Patent Publication Number: US-2010118283-A1

Title: Light source unit and image displaying apparatus using the same

Description:
TECHNICAL FIELD 
     The present invention relates to light source units for use in a laser device requiring a laser beam transferred through an optical fiber, for example, a projector or a rear projection television in which images are projected onto a screen using the laser beam as a light source, or in a liquid-crystal television using it as a backlight. 
     BACKGROUND ART 
     In a conventional light source unit, a collimation lens is used for forming a laser beam emitted from a semiconductor laser into a parallel-ray light beam, which is afterward focused by a plano-convex lens to obtain a light beam having a band-like cross-section. And then, the collimation lens and the plano-convex lens are held by separate lens barrels, and the two lens barrels are further held by their outer supporting part (for example, refer to Japanese Patent Application Publication No. H05-93881, Paragraphs 0024, 0032, FIG. 2). In addition, in another example, a laser beam emitted from a laser-diode (LD) chip having predetermined divergence angles is changed into a parallel-ray light beam by a collimation lens (convex lens), and is subsequently focused onto the front end of an optical fiber by a light-focusing or condenser lens (convex lens). And then, the collimation lens and the condenser lens are individually positioned and held in different lens holders (for example, refer to Japanese Patent Application Publication No. 2000-121888, Paragraphs 0018, 0019, FIG. 1). Moreover, in another example, after having collimated emission light from laser elements by collimation lenses each into a parallel-ray laser beam, focusing onto the front end of an optical fiber is performed using two pieces of light-focusing or condenser lenses (a cylindrical lens and an anamorphic lens). Note that, the two condenser lenses are together held in a condenser lens holder (for example, refer to Japanese Patent Application Publication No. 2007-67271, Paragraphs 0023, 0024, 0038, FIG. 2). 
     Problems to be Solved by the Invention  
     In such light source units disclosed in Japanese Patent Application Publication No. H05-93881 and in Japanese Patent Application Publication No. 2000-121888, a cylindrical lens is not used, so that it is difficult to form a laser beam whose longitudinal and lateral divergence angles are different with each other, into a parallel-ray laser beam, and even when a laser beam is focused by using a light-focusing or condenser lens, after it has passed through a collimation lens, focusing onto an incident end-face of an optical fiber cannot be achieved. In a light source unit in Japanese Patent Application Publication No. 2007-67271, collimation lenses are used to form laser beams into a parallel-ray laser beam, so that it is difficult to form the laser beams having different divergence angles in longitudinal direction and lateral direction, into a parallel-ray laser beam. In addition, as to the light source unit in Japanese Patent Application Publication No. 2007-67271, a cylindrical lens is used; however, it is used for a condensing optical system, and a special anamorphic lens is also used to focus laser beams onto the front end of an optical fiber. 
     Moreover, in the light source unit in Japanese Patent Application Publication No. H05-93881, the collimation lens and the plano-convex lens are held by separate lens barrels, and these lens barrels are individually mounted on the supporting part, so that it is difficult to accurately make the optical axes of these two pieces of lenses coincide with each other. In addition, in the light source unit in Japanese Patent Application Publication No. 2000-121888, a lens barrel that holds the collimation lens and a lens barrel that holds a condenser lens are directly coupled; however, the two lens barrels are not positioned with each other, so that it is difficult to accurately make the optical axes coincide with each other. Moreover, in the light source unit in Japanese Patent Application Publication No. 2007-67271, the condenser lens holder is coupled with a laser unit that holds collimation lenses by way of an interconnecting member, so that there is such a problem that positioning of the condenser lenses and the collimation lenses is difficult. 
     The present invention has been directed at solving those problems described above, and an object of the invention is to focus, without using extra components such as a special lens like an anamorphic lens or a supporting stage other than lens barrels, a laser beam emitted from a laser element, having different divergence angles in longitudinal direction and lateral direction, so as not to allow longitudinally and laterally deviating from an incident end-face of an optical fiber. 
