Light-emitting device, optical device, measuring device, and information processing device

Abstract

The present invention provides a light-emitting device, an optical device, a measuring device, and an information processing device that shorten the rise time of light emission compared to a case where multiple laser element arrays are driven separately by multiple driving units. The light-emitting device includes: multiple driving units; multiple laser element arrays connected to the multiple driving units; and connecting wiring connecting the terminals of the laser element arrays connected to the driving units.

Description

Technical Field

[0001] The present invention relates to a light emitting device, an optical device, a measuring device and an information processing device. Background Art

[0002] Japanese Patent Publication No. 2008-252129 describes a light-emitting device comprising a light-transmitting ceramic substrate; a light-emitting element mounted on the surface of the ceramic substrate; a wiring pattern for supplying power to the light-emitting element; and a metallization layer comprising a reflective metal, the metallization layer being formed within the ceramic substrate to reflect light emitted from the light-emitting element. Summary of the Invention

[0003] When measuring the three-dimensional shape of an object using the so-called Time of Flight (ToF) method, which utilizes the time of flight of light, the light source must have high luminous intensity and a short rise time. To increase luminous intensity, one approach is to use a light source comprised of multiple laser element arrays, each driven separately by multiple driver units. However, this delay in the rise time of each laser element array results in a longer rise time.

[0004] The present invention provides a light emitting device and the like that shortens the rise time of light emission compared to a case where a plurality of laser element arrays are driven separately by a plurality of driving units.

[0005] According to a first embodiment of the present invention, a light-emitting device is provided, comprising: a plurality of driving units; a plurality of laser element arrays, each connected to the plurality of driving units; and connecting wiring, connecting terminals of the laser element arrays connected to the driving units between the plurality of laser element arrays.

[0006] According to a second embodiment of the present invention, the driving unit includes a driving element for turning on / off the current flowing to 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 the downstream side of the current path in the laser element array.

[0007] According to a third embodiment of the present invention, the plurality of laser element arrays are arranged on a circle centered on the center of the plurality of laser element arrays.

[0008] According to a fourth embodiment of the present invention, the plurality of driving units are arranged on another circle centered on the centers of the plurality of laser element arrays.

[0009] According to a fifth embodiment of the present invention, the light emitting device includes a circuit substrate carrying a plurality of the driving units, the circuit substrate including: a reference potential wiring supplied with a reference potential; and the connecting wiring, and the plurality of the driving units are commonly connected to the reference potential wiring and the connecting wiring.

[0010] According to a sixth embodiment of the present invention, the light emitting device includes a heat dissipation substrate provided on the circuit substrate and having a higher thermal conductivity than the circuit substrate, and the plurality of laser element arrays are provided on the heat dissipation substrate.

[0011] According to the seventh embodiment of the present invention, the plurality of driving units are supplied with a common driving signal and driven in parallel.

[0012] According to an eighth embodiment of the present invention, the light emitting device includes a plurality of driving signal lines that branch and supply the driving signal to the plurality of driving units, and the plurality of driving signal lines branch at a central portion of the circuit substrate.

[0013] According to a ninth embodiment of the present invention, the driving signal is supplied as a differential signal, and terminal resistors are provided at branched portions of the plurality of driving signal lines.

[0014] According to a tenth embodiment of the present invention, the light emitting device includes a diffusion member configured to diffuse the light emitted from the plurality of laser element arrays before emitting the light.

[0015] According to an eleventh embodiment of the present invention, the light emitting device includes a diffraction member configured to diffract the light emitted from the plurality of laser element arrays and emit the light.

[0016] According to a twelfth embodiment of the present invention, the light emitting device includes a light-amount monitoring light-receiving element, and the light-amount monitoring light-receiving element monitors the light amount of the plurality of laser element arrays.

[0017] According to a thirteenth embodiment of the present invention, there is provided an optical device including: the light emitting device; and a light receiving unit for receiving reflected light emitted from a plurality of laser element arrays included in the light emitting device and reflected by an object to be measured.

[0018] According to a fourteenth embodiment of the present invention, there is provided a measuring device comprising: the optical device; and a distance determining unit for determining the distance to an object to be measured based on the time from emission from a plurality of laser element arrays included in the optical device to reception by a light receiving unit.

[0019] According to a fifteenth embodiment of the present invention, there is provided an information processing device including: the measuring device; and an authentication processing unit that performs authentication processing related to use of its own device based on a determination result in a distance determination unit included in the measuring device.

[0020] (Effect)

[0021] According to the first embodiment, compared with the case where a plurality of laser units are driven separately by a plurality of driving units, the rise time of light emission is shortened.

[0022] According to the second embodiment, the laser element array can be driven at a higher speed compared to the case where low-side driving is not used.

[0023] According to the third embodiment, compared with the case where the laser elements are not arranged on a circle, a difference in the distance from the center to the laser element array is suppressed.

[0024] According to the fourth embodiment, compared with the case where the drive unit is not arranged on another circle, a difference in the distance from the center to the drive unit is suppressed.

[0025] According to the fifth embodiment, compared with the case where the common connection is not made, the occurrence of a difference in potential is suppressed.

[0026] According to the sixth embodiment, heat conduction from the laser element array is facilitated compared to a case where no heat dissipation substrate is used.

[0027] According to the seventh embodiment, compared with the case where no common drive signal is supplied, the delay in light emission is suppressed.

[0028] According to the eighth embodiment, compared with the case where the branch is not formed at one point in the center, the difference in the distance to the driving portion is suppressed.

[0029] According to the ninth embodiment, compared with the case where the signal is not transmitted using differential signals, a high-speed signal can be transmitted.

[0030] According to the tenth embodiment, a wide irradiation area can be obtained compared with the case where no diffusion member is included.

[0031] According to the eleventh embodiment, a wide irradiation area can be obtained compared to the case where no diffraction member is included.

[0032] According to the twelfth embodiment, the variation in the light amount of the laser element array is suppressed compared to the case where no light receiving element for monitoring the light amount is included.

[0033] According to the thirteenth embodiment, an optical device capable of acquiring a signal corresponding to a distance can be provided.

[0034] According to the fourteenth embodiment, a measuring device capable of measuring the distance to an object to be measured can be provided.

[0035] According to the fifteenth embodiment, it is possible to provide an information processing device equipped with an authentication process based on the determined distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram showing an example of an information processing device.

[0037] Figure 2 This is a block diagram illustrating the structure of an information processing device.

[0038] Figure 3 This is a diagram showing an example of a plan view of a light emitting device.

[0039] Figure 4 This is an enlarged view of a portion of the light-emitting device.

[0040] Figure 5 This is a diagram illustrating the cross-sectional structure of a vertical cavity surface emitting laser (VCSEL) element in a light source.

[0041] Figure 6 A diagram showing an example of a cross-sectional structure of a light-emitting device.

[0042] Figure 7 (a) and Figure 7 (b) is a diagram illustrating an example of a light diffusion member. Figure 7 (a) is a plane diagram, Figure 7 (b) is Figure 7 (a) Cross-sectional view at line VIB-VIB.

[0043] Figure 8 This is a diagram showing an example of an equivalent circuit when a light source is driven by low-side driving.

[0044] Figure 9 This is a diagram illustrating a method of connecting a driving signal line for transmitting a driving signal and a driving unit.

