Switchable polymer-dispersed liquid crystal optical elements

• US 20010033400A1
• Filed: 12/22/2000
• Published: 10/25/2001
• Est. Priority Date: 07/12/1996
• Status: Active Grant

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Sutherland, Richard L., Kelly, William, Hagan, Bill, Epling, Bob
• Granted Patent: US 6,867,888 B2
• Time in Patent Office: Days
• US Class Current: 359/15
• CPC Class Codes: C09K 19/544 as dispersing or encapsulating medium around the liquid crystal
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• CPC Class Codes: G02F 1/1326 Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides
• CPC Class Codes: G02F 1/13342 Holographic polymer dispersed liquid crystals
• CPC Class Codes: G02F 1/13712 the liquid crystal having negative dielectric anisotropy
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: G02F 2201/346 distributed (Bragg) reflector
• CPC Class Codes: G02F 2203/05 wavelength dependent
• CPC Class Codes: G02F 2203/055 wavelength filtering
• CPC Class Codes: G02F 2203/585 Add/drop devices
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 2001/026 Recording materials or recording processes G03H2226/11 takes precedence; corresponding details, see subgroups of G03H2260/00
• CPC Class Codes: G03H 2001/0264 Organic recording material
• CPC Class Codes: G03H 2001/2231 Reflection reconstruction
• CPC Class Codes: G03H 2001/2234 Transmission reconstruction
• CPC Class Codes: G03H 2260/12 Photopolymer
• CPC Class Codes: G03H 2260/33 Having dispersed compound

Abstract

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).

Claims

1. A wavelength selective optical element comprising:

a first polymer-dispersed liquid crystal switchable holographic component for diffracting a wavelength of an incident beam; and

a second polymer-dispersed liquid crystal switchable holographic component for diffracting a wavelength of an incident beam, wherein the first and second polymer-dispersed liquid crystal switchable holographic components are located in stacked relationship with one another and placed in the path of the incident beam.

2. The wavelength selective optical element according to

claim 1

, wherein the incident beam is comprised of multiple wavelengths of radiation.

3. The wavelength selective optical element according to

claim 1

, wherein each of the first and second polymer-dispersed liquid crystal switchable holographic components comprises:

a pair of transparent conductive slides;

a voltage source electrically contacted to the pair of transparent conductive slides;

at least one spacer for separating the pair of transparent conductive slides;

a layer of polymer-dispersed liquid crystal material located within the confines of the pair of transparent conductive slides and the at least one spacer; and

a switchable holographic grating formed within the layer of polymer-dispersed liquid crystal material.

4. The wavelength selective optical element according to

claim 3

, wherein the polymer-dispersed liquid crystal material is made from:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

5. The wavelength selective optical element according to

claim 4

, wherein the polymerizable monomer comprises at least one of a di-, tri-, tetra-, and pentaacrylate.

6. The wavelength selective optical element according to

claim 5

, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

7. The wavelength selective optical element according to

claim 6

, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

8. The wavelength selective optical element according to

claim 7

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

9. The wavelength selective optical element according to

claim 4

, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

10. The wavelength selective optical element according to

claim 9

, wherein the surfactant is octanoic acid.

11. The wavelength selective optical element according to

claim 4

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises at least one cyanobiphenyl, the chain-extending monomer is N- vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal.

12. An optical system for wavelength selection comprising:

at least one coherent light source for inputting multiple wavelengths;

a first polymer-dispersed liquid crystal switchable holographic component for diffracting a first single wavelength of an incident beam;

a second polymer-dispersed liquid crystal switchable holographic component for diffracting a second single wavelength of an incident beam, wherein the first and second polymer-dispersed liquid crystal switchable holographic components are located in stacked relationship with one another and placed in the path of the incident beam; and

an output component for receiving from the first and second polymer-dispersed liquid crystal holographic components at least one of the following from the group consisting of;

(a) at least one of the first and second diffracted single wavelengths;

(b) all undiffracted multiple wavelengths; and

(c) both the first and second diffracted single wavelengths and the undiffracted multiple wavelengths.

13. The optical system for wavelength selection according to

claim 12

, wherein each of the first and second polymer-dispersed liquid crystal switchable holographic components are capable of diffracting a wavelength in the presence of an applied voltage and transmitting the remaining multiple inputted wavelengths in the absence of the applied voltage.

14. The optical system for wavelength selection according to

claim 12

, wherein each of the first and second polymer-dispersed liquid crystal switchable holographic components are capable of transmitting all of the multiple inputted wavelengths in the presence of an applied voltage.

