Showing papers on "Polarization rotator published in 2023"

Perfect linear polarization wave generator based on quasi-bound states in the continuum.

Abstract: Quasi-bound states in the continuum (q-BICs) in optical metasurfaces have been found to carry special radiation polarization properties. Herein, we have studied the relationship between the radiation polarization state of a q-BIC and the polarization state of the output wave, and theoretically proposed a perfect linear polarization wave generator controlled by the q-BIC. The proposed q-BIC has an x-polarized radiation state, and the y co-polarized output wave is completely eliminated by introducing additional resonance at the q-BIC frequency. Finally, a perfect x-polarized transmission wave with very low background scattering is obtained, and the transmission polarization state is not limited by the incident polarization state. The device can be used to efficiently obtain narrowband linearly polarized waves from non-polarized waves, and can also be used for polarization-sensitive high-performance spatial filtering.

Design of a Transmission-Type Polarization-Insensitive and Angularly Stable Polarization Rotator by Using Characteristic Modes Theory

Abstract: A novel design strategy for realizing a transmission-type polarization rotator of linearly polarized (LP) plane waves by exploiting the characteristic modes (CMs) theory is described. Design guidelines for the excitation of two current modes on a frequency selective surface (FSS), both exhibiting a circularly polarized (CP) radiated field, are provided to obtain the polarization rotation. The proposed converter exhibits remarkable performance also in the case of oblique incidence and a polarization-insensitive response thanks to the FSS unit cell compactness along with its fourfold rotational symmetry. Specifically, it provides a 3 dB cross-polar transmission percentage bandwidth up to 16.5% with a minimum insertion loss (IL) of 0.1 dB for a normally impinging plane wave whereas in case of an incidence angle of 60° the 3 dB cross-polar transmission percentage bandwidth turns out to be around 14% with a minimum IL of 0.7 dB. Measurements on a realized prototype are in good agreement with simulations, confirming the reliability of the proposed theoretical study.

Degree and state of polarization control using Brewster’s law in a nematic liquid crystal

Abstract: We theoretically and experimentally investigate the polarization attributes of reflected light from the surface of a nematic liquid crystal (NLC) cell, having light incident at Brewster’s angle. We observe that the degree of polarization (DOP) of reflected light can be controlled by applying suitable voltage across the NLC cell when the incident light at Brewster’s angle is unpolarized. For incident polarized light, with application of suitable voltage across the NLC cell, the state of polarization (SOP) of the reflected light can also be controlled. The experimentally obtained tunability in DOP and SOP of the reflected light fields is found in reasonably well agreement with theory. This effect, utilizing the well known Brewster’s law, can be exploited for designing light sources and optical devices based on NLCs having voltage controllable tunable polarization features.

Switchable in-phase and out-phase polarization rotation vector solitons in a birefringence-managed fiber laser

Abstract: Nonlinear polarization evolution of vector solitons is an interesting subject in nonlinear science and laser dynamics. Here, we demonstrate two types of switchable multiple polarization rotation vector solitons (PRVSs) in a mode-locked fiber laser through birefringence management. It is found that due to the polarization evolution induced gain competition and mode-coupling effect, the intensities of the two orthogonal polarization components of neighboring solitons differ in each round-trip, manifesting as the out-phase PRVSs. By adjusting the polarization orientation of injecting pulses with respect to the principal axis of polarization-maintaining fiber, neighboring solitons can project equal weight of intensity in two orthogonally-polarized directions, thus switching the out-phase PRVSs to the in-phase PRVSs. Real-time spectral measurement results validate the formation of two PRVSs, and reveal the distinct evolution dynamics. This work provides an effective method to control the polarization state of each soliton in multi-pulses mode-locked fiber lasers, and a potential avenue to introduce polarization-coding in optical soliton communications.

Broadband and CMOS-compatible polarization splitter and rotator built on silicon nitride-on silicon multilayer platform

Abstract: A broadband and CMOS-compatible polarization beam splitter and rotator (PSR) built on the silicon nitride-on-silicon multilayer platform is presented. The PSR is realized by cascading a polarization beam splitter and a polarization rotator, which are both subtly constructed with an asymmetrical directional coupler waveguide structure. The advantage of this device is that the function of PSR can be directly realized in the SiN layer, providing a promising solution to the polarization diversity schemes in SiN photonic circuits. The chip is expected to have high power handling capability as the light is input from the SiN waveguide. The use of silicon dioxide as the upper cladding of the device ensures its compatibility with the metal back-end-of-line process. By optimizing the structure parameters, a polarization conversion loss lower than 1 dB and cross talk larger than 27.6 dB can be obtained for TM-TE mode conversion over a wavelength range of 1450 to 1600 nm. For TE mode, the insertion loss is lower than 0.26 dB and cross talk is larger than 25.3 dB over the same wavelength range. The proposed device has good potential in diversifying the functionalities of the multilayer photonic chip with high integration density.

