This application note demonstrates a temperature sensor based on a fiber Bragg grating (FBG) and long-period grating (LPG). The design is a simplified representation of the sensor described in . Figure 1 illustrates the schematic used to simulate the sensor.
In our design, a broadband source over 1545-1560 nm is launched into the sensor. The source is modeled as ASE noise via a Noise Adder. An optical filter implements an LPG transmission spectrum, based on data in  and shown in Figure 2. The pitch and index of the FBG are modeled as functions of temperature. The Optical Monitor measures the ASE power after filtering of the broadband source by the LPG and FBG.
Figure 2. LPG transmission spectrum .
To observe the sensor in action, a sweep in temperature from -50 to 60 °C is carried out. Figure 3 shows the ASE noise power measured by the Optical Monitor. As can be seen, the power changes as a function of temperature. The dependence is approximately linear, with deviations from linearity at higher temperatures.
1. Y. Zhan, H. Cai, R. Qu, S. Xiang, Z. Fang, and X. Wang, “Fiber Bragg grating temperature sensor for multiplexed measurement with high resolution”, Optical Engineering, vol. 43, no. 10, pp. 2358-2361, October 2004.