Periodic Al₂O₃ Nanohole Arrays on MgO (100) for a Low-Reflectivity External Cavity Fabry-Perot Interferometer

Based on nanoimprint lithography and dry etching of stacked three-layer masks, we successfully prepared large-area periodic Al2O3 nanohole arrays on MgO (100) substrates. At 1550 nm, the nanohole arrays increased the interface transmittance of MgO (100) from 93.2% to above 98.8%. Postannealing at 700 C-degrees, the interface transmittance decreased only to 97.8%. Compared with typical multilayer antireflection coating, it is simpler and easier to prepare. Nanoholes are arranged in a square lattice. The radius is 250 nm, the period is 350 nm, and the height is 200 nm. During the etching process, we eliminated the serious impact of shrinking the round hole into a gear hole caused by microloading. The processed nanohole is an inverted truncated cone with a verticality of 83.7(degrees). In addition, the potential of Al2O3 nanohole arrays to interfere with interface reflections was effectively verified using spectrophotometry and the self-built low-reflectivity external cavity Fabry-Perot interference platform. This research provides us with important solutions for developing Fabry-Perot optical fiber devices with a higher demodulation accuracy.