Wide angle optical retarder
First Claim
Patent Images
1. An optical retarder for uniformly retarding visible light incident on the retarder over a relatively wide range of incidence angles varying from an angle normal to a plane of the retarder to a maximum angle φ
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max of at least about 30 degrees, the optical retarder comprising;
a substrate;
a film of an acrylonitrile based polymer and elastomeric copolymer disposed on the substrate, the film having a retardation magnitude δ
which may be expressed by the relationship ##EQU2## where nx and ny are refractive indices of the film for light at a wavelength of interest polarized along orthogonal in-plane axes x and y of the film, d is a thickness of the film in a direction of a z axis mutually orthogonal to the x and y in-plane axis, nz is a refractive index of the film for light at the wavelength of interest polarized along the z axis, and φ
is the angle of incidence in the x-z plane, wherein the magnitude of retardation δ
of the film varies by less than about 25% of the magnitude of retardation at normal incidence as the angle of incidence φ
of light at the wavelength of interest varies from normal to the maximum angle φ
max.
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Abstract
In an acrylonitrile based retarder, relatively uniform performance is obtained as the angle of incidence varies over a wide range. A toughening material may be blended with an acrylonitrile based polymer to facilitate processing of a retarder and improve mechanical properties of the retarder without compromising the optical performance. A rubber-modified acrylonitrile based retarder which provides relatively uniform wide angle can be fabricated using conventional processing techniques. Such retarders are particularly suited for a number of specific applications which use relatively wide ranges of incidence angles.
28 Citations
22 Claims
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1. An optical retarder for uniformly retarding visible light incident on the retarder over a relatively wide range of incidence angles varying from an angle normal to a plane of the retarder to a maximum angle φ
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max of at least about 30 degrees, the optical retarder comprising;
a substrate; a film of an acrylonitrile based polymer and elastomeric copolymer disposed on the substrate, the film having a retardation magnitude δ
which may be expressed by the relationship ##EQU2## where nx and ny are refractive indices of the film for light at a wavelength of interest polarized along orthogonal in-plane axes x and y of the film, d is a thickness of the film in a direction of a z axis mutually orthogonal to the x and y in-plane axis, nz is a refractive index of the film for light at the wavelength of interest polarized along the z axis, and φ
is the angle of incidence in the x-z plane, wherein the magnitude of retardation δ
of the film varies by less than about 25% of the magnitude of retardation at normal incidence as the angle of incidence φ
of light at the wavelength of interest varies from normal to the maximum angle φ
max. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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max of at least about 30 degrees, the optical retarder comprising;
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16. An optical retarder for use in retarding visible light incident on the retarder over a wide range of incidence angles varying from an angle normal to a plane of the retarder to a maximum angle φ
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max of at least about 30 degrees, the optical retarder comprising;
a film comprised of blend of an acrylonitrile based polymer and an elastomeric copolymer, the film having an in-plane retardation magnitude δ
in which may be expressed by the relationship
space="preserve" listing-type="equation">δ
.sub.in =d(n.sub.x -n.sub.y),where nx and ny are refractive indices of the film for light at a wavelength of interest polarized along orthogonal in-plane axes x and y of the film and d is a thickness of the film in a direction of a z axis mutually orthogonal to the x and y in-plane axis, the film further having an out-of-plane retardation magnitude δ
out which may be expressed by the relationship ##EQU3## where nz is a refractive index of the film for light at the wavelength of interest polarized along the z axis, and φ
is an out-of-plane angle of incidence in the x-z plane, wherein a retardation magnitude difference Δ
δ
between the in-plane retardation δ
in and the out-of-plane retardation δ
out for light at the wavelength of interest incident on the film at the maximum angle φ
max is less than about 25% of the in-plane retardation δ
in. - View Dependent Claims (17, 18, 19, 20)
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max of at least about 30 degrees, the optical retarder comprising;
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21. A retarding mirror for reflecting visible light, linearly polarized in an initial polarization direction, in a manner in which the reflected light is substantially linearly polarized in a direction orthogonal to the initial polarization direction, the light being incident on the retarder mirror at angles varying from an angle normal to a plane of the retarding mirror to a maximum angle φ
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max of at least about 15 degrees, the retarding mirror comprising;
a substantially flat reflective substrate; and a stretched acrylonitrile based polymeric retardation film disposed parallel to the reflective substrate, the retardation film having a retardation magnitude δ
which may be expressed by the relationship ##EQU4## where nx and ny are refractive indices of the retardation film for light at a wavelength of interest polarized along orthogonal in-plane axes x and y of the film, d is a thickness of the retardation film in a direction of a z axis mutually orthogonal to the x and y in-plane axis, nz is a refractive index of the retardation film for light at the wavelength of interest polarized along the z axis, and φ
represents an angle in the x-z plane at which the light is incident on the retarding mirror,wherein an ellipticity introduced by the retarding mirror of reflected light at the wavelength of interest which is incident on the retarding mirror at the maximum angle φ
max is within 25% of an ellipticity of the reflected light at the wavelength of interest incident on the retarding mirror at an angle normal to the surface of the retarding mirror.
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max of at least about 15 degrees, the retarding mirror comprising;
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22. An anti-reflective (AR) optical element disposed on a partially reflective surface and effective over a relatively wide range of incidence angles to substantially reduce reflection of visible light from the surface, the AR optical element comprising:
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an absorptive polarizer disposed between a source of incident light and the reflective surface; and a retarder comprised of an acrylonitrile based polymer film, positioned between the polarizer and the reflective surface, the retarder receiving polarized light transmitted by the polarizer and retarding the polarized light by a retardation magnitude δ
which may be expressed by the relationship ##EQU5## where nx and ny are refractive indices of the film for light at a wavelength of interest polarized along orthogonal in-plane axes x and y of the film, d is a thickness of the film in a direction of a z axis mutually orthogonal to the x and y in-plane axis, nz is a refractive index of the film for light at the wavelength of interest polarized along the z axis, and φ
represents an angle in the x-z plane at which the light is transmitted from the polarizer to the film,wherein a retardation magnitude δ
.sub.φ
=0°
for light at the wavelength of interest incident on the blended film at an angle normal to a surface of the blended film is within 15% of a retardation magnitude δ
.sub.φ
max for light at the wavelength of interest incident on the film at a maximum angle of incidence of at least about 30°
, measured from normal incidence.
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Specification
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Current Assignee3M Company
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Original Assignee3M Company
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InventorsBoyd, Gary T., Sahouani, Hassan, Kumar, Ramesh C., Damodaran, Sundaravel
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Primary Examiner(s)Sikes, William L.
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Assistant Examiner(s)NGUYEN, TIEP HUU
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Application NumberUS08/953,128Time in Patent Office473 DaysField of Search349/117, 349/118US Class Current349/117CPC Class CodesG02B 5/3083 Birefringent or phase retar...
