JP2011077849A - Optical communication apparatus and optical transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication apparatus performing stable and high speed optical communication in an optical communication system that uses visible light, and also to provide an optical transmitter to be used for the optical communication apparatus. <P>SOLUTION: The optical communication apparatus 1 is equipped with: the optical transmitter 2; an optical fiber 3; and an optical receiver 4. The optical transmitter 2 includes a light source 11 that emits visible light. The light source 11 includes: a GaN substrate having a non-polar plane or a semi-polar plane as a principal plane; and a light-emitting element (LED or LD) formed on the principal plane of the GaN substrate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical communication device and an optical transmitter. The present invention particularly relates to an optical communication apparatus and an optical transmitter applied to an optical communication system using visible light.

  With the progress of optical communication technology, it has been proposed to apply a short-distance optical communication system using optical fibers to consumer fields such as digital home appliances and in-vehicle networks. In the above-mentioned field, it has been proposed to construct a LAN (Local Area Network) system with a plastic optical fiber (POF) that is cheaper than a glass optical fiber (GOF). Since a wavelength region where transmission loss of POF is low exists in the visible region, a visible light source such as a light emitting diode (LED) that emits visible light is used as a light source for transmitting an optical signal in the optical communication system.

  For example, Non-Patent Document 1 shows an optical communication experiment using a green LED (wavelength 520 nm) and POF. The communication speed in this experiment is 30 Mbit / s.

  For example, Non-Patent Document 2 shows an experiment in which optical signals from both a green LED (wavelength 495 nm) and a red LED (wavelength 650 nm) are transmitted in POF according to a wavelength division multiplexing system. The communication speed in this experiment is 250 Mbit / s.

T.Matusoka, T.Ito and T.Kaino, "First plastic optical fiber transmission experiment using 520nm LEDs with intensity modulation / direct detection", ELECTRONICS LETTERS, October 26th 2000, Vol.26, No.22 Masatoshi Yonemura, Akari Kawasaki, Satoru Kato, and Manabu Kagami, "Polymer waveguide module for visible wavelength division multiplexing plastic optical fiber communication", OPTICS LETTERS, September 1, 2005, Vol. 30, No. 17, p.2206-2208

  In short-distance optical communication systems using POF, an LED or semiconductor laser (LD) that outputs red light is often used as a visible light source.

  As a red light emitting element, an AlInGaP-based semiconductor is well known. However, since it is difficult to increase the conduction band offset in the AlInGaP-based semiconductor, it is not easy to stabilize the output of the light source or the peak emission wavelength. Therefore, when an AlInGaP-based semiconductor is used as a light source for an optical communication system, stable operation of the light source becomes a problem.

  On the other hand, the conduction loss of POF is smaller in the green region than in the red region. Therefore, as disclosed in Non-Patent Document 1 and Non-Patent Document 2, in a short-distance optical communication system using POF, it is preferable to use a green light-emitting element as a light source. However, the existing green LED is formed on a polar surface called a c-plane of a sapphire crystal, for example.

  In a green LED formed on a c-plane sapphire crystal, a piezoelectric field is induced because the strain of the well layer increases due to mismatch of the crystal lattice. Since the luminescence recombination of carriers is less likely to occur due to the piezo electric field, the light emission efficiency is lowered and the light emission lifetime is extended. Since the light emission life is long, it is difficult to operate the light source at high speed (modulate the light source at high speed). Therefore, when the green LED formed on the c-plane sapphire crystal is used as a light source for optical communication, improvement in communication speed becomes a problem.

  Non-Patent Document 2 describes a relatively high communication speed of 250 Mbit / s. However, since there is a trade-off between the output and the operation speed in the LED, the output of the LED is lowered by increasing the operation speed of the LED. When the output of the LED serving as the light source decreases, the received light power at the light receiver that receives the optical signal decreases. As a result, problems such as a high bit error rate (BER) may occur. Therefore, in order to realize high-speed optical communication with the system described in Non-Patent Document 2, it is necessary to further improve the characteristics of the LED as the light source.

  As described above, the conventional optical communication system using visible light has room for improvement in terms of stabilization and speeding up of optical communication.

  An object of the present invention is to provide an optical communication apparatus capable of realizing stable and high-speed optical communication in an optical communication system using visible light, and an optical transmitter used in the optical communication apparatus.

