JP2017076044A - Projection type display device using laser beam and on-vehicle head-up display using the projection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection type display device using laser beams that, when an image having a polarization direction changed in a frame unit to reduce speckle noise is visually recognized through polarized sunglasses, prevents generation of flicker of light with all wavelengths within a range of visible light.SOLUTION: A projection type display device 10 comprises: a light source part 100 that generates a plurality of laser beams with different wavelengths in a predetermined polarization direction; a composition optical part 200 that composes the plurality of laser beams; an image forming part 300 that forms a projection image from the plurality of laser beams; a liquid crystal element 400 that creates a single polarization state in a transmission area through which the plurality of laser beams emitted from the composition optical part 200 transmit, and changes the polarization direction of the plurality of laser beams in the transmission area; and a high retardation film 500 that provides a phase difference to the plurality of laser beams emitted from the liquid crystal element 400.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a projection display device using laser light and an in-vehicle head-up display using the projection display device.

  In recent years, a projection display device using a small and highly efficient laser beam as a light source has been developed. Laser light has high brightness and excellent color reproducibility, and can be applied to head-mounted displays and head-up displays as a projection display device because of its wide angle of view, low power consumption, and high contrast. Progressing.

  Since the laser light has high coherence, when the laser light is scattered by the unevenness of the surface (projection surface) projected by the projection display device, the scattered light interferes with each other and is displayed on the projection surface (display image) Speckle noise, which is a bright and dark spot pattern, may appear. The quality of the displayed image is significantly impaired by speckle noise. Speckle noise is a problem peculiar to a projection display device using a laser light source, and various attempts have been made to solve it.

  One method for reducing speckle noise is to display an image by changing the polarization direction of laser light emitted from a light source by 90 degrees between horizontal polarization and vertical polarization in units of frames. Thereby, although speckle noise is generated in each frame, the location where speckle noise is generated differs depending on the polarization direction, and thus the generated speckle noise is smoothed for the entire display image. As a result, a display image is visually recognized in a state where speckle noise is reduced (for example, Patent Document 1).

  In general, polarizing sunglasses use a polarizing plate that absorbs a horizontally polarized light component. Therefore, in the projection display device that displays the image by switching the laser light emitted from the light source between the horizontal polarization and the vertical polarization as described above, when the display image is viewed through the polarization sunglasses, the display image of the vertical polarization is Although it is visible, a display image with horizontal polarization cannot be visually recognized. Therefore, since a frame that can be visually recognized and a frame that cannot be visually recognized appear alternately in the display image, the display image is recognized as flickering, that is, so-called flicker.

  Patent Document 2 discloses a vehicle display device capable of visually recognizing a horizontally polarized display image while wearing polarized sunglasses. The vehicle display device includes a display that emits output display light having a horizontal polarization plane, an illumination light source that illuminates the display, and 45 degrees with respect to the horizontal polarization plane of the output display light emitted from the display. And a quarter-wave plate provided so as to face the display unit with the high-speed axis tilted. When the ¼ wavelength plate arranged in this way is used, the horizontally polarized outgoing display light becomes circularly polarized after being transmitted through the ¼ wavelength plate. Even with polarized sunglasses that absorb the polarized component of the direction, the display image can be viewed. Therefore, the viewer can visually recognize the display image even when the head or body is tilted.

International Publication No. 2011/037039 JP 2013-057897 A

  However, an actual quarter-wave plate cannot give a quarter-wave phase difference to all wavelengths within the visible light range. For this reason, the output light that has passed through the quarter-wave plate is not circularly polarized but elliptically polarized at wavelengths that do not result in a quarter-wave phase difference, so that the horizontally polarized display image can be viewed visually while wearing polarized sunglasses. The effects that can be done are limited.

  In this way, when an image whose polarization direction is changed in units of frames in order to reduce speckle noise is viewed through polarized sunglasses, the laser does not generate flicker for all wavelengths in the visible light range. There is a need for a projection display device using light.

  One embodiment of a projection display device using laser light according to the present invention includes a light source unit that generates a plurality of laser beams having different wavelengths in a predetermined polarization direction, and a combining optical unit that combines the plurality of laser beams. And a single polarization state in an image forming unit that forms a projection image from the plurality of laser beams, and a transmission region through which the plurality of laser beams emitted from the combining optical unit are transmitted, and in the transmission region A liquid crystal element that changes a polarization direction of the plurality of laser beams; and a high retardation film that gives a phase difference to the plurality of laser beams emitted from the liquid crystal element.

  In a projection display device having a high retardation film, a plurality of laser beams having linearly polarized light are transmitted through the high retardation film, so that light of each wavelength included in the plurality of laser beams after transmission has various polarizations. It includes light of the direction, rotation direction, and polarization type (linearly polarized light, circularly polarized light, elliptically polarized light), and does not include only horizontally polarized light. Therefore, even if a driver wearing polarized sunglasses visually recognizes the image, flicker does not occur.

  In one embodiment of the projection display apparatus using laser light, the optical axis of the high retardation film and the polarization axis in the single polarization state form an angle of 45 degrees, and the plurality of laser lights A phase difference of 4000 nm or more is given.

  If the optical axis (fast axis and slow axis) of the high retardation film and the polarization axis of the linearly polarized laser beam are at an angle of 45 degrees, the multiple laser beams incident on the high retardation film are fast axes. And a component that transmits along the slow axis. In the synthesized light after transmission, a phase difference of 4000 nm or more is generated between the component along the fast axis and the component along the slow axis. The high retardation film according to this embodiment has a characteristic that the phase difference is 4000 nm or more with respect to light of all wavelengths (red light, green light, and blue light) in the visible light range. When the phase difference is 4000 nm or more, a high-quality image can be obtained without causing rainbow unevenness in the projected image.

  In one embodiment of a projection display apparatus using laser light, the liquid crystal element has a liquid crystal layer and a pair of substrates arranged so as to sandwich the liquid crystal layer, and at least of the pair of substrates The high retardation film is formed on the surface of the substrate on the side far from the light source part.

  With such a configuration, a member for holding the high retardation film becomes unnecessary, and the projection display device can be configured at a lower cost.

  One embodiment of a projection display apparatus using laser light further includes an intermediate image portion having a diffusion function on a side farther from the image forming portion when viewed from the light source portion, and at least one surface of the intermediate image portion The high retardation film is formed.

  With such a configuration, a member for holding the high retardation film becomes unnecessary. The intermediate image portion is a transmissive screen and has a function of diffusing incident light and emitting it. By providing the projection display device with the intermediate image portion, it is possible to obtain synthetic light having an emission angle necessary for projection onto the screen.

  One embodiment of a projection display apparatus using laser light further includes a display unit having a half mirror function on the side farther from the image forming unit when viewed from the light source unit, and is close to the light source unit of the display unit The high retardation film is formed on the surface on the side.

  With such a configuration, a member for holding the high retardation film becomes unnecessary. Further, by projecting an image on the display unit, an image without distortion can be displayed regardless of the curvature of the windshield. Furthermore, the magnification of the image can be increased by making the display unit concave.

  In one embodiment of a projection display apparatus using laser light, the liquid crystal element has a liquid crystal layer and a pair of substrates arranged so as to sandwich the liquid crystal layer, and the liquid crystal molecules of the liquid crystal layer are The pair of substrates has a spiral structure, and the product of the spiral pitch of the liquid crystal molecules and the refractive index anisotropy of the liquid crystal layer is 2500 nm or more.

  With such a configuration, the liquid crystal element reduces the optical rotation dispersion of a plurality of laser beams having different wavelengths, and the polarization characteristics are the same. As a result, even if the polarization direction changes during the formation of a one-frame projection image, all the polarization directions of a plurality of laser beams having different wavelengths with respect to the applied voltage change in the same way. Even if the same color is displayed on a plurality of pixels during drawing, the color does not change.

  In one embodiment of the projection display device using laser light, the twist angle of the liquid crystal molecules in the liquid crystal layer is 90 degrees.

  With such a configuration, the polarization direction of light transmitted through the liquid crystal layer can be changed by 90 degrees by turning on and off the voltage application to the liquid crystal layer. Thereby, the effect of reducing speckle noise due to the change in the polarization direction can be maximized.

  In one embodiment of the projection display apparatus using laser light, the liquid crystal layer is formed by laminating a first layer and a second layer, and the twist angle in the first layer and the twist angle in the second layer. Each twist angle is 45 degrees.

  In a liquid crystal element, when two liquid crystal layers are stacked to form a liquid crystal layer, in order to change the polarization direction of light passing through the liquid crystal element by 90 degrees, the voltage applied to each liquid crystal layer is the same voltage. In this case, the change of the polarization direction in each liquid crystal layer due to turning on and off of the applied voltage is 45 degrees. Therefore, the optical rotation dispersion of a plurality of laser beams having different wavelengths can be reduced, and the polarization direction can be changed in a short time. Further, the 45 degree twist angles of the first layer and the second layer may be twisted in the same direction or may be twisted in opposite directions. When twisted in the opposite direction, voltage application to each liquid crystal layer is performed at the timing of alternately applying the same voltage.

  One embodiment of a projection display device using laser light according to the present invention includes a light source unit that generates a plurality of laser beams having different wavelengths in a predetermined polarization direction, and a combining optical unit that combines the plurality of laser beams. And a single polarization state in an image forming unit that forms a projection image from the plurality of laser beams, and a transmission region through which the plurality of laser beams emitted from the combining optical unit are transmitted, and in the transmission region A liquid crystal element that changes a polarization direction of the plurality of laser beams, and the liquid crystal element includes a liquid crystal layer and a pair of substrates disposed so as to sandwich the liquid crystal layer, and the liquid crystal of the liquid crystal layer The molecule has a spiral structure between the pair of substrates, and the polarization direction of the plurality of laser beams in the liquid crystal element is changed by 45 degrees to the right with respect to the horizontal direction in the usage state of the liquid crystal element. When A laser beam is used which alternately changes 45 degrees altered direction.

  In the projection type display device having such a configuration, the liquid crystal element is formed by combined light in which the polarization direction is changed 45 degrees to the right and 45 degrees to the left alternately with respect to the horizontal direction. The projected image is projected on the screen. With such a configuration, since the polarization direction of the projected image changes, speckle noise generated on the screen is smoothed as a whole. As a result, speckle noise is reduced and is visually recognized by the driver. Further, even if the driver wearing the polarized sunglasses visually recognizes the image, the image is not formed by the horizontally polarized synthetic light, and therefore flicker does not occur.

  In one embodiment of the projection display apparatus using laser light, the product of the helical pitch of the liquid crystal molecules and the refractive index anisotropy of the liquid crystal layer is 2500 nm or more.

  With such a configuration, the liquid crystal element reduces the optical rotation dispersion of a plurality of laser beams having different wavelengths, and the polarization characteristics are the same. As a result, even if the polarization direction changes during the formation of a one-frame projection image, all the polarization directions of a plurality of laser beams having different wavelengths with respect to the applied voltage change in the same way. Even if the same color is displayed on a plurality of pixels during drawing, the color does not change.

  In one embodiment of the projection display device using laser light, the twist angle of the liquid crystal molecules in the liquid crystal layer is 90 degrees.

  With such a configuration, the polarization direction of light transmitted through the liquid crystal layer can be changed by 90 degrees by turning on and off the voltage application to the liquid crystal layer. Thereby, the effect of reducing speckle noise due to the change in the polarization direction can be maximized.

  In one embodiment of the projection display apparatus using laser light, the liquid crystal layer is formed by laminating a first layer and a second layer, and the twist angle in the first layer and the twist angle in the second layer. Each twist angle is 45 degrees.

