JPWO2018173507A1 - Optical transceiver and optical communication system - Google Patents

Abstract

An optical transceiver of the present invention includes at least a light source having a light emitting unit that emits a first mode that is a spatial mode or a transverse mode, a receiving unit, and a directional coupler optically coupled to the light source and the receiving unit. Prepare. The directional coupler includes at least a first waveguide region having a first core and a second waveguide region having a second core. The first waveguide region is arranged so that light emitted from the light emitting unit is incident on the first core at a first end of the directional coupler. The second waveguide region is arranged such that at least a part of a second mode having an order different from that of the first mode can transition between the first core and the second waveguide region. The receiving unit includes a light receiving unit into which at least a part of the second mode emitted from the second core is incident at a first end of the directional coupler.

Description

The present invention relates to an optical transceiver and an optical communication system.
This application claims priority based on Japanese Patent Application No. 2017-057327 for which it applied to Japan on March 23, 2017, and uses the content here.

  Conventionally, a single-core bidirectional optical module that can perform bidirectional communication using a single optical fiber has been used in Passive Optical Network (PON), which is subscriber-based communication. In the single-core bidirectional optical module, as shown in Patent Document 1, the laser light is transmitted and received with different wavelengths on the upstream and downstream, and the light is multiplexed or demultiplexed using a long wavelength cut filter or a short wavelength cut filter. Is going. As the filter, a dielectric multilayer film is used by being incorporated in the optical path.

Japanese Unexamined Patent Publication No. 2006-119464

  In a conventional optical communication system, it is necessary to change the wavelength of light upstream and downstream using a wavelength selection device such as a filter. Therefore, since a device for wavelength selection such as a filter is inserted between the laser and the optical fiber or between the light receiving element and the optical fiber, it is inevitable that the device configuration becomes complicated or large.

  An object of one embodiment of the present invention is to provide an optical transmission / reception device and an optical communication system that have a simple structure and can be miniaturized.

  One embodiment of the present invention includes at least a light source having a light emitting unit that emits a first mode that is a spatial mode or a transverse mode, a receiving unit, and a directional coupler optically coupled to the light source and the receiving unit. The directional coupler includes at least a first waveguide region having a first core and a second waveguide region having a second core, and the first waveguide region is formed of the directional coupler. The first end portion is arranged so that light emitted from the light emitting portion is incident on the first core, and the second waveguide region has at least one second mode different in order from the first mode. Is disposed so as to be capable of transition between the first core and the second waveguide region, and the receiver is configured to emit the second light emitted from the second core at a first end of the directional coupler. An optical transmission having a light receiving portion on which at least a part of the mode is incident To provide a communication apparatus.

The second waveguide region has a third core that is optically coupled to the first core so that at least a part of the second mode of the first core can transition, and the third core is configured to be in the second mode. It is preferable that at least a part of the second core is optically coupled to the second core so as to be capable of transition.
The directional coupler includes a first coupling portion whose one end is the first end portion, and a second coupling portion connected to the other end of the first coupling portion, wherein the first coupling portion is Preferably, the first core, the second core, and the third core are included, and the second coupling portion includes the first core and the third core.
The center-to-center distance between the first core and the third core is preferably greater than the center-to-center distance between the third core and the second core.

  According to one embodiment of the present invention, at least a light source having a light emitting unit that emits a second mode having a different order from the first mode that is a spatial mode or a transverse mode, a receiving unit, and the light source and the receiving unit are optically coupled A directional coupler, and the directional coupler includes at least a first waveguide region having a first core and a second waveguide region having a second core, and the second waveguide region. Is arranged such that light emitted from the light emitting part is incident on the second core at the first end of the directional coupler, and the first waveguide region is at least one of the second modes. Is disposed so as to be able to transition between the second core and the first waveguide region, and the receiver is configured to emit the first light emitted from the first core at a first end of the directional coupler. An optical transmission having a light receiving portion on which at least a part of the mode is incident To provide a communication apparatus.