  In summary, the present invention is an optical communication device comprising an optical fiber, at least one optical transmitter, and at least one optical receiver. At least one optical transmitter includes a light source that emits visible light. At least one optical transmitter transmits visible light from the light source as an optical signal propagating through the optical fiber. At least one optical receiver is provided corresponding to the at least one optical transmitter, and receives an optical signal via an optical fiber. The light source includes a gallium nitride substrate having a nonpolar surface or a semipolar surface as a main surface, and a light emitting element formed on the main surface of the gallium nitride substrate.

Preferably, the optical fiber is a plastic optical fiber.
Preferably, the light emission wavelength of the light emitting element is in the range of 500 nm to 580 nm.

  Preferably, the main surface of the gallium nitride substrate is a nonpolar surface. The nonpolar plane is one of the a-plane and the m-plane.

  Preferably, the main surface of the gallium nitride substrate is a semipolar surface. The semipolar plane is any one of a plane having an inclination angle with respect to the c-plane in the range of 63 ° to 80 ° and a plane having an inclination angle from the c-plane in the range of 100 ° to 117 °.

Preferably, the light emitting element is a light emitting diode.
Preferably, the light emitting element is a semiconductor laser.

  Preferably, the at least one optical transmitter is a plurality of optical transmitters. The at least one optical receiver is a plurality of optical receivers. The wavelengths of the plurality of optical signals respectively transmitted from the plurality of optical transmitters are different from each other. An optical communication device includes: a multiplexer for wavelength-multiplexing a plurality of optical signals; a duplexer for separating a plurality of optical signals transmitted by an optical fiber based on a difference in wavelength of each optical signal; Is further provided.

Preferably, the optical communication device is mounted on a vehicle.
In another aspect of the present invention, an optical transmitter for transmitting an optical signal for optical communication to an optical fiber, the light source emitting visible light, and the light source driving the light source so as to transmit the optical signal And a drive circuit. The light source includes a gallium nitride substrate having a nonpolar surface or a semipolar surface as a main surface, and a light emitting element formed on the main surface of the gallium nitride substrate.

Preferably, the optical fiber is a plastic optical fiber.
Preferably, the light emission wavelength of the light emitting element is in the range of 500 nm to 580 nm.

  Preferably, the main surface of the gallium nitride substrate is a nonpolar surface. The nonpolar plane is one of the a-plane and the m-plane.

  Preferably, the main surface of the gallium nitride substrate is a semipolar surface. The semipolar plane is any one of a plane having an inclination angle with respect to the c-plane in the range of 63 ° to 80 ° and a plane having an inclination angle from the c-plane in the range of 100 ° to 117 °.

Preferably, the light emitting element is a light emitting diode.
Preferably, the light emitting element is a semiconductor laser.

  Preferably, the optical transmitter is mounted on a vehicle together with an optical fiber and an optical receiver that receives an optical signal via the optical fiber.

  According to the present invention, stable and high-speed optical communication can be realized in an optical communication system using visible light.

It is a figure explaining the vehicle-mounted LAN system as an application example of the optical communication apparatus which concerns on embodiment of this invention. FIG. 2 is a block diagram illustrating a basic configuration of the optical communication device 1 illustrated in FIG. 1. It is sectional drawing which shows schematically green LED applicable to the light source 11 shown in FIG. It is sectional drawing which shows schematically green LD applicable to the light source 11 shown in FIG. It is the figure which showed roughly one application example of the optical communication apparatus which concerns on embodiment of this invention. It is the figure which showed roughly the other application example of the optical communication apparatus which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a diagram illustrating an in-vehicle LAN system as an application example of an optical communication apparatus according to an embodiment of the present invention.

  With reference to FIG. 1, an optical communication device 1 according to an embodiment of the present invention is mounted on a vehicle 200 as a component of an in-vehicle LAN system 100. The in-vehicle LAN system 100 includes cameras 5a, 5b, 5c, and 5d, a hub (HUB) 6, an optical communication device 1, a controller 7, and a display 8.

  The cameras 5a to 5d image the surroundings of the vehicle 200. Specifically, the camera 5 a captures an area in front of the vehicle 200. The camera 5b and the camera 5c respectively capture a right region and a left region with respect to the traveling direction of the vehicle 200. The camera 5d images an area behind the vehicle 200. The number and arrangement of cameras mounted on the vehicle 200 are not limited as shown in FIG.

