Single-Shot on-Chip Diffractive Speckle Spectrometer with High Spectral Channel Density

The research on chip-scale spectrometers is driven by the growing demand for miniaturized and integrated spectral sensors. The performance trade-off between spectral resolution and bandwidth is one of the primary challenges for the community. While substantial progress has been made toward a vast number of spectral channels to overcome this issue, they either relied on sophisticated tuning mechanisms or required huge chip areas. In this work, a single-shot spectrometer is demonstrated based on all passive on-chip diffractive metasurfaces which is able to create the speckle pattern with richness of spectral information. By scaling the diffractive structure to three layers of metasurfaces, the number of spectral channels resolved from the speckle can be significantly increased due to the cascaded diffraction behaviors. The device is fabricated via a standard silicon photonic foundry with CMOS compatible process. A measured resolution of 47 pm is achieved across the bandwidth of 40 nm, yielding up to 851 spectral channels within a compact footprint of 150 µm × 300 µm. The corresponding spectral channel density reaches 18911 ch mm⁻². It provides a possible means to develop single-shot and compact on-chip spectrometers beyond the resolution-bandwidth limit.