JP2008298951A - Image projection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image projection device which is small in loss of light quantity and irregular color and is compact and excellent in portability. <P>SOLUTION: The image projection device comprises: a light source B eradiating blue light L1; a light source G radiating green light L2; a light source R radiating red light L3; a dichroic mirror DB synthesizing the blue light L1 and the red light L3 by reflecting the blue light L1 and transmitting the red light L3; a dichroic mirror DA synthesizing the blue light L1, the red light L3 and the green light L2 by reflecting the synthesized blue light L1 and red light L3 and transmitting the green light L2; and a projection optical system PL for projecting the synthesized light to an external screen or the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image projection apparatus for combining a plurality of lights having different wavelengths and projecting the light onto, for example, a screen.

  The following Patent Document 1 combines light from a red light source, a green light source, and a blue light source, enters the liquid crystal panel, and synchronizes the time-division driving of the liquid crystal panel with the lighting timing of each light source. A projection-type image display device sharing the same has been proposed.

  In the following Patent Document 2, the first dichroic mirror transmits the light from the red LED and reflects the light from the blue LED, thereby combining the red light and the blue light, and then the second dichroic mirror is combined. An image projection apparatus has been proposed in which red light, blue light, and green light are combined by transmitting the red light and blue light and reflecting the light from the green LED.

JP-A-8-140107 (FIG. 1) Japanese Patent Laying-Open No. 2005-49453 (FIG. 2)

  In Patent Document 1, since the light is synthesized using four mirrors, the synthesis optical system becomes large. Further, since the emission position after combining the three colors of light is located at the center of the apparatus, it is difficult to arrange a projection optical system for miniaturizing the apparatus. Further, the light loss is increased because the light from the green light source passes through the dichroic mirror twice.

  In Patent Document 2, the light amount loss of green light is minimized by combining green light at a point close to the projection optical system. However, since the blue light is synthesized so as to pass through the dichroic mirror, the light amount loss of the blue light tends to increase. In addition, since the projection optical system is arranged along the arrangement direction of the blue LEDs and the red LEDs, the entire apparatus must be elongated in the projection direction, which is inconvenient to carry and store.

  An object of the present invention is to provide an image projection apparatus that is small in size and excellent in portability, with little light loss and color unevenness.

In order to achieve the above object, an image projection apparatus according to the present invention includes a first light source that emits light L1 having a wavelength λ1,
A second light source that emits light L2 having a wavelength λ2 longer than the wavelength λ1,
A third light source that emits light L3 having a wavelength λ3 longer than the wavelength λ2,
A first combining optical element for combining the light L1 and the light L3;
A second combining optical element for combining the light L1, L2, L3 by reflecting the combined light L1, L3 and transmitting the light L2,
A projection optical system for projecting the combined lights L1, L2, and L3.

  In the present invention, the first combining optical element preferably combines the light L1 and the light L3 by reflecting the light L1 and transmitting the light L3.

In the present invention, the second synthetic optical element includes a dichroic film in which a high refractive index film having a refractive index of 2.0 to 2.6 and an intermediate refractive index film having a refractive index of 1.6 to 2.0 are stacked. The difference ΔN _H−L between the refractive index of the high refractive index film and the refractive index of the intermediate refractive index film is
0.55 ≦ ΔN _H−L ≦ 0.7
Is preferably satisfied.

In the present invention, the high refractive index film is preferably formed of one or a mixture of two or more selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and ZrO ₂ .

In the present invention, the intermediate refractive index film is formed of Al ₂ O ₃ or one or more selected from the group consisting of SiO ₂ , TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and ZrO _2. It is preferable to form with the mixture of these.

  In the present invention, the first light source, the second light source, and the third light source are preferably configured by light emitting diodes.

In the present invention, a fourth light source that emits light La having a wavelength λa longer than the wavelength λ2 and shorter than the wavelength λ3;
It is preferable to further include a third synthesis optical element for synthesizing the light La and the light L3.

  In the present invention, it is preferable to further include a lens provided between the first combining optical element and the second combining optical element for adjusting the divergence angle of the lights L1 and L3 combined by the first combining optical element.

