Photonic integrated circuit with multiple waveguide layers for broadband high-efficient 3D OPA.

The traditional photonic integrated circuit (PIC) inherits the mature CMOS fabrication process from the electronic integrated circuit (IC) industry. However, this process also limits the PIC structure to a single-waveguide-layer configuration. In this work, we explore the possibility of the multi-waveguide-layer PIC by proposing and demonstrating a 3D optical phased array (OPA) device, with the light exiting from the edge of the device, based on multi-layer Si3N4/SiO2 stacks. This device is in a multi-waveguide-layer configuration at every single position of the device. This configuration offers the possibility of using edge couplers at both the input and the emitting ends to achieve broadband high efficiency, and its uniqueness provides the potential for a more extended detection range in the lidar application. The device has been studied by numerical simulation, and proof-of-concept samples have been fabricated and tested.

Phase-combining unit for aliasing suppression in an optical phased array.

Integrated optical phased array (OPA) devices have been widely studied as a solution for solid-state light detection and ranging technology in the autonomous driving application. In this work, a phase-combining unit (PCU) is proposed and studied. With a given number (N) of phase shifters, instead of the general N (phase shifters) to N (emitters) control, the PCU can enable an N to 2N-1 control, which efficiently suppresses the aliasing effect. The theoretical analysis, numerical simulation, and experimental proof-of-concept have been completed in this work. The results show that a maximum suppression of 92.54% can be achieved for the grating lobes in simulation, and an average 53.76% is tested for one grating lobe in the experiment. In conclusion, the PCU can be used as a universal aliasing suppression unit on many types of integrated OPA devices.

Off-Resonant Absorption Enhancement in Single Nanowires via Graded Dual-Shell Design.

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.

High-efficiency end-fire 3D optical phased array based on a multi-layer Si3N4/SiO2 platform.

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 ${\rm Si}_{3}{\rm N}_{4}/{\rm SiO}_{2}$Si3N4/SiO2 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.

Compound period grating coupler for double beam generation and steering.

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.