JP2007212733A - Illumination optical system and image projection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination optical system capable of reducing degradation of a polarization converter due to excessive light from a light source. <P>SOLUTION: The illumination optical system is provided with a polarization separation film and a wavelength plate, and contains the polarization converter 4, which converts non-polarized light from the light source 1 to a prescribed polarized light. The illumination optical system comprises a first filter 15 of reflecting ultraviolet region light and a second filter 16 of absorbing ultraviolet region light, on the light source side rather than the polarization converter 4. Therein, the illumination optical system satisfies the conditions: λ<SB>L</SB><λ<SB>B</SB><440nm, λ<SB>O</SB><λ<SB>C</SB><λ<SB>B</SB><440nm. Where λ<SB>O</SB>is luminescent peak wavelength of the light source existing in the range of 400 nm to 420 nm, λ<SB>L</SB>is a wavelength between λ<SB>O</SB>and 440 nm and is closer to λ<SB>O</SB>than to 440 nm, and λ<SB>B</SB>, λ<SB>C</SB>are respectively cut wavelengths of the first and second filters. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an illumination optical system used in an image projection apparatus such as a liquid crystal projector, and more particularly to an illumination optical system capable of removing extraneous light such as ultraviolet light from light from a light source to a polarization conversion element.

  In order to project a brighter image by the image projection apparatus, it is necessary to increase the brightness of the light source and the density of the light flux. However, along with these, deterioration of the optical components in the apparatus due to ultraviolet light or infrared light emitted from the light source increases.

  In order to reduce the burden on such optical components, Patent Document 1 discloses a method of removing extraneous light in the ultraviolet region and infrared region using two filters.

  Specifically, a UVIR filter for removing light in the band from the ultraviolet region to a part of the visible region and infrared light is disposed between the light source and the liquid crystal panel (between the light source and the dichroic mirror). Further, a UV absorption filter that removes light in a band from the ultraviolet region to a part of the visible region is disposed between the UVIR filter and the liquid crystal panel (liquid crystal panel on the blue light path).

Of the light from the light source, light in the band from the ultraviolet region to a part of the visible region and the infrared region light are removed by the UVIR filter. Thereafter, the ultraviolet light that has not been removed by the UVIR filter is removed by the UV absorption filter. Thereby, deterioration of optical components, such as a liquid crystal panel arrange | positioned behind the UV absorption filter, can be reduced.
Japanese Unexamined Patent Publication No. 08-314012 (paragraphs 0016 to 0022, FIG. 1, etc.)

  In a projector or the like using a reflective liquid crystal panel, color separation and color synthesis are performed according to the polarization state. For this reason, before guiding the light from the light source to the color separation / synthesis optical system, non-polarized light from the light source is often aligned with a predetermined linearly polarized light by using an optical component called a polarization conversion element. The polarization conversion element includes a polarization beam splitter having a polarization separation film formed of a multilayer film and a half-wave plate.

  However, with the increase in luminance of the light source, the durability of the polarization separation film of the polarization conversion element, which has not been regarded as a problem in the past, has become a problem. The polarization conversion element is disposed near the light source and is often used together with a lens array having a beam splitting and condensing function. For this reason, the polarization conversion element is exposed to strong light with a high degree of condensing, and the polarization separation film tends to deteriorate.

  In particular, a high-pressure mercury lamp used as a light source has a bright line peak in a region of 400 to 430 nm adjacent to the ultraviolet region, and emits a lot of ultraviolet light.

  In Patent Document 1 described above, a reflective filter is used as the UVIR filter. However, since the reflective filter has a structure in which multiple layers of films are laminated, there is variation (individual difference) in cut wavelength. As a result, there is a drawback that the irradiation amount of the ultraviolet light and infrared light to the optical component also varies.

  An object of the present invention is to provide an illumination optical system capable of reducing deterioration of a polarization conversion element due to extra light from a light source and an image projection apparatus using the illumination optical system.