  According to the present invention, when the three colors of light are combined, the second light source that emits the light L2 having the wavelength λ2 is arranged in a transmission type, the first light source that emits the light L1 having the wavelength λ1, and the light L3 having the wavelength λ3. By arranging the third light source that radiates the light in a reflection type, the entire apparatus including the projection optical system can be configured in a shape close to a square, which is convenient for carrying and storage.

  In addition, when the wavelength λ2 is set in the green wavelength region, it is possible to project a bright image because it is possible to minimize the loss of the amount of green light with high human relative visibility.

  Furthermore, when the light L1 and the light L3 are combined, the light loss of the light L1 can be minimized by adopting an arrangement that reflects the light L1 having the shortest wavelength λ1 and transmits the light L3 having the longest wavelength λ3. A bright image with little color unevenness can be projected.

(First embodiment)
FIG. 1 is a configuration diagram showing a first embodiment of the present invention. This image projection apparatus includes a combining optical system 1 for combining a plurality of lights having different wavelengths, an introducing optical system 2 for introducing the combined light into the modulation panel PA, and the modulated light to an external screen or the like. It comprises a projection optical system PL for projecting.

  The combining optical system 1 reflects the blue light L1, the light source G that emits the blue light L1, the light source G that emits the green light L2, the light source R that emits the red light L3, and the red light L3. The dichroic mirror DB for combining the blue light L1 and the red light L3, the combined blue light L1 and the red light L3 are reflected, and the green light L2 is transmitted, whereby the blue light L1, the red light L3, and the green light are reflected. It is composed of a dichroic mirror DA that synthesizes L2.

  The light source B includes a plurality of (here, four) blue LEDs (light emitting diodes) arranged symmetrically around the optical axis, and a plurality (here, four) partial parabolas focusing on the light emitting point of each blue LED. A surface mirror MP is provided. Each blue LED emits light toward the partial parabolic mirror MP. Each partial parabolic mirror MP reflects the light from each LED, and makes the substantially parallel blue light L1 incident on the dichroic mirror DB as a whole.

  Similarly, the light source R includes a plurality (here, four) of red LEDs arranged symmetrically around the optical axis, and a plurality (here, four) partial paraboloids focusing on the light emission point of each red LED. A mirror MP is provided. Each red LED emits light toward the partial parabolic mirror MP. Each partial parabolic mirror MP reflects the light from each LED, and makes the substantially parallel red light L3 incident on the dichroic mirror DB as a whole.

  The light source G includes a plurality of (here, four) green LEDs arranged symmetrically around the optical axis, and a plurality (here, four) partial paraboloidal mirrors MP that focus on the light emission point of each green LED. Is provided. Each green LED emits light toward a partial parabolic mirror MP. Each partial parabolic mirror MP reflects the light from each LED, and makes the substantially parallel green light L2 incident on the dichroic mirror DA as a whole.

  Between the dichroic mirror DB and the dichroic mirror DA, an adjustment lens LB that can match the divergence angle of the green light L2 by adjusting the divergence angles of the synthesized blue light L1 and red light L3 may be disposed. preferable. As a result, the illumination conditions of the respective color lights on the modulation panel can be made the same, and color unevenness can be prevented. Note that the adjustment lens LB may be omitted when the influence on the color unevenness is small, such as when the difference in divergence angle is small.

  The introduction optical system 2 includes a condenser lens LA, a rod intaglator RI, folding mirrors M1, M2, and M3, a modulation panel PA, and the like.

  The condensing lens LA collects the combined blue light L1, red light L3, and green light L2, and causes the light to enter the rod intaglator RI. The rod intaglator RI is formed of a transparent material in a prismatic shape and has a function of converting into diffused light by repeating internal reflection.

  The folding mirrors M1, M2, and M3 reflect the diffused light from the rod intaglator RI, convert it to a desired size, and enter the modulation panel PA.

  The modulation panel PA has a function in which a plurality of light modulation elements are arranged two-dimensionally and modulates a planar light beam in units of pixels. For example, a DMD (Digital Micromirror Device, Texas Instruments), an LCD (liquid crystal) panel, etc. Consists of. The light modulated by the modulation panel PA is projected onto an external screen or the like by the projection optical system PL.

