Patent Publication Number: US-2023147991-A1

Title: Light emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 17/069,299, filed Oct. 13, 2020, which claims priority under 35 U. S. C. § 119 to Japanese Patent Application No. 2019-198334, filed Oct. 31, 2019. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a light emitting device that includes a plurality of light emitting elements and a plurality of lenses. 
     A light emitting device having a plurality of semiconductor laser elements and a lens array is, for example, described in JP 2007-019301A. 
     SUMMARY 
     JP 2007-019301A describes that, when the position of each light emitting region of two semiconductor laser elements has a mounting error, the angle of tilt of the lens array is adjusted to increase the parallelism of the collimated light. However, merely adjusting the tilt angle of the lens array may not enough to sufficiently improve the adjustment accuracy. Accordingly, a light emitting device allowing further improvement of adjustment accuracy has been needed. 
     A light emitting device according to one embodiment of the present disclosure includes a plurality of light emitting elements including a first light emitting element and a second light emitting element, a case enclosing the plurality of light emitting elements, the case having a light-transmissive region allowing light emitted from the plurality of light emitting elements to pass through, a plurality of main lenses covering at least a portion of the light-transmissive region, the plurality of main lenses including a first main lens to collimate or converge light emitted from the first light emitting element and a second main lens to collimate or converge light emitted from the second light emitting element, and a plurality of sub-lenses disposed in the case, the plurality of sub-lenses including a first sub-lens located in an optical path between the first light emitting element and the first main lens and a second sub-lens located in an optical path between the second light emitting element and the second lens. 
     With the light emitting device described above, the light emitted through the main lenses can be within a target quality range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram schematically showing a light emitting device having a plurality of light emitting elements and a plurality of collimating lenses, but not having a sub-lens. 
         FIG.  2    is a diagram schematically illustrating a plurality of light emitting elements emitting light with different diverging angles in a light emitting device that does not have a sub-lens. 
         FIG.  3    is a diagram schematically showing a basic configuration of a light emitting device according to one embodiment of the present disclosure. 
         FIG.  4 A  is a schematic perspective view of a light emitting device according to a first embodiment of the present disclosure. 
         FIG.  4 B  is a schematic perspective view showing an interior of a light emitting device according to the first embodiment. 
         FIG.  5 A  is a schematic top view of a light emitting device according to the first embodiment, viewed from the positive side of the Z-axis. 
         FIG.  5 B  is a schematic side view of the light emitting device according to the first embodiment, viewed from the positive side of the X-axis. 
         FIG.  5 C  is a schematic side view of the light emitting device according to the first embodiment, viewed from the positive side of the Y-axis. 
         FIG.  6    is a schematic cross-sectional view of a light emitting device according to the first embodiment. 
         FIG.  7    is a schematic plan view showing an internal configuration of a light emitting device according to the first embodiment. 
         FIG.  8    is a schematic perspective view showing an example of a lens array that can be used in the light emitting device according to the first embodiment. 
         FIG.  9 A  is a schematic perspective view of a light emitting device according to a second embodiment of the present disclosure. 
         FIG.  9 B  is a schematic perspective view showing an interior of a light emitting device according to the second embodiment. 
         FIG.  10 A  is a schematic top view of a light emitting device according to the second embodiment, viewed from the positive side of the Z-axis. 
         FIG.  10 B  is a schematic side view of the light emitting device according to the second embodiment, viewed from the positive side of the X-axis. 
         FIG.  10 C  is a schematic side view of the light emitting device according to the second embodiment, viewed from the positive side of the Y-axis. 
         FIG.  11    is a schematic cross-sectional view of the light emitting device shown in  FIG.  9 A . 
         FIG.  12    is a schematic plan view showing an internal configuration of a light emitting device shown in  FIG.  9 A . 
         FIG.  13 A  is a schematic perspective view showing a light emitting device according to a third embodiment of the present disclosure. 
         FIG.  13 B  is a schematic perspective view showing an interior of the light emitting device shown in  FIG.  13 A . 
         FIG.  14 A  is a schematic top view of a light emitting device according to the third embodiment, viewed from the positive side of the Z-axis. 
         FIG.  14 B  is a schematic side view of the light emitting device according to the third embodiment, viewed from the positive side of the X-axis. 
         FIG.  14 C  is a schematic side view of the light emitting device according to the third embodiment, viewed from the positive side of the Y-axis. 
         FIG.  15    is a schematic cross-sectional view of a light emitting device according to the third embodiment. 
         FIG.  16    is a schematic plan view showing an internal configuration of a light emitting device according to the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before describing embodiments of the present disclosure, related art and findings obtained by the present inventors will be described. 
     With reference to  FIG.  1    and  FIG.  2   , difficulties that may occur in a light emitting device configured to collimate or diverge light emitted from a plurality of light emitting elements by using a plurality of lenses will be described. 
