JP4630892B2 - Scanning optical system, scanning image display apparatus, and image display system - Google Patents

Description

  The present invention relates to a scanning optical system suitable for an image display device such as a head mounted display (HMD) or a projector that scans light to form an image in an observer's eye or a screen and observe the image.

  In an image display device such as a head-mounted display (HMD) or a projector, it is common to use a transmissive liquid crystal, a reflective liquid crystal, or an EL element as an original image display element. Recently, however, means for scanning a light beam is used. An image display device that displays a two-dimensional image by using an image has also been proposed (see Patent Document 1).

  Patent Document 1 discloses a scanning image display device that scans RGB light in a horizontal direction and a vertical direction, and forms an image directly on an observer's retina via an optical system.

  However, since the scanning image display device disclosed in Patent Document 1 is required to scan light at a very high speed, a very small device is used as an optical scanning means such as a mirror for scanning light. It has been broken. Therefore, the scanned light beam is very thin, and the light beam at the observer's pupil position is very small in diameter, making it difficult to obtain a sufficiently large exit pupil diameter.

  As a method for enlarging such a small exit pupil diameter, there are techniques disclosed in Patent Documents 2 and 3. In Patent Document 2, an exit pupil enlarging unit such as a lens array or a diffusion plate is disposed on an intermediate image plane having a curvature formed by a scanned beam, and is transmitted through the exit pupil enlarging unit. After that, the spread angle of the light beam is increased.

  Further, in Patent Document 3, although it is not a scanning image display device, the exit pupil is similarly enlarged by transmitting light after being incident on an image display element such as liquid crystal illuminated by parallel light through a diffusion plate. I am doing so.

  However, since the devices disclosed in Patent Documents 2 and 3 use intermediate image transmission type exit pupil enlarging means, the optical path becomes long and the device tends to be large.

Patent Document 4 proposes a relatively small optical system that uses a decentered free-form surface optical system to make light from a light source a slightly thick beam, reflected by an optical scanning unit, and guided to an eyeball. In this patent document, there is a description that the exit pupil is enlarged by a transmission type diffusion plate, but it is inevitable that the size is increased due to the use of the transmission type diffusion plate. That is, in this case, the size can only be reduced to about twice the size of a free-form surface prism (described in Patent Document 5 and Non-Patent Document 1) known as a representative of a small eyepiece optical system.
US Pat. No. 5,467,104 (FIG. 1 etc.) US Pat. No. 5,701,132 (FIG. 1 etc.) US Pat. No. 5,757,544 (FIG. 1 etc.) JP 2001-4955 A (FIG. 1 etc.) Japanese Patent No. 2911750 (FIG. 1 etc.) Optics, Vol. 25, no. 1, p2-7, 1996

  As described above, in the conventional scanning image display device, in order to obtain a sufficiently large exit pupil diameter, the exit pupil is enlarged by using a transmission type diffusion plate to facilitate observation. Sufficient miniaturization of the system has not been achieved.

  An object of the present invention is to provide a scanning optical system that can be further reduced in size even in the case where means for enlarging the exit pupil is used.

In order to achieve the above object, the present invention provides a scanning optical system having an optical scanning unit that scans light from a light source and an optical system that directs the light scanned by the optical scanning unit to an exit pupil. The optical system has a plurality of surfaces including a reflective surface, and the reflective surface has a smaller area than the reflective region inside the reflective region that reflects light from other surfaces, and high light transmittance than the reflection region, light from the optical scanning unit and the transmission region for allowing incident is formed in the optical system, an intermediate image light in the optical system incident from the transmission region A diffuse reflection surface that reflects the light from the transmission region toward the reflection surface is disposed at a position of the intermediate image or a position close thereto, and a conjugate image of an exit pupil of the optical system is the transmission image It is formed at a position on or close to the area. To.

  As described above, according to the present invention, in a scanning optical system that scans light and displays an image, it is possible to achieve downsizing as compared with the conventional one even if a means for sufficiently increasing the exit pupil is used. .

  Prior to the description of the embodiments of the present invention, definitions of the bus bar cross section, the bus bar cross section, the local bus bar cross section, and the local bus bar cross section used in each embodiment will be described.

  In the definition of the conventional system that does not correspond to the eccentric system, if the z-axis is the optical axis in each surface vertex coordinate system, the yz section is the conventional generatrix section (meridional section), and the xz section is the child section (sagittal section). Become. Since the present embodiment is an eccentric system, a local bus cross section and a local sub line cross section corresponding to the eccentric system are newly defined.

  First, a light ray emitted from the light source and passing through the center of the enlarged image and the center of the exit pupil of the display optical system is referred to as a central field angle principal ray. In the drawing corresponding to each embodiment, the central field angle principal ray is indicated as L0.

  Then, on the hit point in each surface of the central field chief ray, the surface including the incident light and the exit light of the central field chief ray is defined as a local bus cross section, and each surface is perpendicular to the local bus cross section including the hit point. A plane parallel to the cross section of the vertex coordinate system (normal subsection) is defined as the local subsection. The focal length in the local bus section and the focal length in the local subsection will be described later.

  Hereinafter, main features of the embodiment of the present invention will be described.

  1. In a scanning optical system having an optical scanning unit that scans light from a light source and an optical system that directs light scanned by the optical scanning unit to an exit pupil plane, the optical system has at least a reflective action, A first surface decentered with respect to the chief ray of view angle; and a second surface that reflects the light beam reflected by the first surface toward the first surface again, the first surface comprising: The central field angle chief ray incident again on the first surface from the second surface is approximately opposite to the previous line with respect to the normal on the hit point of the central field chief ray on the first surface. reflect.

  Thereby, the light from the optical scanning unit is reflected on the optical path (outward path) to the second surface including the first reflection on the first surface and on the second surface (folded reflection surface). It is possible to make the optical system having a long optical path length as a small optical system by substantially overlapping the optical path (return path) including reflection on the surface of 1.

  Here, when focusing on the reflection on the first surface before and after the reflection on the second surface as the return reflection surface, the vector indicating the incident direction on the first surface and the vector indicating the reflection direction are formed. It can be said that the direction of the outer product is almost opposite in both the forward and return directions. It is also possible to form an optical path by providing a plurality of surfaces that function as reflecting surfaces in the forward path and the return path.

