Polarization Division Multiplexing Quadrature Phase Shift Keying Research Articles

FrFT-based estimation of linear and nonlinear impairments using Vision Transformer

To comprehensively assess the conditions of an optical fiber communication system, it is essential to implement joint estimation of the following four critical impairments: nonlinear signal-to-noise ratio (SNRNL), optical signal-to-noise ratio (OSNR), chromatic dispersion (CD), and differential group delay (DGD). However, current studies only achieve identifying a limited number of impairments within a narrow range, due to a lack of high-performance computing algorithms and a unified representation of impairments. To address these challenges, we adopt time-frequency signal processing based on the fractional Fourier transform (FrFT) to achieve the unified representation of impairments, while employing a Transformer-based neural network (NN) to break through network performance limitations. To verify the effectiveness of the proposed estimation method, numerical simulations were conducted on a five-channel polarization-division-multiplexed quadrature phase shift keying (PDM-QPSK) long haul optical transmission system with the symbol rate of 50 GBaud per channel. The mean absolute error (MAE) for SNRNL, OSNR, CD, and DGD estimation is 0.091 dB, 0.058 dB, 117 ps/nm, and 0.38 ps, and the monitoring window ranges from 0−20dB, 10−30dB, 1700−51,000ps/nm, and 0−100ps, respectively. Our proposed method achieves accurate estimation of linear and nonlinear impairments over a broad range, representing a significant advancement in the field of optical performance monitoring (OPM).

Performance analysis of 2λ × 160 Gbps optical single sideband (OSSB) generation in polarization division multiplexed (PDM) QPSK based satellite wireless optical systems (SWOS)

Abstract Capacity enhancement in satellite wireless optical systems (SWOS) systems is an ultimate task to accomplish due to ever-increasing internet services and it can be achieved by incorporating polarization division multiplexed (PDM) quadrature phase shift keying (PDM-QPSK). Herein, 2λ × 160 Gbps intersatellite optical wireless communication (IsOWC) system is proposed using PDM-QPSK. Spectral efficiency is prime requirement to enhance the performance of system and therefore, a suppression of optical single sideband (OSSB) in PDM-QPSK carrier spectrum is performed by employing fiber Bragg grating with 0.99 reflectivity. Proposed system is investigated in terms of log BER and error vector magnitude percentage (EVMP) at varied SWOS distances. Further, effects of the digital signal processing (DSP) in the receiver are analyzed by considering and neglecting the module. Results revealed that suppression of sidebands and employment of DSP enhance the system performance and competent to cover 52,000 km SWOS distance.

Tens to Hundreds of Mrad/s Fast Polarization Tracking and Demultiplexing Using Angle-Plus-Phase Algorithm in Stokes Space

A fast polarization tracking and demultiplexing algorithm in polarization-division-multiplexing (PDM) systems is proposed and demonstrated. The scheme utilizes two optimizing parameters in Stokes Space, including the polarization angle and the phase information. In addition to its transparency to modulation formats, the angle-plus-phase algorithm (APA) could provide fast convergence up to >100-Mrad/s polarization tracking speed. Compared to common polarization demultiplexing algorithms such as constant modulus algorithm (CMA) and linear Kalman filter (LKF), experimental results show that the polarization tracking capability of the proposed APA algorithm is significantly improved without sacrificing the transmission performance. Specifically, compared to CMA, the tracking speed can be improved from 9-Mrad/s to 160-Mrad/s for PDM quadrature phase shift keying (PDM-QPSK) signals. Furthermore, compared to CMA and LKF, APA has the best tracking performance, and the tracking speed can be reached to 34-Mrad/s for PDM 16 quadrature amplitude modulation (PDM-16QAM) signal.

Demonstration of an optical phase conjugation based dual‐hop PDM‐QPSK free‐space optical communication link

The dual-hop free-space optical (FSO) communication link for polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK) signals is proposed and experimentally demonstrated in an atmospheric chamber with the optical phase conjugation (OPC) compensating the turbulence-induced signal distortions. The phase fluctuations can be effectively reduced by the OPC, as the error vector magnitudes are 10.03% and 8.28% decreased for x- and y-polarization. At the bit error rate of 1 × 10–3, the power penalty of the dual-hop link with OPC is 2.85 or 2.34 dB lower than that of each polarization without OPC.