  An illumination optical system as one aspect of the present invention includes a polarization conversion element that includes a polarization separation film and a wave plate, and converts non-polarized light from a light source into predetermined polarized light. A light source side of the polarization conversion element has a first filter that reflects ultraviolet light and a second filter that absorbs ultraviolet light. And it is characterized by satisfying the following conditions.

λ _L <λ _B <440 nm
λ ₀ <λ _C <λ _B <440 nm
However, λ ₀ is the emission line peak wavelength of the light source existing between 400 nm and 420 nm, and λ _L is a wavelength between λ ₀ and 440 nm and closer to λ ₀ than to 440 nm. Is the wavelength. Further, λ _B and λ _C are cut wavelengths of the first and second filters, respectively. Here, the cut wavelength is a wavelength at which the transmittance becomes 50% in a wavelength region where the transmittance of the filter with respect to the ultraviolet light changes from a lower side to a higher side than 50% as the wavelength increases.

  According to the present invention, excess light contained in light incident on the polarization conversion element from the light source can be effectively removed, so that deterioration of the polarization conversion element can be stably reduced. As a result, it is possible to realize an image projection apparatus that can project a brighter image and maintain high reliability over a long period of time.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A shows an optical configuration of a liquid crystal projector (image projection apparatus) that is an embodiment of the present invention.

In FIG. 1A, reference numeral 1 denotes a light source composed of a high-pressure mercury lamp or the like and an arc tube and a reflector that converts a luminous flux from the luminous tube into a parallel luminous flux in a predetermined direction. Here, the spectrum of the high-pressure mercury lamp is shown in FIG. As shown in FIG. 2, the light from the high pressure mercury lamp has an emission line peak wavelength λ ₀ in the vicinity of 407 nm.

  In FIG. 1A, reference numerals 2 and 3 denote a first lens array and a second lens array that divide a light beam from the light source 1 into a plurality of light beams.

  A polarization conversion element 4 converts non-polarized light from the light source 1 into linearly polarized light having a predetermined polarization direction. FIG. 1B shows a configuration example of the polarization conversion element 4. Reference numeral 4a denotes a polarization separation film formed of a dielectric multilayer film. The polarization separation film 4a has a characteristic of reflecting S-polarized light and transmitting P-polarized light. 4b is a reflecting surface. A light shielding plate 4d is provided on a part of the polarization conversion element 4 other than the entrance opening to the polarization separation film 4a on the incident side surface. In addition, a half-wave plate 4c is disposed in an exit opening of light transmitted through the polarization separation film 4a on the exit side surface. The polarization separation cell 4a, the reflection plate 4b, the half-wave plate 4c and the light shielding plate 4d constitute a polarization conversion cell, and the polarization conversion cell is arranged corresponding to the lens cell row of the second lens array 3. Thus, the polarization conversion element 4 is configured.

  Of the non-polarized light incident from the incident aperture, the S-polarized light component is reflected by the polarization separation film 4 a, then reflected by the reflecting surface 4 b and emitted from the polarization conversion element 4. On the other hand, the P-polarized light component of the non-polarized light incident from the incident aperture is transmitted through the polarization separation film 4a and then emitted as S-polarized light with its polarization direction rotated by 90 ° by the half-wave plate 4c. In this way, all non-polarized light from the light source 1 (second lens array 3) is converted to S-polarized light. In addition, you may change the characteristic of the polarization separation film 4a so that the polarization conversion element 4 may convert non-polarized light into P polarized light.

  A condenser lens 5 superimposes the light beams divided by the first and second lens arrays 2 and 3 on the reflective liquid crystal panels 7 to 9 as light modulation elements. An illumination optical system is constituted by optical elements from the light source 1 to the condenser lens 5.

  Light from the illumination optical system enters the dichroic mirror. The dichroic mirror 6 reflects the first light among blue (B: 430 to 500 nm) light, red (R: 600 to 650 nm) light, and green (G: 500 to 600 nm) light. The second and third light is transmitted.

