by

accurate mechanical adjustment of the air gap between the graphene superstrate and the

waveguide core, achieving up to ~2.5 dB and ~6.4 dB for the TE-pass and TM-pass devices,

respectively.

In addition to the aforementioned experimental works, there are a lot of theoretical studies

which designed graphene waveguide optical polarizers based on different structures [107-109].

A compact and broadband TM-pass polarizer was proposed based on a graphene-silicon

horizontal slot waveguide structure [107]. The interaction between light and graphene was

significantly enhanced by strategically placing double-layer graphene sheets in a close

proximity to the slot region, allowing a theoretical PER over 40 dB in the wavelength range

of 1450 ‒ 1650 nm. Similarly, an optical polarizer based on a silicon slot waveguide with

multilayer graphene inserted in the slot region was investigated [108], achieving a theoretical

PER exceeding 20 dB. A tunable optical polarizer based on silicon Mach-Zehnder

interferometers coated with graphene film was also proposed [109]. By varying bias voltages

applied to the graphene layers, distinct alterations in the mode effective index for both TE and

TM polarizations could be achieved, allowing a theoretical PER of ~19 dB for the TE-pass

state and of ~21 dB for the TM-pass state over a wide OBW ranging from ~1500 nm to ~1800

nm.

Apart from graphene, other 2D materials have also been employed in waveguide optical

polarizers. A GO waveguide optical polarizer was fabricated by using drop-casting method to

coat a 2-µm-thick GO film onto an SU8 polymer waveguide (Fig. 5e) [110], which achieved

a high PER of ~40 dB over a wide wavelength range from 1530 nm to 1630 nm. In contrast

to the drop-casting method that was mainly used for coating thick films (typically with a

resolution of hundreds of nanometers), a layer-by-layer film coating method based on self-

assembly was employed to coat GO films onto doped silica waveguides (Fig. 5f) [34], allowing

for accurate control of the film thickness with a high resolution of ~2 nm. This, together with

the use of photolithography and lift-off to precisely control the length and position of the GO

films, enabled the optimization of the device performance as optical polarizers. A high PER of

~53.8 dB was achieved for a 1.5-cm-long doped silica waveguide coated with a 2-mm-long

GO film. A wide OBW extending from visible (~632 nm) to infrared (~1550 nm) wavelengths

was also demonstrated. By coating a 50-μm-long GO film onto a doped silica microring

resonator using the same method, a microring resonator polarizer was also demonstrated (Fig.

5g), achieving a PER of ~8.3 dB between TE and TM-polarized resonances.

Polarization-dependent optical absorption of MoS2 film on an Nd:YAG (neodymium

doped yttrium aluminum garnet) waveguide was also experimentally observed (Fig. 5h) [111].

The MoS2 film with a thickness of ~6.5 nm was coated on the waveguide via pulsed laser

deposition. For a 10-mm-long waveguide uniformly coated with the MoS2 film, a PER ~3 dB

and a low IL ~0.4 dB was achieved. Subsequently, a MoS2-coated waveguide optical polarizer

was demonstrated [112], where the MoS2 was coated on SU-8 polymer strip waveguide by the

drop-casting method. Experimental results showed that a maximum PER of ~12.6 dB at ~980

nm was achieved. In addition, a MoSe2-coated waveguide optical polarizer was demonstrated,

achieving a PER of ~14 dB at ~1480 nm (Fig. 5i) [113]. The device was fabricated by using

the drop-casting method to coat MoSe2 film with a thickness of ~24 µm onto an SU8 polymer

waveguide. By stacking a hybrid metamaterial structure consisting of periodic BP and silica

layers on silicon substrate, a compact tunable optical polarizer was designed to operate within

the visible spectrum from 500 to 800 nm (Fig. 5j) [114]. Simulation results showed that the

polarizer was reconfigurable for either TE-pass or TM-pass by adjusting the orientation of the

BP layers relative to the propagation direction.

Fig. 5. Schematic illustrations of integrated waveguide optical polarizers based on 2D materials.

a. A graphene optical polarizer where a graphene strip was coated on a SiO2 waveguide core with an

air cladding (left panel) and with a UV-curable perfluorinated acrylate polymer resin cladding (right

panel). b. A graphene optical polarizer with a graphene film coated on a glass waveguide assisted by a

ploy(methyl methacrylate) (PMMA) film. c. A graphene waveguide optical polarizer with a graphene

film sandwiched between two chalcogenide layers. d. Graphene optical polarizers assisted by the

micro-opto-mechanical systems (MOMS) technology, where a few-layer graphene film (left panel) and

a thicker graphene film (right panel) were coated on polymer waveguides. e. A graphene oxide (GO)

optical polarizer with a GO film coated on an SU8 polymer waveguide. f. A GO optical polarizer with

a GO film coated on a doped silica waveguide. g. A GO microring polarizer with a GO film coated on

a doped silica microring resonator. h. A MoS2 optical polarizer with a MoS2 film coated on an Nd:YAG

(neodymium doped yttrium aluminum garnet) waveguide. i. A MoSe2 optical polarizer with a MoSe2

film coated on an SU8 polymer waveguide. j. A black phosphorus (BP) optical polarizer with a periodic

BP film stacking on the metamaterial waveguide. a is reprinted with permission from ref. [18]

In Table 1, we summarize 2D-material-based optical polarizers in different device

platforms and compare their performance. Here we compare the key performance parameters

including PER, OBW, and IL, and only show the results for experimental works. From Table

1, it can be seen that the spatial-light and fiber optical polarizers require relatively thick films

of 2D materials as compared to the integrated waveguide polarizers. This is mainly due to the

relatively weak mode overlap with 2D materials in these devices. It is also worth noting that

even for some devices with very thick films beyond the typical thickness of 2D materials, the

anisotropy in the film loss can still remain sufficiently high to facilitate their functions as

optical polarizers.

In contrast to fiber and integrated waveguide polarizers that confine light within

waveguides with mode dispersion, spatial-light optical polarizers have the ability to operate in

free space that has almost no mode dispersion. In addition, they can be designed to function

across different wavelength regions and typically demonstrate wider OBWs compared to fibers

and integrated waveguide devices. On the other hand, the strong mode confinement in fiber

and integrated waveguide optical polarizers makes them attractive in achieving compact

device footprint, and the relatively strong interaction between the light waves and the 2D

materials in these devices also yield relatively high PER values compared to the spatial-light

devices.

