Polarization Mode Dispersion Tolerance Research Articles

PMD tolerance in Stokes space based polarization de-multiplexing algorithms

We numerically investigate the polarization-mode dispersion (PMD) tolerance of Stokes space based polarization-demultiplexing (SSPolDemux) algorithms in optical transmission supported by coherent detection and digital signal processing. The PMD tolerance is evaluated as function of the ratio differential group delay over symbol period, allowing to identify a regime where SSPolDemux is performed practically without penalty (smaller than 1 dB), a regime where SSPolDemux is achievable but induces large penalties, and a third regime where SSPolDemux cannot be accomplished. Results show that coherent access/metro networks are the most evident and potentiating application scenarios for SSPolDemux techniques.

Intensity modulation and direct detection Alamouti polarization-time coding for optical fiber transmission systems with polarization mode dispersion

Alamouti space-time coding is modified in the form of polarization-time coding to combat against polarization mode dispersion (PMD) impairments in exploiting a polarization diversity multiplex (PDM) gain with simple intensity modulation and direct detection (IM/DD) in optical transmission systems. A theoretical model for the proposed IM/DD Alamouti polarization-time coding (APTC-IM/DD) using nonreturn-to-zero on-off keying signal can surprisingly eliminate the requirement of channel estimation for decoding in the low PMD regime, when a two-transmitter and two-receiver channel is adopted. Even in the high PMD regime, the proposed APTC-IM/DD still reveals coding gain demonstrating the robustness of APTC-IM/DD. In addition, this scheme can eliminate the requirements for a polarization state controller, a coherent receiver, and a high-speed analog-to-digital converter at a receiver. Simulation results reveal that the proposed APTC scheme is able to reduce the optical signal-to-noise ratio requirement by ∼3 dB and significantly enhance the PMD tolerance of a PDM-based IM/DD system.

Field Trial Demonstration and Evaluation of a Coherent 100G IP Over WDM Alien Wavelength Across 769 km of Multiple WDM Infrastructures Without Regeneration [Invited

We report the first successful coherent 100G IP over WDM alien wavelength field trial over WDM infrastructures spanning a total distance of 769 km, demonstrating the feasibility and robust performance of a simplified 100G IP over WDM core network architecture. Key performance aspects have been investigated including co-propagation of a 100G IP over WDM alien wavelength and native wavelengths generated from WDM transponders, polarization mode dispersion tolerance, and operation without in-line dispersion compensation modules. We also demonstrated the feasibility of a 100G IP over WDM alien wavelength over multiple WDM systems and optical router or regenerator bypass. In addition, we show evaluation results on the key performance management and monitoring functions with a coherent 100G IP over WDM optical interface in the core router.

PMD mitigation through interleaving LDPC codes with polarization scramblers

The combination of forward error correction (FEC) and distributed fast polarization scramblers (D-FPSs) is approved an effective method to mitigate polarization mode dispersion (PMD) in high-speed optical fiber communication system. The low-density parity-check (LDPC) codes are newly introduced into the PMD mitigation scheme with D-FPSs in this article as one of the promising FEC codes to achieve better performance. The scrambling speed of FPS for LDPC (2040, 1903) codes system is discussed, and the reasonable speed 10MHz is obtained from the simulation results. For easy application in practical large scale integrated (LSI) circuit, the number of iterations in decoding LDPC codes is also investigated. The PMD tolerance and cut-off optical signal-to-noise ratio (OSNR) of LDPC codes are compared with Reed–Solomon (RS) codes in different conditions. In the simulation, the interleaving LDPC codes bring incremental performance of error correction, and the PMD tolerance is 10ps at OSNR=11.4dB. The results show the meaning of the work is that LDPC codes are a substitute for traditional RS codes with D-FPSs and all of the executable code files are open for researchers who have practical LSI platform for PMD mitigation.

A combined scheme of polarization mode dispersion compensation and polarization de-multiplexing in a polarization division multiplexing system with direct detection

A model of polarization mode dispersion (PMD) and state of polarization (SOP) variation induced coherent crosstalk is established in a polarization division multiplexing system. The properties of radio frequency power of one channel in the presence of PMD are investigated. A combined scheme of PMD compensation and polarization de-multiplexing in optical domain is proposed, which is based on monitoring of the feedback signal of RF power. A modified particle swarm optimization algorithm is also used for the adaptive polarization control. The validity of the PMD compensation and polarization de-multiplexing scheme proposed here is demonstrated in a 112Gb/s-PDM-DQPSK simulation system. Results show that the PMD tolerance of the transmission system is increased by 20 ps with 1 dB OSNR margin and the channel separation is accomplished as well.

