JP2016099390A - Illumination optical system and picture display unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illumination optical system and a picture display unit capable of enhancing a contrast ratio of image light by reducing diffraction light.SOLUTION: An illumination optical system (1) includes: a light source (11); and a light uniformizing element (14) configured to uniformize luminous intensity of light from the light source (11) and emit the light. A spatial optical modulation element (2) is irradiated with the light emitted from the light uniformizing element (14). The illumination optical system (1) further includes, between the light uniformizing element (14) and the spatial optical modulation element, a phase conversion element (141) configured to convert a phase of the light in part .SELECTED DRAWING: Figure 10

Description

  The present invention relates to an illumination optical system and an image display device.

  One of the indexes representing the image quality of an image (projected image) displayed by an image display device such as a projector is “contrast ratio”. The contrast ratio is the brightness of the entire image displayed on the projection object (for example, a screen) when the entire projected image is white and the brightness of the entire image when the entire projected image is black. Calculated by ratio. For example, the contrast ratio can be calculated using an average value of the luminance of the white portion and the luminance of the black portion in the entire image when a checker pattern image composed of white and black is displayed as a projection image.

  Since an image with a high contrast ratio is an image with a low luminance in the black portion, the fidelity of the reproducibility of the original image tends to be high. Therefore, it can be said that the image quality of an image having a high contrast ratio is “good”. On the other hand, an image with a low contrast ratio is an image with a high luminance in the black portion, and thus the fidelity of the reproducibility of the original image tends to be low. For example, even when a dark image is displayed, “black floating” occurs. Therefore, it can be said that the image quality of an image with a low contrast ratio is “bad”.

  There are a plurality of known factors for reducing the contrast ratio of the display image by the projector. For example, stray light or ghost light generated in an optical system provided in the projector is one of the causes. Stray light or ghost light refers to light other than image light that forms a projected image. Here, “image light” refers to light that contributes to the formation of a display image among the light that reaches the screen from the spatial light modulator.

  Stray light and ghost light are generated by multiple reflections of light in an optical system provided in the projector, light scattering, light diffraction, and the like, and these are mixed with image light to lower the contrast ratio. There are a number of causes for the generation of ghost light and stray light, but they are particularly likely to occur due to light diffraction in the spatial light modulator.

  If stray light and ghost light can be suppressed, adverse effects on the contrast ratio can be eliminated, and deterioration of image quality in the displayed image can be prevented. There is known an image display device that shields stray light or ghost light that attempts to reach a screen by a light shielding means provided inside a projection optical system (see, for example, Patent Document 1).

  If the light shielding means is provided inside the projection optical system as in the image display device of Patent Document 1, not only ghost light and stray light but also image light is shielded. When the image light is blocked, the amount of light reaching the screen is reduced, and the light use efficiency is lowered. When the light use efficiency decreases, the display image becomes dark on the screen, and the image decreases. When preventing a decrease in contrast ratio due to ghost light or stray light, it is desirable to suppress the generation of ghost light or stray light itself without reducing light utilization efficiency.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an illumination optical system and an image display device that can increase the contrast ratio of image light by reducing diffracted light.

  The present invention is an illumination optical system having a light source and a light uniformizing element that uniformizes and emits the illuminance of light from the light source, and a spatial light modulation element is formed by light emitted from the light uniformizing element. The main feature is that a phase conversion element that illuminates and converts the phase of a part of the light is provided between the light uniformizing element and the spatial light modulation element.

  According to the present invention, the contrast ratio of image light can be increased by reducing diffracted light.

