Nanoscale liquid crystal polymer Bragg polarization gratings

作者：Xiang Xiao; Kim Jihwan; Komanduri Ravi; Escuti Michael J^*

来源：Optics Express, 2017, 25(16): 19298-19308.

DOI：10.1364/OE.25.019298

We experimentally demonstrate nearly ideal liquid crystal (LC) polymer Bragg polarization gratings (PGs) operating at a visible wavelength of 450 nm and with a sub-wavelength period of 335 nm. Bragg PGs employ the geometric (Pancharatnam-Berry) phase, and have many properties fundamentally different than their isotropic analog. However, until now Bragg PGs with nanoscale periods (e.g., < 800 nm) have not been realized. Using photo-alignment polymers and high-birefringence LC materials, we employ multiple thin sublayers to overcome the critical thickness threshold, and use chiral dopants to induce a helical twist that effectively generates a slanted grating. These LC polymer Bragg PGs manifest 85-99% first-order efficiency, 19-29. field-of-view, Q approximate to 17, 200 nm spectral bandwidth, 84 degrees deflection angle in air (in one case), and efficient waveguide-coupling (in another case). Compared to surface-relief and volume-holographic gratings, they show high efficiency with larger angular/spectral band-widths and potentially simpler fabrication. These nanoscale Bragg PGs manifest a 6 pi rad/mu m phase gradient, the largest reported for a geometric-phase hologram while maintaining a first-order efficiency near 100%.

• 出版日期2017-8-7