Design of Si-based flat-top steep-edge RCE photodetector with two-coupled-cavity grating filter

This paper presents the design and analysis of a Si-based flat-top steep-edge RCE photodetector realized by the introduction of a two-coupled-cavity grating filter. A greatly improved rectangular spectral response which can be achieved via adjusting parameters of the filter is shown. Reflectivity spectrums of the one-cavity and the two-coupled-cavity grating filters as well as quantum efficiencies of corresponding photodetectors are simulated in detail. In the final design of the photodetector, the ratio of the linewidth at 0.9 times the peak efficiency to the linewidth at 0.1 times the peak efficiency is 0.72, 3-dB linewidth is 2.2 nm, flat-top quantum efficiency is as high as 90% and sideband value is extremely low.

► We propose a novel Si-based flat-top steep-edge RCE photodetector.
► We introduce a reflective two-coupled-cavity grating filter in the final design.
► A rectangular spectral response with Δλ0.9/Δλ0.1=0.72, FWHM=2.2 nm is achieved.
► Flattop QE is 90% tradeoff between QE and spectral linewidth is solved.
► Side lobes of the spectral response are suppressed to an extremely low value.