  Reference numerals 10, 11, and 12 denote first, second, and third polarization beam splitters each having a polarization separation film. Note that color separation and color synthesis in each polarization beam splitter, which will be described below, are performed by reflection action and transmission action in a polarization separation film corresponding to the polarization direction of light. In order to cause the second polarization beam splitter 11 to perform such color separation and color synthesis, the light polarization side of the light beam and the projection lens side of the second polarization beam splitter 11 are respectively set to a polarization direction of 90 degrees. A color-selective phase difference plate (not shown) that is rotated by a predetermined degree is disposed. However, in the following description, description of the polarization direction is omitted. The first, second and third polarization beam splitters 10, 11, 12 and the color selective phase difference plate constitute a color separation / synthesis optical system.

  The first light passes through the polarization separation film of the first polarization beam splitter 10 and enters the reflective liquid crystal panel 7. Here, an image supply device 30 such as a personal computer, a DVD player, or a TV tuner is connected to the liquid crystal driving circuit 20 mounted on the projector of this embodiment. The liquid crystal drive circuit 20 drives each reflection type liquid crystal panel based on image (video) information input from the image supply device 30 to form an original image for each color. Thereby, the light incident on each reflective liquid crystal panel is reflected and modulated (image modulation) according to the original image.

  The first light reflected and image-modulated by the reflective liquid crystal panel 7 is incident on the first polarizing beam splitter 10 again. Then, the light is reflected by the polarization separation film of the first polarization beam splitter 10 and enters the third polarization beam splitter 12. The first light is reflected by the polarization separation film of the third polarization beam splitter 12 and travels toward the projection lens 13.

  On the other hand, the second light transmitted through the dichroic mirror 6 is reflected by the polarization separation film of the second polarization beam splitter 11, is reflected and image-modulated by the reflective liquid crystal panel 8, and is incident on the second polarization beam splitter 11 again. Then, the light passes through the polarization separation film of the second polarization beam splitter 11 and enters the third polarization beam splitter 12. The second light passes through the polarization separation film of the third polarization beam splitter 12 and travels toward the projection lens 13.

  The third light that has passed through the dichroic mirror 6 passes through the polarization separation film of the second polarization beam splitter 11, is reflected and image-modulated by the reflective liquid crystal panel 9, and is incident on the second polarization beam splitter 11 again. Here, the third light described above is the second light in a state in which the polarization direction of only the third light is rotated 90 degrees by a color-selective phase difference plate (not shown) (retarder stack of Japanese Patent Laid-Open No. 2002-357708). The light enters the polarization beam splitter 11. Then, the light is reflected by the polarization separation film of the second polarization beam splitter 11 and enters the third polarization beam splitter 12. The third light passes through the polarization separation film of the third polarization beam splitter 12 and travels toward the projection lens 13. Here, the third light emitted from the second polarizing beam splitter is rotated 90 degrees in the polarization direction of only the third light by a color-selective retardation plate (not shown) (retarder stack of Japanese Patent Laid-Open No. 2002-357708). In this state, the light enters the third polarizing beam splitter 11.

  The first to third lights (color images) color-combined by the third polarization beam splitter 13 are projected onto a projection surface such as a screen (not shown) by the projection lens 13.

  In the projector configured as described above, the filter A14, the filter B15, and the filter C16 are arranged in this order from the light source side between the light source 1 and the polarization conversion element 4 in the illumination optical system.

  The filter A (third filter) 14 is deposited on the surface of the first lens array 2 opposite to the light source side (polarization conversion element side). The filter A14 has a UVIR reflection characteristic as shown in FIG. 3, and has a function of roughly removing excess ultraviolet light and infrared light that cannot be effectively used as projection light in the projector.

  The filter B (first filter) 15 is deposited on the light source side surface of the filter C described later. The filter B15 has UV reflection characteristics and has a function of determining the wavelength of the blue short wavelength side.

