High-power low-divergence superradiance diode

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Abstract
Using a combination of antireflection coating and proton implantation techniques, GaAlAs double-heterostructure lasers are fabricated to operate in superradiant mode. Light output, in excess of seven milliwatts, is obtained with spectral half-power widths of 15–20 nm. This implies extremely short coherence lengths of less than 50 μm. Such a short coherence length light source should be very useful for many applications in fiber sensors and fiber optic communications. In particular, it has produced marked reduction (better than 15 dB) of coherent Rayleigh backscattering noise in a single-mode fiber. Since the laser operates in superradiant mode, the output light is only partially polarized, another unique characteristic that is important for fiber gyroscopes. The typical light output angle of 30°×50° also provides easy coupling into fibers. Coupling efficiencies of 80% into multimode fiber and over 20% into single-mode fiber have been achieved.