Intelligent design of large angle deflection beam splitter based on method of moving asymptotes

Abstract

Photonic chip is a kind of integrated device that uses light as a carrier for information transportation and processing. Owing to its advantages of small size, lightweight, and low power consumption, photonic chip has become the most popular research topic nowadays. The beam splitter is a vital part of on-chip integration. For conventional beam splitting elements, Y-type and tree-branch output are the main elements, which are usually realized by interference principles. However, it is appropriate only for simple conventional beam splitter because the propagation direction of light cannot achieve large angle deflection. In the case of relay loading, optical amplification, pumping, and frequency upconversion, the vertical loading is often required without affecting the main optical path. To complete the large-angle deflection beam splitting, one needs to add a mirror to realize it or use a right-angle mirror structure for geometric double-sided reflection and splitting in traditional ways, but these structures are relatively complicated and difficult to complete on-chip integration. Based on previous work on inversely designed multi-channel wavelength routers and wide spectrum efficient focusing devices by using the intelligent algorithm, and combining the years of research on the coherent superposition theory of multi-scattering of the disordered medium, a large angle beam splitter that can realize from the near-infrared band is designed through using the intelligent algorithm. The beam splitter structure is based on AMTIR-1 glass, the part to be etched is air. The composition of AMTIR-1 is Ge<sub>33</sub>As<sub>12</sub>Se<sub>55</sub>. And the size of the structure is only 1 μm × 2 μm. The beam splitter can achieve 180° linear separation of beams in a range from 800 nm to 1100 nm, the beam splitting ratio of the entire waveband is approximately 1∶1, and the gross beam splitting efficiency is stable between 85% and 92%. Compared with several conventional structures with the same size, the efficiency of the beam splitter designed by this algorithm is higher. At the same time, the algorithm has the advantages of fast computation speed and small computation amount, and it can be completed only by ordinary personal computers without the support of hardware such as workstations. This intelligent algorithm can also be applied to the design of various passive photonic devices such as optical polarization splitters, routers, optical isolators, etc., providing an idea and reference for the design of integrated micro-nano photonic devices on high-density sheets.