Design and optimization of a silica waveguide based visible etched diffraction grating with uniform loss

A novel method for designing a silica waveguide based visible etched diffraction grating (EDG) with uniform loss is proposed. The designed 1st-order EDG comprises 121 output waveguides with a 2.5 nm channel spacing at a wavelength range from 400 nm to 700 nm. Using the conventional flat-field design with two-stigmatic-points method, the simulated channel loss non-uniformity of a conventional EDG is 2.66 dB. By changing the central output waveguide position and rotating the angles of grating facets according to an appropriately designed distribution function, the loss non-uniformity is reduced to 1.36 dB and the highest loss of marginal channels is decreased from 2.69 dB to 2.13 dB simultaneously. With a total chip size of 30 mm×16 mm, this visible EDG is suitable for realization of spectrometer-on-chip. The proposed design method can achieve insertion loss uniformity in a wide wavelength range with no additional element or extra fabrication step.

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