Design tradeoffs and challenges in practical coherent optical transceiver implementations

This tutorial discusses the design and ASIC implementation of coherent optical transceivers. Algorithmic and architectural options and tradeoffs between performance and complexity/power dissipation are presented. Particular emphasis is placed on flexible (or reconfigurable) transceivers because of their importance as building blocks of software-defined optical networks. The paper elaborates on some advanced digital signal processing (DSP) techniques such as iterative decoding, which are likely to be applied in future coherent transceivers based on higher order modulations. Complexity and performance of critical DSP blocks such as the forward error correction decoder and the frequency-domain bulk chromatic dispersion equalizer are analyzed in detail. Other important ASIC implementation aspects including physical design, signal and power integrity, and design for testability, are also discussed.Fil: Morero, Damián Alfonso. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; ArgentinaFil: Castrillon, Alejandro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Aguirre, Alejandro. ClariPhy Argentina S.A.; ArgentinaFil: Hueda, Mario Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Agazzi, Oscar Ernesto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; Argentin

Maximum-likelihood sequence estimation in dispersive optical channels

This paper discusses the investigation of maximum-likelihood sequence estimation (MLSE) receivers operating on intensity-modulated direct-detection optical channels. The study focuses on long-haul or metro links spanning several hundred kilometers of single-mode fiber with optical amplifiers. The structure of MLSE-based optical receivers operating in the presence of dispersion and amplified spontaneous emission (ASE), as well as shot and thermal noise, are discussed, and a theory of the error rate of these receivers is developed. Computer simulations show a close agreement between the predictions of the theory and simulation results. Some important implementation issues are also addressed. Optical channels suffer from impairments that set them apart from other channels, and therefore they need a special investigation. Among these impairments are the facts that the optical channel is nonlinear, and noise is often non-Gaussian and signal dependent. For example, in optically amplified single-mode fiber links, the dominant source of noise is ASE noise, which after photodetection is distributed according to a noncentral chi-square probability density function. In addition, optical fibers suffer from chromatic and polarization-mode dispersion (PMD). Although the use of MLSE in optical channels has been discussed in previous literature, no detailed analysis of optical receivers using this technique has been reported so far. This motivates the study reported in this paper.Fil: Agazzi, Oscar Ernesto. Broadcom Corporation; Estados Unidos. ClariPhy Communications; Estados UnidosFil: Hueda, Mario Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Carrer, Hugo Santiago. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Departamento de Electronica. Laboratorio de Comunicaciones; ArgentinaFil: Crivelli, Diego Ernesto. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Departamento de Electronica. Laboratorio de Comunicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Reduced complexity MLSD receivers for nonlinear optical channels

We present a novel maximum likelihood sequence detection (MLSD) receiver structure for nonlinear channels. This scheme is derived by treating the NLC as a multiple input/multiple output system. Then, orthogonal signal components are computed using a special form of space-time whitened matched filter (ST-WMF) obtained by a modified Gram-Schmidt orthogonalization of the Volterra kernels of the NLC. The MLSD receiver consists of the ST-WMF followed by a Viterbi detector (VD) with multidimensional branch metrics. The space orthogonalization and noise whitening achieved by the ST-WMF provide an efficient way to reduce the receiver complexity in the presence of highly dispersive NLC. Complexity reduction is crucial in practical applications such as intensity modulation/direct detection (IM/DD) optical channels. As an example, the number of states of the VD in ST-WMF-MLSD required on a 10 Gb/s, 700 km, IM/DD fiber-optic link is reduced eight times compared with an oversampled MLSD.Fil: Maggio, Gabriel Nicolás. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Departamento de Electronica. Laboratorio de Comunicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hueda, Mario Rafael. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Departamento de Electronica. Laboratorio de Comunicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Agazzi, Oscar Ernesto. ClariPhy Communications; España. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

On the performance of joint iterative detection and decoding in coherent optical channels with laser frequency fluctuations

The joint iterative detection and decoding (JIDD) technique has been proposed by Barbieri et al. (2007) with the objective of compensating the time-varying phase noise and constant frequency offset experienced in satellite communication systems. The application of JIDD to optical coherent receivers in the presence of laser frequency fluctuations has not been reported in prior literature. Laser frequency fluctuations are caused by mechanical vibrations, power supply noise, and other mechanisms. They significantly degrade the performance of the carrier phase estimator in high-speed intradyne coherent optical receivers. This work investigates the performance of the JIDD algorithm in multi-gigabit optical coherent receivers. We present simulation results of bit error rate (BER) for non-differential polarization division multiplexing (PDM)-16QAM modulation in a 200 Gb/s coherent optical system that includes an LDPC code with 20% overhead and net coding gain of 11.3 dB at BER = 10-15. Our study shows that JIDD with a pilot rate ≤ 5% compensates for both laser phase noise and laser frequency fluctuation. Furthermore, since JIDD is used with non-differential modulation formats, we find that gains in excess of 1 dB can be achieved over existing solutions based on an explicit carrier phase estimator with differential modulation. The impact of the fiber nonlinearities in dense wavelength division multiplexing (DWDM) systems is also investigated. Our results demonstrate that JIDD is an excellent candidate for application in next generation high-speed optical coherent receivers.Fil: Castrillón, Mario Alejandro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Morero, Damián Alfonso. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Agazzi, Oscar Ernesto. ClariPhy Communications; Estados UnidosFil: Hueda, Mario Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados En Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias exactas Físicas y Naturales. Instituto de Estudios Avanzados En Ingeniería y Tecnología; Argentin

Architecture of a single-chip 50 gb/s DP-QPSK/BPSK transceiver with electronic dispersion compensation for coherent optical channels

The architecture of a single-chip dual-polarization QPSK/BPSK 50 Gigabits per second (Gb/s) DSP-based transceiver for coherent optical communications is presented. The receiver compensates the chromatic dispersion (CD) of more than 3,500 km of standard single-mode fiber using a frequency-domain equalizer. A time-domain four-dimensional MIMO transversal equalizer compensates up to 200 ps of differential group delay (DGD) and 8000 ps of second-order polarization-mode dispersion (SOPMD). Other key DSP functions of the receiver include carrier and timing recovery, automatic gain control, channel diagnostics, etc. A novel low-latency parallel-processing carrier recovery implementation which is robust in the presence of laser phase noise and frequency jitter is proposed. The chip integrates the transmitter, receiver, framer and host interface functions and features a 4-channel 25 Gs/s 6-bit ADC with a figure of merit (FOM) of 0.4 pJ/conversion. Each ADC channel is based on an 8-way interleaved flash architecture. The DSP uses a 16-way parallel processing architecture. Extensive measurement results are presented which confirm the design targets. Measured optical signal-to-noise ratio (OSNR) penalty when compensating 200 ps DGD and 8000 ps is 0.1 dB, while OSNR penalty when compensating 55 ns/nm CD (corresponding to 3,500 km of standard single-mode fiber) is 0.5 dB.Fil: Crivelli, Diego Ernesto. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. ClariPhy; ArgentinaFil: Hueda, Mario Rafael. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. ClariPhy; ArgentinaFil: Carrer, Hugo Felipe. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. ClariPhy; ArgentinaFil: Del Barco, Martín. ClariPhy; ArgentinaFil: López, Ramiro. ClariPhy; ArgentinaFil: Gianni, Pablo. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Finochietto, Jorge Manuel. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Swenson, Norm. ClariPhy Communications; Estados UnidosFil: Voois, Paul. ClariPhy Communications; Estados UnidosFil: Agazzi, Oscar Ernesto. ClariPhy Communications; Estados Unido