Showing papers on "Polarization rotator published in 2015"

Efficient polarization beam splitter pixels based on a dielectric metasurface

Abstract: The polarization dependence of the reflection, refraction, and diffraction of electromagnetic waves from materials is measured in applications that extend from small (e.g., ellipsometry of semiconductor chips) to large scales (e.g., remote sensing for planetary science and weather radar). Such applications employ polarimeters that are in turn based on devices with polarization-selective absorption or reflection/refraction properties (e.g., prisms). The latter devices are generally bulky, thereby limiting their integration into compact systems. The former devices are inherently lossy, as they function by absorbing the unwanted polarization. Here, we experimentally demonstrate a conceptually novel method for pixel-level polarimetry. Each pixel contains amorphous-silicon nanoridges and deflects incident light in a polarization-dependent manner. As photons are sorted by polarization rather than filtered, the approach permits high efficiency. A high transmission efficiency of 90% and a high extinction ratio of 15 times are demonstrated.

Metasurface for characterization of the polarization state of light

Abstract: The miniaturization of measurement systems currently used to characterize the polarization state of light is limited by the bulky optical components used such as polarizers and waveplates. We propose and experimentally demonstrate a simple and compact approach to measure the ellipticity and handedness of the polarized light using an ultrathin (40 nm) gradient metasurface. A completely polarized light beam is decomposed into a left circularly polarized beam and a right circularly polarized beam, which are steered in two directions by the metasurface consisting of nanorods with spatially varying orientations. By measuring the intensities of the refracted light spots, the ellipticity and handedness of various incident polarization states are characterized at a range of wavelengths and used to determine the polarization information of the incident beam. To fully characterize the polarization state of light, an extra polarizer can be used to measure the polarization azimuth angle of the incident light.

Ultra-Thin Reflective Metamaterial Polarization Rotator Based on Multiple Plasmon Resonances

Abstract: We propose the design, simulation, and measurement of a broadband reflective metamaterial polarization rotator in the microwave region based on multiple plasmon resonances. An utra-thin wideband polarization conversion composing of arrays of oval ring pattern, a dielectric layer and a continuous metallic layer is further demonstrated both numerically and experimentally. Two plasmon resonances are generated by magnetic and electric resonances, leading to bandwidth expansion of cross-polarization reflection. The simulated results show that the polarization conversion ratio (PCR) is greater than 68.6% in 8.0–18.0 GHz with incidence angle up to $30^{\circ}$ for both $y$ -and $x$ -polarized waves and the maximum conversion efficiency is nearly 100% at the two plasmon resonance frequencies. Experimental results under normal and oblique incidence agree well with simulated ones. The proposed rotator has applications in the area of polarization control.

Vortex phase elements as detectors of polarization state.

Abstract: We suggest vortex phase elements to detect the polarization state of the focused incident beam. We analytically and numerically show that only the types of polarization (linear, circular, or cylindrical) can be distinguished in the low numerical aperture (NA) mode. Sharp focusing is necessary to identify the polarization state in more detail (direction or sign). We consider a high NA micro-objective and a diffractive axicon as focusing systems. We show that the diffractive axicon more precisely detects the polarization state than does the micro-objective with the same NA.

Incident-polarization-sensitive and large in-plane-photonic-spin-splitting at the Brewster angle.

Abstract: In this Letter, we report a phenomenon of large in-plane-photonic-spin-splitting (IPPSS) in the case of a linear polarized Gaussian light beam reflected from an air-glass interface at the Brewster angle. The IPPSS-induced displacement reaches ∼12.4 μm, which is quite larger than the previously reported value. Particularly, the IPPSS is extremely sensitive (∼70 μm/deg) to the incident polarization. We also find that the direction of the spin accumulation can be switched by adjusting the incident polarization slightly. These findings may have useful applications in spin manipulation and precise polarization metrology.

Compact monolithically-integrated hybrid (de)multiplexer based on silicon-on-insulator nanowires for PDM-WDM systems.

Abstract: A compact silicon hybrid (de)multiplexer is designed and demonstrated by integrating a single bi-directional AWG with a polarization diversity circuit, which consists of an ultra-short polarization-beam splitter (PBS) based on a bent coupler and a polarization rotator (PR) based on a silicon-on-insulator nanowire with a cut corner. The present hybrid (de)multiplexer can operate for both TE- and TM- polarizations and thus is available for PDM-WDM systems. An 18-channel hybrid (de)multiplexer is realized with 9 wavelengths as an example. The wavelength-channel spacing is 400GHz (i.e., Δλch = 3.2nm) and the footprint of the device is about 530μm × 210μm. The channel crosstalk is about −13dB and the total excess loss is about 7dB. The excess loss increases by about 1~2dB due to the cascaded polarization diversity circuit in comparison with a single bi-directional AWG.

