Sensitivity-enhanced Temperature Sensor Based on Cascaded Polymer-infiltrated Mach-Zehnder Interferometers Created in Graded Index Fibers

A sensitive-enhanced temperature sensor based on cascading two polymer-infiltrated MZIs created in two half-pitch graded index fibers (GIFs) is presented in this letter. A single MZI was constructed by splicing a half-pitch GIF between two single-mode fibers (SMFs) and creating an open cavity in one lateral side of the GIF core by means of femtosecond laser micromachining. The cavity and the residual GIF core functioned as two interference arms. Two single MZIs were constructed by creating two cavities with different lengths, respectively. Thermo-sensitive polymer were infiltrated in two cavities, respectively. Subsequently, two MZIs were cascaded by splicing together. Two interference dips were obtained in transmission spectrum. The shift of two dips during temperature variation led to wavelength differential amplification effect. The temperature sensitivity was increased greatly. The temperature sensitivity of the cascaded polymer-infiltrated MZIs is -24.86 nm/°C, two times of the single MZI.