Performance evaluation of free space optical link by incorporating the device parameters of quantum cascade laser based transmitter

This article investigates the performance of a free space optical (FSO) communication link by incorporating the device parameters that influence the optical output power of the quantum cascade laser (QCL). The transmitter side of the FSO link consists of gain-switched QCL operating at 9 mu m. Short optical pulses possessing minimum full width half maximum (FWHM) and peak power as a result of ON-OFF keying are transmitted into the channel. The pulses are attenuated by medium bound losses and reach the receiver which employs quantum well infrared photodetector operating in the same wavelength. Average signal-to-noise ratio (SNRavg), bit error rate (BER) and Channel Capacity are computed for the FSO link for all the variations in the device parameters namely optical confinement factor (Gamma), spontaneous emission factor (beta) and mirror reflectivity (R). The combination of device parameters that gives the best link performance is assessed. From the analysis it is observed that, under minimum FWHM condition, QCL with Gamma = 0.32 provides the best average SNR of 4.04 dB, lowest BER of 13.02 x 10(-2) and maximum capacity of 1.82 bps Hz(-1). When peak power is the constraint, QCL with mirror reflectivity of Gamma = 0.45 provides the best average SNR of 24.78 dB, lowest BER of 7.75 x 10(-35) and a peak capacity of 8.24 bps Hz(-1).