Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2000-06-22
2002-06-11
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C349S009000, C359S487030
Reexamination Certificate
active
06402322
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a polarization conversion element for converting an unpolarized light beam incident thereto into a predetermined polarized light beam, a method of producing the polarization conversion element, and a projector including the polarization conversion element.
2. Description of Related Art
A light-modulation element, which can be referred to as a light valve, is used in a projector in order to modulate a light beam in accordance with an image signal. A light valve of the type which uses only one type of linearly polarized light beam, such as a transmissive liquid crystal panel or a reflection liquid crystal panel, is often used. Accordingly, a projector, which uses one type of linearly polarized light beam, includes a polarization conversion element for converting an unpolarized light beam, which has exited a light source, into one type of linearly polarized light beam (such as an s-polarized light beam or a p-polarized light beam).
Examples of conventional polarization conversion elements are described in Japanese Unexamined Patent Application Publication No. 10-177151 and Japanese Unexamined Patent Application Publication No. 10-90520 disclosed by the Applicant.
A conventional polarization conversion element is produced, for example, by cutting out a polarization beam splitter array, making up the polarization conversion element from a composite plate formed by alternately bonding, with an adhesive, a transmissive plate having a polarization separation film and a reflection film formed thereon, and a transmissive plate which does not have anything formed thereon.
The step of bonding multiple transmissive members together takes a relatively long time to perform because it is ordinarily performed by repeatedly bonding the plates together with ultraviolet curing optical adhesive and curing the optical adhesive. In order to increase the efficiency with which the polarization conversion element is produced, there has been a desire to increase the efficiency with which the bonding step is performed.
SUMMARY OF THE INVENTION
The present invention overcomes the aforementioned conventional problem. An object of the invention is to provide a technology which makes it possible to produce a polarization conversion element with high efficiency.
To solve at least part of the aforementioned problem, a first producing method in accordance with the present invention is a method of producing a polarization conversion element that converts an unpolarized light beam incident thereto to a predetermined polarized light beam, the method comprising the steps of:
(a) providing a plurality of first transmissive plates;
(b) providing a plurality of second transmissive plates;
(c) forming a plurality of polarization separation films and a plurality of reflection films on surfaces of portions of the first transmissive plates or the second transmissive plates, so that the plurality of polarization separation films and the plurality of reflection films are alternately disposed on interfaces of the transmissive plates, when the plurality of first transmissive plates and the plurality of second transmissive plates are alternately disposed and bonded together;
(d) producing a composite plate, having the plurality of polarization separation films and the plurality of reflection films alternately disposed on each of the interfaces of each of the transmissive plates, as a result of alternately disposing and bonding together the plurality of first transmissive plates and the plurality of second transmissive plates; and
(e) producing a transmissive block having a light-incident surface and a light-exiting surface, formed parallel to cut surfaces formed by cutting the composite plate along cutting planes parallel to planes at a predetermined angle from planar surfaces of the composite plate;
wherein the step (d) includes the step of forming the polarization separation films so that a transmittance ratio of each polarization separation film, for an ultraviolet light beam of a particular wavelength region, incident on a surface of each polarization separation film at an angle of incidence of approximately 0 degrees, is approximately 40% or more.
According to the above-described first producing method, the transmittance ratio of each polarization separation film for an ultraviolet light beam can be increased, so that, in step (d), an optical adhesive used to bond the first transmissive plates and the second transmissive plates can be efficiently irradiated with ultraviolet light beams, making it possible to decrease the number of man-hours required to cure the adhesive. Therefore, the polarization conversion element can be produced with high efficiency.
It is preferable that the particular wavelength region lie in a range of 365 nm±30 nm.
It is preferable that the step of forming the polarization separation films include the step of forming multilayered structural sections formed by alternately placing first and second layers upon each other, with a refractive index of each first layer being smaller than a refractive index of each transmissive member and a refractive index of each second layer being greater than the refractive index of each transmissive member; the refractive index of each transmissive member be approximately 1.48 to approximately 1.58; and the first layers of the polarization separation films each be formed of MgF
2
, and the second layers of the polarization separation films each be formed of MgO.
By forming the polarization separation films as described above, each polarization separation film can have a transmittance ratio for an ultraviolet light beam of a particular wavelength range of approximately 40% or more.
In the first producing method, it is preferable that the step (d) comprise the step of forming the reflection films so that a transmittance ratio of each reflection film for an ultraviolet light beam of a particular wavelength region incident to a surface of each reflection film at an angle of incidence of approximately 0 degrees is approximately 40% or more.
According to the foregoing description, the transmittance ratio of each reflection film for an ultraviolet light beam can be increased, so that, in step (d), the optical adhesive used to bond the first transmissive plates and the second transmissive plates together can even be more efficiently irradiated with ultraviolet light beams, making it possible to further decrease the number of man-hours required to cure the adhesive. Therefore, the polarization conversion element can be produced with even higher efficiency.
It is preferable that the particular wavelength region lie in a range of 365 nm±30 nm.
It is preferable that the step of forming the reflection layers include the step of forming multilayered structural sections formed by alternately placing third and fourth layers upon each other, with a refractive index of each third layer being smaller than a refractive index of each transmissive member and a refractive index of each fourth layer being greater than the refractive index of each transmissive member; each transmissive member have a refractive index of approximately 1.48 to approximately 1.58; and the third layers of the reflection films each be formed of SiO
2
, and the fourth layers of the reflection films each be formed of TiO
2
or Ta
2
O
5
.
By forming the reflection films as described above, the transmittance ratio of each reflection film for an ultraviolet beam in a particular wavelength region can be approximately 40% or more.
A second producing method in accordance with the present invention is a method of producing a polarization conversion element that converts an unpolarized light beam incident thereto to a predetermined polarized light beam, the method comprising the steps of:
(a) providing a plurality of first transmissive plates;
(b) providing a plurality of second transmissive plates;
(c) forming a plurality of polarization separation films and a plurality of reflection films on surfaces of portions of the first
Adams Russell
Koval Melissa J.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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