Analysis and Compensation of Chromatic Dispersion in Long-hauls Optical Coherent System

In this paper, we demonstrate the efficiency of Electronic Dispersion Compensation (EDC) for coherent optical systems based on Polarization Division Multiplexed Quadrature Phase Shift Keying (PDM-QPSK). The performance of the proposed system is tested using a pulse that has been recently used in the presence of nonlinear effects.The proposed system is compared to the 0.3RZ-PDM-QPSK system at the optimum launched power under different symbol-rates and lengths of transmission. The simulation results confirm that the proposed method enhances the system performance. In addition, it secures a low penalty that is below 0.6 dB. As a result, the feasible transmission distance is improved by 29 %, 20.15 %, and 26.7 %, at 14 GBaud, 28 Gbaud, and 56 Gbaud, respectively.

Design and evaluation of 2.3 Tb/s (23 ch. × 100 Gb/s) multi-carrier WDM optical transmission systems

Multilevel phase modulation formats with coherent detection enable a new generation of high speed optical transport platform. We demonstrate 23 × 100 Gbps (2.3 Tb/s) WDM Optical systems employing multicarrier generation concept. Three lasers are used to generate 23 sub-carriers using multicarrier generator at transmitter section. Each sub-carrier transmits at a transmission rate of 100 Gbps using polarization division multiplexed quadrature phase shift keying (PDM-QPSK) modulation format with spacing of 25 GHz between sub carriers. The analysis is carried out for 23 × 100 Gb/s (2.3 Tb/s) PDM-QPSK WDM optical systems with ultra large area fiber (ULAF), standard single mode fiber (SSMF) and large effective area fiber (LEAF) at transmission reach from 600 to 5000 km. Coherent detection with DSP is used for all the systems at receiving end. Systems are verified with parameters like symbol error rate, error vector magnitude (EVM) and Q-factor using analytical and simulation results. Improvement of 1.66 dB to 3.21 dB and 2.08 dB to 4.63 dB is noted in Q-factor for system with ULAF in comparison with system using SSMF and LEAF respectively over 600 km to 5000 km transmission reach. EVM values are found 2.24% to 2.68% and 2.68% to 12.43% lower in system with ULAF than system with SSMF and LEAF respectively. Log of estimated symbol error is observed less for system with ULAF than systems with SSMF and LEAF fibers, respectively, at transmission distance of 5000 km. The results clearly show that WDM optical system with ULAF fiber gives better performance.

Efficient preamble design and digital signal processing in upstream burst-mode detection of 100G TDM coherent-PON

Coherent optics has been proved to be a promising candidate for 100 Gb/s and even beyond single-wavelength time-division multiplexing passive optical networks (TDM-PONs). However, one of the key issues in TDM coherent-PON is how to efficiently and robustly achieve upstream burst-mode coherent detection. To solve this problem, we proposed and demonstrated a reliable and efficient preamble design with corresponding burst-mode digital signal processing (DSP) for coherent upstream burst-mode detection in TDM coherent-PON. To reduce the preamble length, a special designed preamble unit is used for three burst-mode DSP functions including frame synchronization, state-of-the polarization estimation, and frequency-offset estimation. The efficiency of the designed preamble and the overall performances under different test conditions are experimentally verified. We also confirmed the robust performance in large frequency offset, residual fiber dispersion, and long-time running. As a proof-of-concept, we demonstrate the coherent upstream burst-mode detection of 100-Gb/s polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) signals based on a 71.68-ns preamble and corresponding burst-mode DSP, achieving a 36-dB power budget after 50-km single-mode fiber transmission. Around 20-dB dynamic range of received power is also experimentally verified for burst signals in the 100 Gb/s/ λ TDM coherent-PON.

