Single-cycle contact-interference hybrid lithography for scalable fabrication of arrayed quadrant micro-polarizer structures

The advantages of polarization imaging can be readily leveraged in remote sensing applications by applying subwavelength metal grating arrays in standard optical imaging systems. However, the efficient fabrication of these arrays remains a significant challenge due to their dual size-scale features, periodic subwavelength grating structures with feature sizes of hundreds of nanometers, and pixel quadrants with dimensions on the order of tens of micrometers. The present study addresses this issue by introducing contact-interference assembly hybrid lithography. With this method, fine grating structures are fabricated using the interference fringes generated by two coherent laser beams having a wavelength close to the feature size. By using a specially designed, flexible mask, the interference wavefront is then segmented to produce the grating structures in each quadrant of the array unit via a single-cycle process. Notably, sub-micron alignment accuracy is guaranteed by introducing an overlay measurement system. The adverse effects of the gap between the mask and the substrate are suppressed by a mechanism in which the refractive index is smoothed out. A fabrication platform was developed, and a double-layer metal grating with a 20 mm × 20 mm four-quadrant array having a period of 950 nm and a unit size of 15 µm × 15 µm was constructed using a total exposure time of 180 s. This represents a 3-4 orders of magnitude reduction in the fabrication time compared to that of electron beam lithography. The quadrant micro-polarizer was characterized, where the produced sample exhibited a polarization extinction ratio of over 20 dB and an equivalent transmittance of approximately 50%. The results reveal the feasibility of the proposed method for scalable fabrication.