WO2011132406A1 - シースルーディスプレイ及びヘッドアップディスプレイ - Google Patents
シースルーディスプレイ及びヘッドアップディスプレイ Download PDFInfo
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- WO2011132406A1 WO2011132406A1 PCT/JP2011/002289 JP2011002289W WO2011132406A1 WO 2011132406 A1 WO2011132406 A1 WO 2011132406A1 JP 2011002289 W JP2011002289 W JP 2011002289W WO 2011132406 A1 WO2011132406 A1 WO 2011132406A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
- G02B27/0103—Head-up displays characterised by optical features comprising holographic elements
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/12—Picture reproducers
- H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
- H04N9/3141—Constructional details thereof
- H04N9/315—Modulator illumination systems
- H04N9/3161—Modulator illumination systems using laser light sources
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
- G02B2027/0112—Head-up displays characterised by optical features comprising device for genereting colour display
Definitions
- the present invention mainly relates to a see-through display used in a video display device such as a head-up display (HUD) or a head-mounted display (HMD).
- a video display device such as a head-up display (HUD) or a head-mounted display (HMD).
- HUD head-up display
- HMD head-mounted display
- a video display device called a head-up display mainly displays information required for a steering operation in a cockpit of an automobile or an aircraft.
- An automobile driver or an aircraft pilot can perceive the information displayed by the HUD as if the display information exists in front of the windshield.
- a video display device called a head mounted display (HMD) is mounted in the same manner as general eyeglasses for correcting vision.
- a user wearing the HMD can perceive an image displayed by the HMD as if the display information exists in the space in front of the lens portion.
- Both the HUD and the HMD allow the user to visually recognize an image through a substantially transparent member such as a windshield and a lens member. Therefore, these video display devices are referred to as “see-through displays”. In recent years, the development of these video display devices has become active.
- HUD can provide high safety and convenience.
- the HMD can provide a user with a large-sized image with a very small power consumption. Further, the user can view the image regardless of the place, and can obtain necessary information anytime and anywhere.
- the see-through display needs to mix external light (natural light) incident from the outside such as scenery with the image to be displayed.
- external light natural light
- an HUD used in an automobile mixes an image to be displayed and external light incident from the outside using a combiner in the vicinity of the windshield.
- the light loss of the external light incident from the external world and the light to be displayed is reduced.
- a conventional see-through display uses a volume hologram as a combiner (see, for example, Patent Document 1). If a hologram is used as a combiner, the image displayed by the HUD is enlarged as a result of the lens action of the hologram. As a result, the user can visually recognize a large size image.
- the volume hologram does not generate higher-order diffracted light. Therefore, the rate of loss of external light incident from the outside due to diffraction by the volume hologram is relatively small.
- the volume hologram has a high diffraction efficiency for a predetermined wavelength. For example, if a laser light source is used as the light source, the HUD has high light utilization efficiency as a result of the narrow wavelength width of the laser light.
- Interference fringes are recorded on volume holograms used in conventional see-through displays.
- the diffraction angle slightly shifts from the desired direction. Therefore, when the wavelength of the light emitted from the light source of the see-through display including the volume hologram deviates from the wavelength of the recording light used for recording the interference fringe of the volume hologram, the image display position is shifted from the desired position. Will be.
- the see-through display typically includes a plurality of light sources.
- a plurality of light sources emit light of different hues. Due to factors such as the wavelength of light emitted from multiple light sources in the see-through display and the variation in wavelength due to temperature, the position of the image drawn by the light from the multiple light sources may be individually shifted for each hue. . If an image is formed by color mixing, color misregistration in the image is likely to be visually recognized due to factors such as solid-state variations in the light source wavelength and wavelength variations caused by temperature. In addition, if the light source wavelength changes, for example, due to temperature fluctuations, the diffraction efficiency decreases and the luminance distribution and color distribution in the image become non-uniform. In addition, the brightness of the entire image may be reduced.
- An object of the present invention is to provide a see-through display capable of displaying a high-quality image.
- a see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, and a volume hologram that deflects light projected from the projection optical system.
- the volume hologram has a linear expansion coefficient of ⁇ (/ ° C.) and interference fringes recorded with recording light having a wavelength of ⁇ (nm), and the wavelength of the light emitted from the light source is It has a temperature dependency of K (nm / ° C.), and the wavelength ⁇ (nm) and the temperature dependency K (nm / ° C.) satisfy the relationship of 0 ⁇ K / ⁇ ⁇ 2 ⁇ .
- a see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, a volume hologram that deflects light projected from the projection optical system, and An adjustment element for adjusting the temperature of the light source, and the wavelength of the light emitted from the light source has temperature dependence, and the volume hologram has a linear expansion coefficient of ⁇ and a recording light having a center wavelength of ⁇ .
- the adjustment element adjusts the temperature of the light source based on the linear expansion coefficient ⁇ and the center wavelength ⁇ of the recording light.
- a see-through display includes a light source including n light source elements (n is an integer greater than 1) that emits light, a projection optical system that projects light emitted from the light source, A volume hologram that deflects the light projected from the projection optical system, and the volume hologram includes ⁇ 1, ⁇ 2, ..., ⁇ n for diffracting the light emitted from the n light source elements, respectively. Having interference fringes formed using recording light of a wavelength, and emitted by the n light source elements, and by interference fringes formed using recording light of the wavelengths ⁇ 1, ⁇ 2,.
- Each wavelength of the diffracted light has temperature dependency of K1 (nm / ° C.), K2 (nm / ° C.),..., Kn (nm / ° C.), and K1 / ⁇ 1, K2 / ⁇ 2,.
- the difference value between the maximum value and the minimum value of Kn / ⁇ n is 0.0 Wherein the 01 or less.
- a see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, a volume hologram that deflects light projected from the projection optical system, and
- the light source includes: a first light source element that emits first light having a first wavelength; and a second light source element that emits second light having a wavelength different from the first wavelength, and is drawn by the first light.
- the first image to be displayed is displayed at a position separated from the second image drawn by the second light.
- a see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, a volume hologram that deflects light projected from the projection optical system, and
- the projection optical system includes: a MEMS mirror that reflects light from the light source; and a modulation that modulates a polarization direction of light from the light source before the MEMS mirror reflects light emitted from the light source. And an element.
- a see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source and forms a frame image, and light projected from the projection optical system.
- a volume hologram that deflects, wherein the projection optical system includes a MEMS mirror, the frame image is formed using a plurality of time-divided subframes, and at least one of the plurality of subframes is displayed. The amount of light emitted from the light source when the light is emitted is 0 or a maximum value.
- a head-up display mounted on a vehicle having a windshield interposing an intermediate film that selectively adjusts a wavelength component of light incident on a vehicle interior includes the above-described see-through display.
- the volume hologram is disposed between the passenger compartment and the intermediate film.
- FIG. 11 is a schematic cross-sectional view of a reflection hologram of the head-up display shown in FIG. 10. It is a schematic sectional drawing of the windshield which clamps a volume hologram.
- FIG. 18B draws on a screen. It is the schematic of the virtual image which a driver
- FIG. 1 is a schematic diagram of a head-up display (hereinafter referred to as HUD) exemplified as a see-through display according to the first embodiment.
- HUD head-up display
- FIG. 1 shows a windshield 210 of an automobile.
- the windshield 210 includes an inner surface 211 that defines an inner boundary of the passenger compartment, and an outer surface 212 opposite to the inner surface 211.
- the HUD 100 includes a laser light source 110 that emits a laser light LB, a projection optical system 120 that projects the laser light LB emitted from the laser light source 110, and a volume hologram 200 attached to the inner surface 211 of the windshield 210.
- the projection optical system 120 includes a lens 121, a folding mirror 122, a liquid crystal panel 123, a projection lens 124, and a screen 125.
- the laser light source 110 is exemplified as a light source that emits light.
- the HUD 100 further includes a control unit 130.
- the control unit 130 is electrically connected to the laser light source 110 and the liquid crystal panel 123.
- the laser light source 110 and the liquid crystal panel 123 operate under the control of the control unit 130.
- the control unit 130 outputs a control signal for causing the laser light source 110 to emit the laser light LB.
- the laser light source 110 emits the laser light LB toward the lens 121 in accordance with a control signal from the control unit 130.
- the laser beam LB that has passed through the lens 121 is reflected toward the liquid crystal panel 123 by the folding mirror 122. As a result, the liquid crystal panel 123 is illuminated two-dimensionally by the laser beam LB.
- the lens 121 expands the laser beam LB so that the liquid crystal panel 123 is illuminated without waste. Since the folding mirror 122 is arranged to fold the laser beam LB, a small HUD 100 is formed.
- the lens for enlarging the laser beam and the folding mirror for folding the laser beam may be omitted depending on the specifications of the HUD and the characteristics of the laser light source.
- the control unit 130 outputs a control signal for causing the liquid crystal panel 123 to display a pattern of an image to be displayed.
- the liquid crystal panel 123 creates a pattern of a displayed image in response to a control signal from the control unit 130.
- the laser beam LB illuminates the liquid crystal panel 123
- the laser beam LB is intensity-modulated two-dimensionally and emitted from the liquid crystal panel 123 as the image light IL.
- the projection lens 124 images the video light IL emitted from the liquid crystal panel 123 on the screen 125. As a result, an image is displayed on the screen 125.
- the volume hologram 200 diffracts the image light IL emitted from the screen 125 and deflects it toward the driver DR. As a result, the driver DR can visually recognize the virtual image VI enlarged by the volume hologram 200 through the windshield 210.
- the optical configuration of the projection optical system 120 shown in FIG. 1 does not limit the principle of this embodiment at all.
- FIG. 2A is a schematic view of the volume hologram 200 under the interference fringe formation process.
- FIG. 2B is a schematic diagram of the volume hologram 200 in which the laser beam LB is incident after the formation of the interference fringes. The diffraction principle of the volume hologram is described with reference to FIGS. 1 to 2B.
- Interference fringes 201 are formed on the volume hologram 200.
- laser light having a wavelength substantially equal to that of the laser light LB described with reference to FIG. 1 (hereinafter referred to as recording light RL) is separated into two light beams.
- the recording light RL separated into two light beams is incident on the volume hologram 200 at an angle ⁇ 1 and an angle ⁇ 2, as shown in FIG. 2A.
- interference fringes 201 having an interference fringe spacing ⁇ are formed on the volume hologram 200.
- the volume hologram 200 diffracts the laser beam LB with a predetermined diffraction efficiency. As a result, the laser beam LB is emitted from the volume hologram 200 in the direction of the angle ⁇ 2. This condition is generally called the Bragg condition.
- the elements that are easily affected by temperature fluctuations around the HUD 100 are mainly the volume hologram 200 and the laser light source 110.
- the influence of the volume hologram 200 and the laser light source 110 on the fluctuation of the temperature around the HUD 100 will be described.
- the volume hologram 200 expands or contracts according to a change in the temperature around the HUD 100.
- the interference fringe spacing ⁇ varies. Variations in the interference fringe spacing ⁇ result in variations in the diffraction angle and diffraction efficiency of the volume hologram 200. For example, if the volume hologram 200 expands isotropically due to a constant wavelength of the laser beam LB and an increase in the temperature around the HUD 100, as shown in FIG. When ⁇ 2 is large, the laser beam LB incident at an angle ⁇ 1 is emitted from the volume hologram 200 at an angle smaller than the angle ⁇ 2 before the volume hologram 200 expands.
- the diffraction efficiency also decreases compared to before the temperature around the HUD 100 increases.
- the laser beam LB incident on the volume hologram 200 at the angle ⁇ 1 is emitted from the volume hologram 200 at an angle larger than the angle ⁇ 2.
- the angle ⁇ 1 is smaller than the angle ⁇ 2
- the laser beam LB is emitted from the volume hologram 200 at an angle larger than the angle ⁇ 2 before the volume hologram 200 is expanded.