Birefringent dielectric multi-foci metalens for polarization detection

Abstract: We propose a birefringent dielectric multi-foci metalens for polarization detection utilizing different transmission phases in two orthogonal directions, which consists of Si nanopillars with different sizes and more than 80% transmission efficiency. Implementing the superposition of the phase profiles in the x- and y-direction, the polarization states of the focal points include linear polarization state in the x-direction, linear polarization state in the y-direction, the incident polarization state, and the polarization state whose y-polarization component more shifted by π/2 compared with the incident polarization state. Based on the intensities of the deflected and converged focal points on the same focal plane, the full polarization information of the incident polarized light can be determined with an analyzer. The multiplexing design method with compact and efficient features renders this technique very attractive for polarization detection and information processing.

High Performance Broadband Full Linear Polarimeter based on ReS 2 Nanobelts

Abstract: Polarization-sensitive photodetectors can simultaneously sense the polarization states and intensity of light. Traditional polarimeters integrate photodetectors with complex and bulky optical systems such as polarizers and waveplates, which can not meet the current demand of on-chip polarization photonic devices. This work has demonstrated a full linear polarization polarimeter based on two independent ReS2 nanobelt devices vertically stacked with a designed twist angle. The device achieves a high responsivity (959 A W−1) without applying an external gate voltage. In addition, the ReS2 nanobelt photodetector displays a strong polarization-sensitive photoresponse with a linear dichroic ratio of 1.72 at 665 nm. By utilizing those two vertically stacked nanobelt devices, the linear polarization states of the incident light can be distinguished in a wide range of wavelengths from 590 to 800 nm. This study provides a simple route for future polarization-sensitive optoelectronic devices.

Development of a Stokes vector polarization speckle system for in vivo clinical applications (Conference Presentation)

Abstract: This presentation reports a snapshot polarimetry system, capable of measuring a Stokes vector distribution within a millisecond timescale. The proposed system measures at a perpendicular backscattering angle and features a polarization state analyzer with no moving parts, comprised of a pair of quarter waveplates and pixel polarization cameras. An additional novel design aspect of the system is its capability to register polarization speckle. Polarization speckle contains both polarization and phase information that is not available from conventional techniques. The device’s acquisition speed and small form factor enable future studies of polarization speckle for biomedical applications.

Design of a Reconfigurable Ultra-Wideband Terahertz Polarization Rotator Based on Graphene Metamaterial

Abstract: In this work, a reconfigurable ultra-wideband transmissive terahertz polarization rotator based on graphene metamaterial is proposed that can switch between two states of polarization rotation within a broad terahertz band by changing the Fermi level of graphene. The proposed reconfigurable polarization rotator is based on a two-dimensional periodic array of multilayer graphene metamaterial structure, which is composed of metal grating, graphene grating, silicon dioxide thin film, and a dielectric substrate. The graphene metamaterial can achieve high co-polarized transmission of a linearly polarized incident wave at the off-state of the graphene grating without applying the bias voltage. Once the specially designed bias voltage is applied to change the Fermi level of graphene, the polarization rotation angle of linearly polarized waves is switched to 45° by the graphene metamaterial at the on-state. The working frequency band with 45-degree linear polarized transmission remaining above 0.7 and the polarization conversion ratio (PCR) above 90% is from 0.35 to 1.75 THz, and the relative bandwidth reaches 133.3% of the central working frequency. Furthermore, even with oblique incidence at large angles, the proposed device retains high-efficiency conversion in a broad band. The proposed graphene metamaterial offers a novel approach for the design of a terahertz tunable polarization rotator and is expected to be applied in the applications of terahertz wireless communication, imaging, and sensing.

Wideband switchable linear polarization rotator based on metasurface

Abstract: The realization of dynamic polarization rotation based on the metamaterial or metasurface is always a concerned issue in electromagnetic manipulation. In this Letter, a transmission-type switchable metasurface is proposed, which can rotate the linear polarized (LP) wave to arbitrary angle among ±45° in a wide frequency band. The polarization rotation metasurface (PRM) consists of a polarization conversion surface and a partially reflective surface. By controlling the resistances of PIN diodes, the PRM can change the polarization angle of transmitted LP wave. To verify the design, a prototype of the proposed PRM is fabricated and tested, and the simulated and measured results are in good agreement. According to the measured results, the fractional bandwidth at each state of prototype is larger than 20.4%. The overlapping operational band of the prototype is from 3.03 to 3.60 GHz, where the transmission coefficient remains higher than –2 dB, and the axial ratio of transmitted wave is higher than 15 dB. The proposed design may have the application potential in target detection, wireless communication, and polarimetric imaging.