It is an optical arrangement | positioning figure which shows the example of embodiment of the image display apparatus which concerns on this invention. It is an optical arrangement | positioning figure which shows the example of embodiment of the illumination optical system which concerns on this invention. It is (a) top view and (b) side view which show the example of the color wheel with which the said illumination optical system is provided. It is an example of the light equalization element with which the said illumination optical system is provided, Comprising: (a) The perspective view of the state which removed the phase conversion element, (b) The perspective view of the state which attached the phase conversion element. It is an example of the spatial light modulation element with which the said image display apparatus is provided, Comprising: (a) Top view, (b) Partial enlarged plan view, (c) Plan view of a micromirror, (d) Example of light reflection state It is the side view shown, (e) The side view of a spatial light modulation element. Examples of diffraction occurring in the spatial light modulation element, wherein (a) an example of reflection of light at a micromirror, (b) an example of diffraction at a specific micromirror, (c) an example of diffraction at a plurality of micromirrors, (D) It is a side view of the spatial light modulation element which shows the example of the diffraction which arises in a spatial light modulation element. It is an example of diffraction in the micromirror, and is a side view of a micromirror array showing (a) an example of diffraction in a micromirror in an ON state and (b) an example of diffraction in a micromirror in an OFF state. It is a side view of the micro mirror arrangement | sequence which shows the example of the optical path length of the diffracted light in the said micro mirror. It is a side view of a micromirror arrangement showing an example of stray light generated by diffracted light in the micromirror. It is an example of embodiment of the phase conversion element with which the said illumination optical system is provided, Comprising: (a) Top view, (b) Side view. It is explanatory drawing which shows the example of the effect | action of the light in the said phase conversion element. It is a side view which shows the example of the structure of the said phase conversion element. It is an expansion perspective view which shows the example of another structure of the said phase conversion element. It is a side view of the spatial light modulation element which shows another example of the stray light produced by the diffracted light in the said micromirror.

  Hereinafter, embodiments of an illumination optical system according to the present invention and embodiments of an image display apparatus according to the present invention will be described with reference to the drawings.

● Image display device ●
First, an embodiment of an image display device according to the present invention will be described. As shown in FIG. 1, the projector 100 includes an illumination optical system 1, a spatial light modulation element 2, and a projection optical system 3.

  The illumination optical system 1 illuminates the spatial light modulator 2 by emitting light according to a signal related to the display image. Detailed description will be given later.

  The spatial light modulator 2 operates in accordance with a signal related to the display image, and forms image light using illumination light. The spatial light modulator 2 emits the formed image light toward the projection optical system 3.

  The projection optical system 3 projects the image light (projected image) formed in the spatial light modulation element 2 in an enlarged manner toward a projection object (for example, a screen).

● Illumination optics 1
Next, the illumination optical system 1 will be described in detail. As shown in FIG. 2, the illumination optical system 1 includes a light source 11, an explosion-proof glass 12, a color wheel 13, a light uniformizing element 14, a first relay lens 15, a second relay lens 16, and a first relay lens. A folding mirror 17 and a second folding mirror 18 are provided.

  The light source 11 includes an arc tube and a reflector. The arc tube may be a white light source such as an ultra high pressure mercury lamp or a laser light source that emits a laser. The reflector is a reflector for emitting the light from the arc tube in a certain direction and collecting it.

  If the light source 11 is a laser light source, the coherence becomes higher than that of a mercury lamp or the like, and the phase of light can be efficiently controlled using a phase conversion element 141 described later.

  The explosion-proof glass 12 is disposed in front of the light source 11, and prevents the fragments and the like from scattering into the projector 100 when the arc tube of the light source 11 is broken.

  The color wheel 13 is an optical filter that converts light from the light source 11 into light of a specific color. The color wheel 13 is disposed on the optical path between the light source 11 and the light uniformizing element 14.

  Here, the color wheel will be described in detail. As shown to Fig.3 (a), the color wheel 13 has the glass disc 131 which consists of glass materials. As shown in FIG. 3B, a motor 133 is mounted on the back surface of the glass disc 131. The rotation axis of the motor 133 is disposed at the rotation center of the glass disk 131, and the glass disk 131 is rotated by the rotation of the motor 133.

  As shown in FIG. 3A, the glass disk 131 is obtained by dividing the surface on which the light from the light source 11 strikes into a plurality of regions, and arranging optical filters of different colors in each region. The optical filter is obtained by depositing a multilayer film on the glass surface of the glass disc 131. In each divided region formed on the glass disc 131, a color filter for converting the color of light into each color of red (R), green (G), and blue (B) is formed. The color filter formed on the glass disc 131 may be provided with other colors as described above. For example, a white (W) region may be arranged. When forming a white (W) color filter, a multilayer film is not formed in the region, and the light is simply transmitted through the glass disk 131. In order to improve color reproducibility, regions such as yellow (Y), magenta (M), and cyan (C) may be further provided. The purpose of providing the white (W) region is to increase the brightness of the image light.

  The light from the light source 11 is adjusted so as to strike the same position on the surface of the glass disk 131 as the light spot 132. Therefore, the optical filter corresponding to the position of the light spot 132 changes in a time-division manner by rotation, so that the light from the light source 11 is converted into a specific color by the color wheel 13.

