阅读说明：本技术 发光装置、光学装置、计测装置及信息处理装置 (Light emitting device, optical device, measuring device, and information processing device ) 是由 井口大介 逆井一宏 皆见健史 于 2020-11-09 设计创作，主要内容包括：本发明提供发光装置、光学装置、计测装置及信息处理装置。发光装置具备平面形状为四边形的激光元件阵列、供给使所述激光元件阵列发光的电流的1对电容器、以及将使所述激光元件阵列发光的电流导通/截止而进行驱动的驱动部,在所述激光元件阵列的对置的2个边侧,夹着该激光元件阵列而配置有1对所述电容器,在该激光元件阵列的另一边侧配置有所述驱动部。(The invention provides a light emitting device, an optical device, a measuring device and an information processing device. The light emitting device includes a laser element array having a rectangular planar shape, 1 pair of capacitors for supplying a current for causing the laser element array to emit light, and a driving unit for driving the laser element array by turning on/off the current for causing the laser element array to emit light, wherein the 1 pair of capacitors are disposed on 2 sides of the laser element array facing each other with the laser element array interposed therebetween, and the driving unit is disposed on the other side of the laser element array.)

1. A light-emitting device is provided with:

a laser element array having a quadrangular planar shape;

1 pair of capacitors for supplying a current for causing the laser element array to emit light; and

a drive unit that drives the laser element array by turning on/off a current for emitting light,

on the 2 opposite sides of the laser element array, 1 pair of the capacitors are disposed with the laser element array therebetween, and the driving section is disposed on the other side of the laser element array.

2. The light emitting device according to claim 1,

the drive unit includes a drive element for turning on/off a current for causing the laser element array to emit light,

the laser element array and the driving element are connected so as to be driven by a low-side drive provided on the downstream side of the current path in the laser element array.

3. The light-emitting device according to claim 1 or 2,

the light-emitting device includes a circuit board on which the laser element array and the driver are mounted,

the laser element array and the driving unit are disposed on the surface of the circuit board,

the reference potential wiring is provided in a layer shape on the circuit board.

4. The light emitting device according to claim 3,

the light emitting device includes a heat dissipation base material having a thermal conductivity greater than that of the circuit board,

the laser element array is arranged on the heat dissipation base material, and the heat dissipation base material is carried on the circuit substrate.

5. The light emitting device according to claim 4,

the laser element array includes a plurality of surface-emitting laser elements connected in parallel,

a cathode electrode is provided on the back surface side, and an anode electrode is provided on the front surface side.

6. The light emitting device according to claim 5,

the heat dissipation base material is provided with a front side cathode wiring connected to the cathode electrode of the laser element array on the front side, and is provided with a pair of front side anode wirings 1 connected to the anode electrode of the laser element array so as to sandwich the front side cathode wiring,

the heat dissipation substrate is provided with a back-side cathode wiring and 1 pair of back-side anode wirings on the back side, wherein the back-side cathode wiring and the 1 pair of back-side anode wirings are respectively provided corresponding to the front-side cathode wiring and the 1 pair of front-side anode wirings, and are electrically connected to the front-side cathode wiring and the 1 pair of front-side anode wirings.

7. The light-emitting device according to any one of claims 1 to 6,

the light-emitting device includes a diffusion member that diffuses and emits light emitted from the laser element array.

8. The light-emitting device according to any one of claims 1 to 6,

the light emitting device includes a diffraction member that diffracts and emits light emitted from the laser element array.

9. The light-emitting device according to any one of claims 1 to 8,

the light emitting device includes a light quantity monitoring light receiving element that monitors a light quantity of the laser element array.

10. An optical device, comprising:

the light-emitting device according to any one of claims 1 to 8; and

and a light receiving unit that receives reflected light emitted from the laser element array included in the light emitting device and reflected by an object to be measured.

11. A measurement device is provided with:

the optical device of claim 10; and

and a distance determining unit that determines a distance to the object based on a time from emission from the laser element array provided in the optical device to reception of the light by the light receiving unit.

12. An information processing apparatus, comprising:

a measuring device according to claim 11; and

and an authentication processing unit that performs authentication processing relating to use of the measurement device on the basis of a determination result of the distance determination unit provided in the measurement device.

Technical Field

The invention relates to a light emitting device, an optical device, a measuring device and an information processing device.

Background

Jp 2008-252129 a describes a light-emitting device including a ceramic substrate having light-transmitting properties, a light-emitting element mounted on a surface of the ceramic substrate, a wiring pattern for supplying power to the light-emitting element, and a metalized layer made of a metal having light-reflecting properties, the metalized layer being formed inside the ceramic substrate so as to reflect light emitted from the light-emitting element.

Disclosure of Invention

Problems to be solved by the invention

According to the so-called tof (time of flight) method based on the flight time of light, when measuring the three-dimensional shape of an object to be measured, it is required that the rise time of light emission of a light source is short. This is effective in reducing the effective inductance of the path through which the current for light emission flows.

The present disclosure provides a light emitting device and the like, in which the effective inductance of a path through which a current for light emission flows is reduced as compared with a case where 1 pair of capacitors are disposed on both sides of a light source with the light source interposed therebetween and a driving portion is not disposed on the other side of the light source.

Means for solving the problems

According to the 1 st aspect of the present disclosure, there is provided a light-emitting device including: a laser element array having a quadrangular planar shape; 1 pair of capacitors for supplying a current for causing the laser element array to emit light; and a driving unit that drives the laser element array by turning on/off a current for emitting light, wherein 1 pair of the capacitors are disposed on 2 sides of the laser element array facing each other with the laser element array interposed therebetween, and the driving unit is disposed on the other side of the laser element array.

According to claim 2 of the present disclosure, the driving unit includes a driving element that turns on/off a current for emitting light from the laser element array, and the laser element array and the driving element are connected so as to be driven by a low-side drive provided on a downstream side of a current path in the laser element array.

According to claim 3 of the present disclosure, the light-emitting device includes a circuit board on which the laser element array and the driver are mounted, the laser element array and the driver are disposed on a surface of the circuit board, and the reference potential wiring is provided in a layer shape on the circuit board.

According to claim 4 of the present disclosure, the light-emitting device includes a heat dissipation base material having a thermal conductivity greater than that of the circuit board, the laser element array is provided on the heat dissipation base material, and the heat dissipation base material is mounted on the circuit board.

According to claim 5 of the present disclosure, the laser element array includes a plurality of surface-emitting laser elements connected in parallel, a cathode electrode is provided on the back surface side, and an anode electrode is provided on the front surface side.

According to claim 6 of the present disclosure, the heat dissipation base material is provided with a front side cathode wiring connected to a cathode electrode of the laser element array on a front side, and is provided with 1 pair of front side anode wirings connected to an anode electrode of the laser element array so as to sandwich the front side cathode wiring, the heat dissipation base material is provided with a back side cathode wiring and 1 pair of back side anode wirings on a back side, and the back side cathode wiring and the 1 pair of back side anode wirings are provided corresponding to the front side cathode wiring and the 1 pair of front side anode wirings, respectively, and are electrically connected to the front side cathode wiring and the 1 pair of front side anode wirings.

According to claim 7 of the present disclosure, the light-emitting device includes a diffusing member that diffuses and emits light emitted from the laser element array.

According to the 8 th aspect of the present disclosure, the light emitting device includes a diffraction member that diffracts light emitted from the laser element array to be emitted.

According to the 9 th aspect of the present disclosure, the light emitting device includes a light quantity monitoring light receiving element that monitors the light quantity of the laser element array.

According to a 10 th aspect of the present disclosure, there is provided an optical device including: the light emitting device; and a light receiving unit that receives reflected light emitted from the laser element array included in the light emitting device and reflected by an object to be measured.

According to an 11 th aspect of the present disclosure, there is provided a measurement device including: the optical device; and a distance determining unit that determines a distance to the object to be measured based on a time from emission from the laser element array provided in the optical device to reception of light by the light receiving unit.

