Performance evaluation of free space optical link driven by gain switched temperature dependent quantum cascade lasers

Abstract

Abstract Temperature dependent terahertz frequency quantum cascade lasers (QCLs) offer huge potential in a large number of new applications. Reduced rate equations are used for better understanding of their behavior and to predict the optical output power under changing current drive and chip temperature. This letter reports the complete end-to-end free space optical (FSO) link driven by a gain switched temperature dependent QCL as transmitter. The device used in the FSO link consists of 90 periods of injector and active regions, emitting light at 116 µm. The device is driven by various electrical inputs such as square, haversine and tangential hyperbolic pulses. The short pulses generated by gain switching travel 1500 m to reach the quantum well infrared photodetector operating in the same wavelength as the source. The performance parameters; namely signal-to-noise ratio (SNR), bit error rate (BER) and capacity are computed for the various input signals. Under the minimum full width half maximum condition, haversine input provides a better performance providing a BER of 7.8 × 10−5, with a peak SNR of 14.56 dB and a capacity of 4.89 bps Hz−1 at a cold finger temperature of 45 K. When peak power is the criterion, tangential hyperbolic input performs well with a minimum BER of 7.66 × 10−9, a peak SNR of 18.06 dB and a capacity of 6.02 bps Hz−1 at a cold finger temperature of 45 K.