Polarization Division Multiplexing Signal Research Articles

Nonlinear interaction between non-orthogonally polarization-multiplexed signals in fiber transmission with polarization-dependent loss

Polarization-division-multiplexing (PDM) is widely used in fiber transmission systems, wherein fiber nonlinearity is a crucial issue to be considered. Conventionally, the Manakov equation has been used to analyze the nonlinear propagation properties of PDM signal lights, which describes the nonlinear interaction between orthogonally polarized lights. However, because the polarization states of PDM signals are not necessarily orthogonal in transmission systems with polarization-dependent loss (PDL), it is not certain if the Manakov equation is applicable to such systems. Therefore, this study presents a wave equation that describes the nonlinear interaction between non-orthogonally polarized PDM signal lights. We derive a formula that considers the nonorthogonality resulting from PDL. Calculation based on the formula is carried out, the result of which shows that the nonlinear wave equation assuming orthogonal PDM signals results in negligible errors in effect when treating nonorthogonal PDM signals.

Beyond 300-Gbps/λ photonics-aided THz-over-fiber transmission employing MIMO single-carrier frequency-domain equalizer.

We experimentally realized a 320-GHz 320-Gbps/λ terahertz (THz) radio-over-fiber (RoF) system based on a photonics-aided scheme with the help of polarization-division multiplexing (PDM) technology and multiple-input, multiple-output (MIMO) transmission. In this system, the low-complexity MIMO single-carrier frequency-domain equalizer (SCFDE) is implemented to compensate for the polarization-related impairments of the PDM signal, and the demultiplexing performances between SCFDE and the commonly used constant modulus algorithm (CMA) are also compared in this proposed system. After 20-km standard single-mode fiber (SSMF) and 3-m 2 × 2 MIMO wireless link transmission, the bit error rate (BER) of the received 46-GBaud PDM 16-ary quadrature amplitude modulation (16QAM) signal satisfies the soft-decision forward error correction (SD-FEC) threshold with 15% overhead, which corresponds to a record-breaking net bit rate of 320 Gbit/s.

Ultra‐Compact High‐Speed Polarization Division Multiplexing Optical Receiving Chip Enabled by Graphene‐on‐Plasmonic Slot Waveguide Photodetectors

AbstractPolarization multiplexing technology is widely adopted for increasing the capacity in optical communication systems. Especially, silicon‐based integrated polarization division multiplexing (PDM) optical receivers with large bandwidth therein play an important role, which are crucial for on‐chip large‐capacity optical interconnection. Here, a silicon‐based PDM optical receiving chip is enabled by two‐dimensional grating couplers and graphene‐on‐plasmonic slot waveguide photodetectors. Utilizing the advantages of the designed focusing two‐dimensional grating couplers and plasmonic‐slot‐waveguide‐enhanced graphene–light interaction, the optical receiving chip is achieved with an ultra‐small footprint, a bandwidth exceeding 70 GHz and a reception of PDM signals in a line rate of 128 Gbit s−1 non‐return‐to‐zero and 224 Gbit s−1 four‐level pulse‐amplitude‐modulation at 1550 nm, accompanied by the bit error rates lower than the KP4 forward error correction threshold and 15% soft‐decision forward error correction threshold, respectively. Comparing with receiving the single‐polarization state, simultaneous receiving dual‐polarization state introduces about 1 dB additional power penalty because of inter‐polarization crosstalk. The graphene‐plasmonic PDM optical receiving chip can greatly improve the line rate of the system, showing its unique advantages of small footprint, high speed, large bandwidth, low crosstalk and complementary metal–oxide–semiconductor compatibility, which can be potentially used in the next generation silicon‐based high‐speed optical communication.

Crossing-free on-chip 2 × 2 polarization-transparent switch with signals regrouping function.

We propose and demonstrate an on-chip 2×2 polarization-transparent switch for simultaneously handling two-group polarization-division multiplexing (PDM) signals. By introducing the polarization-transparent power splitter/combiner (PPS/PPC), waveguide crossings such as those in conventional PDM switches can be avoided and, thus, the insertion losses and complexity of the device can be reduced. Furthermore, each input polarization tributary can be independently switched and routed thanks to the output selectivity of the PPS/PPC. Thus, not only a basic switch between the dual-group PDM signals, but also a precise four-channel-signal regrouping can be achieved, enabling a complete and non-redundant switching functionality. A polarization extinction ratio larger than 15dB with reasonable insertion losses is experimentally observed. Clear and open eye diagrams can be obtained with less than 1dB power penalties for all the measured paths.