- the temperature around the HUD 100 decreases, the laser beam LB is emitted from the volume hologram 200 at an angle smaller than the angle ⁇ 2 before the volume hologram 200 contracts.
- the departure direction from the Bragg condition differs depending on the magnitude relationship between the angle ⁇ 1 and the angle ⁇ 2.
- a deviation from the Bragg condition occurs, so that the diffraction efficiency is lowered as compared to before the temperature around the HUD 100 fluctuates.
- a semiconductor laser light source is exemplified as the laser light source 110 of this embodiment.
- the wavelength of the laser beam LB emitted from the semiconductor laser light source varies.
- the higher the temperature around the semiconductor laser light source the narrower the band gap of the semiconductor band structure.
- the oscillation wavelength of the laser beam LB from the semiconductor laser light source is shifted to the low energy side (long wavelength side).
- the change in the wavelength of the laser beam LB results in a change in the diffraction angle and diffraction efficiency in the volume hologram.
- the wavelength of the laser beam LB shifts to the long wavelength side due to the increase in the temperature around the semiconductor laser light source used as the laser light source 110, and As shown in FIG. 2B, if the angle ⁇ 2 is larger than the angle ⁇ 1, the laser beam LB incident on the volume hologram 200 at the angle ⁇ 1 is larger than the angle ⁇ 2 before the wavelength of the laser beam LB fluctuates. Then, the light is emitted from the volume hologram 200. As a result of deviation from the Bragg condition, the diffraction efficiency is reduced as compared to before the temperature around the laser light source 110 is increased.
- the laser beam LB is emitted from the volume hologram 200 at an angle smaller than the angle ⁇ 2. If the angle ⁇ 2 is smaller than the angle ⁇ 1 and the temperature around the laser light source 110 rises, the laser beam LB is emitted from the volume hologram 200 at an angle smaller than the angle ⁇ 2 before the wavelength of the laser beam LB fluctuates. To do. Conversely, if the temperature around the laser light source 110 decreases, the laser beam LB is emitted from the volume hologram 200 at an angle larger than the angle ⁇ 2.
- the departure direction from the Bragg condition differs depending on the magnitude relationship between the angle ⁇ 1 and the angle ⁇ 2.
- the diffraction efficiency is lowered as compared with the case before the temperature around the laser light source 110 fluctuates.
- the deviation direction from the Bragg condition caused by the expansion or contraction of the volume hologram 200 due to the temperature variation around the HUD 100 is preferably the laser light source 110 due to the temperature variation around the laser light source 110. It is set so as to be opposite to the direction of deviation from the Bragg condition caused by the wavelength fluctuation. If the expansion or contraction of the volume hologram 200 and the wavelength shift of the laser beam LB occur simultaneously as a result of temperature fluctuations around the HUD 100 and / or the laser light source 110, the deviation from the Bragg condition is offset.
- the volume hologram expands or contracts singly due to the temperature fluctuation or the temperature fluctuation.
- the image quality such as the shift of the display position of the image due to the fluctuation of the diffraction angle and the decrease in the brightness due to the reduction of the diffraction efficiency is improved. Deterioration is less likely to occur.
- the temperature fluctuation amount of the wavelength of the laser light emitted from the semiconductor laser light source generally depends on the type of semiconductor used for the semiconductor laser light source.
- a semiconductor laser light source having an active layer having a composition composed of aluminum (Al), gallium (Ga), indium (In), and phosphorus (P) is exemplified.
- the temperature dependence K of the wavelength of laser light emitted from the semiconductor laser light source is about 0.2 nm / ° C.
- the linear expansion coefficient ⁇ of a volume hologram generally used for a see-through display is about 2.0 ⁇ 10 ⁇ 4 / ° C.
- FIG. 3 is a graph schematically showing the temperature expansion characteristic of the volume hologram and the temperature dependence characteristic of the wavelength of the laser beam. The temperature expansion characteristic of the volume hologram and the temperature dependence characteristic of the wavelength of the laser beam will be described with reference to FIG.
- the temperature expansion characteristic shown in FIG. 3 is obtained from a volume hologram having a linear expansion coefficient ⁇ of 2.0 ⁇ 10 ⁇ 4 / ° C. Further, the temperature dependence characteristic of the wavelength of the laser light shown in FIG. 3 is obtained from the red laser light emitted from the red semiconductor laser light source having the temperature dependence K of the wavelength of 0.2 nm / ° C.
- the horizontal axis of the graph in Fig. 3 represents temperature.
- the vertical axis on the left of the graph in FIG. 3 represents the fluctuation ratio of the wavelength that fluctuates due to temperature fluctuation.
- the vertical axis on the right side of the graph in FIG. 3 represents the fluctuation ratio of the interference fringe spacing ⁇ of the volume hologram that expands due to temperature fluctuation.
- the wavelength of the red laser beam at 25 ° C. is 637 nm.
- the semiconductor laser light source having the above-mentioned wavelength dependency is used together with the volume hologram, the deviation from the Bragg condition due to temperature fluctuation is suitably reduced. Therefore, if a light source (for example, a semiconductor laser light source) whose wavelength is shifted to a longer wavelength side as the temperature rises is used as a light source for a see-through display such as a HUD that uses a volume hologram, even if temperature fluctuation occurs, the diffraction angle Image quality deterioration such as a shift in the display position of an image due to fluctuations and a decrease in luminance due to a decrease in diffraction efficiency is less likely to occur.
- a light source for example, a semiconductor laser light source
- a see-through display such as a HUD that uses a volume hologram
- Semiconductor laser light sources are generally the cheapest among laser light sources. Therefore, if a semiconductor laser light source is used as the HUD light source, an inexpensive HUD is provided. It is obvious that the above-described effects can be obtained even with a semiconductor laser light source using a semiconductor having a composition other than that described above. Therefore, the principle of the present embodiment is not limited to a red semiconductor laser light source having a semiconductor having the above composition. Furthermore, if the wavelength of light from the light source has temperature characteristics similar to those described above, the above-described effects can be obtained even with a light source other than the semiconductor laser light source.
- the present inventor hardly causes image quality deterioration such as a shift in the display position of an image due to a variation in diffraction angle and a decrease in luminance due to a decrease in diffraction efficiency under the following conditions. I found out that The conditions for suppressing the deterioration of image quality will be described with reference to FIGS.
- the volume hologram 200 has an interference fringe 201 recorded with recording light RL having a linear expansion coefficient of ⁇ (/ ° C.) and a wavelength of ⁇ (nm) (see FIG. 2A), and a laser emitted from the laser light source 110. If the wavelength of the light LB has a temperature dependency of K (nm / ° C.), the volume ⁇ (nm) and the temperature dependency K (nm / ° C.) satisfy the relationship shown in the following Equation 1 In the see-through display (HUD 100) using the hologram 200, deviation from the Bragg condition due to temperature fluctuation is reduced.
- Equation 1 In the see-through display (HUD 100) using the hologram 200, deviation from the Bragg condition due to temperature fluctuation is reduced.
- FIG. 4 is a schematic diagram of a HUD exemplified as another see-through display of this embodiment. HUD is demonstrated using FIG.1 and FIG.4.
- the HUD 100A includes a light source 150 including a red semiconductor laser light source 110R, a green semiconductor laser light source 110G, and a blue semiconductor laser light source 110B.
- the red semiconductor laser light source 110R emits red laser light LB (r).
- the green semiconductor laser light source 110G emits green laser light LB (g).
- the blue semiconductor laser light source 110B emits blue laser light LB (b).
- each of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B is exemplified as a light source element.
- the HUD 100A further includes a control unit 130A.
- the control unit 130A is electrically connected to each of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, the blue semiconductor laser light source 110B, and the liquid crystal panel 123.
- the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, the blue semiconductor laser light source 110B, and the liquid crystal panel 123 operate under the control of the control unit 130A.
- the HUD 100A further includes dichroic mirrors 151 and 152.
- the red semiconductor laser light source 110 ⁇ / b> R emits red laser light LB (r) toward the dichroic mirror 151.
- the blue semiconductor laser light source 110B also emits blue laser light LB (b) toward the dichroic mirror 151.
- the dichroic mirror 151 combines the red laser beam LB (r) and the blue laser beam LB (b).
- the laser beam combined by the dichroic mirror 151 propagates toward the dichroic mirror 152.
- the green semiconductor laser light source 110 ⁇ / b> G emits the green laser light LB (g) toward the dichroic mirror 152.
- the dichroic mirror 152 combines the laser beam combined by the dichroic mirror 151 and the green laser beam LB (g).
- the three colors of laser light combined by the dichroic mirror 152 enter the projection optical system 120.
- the projection optical system 120 includes a lens 121, a folding mirror 122, a liquid crystal panel 123, a projection lens 124, and a screen 125, as described with reference to FIG.
- the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) illuminate the liquid crystal panel 123.
- the image light IL including the red laser light LB (r), the green laser light LB (g), and the blue laser light LB (b) is emitted from the liquid crystal panel 123.
- an image drawn by the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) is displayed on the screen 125.
- the HUD 100A further includes a volume hologram 200A attached to the inner surface 211 of the windshield 210.
- the red laser beam LB (r), green laser beam LB (g), and blue laser beam LB (b) emitted from the screen 125 are diffracted by the volume hologram 200A and deflected toward the driver DR.
- the driver DR can visually recognize the virtual image VI enlarged by the volume hologram 200 ⁇ / b> A through the windshield 210.
- the volume hologram 200A may be a single hologram element in which interference fringes corresponding to the respective hues of red, green, and blue are recorded in a multiplexed manner.
- the volume hologram 200A is formed with a hologram element in which an interference fringe corresponding to a red hue is formed, a hologram element in which an interference fringe corresponding to a green hue is formed, and an interference fringe corresponding to a blue hue.
- the hologram elements may be stacked.
- the red laser light LB (r) and the green laser light LB are shifted to the long wavelength side.
- FIG. 5 is a graph schematically showing temperature-dependent characteristics of the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b).
- the temperature dependence characteristics of the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) will be described with reference to FIGS. 2B, 4, and 5.
- the horizontal axis of the graph in Fig. 5 represents temperature.
- the vertical axis of the graph in FIG. 5 represents the variation rate of the wavelength that varies due to the temperature variation around the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and / or the blue semiconductor laser light source 110B.
- the graph of FIG. 5 shows how much the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) at 25 ° C. have changed with temperature variation.
- the temperature dependence of the wavelength of the red laser beam LB (r) from the red semiconductor laser light source 110 ⁇ / b> R is represented using the symbol “Kr”.
- the temperature dependence of the wavelength of the green laser beam LB (g) from the green semiconductor laser light source 110G is expressed using the symbol “Kg”.
- the temperature dependence of the wavelength of the blue laser beam LB (b) from the blue semiconductor laser light source 110B is expressed using the symbol “Kb”.
- the red semiconductor laser light source 110R may be a semiconductor laser light source having an active layer having a composition made of, for example, aluminum (Al), gallium (Ga), indium (In), or phosphorus (P).
- the temperature dependence Kr of the wavelength of the red laser beam LB (r) is about 0.2 nm / ° C.
- the green semiconductor laser light source 110G and the blue semiconductor laser light source 110B may be well-known semiconductor laser light sources having an active layer composed of indium (In), gallium (Ga), and nitrogen (N).
- the temperature dependency Kg of the wavelength of the green laser beam LB (g) is about 0.04 nm / ° C.
- the temperature dependency Kb of the wavelength of the blue laser beam LB (b) is also about 0.04 nm / ° C.
- the wavelength of the red laser beam LB (r) from the red semiconductor laser light source 110R is 637 nm at a temperature of 25 ° C.
- the wavelength of the green laser light LB (g) from the green semiconductor laser light source 110G is 532 nm.
