Abstract:
An optical system includes a plurality of separate light sources with a number M of the light sources arranged in a first direction and a number N of the light sources arranged in a second direction. Each of the light sources has an asymmetric light emission area. The light sources are arranged so that a light beam passing a collimator optical element has a beam width in the first direction greater than a beam width in the second direction. An anamorphic optical element is arranged to have a beam-size reduction rate in the first direction greater than a beam-size reduction rate in the second direction and converts the plurality of light beams from the light sources into a light beam having a symmetric beam cross-section. A light-condensing optical element condenses the light beam having the symmetric beam cross-section into a light receiving element, and the anamorphic optical element includes an array of a number of prisms integrally arranged.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an optical system capable of efficiently condensing light from a plurality of light sources into an optical element, and a light source module including such an optical system. 
   2. Description of the Related Art 
   In the related art, for example, Japanese Patent Gazette No. 3228098, Japanese Patent Gazette No. 2848279, and Japanese Laid-Open Patent Application No. 2002-202442 disclose an optical system that condenses light from a plurality of light sources, such as semiconductor lasers (LD) or light emission diodes (LED), into an optical element, such as an optical fiber. Specifically, in the optical system, light beams from the light sources are converted to a parallel light beam by a collimator lens, the parallel light beam is condensed by a condensing lens having a large diameter, and then the condensed light is directed into the optical fiber. 
   When it is desired to make the optical system compact by reducing the thickness of the optical system, it may be attempted to reduce the number of the light sources in the optical system arranged in the perpendicular direction, but this results in an increase of the number of the light sources arranged in the horizontal direction in the optical system (for example, the optical system has a rectangular shape). 
   In order to direct the condensed light into an optical element having a limited NA (Numerical Aperture), such as an optical fiber, it is necessary to limit the NA of the condensed light obtained by the condensing lens to be less than the NA of the optical element, and this requires the NA of the condensed light to be optimized in the horizontal direction, in which way many light sources are arranged. For this purpose, the diameter and focal length of the condensing lens become large, the optical path of the optical system becomes long, and this makes the optical system large. When the focal length of the condensing lens is large, the magnification of the optical system increases, and the diameter of the light beam increases. If the area of the optical element for receiving the condensed light is small, such as the core of the optical fiber, the condensed light cannot be completely directed within the receiving area, and hence the efficiency of light transmission decreases. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to solve one or more problems of the related art. 
   A specific object of the present invention is to provide an optical system that can be made small, has a short light path, and is capable of efficiently condensing light from a plurality of light sources into a light receiving optical element; and a light source module including such an optical system. 
   According to a first aspect of the present invention, there is provided an optical system for condensing a plurality of light beams and directing the condensed light beam to a light-receiving optical element. The optical system includes a plurality of light sources that generates the light beams, and a light condensing portion that condenses the light beams from the light sources and directs the condensed light beam to the light receiving optical element. 
   The light sources are arranged as an array with a number of M light sources being arranged in a first direction and a number of N light sources being arranged in a second direction (assuming M&gt;N, and M, N&gt;1). 
   The light condensing portion includes a collimator optical element, an anamorphic optical element, and a light-condensing optical element. The anamorphic optical element is arranged such that the magnification of the anamorphic optical element in the first direction is greater than the magnification of the anamorphic optical element in the second direction. 
   As an embodiment, a reflection optical element is arranged between the anamorphic optical element and the light-condensing optical element. 
   As an embodiment, the light-condensing optical element includes at least one of a condensing lens, a lens having a refractive index distribution, a Fresnel lens, a diffractive optical element, and a hologram element. 
   As an embodiment, the light-condensing optical element includes at least one of a glass lens fabricated by grinding, a glass molded lens, a resin molded lens, and a lens fabricated by etching. 
   As an embodiment, the light-condensing optical element and the reflection optical element are integrated to be a reflection-condensing optical element. For example, the reflection-condensing optical element includes at least one of a concave mirror and a hologram element. 
   As an embodiment, each of the light sources includes a semiconductor laser, and the light-receiving optical element includes an optical fiber. 
   As an embodiment, each of the semiconductor lasers has a light emission area of different widths in different directions, and the semiconductor lasers are arranged to have such an orientation that a direction corresponding to a larger width of the light emission area is in the direction of the smaller magnification of the anamorphic optical element, and a direction corresponding to a smaller width of the light emission area is in the direction of the larger magnification of the anamorphic optical element. 
