JP2020077001A - Optical element and projector - Google Patents

Abstract

To provide an optical element which can capture the whole virtual image without fail from any point of view.SOLUTION: The optical element is used as an optical screen, for example, and diffuses and outputs a laser beam coming from a laser light source. The optical element has a micro lens array or a diffraction grating, and the pitch is set according to the incidence numerical aperture of the laser beam and the wavelength of the laser beam so that the distribution of a diffraction light emitted from the optical element will be uniform.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an optical screen of a laser projector.

  A head-up display (hereinafter, also referred to as "HUD") uses an image (real image) on a screen of a liquid crystal display or a screen projected by a laser projector by a half mirror called a combiner placed in front of the driver's view. This is a device that the driver visually recognizes as a virtual image. As a result, the driver can visually recognize the instruments, navigation information and the like while superimposing them on the landscape without lowering the line of sight while looking ahead.

  In a HUD using a laser projector, laser light from a light source is projected on an optical screen to generate an image that the driver visually recognizes as a virtual image. Patent Documents 1 and 2 are mentioned as prior arts related to a HUD optical screen using a laser projector.

  In Patent Document 1, an optical element forming an optical screen includes a plurality of optical element portions having curved surfaces, and the pitch of the optical element portions is adjusted so that the diffraction width of the light beam diffused by the optical elements is equal to or smaller than the pupil diameter of the viewer. The method of setting is described.

  Patent Document 2 describes a method in which speckle noise is considered to be generated by the edge of the lens, and the lens pitch is made larger than the diameter of the laser light so that the edge of the lens is not hit by the laser light.

JP, 2013-64985, A Japanese Patent No. 5075595

  In Patent Document 1, the incident NA (numerical aperture) of the laser light incident on the optical element is not taken into consideration when setting the pitch of the optical element section that constitutes the optical element. Further, although the viewer's pupil diameter is used as a reference in setting the pitch, there is a problem that the appearance changes depending on the change in the position of the viewer, particularly the change in the position in the front-back direction.

  In Patent Document 2, since the edge of the lens is not exposed to the laser light, there is a problem that the entire lens cannot be effectively used.

  Examples of the problems to be solved by the present invention include the above. An object of the present invention is to provide an optical element capable of surely seeing the entire virtual image at any viewpoint position.

  The invention described in claim is an optical element for diffusing laser light incident from a laser light source, comprising a microlens array or a diffraction grating, and a pitch of the microlens array or the diffraction grating has an entrance aperture of the laser light. It is characterized in that the distribution of the diffracted light emitted from the optical element is determined to be uniform based on the number and the wavelength of the laser light.

1 shows a schematic configuration of a HUD according to an example. The mode which scans a laser beam on an optical screen is shown typically. It is a figure explaining a lens pitch and incidence NA of a laser beam. It is a figure explaining the appearance of the emitted light from an optical screen. The relationship between a lens array and a diffracted light distribution is shown. The relationship between the incident NA of laser light and diffracted light is shown. 7 shows a distribution of diffracted light according to an example. It is a figure explaining the other conditions for obtaining desired emitted light. The structure of a reflection type optical screen is shown. The structure of the optical screen using a diffraction grating is shown.

  A preferred embodiment of the present invention is an optical element for diffusing laser light incident from a laser light source, comprising a microlens array or a diffraction grating, and the pitch of the microlens array or the diffraction grating is the incidence of the laser light. The distribution of diffracted light emitted from the optical element is set to be uniform based on the numerical aperture and the wavelength of the laser light.

  The above optical element is used, for example, as an optical screen, and diffuses and outputs the laser light incident from the laser light source. The optical element includes a microlens array or a diffraction grating, and its pitch is set based on the incident numerical aperture of the laser light and the wavelength of the laser light so that the distribution of the diffracted light emitted from the optical element becomes uniform. Has been done. This makes it possible to make the light quantity distribution of the light emitted from the optical element uniform regardless of the position of the viewpoint and without depending on the optical system arranged in the subsequent stage.

  In one aspect of the above-mentioned optical element, the optical element is a microlens array or a diffraction grating, and based on the spot diameter of the laser light with which the microlens array or the diffraction grating is irradiated, the microlens array or the diffraction grating The pitch is equal to or smaller than the spot diameter. As a result, the performance of the microlens itself designed to the desired specifications can be exhibited.