     SUMMARY OF THE INVENTION 
     Means for Solving the Problems  
     A light source unit according to the present invention comprises a laser element for emitting a laser beam having different divergence angles in longitudinal direction and lateral direction; at least one cylindrical lens placed with its generatrix perpendicular to an optical axis of the laser beam for forming the laser beam into a parallel-ray laser beam; a first lens barrel for holding the at least one cylindrical lens; a condenser lens placed downstream of the at least one cylindrical lens for focusing the parallel-ray laser beam; and a second lens barrel for holding the condenser lens; wherein the first lens barrel and the second lens barrel are positioned and coupled with each other so that an optical axis of the at least one cylindrical lens coincides with an optical axis of the condenser lens. 
     Effects of the Invention  
     According to the present invention, a laser beam emitted from a laser element having different divergence angles in longitudinal direction and lateral direction is refracted by at least one cylindrical lens so as to form the beam into a longitudinally and laterally parallel-ray laser beam, and therefore, the laser beam can be focused into a smaller spot diameter when focusing is performed by a condenser lens after having the beam passed through the cylindrical lens. In addition, the at least one cylindrical lens and the condenser lens are held by separate lens barrels, so that it becomes possible to adopt the shape of the lens barrels that are individually made suitable for the cylindrical lens and the condenser lens. 
     Moreover, a lens barrel that holds the cylindrical lens and a lens barrel that holds a condenser lens are regularly positioned and coupled with each other, so that such effects can be obtained in which optical axes of the cylindrical lens and the condenser lens that are held by two respective lens barrels can be accurately coincided with each other, and performance may not be degraded due to displacement between the optical axes. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective diagram illustrating a light source unit in Embodiment 1 of the present invention; 
         FIG. 2  is a lateral section diagram illustrating the light source unit in Embodiment 1 of the present invention; 
         FIG. 3  is a longitudinal section diagram illustrating the light source unit in Embodiment 1 of the present invention; 
         FIG. 4  is a lateral section diagram illustrating a lens unit that holds cylindrical lenses of the light source unit in Embodiment 1 of the present invention; 
         FIG. 5  is a perspective view showing the lens unit that holds the cylindrical lenses of the light source unit in Embodiment 1 of the present invention; 
         FIG. 6  is a perspective view showing a lens unit that holds circular lenses of the light source unit in Embodiment 1 of the present invention, where part of the unit is taken to show the cross section; 
         FIG. 7  is a longitudinal section diagram showing the lens unit that holds the circular lenses of the light source unit in Embodiment 1 of the present invention; 
         FIG. 8  is a perspective view showing a state in which the lens unit holding the cylindrical lenses and the lens unit holding the circular lenses are coupled with each other in the light source unit in Embodiment 1 of the present invention; 
         FIG. 9  is a perspective diagram for explaining a positioning method of the lens unit holding the cylindrical lenses and the lens unit holding the circular lenses in the light source unit in Embodiment 1 of the present invention; 
         FIG. 10  is a perspective diagram for explaining another positioning method of a lens unit holding the cylindrical lenses and a lens unit holding the circular lenses in the light source unit in Embodiment 1 of the present invention; 
         FIG. 11  is a perspective diagram for explaining an adjustment method of an optical fiber holder in the light source unit in Embodiment 1 of the present invention; 
         FIG. 12  is a partially cross-sectional view of a lens-barrel portion for explaining a configuration of a light sensor unit in the light source unit in Embodiment 1 of the present invention; and 
         FIG. 13  is a diagram illustrating a configuration of a projection displaying apparatus  500  using light source units according to Embodiment 1 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     Hereunder, a light source unit according to Embodiment 1 of the present invention will be described in detail with reference to the accompanying drawings.  FIG. 1  is a perspective view of the light source unit according to the embodiment;  FIG. 2 , a cross-sectional or lateral section diagram of the unit;  FIG. 3 , a longitudinal section diagram of the unit;  FIG. 4 , a lateral section diagram of a lens unit  100  that holds cylindrical lenses;  FIG. 5 , a perspective view showing the lens unit  100  viewed from behind it, which holds the cylindrical lenses;  FIG. 6 , a perspective view of a lens unit  200  that holds round or circular lenses (only a lens barrel part is taken to show the cross section);  FIG. 7 , a longitudinal section diagram of the lens unit  200  that holds the circular lenses;  FIG. 8 , a perspective view when the lens unit  100  that holds the cylindrical lenses and the lens unit  200  that holds the circular lenses are coupled with each other;  FIG. 9  and  FIG. 10 , perspective diagrams for explaining positioning methods between the lens unit  100  that holds the cylindrical lenses and the lens unit  200  that holds the circular lenses;  FIG. 11 , a perspective diagram for explaining an adjustment method of an optical fiber holder  5 ; and  FIG. 12 , a partially cross-sectional view of a lens-barrel portion for explaining a configuration of a light sensor unit  400 . 
