Wide band variable transmittance optical device and mixture

1. An optical device comprising:

a cell comprising a guest-host mixture of a liquid crystal host and a dichroic guest dye material contained between a pair of plastic substrates,

wherein the liquid crystal host has an axis orientation that is alterable between a clear state orientation when no voltage is applied to the cell and a dark state orientation perpendicular thereto when a voltage is applied to the cell;

wherein the liquid crystal host comprises a chiral nematic material with a thickness to pitch ratio (d/p) of less than 0.9 but greater than 0.25;

wherein the dichroic guest dye material comprises one or more dichroic dyes;

wherein said guest-host mixture has an order parameter, S mix , greater than 0.78 and a nematic-isotropic transition temperature T NI greater than 40° C.;

wherein said pair of plastic substrates have an optical retardation with less than ±20% variation in uniformity for any given wavelength of incident light;

wherein the optical device does not use polarizers;

wherein the optical device exhibits a wide absorption band having an aggregate full width at half maximum (A-FWHF) that is greater than 175 nm within a visible wavelength range of 400-700 nm; and

wherein the optical device has a variable transmission with a dark state transmission equal to or below 40% and a transmission swing between the clear state orientation and the dark state orientation greater than or equal to 30%.

2. The optical device of claim 1 , wherein said guest-host mixture has a dichroic ratio D mix greater than 11.5.

3. The optical device of claim 1 , wherein said one or more dichroic dyes in the dichroic guest dye material are azo-based dyes having at least two azo groups.

4. The optical device of claim 3 , wherein said azo-based dyes have 2-6 azo groups.

5. The optical device of claim 1 , wherein said cell has a cell gap greater than 3 but less than 20 microns.

6. The optical device of claim 1 , further having a transmission swing greater than or equal to 40%.

7. The optical device of claim 1 , wherein said guest-host mixture has an order parameter, S mix , greater than or equal to 0.79.

8. The optical device of claim 1 , wherein said guest-host mixture has an order parameter, S mix , greater than or equal to 0.8.

9. The optical device of claim 1 , wherein:

said guest-host mixture comprises one or more dichroic dyes with a dichroic ratio greater than 11.5;

said guest-host mixture has a nematic-isotropic transition temperature T NI greater than 60° C.;

said cell has a cell gap greater than 3 but less than 20 microns; and

said device has a transmission swing greater than or equal to 40%.

10. A guest-host mixture comprising a mixture of a liquid crystal host having a negative dielectric anisotropy and a dichroic guest dye material having positive dichroism;

wherein the liquid crystal host has an axis orientation that is alterable between a clear state orientation in the absence of a voltage and a dark state orientation perpendicular thereto when a voltage is applied;

wherein the dichroic guest dye material comprises one or more dichroic dyes;

wherein said guest-host mixture has an order parameter, S mix , greater than 0.78 and a nematic-isotropic transition temperature T NI greater than 40° C.;

wherein the gust-host mixture exhibits a wide absorption band that is greater than 175 nm within a visible wavelength range of 400-700 nm; and

wherein the guest-host mixture has a dark state transmission equal to or below 40% and a transmission swing between the clear state orientation and the dark state orientation greater than or equal to 30%.

11. The guest-host mixture of claim 10 wherein said guest-host mixture has a transmission swing of greater than 50%.

12. The guest-host mixture of claim 11 , wherein said guest-host mixture comprises one or more dichroic dyes with a dichroic ratio greater than 13.

13. The guest-host mixture of claim 10 , wherein said guest-host mixture has a clear state transmission equal to or above 60% and a dark state transmission equal to or below 30%.

14. The optical device of claim 1 , wherein said optical device exhibits a wide absorption band with a A-FWHF that is greater than 190 nm within said visible wavelength range.

15. The optical device of claim 1 , wherein the liquid crystal host has negative dielectric anisotropy and the dichroic dye guest has positive dichroism.