Polarization-multiplexed Research Articles

Performance analysis of VLC-based underwater optical communication using polarization division multiplexing and advanced modulation techniques

Abstract Underwater wireless optical communication (UWOC) has emerged as a promising solution for high-speed, low-latency communication in underwater environments. This study investigates the performance of a visible light communication (VLC)-based UWOC system incorporating polarization division multiplexing (PDM) and advanced modulation schemes, including non-return-to-zero (NRZ) and return-to-zero (RZ). The system, utilizing red, green, and blue (RGB) wavelengths, was evaluated under three distinct environmental conditions: Pure Sea, Clear Ocean, and Coastal Ocean, each characterized by varying levels of attenuation due to differences in scattering and absorption coefficients. Through comprehensive simulations, key performance metrics such as bit error rate (BER), transmission range, and eye patterns were analyzed. Results reveal that RZ modulation consistently outperformed NRZ, providing superior signal clarity and lower BER across all conditions. Among the wavelengths, blue light demonstrated the best performance due to its lower susceptibility to attenuation, making it ideal for high-speed communication. These findings contribute to the development of robust UWOC systems for applications in environmental monitoring, underwater exploration, and autonomous vehicle communication.

Using artifact suppression OCT based on polarization multiplexing for tomographic imaging of LCD screens

Defect detection in the inner layers of liquid crystal display (LCD) panels is crucial for the quality control of displays. Optical coherence tomography (OCT), a nondestructive, high-resolution tomographic imaging technique, has been applied in the inspection of display panels. However, the artifacts that arise in imaging multilayer samples remain a challenge. In this study, we propose and validate a method for artifact removal in coherent imaging of multilayer refractive samples. These samples exhibit complex autocorrelation artifacts due to self-interference and multiple reflections. Two orthogonally polarized reference beams with fixed phase shifts, combined with the proposed algorithm, are employed to suppress the autocorrelation in the sample light path. To address the issue of mirror artifacts caused by real spectrum signals, the intensity ratio of the two orthogonally polarized reference beams is adjusted, allowing distinction between real signals and mirror artifacts, thus achieving full-range imaging. Experiments were conducted to measure 3D images of multilayer quartz glass sheets, inclined ceramic blocks, and LCD panels, validating the reliability of the proposed approach and demonstrating its advantages in display defect detection.

Compact and broadband polarization splitter-rotator on thin-film lithium niobate minimized with the fast quasi-adiabatic algorithm.

Polarization splitter-rotators (PSRs) are crucial for on-chip polarization-division multiplexing (PDM) systems. Here, we design and experimentally demonstrate a compact and broadband PSR based on adiabatic mode evolution on a thin-film lithium niobate (TFLN) platform. A novel, to the best of our knowledge, quasi-adiabatic algorithm is proposed to minimize the device size. The fabricated PSR, with an adiabatic waveguide length of only 0.4 mm, exhibits an insertion loss of <0.64 dB and a polarization extinction ratio of >20 dB over a 122-nm bandwidth.

Multipolar multifunction terahertz tunable metasurface

A terahertz coded metasurface composed of VO2, polyimide, and Au is proposed. Based on line polarization multiplexing, seven functions in all are realized by designing the structure of the top VO2 resonator and the middle gold pattern. The simulation results show that when VO2 is metallic and the linearly polarized wave of f=1−2THz is vertically incident, the unit exhibits broadband absorption with an absorption rate (AR) greater than 84%. The AR in the range of 1.56–2 THz can reach more than 90%. When VO2 is insulated, the unit can achieve narrowband absorption at 1.57 THz, with an AR of nearly 100%. Meanwhile, the same coded metasurface can realize one of the five functions of beam deflection, vortex beam, deflected vortex beam, beam splitting, and superimposed vortex beam under x and y polarization modes. This work can provide certain reference for the design of multifunctional devices with metamaterial in the terahertz field.

