Single-Shot Integrated Speckle Spectrometer with Ultrahigh Bandwidth-to-Resolution

Abstract

Miniaturized spectrometers employing chip solutions are essential for a wide range of applications, such as wearable health monitoring, biochemical sensing, and portable optical coherence tomography. However, the development of integrated spectrometers is hampered by the inherent trade-off between bandwidth-to-resolution, footprint, sampling channels, and operation speed. Here, we demonstrate that an ultrahigh bandwidth-to-resolution reconstructive spectrometer can be easily implemented through a single image capture of the speckle pattern diffracted from a passive silicon photonic chip. By leveraging the high pixel count of an image sensor, we can instantly acquire a significant number of distinct spatial sampling channels. Those sampling channels are spatially decorrelated by using our passive optical network on chip including cascaded unbalanced Mach-Zehnder interferometers, random diffraction by an antenna array, and mutual interference in free space before being captured. Hence, each speckle pattern contains wavelength-specific information across its spatial distribution to enhance the effectiveness of the global sampling strategy. Experimentally, we achieve a spectral resolution of 10 pm and an operational bandwidth of 200 nm, with sampling channels up to 2730. Multiple unknown narrowband and broadband spectra can also be precisely obtained.