  In a preferred example, when the pitch is p, the incident numerical aperture is NAinc, and the wavelength is λ, the pitch p is

To be satisfied.

  In another preferred example, the laser light includes laser light of three colors of red, green, and blue, the pitch is p, the incident numerical aperture is NAinc, the wavelength of the red laser light is λRED, and When the wavelength of blue laser light is λ BLUE, the pitch p is

To be satisfied.

  In another preferred embodiment of the present invention, a head-up display is composed of a laser light source and the above optical element, and an optical screen for irradiating laser light emitted from the laser light source, and an optical screen emitted from the optical screen. And a combiner that reflects laser light.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Example]
FIG. 1 shows the configuration of a HUD according to an embodiment of the present invention. The HUD includes a laser projector 10 and a combiner 5. Laser light forming an image to be visually recognized by the driver is emitted from the laser projector 10, reflected by the combiner 5 which is a concave mirror, and reaches the viewpoint of the driver. As a result, the driver visually recognizes the image as a virtual image.

  The laser projector 10 includes a laser light source 11, an optical screen 12, and a MEMS mirror 13. The laser light source 11 includes three color laser light sources of R (red), G (green), and B (blue), and emits RGB laser light L corresponding to an image to be visually recognized by the driver. As shown in FIG. 3A, the optical screen 12 is composed of a lens array in which a plurality of microlenses (hereinafter, also simply referred to as “lenses”) 12x are arranged.

  FIG. 2 shows how the laser light L is scanned on the optical screen 12. The laser light L emitted from the laser light source 11 is scanned on the optical screen 12 by the MEMS mirror 13. As a result, an image to be visually recognized by the driver is drawn on the optical screen 12.

  In this embodiment, the lens pitch p of the lens array forming the optical screen 12 is focused on the lens array so that the driver can see the entire virtual image at any viewpoint position. It is characterized in that it is determined based on the incident NA (numerical aperture) of the laser light (incident light) and the wavelength of the laser light. Specifically, the lens pitch p of the lens array forming the optical screen 12 is determined so as to satisfy the following expression (1).

  Here, the lens pitch p is defined as the distance p between the centers of the adjacent lenses 12x among the plurality of lenses 12x forming the lens array, as shown in FIG. Further, the incident NA is given as “incident NA = sin θ” by using an angle θ indicating the spread of the incident light L incident on the optical screen 12, as shown in FIG.

  The formula (1) will be described below. FIG. 4A shows emitted light when an ideal optical screen is used. Since an ideal optical screen uniformly diffuses incident light, a laser spot for one pixel spreads evenly in emitted light. Therefore, the image by the incident light can be viewed in the same manner at any viewpoint position.

  FIG. 4B shows emitted light when a lens array is used as the optical screen. When a lens array is used, diffraction occurs due to the periodic structure of microlenses forming the lens array, and the emitted light does not spread evenly. Therefore, depending on the viewpoint position, the image may or may not be visible.

  5A shows the lens pitch p of the lens array, and FIG. 5B shows the distribution of the diffracted light emitted from the lens array. According to the grating law, the interval of diffracted light emitted from the lens array depends on the lens period. For example, when the lens array having the lens pitch p shown in FIG. 5A is used, the interval of the diffracted light is (2 / √3) · (λ / p).

  On the other hand, according to the scalar diffraction theory, the size of each diffracted light is determined by the incident NA of the incident light. Specifically, as shown in FIG. 6A, when the incident NA is large, the size (angle θ) of the diffracted light becomes large. Further, as shown in FIG. 6B, when the incident NA is small, the size of the diffracted light (angle θ ′) becomes small.

  From the above, as shown in FIG. 7, if the incident NA is increased to fill the gap of the diffracted light, the emitted light in which the diffracted light is distributed almost uniformly can be obtained. That is, under the condition that the magnitude of the diffracted light is equal to or larger than the interval of the diffracted light, that is, when the relationship of the following expression (2) is satisfied, the light quantity (luminance) distribution of the emitted light is uniform, and is almost ideal. You can get a screen.

  Further, in the emitted light, the emission NA as shown in FIG. 8B is also an important design element. If the emission NA is too small, the viewpoint range becomes narrow, and if it is too large, the brightness of the virtual image becomes insufficient. The following condition (A) is further required to obtain the injection NA that meets the system specifications.

