Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-02-23
2001-03-27
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S246000
Reexamination Certificate
active
06208451
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a polarization conversion system that converts unpolarized light to a specifically polarized light, and to an optical system using the polarization conversion system.
2. Description of the Related Art
Liquid crystal panels are extensively utilized in direct-view display apparatuses and projectors. In a projector, for example, liquid crystal panels (liquid crystal light valves) are used to modulate illumination light in accordance with image information, and the modulated light is projected onto a screen to thereby display images. Generally, since the images are displayed by modulating specific linearly polarized light, it is necessary to provide a polarization plate at the light entry side of the liquid crystal panel in order to convert the unpolarized light emitted by a light source to the requisite linearly polarized light. However, this results in the loss of half or more of the light due to absorption by the polarization plate. To increase the light utilization efficiency of the illumination system with respect to the liquid crystal panel, an optical polarization conversion system is typically employed to convert the light from the light source to one type of linearly polarized light.
Japanese Patent Laid-open Gazette No. 8-304739 discloses an illumination system using a polarization conversion system. This polarization conversion system comprises a polarization splitting prism array consisting of a plurality of polarization beam splitters and a plurality of reflecting mirrors, and a &lgr;/2 retardation film provided on the exit side of the polarization beam splitting prism array. In this polarization conversion system, the polarization splitting prism array is used to split the unpolarized light into two types of linearly polarized light in which the plane of polarization of one is perpendicular to that of the other, and a &lgr;/2 retardation film is then used to align the polarization direction of one of these beams of linearly polarized light with the polarization direction of the other beam of linearly polarized light, whereby the light is converted into substantially one type of linearly polarized light.
The problem with the polarization conversion system of the prior art is the need to use a complex polarization splitting prism array including multiple polarization beam splitters and reflecting mirrors in order to effect the conversion of the unpolarized light to the two types of linearly polarized light.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide a polarization conversion system having a simpler structure than the conventional ones, and an optical system that uses this polarization conversion system.
At least part of the above and the other related object are attained by a polarization conversion system that converts unpolarized light to light of a specific polarization. The polarization conversion system comprises: a polarized light selective reflector that separates incident unpolarized light into first and second types of polarized light, transmits the first type of polarized light and reflects the second type of polarized light, a relay optical system that relays an incident light beam onto the polarized light selective reflector, a polarized light reflector, disposed on an optical path of a reflected light beam reflected by the polarized light selective reflector, that reflects the reflected light beam back to the polarized light selective reflector while converting the second type of polarized light to polarized light of the first type.
In accordance with the above structure, a polarization conversion system having a simpler structure than previous ones can be achieved.
In accordance with the polarization conversion system, it is preferable that the relay optical system includes: a first lens array having a plurality of first small lenses that divides an incident light beam into a plurality of partial light beams, and a relay lens array, disposed on a light emission side of the first lens array, having a plurality of relay lenses corresponding to the plurality of first small lenses. The second lens array is positioned in proximity to entry side of the polarized light selective reflector so that each of reflected partial light beams that exit the second small lenses and are reflected by the polarized light selective reflector is reflected back to the same second small lens from which each of the partial light beams exited prior to being reflected by the polarized light selective reflector. Each of the plurality of relay lenses is located at an each specified position that is in proximity to an exit side focal point of the corresponding first small lens and to an entry side focal point of the corresponding second small lens, and the corresponding first small lens and the corresponding second small lens are located at conjugate points of the relay lens. The polarized light reflector includes a plurality of polarized light reflection portions, disposed on optical paths of a plurality of reflected partial light beams exiting from the plurality of second small lenses, each reflects a corresponding reflected partial light beam and converts the second type of polarized light within the corresponding reflected partial light beam to polarized light of the first type, and a plurality of third small lenses that direct reflected partial light beams reflected by the polarized light reflection portions to go back to the same second small lenses from which the reflected partial light beams exited prior to being reflected by the polarized light reflection portions.
Thus using a the first lens array to divide the incident light beam into a plurality of partial light beams and condense the beams makes it possible to keep the partial light beams small, thereby also enabling the size of the relay lenses to be set to a correspondingly small size. Moreover, the polarization conversion system can be disposed using the spaces between the relay lenses. In addition, the polarized light reflection portions are arranged so that they reflect incident light from the second lens array back to the second lens array, which ensures that the light beam incident on the polarization conversion system can be converted to one type of polarized light and emitted with hardly any change to the size of the incident beam.
Moreover, the relay optical system includes a relay lens array, which makes it possible to also project onto the second lens array partial light beams from the first lens array, thereby increasing the light utilization efficiency.
Here, it is preferable that the plurality of polarized light reflection portions are each positioned in proximity to a focal point of a corresponding second small lens, and the plurality of third small lenses each has a focal distance substantially equal to that of corresponding the second small lenses and are disposed in proximity to a corresponding polarized light reflection portion.
This provides a further improvement in the light utilization efficiency.
In accordance with above configurations, it is preferable that the first and second types of polarized light are first and second types of linearly polarized light having mutually orthogonal polarization planes, and each of the plurality of polarized light reflection portions includes a reflecting mirror and a &lgr;/4 retardation film positioned between the third small lenses and the reflecting mirror.
It is almost preferable that the first and second types of polarized light are first and second types of circularly polarized light circularly polarized in reverse rotations and the plurality of polarized light reflection portions are reflecting mirrors.
In this configuration, the polarization conversion system may further comprise a &lgr;/4 retardation film that converts the first type of circularly polarized light transmitted by the polarized light selective reflector to a predetermined type of linearly polarized light.
In each case, incident unpolarized light can be converted to one ty
Dang Hung Xuan
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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