Microwave Photonic Temperature Sensing Based on Fourier Domain Mode-Locked OEO and Temperature-to-Time Mapping

We report a novel temperature sensor based on a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) and temperature-to-time mapping. In the proposed scheme, a narrow bandpass electrical filter is inserted into the FDML OEO cavity. The temperature information is mapped to the time interval of the output pulses due to the temperature-sensitive bidirectional scanning property of the FDML OEO. Compared with other OEO-based temperature sensors, the proposed scheme avoids the needs of wideband electrical spectrum analyzers, since the temperature-sensitive output pulses can be interrogated using a low-speed oscilloscope working under sub-Nyquist sampling condition. In the proof-of-concept experiment, a high sensitivity of 8.166 μs/°C and resolution of 0.03°C is achieved, demonstrating a good temperature sensing performance.

I. Introduction

Numerous optical sensors have been proposed and demonstrated in recent years to realize parameter interrogation with advantages of light weight, high sensitivity, immunity to electromagnetic interference, and resistance to chemical erosion [1], [2]. Generally, the optical sensors are implemented by translating the variation of the parameters to the change of the optical power or wavelength in optical domain, and it can be analyzed by an optical spectrum analyzer (OSA). However, the resolution of the OSA is usually limited as several tens of pico meters, which is difficult to meet the requirement of sensors with good performance. In the past few decades, optoelectronic oscillators (OEOs) have been intensively investigated as an optical sensor with high resolution. For OEO-based sensors, interrogation are implemented by mapping the parameters such as temperature, acoustic, strain, transverse load, refractive index and so on, to the frequency variation of the microwave signal generated by self-excited oscillation [3]–[8].