LIGHT SCANNING DEVICE

A light scanning device includes a light source that emits laser light, a mirror device that includes a movable mirror swinging about at least one axis and directionally changes the laser light emitted from the light source by reflecting the laser light using the movable mirror, and a condensing optical system that condenses the laser light directionally changed by the mirror device. The condensing optical system includes a half-silvered mirror that has a concave surface, and a diffusion plate in which a plurality of micromirrors that diffuse the laser light transmitted through the half-silvered mirror from the concave surface side are formed.

BACKGROUND

1. Technical Field

The disclosed technology relates to a light scanning device.

2. Description of the Related Art

In recent years, augmented reality (AR) glasses that display a virtual image, various information, and the like in a superimposed manner on an actual view have been in practical use. The AR glasses are also referred to as smart glasses, a head mounted display (HMD), AR eyeglasses, and the like.

Some AR glasses employ a method of directly scanning laser light emitted from a light source to retinas of eyes of a user by directionally changing the laser light using a movable mirror (also referred to as a micro electro mechanical systems (MEMS) mirror) configured with MEMS. This method is referred to as a retinal scanning method. In the AR glasses of the retinal scanning method, the laser light directionally changed by the movable mirror is condensed to pupils of the eyes of the user by a condensing optical system and is scanned to the retinas. Since the retinal scanning method does not depend on a focus adjustment function of crystalline lenses of the eyes, the user can clearly see a video projected to the retinas even in a case where the user is nearsighted or farsighted or has presbyopia. In addition, the AR glasses of the retinal scanning method have high energy efficiency and thus, can be driven for a long time period.

On the other hand, the AR glasses of the retinal scanning method have a problem in that the video is not seen in a case where a condensing point of the laser light by the condensing optical system does not match positions of the pupils. That is, the video is not seen in a case where the positions of the pupils deviate from the condensing point because the user moves the eyes. This problem is known as a narrow movable range of the eyes for clearly seeing the video, that is, a narrow eyebox.

Accordingly, an objective for the AR glasses of the retinal scanning method is to expand the eyebox. US2018/0299680A discloses a technology for expanding an eyebox by replicating laser light directionally changed by a movable mirror using a prism or a light guide plate. In addition, Changwon Jang, Kiseung Bang, Seokil Moon, Jonghyun Kim, Seungjae Lee, and Byoungho Lee. 2017. Retinal 3D: augmented reality near-eye display via pupil-tracked light field projection on retina. ACM Trans. Graph. 36, 6, Article 190 (November 2017). Retrieved from the Internet: <URL: http://library.usc.edu.ph/ACM/TOG%2036/content/papers/190-0330-jang.pdf> discloses a technology for expanding an eyebox by condensing laser light to positions of pupils using a mirror while tracking the positions of the pupils using eye tracking.

SUMMARY

However, the technologies disclosed in US2018/0299680A and Changwon Jang, Kiseung Bang, Seokil Moon, Jonghyun Kim, Seungjae Lee, and Byoungho Lee. 2017. Retinal 3D: augmented reality near-eye display via pupil-tracked light field projection on retina. ACM Trans. Graph. 36, 6, Article 190 (November 2017). Retrieved from the Internet: <URL: http://library.usc.edu.ph/ACM/TOG%2036/content/papers/190-0330-jang.pdf> have a complicated configuration for expanding the eyebox. Thus, a technology that can expand the eyebox with a simple configuration is desired. Furthermore, a technology that can expand the eyebox and also expand an angle of view is desired.

An object of the disclosed technology is to provide a light scanning device that can expand an eyebox and expand an angle of view with a simple configuration.

In order to accomplish the above object, a light scanning device according to an aspect of the present disclosure comprises a light source that emits laser light, a mirror device that includes a movable mirror swinging about at least one axis and directionally changes the laser light emitted from the light source by reflecting the laser light using the movable mirror, and a condensing optical system that condenses the laser light directionally changed by the mirror device, in which the condensing optical system includes a half-silvered mirror that has a concave surface, and a diffusion plate in which a plurality of micromirrors that diffuse the laser light transmitted through the half-silvered mirror from the concave surface side are formed.

