JP2022045811A - Head-up display - Google Patents

Abstract

To reduce performance deterioration of a hologram generated caused by deviations in an incident angle and a reproduction wavelength.SOLUTION: A head-up display (1) mounted on a moving body, comprises a hologram (3) provided in front of an occupant, and an image light irradiation unit (2) that projects light toward the hologram. The hologram is volumetric, and contains a plurality of coherent fringes (31 to 35) with different coherent fringe spacing (d1 to d5).SELECTED DRAWING: Figure 7

Description

The present disclosure relates to a head-up display.

A technique for imparting desired characteristics to a hologram using a laser interference exposure apparatus is known (see, for example, Patent Document 1).

Further, since the interference fringes formed by the light reflected at the interface of the volume hologram cause stray light, a configuration is known in which a transmissive hologram is attached to the windshield for the purpose of preventing such stray light (for example). See Patent Document 2).

Japanese Unexamined Patent Publication No. 2001-154179 International Patent Publication No. 2012/042793 Pamphlet

By the way, in the mounted state, the incident angle of the display light (incident angle with respect to the hologram) and the reproduction wavelength may deviate from the design value (for example, the design value satisfying the Bragg condition). Such deviation may occur due to, for example, initial deviation, temperature, or the like. If such a deviation occurs, the performance of the hologram may deteriorate (for example, when the intensity of the diffracted light is increased).

Therefore, it is an object of the present disclosure to reduce the deterioration of hologram performance that may occur due to the deviation of the incident angle and the reproduction wavelength.

On one side, it is a head-up display (1) mounted on a moving body.
The hologram (3) provided in front of the occupant and
It includes an image light irradiation unit (2) that projects light toward the hologram.
The hologram is volumetric and provides a heads-up display that includes a plurality of interference fringes (31-35) with different interference fringe spacing (d1–d5).

According to the present disclosure, it is possible to reduce the deterioration of hologram performance that may occur due to the deviation of the incident angle and the reproduction wavelength.

It is a figure which shows roughly the vehicle-mounted state of a head-up display in the vehicle side view. It is a schematic diagram which shows the structure of the image light irradiation apparatus. It is explanatory drawing which shows the alternative example with respect to the dichroic mirror unit. It is explanatory drawing of the characteristic of the laser beam for recording the interference fringe which concerns on a hologram. It is explanatory drawing of the characteristic of the laser beam incident on the hologram from the image light irradiation apparatus. It is explanatory drawing of the characteristic of a hologram with respect to an incident angle. It is a figure which shows the structure of the hologram of this Example approximately in a cross-sectional view. It is explanatory drawing of the characteristic of the hologram of this Example about the incident angle. It is a figure which shows the analysis result of the hologram by this Example. It is a figure which shows the analysis result of the hologram by the comparative example. It is explanatory drawing of the size of the eye box by the hologram of this Example. It is explanatory drawing of the size of the eye box by the hologram of the comparative example. It is explanatory drawing of the characteristic of the hologram of this Example regarding a reproduction wavelength. It is a graph of the normalized diffraction efficiency of a volume reflection type phase lattice expressed as a function of a parameter _χr . It is explanatory drawing of the modulation parameter.

Hereinafter, each embodiment will be described in detail with reference to the accompanying drawings.

[Head-up display configuration]
FIG. 1 is a diagram schematically showing a state in which the head-up display 1 is mounted on a vehicle VC (an example of a moving body) when viewed from the side of the vehicle. FIG. 2 is a schematic view showing the configuration of the image light irradiation device 2. In FIG. 2, the dotted arrows R0 to R4 schematically show the flow of electric signals.

In the head-up display 1, as shown in FIG. 1, when the windshield WS is irradiated with the display light, the display obtained by the irradiation is in front of the windshield WS for the driver driving the vehicle VC. Image (virtual image display) VI can be seen. As a result, the driver can visually recognize the display image VI by superimposing it on the landscape in front. Therefore, the driver can grasp the vehicle information and the like in a mode in which the line-of-sight movement is smaller than when looking at the meter in the instrument panel 9, and the convenience and safety are improved.

The head-up display 1 includes an image light irradiation device 2 (an example of an image light irradiation unit) and a hologram 3.

The image light irradiating device 2 projects the light related to the image toward the hologram 3 on the windshield WS located in front of the driver. The hologram 3 on the windshield WS reflects the light related to the image in the driver's eye box. In this case, a display image VI based on the light related to the image is formed in front of the driver's field of view when viewed from the viewpoint related to the eye box.

