JP2008268639A - Projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector capable of improving color reproducibility. <P>SOLUTION: The projector is equipped with: an image forming means 5 which has color filters of a plurality of colors, to form a color image; a light emitting diode 1 which generates light having a wide band wavelength; a projection optical system 6 which projects a projected image produced by irradiating the image forming means 5 with the light generated by the light emitting diode 1; and a light reducing filter 3 which is arranged in the optical path between the light emitting diode 1 and the image forming means 5 or in the optical path between the image forming means 5 and the projection optical system 6 and reduces the light near at least one boundary of the respective transparent wavelength regions of the plurality of color filters, of the light generated by the light emitting diode 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a projector.

  Conventionally, various projectors that project an image formed on a liquid crystal display panel onto a screen using a projection optical system are known. In recent years, a configuration has been proposed in which a projector unit is miniaturized using a high-intensity white LED as a light source, and the projector is incorporated into a mobile phone or the like (see, for example, Patent Document 1).

  The high-intensity white LED is generally realized by a blue LED and a YAG (yttrium, aluminum, garnet) -based phosphor layer disposed in front of the blue LED. The phosphor layer absorbs blue LED light and generates yellow component light. The generated yellow component light and the unabsorbed blue component light are mixed to obtain white light. The white light is irradiated onto a liquid crystal display panel provided with an RGB filter so as to project a color image.

JP 2006-93801 A

  However, the white light emitted from the white LED described above has light intensity peaks at the wavelength of the blue component and the wavelength of the yellow component. For this reason, the light (green component and red component) transmitted through each of the G (green) filter and the R (red) filter has an uneven intensity distribution, and there is a problem in color reproducibility.

According to the first aspect of the present invention, there is provided an image forming means for forming a color image with a plurality of color filters, a light emitting diode for generating light having a broad wavelength, and irradiating the image forming means with light generated by the light emitting diode. The projection optical system that projects the projection image generated in this manner, and the light generated by the light emitting diode, disposed in the optical path between the light emitting diode and the image forming means, or in the optical path between the image forming means and the projection optical system. And a neutral density filter that attenuates light in the vicinity of at least one boundary of the transmission wavelength regions of the plurality of color filters.
According to a second aspect of the present invention, in the projector according to the first aspect, the light emitting diode absorbs a part of the blue light generated from the blue light emitting diode that generates blue light and generates yellow light. And a neutral density filter, wherein the neutral density filter attenuates light near the boundary of the transmission wavelength range of the color filter in the wavelength range of yellow light.
According to a third aspect of the present invention, in the projector according to the second aspect, each pixel of the image forming means has a red display element having a red filter, a green display element having a green filter, and a blue display element having a blue filter. And are provided respectively.
According to a fourth aspect of the present invention, in the projector according to the second aspect, each pixel of the image forming means has a red display element having a red filter, a green display element having a green filter, and a blue display element having a blue filter. And a white display element that emits incident light almost as it is.
According to a fifth aspect of the present invention, in the projector according to any one of the first to fourth aspects, the image forming means is a reflective liquid crystal display panel, and separates light generated by the light emitting diode into two different polarized lights. And a polarization beam splitter that emits one polarized light to the reflective liquid crystal display panel.
According to a sixth aspect of the present invention, in the projector according to the fifth aspect, the neutral density filter includes a color filter so as to suppress a color change of the light caused by the incident angle dependency of the separation characteristic of the polarization beam splitter. It is characterized by dimming light in the vicinity of the boundary of the transmission wavelength range.
According to a seventh aspect of the invention, in the projector according to the sixth aspect, the neutral density filter substantially uniformly attenuates the light in the yellow wavelength range and emits light in the vicinity of the boundary of the transmission wavelength range of the color filter. Further, the light is reduced.
According to an eighth aspect of the present invention, in the projector according to any one of the fifth to seventh aspects, an illumination optical system is provided in which light generated by the light emitting diode is substantially parallel.
According to a ninth aspect of the present invention, in the projector according to any one of the fifth to eighth aspects, the neutral density filter is formed integrally with the polarizing beam splitter.

  According to the present invention, the color reproducibility of the projector can be improved.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
-First embodiment-
FIG. 1 is a schematic configuration diagram showing a first embodiment of a projector according to the present invention. The projector includes a white LED 1, a condensing lens 2, a filter 3, a polarizing beam splitter (hereinafter referred to as PBS) block 4, a reflective liquid crystal display panel LCOS (Liquid Crystal on Silicon) 5, a projection lens 6, and a display control unit. 7 is provided.