       FIG.  1    is a diagram schematically showing a configuration of a light emitting device  100 P having a plurality of laser diodes  110  and a plurality of lenses  140 . The light emitting device  100 P does not have sub-lenses, such that light L emitted from each of the laser diodes  110  reaches a corresponding one of the lenses  140 . The lenses  140  employed in this example are optical elements configured to collimate light L emitted from a corresponding one of the laser diodes  110 . In this case, the light emitting device  100 P is designed to collimate the light from each lens  140  into a substantially parallel beam shape. Therefore, the design position and orientation of each laser diode  110  is determined such that the “light emitting region” at the emission edge of each of laser diode  110  is aligned with or near the focal point of the lens  140  and the center portion of the light L perpendicular to the light incidence surface of lens  140 . The light-emitting region of a laser diode is also referred to as the emitter region. In the description below, the design position of the light emitting region may be referred to as the target position. The target position of the light-emitting region of each laser diode  110  does not necessarily have to be exactly the same as the focal point of lens  140 , and can be determined to form a desired light beam. For example, to control the beam shape of collimated light L, a target position may be intentionally set to slightly away from the focal point and place the light emitting region at that target position. In such a case, it is necessary to accurately position the light emitting region of the laser diode  110  at the design position, that is, the target position determined based on the optical design. 
     When mounting the laser diode  110 , the position of laser diode  110  may deviate from the target position. Such a positional deviation can be caused by variations in the mounting of the laser diode  110 . If the laser diode  110  deviates from its design position, such as the light emitting region offset from the target position, the direction and/or diverging angle of light passing through the lens  140  may deviate from the designed range. In the example shown in  FIG.  1   , the light-emitting region of each laser diode  110  is out of the target position, by which the light beam passing through the lens  140  is not collimated as designed, and the direction and diverging angle of the light beam are out of the target. 
     The positional deviation of the laser diodes  110  can occur separately at each laser diode  110 . After mounting the laser diodes  110 , if the position or orientation of individual lenses  140  can be adjusted to match the position of the light emitting region, desired collimation light can be obtained. However, if each lens  140  is secured to a common member or formed from the same material monolithically, such individual adjustments cannot be performed. Also, if the lenses  140  are secured on the light-transmissive member of the package, a smaller range is allowed for adjusting each lens  140 , so the alignment of individual lens  140  may not be able to compensate for the positional deviation of the light emission area. 
       FIG.  2    is a diagram schematically illustrating a plurality of laser diodes  110  in the light emitting device  100 P emitting light L with different diverging angles. As in the example illustrated in  FIG.  1   , the light emitting device  100 P illustrated in  FIG.  2    does not have a sub-lens. The laser diodes  110  emit light L with uneven diverging angles, for example, when the laser diodes  110  emit light of different colors. In such a case, the structures and sizes of the laser diodes  110  may differ from one another, and accordingly, the diverging angles of the emitted light may from one another. In such a case, the beam diameters of the light beam passing through the lenses  140  may differ from one another. In order to obtain collimated lights of closely uniform beam diameters by changing the focal distances of the lens  140  according to the types of laser diodes  110 , the size of the light emitting device  100 P along the optical axis must be increased. 
     Such concerns may occur not only when various types of laser diodes  110  are combined with lenses, but also when various types of light emitting elements are combined with lenses. 
     Basic Configuration 
     Certain embodiments of the present disclosure will be described below with reference to the drawings. An example of a basic configuration of a light emitting device common to certain embodiments will be described with reference to  FIG.  3   .  FIG.  3    is a diagram schematically showing an example of a configuration of a light emitting device. In certain drawings, an X-axis, a Y-axis, and a Z-axis that are orthogonal to one another are schematically shown for reference. The orientation of the light emitting device during use is arbitrary and is not limited by the orientation of the light emitting device shown in the drawings. 
     The light emitting device  100  includes a plurality of light emitting elements  10 , including a first light emitting element  10 A and a second light emitting element  10 B, and a case  20 , which encloses the plurality of light emitting elements  10 . The plurality of light emitting elements  10  may be hermetically sealed by the case  20 . Although two light emitting elements  10  are illustrated in  FIG.  3   , the number of the light emitting elements  10  may be three or more, as shown in other examples illustrated below. The light emitting elements  10  may be laser elements, such as edge-emitting semiconductor laser elements or vertical cavity surface emitting laser (VCSEL) elements. For such laser elements, laser diodes (LDs) having semiconductor layers can be used. Light emitting elements  10  may be light emitting light emitting diodes (LEDs) configured to emit incoherent light. The light emitting elements  10  are preferably laser elements, because a laser light emitted from a laser element has higher rectilinear propagation than light emitted from an LED, allowing more light to be irradiated into the lens. The term “light-emitting region” of each of the light emitting element  10  refers to a region in a surface of each of the light emitting elements  10  from where light L is emitted. When the light emitting elements  10  are laser elements, the term “light-emitting region” of each of the light emitting elements  10  refers to a region in a surface of each of the light emitting elements  10  from where a laser beam is emitted. The light emitted from each of the light emitting elements  10  is visible light, for example. The wavelength of the light is not limited to the visible light range, but can be in the infrared or ultraviolet range. In addition, the plurality of light emitting elements  10  may respectively emit light in different wavelength ranges or may respectively emit light of different colors. In the example shown in  FIG.  3   , the peak wavelength of the light emitted from the first light emitting element  10 A is different from the peak wavelength of the light emitted from the second light emitting element  10 B. 
     The case  20  has a light-transmissive region  30  to allow the light L emitted from the plurality of light emitting elements  10  to pass therethrough. The light-transmissive region  30  is, for example, formed with glass. The case  20  may be referred to as a package. A specific example of the configuration of the case  20  will be described below. 
     The light emitting device  100  has a plurality of main lenses  40  respectively covering at least portions of the light-transmissive region  30 . The plurality of main lenses  40  include a first main lens  40 A configured to collimate or converge the light L emitted from the first light emitting element  10 A, and a second main lens  40 B configured to collimate or converge the light L emitted from the second light emitting element  10 B. In the example shown in  FIG.  3   , the main lenses  40  are collimating lenses. 
