Angular sensing system based on Y-type twin-core fiber and reflective varied-line spacing grating fabricated by electron beam lithography

Abstract

A varied-line spacing grating (VLSG) inscribed by electron beam lithography was proposed and used for an experimental demonstration of angular sensing. The designed VLSG central groove density was 655 L/mm, and it had an aluminized surface to reflect light. A Y-type twin-core fiber of 600 μm diameter cores connected with a collimator lens was used to input and collect reflected light from the VLSG. The Y-type fiber input and output paths were connected to a white light source and an optical spectrum analyzer, respectively. The fabricated quasi-continuous VLSG size was 70 × 30 mm, with a fixed 23° input angle. The reflected wavelength changed from 917.3 to 1656.9 nm as the incident light spot moved to different grating positions, with a displacement sensitivity of 14.812 nm/mm. As the input angle was adjusted from 23° to 35° in 1° increments, the spot location on the VLSG changed simultaneously, and the reflection wavelength peak positions changed from 917.3 to 1584.5 nm, with a sensitivity of 57.544 nm/° and linearity of 0.993.