  The white LED 1 has a blue LED therein and a YAG (yttrium, aluminum, garnet) -based phosphor layer disposed in front of the blue LED. When blue component light is emitted from the blue LED, part of the blue component light is absorbed by the phosphor, and yellow component light is generated from the phosphor. White light is realized by mixing the yellow component light and the remaining blue component light.

  FIG. 2A is a diagram showing a spectral intensity distribution of white light emitted from the white LED 1. The white LED 1 emits broadband light having a wide wavelength range, but there are two peaks in the spectral intensity distribution. One of them is a relatively narrow peak corresponding to the blue component light emitted from the blue LED, and the peak wavelength is about 460 nm. The second peak is a broad peak corresponding to the yellow component light generated from the phosphor, and the peak wavelength is about 580 nm.

  The illumination light emitted from the white LED 1 is converted into substantially parallel light by the condenser lens 2. The illumination light that has been made substantially parallel light enters the PBS block 4 via the filter 3. The PBS block 4 is formed with a polarization separation portion 4a at an angle of 45 degrees with respect to the incident optical axis. The filter 3 is formed integrally with the incident surface 4 b of the PBS block 4. Details of the filter 3 will be described later.

  The light transmitted through the filter 3 enters the PBS block 4 and enters the polarization separation unit 4a at an angle of 45 degrees. The light incident on the polarization separation unit 4a is separated into P-polarized light that passes through the polarization separation unit 4a and S-polarized light reflected by the polarization separation unit 4a. The P-polarized light transmitted through the polarization separation unit 4a is incident on the LCOS 5 which is a reflective liquid crystal. On the other hand, the S-polarized light reflected by the polarization separation unit 4a is emitted from the surface 4c of the PBS block 4 as unnecessary light that is not used for projection. For example, non-reflective processing such as black processing may be performed on the surface 4c. Further, a polarizing plate that converts illumination light into linearly polarized light (P-polarized light) or extracts linearly polarized light from the illumination light may be disposed between the filter 3 and the illumination lens 2.

  As described above, the LCOS 5 is a reflective liquid crystal display panel, and the light incident on the LCOS 5 travels through the liquid crystal layer upward in the figure, then is reflected by the reflective surface of the LCOS 5 and travels again down the liquid crystal layer in the figure. It is emitted from. The video signal is input to the LCOS 5 from the display control unit 7, and a voltage is applied to each display element according to the level of the video signal. At that time, the arrangement of the liquid crystal molecules in the liquid crystal layer changes according to the voltage application state, and the liquid crystal layer serves as a phase plate. As a result, the light emitted from the LCOS 5 to the PBS block 4 is a mixed light of modulated light that is S-polarized light and unmodulated light that is P-polarized light.

  The LCOS 5 is a color display panel. As shown in FIG. 4A, each of the two-dimensionally arranged display elements has red (R), green (G), and blue (b) color filters. , And one pixel is composed of display elements of three colors of R, G, and B. For example, when all of the R display element, the G display element, and the B display element are on-displayed, the colors of red, green, and blue are mixed, and the pixel is in a state of displaying white.

  The polarization separation unit 4 a of the PBS block 4 reflects only the modulated light that is S-polarized light out of the mixed light incident from the LCOS 5 and guides it to the projection lens 6. The projection lens 6 projects the modulated light from the PBS block onto a screen (not shown) as projection light. On the other hand, the unmodulated light that is P-polarized light is transmitted through the polarization separation unit 4a.

[Detailed description of filter 3]
Next, the function of the filter 3 will be described in detail. The color filters (R filter, G filter, and B filter) provided in the LCOS 5 generally have transmission characteristics as shown in FIG. In the transmission characteristics shown in FIG. 2B, the B filter transmits light in the wavelength region centered on wavelength = 460 nm, the G filter transmits light in the wavelength region centered on wavelength = 530 nm, and the R filter. Transmits light in a wavelength region centered on wavelength = 630 nm.

  On the other hand, the illumination light emitted from the white LED 1 has a spectral intensity distribution as shown in FIG. In the example shown in FIG. 2A, the boundary between the wavelength range of the G filter and the wavelength range of the R filter, that is, the line where the transmittance of the G filter decreases and the line where the transmittance of the R filter decreases intersect. The wavelength of the valley portion and the peak wavelength on the long wavelength side of the illumination light substantially coincide.

  Therefore, when the illumination light emitted from the white LED 1 is passed through the R filter, G filter, and B filter, the R light component, G light component, and B light component transmitted through the R, G, and B filters are shown in FIG. ) Distribution as shown below. That is, the R light component and G light component in FIG. 2C have a distribution biased toward the wavelength = 580 nm side. As a result, the conventional projector in which the filter 3 is not provided has a problem that red and green color reproducibility deteriorates.