  In a liquid crystal element, when two liquid crystal layers are stacked to form a liquid crystal layer, in order to change the polarization direction of light passing through the liquid crystal element by 90 degrees, the voltage applied to each liquid crystal layer is the same voltage. In this case, the change of the polarization direction in each liquid crystal layer due to turning on and off of the applied voltage is 45 degrees. Therefore, the optical rotation dispersion of a plurality of laser beams having different wavelengths can be reduced, and the polarization direction can be changed in a short time. Further, the 45 degree twist angles of the first layer and the second layer may be twisted in the same direction or may be twisted in opposite directions. When twisted in the opposite direction, voltage application to each liquid crystal layer is performed at the timing of alternately applying the same voltage.

  One embodiment of a projection display apparatus using laser light further includes a high retardation film that gives a phase difference to the plurality of laser lights emitted from the liquid crystal element, and the optical axis of the high retardation film and the single The polarization axis in this polarization state forms an angle of 45 degrees, and gives a phase difference of 4000 nm or more to the plurality of laser beams.

  In a projection display device having a high retardation film, a plurality of laser beams having linearly polarized light are transmitted through the high retardation film, so that light of each wavelength included in the plurality of laser beams after transmission has various polarizations. It includes light of the direction, rotation direction, and polarization type (linearly polarized light, circularly polarized light, elliptically polarized light), and does not include only horizontally polarized light. Therefore, even if a driver wearing polarized sunglasses visually recognizes the image, flicker does not occur.

  In addition, if the optical axis (the fast axis and the slow axis) of the high retardation film and the polarization axis of the linearly polarized laser beam form an angle of 45 degrees, a plurality of laser beams incident on the high retardation film advance. It has a component that permeates along the phase axis and a component that permeates along the slow axis. In the synthesized light after transmission, a phase difference of 4000 nm or more is generated between the component along the fast axis and the component along the slow axis. The high retardation film according to this embodiment has a characteristic that the phase difference is 4000 nm or more with respect to light of all wavelengths (red light, green light, and blue light) in the visible light range. When the phase difference is 4000 nm or more, a high-quality image can be obtained without causing rainbow unevenness in the projected image.

  In one embodiment of the projection display apparatus using laser light, the high retardation film is formed on the surface of the substrate that is at least on the side farther from the light source unit among the pair of substrates.

  With such a configuration, a member for holding the high retardation film becomes unnecessary, and the projection display device can be configured at a lower cost.

  One embodiment of a projection display apparatus using laser light further includes an intermediate image portion having a diffusion function on a side farther from the image forming portion when viewed from the light source portion, and at least one surface of the intermediate image portion The high retardation film is formed.

  With such a configuration, a member for holding the high retardation film becomes unnecessary. The intermediate image portion is a transmissive screen and has a function of diffusing incident light and emitting it. By providing the projection display device with the intermediate image portion, it is possible to obtain synthetic light having an emission angle necessary for projection onto the screen.

  One embodiment of a projection display apparatus using laser light further includes a display unit having a half mirror function on the side farther from the image forming unit when viewed from the light source unit, and is close to the light source unit of the display unit The high retardation film is formed on the surface on the side.

  With such a configuration, a member for holding the high retardation film becomes unnecessary. Further, by projecting an image on the display unit, an image without distortion can be displayed regardless of the curvature of the windshield. Furthermore, the magnification of the image can be increased by making the display unit concave.

  One embodiment of a projection display device using laser light further includes a liquid crystal cell that changes the transmittance of the plurality of laser lights between the combining optical unit and the liquid crystal element.

  When the emission intensity of laser light is controlled by current, if the emission intensity is changed from a strong state to a weak state, the oscillation stops at a certain current value, so that a weak laser beam cannot be obtained. That is, the dynamic range of the emission intensity is small. Therefore, by changing the transmittance of the laser beam that passes through the inside of the liquid crystal cell, the emission intensity of the transmitted laser beam can be changed from a strong state to a weak state without performing current control. The dynamic range can be increased.

  In one embodiment of the projection display apparatus using laser light, the liquid crystal cell has a vertically aligned nematic liquid crystal layer.

  When the transmittance of a plurality of laser beams is changed using the vertically aligned nematic liquid crystal, the intensity of the laser beam incident on the liquid crystal element can be controlled in accordance with the intensity of external light. Further, by adopting a configuration in which laser light does not pass through when the voltage is not applied to the liquid crystal layer (normally black), a high contrast ratio (extinction ratio) is obtained and safety against the laser light is ensured.

  One embodiment of a projection display device using laser light further includes a light detection unit that detects colors and intensities of the plurality of laser beams on a side farther from the liquid crystal cell when viewed from the light source unit. The light source unit further includes a control unit to which a detection result of the light detection unit is input, and the light source unit includes a red laser light source that generates red light, a green laser light source that generates green light, and a blue light that generates blue light. A laser light source, and the control unit performs control to change the intensity of light emitted from the red laser light source, the green laser light source, and the blue laser light source based on a detection result of the light detection unit. It is preferred to do so.

  When vertically aligned nematic liquid crystal is used in the liquid crystal cell, the intensity of multiple laser beams can be greatly changed and safety against the laser beam can be ensured. However, vertical aligned nematic liquid crystals have different wavelengths of red light and green light. The difference in the modulation factor (wavelength dispersion) is large when blue light transmits when the same voltage is applied to the liquid crystal layer. For this reason, the color of the combined light before entering the liquid crystal cell, that is, the color to be displayed in the image, and the color of the combined light after passing through the liquid crystal cell change, and the color balance of the projected image is changed. It will deteriorate. Therefore, by having such a configuration, it is possible to always optimize the brightness and color balance of the image viewed by the driver according to the intensity of external light.

  The projection display device using any one of the above laser beams can be applied to an in-vehicle head-up display.

  With such a characteristic configuration, a high-quality image with little speckle noise can be displayed, and a head-mounted display that does not generate flicker even when a driver wearing polarized sunglasses visually recognizes the image. Can be obtained.

It is a block diagram showing the structure of the projection type display apparatus which concerns on 1st Embodiment. It is sectional drawing showing the structure of the liquid crystal element which concerns on 1st Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on 1st Embodiment. It is a figure which represents the polarization direction of the light after horizontally polarized light permeate | transmits the high retardation film, the rotation direction, and the kind of polarization with a Poincare sphere. It is a graph showing the intensity | strength of incident light when the linearly polarized red light, green light, and blue light inject into the orthogonal Nicol polarizing plate which pinches | interposes a high retardation film. It is a graph showing the intensity | strength of the emitted light when a linearly polarized red light, green light, and blue light are radiate | emitted from the orthogonal Nicol polarizing plate which pinches | interposes a high retardation film. It is a graph showing the approximate curve of the intensity | strength of the emitted light when the linearly polarized red light, green light, and blue light are radiate | emitted from the crossed Nicol polarizing plate which pinches | interposes a high retardation film. It is a figure showing the polarization direction, the rotation direction, and the kind of polarization of each light after horizontal polarized light and vertical polarized light are transmitted through the high retardation film by Poincare spheres. A graph showing polarization characteristics when red light, green light, and blue light are transmitted through a liquid crystal element having a twist angle of 90 degrees and a product of the spiral pitch of the liquid crystal molecules and the refractive index anisotropy of the liquid crystal layer of 2500 nm or more. is there. It is a block diagram showing the structure of the projection type display apparatus which concerns on the modification 1 of 1st Embodiment. It is a block diagram showing the structure of the projection type display apparatus which concerns on the modification 2 of 1st Embodiment. It is sectional drawing showing the structure of the liquid crystal element which concerns on the modification 3 of 1st Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 3 of 1st Embodiment. It is sectional drawing showing the structure of the liquid crystal element which concerns on the modification 4 of 1st Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 4 of 1st Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 4 of 1st Embodiment. It is a graph showing the optical response of the liquid crystal element which concerns on the modification 4 of 1st Embodiment. It is a block diagram showing the structure of the projection type display apparatus which concerns on the modification 5 of 1st Embodiment. It is a graph showing the transmittance | permeability of red light with respect to the applied voltage of the liquid-crystal layer using a vertical alignment nematic liquid crystal, green light, and blue light. It is a block diagram showing the structure of the projection type display apparatus which concerns on 2nd Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on 2nd Embodiment. It is sectional drawing showing the structure of the liquid crystal element which concerns on the modification 1 of 2nd Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 1 of 2nd Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 1 of 2nd Embodiment. It is sectional drawing showing the structure of the liquid crystal element which concerns on the modification 2 of 2nd Embodiment. It is the schematic showing the change of the polarization direction when light permeate | transmits the liquid crystal element which concerns on the modification 2 of 2nd Embodiment. It is a block diagram showing the structure of the projection type display apparatus which concerns on 3rd Embodiment.

1. First Embodiment [Configuration of Head-Up Display for Vehicle]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an in-vehicle head-up display (hereinafter simply referred to as “head-up display”) 50. The head-up display 50 is a device that displays information superimposed on the human visual field. The head-up display 50 includes the projection display device 10 according to the first embodiment and a reflection mirror 340.

[Overall configuration of projection display device]
The projection display device 10 includes a light source unit 100, a synthetic optical unit 200, an image forming unit 300, a liquid crystal element 400, and a high retardation film 500. The projection type display device 10 combines the light generated by the light source unit 100 with the combining optical unit 200 to generate combined light, and transmits the high retardation film 500 after changing the polarization direction of the combined light with the liquid crystal element 400. Then, the image forming unit 300 forms a projection image from the synthesized light.

  The formed projection image is reflected by the reflection mirror 340 and then projected onto the windshield 700 of the vehicle. Since this projection image includes information to be recognized by the driver 40, hereinafter, the projection image is also referred to as an information image.

  The information image projected on the windshield 700 forms an image at a point at infinity, and it appears to the driver 40 that the information image is displayed on the virtual screen 600 located far away. Therefore, the driver 40 can recognize the information displayed there while focusing on the information image while gazing at a distance in the traveling direction while driving the vehicle.

[Configuration of light source section]
The light source unit 100 includes a laser diode (LD) 110 that generates green light, an LD 120 that generates blue light, and an LD 130 that generates red light. The light of each color is linearly polarized light having the same polarization direction, and is modulated and emitted corresponding to the pixels of the projected image displayed on the windshield 700. Each color light has high coherence. By providing the LDs 110 to 130, the projection display apparatus 10 can project a color image. The LD 110 is an example of a green laser light source, the LD 120 is an example of a blue laser light source, and the LD 130 is an example of a red laser light source.

  In the present embodiment, a dedicated LD is used for each of the three color light sources, but a two-color or three-color light source may be configured by separating the LD generating white light by a dichroic mirror or the like. In the present embodiment, the LDs 110 to 130 are used, but the light source unit 100 may be configured using LDs that generate other colors. Further, the number of light emitted from the light source unit 100 is not limited to three, and may be two or four or more.

(Composition of the synthesis optical unit)
The combining optical unit 200 includes a mirror 210 that reflects green light generated from the LD 110, a dichroic mirror 220 that transmits green light and reflects blue light generated from the LD 120, and transmits green light and blue light and is generated from the LD 130. And a dichroic mirror 230 that reflects red light. The combining optical unit 200 combines the green light, the blue light, and the red light to generate combined light. In the combined light state, green light, blue light, and red light all have the same polarization direction.

