An on-chip spectral filter is a wavelength-selective optical structure fabricated directly onto an image sensor or photonic die so that spectral discrimination happens in the chip rather than in bulk optics; the sources supplied for this page do not address that technology at all, so no evidence-based assessment of it is possible here.
Summary
In the sensing and imaging taxonomy, an on-chip spectral filter refers to wavelength-selective optical structure built into the sensor stack itself: interference films, plasmonic or metasurface nanostructures, photonic resonators or lithographically patterned filter mosaics deposited over or alongside photodiodes. The intent is to replace bulk components (filter wheels, prisms, free-space gratings, discrete interferometers) so that a spectrometer or multispectral camera collapses into a single fabricated die. Where a conventional colour camera uses three or four broad filters, an on-chip spectral filter array aims for tens to hundreds of narrower channels, often with computational reconstruction recovering a spectrum from a set of deliberately overlapping, non-ideal filter responses.
The honest position on this page is that the supplied source set does not describe this technology. Every source tagged to the concept uses “spectral” in an unrelated sense: power-spectral analysis of EEG signals, mass-spectral features in metabolomics and plant volatile profiling, spectral graph theory in spatial transcriptomics, a spectral framework for epidemic inverse problems, and spectral computed tomography. The single source with any optical-hardware content, on photon-counting CT, concerns spectral separation achieved by energy-resolving detection rather than by an integrated filter. The concept tag appears to have been assigned by keyword rather than by subject matter, and no dimension below can be scored from this corpus.