Submillisecond-response IR spatial light modulators with polymer network liquid crystal

Jie Sun; Yuan Chen; Shin-Tson Wu

doi:10.1117/12.2004306

5 March 2013 Submillisecond-response IR spatial light modulators with polymer network liquid crystal

Jie Sun, Yuan Chen, Shin-Tson Wu

Proceedings Volume 8642, Emerging Liquid Crystal Technologies VIII; 864207 (2013) https://doi.org/10.1117/12.2004306
Event: SPIE OPTO, 2013, San Francisco, California, United States

Abstract

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.

Citation Download Citation

Jie Sun, Yuan Chen, and Shin-Tson Wu "Submillisecond-response IR spatial light modulators with polymer network liquid crystal", Proc. SPIE 8642, Emerging Liquid Crystal Technologies VIII, 864207 (5 March 2013); https://doi.org/10.1117/12.2004306

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KEYWORDS

Liquid crystals

Scattering

Polymers

Light scattering

Reflectivity

Modulators

Phase shifts

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