Polarization Extinction Ratio Research Articles

Full-Stokes polarization mid-wave infrared photodetector based on the polarization-converting metasurface

It is very challenging to achieve direct capture of the circular polarization due to the complex mechanism of the chiral materials. We numerically demonstrate a circular polarization photodetector composed of the silicon (Si) metasurfaces rotated 45° clockwise presenting as the phase delayer and the grating-coupled quantum well infrared photodetectors (QWIP) chip detecting the transverse magnetic (TM) mode. The circular dichroism and extinction ratio of the circular polarization (CP) photodetector are 0.25 and 20 dB at 4 μm operation wavelength, respectively. In addition, the linear dichroism (LD) and extinction ratios (ER) of the linear polarization device are 0.22 and 60 dB, respectively. The excellent LD performance is caused by the Fano resonance of the Si/SiO2 linear grating corresponding to the interference of the bright electric dipole mode and the dark electric quadrupole mode. The full Stokes pixel of the six-image-element technique can almost accurately obtain arbitrary polarized light at 4 μm operation wavelength. The errors of the degree of linear polarizations (Dolp) and the degree of circular polarizations (Docp) are less than −30 dB and −20 dB, respectively.

Design and experimental demonstration of a high-performance all-silicon transverse magnetic polarizer using tilted-elliptical-hole arrays

This study presents the design and experimental demonstration of a high-performance all-silicon transverse magnetic (TM) polarizer. The tilted-elliptical-hole arrays are designed to effectively reflect transverse electric (TE) modes while propagating TM modes with low loss. The device bandwidth (BW) is controlled by changing the tilting angle of the elliptical hole or by combining it with changes in other parameters. The device operates beyond 326 nm (1385–1711 nm) in BW, achieving an average insertion loss (IL) below 1.0 dB and a polarization extinction ratio (PER) over 20 dB. A 20 nm shift in BW can be obtained with a 30° deflection, and an 80 nm shift can be achieved with multiple parameter changes. The experimental results confirm the theoretical analysis. The present device with the advantages of simple structure, flexible design, and broad BW has great potential applications in silicon photonics.

A >20-W, linearly polarized single-frequency continuous-wave all-fiber laser at ∼1540 nm

We have developed both theoretically and experimentally an all polarization-maintaining fiber-based master oscillator power amplifier (MOPA) system, which allows for amplifying the single-frequency continuous-wave (CW) fiber laser to >20 W without compromising the laser intensity noise (−110 dBc/Hz@ relaxation oscillation peak) at the specific wavelength of ∼1540 nm. The experimental results agree well with the simulated results. To the best of our knowledge, this is the first demonstration of a ∼1540-nm single-frequency all fiber laser and reaching such a high-power level. The amplified laser features a narrow linewidth of ∼1.4 kHz and a spectral side-mode-suppression ratio of >38 dB, even as the laser wavelength is tuned from 1538.216 nm to 1540.616 nm. It is believed to be the narrowest laser linewidth realized in the <1550-nm wavelength band of an Erbium-Ytterbium co-doped fiber MOPA system. The all polarization-maintaining configuration of the MOPA ensures the amplified laser linearly polarized with the polarization extinction ratio of >22 dB and power root mean square fluctuations of <0.2 %@1h. This high-performance single-frequency fiber laser is expected to be an ideal pump source in the spin-exchange relaxation-free (SERF)-based atomic sensors after second harmonic generation.

Polarization splitter-rotator on thin film lithium niobate based on multimode interference.

Polarization splitter-rotators (PSRs) are the key elements to realize on-chip polarization manipulation. Current PSRs on thin film lithium niobate (TFLN) rely on sub-micron gaps to realize mode separation, which increases the difficulties of lithography and etching. In this paper, a PSR on TFLN based on multimode interference (MMI) is demonstrated. Mode division is achieved by an MMI-based mode demultiplexer. The minimum feature size of the PSR is 1.5 µm, which can be fabricated with low-priced i-line contact aligners. Experimental results show a polarization extinction ratio (PER) > 16 dB and an insertion loss (IL) < 1.0 dB are achieved in a wavelength range of 1530-1578 nm for TE-polarized light. And a PER > 10.0 dB and an IL <2.1 dB are achieved in a wavelength range of 1530-1569 nm for TM-polarized light. This PSR could find application in the low-cost fabrication of dual-polarization TFLN-integrated photonic devices.