[0045] Figure 10 This is a diagram illustrating an example of a light-emitting device to which the second embodiment is applied. DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0047] Among the measuring devices that measure the three-dimensional shape of the object to be measured, there is a device that measures the three-dimensional shape based on the so-called time of flight (ToF) method using the time of flight of light. In the ToF method, the time from the time when light is emitted from the light-emitting device included in the self-measuring device to the time when the irradiated light is reflected by the object to be measured and received by the three-dimensional sensor (hereinafter referred to as 3D sensor) included in the measuring device is measured, and the three-dimensional shape of the object to be measured is determined based on the measured three-dimensional shape. In addition, the object whose three-dimensional shape is measured is called the object to be measured. Sometimes the three-dimensional shape is called a three-dimensional image. Moreover, sometimes measuring the three-dimensional shape is called three-dimensional measurement, 3D measurement or 3D perception.

[0048] This type of measurement device is installed in mobile information processing devices and is used for facial recognition of users seeking access. Previously, mobile information processing devices used methods such as passwords, fingerprints, and iris scans to authenticate users. In recent years, there has been a demand for more secure authentication methods. Therefore, a measurement device that measures three-dimensional shapes is now installed in mobile information processing devices. Specifically, the device acquires the three-dimensional shape of the user's face, determines whether access is permitted, and only allows access to the user if the user is authenticated as permitted.

[0049] Here, the information processing device is described as an example of a mobile information processing terminal, and the user is authenticated by recognizing a facial shape captured as a three-dimensional shape. Furthermore, the information processing device can be applied to information processing devices other than mobile information processing terminals, such as personal computers (PCs).

[0050] Furthermore, the ToF method measures the time from the moment light is emitted from the light-emitting device included in the measurement device until the light is reflected by the object to be measured and received by the 3D sensor included in the measurement device. Therefore, a short rise time of the emission is required. The shorter the rise time of the emission, the higher the measurement accuracy. Here, the rise time of the emission refers to the time from the start of emission until the light intensity reaches 90% of its maximum value.

[0051] The structure, function, method, etc. described in this embodiment can also be applied to situations where an object other than the face is used as the measured object and the measured object is identified based on the measured three-dimensional shape. Moreover, this measuring device is also applicable to situations where the three-dimensional shape of the measured object is continuously measured in augmented reality (AR). Moreover, the distance to the measured object is irrelevant. In facial authentication, it is sufficient to irradiate light from a light source toward the face at a close distance, but in augmented reality, it is required to irradiate light toward the measured object at a distance farther than the face. Therefore, a large amount of light is required for the light source.

[0052] The configuration, function, method, and the like described in the present embodiment described below can be applied to measurement of the three-dimensional shape of an object to be measured other than face authentication or augmented reality.

[0053] [First embodiment]

[0054] (Information Processing Device 1)

[0055] Figure 1 1 is a diagram showing an example of the information processing device 1. As described above, the information processing device 1 is, as an example, a mobile information processing terminal.

[0056] An information processing device 1 includes a user interface unit (hereinafter referred to as a UI unit) 2 and an optical device 3 for measuring three-dimensional shapes. The UI unit 2 is, for example, an integrated device that displays information to the user and an input device that inputs instructions for information processing through user operations. The display device is, for example, a liquid crystal display or an organic electroluminescence (EL) display, and the input device is, for example, a touch panel.

[0057] The optical device 3 includes a light-emitting device 4 and a three-dimensional sensor (hereinafter referred to as a 3D sensor) 5. The light-emitting device 4 irradiates light toward the object to be measured, in this example, the face. The 3D sensor 5 captures the light emitted from the light-emitting device 4 and reflected by the face. Here, the three-dimensional shape is measured based on the so-called ToF method using the time of flight of light. The three-dimensional shape of the face is then determined based on the three-dimensional shape. As described above, the three-dimensional shape can also be measured using an object other than the face. The 3D sensor 5 is an example of a light receiving unit.

[0058] Information processing device 1 is configured as a computer including a central processing unit (CPU), read-only memory (ROM), and random access memory (RAM). ROM includes nonvolatile, rewritable memory, such as flash memory. Information processing device 1 operates by expanding programs and constants stored in ROM into RAM and executing them with the CPU, thereby performing various information processing operations.

[0059] Figure 2 It is a block diagram illustrating the configuration of the information processing device 1 .

[0060] The information processing device 1 includes the optical device 3, a measurement control unit 8, and a system control unit 9. As described above, the optical device 3 includes a light emitting device 4 and a 3D sensor 5. The measurement control unit 8 controls the optical device 3. In addition, the measurement control unit 8 includes a three-dimensional shape determination unit 81. The system control unit 9 controls the information processing device 1 as a system. In addition, the system control unit 9 includes an authentication processing unit 91. In addition, the system control unit 9 is connected to the UI unit 2, the speaker 92, the two-dimensional camera ( Figure 2 called 2D camera)93 etc.

[0061] The three-dimensional shape determination unit 81 included in the measurement control unit 8 determines the three-dimensional shape of the object to be measured based on the three-dimensional shape measured by the reflected light from the object. The authentication processing unit 91 included in the system control unit 9 determines whether access is permitted based on the three-dimensional shape determined by the three-dimensional shape determination unit 81, and authenticates the user if access is permitted.

[0062] Figure 2 In FIG, the measuring device 6 includes an optical device 3 and a measurement control unit 8 . Figure 2 In FIG. 1 , the optical device 3 and the measurement control unit 8 are shown separately, but they may be integrally configured.

[0063] The following is an explanation in order.

[0064] (Light-emitting device 4)

[0065] Figure 3 1 is a diagram showing an example of a plan view of the light emitting device 4. The right direction of the paper is defined as the x direction, the upper direction of the paper is defined as the y direction, and the surface direction of the paper is defined as the z direction.

[0066] The light emitting device 4 includes a circuit board 10, four light sources 20, and a light receiving element for monitoring light quantity (in Figure 3In the following text, the following are referred to as the PD 40, four driving units 50 that drive the four light sources 20, capacitors 71 and 72 that are provided for each light source 20 and supply current for light emission, and a heat dissipation substrate 100. When the four light sources 20 are distinguished, they are referred to as light source 20-1, light source 20-2, light source 20-3, and light source 20-4; when they are not distinguished, they are referred to as light source 20. Similarly, when the driving units 50 are distinguished, they are referred to as driving units 50-1, driving units 50-2, driving units 50-3, and driving units 50-4; when they are not distinguished, they are referred to as driving units 50. In addition, the light emitting device 4 includes capacitors equivalent to capacitors 71 and 72, but the reference numerals are omitted.

[0067] Furthermore, the light emitting device 4 includes a light diffusion member 30 and a holding portion 60. The heat dissipation substrate 100 and the driving portion 50 are provided on the surface of the circuit board 10. The four light sources 20, the PD 40, and the capacitors 71 and 72 are provided on the surface of the heat dissipation substrate 100. The light diffusion member 30 is held by the holding portion 60 on the surface side of the heat dissipation substrate 100. The light diffusion member 30 is held at a predetermined distance from the light sources 20, the PD 40, and the capacitors 71 and 72 (see the following description). Figure 6 ). Here, the surface refers to Figure 3 The front side of the paper. More specifically, the portion of the circuit board 10 where the driver 50 and the heat dissipation substrate 100 are provided is referred to as the surface, the front side, or the front side. The portion of the heat dissipation substrate 100 where the light source 20, the PD 40, and the capacitors 71 and 72 are provided is referred to as the surface, the front side, or the front side. Furthermore, the center of the four light sources 20 in the light-emitting device 4, i.e., the center in the x and y directions, is referred to as the center O. Hereinafter, viewing each component from the front side through perspective is referred to as a top view.