     Further, the light emitting device  100  has a plurality of sub-lenses  50  disposed in the interior of the case  20 . The plurality of sub-lenses  50  include a first sub-lens  50 A disposed in an optical path between the first light emitting element  10 A and the first main lens  40 A, and a second sub-lens  50 B disposed in an optical path between the second light emitting element  10 B and the second main lens  40 B. Accordingly, the light emitted from the first light emitting element  10 A passes through the first sub-lens  50 A and enters the first main lens  40 A. The first sub-lens  50 A provides an auxiliary function of the first main lens  40 A. The first main lens  40 A in combination with the first sub-lens  50 A can achieve a desired collimation or conversion. Similarly, the light emitted from the second light emitting element  10 B passes through the second sub-lens  50 B and enters the second main lens  40 B. The second sub-lens  50 B provides an auxiliary function of the second main lens  40 B. The second main lens  40 B in combination with the second sub-lens  50 B can achieve a desired collimation or conversion. Accordingly, the main lenses  40  used in combination with the sub-lenses  50  may have a shape different from that of the main lenses used without the sub-lenses  50 . 
     In  FIG.  3   , light L emitted from each of the light emitting element is represented graphically by the area enclosed by two dashed lines. The intensity of light L, such as a laser beam, can be approximately represented as, for example, a Gaussian distribution at a plane perpendicular to the direction of propagation of the center of the light L. The diameter of the beam of such light L can be determined by the size of the region with the light intensity, for example, equal or greater than 1/e 2 , relative to the light intensity of the center of the beam, where “e” is Napier&#39;s constant (about 2.71). The diameter of the beam may be defined by other criteria. 
     The plurality of sub-lenses  50  can be disposed independently of each other in the case  20 . Therefore, the position and orientation of the individual sub-lenses  50  can be adjusted without being constrained to each other. In  FIG.  3   , components supporting the sub-lenses  50  are not shown for simplicity. The individual sub-lenses  50  can be secured directly or indirectly to the case  20 . 
     The position and orientation of the first sub-lens  50 A are determined according to the position and orientation of the first light-emitting element  10 A after the first light emitting element  10 A is disposed in the case  20 . Similarly, the position and orientation of the second sub-lens  50 B are determined according to the position and orientation of the second light-emitting element  10 B after the second light emitting element  10 B is disposed in the case  20 . The plurality of sub-lenses  50  can each compensate positional deviation and/or orientation deviation of the plurality of light emitting elements  10 . Also, even when the plurality of light emitting elements  10  are disposed without positional deviation, differences in the beam diameters or in the conversion point of the light may occur due to differences in the properties such as wavelengths and diverging angles of light emitted from the plurality of light emitting element  10 . Such differences in the beam diameter or in the conversion point of light emitted from each of the plurality of light emitting elements  10  can be adjusted by a respective corresponding one of the plurality of sub-lenses  50 . From these features, the sub-lenses  50  may be referred to as correcting lenses or adjusting lenses. 
     Adjustment of the position and orientation of each of the sub-lenses  50  can be performed by measuring light L passing through the sub-lens  50  by using a device such as a beam profiler, while maintaining emission of light L from the light emitting element  10 . For example, when an ultraviolet curable resin is used to secure the sub-lenses  50  to the case  20 , the adjustment described above is carried out with the uncured ultraviolet curable resin between the sub-lenses  50  and the case  20 . After determining the position and orientation of the sub-lenses  50 , the resin can be cured by irradiating ultraviolet light to the resin while maintaining the positions and orientations of the sub-lenses  50  by using a jig or a holding device. Instead of using the resin, a bonding material containing a metal that is softened or melted by heating may be used. Adjusting the direction and/or diverging angle of light L emitted from the light emitting device  100  by disposing the sub-lenses  50  while maintaining emission of light L from the light emitting elements  10  can be referred to as “active alignment.” After such active alignment is completed, the main lenses  40  are disposed. 
     Lights L that have been corrected through the sub-lenses  50  enter the main lenses  40  respectively. This allows the lights passed through the main lenses  40  to be within the target quality range. The quality of light includes propagating direction of light, diverging angle of light, and intensity of light. The expression “within the target quality” means one or more of these are within the target range, and it is preferable that all of them are within the target range. 
     In addition, even if the main lenses  40  are provided as a lens array in which the main lenses  40  are connected to one other, it is possible to obtain a plurality of light beams each satisfying the desired quality, by adjusting the position of the lens array within a range that is allowed for the lens array. 
     In  FIG.  3   , the main lenses  40  are secured directly or indirectly to an outside of the case  20 . If the main lenses  40  are disposed to the interior of the case  20 , the light collimated or converged by the main lenses  40  are extracted to the outside of the case  20  through the light-transmissive region  30 . In such a case, the possibility of degradation in the quality of the light beam caused by the light-transmissive region  30  cannot be ruled out. Therefore, it is preferable to dispose the main lenses  40  outside of the case  20  as shown in  FIG.  3   . With this arrangement, degradation in the quality of the light beams can be reduced or avoided. Meanwhile, the sub-lenses  50  are disposed to the interior of the case  20 , not to the outside. The light L emitted from each of the light emitting elements  10  spreads in a wider range as the distance from the light emitting region increases. By disposing the sub-lenses  50  inside the case  20 , the sub-lenses  50  can be placed closer to the light-emitting regions of the light emitting elements  10 , which allows the correction by the sub-lenses  50  having dimensions smaller than that required for the sub-lenses  50  placed outside of the case  20 . This can be advantageous for miniaturizing the light emitting device  100 . 