  Each of the cameras 5a to 5d is connected to the hub 6 via a metal cable. An image acquired by each camera is output from the camera as an electrical signal, and the electrical signal is transmitted to the hub 6 via a metal cable. The hub 6 sends the electrical signal output from each camera to the optical communication device 1 via a metal cable.

  The optical communication device 1 includes an optical transmitter 2, an optical fiber 3, and an optical receiver 4. The optical transmitter 2 generates an optical signal by performing electrical / optical conversion (E / O conversion) on the electrical signal output from the hub 6 and sends the optical signal to the optical fiber 3.

  The optical fiber 3 is a transmission medium for transmitting the optical signal sent from the optical transmitter 2. According to the configuration shown in FIG. 1, the optical fiber 3 is relatively short, and its length is, for example, about several m to 10 m. However, this numerical value is an example, and the range of the length of the optical fiber 3 is not particularly limited.

  In the in-vehicle LAN system 100 shown in FIG. 1, a plastic optical fiber (POF) is applied to the optical fiber 3. Generally, an optical fiber includes a core for transmitting an optical signal and a clad covering the core. In the case of POF, the core is made of, for example, acrylic resin (PMMA), and the cladding is made of fluororesin.

  The optical receiver 4 converts the optical signal propagated through the optical fiber 3 into an electrical signal by optical / electrical conversion (O / E conversion), and outputs the electrical signal to the controller 7.

  The controller 7 performs predetermined arithmetic processing on the electrical signal output from the optical receiver 4. The display 8 displays the calculation result by the controller 7. For example, the display 8 displays an area around the vehicle 200 captured by the cameras 5a to 5d.

  In the in-vehicle LAN system 100 shown in FIG. 1, the information of the images acquired by the cameras 5a to 5d is transmitted, so the communication information amount of the in-vehicle LAN system 100 is relatively large. For this reason, the in-vehicle LAN system 100 is required to perform high-speed communication.

  An in-vehicle LAN system 100 according to an embodiment of the present invention includes an optical communication device 1. In the optical communication device 1, optical communication using the optical fiber 3 is performed. As a result, the communication capacity can be increased, and high-speed communication can be realized. Furthermore, the optical signal transmitted through the optical fiber is not easily affected by electromagnetic noise. Therefore, according to the embodiment of the present invention, high-speed communication can be stably realized.

  In particular, according to the embodiment of the present invention, since the optical communication device 1 includes the optical transmitter 2 that can operate stably at high speed, high-speed and stable optical communication can be realized. Therefore, according to the embodiment of the present invention, communication reliability can be improved.

  Various communication protocols can be applied to the in-vehicle LAN system 100 including the optical communication device 1 according to the embodiment of the present invention. As an example, a communication protocol applicable to the in-vehicle LAN system 100 is IDB-1394.

  According to IDB-1394, the communication speed is defined as 400 Mbit / s. According to the embodiment of the present invention, since the high-speed communication can be realized by the optical communication device 1, the IDB-1394 described above can be applied as the communication protocol of the in-vehicle LAN system 100.

  In many cases, in a vehicle-mounted LAN system, a wire harness is used for information transmission. However, the number of wire harnesses increases as the amount of information transmitted increases. Increasing the number of wire harnesses increases the weight of the in-vehicle LAN system.

  On the other hand, according to the embodiment of the present invention, since a large amount of information can be transmitted by the optical communication device 1, an increase in the number of wire harnesses can be suppressed. By suppressing the increase in the number of wire harnesses, the weight of the in-vehicle LAN system can be reduced, and the space in the in-vehicle LAN system can be saved. According to the embodiment of the present invention, improvement in fuel efficiency of the vehicle can be expected by reducing the weight of the in-vehicle LAN system.

  Furthermore, POF is not only cheaper than glass optical fibers, but also has a feature of flexibility. According to the embodiment of the present invention, since POF is applied to the optical fiber 3, not only an inexpensive optical communication system can be constructed, but also the optical fiber can be easily wired inside the vehicle.

  As described above, by applying the optical communication apparatus according to the embodiment of the present invention to an in-vehicle LAN system, communication speed is improved, communication reliability is improved, vehicle fuel efficiency is improved, and in-vehicle LAN system is saved. Space becomes possible.

  FIG. 2 is a block diagram showing a basic configuration of the optical communication apparatus 1 shown in FIG. With reference to FIG. 2, the optical communication device 1 includes an optical transmitter 2, an optical fiber 3, and an optical receiver 4. The optical transmitter 2 includes a light source 11 and a drive circuit 12 for driving the light source 11.