In this embodiment, as an example, as shown in FIG. 2, the image light irradiation device 2 includes a laser unit 10, a dichroic mirror unit 20, a condenser lens 28, a MEMS (Micro Electro Electrical Systems) scanner 29, and the image light irradiation device 2. The screen 40 and the control device 50 are included.

The laser unit 10 includes laser irradiation devices 11, 12, and 13 for each color of red, blue, and green. The laser irradiation device 11 emits laser light in the red wavelength region. The laser irradiation device 12 emits laser light in the blue wavelength range. The laser irradiation device 13 emits laser light in the green wavelength range. In this embodiment, since the laser beams of these three colors can be emitted, a full-color display image VI can be generated. However, in the modified example, the variation of the displayable color may be small.

The dichroic mirror unit 20 has dichroic mirrors 21, 22, and 23 corresponding to the laser irradiation devices 11, 12, and 13, respectively. The dichroic mirror 21 reflects only the red wavelength range. Therefore, the dichroic mirror 21 can reflect only the laser light incident from the laser irradiation device 11 toward the condenser lens 28. The dichroic mirror 22 transmits the red wavelength region and reflects the blue wavelength region. Therefore, the dichroic mirror 22 can reflect the laser light incident from the laser irradiation device 12 toward the condenser lens 28 while transmitting the laser light incident from the dichroic mirror 21. Similarly, the dichroic mirror 23 transmits the red and blue wavelength regions and reflects the green wavelength region. Therefore, the dichroic mirror 23 can reflect the laser light incident from the laser irradiation device 13 toward the condenser lens 28 while transmitting the laser light incident from the dichroic mirror 22.

As described above, the condenser lens 28 collects the laser light (laser light of each color of red, blue, and green) incident from the dichroic mirror unit 20 and emits it toward the MEMS scanner 29.

The condenser lens 28 is configured such that the laser light incident from the dichroic mirror unit 20 is projected onto the screen 40 with a spot diameter (diameter) smaller than the size of each of the plurality of microlenses forming the screen 40.・ Be placed.

The MEMS scanner 29 projects the laser beam incident from the condenser lens 28 onto the screen 40. The MEMS scanner 29 includes a MEMS mirror that is rotatable about two orthogonal axes. The projection position of the laser beam on the screen 40 changes according to the orientation of the MEMS mirror. Therefore, the MEMS scanner 29 can arbitrarily change the projection position of the laser beam on the screen 40.

The screen 40 extends in a plane. In this embodiment, as an example, the screen 40 extends in the horizontal plane, but may be arranged in a direction slightly inclined with respect to the horizontal plane. The screen 40 includes a plurality of microlenses (not shown) that are regularly arranged in a plane. That is, the screen 40 includes a two-dimensional microlens array.

The control device 50 may be realized by a computer such as an ECU (Electronic Control Unit). The control device 50 includes a laser control unit 51 and a scanner control unit 52.

The laser control unit 51 controls the laser unit 10 based on an image signal for generating a display image VI (see arrows R1 to R3 in FIG. 2). The image signal may be generated by an external ECU and given to the control device 50 (see arrow R0 in FIG. 2), or may be generated by the control device 50 by itself.

The image signal is, for example, a signal representing a pixel value (luminance or color) of each pixel of an image having a predetermined size and a predetermined resolution. The second image signal is, for example, a signal representing a pixel value (luminance or color) of each pixel of an image having a predetermined size and a predetermined resolution. Each pixel of the image is associated with each position of the screen 40 (each position on the scanning surface). For example, each pixel of the image may be associated with each position of the screen 40 (each position on the scanning surface) in a one-to-one relationship. Each position of the screen 40 is associated with each orientation of the MEMS mirror of the MEMS scanner 29.

When the laser control unit 51 controls the laser unit 10 based on the image signal, the laser unit 51 sets the laser unit 10 to each pixel value at a timing corresponding to each pixel based on the pixel value of each pixel included in the image signal. The laser unit 10 is controlled so that the laser beam of the corresponding color is emitted.

The scanner control unit 52 controls the MEMS scanner 29 (see arrow R4 in FIG. 2). That is, the scanner control unit 52 scans the laser beam on the screen 40 by controlling the direction of the MEMS mirror of the MEMS scanner 29. Here, "scanning the laser beam on the screen 40" means changing the projection position of the laser beam on the plane of the screen 40 (the projection position when viewed perpendicular to the plane of the screen 40). Point to. Further, in the following, the "scanning pattern" refers to the locus of the projection position (the locus of the projection position of the laser beam on the plane of the screen 40). Further, the plane related to the screen 40 (that is, the plane on which a plurality of microlenses are arranged) is also referred to as a “scanning surface”.

