Based on a model for the calculation of the variance of relaxation noise we show that it is possible in principle to modulate a miniature solid state laser at data rates (random) of 50 Mbit s-' and higher by modulating the cavity loss, while keeping the relaxation oscillation noise small enough to permit a 10 -9 error rate. Because of the small transit time through the miniature cavity a large modulation index (M ~ 45) can be achieved, and although the laser power output suffers this can be compensated for in data transmission by the narrow output pulse shape that characterizes our intra-cavity modulation scheme.We discuss the design of a proposed miniature laser based on an acousto-optic intracavity modulator and compare its predicted performance with that of a modulated laser source based on an external modulator. Its major advantages are a somewhat lower electrical operating power and the simple construction which is based on an all-planar technology.
I. IntroductionIt was recognized [1] early in the development of the laser that relaxation oscillation noise can appear during its operation in a synchronous pulsed mode, such as Q-switching 1-2] or cavity dumping [2]. The noise is excited during the laser pulse extraction process when the loss that is introduced by the modulator in the cavity is not perfectly reproducible from pulse to pulse. Based on that experience it would at first appear that intra-cavity modulation in a random on-off sequence (such as is required in a data transmission application) would be severely hampered by relaxation noise.In the present paper we analyse this problem quantitatively. In Section 2 we consider a miniature solid state laser [3] and show that, contrary to expectation, it is possible to modulate the output at a data rate of 50 Mbit s-1 by varying the cavity loss, without exciting severe relaxation oscillations. Our approach will be to start with