According to a 12 th aspect of the present disclosure, there is provided an information processing apparatus including: the measuring device; and an authentication processing unit that performs authentication processing relating to use of the measurement device on the basis of a determination result of the distance determination unit provided in the measurement device.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above aspect 1, the effective inductance of the path through which the current for light emission flows is reduced as compared with a case where 1 pair of capacitors is not disposed on the 2 side of the light source with the light source interposed therebetween and the driving section is disposed on the other side of the light source.

According to the above-described aspect 2, the laser element array can be driven at a higher speed than the case where the low-side drive is not used.

According to the above aspect 3, the return current path is configured to be shorter than in the case where the reference potential wiring is not provided in a layer shape.

According to the above-mentioned aspect 4, heat generated by the laser element array is easily dissipated as compared with the case where the heat dissipation base material is not provided.

According to the above aspect 5, the emission intensity from the laser element array can be increased as compared with the case where the laser elements are not connected in parallel.

According to the above-mentioned aspect 6, the effective inductance of the path through which the current for light emission flows is reduced as compared with the case where the surface-side anode wiring 1 is not provided so as to sandwich the surface-side cathode wiring.

According to the above-mentioned aspect 7, a wider irradiation region is obtained as compared with the case where the diffusion member is not provided.

According to the above-mentioned aspect 8, a wider irradiation region is obtained as compared with the case where the diffraction element is not provided.

According to the above-mentioned aspect 9, variation in the light quantity of the laser element array is suppressed as compared with the case where the light receiving element for monitoring the light quantity is not provided.

According to the 10 th aspect, there is provided an optical device capable of acquiring a signal corresponding to a distance.

According to the 11 th aspect, there is provided a measuring device capable of measuring a distance to an object to be measured.

According to the above-described 12 th aspect, there is provided an information processing apparatus having an authentication process performed based on a specified distance.

Drawings

Fig. 1 is a diagram showing an example of an information processing apparatus.

Fig. 2 is a block diagram illustrating the configuration of the information processing apparatus.

Fig. 3 is a top view of a light source.

Fig. 4 is a diagram illustrating a cross-sectional configuration of 1 VCSEL in the light source.

Fig. 5 is a diagram illustrating an example of the light diffusion member. Fig. 5 (a) is a plan view, and fig. 5 (b) is a cross-sectional view taken along line VB-VB of fig. 5 (a).

Fig. 6 is a diagram showing an example of an equivalent circuit in the case where the light source is driven by low-side driving.

Fig. 7 is a diagram illustrating a light-emitting device to which the present embodiment is applied. Fig. 7 (a) is a plan view, and fig. 7 (b) is a sectional view taken along line VIIB-VIIB of fig. 7 (a).

Fig. 8 is a diagram schematically illustrating a current path in the light emitting device.

Fig. 9 is a diagram illustrating a light-emitting device as a modification to the light-emitting device to which the present embodiment is applied. Fig. 9 (a) is a plan view, and fig. 9 (b) is a sectional view taken along the IXB-IXB line of fig. 9 (a).

Fig. 10 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of a heat dissipation base material in a light-emitting device as a modification. Fig. 10 (a) shows the front-side wiring, and fig. 10 (b) shows the rear-side wiring.

Fig. 11 is a diagram illustrating a light-emitting device of comparative example 1 to which the present embodiment is not applied. Fig. 11 (a) is a plan view, and fig. 11 (b) is a sectional view taken along line XIB-XIB of fig. 11 (a).

Fig. 12 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of the heat dissipation base material in the light-emitting device of comparative example 1. Fig. 12 (a) shows the front-side wiring, and fig. 12 (b) shows the rear-side wiring.

Fig. 13 is a diagram schematically illustrating a current path in the light-emitting device of comparative example 1.

Fig. 14 is a diagram illustrating a light-emitting device of comparative example 2 to which the present embodiment is not applied. Fig. 14 (a) is a plan view, and fig. 14 (b) is a sectional view taken along the XIVB-XIVB line of fig. 14 (a).

Fig. 15 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of a heat dissipation base material in a light-emitting device as comparative example 2. Fig. 15 (a) shows the front-side wiring, and fig. 15 (b) shows the rear-side wiring.

Fig. 16 is a diagram schematically illustrating a current path in the light-emitting device of comparative example 2.

Detailed Description

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

A measuring device for measuring a three-dimensional shape of an object to be measured includes a device for measuring a three-dimensional shape by a so-called tof (time of flight) method based on a flight time of light. In the ToF method, the time from the timing when light is emitted from a light emitting device provided in a measurement device to the timing when the irradiated light is reflected by an object to be measured and received by a three-dimensional sensor (hereinafter, referred to as a 3D sensor) provided in the measurement device is measured, and the three-dimensional shape of the object to be measured is determined from the measured three-dimensional shape. In addition, an object to be measured for a three-dimensional shape is represented as a measured object. A three-dimensional shape is sometimes referred to as a three-dimensional image. Note that the table for measuring a three-dimensional shape may be referred to as three-dimensional measurement, 3D measurement, or 3D sensing.

Such a measurement device is mounted on a portable information processing device or the like, and is used for authentication of a face of a user to be accessed. Conventionally, in portable information processing devices and the like, methods of authenticating users using passwords, fingerprints, irises, and the like have been used. In recent years, authentication methods with higher security have been demanded. On the other hand, a measurement device for measuring a three-dimensional shape is mounted on the portable information processing device. That is, the three-dimensional shape of the face of the user who performs access is acquired, whether or not access is permitted is identified, and use of the device (portable information processing device) is permitted only when the user is authenticated as a user who permits access.

Here, a case where the information processing device is a portable information processing terminal will be described as an example, and the user is authenticated by recognizing the shape of the face captured as a three-dimensional shape. The information processing device can be applied to an information processing device such as a Personal Computer (PC) other than the portable information processing terminal.

In the ToF method, the time from the timing when light is emitted from the light emitting device provided in the measurement device to the timing when the irradiated light is reflected by the measurement object and received by the 3D sensor provided in the measurement device is measured, and therefore, the rise time of the light emission of the light source is required to be short. The shorter the rise time of light emission, the higher the measurement accuracy. The smaller the effective inductance of the current path for supplying the current for light emission to the light source, the shorter the rise time of light emission of the light source. That is, as the effective inductance of the current path is larger, it becomes more difficult to flow a current of a high frequency (hereinafter referred to as a high frequency), and the rise time of the current for light emission of the light source becomes longer. The rise time of light emission is a rise time of a current flowing for light emission, and is, for example, a time from a timing when a current for light emission starts to rise until the light emission reaches 90% of the maximum light amount.

The configuration, function, method, and the like described in the present embodiment can also be applied to a case where an object other than the face is regarded as an object and the object is recognized from the measured three-dimensional shape. Such a measurement device is also applied to a case where the three-dimensional shape of the object to be measured is continuously measured, such as Augmented Reality (AR). The distance to the object to be measured is not limited. In the face authentication, light may be irradiated from a light source to a face located at a short distance, but in augmented reality or the like, light is required to be irradiated to an object located at a longer distance from the face. Therefore, the light source is required to have a large light amount.

The structures, functions, methods, and the like described in the following embodiments can be applied to face authentication and measurement of a three-dimensional shape of an object to be measured other than augmented reality.

(information processing apparatus 1)

Fig. 1 is a diagram showing an example of the information processing apparatus 1. As described above, the information processing device 1 is, for example, a portable information processing terminal.

The information processing apparatus 1 includes a user interface unit (hereinafter, UI unit) 2 and an optical device 3 for measuring a three-dimensional shape. The UI unit 2 is configured by integrating, for example, a display device that displays information to a user and an input device that inputs an instruction for information processing by a user operation. The display device is, for example, a liquid crystal display or an organic EL display, and the input device is, for example, a touch panel.