   As an embodiment, a core of the optical fiber has a diameter less than 100 μm, and a numerical aperture (NA) less than 0.35. 
   As an embodiment, each of the light sources has a light emission area having different widths in different directions, and the light sources are arranged to have such an orientation that a direction corresponding to a larger width of the light emission area is in the direction of the smaller magnification of the anamorphic optical element, and a direction corresponding to a smaller width of the light emission area is in the direction of the larger magnification of the anamorphic optical element. 
   As an embodiment, each of the light sources includes at least one of a light emission diode, an electro-luminescence emitter, a VCSEL (Vertical Cavity Surface Emitting Laser), and a lamp. 
   As an embodiment, the light beams include light beams output from an optical fiber or a light wave guide which propagates light emitted from at least one of a semiconductor laser, a light emission diode, an electro-luminescence emitter, a VCSEL (Vertical Cavity Surface Emitting Laser), and a lamp. 
   As an embodiment, the light-receiving optical element is an optical element having an opening such as an optical fiber, an optical wave guide, a light tunnel, and a pin hole. 
   As an embodiment, the anamorphic optical element includes a prism. For example, the anamorphic optical element includes a large-size integral prism, or an array of a number of independent small prisms, or an integrated array of the small prisms. Alternatively, the anamorphic optical element includes at least one of a cylindrical lens, a cylindrical mirror, a hologram element, and a diffractive optical element. 
   As an embodiment, the collimator optical element includes at least one of a collimator lens, a lens having a refractive index distribution, a Fresnel lens, a diffractive optical element, and a hologram element. 
   As an embodiment, the collimator optical element includes at least one of a glass lens fabricated by grinding, a glass molded lens, a resin molded lens, and a lens fabricated by etching. 
   As an embodiment, the collimator optical element includes one of an assembly of a plurality of single lenses and an integrated lens array. 
   According to a second aspect of the present invention, there is provided a light source module including a power combination optical system. The power combination optical system includes plural light sources that generate the light beams, and a light condensing portion that condenses the light beams from the light sources and directs the condensed light beam to a light receiving optical element. 
   The light sources are arranged as an array with a number of M light sources arranged in a first direction and a number of N light sources arranged in a second direction (assuming M&gt;N, and M, N&gt;1). The light condensing portion includes a collimator optical element, an anamorphic optical element, and a light-condensing optical element. The anamorphic optical element is arranged such that the magnification of the anamorphic optical element in the first direction is greater than the magnification of the anamorphic optical element in the second direction. 
   As an embodiment, the light source module further includes a beam-processing optical element provided at an output end of the light-receiving optical element for processing a light beam from the light-receiving optical element. 
   As an embodiment, the beam-processing optical element includes one of a condensing coaxial optical element and a condensing anamorphic optical element to condense the light beam from the light-receiving optical element. 
   As an embodiment, the beam-processing optical element includes one of a collimator coaxial optical element and a collimator anamorphic optical element to covert the light beam from the light-receiving optical element to a parallel light beam. 
   As an embodiment, the beam-processing optical element includes one of a divergent coaxial optical element and a divergent anamorphic optical element to diverge the light beam from the light-receiving optical element. 
   As an embodiment, the light source module further includes an illuminance unification optical element that makes uniform the illuminance distribution of the light beam from the light-receiving optical element or the light beam from the beam-processing optical element. 
   According to the present invention, the optical system includes a plurality of light sources that generates a plurality of light beams, and a light condensing portion that condenses the light beams from the light sources and directs the condensed light beam to the light receiving optical element. The light sources are arranged as an array with a number of M light sources arranged in a first direction and a number of N light sources arranged in a second direction (assuming M&gt;N, and M, N&gt;1). The light condensing portion includes a collimator optical element, an anamorphic optical element, and a light-condensing optical element. The anamorphic optical element is arranged such that the magnification of the anamorphic optical element in the first direction is greater than the magnification of the anamorphic optical element in the second direction. 
   Due to the anamorphic optical element, the width of the light beam in the horizontal direction becomes approximately equal to that in the vertical direction, and this reduces the diameter and the focal length of the condensing lens (in turn, the light path of the optical system) compared with the optical system in the related art, thereby enabling reduction of the size of the whole optical system. 
