Cavity-enhanced scalable integrated temporal random-speckle spectrometry
Hongnan Xu, Yue Qin, Gaolei Hu, Hon Ki Tsang
Abstract
Chip-scale integrated spectrometers have many prospective applications, such as in situ biochemical analysis, optical coherence tomography, and remote hyperspectral sensing. Most reported monolithically integrated spectrometers support spectral resolutions of 10 1 −10 2 pm with 10 2 −10 3 wavelength channels. In this work, we propose and demonstrate a scalable integrated spectrometer that achieves ultrahigh resolution and improves the channel capacity by around one order of magnitude. The approach is based on a spatially reconfigurable multimode cavity formed by a waveguide array and delay lines. The mode mixing is enhanced through cavity resonance and intermodal coupling, producing chaotic spectral responses. The orthogonal resonant state can be arbitrarily switched by tuning the phase shifters within the cavity. Each wavelength channel is associated with a unique random temporal speckle. Notably, for the proposed design, all the speckle “signatures” can be detected at a single spatial port and generated purely in the time domain, resulting in an extremely large number of usable speckles (>2×10 4 ) beyond the capacity limit of multimode interference. Any arbitrary input spectrum can be computationally retrieved from the recorded output signal. Due to the full randomization of the singular space, the sampling steps can be decreased to <2×10 3 , which efficiently reduces the computational requirement. Our experimental results show an ultrahigh resolution of 5 pm over >2×10 4 wavelength channels, with a peak signal-to-noise ratio of ≈30dB. To the best of our knowledge, these results represent the largest channel capacity among all demonstrated monolithically integrated spectrometers.