Abstract:
A microprojector comprising an illumination optical system, including light sources for green, red and blue laser light beams, first through third focusing lenses arranged in the optical path of the light beams, first through third mirrors diverting the light beams to a rear side of the microprojector, a reflection mirror diverting the light beams upward, a unifying unit, and a polarizing beam splitter; an image display panel reflecting the linearly polarized green, red and blue light beams in the opposite direction to the incident direction as well as selectively rotating the polarization of linearly polarized green, red and blue light beams in accordance with an externally input image signal; and a projection optical system having a plurality of lenses linearly arranged to project the light beams, thereby forming an image onto an external surface. The microprojector includes components arranged in such a way that they occupy a relatively small space.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0084830, filed on Sep. 4, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a microprojector, and more particularly, to an ultracompact portable microprojector for displaying magnified images on an external screen by connecting portable multimedia apparatuses such as digital cameras, digital camcorders, portable multimedia players (PMPs), laptop computers, and mobile phones to the microprojector. 
         [0004]    2. Description of the Related Art 
         [0005]    Projectors can be classified into reflection type projectors and transmission type projectors. In reflection type projectors, light beams are reflected by an image display panel, while in transmission type projectors, light beams are transmitted by an image display panel. Projectors can also be classified into single-panel type, two-panel type, and three-panel type projectors according to the number of image display panels. 
         [0006]    Some projectors use lamp light sources, while other projectors use laser light sources. Lamp light sources are generally larger in size than laser light sources. Thus, projectors using lamp light sources are typically large and difficult to carry. To overcome this disadvantage, technology and configurations for projectors using laser light sources that are relatively smaller in size are being actively developed. Japanese Patent Publication Nos. 2000-347291 and 2001-264662, Japanese Patent Publication No. Hei 11-64789, and Korean Patent Registration No. 0519348 disclose projectors using one or more laser light sources. 
         [0007]    Currently, there is a growing trend in the use of portable multimedia apparatuses such as digital cameras, digital camcorders, portable multimedia players (PMPs), laptop computers, and mobile phones. As the use of portable multimedia apparatuses increases, so do the opportunities for users of portable multimedia apparatuses to share images by using projectors. However, the portability and mobility of projectors must improve in order to increase their use with portable multimedia apparatuses. Since portable multimedia apparatuses are compact and easy to carry, projectors also need to be compact and easy to carry, so that they can be easily carried with portable multimedia apparatuses. A projector may even need to be small enough to be carried in a coat pocket or to be integrated into a portable multimedia apparatus. Thus, to increase the use of projectors with portable media apparatuses, improved technology and configurations of projectors using laser light sources are needed. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention overcomes the deficiencies of the prior art by providing a compact microprojector including optical components arranged in such a way that they occupy a relatively small space. In one embodiment, the microprojector contains an illumination optical system, a reflection type image display panel and a projection optical system. In this embodiment, the illumination optical system includes light sources having downward-facing exit holes for green (G), red (R), and blue (B) laser light beams, first through third focusing lenses arranged under the respective light sources and controlling the width of each of the light beams, first through third mirrors arranged under the first through third focusing lenses and reflecting the light beams by about 90° so the light beams proceed to a rear side of the microprojector, a reflection mirror reflecting the reflected light beams by about 90° so the light beams proceed upward, a unifying unit producing a uniform light strength distribution of each of the light beams proceeding upward of the microprojector, and a PBS (polarizing beam splitter) reflecting a linearly polarized light beam of the unified light beams so the polarized light beam proceeds to the rear side of the microprojector. The image display panel of this embodiment has pixels forming a plurality of rows and columns and reflects the linearly polarized G, R, and B light beams in a direction opposite to the incident direction and also selectively rotates the polarization of linearly polarized G, R, and B light beams output from the illumination optical system that are incident on selected pixels in accordance with an image signal received from an internal or external source, such as a portable multimedia apparatus. The projection optical system of this embodiment has a plurality of lenses linearly arranged to project the G, R, and B light beams forming an image onto an external screen. 