  The light source 11 is an LED (light emitting diode) that emits visible light or an LD (semiconductor laser) that emits visible light. Specifically, the emission wavelength of the light source 11 is in the green region. In the description of the embodiment of the present invention, the “green region” is a wavelength region of 500 nm or more and 580 nm or less. More specifically, the light emission wavelength of the light source 11 is, for example, 530 nm.

  Since there is a region in the visible light region where the transmission loss of POF is low, a light source that generates visible light is generally used in an optical communication system using POF. Furthermore, the conduction loss of POF is smaller in the green region than in the red region. Therefore, in the embodiment of the present invention, a green LED or a green LD is used as the light source 11.

  The drive circuit 12 drives the light source 11 by supplying a current 111 to the light source 11. The drive circuit 12 changes the current 111 in response to the electrical signal sent from the hub 6 shown in FIG. When the current supplied to the light source 11 is changed by the drive circuit 12, the intensity of the light emitted from the light source 11 is changed. As a result, an optical signal 101 is emitted from the light source 11. For example, a digital signal is input to the drive circuit 12. The drive circuit 12 supplies a pulse current corresponding to the digital signal to the light source 11. The light source 11 outputs an optical signal 101 composed of an optical pulse according to the pulse current.

  As described above, the optical fiber 3 is a POF, more preferably a graded index (GI) POF. The GI POF is a fiber in which the refractive index of the core gradually decreases from the center of the core toward the peripheral edge of the core (the boundary between the core and the clad). By applying the GI-type POF to the optical fiber 3, modal dispersion (difference in arrival time of optical pulses depending on wavelength) can be reduced. This can be expected to increase the speed of optical communication.

  The optical receiver 4 includes a light receiving circuit 21 and a current detection circuit 22. The light receiving circuit 21 is constituted by a photodiode, for example, and converts the optical signal 102 from the optical fiber 3 into a current signal 103. The current detection circuit 22 includes, for example, a resistance element (not shown), converts the current signal 103 output from the light receiving circuit 21 into a voltage signal 104, and outputs the voltage signal 104.

FIG. 3 is a cross-sectional view schematically showing a green LED applicable to the light source 11 shown in FIG.
With reference to FIG. 3, LED 11 </ b> A includes a substrate 31 and a light emitting element formed on the main surface of substrate 31. The light emitting element includes an n-type buffer layer 32, a well layer 33, a barrier layer 34, a p-type electron block layer 35, a p-type contact layer 36, a p-type electrode 37, and an n-type electrode 38.

  The substrate 31 is a GaN (gallium nitride) substrate. The main surface of the substrate 31 is a nonpolar surface or a semipolar surface. The “nonpolar plane” is a plane in the normal direction to the polar plane (c-plane of the GaN crystal), and specifically, is an a-plane or m-plane perpendicular to the c-plane of the GaN crystal. The “c plane” is the {1000} plane, the “a plane” is the {11-20} plane, and the “m plane” is the {1-100} plane. Here, {} indicates an aggregation plane, and for a negative index, “−” (bar) is attached on the number in terms of crystallography, but in this specification, before the number. It has a negative sign. The “semipolar plane” is a plane inclined by a predetermined angle with respect to the polar plane, that is, the c-plane of the GaN crystal. This angle is preferably a value within a numerical range of 63 ° to 80 °, or 100 ° to 117 °.

  The n-type buffer layer 32 is formed on the main surface (nonpolar surface or semipolar surface) of the substrate 31. N-type buffer layer 32 has a thickness of 2000 nm, for example, and is made of n-type GaN.

The well layer 33 is formed on the n-type buffer layer 32, has a thickness of, for example, 3 nm, and is made of, for example, In _x Ga _1-x N (0 <x <1). By changing the value of x within the range of 0 <x <1, the composition ratio of In and Ga in the well layer 33 changes. Accordingly, the emission wavelength of the light emitting element can be changed in a range from about 360 nm (GaN) to about 1700 nm (InN). In the embodiment of the present invention, x is preferably in the range of 0.2 <x <0.3 from the viewpoint of the emission wavelength range and the emission efficiency.

  The barrier layer 34 is formed on the well layer 33, has a thickness of 15 nm, for example, and is made of undoped GaN, for example.

