Polarization Crosstalk Research Articles

High-sensitivity fiber temperature sensor based on composite film structure and lossy mode resonance

In this work, we proposed and demonstrated a high-sensitivity optical fiber temperature sensor based on lossy mode resonance (LMR). The sensor is composed of a D-shaped fiber and a thin composite film. The composite film consists of tin dioxide (SnO2) and polydimethylsiloxane (PDMS). PDMS is inserted as an intermediate layer between D-shaped fiber and SnO2 layer, realizing the separation of TM and TE polarization to reduce polarization crosstalk, while also serving as a temperature sensitive layer. The polarization state of the excited LMR can be freely controlled by adjusting the thickness of the composite film. The proposed sensor exhibits a high temperature sensitivity of −1.1883 nm/°C with a measurement range of 10–90 °C. Meanwhile, a fast response time of ∼ 109 ms was observed due to the ultra-thin PDMS interlayer.

8K Real-Time Video-Transmission Using PDM and FDM in 220-GHz Band Based on Polarization Crosstalk Model and Optimization Strategy

8K Real-Time Video-Transmission Using PDM and FDM in 220-GHz Band Based on Polarization Crosstalk Model and Optimization Strategy

Ultra‐Low Loss Lithium Niobate Polarizer with Enhanced Anti Bound State in the Continuum

AbstractThin film lithium niobate (TFLN) has emerged as a promising platform for photonic integrated circuits (PICs). However, the polarization crosstalk is usually inevitable owing to its birefringence. Polarizers, as key polarization handling devices, are essential to ensure polarization purity in PICs. In this work, a novel ultra‐low loss polarizer is proposed and demonstrated based on the enhanced anti‐bound state in the continuum (anti‐BIC) on TFLN. With meticulously designed waveguide width, constructive interference occurs for the leaky modes, such that transverse magnetic (TM) bound mode can drastically couple into the continuum modes, leading to high propagation loss for TM polarization. Meanwhile transverse electric (TE) polarization remains bound with high optical confinement, hence low propagation loss. Furthermore, it have demonstrated that angled sidewalls can facilitate the mode conversion from bound mode into continuum mode in lithium niobate (LN), which can be an efficient method for controlling the bound mode coupling into the continuum. Ultra‐low loss of <≈0.04 dB and compact footprint of 46 µm are experimentally demonstrated from 1460 to 1600 nm for the fabricated polarizer.

Multimode interference coupler based on general interference for integrated optical and quantum optic devices: a review

Integrated optics play important role in the development for optical network devices, optical processing, instrumentation and quantum information device. Here, multimode interference (MMI) coupler is one of basic component preferred for these integrated optic devices in which MMI coupler based on general interference (GIMMI) has been focused for large scale integrated optic devices because of compact size in comparison to MMI coupler based restricted interference (RIMMI). In this paper, we have reviewed different GIMMI structures reported previously. Different waveguide materials are mentioned and compared for fabrication of GIMMI device. The coupling behaviors and modal analysis of GIMMI couplers and their different tapered structures are estimated by using simple model based on sinusoidal modes showing reduced coupling lengths in down tapered structures in comparison to other structures. The excess loss, polarization dependence loss and crosstalk versus fabrication tolerances are obtained to compare their performances revealing almost same losses and fabrication tolerance. The paper reports the use of the GIMMI coupler in wavelength multiplexing, power splitting, switching, optical processing. Finally, Quantum optic application of GIMMI coupler is shown indicating high quantum fidelity of 50:50 coupling ratio.

Compact and broadband silicon polarization splitter-rotator using adiabaticity engineering.

We propose and demonstrate a short and broadband silicon mode-conversion polarization splitter-rotator (PSR) consisting of a mode-conversion taper and an adiabatic coupler-based mode sorter both optimized by adiabaticity engineering (AE). AE is used to optimize the distribution of adiabaticity parameter over the length of the PSR, providing shortcut to adiabaticity at a shorter device length. The total length of the PSR is 85 µm. The design is compatible with standard silicon photonics platforms and requires only one patterning step. Fabricated PSR has a polarization cross talk of less than -20 dB over the entire O-band for the TE polarization and a polarization cross talk of less than -15 dB from 1267 to 1348 nm for the TM polarization. Overall, the PSR shows low polarization cross talk (-15 dB) over a bandwidth of 81 nm in the O-band. Cross-wafer measurements show that the PSR has good fabrication tolerance.

