Polarization Extinction Ratio Research Articles

Watt-level broadband PM Tm-doped fiber amplifier for the 1750–1910 nm window

We report broadband experimental and simulated performance of a single-clad polarization-maintaining (PM) thulium-doped fiber amplifier (TDFA) optimized for operation in the 1750–1910 nm wavelength band. With the two-stage amplifier architecture, a maximum output power of 2.4 W was obtained at 1850 nm for 7.0 W of launched pump power at 1567 nm, with a corresponding optical-to-optical efficiency of 31.4 %. The measured polarization extinction ratio (PER) was larger than 22.6 dB, and the long-term power stability exhibited a peak-to-peak variation of 2.4 %. By employing a tunable seed laser covering the 1750–1910 nm wavelength range, we measured a maximum output power level of 2.38 W with an optical signal-to-noise ratio (OSNR) greater than 53 dB/0.1 nm. Our simulations are in good agreement with the experimental data over the whole 160 nm operating spectral bandwidth.

Single-frequency pulsed fiber laser based on an electro-optic modulator with injection seeding technique.

A single-frequency linearly polarization pulsed fiber laser based on an electro-optic modulator with injection seeding technique is demonstrated. The single-frequency performance of the fiber ring-cavity laser is guaranteed by the seed source, which is a distributed-feedback fiber laser based on the π-phase-shifted fiber Bragg grating. The electro-optic modulator triggers active Q-switching of the laser for pulse generation. The devices used in the fiber laser are all polarization-maintaining to ensure linear polarization laser output. Through parameter optimization, the laser generates a single-frequency linearly polarization pulsed laser with a central wavelength of 1064.22nm, linewidth of 35MHz, and polarization extinction ratio of better than 40dB. This type of fiber laser can be applied in lidar, beam combining, nonlinear frequency conversion, and other fields.

Linear polarization and narrow-linewidth external-cavity semiconductor laser based on birefringent Bragg grating optical feedback

We demonstrate an external-cavity semiconductor laser (ECSL) with linear polarization and a narrow linewidth. A birefringent Bragg grating prepared by a femtosecond laser point-by-point technique in a polarization-maintaining fiber (PMF) is used to provide external-cavity feedback, and its polarization-dependent characteristics enable selection of the main polarization mode and linewidth narrowing of the ridge waveguide emission gain chip (GC). This compact and robust ECSL achieves an output power of > 60 mW and a polarization extinction ratio (PER) of > 30 dB. We simulate and calculate the linewidth and injection current, while a Lorentz linewidth of 2.58 kHz is obtained based on delayed self-heterodyne beat frequency measurement. This flexible and cost-effective solution allows realization of a compact ECSL with linear polarization and a narrow linewidth.

Simultaneous broadband and high circular dichroism with two-dimensional all-dielectric chiral metasurface

Abstract Chiral metasurfaces have great potential in various applications such as polarimetric imaging and biomedical recognition. However, simultaneous broadband and high circular dichroism (CD) with high polarization extinction ratio (PER) remains a challenge. Here, we present a novel approach to realize simultaneous broadband and high CD with high PER in the optical communication band using a two-dimensional all-dielectric chiral metasurface. The structure is formed by a two-level chiral structure of split cross (first-order) and trapezoid-shaped (second-order) of Si nano ribs, respectively, in which constructively coupled first- and second-order of chirality occurs, resulting in the broad chiral response in the far field of multipoles excited by incident light of different chiralities. Theoretical results show that a CD in transmission reaching 0.9 (up to 0.993) and a PER exceeding 20 dB (up to 35 dB) over the entire wavelength range from 1.39 to 1.61 μm can be achieved simultaneously, consistent with the experimental results of CD ∼0.9 and PER of 10 dB (up to 19.7 dB). Our design paves the way for chiral metasurfaces toward practical applications in terms of working bandwidth, high CD and PER as well as integrality of the devices in many fields.

On-chip multifunctional polarizer based on phase change material.