   In addition, because the focal length becomes short, the magnification in the vertical direction is reduced, thus reducing the diameter of the condensed light beam. This reduced diameter increases the efficiency of light transmission to the light-receiving optical element, and makes it possible to obtain a light beam from the light-receiving optical element having a high output power. 
   The anamorphic optical element and the light sources are arranged while considering the numerical apertures and magnifications. Specifically, because the anamorphic optical element has different magnifications in the horizontal direction and the vertical direction, even when light sources like the semiconductor laser, whose light emission area has different widths in different directions, is used as the light source, provided that the semiconductor laser is arranged such that a direction corresponding to a larger width of the light emission area is in the direction of the smaller magnification of the anamorphic optical element, and a direction corresponding to a smaller width of the light emission area is in the direction of the larger magnification of the anamorphic optical element, the spot size of the condensed light beam can be reduced to be equal in all directions, and thus it is possible to efficiently direct the condensed light beam to a light-receiving optical element, such as an optical fiber or a light wave guide. 
   These and other objects, features, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments given with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A and 1B  are schematic views of a general configuration of an optical system according to an embodiment of the present invention, where  FIG. 1A  shows the optical system in the horizontal plane (plan view), and  FIG. 1B  shows the optical system in the vertical direction viewed from the bottom to the top in  FIG. 1A ; 
       FIG. 2  is a table showing characteristics of the constituent elements of the optical system according to the present embodiment; 
       FIGS. 3A and 3B  are schematic views of an optical system according to a first embodiment of the present invention, where  FIG. 3A  is a view of the optical system in the horizontal plane, and  FIG. 3B  is a view of the optical system in the vertical direction viewed along an arrow A in  FIG. 3A ; 
       FIG. 4  is a schematic view illustrating an optical system in the horizontal plane according to a second embodiment of the present invention; 
       FIG. 5  is a schematic view illustrating an optical system in the horizontal plane according to a third embodiment of the present invention; 
       FIG. 6  is a schematic view illustrating an optical system in the horizontal plane according to a fourth embodiment of the present invention; 
       FIG. 7  is a schematic view illustrating an optical system in the horizontal plane according to a fifth embodiment of the present invention; 
       FIG. 8  is a schematic view illustrating an optical system in the horizontal plane according to a sixth embodiment of the present invention; 
       FIG. 9  is a schematic view illustrating an optical system in the horizontal plane according to a seventh embodiment of the present invention; 
       FIGS. 10A and 10B  are schematic views illustrating an optical system according to an eighth embodiment of the present invention, where  FIG. 10A  is a view of the optical system in the horizontal plane, and  FIG. 10B  is a view of the optical system in the vertical direction; 
       FIGS. 11A and 11B  are a top view and a side view of a light source module according to a ninth embodiment of the present invention; 
       FIG. 12  is a perspective view of a light source module according to a 10th embodiment of the present invention; 
       FIG. 13  illustrates illuminance distributions and beam shapes of a condensed beam obtained by a condensing coaxial optical element or a condensing anamorphic optical element according to the 10th embodiment of the present invention; 
       FIG. 14  illustrates illuminance distributions and beam shapes of a parallel beam obtained by a collimator coaxial optical element or a collimator anamorphic optical element according to the 10th embodiment of the present invention; and 
       FIG. 15  illustrates illuminance distributions and beam shapes of a divergent beam obtained by a divergent coaxial optical element or a divergent anamorphic optical element according to the 10th embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Below, a fundamental configuration of an optical system according to the present invention and a method of designing the optical system are explained, first. 
     FIGS. 1A and 1B  are schematic views of a general configuration of an optical system according to an embodiment of the present invention, where,  FIG. 1A  is a view of the optical system in the horizontal plane, and  FIG. 1B  is a view of the optical system in the vertical direction viewed from the bottom to the top in  FIG. 1A . 
   In the optical system illustrated in  FIG. 1A  and  FIG. 1B , light from a light source portion  1  having a plurality of light-sources is condensed by a light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light source portion  1  includes a number of M light sources arranged in the horizontal direction and a number of N light sources arranged in the vertical direction. Here, assume M is greater than N (M&gt;N), and both M and N are greater than 1 (M, N&gt;1). 
   The light condensing portion includes a collimator optical element  2 , an anamorphic optical element  3 , and a light-condensing optical element  4 . The anamorphic optical element  3  is arranged in such way that the magnification of the anamorphic optical element  3  in the direction in which M light sources are arranged is larger than the magnification of the anamorphic optical element  3  in the direction in which N light sources are arranged. 