  FIG. 3A shows an example of the transmission characteristics of the filter 3. The filter 3 has a characteristic as a so-called notch filter, and attenuates light having a predetermined wavelength width (for example, about ± 20 nm) centered on a wavelength = 580 nm. Regarding the transmission characteristics of the filter 3, for example, the wavelength range for dimming and the degree of dimming are set so that the G light component and the R light component are appropriately separated according to the height and shape of the peak of the yellow component. Just do it.

  When the illumination light having the characteristics as shown in FIG. 2A is passed through the filter 3 as shown in FIG. 3A, the transmitted light has a distribution as shown in FIG. 3B. In the vicinity of the wavelength of 580 nm, the distribution changes as indicated by the symbol A, and the hatched portion is cut. Therefore, when such illumination light is passed through the R, G, and B filters, the R light component, the G light component, and the B light component are distributed as shown in FIG. Compared with the case where the filter 3 is not used (the case of FIG. 2 (c)), the broken line shows the intensity of the G light component and the R light component in the vicinity of the wavelength of 580 nm by the amount corresponding to the shaded portion in FIG. Decrease. As a result, the separation of the R light component and the G light component is improved, and the red and green color reproducibility is improved.

-Second Embodiment-
In the above-described LCOS5, three display elements having R, G, and B filters are provided in one pixel. However, in order to increase the luminance of the image, the “RGBW” method in which a white (W) display element is further added. May be adopted. FIG. 4B shows an example of an “RGBW” type filter array. No color filter is arranged on the W display element. In the W display element, the incident illumination light is reflected as it is when a voltage is applied. Therefore, the white color formed by the W display element has the same spectral intensity distribution as that of the illumination light shown in FIG.

  On the other hand, the white color generated by the R, G, and B display elements is a white color obtained by mixing the R light component, the G light component, and the B light component in FIG. Comparing the distribution shown in FIG. 2 (a) with the distribution shown in FIG. 2 (c), the distribution around the wavelength of 580 nm is different by passing through the RGB filter. Become. As a result, when a W display element is used, the color temperature varies depending on how much light from the W display element is mixed, and color reproduction becomes difficult.

  However, when light having a wavelength of about 580 nm is cut by providing the filter 3 as described above, the white color generated by the R, G, and B display elements is the R light component, G light component, and B in FIG. A white color obtained by mixing light components. On the other hand, the white spectrum intensity distribution by the W display element is obtained by cutting the hatched portion in FIG. That is, as a result, the filter 3 is provided to cut the light in the vicinity of the wavelength 580 nm of the illumination light that illuminates the LCOS 5, so that the wavelength between the white color by the conventional RGB display element and the white color by the W display element is 580 nm. Differences in the distribution in the vicinity can be reduced, and color reproducibility can be improved.

-Third embodiment-
By the way, as a cause of impairing the color reproducibility, in addition to the distribution of the color components of the illumination light described above, there is a variation in the incident angle of the illumination light with respect to the polarization separation unit 4a of the PBS block 4. As shown in FIG. 5A, the PBS separation performance is designed to be exhibited when the angle α between the light traveling direction and the polarized light separating portion 4a is 45 °. FIG. 5B schematically shows the angle dependency of the transmittance of the P-polarized light to be transmitted, and shows the cases where the angle α is 45 ° and 35 °. When the angle α is as small as 35 °, the transmittance is reduced on the short wavelength side (blue component wavelength). As a result, the intensity of the blue component of the spectral intensity distribution of the P-polarized light transmitted through the PBS block 4 not provided with the filter 3 is reduced as indicated by the one-dot chain line in FIG. For this reason, the illumination light becomes yellowish white light, and the white color reproducibility is lowered.

  Therefore, in the third embodiment, the transmission characteristic of the filter 3 is a characteristic having both the transmission characteristic shown by the broken line in FIG. 6A and the transmission characteristic shown by the solid line. Specifically, the filter 3a having the broken line characteristic and the filter 3b having the solid line transmission characteristic may be formed on the illumination light incident surface of the PBS block 4. As shown by the broken line in FIG. 6B, the use of the filter 3b reduces the yellow component centered on the wavelength = about 580 nm in the intensity of the illumination light. Roughly, the area of the portion indicated by S1 corresponding to the decrease of the blue component and the area of the portion indicated by S2 corresponding to the decrease of the yellow component may be approximately the same.

