Miniaturized Spectral Sensor based on Gate‐Tunable PdSe ₂ /MoSe ₂ Heterostructure Integrated on a Fiber Endface

Wavelength‐division multiplexing (WDM) continues to drive the need for optical receivers with compact and integrated spectral discrimination. Conventional demultiplexers based on gratings, or filter arrays remain bulky, sensitive to alignment, and difficult to co‐package with fibers. Here we report a proof‐of‐concept fiber‐endface heterojunction spectral sensor (FIHSS) with an electrically tunable transport‐mediated spectral response. In the continuous regime, the FIHSS reconstructs spectra over the wavelength of 1510–1610 nm with a root mean square error of 0.11 relative to a commercial spectrometer. In the discrete regime, it resolves CWDM‐type channels with wavelength spacings down to 1 nm and channel power ratios from 1:1 to 1:100. Further, benefiting from a robust fabrication process that shields the vdW layers from developer exposure, rapid rise (155 µs) and decay times (125 µs) are obtained, representing an outcome one order of magnitude faster than the values currently in the literature. Ultracompact device structure, free from external optical and mechanical modules, makes the FIHSS a promising configuration for portable spectrometer applications.