All-polarization-maintaining passively mode-locked Ho-doped fiber laser oscillator and amplifier based on a nonlinear optical loop mirror

Our study reveals results from an all-polarization-maintaining Ho-doped fiber laser that is passively mode-locked, consisting of both an oscillator and an amplifier. A stable, self-starting, noise-like mode-locked pulse is achieved in the Ho-doped fiber laser oscillator based on a nonlinear optical loop mirror at a wavelength of 2.05 μm. The mode-locked oscillator achieves a peak output power of 20.2 mW, generating pulses with a duration of 284 ps and exhibiting a coherence peak at 690 fs. Moreover, with the use of Ho-doped fiber amplifier, the mode-locked pulse can reach a peak output of 1.05 W while maintaining a power stability of 1.43 % over the course of an hour. The highest pulse energy reaches approximately 333.6 nJ, which equates to a peak power of 1.18 kW. The polarization extinction ratio is approximately 24.9 dB.

Nano-pixel polarization rotator for a photonic integrated breath sensor

In response to the global aging population, a photonic-integrated-circuit sensor is investigated for the detection of disease markers within human breath content. The device relies on cavity-ring-down spectroscopy with an amplifying medium and loop feedback to secure sufficient sensitivity down to ppm-order concentration detection. This configuration, however, might cause unwanted oscillation, and the polarization rotation method has been proposed to prevent this issue. We have researched a waveguide-based polarization rotator using nano-pixels. The device consists of two regions: (1) From TE00 mode TE10 modes conversion and (2) TE10 to TM00 modes conversion. As the intermediary TE10 mode quality is key to realizing polarization rotation performance, the purpose of this study is to realize high-quality TE10 by employing the mean-squared-error criterion for waveguide design optimization. A finite-difference time-domain simulation with this method reveals a TE10 mode with 1% accuracy that results in a polarization extinction ratio improved from 4.3 to 8.6 dB.

High Performance Balanced Linear Polarization Photodetector Based on 2D ReS2

AbstractConventional research on linear polarization photodetector for 2D materials has focused on the search for different anisotropic materials, combinations between materials, introducing plasmonic structures, and patterning 2D materials to improve performance. However, these methods provide limited improvement in polarization sensitivity. Here, a balanced photodetector structure is proposed that does not require an additional process and relies only on the presence of anisotropy in the material itself to substantially improve the polarization sensitivity. The balanced photodetector consists of two ReS2 photodetectors, where the single ReS2 photodetector exhibits excellent performance at 650 nm illumination, including a responsivity and detectivity of 0.28 A W−1 and 4.22 × 109 Jones. Benefiting from the anisotropy of ReS2, the single photodetector achieves excellent polarization sensitivity of 2.79 at 650 nm. The balanced photodetector system achieves an excellent performance of ≈20 dB linear polarization extinction ratio and 0.003° Hz−1/2 noise equivalent light polarization difference at 100 kHz. These performances can also be further optimized by adjusting the gate voltage. The results provide a basis for further development of high‐performance polarization photodetector for 2D materials.

Scalable Nanoimprint Manufacturing of Functional Multilayer Metasurface Devices

AbstractOptical metasurfaces, consisting of subwavelength‐scale meta‐atom arrays, hold great promise of overcoming the fundamental limitations of conventional optics. Due to their structural complexity, metasurfaces usually require high‐resolution yet slow and expensive fabrication processes. Here, using a metasurface polarimetric imaging device as an example, the photonic structures and the Nanoimprint lithography (NIL) processes are designed, creating two separate NIL molds over a patterning area of &gt; 20 mm2 with designed Moiré alignment markers by electron‐beam writing, and further subsequently integrate silicon and aluminum metasurface structures on a chip. Uniquely, the silicon and aluminum metasurfaces are fabricated by using the nanolithography and 3D pattern‐transfer capabilities of NIL, respectively, achieving nanometer‐scale linewidth uniformity, sub‐200 nm translational overlay accuracy, and &lt;0.017 rotational alignment error while significantly reducing fabrication complexity and surface roughness. The micro‐sized multilayer metasurfaces have high circular polarization extinction ratios as large as ≈20 and ≈80 in blue and red wavelengths. Further, the metasurface chip‐integrated CMOS imager demonstrates high accuracy in broad‐band, full Stokes parameter analysis in the visible wavelength ranges and single‐shot polarimetric imaging. This novel, NIL‐based, multilayered nanomanufacturing approach is applicable to the scalable production of large‐area functional structures for ultra‐compact optic, electronic, and quantum devices.

