Polarization-multiplexed Transmission Research Articles

Optical Polarization Division Multiplexing Transmission System Based on Simplified Twin-SSB Modulation.

Optical twin-single sideband (Twin-SSB) modulation, due to the left sideband (LSB) and right sideband (RSB) signal carrying individual data, has become an attractive technique in fiber transmission because it satisfies the demand of the explosive increase in data traffic. This paper focuses on reducing the complexity of Twin-SSB system and further enhancing the spectral efficiency by proposing a polarization division multiplexing (PDM) Twin-SSB modulation scheme. LSB and RSB signals are extracted using de-mapping algorithm instead of optical bandpass filters (OBPFs) to reduce system complexity. To further improve spectral efficiency, PDM is employed to meet the polarization multiplexing transmission and achieve a higher transmission capacity. Based on the PDM Twin-SSB system, the LSB is 3-arr phase-shift-keying (3PSK) modulated, while RSB is quadrature phase-shift keying (QPSK) modulated. We simulated that the bit error ratio (BER) performance of LSB and RSB of X-polarization (X-Pol) and Y-polarization (Y-Pol) at 8-Gbaud, 10-Gbaud, 12-Gbaud, 14-Gbaud, and 16-Gbaud in the case of back-to-back (BTB) and 2 km standard single-mode fiber (SSMF) transmission. The simulation results verify the effectiveness and practical feasibility of the proposed PDM Twin-SSB scheme for future short-distance transmission owing to low cost, simplified structure, low algorithm complexity, and high data transmission capacity.

Single-shot dual-wavelength phase reconstruction in off-axis digital holography with polarization-multiplexing transmission.

A new system for single-shot dual-wavelength digital holographic microscopy with polarization-multiplexing path-shared transmission is presented. The key feature of the optical configuration is that the interference waves of two wavelengths having orthogonal polarization can transmit in the same interferometer paths at the same time, and two polarizers orthogonal to each other are placed in front of the CCD to realize single-shot recording of two holograms. The correlative filtering algorithm of the spatial-frequency spectrum for dual-wavelength digital holograms is reliable and efficient in the dual-wavelength path-shared configuration. The phase reconstruction in dual-wavelength digital holographic imaging is achieved by using this filtering algorithm. The experiment results of phase reconstruction of a groove grating demonstrate the reliability and validity of this optical configuration and the correlative filtering algorithm. This polarization-multiplexing configuration for dual-wavelength digital holography is compact and has more flexibility for the replacement of different-wavelength lasers.

Polarization Drift Channel Model for Coherent Fibre-Optic Systems.

A theoretical framework is introduced to model the dynamical changes of the state of polarization during transmission in coherent fibre-optic systems. The model generalizes the one-dimensional phase noise random walk to higher dimensions, accounting for random polarization drifts, emulating a random walk on the Poincaré sphere, which has been successfully verified using experimental data. The model is described in the Jones, Stokes and real four-dimensional formalisms, and the mapping between them is derived. Such a model will be increasingly important in simulating and optimizing future systems, where polarization-multiplexed transmission and sophisticated digital signal processing will be natural parts. The proposed polarization drift model is the first of its kind as prior work either models polarization drift as a deterministic process or focuses on polarization-mode dispersion in systems where the state of polarization does not affect the receiver performance. We expect the model to be useful in a wide-range of photonics applications where stochastic polarization fluctuation is an issue.

256 Tbit/s/ch (640 Gbaud) polarization-multiplexed DQPSK non-coherent Nyquist pulse transmission over 525 km

We demonstrate a single-channel 2.56 Tbit/s polarization-multiplexed DQPSK transmission using 640 Gbaud non-coherent optical Nyquist pulses. By virtue of a large tolerance to polarization-mode dispersion, the detrimental depolarization-induced crosstalk was reduced by 3.8 dB compared with RZ pulses. As a result, the transmission distance was substantially extended to 525 km compared with the distance of 300 km obtained with a Gaussian pulse.

1024 QAM, 7-core (60 Gbit/s x 7) fiber transmission over 55 km with an aggregate potential spectral efficiency of 109 bit/s/Hz.

We report the first 1024 QAM polarization-multiplexed transmission at 3 Gsymbol/s over a 55 km 7-core fiber, with a total bit rate of 420 Gbit/s (60 Gbit/s x 7 cores). The potential spectral efficiency per core reached 15.6 bit/s/Hz, which corresponds to an aggregate spectral efficiency as high as 109 bit/s/Hz in a multi-core single-mode fiber.

