The proposal of this study is demonstrating a simple vapor sensor for chloroform (CHCI3) utilitizing air gap region of the Mach-Zehnder interferometer (MZI) by using a single mode optical fiber coupler (3 dB) structure. In the last few decades, flammable liquids such as chloroform have been highly used. This chemical liquid has some degrees of carcinogenic effects in humans in addition to acute and chronic exposure results like blurred vision and nausea. The two arms of MZI contain a free space gap utilized to serve the sensing mechanism by adding chemical liquid volumes (0.2, 0.4, 0.6, 0.8, and 1) ml and to set the phase difference with air-gap distance 0.5 mm. The small variation in the effective refractive index of chloroform is due to changing the propagation of the transmitted light in the MZI’s gap that will further shift the optical phase of the signal. The experimental results indicate that the output power decreased when the air gap distance is 0.5 mm, and the shifting of wavelength will increase toward blue shift when increasing the chloroform liquid volumes. A maximum wavelength shift of chloroform is 0.0251 nm when the liquid volume is 1 ml and sensitivity of chloroform is 0.0223 nm/ml at air gap distance 0.5 mm for different chloroform liquid volumes.