The p-type electron block layer 35 is formed on the barrier layer 34, has a thickness of, for example, 20 nm, and is made of p-type Al _x Ga _1-x N (0 <x <1). The value of x in p-type Al _x Ga _1-x N is, for example, 0.18.

  The p-type contact layer 36 is formed on the p-type electron block layer 35, has a thickness of, for example, 100 nm, and is made of p-type GaN.

  The p-type electrode 37 is formed on the p-type contact layer 36 and has a feature of high transmittance. For example, when the p-type electrode 37 is made of nickel (Ni) and gold (Au), it may be made of ITO (indium tin oxide) or the like. The n-type electrode 38 is formed on the surface of the substrate 31 located opposite to the surface of the substrate 31 on which the n-type buffer layer 32 is formed, and is made of, for example, titanium (Ti) and Al.

FIG. 4 is a cross-sectional view schematically showing a green LD applicable to the light source 11 shown in FIG.
Referring to FIG. 4, LD 11 </ b> B includes a substrate 41 and a light emitting element formed on the main surface of substrate 41. The light emitting device includes an n-type cladding layer 42, a guide layer 43, a well layer 44, a guide layer 45, a p-type electron blocking layer 46, a guide layer 47, a p-type cladding layer 48, and a p-type contact layer. 49, a p-type electrode 50, an n-type electrode 51, and an insulating film 52.

  The substrate 41 is a GaN substrate. The main surface of the substrate 41 is a nonpolar surface or a semipolar surface. Since the configuration of substrate 41 is the same as the configuration of substrate 31, the description thereof will not be repeated.

The n-type cladding layer 42 is formed on the main surface of the substrate 41, has a thickness of, for example, 2300 nm (2.3 μm), and has n-type In _y Al _x Ga _(1-xy) N (0 <x <1, 0 <y <1, x + y <1). Hereinafter, In _y Al _x Ga _(1-xy) N (0 <x <1, 0 <y <1, x + y <1) is referred to as “InAlGaN”.

The guide layer 43 includes a first layer 43a formed on the n-type cladding layer 42 and a second layer 43b formed on the first layer 43a. The first layer 43a has a thickness of, for example, 250 nm and is made of n-type GaN. The second layer 43b has a thickness of 115 nm, for example, and is made of undoped In _x Ga _1-x N (0 <x <1). The value of x in In _x Ga _1-x N is, for example, 0.02.

The well layer 44 is formed on the guide layer 43, has a thickness of 3 nm, for example, and is made of In _x Ga _1-x N (0 <x <1), for example. Similar to the well layer 33, x is preferably in the range of 0.25 <x <0.3 from the viewpoint of the emission wavelength range and the emission efficiency. Hereinafter, In _(1-x) Ga _x N (0 <x <1) is also referred to as “InGaN”.

  The guide layer 45 is formed on the well layer 44, has a thickness of, for example, 65 nm, and is made of undoped InGaN.

The p-type electron block layer 46 is formed on the guide layer 45, has a thickness of, for example, 20 nm, and is made of p-type Al _x Ga _1-x N (0 <x <1). The value of x in p-type Al _x Ga _1-x N is, for example, 0.18.

  The guide layer 47 includes a first layer 47a formed on the p-type electron block layer 46 and a second layer 47b formed on the first layer 47a. The first layer 47a has a thickness of 50 nm, for example, and is made of p-type InGaN. Second layer 47b has a thickness of, for example, 250 nm and is made of p-type GaN.

  The p-type cladding layer 48 is formed on the guide layer 47, has a thickness of, for example, 400 nm (0.4 μm), and is made of p-type InAlGaN.

  The p-type contact layer 49 is formed on the p-type cladding layer 48, has a thickness of, for example, 50 nm, and is made of p-type GaN.

  The p-type electrode 50 is formed on the p-type contact layer 49 and is made of, for example, Ni and Au. The n-type electrode 51 is formed on the surface of the substrate 41 located on the opposite side of the surface of the substrate 41 on which the n-type cladding layer 42 is formed, and is made of, for example, Ti and Al.

  Except for the contact portion between the p-type electrode 50 and the p-type contact layer 49, a mesa structure is formed by dry etching. In addition to the contact portion, for example, SiO2 is formed as the insulating film 52 by vapor deposition.

  In a light-emitting element formed on a polar plane (c-plane), a piezoelectric field is induced because strain of a well layer increases due to mismatch of crystal lattices. Due to the influence of the piezoelectric field, the longer the emission wavelength, the longer the emission lifetime. For example, the emission lifetime of a green LED formed on the c-plane of a sapphire crystal is about 100 nanoseconds.

