Jason Hurley

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.

25 Gb/s transmission over 820 m of MMF using a multimode launch from an integrated silicon photonics transceiver

A new high bandwidth bend-insensitive MMF optimized for 1310 nm is designed and characterized. 25 Gb/s transmission over a record 820 m length using a multimode launch from an integrated SiPh transceiver at 1310 nm through the new fiber is demonstrated with a power penalty of 3.4 dB at 10(-12) BER. Detailed characteristics of the fiber and transceiver are presented along with BER measurements.

Transmission of 112 Gb/s PM-QPSK signals over up to 635 km of multimode optical fiber.

We investigate transmission of 112 Gb/s PM-QPSK signals over 50 μm core diameter OM3 multimode fiber using the center launch approach. We demonstrate successful transmission of 16 DWDM channels over a distance of 635 km.

Pulse shaping for 112 Gbit/s polarization multiplexed 16-QAM signals using a 21 GSa/s DAC

The implications of increasing the symbol rate for a given digital-to-analog converter (DAC) sampling rate are investigated by considering the generation of 112 Gbit/s PM 16-QAM signals (14 Gsym/s) using a 21 GSa/s DAC with 6-bit resolution.

40 × 112 Gb/s transmission over an unrepeatered 365 km effective area-managed span comprised of ultra-low loss optical fibre

We experimentally demonstrate transmission of 40 × 112 Gb/s PM-QPSK channels over a 365 km unrepeatered span enabled by ultra-low loss fibres in an effective area-managed configuration using only backward-pumped Raman with 25 dB gain and EDFA amplification.

Experimental Measurements of the Effectiveness of MLSE against Narrowband Optical Filtering Distortion

We experimentally investigate the application of MLSE-EDC to signals transmitted through narrowband optical filters. We find MLSE affords significant OSNR improvement of ~5 dB for NRZ signals, but less or none for duobinary and DPSK.

Unrepeatered 256 Gb/s PM-16QAM transmission over up to 304 km with simple system configurations

We study unrepeatered transmission of 40x256 Gb/s systems with polarization-multiplexed 16-quadrature amplitude modulation (PM-16QAM) channels using simple coherent optical system configurations. Three systems are investigated with either a homogeneous fiber span, or simple two-segment hybrid fiber designs. Each system relies primarily on ultra-low loss, very large effective area fiber, while making use of only first-order backward pumped Raman amplification and no remote optically pumped amplifier (ROPA). For the longest span studied, we demonstrate unrepeatered 256 Gb/s transmission over 304 km with the additional aid of nonlinear compensation using digital backpropagation. We find an average performance improvement in terms of the Q-factor of 0.45 dB by using digital backpropagation compared to the case of using chromatic dispersion compensation alone for an unrepeatered span system.

Behavior of MLSE-EDC With Self-Phase Modulation Limitations and Various Dispersion Levels in 10.7-Gb/s NRZ and Duobinary Signals

We investigate experimentally the effectiveness of maximum likelihood sequence estimation electronic dispersion compensation (MLSE-EDC) for signals limited by self-phase modulation (SPM) and with various dispersion levels. We study nonreturn-to-zero (NRZ) and duobinary signals modulated at 10.7Gb/s and find that the improvement obtained with an MLSE-EDC receiver depends strongly on the level of residual chromatic dispersion (after partial optical compensation) in both cases. In general, greater SPM tolerance to high channel powers is derived from the MLSE in the presence of larger residual dispersion values. An increase in the allowable channel launch power of more than 2 dB is observed for NRZ signals, whereas, the increase for duobinary may be almost 6 dB.

Experimental investigation of multimode fiber bandwidth requirements for 5.2 GHz WLAN signal transmission

We investigate the specification requirements of MMF for 5.2 GHz WLAN signal transmission and show that at minimum 1400 MHz-km are required for EVM distortion <1%. Low-bandwidth 62.5 mum MMF is not suited for this application

Experimental measurements of uncompensated reach increase from MLSE-EDC with regard to measurement BER and modulation format

Comprehensive experimental measurement data are presented comparing the performance of an optical receiver with MLSE-EDC technology against a standard receiver for signals with uncompensated chromatic dispersion. Signals with the NRZ and duobinary modulation formats are investigated. We find that the MLSE-EDC technology provides greater uncompensated reach advantage for both formats as the allowable measured BER is increased, demonstrating the EDC technology has greatest effect and application in conjunction with strong forward error correction. We also measure signal quality vs. dispersion with constant OSNR and draw similar conclusions along with further insights into the application space of the EDC technology for both modulation formats.