Fabrication of an optical directional coupler of CdTe by electron beam lithography and ion etching

Various kinds of high resolution techniques such as ion etching, chemical etching, ion implantation, and electron beam lithography are studied for fabricating CdTe optical integrated circuits. It is found that the ion-etching rate of CdTe is high and has only a small dependence on crystal orientation. A special chemical etching solution for aluminum on CdTe that does not corrode CdTe and proton implanted CdTe is used for high resolution patterning of CdTe. The smooth patterns in PMMA resist produced by an electron beam exposure is replicated deep into 2.5 μm of CdTe face through the aluminum layer. Rib guides and a rib-type optical directional coupler are fabricated from planar guides by using proton implantation which makes refractive index change on CdTe face. The two-dimensional optical confinement is observed. A coupling coefficient of
k \simeq 0.39
mm
^-1
is observed in the rib-type optical directional coupler.