REFRACTIVE-INDEX AND LOSS CHANGES PRODUCED BY CURRENT INJECTION IN INGAAS(P)-INGAASP MULTIPLE-QUANTUM-WELL (MQW) WAVE-GUIDES

We have theoretically estimated the carrier-induced changes in the ref ractive index delta n and the optical loss delta alpha produced by the injection of free carriers in InGaAs(P)-InP multiple quantum-well (MQ W) optical waveguides, MQW structures are specially designed for the t uning layer in carrier injection type tunable laser diodes, such as tu nable twin-guide laser diode (TTG-LD), at the lasing wavelength lambda of 1.55 mu m. Anomalous dispersion and plasma effect for delta n and IVBA (intervalance band absorption) for delta alpha were included, A v alance-band mixing, an overlap integral of electron-hole, and confinem ent factors of carriers in the web were considered to include quantum- size effect of carriers in delta n and delta alpha. Predictions of del ta n are in reasonably good agreement with the experimental results, S ystematic analysis shows that the following InGaAs(P)(well)-InGaAsP (b arrier) MQW structures are promising in order to obtain a large delta n at a given injection current density J: 1) well materials: InGaAsP a lloy with its bulk bandgap wavelength of around 1.55 mu m, 2) barrier materials: InGaAsP alloy with its bulk bandgap wavelength of around 1. 4 mu m, 3) as many as possible number of wells, typically about 15. de lta alpha is also estimated by calculating the carrier distributions i n MQW structures and by fitting experimental data of bulk and MQW wave guides, The maximum well number is limited by the increase of optical loss, According to these results, we have found that 1,55-mu m InGaAsP (well 1,8-nm thick)/1.40-mu m InGaAsP (barrier 14-nm thick) MQW, with the well number of around 15, will be the optimum tuning layer struct ure for 1.55-mu m band tunable LD's, Over 10 mn continuous tuning rang e, with moderate output power, is expected for TTG-LD's.