Spectrum-controllable reflective polarizers having electrically-switchable modes of operation

• US 20040095523A1
• Filed: 09/05/2003
• Published: 05/20/2004
• Est. Priority Date: 11/27/1991
• Status: Active Grant

• Current Assignee: Bunsen Fan, Jian-Feng Li, Le Li, Sadeg M. Faris, Sameer Vartak, Yingqiu Jiang
• Original Assignee: Bunsen Fan, Jian-Feng Li, Le Li, Sadeg M. Faris, Sameer Vartak, Yingqiu Jiang
• Inventors: Li, Jian-Feng, Faris, Sadeg M., Li, Le, Jiang, Yingqiu, Fan, Bunsen, Vartak, Sameer
• Granted Patent: US 6,965,420 B2
• Time in Patent Office: Days
• US Class Current: 349/86
• CPC Class Codes: B82Y 15/00 Nanotechnology for interacting, sensing or actuating, e.g. quantum dots as markers in protein assays or molecular motors
• CPC Class Codes: C09B 67/0098 Organic pigments exhibiting interference colours, e.g. nacrous pigments
• CPC Class Codes: C09D 11/037 characterised by the pigment
• CPC Class Codes: C09D 11/17 characterised by colouring agents
• CPC Class Codes: C09K 19/00 Liquid crystal materials
• CPC Class Codes: C09K 19/52 characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
• CPC Class Codes: E06B 2009/2464 featuring transparency control by applying voltage, e.g. LCD, electrochromic panels
• CPC Class Codes: E06B 9/24 Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blindsoperating, guiding or securing devices or arrangements for roll-type closures E06B9/56; free-hanging flexible screens A47H23/00
• CPC Class Codes: F24S 50/80 for controlling collection or absorption of solar radiation
• CPC Class Codes: G01D 11/28 Structurally-combined illuminating devices
• CPC Class Codes: G02B 27/0093 with means for monitoring data relating to the user, e.g. head-tracking, eye-tracking
• CPC Class Codes: G02B 5/3016 involving passive liquid crystal elements optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528
• CPC Class Codes: G02F 1/133365 Cells in which the active layer comprises a liquid crystalline polymer
• CPC Class Codes: G02F 1/1334 based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
• CPC Class Codes: G02F 1/13345 Network or three-dimensional gels
• CPC Class Codes: G02F 1/133514 Colour filters
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133543 Cholesteric polarisers
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence
• CPC Class Codes: G02F 1/133623 : Inclined coloured light beams
• CPC Class Codes: G02F 1/13471 : in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells G02F1/13475 takes precedence
• CPC Class Codes: G02F 1/13718 : based on a change of the texture state of a cholesteric liquid crystal
• CPC Class Codes: G02F 1/1393 : the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 2203/07 : Polarisation dependent
• CPC Class Codes: Y02E 10/40 : Solar thermal energy, e.g. solar towers

Abstract

A light controlling film is disclosed, comprising a polymerized polymer network varying spatially in a direction normal to the film surface, where the polymerized polymer network is a crosslinked high molecular weight polymeric material mixed with a low molecular weight nematic material exhibiting cholesteric liquid crystal (CLC) order, wherein an electric field impressed in the film controls the reflection bandwidth of circularly polarized light.

Claims

1. A light controlling film, the film having a first surface and a second surface, comprising:

a polymerized polymer network, the polymer network varying spatially in a direction normal to the first surface, the polymerized polymer network comprising;

a crosslinked high molecular weight polymeric material; and

a low molecular weight polymeric material, wherein the high molecular weight and the low molecular weight form a material having cholesteric liquid crystal (CLC) order, the CLC order oriented with respect to the first and the second surfaces, the pitch of the CLC order varying non-linearly in a direction perpendicular to the first surface, and

wherein light having a first polarization and a broad bandwidth incident on the first surface is substantially reflected from the film, and wherein light having a second polarization and the broad bandwidth incident on the first surface is not substantially reflected from the film, and wherein an electric field impressed in the film controls the reflection of light having the first polarization when the electric field has a component in a direction normal to the first surface.

5. The light controlling film of claim 1, further comprising electrically conducting material adjacent to the first surface for impressing an electric field in the film, the electrically conducting material transmitting the light having the broad bandwidth and the first polarization.

6. The apparatus of claim 5, further comprising a second electrically conducting material adjacent to the second surface, wherein a voltage applied between the first and the second electrically conducting material impresses an electric field on in the film.

7. The apparatus of claim 6, wherein the second electrically conducting material transmits light having the first bandwidth.

