On-chip ultra-high rejection and narrow bandwidth filter based on coherency-brokencascaded cladding-modulated gratings

  Bragg filters are of essential importance for chip-scale photonic systems, However, the implementation of filterswith sub-nanometer bandwidth and rejection beyond 70 dB is hindered by the high index contrast of the siliconon-insulator platform, which makes filters prone to fabrication imperfections, In this papet, we propose to combine cohereney-broken cascading architecture and cladding modulation to circumvent the intrinsic limitationThe cascading architecture effectively prevents the accumulation of phase errors, while the cladding modulationoffers additional design freedom to reduce the coupling coefficient, A bimodal Bragg filter with a testingequipment-limited rejection level of 74 dB and a 40 dB bandwidth of 0.44 nm is experimentally demonstratedThe minimum feature size is 90 nm, which significantly relieves the fabrication constraints.

DOI: 10.1364/PRJ.510899