Regarding the 2D materials selected for these optical polarizers, most studies opted for

graphene, likely due to its earlier discovery and more extensive investigation. Along with the

rapid advancements in the studies and fabrication of 2D materials over the past decade, an

increasing variety of 2D materials are being utilized for implementing optical polarizers, which

demonstrate their own advantages and address a broader application scope. The future

development in this field hinges on overcoming the specific limitations to materials and

platforms, thereby paving the way for more versatile and broadly applicable polarizing

technologies.

Table 1 Comparison of 2D-material-based polarizers in different device platforms. PER:

polarization extinction ratio. OBW: operational bandwidth. IL: insertion loss. WG: waveguide.

Materials

Platforms

Thickness

PER (dB)

OBW (µm)

IL (dB)

Ref.

Graphene

Spatial-light

Monolayer

‒ a

~188 – 500

‒ a

[20]

Graphene

Spatial-light

Monolayer

~10

~120 – 600

‒ a

[26]

Spatial-light

~96 nm

‒ a

[90]

Spatial-light

~1000 nm

~20

~2 – 14

‒ a

[89]

MXene

Spatial-light

~30 nm

~150 – 1000

<2.0

[66]

Perovskite

Spatial-light

~40 nm

‒ a

~0.20 – 0.60

‒ a

[75]

Graphene

Fiber

Monolayer

~27

~0.50 – 1.63

~5.0

[17]

Graphene

Fiber

~1.0 nm

~16

~1.20 – 1.65

‒ a

[19]

Graphene

Fiber

Monolayer

~38

~1.43 – 2.00

~1.0

[99]

Graphene

Fiber

2 layers

~44

~1.56 – 1.63

>5.0

[98]

Graphene

Fiber

Monolayer

~31

‒ a

[103]

Graphene/MoS2

Fiber

Monolayer

~19

~0.98 – 1.62

<10.5

[78]

Fiber

~24000 nm

~36

~1.30 – 1.60

~2.2

[100]

ReS2

Fiber

Monolayer

‒ a

<4.4

[101]

Graphene

Polymer WG

‒ a

~19

‒ a

~26.0

[18]

Graphene

Glass WG

‒ a

~27

~1.23 – 1.61

~9.0

[106]

Graphene

Chalcogenide

glass-on-

graphene WG

Monolayer

~23

~0.94 – 1.60

~0.8

[21]

Graphene

Polymer WG

> or < 10 nm b

‒ a

~9.0

[22]

Polymer WG

~2000 nm

~40

~1.53 – 1.63

~6.5

[110]

Doped silica

~2 – 200 nm

~54

~0.63 – 1.60

~7.5

[34]

MoS2

Nd:YAG

waveguide

~6.5 nm

‒ a

~0.4

[111]

MoS2

Polymer WG

~2.5 nm

~12.6

~0.65 – 0.98

<10

[112]

Metamaterial

~0.5 nm

~30

~0.50 – 0.80

~0.3

[114]

MoSe2

Polymer WG

~24000 nm

~14

~0.98 – 1.55

‒ a

[113]

60. a There is no reported value for this parameter in the literature.

61. b The polymer waveguides with a few-layer graphene film (< 10 nm) and a thicker graphene film (> 10

nm) worked as TM- and TE-pass optical polarizers, respectively.

Challenges and perspectives

As can be seen from the substantial works reviewed in previous section, the past decade

has seen remarkable advancements in optical polarizers based on 2D materials. Despite the

significant progress, this field still faces challenges and has new demands for further

developments. In this section, we discuss the current challenges and future opportunities.

Fig. 6. Development roadmap of 2D-material-based optical polarizers with different platforms.

WG: waveguide. Values of wavelength ranges are taken from: Ref. [17] for 2011 (Graphene), Ref. [110]

for 2014 (GO), Ref. [19] for 2014 (Graphene), Ref. [112] for 2015 (MoS2), Ref. [106] for 2015

(Graphene), Ref. [99] for 2016 (Graphene), Ref. [114] for 2017 (BP), Ref. [21] for 2017 (Graphene,

integrated WG), Ref. [98] for 2017 (Graphene, fiber), Ref. [20] for 2017 (Graphene, spatial-light), Ref.

[34] for 2019 (GO), Ref. [113] for 2019 (MoSe2), Ref. [26] for 2019 (Graphene), Ref. [89] for 2020

(GO), Ref. [66] for 2020 (MXene), Ref. [78] for 2022 (Graphene / MoS2), Ref.[75] for 2023

(Perovskite).

Fig. 6 shows a development roadmap of optical polarizers based on 2D materials, which

includes typical experimental works on different 2D materials and in different device platforms.

Here, we focus on comparing the operating wavelength ranges of these devices, and it can be

seen that the fiber and integrated waveguide optical polarizers are limited to work within the

visible and near-infrared regions. This is mainly because these devices with compact footprint

and small mode area cannot support the propagation of THz waves. In contrast, spatial-light

devices dominate the optical polarizers working in the THz region. In these devices with light

propagating freely in space, more efficient interaction with THz waves can be achieved.

Developing THz optical polarizers with a more compact footprint is a direction for future

advancements. To achieve this, incorporating 2D materials into plasmonic devices that provide

sub-wavelength confinement beyond the diffraction limit [115, 116] could be a possible

approach, while the yield needs to be balanced with the relatively high propagation loss in

these devices.

In practical applications, the stability of 2D materials is critical for devices incorporating

them, and this is also true for 2D-material-based optical polarizers. 2D materials with large

surface area and ultrathin film thicknesses may be susceptible to environmental factors

including changes in temperature, humidity, mechanical strain, and exposure to chemicals.

This sensitivity is particularly pronounced in 2D materials like BP and TMDCs, which exhibit

limited stability in air. To improve the environmental stability of 2D materials, two strategies

are usually employed. The first is adopting encapsulation materials to effectively isolate the

2D materials from ambient conditions. For instance, dielectrics (e.g., Al2O3) [117] and

polymers (e.g., PMMA and PVB) [118, 119] were used as encapsulation layers. The second

involves introducing robust 2D materials such as hBN and GO to render the surface of sensitive

2D materials inert to environmental influences [120]. For example, few-layer holey GO

membranes were utilized as passivation layers to protect BP and MXene from oxidative

degradation [121]. It should also be noted that the incorporation of polymer or other 2D

materials might decrease thermal dissipation in layered 2D films, which should be considered

for devices operating at high light intensities and with temperature-sensitive 2D materials.

