Expansion of Measurement Range of Low-Cost Ethernet-Based Temperature Sensing System Using Long-Period Fiber Grating

It is important to reduce the cost of the sensing system to promote the social implementation of optical fiber sensors. The light source and the photodetector with analysis functions, e.g., optical spectrum analyzer, are the most expensive components of an optical fiber sensing system. To solve this problem, we have proposed an Ethernet-based temperature sensing system. This system uses an inexpensive optical transceiver (OTR) as a light source for the Ethernet and a photodetector and a single-board computer with temperature evaluation functions to reduce the system cost. In this letter, we propose a method to enhance the temperature sensing function in our proposed Ethernet-based temperature sensing system by using multiple OTRs with different output wavelengths and an optical switch to expand the measurement temperature range. In addition, we constructed the proposed system and conducted a demonstration experiment to expand the temperature range that can be measured using five OTRs, one optical switch, Raspberry Pi, and a long-period fiber grating as an optical fiber sensor. The experimental results show that the temperature range from 60 to 760 °C can be expanded with an error of approximately ±5 °C.