Polarizers are used to eliminate the undesired polarization state and maintain the other one. The phase change material Ge2Sb2Se4Te1 (GSST) has been widely studied for providing reconfigurable function in optical systems. In this paper, based on a silicon waveguide embedded with a GSST, which is able to absorb light by taking advantage of the relatively large imaginary part of its refractive index in the crystalline state, a multifunctional polarizer with transverse electric (TE) and transverse magnetic (TM) passages has been designed. The interconversion between the two types of polarizers relies only on the state switching of GSST. The size of the device is 7.5µm∗4.3µm, and the simulation results showed that the extinction ratio of the TE-pass polarizer is 45.37dB and the insertion loss is 1.10dB at the wavelength of 1550nm, while the extinction ratio (ER) of the TM-pass polarizer is 20.09dB and the insertion loss (IL) is 1.35dB. For the TE-pass polarizer, a bandwidth broader than 200nm is achieved with ER>20dB and IL<2.0dB over the wavelength region from 1450 to 1650nm and for the TM-pass polarizer, ER>15dB and IL<1.5dB in the wavelength region from 1525 to 1600nm, with a bandwidth of approximately 75nm.

Performance Study of Polarization Beam Splitters Based on Horizontal Slot Waveguide Operating at 700nm Wavelength

Abstract: Polarization beam splitter (PBS) integrated waveguides are the key components in the receiver of quantum key distribution (QKD) systems. Their function is to analyze the polarization of polarized light and separate the transverse-electric (TE) and transverse-magnetic (TM) polarizations into different waveguides. In this paper, a performance study of polarization beam splitters based on horizontal slot waveguide has been investigated for a wavelength of . PBS based on horizontal slot waveguide structure shows a polarization extinction ratio for quasi-TE and quasi-TM modes larger than with insertion loss below and a bandwidth of . Also, the fabrication tolerance of the structure is analyzed.

Passively Q-switching an all polarization-maintaining erbium-doped fiber laser with a rhenium disulfide (ReS2) saturable absorber

This study demonstrates a linearly polarized Er-doped fiber laser system featuring an all-polarization-maintaining (all-PM) architecture. Short pulses were generated by Q-switching operation based on drop-casting rhenium disulfide (ReS2) saturable absorber (SA) onto a fiber connector placed inside the laser cavity. The Q-switching operation of the laser was able to self-start at a low (23 mW) threshold power of the pump and without the need to use a polarization controller. The proposed laser was able to produce stable pulses with a center wavelength and 3-dB bandwidth of 1558.4 nm and 0.13 nm, respectively. The shortest pulse duration measured (2.8 μs) was achieved at a repetition rate of 37.6 kHz while the highest average output power and pulse energy were 2.2 mW and 76.5 nJ, respectively. Furthermore, as the cavity of the laser was designed to be all-PM the laser that it produced was linearly polarized and had a degree of polarization (DOP) at the level of 94.5 % and 40 dB polarization extinction ratio (PER). Therefore, the proposed laser is a suitable light source for optical applications in environments that are complex.

Silicon Photonics Multi-Function Integrated Optical Circuit for Miniaturized Fiber Optic Gyroscope

Interferometric fiber optic gyroscope (IFOG) is advantageous for inertial navigation due to its high reliability as a solid-state technology with no moving parts. The size, weight, power, and cost of IFOG can be improved by employing photonic integration technology. Here, by leveraging the foundry-enabled silicon photonics platform, we demonstrate a silicon multi-function integrated optical circuit (Si-MIOC) with a fingertip size that can easily interfaces with light source and fiber coil to perform a tactical-grade gyroscope (0.1 °/hr bias instability). This achievement comes from the pros of high-index-contrast silicon waveguide that enables high polarization extinction ratio of > 60 dB and high electro-optic efficiency in silicon phase modulator, while the cons of the signature lead to non-negligible optical back-reflection at silicon/fiber interfaces and generate spurious bias voltage offset at the gyroscope outputs. Nevertheless, the results of earth rotation measurement and Allan deviation analysis confirmed that Si-MIOC based IFOG is a promising angular sensor and can be utilized to construct a compact and low-cost inertial measurement unit.

All-fiberized linearly polarized superfluorescent fiber source with 5 kW power output.

A superfluorescent fiber source (SFS) is a special fiber source that commonly possesses high temporal stability and a wide spectral linewidth. In this work, an all-fiberized linearly polarized SFS with, to our knowledge, record output power and near-diffraction-limited beam quality is presented. Up to 5.03kW SFS is achieved at a pump power of 6.18kW with a corresponding conversion efficiency of ∼81.1%. At maximum output power, the signal-to-noise ratio to background spectral noise is over 50dB, the polarization extinction ratio is ∼17d B, and the beam quality factor is M x 2=1.49, M y 2=1.44. Further comparisons confirm the power scalability of fiber amplifiers employing SFSs as seed lasers. Overall, this work could provide a good reference for potential exploration of high-power fiber laser systems.