- the wavelength of the blue laser light LB (b) from the blue semiconductor laser light source 110B is 445 nm.
- the ambient temperature of the semiconductor laser light source rises. Then, the wavelength of the laser light emitted from the semiconductor laser light source is shifted to the long wavelength side. As a result, the Bragg condition is not satisfied and the diffraction angle varies.
- the wavelength of the laser beam LB is When it becomes longer, as described above, the emission angle of the laser beam LB emitted from the volume hologram 200A from the volume hologram 200A becomes larger than the angle ⁇ 2.
- a laser light source having a characteristic that the wavelength is constant regardless of temperature fluctuation for example, wavelength conversion is performed on a fundamental wave emitted from a solid-state laser element, and green If a wavelength conversion laser light source that generates laser light is used, the wavelength of the green laser light hardly fluctuates even when the temperature around the laser light source is 45 ° C., for example.
- the wavelength of the red laser beam LB (r) is longer by about 0.0062 times the wavelength under the condition of 25 ° C.
- the driver DR is 0 between the red image drawn with the red laser beam LB (r) and the green image drawn with the green laser beam emitted from the green laser light source that is not easily affected by temperature fluctuations.
- a virtual image VI that is color-shifted by an amount corresponding to a wavelength variation ratio of .0062 times is visually recognized.
- the HUD 100A of the present embodiment is a light source (light source 150R, green semiconductor laser light source 110G, and blue semiconductor laser light source 110B) in which the wavelength of emitted light shifts to the longer wavelength side as the temperature rises as the light source 150.
- the wavelength of the green laser light LB (g) emitted from the green semiconductor laser light source 110G is longer by about 0.0016 times the wavelength at 25 ° C.
- the green semiconductor laser light source 110G is used as a light source that emits light of a green hue
- the principle of reducing the amount of image shift described above is not limited to the hue emitted by the light source.
- the principle of reducing the amount of image shift described above is similarly applied to a light source that emits laser light having an arbitrary hue.
- n is an integer greater than 1
- light source elements that emit light of different hues (different wavelengths). If all n light source elements cause a wavelength shift to the longer wavelength side as the temperature rises, the relative displacement between images (between images of different hues) due to temperature fluctuations is reduced. Is done. Therefore, the HUD can display a high-quality image.
- the wavelength of the laser beam used for image formation is smaller than the wavelength of the recording beam used to record the interference fringes on the volume hologram. If they are different, for the same reason as described above, the polarization direction of the laser light used for image formation is different from the direction set at the time of recording the interference fringes.
- a laser beam having a plurality of hues is deflected at a predetermined temperature in the same direction as when recording interference fringes to form an image (for example, like HUD100A), it is used for recording interference fringes at a predetermined temperature.
- a laser light source that emits laser light having the same wavelength as the recording light is required. This narrows the range of usable wavelengths. Therefore, for example, when an inexpensive semiconductor laser light source is used as a light source for image formation, the yield is deteriorated.
- the usable wavelength range is expanded by the inventor's study described below.
- the wavelength of laser light emitted from a plurality of semiconductor laser light sources is measured under a temperature condition of 25 ° C.
- the plurality of semiconductor laser light sources are formed to emit laser beams having different wavelengths ( ⁇ 1, ⁇ 2,..., ⁇ n).
- the ratio of deviation between the measured wavelength and the wavelength of recording light ( ⁇ 1, ⁇ 2,..., ⁇ n) used for recording the interference fringes of the volume hologram is then calculated.
- laser light having different wavelengths ( ⁇ 1, ⁇ 2,..., ⁇ n) relative to the angle ⁇ 2 can be selectively combined if the calculated deviation ratios are close to each other. Folding angle deviation is reduced.
- the wavelength ⁇ 1 is the wavelength of the recording light used for recording the interference fringes for diffracting the wavelength ⁇ 1 of the laser light used for image formation.
- the wavelength ⁇ 2 is the wavelength of the recording light used for recording the interference fringes for diffracting the wavelength ⁇ 2 of the laser light used for image formation.
- the wavelength ⁇ n is the wavelength of the recording light used for recording the interference fringes for diffracting the wavelength ⁇ n of the laser light used for image formation.
- the wavelength emitted from the red laser light source used for forming the interference fringes for diffracting the laser light of red hue is represented by the symbol “ ⁇ r” in the following description.
- the wavelength emitted from the green laser light source used for forming the interference fringes for diffracting the laser light of the green hue is represented by the symbol “ ⁇ g” in the following description.
- the wavelength emitted from the blue laser light source used to form the interference fringes for diffracting the laser light of the blue hue is represented by the symbol “ ⁇ b” in the following description.
- the wavelength of the red laser beam LB (r) emitted from the red semiconductor laser light source 110R mounted on the HUD 100A is represented using the symbol “ ⁇ r” in the following description.
- the wavelength of the green laser light LB (g) emitted from the green semiconductor laser light source 110G mounted on the HUD 100A is expressed using the symbol “ ⁇ g” in the following description.
- the wavelength of the blue laser light LB (b) emitted from the blue semiconductor laser light source 110B mounted on the HUD 100A is represented using the symbol “ ⁇ b” in the following description.
- the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B are selected so that the dimensionless numbers calculated based on the following formulas 2 to 4 are close, the red laser from the angle ⁇ 2 is selected.
- the diffraction angle shifts of the light LB (r), the green laser light LB (g), and the blue laser light LB (b) are substantially equal. Therefore, the relative shift between the red image, the green image, and the blue image at a predetermined temperature is reduced.
- the driver DR hardly perceives a relative shift between a red image, a green image, and a blue image at a predetermined temperature.
- the difference between the maximum value and the minimum value of the dimensionless number obtained from the combination of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B is 0.005 or less.
- the driver DR Under the temperature condition of ° C., the driver DR hardly perceives a relative shift between the red image, the blue image, and the green image.
- the HUD includes a plurality of light sources that emit different wavelengths (for example, the HUD 100A described with reference to FIG. 4), the result of appropriately combining the light source elements based on the wavelength data measured at a predetermined temperature The relative shift between images drawn with different hues is reduced.
- the relationship with the linear expansion coefficient is set so as to satisfy the relationship defined by Equation 1 above, the HUD displays an image with little color shift regardless of temperature fluctuations. Can do.
- the temperature of 25 ° C. is exemplified as the predetermined temperature.
- wavelength data measured at other temperatures may be used to determine the combination of light source elements.
- ⁇ r, ⁇ g, ⁇ b, ⁇ r, ⁇ g, and ⁇ b described above are merely examples, and other values of wavelengths may be used.
- three color light source elements are mainly described. However, more than two or more light source elements may be used.
- the hue of light emitted from the light source element is not limited to red, green, and blue, and light of other hues may be emitted from the light source element.
- a semiconductor laser light source is exemplified as a light source having wavelength dependency.
- a light source having a similar wavelength dependency may be incorporated in the HUD.
- the HUD 100 may include an adjustment element that adjusts the temperature of the laser light source 110.
- the HUD 100A may include adjustment elements that adjust the temperatures of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B, respectively.
- the volume hologram has a linear expansion coefficient ⁇ of 2.0 ⁇ 10 ⁇ 4 / ° C. as described in connection with the graph of FIG.
- the temperature dependence K of the wavelength of the laser light emitted from the semiconductor laser light source is 0.2 nm / ° C.
- the interference fringe spacing ⁇ is widened by 0.005 times the interference fringe spacing compared to the temperature of 25 ° C.
- the temperature around the semiconductor laser light source used as the laser light source 110 is adjusted to about 41 ° C., it is about 0.005 times the wavelength of the laser beam LB at 25 ° C.
- a long wavelength laser beam LB is emitted.
- the wavelength of the laser light emitted from the laser light source has a temperature dependency as in the semiconductor laser light source, based on the linear expansion coefficient ⁇ of the volume hologram and the temperature dependency K of the wavelength of the laser light
- the temperature of the laser light source is preferably determined.
- a semiconductor laser light source having a temperature dependency in which the wavelength shifts to the longer wavelength side when the temperature rises is exemplified as the HUD light source.
- the temperature dependence is not limited to the characteristic that the wavelength shifts to the longer wavelength side when the temperature rises. If the wavelength of the laser beam emitted from the laser light source has some temperature dependence, the above-described effect can be obtained.
- FIG. 6 is a schematic diagram of a HUD having a temperature adjustment function for a laser light source.
- a HUD having a temperature adjustment function will be described with reference to FIG.
- the HUD 100B shown in FIG. 6 includes the temperature of the volume hologram 200 itself and / or the volume hologram 200 in addition to the laser light source 110, the projection optical system 120, and the volume hologram 200 similar to the HUD 100 described with reference to FIG.
- a temperature sensor 160 that measures the ambient temperature and an adjustment unit 165 for adjusting the temperature of the laser light source 110 are provided.
- the HUD 100B further includes a control unit 130B.
- the control unit 130B is electrically connected to the laser light source 110 and the liquid crystal panel 123 in the same manner as the control unit 130 described with reference to FIG.
- the control unit 130B is also electrically connected to the temperature sensor 160 and the adjustment unit 165.
- the control unit 130B and the adjustment unit 165 are exemplified as adjustment elements.
- the temperature sensor 160 measures the temperature of the volume hologram 200 itself and / or the temperature around the volume hologram 200, and outputs temperature information regarding the measured temperature to the control unit 130B.
- Control unit 130B sets a target temperature for the temperature of laser light source 110 based on the temperature information.
- the adjustment unit 165 adjusts the temperature of the laser light source 110 so that the temperature of the laser light source 110 becomes the target temperature under the control of the control unit 130B.
- FIG. 7 is a schematic diagram of the adjustment unit 165.
- the adjustment unit 165 will be described with reference to FIGS. 6 and 7.
- the adjustment unit 165 includes a Peltier element 166 attached to the laser light source 110 and a heat dissipation plate 167 attached to the Peltier element 166.
- the Peltier element 166 electrically connected to the control unit 130B adjusts the temperature of the laser light source 110 under the control of the control unit 130B.
- control unit 130B can set an appropriate target temperature for the laser light source 110 in substantially real time based on the temperature data from the temperature sensor 160.
- a Peltier element is used as the adjustment unit 165.
- other temperature control elements eg, heaters, fans, compressors
- the temperature of the laser light source is appropriately set based on the linear expansion coefficient ⁇ of the volume hologram and the temperature dependence of the laser light emitted from the laser light source, not limited to the temperature control structure shown in FIGS.
- Other temperature control techniques that can be used may be used.
- FIG. 8 is a schematic diagram of another HUD having a temperature adjustment function for the laser light source.
- a HUD having a temperature adjustment function will be described with reference to FIG.
- the HUD 100C shown in FIG. 8 includes the temperature of the volume hologram 200A itself and / or the periphery of the volume hologram 200A in addition to the light source 150, the projection optical system 120, and the volume hologram 200A similar to the HUD 100A described with reference to FIG.
- the HUD 100C further includes a control unit 130C.
- the control unit 130C is electrically connected to the light source 150 and the liquid crystal panel 123 in the same manner as the control unit 130A described with reference to FIG.
- the control unit 130C is also electrically connected to the temperature sensor 160 and the adjustment units 165R, 165G, and 165B.
- the control unit 130C and the adjustment units 165R, 165G, and 165B are exemplified as adjustment elements.
- the temperature sensor 160 measures the temperature of the volume hologram 200A itself and / or the temperature around the volume hologram 200A, and outputs temperature information regarding the measured temperature to the control unit 130C.
- the controller 130C individually sets target temperatures for the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B based on the temperature information.
- the adjustment units 165R, 165G, and 165B control the red semiconductor laser light source 110R so that the temperatures of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B become the target temperatures, respectively, under the control of the control unit 130C.
- the temperatures of the green semiconductor laser light source 110G and the blue semiconductor laser light source 110B are adjusted.
