Patent Publication Number: US-2013243019-A1

Title: Laser diode array and laser diode unit

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to Japanese Priority Patent Application JP 2012-058213 filed in the Japan Patent Office on Mar. 15, 2012, the entire content of which is hereby incorporated by reference. 
     BACKGROUND 
     The present disclosure relates to a laser diode array including a plurality of laser diode devices on a heat sink, and a laser diode unit including the laser diode array. 
     A laser diode is used as a light source for a display or the like because of its small light-emitting point and its sharp spectrum (its high color rendering properties). For example, in Japanese Unexamined Patent Application Publication No. 2006-32406, a laser array including a plurality of laser diode devices which are one-dimensionally arranged is used as a high-power laser. 
     However, when the laser diode is used as a light source, there are two issues, i.e., screen glare (speckle noise) and deterioration in characteristics due to heat generation. 
     A typical laser diode has a characteristic in which an oscillation wavelength thereof is shifted to a longer wavelength with an increase in an internal temperature of an active layer. For example, in Japanese Unexamined Patent Application Publication No. 2008-4743, there is disclosed a method of reducing speckle noise with use of the characteristics. In the method, distances between light-emitting points are varied to cause thermal interference in an array laser, and a thermal distribution is provided to vary wavelengths from respective light-emitting points, thereby expanding an emission spectrum. Thus, speckle noise is reduced. 
     Moreover, for example, in Japanese Unexamined Patent Application Publication No. H9-252166, there is disclosed a configuration of a semiconductor light-emitting device in which chips (laser diode devices) are separated, and a heat dissipater (heat sink) disposed between a substrate and the chips has a smaller thickness than a distance between chips to thereby reduce thermal interference. 
     SUMMARY 
     However, in a technique of expanding a spectrum of a laser diode device through providing a thermal distribution as in Japanese Unexamined Patent Application Publication No. 2008-4743, it is difficult to produce a thermal distribution large enough to sufficiently reduce speckle noise, and an issue, i.e., a decline in reliability of a device in a high-temperature region arises. Moreover, in the semiconductor light-emitting device in Japanese Unexamined Patent Application Publication No. H9-252166, a reduction in thermal interference causes an increase in coherence of light from each light-emitting point, resulting in an increase in speckle noise. 
     It is desirable to provide a laser diode array capable of reducing speckle noise and suppressing deterioration in characteristics of a laser diode device, and a laser diode unit including the laser diode array. 
     According to an embodiment of the disclosure, there is provided a laser diode array including: a heat dissipator; a plurality of submounts disposed independently of one another on the heat dissipator; and a plurality of laser diode devices including two or more kinds of laser diode devices with different oscillation wavelengths, the laser diode devices being disposed on the respective submounts, and being electrically connected to one another. 
     According to an embodiment of the disclosure, there is provided a laser diode unit including a plurality of laser diode arrays, each of the laser diode arrays including: a heat dissipator; a plurality of submounts disposed independently of one another on the heat dissipator; and a plurality of laser diode devices including two or more kinds of laser diode devices with different oscillation wavelengths, the laser diode devices being disposed on the respective submounts, and being electrically connected to one another. 
     In the laser diode array and the laser diode unit according to the embodiments of the disclosure, the plurality of laser diode devices are disposed on the heat dissipator with the respective submounts in between; therefore, heat dissipation efficiency of the laser diode devices is improved. Moreover, when laser diode devices with different oscillation wavelengths are disposed in the laser diode array, a wavelength width of the laser diode array is increased, and coherency is reduced. 
     In the laser diode array and the laser diode unit according to the embodiments of the disclosure, since the plurality of laser diode devices are disposed on the heat dissipator with the respective submounts in between, heat dissipation efficiency of the laser diode devices is improvable, and deterioration in characteristics due to heat generation is allowed to be suppressed. Moreover, since the laser diode devices with different wavelengths are disposed on the heat dissipator, the wavelength width of the laser diode array is increased, and speckle noise is allowed to be reduced. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the technology as claimed. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are included to provide a further understanding of the technology, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the technology. 
         FIG. 1  is a perspective view illustrating a configuration of a laser diode array according to an embodiment of the disclosure. 