The optical device 3 includes a light-emitting device 4 and a 3D sensor 5. The light emitting device 4 emits light toward the object to be measured, and in this example, emits light toward the face. The 3D sensor 5 acquires light emitted from the light emitting device 4 and reflected by the surface portion to return. Here, the three-dimensional shape is measured by a so-called ToF method based on the time of flight of light. Then, the three-dimensional shape of the face is determined from the three-dimensional shape. Then, whether or not access is permitted is identified based on the three-dimensional shape of the determined face, and in the case where the user who permits access is authenticated, use of the information processing apparatus 1 is permitted. As described above, the three-dimensional shape may be measured using the object other than the face. The 3D sensor 5 is an example of a light receiving portion.

The information processing apparatus 1 is configured as a computer including a CPU, a ROM, a RAM, and the like. In addition, the ROM includes a nonvolatile rewritable memory such as a flash memory. Then, the information processing apparatus 1 operates and executes various information processes by expanding the programs and constants stored in the ROM into the RAM and executing the programs by the CPU.

Fig. 2 is a block diagram illustrating the configuration of the information processing apparatus 1.

The information processing apparatus 1 includes the optical apparatus 3, a measurement control unit 8, and a system control unit 9. As described above, the optical device 3 includes the light-emitting device 4 and the 3D sensor 5. The measurement control unit 8 controls the optical device 3. The measurement control unit 8 includes a three-dimensional shape specifying unit 81. The system control unit 9 controls the entire information processing apparatus 1 as a system. The system control unit 9 includes an authentication processing unit 91. The system control unit 9 is connected to a UI unit 2, a speaker 92, a two-dimensional camera (2D camera in fig. 2) 93, and the like.

The light-emitting device 4 included in the optical device 3 includes a circuit board 10, a light source 20, a light-diffusing member 30, a light-quantity-monitoring light-receiving element (hereinafter, referred to as PD.) 40, a driving unit 50, a holding unit 60, and capacitors 71A, 71B, 72A, and 72B. The capacitors 71A and 71B are capacitors having a reduced equivalent Series inductance ESL (equivalent Series inductance), and the capacitors 72A and 72B are capacitors having a larger equivalent Series inductance ESL than the capacitors 71A and 71B (hereinafter referred to as non-low ESL capacitors). When the capacitors 71A and 71B are not distinguished, they are referred to as a capacitor 71, and when the capacitors 72A and 72B are not distinguished, they are referred to as a capacitor 72. The light emitting device 4 may include a passive element such as a resistor element or another capacitor in order to operate the driving unit 50.

The light source 20, the PD40, the driving unit 50, the capacitors 71, 72, and the holding unit 60 are provided on the surface of the circuit board 10. In fig. 2, the 3D sensor 5 is not provided on the surface of the circuit board 10, but may be provided on the surface of the circuit board 10. The light diffusion member 30 is provided on the holder 60. Here, the front surface refers to the front side of the paper surface of fig. 2. More specifically, in the circuit board 10, the side on which the light source 20 and the like are provided is referred to as a front surface, a front side, or a front surface side. The same applies to other components. Hereinafter, a case where the member is viewed from the front side as viewed in perspective is referred to as a plan view.

The light source 20 is configured as a surface-emission laser element array in which a plurality of surface-emission laser elements are two-dimensionally arranged (see fig. 3 described later). For example, the Surface Emitting laser element is a vertical resonator Surface Emitting laser element vcsel (vertical Cavity Surface Emitting laser). Hereinafter, a case where the surface-emitting laser element is a vertical resonator surface-emitting laser element VCSEL will be described. The vertical resonator surface emitting laser element VCSEL is denoted as a VCSEL. Since the light source 20 is provided on the surface on the circuit substrate 10, the light source 20 emits light to the outside in a direction (surface side) perpendicular to the surface of the circuit substrate 10. The surface of the light source 20 from which light is emitted may be referred to as an emission surface. The light source 20 is an example of a laser element array.

The light diffusion member 30 is provided on the light exit path of the light source 20. The light diffusion member 30 diffuses the light emitted from the incident light source 20 and emits the diffused light. The light diffusion member 30 is provided so as to cover the light source 20 and the PD 40. The light diffusion member 30 is provided at a predetermined distance from the light source 20 and the PD40 provided on the circuit board 10 by the holding portion 60 provided on the surface of the circuit board 10. Therefore, the light emitted from the light source 20 is diffused by the light diffusion member 30 and is irradiated to the object to be measured. That is, the light emitted from the light source 20 is diffused by the light diffusion member 30 and is irradiated over a wider range than in the case where the light diffusion member 30 is not provided. The PD40 receives light reflected by the back surface of the light diffusion member 30.

The PD40 is a photodiode made of silicon or the like and outputting an electric signal according to the amount of received light (hereinafter referred to as the amount of received light). The PD40 is arranged to receive light emitted from the light source 20 and reflected by the back surface (surface on the-z direction side in fig. 6 described later) of the light diffusion member 30. The light source 20 is controlled to constantly emit a predetermined amount of light based on the amount of light received by the PD 40. That is, the measurement control unit 8 monitors the light receiving amount of the PD40, and controls the drive unit 50 to control the light amount emitted from the light source 20.

In the case of performing three-dimensional measurement by the ToF method, the light source 20 is required to emit pulsed light (hereinafter referred to as emitted light pulse) having a rise time of 1ns or less at 100MHz or more, for example, by the driving unit 50. That is, the light source 20 is driven by flowing current and emits light pulses. In the case of face authentication, for example, the distance over which light is emitted is about 10cm to about 1 m. The range of light irradiation is about 1m square. The distance to which light is irradiated is referred to as a measurement distance, and the range to which light is irradiated is referred to as an irradiation range or a measurement range. In addition, a surface virtually set in the irradiation range or the measurement range is referred to as an irradiation surface. In the case other than the face authentication, the measurement distance to the object and the irradiation range to the object may be other than the above-described measurement distance and irradiation range.

The 3D sensor 5 includes a plurality of light receiving units, and outputs a signal corresponding to a time from a timing of light emitted from the light source 20 to a timing of light reception by the 3D sensor 5. For example, each light receiving unit of the 3D sensor 5 receives pulse-shaped reflected light (hereinafter referred to as light receiving pulse) reflected from the object with respect to the light pulse emitted from the light source 20, and stores electric charge corresponding to the time until light reception for each light receiving unit. The 3D sensor 5 is configured as a CMOS device in which each light receiving cell includes 2 gates and charge storage units corresponding to the gates. Then, by alternately applying pulses to the 2 gates, generated photoelectrons are transferred to any one of the 2 charge storage units at high speed. The 2 charge storage units store charges corresponding to the phase difference between the outgoing light pulse and the received light pulse. Then, the 3D sensor 5 outputs, as a signal, a digital value corresponding to the phase difference between the emitted light pulse and the light reception pulse for each light reception unit via the AD converter. That is, the 3D sensor 5 outputs a signal corresponding to the time from the timing of light emitted from the light source 20 to the timing of light received by the 3D sensor 5. That is, a signal corresponding to the three-dimensional shape of the object to be measured is acquired from the 3D sensor 5. Therefore, it is required that the rise time of the emitted light pulse is short and the rise time of the received light pulse is short. That is, the rise time of the current pulse supplied to drive the light source 20 is required to be short. The AD converter may be provided in the 3D sensor 5, or may be provided outside the 3D sensor 5. The 3D sensor 5 is an example of a light receiving portion.

When the 3D sensor 5 is, for example, a device having the above-described CMOS structure, the three-dimensional shape determining unit 81 of the measurement control unit 8 acquires a digital value obtained for each light receiving cell and calculates a distance to the object for each light receiving cell. Then, the three-dimensional shape of the object is specified based on the calculated distance, and the specified result is output. Here, the three-dimensional shape specifying unit 81 functions as a distance specifying unit that specifies a distance to the object to be measured.

The authentication processing unit 91 provided in the system control unit 9 recognizes whether or not access is permitted based on the three-dimensional shape specified by the three-dimensional shape specifying unit 81, and authenticates the user who is permitted to access.

In fig. 2, the measurement device 6 includes an optical device 3 and a measurement control unit 8. In fig. 2, the optical device 3 and the measurement control unit 8 are shown separately, but may be integrally configured.