(Configuration of image forming unit)
The image forming unit 300 includes a horizontal scanning mirror 310 and a vertical scanning mirror 320, which are examples of a scanning mechanism, and scans incident combined light in a two-dimensional direction. In the present embodiment, the horizontal scanning mirror 310 is a MEMS (Micro Electro Mechanical System) mirror manufactured using semiconductor manufacturing technology or the like, and can be reciprocally oscillated (resonant vibration) using electromagnetic force or the like. Use what you can. Further, a galvanometer mirror is used as the vertical scanning mirror 320. The horizontal scanning mirror 310 and the vertical scanning mirror 320 are driven by a driving source (not shown). Thus, the combined light is scanned from the upper left end to the lower right end by sequentially repeating the scanning in the horizontal direction and the scanning in the vertical direction in the display range of the information image on the windshield 700, and is formed by the image forming unit 300. The one frame information image is projected and displayed. Thereafter, the scanning position returns to the upper left end again, and scanning for projecting and displaying the information image of the next frame starts. Note that one frame of the information image may be displayed by scanning the combined light from the upper right end to the lower left end. Further, as another example of the scanning mechanism, the image forming unit 300 may be configured to swing so as to scan in the horizontal direction and the vertical direction with a single mirror.

[Configuration of liquid crystal element]
As shown in FIG. 2, the liquid crystal element 400 includes a light-transmitting liquid crystal layer 441 between the light-transmitting substrates 411 and 412, and a liquid crystal layer 441 between the liquid crystal layer 441 and the substrates 411 and 412. Light-transmitting alignment layers 431 and 432 for aligning molecules, and electrode layers 421 and 422 made of a light-transmitting material such as ITO (Indium Tin Oxide) and generating an electric field applied to the liquid crystal layer 441 by applying a voltage. I have. The liquid crystal element 400 is disposed between the combining optical unit 200 and the image forming unit 300, and transmits the combined light emitted from the combining optical unit 200 to enter the image forming unit 300. When a voltage is applied to the electrode layers 421 and 422 by the AC power supply 450, the alignment state of the liquid crystal molecules of the liquid crystal element 400 is changed by the generated electric field, thereby changing the polarization direction of the transmitted synthesized light. Note that Δn in FIG. 2 represents the refractive index anisotropy of the liquid crystal layer 441, and d represents the thickness of the liquid crystal layer 441. In the figure, the arrow from the left to the right represents the traveling direction of the combined light.

  FIG. 3 shows a change in the polarization direction of the light X transmitted through the liquid crystal element 400 when no voltage is applied. The alignment layers 431 and 432 of the liquid crystal element 400 have a function of aligning liquid crystal molecules in a certain direction. In this embodiment, the alignment layer 431 is aligned so that the liquid crystal molecules are aligned in the vertical direction (arrow B), and the alignment layer 432 is aligned so that the liquid crystal molecules are aligned in the horizontal direction (arrow C). ). Therefore, the liquid crystal molecules in the liquid crystal layer 441 have a helical structure in which the liquid crystal molecules are twisted by 90 degrees and arranged from the alignment layer 431 toward the alignment layer 432. The polarization direction of the light X transmitted through the liquid crystal layer 441 rotates along the alignment of the liquid crystal molecules.

  As shown in FIG. 3, the polarization direction of the light X indicated by the arrow A is vertical polarization, and the polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 431 indicated by the arrow B. And enters the liquid crystal layer 441. While the light X is transmitted through the liquid crystal layer 441, the polarization direction changes by 90 degrees along the alignment of the liquid crystal molecules, becomes horizontal polarized light indicated by the arrow D, and passes through the alignment layer 432 indicated by the arrow C to be emitted. In each embodiment and modification of the present specification, in the state where the light source unit 100 and the liquid crystal element 400 in the projection display device 10 are used, the polarization in the direction along the direction of gravity (vertical direction) is vertically polarized. The polarized light in the direction perpendicular to the direction of gravity (direction parallel to the ground, horizontal direction) is referred to as horizontal polarized light.

  On the other hand, when a voltage is applied to the electrode layers 421 and 422 by the AC power source 450, the liquid crystal molecules are aligned along the traveling direction of the light X under the action of the generated electric field. The polarization direction of X remains the vertical polarization indicated by arrow A and does not change. As described above, the polarization direction of the light X transmitted through the liquid crystal element 400 changes by 90 degrees from vertical polarization to horizontal polarization by turning on and off the voltage applied by the AC power supply 450. This change in the polarization direction also occurs in the combined light. In the present embodiment, the polarization direction is changed once during drawing of an information image of one frame.

  In the present embodiment, the liquid crystal layer 441 of the liquid crystal element 400 has a structure that forms a single pixel in order to simultaneously and similarly change the polarization direction of the combined light. According to the liquid crystal element 400 having such a configuration, the polarization direction of the transmitted composite light is the same regardless of the transmission location, and the change in the polarization direction occurs simultaneously and similarly. In other words, the liquid crystal element 400 generates only one polarization state in the combined light.

[Configuration of high retardation film]
As shown in FIG. 1, the high retardation film 500 is disposed between the liquid crystal element 400 and the image forming unit 300, and is held by a holding member (not shown). The high retardation film 500 is a film made of a polymer such as polyethylene terephthalate (PET), polyester or polycarbonate having birefringence characteristics. In this embodiment, the high retardation film 500 has an optical axis (fast axis and slow axis) of 45 degrees with respect to the horizontal polarization axis and the vertical polarization axis of the combined wave emitted from the liquid crystal element 400. It is arranged to make an angle.

  Since the angle between the fast axis and the slow axis in the high retardation film 500 is 90 degrees, the combined light incident on the high retardation film 500 so that the polarization axis and the optical axis form an angle other than orthogonal or parallel is the fast axis. And a component that transmits along the slow axis. Since the component along the slow axis passes through the high retardation film 500 at a relatively slower transmission speed than the component along the fast axis, the synthesized light after transmission has a component along the fast axis and a slow axis. There is a phase difference (retardation) between the components along. This phase difference can be calculated by multiplying the difference between the refractive index of light transmitted through the fast axis and the refractive index of light transmitted through the slow axis by the thickness of the high retardation film 500.

  The high retardation film 500 has a characteristic that the phase difference is 4000 nm or more with respect to light of all wavelengths (red light, green light, blue light) in the visible light range. When the phase difference is 4000 nm or more, a high-quality information image can be obtained without causing rainbow unevenness in the projected information image. In addition, since such a large phase difference occurs between the component along the fast axis and the component along the slow axis of the synthesized light, the synthesized light after transmission has various polarization directions, rotational directions, And the kind of polarized light (linearly polarized light, circularly polarized light, elliptically polarized light) is included.

  Hereinafter, the fact that the combined light after passing through the high retardation film 500 includes various polarization directions, rotation directions, and types of polarization will be described using Poincare spheres. In FIG. 4, horizontally polarized light having a wavelength λ is incident on a high retardation film 500 having an optical axis having an angle ψ of 45 degrees with the polarization direction and a retardation value (absolute value of phase difference). A Poincare sphere representing that the horizontally polarized incident light at the point P is converted into a polarization direction, a rotation direction, and a polarization type at the position of the point M and is emitted by being transmitted. When Poincare sphere is compared to the earth, (i) all of the equator H represents linearly polarized light, (ii) the north pole N and the south pole S represent circularly polarized light, and (iii) other than the equator H, north pole N, and south pole S. All represent elliptically polarized light, (iv) the angle of half the longitude from point P corresponds to the azimuth angle of a straight line or elliptically polarized light, and the same longitude represents the same azimuth angle, (v) the northern hemisphere rotates clockwise Polarized light and the southern hemisphere represent left-handed polarized light.

  Drawing on the Poincare sphere is performed as follows. (1) The point of the Poincare sphere at an angle (2ψ = 90 degrees) that is twice the angle ψ (= 45 degrees) between the polarization direction of the incident light and the optical axis of the high retardation film 500 from the point P (horizontally polarized incident light). A straight line L1 representing the rotation axis passing through the center is drawn. (2) A straight line L2 perpendicular to the straight line L1 and passing through the point P is drawn. (3) A point M rotated from the point P by an angle δ (= 2π · Re / λ) about the straight line L1 along the circle Cr on the Poincare sphere formed by a cross section perpendicular to the equator H including the straight line L2. Determine.

  The point M converted from the point P when the horizontally polarized light having the wavelength λ is transmitted through the high retardation film 500 changes the angle δ depending on the wavelength λ and / or the retardation value Re. Take position. For example, when the point M is on the equator H, the outgoing light is horizontally or vertically polarized light, and when the point M is at the north pole N, the outgoing light is right-handed circularly polarized light, and the point M is other than the equator H and the north pole N. When it is in the northern hemisphere, the outgoing light is right-handed elliptically polarized light. When the point M is at the south pole S, the outgoing light is counterclockwise circularly polarized light, and when the point M is in the southern hemisphere other than the equator H and the south pole S, the outgoing light is counterclockwise elliptically polarized light. When the synthetic light is incident on the high retardation film 500 having a constant retardation value Re, the red light, the green light, and the blue light included in the synthetic light have different wavelength widths and different wavelengths λ. It is understood that red light, green light, and blue light included in the combined light after transmission are light having different polarization directions, rotation directions, and polarization types.

Generally, in those high retardation film 500 of the retardation value R _e so that both the polarization axis of the polarizing plate polarizing plates crossed Nicols and the optical axis form an angle of 45 degrees are arranged, linearly polarized light of wavelength λ light Is incident on the incident-side polarizing plate with the intensity I _o in a state where the polarization direction is parallel, passes through the high retardation film 500 and is emitted from the output-side polarizing plate with the intensity I, the following relationship is established.
I = I _o · sin ² (π · R _e / λ) (1)

  Among the crossed Nicols polarizing plates, the incident side polarizing plate is a polarizing plate that transmits the incident light as it is, and the outgoing side polarizing plate is a polarizing plate that absorbs the horizontal polarization component. The exit side polarizing plate corresponds to the polarized sunglasses 42 of the driver 40. Here, if the high retardation film 500 is not disposed between the crossed Nicols polarizing plates, the light incident as the horizontally polarized light is absorbed (blacked out) by the output side polarizing plate corresponding to the polarized sunglasses 42, and the display image cannot be visually recognized. . Therefore, it can be understood from the expression (1) that the high retardation film 500 is arranged so that the display of the horizontally polarized light can be visually recognized with the polarized sunglasses 42 on.

Further, as can be seen from the equation (1), since the transmitted light intensity I changes when the wavelength λ changes, red light, green light, which are light of different wavelengths included in the synthesized light transmitted through the high retardation film 500, Blue light has different polarization direction, rotation direction, and polarization type (linearly polarized light, circularly polarized light, elliptically polarized light) due to transmission through the high retardation film 500. Further, a retardation value R _e is large (more than 4000 nm), the transmitted light intensity even a small variation of the wavelength λ is I varies greatly.

FIG. 5 shows the intensity I _o of the incident light when linearly polarized red light, green light, and blue light having the same intensity are incident on the high retardation film 500 disposed between the crossed Nicols polarizing plates. FIG. 6 shows the intensity I, and FIG. 7 shows an approximate curve of the intensity of transmitted light. As can be seen from FIGS. 5 and 6, the envelope of the spectrum of the transmitted light intensity I has the same shape as the spectrum of the incident light intensity I _o . This is because when the retardation value Re is large (4000 nm or more), the transmitted light intensity I changes greatly even if the amount of change in the wavelength λ is small (the half-wave width of the waveform indicating the intensity in FIG. 6 becomes narrow). ) If the retardation value Re is small (less than 4000 nm), the transmitted light intensity I slightly changes even if the change amount of the wavelength λ is large (the wavelength half-value width of the waveform showing the intensity in FIG. 6 becomes wide). Therefore, the envelope of the spectrum of the transmitted light intensity I and the spectrum of the incident light intensity _Io are not the same shape. Further, comparing FIG. 7 with FIG. 5, the peak of the approximate curve of the transmitted light intensity I is about half of the peak of the incident light intensity I _o , but any of the red light, green light, and blue light peaks of the approximate curve. Is equivalent. Therefore, it can be seen that the light transmitted through the high retardation film 500 having a phase difference of 4000 nm or more has not changed from the hue of the incident light. Therefore, rainbow spots are not observed in the information image projected with the transmitted light.