A modulation format identification method based signal amplitude sorting and ratio calculation

Modulation format identification (MFI) is an indispensable part of next generation optical networks such as elastic optical networks (EON). We propose a simple MFI method based on signal amplitude sorting and ratio calculation. After sorting the amplitude of signals, three MFI feature values are extracted to identify polarization division multiplexing (PDM) quadrature phase shift keying (PDM-QPSK) and three commonly used quadrature amplitude modulation (QAM) signals (PDM-16QAM, PDM-32QAM and PDM-64QAM). Numerical simulations verify the effectiveness of proposed MFI method with the required optical signal noise ratio (OSNR) lower than 7% forward error correction (FEC) threshold. Proof-of-concept experiments using QPSK, 16QAM, 32QAM and 64QAM signals with 100 km fiber transmission demonstrate the feasibility of proposed MFI method. We also investigate the influence of fiber transmission distance, fiber nonlinearity and symbol numbers on the proposed method and the results show that the proposed MFI methods can achieve accurate identification at different fiber transmission length, a range of fiber nonlinearity and small requirement of symbol number. The method is simple and insensitive to phase impairments caused by laser phase noise and frequency offset (FO), which will bring convenience into future EONs.

Performance analysis of 160 Gbit/s single-channel PDM-QPSK based inter-satellite optical wireless communication (IsOWC) system

Inter-satellite optical wireless communication (IsOWC) links have been exploited by many researchers as a viable technology to transmit information amongst two or more satellites using optical carrier signals and outer space as the medium of propagation medium. IsOWC links can securely transmit information all over the globe. The present study discusses a spectral-efficient large-speed single-channel IsOWC system using polarization division multiplexed-quadrature phase shift keying (PDM-QPSK) scheme. Coherent detection has been used at the receiver terminal for receiver sensitivity improvement. A digital signal processing (DSP) module to mitigate losses due to nonlinearity effects and for estimating carrier phase has been used at the receiver. We have analyzed the proposed link performance by investigating the required optical signal to noise ratio (OSNR) to achieve a target bit error rate (BER). The reported results show a faithful 160 Gbit/s transmission at 40,000 km with good BER. Also, we numerically investigate the OSNR performance of link for increasing pointing errors. Further, a comparative analysis of the proposed link with previous literature illustrates a better performance in terms of spectral efficiency and figure of merit (maximum transmission range $${\times} $$ information transmission rate). The integration of PDM-QPSK with coherent detection and DSP provides a viable platform to develop spectral-efficient IsOWC links.

All-fiber polarization-division multiplexing to mode-division multiplexing conversion for hybrid optical networks.

This paper proposes and experimentally demonstrates an all-fiber conversion method that transfers the polarization-division multiplexing (PDM) signals to the mode-division multiplexing (MDM) signals. The conversion scheme is based on a mode converter and a polarization-mode controller. The input X-polarized/Y-polarized fundamental modes are converted to the first-order linear-polarized LP11A/LP11B modes with crosstalk of -10 dB/-18 dB and insertion losses of 3.04dB/3.1dB at 1550nm, respectively. Using the proposed converter, 11.2GBaud/s polarization-division-multiplexed quadrature-phase-shift keying (PDM-QPSK) and 16 quadrature-amplitude-modulation (PDM-16QAM) signals are successfully converted to 11.2GBaud/s MDM-QPSK and MDM-16QAM signals.

Pulse-Overlapping Super-Nyquist WDM System

In this paper, a pulse-overlapping super-Nyquist (Pol-SN) wavelength-division multiplexing (WDM) scheme is proposed to improve spectral efficiency of coherent optical transmission. In this scheme, two tributaries of polarization-division multiplexing quadrature phase-shift keying (PDM-QPSK) signals at the transmitter, carried by the same wavelength, are grouped together to allow for pulse overlapping in the time domain. Then, several wavelength channels are packed tightly in the frequency domain to form a super-Nyquist WDM system. At the receiver, three partial-response detection schemes are investigated and compared: (1) constant modulus algorithm (CMA) + duobinary shaping + maximum likelihood sequence estimation (MLSE); (2) duobinary shaping + multimodulus algorithm (MMA) + MLSE; and (3) channel shortening filter. Among these schemes, the easy-to-implement duobinary shaping +MMA + MLSE is selected by virtue of its best performance and lowest complexity. A 224-Gb/s Pol-SN PDM-QPSK system is investigated through numerical simulations. The simulation results show that the channel spacing of the 224 Gb/s Pol-SN PDM-QPSK system can be reduced to 20 GHz (11.2 bit/s/Hz SE) with 7% overhead hard-decision forward-error correction (HD-FEC, 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ). At 26-GHz channel spacing, Pol-SN PDM-QPSK signals show 5.5-dB OSNR improvement, as compared with the signals of 224-Gb/s super-Nyquist PDM-16QAM. The simulation results also show that 224-Gb/s Pol-SN PDM-QPSK system, with 20-GHz spacing, can transmit up to 1000-km SSMF with 7% overhead HD-FEC.