[0068] The four light sources 20 (light source 20-1, light source 20-2, light source 20-3, light source 20-4) are arranged on a circle S1 with a center O. Furthermore, the driving unit 50 (driving unit 50-1, driving unit 50-2, driving unit 50-3, driving unit 50-4) is arranged on a circle S2 with a center O. That is, the light sources 20 and the driving unit 50 are arranged on concentric circles with a center O. Thereby, the situation in which the distance between the light source 20 and the driving unit 50, such as the distance between the light source 20-1 and the driving unit 50-1, is different is suppressed. That is, the center O of the plurality of light sources 20 can also be arranged to deviate from the center of the heat dissipation substrate 100, and the center O of the plurality of light sources 20 can also be arranged to deviate from the center of the circuit substrate 10.

[0069] Alternatively, the center O may be the center of the heat dissipation substrate 100. That is, the multiple light sources 20 may be arranged on a circle centered on the center of the heat dissipation substrate 100. Furthermore, the multiple driving units 50 may be arranged on another circle centered on the aforementioned center. Furthermore, the center O may be the center of the circuit board 10. That is, the multiple light sources 20 may be arranged on a circle centered on the center of the circuit board 10. Furthermore, the multiple driving units 50 may be arranged on another circle centered on the aforementioned center.

[0070] The light source 20 is configured as a light emitting element array in which a plurality of light emitting elements are arranged in two dimensions. As an example, the light emitting element is a vertical cavity surface emitting laser element (VCSEL). Hereinafter, the light emitting element will be described as a vertical cavity surface emitting laser element VCSEL. In addition, the vertical cavity surface emitting laser element VCSEL is referred to as VCSEL. The light source 20 is provided on the surface of the heat dissipation substrate 100, so the light source 20 emits light perpendicularly relative to the surface of the heat dissipation substrate 100 in a direction away from the heat dissipation substrate 100. That is, the light emitting element array is a surface emitting laser element array. In addition, the surface of the light source 20 from which the plurality of light emitting elements in the light source 20 are arranged in two dimensions and emit light is sometimes referred to as an emission surface. The light source 20 is an example of a laser element array.

[0071] The light diffuser 30 is positioned in the emission path of light from the light source 20. The light diffuser 30 receives light emitted by the light source 20 and diffuses the incident light before emitting it. Thus, the light emitted by the light source 20 is diffused by the light diffuser 30 and irradiated onto the object being measured. In other words, compared to a case where the light diffuser 30 is not included, the light emitted by the light source 20 is diffused by the light diffuser 30 and irradiated over a wider area.

[0072] The PD 40 is a photodiode made of silicon or the like that outputs an electrical signal corresponding to the amount of light received (hereinafter referred to as the amount of received light). The PD 40 is configured to receive light emitted from the light source 20 and received by the back surface of the light diffusion member 30 (hereinafter referred to as the back surface of the light diffusion member 30). Figure 6 Light source 20 is controlled based on the amount of light received by PD 40 to maintain a predetermined light intensity. Specifically, measurement control unit 8 monitors the amount of light received by PD 40 and controls drive unit 50 to control the amount of light emitted by light source 20.

[0073] In the case of three-dimensional measurement by the ToF method, the light source 20 is required to emit pulsed light (hereinafter referred to as the emitted light pulse) of, for example, 100 MHz or more and a rise time of 1 ns or less through the driving unit 50. In addition, in the case of facial recognition as an example, the distance of the irradiated light is about 10 cm to about 1 m. And, the range of the irradiated light is about 1 m square. In addition, the distance of the irradiated light is referred to as the measurement distance, and the range of the irradiated light is referred to as the irradiation range or the measurement range. And, the surface hypothetically set in the irradiation range or the measurement range is called the irradiation surface. In addition, in cases other than facial recognition, the measurement distance to the object to be measured and the irradiation range for the object to be measured may also be other than those described above.

[0074] Figure 2 The illustrated 3D sensor 5 is a component comprising a plurality of light-receiving cells that output a signal corresponding to the time from when light is emitted from the light source 20 in the light-emitting device 4 until it is received by the 3D sensor 5. For example, each light-receiving cell of the 3D sensor 5 receives pulsed reflected light from the object being measured (hereinafter referred to as a light-receiving pulse) relative to the outgoing light pulse from the light source 20, and stores a charge corresponding to the time until light reception in each light-receiving cell. The 3D sensor 5 is constructed as a complementary metal oxide semiconductor (CMOS) device, with each light-receiving cell comprising two gates and a corresponding charge storage unit. By alternately applying pulses to the two gates, the generated photoelectrons are transferred at high speed to one of the two charge storage units. The two charge storage units store charge corresponding to the phase difference between the outgoing light pulse and the light-receiving pulse. Furthermore, the 3D sensor 5 outputs a digital value corresponding to the phase difference between the outgoing light pulse and the received light pulse as a signal for each photodetecting cell via an analog-to-digital (AD) converter. Specifically, the 3D sensor 5 outputs a signal corresponding to the time from when light is emitted from the light source 20 to when it is received by the 3D sensor 5. In other words, the 3D sensor 5 acquires a signal corresponding to the three-dimensional shape of the object being measured. The AD converter can be included in the 3D sensor 5 or located externally.

[0075] Furthermore, if the 3D sensor 5 is, for example, a device with the aforementioned CMOS structure, the three-dimensional shape determination unit 81 of the measurement control unit 8 acquires the digital value obtained for each light-receiving cell and calculates the distance to the object being measured for each light-receiving cell. The three-dimensional shape of the object being measured is then measured based on the calculated distances, thereby determining the three-dimensional shape of the object being measured and outputting the determination result. Here, the three-dimensional shape determination unit 81 functions as a distance determination unit that determines the distance to the object being measured.

[0076] As previously described, the measurement control unit 8 is configured as a computer, and the three-dimensional shape determination unit 81 is implemented by a program. However, these units may also include integrated circuits such as application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs). Furthermore, they may also include software such as programs and integrated circuits such as ASICs.

[0077] As described above, the information processing device 1 diffuses the light emitted by the light source 20 and illuminates the object to be measured. The 3D sensor 5 then receives the reflected light from the object. In this way, the information processing device 1 measures the three-dimensional shape. Therefore, regardless of facial recognition, in three-dimensional shape measurement, such as in augmented reality, the light emitting device 4 requires a high light output. Therefore, in the first embodiment, multiple light sources 20 are used. Such light emitting devices 4 are required to efficiently dissipate heat from the light sources 20.

[0078] The heat dissipation substrate 100 is provided with a cathode wiring 111F (denoted as [K]) connected to the cathode of the light source 20 (described later). Figure 5 anode wiring 112F (labeled as [A]), connected to the anode of the light source 20 ( Figure 5 and a reference potential wiring 113F (labeled as [G]), which is supplied with a reference potential. The reference potential is, for example, the ground potential (GND). Figure 3 As shown, multiple reference potential wirings 113F are provided. Furthermore, cathode wiring 111F, anode wiring 112F, and reference potential wiring 113F are sometimes referred to as wirings without distinguishing them from each other. The same applies to other situations. Furthermore, wiring refers to a conductor pattern that connects an electrical circuit, and its shape is not limited.

[0079] Figure 4 It is an enlarged view of a portion of the light emitting device 4 . Figure 4The portion of light source 20-1 in light-emitting device 4 is shown enlarged. Capacitors 71 and 72 are shown, which supply current to light source 20-1 and 20-1 for light emission. Capacitor 71 is referred to as capacitor 71A and capacitor 71B, and capacitor 72 as capacitor 72A and capacitor 72B. Furthermore, reference potential wiring 113F is referred to as reference potential wiring 113FA and reference potential wiring 113FB.

