Figure 3
From: Highly efficient dual-level grating couplers for silicon nitride photonics
(a) Numerically simulated directionality at 1550 nm as a function of the etching depth e and bottom linear apodization factor \(R_1\) considering a single level Si\(_3\)N\(_4\) GC with a thickness of 400 nm (step 1 of the design); (b) numerically simulated directionality at 1550 nm as a function of the top layer thickness \(h_2\) and top linear apodization factor \(R_2\) for a dual level Si–Si\(_3\)N\(_4\) GC with a Si\(_3\)N\(_4\) thickness \(h_1\) = 400 nm, e = 250 nm and \(R_1\) = 0.016 \(\upmu\)m\(^{-1}\) (step 2 of the design). For both simulations campaigns: B = 3 \(\upmu\)m, T = 1 \(\upmu\)m and s = 20 nm.