The trade-off between PER and IL presents another challenge in the design and

fabrication of 2D-material-based optical polarizers, particularly for fiber and integrated

waveguide devices. Typically, a device with a thicker 2D material film exhibits a higher PER

and IL, where the former is advantageous, but the latter is undesirable. In some literatures, the

figure of merit (FOM) for optical polarizers based on 2D materials was defined as the ratio of

PER to IL [21, 34]. To balance the trade-off between these two parameters, it is important to

engineer the mode overlap with 2D materials, and this can be achieved by optimizing the

waveguide geometry as well as the thickness and position of the 2D films. Given that the IL

accumulates over a certain length, it can always be minimized by shortening the lengths of the

2D films, although this may also result in decreased PERs. Recently, some methods to

manipulate the optical anisotropy of 2D materials have been proposed [13, 122]. For example,

by adjusting the twist angle between adjacent layers, BP exhibited distinctive properties in its

optical anisotropy [123]. The change of the intrinsic optical anisotropy of 2D materials can

also be realized by introducing external factors, such as stain, electric field, and surface

plasmon [124-126].

In terms of device fabrication, currently there are mainly two fabrication strategies to

incorporate 2D materials into different device platforms. The first involves the transfer of 2D

materials to the target device substrates, which is represented by the dry transfer method (using

a transfer stamp [127, 128] to obtain 2D films from bulk materials) and the wet transfer method

(typically for CVD-grown 2D materials on metal substrates or foils [129, 130]). The second

features directly coating 2D materials onto the target devices, which is exemplified by the

solution dropping method [131] and the self-assembly method [38]. Despite the wide use of

the transfer methods in lab experiments, they face limitations in achieving high efficiency for

large-scale manufacturing and precise control of the 2D film parameters. In addition, the

transfer process can easily lead to stretching, bending, and wrinkling of the 2D films, posing

challenges in achieving high film uniformity. On the other hand, although the solution

dropping method offer a simple and rapid way to coated 2D material films onto the target

devices, it faces limitations due to low film uniformity and considerable film thickness. In

contrast, the self-assembly coating method allows for layer-by-layer film coating with precise

control over the thicknesses of 2D material films. It also shows attractive abilities to achieve

large-area film coating, high film uniformity, and conformal coating on complex structures. To

date, the self-assembly method has been employed for coating graphene, GO, TMDC, and

MXene films, with more 2D materials remaining to be explored [34, 39, 132, 133].

The precise control of 2D material film parameters, such as thickness, length, and

placement, is crucial for optimizing the performance of optical polarizers. The ability to pattern

2D materials can also introduce more complex polarization functionalities that go beyond what

traditional polarization mechanisms can provide. For example, uniformly spaced and well-

aligned free-standing 2D materials patterns are needed for 2D-material-based wire grid

polarizers to achieve a high PER [75, 88], and a THz spatial light optical polarizer with

graphene patches in different patterns can convert the linearly polarized waves into different

polarization states [87]. So far, many approaches have been employed to pattern 2D materials,

such as laser patterning, lithography, nanoimprinting, inkjet printing, and focused ion beam

(FIB) milling [134-137]. Each of these approaches has its advantages for specific purposes.

For example, the laser patterning approach provides a mask-free and chemical-free method

with simple fabrication process, along with the ability to pattern a variety of 2D materials. The

lithography and nanoimprinting approaches leverage the well-developed patterning techniques

for the fabrication of integrated circuits, and show better compatibility with the integrated chip

industry. Inkjet printing allows for rapid and in situ patterning, and is attractive for fabricating

large-area patterns with relatively low resolution (typically > 1 μm [138]). FIB milling can

achieve ultrahigh patterning resolution (< 10 nm [139]), but this normally comes at the expense

of a lower patterning speed than other patterning approaches.

Although in this review we focus on optical polarizers based on 2D materials, it is worth

noting that 2D materials have also been employed to improve the performance of other

polarization sensitive devices such as photodetectors, light-emitting devices, and mode-locked

lasers. Fig. 7 shows typical polarization sensitive devices incorporating 2D materials.

Polarization-sensitive photodetectors with 2D materials such as perovskite, germanium

selenide (GeSe2), germanium arsenide (GeAs2), and MXene have been reported (Fig. 7a) [65,

140-142]. The 2D materials with strong optical anisotropy in these photodetectors allow them

to exhibit prominent ability to capture light with high responsivity, fast response speed, and

broad response bandwidth. In addition, 2D materials such as TMDCs and BP have been

utilized in polarization sensitive light emitting devices (Fig. 7b) [143-146]. The direct bandgap

of these 2D materials allows for photon emission upon excitation, and their optical anisotropy

offers the capability to control the polarization state of the emitted light. 2D materials such as

BP and GO have been employed in mode-locked fiber lasers (Fig. 7c) [147, 148], where the

2D materials featured with both high saturable absorption and high anisotropic optical

absorption enable the generation of mode-locked optical pulses via simple polarization control.

In addition to the above devices, 2D materials such as graphene, BP, and vdW heterostructures

have also been used for implementing other polarization sensitive optical devices, such as

converters, waveplates, beam splitters, and polarization switches (Figs. 7d-7g) [149-152].

These results have wide applications to GO based devices as well as other novel photonic

platforms. 153-200 Ultimately this could be useful for both classical and quantum microcomb

based applications. 201-277

Finally, while 2D materials have already seen extensive uses in optical polarizers and

polarization sensitive devices, the quest for enhanced performance of these devices continues.

To further improve performance, there are mainly two strategies. One involves modification

of the properties of 2D materials (e.g., by optimizing their fabrication processes) to enhance

their optical anisotropy, and the other is to optimize the device configuration and facilitate

more efficient interaction between light and the anisotropic 2D materials. In addition, with the

rapid expansion of the 2D materials family, there will also be new opportunities for the

development of optical polarizers incorporating newly emerging 2D materials. Considering

the extensive applications of optical polarizers highlighted at the start of this review, the

continuous advancement of optical polarizers incorporating 2D materials is expected to

significantly impact and facilitate a broad range of optical systems with miniatured size and

reduced power consumption.