Radio-Over-Fiber Optical Polarization-Multiplexed Networks for 3GPP Wireless Carrier-Aggregated MIMO Provision

This paper proposes and demonstrates experimentally the application of optical polarization-multiplexed radio-over-fiber wireless backhauling of fully standard 3GPP carrier-aggregated multiple-input multiple-output (MIMO) signals. The experimental work demonstrates successful long-reach optical transmission of 3GPP carrier-aggregated LTE-Advanced (LTE-A) signals using 2×2 MIMO spatial diversity. The suitability of MIMO provision using radio-over-fiber optical links is demonstrated over different E-UTRA frequency division duplex frequency bands. The performance of electrical carrier aggregation is evaluated in different configurations comprising one, three and five LTE-A component carriers of 10 and 20 MHz bandwidth each. The experimental results demonstrate successful 2×2 MIMO radio-over-fiber polarization-multiplexed transmission of five LTE-A carriers over 25 km, three LTE-A carriers over 75 km and an LTE-A carrier over 100 km of standard single mode fiber to provide pervasive MIMO wireless service to a large number of users.

Doubling direct-detection data rate by polarization multiplexing of 16-QAM without active polarization control

We introduce and simulate a technique enabling to utilize the polarization dimension in direct-detection optical transmission, supporting polarization multiplexing (POL-MUX) over direct-detection (DD) methods previously demonstrated for a single polarization such as direct-detection OFDM. POL-MUX is currently precluded in self-coherent DD with remotely transmitted pilot, as signal x pilot components may randomly fade out. We propose POL-MUX transmission of advanced modulation formats, such as 16-QAM and higher, by means of a novel low-complexity photonic integrated optical front-end and adaptive 3x2 MIMO DSP. The principle of operation is as follows: an additional X x Y cross-polarizations signal is generated, providing three projections onto an over-complete frame of three dependent vectors. This enables to resiliently reconstruct the received state of polarization even when the remotely transmitted pilot fades along one of the received polarization axes.

Polarization-time coding for PDL mitigation in long-haul PolMux OFDM systems

In this paper, we present a numerical, theoretical and experimental study on the mitigation of Polarization Dependent Loss (PDL) with Polarization-Time (PT) codes in long-haul coherent optical fiber transmissions using Orthogonal Frequency Division Multiplexing (OFDM). First, we review the scheme of a polarization-multiplexed (PolMux) optical transmission and the 2 × 2 MIMO model of the optical channel with PDL. Second, we introduce the Space-Time (ST) codes originally designed for wireless Rayleigh fading channels, and evaluate their performance, as PT codes, in mitigating PDL through numerical simulations. The obtained behaviors and coding gains are different from those observed on the wireless channel. In particular, the Silver code performs better than the Golden code and the coding gains offered by PT codes and forward-error-correction (FEC) codes aggregate. We investigate the numerical results through a theoretical analysis based on the computation of an upper bound of the error probability of the optical channel with PDL. The derived upper bound yields a design criterion for optimal PDL-mitigating codes. Furthermore, a transmission experiment of PDL-mitigation in a 1,000 km optical fiber link with inline PDL validates the numerical and theoretical findings. The results are shown in terms of Q-factor distributions. The mean Q-factor is improved with PT coding and the variance is also narrowed.

Second-Order PMD-Induced Crosstalk Between Polarization-Multiplexed Signals and Its Impact on Ultrashort Optical Pulse Transmission

We present an analytical description and experimental demonstration of inter-polarization crosstalk caused by second-order polarization-mode dispersion (PMD). Even if the first-order PMD is completely compensated for, second-order PMD leads to large transmission impairments in ultrashort optical pulse transmissions through signal depolarization, which is caused by the frequency dependence of the principal state of polarization. In particular, depolarization in a polarization-multiplexed transmission inevitably prevents the complete separation of the two channels at the polarization demultiplexing. The analytical results show that the crosstalk increases in proportion to the fourth power of the signal bandwidth and grows by the square of distance as also verified by the experiments.