  Regarding the electric circuit system, a drive circuit 11 for driving the light source B, a drive circuit 12 for driving the light source G, a drive circuit 13 for driving the light source R, and the modulation panel PA according to the image signal Sv. And a control circuit 20 for outputting operation timing signals Sr, Sb, Sg of the drive circuits 11, 12, 13 and the like.

  The control circuit 20 modulates the blue light L1, the green light L2, and the red light L3 in a time division manner. Specifically, when a blue image is projected, the light source B is turned on, the light source G and the light source R are turned off, the modulation panel PA is driven according to the blue signal component, and the blue light L1 modulated by the blue signal component Project. When projecting a green image, the light source G is turned on, the light sources B and R are turned off, the modulation panel PA is driven according to the green signal component, and the green light L2 modulated by the green signal component is projected. When projecting a red image, the light source R is turned on, the light sources B and G are turned off, the modulation panel PA is driven according to the red signal component, and the red light L3 modulated by the red signal component is projected. In this way, full-color image projection is realized by projecting the blue light L1, the green light L2, and the red light L3 in a time-sharing manner.

  In this embodiment, a bright data projector or the like can be realized by using high-luminance type LEDs called power LEDs as the light sources B, G, and R. The size of the high-brightness LED is usually about 1 mm to several mm. Therefore, even if collimation can be performed using an optical element such as a lens or a reflecting mirror to reduce the directivity, a certain area exists in the light-emitting portion, so that the influence has a certain divergence angle. Resulting in.

  Increasing the size of the optical element improves directivity, but enlarges the entire device. Usually, for example, the directivity is often improved with a lens or a reflecting mirror of about φ10 to 20 mm. The reason is that a certain degree of directivity can be secured while being compact.

  The focal length of the optical element that satisfies the above conditions is about 5 mm. When an LED having a light emitting area of 2 mm square is used, the divergence angle is Y = f × tan θ, and Y = 1 mm (2 mm Half), f = 5 mm is substituted, and θ = 11 degrees.

  Therefore, the divergence angle after collimating a normal high-brightness LED with an optical element is about ± 10 degrees. That is, light is incident on the dichroic film so as to have a spread of about 45 ± 10 °.

  Furthermore, the wavelength distribution of each color of the LED partially overlaps around the emission spectrum as shown in FIG. The vertical axis in FIG. 2 is the relative intensity of light, and the horizontal axis is the wavelength (nm).

  When performing full color image projection, in general, a blue (BLUE) LED having a central wavelength of about 460 nm, a green (GREEN) LED having a central wavelength of about 530 nm, and a red (RED) LED having a central wavelength of about 640 nm Use a combination with.

  Therefore, the reflection band and the transmission band of the dichroic film in the synthesis optical system 1 ensure an appropriate wavelength range, and the 50% transmission wavelength is less likely to lose the light amount as the shift amount with respect to the incident angle is smaller.

  The shift amount of the dichroic film with respect to the incident angle of the 50% transmission wavelength has a characteristic that it increases as the difference in refractive index between the high refractive index material and the low refractive index material increases. Therefore, when the dichroic film is formed with the intermediate refractive index material and the high refractive index material, the shift amount with respect to the incident angle becomes small.

The high refractive index film is a material having a refractive index of 2.0 to 2.6 at a wavelength of 550 nm, for example, TiO ₂ (refractive index: 2.3 to 2.55), Nb ₂ O ₅ (refractive index: 2). .348), Ta ₂ O ₅ (refractive index: 2.16), and ZrO ₂ (refractive index: 2.05), and is preferably formed of one or a mixture of two or more.

The intermediate refractive index film is a material having a refractive index of 1.6 to 2.0 at a wavelength of 550 nm, for example, Al ₂ O ₃ (refractive index: 1.63), or SiO ₂ (low refractive index material). Refractive index: 1.479) and a mixture of at least one selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and ZrO ₂ which are high refractive index materials.

