Sub-100 fε resolution strain sensing based on optical fiber frequency comb

In this paper, we introduced a high-resolution optical fiber strain sensing system capable of detecting both static and dynamic strain through optical frequency comb (OFC) beat frequency demodulation. The system employed a fiber Fabry-Perot interferometer (FFPI) as the strain sensing element, which was probed by a narrow-linewidth laser stabilized to it using the Pound-Drever-Hall (PDH) locking technique. By leveraging the concept of beat frequency demodulation, the OFC, characterized by its stable repetition rate and offset frequency, translated the optical frequency shifts within the strain sensor into the radio frequency (RF) domain for detection. Our findings revealed a static strain resolution of 247 pε over a 10-second period, and a dynamic strain resolution of 87 fε/Hz-1/2 at 8 kHz. Additionally, we investigated the potential of a free-running OFC with a stable repetition rate for high-resolution static strain sensing. By actively sweeping the OFC’s offset frequency in conjunction with the FFPI, we achieved a static strain resolution of 630 pε within 10 seconds. This sensor system offers high resolution, moderate cost, and a degree of portability, rendering it suitable for a range of geophysical research applications.