  For example, the glass disk 131 has a diameter of about 40 mm and a thickness of about 1 mm. The optical filters of the respective colors provided on the surface of the glass disk 131 are rotated by the motor 133 at a rotational speed of about several thousand rpm to about 10,000 rpm. The color wheel 13 includes a sensor so that the position of each color optical filter can be grasped. The position of the optical filter is controlled in synchronization with the image forming operation by the spatial light modulator 2. The color wheel 13 generates light of each color by time division (field sequential). Since the response speed of the mirror of the spatial light modulator 2 is high, even if a color image is formed by field sequential, it can be performed without any problem.

  Returning to FIG. The light homogenizing element 14 is an optical element that emits light with a uniform illuminance distribution (orientation distribution) of light from the light source 11, and is called a rod integrator, light tunnel, light pipe, or the like. The light uniformizing element 14 will be described with reference to FIG. As shown in FIG. 4A, the light homogenizing element 14 is a quadrangular columnar member formed by combining four strip-shaped mirror plates 142. The inner wall surface of the light uniformizing element 14 is the mirror surface of the mirror plate 142.

  The light incident on the light uniformizing element 14 from the incident end (incident surface) is reflected by the inner wall surfaces (mirror surfaces) of the four mirror plates 142, and the light orientation distribution is uniformized. As a result, the emission surface 143 serving as the emission end can be regarded as a surface light source. As shown in FIG. 4B, the phase conversion element 141 is disposed on the emission surface 143 of the light homogenizing element 14. That is, the phase conversion element 141 is configured to block the opening of the emission surface 143. Since the phase conversion element 141 is a member that transmits light, even when the phase conversion element 141 is disposed on the emission surface 143, light having the emission surface 143 of the light uniformizing element 14 as a surface light source is emitted. A detailed description of the phase conversion element 141 will be described later.

  Returning to FIG. A first relay lens 15, a second relay lens 16, a first folding mirror 17, and a second folding mirror 18 are arranged in this order after the light uniformizing element 14. With these configurations, the emission end face of the light homogenizing element 14 (light emission face with uniform orientation distribution) and the incident / exit face of the spatial light modulator 2 have an optically conjugate relationship.

  The light emitted from the light uniformizing element 14 passes through the first relay lens 15 and the second relay lens 16 and is three-dimensionally reflected (folded back) obliquely upward by the first folding mirror 17. The reflected light is reflected (folded back) three-dimensionally and obliquely downward by the second folding mirror 18. The light reflected by the second folding mirror 18 is directed to the spatial light modulator 2 and enters the spatial light modulator 2 with a predetermined incident angle. This light illuminates the effective image area of the spatial light modulator 2.

  The illumination optical system 1 may use a total reflection prism or may not use a total reflection prism.

● Spatial light modulator 2
The spatial light modulation element 2 will be described with reference to FIG. The spatial light modulator 2 selectively reflects light for each pixel using the light beam from the illumination optical system 1 to form image light. The spatial light modulator 2 is, for example, a DMD (Digital Micromirror Device, Texas Instruments) configured by a group of micromirrors arranged two-dimensionally.

  FIG. 5A is a plan view of the spatial light modulator 2 as viewed from the light incident side (above). As shown in FIG. 5A, a certain plane area of the spatial light modulator 2 is an effective image area, and image light is formed from illumination light in this area. The size of the displayed image is determined by the length of the diagonal line of the effective image area. For example, the length of the diagonal line of the spatial light modulator 2 is 0.5 inch, 0.65 inch, or the like. The size of the spatial light modulator 2 is expressed as 4: 3, 16:10, or the like by using the ratio of the long side to the short side of the external shape (rectangle) of the spatial light modulator 2. The

  The spatial light modulation element 2 is formed by arranging a plurality of micromirrors 21 as shown in FIG. The outline of the micromirror 21 in plan view is a square, and each corresponds to a pixel of the display image. The period of the arrangement of the micromirrors 21 is called a pixel pitch. Note that the pixel pitch of the spatial light modulator 2 is around 10 μm. The actual size of the micromirror 21 is slightly smaller than the pixel pitch. The number of arrangement of the micro mirrors 21 is 1024 pixels × 768 pixels (or pixels) when the image display size is XGA standard. Similarly, in the case of the WXGA standard, it is 1280 × 768 pixels.

