Compact Polarization Research Articles

Generalized polarization transformations with metasurfaces.

Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control the many degrees-of-freedom of light on an unprecedented scale. In this work, we design meta-gratings where the diffraction orders can perform general, arbitrarily specified, polarization transformation without any reliance on conventional polarization components, such as waveplates and polarizers. We use matrix Fourier optics to design our devices and introduce a novel approach for their optimization. We implement the designs using form-birefringent metasurfaces and quantify their behavior - retardance and diattenuation. Our work is of importance in applications, such as polarization abberation correction in imaging systems, and in experiments requiring novel and compact polarization detection and control.

Broadband and CMOS compatible polarization splitter-rotator based on a bi-level taper.

A silicon-on-insulator polarization diversity scheme is proposed. Based on an asymmetrical evanescent coupler, a broadband and compact polarization splitter-rotator comprising mode conversion tapers and mode sorting asymmetric Y junctions is optimized with silicon dioxide upper cladding and a silicon nitride waveguide. The simulation results show mode conversion loss is less than 0.2 dB, and the extinction ratio is lower than -17dB in the wavelength range of 1.48µm to 1.67µm.

Intrinsic Linear Dichroism of Organic Single Crystals toward High-Performance Polarization-Sensitive Photodetectors.

The ability to detect light in photodetectors is central to practical optoelectronic applications, which has been demonstrated in inorganic semiconductor devices. However, so far, the study of polarization-sensitive organic photodetectors, which have unique applications in flexible and wearable electronics, has not received much attention. Herein, the construction of polarization-sensitive photodetectors based on the single crystals of a superior optoelectronic organic semiconductor, 2,6-diphenyl anthracene (DPA), is demonstrated. The systematic characterization of two-dimensionally grown DPA crystals with various techniques definitely show their strong anisotropy in molecular vibration, optical reflectance and optical absorption. In terms of polarization sensitivity, DPA-crystal based photodetectors exhibit a linear dichroic ratio up to ≈1.9. Theoretical calculations confirm that intrinsic linear dichroism, originated from the anisotropic in-plane crystal structure, is responsible for the polarization sensitivity of DPA crystals. This work opens up a new door for exploiting organic semiconductors for developing highly compact polarization photodetectors and providing new functionalities in novel flexible optical and optoelectronic applications.

Development and optimization of microwave guide polarizers using equivalent network method

In this article, we have developed a new mathematical model of a microwave square guide polarization converter with diaphragms. The applied model was created using the microwave theory of equivalent networks. The novelty of the developed theoretical model consists in its possibility to take into account the thickness of the diaphragms. This feature is achieved by using more accurate but complicated T- and Π-shaped equivalent networks. Theoretical analysis and optimization of a guide polarizer were performed using the scattering and transmission matrices of the diaphragms in a square guide. The parametric optimization of a guide polarizer was performed by means of the developed equivalent networks and using finite elements method in the frequency domain. The optimal sizes and electromagnetic characteristics of the polarizer, which were obtained by both methods, are in good agreement. The main advantage of the suggested mathematical model consists in the calculation time reduction. Developed compact waveguide polarizer can be used in modern satellite and radar antenna systems with circular polarization of applied electromagnetic waves.

Compact common-path polarisation holographic microscope for measuring spatially-resolved Jones matrix parameters of dynamic samples in microfluidics

In this study, we propose a compact four-channel angular-multiplexing polarisation holographic microscope to quantify the spatially resolved Jones matrix of a dynamic sample in a microfluidic channel. To make the imaging system compact, a common-path off-axis configuration based on a simple object and a reference beam generator unit, consisting of a Wollaston prism and a converging lens, was introduced in the holographic microscope. Using this system and the retrieval method described in this paper, the spatially resolved Jones matrix parameters, as well as the polarisation information, including the diattenuation and phase retardation, of the target sample could be simultaneously retrieved from a single-shot hologram. We experimentally demonstrated the feasibility of our method by quantitatively measuring the birefringence parameters of a quarter-wave plate and extracting the 2-D Jones matrix and polarisation parameters of potato starch particles and C. elegans worms. The simple optical structure and common-path design reduce the system requirements for light source coherence and system stability, which provides a feasible approach for the development of a portable polarisation holographic microscope for microfluidics.

