## 3 Discussion of the Obtained Results  
The experiments showed a dramatic decrease in the output optical power being observed when the cooled sample is fast heating (Figure 3). The spectral analysis showed that the decrease occurs uniformly in the measured spectral range (Figure 6). It confirms the legitimacy of the used OFDR technique with tunable radiation. Reflectometric measurements demonstrated the changes in the intensities of the return signals in different parts of the IOM during the thermal cycle. Initially, it was assumed that a sharp change in the reflectogram would be observed in the waveguides branching area because it is there that the dislocation grid surrounding the waveguides has the greatest width, facilitating the movement of the charged defects, which affect the waveguide refractive index. Further, we analyzed the temperature behavior in different areas of the IOM (Figure 10):  
1. The input peak (A) corresponding to the transition from fiber to IOM. The magnitude of the peak has a relatively stable value at \(-90\) dB and has no features. This behavior is because temperature changes do not affect the fiber feeding the IOM. 2. The input side of the IOM (B). During the period of uniform cooling from room temperature to \(-60\)\({}^{\circ}\)C, the almost constant growth of the optical intensity in this location from \(-110\) to \(100\) dB was observed. When changing cooling to heating, the dependence demonstrates at first a dip to \(-112\) dB (at about \(100\) min) and immediately thereafter a rise to \(-97\) dB (at about \(110\) min). It should be noted that topologically there are no significant events in the modulator in this location, such as channel splitting or a sharp drop in the refractive index. The length of the area with similar behavior is about \(5\) mm (Figure 8). We assume that the pyroelectric effect introduced the most remarkable surge of the refractive index at this location in this chip design. Further, the nature of the temperature behavior changes. The second area inside the IOM is about \(20\) mm and ends at the output side of the IOM. 3. The output side of the chip (C). There is a topologically important point in this area, which is responsible for combining the channels. Previously, it was assumed that the pyroelectric effect could make the most significant changes in the waveguide properties of the chip precisely in this area. However, in both experiments conducted, the radiation intensity in this area has only a moderate correlation with the intensity in the input part of the chip and before the cooling is replaced by heating. During the period of sharp heating, the character of this curve does not change in both cases as well, which may indicate that the signal intensity in this area is not related to the pyroelectric effect. It should be noted, however, more intensive fluctuations  
Figure 10: Temperature dynamics of the intensity in the IOM different areas. Locations A,B,C,D are presented at Figure 9.  
of the signal (about 10 dB), the amplitude of which grows with cooling, and the character itself visually resemble a periodic one. This is quite clearly observed both on individual graphs and on the heat map. The authors cannot explain their nature now. 4. The output peak (D) corresponds to the radiation output from the IOM into the optical fiber. It should be noted that the intensity of this peak has a solid and commensurate inverse relationship with the intensity of artifacts in the input part of the chip. At the start of intensive heating, the output peak significantly decreases in intensity, while the intensity in the assumed area of the pyroelectric effect grows just as sharply. That is, an anti-correlation is observed at line B and line D, especially between 100 and 110 min of experiment. This is explained by the fact that a significant portion of the radiation is scattered or reflected in this location and does not reach the output end of the IOM.