  The filter C (second filter) 16 is an absorption filter made of glass having UV absorption characteristics. The filter C16 is disposed closer to the light source than the polarization conversion element 4, and removes excess light for removal with a small error.

  The optical characteristics of these three filters will be described in more detail below.

The filter A14 is a reflection type filter, and includes light in a band (hereinafter, collectively referred to as UV light) and an infrared light range (hereinafter, referred to as UV light) included in light from the light source 1 to a part of the visible range. Part of excess light that cannot be effectively used as projection light. Filter A14 has a transmittance characteristic shown by the curve A in FIG. 4, the cut wavelength lambda _A is 420 nm. The cut wavelength refers to the transmittance in the wavelength region where the transmittance of the filter with respect to UV light changes from substantially 0% (a side lower than 50%) to substantially 100% (a side higher than 50%) as the wavelength increases. The wavelength at which the rate is 50%. The same applies to the other filters.

The filter A14 is designed to have both UV light and IR light removal characteristics in one filter. Therefore, as shown in FIG. 4, in the variation of the cut wavelength lambda _A Figure A ', as large as about ± 5nm as A ". Moreover, in the range of 5nm indicated by a region P in the figure, the curve A The change in transmittance shown is gentle at 3.5%.

The filter B15 is a filter that determines the wavelength on the short wavelength side of blue, and is a reflective filter. The filter B15 has a transmittance characteristic indicated by a curve B in FIG. 5, and the cut wavelength λ _B is 426 nm. By using a reflective filter specialized only for removing UV light as the filter B15, the variation in wavelength is less than that of the filter A14, which is about ± 3 nm as indicated by B ′ and B ″ in FIG. Further, the wavelength range of the region where the transmittance changes from substantially 0% to substantially 100% is dB = 15 nm, which is narrower than dBA = 25 nm of the filter A14 shown in Fig. 4. That is, the filter B15 is the filter A14. Compared to the above, since it has the characteristic that the transmittance change is steep, it is suitable as a filter for determining the color.

Filter C16 is the absorption type filter to remove excess light that could not be removed by the filter A14 and filter B15, cut wavelength lambda _C is 418 nm. The filter C16 has a transmittance characteristic indicated by a curve C in FIG. The filter C16 is formed using absorption glass, and its transmittance characteristic is determined by the thickness of the glass substrate, so that there is no large variation in cut wavelength unlike other filters. For this reason, excess light in the intended wavelength band can be reliably removed.

Next, the influence of variations in the characteristics of each filter will be described. The filter characteristic (transmittance characteristic) of the design center wavelength of the filter B15 is shown by a curve B in FIG. The transmittance in the vicinity of λ ₀ = 407 nm is suppressed to about 0.02%.

Furthermore, the characteristics of the filter B15 at which the cut wavelength lambda _B is 5nm shifted in the short wavelength direction, indicated by a curve B 'in FIG. It can be seen that the transmittance in the vicinity of λ ₀ = 407 nm is about 0.04%, and about twice as much leakage light is generated with respect to the filter characteristic of the design center wavelength.

Although not shown, the transmittance of the filter A14 also, the shift to the short wavelength side of the cut wavelength lambda _A, similarly increased filter B15. When the extra light in the wavelength range from the ultraviolet range to a part of the visible range is maximized, the cut wavelengths λ _A and λ _B of the filters A14 and B15 are greatly shifted to the shorter wavelength side than the design center value. This is the case. Specifically, as shown in FIG. 8 and FIG. 9, the curves A ′ and the curves A ′ and B1 in which the cut wavelengths λ _A and λ _B of the filters _A 14 and B 15 are shifted to the short wavelength side with respect to the design center value of each filter In this state, the characteristic relationship is indicated by B ′. FIG. 9 is an enlarged view of the vicinity of the region H in FIG. In this embodiment, since the absorption glass is used as the filter C16, even when the cut wavelengths of the filters A and B are shifted to the short wavelength side, as shown by the curve C in FIG. There is no shift of the cut wavelength due to the variation of. Therefore, even if the characteristics of the filters A and B are shifted as shown by the curves A ′ and B ′ and the excess light (leakage light) near λ ₀ = 407 nm transmitted through the filters A and B increases, the filter C The leakage light can be surely removed.