Meta-coupler empowered dynamic wavefront control with on-chip polarization reconfiguration.

Metasurfaces consisting of subwavelength structures have shown unparalleled capability in light field manipulation. However, their functionalities are typically static after fabrication, limiting their practical applications. Though persistent efforts have led to dynamic wavefront control with various materials and mechanisms, most of them work in free space and require specialized materials or bulky configurations for external control. This deviates from the original intention of metasurface to realize compact and integrated devices. Here, we leverage the on-chip geometric metasurface associated with polarization reconfiguration of the guided wave, enabling three functions simultaneously: guided wave radiation, polarization multiplexing, and dynamic wavefront manipulation. We demonstrate proof-of-principle functionalities, including intensity-continuously tunable multifocal metalens, and dynamic zoom metalens as well as dynamic holography, based on a metasurface dressed lithium-niobate-on-insulator waveguide. Such an integrated platform for dynamic wavefront shaping implies the prospect of advancements in chip-integrated multifunctional meta-devices.

Quadruplex Independent Vector Microwave Signal Transmission Over 100 km Using DSM and Optical Polarization Multiplexing

Quadruplex Independent Vector Microwave Signal Transmission Over 100 km Using DSM and Optical Polarization Multiplexing

Radial angular polarization multiplexing and wavefront correction in partially coherent vortex optical communication

Radial angular polarization multiplexing and wavefront correction in partially coherent vortex optical communication

Expanding field-of-view of near-to-eye display by hybrid angular and wavelength multiplexing.

Field-of-view (FOV) and resolution are two critical performance metrics of a near-to-eye display (NED) and are primarily limited by the refractive index (RI) of the waveguide combiner and the number of available pixel counts of the micro display. A high RI material (n = 2.0) is required to transfer an image exceeding a 60 degree full FOV using traditional techniques. We decouple FOV from resolution by wavelength-multiplexing multiple high-resolution FOVs followed by de-multiplexing those FOVs by volume holographic gratings. This approach increases the entire effective FOV beyond the RI-limited FOV while maintaining resolution. Using our new approach we experimentally demonstrate the transfer of images across a 60 degree full FOV through a waveguide with a RI-limited FOV of 30 degrees, which is a common limit for n = 1.5 material. Additional polarization multiplexing enables transferring a 90 degree FOV image over the n = 1.5 waveguide combiner.

Feasibility of Polarization Division Multiplexing for Bidirectional Optical Links in 5G Radio over Fiber Cloud Access Networks

Objective: To investigate the potential of polarization division multiplexing in a 5G radio over fiber cloud access network to enable bidirectional optical links in the front-haul segment. Methodology: An optically centralized cloud radio access network based on polarization division multiplexing and radio-over-fiber transport is proposed. The exploitation of the polarization domain enables independent optical wavelength channels for the downlink and uplink. The experimental demonstration assesses the feasibility of the radio-over-fiber transport of information in a 5G-cloud radio access network. The demonstration evaluated the Error Vector Magnitude measurements for optical carrier linewidths of 0.1 nm. Data was experimentally measured for QPSK and 64QAM signals onto 3.5 GHz radio frequency across 10 km and 20 km of single mode optical fiber. Results: The experimental results evaluated the quality of the QPSK and 64QAM signals transported onto a polarization division multiplexing environment for an optically centralized transport in a 5G-cloud radio access network. 64QAM featured an EVM below 6% with a degradation of 2.8% and QPSK presented and EVM below 8% with a degradation of roughly 4.8% with respect to the back-to-back signal across a propagation length of 20 km. Conclusions: The results demonstrated that polarization multiplexing for an optically centralized transport in a 5G-cloud radio access network is feasible. Despite the relatively low optical power received in the uplink, the power penalties of the polarized components did not compromise the power budget so that optical amplification was not included in the measurements. Both QPSK and 64QAM fulfills the requirements of the 3GPP in terms of quality and signal integrity.