         FIG. 2  is a sectional view of the laser diode array taken along a line I-I of  FIG. 1 . 
         FIG. 3  is a sectional view of a device illustrated in  FIG. 1 . 
         FIG. 4  is a characteristic diagram illustrating a relationship between device interval and temperature increase. 
         FIG. 5  is a characteristic diagram illustrating a relationship between spectrum width and speckle contrast. 
         FIGS. 6A and 6B  are schematic views illustrating connection of devices located at both ends of the laser diode array illustrated in  FIG. 1 . 
         FIG. 7  is a perspective view illustrating a configuration of a laser diode array according to a modification of the disclosure. 
         FIG. 8  is a perspective view illustrating a configuration of a laser diode unit including a plurality of laser diode arrays illustrated in  FIG. 1  or  7 . 
         FIG. 9  is a perspective view describing mounting of the laser diode array in the laser diode unit illustrated in  FIG. 8 . 
         FIG. 10  is a perspective view illustrating another configuration of the laser diode unit including a plurality of laser diode arrays illustrated in  FIG. 1  or  7 . 
     
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment of the disclosure will be described in detail below referring to the accompanying drawings. It is to be noted that description will be given in the following order. 
     1. Embodiment
         1-1. Configuration of laser diode array   1-2. Manufacturing method       

     2. Modification 
     3. Application Examples 
     1. EMBODIMENT 
     1-1. Configuration of Laser Diode Array 
       FIG. 1  illustrates an entire configuration of a laser diode array (a laser diode array  1 ) according to an embodiment of the disclosure.  FIG. 2  illustrates a sectional configuration taken along a line I-I in  FIG. 1 . In the laser diode array  1 , a plurality of laser diode devices (devices  10 ) are mounted along one direction on a heat dissipator (a heat sink  20 ) with submounts  21  in between. The submounts  21  are disposed independently of one another, and in this case, one device  10  is disposed on one submount  21 . The devices  10  are connected to one another in series. More specifically, as will be described in detail later, for example, a first electrode (for example, a p-side electrode  13 ) of a pair of electrodes of a device  10   a  and a second electrode (for example, an n-side electrode  14 ) of a pair of electrodes of a device  10   b  are electrically connected to each other through a wire  22  (refer to  FIG. 2 ). 
       FIG. 3  illustrates a sectional configuration of the device  10 . The device  10  is, for example, an edge-emitting laser diode device, and includes, on one surface (an upper surface) of a substrate  11 , a laser structure section  10 A configured of a semiconductor laminate structure  12  and a p-side electrode  13  formed on the semiconductor laminate structure  12 . An n-side electrode  14  is disposed on the other surface (a lower surface) of the substrate  11 . 
     In the device  10 , the semiconductor laminate structure  12  disposed on the upper surface of the substrate  11  made of, for example, GaAs includes, for example, a buffer layer  12 A, an n-type cladding layer  12 B, an n-type guide layer  12 C, an active layer  12 D, a p-type guide layer  12 E, a p-type cladding layer  12 F, and a contact layer  12 G in this order of closeness to the substrate  11 . The n-type electrode  14  disposed on the lower surface of the substrate  11  is electrically connected to the n-type cladding layer  12 A, and the p-type electrode  14  is electrically connected to the contact layer  12 G. 
     The semiconductor laminate structure  12  is made of, for example, an AlGaInP-based material emitting light in a red region. As used herein, the term “AlGaInP-based compound semiconductor” refers to a quaternary semiconductor including one or both of aluminum (Al) and gallium (Ga) from Group 3B elements and one or both of indium (In) and phosphorus (P) from Group 5B elements in the long form of the periodic table of the elements, and examples of the AlGaIn-based compound semiconductor include an AlGaInP mixed crystal, a GaInP mixed crystal, and an AlInP mixed crystal. These mixed crystals may include an n-type impurity such as silicon (Si) or selenium (Se) or a p-type impurity such as magnesium (Mg), zinc (Zn), or carbon (C), if necessary. The device  10  emits light with a wavelength of about 630 nm to about 645 nm both inclusive. It is to be noted that an oscillation wavelength of the device  10  is not limited thereto, and the oscillation wavelength of the device  10  may be within a range of about 600 nm to about 630 nm both inclusive or a range of about 645 nm to about 700 nm both inclusive. Moreover, in addition to the AlGaInP-based material, a III-N-based material such as an AlInGaN-based material may be used. The device  10  has, for example, a width of about 0.3 mm to about 3 mm both inclusive, a length of about 0.3 mm to about 3 mm both inclusive, and a thickness of about 50 μm to about 300 μm both inclusive. 