15. The optical system for wavelength selection according to

claim 12

, wherein each of the first and second polymer-dispersed liquid crystal switchable holographic components are capable of diffracting a wavelength in the absence of an applied voltage and transmitting the remaining multiple inputted wavelengths in the presence of the applied voltage.

16. The optical system for wavelength selection according to

claim 12

, wherein each of the first and second polymer-dispersed liquid crystal switchable holographic components are capable of transmitting all of the multiple inputted wavelengths in the absence of an applied voltage.

17. The optical system for wavelength selection according to

claim 12

, wherein the multiple wavelength input component is a laser.

18. The optical system for wavelength selection according to

claim 12

, wherein the multiple wavelength input component is a fiber.

19. The optical system for wavelength selection according to

claim 12

, wherein the multiple wavelength input component is a waveguide.

20. The optical system for wavelength selection according to

claim 12

, wherein the output component is a single-mode fiber.

21. The optical system for wavelength selection according to

claim 12

, wherein the output component is an array of single-mode fibers.

22. The optical system for wavelength selection according to

claim 12

, wherein the output component is a single-mode waveguide.

23. The optical system for wavelength selection according to

claim 12

, wherein the output component is an array of single-mode waveguides.

24. The optical system for wavelength selection according to

claim 12

, wherein the output component is a detector.

25. The optical system for wavelength selection according to

claim 12

, wherein the output component is a combiner.

26. The optical system for wavelength selection according to

claim 12

, wherein each of the multiple polymer-dispersed liquid crystal switchable holographic components comprises:

a pair of transparent conductive slides;

a voltage source electrically contacted to the pair of transparent conductive slides;

at least one spacer for separating the pair of transparent conductive slides;

a layer of polymer-dispersed liquid crystal material located within the confines of the pair of transparent conductive slides and the at least one spacer; and

a switchable holographic grating formed within the layer of polymer-dispersed liquid crystal material.

27. The optical system for wavelength selection according to

claim 26

, wherein the polymer-dispersed liquid crystal material is made from:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

28. The optical system for wavelength selection according to

claim 27

, wherein the polymerizable monomer comprises at least one of a di-, tri-, tetra-, and pentaacrylate.

29. The optical system for wavelength selection according to

claim 28

, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

30. The optical system for wavelength selection according to

claim 29

, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

31. The optical system for wavelength selection according to

claim 30

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

32. The optical system for wavelength selection according to

claim 27

, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

33. The optical system for wavelength selection according to

claim 32

, wherein the surfactant is octanoic acid.

34. The optical system for wavelength selection according to

claim 27

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises at least one cyanobiphenyl, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal.

35. An optical connector comprising:

a first matrix comprising N×

N polymer-dispersed liquid crystal switchable holographic components for deflecting and transmitting incident radiation; and

a second matrix comprising N×

N optical components for accepting the deflected and transmitted incident radiation.

36. The optical connector according to

claim 35

, wherein each of the N×

N polymer-dispersed liquid crystal switchable holographic components is capable of deflecting incident radiation in at least one of the following directions;

(a) up;

(b) down;

(c) right; and

(d) left.

37. An optical connector according to

claim 35

, wherein each of the N×

N polymer-dispersed liquid crystal switchable holographic components comprises;

a pair of transparent conductive slides;

a voltage source electrically contacted to the pair of transparent conductive slides;

at least one spacer for separating the pair of transparent conductive slides;

a layer of polymer-dispersed liquid crystal material located within the confines of the pair of transparent conductive slides and the at least one spacer; and

a switchable holographic grating formed within the layer of polymer-dispersed liquid crystal material.

38. An optical connector according to

claim 37

, wherein the polymer-dispersed liquid crystal material is made from:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

39. The optical connector according to

claim 38

, wherein the polymerizable monomer comprises at least one of a di-, tri-, tetra-, and pentaacrylate.

40. The optical connector according to

claim 39

, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

41. The optical connector according to

claim 40

, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

42. The optical connector according to

claim 41

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

43. The optical connector according to

claim 38

, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

44. The optical connector according to

claim 43

, wherein the surfactant is octanoic acid.

45. The optical connector according to

claim 38

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises at least one cyanobiphenyl, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal.

46. The optical connector according to

claim 35

, wherein N equals at least 2 and the optical connector further comprises:

a third matrix comprised of N×

N polymer-dispersed liquid crystal switchable holographic components capable of accepting deflected and transmitted radiation from the second matrix and capable of further deflecting and transmitting the accepted radiation; and

a fourth matrix comprised of N×

N polymer-dispersed liquid crystal switchable holographic component capable of accepting from the third matrix the further deflected and transmitted radiation.

