A.K. Mishra

All-optical logic based on ultrafast gain and index dynamics in a semiconductor optical amplifier

We investigate nonlinear carrier dynamics in a multiquantum-well semiconductor optical amplifier (SOA) in the context of ultrafast all-optical logic. A rate-equation model is presented that accounts for two-photon absorption, free-carrier absorption, self- and cross phase modulation, carrier heating, spectral, spatial hole burning, and self- and cross polarization modulation. The nonlinear refractive index dynamics is investigated theoretically and experimentally. We find nonlinear phase changes larger than /spl pi/ radians, which recovers on a timescale in the order of 1 ps. We also investigate a nonlinear AND gate that consists of an SOA that is placed in an asymmetric Mach-Zehnder interferometer. We show that the gate can be operated using 800-fJ optical pulses with duration of 200 fs while having a contrast ratio larger than 11 dB.

Cross-Channel Interference Due to Wavelength Drift of Tunable Lasers in DWDM Networks

The authors present an investigation of the wavelength stability of a tunable laser (TL) transmitter and its impact on the performance of a 2.5-Gb/s dense wavelength-division-multiplexed (DWDM) system. Performance of a DWDM system, employing such a TL, is characterized by examining the cross-channel interference caused by this drift when the channel spacing is set to 12.5 and 25 GHz. Results obtained show that the wavelength drift affects the system performance by introducing an error floor in the case of 12.5-GHz spacing. This error floor can be mitigated by increasing the blanking time of the TL during the channel transition, in order to reduce the wavelength drift

Time-resolved linewidth measurements of a wavelength switched SG-DBR laser for optical packet switched networks

We report time-resolved linewidth measurements of different sizes of optical packets under wavelength-switching for the first time and show that laser linewidth is significantly broadened during switching transition requiring ~3 μs to attain its minimum value.

Wavelength conversion employing 120-fs optical pulses in an SOA-based nonlinear polarization switch

We demonstrate wavelength conversion based on nonlinear polarization rotation driven by ultrafast carrier relaxation in an InGaAsP-InGaAs multiquantum-well semiconductor optical amplifier. We use a continuous-wave (CW) probe beam at a center wavelength of 1555 nm, and a control pulse of duration of 120 fs at a center wavelength of 1520 nm. We have investigated wavelength conversion for different injection currents and for different control pulse energies. We show that a conversion efficiency of 12 dB can be obtained for control pulse energies of 10 pJ.

Adaptive modulation schemes

In this presentation we will discuss recent advances in adaptive modulation schemes for ultra high bit capacity optical networks. This paper focuses on optimising the sub-carrier spacing for such high capacity networks..

Time-Resolved

We demonstrate a novel time-resolved Q-factor measurement technique and demonstrate its application in the analysis of optical packet switching systems with high information spectral density. For the first time, we report the time-resolved Q-factor measurement of 42.6 Gbit/s AM-PSK and DQPSK modulated packets, which were generated by a SGDBR laser under wavelength switching. The time dependent degradation of Q-factor performance during the switching transient was analyzed and was found to be correlated with different laser switching characteristics in each case.

Q

Crosstalk caused by switching events in fast tunable lasers in an optical label switching (OLS) system is investigated for the first time. A wavelength-division-multiplexed OLS system based on subcarrier multiplexed labels is presented which employs a 40-Gb/s duobinary payload and a 155-Mb/s label on a 40-GHz subcarrier. Degradation in system performance as the transmitters switch between different channels is then characterized in terms of the frequency drift of the tunable laser

-factor Measurement and Its Application in Performance Analysis of 42.6 Gbit/s Packets Generated by SGDBR Lasers

The use of amplitude-modulated phase-shift-keyed (AM-PSK) optical data transmission is investigated in a sequence of concatenated links in a wavelength-division-multiplexed clockwork-routed network. The narrower channel spacing made possible by using AM-PSK format allows the network to contain a greater number of network nodes. Full differential precoding at the packet source reduces the amount of high-speed electronics required in the network and also offers simplified header recognition and time-to-live mechanisms.

Effects of Crosstalk in WDM Optical Label Switching Networks Due to Wavelength Switching of a Tunable Laser

A novel approach to optical subcarrier multiplexing with compact spectrum is demonstrated using a 42.6 Gb/s duobinary payload and 2.5 Gb/s NRZ label. The label causes ≪1 dB penalty on the payload receiver sensitivity.

Optical packet transmission in 42.6 Gbit/s wavelength-division-multiplexed clockwork-routed networks

We demonstrate wavelength conversion based on nonlinear polarization rotation driven by ultrafast carrier relaxation in an InGaAsP-InGaAs multi-quantum-well (MQW) semiconductor optical amplifier (SOA). A continuous wave probe beam at a center wavelength of 1555 nm, and a control pulse of duration of 120 fs (FWHM) at a center wavelength of 1520 nm were used. We have presented wavelength conversion for different injection currents and for different control pulse energies. The conversion efficiency of 12 dB was obtained for the control pulse energies of 10 pJ.