Low-loss in-line microfilter fabricated by precision trench machining

A machining technique has been developed that enables a narrow, smooth damage-free walled trench to be cut into an optical fiber engraved in a silica substrate by using a fine silica powder effect. This technique allows a very low insertion loss (0.21 dB) in-line microfilter to be made by inserting a thin filter plate into a trench cut into an optical fiber already fixed to a substrate.