  As described above, the synthesized light transmitted through the high retardation film 500 includes light of various polarization directions, rotation directions, and types of polarization, which has a phase difference according to the birefringence characteristics of the high retardation film 500. This is due to the fact that light of each wavelength (red light, green light, and blue light) included in the combined light after transmission still has coherence. For this reason, when the information image formed by the synthesized light is projected onto the windshield 700, the scattered light of the respective wavelengths included in the synthesized light interferes with each other due to the unevenness of the surface of the windshield 700, and speckle noise is generated. Occur. Speckle noise appears as a bright and dark speckled pattern on the information image on the windshield 700, thereby reducing the quality of the information image.

  In this embodiment, the liquid crystal element 400 changes the combined light into vertical polarization and horizontal polarization in units of frames. The vertically polarized light and the horizontally polarized light respectively have a polarization direction inclined 45 degrees to the upper right and a polarization direction inclined 45 degrees to the upper left with respect to the optical axis of the high retardation film 500. In this case, light having a polarization direction tilted 45 degrees to the upper right and a polarization direction tilted 45 degrees to the upper left is an angle ψ (= ±) between the polarization direction of the incident light and the optical axis of the high retardation film 500 in the Poincare sphere. 45 degrees). When these lights pass through the high retardation film 500, as shown in FIG. 8, the light after the transmission has an angle twice as large as the angle ψ from the point P1 (horizontal polarization) and the point P2 (vertical polarization) (2ψ = Positions of points M1 and M2 rotated by the same angle δ (δ = 2π · Re / λ) from the point P on the circle Cr with the straight line L1 passing through the center of the Poincare sphere at ± 90 degrees as the rotation center axis The polarization direction, the rotation direction, and the polarization type of light. As described above, the points P1 and P2 are converted into the northern hemisphere (right-handed polarized light) or the southern hemisphere (left-handed polarized light) indicated by the points M1 and M2, respectively. It is understood that the outgoing light after passing through the light becomes circularly polarized light or elliptically polarized light having opposite rotation directions (left-handed and right-handed).

  Therefore, the location where speckle noise occurs in an information image formed with vertically-polarized synthesized light is different from the location where speckle noise occurs in an information image formed with horizontally-polarized synthesized light. As a result, speckle noise generated at different locations in each frame is smoothed as a whole, and speckle noise appearing in the information image displayed on the windshield 700 is reduced and visually recognized by the driver 40. In this embodiment, since the polarization direction changes by 90 degrees, the effect of reducing speckle noise is maximized compared to changes in other angles.

  Further, as described above, the light of each wavelength included in the synthesized light transmitted through the high retardation film 500 is light of various polarization directions, rotation directions, and types of polarization (linearly polarized light, circularly polarized light, elliptically polarized light). Since it is not formed only by the combined light of the horizontally polarized light, the driver 40 wearing the polarized sunglasses 42 whose light absorption axis is the horizontal direction visually recognizes the information image formed by the combined light. However, no flicker occurs.

  In this embodiment, although the high retardation film 500 is hold | maintained at the holding member, it is not restricted to this. The high retardation film 500 may be formed on the surface of the substrate 412 of the liquid crystal element 400 instead of being held by the holding member. With such a configuration, the holding member is unnecessary, and the projection display device 10 can be configured at a lower cost.

[Polarization characteristics of light transmitted through the liquid crystal layer]
In general, when the color (wavelength) of light is different, different optical rotatory dispersion occurs in the liquid crystal layer 441 depending on the wavelength, and the characteristics of the polarization direction with respect to the applied voltage (hereinafter referred to as “polarization characteristics”) are different. If the polarization characteristics are different, when the polarization direction is changed during drawing of an information image of one frame as in this embodiment, a plurality of colors that should display the same color in the projected image depending on the value of the applied voltage. In a pixel, a color change may occur due to a difference in polarization characteristics of green light, blue light, and red light, which may give an uncomfortable feeling to a person viewing the image. In order to prevent color change, it is necessary to form and project a projection image with the same polarization characteristics of green light, blue light, and red light.

  Therefore, in this embodiment, p × Δn ≧ 2500 nm (Δn is the refractive index anisotropy of the liquid crystal layer 441 described above) where p is the helical pitch of the helical structure of the liquid crystal molecules of the liquid crystal layer 441 of the liquid crystal element 400. It is configured to satisfy. The helical pitch p has a relationship of p = d × 360 / θ where d is the twist angle of the liquid crystal molecules (d is the thickness of the liquid crystal layer 441 described above). In the present embodiment, the twist angle θ is 90 degrees from the relationship between the arrow B and the arrow C shown in FIG.

  When the liquid crystal element 400 satisfies the relationship of p × Δn ≧ 2500 nm, as shown in FIG. 9, the polarization direction changes by the same amount when all the green light, blue light, and red light are applied with the same voltage. ing. As a result, it is understood that the optical rotation dispersion is reduced and the polarization characteristics are the same. As a result, even if the polarization direction is changed during drawing of an information image of one frame as in the present embodiment, all the polarization directions of green light, blue light, and red light are the same with respect to the applied voltage. Therefore, even if the same color is displayed on a plurality of pixels during drawing of one frame of the information image, the color does not change.

2. Modified Example of First Embodiment Hereinafter, a projection display device 10 according to a modified example of the first embodiment of the present invention will be described in detail based on the drawings. In the description of each modified example, the same reference numerals are given to the same components as those in the first embodiment, and the descriptions regarding the same components are omitted.

[Modification 1]
As shown in FIG. 10, in the projection display device 10 according to the first modification, the high retardation film 500 is not between the liquid crystal element 400 and the image forming unit 300 but between the image forming unit 300 and the reflecting mirror 340. Are formed on the surface of the intermediate image portion 350 facing the image forming portion 300. The intermediate image portion 350 is a transmissive screen, and a light diffusing layer is provided on a glass substrate or a resin substrate by surface processing or coating to improve the light diffusibility while suppressing a decrease in light transmittance. It is configured as follows. The intermediate image unit 350 is made of, for example, frosted glass or a microlens array, and has a function of diffusing incident light and emitting it. When the high retardation film 500 is formed on the intermediate image portion 350, light of various polarization directions, rotation directions, and types of polarization (linearly polarized light, circularly polarized light, elliptically polarized light) is included due to the transmission of the high retardation film 500. The combined light is transmitted through the intermediate image portion 350 and emitted.

  According to the configuration of the first modification, synthetic light having an emission angle necessary for projection onto the windshield 700 can be obtained, the generation of speckle noise is reduced, and flicker even when the driver 40 sees through the polarized sunglasses 42. It is possible to obtain an information image in which no occurrence occurs. Note that the high retardation film 500 may be formed not on the surface of the intermediate image portion 350 facing the image forming portion 300 but on the surface facing the reflection mirror 340. Alternatively, the intermediate image portion 350 may be formed on both surfaces.

[Modification 2]
As shown in FIG. 11, in the projection display device 10 according to the modified example 2, the high retardation film 500 is not between the liquid crystal element 400 and the image forming unit 300 but between the reflection mirror 340 and the windshield 700. The formed combiner 360 having a half mirror function is formed on a surface facing the reflection mirror 340. When the head-up display 50 includes the combiner 360, the information image is projected on the combiner 360 instead of the windshield 700. The driver 40 visually recognizes the information image displayed on the virtual screen 600 far away from the vehicle through the combiner 360 by the combined light that is transmitted through the high retardation film 500 and reflected by the surface of the combiner 360. By projecting the information image onto the combiner 360, an information image without distortion can be displayed regardless of the curvature of the windshield 700. Furthermore, the magnification of the information image can be increased by making the combiner 360 concave.

  Also with the configuration of the modified example 2, the generation of speckle noise is reduced, and an information image in which flicker does not occur even when the driver 40 looks through the polarized sunglasses 42 can be obtained. The combiner 360 is an example of a display unit.

[Modification 3]
In the projection display device 10 according to the modification 3, the configuration of the liquid crystal element 400 is different from that of the first embodiment. Specifically, as illustrated in FIG. 12, the liquid crystal element 400 includes a light-transmitting liquid crystal layer 441 and a light-transmitting liquid crystal layer 442. The liquid crystal layer 441 is provided between the light-transmitting substrates 411 and 413, and the liquid crystal layer 442 is provided between the substrates 413 and 412. The refractive index anisotropy of the liquid crystal layer 441 and the liquid crystal layer 442 may be the same value or different values. The thickness of the liquid crystal layer 441 is d1, and the thickness of the liquid crystal layer 442 is d2. In the figure, the arrow from the left to the right represents the traveling direction of the combined light. In Modification 3, the liquid crystal layer 441 is an example of a first layer, and the liquid crystal layer 442 is an example of a second layer. The thickness d1 of the liquid crystal layer 441 and the thickness d2 of the liquid crystal layer 442 do not have to be the same, but when the characteristics of the liquid crystal layer 441 and the liquid crystal layer 442 are made equal, the thickness of the liquid crystal layer 441 is It is desirable that d1 and the thickness d2 of the liquid crystal layer 442 be the same.

  A translucent alignment layer 431 and an alignment layer 433 that align liquid crystal molecules of the liquid crystal layer 441 are provided on both sides of the liquid crystal layer 441, and a translucent property that aligns the liquid crystal molecules of the liquid crystal layer 442 on both sides of the liquid crystal layer 442. The alignment layer 433 and the alignment layer 432 are provided. Further, outside the alignment layer 431 and the alignment layer 433 and outside the alignment layer 433 and the alignment layer 432, electrode layers 421 and 422 made of a light-transmitting material such as ITO and applying a voltage to the liquid crystal layers 441 and 442 are provided. Are provided.

  FIG. 13 shows a change in the polarization direction of the light X transmitted through the liquid crystal element 400 when no voltage is applied. The alignment layer 431 is aligned so that the liquid crystal molecules are aligned in the vertical direction (arrow B), and the alignment layer 432 is aligned so that the liquid crystal molecules are aligned in the horizontal direction (arrow E). The alignment layer 433 is aligned so that liquid crystal molecules are aligned at an angle of 45 degrees with respect to the alignment layers 431 and 432 (arrow C). As shown in FIG. 13, the polarization direction of the light X indicated by the arrow A is vertical polarization, and this polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 431 indicated by the arrow B. And enters the liquid crystal layer 441. While the light X passes through the liquid crystal layer 441, the polarization direction changes by 45 degrees as indicated by the arrow C along the alignment of the liquid crystal molecules, and passes through the two alignment layers 433 indicated by the arrow C while maintaining the polarization direction indicated by the arrow D. Then, the light enters the liquid crystal layer 442. Then, while passing through the liquid crystal layer 442, the polarization direction further changes by 45 degrees along the arrangement of the liquid crystal molecules, becomes horizontal polarized light indicated by the arrow F, and passes through the alignment layer 432 indicated by the arrow E to be emitted. That is, when the light X is transmitted through the liquid crystal element 400, the polarization direction of the light X is changed by 90 degrees as in the first embodiment.