8. The apparatus of claim 6, wherein the first polarization is a circular polarization.

9. The apparatus of claim 8, further comprising a transparent quarter wave retardation plate in close proximity to the first surface, whereby linearly polarized light incident on the transparent quarter wave retardation plate is controllably reflected.

10. The apparatus of claim 5, further comprising a means for applying an electric field in the film, the electric field varying spatially over the first surface, whereby polarized light is controllably reflected for display purposes.

11. The apparatus of claim 5, further comprising a means for applying an electric field in the film, the electric field having a controllable bias field and a controllable adjustment field, whereby the reflectivity of polarized light may be substantially changed by changing the controllable adjustment field.

12. The apparatus of claim 5, further comprising optical communication means, whereby the light in the optical communication means is controlled.

13. The apparatus of claim 5, further comprising means for directing light on to the first surface, and means for receiving reflected light from the first surface, whereby polarized light with a controllable bandwidth produced in the means for receiving reflected light.

14. The apparatus of claim 5, further comprising laser cavity means, whereby the output of the laser cavity means is controlled by the film when the film is used as a reflective element in the laser cavity.

15. The apparatus of claim 5, further comprising a transparent quarter wave retardation plate in close proximity to the first surface, whereby linearly polarized light incident on the transparent quarter wave retardation plate is controllably reflected.

2. The light controlling film of claim 1, wherein the crosslinked high molecular weight polymeric material is less than 20% by weight of the film.

3. The light controlling film of claim 2, wherein the crosslinked high molecular weight polymeric material is less than 15% by weight of the film.

4. The light controlling film of claim 3, wherein the crosslinked high molecular weight polymeric material is less than 10% by weight of the film.

16. A method of making a light controlling film, the film having a first surface and a second surface, comprising:

applying a mixture of high molecular weight polymeric material and low molecular weight polymeric material on a surface which produces a CLC order in the mixture; and

crosslinking the high molecular weight polymeric material so that the low molecular weight material significantly diffuses throughout the film and remains distributed in a non uniform fashion across the film from the first surface to the second surface;

wherein light having a first polarization and a broad bandwidth incident on the first surface is substantially reflected from the film, and wherein light having a second polarization and the broad bandwidth incident on the first surface is not substantially reflected from the film, and wherein an electric field impressed in the film substantially decreases the reflection of light of the first polarization and broad bandwidth.

17. The method of claim 16, wherein the step of crosslinking takes place in a time t1 long compared to the time t2 in which the low molecular weight material can significantly diffuse.

18. The method of claim 17, wherein the step of crosslinking takes place includes irradiation of the film by low intensity ultraviolet radiation.

19. The method of claim 18, wherein the step of crosslinking takes place includes irradiation of the film by high intensity ultraviolet radiation having a radiation intensity of less than 1 mw/cm2.

20. The method of claim 17, wherein the step of crosslinking takes place includes irradiation of the film by high energy electrons where the electron where the electron energy deposition varies substantially throughout the film.

21. The method of claim 17, wherein the step of crosslinking takes place includes irradiation of the film by light which is substantially nonuniformly absorbed throughout the film.

22. The method of claim 17, wherein the step of crosslinking takes place includes heating the film substantially nonuniformly across the film.

23. A system for controlling EM radiation comprising:

a substrate;

a single layer of material on the substrate, the material reflecting the electromagnetic (EM) radiation, the reflected EM radiation being polarized, the reflected EM radiation having a broad bandwidth;

an electric field generator for generating a variable electric field in the layer of material; and

a controller for controlling the electric field generator;

whereby the controller controls the electric field generator to generate a field in the layer of material and whereby the reflected EM radiation changes in response to the change of the electric field.

24. A switchable single layer reflective polarizer for reflecting light of a first polarization, the single layer reflective polarizer having a non linear distribution of polarized light reflecting molecules such that the bandwidth of polarized light reflected from the reflective polarizer is very broad, and wherein an electric field impressed across the single layer changes the reflectivity of the single layer.

25. The switchable reflective polarizer of claim 24 in combination with an additional switchable reflective polarizer reflecting the opposite polarization, whereby the bandwidth of both polarizations of light reflected from the combination is very broad, and whereby the reflectivity of light in the broad bandwidth may be controlled by the electric field.

26. The switchable reflective combination of claim 25 controllably reflecting visible light in combination with a broad band infra-red reflecting and visible transmitting component, whereby visible light may be controllably transmitted and infra-red light may be reflected.

