Abstract

The direct modulation response of a semiconductor laser is of great importance to optical fiber communication systems employing these devices as sources. It has been studied extensively and is determined by two mechanisms. The first is simply device parasitics, e.g., resistance and capacitance associated with the laser packaging, sub-mount, and the device itself. The second is the interaction of carriers and lasing mode photons in the active layer of the device. We demonstrate a technique that is able to measure the response associated with the latter, the intrinsic response function, independently of parasitic effects. In it, a semiconductor laser having a transparent contact layer is modulated by photomixing two optical frequencies in the device active layer. This technique has been used in the past to calibrate photo-detectors over large-frequency bandwidths.^1,2 In those cases, however, both the intrinsic device response and the parasitic response are measured simultaneously, since the photomix-generated signal is dependent on the current transport out of the detector. With the semiconductor laser the photo-mixing process delivers gain modulation precisely where it is needed, inducing modulation of the emitted Iasing light without the deleterious effects of parasitics associated with carrier transport. We believe for this reason that the modulation response curves presented here are the first measurements of the intrinsic response of a semiconductor laser.

© 1988 Optical Society of America