Showing papers on "Polarization rotator published in 2019"

Tunable Metasurfaces: A Polarization Rotator Design

Abstract: An electronically tunable metasurface can rotate the polarization angle of an incident polarized electromagnetic wave, showing promise for a new paradigm of real-time wave manipulation.

Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding

Abstract: Optical isolators and circulators are fundamental building block in photonic integrated circuits to block undesired reflections and routing light according to a prescribed direction. In silicon photonics, heterogeneous integration of magneto-optic garnet bonded on a pre-patterned silicon layer has been demonstrated to be an effective solution for manufacturing optical isolators and circulators for TM polarized light. However, most integrated semiconductor lasers emit TE polarized light, which indicates the need to find a reliable solution for this polarization. In this paper, we demonstrated broadband optical isolators and circulators for TE polarized light based on heterogeneous bonding on the silicon photonics platform. To achieve this goal, an integrated adiabatic coupler and a broadband polarization rotator are designed and optimized. The nonreciprocal behavior is induced through an energy-efficient integrated electromagnet with a minimum power consumption of 3 mW. Two isolators/circulators are fabricated with small and large free spectral range, respectively. In the former case, an optical isolation ratio as large as 30 dB is measured at 1555 nm with an insertion loss of 18 dB, while for the broadband circulator, an optical isolation larger than 15 dB is guaranteed over more than 14 nm (1.75 THz) for all port combinations with an insertion loss between 14 and 18 dB at 1560 nm. Finally, it has been theoretically shown that the insertion loss can be reduced below 6 dB with design and fabrication improvements. To the best of the authors’ knowledge, the proposed integrated TE optical circulator is the first experimental demonstration of this device in silicon photonics.

Triple-Band Polarization Angle Independent 90° Polarization Rotator Based on Fermat's Spiral Structure Planar Chiral Metamaterial

Abstract: We propose a planar chiral metamaterial (PCMM), which can function as a triple-band polarization angle independent 90◦ polarization rotator. The unit cell of the PCMM is composed of bi-layered mutual twisted Fermat’s spiral structure (FSS) resonators with four-fold rotation symmetry. The simulated and measured results show that the PCMM can work in triple-band and convert a linearly polarized (y-/x-polarized) wave to its cross-polarization (x-/y-polarized) or experience a near 90◦ polarization rotation with a polarization conversion ratio of over 90%. The electric field and surface current distributions of the unit-cell structure are analyzed to study its physics mechanism. Compared with previous CMM-based rotator, our design has more operation frequencies in a single PCMM structure, a relative thinner thickness, and higher Q-factor. Good performances of the PCMM suggest promising applications in the polarization rotator or convertor that need to be integrated with other compact devices.

Ultra-wideband and wide-angle polarization rotator based on double W-shaped metasurface

Abstract: In this work, we design a novel polarization converter based on a metasurface with double w-shaped unit cells. The proposed polarization converter can convert linearly polarized incident waves into its cross polarized reflective counterparts in a very wide band with high efficiency. Theoretical analysis and simulation results show that the proposed polarization converter can achieve a 90° polarization rotation, while the polarization conversion ratio (PCR) is above 90% in the frequency range from 8.44 GHz to 24.96 GHz, and the relative bandwidth can be up to 99%. The measured results agree well with simulation results. The designed double w-shaped metasurface has a very simple geometry, and can realize a highly-efficient and broadband polarization rotation. Therefore, it has practical applications in wireless communication systems, imaging, radar stealth technology, and other fields.

Subwavelength-grating-assisted silicon polarization rotator covering all optical communication bands

Abstract: We propose an ultra-broadband and ultra-compact polarization rotator (PR) structure on the silicon-on-insulator platform. The subwavelength gratings (SWGs) are introduced at the waveguide corner in order to excite the hybridized modes and realize the polarization rotation. The dispersion-engineered SWG can dramatically reduce the polarization conversion length deviation. High polarization extinction ratio > 20 dB and low excess loss < 1 dB can be achieved over 1.26-1.675 μm wavelength range, which covers O-, E-, S-, C-, L-, and U-bands. The total device size is as small as 4.8 × 0.34 μm2. To the best of our knowledge, the proposed structure is the first silicon PR that could cover all of the optical communication bands.