  As shown in FIG. 5C, the micro mirror 21 is configured to rotate about a diagonal line as a rotation axis. The rotation direction of the micro mirror 21 is both a clockwise direction and a counterclockwise direction with respect to the rotation axis. For example, clockwise rotation is “plus rotation”, and counterclockwise rotation is “minus rotation”.

  The rotation angle of the micro mirror 21 is ± 10 ° to 12 °. This rotation is sometimes referred to as “tilt”. As shown in FIG. 5D, the direction of the reflected light with respect to the incident light is different between the plus rotation and minus rotation of the rotated micromirror 21. Since the micromirrors 21 can rotate independently, image light can be formed by rotating each of the micromirrors 21 in a predetermined direction while receiving light from the illumination light.

  The rotation of the micro mirror 21 is a binary value of ON and OFF. The light (ON light) reflected by the micro mirror 21 in the ON state enters the projection optical system 3 and reaches the projection object. The light (OFF light) reflected by the micro mirror 21 in the OFF state reaches the light absorbing member provided at an appropriate position without entering the projection optical system 3. Pixels corresponding to micromirrors that reflect OFF light are displayed in black on the screen. Therefore, an image is formed by ON light and OFF light.

  In addition, the rotation angle and rotation axis of each micromirror are not limited to those described above. Although not used for image formation, there is a flat state between ON and OFF.

  The actual mirror size with respect to the pixel pitch is called the aperture ratio. When the arrangement of the micromirrors 21 is viewed from the side, the protective cover glass 22 is disposed on the upper side of the micromirrors 21 as shown in FIG.

  Next, reflection of light at the spatial light modulation element 2 and diffraction of light generated at each of the micro mirrors 21 of the spatial light modulation element 2 will be described. As shown in FIG. 6A, the arrangement interval d of the micromirrors 21 is a pixel pitch. The length of one side in the arrangement direction of the micromirrors 21 is shorter than the arrangement interval d. The arrangement of the micromirrors 21 of the spatial light modulator 2 can be regarded as a diffraction grating.

As shown in FIG. 6, assuming a flat state in which the micromirror 21 is neither positively rotated nor negatively rotated, light (incident light L _i ) incident on the micromirror 21 from the illumination optical system 1 in this case is very small. Incident at an angle θ with respect to the normal of the mirror 21 (indicated by a broken line). The incident light _Li is reflected by the micro mirror 21 at an angle θ. The incident light _Li is a plane wave, and the light incident on any minute mirror 21 has the same phase.

As shown in FIG. 6, the spatial light modulator 2 constitutes a micromirror array in which micromirrors 21 are arranged. As already described, the length of one side of the micromirror 21 is shorter than the arrangement interval d. Therefore, a slight gap is generated between the adjacent micromirrors 21. Therefore, even light illuminating the effective image area, the portion of the incident light L _i of the spatial light modulator 2 may hit the end of the micro mirror 21. Light impinging on the end of the micro mirror 21, the diffracted light L _d cause diffraction, as shown in Figure 6 (b). This diffracted light L _d is generated in each of the micromirrors 21 as shown in FIG. The diffracted light L _d include interfere with each other where it is synthesized where is offset (highlighted is at) and (weakened place) each other.

Diffracted light L _d is generated in the entire array of micromirrors 21. The interference of light in the diffracted light L _d as described above is expressed by a diffraction formula (d sin θ = nλ) by a diffraction grating. The interference as described above is referred to as “diffraction” in this specification. The pixel pitch of the micro mirrors 21 "d", an angle (diffraction angle) of the diffracted light L _d "θ", the order of the diffracted light L _d "n", a wavelength of light and "λ". The order “n” is an integer and takes a positive or negative value.

In FIG. 6D, the diffracted light L _d with the order “n” between +2 and −2 is shown. The actual diffracted light L _d is generated up to higher order. Note that 0-order diffracted light is consistent with the outgoing light L _o emitted is reflected by the micro mirror 21.

Diffraction occurs as described above regardless of whether the micromirror 21 is in the ON state or the OFF state. In this case, arrangement of the micro mirror 21 becomes a blazed diffraction grating, the direction of the diffracted light L _d are different by the respective tilt angles of the micro mirrors 21.

As shown in FIG. 7A, the outgoing light L _{o from} the micro mirror 21 in the ON state enters the projection optical system 3 including the diffracted light L _d . In this case, even if the entire image to be displayed is white (all the micromirrors 21 are in the ON state), the entire image is bright, so even if the diffracted light L _d is incident on the projection optical system 3 as stray light, The contrast ratio of the display image is not affected.