Efficient silicon polarization rotator based on mode-hybridization in a double-stair waveguide.

Abstract: We present a compact silicon polarization rotator (PR) based on mode-hybridization by breaking the cross-sectional symmetry of a double-stair waveguide. The device fabrication is fully compatible with the commonly used silicon photonics processes with no extra masks required. The dependence of device performance on the double-stair waveguide dimensions is investigated using FDTD simulations. Characterizations of the fabricated devices reveal that the 23-μm-long PR exhibits a polarization extinction ratio (PER) of >17 dB in the wavelength range of 1500-1540 nm. The maximum PER exceeds 30 dB at 1518 nm.

Complete Characterization of Polarization-Maintaining Fibers Using Distributed Polarization Analysis

Abstract: We present methods and processes of using a ghost-peak-free distributed polarization crosstalk analyzer (DPXA) to accurately obtain all polarization related parameters of polarization-maintaining (PM) fibers. We show that by first inducing a series equidistant periodic polarization crosstalk peaks along a PM fiber and then measuring the positions and the widths of these peaks using the analyzer, all birefringence related parameters of the PM fiber, including group birefringence, group birefringence variation along the fiber, group birefringence dispersion, and group birefringence temperature coefficient , can be accurately obtained. We further show that the DPXA has the ability to identify and eliminate polarization crosstalk contributions of connectors or splices in the measurement system and therefore can be used to obtain high accuracy measurement of the polarization extinction ratio (PER) of PM fibers. Finally, we propose a set of parameters based on the distributed polarization analysis to quantitatively evaluate the quality of PM fibers. We believe that the methods and processes described in this paper can be widely applied in the industry for the complete characterization of PM optical fibers.

Generation and propagation of a vector cosine-Gaussian correlated beam with radial polarization.

Abstract: Scalar cosine-Gaussian-correlated Schell-model (CGCSM) beams of circular or rectangular symmetry were introduced just recently. In this paper, a new kind of partially coherent vector beam named vector CGCSM beam with radial polarization (i.e., radially polarized CGCSM beam) is introduced. The realizability conditions for a radially polarized CGCSM source and the beam condition for radiation generated by such source are derived. The statistical properties, such as the average intensity, the degree of coherence, the degree of polarization and the state of polarization, of a radially polarized CGCSM beam focused by a thin lens are analyzed in detail. It is found that the statistical properties of a radially polarized CGCSM beam are quite different from those of a conventional radial polarized partially coherent beam with Gaussian correlated Schell-model function. Furthermore, we first report experimental generation of a radially polarized CGCSM beam and measure its focusing properties. Our experimental results are consistent with the theoretical predictions.

Analysis of a segmented q-plate tunable retarder for the generation of first-order vector beams.

Abstract: In this work we study a prototype q-plate segmented tunable liquid crystal retarder device. It shows a large modulation range (5π rad for a wavelength of 633 nm and near 2π for 1550 nm) and a large clear aperture of one inch diameter. We analyze the operation of the q-plate in terms of Jones matrices and provide different matrix decompositions useful for its analysis, including the polarization transformations, the effect of the tunable phase shift, and the effect of quantization levels (the device is segmented in 12 angular sectors). We also show a very simple and robust optical system capable of generating all polarization states on the first-order Poincare sphere. An optical polarization rotator and a linear retarder are used in a geometry that allows the generation of all states in the zero-order Poincare sphere simply by tuning two retardance parameters. We then use this system with the q-plate device to directly map an input arbitrary state of polarization to a corresponding first-order vectorial beam. This optical system would be more practical for high speed and programmable generation of vector beams than other systems reported so far. Experimental results are presented.

Low-loss partial rib polarization rotator consisting only of silicon core and silica cladding.

Abstract: We present a low-loss and small-footprint polarization rotator based on mode evolution. The polarization rotator is composed of an asymmetric-rib waveguide and a tapered waveguide, both of which consist only of a silicon core and a silica cladding. The rotator is fabricated under the same design rules as other device blocks, such as rib-waveguide phase shifters for photonic integration. The polarization rotator is fabricated using CMOS-based processes and provides polarization rotations with an on-chip insertion loss lower than 0.5 dB from transverse-electric (TE) to transverse-magnetic (TM) polarization and a loss lower than 1.0 dB from the TM to TE polarization in a 200 nm wavelength range extending over C and L bands.

Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale

Abstract: Probing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV photons to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe $\gamma$-rays which can also be interpreted as phase retardation of probe photons. We provide theoretically how to extract phase retardation of GeV probe photons via pair-wise topology of the Bethe-Heitler process in a polarimeter and then evaluate the measurability of the vacuum birefringence via phase retardation given a concrete polarimeter design with a realistic set of laser parameters and achievable pulse statistics.

