Ultracompact and Sensitive Fiber Michelson Temperature Sensor-Based Parallel Polymer Cavities With Vernier Effect

In this article, an ultracompact fiber Michelson interferometer (MI) based on parallel polymer cavities with Vernier effect is proposed. A series of high-frequency fringes in the reflection spectrum with different amplitudes form the envelope. Theoretical temperature sensitivities of the envelope and the high-frequency fringes are 2.750 and −0.136 nm/°C, respectively. The theoretical differential sensitivity of the MI obtained by subtracting the high-frequency fringes sensitivity from the envelope sensitivity reaches 2.886 nm/°C. Two-photon polymerization (TPP) technique is used to fabricate the parallel polymer cavities: a liquid polymer cavity and a solid polymer cavity on the end face of a single-mode fiber (SMF). The size of the proposed sensor can be controlled precisely, and the total length along the fiber axis is only $44 ~\mu \text{m}$ . The interface of liquid and solid polymer cavities just locates on the center of SMF. Since the optical paths between liquid polymer cavity and solid polymer cavity are slightly different, the Vernier effect is generated. Experimental results show that the temperature sensitivities of the envelope and the high-frequency fringes are 2.782 and −0.097 nm/°C, respectively. The final differential sensitivity of the structure reaches 2.879 nm/°C. Theoretical and experimental results agree well. The proposed sensor is with a high-temperature sensitivity and an ultracompact volume. It can have important application prospects in fields, such as microfluid chip and biomedicine.