Liquid crystal lens with doping of rutile titanium dioxide nanoparticles

Abstract

A 4 mm-aperture hole-patterned liquid crystal (LC) lens has been fabricated using a LC mixture, which consisted of rutile titanium dioxide (TiO2) nanoparticles (NPs) and nematic LC E7, for the first time. The TiO2 NP dopant improves the addressing and operation voltages of the LC lens significantly because it strengthens the electric field surrounding the TiO2 NP and increases the capacitance of lens cell. Unlike the doping of common colloidal NPs, that of rutile TiO2 NPs increases the phase transition temperature and birefringence of the LC mixture, thereby helping enhance the lens power of LC lens. In comparison with a pure LC lens, the TiO2 NP-doped one has approximately 50% lower operation voltage because of the strengthened electric field around the NPs and has roughly 2.8 times faster response time because of the decreased rotational viscosity of the LC mixture and the increased interaction between the LC molecules by the NP dopants. Notably, the doping of rutile TiO2 NPs improves the operation voltage, tunable focusing capability, and response time of LC lens simultaneously. Meanwhile, this method does not degrade the focusing and lens qualities. The imaging performances of TiO2 NP-doped LC lens at various voltages are demonstrated practically by tunable focusing on three objectives at different positions. These results introduce NP in the application of LC lenses.

Superior improvement in dynamic response of liquid crystal lens using organic and inorganic nanocomposite

“…The response time of the HLC lenses was obtained by measuring the focus and defocus transient intensities. In comparison with previous manners 15 , 16 , BR composite doping further enhances the response speed of HLC lens; accordingly, the BR composite-doped HLC lens has the short focus and defocus times, which are 8.5× and 14× faster than the pristine HLC lens, respectively. Meanwhile, the focus and defocus times of the BR composite-doped HLC lens reach the order of milliseconds.…”

“…The ITO surface of the top glass substrate was etched with a circular-hole pattern of 4 mm diameter by the photolithography process. The inner surfaces of both substrates were coated with a homogeneous polyimide (PI) AL 1426 CA (Daily Polymer Kaohsiung, Taiwan) and rubbed in antiparallel directions 15 . The cell gap of lens cell was controlled at ~ 40 μm thick by Mylar spacer.…”

“…Ltd, Australia) at the concentration ratio of 96.5:0.5:3. The concentration ratios of TiO 2 NP and BNA were decided according to our previous works 15 , 16 . The supplier information indicated that LC E7 had a dielectric anisotropy Δε of 14.5, birefringence Δn of 0.216 at room temperature, and elastic constants K 11 , K 22 , and K 33 of 11.1, 5.9, and 17.1 pN, respectively; the average diameter of the rutile TiO 2 NP was ~ 20 nm 14 .…”

“…The focus (defocus) time was defined as the time during which the intensity of the HLC lens reached stable when the supplied voltage (100 V) was suddenly turned on (off). With the measurement method, the response speed of the BR composite-doped HLC lens can be compared with those of the HLC lenses demonstrated in our previous works 15 , 16 . The measurement in focus and defocus times of HLC lens evaluate the wavefront bending characteristics, but that in rise and fall times of LC cell evaluate the transmissions.…”

“…Other manners, such as polymer-stabilized LCs 13 and nanoparticle (NP) dispersion 14 , were also reported to improve the dynamic response of LC devices. In our recent studies, the inorganic rutile titanium dioxide (TiO 2 ) NP doping was used to fabricate the 4 mm aperture HLC lens 15 . The TiO 2 NP-doped HLC lens had the focus and defocus times, which were 3.6× and 2.3× faster than the pristine HLC lens, respectively.…”