  On the other hand, when a voltage is simultaneously applied to the electrode layers 421 and 422 sandwiching the liquid crystal layer 441 and the electrode layers 421 and 422 sandwiching the liquid crystal layer 442 by the AC power supply 450, the liquid crystal molecules are subjected to the action of the generated electric field. Since the light is arranged along the X traveling direction, the polarization direction of the light X remains unchanged as the vertical polarization indicated by the arrow A before and after transmission through the liquid crystal element 400. As described above, the polarization direction of the light X transmitted through the liquid crystal element 400 is changed by 90 degrees between vertical polarization and horizontal polarization by switching the applied voltage on and off by the AC power supply 450. This change in the polarization direction also occurs in the combined light. In the third modification, the polarization direction is changed once during the drawing of the information image of one frame.

  In Modification 3, the alignment layer 433 facing the alignment layer 431 of the liquid crystal layer 441 when viewed from the downstream side in the traveling direction of the light X (right side in FIG. 13) to the upstream in the traveling direction (left side in FIG. 13). Is inclined 45 degrees to the right, and the alignment layer 432 facing the alignment layer 433 of the liquid crystal layer 442 is also inclined 45 degrees to the right. That is, when an AC voltage is not applied to the AC power supply 450, the twist angle of each liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 is 45 degrees, and any liquid crystal molecule moves from the incident side of the light X to the outgoing side. It has a spiral structure that is twisted and arranged in the same direction.

  If the liquid crystal element 400 includes the liquid crystal layers 441 and 442 as in the third modification, the voltage applied to the liquid crystal layers 441 and 442 by the AC power source 450 is performed at the same timing and at the same timing, thereby The change in the polarization direction of the light transmitted through the liquid crystal layers 441 and 442 by turning on and off is 45 degrees. Therefore, the polarization dispersion of red light, green light, and blue light can be reduced, and the liquid crystal element 400 can complete the change in the polarization direction of vertical polarization and horizontal polarization in a short time. The configuration of the third modification also reduces the generation of speckle noise, and an information image in which flicker does not occur even when the driver 40 looks through the polarized sunglasses 42 can be obtained.

  In general, in a projection type display device, the optical system constituting it makes it difficult to adjust the alignment of optical components such as mirrors arranged on a horizontal plane when there is light in an oblique polarization direction. Therefore, in many cases, the polarization direction of light transmitted through the optical component or reflected by the optical component is set to the horizontal direction or the vertical direction. The projection display device 10 has a configuration in which the twist direction in the liquid crystal layer 441 and the twist direction in the liquid crystal layer 442 are the same direction, so that the outgoing light with respect to the vertically polarized incident light to the liquid crystal element 400. It is possible to easily realize that the polarization direction is alternately changed between horizontal polarization and vertical polarization. When the polarization direction of the incident light is horizontal polarization, the same effect can be obtained by rotating the liquid crystal element 400 by 90 degrees.

  In the liquid crystal element 400 of Modification 3, the spiral pitch of the spiral structure of the liquid crystal molecules in the liquid crystal layer 441 is p1, the refractive index anisotropy is Δn1, and the spiral pitch of the spiral structure of the liquid crystal molecules in the liquid crystal layer 442 is p2. When the refractive index anisotropy is Δn2, p1 × Δn1 ≧ 2500 nm and p2 × Δn2 ≧ 2500 nm are satisfied. Thereby, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9). FIG. 9 shows that the liquid crystal element 400 having a twist angle of 90 degrees can have the same polarization characteristics in which the polarization direction changes by 90 degrees. However, in the liquid crystal element 400 of Modification Example 3 having a twist angle of 45 degrees, FIG. However, it is natural that the polarization characteristics whose polarization direction changes by 45 degrees can be made the same.

[Modification 4]
In the projection display device 10 according to the modification 4, the configuration of the liquid crystal element 400 is different from that of the first embodiment. Specifically, as illustrated in FIG. 14, the liquid crystal element 400 includes a light-transmitting liquid crystal layer 441 and a light-transmitting liquid crystal layer 442. The structure of the liquid crystal element 400 is similar to that of the liquid crystal element 400 shown in FIG. 12, but the AC power source 450 applied to the liquid crystal layer 441 and the AC power source 450 applied to the liquid crystal layer 442 are independent. The point is different. Further, a translucent alignment layer 433 and an alignment layer 431 for aligning liquid crystal molecules of the liquid crystal layer 441 are provided on both sides of the liquid crystal layer 441, and a transparent layer for aligning the liquid crystal molecules of the liquid crystal layer 442 is provided on both sides of the liquid crystal layer 442. An optical alignment layer 433 and an alignment layer 432 are provided.

  In Modification 4, an alternating voltage is applied alternately to the liquid crystal layer 441 and the liquid crystal layer 442. FIG. 15 shows a change in the polarization direction of light transmitted through the liquid crystal element 400 when a voltage is applied to the liquid crystal layer 441 and no voltage is applied to the liquid crystal layer 442. FIG. 16 shows a change in the polarization direction of light transmitted through the liquid crystal element 400 when a voltage is applied to the liquid crystal layer 442 and no voltage is applied to the liquid crystal layer 441.

  As shown in FIG. 15, in the fourth modification, the polarization direction of the light X incident on the liquid crystal layer 441 is inclined 45 degrees with respect to the horizontal direction as indicated by an arrow A. Hereinafter, in the light X and the combined light, the polarization direction tilted 45 degrees in the direction indicated by the arrow A with respect to the horizontal direction is “right 45 degree polarization”, and 45 degrees in the direction opposite to the direction indicated by the arrow A with respect to the horizontal direction. The tilted polarization direction is referred to as “left 45 degree polarization”.

  15 and 16, the alignment layer 433 is aligned so that the liquid crystal molecules are aligned at an angle of 45 degrees to the right (arrow B), and the alignment layer 431 is aligned so that the liquid crystal molecules are aligned in the vertical direction. (Arrow C). The alignment layer 432 is aligned so that liquid crystal molecules are aligned in the horizontal direction (arrow E). In FIG. 15, the polarization direction of the light X indicated by the arrow A is right 45 ° polarization, and this polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 433 indicated by the arrow B, and the light X is the alignment layer 433. And enters the liquid crystal layer 441. Since voltage is applied to the liquid crystal layer 441, the liquid crystal molecules of the liquid crystal layer 441 are aligned along the traveling direction of the light X under the action of the generated electric field, and the polarization of the light X before and after transmission through the liquid crystal layer 441. The direction passes through the alignment layer 431 and is incident on the alignment layer 433 without changing with the right 45-degree polarized light indicated by the arrow A.

  Since no voltage is applied to the liquid crystal layer 442, the polarization direction of the light X changes by 45 degrees along the alignment of the liquid crystal molecules while passing through the liquid crystal layer 442, as indicated by the arrow F. Is transmitted through the alignment layer 432 indicated by the arrow E and emitted. That is, when the light X passes through the liquid crystal element 400, the polarization direction of the light X changes 45 degrees from right 45-degree polarized light to horizontal polarized light.

  In FIG. 16, the polarization direction of the light X indicated by the arrow A is right 45 ° polarization, and this polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 433 indicated by the arrow B, and the light X is the alignment layer 433. And enters the liquid crystal layer 441. Since no voltage is applied to the liquid crystal layer 441, the light X changes its polarization direction by 45 degrees as indicated by the arrow D along the alignment of the liquid crystal molecules while passing through the liquid crystal layer 441. Then, the light passes through the alignment layer 431 indicated by the arrow C and enters the alignment layer 433.

  Since a voltage is applied to the liquid crystal layer 442, the liquid crystal molecules of the liquid crystal layer 442 are aligned along the traveling direction of the light X under the action of the generated electric field, and the polarization of the light X before and after transmission through the liquid crystal layer 442. The direction is transmitted through the alignment layer 432 indicated by the arrow E without changing while maintaining the vertical polarization indicated by the arrow D. That is, when the light X is transmitted through the liquid crystal element 400, the polarization direction of the light X changes 45 degrees from right 45-degree polarized light to vertical polarized light.

  Thus, by alternately switching on and off the AC power supply 450 of the liquid crystal layer 441 and the liquid crystal layer 442, the polarization direction of the light X transmitted through the liquid crystal element 400 changes by 90 degrees between horizontal polarization and vertical polarization. This change in the polarization direction also occurs in the combined light. In the fourth modification, the polarization direction is changed once during the drawing of the information image of one frame.

  In Modification 4, the alignment layer 431 facing the alignment layer 433 of the liquid crystal layer 441 when viewed from the downstream side in the traveling direction of the light X (right side in FIG. 15) to the upstream in the traveling direction (left side in FIG. 15). Is inclined 45 degrees to the left, and the alignment layer 432 facing the alignment layer 433 of the liquid crystal layer 442 is inclined 45 degrees to the right. That is, when no AC voltage is applied to any AC power supply 450, the twist angle of each liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 is 45 degrees, and the liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 The liquid crystal molecules have a helical structure in which they are twisted in opposite directions from the incident side of the light X toward the outgoing side.

  If the liquid crystal element 400 is configured to include the liquid crystal layers 441 and 442 as in the fourth modification example, the AC power supply 450 alternately applies a voltage to the liquid crystal layers 441 and 442, thereby switching the applied voltage. The change in the polarization direction of the light transmitted through 441 and 442 may be 45 degrees. Therefore, the polarization dispersion of red light, green light, and blue light can be reduced, and the liquid crystal element 400 can complete the change in the polarization direction of vertical polarization and horizontal polarization in a short time. The configuration of the fourth modification also reduces the generation of speckle noise, and an information image in which flicker does not occur even when the driver 40 looks through the polarized sunglasses 42 can be obtained.

  In the fourth modification, as shown in FIG. 17, the applied voltage switching time includes the rise response time tr of the liquid crystal layer 441, the fall response time td of the liquid crystal layer 442, and the fall response of the liquid crystal layer 441. The time td and the rise response time tr of the liquid crystal layer 442 overlap. Therefore, in each frame, the rise time tr that the liquid crystal layer 441 responds and the start of the fall time td that the liquid crystal layer 442 responds, and the fall response time td of the liquid crystal layer 441 and the rise response time tr of the liquid crystal layer 442 The start can be at the same time. That is, since the time for changing the polarization directions of the liquid crystal layer 441 and the liquid crystal layer 442 by 45 degrees is the same, the display time of the information images of the temporally adjacent frames can be made the same. As a result, no brightness or darkness occurs in the information image, so that the visibility of the information image by the driver 40 can be improved.

  Note that in the liquid crystal element 400 of the modification example 4, the helical pitch of the helical structure of the liquid crystal molecules of the liquid crystal layer 441 is p1, the refractive index anisotropy is Δn1, and the helical pitch of the helical structure of the liquid crystal molecules of the liquid crystal layer 442 is p2. When the refractive index anisotropy is Δn2, p1 × Δn1 ≧ 2500 nm and p2 × Δn2 ≧ 2500 nm are satisfied. Thereby, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9). FIG. 9 shows that the liquid crystal element 400 with a twist angle of 90 degrees can have the same polarization characteristic with the polarization direction changing by 90 degrees. In the liquid crystal element 400 of the modification example 4 with the twist angle of 45 degrees, FIG. However, it is natural that the polarization characteristics whose polarization direction changes by 45 degrees can be made the same.

[Modification 5]
As shown in FIG. 18, the projection display device 10 according to the modification 5 includes a liquid crystal cell 140, a half mirror 150, a light between the synthesis optical unit 200 and the liquid crystal element 400 in addition to the configuration of the first embodiment. A detection unit 160 and a control unit 170 are provided.