Refractive Index Morphology Imaging Microscope System Utilizing Polarization Multiplexing for Label-Free Single Living Cells.

Detections of internal substances and morphologies for label-free living cells are crucial for revealing malignant diseases. With the phase serving as a coupling of refractive index (RI) (marker for substances) and thickness (morphology), existing decoupling methods mainly rely on complex integrated systems or extensive optical field information. Developing simple and rapid decoupling methods remains a challenge. This study introduces a refractive index morphology imaging microscope (RIMIM) system utilizing polarization multiplexing for label-free single living cells. By simultaneous degree of circular polarization (DOCP) imaging and noninterferometric quantitative phase imaging (QPI), the intracellular refractive index distribution (IRID) and morphology can be decoupled. The optical thickness calculated from the phase is input into the circular depolarization decay model (CDDM) of degree of circular polarization to retrieve IRID. Subsequently, the thickness can be decoupled from phase result using retrieved IRID. Experiments conducted on mouse forestomach carcinoma (MFC) cells and human kidney-2 cells (HK-2) demonstrated the RIMIM system's ability to retrieve IRID and decouple fine morphology. Additionally, the RIMIM system effectively detected membrane damage and changes in erastin-induced ferroptotic HK-2 cells, with average and root-mean-square of surface folds 65.5% and 70.0% higher than those of normal HK-2 cells. Overall, the RIMIM system provides a simple and rapid method for decoupling RI and fine morphology, showing great potential for label-free live cells' cytopathology detection.

Single-pixel imaging through scattering media employing a circular polarization multiplexing metasurface

We propose a scheme of single-pixel imaging through scattering media employing an all-dielectric metasurface, which provides the functions of circular polarization multiplexing and random sampling for single-pixel imaging simultaneously. The former and latter functions are implemented through focusing two orthogonal circular polarization lights with different focal lengths and relative displacements of the metasurface, respectively. Numerical simulations are performed to demonstrate the performance of the metasurface. Whereafter, we simulate the target images projected onto the metasurface and single-pixel imaging reconstructions with these simulated sampling patterns by using the Monte Carlo method, thereby verifying the proposed approach. This technology holds significant potential for applications in microscopic imaging and biological tissue recognition.

Enhanced photonic reservoir computing using an optically injected VCSEL with random polarized optical feedback.

We propose and numerically demonstrate a photonic time-delay reservoir computing (TDRC) system exhibiting enhanced parallel task processing performance, where an optically injected vertical-cavity surface-emitting laser (VCSEL) under random distributed optical feedback acts as the reservoir computer. To assess its effectiveness, we perform two benchmark tasks including chaotic time-series prediction and waveform recognition task, where the TDRC is associated with two different random feedback structures, i.e., orthogonally polarized optical feedback (OPOF) and parallelly polarized optical feedback (PPOF). Benefiting from the enhanced nonlinearity offered by the random distributed optical feedback, the proposed TDRC excels at parallel task processing with the PPOF structure, whereas the performance of the OPOF structure may be deteriorated. Additionally, we reveal the effect of the injection strength, feedback strength, pump current, and number of virtual nodes on the proposed TDRC. Our work paves the way for the performance enhancement of parallel task processing based on polarization multiplexing in a VCSEL-based TDRC.

100 Gb/s/λ polarization multiplexing PON downlink based on simplified heterodyne coherent reception

In this work, we experimentally demonstrate a 100Gb/s/λ downstream transmission link for coherent passive optical networks (PONs) up to 50 km, achieving an optical power budget of 29 dB through polarization multiplexing (PolMux) of two 50 Gb/s channels using multiband carrierless amplitude phase modulation (multiCAP) and optical single side band (OSSB) modulation. Additionally, we introduce a separate PolMux 50 Gb/s link that presents an optical power budget of 38.7 dB. Both links have been achieved using a simplified polarization-demultiplexing heterodyne coherent receiver. The robustness of the system is experimentally evaluated by analyzing its response to various input states of polarization. The transmission has been accomplished using 10 GHz electrical bandwidth devices at both the transmission and receiving ends, thereby paving the way for low-cost 100G links suitable for applications such as PONs.

