Optimization of optical transmission capacity

A method for transmitting a coherent optical data signal includes receiving a data signal from an interface, and encoding the data signal with a forward error correcting (FEC) encoder according to a mix of modulation formats. The FEC encoder generates an FEC encoded signal which is used to generate modulation symbols according to the modulation formats. The FEC encoded signal of modulation symbols is spectrally shaped to generate a shaped signal, and pre-distorted before transmission. The shaped signal is pre-distorted by adding a predetermined amount of chromatic dispersion to generate a smoothed signal, and the smoothed signal is transmitted according to the modulation formats

Impact of finite-resolution DAC and ADC on probabilistically-shaped QAM constellations

We analyze the impact of finite resolution of DAC and ADC on the performance of coherent-detection optical communication systems using probabilistically-shaped 64-QAM constellations. We show that no substantial additional penalty is incurred with respect to uniformly distributed constellations with the same net data rate

Dual Stage CPE for 64-QAM Optical Systems Based on a Modified QPSK-Partitioning Algorithm

In this letter, a novel two-stage digital feed forward carrier recovery algorithm for 64-ary quadrature amplitude modulation (QAM) is proposed and analyzed. Due to the absence of any feedback loop, the approach shows a high tolerance toward laser phase noise. Different steps involving partition, selection, and rotation of symbols are also discussed. For an OSNR penalty of 1 dB at bit error rate of 10-3, the proposed scheme can tolerate linewidth times symbol duration product equal to 3.3×10-5 and hence can be used with the commercially available state-of-the-art tunable lasers for 64-QAM transmission at 400 Gb/

Multi-Stage CPE Algorithms for 64-QAM Constellations

We propose and analyze a multi-stage architecture for carrier phase-estimation in 64-QAM systems, based on the cascade of several feed-forward elementary blocks. We outline the beneficial effect of increasing the number of elementary blocks

Multistage carrier phase estimation algorithms for phase noise mitigation in 64-quadrature amplitude modulation optical systems

Two novel low-complexity multi-stage digital feedforward carrier phase estimation (CPE) algorithms for 64-ary quadrature amplitude modulation (QAM) are proposed and analyzed by numerical simulations. The first stage is composed of a Viterbi&Viterbi block, based on either the standard quadrature phase shift keying (QPSK) partitioning algorithm using only Class-1 symbols or a modified QPSK partitioning scheme utilizing both Class-1 and outer most triangle-edge (TE) symbols. The second stage applies the Viterbi&Viterbi algorithm after a 64-QAM-to-QPSK transformation, while the subsequent stages iterate a maximum likelihood estimation (MLE) algorithm for phase estimation. All proposed techniques are characterized by a high tolerance to laser phase noise: an OSNR penalty of 1 dB at bit error rate (BER) of 10−2, the proposed schemes can tolerate a linewidth times symbol duration product equal to 5.6e−5 and 7.1e−5, respectively. At 32 Gbaud, all of the above linewidth requirements can be met using commercial tunable lasers. The proposed schemes achieve a similar linewidth. tolerance with a reduced implementation complexity with respect to algorithms based on the blind phase search (BPS) method

Hybrid modulation formats enabling elastic fixed-grid optical networks

In this paper, we analyze hybrid modulation formats as an effective technology for the implementation of flexible transponders that are capable of trading off the delivered data rate by the lightpath quality of transmission with fine granularity. Flexible transponders are an enabling technology that can introduce the elastic paradigm in state-of-the-art networks while maintaining compatibility with the installed equipment, including fibers, mux-demux, and reconfigurable optical add-drop multiplexers, as required by telecom operators willing to exploit fixed-grid wavelength-division multiplexed (WDM) transmission. We consider two solutions achieving different levels of flexibility and employing different hybridization approaches: time-division (TDHMF) and quadrature-division (Flex-PAM) hybrid modulation formats. We introduce a comprehensive theoretical assessment of back-to-back performances, analyzing different transmitter operating conditions, and we provide an extensive simulation analysis on the propagation of a Nyquist-WDM channel comb over an uncompensated and amplified fiber link. After assessing the impact of nonlinear propagation on the maximum signal reach, we present simple countermeasures for non-linear mitigation and discuss their effectiveness for both TDHMF and Flex-PA