  The liquid crystal cell 140 has a function of changing the transmittance of light transmitted through the inside. Although the configuration of the liquid crystal cell 140 is known and omitted, an alternating voltage is applied to the electrode layers provided at both ends of the liquid crystal layer (not shown) to change the alignment state of the liquid crystal molecules in the liquid crystal layer to The polarization direction of the transmitted light is changed, thereby changing the transmittance of the synthesized light transmitted through the inside. The liquid crystal layer is a vertically aligned nematic liquid crystal layer and has a structure for forming a single pixel.

  The transmittance of the liquid crystal cell 140 is controlled by the intensity of outside light from the vehicle. For example, the liquid crystal cell 140 may be connected to a solar cell (not shown) that generates electric power according to the intensity of external light of the vehicle via an inverter (not shown). As a result, an AC voltage corresponding to the intensity of outside light outside the vehicle is applied to the liquid crystal cell 140. In addition, a detection signal having a magnitude corresponding to the intensity of external light (power generated by the solar cell) is input to the controller 170.

  In the liquid crystal cell 140, when the intensity of external light is high, that is, when the voltage value applied to the liquid crystal layer is large, the transmittance is high, and when the intensity of external light is low, that is, applied to the liquid crystal layer. The transmittance is low when the voltage value is small. In addition, the liquid crystal cell 140 is configured so that the combined light does not transmit (normally black) when no voltage is applied to the liquid crystal layer. Thereby, a high contrast ratio (extinction ratio) is obtained, and safety against laser light is ensured.

  The half mirror 150 has a function of reflecting a part of the combined light transmitted through the liquid crystal cell 140 and transmitting the rest. The light detection unit 160 receives the combined light reflected by the half mirror 150 and detects the intensity of each of red light, green light, and blue light included in the combined light and the color as the combined light. Thereafter, a signal representing the detection result is output toward the control unit 170.

  The control unit 170 changes the intensity of light emitted from the LD 110 (green light), the LD 120 (blue light), and the LD 130 (red light) based on the detection signal from the solar cell and the detection signal from the light detection unit 160. Controls by outputting instructions. Thereby, the brightness | luminance and color balance of the information image which the driver | operator 40 visually recognizes can be optimized.

  In order to increase the visibility of the information image by the driver 40, for example, when the intensity of outside light is high, such as in fine weather, it is necessary to increase the brightness of the information image. At this time, since the transmittance of the liquid crystal cell 140 is increased, the intensity of the emitted light from the LDs 110 to 130 transmitting through the liquid crystal cell 140 is increased, and the luminance of the information image is increased. Conversely, when the intensity of external light is low, such as at night, the brightness of the information image needs to be reduced. At this time, since the transmittance of the liquid crystal cell 140 is low, the intensity of the emitted light of the LDs 110 to 130 that is transmitted through the liquid crystal cell 140 is small, and the luminance of the information image is small.

  Although the transmittance of the liquid crystal cell 140 cannot be controlled by the control unit 170, the control unit 170 determines the driver from the intensities of red light, green light, and blue light transmitted through the liquid crystal cell 140 detected by the light detection unit 160. The luminance of the information image visually recognized by 40 can be estimated. Therefore, in order to obtain the optimum brightness of the information image according to the intensity of the external light, the control unit 170 determines whether the light detection unit 160 detects the intensity of each of the red light, the green light, and the blue light. Control is performed to change the intensity of the emitted light 130.

  The intensity of the emitted light from the LDs 110 to 130 can be controlled by the current supplied to the LDs 110 to 130. However, when the intensity is controlled by the current, there is a change in the intensity of the emitted light from a strong state to a weak state. Since oscillation stops at the current value, it is not possible to obtain weak emission light. That is, the dynamic range of the intensity of the emitted light is small. Therefore, by changing the transmittance of the light transmitted through the inside of the liquid crystal cell 140, the intensity of the combined light transmitted without changing the current can be changed from a strong state to a weak state, so that the dynamic range is increased. can do.

  As described above, by using the vertically aligned nematic liquid crystal in the liquid crystal cell 140, the intensity of the emitted light can be greatly changed and the safety against the laser light can be secured, but the vertically aligned nematic liquid crystal has red light having a different wavelength, There is a large difference (wavelength dispersion) in the modulation factor when green light and blue light transmit when the same voltage is applied to the liquid crystal layer (see FIG. 19). Therefore, the color of the synthesized light before entering the liquid crystal cell 140, that is, the color to be displayed in the information image, and the color of the synthesized light after passing through the liquid crystal cell 140 change, and the projected information image Color balance will deteriorate. Therefore, based on the detection result of the color of the synthesized light by the photodetecting unit 160, the control unit 170 determines that the actual transmittance is other than that so that the color of the synthesized light transmitted through the liquid crystal cell 140 becomes a color that is originally displayed. The intensity of the emitted light is controlled to be larger for the LD of the color smaller than the transmittance of the other color, or the intensity of the emitted light for the LD of the color whose actual transmittance is larger than the transmittance of the other colors. Control to make it smaller. As described above, the color balance of the information image can be maintained satisfactorily by detecting the color of the combined light transmitted through the liquid crystal cell 140 by the light detection unit 160 and changing the emission intensity of the LDs 110 to 130. it can.

  As described above, in Modification 5, the detection result of the intensity of the external light, and the intensity of each of the red light, the green light, and the blue light included in the combined light after passing through the liquid crystal cell 140 and the combined light are used. Based on the color detection result, the control unit 170 controls the intensity of the emitted light from the LD 110, LD 120, and LD 130 to change. As a result, the brightness and color balance of the information image visually recognized by the driver 40 can always be optimized, the generation of speckle noise is reduced, and flicker does not occur even when the driver 40 looks through the polarized sunglasses 42. An information image can be obtained.

3. Second Embodiment Hereinafter, a projection display device 20 according to a second embodiment of the present invention will be described in detail with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same components as those in the first embodiment and the respective modifications, and the description regarding the same components is omitted.

  The projection display device 20 according to the second embodiment does not include the high retardation film 500 as shown in FIG. The liquid crystal element 410 in this embodiment has a structure similar to that of the liquid crystal element 400 shown in FIG. However, unlike the first embodiment, alignment layers 433 and 434 for arranging the liquid crystal molecules of the liquid crystal layer 441 in a direction inclined by 45 degrees with respect to the horizontal direction are arranged as the alignment layers (arrows in FIG. 21). C and B). However, the alignment directions of the alignment layer 433 and the alignment layer 434 are orthogonal to each other. Therefore, the liquid crystal molecules have a spiral structure in which the liquid crystal molecules are twisted by 90 degrees and arranged from the alignment layer 434 toward the alignment layer 433.

  As shown in FIG. 21, in this embodiment, the polarization direction of the light X incident on the liquid crystal layer 441 is 45 degrees left polarization, and this polarization direction is the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 434 indicated by the arrow B. Since they are the same, the light X passes through the alignment layer 434 and enters the liquid crystal layer 441. While the light X is transmitted through the liquid crystal layer 441, the polarization direction changes by 90 degrees along the alignment of the liquid crystal molecules, becomes right 45-degree polarized light indicated by the arrow D, and passes through the alignment layer 433 indicated by the arrow C to be emitted. .

  On the other hand, when a voltage is applied to the electrode layers 421 and 422 by the AC power source 450, the liquid crystal molecules are aligned along the traveling direction of the light X under the action of the generated electric field. The polarization direction of X remains 45 degrees left polarization and does not change. As described above, when the voltage applied by the AC power supply 450 is turned on and off, the polarization direction of the light X transmitted through the liquid crystal element 410 changes from 45 degrees left polarized light to 45 degrees right polarized light by 90 degrees. This change in the polarization direction also occurs in the combined light. In the present embodiment, the polarization direction is changed once during drawing of an information image of one frame.

  In the projection display device 20, the information image formed by the combined light in which the polarization direction is changed by the liquid crystal element 410 to the left 45 degree polarization direction and the right 45 degree polarization direction in units of frames is projected onto the windshield 700. . Also in this embodiment, since the polarization direction is different for each frame, speckle noise generated in different places in each frame is smoothed as a whole, and speckle noise appearing in the information image displayed on the windshield 700 is reduced. And is visually recognized by the driver 40.

  Further, in the projection display device 20, horizontal polarization is not included in the polarization direction of the information image projected on the windshield 700. Therefore, when the driver 40 wearing the polarized sunglasses 42 visually recognizes the information image, the information image of all the frames can be visually recognized, and thus flicker does not occur.

  Note that the liquid crystal element 410 of the present embodiment is configured to satisfy p × Δn ≧ 2500 nm, where p is the helical pitch of the helical structure of the liquid crystal molecules of the liquid crystal layer 441 and Δn is the refractive index anisotropy. Yes. Thereby, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9).

4). Modification of Second Embodiment Hereinafter, a projection display device 20 according to a modification of the second embodiment of the present invention will be described in detail based on the drawings. In the description of each modification, the same reference numerals are given to the same components as those in the first embodiment, the second embodiment, and each modification, and the description regarding the same configuration is omitted.

[Modification 1]
In the projection display device 20 according to the first modification, the configuration of the liquid crystal element 410 is different from that of the second embodiment. Specifically, as illustrated in FIG. 22, the liquid crystal element 410 includes a light-transmitting liquid crystal layer 441 and a light-transmitting liquid crystal layer 442. The liquid crystal element 410 has a structure similar to that of the liquid crystal element 400 illustrated in FIG. 14, and the AC power source 450 applied to the liquid crystal layer 441 and the AC power source 450 applied to the liquid crystal layer 442 are independent. Further, a translucent alignment layer 432 and an alignment layer 433 that align liquid crystal molecules of the liquid crystal layer 441 are provided on both sides of the liquid crystal layer 441, and a transparent layer that aligns the liquid crystal molecules of the liquid crystal layer 442 is provided on both sides of the liquid crystal layer 442. An optical alignment layer 432 and an alignment layer 434 are provided.

  In the first modification, an alternating voltage is applied alternately to the liquid crystal layer 441 and the liquid crystal layer 442. FIG. 23 shows a change in the polarization direction of light transmitted through the liquid crystal element 410 when a voltage is applied to the liquid crystal layer 441 and no voltage is applied to the liquid crystal layer 442. FIG. 24 shows a change in the polarization direction of light transmitted through the liquid crystal element 410 when a voltage is applied to the liquid crystal layer 442 and no voltage is applied to the liquid crystal layer 441.

  23 and 24, the alignment layer 432 is aligned so that liquid crystal molecules are aligned in the horizontal direction (arrow B), and the alignment layer 433 is aligned so that the liquid crystal molecules are aligned at an angle of 45 degrees to the right. (Arrow C). The alignment layer 434 is aligned so that liquid crystal molecules are aligned at an inclination of 45 degrees to the left (arrow E). In FIG. 23, the polarization direction of the light X indicated by the arrow A is horizontal polarization, the polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 432 indicated by the arrow B, and the light X is transmitted through the alignment layer 432. Then, the light enters the liquid crystal layer 441. Since voltage is applied to the liquid crystal layer 441, the liquid crystal molecules of the liquid crystal layer 441 are aligned along the traveling direction of the light X under the action of the generated electric field, and the polarization of the light X before and after transmission through the liquid crystal layer 441. The direction passes through the alignment layer 433 and remains incident on the alignment layer 432 without changing with the horizontal polarization indicated by the arrow A.

  Since no voltage is applied to the liquid crystal layer 442, the polarization direction of the light X changes 45 degrees along the alignment of the liquid crystal molecules while passing through the liquid crystal layer 442, as indicated by the arrow F. The light is transmitted through the alignment layer 434 indicated by the arrow E after being polarized. That is, when the light X passes through the liquid crystal element 410, the polarization direction of the light X changes by 45 degrees from the horizontal direction.

