Optical phased arrays (OPAs) have attracted much attention due to its potential applications in a series of advanced technologies such as LIDAR, free space communication. OPAs have many advantages, such as non-mechanical, arbitrary beam shaping and control. It has been proved that it is feasible to process OPAs with integrated optical platform. Among all the integrated optical platforms, silicon photonic platform has attracted the attention of most researchers and has achieved many important results. However, silicon photonic platform is very sensitive to processing errors and is not suitable for high power input because of its strong nonlinear effect. Silicon nitride (Si3N4) has become a research hotspot in integrated photonics due to its weak nonlinear effect and low-loss. Compared with silicon, because of its lower refractive index contrast, it is more tolerant to process changes and because of its weak nonlinear effect, it can allow higher power input, which is very suitable for processing OPAs. In this work, we propose an OPA based on 200 nm silicon nitride platform to control the two-dimensional direction of the beam by wavelength tuning. The system is simulated by FDTD solution. Finally, the scanning range of 46°×12° is realized in the wavelength range of 1500 nm to 1600 nm. The 3 dB size of a single spot is 1.8°×0.5° and a total of 600 scanning points can be obtained. This OPA can find applications in laser scanning, spectroscopy, demultiplexing and spectral pulse shaping applications.
Metalens can reconstruct the wavefront of a beam arbitrarily, and on-chip metalenses are more conducive to integration. We now propose a metalens based on silicon substrate. The lens consists of several silicon nitride (Si3N4) waveguides and annular coupling gratings (ACG). It can achieve off-chip far-field focusing at a wavelength of 780 nm. The radii and the grating periods of the ACG can be selected respectively according to Fermat’s Principle and Bragg’s Law. The key to designing the metalens lies in the precise control of the on-chip phase delay and the off-chip phase delay. When the total phase delay caused by the on-chip and off-chip light propagation is an integer multiple of 2π, the metalens can reconstruct a specific wavefront and capture the expected focal point in the off-chip free space. The theoretical calculation and simulation results of the designed metalens are well consistent. From the simulation results, the metalens has a focal spot size of FWHMx = 1.18 μm, FWHMy = 0.76 μm, focal depth of 3.25 μm, focal length of 19.6 μm, and transmission of 25.1% at the focal plane. Moreover, the focal length of the metalens can be controlled flexibly by engineering the radii and the grating periods of the ACG. This metalens is of great significance to the integration of modern optoelectronic devices, and it would promote potential applications in controllable focusing, optical interconnection devices, and biosensor imaging.
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