Coherent 100G Field Trial Over Installed Fiber Links: Investigating Key Network Scenarios and Applications [Invited

We report a successful coherent 100G field trial over installed fiber links of a total of 769 km, investigating the performance of coherent technology for key network scenarios and applications including network upgrade, a new dispersion-compensation-module-less network design, polarization mode dispersion tolerance and support for alien wavelengths. In addition, we evaluated the end to end transport performance of 100GE and 10GE client signals.

Polarization mode dispersion tolerance of Miller and Manchester signals

Polarization mode dispersion (PMD) which is the time space varying nature of two parallel splitting rays polarized perpendicularly in single mode fiber, causes a serious problem in high bit rate transmission. We evaluated the PMD induced system penalty by means of simulations for Miller and Manchester signals under similar conditions and found that Miller is more tolerant to PMD than Manchester.

PMD mitigation through interleaving LDPC codes with polarization scramblers

The combination of forward error correction (FEC) and distributed fast polarization scramblers (D-FPSs) is approved as an effective method to mitigate polarization mode dispersion (PMD) in high-speed optical fiber communication system. The low-density parity-check (LDPC) codes are newly introduced into the PMD mitigation scheme with D-FPSs in this paper as one of the promising FEC codes to achieve better performance. The scrambling speed of FPS for LDPC (2040, 1903) codes system is discussed, and the reasonable speed 10MHz is obtained from the simulation results. For easy application in practical large scale integrated (LSI) circuit, the number of iterations in decoding LDPC codes is also investigated. The PMD tolerance and cut-off optical signal-to-noise ratio (OSNR) of LDPC codes are compared with Reed–Solomon (RS) codes in different conditions. In the simulation, the interleaving LDPC codes brings incremental performance of error correction, and the PMD tolerance is 10ps at OSNR=11.4dB. The results show that the meaning of the work is that LDPC codes are a substitute for traditional RS codes with D-FPSs and all of the executable code files are open for researchers who have practical LSI platform for PMD mitigation.

Polarization mode dispersion compensation in a novel dual polarization differential quadrature phase shift keying system

A novel dual polarization differential quadrature phase shift keying (DP-DQPSK) system is proposed, whose receiver is the same as the single polarization DQPSK system, while it does not need polarization de-multiplexing like the conventional polarization division multiplexing QPSK (PDM-QPSK). Polarization mode dispersion (PMD) is mainly considered and PMD compensation for the DP-DQPSK system is studied. As the feedback signal for PMD compensation, the degree of polarization of the signals is discussed in detail. The results show that PMD tolerance can be improved by 89 ps within 1 dB optical signal noise ratio penalty after PMD compensation for the DP-DQPSK system.

An IIR adaptive electronic equalizer for polarization multiplexed fiber optic communication systems

An electronic digital equalizer for polarization multiplex coherent fiber optic communication systems is designed to compensate polarization mode dispersion (PMD) and residual chromatic dispersion (CD) of transmission channel. The proposed equalizer is realized with fraction spaced infinite impulse response (IIR) butterfly structure with 21 feedforward taps and 2 feedback taps. Compared with finite impulse response (FIR) structure, this structure can reduce implementation complexity of hardware under the same condition. To keep track of the random variation of channel characteristics, the filter weights are updated by least mean square (LMS) algorithm. The simulation results show that the proposed equalizer can compensate residual chromatic dispersion (CD) of 1600 ps/nm and differential group delay (DGD) of 90 ps simultaneously, and also can increase the PMD and residual CD tolerance of the whole communication system.

High-speed polarization mode dispersion compensation in a 43-Gb/s RZ-DQPSK transmission system over 1200 km of standard single-mode fibre

This paper reports that the designed optical polarization mode dispersion compensator shows a good performance under the real-time variation of differential group delay, state of polarization and principal state of polarization in a (40×43)-Gb/s dense-wavelength-multiplexing, 1200-km enhanced return-to-zero differential-quadrature-phase-shift-keying (RZ-DQPSK) system. The polarization mode dispersion tolerance of the system is improved by 26 ps using the optical polarization mode dispersion compensator. The short and long time stabilities are tested with the bit error ratio recorded.

An optical OFDM multiplexer and 16 × 10 Gb/s OOFDM system using serrodyne optical frequency translation based on LiNbO 3 phase modulator

This paper proposes an all-optical orthogonal frequency division multiplexing (OFDM) multiplexer based on sawtooth wave driving LiNbO 3 phase modulators by using serrodyne optical frequency translation. This multiplexer has high integration ability. The designing concept and implementation method have been discussed. A 16 × 10 Gb/s optical OFDM system is designed based on this multiplexer. Transmission characteristics, including tolerances of polarization mode dispersion (PMD) and nonlinear impairments have been studied numerically. Simulations show that the PMD tolerance is about 42 ps. The spectral efficiency reaches 1 bit/s/Hz with binary modulation format.

Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization

This paper presents a new channel estimation/equalization algorithm for coherent OFDM (CO-OFDM) digital receivers, which enables the elimination of the cyclic prefix (CP) for OFDM transmission. We term this new system as the zero-guard-interval (ZGI)-CO-OFDM. ZGI-CO-OFDM employs an overlapped frequency-domain equalizer (OFDE) to compensate both chromatic dispersion (CD) and polarization mode dispersion (PMD) before the OFDM demodulation. Despite the zero CP overhead, ZGI-CO-OFDM demonstrates a superior PMD tolerance than the previous reduced-GI (RGI)-CO-OFDM, which is verified under several different PMD conditions. Additionally, ZGI-CO-OFDM can improve the channel estimation accuracy under high PMD conditions by using a larger intra-symbol frequency-averaging (ISFA) length as compared to RGI-CO-OFDM. ZGI-CO-OFDM also enables the use of ever smaller fast Fourier transform (FFT) sizes (i.e. <128), while maintaining the zero CP overhead. Finally, we provide an analytical comparison of the computation complexity between the conventional, RGI- and ZGI- CO-OFDM. We show that ZGI-CO-OFDM requires reasonably small additional computation effort (~13.6%) compared to RGI-CO-OFDM for 112-Gb/s transmission over a 1600-km dispersion-uncompensated optical link.

Loss of polarization entanglement in a fiber-optic system with polarization mode dispersion in one optical path

We characterize theoretically and experimentally the degradation of polarization entanglement in a fiber-optic entanglement distribution system where one of the optical fibers is exposed to the effects of polarization mode dispersion (PMD). We show gradual reduction of entanglement with increasing PMD and find that the highest PMD tolerance is achieved when the bandwidth of the pump used to generate the entangled photons in a χ((3)) process is approximately half the bandwidth of the quantum channels.

PMD tolerance of 288 Gbit/s Coherent WDM and transmission over unrepeatered 124 km of field-installed single mode optical fiber

Low-cost, high-capacity optical transmission systems are required for metropolitan area networks. Direct-detected multi-carrier systems are attractive candidates, but polarization mode dispersion (PMD) is one of the major impairments that limits their performance. In this paper, we report the first experimental analysis of the PMD tolerance of a 288Gbit/s NRZ-OOK Coherent Wavelength Division Multiplexing system. The results show that this impairment is determined primarily by the subcarrier baud rate. We confirm the robustness of the system to PMD by demonstrating error-free performance over an unrepeatered 124km field-installed single-mode fiber with a negligible penalty of 0.3dB compared to the back-to-back measurements.

Optimal Polarization Demultiplexing for Coherent Optical Communications Systems

Spectrally-efficient optical communications systems employ polarization division multiplexing (PDM) as a practical solution, in order to double the capacity of a fiber link. Polarization demultiplexing can be performed electronically, using polarization-diversity coherent optical receivers. The primary goal of this paper is the optimal design, using the maximum-likelihood criterion, of polarization-diversity coherent optical receivers for polarization-multiplexed optical signals, in the absence of polarization mode dispersion (PMD). It is shown that simultaneous joint estimation of the symbols, over the two received states of polarization, yields optimal performance, in the absence of phase noise and intermediate frequency offset. In contrast, the commonly used zero-forcing polarization demultiplexer, followed by individual demodulation of the polarization-multiplexed tributaries, exhibits inferior performance, and becomes optimal only if the channel transfer matrix is unitary, e.g., in the absence of polarization dependent loss (PDL), and if the noise components at the polarization diversity branches have equal variances. In this special case, the zero-forcing polarization demultiplexer can be implemented by a 2 ? 2 lattice adaptive filter, which is controlled by only two independent real parameters. These parameters can be computed recursively using the constant modulus algorithm (CMA). We evaluate, by simulation, the performance of the aforementioned zero-forcing polarization demultiplexer in coherent optical communication systems using PDM quadrature phase shift keying (QPSK) signals. We show that it is, by far, superior, in terms of convergence accuracy and speed, compared to conventional CMA-based polarization demultiplexers. Finally, we experimentally test the robustness of the proposed constrained CMA polarization demultiplexer to realistic imperfections of polarization-diversity coherent optical receivers. The PMD and PDL tolerance of the proposed demultiplexer can be used as a benchmark in order to compare the performance of more sophisticated adaptive electronic PMD/PDL equalizers.

An experiment of PMD compensation in 40-Gb/s PSBT transmission system

An adaptive polarization mode dispersion (PMD) compensation experiment is reported in a 40-Gb/s phase shaped binary transmission (PSBT) communication system, with the use of a new digital signal processor (DSP)-based optical PMD compensator. PMD tolerance is found to be enhanced by 8 ps after PMD compensation with 1-dB optical signal-to-noise ratio (OSNR) penalty. Under the condition of fast change of states of polarization up to 85 rad/s in the fiber link, the performance of our PMD compensator undergoes the bit error ratio (BER) test for as long as 10 h.