     The heat sink  20  is made of, for example, a material having thermal conductivity and electrical conductivity such as copper (Cu) (with a linear expansion coefficient of 16.8×10 −6 /° C.), and, for example, a thin film made of gold (Au) is deposited on a surface of the heat sink  20 . Thermal conductivity is a necessary characteristic to release a large amount of strong heat generated in the laser diode device to maintain the laser diode device at an appropriate temperature, and electrical conductivity is a necessary characteristic to efficiently conduct a current to the laser diode device. 
     The submounts  21  are made of an insulating material. More specifically, for example, aluminum nitride (AlN), silicon carbide (SiC), or the like is used. Each of the submounts  21  has, for example, a width of about 0.3 mm to about 4 mm both inclusive, a length of about 0.5 mm to about 5 mm both inclusive, and a thickness of about 50 μm to about 500 μm both inclusive. Metal thin films made of titanium (Ti), platinum (Pt), or Au are formed on a front surface and a back surface of each of the submounts  21 , and the metal thin films on the front surface and the back surface are bonded to the device  10  and the heat sink  20 , respectively, with solder. Examples of the solder used herein include gold-tin (AuSn) solder and tin-silver (SnAg) solder. 
     As described above, the submounts  21  are disposed separately from one another, and are arranged on the heat sink  20  at predetermined intervals.  FIG. 4  illustrates a relationship between arrangement interval and temperature increase while the devices  10  emit light. As can be seen from  FIG. 4 , when a distance between the devices  10  is increased, an increase in temperature of each of the devices  10  is suppressed. More specifically, when each interval between the devices  10  is about 2 mm, an increase in temperature while the devices  10  emit light is about 10° C., and the temperature of each device  10  is hardly affected by the adjacent devices  10 . In the case where each interval between the devices  10  is smaller than about 2 mm, thermal interference from the adjacent devices  10  is highly influential, and easily causes deterioration in characteristics. Moreover, when each interval between the devices  10  is increased to be about 2 mm or more, for example, in the case where the laser diode array  1  according to the embodiment is used in an illumination device of a projector, light is easily uniformized in the projector using a fly-eye lens or the like. Moreover, a high-priced lens such as a microlens array is not necessary, thereby resulting in a reduction in cost. 
     An upper limit of each interval between the devices  10  is preferably about 10 nm. For example, in the case where each interval between the devices  10  is larger than about 10 mm, it is necessary to increase light emission intensity per device to secure necessary light emission intensity in the same area, and this may cause damage to a laser facet. On the other hand, in the case where the devices  10  are used without increasing light emission intensity per device, light emission intensity per unit area is reduced, and it is necessary to upsize an entire light source accordingly. Therefore, each interval between the devices  10  is preferably within a range of about 2 mm to about 10 mm both inclusive. 
     As an example of arrangement of the devices  10  at intervals within the above-described range in the laser diode array  1 , the devices  10  are arranged at 4-mm intervals on the heat sink  20  with a width of, for example, 35 mm with the submounts  21  in between. At this time, eight devices  10  are mounted on the heat sink  20 . 
     It is to be noted that a plurality of devices  10  mounted on one heat sink  20  have slightly different oscillation wavelengths from one another, and a half-width of a wavelength spectrum of a superimposition of the oscillation wavelengths is adjusted to be about 2 nm or more. Thus, in the laser diode array  1  according to the embodiment, two or more kinds of devices  10  with different emission spectra from one another are arranged on one heat sink  20  to allow the spectra thereof to be superimposed on one another. Accordingly, a wavelength width of the entire laser diode array  1  is increased, and coherency declines. As a result, speckle noise is reduced.  FIG. 5  illustrates a relationship between a spectrum width of the laser diode array  1  and speckle contrast. As can be seen from  FIG. 5 , when the spectrum width is within a range of about 2 nm to about 3 nm both inclusive, a sufficient effect on suppressing speckle contrast is obtainable. 