The second waveguide region includes a third core that is optically coupled to the second core so that at least a part of the second mode of the second core can transition, and the third core is configured to be in the second mode. Preferably, at least a part of the first core is optically coupled to the first core so as to be capable of transition.
The directional coupler includes a first coupling portion whose one end is the first end portion, and a second coupling portion connected to the other end of the first coupling portion, wherein the first coupling portion is Preferably, the first core, the second core, and the third core are included, and the second coupling portion includes the first core and the third core.
The center-to-center distance between the first core and the third core is preferably greater than the center-to-center distance between the third core and the second core.

  One embodiment of the present invention includes a first optical transmission / reception device that is the above-described optical transmission / reception device, a second optical transmission / reception device that is the above-described optical transmission / reception device, the first optical transmission / reception device, and the second optical transmission / reception device. An optical communication system comprising an optical transmission line to be connected is provided.

  According to one embodiment of the present invention, an optical transceiver and an optical communication system that have a simple structure and can be reduced in size are provided.

1 is a configuration diagram of an optical communication system according to a first embodiment of the present invention. It is sectional drawing which follows the II line | wire shown in FIG. It is sectional drawing which follows the II-II line | wire shown in FIG. It is sectional drawing which follows the III-III line | wire shown in FIG. It is sectional drawing which follows the IV-IV line | wire shown in FIG. It is sectional drawing which follows the VV line shown in FIG. It is sectional drawing which follows the VI-VI line shown in FIG. It is sectional drawing which shows typically schematic structure of the 1st transmission / reception part of the optical communication system shown in FIG. It is a figure which shows the mode in the code | symbol A shown in FIG. 3A. It is a figure which shows the mode in the code | symbol B shown to FIG. 3A. It is a figure which shows the mode in the code | symbol C shown to FIG. 3A. It is a figure which shows the mode in the code | symbol D shown to FIG. 3A. It is sectional drawing which follows the VII-VII line shown to FIG. 3A. It is a top view which shows typically schematic structure of the 1st transmission / reception part of the optical communication system shown in FIG. It is the enlarged view which expanded the part which the code | symbol E shows in FIG. 5A. It is sectional drawing which shows typically schematic structure of the 1st transmission / reception part of the optical communication system shown in FIG. It is a figure which shows the example of the spectrum of the light radiate | emitted from the light source of the 1st transmission / reception part. It is sectional drawing which shows typically schematic structure of the 2nd transmission / reception part of the optical communication system shown in FIG. It is a figure which shows the mode in the code | symbol F shown to FIG. 7A. It is a figure which shows the mode in the code | symbol G shown to FIG. 7A. It is a figure which shows the mode in the code | symbol H shown to FIG. 7A. It is a figure which shows the mode in the code | symbol I shown to FIG. 7A. It is sectional drawing which follows the VIII-VIII line shown to FIG. 7A. It is a top view which shows typically schematic structure of the 2nd transmission / reception part of the optical communication system shown in FIG. It is a figure which shows the example of the spectrum of the light radiate | emitted from the light source of the 2nd transmission / reception part. It is a figure which shows the example of the relationship between the distance between centers of a pair of core of a directional coupler, and coupling length. It is a figure which shows the example of the relationship between the center-center distance of a pair of core of a directional coupler, and the residual amount of the LP01 mode in a 1st core. It is a block diagram of the optical communication system which concerns on 2nd Embodiment of this invention.

Hereinafter, an optical communication system according to an embodiment of the present invention will be described with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for the sake of convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. Absent. Further, the present invention is not limited to the following embodiment.
In general, a plurality of modes such as a longitudinal mode and a transverse mode, which are laser oscillation modes, and a spatial mode, which is a fiber propagation mode, are known as modes used in optical transmission. Among these modes, the “first mode” of the present invention is a spatial mode or a transverse mode.
In particular, an LP (Linear Polarized mode) mode described later, that is, an “LP11 mode”, an “LP12 mode”, and an “LP01 mode” correspond to a “spatial mode” that is one of the first modes of the present invention.
Note that the “lateral mode” which is one of the first modes of the present invention may be applied to the present embodiment.

<Optical Transceiver and Optical Communication System (First Embodiment)>
FIG. 1 is a configuration diagram of an optical communication system 10 according to the first embodiment. 2A to 2F are a cross-sectional view taken along line II, a cross-sectional view taken along line II-II, a cross-sectional view taken along line III-III, a cross-sectional view taken along line IV-IV, and V- It is sectional drawing which follows the V line, and sectional drawing which follows a VI-VI line.

