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Abstract and Figures
We propose an optical wave plate using a metal nano-grid. The wave plate operates in reflection mode. A single-mode truncated modematching theory is presented as a general method to design such nano-grid wave plates with the desired phase difference between the reflected TM and TE polarizations. This analytical theory allows angled incidence calculations as well, and numerical results agree-well with comprehensive finite-difference time-domain electromagnetic simulations. Due to the subwavelength path-length, the reflective wave plate is expected to have improved broad-band functionality over existing zero-order transmissive wave plates, for which an example is provided. The proposed wave plate is simple and compact, and it is amenable to existing nanofabrication techniques. The reflective geometry is especially promising for applications including liquid-crystal displays and laser feedback experiments.
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... Metal oxidation after LIPSS processing is usually not studied or reported. However, in optical applications, and specifically in SWG, it is to expect an influence of the refractive index of the material [45]. Additionally, changes in the refractive index of other materials with different degrees of oxidation have been reported [46]. ...
... The observed behavior of the samples concerning change in polarization is in agreement with subwavelength gratings causing phase retardation [9,45], so our conclusion is that these properties must be caused by the LIPSS, with their geometry or composition being the key factor to their specific optical behavior. ...
... By changing the processing parameters, we can control these factors, as shown in this work, and therefore tailor the properties of the resulting polarization grating. Other factors could be studied as well, such as changes in height, which is another property of polarization gratings that influence the polarization change [45]. ...
A fast and reliable method for the fabrication of polarization modifying devices using femtosecond laser is reported. A setup based on line focusing is used for the generation of LIPSS on stainless steel, processing at different speeds between 0.8 and 2.4 mm/s with constant energy per pulse of 1.4 mJ. SEM and AFM characterizations of the LIPSS show a progressive increase in period as the processing speed increases, while height remains approximately constant in the studied range. Optical characterization of the devices shows an induced change in the polarization of the reflected beam that varies with the processing speed, which allows a controlled fabrication of these devices.
... Metal oxidation after LIPSS processing is usually not studied or reported. However, in optical applications, and specifically in SWG, it is to expect an influence of the refractive index of the material [45]. Additionally, changes in the refractive index of other materials with different degrees of oxidation have been reported [46]. ...
... The observed behavior of the samples concerning change in polarization is in agreement with subwavelength gratings causing phase retardation [9,45], so our conclusion is that these properties must be caused by the LIPSS, with their geometry or composition being the key factor to their specific optical behavior. ...
... By changing the processing parameters, we can control these factors, as shown in this work, and therefore tailor the properties of the resulting polarization grating. Other factors could be studied as well, such as changes in height, which is another property of polarization gratings that influence the polarization change [45]. ...
Surface nanostructuring has received increasing attention in recent years due to the wide range of applications in which it offers advantages. Particularly, Laser-Induced Periodic Surface Structures (LIPSS) have proven useful for surface functionalization. LIPSS are periodic formations generated in most materials when irradiated with linearly polarized radiation. The orientation of these structures is directly linked to the polarization of the incident light, while other parameters of their morphology such as period and depth can be controlled with the number of pulses, fluence, wavelength and pulse duration of the incident light.
... Hence, alternative principles of optical wave retardation by nanostructures are of great interest. Previously, also nanopatterned metal surfaces have been demonstrated to provide wave retardation for reflected light [14][15][16][17]. However, they cannot be used in the usually more convenient transmission mode. ...
... On the other hand, for TM polarization (along the x axis), the boundary conditions are different and the field is approximately transversely uniform in the dielectric region, giving an effective refractive index n TM ≈ n d . With realistic metal that does not conduct perfectly, both modes slightly penetrate into the metal, and the TM mode is slightly concentrated on the metal surfaces due to coupling to surface plasmon polaritons [14]. ...
... where k 0 is the wavenumber in vacuum [14]. These are valid for the fundamental, symmetric TE and TM modes that do not have electric-field nodes at the centers of the dielectric and metal parts. ...
