1. Field of the Invention
The present disclosure relates to projection display devices and optical systems thereof, and in particular, relates to a projection display device and an optical system thereof both of which can provide high-contrast images for a projection type projector.
2. Description of Related Art
Conventionally, a 3-panel type projector using three pieces (red, green, blue) of modulation devices is general in the projection display device (projector). Depending on the kind of devices, the 3-panel type projectors comprise LCD (Liquid Crystal Display) projector, DLP (Digital Light Processing) projector, LCOS (Liquid Crystal on Silicon) projector and so on.
FIG. 1 is a structural view of a conventional optical system. In FIG. 1, white light is emitted from a specified lamp (e.g. xenon lamp, ultra-high pressure mercury lamp, laser diode, light emission diode, etc.) in a lamp house 11. Then, the white light is changed to a parallel light by a condenser lens 12 and successively reflected by a cold mirror 13 for eliminating UV light or IR light unnecessary for a display device or interposed optical components. Then, the so-reflected light is transmitted through an integrator (rod integrator, flyeye integrator, etc.) 14 and a sequent field lens 15 thereby to enter a B/RG dichroic mirror 16.
The B/RG dichroic mirror 16 resolves incident illumination light to a light containing the wave bands of both red light and green light and a blue light, so that the former light (red and green) enters a RG mirror 17, while the latter light (blue) enters a B mirror 18. In the former light reflected by the RG mirror 17, its red light component is transmitted through a R/G dichroic mirror 19 thereby to enter an R field lens 24, while the green light component is reflected by the R/G dichroic mirror 19 thereby to enter a G field lens 20.
Regarding the green light component transmitted through the G field lens 20 and the red light component transmitted through R field lens 24, their S-polarization components are reflected by wire grids 21, 25 as polarization split elements thereby to enter a G device 23 and an R device 27 through a G quarter-wave (λ/4) plate 22 and an R quarter-wave (λ/4) plate 26, respectively. After light modulation at the G device 23 and the R device 27 with green signal and red signal of an image to be displayed from the 3-primary color signal processing and converting block 1, their P-polarized lights on light modulation are transmitted through the G, R quarter-wave (λ/4) plates 22, 26 and the wire grids 21, 25 thereby to enter an RGB composite dichroic prism 32.
On the other hand, regarding the blue light component reflected by the B mirror 18, it is transmitted through a B field lens 28 and the light's S-polarization component is reflected by a wire grid 29 thereby to enter a B device 31 through a B quarter-wave (λ/4) plate 30. After light modulation at the B device 31 with blue signal of the image to be displayed from the 3-primary color signal processing and converting block 1, the S-polarized light on light modulation is transmitted through the B quarter-wave (λ/4) plate 30 and the wire grid 29 thereby to enter the RGB composite dichroic prism 32.
The RGB composite dichroic prism 32 recombines respective P-polarization components of incident green, red and blue lights on light modulation. The so-combined light is transmitted through a PJ lens 33 to form an image on a screen.
Here, in a projector using the above-mentioned optical system, contrast influencing the definition of images is determined by the performances of the optical system and the individual device. In this view, there are recently proposed a projector and a liquid crystal display that the contrast of images are improved by double modulation dramatically (e.g. Japanese Patent Laid-Open Publication Nos. 2005-181437 and 2005-241738).
FIG. 2 shows the constitution of such an optical system adopting double modulation. In this example, elements identical to those of FIG. 1 are indicated with the same reference numerals respectively and their overlapping descriptions are eliminated. The conventional optical system of FIG. 2 is equivalent to the previously-mentioned optical system of FIG. 1 but the interposition of a Y-modulation system part between the RGB composite dichroic prism 32 and the PJ lens 33, the Y-modulation optical system comprising an aberration correcting lens 34, an 1:1 (one-to-one) relay lens 35, a mirror 36, an aberration correcting lens 37, a Y wire grid (WG) 38, a Y wavelength plate 39, a Y device 40 and a WG analyzer 41. The aberration correcting lenses 34, 37 are formed by cylindrical lenses for correcting aberrations that would be produced since the optical axis is slanted to the Y wire grid (WG) 38 by 45 degrees.