  Furthermore, by using the filter 3a, the intensity in the vicinity of the wavelength of 580 nm is further reduced, and the separation characteristic between the G light component and the R light component can be improved. Even when only the filter 3a is used, it is possible to give the same function as the filter 3b by increasing the wavelength range of the light to be cut.

  In the above-described embodiment, the filter 3 is formed on the illumination light incident surface 4b of the PBS block 4. However, the filter 3 is formed on the projection light exit surface 4d of the PBS block 4, the surface of the projection lens 6, the exit surface of the condenser lens 2, and the like. You may do it. Furthermore, the filter 3 may be disposed as an independent filter member in the optical path between the condenser lens 2 and the PBS block 4 or in the optical path between the PBS block 4 and the projection lens 6. As a means for forming an image, a transmissive liquid crystal display panel can be used in addition to the above-described reflective liquid crystal display panel. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims.

1 is a schematic configuration diagram showing a first embodiment of a projector according to the present invention. It is a figure explaining illumination light, (a) shows the spectral intensity distribution of illumination light, (b) shows the transmission characteristic of an RGB filter, (c) shows the B light component of the illumination light which passed the RGB filter, The distribution of the G light component and the R light component is shown. It is a figure explaining the effect of the filter 3, (a) shows the permeation | transmission characteristic of the filter 3, (b) shows the spectrum intensity distribution of the illumination light which passed the filter 3, (c) is illumination of (b) The distribution of the B light component, G light component, and R light component after passing light through the RGB filter is shown. It is a figure which shows an example of the filter arrangement | sequence in LCOS5, (a) shows the case of RGB system, (b) shows the case of RGBW system. It is a figure explaining the angle dependence of the isolation | separation characteristic of PBS block 4, (a) shows the relationship between PBS block 4 and incident light, (b) The transmittance | permeability in the case of angle 35 degrees and angle 45 degrees FIG. It is a figure explaining the effect of filter 3a, 3b, (a) shows the transmission characteristic of filter 3a, 3b, (b) shows the spectrum intensity distribution of the illumination light at the time of using filter 3b, (c) Indicates the spectral intensity distribution of the illumination light when the filters 3a and 3b are used.

Explanation of symbols

  1: white LED, 2: condensing lens, 3: filter, 4: PBS block, 5: LCOS, 6: projection lens, 7: display control unit,

Claims (9)

Image forming means for forming a color image with a plurality of color filters;
A light emitting diode that generates light of a broad wavelength range;
A projection optical system for projecting a projection image generated by irradiating the image forming means with light generated by the light emitting diode;
Among the light generated by the light emitting diodes, disposed in the optical path between the light emitting diode and the image forming unit or in the optical path between the image forming unit and the projection optical system, A projector comprising: a neutral density filter that attenuates light in the vicinity of at least one boundary of each transmission wavelength region. The projector according to claim 1, wherein
The light emitting diode includes a blue light emitting diode that generates blue light, and a phosphor that generates yellow light by absorbing part of the blue light generated from the blue light emitting diode.
The projector is characterized in that the neutral density filter attenuates light in the vicinity of a boundary of a transmission wavelength range of the color filter in the wavelength range of the yellow light. The projector according to claim 2,
Each of the pixels of the image forming unit is provided with a red display element having a red filter, a green display element having a green filter, and a blue display element having a blue filter. The projector according to claim 2,
Each pixel of the image forming unit includes a red display element having a red filter, a green display element having a green filter, a blue display element having a blue filter, and a white display element that emits incident light almost as it is. A projector characterized by being provided. In the projector as described in any one of Claims 1-4,
The image forming means is a reflective liquid crystal display panel,
A projector comprising: a polarization beam splitter that separates light generated by the light emitting diode into two different polarized lights and emits one polarized light to the reflective liquid crystal display panel. The projector according to claim 5, wherein
The neutral density filter attenuates light in the vicinity of the boundary of the transmission wavelength region of the color filter so as to suppress the color change of light caused by the incident angle dependency of the separation characteristic of the polarization beam splitter. Projector. The projector according to claim 6, wherein
The projector according to claim 1, wherein the neutral density filter substantially uniformly attenuates the light in the yellow light wavelength range and further reduces the light in the vicinity of the boundary of the transmission wavelength range of the color filter. In the projector as described in any one of Claims 5-7,
A projector comprising an illumination optical system that makes light generated by the light emitting diode substantially parallel light. The projector according to any one of claims 5 to 8,
A projector characterized in that the neutral density filter is formed integrally with the polarizing beam splitter.

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