     As shown in  FIG. 1 , the light source unit in Embodiment 1 is constituted of the lens unit  100  having a first lens barrel  1  that holds the cylindrical lenses, the lens unit  200  having the second lens barrel  2  that holds the circular lenses, the optical fiber holder  5  for fixing by a cap nut  4   a  a connector  4  that holds an optical fiber  3 , a laser module  300  mounted at the rear end of the first lens barrel  1  for emitting a laser beam, and the light sensor unit  400  mounted on a lateral side of the first lens barrel  1  for detecting the laser beam. 
     As shown in  FIG. 2  and  FIG. 3 , the laser module  300  is constituted of a base plate  6 , a laser element  7  mounted thereon and a cap  8  mounted on the base plate  6  to seal the laser element  7 , and is mounted being regularly positioned at the rear end of the first lens barrel  1 . In the first lens barrel  1 , three pieces of the cylindrical lenses  10 ,  11  and  12  are held. The cylindrical lens  10  and the cylindrical lens  11  are set having their generating lines or generatrices common in the same orientation, and are held in the first lens barrel  1  by way of a lens holder  15 . In addition, the cylindrical lens  12  is held to have its generatrix perpendicular to the generatrices of the cylindrical lenses  10  and  11 . 
     In the second lens barrel  2 , two pieces of round or circular lenses  13  and  14  are held. The second lens barrel  2  is regularly positioned and mounted with respect to the first lens barrel  1  so that optical axes of the circular lenses  13  and  14  coincide with those of the cylindrical lenses  10 ,  11  and  12 . Note that, in Embodiment 1, an example is described in which three pieces of the cylindrical lenses are held in the first lens barrel  1 , and two pieces of the circular lenses are held in the second lens barrel  2 ; however, the number of each of the lenses may be changed depending on the constraining conditions such as required performance, and costs or size. In addition, in Embodiment 1, the cylindrical lenses  10  and  11  are placed in the lens holder  15 , which is held by the first lens barrel  1 ; however, in a case in which one cylindrical lens is used, which may be directly held by a lens barrel, i.e. without intervening the lens holder, like the state of the cylindrical lens  12 . 
     The optical fiber  3  is inserted into the connector  4  so that the front end of the fiber on the side of the second lens barrel  2  coincides with the front end of the connector  4 , and is fixed to the connector  4  by adhesive or the like. In addition, on the front end, i.e., on the exit side of the second lens barrel  2 , the optical fiber holder  5  is mounted. Into the optical fiber holder  5 , the front end of the connector  4  is inserted, which is fixed by the cap nut  4   a.  At this time, the front end of the connector  4  is stopped by touching at the bottom in a hole of the optical fiber holder  5 , so that positioning of the front end of the optical fiber  3  is achieved in the axial direction thereof (in depth) with respect to the optical fiber holder  5 . Note that, the optical fiber  3  shown in  FIG. 1  through  FIG. 3  indicates a state being cut partway for explanatory purposes; however, it is a general practice that the optical fiber is actually long with desired length and is also coated with covering material. 
     Next, the operations of the light source unit will be explained. A laser beam  9  is emitted from the laser element  7 . The laser element  7  emits the laser beam  9  whose light-rays spread in lateral directions to a large extent as shown in  FIG. 2  that is a lateral section diagram, and also spread in longitudinal directions to a small extent as shown in  FIG. 3  that is a longitudinal section diagram. Next, the laser beam  9  emitted from the laser element  7  passes through a glass window  8   a  provided in the cap  8 , and is made incident to the cylindrical lens  10 . As shown in  FIG. 2 , the laser beam  9  made incident to the cylindrical lens  10  is refracted by the cylindrical lenses  10  and  11 , so that the spread in the lateral directions is compensated, resulting in a parallel-ray laser beam. On the other hand, the cylindrical lenses  10  and  11  each do not have the curvature in longitudinal directions, so that, as shown in  FIG. 3 , light-rays of the laser beam  9  in the longitudinal directions hardly change their angles, i.e., pass through the cylindrical lenses  10  and  11 . 