Circular Waveguide Polarizer for Weather Radars and Satellite Information Systems

This research presents the design and main electromagnetic characteristics of the novel compact microwave waveguide polarizer. The developed device's structure is based on a circular waveguide and anti-phase conducting posts located in it. The application of a circular waveguide instead of a square one allowed simple integration of a polarizer with corrugated horn antennas. The obtaining of required phase difference using a posts-based design provides the possibility of fine tuning of the developed circular waveguide polarizer after its manufacturing process. In addition, simultaneous adaptive operation at orthogonal circular and linear polarizations is available in the antenna system including a polarizer with posts. An automatic control of posts height must be applied in a waveguide in order to provide this option. Numerical simulation, optimization, manufacture and measurements of the polarizer's characteristics were carried out in the operating band 7.4-8.5 GHz. Measured characteristics proved that the suggested circular waveguide polarizer provides good matching and polarization performance. Developed circular waveguide polarizer can be integrated in corrugated horn antenna systems and applied in modern weather radars and satellite information systems.

High-performance and fabrication friendly polarization demultiplexer

A compact and fabrication friendly polarization demultiplexer (P-DEMUX) is proposed and characterized to enable wavelength-division-multiplexing and polarization-division-multiplexing simultaneously. The proposed structure is composed of a polarization-selective microring resonator in ultrathin waveguide and two bus channels in the silicon nitride-silica-silicon horizontal slot waveguides. In the slot waveguide, the transverse electric (TE) mode propagates through the silicon layer, while the transverse magnetic (TM) mode is confined in the slot region. In the designed ultra-thin waveguide, the TM mode is cut-off. The effective indexes of the TE modes for ultrathin and slot waveguides have comparable values. Thanks for these distinguishing features, the input TE mode can be efficiently filtered through the ultra-thin microring at the resonant wavelength, while the TM mode can directly output from the through port. Simulation results show that the extinction ratio of the proposed P-DEMUX for TE and TM modes are 33.21 dB and 24.97 dB, and the insertion losses are 0.346 dB and 0.324 dB, respectively, at the wavelength of 1551.64 nm. Furthermore, the device shows a broad bandwidth (>100 nm) for an extinction ratio (ER) of >20 dB. In addition, the proposed P-DEMUX also has a good fabrication tolerance for the waveguide width variation of –20 nm ≤ Δ w g ≤ 20 nm and the microring width variation of –20 nm ≤ Δ w r ≤ 20 nm for a low insertion loss of <0.75 dB and low ER of <–18 dB.

Low loss and high extinction ratio all-silicon TM-pass polarizer with reflection removal enabled by contra-mode conversion Bragg-gratings

Bragg-gratings have been frequently used to design compact and high extinction ratio (ER) on-chip polarizers. However, the strong reflection of the unwanted polarization may deteriorate the performance of the light source or cause unwanted interferences. In this paper, we propose a Bragg-grating-based all-silicon TM-pass polarizer with low reflection, low insertion loss (IL) and high ER. Unlike previously reported polarizers based on single mode waveguides, we construct the Bragg grating with a multimode waveguide, which not only acts as a Bragg reflector, but also a mode-order converter to convert the reflected TE light into higher order modes to be eventually filtered out by utilizing a tapered transition. On the other hand, the grating has little adverse influence on the TM input light since it works at sub-wavelength-guided wave propagation regime. Finally, the polarizer obtained has a length of 30µm, an ER of 51.83dB, an IL of 0.08dB, and an operating bandwidth of ∼61nm for ER > 30dB at the wavelength of 1.55µm. More importantly, the reflection of the unwanted polarization is suppressed to -12.6dB, which can be further lowered via additional design optimization. Our work points to a new direction for making better on-chip polarizers.

