Patent Publication Number: US-11656543-B2

Title: Projection device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-151706 filed on Sep. 10, 2020, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The technical field relates to a projection device. 
     Description of Related Art 
     Conventionally, there is a light source device that adjusts direction of light rays emitted by a light source in an appropriate direction and outputs it with high directionality. In a device that outputs desired color images, such as a projector, light of multiple wavelength bands is combined and output. JP 2016-57375 A discloses a projector that diffuses a part of light emitted by a laser light source of a blue wavelength band, converts the rest of the light into light of a green wavelength band using phosphors, and then combines them again for output. 
     SUMMARY 
     According to an aspect of the present disclosure, there is provided a projection device including: 
     an optical lens that has an incident surface of light, a reflecting surface that has a concave curved surface and internally reflects light that has entered through the incident surface, and an exit surface of light that has been reflected by the reflecting surface; and 
     a light source that emits light that enters the optical lens. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure, wherein: 
         FIG.  1    is a diagram illustrating configurations of a projector and light emission paths; 
         FIG.  2 A  is a diagram illustrating an irregular-shaped lens; 
         FIG.  2 B  is a diagram illustrating the irregular-shaped lens; 
         FIG.  2 C  is a diagram illustrating the irregular-shaped lens; 
         FIG.  3 A  is a diagram illustrating a light path in the irregular-shaped lens; and 
         FIG.  3 B  is a diagram illustrating a light path in the irregular-shaped lens. 
     
    
    
     DETAILED DESCRIPTION 
     In the followings, an embodiment of a projection device will be described. 
       FIG.  1    is a diagram of the projection device of this embodiment, explaining configurations of a projector  1  including a light source device and the light output path. 
     The projector  1 , which is a projection device, includes a laser diode (LD 11 ; light source) and a light-emitting diode (LED 17 ) as light sources, and emits light of RGB colors using these light sources. The LD 11  emits light of a blue wavelength band. Here, for example, four TO-CAN type LDs  11  are aligned and emit parallel rays of light. An LED  17  emits light of a red wavelength band. The light of a green wavelength band is obtained by a phosphor based on the light of the blue wavelength band, as described later. In  FIG.  1   , the light path of the blue wavelength band is shown with solid arrows, the light path of the green wavelength band is shown with dashed-dotted arrows, and the light path of the red wavelength band is shown with dashed arrows. 
     Various optical devices are located on the optical paths. The optical devices here include a reflective mirror group  21 , a collimating lens  22 , collimating lens groups  23 ,  25 ,  28 ,  29 , dichroic filters  24 ,  30 , an irregular-shaped lens  26 , a reflective mirror  27 , and the like. On the light path of the blue wavelength band, a fluorescent wheel  40  is located. 
     After the light of the three wavelength bands has been combined (merged) by the dichroic filter  30 , the light is emitted through the merged light guide  50 , a display element  60 , and a projection lens group  70 . The merged light guide  50  reflects the merged parallel rays of light of respective wavelength bands in an appropriate direction and guides it to the display element  60 . 
     The display element  60  is a spatial optical modulator (SOM), for example, a digital micromirror device (DMD). The DMD switches tilt angles of respective micromirrors arranged in an array at high speed one by one, determines whether or not light is reflected toward the projection lens group  70  for each pixel unit or each image frame unit, and forms an optical image with the reflected light. 
     The projection lens group  70  guides and emits the optical image emitted by the display element  60  in the output direction. The projection lens group  70  includes a plurality of lenses whose combination or positional relationship can be changed such that its focal position, the magnification (zoom) of the output image, and the like can be adjusted. 
     The fluorescent wheel  40  is a circular metal plate that has an area with a phosphor layer and a diffusion transmission surface. When the phosphor layer is irradiated with light of the blue wavelength band, light of the green wavelength band is excited and emitted. The diffusion transmission surface transmits the light of the blue wavelength band while diffusing it. The fluorescent wheel  40  is rotatably driven by a motor  41 . As a result, the fluorescent wheel  40  emits light of the green wavelength band (of a different wavelength) based on a part of the light of the blue wavelength band, and causes light other than the part to enter the diffusion transmission surface as it is. 