  As shown in FIG. 1, an optical communication system 10 includes a first transmission / reception unit 1 (optical transmission / reception device), an optical transmission line 2 optically coupled to the first transmission / reception unit 1, and an optical transmission line 2 And a second transmitter / receiver 3 (optical transmitter / receiver). That is, the optical communication system 10 includes a first transmission / reception unit 1, a second transmission / reception unit 3, and an optical transmission path 2 that connects the first transmission / reception unit 1 and the second transmission / reception unit 3.

The light coupling between the light source (light emitting unit) and the first core, or the light coupling between the light source and the second core means that the light emitted from the light source enters the first core or the second core.
For example, the light source (light emitting unit) and the first core are optically coupled, or the light source and the second core are optically coupled means the following cases (i), (ii), and (iii). .
(I) The light source and the first core are separated from each other, or the light source and the second core are separated from each other, and light emitted from the light source enters the first core or the second core.
(Ii) The light source and the first core are separated from each other, or the light source and the second core are separated from each other, and the light source and the first core are connected to each other through a relay optical transmission line such as an optical fiber, or The light source and the second core are connected to each other through a relay optical transmission line such as an optical fiber, and light emitted from the light source enters the first core or the second core through the relay optical transmission line.
(Iii) The light source and the first core are installed in contact with each other, or the light source and the second core are installed in contact with each other, and light emitted from the light source enters the first core or the second core.

When the receiving unit (light receiving unit) and the first core are optically coupled, or when the receiving unit and the second core are optically coupled, the light emitted from the first core or the second core is the receiving unit (light receiving unit). To be incident on.
For example, the receiving unit (light receiving unit) and the first core are optically coupled or the receiving unit and the second core are optically coupled in the following cases (i), (ii), and (iii): Say that.
(I) The first core and the receiving unit are separated from each other, or the second core and the receiving unit are separated from each other, and light emitted from the first core or the second core enters the receiving unit (light receiving unit). To do.
(Ii) The first core and the receiving unit are separated from each other, or the second core and the receiving unit are separated from each other, and the first core and the receiving unit are connected to each other through a relay optical transmission line such as an optical fiber. Alternatively, the second core and the receiving unit are connected to each other through a relay optical transmission path such as an optical fiber, and light emitted from the first core or the second core is received through the relay optical transmission path (light receiving unit). Is incident on.
(Iii) The first core and the receiving unit are installed in contact with each other, or the second core and the receiving unit are installed in contact with each other, and light emitted from the first core or the second core is received by the receiving unit (light receiving). To the center).
In addition, two cores optically couple so that at least part of the light can transition, for example, means that at least part of the light propagating in one of the two cores can transition to the other core. .

The optical coupling between the first coupling portion and the second coupling portion means that, for example, light emitted from the core of the first coupling portion enters the core of the second coupling portion, or from the core of the second coupling portion. It means that the emitted light is incident on the core of the first coupling portion.
The optical coupling between the second coupling unit and the relay unit means, for example, that light emitted from the core of the second coupling unit is incident on the core of the relay unit or light emitted from the core of the relay unit is the first It is incident on the core of the two joints.
The optical coupling between the relay unit and the optical transmission path means that, for example, light emitted from the core of the relay section enters the core of the optical transmission path, or light emitted from the core of the optical transmission path is relayed To be incident on the core.

FIG. 3A is a cross-sectional view schematically showing a schematic configuration of the first transmission / reception unit 1 of the optical communication system 10. FIG. 3B is a diagram illustrating modes (LP11 mode and LP12 mode) in the code A illustrated in FIG. 3A. FIG. 3C is a diagram illustrating a mode (LP01 mode) in the code B illustrated in FIG. 3A. FIG. 3D is a diagram illustrating modes (LP11 mode and LP12 mode) in the code C illustrated in FIG. 3A. FIG. 3E is a diagram showing a mode (LP01 mode) in the symbol D shown in FIG. 3A. 4 is a cross-sectional view taken along line VII-VII shown in FIG. 3A.
As illustrated in FIG. 3A, the first transmission / reception unit 1 includes a light source 11, a reception unit 12, a directional coupler 13, and a relay unit 14.
The light source 11 is, for example, a surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser). By using the VCSEL, the structure of the first transmission / reception unit 1 can be simplified.