Specifically, the scanner control unit 52 cooperates with the laser control unit 51 to scan the laser beam corresponding to the image signal in a predetermined scanning pattern. That is, the scanner control unit 52 MEMS so that the laser light from the laser unit 10 is projected to each position on the scanning surface corresponding to each pixel based on the pixel value of each pixel included in the image signal. Controls the scanner 29.

The image light irradiation device 2 shown in FIG. 2 has a specific configuration, but the configuration of the image light irradiation device 2 is arbitrary as long as it has a light source related to laser light of a plurality of colors. Therefore, as the image light irradiation device 2, the cross prism 20A may be used instead of the dichroic mirror unit 20, for example, as shown in FIG. Note that, in FIG. 3, the laser irradiation devices 11, 12, and 13 are illustrated in a mode including light sources 111, 121, 131 (an example of a laser light source) and collimator lenses 112, 122, 132, respectively. Further, although the image light irradiation device 2 shown in FIG. 2 directly projects light on the hologram 3 on the windshield WS, it may be projected via an optical member. For example, the light from the screen 40 may be reflected by the concave mirror and then projected onto the hologram 3 on the windshield WS. Further, the image light irradiation device 2 shown in FIG. 2 projects light only on the hologram 3 on the windshield WS, but forms a display image VI by projecting light on both the hologram 3 and the windshield WS. You may.

The hologram 3 is provided on the windshield WS. The hologram 3 may be attached to the indoor surface of the windshield WS, or may be provided on the inner layer (for example, in the interlayer film) of the windshield WS.

The hologram 3 may be formed of, for example, a photopolymer. The types of hologram 3 are reflection type, phase change type, and volume type. The hologram 3 may be formed by utilizing a hologram film having a thickness of several microns. Interference fringes are recorded on the hologram 3, for example, in the form of a change in refractive index. That is, in the hologram 3, the interference fringes are stored in layers inside the material as a bending rate distribution. In this embodiment, interference fringes related to each of the RGB wavelengths are recorded in the hologram 3 corresponding to the three colors of laser light. In this case, a laminated hologram 3 may be formed by creating a hologram layer for each interference fringe corresponding to each of the RGB wavelengths and laminating the hologram layers related to each. Alternatively, a multi-type hologram 3 in which RGB interference fringes are superimposed and recorded may be realized. Any laser interference exposure apparatus may be used for recording (exposure) such interference fringes.

The hologram 3 preferably has a transmittance of 70% or more and a diffraction efficiency of 30% or less. As a result, it is possible to generate a display image VI with high visibility in a manner that does not impair the transparency of the windshield WS.

[Characteristics of hologram 3 with respect to wavelength and incident angle]
Next, the deviation between the exposure wavelength and the reproduction wavelength will be described with reference to FIGS. 4 and later.

FIG. 4 is an explanatory diagram of the characteristics of the laser beam for recording the interference fringes related to the hologram 3, and FIG. 5 is an explanatory diagram of the characteristics of the laser beam incident on the hologram 3 from the image light irradiation device 2.

In FIGS. 4 and 5, the incident angle θ is taken on the horizontal axis and the diffraction efficiency η is taken on the vertical axis, respectively. As an example, the characteristics L400 and L401 of the laser beam for recording the interference fringes related to G (green). And the characteristics L500 and L501 of the laser beam for recording the interference fringes related to R (red) are shown. As shown in FIG. 4, the characteristics L400 and L500 of the laser beam for recording both have a peak diffraction efficiency at a predetermined incident angle α0. The predetermined incident angle α0 may correspond to the incident angle of the laser beam incident on the hologram 3 from the image light irradiation device 2, and the regular positional relationship between the image light irradiation device 2 and the hologram 3 (in the design drawing). It is uniquely determined from the positional relationship of). On the other hand, as shown in FIG. 5, the characteristic L401 of the laser beam from the image light irradiation device 2 has a diffraction efficiency peak at a predetermined incident angle α0, while the characteristic L501 has a characteristic L501 from a predetermined incident angle α0. Diffraction efficiency peaks at a deviated incident angle α1. Note that FIG. 5 illustrates the characteristics of a certain individual, and when other individuals are used, different characteristics may be shown.

