JPH04198980A - Holographic headup display - Google Patents

Abstract

PURPOSE:To form a holographic headup display without a noise by forming a hologram by making signal light and reference light which aremade incident on a hologram dry plate incident nearly at the angle of polarization at the time of forming the hologram. CONSTITUTION:At the time of forming the hologram, the signal light S and the reference light R which the made incident on the hologram dry plate 1 are made incident nearly at the angle of polarization. Therefore, reflection is not caused and the signal light S and the reference light R which are made incident are nearly perfectly transmitted through a substrate, so that ghost hologram caused from five types shown by Figure is prevented from occurring. Thus, the image without the noise is visually recognized when the hologram is used as the holographic headup display.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention reflects the displayed image of a display device that displays driving information such as vehicle speed toward the driver's seat side using a hologram having concave mirror characteristics, and displays the above-mentioned information within the field of view. The present invention relates to a holographic head-up display that displays an enlarged display image of a device at a distance.

[Conventional technology]

Conventionally, the manufacturing method of holograms having concave mirror characteristics used in holographic head-up displays, etc. is as shown in FIG. One part is reflected by a mirror 5 and further diverged by a lens 8, and the reference light R is irradiated onto the surface of a hologram dry plate 1 made of a transparent substrate coated with mammography, and the other part is reflected by a mirror 4 and further diverged by a lens. 6, the signal light S is made into a parallel wave by a large lens 7, and is irradiated onto the back surface of the hologram dry plate 1 as a signal light S. When viewed from the side of the reference beam R, which is a diverging beam, the hologram recorded by this method has a curvature R (=2L) that depends on the distance ML to the hologram dry plate 1 during recording for a specific wavelength band. Acts as a concave mirror.

When the hologram 1 obtained in this way is used in a head-up display of a vehicle, an aircraft, etc., as shown in FIG. When placed inside the hologram 1, an enlarged virtual image P' is observed behind the hologram 1 when viewed from the viewpoint 9. Therefore, the driver who is looking at a distant external scene can visually recognize the displayed image on the display device or the like with less movement of the line of sight and focus.

However, when viewed from viewpoint 9, in addition to this virtual image P', there is a second
Specular reflection images P, , P2 shown in the figure are observed. This is because the displayed image P is reflected by the front and back surfaces of the substrate of the hologram l and reaches the viewpoint 9, and prisms are attached to both sides of the substrate to create a specularly reflected image P3. This can be prevented by letting Pz escape so that it does not overlap with the virtual image P', or by applying an AR (anti-reflection) coating.

In addition, as shown in FIG. 3, many images are observed from the viewpoint 9. These images are caused by the fact that when recording concave mirror characteristics on the hologram dry plate 1, the signal light S and reference light R are reflected on the front and back surfaces of the substrate, forming unnecessary holograms (hereinafter referred to as ghost holograms). This is visible as noise and becomes an eyesore.

This ghost hologram will be explained in more detail.

Usually, the hologram dry plate 1 is composed of a transparent substrate B and an emulsion layer E, as shown in FIG. 4(a).
When parallel light represented by a ray I is incident on the emulsion layer E from the side opposite to the emulsion layer E, a part of the ray I is reflected at the boundary b' between the substrate B and the outside air, and the rest travels inside the substrate B and passes through the emulsion layer. A part of the reflected light r is reflected at the boundary b' between E and the outside air and becomes reflected light r, and a part of this reflected light r is further reflected again at the boundary b'' and becomes reflected light r'. By repeating this process, the light undergoes multiple reflections within the dry plate. Note that the reflection of light at the boundary between the substrate B and the emulsion layer E can be ignored in the case of ordinary silver salt dry plates.

This kind of reflection situation depends on the polarization direction of the incident light, but
For example, if the refractive index of substrate B is n = 1.5 and the incident angle is 60° or less with non-polarized light, the reflectance will be 10% or less,
Since the intensity of the multiple reflected lights r' and r'' is sufficiently weak, there is no need to consider them as a cause of the ghost hologram.

Furthermore, the same thing can be said for the case where light is incident from the emulsion layer E side of the hologram dry plate 1, as shown in FIGS.

From these facts, five types as shown in FIGS. 5(a) to 5(e) can be considered as causes of ghost holograms.

