Milen Paskov

Spectral shaping for mitigating backreflections in a bidirectional 10 Gbit/s coherent WDM-PON

Receiver sensitivity penalty due to backreflections in a 10 Gbit/s bidirectional coherent WDM-PON is evaluated for 3 GBd PDM-QPSK. Pulse shaping is applied to reduce the impact of backreflections and enable tolerance to reflections up to -20 dBm.

Blind Equalization of Receiver In-Phase/Quadrature Skew in the Presence of Nyquist Filtering

In-phase and quadrature skew inside a coherent receiver, caused by misalignments, can severely limit performance. Future 400G systems employing higher order modulation formats and Nyquist filtering are especially sensitive to this. A blind adaptive equalizer is proposed to track and compensate the skew while also performing matched filtering. Performance is investigated in simulation for 56 GBd polarization division multiplexed 16-quadrature amplitude modulation (PDM-16QAM) and experimentally for 6 GBd PDM quadrature phase shift keying (PDM-QPSK) and PDM-16QAM, where compensation for delays up to half a symbol period are demonstrated without penalty. At 30% delay skew, the maximum skew recommended by Optical Internetwork Forum (OIF) for PDM-QPSK, a gain of 1.6 dB for PDM-QPSK, and a gain of more than 5 dB for PDM-16QAM is observed compared with using a conventional equalizer.

Nyquist-shaped dispersion-precompensated subcarrier modulation with direct detection for spectrally-efficient WDM transmission

We report on the first experimental demonstration of 14 Gb/s direct detection single-sideband subcarrier modulated Nyquist QPSK transmission. Using electronic pre-compensation, transmission over 800 km of dispersion-uncompensated standard single-mode fiber was achieved.

Experimental demonstration of 24-dimensional extended Golay coded modulation with LDPC

We experimentally demonstrate ultra-long haul transmission of 24-D extended Golay coded modulation with LDPC. Compared with LDPC coded DP-BPSK, an increase of 15% in reach was shown, with a 3 dB increase in launch power margin at a transmission distance of more than 16,000 km.

Design of a 1 Tb/s Superchannel Coherent Receiver

We describe the design of a trained and pilot-aided digital coherent receiver, capable of detecting a 1 Tb/s superchannel with a single optical front-end. Algorithms for receiver training are described, which calculate the equalizer coefficients, subchannel SNRs, and centroids of the transmitted constellations. Algorithms for pilot-aided operation are then described in detail, providing pilot-aided constant modulus equalization and joint carrier-phase estimation over several coherent subchannels. We demonstrate the detection of a superchannel with net bit rate in excess of 1 Tb/s with a single coherent receiver. An 11 × 10 GBd DP-64QAM Nyquist superchannel is used, with 1.32 Tb/s gross bit rate.

Achievable information rates estimates in optically amplified transmission systems using nonlinearity compensation and probabilistic shaping

Achievable information rates (AIRs) of wideband optical communication systems using a ∼40  nm (∼5  THz) erbium-doped fiber amplifier and ∼100  nm (∼12.5  THz) distributed Raman amplification are estimated based on a first-order perturbation analysis. The AIRs of each individual channel have been evaluated for DP-64QAM, DP-256QAM, and DP-1024QAM modulation formats. The impact of full-field nonlinear compensation (FF-NLC) and probabilistically shaped constellations using a Maxwell-Boltzmann distribution were studied and compared to electronic dispersion compensation. It has been found that a probabilistically shaped DP-1024QAM constellation, combined with FF-NLC, yields achievable information rates of ∼75  Tbit/s for the EDFA scheme and ∼223  Tbit/s for the Raman amplification scheme over a 2000 km standard single-mode fiber transmission.

80-km Coherent DWDM-PON on 20-GHz Grid With Injected Gain Switched Comb Source

We have proposed and experimentally demonstrated a 6 × 40-Gb/s long reach dense wavelength division multiplexed passive optical network downlink system operating over 80 km of standard single mode fiber. The six optical channels with 20 GHz spacing are generated by an externally injected gain switched optical comb source. Each comb line is imposed with a 6-GBd polarization division multiplexed quadrature amplitude modulation, which included a 20% overhead for forward error correction. A worst case channel sensitivity of -35.6 dBm (54 photons/bit) at a bit error rate of 1.5×10-2 was achieved, yielding a system loss budget of 40 dB.

Digital Coherence Enhancement Enabling 6-GBd DP-64QAM Using a 1.4-MHz Linewidth Laser

This letter demonstrates the possibility of using digital coherence enhancement-a means of estimating and digitally compensating local oscillator laser phase noise using a secondary, low speed coherent receiver-to enable the reception of high order quadrature amplitude modulation (QAM) using a monolithically integrated tunable semiconductor laser as local oscillator. We show that this coherence enhancement technique compensates both the Lorentzian and non-Lorentzian distributed phase noise of this laser, enabling reception of DP-64QAM without differential decoding, and with a record (linewidth)×(symbol duration) product of 2.3×10-4.

Degenerate mode-group division multiplexing using MIMO digital signal processing

MIMO DSP is employed to improve the performance of degenerate mode-group division multiplexing in 8 km of conventional GI-MMF. Compensation of the mode coupling, induced by the launch and propagation, between and inside each degenerate mode-group is investigated in order to reduce the DSP complexity.

Polarization-insensitive single balanced photodiode coherent receiver for passive optical networks

Alamouti polarization-time block coding, combined with heterodyne detection, enables phase-diverse coherent detection using a single balanced photodiode without optical polarization tracking. A 10.7Gb/s OFDM signal is experimentally rotated over the full Poincare sphere achieving a mean receiver sensitivity of -35.8dBm.