Electrical Polarization Control of VCSEL Based on Orthogonal Switching Liquid Crystal Layer

Abstract: Stable polarization has been regarded as a key element for improving the beam quality of vertical cavity surface emitting lasers (VCSELs). However, gain isotropy in the active layer of VCSELs ineluctably leads to the uncertainty of the polarization direction. In this paper, a liquid crystal (LC)-VCSEL laser with polarization control characteristics is designed and fabricated based on the optical rotation effect and electrically controlled birefringence characteristics of orthogonal LC. The experimental results show that, electrically controlled LC could flexibly realize the scheme of polarization stable output and the switching ratio of polarization output could reach 164:1. Based on the electrically controlled birefringence characteristics of LC, the linear polarization angle of VCSEL is further regulated by applying a deflection voltage, and the polarization angle tuning range is between 0° and 90°.

Black Phosphorus‐Based Absorbing Bionic Stacked Structured Linear Polarization Detector

Abstract: Polarization detection technology is developing toward miniaturization and high integration from the early time‐division type, amplitude‐division type, aperture‐division type, etc., to a more integrated focal plane‐integrated array type. Focal plane detectors that rely on metal nanogrids are not able to guarantee both temporal and spatial resolution for lossless polarized light detection with a guaranteed level of integration. Inspired by Agabus japonicus, the black phosphorus (BP)‐based absorbing bionic stacked structured linear polarization detector (BSLD) is proposed. The BSLD exploits the polarization absorption properties of BP to achieve near‐lossless linear polarization detection. The design includes two orthogonally aligned polarization‐ and angle‐sensitive BP photodetectors. The detection performance of the detector is investigated and analyzed under a green laser beam (wavelength 532 nm). The BSLD designed in this paper can simultaneously measure the multi‐angle component information of the incident light at one point in space in order to resolve the polarization state of the incident light, providing a potential solution for an integrated, real‐time, and high‐resolution loss‐free polarization image sensor.

Broadband terahertz linear cross-polarization conversion in transmission mode using planar coupled metamaterials

Abstract: We demonstrate a metamaterial (MM) design capable of showing linear broadband polarization conversion over the terahertz (THz) frequency range. The building block of the proposed MM structure is composed of a strip and four split ring resonators (SRRs), which are coupled through their near fields. To examine co- and cross-polarization transmission amplitudes, we gradually increase the distance between the strip and SRRs. When the SRRs are near (S = 2 [Formula: see text]m) the strip, maximum cross-polarization conversion is attained with a resonance mode hybridization effect in the co-polarization transmission due to strong near-field coupling between the strip and SRRs. When the SRRs moved away from the strip (S = 22 [Formula: see text]m), minimum cross-polarization conversion is attained due to weak coupling between the strip and SRRs. This MM system exhibits a transition from a strongly coupled state to a weakly coupled state with the rise in displacement between the strip and SRRs. The ability to tune the linear polarization conversion can be useful in the improvement of efficient THz polarization rotation devices. The proposed MM structure can be used in other frequency domains, like the microwave and visible range, by scaling up/down the structure.

Control over polarization of vertically emitting random lasers based on dye doped nematic liquid crystals by applying a transverse electric field locally

Abstract: Flexible control over random lasers (RLs) is highly desired. In this manuscript, a control over the polarization of random lasing emitted vertically from dye doped nematic liquid crystal (NLC) cell by the transverse component of a local ac electric field was demonstrated. The polarizing direction of the RL could be tuned continuously and monotonously with the increase of the field strength, from the direction along the NLC director without an applied electric field. The maximum rotation angle of the polarizing direction reached nearly 90° at the applied voltage of 200 V (root-mean-square value) across the 230 μm wide slit. The degree of polarization declined from 1 at zero voltage, and after reaching the minimum rose with the field strength. The lasing spectrum consists of sharp spikes corresponding to the resonant modes for all the applied voltages. The mechanisms responsible for electrically tuning the polarization of the RL were discussed. Optimizing the voltage characteristic of the polarization tunability was suggested by the preliminary experimental results.

A multifunctional broadband polarization rotator based on reflective anisotropic metasurface

Abstract: In this paper, both linear cross-polarization conversion (CPC) and linear-to-circular or circular-to-linear polarization conversion based on a single reflective anisotropic metasurface are realized and experimentally demonstrated. The multifunctional CPC metasurface in the frequency range of 5.9-6.4 GHz and 8.7-17.7 GHz has a fractional band of 68.2%, and the efficiency reaches almost 100% under plasma resonance. In addition, the metasurface acts as a high efficiency circular-polarizer in the range of 6.7–8.4 GHz. Moreover, the polarization transforming functionality of the structure is stable for the change of incident angle for both x-polarized or transverse-electric (TE) and y-polarized or transverse-magnetic (TM) illumination up to 45∘. It can be seen that the anticipated hypersurface has potential applications in reflector antenna, satellite communication and radar.