Further, the difference ΔN _H−L between the refractive index of the high refractive index film and the refractive index of the intermediate refractive index film is preferably 0.55 or more and 0.7 or less. By satisfying this conditional expression, the securing of the reflection band and the shift amount with respect to the incident angle can be satisfied at the same time. Further, the refractive index difference ΔN _H−L is more preferably 0.6 or more and 0.7 or less.

  As shown in FIG. 3C, when the refractive index difference of the laminated film is reduced, the shift amount Sa of the 50% transmission wavelength is reduced, but the reflection band Bw is reduced. Therefore, regarding the arrangement of the dichroic film and the light source, the wavelength band is different as means for securing the reflection band Bw in the configuration of BG reflection with R transmission (see FIG. 3B) or the configuration of GR reflection with B transmission. Generally, two reflection bands Bw are overlapped to secure a reflection band (see FIG. 3D). However, ripples are likely to occur at the connection between the different reflection bands Bw (see FIG. 3E), making it difficult to produce a dichroic film.

  On the other hand, in the case of the G transmission and BR reflection configuration (see FIG. 3A), the reflection band Bw is not continuous, and there is no need to overlap the reflection band Bw (see FIG. 3F). A film with less ripple can be manufactured (see FIG. 3G).

The following (Table 1) shows the multilayer structure of the dichroic mirror DA. BK7 is used as a substrate, and Nb ₂ O ₅ having a predetermined thickness (represented as Nb ₂ O ₅ , refractive index: 2.348), SiO ₂ having a predetermined thickness (molar ratio 80%) and Nb ₂ O ₅ ( A mixture having a molar ratio of 20% (denoted as mixture A, refractive index: 1.7) is alternately laminated to form a total of 58 multilayer films.

The following (Table 2) shows the multilayer structure of the dichroic mirror DB. BK7 is used as a substrate, and Nb ₂ O ₅ having a predetermined thickness (represented as Nb ₂ O ₅ , refractive index: 2.33), SiO ₂ having a predetermined thickness (molar ratio 80%) and Nb ₂ O ₅ ( A mixture having a molar ratio of 20% (denoted as mixture A, refractive index: 1.7) is alternately laminated to form a total of 30 multilayer films.

  FIG. 4A is a graph showing the wavelength dependence of the dichroic mirror DA according to (Table 1). FIG. 4B is a graph showing the wavelength dependence of the dichroic mirror DB according to (Table 2).

  First, referring to FIG. 4A, the dichroic mirror DA transmits a green emission spectrum having a center wavelength of about 530 nm, reflects a blue emission spectrum having a center wavelength of about 460 nm, and has a center of about 640 nm. It can be seen that the red emission spectrum having the wavelength is reflected.

  Next, referring to FIG. 4B, it can be seen that the dichroic mirror DB reflects a blue emission spectrum having a center wavelength of about 460 nm and transmits a red emission spectrum having a center wavelength of about 640 nm.

  In the present embodiment, since the blue light and the red light are employed as the reflection band Bw of the dichroic mirror DA, the occurrence of ripple as described above can be suppressed. In the dichroic mirror DB, since it is not necessary to consider green light, a blue light reflection band and a red light transmission band can be realized with a relatively simple film configuration.

  Next, the difference between the light source arrangement according to the present embodiment and the light source arrangement according to Japanese Patent Application Laid-Open No. 2005-49453 will be described.

Generally, a dichroic film has a transmittance of p-polarized light and s-polarized light with respect to an incident angle as a refractive index difference ΔN _H−L between a high refractive index material (refractive index H) and a low (intermediate) refractive index material (refractive index L) is small. The shift amount of the average value of 50% (half-value wavelength shift amount) becomes small.

Further, the smaller the refractive index difference ΔN _H−L, the narrower the half-value wavelength width of p-polarized light and s-polarized light, and the smaller the 20% and 80% wavelength width (gradient wavelength width) of the average transmittance.

