Ultimate coupling performances for microlensed fibres

The authors have analysed the coupling efficiency of highly diverging Gaussian beams into the LP₀₁ mode of a typical singlemode fibre, through a microlens on the end of the fibre. Hyperbolic and spherical lenses have been investigated. In both cases, it should be possible to obtain less than 0.2 dB coupling loss with a Gaussian beam of half width 1 mu m, with a positioning tolerance of about 6 mu m for less than 1 dB loss.