SPECTROMETER: Photonic-crystal-based spectrometer is small and simple

Although photonic crystals (PCs) are inherently intricate, they can result in optical devices of great simplicity. For example, a spectrometer created by engineers at Columbia University and the Cooper Union for the Advancement of Science and Art (both in New York, NY) consists merely of various PC patterns on a glass substrate, with a camera focused on the patterns. Different patterns correspond to different wavelengths; light introduced into the edge of the substrate gets coupled out at wavelength-dependent locations seen by the camera. The device works well for measuring broadband light sources used for illumination.

In the prototype, nine PC patterns with different lattice constants ranging from 300 to 420 nm were fabricated in a square grid in polymer film on glass; each PC pattern was 30 × 30 µm in size. The USB camera, which had a 4x objective, was first characterized with a programmable light source. The spectrometer was used to test a 5 mm white LED; the recovered spectrum matched well with measurements made with a standard commercial spectrometer. Increasing the number of different PC patterns will increase the accuracy and resolution of future versions of this device. Contact Nadia Pervez at [email protected].

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