[0080] As described above, the light source 20 - 1 and the capacitors 71A, 71B, 72A, and 72B are provided on the surface of the heat dissipation substrate 100 . Figure 4 In the following, the connection relationship between the light source 20 - 1 , the wiring provided on the surface of the heat dissipation substrate 100 , and the capacitor 71A, the capacitor 71B, the capacitor 72A, and the capacitor 72B is described.

[0081] The light source 20-1 has a rectangular planar shape, with the +y direction side 21A, the -y direction side 21B, the -x direction side 22A, and the +x direction side 22B. As described above, the light source 20 is composed of a plurality of VCSELs arranged in a two-dimensional array.

[0082] VCSEL is a light emitting element as described below, that is, a light emitting element is stacked on a semiconductor substrate 200 (see Figure 5 ) is provided between the lower multilayer film reflector and the upper multilayer film reflector, which becomes the active region of the light emitting region, so that the laser light is emitted in a direction perpendicular to the surface. As a result, VCSEL is easier to form a two-dimensional array than when using an end-emitting laser. On the surface of the light source 20, a plurality of VCSELs share an anode electrode 218 (see Figure 5 ). On the back of the light source 20, a cathode electrode 214 is provided (see Figure 5 ). That is, a plurality of VCSELs are connected in parallel. By connecting a plurality of VCSELs in parallel and driving them, light with a greater intensity can be emitted compared to the case where the VCSELs are driven independently. As an example, the number of VCSELs included in the light source 20 is 100 to 1000. The number of VCSELs described above is an example. In the light source 20, the side on which the epitaxial layer functioning as the light-emitting layer (active region 206 described later) is formed is referred to as the surface, surface side, or surface side of the light source 20.

[0083] In the portion of the light source 20-1 on the surface of the heat dissipation substrate 100, there are provided: a cathode wiring 111F connected to the cathode of the light source 20; an anode wiring 112F connected to the anode of the light source 20; and reference potential wiring 113FA and reference potential wiring 113FB connected to a reference potential.

[0084] The cathode wiring 111F is set larger than the planar shape of the light source 20-1 so that the light source 20-1 is provided on its surface. In addition, the light source 20-1 is provided on the surface of the cathode wiring 111F by a conductive member such as solder. Figure 5 The cathode electrode 214) is connected to the cathode wiring 111F.

[0085] The anode wiring 112F is provided so as to surround the three side surfaces (side surface 21A, side surface 21B, and side surface 22A) of the light source 20-1. The anode wiring 112F is connected to the anode of the light source 20 (described later) by bonding wires 23A and 23B on two side surfaces (side surface 21A and side surface 21B) of the light source 20-1. Figure 5 The anode electrode 218 is connected.

[0086] Reference potential wirings 113FA and 113FB are provided outside anode wiring 112F on the side faces 21A and 21B of light source 20-1. Furthermore, capacitors 71A and 72A are provided between reference potential wiring 113FA and anode wiring 112F on the side face 21A of light source 20-1. Capacitors 71B and 72B are provided between reference potential wiring 113FB and anode wiring 112F on the side face 21B of light source 20-1.

[0087] Capacitor 71 (capacitor 71A, capacitor 71B) is a capacitor that reduces the equivalent series inductance (ESL) (hereinafter referred to as a low-ESL capacitor), and capacitor 72 (capacitor 72A, capacitor 72B) is a capacitor with an equivalent series inductance (ESL) greater than that of capacitor 71 (hereinafter referred to as a non-low-ESL capacitor). In order to shorten the rise time of the light source 20, the driver circuit that supplies the current for light emission to the light source 20 requires low impedance at high frequencies. Therefore, capacitors configured to reduce the equivalent series inductance (ESL), namely low-ESL capacitors, can be used. However, low-ESL capacitors are often large in planar shape (large in mounting area on the heat dissipation substrate 100) but have small capacitance. On the other hand, non-low-ESL capacitors are made of ceramic sheets with high dielectric constants and are often small in planar shape (small in mounting area on the heat dissipation substrate 100) but have large capacitance. Therefore, capacitor 71, which is a low-ESL capacitor, and capacitor 72, which is a non-low-ESL capacitor, are used together. Specifically, the current for the rise time of light source 20's luminescence is supplied by capacitor 71, a low-ESL capacitor with a small capacitance. Furthermore, the current required to ensure the amount of light after the rise time is supplied by capacitor 72, a non-low-ESL capacitor with a large capacitance. This shortens the rise time of light source 20 while ensuring the amount of light. Low-ESL capacitors are sometimes referred to as LW inversion capacitors.

[0088] Furthermore, the capacitors 71A and 71B, which are low-ESL capacitors, are located on the center line (one-dot chain line) of the light source 20-1 in the x direction. On the other hand, the capacitors 72A and 72B, which are non-low-ESL capacitors, are located at positions offset from the center line toward the -x direction. Thus, the anode electrode ( Figure 5 The distance between anode electrode 218 (shown) and capacitors 71A and 71B, which are low-ESL capacitors, is shorter than the distance between light source 20-1 and capacitors 72A and 72B, which are non-low-ESL capacitors. Consequently, the inductance of the current path (sometimes referred to as a drive circuit) that supplies the light-emitting current from capacitors 71A and 71B, which are low-ESL capacitors, to light source 20-1 is smaller than the inductance of the current path that supplies the light-emitting current from capacitors 72A and 72B, which are non-low-ESL capacitors. This further shortens the rise time of light source 20-1.

[0089] While the above description focuses on light source 20-1, the connection relationship between light source 20 and capacitors 71 and 72 is similar for other light sources 20-2 through 20-4. Furthermore, for one light source 20 (light source 20-1), two capacitors 71 (capacitor 71A and capacitor 71B) are used as low-ESL capacitors, and two capacitors 72 (capacitor 72A and capacitor 72B) are used as non-low-ESL capacitors. However, either may be one, or three or more.

[0090] And, as Figure 3 As shown, on the surface of the heat dissipation substrate 100 , cathode wiring 111F and anode wiring 112F are connected to each other between the light sources 20 - 1 to 20 - 4 .

[0091] (VCSEL structure)

[0092] Figure 5 1 is a diagram illustrating a cross-sectional structure of one VCSEL in the light source 20. The VCSEL is a VCSEL having a λ resonance structure. The upward direction on the paper is the z direction.

[0093] A VCSEL is constructed by sequentially stacking an n-type lower distributed Bragg reflector (DBR) 202, an active region 206, and a p-type upper distributed Bragg reflector 208 on an n-type semiconductor substrate 200, such as GaAs. The n-type lower distributed Bragg reflector 202 is formed by alternating layers of AlGaAs with varying Al content. The active region 206 includes a quantum well layer sandwiched between an upper diaphragm layer and a lower diaphragm layer. The p-type upper distributed Bragg reflector 208 is formed by alternating layers of AlGaAs with varying Al content. Hereinafter, a distributed Bragg reflector is referred to as a DBR.

[0094] The n-type lower DBR 202 is constructed so that Al 0.9 Ga 0.1 The thickness of each layer of the lower DBR 202 is λ / 4n. r (where λ is the oscillation wavelength, n r is the refractive index of the medium), and 40 periods are alternately stacked. As a carrier, silicon is doped as an n-type impurity. The carrier concentration is, for example, 3×10 18 cm -3 .