Multifunctional Meta-Devices for Full-Polarization Rotation and Focusing in the Near-Infrared.

The creation of multi-channel focused beams with arbitrary polarization states and their corresponding optical torques finds effective applications in the field of optical manipulation at the micro-nanoscale. The existing metasurface-based technologies for polarization rotation have made some progress, but they have been limited to single functions and have not yet achieved the generation of full polarization. In this work, we propose a multi-channel and spatial-multiplexing interference strategy for the generation of multi-channel focusing beams with arbitrary polarization rotation based on all-dielectric birefringent metasurfaces via simultaneously regulating the propagation phase and the geometric phase and independently controlling the wavefronts at different circular polarizations. For the proof of concept, we demonstrate highly efficient multi-channel polarization rotation meta-devices. The meta-devices demonstrate ultra-high polarization extinction ratios and high focusing efficiencies at each polarization channel. Our work provides a compact and versatile wavefront-shaping methodology for full-polarization control, paving a new path for planar multifunctional meta-optical devices in optical manipulation at micro-nano dimensions.

871 nm single-frequency fiber laser for Yb+ ion optical clock

In recent years, there has been a dramatically increasing demand for high-performance narrow-linewidth lasers for optical atomic clock and quantum applications. In this paper, we report on a single-frequency distributed Bragg reflector fiber laser operating at 871 nm that can be used to produce a 435.5 nm narrow-linewidth laser for a Yb+ clock via second-harmonic generation. Linearly polarized single-longitudinal-mode laser output with a power of 6.7 mW and a polarization extinction ratio of 29 dB was obtained by using a 3-cm long 1 wt. % neodymium (Nd3+)-doped phosphate fiber as the gain fiber.

Compact, low-loss, and high-polarized-extinction ratio terahertz TM-pass polarizer based on a hybrid plasmonic waveguide with a graphene ridge

A compact, low-loss, and high-polarized-extinction ratio TM-pass polarizer based on a graphene hybrid plasmonic waveguide (GHPW) has been demonstrated for the terahertz band. A ridge coated by a graphene layer and the hollow HPW with a semiround arch (SRA) Si core is introduced to improve structural compactness and suppress the loss. Based on this, a TM-pass polarizer has been designed that can effectively cut off the unwanted TE mode, and the TM mode passes with negligible loss. By optimizing the angle of the ridge, the height of the ridge, air gap height, and the length of the tapered mode converter, an optimum performance with a high polarization extinction ratio of 30.28 dB and a low insert loss of 0.4 dB is achieved in the 3 THz band. This work provides a scheme for the design and optimization of polarizers in the THz band, which has potential application value in integrated terahertz systems.

Strain-Prompted Giant Flexo-Photovoltaic Effect in Two-Dimensional Violet Phosphorene Nanosheets.

As a second-order nonlinear optical phenomenon, the bulk photovoltaic (BPV) effect is expected to break through the Shockley-Queisser limit of thermodynamic photoelectron conversion and improve the energy conversion efficiency of photovoltaic cells. Here, we have successfully induced a strong flexo-photovoltaic (FPV) effect, a form of BPV effect, in strained violet phosphorene nanosheets (VPNS) by utilizing strain engineering at the h-BN nanoedge, which was first observed in nontransition metal dichalcogenide (TMD) systems. This BPV effect was found to originate from the disruption of inversion symmetry induced by uniaxial strain applied to VPNS at the h-BN nanoedge. We have revealed the intricate relationship between the bulk photovoltaic effect and strain gradients in VPNS through thickness-dependent photovoltaic response experiments. A bulk photovoltaic coefficient of up to 1.3 × 10-3 V-1 and a polarization extinction ratio of 21.6 have been achieved by systematically optimizing the height of the h-BN nanoedge and the thickness of VPNS, surpassing those of reported TMD materials (typically less than 3). Our results have revealed the fundamental relationship between the FPV effect and the strain gradients in low-dimensional materials and inspired further exploration of optoelectronic phenomena in strain-gradient engineered materials.