  By utilizing the reflection at the folded reflection surface characterized in this way, compared with the so-called zigzag reflection performed between two normal facing surfaces, a long optical path is formed in a narrow space while suppressing the occurrence of distortion. Can fit. Further, the reflection on the first surface is not limited to two times, and the optical power of the first surface may be used by reflecting three or more times.

  Moreover, in the central field angle chief ray, the incident light on each surface including the folded reflection surface and the planes including the reflected light are typically all in the same plane, but the incident light and the reflected light are included. The planes do not necessarily have to be in the same plane. In other words, the component reflected in the direction perpendicular to the plane may be given to the light reflected by the folded reflecting surface by the folded reflecting surface. In this case, for example, when attention is paid to the first surface on which the light beam is reflected toward the return reflection surface and the light beam reflected by the return reflection surface is incident, the vector indicating the incident direction on the first surface and the reflection direction are indicated. The direction of the outer product formed by the vector makes an obtuse angle in each of the forward path and the return path. The configuration of the optical path can also be characterized by the negative inner product formed by the outer products (outer products).

  Further, not only on the folded reflection surface, but also on other reflection surfaces, the reflected light may be given a component in a direction perpendicular to the plane.

  By doing so, each reflecting surface also has an eccentricity in the direction perpendicular to the plane with respect to the light beam, and the degree of freedom in optical design can be increased.

  1-2. The light from the light source forms an intermediate imaging plane through the optical scanning means, and the optical scanning means is arranged at a position conjugate with the exit pupil of the optical system, and the light from the optical scanning means is on the intermediate imaging plane. A two-dimensional image is formed.

  There is an optical system (relay optical system) that forms a light source image on an intermediate image plane, and an optical scanning means is arranged at the position of the stop of the relay optical system, and the stop (optical scanning means) of the relay optical system and the emission of the optical system If the pupils are in a conjugate relationship, no light will be lost when the observer places his eyes on the exit pupil plane.

  1-3. After the light beam travels in the forward path, reflected reflection, and return path, the optical system is reflected by another reflecting surface decentered with respect to the light beam, and forms an optical path different from the forward path.

  As a result, the light beam emitted from the round-trip optical path can be guided in a different direction from the light beam incident on the round-trip optical path, and interference with the incident light on the round-trip optical path can be avoided.

  1-4. The optical scanning means is a two-dimensional scanning minute reflecting member.

  When the reflecting member that is scanned only in the one-dimensional direction is used for each of horizontal scanning and vertical scanning, one reflecting member is arranged at a position conjugate with the exit pupil, and another reflecting member is conjugated with the exit pupil. Since it must be arranged at a position (second pupil imaging plane), the optical system becomes large. In addition, since two elongated reflecting members are required, the optical scanning means is also increased in size. On the other hand, if horizontal scanning and vertical scanning are performed with a two-dimensional scanning micro-reflecting member that is one reflecting member capable of scanning in a two-dimensional direction, a micro device can be used as an optical scanning means, and high-speed scanning is also possible. It becomes. Further, since the optical system only needs to have a one-time pupil imaging conjugate relationship, it can be reduced in size.

  2. In a scanning optical system having an optical scanning unit that scans light from a light source and an optical system that directs light scanned by the optical scanning unit to an exit pupil plane, the optical system has at least a reflective action, A first surface decentered with respect to the chief ray of view angle; and a second surface that reflects the light beam reflected by the first surface toward the first surface again, the first surface comprising: The central field angle chief ray incident again on the first surface from the second surface is approximately opposite to the previous line with respect to the normal on the hit point of the central field chief ray on the first surface. In addition, the second surface has a diffuse reflection effect, and an intermediate imaging surface is formed on or near the second surface.

  In other words, the optical system includes a case where the inner product formed by the outer product formed by the vector indicating the incident direction to the first surface and the vector indicating the reflection direction is negative, and the second surface has a diffuse reflection effect. And an intermediate imaging plane is formed on the second surface or at a position close thereto.

  In an optical system having an intermediate image plane with a long optical path length, by overlapping the optical paths (forward path and return path), the optical systems having long optical path lengths can be combined as a small optical system, and a small display optical system can be realized. Then, by providing an intermediate imaging surface and a diffusing surface on the return reflection surface between the forward path and the return path, an optical system that guides a thin beam on the forward path, and a diffusion optical system that can cover a wide exit pupil on the return path, respectively. As a result, it is possible to achieve both downsizing of the optical system and enlargement of the exit pupil.

  2-2. The optical system has a transparent body on which at least three surfaces including a plurality of non-rotationally symmetric reflecting surfaces are formed.

  Since the optical system of this embodiment is a decentered optical system, decentration aberrations occur. However, by providing a plurality of non-rotationally symmetric reflecting surfaces, the generated decentration aberrations can be canceled or reduced. Further, even if the horizontal and vertical aspect ratios by the optical scanning means are set freely, there are a plurality of non-rotationally symmetric reflecting surfaces, so that the aspect ratio of the enlarged display screen is a required value (3: 4 or 9:16). Etc.), and the degree of freedom in design increases.

  The non-rotationally symmetric surface is preferably a plane-symmetric shape having a local generatrix cross section as the only symmetric surface. This is because processing and fabrication are easier than in the case of no symmetry. Furthermore, by using a transparent body having at least three surfaces, a plurality of conventional parts can be replaced with one transparent body, so that assembly and adjustment are facilitated.

  2-3. The optical system has at least one internal total reflection surface and performs total internal reflection at least twice.

  The internal total reflection surface is a phenomenon in which light is theoretically reflected by 100% when light is incident at a critical angle or more with respect to the normal of the surface when reflected in a transparent body. Since the light utilization efficiency is higher than the film reflection, it is possible to eliminate the light amount loss on the surface. If an internal total reflection surface is provided in the reciprocating optical path, total internal reflection is performed at least twice, and the light amount loss in the entire optical system can be reduced.

