Highly efficient ultra-broad beam silicon nanophotonic antenna based on near-field phase engineering

Abstract

Optical antennas are a fundamental element in optical phased arrays (OPA) and free-space optical interconnects. An outstanding challenge in optical antenna design lies in achieving high radiation efficiency, ultra-compact footprint and broad radiation angle simultaneously, as required for dense 2D OPAs with a broad steering range. Here, we demonstrate a fundamentally new concept of a nanophotonic antenna based on near-field phase-engineering. By introducing a specific near-field phase factor in the Fraunhofer transformation, the far-field beam is widened beyond the diffraction limit for a given aperture size. We use transversally interleaved subwavelength grating nanostructures to control the near-field phase. A Bragg reflector is used at the end of the grating to increase both the efficiency and the far-field beam width. The antenna has a compact footprint of 3.1 µm × 1.75 µm and an ultra-broad far-field beam width of 52° and 62° in the longitudinal and transversal direction, respectively, while the radiation efficiency reaches 82% after incorporating a bottom reflector to further improve the directionality. This unprecedented design performance is achieved with a single-etch grating nanostructure in a 300-nm SOI platform.

Silicon-based surface gratings for efficient fiber-chip and free-space beam coupling

“…Surface gratings as optical antennas are designed to radiate the light out of the chip, facilitating free-space beam shaping and steering, which is desired for surging applications in LIDARs or free-space optical communications. Both very long (mm-scaled) andultra-short (μm-scaled) surface gratings with weak and strong radiation can be advantageously utilized as efficient optical antennas in one-dimensional (1-D) or two-dimensional (2-D) OPAs [35][36][37][38]. Figure 2a show a schematic view the optical nano-antenna implemented on a 220 nm thick SOI platform.…”

Toward Practical Optical Phased Arrays through Grating Antenna Engineering

“…The results showed that the unidirectional transmission efficiency of the grating antenna increased from 46% to 95% after the DBR were added. Shahrzad Khajavi et al achieved an emission efficiency of 82% while designing a nanophotonic antenna based on near-field phase engineering, by incorporating a bottom Bragg reflector into the structure [35], but this structure in the process of production is more complicated.…”

Low‐Temperature Synthesis of Silicon Oxynitride‐Doped Si for Tunable Bragg Gratings Homogeneously Deposited on Si, SiO2, and Borosilicate Substrates and the tip of SM and PM Optical Fibers

“…Earlier works on silicon (Si) [1][2][3][4][5][6] stimulated the progress in numerous Si-photonics devices, including vertical-cavity surfaceemitting lasers (VCSELs), [7] distributed feedback (DFB) lasers [8] and efficient nanophotonic antennas, [9] supercontinuum generation, [10] and optoacoustic detection. [11] Within these photonic devices, Bragg gratings (BGs) are critical and used to improve the efficiency of the devices.…”