  Specifically, the relationship between the refractive index difference and the half-value wavelength shift amount depending on the incident angle is examined. As an example, the main wavelength λ is determined so that the half angle wavelength is 540 nm at an incident angle of 45 degrees, the first layer and the last layer are made of a high refractive index material having an optical film thickness λ / 8, and the intermediate layer is an optical film. A total of 31 multilayer films (FIG. 5) in which low-refractive index materials and high-refractive index materials having a thickness of λ / 4 are alternately coated will be considered.

The following (Table 3) shows (1) a combination in which the high refractive index material is Nb ₂ O ₅ (refractive index: 2.348) and the low refractive index material is SiO ₂ , and (2) the high refractive index material is the same. Nb ₂ O ₅ , intermediate refractive index material is a mixture of Nb ₂ O ₅ (molar ratio 19%) and SiO ₂ (molar ratio 81%) (refractive index: 1.690), (3) high refractive index material is the same With respect to a mixture (refractive index: 1.720) of Nb ₂ O ₅ and an intermediate refractive index material of Nb ₂ O ₅ (molar ratio 22%) and SiO ₂ (molar ratio 78%), the half-value wavelength shift amount and the tilt wavelength width The result of calculating is shown.

Further, bandwidth reflection is determined by the refractive index difference .DELTA.N _H-L, the larger the refractive index difference reflectivity of 99% or more of the width (reflection bandwidth) increases. Specifically, the main wavelength λ is adjusted so that the wavelength 530 nm at the center of the reflection band does not change at an incident angle of 45 degrees, and a high refractive index material and a low (intermediate) refraction are formed on the substrate BK7 by a film thickness λ / 4. A multi-layered film having a total of 30 layers was formed by alternately coating the rate material.

  The following (Table 4) shows the results of calculating the reflection bandwidth for the combinations (1) to (3). From Table 4, it can be seen that the greater the difference in refractive index, the greater the reflection bandwidth.

  When synthesizing red and blue colors and green colors, it is synthesized by a dichroic film that reflects red and blue and transmits green, and by a dichroic film that transmits red and blue and reflects green Can be considered. In general, in the case of an LED, the wavelength where blue and green overlap is about 490 nm, and the wavelength where green and red overlap is about 600 nm. Therefore, the average transmittance wavelength (half-value wavelength) of 50% of the p-polarized light and s-polarized light of the dichroic film to be synthesized is about 490 nm and about 600 nm, so that the amount of light loss can be reduced.

When color synthesis is performed using a dichroic film that reflects green and transmits red and blue, the green wavelength band is reflected and the half-value wavelength is coated so as to be the wavelength between blue and green and between green and red. In order to reduce the light loss, it is necessary to secure a sufficient green reflection band. For that purpose, when Nb ₂ O ₅ is used as the high refractive index material, the refractive index of the low (intermediate) refractive index material needs to be 1.69 or less. The red and blue transmission bands can be set to desired values by adjusting the film thickness by overlapping the number of layers.

On the other hand, when color synthesis is performed using a dichroic film that transmits green and reflects blue and red, the refractive index difference ΔN that reflects the blue wavelength band of 430 nm to about 490 nm and the red reflection band of 600 nm to 670 nm. _HL is desirable.

When Nb ₂ O ₅ is used as the high refractive index material, the refractive index of the low (intermediate) refractive index material is desirably 1.72 or less in order to sufficiently secure the red reflection band and the blue reflection band. . By the way, in the band of 430 nm or less on the short wavelength side of blue and the wavelength of 670 nm or more on the long wavelength side of red, the light emission intensity of the LED is small and the relative visibility is low. There is little impact on. From this point, when Nb ₂ O ₅ is used as the high refractive index material, the refractive index of the low (intermediate) refractive index material is desirably 1.8 or less. On the other hand, the green transmission band can be set to a desired value by adjusting the film thickness by overlapping the number of layers.

  Comparing both light source arrangements, the dichroic film that transmits green and reflects blue and red can be designed and coated such that the refractive index ratio is smaller. Since the design can be made with a small difference in refractive index, a dichroic film with a small half-value wavelength shift amount and a small tilt wavelength width can be coated, and as a result, a film with little light loss can be manufactured. Therefore, a dichroic film that transmits green and reflects red and blue as in the configuration of the present embodiment, rather than a dichroic film that reflects green and transmits blue and red as in the configuration of Patent Document 2. However, color composition is possible with little loss of light.

