Patent Publication Number: US-2023134378-A1

Title: Integrated optical device, integrated optical module, and method for manufacturing integrated optical device

Description:
TECHNICAL FIELD 
     The present invention relates to an integrated optical device, an integrated optical module using the integrated optical device, and a method for manufacturing the integrated optical device. 
     Priority is claimed on Japanese Patent Application No. 2020-007205, filed Jan. 21, 2020 and Japanese Patent Application No. 2020-056032, filed Mar. 26, 2020, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     With the increase in data traffic, the functions of optical communication systems and various optical devices around us that utilize them are becoming more multifunctional. Recently, there has been a demand for high density as well as multifunctionality, and multi-functional and compact optical devices are being studied. 
     In optical communication systems, silicon photonics has been technically examined. This integrates a light-emitting element, a light-receiving element, and the like in a silicon optical waveguide. 
     In addition, compact optical modules are required for devices around us that are multifunctional and portable, such as wearable devices and compact projectors. 
     Conventionally, a mirror and a lens have been used to integrate a plurality of optical elements into one. For example, Patent Literature 1 discloses an optical module in which a laser diode (LD), an optical lens, a total reflection wavelength filter, a wavelength separation filter, a fiber collimator, and a photodiode are integrated in a housing. 
     In such an optical module of Patent Literature 1, light having a wavelength of 1.3 μm emitted from the LD passes through a condenser lens, a capillary, and a collimator lens, passes through the total reflection wavelength filter, is totally reflected by the wavelength separation filter, and is received by the fiber collimator. Light having wavelengths of 1.49 μm and 1.55 μm input from the fiber collimator passes through the wavelength separation filter and is separated by a total reflection/wavelength separation filter. The separated light having a wavelength of 1.55 μm is folded back by the total reflection wavelength filter and is incident on the photodiode by a coupling lens. The separated light having a wavelength of 1.49 μm is incident on the photodiode by the coupling lens. 
     Further, Patent Literature 2 discloses an optical transmission/reception module in which a plurality of light having a predetermined wavelength is incident to a wavelength combiner/demultiplexer having a wavelength selection filter and a mirror mounted on front and back surfaces of a transparent substrate in accordance with the arrangement of the wavelength selection filter and the mirror to combine them with each other by the wavelength combiner/demultiplexer. 
     As a structure different from the integration using the mirror or the lens as in Patent Literatures 1 and 2, for example, Patent Literatures 3 and 4 disclose an optical device having a waveguide structure. In a combiner disclosed in Patent Literature 3, fiber strands with any N thin cladding are fixed to a chip template and emission ends of the plurality of fiber strands are bundled with each other. Patent Literature 4 discloses a hybrid integrated optical module in which a semiconductor chip having a semiconductor waveguide and mounted on a first substrate and a PLC chip are integrated. 
     In the hybrid integrated optical module of Patent Literature 4, an end surface facing the PLC chip in the semiconductor chip and an end surface facing the semiconductor chip in the PLC chip are separated from each other with a gap. Further, the semiconductor chip and the PLC chip are bonded with an ultraviolet-curable adhesive. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] 
     Japanese Unexamined Patent Application No. 2005-309370 
     [Patent Literature 2] 
     Japanese Unexamined Patent Application No. 2009-105106 
     [Patent Literature 3] 
     Japanese Unexamined Patent Application No. 2016-118750 
     [Patent Literature 4] 
     Japanese Unexamined Patent Application No. 2011-102819 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the optical devices disclosed in Patent Literatures 1 and 2 there are a large number of components, the size of each component is large, and the optical device is composed of a free space optical system using a mirror and a lens. Considering the size of each component and the configuration of the free space optical system, there is a limit to the miniaturization of the optical devices disclosed in Patent Literatures 1 and 2. On the other hand, as disclosed in Patent Literatures 3 and 4, the integrated optical device using the waveguide can be easily reduced in size as compared with the free space optical system. 
     However, in a hybrid integrated optical module  1  described in Patent Literature 4, a semiconductor chip  2  is bonded to a PLC chip  3  and a Si bench  5  is bonded to a PLC substrate  6  by an ultraviolet-curable adhesive  8  ( FIG.  1   , paragraph 0025 and the like). Therefore, since the UV-curable adhesive expands and contracts due to temperature changes according to the wire-bonding process of the light source, there is a risk that the alignment accuracy of the components bonded to each other will decrease and the reliability of the integrated optical device will decrease. Further, in order to operate an optical semiconductor device such as LD, it is necessary to conduct electricity and it is necessary to connect the optical semiconductor element to a power supply on a substrate by using a method such as wire-bonding. However, if the strength for fixing the optical semiconductor element to the optical waveguide is not sufficient, the optical semiconductor element may slip off the optical waveguide during wire-bonding. 
     Further, the heat generated by the semiconductor chip  2  and the PLC chip  3  is mainly dissipated through the package on which the chips are mounted. However, since at least one of the semiconductor chip  2  and the PLC chip  3  has a large separation from the package due to the expansion and contraction of the UV-curable adhesive, there is a problem in that stable laser beam output cannot be obtained when emitting a laser beam that has insufficient heat dissipation and has temperature dependence. 
     The present invention has been made in view of such circumstances and an object thereof is to provide an integrated optical device in which temperature dependence in laser emission is suppressed and a bonding strength of components to a package is improved and an integrated optical module using the same. 
     Solution to Problem 
     An integrated optical device according to a first aspect of the present invention includes: a mounting base; an optical semiconductor device which is provided on a surface of the mounting base; a substrate; and an optical waveguide which is provided on a surface of the substrate, wherein an incident surface of the optical waveguide is disposed to face an emission surface of the optical semiconductor device, wherein light emitted from the optical semiconductor device is able to be incident to the optical waveguide, wherein the optical semiconductor device is connected to the mounting base through a metal layer, wherein the mounting base is connected to the substrate through the other metal layer, and wherein a mounting base bottom surface on the side opposite to a surface of the mounting base and a substrate bottom surface on the side opposite to a surface of the substrate are provided on the substantially same plane. 
     In the integrated optical device according to the above-described aspect, an antireflection film may be provided between the optical semiconductor device and the optical waveguide. 
     In the integrated optical device according to the above-described aspect, a plurality of the optical semiconductor devices may be provided, the plurality of optical semiconductor devices may emit light having different wavelengths, the optical waveguide may be provided with a core into which light emitted from the plurality of optical semiconductor devices is able to be incident, and the plurality of cores may be gathered together on the front side reaching the emission surface of the optical waveguide. 
     In the integrated optical device according to the above-described aspect, the mounting base may include first to third outer surfaces, the first outer surface may be a surface of the mounting base, the optical semiconductor device may be mounted on the first outer surface of the mounting base, the optical semiconductor device may be disposed to be optically coupled to the optical waveguide, the second outer surface of the mounting base may be connected to a side surface of the substrate through the metal layer, and at least a part of the third outer surface of the mounting base may include a roughened region. 
     In the integrated optical device according to the above-described aspect, the surface roughness of the roughened region may be larger than the surface roughness of the first and second outer surfaces. 
     In the integrated optical device according to the above-described aspect, the roughened region may have a maximum cross-sectional height (Rt) of 5 μm or more and 50 μm or less or 5 μm or more and 30 μm or less. 
     In the integrated optical device according to the above-described aspect, the mounting base may have a substantially rectangular parallelepiped shape, the second outer surface may be a first side surface of the mounting base, and the third outer surface may include a second side surface which faces the first side surface, third and fourth side surfaces which are respectively adjacent to the first and second side surfaces to face them, and the mounting base bottom surface which faces the upper surface. 
     In the integrated optical device according to the above-described aspect, the roughened region may be provided on the third and fourth side surfaces, and the second side surface and the mounting base bottom surface may be smooth surfaces not provided with the roughened region. 
     In the integrated optical device according to the above-described aspect, the roughened region may be provided in the entire surfaces of the third and fourth side surfaces. 
     In the integrated optical device according to the above-described aspect, the roughened region may be provided in a front region near the first side surface in relation to a middle position between the first side surface and the second side surface. 
     In the integrated optical device according to the above-described aspect, the roughened region may be provided in a lower region near the mounting base bottom surface in relation to a middle position between the upper surface and the mounting base bottom surface. 
     In the integrated optical device according to the above-described aspect, two or more optical semiconductor devices may be provided. 
     In the integrated optical device according to the above-described aspect, the optical semiconductor device may include a first optical semiconductor device which outputs red light, a second optical semiconductor device which outputs green light, and a third optical semiconductor device which outputs blue light. 
     An integrated optical module according to a second aspect of the present invention includes: the above-described integrated optical device; and a package which accommodates the integrated optical device, wherein in the integrated optical device, both the mounting base bottom surface and the substrate bottom surface are fixed to one inner surface of the package through an adhesive layer containing metal or resin. 
     In the integrated optical module according to the above-described aspect, the adhesive layer may be made of a material in which a filler is mixed with a resin. 
     In the integrated optical module according to the above-described aspect, the adhesive layer may have thermal conductivity of 4 W/m·K or more. 
     A method for manufacturing an integrated optical device according to a third aspect of the present invention includes: preparing a mounting base including first to third outer surfaces, having an optical semiconductor device mounted on the first outer surface, having a metal bonding material provided in the second outer surface, and having a roughened region formed in at least a part of the third outer surface; adjusting a position of the optical semiconductor device to be optically coupled to an optical waveguide while heating the metal bonding material together with the mounting base by irradiating the roughened region with a laser beam in a state in which a side surface of a substrate provided with the optical waveguide is in contact with the second outer surface of the mounting base; and fixing the optical semiconductor device by stopping the irradiation of the laser beam to cool the mounting base and metal-bonding the mounting base and the substrate. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to provide an integrated optical device which efficiently dissipates heat generated by the operation of an optical semiconductor device and does not cause operational instability due to a temperature change and an integrated optical module using the same. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a perspective view of an integrated optical device of a first embodiment of the present invention. 
         FIG.  2    is a cross-sectional view of an incident surface of a PLC of the integrated optical device of the first embodiment. 
         FIG.  3    is a plan view of a part of the integrated optical device of the first embodiment. 
         FIG.  4    is a cross-sectional view taken along a line A-A′ of the integrated optical device of the first embodiment. 
         FIG.  5    is a cross-sectional view illustrating an example of a method for manufacturing the integrated optical device of the first embodiment. 
         FIG.  6    is a plan view of an integrated optical module obtained by packaging the integrated optical device of the first embodiment. 
         FIG.  7    is a side view of the integrated optical module. 
         FIG.  8    is a plan view in a state in which a cover of the integrated optical module is excluded. 
         FIG.  9    is a side view of the integrated optical module as viewed from an emitting portion side. 
         FIG.  10    is a perspective view showing a state when the integrated optical module is used. 
         FIG.  11    is a perspective view of an integrated optical device of a second embodiment. 
         FIG.  12    is a cross-sectional view of an incident surface of a PLC of the integrated optical device of the second embodiment. 
         FIG.  13    is a plan view of a part of the integrated optical device of the second embodiment. 
         FIG.  14    is a cross-sectional view taken along a line B-B′ of the integrated optical device of the second embodiment. 
         FIG.  15    is a diagram illustrating the surface roughness of each surface of a subcarrier. 
