Simulation of mid infrared quantum cascade laser and its application to free space optical links

Abstract

The research work described in this thesis is devoted to explore the potential applications of mid infrared Quantum Cascade Lasers (QCLs) in Free Space Optics (FSO) based communication. The main contributions of this thesis have expanded in three main areas: device modelling and simulation of QCL to study its characteristics, short pulse generation by Gain Switching for application in FSO links, design of QCL based repeater for FSO links. The device parameters of QCL namely spontaneous emission coefficient, optical confinement factor and mirror reflectivities are varied to study their effects on steady state and transient characteristics. From these studies, the device parameters that give the lowest threshold current and maximum power are deduced. QCL devices are semiconductor sources of terahertz radiation, which can be made to generate short optical pulses by gain switching. This characteristic is also investigated. Optical pulses propagate in free space without electromagnetic interference and minimal dispersion, which are important in optical wireless communication. Both single wavelength QCLs and Dual-Wavelength (DW) QCLs ar analyzed with various electrical input signals to determine the optimum pulse characteristics. In the case of conventional single wavelength QCLs, it is evident that tangential hyperbolic input current provides the maximum peak power and minimum pulse width, for the device considered in this thesis. In the case of DW-QCLs, it is observed that square input current having peak amplitude of 11.12mA and 0.1ns produces short optical pulses of width 15.89ps with peak power of 2.2mW at 10.5and#956;m. newline