Optical: systems and elements – Polarization without modulation – Polarization variation over surface of the medium
Reexamination Certificate
2002-09-30
2004-12-07
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarization variation over surface of the medium
C359S566000, C353S020000, C349S009000
Reexamination Certificate
active
06829090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a prism for separating the illuminated light from a light source depending on the wavelength or polarized light components, a projection device for modulating the illuminated light radiated from the light source using a reflection type optical modulating element and for projecting the light to an enlarged scale using a lens and an optical component used in this prism and in the projection device.
2. Description of Related Art
For enabling display on a large sized screen, there has so far been known a projection device in which illuminated light is radiated from a lamp to a liquid crystal panel, on which a pattern consistent with input picture signals is displayed, and in which the illuminated light is modulated and reflected by the liquid crystal panel so as to be projected to an enlarged scale using a projector lens.
In this projection device, a polarized beam splitter (PBS) for separating the forward and return optical paths is provided in the optical path so that the optical path for the illuminated light towards the liquid crystal panel and that for the reflected light modulated by the liquid crystal panel will not be the same optical path. In this PBS
200
, a pair of corner prisms
202
, as substrates, are bonded together to hold a dielectric multi-layer film
201
in-between as shown in FIG.
1
. Moreover, in this PBS
200
, the dielectric multi-layer film
201
is formed to have different reflectance and transmittance values, depending on the wavelength or the direction of light polarization, and operates as a beam splitter for separating a light beam depending on the wavelength or the direction of light polarization.
The PBS
200
can be classified into a McNeill type in which the dielectric multi-layer film
201
separates the light beam depending on the polarized light component, and a dichroic type, in which the light beam is separated depending on the wavelength.
In the McNeill or dichroic type PBS, exploiting the interference of multi-layer dielectric films, the performance is determined by the refractive index of the substrate and the combination of the layered dielectric materials, so that the performance beyond a certain limit cannot be achieved. In such PBS, it is extremely difficult to maintain separation characteristics between the P-polarized light and the S-polarized light over a wide angle of incidence. Thus, if this PBS is built into an optical system with a large angular distribution, that is with a small F-value, light separation characteristics as well as the light exploitation efficiently is lowered.
As a solution, a flat plate shaped diffraction grid PBS
210
, shown in
FIG. 2
, may be used. In this diffraction grid PBS
210
, a diffraction grid
212
of e.g., aluminum is provided on a glass substrate
211
. By this diffraction grid
212
, light is separated depending on polarized components. However, if the grid is used as a beam splitter, the diffraction grid PBS
210
needs to be arranged obliquely relative to the main light beam, so that, if the diffraction grid PBS is inserted into the optical path, astigmatic aberration is produced.
In the case of the McNeill or dichroic prism, distortion is produced in the prism due to temperature rise in the prism or by a holding mechanism, so that diffraction distribution in the substrate becomes nonuniform with the result that phase difference is produced in the light transmitted through the substrate and hence the extinction ratio is partially lowered. With the projection device, employing this prism, so-called black spots are produced in the projected image such that clear images cannot be projected.
Thus, as a prism substrate, such a material having a low modulus of opto-elasticity and less susceptible to distortion in the prism needs to be selected. However, a material having a low modulus of opto-elasticity is costly, such that the prism employing the low modulus of opto-elasticity or the projection device employing such prism is expensive. On the other hand, it is extremely difficult to produce a prism of high performance from an inexpensive vitreous material having a high modulus of opto-elasticity.
SUMMARY OF THE INVENTION
In view of the above-depicted status of the art, it is an object of the present invention to provide a prism or an optical component, in which astigmatic aberration is suppressed and which has uniform distribution of the modulus of elasticity in the substrate, and a projection device employing such prism or optical component.
In one aspect, the present invention provides a prism for transmitting or reflecting incident light depending on polarized light components thereof, including a substantially grid-shaped diffraction grid, formed of metal, a pair of diffraction grid substrates sandwiching the diffraction grid in-between, an adhesive layer provided on each surface of each diffraction grid substrate facing the diffraction grid, and a pair of block members secured through the adhesive layer to each of the paired diffraction grid substrates, wherein a medium having a refractive index approximately equivalent to that of the block members is charged in a gap defined between the diffraction grid and the paired grid substrates.
With the prism of the present invention, the diffraction grid is sandwiched between a pair of the block members to suppress the astigmatic aberration in the image-forming optical system. The incident light may be transmitted or reflected depending on the polarized light components as optimum polarized light separation characteristics are maintained over a wide angle of incidence.
In another aspect, the present invention provides a projector device including a light source for radiating illuminated light, a light collecting lens for collecting the illuminated light radiated from the light source, a prism for transmitting or reflecting the light from the light collecting lens depending on polarized light components thereof, a light modulating element for modulating the illuminated light transmitted or reflected by the prism and for reflecting the modulated light, and a projector lens for enlarging and projecting the reflected light reflected or transmitted by the prism and modulated by the light modulating element, wherein the prism includes a substantially grid-shaped diffraction grid, formed of metal, a pair of diffraction grid substrates sandwiching the diffraction grid in-between, an adhesive layer provided on each surface of each diffraction grid substrate facing the diffraction grid, a pair of block members secured through the adhesive layer to each of the paired diffraction grid substrates, and a medium having a refractive index approximately equivalent to that of the block members, the medium being charged in a gap defined between the diffraction grid and the paired grid substrates.
With the projection device of the present invention, when the reflected light modulated by the optical modulation element is transmitted through or reflected by the prism, the image of the reflected light may be projected as reflected light is optimally separated into polarized light components and as astigmatic aberration is prevented from occurring.
In still another aspect, the present invention provides an optical component in which the light of preset polarization state is transmitted and radiated, wherein plural plate shaped members, having the surfaces polished to mirror finish, are layered together with interposition of soft type adhesives.
With this optical component of the present invention, in which the plural plate shaped members are layered together with interposition of soft type adhesives, the internal stress produced by strain may be suppressed to maintain the refractive index distribution constant to permit light to be transmitted without disturbing the state of polarization.
In another aspect, the present invention provides a prism including a light separating layer provided on a plate-shaped substrate and having the properties of transmitting or reflecting light depending on p
Katsumata Masao
Yamamoto Hideki
Frommer William S.
Frommer & Lawrence & Haug LLP
Lavarias Arnel C.
Lee Samuel S.
Nguyen Thong
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