         FIG.  16    is a cross-sectional view illustrating an example of a method for manufacturing the integrated optical device of the second embodiment. 
         FIG.  17    is a plan view illustrating a method for manufacturing the integrated optical device of the second embodiment. 
         FIG.  18    is a graph showing a relationship between light utilization efficiency and a distance between the incident surface of the PLC and an emission surface of an LD of the integrated optical device of the second embodiment. 
         FIG.  19    is a plan view showing a state in which the LD of the integrated optical device of the second embodiment is wire-bonded. 
         FIG.  20    is a development view showing a modified example of a configuration of the subcarrier. 
         FIG.  21    is a development view showing a modified example of a configuration of the subcarrier. 
         FIG.  22    is a cross-sectional view of an integrated optical device of a third embodiment. 
         FIG.  23    is a schematic perspective view transparently showing an example of a structure of an integrated optical module obtained by packaging the integrated optical device of the third embodiment. 
         FIG.  24    is a heat distribution diagram showing a verification example of the present invention. 
         FIG.  25    is a graph showing a verification example of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. Additionally, the embodiments shown below are specifically described in order to better understand the gist of the invention and do not limit the present invention unless otherwise specified. Further, the drawings used in the following description may be shown by enlarging the main parts for convenience in order to make the features of the present invention easy to understand and the dimensional ratios of each component are not limited to the same as the actual ones. That is, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited thereto. These can be appropriately modified and implemented within the range in which the effects of the present invention are exhibited. 
     First Embodiment 
     (Integrated Optical Device) 
     As shown in  FIG.  1   , an integrated optical device  10  according to this embodiment includes a subcarrier (mounting base)  20 , an optical semiconductor device (LD)  30  which is provided on an upper surface (surface)  21  of the subcarrier  20 , a substrate  40 , and an optical waveguide (PLC)  50  which is provided on an upper surface (surface)  41  of the substrate  40 . 
     The integrated optical device  10  is a combiner that combines light of each of the three primary colors of light, red (R), green (G), and blue (B). The integrated optical device  10  can be applied as, for example, a combiner mounted on a head-mounted display. The optical semiconductor device (LD)  30  which is a light source to be used is not limited to red (R), green (G), and blue (B) and in this embodiment, as the optical semiconductor device (LD)  30  of the three primary colors of light shown as an example, various commercially available laser elements of red light, green light, and blue light can be used. It may be selected as appropriate according to the desired application. For example, light having a peak wavelength of 610 nm or more and 750 nm or less can be used as the red light, light having a peak wavelength of 500 nm or more and 560 nm or less can be used as the green light, and light having a peak wavelength of 435 nm or more and 480 nm or less can be used as the blue light. 
     The integrated optical device  10  includes an LD  30 - 1  which emits red light, an LD  30 - 2  which emits green light, and an LD  30 - 3  which emits blue light. The LDs  30 - 1 ,  30 - 2 , and  30 - 3  are arranged at intervals in a direction substantially orthogonal to the emission direction of the light emitted from each LD and are provided on upper surfaces  21  of the individual subcarriers  20 . The LD  30 - 1  is provided on an upper surface  21 - 1  of a subcarrier  20 - 1 . The LD  30 - 2  is provided on an upper surface  21 - 2  of a subcarrier  20 - 2 . The LD  30 - 3  is provided on an upper surface  21 - 3  of a subcarrier  20 - 3 . Hereinafter, in the reference numeral Z of any component of the integrated optical device  10 , the contents common to the components of the reference numerals Z- 1 , Z- 2 , . . . , Z-K may be collectively referred to as the reference numeral Z. The K is a natural number of 2 or more. 
     Needless to say, light other than red (R), green (G), and blue (B) shown in this embodiment can also be used, and the mounting order of red (R), green (G), and blue (B) described with reference to the drawings does not need to be in this order and can be changed as appropriate. 
     The LD  30  is a bare chip mounted on the subcarrier  20 . The subcarrier  20  is made of, for example, aluminum nitride (AlN), aluminum oxide (Al 2 O 3 ), silicon (Si), or the like. As shown in  FIG.  4   , metal layers  75  and  76  are provided between the subcarrier  20  and the LD  30 . The subcarrier  20  and the LD  30  are connected to each other via the metal layers  75  and  76 . As a method of forming the metal layers  75  and  76 , a known method can be used and is not particularly limited, but a known method such as sputtering, vapor deposition, or coating of a paste-like metal can be used. The metal layers  75  and  76  may contain one or more metals selected from the group composed of, for example, gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti), tantalum (Ta), tungsten (W), an alloy of gold (Au) and tin (Sn), tin (Sn)-silver (Ag)-copper (Cu)-based solder alloys (SAC), SnCu, InBi, SnPdAg, SnBiln, and PbBiln and may be made of one or more metals selected from the group. 
     The substrate  40  is made of silicon (Si). The PLC  50  is manufactured to be integrated with the substrate  40  on the upper surface  41  by a semiconductor process including known photolithography and dry etching used when forming a fine structure such as an integrated circuit. As shown in  FIGS.  1  and  2   , the PLC  50  is provided with as many cores  51 - 1 ,  51 - 2 , and  51 - 3  as the LDs  30 - 1 ,  30 - 2 , and  30 - 3  constituting the optical waveguide and a clad  52  surrounding the cores  51 - 1 ,  51 - 2 , and  51 - 3 . The thickness of the clad  52  and the widthwise dimensions of the cores  51 - 1 ,  51 - 2 , and  51 - 3  are not particularly limited. For example, the cores  51 - 1 ,  51 - 2 ,  51 - 3  having widthwise dimensions of about several microns are arranged in the clad  52  having a thickness of about 50 μm. 
     The cores  51 - 1 ,  51 - 2 , and  51 - 3  and the clad  52  are made of, for example, quartz. The refractive index of the cores  51 - 1 ,  51 - 2 , and  51 - 3  is higher than the refractive index of the clad  52  by a predetermined value. Accordingly, the light incident on each of the cores  51 - 1 ,  51 - 2 , and  51 - 3  propagates through each core while being totally reflected at the interface between each core and the clad  52 . The cores  51 - 1 ,  51 - 2 , and  51 - 3  are doped with impurities such as germanium (Ge) in an amount corresponding to the above-described predetermined values. 
     Hereinafter, the emission direction of the light emitted from the LD  30  is the y direction. The direction which is orthogonal to the y direction in the plan including the y direction and in which the LDs  30 - 1 ,  30 - 2 , and  30 - 3  are arranged at intervals is the x direction. The direction orthogonal to the x direction and the y direction and directed from the subcarrier  20  to the LD  30  is the z direction. In an incident surface  61  of the PLC  50 , the cores  51 - 1 ,  51 - 2 , and  51 - 3  are arranged to match the optical axis of the light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  in the x direction and the z direction. 
     As shown in  FIGS.  1  and  4   , the cores  51 - 1 ,  51 - 2 , and  51 - 3  are gathered together on the front side reaching the emission surface  64  of the PLC  50 . That is, the cores  51 - 1 ,  51 - 2 , and  51 - 3  approach each other sequentially toward the front side in the y direction and merge with one core  51 - 4 . It is preferable that each of the cores  51 - 1 ,  51 - 2 , and  51 - 3  be connected to the core  51 - 4  at a curvature radius equal to or larger than a predetermined curvature radius so that light does not leak from the cores  51 - 1 ,  51 - 2 , and  51 - 3 . 
     As shown in  FIG.  3   , the incident surface  61  of the PLC  50  is disposed to face the emission surface  31  of the LD  30 . Specifically, the emission surface  31 - 1  of the LD  30 - 1  faces the incident surface  61 - 1  of the core  51 - 1 . In the x direction and the z direction, the optical axis of the red light emitted from the LD  30 - 1  substantially overlaps with the center of the incident surface  61 - 1 . Similarly, the emission surface  31 - 2  of the LD  30 - 2  faces the incident surface  61 - 2  of the core  51 - 2 . In the x direction and the z direction, the optical axis of the green light emitted from the LD  30 - 2  substantially overlaps with the center of the incident surface  61 - 2 . The emission surface  31 - 3  of the LD  30 - 3  faces the incident surface  61 - 3  of the core  51 - 3 . In the x direction and the z direction, the optical axis of the blue light emitted from the LD  30 - 3  substantially overlaps with the center of the incident surface  61 - 3 . With such a configuration and arrangement, at least a part of the red light, the green light, and the blue light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  can be incident to the cores  51 - 1 ,  51 - 2 , and  51 - 3 . 
     As shown in  FIG.  1   , the red light, the green light, and the blue light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  are respectively incident to the cores  51 - 1 ,  51 - 2 , and  51 - 3  and propagate through the cores. The cores  51 - 1  and  51 - 2  and the red light and the green light propagated through these cores merge at a predetermined merging position  57 - 1  (see  FIG.  3   ) behind a merging position  57 - 2  in the y direction. The core  51 - 7  (see  FIG.  3   ) at which the cores  51 - 1  and  51 - 2  merge with each other, the core  51 - 3 , and the red light, the green light and the blue light propagating through these cores meet at a merging position  57 - 2 . The red light, the green light, and the blue light collected at the merging position  57 - 2  propagated through the core  51 - 4  and reaches the emission surface  64 . The three-color light emitted from the emission surface  64  is used, for example, as signal light or the like depending on the purpose of use of the integrated optical device  10 . 
     As shown in  FIG.  4   , the subcarrier  20  is connected to the substrate  40  through a first metal layer  71 , a second metal layer  72 , and a third metal layer  73 . In this embodiment, a side surface (first side surface)  22  ( 22 - 1 ,  22 - 2 ,  22 - 3 ) facing the substrate  40  in the subcarrier  20  and a side surface (second side surface)  42  facing the subcarrier  20  in the substrate  40  are connected to each other through the first metal layer  71 , the second metal layer  72 , the third metal layer  73 , and an antireflection film  81 . The melting point of the metal layer  75  is higher than the melting point of the third metal layer  73 . 
     The first metal layer  71  is provided while being in contact with a side surface  22  by sputtering, vapor deposition, or the like, may contain one or more metals selected from the group composed of, for example, gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti), and tantalum (Ta), and may be made of one or more metals selected from the group. Preferably, the first metal layer  71  contains at least one metal selected from the group composed of gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), and nickel (Ni). The second metal layer  72  is provided while being in contact with a side surface  42  by sputtering, vapor deposition, or the like, may contain one or more metals selected from the group composed of, for example, titanium (Ti), tantalum (Ta), and tungsten (W), and may be made of one or more metals selected from the group. Preferably, tantalum (Ta) is used for the second metal layer  72 . The third metal layer  73  is interposed between the first metal layer  71  and the second metal layer  72 , may contain one or more metals selected from the group composed of, for example, aluminum (Al), copper (Cu), AuSn, SnCu, InBi, SnAgCu, SnPdAg, SnBiln, and PbBiln, and may be made of one or more metals selected from the group. Preferably, AuSn, SnAgCu, and SnBiln are used for the third metal layer  73 . 
