Patent Publication Number: US-2023140458-A1

Title: Measurement apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-179309 filed Nov. 2, 2021. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a measurement apparatus. 
     (ii) Related Art 
     As a related art, JP2020-136655A discloses a semiconductor light amplifier including a light source unit that emits laser light and a light amplification unit that includes an active region formed on a substrate and formed in an extended manner from the light source unit in a direction set in advance along a surface of the substrate, amplifies propagation light propagating from the light source unit in the direction set in advance, and emits the amplified propagation light in a direction intersecting the substrate surface. 
     SUMMARY 
     In a case where a light emitter including a light emission unit that emits light in an oblique direction inclined with respect to the substrate and a normal line of the substrate emits light to an object and a light receiver receives reflected light reflected by the object to be measured, the reflected light may be difficult to be received by the light receiver depending on an orientation of the substrate of the light emitter. 
     Aspects of non-limiting embodiments of the present disclosure relate to a measurement apparatus that enables a light receiver to easily receive reflected light in a case where a light emitter that emits light in an oblique direction emits light to an object to be measured and the light receiver receives the reflected light reflected by the object to be measured, as compared with a case where a substrate of the light emitter is parallel to a light reception surface of the light receiver. 
     Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above. 
     According to an aspect of the present disclosure, there is provided a measurement apparatus including a light emitter including a substrate and a light emission unit that emits light in an inclined direction inclined with respect to the substrate and a normal line of the substrate, and a light receiver that receives, on a light reception surface, reflected light emitted from the light emitter and reflected by an object to be measured, in which in a case where an angle formed by the light emitted from the light emitter and the substrate of the light emitter is an angle θ 1  (0°&lt;θ1&lt;90°), an angle θ 2  formed by the substrate and the light reception surface of the light receiver satisfies 0°&lt;θ2&lt;180°−2ƒ 1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG.  1    is a diagram showing an example of a configuration of a distance measurement apparatus to which a first exemplary embodiment is applied; 
         FIG.  2    is a view of the distance measurement apparatus shown in  FIG.  1    as viewed from a II direction; 
         FIG.  3    is a plan view of a semiconductor multilayer structure to which the present exemplary embodiment is applied; 
         FIG.  4    is a cross-sectional view taken along a line IV-IV shown in  FIG.  3   ; 
         FIG.  5    is a diagram showing an example of a configuration of a distance measurement apparatus different from the distance measurement apparatus according to the present exemplary embodiment; 
         FIG.  6    is a diagram showing an example of a configuration of a distance measurement apparatus to which a second exemplary embodiment is applied; 
         FIG.  7    is a diagram showing a modification example of the distance measurement apparatus to which the second exemplary embodiment is applied; 
         FIG.  8    is a diagram for describing an optical path length and the like until light emitted from a semiconductor multilayer structure reaches an object to be measured in the distance measurement apparatus; 
         FIG.  9    is a diagram for describing a configuration of a distance measurement apparatus to which a third exemplary embodiment is applied and is a diagram showing a configuration between a light emitter and the object to be measured; 
         FIG.  10    is a diagram showing an example of a configuration of a distance measurement apparatus to which a fourth exemplary embodiment is applied; 
         FIG.  11    is a diagram showing a modification example of the distance measurement apparatus to which the fourth exemplary embodiment is applied; 
         FIG.  12    is a plan view of a semiconductor multilayer structure to which a fifth exemplary embodiment is applied; and 
         FIG.  13    is a cross-sectional view taken along a line XIII-XIII shown in  FIG.  12   . 
     
    
    
     DETAILED DESCRIPTION 
     First Exemplary Embodiment 
     Distance Measurement Apparatus  1   
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. 
       FIG.  1    is a diagram showing an example of a configuration of a distance measurement apparatus  1  to which a first exemplary embodiment is applied.  FIG.  2    is a view of the distance measurement apparatus  1  shown in  FIG.  1    as viewed from a II direction. 
     The distance measurement apparatus  1  according to the present exemplary embodiment is used to measure a distance between the distance measurement apparatus  1 , which is an example of a measurement apparatus, and an object to be measured OB disposed via a gap with respect to the distance measurement apparatus  1 . As shown in  FIG.  1   , the distance measurement apparatus  1  includes a light emitter  2  that emits light and a light receiver  3  that receives reflected light emitted from the light emitter  2  and reflected by the object to be measured OB. Further, the distance measurement apparatus  1  includes a PCB board  4  on which wiring for supplying electric power to the light emitter  2  and the like is formed, and a pedestal  5  that supports the light emitter  2 , the light receiver  3 , and the PCB board  4 . Furthermore, the distance measurement apparatus  1  includes an angle adjustment member  6  that adjusts an angle of the light emitter  2  with respect to the light receiver  3 . 
     Light Emitter  2   
     As shown in  FIG.  1   , the light emitter  2  includes a semiconductor multilayer structure  10  that emits the light, an emission-side substrate  21  on which the semiconductor multilayer structure  10  is loaded (hereinafter simply referred to as a substrate  21 ), and a diffusion plate  22  that is provided between the semiconductor multilayer structure  10  and the object to be measured OB and diffuses and transmits the light emitted from the semiconductor multilayer structure  10  toward the object to be measured OB. 
     Semiconductor Multilayer Structure  10   
     The semiconductor multilayer structure  10  is an example of a light emission unit and emits the light in an oblique direction inclined with respect to the substrate  21  having a flat plate shape and a normal line of the substrate  21 . The normal line of the substrate  21  means a line extending in a perpendicular direction from a surface, in the substrate  21  having a flat plate shape, on which the semiconductor multilayer structure  10  is loaded. 
       FIG.  3    is a plan view of the semiconductor multilayer structure  10  to which the present exemplary embodiment is applied, and  FIG.  4    is a cross-sectional view taken along a line IV-IV shown in  FIG.  3   . As shown in  FIG.  3   , the semiconductor multilayer structure  10  has a longitudinal direction LD and a lateral direction SD orthogonal to the longitudinal direction LD, and includes an optical coupling portion  11  provided at one end in the longitudinal direction LD and a light amplification unit  12  extending from the optical coupling portion  11  along the longitudinal direction LD. 
     The optical coupling portion  11  couples a light source that generates seed light Ls, which is input light to the semiconductor multilayer structure  10 . In the semiconductor multilayer structure  10  according to the present exemplary embodiment, the input light is propagated from an external light source (not shown) via an optical fiber OF, and an output end of the optical fiber OF is coupled to the optical coupling portion  11  to introduce the input light to the light amplification unit  12 . For example, a vertical cavity surface emitting laser (VCSEL) is used as the external light source. A lensed fiber may be used as the optical fiber OF from the viewpoint of light coupling efficiency. 