     The wavelength width of laser light emitted from each of the devices  10  in the laser diode array  1  is about 1 nm. As an example of a combination of the devices  10  in the laser diode array  1 , for example, as described above, in the case where eight devices  10  are mounted on one heat sink  20 , the devices  10  with oscillation wavelengths different by, for example, 0.5 nm from one another are used. When the eight devices  10  with oscillation wavelengths different by 0.5 nm from one another are selected and mounted, the spectrum width of the laser diode array  1  is about 4.5 nm (1 nm+0.5 nm×(8−1)) as a whole. 
     An example of a method of manufacturing the laser diode array  1  according to the embodiment will be described below. First, for example, the substrate  11  made of GaN is prepared, and, for example, semiconductor layers including the active layer  12 D made of an AlGaInP-based material are grown on the front surface of the substrate  11  by, for example, an MOCVD (Metal Organic Chemical Vapor Deposition) method to form the semiconductor laminate structure  12 . Next, a metal layer made of Ti, Pt, Au, or the like is laminated on the semiconductor laminate structure  12  by, for example, an evaporation method to form the p-side electrode  13 . 
     Then, an Au-germanium (Ge) array layer or the like is formed on the back surface of the substrate  11  by, for example, an evaporation method to form the n-side electrode  14 . 
     After that, separation and cleavage is performed to form a pair of resonator facets, and then the resonator facets are subjected to facet coating as appropriate. More specifically, for example, dielectric films made of Al 2 O 3  or the like are deposited on the resonator facets by an evaporation method to adjust reflectivity of the resonator facets. Thus, the laser diode device (the device  10 ) illustrated in  FIG. 3  is completed. 
     Next, each device  10  is disposed on each submount  21  made of AlN on which AuSn solder is evaporated to allow the p-side electrode  13  to be in contact with the submount  21 , and then the device  10  and the submount  21  is heated by, for example, a heater to be integrated (into a laser-on-submount, i.e., LOS). Electrode probes are set up at a p-side (a metalized surface of an upper surface of the submount) and an n-side (the n-side electrode  14  of the device  10 ) of the LOS to pass a current through the device  10 , and an oscillation wavelength at a predetermined current value of the device  10  is measured. Thus, the devices  10  are classified by wavelength. 
     In the case where a sufficient wavelength distribution is not obtained, a crystal is grown on the GaAs substrate again. At this time, the composition of Ga or In in the active layer  12 D is adjusted to vary the oscillation wavelength after fabricating the device  10 . This process is repeatedly performed until a necessary oscillation wavelength width is obtained. The wavelength of the device  10  may be measured before the device  10  is mounted on the submount  21 , but the wavelength of the device  10  may vary by stress at the time of mounting. Therefore, it is desirable to measure the wavelength after the device  10  and the submount  21  are bonded together. 
     Next, the devices  10  (LOSs) with different wavelengths from one another are selected from a plurality of devices  10  classified by wavelength, and are accurately bonded, at 4-mm intervals, onto the heat sink  20  having a metal-plated surface with, for example, SnAg solder. 
     Then, the devices  10  are electrically connected to one another in series through the wires  22  made of, for example, Au. More specifically, as illustrated in  FIG. 2 , the n-side (the n-side electrode  14 ) of the device  10   a  and the p-side (herein, a metal in contact with the p-side electrode  13 ) of the device  10   b  are connected to each other through the wire  22 . Thus, the laser diode array  1  illustrated in  FIG. 1  is completed. 
     As described above, the devices  10  in the laser diode array  1  according to the embodiment are connected to one another in series. When the devices  10  are connected to one another in series in such a manner, even in the case where an operation voltage varies during crystal growth or a manufacturing process, the devices  10  are operable according to an operation current. Moreover, the devices  10  are allowed to be driven at a small current for an entire unit. Further, even in the case where one of the devices  10  in the laser diode array  1  is short-circuited and damaged, not all the devices  10  stop light emission, and the laser diode array  1  is allowed to be driven with use of undamaged devices  10 . 