[0095] The active region 206 is composed of a lower diaphragm layer, a quantum well active layer and an upper diaphragm layer. For example, the lower diaphragm layer is an undoped Al0.6 Ga 0.4 As layer, the quantum well active layer is a non-doped InGaAs quantum well layer and a non-doped GaAs barrier layer, and the upper diaphragm layer is a non-doped Al 0.6 Ga 0.4 As layer.

[0096] The p-type upper DBR 208 is configured so that the p-type Al 0.9 Ga 0.1 The thickness of each layer of the upper DBR 208 is λ / 4n. r , and 29 cycles are alternately stacked. As a carrier, carbon is doped as a p-type impurity. The carrier concentration is, for example, 3×10 18 cm -3 Preferably, a contact layer made of p-type GaAs is formed at the uppermost layer of the upper DBR 208 , and a current constriction layer 210 made of p-type AlAs is formed at the lowermost layer of the upper DBR 208 or inside the upper DBR 208 .

[0097] By etching the semiconductor layers stacked from the upper DBR 208 to the lower DBR 202, a cylindrical mesa M is formed on the semiconductor substrate 200. This exposes the current constriction layer 210 on the side of the mesa M. Through the oxidation process, an oxidized region 210A, formed from the side of the mesa M, and a conductive region 210B surrounded by the oxidized region 210A are formed in the current constriction layer 210. Furthermore, during the oxidation process, the AlAs layer oxidizes faster than the AlGaAs layer, and the oxidized region 210A oxidizes at a substantially constant rate from the side of the mesa M toward the interior. As a result, the cross-sectional shape of the conductive region 210B is a circular shape reflecting the outer shape of the mesa M, with its center roughly aligned with the axis of the mesa M indicated by the dotted line. In this embodiment, the mesa M has a columnar structure.

[0098] On the top layer of the mesa M, a ring-shaped p-side electrode 212 made of a metal stacked with Ti / Au or the like is formed. The p-side electrode 212 is in ohmic contact with a contact layer provided in the upper DBR 208. The inner side of the ring-shaped p-side electrode 212 becomes a light exit port 212A from which the laser light is emitted to the outside. That is, the VCSEL emits light in a direction perpendicular to the surface (the surface on the +z direction side) of the semiconductor substrate 200. In addition, the axis of the mesa M becomes the optical axis. Furthermore, a cathode electrode 214 serving as an n-side electrode is formed on the back side of the semiconductor substrate 200. In addition, the surface (the surface on the +z direction side) of the upper DBR 208 on the inner side of the p-side electrode 212 serves as a light exit surface. That is, the optical axis direction of the VCSEL becomes the light exit direction.

[0099] Furthermore, an insulating layer 216 is provided in such a manner as to cover the surface of the mesa M except for the portion where the anode electrode 218 is connected to the p-side electrode 212 and the light emitting port 212A. Furthermore, the anode electrode 218 is provided in such a manner as to be in ohmic contact with the p-side electrode 212 except for the light emitting port 212A. In addition, the anode electrode 218 is provided in common to a 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 addition, Figure 5 In FIG. 1 , the portion of the anode electrode 218 is marked with [A] indicating that it is an anode, and the portion of the cathode electrode 214 is marked with [K] indicating that it is a cathode.

[0100] VCSELs can oscillate in either a single transverse mode or multiple transverse modes. For example, the optical output of a single VCSEL is 4 to 8 mW. Therefore, if light source 20 includes 500 VCSELs, the optical output of light source 20 is 2 to 4 W. Furthermore, if there are four light sources 20, the optical output of light-emitting device 4 is 8 to 16 W. This high-output light source 20 generates a lot of heat. Therefore, efficient heat dissipation from light source 20 is required.

[0101] Figure 6 1 is a diagram showing an example of a cross-sectional structure of the light emitting device 4 . Figure 6 The cross-section shown is Figure 3 The cross-sectional view at line VI-VI in FIG. That is, Figure 6 , the driving unit 50 - 1 , the light source 20 - 1 , the PD 40 , the light source 20 - 3 , and the driving unit 50 - 3 are shown from the left side of the paper.

[0102] As described above, the light emitting device 4 is provided with a driving unit 50 ( Figure 6 In the figure, there are driving parts 50-1 and 50-3) and a heat dissipation substrate 100. In addition, a light source 20 ( Figure 6 In the figure, there are light source 20-1, light source 20-3), PD 40, and holding part 60. In addition, on the holding part 60, Figure 6 In the embodiment, a light diffusion member 30 provided so as to cover the light source 20 - 1 , the light source 20 - 3 , and the PD 40 is held.

[0103] The circuit board 10 is constructed by providing a wiring layer on an insulating substrate such as glass epoxy resin, with the wiring layer forming metal wiring such as copper (Cu) foil. Here, the circuit board 10 is described as a two-layer printed wiring board with wiring layers provided on both the front and back sides of the substrate. Meanwhile, the heat dissipation substrate 100 comprises an insulating substrate having a higher thermal conductivity than the circuit board 10.

[0104] On the surface side of the circuit board 10, a cathode wiring 11, a reference potential wiring 13F and an anode wiring are provided. Figure 6 In the figure, the anode wiring is omitted. A reference potential wiring 13B is provided on the back side of the circuit substrate 10. In addition, the reference potential wiring 13F is connected to the reference potential wiring 13B via a through conductor 13V. The so-called through conductor is a conductor formed by filling a hole provided by copper (Cu) or the like through the electrically insulating base material constituting the circuit substrate 10. In addition, the through conductor is a component that electrically connects the wiring provided on the base material surface side of the circuit substrate 10 with the wiring provided on the back side. In addition, the through conductor is sometimes called a through hole.

[0105] As described above, cathode wiring 111F, anode wiring 112F, and reference potential wiring 113F are provided on the front surface of heat dissipation substrate 100. Cathode wiring 111B and reference potential wiring 113B are provided on the back surface of heat dissipation substrate 100. Cathode wiring 111F and cathode wiring 111B are electrically connected via a through conductor 111V provided through heat dissipation substrate 100. Reference potential wiring 113F and reference potential wiring 113B are electrically connected via a through conductor (not shown) provided through heat dissipation substrate 100.

[0106] Furthermore, cathode wiring 11, provided on the surface of circuit board 10, is connected to driver 50 at one end via a conductive member such as solder, and is connected at the other end to cathode wiring 111B provided on the back side of heat dissipation substrate 100. Specifically, cathode wiring 11 is provided so as to extend from driver 50 to cathode electrode 214 of light source 20. Cathode wiring 111B is connected to cathode wiring 111F via through-conductor 111V provided on heat dissipation substrate 100. Cathode wiring 111F is, in turn, connected to cathode electrode 214 of light source 20.

[0107] Figure 6 Although not shown in the figure, the anode wiring 112F provided on the surface side of the heat dissipation substrate 100 is connected to the anode wiring provided on the back side via a through conductor. The anode wiring provided on the back side of the heat dissipation substrate 100 is connected to the anode wiring provided on the surface of the circuit substrate 10. In addition, the anode wiring provided on the surface of the circuit substrate 10 is connected to the power supply 82 (see the following description). Figure 8 ) on the + side.

[0108] On the other hand, the reference potential wiring 113B provided on the back side of the heat dissipation substrate 100 is connected to the reference potential wiring 13F provided on the front side of the circuit board 10. Furthermore, the reference potential wiring 13F is connected to the reference potential wiring 13B provided on the back side via the through conductor 13V. Furthermore, the reference potential wiring 13B is connected to the power supply 82 (see the following description). Figure 8 )'s side.

[0109] Furthermore, the PD 40 is connected to the anode wiring 112F on the surface of the heat dissipation substrate 100 at its cathode side.