Advanced decision scheme to mitigate phase impairments in coherent optical transmission systems

An advanced decision scheme is proposed to mitigate phase impairments in coherent optical communication systems. First, the centers of received signals affected by nonlinear impairment are calculated using tangential and radial hierarchical clustering. Then signal decisions with phase noise and nonlinear impairment tolerance are achieved through phase subsequence clustering, resulting in the improvement of transmission performance and the reduction of the computational complexity. The proposed scheme was simulated and experimentally verified in a 216 Gbit/s uniform and probabilistic-shaped (PS) polarization division multiplexing (PDM) 64-quadrature amplitude modulation (64-QAM) coherent optical communication system. The results indicate that the proposed scheme achieves a power budget increase of 0.1 dB in the uniform 64-QAM system and 1.7 dB in the PS 64-QAM system, respectively, compared to the cascaded schemes of 2-stage blind phase search and K-means. Furthermore, the proposed scheme reduces the computational complexity by 86.5% and 93.9%, respectively.

An 80 Gbps Integrated PDM‐OAM‐Enabled‐FSO Transmission for Implementing 5G Services Under Riyadh Weather Conditions

ABSTRACTThe surge in demand of high‐capacity wireless information transmission links has led to emergence of novel multiplexing techniques for free space optics (FSO) over the past few years. Two such important techniques are polarization division multiplexing (PDM) and orbital angular momentum (OAM) multiplexing. This article investigates the integration of PDM and OAM techniques in a FSO transmission system to enable 5G communication services in Riyadh City, Saudi Arabia. Four OAM beams () of 2‐polarization states of a single frequency laser beam are used to transport 10 Gbps data independently. A total of 80 Gbps net transmission rate is achieved. The visibility data for Riyadh city are collected from Saudi Meteorological Department and the attenuation coefficient is calculated using Kim, Kruse, and Al‐Naboulsi attenuation models. The performance of all the PDM‐OAM modulated signals is compared for the three‐attenuation models in terms of bit error rate, eye diagrams, and Q Factor of the signal at the receiver. The results show that using Kim and Kruse models, with attenuation of 0.62 and 0.64 dB/km, the maximum range of 3.8 km is achieved. This is, however, reduced to 2.4 km using Al‐Naboulsi model having attenuation of 2.03 dB/km with acceptable limits of Q Factor (∼6 dB) and BER (∼9).

Theoretical and experimental study on optical polarization states in overhead optical cables under complex weather conditions such as real lightning

Abstract By analyzing the changes in three Stokes vectors, the trajectory of polarization state on the Poincaré sphere, and the polarization change rate, both theoretical and practical aspects of polarization state variations in signal light within optical fiber composite overhead power ground wires (OPGWs) during real thunderstorm conditions, were examined. Our findings reveal that lightning and mechanical vibrations both impact the polarization state of the signal light in OPGW. Theoretical models demonstrate that lightning induces polarization changes through the Faraday magneto-optic effect and exhibits nonlinear electro-optic effects, leading to a maximum polarization change rate of Mrad s−1. In contrast, mechanical vibrations cause long-term, low-intensity polarization rate changes, with a maximum polarization rate of Krad s−1, highlighting a significant optical birefringence effect. Digital signal processing algorithms for coherent receivers with over 100G polarization multiplexing provide valuable guidance for recovering polarization states.

Polarization division multiplexing link using a high-speed lithium niobate automatic polarization demultiplexer.

