Matching of injection lasers to single-mode fiber waveguides

A study was made of the efficiency of coupling of radiation from a heterostructure laser into a single-mode fiber waveguide with the aid of a hemispherical microlens formed at the entry end of the waveguide. This microlens was produced in the course of thermal melting of a cone-shaped tapered end of the fiber. The highest coupling-in efficiency achieved using such a microlens was 31% for a laser beam with an elongated elliptic cross section (wavelength λ = 0.85 μm). The optimal matching parameters were calculated and found experimentally. The permissible displacement of the fiber axis from its optimal position, which would result in additional losses not exceeding ~ 1 dB, was also determined.