Optimizing performance parameters for switchable polymer dispersed liquid crystal optical elements

• US 6,950,173 B1
• Filed: 04/08/2003
• Issued: 09/27/2005
• Est. Priority Date: 04/08/2003
• Status: Active Grant

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Siwecki, Stephen A., Tondiglia, Vince P., Sutherland, Richard L.
• Primary Examiner(s): CHOWDHURY, TARIFUR RASHID
• Application Number:
  US10/408,259
• Time in Patent Office: 903 Days
• Field of Search: 349/86, 349/201, 359/3, 359/7, 359/15, 430/1
• US Class Current: 349/201
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G03H 1/22 Processes or apparatus for obtaining an optical image from holograms G03H1/26 - G03H1/34 take precedence
• CPC Class Codes: G03H 2250/38 Liquid crystal

Abstract

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.

Claims

1. An inverse mode switchable grating system comprising:

a holographically polymerized polymer dispersed liquid crystal material having a switchable grating formed therein;

at least a first and a second electrode for applying a switching field to the switchable grating in order to vary a diffraction efficiency thereof, wherein application of the switching field increases the diffraction efficiency of the switchable grating and removal of the switching field decreases the diffraction efficiency of the switchable grating;

a light signal having a p-polarization component and an s-polarization component; and

wherein the grating is oriented such that an internal angle of p-polarized light incident thereon satisfies the following condition for a switching field of zero, $\tan <br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\theta <br><br>}}_{\mathrm{\rho <br><br>}}={\left(\frac{{\mathrm{\epsilon <br><br>}}_{\mathrm{xx}}^{\left(1\right)}}{{\mathrm{\epsilon <br><br>}}_{\mathrm{zz}}^{\left(1\right)}}\right)}^{1/2}$

wherein θ

_p is the angle of incidence of a reference wave of the incident light and ∈

_xx⁽¹⁾ and ∈

_zz⁽¹⁾ are the x and z components of the modulation of a dielectric tensor for a material comprising the grating.

2. The inverse mode switchable grating system of claim 1, wherein the light signal is incident upon the switchable grating at an incident angle greater than zero.

3. The inverse mode switchable grating system of claim 2, wherein the application of the switching field to the switchable grating increases the diffraction efficiency of the p-polarization component of the incident light signal.

4. The inverse mode switchable grating system of claim 1, wherein the holographically polymerized polymer dispersed liquid crystal material is anisotropic.

5. The inverse mode switchable grating system of claim 1, wherein the switchable grating is a reflection grating.