High-Resolution Random Laser Dynamic-Strain Sensor Based on Two-Cavity FBG-FP Interferometer

A high-resolution optic fiber dynamic strain sensor based on a two-cavity fiber Bragg grating Fabry-Perot (FBG-FP) interferometer and random fiber laser (RFL) is demonstrated. The specially designed two-cavity FBG-FP interferometer acts as a sensing element and can effectively suppress the competition-induced multi-spike lasing modes and frequency jitter, which contributes to establish single-wavelength laser and suppress frequency noise of RFL. The frequency noise is reduced from about 12 to 3 Hz/<inline-formula> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula>Hz above 4 kHz. An ultrahigh dynamic-strain detecting resolution of 30 femto-strain (<inline-formula> <tex-math notation="LaTeX">$\text{f}\varepsilon)/\surd $ </tex-math></inline-formula>Hz is achieved. To the best of our knowledge, it is the first time that two-cavity FBG-FP interferometer has been used in sensing field.