Compact Lithium-Niobate-on-Insulator Polarization Rotator Based on Asymmetric Hybrid Plasmonics Waveguide

We proposed a compact and efficient polarization rotator (PR) based on an asymmetric hybrid plasmonics waveguide (HPW) on the lithium-niobate-on-insulator (LNOI) platform. We focus on the design of rotation angle and balance between the two hybrid modes. The presented device exhibits a polarization extinction ratio as high as 59.58 dB and an insertion loss of 1.44 dB with the rotation length of only 13.7 μm. The fabrication tolerances and a suitable process are also discussed to meet the state-of-art technology.

A Compact Low-Loss Broadband Polarization Independent Silicon 50/50 Splitter

We present a low-loss, compact, polarization insensitive 3-dB optical power-splitter for submicron silicon waveguides. The splitter is optimized over a broad wavelength span ranging from 1300 to 1700 nm through finite difference time domain simulations. The splitter junction footprint is only 1.8 × 1.3 μm, which is smaller than previously reported broadband multimode junction splitters. Furthermore, the demonstrated device overcomes the fabrication limitations of previous splitters while maintaining a compact size without any sharp angles. The device was fabricated using electron beam lithography. The experimental results show a small insertion loss of less than 0.3 dB for both the TE and TM polarizations.

Comparative Analysis of Compact Satellite Polarizers Based on a Guide with Diaphragms

In this article we carry out the comparative analysis of new compact satellite polarisers based on a square guide with diaphragms. The main electromagnetic parameters of the developed microwave guide devices with various amount of diaphragms were obtained within the satellite frequency interval from 10.7 GHz to 12.75 GHz. Waveguide polarization converters with different amount of diaphragms from 2 to 5 have been designed and optimized. The main parameters of the presented polarizer were calculated applying the numerical method of finite integration in the frequency domain. Optimization of the electromagnetic parameters of the developed waveguide devices was carried out using the software CST Microwave Studio. As a result, sizes of the device designs have been optimized for the provision of improved polarization and phase parameters. The performed analysis showed that a waveguide polarizer with five diaphragms has the best electromagnetic parameters. The developed compact polarizer with five diaphragms based on a square guide provides a minimum deviation of the output phase difference from 90 degrees and high level of isolation between linear polarization over the entire operating frequency range. Presented in the article compact waveguide polarization converters can be applied in satellite systems, which require efficient polarization separation of signals.

Metalens‐Assisted System for Underwater Imaging

AbstractThe ability to image under water is highly desirable for a variety of applications including biological monitoring and seafloor survey, yet the image quality is usually hampered by the presence of scattering medium in water. Polarization imaging has proven to be an effective method for image enhancement; however, conventional systems require mechanically rotating polarizers which compromises the system's footprint or a set of polarization filters which limits the system's efficiency. Here, a compact polarization imaging apparatus that leverages a multifunctional planar dielectric metalens to simultaneously capture two orthogonally polarized images of an underwater scene is presented. Using a metalens to image target objects through milky water in a single shot, large enhancement of image contrast and depth estimation of target objects in real‐time are demonstrated. This work shows the effectiveness of metalens for tackling challenging imaging tasks in complex environments.

Compact Photonic Crystal Polarization Beam Splitter Based on the Self-Collimation Effect

We propose a new compact polarization beam splitter based on the self-collimation effect of two-dimensional photonic crystals and photonic bandgap characteristics. The device is composed of a rectangular air holes-based polarization beam splitting structure and circular air holes-based self-collimating structure. By inserting the polarization beam splitting structure into the self-collimating structure, the TE and TM polarized lights are orthogonally separated at their junction. When the number of rows in the hypotenuse of the inserted rectangular holes is 5, the transmittance of TE polarized light at 1550 nm is 95.4% and the corresponding polarization extinction ratio is 23 dB; on the other hand, the transmittance of TM polarized light is 88.5% and the corresponding polarization extinction ratio is 37 dB. For TE and TM polarized lights covering a 100 nm bandwidth, the TE and TM polarization extinction ratios are higher than 18 dB and 30 dB, respectively. Compared with the previous polarization beam splitters, our structure is simple, the size is small, and the extinction ratio is high, which meets the needs of modern optical communications, optical interconnection, and optical integrated systems.

