By cleverly applying the guided-mode resonance (GMR) effect, Hung and colleagues demonstrate a compact spectrometer with excellent attributes. Using first a chirped resonant grating on a waveguide film with a fixed thickness, there results a spectrum with varying resonance linewidth and efficiency relative to period, or position, along the spectrometer. In contrast, combining the chirped grating with a waveguide film that is mildly graded in thickness along the grating vector yields a constant linewidth and efficiency. Natural for GMR filters, the resonance linewidth depends on the polarization state of the input light. Thus, this chip-type spectrometer exhibits sub-nm resolution in TM polarization and around 4 nm in TE polarization while working across the 500- to 700-nm spectral range. The authors verify successful operation of their instrument by measuring spectra of a white LED as well as laser sources and then comparing these with spectra obtained with a commercial spectrum analyzer. This work exemplifies the potential of the GMR effect to enable platform technologies on which many beneficial applications could be based.
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