  3. In a scanning optical system having an optical scanning unit that scans light from a light source and an optical system that directs the light scanned by the optical scanning unit to the exit pupil plane, the optical system is decentered with respect to the optical path, and It has a plurality of non-rotationally symmetric reflecting surfaces facing each other and a diffuse reflecting surface having a diffuse reflecting action, and forms an intermediate imaging surface on or near the diffuse reflecting surface and reflects on the diffuse reflecting surface. The enlarged light is guided to the exit pupil plane by the light thus formed, and an enlarged image is formed.

  If a plurality of non-rotationally symmetric reflecting surfaces are arranged to face each other, the optical path can be made zigzag, and the optical system can be made thin. Furthermore, if a diffuse reflection surface is provided in the vicinity of the intermediate image plane, it is possible to achieve both reduction in the thickness of the optical system and enlargement of the exit pupil.

  3-2. In the optical system, there are a plurality of shared surfaces shared by the optical path from the optical scanning unit to the intermediate image plane and the optical path from the intermediate image plane to the magnified image.

  Thereby, an unnecessary optical surface can be reduced and an optical system can be reduced in size. The optical system from the intermediate image plane to the magnified image is an eyepiece optical system, and the optical system from the light source to the intermediate image plane is a relay optical system. In general, a relay optical system requires about two optical powers of the eyepiece optical system (reciprocal of the focal length). Therefore, some surfaces of the eyepiece optical system and the relay optical system (especially those near the intermediate image plane) Surface) is preferably shared by both optical paths. When there are a plurality of shared surfaces, the light beam can be folded by both the relay optical system and the eyepiece optical system, so that the entire optical system can be thinned.

  3-3. The plurality of shared surfaces are non-rotationally symmetric reflecting surfaces.

  A non-rotationally symmetric reflecting surface as a relay system can reduce decentration aberrations at the intermediate image plane, and a non-rotationally symmetric reflecting surface as an eyepiece optical system can reduce decentration aberrations at the eyepiece optical system.

  3-4. The optical system includes a transparent body on which at least three surfaces including a plurality of shared surfaces are formed, and the reflecting surface having a diffusing action is separate from the transparent body.

  By configuring the reflecting surface having the diffusing action as one member, it can be made independent of the transparent body and exchangeable with a diffusing member having various diffusing characteristics. Further, the transparent body and the diffusing member may be integrated by forming an intermediate imaging surface in the vicinity of the reflecting surface of the transparent body and giving the reflecting surface a diffusing action. Thereby, a number of parts can also be reduced and adjustment between a diffusing member and a transparent body becomes unnecessary. Further, if the reflecting surface is set to the above-described folding reflecting surface of the reciprocating optical path, the optical system can be miniaturized.

  4). In a scanning optical system having an optical scanning unit that scans light from a light source and an optical system that directs light scanned by the optical scanning unit to an exit pupil plane, the optical system includes a plurality of surfaces including a reflective surface. The light from the optical scanning means is provided on the reflective surface and has a smaller area than the reflective region and higher light transmittance than the reflective region inside the reflective region that reflects light from other surfaces. Is formed in the optical system.

  A half mirror is generally considered as an optical path separation unit that transmits light from the optical scanning unit and reflects light that has returned from another surface. However, when the light that has passed through the half mirror returns and is reflected, the amount of light becomes ¼ (25%) in principle, and the light utilization efficiency is low.

  Therefore, in the present embodiment, a reflection surface having the reflection region and the transmission region is used as the optical path separation unit. In the part of the optical system where the light from the optical scanning unit is incident, the area of the part through which the light (beam) passes may be very small, so that only the small part is not a reflection area but a transmission area (only that area) Uses a reflective surface (not coated with a metal film). When the light returns to the reflecting surface, the light beam spreads by a diffuser plate or the like, so that most of the light beams other than the light beam that passes through the minute transmission region are reflected. For this reason, when the magnified image is observed, the transmission region is very small, so that the observer does not feel a substantial decrease in the amount of light, and the light utilization efficiency is increased compared to the case where the half mirror is used. be able to.

  Here, the ratio (Db / Da) of the area Da of the reflection area (effective area where light rays are incident) and the area Db of the transmission area on the reflection surface is preferably 10% or less. When this value is 10%, 100% of the light beam from the optical scanning means is transmitted through the transmission region and returned to the optical system when surface reflection or light absorption by the reflection film is not considered. Since 90% of the light beam is reflected by the reflecting surface, the light utilization efficiency is 90%. On the other hand, if Db / Da exceeds 10%, the portion of the returned light beam that is transmitted (not reflected) through the minute transmission region becomes relatively large, and the magnified image to be observed becomes bright and dark, which is not preferable.

  If Db / Da is 5% or less (light utilization efficiency of 90% or more), almost no reduction in the amount of light due to the transmission region is felt.

  The shape of the transmissive region is preferably a circle or an ellipse, but may be a quadrangle. Further, it is desirable that the position of the transmissive region is within the reflective region, and the entire reflective surface including the transmissive region and the reflective region is symmetric in the horizontal direction or the vertical direction. This makes it easy to obtain positional accuracy when creating a transmissive region. FIG. 7 shows (a) when Db / Da is 10% on the reflecting surface and (b) when Db / Da is 5% (5a is a reflection region, and 5b is a transmission region). .

  In the head mounted display, the position where the magnified image is formed is away from the observer's eyes (for example, 50 cm to ∞), and the position of the transmission region 5b is close to the observer's eyes. Since the focus of the observer's eye is not aligned with the transmissive area and the transmissive area is very small, the presence of the transmissive area is hardly noticeable.

  Further, by performing a process in which the transmittance gradually decreases toward the reflection region and the reflectance increases in the vicinity of the boundary between the transmission region and the reflection region, the boundary can be made less noticeable.

  4-2. The optical system forms an intermediate imaging plane in the vicinity of the reflecting surface having a diffusing action (the position of the reflecting surface or a position close thereto).

  As a result, even when light is incident as a thin beam up to the intermediate imaging plane, the exit pupil can be enlarged and observation becomes easy. In addition, the area Da of the reflective region on the reflective surface having the transmissive region can be increased with respect to the area Db of the transmissive region (Db / Da can be reduced), and the light utilization efficiency can be increased.