Photonics-aided 2 × 2 MIMO wireless terahertz-wave signal transmission system with optical polarization multiplexing

We experimentally demonstrate a photonics-aided 2 × 2 multiple-input multiple-output (MIMO) wireless transmission system at a terahertz-band (THz-band). In our demonstrated system, the generated 4-Gbaud polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) signal at 450GHz by photonic remote heterodyning can be delivered over a 142-cm 2 × 2 MIMO wireless transmission link, with a bit-error ratio (BER) less than the hard-decision forward-error-correction (HD-FEC) threshold of 3.8 × 10−3. The further introduction of up to a 50-km single-mode fiber-28 (SMF-28) transmission causes a negligible power penalty. To the best of our knowledge, this is the first time a 2 × 2 MIMO wireless transmission of a polarization-multiplexing terahertz-wave (THz-wave) signal has been realized.

Experimental Demonstration of Ultra-Dense WDM-PON With Seven-Core MCF-Enabled Self-Homodyne Coherent Detection

We demonstrate an ultra-dense wavelength-division-multiplexing (UDWDM) passive optical network (PON) in a spatial-division-multiplexing system utilizing our home-made seven-core multicore fiber (MCF) with a self-homodyne coherent detection (SHCD) scheme. In the SHCD system, we transmit 12 channels of 40-Gb/s UDWDM-PON signals using polarization-division-multiplexing quadrature phase-shift keying (PDM-QPSK) with a 12-GHz grid through the six outer cores of the seven-core MCF with the central core used to transmit the pilot tone. An optical frequency comb generator is employed to supply the multi-carriers for cost saving. After 37-km low-crosstalk seven-core MCF long-reach transmission with compact fan-in/fan-out multiplexers, a large transmission capacity of 2.88 Tb/s and a power budget of 26 dB are obtained. At the optical network unit side, a narrow linewidth local oscillator laser is no longer necessary since SHCD is adopted in our system. The complexity of the digital signal processing procedure at the coherent receiver is also greatly reduced as the carrier phase recovery and carrier frequency offset estimation are not needed.

Optical wireless integration based on phase modulator down-conversion for W-band QPSK signal delivery

We demonstrate one optical wireless integration system for 44Gb/s polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signal down-conversion based on phase modulators. 2×100km single-mode fiber-28 (SMF-28) fiber transmission and 3m wireless delivery at 88GHz W-band are realized in our experiment. We also compare the different modulation formats with the same bit rate transmission in this optical wireless integration link.

Sub-symbol-rate sampling for PDM-QPSK signals in super-Nyquist WDM systems using quadrature poly-binary shaping.

We compare the performance of sub-symbol-rate sampling for polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) signals in super-Nyquist wavelength division multiplexing (WDM) system by using quadrature duo-binary (QDB) and quadrature four-level poly-binary (4PB) shaping together with maximum likelihood sequence estimation (MLSE). PDM-16QAM is adopted in the simulation to be compared with PDM-QPSK. The numerical simulations show that, for a software defined communication system, the level number of quadrature poly-binary modulation should be adjusted to achieve the optimal performance according to channel spacing, required OSNR and sampling rate restrictions of optics. In the experiment, we demonstrate 3-channel 12-Gbaud PDM-QPSK transmission with 10-GHz channel spacing and only 8.4-GSa/s ADC sampling rate at lowest. By using QDB or 4PB shaping with 3tap-MLSE, the sampling rate can be reduced to the signal baud rate (1 samples per symbol) without penalty.