     It is to be noted that, as illustrated in  FIG. 6A , as connection of the devices  10  located at both ends of the laser diode array  1 , the device  10  located at one of the ends of the laser diode array  1  may be connected to an electrode pin  23 A, and the device  10  located at the other end of the laser diode array  1  may be connected to the heat sink  20  with electrical conductivity. Moreover, as illustrated in  FIG. 6B , the devices  10  located at both ends of the laser diode array  1  may be connected to respective independent electrode pins  23 A and  23 B. The device  10  may be directly connected to the electrode pin  23 A (or  23 B) through the wire  22 ; however, the device  10  may be connected to the electrode pin  23 A (or  23 B) through, for example, a lead wire, a flexible electrode, or the like. 
     Moreover, in the case where the devices  10  in the laser diode array  1  are connected to one another in series as in the embodiment, an issue of a large difference between light outputs from the devices  10  may be caused. In this case, adjustment is possible through varying stripe widths Ws or resonator lengths  1  of the devices  10 . For example, in the case where an AlGaInP-based material is used, light emission efficiency pronouncedly declines at a shorter wavelength than about 640 nm. Therefore, light intensity pronouncedly declines at a wavelength shorter than about 640 nm. In this case, the stripe width Ws of the device  10  of a short wavelength which causes a decline in light emission efficiency is reduced. Moreover, when the device  10  with a shorter resonator length l is used, current density during operation is increased to improve a light output. 
     When a predetermined voltage is applied between the n-side electrode  14  (the n-side) and the p-side electrode  13  (the p-side) in each of the devices  10  configuring the laser diode array  1  according to the embodiment, a current is injected into the active layer  12  to allow the device  10  to emit light by the recombination of electrons and holes. The light is reflected by a pair of resonator facets, and travels back and forth between the pair of resonator facets to cause laser oscillation. Thus, the light exits from the device  10  as a laser beam. 
     In a laser diode array in related art, the above-described various techniques are used to reduce deterioration in characteristics of the device due to speckle noise or thermal interference caused by coherent light interference. However, in any of the techniques, it is difficult to sufficiently reduce speckle noise and deterioration in characteristics of the device, and it is difficult to solve these two issues concurrently. 
     On the other hand, in the embodiment, the plurality of devices  10  are mounted on the heat sink  20  with the respective submounts  21  in between; therefore, heat dissipation efficiency is improved, and thermal interference by the adjacent devices  10  is reduced. Moreover, since a combination of two or more kinds of devices  10  with different oscillation wavelengths from one another is used in the laser diode array  1 , the wavelength width of the entire laser diode array  1  is increased; therefore, coherency of the laser diode array  1  is allowed to be reduced. 
     Thus, in the laser diode array  1  according to the embodiment, a plurality of devices  10  are disposed on the heat sink  20  with the respective independent submounts  21  in between; therefore, heat dissipation efficiency of the devices  10  is improvable. Thus, deterioration in characteristics due to thermal interference of the adjacent devices  10  is suppressed. Moreover, since the devices  10  with different wavelengths from one another are combined together, the width of the oscillation wavelength of the laser diode array  1  is allowed to be increased, and speckle noise is allowed to be reduced. 
     Moreover, when the devices  10  are arranged at equal intervals within a predetermined range, in particular, at intervals of about 2 mm to about 10 mm both inclusive, heat of the devices  10  is allowed to be efficiently dissipated while maintaining light emission intensity of the devices  10  without upsizing an entire light source. Further, when the devices  10  with different oscillation wavelengths from one another are combined together to allow the wavelength width (half-width) of the laser diode array  1  to be about 2 nm, speckle noise is allowed to be efficiently reduced. 
     Next, a modification of the above-described embodiment will be described below. Like components are denoted by like numerals as of the above-described embodiment and will not be further described, and effects common to the above-described embodiment and the modification will not be further described. 
     2. MODIFICATION 
       FIG. 7  illustrates an entire configuration of a laser diode array  2  according to a modification. The laser diode array  2  according to the modification is different from the laser diode array  1  according to the above-described embodiment in that a plurality of devices  10  mounted on the heat sink  20  are connected to one another in parallel. 
