Abstract

A lot of research interest is presently focused on microcavity lasers. These structures are resonators having at least one dimension of the order of a wavelength. So far, attention has been paid mainly to controlling spontaneous emission and the threshold-less feature of the microcavity laser [1], i.e. the advantage of low power consumption. However, the microcavity laser offers another attractive feature: the ultrafast response of possibly over 100 gigabit-per-second (Gbps). One reason is due to the extremely short photon lifetime in an appropriately designed microcavity accompanied by the extremely short cavity length. The other reason for the response speed increase is the cavity-enhanced spontaneous emission rate. Assuming a linear gain, the resonant relaxation oscillation frequency is inversely proportional to the square-root of both lifetimes. A three-dimensionally or two-dimensionally confined microcavity could induce a marked reduction in the spontaneous emission lifetime. In a planar microcavity, although the enhancement in the spontaneous emission rate is at most a factor of ~2 [2], ultrafast response is still expected. For example, a symmetric Fabry-Perot cavity having a 0.99 reflectivity and λ/2 length gives a 0.2 ps photon lifetime. This value is ~1/10 of a conventional diode laser. Assuming a 1 ns spontaneous emission lifetime and an excitation level of 20 times higher than the threshold, the above photon lifetime gives a relaxation oscillation frequency of ~100 GHz. Under these conditions, large signal analysis has shown that the light output follows a series of 100 Gbps excitation pulses without serious distortions [3].

© 1992 The Author(s)