Generalized Rayleigh quotient optimization method for inter-channel nonlinearity compensation in coherent optical communication systems.

Inter-channel nonlinearity compensation plays a crucial role in wavelength division multiplexing (WDM) systems for improving transmission capacity and distance. In this work, we propose a novel, to the best of our knowledge, inter-channel nonlinearity compensation method called generalized Rayleigh quotient optimization (GRQO) method with two different working modes. In an 8 × 64 GBaud 16-ary quadrature amplitude modulation (16-QAM) experimental system over 1600 km standard single-mode fiber (SSMF), the proposed method shows a 0.40 dB Q2 factor improvement over nonlinear polarization cross talk canceller (NPCC) with a moderately low computational complexity of about 2000 real multiplications per bit (RMb).

Integration of Sensing and Communication in a W-Band Fiber-Wireless Link Enabled by Electromagnetic Polarization Multiplexing

The coexistence needs of sensing and communication in millimeter-wave (mmW) bands have urgently driven the seamless integration of sensing and communication in the upcoming mmW era. However, the time-frequency competition between the two functions makes it difficult to accommodate both high sensing resolution and large communication capacity. In this paper, we have designed a W-band fiber-wireless link with the integrated sensing and communication functions enabled by electromagnetic polarization multiplexing. The ultra-wideband fiber-wireless link in W band is enabled by the asymmetrical single-sideband modulation along with the optical heterodyne up-conversion. The electromagnetic polarization multiplexing allocates the sensing and communication functions on two orthogonal electromagnetic polarizations, respectively. Thus, all time-frequency resources of the fiber-wireless link can simultaneously serve these two functions without any resource competition, contributing to an ultra-high spatial resolution and an ultra-large data capacity at the same time. Our experimental results show the spatial resolution of up to 15 mm and data rate as high as 92 Gbit/s were simultaneously realized in W band after delivering over a 10.8-m wireless distance. The overall improvement of both the sensing and communication performance, to the best of our knowledge, led to a record capacity-resolution quotient of 61.333 Gbit/s/cm. In addition, we have qualitatively investigated the integrated sensing and communication fiber-wireless link, in terms of the carrier frequency, system bandwidth, multi-mmW access, and electromagnetic polarization crosstalk.

ECM-Engineered Electrospun Fibers with an Immune Cascade Effect for Inhibiting Tissue Fibrosis.

Tissue regeneration/fibrosis after injury is intricately regulated by the immune cascade reaction and extracellular matrix (ECM). Dysregulated cascade signal could jeopardize tissue homeostasis leading to fibrosis. Bioactive scaffolds mimicking natural ECM microstructure and chemistry could regulate the cascade reaction to achieve tissue regeneration. The current study constructed an ECM-engineered micro/nanofibrous scaffold using self-assembled nanofibrous collagen and decorin (DCN)-loaded microfibers to regulate the immune cascade reaction. The ECM-engineered scaffold promoted anti-inflammatory and pro-regenerative effects, M2 polarization of macrophages, by nanofibrous collagen. The ECM-engineered scaffold could release DCN to inhibit inflammation-associated fibrous angiogenesis. Yet, to prevent excessive M2 activity leading to tissue fibrosis, controlled release of DCN was expected to elicit M1 activity and achieve M1/M2 balance in the repair process. Regulated cascade reaction guided favorable crosstalk between macrophages, endothelial cells and fibroblasts by proximity. Additionally, decorin could also antagonize TGF-β1 via TGF-β/Smad3 pathway to suppress fibrotic activity of fibroblasts. Hence, ECM-engineered scaffolds could exert effective regulation of the immune cascade reaction by microstructure and DCN release and achieve the balance between tissue fibrosis and regeneration. STATEMENT OF SIGNIFICANCE: : With the incidence of up to 74.6%, failed back surgery syndrome (FBSS) has been a lingering issue in spine surgery, which poses a heavy socio-economic burden to society. Epidural fibrosis is believed to be responsible for the onset of FBSS. Current biomaterial-based strategies treating epidural fibrosis mainly rely on physical barriers and unidirectional suppression of inflammation. Regulation of the immune cascade reaction for inhibiting fibrosis has not been widely studied. Based on the simultaneous regulation of M1/M2 polarization and intercellular crosstalk, the ECM-engineered micro/nanofibrous scaffolds constructed in the current study could exert an immune cascade effect to coordinate tissue regeneration and inhibit fibrosis. This finding makes a significant contribution in the development of a treatment for epidural fibrosis and FBSS.