Wave retarders, including quarter- and half-wave plates, are used in many optical systems for polarization conversion. They are usually realized with anisotropic crystalline materials. However, much thinner and possibly also less expensive wave plates can be made of micro- and nanostructures. We present a new way to create thin-film optical retarders based on a highly birefringent metamaterial. The wave plate is capable of low-loss, broadband operation, which we verify both numerically and experimentally. Owing to the remarkable simplicity of our design, the wave plates operating on the proposed principle can meet the requirements of large-scale production and find widespread application in optics and photonics.
... Metal oxidation after LIPSS processing is usually not studied or reported. However, in optical applications, and specifically in SWG, it is to expect an influence of the refractive index of the material [45]. Additionally, changes in the refractive index of other materials with different degrees of oxidation have been reported [46]. ...
... The observed behavior of the samples concerning change in polarization is in agreement with subwavelength gratings causing phase retardation [9,45], so our conclusion is that these properties must be caused by the LIPSS, with their geometry or composition being the key factor to their specific optical behavior. ...
... By changing the processing parameters, we can control these factors, as shown in this work, and therefore tailor the properties of the resulting polarization grating. Other factors could be studied as well, such as changes in height, which is another property of polarization gratings that influence the polarization change [45]. ...
Birefringence induced by nanoripples generated by laser (Laser Induced Periodic Surface Structures, LIPSS), enables their use as polarization gratings. Their fabrication is simple, as LIPSS geometry is defined by the characteristics of the laser and the substrate in a one-step process. In this work LIPPS generated on stainless steel have been used to measure the change in polarization of the light reflected on them. Parameters such as period, depth or width of the ripples define the optical properties of these polarization gratings. As the fabrication parameters change, results show a gradual change in polarization. Our experiments, performed with a setup based in cylindrical focusing lens, demonstrate the fast fabrication of samples for different applications, such as waveplates.
... The ability of a QWP hinges on its capacity to induce an exact phase shift, which is contingent on the birefringence of the structure. Grating structures have been extensively studied in the literature [53][54][55][56][57]. Building upon this, we design a grating-based QWP. ...
Metamaterial-based quarter-wave plates (QWPs) have emerged as promising candidates for advanced polarization control in a variety of optical applications, owing to their unique properties, such as ultra-thin profiles and tailored spectral responses. We design an ultra-thin, high-efficiency, and broadband QWP in transmission mode based on a TiO2/Au grating structure. We show that multiple reflections and the near-field effects associated with the integration of these devices pose challenges that must be considered when combining multiple metamaterials. We present insights that facilitate improved design methodology and the optimization of integrated metamaterial QWPs and other metadevices. Our results contribute to the development of miniaturized and high-density advanced lightwave and polarization control devices in optical systems.
... The width, height and separation of the nanostripes are w, h and d, respectively. We start by assuming that the height h of the stripes is infinite and calculate the effective refractive indices n TE and n TM for fundamental TE and TM modes of the structure using the following equations [33]: ...
We consider a highly anisotropic metamaterial structure, composed of parallel metal nanostripes, and show that a thin layer of the material can be used as a tunable partial polarizer. The transmittance of the structure for TE-polarized waves depends strongly on the incidence angle, while for TM-polarized waves, it stays high and essentially constant. In particular, using the structure, the degree of polarization of a partially polarized or unpolarized light can be tuned by changing the incidence angle. The TE-wave transmittance drops from, c.a., 1 to 0 when the incidence angle increases by 5 deg only, owing to the presence of an unusual higher-order odd-symmetric TM mode that we have revealed in the structure. The tuning can be made smoother by introducing another layer of a similar metal-nanostripe structure on top of the first one. The new design allows the TE-wave transmittance to decrease gradually towards 0 with the incidence angle increasing from 0 to about 30 deg. Our structures serve as an essential optical component for studies involving partially polarized light.