High-performance bifunctional polarization switch chiral metamaterials by inverse design method

Abstract: Multifunctional polarization controlling plays an important role in modern photonics, but their designs toward broad bandwidths and high efficiencies are still rather challenging. Here, by applying the inverse design method of model-based theoretical paradigm, we design cascaded chiral metamaterials for different polarization controls in oppositely propagating directions and demonstrate their broadband and high-efficiency performance theoretically and experimentally. Started with the derivation of scattering matrix towards specified polarization control, a chiral metamaterial is designed as a meta-quarter-wave plate for the forward propagating linearly polarized wave, which converts the x- or y-polarized wave into a nearly perfect left- or right-handed circularly polarized wave; intriguingly, it also serves as a 45° polarization rotator for the backward propagating linearly polarized waves. This bifunctional metamaterial shows a high transmission as well as a broad bandwidth due to the Fabry–Perot-like interference effect. Using the similar approach, an abnormal broadband meta-quarter-wave plate is achieved to convert the forward x- and y-polarized or the backward y- and x-polarized waves into left- and right-handed circularly polarized waves with high transmission efficiencies. The integration of multiple functions in a single structure endows the cascaded chiral metamaterials with great interests for the high-efficiency polarization-controlled applications.

Silicon On-Chip PDM and WDM Technologies Via Plasmonics and Subwavelength Grating

Abstract: Silicon photonics, which is compatible with standard CMOS technology, is the most promising platform for large-scale photonic integration. The rapid growth of data volume demands larger link capacity and higher integration density of photonic integrated circuits. Multiplexing technology is an effective approach to enhance the capacity of on-chip optical interconnects. This review provides an introduction to the silicon on-chip multiplexing devices using plasmonics and subwavelength grating (SWG). To expand the data transmission capacity, one solution is introducing wavelength-division-multiplexing structures where diplexer and triplexer are fundamental elements. Another is adopting polarization-division-multiplexing (PDM) technology. Polarizer, polarization beam splitter, polarization rotator, polarization beam splitter-rotator, and polarization-independent directional coupler are all essential components for integrated PDM scheme. By using plasmonics and SWG, the mode profile distribution, refractive index, birefringence, and dispersion can all be manipulated, which enables compact devices with high performance.

Adiabatic mode converters for silicon photonics: Power and polarization broadband manipulators

Abstract: Broadband, low-loss, and fabrication-tolerant photonic passives are of paramount importance in any photonic integrated circuit (PIC). Among others, the adiabatic couplers can have those merits premised on their one-to-one mode transformation characteristics. These devices are usually designed comprising linear waveguide tapers and have typical lengths of 1 mm, in order to minimize inter-modal coupling along the device. The large footprints and, therefore, the fabrication sensitivity can eventually become a barrier toward their widespread applications. Here, we discuss an intuitive generic method for designing compact broadband adiabatic mode converters. The method can be used to design broad types of adiabatic devices for power and polarization manipulations on silicon PICs. Exemplary devices such as polarization beam splitters and polarization rotator splitters, 3 dB power splitters/combiners for quasi-TE and for quasi-TM polarizations, and power tapper for quasi-TE polarization are discussed. The devices provide insertion losses of <1 dB and extinction ratios in the range of 10–20 dB across the 85 nm measurement window. As an important application of the adiabatic devices, we also report on a broadband optical 90° hybrid with an operating bandwidth of 85 nm.

Anisotropic Metasurface-Based Beam-Scanning Dual-Polarized Fan-Beam Integrated Antenna System

Abstract: This paper presents a novel anisotropic metasurface (AMS)-based integrated antenna system to facilitate dual-polarized fan-beam patterns with independent beam-scanning ability. In the proposed configuration, the antenna subsystem comprises a specially designed differentially fed microstrip patch antenna (source antenna) along with a polarization rotator (PR). The differential antenna arrangement is realized using a square shaped microstrip patch capacitively coupled with two metallic strips, which are connected to a specially designed wideband hybrid coupler using two metallic vias for the microstrip feeding. This source antenna is loaded with a PR by placing it at a height of $0.35\lambda _{0}$ from the radiating aperture. The PR comprised two identical metallic layer patterns, separated by two substrates. Depending upon the relative orientation of these layers, the polarization of the linearly polarized impinging spherical electromagnetic (EM) waves (originating from the source antenna) either remains preserved or gets rotated by 90° while transmitting through this PR. After realizing the antenna subsystem, a novel AMS lens is designed and placed above the PR. The proposed AMS lens is realized by integrating two cylindrical MS (CMS) lenses, $\text {CMS}_{Y}$ and $\text {CMS}_{X}$ . This integration provides a unique phase profile to the AMS lens, thus introducing appropriate phase correction to the incident orthogonally polarized spherical EM waves along their respective polarization direction. The proposed configuration of AMS lens, thus, results into formation of the independent dual-polarized fan-beam radiation beams. Finally, the steering of the generated fan-beams along the direction of their respective polarization is facilitated using the proposed system by translating the AMS lens parallel to the source antenna.