Hardware-Efficient and Robust DSP Scheme for Coherent DSCM System in Presence of Transmitter IQ Impairments

In this paper, a hardware-efficient and robust DSP scheme for the coherent digital subcarrier multiplexing (DSCM) system in presence of transmitter (Tx) in-phase/quadrature (IQ) impairments is introduced and demonstrated. An analytic complex model is given to describe the effects of IQ skew, IQ amplitude and phase imbalance (referred to as IQ mixing) on the DSCM signal. Based on the model, residual frequency offset, polarization and carrier phase noise are jointly recovered using frequency pilot tones (FPT) in presence of IQ mixing. This process avoids the coupling effect of phase noise and Tx IQ mixing in conventional schemes, which allows the Tx IQ mixing to be compensated for by the following joint equalization of conjugate symmetric subcarriers. Compared to the conventional scheme based on widely linear equalizer, the polarization and carrier phase tracking capability of the proposed scheme is robust to IQ mixing. Meanwhile, the proposed scheme can tolerate a wide range of Tx IQ mixing in the presence of residual frequency offset and carrier phase noise. Since polarization crosstalk is eliminated, the signals of the two polarizations can be equalized separately in the proposed scheme, thus reducing the computational complexity by half. For a 4-subcarrier DSCM system with baud rate of 32 Gbaud, experimental results show that the Q-factor degradation of the proposed scheme is less than 0.5dB in the presence of Tx IQ time skew within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 15 ps, IQ phase imbalance within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 20 degrees or IQ amplitude imbalance within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 3 dB. With 1dB Q-factor degradation, the proposed scheme can track polarization variation up to 10 Mrad/s, residual frequency offset of 10 MHz or carrier phase noise with 3dB linewidth of 200 kHz in the presence of Tx IQ mixing. Therefore, the proposed scheme provides a hardware-efficient and robust DSP solution for coherent DSCM targeting access network applications.

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.

Simplified analysis and suppression of polarization aberration in planar symmetric optical systems.

Polarized remote sensing imaging has attracted more attention in recent years due to its wider detection information dimension compared to traditional imaging methods. However, the inherent instrument errors in optical systems can lead to errors in the polarization state of the incident and outgoing light, which is the polarization aberration of the optical system, resulting in a decrease in polarization detection accuracy. We propose a polarization aberration simplification calculation method for planar symmetric optical systems, by what only three ray samples are needed to obtain the distribution of polarization aberrations within the pupil. This method has a calculation accuracy close to traditional methods, and the sampling rate is 0.003 times that of traditional methods. Based on this, we designed a merit function that optimizes both wavefront and polarization aberrations simultaneously. It is found that diattenuation and retardance of the optical system are 62% and 58% of the original, and the polarization crosstalk term is reduced by 37% when the polarization weight factor takes an appropriate value. And at the same time, the wavefront aberration has also been well optimized.

Silicon-Nanowire-Type Polarization-Diversified CWDM Demultiplexer for Low Polarization Crosstalk.

Coarse wavelength division multiplexing (CWDM)-targeted novel silicon (Si)-nanowire-type polarization-diversified optical demultiplexers were numerically analyzed and experimentally verified. The optical demultiplexer comprised a hybrid mode conversion-type polarization splitter rotator (PSR) and a delayed Mach-Zehnder interferometric demultiplexer. Si-nanowire-based devices were fabricated using a commercially available Si photonics foundry process, exhibiting nearly identical spectral responses regardless of the polarization states of the input signals under the PSR. The experiment demonstrated a low insertion loss of 1.0 dB and a polarization-dependent loss of 1.0 dB, effectively suppressing spectral crosstalk from other channels by less than -15 dB. Furthermore, a TM-mode rejection-filter-integrated optical demultiplexer was designed and experimentally validated to mitigate unwanted TM-mode-related polarization crosstalk that arose from the PSR. It exhibited an improved polarization crosstalk rejection efficiency of -25 dB to -50 dB within the whole CWDM spectral range.

