Abstract: We present an L3-type photonic crystal cavity in silicon with a theoretical quality factor of 20.9 million. This highly-optimized design is made by shifting the positions of the holes surrounding the cavity, and was obtained through an automated global optimization procedure.
In Ref. (Minkov 2014) we presented a global optimization of the quality factors (\(Q\)) of several of the most widely-used photonic crystal (PhC) cavities. This resulted in a tremendous improvement – typically of one or more orders of magnitude – in this important figure of merit. In particular, the L3-type cavity, consisting of three missing holes in the PhC, was optimized to a theoretical \(Q\) of 4.1 million, and a \(Q\) of 2 million for this design was measured in a subsequent experiment (Lai 2014). Here, we present an additional improvement of the theoretical \(Q\) of this cavity, accomplished by including three extra parameters in the optimization. We use the same overall PhC parameters as in Ref. (Minkov 2014): slab refractive index \(n=3.46\) (as for silicon); hole radius \(R=0.25a\); slab thickness \(d=0.55a\), with \(a\) the PhC lattice constant.