Proof of Concept of Polarization-Multiplexed PAM Using a Compact Si-Ph Device

Abstract: We experimentally propose and demonstrate how to double the capacity per wavelength in short distance data center interconnect fiber links by polarization multiplexing two pulse-amplitude modulation streams and by using a very compact silicon photonic polarization rotator driven by an algorithm implemented in a low-speed digital signal processing platform, avoiding more complex coherent and/or Stokes receiver structures. Tackling up to 100 rad/s, the system gives automatic stabilization against polarization fluctuations. We also report on the experimentally measured evolution of the state of polarization in an installed data center link.

Highly efficient passive InP polarization rotator-splitter.

Abstract: Monolithically integrated polarization beam splitters (PBSs) are needed to reduce the form-factor and assembly cost of optical coherent receivers. A highly efficient passive polarization rotator and splitter based on mode-evolution is demonstrated. The device is fabricated on InP substrate with a single etch-step and uses an adiabatic mode-converter and an asymmetric Y-coupler. Despite its simple fabrication process, the device shows a polarization extinction ratio (PER) better than 19 dB over 1520 nm to 1620 nm, thus covering both C- and L-band. The peak value of 24 dB is obtained for TE and TM polarizations. Its fabrication tolerance is large, so that even under a width variation of +/- 200 nm the PER remains above 17 dB over the entire C- and L-band.

On-chip polarization rotator for type I second harmonic generation

Abstract: We demonstrate a polarization rotator integrated at the output of a GaAs waveguide producing type I second harmonic generation (SHG). Form-birefringent phase matching between the pump fundamental transverse electric (TE) mode near 2.0 µm wavelength and the signal fundamental transverse magnetic (TM) mode efficiently generates light at 1.0 µm wavelength. A SiN waveguide layer is integrated with the SHG device to form a multifunctional photonic integrated circuit. The polarization rotator couples light between the two layers and rotates the polarization from TM to TE or from TE to TM. With a TE-polarized 2.0 µm pump, type I SHG is demonstrated with the signal rotated to TE polarization. Passive transmission near 1.0 µm wavelength shows ∼80% polarization rotation across a broad bandwidth of ∼100 nm. By rotating the signal polarization to match that of the pump, this SHG device demonstrates a critical component of an integrated self-referenced octave-spanning frequency comb. This device is expected to provide crucial functionality as part of a fully integrated optical frequency synthesizer with resolution of less than one part in 1014.

Ultra-wideband Ge-rich silicon germanium mid-infrared polarization rotator with mode hybridization flattening

Abstract: In this work we investigate the implementation of ultra-wideband polarization rotator in the mid-infrared spectral region. A new design method of the rotation section is proposed, yielding a polarization rotator with an extinction ratio of at least 15 dB in a wavelength range of 2 µm. For a spectral range wider than 3.8 µm, an extinction ratio of at least 10 dB is achieved for this design. The device is 1660 µm long and the associated insertion loss is below 1.2 dB on the full operational wavelength range. The influence of geometrical parameters with respect to the design method to obtain such a broadband behavior is discussed. Finally, to increase the tolerance to fabrication errors, a tapered rotator design is proposed. Such a device can support up to ± 100 nm fabrication errors and still guarantees remarkable broadband behavior. To the best of our knowledge, this is the first time an integrated polarization rotator is designed to operate for the wavelength range of 4 to 9 µm with a bandwidth exceeding 2 µm.

Polarization-insensitive tunable terahertz polarization rotator.

Abstract: A rotation-angle variable polarization rotator is proposed and demonstrated using an all-dielectric metasurface doublet. Such a transmissive device can conveniently rotate the polarization of incident light by any desired angles by mechanically changing the relative angle of the double metasurface layers regardless of the incident state of polarization. Under certain conditions the device acts as a full phase modulator for the circularly polarized incident wave. Hence, it has a promising application in polarization and phase control.

Grating-Coupled Silicon-on-Sapphire Polarization Rotator Operating at Mid-Infrared Wavelengths

Abstract: We provide an experimental demonstration of mid-infrared polarization rotators built on a silicon-on-sapphire platform at the mid-infrared wavelength of $4.55~\mu \text{m}$ to enable integration of quantum cascade lasers (QCLs) and detectors with slotted photonic crystal waveguide (PCW) gas sensors for on-chip optical spectroscopy applications. The polarization rotators are essential to convert the preferentially transverse magnetic (TM) polarized light from a QCL to transverse electric (TE) polarization to interface with the preferential TE-guiding slotted PCW sensors. The polarization rotator consists of an adiabatic-tapered mode converter followed by a phase shifter and a multimode interferometer that effectively transfers energy from an input fundamental TM00 polarization to a first-order TE10 polarization that is then converted to the fundamental TE00 mode. Polarization-selective sub-wavelength grating couplers are designed and fabricated to effectively couple TE or TM polarizations at the designed wavelengths into and out of the polarization rotator device for efficient device characterization. TM00–TE10 conversion efficiency of 100% is simulated. Fabrication tolerances in the phase shifter result in an experimental 80:20 splitting ratio of the measured output TE00-polarized light between two output arms.

