Single-Pixel Multimode Fiber Spectrometer via Wavefront Shaping

When light passesthrough a multimode fiber, two-dimensional randomintensity patterns are formed due to complex interference withinthe fiber. The extreme sensitivity of speckle patterns to the frequencyof light paved the way for high-resolution multimode fiber spectrometers.However, this approach requires expensive IR cameras and impedes theintegration of spectrometers on-chip. In this study, we propose asingle-pixel multimode fiber spectrometer by exploiting wavefrontshaping. The input light is structured with the help of a spatiallight modulator, and optimal phase masks, focusing light at the distalend of the fiber, are stored for each wavelength. Variation of theintensity in the focused region is recorded by scanning all wavelengthsunder fixed optimal masks. Based on the intensity measurements, weshow that an arbitrary input spectrum having two wavelengths 20 pmapart from each other can be reconstructed successfully (with a reconstructionerror of & SIM;3%) in the near-infrared regime, corresponding toa resolving power of R & AP; 10(5). Wealso demonstrate the reconstruction of broadband continuous spectrawith varying bandwidths. With the installation of a single-pixel detector,our method provides compact detection and a lower budget alternativeto conventional systems, with potential promise to operate at low-signallevels.