Optical pump-rejection filter based on silicon sub-wavelength engineered photonic structures

Abstract

The high index contrast of the silicon-on-insulator (SOI) platform allows the realization of ultra-compact photonic circuits. However, this high contrast hinders the implementation of narrow-band Bragg filters. These typically require corrugations widths of a few nanometers or double-etch geometries, hampering device fabrication. Here we report, for the first time, on the realization of SOI Bragg filters based on sub-wavelength index engineering in a differential corrugation width configuration. The proposed double periodicity structure allows narrow-band rejection with a single etch step and relaxed width constraints. Based on this concept, we experimentally demonstrate a single-etch, $220\mathbf{nm}$ thick, Si Bragg filter featuring a corrugation width of $150\mathbf{nm}$, a rejection bandwidth of $1.1\mathbf{nm}$ and an extinction ratio exceeding $40\mathbf{dB}$. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch counterparts with similar bandwidths.

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• Ultra-low power generation of twin photons in a compact silicon ring resonator
• 60dB high-extinction auto-configured Mach--Zehnder interferometer
• High-quality photonic entanglement for wavelength-multiplexed quantum communication based on a silicon chip