Ilya Lyubomirsky

DPSK demodulator based on optical discriminator filter

A 10-Gb/s differential phase-shift-keying (DPSK) demodulator is demonstrated based on an ultranarrow 6.2-GHz optical discriminator filter. The DPSK demodulator operates with a conventional direct detection p-i-n receiver, while still outperforming on-off keying by 1.2 dB.

Quadrature Duobinary for High-Spectral Efficiency 100G Transmission

This paper proposes and analyzes a quadrature duobinary modulation format with coherent detection for high-spectral efficiency wavelength-division-multiplexing transmission systems at 112 Gb/s per channel. A practical system design of a dual polarization quadrature duobinary (DP-QDB) format with coherent heterodyne detection is analyzed and compared with the DP-differential quadrature phase-shift keying format for feasibility of 112 Gb/s transmission. Using simulation analysis, we show that the relatively narrow spectrum of quadrature duobinary modulation provides an effective practical means for realizing high-spectral efficiency transmission, approaching the theoretical limit of 4 bits/s/Hz, while also providing excellent tolerance to optical filter cascades for a robust optical networking functionality.

Impact of optical filtering on duobinary transmission

An experimental investigation into the effects of optical filtering on 10-Gb/s duobinary transmission is presented. It is found that duobinary transmission systems benefit substantially from narrow optical filtering at the receiver. A 2-3- dB Q improvement in amplified spontaneous emission (ASE) noise-limited performance is obtained by optimizing the optical filter bandwidth. The duobinary modulation is compared to nonreturn-to-zero modulation as a function of optical filter bandwidth in ASE noise-limited and dispersion-limited regimes.

Optical DQPSK Receiver With Enhanced Dispersion Tolerance

We propose and analyze a novel differential quadrature phase-shift-keying (DQPSK) receiver architecture based on optical frequency discriminator filtering and direct detection. Our simulations show that such a receiver provides significantly enhanced tolerance to chromatic dispersion compared with the conventional delay-interferometer-based receiver. Preliminary measurement results demonstrate the novel DQPSK demodulator concept at 20 Gb/s.

Comparison of RZ Versus NRZ Pulse Shapes for Optical Duobinary Transmission

This paper presents an experimental study and comparison of return-to-zero (RZ) versus nonreturn-to-zero (NRZ) pulse shapes for optical duobinary systems. Surprisingly, and contrary to the case of on-off keying, we find the NRZ pulse shape to be superior, compared with RZ, for duobinary transmission in all the cases that were studied, including systems that are limited by amplified-spontaneous-emission noise, fiber chromatic dispersion, and self-phase modulation.

Impact of DP-QPSK Pulse Shape in Nonlinear 100 G Transmission

This paper reports results of an extensive Monte Carlo simulation analysis on the impact of DP-QPSK pulse shape in high-spectral efficiency WDM transmission at 112 Gb/s per channel. The pulse shapes studied include NRZ, 50% duty cycle RZ and 67% duty cycle RZ. Both symbol-aligned and symbol-interleaved formats are investigated and compared for nonlinear transmission tolerance on common dispersion maps used in terrestrial long-haul systems. The RZ pulse shape shows the greatest improvement in nonlinear tolerance with symbol-interleaving. However, symbol-interleaving only provides significant benefit in optical line systems designed to preserve the pulse shape during transmission, such as systems based on distributed dispersion compensating fiber (DCF). The duty cycle of the RZ pulse has only a minor impact on nonlinear performance, and even systems based on the NRZ pulse shape can gain significant benefit from symbol-interleaving.

Tailoring the duobinary pulse shape for optimum performance

This paper presents an experimental investigation on the optimum optical duobinary system for amplified spontaneous emission (ASE)-noise-limited transmission at 10 Gb/s. Optical filtering is used at the transmitter and receiver to optimize the duobinary pulse shape, while suppressing the effects of ASE noise. The optimized system shows excellent ASE-noise-limited performance, approaching to within 3.4 dB of the theoretical matched filter limit for the duobinary system.

Coherent detection for optical duobinary communication systems

We propose and analyze coherent detection schemes for optical duobinary modulation. Thus, new quantum limits are established at 15, 30, and 31 photons/bit for coherent duobinary based on homodyne, heterodyne synchronous, and heterodyne asynchronous detection, respectively.

Ideal duobinary generating filter for optically amplified systems

We develop a simple analytical model of an ideal duobinary generating low-pass filter. The model provides important physical insight into the design of optically amplified duobinary systems. We verify the theory with experimental data at 10 Gb/s

Optical duobinary spectral efficiency versus transmission performance: is there a tradeoff?

Tradeoffs between optical spectral efficiency, ASE noise-tolerance, and dispersion tolerance are investigated experimentally for three modulation formats - RZ, NRZ, and duobinary. Duobinary does not follow conventional wisdom - achieving excellent performance with the narrowest bandwidth.