Characteristics of (GaAℓ)As Injection Lasers Operating with an Optical Fiber External Resonator

Abstract

The operation of injection lasers with an external optical cavity has become an important subject because it can lead to the generation of short optical pulses at Ghz rates. Potential applications for such pulses are optic logic circuits and the phase locking of microwave semiconductor sources. Conventional external cavities, composed of lenses and mirrors, are bulky and difficult to align. In this talk we report the characteristics of a novel external cavity configuration which is mechanically stable and simple to construct. The external cavity consists of a piece of multimode graded index fiber with both ends cleaved. One end of the fiber is coated with a thin layer of Au to form a reflector. A spherical lens (typically 80-100 µ in radius) is formed on the other end of the fiber. By aligning the lase(1) to the lens end of the fiber we have obtained laser oscillation in the composite cavity whose threshold was typically 6-10% less than without the fiber resonator. The light output vs. current is shown in Figure 1.