It is preferable that the condensing optical system condenses the laser light directionally changed by the mirror device to a center of an eyeball.

It is preferable that the concave surface is an elliptical surface, and a swinging axis of the movable mirror is positioned at one focal point of the elliptical surface, and the center of the eyeball is positioned at the other focal point of the elliptical surface.

It is preferable that the diffusion plate diffuses the laser light transmitted through the half-silvered mirror from the concave surface side in a direction other than a specular reflection direction.

It is preferable that the half-silvered mirror and the diffusion plate are formed of a material having the same refractive index.

It is preferable that the movable mirror is configured to be swingable about a first axis and a second axis that are orthogonal to each other.

According to the disclosed technology, a light scanning device that can expand an eyebox and expand an angle of view with a simple configuration can be provided.

DETAILED DESCRIPTION

Hereinafter, an embodiment according to the disclosed technology will be described in detail with reference to the drawings. As an example, a form of applying a light scanning device according to the embodiment of the disclosed technology to AR glasses will be described in the embodiment below.

FIG.1illustrates a configuration of AR glasses10according to the present embodiment. As illustrated inFIG.1, the AR glasses10are configured with a frame11, two lenses12, two temples13, a module14, and a condensing optical system15. The two lenses12are held in the frame11. Each of the two temples13is connected to an end part of the frame11through a hinge (not illustrated).

The module14is provided in one of the two temples13. In addition, the condensing optical system15is provided in the lens12on a temple13side in which the module14is provided out of the two lenses12. In the present embodiment, the module14is provided in the temple13on a right eye side, and the condensing optical system15is provided in the lens12on the right eye side. The module14may be provided in both of the two temples13, and the condensing optical system15may be provided in both of the two lenses12.

The module14emits laser light L modulated in accordance with an image signal toward the condensing optical system15. The condensing optical system15reflects and condenses a part of the laser light L incident from the module14to a center of an eyeball of a user wearing the AR glasses10. Reference numeral P denotes a condensing point of the laser light L by the condensing optical system15. As will be described in detail later, the condensing optical system15is configured to reflect a part of the laser light L incident from the module14and diffuse a part of the laser light L.

FIG.2illustrates configurations of the module14and the condensing optical system15. As illustrated inFIG.2, the module14comprises a control device20, a micro electro mechanical systems (MEMS) driver22, a light emitting device24, a multiplexing optical system26, a collimator28, and a MEMS mirror30. The MEMS mirror30is an example of a “mirror device” according to the embodiment of the disclosed technology.

The light emitting device24includes a laser driver25and a laser light source27. The laser driver25of the present embodiment drives the laser light source27based on an intensity modulation signal supplied from the control device20and causes the laser light L for forming an image to be output from the laser light source27. For example, the laser light source27outputs the laser light L of three colors of red (R), green (G), and blue (B). The laser light source27is an example of “light source” according to the embodiment of the disclosed technology.

The laser light L output from the laser light source27is multiplexed by the multiplexing optical system26. Then, the MEMS mirror30is irradiated with the multiplexed laser light L through the collimator28. The laser light L with which the MEMS mirror30is irradiated is reflected toward the condensing optical system15by the MEMS mirror30.

The MEMS driver22drives the MEMS mirror30under control of the control device20. In the MEMS mirror30, a mirror portion40(refer toFIG.3) that reflects the laser light L independently swings about each of two axes orthogonal to each other as a central axis. In the present embodiment, the laser light L is scanned in a state of drawing a Lissajous curve on the condensing optical system15by the swing of the mirror portion40based on a driving signal. The Lissajous curve is a curve that is decided by a swing frequency about a first axis, a swing frequency about a second axis, and a phase difference therebetween. The mirror portion40is an example of a “movable mirror” according to the embodiment of the disclosed technology. The MEMS mirror30directionally changes the laser light L by reflecting the laser light L using the mirror portion40. Directional changing refers to changing a traveling direction of the laser light L.