  (A) The spot of incident light needs to be larger than the diameter of a single lens. This is because unless the incident light is made incident on the entire surface of each lens, the performance of the lens itself cannot be sufficiently exhibited. Therefore, as shown in FIG. 8A, the diameter of the incident light L is made larger than the diameter of the lens 12x. Here, if the diameter of the Airy disk (r = 1.22λ / NA) is used as the spot diameter of the laser light, the following expression (3) must be established.

  From the above equations (2) and (3), when the equation (1) is satisfied, the light amount distribution of the emitted light becomes uniform and a desired emission NA can be obtained.

  The equation (1) includes a parameter of the laser wavelength. When the laser light from the laser light source 11 is laser light of RGB colors, the laser wavelength has a relation of red> green> blue, and therefore the following formula (4) is obtained. Here, λRED is the wavelength of the red laser light, and λBLUE is the wavelength of the blue laser light.

  Next, a numerical example satisfying the above equation (4) will be examined. As an example, the incident NA of the laser light is set to 0.003. When the wavelength λ RED of the red laser light in Expression (4) is 0.638 nm, the lens pitch p is about 123 μm. Further, when the blue laser wavelength λ BLUE of the formula (4) is 0.450 nm, the lens pitch p is about 183 μm. Therefore, the lens pitch of the optical screen 12 for making the emitted light uniform is p = 123 to 183 μm.

  As described above, by setting the lens pitch p so as to satisfy the above formula (1) or (4), an optical system (for example, an optical system arranged at the subsequent stage of the optical screen 12 regardless of the viewpoint position). The light quantity distribution of the light emitted from the optical screen 12 can be made uniform without depending on a combiner or the like.

  Although it is ideal that the diffracted lights be lined up without any gap, in reality, there is a gap between adjacent diffracted lights, or some of the adjacent diffracted lights will overlap each other. Such gaps or overlaps are not strictly uniform. However, since the human eye visually recognizes an object with a certain amount of spread, not with dots, such minute gaps and overlaps are visually averaged and recognized, so in reality the human eye does not. It will look uniform. In the present invention, the diffracted light is uniform in this sense.

(Modification)
Although the optical screen 12 is of a transmissive type in the above embodiment, the optical screen 12 may be of a reflective type. FIG. 9 shows an example of the reflection type optical screen 12R. The reflective optical screen 12R is manufactured by forming the reflective film 12a on the curved surface of the lens array of the transmissive optical screen 12. The laser light incident on the lens array is reflected by the reflection film 12a on the lens array. By making the optical screen a reflective type, the degree of freedom in arranging components in the HUD can be increased.

  Further, in the above optical screen 12, the individual lenses 12x forming the lens array are hexagonal, but the application of the present invention is not limited to this. That is, each lens 12x may be a quadrangle or another polygon.

  Further, in the above optical screen 12, the pitch of the lens array in all directions need not be the same. For example, even if the lens 12x has a hexagonal shape that is collapsed in the vertical or horizontal direction, if both the vertical lens pitch and the horizontal lens pitch satisfy the expressions (1) and (4), the emitted light The light intensity distribution can be made uniform. Further, there may be a space between the adjacent lenses 12x.

[Other embodiments]
In the above embodiment, the optical screen 12 is composed of the lens array, but the application of the present invention is not limited to this. The optical screen may have a periodic array, and for example, a diffraction grating may be used. FIG. 10 shows the configuration of the optical screen 22 using a diffraction grating. FIG. 10A is a perspective view of the optical screen 22, and FIG. 10B is a plan view of the optical screen 22. The optical screen 22 using a diffraction grating also diffracts and emits incident light. At this time, by setting the grating pitch p so as to satisfy the above equations (1) and (4), it is possible to make the light quantity distribution of the emitted light uniform, as in the embodiment of the lens array.

5 Combiner 10 Laser Projector 11 Laser Light Source 12, 22 Optical Screen 12x Microlens 13 MEMS Mirror

Claims (2)

An optical element that diffuses laser light incident from a laser light source,
Equipped with a microlens array or diffraction grating,
The laser light includes laser light of three colors of red, green and blue,
When the pitch of the microlens array or the diffraction grating is p, the incident numerical aperture is NAinc, the wavelength of the red laser light is λRED, and the wavelength of the blue laser light is λBLUE,
The pitch p is

An optical element that satisfies the requirements. A laser light source for emitting the laser light;
An optical screen configured by the optical element according to claim 1, which diffuses and outputs the laser light emitted from the laser light source,
Projector equipped with.

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