- the volume hologram 200A includes an interference pattern for diffracting the red laser beam LB (r), an interference pattern for diffracting the green laser beam LB (g), and an interference pattern for diffracting the blue laser beam LB (b). Is recorded.
- the red semiconductor laser light source 110R is a red laser beam having a wavelength substantially equal to the center wavelength of the recording light used for recording the interference fringes for diffracting the red laser light LB (r) under the temperature condition of 25 ° C.
- LB (r) is emitted.
- the green semiconductor laser light source 110G is a green laser light having a wavelength substantially equal to the center wavelength of the recording light used for recording the interference fringes for diffracting the green laser light LB (g) under the temperature condition of 25 ° C.
- the blue semiconductor laser light source 110B is a blue laser beam having a wavelength substantially equal to the center wavelength of the recording light used for recording the interference fringes for diffracting the blue laser light LB (b) under a temperature condition of 25 ° C. LB (b) is emitted.
- the control unit 130C sets, for example, the target temperature of the blue semiconductor laser light source 110B to about 35 ° C. and the target temperature of the green semiconductor laser light source 110G to about 37 ° C.
- the temperature of the red semiconductor laser light source 110R may be set to about 28 ° C.
- the wavelength fluctuation ratios of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) emitted from the light source 150 are all about 0. .001 (see FIG. 5).
- the red semiconductor laser light source 110R and the green semiconductor laser are selected according to the temperature dependence of the wavelengths of the red laser light LB (r), the green laser light LB (g), and the blue laser light LB (b) emitted from the light source 150.
- the target temperatures for the light source 110G and the blue semiconductor laser light source 110B are individually set, the relative shift between the red image, the green image, and the blue image due to temperature fluctuation is reduced. Therefore, the HUD 100C can display a high-quality image.
- the target temperatures for the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B are set so that the wavelength variation ratio is about 0.001.
- the target temperatures for the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B may be set based on other values of the wavelength variation ratio. For example, if the temperature measured by the temperature sensor 160 is relatively high, the target temperatures for the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B may be set higher.
- control unit 130C sets the target temperature of the blue semiconductor laser light source 110B to 47 ° C., sets the target temperature of the green semiconductor laser light source 110G to 51 ° C., and sets the temperature of the red semiconductor laser light source 110R to 31 ° C. May be.
- the control unit 130C may set other target temperature combinations. If the target temperature set by the control unit 130C increases or decreases according to the temperature measured by the temperature sensor 160, it is consumed by adjusting the temperatures of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B. The amount of power is reduced. Therefore, the power consumption of HUD 100C is reduced.
- the control unit 130C determines not only the linear expansion coefficient of the volume hologram 200A but also the center wavelength of the recording light used for recording the interference fringes of the volume hologram 200A and the wavelength of the light emitted from the light source 150 at a predetermined temperature.
- the temperature of the light source 150 is adjusted.
- the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) from the light source 150 are 25 ° C., and the interference fringes of the volume hologram 200A are recorded. Is set to be substantially equal to the center wavelength of the recording light used in the above.
- the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) are shifted from the center wavelength of the recording light used for recording the interference fringes of the volume hologram 200A. If so, the control unit 130C may set the target temperature for the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) at 25 ° C.
- the wavelength of the red laser beam LB (r) emitted from the red semiconductor laser light source 110R under a temperature condition of 25 ° C. is 638 nm, and recording of interference fringes for diffracting the red laser beam LB (r)
- a lower target temperature may be set. That is, the target temperature set for the red semiconductor laser light source 110R is 20 ° C.
- control unit 130C may set a target temperature with respect to red semiconductor laser light source 110R based on 20 ° C.
- the controller 130C can set the target temperature for other semiconductor laser light sources (the green semiconductor laser light source 110G and the blue semiconductor laser light source 110B) according to the same method.
- a semiconductor laser light source is exemplified as a laser light source that emits a laser beam having a temperature dependency.
- a light source that emits light of a wavelength having a similar temperature dependency may be used.
- FIG. 9 is a graph schematically showing the temperature expansion characteristic of the volume hologram and the temperature dependence characteristic of the wavelength of the laser beam.
- the graph shown in FIG. 9 is a graph in which the fluctuation ratio of the interference fringe spacing ⁇ of the volume hologram is added to the graph shown in FIG. 5 as the right vertical axis.
- the temperature expansion characteristic of the volume hologram and the temperature dependence characteristic of the wavelength of the laser beam will be described with reference to FIGS.
- the linear expansion coefficient of the volume hologram 200A is 2 ⁇ 10 ⁇ 4 (/ ° C.) similarly to the above description.
- the wavelength of the red laser light used as recording light for recording interference fringes on the volume hologram 200A is indicated by the symbol “ ⁇ r (nm)” in the following description.
- the wavelength of the green laser light used as the recording light for recording the interference fringes on the volume hologram 200A is indicated by the symbol “ ⁇ g (nm)” in the following description.
- the wavelength of the blue laser light used as recording light for recording interference fringes on the volume hologram 200A is indicated by the symbol “ ⁇ b (nm)” in the following description.
- the temperature dependence of the wavelength of the red laser light LB (r) from the red semiconductor laser light source 110R mounted on the HUD 100C is expressed using the symbol “Kr (nm / ° C.)”.
- the temperature dependence of the wavelength of the green laser light LB (g) from the green semiconductor laser light source 110G mounted on the HUD 100C is expressed using the symbol “Kg (nm / ° C.)”.
- the temperature dependence of the wavelength of the blue laser beam LB (b) from the blue semiconductor laser light source 110B mounted on the HUD 100C is expressed using the symbol “Kb (nm / ° C.)”.
- the linear expansion coefficient of the volume hologram is expressed using the symbol “ ⁇ (/ ° C.)”.
- the interference fringe interval ⁇ is widened by 0.002 times the interference fringe interval compared to 25 ° C. . If the control unit 130C sets the target temperature for the red semiconductor laser light source 110R to 32 ° C., sets the target temperature for the blue semiconductor laser light source 110B to 47 ° C., and sets the target temperature for the green semiconductor laser light source 110G to 51 ° C. In this case, the deviation from the Bragg condition is cancelled.
- the HUD 100C can display a high-quality image.
- the temperature sensor 160 shown in FIG. 8 may be a radiation thermometer, for example.
- the radiation thermometer outputs temperature information regarding the measured temperature to the control unit 130C.
- the temperature measured by the radiation thermometer is reflected in the temperature control of the red semiconductor laser light source 110R, the green semiconductor laser light source 110G, and the blue semiconductor laser light source 110B.
- the temperature of the volume hologram 200A itself or the ambient temperature of the volume hologram 200A may be measured by other measurement methods.
- FIG. 10 is a schematic diagram of a HUD having a function for reducing a relative shift between a red image, a blue image, and a green image.
- a HUD having a function for reducing a relative shift between the red image, the blue image, and the green image will be described with reference to FIGS. 4 and 10.
- the HUD 100D shown in FIG. 10 has substantially the same structure as the HUD 100A described in relation to FIG.
- the HUD 100D includes the volume hologram 200A, the light source 150, the control unit 130A, the dichroic mirrors 151 and 152, and the projection optical system 120, similarly to the HUD 100A described with reference to FIG. For clarity of the drawings, these elements are not shown in FIG. FIG. 10 shows the screen 125 of the projection optical system 120.
- the HUD 100D further includes a reflection hologram 170 disposed between the screen 125 and the volume hologram 200A.
- FIG. 10 shows red laser beams LB (r) and LB (r +) emitted from the screen 125.
- the red laser light LB (r) has the same wavelength as the recording light used for recording the interference fringes of the volume hologram 200A.
- the red laser beam LB (r +) has a wavelength shifted to the long wavelength side by, for example, 5 nm from the red laser beam LB (r).
- the reflection hologram 170 has a characteristic of canceling the wavelength dependence line of the diffraction angle of the volume hologram 200A. As shown in FIG. 10, the red laser beam LB (r) and the red laser beam LB (r +) are incident on different points on the reflection hologram 170. The reflection hologram 170 causes the red laser light LB (r) and the red laser light LB (r +) incident on different points to be incident on substantially the same point on the volume hologram 200A. As a result, the red laser beam LB (r) and the red laser beam LB (r +) are emitted from the volume hologram 200A at substantially the same angle.
- the driver DR can visually recognize the image comfortably without substantially perceiving the positional shift between the images in the virtual image VI.
- the principle described above is similarly applied to blue laser light and green laser light.
- the HUD 100D can display a high-quality image. If a reflection hologram having the above-described characteristics is used, even if the wavelength of the laser beam is temperature-dependent, such as a semiconductor laser light source, the image misalignment is unlikely to occur without temperature adjustment. Become. Therefore, the HUD can display a high-quality image.
- FIG. 11 is a schematic cross-sectional view of the reflection hologram 170.
- the reflection hologram 170 is described with reference to FIGS. 10 and 11.
- the reflection hologram 170 shown in FIG. 11 is a relief hologram. Note that a volume hologram may be used as the reflection hologram 170.
- the 11 includes a laminated resin material 171, 172, 173.
- the resin materials 171, 172, and 173 have substantially the same refractive index.
- Complementary surface reliefs are engraved on the surfaces of the resin materials 171, 172, and 173.
- the surfaces of the resin materials 171, 172, and 173 engraved with the surface relief are in close contact with each other without a gap.
- a reflection coat 174r that reflects the red laser beam LB (r) is provided on the outer surface of the resin material 171.
- a reflective coat 174g that allows the transmission of the red laser beam LB (r) while reflecting the green laser beam LB (g) is provided.
- a reflective coat 174b that allows the red laser beam LB (r) and the green laser beam LB (g) to pass therethrough while reflecting the blue laser beam LB (b). Is provided.
- the reflective coats 174r, 174g, and 174b shown in FIG. 11 are formed, for example, by vapor deposition of a dielectric multilayer film.
- the reflective coats 174r, 174g, and 174b may be formed using other methods.
- the reflective coat 174r may be a metal coat.
- the relief structure of the contact surface between the resin material 171 and the resin material 172 may be a blazed structure formed so that the green laser beam LB (g) can be efficiently diffracted in a desired direction.
- the relief structure of the contact surface between the resin material 172 and the resin material 173 may be a blazed structure formed so that the blue laser beam LB (b) can be efficiently diffracted in a desired direction.
- the relief structure formed on the outer surface of the resin material 171 may also be a blaze structure formed so that the red laser beam LB (r) can be efficiently diffracted in a desired direction.
- characteristics described with reference to FIG. 10 are various relief structures (relief pitch, thickness, angle, etc.) of the resin materials 171, 172, 173. To optimize the dimensional parameters).
- the red laser light LB (r) of the image light IL passes through the reflection coats 174b and 174g and reaches the reflection coat 174r.
- the reflective coat 174r reflects and diffracts the red laser beam LB (r).
- the red laser beam LB (r) is emitted in a desired direction.
- the green laser beam LB (g) of the image light IL passes through the reflection coat 174b and reaches the reflection coat 174g.
- the reflective coat 174g reflects and diffracts the green laser beam LB (g). As a result, the green laser beam LB (g) is emitted in a desired direction.
- the reflection coat 174b reflects and diffracts the blue laser beam LB (b). As a result, the blue laser beam LB (b) is emitted in a desired direction.
- the reflection hologram 170 shown in FIG. 11 is used, as described with reference to FIG. 10, for example, even if the ambient temperature varies, the relative position between the red image, the green image, and the blue image The deviation is cancelled.
- the HUD 100D can display a high-quality image.
- the relief hologram 170 is exemplified by a relief hologram shown in FIG.
- another structure that can compensate the wavelength dependence of the diffraction angle of the volume hologram 200 ⁇ / b> A may be used as the reflection hologram 170.
- FIG. 12 is a schematic cross-sectional view of a windshield that sandwiches a volume hologram. The arrangement of the volume hologram will be described with reference to FIG.