The control device20of the present embodiment includes a field programmable gate array (FPGA)20A and a memory20B. For example, the memory20B is a volatile memory and stores various information such as the image signal representing the image projected to the condensing optical system15. For example, the memory20B stores the image signal input from an outside of the AR glasses10.

The condensing optical system15is composed of a half-silvered mirror16and a diffusion plate17. The laser light L directionally changed by the MEMS mirror30is incident on the half-silvered mirror16. The diffusion plate17is bonded to a surface of the half-silvered mirror16on an opposite side from a surface on which the laser light L is incident.

A concave surface16A that specularly reflects a part of the laser light L incident from the MEMS mirror30is formed in the half-silvered mirror16. The half-silvered mirror16specularly reflects a part of the laser light L and transmits a part of the laser light L. The laser light L transmitted through the half-silvered mirror16is incident on the diffusion plate17. InFIG.2, the laser light L transmitted through the half-silvered mirror16is not illustrated.

In the present embodiment, the concave surface16A is an elliptical surface. More specifically, the concave surface16A is a surface of a part of a rotational ellipsoid obtained by rotating an ellipse about an axis passing through two focal points of the ellipse as a center. That is, the concave surface16A is an off-axis elliptical surface. Light output from one focal point always reaches the other focal point in a case where the light is specularly reflected by the concave surface16A.

The AR glasses10are configured such that a swinging axis of the MEMS mirror30is positioned at one focal point of the concave surface16A and a center of an eyeball EB of the user is positioned at the other focal point. Based on this geometrical relationship, a part of the laser light L incident on the condensing optical system15from the MEMS mirror30is reflected by the concave surface16A of the half-silvered mirror16and is condensed to the center of the eyeball EB.

A plurality of micromirrors17A that diffuse the laser light L transmitted through the half-silvered mirror16are formed in the diffusion plate17. For example, each micromirror17A has an approximately hemispherical shape and is arranged to have a convex shape toward the concave surface16A of the half-silvered mirror16. For example, the plurality of micromirrors17A are in contact with a surface of the half-silvered mirror16on an opposite side from the concave surface16A. In addition, the plurality of micromirrors17A are arranged adjacent to each other in two dimensions.

For example, the half-silvered mirror16and the diffusion plate17are formed of a material such as resin or glass that transmits the laser light L. In addition, for example, the half-silvered mirror16and the diffusion plate17are formed of a material having the same refractive index. The diffusion plate17reflects a part of the laser light L transmitted through the half-silvered mirror16on surfaces (that is, an interface between the half-silvered mirror16and the diffusion plate17) of the micromirrors17A. The condensing optical system15has a light-transmitting property as a whole and transmits a part of external light incident from an outside toward the eyeball EB.

Each micromirror17A diffuses the laser light L transmitted through the half-silvered mirror16in a specular reflection direction and a direction other than the specular reflection direction. The specular reflection direction is a reflection direction in a case where light is reflected in a direction equal to an incidence angle. Since each micromirror17A also diffuses the laser light L in the direction other than the specular reflection direction, a part of the laser light L diffused by the micromirrors17A passes through a pupil of the eyeball EB and is incident on a retina without passing through the condensing point P that is the center of the eyeball EB.

FIG.3illustrates an example of a configuration of the MEMS mirror30. The MEMS mirror30includes the mirror portion40, a first support portion41, a first movable frame42, a second support portion43, a second movable frame44, a connecting portion45, and a fixed frame46.

The mirror portion40has a reflecting surface40A on which an incidence ray is reflected. For example, the reflecting surface40A is formed with a thin metal film of gold (Au), aluminum (Al), silver (Ag), or a silver alloy. For example, a shape of the reflecting surface40A is a circular shape.