     The light amplification unit  12  has a function of amplifying and emitting the seed light Ls coupled to the optical coupling portion  11 . The light amplification unit  12  according to the present exemplary embodiment is a surface-emission light amplification unit using a distributed Bragg reflector waveguide (hereinafter referred to as a DBR waveguide) having a GaAs diameter as an example. Specifically, the light amplification unit  12  includes an N electrode  121  stacked on one surface (back surface) of a base layer  120 . The light amplification unit  12  includes a lower DBR layer  122 , an active layer  123 , an oxidization constriction layer  124 , an upper DBR layer  125 , and a P electrode  126 , which are sequentially stacked on the other surface (front surface) of the base layer  120 . 
     In the present exemplary embodiment, the base layer  120  is an n-type GaAs substrate, and an N electrode  121  that is in ohmic contact with the n-type GaAs substrate is provided on the back surface of the base layer  120 . 
     The lower DBR layer  122  is n-type, and the upper DBR layer  125  is p-type. In a case where the semiconductor multilayer structure  10  is driven, a positive electrode of a driving power source is applied to the P electrode  126  and a negative electrode thereof is applied to the N electrode  121  to cause a drive current to flow from the P electrode  126  to the N electrode  121 . However, the polarities of the base layer  120 , the lower DBR layer  122 , and the upper DBR layer  125  are not limited thereto. The polarities may be reversed, that is, the base layer  120  may be a p-type GaAs substrate, the lower DBR layer  122  may be a p-type, and the upper DBR layer  125  may be an n-type. 
     The lower DBR layer  122  is paired with the upper DBR layer  125  described below to form a resonator that contributes to light emitting in the semiconductor multilayer structure  10 . The lower DBR layer  122  is a multilayer film reflector configured by alternately and repeatedly stacking two semiconductor layers having a thickness of 0.25 λ/n each and different refractive indexes in a case where an oscillation wavelength of the semiconductor multilayer structure  10  is λ and a refractive index of a medium (semiconductor layer) is n. As a specific example, the lower DBR layer  122  is configured by alternately and repeatedly stacking an n-type low refractive index layer made of Al 0.9 Ga 0.1 As and an n-type high refractive index layer made of Al 0.2 Ga 0.8 As. 
     The active layer  123  according to the present exemplary embodiment may be configured to include, for example, a lower spacer layer, a quantum well active region, and an upper spacer layer, which are not shown. The quantum well active region according to the present exemplary embodiment may be configured of, for example, barrier layers consist of four layers of Al 0.3 Ga 0.7 As and quantum well layers consist of three layers of GaAs provided between the barrier layers. The lower spacer layer and the upper spacer layer are respectively disposed between the quantum well active region and the lower DBR layer  122  and between the quantum well active region and the upper DBR layer  125  to have a function of adjusting a length of the resonator and a function as a clad layer to confine a carrier. 
     The oxidization constriction layer  124  provided on the active layer  123  includes a non-oxidized region  124   a  and an oxidized region  124   b.  The oxidized region  124   b  is a region where a current does not easily flow, and the non-oxidized region  124   a  is a region where a current easily flows. That is, the oxidization constriction layer  124  constricts a path through which the current flows in the semiconductor multilayer structure  10 . 
     In the present exemplary embodiment, the oxidization constriction layer  124  is composed of one layer on a base layer  120  side among multilayer films constituting the upper DBR layer  125  described below. That is, with oxidization of a part of the one layer constituting the upper DBR layer  125 , the oxidized region  124   b  is formed, and an unoxidized region other than the oxidized region  124   b  becomes the non-oxidized region  124   a.  In the present exemplary embodiment, the oxidization constriction layer  124  is formed in one layer of the upper DBR layer  125  has been described as an example, but the present invention is not limited thereto. The oxidization constriction layer  124  may be formed into a plurality of layers of the upper DBR layer  125  or in the lower DBR layer  122 . 
     The upper DBR layer  125  is a multilayer film reflector configured by alternately and repeatedly stacking two semiconductor layers having a film thickness of 0.25 λ/n each and having different refractive indexes. As a specific example, the upper DBR layer  125  is configured by alternately and repeatedly stacking an n-type low refractive index layer made of Al 0.9 Ga 0.1 As and an n-type high refractive index layer made of Al 0.2 Ga 0.8 As. 
     The light amplification unit  12  according to the present exemplary embodiment, which is a DBR waveguide, will be described in more detail. The seed light Ls introduced from the optical coupling portion  11  propagates, in the light amplification unit  12 , in a propagation direction (longitudinal direction LD of the semiconductor multilayer structure  10 ) from a left side to a right side of a paper surface of  FIGS.  3  and  4   . In this case, the propagation light propagates mostly in the lower DBR layer  122 , the active layer  123 , the non-oxidized region  124   a  of the oxidization constriction layer  124 , and the upper DBR layer  125  with a distribution set in advance, as shown in  FIG.  4   . Therefore, the “DBR waveguide” is configured to include the above parts. 
     The semiconductor multilayer structure  10  using the light amplification unit  12  which is the DBR waveguide is configured of a pair of DBRs (lower DBR layer  122  and upper DBR layer  125 ), which is provided on the base layer  120 , and the active layer  123  and the oxidization constriction layer  124  between the pair of DBRs. A region sandwiched between the DBRs functions as an optical waveguide, and the light input into the optical waveguide propagates in a slow light mode while being multiple-reflected in an oblique direction. In this case, in a case where a current is injected into the active layer  123  by the P electrode  126  and the N electrode  121  provided on both sides of the DBR waveguide, the input light is amplified. The amplified light is output in a direction that intersects the base layer  120  and a normal line of the base layer  120  and is inclined forward in the propagation direction (longitudinal direction LD) of the propagation light in the light amplification unit  12 . In  FIG.  4    and  FIG.  1    described above, the light output from the light amplification unit  12  and emitted to the outside from the semiconductor multilayer structure  10  is shown as emission light Lf. 
     That is, the light amplification unit  12 , which is a region (region sandwiched between the P electrode  126  and the N electrode  121 ) where the P electrode  126  and the N electrode  121  are provided in the semiconductor multilayer structure  10 , has a function of propagating the light and a function of amplifying the light. The light amplified by the light amplification unit  12  of the semiconductor multilayer structure  10  is emitted, as the emission light Lf, in the direction intersecting the base layer  120  and the normal line of the base layer  120 . 
