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 ultracompact 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 singleetch, 220 nm thick, Si Bragg filter featuring a corrugation width of 150 nm, a rejection bandwidth of 1.1 nm and an extinction ratio exceeding 40 dB. This represents a ten-fold width increase compared to conventional single-periodicity, single-etch counterparts with similar bandwidths. The silicon-on-insulator (SOI) platform with submicrometric thick Si layer has shown outstanding results in the miniaturization of photonic circuits [1]. Highquality materials and mature fabrication processes, together with the potential to leverage already existing CMOS facilities, make it a promising candidate for the large volume production of performant photonic devices. In addition to datacom [2] or sensing applications [3,4], SOI shows a great potential for the generation and manipulation of photonic entanglement [5][6][7][8][9][10]. Such a technology would enable monolithic integration of quantumprocessing circuits, opening new routes for envisioned quantum-based applications, including quantum key distribution [11] and optical quantum computing [12].

Coherency‐Broken Bragg Filters: Overcoming On‐Chip Rejection Limitations

“…More specifically, the bandwidth of the cascaded Bragg filter is mainly determined by the length of the single section, while the rejection depth is set by the number of sections. Hence, previously reported strategies to reduce Bragg bandwidth, based on subwavelength engineering, could be combined with the broken‐coherency approach proposed here, allowing to simultaneously yield narrowband operation and ultra‐high rejection. This unique capability to overcome bandwidth‐rejection trade‐off in conventional Bragg filters opens exciting opportunities for the development of efficient and fabrication tolerant Si wavelength filters, with a great potential for integrated nonlinear applications, for example, next generation Si‐based photon‐pair sources for quantum photonic circuits.…”

Quantum optical frequency up-conversion for polarisation entangled qubits: towards interconnected quantum information devices

“…Further stability improvements could be made with a fully integrated QFC device, and promising efforts in this direction have recently been demonstrated, e.g. on-chip combination of PPLN/Ws and PBS [38] or high-rejection spectral filtering stages [39].…”

Low loss grating coupled optical interfaces for large volume fabrication with deep ultraviolet optical lithography

“…This technologically profound concept was demonstrated for the first time in Refs. [43][44][45] , and most recently, extensively utilized in a variety of photonic devices 46 , including components for wideband [47][48][49] and narrowband [50][51][52] spectral operation, sensing structures [53][54][55] , or waveguides for extended mid-infrared (mid-IR) wavelengths 56,57 , to name a few outstanding implementations.…”