A. Hadjifotiou

Laser linewidth requirements for optical DQPSK systems

A differential quadrature phase-shift-keying (DQPSK) system is analyzed in the presence of additive optical noise and phase noise. In DQPSK, the impact of laser linewidth is frequently neglected: This letter aims to determine whether this assumption is valid. Using asymptotic techniques, we determine the effect that phase noise has on the bit-error rate (BER); this leads to a simple condition for when laser linewidth may be neglected. For a 10-GBd DQPSK system operating at a BER of 10/sup -3/, a linewidth of less than 3 MHz is required for the signal-to-noise-ratio penalty to be less than 0.1 dB.

Single channel 160 GB/s OTDM propagation over 480 km of standard fiber using a 40 GHz semiconductor mode-locked laser pulse source

We have successfully demonstrated the propagation of 160 GB/s over 480 km of NDSF using a 40 GHz semiconductor mode locked laser (MLL) as a pulse source and a two stage, dual drive, electroabsorption modulator (EAM) based optical time domain demultiplexer (OTDD). Theoretical predictions show that the reach can be significantly extended by using distributed Raman amplification, and that the WDM penalties due to nonlinear effects are negligible.

Twin fiber grating tunable dispersion compensator

A new tunable dispersion compensator that does not suffer from higher order dispersion is reported. The device consists of two quadratically chirped fiber Bragg gratings, each with linear strain actuators. The module has a tuning range of 500 ps/nm and a bandwidth of 0.5 nm. In a 40-Gb/s return-to-zero system, the dispersion penalty tolerance is extended from 100 to 600 ps/mm.

Estimating Outages Due to Polarization Mode Dispersion Using Extreme Value Statistics

Polarization mode dispersion (PMD) is a time varying phenomenon, which in a network can result in system outages. In this paper, it is demonstrated that the method of extreme value statistics can be used to model the occurrence of these rare events. The extreme value behavior of the bit error rate (BER) due to PMD is analyzed both theoretically and experimentally, revealing that the logarithm of the BER follows a Gumbel distribution

40-Gbit/s TDM transmission over 160 km (2/spl times/80 km) of standard nondispersion-shifted fiber

It is anticipated that fiber chromatic dispersion is one of the key performance-limiting factors in the next generation high-speed time-division multiplexing (TDM) systems operating at 40 Gbit/s. To date, much effort has been focused on the issue of signal propagation using dispersion-shifted fiber (DSF). In reality, the existing fiber base is predominantly nondispersion-shifted fiber (NDSF) exhibiting dispersion values between 15 and 17 ps/nm/km with respect to the erbium-doped fiber amplifier wavelength window. Some ways of compensating this level of dispersion will be necessary. In this paper, we report the TDM transmission of 40-Gbit/s data on these high-dispersion-standard NDSF. The optimum position of the dispersion-compensating fiber was evaluated in single- and multi-span configurations. System results for operation up to two spans of NDSF are presented. Comparison with system simulation is also be made.

Interaction between polarization mode dispersion and polarization-dependent losses in optical communication links

The interplay between polarization mode dispersion (PMD) and polarization-dependent losses (PDLs) is systematically analyzed by a model that assumes the concatenation of independent birefringent and PDL elements in a distributed way. It is shown that PDL enhances the differential group delay for the optical link and also induces a faster frequency decorrelation that increases the magnitude of higher-order PMD. In addition, PDL converts the real-valued PMD vector into a complex vector, giving rise to a loss of orthogonality between the principal states of polarization that scales with the link PDL. The dynamic equation for the global PDL vector that characterizes the polarization states with maximum and minimum attenuation is also solved. The frequency dependence of this vector is found to be a function of the total link PMD. Finally, the probability density functions for both the PMD and the PDL vectors will be discussed.

Widely tunable twin fiber grating dispersion compensator for 80 Gbit/s

The dispersion tolerance of an 80 Gbit/s system is broadened 27-fold, from 32.7 ps/nm to 884.9 ps/nm, using an adjustable dispersion compensator with novel grating design. This is the largest reported broadening of any system.

Polarisation-channel-interleaved carrier-suppressed RZ ETDM/DWDM transmission at 40 Gbit/s with 0.8 bit/s/Hz spectral efficiency

We report experimental results of 8/spl times/40 Gbit/s polarization-channel-interleaved carrier-suppressed RZ transmission over 2/spl times/160 km NDSF, with 0.8 bit/s/Hz spectral efficiency. Average system linear Q of 6.5 (2/sup 31/-1 PRBS) and tolerance of at least 50% degradation in orthogonality were demonstrated.

All-Raman unrepeatered transmission of 1.28 Tbit/s (32/spl times/40 Gbit/s) over 240 km conventional 80-/spl mu/m/sup 2/ NDSF employing bi-directional pumping

A total of 32 channels of 40 Gbit/s CS-RZ ETDM signals have been successfully transmitted over an unrepeatered span of 240 km conventional 80-/spl mu/m/sup 2/ NDSF employing all-Raman amplification and bi-directional pumping. No large-effective-area fibres, hybrid transmission lines, or intraspan remotely pumped EDFAs were used. Up to 65 dB span loss, out of a total span loss of 93.8 dB, has been compensated. Individual channel Q-factors between 12.5 dB and 14.5 dB, at a PRBS pattern length of 2/sup 31/-1, were achieved without using FEC. Bi-directional pumping with pump laser RINs around -140 dB/Hz has allowed an average OSNR improvement by 6 dB in the transmission fibre, compared to either counter-pumping or co-pumping alone. This highlights the prospect of possible performance enhancement in high bit rate multiple long-span systems by bi-directionally pumped distributed Raman amplification, as compared to counter-pumping only, or unrepeatered transmissions with additional adoption of fibre effective area management and remote pumping.

Experimental comparison of all-Raman vs. Raman/EDFA hybrid amplification with 40 Gb/s-based ETDM/DWDM transmissions over 400 km TW-RS fibre

Summary form only given. A 400 km TW-RS fibre system with 16 channels of 40 Gbit/s CS-RZ ETDM signals has been used to experimentally compare the relative merits of all Raman and Raman/EDFA hybrid amplification. In the cases of counter-pumped 10 /spl times/ 40 km and 5 /spl times/ 80 km spans, all Raman distributed amplification has allowed best transmission performance, compared to Raman/EDFA hybrid amplification. All Raman transmission yielded up to 1.3 dB system Q improvement in the 40 and 80 km span length systems, compared to systems without Raman gain. The MPI impairment associated with the double Rayleigh scattering effect in all-Raman counter-pumped long span systems, was significantly reduced in an experimental demonstration over 1 /spl times/ 160 + 2 /spl times/ 120 km TW-RS fibre, by employing multi-span bidirectionally pumped all Raman amplification.