On-field measurement trial of 4×128 Gbps PDM-QPSK signals by linear optical sampling

Linear optical sampling is a promising characterization technique for advanced modulation formats, together with digital signal processing (DSP) and software-synchronized algorithm. We theoretically investigate the acquisition of optical sampling, when the high-speed signal under test is either periodic or random. Especially, when the profile of optical sampling pulse is asymmetrical, the repetition frequency of sampling pulse needs careful adjustment in order to obtain correct waveform. Then, we demonstrate on-field measurement trial of commercial four-channel 128Gbps polarization division multiplexing quadrature phase shift keying (PDM-QPSK) signals with truly random characteristics by self-developed equipment. A passively mode-locked fiber laser (PMFL) with a repetition frequency of 95.984MHz is used as optical sampling source, meanwhile four balanced photo detectors (BPDs) with 400MHz bandwidth and four-channel analog-to-digital convertor (ADC) with 1.25GS/s sampling rate are used for data acquisition. The performance comparison with conventional optical modulation analyzer (OMA) verifies that the self-developed equipment has the advantages of low cost, easy implementation, and fast response.

Performance of coherent detection for FTN-DFTs-OFDM signal using receiver-side quadrature duobinary shaping

Abstract In this paper we investigate Faster-than-Nyquist Discrete-Fourier-Transform spread Orthogonal Frequency Division Multiplexing (FTN-DFTs-OFDM) signaling which combines the features of both single carrier FTN and OFDM system. By introducing the quadrature duo-binary (QDB) filtering at the receiver side, the transmitted OFDM signal can be packed in a sub-Nyquist spacing, which improves the spectral efficiency (SE) compared to conventional detection schemes. Maximum a posteriori (MAP) and maximum likelihood sequence estimation (MLSE) criteria have been both used and compared to find an optimal equalization scheme for combating FTN multiplexing at transmitter side and QDB filtering at receiver side. The simulations result show that by applying QDB filtering at the receiver side, the back-to-back (BTB) required optical signal noise ratio (OSNR) at bit error rate (BER) of 1 × 10 −2 is reduced by 1.5-dB for 20-GHz spaced 128-Gb/s polarization-division-multiplexed quadrature-phase-shift-keying (PDM-QPSK) signal, achieving a SE of 6.4-b/s/Hz.

Over 100 Gb/s Ultrabroadband MIMO Wireless Signal Delivery System at the D-Band

We propose and experimentally demonstrate an ultrabroadband wireless millimeter-wave (mm-wave) signal delivery system at the D-band (110–170 GHz), employing the techniques of photonics-aided mm-wave generation, wireless multiple-input multiple-output (MIMO), and high-level vector signal modulation, combined with digital heterodyne coherent detection. Our demonstrated system not only can deliver up to 46-Gbaud (184-Gbit/s) polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) signal over 80-km single-mode fiber-28 (SMF-28) and 0.6-m 2 × 2 MIMO wireless link at the D-band but can deliver up to a 16-Gbaud (128-Gbit/s) polarization-division-multiplexing 16-ary quadrature-amplitude-modulation (PDM-16QAM) signal over 10-cm $2\times 2$ MIMO wireless link at the D-band as well. To the best of our knowledge, we have realized a record bit rate of 184 Gbit/s for the D-band wireless mm-wave signal delivery.

Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system**Project supported by the National Natural Science Foundation of China (Grant Nos. 61271192, 61427813, and 61331010) and the National Basic Research Program of China (Grant No. 2013AA013401).

The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing (PDM) coherent optical systems by mid-span optical phase conjugation (OPC) based on four wave mixing (FWM) effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing (CO-OFDM) system and the single carrier (SC) PDM quadrature phase shift keying (QPSK) system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system.

Generation and Transmission of High Symbol Rate Single Carrier Electronically Time-Division Multiplexing Signals

We experimentally investigate the generation and transmission of high-symbol-rate single-carrier signals based on the electronically time-division multiplexing (ETDM) method. We have successfully increased the operating bandwidth limit of ETDM-based optoelectronic subsystems to the symbol rate of 128.8 and 138.4 GBaud over a long-haul SMF-28 link. We experimentally demonstrate 8 $\times$ 128.8 Gbaud polarization-division multiplexed quadrature phase-shift keying (PDM-QPSK) signals over 2800 km SMF-28 and 4 $\times$ 138.4 GBaud over 1200 km with EDFA-only amplification. To the best of our knowledge, 138.4 GBaud is the highest symbol rate of all-ETDM-based optical coherent system reported so far.