Wide-angle high-performance polarizers based on all-elliptical-metamaterial one-dimensional photonic crystals

As a class of all-dielectric metamaterials, elliptical metamaterials (EMMs) with elliptical iso-frequency curves provide a lossless platform to manipulate light with unity efficiency. Herein, we select two kinds of EMMs as the elements to constitute a special class of one-dimensional (1D) photonic crystals (PCs) called all-EMM 1D PCs and realize polarization-sensitive photonic bandgaps (PBGs). Enabled by the polarization-sensitive property of the PBG, we achieve a wide-angle high-performance polarizer. The maximum polarization extinction ratio reaches 1.82 × 104 and the width of the operating angle range reaches 36.07°. Besides, the performance of the polarizer demonstrates robustness against the layer thickness. The all-EMM 1D PCs are 1D nanostructures completely consisting of dielectric thin films, which can be much easily fabricated compared with 2D and 3D nanostructures. Our work provides a lithography-free recipe to design wide-angle high-performance polarizers.

SNR Improvement of Optical Frequency Domain Polarimetry Against Laser Frequency Sweep Nonlinearity

A high-precision measurement of distributed polarization crosstalk (DPC) is necessary for developing the device with an ultrahigh polarization extinction ratio of even more than 80 dB. Optical frequency domain polarimetry (OFDP) is a novel DPC measurement method with a potential ultra-wide dynamic range. The degradation of dynamic range caused by interference phase error is a common issue in optical frequency domain measurement techniques. In this work, we enhanced the dynamic range by solving the phase error problem induced by the laser frequency sweep nonlinearity to improve the measurement precision of weak polarization crosstalk. The aliasing issue caused by the fluctuation of the frequency sweep rate is the primary reason for the limited dynamic range. We proposed a modified dynamic range limit model of OFDP considering the aliasing issue. The experimental results agree with the inflection points predicted by the modified dynamic range limit model. Under the guidance of the model, we achieved a dynamic range of more than 115 dB with different optical path differences of the interferometer and various sweep rates of the laser. Compared to the DPC measurement method with a dynamic range of 100 dB, the measurement repeatability is improved from 7.0 dB to <1.0 dB for polarization crosstalk less than -95 dB.

A bi-Layered chiral metasurface as a multi-functional polarization convertor with high incidence angle stability

This paper introduces a polarization converter with multiple functions constructed using a bi-layered chiral metasurface. The chiral metasurface has double-modified metal layers on a dielectric substrate. The results authenticate the superior efficiency of the structure in achieving both circular birefringence and circular dichroism characteristics. The chiral metasurface can convert y-(x-) polarized electromagnetic lights to circularly polarized waves at 7.18 GHz and 8.85 GHz. When the x-(y-) polarized wave interacts with chiral metamaterial in –z(+z) orientations, it results in a transmitted wave of y-(x-) polarized light (15–17 GHz). The extracted significant polarization conversion ratio above 0.9 (15–17 GHz) and the considerable polarization extinction ratio (PER) over 40 dB (7.18 GHz) and -22dB (8.85 GHz) confirm the considerable potential of the offered chiral metasurface in acquiring the transmitted waves with approximately pure circular and linear polarization. The proposed structure has reliable asymmetric transmission properties and can function as a stable polarizer in the microwave spectrum.

Multi-mode polarization-filtering hollow core anti-resonance fiber using SPR

A multi-mode polarization-filtering hollow core anti-resonance fiber whose cladding is composed of four circular tubes and four elliptical tubes is demonstrated. In the vertical directions, two small nested elliptical tubes are coated with gold films in the inner wall. This fiber can filter x-polarized LP01, LP21 and LP02 modes in different wavelengths through surface plasmon resonance which, is produced by two gold films. The polarization extinction ratio of LP01, LP21 and LP02 modes can reach 293, 116 and 30 at the wavelength of 1550 nm, 1570 nm and 1574 nm, respectively. We can adjust the polarization-filtering operation wavelength by changing the ellipticity of elliptical tubes in the cladding. Thus, this fiber can achieve polarization-filtering operation in the whole C and L bands.