         [0009]    A second embodiment of the microprojector is adapted to use a transmission type image display panel. A third embodiment is adapted to be embedded in a portable media apparatus. The disclosed microprojector embodiments have small volumes, making them relatively easy to carry. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
           [0011]      FIG. 1  is a perspective view of a microprojector according to an embodiment of the present invention; 
           [0012]      FIG. 2  shows a configuration of an optical system viewed from the side of the microprojector of  FIG. 1 ; 
           [0013]      FIG. 3A  shows the path of a light beam emitted from a green (G) light source and passing through a first focusing lens; 
           [0014]      FIG. 3B  shows the path of a light beam emitted from a red (R) light source and passing through a second focusing lens; 
           [0015]      FIG. 3C  shows the path of a light beam emitted from a blue (B) light source and passing through a third focusing lens; 
           [0016]      FIG. 4  shows the shapes and polarization directions of the light beams emitted from the G, R, and B light sources; 
           [0017]      FIG. 5  is a perspective view of a heat radiation portion of the microprojector of  FIG. 1 ; 
           [0018]      FIG. 6  shows paths of the rays of a light beam passing through a unifying unit of the microprojector of  FIG. 1 ; 
           [0019]      FIG. 7  shows the G, R, and B light beams which are incident on the effective area of a micro fly-eye lens of the unifying unit of  FIG. 6 ; 
           [0020]      FIG. 8  is a section view of an LCoS (liquid crystal on silicon) panel; 
           [0021]      FIG. 9A  shows a PBS (polarizing beam splitter) and the proceeding direction and polarization direction of light incident on an image display panel; 
           [0022]      FIG. 9B  shows the proceeding direction and polarization direction of the incident light of  FIG. 9A  when pixels are OFF in the image display panel; 
           [0023]      FIG. 9C  shows the proceeding direction and polarization direction of the incident light of  FIG. 9A  when pixels are ON in the image display panel; and 
           [0024]      FIG. 10  shows the configuration of an optical system viewed from the side of a microprojector according to another embodiment of the present invention which uses a transmission type image display panel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]      FIG. 1  is a perspective view of a microprojector  1  according to an embodiment of the present invention. The microprojector  1  has a cubic shape. A beam emission hole  3  through which a light beam is emitted toward an external screen is positioned in the upper portion of a front surface of the microprojector  1 . A menu button portion  2  for operating the microprojector  1  is arranged on the upper surface of the microprojector  1 . Although it is not shown in the drawing, an input port is positioned on the rear surface of the microprojector  1  for receiving an image signal from a portable multimedia apparatus, such as a digital camera, a digital camcorder, a portable multimedia player (PMP), a laptop computer, a mobile phone, or any other apparatus capable of displaying an image or outputting an image signal. 
         [0026]      FIG. 2  shows a configuration of an optical system viewed from the side of the microprojector of  FIG. 1 . It is important to note that the configurations disclosed in the embodiment in  FIG. 2  and the other embodiments disclosed herein may also be used for optical systems contained within portable multimedia apparatuses. Referring to  FIG. 2 , the optical system of the microprojector  1  includes an illumination optical system  20  and a projection optical system  10 . The illumination optical system  20  includes a green (G) light source  21 , a red (R) light source  22 , a blue (B) light source  23 , first through third focusing lenses  24 ,  25 , and  26 , first through third mirrors  27 ,  28 , and  29 , a reflection mirror  31 , a unifying unit  35 , a PBS (polarizing beam splitter)  36 , and an image display panel  40 . The projection optical system  10  includes a series of lenses through which the light beam from the image display panel  40  passes. 
         [0027]    A light source is a laser light source and includes the G light source  21 , the R light source  22 , and the B light source  23 . In the present embodiment, the G light source  21  is a diode pumping solid state (DPSS) laser and the R light source  22  and the B light source  23  are laser diodes (LDs). The LD and DPSS lasers are smaller than other laser light sources. The G light beam emitted by the DPSS laser has a smaller radial distance than those of the R and B light beams emitted by the LD laser due to superior linearity of the DPSS laser. 
         [0028]      FIGS. 3A through 3C  show in detail the width of each of the G, R, and B light beams emitted from the G light source  21 , the R light source  22 , and the B light source  23 . As shown in the drawings, the width of the light beam of the G light source  21  is narrower than that of the light beam emitted from the R light source  22  or the B light source  23 . However, each of the light beams is incident on a micro fly-eye lens  32  with a predetermined size. Thus, as shown in  FIG. 3A , the of the light beam from the G light source  21  needs to be increased and the first focusing lens  24  is used for this purpose. The first focusing lens  24  is arranged at a side of the G light source  21  through which the light beam exits, that is, under the G light source  21 . The first focusing lens  24  increases the radial distance of the G light beam so that radial distance of the G light beam corresponds to the width of the micro fly-eye lens  32 . 
         [0029]    The radial distance of each of the light beams from the R light source  22  and the B light source  23  is greater than that of the light beam of the G light source  21 . Likewise, as shown in  FIGS. 3B and 3C , the second focusing lens  25  and the third focusing lens  26  are used to adjust the width of the R light beam and the G light beam respectively to be a predetermined size. The second focusing lens  25  is arranged at a side of the R light source  22  through which the light beam exits and the third focusing lens  26  is arranged at a side of the B light source  23  through which the light beam exits. The predetermined size means a size at which the radial distance of each light beam matches the width of the micro fly-eye lens  32  which will be described later. 