   In the optical system illustrated in  FIG. 1A  and  FIG. 1B , light sources generating light in the same wavelength region are used as the M×N light sources of the light source portion  1 . Specifically, the light sources may be semiconductor lasers (LD), light emission diodes (LED), electro-luminescence (EL) emitters, VCSELs (Vertical Cavity Surface Emitting Laser), or lamps. In addition, the semiconductor lasers, light emission diodes, and so on, may also be arranged as a light source array (an LD array or an LED array) to form the light source portion  1 . 
   In the present embodiment, for example, the collimator optical element  2  includes the number M×N collimator lenses L 1 , which are arranged in correspondence to the light sources of the light source portion  1 . The collimator lens L 1  may be a common lens having a continual curved surface and a refractive index difference, or a lens having a refractive index distribution, or a Fresnel lens, or a diffractive optical element, or a hologram element. In addition, from the point of view of the fabrication method, the collimator lens L 1  may be a glass lens fabricated by grinding, or a glass molded lens, or a resin molded lens, or a lens fabricated by etching. Further, each collimator lens L 1  may be an assembly of a number of single lenses, or an integral lens array. 
   In the present embodiment, the anamorphic optical element  3  may include a prism. Specifically, the anamorphic optical element  3  may include a large-size one-piece prism, or an array of a number of independent small prisms, or an integrated array of the small prisms. Alternatively, the anamorphic optical element  3  may also include a cylindrical lens, or a cylindrical mirror, or a hologram element, or a diffractive optical element. 
   In the present embodiment, the light-condensing optical element  4  may be a common lens (L 2 ) having a continual curved surface and a refractive index difference, or a lens having a refractive index distribution, or a Fresnel lens, or a diffractive optical element, or a hologram element. In addition, the collimator lens L 1  may be a glass lens fabricated by grinding, or a glass molded lens, or a resin molded lens, or a lens fabricated by etching. 
   The light receiving optical element  5  may be an optical fiber, or an optical wave guide, or a light tunnel, or a pin hole. 
   In the following descriptions, it is assumed that the light source portion  1  includes M×N semiconductor lasers (LD) generating laser beams in the same wavelength region, and in the light condensing portion, the collimator optical element  2  includes M×N collimator lenses L 1 , the anamorphic optical element  3  includes a prism, the light-condensing optical element  4  includes a condensing lens (L 2 ), the light receiving optical element  5  is an optical fiber, and light beams from the semiconductor lasers LD are condensed by the light condensing portion and are efficiently directed to the optical fiber  5 . 
   In the present embodiment, in order to efficiently condense the light beams from the semiconductor lasers LD, (1) the total NA (Numerical Aperture) of the light beams is set to be less than the NA of the optical fiber, and (2) the magnification of the optical system is set to be sufficiently small so that the spot of the light beam condensed by the condensing lens L 2  is less than the diameter of the core of the optical fiber  5 . 
   Further, in order to make the optical system compact, (1) the light source portion  1  includes an array of M×N semiconductor lasers LD, wherein M semiconductor lasers LD are arranged in the horizontal direction, and N semiconductor lasers LD are arranged in the vertical direction (M&gt;N, and M, N&gt;1), (2) the anamorphic optical element  3  is used and arranged so that the width of the condensed light beam in the horizontal direction is approximately equal to that in the vertical direction, and this reduces the diameter and the focal length f2 of the condensing lens L 2 , hence reducing the size of the whole optical system, and (3) the direction corresponding to a larger width of the light emission area of each semiconductor laser LD is arranged in the direction in which the anamorphic optical element  3  has the smaller magnification, and the direction corresponding to a smaller width of the light emission area of each semiconductor laser LD is arranged in the direction in which the anamorphic optical element  3  has the larger magnification. Because of such an arrangement, the spot size of the condensed light beam is reduced to be equal in all directions. 
     FIG. 2  is a table showing characteristics of the constituent elements of the optical system according to the present embodiment. Some of the characteristics are specified as design conditions of the optical system, and the others are determined when designing the optical system. 
   The optical system illustrated in  FIG. 1A  and  FIG. 1B  is designed as follows. The quantities appearing below are described in the table in  FIG. 2 . 
   (1) Arranging the M×N Semiconductor Lasers LD 
   The V (vertical) direction of each semiconductor laser LD is set along the horizontal direction of the optical system, the H (horizontal) direction of each semiconductor laser LD is set along the vertical direction of the optical system, M semiconductor lasers LD are arranged along the direction (EA V ) corresponding to the smaller width of the light emission areas of the semiconductor lasers LD, and N semiconductor lasers LD are arranged along the direction (EA H ) corresponding to the larger width of the light emission areas of the semiconductor lasers LD. 
   (2) Calculating the Focal Length f1 of the Collimator Lens L 1   
   By using the following equation (1) and an object value Y 0  of the thickness of the optical system, that is, the width of an optical effective area in the direction in which N semiconductor lasers LD are arranged, the quantity D Y  (vertical collimator diameter after the lens L 1 ) as shown in the table in  FIG. 2  is obtained.
 
