Interferometric Sensor Based On Photonic Crystal Fiber

With the rapid development of optical fiber communication technology,optical fiber sensing technology has attracted more and more attention from researchers because of its advantages,such as high sensitivity,small size,and free of electromagnetic influence.It has been applied to biochemistry and environmental testing,medical and other fields.How to improve the sensitivity of refractive index and eliminate the cross-effect of temperature has become a hot topic for researchers.In this paper,two new hybrid waveguide structures have been fabricated investigated by combining photonic crystal fiber,hollow fiber and graphene.Firstly,a dual-parameter sensor based on a composite interferometer structure has been proposed and studied.Cascaded Fabry-Perot interferometer and Mach-Zehnder interferometer are simultaneously formed by cascading single-mode fiber,hollow-core fiber,and photonic crystal fiber.Therefore,by simultaneously measuring the reflection and transmission spectra,it is possible to monitor the changes in the temperature and refractive index at the same time.Because the reflection and transmission spectra do not interfere with each other,the demodulation method does not require complicated fast Fourier transform and matrix calculation.Based the sensitivity of the transmission spectrum to the refractive index and the sensitivity of the reflection spectrum to temperature,the refractive index and temperature sensitivities of this sensor are approximately 127 nm/RIU and 52.3 pm/?,respectively.Secondly,we demonstrated a photonic crystal fiber based refractive index(RI)sensor involving the deposition of graphene onto the surface of a segment of photonic crystal fiber(PCF)in a fiber-based Mach-Zehnder Interferometer(MZI).The fabrication process is relatively simple and only involves the fusion splicing of a PCF between two single mode fibers.The depostition process relies on the Plasma Enhanced Chemical Vapor Deposition(PECVD).The graphene overlay modified the sensing scheme of the MZI RI sensor,allowing the sensor to overcome the limitation to its detectable RI range due to free spectral range issue and having the potential for simultaneous dual parameter sensing.Overall,the RI sensor is able to achieve a RI sensitivity of 12.6 dB/RIU for the RIs of 1.30-1.41 and a sensitivity of 90.3 dB/RIU for the RIs of 1.41-1.44.