     The laser beam  9  that propagates through a hollow within the first lens barrel  1  is made incident to the cylindrical lens  12 . The cylindrical lens  12  is placed to have its generating line or generatrix perpendicular to the generatrices of the cylindrical lenses  10  and  11 , so that light-rays of the laser beam  9  that spread in lateral directions do not turn as shown in  FIG. 2 , and light-rays of the laser beam  9  that spread in longitudinal directions are refracted to be compensated in the longitudinal directions as shown in  FIG. 3 , resulting in a parallel-ray laser beam. According to the operations described above, the laser beam  9  emitted from the exit side of the cylindrical lens  12  is formed into the longitudinally and laterally parallel-ray laser beam. 
     Subsequently, the longitudinally and laterally parallel laser beam  9  incident to the circular lens  14  is refracted in longitudinal direction and lateral direction by the circular lens  14  and the circular lens  13 , and is focused onto an entrance of the optical fiber  3 . The laser beam  9  being incident to the optical fiber  3  is propagated within the optical fiber  3  so as to be transferred. As described above, the laser beam  9  emitted from the laser element  7 , having different divergence angles in longitudinal direction and lateral direction, is formed into a longitudinally and laterally parallel-ray beam by a plurality of such cylindrical lenses  10  and  11 , and  12  that are placed to have their respective generatrices perpendicular to one another, so that the laser beam can be easily focused onto the front end of the optical fiber  3  by subsequently focusing the parallel-ray beam using the circular lenses  13  and  14 . 
     Next, configurations of each of the lens units will be explained. In the lens unit  100  shown in  FIG. 4 , the cylindrical lens  10  and the cylindrical lens  11  are placed in the lens holder  15 , and are held on the entrance side of the first lens barrel  1  to which the laser beam  9  is made incident. On the other hand, the cylindrical lens  12  is held on the exit side of the first lens barrel  1  from which the laser beam  9  is emitted. In addition, the cylindrical lens  11  is pressed by a plate spring  16  toward protrusions  15   a  and  15   b  provided inside the lens holder  15 , and is securely held without looseness and excess play. The plate spring  16  is fastened onto the lens holder  15  by screws  17   a  and  17   b.    
     The cylindrical lens  12  is directly fitted in the first lens barrel  1 , and is fixed being spring-biased toward the lens-barrel side by a plate spring  18 . The plate spring  18  is fastened onto the first lens barrel  1  by four pieces of screws  19   a  through  19   d  shown in  FIG. 9 . In addition, the cylindrical lens  12  is placed to have its generatrix perpendicular to the generatrices of the cylindrical lenses  10  and  11 . This is because the spread of the laser beam  9  in lateral directions is collimated by the cylindrical lenses  10  and  11 , and the spread of the laser beam  9  in longitudinal directions is collimated by the cylindrical lens  12 , so that the laser beam  9  is formed into a parallel-ray laser beam. 
     The cylindrical lens  10  is placed in the lens holder  15  from the opposite side to the cylindrical lens  11 , and is made contact with the protrusions  15   a  and  15   b  from the incident side of the laser beam  9 , so that positioning in optical axis directions is achieved. And then, the cylindrical lens  10  is held, as shown in  FIG. 5 , by fixing a plate spring  20  from the entrance side of the first lens barrel  1  using four pieces of screws  21   a  through  21   d.  The cylindrical lens  10  is positioned as its planar side face being positioned beyond to some extent from an end-face of the lens holder  15 , and is thus securely held without looseness and excess play by spring-biasing by means of the plate spring  20 . Moreover, in the plate spring  20 , a window  20   a  is provided so that the laser beam  9  passes therethrough. 
     As described above, the cylindrical lenses  10  and  11 , and  12  are held in proximities to the respective entrance and exit sides of the first lens barrel  1 , so that the first lens barrel  1  can be made as a single component in a tubular shape, and it is not only possible to reduce the number of components, but also easy to secure positional accuracy among a plurality of lenses. Moreover, the stiffness of the lens barrel can be enhanced, so that it becomes possible to reduce the thickness of material and also to lower costs. 
