Search

Planar optical device with continuous phase shifting (CPS) has raised widespread interest recently. Formed by subwavelength micro/nano structures, planar optics are able to control wavefront in multi aspects including phase and polarization. Most phase shifters for CPS devices are individual structures such as cylinders or cuboids. In this study, we specifically discuss grating based continuous phase shifting lenses comparing with aforementioned counterparts, in terms of differences of design mechanism and polarization responses. In addition we found that grating based metalens has outstanding potential in generating emerging artificial focus pattern. A grating based CPS lens with ‘U’ shaped focus was fabricated and characterized for prove of concept. Planar optics with artificial focus pattern has great potential for future applications including micro beam shaping and maskless nano lithography.

OPA device has been widely studied for solid-state Lidar. We have investigated a multi-layers SiN/SiO structure to end-fire the beam with high efficiency. The advantage of the structure, simulation result and fabrication feasibility are discussed. In addition, the latest fabrication progress is also presented.

Single nanowires (NWs) are of great importance for optoelectronic applications, especially solar cells serving as powering nanoscale devices. However, weak off-resonant absorption can limit its light-harvesting capability. Here, we propose a single NW coated with the graded-index dual shells (DSNW). We demonstrate that with appropriate thickness and refractive index of the inner shell, the DSNW exhibits significantly enhanced light trapping compared with the bare NW (BNW), and the NW only coated with the outer shell (OSNW) and the inner shell (ISNW), which can be attributed to the optimal off-resonant absorption mode profiles due to the improved coupling between the reemitted light of the transition modes of the leak mode resonances of the Si core and the nanofocusing light from the dual shells with the graded refractive index. We found that the light absorption can be engineered via tuning the thickness and the refractive index of the inner shell, the photocurrent density is significantly enhanced by 134% (56%, 12%) in comparison with that of the BNW (OSNW, ISNW). This work advances our understanding of how to improve off-resonant absorption by applying graded dual-shell design and provides a new choice for designing high-efficiency single NW photovoltaic devices.

Photonic-based reservoir computing (RC) systems have attracted significant attention. Integrated and purely passive systems are compatible with complementary metal-oxide-semiconductor devices, but are limited by the lack of non-linear components. This study consists of two parts: firstly, a review on the published integrated and passive RC system is presented. The review focuses on the structural configuration (rather than the mathematical model) of the neural network; secondly, a new approach for achieving an integrated and passive photonic RC system is introduced and discussed. This approach employs a mode combiner in front of the reservoir to achieve an extra non-linearity in a purely passive device. Moreover, the approach is numerically investigated, and an XOR (exclusive or) task is used to test the device, and the result shows that the new approach satisfies the requirement of an RC system.

Beam-steering devices such as optical phased arrays (OPAs) are key components in the applications of solid-state Lidar and wireless communication. The traditional single-layer OPA results in a significant energy loss due to substrate leakage caused by the downward coupling from the grating coupler structure. In this work, we have investigated a structure based on a multi-layer S i 3 N 4 / S i O 2 platform that can form a 3D OPA to emit light from the edge of the device with high efficiency; a 2D converged out-coupling beam will be end-fired to the air. High efficiency and wide horizontal beam steering are demonstrated numerically, and the influence of vertical crosstalk, delay length, and number of waveguide layers are discussed, as well as the fabrication feasibility.

Grating couplers are one of the most basic integrated photonic structures. They have raised tremendous research interest due to their outstanding performance in compact nonmechanical beam steering. Here we propose a new compound period grating coupler formed by combining two grating structures with different periodicities. The new compound period grating coupler structure can couple the waveguide mode into two radiation modes with different angles. Therefore, the beam steering range is doubled due to the extra beam. We numerically demonstrate this idea, and a 26.20° steering range is observed within a wavelength tuning range of 1500 to 1600 nm. The compound period grating structure with a distributed Bragg reflector as the substrate is also numerically demonstrated, and its energy leakage to the substrate is highly suppressed. In addition, the investigation of fabrication tolerance shows that the new structure can be fabricated with the current CMOS technology.