Investigation on random distributed feedback Raman fiber laser with linear polarized output

Abstract: A random distributed feedback fiber laser with linear polarized output at 1178 nm is presented. Linear polarization is realized by fiber coiling in a half-opened cavity of a polarization maintaining random fiber laser structure. The single linear polarization laser output power reaches ∼3 W with polarization extinction ratio >14 dB. Further investigations on the coiling technique and additional feedback are also studied. So far as we know, this is the first reported linear polarized random distributed feedback Raman fiber laser.

Polarization Rotator-Splitter/Combiner Based On Silicon Rib-Type Waveguides

Abstract: Various embodiments of an integrated polarization rotator-splitter/combiner apparatus are described. An integrated polarization rotator-splitter apparatus may include an input waveguide section, a polarization rotator section, a polarization splitter section and an outgoing waveguide section, which can also be reversely connected as a polarization rotator-combiner.

Coherent optical control of polarization with a critical metasurface

Abstract: We describe the mechanism by which a metamaterial surface can act as an ideal phase-controlled rotatable linear polarizer. With equal-power linearly polarized beams incident on each side of the surface, varying the relative phase rotates the polarization angles of the output beams, while keeping the polarization exactly linear. The explanation is based on coupled-mode theory and the idea of coherent perfect absorption into auxiliary polarization channels. The polarization-rotating behavior occurs at a critical point of the coupled-mode theory, which can be associated with the exceptional point of a parity-time (PT) symmetric effective Hamiltonian.

High Performance Broadband Asymmetric Polarization Conversion Due to Polarization-dependent Reflection

Abstract: We present the underlying theory, the design specifications, and the simulated demonstration of a high performance broadband asymmetric polarization conversion composed of an L-shaped gold particle and a gold nanoan- tenna array for the near-infrared regime. It can transform linearly polarized light to its cross polarization in the trans- mission mode for one propagation direction and efficiently reflect the light for the opposite propagation direction. The broadband asymmetric polarization conversion can be attributed to the polarization-dependent reflection of the nanoantenna array, which enhances the polarization con- version efficiency of the L-shaped particle and makes it asymmetric and devisable. This work offers a further step in the development of a high efficiency broadband optical activity device.

Compact LCOS–SLM Based Polarization Pattern Beam Generator

Abstract: In this paper, a compact optical system for generating arbitrary spatial light polarization patterns is demonstrated. The system uses a single high-resolution liquid crystal (LC) on silicon (LCOS) spatial light modulator. A specialized optical mount is designed and fabricated using a 3D printer, in order to build a compact dual optical architecture, where two different phase patterns are encoded on two adjacent halves of the LCOS screen, with a polarization transformation in between. The final polarization state is controlled via two rotations of the Poincare sphere. In addition, a relative phase term is added, which is calculated based on spherical trigonometry on the Poincare sphere. Experimental results are presented that show the effectiveness of the system to produce polarization patterns.

Diffractive optical element using polarization rotation grating for in-coupling

Abstract: In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), an in-coupling DOE couples light into the waveguide, an intermediate DOE provides exit pupil expansion in a first direction, and an out-coupling DOE provides exit pupil expansion in a second direction and couples light out of the waveguide. The in-coupling DOE is configured with two portions—a first portion includes a grating to rotate a polarization state of in-coupled light while a second portion couples light into the waveguide without modulation of the polarization state. The in-coupled light beams with different polarization states are combined in the waveguide after undergoing total internal reflection. However, as the difference in optical path lengths of the constituent light beams exceeds the coherence length, the combined light has random polarization (i.e., a degree of polarization equal to zero).

Complex light fields enter a new dimension: holographic modulation of polarization in addition to amplitude and phase

Abstract: We present a method to tailor not only amplitude and phase of a complex light field, but also the transverse states of polarization. Starting from the implementation of spatially inhomogeneous distributions of polarization, so called Poincare beams, we realized a holographic optical technique that allows arbitrarily modulating the states of polarization by a single phase-only spatial light modulator (SLM). Moreover, the effective amplitude modulation of higher order beams performed by a phase-only SLM is shown. We will demonstrate the capabilities of our method ranging from the modulation of higher order Gaussian modes including desired polarization characteristics to the generation of polarization singularities at arbitrary points in the transverse plane of Poincare beams.

Characterization of polarizer made of the deep-UV birefringent crystal Ba2Mg(B3O6)2.

Abstract: In optical communications and the laser industry, modulating the polarization of light requires crystals with both large birefringence and a wide transparent range. A good candidate for a deep-UV birefringent crystal is Ba2Mg(B3O6) because it has a large birefringence and short UV cutoff edge. We grew Ba2Mg(B3O6)2 crystals with sizes up to 41 mm×40 mm×7 mm using the top-seeded solution growth method. We obtained the thermal-expansion coefficients in different directions and the thermo-optic coefficients and then designed and manufactured a Glan–Taylor type polarizer to fulfill the commercial requirements.

