Switchable polymer-dispersed liquid crystal optical elements
View Patent ↗Transmission and reflection type holograms may be formed utilizing a novel polymer-dispersed liquid crystal (PDLC) material and its unique switching characteristics to form optical elements. Applications for these switchable holograms include communications switches and switchable transmission, and reflection red, green, and blue lenses. The PDLC material of the present invention offers all of the features of holographic photopolymers with the added advantage that the hologram can be switched on and off with the application of an electric field. The material is a mixture of a polymerizable monomer and liquid crystal, along with other ingredients, including a photoinitiator dye. Upon irradiation, the liquid crystal separates as a distinct phase of nanometer-size droplets aligned in periodic channels forming the hologram. The material is called a holographic polymer-dispersed liquid crystal (H-PDLC).
1. A method for forming a switchable holographic waveguide filter comprising:
etching a channel into a substrate;
filling the channel with a polymerizable material;
forming at least two sets of electrodes on the substrate, wherein forming the at least two sets of electrodes further comprises:
coating the substrate with an electrically conductive material;
covering the electrically conductive material with a photoresist;
exposing the photoresist to light and dark regions of radiation;
etching the photoresist to form alternating regions of electrically conductive material and substrate; and
exposing the polymerizable material to at least two interfering light beams in order to form a hologram therein.
2. The method according to claim 1 , wherein the substrate is selected from the following group consisting of glass and a polymer material.
3. The method according to claim 1 , wherein the polymerizable material comprises at least one type of liquid crystal material.
4. The method according to claim 3 , wherein the polymerizable material further is made from;
(a) a polymerizable monomer comprising at least one acrylate;
(b) a chain-extending monomer;
(c) a coinitiator; and
(d) a photoinitiator.
5. The method according to claim 1 , wherein the at least two interfering light beams are incident upon the polymerizable material from the same side of the substrate.
6. The method according to claim 1 , further comprising curing the exposed polymerizable material.
7. The method according to claim 1 , wherein the hologram is a grating.
8. The method according to claim 1 , wherein forming the at least two sets of electrodes comprises sputtering an electrically conductive material onto the substrate.
9. The method according to claim 8 , wherein the electrically conductive material is selected from the group consisting of gold, aluminum, and indium-tin-oxide.
10. The method according to claim 1 , wherein exposing the polymer-dispersed liquid crystal material and exposing the substrate coated with the electrically conductive material occur simultaneously with a single source of radiation.