     For the light input to the light amplification unit  12 , a part of the DBR is removed by etching to create a light incident portion (optical coupling portion  11 ) having a reduced reflectance and external light is obliquely incident for coupling. Further, for the light input to the light amplification unit  12 , although the details will be described below, a light source (seed light unit) is laterally integrated as a part of the semiconductor multilayer structure  10  and light exuded to the light amplification unit  12  may be propagated. 
     Substrate  21   
     Returning to  FIGS.  1  and  2   , the semiconductor multilayer structure  10  is loaded on one surface (upper surface in  FIG.  1   ) of the substrate  21  of the light emitter  2 . 
     The substrate  21  is formed with wiring for supplying electric power to the semiconductor multilayer structure  10 . Specifically, the substrate  21  is formed with anode wiring  211  connected to the P electrode  126  (refer to  FIG.  4   ) in the semiconductor multilayer structure  10  and cathode wiring  212  connected to the N electrode  121  (refer to  FIG.  4   ) in the semiconductor multilayer structure  10  A, as shown in  FIG.  2   . In this example, the anode wiring  211  of the substrate  21  and the P electrode  126  of the semiconductor multilayer structure  10  are connected via a plurality of bonding wires  213 . The cathode wiring  212  of the substrate  21  and the N electrode  121  of the semiconductor multilayer structure  10  are connected with the loading of the semiconductor multilayer structure  10  on the cathode wiring  212  of the substrate  21 . 
     As described above, the semiconductor multilayer structure  10  loaded on the substrate  21  emits the emission light Lf in the direction intersecting the base layer  120  and the normal line of the base layer  120 . Therefore, in the light emitter  2  according to the present exemplary embodiment, the semiconductor multilayer structure  10  emits the emission light Lf in the oblique direction inclined with respect to the substrate  21  and the normal line of the substrate  21 . In the following, an angle formed by the substrate  21  and the emission light Lf in a cross section of the semiconductor multilayer structure  10  perpendicular to the lateral direction SD may be referred to as an emission angle θ 1 . 
     The emission angle θ 1  satisfies 0&lt;θ1&lt;90°. The emission angle θ 1  varies depending on the configuration of the semiconductor multilayer structure  10  and the like, but is, for example, preferably 30°&lt;θ1&lt;60°. 
     Diffusion Plate  22   
     The diffusion plate  22  of the light emitter  2  diffuses the emission light Lf emitted from the semiconductor multilayer structure  10  at a diffusion angle θt set in advance and transmits the emission light toward the object to be measured OB. The diffusion angle θt is an angle at which the light transmitted through the diffusion plate  22  diffuses with respect to an optical axis direction of the light incident on the diffusion plate  22 . 
     The diffusion plate  22  is supported at an angle set in advance with respect to the semiconductor multilayer structure  10  such that the emission light Lf emitted from the semiconductor multilayer structure  10  is perpendicularly incident. 
     Light Receiver  3   
     The light receiver  3  includes a light-receiving side substrate  31  loaded on the pedestal  5 , a light reception sensor  32  that is loaded on the light-receiving side substrate  31 , receives the reflected light from the object to be measured, and outputs an electric signal, and a filter  33  that is provided between the light reception sensor  32  and the object to be measured and transmits the light having a wavelength set in advance. 
     The light reception sensor  32  receives the light (reflected light) reflected by the object to be measured OB and transmitted through the filter  33  on a light reception surface  32   a,  and outputs the electric signal according to an amount of light received. The light reception sensor  32  is composed of, for example, a photodiode or a phototransistor. The electric signal from the light reception sensor  32  is output to a calculation unit (not shown) composed of a central processing unit (CPU), an application specific integrated circuit (ASIC), or the like. The calculation unit performs calculation processing set in advance on the electric signal from the light reception sensor  32  to calculate the distance between the distance measurement apparatus  1  and the object to be measured OB. 
     In this example, the light reception sensor  32  is horizontally disposed along a left-right direction in the figure such that the light reception surface  32   a  faces the object to be measured OB, as shown in  FIG.  1   . The light reception sensor  32  can receive light within a range of a light-receiving viewing angle θr set in advance with respect to a normal line of the light reception surface  32   a.    
     PCB Board  4   
     Wiring connected to the wiring formed on the substrate  21  of the light emitter  2  is formed on the PCB board  4 . Specifically, anode wiring  41  connected to the anode wiring  211  of the substrate  21  and cathode wiring  42  connected to the cathode wiring  212  of the substrate  21  are formed on the PCB board  4 . In this example, the anode wiring  211  of the substrate  21  is connected to the anode wiring  41  of the PCB board  4  by a solder  45 . Similarly, the cathode wiring  212  of the substrate  21  is connected to the cathode wiring  42  of the PCB board  4  by the solder  45 . Further, the anode wiring  41  and the cathode wiring  42  of the PCB board  4  are connected to a power supply (not shown). 
     Accordingly, in the distance measurement apparatus  1  according to the present exemplary embodiment, the electric power is supplied to the semiconductor multilayer structure  10  of the light emitter  2  via the anode wiring  41  and the cathode wiring  42  formed on the PCB board  4  and the anode wiring  211  and the cathode wiring  212  formed on the substrate  21 . 
     Pedestal  5   
     The pedestal  5  collectively supports the light emitter  2 , the light receiver  3 , the PCB board  4 , and the angle adjustment member  6 . In addition, the pedestal  5  supports the light emitter  2  and the light receiver  3  such that a distance between the light emitter  2  and the light receiver  3  is a distance set in advance. 
     Angle Adjustment Member  6   
     The angle adjustment member  6  is a member that supports the substrate  21  of the light emitter  2  and adjusts the substrate  21  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  to have an angle set in advance. 
     The angle adjustment member  6  has a cross-sectional shape similar to the shape shown in  FIG.  1    from one end to the other end in the lateral direction SD of the semiconductor multilayer structure  10 . As shown in  FIG.  1   , the angle adjustment member  6  has an inclined surface  6   a  forming an angle set in advance with respect to the light reception surface  32   a  in the light reception sensor  32 . In the distance measurement apparatus  1  according to the present exemplary embodiment, the substrate  21  is loaded on the inclined surface  6   a  of the angle adjustment member  6 , and thus the substrate  21  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  have the angle set in advance. Hereinafter, the angle formed by the substrate  21  of the light emitter  2  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  is referred to as a substrate angle θ 2 . The substrate angle θ 2  will be described below in detail. 
     By the way, in a case where the light emitter  2  including the semiconductor multilayer structure  10  that emits the light in the oblique direction inclined with respect to the substrate  21  and the normal line of the substrate  21  emits the light to the object to be measured OB and the light receiver  3  receives the reflected light reflected by the object to be measured is OB, the reflected light may be difficult to be received by the light receiver  3  depending on an orientation of the substrate  21  of the light emitter  2 . 