- the vehicle windshield 210E typically includes an inner glass 215 forming an inner surface 211, an outer glass 216 forming an outer surface 212, and an intermediate film 217 disposed between the inner glass 215 and the outer glass 216. And comprising.
- the intermediate film 217 selectively adjusts the wavelength component of external light incident on the vehicle interior.
- the intermediate film 217 has absorption characteristics that absorb infrared rays and ultraviolet rays.
- the volume hologram 200E shown in FIG. 12 is arranged between the inner glass 215 and the intermediate film 217.
- the volume hologram 200E shown in FIG. The volume hologram 200E typically has a characteristic of absorbing light in the infrared region. In many cases, an infrared absorber is added to the intermediate film 217. Therefore, as shown in FIG. 12, if the volume hologram 200E is disposed between the passenger compartment (inner glass 215) and the intermediate film 217, the volume hologram 200E hardly undergoes thermal expansion.
- the arrangement of the volume hologram 200E shown in FIG. 12 reduces the influence of the temperature rise and thermal expansion of the volume hologram 200E caused by infrared rays included in sunlight. If the arrangement of the volume hologram 200E shown in FIG. 12 is applied to the above-described HUDs 100 to 100D, the HUDs 100 to 100D can display high-quality images.
- the temperature of the laser light source is adjusted according to the temperature of the windshield as in the above-described HUDs 100B and 100C, the rise in the temperature of the laser light source is also suppressed as a result of the suppression of the temperature increase of the volume hologram. Therefore, the energy required for temperature adjustment is reduced.
- a light source whose luminous efficiency is reduced under a high temperature environment such as a semiconductor laser light source, the luminous efficiency is hardly reduced due to the temperature rise as a result of suppressing the temperature rise of the volume hologram. Therefore, the energy consumption of HUD is suitably reduced.
- volume 12 is arranged between the inner glass 215 and the intermediate film 217.
- the volume hologram 200E shown in FIG. Alternatively, the volume hologram may be attached to the inner surface 211 of the inner glass 215.
- the volume hologram 200E is less likely to be deteriorated due to ultraviolet rays. Therefore, the arrangement of the volume hologram 200E described with reference to FIG. 12 improves the durability of the HUD.
- FIG. 13 is a schematic diagram of a HUD exemplified as a see-through display according to the second embodiment. The HUD is described with reference to FIGS. 4 and 13.
- the HUD 300 includes a control unit 130A, the dichroic mirrors 151 and 152, and the projection optical system 120 similar to the HUD 100A described with reference to FIG. 4, a red wavelength conversion laser light source 310R, and a green wavelength conversion laser light source.
- the light source 350 including 310G and the blue wavelength conversion laser light source 310B, and the volume hologram 320 attached to the inner surface 211 of the windshield 210 are provided.
- the red wavelength conversion laser light source 310R, the green wavelength conversion laser light source 310G, and the blue wavelength conversion laser light source 310B are electrically connected to the control unit 130A and operate under the control of the control unit 130A.
- the red wavelength conversion laser light source 310R converts the fundamental wave into a harmonic using a wavelength conversion element, and emits red laser light LB (r).
- the green wavelength conversion laser light source 310G converts the fundamental wave into a harmonic using a wavelength conversion element, and emits green laser light LB (g).
- the blue wavelength conversion laser light source 310B converts the fundamental wave into a harmonic using a wavelength conversion element, and emits blue laser light LB (b).
- the HUD 300 is different from the HUD 100A described in relation to FIG. 4 in that a wavelength conversion laser light source is provided as a light source instead of the semiconductor laser light source. Since the description related to the other elements is the same as that of the HUD 100A, the description of the HUD 100A is incorporated in the HUD 300.
- FIG. 14A is a schematic diagram of a green wavelength conversion laser light source 310G.
- the green wavelength conversion laser light source 310G will be described with reference to FIGS. 13 and 14A.
- the following description related to the green wavelength conversion laser light source 310G can be similarly applied to the red wavelength conversion laser light source 310R and the blue wavelength conversion laser light source 310B.
- Green wavelength conversion laser light source 310G includes a semiconductor laser light source 311 for excitation that emits excitation laser light PL, a condensing lens 312, a solid-state laser crystal 313, and a wavelength conversion element 314.
- the excitation laser light PL emitted from the semiconductor laser light source 311 is condensed by the condenser lens 312 and enters the solid-state laser crystal 313.
- the semiconductor laser light source 311 incorporated in the green wavelength conversion laser light source 310G typically has a center wavelength of about 808 nm in accordance with the absorption wavelength of the solid-state laser crystal 313 in order to obtain the green laser light LB (g).
- the excitation laser beam PL that it has is emitted.
- the solid-state laser crystal 313 typically includes YAG (a compound oxide of yttrium (Y) and aluminum (Al) doped with neodymium (Nd)) or YVO 4 (yttrium (Y) and vanadium (V).
- YAG a compound oxide of yttrium (Y) and aluminum (Al) doped with neodymium (Nd)
- YVO 4 yttrium (Y) and vanadium (V).
- a composite oxide may be doped with neodymium (Nd).
- the solid-state laser crystal 313 using YAG or YVO 4 emits a fundamental wave light FL of about 1064 nm.
- the solid-state laser crystal 313 includes an incident surface 315 on which the excitation laser beam PL is incident, and an exit surface 316 opposite to the incident surface 315.
- a resonator is formed between the entrance surface 315 and the exit surface 316.
- the fundamental wave light FL having a wavelength of about 1064 nm oscillates.
- the wavelength conversion element 314 may typically be lithium niobate (LiNbO 3 ) doped with magnesium oxide.
- a polarization inversion structure is formed in the wavelength conversion element 314.
- the fundamental wave light FL incident on the wavelength conversion element 314 is converted into a second harmonic wave having a wavelength of 532 nm corresponding to half the wavelength of the fundamental wave light FL in the wavelength conversion element 314.
- the second harmonic is emitted from the wavelength conversion element 314 as green laser light LB (g).
- the oscillation wavelength of the green laser beam LB (g) is mainly determined by the peak wavelength of the solid-state laser crystal 313.
- the peak wavelength of the solid state laser crystal 313 typically varies only about 0.01 nm / ° C. That is, the wavelength of the green laser beam LB (g) varies only about 0.005 nm / ° C. Therefore, even if the ambient temperature fluctuates, the oscillation wavelength of the green wavelength conversion laser light source hardly fluctuates. If the red wavelength conversion laser light source 310R and the blue wavelength conversion laser light source 310B have the same structure, even if the ambient temperature fluctuates, these oscillation wavelengths will hardly fluctuate.
- the volume hologram 320 expands or contracts as described in connection with the first embodiment.
- the wavelengths of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) incident on the volume hologram 320 hardly change.
- the temperature around the volume hologram 320 rises and the volume hologram 320 expands, the diffraction angles of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) change.
- the HUD 300 can display a high-quality image.
- FIG. 14B is a schematic diagram of a green wavelength conversion laser light source 310G having another configuration.
- the green wavelength conversion laser light source 310G will be described with reference to FIGS. 13 to 14B.
- the following description related to the green wavelength conversion light source 310G can be similarly applied to the red wavelength conversion laser light source 310R and the blue wavelength conversion laser light source 310B.
- FIG. 14B schematically shows a green wavelength conversion laser light source 310G incorporating a fiber laser.
- the green wavelength conversion laser light source 310G includes a semiconductor laser light source 311 for excitation that emits the excitation laser light PL, a condensing lens 312 and a fiber laser 317.
- the excitation laser light PL emitted from the semiconductor laser light source 311 is collected by the condenser lens 312 and enters the fiber laser 317.
- the fiber laser 317 typically has a double clad structure.
- the fiber laser 317 typically includes a core doped with, for example, yttrium (Yb).
- the inner clad portion is typically made of quartz, for example.
- the excitation laser beam PL usually propagates through the inner cladding part.
- the excitation laser light PL propagating through the inner cladding part excites Yb contained in the core.
- a fiber grating 318 is formed in the vicinity of both ends of the fiber laser 317.
- the fiber grating 318 selectively resonates within the core of the fiber laser 317 and is emitted from the fiber laser 317 as the fundamental light FL.
- the green wavelength conversion laser light source 310G includes a wavelength conversion element 314.
- the wavelength conversion element 314 may typically be lithium niobate (LiNbO 3 ) doped with magnesium oxide.
- a polarization inversion structure is formed in lithium niobate (LiNbO 3 ).
- the wavelength conversion element 314 has a green laser beam LB having a wavelength of 532 nm as the second harmonic, as described with reference to FIG. 14A. (G) is generated.
- the green laser beam LB (g) is emitted from the wavelength conversion element 314.
- the wavelength of the fundamental wave light FL emitted from the fiber laser 317 is determined by the period of the fiber grating 318.
- the core of the fiber laser 317 is usually made of quartz, and the linear expansion coefficient of quartz is about 6 ⁇ 10 ⁇ 7 , so the wavelength of the fundamental wave light FL emitted from the fiber laser 317 is Despite the change in ambient temperature, it hardly fluctuates. Since the wavelength of the fundamental wave light FL hardly fluctuates regardless of the fluctuation of the ambient temperature, the wavelength of the green laser light LB (g) emitted as the second harmonic of the fundamental wave light FL is also affected by the fluctuation of the ambient temperature. Despite this, it hardly fluctuates.
- the HUD 300 can display a high-quality image.
- the principle of this embodiment is applied to a see-through display including a light source including n light source elements (n is an integer greater than 1). If the wavelength of the n light source elements hardly fluctuates regardless of the variation of the ambient temperature, the relative misalignment between the images drawn by the light emitted from the n light source elements is the variation of the ambient temperature. Regardless of, it becomes difficult to occur.
- the wavelength of the recording light (laser light) used for recording the interference fringes of the volume hologram 320 for diffracting the red laser light LB (r) is represented by the symbol “ ⁇ r (nm)”.
- the wavelength of the recording light (laser light) used for recording the interference fringes of the volume hologram 320 for diffracting the green laser light LB (g) is represented by the symbol “ ⁇ g (nm)”.
- the wavelength of the recording light (laser light) used for recording the interference fringes of the volume hologram 320 for diffracting the blue laser light LB (b) is represented by the symbol “ ⁇ b (nm)”.
- the wavelength dependency of the red laser beam LB (r) emitted from the red wavelength conversion laser light source 310R is represented by a symbol “Kr (nm / ° C.)”.
- the wavelength dependence of the green laser beam LB (g) emitted from the green wavelength conversion laser light source 310G is represented by the symbol “Kg (nm / ° C.)”.
- the wavelength dependence of the blue laser beam LB (b) emitted from the blue wavelength conversion laser light source 310B is represented by a symbol “Kb (nm / ° C.)”.
- the driver DR can recognize the red image, the green image, and the Little perception of relative displacement between blue images. Therefore, the HUD 300 can display a high-quality image.
- a light source including a solid-state laser light source for generating fundamental light and a light source including a fiber laser for generating fundamental light are illustrated.
- another light source having a configuration in which the wavelength of the fundamental light hardly fluctuates regardless of variations in the ambient temperature may be used as the light source element.
- FIG. 15 is a schematic cross-sectional view of a volume hologram 320 fixed on a base material. The further advantageous effect of this embodiment is demonstrated using FIG.13 and FIG.15.
- FIG. 15 shows a substrate 210B including a flat upper surface 211B to which the volume hologram 320 is fixed.
- FIG. 15 shows a first direction perpendicular to the upper surface 211B and a second direction parallel to the upper surface 211B.
- the linear expansion coefficient of the substrate 210B is represented by the symbol “ ⁇ (/ ° C.)”.
- the linear expansion coefficient of the volume hologram 320 is represented by the symbol “ ⁇ (/ ° C.)”. If the substrate 210B is a glass plate, the linear expansion coefficient ⁇ is typically about 8 ⁇ 10 ⁇ 6 (/ ° C.).