47. A polarization diversity system comprising:

a first polarizing beam splitter for receiving an input beam of light and splitting the input beam of light into a first beam of light polarized in first direction and a second beam of light polarized in a second direction;

a first optical path comprising;

a first deflector;

a half-wave plate;

a second deflector; and

a mirror, wherein the first optical path receives the first beam of light polarized in a first direction from the first polarizing beam splitter and outputs the first beam of light polarized in a second direction;

a second optical path comprising;

a mirror;

a third deflector;

a half-wave plate; and

a fourth deflector, wherein the second optical path receives the second beam of light polarized in a second direction from the first polarizing beam splitter and outputs the second beam of light polarized in a first direction; and

a second polarizing beam splitter for receiving the outputted first beam of light polarized in a second direction from the first optical path and the outputted second beam of light polarized in a first direction from the second optical path.

48. The polarization diversity scheme according to

claim 47

, wherein the first and fourth deflectors are capable of deflecting light in a first and second direction.

49. The polarization diversity system according to

claim 48

, wherein the second and third deflectors are capable of deflecting light in a third and fourth direction.

50. The polarization diversity system according to

claim 47

, wherein the first, second, third and fourth deflectors are ma de from polymer-dispersed liquid crystal elements.

51. The polarization diversity system according to

claim 47

, wherein the first and second optical paths are symmetrical in length.

52. An optical switch comprising:

a pair of conductive slides at least one of which is transparent;

a voltage source electrically contacted to the pair of conductive slides;

at least one spacer for separating the pair of conductive slides;

a layer of polymer-dispersed liquid crystal material located within the confines of the pair of conductive slides and the at least one spacer; and

a switchable holographic grating formed within the layer of polymer- dispersed liquid crystal material.

53. The optical switch according to

claim 52

, wherein the polymer-dispersed liquid crystal material is made from:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

54. The optical switch according to

claim 53

, wherein the polymerizable monomer comprises at least one of a di-, tri-, tetra-, and pentaacrylate.

55. The optical switch according to

claim 54

, wherein the polymerizable monomer is at least one acrylate selected from the group consisting of triethyleneglycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, and dipentaerythritol pentaacrylate.

56. The optical switch according to

claim 55

, wherein the polymerizable monomer comprises a mixture of tri- and pentaacrylates.

57. The optical switch according to

claim 56

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate.

58. The optical switch according to

claim 53

, wherein the polymer-dispersed liquid crystal material further comprises a surfactant.

59. The optical switch according to

claim 58

, wherein the surfactant is octanoic acid.

60. The optical switch according to

claim 53

, wherein the polymerizable monomer comprises dipentaerythritol pentaacrylate, the at least one liquid crystal comprises a mixture of cyanobiphenyls, the chain-extending monomer is N-vinyl pyrrolidone, the coinitiator is N-phenylglycine, and the photoinitiator is rose bengal.

61. 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; and

exposing the polymerizable material to at least two interfering light beams in order to form a hologram therein.

62. The method according to

claim 61

, wherein the substrate is selected from the following group consisting of glass and a polymer material.

63. The method according to

claim 61

, wherein the polymerizable material comprises at least one type of liquid crystal material.

64. The method according to

claim 63

, 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.

65. The method according to

claim 61

, wherein the at least two interfering light beams are incident upon the polymerizable material from the same side of the substrate.

66. The method according to

claim 61

, further comprising curing the exposed polymerizable material.

67. The method according to

claim 61

, wherein the hologram is a grating.

68. The method according to

claim 61

, wherein forming the at least two sets of electrodes comprises sputtering an electrically conductive material onto the substrate.

69. The method according to

claim 68

, wherein the electrically conductive material is selected from the group consisting of gold, aluminum, and indium-tin-oxide.

70. The method according to

claim 61

, wherein forming the at least two sets of electrodes 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.

71. The method according to

claim 70

, 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.

72. A holographic switch comprising:

a substrate;

a waveguide within the substrate having a polymer-dispersed liquid crystal holographic layer therein; and

at least two sets of electrodes attached to the substrate and electrically contacting the polymer-dispersed liquid crystal holographic layer.

73. The holographic switch according to

claim 72

, wherein the substrate is selected from the following group consisting of glass and a polymer material.

74. The holographic switch according to

claim 72

, wherein within the waveguide, the polymer-dispersed liquid crystal holographic material includes alternating regions of pure polymer material and polymer-dispersed liquid crystal material.

75. The holographic switch according to

claim 74

, wherein the at least two sets of electrodes comprise finger electrodes.

76. The holographic switch according to

claim 75

, wherein the finger electrodes are in electrical contact with the regions of pure polymer material.

77. The holographic switch according to

claim 72

, wherein the waveguide is a channel waveguide.

