Coupling between angled-facet amplifiers and tapered lens-endedfibers

The coupling between angled facet amplifiers and tapered lens-ended fibers is investigated theoretically and experimentally. The theoretical investigation is based on a three-dimensional plane wave model which accounts for the phase differences introduced by the angled facets. The coupling is investigated with respect to the beam parameters of the amplifier waveguide and the tapered lens-ended fiber, and with respect to the fiber position. The excess coupling losses due to the facet angle and to the variation of the fiber lens radius are investigated theoretically and found to be in good agreement with experimental results. For optimized lens radii, the excess loss for a 10° facet angle is found to be less than 0.5 dB compared to a normal facet amplifier