The first support portion41is arranged outside the mirror portion40at each of positions that face with a second axis a2interposed therebetween. The first support portions41are connected to the mirror portion40on a first axis a1and support the mirror portion40in a swingable manner about the first axis a1.

The first movable frame42is a rectangular frame surrounding the mirror portion40and is connected to the mirror portion40through the first support portions41on the first axis a1. A piezoelectric element50is formed on the first movable frame42at each of positions that face with the first axis a1interposed therebetween. In such a manner, a pair of first actuators51are configured by forming two piezoelectric elements50on the first movable frame42.

The pair of first actuators51are arranged at positions that face with the first axis a1interposed therebetween. The first actuators51cause the mirror portion40to swing about the first axis a1by applying rotational torque about the first axis a1to the mirror portion40.

The second support portion43is arranged outside the first movable frame42at each of positions that face with the first axis a1interposed therebetween. The second support portions43are connected to the first movable frame42on the second axis a2and support the first movable frame42and the mirror portion40in a swingable manner about the second axis a2. In the present embodiment, the second support portions43are torsion bars that stretch along the second axis a2.

The second movable frame44is a rectangular frame surrounding the first movable frame42and is connected to the first movable frame42through the second support portions43on the second axis a2. The piezoelectric element50is formed on the second movable frame44at each of positions that face with the second axis a2interposed therebetween. In such a manner, a pair of second actuators52are configured by forming two piezoelectric elements50on the second movable frame44.

The pair of second actuators52are arranged at positions that face with the second axis a2interposed therebetween. The second actuators52cause the mirror portion40to swing about the second axis a2by applying rotational torque about the second axis a2to the mirror portion40and the first movable frame42.

The connecting portion45is arranged outside the second movable frame44at each of positions that face with the first axis a1interposed therebetween. The connecting portions45are connected to the second movable frame44on the second axis a2.

The fixed frame46is a rectangular frame surrounding the second movable frame44and is connected to the second movable frame44through the connecting portions45on the second axis a2.

In the present embodiment, the first axis a1and the second axis a2are orthogonal to each other. In the following description, a direction parallel to the first axis a1will be referred to as an X direction, a direction parallel to the second axis a2will be referred to as a Y direction, and a direction orthogonal to the first axis a1and the second axis a2will be referred to as a Z direction.

FIG.4illustrates a positional relationship among the MEMS mirror30, the condensing optical system15, and the eyeball EB. As illustrated inFIG.4, the MEMS mirror30is arranged such that the first axis a1that is one swinging axis passes through one focal point of the concave surface16A that is an elliptical surface. Specifically, the MEMS mirror30is arranged such that an intersection between the first axis a1and the second axis a2matches one focal point of the concave surface16A that is an elliptical surface. Based on this geometrical relationship, a condensing point P of the laser light L reflected by the concave surface16A matches the other focal point of the concave surface16A.

The AR glasses10are configured such that the center of the eyeball EB matches the condensing point P in a case where the user wears the AR glasses10. Thus, in a case where the user sees the concave surface16A of the half-silvered mirror16in a state of wearing the AR glasses10, a part of the laser light L reflected by the concave surface16A is incident into the eyeball EB through the pupil and is condensed to the condensing point P and then, is incident on the retina. The laser light L incident into the eyeball EB is mainly incident on a region corresponding to a macula lutea including a fovea centralis in the retina. The fovea centralis is a part in which cells for recognizing colors and shapes are concentrated and has the highest resolution in the retina. The user recognizes a video based on the laser light L projected to the retina.

In the video projected to the concave surface16A of the half-silvered mirror16by the MEMS mirror30, the user can clearly recognize a part positioned at a center in a visual line direction.