FIG. 5A is a plan view schematically showing a schematic configuration of the first transmission / reception unit 1. FIG. 5B is an enlarged view in which a portion indicated by a symbol E in FIG. 5A is enlarged. FIG. 5C is a cross-sectional view schematically showing a schematic configuration of the first transmission / reception unit 1.
As shown in FIGS. 5A to 5C, the light source 11 includes a base portion 16, a light emitting portion 17, a cathode electrode 18, and an anode electrode 19. The light emitting unit 17, the cathode electrode 18, and the anode electrode 19 are provided on the base unit 16. The cathode electrode 18 and the anode electrode 19 are connected to a driver 21 via a wire 20.
The base unit 16 and the driver 21 are provided on the substrate 31. The substrate 31 is connected to a card edge connector 33 via an FPC (flexible printed wiring board) 32.
The electric signal is amplified by the driver 21 and input from the electrodes 18 and 19 to the base unit 16, whereby the light emitting unit 17 emits the modulated first light L1 (see FIGS. 3A and 3E). .

FIG. 6 is a diagram illustrating an example of a spectrum of the first light L1 emitted from the light source 11 of the first transmission / reception unit 1.
As shown in FIG. 6, the light L1 includes a fundamental mode (LP01 mode) (first mode) having the longest wavelength. The light L1 is substantially single mode light because the power of modes other than the fundamental mode is significantly lower than the power of the fundamental mode. When the light L1 is a single mode light, it is possible to reduce the crosstalk noise between the upstream signal and the downstream signal in optical transmission.
The light L1 may include a higher order mode (for example, LP11 mode, LP12 mode, etc.) (second mode) having a higher order than the basic mode.

As illustrated in FIGS. 5A and 5B, the receiving unit 12 is, for example, a photodiode (PD: Photo Diode). Examples of the PD include a GaAs PIN type photodiode (PIN-PD) and an avalanche photodiode (APD). The receiving unit 12 includes a base unit 36, a light receiving unit 37, a cathode electrode 38, and an anode electrode 39.
At least a part of the higher-order mode emitted from the second core 29A is incident on the light receiving unit 37 at the first end 13a (see FIG. 3A) of the directional coupler 13.
The light receiving unit 37, the cathode electrode 38, and the anode electrode 39 are provided on the base unit 36. The cathode electrode 38 and the anode electrode 39 are connected to a TIA (Trans-Impedance Amplifier) 41 through a wire 40.
The base part 36 and the TIA 41 are provided on the substrate 31.

As shown in FIG. 3A, the directional coupler 13 includes first and second waveguide regions 26 and 27, and a clad 25 surrounding the first and second waveguide regions 26 and 27.
The first waveguide region 26 has a first core 28A. The first core 28 </ b> A extends along the longitudinal direction of the directional coupler 13.
The first waveguide region 26 is arranged so that the light L1 emitted from the light emitting unit 17 of the light source 11 is incident on the first core 28A at the first end 13a of the directional coupler 13.
Specifically, since the first core 28A is located at a position where at least a part of the start end 28Aa at the first end portion 13a overlaps the light emitting portion 17 of the light source 11 in plan view, the light L1 emitted from the light emitting portion 17 is the start end. Incident from 28Aa. In other words, the first core 28 </ b> A is disposed so as to be optically coupled to the light emitting unit 17. In addition, planar view means seeing from the length direction of the directional coupler 13 or the relay part 14.
Since the terminal 28Ab of the first core 28A is at least partially overlapped with the first end 23a of the transmission line core 23 of the optical transmission line 2 in plan view (see FIG. 1), the first core 28A is the optical transmission line. Two transmission path cores 23 are optically coupled.
The first waveguide region 26 has only the first core 28A, but the first waveguide region may have two or more cores.

