This dissertation describes the development of optical fiber sensor system for application temperature sensor by using Mach-Zehnder interferometer．The Mach-Zehnder interferometer acquires fundamental importance because it can be used as a building block of more complex optical devices and functionalities such as optical filters，wavelength demultiplexers，intensity modulators，switches and optical gates． Mach-Zelmder interferometers (MZIs) are optical devices that make use of the interference between two optical signals from a same origin traveling through different effective path lengths． In this work，the performance of a Mach-Zehnder interferometer consisting of two coupled-cavity wave guides with different lengths created． In present work we first make two couplers and then a M-Z fiber filter is made by using these couplers with fusion splicer machine．We applied the M-Z fiber filter in two stages a)used M-Z fiber filter without metal sheet, b) used the M-Z fiber filter with attached metal sheets．Results for this experience showed that after using the metal sheets，the variations of frequency separation (fs) can be increased．In stage without metal sheet for temperature from 30℃ to 70℃ the fs only from 0.159 THz to 0.158 THz were changed whereas for attached 20 cm A1，the fs were changed from 1.45 THz to 0.82 THz and for attached 20 cm Pb the fs were changed from 0.62 THz to 1.49 THz respectively． The present work is easily implemented in any environmental where the high sensitivity of temperature is necessary．