     FIRST EMBODIMENT 
     A first embodiment will be described below with reference to  FIG.  4 A  through  FIG.  8   . 
     A general structure of a light emitting device  100  according to the first embodiment will be described below with reference to  FIG.  4 A ,  FIG.  4 B ,  FIG.  5 A ,  FIG.  5 B , and  FIG.  5 C . FIG.  4 A is a schematic perspective view of a light emitting device according to the first embodiment.  FIG.  4 B  is a schematic perspective view showing an interior of the light emitting device  100  according to the first embodiment.  FIG.  5 A  is a schematic top view of a light emitting device  100  according to the first embodiment, viewed from the positive side of the Z-axis.  FIG.  5 B  is a schematic side view of the light emitting device  100  according to the first embodiment, viewed from the positive side of the X-axis.  FIG.  5 C  is a schematic side view of the light emitting device  100  according to the first embodiment, viewed from the positive side of the Y-axis. 
     The light emitting device  100  according to the first embodiment includes a plurality of light emitting elements  10  including a first light emitting element  10 A, a second light emitting element  10 B, and a third light emitting element  10 C, and a case  20  that encloses the plurality of light emitting elements  10 . 
     In the example placement shown in  FIG.  4 B , each of the light emitting elements  10 A,  10 B, and  10 C emits light in the negative direction of the Y-axis. Three reflectors R are disposed in the interior of the case  20 , each configured to reflect the light emitted from a corresponding one of the three light emitting elements  10  in the positive direction of the Z-axis. Also, as shown in  FIG.  4 A , the case  20  has a cover  32  including a light-transmissive region that allows light reflected by the reflector R passes therethrough. In this example, the entire cover  32  is formed from a light-transmissive material and serves as the light-transmissive region. Instead of the entire part of the cover  32 , a portion of the cover  32  may serve as a light-transmissive region. The light emitting device  100  includes a plurality of main lenses  40 : a first main lens  40 A, a second main lens  40 B, and a third main lens  40 C, covering at least portions of the cover  32 , and a plurality of sub-lenses  50  disposed in the interior of the case  20 : a first sub-lens  50 A, a second sub-lens  50 B and a third sub-lens  50 C. In this example, each of the plurality of sub-lenses  50  is disposed between a corresponding one of the plurality of light emitting elements  10  and a corresponding one of the plurality of reflectors R. 
     Next, with reference to  FIG.  6   ,  FIG.  7    and  FIG.  8   , the configuration of the light emitting device  100  according to the first embodiment will be described in detail.  FIG.  6    is a schematic cross-sectional view of the light emitting device  100  according to the first embodiment.  FIG.  7    is a schematic plan view showing the internal configuration of the light emitting device  100 , in which the cover  32  and the main lenses  40  are not shown.  FIG.  8    is a schematic perspective view showing a configuration example of a lens array  400  that can be used in the light emitting device  100 . 
     As shown in  FIG.  6   , case  20  of light emitting device  100  has a base  22  supporting light emitting element  10  and a cover  32  covering light emitting element  10 . The cover  32  can be formed from a light-transmissive material such as sapphire. The cover  32  includes, for example, a plate formed from a light-transmissive material. A metal layer may be disposed on a surface of the plate. The base  22  includes a bottom portion  24  having a first upward-facing surface on which a plurality of light emitting elements  10  are disposed, and a frame portion  26  surrounding the plurality of light emitting elements  10  and having a second upward-facing surface. The main lenses  40  are disposed on the cover  32  and the cover  32  is supported by the second upward-facing surface of the frame portion  26 . 
     The base  22  includes an electrode structure to electrically connect the light emitting elements  10  to an external power source. The plurality of light emitting elements  10  are electrically connected to the electrode structure. Therefore, the base  22  also serves to electrically connect the light emitting elements  10  to the external power supply. The base  22  can be formed from a composite of an electrically insulating material and an electrically conductive material. The base  22  includes, for example, an electrically insulating ceramic body and an electrically conductive metal part that serves as electrodes. 
     In the example shown in  FIG.  6   , the frame portion  26  has a step portion having a third upward-facing surface  28  between the second upward-facing surface supporting the cover  32  and the first upward-facing surface of the bottom portion  24 . At least portions of the electrode structure for connecting the light emitting elements  10  to the external power supply can be disposed on the third upward-facing surface  28  of the step portion. A portion of the electrode structure can be a via electrode that penetrates the base  22 . The electrode structure and the light emitting elements  10  can be electrically connected, for example, via respective wires. In  FIG.  6   , the wires are not shown. In  FIG.  7   , six wires  60  are schematically illustrated. The wires  60  electrically connect the electrically conductive layers that are parts of the electrode structure disposed on the third upward-facing surface  28  of the step portion and the light emitting elements  10  respectively. In  FIG.  7   , the wires  60  are shown in the shape of straight lines, but the wires  60  may have, for example, curved portion(s) or bent portion(s). 
