Graham Swift

Performance of the passive recirculating fiber loop buffer within an OTDM transmission link

In this paper, we examine the propagation of both standard soliton and the Gaussian-soliton shaped pulses within a recirculating fiber loop buffer. We believe that this is the first time Gaussian-soliton pulses are considered for the transmission of OTDM signals within a communication system. The simulation model is based on the nonlinear Schrodinger equation (NLSE) and accounts for fiber loss within the communications channel. At this stage pulse interactions are not considered and direct modulation of the launched pulses is assumed. Simulation results for bit error rate (BER) performance at different buffer loop numbers and eye diagrams for buffered and unbuffered cases are presented.

Simulation of all-optical time division multiplexed router

In this paper we have developed a model of an all optical router based on the terahertz optical asymmetric demultiplexer (TOAD). The model architecture is based on a system which has as its input on OTDM packet containing header and payload information. The model simulates extraction of header information from the data stream using one TOAD, which is subsequently used to make a routing decision. The payload information is routed through a second TOAD according to the information contained in the header.

Simulation of an all optical time division multiplexing router employing symmetric Mach-Zehnder (SMZ)

Synchronisation is an important and critical issue in high-speed all optical time division multiplexed (OTDM) packet routing and transmission. In this paper we present a technique for separating the clock synchronization pulse from an incoming optical time division multiplexed data packet, based on all-optical switching devices with optical feedback. A 1/spl times/2 OTDM router composed of three symmetric Mach-Zehnders (SMZs) is proposed. Simulation results show that synchronization between clock and data packet is achievable and the packet payload can be successfully switched to the correct destination port.

Bit-error-rate analysis for a 100-Gbit/s nonlinear optical loop mirror demultiplexer employing soliton control and signal pulses

On the basis of a previously derived mathematical model, the power penalty associated with a nonlinear optical loop mirror (NOLM) demultiplexer was calculated, with timing jitter noise, bit-to-bit cross talk, and channel cross talk taken into consideration. Simulation results show that a 3-dBm improvement in the receiver sensitivity at a bit error rate of 10(-9) can be achieved by choice of the appropriate walk-off time between the control and the signal pulses within the NOLM demultiplexer.

Cascaded optical delay line architectures in the performance of optical MIN

Internally buffered multistage interconnection network (MIN) architectures have been widely used in parallel computer systems and large switching fabrics. Migration from electrical domain to optical domain has raised the necessity of developing node architectures with optical buffers. Cascaded optical delay line(COD) emulates output buffering in a 2/spl times/2 switching element. Two versions of COD are track changer (TC) and twin track changer (TTC). These approaches can be used as a buffered switching element in a Banyan like MIN. We investigate and compare these approaches by using simulation methods. Different performance metrics, such as throughput-delay ratio, packet loss rate have been used under uniform and nonuniform traffic models. Results show that TC-chain node Banyan network offer an improved throughput-delay ratio performance under both traffic models.

MODELING OF AN ALL-OPTICAL TIME-DIVISION DEMULTIPLEXER

The communication Networks of the future will require signal switching in the optical domain to avoid the inherent speed bottleneck of optical-electronic-optical conversions. This has resulted in an intense research effort in this area. Of particular interest are wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). The latter offers the advantage that it operates over a single wavelength, removing the problems associated with dispersion in fibre systems whilst the former operates over a number of wavelengths. This thesis concentrates on the modelling and simulation of one particular system: the asymmetric semiconductor laser amplifier loop mirror (ASLALOM) for OTDM.Initially, a literature review looks at the theory of laser operation which complements the following chapter on laser amplifiers. A review of current optical switching devices will be examined next with regard to switching speeds, crosstalk and the possibility of integration. Also wavelength division multiplexing and time division multiplexing are reviewed, comparing the different systems in current use.At the present time, no complete models of an asymmetric semiconductor laser amplifier loop mirror have been developed. The intention of this work is to determine the equations necessary for a model to be developed and thus enable the system to be simulated. Computer modelling of a system prior to implementation is advantageous in all aspects of engineering. As this system is still confined to the laboratory a model would complement any practical work and identify critical design parameters.In this work the Travelling Wave Semiconductor Laser Amplifier (TWSLA) is first modelled in a form which is appropriate for the asymmetric semiconductor laser amplifier loop mirror architecture. The simulations are then used to demonstrate the switching speeds for different configurations and identify any areas needing further work, such as crosstalk, birefringence and polarisation, a method for multi-channel output is also presented. A further aim is to lay a foundation for future work to enable the system to be fully characterised with regard to noise, dispersion and integration.