That is, in the mold shown in FIG. 5(a), the reference light R incident on the substrate in the hologram forming apparatus shown in FIG. The light that forms a hologram through interference with the hologram becomes a specular reflection hologram, and in the apparatus shown in FIG. 3, a specular reflection image Pa is visible from a viewpoint 9. Figure 5(b)
In the type shown in , the signal light S incident on the substrate is reflected on the substrate surface, and the reflected light S' interferes with the signal light S that comes immediately after, resulting in light that forms a hologram. It becomes a reflection type hologram, and a regular reflection image Pb shown in FIG. 3 is visually recognized. The type shown in FIG.
Since the relationship between the original signal light S and the reference light R is reversed in the hologram created by like,
The reduced image Pc is visually recognized in front of the regular reflection images Pa and Pb. Figure 5(d) shows the reflected light S of the reference light R and the signal light S.
The transmission hologram formed by ' becomes a convex lens with a focal length of 1, and when viewed from the back side of the hologram l in FIG. 3, an enlarged virtual image of the display image P can be observed behind the image P. In this case, the back surface b of the substrate of the hologram I (see Fig. 4)
When the reflectance of the substrate is high or the surroundings are extremely dark, this enlarged virtual image is visible from the viewpoint 9 as an enlarged virtual image Pd reflected by the back surface b of the substrate. Fig. 5(e) shows the reference light R.
The transmission hologram formed by the reflected light R' and the signal light S forms a convex lens with a focal length of 1, and is visually recognized as an enlarged virtual image Pe similar to that shown in FIG. 5(d).

In order to prevent the formation of these ghost holograms, when forming hologram 1, an anti-reflection coating is applied to the back surface of the substrate, the entire substrate is immersed in index matching liquid to prevent surface reflections, or silicone oil is interposed. Techniques have been proposed in which the Cacher glass and the emulsion surface are brought into close contact with each other, and furthermore, an AR coating is applied to the side opposite to the contact surface to prevent surface reflection of the cover glass.

[Problems to be Solved by the Invention] However, since the above-mentioned AR coat can only be used on the back side of the substrate, the problem shown in FIG. 5(a).

Although the situations shown in (C) and (e) can be avoided, the situations shown in FIGS. 5(b) and (d) cannot be prevented. Also, for the method using silicone oil, see Figure 5■)
, (C), and (d) can be avoided, but it is difficult to hold the dry plate during exposure, and there is concern that it will affect the yield. In addition, the process of removing silicone oil after exposure will be increased, and the process of removing silicone oil will be difficult. The problem is the effect of the chemicals used on the hologram.

Therefore, the present invention utilizes the reflectance characteristics depending on the polarization direction of light when forming a hologram to form a hologram under conditions where there is no surface reflection, and uses the hologram to provide a noise-free holographic head-up display. The purpose is

[Means to solve the problem]

The present invention relates to a holography system in which a display image of a display device that displays driving information is reflected toward the driver's seat side by a hologram having concave mirror characteristics, and an enlarged display image of the display device is displayed at a distance within the visual field. The hologram is characterized in that the hologram is formed by making both the signal light and the reference light incident on the hologram dry plate at approximately Brewster's angle when forming the hologram.

[Function] Based on the above configuration, since both the signal light and the reference light are incident on the hologram dry plate at approximately Brewster's angle during hologram formation, no reflection occurs, so unnecessary holograms with other than the desired concave mirror characteristics are formed. First, when the display image reflected by the hologram is viewed from the driver's side, it is visually recognized as a noise-free distant display image.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In the present invention, when forming a hologram as shown in FIG. 1, a signal beam S and a reference beam R are incident on a hologram dry plate 1 at approximately Brewster's angle to form a hologram as shown in FIGS. 5(a) to (e). This is intended to prevent the occurrence of ghost holograms resulting from five types.

Figure 10 shows the refractive index nz from the air layer (refractive index n+=1).
The reflectance characteristics depending on the incident angle of S-polarized light (polarized light perpendicular to the plane of incidence) and P-polarized light (polarized light parallel to the plane of incidence) when light is incident on the transparent material of =i, 5 are shown. The reflectance of the P-polarized light becomes 0 near the incident angle θ-56°, and all of the light enters the substance. This angle θB is called the Brewster angle or the polarization angle, and the refractive index of the material before and after the incident boundary is nl,
If n2 is defined as tanθB=n2/n1. As shown in Fig. 11, an air layer (refractive index nI =
Since the P-polarized light incident from 1) at the Brewster angle is also emitted from the back surface of the substrate to the air layer at the Brewster angle, the incident light is almost completely transmitted through the substrate.

Several experiments were conducted to verify the effect of the Brewster angle incidence during hologram formation.