       FIG.  5    is a diagram showing an example of a configuration of a distance measurement apparatus (hereinafter referred to as a distance measurement apparatus LA) different from the distance measurement apparatus  1  according to the present exemplary embodiment. In  FIG.  5   , the same reference numerals are used for the same configurations as the configurations of the distance measurement apparatus  1  according to the present exemplary embodiment shown in  FIGS.  1  and  2   . 
     In the distance measurement apparatus  1 A shown in FIG.  5 , the light emitter  2  and the light receiver  3  are disposed on the pedestal  5  such that the substrate  21  of the light emitter  2  is parallel to the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3 . In a case where the substrate  21  is parallel to the light reception surface  32   a,  for the reflected light emitted from the semiconductor multilayer structure  10  of the light emitter  2  and reflected by the object to be measured OB, an angle formed with the light reception surface  32   a  tends to be smaller than the light-receiving viewing angle θr in the distance measurement apparatus LA. In this case, the reflected light from the object to be measured OB is difficult to be received by the light reception sensor  32 . 
     In the distance measurement apparatus  1 A shown in  FIG.  5   , in order to enable the light reception sensor  32  of the light receiver  3  to easily receive the reflected light emitted from the light emitter  2  and reflected by the object to be measured OB, the light-receiving viewing angle θr of the light reception sensor  32  is, for example, preferably made larger by the emission angle θ 1  than the diffusion angle θt of the diffusion plate  22  in the light emitter  2 . However, in a case where the light-receiving viewing angle θr of the light reception sensor  32  is increased, the light reception sensor  32  easily receives the reflected light. However, a range that does not contribute to the reception of the reflected light of a range within the light-receiving viewing angle θr in the light reception sensor  32  is widened, and waste tends to increase. 
     On the contrary, in the distance measurement apparatus  1  according to the present exemplary embodiment, the angle of the light emitter  2  with respect to the light receiver  3  is adjusted by using the angle adjustment member  6  to enable the light receiver  3  to easily receive the light reflected from the object to be measured OB, for example, as compared with a case where the substrate  21  of the light emitter  2  is parallel to the light reception surface  32   a  of the light receiver  3 . 
     Hereinafter, a relationship between the light emitter  2  and the light receiver  3  in the distance measurement apparatus  1  will be described in more detail with reference to  FIG.  1   . Each angle described in the present exemplary embodiment means an angle in a cross section of the distance measurement apparatus  1  cut along a plane perpendicular to the lateral direction SD in the semiconductor multilayer structure  10  of the light emitter  2 . 
     As described above, the angle formed by the emission light Lf emitted from the semiconductor multilayer structure  10  of the light emitter  2  and the substrate  21  of the light emitter  2  is assumed as the emission angle θ 1 . Since the semiconductor multilayer structure  10  emits the light in the oblique direction inclined with respect to the substrate  21  and the normal line of the substrate  21 , the emission angle θ 1  is 0°&lt;θ1&lt;90°. 
     As described above, assuming that the angle formed by the substrate  21  of the light emitter  2  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  is the substrate angle  82 , in the distance measurement apparatus  1  according to the present exemplary embodiment, the emission angle θ 1  and the substrate angle  82  satisfy the following equation (1). 
       0°&lt;θ2&lt;180°−2θ1   (1)
 
     In the distance measurement apparatus  1  according to the present exemplary embodiment, in a case where the emission angle θ 1  and the substrate angle θ 2  satisfy equation (1), an advancing direction of the light emitted from the semiconductor multilayer structure  10  is close to a direction perpendicular to the light reception surface  32   a  (upper-lower direction in  FIG.  1   ), as compared with a case where equation (1) is not satisfied, for example, the substrate  21  of the light emitter  2  is parallel to the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  (that is, in a case where θ 1 =0°). Accordingly, in the distance measurement apparatus  1  according to the present exemplary embodiment, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the emission angle θ 1  and the substrate angle θ 2  do not satisfy equation (1). 
     In addition, in the distance measurement apparatus  1  according to the present exemplary embodiment, even in a case where the light-receiving viewing angle θr of the light reception sensor  32  is not larger than the diffusion angle θt of the diffusion plate  22  in the light emitter  2 , the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB. Accordingly, the range that does not contribute to the reception of the reflected light within the range of the light-receiving viewing angle θr of the light reception sensor  32  is less likely to occur. 
     In the distance measurement apparatus  1 , a sum of the emission angle θ 1  and the substrate angle θ 2  is, for example, preferably 90° (θ 1 +θ 2 =90°). With the sum of the emission angle θ 1  and the substrate angle θ 2  of 90°, the direction in which the light is emitted from the semiconductor multilayer structure  10  of the light emitter  2  and the direction perpendicular to the light reception surface  32   a  of the light reception sensor  32  are easier to match. Accordingly, the light reception sensor  32  more easily receives the reflected light emitted from the semiconductor multilayer structure  10  of the light emitter  2  and reflected by the object to be measured OB. In a case where the object to be measured OB is disposed in a vertical direction with respect to the light emitter  2 , with the sum of the emission angle θ 1  and the substrate angle θ 2  of 90°, the light emitted from the semiconductor multilayer structure  10  of the light emitter  2  is likely to be evenly emitted with respect to the object to be measured OB. Accordingly, a measurement accuracy of the distance measurement apparatus  1  is improved. 
     The fact that the sum of the emission angle θ 1  and the substrate angle θ 2  is 90° (θ 1 +θ 2 =90°) means that all the light emitted from the semiconductor multilayer structure  10  does not need to strictly satisfy θ 1 +θ 2 =90° and at least a part of the light may be in a range in which the same result as the light at θ 1 +θ 2 =90° can be obtained. Even though the laser light has a strong straightness, the laser light spreads to some extent. Therefore, the direction of the light emitted from the semiconductor multilayer structure  10  changes also depending on the variation in the emission surface, the accuracy or variation of parts, and the like. 
     Further, in the distance measurement apparatus  1 , the light emitter  2  is disposed so as to be away from the object to be measured OB as the substrate  21  and the semiconductor multilayer structure  10  loaded on the substrate  21  are closer to the anode wiring  41  and the cathode wiring  42 , which are examples of a supply unit formed on the PCB board  4 . In addition, in the light emitter  2 , the anode wiring  211  and the cathode wiring  212  formed on the substrate  21  are respectively connected to the anode wiring  41  and the cathode wiring  42  of the PCB board  4  at a position farthest from the object to be measured OB on the substrate  21  (that is, position closest to the PCB board  4 ). 