     The thickness of the first metal layer  71 , that is, the size of the first metal layer  71  in the y direction is, for example, 0.01 μm or more and 5.00 μm or less. The thickness of the second metal layer  72 , that is, the size of the second metal layer  72  in the y direction is, for example, 0.01 μm or more and 1.00 μm or less. The thickness of the third metal layer  73 , that is, the size thereof in the y direction is, for example 0.01 μm or more and 5.00 μm or less. Further, it is preferable that the thickness of the third metal layer  73  be larger than the thickness of each of the first metal layer  71  and the second metal layer  72 . In such a configuration, each of the above-described roles of the first metal layer  71 , the second metal layer  72 , the third metal layer  73  is well expressed and the entry of the material of the first metal layer  71  into the substrate  40  and the decrease in the adhesive strength between the metal layers are suppressed. The thicknesses of the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  are measured, for example, by spectroscopic ellipsometry. 
     In this embodiment, the first metal layer  71  is provided on the side surface facing the PLC  50  or the substrate  40  in the substantially entire area of the side surface  22  while not being in contact with the metal layer  75 . The front ends, that is, the upper ends of the second metal layer  72  and the third metal layer  73  in the z direction reach, for example, the same position as the upper end of the first metal layer  71  on the front side of the z direction. The rear ends, that is, the lower ends of the second metal layer  72  and the third metal layer  73  in the z direction reach, for example, the same positions as the lower ends of the subcarrier  20 , the first metal layer  71 , and the substrate  40 . When viewed from the y direction, the first metal layer  71  is formed to be larger than the subcarrier  20  in the x direction. 
     As in the above-described configuration, it is preferable that the area of the first metal layer  71 , that is, the size thereof in the plane including the x direction and the z direction be substantially the same as the area of the second metal layer  72  and the third metal layer  73  and the lower end thereof reach the same position as the lower end of the subcarrier  20 . In such a configuration, the connection strength of the subcarrier  20  to the substrate  40  is secured to the maximum. That is, it is possible to suppress the connection between the subcarrier  20  and the substrate  40  from being disconnected, for example, even when each of the LD  30  and the subcarrier  20  is connected to an internal electrode pad  202  corresponding to each LD  30  in a plurality of internal electrode pads  202  by wire-bonding using a wire  95  as described below. Further, since the lower ends of the subcarrier  20 , the first metal layer  71 , the second metal layer  72 , the third metal layer  73 , and the substrate  40  reach the same position, the heat dissipation path from the subcarrier  20  can be increased. In addition, the area of the first metal layer  71  may be smaller than the area of the second metal layer  72  and the third metal layer  73 . 
     In the integrated optical device  10  according to this embodiment, the antireflection film  81  is provided between the LD  30  and the PLC  50 . For example, the antireflection film  81  is integrally formed with the side surface  42  of the substrate  40  and the incident surface  61  of the PLC  50 . However, the antireflection film  81  may be formed only on the incident surface  61  of the PLC  50 . 
     In the integrated optical device  10 , the antireflection film  82  is also formed on the emission surface  64  in addition to the incident surface  61 . Additionally,  FIG.  1    shows a schematic configuration of the integrated optical device  10  and the first metal layer  71 , the second metal layer  72 , the third metal layer  73 , and the antireflection films  81  and  82  are omitted. 
     The antireflection films  81  and  82  are films for preventing the light incident to or emitted from the PLC  50  from being reflected from the incident surface  61  or the emission surface  64  in the direction opposite to the direction in which the light is incident to each surface and increasing the transmittance of the incident light or emitted light. The antireflection films  81  and  82  are multilayer films formed by alternately laminating, for example, a plurality of types of dielectrics corresponding to the wavelengths of the red light, the green light, and the blue light which are the incident light in a predetermined thickness. Examples of the above-described dielectric include titanium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), and the like. 
     The emission surface  31  of the LD  30  and the incident surface  61  of the PLC  50  are arranged at a predetermined interval. The incident surface  61  faces the emission surface  31  and a gap  70  is formed between the emission surface  31  and the incident surface  61  in the y direction. Since the integrated optical device  10  is exposed to air, the gap  70  is full of air. Considering the point that the integrated optical device  10  is used for the head-mounted display and the amount of light required for the head-mounted display, the size of the gap (distance)  70  in the y direction is, for example, larger than 0 μm and 5 μm or less. 
     As shown in  FIG.  4   , in the integrated optical device  10  of this embodiment, a bottom surface (mounting base bottom surface)  23  facing the upper surface (surface)  21  of the subcarrier (mounting base)  20  and a bottom surface (substrate bottom surface)  43  facing the upper surface (surface)  41  of the substrate  40  are provided to be located on the substantially same plane S. In the integrated optical device  10  of this embodiment, since the subcarrier (mounting base)  20  and the substrate  40  are connected through the metal layer, the occurrence of positional deviation due to the heating process is remarkably suppressed compared with the hybrid integrated optical module of Patent Document 4 having a structure connected by an adhesive. 
     Additionally, the substantially same plane S described herein allows a slight deviation between the bottom surface (mounting base bottom surface)  23  and the bottom surface (substrate bottom surface)  43 . Specifically, the deviation in the range of 20 μm or less with respect to the thickness of the substrate  40  in the z direction is allowed. However, since it is preferable that the deviation become smaller, the deviation is more preferably 10 μm or less and further preferably 5 μm or less. 
     In this embodiment, when a bottom surface  23  of the subcarrier  20  and a bottom surface  43  of the substrate  40  are formed on the substantially same plane S, both the subcarrier  20  and the substrate  40  can be bonded, for example, on one plane of a package or heat sink. Accordingly, compared with the conventional integrated optical device in which the bottom surface of the subcarrier and the bottom surface of the substrate are not on the substantially same plane and any one bottom surface is bonded, the integrated optical device  10  of this embodiment can efficiently dissipate the heat generated by the operation of the optical semiconductor device (LD)  30  to both the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40 . 
     Further, since the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  are provided on the substantially same plane S in this embodiment, both the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  can be bonded to one plane of the substrate or the like when the integrated optical device  10  is bonded to one plane of another substrate or the like. Accordingly, it is possible to maintain a high bonding strength and to realize the integrated optical device  10  having excellent impact resistance. 
     For example, when the bottom surface of the subcarrier is located in the +z direction in relation to the bottom surface of the substrate, that is, the bottom surface of the subcarrier is disposed to be separated upward from a base  180  (see  FIG.  7   ) of a package  110  in relation to the bottom surface of the substrate, the subcarrier may slip off when wire-bonding described later is performed in a state in which the size of the first side surface of the subcarrier is small, heat dissipation cannot be performed efficiently, and the bonding strength with the substrate is not sufficient. However, in the integrated optical device  10  according to this embodiment, since it is possible to sufficiently perform the heat dissipation from the bottom surface  23  and the side surface  22  or the bonding with the substrate  40  by sufficiently ensuring the size of the side surface  22 , it is possible to improve heat dissipation or impact resistance. Since the impact resistance is improved, for example, the LD  30  is maintained at an optimal position with respect to the PLC  50 . Thus, it is possible to improve the reliability of the integrated optical device  10  by exhibiting desired light utilization efficiency and optical characteristics in the integrated optical device  10 . 
     Next, a method for manufacturing the integrated optical device  10  will be simply described.  FIG.  5    is a diagram illustrating a method for manufacturing the integrated optical device  10 . First, the LD  30  of the bare chip is mounted on the upper surface  21  of the subcarrier  20  by a known method. For example, the metal layer  75  is formed on the upper surface  21  of the subcarrier  20  by sputtering, vapor deposition, or the like. Further, the metal layer  76  is formed on a lower surface  33  of the LD  30  (for example, a lower surface  33 - 1  of the LD  30 - 1 ) by sputtering, vapor deposition, or the like. Next, as shown in  FIG.  5 ( a ) , for example, the subcarrier  20  is irradiated with a laser beam from a laser  90  so that only the subcarrier  20  is heated to a degree that melting or deforming does not occur. Heat transfer from the subcarrier  20  softens or melts the metal layers  75  and  76  and then cools them. Accordingly, the LD  30  is bonded to the upper surface  21  of the subcarrier  20  through the metal layers  75  and  76 . Further, the first metal layer  71  is formed on the side surface  22  of the subcarrier  20  by sputtering, vapor deposition, or the like before or after the LD  30  is mounted on the subcarrier  20 . 
     Next, the PLC  50  is formed on the upper surface  41  of the substrate  40  by a known semiconductor process. Next, the antireflection films  81  and  82  and the antireflection film (not shown) are formed on the incident surface  61  and the emission surface  64 . Further, the second metal layer  72  and the third metal layer  73  are formed in this order behind the antireflection film  81  in the y direction by sputtering, vapor deposition, or the like. 
     Next, the emission surface  31  and the incident surface  61  in the LDs  30  and the cores  51 - 1 ,  51 - 2 , and  51 - 3  corresponding to each other in the x direction and the z direction are allowed to face each other in the y direction with a distance therebetween. The optical axis of each color light emitted from the LD  30  and the center of the incident surface  61  of the corresponding core are substantially overlapped with each other. At this time, the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  are arranged so that the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  are substantially on the same plane. 
     Next, as shown in  FIG.  5 ( b ) , the subcarrier  20  is irradiated with a laser beam from the laser  90  to soften or melt the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  due to the heat transfer from the subcarrier  20 . The relative positions of the LD  30  and the PLC  50  are adjusted and the subcarrier  20  having the LD  30  mounted thereon is bonded to the substrate  40  provided with the PLC  50  so that the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  are substantially on the same plane. By these steps, it is possible to manufacture the integrated optical device  10  in which the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  are located on the substantially same plane. 
     (Integrated Optical Module) 
     Next, an integrated optical module including the integrated optical device of this embodiment will be described. 
     An integrated optical module  100  of this embodiment may be accommodated in, for example, the package  110  as shown in  FIGS.  6  and  7   . The integrated optical module  100  includes the integrated optical device  10  and the package  110 . The package  110  includes a main body  102  having a cavity structure and a cover  105  covering the main body  102 . 
     The main body  102  includes a box-shaped accommodating portion  107  which accommodates the integrated optical device  10  and an electrode portion  108  which is adjacent to the accommodating portion  107 . The main body  102  is made of, for example, ceramic or the like. An opening is formed on the upper surface of the accommodating portion  107 . A metal film  112  such as Kovar is formed on the upper surface of the accommodating portion  107  at the periphery of the opening when viewed from above. The cover  105  completely covers the opening formed on the upper surface of the accommodating portion  107  via the metal film  112 . When the accommodating portion  107  is hermetically sealed with the cover  105 , an inert gas such as nitrogen (N 2 ) is enclosed in the internal space of the accommodating portion  107 . That is, the accommodating portion  107  is hermetically sealed by the cover  105 . The internal space of the accommodating portion  107  is filled with an inert gas. Accordingly, the gap  70  (see  FIG.  4   ) is filled with an inert gas. 
     The electrode portion  108  is disposed on the front side of the accommodating portion  107  in the y direction, that is, on the rear side in the y direction. The upper surface of the electrode portion  108  is located below the upper surface of the accommodating portion  107 . The bottom surface of the electrode portion  108  is located at the substantially same height as the bottom surface of the accommodating portion  107 . A plurality of external electrode pads  210  are provided on the electrode portion  108  at intervals in the x direction. 