  In FIG. 24, the polarization direction of the light X indicated by the arrow A is horizontal polarization, the polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 432 indicated by the arrow B, and the light X is transmitted through the alignment layer 432. Then, the light enters the liquid crystal layer 441. Since no voltage is applied to the liquid crystal layer 441, the light X changes its polarization direction by 45 degrees as indicated by the arrow D along the alignment of the liquid crystal molecules while passing through the liquid crystal layer 441. It becomes polarized light and passes through the alignment layer 433 indicated by the arrow C to enter the alignment layer 432.

  Since a voltage is applied to the liquid crystal layer 442, the liquid crystal molecules of the liquid crystal layer 442 are aligned along the traveling direction of the light X under the action of the generated electric field, and the polarization of the light X before and after transmission through the liquid crystal layer 442. The direction is transmitted through the alignment layer 434 indicated by the arrow E without changing with the right 45-degree polarized light indicated by the arrow D. That is, when the light X is transmitted through the liquid crystal element 410, the polarization direction of the light X changes 45 degrees from the horizontal direction to the direction opposite to the direction shown in FIG.

  Thus, by alternately switching on and off the AC power supply 450 of the liquid crystal layer 441 and the liquid crystal layer 442, the polarization direction of the light X transmitted through the liquid crystal element 410 is changed from the left 45 degree polarization direction to the right 45 degree polarization direction. Change by 90 degrees. This change in the polarization direction also occurs in the combined light. In the first modification, the polarization direction is changed once during the drawing of the information image of one frame.

  In the first modification, the alignment layer 433 facing the alignment layer 432 of the liquid crystal layer 441 when viewed from the downstream side in the traveling direction of the light X (right side in FIG. 23) to the upstream in the traveling direction (left side in FIG. 23). Is inclined 45 degrees to the left, and the alignment layer 434 facing the alignment layer 432 of the liquid crystal layer 442 is inclined 45 degrees to the right. That is, when no AC voltage is applied to any AC power supply 450, the twist angle of each liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 is 45 degrees, and the liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 The liquid crystal molecules have a helical structure in which they are twisted in opposite directions from the incident side of the light X toward the outgoing side.

  In the projection display device 20, an information image formed by the combined light in which the polarization direction is changed by the liquid crystal element 410 into 45-degree left polarization and 45-degree right polarization in a frame unit is projected onto the windshield 700. Also in the first modification, since the polarization direction is different for each frame, speckle noise generated at different locations in each frame is smoothed as a whole, and speckle noise appearing in the information image displayed on the windshield 700 is reduced. And is visually recognized by the driver 40.

  Further, in the projection display device 20, horizontal polarization is not included in the polarization direction of the information image projected on the windshield 700. Therefore, when the driver 40 wearing the polarized sunglasses 42 visually recognizes the information image, the information image of all the frames can be visually recognized, and thus flicker does not occur.

  If the liquid crystal element 410 has a configuration including the liquid crystal layers 441 and 442 as in the first modification, the liquid crystal layer is formed by switching the applied voltage by alternately applying a voltage to the liquid crystal layers 441 and 442 by the AC power source 450. The change in the polarization direction of the light transmitted through 441 and 442 may be 45 degrees. Therefore, the polarization dispersion of red light, green light, and blue light can be reduced, and the change in the polarization direction of the left 45-degree polarized light and the right 45-degree polarized light as the liquid crystal element 410 can be completed in a short time.

  In the first modification, as shown in FIG. 17, the applied voltage switching time includes the rise response time tr of the liquid crystal layer 441, the fall response time td of the liquid crystal layer 442, and the fall response of the liquid crystal layer 441. The time td and the rise response time tr of the liquid crystal layer 442 overlap. Therefore, in each frame, the rise time tr that the liquid crystal layer 441 responds and the start of the fall time td that the liquid crystal layer 442 responds, and the fall response time td of the liquid crystal layer 441 and the rise response time tr of the liquid crystal layer 442 The start can be at the same time. That is, since the time for changing the polarization directions of the liquid crystal layer 441 and the liquid crystal layer 442 by 45 degrees is the same, the display time of the information images of the temporally adjacent frames can be made the same. As a result, no brightness or darkness occurs in the information image, so that the visibility of the information image by the driver 40 can be improved.

  As described above, in the projection display device, the optical system constituting it becomes difficult to adjust the alignment of optical components such as mirrors arranged on a horizontal plane when there is light in an oblique polarization direction. In order to facilitate, the polarization direction of the light transmitted through the optical component or reflected by the optical component is often set to the horizontal direction or the vertical direction. In the projection display device 20, since the twist direction in the liquid crystal layer 441 and the twist direction in the liquid crystal layer 442 are opposite to each other, the polarization direction of the emitted light is 45 degrees to the right with respect to the horizontal direction. It is possible to easily change between polarized light and left 45-degree polarized light alternately.

  In the liquid crystal element 410 of the first modification, the spiral pitch of the spiral structure of the liquid crystal molecules of the liquid crystal layer 441 is p1, the refractive index anisotropy is Δn1, and the spiral pitch of the spiral structure of the liquid crystal molecules of the liquid crystal layer 442 is p2. When the refractive index anisotropy is Δn2, p1 × Δn1 ≧ 2500 nm and p2 × Δn2 ≧ 2500 nm are satisfied. Thereby, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9). FIG. 9 shows that the liquid crystal element 400 having a twist angle of 90 degrees can have the same polarization characteristics in which the polarization direction changes by 90 degrees. In the liquid crystal element 410 of the first modification example, the twist angle is 45 degrees. However, it is natural that the polarization characteristics whose polarization direction changes by 45 degrees can be made the same.

[Modification 2]
In the projection display device 20 according to the second modification, the configuration of the liquid crystal element 410 is different from that of the second embodiment. Specifically, as illustrated in FIG. 25, the liquid crystal element 410 includes a light-transmitting liquid crystal layer 441 and a light-transmitting liquid crystal layer 442. The liquid crystal element 410 has a structure similar to that of the liquid crystal element 400 illustrated in FIG. 12, and a voltage is applied to the liquid crystal layer 441 and the liquid crystal layer 442 by one AC power supply 450. Further, a light-transmitting alignment layer 433 and an alignment layer 432 for aligning liquid crystal molecules of the liquid crystal layer 441 are provided on both sides of the liquid crystal layer 441, and a liquid crystal layer for aligning liquid crystal molecules of the liquid crystal layer 442 is provided on both sides of the liquid crystal layer 442. An optical alignment layer 432 and an alignment layer 434 are provided.

  FIG. 26 shows a change in the polarization direction of the light X transmitted through the liquid crystal element 410 when no voltage is applied. The alignment layer 433 is aligned so that the liquid crystal molecules are aligned at an angle of 45 degrees to the right (arrow B), and the alignment layer 434 is aligned so that the liquid crystal molecules are aligned at an angle of 45 degrees to the left (arrow E). The alignment layer 432 is aligned so that liquid crystal molecules are aligned in the horizontal direction (arrow C). As shown in FIG. 26, the polarization direction of the light X indicated by the arrow A is right 45-degree polarization, and this polarization direction is the same as the alignment direction of the liquid crystal molecules in the vicinity of the alignment layer 433 indicated by the arrow B. The light passes through the layer 433 and enters the liquid crystal layer 441. While the light X is transmitted through the liquid crystal layer 441, the polarization direction changes by 45 degrees as indicated by the arrow C along the alignment of the liquid crystal molecules, and is transmitted through the two alignment layers 432 indicated by the arrow C with the horizontal polarization indicated by the arrow D. Then, the light enters the liquid crystal layer 442. Then, while passing through the liquid crystal layer 442, the polarization direction further changes by 45 degrees along the arrangement of the liquid crystal molecules, becomes 45 degrees left polarized light indicated by the arrow F, and transmits through the alignment layer 434 indicated by the arrow E to be emitted. That is, when the light X passes through the liquid crystal element 410, the polarization direction of the light X changes by 90 degrees.

  On the other hand, when a voltage is simultaneously applied to the electrode layers 421 and 422 sandwiching the liquid crystal layer 441 and the electrode layers 421 and 422 sandwiching the liquid crystal layer 442 by the AC power supply 450, the liquid crystal molecules are subjected to the action of the generated electric field. Since the light is arranged along the X traveling direction, the polarization direction of the light X remains 45 degrees right polarization indicated by the arrow A and does not change before and after transmission through the liquid crystal element 410. As described above, the polarization direction of the light X transmitted through the liquid crystal element 410 is changed by 90 degrees between the left 45-degree polarized light and the right 45-degree polarized light by switching the applied voltage on and off by the AC power supply 450. This change in the polarization direction also occurs in the combined light. In the second modification, the polarization direction is changed once during the drawing of one frame of the information image.

  In the second modification, the alignment layer 432 facing the alignment layer 433 of the liquid crystal layer 441 when viewed from the downstream side in the traveling direction of the light X (right side in FIG. 26) to the upstream in the traveling direction (left side in FIG. 26). Is inclined 45 degrees to the right, and the alignment layer 434 facing the alignment layer 432 of the liquid crystal layer 442 is also inclined 45 degrees to the right. That is, when an AC voltage is not applied to the AC power supply 450, the twist angle of each liquid crystal molecule in the liquid crystal layer 441 and the liquid crystal layer 442 is 45 degrees, and any liquid crystal molecule moves from the incident side of the light X to the outgoing side. It has a spiral structure that is twisted and arranged in the same direction.

  In the projection display device 20, an information image formed by the combined light in which the polarization direction is changed by the liquid crystal element 410 into 45-degree left polarization and 45-degree right polarization in a frame unit is projected onto the windshield 700. Also in the second modification, since the polarization direction is different for each frame, speckle noise generated in different places in each frame is smoothed as a whole, and speckle noise appearing in the information image displayed on the windshield 700 is reduced. And is visually recognized by the driver 40.

  Further, in the projection display device 20, horizontal polarization is not included in the polarization direction of the information image projected on the windshield 700. Therefore, when the driver 40 wearing the polarized sunglasses 42 visually recognizes the information image, the information image of all the frames can be visually recognized, and thus flicker does not occur.

  If the liquid crystal element 410 includes the liquid crystal layers 441 and 442 as in the second modification, voltage application to the liquid crystal layers 441 and 442 by the AC power source 450 is performed at the same timing and at the same timing, thereby The change in the polarization direction of the light transmitted through the liquid crystal layers 441 and 442 by turning on and off is 45 degrees. Therefore, the polarization dispersion of red light, green light, and blue light can be reduced, and the change in the polarization direction of the left 45-degree polarized light and the right 45-degree polarized light as the liquid crystal element 410 can be completed in a short time.

  In the liquid crystal element 410 of the second modification, the spiral pitch of the spiral structure of the liquid crystal molecules of the liquid crystal layer 441 is p1, the refractive index anisotropy is Δn1, and the spiral pitch of the spiral structure of the liquid crystal molecules of the liquid crystal layer 442 is p2. When the refractive index anisotropy is Δn2, p1 × Δn1 ≧ 2500 nm and p2 × Δn2 ≧ 2500 nm are satisfied. Thereby, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9). FIG. 9 shows that the liquid crystal element 400 with a twist angle of 90 degrees can have the same polarization characteristics with the polarization direction changing by 90 degrees. In the liquid crystal element 410 of the second modification example with the twist angle of 45 degrees, FIG. However, it is natural that the polarization characteristics whose polarization direction changes by 45 degrees can be made the same.

