Multi-Poly-Silicon-Layer-Based Spot-Size Converter for Efficient Coupling Between Silicon Waveguide and Standard Single-Mode Fiber

Abstract

A novel spot-size converter (SSC) incorporating phase matched polycrystalline-silicon (Poly-Si) multi-layer is proposed and optimised for efficient nanophotonic coupling, which can be fabricated by using the CMOS compatible process and can be directly integrated. An efficient algorithm, combining the rigorous H-field based full-vectorial finite element method and the least squares boundary residual method, is developed for the design optimization of the SSC. Use of simple single layer and multi-layer Poly-Si based SSCs are investigated, in which the coupling process, phase matching for isolated and composite waveguides are also carried out. The coupling loss can be reduced to 2.72 dB by using an eleven Poly-Si layers based SSC. The on-chip integrated SSC opens up the feasibility of a low cost passive aligned fiber-pigtailed electronic-photonics integrated circuits platform.

Improved design for SOI based evanescently coupled multilayer spot-size converter

“…In the previous design of Jiang et al (2016), an 11 layer based SSC with h = 105 nm, s = 400 nm, and s = 200 nm was studied. Although the Poly Si layers were single moded vertically but it should be noted that they can support higher order modes laterally.…”

“…A spot size converter (SSC) based on a different design concept (Jiang et al 2016) has been recently reported. This SSC comprises of two evanescently coupled waveguides: a standard nanowire and a phase matched array of Polycrystalline Silicon waveguides.…”

“…The refractive indices for Si, Poly Si and SiO are taken as 3.47548, 3.48 and 1.46 (Preston et al 2007; Barh et al 2013) respectively, at the operating wavelength of 1.55 μm. multilayer Poly Si structure (Jiang et al 2016) The CMOS compatible fabrication for this SSC would require the plasma enhanced chemical vapor deposition (PECVD) of silica. Poly Si layers can be deposited as thin films of amorphous silicon by LPCVD and then crystallized by annealing at 600 °C and again at 1100 °C as shown by Preston et al (2007).…”

“…In Jiang et al (2016) this SSC has been analyzed numerically using the first two supermodes of the composite structure, where the first supermode is the symmetric mode of the NW and array fundamental mode, and the second supermode is the antisymmetric mode. The height h of the Poly Si layers in the array can be tuned to obtain the point of minimum separation between these two supermodes.…”

“…Since the array is multimoded, we have now taken also into consideration the existence of possible higher order modes of the composite structure. The assumption taken into account in Jiang et al (2016) that only two modes of the SSC can be used in the analysis may not be valid in some cases. In this paper we present these design criteria in detail based on which a new optimized design with improved coupling efficiency with the fiber is proposed.…”