Optimizing performance parameters for switchable polymer dispersed liquid crystal optical elements
View Patent ↗Described herein are the materials, mechanisms and procedures for optimizing various performance parameters of HPDLC optical devices in order to meet differing performance requirements. These optimization tailoring techniques include control and independent optimization of switchable HPDLC optical devices to meet the demanding requirements of anticipated applications for, inter alia, the telecommunications and display industries. These techniques include optimization of diffraction efficiency, i.e., index modulation, polarization dependence control, haze, cosmetic quality, control of response and relaxation time, voltage driving for on and off switching, and material uniformity. This control and independent optimization tailors properties of switchable HPDLC optical devices according to the specific requirements of the application of the switchable HPDLC optical device. The invention disclosed herein retains the desirable attributes of the multi-functional acrylate system for forming HPDLC optical devices, but adds new materials to the acrylate system and/or new process control to the recording to optimize performance parameters as may be needed for specific applications. This results in high optical quality switchable holograms with good diffraction efficiency and low, stable switching voltage.
1. A method for driving a polymer dispersed liquid crystal hologram comprising:
providing a polymer dispersed liquid crystal hologram between a first and second substrate, the first and second substrate having a first and second electrode pattern thereon, respectively, for applying a switching voltage to the polymer dispersed liquid crystal hologram, wherein the first and second electrode patterns consist of interdigitated electrodes;
applying a first voltage scheme, wherein a voltage approximately equal to the switching voltage is applied to the interdigitated electrodes on the first substrate and the interdigitated electrodes on the second substrate are connected to ground in order to drive the polymer dispersed liquid crystal hologram off; and
removing the first voltage scheme and applying a second voltage scheme, wherein a voltage approximately equal to the switching voltage is applied to every other interdigitated electrode on the first and second substrates and the intermittent electrodes therebetween are connected to ground in order to drive the polymer dispersed liquid crystal hologram on.
2. The method of claim 1 , wherein a response time to the application of the first and second voltage schemes is approximately given by
τ
on
∼
γ
1
Δ
ɛ
E
2
wherein γ 1 is the rotational viscosity coefficient of the liquid crystal, Δ∈ is the dielectric anisotropy, and E is the electric field established between the first and second electrode patterns.
3. The method of claim 2 , wherein the electric field is greater than the critical electric field for switching.
4. The method of claim 2 , further comprising the step of driving the polymer dispersed liquid crystal hologram to produce a waveform that is longer than the response time.
5. The method of claim 4 , wherein a first cycle of the waveform has a faster response time than a second cycle of the waveform.
6. The method of claim 4 , wherein the first cycle of the waveform has a faster response time than later cycles of the waveform.
7. The method of claim 6 , wherein the later cycles are approximately equal to E c , the critical electric field established between the first and second electrode patterns.
8. The method of claim 1 , wherein the polymer dispersed liquid crystal hologram is driven at approximately 500 to 2000 Hz.
9. The method of claim 1 , wherein the polymer dispersed liquid crystal hologram, the first and second substrate, and the first and second electrode patterns comprise a device; wherein the desired response time of the device is faster than 500 Hz.
10. The method of claim 1 , wherein the polymer dispersed liquid crystal hologram, the first and second substrate, and the first and second electrode patterns comprise a device; wherein the desired response time of the device is faster than 2000 Hz.
11. The method of claim 1 , wherein the interdigitated electrodes of the first electrode pattern are staggered with respect to the interdigitated electrodes of the second electrode pattern.
12. The method of claim 1 , wherein the first electrode pattern is a solid planar patttern.
13. The method of claim 1 , wherein the second electrode pattern is a solid planar pattern.
14. The method of claim 1 , wherein each of the interdigitated electrodes has a height (h) and each of the interdigitated electrodes are separated by a separation (b), wherein each of (h) and (b) are approximately equal to the width of the polymer dispersed liquid crystal optical material.
15. The method of claim 14 , wherein h is about 10 μm.
16. The method of claim 14 , wherein b is about 10 μm.
17. The method of claim 1 , wherein the first and second substrates comprise a glass plate.
18. The method of claim 1 , wherein the second voltage scheme produces an in-plane electric field.
19. The method of claim 1 , wherein a response time when a critical electric field is applied is approximately given by
τ
on
∼
γ
1
4
Δ
ɛ
E
c
2
wherein γ 1 is the rotational viscosity coefficient of the polymer dispersed liquid crystal hologram, Δ∈ is the dielectric anisotropy, and E c is the critical electric field established between the first and second electrode patterns.
20. The method of claim 19 , wherein (2+σ LC /σ p )/3 is approximately equal to 1, wherein σ LC is the electrical conductivity of the liquid crystal and σ p is the electrical conductivity of the polymer.