     The diffused and transmitted light of the blue wavelength band enters the irregular-shaped lens  26 , passes through the reflective mirror  27 , the collimating lens  28 , and then the dichroic filter (second dichroic filter)  30  (first light guide), and is guided to the merged light guide  50 . The light of the green wavelength band emitted from the phosphor layer returns to the collimating lens group  25 , is reflected by the dichroic filter  24  (first dichroic filter), passes through the collimating lens  29 , is then reflected by the dichroic filter  30  (second light guide), and is guided to the merged light guide  50 . 
     The light of the red wavelength band that is emitted by the LED  17  and is less diffused because of the collimating lens group  23 , passes through the dichroic filter  24 , is then reflected by the dichroic filter  30 , and is guided to the merged light guide  50 . 
     In other words, the dichroic filter  24  transmits the light of the blue and red wavelength bands and selectively reflects the light of the green wavelength band. The dichroic filter  30  selectively transmits the light of the blue wavelength band and reflects the light of the green and red wavelength bands. 
     The light source device of this embodiment includes, among the above-described configurations, those along the respective paths of light of the blue wavelength band and the light of the green wavelength band from LD  11  where light of the blue wavelength band is emitted, to the dichroic filter  30  where light of the blue and green wavelength bands are combined, in particular, the fluorescent wheel  40 , the motor  41 , and the irregular-shaped lens  26 . 
     Next, the irregular-shaped lens  26 , which is an optical lens of this embodiment, will be explained. 
       FIG.  2 A  to  FIG.  2 B  show the irregular-shaped lens  26 . As shown in  FIG.  2 A , the irregular-shaped lens  26  is different from other lenses in that its optical axis on a side of an incident surface P 1  (incident optical axis X 1 ) is oriented differently from its optical axis on a side of an exit surface P 3  (outgoing optical axis X 3 ). Here, the incident optical axis X 1  (here, along the Z direction) and the outgoing optical axis X 3  (here, along the X direction) are perpendicular to each other. The irregular-shaped lens  26  has a reflecting surface P 2  at which orientation of the optical axis changes inside the irregular-shaped lens  26 . 
     As shown in  FIG.  2 B ,  FIG.  2 C , etc., the incident surface P 1  has a convex portion B (protrusion) that protrudes from a flat surface. The convex portion B has a spherical surface (three-dimensional shape of a spherical cap) and functions as a convex lens that collimates the incident light. Here, the convex portion B has a shape (curvature) that at least reduces diffusion of the light that has been transmitted while being diffused through the diffusion transmission surface of the fluorescent wheel  40 . The position and size of the convex portion B are determined such that almost all the light of the blue wavelength band from the diffusion transmission surface of the fluorescent wheel  40  enters the convex portion B. 
     The incident light entering the irregular-shaped lens  26  through the incident surface P 1  is reflected by the reflecting surface P 2  in the irregular-shaped lens  26 . The reflecting surface P 2  has a concave curved surface (convex shape when viewed from the outside) having a shape formed by extending a quadratic curve perpendicular to a plane on which the quadratic curve is present. Here, the reflecting surface P 2  has a shape of a portion of a cylinder surface (quadratically curved surface). The cross section of the curved surface cut by a plane parallel to the incident optical axis X 1  and the outgoing optical axis X 3  (XZ plane or first plane) has a shape of a quadratic curve having a focus on the diffusion transmission surface of the fluorescent wheel  40 , for example, a parabola shape. The reflection surface P 2  extends in a straight line in the direction perpendicular to both the incident optical axis X 1  and the outgoing optical axis X 3  (Y-axis direction, normal to the first surface). The irregular-shaped lens  26  is made of optical glass whose refractive index is approximately 1.5. The reflecting surface P 2  is oriented depending on the material so that most of the incident light is totally reflected. However, because not all the incident light is reflected depending on the direction of the incident light, the irregular-shaped lens  26  may have a reflective layer R on the outer side of the reflecting surface P 2 . Depending on an incident angle on the incident surface P 1 , positional relationship between the incident surface P 1  and the reflecting surface P 2 , and the refractive index, the area in the reflecting surface P 2  where total reflection may not occur is limited. 