Optical Coherent Receiver With a Switchable Electrical Dispersion Compensator for 10 Gb/s DPSK Transmission up to 300 km of SSMF in Metro Optical Networks

The purpose of this paper is to demonstrate the potential of an electrical signal processing technique to mitigate the effect of intersymbol interference in metro optical networks, using optical coherent detection. Intersymbol interference in fiber-optic systems can severely degrade the system performance and subsequently limit both the maximum transmission distance and data rate. The main sources of intersymbol interference include chromatic dispersion (CD) and polarization mode dispersion (PMD). The typical reach for 10 Gb/s metro optical systems is on the order of 300 km. To bridge this distance either with or without repeaters, we demonstrate the potential use of 10 Gb/s differential phase-shift keying (DPSK) modulation format in conjunction with an optical coherent receiver with a built-in switchable electrical dispersion compensator. The overall performance of the optical coherent receiver is compared with that of the corresponding direct detection (DD) receiver based on Mach-Zehnder delay interferometer. The optical signal-to-noise (OSNR) required to operate the optical coherent receiver at the enhanced forward error correction (EFEC) threshold of 2.1 X 10-3 is 6 dB/0.1 nm resolution bandwidth. The optical coherent receiver outperforms in absolute required OSNR by 0.5 dB at the EFEC threshold when compared to a DD receiver. A four position switchable CD compensator compensates up to ?5100 ps/nm of CD, using the method of heterodyne detection. The optical coherent receiver has a first-order PMD tolerance of 36.2 ps for 1 dB OSNR penalty. The utility of our optical coherent receiver is demonstrated by doing transmission experiments over 304 km of standard single-mode fiber (SSMF) in both repeatered (multiple spans) and repeaterless (single span) to measure the self-phase modulation (SPM) tolerance of 10 Gb/s nonreturn-to-zero (NRZ)-DPSK. The measured SPM tolerance of NRZ-DPSK over 304 km of SSMF in three spans of ~100 km each is +8.8 dBm fiber launch power for 1.5 dB OSNR penalty. In addition, the best Q factor of ~12 dB is obtained for the fiber launch power of +18 dBm over single repeaterless span of 304 km of SSMF, which gives ~3 dB of system margin at the second generation EFEC threshold of 9.1 dB.

Theoretical Investigation of First-order and Second-order Polarization-mode Dispersion Tolerance on Various Modulation Formats in 40 Gb/s Transmission Systems with FEC Coding

We investigated the polarization-mode dispersion (PMD) tolerance for 40Gb/s non-return to zero (NRZ), duobinary NRZ, return to zero (RZ), carrier-suppressed RZ (CS-RZ), and duobinary-carrier-suppressed RZ (DCS-RZ) modulation formats with a forward error correction (FEC) coding. The power penalty has been calculated as a measure of the system performance due to PMD. After comparison of the PMD tolerance of various modulation formats, our results suggest that RZ signals have the best tolerance against the effect of first-order PMD only. The duobinary NRZ modulation format is most resilient to PMD when both first- and second-order PMD are considered. However, the duobinary NRZ modulation format is the most sensitive to the incident angle of the input signal to a fiber axis in the presence of first- and second-order PMD, leading to incident angle-dependent power penalty. The coding gain by FEC can cope with the power penalties induced by first- and second-order PMD up to a DGD value of 16ps.

PMD Tolerance of 10 Gbps Modulated Signals due to SOA-Induced Chirp in SOA Booster Amplifiers

We investigated how the polarization-mode dispersion (PMD) tolerance was degraded by semiconductor optical amplifier (SOA)-induced chirp for the 10 Gb/s nonreturn-to-zero (NRZ), duobinary NRZ, return-to-zero (RZ), and carrier-suppressed RZ (CS-RZ) modulation formats. The power penalty was calculated as a measure of the system performance due to PMD for a given SOA-induced chirp. Considering only first-order PMD, all modulation formats have a similar PMD tolerance regardless of SOA-induced chirp. On the other hand, when both first- and second-order PMD are considered, the PMD tolerance of all modulation formats with the exception of the CS-RZ modulation format are degraded by SOA-induced chirp. Among all modulation formats considered here, the NRZ modulation format has the PMD tolerance with the highest sensitivity to SOA-induced chirp. When the peak-to-peak chirp induced by SOAs is $0.28{\AA}$ , its PMD tolerance is degraded up to 4 dB for a differential group delay (DGD) of 50 ps. However, the PMD tolerance of the CS-RZ modulation format is largely unaffected by SOA-induced chirp.