Coupling Si3N4 waveguide to SOI waveguide using transformation optics

Abstract

Silicon nitride (Si3N4) planar waveguide platform combined with silicon-on-insulator (SOI) devices offer a whole new generation of system-on-chip applications. Therefore, efficient coupling of an Si3N4 waveguide to an SOI waveguide is essential. We present a coupler to interface a 1.8 µm-wide Si3N4 waveguide to a 0.5 µm-wide SOI waveguide based on the focusing property of the Luneburg lens. In order to match the refractive indices of the waveguides with the edges of the lens, one side of the lens is flattened with quasi-conformal transformation optics. The designed coupler is implemented by graded photonic crystals. The three-dimensional numerical simulations indicate that the 1.93 µm-long coupler has an average coupling loss of 0.13 dB in the C-band.

Overcoming the challenges of performing metasurface-based general spatial transfer functions

“…Nowadays, GRIN materials can be employed for Fourier transform implementation, inspired by conventional lenses. Numerous studies have been conducted for practical implementations, including the implementation of GRIN using, Maxwell's fisheye lenses [30], and Luneburg lenses [31,32]. To obtain the Fourier transform, we utilize a layer with a graded permittivity profile which is given in relation ( )…”

Surface wave direction control on curved surfaces

“…To overcome the requirement of anisotropic materials, one implementation is the quasi-conformal TO proposed by Leonhardt [23]. Quasi-conformal TO has offered an alternative to TO designs using all dielectric materials and has been widely used in numerous applications such as conformal lens [24], Maxwell-fisheye lens [25] and waveguides [26]. However, the quasi-conformal TO method assumes approximations and is limited to omnidirectional sources when directly designing a new lens [3,27].…”

“…In this work, we designed a TO device with a rotationally symmetric curved surface to partially control the propagation direction of surface waves. Such a surface wave propagation direction controlling device could be of use in various potential application areas such as waveguides [26] and cloaking [31]. Compared to previous studies [18], the proposed TO device can be realized on multiple curved surfaces, which expands the range of options in application.…”