Recent advances in polymer network liquid crystal spatial light modulators

Abstract

Polymer network liquid crystal (PNLC) spatial light modulators are attractive for display and photonic applications because they can achieve submillisecond response time while keeping a large phase change. However, their on-state scattering caused by the grain boundary of LC multidomains hinders their applications. In this article, we review recent progress on the development of scattering-free PNLCs extending from short-wavelength infrared to visible region by reducing the domain sizes to $200 nm through low temperature curing process. To reduce operation voltage, both transmissive and reflective modes, LC material properties (birefringence and dielectric anisotropy), polymer composition and concentration, and pretilt angle effect are analyzed.

Doping Liquid Crystal Cells with Photocurable Monomer via Holographic Exposure to Realize Optical-Scattering-Free Infrared Phase Modulators with Fast Response Time

“…In this method, the molecules of an anisotropic monomer like RM257 possessing an LC building block structure are usually doped with LCs and processed with UV exposure, so that the generated polymer networks provide constraints to LCs to effectively speed up the falling time during the relaxation of LC molecular reorientations. However, light scattering occurs due to the refractive index mismatch of polymer networks and LC microdomains [1]. The degree of light scattering can be reduced by using much smaller LC microdomains via optimal processing conditions such as monomer concentrations and photopolymerization conditions [9][10][11][12][13].…”

“…They are widely applied in various electro-optical devices including spatial light modulators, LC lenses, and displays [1][2][3]. For typical optical phase modulation, a homogeneous LC cell is usually adopted to provide maximum phase retardation (δ) using the equation δ = 2π∆nd/λ, where ∆n is LC birefringence, d is cell gap, and λ is incident wavelength [4].…”

Nematic copolymer network LCs for swift continuous phase modulation and opaque scattering states

“…Although the response times are sometimes found to be predetermined by the polymer content rather than the cell gap [5,[9][10][11], a thinner cell gap can still lead to even faster responses. A scattering state was induced in samples with a relatively low polymer content at low driving voltages of 8 -12 V, which might be useful in the development of multilayered privacy windows or modulators, where scattering can be enhanced through use of two or three copolymer network LC layers.…”

“…As compared with a polymer network LC, a copolymer network LC will have a higher responsiveness at the same overall polymer concentration [1]. For uses in electro-optical phase modulators [1][2][3][4][5][6][7][8][9][10][11] continuous phase modulation is highly desirable, where the optical phase shift can be varied reliably by varying the driving voltage. Although polymer network and copolymer network LCs show promising properties, they also may scatter light much more than a neat nematic LC, especially if addressed with intermediate driving voltages that lead to a partial realignment of the LC director in the cell (that is both the initial and high voltage state are scattering free).…”

A low voltage submillisecond-response polymer network liquid crystal spatial light modulator

“…Various LC technologies have been explored, such as ferroelectric LC, 10 dual frequency liquid crystal (DFLC), 11 stressed LC, 12,13 and polymer network liquid crystal (PNLC). 14,15 Each approach has its own pros and cons. Ferroelectric LC shows microsecond response time, but it is a bistable device and is difficult to obtain continuous phase-only modulation.…”