Fabrication and characterization of diffractive optical elements in InP for monolithic integration with surface-emitting components

We report on the fabrication and subsequent characterization of binary diffractive optical elements (DOE's) in InP for operation at 1.3 microm. Fresnel lenses of different focal lengths and a DOE that splits and focuses an incident beam into a 1 x 4 array of spots (optical fan-out) were fabricated. We realized the surface reliefs by patterning resist, using electron-beam lithography and etching with a chemically assisted ion beam, which produced well-defined patterns with smooth sidewalls and little if no surface roughness. The measured efficiency for the lenses was 36%. For the fan-out element the efficiency and the uniformity error were 26% and 30%, respectively. Spot sizes as small as 16 microm were measured.