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 singlemode 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 µm, numerical aperture 0.37) into a single-mode fiber (core diameter 2.9 µm, numerical aperture 0.11), with an efficiency of ~15% and an alignment tolerance of ~100 µm. 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.
© 1995 Optical Society of America
Arthur Chiou, Pochi Yeh, Changxi Yang, and Claire Gu, "Photorefractive spatial mode converter for multimode-to-single-mode fiber-optic coupling," Opt. Lett. 20, 1125-1127 (1995)