     Therefore, the reflective layer R does not need to cover the entire outer surface of the reflecting surface P 2 , but only needs to be provided in such a way that reflection occurs with a small loss in the area where total reflection does not occur. Because of the reflecting surface P 2  shaped as described above, the incident light is collimated (diffusion is suppressed) in the XZ plane (first plane) in the direction of the outgoing optical axis X 3 . 
     The convex portion B is sized and located such that the incident light on the incident surface P 1  can efficiently strike the appropriate area of the reflecting surface P 2 . Here, the convex portion B is located at the center of the incident surface P 1  in the Y direction, and is shifted from the center toward the −X side in the X direction. Accordingly, the convex portion B may have a shape of a trimmed spherical cap, that is, a spherical cap from which a part protruding from the incident surface P 1  is removed. The removed part specifically corresponds to a part of the spherical cap on the −X side of an YZ plane. The YZ plane is perpendicular to the bottom of the spherical cap shape and includes the −X side edge of the incident surface P 1 . 
     The exit surface P 3  is straight in the Z direction (the direction normal to the second plane) and has a shape of a portion of a cylinder whose cross-section parallel to the XY plane (a second plane that is parallel to the normal of the first plane) has a shape of a quadratic curve (here, a circular arc shape). As a result, the incident light is not collimated by the reflecting surface P 2  when viewed in the XY plane but is collimated so as to be in parallel with the outgoing optical axis X 3  by the exit surface P 3 , thereby the outgoing light is parallel rays of light. Here, the incident optical axis X 1  is perpendicular to the outgoing optical axis X 3 . 
     The incident surface P 1  and the exit surface P 3  may have an anti-reflection layer. The anti-reflection layer may be a well-known coating layer. 
       FIG.  3 A  and  FIG.  3 B  are diagrams illustrating light paths in the irregular-shaped lens  26 .  FIG.  3 A  illustrates the light path in the XZ plane, and  FIG.  3 B  illustrates the light path in the XY plane. 
     As shown in  FIG.  3 A , in the XZ plane, the light of the blue wavelength band from the fluorescent wheel  40  is collimated so as to be almost parallel rays of light, and is output from the exit surface P 3  because of the convex surface of the convex portion B and the concave surface of the reflecting surface P 2 . As shown in  FIG.  3 B , in the XY plane, diffusion of the light of the blue wavelength band from the fluorescent wheel  40  is not reduced by reflection at the reflecting surface P 2 , but is reduced at the exit surface P 3 . Thus, the irregular-shaped lens  26  of this embodiment uses a combination of the reflecting surface P 2  and exit surface P 3  to emit collimated light. 
     As described above, the irregular-shaped lens  26 , the optical lens of this embodiment, has the incident surface P 1  where light enters, the reflecting surface P 2  that internally reflects the light having entered from the incident surface P 1 , and the exit surface P 3  of the light having been reflected by the reflecting surface P 2 . The reflecting surface P 2  has a shape of a concave curved surface. 
     The conventional optical system including combination of a collimating lens and a mirror to output light in an appropriate direction has been facing a problem of difficulty in downsizing the system because the system requires a space to bend the light while suppressing diffusion of the light. 
     The irregular-shaped lens  26  in the above embodiment enables collimation and change in the optical axis direction due to reflection collectively and in a compact manner. In particular, since a convex portion of a conventional convex lens for collimation occupies a large space, it is necessary to leave a large space between such convex lens and other configurations such as mirrors. Therefore, according to the irregular-shaped lens  26  of this application, the components of the optical system can be arranged with less limitations. Furthermore, almost total reflection of the incident light inside the irregular-shaped lens  26  can cause less losses than the reflection using a conventional mirror. Therefore, the irregular-shaped lens  26  can change the direction of light while efficiently collimating light (reducing light diffusion). 