The following description will be made in order.

(Structure of light Source 20)

Fig. 3 is a top view of the light source 20. The planar shape of the light source 20 is a quadrangle. The quadrangle refers to a rectangle, a square, a parallelogram, or the like. The light source 20 is configured by arranging a plurality of VCSELs in a two-dimensional array. In fig. 3, the VCSELs are arranged at the vertices (lattice points) of a square, but may be arranged by another arrangement method. As described above, the light source 20 is configured as a surface-emitting laser element array including VCSELs as surface-emitting laser elements. Here, the right direction of the paper surface is defined as the x direction, and the upper direction of the paper surface is defined as the y direction. The z direction is a direction perpendicular to the x direction and the y direction counterclockwise. The front surface of the light source 20 is the front side of the paper surface, i.e., the + z direction side surface, and the back surface of the light source 20 is the back side of the paper surface, i.e., the-z direction side surface. The plan view of the light source 20 is a view of the light source 20 viewed from the front surface side. In the light source 20, the epitaxial layer functioning as a light-emitting layer (active region 206 described later) is formed on the surface, front side, or front side of the light source 20.

The VCSEL is a surface-emitting laser element in which an active region to be a light-emitting region is provided between a lower multilayer film mirror and an upper multilayer film mirror stacked on a semiconductor substrate 200 (see fig. 4 described later), and laser light is emitted in a direction perpendicular to the surface. Therefore, the VCSEL can be easily arrayed in two dimensions as compared with the case of using an end-face emission type laser element. For example, the number of VCSELs included in the light source 20 is 100 to 1000. In addition, the plurality of VCSELs are connected in parallel with each other and driven in parallel. The number of VCSELs is an example, and may be set according to the measurement distance and the irradiation range.

An anode electrode 218 common to the plurality of VCSELs is provided on the surface of the light source 20. A cathode electrode 214 is provided on the rear surface of the light source 20 (see fig. 4 described later). I.e. a plurality of VCSELs are connected in parallel. By connecting a plurality of VCSELs in parallel to drive, light having a higher intensity is emitted as compared with the case where the VCSELs are driven individually.

Here, the side surface on the + y direction side of the light source 20 is denoted as a side surface 21A, the side surface on the-y direction side is denoted as a side surface 21B, the side surface on the-x direction side is denoted as a side surface 22A, and the side surface on the + x direction side is denoted as a side surface 22B. The side surface 21A faces the side surface 21B. The side surface 22A and the side surface 22B connect and face the side surface 21A and the side surface 21B, respectively.

(construction of VCSEL)

Fig. 4 is a diagram illustrating a cross-sectional configuration of 1 VCSEL in the light source 20. The VCSEL is a VCSEL of lambda resonator construction. The upper direction of the paper surface is the z direction, the + z direction is indicated as the upper side, and the-z direction is indicated as the lower side.

The VCSEL is configured by sequentially stacking, on an n-type semiconductor substrate 200 made of GaAs or the like: an n-type lower portion of which is formed by alternately overlapping AlGaAs layers having different Al compositions is provided with a black reflector (DBR) 202; an active region 206 including a quantum well layer sandwiched by an upper spacer layer and a lower spacer layer; and a p-type upper distribution black mirror 208 in which AlGaAs layers having different Al compositions are alternately stacked. Hereinafter, the distributed black type mirror is referred to as DBR.

The n-type lower DBR202 is formed of Al_0.9Ga_0.1And a stack of an As layer and a GaAs layer in pair. The thickness of each layer of the lower DBR202 is lambda/4 n_r(where. lambda. is an oscillation wavelength, n_rIs the refractive index of the medium) and 40 periods are alternately stacked. As the carrier, silicon (Si) as an n-type impurity is doped. The concentration of the carrier is, for example, 3X 10¹⁸cm^-3。

The active region 206 is formed by stacking a lower spacer layer, a quantum well active layer, and an upper spacer layer. For example, the lower spacer layer is undoped Al_0.6Ga_0.4An As layer, an undoped InGaAs quantum well layer and an undoped GaAs barrier layer As the quantum well active layer, and an undoped Al layer As the upper spacer layer_0.6Ga_0.4And an As layer.

The p-type upper DBR208 is formed of p-type Al_0.9Ga_0.1And a stack of an As layer and a GaAs layer in pair. The layers of the upper DBR208 have a thickness of lambda/4 n_rAnd 29 cycles are alternately stacked. As the carriers, carbon (C) as a p-type impurity is doped. The carrier concentration is, for example, 3X 10¹⁸cm^-3. Preferably, a contact layer made of p-type GaAs is formed on the uppermost layer of the upper DBR208, and a current narrowing layer 210 of p-type AlAs is formed on the lowermost layer of the upper DBR208 or inside thereof.

By etching the semiconductor layers stacked from the upper DBR208 to the lower DBR202, a columnar mesa M is formed on the semiconductor substrate 200. Thereby, the current constriction layer 210 is exposed on the side surface of the mesa M. By the oxidation process, an oxidized region 210A oxidized from the side surface of the mesa M and a conductive region 210B surrounded by the oxidized region 210A are formed in the current constriction layer 210. In the oxidation step, the oxidation rate of the AlAs layer is higher than that of the AlGaAs layer, and the oxidized region 210A is oxidized at a substantially constant rate from the side surface of the mesa M toward the inside, so that the cross-sectional shape of the conductive region 210B is a shape reflecting the outer shape of the mesa M, that is, a circular shape, and the center thereof substantially coincides with the axis of the mesa M indicated by the dashed-dotted line. In the present embodiment, the mesa M has a columnar structure.

An annular p-side electrode 212 made of a metal, which is formed by stacking Ti/Au or the like, is formed on the uppermost layer of the mesa M. The p-side electrode 212 is in ohmic contact with a contact layer provided in the upper DBR 208. The inside of the annular p-side electrode 212 is a light exit port 212A through which laser light exits to the outside. That is, the VCSEL emits light in the + z direction perpendicular to the surface (+ z direction side surface) of the semiconductor substrate 200. The axis of the table M is the optical axis. A cathode electrode 214 is formed as an n-side electrode on the back surface of the semiconductor substrate 200. The surface of the upper DBR208 inside the p-side electrode 212 (+ z-direction surface) is a light exit surface.

Further, the insulating film 216 is provided so as to cover the surface of the mesa M except for the portion of the anode electrode 218 connected to the p-side electrode 212 and the light exit port 212A. Further, the anode electrode 218 is disposed in ohmic contact with the p-side electrode 212 except for the light exit port 212A. In addition, the anode electrode 218 is provided commonly in the plurality of VCSELs. That is, the p-side electrodes 212 of the plurality of VCSELs constituting the light source 20 are connected in parallel via the anode electrode 218.

In fig. 4, the portion of the anode electrode 218 is denoted by "a" indicating the anode, and the portion of the cathode electrode 214 is denoted by "K" indicating the cathode.

The VCSEL may oscillate in a single transverse mode or in multiple transverse modes. For example, the light output of 1 VCSEL is 4mW to 8 mW. Therefore, when the light source 20 is configured by 500 VCSELs, the light output of the light source 20 is 2W to 4W.

(Structure of light-diffusing member 30)

Fig. 5 is a diagram illustrating an example of the light diffusion member 30. Fig. 5 (a) is a plan view, and fig. 5 (b) is a cross-sectional view taken along line VB-VB of fig. 5 (a). In fig. 5 (a), the right direction of the paper surface is defined as the x direction, the upper direction of the paper surface is defined as the y direction, and the front direction of the paper surface is defined as the z direction. In the light-diffusing member 30, the + z direction side is referred to as the front surface or the front surface side, and the-z direction side is referred to as the back surface or the back surface side. Therefore, in fig. 5 (b), the right direction on the paper surface is the x direction, the back direction on the paper surface is the y direction, and the upper direction on the paper surface is the z direction.