Experimental demonstration of a frequency-domain Volterra series nonlinear equalizer in polarization-multiplexed transmission

Employing 100G polarization-multiplexed quaternary phase-shift keying (PM-QPSK) signals, we experimentally demonstrate a dual-polarization Volterra series nonlinear equalizer (VSNE) applied in frequency-domain, to mitigate intra-channel nonlinearities. The performance of the dual-polarization VSNE is assessed in both single-channel and in wavelength-division multiplexing (WDM) scenarios, providing direct comparisons with its single-polarization version and with the widely studied back-propagation split-step Fourier (SSF) approach. In single-channel transmission, the optimum power has been increased by about 1 dB, relatively to the single-polarization equalizers, and up to 3 dB over linear equalization, with a corresponding bit error rate (BER) reduction of up to 63% and 85%, respectively. Despite of the impact of inter-channel nonlinearities, we show that intra-channel nonlinear equalization is still able to provide approximately 1 dB improvement in the optimum power and a BER reduction of ~33%, considering a 66 GHz WDM grid. By means of simulation, we demonstrate that the performance of nonlinear equalization can be substantially enhanced if both optical and electrical filtering are optimized, enabling the VSNE technique to outperform its SSF counterpart at high input powers.

1024 QAM (60 Gbit/s) single-carrier coherent optical transmission over 150 km

We demonstrate a record QAM multiplicity of 1024 levels in a single-carrier coherent transmission. A frequency-domain equalization technique and a back-propagation method are adopted to compensate for distortions caused by hardware imperfections and fiber impairments, respectively. As a result, 60 Gbit/s polarization-multiplexed transmission over 150-km has been achieved at 3 Gsymbol/s within an optical bandwidth of only 4.05 GHz.

PMD-Induced Crosstalk in Ultrahigh-Speed Polarization-Multiplexed Optical Transmission in the Presence of PDL

We present a new type of crosstalk in a polarization-multiplexed ultrahigh-speed transmission caused by polarization-mode dispersion (PMD) in the presence of polarization-dependent loss (PDL). When PMD and PDL are both present, the orthogonality between two principal states of polarization (PSP) is reduced. As a result, crosstalk inevitably occurs between two polarizations and prevents the two channels from being separated completely during polarization demultiplexing. The system impact of these effects in a polarization-multiplexed terabit/s transmission is also demonstrated experimentally.

Nonlinear Compensation Using Backpropagation for Polarization-Multiplexed Transmission

Digital backpropagation (BP) is a universal method for jointly compensating dispersion and nonlinear impairments in optical fiber and is applicable to signals of any modulation format. In this paper, we compare single carrier (SC) versus orthogonal frequency-division multiplexing (OFDM) for polarization-multiplexed transmission. We show that at realistic data rates and transmission distances, polarization mode dispersion does not significantly degrade the performance of BP and can be mitigated by a post-BP linear equalizer. Dispersion unmanaged transmission can significantly reduce nonlinearity, and in this transmission regime, SC and OFDM have similar nonlinear tolerance. Multichannel BP is effective at mitigating interchannel nonlinearity for point-to-point links.

All-Optical Wavelength Conversion of a 100-Gb/s Polarization-Multiplexed Signal

We present the results of an in-depth experimental investigation about all-optical wavelength conversion of a 100-Gb/s polarization-multiplexed (POLMUX) signal. Each polarization channel is modulated at 25 Gbaud by differential quadrature phase-shift keying (DQPSK). The conversion is realized exploiting the high nonlinear chi((2)) coefficient of a periodically poled lithium niobate waveguide, in a polarization-independent configuration. We find that slight non-idealities in the polarization independent setup of the wavelength converter can significantly impair the performance of POLMUX systems. We show that high-quality wavelength conversion can be nevertheless achieved for both the polarization channels, provided that an accurate optimization of the setup is performed. This is the first demonstration, to the best of our knowledge, of the possibility to obtain penalty-free all-optical wavelength conversion in a 100-Gb/s POLMUX transmission system using direct-detection.

PMD Monitoring in Polarization-Multiplexed Transmission Systems by Spectral Polarimetric Analysis

A polarization-mode dispersion (PMD) monitoring technique tailored for polarization-multiplexed high capacity optical transmission systems is proposed and experimentally demonstrated. First-order PMD is evaluated calculating the vector product of the spectral components of the two state-of-polarization transmitted in the polarization-multiplexed system. The spectral components in each state-of-polarization are resolved by a real-time optical Fourier transformer. The technique is demonstrated measuring first-order PMD in an proof-of-concept experiment implementing an alternate-polarization return-to-zero modulation. The results indicate an improved accuracy over the conventional Poincare-arc measurement method applied to a single polarization. Successful differential group-delay (DGD) measurements have been performed from 0.68 to 30.78 ps with 2.5% maximum relative error. A high degree of independence with the SOP/PSP angle is observed. The technique can be used to generate a feedback signal for PMD compensators in generic polarization-multiplexed transmission systems.