     Accordingly, a connection path for connecting the anode wiring  211  and the cathode wiring  212  formed on the substrate  21  of the light emitter  2  and the anode wiring  41  and the cathode wiring  42  formed on the PCB board  4  can be shortened, which leads to miniaturization of the distance measurement apparatus  1 . 
     In the distance measurement apparatus  1 , the light receiver  3  is disposed on an opposite side (right side in  FIG.  1   ) of the anode wiring  41  and the cathode wiring  42  formed on the PCB board  4  with respect to the light emitter  2 . In this case, the light receiver  3  is less likely to interfere with the anode wiring  41  and the cathode wiring  42  on the PCB board  4 , the power supply that supplies the electric power to the anode wiring  41  and the cathode wiring  42 , or the like. Accordingly, as compared with a case where the light receiver  3  is disposed on the same side (left side in  FIG.  1   ) as the anode wiring  41  and the cathode wiring  42  of the PCB board  4  with respect to the light emitter  2 , the distance between the light emitter  2  and the light receiver  3  can be reduced, which leads to the miniaturization of the distance measurement apparatus  1 . 
     Second Exemplary Embodiment 
     Subsequently, a second exemplary embodiment of the present invention will be described.  FIG.  6    is a diagram showing an example of a configuration of the distance measurement apparatus  1  to which the second exemplary embodiment is applied, and, as in  FIG.  1   , corresponds to a diagram of the distance measurement apparatus  1  as viewed along the lateral direction SD of the semiconductor multilayer structure  10  in the light emitter  2 . In  FIG.  6   , the description of the wiring and the like formed on the PCB board  4  and the substrate  21  is omitted. In the second exemplary embodiment, the same reference numerals are used for the same configurations as the configurations of the first exemplary embodiment, and a detailed description thereof will be omitted here. 
     In the distance measurement apparatus  1  according to the first exemplary embodiment described above, the emission light Lf emitted from the semiconductor multilayer structure  10  is diffused by the diffusion plate  22 , the diffused light is emitted to the object to be measured OB to be measured, and the reflected light from the object to be measured OB to be measured is received by the light receiver  3 . 
     On the contrary, the distance measurement apparatus  1  according to the second exemplary embodiment shown in  FIG.  6    does not have the diffusion plate  22  (refer to  FIG.  1   ) that diffuses the emission light Lf emitted from the semiconductor multilayer structure  10 . In the distance measurement apparatus  1  according to the second exemplary embodiment, the emission light Lf emitted from the semiconductor multilayer structure  10  is directly emitted to the object to be measured OB, and the light receiver  3  receives the reflected light that is specularly reflected by the object to be measured OB. 
     In the distance measurement apparatus  1  according to the second exemplary embodiment, similarly to the first exemplary embodiment, the emission angle θ 1  formed by the emission light Lf emitted from the semiconductor multilayer structure  10  and the substrate  21  and the substrate angle θ 2  formed by the substrate  21  and the light reception surface  32   a  of the light reception sensor  32  satisfy equation (1) described above. 
     Accordingly, in the distance measurement apparatus  1  according to the second exemplary embodiment, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the emission angle θ 1  and the substrate angle θ 2  do not satisfy equation (1). In the distance measurement apparatus  1  according to the second exemplary embodiment, as compared with a case where the emission angle θ 1  and the substrate angle θ 2  do not satisfy equation (1), a distance between the light emitter  2  and the light receiver  3  (distance X described below, refer to  FIG.  6   ) at which the reflected light is incident on the light reception sensor  32  of the light receiver  3  is shortened, which leads to the miniaturization of the distance measurement apparatus  1 . 
     In the distance measurement apparatus  1  shown in  FIG.  6   , the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  is less than 90° (0°&lt;θ 1 +θ 2  &lt;90°). 
     In this case, in the distance measurement apparatus  1 , from the viewpoint of easily receiving the reflected light from the object to be measured OB by the light reception sensor  32  of the light receiver  3 , the light receiver  3  is, for example, preferably disposed adjacent to a side of the light emitter  2  close to the object to be measured OB (right side in  FIG.  6   ) with respect to the light emitter  2 . 
     In the distance measurement apparatus  1  according to the second exemplary embodiment, in a relationship between the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  and the light-receiving viewing angle θr of the light receiver  3 , the following equation (2) is, for example, preferably satisfied. 
       90°−θr&lt;θ1+θ2&lt;90°  (2)
 
     In a case where the sum of the emission angle θ 1  and the substrate angle θ 2  satisfies equation (2), the reflected light from the object to be measured OB easily enters the inside of the light-receiving viewing angle θr of the light receiver  3 . Accordingly, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the sum of the emission angle θ 1  and the substrate angle θ 2  does not satisfy equation (2). 
     Assuming that a distance between the semiconductor multilayer structure  10  of the light emitter  2  and the object to be measured OB is a distance L 1  and a distance between the light reception surface  32   a  of the light receiver  3  and the object to be measured OB is a distance L 2 , the distance X along the light reception surface  32   a  between the semiconductor multilayer structure  10  of the light emitter  2  and the light reception surface  32   a  of the light receiver  3 , for example, preferably satisfies the following equation (3). 
         X =( L 1+ L 2)×tan(θ1+θ2)   (3)
 
     In a case where the distance X satisfies equation (3), in the distance measurement apparatus  1  according to the second exemplary embodiment, the light reception surface  32   a  of the light reception sensor  32  is easily disposed in the advancing direction of the reflected light from the object to be measured OB. Accordingly, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the distance X does not satisfy equation (3). 
     The distance L 1  is a distance along a direction perpendicular to the light reception surface  32   a  of the light receiver  3  between a center of the semiconductor multilayer structure  10  in the longitudinal direction LD (refer to  FIG.  2   ) and the object to be measured OB (distance along upper-lower direction in  FIG.  6   ). The distance L 2  is a distance along a direction perpendicular to the light reception surface between a center of the light reception surface  32   a  and the object to be measured OB (distance along upper-lower direction in  FIG.  6   ). Further, the distance X is a distance along the light reception surface  32   a  between the center of the semiconductor multilayer structure  10  and the center of the light reception surface  32   a  (distance along left-right direction in  FIG.  6   ). 
     Subsequently, a modification example of the distance measurement apparatus  1  according to the second exemplary embodiment will be described.  FIG.  7    is a diagram showing the modification example of the distance measurement apparatus  1  to which the second exemplary embodiment is applied, and, as in  FIG.  6   , is a diagram of the distance measurement apparatus  1  as viewed along the lateral direction SD of the semiconductor multilayer structure  10  in the light emitter  2 . In  FIG.  7   , the same reference numerals are used for the same configurations as the configurations of the distance measurement apparatus  1  shown in  FIG.  6   . 
