4. Fiber-optic temperature sensor with chalcogenidic glass sensitive element

The operation principle of such fiber-optic sensors is similar to the one discussed above. Change in the light transmission in chalcogenide vitreous semiconductor (ChVS) with temperature change. The use of as sensitive elements of ChVS gives the possibility for better optic coordination of emission source (LED), temperaturesensitive element, and emission detector (photodiode), since the physical and chemical, optic properties of glass can be changed in wide range by changing their composition within the region of glass formation. Developed FOTS are using a film of single crystals GaAs and Ge, with given optic constants, as a sensitive element. Our previous studies [18] have shown that, as an active element of FOTS, from a large number of ChVS can be used As-Se glass system.

In few scientific and technical publications, several analogues of FOS with semiconductor crystals as a temperature-sensitive element were published [5, 15–17]. Often, these are two-wave single-channel fiber-optic circuits, which use two LEDs

Figure 3.

Optic scheme of the primary converter: 1, radiation source (LED); 2, fiber-optic coupler; 3, place of optic signal division; 4, temperature-sensitive element; 5, the first photodiode (FD1); and 6, the second photodiode (FD2).

with different wavelengths (operating and reference). If the ambient temperature changes, the change in characteristics will not be the same, and the compensation scheme will not be able to eliminate the measurement error in this case. In our view, a more stable scheme of temperature measurement with a fiber-optic sensor is a single-LED dual-channel circuit, which is shown in Figure 3.

The operation principle of this type of FOS is that light signal after passing through the Y-cutter on two channels (working and reference) is received by two identical photodiodes. The registration system measures the ratio of signals from photodiodes 5 and 6 (Figure 3). Therefore, changes that can occur in the fiber-optic line for a given temperature will not affect the ratio of signals on photodiodes.

In scientific work (article) [18], we developed a method for performing calculations of the transmission characteristics of the fiber-optic temperature sensor. In this chapter, a method of selecting the elements of the primary measuring transformer and the optic parameters of LED, photodiode, and sensitive element of such fiber-optic temperature sensor was simulated. The results of the transfer characteristic in the form of a plot of the dependence of the change in the voltage of the emission detector (photodiode) on the temperature of the medium in which the temperature-sensitive element is shown demonstrate the performance of this technique.

In this chapter, a plate of ChVS As-Se was used as a temperature-sensitive element. The change in the composition of the components of the temperaturesensitive element allowed us to ensure the optimum harmonization of the spectral characteristics of the receiver source and the temperature-sensitive element, which are very convenient for the construction of fiber-optic thermometers. However, not only ChVS can be used as a temperature-sensitive element in a fiber-optic temperature sensor; some crystalline materials can also be effectively implemented in these devices.
