This work presents a research in which a Twin Core Fiber (TCF) has been employed for designing a Mach- Zehnder interferometer and its behavior under the effect of thermal gradients has been regarded. From the coupled modes theory can be deduced that under the phase-matched condition-that is similar propagation constants in both cores of a TCF, the energy transported in the cores is the same, which is fundamental for developing this interferometer. This research required to design a thermal cavity and an automation circuit for applying thermal cycles to a segment of the TCF. The temperature was recorded by means of a thermocouple placed inside the thermal cavity and its signal was introduced into the computer where an instrumentation software (Lab View) designed for monitoring and controlling variables used this signal for controlling the on-off states of a power resistor and a refrigeration system for raising and lowering the temperature, respectively. It was observed that the optical power variations in a point of the interference pattern presented a weak dependence with the thermal cycles.