First, as shown in FIGS. 6 and 7, diverging light was made to enter the hologram dry plate 1 from the emulsion side. In the case shown in Fig. 6, the surface of the hologram dry plate 1 is arranged at an angle θ1 = 20° with respect to the laser source 2, and the emitted laser is vibrated with an electric field 20 perpendicular to the plane of the paper and converted into S-polarized light. The light is diverged by a lens 21 and irradiated onto the hologram dry plate 1. In the case shown in Fig. 7, the surface of the hologram dry plate 1 is arranged at an angle θ1 = 56° with respect to the laser source 2, and the emitted laser is vibrated with an electric field 22 parallel to the plane of the paper, and then the P-polarized light is transmitted to the objective. The light is diverged by a lens 21 and irradiated onto the hologram dry plate 1. Note that the distance between the objective lens 21 and the hologram dry plate 1 was 300 mm.

Furthermore, as shown in the eighth and ninth sections, parallel light was incident alone on the surface of the hologram dry plate 1 opposite to the emulsion surface.

In the case shown in FIG. 8, the surface of the hologram dry plate I is arranged at an angle θ1 = 20' with respect to the laser source 2, and the emitted laser is converted into S-polarized light with an electric field 20 perpendicular to the plane of the paper by the objective lens 21. The light is diverged by a large convex lens 23, and then converted into parallel light and irradiated onto the hologram dry plate 1.

In the case shown in FIG. 7, the surface of the hologram dry plate 1 is tilted at an angle θ1-56° with respect to the laser source 2, and the emitted laser is converted into P-polarized light with an electric field 22 parallel to the plane of the paper by the objective lens 21. The light is diverged, and then converted into parallel light by a large convex lens 23 and irradiated onto the hologram dry plate 1.

The hologram dry plate l used in this experiment was a high resolution type for reflection holograms, with silver salt emulsion E coated on a glass substrate, and the irradiated recording light was He-N.
The CWC2 and PBQ2 methods were used for development and bleaching using an e-laser (wavelength: 632°, 8 nm) because of their high diffraction efficiency.

The ghost hologram of hologram I irradiated with light in this way is created by assembling a system as shown in Figure 2, and by bringing the emulsion surface into close contact with a cover glass via silicone oil, etc. This can be confirmed by observing whether or not another image exists between the reflected images P, , P. Also, if a specular reflection hologram is formed when the image of a fluorescent lamp on the ceiling is lit is reflected on the emulsion surface, an image colored by light of a wavelength that matches the reproduction conditions will overlap the specular reflection image. You can also check whether you can see it or not.

As a result, specular reflection ghost holograms are created for S-polarized light with an incident angle of θ1-20° for both divergent and parallel light, and P-polarized light with an incident angle of θ1 = 56° for divergent and parallel light. In neither case could a ghost hologram be created.

Next, in the recording system shown in FIG. 1, the emulsion surface of the hologram dry plate 1 is irradiated with a reference beam R consisting of diverging light, and the surface opposite to the emulsion surface is irradiated with a signal beam S consisting of parallel light. was formed.

The incident angle θi is 20° and 56°, the SR ratio is 1:1, and the polarization direction is the same as the above experiment.As a result, when θ1 = 20°, Fig. 5 (a) to (e) Ghost holograms generated from five types as shown in Figure 1 were confirmed, but no ghost holograms occurred at θ1-56°.

From the above, it has been confirmed that the formation of ghost holograms can be prevented by making light incident at the Brioster angle.

The holographic head-up display according to the present invention is a head-up display as shown in FIG. 2, using a hologram formed by incident light at the Briuster angle.

Note that in the hologram recording system shown in Figure 1, the signal light S is parallel light and can be set to a positive @L Koblius star angle, so surface reflection can be almost completely prevented, but the reference light R is a divergent light. Since it is light and has a wide range of incident angles, in order to prevent surface reflection, it is desirable to make the diverging light enter from the emulsion layer E side and remove residual reflection due to deviation from the Brillister angle with an AR coating or the like provided on the back surface of the substrate. therefore,
It is convenient to adopt a configuration in which the parallel light serving as the signal light S is made incident from the side opposite to the emulsion surface.

Formation of such a hologram is particularly effective with a specular reflection type hologram combiner, but even with a non-specular reflection type hologram combiner as shown in Fig. 12, the signal beam S during recording must be set at the Briuster angle. You can eliminate some ghosts with this.

Furthermore, since the angle of incidence of light during recording of the hologram l used in the present invention is limited, the degree of freedom in designing the optical system may be reduced. The angle of the emitted light may be changed by attaching a prism 30 to the emulsion surface. Alternatively, as shown in FIG. 14, a transmission hologram 40 may be used to diffract the emitted light. Unlike the reflection type, the transmission type hologram 40 does not have problems such as the generation of double images due to specular reflection. In addition, transmission holograms usually have a problem with chromatic aberration, but since the reflection hologram limits the wavelength of the diffracted light, this problem is also avoided.