- the linear expansion coefficient ⁇ of the volume hologram 320 is typically about 2 ⁇ 10 ⁇ 4 (/ ° C.).
- the volume hologram 320 is much softer than the substrate 210B such as a glass plate. Therefore, even if the ambient temperature varies, the expansion width or contraction width of the volume hologram 320 in the second direction does not exceed the expansion width or contraction width of the base material 210B in the second direction. However, the volume hologram 320 can freely expand or contract in the first direction.
- the laser beam red laser beam LB ( r) If the angle ⁇ 1 and the wavelength of the green laser beam LB (g) and the blue laser beam LB (b) are not changed, the laser beam is emitted even if the volume hologram 320 expands or contracts in the first direction.
- the angle ⁇ 2 hardly varies. Therefore, if the linear expansion coefficient ⁇ of the base material 210B is smaller than the linear expansion coefficient ⁇ of the volume hologram 320, the angle ⁇ 2 at which the laser beam is emitted from the volume hologram 320 hardly changes even if the ambient temperature fluctuates.
- the HUD 300 can display a high-quality image.
- glass is exemplified as the substrate 210B.
- another material having a linear expansion coefficient ⁇ smaller than the linear expansion coefficient ⁇ of the volume hologram 320 may be used as the substrate 210B.
- the windshield 210 shown in FIG. 13 also serves as a base material. Accordingly, as shown in FIG. 13, the volume hologram 320 attached to the windshield 210 provides the effects described in connection with FIG.
- the temperature dependence of the wavelength of light emitted from the light source is considered.
- the principle of the present embodiment is limited to the temperature dependence of the wavelength of light emitted from the light source. It is applicable without.
- FIG. 16 is a schematic diagram of a HUD exemplified as a see-through display according to the third embodiment. The HUD is described with reference to FIGS. 4 and 16.
- the HUD 400 of the present embodiment includes a red laser light source 410R, a green laser light source 410G, and a blue laser in addition to the dichroic mirrors 151 and 152, the projection optical system 120, and the volume hologram 200A similar to the HUD 100A described with reference to FIG.
- a light source 450 including the light source 410B and a control unit 430 are included.
- the controller 430 is electrically connected to the liquid crystal panel 123, the red laser light source 410R, the green laser light source 410G, and the blue laser light source 410B.
- the liquid crystal panel 123, the red laser light source 410R, the green laser light source 410G, and the blue laser light source 410B operate under the control of the control unit 430.
- the red laser light source 410R, the green laser light source 410G, and the blue laser light source 410B may be the semiconductor laser light sources described in connection with the first embodiment.
- the red laser light source 410R, the green laser light source 410G, and the blue laser light source 410B may be the wavelength conversion laser light source described in connection with the second embodiment.
- the light source 450 may be a combination of a semiconductor laser light source and a wavelength conversion laser light source. Further alternatively, other laser light sources may be used as the light source 450.
- the red laser light source 410R emits red laser light LB (r) under the control of the control unit 430.
- the green laser light source 410G emits the green laser light LB (g) under the control of the control unit 430.
- the blue laser light source 410B emits the blue laser light LB (b) under the control of the control unit 430.
- one of the red laser light source 410R, the green laser light source 410G, and the blue laser light source 410B is exemplified as the first light source element, and the other is exemplified as the second light source element.
- One of the red laser light LB (r), the green laser light LB (g), and the blue laser light LB (b) is exemplified as the first light, and the other is exemplified as the second light.
- FIG. 17 is a schematic diagram of display content displayed by the HUD 400. The display content is described with reference to FIGS. 16 and 17.
- Control unit 430 controls light source 450 and liquid crystal panel 123 to display display content including attention content CT1, speed content CT2, and guidance content CT3. As shown in FIG. 17, the control unit 430 controls the liquid crystal panel 123 to separate the attention content CT1 and the speed content CT2 in the vertical direction by a predetermined distance “W”. In addition, the control unit 430 controls the liquid crystal panel 123 to separate the attention content CT1 and the speed content CT2 from the guidance content CT3 in the horizontal direction, thereby eliminating the overlap therebetween.
- the attention content CT1 is drawn using the red laser beam LB (r).
- the speed content CT2 is drawn using the green laser light LB (g).
- the guidance content CT3 is drawn using the blue laser beam LB (b).
- one of the attention content CT1, the speed content CT2, and the guidance content CT3 is exemplified as the first image, and the other is exemplified as the second image.
- the HUD 400 displays the display content. Therefore, even if the emission angles of the red laser beam LB (r), the green laser beam LB (g), and the blue laser beam LB (b) with respect to the volume hologram 200A are changed according to environmental changes such as changes in the ambient temperature, the operation is performed. The person DR does not perceive changes in the positions of the attention content CT1, the speed content CT2, and the guidance content CT3 as color shifts.
- the attention content CT1 and the speed content CT2 aligned in the vertical direction are separated by a predetermined distance “W”. Therefore, even if the positions of the attention content CT1 and the speed content CT2 relatively change due to the temperature fluctuation, the attention content CT1 and the speed content CT2 are unlikely to overlap. Therefore, the HUD 400 can display an image that is difficult to be visually recognized as a color shift using various types of light source elements. Thus, a high-quality image is provided to the driver DR.
- the HUD may display other content images and / or more or fewer types of images.
- the HUD may display other content images and / or more or fewer types of images.
- the HUD creates display content with four hues, four types of laser light sources are used. If an image is displayed with a hue other than red, green, and blue (for example, yellow), a yellow laser light source may be used as the light source. If a combination of light sources having substantially the same temperature dependency of wavelengths is used, only colors represented by these light sources may be represented by color mixing.
- FIG. 18A is a schematic diagram of a HUD exemplified as a see-through display according to the fourth embodiment. The HUD of the fourth embodiment will be described using FIG. 18A.
- the HUD 500 of this embodiment is attached to a laser light source 510 that emits a laser beam LB, a projection optical system 520 that projects the emitted laser beam LB emitted from the laser light source 510, and an inner surface 211 of the windshield 210.
- the projection optical system 520 includes a MEMS mirror 523 and a screen 525.
- the laser light source 510 is exemplified as a light source that emits light.
- the HUD 500 includes a half-wave plate 540 disposed between the laser light source 510 and the MEMS mirror 523, and a control unit electrically connected to the laser light source 510, the MEMS mirror 523, and the half-wave plate 540, respectively. 550 is further provided.
- the laser light source 510, the MEMS mirror 523, and the half-wave plate 540 operate under the control of the control unit 550.
- the laser light source 510 emits a laser beam LB under the control of the control unit 550.
- the laser beam LB passes through the half-wave plate 540 and is reflected toward the volume hologram 530 by the MEMS mirror 523.
- the half-wave plate 540 modulates the polarization direction of the laser light LB before the MEMS mirror 523 reflects the laser light LB.
- the half-wave plate 540 is exemplified as a modulation element.
- the MEMS mirror 523 operated under the control of the control unit 550 scans the laser beam LB two-dimensionally on the screen 525 and illuminates the screen 525.
- the laser light source 510 modulates the laser light LB in synchronization with the scanning of the MEMS mirror 523 in accordance with the displayed image.
- a desired image is displayed on the screen 525.
- video light IL corresponding to the image drawn on the screen 525 is emitted from the screen 525 to the volume hologram 530.
- the volume hologram 530 diffracts the image light IL toward the driver DR.
- the driver DR visually recognizes the virtual image VI through the windshield 210.
- FIG. 18B is a schematic diagram of a HUD that does not include the half-wave plate 540.
- a HUD that does not include the half-wave plate 540 will be described with reference to FIGS. 18A and 18B.
- the HUD 900 shown in FIG. 18B includes a laser light source 510, a projection optical system 520, a volume hologram 530, and a control unit 950, as with the HUD 500 shown in FIG. 18A.
- HUD 900 does not include half-wave plate 540.
- the control unit 950 controls the MEMS mirror 523 and the laser light source 510 of the projection optical system 520 and does not control the half-wave plate 540.
- the operation of HUD 900 is similar to that of HUD 500, except for the operation of half-wave plate 540 described with reference to FIG. 18A.
- FIG. 19A is a schematic view of an image drawn on the screen 525 by the HUD 900.
- FIG. 19B is a schematic diagram of a virtual image VI visually recognized by the driver DR. The effect of the half-wave plate 540 is described with reference to FIGS. 2B and 18A to 19B.
- the laser light source 510 may be, for example, a semiconductor laser light source. It is known that the wavelength of laser light emitted from a semiconductor laser light source varies depending on the power of the laser light.
- Examples of the semiconductor laser light source include a red semiconductor laser light source that emits red laser light having an active layer having a composition composed of aluminum (Al), gallium (Ga), indium (In), and phosphorus (p).
- a red semiconductor laser light source typically has a power dependency of about 0.005 nm / mW.
- the image shown in FIG. 19A includes a low luminance area LBA drawn by a low luminance laser beam and a high luminance area HBA drawn by a high luminance laser beam.
- the low luminance area LBA and the high luminance area HBA are alternately arranged.
- the wavelength of the laser light that draws the high brightness area HBA is longer than the wavelength of the laser light that draws the low brightness area LBA in accordance with the above-described characteristics of the semiconductor laser light source.
- the position of the high luminance area HBA is shifted with respect to the low luminance area LBA.
- the relative moving direction (vertical direction) of the low luminance area LBA and the high luminance area HBA in the virtual image VI is determined by the relationship between the incident angle and the outgoing angle of the laser beam LB under the Bragg condition shown in FIG. 2B. It is done. For example, as shown in FIG. 2B, if the angle ⁇ 1 incident on the volume hologram is smaller than the angle ⁇ 2 emitted from the volume hologram, the longer the wavelength (the higher the luminance), the larger the angle ⁇ 2 the laser beam LB. Exits. Conversely, if the angle ⁇ 1 is smaller than the angle ⁇ 2, the laser beam LB is emitted at an angle smaller than the angle ⁇ 2 as the wavelength is longer (the luminance is higher).
- the HUD 500 shown in FIG. 19A includes the half-wave plate 540 disposed between the laser light source 510 and the MEMS mirror 523 as described above.
- the half-wave plate 540 operates under the control of the control unit 550.
- the laser light source 510 outputs single-polarized laser light LB in a predetermined direction with the same power for image formation.
- the control unit 550 rotates the half-wave plate 540 according to the image data to be displayed and the scanning position of the MEMS mirror 523, and modulates the polarization direction of the laser beam LB that passes through the half-wave plate 540.
- the half-wave plate 540 disposed immediately before the MEMS mirror 523 sets the polarization direction of the laser light LB in a direction perpendicular to the paper surface of FIG. 18A.
- the laser beam LB is incident on the volume hologram 530 as S-polarized light.
- Volume holograms generally achieve high diffraction efficiency when S-polarized light is incident, but have low diffraction efficiency for P-polarized light. Therefore, only the portion incident as S-polarized light is brightly lit.
- the control unit 550 sets the angle of the half-wave plate 540 so that the half-wave plate 540 sets the polarization direction of the laser beam LB vertically in the plane of FIG. 18A, the laser beam LB The light is incident on the hologram 530 as P-polarized light. As a result, the portion where the P-polarized light is incident becomes dark.
- the controller 550 appropriately adjusts the angle of the half-wave plate 540, the ratio of the P-polarized light and the S-polarized light of the laser light LB incident on the volume hologram 530 is adjusted, and an image expressed in an arbitrary gradation is obtained. Is displayed.
- the wavelength of the laser light LB incident on the volume hologram 530 is also substantially constant. Therefore, the image shift due to the luminance difference described with reference to FIG. 19B is less likely to occur.