     In the distance measurement apparatus  1  shown in  FIG.  6   , the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  is less than 90°, whereas in the distance measurement apparatus  1  of the modification example shown in  FIG.  7   , the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  is 90° or more and less than 180° (90°≤θ 1 +θ&lt;80°). 
     In the distance measurement apparatus  1  shown in  FIG.  7   , from the viewpoint of easily receiving the reflected light from the object to be measured OB by the light reception sensor  32  of the light receiver  3 , the light receiver  3  is, for example, preferably disposed adjacent to a side of the light emitter  2  far from the object to be measured OB (left side in  FIG.  7   ) with respect to the light emitter  2 . 
     Also in the distance measurement apparatus  1  shown in  FIG.  7   , the emission angle θ 1  formed by the emission light Lf emitted from the semiconductor multilayer structure  10  and the substrate  21  and the substrate angle θ 2  formed by the substrate  21  and the light reception surface  32   a  of the light reception sensor  32  satisfy equation (1) described above. 
     Accordingly, in the distance measurement apparatus  1  according to the second exemplary embodiment, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the emission angle θ 1  and the substrate angle θ 2  do not satisfy equation (1). 
     In the distance measurement apparatus  1  shown in  FIG.  7   , in a relationship between the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  and the light-receiving viewing angle er of the light receiver  3 , the following equation (4) is, for example, preferably satisfied. 
       90°≤θ 1 +θ 2 &lt;90°+θr   (4)
 
     In a case where the sum of the emission angle θ 1  and the substrate angle θ 2  satisfies equation (4), the reflected light from the object to be measured OB easily enters the inside of the light-receiving viewing angle er of the light receiver  3 . Accordingly, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the sum of the emission angle θ 1  and the substrate angle θ 2  does not satisfy equation (4). 
     As in the example shown in  FIG.  6   , assuming that a distance between the semiconductor multilayer structure  10  of the light emitter  2  and the object to be measured OB is a distance L 1  and a distance between the light reception surface  32   a  of the light receiver  3  and the object to be measured OB is a distance L 2 , the distance X along the light reception surface  32   a  between the semiconductor multilayer structure  10  of the light emitter  2  and the light reception surface  32   a  of the light receiver  3 , for example, preferably satisfies equation (3) described above. 
     In a case where the distance X satisfies equation (3), the light reception surface  32   a  of the light reception sensor  32  is easily disposed in the advancing direction of the reflected light from the object to be measured OB also in the distance measurement apparatus  1  shown in  FIG.  7   . Accordingly, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where the distance X does not satisfy equation (3). 
     As described above, as in the distance measurement apparatus  1  shown in  FIGS.  6  and  7   , even in a case where the light emitter  2  does not include the diffusion plate  22  (refer to  FIG.  1   ) and the light receiver  3  receives the reflected light that is emitted from the light emitter  2  and is specularly reflected by the object to be measured OB, equation (1) described above is satisfied. Therefore, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB. 
     Further, in the distance measurement apparatus  1  shown in  FIGS.  6  and  7   , in a case where the relationships, shown in equations (2) and (4) described above, between the sum (θ 1 +θ 2 ) of the emission angle θ 1  and the substrate angle θ 2  and the light-receiving viewing angle θr of the light receiver  3  are summarized, the following equation (5) is, for example, preferably satisfied. 
       90°−θr&lt;θ 1 +θ 2 &lt;90°+θr   (5)
 
     In the distance measurement apparatus  1 , in a case where equation (5) is satisfied, the light reception sensor  32  of the light receiver  3  easily receives the reflected light from the object to be measured OB, as compared with a case where equation (5) is not satisfied. 
     Third Exemplary Embodiment 
     By the way, in the distance measurement apparatus  1 , in a case where the semiconductor multilayer structure  10  having the longitudinal direction LD is used to emit the light to the object to be measured OB, there may be a difference in an optical path length, between one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD, until the light emitted from the semiconductor multilayer structure  10  reaches the object to be measured OB. In addition, in the distance measurement apparatus  1 , there may be a difference in a time, between one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD, until the light emitted from the semiconductor multilayer structure  10  reaches the object to be measured OB. In this case, there may be an error in an output result of the light reception sensor  32  that receives the reflected light from the object to be measured OB. 
       FIG.  8    is a diagram for describing the optical path length and the like until the light emitted from the semiconductor multilayer structure  10  reaches the object to be measured OB in the distance measurement apparatus  1 . The distance measurement apparatus  1  shown in  FIG.  8    has the same configuration as the distance measurement apparatus  1  shown in  FIG.  6   . 
     As shown in  FIG.  8   , in the distance measurement apparatus  1 , assuming that a length of the semiconductor multilayer structure  10  along the longitudinal direction LD is Z, a difference Δd 1  in the optical path length until the light emitted from one end (left side in  FIG.  8   ) and the other end (right side in  FIG.  8   ) of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB is expressed by the following equation (6). 
       Δ d 1= Z ×cos θ1− Z ×sin θ1/tan(θ1+θ2)   (6)
 
     The time difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB is expressed as Δd 1 /c, where c is the speed of light. 
       FIG.  9    is a diagram for describing a configuration of the distance measurement apparatus  1  (refer to  FIG.  8   ) to which the third exemplary embodiment is applied, and is a diagram showing the configuration between the light emitter  2  and the object to be measured OB. 
     In the distance measurement apparatus  1  according to the third exemplary embodiment, from the viewpoint of reducing the time difference Δd 1 /c until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB, a prism  9  which is an example of a light adjustment unit is provided between the light emitter  2  and the object to be measured OB. 
     Specifically, as shown in  FIG.  9   , the prism  9  includes an incident surface  91  that faces the semiconductor multilayer structure  10  and is incident with the light emitted from the semiconductor multilayer structure  10  and an emission surface  92  that forms an inclination angle θ 3  (0°&lt;θ 3  &lt;90°) set in advance with respect to the incident surface  91  and emits light passing through the prism  9 . In addition, as shown in  FIG.  9   , the prism  9  has a triangular cross-sectional shape on a plane of the semiconductor multilayer structure  10  perpendicular to the lateral direction SD. 
     In the distance measurement apparatus  1  according to the present exemplary embodiment, the prism  9  is disposed such that the emission light Lf emitted from the semiconductor multilayer structure  10  is perpendicularly incident on the incident surface  91 . 