  On the other hand, according to the embodiment of the present invention, the light emitting element (specifically, LED or LD) is formed on the nonpolar or semipolar surface of the GaN substrate. Thus, the influence of the piezoelectric field can be reduced, so that the light emission efficiency of the light emitting element can be improved and the light emission lifetime can be shortened. For example, the emission lifetime of the green LED shown in FIG. 3 is on the order of nanoseconds (about 1 to 10 nanoseconds). In the case of the green LD shown in FIG. 4, in the mode in which laser light is emitted, the light emission lifetime is on the order of picoseconds (about 1 to 100 picoseconds).

  The operating speed of the light source can be increased by shortening the light emitting lifetime of the light emitting element. That is, light can be turned on / off at high speed. Therefore, according to the embodiment of the present invention, high-speed optical communication can be realized.

  When a semipolar plane is selected as the main surface of the GaN substrate, the predetermined angle from the c plane is preferably a value within a numerical range such as 63 ° to 80 °, or 100 ° to 117 °. The light emission lifetime can be shortened by selecting the inclination angle of the semipolar surface with respect to the c-plane within the above range.

  According to the embodiment of the present invention, a GaN substrate is used as a substrate for forming a light emitting element. By using a GaN substrate that has fewer dislocations (disturbance of atomic arrangement in the crystal) than a sapphire substrate, the reliability of a light-emitting element formed on the substrate can be increased. Specifically, the light emitting element can be stably operated and the heat dissipation of the light emitting element can be improved.

  Furthermore, the light emitting device according to the embodiment of the present invention includes a single well layer. That is, the light emitting device according to the embodiment of the present invention has an SQW (Single Quantum Well) structure. Thereby, the light emission lifetime can be shortened compared with the light emitting element of MQW (Multi Quantum Well) structure.

  The LD 11B shown in FIG. 4 has the following characteristics in addition to the above characteristics. First, the thickness of at least the guide layer 43 formed on the n-type cladding layer 42 is larger than the thickness of a general guide layer (50 nm), and the p-type electron block layer 46 includes two guide layers (the guide layer 45 and the guide layer 45). Sandwiched between layers 47). With such a configuration, the light emission efficiency can be increased.

  Next, since the pn junction area is small, the junction capacitance can be reduced. Thereby, since CR time constant can be made small, responsiveness can be improved.

  Reliability is particularly required for a light source used for optical communication. According to the embodiment of the present invention, a light source excellent in reliability as described above can be realized. By using this light source, an optical transmitter having excellent reliability can be realized. Therefore, according to the embodiment of the present invention, an optical transmitter and an optical communication device excellent in reliability can be realized. In order to further improve the reliability, control for keeping the element temperature constant may be executed. For example, by keeping the temperature of the light source constant using a Peltier element, it is possible to realize control for keeping the element temperature constant.

  Furthermore, according to the embodiment of the present invention, a light-emitting element with a short light emission lifetime as described above can be realized. Therefore, the light source can be operated at high speed. By using this light source for an optical transmitter, high-speed optical communication can be realized. In particular, the speed of optical communication can be further increased by using an LD as a light source (light emitting element) for an optical transmitter.

  The optical communication apparatus according to the embodiment of the present invention is not limited to the one having the configuration shown in FIG. Several configurations of the optical communication apparatus according to the embodiment of the present invention are exemplified below.

  FIG. 5 is a diagram schematically showing one application example of the optical communication apparatus according to the embodiment of the present invention.

  With reference to FIG. 5, the optical communication device 1 </ b> A is an optical communication system according to a wavelength division multiplexing (WDM) system. Specifically, the optical communication apparatus 1A includes n optical transmitters 2.1, 2.2,... n, optical multiplexer 9a, optical fiber 3, optical demultiplexer 9b, and n optical receivers 4.1, 4.2,. n.

Optical transmitters 2.1, 2.2,... n emits optical signals having different wavelengths. Specifically, the optical transmitters 2.1, 2.2,. n emits optical signals of wavelengths λ ₁ , λ ₂ ,..., λ _n , respectively.

  The optical multiplexer 9 a combines (combines) a plurality of optical signals having different wavelengths and sends them to the optical fiber 3. The optical demultiplexer 9b demultiplexes a plurality of optical signals having different wavelengths transmitted by the optical fiber 3 for each wavelength.

