On-Chip Passive Optical Spectrometer with Multimode Photonic Devices

On-chip optical spectrometers are widely regarded as a highly promising solution for portable and wearable sensing applications. In particular, optical spectrometers are often preferred to operate passively without the need for external power for tuning, thereby significantly reducing system complexity and power consumption. This is vital for promoting the widespread adoption of spectroscopic technology in resource-constrained scenarios demanding ultralow power consumption. In addition, achieving on-chip spectrometers with both a large bandwidth and high resolution remains a significant challenge, particularly when the physical channel number is limited. In this work, we propose and demonstrate a high-performance on-chip passive spectrometer leveraging advanced multimode photonics. The spectral information is decorrelated through stochastic mode generation, coupling/mixing, wavelength-selective resonance, and demultiplexing enabled by multiple distinct modes (e.g., the TE 0, TE 1, and TE 2 mode) in a spiraled multimode waveguide system, significantly enhancing transmission matrix decorrelation across a broad bandwidth. Experimentally, it is demonstrated that the present optical spectrometer successfully achieves a remarkable resolution of 10 pm and a broad bandwidth of 80 nm with only 36 synthetic physical channels. This performance corresponds to a wavelength-channel capacity of 8 × 10 3 and a reconstructive compression ratio of 222, setting a new benchmark for on-chip passive optical spectrometers reported to date.