Fig. 7. Typical polarization-sensitive devices incorporating 2D materials: a. Photodetectors with (i)

perovskite, (ii) germanium selenide (GeSe2), (iii) germanium arsenide (GeAs2), and (iv) MXene b.

Light emitting devices with (i) tungsten diselenide (WSe2), (ii) rhenium disulfide (ReS2), (iii) black

phosphorus (BP) / molybdenum disulfide (MoS2), and (iv) MoS2 / WSe2. c. Mode-locked fiber lasers

with (i) BP and (ii) graphene oxide (GO). d. Converters with graphene. e. Waveplates with BP. f. Beam

splitters with BP. g. Polarization switches with molybdenum diselenide (MoSe2) / WSe2. a-i is reprinted

Springer Nature.

Conclusion

2D-material-based optical polarizers represent an emerging interdisciplinary field at the

intersection of polarization optics and material science. Over the past decade, significant

advancements in this field have been made, facilitated by the distinctive properties of advanced

2D materials and the rapid progress in their fabrication technologies. In this review, we provide

an overview for recent progress in 2D-material-based optical polarizers. First, we introduce

the distinctive material properties of 2D materials for implementing optical polarizers. Next,

we review 2D-material-based optical polarizers in different device platforms, including

spatial-light devices, fiber devices, and integrated waveguide devices. Finally, we discuss the

current challenges and future perspectives of this field. In the future, along with advances in

device fabrication technologies and expanded applications with demanding requirements, we

believe that there will be more and more new breakthroughs in this field.

Competing interests

The authors declare no competing interests.

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178. Linnan Jia, Jiayang Wu, Yunyi Yang, Yi Du, Baohua Jia, David J. Moss, “Large Third-Order Optical

Kerr Nonlinearity in Nanometer-Thick PdSe2 2D Dichalcogenide Films: Implications for Nonlinear

Photonic Devices”, ACS Applied Nano Materials vol. 3 (7) 6876–6883 (2020).

DOI:10.1021/acsanm.0c01239.

179. E.D Ghahramani, DJ Moss, JE Sipe, “Full-band-structure calculation of first-, second-, and third-

harmonic optical response coefficients of ZnSe, ZnTe, and CdTe”, Physical Review B 43 (12), 9700

(1991)

180. A. Pasquazi, et al., “Sub-picosecond phase-sensitive optical pulse characterization on a chip”, Nature

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chalcogenide glass photonic crystal waveguides via silica optical fiber nanowires”, Optics Express vol.

14 (3), 1070-1078 (2006).

182. S Tomljenovic-Hanic, MJ Steel, CM de Sterke, DJ Moss, “High-Q cavities in photosensitive photonic

crystals” Optics Letters vol. 32 (5), 542-544 (2007).

183. 83. E Ghahramani, DJ Moss, JE Sipe, “Second-harmonic generation in odd-period, strained,

(Si(Ge/Si superlattices and at Si/Ge interfaces”, Physical Review Letters vol. 64 (23), 2815 (1990).

184. M Ferrera et al., “On-Chip ultra-fast 1st and 2nd order CMOS compatible all-optical integration”,

Optics Express vol. 19 (23), 23153-23161 (2011).

185. VG Ta’eed et al., “Error free all optical wavelength conversion in highly nonlinear As-Se chalcogenide

glass fiber”, Optics Express vol. 14 (22), 10371-10376 (2006).

186. M Rochette, L Fu, V Ta'eed, DJ Moss, BJ Eggleton, “2R optical regeneration: an all-optical solution

for BER improvement”, IEEE Journal of Selected Topics in Quantum Electronics vol. 12 (4), 736-744

(2006).

187. TD Vo, et al., “Silicon-chip-based real-time dispersion monitoring for 640 Gbit/s DPSK signals”,

Journal of Lightwave Technology vol. 29 (12), 1790-1796 (2011).

188. C Monat, C Grillet, B Corcoran, DJ Moss, BJ Eggleton, TP White, ..., et al., “Investigation of phase

matching for third-harmonic generation in silicon slow light photonic crystal waveguides using Fourier

optics”, Optics Express vol. 18 (7), 6831-6840 (2010).

189. L Carletti, P Ma, Y Yu, B Luther-Davies, D Hudson, C Monat, .... , et al., “Nonlinear optical response

of low loss silicon germanium waveguides in the mid-infrared”, Optics Express vol. 23 (7), 8261-8271

(2015).

190. Bao, C., et al., Direct soliton generation in microresonators, Opt. Lett, 42, 2519 (2017).

191. M.Ferrera et al., “CMOS compatible integrated all-optical RF spectrum analyzer”, Optics Express, vol.

22, no. 18, 21488 - 21498 (2014).

192. M. Kues, et al., “Passively modelocked laser with an ultra-narrow spectral width”, Nature Photonics,

vol. 11, no. 3, pp. 159, 2017.

193. M.Ferrera et al.“On-Chip ultra-fast 1st and 2nd order CMOS compatible all-optical integration”, Opt.

Express, vol. 19, (23)pp. 23153-23161 (2011).

194. D. Duchesne, M. Peccianti, M. R. E. Lamont, et al., “Supercontinuum generation in a high index

doped silica glass spiral waveguide,” Optics Express, vol. 18, no, 2, pp. 923-930, 2010.

195. H Bao, L Olivieri, M Rowley, ST Chu, BE Little, R Morandotti, DJ Moss, ... “Turing patterns in a fiber

laser with a nested microresonator: Robust and controllable microcomb generation”, Physical Review

Research vol. 2 (2), 023395 (2020).

196. M. Ferrera, et al., “On-chip CMOS-compatible all-optical integrator”, Nature Communications, vol. 1,

Article 29, 2010.

197. A. Pasquazi, et al., “All-optical wavelength conversion in an integrated ring resonator,” Optics

Express, vol. 18, no. 4, pp. 3858-3863, 2010.