Perfect terahertz-wave polarization rotator using dual Fabry–Perot-like cavity resonance metamaterial

Abstract: A novel kind of terahertz ultrathin perfect polarization rotator (UPPR) based on the composite metamaterial is proposed and numerically demonstrated in this paper. The proposed UPPR is constructed by two electric dipole resonant polarization selectors on the two sides and a cross-shaped polarization converter in the center between two dielectric layers as spacers. This typical structure forms a dual Fabry–Perot cavity-like resonance, leading to an enhanced 90° polarization rotation with polarization conversion ratio reaching 99.9%. Quantitative analysis is given to reveal the underlying principle of the UPPR and the detailed design guidelines are also provided for the others to accomplish this kind of UPPR in other frequency bands at will, such as in microwave and infrared regions. In a way, we believe this kind of UPPR, i.e., the polarization selector–polarization converter–polarization selector type, can enrich the metamaterial community for achieving the perfect polarization rotation.

InP-based polarization rotator-splitter for mid-infrared photonic integration circuits

Abstract: We design and experimentally demonstrate the propagation loss of waveguides and the operation of a single-step etched polarization rotator-splitter (PRS) in low index contrast InGaAs-InP material system at 6.15 μm. Propagation losses 4.19 dB/cm for TM mode and 3.25 dB/cm for TE mode are measured. The designed PRS can achieve near 100% conversion efficiency. This study enables the possibility of monolithic integration of quantum cascade devices with TM-polarized characteristics and TE-guiding two-dimensional slotted photonic crystal waveguide gas sensors for on-chip monolithic absorption spectroscopy.

Fabrication Tolerant Integrated Polarization Rotator Design Using the Jones Calculus

Abstract: A fabrication tolerant polarization rotator (PR) building block is added to our generic photonic integration technology. Using asymmetric waveguides, we propose a PR with guided modes that do not enclose a 45° angle with the substrate. Rather, we find that polarization performance and loss can be improved substantially by allowing the mode angles to vary along the device. We numerically optimize PR designs, targeting at high extinction and high fabrication tolerance. The optimization makes use of the Jones formalism and the fact that Jones calculus is numerically much faster than beam propagation methods. A comparison of our Jones model and commercial simulation software shows excellent agreement. Fabricated devices show a polarization extinction between 10 and 14 dB across different wafers, at an excess loss of 1 dB. Compared to PR designs without tapers, the loss is 3 dB lower and the polarization extinction is now reproducible from wafer to wafer.

High-efficiency and broadband photonic polarization rotator based on multilevel shape optimization.

Abstract: We report on a novel photonic polarization rotator design obtained by multilevel shape optimization. The numerical method consists of a topological optimization scheme, improving iteratively the efficiency of the component by modifying its shape on two discrete levels along the etching direction. We numerically show that, compared to state-of-the-art single-level shape optimization, the performances can be drastically improved for a given device length. Next, the polarization conversion efficiency can be further improved up to a computed value of 98.5% with less than 0.35 dB insertion losses on a 100 nm bandwidth for a 6 μm×1 μm footprint.

Achromatic polarization rotator with tunable rotation angle

Abstract: We theoretically suggest and experimentally demonstrate a broadband composite optical rotator that is capable of rotating the polarization plane of a linearly-polarized light at any chosen angle. The device is composed of an even number of half-wave plates rotated at specific angles with respect to their fast-polarization axes. The frequency bandwidth of the polarization rotator in principal increases with the number of half-wave plates. Here we experimentally examine the performance of rotators composed of two, four, six, eight and ten half-wave plates.

Broadband polarization rotator with tunable rotation angle composed of three wave-plates

Abstract: A simple scheme for a broadband polarization rotator with tunable rotation angle is proposed and verified experimentally. The rotator consists of only three wave-plates, one of which is a full-wave plate. The robust approach inspired by the composite pulses analogy allows to compensate the wave-plate dispersion in large extent.

