Ultracompact Spatial Speckle Reconstructive Spectrometer Based on a Waveguide Corner with Chaotic Reflection

On-chip spectrometers offer significant advantages in terms of compactness and portability, paving the way for advancements in both industrial applications and scientific research. The growing demand for high-performance and miniaturized spectral sensing modules is particularly evident in applications such as smartphones and wearable sensors. In this paper, we introduce and demonstrate an ultracompact and high-performance spatial speckle reconstructive spectrometer, which utilizes chaotic reflection achieved with a waveguide corner consisting of a randomly rough reflecting facet, resulting in chaotic spectral responses at multiple output ports within an ultracompact footprint. Additionally, we propose the concept of segmenting and switching the working window to enable enhanced spectral resolution by sacrificing a certain amount of working bandwidth. This also facilitates the combination of multiple sub-bands to achieve both high resolution and broad bandwidth. We combine innovative schemes and a convex optimization algorithm, leading to a remarkable resolution of 0.02 nm for the spectral range of 1520–1610 nm even with an ultracompact size of 250 μm2 for the fabricated chip. To the best of our knowledge, the present spatial-domain speckle reconstructive spectrometer shows the highest channel-number-to-footprint ratio (λbandwidth/(λres·footprint)) of up to 1.8 × 107 mm–2, offering a promising option for on-chip spectral analysis.