     As shown in  FIGS.  7  and  8   , the base  180  for installing the integrated optical device  10  is provided at a predetermined position of a bottom wall portion  131  of the accommodating portion  107 . The integrated optical device  10  is provided on the base  180 . That is, the integrated optical device  10  is disposed in the internal space of the accommodating portion  107 . In the integrated optical device  10 , since the bottom surface (mounting base bottom surface)  23  of the subcarrier (mounting base)  20  and the bottom surface (substrate bottom surface)  43  of the substrate  40  are formed to be located on the substantially same plane S, both the subcarrier  20  and the substrate  40  of the integrated optical device  10  are bonded to an upper surface  180   a  (one inner surface) of the base  180 . 
     The bottom surface (mounting base bottom surface)  23  of the subcarrier (mounting base)  20  and the bottom surface (substrate bottom surface)  43  of the substrate  40  may be bonded through an adhesive layer  182  with respect to the upper surface  180   a  (one inner surface) of the base  180 . The adhesive layer  182  is made of a material in which a filler is mixed with a resin in order to enhance thermal conductivity. Examples of the resin constituting the adhesive layer  182  include an epoxy resin. Further, as the filler for improving the thermal conductivity of the resin, copper powder, aluminum powder, alumina powder or the like can be used. 
     Additionally, in order to maintain a certain level of thermal conductivity or more of the adhesive layer  182 , the thermal conductivity is preferably 0.5 W/m·K or more, more preferably 1 W/m·K or more, and particularly preferably 4 W/m·K or more. 
     In this way, since both the substrate  40  and the subcarrier (mounting base)  20  of the integrated optical device  10  are bonded to the upper surface  180   a  of the base  180  of the package  110 , heat generated by the operation of the LD  30  can be efficiently dissipated from both the bottom surface (mounting base bottom surface)  23  of the subcarrier (mounting base)  20  and the bottom surface (substrate bottom surface)  43  of the substrate  40  toward the base  180 . Further, since both the bottom surface (mounting base bottom surface)  23  of the subcarrier (mounting base)  20  and the bottom surface (substrate bottom surface)  43  of the substrate  40  are bonded by an adhesive layer made of a resin mixed with a filler, heat can be efficiently propagated from both the bottom surface (mounting base bottom surface)  23  of the subcarrier (mounting base)  20  and the bottom surface (substrate bottom surface)  43  of the substrate  40  toward the base  180 . 
     The plurality of internal electrode pads  202  are provided at intervals in the x direction in the bottom wall portion  131  between the external electrode pad  210  and the base  180  below the subcarrier  20  in the y direction. 
     Each of the LD  30  and the subcarrier  20  is connected to the internal electrode pad  202  corresponding to each LD  30  in the plurality of internal electrode pads  202  by a method such as wire-bonding using the wire  95 . For example, each of the LD  30 - 1  and the subcarrier  20 - 1  is individually connected to each of two internal electrode pads  202 - 1  by a wire  95 - 1 . Each of the LD  30 - 2  and the subcarrier  20 - 2  is individually connected to each of two internal electrode pads  202 - 2  by a wire  95 - 2 . Each of the LD  30 - 3  and the subcarrier  20 - 3  is individually connected to each of two internal electrode pads  202 - 3  by a wire  95 - 3 . 
     The internal electrode pads  202 - 1 ,  202 - 2 , and  202 - 3  are each connected to different external electrode pads  210 . As described above, the external electrode pad  210  electrically connected to each of the internal electrode pads  202 - 1 ,  202 - 2 , and  202 - 3  is electrically connected to a power supply (not shown) or the like. That is, in the integrated optical device  10 , the LD  30  and the power supply (not shown) are connected by the wire  95 , the internal electrode pads  202 - 1 ,  202 - 2 , and  202 - 3 , and the external electrode pad  210 . When electric power is supplied from the power supply (not shown) to the external electrode pad  210  corresponding to each of the internal electrode pads  202 - 1 ,  202 - 2 , and  202 - 3 , the red light, the green light, and the blue light are emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3 . 
     In a side wall portion  132  of the accommodating portion  107 , the side wall portion  132  facing the emission surface  31  of the PLC  50  of the integrated optical device  10  is provided with an opening  133 . The opening  133  is formed substantially around a position intersecting the optical axis of the three-color light emitted from the core  51 - 4  of the PLC  50  on the side wall portion  132 . The opening  133  is formed to be larger than the size on the surface of the side wall portion  132  of the three-color light emitted from the core  51 - 4  and spread in the internal space of the accommodating portion  107 . As shown in  FIGS.  12  and  13   , the opening  133  is covered by a glass plate  220  from the outside of the side wall portion  132  without any gap. That is, the accommodating portion  107  is hermetically sealed by the glass plate  220  in addition to the cover  105 . Antireflection films (not shown) are provided on both surfaces of the glass plate  220 . 
     The opening  133  is a window through which the three-color light emitted from the core  51 - 4  of the PLC  50  passes and propagates to the outside of the package  110 . As shown in  FIG.  14   , the three-color light LL emitted from the core  51 - 4  of the PLC  50  passes through the opening  133  and the glass plate  220  while diffusing around the y direction and travels in the y direction of the package  110  to the inside, that is, to the front side in the y direction. For example, a collimating device  300  including a collimating lens  310  can be disposed on the inside of a side wall portion  132 - 1  of the package  110  in the y direction. The three-color light LL emitted from the core  51 - 4  is collimated to become parallel light by aligning the distance between the emission surface  31  and the collimating lens  310  in the y direction with the focal length of the collimating lens  310  and aligning the center of the collimating lens  310  on the optical axis of the three-color light LL. 
     Second Embodiment 
     (Integrated Optical Device) 
       FIGS.  11  to  14    are diagrams illustrating an integrated optical device  10 A according to a second embodiment.  FIG.  11    is a perspective view of the integrated optical device  10 A.  FIG.  12    is a cross-sectional view of the incident surface  61  of the PLC  50  of the integrated optical device  10 A shown in  FIG.  11   .  FIG.  13    is a plan view of a part of the integrated optical device  10 A shown in  FIG.  11   .  FIG.  14    is a cross-sectional view taken along a line B-B′ of the integrated optical device  10 A shown in  FIG.  11   .  FIG.  15    is a diagram illustrating the surface roughness of each surface of the subcarrier  20 . In the integrated optical device  10 A according to the second embodiment, a configuration of a subcarrier  420  is different from that of the subcarrier  20  of the integrated optical device  10  according to the first embodiment. In the integrated optical device  10 A, the same configurations as those of the integrated optical device  10  are designated by the same reference numerals, and the description thereof may be omitted. 
     As shown in  FIG.  11   , the integrated optical device  10 A according to this embodiment includes the subcarrier (mounting base)  420 , the optical semiconductor device (LD)  30  provided on an upper surface  421  of the subcarrier  420 , the substrate  40 , and the optical waveguide device (PLC)  50  provided on the upper surface  41  of the substrate  40 . 
     The integrated optical device  10 A is a combiner that combines light of each of the three primary colors of light, red (R), green (G), and blue (B). Therefore, the integrated optical device  10 A includes the LD  30 - 1  that emits red light, the LD  30 - 2  that emits green light, and the LD  30 - 3  that emits blue light. Such an integrated optical device  10 A can be applied as a combiner mounted on, for example, a head-mounted display or smart glasses. In this embodiment, the red light means light having a peak wavelength of 690 nm or more and 710 nm or less. The green light means light having a peak wavelength of 535 nm or more and 555 nm or less. The blue light means light having a peak wavelength of 425 nm or more and 445 nm or less. 
     The LDs  30 - 1 ,  30 - 2 , and  30 - 3  are arranged at intervals in a direction substantially orthogonal to the emission direction of the light emitted from each LD and are provided on the upper surface  421  of the individual subcarrier  420 . The LD  30 - 1  is provided on an upper surface  421 - 1  of a subcarrier  420 - 1 . The LD  30 - 2  is provided on an upper surface  421 - 2  of a subcarrier  420 - 2 . The LD  30 - 3  is provided on an upper surface  421 - 3  of a subcarrier  420 - 3 . Hereinafter, in the reference numeral Z of any component of the integrated optical device  10 A, the contents common to the components of the reference numerals Z- 1 , Z- 2 , . . . , Z-K may be collectively referred to as the reference numeral Z. K is a natural number of 2 or more. 
     The LD  30  is a bare chip mounted on the subcarrier  420 . The subcarrier  420  is made of, for example, aluminum nitride (AlN), aluminum oxide (Al 2 O 3 ), silicon (Si), or the like. As shown in  FIG.  14   , the metal layers  75  and  76  are provided between the subcarrier  420  and the LD  30 . The subcarrier  420  and the LD  30  are connected to each other through the metal layers  75  and  76 . 
     As a method of forming the metal layers  75  and  76 , a known method can be used and is not particularly limited, but a known method such as sputtering, vapor deposition, or coating of a paste-like metal can be used. The metal layers  75  and  76  contain one or more metals selected from the group composed of, for example, gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti), tantalum (Ta), tungsten (W), an alloy of gold (Au) and tin (Sn), tin (Sn)-silver (Ag)-copper (Cu)-based solder alloys (SAC), SnCu, InBi, SnPdAg, SnBiln, and PbBiln. 
     The substrate  40  is made of silicon (Si). The PLC  50  is manufactured to be integrated with the substrate  40  on the upper surface  41  by a semiconductor process including known photolithography and dry etching used when forming a fine structure such as an integrated circuit. As shown in  FIGS.  11  and  12   , the PLC  50  is provided with as many cores  51 - 1 ,  51 - 2 , and  51 - 3  as the LDs  30 - 1 ,  30 - 2 , and  30 - 3  constituting the optical waveguide and a clad  52  surrounding the cores  51 - 1 ,  51 - 2 , and  51 - 3 . The thickness of the clad  52  and the widthwise dimensions of the cores  51 - 1 ,  51 - 2 , and  51 - 3  are not particularly limited. For example, the cores  51 - 1 ,  51 - 2 ,  51 - 3  having widthwise dimensions of about several microns are arranged in the clad  52  having a thickness of about 50 μm. 
     The cores  51 - 1 ,  51 - 2 , and  51 - 3  and the clad  52  are made of, for example, quartz. The refractive index of the cores  51 - 1 ,  51 - 2 , and  51 - 3  is higher than the refractive index of the clad  52  by a predetermined value. Accordingly, the light incident on each of the cores  51 - 1 ,  51 - 2 , and  51 - 3  propagates through each core while being totally reflected at the interface between each core and the clad  52 . The cores  51 - 1 ,  51 - 2 , and  51 - 3  are doped with impurities such as germanium (Ge) in an amount corresponding to the above-described predetermined values. 
     Hereinafter, the emission direction of the light emitted from the LD  30  is the y direction. The direction which is orthogonal to the y direction in the plan including the y direction and in which the LDs  30 - 1 ,  30 - 2 , and  30 - 3  are arranged at intervals is the x direction. The direction orthogonal to the x direction and the y direction and directed from the subcarrier  420  to the LD  30  is the z direction. In an incident surface  61  of the PLC  50 , the cores  51 - 1 ,  51 - 2 , and  51 - 3  are arranged to match the optical axis of the light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  in the x direction and the z direction. 