     An assembling method of the lens unit  200  will be explained using  FIG. 6  and  FIG. 7 . First, the circular lens  13  is inserted into the second lens barrel  2 , and next, a doughnut-shaped spacer  22   a  is inserted thereinto. Subsequently, the circular lens  14  is inserted and then fixed by a screw-thread ring  23  that is externally threaded. Under actual circumstances, the exit side of the second lens barrel  2  is lowered, and each of the components is built up by a drop-in technique. And then, the second lens barrel  2  is finally fastened from the circumferentially lateral side by a setscrew  24 , so that the screw-thread ring  23  is prevented from loosening due to vibrations or the like. 
     As described above, the cylindrical lenses  10  through  12 , and the circular lenses  13  and  14  are held by the separate lens barrels, so that it becomes possible to adopt the shape of the lens barrels that are individually made suitable for the cylindrical lenses  10  through  12 , and the circular lenses  13  and  14 . As for a lens barrel that holds the circular lenses, a lens barrel whose cross-section is circular can be used, and thus cylindrical machining is possible to apply using a lathe during additional machining such as on the inner surface, so that machining accuracy can be made high, a machining time can be also shortened, and costs can be reduced as well. In addition, when a lens barrel in a circular cross-section is used, it is easy to secure optical axes of the lenses, and at the time of assembling, each of the components can be assembled by a drop-in technique, so that assembling is easy, the assembly time can be shortened, and assembly costs can be reduced. 
     In addition, because the lens barrel that holds the cylindrical lenses can have a shape of rectangular cross-section and be made to adopt the shape suitable for an external shape of the cylindrical lenses, material thickness can be made uniform, and the material can be efficiently used. When cylindrical lenses and circular lenses are used in combination, a lens barrel takes a complex shape, and thus it is hard to form the lens barrel and also to additionally machine it; therefore, it is difficult to secure machining accuracy, resulting in rising costs. 
     In addition, the laser beam  9  emitted from the laser element  7  having different divergence angles in longitudinal direction and lateral direction is refracted by the cylindrical lenses  10  and  11 , and  12  so as to from the beam into a longitudinally and laterally parallel-ray laser beam, so that it is possible to focus the laser beam  9  that has passed through the cylindrical lenses  10  and  11 , and  12  by using the circular lenses  13  and  14 . Thus, focusing a smaller spot diameter can be achieved when the laser beam  9  is focused by the circular lenses  13  and  14 . 
     Moreover, the laser beam  9  emitted from the laser element  7  having different divergence angles in longitudinal direction and lateral direction is formed into a parallel-ray laser beam by the cylindrical lenses  10  and  11 , and  12 , and therefore, displacement occurred between the two lens barrels in direction parallel to their optical axes may provides a little influence. Namely even if the second lens barrel is shifted from the first lens barrel in the direction to depart therefrom, the laser beam  9  is a parallel-ray laser beam, so that it is possible to focus the laser beam  9  onto the incident end-face of the optical fiber  3  by means of the circular lenses  13  and  14 . 
     Next, a positioning method of the first lens barrel  1  and the second lens barrel  2  will be explained. In  FIGS. 8 and 9 ,  FIG. 8  illustrates a state after the assembly, and  FIG. 9 , a state before the assembly. In  FIG. 9 , two pieces of positioning bosses  25  and  26  are provided on the exit end-face of the first lens barrel  1 . On an entrance end-face of the second lens barrel  2 , a positioning hole  27  and a positioning oblong hole  28  are provided at the positions opposing to the positioning bosses  25  and  26  of the first lens barrel  1 , and both optical axes of the lens unit  100  and the lens unit  200  indicated by alternate long and short dashed lines in the figure are positioned so as to coincide with each other. After having the lens units  100  and  200  coupled, they are fixed by two pieces of screws  29   a  and  29   b.    
       FIG. 10  illustrates a different exemplary embodiment from that in  FIG. 8  and  FIG. 9 . In  FIG. 10 , such positioning bosses and a positioning hole are provided for the lens units in reversed relation to that in  FIG. 8  and  FIG. 9 , that is, on the entrance end-face of the second lens barrel  2 , the two positioning bosses  30  and  31  are provided, and on the entrance end-face of the first lens barrel  1 , the positioning hole  32  and a positioning oblong hole  33  are provided at the positions opposing to the positioning bosses  30  and  31  of the second lens barrel  2 . Positioning is performed by fitting the positioning boss  30  and the positioning hole  32 , and the positioning boss  31  and the positioning oblong hole  33 , respectively. 
