An on-chip micro-spectrometer is demonstrated based on a circular diffraction grating consisting of an elliptical Bragg mirror. This structure results in a highly efficient and compact device with simplified processing requirements, useful for sensing, spectroscopy, telecom demultiplexing, and optical interconnects. The computed efficiency for a realistic geometry is 0.14 dB, which represents to the best of our knowledge the highest predicted efficiency for concave diffraction gratings (echelle/echelette gratings). The first realization of the elliptical Bragg mirror diffraction grating spectrometer is presented on silicon on insulator at a wavelength of 1.55 µm. Measurements show a full device efficiency of 3.0 dB, including all in-line losses, with a band flatness of 0.4 dB over 30 nm.
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