     In the example shown in  FIG.  6   , each of the light emitting elements  10  is secured to a corresponding one of the sub-mounts  12 , and the sub-mounts  12  are secured to the base  22 . The sub-mounts  12  can be omitted from the configuration of the light emitting device  100 . The sub-mounts  12  can be formed from a material having a thermal conductivity higher than the thermal conductivity of the base  22  to increase heat dissipation. The light-emitting region of each of the light emitting elements  10  is located opposite to the corresponding reflector R such that the light L is emitted toward the reflector R. In  FIG.  6   , an optical axis (center) of light L is schematically depicted as a straight arrow. A plurality of sub-lenses  50  are disposed between the light-emitting regions of the light emitting elements  10  and the reflectors R, respectively. The positions of the sub-lenses  50  are adjusted to compensate for positional deviations of corresponding one of the light emitting elements  10 , and then the sub-lenses  50  are secured to the base  22 . The expression “compensation” shown above does not necessarily mean strict matching of the focal point of the lens system formed by a combination of one of the main lenses  40  and a corresponding one of the sub-lenses  50  onto the light-emitting region of a corresponding one of the light emitting elements  10 . “Compensation” includes adjusting the position and/or orientation of the sub-lens  50  such that the focal point of the lens system is brought relatively close to the light-emitting region of the light emitting element  10  compared to that without the sub-lenses  50 . 
     The position and orientation of each of the sub-lenses  50  are preferably adjusted such that the focal point of the lens system formed by a combination of one of the main lenses  40  and a corresponding one of the sub-lenses  50  matches the light-emitting region of the light emitting element  10 . This allows each portion of light L that has passed through the corresponding one of the sub-lenses  50  to be more reliably collimated or converged by the corresponding one of the main lenses  40 . It is also preferable that at least one of the main lenses  40  and the sub-lenses  50  is not a lens array with a plurality of lenses mechanically connected together, but that the lenses are separate lens components. This allows for a wider adjustment range for the focal point of each combination of the main lens  40  and the sub-lens  50 , compared to a case in which both the main lenses  40  and the sub-lenses  50  are respectively provided as lens arrays. Accordingly, the focal point can be easily matched to the light emitting region of a corresponding one of the light emitting elements  10 . 
     Each of the reflectors R has a light-reflecting surface on at least one side. The light-reflecting surface is inclined with respect to the bottom surface of the reflector R to reflect light L from the light emitting element  10  toward the light-transmissive region. The reflector R receives the radiation light from the light emitting element  10 , therefore preferably be formed from a heat-resistant material. The light-reflecting surface can be formed with a layer of a material having high reflectance. The main body part of the reflector R can be formed from glass such as quartz or BK7 (borosilicate glass), a metal such as aluminum, or Si. The light-reflecting surface can be formed from a metal layer and/or a dielectric multilayer film. 
     It is preferable that a portion of each of the sub-lenses  50  has a shape that allows bonding to the base  22 , for example, a rectangular parallelepiped shape. Each of the sub-lenses  50  has a curved-surface lens portion. This curved surface can be convex or concave. The sub-lenses  50  can be made of, for example, glass such as BK7 or B270. The main lenses  40  can also be made of, for example, glass such as BK7 or B270. The main lens  40  contains three main lenses  40 A,  40 B and  40 C arranged in an X axis direction as shown in  FIG.  4 A . Each of the main lenses  40 A,  40 B, and  40 C has a spherical or an aspherical lens shape at a portion where light L passes through, and has appropriate shapes at other portions. In the example shown in  FIG.  4 A , the lens shape portion of each of the main lenses  40  is a convex portion protruding upward from a plate-like portion. Close arrangement of the convex portions of the plurality of main lenses  40  can facilitate miniaturization of the light emitting device  100 . The distance between each of the convex portions of the plurality of main lenses  40  can be, for example, smaller than the width in the X-axis direction of a single convex portion. 
     The main lenses  40 A,  40 B, and  40 C may be bonded to the cover  32  as separate lens components, or may be secured to the cover  32  as a single integrated lens array.  FIG.  8    is a schematic perspective view showing a configuration example of a lens array  400  in which the main lenses  40 A,  40 B, and  40 C are connected to each other. The lens array  400  is a one-piece body with the main lenses  40 A,  40 B, and  40 C in a tightly aligned structure along the X-axis. There may be a gap between the first main lens  40 A and the second main lens  40 B, and between the second main lens  40 B and the third main lens  40 C, or the three main lenses  40 A,  40 B, and  40 C may be connected without a gap. 
     As shown in  FIG.  6   , the main lenses  40  can be secured to the cover  32  via a bonding layer  34 . The bonding layer  34  can be formed from ultraviolet curable resin, for example. The lens array  400  shown in  FIG.  8    can also be secured to the cover  32  via a similar bonding layer. In the lens array  400 , the relative positional relationship among the main lenses  40 A,  40 B, and  40 C are in a fixed state, such that the main lenses  40 A,  40 B, and  40 C are not required to be secured separately to the cover  32 . The lens array  400  can be handled as a single component and thus can facilitate mounting. 
     The plurality of light emitting elements  10  may emit light of different colors. For example, light emitting elements  10  respectively emitting light of blue color, green color, and red color can be employed. In the first embodiment, the first light emitting element  10 A, the second light emitting element  10 B, and the third light emitting element  10 C can be respectively a green semiconductor laser element to emit a green laser beam, a blue semiconductor laser element to emit a blue laser beam, and a red semiconductor laser element to emit a red laser beam. All of them are edge-emitting semiconductor laser elements. 
