Fabrication of a concave grating with a large line spacing via a novel dual-beam interference lithography method

We introduce a novel dual-beam interference lithography (IL) method that makes it possible to fabricate a concave grating with a large line spacing. A concave lens is placed between two point sources for spatial interference and a concave substrate to produce the grating pattern. The original positions of the two point sources are separated by the concave lens, which permits the IL method to fabricate a concave grating that bypasses the line spacing limitation of the conventional IL system. A concave grating with a line spacing of about 3.8 μm was fabricated and fitted inside a miniature spectrometer. The enlarged line spacing reduces the detector length by 66.5%, while keeping the resolution better than 1.5 nm over a wide spectral band (360 - 825 nm).