Measurement of temperature and refractive index based on surface long-period gratings deposited onto a D-shaped photonic crystal fiber

Abstract

We propose a surface long-period grating (LPG) based on a D-shaped photonic crystal fiber (PCF). The D-shaped PCF is fabricated by a side-polishing technique. The surface LPG based on periodic patterns of photoresist (PR) is formed by using the spin-coating and the standard contact lithography methods. Resonant coupling is created by the surface PR-LPG in the D-shaped PCF. The resonant peak shifts to longer wavelength as the ambient index is increased and shifts to shorter wavelength as the temperature is increased. The total wavelength shift is measured to be 122 nm in the refractive index range from 1 to 1.45 and the temperature sensitivity is measured to be −0.3 nm/°C in the temperature range from 30 to 100°C.