[0110] Hereinafter, the heat dissipation substrate 100 and the light diffusion member 30 will be described.

[0111] (Heat Dissipation Substrate 100)

[0112] The glass epoxy resin substrate used for circuit board 10 is called FR-4. The thickness of this substrate is approximately 100 μm. Furthermore, its thermal conductivity is approximately 0.4 W / m·K. Furthermore, the thermal conductivity of copper (Cu) is approximately 360 W / m·K. Unless otherwise specified, the thermal conductivity values ​​shown here are at 25°C.

[0113] The heat dissipation substrate 100 is an insulating substrate having a higher thermal conductivity than the circuit board 10. For example, the heat dissipation substrate 100 is preferably a substrate having a thermal conductivity of 10 W / m·K or more, and further preferably a substrate having a thermal conductivity of 50 W / m·K or more. Furthermore, a substrate having a thermal conductivity of 100 W / m·K or more is more preferred. As a substrate having a thermal conductivity of 10 W / m·K or more, aluminum oxide (Al2O3) having a thermal conductivity of 20 W / m·K to 30 W / m·K can be cited. Furthermore, as a substrate having a thermal conductivity of 50 W / m·K or more, silicon nitride (Si3N4) having a thermal conductivity of about 85 W / m·K can be cited. Furthermore, as a substrate having a thermal conductivity of 100 W / m·K or more, aluminum nitride (AlN) having a thermal conductivity of 150 W / m·K to 250 W / m·K can be cited. They are sometimes referred to as ceramic materials. That is, the heat dissipation substrate 100 may include ceramic material as a whole. The heat dissipation substrate 100 may be made of any insulating material with high thermal conductivity, such as silicon (Si) not doped with impurities. Here, the heat dissipation substrate 100 is made of aluminum nitride (AlN).

[0114] When the light source 20 is disposed on the surface of the heat dissipation substrate 100, the heat generated by the light source 20 is dissipated from the cathode electrode 214 via the cathode wiring 111F disposed on the surface side of the heat dissipation substrate 100, the heat dissipation substrate 100, the reference potential wiring 113B disposed on the back side of the heat dissipation substrate 100, the reference potential wiring 13F on the circuit substrate 10, the through conductor 13V, and the reference potential wiring 13B. Specifically, by disposing the reference potential wiring 113B on the back side of the heat dissipation substrate 100, the heat generated by the light source 20 is conducted to the reference potential wiring 13B disposed on the back side of the circuit substrate 10. Generally speaking, on the back side of the circuit substrate 10, the reference potential wiring 13B is disposed across the entire back side of the circuit substrate 10. Therefore, heat is dissipated from the reference potential wiring 13B disposed on the back side of the circuit substrate 10 to the outside. This facilitates heat dissipation from the light source 20. Furthermore, if the reference potential wiring 113B is not provided on the back side of the heat dissipation substrate 100, the heat generated by the light source 20 is difficult to be transferred to the reference potential wiring 13B provided on the back side of the circuit board 10. Therefore, even if the heat dissipation substrate 100 is used, it is difficult to dissipate the heat generated by the light source 20.

[0115] (Light Diffusing Member 30)

[0116] Figure 7 (a) and Figure 7 (b) is a diagram illustrating an example of the light diffusion member 30 . Figure 7 (a) is a plane graph, Figure 7 (b) is Figure 7 (a) Cross-sectional view at line VIB-VIB. Figure 7 In (a), the right direction of the paper is the x direction, and the upper direction of the paper is the y direction. In the light diffusion member 30, the +z direction side is the front surface or the front side, and the -z direction side is the back surface or the back side. Figure 7 In (b), the right direction of the paper is the x direction, the back direction of the paper is the y direction, and the upper direction of the paper is the z direction.

[0117] like Figure 7 As shown in (b), the light diffusion member 30 includes, for example, a glass substrate 31 having two parallel and flat surfaces, and a resin layer 32 having a concave and convex portion formed on the back side (-z direction) of the glass substrate 31 for diffusing light. The light diffusion member 30 widens the spread angle of light incident from the VCSEL of the light source 20 and emits the light. That is, the concave and convex portion formed on the resin layer 32 of the light diffusion member 30 refracts or scatters the light, thereby causing the incident light to be emitted as light with a wider spread angle. That is, as shown in FIG. Figure 7 As shown in (b), the light diffusion member 30 makes the light with a spread angle θ incident from the back side and emitted from the VCSEL have a spread angle larger than the spread angle θ from the front side. The light emitted Therefore, when the light diffusion member 30 is used, the irradiation area irradiated by the light emitted from the light source 20 is expanded compared to the case where the light diffusion member 30 is not used. is the full width at half maximum (FWHM).

[0118] Here, the planar shape of the light diffusion member 30 is assumed to be the same as the planar shape of the heat dissipation substrate 100. In addition, the thickness (thickness in the z direction) t of the light diffusion member 30 is d The planar shape of the light diffusion member 30 may not be the same as the planar shape of the heat dissipation substrate 100 , and may be another planar shape such as a polygon or a circle.

[0119] like Figure 3 、 Figure 6 As shown, the light diffuser 30 is provided so as to cover the light source 20, the PD 40, and the capacitors 71 and 72. Here, "the light diffuser 30 covers the light source 20" means that the light diffuser 30 is provided on the emission path of light emitted by the light source 20, so that the light emitted by the light source 20 passes through the light diffuser 30. In other words, when viewed from above through the light diffuser 30 from the front side of the light diffuser 30, the light source 20 and the light diffuser 30 overlap.

[0120] Since the PD 40 is covered by the light diffuser 30, the PD 40 receives light emitted from the light source 20 and reflected by the back surface (the surface in the -z direction) of the light diffuser 30. Therefore, the measurement control unit 8 controls the light source 20 based on an electrical signal corresponding to the amount of light received by the PD 40 so that the light source 20 emits a predetermined amount of light.

[0121] Alternatively, the light diffuser 30 may be provided so as to cover the light source 20 and the PD 40. That is, it may not cover the capacitors 71 and 72. In this case, the portion covering the capacitors 71 and 72 may be a cover made of the same member as the retaining portion 60. If the light diffuser 30 covers the light source 20 and the PD 40 but does not cover the capacitors 71 and 72, the area of ​​the expensive light diffuser 30 can be reduced, thereby reducing the cost of the light emitting device 4.

[0122] The holding portion 60 is formed, for example, as a molded member made of resin or the like. Furthermore, the holding portion 60 can be colored, for example, black to absorb the light emitted by the light source 20. This absorbs the light emitted by the light source 20 that strikes the holding portion 60, thereby preventing light from passing through or being reflected by the holding portion 60 and striking the object to be measured.

[0123] Next, the driving circuit of the light source 20 will be described.

[0124] (Drive Circuit of Light Source 20)

[0125] To drive the light source 20 at a higher speed, low-side drive can be used. Low-side drive refers to a configuration in which a driver element, such as a MOS transistor, is located downstream of the current path relative to the drive target, such as a VCSEL. Conversely, a configuration in which the driver element is located upstream is called high-side drive.

[0126] Figure 8 This is a diagram showing an example of an equivalent circuit when the light source 20 is driven by low-side driving. Figure 8 Here, the case of two light sources 20 (light source 20 - 1 and light source 20 - 2 ) is described as an example. Figure 8 , two light sources 20 (light source 20-1 and light source 20-2), capacitors 71 and 72 provided respectively, two driving units 50-1 and 50-2 for driving the two light sources 20, PD 40, and power supply 82 are shown. Furthermore, power supply 82 is provided in measurement control unit 8. Power supply 82 generates a DC voltage with a power supply potential on the positive side and a reference potential on the negative side. The power supply potential is supplied to power line 83, and the reference potential is supplied to reference line 84.