- the laser beam is scanned in a dotted manner using a scanning optical system such as a MEMS mirror, and an image with little image shift due to a luminance difference is displayed. Therefore, the HUD 500 can display a high quality image.
- a half-wave plate 540 is exemplified as a modulation element that adjusts the polarization direction.
- another optical element that can adjust the polarization direction of the laser light at an arbitrary timing may be used as the modulation element.
- a semiconductor laser is exemplified as a light source that emits laser light whose wavelength varies according to the output. If a light source having similar characteristics is used, a high-quality image is displayed according to the principle of this embodiment.
- FIG. 20 is a schematic diagram of another HUD exemplified as the see-through display of the fourth embodiment. Another HUD of the fourth embodiment will be described with reference to FIGS. 18A and 20.
- a HUD 500A shown in FIG. 20 includes a half-wave plate 540 in addition to a laser light source 510, a projection optical system 520, a volume hologram 530, a half-wave plate 540 and a control unit 550 similar to the HUD 500 shown in FIG. 18A. And a MEMS mirror 523, a polarizing plate 545 is provided.
- the polarizing plate 545 absorbs or reflects the vertically polarized component in FIG.
- the polarizing plate 545 allows transmission of a polarization component in a direction perpendicular to the paper surface of FIG.
- the laser beam LB enters the volume hologram 530 as S-polarized light.
- the driver DR can visually recognize an image with high luminance and little image shift due to the luminance difference.
- the HUD 500A can display a high-quality image.
- the frame image displayed by the see-through display according to the fifth embodiment is formed using time-divided subframes.
- the see-through display reduces image displacement by adjusting the luminance for each subframe.
- FIG. 21A is a schematic diagram of a frame image drawn on the screen 525 by the HUD 900 shown in FIG. 18B.
- FIG. 21B is a schematic diagram of a virtual image VI corresponding to the frame image shown in FIG. 21A.
- the problems included in the HUD 900 will be described with reference to FIGS. 18B, 21A, and 21B.
- FIG. 21A shows a high luminance point HBP and a low luminance point LBP displayed on the screen 525.
- the gradation of the high luminance point HBP is 230 with 8 bits.
- the gradation of the low luminance point LBP is 80 with 8 bits.
- the HUD 900 drives the laser light source 510 at a desired brightness at each scanning position in order to draw one frame image. If a semiconductor laser light source is used as the laser light source 510, the wavelength of the semiconductor laser light source varies depending on the power as described above. Therefore, as shown in FIG. 21B, in the virtual image VI, the high luminance point HBP The positional deviation amount is larger than the positional deviation amount of the low luminance point LBP. Therefore, the relative positions of the high luminance point HBP and the low luminance point LBP are shifted.
- FIG. 22 is a schematic diagram of a HUD exemplified as the see-through display of this embodiment.
- the HUD of this embodiment will be described with reference to FIGS. 18B and 22.
- the HUD 600 of this embodiment is electrically connected to the laser light source 510 and the MEMS mirror 523 in addition to the laser light source 510, the projection optical system 520, and the volume hologram 530 similar to the HUD 900 described with reference to FIG. 18B.
- a control unit 650 is provided.
- the laser light source 510 and the MEMS mirror 523 operate under the control of the control unit 650, and form a one-frame image using a plurality of time-divided subframes.
- FIG. 23A is a timing chart schematically showing a lighting pattern of the laser light source 510 of the HUD 900.
- FIG. 23B is a timing chart schematically showing a lighting pattern of the laser light source 510 of the HUD 600. Differences in the lighting pattern of the laser light source 510 will be described with reference to FIGS. 18B and 21A to 23B.
- the control unit 650 of the HUD 600 divides one frame into a plurality of subframes and controls the laser light source 510 as shown in FIG. 18B. As a result, the relative difference in the amount of positional deviation between the high luminance point HBP and the low luminance point LBP is reduced.
- one frame is divided into four subframes (subframe 1, subframe 2, subframe 3, subframe 4).
- the MEMS mirror 523 scans the entire surface of the screen 525 once in one subframe.
- the gradation of the high luminance point HBP is 230 with 8 bits.
- conversion represented by the following Equation 6 is possible.
- control unit 650 turns on laser light source 510 at a gradation of 256, and lights up at a gradation of 152 in subframe 4. .
- the lighting time of the high luminance point HBP per subframe is 1 ⁇ 4 of the lighting time of the high luminance point HBP shown in FIG. 23A. Therefore, the luminance of the high luminance point HBP per frame is equal between FIG. 23A and FIG. 23B.
- the gradation of the low luminance point LBP is 8 bits and 80.
- the conversion expressed by the following Equation 7 is possible for the total gradation of the low luminance point LBP obtained by four scans.
- the luminance of the low luminance point LBP per frame is the same between FIG. 23A and FIG. 23B.
- the laser light source 510 when the laser light source 510 is turned on during the period from the sub-frame 1 to the sub-frame 3, the laser light source 510 is lit only with 256 gradations. Therefore, during the period from subframe 1 to subframe 3, the relative position of the point (high luminance point HBP and / or low luminance point LBP) in the virtual image VI does not vary at any gradation. Thus, if one frame is divided into a plurality of sub-frames, the time during which the laser light source 510 is lit at the intermediate gradation is shortened, and the relative position shift in the virtual image VI caused by the gradation difference is appropriate. Reduced to Thus, the HUD 600 can display a high-quality image.
- the amount of light emitted from the laser light source 510 between the subframes 1 to 3 is the maximum value for displaying the high luminance point HBP.
- the light amount emitted from the laser light source 510 in the subframe 1 is set to the maximum value, and the light amount emitted from the laser light source 510 in the subframe 2 and the subframe 3 is “0”. "Is set.
- the subframe in which the light amount emitted from the laser light source 510 is set to the maximum value or 0 may be arbitrarily set. In at least one of the plurality of subframes, if the amount of light emitted from the laser light source 510 is set to the maximum value or 0, the displayed image is less likely to be misaligned.
- one frame is divided into four subframes.
- a frame may be divided into less than 4 or more than 4 subframes. As the number of divisions per frame increases, the effect of reducing the relative position shift becomes more prominent.
- the HUD 600 includes a single light source.
- the HUD may include a plurality of laser light sources that emit laser beams having different wavelengths.
- a semiconductor laser light source is exemplified as the laser light source 510.
- the HUD may comprise a light source having similar wavelength-output power characteristics. Even in this case, the above-described effect of reducing the relative position shift is brought about.
- a laser light source is exemplified as the light source or the light source element.
- other light sources eg, LEDs
- the principle of the series of embodiments described above is preferably applied as long as the light source has characteristics similar to the wavelength characteristics of the laser light source described above.
- the embodiment described above mainly includes the following configuration.
- a see-through display having the following configuration is less likely to cause a decrease in luminance, a luminance distribution, and a deterioration in color distribution due to variations in light source wavelength, color shift due to wavelength fluctuations, and a decrease in diffraction efficiency. Therefore, a see-through display having the following configuration can display a high-quality image with almost no deterioration in image quality.
- the see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, a volume hologram that deflects light projected from the projection optical system, and
- the volume hologram has a linear expansion coefficient of ⁇ (/ ° C.) and interference fringes recorded with recording light having a wavelength of ⁇ (nm), and the wavelength of the light emitted from the light source is , K (nm / ° C.), and the wavelength ⁇ (nm) and the temperature dependency K (nm / ° C.) satisfy the relationship 0 ⁇ K / ⁇ ⁇ 2 ⁇ . .
- the projection optical system projects light emitted from the light source.
- a volume hologram that deflects light projected from the projection optical system has a linear expansion coefficient of ⁇ (/ ° C.) and interference fringes recorded with recording light having a wavelength of ⁇ (nm).
- the wavelength of light emitted from the light source has a temperature dependence of K (nm / ° C.). Since the wavelength ⁇ (nm) and the temperature dependence K (nm / ° C.) satisfy the relationship of 0 ⁇ K / ⁇ ⁇ 2 ⁇ , the deviation from the Bragg condition due to temperature fluctuation is reduced. Therefore, image quality deterioration such as a shift in the display position of an image due to a variation in diffraction angle and a decrease in luminance due to a decrease in diffraction efficiency is less likely to occur.
- the light source includes n (n is an integer greater than 1) light source elements, and the plurality of light source elements emit light having wavelengths ⁇ 1, ⁇ 2,..., ⁇ n at a predetermined temperature.
- the interference fringes are formed using recording light having wavelengths ⁇ 1, ⁇ 2,..., ⁇ n in order to diffract light having wavelengths ⁇ 1, ⁇ 2,.
- the difference value between the maximum value and the minimum value of ⁇ 1- ⁇ 1) / ⁇ 1, ( ⁇ 2- ⁇ 2) / ⁇ 2,... ( ⁇ n ⁇ n) / ⁇ n is preferably 0.005 or less.
- the light source includes n (n is an integer greater than 1) light source elements.
- the plurality of light source elements emit light having wavelengths ⁇ 1, ⁇ 2,..., ⁇ n at a predetermined temperature.
- the interference fringes are formed using recording light having wavelengths ⁇ 1, ⁇ 2,..., ⁇ n in order to diffract light having wavelengths ⁇ 1, ⁇ 2,. Since the difference value between the maximum and minimum values of ( ⁇ 1- ⁇ 1) / ⁇ 1, ( ⁇ 2- ⁇ 2) / ⁇ 2,... ( ⁇ n- ⁇ n) / ⁇ n is 0.005 or less, ⁇ 1, A relative shift between images drawn using light of wavelengths ⁇ 2,..., ⁇ n is less likely to be perceived by the viewer.
- the see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, and a volume hologram that deflects light projected from the projection optical system;
- An adjustment element for adjusting the temperature of the light source, and the wavelength of the light emitted from the light source has temperature dependence, and the volume hologram has a linear expansion coefficient of ⁇ and a center wavelength of ⁇ . Interference fringes recorded with recording light, and the adjusting element adjusts the temperature of the light source based on the linear expansion coefficient ⁇ and the center wavelength ⁇ of the recording light.
- the projection optical system projects light emitted from the light source.
- a volume hologram that deflects light projected from the projection optical system has a linear expansion coefficient of ⁇ and interference fringes recorded with recording light having a center wavelength of ⁇ .
- the adjustment factor that adjusts the temperature of the light source adjusts the temperature of the light source based on the linear expansion coefficient ⁇ and the central wavelength ⁇ of the recording light. It is difficult for image quality deterioration such as a decrease in luminance due to a decrease in image quality to occur.
- the light source includes a plurality of light source elements, the plurality of light source elements respectively emit light having different wavelengths, and the adjustment element individually sets a target temperature for each of the plurality of light source elements. It is preferable to set and adjust the temperatures of the plurality of light source elements so as to achieve the target temperature.
- the light source includes a plurality of light source elements.
- the plurality of light source elements respectively emit light having different wavelengths.
- the adjustment element sets the target temperature individually for each of the plurality of light source elements, and adjusts the temperature of each of the plurality of light source elements so as to be the target temperature. Therefore, the adjustment elements are drawn using light of different wavelengths. A relative shift between images is less likely to be perceived by the viewer.
- the adjustment element adjusts the temperature of the light source based on the wavelength of light emitted from the light source at a predetermined temperature in addition to the linear expansion coefficient ⁇ and the center wavelength ⁇ .
- the adjustment element adjusts the temperature of the light source based on the wavelength of light emitted from the light source at a predetermined temperature in addition to the linear expansion coefficient ⁇ and the center wavelength ⁇ .
- Image quality deterioration such as a decrease in luminance due to a shift in display position and a decrease in diffraction efficiency.
- the see-through display further includes a temperature sensor that measures at least one of a temperature of the volume hologram and a temperature around the volume hologram, and the adjustment element is based on the temperature measured by the temperature sensor, It is preferable to set a target temperature.
