Frequency response of a continuously tuning narrow-band optical filter based on stimulated Brillouin scattering.

Tunable narrow-band optical filter (TNOF) based on stimulated Brillouin scattering (SBS) has been applied in various applications such as microwave photonics and a high-resolution optical spectrum analyzer (OSA). While the frequency response of a SBS-based filter has always been an important characteristic in the reported studies, few have addressed the issue of the filter response under a continuously tuning condition. When the tuning speed is too fast, the filter response will change and cause spectral distortion. In this paper, the frequency response of SBS-TNOF under a wavelength-swept pump (i.e., continuously tuning) condition is investigated and modeled. Experimental results are in good agreement with the theoretical analysis and verify that the broadening of the SBS-TNOF response is induced by the pump wavelength difference along different positions of the fiber, which can be explained as convolution with broadband pump as well. Based on the widely used Richardson-Lucy deconvolution algorithm and proposed SBS-TNOF response model, the distorted responses are successfully reconstructed and the sweep speed dependency is almost eliminated. Commonly used on-off keying signal is tested using the proposed reconstruction method to assess its performance in the SBS-OSA. Both the overall profile and the detail of the signal spectra are significantly recovered, and the quantitatively evaluation illustrates that the feasible sweep speed can be improved from ∼45 nm/s to over 95 nm/s.