An ultra-thin optical polarizer based on weyl semimetals

Recently, Weyl semimetals have been extensively studied due to their unique optical responses, especially in the mid-infrared region. However, the possibility of developing optical polarizers based on Weyl semimetals remains unexplored. In this paper, under the Voigt geometry, we numerically show that an ultra-thin Weyl semimetal film with thickness L = 100 nm can achieve an impressive polarization extinction ratio (more than 40 dB) with a wide acceptance angle. Further, the proposed sandwich structure can effectively adjust the position of the TE mode transmission peak alone, thus obtaining lower insertion loss (from 0.06 dB to 0.03 dB) and wider acceptance range of angle (from 49.5∘ to 71∘). The proposed gradient Fermi level structure eliminates the Fabry-Perot cavity resonance, thus resulting a wider bandwidth (approximately 60 % improvement). Our proposed ultra-thin and wide-angle polarizer may have potential applications in optical communication and omnidirectional polarization detectors.

Broadband silicon nitride integrated polarization rotators at 780 nm

Polarization management, and in particular polarization rotation, is becoming increasingly important for photonic integrated circuits (PICs). While fiber-optic networks are generally polarization insensitive, the large aspect ratio of high-index-contrast PIC waveguides leads to a large polarization-dependent response of integrated components such as waveguides, optical cavities, couplers, etc. Although foundry-processed polarization rotators operating at telecom and datacom wavelengths (C- and O-band) have been demonstrated, to date, there have been few reports of devices operating at shorter wavelengths. This work demonstrates silicon nitride (SiN) polarization rotators operating from λ=700-1000 nm (the I/Z-band) that take advantage of optical coupling between two waveguiding layers in a standard foundry process. We demonstrate a broadband white-light polarization measurement setup that enables precise characterization of the polarization-dependent transmission of photonic waveguide devices. Measurements on foundry-processed devices confirm full TE-to-TM rotation exhibiting a maximum polarization extinction ratio (PER) approaching 20 dB (limited by our measurement setup), and an exceptionally large bandwidth of up to 160 nm with an insertion loss less than 0.2 dB. Beam propagation method (3D-BPM) simulations show good agreement with experimental data and enable the device parameters to be adjusted to accommodate different operating wavelengths and geometries with no changes to the existing foundry process. This work opens up opportunities for applications in quantum information and bio-sensing where operation at λ&lt;1000nm is needed.

Compact polarization transceiver module for fiber optic gyroscopes

This paper reports a transceiver module with a high polarization extinction ratio (PER) for the polarization-maintaining interferometric fiber optic gyroscope (PM-IFOG). This transceiver utilizes a graded-index lens featuring a slanted face coated with a multilayer film, enabling simultaneous collimation and beam splitting. Configurations of the graded-index splitter lens and the corresponding transceiver module are simulated and designed using the ray matrix method and physical optical propagation. The optical loss of the transceiver module is about 3.77 dB, and the PER exceeds 25 dB. The IFOG prototype is implemented by integrating the transceiver module with a PM sensing coil. The bias instability of the IFOG prototype is evaluated to be 0.51°/h by Allan variance. This research contributes to the reduction in size, weight, power consumption, and cost of PM-IFOG systems.

