Tilted Fiber Bragg Grating Sensors Based on Time-Domain Measurements with Microwave Photonics

Tilted fiber Bragg gratings (TFBGs) have garnered substantial research attention and have found widespread applications for sensing a diverse array of physical, chemical, and biological parameters based on optical spectrum measurements. The interrogation of a TFBG sensor typically requires a high-resolution bulky optical spectrum analyzer (OSA) due to the extremely narrow dips caused by the resonance of cladding modes. However, high-resolution OSAs can be costly and have limitations on measuring speed, limiting their practicality. In this paper, a new approach to interrogating TFBG sensors is proposed and experimentally demonstrated based on a microwave photonics technique. Instead of measuring the optical transmission spectrum, the frequency response of the TFBG sensor is acquired using a vector network analyzer. Followed by time domain analysis, sensing information embedded in the transmission spectra of the TFBG sensor subject to external perturbations is successfully extracted. Monitoring of variations in temperature, strain, and liquid level is experimentally demonstrated, and the potential for multi-parameter discrimination is also discussed. The introduced technique is easy to implement and the corresponding characteristic sensing signal is easy to demodulate, offering a promising solution for TFBG-based sensor systems.