Power Coupling from GaAs Injection Lasers into Optical Fibers

Abstract

Measurements have been made to determine the efficiency of coupling light from GaAs injection lasers (λ = 9000 Å) of stripe geometry into the cores of optical fibers. Laser light was coupled into a fiber across a small air gap which separated the laser from the fiber. The power coupling efficiency was calculated by extrapolating the lasing light power emitted at the end of a short length of fiber back to its input tip and comparing it with the total laser beam power. Experiments were performed with several diffused junction (DJ) lasers and with low-threshold double-heterostructure (DH) lasers having stripes formed by proton bombardment or oxide masking. The beam profile, scanned in its near and far field region, was approximately Gaussian. The beam dimensions at the surface of the laser were estimated from far field measurements and were used to predict the coupling efficiency of single-mode and multimode fibers. Power coupling efficiencies of about 70 percent were measured for DJ lasers feeding 10-µm multimode fibers. A coupling efficiency of 25 percent, almost identical to the theoretical estimate, was achieved with a DH laser having a 1-µm × 13-µm proton-bombarded stripe, feeding the 3.2-µm core of a single-mode fiber. The coupling efficiency was greater than 40 percent when a DJ laser fed the same fiber. A cylindrical lens is proposed to increase the power coupling perpendicular to the junction plane. Permanent self-supporting couplers were made by applying epoxy between structures which supported the fiber and the laser.