Reconstructive spectrometer using double-layer disordered metasurfaces.

Conventionally, optical spectrometers rely on traditional dispersive elements like grating and prism, which pose inherent challenges for miniaturizing spectrometers, including the trade-off between propagation distance and spectral resolution and calibration ambiguity. Here, we present a random dispersive element-double-layer disordered metasurfaces-where wavelength-specific speckle patterns can be uniquely determined a priori without ambiguity in wavelength and propagation distance. By directly mounting this element on an image sensor, we implement a spectrometer with a spectral resolution of around 1 nanometer and an operable range of 440 to 660 nanometers, comprising 221 spectral channels, within a form-factor of less than 1 centimeter. Our results firmly establish that the versatility of multilayer disordered metasurfaces in the spatio-spectral domain can be fully exploited for on-sensor spectroscopic applications.