5. Third Embodiment Hereinafter, a projection display device 30 according to a third embodiment of the present invention will be described in detail with reference to the drawings. In the description of this embodiment, the same reference numerals are given to the same components as those in the first embodiment, the second embodiment, and the respective modifications, and the description regarding the same components is omitted.

  This embodiment is a combination of the first embodiment and the second embodiment. As shown in FIG. 27, the liquid crystal element includes the liquid crystal element 410 used in the second embodiment and its modification, and the liquid crystal element 410 The high retardation film 500 used in the first embodiment and its modifications is provided between the image forming unit 300 and the image forming unit 300. The high retardation film 500 is held by a holding member (not shown).

  In the present embodiment, the composite light is changed by the liquid crystal element 410 into the left 45 degree polarization direction and the right 45 degree polarization direction in units of frames. The left 45 degree polarization direction combined light and the right 45 degree polarization direction combined light form a polarization direction inclined 45 degrees to the upper right and a polarization direction inclined 45 degrees to the upper left with respect to the optical axis of the high retardation film 500, respectively. . In this case, the combined light with the polarization direction tilted 45 degrees to the upper right and the combined light with the polarization direction tilted 45 degrees to the upper left have an angle ψ (the angle between the polarization direction of the incident light and the optical axis of the high retardation film 500 in the Poincare sphere. = ± 45 degrees). When these lights pass through the high retardation film 500, as shown in FIG. 8, the light after the transmission has an angle twice as large as the angle ψ from the point P1 (horizontal polarization) and the point P2 (vertical polarization) (2ψ = Positions of points M1 and M2 rotated by the same angle δ (δ = 2π · Re / λ) from the point P on the circle Cr with the straight line L1 passing through the center of the Poincare sphere at ± 90 degrees as the rotation center axis The polarization direction, the rotation direction, and the polarization type of light. As described above, the points P1 and P2 are converted into the northern hemisphere (right-handed polarized light) or the southern hemisphere (left-handed polarized light) indicated by the points M1 and M2, respectively. It is understood that the outgoing light after passing through the light becomes circularly polarized light or elliptically polarized light having opposite rotation directions (left-handed and right-handed).

  Therefore, the location where speckle noise occurs in the information image formed with the combined light having the 45-degree polarization direction on the left is different from the location where speckle noise occurs in the information image formed with the combined light having the 45-degree polarization direction on the right. As a result, speckle noise generated at different locations in each frame is smoothed as a whole, and speckle noise appearing in the information image displayed on the windshield 700 is reduced and visually recognized by the driver 40. In this embodiment, since the polarization direction changes by 90 degrees, the effect of reducing speckle noise is maximized compared to changes in other angles.

  As described above, in the projection display device 30, the polarization direction of the combined light transmitted through the liquid crystal element 410 is switched between the left 45 degree polarization direction and the right 45 degree polarization direction in units of frames, and high retardation is achieved in the polarization direction. The film 500 is transmitted. As a result, the light of each wavelength included in the combined light after transmission includes light of various polarization directions, rotation directions, and types of polarization (linearly polarized light, circularly polarized light, elliptically polarized light). It does not contain only light. Since the information image formed by the combined light is projected onto the windshield 700, flicker does not occur even when the driver 40 wearing the polarized sunglasses 42 visually recognizes the information image.

  Also in this embodiment, as in the first embodiment, the high retardation film 500 may be formed on the surface of the substrate 412 of the liquid crystal element 410 instead of being held by the holding member. With such a configuration, the holding member is unnecessary, and the projection display device 30 can be configured at a lower cost.

  In the case where the liquid crystal element 410 of the second embodiment is used as the liquid crystal element, p × Δn ≧ when the spiral pitch of the spiral structure of the liquid crystal molecules of the liquid crystal layer 441 is p and the refractive index anisotropy is Δn. It is comprised so that 2500 nm may be satisfied. When the liquid crystal element 410 according to the modification of the second embodiment is used, the spiral pitch of the liquid crystal molecules of the liquid crystal layer 441 is p1, the refractive index anisotropy is Δn1, and the liquid crystal of the liquid crystal layer 442 is When the helical pitch of the molecular helical structure is p2 and the refractive index anisotropy is Δn2, p1 × Δn1 ≧ 2500 nm and p2 × Δn2 ≧ 2500 nm are satisfied. Accordingly, the polarization characteristics of green light, blue light, and red light can be made the same (see FIG. 9).

  Further, similarly to the first modification of the first embodiment, the projection display device 30 may include the intermediate image portion 350, and the high retardation film 500 may be formed on the intermediate image portion 350. Further, similarly to the second modification of the first embodiment, the projection display device 30 may include a combiner 360, and the high retardation film 500 may be formed on the combiner 360.

  In any of the second embodiment, its modification, and the third embodiment, the liquid crystal cell 140, the half mirror 150, the light detection unit 160, and the control unit 170 are provided as in the fourth modification of the first embodiment. It may be. With such a configuration, the brightness and color balance of the information image visually recognized by the driver 40 can always be optimized, the generation of speckle noise can be reduced, and the driver 40 can see through the polarized sunglasses 42. However, an information image that does not cause flicker can be obtained.

  The configurations of the above embodiments and modifications can be combined as much as possible.

  The projection display devices 10, 20, and 30 are not limited to the in-vehicle head-up display 50, but can be applied to head-up displays of any transportation equipment that uses laser light as a light source, such as an aircraft or a train. Further, the present invention can be applied to any projection display device or display device that uses laser light as a light source. For example, the present invention can be applied to a projector, a projector television, a projection mapping device, a digital signage, a head mounted display, a micro projector, a portable information terminal incorporating the projector, and the like.

  INDUSTRIAL APPLICABILITY The present invention can be used for a projection display device using laser light and an in-vehicle head-up display using the projection display device.

10, 20, 30 Projection type display device 50 On-vehicle head-up display 100 Light source unit 110 Laser diode (green laser light source)
120 Laser diode (blue laser light source)
130 Laser diode (red laser light source)
140 Liquid Crystal Cell 160 Photodetector 170 Controller 200 Synthetic Optical Unit 300 Image Forming Unit 350 Intermediate Image Unit 360 Combiner (Display Unit)
400, 410 Liquid crystal element 411 Substrate 412 Substrate 441 Liquid crystal layer (first layer)
442 Liquid crystal layer (second layer)
500 High retardation film Δn Refractive index anisotropy p Spiral pitch

Claims (21)

A light source unit that generates a plurality of laser beams having different wavelengths in a predetermined polarization direction;
A combining optical unit for combining the plurality of laser beams;
An image forming unit that forms a projection image from the plurality of laser beams;
A liquid crystal element that generates a single polarization state in a transmission region through which the plurality of laser beams emitted from the combining optical unit are transmitted, and changes a polarization direction of the plurality of laser beams in the transmission region;
And a high retardation film that gives a phase difference to the plurality of laser beams emitted from the liquid crystal element.   2. The laser beam according to claim 1, wherein an optical axis of the high retardation film and a polarization axis in the single polarization state form an angle of 45 degrees and give a phase difference of 4000 nm or more to the plurality of laser beams. Projection type display device used. The liquid crystal element has a liquid crystal layer and a pair of substrates arranged so as to sandwich the liquid crystal layer,
The projection display device using laser light according to claim 1 or 2, wherein the high retardation film is formed on a surface of at least a side of the pair of substrates which is far from the light source unit.   4. The apparatus according to claim 1, further comprising an intermediate image portion having a diffusion function on a side farther from the image forming portion when viewed from the light source portion, wherein the high retardation film is formed on at least one surface of the intermediate image portion. A projection display device using the laser light according to any one of the above.   The display device having a half mirror function is further provided on a side farther from the image forming unit as viewed from the light source unit, and the high retardation film is formed on a surface of the display unit closer to the light source unit. 5. A projection display device using the laser beam according to any one of 1 to 4. The liquid crystal element has a liquid crystal layer and a pair of substrates arranged so as to sandwich the liquid crystal layer,
The liquid crystal molecules of the liquid crystal layer have a spiral structure between the pair of substrates,
6. The projection display device using laser light according to claim 1, wherein the product of the helical pitch of the liquid crystal molecules and the refractive index anisotropy of the liquid crystal layer is 2500 nm or more.   The projection display device using laser light according to claim 6, wherein a twist angle of the liquid crystal molecules in the liquid crystal layer is 90 degrees.   The liquid crystal layer is configured by laminating a first layer and a second layer, and the twist angle in the first layer and the twist angle in the second layer are both 45 degrees. Projection display device using laser light. A light source unit that generates a plurality of laser beams having different wavelengths in a predetermined polarization direction;
A combining optical unit for combining the plurality of laser beams;
An image forming unit that forms a projection image from the plurality of laser beams;
A liquid crystal element that generates a single polarization state in a transmission region through which the plurality of laser beams emitted from the combining optical unit are transmitted, and changes a polarization direction of the plurality of laser beams in the transmission region;
The liquid crystal element has a liquid crystal layer and a pair of substrates arranged so as to sandwich the liquid crystal layer,
The liquid crystal molecules of the liquid crystal layer have a spiral structure between the pair of substrates,
The polarization direction of the plurality of laser beams in the liquid crystal element is a laser beam that alternately changes in a direction that changes 45 degrees to the right and a direction that changes 45 degrees to the left with respect to the horizontal direction when the liquid crystal element is used. Projection type display device.   The projection display device using laser light according to claim 9, wherein a product of the helical pitch of the liquid crystal molecules and the refractive index anisotropy of the liquid crystal layer is 2500 nm or more.   The projection display device using laser light according to claim 9 or 10, wherein a twist angle of the liquid crystal molecules in the liquid crystal layer is 90 degrees.   The liquid crystal layer is formed by laminating a first layer and a second layer, and the twist angle in the first layer and the twist angle in the second layer are both 45 degrees. A projection display device using the laser beam described. A high retardation film that gives a phase difference to the plurality of laser beams emitted from the liquid crystal element;
The optical axis of the high retardation film and the polarization axis in the single polarization state form an angle of 45 degrees, and give a phase difference of 4000 nm or more to the plurality of laser beams. A projection type display device using the laser beam described in the item.   The projection display apparatus using laser light according to claim 13, wherein the high retardation film is formed on a surface of at least a side of the pair of substrates that is far from the light source unit.   The intermediate retardation part which further has a diffusion function in the side far from the image formation part seeing from the light source part is provided, and the high retardation film is formed in at least one surface of the intermediate image part. A projection display device using the laser beam described in 1.   The display device having a half mirror function is further provided on a side farther from the image forming unit as viewed from the light source unit, and the high retardation film is formed on a surface of the display unit closer to the light source unit. A projection display device using the laser beam according to any one of 13 to 15.   The projection type using a laser beam according to any one of claims 1 to 16, further comprising a liquid crystal cell that changes a transmittance of the plurality of laser beams between the synthetic optical unit and the liquid crystal element. Display device.   The projection display device using laser light according to claim 17, wherein the liquid crystal cell has a vertically aligned nematic liquid crystal layer.   The projection display device using laser light according to claim 17 or 18, further comprising a light detection unit that detects colors and intensities of the plurality of laser beams on a side farther from the liquid crystal cell as viewed from the light source unit. A control unit to which the detection result of the light detection unit is input;
The light source unit includes a red laser light source that generates red light, a green laser light source that generates green light, and a blue laser light source that generates blue light,
The said control part performs control which changes the intensity | strength of the light radiate | emitted from the said red laser light source, the said green laser light source, and the said blue laser light source based on the detection result of the said light detection part. Projection display device using laser light.   21. A vehicle-mounted head-up display comprising the projection display device using the laser beam according to claim 1.

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