Analysis of optical time division multiplexed transmission

Wavelength division multiplexing (WDM) is making a major impact on current high-speed optical communications and configurable network applications. Its counterpart optical time division multiplexing (OTDM) promises high-speed short pulse transmission with the fiber capacity utilized more efficiently. This paper looks at simulations of OTDM data in a time division demultiplexer. The system used to demultiplex the data is the Asymmetric Semiconductor laser Amplifier Loop Mirror (ASLALOM) which is capable of selecting high-speed optical pulses within a data train. The authors use a model of the ASLALOM which includes a time and space analysis of a traveling wave semiconductor laser amplifier. Our investigations show that this system produces crosstalk that is dependent on the data rate, which we analyzed over a range of 200 to 300 Gbit/s. Investigations also show that the crosstalk profile is dependent of the control pulse energy. We also investigate the effect of the switching window width and note two types of crosstalk are evident. The control pulse rate is varied and the effect analyzed.

Performance analysis of all-optical time division multiplexed router based on terahertz optical asymmetric demultiplexer

Growing demands for bandwidth have stimulated the development of high-speed optical shared media networks. At present, most research on optical networking has concentrated on wavelength- division multiplexing (WDM). Optical time-division multiplexing (OTDM) is considered as an alternative to WDM offering data rates greater than 100 Gb/s using just a single wavelength. In such systems all optical routers, which overcomes the bottleneck of optoelectronic conversion, play an important role. This paper investigates TOAD based 1 X 4 optical router by developing a mathematical model. The proposed model is simulated and results for crosstalk are presented and compared with 1 X 2 router.

Cross-talk analysis of optical time-division demultiplexer

We have developed a simulation model to investigate the demultiplexing of all-optical-time-division-multiplexed data, employing an optical time-division demultiplexer. Particular attention is paid to the cross-talk performance when selected parameters of the system are varied. The system used to demultiplex the data is the asymmetric semiconductor laser amplifier loop mirror (ASLALOM), which is capable of selecting high-speed optical pulses within a data train. The authors use a model of the ASLALOM that includes a time and space analysis of a traveling-wave semiconductor laser amplifier. Our investigation shows that this system produces cross talk that is dependent on the data rate, control pulse energy, and control pulse rate.

Effect of Gordon-Haus jitter on nonlinear optical loop mirror (NOLM) demultiplexing

One of the major problems associated with high-speed optical time division multiplexed soliton transmission systems is the timing jitter error associated with individual soliton pulses. The two physical effects that cause soliton jitters are the amplified spontaneous emission (ASE) noise in in- line optical amplifiers and soliton interaction. While soliton interaction is negligible when the duty cycle of transmitted pulses is small enough, the root-mean-square (rms) soliton jitter due to culminated ASE noise is a fundamental factor that limits the bit-rate distance product in high-speed long-haul data transmission systems. Soliton jitter is detrimental to all-optical time division demultiplexing as it would manifest itself into a relative intensity noise in the data recovery process at the optical receiver. This paper investigates the possibility of minimizing the ASE-induced soliton jitter by changing the spacing between in-line optical amplifiers. It is found that the rms soliton jitter decreases with the amplifier spacing and the minimum soliton jitter can be attained in the case of distributed amplification. These results have significant implications to all-optical time division demultiplexing in the sense of taking into account the amplifier spacing in the process of optimizing system parameters to achieve minimum power penalty of the all-optical demultiplexer. The optical demultiplexer used in the analysis is a non-linear optical loop mirror.