Temperature activated optical films
First Claim
1. A multilayer dielectric optical structure, for selectively reflecting a predetermined wavelength, comprising:
- a transparent substrate;
a plurality of alternating first layers and second layers on the substrate, wherein the first layers comprise a first optical material having a first optical axis and a first refractive index along the first optical axis, and wherein the second layers comprise a second optical material having a second optical axis and a second refractive index along the second optical axis below a characteristic transition temperature (Tc) and a third refractive index above the Tc, wherein the second optical material includes a liquid crystal material having an isotropic-to-ordered state transition temperature between 15 and 35 degrees Celsius, wherein the first and second optical axes are substantially parallel and the first and second refractive indices are substantially equal, and wherein the third refractive index differs from the second refractive index and from the first refractive index; and
wherein the optical thickness of each of the first layers is equal to ¼
times the predetermined wavelength and the optical thickness of each of the second layers is equal to ¼
times the predetermined wavelength when the temperature is above the Tc.
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Abstract
The present invention discloses a multilayer dielectric optical structure wherein one of the optical materials in the multilayer structure shows an optically isotropic state above and a birefringent state below a characteristic temperature Tc near the room temperature. The optical structure reflects a predetermined wavelength range of electromagnetic radiation above the Tc but allow the same to transmit through below the Tc. The predetermined wavelength can be the near infrared radiation from 700 nm to 2500 nm, and the optical structure rejects solar heat in warm summer days but admits the same to interior on a colder winter day.
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Citations
20 Claims
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1. A multilayer dielectric optical structure, for selectively reflecting a predetermined wavelength, comprising:
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a transparent substrate; a plurality of alternating first layers and second layers on the substrate, wherein the first layers comprise a first optical material having a first optical axis and a first refractive index along the first optical axis, and wherein the second layers comprise a second optical material having a second optical axis and a second refractive index along the second optical axis below a characteristic transition temperature (Tc) and a third refractive index above the Tc, wherein the second optical material includes a liquid crystal material having an isotropic-to-ordered state transition temperature between 15 and 35 degrees Celsius, wherein the first and second optical axes are substantially parallel and the first and second refractive indices are substantially equal, and wherein the third refractive index differs from the second refractive index and from the first refractive index; and wherein the optical thickness of each of the first layers is equal to ¼
times the predetermined wavelength and the optical thickness of each of the second layers is equal to ¼
times the predetermined wavelength when the temperature is above the Tc. - View Dependent Claims (2, 3, 4, 5, 6, 11, 12, 13, 14, 15, 17, 18, 19, 20)
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7. A multilayer dielectric optical structure, for selectively reflecting a predetermined wavelength, comprising:
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a transparent substrate; a plurality of alternating first layers and second layers on the substrate, wherein the first layers comprise a first optical material having a first optical axis and a first refractive index along the first optical axis, and wherein the second layers comprise a second optical material having a second optical axis and a second refractive index along the second optical axis below a characteristic transition temperature (Tc) and a third refractive index above the Tc, wherein the second layer includes a polymer mesh at less than 10 weight % for maintaining mechanical stability and for limiting mobility of a liquid crystal material, wherein the first and second optical axes are substantially parallel and the first and second refractive indices are substantially equal, wherein the third refractive index differs from the second refractive index and from the first refractive index; and wherein the optical thickness of each of the first layers is equal to ¼
times the predetermined wavelength and the optical thickness of each of the second layers is equal to ¼
times the predetermined wavelength when the temperature is above the Tc. - View Dependent Claims (8, 9, 10)
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16. A multilayer dielectric optical system, comprising:
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a transparent substrate; a plurality of dielectric pairs, wherein each pair comprises a first layer of a first optical material having a first refractive index and a liquid crystal layer having a third isotropic refractive index when temperature is above a transition temperature, wherein the optical thickness of the first layer equals the optical thickness of the liquid crystal layer which equals ¼
of a predetermined wavelength λ
0, wherein the number of dielectric pairs is between 1 to 500; andthe optical thickness of each adjacent pair is in accordance to the formula;
dN+1=r dNfirst layer =¼
λ
0where dN is the optical thickness of Nth pair, it is the two times the optical thickness of each layer in the pair and r is a numerical number between 0.85 to 0.999.
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Specification