  4-3. A conjugate image of the exit pupil of the optical system is formed on or near the transmission region of the reflecting surface.

  As a result, the area Db of the transmissive region can be reduced (Db / Da can be reduced), and a decrease in light amount due to the transmissive region can be suppressed. Specifically, the distance from the transmission region to the conjugate image of the exit pupil is preferably 10 mm or less.

Others.
Further, in the plurality of non-rotationally symmetric reflecting surfaces, the absolute value of the focal length in the local bus section is larger than the absolute value of the focal length in the local subsection.

  Since the local bus cross section is an eccentric cross section, the occurrence of decentration aberration is larger than the local sub cross section. Therefore, the occurrence of decentration aberrations on the local bus cross section can be reduced by using a power arrangement in which the optical power on the local bus cross section of multiple surfaces is made weaker than the optical power on the local bus cross section. It becomes.

  In addition, when the above-described folding reflection surface is a curved surface, the direction of the light beam of the peripheral image can be individually controlled at the time of reflection, compared to the case where the folding reflection surface is a flat surface, so that the optical system can be downsized.

  Furthermore, if the return reflection surface is a non-rotationally symmetric surface, the direction of the light beam in the peripheral image can be freely controlled, so that the size can be further reduced as compared with the case of a rotationally symmetric curved surface.

  It is desirable to apply a metal mirror coating that reflects almost 100% of light to the folded reflection surface so as to reduce the light loss as much as possible. The folded reflection surface may be provided separately from the transparent body having a plurality of surfaces, or may be provided integrally with the transparent body.

  Further, the folded reflection surface reflects the light beam almost to the opposite side, but the angle θ formed by the incident light beam and the reflected light beam in the central field angle principal light beam preferably satisfies the following equation.

| Θ | <60 ° (1)
When the upper limit of the conditional expression (1) is exceeded, the optical path after return reflection (return path) does not return to the forward path, but becomes a zigzag optical path rather than a reciprocating optical path, and the optical system becomes large.

  Further, θ preferably satisfies the following formula.

| Θ | <30 ° (2)
If the condition of conditional expression (2) is not met, the light beam can be reversed, but the forward path and the return path do not overlap sufficiently, and the optical system becomes larger, making it difficult to reduce the size of the entire scanning optical system.

  Furthermore, it is desirable that θ satisfies the following formula.

| Θ | <20 ° (3)
When the conditional expression (3) is satisfied, the optical system and thus the entire scanning optical system can be sufficiently downsized.

  In the optical system, the return reflection surface and the eccentric reflection surface through which the forward path and the return path pass may be shared. In this case, the optical surface can be reduced and the optical system can be further downsized.

  In addition, when the scanning optical system of the present embodiment is applied to a head mounted display (HMD), it is preferable to provide independent optical scanning means and optical systems for the left and right eyes of the observer. That is, it is preferable to provide two identical optical scanning means and two identical optical systems corresponding thereto. As a result, a brighter image can be displayed as compared with the case where light is divided from one optical scanning unit to the left and right optical systems.

  In the scanning optical system, it is preferable that a local bus cross section that is an eccentric cross section for both the left eye and the right eye is arranged in the vertical direction of the observer's face (the light beam is folded in the vertical direction). Usually, the enlarged display image has a wide angle of view in the left-right direction and a narrow angle of view in the up-down direction (for example, left and right 4: up and down 3). By setting a small vertical direction, the occurrence of decentration aberrations in the enlarged display image can be reduced.

  In the present invention, the local bus section focal length of the eyepiece optical system from the intermediate imaging plane to the exit pupil, which will be described later, is local-fy1, and the local bus section focal length from the two-dimensional scanning member to the intermediate imaging plane is local-fy2. It is desirable that the following conditional expression is satisfied.

-2 <local-fy1 / local-fy2 <1
Below the lower limit of the above formula, the negative optical power from the two-dimensional scanning member to the intermediate image plane becomes strong, and it is necessary to increase the positive optical power of the collimator optical system to form the intermediate image plane. As a result, the generation of aberrations in the collimator optical system increases.

  On the other hand, when the value is equal to or greater than the upper limit, the positive optical power from the two-dimensional scanning member to the intermediate image plane becomes strong, and the optical swing angle of the two-dimensional scanning member is reduced, so that widening the angle becomes difficult.

  Hereinafter, specific embodiments will be described together with numerical examples.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a beam optical path from the light source 8 to the exit pupil 1 of the scanning optical system according to the first embodiment of the present invention. FIG. 2 shows an optical path diagram of diffusely reflected light from the diffuse reflection surface 2 that is an intermediate imaging surface. This scanning optical system is used in an image display device such as a head mount display (HMD) or a projector that performs screen projection.

  Although the light source 8 is shown as a single light source in the figure, it is actually composed of LEDs of three colors of red (r), green (g), and blue (b) (laser diodes may be used). The three color LEDs are arranged at optically equivalent positions via a dichroic prism that performs color synthesis. These three color LEDs can change (modulate) their intensities.

  A driving circuit 10 for driving the light source 8 (three color LEDs) is connected to the light source 8. The driving circuit 10 receives images from an image information supply device 12 such as a personal computer, a DVD player, a video, and a television. Information is entered. The drive circuit 10 modulates and drives the light source 8 according to the input image information (the same applies to the following embodiments). An image display system is configured by the image display device and the image information supply device of the present embodiment.

  The light from the light source 8 is made into a substantially parallel light beam (beam) by the collimator lens 7 and reflected by the minute two-dimensional scanning mirror 4. As the size of the two-dimensional scanning mirror 4 in this embodiment, a very small mirror having a maximum effective dimension of 3 mm or less is used (the same applies to the following embodiments).

  As the scanning mirror 4, a micro device such as a MEMS (Micro-Electro Mechanical System) is used, and the mirror surface can be scanned and driven in a two-dimensional direction. The scanning mirror 4 is also driven by the driving circuit 10 based on a vertical synchronization signal from the image information supply device 12.