On the other hand, as shown in FIG. 7 (b), if all the micromirrors 21 is OFF, the outgoing light _{L o} in the micro mirror 21 in the ON state does not enter the projection optical system 3. However, some of the diffracted light L _d is thus incident on the projection optical system 3. In this case, even if the displayed image is entirely black, a part of the diffracted light L _d is projected onto the screen, causing a so-called “black float” and affecting the contrast ratio.

In this way, mainly the diffracted light L _d in the OFF state becomes stray light, and the contrast ratio is lowered. In FIGS. 7A and 7B, only three micro mirrors 21 are used for explanation, but the actual number of micro mirrors 21 provided in the spatial light modulator 2 is large. In FIG. 7, the size of the micro mirror 21 is exaggerated with respect to the size of the lens of the projection optical system 3.

Here, consider the optical path difference of the diffracted light L _d caused by the light incident on the adjacent micromirrors 21. As shown in FIG. 8, assuming that the adjacent micromirrors 21 are both in the OFF state, the tilt angle (θ _tilt ) of the micromirrors 21 is, for example, 12 degrees. Further, the angle of incidence of the incident light _{L i} to the micro mirror 21 (θ _in) is, for example, 24 degrees _{(θ in = 2 · θ tilt} ). The outgoing angle (θ _out ) of the outgoing light L _o reflected by the micro mirror 21 is a value obtained by subtracting an angle twice as large as the incident angle (θ _in ) from 90 degrees.

Therefore, the optical path difference (δ) of the diffracted light by the adjacent micromirrors 21 is “δ = d × cos θ _out ”. “D” is the interval of the arrangement of the micromirrors 21. Since θ _out takes a value from 0 ° to 180 °, δ also changes according to the value of θ _out . When δ is an integer multiple of the wavelength λ is ready constructive diffracted light L _d, a state destructive diffracted light L _d otherwise. It is assumed that the phases of the incident plane waves are uniform, and the angle 12 ° of the micro mirror 21 and the angle 24 ° of the incident angle (θ _in ) are not limited to this. These angles vary depending on the design of the illumination optical system 1 and the spatial light modulator 2.

As described in the above, if the light is a plane wave incident on the micro mirror 21, the diffracted light L _d includes a portion weakened the portion to be highlighted by interference. However, the phase of the incident light L _i if it is possible to cheat each micro mirror 21, it is possible to reduce interference of the diffracted light L _d. That is, it is possible to reduce the stray light, it is possible to prevent a reduction in contrast ratio due to diffraction light L _d.

As described above, the illumination optical system 1 of the present embodiment in order to reduce diffracted light L _d is have a phase conversion element 141 between the exit surface 143 of the spatial light modulator 2 and the light equalizing element 14 doing. Phase conversion element 141 is provided with the function of shifting the phase of the incident light L _i for each micro mirror 21 provided in the spatial light modulator 2.

Here, the phase conversion element 141 provided in the illumination optical system 1 according to the present embodiment will be described in detail. As shown in FIG. 10, the phase conversion element 141 includes a first conversion unit 1411 to shift the phase of incident light _{L i,} not shifted the phase of the incident light _{L i,} or, in a different phase from the first conversion unit 1411 And a second conversion unit 1412 that gives a shift. The first conversion unit 1411 that is the first part and the second conversion unit 1412 that is the second part have a square shape in plan view, and have the same dimensions. Here, the length of one side of the first conversion unit 1411 and the second conversion unit 1412 is “D”.

  As shown in FIG. 10A, the first conversion unit 1411 and the second conversion unit 1412 are alternately arranged on the plane of the phase conversion element 141. The number of arrangements of the first conversion unit 1411 and the second conversion unit 1412 is the same as the number of arrangement of the pixels (micromirrors 21) of the spatial light modulation element 2 at the maximum. The light emitted from the emission end of the light uniformizing element 14 passes through the phase conversion element 141 and illuminates the effective image area of the spatial light modulation element 2 through each optical element already described.

