S. Ishikawa, H. Kanamori, T. Kohgo, M. Nishimura, and H. Yokota, "New mode-field conversion technique in optical fiber using thermal relaxation of residual stress,"
in Conference on Optical Fiber Communication/International Conference on Integrated Optics and Optical Fiber Communication,
Vol. 4 of 1993 OSA Technical Digest Series
(Optical Society of America, 1993), paper TuB4.