Compact in-line interferometeric temperature sensor composed of a hollow optical fiber and photonic crystal fibers

We propose a simple but effective in-line interferometeric sensor based on photonic crystal fiber (PCFs) and hollow optical fiber (HOF). A short piece of HOF was spliced between PCFs for inducing modal interference. The temperature-induced shift of the interference fringes was experimentally monitored. It was linearly shifted toward the longer wavelength direction with a sensitivity of about 8 pm/°C.