         [0030]    The light sources are arranged such that the G light source  21  is farthest from the unifying unit  35 , followed by the R light source  22 , followed by the B light source  23 . This is to secure a proceeding distance sufficient to enable the width of the G light beam that is relatively narrow to increase to a predetermined width as a result of the first focusing lens  24 . In case that the radial distance of the R light beam is shorter than that of the B light beam, since the proceeding distance of the R light beam must be greater than the proceeding distance of the B light beam, the R light source  22  can be arranged farther from the unifying unit  35  than the B light source  23 . However, it must be understood that the arrangement of the light sources is not limited to the above description but can be modified according to the type of the light source to be adopted. 
         [0031]    The first through third mirrors  27 ,  28 , and  29  are respectively arranged under the first through third focusing lenses  24 ,  25 , and  26 . The first mirror  27  reflects the G light beam by about 90° counterclockwise. That is, the G light beam proceeding downward proceeds to the rear side of the microprojector  1 . The second mirror  28  is a dichroic filter that reflects the R light beam by about 90° to the rear side of the microprojector  1  and transmits the G light beam. The third mirror  29  is a dichroic filter that reflects the B light beam by about 90° to the rear side of the microprojector  1  and transmits the G light beam and the R light beam. As a result, the G, R, and B light beams respectively emitted from the G, R, and B light sources  21 ,  22 , and  23  all proceed toward the reflection mirror  31 . 
         [0032]      FIG. 4  shows the shapes and polarization directions of the light beams emitted from the G, R, and B light sources  21 ,  22 , and  23 . Referring to  FIG. 4 , the G light source  21  has a roughly circular shape and a polarization in the vertical direction in a section perpendicular to the proceeding direction. The R light source  22  has an oval shape and a polarization in the vertical direction in a section perpendicular to the proceeding direction. The B light source  23  has an oval shape and a polarization in the horizontal direction in a section perpendicular to the proceeding direction. 
         [0033]    However, to ensure the light incident on the PBS  36 , which will be described later, is not lost the polarization of the light beam incident on the micro fly-eye lens  32 , as shown in  FIG. 7 , must be in the vertical direction in a section perpendicular to the proceeding direction. Thus, there is a need to convert the polarization of the B light beam in the horizontal direction to a polarization in the vertical direction. For this purpose, a λ/2 filter (half wave plate)  30  is arranged under the B light source  23 . Thus, after the B light beam passes through the λ/2 filter  30 , the G, R, and B light beams are polarized in the same vertical direction, perpendicular to the proceeding direction so that light incident on the PBS  36  is not lost. 
         [0034]    The G, R, and B light beams are emitted from the G, R, and B light sources  21 ,  22 , and  23  according to an output signal from a control portion (not shown) which will be described later. The output signal from the control portion is based on an image signal received through an input channel connected to a source, such as a portable multimedia apparatus. 
         [0035]    The microprojector  1  according to the present embodiment further includes the control portion and a heat radiation portion  50  in addition to the illumination optical system  20  and the projection optical system  10 . The control portion controls the operations of the G, R, and B light sources  21 ,  22 , and  23  and the operation of the image display panel  40  according to image signals from a source, such as a portable multimedia apparatus. The heat radiation portion  50  radiates heat generated from the G, R, and B light sources  21 ,  22 , and  23 . For this purpose, the heat radiation portion  50  encompasses or is adjacent to the G, R, and B light sources  21 ,  22 , and  23  and has a plurality of heat radiation fins  50   a  formed on the surface of the heat radiation portion  50  to increase the area through which heat may be radiated. 
         [0036]    The reflection mirror  31  reflects the G, R, and B light beams emitted from the respective light sources  21 ,  22 , and  23  and reflected by the first through third mirrors  27 ,  28 , and  29  by about 90° upward. That is, all the light beams proceeding to the rear side proceed upward after reflection by the reflection mirror  31 . The reflection mirror  31  reflects all of the G, R, and B light beams. 
         [0037]    The respective light beams reflected by the reflection mirror  31  are incident on the unifying unit  35 . The purpose of the unifying unit is to give the G, R, B and B light beams a substantially uniform light strength, and it can be implemented in a number of ways.  FIG. 6  shows one embodiment of a unifying unit  35  and the path of the rays of a light beam passing through the unifying unit  35 . As an example of the unifying unit  35 , the micro fly-eye lens  32 , a fourth focusing lens  33 , and a collimation lens  34  are used. The micro fly-eye lens  32  is arranged above the reflection mirror  31 , the fourth focusing lens  33  is arranged above the micro fly-eye lens  32 , and the collimation lens  34  is arranged above the fourth focusing lens  33 . 
