Focused ion beam fabricated microgratings for integrated optics applications

Miniature diffraction gratings (μgratings) have been fabricated using focused ion beam (FIB) milling. This FIB "direct write" (maskless/resistless) patterning technique is very well suited for the fabrication of micrometer-scale gratings and for their on-chip integration with other photonic components for fiber-optic communications applications. μgratings in sizes from 20 to 250 μm with groove center-to-center spacing from 200 nm to 2 μm have been fabricated. The diffraction efficiency of the μgratings was investigated as a function of FIB dose. A maximum of 40% efficiency was obtained for nonpolarized 632.8-nm light and 50% for P-polarized light. A technique was developed for the fabrication of μgratings on angled facets and for their integration with optical fibers. The fiber-coupled μgrating was operated as a diffractive optical element (DOE) at 1.5 μm. The diffractive wavelength resolution in these first FIB-fabricated DOEs was measured to be ∼10 nm using a tunable laser in the range 1510-1580 nm. Future such DOEs have the potential to reach the sub-nm resolution level.