A 32-Channel C-Band Hybrid Wavelength/ Polarization Division (de)multiplexer on Silicon

A 32-channel hybrid (de)multiplexer on silicon is designed and experimentally demonstrated to enable polarization division multiplexing (PDM) and wavelength division multiplexing (WDM) for improving the capacity of optical communication links. The hybrid (de)multiplexer is realized by monolithically integrating a polarization rotator and splitter (PRS) and two 16-channel microring resonators (MRRs) arrays. The through and cross ports of the PRS are connected to the bus waveguide of the MRR arrays, respectively. In order to ensure a larger free spectrum range (FSR) to cover all wavelength channels, the radius of the microring is about 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m and the wavelength-channel spacing is 1.6 nm. For the hybrid (de)multiplexer, the crosstalk between the adjacent channels and the non-adjacent channels are -20 dB and -25 dB, respectively. When TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode input, the insertion loss is 1.5 dB - 3.8 dB, the crosstalk between the through and cross port is less than -24 dB. When TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{0}$</tex-math></inline-formula> mode inputs, the insertion loss is 1.9 dB - 4.5 dB and the polarization crosstalk is less than -22 dB. In order to eliminate the influence of the fabrication errors and temperature on resonance wavelength, a TiN thermal tuning electrode is added to calibrate the deviation of the wavelength.

Monolithically Integrated O-Band Coherent ROSA Featuring 2D Grating Couplers for Self-Homodyne Intra Data Center Links

In this work, we present an O-band dual-polarization coherent receiver optical sub-assembly (cROSA), monolithically integrated in a 0.25 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> m BiCMOS technology. The receiver features 248 nm deep ultra violet compatible 2-dimensional grating couplers (2D-GRCs), and an adaptive polarization controller, suitable for mitigation of local oscillator induced power fading in self-homodyne transmission systems. The cROSA is evaluated in system experiments at 64 GBd quadrature-phase shift-keying. Experimental results are related to grating coupler induced polarization crosstalk through Monte-Carlo simulations. Second generation 2D-GRCs are proposed.

Optical frequency domain polarimetry based on a self-referenced unbalanced Mach-Zehnder interferometer.

Optical frequency domain polarimetry (OFDP) is an emerging distributed polarization crosstalk rapid measurement method with an ultrawide dynamic range. However, interferometric phase noise induced by the laser source and ambient noise results in a trade-off between measurement length and dynamic range. In this Letter, we solve this problem with a self-referenced unbalanced Mach-Zehnder interferometer. The features of long distance (9.8 km), ultrawide dynamic range (107.8 dB), short measurement time (2 sec), and signal-to-noise ratio improvement against ambient noise are experimentally demonstrated. The method makes it possible to evaluate a long polarization-maintaining fiber in an environment whose state changes rapidly.

A Photonics-Assisted Binary/Quaternary Phase-Coded Microwave Signal Generator Applicable to Digital I/O Interfaces.

A photonics-assisted binary/quaternary phase-coded microwave signal generator with fundamental/doubling reconfigurable carrier frequency applicable to digital I/O interfaces is proposed and has been verified by experiments. This scheme is based on a cascade modulation scheme, which is used to reconfigure fundamental/doubling carrier frequency and load the phase-coded signal, respectively. By controlling the radio frequency (RF) switch and the bias voltages of the modulator, the switching of the fundamental or doubling carrier frequency can be realized. When the amplitudes and sequence pattern of the two independent coding signals are set reasonably, binary or quaternary phase-coded signals can be realized. The sequence pattern of coding signals is applicable to digital I/O interfaces and can be directly generated through the IO interfaces of FPGA instead of an expensive high-speed arbitrary waveform generator (AWG) or other digital-to-analog conversion (DAC) systems. A proof-of-concept experiment is carried out, and the performance of the proposed system is evaluated from the aspects of phase recovery accuracy and pulse compression capability. In addition, the influence of residual carrier suppression and polarization crosstalk in non-ideal states on phase shifting based on polarization adjustment has also been analyzed.

Nonlinear polarization crosstalk canceled wavelength conversion for Pol-Mux OFDM signal with polarization-diversity FWM.

We present a model that is capable of describing the polarization crosstalk in terms of nonlinear polarization rotation (NPR) of semiconductor optical amplifier (SOA) in wavelength conversion for polarization multiplexing (Pol-Mux) orthogonal frequency division multiplexing (OFDM) signal. Then a simple nonlinear polarization crosstalk canceled wavelength conversion (NPCC-WC) with polarization-diversity four-wave mixing (FWM) is proposed. The effectiveness is achieved successfully in the proposed wavelength conversion for the Pol-Mux OFDM signal by using simulation. In addition, we studied the influence of several system parameters on the performance, including the power of the signal, SOA's injection current, frequency spacing, polarization angle of signal, laser linewidth, and modulation order. The results show that the proposed scheme has better performance due to crosstalk cancellation than the conventional scheme, such as wider wavelength tunability, lower polarization sensitivity, and wider laser linewidth tolerance.