Tunable optical multicasting of PDM-OFDM signals by novel polarization-interleaved multi-pump FWM scheme.

Optical multicasting that supports point-to-multipoint traffic replication can be one of the necessary techniques in next-generation all-optical elastic networks. In this paper, we propose an optical multicasting approach for polarization-division-multiplexing (PDM) orthogonal frequency division multiplexing (OFDM) signals based on a novel polarization-interleaved multi-pump (PIMP) four-wave mixing (FWM) scheme in highly nonlinear fiber (HNLF). Besides format transparency and the support of PDM signals, the scheme further enables wide spectral tunability of generated replicas. The pump frequency arrangement for the scheme is presented, which successfully prevents the replicas from being superimposed by unwanted FWM components during tuning. We experimentally demonstrate multicasting operation of a 3-band 100-Gb/s PDM-OFDM signal. With different input positions, 1.4 and 1.6 Terahertz tuning ranges of four replicas are achieved with Q-factor performance better than the forward error correction threshold. Tunable replica spacing from 100-GHz to 250-GHz are also verified. In addition, the scalability of the scheme is demonstrated via 5-pump multicasting, successfully generating a total of 14 replicas.

PDM Signal Amplification Using PPLN-Based Polarization-Independent Phase-Sensitive Amplifier

We demonstrate the first polarization-independent phase-sensitive amplification of a polarization-division multiplexing (PDM) signal. A novel polarization-diversity loop configuration using periodically poled LiNbO3 waveguides is proposed to achieve the polarization-independent amplification of both a single-polarized signal and a PDM signal. The proposed configuration provides two independent optical parametric amplification processes for two orthogonal polarization components in the loop, while preventing the amplification of the reflection noise by a counter-propagating pump. Polarization-independent error-free operation was confirmed with a bit-error-rate measurement for a 40-Gb/s quadrature phase-shift keying (QPSK) signal. We then demonstrated the phase regenerative amplification of an 80-Gb/s PDM-QPSK signal with artificial phase noise.

Phase regeneration for polarization-division multiplexed signals based on vector dual-pump nondegenerate phase sensitive amplification.

The polarization-division multiplexing (PDM) technology is a practical method to double the transmission capacity, and the corresponding phase regeneration (PR) for PDM signals is meaningful and necessary to extend the transmission distance and increase the transparency for the phase-encoded PDM system. Those reported PDM PR schemes either utilized polarization-diversity technique or required special PDM format. In order to overcome these issues, the PR for the PDM phase-modulated signals is proposed and theoretically demonstrated in this paper, based on the vector dual-pump nondegenerate phase sensitive amplification (PSA). The theoretical model is established and the detailed characteristics are investigated to optimize the PR performance. Results show an obvious phase squeezing for the degraded 80 Gbit/s PDM differential phase-shift keying (DPSK) signals, and the error vector magnitude (EVM) of the regenerated signals on dual polarization states can be improved from 22.58% and 21.39% to 4.57% and 4.63%, respectively. Furthermore, the applicability of the proposed scheme for PDM quaternary-phase shift keying (QPSK) signals is investigated. The proposed scheme can be useful and promising in current PDM based coherent fiber-optic communication.

Experimental demonstration of half cycle 64-QAM Nyquist-SCM direct-detection optical communication system with data-aided estimation and overlap frequency-domain equalization

A half cycle 64-quadrature amplitude modulation (QAM) Nyquist subcarrier modulation (SCM) polarization division multiplexing (PDM) intensity modulation direct detection optical communication system is experimentally demonstrated. At the receiver, training sequences-based channel estimation and an overlap frequency domain equalization method are proposed to enhance the system performance. The experimental results show that the half cycle 64-QAM Nyquist-SCM PDM signal can be transmitted over 43-km standard single-mode fibers with a bit error rate below the forward error coding threshold of 2.4×10−2.

Dispersion insensitive optical signal to noise ratio monitoring of PDM signal by using uncorrelated signal power.