The phase conversion element 141 will be described in more detail. When the incident light L _i is a plane wave from the left side of the drawing of the phase conversion element 141 as shown in FIG. 11 passes through the phase conversion element 141 is incident, the phase of the outgoing light L _o emitted from the right side of the drawing, the incident light L _i A portion different from the phase of is included. The phase conversion element 141 is arranged on a plane that intersects the traveling direction of the light. That is, the first conversion unit 1411 and the second conversion unit 1412 are alternately arranged in the crossing direction of the light traveling direction. In other words, the phase conversion element 141 is disposed so as to be parallel to the emission end face 143 of the illumination uniformizing element 14, and the first conversion unit 1411 and the second conversion part 1412 are also parallel to the emission end face 143.

11, a solid line and a dashed line across the arrow indicating the incident light L _i illustrates a mountain L _T and valleys L _B of the amplitude of the incident light L _i is a plane wave. Similarly, solid and dashed lines across the arrow indicating the outgoing light L _o illustrate the mountain L _T and valleys L _B of each of the amplitude of light passing through a first conversion unit 1411 and the second conversion unit 1412.

As shown in FIG. 11, the phase of the outgoing light L _o which has passed through the first conversion unit 1411 is a first portion, the phase of the outgoing light L _o which has passed through the second conversion unit 1412 is a second part It is late compared. Therefore, even light entering the phase conversion element 141 is a plane wave, a light emitted L _o which has passed through the phase conversion element 141, the emitted light which has passed through the first converter 1411 adjacent the second conversion unit 1412 The peaks L _T and valleys L _B of the amplitude between L _o exist alternately.

As described above, when the phases of lights passing through adjacent regions in the phase conversion element 141 are different from each other, and the peaks L _T and valleys L _B of the amplitudes of the adjacent lights are shifted, the light is caused by interference. Intensified parts are less likely to occur. Therefore, even if diffraction is caused by this light, the stray light becomes weak and the influence on the image quality is small.

  FIG. 12 is a side view of the phase conversion element 141. As shown in FIG. 12, the phase conversion element 141 is obtained by providing dielectric thin films 1414 in a staggered pattern on a portion (first portion) that gives a phase difference on a glass substrate 1413. The portion where the dielectric thin film 1414 is provided becomes the first converter 1411. A portion where the dielectric thin film 1414 is not provided becomes the second conversion unit 1412.

  When the wavelength of light passing through the phase conversion element 141 is “λ”, the thickness of the dielectric thin film 1414 is “t”, and the refractive index of the dielectric thin film 1414 is “n”, the light passing through the first conversion unit 1411 and the first The phase difference δ of the light passing through the two converting unit 1412 is obtained by δ = (2π / λ) (n−1) t.

  If the dielectric thin film 1414 is formed so that the above phase difference δ becomes “λ / 2”, the zero-order light of the diffracted light disappears. Further, if the dielectric thin film 1414 is formed so that the phase difference δ is other than “λ / 2”, higher-order diffracted light can be weakened. That is, the stray light generated in the spatial light modulation element 2 can be reduced by the phase conversion element 141, and thereby the contrast ratio can be increased.

  The half angle of the light beam emitted from the light uniformizing element 14 is 30 °, the tilt angle of the minute mirror 21 of the spatial light modulator 2 is 12 °, and the half angle reflected by the minute mirror 21 and incident on the projection optical system 3 is 12 °. Then, the lateral magnification β becomes 2.5. Since the outer shape of the micromirror 21 is square and one side is, for example, 10.8 μm, the length D of one side of the first conversion unit 1411 and the second conversion unit 1412 of the phase conversion element 141 is 10.8 / 2. .5 = 4.32 μm is sufficient. By matching with this size, each of the first conversion unit 1411 and the second conversion unit 1412 of the phase conversion element 141 corresponds to each of the micro mirrors 21 of the spatial light modulation element 2 that is a square pixel, which is efficient. The phase can be controlled.

  The illumination optical system 1 including the phase conversion element 141 has a length “D” of one side of the phase conversion element 141, a length “d” of one side of the micromirror of the spatial light modulation element 2, and a horizontal length in the illumination optical system 1. A condition in which the relationship of the magnification “β” is “D≈β · d” is a preferable condition.

  Next, another embodiment of the phase conversion element 141 will be described. FIG. 13 is an enlarged perspective view of the first conversion unit 1411 included in the phase conversion element 141. As illustrated in FIG. 13, the first conversion unit 1411 of the phase conversion element 141 according to the present embodiment is configured by a subwavelength structure (SWS: Subwavelength Structure).