     As shown in  FIGS.  11  and  13   , the cores  51 - 1 ,  51 - 2 , and  51 - 3  are gathered together on the front side reaching the emission surface  64  of the PLC  50 . That is, the cores  51 - 1 ,  51 - 2 , and  51 - 3  approach each other sequentially toward the front side in the y direction and merge with one core  51 - 4 . It is preferable that each of the cores  51 - 1 ,  51 - 2 , and  51 - 3  be connected to the core  51 - 4  at a curvature radius equal to or larger than a predetermined curvature radius so that light does not leak from the cores  51 - 1 ,  51 - 2 , and  51 - 3 . 
     As shown in  FIG.  13   , the incident surface  61  of the PLC  50  is disposed to face the emission surface  31  of the LD  30 . Specifically, the emission surface  31 - 1  of the LD  30 - 1  faces the incident surface  61 - 1  of the core  51 - 1 . In the x direction and the z direction, the optical axis of the red light emitted from the LD  30 - 1  substantially overlaps with the center of the incident surface  61 - 1 . The emission surface  31 - 2  of the LD  30 - 2  faces the incident surface  61 - 2  of the core  51 - 2 . In the x direction and the z direction, the optical axis of the green light emitted from the LD  30 - 2  substantially overlaps with the center of the incident surface  61 - 2 . The emission surface  31 - 3  of the LD  30 - 3  faces the incident surface  61 - 3  of the core  51 - 3 . In the x direction and the z direction, the optical axis of the blue light emitted from the LD  30 - 3  substantially overlaps with the center of the incident surface  61 - 3 . With such a configuration and arrangement, at least a part of the red light, the green light, and the blue light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  can be incident to the cores  51 - 1 ,  51 - 2 , and  51 - 3 . 
     As shown in  FIG.  11   , the red light, the green light, and the blue light emitted from the LDs  30 - 1 ,  30 - 2 , and  30 - 3  are respectively incident to the cores  51 - 1 ,  51 - 2 , and  51 - 3  and propagate through the cores. The cores  51 - 1  and  51 - 2  and the red light and the green light propagated through these cores merge at a predetermined merging position  57 - 1  (see  FIG.  13   ) behind a merging position  57 - 2  in the y direction. The core  51 - 7  (see  FIG.  13   ) at which the cores  51 - 1  and  51 - 2  merge with each other, the core  51 - 3 , and the red light, the green light and the blue light propagating through these core meet at a merging position  57 - 2 . The red light, the green light, and the blue light collected at the merging position  57 - 2  propagate through the core  51 - 4  and reach the emission surface  64 . The three-color light emitted from the emission surface  64  is used, for example, as signal light or the like depending on the purpose of use of the integrated optical device  10 A. 
     As shown in  FIG.  14   , the subcarrier  420  is connected to the substrate  40  through the first metal layer  71 , the second metal layer  72 , and the third metal layer  73 . In this embodiment, a side surface (first side surface)  422  ( 422 - 1 ,  422 - 1 ,  422 - 3 ) of the subcarrier  420  facing the substrate  40  is connected to the side surface  42  of the substrate  40  through the first metal layer  71 , the second metal layer  72 , the third metal layer  73 , and the antireflection film  81 . The melting point of the metal layer  75  is higher than the melting point of the third metal layer  73 . 
     The first metal layer  71  is provided while being in contact with a first side surface  422  by sputtering, vapor deposition, or the like and is made of one or more metals selected from the group composed of, for example, gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), nickel (Ni), titanium (Ti), and tantalum (Ta). Preferably, gold (Au), platinum (Pt), silver (Ag), lead (Pb), indium (In), and nickel (Ni) are used for the first metal layer  71 . The second metal layer  72  is provided while being in contact with a side surface  42  by sputtering, vapor deposition, or the like and is made of one or more metals selected from the group composed of, for example, titanium (Ti), tantalum (Ta), and tungsten (W). Preferably, tantalum (Ta) is used for the second metal layer  72 . The third metal layer  73  is interposed between the first metal layer  71  and the second metal layer  72  and is made of one or more metals selected from the group composed of, for example, aluminum (Al), copper (Cu), AuSn, SnCu, InBi, SnAgCu, SnPdAg, SnBiln, and PbBiIn. Preferably, AuSn, SnAgCu, and SnBiIn are used for the third metal layer  73 . 
     The thickness of the first metal layer  71 , that is, the size of the first metal layer  71  in the y direction is, for example, 0.01 μm or more and 5.00 μm or less. The thickness of the second metal layer  72 , that is, the size of the second metal layer  72  in the y direction is, for example, 0.01 μm or more and 1.00 μm or less. The thickness of the third metal layer  73 , that is, the size thereof in the y direction is, for example 0.01 μm or more and 5.00 μm or less. Further, it is preferable that the thickness of the third metal layer  73  be larger than the thickness of each of the first metal layer  71  and the second metal layer  72 . In such a configuration, each of the above-described roles of the first metal layer  71 , the second metal layer  72 , the third metal layer  73  is well expressed and the entry of the material of the first metal layer  71  into the substrate  40  and the decrease in the adhesive strength between the metal layers are suppressed. 
     In this embodiment, the first metal layer  71  is provided on the side surface facing the PLC  50  or the substrate  40  in the substantially entire area of the first side surface  422  while not being in contact with the metal layer  75 . The front ends, that is, the upper ends of the second metal layer  72  and the third metal layer  73  in the z direction reach the same position as the upper end of the first metal layer  71  on the front side in the z direction. The rear ends, that is, the lower ends of the second metal layer  72  and the third metal layer  73  in the z direction reach the same positions as the lower ends of the metal layer  71 , the subcarrier  420 , and the substrate  40 . When viewed from the y direction, the first metal layer  71  is formed to be larger than the subcarrier  420  in the x direction. 
     As in the above-described configuration, it is preferable that the area of the first metal layer  71 , that is, the size thereof in the plane including the x direction and the z direction be substantially the same as the area of the second metal layer  72  and the third metal layer  73  and the lower end thereof reach the same position as the lower end of the subcarrier  20 . In such a configuration, the connection strength of the subcarrier  420  to the substrate  40  is secured to the maximum. In addition, the lower ends of the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  may be located above the lower ends of the subcarrier  420  and the substrate  40 . 
     In this embodiment, the antireflection film  81  is provided between the LD  30  and the PLC  50 . For example, the antireflection film  81  is integrally formed with the side surface  42  of the substrate  40  and the incident surface  61  of the PLC  50 . However, the antireflection film  81  may be formed only on the incident surface  61  of the PLC  50 . 
     The antireflection film  82  is also formed on the emission surface  64  in addition to the incident surface  61 . Additionally, the antireflection film (not shown) is also provided on the emission surface  64 . Additionally,  FIG.  11    shows a schematic configuration of the integrated optical device  10 A and the first metal layer  71 , the second metal layer  72 , the third metal layer  73 , and the antireflection films  81  and  82  are omitted. 
     The antireflection films  81  and  82  are films for preventing the light incident to or emitted from the PLC  50  from being reflected from the incident surface  61  or the emission surface  64  in the direction opposite to the direction in which the light is incident to each surface and increasing the transmittance of the incident light or emitted light. The antireflection films  81  and  82  are multilayer films formed by alternately laminating, for example, a plurality of types of dielectrics corresponding to the wavelengths of the red light, the green light, and the blue light which are the incident light in a predetermined thickness. Examples of the above-described dielectric include titanium oxide (TiO 2 ), silicon oxide (SiO 2 ), aluminum oxide (Al 2 O 3 ), and the like. 
       FIG.  15    is a diagram illustrating the surface roughness of each surface of the subcarrier  420 . 
     As shown in  FIG.  15   , the subcarrier  420  has a substantially rectangular parallelepiped shape and includes the upper surface  421  which constitutes a mounting surface of the LD  30 , the first side surface  422  which is connected to the side surface of the substrate  40  through the metal layers  71 ,  73 , and  72 , a second side surface  423  which is on the side opposite to the first side surface  422 , a third side surface  424  and a fourth side surface  425  which are respectively adjacent to the first side surface  422  and the second side surface  423  to face them, and a bottom surface (mounting base bottom surface)  26  which is on the side opposite to the upper surface  421 . The LD  30  is disposed closer to the first side surface  422  of the subcarrier  420  (that is, the front end portion of the upper surface  421 ) and is connected to the subcarrier  420  through the metal layers  75  and  76 . 
     In this embodiment, the upper surface  421 , the first side surface  422 , the second side surface  423 , and the bottom surface  26  of the subcarrier  420  are smooth surfaces, but the entire surfaces of the third side surface  424  and the fourth side surface  425  are provided with a roughened region  420 S. The roughened region  420 S is a region in which the surface roughness is larger than that of the smooth surface such as the upper surface  421  of the subcarrier  420 . Specifically, the maximum cross-sectional height (Rt) of the smooth surface such as the upper surface  421  of the subcarrier  420  is 0.01 μm or more and 5 μm or less, but the maximum cross-sectional height (Rt) of the roughened region  420 S is 5 μm or more and 50 μm or less. The maximum cross-sectional height (Rt) of the roughened region  420 S may be 10 μm or more and 50 μm or less, 20 μm or more and 40 μm or less, and preferably 5 μm or more and 30 μm or less. 
     In the present specification, the “maximum cross-sectional height” means the sum of the maximum value of the peak height and the maximum value of the valley depth of the contour curve in the evaluation length in accordance with JIS B601. 
     The maximum cross-sectional height (Rt) of the roughened region  420 S of the subcarrier  420  is measured non-contactly by a method using a device of the same principle as a white light interference type microscope (for example, “Wyko-HD9800” manufactured by BRUKER). 
     The samples 1 to 5 shown in Table 1 are examples in which the maximum cross-sectional height (Rt) of the surface before and after performing a roughening treatment on the surface of the subcarrier made of silicon by sandblasting is measured by a white light interference type microscope (“Wyko-HD9800” manufactured by BRUKER). The measurement used a VSI mode, the Rt before the roughening treatment was measured at a magnification of 7.5 times and a measurement range of (400) μm×(400) μm, and the Rt after the roughening treatment was measured at a magnification of 10 times and a measurement range of (400) μm×(400) μm. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Rt (μm) before roughening 
                 Rt (μm) after roughening 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Sample 1 
                 0.82 
                 11.60 
               
               
                 Sample 2 
                 1.51 
                 7.36 
               
               
                 Sample 3 
                 0.99 
                 12.95 
               
               
                 Sample 4 
                 2.48 
                 14.61 
               
               
                 Sample 5 
                 1.46 
                 14.11 
               
               
                   
               
            
           
         
       
     
     When the entire surface of the subcarrier  420  is a smooth surface, the laser beam is reflected on the smooth surface of the subcarrier  420  during the irradiation of the laser on the subcarrier  420  to be described later. Accordingly, the heating efficiency is not good and the bonding strength between the subcarrier  420  and the substrate  40  through the metal layers  71 ,  73 , and  72  is not sufficient in some cases. However, when the third and fourth side surfaces  424  and  425  of the subcarrier  420  are roughened, the heat capacity is suppressed, the reflection of the laser beam irradiating the third and fourth side surfaces  424  and  425  of the subcarrier  420  is suppressed, and the heating efficiency of the subcarrier  420  can be improved. Accordingly, it is possible to improve the metal bonding strength. 
