Compact speckle spectrometer using femtosecond laser-induced double-sided surface nanostructures

The utilization of light scattering in disordered media has shown promise in the design of highly sensitive speckle spectrometers. Significant advances have been made in the research of all-fiber speckle spectrometers, and various planar scattering media have also garnered the attention of many researchers. In this study, we designed a compact speckle spectrometer employing a femtosecond laser to induce double-sided nanostructures on a quartz glass as a scattering medium. Once the transmission matrix is calibrated, the spectrum can be reconstructed over a bandwidth of 100 nm, achieving a spectral resolution of 0.1 nm. A 5 pm spectral resolution has been demonstrated by integrating a neural network to recognize speckle patterns in 100 pm bandwidths at 1500, 1550, and 1600 nm. By combining ResNet-50 and GRU, a simulated continuous spectrum spinning a bandwidth of 2 nm can be accurately reconstructed. This innovative, compact spectrometer features low cost, small size, simple preparation, and repeatability.