... In this case, we anticipate only low absorption during the UC process because the electric field is weak near the surface of the mirror where the UC layer is placed. However, the metamaterial mirror can locate the maximum of the electric field near the surface of the metal by controlling the phase of reflected light [5,9,[11][12][13][14]. Since the highly concentrated electric field is in the UC layer, the absorption and emission of UC material can be enhanced by stronger light-matter interactions and the Purcell effect, respectively. ...
Because of finite bandgap, useful spectral ranges of semiconductors are limited for photovoltaic applications. The upconversion (UC) process is one of alternatives to extend the useful spectral range by converting long wavelength photons to short wavelength photons. For example, NaYF4 codoped Yb³⁺/Er³⁺ converts photons from near-infrared (970 nm) to visible (660 nm). However, in the form of a thin layer on a flat metal mirror, which is a representative structure to add UC layer into photovoltaic devices, the UC material exhibits low efficiency in optical devices because of its low absorption and conversion efficiencies. In this paper, the UC process is highly enhanced by a metamaterial mirror consisting of grooved silver surfaces. The absorption of UC material is improved by a factor of 5.3 due to increased light-matter interaction because the electric field is highly concentrated in the UC layer near the metal surface. The surface plasmon polariton (SPP) modes induced by a dipole emitter to a metal grooved surface enhance the spontaneous emission (SE) rate of the emission wavelength of UC material by a factor of 65 compared with a thin UC layer on flat mirror. Consequently, total efficiency of the UC process is 400 times more enhanced than the reference structure by magnetic mirror property and SPP modes of metamaterial mirror.
We propose a novel cross bowtie antenna using phase-shift lines to realize circular polarization (CP) in the infrared (IR) spectrum. The CP antenna consists of a vertical, a horizontal antenna, and two elliptical loops connecting adjacent tips of the antennas to create a 90° phase shift. The phase-shift lines are conceived to realize a single terminal of the antenna where a detecting material can be mounted and enable the detecting material to fully utilize the field enhancement from the antenna. In full-wave simulations, a nanometer-scale low-bandgap semiconductor, i.e., indium gallium arsenide antimonide (InGaAsSb) capable of detecting IR wave is loaded at the antenna terminal and the antenna structure is designed to achieve CP absorption at 180 THz. The antenna includes a transmission line-based impedance matching structure to compensate for the reactance of the InGaAsSb semiconductor load. To verify the CP detection of the antenna near 180 THz, we numerically show a higher field enhancement value and absorption rate in the antenna terminal in a specific CP case when the antenna is illuminated with incident waves with various polarization states. Also, we design 2 × 1 and 2 × 2 antenna arrays using the CP antennas connected with metallic traces and show that the CP absorption at 180 THz is maintained. Finally, an illustration of a focal plane array based on the proposed CP cross bowtie antennas coupled with the InGaAsSb for a full Stokes polarimeter is presented.
Broadband nanowire-grid polarizers were designed and numerically simulated using the finite difference time domain (FDTD) method. Using a broadband stimulation source, optical properties of the polarizers were analyzed in the ultraviolet (UV)-visible-near infrared (NIR) regions. Specifically, the extinction ratios and optical transmittances of transverse magnetic (TM) and transverse electric (TE) modes were characterized for different metal materials and geometrical parameters including wire-grid periods, metal-wire fill ratios, and spacing between wire-grid layers. Based on the simulation results, an extra broadband polarizer with an average extinction ratio higher than 70 dB and transmission efficiency over 64% in the range of 0.3 to 5 mum was proposed.
We have fabricated, characterized and theoretically analyzed the performance of bilayer (or stacked) metallic wire-grids. The samples with 100 nm period were fabricated with extreme-ultraviolet interference lithography. Transmission efficiency over 50% and extinction ratios higher than 40 dB were measured in the visible range with these devices. Simulations using a finite-difference time-domain algorithm are in agreement with the experimental results and show that the transmission spectra are governed by Fabry-Perot interference and nearfield coupling between the two layers of the structure. The simple fabrication method involves only a single lithographic step without any etching and guarantees precise alignment and separation of the two wire-grids with respect to each other.