  In order to give a suitable phase difference to each of R, G, and B, it is necessary to form the first converter 1411 corresponding to each color (wavelength). Therefore, the first conversion unit 1411 may be configured with a sub-wavelength structure like the phase conversion element 141 according to the present embodiment. The subwavelength structure is designed so that a phase difference is given to a specific wavelength by setting the pitch (p), groove width “w”, and height “t” to optimum values as parameters. be able to.

  Since the human eye has the maximum relative visibility with respect to green (wavelength = 555 nm), if the phase difference is given to this wavelength, the effect is maximized, and the structure that gives the phase difference is also one. One is enough.

  Next, still another embodiment of the phase conversion element 141 will be described. Whether the diffracted light enters the projection optical system 3 differs depending on the incident position of the incident light with respect to the spatial light modulator 2. Consider the incident light on the end of the spatial light modulation element 2 as shown in FIG. Of the end portions of the spatial light modulator 2, the end portion on the side close to the second folding mirror 18 is referred to as “position p1”, and the end portion on the far side is referred to as “position p2”. Of the incident light incident on the spatial light modulator 2 from the second folding mirror 18, the optical path of the incident light to the position p1 is longer than the optical path of the incident light to the position p2.

  Therefore, the diffracted light by the incident light incident on the position p1 is generated in a direction that does not reach the entrance pupil of the projection optical system 3. Therefore, the diffracted light at the position p 1 does not enter the projection optical system 3. However, a part of the diffracted light by the incident light incident on the position p2 is generated in a direction reaching the entrance pupil of the projection optical system 3. Therefore, the diffracted light at the position p <b> 2 enters the projection optical system 3.

  As described above, since the degree of influence of the image quality due to the diffracted light differs depending on the incident position on the spatial light modulator 2, the illumination optical system 1 is configured so that the phase difference is given only to the incident light corresponding to the position p2. do it. That is, the phase conversion element 141 disposed on the emission surface 143 of the light uniformizing element 14 may be disposed at a position corresponding to the position p2 on the spatial light modulation element 2. As described above, even if the small phase conversion element 141 is arranged on a part of the emission surface 143 without arranging the phase conversion element 141 so as to cover the entire emission surface 143 of the light uniformizing element 14, stray light can be obtained. The effect which prevents can be acquired. That is, it is possible to prevent a reduction in contrast ratio and reduce costs.

DESCRIPTION OF SYMBOLS 1 Illumination optical system 11 Light source 13 Color wheel 14 Light uniformizing element 2 Spatial light modulation element 3 Projection optical system 100 Projector

JP 2004-258439 A

Claims (10)

A light source;
A light uniformizing element that emits light with uniform illuminance from the light source;
An illumination optical system comprising:
Illuminating the spatial light modulator with the light emitted from the light homogenizer,
Between the light uniformizing element and the spatial light modulation element, a phase conversion element that converts the phase of a part of the light,
An illumination optical system characterized by that. The phase conversion element is
A first converter that converts a part of the phase of the light into a first phase;
A second converter that converts the phase of the other part of the light into a second phase;
Having
The illumination optical system according to claim 1. The first conversion unit and the second conversion unit are alternately arranged on a plane in a direction crossing the traveling direction of the light,
The illumination optical system according to claim 2. The shape of the first conversion unit and the second conversion unit in plan view is a rectangle.
The illumination optical system according to claim 2 or 3. The outer shape of the phase conversion element is square,
A length D of one side of the phase conversion element;
A length d of one side of the square pixel of the spatial light modulator;
Lateral magnification β in the illumination optical system,
Where D≈β · d.
The illumination optical system according to claim 1. The phase conversion element is provided on a part of the emission surface of the light uniformizing element,
The illumination optical system according to claim 1. A color wheel that converts light from the light source into light of a specific color between the light source and the incident surface of the light uniformizing element;
The phase conversion element converts the phase of the light of the specific color.
The illumination optical system according to any one of claims 1 to 6. The phase conversion element has a subwavelength structure,
A part of the light whose phase is converted, the phase of which is converted in the sub-wavelength structure;
The illumination optical system according to claim 1. The light source is a laser;
The illumination optical system according to claim 1. An image display apparatus comprising: an illumination optical system; a spatial light modulation element that forms a projection image based on light from the illumination optical system; and a projection optical system that projects the projection image toward a projection object. ,
The illumination optical system is the illumination optical system according to any one of claims 1 to 9.
An image display device characterized by that.

Images