 Y   0 =( N− 1)* P   Y   +D   Y   (1)
 
   Substitute D Y  and NA H (NA of the LD in the H direction) into a common formula NA=D/2f, and the focal length f1 of the collimator lens L 1  is obtained.
 
 f 1 =D   Y /(2* NA   H )  (2)
 
(3) Calculating the Beam Width X 0  Before the Anamorphic Optical Element  3 
 
   Substitute f1 and NA V  (NA of the LD in the V direction) into the common formula NA=D/2f, and the quantity D X (horizontal collimator diameter after the lens L 1 ) is obtained.
 
 D   X =2 f 1 *NA   V   (3)
 
   Using the following equation (4), X 0  is obtained.
 
 X   0 =( M− 1)* P   X   +D   X   (4)
 
(4) Calculating the Beam Reduction Rate MX of the Anamorphic Optical Element  3 
 
   MX is determined to make X 1 =Y 0 . 
   Substitute f1 and NA V  into the common formula NA=D/2f, and a quantity D X  is obtained.
 
 D   X =2 f 1 *NA   V   (3)
 
   Using the following equation (5), MX is obtained.
 
 MX=X   1   /X   0   =Y   0   /X   0   (5)
 
(5) Calculating the Focal Length f2 of the Condensing Lens L 2 
 
   Substitute √{square root over ( )}2*X 1  and NA F  into the common formula NA=D/2f, and the focal length f2 of the condensing lens L 2  is obtained.
 
 f 2=(√{square root over ( )}2 *X   1 )/(2* NA   F )  (6)
 
(6) Calculating the Size of the Condensed Beam
 
   First, calculate magnifications β X , β Y  of the optical system.
 
β X =( f 2/ f 1)*1 /MX   (7)
 
β Y   =f 2 /f 1  (8)
 
   Then, calculate the size of the condensed beam from the light emission area of the semiconductor laser LD and the magnifications β X , β Y  of the optical system.
 
 W   X =β X   *EA   V   (9)
 
 W   Y =β Y   *EA   H   (10)
 
(7) Confirming that the Size of the Condensed Beam is Less than that of the Core of the Optical Fiber
 
W X &lt;FD  (11)
 
W Y &lt;FD  (12)
 
   By the above design, it is possible to obtain a compact optical system that is capable of efficiently directing light beams to the optical fiber  5  having a certain NA and a certain core diameter. 
   It should be noted that the light source portion  1  may also be formed from light sources generating light in different wavelength regions. However, when using light sources generating light in the same wavelength region, by condensing the light beams, it is possible to transmit a high power laser beam at the same wavelength region to the optical element  5 , and obtain a high power outgoing light beam from the optical element  5  at the same wavelength region. 
   In the above, descriptions are made of the fundamental structure of and a method of designing the optical system of the present invention. Below, specific embodiments of the present invention are explained with reference to the accompanying drawings. 
   First Embodiment 
     FIGS. 3A and 3B  are schematic views illustrating an optical system according to a first embodiment of the present invention, where  FIG. 3A  is a view of the optical system in the horizontal plane, and  FIG. 3B  is a view of the optical system in the vertical direction viewed along an arrow A in  FIG. 3A . 
   In the optical system illustrated in  FIG. 3A  and  FIG. 3B , light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a prism array formed from eight small prisms  3 A, the light-condensing optical element  4  includes one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The details of the optical system are below.
     (1) Light sources: semiconductor lasers (LD)
       LD light emission power: 30 mW   
       (2) LD wavelength (λ): 408±10 nm   (3) LD divergence angle:
       8 degrees in the horizontal direction   24 degrees in the vertical direction   
       (4) NA (1/e 2 ) of LD:
       0.12 in the horizontal direction   0.35 in the vertical direction   
       (5) light emission area of LD:
       2.2 μm in the horizontal direction   0.7 μm in the vertical direction   
       (6) number of LDs:
       eight in the horizontal direction   two in the vertical direction   
       (7) pitch of LDs:
       pitch in the horizontal direction (P X ): 7.5 mm   pitch in the vertical direction (P Y ): 7.5 mm   
       (8) LD orientation:
       V direction of LD in the horizontal direction, and H direction of LD in the vertical direction   
       (9) collimator lens L 1 : non-spherical lens
       focal length: 5.5 mm   effective diameter 5.5 mm   
       (10) anamorphic optical element:
       prism array made from quartz   beam size reduction rate: 0.18 in the horizontal direction, 1.0 in the vertical direction   
       (11) condensing lens L 2 : non-spherical lens
       focal length: 35 mm   effective diameter 15 mm   
       (12) light receiving optical element:
       multiple mode optical fiber,   core diameter: 50 μm   NA 0.2   
       (13) anti-reflection (AR) coating on incident and outgoing surfaces of all optical elements (reflectivity: &lt;0.5%)   (14) magnification of the whole optical system:
       35.4 in the horizontal direction,   6.4 in the vertical direction   
       