     The reflecting surface P 2  has a quadratically curved surface. As a result, the irregular-shaped lens  26  having a simple shape can efficiently collimate the incident light and convert it into parallel rays of light. 
     The reflecting surface P 2  has a shape of a portion of a cylinder (parabolic curved cylinder) surface that extends linearly in a direction of a normal to the first plane (Y direction). The cross-section of the cylinder surface has a quadratically curved (for example, parabolic) shape when cut by a plane parallel to the first plane (XZ plane). The exit surface P 3  has a shape of a portion of a cylinder (circular cylinder) surface that extends linearly in a direction of a normal to the second plane (Z direction). The cross-section of the cylinder surface has a quadratically curved shape (circular arc) when cut by a plane parallel to the second plane (XY plane) parallel to a normal to the first plane. 
     Since the reflecting surface P 2  and the exit surface P 3  individually perform collimation of light in this manner, they each can be formed in a two dimensionally curved shape. Therefore, it is easy to manufacture the irregular-shaped lens and to efficiently set the path of the light. 
     The exit surface P 3  has a shape of a portion of a cylinder surface. This allows the irregular-shaped lens  26  to convert the diffused incident light into parallel rays of light easily and in a short distance. 
     The irregular-shaped lens  26  emits parallel rays of light from the exit surface P 3 . In this way, the irregular-shaped lens  26  not only reflects and bends the light as a prism does, but also reduces diffusion of light and emits the light. Because a mirror and a collimating lens do not need to be arranged separately, it is possible to set the light path in a more space-saving manner. 
     The outgoing optical axis X 3  of the light emitted from the exit surface P 3  is perpendicular to the incident optical axis X 1  of the incident light on the incident surface P 1 . That is, this irregular-shaped lens  26  can perform bending of the light path in 90 degrees and the light collimation (suppressing light diffusion to forma parallel rays of light) simultaneously in a space-saving manner. 
     The irregular-shaped lens  26  has the reflective layer R at least at a part of the outer side of the reflecting surface P 2  to reflect light that is not reflected by the reflecting surface P 2 . The irregular-shaped lens  26  may not fully reflect the light depending on the angle of incidence, because the reflecting surface P 2  is not flat, the phosphor layer is quite close to the incident surface P 1 , and so on. In such cases, the reflective layer R is preferably provided in a required area. With such a configuration, losses can be reduced as compared to reflection using a mirror only, and light can be reflected and collimated in a compact manner. 
     Furthermore, the incident surface P 1  has the convex portion B of a spherical surface shape. This allows the irregular-shaped lens  26  to reduce diffusion degree of the diffused incident light to a certain extent. As a result, the reflecting surface P 2  and the exit surface P 3  can be shaped more freely. 
     The convex portion B has a shape of a trimmed spherical cap. If a spherical cap that is located corresponding to an incident area that efficiently allows light to reach the reflecting surface P 2  protrudes from the incident surface P 1 , the convex portion B of the incident surface P 1  may have a shape of the spherical cap from which this protruding portion is removed. This does not cause any optical inconvenience and allows the irregular-shaped lens  26  to have a compact shape without an extra protruding portion. 
     The light source device included in the projector  1  (projection device) of this embodiment includes the above-mentioned irregular-shaped lens  26  and the LD  11  that emits light that enters the irregular-shaped lens  26 . In other words, this light source device can be compact and output light emitted by the LD 11  in an appropriate direction. 
     The light source device also includes fluorescent wheel  40  having the phosphor layer that emits, based on a part of the light of the blue wavelength band emitted by the LD  11 , light of the different wavelength band (green), and the diffusion transmission surface that transmits the light of the blue wavelength band while diffusing it. Light transmitted by the diffusion transmission surface enters the irregular-shaped lens  26 . The quadratically curved cylinder surface of the reflecting surface P 2  has its focus on the diffusion transmission surface (assuming a cross section of the reflecting surface P 2  cut by the XZ plane in the drawing). In other words, by compactly setting a path for a part of the light to be emitted, the size of the entire light source device can be reduced. 
