Cascaded nanobeam spectrometer with high resolution and scalability

An on-chip reconstruction spectrometer provides a powerful approach for miniaturized and portable applications. Owing to the cross-correlation and line shape of broadband responses, the reconstruction spectrometer exhibits limited resolution and a fixed bandwidth. Here we demonstrate a cascaded nanobeam spectrometer with assistance of a reconstruction algorithm. The transmissions of tunable Fano-enhanced nanobeams (FENs) are of good orthogonality and have improved quality factors. We retrieved a narrowband signal of 0.16 nm linewidth and a dual peak at 0.32 nm distance for resolution characterization. This result breaks the limit of the full width at half maximum for narrowband filter spectrometers. An expanded bandwidth is realized by a three-channel cascaded device, and signal spectra in the 16 nm range are reconstructed successfully. Each FEN unit has an ultra-compact footprint of 18 × 18 µ m 2 . In view of the improved performance and flexibility, our concept is an ideal candidate for precise and miniaturized applications.