Optimum electrical pulse characteristics for efficient gain switching in QCL

Numerical simulation of Gain Switching in Quantum Cascade Lasers (QCLs) for short pulse generation in the mid-Infrared region is reported. Standard two-level rate equation model is used to analyse the QCL which consists of 48 periods of injector and active regions, emitting at 9 μm. The device is simulated for various inputs such as sinusoidal, tangential hyperbolic, trapezoidal and square electrical pulses. The optimum electrical pulse characteristics pertaining to generation of short pulses with maximum power and minimum pulse width are determined using Golden Section Search (GSS) and Parabolic Interpolation (PI) methods Optical pulses of width 10.1 ps at a power of 66.9 mW are obtained, when a square electrical signal of amplitude 1.57A is given to the device. Simulations carried out with sinusoidal input of peak value 0.93A predict generation of 27.62 ps, 49.2 mW optical pulses. Optical pulses of width 17 ps at a power level of 122.1 mW are obtained when trapezoidal electrical pulse of amplitude 1.87A is given to the device. Analysis done with tangential hyperbolic electrical signal resulted in generation of 13.15 ps, 178.3 mW optical pulses. From the numerical simulation, it is observed that tangential hyperbolic input provides the maximum power along with minimum FWHM. However, square wave input provides the shortest pulse width for power less than 0.5 W.