Process calibration method for designing silicon-on-insulator contra-directional grating couplers

Abstract

We present a process calibration method for designing silicon-on-insulator (SOI) contra-directional grating couplers (contra-DCs). Our method involves determining the coupling coefficients of fabricated contra-DCs by using their full-width-at-half-maximum (FWHM) bandwidths. As compared to the null method that uses the bandwidth measured at the first nulls, our FWHM method obtains more consistent results since the FWHM bandwidth is more easily determined. We also extract the coupling coefficients using curve-fitting which provide values that are in general agreement with the values obtained using our method. However, as compared to the curve-fitting method, our method does not require knowledge of the insertion loss and is easier to implement. Our method can be used to predict the FWHM bandwidths, the maximum power coupling factors, the minimum power transmission factors, and the through port group delays and dispersions of subsequent, fabricated devices, which is useful in designing filters.

Hybrid multimode resonators based on grating-assisted counter-directional couplers

“…These fine structures are hardly reproduced with fidelity by the lithography tools and the resulting experimental device often deviates from the design. Methods based on computational lithography [31] and empirical models [31,32] can be employed in the design process to overcome strong discrepancies. This is especially important for achieving high extinction ratio and a desired bandwidth as they are dictated by the coupling strength which in turn depends on the sidewall modulation and on the grating length (or the number of periods).…”

“…In this example, the waveguide widths w 1 and w 2 are chosen to allow single mode operation in waveguide 1 and multimode operation in waveguide 2, while the grating is designed to allow phase-matching between the forward-propagating fundamental mode (TE 0 ) of waveguide 1 and the backwardpropagating second order mode (TE 1 ) of waveguide 2 around a targeted wavelength λ 0 . At phase-matching, the grating period Λ is related to λ 0 and to the effective indices n 1 and n 2 of the two modes by the well-known relation [23][24][25][26][27] ( )…”