[0127] Hereinafter, the light source 20 - 1 and the driving unit 50 - 1 are referred to as the light source 20 and the driving unit 50 , and the driving circuit of the light source 20 is described with reference to the light source 20 - 1 .

[0128] As mentioned above, the light source 20 is composed of a plurality of VCSELs connected in parallel. Figure 8 Marked as [A] in the figure) is connected to the power line 83.

[0129] The driving unit 50 includes an n-channel MOS transistor 51 and a buffer circuit 52 for supplying a driving signal to the gate of the MOS transistor 51. The drain of the MOS transistor 51 (denoted by [D]) is connected to the cathode electrode 214 ( Figure 8 84). The source of MOS transistor 51 (denoted as [S]) is connected to reference line 84. Furthermore, the gate of MOS transistor 51 is connected to the output terminal of buffer circuit 52. Specifically, MOS transistor 51 of VCSEL and driver 50 is connected in series between power supply line 83 and reference line 84. In response to a drive signal input from measurement control unit 8, buffer circuit 52 outputs an "H level" to turn on MOS transistor 51 and an "L level" to turn off MOS transistor 51.

[0130] Furthermore, the cathodes ([K]) of the plurality of light sources 20 are connected to each other. Figure 8In FIG. 8 , the cathode of the light source 20-1 and the cathode of the light source 20-2 are connected by a connecting wire 88. Specifically, Figure 3 As shown, the connection line 88 is a cathode wiring 111F provided on the surface side of the heat dissipation substrate 100, and connects the cathodes of the four light sources 20. That is, the cathode wiring 111F is an example of a connection wiring.

[0131] One terminal of the capacitor 71 and the capacitor 72 is connected to the power supply line 83, and the other terminal is connected to the reference line 84. Here, the capacitor 71 and the capacitor 72 are connected in parallel.

[0132] The cathode of PD 40 is connected to power line 83, and the anode is connected to one terminal of detection resistor element 41. Furthermore, the other terminal of detection resistor element 41 is connected to reference line 84. That is, PD 40 and detection resistor element 41 are connected in series between power line 83 and reference line 84. Furthermore, output terminal 42, the connection point between PD 40 and detection resistor element 41, is connected to measurement control unit 8. Output terminal 42 transmits an electrical signal corresponding to the amount of light received by PD 40 to measurement control unit 8.

[0133] Each buffer circuit 52 of the plurality of driving units 50 is connected to the measurement control unit 8 via a driving signal line 85. Furthermore, the measurement control unit 8 sends a driving signal to the driving signal line 85. In addition, a differential signal such as a low voltage differential signal (LVDS) or a current mode logic (CML) is supplied to the driving signal line 85. In addition, if a differential signal is used, it is less likely to be affected by noise and the driving signal can be transmitted at high speed. Here, the driving signal line 85 is terminated by a terminal resistor 86 and is branched into a plurality of driving signal lines 87 in this part. Furthermore, the plurality of driving signal lines 87 are respectively connected to each buffer circuit 52 of the plurality of driving units 50. That is, the same driving signal is supplied to each buffer circuit 52 of the plurality of driving units 50 in common.

[0134] Next, a method of driving the light source 20 by low-side driving will be described.

[0135] First, assume that the output of buffer circuit 52 in driver 50 is set to "L" level in response to a drive signal from measurement control unit 8. This turns MOS transistor 51 off, and no current flows between its source ([S]) and drain ([D]). Consequently, no current flows through the VCSEL connected in series with MOS transistor 51. In other words, the VCSEL does not emit light.

[0136] One terminal of capacitor 71 and capacitor 72 is connected to power supply line 83 at a power supply potential, and the other terminal is connected to reference line 84 at a reference potential. Therefore, current flows from power supply 82 (charge is supplied) to capacitors 71 and 72, and they are charged.

[0137] Next, when the output of the buffer circuit 52 in the driver 50 transitions from an "L" level to an "H" level, the MOS transistor 51 transitions from an "off" state to an "on" state. This creates a closed loop consisting of capacitors 71 and 72, the MOS transistor 51 connected in series, and the VCSEL. The charge stored in capacitors 71 and 72 is supplied to the MOS transistor 51 and the VCSEL connected in series. This causes a drive current to flow through the VCSEL, causing it to emit light. This closed loop constitutes the drive circuit for the light source 20.

[0138] When the output of buffer circuit 52 in driver 50 transitions from "H" to "L," MOS transistor 51 transitions from on to off. This opens the closed loop (drive circuit) of capacitors 71 and 72, the MOS transistor 51 connected in series, and the VCSEL, and stops driving current from flowing to the VCSEL. Consequently, the VCSEL stops emitting light. Then, capacitors 71 and 72 are charged by the charge supplied from power supply 82.

[0139] As described above, every time the output of the buffer circuit 52 transitions between "H level" and "L level", the MOS transistor 51 repeatedly turns on and off, and the VCSEL repeatedly emits and does not emit light. The repeated on and off of the MOS transistor 51 is sometimes called switching.

[0140] As described above, when MOS transistor 51 is switched from the off state to the on state, the charge stored in capacitors 71 and 72 is discharged all at once and supplied as drive current to the VCSEL, thereby causing the VCSEL to emit light with a short rise time. As previously described, capacitor 71 is a low-ESL capacitor with small capacitance, and capacitor 72 is a non-low-ESL capacitor with large capacitance. Therefore, when MOS transistor 51 is switched from the off state to the on state, charge is first supplied from capacitor 71, a low-ESL capacitor with small inductance, thereby supplying the current for the rise portion of the light emission of light source 20. Subsequently, charge is supplied from capacitor 72, a non-low-ESL capacitor with large inductance but large capacitance, thereby ensuring the amount of light emitted by light source 20. This shortens the rise time of the light emission of light source 20.

[0141] And, as Figure 3As shown, when the light-emitting device 4 includes multiple light sources 20, the measurement control unit 8 transmits a common control signal to the multiple driver units 50. This synchronizes the signals ("H level") output from the buffer circuits 52 in the driver units 50. However, the characteristics of the multiple light sources 20 or the multiple driver units 50 inevitably differ. Therefore, there is a possibility of light emission delay between the multiple light sources 20. The rise time of light emission in the light-emitting device 4 is the sum of the light emission of each light source 20. Therefore, if there is a delay in light emission, the rise time of light emission will be longer.

[0142] Therefore, in the light emitting device 4 of the first embodiment, the cathodes of the plurality of light sources 20 are connected to each other by connecting wires 88 (see Figure 8 ) are connected so that the potential difference of the cathode of the light source 20 is unlikely to occur. Thereby, the rise time of the light emission in the light emitting device 4 will be shortened.

[0143] In addition, it is considered to connect multiple light sources 20 in parallel and use one driving unit 50 to drive them. However, as mentioned above, the output of the four light sources 20 is about 10W. In such a high-output driving unit, the rise time is reduced from 1ns to 2ns. Therefore, a driving unit 50 is provided for each light source 20 so as to drive them in parallel. At this time, in order to shorten the rise time, a control signal as a differential signal is sent to the multiple driving units 50 in common, and the cathodes of the multiple light sources 20 driven by each of the multiple driving units 50 are connected to each other.

[0144] Figure 9 1 and 2 are diagrams for explaining a method of connecting a driving signal line 85 for transmitting a driving signal and the driving unit 50 . Figure 9 is Figure 3 Four driving units 50 are shown.