Development and analysis of a nano-triangular wave-shaped polarizer

As society becomes smarter, advanced optical sensing and imaging technologies utilizing visible and near-infrared regions have become increasingly prevalent. Wire-grid polarizers, which are available for broadband electromagnetic waves, are effective in improving the signal-to-noise ratio of such optical systems and enabling more advanced object detection and analysis. However, to be implemented in everyday products, low-cost manufacturing methods must be developed while maintaining high-performance optical functions. To meet these requirements, we conducted an analysis of the geometry of wire-grid polarizers, and designed and developed a wire-grid polarizer with a nano-triangular wave-shaped structure that can be fabricated using general-purpose manufacturing equipment. Once the mould is prepared, this polarizer can be fabricated via nanoimprinting and metal deposition with a normal angle or electroless plating processes. The polarizer fabricated through electroless Ni plating achieves a transmittance of 40%, which is approximately 1.4 times higher than that achieved in a previous study using electroless Ni plating on a rectangular structure with the same period. In addition, the polarizer fabricated through normal angle Al deposition operates over a wide range of wavelengths from visible light to near-infrared, and achieves a polarization extinction ratio of 24 dB at a wavelength of 550 nm and a high transmittance of 81%. High-performance polarizers can be obtained through normal-angle deposition using general-purpose equipment in contrast to the oblique-angle deposition method employed in the manufacture of conventional rectangular structure-based wire-grid polarizers, thereby contributing to cost reduction and improved manufacturability.

Over 60% Optical-to-Optical Conversion Efficiency Linearly Polarized Single-Frequency Fiber Laser Based on Yb: YAG Crystal-Derived Silica Fiber

Silica optical fiber derived from yttrium-aluminum-garnet (YAG) crystals is an excellent high-gain fiber due to their high rare earth ions doping concentration. It offers a new opportunity of addressing the constraints on optical-to-optical conversion efficiency and output power in silica gain fiber-based linearly polarized single-frequency fiber lasers (LPSFFL). Here, we fabricated a 6.57 wt.% Yb: YAG crystal-derived silica fiber (YCDSF) with a gain coefficient of 6.0 dB/cm at 1030 nm. Using a 0.8-cm-long YCDSF, a stable LPSFFL has been constructed, having an output power of over 350 mW and an optical-to-optical conversion efficiency as high as 63.0%. Among the similar YCDSF-based SFFLs, it has the highest output power and the largest conversion efficiency, to the best of our knowledge. By controlling the polarization state in the cavity, the optimum performances of the laser were accomplished with a relative intensity noise of <-143.5 dB/Hz, and a polarization extinction ratio of >21 dB. The approach presented here could be applicable to other RE: YAG crystal-derived silica fibers-based LPSFFLs operating at different wavelengths, paving the way for their applications in areas such as industrial processing, bioanalytic, metrology, and precision detection.

On-chip long-wavelength infrared polarimeter for full-Stokes polarization detection

Polarization detection is a critical technique in various research and application fields, especially in the long-wavelength infrared regime for target discrimination from complex backgrounds. With the trend of miniaturization and integration, on-chip full-Stokes polarimeters are eagerly pursued. However, how to achieve efficient linear and circular polarimetry simultaneously on the same detection material chip with sufficient polarization extinction ratios and responsivities still remains a challenge. In this work, we propose an on-chip long-wavelength infrared full-Stokes polarimeter based on the integration of anisotropic and twisted metamaterials on the same quantum well material chip. The device consists of six subpixels with different principle detection polarization states. Based on the dual polarization selection by the structure and the detection material, the linear polarization extinction ratio exceeds 106 and the circular polarization extinction ratio reaches 150. In addition, the absorptance of the detection material is enhanced by more than 16 times. Through simple subtracting and normalization operations on the photocurrents of the subpixels, the Stokes parameters are obtained with small root mean square errors. The device performance remains at a high level over the incident angle range of ±5°. This work points out a promising way for on-chip long-wavelength infrared full-Stokes detection. The device architecture is compatible with focal plane arrays.

