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![Far-field excitations of hyperbolic phonon polaritons (HPhPs) in in-plane hyperbolic polariton tuners
a Schemes of the tuners comprised of van der Waals (vdW) α-MoO3 periodic ribbon patterns and Fourier transform infrared spectroscopic (FTIR) measurements. b Photograph of a typical α-MoO3 flake grown on a silicon substrate with a 300-nm oxide layer. The largest lateral length of the flake is 1 cm. c Scanning electron microscopy image of periodic ribbon patterns with a fixed width w = 800 nm and different skew angles θ of 0°, 30°, 60°, and 90°. d Polarized reflectance spectra of the pristine α-MoO3 thin flake shown in (b). The electric fields of the incident light, Einc, are along [001] (red curve) and [100] (blue curve) crystallographic directions, respectively. e, f Experimental polarized reflectance spectra of one-dimensional periodic tuner patterns with θ = 0° (e) and 90° (f). The polarization of the incident light is paralleled to [001] (red curves) and [100] (blue curves) directions, respectively. Insets: enlarged reflectance spectra in the range of 995 to 1020 cm⁻¹. The ω0 represents the resonant frequency of polariton tuners. The ωTO001\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{TO}}}}}}}^{001}$$\end{document} and ωTO100\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{TO}}}}}}}^{100}$$\end{document} represent the transverse optical (TO) phonon frequencies along the [001] and [100] crystallographic directions, respectively, and the ωLO010\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{LO}}}}}}}^{010}$$\end{document} indicates the longitudinal optical (LO) phonon frequency along the [010] crystallographic direction. Colored shaded regions in (d), (e), and (f) mark the frequency ranges of different Reststrahlen bands of α-MoO3.](publication/370687823/figure/fig1/AS:11431281157631783@1683859942500/Far-field-excitations-of-hyperbolic-phonon-polaritons-HPhPs-in-in-plane-hyperbolic.png)
Far-field excitations of hyperbolic phonon polaritons (HPhPs) in in-plane hyperbolic polariton tuners a Schemes of the tuners comprised of van der Waals (vdW) α-MoO3 periodic ribbon patterns and Fourier transform infrared spectroscopic (FTIR) measurements. b Photograph of a typical α-MoO3 flake grown on a silicon substrate with a 300-nm oxide layer. The largest lateral length of the flake is 1 cm. c Scanning electron microscopy image of periodic ribbon patterns with a fixed width w = 800 nm and different skew angles θ of 0°, 30°, 60°, and 90°. d Polarized reflectance spectra of the pristine α-MoO3 thin flake shown in (b). The electric fields of the incident light, Einc, are along [001] (red curve) and [100] (blue curve) crystallographic directions, respectively. e, f Experimental polarized reflectance spectra of one-dimensional periodic tuner patterns with θ = 0° (e) and 90° (f). The polarization of the incident light is paralleled to [001] (red curves) and [100] (blue curves) directions, respectively. Insets: enlarged reflectance spectra in the range of 995 to 1020 cm⁻¹. The ω0 represents the resonant frequency of polariton tuners. The ωTO001\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{TO}}}}}}}^{001}$$\end{document} and ωTO100\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{TO}}}}}}}^{100}$$\end{document} represent the transverse optical (TO) phonon frequencies along the [001] and [100] crystallographic directions, respectively, and the ωLO010\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\omega }_{{{{{{\rm{LO}}}}}}}^{010}$$\end{document} indicates the longitudinal optical (LO) phonon frequency along the [010] crystallographic direction. Colored shaded regions in (d), (e), and (f) mark the frequency ranges of different Reststrahlen bands of α-MoO3.
Source publication
One of the main bottlenecks in the development of terahertz (THz) and long-wave infrared (LWIR) technologies is the limited intrinsic response of traditional materials. Hyperbolic phonon polaritons (HPhPs) of van der Waals semiconductors couple strongly with THz and LWIR radiation. However, the mismatch of photon − polariton momentum makes far-fiel...
Citations
... This inherent property impedes the development of photonic devices compatible with on-chip planar fabrication processes. Recently, a natural -MoO 3 crystal, exhibiting inplane hyperbolicity within the mid-IR and terahertz frequency ranges [34], [35], has been identified. This unique crystal sustains in-plane hyperbolic PhPs (HPhPs) and offers a versatile platform for wavefront control, directional canalization, negative refraction, and focusing. ...
