Photon pair generation via spontaneous four wave mixing in silicon waveguides or microring resonators (MRR) integrated with a high extinction pump rejection filter is very much demanding for futuristic large-scale integrated quantum photonics circuits. As the photon pair generation is poor in silicon waveguide via χ(3) process ( ~ MHz ), the nearly un-depleted pump laser light needs to be immediately filtered or attenuated (> 100 dB) to avoid any noise to the originally created photon pairs along the path. To offer desired pump rejection, a suitably designed distributed Bragg reflector (DBR) can be integrated on chip offering an extinction of > 150 dB. However, fabricated DBRs suffer degradation because of roughness induced in-band forward scattering waves which limits the extinction ratio below 50 dB. Therefore, several single stage DBRs need to be cascaded incoherently. This approach is detrimental as it increases the overall footprint and insertion loss of the filters.

In this talk, we are going to present a DBR design in multimode rib waveguide structures offering relatively lower forward scattering waves due to waveguide side-wall roughness. This design concept has been validated with experimental demonstration recording the single-stage DBR filter extinction of 65 dB, which is 15 dB higher than those of earlier reported results by others. It has been also shown with a four wave mixing experiment that the DBR design is very much effective in attenuating the pump laser significantly without affecting the transmission of signal and idler photons.