Photonic Crystal Fiber Sensor Based On Multi-beam Interference

Part IPhotonic crystal fibre (PCF) modal interferometers are widely used for sensing applications. Owing to the intrinsic Mach-Zehnder-like dual mode interference there is a trade-off between sharp spectral response and wide sensing range. A three-beam path interferometer induced by mode-conversion in a single dual mode PCF end face is experimentally demonstrated. Doubled free spectral range is obtained owing to the three-beam path interference, which is suitable in sensing large index change, wide temperature variation and strong applied pressures. As an example, a temperature sensor with the sensitivity of8.17pm/°C is demonstrated ranging from room temperature to520°C. Then further improvements of the multi-beam path interferometers are also discussed. A splicing approach is proposed and demonstrated to achieve unique four-beam interference so that quadrupled sensing range is obtained without reduction in detection limit, which would be much desired in wide range refractive index, pressure and temperature sensing. As an example, a high-temperature sensor ranging from28to484°C is demonstrated. Part IIA dispersion control unit is proposed and employed to enhance the dispersion and compensate the intrinsic nonlinear dispersion of the grating. A40-channel,100-GHz channel-spacing dynamic wavelength blocker/equalizer is thus demonstrated with-5dB insertion loss and over40dB extinction ratio. The maximum center frequency shift of all40channels is±2GHz, which means our dispersion control technology works very well for grating-based DWDM devices. We also utilize this module to measure the surface plasmon polariton (SPP) enhanced Goos-Hanchen (GH) shift based on liquid crystal (LC) and grating technologies. An optical setup is used to convert the spatial displacement to incidence angle variation to a Littrow mounted diffraction grating. As a consequence, the GH shift information could be obtained from the back-reflected center wavelength that fulfills the Littrow condition. About10μm GH shift difference between TE (Transverse Electric) and TM (Transverse Magnetic) mode lights were measured associated with the SPP excitation. The corresponding center wavelength shift of the returned beam is404pm.