Design System of Optical Heterodyne Detection Based on Temperature Sensor

Optical Heterodyne Detection (OHD) technique is based on two separate sources with optical interference between them. The optical signal from a specific light source is compared with a separate reference signal from another source. The Fiber Bragg grating (FBG) reflect a specific wavelength λ_B and transmit the other wavelengths within the laser source spectral. This is achieved by changing the refractive index generated by periodic variation of optical fiber core, which reflect a specific wavelength, so FBG can be used to withhold a certain wavelength and allow other wavelengths to transmit. In this paper, a new method of an OHD has been designed using Optisystem software. Optical fiber as a temperature sensor element with single source and two FBGs have used in this system. the first FBG used as a tunable source and the other has used as a sensing element. The two optical signals have been combined utilizing a photodetector. It has a linear response to the light energy, while having a quadratic response with the amplitude of the electromagnetic field. The results show that the beat frequency shift has a linear response to the temperature with sensitivity about 2.24 GHz/C^o. (paper)