Inverse Design and Demonstration of Ultracompact Silicon Polarization Rotator

Abstract: An ultra-compact silicon polarization rotator based on inverse-designed subwavelength structures is proposed and experimentally exhibited high performance with high extinction ratio of 19 dB, a footprint of 1.2 × 7.2 μm2 and only one-step etching.

A Tunable Graphene 0–90° Polarization Rotator Achieved by Sine Equation Voltage Adjustment

Abstract: Polarization Manipulation has been widely used and plays a key role in wave propagation and information processing. Here, we introduce a polarization rotator in the terahertz range with a polarization conversion ratio up to 99.98% at 4.51 terahertz. It has a single graphene layer on top of the structure patterned by 45° tilted space elliptical rings. By changing the Fermi level from 0.3 ev to 0.7 ev of the graphene, we can turn the reflective light polarization direction between 0° to 90° with nearly unique magnitude. Surface currents theories and graphene characteristics clarify the relationship between polarization angle and Fermi level to be a sine equation adjusted voltage. We firstly put forward an equation to thetunable graphene changing the reflective light polarization angle. It can be widely used in measurement, optic communication, and biology. Besides, with nearly the unique reflective light in different directions, the rotator is designed into a novel radially polarization converter. The latter can be switched from radially polarized light to linearly polarized light, and vice versa, in the terahertz region.

Liquid crystal phased array-based laser radar system

Abstract: The invention provides a liquid crystal phased array-based laser radar system, and relates to the technical field of laser phase control By the liquid crystal phased array-based laser radar system, the problem that incident light and emergent light are separated by a light splitter in an existing light path and the light intensity loss can be caused by introduction of the light splitter so that the application of a beam deflection system is limited are solved The liquid crystal phased array-based laser radar system comprises a central processing unit, a laser emission system and an echo receiving system, wherein the laser emission system comprises a laser A and an emission light path, the emission light path comprises a beam expansion collimation system A, a refined deflection system, aone fourth wave plate and a rough deflection system, the refined deflection system comprises a one second wave plate, a liquid crystal spatial light modulator (LCSLM) and a DSP controller, the rough deflection system comprises a liquid crystal polarization rotator, a liquid crystal spatial light modulator (LCPG) and a polarization grating controller, and the echo receiving system comprises a fieldprogrammable gate array (FPGA), an MPPC and a receiving light path An oblique incidence mode is employed, an included angle between light irradiating the liquid crystal spatial light modulator and emergent light is increased, the light path is simplified, the system volume is reduced, the light intensity loss caused by the light splitter is also reduced, and the application range of the liquid crystal spatial light modulator is expanded

Perfect Anomalous Reflection and Refraction Accompanied by an Ideal Polarization Conversion: Potential of a Chiral Metasurface

Abstract: Electrically thin layers, composed of sub-wavelength-size inclusions known as metasurfaces, are exploited to shape the wavefront of electromagnetic waves. In this work, we engineer ideal polarization rotator metasurfaces which perfectly reflects or refracts a normally illuminated electromagnetic plane wave into an anomalous direction. Our approach is based on applying boundary conditions to relate the induced electric and magnetic equivalent dipole polarizations per unit-cell to the jump of both electric and magnetic fields at the metasurface boundary, and to find the required electric and magnetic polarization densities, and finally to allocate a desired topology to achieve the aforementioned goals of anomalous scattering. We use an analytical model and demonstrate that such design realizations are achievable using metasurfaces with scatterers possessing a chiral topology.

Achromatic polarization rotator with tunable rotation angle

Abstract: We theoretically suggest and experimentally demonstrate a broadband composite optical rotator that is capable of rotating the polarization plane of a linearly-polarized light at any chosen angle. The device is composed of an even number of half-wave plates rotated at specific angles with respect to their fast-polarization axes. The frequency bandwidth of the polarization rotator in principal increases with the number of half-wave plates. Here we experimentally examine the performance of rotators composed of two, four, six, eight and ten half-wave plates.

Design of Polarization Rotator Based on Asymmetric Slot-Waveguide

Abstract: In this study, a slot-waveguide based polarization rotator (PR) is proposed and designed on silicon-on-isulator platform. Since the entire structure is symetrically distributed along the y = x axis, the optical axies of the excited modes are rotated by 45° with respect to the x-axis, which leads to a high polarization conversion efficiency. Simulation results using 3D-FDTD method illustrate that a polarization conversion efficiency of 99.7% is obtained with a device length of only 8 μm at wavelength of 1.55 µm. The corresponding extinction ratio is − 25.9dB and insertion loss is 1.19dB. Additionally, the wavelength dependence of the proposed PR is also discussed in detail.