By the way, in general, the diffraction efficiency of light peaks when the incident angle is an angle that satisfies the Bragg condition (Bragg condition). Bragg conditions are as follows.
2dsinθ = nλ equation (1)
Here, d is the interval between the interference fringes (hereinafter, also referred to as “interference fringe interval”), θ is the angle formed by the light with respect to the hologram 3 (incident angle), λ is the wavelength of the light, and n is a natural number. Therefore, under the condition that d and θ do not change, it can be seen that the difference in characteristics as shown in FIGS. 4 and 5 is due to the difference in λ. That is, the wavelength of the laser beam for recording the interference fringes (exposure wavelength) and the wavelength of the laser beam incident on the hologram 3 from the image light irradiation device 2 (reproduction wavelength) are different, so that such a characteristic difference occurs.

In this way, if the wavelength of the laser beam for recording the interference fringes and the wavelength of the laser beam incident on the hologram 3 from the image light irradiation device 2 are different, the desired performance of the hologram 3 cannot be realized (that is,). There is a case where the performance deteriorates).

In this respect, it is designed so that there is originally no difference between the exposure wavelength and the reproduction wavelength. That is, the laser unit 10 is designed so that there is substantially no significant difference between the exposure wavelength and the reproduction wavelength.

However, in reality, there may be a significant difference between the exposure wavelength and the reproduction wavelength due to individual differences in the laser unit 10, secular variation, and the like.

FIG. 6 is an explanatory diagram of the characteristics of the hologram 3 with respect to the incident angle, in which the incident angle θ is taken on the horizontal axis and the diffracted light intensity I is taken on the vertical axis, and the relationship between the incident angle θ and the diffracted light intensity I is shown.

As can be seen from FIG. 6 and the equation (1), even when the incident angle does not satisfy the Bragg condition, the desired performance of the hologram 3 may not be realized (for example, the intensity may decrease).

In this respect, the configuration of the image light irradiation device 2 is originally designed so that the incident angle satisfies the Bragg condition in relation to the windshield WS.

However, in reality, the incident angle may not satisfy the Bragg condition due to individual differences (initial deviation), temperature, secular variation, etc. of the image light irradiation device 2. That is, the incident angle may deviate from the original angle (design value) that satisfies the Bragg condition.

Therefore, in the head-up display 1 according to the present embodiment, even when such a significant difference between the exposure wavelength and the reproduction wavelength or the significant difference between the incident angle and the angle satisfying the Bragg condition occurs. The hologram 3 is configured so that the desired performance is realized.

Specifically, in the head-up display 1 according to the present embodiment, as described in detail below, the hologram 3 records interference fringes having different interference fringe intervals.

FIG. 7 is an explanatory diagram of the hologram 3 of the present embodiment, and is a diagram schematically showing the structure of the hologram 3 in a cross-sectional view.

The hologram 3 records interference fringes 310 to 350 with different interference fringe intervals. In this embodiment, as shown in FIG. 7, the hologram 3 includes a first interference fringe layer 31, a second interference fringe layer 32, a third interference fringe layer 33, a fourth interference fringe layer 34, and a fifth. Includes an interference fringe layer 35. The hologram 3 has a structure in which the first interference fringe layer 31 to the fifth interference fringe layer 35 are laminated.

In the first interference fringe layer 31, interference fringes having an interference fringe interval d1 are recorded. In the second interference fringe layer 32, the interference fringes having the interference fringe interval d2 are recorded. Similarly, in the third interference fringe layer 33 to the fifth interference fringe layer 35, interference fringes having interference fringe intervals d3 to d5 are recorded, respectively. The interference fringe intervals d1 to d5 are different from each other.

In this embodiment, the hologram 3 includes five types of interference fringe layers from the first interference fringe layer 31 to the fifth interference fringe layer 35, but as long as it includes two or more types of interference fringe layers having different interference fringe intervals. , The number of types is arbitrary.

FIG. 8 is an explanatory diagram of the characteristics of the hologram 3 of this embodiment. In FIG. 8, the incident angle θ is taken on the horizontal axis, the diffraction light intensity I is taken on the vertical axis, and the diffraction efficiency curves L1 to L5 relating to each of the _first interference fringe layer 31 to the _fifth interference fringe layer 35 are shown. It is shown.

