Optical: systems and elements – Polarization without modulation – By relatively adjustable superimposed or in series polarizers
Reexamination Certificate
1999-06-15
2001-02-06
Schuberg, Darren (Department: 2872)
Optical: systems and elements
Polarization without modulation
By relatively adjustable superimposed or in series polarizers
C359S494010, C359S490020, C359S352000
Reexamination Certificate
active
06185039
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of light control devices and methods. More particularly, the present invention provides polarizing elements and light valves which use one or more polarizing elements that rotate about an in-plane axis to control the passage of light through the device.
BACKGROUND OF THE INVENTION
Manual control of light trnsmission is generally required for many purposes, including industrial, commercial, and residential applications. One common application is the control of light passing through a window, skylight, or other opening for a variety of reasons, e.g., controlling visible light transmission, ensuring privacy, reducing heat build-up in a room, etc. Many types of curtains, venetian blinds, shades, draperies, shutters, and the like are used to control the amount of light admitted into a room or building through a window, skylight, or other opening.
In many cases, the devices used as light valves are totally or partially opaque and function by absorbing incident light. Because the light is absorbed by the devices, they typically convert light energy into heat, which can then be radiated into the building or space in which the devices are located. In addition, while some of the devices, e.g., venetian blinds and shutters, are effective at ensuring privacy, they may also excessively restrict the view through the window.
The use of polarizers as light valves in many different applications is well-known. Typically, two polarizers are used, at least one of which can be translated or rotated. In general, the transmission axis of the front polarizer is “crossed” with the transmission axis of the rear polarizer at angles that can vary between 0 and 90° to adjust the amount of light transmitted through the polarizers. The rotation is typically about an axis that is normal to the plane in which the polarizer is located, i.e., the axis of rotation is out of the plane in which the rotating polarizer is located. As a result, the rotating light valves typically require that the window or other opening in which they are placed be generally circular. In other words, such devices are not particularly useful for windows which have a generally square or rectangular outline.
Other approaches at controlling light transmission through a window include the use of privacy films, such as those described in U.S. Pat. No. 5,686,979 (Weber et al.). Such privacy films use an electronically switched columnar dispersed liquid crystal film that provides reversible opacity with or without mechanical movement.
In addition, although the use of polarization to control the transmission of light has been discussed in many different manners, most of the discussions focus on the use of absorptive polarizers. Typically, absorptive polarizers use dichroic dyes which absorb light of one polarization orientation more strongly than that of the orthogonal polarization orientation. Because absorptive polarizers absorb light having one polarization orientation, they can also present the problems of conversion of absorbed solar energy into thermal energy which is then radiated into the interior of a room.
As a result, a need exists for a light valve that can a) control the amount of light passing through an opening, b) provide high contrast between its open and closed states, c) provide for absorption or reflection to improve energy efficiency, and/or d) provide control over viewing angle to either limit or expand viewing angles.
SUMMARY OF INVENTION
The present invention provides polarizing elements including at least one reflective polarizer in combination with an infred reflective material or an infrared absorptive material. The polarizing elements can be included in light valves to control light transmission by rotating at least one of the polarizing elements about an in-plane axis.
The light valves according to the present invention may find use in any application in which the transmission of light (visible or otherwise) is to be controlled. Examples of specific applications include, but are not limited to: windows, luninaires, skylights, etc.
In one aspect, the present invention provides a polarizing element including at least one of an infrared absorptive material that absorbs substantially all of the infrared light incident thereon or an infrared reflective material that reflects substantially all of the infared light incident thereon. The polarizing element further includes a reflective polarizer including first and second materials, at least one of the first and second materials being birefringent, wherein a refractive index difference between the first and second materials for light having a first polarization orientation is large enough to substantially reflect the light having the first polarization orientation, and firther wherein a refractive index difference between the first and second materials for light having a second polarization orientation is small enough to substantially transmit the light having the second polarization orientation.
The reflective polarizer of the polarizing element may be a diffusely reflective polarizer that diffusely reflects the light having the first polarization orientation. Polarizing elements that include a diffuisely reflective polarizer may also include a spectrally reflective polarizer comprising third and fourth materials in different layers within the spectrally reflective polarizer, at least one of the third and fourth materials being birefringent, wherein a refractive index difference between the third and fourth materials for light having a first polarization orientation is large enough to substantially spectrally reflect the light having the first polarization orientation, and further wherein a refractive index difference between the third and fourth materials for light having a second polarization orientation is small enough to substantially transmit the light having the second polarization orientation.
In another aspect, the present invention provides a light valve including a first polarizing element having a first transmission axis; and a second polarizing element having an axis of rotation and a second transmission axis intersecting the axis of rotation at a fixed angle. Rotation of the second polarizing element about the axis of rotation to a first orientation relative to the first polarizing element provides maximum transmission of light through the first and second polarizing elements, and rotation of the second polarizing element of about 180 degrees around the axis of rotation to a second orientation provides minimum transmission of incident light through the first and second polarizing elements.
The fixed angle at which the second transmission axis intersects the axis of rotation may be about 45 degrees and/or the first transmission axis may form an angle of about 45 degrees with the axis of rotation of the second polarizing element. The first polarizing element may be stationary relative to the axis of rotation of the second polarizing element.
The light valve may also include two or more second polarizing elements. In some embodiments, the first polarizing element may be provided in the form of a single sheet having a surface, and the second polarizing elements may be located proximate the surface of the first polarizing element.
Either or both of the first and second polarizing elements may include a reflective polarizer. The second polarizing element may include an infrared selective material, e.g., at least one of an infrared absorptive material and an infrared reflective material. The reflective polarizer may include first and second materials, at least one of the first and second materials being birefringent, wherein a refractive index difference between the first and second materials for light having a first polarization orientation is large enough to substantially reflect the light having the first polarization orientation, and frrther wherein a refractive index difference between the first and second materials for light having a second polarization orientation is small enough to substantia
Allen Richard C.
Hietpas Gregg A.
Stickrod Jon E.
Wheatley John A
3M Innovative Properties Co.
Patchett David B.
Schuberg Darren
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