  When the scanning mirror 4 is driven, the beam reflected by the scanning mirror 4 is simultaneously deflected and scanned in the horizontal direction and the vertical direction to generate a field-angle light beam. Each field-angle light beam passes through the correction prism 6 and then enters the reciprocating prism 3.

  Here, the boundary surface between the correction prism 6 and the reciprocating prism 3 has substantially the same surface shape, and the correction prism 6 and the reciprocating prism 3 are arranged via a minute air layer. However, the correction prism 6 and the reciprocating prism 3 may be joined without an air layer.

  The reciprocating prism 3 is a transparent body having three optical surfaces and filled with an optical medium such as glass or plastic. The surface A1 has an internal total reflection surface having a reflection function and a transmission function, and the surface B has a minute transmission region (pinhole) 5b in the reflection region 5a as shown in FIGS. 7 (a) and 7 (b). It is a reflective surface. Surface A2 is a reflective surface. Reference numeral 2 denotes a diffuse reflection surface provided as a separate body from the reciprocating prism 3, which is a folded reflection surface having a diffusion action.

  A reflection film is formed on the surface A2 and the diffuse reflection surface 2, and a reflection film is formed on a portion of the surface B other than the minute transmission region 5b (reflection region 5a). The reflective film is preferably a metal film. This is because the metal film has a flat spectral reflectance characteristic, a color is hardly noticeable, and a difference in reflectance with respect to light having different polarization directions is small.

  In the present embodiment, the surface B functions as an incident surface and a reflecting surface, and the surface A1 is a light exit surface toward the diffuse reflecting surface 2, a light exit surface toward the exit pupil 1, and light incident from the diffuse reflecting surface 2. It functions as a reflective surface shared by the surface and the round-trip optical path. Further, the surface A2 functions as a reflecting surface shared by the reciprocating optical path.

  In the first embodiment, all optical surfaces are rotationally symmetric surfaces.

  Each angle-of-view beam incident on the reciprocating prism 3 from the minute transmission region 5b on the surface B is incident on the surface A1 at an incident angle greater than the critical angle and totally internally reflected, and then is reflected on the surface A2 and is reflected on the surface A1. The light is incident at an incident angle less than that and exits from the reciprocating prism 3. Then, each angle-of-view light beam emitted from the reciprocating prism 3 forms an intermediate image on the diffuse reflection surface 2 or a position close to the diffuse reflection surface 2 and diffusely reflects on the diffuse reflection surface 2, as shown in FIG. A small number (ie, bright) and a thick light beam are formed.

  The diffuse reflection surface 2 is a folded reflection surface that reflects incident light so as to return it to a direction substantially opposite to the incident direction. Here, the angle formed between the incident light of the central field angle principal ray L0 on the reflection surface and the reflected light is θ described above.

  After that, each field angle ray re-enters the reciprocating prism 3 from the surface A1, is reflected by the surfaces A2 and A1, and is reflected by the surface B toward the exit pupil 1 (the eyeball of the observer in the head-mounted display and the screen in the projector). After being reflected, the reciprocating prism 3 exits from the surface A 1 and reaches the exit pupil 1.

  In the head-mounted display, an enlarged image can be observed when the observer puts his eyes near the position of the exit pupil 1.

  In the reciprocating prism 3, the light is surface B (transmission of the transmission region 5b) → surface A1 (reflection) → surface A2 (reflection) → surface A1 (transmission) → diffuse reflection surface 2 (folded reflection + diffusion) → surface A1 ( Re-transmission) → surface A2 (re-reflection) → surface A1 (re-reflection) → surface B (reflection on the reflection region 5a) → surface A1 (re-transmission), and the reflection on the return reflection surface The light path up to that point is traced backwards. From the surface B (transmission of the transmission region 5b) to the return reflection surface is the forward path, and from the return reflection surface to the surface B (reflection) is the return path, and a round-trip optical path in which the forward path and the return path substantially overlap is formed.

  In the first embodiment, the mechanical deflection angle of the micro-scanning mirror 4 is ± 4.25 ° on the cross section of the local bus (on the paper surface of FIGS. 1 and 2), and the optical deflection angle is ± 8. .5 °. At this time, ± 10 ° (vertical) field angle rays are obtained on the exit pupil plane. The horizontal direction is also scanned simultaneously.

  FIG. 1 is a beam trace diagram in the case where the light beam is not diffused on the diffuse reflection surface 2, and the exit pupil diameter is φ1 mm. However, in the diffuse reflection light trace shown in FIG. φ8 mm.

(Embodiments 2 to 5)
3 is a beam optical path cross-sectional view (beam trace diagram) of the scanning optical system according to the second embodiment of the present invention, and FIG. 4 is a beam optical path cross-sectional view of the scanning optical system according to the third embodiment of the present invention. 5 shows a beam optical path cross-sectional view of the scanning optical system that is Embodiment 4 of the present invention, and FIG. 6 shows a beam optical path cross-sectional view of the scanning optical system that is Embodiment 5 of the present invention.

  3 to 6 are trace diagrams up to the exit pupil 1 and the two-dimensional micro scanning mirror 4, and the collimator lens 7 and the light source 8 are omitted. Further, a trace diagram of the reflected diffused light from the diffuse reflection surface 2 that is the intermediate image formation surface to the exit pupil 1 is also omitted.

  In the second to fifth embodiments, the angle of view to the exit pupil 1 is common, the horizontal angle of view is ± 15 °, and the vertical angle of view is ± 11.3 °.

  Furthermore, the exit pupil diameter when diffusely reflected by the diffuse reflection surface 2 is also common and is φ8 mm. In addition, the exit pupil diameter in the beam trace diagrams of FIGS. 3 to 6 is φ1 to 1.3 mm, and the size of the transmission region 5b of the reflection surface B at that time is φ2 to 5 mm.

  The configurations of Embodiment 2 and Embodiment 3 shown in FIGS. 3 and 4 are basically the same as the configurations of Embodiment 1, except that all optical surfaces other than the diffusion folding surface 2 are free-form surfaces (non-rotationally symmetric surfaces). ) Is different from the first embodiment. Moreover, both surfaces of the correction prism 6 are also free-form surfaces.