WhileFIG.4illustrates a state where the concave surface16A condenses the laser light L to the condensing point Pin a YZ plane orthogonal to the first axis a1, the concave surface16A is not limited to the YZ plane and also condenses the laser light L to the condensing point P in a plane other than the YZ plane including the two focal points.

InFIG.4, reference numeral Ld denotes a part of the laser light L (hereinafter referred to as diffused light Ld) that is transmitted through the half-silvered mirror16and diffused by the diffusion plate17. As described above, the diffusion plate17diffuses the laser light L that is transmitted through the half-silvered mirror16and incident in the specular reflection direction and the direction other than the specular reflection direction by the micromirrors17A. Thus, a part of the diffused light Ld is incident on the retina without passing through the condensing point P that is the center of the eyeball EB. That is, the diffused light Ld is also incident on a region other than a region on which the laser light L reflected by the concave surface16A is incident in the retina.

FIG.5toFIG.7are diagrams for describing expansion of an eyebox and expansion of an angle of view by the AR glasses10according to the present embodiment.

FIG.5illustrates a state where the user sees the front. In this case, the laser light L mainly related to the video at the center of the video projected to the concave surface16A of the half-silvered mirror16is reflected by the concave surface16A and is incident near the fovea centralis of the retina through the pupil. Reference numeral60denotes an image recognized by the user in a brain. Reference numeral61denotes a region (hereinafter, referred to as a high-definition region) that can be clearly recognized by the user in the entire image60. The high-definition region61corresponds to a region near the fovea centralis of the retina. InFIG.5, the high-definition region61is positioned at a center of the image60.

FIG.6illustrates a state where the user moves a visual line to a right side from the front. In this case, the laser light L mainly related to the video on a right side of the video projected to the concave surface16A of the half-silvered mirror16is incident near the fovea centralis of the retina through the pupil. InFIG.6, the high-definition region61is positioned on a right side of the image60.

FIG.7illustrates a state where the user moves the visual line to a left side from the front. In this case, the laser light L mainly related to the video on a left side of the video projected to the concave surface16A of the half-silvered mirror16is incident near the fovea centralis of the retina through the pupil. InFIG.7, the high-definition region61is positioned on a left side of the image60.

As illustrated inFIG.5toFIG.7, in the AR glasses10according to the present embodiment, since the laser light L reflected by the concave surface16A of the half-silvered mirror16is condensed to the center of the eyeball EB, the laser light L of a region (corresponds to the high-definition region61) on which the user focuses in the video projected to the concave surface16A is always incident near the fovea centralis of the retina even in a case where a position of the pupil is moved because the user moves the visual line. In the embodiment of the disclosed technology, while the region that can be clearly recognized by the user in the video projected to the concave surface16A of the half-silvered mirror16is slightly narrow, the region on which the user focuses can be always clearly recognized even in a case where the visual line is moved. That is, according to the embodiment of the disclosed technology, the eyebox can be expanded with a simple configuration.

In addition, the diffused light Ld is mainly incident on a region other than the region corresponding to the macula lutea including the fovea centralis in the retina. The diffused light Ld includes light generated by diffusion, by the diffusion plate17, of the laser light L related to an edge part region other than the region on which the user focuses in the video projected to the concave surface16A. Thus, in addition to the laser light L related to the video at the center of the video projected to the concave surface16A, the laser light L related to the video in an edge part is incident on the retina as the diffused light Ld. Accordingly, while the video in the edge part of the region on which the user focuses has low resolution, the user can also recognize the video in the edge part. Thus, the angle of view is expanded.

In addition, as described above, by having the same refractive index for the half-silvered mirror16and the diffusion plate17, refraction in the interface between the half-silvered mirror16and the diffusion plate17in a case where the external light is transmitted through the condensing optical system15from a diffusion plate17side is suppressed. By suppressing the refraction of the external light, the condensing optical system15enables the user to observe a view of an outer world without distortion together with the video based on the laser light L.

