Minute Wavelength Shift Detection of Actively Mode-Locked Fiber Laser Based on Stimulated Brillouin Scattering Effect

We analyze theoretically and verify experimentally an effective approach to detect slight wavelength shift based on stimulated Brillouin scattering (SBS) effect. The concerned wavelength variation in an actively mode-locked fiber laser (MLFL) is caused by a π-phase-shifted fiber Bragg grating (π-PSFBG) under different temperatures. Based on the microwave photonics technology, the weak variations of the MLFL wavelength are converted into the amplitude changes of the beat signal generated by the mode-locked fiber laser. With the aid of the SBS effect, the beat signal is amplified larger than 20 dB, enhancing the measurement sensitivity. Through seeking the maximum beat signal, approximately 359.6 MHz modulation frequency shift of pump light with 0.2 °C temperature raise, corresponding to 2.876 pm wavelength shift in the 1550 nm band, is experimentally realized. Our proposed scheme achieves detection of minute wavelength shift with ultrahigh accuracy and convenient operation, which has potential applications for optical spectrum analysis of silicon-based integrated chips, biomedical fields and high sensitive optical sensing.