Fabrication of two-dimensional micro-nano photonic structures by symmetry-lost beams interference
Authors: L&uuml; Hao  , You Kai  , Lan Yan-Yan  , Gao Dong  , Zhao Qiu-Ling  , Wang Xia  ,   College of Mathematics and Physics, Qingdao University of Science and Technology, Qingdao 266061, China;,   Shandong Advanced Optoelectronic Materials and Technologies Engineering Laboratory, Qingdao 266061, China
Published: December 2020

Micro-nano photonic structures, such as meta-materials and photonic crystals, having special effects on light generation, transmission, detection and sensing on a submicron scale, play an increasingly significant role in optical information fields. Micro-nano photonic structures have great potential applications in surface laser emission, optical waveguide and high-Q laser. There are several methods to fabricate micro-nano photonic structures, including laser direct writing, electron beam direct writing, electrochemical corrosion, and holographic lithography and so on. Holographic lithography employs multi-beam interference to generate periodic patterns and records them on photosensitive materials to form typical structures. What is more, it has advantages of low cost, large area and high efficiency. However, there are still some challenges in fabricating typical micro-nano photonic structures, especially the precise optical alignment, beam polarization and control of the details of local interference pattern. A specially designed prism is employed in this work and we propose a compact symmetry-lost setup with the rapid adjustment of beam configuration and polarization.
Based on the theory of multi-beam interference, symmetry-lost four-and five-beam interference with different polarizations are simulated. By changing the combination of beam configuration and polarization, novel two-dimensional micro-nano photonic structures can be achieved. The variations of azimuthal angle and polarization of beam in symmetry-lost system affect the wave vector difference, and thus changing the lattice shape and structure contrast. Branch-like and wave-like structures are generated by symmetry-lost four beams with polarizations of (90, 90, 90, 90) and five beams with polarizations of (90, 90, 90, 90, 0), respectively. An appropriate threshold is selected in simulation, such that the intensity data larger than the threshold are removed, while the smaller data are remained, which is transformed into an optical lattice pattern. The interference structures show different morphologies and structural contrasts, and have a period of several hundred nanometers.
In experimental fabrication, a top-cut hexagonal prism is used to generate two-dimensional micro-nano photonic structure on CHP-C positive photoresist by single exposure. The intensity of each beam is about 18-20 mW, and the incident angle is 42. The beam polarization is adjusted by rotating a half waveplate inside the holes of the mask and structure volume fraction is determined by exposure dose controlled by beam intensity and exposure time. The scanning electron microscope images of the samples show good agreement with simulation results. This study could provide an effective method of fabricating novel photonic structures, which can be used as templates of fabricating different types of metal lattice structures, thereby promoting the development and applications of novel photonic devices.