   In the optical system illustrated in  FIGS. 3A and 3B , the anamorphic optical element  3  is a prism array formed from a number of small prisms  3 A. Because the transmission path of the beam is short in the small prisms  3 A, loss of light due to absorption inside the prisms  3 A is low. 
   In  FIGS. 3A and 3B , if assuming that the total loss of light is 8% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 428 mW, corresponding to an efficiency of 89%. 
   By way of comparison, if assuming that loss of light is zero in the anti-reflection (AR) coating or due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  is 465 mW, corresponding to an efficiency of 97%. 
   Characteristic parameters of the optical system of the present embodiment according to the scheme of design described above are as follows.
     (1) 8×2 Semiconductor laser array.   

   Each semiconductor laser is arranged so that the width of the light emission area of the semiconductor laser along the direction of the arrangement of the eight semiconductor lasers, that is, EA V  equals 0.7 μm, and the width of the light emission area of the semiconductor laser along the direction of the arrangement of the two semiconductor lasers, that is, EA H  equals 2.2 μm.
     (2) The object value of the thickness of the optical system, that is, Y 0 =10 mm. From equation (1) and Y 0 , it is obtained that D Y =2.5 mm.   

   NA of the semiconductor laser in the horizontal direction (NA H ) is originally 0.12 (in units of 1/e 2 ) here, however, in order to increase the efficiency, NA H  is increased to 0.23. Hence, from equation (2), it is obtained that the focal length f1 of the collimator lens L 1  is 5.43 mm.
     (3) NA of the semiconductor laser in the vertical direction (NA V ) is originally 0.35 (in units of 1/e 2 ) here, however, in order to increase the efficiency, NA V is increased to 0.5. Hence, from equation (3), it is obtained that D X =5.5 mm. and from equation (4), it is obtained that X 0 =58 mm.   (4) MX=10/58=0.172≈0.18   (5) f2=(√{square root over ( )}2*10)/(2*0.2)=35.4≈35 mm   (6) β X =(35/5.5)*1/0.18=35.4
       β Y =35/5.5=6.4   W X =35.4 *0.7=24.8   W Y =6.4*2.2=14.1   
       (7) since FD=50 μm, it is confirmed that W X &lt;FD, and W Y &lt;FD.   

