LONG-WORKING-DISTANCE EXPANDED-BEAM FIBER MICROLENSES

Single-mode-fibre output couplers for diode lasers have been fabricated to have long working distances. The fibres have (i) tapered cores expanded at one end to 25-mu-m diameter by thermal diffusion of the core dopant and (ii) outside diameters etched down to 30-60-mu-m. Hemispherical lenses were made by melting the ends. The resulting working distances are 35-40-mu-m, and coupling losses, as low as 3 dB, are mostly between 3.5 and 5.5 dB.