We propose and experimentally demonstrate a polarization division multiplexing (PDM) link employing an integrated dual-polarization thin-film lithium niobate (TFLN) modulator and an on-chip automatic polarization demultiplexer. The tracking speed of an 80-Gb/s PDM link achieves a maximum of 600 rad/s with a bit error rate (BER) below 2.4 × 10-2. Furthermore, at a polarization scrambling rate (SR) of 100 rad/s, BERs maintain around 1.7 × 10-3 over a period of half an hour. This configuration takes advantage of the TFLN platform, which includes high-speed modulation, fast polarization control, and a compact footprint, effectively doubling capacity per wavelength using simple direct detection. The demonstration highlights the effectiveness of on-chip polarization multiplexing and demultiplexing, particularly in scenarios involving polarization fluctuations, offering promising prospects for applications in commercial short-reach data centers.

Polarization Division Multiplexing CV-QKD with Pilot-Aided Polarization-State Sensing

Continuous-variable quantum key distribution (CV-QKD) with local local oscillator (LLO) is well-studied for its security and simplicity, but enhancing performance and interference resistance remains challenging. In this paper, we utilize polarization division multiplexing (PDM) to enhance spectral efficiency and significantly increase the key rate of the CV-QKD system. To address dynamic changes in the state of polarization (SOP) in Gaussian modulated coherent states (GMCS) signals due to polarization impairment effects, we designed a time-division multiplexing pilot scheme to sense and recover changes in SOP in GMCS signals, along with other digital signal processing methods. Experiments over 20 km show that our scheme maintains low excess noise levels (0.062 and 0.043 in shot noise units) and achieves secret key rates of 4.65 Mbps and 5.66 Mbps for the two polarization orientations, totaling 10.31 Mbps. This work confirms the effectiveness of PDM GMCS-CV-QKD and offers technical guidance for high-rate QKD within metropolitan areas.

Thin-film lithium niobate polarization-independent modulators for mode and polarization multiplexing

We demonstrated a high-order mode modulator based on thin-film lithium niobate (TFLN). By introducing a mode converter and a polarization splitter-rotator (PSR), the modulator can achieve dual-mode modulation. Additionally, we designed a periodic capacitively loaded traveling-wave electrode on TFLN to enhance modulation efficiency and bandwidth. The modulator exhibits a polarization extinction ratio greater than 20 dB at a wavelength of 1550 nm, a modulation efficiency of V π LTE0=2.541V⋅cm and V π LTM0=2.570V⋅cm, and a 3 dB bandwidth exceeding 60 GHz. This not only meets the requirements for polarization-independent modulators but also supports on-chip multimode applications such as mode and polarization multiplexing.

MIMO and PDM-based intersatellite optical link for high-speed data transfer and remote sensing application.

Inter-Satellite Optical Wireless Communication (Is-OWC) is a pivotal technology for advancing global connectivity and the effectiveness of space-based operations. It serves as the linchpin for various applications such as global internet coverage, Earth observation, and remote sensing, bolstering our capacity to monitor the planet and deliver essential services. This paper presents the design and performance evaluation of a Polarization Division Multiplexing (PDM) and Multiple Input Multiple Output (MIMO)-based Is-OWC system operating at a data rate of 60 Gbps. The system was tested under varying transmission distances, atmospheric turbulence, and pointing error conditions. At a transmission distance of 10,000 km, the system achieved a Bit Error Rate (BER) of 6.76 × 10⁻3 for Channel 1 (X polarization) and 7.1 × 10⁻3 for Channel 4 (Y polarization), both within Forward Error Correction (FEC) limits. The introduction of a 4 × 4 MIMO configuration extended the transmission range to 14,000 km, with a corresponding BER of 9.1 × 10⁻3 for Channel 1 and 8.7 × 10⁻⁵ for Channel 4. Eye diagrams confirm successful signal reception, demonstrating that the system can maintain high data rates and low error rates over long distances. The proposed PDM-MIMO system showcases high-capacity, robust performance under challenging conditions, such as turbulence and pointing errors, validating its suitability for space-based communication applications. These findings highlight the potential of the system for future deployments in satellite networks, offering reliable, high-throughput, and low-latency data transmission over extended distances.