PMD Monitoring in Polarization-Multiplexed Transmission Systems by Spectral Polarimetric Analysis

A polarization-mode dispersion (PMD) monitoring technique tailored for polarization-multiplexed high capacity optical transmission systems is proposed and experimentally demonstrated. First-order PMD is evaluated calculating the vector product of the spectral components of the two state-of-polarization transmitted in the polarization-multiplexed system. The spectral components in each state-of-polarization are resolved by a real-time optical Fourier transformer. The technique is demonstrated measuring first-order PMD in an proof-of-concept experiment implementing an alternate-polarization return-to-zero modulation. The results indicate an improved accuracy over the conventional Poincare-arc measurement method applied to a single polarization. Successful differential group-delay (DGD) measurements have been performed from 0.68 to 30.78 ps with 2.5% maximum relative error. A high degree of independence with the SOP/PSP angle is observed. The technique can be used to generate a feedback signal for PMD compensators in generic polarization-multiplexed transmission systems.

Electrical Joint Equalization for PMD-Induced Performance Degradation in Direct-Detection Polarization-Multiplexed Transmission Systems

Polarization-division-multiplexed (PDM) systems are sensitive to polarization-mode dispersion (PMD), since PMD induces not only intersymbol distortion but also interchannel crosstalk. Electrical equalization for individual channels is not sufficient for the lack of information from another channel. In this letter, electrical joint equalization including both the decision-feedback equalizer and Viterbi equalizer for PMD compensation in direct-detection PDM systems is investigated. Simulation shows that joint equalizers can effectively combat PMD-induced performance degradation and lower the requirement for dynamic polarization control.

PMD-induced transmission penalties in polarization-multiplexed transmission

In this paper, we investigate for the first time chromatic dispersion and nonlinearity tolerances in the presence of polarization-mode dispersion (PMD) for polarization-multiplexed (POLMUX) 2 /spl times/ 10-Gb/s nonreturn-to-zero (NRZ) transmission. In polarization-multiplexing, the interaction between fiber nonlinearity and PMD can lower the nonlinear tolerance beyond the tolerances evident when considering both transmission penalties separately; the combined penalties are significantly worse than in the case for non-POLMUX transmission. In this paper, we show, through simulations comparing POLMUX with non-POMUX transmission in the presence of nonlinearity, a reduction of about a factor of three in PMD tolerance. In addition, we show that the dispersion tolerance of POLMUX transmission is severely limited in the presence of PMD. For example, a 40-ps differential group delay (DGD) with worst case coupling of the polarization channels into the fiber lowers the dispersion tolerance, resulting in a 1-dB eye-opening penalty (EOP), from 1200 to 450 ps/nm. We conclude that the interaction between PMD, chromatic dispersion, and nonlinearity leads to the worst signal impairments in POLMUX transmission and increases the effort of using polarization-multiplexing as a modulation format.

Interchannel nonlinear transmission penalties in polarization-multiplexed 2×10Gbit?s differential phase-shift keying transmission

We discuss the performance of a multichannel 2 x 10 Gbit/s polarization-multiplexed differential phase-shift keying transmission system. Through simulations and transmission experiments we find that, despite the constant power envelope of non-return-to-zero phase-shift keying modulation formats, polarization multiplexing strongly reduces the nonlinear tolerance and transmission performance at a 2 x 10 Gbit/s line rate with multichannel transmission. This results in a 10 dB power penalty when comparing single- and nine-channel transmission. Additionally, multichannel impairments in differential phase-shift keying and on-off keying are compared for 2 x 10 Gbit/s polarization-multiplexed transmission.

Reduction of nonlinear penalties through polarization interleaving in 2/spl times/10 gb/s polarization-multiplexed transmission

We simulated the nonlinear transmission penalties induced through cross-phase modulation related depolarization in 2/spl times/10 Gb/s polarization-multiplexed (POLMUX) transmission. We find that launching adjacent wavelength-division-multiplexed channels with a 180/spl deg/ relative state of polarization shift results in a significant decrease in nonlinear transmission penalties and allows for longer distance POLMUX transmission.