1. F. P. Kapron, D. B. Keck, R. D. Maurer, Appl. Phys. Lett. 17 (10), p. 423–425 (1970).
2. D. B. Keck, R. Bouillie, Optics Communications 25 (1), p. 43–48, (April 1978).
3. S. Horiguchi, et al., Nat. Cony. IECE J. 821 (March, 1977 ).
4. Fiber Optics and Communications Newsletter, 1 (7), 8–17 (August 1978).
5. D. R. Powers, J. Am. Ceram. Soc. 61 (7–8), p. 295–297 (July, 1978 ).