     A difference in the optical path length in which the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD and entering the prism  9  advances in the prism  9  (difference in optical path length from the incident surface  91  to the emission surface  92 ) Δd 2  is expressed by the following equation (7). 
       Δ d 2= Z ×sin θ1×tan θ3   (7)
 
     A speed of the light advancing in the prism  9  is c/n, where n is the refractive index of the prism  9 . Therefore, a time difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD and entering the prism  9  reaches the emission surface  92  from the incident surface  91  is expressed as Δd 2 ×n/c. 
     In the present exemplary embodiment, a shape of the prism  9  (angle Θ 3  formed by the incident surface  91  and the emission surface  92  of the prism  9 ) and the refractive index n of the prism  9  are, for example, preferably determined such that Δd 1 =Δd 2 ×n. 
     Accordingly, in the distance measurement apparatus  1 , the optical path length difference and the time difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB are reduced, and thus the error in an output result of the light reception sensor  32  that receives the reflected light from the object to be measured OB is less likely to occur. 
     In the distance measurement apparatus  1 , even in a case where the prism  9  satisfying Δd 1 =Δd 2 ×n described above is disposed between the semiconductor multilayer structure  10  and the object to be measured OB, the optical path length difference and the time difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB may remain. Although a detailed calculation is omitted, from the viewpoint of more reducing the optical path length difference and the time difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB, for example, selection of the prism  9  satisfying the following equation (8) is more preferable. 
         Z ×cos θ1+Δ d 2×cos θ4/sin θ3=Δ d 2× n+Δd 2×sin θ4/{sin θ3×tan(θ4+θ5)}  (8)
 
     In equation (8), an angle θ 4  is formed by the emission surface  92  of the prism  9  and the light refracted by the prism  9  and emitted from the prism  9 . In equation (8), an angle θ 5  is formed by the light reception surface  32   a  of the light receiver  3  (both refer to  FIG.  6   ) and the emission surface  92  of the prism  9 . 
     In the third exemplary embodiment, the distance measurement apparatus  1  has been described as an example in which the emission light Lf emitted from the semiconductor multilayer structure  10  is directly emitted to the object to be measured OB, and the light receiver  3  receives the reflected light that is specularly reflected by the object to be measured OB. However, the present invention is not limited thereto. The prism  9  according to the third exemplary embodiment may be applied to a distance measurement apparatus  1  provided with the light emitter  2  including the diffusion plate  22 . In this case, for example, the prism  9  may be provided between the semiconductor multilayer structure  10  of the light emitter  2  and the diffusion plate  22 . 
     In the third exemplary embodiment, the prism  9  having the triangular cross-sectional shape is used as an example of an optical path length adjustment unit that reduces the optical path length difference until the light emitted from one end and the other end of the semiconductor multilayer structure  10  in the longitudinal direction LD reaches the object to be measured OB. However, the prism  9  having a different shape may be used, or an optical component other than the prism  9  may be used. The optical path length adjustment unit may be formed by combining a plurality of optical components and the like. 
     Fourth Exemplary Embodiment 
     Subsequently, a fourth exemplary embodiment of the present invention will be described.  FIG.  10    is a diagram showing an example of a configuration of the distance measurement apparatus  1  to which the fourth exemplary embodiment is applied, and, as in  FIG.  1   , corresponds to a diagram of the distance measurement apparatus  1  as viewed along the lateral direction SD of the semiconductor multilayer structure  10  in the light emitter  2 . In  FIG.  10   , the description of the wiring and the like formed on the PCB board  4  and the substrate  21  is omitted. In  FIG.  10   , although the description of the object to be measured OB (refer to  FIG.  1   ) is omitted, the object to be measured OB is disposed at an upper part of the figure with respect to the distance measurement apparatus  1  as in  FIG.  1   . Further, in the fourth exemplary embodiment, the same reference numerals are used for the same configurations as the configurations of the first exemplary embodiment, and a detailed description thereof will be omitted here. 
     In the first exemplary embodiment described above, the PCB board  4  is loaded on the pedestal  5 , and the angle adjustment member  6  (refer to  FIG.  1   ) is provided on the PCB board  4 . As a result, the substrate  21  of the light emitter  2  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  form the substrate angle θ 2 . 
     On the contrary, in the distance measurement apparatus  1  according to the fourth exemplary embodiment, the pedestal  51  is included as an example of a support member that supports the light emitter  2  such that the substrate  21  of the light emitter  2  and the light reception surface  32   a  of the light receiver  3  form the substrate angle θ 2 , and the light receiver  3  is supported by the pedestal  51  together with the light emitter  2 . 
     Specifically, as shown in  FIG.  10   , the pedestal  51  includes a flat surface  51   a  parallel to the light reception surface  32   a  in the light reception sensor  32  and an inclined surface  51   b  that projects from the flat surface  51   a  toward the object to be measured OB and forms an angle set in advance (substrate angle θ 2 ) with respect to the flat surface  51   a.  In the distance measurement apparatus  1  according to the fourth exemplary embodiment, the light receiver  3  is loaded on the flat surface  51   a,  and the substrate  21  of the light emitter  2  is loaded on the inclined surface  51   b.  As a result, the substrate  21  and the light reception surface  32   a  in the light reception sensor  32  of the light receiver  3  form the substrate angle θ 2 . 
     As described above, in the distance measurement apparatus  1  according to the fourth exemplary embodiment, the light emitter  2  and the light receiver  3  are supported by the common pedestal  51 . As a result, the number of alignments for adjusting the light emitter  2  and the light receiver  3  to have a positional relationship set in advance is reduced. Accordingly, a positional accuracy between the light emitter  2  and the light receiver  3  is improved, and the light receiver  3  easily receives the reflected light emitted from the light emitter  2  and reflected by the object to be measured OB. 
     In the distance measurement apparatus  1  shown in  FIG.  10   , the light emitter  2  is disposed such that the substrate  21  and the semiconductor multilayer structure  10  loaded on the substrate  21  are closer to the object to be measured OB as the substrate  21  and the semiconductor multilayer structure  10  are farther from the light receiver  3 . In other words, in the distance measurement apparatus  1  shown in  FIG.  10   , the light receiver  3  is disposed adjacent to a side of the light emitter  2  far from the object to be measured OB (left side in  FIG.  10   ) with respect to the light emitter  2 . 
     With such a configuration, the reflected light from the object to be measured OB is prevented from being blocked by the inclined surface  51   b  or the like on which the light emitter  2  or the substrate  21  of the light emitter  2  is loaded. Further, a shadow is prevented from being formed on the light reception surface  32   a  of the light receiver  3  due to the inclined surface  51   b  or the like on which the light emitter  2  or the substrate  21  of the light emitter  2  is loaded. 