198. A.Pasquazi, Y. Park, J. Azana, et al., “Efficient wavelength conversion and net parametric gain via

Four Wave Mixing in a high index doped silica waveguide,” Optics Express, vol. 18, no. 8, pp. 7634-

7641, 2010.

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nonlinear chirper,” Optics Express, vol. 18, no. 8, pp. 7625-7633, 2010.

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Glass Micro-Ring Resonator with Q-factor > 1 Million”, Optics Express, vol.17, no. 16, pp. 14098–

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201. M. Peccianti, et al., “Demonstration of an ultrafast nonlinear microcavity modelocked laser”, Nature

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202. A.Pasquazi, et al., “Self-locked optical parametric oscillation in a CMOS compatible microring

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210. Antonio Cutrona, Maxwell Rowley, Debayan Das, Luana Olivieri, Luke Peters, Sai T. Chu, Brent L.

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Issue 22, pp. 39816-39825 (2022). https://doi.org/10.1364/OE.470376.

211. M.Rowley, P.Hanzard, A.Cutrona, H.Bao, S.Chu, B.Little, R.Morandotti, D. J. Moss, G. Oppo, J.

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vol. 608 (7922) 303–309 (2022).

212. A. Cutrona, M. Rowley, A. Bendahmane, V. Cecconi,L. Peters, L. Olivieri, B. E. Little, S. T. Chu, S.

Stivala, R. Morandotti, D. J. Moss, J. S. Totero-Gongora, M. Peccianti, A. Pasquazi, “Nonlocal

bonding of a soliton and a blue-detuned state in a microcomb laser”, Nature Communications Physics

vol. 6 (2023).

213. A. Cutrona, M. Rowley, A. Bendahmane, V. Cecconi,L. Peters, L. Olivieri, B. E. Little, S. T. Chu, S.

Stivala, R. Morandotti, D. J. Moss, J. S. Totero-Gongora, M. Peccianti, A. Pasquazi, “Stability

Properties of Laser Cavity-Solitons for Metrological Applications”, Applied Physics Letters vol. 122

(12) 121104 (2023); doi: 10.1063/5.0134147.

214. X. Xu, J. Wu, M. Shoeiby, T. G. Nguyen, S. T. Chu, B. E. Little, R. Morandotti, A. Mitchell, and D. J.

Moss, “Reconfigurable broadband microwave photonic intensity differentiator based on an integrated

optical frequency comb source,” APL Photonics, vol. 2, no. 9, 096104, Sep. 2017.

215. Xu, X., et al., Photonic microwave true time delays for phased array antennas using a 49 GHz FSR

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216. X. Xu, M. Tan, J. Wu, R. Morandotti, A. Mitchell, and D. J. Moss, “Microcomb-based photonic RF

signal processing”, IEEE Photonics Technology Letters, vol. 31 no. 23 1854-1857, 2019.

217. Xu, et al., “Advanced adaptive photonic RF filters with 80 taps based on an integrated optical micro-

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223. M. Tan, X. Xu, J. Wu, R. Morandotti, A. Mitchell, and D. J. Moss, “RF and microwave high bandwidth

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224. 123. X. Xu, et al., “Advanced RF and microwave functions based on an integrated optical frequency

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225. M. Tan, X. Xu, J. Wu, B. Corcoran, A. Boes, T. G. Nguyen, S. T. Chu, B. E. Little, R.Morandotti, A.

Lowery, A. Mitchell, and D. J. Moss, “"Highly Versatile Broadband RF Photonic Fractional Hilbert

Transformer Based on a Kerr Soliton Crystal Microcomb”, Journal of Lightwave Technology vol. 39

(24) 7581-7587 (2021).

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Quantum Electronics Vol. 24, 6101020, 1-20 (2018).

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Journal of Lightwave Technology, vol. 36, no. 19, pp. 4519-4526, 2018.

229. X. Xu, et al., “Continuously tunable orthogonally polarized RF optical single sideband generator based

on micro-ring resonators,” Journal of Optics, vol. 20, no. 11, 115701. 2018.

230. X. Xu, et al., “Orthogonally polarized RF optical single sideband generation and dual-channel

equalization based on an integrated microring resonator,” Journal of Lightwave Technology, vol. 36,

no. 20, pp. 4808-4818. 2018.

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source”, Journal of Lightwave Technology, vol. 38 no. 2, pp. 332-338, 2020.

233. M. Tan, et al., “Photonic RF and microwave filters based on 49GHz and 200GHz Kerr microcombs”,

Optics Comm. vol. 465,125563, Feb. 22. 2020.

234. X. Xu, et al., “Broadband photonic RF channelizer with 90 channels based on a soliton crystal

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235. M. Tan et al, “Orthogonally polarized Photonic Radio Frequency single sideband generation with

integrated micro-ring resonators”, IOP Journal of Semiconductors, Vol. 42 (4), 041305 (2021). DOI:

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236. Mengxi Tan, X. Xu, J. Wu, T. G. Nguyen, S. T. Chu, B. E. Little, R. Morandotti, A. Mitchell, and

David J. Moss, “Photonic Radio Frequency Channelizers based on Kerr Optical Micro-combs”, IOP

Journal of Semiconductors Vol. 42 (4), 041302 (2021). DOI:10.1088/1674-4926/42/4/041302.

237. B. Corcoran, et al., “Ultra-dense optical data transmission over standard fiber with a single chip

source”, Nature Communications, vol. 11, Article:2568, 2020.

238. X. Xu et al, “Photonic perceptron based on a Kerr microcomb for scalable high speed optical neural

networks”, Laser and Photonics Reviews, vol. 14, no. 8, 2000070 (2020). DOI:

10.1002/lpor.202000070.

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589, 44-51 (2021).

240. X. Xu et al., “Neuromorphic computing based on wavelength-division multiplexing”, 28 IEEE Journal

of Selected Topics in Quantum Electronics Vol. 29 Issue: 2, Article 7400112 (2023).

DOI:10.1109/JSTQE.2022.3203159.

241. Yang Sun, Jiayang Wu, Mengxi Tan, Xingyuan Xu, Yang Li, Roberto Morandotti, Arnan Mitchell, and

David Moss, “Applications of optical micro-combs”, Advances in Optics and Photonics vol. 15 (1) 86-

175 (2023). DOI:10.1364/AOP.470264.