     The peak wavelength of the laser beam emitted by the blue semiconductor laser element is in a range of 430 to 480 nm and may be in a range of 450 to 470 nm. The peak wavelength of the laser beam emitted by the green semiconductor laser element is in a range of 500 to 550 nm and may be in a range of 520 to 540 nm. The peak wavelength of the laser beam emitted by the red semiconductor laser element is in a range of 620 to 660 nm and may be in a range of 630 to 650 nm. The blue semiconductor laser element and the green semiconductor laser element can be formed mainly from nitride semiconductors. Examples of nitride semiconductors include GaN, InGaN, and AlGaN. The red semiconductor laser element can be formed mainly of a gallium arsenic-based semiconductor. When laser elements are employed as the light emitting elements  10 , the higher the optical energy is, the more accumulation of dust etc., from the environmental atmosphere attracted on the light-emitting surfaces of the laser elements in operation. Dust and other particles on the light-emitting surface can reduce the optical output. The optical energy increases with shorter wavelengths of the laser beam, and with higher optical output. For this reason, when laser elements to emit laser beams of green color or shorter wavelengths are employed as the light emitting elements  10 , the light emitting elements  10  are preferably hermetically sealed within the case  20 . When the light emitting elements  10  are hermetically sealed within the case  20 , outside dust etc., can be prevented from entering the case  20 , such that possibility of dust etc., attaching to the light emitting surfaces of the laser elements can be reduced. 
     Lasing performance fluctuation due to temperature may more likely occur in red semiconductor laser elements than in blue and green semiconductor laser elements. Blue semiconductor laser elements have a power conversion efficiency greater than that of green semiconductor laser elements, and thus the amount of heat generated from the blue semiconductor laser elements is smaller than that from the green semiconductor laser elements. For this reason, the green semiconductor laser elements are preferably disposed spaced apart from the red semiconductor laser elements. As shown in  FIG.  7   , in the first embodiment, the blue semiconductor laser element (a second light emitting element  10 B) is disposed between the red semiconductor laser element (a third light emitting element  10 C) and the green semiconductor laser element (a first light emitting element  10 A). With this configuration, the emission characteristics of the red semiconductor laser element (the third light emitting element  10 C) can be stabilized. 
     One or more semiconductor elements other than the light emitting elements  10  may be disposed in the case  20 . For example, a protective circuit element such as a Zener diode configured to control reverse voltage loaded on respective light emitting elements  10  within a predetermined level and/or a photodetection element such as a photodiode configured to monitor the intensity of light L may also be disposed. 
     In the first embodiment, each of the sub-lenses  50  can be disposed close to the light-emitting region of a corresponding one of the light emitting elements  10 , such that light L emitted from each of the light-emitting regions enters the sub-lens  50  before expanding. This allows for reducing the size of the sub-lenses  50 . Further, adjusting the positions of the sub-lenses  50  within the case  20  allows for compensating for positional deviation of the light-emitting regions. Other than that shown in the figures, the shapes and dimensions of the sub-lenses  50  can be appropriately determined. In addition, when the beam sizes of light L emitted from the plurality of light emitting elements  10  at the light incidence surfaces of the main lenses  40  differ without the sub-lenses  50 , it is possible to adjust the beam size of each portion of light L to approach uniformity by using the sub-lenses  50 . 
     SECOND EMBODIMENT 
     A second embodiment of the present invention will be described below with reference to  FIG.  9 A  through  FIG.  12   . 
     A schematic configuration of a light emitting device  100  according to the second embodiment will be described below with reference to  FIG.  9 A ,  FIG.  9 B ,  FIG.  10 A ,  FIG.  10 B , and  FIG.  10 C .  FIG.  9 A  is a schematic perspective view of a light emitting device according to the second embodiment.  FIG.  9 B  is a schematic perspective view showing an interior of the light emitting device according to the second embodiment.  FIG.  10 A  is a schematic top view of the light emitting device shown in  FIG.  9 A , viewed from the positive side of the Z-axis.  FIG.  10 B  is a schematic lateral view of the light emitting device shown in  FIG.  9 A , viewed from the positive side of the X-axis.  FIG.  10 C  is a schematic lateral view of the light emitting device shown in  FIG.  9 A , viewed from the positive side of the Y-axis. 
     As in the light emitting device  100  according to the first embodiment described above, the light emitting device  100  according to the second embodiment includes a plurality of light emitting elements  10  that includes a first light emitting element  10 A, a second light emitting element  10 B, and a third light emitting element  10 C, a case  20  enclosing the plurality of light emitting elements  10 . The difference from the first embodiment is the configuration of a plurality of sub-lenses  50  disposed in the case  20 . The difference will be described in detail below. 
     As shown in  FIG.  9 B , the light emitting device  100  according to the second embodiment includes a first sub-lens  50 A, a sub-lens  50 B, and a third sub-lens  50 C. In the second embodiment, the plurality of sub-lenses  50  are respectively disposed between the cover  32  and a corresponding one of the reflectors R. 
     Next, with reference to  FIG.  11    and  FIG.  12   , structure of the sub-lenses  50  of the light emitting device  100  according to the second embodiment will be described.  FIG.  11    is a schematic cross-sectional view showing the light emitting device  100  according to the second embodiment.  FIG.  12    is a schematic plan view showing a structure of an interior of the light emitting device  100 . In  FIG.  12   , the cover  32  and the main lenses  40  are not shown. 