In the conventional optical system of FIG. 2, RGB composite light emitted from the RGB composite dichroic prism 32 is transmitted through the aberration correcting lens 34 and the 1:1 relay lens 35 and subsequently reflected by the mirror 36 for coordinating an optical-axis direction of the 1:1 relay lens 35 with an optical-axis direction of the PJ lens 33. Then, the so-reflected light is transmitted through the aberration correcting lens 37. In the so-transmitted RGB composite light, its P-polarized light is transmitted through the Y wire grid (WG) 38 and the Y wavelength plate 39 thereby to enter the Y device 40.
For instance, the Y device 40 is formed by LCOS (Liquid Crystal on Silicon) to modulate incident light by luminance signal of the same image signal as R-signal, G-signal and B-signal modulated by the R device 27, the G device 23 and the B device 31 respectively. Thus, the image signal to be displayed on a screen (not shown) is subjected to twice modulations, that is, one modulation by 3-primary color (R, G and B) signals and another modulation by the luminance signal. The modulated light from the Y device 40 is transmitted to the Y wire WG 38 through the Y wavelength plate 39 and its S-polarized light is reflected by the Y wire WG 38. Thereafter, P-polarized light component mixed in the S-polarized light is eliminated by the WG analyzer 41 so as to maintain its high-contrast and subsequently projected on the not-shown screen through the PJ lens 33.
According to the general optical system of FIG. 1, as the contrast of an image to be displayed on the screen is influenced by an optical F-number and the performance of the display device, there is no possibility that the image is displayed at a contrast value exceeding the proportion of thousands to one (thousands:1) in a situation of ensuring appropriate brightness. On the contrary, the optical system of FIG. 2 is constructed so as to project an image on a screen (not shown) after once forming an image, which has been brought by the first modulation optical system similar to FIG. 1, on the Y device 40 for a further modulation. Consequently, the contrast of the image displayed on the screen becomes equal to or more than the proportion of a million to one (a million: 1) as a result of multiplying a contrast value of the first modulation optical system by a contrast value of the second modulation optical system.
In the projector adopting the optical system of FIG. 2, however, there exists a reality that the resolving power (i.e. number of pixels) of the Y device 40 determines a final resolving power of an image projected on the screen. In even a highest-definition device produced in the market currently, this resolving power would be 4 k×2 k pixels (horizontal: 4,096 pixels, vertical: 2,160 pixels) at the highest.
Under such a situation, there is recently proposed a projector of FIG. 3 in order to attain a higher resolving power (8 k×4 k pixels). This projector is one proposed by Japan Broadcasting Corporation, which is referred to as “Super Hi-Vision (SHV)”. Here, the super Hi-Vision is one of a LSDI (Large Screen Digital Imagery) system with 7680×4320 pixels specified in Recommendation ITU-R BT.1769 “parameter values for an expanded hierarchy of LSDI image formats for production and international program exchange”. We now describe the operation of this projector with reference to FIG. 3. In the illustrated projector, a hard disk recorder (UDR) 45 capable of parallel-recording/reproducing 16 channels of HDTV images is adapted so as to output a G1G2 image signal and a RB image signal to a convergence correction device 46. In the convergence correction device 46, both convergences of the G1G2 image and the PB image are corrected in order to align their registrations with each other on a screen 49. After the convergence correction, light modulated by the RB image is projected by a RB projector 47, while light modulated by the G1G2 image is projected by a GG projector 48, forming an image on the screen 49.
In order to attain the resolving power of 8 k×4 k pixels, the G1G2 projector 48 utilizes two G devices (G1 device and G2 device) each having 4 k×2 k pixels. In common with the G1 and G2 devices, respective pixels are arranged at intervals of pitch Px in the horizontal direction and pitch Py in the vertical direction. As shown in FIG. 4, respective pixels forming the whole G1 device are shifted from respective pixels forming the whole G2 device by Px/2 in the horizontal direction and by Py/2 in the vertical direction. That is, while inputting signals meeting with the resolving power of G1G2 to the GG projector 28, respective images from the G1 and G2 devices are overlaid on each other at a slant of 45 degrees by half pixel, whereby the resolving power equivalent to 8 k pixels is attained. On the other hand, the RB projector 47 utilizes an R device and a B device each having 4 k×2 k pixels.
That is, it is difficult structurally to fabricate an optical system where 2 channels of green images are provided by a single projector. Therefore, the proposed projector of FIG. 3 adopts the shown constitution composed of the GG projector 48 for G1, G2 and the RB projector 47 as a result of eliminating a G-component from the RGB projector. In this projector, by projecting images from two projectors 47, 48 in stack and further combining respective images with each other onto the screen 49, a high resolving power (high-definition) can be attained.