Optical and Quantum Electronics 28 (1996) 1669-1676 Simulation of gain-switched picosecond pulse generation from quantum well lasers H. A. TAFTI School of Electronics and Communication Engineering, Anna University, Guindy, Madras-25, India V. S. SHEEBA, K. K. KAMATH,* F. N. FAROKHROOZ, P. R. VAYA :~ Department of Electrical Engineering, Indian Institute of Technology, Madras-36, India Received 16 June 1995; revised 23 March; accepted 22 April 1996 Circuit models for gain-switched quantum well laser diodes are developed and simulated using the circuit analysis program SPICE2. Effects of cavity length and number of wells on the output pulse shape are analysed. Picosecond pulses of 7 and 2 ps full-width at half-maximum (FWHM) are observed, corresponding to second and third quantized level transitions, respectively. A remarkable reduction in the output pulse width observed for the third quantized level transition, demonstrates the significance of higher sub-band transitions for ultrashort pulse generation. 1. Introduction Picosecond pulse generation in multiple quantum well (QW) semiconductor lasers using the gain switching (GS) technique is gaining popularity, because enhanced differential gain in these lasers is effective for obtaining ultrashort pulses. So far, the gain switching characteristics of QW lasers have been investigated either experimentally or theoretically by the numerical solution of rate equations [1-4]. However, these methods suffer from the limitations of non- inclusion of substrate parasitics, package parasitics and device circuit interactions in the calcu- lations. An alternate approach that overcomes these limitations is to transform the rate equations into a circuit model that can then be solved using standard circuit analysis techniques. In this paper, we have developed circuit models corresponding to multiple quantized state transitions (QST) for the generation of picosecond optical pulses in QW lasers. The model was simulated using the circuit simulation program SPICE2, and the effects of cavity length, L, and number of wells, Nw, on the output pulse shape, for various injection, I, current levels, were investigated. 2. Discussion The optical gain function of single QW lasers shows a step-like behaviour in the transition Present addresses: *Department of EECS, University of Michigan, USA. *Optoelectronics Laboratory, N U.S.. Singapore. 0306-8919 ,C~ 1996 Chapman & Hall 1669