Electro-tunable Metasurface for Tri-State Dynamic Polarization Switching at Near-Infrared Wavelengths

Abstract: Control of polarization states of light is crucial for any photonic system. However, conventional polarization-controlling elements are typically static and bulky. Metasurfaces open a new paradigm to realize flat optical components by engineering meta-atoms at sub-wavelength scale. Tunable metasurfaces can provide enormous degrees-of-freedom to tailor electromagnetic properties of light and thus have the potential to realize dynamic polarization control in nanoscale. In this study, we propose a novel electro-tunable metasurface to enable dynamic control of polarization states of reflected light. The proposed metasurface comprises a two-dimensional array of elliptical Ag-nanopillars deposited on indium-tin-oxide (ITO)-Al2O3-Ag stack. In unbiased condition, excitation of gap-plasmon resonance in the metasurface leads to rotation ofx-polarized incident light to orthogonally polarized reflected light (i.e.,y-polarized) at 1.55μm. On the other hand, by applying bias-voltage, we can alter the amplitude and phase of the electric field components of the reflected light. With 2 V applied bias, we achieved a linearly polarized reflected light with a polarization angle of -45°. Furthermore, we can tune the epsilon-near-zero wavelength of ITO at the vicinity of 1.55μm wavelength by increasing the bias to 5 V, which reducesy-component of the electric field to a negligible amplitude, thus, resulting in anx-polarized reflected light. Thus, with anx-polarized incident wave, we can dynamically switch among the three linear polarization states of the reflected wave, allowing a tri-state polarization switching (viz.y-polarization at 0 V, -45° linear polarization at 2 V, andx-polarization at 5 V). The Stokes parameters are also calculated to show a real-time control over light polarization. Thus, the proposed device paves the way toward the realization of dynamic polarization switching in nanophotonic applications.

Local polarization properties extraction using single incident state, single-mode-fiber-based spectral domain polarization-sensitive optical coherence tomography.

Abstract: We showed the local polarization properties extraction method for the single incident state, all-single-mode-fiber-based spectral domain polarization-sensitive optical coherence tomography (SD-PS-OCT) system that uses the single linear-in-wavenumber spectral camera. Polarization controllers are used in the single-mode-fiber-based SD-PS-OCT system to provide a compact structure with polarization state stability. The local polarization properties of the birefringent sample are extracted from the cumulative polarization properties iteratively. The reconstructed polarization images demonstrate the local polarization properties extraction ability of the system.

Polarization splitter and rotator, and an optical demultiplexer for a polarization-diverse silicon photonic receiver

Abstract: We propose a polarization-diverse receiver for coarse wavelength division multiplexing. We fabricated polarization splitters and rotators as well as demultiplexers. The combined insertion loss and crosstalk were less than 4.0 dB and −10 dB, respectively.

Polarization dynamics in spin‐VCSELs with integrated surface grating for high birefringence splitting

Abstract: Polarization dynamics in spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) with high birefringence have recently been demonstrated to offer very high potential for optical data-transmission systems that outperform their counterparts based on conventional direct current modulation by far. For polarization dynamics in spin-VCSELs, the birefringence determines the resonance frequency and thus the modulation bandwidth. In previous work, birefringence was controlled using mechanical strain, which lacks the ability to be integrated in standard VCSEL manufacturing processes. In this work the polarization dynamics of a VCSEL with an integrated birefringence control mechanism is demonstrated based on custom designed integrated surface gratings. It is found that, despite the surface grating which is commonly known to stabilize the polarization, the presented spin-VCSELs are able to generate polarization oscillations with frequencies corresponding to the birefringence induced by the surface grating and show polarization dynamics up to 68 GHz.

Highly efficient and tunable polarization rotator based on lithium niobate on an insulator.

Abstract: The lithium niobate on an insulator (LNOI) platform has greatly advanced the development of integrated photonics recently, where efficient polarization management components are indispensable. In this work, we propose a highly efficient and tunable polarization rotator based on the LNOI platform and the low-loss optical phase change material antimony triselenide (S b 2 S e 3). The key polarization rotation region is formed by a LNOI waveguide with a cross section of the double trapezoidal shape and a S b 2 S e 3 layer deposited atop the LNOI waveguide in an asymmetrical way, where an isolating layer of silicon dioxide is sandwiched between them to reduce the material absorption loss. Based on such a structure, we have achieved the efficient polarization rotation in a length of only 17.7 µm, where the polarization conversion efficiency and insertion loss are 99.6% (99.2%) and 0.38 dB (0.4 dB) for the trans-electric (TE)-to-trans-magnetic (TM) rotation. If we further change the phase state of the S b 2 S e 3 layer, other polarization rotation angles besides 90° can also be obtained for the same device, revealing a tunable function. We believe that the proposed device and design scheme could offer an efficient method for realizing the polarization management on the LNOI platform.