In this paper, we propose and demonstrate optical signal to noise ratio (OSNR) monitoring method for polarization-division-multiplexing (PDM) signal by using the uncorrelated signal power, which is generated by balanced subtraction in electrical domain. The proposed OSNR monitoring is insensitive to dispersion impairment by using low bandwidth receiver. The proposed OSNR monitoring method is tested from 5 dB to 27.5 dB in 100-Gb/s PDM-QPSK system experimentally.

Simultaneous PMD Mitigation for Two Polarization Tributaries of a PDM Signal using only One All-Optical Regenerator

A scheme of polarization-mode-dispersion (PMD) mitigation in a polarization-division-multiplexing (PDM) system is proposed and demonstrated with 2×10Gb/s return-to-zero on-off-keying (RZ-OOK) transmission. Simultaneous mitigation for two polarization tributaries of the PDM signal is achieved based on the self-phase-modulation (SPM) effect and offset filtering in a polarization nonlinear loop configuration. The improvement of eye-diagram-based signal-to-noise ratio (SNR) is 3.5 dB in the presence of a 7.2-ps differential-group delay (DGD) when the pulsewidth of the PDM signal is ∼16.6ps.

All-Optical Signal Regeneration in Polarization-Division-Multiplexing Systems

Schemes of all-optical regeneration in polarization-division-multiplexing (PDM) systems are proposed and demonstrated with 2 × 10-Gb/s return-to-zero on-off-keying (RZ-OOK) transmission. Regeneration is achieved based on self-phase-modulation (SPM) effect and detuned filtering in highly nonlinear fiber (HNLF) with a polarization-diversified loop configuration. Furthermore, the ability of mitigating polarization-mode-dispersion (PMD) effects in PDM systems is evaluated. More than 3.7-dB eye-diagram-based signal-to-noise-ratio (SNR) improvement is achieved in the presence of 6.3-ps PMD as the pulsewidth of the PDM signal is about 18 ps.

Wavelength Conversion of RZ-OOK PDM Signals Based on XPM in Highly Nonlinear Fiber

Wavelength conversion of return-to-zero on-off keying (RZ-OOK) signals in polarization-division-multiplexing (PDM) systems based on cross-phase modulation (XPM) in highly nonlinear fiber (HNLF) using a polarization-diversified loop configuration is experimentally demonstrated. Eye-diagram-based signal-to-noise-ratio (SNR) results indicate that successful wavelength conversion can be achieved over the whole <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> -band.

Adaptive Receiver Structures for Fiber Communication Systems Employing Polarization-Division Multiplexing

Polarization-division multiplexing (PDM) is emerging as a promising technique for increasing data rates without increasing symbol rates. However, the distortion effects of the fiber transmission medium poses severe barriers for the implementation of this technological alternative. Especially, due to the fiber-induced polarization fluctuation orthogonally transmitted PDM signals are mixed at the receiver input. Therefore, a receiver compensation structure needs to be implemented to recover the original orthogonal transmitted components from their mixtures at the end of the fiber channel. This is in fact the focus of this article where a receiver algorithm is based on a recently proposed blind source separation scheme exploiting magnitude boundedness of digital communication signals. Through the use of this scheme, new receiver algorithms for recovering the original polarization signals in an adaptive manner are proposed. The key feature of these algorithms is that they can achieve high separation performance while maintaining the algorithmic complexity in a fairly low level that is suitable for implementation in optical fiber communication receivers. The performance of these algorithms are illustrated through some simulation examples.

PMD and PDL impairments in polarization division multiplexing signals with direct detection

We investigate polarization mode dispersion (PMD) and polarization dependent loss (PDL) impairments in polarization division multiplexing (PDM) signals with optical polarization demultiplexing and direct detection. We find that the time alignment between the bits in the two polarizations has a significant impact on the PMD impairments, and PMD impairments also depend on the bandwidth of PDM signals, whereas PDL impairments have little dependence on the relative time alignment between the two polarizations and the signal bandwidth. We show that with a proper configuration of the polarization demultiplexing, the PDL-induced crosstalk between the two polarizations can be completely eliminated. The combined effects of PMD and PDL are also studied, and we find that, in the presence of concatenated PMD and PDL, the impairment from one effect does not enhance that from the other.