As shown in fig. 5 (b), the light diffusion member 30 includes, for example, a resin layer 32 having irregularities for diffusing light formed on the back surface (-z direction) side of a flat glass substrate 31 having parallel surfaces. The light diffusion member 30 widens the diffusion angle of light incident from the VCSEL of the light source 20 to emit light. That is, the irregularities formed on the resin layer 32 of the light diffusion member 30 refract or scatter light, and the incident light is emitted as light having a wider diffusion angle. That is, as shown in fig. 5, the light-diffusing member 30 makes the light of the diffusion angle θ incident from the back surface (-z direction side) and emitted from the VCSEL be a light of a diffusion angle larger than the diffusion angle θIs emitted from the surface (+ z direction side)Therefore, when the light-diffusing member 30 is used, the area of the irradiation surface irradiated with the light emitted from the light source 20 is enlarged as compared with the case where the light-diffusing member 30 is not used. The diffusion angle theta,Is the full width at half maximum (FWHM).

Here, the planar shape of the light diffusion member 30 is rectangular. The thickness (thickness in the z direction) t of the light-diffusing member 30_dIs 0.1 mm-1 mm. The planar shape of the light diffusion member 30 may be other shapes such as a polygon and a circle.

(drive unit 50 and capacitors 71 and 72)

In the case where it is desired to drive the light source 20 at a higher speed, it is preferable to perform low-side driving. The low-side drive is a structure in which a driving element such as a MOS transistor is positioned on the downstream side of a path through which a current flows (hereinafter referred to as a current path) with respect to a driving target such as a VCSEL. Conversely, a structure in which the driving element is located on the upstream side is referred to as high-side driving.

Fig. 6 is a diagram showing an example of an equivalent circuit in the case where the light source 20 is driven by low-side driving. Fig. 6 shows the VCSEL of the light source 20, the driving unit 50, the capacitors 71 and 72, and the power supply 82. Fig. 6 also shows the measurement control unit 8 shown in fig. 2. The power supply 82 is provided in the measurement control unit 8. The power supply 82 generates a dc voltage having the + side as a power supply potential and the-side as a reference potential. The power supply potential is supplied to the power supply line 83, and the reference potential is supplied to the reference line 84. The reference potential may be a ground potential (sometimes denoted as gnd, and denoted as [ G ] in fig. 6).

As described above, the light source 20 is configured by connecting a plurality of VCSELs in parallel. The anode electrode 218 (see fig. 4, and [ a ] in fig. 6) of the VCSEL is connected to the power supply line 83.

The driving unit 50 includes an n-channel MOS transistor 51 and a signal generating circuit 52 for turning on/off the MOS transistor 51. The drain electrode (denoted by "D" in fig. 6) of the MOS transistor 51 is connected to the cathode electrode 214 (denoted by "K" in fig. 6 with reference to fig. 4) of the VCSEL. A source (denoted as "S" in fig. 6) of MOS transistor 51 is connected to reference line 84. Further, the gate of the MOS transistor 51 is connected to the signal generation circuit 52. That is, the VCSEL and the MOS transistor 51 of the driver 50 are connected in series between the power supply line 83 and the reference line 84. The signal generation circuit 52 generates a signal of "H level" for turning on the MOS transistor 51 and a signal of "L level" for turning off the MOS transistor 51 under the control of the measurement control unit 8.

One terminal of each of the capacitors 71 and 72 is connected to a power supply line 83 (VCSEL [ a ] in fig. 6), and the other terminal is connected to a reference line 84 (VCSEL [ G ] in fig. 6).

The PD40 has a cathode connected to the power supply line 83 and an anode connected to one terminal of the detection resistance element 41. The other terminal of the detection resistor element 41 is connected to the reference line 84. That is, PD40 and detection resistance element 41 are connected in series between power supply line 83 and reference line 84. The output terminal 42, which is a connection point between the PD40 and the detection resistor element 41, is connected to the measurement control unit 8. The output terminal 42 transmits an electric signal corresponding to the amount of light received by the PD40 to the measurement control unit 8.

Next, a driving method of the light source 20 by low-side driving will be described.

First, the signal generated by the signal generation circuit 52 in the drive unit 50 is set to "L level". In this case, the MOS transistor 51 is in an off state. That is, no current flows between the source (S in fig. 6) and the drain (D in fig. 6) of the MOS transistor 51. Therefore, no current flows in the VCSEL connected in series with the MOS transistor 51. That is, the VCSEL does not emit light.

At this time, the capacitors 71 and 72 are connected to the power supply 82, one terminal (a terminal on the [ a ] side of the VCSEL in fig. 6) of the capacitors 71 and 72 connected to the power supply line 83 is set to a power supply potential, and the other terminal (a terminal on the [ G ] side of fig. 6) of the capacitors 71 and 72 connected to the reference line 84 is set to a reference potential. Therefore, a current (charge) flows from the power supply 82 to the capacitors 71 and 72, and the capacitors 71 and 72 are charged.

Next, when the signal generated by the signal generation circuit 52 in the drive unit 50 becomes "H level", the MOS transistor 51 is switched from the off state to the on state. Thus, a closed loop is formed between the capacitors 71 and 72 and the MOS transistor 51 and the VCSEL connected in series, and the electric charges accumulated in the capacitors 71 and 72 are supplied to the MOS transistor 51 and the VCSEL connected in series. That is, a current flows to the VCSEL, and the VCSEL emits light. The closed loop is a path (sometimes referred to as a current path) through which a current for lighting the light source 20 flows. Further, since a current for emitting light for each of the capacitors 71 and 72 flows, a current path is configured for each of the capacitors 71 and 72. In addition, the current flowing to cause the light source 20 to emit light may be referred to as a driving light source 20.

Then, when the signal generated by the signal generation circuit 52 in the drive section 50 becomes "L level" again, the MOS transistor 51 shifts from the on state to the off state. Thereby, the closed loop (current path) of the capacitors 71 and 72 and the MOS transistor 51 and the VCSEL connected in series becomes an open loop, and the current does not flow to the VCSEL. Thereby, the VCSEL stops emitting light. Thus, a current (charge) flows from the power supply 82 to the capacitors 71 and 72, and the capacitors 71 and 72 are charged.

As described above, every time the signal output from the signal generation circuit 52 shifts between the "H level" and the "L level", the MOS transistor 51 is repeatedly turned on and off, and the VCSEL repeatedly emits and does not emit light. The repetition of on/off of the MOS transistor 51 is sometimes referred to as a switch.

As described above, when the MOS transistor 51 is switched from the off state to the on state, the electric charges stored in the capacitors 71 and 72 are discharged at once to supply a current for light emission to the VCSEL, thereby causing the VCSEL to emit light with a short rise time. As described above, the capacitor 71 is a low ESL capacitor, and the capacitor 72 is a non-low ESL capacitor.

The low ESL capacitor has a large planar shape (a large mounting area on the circuit board 10), but in many cases has a small capacitance. On the other hand, a non-low ESL capacitor uses a ceramic sheet having a high dielectric constant, and even if the planar shape is small (the mounting area on the circuit board 10 is small), the capacitance is large in many cases. In contrast, a capacitor 71 as a low ESL capacitor having a small capacitance and a capacitor 72 as a non-low ESL capacitor having a large capacitance are used at the same time. That is, a current at the time of light emission rise of the light source 20 is supplied through the capacitor 71 which is a low ESL capacitor having a small capacity. Then, a current for securing the light amount after the light emission is increased is supplied through the capacitor 72 which is a non-low ESL capacitor having a large capacity. Thus, the rise time of light emission can be shortened and the amount of light can be secured. In addition, the low ESL capacitor is generally referred to as LW inversion because its width (W) in the lateral direction is larger than its length (L) in the longitudinal direction (between electrodes). On the other hand, a non-low ESL capacitor generally has a width (W) in the lateral direction smaller than the length (L) in the vertical direction (between electrodes).

(light emitting device 4)

Next, the light emitting device 4 will be described in detail.