FIG.8is a diagram for describing a retinal scanning method of the related art. In the retinal scanning method of the related art, the laser light L is condensed near a center of the pupil and then, is incident on the retina.FIG.8illustrates a state where the user sees the front. In this case, since the condensing point P of the laser light L is positioned near the center of the pupil, an incidence angle of the laser light L incident on the retina is wide. That is, in the retinal scanning method of the related art, in a case where the user sees the front, the angle of view is wide, and the entire image60can be recognized. On the other hand, in the retinal scanning method of the related art, in a case where the user moves the visual line, the position of the pupil deviates from the condensing point P. Thus, there is a problem that the eyebox is narrow.

FIG.9illustrates a state where the user moves the visual line to the right side from the front in the retinal scanning method of the related art. In this case, for example, the laser light incident from a right side of the pupil is blocked by an iris positioned on a left side of the pupil. Consequently, the video in a region on the right side of the image60is not seen. Since the video on the right side is not seen even in a case where the user moves the visual line to the right side in order to see the right side, the user feels stressed.

On the other hand, in a retinal scanning method according to the embodiment of the present disclosure, the laser light L is condensed to the center of the eyeball EB. Thus, even in a case where the position of the pupil is moved because the user moves the visual line, the user can always clearly recognize near a center of the visual line and does not feel stressed unlike in the related art. In the retinal scanning method according to the embodiment of the present disclosure, the resolution of the edge part region is low, and the edge part cannot be clearly recognized, compared to the retinal scanning method of the related art. However, generally, a person can only clearly recognize near a center of the visual field and needs to move eyes in accordance with a region of interest in a case of, for example, reading a text. Thus, as long as the user can always clearly recognize near the center of the visual line as in the retinal scanning method according to the embodiment of the present disclosure, there is no practical problem even in a case where the edge part region cannot be clearly recognized.

Modification Example

Next, various modification examples of the embodiment will be described. In the embodiment, while the diffusion plate17is configured to diffuse the laser light L that is transmitted through the half-silvered mirror16and incident in the specular reflection direction and the direction other than the specular reflection direction, the diffusion plate17may be configured to diffuse the laser light L in only the direction other than the specular reflection direction. For example, each micromirror17A may have a shape in which the laser light L is diffused in only a direction outside an angular range of ±5° about the specular reflection direction as a center. By having such a configuration for the diffusion plate17, the diffused light Ld is incident on only the edge part region of the retina without passing through the condensing point P that is the center of the eyeball EB. Thus, a decrease in resolution of the high-definition region61because of the incidence of the diffused light Ld is suppressed. Accordingly, a contrast of the image60is improved.

In addition, in the embodiment, while the diffusion plate17has the light-transmitting property, the diffusion plate17may have light reflectivity. For example, a light reflection film such as a metal film that highly reflects the laser light L is formed in the interface (that is, the surfaces of the micromirrors17A) between the half-silvered mirror16and the diffusion plate17. In addition, the diffusion plate17may be formed with a member of metal or the like having the light reflectivity. In a case where the diffusion plate17has the light reflectivity, the external light is not transmitted through the condensing optical system15. Thus, a light scanning device that projects an immersive video can be configured.

In addition, the configuration of the MEMS mirror30illustrated in the embodiment can be appropriately changed. For example, in the embodiment, while the first actuator51and the second actuator52have a ring shape, one or both of the first actuator51and the second actuator52can have a meander structure. In addition, a support member having a configuration other than a torsion bar can be used as the first support portion41and the second support portion43.

In addition, various modifications can be made to a hardware configuration of the control device20. A processing unit of the control device20may be configured with one processor or may be configured with a combination of two or more processors of the same type or different types (for example, a combination of a plurality of field programmable gate arrays (FPGAs) and/or a combination of a CPU and an FPGA).

All documents, patent applications, and technical standards disclosed in the present specification are incorporated in the present specification by reference to the same extent as in a case where each of the documents, patent applications, technical standards are specifically and individually indicated to be incorporated by reference.