     As shown in  FIG.  11   , the case  20  of the light emitting device  100  in the second embodiment also includes a base  22  configured to support the plurality of light emitting elements  10 , and a cover  32  configured to cover the plurality of light emitting elements  10 . The base  22  includes a bottom portion  24  having a first upward-facing surface on which a plurality of light emitting elements  10  and a plurality of reflectors R are disposed, and a frame portion  26  surrounding the plurality of light emitting elements  10  and having a second upward-facing surface. The light emitting elements  10  are surrounded by the frame portion  26 . The main lenses  40  are disposed on the cover  32  and the cover  32  is supported by the second upward-facing surface of the frame portion  26 . The main lenses  40  may be provided as the lens array  400  shown in  FIG.  8   . 
     In the example shown in  FIG.  11   , the frame portion  26  has two step portions (an upper step portion and a lower step portion) respectively having an upward-facing surface between the second upward-facing surface supporting the cover  32  and the first upward-facing surface of the bottom portion  24 . At least a portion of the electrode structure to connect the light emitting elements  10  to an external power source can be disposed on the upward-facing surface  28 A of the lower step portion. In the second embodiment, each of the plurality of sub-lenses  50  is supported by the upward-facing surface  28 B of the upper step portion of the frame portion  26 . 
     In  FIG.  11    and  FIG.  12   , the wires are not shown. The light emitting device  100  according to the second embodiment also includes the electrode structure and wires as described in the first embodiment, and the repetitive description of which will be omitted. 
     As shown in  FIG.  12   , each of the sub-lenses  50 A,  50 B, and  50 C has a plate-like flat extending portion  52  and a lens shape having convex portion with a curved surface. The convex portion serves as a lens. The sub-lenses  50 A,  50 B, and  50 C are respectively discrete components and, for example, made of a glass material. Each of the sub-lenses  50 A,  50 B, and  50 C has a substantially rectangular shape in a plan view, with a length L 1  in a Y-axis direction that allows each of the sub-lens  50 A,  50 B, and  50 C to rest on the left portion and the right portion of the upward-facing surface  28 B of the frame portion  26 . Both ends of each of the sub-lenses  50 A,  50 B, and  50 C are slidably supported by the upward-facing surface  28 B of the frame portion  26  and can be slid in an X-axis direction before being secured to the frame portion  26 . Before being secured to the frame portion  26 , each of the sub-lenses  50 A,  50 B, and  50 C can also be slid in a Y-axis direction. In order to allow such sliding in the Y-axis direction, the length L 1  in a Y-axis direction of lateral surfaces extending from outer edges of the upward-facing surface  28 B in a positive Z-axis direction is greater than the length L 2  of each of the sub-lenses  50 A,  50 B, and  50 C. The length L 1  may also be referred to a distance between the left end of the left side portion of the upward-facing surface  28 B and the right end of the right side portion of the upward-facing surface  28 B in the Y-axis direction. A difference in the lengths (L 1 -L 2 ) determines an upper limit of shiftable range of the sub-lenses  50 A,  50 B, and  50 C in the Y-axis direction. The difference in the lengths (L 1 -L 2 ) can be set within a range appropriate for the dimensions of the light emitting device  100 . The length L 2  may be set, for example, in a range of 0.5 to 0.95 times with respect to the length L 1 . The difference in the lengths (L 1 -L 2 ) can be set, for example, within a range of 0.2 to 3 mm. In order to allow the upward-facing surface  28 B to support the both ends of the sub-lenses  50 A,  50 B, and  50 C, the length L 3  in the Y-axis direction of lateral surfaces extending from inner edges of the upward-facing surface  28 B in a negative Z-axis direction is less than the length L 2  of each of the sub-lenses  50 A,  50 B, and  50 C. The length L 3  may also be referred to a distance between the right end of the left side portion of the upward-facing surface  28 B and the left end of the right side portion of the upward-facing surface  28 B in the Y-axis direction. The length L 3  may be set, for example, in a range of 0.5 to 0.95 times with respect to the length L 2 . The difference in the lengths (L 2 -L 3 ) can be set, for example, within a range of 0.02 to 3 mm. 
     In the second embodiment, at the time of securing the sub-lenses  50 A,  50 B, and  50 C to the frame portion  26 , each of the sub-lenses is allowed to be slided in the two dimensions along the upward-facing surface  28 B of the step portion, which facilitates the positional adjustment of the sub-lenses  50 A,  50 B, and  50 C. 
     The positions of the sub-lenses  50 A,  50 B, and  50 C in the Z-axis direction can be adjusted by a thickness of a bonding layer disposed between the upward-facing surface  28 B of the step portion and the lower surfaces of the sub-lenses  50 A,  50 B, and  50 C. 
     As described in the first embodiment, when the sub-lenses  50 A,  50 B,  50 C are secured to the case  20  by using a ultraviolet curable resin, adjustment can be performed with uncured ultraviolet curable resin being disposed between the sub-lenses  50 A,  50 B, and  50 C and the upward-facing surface  28 B of the step portion. After the positions and the orientations of the sub-lenses  50 A,  50 B, and  50 C are adjusted, the positions and the orientations of the sub-lenses  50 A,  50 B, and  50 C are held by a jig or a holding device, and ultraviolet light is irradiated to harden the resin. 