         [0038]    As shown in  FIG. 7 , each incident light beam must be accurately disposed on the whole of an effective area  32 a of the micro fly-eye lens  32 , which can be achieved by adjusting the focusing lenses  24 ,  25 , and  26  arranged under the respective light sources. 
         [0039]    The light strength distribution of the light beam incident on the micro fly-eye lens  32  is great in the central portion and small in the circumferential portion as shown in  FIG. 6 . The incident light beam is split by the micro fly-eye lens  32 . Each of the split light beams pass through the fourth focusing lens  33  and are incident on the whole of the collimation lens  34 . That is, as each ray of the split light beams at the central portion and each ray of the split light beams of both circumferential portions are incident on the whole of the collimation lens  34  as a result of the fourth focusing lens  33 , the light strength distribution of the light beam passing through the collimation lens  34  is made uniform. Thus, the light strength distribution of the light beam incident on the PBS  36  is uniform. 
         [0040]    Although in the embodiment shown in  FIG. 2 , the unifying unit  35  includes the micro fly-eye lens  32 , a diffraction optical element (DOE, not shown) may be included instead. The DOE separates the incident light by diffracting the same. To this end, the DOE includes a diffraction grid and the shape of the diffraction grid can be modified in various ways by those skilled in the art. 
         [0041]    The image display panel  40  forms an image by modulating a light beam according to an image signal input from the outside. The image display panel  40  may be, for example, a DMD (digital micromirror display) panel, an LCoS (liquid crystal on silicon) panel, and a diffractive optical display device. In the embodiment shown in  FIG. 2 , the image display panel  40  is an LCoS panel. 
         [0042]      FIG. 8  is a sectional view of the LCoS panel. Referring to  FIG. 8 , an LCoS panel  40  includes ITO (indium tin oxide) glass  41 , liquid crystal  42 , aluminum pixels  43 , and a CMOS substrate  44 . The incident light passing through the ITO glass  41  is reflected from the aluminum pixels  43  while the polarization direction thereof is rotated by 90°, or maintained as it is, according to the arrangement of molecules of the liquid crystal  42  corresponding to each aluminum pixel  43 . The arrangement of molecules of the liquid crystal  42  is controlled according to a voltage applied to electrodes (not shown) of each aluminum pixel  43  through the CMOS substrate  44 . That is, the control portion applies a voltage to a particular aluminum pixel  43  corresponding to the image signal input from the external source. As the arrangement of molecules of the liquid crystal  42  corresponding to the particular aluminum pixel  43  changes, according to the applied potential difference, the polarization direction of the light beam is controlled. 
         [0043]    Unlike in the transmission type LCD, in the LCoS panel  40 , the light beam input through the liquid crystal  42  is reflected and emitted. That is, the light beam does not the pass through the CMOS, but is instead reflected and emitted through the ITO glass  41 . Thus, the numerical aperture (NA) is high and the LCoS panel  40  has high brightness compared to that of the transmission type LCD. 
         [0044]    Referring to  FIGS. 9A through 9C , the method via which the PBS  36  and the image display panel  40  make the respective light beams output from the unifying unit  35  proceed toward the projection optical system  10  is described. As shown in  FIG. 9A , the respective light beams having a uniform light strength and a polarization in the vertical direction in a section perpendicular to the proceeding direction are incident on the PBS  36 . The PBS  36  reflects only one of the light beams output from the unifying unit  35 , which has a polarization in a predetermined direction, that is, in the present embodiment, a polarization in the vertical direction in a section perpendicular to the proceeding direction of the light beam, by about 90° counterclockwise. That is, the PBS  36  reflects only the light beam having a polarization in the vertical direction causing it to proceed to the rear side while transmitting the other light beams. The reflected light beam having a polarization in the vertical direction is incident on the image display panel  40 . 
         [0045]    As shown in  FIG. 9B , the light beam incident on an aluminum pixel  43  in a black state (OFF state) of the image display panel  40  is reflected by the image display panel  40  maintaining the same polarization direction. As a result, since the reflected light beam is reflected again by the PBS  36 , the light beam no longer proceeds toward the projection optical system  10 . Thus, the G, R, and B light beams are not projected to the external screen in the black state. 