Compact polarisation insensitive wide angular stable triple band absorber for RF energy harvesting, RCS reduction, and sensor applications

This paper presents a new compact ultra-thin triple-band absorber which shows near-unity absorption in C, X and Ku-bands. It consists of an inductive stub loaded circular ring resonator and a flower-shaped resonating patch on top of 0.8 mm thin FR-4 grounded dielectric substrate. A transmission line equivalent is proposed, and circuit simulation response is in good agreement with the full-wave analysis. The unit-cell architect's 4fold symmetry makes it polarisation-insensitive for different polarisation angles in the azimuthal plane (𝜃 = 0°) under normal incidence. Its good shows angular stability up to 45° under TE (75° under TM) incidences for all three frequencies. Surface current patterns are analysed at resonant frequencies to illustrate the mechanism behind the electromagnetic absorption. This design's novelty lies in the centre patch's dual-resonating behaviour, making this design compacted one. The absorber has low-profile nature with cell periodicity of 0.163λL and thickness 0.013λL, where λL is the lowest resonating peak wavelength. An X-band conventional MSA is fabricated on a thin FR-4 substrate. In-band RCS reduction (nearly 18 dBsm) of the antenna is verified after loading with the proposed absorber. The absorptivity peaks are optimised such that the same structure would be used in different applications like RF energy harvesting, RCS reduction and sensor applications.

Efficient, compact, and robust GeOI-based photonic polarization rotator in the 2 [formula omitted]m waveband

Based on the germanium-on-insulator (GeOI) platform, we numerically demonstrate a photonic polarization rotator (PR) operating in the 2 μm waveband. Utilizing the partial-height etching to break the symmetry of germanium waveguide cross section, the proposed PR realizes a 90° polarization rotation between the fundamental transverse electric (TE) and magnetic (TM) modes. The device footprint occupies only 0.4 μm ×0.4μm ×3μm. This PR shows a low insertion loss of 0.096 dB, a remarkably high polarization conversion efficiency (PCE) of 98.9%, and an extremely high extinction ratio of 33.45 dB at the wavelength of 2005 nm The PCE keeps above 95.4% within the waveband between 1.9 μm and 2.1 μm. Furthermore, a reasonable robustness is demonstrated.

Multiband and multifunctional polarization converter using an asymmetric metasurface

A compact and asymmetric multi-band reflective polarization converter metasurface has been offered in this paper. The proposed simple converter can effectively convert an incident linearly polarized EM wave to its orthogonal counterpart and circular polarized waves (RHCP and LHCP) at two frequency bands. The design consists of a square with two curves on the top right and lower left corners and a square Split Ring Resonator (SRR) responsible for linear-to-linear and linear-to-circular polarization conversions, respectively. The simulated results show that the converter successfully transforms a y-polarized incident wave to its orthogonal counterpart in a frequency range of 15.5–16.5 GHz with unity conversion at 16 GHz and circularly-polarized (RHCP) wave at 13 GHz and (LHCP) at 18 GHz, verified through the fabricated and measured sample. Wide angular stability up to 60° oblique incidence along with high efficiency reveals the good applicability of the structure. Moreover, the root cause of the cross-polarization conversion has been analyzed and confirmed through Bi-Mode Foster equivalent circuit and surface current distribution as well. Finally, a fabricated prototype is tested to validate the simulated results through measurement.

Ultra-high extinction ratio polarization beam splitter with extreme skin-depth waveguide.

