Spectral Response Pixels in Lithium Niobate for Spectroscopic Applications.

Spectral encoding units are pivotal for computationally augmented spectroscopic applications across sensing, measuring, and imaging domains. Recent advancements in miniaturized spectroscopic systems have dramatically reduced the size of spectral encoding units, rendering them increasingly compatible with field-deployable, wearable, and customer platforms. However, the miniaturization of spectral encoding units is often accompanied by the deterioration of manufacturability, stability, and operational bandwidth. Here, we present a single-step approach to inscribe spectral response pixels in lithium niobate crystals. By employing ultrafast laser-induced pixelated amorphous phase transition in birefringent substrates, we achieve localized frequency-dependent optical modulation, generating dispersion signals at the microscale. These pixels function over a broad bandwidth (400-1550 nm), occupy an ultra-compact footprint (5 × 5 µm2), and are viewing angle independent, offering rich, varied spectral responses for efficient sampling. They also exhibit considerable stability against harsh conditions. We demonstrate their potential in precise spectral detection and liveness recognition applications, paving the way for versatile, affordable, and robust micro-spectroscopic devices.