INTEGRATED COUPLING DEVICE BETWEEN A LASER-DIODE AND AN OPTICAL-FIBERUSING A MICROLENS

An integrated coupling device between a GaAs/AlGaAs laser diode and an optical fiber using a microlens is described. It is calculated that t he high single-mode fiber coupling efficiency of 81 percent is obtaine d for the microlens with RMSA of 0.4 lambda and that the large alignme nt tolerance of 55 mu m is obtained in the z-direction. It is demonstr ated experimentally for single-mode fiber coupling that the coupling e fficiency is 26 percent and that the alignment tolerance in the z-dire ction is 19 mu m. The differences in the coupling efficiency and align ment tolerance between the calculation and experiment are due to a mis match of beamwidth and the fabrication error of the fiber guide. Addit ionally, measurement of: the oscillation spectrum of this coupling dev ice, which has a composite cavity, showed that an LD with a microlens and fiber causes multimode oscillation due to reflection from the fibe r facet.