Optimisation of InGaN narrow stripe self-pulsating laser diodes [for DVD

Abstract

Summary form only given. In optical disc storage devices excessive noise caused by optical feedback can be a problem. An economical and compact solution can be found by creating semiconductor laser diode that self-pulsates. These lasers have a lower coherence length than CW lasers making than relatively insensitive to feedback. To obtain self pulsation, saturable absorption needs to be introduced into the optical laser cavity. A very effective process has been theoretically treated by M. Yamada [1993]. He modelled a narrow stripe laser which ensure that the optical mode extends beyond the central electrically pumped, active region to the neighbouring unpumped region which acts as an absorber. Device specifications require the laser to self-pulsate at temperature greater than 70/spl deg/C. A low operating threshold current density is also demanded combined with a wide operating current range. In this paper we model a 420 nm narrow stripe self-pulsating laser fabricated in the GaN material system. The laser structure is optimised for optical storage applications. We do this by optimising the amount of absorption by varying the cavity length, stripe width and the width of the InGaN quantum wells. Initial results indicate that the 70/spl deg/C threshold can be achieved, however, certain tradeoffs are necessary to combine high temperature and low threshold current density operation. Our findings also show that the reduced gain available in the short wavelength GaN material results in optimised structures that are very different to those found for GaAs and GaInP devices.