Fig. 7 is a diagram illustrating a light-emitting device 4 to which the present embodiment is applied. Fig. 7 (a) is a plan view, and fig. 7 (b) is a sectional view taken along line VIIB-VIIB of fig. 7 (a). Fig. 7 (a) is a plan view of the light diffusion member 30 viewed through the light diffusion member. Here, in fig. 7 (a), the right direction of the paper surface is defined as the x direction, the upper direction of the paper surface is defined as the y direction, and the front direction of the paper surface is defined as the z direction. In fig. 7 (b), the right direction on the paper surface is the x direction, the back direction on the paper surface is the y direction, and the upper direction on the paper surface is the z direction.

As shown in fig. 7 (a) and (B), the light source 20, the PD40, the driving unit 50, the capacitors 71 and 72 (capacitors 71A, 71B, 72A, and 72B), and the holding unit 60 are provided on the surface of the circuit board 10. The light diffusion member 30 is provided in the holder 60.

The circuit board 10 is configured by providing a wiring layer in which a wiring made of a metal such as copper (Cu) foil is formed on an insulating base material (sometimes referred to as an insulating layer) such as glass epoxy. The wiring refers to a conductor pattern for circuit connection, and the shape is not limited. Here, a case where the circuit board 10 is a printed wiring board having 2 wiring layers will be described. For example, the base material such as glass epoxy resin includes a glass composite substrate (CEM-3) and a glass epoxy substrate (FR-4).

On the front surface side of the circuit board 10, a cathode wiring 11, anode wirings 12A and 12B, and reference potential wirings 13FA and 13FB are provided. The cathode wiring 11 has a rectangular planar shape and is provided in the center of the circuit board 10. The anode wirings 12A and 12B are provided so as to sandwich the cathode wiring 11 in the x direction. The reference potential wirings 13FA and 13FB are provided outside the anode wirings 12A and 12B so as to sandwich the cathode wiring 11 in the x direction. Note that, when the anode lines 12A and 12B are not distinguished, they are referred to as anode lines 12. Similarly, the reference potential wirings 13FA and 13FB are denoted as reference potential wirings 13F without being distinguished from each other. A reference potential wiring 13B is provided on the back surface side of the circuit board 10. The reference potential wiring 13B (indicated by a broken line in fig. 7 a) is provided on the entire rear surface of the circuit board 10. That is, the reference potential wiring 13B is provided in a layered form as a reference potential wiring layer. The reference potential wiring 13F and the reference potential wiring 13B are connected by a through conductor 13V provided through the base material of the circuit board 10. The through conductor is a conductor obtained by filling a hole provided through an electrically insulating base material constituting the circuit board 10 with copper (Cu) or the like. The through conductor is a member that electrically connects a wiring provided on the front side of the base material of the circuit board 10 and a wiring provided on the back side. In addition, the through conductor is sometimes referred to as a via.

Further, although the reference potential wiring 13B is provided on the back surface of the circuit board 10, it may be provided in a layer form as a reference potential wiring layer in the circuit board 10 so as to occupy a wide area of the circuit board 10.

The cathode wiring 11 provided on the surface of the circuit board 10 is connected at one end to the driving unit 50 via a conductive member such as solder or silver paste, and is connected at the other end to the cathode electrode 214 (see fig. 4) of the light source 20 while mounting the light source 20 thereon.

The anode wirings 12A and 12B are connected to an anode electrode 218 (see fig. 4) of the light source 20 by bonding wires 23A and 23B. When the bonding wires 23A and 23B are not distinguished, they are denoted as bonding wires 23. Capacitors 71A and 72A are provided between the anode wiring 12A and the reference potential wiring 13FA, and capacitors 71B and 72B are provided between the anode wiring 12B and the reference potential wiring 13 FB.

As shown in fig. 7 (a), the capacitors 71A, 72A and the capacitors 71B, 72B are provided so as to sandwich the light source 20 in the x direction. That is, the capacitors 71A and 72A and the capacitors 71B and 72B are arranged symmetrically with respect to the center line C-C of the light source 20 in the x direction. Specifically, the capacitors 71A and 72A are provided on the side surface 22A of the light source 20, and the capacitors 71B and 72B are provided on the side surface 22B of the light source 20. The driving unit 50 is disposed on the center line C-C of the light source 20 in the x direction in the-y direction of the light source 20. Specifically, the driving unit 50 is provided on the side surface 21B of the light source 20. Also, the PD40 is disposed on the y-direction side of the light source 20. That is, the PD40 and the driving section 50 are disposed so as to sandwich the light source 20 in the y direction.

As described above, the light source 20, the capacitors 71A, 71B, 72A, 72B, and the driving unit 50 are arranged in a T shape. Hereinafter, description of PD40 will be omitted.

Fig. 8 is a diagram schematically illustrating a current path in the light-emitting device 4. Here, the solid-line arrows show paths (current paths) of currents flowing on the front surface side of the circuit board 10, and the broken-line arrows show paths (current paths) of currents flowing in the reference potential wiring 13B provided on the back surface side of the circuit board 10. In addition, a current flowing through the reference potential wiring 13B may be referred to as a return current. These current paths were found by simulation. In fig. 8, the bonding wire 23 is shown as a thin wire. The light diffusion member 30 is not described.

As shown in fig. 8, a current flows from the capacitors 71A and 72A to the anode electrode 218 of the light source 20 via the anode line 12A and the bonding wire 23A. Similarly, a current flows from the capacitors 71B and 72B to the anode electrode 218 of the light source 20 through the anode wiring 12B and the bonding wire 23B. Then, a current flows from the light source 20 to the driving unit 50 via the cathode wiring 11. Then, the current returns (returns) from the driving unit 50 to the light source 20 side along the cathode wiring 11 on the front side among the reference potential wirings 13B on the back side of the circuit board 10. Then, the anode wiring 12A along the surface side returns (returns) to the capacitors 71A, 72A. At the same time, the current returns (returns) to the capacitors 71B, 72B along the anode wiring 12B on the surface side.

As described above, in the light-emitting device 4 to which the present embodiment is applied, even if the reference potential wiring 13B is provided on the entire surface on the back side of the circuit board 10, the current flows not in a diffused manner over a wide range of the reference potential wiring 13B but in a current path determined by the arrangement of the light source 20, the capacitors 71 and 72, and the driving unit 50. In the light-emitting device 4, the current path in the reference potential wiring 13B on the back surface side of the circuit board 10 is formed in a portion facing the current path on the front surface of the circuit board 10 from the capacitors 71 and 72 to the light source 20 via the anode wirings 12A and 12B and the current path from the light source 20 to the driver 50 via the cathode wiring 11. In the light source 20, the entire light source flows from the anode electrode 218 to the cathode electrode 214 in a diffused manner. That is, the current flows with minimal impedance, thus reducing the effective inductance of the current path. Moreover, variations in light emission in the light source 20 are suppressed.

Next, a light-emitting device 4' which is a modification of the light-emitting device 4 according to the present embodiment will be described.

Fig. 9 is a diagram illustrating a light-emitting device 4' which is a modification of the light-emitting device 4 to which the present embodiment is applied. Fig. 9 (a) is a plan view, and fig. 9 (b) is a sectional view taken along the IXB-IXB line of fig. 9 (a). Fig. 9 (a) is a plan view of the light diffusion member 30 viewed through the light diffusion member. The light-emitting device 4' further includes a heat dissipation base material 100 in addition to the light-emitting device 4. Since other configurations are the same as those of the light emitting device 4, the same portions are denoted by the same reference numerals, and description thereof is omitted, and the heat dissipating base material 100 as a different portion will be described.

The heat dissipation base material 100 is an insulating base material having a thermal conductivity greater than that of the circuit board 10. As the light intensity becomes larger, the amount of heat generation of the light source 20 also becomes larger. In order to efficiently dissipate heat generated from the light source 20, the light source 20 is preferably mounted on the heat dissipation substrate 100.

FR-4, which is an example of a base material of glass epoxy resin used for the circuit board 10, has a thickness of about 100 μm and a thermal conductivity of about 0.4W/m.K. Further, the thermal conductivity of copper (Cu) is about 360W/m.K. The thermal conductivity shown here is a value at 25 ℃ unless otherwise specified.

