Integrated coupling device between a laser diode and an optical fiber using a microlens

An integrated coupling device between a GaAs/Al-GaAs laser diode and an optical fiber using a microlens is described. It is calculated that the high single-mode fiber coupling efficiency of 81 percent is obtained for the microlens with RMSA of 0.4 λ and that the large alignment tolerance of 55 μm is obtained in the z-direction. It is demonstrated experimentally for single-mode fiber coupling that the coupling efficiency is 26 percent and that the alignment tolerance in the z-direction is 19 μm. the differences in the coupling efficiency and alignment tolerance between the calculation and experiment are due to a mismatch of beamwidth and the fabrication error of the fiber guide. Additionally, measurement of the oscillation spectrum of this coupling device, which has a composite cavity, showed that an LD with a microlens and fiber causes multimode oscillation due to reflection from the fiber facet.