Note that when the hologram 1 formed with the recording system shown in FIG. 1 is reproduced by assembling a holographic head-up display as shown in FIG. 2, a ghost image due to the ghost hologram shown in FIG. In addition to P, ~P8, there is a ghost image P" P // as shown in FIG.
/ etc. are confirmed behind the image P'. As the display image P moves away from the hologram 1, these images P" P /// further expand in the distant display and change to a real image in front of the hologram 1 at a certain point. In this case,
The image P'' is the earliest, followed by P'' and P'. From this, the image P'' P /// has a shorter focal length than the concave mirror (focal length 300 mm) involved in the reproduction of the image P'. It is clear that it has a concave mirror effect.

This is because, as shown in Figure 16, when parallel light is incident from the direction of the original reproduction conditions, the originally recorded hologram is reflected by the concave mirror action with f = 300 mm, and the P0 is located in the regular reflection direction and 300 mm from the center of the hologram surface. It becomes light that converges in a certain place. At this time, a part of the convergent light is reflected at the boundary H between the hologram substrate and the air and returns to the hologram layer, and again f =
It is reflected by a 300mm concave mirror and becomes P. The light converges at the position ′. A part of the convergent light toward P0' is reflected again at the boundary H, is again subjected to the action of the concave mirror, and converges to P0/7. Therefore, if the reflectance of the boundary H is high, multiple convergent lights and point sequences p0', p,'', etc. will appear due to multiple reflections.In other words, multiple concave mirrors with different focal lengths will be recorded. It has a similar effect, and becomes noise in the enlarged virtual image or real image when performing a holographic throat-up display.

These ghosts are specular reflection images P+ and P shown in Figure 2.
When removing z, it can be removed by AR coating used on the front and back surfaces of the substrate.

〔Effect of the invention〕

As explained above, according to the present invention, since a hologram is formed by making both the signal light and the reference light incident on the hologram dry plate approximately at Brewster's angle, unnecessary holograms other than the desired hologram are eliminated. Since no noise is formed, a noise-free image can be viewed when the hologram is used in a holographic head assembling display.

[Brief explanation of the drawing]

Fig. 1 shows the hologram recording system, Fig. 2 shows the holographic head-up display, Fig. 3 shows how ghosts produced by ghost holograms appear, Fig. 4 (a) ), (b) are diagrams explaining multiple reflections within the hologram substrate, Figures 5 (a) to (e) are diagrams illustrating the causes of ghost hologram formation, and Figure 6 is a diagram showing divergent S-polarized light on the hologram dry plate. Figure 7 is a diagram of irradiating a hologram dry plate with divergent P-polarized light, Figure 8 is a diagram of irradiating a hologram dry plate with parallel S-polarized light, Figure 9 is a diagram of irradiating a hologram dry plate with parallel P-polarized light, Figure 10 shows that S-polarized light and P-polarized light are transmitted from an air layer with a refractive index of 1.
Figure 11 is a diagram showing the relationship between the angle of incidence and reflectance when entering a substance in No. 5. Figure 11 is a diagram showing the state in which light passes through materials with refractive index n to n2. Figure 12 is non-specular reflection. Figure 13 is a diagram showing a prism attached to the surface of a hologram, Figure 14 is a diagram showing a holographic head-up display that uses a transmission hologram in addition to a reflection hologram, FIG. 15 is a diagram showing the existence of an enlarged ghost other than the ghost shown in FIG. 3, and FIG. 16 is a diagram showing the principle of occurrence of short-focus concave mirror action. , ■...Hologram (hologram dry plate), 2...Laser source, 9...Viewpoint, P...Display image. 1. Honguchi q'crum Faq"t411'tt&)2°
° S-se°°- Fig. 1 Fig. 3 Fig. 4
C) Figure 5 Figure 6 Figure 7 Figure 9 Figure 10 Trout g day of BREWSTERfA Figure 11 Figure 12. Figure 13

Claims (1)

[Scope of Claims] A hologram in which a display image of a display device that displays driving information is reflected toward the driver's seat side by a hologram having concave mirror characteristics, so that an enlarged display image of the display device is displayed at a distance within the visual field. A holographic head-up display, characterized in that the hologram is formed by making both the signal light and the reference light incident on the hologram dry plate at approximately Brewster's angle when forming the hologram.