  In the second embodiment, the optical power of each surface is set so that the transmission region 5b is smaller than that in the third embodiment. Although not shown, if a free curved surface is adopted for the collimator lens 7, light from the light source 8 can be collected efficiently. In the second and third embodiments, the optical deflection angle of the micro scanning mirror 4 in the local cross section (horizontal direction, the direction perpendicular to the drawing sheet) is ± 10.5 °.

  Further, the configurations of the fourth embodiment illustrated in FIG. 5 and the fifth embodiment illustrated in FIG. 6 are different from the configurations of the first to third embodiments (FIGS. 1 to 4) in that the correction prism 6 is not provided.

  In the fourth and fifth embodiments, the light from the micro scanning mirror 4 directly enters the reciprocating prism 3 through the transmission region 5 b of the reflection surface B of the reciprocating prism 3. The optical path after entering the reciprocating prism 3 is the same as in the first to third embodiments.

  In the fourth embodiment and the fifth embodiment, free-form surfaces are adopted for all optical surfaces other than the diffuse reflection surface 2.

  In the fourth embodiment, the optical power of each surface is set so that the transmission region 5b is smaller than that in the fifth embodiment. The optical deflection angle of the micro-scanning mirror 4 of the fourth embodiment in the cross section of the local line (horizontal direction, the direction perpendicular to the drawing sheet) is ± 14 °, and in the fifth embodiment, it is ± 13 °.

  In addition, in these Embodiments 2 to 5, the angle of view of the exit pupil plane in the local child line cross section is ± 15 °. As can be seen from FIGS. 3 to 4, the optical surface on which light is incident immediately after being reflected by the micro scanning mirror 4 (in the second and third embodiments, the surface on the scanning mirror side of the correction prism 6) has negative optical power. Good. Thereby, even if the optical deflection angle of the micro scanning mirror 4 is small, the angle of view is enlarged by this negative optical power, so that it is easy to obtain a wide angle of view.

  Further, as a matter common to the first to fifth embodiments, it is preferable that the reflection on the surface A1 is total internal reflection because the loss of light amount is reduced. Further, reflection at least in a region where the reflected light beam and the emitted light beam are shared on at least the surface A1 (a lower portion of the surface A1 where the light beam toward the exit pupil 1 is emitted and an upper portion of the surface A1 where the light beam toward the diffuse reflection surface 2 is emitted). When total internal reflection is used and reflection outside the common area is reflected by a reflective film such as a metal film, the degree of freedom of design is increased and the same degree as in the case where all of the reflected light beam on the surface A1 is totally reflected internally. The brightness can be secured.

  In addition, the boundary between the reflective film area and the common area may be clearly visible to the observer, so the vicinity of the boundary (the lower side and the upper side in the reflective film area) is shared. It is desirable to increase the reflectance gradually as the distance from the region increases so that the boundary becomes less noticeable.

(Numerical example)
Hereinafter, numerical examples of the above embodiments will be described. In each numerical example, a local paraxial is used, which will be described first.

  1 to 6 are cross-sectional views of the main part of the above embodiments (local bus bar cross-sectional view, subscript y), and the surface vertex coordinate system of the first surface (exit pupil 1) is shown in FIG. . In each embodiment, since the surface vertex of each surface is only shifted in the y-axis direction and tilted about the x-axis, the conventional bus cross section and the local bus cross section are the same cross section. The child wire cross section and the local wire cross section are different. The above-described conventional busbar cross section and child cross section are the definitions of the conventional paraxial (general-paraxial axis), and the local busbar cross section and local subsection are the definitions of the local paraxial (local-paraaxial) described below. It is. In addition, the definitions of local curvature radius, local surface spacing, local focal length, and local refractive power corresponding to the eccentric system in the local paraxial will be described below.

  In each embodiment, a light ray emitted from the light source 8 and passing through the center of the magnified image and the center of the exit pupil 1 of the optical system is used as a reference light ray (central field angle principal ray), and the conventional surface vertex-based radius of curvature of each surface is used. , Local curvature radius, local surface distance, local focal length, and local refractive power based on the hit point (incident point) on each surface of the reference ray are used instead of the surface distance, focal length, and refractive power.

  Here, the local radius of curvature refers to the local radius of curvature on the hit point of the optical surface (the radius of curvature on the cross section of the local generatrix, the radius of curvature on the cross section of the local subwire). The local surface interval is the distance between two hit points on the current surface and the next surface (distance on the reference ray, value without air conversion). The local focal length is a value calculated by a conventional focal length calculation method (paraxial tracking) from the local curvature radius, the refractive index before and after the surface, and the local surface spacing. The local refractive power (optical power) is the reciprocal of the local focal length.

  In each numerical example, the conventional curvature radius, surface interval, eccentricity, refractive index, Abbe number, local curvature radius, surface refractive index, local surface interval, and local focal length are shown.

  Further, data of numerical examples corresponding to the above-described five embodiments are shown in Table 1 (Numerical Example 1), Tables 2 and 3 (Numerical Example 2), Tables 4 and 5 (Numerical Example 3), and Table 6. 7 (Numerical Example 4) and Tables 8 and 9 (Numerical Example 5), and optical path cross-sectional views are shown in FIGS. In the conventional paraxial axes of Tables 1 to 9, the bus section radius of curvature ry, the subsection radius of curvature rx, the surface interval d (distance parallel to the surface vertex coordinate system of the first surface), and the amount of eccentricity (The parallel decentering amount of the surface vertices of each surface with respect to the surface vertex coordinate system of the first surface on the generatrix cross section is shift, and the tilt eccentricity (degree) is tilt), the d-line refractive index nd, and the Abbe number νd Show. FFS represents a free-form surface (non-rotationally symmetric surface). Further, the surface with “M” attached to the left end of each table is a reflecting surface, and the surface with “M (dif)” is a diffuse reflecting surface. The refractive index nd of the d line has an opposite sign. Tables 1 to 9 show numerical data when the optical path is traced backward from the exit pupil 1 toward the scanning mirror 4 and the light source 8.

  The definition formula of FFS (free-form surface) is shown below. The following expression is a definition expression in the surface vertex coordinate system of each surface.