As shown in FIG. 8, when the first interference fringe layer 31 has a normal reproduction wavelength (reproduction wavelength based on the design value), the diffracted light intensity I peaks when the incident angle θ = θ ₁ , and the following Similarly, in the second interference fringe layer 32 to the fifth interference fringe layer 35, the diffracted light intensity I peaks when the incident angles θ = θ ₂ , θ ₃ , θ ₄ , and θ ₅ , respectively. In other words, when the interference fringe intervals d1 to d5 of the first interference fringe layer 31 to the fifth interference fringe layer 35 are normal reproduction wavelengths, the incident angles θ = θ ₁ , θ ₂ , θ ₃ , and θ, respectively. _4. At θ ₅ , it is adapted so that the diffracted light intensity I peaks.

Therefore, according to this embodiment, when the reproduction wavelength is normal, the incident angle θ is the same as (that is, the Bragg angle) any one of the angles θ ₁ , θ ₂ , θ ₃ , θ ₄ , and θ ₅ . If this is the case, a relatively high diffracted light intensity I can be realized. As a result, even if the incident angle θ fluctuates due to individual differences (initial deviation), temperature, aging, etc. of the image light irradiation device 2, the incident angles θ are angles θ ₁ , θ ₂ , θ ₃ , and θ. _4. If it is the same as or in the vicinity of any one of θ ₅ , the angle that satisfies or satisfies the Bragg condition is satisfied, and therefore a relatively high diffracted light intensity I can be realized. Since a relatively high diffracted light intensity I can be realized, good quality of the display image VI can be ensured.

By the way, as can be seen from the above equation (1), when the incident angle θ is fixed, when the wavelength fluctuates, the interference fringe interval d that satisfies the Bragg condition changes. Therefore, according to the present embodiment, since the hologram 3 includes the interference fringes recorded at the plurality of interference fringe intervals d1 to d5 as described above, the reproduction wavelength varies from the normal wavelength (reproduction wavelength based on the design value). Even in this case, a relatively high diffracted light intensity I can be realized. Since a relatively high diffracted light intensity I can be realized, good quality of the display image VI can be ensured.

In this way, according to the present embodiment, since the hologram 3 records the interference fringes 310 to 350 having different interference fringe intervals, the incident angle θ and / or the reproduction wavelength is set to the normal incident angle θ (design value). Based on the incident angle) and / or even when deviated from the normal reproduction wavelength, it is possible to realize a relatively high diffracted light intensity I that can realize a relatively high diffracted light intensity I, and it is possible to secure good quality of the display image VI. That is, it is possible to realize a head-up display 1 having a hologram 3 that is robust against fluctuations in the incident angle θ and the reproduction wavelength.

Here, the effects of this embodiment will be further described with reference to FIGS. 9A to 10B.

FIG. 9A is a diagram showing the analysis result of the hologram 3 according to the present embodiment, and FIG. 9B is a diagram showing the analysis result of the hologram (not shown) according to the comparative example. In FIGS. 9A and 9B, Δθ (amount of deviation with respect to the normal incident angle θ) is taken on the horizontal axis, and Δλ (amount of deviation with respect to the normal reproduction wavelength) is taken on the vertical axis, and the distribution of the diffracted light intensity I is shown. be. The region I1 has the highest diffracted light intensity I, and the region I2 has the next highest diffracted light intensity I, and so on. Further, the region _IB is a region where the diffracted light intensity I is very low, and is a region where the diffracted light intensity I is at a level at which the displayed image VI is not substantially visible.

As described above, FIGS. 9A and 9B schematically show an allowable fluctuation range Q1 as a range of an incident angle θ and a reproduction wavelength that can deviate from the normal value due to various factors. The allowable fluctuation range Q1 is appropriately determined according to the design conditions and the like.

The hologram according to the comparative example includes an interference fringe layer having a single interference fringe interval d0, unlike the hologram 3 of the present embodiment. The interference fringe interval d0 is set so as to satisfy the Bragg condition based on the normal incident angle θ and the normal reproduction wavelength.

In the case of such a comparative example, the diffracted light intensity I becomes relatively large only in a narrow range around the position where the Bragg condition is satisfied. That is, as shown in FIG. 9B, within the permissible fluctuation range Q1, only a part of the region _I1 and the like is included, and most of the region IB is included. Therefore, in such a comparative example, if the incident angle θ and / or the reproduction wavelength deviates from the normal incident angle θ and / or the normal reproduction wavelength, the possibility of belonging to the region _IB increases. Therefore, in the case of the comparative example, it is difficult to realize a head-up display provided with a hologram that is robust against fluctuations in the incident angle θ and the reproduction wavelength.