     The upper surface  421  and the first side surface  422  of the subcarrier  420  are formed as smooth surfaces. Since the upper surface  421  of the subcarrier  420  is formed as a smooth surface, it is possible to form the metal layer having a uniform thickness on the upper surface  421  and to reliably and strongly mount the LD  30  onto the subcarrier  420  through the metal layer. Further, since the first side surface  422  of the subcarrier  420  is formed as a smooth surface, it is possible to form the metal layer  71  having a uniform thickness on the first side surface  422  and to reliably and strongly connect the subcarrier  420  to the side surface of the substrate  40  through the metal layers  71 ,  73 , and  72 . 
     It is preferable that the second side surface  423  and the bottom surface  26  of the subcarrier  420  also be smooth surfaces. Accordingly, the second side surface  423  and the bottom surface  26  of the subcarrier  420  can be held by vacuum suction. Thus, the position of the subcarrier  420  can be adjusted while irradiating the third and fourth side surfaces  424  and  425  of the subcarrier  420  with a laser beam. 
     The roughening method for forming the roughened region is not particularly limited and a known method for roughening the surface of the inorganic member can be used by either a wet method or a dry method. For example, the roughened region can be formed at any place by a method such as sandblasting. Instead of sandblasting, sandpaper or the like may be used to form scratches on the side surfaces of the subcarrier. 
     Further, the roughened region may be formed by a method adopting a processing condition in which a cut surface becomes rough when a collective substrate of the subcarrier  420  is diced and individualized. Specifically, roughening can be performed by adjusting the size of the diamond abrasive grains adhered to the blade of the diamond cutter. In addition, the roughened region can be formed under predetermined conditions by using a cutting method using a laser. 
     The emission surface  31  of the LD  30  and the incident surface  61  of the PLC  50  are arranged with a predetermined distance therebetween (see  FIG.  15 ( b ) ). The incident surface  61  faces the emission surface  31  and the gap  70  is formed between the emission surface  31  and the incident surface  61  in the y direction. When the integrated optical device  10 A is exposed to air, the gap  70  is full of air. Considering the amount of light required when the integrated optical device  10 A is used for a head-mounted display or the like, the size of the gap (distance)  70  in the y direction is, for example, larger than 0 μm and 5 μm or less. 
     Next, a method for manufacturing the integrated optical device  10 A will be simply described.  FIG.  16    is a diagram illustrating a method for manufacturing the integrated optical device  10 A. First, the LD  30  of the bare chip is mounted on the upper surface  421  of the subcarrier  420  by a known method. For example, the metal layer  75  is formed on the upper surface  421  of the subcarrier  420  by sputtering, vapor deposition, or the like. Further, the first metal layer  76  is formed on the lower surface  33  of the LD  30  (for example, the lower surface  33 - 1  of the LD  30 - 1 ) by sputtering, vapor deposition, or the like. Next, as shown in  FIG.  16 ( a ) , for example, the subcarrier  420  is irradiated with a laser beam from the laser device  90  so that only the subcarrier  420  is heated to a degree that melting or deforming does not occur. Heat transfer from the subcarrier  420  softens or melts the metal layers  75  and  76  and then cools them. Accordingly, the LD  30  is bonded to the upper surface  421  of the subcarrier  420  through the metal layers  75  and  76 . Further, the first metal layer  71  is formed on the first side surface  422  of the subcarrier  420  by sputtering, vapor deposition, or the like before or after the LD  30  is mounted on the subcarrier  420 . 
     Next, the PLC  50  is formed on the upper surface  41  of the substrate  40  by a known semiconductor process. Next, the antireflection films  81  and  82  and the antireflection film (not shown) are formed on the incident surface  61  and the emission surface  64 . Further, the second metal layer  72  and the third metal layer  73  are formed in this order behind the antireflection film  81  in the y direction by sputtering, vapor deposition, or the like. 
     Next, the emission surface  31  and the incident surface  61  in the LDs  30  and the cores  51 - 1 ,  51 - 2 , and  51 - 3  corresponding to each other in the x direction and the z direction are allowed to face each other in the y direction with a distance therebetween. The optical axis of each color light emitted from the LD  30  and the center of the incident surface  61  of the corresponding core are substantially overlapped with each other. At this time, the bottom surface  423  of the subcarrier  420  and the bottom surface  43  of the substrate  40  are arranged so that the bottom surface  423  of the subcarrier  420  and the bottom surface  43  of the substrate  40  are substantially on the same plane. 
     Next, as shown in  FIG.  16 ( b ) , the subcarrier  420  is irradiated with a laser beam from the laser device  90  to soften or melt the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  due to the heat transfer from the subcarrier  420 . The relative positions of the LD  30  and the PLC  50  are adjusted and the subcarrier  420  having the LD  30  mounted thereon is bonded to the substrate  40  provided with the PLC  50  so that the bottom surface  423  of the subcarrier  420  and the bottom surface  43  of the substrate  40  are substantially on the same plane. By these steps, it is possible to manufacture the integrated optical device  10 A in which the bottom surface  423  of the subcarrier  420  and the bottom surface  43  of the substrate  40  are located on the substantially same plane. 
     Specifically, as shown in  FIG.  17   , the laser device  90  is disposed on both sides of the subcarrier  420  in the X direction, a laser beam emitted from the laser device  90  is applied to the third side surface  424  and the fourth side surface  425  of the subcarrier  420  in a direction indicated by an arrow so that only the subcarrier  420  is heated to a degree that melting or deforming does not occur. At the same time, each color light is emitted from the LD  30 , the emission intensity is detected, and the emission intensity of the three color light emitted from the core  51 - 4  is detected. As shown in  FIG.  18   , when the distance S between the emission surface  31  and the incident surface  61  in the y direction is at a value on the order of microns and the emission intensity with respect to the light-emitting intensity is the light utilization efficiency [%], the light utilization efficiency decreases as the distance S increases (Sa&lt;Sb&lt;Sc&lt;Sd&lt;Se&lt;Sf&lt;Sg). The “light utilization efficiency” at each distance S means the light utilization efficiency when DT offset of the horizontal axis of the graph of  FIG.  18    is 0 (zero). The optimum distance S changes according to the intended use of the integrated optical device  10 A, the emission pattern of the LD  30 , and the sizes of the cores  51 - 1 ,  51 - 2 , and  51 - 3  in the x direction and the z direction. The positions and orientations of the distance S and the LD  30  are adjusted to satisfy the required light utilization efficiency in consideration of these conditions. Such adjustment of the position and orientation of the LD  30  means performing so-called active alignment and gap control. The adjustment of the distance S and the LD  30  can be performed using a known device having an active alignment function. 
     With the active alignment, the gap control, and the heating of the subcarrier  420 , as shown in  FIG.  17   , the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  disposed between the incident surface  61  and the emission surface  31  of the LD  30  disposed at an optimal position become thinner than each metal layer not interposed between the emission surface  31  and the incident surface  61  due to the alloying and slight heat shrinkage of the third metal layer  73 . By stopping the heating of the subcarrier  420  due to the laser device  90 , the position of the LD  30  is fixed by cooling. By proceeding with the above procedure, the integrated optical device  10 A can be manufactured. 
     As described above, since the third side surface  424  and the fourth side surface  425  of the subcarrier  420  are roughened and the roughened region  420 S is irradiated with the laser beam, it is possible to improve the heating efficiency by suppressing the reflection of the laser beam during the heating of the subcarrier  420 . Thus, it is possible to improve the bonding strength when the subcarrier  420  and the substrate  40  are bonded to each other through the first metal layer  71 , the second metal layer  72 , and the third metal layer  73 . 
     The integrated optical device  10 A of this embodiment described above includes the subcarrier  420 , the LD  30 , the substrate  40 , and the PLC  50 . The incident surface  61  is disposed to face the emission surface  31  so that the light emitted from the LD  30  can be incident to the cores  51 - 1 ,  51 - 2 , and  51 - 3 . Further, the first side surface  422  of the subcarrier  420  and the side surface  42  of the substrate  40  are connected to each other from the rear to the front in the y direction via the first metal layer  71 , the second metal layer  72 , and the third metal layer  73 . 
     According to the above-described configuration, the first metal layer  71  and the second metal layer  72  are strongly bonded to the first side surface  422  and the side surface  42  of the mounting base  40  and the third metal layer  73  is strongly bonded to the first metal layer  71  and the second metal layer  72  in the substantially entire area within the plane including the x direction and the z direction of the first side surface  422  while being alloyed at the interface with the first metal layer  71  and the second metal layer  72 . The connection between the subcarrier  420  and the substrate  40  by the first metal layer  71 , the second metal layer  72 , and the third metal layer  73  due to such alloying is resistant to heat and is difficult to be released even when the ambient environment temperature rises in a process such as wire-bonding, for example, as shown in  FIG.  19   . Thus, the PLC  50  is kept in a strong fixed state to the LD  30  even when the LD  30  and a power supply (not shown) are connected by the wire  95  on the upper surface  421  using a method such as wire-bonding. That is, the LD  30  or the subcarrier  420  does not slip off from the PLC  50  or the substrate  40  and the LD  30  is held at an optimal position with respect to the PLC  50  during wire-bonding. Accordingly, it is possible to improve the reliability of the integrated optical device  10 A by exhibiting desired light utilization efficiency and optical characteristics in the integrated optical device  10 A. 
     On the other hand, in the conventional bonding of the LD and the PLC using a resin or the bonding of the subcarrier and the substrate, hydrogen bonds due to substituents occur in a resin having a high molecular as a molecular structure. Since the density of substituents in the resin is low, local bonding is achieved within the formation plane of the resin. In the application to the configuration of the integrated optical device  10 A, the LD and PLC and the subcarrier and the substrate are locally bonded in the plane including the x direction and the z direction. Therefore, it is presumed that in the conventional connection using a resin, the connection strength is lower than that the full-scale and strong bonding by alloying. 
     Further, according to the integrated optical device  10 A of this embodiment, since the third metal layer  73  is thicker than the first metal layer  71  and the second metal layer  72 , the first metal layer  71  and the third metal layer  73  and/or the third metal layer  73  and the second metal layer  72  are sufficiently alloyed and hence the subcarrier  420  and the substrate  40  can be more strongly bonded to each other. Further, it is possible to ensure the distance between the substrate  40  and the alloy layer of the first metal layer  71  and the third metal layer  73  in the y direction. 
     Further, according to the integrated optical device  10 A of this embodiment, the lower ends of the first metal layer  71 , the second metal layer  72 , and the third metal layer reach the same positions as the lower end of the subcarrier  420  and the lower end of the substrate  40  when viewed from the y direction (light traveling direction). That is, similarly to the integrated optical device  10 A according to the first embodiment, the bonding area of the subcarrier  420  is maximized and the substrate  4  of the subcarrier  420  can be strongly bonded. 
     Further, according to the integrated optical device  10 A of this embodiment, since the antireflection film  81  is provided between the LD  30  and the PLC  50 , it is possible to prevent the reflection of each color light emitted from the LD  30  on the incident surface  61  and to improve the coupling efficiency of each color light to the cores  51 - 1 ,  51 - 2 , and  51 - 3 . 