Improved Thermal Stability of a Fiber Optic Gyroscope Using a Geometric Birefringence-Enhanced Polarization- Maintaining Fiber

In this paper, we propose and experimentally demonstrate an interferometric fiber optic gyroscope (IFOG) composed of an optimized elliptical-core Panda polarization-maintaining fiber (PMF) based on a comprehensive analysis of the design principle of PMFs for IFOGs. The improvement mechanism of the geometric birefringence on the performance of the Panda PMF was analyzed using the finite element model, and the optimized structural parameters were selected for fiber fabrication. The extinction ratio, polarization crosstalk, and assembled closed-loop IFOG output were tested and compared for fiber coils wound by different fiber structures under different temperature loads. An angle random walk performance of 0.001723 °/√h was achieved, which is a significant improvement over the traditional IFOG. The experimental results confirmed the proposed design basis that the elliptical-core Panda PMF with both higher birefringence and lower effective mode refractive index can improve the temperature stability of the IFOG.

Continuous fabrication of polarization maintaining fibers via an annealing improved infinity additive manufacturing technique for THz communications.

We report the design and fabrication of a polarization-maintaining fiber for applications in fiber-assisted THz communications. The fiber features a subwavelength square core suspended in the middle of a hexagonal over-cladding tube by four bridges. The fiber is designed to have low transmission losses, high birefringence, high flexibility, and near-zero dispersion at the carrier frequency of 128 GHz. An infinity 3D printing technique is used to continuously fabricate a 5 m-long polypropylene fiber of ∼6.8 mm diameter. The fiber transmission losses are furthermore reduced by as high as ∼4.4 dB/m via post-fabrication annealing. Cutback measurements using 3 m-long annealed fibers show ∼6.5-11 dB/m and ∼6.9-13.5 dB/m losses (by power) over a 110-150 GHz window for the two orthogonally polarized modes. Signal transmission with bit error rates of ∼10-11-10-5 is achieved at 128 GHz for 1-6 Gbps data rates using a 1.6 m-long fiber link. The average polarization crosstalk values of ∼14.5 dB and ∼12.7 dB are demonstrated for the two orthogonal polarizations in fiber lengths of 1.6-2 m, which confirms the polarization-maintaining property of the fiber at ∼1-2 meter lengths. Finally, THz imaging of the fiber near-field is performed and shows strong modal confinement of the two orthogonal modes in the suspended-core region well inside of the hexagonal over-cladding. We believe that this work shows a strong potential of the infinity 3D printing technique augmented with post-fabrication annealing to continuously produce high-performance fibers of complex geometries for demanding THz communications applications.

ROS mediated pyroptosis-M1 polarization crosstalk participates in inflammation of chicken liver induced by bisphenol A and selenium deficiency

The earth's natural environmental factors and man-made industrial pollution often lead to the co-occurrence of environmental pathogenic factors and malnutrition. Bisphenol A (BPA) is a serious environmental endocrine disruptor, and its exposure can cause liver tissue damage. Selenium (Se) deficiency is a worldwide problem that afflicts thousands of people, and Se deficiency can cause M1/M2 imbalance. In addition, the crosstalk between hepatocyte and immune cell is closely related to the occurrence of hepatitis. Therefore, this study found for the first time that the combined exposure of BPA and Se deficiency caused liver pyroptosis and M1 polarization through ROS, and the crosstalk between pyroptosis and M1 polarization aggravated liver inflammation in chicken. In this study, the BPA or/and Se deficiency chicken liver, single and co-culture model of LMH and HD11 cells were established. The results displayed that BPA or Se deficiency induced liver inflammation accompanied by pyroptosis and M1 polarization through oxidative stress, and increased expressions of chemokines (CCL4, CCL17, CCL19, and MIF) and inflammatory factors (IL-1β and TNF-α). The vitro experiments further verified the above changes and showed that LMH pyroptosis promoted M1 polarization of HD11 cells, and vice versa. NAC counteracted pyroptosis and M1 polarization caused by BPA and low-Se, reducing the release of inflammatory factors. In brief, BPA and Se deficiency treatment can exacerbate liver inflammation by increasing oxidative stress to induce pyroptosis and M1 polarization.