         [0046]    As shown in  FIG. 9C , the light beam incident on an aluminum pixel  43  in a white state (ON state) of the image display panel  40  is reflected by the image display panel  40  with its polarization direction rotated by 90°. As a result, since the reflected light beam has a polarization in the vertical direction in a section perpendicular to the proceeding direction, the PBS  36  transmits the light beam and the light beam then proceeds toward the projection optical system  10 . Thus, the G, R, and B light beams are projected to the external screen in the white state. The aluminum pixel  43  to which a voltage is applied can be set to be in a white state or in a black state. 
         [0047]    The light beam passing through the unifying unit  35  must be perpendicularly incident on an incident surface  36 a of the PBS  36 . However, in an actual situation, a skew ray that is not perpendicular to the incident surface  36 a is present and the skew ray is reflected with its polarization direction slightly being rotated. To correct this, a λ/4 filter  37  can be additionally arranged on an optical path between the PBS  36  and the image display panel  40 . 
         [0048]    Also, a polarizer  38  can be additionally arranged between the PBS  36  and the projection optical system  10 . The polarizer  38  transmits only the light beam having a polarization in the vertical direction in a section perpendicular to the proceeding direction of the light beam. That is, the polarizer  38  filters out polarizations other than a desired polarization. Thus, the A/ 4  filter  37  and/or polarizer  38  improve the contrast of an image. 
         [0049]    Although the reflection type image display panel  40  is used in the embodiment shown in  FIG. 2 , a transmission type image display panel  140 , such as a transmission type LCD panel, can also be used as shown in the embodiment in  FIG. 10 . 
         [0050]      FIG. 10  shows the configuration of an optical system using a transmission type image display panel  140  viewed from the side of a microprojector  100  according to another embodiment of the present invention. The transmission type LCD  140  is arranged on the optical path after the fourth focusing lens  33  and the collimation lens  34  and a second reflection mirror  45  is arranged at the position of the PBS  36  of  FIG. 2 . That is, the transmission type LCD panel  140  is arranged on the optical path between the collimation lens  34  and the second reflection mirror  45 . A first polarization plate  141  and a second polarization plate  142  are arranged under and above the transmission type LCD panel  140  respectively. 
         [0051]    Thus, the light beams incident on pixels of the LCD panel  140  that are selected based on an image signal received from a device, such as a portable media apparatus, pass through the second polarization plate  142  with their polarization directions changed according to changes in the arrangement of liquid crystal corresponding to the selected aluminum pixels. As a result, only the light beams forming an image corresponding to the image signal proceed toward a projection optical system  110 . 
         [0052]    The projection optical system  110  projects the light beam for forming an image onto an external screen (not shown) and includes a plurality of lenses that are linearly arranged. The type, number, and arrangement of the lenses adopted in the projection optical system  110  can be modified by those skilled in the art without departing from the spirit and scope of the present invention. 
         [0053]    The operation of the microprojector  1  according to the above-described first embodiment of the present invention of magnifying an image and projecting the image on the screen will now be described below. 
         [0054]    When the microprojector  1  is connected to a multimedia apparatus, an image signal from the multimedia apparatus is input to the control portion of the microprojector. The control portion outputs an output signal to form an image on the image display panel  40  according to the input image signal. Then, a change in the arrangement of the liquid crystal  42  corresponding to a particular pixel occurs to form an image. The G, R, and B light sources  21 ,  22 , and  23  are operated by the control portion to be engaged with the image display panel  40 . G, R, and B light beams are sequentially emitted from the respective light sources  21 ,  22 , and  23 . 
         [0055]    The respective light beams sequentially pass through the first through third focusing lenses  24 ,  25 , and  26  and are reflected by the first through third mirrors  27 ,  28 , and  29  to be incident on the reflection mirror  31 . The light beams reflected by the reflection mirror  31  are given a uniform light strength by the unifying unit  35 . Of the light beams having the uniform light strength distribution, only a light beam having a polarization in a predetermined direction is reflected by the PBS  36  and incident on a reflection type image display panel  40  such as an LCoS. 
         [0056]    The light beams incident on the particular pixels of the image display panel  40  according to the image signal are reflected, and then proceed in the opposite direction to the incident direction with their polarization directions rotated by 90° and pass through the PBS  36  to be incident on the projection optical system  10 . The incident light beams are magnified while passing through the projection optical system  10  so that a magnified image can be projected onto the external screen. The G, R, and B light beams are sequentially projected onto the external screen for a very short time. That is, a G image, an R image, and a B image are sequentially projected onto the external screen at times separated by very short time intervals. As a result, the projected R image, G image, and B image appear to overlap one another to form a single image. Thus, as the images are continuously projected, a moving image is formed. 
         [0057]    While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.