   Consequently, it is possible to provide an optical system that has a small thickness and a short light path and is capable of efficiently condensing light beams into an optical fiber having a certain numerical aperture NA and a certain core diameter. 
   Second Embodiment 
     FIG. 4  is a schematic view illustrating an optical system in the horizontal plane according to a second embodiment of the present invention. 
   In the optical system illustrated in  FIG. 4 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a large-size prism  3 B, the light-condensing optical element  4  includes one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the first embodiment except that the anamorphic optical element  3  in the present embodiment includes a large-size prism  3 B, instead of a prism array formed from eight small prisms  3 A, as in the first embodiment. Due to this, it is easy to mount and adjust the prism  3 B. 
   In the optical system illustrated in  FIG. 4 , if assuming that the loss of light is totally 9.5% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 421 mW, corresponding to an efficiency of 88%. 
   Third Embodiment 
     FIG. 5  is a schematic view illustrating an optical system in the horizontal plane according to a third embodiment of the present invention. 
   In the optical system illustrated in  FIG. 5 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , a reflection optical element  6 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a prism array formed from eight small prisms  3 A, the reflection optical element  6  includes a reflecting mirror, the light-condensing optical element  4  include one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the first embodiment except that the reflection optical element  6  is arranged between the anamorphic optical element  3  and the light-condensing optical element  5  in the present embodiment. The reflection optical element  6  is used to reflect the light beam so as to change the direction of light beam. 
   In the optical system illustrated in  FIG. 5 , if assuming that the reflectivity of the reflection optical element  6  is 99%, and the loss of light is totally 9% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 423 mW, corresponding to an efficiency of 88%. 
   Fourth Embodiment 
     FIG. 6  is a schematic view illustrating an optical system in the horizontal plane according to a fourth embodiment of the present invention. 
   In the optical system illustrated in  FIG. 6 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , and a reflection condensing optical element  7 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a prism array formed from eight small prisms  3 A, the reflection condensing optical element  7  includes a concave lens, and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the third embodiment except that instead of the reflection optical element  6  and the light-condensing optical element  4  in the third embodiment, the reflection condensing optical element  7  is arranged which integrates functions of the reflection optical element  6  and the light-condensing optical element  4 . 
   Due to this, one optical element is removed, and this makes it possible to further reduce the size and cost of the optical system compared with the third embodiment. 
   In the optical system illustrated in  FIG. 6 , if assuming that the reflectivity of the reflection condensing optical element  7  is 99%, and the loss of light is totally 4% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 446 mW, corresponding to an efficiency of 93%. That is, because of absence of the condensing lens, loss of light due to absorption in the optical elements is lowered, thus increasing the power of the light beam from the light-receiving optical element  5 . 
   Fifth Embodiment 
     FIG. 7  is a schematic view illustrating an optical system in the horizontal plane according to a fifth embodiment of the present invention. 
   In the optical system illustrated in  FIG. 7 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , and a reflection condensing optical element  8 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a prism array formed from eight small prisms  3 A, the reflection condensing optical element  8  includes a hologram element, and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the third embodiment except that instead of the reflection optical element  6  and the light-condensing optical element  4  in the third embodiment, the hologram element  8  is arranged which integrates functions of the reflection mirror  6  and the condensing lens  4 . 
   Due to this, one optical element is removed, and this makes it possible to further reduce the size and cost of the optical system compared with the third embodiment. 
   In the optical system illustrated in  FIG. 7 , because essentially there is not loss of light in the hologram element  8 , if assuming that the loss of light is totally 8% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 446 mW, corresponding to an efficiency of 93%. That is, because of absence of the condensing lens and usage of the hologram element  8 , loss of light due to absorption in the optical elements is lowered, thus increasing the power of the light beam from the light-receiving optical element  5 . 
   Sixth Embodiment 
     FIG. 8  is a schematic view illustrating an optical system in the horizontal plane according to a sixth embodiment of the present invention. 
   In the optical system illustrated in  FIG. 8 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , an anamorphic optical element  9 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  9  includes two cylindrical lenses  9   a  and  9   b , the light-condensing optical element  4  include one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the first embodiment except that the anamorphic optical element  9  is formed from two cylindrical lenses  9   a  and  9   b  in the present embodiment instead of a prism array as in the first embodiment. 
   In the optical system illustrated in  FIG. 8 , if assuming that the loss of light is totally 19% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 377 mW, corresponding to an efficiency of 79%. That is, when using the anamorphic optical element  9  formed from two cylindrical lenses  9   a  and  9   b , since loss of light due to absorption in the cylindrical lenses  9   a  and  9   b  and other optical elements is greater, the efficiency of light transmission decreases more or less, and the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) decreases. 
   Seventh Embodiment 
     FIG. 9  is a schematic view illustrating an optical system in the horizontal plane according to a seventh embodiment of the present invention. 
   In the optical system illustrated in  FIG. 9 , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , an anamorphic optical element  10 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  10  includes a diffractive optical element, the light-condensing optical element  4  include one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the first embodiment except that the anamorphic optical element  10  is formed from a diffractive optical element in the present embodiment instead of a prism array as in the first embodiment. 
   In the optical system illustrated in  FIG. 9 , because there is essentially not any light loss in the diffractive element  10 , if assuming that the loss of light is totally 8% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 426 mW, corresponding to an efficiency of 89%. 