FIG. 10 shows the effect of the UV absorption filter C16 when the cut wavelength of the UV reflection filter B15 is actually shifted to the short wavelength side. A curve D in the figure indicates the amount of leaked light when the UV absorption filter C16 is not used, and a curve E indicates the amount of leaked light when the UV absorption filter C16 is used. When compared at λ ₀ = 407 nm, the transmittance of 0.05% in curve D is 0.0002% in curve E, and the leakage light is greatly reduced.

  Next, the relationship between the cut wavelengths of the filters will be described.

The cut wavelength λ _A = 420 nm of the UVIR reflection filter A is a wavelength shifted from λ ₀ to the longer wavelength side by approximately ¼ (≈8 nm) of the width of the bright line peak wavelength λ ₀ = 407 nm to 440 nm of the high pressure mercury lamp = 33 nm. λ _L = set to a longer wavelength side than 415 nm. As a result, the transmittance of the UVIR reflection filter A at λ ₀ is 2% or less when λ _A = 420 nm, and 6% or less when λ _A = 415 nm, and the amount of leakage light is triple the design value. It can be suppressed to the extent.

Further, the cut wavelength λ _A = 420 nm of the UVIR reflection filter A is set to a shorter wavelength side than the cut wavelength λ _B = 426 nm of the UV reflection filter B that determines the wavelength of the blue short wavelength side. This is because the UVIR reflection filter A has a structure in which a plurality of layers are laminated, and thus the transmittance change has a gentle characteristic with respect to the UV reflection filter B. That is, when the cut wavelengths of both reflection filters are set to be the same, the transmittance of the UVIR reflection filter A near 440 nm is lower than that of the UV reflection filter B.

For example, as shown in FIG. 11, the transmittance of the UV reflecting filter B having the characteristic of the curve B ″ at 433 nm under the condition of the cut wavelength λ _B = 426 nm is 98.5%. The transmittance at 433 nm at the cut wavelength λ _A = 426 nm of the UVIR reflection filter A having the “″ characteristic is greatly reduced to 91%. FIG. 11 is an enlarged view of a region corresponding to the region I in FIG.

Further, the cut wavelength λ _B = 426 nm of the UV reflection filter B is set to a shorter wavelength side than 440 nm. This is because when λ _B is 440 nm or more, the transmittance at 440 nm, which is greatly involved in determining blue, is reduced to 50% or less.

The cut wavelength λ _C = 418 nm of the UV absorption filter C is the peak wavelength λ ₀ = 407 nm of the bright line of the high-pressure mercury lamp, and the cut wavelength λ _B of the UV reflection filter B that determines the wavelength on the short wavelength side of blue in the projector. Set between 426 nm. This is because if the cut wavelength λ _C = 418 nm of the UV absorption filter C is set on the shorter wavelength side than the emission line peak wavelength λ ₀ = 407 nm, the transmittance at λ ₀ = 407 nm of the filter C becomes 50% or more, This is because only 50% or less of the leakage light of the bright line that is light can be removed.

Further, when the cut wavelength λ _C = 418 nm of the UV absorption filter C is set on the longer wavelength side than the cut wavelength λ _B = 426 nm of the UV reflection filter B, it is not preferable for the following reason. As can be seen from FIG. 11, the transmittance of the UV reflection filter B having the characteristics of the curve B ″ at the wavelength of 433 nm under the condition of the cut wavelength λ _B = 426 nm is 98.5%. The transmittance at 433 nm under the condition of the cut wavelength λ _C = 426 nm of the UV absorption filter C having the above characteristics is greatly reduced to 94%. In this case, it is not possible to sufficiently secure the transmittance around 430 nm.

