Inverse Design of a Polarization Demultiplexer Photonic Circuit

Single quantum dots are excellent candidates for on-chip production of entangled photon pairs.

Such sources are essential for optical quantum computation and require high indistinguishability,

purity, and brightness. To meet these requirements, the source must efficiently funnel the emitted

photons into appropriate collection channels (e.g., free space optics or on-chip waveguides). We

present an inverse design approach to develop a polarization demultiplexer, a nanophotonic device

that converts the QD’s polarization-entangled photons into a path-entangled pair coupled into or-

thogonal waveguides. Our approach utilizes a multi-objective optimization which simultaneously

maximizes two important figures of merit for on-chip photon sources: the coupling efficiency into

the desired waveguides, and the Purcell factor that increases the radiative rate. Using open-source,

adjoint method inverse design software, and modelling the QD as a linear electric dipole, the final

design results in a Purcell factor of ≈ 14 and a coupling efficiency of ≈ 95%. Our results demon-

strate the benefits that a multi-objective inverse design approach has over the previously established

nanophotonic design methods.