Simplified V-grooving aids optical-fiber alignment

Simplified V-grooving aids optical-fiber alignment

V-grooves are considered a possible route to a low-loss, high-stability fiber-alignment technique for devices with hybrid integrated-optical components. Researchers at Toyota Central R&D Laboratories (Aichi, Japan) have developed a new way of incorporating V-grooves into a lithium niobate substrate for fiber alignment or vertical grooves for waveguide end-face formation. The method involves defining the waveguiding region with conventional photolithographic techniques, then depositing a thin titanium film (about 50 nm) that is diffused into the substrate. Electrodes are then patterned on the substrate. An excimer laser with a rhombus-shaped output beam then forms a V-groove along the waveguide from substrate edge to waveguide edge. The beam is projected onto a moving substrate by a lens and a mask to control window shape. Instead of conventional polishing, a high-speed diamond saw cuts a swath 100 µm deep along the normal direction of the waveguide, producing an almost optical-quality surface. Test cuts produced no chipping or cracking at the end face, and the coupling loss with a single-mode fiber was 0.5 dB/facet--the same as the coupling loss with a polished end face.

Regardless of the substrate material and its crystal orientations, the technique can form various cross-sectional groove shapes with a change in the ablation mask shape. This extends its application to low-cost optical platforms for glasses, polymers, and semiconductors.