The heat dissipation base material 100 is preferably a heat dissipation base material having a thermal conductivity of 10W/mK or more, and more preferably a heat dissipation base material having a thermal conductivity of 50W/mK or more. Further, a heat-dissipating substrate having a thermal conductivity of 100W/mK or more is more preferable. As the heat dissipation base material having a thermal conductivity of 10W/mK or more, there is mentioned alumina (Al) having a thermal conductivity of 20 to 30W/mK₂O₃). Further, as a heat dissipating base material having a thermal conductivity of 50W/mK or more, silicon nitride (Si) having a thermal conductivity of about 85W/mK is mentioned₃N₄). Further, the heat dissipation base material having a thermal conductivity of 100W/mK or more is aluminum nitride (AlN) having a thermal conductivity of 150 to 250W/mK. They are sometimes referred to as ceramic materials. That is, the heat dissipation substrate 100 may be entirely composed of a ceramic material. The heat dissipation base material 100 may be an insulating material having high thermal conductivity, such as silicon (Si) that is not doped with impurities. Here, the heat dissipation substrate 100 is aluminum nitride (AlN).

As shown in fig. 9 (a) and (B), the cathode wiring 111F and the anode wirings 112FA and 112FB are provided on the front surface side of the heat dissipation base material 100, and the cathode wiring 111B and the anode wirings 112BA and 112BB are provided on the back surface side. Note that the anode wiring 112F is denoted when the anode wirings 112FA and 112FB are not distinguished, and the anode wiring 112B is denoted when the anode wirings 112BA and 112BB are not distinguished. The cathode wiring 111F and the cathode wiring 111B are connected to each other via a through conductor 111V provided through the heat dissipation substrate 100. Similarly, the anode wiring 112F and the anode wiring 112B are connected via a through conductor 112V. Here, the cathode wiring 111F is an example of a front-side cathode wiring, and the cathode wiring 111B is an example of a rear-side cathode wiring. Anode wirings 112FA and 112FB exemplify 1 pair surface side anode wirings, and anode wirings 112BA and 112BB exemplify 1 pair back side anode wirings.

The cathode wiring 111F provided on the front surface side of the heat sink base material 100 is mounted with a conductive member on the light source 20 and connected to the cathode electrode 214 (see fig. 4) of the light source 20. The anode wirings 112FA and 112FB provided on the surface of the heat dissipation substrate 100 are connected to the anode electrode 218 (see fig. 4) of the light source 20 by bonding wires 23A and 23B.

The cathode wiring 111B provided on the back surface side of the heat dissipation base material 100 is connected to the cathode wiring 11 on the front surface side of the circuit board 10 via a conductive member. Similarly, anode wirings 112BA and 112BB provided on the back surface side of heat dissipation base material 100 are connected to anode wirings 12A and 12B provided on the front surface side of circuit board 10 by conductive members.

Fig. 10 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of the heat dissipation substrate 100 in the light emitting device 4' as a modification. Fig. 10 (a) shows the front-side wiring, and fig. 10 (b) shows the rear-side wiring. The wiring on the back side shown in fig. 10 (b) is a plan view seen through the heat dissipation substrate 100. Therefore, in fig. 10 (a) and (b), the right direction of the paper surface is the x direction, the upward direction of the paper surface is the y direction, and the front direction of the paper surface is the z direction.

As shown in fig. 10 (a), a cathode wiring 111F and anode wirings 112FA and 112FB are provided on the surface side of the heat dissipating base material 100. As shown in fig. 10 (B), on the back surface side of the heat dissipation substrate 100, a cathode wiring 111B and anode wirings 112BA and 112BB are provided. The cathode wiring 111F and the cathode wiring 111B are connected by a through conductor 111V. The anode wiring 112F (anode wirings 112FA and 112FB) and the anode wiring 112B (anode wirings 112BA and 112BB) are connected by a through conductor 112V. Further, the cathode wiring 111B and the anode wirings 112BA and 112BB provided on the back surface side have a larger planar shape (area) than the cathode wiring 111F and the anode wirings 112FA and 112FB provided on the front surface side. In this way, the mounting on the circuit board 10 is facilitated.

Further, as shown in fig. 10 (a), the anode wirings 112FA, 112FB are disposed symmetrically with respect to the center line C-C in the x direction of the cathode wiring 111F. That is, the anode wirings 112FA and 112FB are provided so as to sandwich the cathode wiring 111F. The relationship between the cathode wiring 111B and the anode wirings 112BA and 112BB provided on the back surface side is also the same as that on the front surface side.

The path of the current for light emission in the light emitting device 4' is the same as that of the light emitting device 4 described above. The effective inductance of the current path in this case is 0.4nH, and the rise time of the current for light emission is 330 ps.

(light-emitting devices 4A and 4B of comparative examples 1 and 2)

Next, light-emitting devices 4A and 4B shown as comparative examples to which the present embodiment is not applied will be described.

Fig. 11 is a diagram illustrating a light-emitting device 4A of comparative example 1 to which the present embodiment is not applied. Fig. 11 (a) is a plan view, and fig. 11 (b) is a sectional view taken along line XIB-XIB of fig. 11 (a). Fig. 11 (a) is a plan view of the light diffusion member 30 viewed through the light diffusion member. The light emitting device 4A includes the heat dissipation substrate 100 in the same manner as the light emitting device 4'. Since other configurations are the same as those of the light emitting device 4', the same portions are denoted by the same reference numerals, and description thereof is omitted, and different portions are described.

The light emitting device 4A includes capacitors 71 and 72 only on the side surface 22B of the light source 20. Therefore, the anode line 12 and the reference potential line 13F are provided only on the side surface 22B of the light source 20 on the circuit board 10. In addition, the PD40 is provided on the side face 22A side of the light source 20. Description about the PD40 is omitted.

Similarly, the heat dissipation substrate 100 is provided with the anode wiring 112F only on the side surface 22B of the light source 20 on the front side, and is provided with the anode wiring 112B only on the side surface 22B of the light source 20 on the back side. On the front surface side of the heat dissipation substrate 100, an anode electrode 218 (see fig. 4) of the light source 20 and the anode wiring 112F are connected by a bonding wire 23.

Fig. 12 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of the heat dissipation substrate 100 in the light-emitting device 4A as comparative example 1. Fig. 12 (a) shows the front-side wiring, and fig. 12 (b) shows the rear-side wiring. The wiring on the back side shown in fig. 12 (b) is a plan view seen through the heat dissipation substrate 100. Therefore, in fig. 12 (a) and (b), the right direction of the paper surface is the x direction, the upward direction of the paper surface is the y direction, and the front direction of the paper surface is the z direction.

As shown in fig. 12 (a), a cathode wiring 111F and an anode wiring 112F are provided on the front surface side of the heat dissipation substrate 100. As shown in fig. 12 (B), a cathode wiring 111B and an anode wiring 112B are provided on the back surface side of the heat dissipation substrate 100. The cathode wiring 111F and the cathode wiring 111B are connected by a through conductor 111V. Anode wiring 112F and anode wiring 112B are connected by through conductor 112V. The cathode wiring 111B and the anode wiring 112B provided on the back surface side have a larger planar shape (area) than the cathode wiring 111F and the anode wiring 112F provided on the front surface side. In this way, the mounting on the circuit board 10 is facilitated.

Fig. 13 is a diagram schematically illustrating a current path in the light-emitting device 4A of comparative example 1. Here, the solid-line arrows also show the paths (current paths) of the currents flowing on the front surface side of the circuit board 10, and the broken-line arrows also show the paths (current paths) of the currents flowing in the reference potential wirings 13B provided on the back surface side of the circuit board 10. In fig. 13, the bonding wire 23 is shown as a thin wire. The light diffusion member 30 is not described.