78. The holographic switch according to

claim 72

, wherein the polymer-dispersed liquid crystal holographic layer is made from:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

79. A crossbar switch comprising:

N×

M polymer-dispersed liquid crystal holographic elements, where N=M and N is equal to at least 2, and further wherein each of the polymer-dispersed liquid crystal holographic elements deflects light in a first state and transmits light in a second state, such that light input at any N is capable of output at any M by alternating between the first and second states of the polymer-dispersed liquid crystal holographic elements.

80. A non-blocking switch comprising:

multiple polymer-dispersed liquid crystal holographic elements arranged into an N input and an M output configuration, wherein each of the elements alternates between either a first state and a second state or a first state and a third state, and further wherein, light incident upon any N input is coupled to any M output without blocking the path of any other N input to M output coupling.

81. The non-blocking switch of

claim 80

, wherein the first state is transmission of incident light along an incident path, the second state is deflection of incident light in a first direction, and the third state is deflection of incident light in a second direction.

82. A method for forming a switchable holographic filter comprising:

inserting a first end of a first optical fiber into a first end of a capillary tube and inserting a first end of a second optical fiber into a second end of a capillary tube, leaving a space within the capillary tube between the first end of the first optical fiber and the first end of the second optical fiber;

filling the space within the capillary tube with a polymerizable material; and

exposing the polymerizable material to radiation, thereby forming a switchable holographic filter within the capillary tube.

83. The method according to

claim 82

, further comprising:

attaching a first GRIN lens to the first end of the first optical fiber and a second GRIN lens to the first end of the second optical fiber, prior to inserting the first end of the first optical fiber and the first end of the second optical fiber into the capillary tube.

84. The method according to

claim 82

, wherein filling the space within the capillary tube includes injecting the polymerizable material into the capillary tube via a syringe.

85. The method according to

claim 84

, further comprising:

positioning the filled capillary tube between at least two optical flats;

clamping the at least two optical flats together with the filled capillary tube therebetween; and

injecting an index matching solution in all spaces between the filled capillary tube and the at least two optical flats.

86. The method according to

claim 85

, wherein exposing the polymerizable material to radiation includes irradiating the filled capillary tube with two beams of radiation.

87. The method according to

claim 86

, wherein the two beams of radiation are incident upon the filled capillary tube from the same side.

88. The method according to

claim 82

, wherein the polymerizable material comprises:

(a) a polymerizable monomer comprising at least one acrylate;

(b) at least one type of liquid crystal material;

(c) a chain-extending monomer;

(d) a coinitiator; and

(e) a photoinitiator.

89. The method according to

claim 87

, further comprising:

positioning the exposed capillary within a groove etched into a substrate; and

depositing a set of finger electrodes on the surface of the substrate on either side of the groove containing the exposed capillary.

90. The method according to

claim 87

, further comprising wrapping a coil of wire around the exposed capillary.

91. The method according to

claim 87

, further comprising positioning the exposed capillary between at least two heating elements.

92. An electrically switchable holographic filter comprising:

a substrate containing an etched groove;

a first and second set of finger electrodes positioned on the surface of the substrate on either side of the etched groove;

a capillary tube containing a switchable grating positioned within the etched groove; and

first and second optical fibers, wherein the first optical fiber is inserted into one end of the capillary tube and the second optical fiber is inserted into the other end of the capillary tube, such that the switchable grating is positioned between the inserted first and second optical fibers.

95. The electrically switchable holographic filter according to

claim 92

, wherein the switchable grating is made of a polymer-dispersed liquid crystal material.

98. The electrically switchable holographic filter according to

claim 92

, wherein a first GRIN lens is attached to at least a first inserted end of the first optical fiber and a second GRIN lens is attached to at least a first inserted end of the second optical fiber.

93. A magnetically switchable holographic filter comprising:

a capillary tube containing a switchable grating;

a coil of wire wrapped around the capillary tube; and

first and second optical fibers, wherein the first optical fiber is inserted into one end of the capillary tube and the second optical fiber is inserted into the other end of the capillary tube, such that the switchable grating is positioned between the inserted first and second optical fibers.

96. The magnetically switchable holographic filter according to

claim 93

, wherein the switchable grating is made of a polymer-dispersed liquid crystal material.

94. A thermally switchable holographic filter comprising:

a capillary tube containing a switchable grating positioned between at least two heating elements; and

first and second optical fibers, wherein the first optical fiber is inserted into one end of the capillary tube and the second optical fiber is inserted into the other end of the capillary tube, such that the switchable grating is positioned between the inserted first and second optical fibers.

97. The thermally switchable holographic filter according to

claim 94

, wherein the switchable grating is made of a polymer-dispersed liquid crystal material.