PHOTOREFRACTIVE SPATIAL MODE CONVERTER FOR MULTIMODE-TO-SINGLE-MODE FIBEROPTIC COUPLING

We report what is to our knowledge the first experimental demonstration of a photorefractive spatial mode converter (based on mutually pumped phase conjugation) that couples light efficiently from a multimode fiber into a single-mode fiber with an extremely large degree of tolerance to misalignment. Using an argon laser (514.5 nm) and a barium titanate crystal, we have demonstrated that the laser light can be coupled from a multimode fiber (core diameter 100 mu m, numerical aperture 0.37) into a single-mode fiber (core diameter 2.9 mu m, numerical aperture 0.11), with an efficiency of similar to 15% and an alignment tolerance of similar to 100 mu m The coupling efficiency is more than 2 orders of magnitude, and the tolerance to misalignments is more than 30 times better than the corresponding values achievable by conventional techniques.