Microlasers based on photonic crystal concept

Abstract

The recent development of photopumped 1.5 - 1.65 μm GaInAsP microdisk, microgear and photonic crystal lasers is re-viewed. For the former two lasers, room temperature cw lasing characteristics are presented. Their small cavity volume and high Q factor simply reduced the threshold pump power to a record low value of 10 microwatt order, and provided a large sponta-neous emission factor of over 0.1 potentially with the Purcell effect. In the microdisk, nonlasing resonant modes with differ-ent order and different phase often appear. Rate equation analysis indicated that such modes with a high Q affect the laser performance. The microgear having a rotational periodic structure is unique because it not only suppresses such modes, but also increases the Q factor by the minute control of electromagnetic fields so that the radiation field is minimized. The latter advantage will allow a further reduction in cavity size from the smallest limit of the microdisk. A couple of microdisks lased even in a form of a coupled cavity, which can be treated as a photonic molecule. The photonic crystal cavity is also unique because it is easy to construct various types of cavities by the composite of line and point defects inside the uniform photonic crystal slab. The pulsed lasing was obtained in some of them, while we found a large thermal resistance that dis-turbed the cw lasing. We also found through the rate equation analysis that carriers are effectively confined in the microdisk by the strain relaxation effect in compressively-strained quantum wells. However, the result also suggested that the carrier confinement is rather degraded by this effect, so a structural optimization is necessary in the photonic crystal laser.