     The light source device also includes the first light guide that guides the light emitted through the irregular-shaped lens  26 , the second light guide that guides the light emitted by the phosphor layer, and the merged light guide  50  where the light through the first light guide and the light through the second light guide are merged and guided. That is, when light of a certain wavelength and light of another wavelength pass through different paths to be merged, one of the paths, in particular the longer path, can be compactly set using the irregular-shaped lens  26  so that the size of the light source device can be reduced. 
     The present invention is not limited to the above embodiment, and various changes can be made. 
     For example, the reflecting surface P 2  and the exit surface P 3  have respective quadratically curved cylinder surface shapes so as to make the light rays parallel to respective planes that are orthogonal to each other in the above embodiment, but the present invention is not limited thereto. The reflecting surface P 2  may have a quadratically curved surface such as a paraboloid to orient the light rays parallel to a straight line at a time. In this case, the exit surface P 3  may be just a flat surface. Alternatively, reflecting surface P 2  and the exit surface P 3  each may be such a quadratically curved surface that collimates light step by step. The reflecting surface P 2  and the exit surface P 3  are not limited to the quadratically curved surfaces, but may be, for example, third-order or higher-order surfaces such that fine aberrations are reduced, and the like. 
     In the above-described embodiment, parallel rays of light are emitted as an example, but the present invention is not limited thereto, as long as diffusion of the emitted light is suppressed compared to that of the incident light. Alternatively, the light may be emitted in a more converged manner. 
     In the above-described embodiment, the irregular-shaped lens  26  bends the optical axis at a right angle and has the exit surface P 3  and the incident surface P 1  perpendicular to each other, but the present invention is not limited thereto. The irregular-shaped lens can be configured to bend the optical axis of the outgoing light by appropriately 90 degrees taking manufacturing errors into account, or any other angle. 
     In the above-described embodiment, the irregular-shaped lens  26  has the reflecting layer R, but does not have to have the reflecting layer R if not necessary, considering the relationship between the incident angle of the incident light, the reflection angle at the reflecting surface P 2 , and the material (refractive index) of the irregular-shaped lens  26 . 
     In the above-described embodiment, the incident surface P 1  has a convex portion B having a spherical surface shape to suppress light diffusion, but the present invention is not limited thereto. When the incident light is not diffused so much, the incident surface P 1  may not have the convex portion B. The incident surface of the convex portion B may have any other quadratically curved surface shape. The convex portion B may not have a partially removed spherical cap shape, depending on the position and size of the spherical cap shape that constitutes the convex portion B. 
     In the above-described embodiment, the light emitted by the LD  11  enters the irregular-shaped lens  26 , but the present invention is not limited thereto. Any other light source may be used. 
     In the above-described embodiment, light of the green wavelength band is emitted by the phosphor layer, but the present invention is not limited thereto. There may be a further light source that emits light of the green wavelength band. Alternatively, light of the green wavelength band may be generated not by the phosphor layer but by a filter or the like. 
     In the above-described embodiment, light of the blue wavelength band enters the irregular-shaped lens  26 , but light of other wavelength bands may enter the irregular-shaped lens  26 . Also, the incident light is not limited to light of a single wavelength band. In this case, the incident angle of the light may be different for each wavelength band. 
     In the above-described embodiment, the light source device emits light of multiple wavelength bands, but may emit light of only a single wavelength band. Furthermore, the light is not limited to visible light as long as it is light of a wavelength band that can pass through a lens and can be reflected by a mirror. For example, infrared light may be included. Also, light of multiple wavelength bands does not necessarily have to be merged and output. 
     In the above-described embodiment, the light source device is one for the projector  1 , but the present invention is not limited thereto. The light source device may be used in various applications such as lighting devices, signs, inspection devices, and the like. 
     In addition, the specific configuration, contents and procedures of processing, and the like described in the above embodiment can be changed as necessary without departing from the gist of the present invention. 
     Although several embodiments of the present invention have been described above, the scope of the present invention is not limited to the embodiments described above, but includes the scope of the present invention described in the claims and the scope of their equivalents.