     Further, in the integrated optical device  10 A of this embodiment, since the emission surface  31  of the LD  30  and the incident surface  61  of the PLC  50  are arranged with a predetermined distance therebetween, the relative arrangement between the LD and the PLC is not influenced by the inclusions between the emission surface of the LD and the incident surface of the PLC as in the conventional integrated optical element in which a resin is interposed between the emission surface of the LD and the incident surface of the PLC. Accordingly, it is possible to prevent the occurrence of a deviation in the relative arrangement between the LD  30  and the PLC  50 . 
     Further, the integrated optical device  10 A of this embodiment includes the plurality of LDs  30  that emit light having different peak wavelengths (wavelengths). That is, the integrated optical device  10 A includes the plurality of LDs  30 - 1 ,  30 - 2 , and  30 - 3 , the PLC  50  is provided with the plurality of cores  51 - 1 ,  51 - 2 , and  51 - 3  into which the light emitted from the plurality of LDs  30 - 1 ,  30 - 2 , and  30 - 3  can be incident, and the plurality of cores  51 - 1 ,  51 - 2 , and  51 - 3  are gathered together on the front side reaching the emission surface  64 . According to such a configuration, three-color light having different peak wavelengths (wavelengths) can be efficiently incident to the plurality of cores  51 - 1 ,  51 - 2 , and  51 - 3  and the light utilization efficiency of the three-color light emitted from the emission surface  64  can be improved. 
     Further, in the integrated optical device  10 A of this embodiment, the bottom surface  423  of the subcarrier  420  and the bottom surface  43  of the substrate  40  are formed in the state on the substantially same plane S. That is, even in the integrated optical device  10 A of this embodiment, similarly to the integrated optical device  10  of the first embodiment, the heat generated by the operation of the optical semiconductor device (LD)  30  can be efficiently dissipated to both the first side surface  422  and the bottom surface  423  of the subcarrier  420 . 
       FIGS.  20 ( a ) to  20 ( f )  and  FIGS.  21 ( a ) to  21 ( f )  are development views showing modified examples of the configuration of the subcarrier  420 . 
     In the subcarrier  420  shown in  FIG.  20 ( a ) , the upper surface  421 , the first side surface  422 , and the bottom surface  426  are formed as smooth surfaces and the entire surfaces of the second side surface  423 , the third side surface  424 , and the fourth side surface  425  are formed as the roughened region  420 S. That is, the roughened region  420 S is further added to the second side surface  423  of the subcarrier  420  shown in  FIG.  15   . 
     In the subcarrier  420  shown in  FIG.  20 ( b ) , the upper surface  421 , the first side surface  422 , and the second side surface  423  are formed as smooth surfaces and the entire surfaces of the third side surface  424 , the fourth side surface  425 , and the bottom surface  426  are formed as the roughened region  420 S. That is, the roughened region  420 S is further added to the bottom surface  426  of the subcarrier  420  shown in  FIG.  15   . 
     In the subcarrier  420  shown in  FIG.  20 ( c ) , only the second side surface  423  is formed as the roughened region  420 S and all other outer surfaces are formed as smooth surfaces. In  FIG.  20 ( d ) , only the bottom surface  426  is formed as the roughened region  420 S and all other outer surfaces are formed as smooth surfaces. 
     In  FIG.  20 ( e ) , only the second side surface  423  and the bottom surface  426  are formed as the roughened region  420 S and all other outer surfaces are formed as smooth surfaces. Thus, the third side surface  424  and the fourth side surface  425  are smooth surfaces. 
     In  FIG.  20 ( f ) , the upper surface  421  and the first side surface  422  are formed as smooth surfaces and all surfaces other than the upper surface  421  and the first side surface  422  are formed as the roughened region  420 S. 
     In the subcarrier  420  shown in  FIG.  21 ( a ) , the roughened region  420 S is provided only on the center portion of each surface instead of the entire surfaces of the third side surface  424  and the fourth side surface  425 . Therefore, a smooth surface is formed in the vicinity of the edges of the third side surface  424  and the fourth side surface  425 . 
     In the subcarrier  420  shown in  FIG.  21 ( b ) , the same roughened region  420 S as the third side surface  424  and the fourth side surface  425  is also provided on the second side surface  423  and the bottom surface  426 . In this way, the roughened region  420 S does not have to be formed on the entire surface of the target surface, but may be formed only on a part of the target surface, that is, the laser irradiation region. 
     In the subcarrier  420  shown in  FIG.  21 ( c ) , the front half region near the first side surface  422  is formed as the roughened region  420 S and the rear half region near the second side surface  423  is formed as a smooth surface in the third side surface  424  and the fourth side surface  425 . Further, in the subcarrier  420  shown in  FIG.  21 ( d ) , the same roughened region  420 S is also formed on the front half region of the bottom surface  426 . In this way, the roughened region  420 S may be provided only in the front region near the first side surface  422  in relation to the middle position between the first side surface  422  and the second side surface  423 . 
     In the subcarrier  420  shown in  FIG.  21 ( e ) , the lower half region near the bottom surface  426  is formed as a roughened region and the upper half region near the upper surface  421  is formed as a smooth surface in the third side surface  424  and the fourth side surface  425 . The subcarrier  420  shown in  FIG.  21 ( f )  forms the same roughened region  420 S also in the lower half region of the second side surface  423  and the entire surface of the bottom surface  426 . In this way, the roughened region  420 S may be provided only in the lower region near the bottom surface  426  in relation to the middle position between the upper surface  421  and the bottom surface  426 . 
     As described above, the subcarrier  420  has a substantially rectangular parallelepiped shape and includes the upper surface  421 , the first to fourth side surfaces  422  to  425 , and the bottom surface  426 . Here, when the upper surface  421  on which the LD  30  is mounted is a first outer surface, the first side surface  422  which is connected to the substrate  40  is a second outer surface, and the remaining surface is a third outer surface, the roughened region  420 S may be provided in at least a part of the third outer surface. That is, in the present invention, the roughened region  420 S may be formed on at least a part of any one of the second side surface  423 , the third side surface  424 , the fourth side surface  425 , and the bottom surface  426 . 
     Third Embodiment 
       FIG.  22    is a cross-sectional view of an integrated optical device  10 B according to a third embodiment. In the integrated optical device  10 B according to the third embodiment, the lengths of a subcarrier  520 , a first metal layer  571 , a second metal layer  572 , and a third metal layer  573  in the z direction are different from those of the integrated optical device  10 A of the second embodiment. In the integrated optical device  10 B, the same configuration as the integrated optical device  10 A is designated by the same reference numerals, and the description thereof will be omitted. 
     In this embodiment, the first metal layer  571  is provided on the side surface facing the substrate  40  or the PLC  50  in the substantially entire area of the first side surface  522  while not being in contact with the metal layer  575 . The front ends, that is, the upper ends of the second metal layer  572  and the third metal layer  573  in the z direction reach the same position as the first metal layer  571  on the front side in the z direction. The rear ends, that is, the lower ends of the second metal layer  572  and the third metal layer  573  in the z direction reach the position on the rear side of the first metal layer  571  and the front side of the antireflection film  81 . When viewed from the y direction, the first metal layer  571  is formed to be larger than the subcarrier  520  in the x direction. 
     It is preferable that the area of the first metal layer  571 , that is, the size thereof in the plane including the x direction and the z direction be substantially the same as the area of the second metal layer  572  and the third metal layer  573  or smaller than the area of the second metal layer  572  and the third metal layer  573 . 
     The integrated optical device  10 B according to this embodiment is manufactured by the same method as that of the integrated optical device  10 A. In addition, in manufacturing the integrated optical device  10 B, a bottom surface  523  of the subcarrier  520  and the bottom surface  43  of the substrate  40  may be offset from each other so that the bottom surface  523  of the subcarrier  520  and the bottom surface  43  of the substrate  40  are on the substantially same plane. Further, when bonding the subcarrier  520  having the LD  30  mounted thereon to the substrate  40  provided with the PLC, the bottom surface  523  of the subcarrier  520  and the bottom surface  43  of the substrate  40  do not have to be on the same plane. 
     Even in the integrated optical device  10 B according to this embodiment, similarly to the integrated optical device  10 A, the LD  30  or the subcarrier  520  does not slip off from the PLC  50  or the substrate  40  and the LD  30  is held at an optimal position with respect to the PLC  50 , for example, during wire-bonding. Accordingly, it is possible to improve the reliability of the integrated optical device  10 B by exhibiting desired light utilization efficiency and optical characteristics in the integrated optical device  10 B. 
     Further, even in the integrated optical device  10 B of this embodiment, the first metal layer  571  and the third metal layer  573  and/or the third metal layer  573  and the second metal layer  572  are sufficiently alloyed and the subcarrier  520  and the substrate  40  can be more strongly bonded to each other. Further, it is possible to ensure the distance between the substrate  40  and the alloy layer between the first metal layer  571  and the third metal layer  573  in the y direction. 
     Further, according to the integrated optical device  10 B of this embodiment, since the area of the first metal layer  571  is smaller than the area of the second metal layer  572  when viewed from the y direction (light traveling direction), the bonding area between the subcarrier  520  and the substrate  40  can be ensured to be equal to or larger than at least the area of the first metal layer  571 . Since the first metal layer  571  is provided in the substantially entire area of the first side surface  52 B, the subcarrier  520  and the substrate  40  can be more strongly bonded to each other by maximizing the bonding area of the subcarrier  520 . 
     (Integrated Optical Module) 
       FIG.  23    is a schematic perspective view transparently showing an example of a structure of the integrated optical module  100 B. As shown in  FIG.  23   , the integrated optical module  100 B includes the integrated optical device  10 B having a combination of the LD  30  on the subcarrier  20  and the PLC  50  of the substrate  40  and a package  91  accommodating the integrated optical device  10 B. Then, the integrated optical device  10 B is accommodated in the package  91  together with other components (not shown) such as a photo detector (PD) module and a controller IC chip, and is hermetically sealed together with an inert gas. 
     The package  91  includes a main body  91   a  which has an opening formed on the upper surface side and is made of resin or ceramic and a cover  92  which covers the opening formed on the upper surface of the main body  91   a  without a gap. A laser beam emission window  93  is provided at one end side surface of the main body  91   a  in the longitudinal direction. A portion corresponding to the emission window  93  in the main body  91   a  is provided with an opening. A laser beam emitted from the PLC  50  passes through the emission window  93  and is output to the outside. Further, a terminal block  91   b  integrated with the main body  91   a  is formed on the side surface side opposite to the side surface provided with the emission window  93  and a plurality of external electrode pads  94  are formed on the upper surface of the terminal block  91   b . The plurality of external electrode pads  94  are electrically connected to any one of the plurality of internal terminal electrodes  96  in the package  91  and the LD  30  is connected to the internal terminal electrode  96  via a bonding wire (wire)  95 . 
     The plurality of external electrode pads  94  are electrically connected to any one of the plurality of internal terminal electrodes  96  in the package  91  and the LD  30  is connected to the internal terminal electrode  96  via the wire  95 . In this way, wire-bonding is used in the connection between the pad of the LD  30  and the internal terminal electrode  96 , but when the bonding strength of the subcarrier  20  to the substrate  40  is weak, the subcarrier  20  may be peeled off from the substrate  40  due to the pressure applied during wire-bonding. However, in this embodiment, since the subcarrier  20  is strongly bonded to the substrate  40 , the electrical connection between the casing-side terminal and the optical semiconductor device  30  by wire-bonding can be reliably performed. 