     In each cases of  FIG. 8  and  FIG. 9 , and of  FIG. 10 , the positioning bosses, the positioning holes and the oblong holes are each provided at a position apart from a midline of respective lens-barrel end-faces, whereby the orientation of the second lens barrel  2  is uniquely determined with respect to the first lens barrel  1 . If at all positioning is made on the midline, the second lens barrel  2  can be assembled even when it is upside down, resulting in not uniquely determining the orientation. 
     In addition, the first lens barrel  1  and the second lens barrel  2  are regularly positioned and directly coupled with each other, so that it is possible to accurately make optical axes of the cylindrical lenses  10  through  12  held by the first lens barrel  1 , and those of the circular lenses  13  and  14  held by the second lens barrel  2  coincide with each other. Therefore, performance may not be degraded due to displacement between the optical axes. Moreover, as in Embodiment 1, when the lenses are held at positions near to respective lens-barrel end-faces, and positioning is thus difficult using the outer circumference and the inner circumference of the lens barrels, the positioning method according to Embodiment 1 is effective. 
     A mounting method of the optical fiber holder  5  and a position adjustment method of the optical fiber  3  will be explained referring to  FIG. 11 . The optical fiber holder  5  is fastened on an exit surface  2   a  of the second lens barrel  2  by three pieces of screws  34   a  through  34   c.  The exit surface  2   a  of the second lens barrel  2  is planar, and further female screw-threads  35   a  through  35   c  are cut therein at the segment angle of 120 degrees therebetween. The optical fiber holder  5  is attached on such an exit surface, and the screws  34   a  through  34   c  are loosely secured. Next, the connector  4  is plugged into the optical fiber holder  5  so as to be fixed. Note that, the position adjustment of the optical fiber  3  is performed in a state in which the laser module  300  shown in  FIG. 1  through  FIG. 3  is mounted and the laser beam  9  is emitted to an incident end of the optical fiber holder  5 . 
     The screws  34   a  through  34   c  having been tentatively secured are loosened, so that the optical fiber holder  5  is allowed movable in the plane of the surface. The optical fiber holder  5  can be moved by the amount of looseness and play of holes  5   a  through  5   c  drilled in the planar bottom portion, and the screws  34   a  through  34   c.  As shown in  FIGS. 2 and 3 , the laser beam  9  is focused onto the point at which the optical fiber  3  should be positioned normally, so that, by moving the optical fiber holder  5  in the plane of the surface, it is possible to make the incident end-face of the optical fiber  3  coincide with the focusing point of the laser beam  9 . The determination whether or not the front end of the optical fiber  3  coincides with the focusing point is carried out by measuring intensity of the laser beam  9  outputted from the exit of the optical fiber  3 , that is, at the position where the intensity is maximized, the optical fiber holder  5  is fixed by tightly fastening the screws  34   a  through  34   c.    
     The optical fiber holder  5  is movably held in the plane of the surface, i.e., on the exit surface  2   a  of the second lens barrel  2  by the amount of looseness and play of the holes  5   a  through  5   c  and the screws  34   a  through  34   c , so that a complex adjustment mechanism is not required, and the number of components can be reduced. Therefore, a position adjustment mechanism for the optical fiber  3  is realized with lower costs and higher reliability. In addition, the position adjustment of the optical fiber  3  is performed by sliding, with respect to the exit surface  2   a,  the optical fiber holder  5  on which the optical fiber  3  is mounted by way of the connector  4 , and therefore, the position adjustment of the optical fiber  3  is proceeded without deviating the incident end-face of the optical fiber  3  in optical axis directions, and highly precise positioning is made possible. 
     Shown in  FIG. 12  is an enlarged view of the light sensor unit  400  shown in  FIG. 2 , where a light sensor  36  is mounted on a board  37 , and the board  37  is fixed on a board holder  38  by a screw  39   a.    