On the other hand, in the hologram 3 according to the present embodiment, as described above, interference fringes 310 to 350 with different interference fringe intervals are recorded. In the case of this embodiment as shown in FIG. _9A , in contrast to the above-mentioned comparative example, the allowable fluctuation range Q1 does not include the region IB, and most of the region I1 is included. Become. Therefore, according to this embodiment, it is possible to realize a head-up display 1 having a hologram 3 that is robust against fluctuations in the incident angle θ and the reproduction wavelength. In other words, according to the present embodiment, the permissible fluctuation range Q1 capable of generating the display image VI of appropriate luminance can be efficiently expanded as compared with the comparative example.

FIG. 10A is an explanatory diagram of the size of the eyebox EB by the hologram 3 of the present embodiment, and a part of the display lights L100, L110, and L120 from the image light irradiation device 2 are directed toward the eyebox EB in a side view. It is a figure which shows the state of reflection schematically. FIG. 10B is an explanatory diagram of the size of the eye box EB'by the hologram 3'of the comparative example. 10A and 10B each show an enlarged view of the Q10 portion.

The hologram 3'according to the comparative example has an interference fringe layer having a single interference fringe spacing d0, unlike the hologram 3 of the present embodiment, as in the case of FIG. 9B.

In the case of such a comparative example, as described above, the diffracted light intensity I becomes relatively large only in a narrow range around the position where the Bragg condition is satisfied. Therefore, of the display lights L100, L110, and L120 that are incident on the hologram 3'at different angles of incidence, only the specific display light (in this example, the display light L100) that matches the interference fringe interval d0 is the driver (in this example). (See Fig. 1). As a result, the eye box EB'tends to become narrower.

On the other hand, in the hologram 3 according to the present embodiment, as described above, interference fringes 310 to 350 with different interference fringe intervals are recorded. In the case of this embodiment, as shown in FIG. 10A, in contrast to the above-mentioned comparative example, each of the indicator lights L100, L110, and L120 incident on the hologram 3 at different angles of incidence is the driver ( (See Fig. 1). Therefore, according to this embodiment, a relatively wide eye box EB can be realized.

Next, a preferable example of the diffraction efficiency curve related to each of the first interference fringe layer 31 to the fifth interference fringe layer 35 will be described with reference to FIG. 11 again with reference to FIG. 8 described above.

FIG. 11 is an explanatory diagram of the characteristics of the hologram 3 of the present embodiment, as in FIG. In FIG. 11, the wavelength is taken on the horizontal axis, the diffraction light intensity I is taken on the vertical axis, and the diffraction efficiency curve L relating to each of the first interference fringe layer 31 to the fifth interference fringe layer 35 of the hologram 3 of this embodiment. ₁₁ to L ₁₅ are shown.

Note that FIG. 8 shows the characteristics of the diffracted light intensity I according to the incident angle, while FIG. 11 shows the characteristics of the diffracted light intensity I according to the reproduction wavelength.

As shown in FIG. ₈ , the diffraction efficiency curves L1 to L5 relating to each of the _first interference fringe layer 31 to the fifth interference fringe layer 35 overlap each other with at least two diffraction efficiency curves (see hatch region R8). Have. For example, the diffraction efficiency curve L ₁ and the diffraction efficiency curve L ₂ have an overlap (see the hatching region R8), and have an overlap (see the hatching region R8) within a range in which the diffraction light intensity is a predetermined value I ₀ or more. However, the same applies below.

Specifically, as described above, when the interference fringe intervals d1 to d5 of the first interference fringe layer 31 to the fifth interference fringe layer 35 are normal reproduction wavelengths, the incident angles θ = θ ₁ , respectively. It is adapted so that the diffracted light intensity I peaks at θ ₂ , θ ₃ , θ ₄ , and θ ₅ . At this time, the angles θ ₁ , θ ₂ , θ ₃ , θ ₄ , and θ ₅ are adapted to have such an overlap (see hatch region R8).

By having such an overlap (see the hatch region R8), it is possible to secure a diffracted light intensity I of a certain level or more over the entire allowable fluctuation range Q1 (see FIG. 9A), and it is robust against fluctuations in the incident angle θ and the reproduction wavelength. It can enhance the sex.