   Therefore, when using the anamorphic optical element  10  formed from a diffractive element, it is possible to make the optical system small and light compared with the optical system employing the anamorphic optical element  9  formed from two cylindrical lenses  9   a  and  9   b.    
   Eighth Embodiment 
     FIGS. 10A and 10B  are schematic views illustrating an optical system according to an eighth embodiment of the present invention, where  FIG. 10A  is a view of the optical system in the horizontal plane, and  FIG. 10B  is a view of the optical system in the vertical direction. 
   In the optical system illustrated in  FIG. 10A  and  FIG. 10B , the same as that in the first embodiment, light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , an anamorphic optical element  11 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  11  includes two cylindrical mirrors  11   a  and  11   b , the light-condensing optical element  4  include one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   The optical system of the present embodiment is basically the same as that of the first embodiment except that the anamorphic optical element  11  is formed from two cylindrical mirrors  11   a  and  11   b  in the present embodiment instead of a prism array as in the first embodiment. 
   In the optical system illustrated in  FIGS. 10A and 10B , if assuming that the loss of light is totally 9% in the anti-reflection (AR) coating and due to absorption inside the optical elements, the power of the light beam from the light-receiving optical element  5  (here, an optical fiber) is 423 mW, corresponding to an efficiency of 88%. 
   Ninth Embodiment 
     FIGS. 11A and 11B  are a top view and a side view of a light source module according to a ninth embodiment of the present invention. 
   In the present embodiment, the light source module includes an optical system as disclosed in the third embodiment ( FIG. 5 ) accommodated in a housing  18 . 
   That is, in the optical system of the light source module illustrated in  FIG. 11A  and  FIG. 11B , light from the light source portion  1 , which includes eight light sources arranged in the horizontal direction and two light sources arranged in the vertical direction, is condensed by the light condensing portion, and is then directed to a light receiving optical element  5 . 
   The light condensing portion includes the collimator optical element  2 , the anamorphic optical element  3 , a reflection optical element  6 , and the light-condensing optical element  4 . 
   Specifically, the light source portion  1  includes 8×2 semiconductor lasers (LD) which generate laser beams in the same wavelength region. In the light condensing portion, the collimator optical element  2  includes 8×2 collimator lenses L 1 , the anamorphic optical element  3  includes a prism array formed from eight small prisms  3 A, the reflection optical element  6  includes a reflecting mirror, the light-condensing optical element  4  includes one condensing lens (L 2 ), and the light receiving optical element  5  is an optical fiber. 
   In addition, the 16 semiconductor lasers are mounted on a block  15  for driving the semiconductor lasers and releasing heat, the sixteen collimator lenses L 1  are mounted on a mounting member  12 , the prism array of eight prisms  3 A of the anamorphic optical element  3  is mounted on a mounting member  13 , the reflecting mirror  6  is mounted on a mounting member  16 , the condensing lens L 2  is mounted on a mounting member  14 , and the optical fiber  5  is fixed to the side wall of the housing  18 . The above mounting members are fixed on a base member  18   a  of the housing  18 . 
   A fan  17  is installed near the block  15  to cool the block  15 . Cables  19  from the block  15  and the fan  17  are connected to a connector  20  fixed on the housing  18 . In addition, not-illustrated cables from a controller and a power cable are connected to the connector  20 . 
   In the present embodiment, by employing the optical system in the third embodiment, it is possible to realize a thin and small light source module having high output power. 
   As an example, the dimensions of the housing in  FIGS. 11A and 11B  are as follows: LX=105 mm, LY=40 mm, LZ=165 mm. 
   Certainly, instead of the optical system of the third embodiment, any optical system of other embodiments of the present invention may also be installed in a housing to form a light source module. 
   10th Embodiment 
     FIG. 12  is a perspective view of a light source module according to a 10th embodiment of the present invention. 
   In the present embodiment, the light source module  21  is basically the same as that in the ninth embodiment, except that an optical element  22  is provided at an output end of the optical fiber  5 . 
   The optical element  22  may be a condensing coaxial optical element or a condensing anamorphic optical element to condense the outgoing light beam from the light-receiving optical element  5 . The beam condensed by the optical element  22  is illustrated in  FIG. 13  in terms of illuminance distribution and beam shape. 
   The optical element  22  may also be a collimator coaxial optical element or a collimator anamorphic optical element to covert the outgoing light beam from the light-receiving optical element  5  to a parallel beam, which is illustrated in  FIG. 14  in terms of illuminance distribution and beam shape. 
   The optical element  22  may also be a divergent coaxial optical element or a divergent anamorphic optical element to diverge the outgoing light beam from the light-receiving optical element  5 . The thus obtained diverged beam is illustrated in  FIG. 15  in terms of illuminance distribution and beam shape. 
   Furthermore, an illuminance unification optical element may be provided at the output end of the optical element  22  to make the illuminance distribution of the outgoing light beam from the optical element  22  uniform. For example, the illuminance unification optical element may be a diffusion plate, a lens, a hologram, or others. 
   The influences of the illuminance unification optical element on the outgoing light beam are also illustrated in  FIG. 13  through  FIG. 15 . 
   Further, the illuminance unification optical element may also be provided at the output end of the light-receiving optical element  5  to make the light beam from the light-receiving optical element  5  uniform. 
   The optical element  22  and the illuminance unification optical element may be appropriately installed in the light source module of the present invention depending on the applications. 
   While the present invention is described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that the invention is not limited to these embodiments, but numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. 
   According to the present invention, it is possible to provide an optical system that can be made compact and is capable of efficiently condensing light from plural light sources into a light-receiving optical element, and a light source module that is compact and has high output power. 
   The optical system and the light source module according to the present invention can be used in applications related to optical communication, optical computers, laser processing, photo-lithography, illumination, image display, optical molding, medical services, and many other fields. 
   This patent application is based on Japanese Priority Patent Application No. 2003-348287 filed on Oct. 7, 2003, the entire contents of which are hereby incorporated by reference.