     As illustrated in  FIG. 7 , the p-side electrode  13  of each of the devices  10  is bonded onto the upper surface of each of the submounts  21  (to form an LOS), and the device  10  is connected to the heat sink  20 , and the n-side of the LOS is a surface of the n-side electrode  14  (refer to  FIG. 3 ). It is to be noted that the submount  21  is made of a conductive material or an insulating material. In the case where the submount  21  is made of an insulating material, a surface of the submount  21  is coated with a conductive material to allow the p-side electrode  13  of the device  10  and the heat sink  20  to be electrically connected to each other. Alternatively, the p-side electrode  13  of the device  10  and the heat sink  20  may be electrically connected to each other through a wire drawn from the upper surface of the submount  21 . For example, the n-side electrodes  14  of the devices  10  are connected to one another through an electrode plate  25  fixed on the heat sink  20  with an insulating plate  24  in between and the wires  22 . It is to be noted that, as the electrode plate  25 , for example, a copper plate having a gold-plated surface may be used. 
     In the laser diode array  2  according to the modification, even in the case where one of the devices  10  in the laser diode array  2  has an open-circuit failure, not all the devices  10  stop light emission, and undamaged devices  10  are allowed to be driven. Moreover, typically, in the case where a voltage varies during crystal growth or a manufacturing process, an increase in a resistance value at a crystal interface or in a crystal frequently takes place, thereby frequently causing heat generation during operation. When the laser diode array  1  according to the above-described embodiment operates at a constant current, the device  10  with a higher operation voltage causes larger heat generation; therefore, the rate of deterioration may vary between the devices  10  in the laser diode array  1 . On the other hand, in the modification, the devices  10  are so mounted as to be electrically connected to one another in parallel to equalize the voltage values of the devices  10 . Therefore, in addition to the effects in the above-described embodiment, a current flowing through the device  10  with a high rate of deterioration is reduced to suppress variations in longevity between the devices  10 . 
     3. APPLICATION EXAMPLES 
     Application Example 1 
       FIG. 8  illustrates a configuration example of a laser diode unit  100 A using the laser diode arrays  1  and  2  according to the above-described embodiment and the above-described modification. In the laser diode unit  100 A, for example, six laser diode arrays  1  described above are one-dimensionally arranged along a direction orthogonal to a direction where the devices  10  are mounted on the heat sink  20 . As illustrated in  FIG. 9 , a tapped hole  20 A is formed on a side surface, i.e., a surface orthogonal to the surface where the devices  10  are mounted of the heat sink  20 , and the laser diode array  1  is fixed to a base plate  101  by a screw. 
     Application Example 2 
       FIG. 10  illustrates a configuration example of a laser diode unit  100 B using the laser diode arrays  1  and  2  according to the above-described embodiment and the above-described modification. In the laser diode unit  100 B, for example, the above-described laser diode arrays  1  are two-dimensionally arranged along directions the same as and orthogonal to the direction where the devices  10  are mounted on the heat sink  20 . 
     As described above, the laser diode units  100 A and  100 B according to the embodiment are allowed to achieve high power through one-dimensionally or two-dimensionally arranging the above-described laser diode arrays  1  and  2 . Moreover, when the laser diode arrays  1  and  2  with different central wavelengths are combined and arranged, the oscillation wavelengths of the entire laser diode units  100 A and  100 B are allowed to be further increased. More specifically, for example, in the laser diode unit  100 B illustrated in  FIG. 10 , the laser diode arrays  1  may be arranged in decreasing order of central wavelength from an upper-left stage toward the direction where the devices  10  are mounted, and may be arranged in increasing order of central wavelength from the upper-left stage toward a bottom stage. In particular, when the wavelength widths of the entire laser diode units  100 A and  100 B are about 4 nm or more, speckle noise is effectively reduced. 