Here, the overlap of the diffraction efficiency curves L1 to L5 has been described with reference to FIG. ₈ , but the _same applies to the overlap of the diffraction efficiency curves _L11 to _L15 . That is, as can be seen from the above equation (1), when the incident angle θ changes, the reproduction wavelength λ that satisfies the Bragg condition also changes with respect to the changed incident angle θ, so that the diffraction efficiency curves L ₁₁ to L The relationship according to ₁₅ substantially corresponds to the relationship according to the diffraction efficiency curves _L1 to _L5 . In other words, the relationship between the wavelengths λ ₁ , λ ₂ , λ ₃ , λ ₄ , and λ ₅ at which the diffraction light intensity I peaks in each of the diffraction efficiency curves L ₁₁ to L ₁₅ is based on the above equation (1). It correlates with the relationship between the angles θ ₁ , θ ₂ , θ ₃ , θ ₄ , and θ ₅ .

FIG. 12 is an explanatory diagram of a setting method for setting the interference fringe intervals d1 to d5 of the first interference fringe layer 31 to the fifth interference fringe layer 35 so as to have the above-mentioned overlap (see the hatching region R8). .. FIG. 13 is an explanatory diagram of modulation parameters. FIG. 12 is a graph of the normalized diffraction efficiency (η / η _B ) of the volumetric reflection type phase lattice expressed as a function of the parameter _χr . Specifically, the horizontal axis is the parameter _χr , the vertical axis is the normalized diffraction efficiency (η / η _B ), and the characteristic curve L140 showing the relationship between the two is shown. The characteristic curve L140 changes depending on the value of the predetermined modulation parameter Φ. The modulation parameter Φ is represented by Φ = πΔnd / λcosθ ₀ using Δn, which is the amplitude of the change in the refractive index, and as shown in FIG. 13, the diffraction efficiency increases toward the upper limit of 1 as the value increases. It has a monotonically increasing relationship. Here, it is assumed that the value of the modulation parameter is 1 / 4π. The efficiency η _B for normalization is represented by η _B = tanh ² Φ.

The parameter _χr represents the amount of deviation from the Bragg condition, and is as shown in the following equation.

ここでは、上記の数１の式に基づいて、正規の再生波長をλ_０、ブラッグ角度がθ_０であるホログラム３を設計する場合について、上述した図１１を参照して、説明する。

Here, a case of designing a hologram 3 having a normal reproduction wavelength of λ ₀ and a Bragg angle of θ ₀ based on the above equation of Equation 1 will be described with reference to FIG. 11 described above.

First, the interference fringe interval d ₀ having a wavelength λ ₀ is obtained from the Bragg condition as follows.
d ₀ = λ ₀ / 2cosθ ₀
The amount of diffracted light at this time changes as shown in the characteristic curve L140 with respect to the wavelength shift. Therefore, the amount of diffracted light becomes 0 when the parameter _χr = 3.2 in the above equation (see P1 in FIG. 12). Substituting the parameter _χr = 3.2 into the equation of equation 1, Δλ can be expressed as follows.
Δλ = 3.2λ ₀ / cosθ ₀ × λ ₀ / 2πD
The wavelengths λ ₁ , λ ₂ , λ ₃ , λ ₄ , and λ ₅ described above with reference to FIG. 11 are diffracted by having a relationship of offsetting each of the adjacent wavelengths in the horizontal axis direction by Δλ. It is possible to have an overlap (see the hatching region R8) so that the amount of light does not become zero.

Specifically, assuming that the wavelength λ ₃ is the central wavelength (λ ₀ ), the wavelengths λ ₄ and λ ₅ are as follows.

また、波長λ_３を中心波長（λ_０）とすると、波長λ_２、λ_１は、以下の通りである。

Further, assuming that the wavelength λ ₃ is the central wavelength (λ ₀ ), the wavelengths λ ₂ and λ ₁ are as follows.

このようにして、例えば波長λ_３を中心波長（λ_０）として、波長λ_１、λ_２、λ_４、λ_５を設定すれば、図１２に示した特性に基づいて、回折効率曲線Ｌ_１１からＬ_１５の重なり（ハッチング領域Ｒ８参照）を適切に設定できる。そして、波長λ_１、λ_２、λ_３、λ_４、λ_５が求まると、上述した式（１）に基づいて、各波長に対応した干渉縞間隔ｄ１からｄ５を求めることができる。例えば、波長λ_３を６５０ｎｍ、入射角度θ_０を３０度、媒体厚Ｄを３０ｕｍとしたとき、干渉縞間隔ｄ１からｄ５は、ｄ１＝３６６ｎｍ、ｄ２＝３７１ｎｍ、ｄ３＝３７５ｎｍ、ｄ４＝３８０ｎｍ、ｄ５＝３８５ｎｍとなる。