27. The switchable reflective combination of claim 25 controllably reflecting visible light in combination with a switchable reflective combination of claim 25 controllably reflecting infra-red light, whereby visible light may be controllably transmitted and infra-red light may be controllably transmitted.

54. The switchable reflective combination of claim 52 controllably reflecting visible light in combination with a switchable reflective combination of claim 25 controllably reflecting infra-red light, whereby visible light may be controllably transmitted and infra-red light may be controllably transmitted.

28. A light controlling film, the film having a first surface and a second surface, comprising:

a polymerized polymer network, comprising;

a crosslinked high molecular weight polymeric material; and

a low molecular weight cholesteric liquid crystal (CLC) material, wherein the high molecular weight and the low molecular weight form a material having cholesteric liquid crystal (CLC) order, the CLC order oriented with respect to the first and the second surfaces, and

wherein light having a first polarization and a first bandwidth incident on the first surface is substantially reflected from the film, and wherein light having a second polarization and the first bandwidth incident on the first surface is not substantially reflected from the film, and wherein an electric field impressed in the film substantially changes the first bandwidth of reflection of light having the first polarization.

29. The light controlling film of claim 28, wherein the crosslinked high molecular weight polymeric material is less than 20% by weight of the film.

30. The light controlling film of claim 29, wherein the crosslinked high molecular weight polymeric material is less than 15% by weight of the film.

31. The light controlling film of claim 30, wherein the crosslinked high molecular weight polymeric material is less than 12% by weight of the film.

32. The light controlling film of claim 28, wherein the proportion of crosslinked high molecular weight material to low molecular weight material is substantially constant across the film from the first surface to the second surface.

33. The light controlling film of claim 28, further comprising a first electrically conducting material adjacent to the first surface, the first electrically conducting material for impressing an electric field in the film, the first electrically conducting material transmitting light having the first bandwidth.

34. The apparatus of claim 33, further comprising a second electrically conducting material adjacent to the second surface, wherein a voltage applied between the first and the second electrically conducting material impresses an electric field on in the film.

35. The apparatus of claim 34, wherein the second electrically conducting material transmits light having the first bandwidth.

36. The apparatus of claim 34, wherein the first polarization is a circular polarization.

37. The apparatus of claim 36, further comprising a transparent quarter wave retardation plate in close proximity to the first surface, whereby linearly polarized light incident on the transparent quarter wave retardation plate is controllably reflected.

38. The apparatus of claim 33, further comprising a means for applying an electric field in the film, the electric field varying spatially over the first surface, whereby polarized light is controllably reflected for display purposes.

39. The apparatus of claim 33, further comprising optical communication means, whereby the bandwidth of light in the optical communication means is controlled.

40. The apparatus of claim 33, further comprising means for directing light on to the first surface, and means for receiving light from the first surface, whereby polarized light with a controllable bandwidth produced in the means for receiving light.

41. The apparatus of claim 33, further comprising laser cavity means, whereby the bandwidth of the light output of the laser cavity means is controlled by the film when the film is used as a reflective element in the laser cavity.

42. The apparatus of claim 33, further comprising a transparent quarter wave retardation plate in close proximity to the first surface, whereby linearly polarized light incident on the transparent quarter wave retardation plate is controllably reflected.

43. A method of making a light controlling film, the film having a first surface and a second surface, comprising:

applying a mixture of high molecular weight polymeric material and

low molecular weight polymeric material on a surface which produces a CLC order in the mixture; and

crosslinking the high molecular weight polymeric material so that the low molecular weight material does not significantly diffuse and remains uniformly distributed in the film;

wherein light having a first polarization and a first bandwidth incident on the first surface is substantially reflected from the film, and wherein light having a second polarization and the first bandwidth incident on the first surface is not substantially reflected from the film, and wherein an electric field impressed in the film substantially increases the first bandwidth of reflection of light having the first polarization.

44. The method of claim 43, wherein the step of crosslinking takes place in a time t1 short compared to the time t2 in which the low molecular weight material can significantly diffuse.

45. The method of claim 44, wherein the step of crosslinking takes place includes irradiation of the film by high intensity ultraviolet radiation.

46. The method of claim 45, wherein the step of crosslinking takes place includes irradiation of the film by high intensity ultraviolet radiation having a radiation intensity of greater than 0.1 watts/cm2.

47. The method of claim 43, wherein the step of crosslinking takes place includes irradiation of the film by high energy electrons where the electron where the electron energy deposition is substantially constant throughout the film.