     Although the present disclosure is described referring to the embodiment and the modification, the disclosure is not limited thereto, and may be variously modified. For example, the material and thickness of each layer, the method and conditions of forming each layer are not limited to those described in the above-described embodiment and the like, and each layer may be made of any other material with any other thickness by any other method under any other conditions. For example, in the above-described embodiment, the case where semiconductor layers including the active layer  12 D are formed by an MOCVD method is described; however, the semiconductor layers may be formed by any other metal organic chemical vapor deposition method such as an MOVPE method, an MBE (Molecular Beam Epitaxy) method, or the like. 
     In addition, for example, in the above-described embodiment and the like, the specific configuration of the laser diode device (the device  10 ) is described; however, it is not necessary for the laser diode device to include all of the layers described in the above-described embodiment and the like, and the laser diode device may further include any other layer. 
     Moreover, the disclosure is applicable to not only the AlGaInP-based device  10  described in the above-described embodiment and the like but also a blue or blue-violet laser diode made of a nitride-based Group III-V compound semiconductor including at least gallium (Ga) from Group III elements and at least nitrogen (N) from Group V elements, a higher-power laser diode, a laser diode with any other oscillation wavelength, and a laser diode made of any other material. 
     It is to be noted that the present technology is allowed to have the following configurations. 
     (1) A laser diode array including: 
     a heat dissipator; 
     a plurality of submounts disposed independently of one another on the heat dissipator; and 
     a plurality of laser diode devices including two or more kinds of laser diode devices with different oscillation wavelengths, the laser diode devices being disposed on the respective submounts, and being electrically connected to one another. 
     (2) The laser diode array according to (1), in which the plurality of laser diode devices are arranged at equal intervals. 
     (3) The laser diode array according to (1) or (2), in which the plurality of laser diode devices are arranged at intervals of about 2 mm to about 10 mm both inclusive. 
     (4) The laser diode array according to any one of (1) to (3), in which a half-width of a superimposition of wavelength spectra of the plurality of laser diode devices is about 2 nm or more. 
     (5) The laser diode array according to any one of (1) to (4), in which the plurality of laser diode devices are electrically connected to one another in series. 
     (6) The laser diode array according to any one of (1) to (4), in which the plurality of laser diode devices are electrically connected to one another in parallel. 
     (7) The laser diode array according to any one of (1) to (6), in which the plurality of laser diode devices are configured of the same material-based devices. 
     (8) The laser diode array according to any one of (1) to (7), in which the laser diode devices are made of an AlGaInP-based material. 
     (9) The laser diode array according to (7), in which the laser diode devices are made of a GaN-based material. 
     (10) The laser diode array according to any one of (1) to (9), in which the plurality of laser diode devices include two or more kinds of laser diode devices with different stripe widths. 
     (11) The laser diode array according to any one of (1) to (10), in which the plurality of laser diode devices each have a pair of resonator facets at two facing side surfaces, and include two or more kinds of laser diode devices with different resonator lengths. 
     (12) The laser diode array according to any one of (1) to (11), further including a base plate for fixing, 
     in which a surface different from a surface where the laser diode devices are mounted of the heat dissipator is fixed on the base plate. 
     (13) The laser diode array according to any one of (1) to (11), further including a base plate for fixing, 
     in which a surface inclined at about 90° from a surface where the laser diode devices are mounted of the heat dissipator is fixed on the base plate. 
     (14) The laser diode array according to any one of (1) to (13), in which the submounts are made of an insulating material. 
     (15) A laser diode unit including a plurality of laser diode arrays, each of the laser diode arrays including: 
     a heat dissipator; 
     a plurality of submounts disposed independently of one another on the heat dissipator; and 
     a plurality of laser diode devices including two or more kinds of laser diode devices with different oscillation wavelengths, the laser diode devices being disposed on the respective submounts, and being electrically connected to one another. 
     (16) The laser diode unit according to (15), in which the plurality of laser diode arrays are disposed along a direction orthogonal to a direction where the plurality of laser diode devices are arranged. 
     (17) The laser diode unit according to (15) or (16), in which the plurality of laser diode arrays are arranged along directions the same as and orthogonal to a direction where the plurality of laser diode devices are arranged. 
     (18) The laser diode unit according to any one of (15) to (17), in which a half-width of a superimposition of wavelength spectra of the plurality of laser diode arrays is about 4 nm or more. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.