Optical receivers 4.1, 4.2,. n is an optical transmitter 2.1, 2.2,. Each of them is provided corresponding to n. Each optical receiver receives a corresponding optical signal among a plurality of optical signals (optical signals of wavelengths λ ₁ , λ ₂ ,..., Λ _n ) transmitted from the optical demultiplexer 9b. Specifically, the optical receivers 4.1, 4.2,. n receives optical signals of wavelengths λ ₁ , λ ₂ ,..., λ _n , respectively.

  Optical transmitters 2.1, 2.2,... Each configuration of n is the same as the configuration of optical transmitter 2 shown in FIG. 2, and therefore detailed description will not be repeated hereinafter. Similarly, optical receivers 4.1, 4.2,. Each configuration of n is the same as the configuration of optical receiver 4 shown in FIG. 2, and therefore detailed description will not be repeated hereinafter.

The wavelengths λ ₁ , λ ₂ ,..., Λ _n are all in the green region (the above-described range of 500 nm to 580 nm), and more preferably in the range centered on 530 nm. The wavelength interval between the wavelengths λ ₁ , λ ₂ ,..., Λ _n is not particularly limited. Note that at least one of the wavelengths λ ₁ , λ ₂ ,..., Λ _n may be in a region different from the green region, for example, in the red region.

  As shown in FIG. 5, in the embodiment of the present invention, the optical communication device can be configured so that optical communication according to the wavelength division multiplexing communication system is possible. By executing the wavelength division multiplexing communication, the transmission capacity of the optical communication device can be further increased.

  FIG. 6 is a diagram schematically showing another application example of the optical communication apparatus according to the embodiment of the present invention. Referring to FIG. 6, an optical communication device 1B is an optical communication system in accordance with a time division multiplexing (TDM) system. Specifically, the optical communication device 1B includes a multiplexing device 9c, an optical transmitter 2, an optical fiber 3, an optical receiver 4, and a demultiplexing device 9d.

  The multiplexing device 9c sequentially assigns a plurality of data (indicated as “data 1”, “data 2”,..., “Data n” in FIG. 6) to time slots divided at predetermined time intervals. , “Data 1”, “data 2”,..., “Data n” are time-division multiplexed. The signal multiplexed by the multiplexing device 9 c is input to the optical transmitter 2.

  Since the configuration of optical transmitter 2 is the same as that shown in FIG. 2, the following description will not be repeated. The optical transmitter 2 converts the electrical signal output from the multiplexing device 9 c into an optical signal and sends the optical signal to the optical fiber 3.

  The optical receiver 4 receives an optical signal transmitted through the optical fiber 3 and converts the optical signal into an electrical signal. Since the configuration of optical receiver 4 is the configuration shown in FIG. 2, the following description will not be repeated. The demultiplexer 9d separates the electrical signal output from the optical receiver 4 into a plurality of electrical signals using a signal synchronized with the time slot. As a result, a plurality of data (“data 1”, “data 2”,..., “Data n”) are extracted. The transmission capacity of the optical communication apparatus is increased also by the time division multiplexing method shown in FIG. Can do.

  Applications of the optical communication device 1A shown in FIG. 5 and the optical communication device 1B shown in FIG. 6 are not particularly limited. For example, the optical communication device 1A can be mounted on the in-vehicle LAN system 100 shown in FIG.

  As described above, according to the embodiment of the present invention, the optical communication device includes the optical transmitter, the optical fiber, and the optical receiver. The optical transmitter includes a light source that emits visible light. The light source includes a GaN substrate having a nonpolar or semipolar surface as a main surface and a light emitting element (LED or LD) formed on the main surface of the GaN substrate. By using a light emitting element (LED or LD) formed on the main surface of a GaN substrate as a light source (light source of an optical transmitter) of an optical communication device, in a short-distance optical communication system using visible light, High-speed optical communication can be realized.

  The optical communication apparatus and the optical transmitter according to the present invention are not limited to being applied only to an in-vehicle LAN system, but are used in fields where optical fiber communication using POF is used, or optical fiber communication using POF. It is possible to apply to the field where is expected. For example, the optical communication apparatus and the optical transmitter according to the present invention can be applied to an interface of a digital AV device, a home appliance network, and the like.

