## 4 Experiment and Results Discussion
### Results and Discussions  
To conduct the temperature measurement experiment, we first placed the whole FUT at room temperature (21.2 \({}^{\circ}\)C) to obtain the calibration trace data. Then the fiber section for the heating zone was put into hot water, and the temperature, which ranged from 30.0 \({}^{\circ}\)C to 80.0 \({}^{\circ}\)C, was tested. OTDR traces of the Raman anti-Stokes light are shown in Figure 4. It was found that the OTDR traces corresponding to the fiber section at room temperature are not coincident, which means that the output power of the PL or the gain factor of the APD is instable. In particular, the OTDR trace with the temperature of the heating zone at 30.0 \({}^{\circ}\)C is far below the others. We infer that the PL is the key problem because it contains a directly modulated laser diode (LD) and an erbium-doped fiber amplifier (EDFA) module, which makes it quite difficult to control the pulse shape and stabilize the gain of the EDFA. Therefore, with the temperature measurement method that only adopts the Raman anti-Stokes light, it is essential to correct the coefficient \(R\) in Formula (13). Next, the temperature measurement results along the whole FUT are computed, as shown in Figure 5, where the room temperature in the experiment is nearly kept stable at  
Figure 4: The OTDR traces of the Raman anti-Stokes light at different heating temperatures. 21.2 \({}^{\circ}\)C. The temperature traces (except the heating zone) are almost coincident; however, there is a fluctuation of approximately \(\pm\)1.0 \({}^{\circ}\)C, which is caused by the randomness of light scattering and can be reduced by increasing the OTDR trace average number. The details of the temperature measurement result in the heating zone are shown in Figure 6. At the transition positions between the heating zone and non-heating zone, there is a temperature peak that is caused by light scattering with simultaneous light pulses in two different temperature zones. This disturbs the temperature-power relationship \(R_{a}(T)\) in Formula (4). The average values of temperature measurement are marked on the right side in Figure 6. The maximum temperature deviation range is \(-\)1.5 \({}^{\circ}\)C to +1.6 \({}^{\circ}\)C, and the root mean square (RMS) error within the whole temperature measurement range is 0.3 \({}^{\circ}\)C. Considering the accuracy of the thermometer (approximately \(\pm\)0.5 \({}^{\circ}\)C), we believe that the measurement results are reliable and the scheme proposed is feasible for practical use. In the experiment, the temperature measurement range adopted is just within 30.0 to 80.0 \({}^{\circ}\)C, which is relatively small for a practical temperature measurement application. However, we think that it also possesses the performance for temperature measurement  
Figure 5: The temperature measurement results along the whole FUT. Figure 6: The temperature measurement results in a heating zone. with large temperature ranges, such as \(-30.0\)\({}^{\circ}\)C to \(120.0\)\({}^{\circ}\)C, because the basic principle originates from temperature sensitivity Formulas (3), (4), (6) and (8) in the traditional dual-channel-based scheme. Moreover, the newly proposed scheme based on Raman anti-Stokes light shall possess the same temperature measurement range in theory. In our work, the reliability of the temperature demodulation algorithm that simply adopts the data of Raman anti-Stokes signals has been experimentally demonstrated, so we believe that the temperature measurement range of the proposed sensing system should be the same as the commonly used Raman Stokes and anti-Stokes light-based scheme. As the distributed optical fiber temperature sensing scheme only adopts one channel for the Raman anti-Stokes light signal sampling and processing, it brings two advantages. The first advantage is that it can completely overcome the walk-off effect in traditional dual-channel-based schemes.