Ultra-low loss, single polarization hollow-core anti-resonant fiber

In this paper we present a new hollow-core anti-resonant fiber (HC-ARF). The structural asymmetry is constructed by the introduction of elliptical quartz tubes in the core region, which can greatly improve the birefringence and enhance the polarization extinction ratio. Meanwhile, the semicircular and circular nested quartz tubes in the cladding region also contribute to the decrease of the confinement loss of the fundamental mode. A finite element algorithm is used to analyze the effects of each parameter on the performance of the designed HC-ARF. The final simulation results illustrate that the designed structure achieves the values of birefringence and polarization extinction ratio of 2.4×10−5 and 257 in the common wavelength band of 1550 nm, and polarization filtering with a bandwidth of 4 nm. It is worth mentioning that the loss of the y-polarized fundamental mode in the 1550 nm wavelength band reaches an ultra-low value of 0.014 dB/m. The corresponding fundamental mode loss has remained extremely low in the wavelength range considered. Our proposed device still has good bending resistance, where the loss of the y-polarized mode is about 0.04 dB/m and decreases gradually when the bending radius is 5 cm. We believe that the proposed HC-ARF can be used in polarization-sensitive fiber devices and can be widely applied in polarization-sensitive fiber communication systems such as fiber lasers and fiber gyroscopes.

Superconducting nanowire single-photon detector with polarization insensitivity, ultrafast response, and high efficiency

This study proposed what we believe to be a novel method for fabricating superconducting nanowire single-photon detectors (SNSPDs) with high efficiency, polarization insensitivity, and ultrafast response. To achieve these properties in niobium nitride (NbN) SNSPDs, the periodic four-split rings (PFSR) were positioned above the nanowires. This design uses the localized surface plasmon resonance to enhance the electric field around nanowires. For an incident light with a wavelength of 1550 nm, the PFSR-SNSPD structure achieved a polarization extinction ratio of 1.0064 and absorptions of 88.94% and 88.37% under TE and TM polarizations, respectively. The nanowire length was reduced by 85% using a meandering nanowire arrangement with a fill factor of 0.074.

2.8-µm polarization-maintaining Er fiber laser mode-locked by a GaSb-based SESAM

A GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM) enables continuous-wave picosecond mode-locked operation with excellent stability of a polarization-maintaining mid-infrared Er:ZBLAN fiber laser. The GaSb-based SESAM mode-locked fiber laser delivers an average output power of 190 mW at 2.76 µm at a repetition rate of 32.07 MHz (corresponding to a pulse energy of ∼6 nJ) and exhibits a high signal-to-noise ratio of ∼80 dB. The polarization extinction ratio is more than 23 dB. By employing an intracavity diffraction grating, the laser wavelength is continuously tunable across 2.706–2.816 µm. Passively Q-switched operation of this laser is also demonstrated.

Low loss, wideband, and high extinction ratio TM polarizer based on subwavelength gratings

We propose a low loss, wideband silicon transverse magnetic (TM) polarizer with high polarization extinction ratio and low reflection based on subwavelength grating. By arranging and optimizing a mutually perpendicular subwavelength grating with different duty cycles as the core and cladding, efficient waveguiding and radiation can be achieved for the TM and transverse electric (TE) injection, respectively. In simulation, the proposed TM polarizer has a footprint of 40µm×16.68µm, an insertion loss &lt;0.7dB, a polarization extinction ratio ≥20dB, and an unwanted TE reflection &lt;−17.4dB in the wavelength range of 1230–1700 nm. Moreover, the fabrication tolerance of the proposed device is also investigated.

Broadband infrared polarizer of graphene wire grids with flat PER curves

Since 2004, the flourishing two-dimensional graphene has sparked extensive research on graphene-based optical and optoelectronic devices with high performance due to its ultra-fast photoelectric response, broadband, and tunable optical response. However, up until now, graphene-based wire grid polarizers have not been demonstrated to perform excellent characteristics with flat polarization extinction ratio (PER) curves, while they all exhibited narrow peak-shaped working bands. Here, we propose a broadband polarizer based on graphene wire grids with a flat PER curve of up to ∼84.5 dB in the ultrawide range of 1–10 μm. In the range of &amp;lt;4 μm, the graphene wire grid polarizer exhibits a strong plasmon resonance effect and outputs a linear-polarized state. Its performance is closely related to carrier density that is tuned by the Fermi level (EF) and thickness of graphene.