  Furthermore, in the above-described embodiment of the present invention, the optical fiber applied to the optical communication apparatus is a plastic optical fiber, but instead of the plastic optical fiber, a glass optical fiber is used as the optical communication apparatus according to the embodiment of the present invention. You may apply to.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 1A, 1B optical communication devices, 2, 2.1-2. n Optical transmitter, 3 optical fiber, 4, 4.1-4. n optical receiver, 5a to 5d camera, 6 hub, 7 controller, 8 display, 9a optical multiplexer, 9b optical demultiplexer, 9c multiplexer, 9d demultiplexer, 11 light source, 11A LED, 11B LD, 12 Drive circuit, 21 light receiving circuit, 22 current detection circuit, 31, 41 substrate, 32 n-type buffer layer, 33, 44 well layer, 34 barrier layer, 35, 46 p-type electron block layer, 36, 49 p-type contact layer, 37, 50 p-type electrode, 38, 51 n-type electrode, 42 n-type cladding layer, 43, 45, 47 guide layer, 43a, 47a first layer, 43b, 47b second layer, 48 p-type cladding layer, 52 Insulating film, 100 In-vehicle LAN system, 101, 102 Optical signal, 103 Current signal, 104 Voltage signal, 111 Current, 200 Vehicle

Claims (17)

Optical fiber,
At least one optical transmitter that includes a light source that emits visible light, and transmits the visible light from the light source as an optical signal propagating through the optical fiber;
At least one optical receiver provided corresponding to the at least one optical transmitter and receiving the optical signal via the optical fiber;
The light source is
A gallium nitride substrate having a nonpolar or semipolar surface as a main surface;
And a light emitting element formed on the main surface of the gallium nitride substrate.   The optical communication apparatus according to claim 1, wherein the optical fiber is a plastic optical fiber.   The optical communication apparatus according to claim 1, wherein an emission wavelength of the light emitting element is in a range of 500 nm or more and 580 nm or less. The main surface of the gallium nitride substrate is the nonpolar surface,
The optical communication device according to claim 1, wherein the nonpolar plane is one of an a-plane and an m-plane. The main surface of the gallium nitride substrate is the semipolar surface,
The semipolar plane is any one of a plane having an inclination angle with respect to the c-plane in the range of 63 degrees to 80 degrees and a plane having an inclination angle from the c-plane in the range of 100 degrees to 117 degrees. The optical communication device according to any one of claims 1 to 3.   The optical communication device according to claim 1, wherein the light emitting element is a light emitting diode.   The optical communication device according to claim 1, wherein the light emitting element is a semiconductor laser. The at least one optical transmitter is a plurality of optical transmitters;
The at least one optical receiver is a plurality of optical receivers;
The wavelengths of the plurality of optical signals respectively transmitted from the plurality of optical transmitters are different from each other,
The optical communication device is:
A multiplexer for wavelength multiplexing the plurality of optical signals;
The light according to any one of claims 1 to 7, further comprising a duplexer for separating the plurality of optical signals transmitted by the optical fiber based on a difference in wavelength of each optical signal. Communication device.   The optical communication device according to claim 1, wherein the optical communication device is mounted on a vehicle. An optical transmitter for transmitting an optical signal for optical communication to an optical fiber,
A light source that emits visible light;
A drive circuit for driving the light source so that the light source transmits the optical signal;
The light source is
A gallium nitride substrate having a nonpolar or semipolar surface as a main surface;
And a light emitting device formed on the main surface of the gallium nitride substrate.   The optical transmitter according to claim 10, wherein the optical fiber is a plastic optical fiber.   The optical transmitter according to claim 10 or 11, wherein an emission wavelength of the light emitting element is in a range of 500 nm or more and 580 nm or less. The main surface of the gallium nitride substrate is the nonpolar surface,
The optical transmitter according to claim 10, wherein the nonpolar plane is one of an a-plane and an m-plane. The main surface of the gallium nitride substrate is the semipolar surface,
The semipolar plane is any one of a plane having an inclination angle with respect to the c-plane in the range of 63 degrees to 80 degrees and a plane having an inclination angle from the c-plane in the range of 100 degrees to 117 degrees. The optical transmitter according to any one of claims 10 to 12.   The optical transmitter according to claim 10, wherein the light emitting element is a light emitting diode.   The optical transmitter according to claim 10, wherein the light emitting element is a semiconductor laser.   The optical transmitter according to claim 10, wherein the optical transmitter is mounted on a vehicle together with the optical fiber and an optical receiver that receives the optical signal via the optical fiber.

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