Manipulating the propagation of mid-infrared (mid-IR) light is crucial for optical imaging, biosensing, photocatalysis, and guiding photonic circuits. Artificially engineered metamaterials were introduced to comprehensively control optical waves. However, fabrication challenges and optical losses have impeded the progress. Fortunately, two-dimensional van der Waals (vdW) materials are alternatives because of their inherent optical properties, such as hyperbolic behavior, high confinement, low loss, and atomic-scale thickness. In this research, we conducted theoretical and numerical investigations on the α -phase molybdenum trioxide, a biaxial vdW material, with patterned graphene to assess the potential of the tunable focusing of mid-IR light. Our proposed method directly alters the path of excited light to focus mid-IR light by negative refraction. Further, the patterned graphene in our design offers enhanced focusing characteristics, featuring a significantly reduced waist diameter with 1/92 of the free-space wavelength, an enhanced beam quality without pronounced field ripples, and a fivefold increase in field intensity. Moreover, our approach significantly preserves the waist diameter of the focused beam while facilitating directional steering. Thus, the focused beam can propagate in a canalized manner toward the desired direction. These advancements lay the foundation for promising applications in planar photonics.
... Particularly, the terahertz band is a unique frequency band for detecting the early cold universe, the dark universe, and the environment of life in the universe [18]. In recent years, the development of superior optoelectronic materials and innovative sensor structures has promoted advancements in both infrared and terahertz detector fields [19][20][21][22][23][24], and some have even been commercialized [25][26][27][28][29][30]. However, the expanding range of wavelengths that need to be detected makes conventional single infrared or terahertz photodetectors inadequate for meeting the demands of increasingly sophisticated optoelectronic sensing [31,32]. ...
... Researchers have conducted reviews on the progress of photodetectors related to infrared and terahertz topics. However, these reviews either exclusively summarized broadband detectors based In recent years, the development of superior optoelectronic materials and innovative sensor structures has promoted advancements in both infrared and terahertz detector fields [19][20][21][22][23][24], and some have even been commercialized [25][26][27][28][29][30]. However, the expanding range of wavelengths that need to be detected makes conventional single infrared or terahertz photodetectors inadequate for meeting the demands of increasingly sophisticated optoelectronic sensing [31,32]. ...
The growing need for the multiband photodetection of a single scene has promoted the development of both multispectral coupling and broadband detection technologies. Photodetectors operating across the infrared (IR) to terahertz (THz) regions have many applications such as in optical communications, sensing imaging, material identification, and biomedical detection. In this review, we present a comprehensive overview of the latest advances in broadband photodetectors operating in the infrared to terahertz range, highlighting their classification, operating principles, and performance characteristics. We discuss the challenges faced in achieving broadband detection and summarize various strategies employed to extend the spectral response of photodetectors. Lastly, we conclude by outlining future research directions in the field of broadband photodetection, including the utilization of novel materials, artificial microstructure, and integration schemes to overcome current limitations. These innovative methodologies have the potential to achieve high-performance, ultra-broadband photodetectors.
... The experimental results demonstrate that, while the propagation at the real frequencies suffers strong attenuation, the polariton at the complex frequencies experiences almost no decay along the propagation. We next apply the complex frequency approach to investigate the temporal evolution of more complicated field distributions supported by a thin film of van der Waals crystal α-MoO 3 , which is highly anisotropic and supports natural in-plane hyperbolic polaritons [48][49][50][51][52][53][54] . A gold antenna is placed on the MoO 3 film to excite the PhPs, with the atomic force microscopy (AFM) image displayed in Fig. 2 (details in Supplementary Fig. 4). ...
Surface plasmon polaritons and phonon polaritons offer a means of surpassing the diffraction limit of conventional optics and facilitate efficient energy storage, local field enhancement and highsensitivity sensing, benefiting from their subwavelength confinement of light. Unfortunately, losses severely limit the propagation decay length, thus restricting the practical use of polaritons. While optimizing the fabrication technique can help circumvent the scattering loss of imperfect structures, the intrinsic absorption channel leading to heat production cannot be eliminated. Here, we utilize synthetic optical excitation of complex frequency with virtual gain, synthesized by combining the measurements made at multiple real frequencies, to compensate losses in the propagations of phonon polaritons with dramatically enhanced propagation distance. The concept of synthetic complex frequency excitation represents a viable solution to the loss problem for various applications including photonic circuits, waveguiding and plasmonic/phononic structured illumination microscopy.
... α-MoO 3 enables the ultrahigh confinement (≈1/100 of free-space wavelength) and low optical loss [20][21][22][23]. The hyperbolicity of this material can be incorporated into a variety of nanophotonic applications, such as in-plane focusing [24][25][26][27], Cherenkov radiation generation [28,29], tunable polarization notch filters [30], and photonic crystals [31] 46-18.32 μm with an average absorption of 99 %. ...