In this Letter, we present a high extinction ratio and compact on-chip polarization beam splitter (PBS), based on an extreme skin-depth (eskid) waveguide. Subwavelength-scale gratings form an effectively anisotropic metamaterial cladding and introduce a large birefringence. The anisotropic dielectric perturbation of the metamaterial cladding suppresses the TE polarization extinction via exceptional coupling, while the large birefringence efficiently cross-couples the TM mode, thus reducing the coupling length. We demonstrated the eskid-PBS on a silicon-on-insulator platform and achieved an ultra-high extinction ratio PBS (${\approx} 60\;{\rm dB} $ for TE and ${\approx} 48\;{\rm dB} $ for TM) with a compact coupling length (${\approx} 14.5\,\,\unicode{x00B5}{\rm m}$). The insertion loss is also negligible (${\lt}{0.6}\;{\rm dB}$). The bandwidth is ${\gt}{80}$ (30) nm for the TE (TM) extinction ratio ${\gt}{20}\;{\rm dB}$. Our ultra-high extinction ratio PBS is crucial in implementing efficient polarization diversity circuits, especially where a high degree of polarization distinguishability is necessary, such as photonic quantum information processing.

Compact polarization diversity patch antenna in L and WiMAX bands for IoT applications

A miniaturized stacked patch antenna with circular polarization in GPS L1 band and dual linear polarization in WiMAX band for IoT (Internet of Things) applications is proposed. A novel technique has been introduced to enhance a second mode in dual-band patch antenna, by adding pi shaped slots and stacking another reflective patch, with shorting pins in between. The upper patch, thus, acts as an independent receiver in WiMAX band using enhanced second mode of the lower patch. At GPS L1 frequency of 1.575 GHz, the compact antenna of volume 0.13 λ0 × 0.13 λ0 × 0.067 λ0 (λ0 is the free-space wavelength at 1.575 GHz) achieves a wide half-power beamwidth of 104 ± 5°. The measured results exhibit an impedance bandwidth of 5.71% in WiMAX (3.4 GHz–3.6 GHz) band along with symmetrical radiation patterns for both horizontal and vertical polarizations of the transmitter. The fabricated prototype, with a radiation efficiency greater than 85%, proves to be highly efficient in portable devices for multipath spaces in IoT.

Compact and efficient polarization splitter based on dual core microstructured fiber for THz photonics

We consider a dual core polyethyelene microstructured fiber with teflon and air inclusions in the core region for achieving compact and efficient polarization splitting at THz frequencies. The teflon inclusions form slit-like structure that helps in shifting the degeneracy point to lower frequencies. The y-polarized light couples from one core to the other within a very small device length of a few cm. Modal fields, effective indices, device length, extinction ratio and different losses have been calculated, which provide a handle to reduce the polarization splitting length at frequencies below and above ~ 0.7THz. Extinction ratios are found to be significantly high in a broad frequency range, e.g. a value of ~ 70 dB for x-polarization and ~ 45 dB for the y-polarization with about 2.1 cm device length at 1 THz. This device length is more than 30 times shorter than previously reported values. However, it attains a maximum device length of 21.6 cm at ~ 0.7 THz, which is also shorter than the corresponding earlier reported value.

Compact silicon-based TE-pass polarizer using a symmetrical triple-guide directional coupler including SWG structures and hybrid plasmonic waveguides

A compact and broadband silicon-based transverse-electric (TE)-pass polarizer based on a symmetrical triple-guide directional coupler (TW-DC) is presented and analyzed in detail, assisted with subwavelength gratings (SWGs) and hybrid plasmonic waveguides (HPWs), where the SWGs are involved at the inner part of its central waveguide and two HPWs are introduced and symmetrically located at its outer sides. By carefully improving the structural parameters, only the injected TE mode can be supported by SWGs, and it passes through the device directly due to phase mismatching, while the input TM mode will be supported in the strip waveguides and coupled to the adjacent HPWs due to phase matching and gradually attenuated via the metals. As a result, a compact TE-pass polarizer is realized. Results show that the proposed polarizer has a total coupling length of 6 µm, with an extinction ratio (ER) of 31.2 dB, insertion loss (IL) of 0.1 dB, and reflection loss (RL) of − 26.2 d B at 1.55 µm, and its operation bandwidth can be up to 270 nm (from 1.43 to 1.7 µm) for E R &gt; 20 d B and I L &lt; 1 d B . In addition, fabrication tolerances to the key structural parameters and field evolution through the proposed device are given.