A useful polarizer for the 6-µ to 20-µ region has been designed, fabricated, and tested. A microscopic wire grid was formed by ruling Irtran 2 (ZnS) or Irtran 4 (ZnSe) and evaporating aluminum preferentially on the groove tips. The average transmittance for the crossed polarizers in the 8-µ to 20-µ region was less than 1%. The degree of polarization was insensitive to a wide range of incidence angles. Data showing the spectral polarization efficiency as a function of wavelength are presented.
Both high contrast and high transmittance are preferred for optical polarizers. To achieve high transmittance for aluminum nanowire-grid polarizers, a narrow linewidth is required. In this letter, aluminum nanowire-grid polarizers with 30-nm-wide linewidth and 200 nm depth were fabricated by UV-nanoimprint lithography, which leads to ultrahigh transmittance. To achieve a high contrast, the authors fabricated the 30-nm-wide aluminum nanowire structures on both sides of the glass wafers. An extremely high contrast up to 10 000:1 was achieved, in the visible range, along with good transmittance of 83%–87% for the double-side aluminum nanowire-grid polarizers.
We developed an integrated circular polarizer based on stacking an aluminum nano-wire grid polarizer with a dielectric nano-grating-based quarter waveplate. The polarizer consists of 65 nm wide and 130 nm tall aluminum wires with a period of 148 nm. For integration, the aluminum nanowires were buried into a silicon dioxide matrix by a trench filling and planarization technology. The buried nanowire polarizer achieved excellent optical performance in a broad wavelength range from 400 nm to ≫900 nm . On top of the buried and planarized nanowire polarizer, a visible quarter waveplate based on a 200 nm period silicon nitride nano-grating was fabricated. Both the 148 nm period aluminum grating and the 200 nm period silicon nitride grating were fabricated by an ultraviolet (UV)-nanoimprint lithography. The ability to integrate multiple nanostructure-based optical layers opens a path for novel integrated optical devices, as well as a new strategy for driving both miniaturization and cost.
We report optical transmission and reflection spectral measurements in the visible and near infrared on a one-dimensional transmission grating having a metal film deposited on deep rectangular subwavelength grooves etched in quartz. Measurements are made for both classical and conical diffraction geometry by varying the azimuthal angles (φ) between the plane of incidence and the grating vector. Strong differences for transverse electric (TE) and transverse magnetic (TM) polarized light are seen. We find conditions under which the transmission is negligible irrespective of light polarization and angle of incidence. The transmission spectra show deep dips corresponding to excitation of surface plasmons by TM polarized light when φ=0° , by both TE and TM light when 0°≪φ≪90° and by TE light for φ=90° . We also examine the reciprocity behavior of the optical properties for incidence from the metal and substrate sides and dependence on light polarization.
Polarization self‐modulation at frequencies up to 6 GHz is observed in a vertical‐cavity surface‐emitting laser. This self‐oscillation is observed when a portion of the laser output power is injected back into the laser after having rotated its polarization by 90° with respect to the initial laser polarization state. Our experiment demonstrates a simple technique for generating an ultrahigh frequency optical clock. New applications in optical storage are also envisioned.
A new reflective dichroic display device is described. The only components include a quarter‐wave retarder positioned between an aligned dichroic nematic liquid‐crystal display cell and a diffuse metallic reflector. This configuration allows both polarizations of incident light to be absorbed without affecting the polarizer‐free high brightness voltage activated state.
A chromium wire‐grid duplexer polarizer for CO 2 lasers has been developed using holographic and chemical etching techniques. The reflection and transmission measurements show reasonably good agreement with the theory.
A nematic polymer liquid crystal is used to construct wave plates for use at 1054 nm. Three methods of wave-plate construction are discussed: double substrate with fiber spacers in homogeneous distribution, double substrate with fiber spacers in annular distribution, and single substrate. The polymer liquid crystal shows high laser-damage resistance, making it particularly useful for high-peak-power laser applications. Alignment techniques and measurement of birefringence for the highly viscous polymer are described.