[0145] As described above, the four drive units 50 are arranged on a circle S1, which is the center O of the light-emitting device 4. Furthermore, a terminal resistor 86 is provided on the back side of the circuit board 10, at a location corresponding to the center O of the light-emitting device 4 (the center portion). A drive signal line 85 is provided between the terminal resistor 86 and the measurement control unit 8. Furthermore, four drive signal lines 87 are provided from the two terminals of the terminal resistor 86 for the four drive units 50 (drive unit 50-1, drive unit 50-2, drive unit 50-3, and drive unit 50-4). This minimizes the difference in length L between the drive signal lines 87 connecting the terminal resistors 86 and the drive units 50, and the length of the drive signal lines 87 connecting the terminal resistors 86 and the drive units 50 is shortened. A shorter drive signal line 87 allows the downstream side of the terminal resistor 86 to be treated as a lumped constant circuit. Therefore, even when the terminal resistor 86 is shared by multiple drive units 50, signal scrambling can be suppressed. For example, if the length L of the drive signal line 87 is approximately 1 / 7 of the wavelength λ of the drive signal, for example, when transmitting a pulse signal with a repetition frequency of 200 MHz, and the length L of the drive signal line 87 is 10 mm or less, the terminal resistor 86 can be shared. Furthermore, as an example, the terminal resistor 86 is 100 Ω.

[0146] Furthermore, generally, a terminal resistor 86 is provided for each driver 50. However, if a signal is transmitted to multiple drivers 50 in common, the voltage of the signal supplied to each driver 50 decreases. Therefore, it is preferable to shorten the length L of the drive signal line 87 connecting the multiple drivers 50 and the terminal resistor 86 and provide a common terminal resistor 86.

[0147] As described above, in the light emitting device 4 including the four light sources 20 , when the light emitting device 4 is caused to emit light at a current of 4 A, the rise time of light emission is 500 ps or less.

[0148] In the above, the light emitting device 4 uses four light sources 20 and four driving units 50 . However, the number of these light sources 20 and driving units 50 may be two or six, as long as it is an even number.

[0149] [Second embodiment]

[0150] The light emitting device 4 according to the first embodiment uses the heat dissipation substrate 100. The heat dissipation substrate 100 is not necessarily required. In the light emitting device 4' according to the second embodiment, the light source 20 and the like are provided on the surface of the circuit board 10.

[0151] The other structures are the same as those of the first embodiment, and therefore their description is omitted. A different light emitting device 4 ′ will be described.

[0152] Figure 10 This is a diagram illustrating an example of a light emitting device 4 ′ to which the second embodiment is applied. Figure 101 is a plan view of the light emitting device 4'. Components having the same functions as those of the light emitting device 4 to which the first embodiment is applied are denoted by the same reference numerals.

[0153] The light-emitting device 4' includes a circuit substrate 10, two light sources 20, and four capacitors 73. Furthermore, the light-emitting device 4' includes a retaining portion 60 and a light diffusion member 30. The two light sources 20 and the four capacitors 73 are provided on the surface of the circuit substrate 10. Furthermore, a cathode wiring 11, an anode wiring 12, and a reference potential wiring 13F are provided on the surface of the circuit substrate 10. A reference potential wiring 13B is provided on the back surface of the circuit substrate 10. Furthermore, the reference potential wiring 13F and the reference potential wiring 13B are electrically connected via a through-conductor (not shown).

[0154] In the light-emitting device 4', the light sources 20 are also arranged on a circle S3 with the center of the light source 20 as the center O. The driving unit 50 is arranged on a circle S4 with the center O. Furthermore, the cathode wiring 11 is provided to connect the cathode of the light source 20-1 with the cathode of the light source 20-2. That is, in the light-emitting device 4' according to the second embodiment, the cathode wiring 11 is also an example of a connecting wiring.

[0155] The capacitor 73 may be a low-ESL capacitor or a non-low-ESL capacitor. Similar to the light-emitting device 4 to which the first embodiment is applied, a combination of low-ESL capacitors and non-low-ESL capacitors may be used.

[0156] Figure 10 In the light emitting device 4 ′ according to the second embodiment, two light sources 20 and two driving units 50 are used, but the number may be four or an even number.

[0157] Furthermore, the light emitting device 4 according to this embodiment uses a light diffuser 30, which diffuses the incident light and changes its spread angle to a larger angle before emitting the light. Alternatively, a diffractive optical element (DOE), such as a diffractive optical element (DOE), may be used in place of the light diffuser 30. The diffractive optical element diffracts the light and emits it in a direction different from the incident direction.

Claims

1. A light emitting device, characterized in that: include: multiple drive units; A plurality of laser element arrays are respectively connected to the plurality of driving units, wherein a cathode electrode is provided on the back surface of each of the laser element arrays; as well as The connection wiring connects cathode electrodes of the respective laser element arrays, which are terminals connected to the driving unit, between the plurality of laser element arrays arranged on a surface of the connection wiring.

2. The light emitting device according to claim 1, wherein The driving unit includes a driving element for turning on and off the current flowing to the laser element array. The laser element array and the driving element are connected so as to be driven by a low-side driver provided on a downstream side of a current path in the laser element array.

3. The light emitting device according to claim 1 or 2, characterized in that: The plurality of laser element arrays are arranged on a circle centered on the center of the plurality of laser element arrays. The plurality of driving units are arranged on another circle centered on the centers of the plurality of laser element arrays.

4. The light emitting device according to claim 1 or 2, characterized in that: comprising a circuit substrate carrying a plurality of the driving units, The circuit substrate includes: a reference potential wiring to which a reference potential is supplied; and the connection wiring, The plurality of driving units are commonly connected to the reference potential wiring and the connection wiring.

5. The light emitting device according to claim 4, characterized in that include: The heat dissipation substrate is provided on the circuit substrate and has a thermal conductivity greater than that of the circuit substrate. The plurality of laser element arrays are provided on the heat dissipation substrate.

6. The light emitting device according to claim 4, characterized in that The plurality of driving units are supplied with a common driving signal and driven in parallel.

7. The light emitting device according to claim 6, characterized in that include: A plurality of driving signal lines, which branch and supply the driving signal to the plurality of driving parts, The plurality of driving signal lines are branched at one point in the center of the circuit substrate.

8. The light emitting device according to claim 7, characterized in that The driving signal is supplied as a differential signal. Terminal resistors are provided at the portions where the plurality of drive signal lines branch.

9. The light emitting device according to claim 1 or 2, characterized in that: include: The diffusion member diffuses the light emitted from the plurality of laser element arrays and emits the light.

10. The light emitting device according to claim 1 or 2, characterized in that: include: The diffraction member diffracts the light emitted from the plurality of laser element arrays and emits the light.

11. The light emitting device according to claim 1 or 2, characterized in that: include: The light-amount monitoring light-receiving element monitors the light amount of the plurality of laser element arrays.

12. An optical device, characterized in that: include: The light-emitting device according to claim 1 or 2; as well as The light receiving unit receives reflected light emitted from the plurality of laser element arrays included in the light emitting device and reflected by the object to be measured.

13. A measuring device, characterized in that: include: The optical device according to claim 12; as well as The distance determining unit determines the distance to the object to be measured based on the time from when light is emitted from the plurality of laser element arrays included in the optical device to when light is received by the light receiving unit.

14. An information processing device, characterized in that: include: The measuring device according to claim 13; as well as The authentication processing unit performs authentication processing related to use of the own device based on the determination result of the distance determination unit included in the measurement device.

Images