  In the above definition, c1, c5,... Are free-form surface coefficients. However, in the case of this free-form surface, since there are coefficients related to the paraxial in the free-form surface coefficients, the values of the conventional paraxial (general-paraxial axis) generatrix cross-section radius of curvature ry and child-line cross-section radius of curvature rx are surfaces. It does not coincide with the actual busbar section radius of curvature ry and child section radius of curvature rx on the vertex. Therefore, an actual generatrix section radius of curvature ry and subsection cross section radius of curvature rx on the point (0, 0), that is, on the surface vertex are also shown.

  Further, in the local paraxial (local-paraxal axis), the local curvature radius (local-ry, local-rx), the local surface interval (local-d) (the reflecting surface has the opposite sign), the local focal length (local-fy, local-fx) and the refractive index nd of the surface (the reflecting surface has the opposite sign). Furthermore, the hit point coordinates on each surface (with the surface vertex set to (0, 0)) and the field angles 2ωy and 2ωx at the exit pupil (the total angle of view on the + and − sides in total) are also shown.

  Since all rotationally symmetric surfaces are used for Table 1 (Numerical Example 1), only the conventional paraxial (general-paraaxial axis) is shown (actual bus section cross-section radius of curvature ry and child line on the surface vertex). (The section curvature radius rx is also omitted).

  Further, the 18th surface in Table 1 is a two-dimensional scanning mirror. In ZOOM1, the surface data when the field angle ωy on the local bus section and the field angle ωx on the local child section to the exit pupil are both 0 ° are surface data. is there. ZOOM2 is surface data when the angle of view ωy on the local bus section to the exit pupil is + 10 °, and ZOOM3 is surface data when the angle of view ωy on the local bus section to the exit pupil is −10 °.

  Further, the eyepiece optical system local focal length local-fy1, local-fx1 (3 to 7) and the local focal length local-fy2, local-fx2 (10 in Table 1) from the two-dimensional scanning means to the intermediate image plane. To 14 surfaces, 11 to 16 surfaces in Tables 2 to 5, and 11 to 14 surfaces in Tables 6 to 9). Table 1 also shows the relay system local focal length (planes 10 to 21) from the light source to the intermediate image plane.

  (Numerical example 1)

  (Numerical example 2)

  (Numerical Example 3)

  (Numerical example 4)

  (Numerical example 5)

(Embodiment 6)
FIG. 8 shows a configuration of the scanning optical system according to the sixth embodiment of the present invention and an optical path cross-sectional view of the central field angle principal ray. In addition, in this embodiment, the member which attached | subjected the same code | symbol as Embodiment 1-5 is the same as that of Embodiment 1-5 except the reciprocating prism 3. FIG.

  The light from the light source 8 is converted into a substantially parallel light beam (beam) by the collimator lens 7, then reflected and deflected by the two-dimensional scanning mirror 4, and converted into a field angle light beam and transmitted through the correction prism 6. The light enters the reciprocating prism 3 from the transmission region 5b of the reflection surface B.

  The surface B of the reciprocating prism 3 is a light incident surface from the two-dimensional scanning mirror 4 and also functions as a final reflection surface to the exit pupil 1. On the surface B, as in the first to fifth embodiments, the transmission region 5b shown in FIGS. 7A and 7B is formed in the reflection region 5a.

  The surface A1 is a reflective surface that reflects the light incident from the transmissive region 5b of the surface B and guides it to the surface A2, and further reflects the light from the surface A2 back to the surface B. Furthermore, it also functions as an exit surface for emitting the light reflected by the surface B from the reciprocating prism 3.

  The surface A2 is a transmission surface that transmits and emits the light from the surface A1 and transmits the light reflected by the diffuse reflection surface 2 so as to enter the reciprocating prism 3 again.

  The diffuse reflection surface 2 is a folded reflection surface that diffuses the incident light and reflects the incident light so as to return the light to approximately the opposite direction.

  Each angle-of-view beam incident on the reciprocating prism 3 from the minute transmission region 5b on the surface B is incident on the surface A1 at an incident angle greater than the critical angle and totally internally reflected, then passes through the surface A2 and is incident on the diffuse reflection surface 2. It reaches. At this time, each light beam with an angle of view forms an intermediate image on the diffuse reflection surface 2 or at a position close thereto. Then, each angle-of-view light beam diffusely reflected by the diffuse reflection surface 2 is again transmitted through the surface A2 and enters the reciprocating prism 3, and is incident on the surface A1 at an incident angle greater than the critical angle and totally internally reflected. The light is reflected by the reflection area 5 a of the surface B, exits the reciprocating prism 3 from the surface A 1, and reaches the exit pupil 1. The angle formed between the incident light that is the central field angle principal ray L0 and the reflected light on the diffuse reflection surface 2 is θ.

  In the reciprocating prism 3, light is transmitted from the surface B (transmission of the transmission region 5b) → surface A1 (reflection) → surface A2 (transmission) → diffuse reflection surface 2 (folded reflection + diffusion) → surface A2 (retransmission) → surface A1. Each surface is traced in the order of (re-reflection) → surface B (reflection on the reflection region 5a) → surface A1 (transmission), and the optical path up to that point is traced in reverse from the reflection on the reflection surface. . From the surface B (transmission of the transmission region 5b) to the return reflection surface is the forward path, and from the return reflection surface to the surface B (reflection) is the return path, and a round-trip optical path in which the forward path and the return path substantially overlap is formed.

In addition, the range of the angle θ formed by the incidence / reflection of the central field angle principal ray L0 with respect to the diffuse reflection surface 2 that is the reflection reflection surface is:
| Θ | <45 ° (4)
It is desirable that Exceeding this condition is not preferable because it is difficult to form a round-trip optical path by reflected reflection. On the other hand, when configured so as to satisfy (4), a reciprocating optical path is formed by folded reflection regardless of the arrangement configuration of other surfaces, etc., so it is relatively easy to reduce the size of the optical system with respect to the optical path length. .

More preferably,
| Θ | <30 ° (5)
It is good to be. When this condition is satisfied, the degree of overlap between the forward path and the return path increases, so that the optical system can be made more compact.