Multiple‐band reflective polarization converter based on complementary L‐shaped metamaterial

Abstract: In this article, we numerically and experimentally investigate the electromagnetic responses of multiple-band reflective polarization based on complementary L-shaped metamaterial. The proposed reflective polarization converter can convert a linearly polarized wave to its cross-polarized wave at the five resonant frequencies, which is also can convert the linearly polarized wave to circularly polarized wave at other six resonant frequencies. Furthermore, the incident circularly polarized wave can be transformed into the same rotational direction at five resonant frequencies after reflection, which is different from reflection by conventional materials. Simulations are in reasonable agreements with the experimental results in the entire frequency range, and the polarization conversion ratio is over 90% for both linear and circular polarizations in simulation. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:978–983, 2015

Current-induced spin polarization and spin-orbit torque in graphene

Abstract: Using the Green-function formalism, we calculate a current-induced spin polarization of weakly magnetized graphene with Rashba spin-orbit interaction. In a general case, all components of the current-induced spin polarization are nonzero, contrary to the nonmagnetic limit, where the only nonvanishing component of spin polarization is that in the graphene plane and normal to the electric field. When the induced spin polarization is exchange coupled to the magnetization, it exerts a spin-orbit torque on the latter. Using the Green-function method, we have derived some analytical formulas for the spin polarization and also determined the corresponding spin-orbit torque components. The analytical results are compared with those obtained numerically. Vertex corrections due to scattering on randomly distributed impurities are also calculated and shown to enhance the spin polarization calculated in the bare bubble approximation.

Multiple-band reflective polarization converter based on deformed F-shaped metamaterial

Abstract: A three-layered deformed F-shaped metamaterial reflective polarization converter (RPC) is proposed to realize linear and circular polarization conversions. The proposed F-shaped RPC can convert a linearly polarized wave to its cross-polarized wave at the four resonant frequencies. It also can convert the linearly polarized wave to a circularly polarized wave at the other four resonant frequencies. In addition, the proposed F-shaped RPC can maintain the same rational direction at the five resonant frequencies when the incident is a circularly polarized wave and higher reflective coefficients can be obtained with the increase of the thickness of the dielectric layer. The simulated and measured results are in agreement in the entire frequency range, and the polarization conversion ratio is more than 85% for both linear and circular polarizations. Further simulations reveal that the polarization in the terahertz range can also be obtained by changing the thickness of the dielectric layer and the unit of the reflective polarization converter.

Automated mode locking in nonlinear polarization rotation fiber lasers by detection of a discontinuous jump in the polarization state.

Abstract: A strategy to align a mode-locked fiber laser with nonlinear polarization rotation is presented. This strategy is based on measurements of the output polarization state. It is shown that, as the angle of a motorized polarization controller inside the cavity is swept, the laser eventually reaches a mode-locked regime and the values of the Stokes parameters undergo an abrupt change. The sensing of this sudden variation is thus used to detect the mode-locking condition and a feedback mechanism drives the alignment of the polarization controller to force mode locking.

Simple Method for the Elimination of Polarization Noise in BOTDA Using Balanced Detection and Orthogonal Probe Sidebands

Abstract: Polarization noise arises in Brillouin optical time-domain analysis due to the strong polarization sensitivity of stimulated Brillouin scattering. To avoid this noise, it turns out to be indispensable to perform some kind of polarization scrambling, either in the pump pulse, the probe signal or both. This is usually achieved using polarization scrambling/switching systems, which, being mechanical, tend to be not as robust as it would be desirable. In this paper, we propose a completely passive system, with no moving parts, to eliminate polarization noise in a BOTDA. It is based on the use of passive depolarization of the pump pulse together with balanced detection among orthogonally polarized Stokes and anti-Stokes bands of the probe signal. The setup requires no alignment readjustment over time and provides a performance similar to a conventional BOTDA using scrambler.

Linear polarization optimized Stokes polarimeter based on four-quadrant detector

Abstract: A four-quadrant detector (4QD) consists of four well-balanced detectors. We report on a Stokes polarimeter with optimal linear polarization measurements based on a 4QD. We turned the four intensity-detection channels into four polarization-analyzing channels by placing four polarizers and one quarter-wave plate in front of the individual detectors. An optimization method for the four polarization-analyzing channels is proposed to improve measurement accuracy. Considering applications in favor of linear polarization measurements instead of global optimization for all the possible states of polarization (SOP), we optimize the polarimeter first for the linear polarization components and then for the circular polarization component. The polarimeter is capable of simultaneous measurements of fast varying SOP with improved performance for the linear polarizations.