In this way, for example, if the wavelengths λ ₃ are set as the central wavelength (λ ₀ ) and the wavelengths λ ₁ , λ ₂ , λ ₄ , and λ ₅ are set, the diffraction efficiency curve L ₁₁ is based on the characteristics shown in FIG. The overlap of L ₁₅ (see hatch area R8) can be appropriately set. Then, when the wavelengths λ ₁ , λ ₂ , λ ₃ , λ ₄ , and λ ₅ are obtained, the interference fringe intervals d1 to d5 corresponding to each wavelength can be obtained based on the above-mentioned equation (1). For example, when the wavelength λ ₃ is 650 nm, the incident angle θ ₀ is 30 degrees, and the medium thickness D is 30 um, the interference fringe intervals d1 to d5 are d1 = 366 nm, d2 = 371 nm, d3 = 375 nm, d4 = 380 nm, d5. = 385 nm.

Here, the interference fringe intervals d1 to d5 are adapted so as to have an overlap (see the hatching region R8) so that the amount of diffracted light (normalized diffraction efficiency) does not become 0, but the present invention is not limited to this. For example, the interference fringe spacing d1 to d5 may be adapted based on the range of parameters _χr where the normalized diffraction efficiency is 0 to 0.4. By fitting within such a range, the diffraction light intensity I in the desired allowable fluctuation range Q1 (see FIG. 9A) without increasing the number of layers such as the first interference fringe layer 31 included in the hologram 3. It is possible to efficiently optimize the distribution of light.

Although each embodiment has been described in detail above, the present invention is not limited to a specific embodiment, and various modifications and changes can be made within the scope of the claims. It is also possible to combine all or a plurality of the components of the above-described embodiment.

In the above-described embodiment, the multiplexing of a plurality of interference fringes is realized by laminating the interference fringe layers 31 to 35 having different interference fringe intervals (d1 to d5), but the present invention is not limited to this.
Specifically, interference fringes having different interference fringe intervals (d1 to d5) may be multiple-recorded at the same location by various volume multiplex recording methods. As the volume multiplex recording method, various recording methods such as an angle multiplex method and a spherical reference wave shift multiplex method can be adopted.

When the above-mentioned volume multiple recording method is adopted, the diffraction efficiency may deteriorate due to the multiple recording. When considering the deterioration of diffraction efficiency due to multiple recording, the deterioration of the interference fringes corresponding to the center wavelength (λ ₀ ) is the smallest, and the deterioration is as large as the interference fringes corresponding to the wavelength with a large deviation from the center wavelength (λ ₀ ). It is preferable to control the recording exposure amount so that the recording exposure amount becomes large.

Further, the plurality of interference fringes to be multiplexed may be a multiplexing of two or more interference fringes, and is not limited to the multiplexing of the five interference fringes of the above-described embodiment.

1 Head-up display 2 Image light irradiation device 3 Hologram 9 Instrument panel 10 Laser unit 11 Laser irradiation device 12 Laser irradiation device 13 Laser irradiation device 20 Dichroic mirror unit 20A Cross prism 21 Dichroic mirror 22 Dichroic mirror 23 Dichroic mirror 28 Condensing lens 29 MEMS Scanner 31 1st interference fringe layer 32 2nd interference fringe layer 33 3rd interference fringe layer 34 4th interference fringe layer 35 5th interference fringe layer 40 screen

Claims (6)

A head-up display (1) mounted on a moving body.
The hologram (3) provided in front of the occupant and
It includes an image light irradiation unit (2) that projects light toward the hologram.
The hologram is a volumetric type and is a head-up display including a plurality of interference fringes (31 to 35) having different interference fringe intervals (d1 to d5). The head-up display according to claim 1, wherein the hologram is a reflection type and a phase change type. 1. The head-up display according to 2. Each wavelength when the diffraction light intensity in the diffraction efficiency curve relating to the plurality of interference fringes peaks is a characteristic of the normalized diffraction efficiency (η / η _B ) of the volumetric reflection type phase lattice expressed as a function of the parameter _χr. It is adapted based on the range of the parameter _χr where the normalized diffraction efficiency is 0 to 0.4.
The head-up display according to claim 3, wherein the parameter _χr represents the amount of deviation from the Bragg condition. The head-up display according to claim 4, wherein the image light irradiation unit includes a laser light source (111, 121, 131). The head-up display according to claim 5, wherein the laser light source is an RGB laser light source (111, 121, 131).

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