242. Yunping Bai, Xingyuan Xu,1, Mengxi Tan, Yang Sun, Yang Li, Jiayang Wu, Roberto Morandotti,

Arnan Mitchell, Kun Xu, and David J. Moss, “Photonic multiplexing techniques for neuromorphic

computing”, Nanophotonics vol. 12 (5): 795–817 (2023). DOI:10.1515/nanoph-2022-0485.

243. Chawaphon Prayoonyong, Andreas Boes, Xingyuan Xu, Mengxi Tan, Sai T. Chu, Brent E. Little,

Roberto Morandotti, Arnan Mitchell, David J. Moss, and Bill Corcoran, “Frequency comb distillation

for optical superchannel transmission”, Journal of Lightwave Technology vol. 39 (23) 7383-7392

(2021). DOI: 10.1109/JLT.2021.3116614.

244. Mengxi Tan, Xingyuan Xu, Jiayang Wu, Bill Corcoran, Andreas Boes, Thach G. Nguyen, Sai T. Chu,

Brent E. Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, “Integral order photonic RF

signal processors based on a soliton crystal micro-comb source”, IOP Journal of Optics vol. 23 (11)

125701 (2021). https://doi.org/10.1088/2040-8986/ac2eab

245. Yang Sun, Jiayang Wu, Yang Li, Xingyuan Xu, Guanghui Ren, Mengxi Tan, Sai Tak Chu, Brent E.

Little, Roberto Morandotti, Arnan Mitchell, and David J. Moss, “Optimizing the performance of

microcomb based microwave photonic transversal signal processors”, Journal of Lightwave

Technology vol. 41 (23) pp 7223-7237 (2023). DOI: 10.1109/JLT.2023.3314526.

246. Mengxi Tan, Xingyuan Xu, Andreas Boes, Bill Corcoran, Thach G. Nguyen, Sai T. Chu, Brent E.

Little, Roberto Morandotti, Jiayang Wu, Arnan Mitchell, and David J. Moss, “Photonic signal

processor for real-time video image processing based on a Kerr microcomb”, Communications

Engineering vol. 2 94 (2023). DOI:10.1038/s44172-023-00135-7

247. Mengxi Tan, Xingyuan Xu, Jiayang Wu, Roberto Morandotti, Arnan Mitchell, and David J. Moss,

“Photonic RF and microwave filters based on 49GHz and 200GHz Kerr microcombs”, Optics

Communications, vol. 465, Article: 125563 (2020). doi:10.1016/j.optcom.2020.125563.

doi.org/10.1063/1.5136270.

248. Yang Sun, Jiayang Wu, Yang Li, Mengxi Tan, Xingyuan Xu, Sai Chu, Brent Little, Roberto

Morandotti, Arnan Mitchell, and David J. Moss, “Quantifying the Accuracy of Microcomb-based

Photonic RF Transversal Signal Processors”, IEEE Journal of Selected Topics in Quantum Electronics

vol. 29 no. 6, pp. 1-17, Art no. 7500317 (2023). 10.1109/JSTQE.2023.3266276.

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doi:10.1038/s41566-019-0363-0

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parametric oscillation on a chip”, Nature Communications, vol. 6, Article 8236, 2015. DOI:

10.1038/ncomms9236.

252. L. Caspani, C. Reimer, M. Kues, et al., “Multifrequency sources of quantum correlated photon pairs

on-chip: a path toward integrated Quantum Frequency Combs,” Nanophotonics, vol. 5, no. 2, pp. 351-

362, 2016.

253. C. Reimer et al., “Generation of multiphoton entangled quantum states by means of integrated

frequency combs,” Science, vol. 351, no. 6278, pp. 1176-1180, 2016.

254. M. Kues, et al., “On-chip generation of high-dimensional entangled quantum states and their coherent

control”, Nature, vol. 546, no. 7660, pp. 622-626, 2017.

255. P. Roztocki et al., “Practical system for the generation of pulsed quantum frequency combs,” Optics

Express, vol. 25, no. 16, pp. 18940-18949, 2017.

256. Y. Zhang, et al., “Induced photon correlations through superposition of two four-wave mixing

processes in integrated cavities”, Laser and Photonics Reviews, vol. 14, no. 7, pp. 2000128, 2020.

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257. C. Reimer, et al., “High-dimensional one-way quantum processing implemented on d-level cluster

states”, Nature Physics, vol. 15, no.2, pp. 148–153, 2019.

258. P.Roztocki et al., “Complex quantum state generation and coherent control based on integrated

frequency combs”, Journal of Lightwave Technology vol. 37 (2) 338-347 (2019).

259. S. Sciara et al., “Generation and Processing of Complex Photon States with Quantum Frequency

Combs”, IEEE Photonics Technology Letters vol. 31 (23) 1862-1865 (2019). DOI:

10.1109/LPT.2019.2944564.

260. Stefania Sciara, Piotr Roztocki, Bennet Fisher, Christian Reimer, Luis Romero Cortez, William J.

Munro, David J. Moss, Alfonso C. Cino, Lucia Caspani, Michael Kues, J. Azana, and Roberto

Morandotti, “Scalable and effective multilevel entangled photon states: A promising tool to boost

quantum technologies”, Nanophotonics vol. 10 (18), 4447–4465 (2021). DOI:10.1515/nanoph-2021-

0510.

261. L. Caspani, C. Reimer, M. Kues, et al., “Multifrequency sources of quantum correlated photon pairs

on-chip: a path toward integrated Quantum Frequency Combs,” Nanophotonics, vol. 5, no. 2, pp. 351-

362, 2016.

262. Hamed Arianfard, Saulius Juodkazis, David J. Moss, and Jiayang Wu, “Sagnac interference in

integrated photonics”, Applied Physics Reviews vol. 10 (1) 011309 (2023). doi: 10.1063/5.0123236.

(2023).

263. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, and David J. Moss, “Optical analogs of Rabi

splitting in integrated waveguide-coupled resonators”, Advanced Physics Research 2 (2023). DOI:

10.1002/apxr.202200123.

264. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, and David J. Moss, “Spectral shaping based on

optical waveguides with advanced Sagnac loop reflectors”, Paper No. PW22O-OE201-20, SPIE-Opto,

Integrated Optics: Devices, Materials, and Technologies XXVI, SPIE Photonics West, San Francisco

CA January 22 - 27 (2022). doi: 10.1117/12.2607902

265. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis, David J. Moss, “Spectral Shaping Based on

Integrated Coupled Sagnac Loop Reflectors Formed by a Self-Coupled Wire Waveguide”, IEEE

Photonics Technology Letters vol. 33 (13) 680-683 (2021). DOI:10.1109/LPT.2021.3088089.

266. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, “Three Waveguide Coupled

Sagnac Loop Reflectors for Advanced Spectral Engineering”, Journal of Lightwave Technology vol.

39 (11) 3478-3487 (2021). DOI: 10.1109/JLT.2021.3066256.

267. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, “Advanced Multi-Functional

Integrated Photonic Filters based on Coupled Sagnac Loop Reflectors”, Journal of Lightwave

Technology vol. 39 Issue: 5, pp.1400-1408 (2021). DOI:10.1109/JLT.2020.3037559.

268. Hamed Arianfard, Jiayang Wu, Saulius Juodkazis and David J. Moss, “Advanced multi-functional

integrated photonic filters based on coupled Sagnac loop reflectors”, Paper 11691-4, PW21O-OE203-

44, Silicon Photonics XVI, SPIE Photonics West, San Francisco CA March 6-11 (2021).

doi.org/10.1117/12.2584020

269. Jiayang Wu, Tania Moein, Xingyuan Xu, and David J. Moss, “Advanced photonic filters via cascaded

Sagnac loop reflector resonators in silicon-on-insulator integrated nanowires”, Applied Physics Letters

Photonics vol. 3 046102 (2018). DOI:/10.1063/1.5025833

270. Jiayang Wu, Tania Moein, Xingyuan Xu, Guanghui Ren, Arnan Mitchell, and David J. Moss, “Micro-

ring resonator quality factor enhancement via an integrated Fabry-Perot cavity”, Applied Physics

Letters Photonics vol. 2 056103 (2017). doi: 10.1063/1.4981392.

271. TM Monro, D Moss, M Bazylenko, CM De Sterke, L Poladian, “Observation of self-trapping of light

in a self-written channel in a photosensitive glass”, Physical Review Letters vol. 80 (18), 4072 (1998).

272. MD Pelusi, F Luan, E Magi, MRE Lamont, DJ Moss, BJ Eggleton, ... et al., “High bit rate all-optical

signal processing in a fiber photonic wire”, Optics Express vol. 16 (15), 11506-11512 (2008).

273. M Shokooh-Saremi, VG Ta'Eed, NJ Baker, ICM Littler, DJ Moss, ... et al., “High-performance Bragg

gratings in chalcogenide rib waveguides written with a modified Sagnac interferometer”, JOSA B vol.

23 (7), 1323-1331 (2006).

274. MRE Lamont, VG Ta'eed, MAF Roelens, DJ Moss, BJ Eggleton, DY Choi, ... et al., “Error-free

wavelength conversion via cross-phase modulation in 5cm of As2S3 chalcogenide glass rib

waveguide”, Electronics Letters vol. 43 (17), 945-947 (2007).

275. M Ferrera, Y Park, L Razzari, BE Little, ST Chu, R Morandotti, DJ Moss, ... et al., “All-optical 1st and

2nd order integration on a chip”, Optics Express vol. 19 (23), 23153-23161 (2011).

276. C Grillet, C Monat, CLC Smith, BJ Eggleton, DJ Moss, S Frédérick, ... et al., “Nanowire coupling to

photonic crystal nanocavities for single photon sources”, Optics Express vol. 15 (3), 1267-1276

(2007).

277. VG Ta'Eed, MRE Lamont, DJ Moss, BJ Eggleton, DY Choi, S Madden, ... et al., “All optical

wavelength conversion via cross phase modulation in chalcogenide glass rib waveguides”, Optics

Express vol. 14 (23), 11242-11247 (2006).

ResearchGate has not been able to resolve any citations for this publication.

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Jun 2023
J OPT SOC AM B

An electrically tunable surface plasmon resonance based graphene ribbon (GR) terahertz (THz) polarizer with an adjustable operating frequency, high extinction ratio, and low insertion loss is reported here, and is simple and fabrication feasible. The proposed metasurface structure comprises a periodic array of graphene ribbons deposited on a quartz–silicon substrate. The operating frequency of the GR-polarizer can be tuned by varying the gap between GRs, GR pitch, GR width, and Fermi level in graphene. Beyond the available graphene-based polarizers, the proposed device exhibits a high extinction ratio (ER) of up to 75 dB with simultaneous insertion loss of ${\sim}{1.5}\;{\rm{dB}}$ ∼ 1.5 d B at the optimized frequency of 1.69 THz. In addition, an average ER of ${\sim}{{30}}\;{\rm{dB}}$ ∼ 30 d B with insertion loss of ${\sim}{{2}}\;{\rm{dB}}$ ∼ 2 d B in the broad frequency range of 0.8–2.5 THz is demonstrated. Such metastructure polarizing devices, enriched with the nontrivial functionalities of graphene, would open up a fertile platform for designing a range of integrated photonic components for useful applications in THz optoelectronics, biomedical engineering, and microfluidics.

Optical Analogs of Rabi Splitting in Integrated Waveguide‐Coupled Resonators

Article

Full-text available

Mar 2023

Realizing optical analogs of quantum phenomena in atomic, molecular, or condensed matter physics has underpinned a range of photonic technologies. Rabi splitting is a quantum phenomenon induced by a strong interaction between two quantum states, and its optical analogs are of fundamental importance for the manipulation of light–matter interactions with wide applications in optoelectronics and nonlinear optics. Here, purely optical analogs of Rabi splitting in integrated waveguide‐coupled resonators formed by two Sagnac interferometers are proposed and theoretically investigated. By tailoring the coherent mode interference, the spectral response of the devices is engineered to achieve optical analogs of Rabi splitting with anti‐crossing behavior in the resonances. Transitions between the Lorentzian, Fano, and Rabi splitting spectral lineshapes are achieved by simply changing the phase shift along the waveguide connecting the two Sagnac interferometers, revealing interesting physical insights about the evolution of different optical analogs of quantum phenomena. The impact of the device's structural parameters is also analyzed to facilitate device design and optimization. These results suggest a new way for realizing optical analogs of Rabi splitting based on integrated waveguide‐coupled resonators, paving the way for many potential applications that manipulate light–matter interactions in the strong coupling regime.

