Polymer network liquid crystal (PNLC) is attractive for many photonic applications because of its fast response time and
large phase modulation. However, the voltage-on state light scattering caused by multi-domains of LC molecules hinders
its applications in the visible and near infrared regions. To reduce domain sizes and eliminate scattering for λ=1.06 μm
and 1.55 μm, we studied the effect of LC viscosity on domain sizes. PNLCs based on five different LC hosts were
prepared. The LC host was first mixed with 6% reactive mesogen and then filled into a 12-μm cell with homogeneous
alignment. After UV curing, we measured the on-state transmission spectra of these five PNLCs. By fitting the
transmission spectra with Rayleigh-Gans-Debye model, we can estimate the average domain sizes. We found that the
domain sizes of PNLC are inversely proportional to the rotational viscosity of the LC host. This finding can be explained
by the Stokes-Einstein equation. As a result, PNLC with a slower diffusion rate would cause smaller domain sizes,
which in turn lead to faster response time. To achieve a slower diffusion rate, we cured the PNLC samples at a lower
temperature. By selecting a high viscosity and high Δε LC host, we demonstrate a scattering-free (<3%) 2π phase
modulator at λ=1.06 μm and λ=1.55 μm. Temperature affects the PNLC performance significantly. As the operation
temperature increases from 25oC to 70oC, the response time drops from 220 μs to 30 μs. 2π operating voltage for λ=1.06
μm slightly increases from 65V to 85V. Meanwhile, hysteresis decreases from 7.7% to 2%. For λ=1.55μm, operating
voltage is 100V. If reflective mode is employed, operating voltage can be reduced to 55V.
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