Olga Vassilieva

Optimal 40 Gb/s modulation formats for spectrally efficient long-haul DWDM systems

Three modulation formats are compared by numerical simulation of highly dense (75-GHz-spaced for 40 Gb/s channel), long-haul (600-1800 km) wavelength division multiplexed systems with three fiber types. Nonreturn-to-zero (NRZ) format, being the most spectrally compact and the simplest in transmitter and receiver configuration of the three, seems to be capable enough at shorter transmission distances than 1000 km regardless of fiber type. Carrier-suppressed return-to-zero (RZ) format, being the most tolerant to the self-phase modulation effect, showed better performance with fibers having larger chromatic dispersion. However, its transmission distance with low dispersion fibers is severely limited by the four-wave mixing effect. Bit-synchronous intensity modulated differential phase shift keying (IM-DPSK) format seems to be the best choice for a transmission distance beyond 1000 km because of its superior tolerance to optical noise and fiber nonlinear effects regardless of fiber types, despite slightly more complex transmitter and receiver configurations.

Numerical comparison of NRZ, CS-RZ and IM-DPSK formats in 43 Gbit/s WDM transmission

We have compared by numerical simulations the performance of NRZ, CS-RZ and IM-DPSK modulation formats for 480 km of 40 channels WDM transmission with SMF and NZ-DSF fibers. IM-DPSK has shown the best tolerance to non-linear effects and dispersion for the both types of fibers. IM-DPSK is an extremely attractive format for long-haul 40 Gbit/s WDM systems.

Impact of Polarization Dependent Loss and Cross-Phase Modulation on Polarization Multiplexed DQPSK Signals

We investigated PolMux-RZ-DQPSK signal degradation modes due to PDL and XPM in WDM transmission with co-propagating NRZ signals. SNR degradation due to PDL and XPM-induced polarization dependent phase noise greatly impact transmission system.

Systematic analysis of intra-superchannel nonlinear crosstalk in flexible grid networks

Intra-superchannel nonlinear crosstalk affects center subcarriers of multi-carrier superchannels more than the edge subcarriers; its impact on center subcarriers significantly increases with increase of the number of subcarriers. Power pre-emphasis of subcarriers effectively equalizes performance and extends reach by 20%.

Symbol rate dependency of XPM-induced phase noise penalty on QPSK-based modulation formats

Systematic investigation of XPM impact on QPSK signals reveals that higher symbol rates are advantageous for reducing both intra-span generation and multi-span accumulation of phase noise.

Transmission Characteristics of 43 Gb/s Single-Polarization and Dual-Polarization RZ-DQPSK Signals with Co-propagating 11.1 Gb/s NRZ Channels over NZ-DSF

XPM impairments on 43 Gb/s single-polarization and dual-polarization RZ-DQPSK signals were compared under co-propagation of 11.1 Gb/s NRZ channels with direct-detection. The higher symbol rate, single-polarization format, showed a larger tolerance than the dual-polarization case.

Interplay between PDL and nonlinear effects in coherent polarization multiplexed systems.

We analyzed the mechanism of the interplay between PDL and fiber nonlinear effects and showed that PDL can generate large data-dependent optical peak power variations that can worsen nonlinear tolerance and cause additional 1.4dB Q-penalty.

Nonlinear tolerant and spectrally efficient 86 Gbit/s RZ-DQPSK format for a system upgrade

We propose a method employing 86 Gbit/s RZ-DQPSK format to enable doubling the capacity of 43 Gbit/s WDM systems. Its relaxed OSNR, chromatic dispersion and PMD requirements allow the upgrade without changing WDM optics, using 43 Gbit/s electronics.

Requirement of filter characteristics for 40 Gbit/s-based DWDM systems

The impact of WDM filter characteristics on 40 Gbit/s signals with various channel spacing is investigated for NRZ, CS-RZ, and RZ modulation formats. The basic limitations imposed by channel spacing, slope, detuning, and cascade of filters are presented.

Accurate bit error ratio monitor by spectral filtering and optical power measurements

We propose a novel bit error ratio monitoring method by optical bandpass filter and optical power measurements and experimentally demonstrate its sufficient accuracy with various fiber launched powers and wavelengths in WDM dispersion-uncompensated transmission link.