     In the light emitting device  100  according to the second embodiment, the plurality of sub-lenses  50  are respectively held by the step portion of the frame portion  26 . This arrangement allows for arranging the sub-lenses  50  at higher locations than the light emitting elements  10  and the reflectors R, which can facilitate handling of the sub-lenses  50 A,  50 B, and  50 C, and which can facilitate positioning of the sub-lenses  50 A,  50 B, and  50 C in X-Y plane. Meanwhile, the shiftable range of the sub-lenses  50 A,  50 B, and  50 C along the propagation direction of light, that is, along the optical axis can be greater in the first embodiment than in the second embodiment. Also, the first embodiment is more advantageous in view of miniaturizing of the light emitting device. This is because in the second embodiment, distances between the light-emitting regions of the light emitting elements  10  and a corresponding one of the sub-lenses  50  becomes relatively great, resulting in relatively large convex portions that serve as lenses in the sub-lenses  50 . 
     In the embodiments described above, the light emitting devices  100  are provided with the reflectors R, but the reflectors R can be optional. 
     THIRD EMBODIMENT 
     A third embodiment of the present invention will be described below with reference to  FIG.  13 A  to  FIG.  16   . A light emitting device  100  according to the third embodiment is not provided with a reflector R. 
     A general structure of a light emitting device  100  according to the third embodiment will be described below with reference to  FIG.  13 A ,  FIG.  13 B ,  FIG.  14 A ,  FIG.  14 B , and  FIG.  14 C .  FIG.  13 A  is a schematic perspective view showing a light emitting device according to the third embodiment.  FIG.  13 B  is a schematic perspective view showing an interior of the light emitting device according to the third embodiment.  FIG.  14 A  is a schematic top view of and the emitting device according to the third embodiment, viewed from the positive Z-axis.  FIG.  14 B  is a schematic lateral view of the light emitting device according to the third embodiment, viewed from the positive X-axis.  FIG.  14 C  is a schematic lateral view of the light emitting device according to the third embodiment, viewed from the positive Y-axis. 
     As in the first embodiment and the second embodiment described above, the light emitting device  100  according to the third embodiment includes a plurality of light emitting elements  10 , which include a first light emitting element  10 A, a second light emitting element  10 B, and a third light emitting element  10 C, as well as a case  20  enclosing the plurality of light emitting elements  10 . The light emitting device  100  according to the third embodiment is not provided with a reflector R. Light emitted from each of the plurality of light emitting elements  10  disposed in the case  20  is extracted from a lateral surface of the case  20 . This will be described in detail below. The case  20  has a lid  70  covering a frame portion  26 . In  FIG.  13 B , the lid  70  and main lenses  40  are not shown. 
     As shown in  FIG.  13 A , the light emitting device  100  according to the third embodiment includes a first main lens  40 A, a second main lens  40 B, and a third main lens  40 C, respectively secured on a cover  32  located on a lateral surface of the case  20 . The light emitting device  100  according to the third embodiment includes a first sub-lens  50 A, a sub-lens  50 B, and a third sub-lens  50 C located in the case  20 . In the third embodiment, the first sub-lens  50 A is located in the optical path between the first light emitting element  10 A and the first main lens  40 A. The second sub-lens  50 B is located in the optical path between the second light emitting element  10 B and the second main lens  40 B. The third sub-lens  50 C is located in the optical path between the third light emitting element  10 C and the third main lens  40 C. 
     Next, with reference to  FIG.  15    and  FIG.  16   , the structure of the light emitting device  100  according to the third embodiment will be further described.  FIG.  15    is a schematic cross-sectional view showing the light emitting device  100  according to the third embodiment.  FIG.  16    is a schematic plan view showing a structure of an interior of the light emitting device  100 , in which a lid  70  is not shown. 
     As shown in  FIG.  15   , in the third embodiment, a through opening  26 X is formed in a lateral surface, more specifically, a portion of the frame portion  26  of the case  20 . The through opening  26 X of the frame portion  26  is covered by a cover  32 . The main lenses  40  are secured to the frame portion  26  via a bonding layer  34 . Alternatively, the main lenses  40  may be secured to the cover  32 . 
     Light L is emitted from each of the light emitting elements  10 A,  10 B, and  10 C in the positive Y-axis. Three sub-lenses  50  are disposed in the interior of the case  20  to transmit light emitted from a corresponding one of the three light emitting elements  10 . 
     The lid  70  is not required to have a light-transmissive portion, but the cover  32  is required to have a light-transmissive portion. At least a portion of the cover  32  to transmit light L is made of a light-transmissive material. Light L that has passed through each one of the sub-lenses  50  can be collimated or converged by a corresponding one of the main lenses  40 . Adjustment and securing of each of the sub-lenses  50  can be performed as described in the first embodiment. The light emitting device  100  according to the third embodiment also includes the electrode structure and wires as described above. 
     According to the structure in the third embodiment, a reflector R is not required in the light emitting device  100 , which allows a reduction in the number of components, which in turn allows a reduction in the dimensions of the light emitting device  100 . 
     The embodiments described above are intended as illustrative of a light emitting device to give a concrete form to technical ideas of the present invention, and the scope of the invention is not limited to those described below. Further, the members shown in claims attached hereto are not specifically limited to members according to embodiments. The sizes, materials, shapes and the relative configuration etc. of components described in the embodiments are given as an example and not as a limitation to the scope of the invention, unless specifically described otherwise. 
     In addition, in the present disclosure, a plurality of structural elements may be configured as a single part that serves the purpose of a plurality of elements, and on the other hand, a single structural element may be configured as a plurality of parts that serve the purpose of a single element. 
     The light emitting devices according to the present disclosure can be used as light sources of projectors, vehicular headlights, lighting devices, communication devices, laser machining devices, etc. 
     It is to be understood that although the present invention has been described with regard to preferred embodiments thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims.