Unrepeated 200-km transmission of 40-Gbit/s 16-QAM signals using digital coherent receiver

Abstract

We demonstrate unrepeated 200-km transmission of 40-Gbit/s 16-QAM signals using a digital coherent receiver, where the decision-directed carrier-phase estimation is employed. The phase fluctuation is effectively eliminated in the 16-QAM system with such a phase-estimation method, when the linewidth of semiconductor lasers for the transmitter and the local oscillator is 150 kHz. Finite-impulse-response (FIR) filters at the receiver compensate for 4,000-ps/nm group-velocity dispersion (GVD) of the 200-km-long single-mode fiber and a part of self-phase modulation (SPM) in the digital domain. In spite of the launched power limitation due to SPM, the acceptable bit-error rate performance is obtained owing to high sensitivity of the digital coherent receiver.

Effects of phase noise of monolithic tunable laser on coherent communication systems

“…The non-data-aided frequency correction removed the frequency offset between the lasers [8] and a 20-symbol training sequence was employed to achieve symbol synchronization. Many algorithms have been developed for carrier phase recovery in digital coherent receiver including the least mean-squared (LMS) algorithm [1], decisiondirected phase-locked loop [9,10], decision-aided maximum likelihood phase estimation [11], blind phase search technique [12], and QPSK partitioning algorithm [13]. In this work, we developed a first order decision-directed phase-locked loop (DD-PLL) [9] as shown by the block diagram in Fig.…”

“…Multi-level modulation has been identified as one of the key technologies to address the capacity increase in Dense Wavelength Division Multiplexing (DWDM) optical networks [1,2]. Higher order quadrature amplitude modulation (QAM) schemes such as 16-QAM [1] and 64-QAM [2] with digital coherent receivers have attracted research attention recently as the potential candidates for next generation optical networks.…”

“…Higher order quadrature amplitude modulation (QAM) schemes such as 16-QAM [1] and 64-QAM [2] with digital coherent receivers have attracted research attention recently as the potential candidates for next generation optical networks. One of the key elements in these systems will be the laser transmitter, and phase noise of the laser sources has been identified as a crucial characteristic that affects the ultimate performance of these coherent systems.…”

Analytical BER performance in differential n-PSK coherent transmission system influenced by equalization enhanced phase noise

“…It has been verified that the behavior of the feedback carrier phase estimation using the one-tap normalized least-mean-square (NLMS) algorithm resembles the differential phase estimation [5,10,25]. Therefore, the theoretical BER evaluation based on this model is also suitable for the one-tap NLMS carrier phase estimation.…”

“…The carrier phase estimation (CPE) can be effectively implemented by employing the feedforward and the feedback algorithms [7][8][9][10][11]. As a conventional feedforward algorithm, the differential phase estimation has been validated as a simple and effective method for the phase noise compensation (PNC) in the coherent transmission system, which is also regarded as a benchmark for evaluating the CPE approaches [12][13][14][15][16][17].…”