Stability of laser cavity-solitons for metrological applications

Article

Full-text available

Mar 2023
APPL PHYS LETT

Laser cavity-solitons can appear in systems comprised of a nonlinear microcavity nested within an amplifying fiber loop. These states are robust and self-emergent and constitute an attractive class of solitons that are highly suitable for microcomb generation. Here, we present a detailed study of the free-running stability properties of the carrier frequency and repetition rate of single solitons, which are the most suitable states for developing robust ultrafast and high repetition rate comb sources. We achieve free-running fractional stability on both optical carrier and repetition rate (i.e., 48.9 GHz) frequencies on the order of [Formula: see text] for a 1 s gate time. The repetition rate results compare well with the performance of state-of-the-art (externally driven) microcomb sources, and the carrier frequency stability is in the range of performance typical of modern free-running fiber lasers. Finally, we show that these quantities can be controlled by modulating the laser pump current and the cavity length, providing a path for active locking and long-term stabilization.

Sagnac interference in integrated photonics

Article

Full-text available

Mar 2023

As a fundamental optical approach to interferometry, Sagnac interference has been widely used for reflection manipulation, precision measurements, and spectral engineering in optical systems. Compared to other interferometry configurations, it offers attractive advantages by yielding a reduced system complexity without the need for phase control between different pathways, thus offering a high degree of stability against external disturbance and a low wavelength dependence. The advance of integration fabrication techniques has enabled chip-scale Sagnac interferometers with greatly reduced footprint and improved scalability compared to more conventional approaches implemented by spatial light or optical fiber devices. This facilitates a variety of integrated photonic devices with bidirectional light propagation, showing new features and capabilities compared to unidirectional-light-propagation devices, such as Mach–Zehnder interferometers (MZIs) and ring resonators (RRs). This paper reviews functional integrated photonic devices based on Sagnac interference. First, the basic theory of integrated Sagnac interference devices is introduced, together with comparisons to other integrated photonic building blocks, such as MZIs, RRs, photonic crystal cavities, and Bragg gratings. Next, the applications of Sagnac interference in integrated photonics, including reflection mirrors, optical gyroscopes, basic filters, wavelength (de)interleavers, optical analogues of quantum physics, and others, are systematically reviewed. Finally, the open challenges and future perspectives are discussed.

van der Waals forces enhanced light–graphene interaction in optical microfiber polarizer

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Full-text available

Apr 2022

A facile and efficient approach to manufacturing optical devices with a plane graphene-coupled microfiber structure is proposed—attaching the optical microfiber onto a monolayer graphene-coated polydimethylsiloxane substrate. Such devices exhibit strong light–graphene interaction via the evanescent fields of the guided light in microfibers and show evident optical polarization and polarization-dependent saturable absorption effect. When the monolayer graphene with propagation distance is 2.5 mm, and the microfiber diameter is 3.9 μm, the polarization extinction ratio can reach up to 31.0 dB with the light wavelength at 1550 nm. The transmission in TM modes could be increased continuously by increasing the input power of light at 980 nm. The transmission with 3 and 10 dB modulation depths in TM modes could be achieved via 980 nm pump power of 15.1 and 66.1 mW, respectively, which is advantageous over unpolarized graphene-coupled microfiber devices. The proposed microfiber on graphene structure could efficiently integrate optical waveguides with two-dimensional materials, with great potential applications in optical polarizers, all-optical modulators, mode-locked fiber lasers, and sensors, especially for all-fiber systems.

Broadband Vis–NIR Circular Polarizer with Cascaded Aluminum Wire‐Grid

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Full-text available

Jan 2023

A universal design and fabrication scheme is proposed for a cascaded aluminum wire‐grid‐based vis–NIR circular polarizer. The aluminum wire‐grid is designed as a broadband circular‐linear polarization converter and a broadband linear polarizer, which is further cascaded to form a circular polarizer with strong circular polarization transmittance difference (CPTD) and circular polarization extinction ratio (CPER) in vis–NIR. By increasing the distance between the circular‐linear polarization converter and the linear polarizer, the redshift of the CPTD and CPER peaks is realized and used to design a novel circular polarizer to work better in the operating wavelength. Anisotropic thin‐film interference is revealed to be responsible for the redshift phenomenon. Furthermore, the circular polarizer is fabricated by nano imprint lithography and nano transfer printing with the merits of relatively low cost, and high production efficiency. With such flexibility in the design and fabrication, cascaded aluminum wire‐grid may serve as a tunable compact circular polarizer, and it is also easy to integrate with the wire‐grid‐based linear polarizer to realize the fabrication of the division‐of‐focal‐plane full Stokes polarimeter.

Synthesis of 2D perovskite crystals via progressive transformation of quantum well thickness

Article

Oct 2023

Optimizing the Accuracy of Microcomb-Based Microwave Photonic Transversal Signal Processors

Article

Dec 2023

Microwave photonic (MWP) transversal signal processors offer a compelling solution for realizing versatile high-speed information processing by combining the advantages of reconfigurable electrical digital signal processing and high-bandwidth photonic processing. With the capability of generating a number of discrete wavelengths from micro-scale resonators, optical microcombs are powerful multi-wavelength sources for implementing MWP transversal signal processors with significantly reduced size, power consumption, and complexity. By using microcomb-based MWP transversal signal processors, a diverse range of signal processing functions have been demonstrated recently. In this paper, we provide a detailed analysis for the processing inaccuracy that is induced by the imperfect response of experimental components. First, we investigate the errors arising from different sources including imperfections in the microcombs, the chirp of electro-optic modulators, chromatic dispersion of the dispersive module, shaping errors of the optical spectral shapers, and noise of the photodetector. Next, we provide a global picture quantifying the impact of different error sources on the overall system performance. Finally, we introduce feedback control to compensate the errors caused by experimental imperfections and achieve significantly improved accuracy. These results provide a guide for optimizing the accuracy of microcomb-based MWP transversal signal processors.

Integrated optical polarizers based on novel 2D materials

Abstract

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