Subwavelength grating Fourier‐transform interferometer array in silicon‐on‐insulator

A planar waveguide Fourier-transform spectrometer with densely arrayed Mach-Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach-Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free-spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of -25 to -30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements.

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