Optical transmitter apparatus 10 comprising a reflective optical amplifier 12, a driver 14, an optical splitter 16, polarisation compensation apparatus 18 and an optical router 20. The reflective optical amplifier is arranged to receive an optical seed signal. The driver is arranged to generate a drive signal arranged to cause the reflective optical amplifier to amplify the optical seed signal to form an optical signal. The optical splitter is arranged to receive the optical signal and to split off a part of the optical signal to form a further optical signal. The polarisation compensation apparatus is arranged to receive the further optical signal and to rotate a polarisation of the further optical signal by a pre-determined amount, to form a further optical seed signal. The optical router is arranged to receive the further optical seed signal and to direct the further optical seed signal to the reflective optical amplifier for amplification thereby.

Passive optical networks

A flip-flop (FF) is a kind of latch and the simplest form of memory device, which stores various values either temporarily or permanently. Optical FF memories form a fundamental building block for all-optical packet switches in next-generation communication networks. An all-optical clocked delay FF using a single terahertz optical asymmetric demultiplexer-based interferometric switch is proposed and described. Numerical simulation results are also reported.

All-optical clocked delay flip-flop using a single terahertz optical asymmetric demultiplexer -based switch: a theoretical study

All-optical cross-bar network architecture using TOAD based interferometric switch and designing of reconfigurable logic unit

All-optical frequency-encoded AND, OR, and NOT logic gates are proposed and their performance simulated to confirm their feasibility. Terahertz optical asymmetric demultiplexer (TOAD)-based logic gates with a control pulse energy as low as 50 fJ are used, and real-time simulations of their input and output pulse patterns reveal a rate of 20 Gbps. Such logic gates could be used for future all-optical logic processors for optical computation and communication systems.

An alternative method for implementation of frequency-encoded logic gates using a terahertz optical asymmetric demultiplexer (TOAD)

Turbo-switched Mach-Zehnder interferometer performance as all-optical signal processing element at 160 Gb/s

Design tool and its experimental validation for SOA-based photonic signal processing

Future interconnection networks will be required to achieve ultra-high bandwidth and low latency communications to cope with the increasing performance requirements of backbone routers, large data storage systems and supercomputing systems. Aiming at achieving ultra-high bandwidth communications and approaching optical time-of-flight processing latency while being robust to cascade impairments, the authors propose an all-optical packet-switched interconnection network, where not only the actual packet switching but also the packet processing is performed in the photonic domain. The authors present two modular architectures, based on the crossbar and the Batcher-Banyan topologies, capable of forwarding fixed-length packets with two classes of service. Both use photonic digital-processing subsystems built by combining a single integrable module which exploits cross gain modulation in a semiconductor optical amplifier. System level simulations on the crossbar switch controller guarantee that the control signals maintain an acceptable quality during the processing. Moreover, the Batcher-Banyan configuration is more cost-effective than the crossbar for increasing port count, while effective network performance in terms of packet loss rate can be obtained by adding just few recirculating delay lines.

All-optical packet-switched interconnection network based on modular photonic digital processing

In the present work we have investigated experimentally and theoretically inter-channel crosstalk in an all-optical de-multiplexer at 50 Gbps using a terahertz optical asymmetric de-multiplexer (TOAD) in presence of continuous wave (CW) assist light. CW assist light substantially reduces gain recovery time and gain depletion in the non linear element present in the TOAD. We found that with assist light ‘on’, power penalty in the de-multiplexing device is reduced and dynamic range of input probe power is raised to 10 dB. Assist light also removes Bit-Error-Rate (BER) floor due to crosstalk and distortion. Lastly the optimum CW assist light wavelength is found to be at the edge of 3-dB gain peak of semiconductor optical amplifier for minimum crosstalk. The experimental results are validated with the theoretical investigation.

http://ieeexplore.ieee.org/iel5/5398767/5407062/05407241.pdf

Theoretical and experimental investigation of inter-channel crosstalk mitigation by assist light in a TOAD de-multiplexer

A bidirectional WDM-PON exploiting reflective semiconductor amplifiers at the optical network unit (ONU) and a multiwavelength RZ pulsed signal comb at the Central Office (CO) is presented. The reflective SOA acts simultaneously as downstream modulation eraser, upstream amplifier and modulator, thus making the ONU wavelength-independent.

Single RSOA based ONU for RZ symmetrical WDM PONs at 2.5 Gb/s

The paper investigates in depth analysis of inter-channel crosstalk in a terahertz optical asymmetric de-multiplexer (TOAD) switch. Large signal multi-wavelength circuit model of semiconductor optical amplifier (SOA) has been developed for crosstalk analysis of the TOAD. The circuit model is particularly suitable for numerical simulation of an integrated TOAD switch in presence of chip and package parasitics. Mitigation of inter-channel crosstalk by continuous wave (cw) assist light is studied experimentally and good prediction accuracy with the numerical result is obtained. It is found that the range of input probe power can be increased by 10 dB when assist light is injected and no error floor is observed. Best performance of crosstalk mitigation is obtained when assist light wavelength is set to the edge of 3 dB bandwidth of the SOA.

A. Das Barman

Papers

Design tool and its experimental validation for SOA-based photonic signal processing

All-optical packet-switched interconnection network based on modular photonic digital processing

Theoretical and experimental investigation of inter-channel crosstalk mitigation by assist light in a TOAD de-multiplexer

Single RSOA based ONU for RZ symmetrical WDM PONs at 2.5 Gb/s

Investigation of inter-channel crosstalk mitigation by assist light in a TOAD switch by using electrical equivalent circuit model of SOA