- the temperature sensor measures at least one of the temperature of the volume hologram and the temperature around the volume hologram. Since the adjustment element sets the target temperature based on the temperature measured by the temperature sensor, image quality degradation such as a shift in the display position of the image due to fluctuations in the diffraction angle and a decrease in luminance due to a decrease in diffraction efficiency occurs. It becomes difficult.
- a see-through display includes a light source including n (n is an integer greater than 1) light source elements that emit light, and a projection optical system that projects the light emitted from the light source.
- Each of the wavelengths of light diffracted by the fringes has temperature dependence of K1 (nm / ° C.), K2 (nm / ° C.),..., Kn (nm / ° C.), and K1 / ⁇ 1, K2 / ⁇ 2 ...
- the difference value between the maximum and minimum values of Kn / ⁇ n is Characterized in that it is 0.0001 or less.
- the projection optical system projects light emitted from a light source including n light source elements that emit light.
- the volume hologram deflects light projected from the projection optical system.
- the volume hologram has interference fringes formed using recording lights having wavelengths of ⁇ 1, ⁇ 2,..., ⁇ n in order to diffract light emitted from n light source elements.
- the wavelength of light emitted from each of the n light source elements has temperature dependency of K1 (nm / ° C.), K2 (nm / ° C.),..., Kn (nm / ° C.). Since the difference value between the maximum value and the minimum value of K1 / ⁇ 1, K2 / ⁇ 2,... Kn / ⁇ n is 0.0001 or less, each is formed using light emitted from n light source elements. The relative shift between the images to be displayed becomes difficult to perceive.
- the see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, and a volume hologram that deflects light projected from the projection optical system.
- the light source includes: a first light source element that emits first light having a first wavelength; and a second light source element that emits second light having a wavelength different from the first wavelength.
- the first image drawn by is displayed at a position separated from the second image drawn by the second light.
- the projection optical system projects light emitted from the light source.
- the volume hologram deflects light projected from the projection optical system.
- the light source includes a first light source element that emits first light having a first wavelength and a second light source element that emits second light having a wavelength different from the first wavelength. Since the first image drawn by the first light is displayed at a position separated from the second image drawn by the second light, color misregistration is hardly perceived.
- the see-through display includes a light source that emits light, a projection optical system that projects light emitted from the light source, and a volume hologram that deflects light projected from the projection optical system. And the projection optical system modulates the polarization direction of the light from the light source before the MEMS mirror reflects the light emitted from the light source. And a modulation element.
- the projection optical system projects light emitted from the light source.
- the volume hologram deflects light projected from the projection optical system.
- the projection optical system includes a MEMS mirror that reflects light from the light source, and a modulation element that modulates the polarization direction of the light from the light source before the MEMS mirror reflects the light emitted from the light source. The shift becomes difficult to occur.
- the see-through display is a light source that emits light, a projection optical system that projects light emitted from the light source, and forms a frame image, and is projected from the projection optical system A volume hologram for deflecting light, wherein the projection optical system includes a MEMS mirror, and the frame image is formed using a plurality of time-divided subframes, and at least one of the plurality of subframes.
- the light quantity emitted from the light source is 0 or a maximum value.
- the projection optical system including the MEMS mirror projects the light emitted from the light source to form a frame image.
- the volume hologram deflects light projected from the projection optical system.
- a frame image is formed using a plurality of time-divided subframes. The amount of light emitted from the light source when at least one of the plurality of sub-frames is displayed is 0 or the maximum value, so that it is difficult to perceive a relative shift in the image display position.
- the light source preferably includes a semiconductor laser light source.
- the light source includes a semiconductor laser light source. Even if the wavelength of the laser light from the semiconductor laser light source fluctuates, it is difficult to perceive the deviation of the image display position.
- a head-up display mounted on a vehicle having a windshield interposing an intermediate film that selectively adjusts a wavelength component of light incident on a vehicle interior is the see-through display described above.
- the volume hologram is arranged between the vehicle compartment and the intermediate film.
- a head-up display mounted on a vehicle having a windshield interposing an intermediate film for selectively adjusting the wavelength component of light incident on the vehicle interior includes the above-described see-through display. Since the volume hologram is disposed between the vehicle compartment and the intermediate film, the volume hologram characteristic change is less likely to occur due to light incident on the vehicle compartment.
- the principle of this embodiment hardly causes a color shift or a decrease in diffraction efficiency due to a change in ambient temperature. Therefore, image quality deterioration such as luminance spots and color spots of the image is less likely to occur. Therefore, the principle of this embodiment is suitably applied to various see-through displays such as HUD and HMD.
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Abstract
Description
図1は、第1実施形態に従うシースルーディスプレイとして例示されるヘッドアップディスプレイ(以下、HUDと称される)の概略図である。図1を用いて、ヘッドアップディスプレイが説明される。
図1に概略的にHUD100は、例えば、自動車に搭載される。図1には、自動車のフロントガラス210が示されている。フロントガラス210は、車室の内側境界を規定する内面211と、内面211とは反対側の外面212と、を含む。
図1を用いて、本実施形態のHUD100の動作が説明される。
図2Aは、干渉縞の形成工程下にある体積ホログラム200の概略図である。図2Bは、干渉縞の形成の後にレーザ光LBが入射された体積ホログラム200の概略図である。図1乃至図2Bを用いて、体積ホログラムの回折原理が説明される。
HUD100の周囲の温度の変化が、体積ホログラム200の回折に与える影響が説明される。
0≦K/Λ≦2α
(λr-Λr)/Λr
(λg-Λg)/Λg
(λb-Λb)/Λb
HUD100は、レーザ光源110の温度を調整する調整要素を備えてもよい。同様に、HUD100Aは、赤色半導体レーザ光源110R、緑色半導体レーザ光源110G及び青色半導体レーザ光源110Bの温度をそれぞれ調整する調整要素を備えてもよい。
0≦Kn/Λn≦2α(n=r、g、b)
図12は、体積ホログラムを挟持するフロントガラスの概略的な断面図である。図12を用いて、体積ホログラムの配置が説明される。
図13は、第2実施形態に従うシースルーディスプレイとして例示されるHUDの概略図である。図4及び図13を用いて、HUDが説明される。
第1実施形態の原理では、光源から出射される光の波長の温度依存性が考慮されているが、本実施形態の原理は、光源から出射される光の波長の温度依存性に限定されることなく適用可能である。
図18Aは、第4実施形態のシースルーディスプレイとして例示されるHUDの概略図である。図18Aを用いて、第4実施形態のHUDが説明される。
第5実施形態に従うシースルーディスプレイが表示するフレーム画像は、時分割されたサブフレームを用いて形成される。シースルーディスプレイは、サブフレームごとの輝度調整により、画像の位置ずれを低減する。
230×4=256×3+152
80×4=256+64
Claims (12)
- 光を発する光源と、
該光源から発せられた光を投射する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、を備え、
該体積ホログラムは、α(/℃)の線膨張係数と、Λ(nm)の波長の記録光で記録された干渉縞と、を有し、
前記光源から発せられた光の波長は、K(nm/℃)の温度依存性を有し、
前記波長Λ(nm)及び前記温度依存性K(nm/℃)は、0≦K/Λ≦2αの関係を満たすことを特徴とするシースルーディスプレイ。 - 前記光源は、n個(nは1より大きい整数)の光源要素を含み、
該複数の光源要素は、所定の温度において、λ1、λ2、・・・、λnの波長の光を出射し、
前記干渉縞は、前記λ1、λ2、・・・、λnの波長の光をそれぞれ回折するために、Λ1、Λ2、・・・、Λnの波長の記録光を用いて形成され、
(λ1-Λ1)/Λ1、(λ2-Λ2)/Λ2、・・・(λn-Λn)/Λnの最大値と最小値との間の差分値は、0.005以下であることを特徴とする請求項1に記載のシースルーディスプレイ。 - 光を発する光源と、
該光源から発せられた光を投射する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、
前記光源の温度を調整する調整要素と、を備え、
前記光源から発せられた光の波長は、温度依存性を有し、
該体積ホログラムは、αの線膨張係数と、Λの中心波長の記録光で記録された干渉縞と、を有し、
前記調整要素は、前記線膨張係数αと前記記録光の中心波長Λとに基づき、前記光源の温度を調整することを特徴とするシースルーディスプレイ。 - 前記光源は、複数の光源要素を含み、
前記複数の光源要素は、異なる波長の光をそれぞれ発し、
前記調整要素は、前記複数の光源要素それぞれに対して、個別に目標温度を設定し、該目標温度となるように前記複数の光源要素の温度をそれぞれ調整することを特徴とする請求項3に記載のシースルーディスプレイ。 - 前記調整要素は、前記線膨張係数α及び前記中心波長Λに加えて、前記光源が所定温度において発する光の波長に基づき、前記光源の温度を調整することを特徴とする請求項4に記載のシースルーディスプレイ。
- 前記体積ホログラムの温度及び前記体積ホログラムの周囲の温度のうち少なくとも一方を測定する温度センサを更に備え、
前記調整要素は、前記温度センサが測定した温度に基づき、前記目標温度を設定することを特徴とする請求項4に記載のシースルーディスプレイ。 - 光を発するn個(nは1より大きい整数)の光源要素を含む光源と、
該光源から発せられた光を投射する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、を備え、
該体積ホログラムは、前記n個の光源要素から発せられる光をそれぞれ回折するために、Λ1、Λ2、・・・、Λnの波長の記録光を用いて形成された干渉縞を有し、
前記n個の光源要素から発せられ、前記Λ1、Λ2、・・・、Λnの波長の記録光を用いて形成された干渉縞によって回折される光の波長それぞれは、K1(nm/℃)、K2(nm/℃)、・・・、Kn(nm/℃)の温度依存性を有し、
K1/Λ1、K2/Λ2、・・・Kn/Λnの最大値と最小値との間の差分値は、0.0001以下であることを特徴とするシースルーディスプレイ。 - 光を発する光源と、
該光源から発せられた光を投射する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、を備え、
前記光源は、第1波長の第1光を発する第1光源要素と、前記第1波長と異なる波長の第2光を発する第2光源要素と、を含み、
前記第1光によって描かれる第1画像は、前記第2光によって描かれる第2画像から離間した位置に表示されることを特徴とするシースルーディスプレイ。 - 光を発する光源と、
該光源から発せられた光を投射する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、を備え、
前記投射光学系は、前記光源からの光を反射するMEMSミラーと、該MEMSミラーが前記光源から発せられた光を反射する前に、前記光源からの光の偏光方向を変調する変調要素と、を含むことを特徴とするシースルーディスプレイ。 - 光を発する光源と、
該光源から発せられた光を投射し、フレーム画像を形成する投射光学系と、
該投射光学系から投射された光を偏向する体積ホログラムと、を備え、
前記投射光学系は、MEMSミラーを含み、
前記フレーム画像は、時分割された複数のサブフレームを用いて形成され、
前記複数のサブフレームのうち少なくとも1つにおいて、前記光源が発する光の光量は、0又は最大値であることを特徴とするシースルーディスプレイ。 - 前記光源は、半導体レーザ光源を含むことを特徴とする請求項1乃至10のいずれか1項に記載のシースルーディスプレイ。
- 車室内に入射する光の波長成分を選択的に調整する中間膜が介在されたフロントガラスを有する車両に搭載されたヘッドアップディスプレイであって、
請求項1乃至11のいずれか1項に記載のシースルーディスプレイを備え、
前記体積ホログラムは、前記車室と前記中間膜との間に配設されることを特徴とするヘッドアップディスプレイ。
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CN102472894A (zh) | 2012-05-23 |
JPWO2011132406A1 (ja) | 2013-07-18 |
US8934159B2 (en) | 2015-01-13 |
CN102472894B (zh) | 2015-01-28 |
US20120099170A1 (en) | 2012-04-26 |
JP5793639B2 (ja) | 2015-10-14 |
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