(Second Embodiment)
Fig.6 (a) is explanatory drawing which shows the light source arrangement | positioning which concerns on 2nd Embodiment of this invention. The image projection apparatus according to the present embodiment has the same configuration as that in FIG. 1, a combining optical system 1 for combining a plurality of lights having different wavelengths, and a function for introducing the combined light into the modulation panel PA. The optical system 2 includes an introduction optical system 2 and a projection optical system PL for projecting modulated light onto an external screen or the like.

  The combining optical system 1 includes a light source B that emits blue light L1, a light source G that emits green light L2, a light source R that emits red light L3, and a dichroic mirror DB that combines the blue light L1 and the red light L3. , A dichroic mirror DA that combines the blue light L1, the red light L3, and the green light L2.

  In the present embodiment, a dichroic mirror DC that reflects the red light L3 is further added to the dichroic mirrors DA and DB shown in FIG.

The following (Table 5) shows the multilayer structure of the dichroic mirror DC. BK7 is used as a substrate, and Nb ₂ O ₅ having a predetermined film thickness and SiO ₂ having a predetermined film thickness are alternately laminated thereon to form a total of 19 multilayer films.

  FIG. 6B is a graph showing the wavelength dependence of the dichroic mirror DC according to (Table 5). From this graph, it can be seen that the red emission spectrum having a center wavelength of about 640 nm is reflected with high reflectance.

  In the present embodiment, since the light source R, the light source B, and the light source G can be arranged linearly, the drive circuits 11, 12, and 13 of each light source are mounted on a single circuit board, or an LED or a partial parabolic mirror MP. Etc. can be mounted on a single cooling mechanism.

(Third embodiment)
Fig.7 (a) is explanatory drawing which shows the light source arrangement | positioning which concerns on 3rd Embodiment of this invention. The image projection apparatus according to the present embodiment has the same configuration as that in FIG. 1, a combining optical system 1 for combining a plurality of lights having different wavelengths, and a function for introducing the combined light into the modulation panel PA. The optical system 2 includes an introduction optical system 2 and a projection optical system PL for projecting modulated light onto an external screen or the like.

  The combining optical system 1 includes a light source B that emits blue light L1, a light source G that emits green light L2, a light source R that emits red light L3, and a dichroic mirror DB that combines the blue light L1 and the red light L3. , A dichroic mirror DA that combines the blue light L1, the red light L3, and the green light L2.

  In the present embodiment, as shown in FIG. 2, a dichroic mirror DC that adds a light source Y including an yellow (AMBER) LED having a center wavelength of about 590 nm, reflects red light L3, and transmits yellow light La is used. Has been added.

The following (Table 6) shows a multilayer film configuration of the dichroic mirrors DA, DB, and DC. The dichroic mirror DA is a mixture of Nb ₂ O ₅ having a predetermined thickness as a high refractive index material and a mixture of Nb ₂ O ₅ and SiO ₂ having a predetermined thickness as an intermediate refractive index material (refractive index: 1.. 70) are alternately laminated to form a total of 48 multilayer films.

The dichroic mirrors DB and DC are formed on a BK7 substrate with a predetermined thickness of Nb ₂ O ₅ as a high refractive index material, and a predetermined thickness of SiO ₂ (molar ratio 80%) and Nb ₂ O ₅ as intermediate refractive index materials. A mixture of (molar ratio 20%) (indicated as mixture A, refractive index: 1.7) is alternately laminated to form a total of 30 multilayer films.

  FIGS. 7B to 7D are graphs showing the wavelength dependence of the dichroic mirrors DA, DB, and DC according to (Table 6), respectively. Referring to FIG. 7B, the dichroic mirror DA transmits a green emission spectrum having a center wavelength of about 530 nm, reflects a blue emission spectrum having a center wavelength of about 460 nm, and has a center wavelength of about 590 nm. It can be seen that it reflects the emission spectrum and reflects the red emission spectrum having a center wavelength of about 640 nm.