  In summary, the following conditions can be obtained.

Condition 1.
The cut wavelength λ _A of the UVIR reflection filter A14 is set to a wavelength closer to 440 nm than the peak wavelength λ ₀ of the bright line of the high-pressure mercury lamp, which is a light source existing in the vicinity of 400 to 420 nm. More specifically, the wavelength is set to the longer wavelength side than the wavelength λ _L shifted from λ ₀ to the longer wavelength by about ¼ of the width from the wavelength λ ₀ to 440 nm. Thereby, the transmittance at λ ₀ can be suppressed.

Condition 2.
The cut wavelength λ _A of the UVIR reflection filter A14 is set to be shorter than the cut wavelength λ _B of the UV reflection filter B15 that determines the blue short wavelength side in the projector. This is because the filter A14 has a gentle transmission characteristic with respect to the filter B15, and the transmittance in the vicinity of 430 nm of the filter A14 is lower than that of the filter B15 when the cut wavelengths of both filters are the same. It is to do.

Condition 3.
The cut wavelength λ _B of the UV reflection filter B15 is set to a shorter wavelength side than 440 nm. This is to prevent the transmittance at 440 nm from dropping to 50% or less when the cut wavelength λ _B is 440 nm or more.

Condition 4.
Cut wavelength lambda _C of the UV-absorbing filter C16 high-pressure mercury lamp is cut wavelength lambda _B of the UV reflection filter B15 which determines the short wavelength side of the blue emission line peak wavelength lambda ₀ and projector with near 400~420nm a light source Set between. This is because when the cut wavelength lambda _C filter C16 than lambda ₀ is set to the short wavelength side, the transmittance at lambda ₀ is 50% or more, can only be removed less than 50% light leakage is redundant light emission line So to avoid this. Furthermore, if the cut wavelength λ _C of the filter C15 is set longer than the cut wavelength λ _B of the filter B15, the transmittance near 430 nm cannot be secured sufficiently, so that sufficient transmittance can be secured. is there.

  Based on these conditions, the following conditional expression can be derived.

Cut wavelength of UVIR filter A14: λ _A
Cut wavelength of UV reflection filter B15: λ _B
Cut wavelength of UV absorption filter C16: λ _C
Bright line peak wavelength of a light source existing in a wavelength region of 400 nm or more and 420 nm or less (for example, around 407 nm for a high pressure mercury lamp): λ ₀
a wavelength between λ ₀ and 440 nm, closer to λ ₀ than to 440 nm (approximately ¼ of the width or spacing of λ ₀ and 440 nm is longer than λ ₀ ) : Λ _L
And when
λ _L <λ _A <λ _B <440 nm (1)
λ ₀ <λ _C <λ _B <440 nm (2)

  By satisfying the above conditions, it is possible to reduce excess light incident on the polarization conversion element 4 stably, that is, without variation, while reducing loss of blue light to be used. As a result, it is possible to suppress the deterioration of the polarization conversion element and further optical components thereafter, and to realize a highly reliable projector over a long period of time.

  Furthermore, it is desirable to satisfy the following conditions.

Condition 5.
Since the UV absorption filter C16 absorbs and removes the energy of the wavelength to be removed, the UV absorption filter C16 is more likely to cause deterioration and breakage of transmittance as compared with the reflective filter. For this reason, in particular, in an ultra-bright projector, the filter C16 among the three filters A14, B15, and C16 may be disposed at a position farthest from the light source, in other words, at a position closest to the polarization conversion element 4. As a result, the deterioration of the absorption filter C16 itself can be reduced, and a more reliable projector can be realized. The order of the other two filters A14 and B15 may be in this order, or may be in the reverse order.

  In the above embodiment, the case where three of the UVIR reflection filter A14, the UV reflection filter B15, and the UV absorption filter C16 are used has been described. However, the following conditional expression may be satisfied when a filter for removing IR light is provided independently or when the heat load of the UV absorption filter C16 does not matter.