(Embodiment 7)
FIG. 9 shows a configuration of the scanning optical system according to the seventh embodiment of the present invention and an optical path cross-sectional view of the central field angle principal ray. In addition, in this embodiment, the member which attached | subjected the same code | symbol as Embodiment 1-5 is the same as that of Embodiment 1-5 except the reciprocating prism 3. FIG.

  The light from the light source 8 is converted into a substantially parallel light beam (beam) by the collimator lens 7, and then reflected and deflected by the two-dimensional scanning mirror 4 to become an angle-of-view light beam and the transmission region of the reflection surface B of the reciprocating prism 3. The light enters the reciprocating prism 3 from 5b.

  The surface B of the reciprocating prism 3 is a light incident surface from the two-dimensional scanning mirror 4 and also functions as a final reflection surface to the exit pupil 1. On the surface B, as in the first to fifth embodiments, the transmission region 5b shown in FIGS. 7A and 7B is formed in the reflection region 5a.

  The surface A1 is a reflective surface that reflects the light incident from the transmissive region 5b of the surface B and guides it to the surface A2, and further reflects the light from the surface A2 back to the surface B. Furthermore, it also functions as an exit surface for emitting the light reflected by the surface B from the reciprocating prism 3.

  Further, the surface A2 is a diffuse reflection surface, and is also a folded reflection surface that reflects the light incident from the surface A1 so as to return the light in a substantially reverse direction.

  Each field angle ray incident on the reciprocating prism 3 from the minute transmission region 5b on the surface B is incident on the surface A1 at an incident angle greater than the critical angle and totally internally reflected, and then reaches the surface A2. At this time, each ray of view angle forms an intermediate image on the surface A2 or at a position close to the surface A2. Then, each angle-of-view ray diffused and reflected by the surface A2 is incident again on the surface A1 at an incident angle equal to or greater than the critical angle and totally internally reflected, and then is reflected by the reflection region 5a of the surface B. To reach the exit pupil 1. The angle formed between the incident light and the reflected light that is the central field angle principal ray L0 on the surface A2 is θ, which satisfies the above formula (4) or (5).

  In the reciprocating prism 3, light is transmitted from the surface B (transmission of the transmission region 5b) → surface A1 (reflection) → surface A2 (folded reflection + diffusion) → surface A1 (rereflection) → surface B (reflection at the reflection region 5a). → Each surface is traced in the order of surface A1 (transmission), and the optical path up to that point is traced in reverse on the basis of the reflection at the return reflection surface. From the surface B (transmission of the transmission region 5b) to the return reflection surface is the forward path, and from the return reflection surface to the surface B (reflection) is the return path, and a round-trip optical path in which the forward path and the return path substantially overlap is formed.

1 is a beam optical path diagram of a scanning optical system that is Embodiment 1 of the present invention. FIG. 3 is an optical path diagram after diffuse reflection in the scanning optical system according to the first embodiment. FIG. 5 is a beam optical path diagram of a scanning optical system that is Embodiment 2 of the present invention. FIG. 6 is a beam optical path diagram of a scanning optical system that is Embodiment 3 of the present invention. FIG. 7 is a beam optical path diagram of a scanning optical system that is Embodiment 4 of the present invention. FIG. 7 is a beam optical path diagram of a scanning optical system that is Embodiment 5 of the present invention. The figure which shows the transmissive area | region formed in the reflective surface in the scanning optical system of each said embodiment. FIG. 10 is a beam optical path diagram of a scanning optical system that is Embodiment 6 of the present invention. FIG. 10 is a beam optical path diagram of a scanning optical system that is Embodiment 7 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exit pupil 2 Diffuse reflection surface 3 Reciprocating prism 4 Two-dimensional micro scanning mirror 5a Reflection area 5b Transmission area 6 Correction prism 7 Collimator lens 8 Light source

Claims (8)

A scanning optical system comprising: an optical scanning unit that scans light from a light source; and an optical system that directs light scanned by the optical scanning unit to an exit pupil,
The optical system has a plurality of surfaces including a reflecting surface,
On the reflection surface, the light from the optical scanning means having an area smaller than that of the reflection region and higher than that of the reflection region inside the reflection region that reflects light from other surfaces. A transmission region for incidence in the optical system is formed;
Light incident from the transmission region forms an intermediate image in the optical system, and a diffuse reflection surface that reflects the light from the transmission region toward the reflection surface is disposed at the position of the intermediate image or a position close thereto. And
A scanning optical system, wherein a conjugate image of an exit pupil of the optical system is formed on the transmission region or at a position close to the transmission region.   2. The optical scanning unit is disposed at a position conjugate with an exit pupil of the optical system, and the light from the optical scanning unit forms a two-dimensional image at the position of the intermediate image. The scanning optical system described.   The scanning optical system according to claim 1, wherein an area of the transmission region is 10% or less of an area of the reflection region. The optical system has a plurality of non-rotationally symmetric reflecting surfaces;
2. The scanning optical system according to claim 1, wherein the reflecting surfaces have an absolute value of a focal length in a local bus section larger than an absolute value of a focal length in the local subsection. The optical system has at least a reflecting action, and a first surface that is decentered with respect to a central field angle principal ray, and a light ray reflected by the first surface is reflected again toward the first surface. 2 planes,
The first surface causes the central field angle chief ray incident on the first surface again from the second surface to be a normal line on the hit point of the central field angle chief ray on the first surface. 2. The scanning optical system according to claim 1, wherein the scanning optical system reflects light on the opposite side to the previous time.   The optical system moves from a forward path, which is an optical path including the first reflection on the first surface, to a return path, which is an optical path including the reflection on the first surface, after being reflected on the second surface. 6. The scanning optical system according to claim 5, wherein after the light travels, the light is reflected by another reflecting surface decentered with respect to the light to form an optical path different from the forward path. A scanning optical system according to any one of claims 1 to 6;
And a driving circuit for driving the optical scanning unit in accordance with input image information. A scanning image display device according to claim 7,
An image display system comprising: an image information supply device that inputs image information to the scanning image display device.

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