     In addition, the package  91  may be filled with an inert gas such as nitrogen (N 2 ). 
     Although the embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. This embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the present invention. For example, the characteristic configurations of the above-described embodiments and modified examples may be combined. 
     For example, in the integrated optical device  10  ( 10 A,  10 B) of this embodiment, three optical semiconductor devices (LD)  30 - 1 ,  30 - 2 , and  30 - 3  are provided on the upper surface (surface)  21  ( 421 , 521 ) of the subcarrier (mounting base)  20  ( 420 ,  520 ), but only at least one optical semiconductor device (LD) (for example, LD emitting white light) may be provided or four or more LDs may be provided. Further, the light emitted from the optical semiconductor devices (LDs)  30 - 1 ,  30 - 2 , and  30 - 3  is not limited to the red light, the blue light, and the green light, and an LD emitting light having an arbitrary wavelength can be used. 
     Further, for example, one common heat sink and the like bonded to the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  located on the substantially same plane may be provided. 
     Further, in the integrated optical module  100  ( 100 A), the heat sink and the like can be further bonded to the bottom surface of the package. Accordingly, the heat propagated from the integrated optical device  10  ( 10 A,  10 B) to the package  110  can be further efficiently dissipated to the outside. 
     Further, for example, in the integrated optical device  10  ( 10 A,  10 B), the subcarrier  20  ( 420 ,  520 ) and the substrate  40  may be connected to each other through a metal composite layer (not shown) including at least the alloy layer of the metal of the first metal layer  71  ( 571 ) and the third metal layer  73  ( 573 ) and/or the alloy layer of the metal of the second metal layer  72  ( 572 ) and the third metal layer  73  ( 573 ). The “metal composite layer including at least the alloy layer of the metal of the first metal layer  71  ( 571 ) and the third metal layer  73  ( 573 ) and/or the alloy layer of the metal of the second metal layer  72  ( 572 ) and the third metal layer  73  ( 573 )” means a layer partially including the alloy layer of the metal of the first metal layer  71  ( 571 ) and the third metal layer  73  ( 573 ) and/or the alloy layer of the second metal layer  72  ( 572 ) and the third metal layer  73  ( 573 ) or a layer entirely including the alloy layer of the metal of the first metal layer  71  ( 571 ) and the third metal layer  73  ( 573 ) and the alloy layer of the metal of the second metal layer  72  ( 572 ) and the third metal layer  73  ( 573 ). As an example, in the integrated optical device  10  ( 10 A,  10 B), there is a case in which the metal of the first metal layer  71  ( 571 ) and the metal of the third metal layer  73  ( 573 ) are alloyed partially or entirely in the y direction to form one alloy layer. 
     Further, for example, there is a case in which the metal of the second metal layer  72  ( 572 ) and the metal of the third metal layer  73  ( 573 ) are alloyed partially or entirely in the y direction to form one alloy layer. In these cases, the subcarrier  20  ( 420 ,  520 ) and the substrate  40  can be connected to each other through any one of or both the alloy layer of the first metal layer  71  ( 571 ) and the third metal layer  73  ( 573 ) and the alloy layer of the second metal layer  72  ( 572 ) and the third metal layer  73  ( 573 ). According to such a configuration, the subcarrier  20  ( 420 ,  520 ) and the substrate  40  can be strongly connected as compared with the conventional resin connection using the alloy layer and the reliability of the integrated optical device can be improved. 
     Further, for example, in the integrated optical device  10  ( 10 A,  10 B), the subcarrier  20  ( 420 ,  520 ) and the LD  30  may be connected to each other through the metal composite layer including at least the alloy layer of the metal layers  75  and  76 . The “metal composite layer including at least the alloy layer of the metal layers  75  and  76 ” means a layer partially including the alloy layer of the metal layer  75  and the metal layer  76  or a layer entirely including the alloy layer. As an example, there is a case in which the metal of the metal layer  75  and the metal of the metal layer  76  are partially or entirely alloyed in the z direction to form an alloy layer in the integrated optical device  10  ( 10 A,  10 B). When the metal of the metal layer  75  and the metal of the metal layer  76  are partially alloyed in the z direction, the alloy layer of the metal layers  75  and  76  and any one of or both the metal layer  75  and the metal layer  76  are interposed between the subcarrier  20  ( 420 ,  520 ) and the LD  30 . When the metal of the metal layer  75  and the metal of the metal layer  76  are entirely alloyed in the z direction, only the alloy layer is substantially interposed between the subcarrier  20  ( 420 ,  520 ) and the LD. Further, although it is preferable that the metal layer  75  and the metal layer  76  be entirely alloyed in the y direction to form the alloy layer, the present invention is not limited to such a configuration. For example, these metal layers may be partially alloyed in the y direction to form the alloy layer. 
     In order to connect the subcarrier  20  ( 420 ,  520 ) and the substrate  40  to each other, the metal material interposed between the subcarrier  20  ( 420 ,  520 ) and the substrate  40  can be appropriately changed in accordance with each material of the subcarrier  20  ( 420 ,  520 ), the substrate  40 , and the first metal layer  71  ( 571 ). Further, the thickness of the metal material of the metal layer or the alloy layer is also appropriately set in accordance with each material of the subcarrier  20  ( 420 ,  520 ), the substrate  40 , and the first metal layer  71  ( 571 ). In accordance with the type and thickness of the metal material, the heating condition of the subcarrier  20  ( 420 ,  520 ), and the like, the configuration of the metal composite layer interposed between the subcarrier  20  ( 420 ,  520 ) and the substrate  40  can be changed. The metal composite layer may be a single alloy layer, a combination of a metal layer and an alloy layer, a combination of alloy layers having different compositions, or a multilayer structure including at least an alloy layer. 
     Although the integrated optical device  10  ( 10 A,  10 B) has been described as a combiner that combines light of the three primary colors in the visible wavelength range, the integrated optical device of the present invention is not limited to the combiner and can be widely used in optical communication applications. 
     Further, it has been described that the integrated optical device  10  ( 10 A,  10 B) can combine three primary colors in the visible wavelength range to be used in applications such as wearable devices and compact projectors, but the wavelength of light processed by the integrated optical device of the present invention is not limited to the visible wavelength range. For example, the wavelength range of light processed by the integrated optical device of the present invention may range from the visible wavelength range to the near infrared wavelength range or may be only in the near infrared wavelength range to be used in optical communication. The materials of the substrate  40 , the PLC  50 , various metal layers, and alloy layers may be selected according to the wavelength of light processed by the integration of the present invention. 
     EXAMPLES 
     The effect of the present invention was verified. 
     EXAMPLE 
     The integrated optical device  10  of the first embodiment shown in  FIG.  1    was prepared and the heat dissipation state when bonding a package to the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  of the integrated optical device  10  through a thermally conductive adhesive was simulated. 
     Subcarrier: Silicon (Si) 
     Substrate: Silicon (Si) 
     Package: Aluminum oxide (Al 2 O 3 ) 
     Adhesive: Epoxy resin 
     COMPARATIVE EXAMPLE 
     An integrated optical device having the same configuration as that of the example except that a bottom surface of a subcarrier was recessed in a thickness direction rather than a bottom surface of a substrate was prepared and a heat dissipation state when bonding a package to the bottom surface of the substrate of the integrated optical device through a thermally conductive adhesive was measured. The bottom surface of the subcarrier was not bonded to the package and a gap between the bottom surface of the subcarrier and an inner surface of the package was 0.5 mm. 
       FIG.  24 ( a )  shows a heat distribution when the LD  30  of the integrated optical device  10  of the example was heated by 1 W and  FIG.  24 ( b )  shows a heat distribution when the LD of the integrated optical device of the comparative example was heated by 1 W. Additionally,  FIG.  24    shows a cross-section of a main part of the integrated optical module in the thickness direction. 
     According to the result shown in  FIG.  24   , since the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40  of the integrated optical device  10  of the example were bonded to the package to be on the substantially same plane S, it was confirmed that the heat generated from the LD  30  was dissipated to the package from each of the bottom surface  23  of the subcarrier  20  and the bottom surface  43  of the substrate  40 . Accordingly, it was confirmed that the temperature of the LD  30  was kept lower than that of the comparative example. 
     On the other hand, in the integrated optical device of the comparative example, since the bottom surface of the subcarrier had a step with respect to the bottom surface of the substrate and only the bottom surface of the substrate was bonded to the package, the heat generated from the LD was dissipated to the package only on the bottom surface of the substrate located at a position separated from the LD. Therefore, the heat dissipation efficiency was poor as compared with the example and the temperature of the LD was higher than that of the example. 
     Next, a relationship between the maximum temperature change value and the thermal conductivity of the adhesive for bonding the integrated optical device to the package in the example and comparative example was measured. This result is shown by the graph in  FIG.  25   . 
     According to the measurement result of  FIG.  25   , it was confirmed that the temperature change amount of the integrated optical module can be minimized by setting the thermal conductivity to 1 W/(m·K) or more and the temperature change amount of the integrated optical module can be suppressed by setting the thermal conductivity to 4 W/(m·K) or more. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  Integrated optical device 
               20 ,  420 ,  520  Subcarrier (mounting base) 
               20 - 1 ,  420 - 1 ,  520 - 1  Subcarrier (mounting base) 
               20 - 2 ,  420 - 2 ,  520 - 2  Subcarrier (mounting base) 
               20 - 3 ,  420 - 3 ,  520 - 3  Subcarrier (mounting base) 
               21 ,  421 ,  521  Upper surface 
               21 - 1  Upper surface 
               21 - 2  Upper surface 
               21 - 3  Upper surface 
               22  Side surface 
               22 - 1  Side surface 
               22 - 2  Side surface 
               22 - 3  Side surface 
               23  Bottom surface (mounting base bottom surface) 
               30  LD (optical semiconductor device) 
               30 - 1  LD 
               30 - 2  LD 
               30 - 3  LD 
               31  Emission surface 
               31 - 1  Emission surface 
               31 - 2  Emission surface 
               31 - 3  Emission surface 
               33  Lower surface 
               33 - 1  Lower surface 
               40  Substrate 
               41  Upper surface (surface) 
               42  Side surface 
               43  Bottom surface (substrate bottom surface) 
               50  PLC (optical waveguide) 
               51 - 1 ,  51 - 2 ,  51 - 3  Core 
               51 - 4 ,  51 - 7  Core 
               52  Clad 
               57 - 1 ,  57 - 2  Merging position 
               61  Incident surface 
               61 - 1  Incident surface 
               61 - 2  Incident surface 
               61 - 3  Incident surface 
               64  Emission surface 
               70  Gap 
               71  First metal layer 
               72  Second metal layer 
               73  Third metal layer 
               75  Metal layer 
               76  Metal layer 
               81 ,  82  Antireflection film 
               100  Integrated optical module 
               102  Main body 
               105  Cover 
               110  Package 
               180  Base 
               180   a  Upper surface (one inner surface) 
               182  Adhesive layer