As shown in fig. 13, a current flows from the capacitors 71 and 72 to the anode electrode 218 of the light source 20 via the anode wiring 12 and the bonding wire 23. Then, a current flows from the light source 20 to the driving unit 50 via the cathode wiring 11. Then, the current returns (returns) from the driving unit 50 to the light source 20 side along the cathode wiring 11 on the front side among the reference potential wirings 13B on the back side of the circuit board 10. Then, the current returns (returns) to the capacitors 71, 72 along the anode wiring 12 on the surface side.

At this time, in the reference potential wiring 13B provided on the back surface side of the circuit board 10, the current (return current shown by a broken line) returning from the driving unit 50 to the light source 20 flows not only along the back surface of the cathode wiring 11 but also flows toward the capacitors 71 and 72 (portion shown by α). Further, since the current flowing through the anode electrode 218 on the surface of the light source 20 also flows toward the driving unit 50 (portion indicated by β), the light emission of the light source 20 tends to be uneven on the surface. This is because of the influence of the arrangement of the light source 20, the driving section 50, and the capacitors 71 and 72. Therefore, the current path of the light emitting device 4A becomes longer than the light emitting device 4 to which the present embodiment is applied, and the effective inductance becomes larger. The effective inductance of the current path of the light-emitting device 4A is 0.5nH, which is larger than 0.4nH of the light-emitting device 4.

The light-emitting device 4A includes the heat dissipation substrate 100, but may be configured without the heat dissipation substrate 100. The current path is the same even without the heat dissipation substrate 100.

Fig. 14 is a diagram illustrating a light-emitting device 4B of comparative example 2 to which the present embodiment is not applied. Fig. 14 (a) is a plan view, and fig. 14 (b) is a sectional view taken along the XIVB-XIVB line of fig. 14 (a). Fig. 14 (a) is a plan view of the light diffusion member 30 viewed through the light diffusion member. The light emitting device 4B includes the heat dissipation substrate 100 in the same manner as the light emitting device 4'. The sectional view shown in fig. 14 (b) is the same as the sectional view of the light-emitting device 4A in fig. 11 (b). Since other configurations are the same as those of the light emitting device 4', the same portions are denoted by the same reference numerals, and description thereof is omitted, and different portions are described.

The light emitting device 4B includes the capacitors 71 and 72 only on the side of one side surface 22B of the light source 20, as in the light emitting device 4A. Therefore, the anode line 12 and the reference potential line 13F are provided only on the side surface 22B of the light source 20 on the circuit board 10. The PD40 is provided on the side surface 22A of the light source 20. Description about the PD40 is omitted.

The anode wiring 112F is provided on the front surface side of the heat dissipation substrate 100 so as to surround the side surfaces 21A, 22B, and 21B of the light source 20, and the anode wiring 112B is provided on the rear surface side of the heat dissipation substrate 100 so as to surround the side surfaces 21A, 22B, and 21B of the light source 20 (see fig. 15 described later). On the front surface side of the heat dissipation substrate 100, the anode electrode 218 (see fig. 4) of the light source 20 and the anode wiring 112F are connected by bonding wires 23C and 23D on 2 sides of the side surfaces 21A and 21B of the light source 20.

The light-emitting device 4B has the following structure: in the light-emitting device 4A, the anode wiring 112F is provided so as to surround the side surfaces 21A, 22B, and 21B of the light source 20, thereby facilitating the supply of current to the light source 20.

Fig. 15 is a diagram illustrating a wiring provided on the front surface side and a wiring provided on the back surface side of the heat dissipation substrate 100 in the light-emitting device 4B as comparative example 2. Fig. 15 (a) shows the front-side wiring, and fig. 12 (b) shows the rear-side wiring. The wiring on the back side shown in fig. 15 (b) is a plan view seen through the heat dissipation substrate 100. Therefore, in fig. 15 (a) and (b), the right direction of the paper surface is the x direction, the upward direction of the paper surface is the y direction, and the front direction of the paper surface is the z direction. The wiring on the back side in fig. 15 (b) is the same as the wiring provided on the back side of the heat dissipation substrate 100 in the light-emitting device 4A shown in fig. 12 (b).

As shown in fig. 15 (a), a cathode wiring 111F and an anode wiring 112F are provided on the front surface side of the heat dissipation substrate 100. As shown in fig. 15 (B), a cathode wiring 111B and an anode wiring 112B are provided on the back surface side of the heat dissipation substrate 100. The cathode wiring 111F and the cathode wiring 111B are connected by a through conductor 111V. Anode wiring 112F and anode wiring 112B are connected by through conductor 112V. The cathode wiring 111B and the anode wiring 112B provided on the back surface side have a larger planar shape (area) than the cathode wiring 111F and the anode wiring 112F provided on the front surface side. In this way, the mounting on the circuit board 10 is facilitated.

Fig. 16 is a diagram schematically illustrating a current path in the light-emitting device 4B of comparative example 2. Here, the solid-line arrows also show the paths (current paths) of the currents flowing on the front surface side of the circuit board 10, and the broken-line arrows show the paths (current paths) of the currents flowing in the reference potential wirings 13B provided on the back surface side of the circuit board 10. In fig. 16, the bonding wires 23C and 23D are shown as thin lines. The light diffusion member 30 is not described.

As shown in fig. 16, a current flows from the capacitors 71 and 72 to the anode electrode 218 of the light source 20 via the anode wiring 12 and the bonding wires 23C and 23D. A current flows from the light source 20 to the driving unit 50 through the cathode wiring 11. Then, the current returns (returns) from the driving unit 50 to the light source 20 side along the cathode wiring 11 on the front side among the reference potential wirings 13B on the back side of the circuit board 10. Then, the current returns (returns) to the capacitors 71, 72 along the anode wiring 12 on the surface side.

At this time, in the reference potential wiring 13B provided on the back surface side of the circuit board 10, the current returning from the driving unit 50 to the light source 20 side (the return current indicated by the broken line) flows not only along the back surface of the cathode wiring 11 but also toward the capacitors 71 and 72 side (the portion indicated by α). Further, since the anode wiring 112F is provided so as to surround the 3 side surfaces (side surfaces 21A, 22B, 21B) of the light source 20, a current flows from the side surface 21A side to the side surface 21B side in the anode electrode 218 on the surface of the light source 20. Therefore, the light emission of the light source 20 does not easily become uneven on the surface. However, in order to cause a current to flow to the side surface 21A of the light source 20 through the anode wiring 112F, the current path is longer in the light-emitting device 4B than in the light-emitting device 4A, and the effective inductance is conversely increased. The effective inductance of the current path of the light-emitting device 4B is 0.6nH, which is larger than 0.4nH of the light-emitting device 4' and the light-emitting device 4A. The rise time of light emission in the light emitting device 4B is 660ps, which is longer than 330ps of the light emitting device 4'.

In the light-emitting device 4B, the heat-radiating base material 100 needs to be used because the anode wiring 112F on the heat-radiating base material 100 intersects with the cathode wiring 11 on the circuit board 10.

As described above, in the light emitting devices 4 and 4' to which the present embodiment is applied, the capacitors 71 and 72 are provided on the 2 sides (the side surfaces 22A and 22B in fig. 7 and 9) of the light source 20 facing each other, and the driving unit 50 is provided on the other side (the side surface 21B in fig. 7 and 9) of the light source 20, whereby the current (return current) returning to the reference potential wiring 13B provided on the rear surface side of the circuit board 10 flows with minimum impedance. This reduces the effective inductance of the current path, and shortens the rise time of light emission. That is, in the light-emitting device 4 (light-emitting device 4') to which the present embodiment is applied, the effective inductance is reduced from 0.6nH to 0.4nH and the rise time of the current for light emission is improved from 660ps to 330ps, as compared with the light-emitting device 4B using the normal heat dissipation base material 100 shown as comparative example 2.

In the light emitting devices 4 and 4' to which the present embodiment is applied, the light diffusion member 30 is used which changes the diffusion angle of incident light so as to widen the angle by diffusion and emits the light. Instead of the light diffusion member 30, a diffraction member such as a Diffractive Optical Element (DOE) that emits incident light by changing the direction of the incident light from the direction of the incident light may be used.