λ _L <λ _B <440 nm (1) ′
λ ₀ <λ _C <λ _B <440 nm (2)
The cut wavelengths λ _B and λ _C of the filters B and C may be set under the conditions.

  The specific cut wavelengths and filter characteristics described in the embodiments described above are merely examples, and the present invention is not limited to these.

  In the present invention, the optical configuration after the polarization conversion element in the projector is not limited to that shown in FIG. 1A.

1 is an optical configuration diagram of a liquid crystal projector that is an embodiment of the present invention. FIG. 1 is a schematic configuration diagram of a polarization conversion element used in an illumination optical system of a projector according to an embodiment. The figure which shows the emission spectrum of the high pressure mercury lamp which is a light source of the projector of an Example. The optical characteristic figure of the UVIR reflection filter in an Example. The optical characteristic figure of the UVIR reflection filter in an Example. The optical characteristic figure of the UV reflection filter in an Example. The optical characteristic figure of the UV absorption filter in an Example. The figure which shows the mode of the transmittance | permeability change by the dispersion | variation in the cut wavelength of the UV reflective filter in an Example. The figure which shows the dispersion | variation in the characteristic of each filter in an Example. The figure which shows the dispersion | variation in the characteristic of each filter in an Example. The figure which shows the effect of a UV absorption filter when the cut wavelength of the UV reflective filter in an Example shifts to the short wavelength side. The figure which shows the transmittance | permeability when the cut wavelength of each filter in an Example is set to the longest wavelength side.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2, 3 1st, 2nd array lens 4 Polarization conversion element 5 Condenser lens 6 Dichroic mirror 7, 8, 9 Reflection type liquid crystal panel 10, 11, 12 Polarization beam splitter 13 Projection lens A, A ', A " , A ″ ′ Optical characteristic curve of filter A B, B ′, B ″ Optical characteristic curve of filter B C, C ′, C ″, C ″ ″ Optical characteristic curve of filter C D, E Leakage light characteristic curve

Claims (7)

An illumination optical system including a polarization conversion element that includes a polarization separation film and a wave plate and converts non-polarized light from a light source into predetermined polarized light,
An illumination having a first filter that reflects ultraviolet light and a second filter that absorbs ultraviolet light, and that satisfies the following conditions, disposed on the light source side of the polarization conversion element: Optical system.
λ _L <λ _B <440 nm
λ ₀ <λ _C <λ _B <440 nm
However, λ ₀ is an emission line peak wavelength λ _L of the light source existing at 400 nm or more and 420 nm or less, a wavelength between λ ₀ and 440 nm, a wavelength closer to λ ₀ than to 440 nm,
λ _B and λ _C are cut wavelengths of the first and second filters, respectively. The cut wavelength is a wavelength at which the transmittance becomes 50% in a wavelength region where the transmittance of the filter with respect to ultraviolet light changes from a lower side to a higher side with a wavelength increase from 50%. 2. The method according to claim 1, further comprising: a third filter that reflects ultraviolet light closer to the light source side than the polarization conversion element and has a cut wavelength different from that of the first filter, and satisfies the following condition. The illumination optical system described.
λ _L <λ _A <λ _B <440 nm
λ ₀ <λ _C <λ _B <440 nm
Where λ _A is the cut wavelength of the third filter.   The illumination optical system according to claim 2, wherein the third filter is a filter that reflects ultraviolet light and infrared light.   The illumination optical system according to any one of claims 1 to 3, wherein the second filter is disposed at a position farthest from the light source than other filters. The illumination optical system according to any one of claims 1 to 4,
An optical system comprising: a projection optical system that guides light from the illumination optical system to a light modulation element and projects the light from the light modulation element.   An image projection apparatus that projects an image using the optical system according to claim 5. An image projection apparatus according to claim 6;
An image display system comprising: an image supply device that supplies image information to the image projection device.