     In the board holder  38 , a window  38   a  is provide so as to accommodate the light sensor  36 , and the board  37  is fixed to a lateral side of the first lens barrel  1  by two pieces of screws  39   b  and  39   c,  with the mounting face of the board for the light sensor  36  facing down. In addition, the board holder  38  has a bathtub-shaped structure so that the light sensor  36  is not brought close contact with the lateral side of the first lens barrel  1 , and is held to provide an interspace to the first lens barrel  1 . Meanwhile, a light detection hole  40  is provided on the lateral side of the first lens barrel  1 , so that, part of the laser beam  9  is introduced into the board holder  38  through the hole. 
     The hole  40  provided in the first lens barrel  1  is placed off the light path of the laser beam  9 , that is, at the position where the laser beam  9  does not directly enter into the hole  40 , so that scattered light that is reflected diffusely in the first lens barrel  1  is introduced into the hole. If intensity of the laser beam  9  incident to the light sensor  36  is too high, the light sensor  36  becomes functionally saturated, so that the intensity of the beam cannot be detected. For this reason, in addition to make the hole  40  in an appropriate size, the light sensor  36  is placed off, and slightly shifted, the axis line of the hole  40 , whereby part of the laser beam  9  to be detected is reflected and attenuated in the board holder  38 . In order to further attenuate the part of the laser beam  9 , the inner surface of the board holder  38  may be roughened or colored in black. 
     According to the configuration in which the hole  40  provided in the first lens barrel  1  to introduce part of the laser beam  9  is placed at the position where the laser beam  9  does not directly enter, the light sensor  36  is placed at a position apart slightly from the axis line of the hole  40 ; and then, a shape of the board holder  38  is designed so that the part of the laser beam  9  is internally reflected and attenuated, and the inner surface of the board holder  38  may be roughened or colored in black, therefore light intensity detection can be stably carried out even when the intensity of the laser beam  9  is strong. In addition, because intensity of the laser beam  9  is detected by the light sensor  36 , and changes in the intensity of the laser beam are monitored, it is possible to determine an unexpected malfunction of the laser element  7  or its operating life. Moreover, when the detected intensity is compared with that of the output of the exit side of the optical fiber  3 , it is also possible to detect a disconnection in the optical fiber  3 , reduction of transmissivity therein, or the like. 
     Embodiment 2 
       FIG. 13  is a diagram illustrating a configuration of a projection displaying apparatus  500  as an image displaying apparatus using light source units according to Embodiment 1 of the present invention. The projection displaying apparatus  500  is a rear projection television that projects images onto a screen using a light valve. 
     As shown in  FIG. 13 , the projection displaying apparatus  500  according to Embodiment 2 includes a condensing optical system  510 , an illumination optical system  540 , a reflection-type light modulation device (reflection-type light valve)  520  as an image displaying device, and a projection optical system  530  that enlarges and projects onto the transmission-type screen  550  images on an illumination surface (image producing area)  520   a  of the reflection-type light modulation device  520  which is illuminated by the illumination optical system  540 . 
     The condensing optical system  510  is constituted of light source units  511  having a plurality of colors (three colors in  FIG. 13 ) and a plurality of pieces (three pieces in  FIG. 13 ) of such optical fibers  3  that guide light beams emitted from the light source units  511  into the illumination optical system  540 . Among the light source units  511  having the plurality of colors, at least one is the light source unit according to Embodiment 1. 
     In the condensing optical system  510 , laser beams emitted from the light source units  511  are guided into the illumination optical system  540  by way of the optical fibers  3  corresponding to the light source units  511 . 
     The illumination optical system  540  includes a light intensity uniformizing device  541  that uniformly distributes the intensity of laser beams emitted from the condensing optical system  510  (optical fibers  3 ), a relay-lens group  542 , a diffusion device  544 , and a mirror group  543  constituted of a first mirror  543   a  and a second mirror  543   b.  The illumination optical system  540  thus guides by means of the relay-lens group  542  and the mirror group  543  a light beam emitted from the light intensity uniformizing device  541  onto the reflection-type light modulation device  520 . 
     The light intensity uniformizing device  541  has a function to uniformize the light intensity of the laser beams (for example, a function to reduce inconsistencies of illuminance) emitted from the condensing optical system  510 . The light intensity uniformizing device  541  is disposed in the illumination optical system  540  so that an incident face (incident end-face) that is an entrance of incident light is set facing toward the optical fibers  3 , and an emission face (emission end-face) that is a light emission exit is set facing toward the relay-lens group  542 . 