... Polaritons in hyperbolic materials open up a new way to study near-field optical phenomena [8][9][10][11]. For instance, in-plane hyperbolic phonon polaritons (PhPs) have been reported in layered biaxial vdW materials such as α-MoO 3 , showing exotic propagating characteristics of long lifetimes, low loss, and strong field confinement [12][13][14][15][16][17][18]. These properties have advantages for some long-range transportation of optical information, which could be combined with structured light [19][20][21] to empower unique opportunities for many nanophotonic functionalities, e.g., on-chip optical switching, routers, and transceivers. ...
In recent years, van der Waals (vdW) polaritons excited by the hybrid of matter and photons have shown great promise for applications in nanoimaging, biosensing, and on-chip light guiding. In particular, polaritons with a flatband dispersion allow for mode canalization and diffractionless propagation, which showcase advantages for on-chip technologies requiring long-range transportation of optical information. Here, we propose a flatband polaritonic router based on twisted α-MoO3 bilayers, which allows for on-chip routing of highly confined and low-loss phonon polaritons (PhPs) along multichannel propagating paths under different circular polarized dipole excitations. Our work combines flatband physics and optical spin– orbit coupling, with potential applications in nanoscale light propagation, on-chip optical switching, and communication.
... Previous studies of the NFRHT based on hyperbolic materials (HMs) show that the NFRHF can be promoted in a wide frequency range owing to the excitation of hyperbolic phonon polaritons (HPPs) [37][38][39][40][41][42][43]. HMs are a kind of materials with opposite signs of the permittivity components and exhibit superior hyperbolic dispersion properties [44][45][46][47][48][49]. Specifically, the natural HMs have remarkable advantages because of manifest hyperbolic dispersion without designing into nanostructures. ...
Coupling of surface plasmon polaritons (SPPs) supported by graphene and hyperbolic phonon polaritons (HPPs) supported by hyperbolic materials (HMs) could effectively promote photon tunneling, and hence the radiative heat transfer. In this work, we investigate the polariton hybridization phenomena on near-field radiative heat transfer (NFRHT) in multilayer heterostructures, which consist of periodic graphene/ α -MoO 3 cells. Numerical results show that increasing the graphene/α-MoO 3 cells can effectively enhance the NFRHT when the vacuum gap is less than 50 nm, but suppresses the enhanced performance with larger gap distance. This depends on the coupling of SPPs and HPPs in the periodic structure, which is analyzed by the energy transmission coefficients distributed in the wavevector space. The influence of the thickness of the α-MoO 3 film and the chemical potential of graphene on the NFRHT is investigated. The findings in this work may guide designing high-performance near-field energy transfer and conversion devices based on coupling polaritons.
Recent advances in twisted photonic structures (e.g., twisted bilayer graphene and twisted anisotropic metasurfaces) have enabled many exotic phenomena of light-matter interactions, such as topological transition of the isofrequency contour of surface waves at the magic angle, photonic flatbands, and localization-to-delocalization transition of light. In general, the optical features of these twisted photonic structures are sensitive to the interlayer twist angle. Here we investigate the mode hybridization of surface waves supported by twisted bilayer anisotropic heterometasurfaces, whose two constituent metasurfaces are nonidentical and support surface waves with similar spatial confinements but distinct polarizations. Counterintuitively, we find that the shape of the isofrequency contour of these hybrid surface waves—eigenmodes with both transverse magnetic and transverse electric wave components—can be insensitive to the twist angle, due to the weak interlayer electromagnetic coupling. Moreover, the interlayer distance provides a unique route to reshape the dispersion of one specific kind of hybrid surface wave, while it has negligible influence on the other kinds. Our finding enriches the physics of light-matter interactions in twisted photonic structures and may open new possibilities to mold the flow of light at the subwavelength scale.
We analyze, from first-principles calculations, the excitonic properties of monolayer black phosphorus (BP) under strain, as well as of bilayer BP with different stacking registries, as a base platform for the observation and use of hyperbolic polaritons. In the unstrained case, our results confirm the in-plane hyperbolic behavior of polaritons coupled to the ground-state excitons in both mono- and bilayer systems, as observed in recent experiments. With strain, we reveal that the exciton-polariton hyperbolicity in monolayer BP is enhanced (reduced) by compressive (tensile) strain in the zig-zag direction of the crystal. In the bilayer case, different stacking registries are shown to exhibit hyperbolic exciton polaritons with different dispersion, while also peaking at different frequencies. This renders both mechanical stress and stacking registry control as practical tools for tuning physical properties of hyperbolic exciton polaritons in black phosphorus, which facilitates detection and further optoelectronic use of these quasiparticles.