High-performance terahertz polarization filter based on the anti-resonant fiber

A novel terahertz polarization filter based on the anti-resonant fiber is designed and analyzed. The polarization extinction ratio (PER) is improved by using high-resistivity silicon (HRS) as the bulk material in conjunction with a double conjoined tube cladding structure. The effects of the structure and material of the anti-resonant fiber on the polarization filtering characteristics are analyzed by the finite element method. The PER of the anti-resonant fiber reaches 100 dB and the insertion loss of y-polarization fundamental mode (YPFM) is less than 0.66 dB at 1 THz when the anti-resonant fiber length is 5.58 cm. The bandwidth can be expanded by changing the fiber length and for a fiber length of 8 cm, the frequency bandwidth is 0.92–1.14 THz and the insertion loss is less than 3 dB. The polarization filter is demonstrated to deliver excellent performance in the terahertz frequency range and has large commercial potential in terahertz communication and biomedical spectroscopy.

The Ultra-Large-Bandwidth Cascade Full-Stokes-Imaging Metasurface Based on the Dual-Major-Axis Circular Dichroism Grating.

A dual-major-axis grating composed of two metal-insulator-metal (MIM) waveguides with different dielectric layer thicknesses is numerically proposed to achieve the function of the quarter-wave plate with an extremely large bandwidth (1.0-2.2 μm), whose optical properties can be controlled by the Fabry-Pérot (FP) resonance. For the TE incident mode wave, MIM waveguides with large (small) dielectric layer thicknesses control the guided-mode resonant channels of long (short) waves, respectively, in this miniaturized optical element. Meanwhile, for the TM incident mode wave, the propagation wave vector of this structure is controlled by the hybrid mode of two gap-SPPs (gap-surface plasmon polaritons) with different gap thicknesses. We combine this structure with a thick silver grating to propose a circularly polarizing dichroism device, whose effective bandwidth can reach an astonishing 1.65 μm with a circular polarization extinction ratio greater than 10 dB. The full Stokes pixel based on the six-image element technique can almost accurately measure arbitrary polarization states at 1.2-2.8 μm (including elliptically polarized light), which is the largest bandwidth (1600 nm) of the full Stokes large-image element to date in the near-infrared band. In addition, the average errors of the degree of linear polarizations (Dolp) and degree of circular polarizations (Docp) are less than -25 dB and -10 dB, respectively.

Multi-frequency polarization and electro-optical modulator based on triple plasmon- induced transparency in monolayer graphene metamaterials

In this paper, a dynamically tunable triple plasmon-induced transparency (PIT) is numerically investigated in a simple monolayer graphene- patterned structure. The structure is composed of five graphene strips and a silicon substrate. Electric field distributions show that the triple PIT effect is originated from the strong destructive interference between three bright modes and one dark mode, coupled mode theory (CMT) is utilized to confirm the finite-difference-time-domain (FDTD) simulation. Results show the maximum figure of merit (FOM) and sensitivity can reach 15.88 and 0.91 THz/RIU. A on-to-off electro-optical modulator is realized by tuning the Fermi levels of the graphene, the modulation degrees of amplitude are 79.3 %, 87.1 %, 70.5 %, 79.2 %, and 84.3 %, corresponding to 2.35 terahertz (THz), 3.12THz, 3.58 THz, 3.91THz, and 4.31 THz, respectively. In addition, the effect of polarized angle on the transmission spectra was studied in detail. A multi-frequency polarization modulator can also be realized with modulation degrees of amplitude (MDA) of 77.6 %, 85.9 %, and 93.7 % at 2.09 THz, 2.82 THz, and 3.59 THz, respectively, and the corresponding polarization extinction ratio (PER) are 6.5 dB, 8.5 dB, and 12.1 dB, respectively. Therefore, the results of the paper are significant to the design of multi-frequency, terahertz sensors, slow light, and modulators.

Ultralow-quantum-defect single-frequency fiber laser.

A single-frequency distributed-Bragg-reflector fiber laser at 980 nm with a quantum defect of less than 0.6% was developed with a 1.5-cm 12 wt% ytterbium-doped phosphate fiber pumped by a 974.5-nm laser diode. Linearly polarized single-longitude-mode laser with a polarization extinction ratio (PER) of nearly 30 dB and spectral linewidth of less than 1.8 kHz was obtained. A maximum output power of 275 mW was measured at a launched pump power of 620 mW. The performance of the single-frequency fiber laser pumped at 909 nm and 976 nm was also characterized. This research demonstrated an approach to high-power single-frequency fiber laser oscillators with mitigated thermal effects.