     The light intensity uniformizing device  541  is made of a transparent material, for example, glass, resin or the like. The light intensity uniformizing device  541  includes a polygonally columned rod (columned member having its cross-sectional shape polygonal) whose sidewall has an internal surface of total reflection, or a polygonal pipe (tubular member) having inwardly arranged light reflection surfaces tubularly combined with its cross-sectional shape polygonal. 
     When the light intensity uniformizing device  541  is a polygonally columned rod, light is emitted from an emission end (emission exit) after having light reflected a number of times by utilizing a total reflection action on an interface between a transparent material and air. 
     When the light intensity uniformizing device  541  is a polygonal pipe, light is emitted from the emission exit after having light reflected a number of times by utilizing a reflection action by the surface mirror inwardly facing. 
     When an appropriate length is secured for the light intensity uniformizing device  541  in the traveling direction of the light beam, the light internally reflected a number of times is superimposed and emitted in proximity to the emission face of the light intensity uniformizing device  541 ; therefore, a substantially uniform intensity distribution can be obtained in the proximity to the emission face of the light intensity uniformizing device  541 . Light emitted from the emission face having the substantially uniform intensity distribution is guided by the relay-lens group  542  and the mirror group  543  onto the reflection-type light modulation device  520 , so that the illumination surface  520   a  of the reflection-type light modulation device  520  is illuminated. 
     In addition, in the illumination optical system  540 , the diffusion device (diffusing portion)  544  is provided downstream of the relay-lens group  542 . The diffusion device  544  is a device that reduces speckle by diffusing the light propagated by way of the relay-lens group  542  and then by sending it to the mirror group  543 . The diffusion device  544  is a holographic diffusion device or the like that can specify light diffusion angles using a hologram pattern provided on the substrate, and that mitigates coherency attributed to the light source units  511 . 
     In addition, by rotating, moving or vibrating the diffusion device  544 , or doing the like, the coherency attributed to the light source units  511  can be effectively mitigated. 
     The reflection-type light modulation device  520  is, for example, a light modulation device of a reflection-type such as a digital micromirror device (DMD). The reflection-type light modulation device  520  is configured in such a manner that a large number of movable micromirrors corresponding to pixels each (for example, hundreds of thousands of pieces) are arranged in a planar surface, and a slope angle (tilt) of each of the micromirrors is changed depending on pixel information. 
     The projection optical system  530  enlarges and projects onto a transmission-type screen  550  images on the illumination surface (image producing area)  520   a  of the reflection-type light modulation device  520 . According to this arrangement, the images are displayed on the transmission-type screen  550 . 
     Note that, shown in  FIG. 13  is a case in which the relay-lens group  542  is configured by one lens; however, the lens number is not limited to one, and a plurality of lenses may be used. Likewise, as for the mirror group  543 , the mirrors are not limited to two, and the mirror group  543  may be configured by one, or by three or more mirrors. 
     Note that in  FIG. 13 , laser beams emitted from the light source units  511  having a plurality of colors are guided into the illumination optical system  540  by way of the optical fibers  3  corresponding to the respective light source units  511 ; however, laser beams emitted from the light source units  511  may be combined using a dichroic mirror or the like, and then be incident to the illumination optical system  540 . 
     While the present invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be realized without departing from the scope of the invention. 
     EXPLANATION OF NUMERALS AND SYMBOLS 
     “ 1 ” designates a first lens barrel; “ 2 ,” second lens barrel; “ 2   a ,” exit surface; “ 3 ,” optical fiber; “ 5 ,” optical fiber holder; “ 7 ,” laser element; “ 9 ,” laser beam; “ 10 ,” “ 11 ,” “ 12 ,” cylindrical lens; “ 13 ,” “ 14 ,” circular lens; “ 25 ,” 
       26 ,” positioning boss; “ 27 ,” positioning hole; “ 28 ,” oblong hole; “ 30 ,” “ 31 ,” positioning boss; “ 32 ,” positioning hole; “ 33 ,” oblong hole; “ 36 ,” light sensor; “ 37 ,” board; “ 38 ,” board holder; “ 40 ,” hole; “ 100 ,” lens unit; “ 200 ,” lens unit; “ 300 ,” laser module; and “ 400 ,” light sensor unit.