Somekh S, Garmire E, Yariv A, Garvin H L, Hunsperger R G
Appl Opt. 1974 Feb 1;13(2):327-30. doi: 10.1364/AO.13.000327.
Two-channel imbedded directional couplers were fabricated with proton implantation, yielding complete light transfer in 2 mm. Ridged channel guides were fabricated by ion-micromachining epitaxial layers, and a method of directional coupling was demonstrated.