Serge Mottet

Theory of signal degradation in semiconductor laser amplifiers in direct detection systems

Theoretical studies are carried out on long haul direct detection optical fiber communication systems, with inline optical semiconductor amplifier repeaters. Calculations are made of the noise, eye diagrams, and bit-error-rate characteristics of lightwave systems with optical amplifiers. Indications are given of the effect of amplifier characteristics such as spontaneous noise and signal distortion due to gain saturation on the system performance. The nonlinear process within semiconductor laser amplifiers leads generally to pulse amplitude-temporal distortions due to gain saturation. This theoretical study demonstrates that the system penalty caused by these nonlinear effects appears progressively as the optical input power at each amplifier is increased. For example, nonregenerated fiber transmission using traveling wave semiconductor laser amplifiers was simulated, and results obtained at 0.5 and 2.5 Gb/s are presented. In order to improve the system performance, the influence of structure and bulk dimensions of the amplifier cavity is also considered. >

2D numerical simulation of a-Si:H TFTS: Application to parasitic contact resistances evaluation

Abstract In this paper, we present a 2D numerical computer program for amorphous silicon thin film transistors (a-Si:H TFTs) simulation, and its application to the bidimensional study of the parasitic channel access resistances. The program solves the transport equation set under non-equilibrium steady state conditions, for given applied voltages. The values of physical parameters describing the internal state of the transistor are calculated at each node of a bidimensionnal mesh and the resulting drain current can therefore be related to the physical characteristics of the materials and to the geometrical and technological parameters of the device. The program allowed us to perform the evaluation of parasitic channel access resistances and their sensitivity to physical and geometrical parameters.

Fast semiconductor optical amplifier modulator design

A time dependent model describing near travelling wave optical amplifiers is presented. This model is used to design and optimize semiconductor optical amplifiers used as fast external modulators with internal gain.

Investigation into the properties of the explicit method for the resolution of the semiconductor device equations

Most simulators use a Newton-like method for solving the semiconductor device equations. The linearized system obtained by this method is then solved either directly or iteratively. However, it is also possible to use an explicit method instead of the implicit Newton method. This method was first introduced by Kurata and Nakamura (see ibid., vol. 11, no. 8, p. 1013-22, 1992) for the semiconductor equations. The authors revise and improve this explicit method and show the properties and limitations of the algorithm. The main limitation of the method is the long computation time needed. However, the method benefits from a very simple algorithm, low memory requirements, and highly parallel properties. >

Design tool for multifunctional semiconductor laser amplifiers

Semiconductor laser amplifiers (SLAs) are multi-functional devices, as they can perform the following functions: amplification, modulation, detection and wavelength conversion. For the optimization of SLAs, a good numerical simulator is required. This gives insight into both the internal behavior of SLAs and the variation of certain system parameters due to changes in the SLA structure or external conditions. This paper describes an extensive numerical model for SLAs. It includes large-signal time dependent analysis, residual mirror reflection, amplified spontaneous emission (ASE) and multiple electrodes. SLAs with active layers made of bulk or MQW material can both be simulated. Important parameters such as the bit-rate, amplification, noise figure, chirp, ASE-spectrum and polarization-dependency can be obtained. It is also possible to use the simulator to investigate the influence of the accumulation of forward and backward propagating ASE in cascaded SLAs. The simulator is used for the design of a fast external modulator and for a wavelength convertor at 1.55 micrometers . Further, a multi-functional two electrode polarization-intensive amplifier-modulator- detector structure is proposed and optimized. This SLA can be used as an insert-drop transparent node for application in LANs and access/distribution networks.