48. The method of claim 43, wherein the step of crosslinking takes place includes irradiation of the film by light which is substantially uniformly absorbed throughout the film.

49. The method of claim 43, wherein the step of crosslinking takes place includes heating the film substantially uniformly throughout the film.

50. A system for controlling unpolarized electromagnetic (EM) radiation comprising:

a substrate;

a single layer of material on the substrate, the material reflecting the electromagnetic (EM) radiation, the reflected EM radiation being polarized, the reflected EM radiation having a bandwidth;

an electric field generator for generating a variable electric field in the layer of material; and

a controller for controlling the electric field generator;

whereby the controller controls the electric field generator to generate a field in the layer of material and whereby the bandwidth of the reflected EM radiation changes in response to the change of the electric field.

51. A switchable reflective polarizer for reflecting light of a first polarization, wherein the bandwidth of polarized light reflected from the reflective polarizer may be changed from a broad bandwidth to a narrower bandwidth by the application of an voltage to the reflective polarizer.

52. The switchable reflective polarizer of claim 51 in combination with an additional switchable reflective polarizer reflecting the opposite polarization, whereby the bandwidth of all light reflected from the combination may be changed from a broad bandwidth to a narrower bandwidth by the application of an voltage to the reflective polarizer.

53. The switchable reflective combination of claim 52 controllably reflecting visible light in combination with a broad band infra-red reflecting and visible transmitting component, whereby visible light may be controllably transmitted and infra-red light may be reflected.

55. A single layer polarizing film having a very wide bandwidth which is switchable.

56. A switchable reflecting polarizing filter having a very wide bandwidth which is controllable by an electric field.

58. A “

smart window”

using a polarizing reflective film having a very wide bandwidth.

59. A smart window using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having a very wide bandwidth.

62. A reflective polarizing film having a bandwidth which is controllable by an electric field.

63. A smart window using a polarizing reflective film having a very wide bandwidth which is controllable by an electric field.

64. An electrically-switchable family of infrared reflective polarizers and filters, based on the remarkable properties of cholesteric liquid crystals (CLCs), having far-reaching dual-use aerospace and window-glazing applications.

65. An electrically controllable polarizer that can be remotely controlled and involves no moving parts, to active-solar-control window glazings having the unheard-of property of infrared switchability while maintaining total visible transparency.

66. A near-infrared switchable polarizer embodied in a remote-controlled optical component.

67. A electrically-switchable infrared reflective polarizer capable of switching from broad-to-narrow band reflective operation over the IR band.

68. A electrically-switchable infrared reflective polarizer, wherein its rise time is about at least 14.5 ms and its fall time is about at least 8.5 ms.

69. A smart window using a polarizing reflective film having a very wide bandwidth combined with a reflective multilayer polymer film having little variation in the reflectivity outside of the reflective bandwidth of the film.

70. A switchable reflective film having little variation in the reflectivity outside of the reflective bandwidth of the film.

70-1. A smart window using a polarizing reflective multilayer polymer film having a very wide bandwidth combined with a light scattering layer for further control of transmitted light.

71. A electrically-switchable infrared reflective polarizer capable of switching from narrow-to-broad band reflective operation over the IR band.

71-2. An electrically switchable IR reflector based on an electrically switchable broadband reflective polarizer that operates in the IR region from 780 nm to 4 microns.

72. An electrically-tunable infrared reflective polarizer.

73. A left and right-handed CLC based switchable broadband polarizers that operate in the IR region from 780 nm to 4 microns.

74. A field-switchable broadband reflective polarizer operable in the NIR spectral region.

75. A field-switchable broadband reflective polarizer operable in the spectral region from 700 to >

1000 nm, and having a polarizing bandwidth and extinction ratio which are changeable via an applied electric field.

76. A method of optimizing the performance of such electro-optical structures in terms of extinction ratio, overall reflectivity, and reflection spectral cutting-off edge.

77. A material recipe for making the switchable, broadband-to-narrow-band polarizers and which enables further expansion of the polarizer bandwidth, shift to longer wavelengths, and increase the extinction ratio to the desired level.

78. A method of making such electrically-switchable IR reflective polarizers, using liquid crystal polymeric compounds having different pitch, cross-linking density, and polymerization rate.

79. An electrically-controllable narrow-band reflective polarizer which undergoes a shift in reflection band, rather than a broadening in bandwidth when a DC voltage is applied.

80. A method of precisely electrically tuning the CLC center wavelength by applying an electric field, without affecting the other specifications of the polarizer, such as polarization, extinction ratio, and bandwidth.