  Referring to FIG. 7C, the dichroic mirror DB reflects a blue emission spectrum having a center wavelength of about 460 nm, transmits a yellow emission spectrum having a center wavelength of about 590 nm, and has a center wavelength of about 640 nm. It can be seen that the red emission spectrum possessed is transmitted.

  Referring to FIG. 7D, it can be seen that the dichroic mirror DC transmits a yellow emission spectrum having a center wavelength of about 590 nm and reflects a red emission spectrum having a center wavelength of about 640 nm.

  In this embodiment, since the light source Y is added to the light source R, the light source B, and the light source G, color reproducibility can be improved.

  In place of the light source Y, as shown in FIG. 2, a light source including a cyan (CYAN) LED having a central wavelength of about 505 nm, or a light source including a blue-violet (ROYAL BLUE) LED having a central wavelength of about 450 nm. It is also possible to add a dichroic mirror DC whose wavelength dependency is appropriately adjusted. With such a configuration, color reproducibility can be improved.

  INDUSTRIAL APPLICABILITY The present invention is extremely useful in that it can provide an image projection apparatus that is small in size and excellent in portability with little light loss and color unevenness.

It is a block diagram which shows 1st Embodiment of this invention. It is a graph which shows wavelength distribution of each color of LED. It is explanatory drawing which shows the relationship between light source arrangement | positioning and the characteristic of a dichroic film | membrane. It is a graph which shows the wavelength dependence of the dichroic mirror DA and DB. It is a block diagram which shows an example of the multilayer film for examining the relationship between refractive index ratio and the half value wavelength shift amount by an incident angle. FIG. 6A is an explanatory diagram showing a light source arrangement according to the second embodiment of the present invention, and FIG. 6B is a graph showing the wavelength dependence of the dichroic mirror DC according to (Table 5). FIG. 7A is an explanatory diagram showing a light source arrangement according to the third embodiment of the present invention, and FIGS. 7B to 7D are views of the dichroic mirrors DA, DB, and DC according to (Table 6). It is a graph which shows wavelength dependence, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Composite optical system 2 Introduction optical system 11, 12, 13 Drive circuit 20 Control circuit DA, DB, DC Dichroic mirror LA Condensing lens LB Adjustment lens RI Rod intaglator M1, M2, M3 Folding mirror PA Modulation panel PL Projection optical system

Claims (8)

A first light source that emits light L1 of wavelength λ1;
A second light source that emits light L2 having a wavelength λ2 longer than the wavelength λ1,
A third light source that emits light L3 having a wavelength λ3 longer than the wavelength λ2,
A first combining optical element for combining the light L1 and the light L3;
A second combining optical element for combining the light L1, L2, L3 by reflecting the combined light L1, L3 and transmitting the light L2,
A projection optical system for projecting the combined lights L1, L2, and L3.   The image projection apparatus according to claim 1, wherein the first combining optical element combines the light L1 and the light L3 by reflecting the light L1 and transmitting the light L3. The second synthetic optical element includes a dichroic film in which a high refractive index film having a refractive index of 2.0 to 2.6 and an intermediate refractive index film having a refractive index of 1.6 to 2.0 are stacked. The difference ΔN _H−L between the refractive index of the refractive index film and the refractive index of the intermediate refractive index film is
0.55 ≦ ΔN _H−L ≦ 0.7
The image projector according to claim 1, wherein: The high refractive index film is formed of one or a mixture of two or more selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and ZrO ₂ . Image projection device. The intermediate refractive index film is formed of Al ₂ O ₃ or a mixture of SiO ₂ and one or more selected from the group consisting of TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ and ZrO _2. The image projection apparatus according to claim 3, wherein   The image projection apparatus according to claim 1, wherein the first light source, the second light source, and the third light source are configured by light emitting diodes. A fourth light source that emits light La having a wavelength λa that is longer than the wavelength λ2 and shorter than the wavelength λ3;
The image projection apparatus according to claim 1, further comprising a third combining optical element for combining the light La and the light L3.   2. A lens provided between the first combining optical element and the second combining optical element, for adjusting the divergence angle of the light L1, L3 combined by the first combining optical element. The image projection apparatus described.

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