In-fiber Rayleigh peak suppression for Brillouin spectroscopy

Brillouin spectroscopy shows great potential for various biomedical applications, but the complexity, high cost, and size of current technologies limit its widespread access. Major complications result from the need to measure weak Brillouin peaks picometers away from the Rayleigh peak, which are larger by many orders of magnitude. We propose and study an ultra-narrow notch filter based on a fiber Bragg grating Fabry-Perot in reflection. L-band and 785 nm devices are prepared, exhibiting good agreement with theory and simulations. Strain tuning enables precise adjustment over nanometers. A suppression of 31 dB is achieved at 785 nm with an intrinsic insertion loss of 2 dB. Brillouin spectra of various samples are acquired, demonstrating the in-fiber module's ability to suppress the otherwise overwhelming Rayleigh light, thus greatly improving measurement capabilities. Overall, this high-performance device is simple, alignment-free, compact, low-cost, tunable, serializable, and its design is flexible, holding promise for democratizing Brillouin spectroscopy and developing field-deployable systems.