     Subsequently, a modification example of the distance measurement apparatus  1  according to the fourth exemplary embodiment will be described.  FIG.  11    is a diagram showing a modification example of the distance measurement apparatus  1  to which the fourth exemplary embodiment is applied, and, as in  FIG.  10   , is a diagram of the distance measurement apparatus  1  as viewed along the lateral direction SD of the semiconductor multilayer structure  10  in the light emitter  2 . In  FIG.  11   , the same reference numerals are used for the same configurations as the configurations of the distance measurement apparatus  1  shown in  FIG.  10   . In  FIG.  11   , although the description of the object to be measured OB (refer to  FIG.  1   ) is omitted, the object to be measured OB is disposed at an upper part of the figure with respect to the distance measurement apparatus  1  as in  FIG.  1   . 
     In the distance measurement apparatus  1  shown in  FIG.  11   , the pedestal  51  includes the inclined surface  51   b  that projects from the flat surface  51   a  toward the object to be measured OB and forms the angle set in advance (substrate angle θ 2 ) with respect to the flat surface  51   a,  as in the distance measurement apparatus  1  shown in  FIG.  10   . In the distance measurement apparatus  1  shown in  FIG.  11   , the substrate  21  of the light emitter  2  is loaded on the inclined surface  51   b  of the pedestal  5 . As a result, the light emitter  2  and the light receiver  3  are both supported by the pedestal  51 . 
     Accordingly, also in the distance measurement apparatus  1  shown in  FIG.  11   , the number of alignments for adjusting the light emitter  2  and the light receiver  3  to have a positional relationship set in advance is reduced. An alignment accuracy between the light emitter  2  and the light receiver  3  is improved, and the light receiver  3  easily receives the reflected light emitted from the light emitter  2  and reflected by the object to be measured OB. 
     In the distance measurement apparatus  1  shown in  FIG.  11   , the pedestal  51  includes a projection portion  51   c  that projects from the flat surface  51   a  toward the object to be measured OB and has an upper surface, which is closest to the object to be measured OB, formed in parallel with the flat surface  51   a.  In the distance measurement apparatus  1  shown in  FIG.  11   , the light receiver  3  is loaded on the projection portion  51   c  of the pedestal  51 . 
     Accordingly, in the distance measurement apparatus  1  shown in  FIG.  11   , the light receiver  3  is provided at a position closer to the object to be measured OB than the light emitter  2 . In this example, the light reception surface  32   a  of the light receiver  3  is provided at a position closer to the object to be measured OB than the semiconductor multilayer structure  10  of the light emitter  2 . With such a configuration, the reflected light from the object to be measured OB is prevented from being blocked by the inclined surface  51   b  or the like on which the light emitter  2  or the substrate  21  of the light emitter  2  is loaded. Further, a shadow is prevented from being formed on the light reception surface  32   a  of the light receiver  3  due to the inclined surface  51   b  or the like on which the light emitter  2  or the substrate  21  of the light emitter  2  is loaded. 
     Fifth Exemplary Embodiment 
     Subsequently, another form of the semiconductor multilayer structure  10  in the light emitter  2  will be described.  FIGS.  12  and  13    are views of configurations of the semiconductor multilayer structure  10  to which the fifth exemplary embodiment is applied.  FIG.  12    is a plan view of the semiconductor multilayer structure  10  to which the fifth exemplary embodiment is applied, and  FIG.  13    is a cross-sectional view taken along a line XIII-XIII shown in  FIG.  12   . 
     The semiconductor multilayer structure  10  according to the fifth exemplary embodiment is a form in which, for example, a light emitting element such as a VCSEL is integrally formed in a region where the optical coupling portion  11  of the semiconductor multilayer structure  10  according to the first exemplary embodiment is disposed. The same reference numerals are used for the same configurations as the configurations of the semiconductor multilayer structure  10  according to the first exemplary embodiment, and a detailed description thereof will be omitted. 
     As shown in  FIGS.  12  and  13   , the semiconductor multilayer structure  10  is divided into a seed light unit  13  and the light amplification unit  12 . As shown in  FIG.  13   , the semiconductor multilayer structure  10  includes the lower DBR layer  122 , the active layer  123 , the oxidization constriction layer  124 , a p-DBR layer  131 , a phase control layer  132 , an i-DBR layer  133 , an insulation portion  134 , and P electrodes  126 - 1  and  126 - 2 , which are stacked on a front surface of the base layer  120 , and the N electrode  121  stacked on the back surface of the base layer  120 . 
     The seed light unit  13  is a portion that generates the seed light Ls and is configured as the VCSEL in the present exemplary embodiment. As shown in  FIG.  13   , the seed light Ls generated from the seed light unit  13  propagates toward the light amplification unit  12 . 
     The p-DBR layer  131  and the i-DBR layer  133  are layers corresponding to the upper DBR layer  125  in the semiconductor multilayer structure  10  according to the first exemplary embodiment. The p-DBR layer  131  is a p-type containing a p-type impurity, and the i-DBR layer  133  does not contain an impurity. 
     The phase control layer  132  is formed between the p-DBR layer  131  and the i-DBR layer  133  and is a layer that adjusts a relationship between a wavelength of the seed light Ls and a perpendicular resonance wavelength in the light amplification unit  12 . In the present exemplary embodiment, the phase control layer  132  is formed by using, for example, a silicon oxide film (SiO 2 ), a silicon nitride film (SiON), or GaAs. In the present exemplary embodiment, the wavelength of the seed light Ls is controlled by etching the phase control layer  132  after the formation thereof to reduce a film thickness of the phase control layer  132 , as an example. 
     The insulation portion  134  is a layer that electrically insulates the seed light unit  13  from the light amplification unit  12  and is formed by ion implantation, as an example, in the present exemplary embodiment. 
     The P electrode  126 - 1  is a P electrode of the light amplification unit  12 , and the P electrode  126 - 2  is a P electrode of the seed light unit  13 . 
     The semiconductor multilayer structure  10  according to the present exemplary embodiment having the above configuration is a form in which the light source of the seed light Ls is integrated into the structure in the semiconductor multilayer structure  10  according to the first exemplary embodiment. The semiconductor multilayer structure  10  according to the present exemplary embodiment has the same functions and actions as the semiconductor multilayer structure  10  according to the first exemplary embodiment. With the semiconductor multilayer structure  10  according to the present exemplary embodiment, an additional light source is not required except for the semiconductor multilayer structure  10 , and thus the function of the light emission unit that emits the light in the light emitter  2  is realized by one chip. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.