Perfectly vertical surface grating couplers using subwavelength engineering for increased feature sizes

Abstract

We present perfectly vertical grating couplers for the 220 nm silicon-on-insulator platform incorporating subwavelength metamaterials to increase the minimum feature sizes and achieve broadband low back-reflection. Our study reveals that devices with high coupling efficiencies are distributed over a wide region of the design space with varied back-reflections, while still maintaining minimum feature sizes larger than 100 nm and even 130 nm. Using 3D-finite-difference time-domain simulations, we demonstrate devices with broadband low back-reflection of less than − 20 d B over more than 100 nm bandwidth centered around the C-band. Coupling efficiencies of 72% and 67% are achieved for minimum feature sizes of 106 nm and 130 nm, respectively. These gratings are also more fabrication tolerant compared to similar designs not using metamaterials.

Circular Optical Phased Arrays with Radial Nano-Antennas

“…The performance of the circular grating coupler was engineered to match the upward radiation beam profile to the Gaussian-like optical fiber mode. The grating coupler was designed using an L-shaped waveguide geometry [ 28 ] with subwavelength grating (SWG) metamaterial sections to reduce back-reflections [ 29 , 30 ]. The SWGs are non-resonant nanophotonic structures with pillar segmentation with dimensions much smaller than the wavelength of light, suppressing reflection and diffraction effects [ 31 ].…”

“…To take advantage of the large maximum theoretical FOV of a circular array, broadband nano-antennas are needed. In this work, we advantageously adopted an L -shaped configuration [ 29 , 30 ], similar to the elements discussed in Section 2.1 . A 3D schematics of the nano-antenna is shown in Figure 3 a.…”

Breaking the Coupling Efficiency–Bandwidth Trade‐Off in Surface Grating Couplers Using Zero‐Order Radiation

“…We considered an MFS of 100 nm, which is compatible with current 193‐nm deep‐UV lithography. [ 40 ] Thus, the grating period is chosen as 200 nm. Additionally, the coupling efficiency is maximized without compromising the bandwidth by tilting the prism 1° with respect to the chip plane.…”

Metamaterial-Engineered Silicon Beam Splitter Fabricated with Deep UV Immersion Lithography

“…Structures sometimes include small features near the resolution limit of dry deep-ultraviolet (DUV) lithography tools [22]. Several demonstrations of SWG-based devices with features larger than about 120 nm and compatible with dry DUV lithography have been proposed in the literature but this normally constraints the available design space and the range of achievable material properties, making the design more complex and ultimately impacting performance [23]. For this reason, most of the successful demonstrations have so far relied on electron-beam lithography that offers higher resolution at the expense of a largely reduced throughput which limits its applicability to research or small volume productions.…”