The second waveguide region 27 has a second core 29A and a third core 29B. The second core 29 </ b> A and the third core 29 </ b> B extend along the longitudinal direction of the directional coupler 13.
The third core 29B is optically coupled to the first core 28A so that at least a part of the higher mode of the first core 28A can transition. Thereby, in the second waveguide region 27, at least a part of the higher-order mode can transition between the first core 28 </ b> A and the second waveguide region 27.
The third core 29B is formed in parallel with the second core 29A at an interval that enables optical coupling. The third core 29B is optically coupled to the second core 29A so that at least a part of the higher-order mode can transition.
In addition, although the 2nd waveguide region 27 is the structure which has 2nd core 29A and 3rd core 29B, the 2nd waveguide region may have three or more cores.

In the third core 29 </ b> B, the terminal end 29 </ b> Bb at the first end portion 13 a (one end portion 43 a of the first coupling portion 43) is located away from the light receiving portion 37 of the receiving portion 12 in plan view. Therefore, the third core 29 </ b> B is not optically coupled to the light receiving unit 37. The starting end 29Ba of the third core 29B is at the other end 44b of the second coupling portion 44.
In FIG. 3A, the end 29Bb of the third core 29B has reached the first end 13a, but does not necessarily have to reach the first end 13a. In FIG. 3A, the start end 29Ba of the third core 29B reaches the other end 44b of the second coupling portion 44, but it does not necessarily have to reach the other end 44b of the second coupling portion 44.

  The end 29Bb of the third core 29B is at a position away from the light emitting unit 17 of the light source 11 in plan view. For this reason, the third core 29 </ b> B is not optically coupled to the light emitting unit 17.

The second core 29A is in a position where at least a part of the terminal end 29Ab at the first end portion 13a (one end portion 43a of the first coupling portion 43) overlaps the light receiving portion 37 of the receiving portion 12 in plan view. Therefore, the light emitted from the terminal end 29Ab enters the light receiving unit 37. That is, the second core 29 </ b> A is disposed so as to be optically coupled to the light receiving unit 37. The starting end 29Aa of the second core 29A is at the other end 43b of the first coupling portion 43.
In FIG. 3A, the end 29Ab of the second core 29A reaches the first end 13a, but it does not necessarily have to reach the first end 13a. In FIG. 3A, the starting end 29Aa of the second core 29A reaches the other end 43b of the first coupling portion 43, but it does not necessarily have to reach the other end 43b of the first coupling portion 43.

The directional coupler 13 includes a first coupling portion 43 and a second coupling portion 44. One end portion 43 a of the first coupling portion 43 is the first end portion 13 a of the directional coupler 13.
As shown in FIG. 4, the first coupling portion 43 includes a first core 28A, a third core 29B, a second core 29A, and a clad 25 surrounding the cores 28A, 28B, and 29A.
The first core 28A, the third core 29B, and the second core 29A are arranged in the radial direction of the directional coupler 13 in this order. The center distance D1 (distance between the central axes) between the first core 28A and the third core 29B is greater than the center distance D2 (distance between the central axes) between the third core 29B and the second core 29A. preferable. Thereby, in the first coupling portion 43, the return amount of the higher order mode from the third core 29B to the first core 28A can be reduced.
As the first coupling portion 43, a three-core multicore optical fiber can be used. The multi-core optical fiber used for the first coupling unit 43 is, for example, a step index (SI) type.

As shown in FIG. 3A, the second coupling portion 44 includes a first core 28A, a third core 29B, and the cladding 28 surrounding the core 28A and the core 29B. As the second coupling portion 44, a two-core multi-core optical fiber can be used. The multi-core optical fiber used for the second coupling unit 44 is, for example, a step index (SI) type.
One end 44 a of the second coupling portion 44 is connected to the other end 43 b of the first coupling portion 43.

The relay unit 14 includes a first core 28A and a clad 25 surrounding the first core 28A. As the relay unit 14, a single core optical fiber can be used. The optical fiber used for the relay unit 14 is, for example, a step index (SI) type.
One end portion 14 a of the relay portion 14 is connected to the other end portion 44 b of the second coupling portion 44.

As shown in FIG. 1, the optical transmission line 2 is, for example, an optical fiber. The optical transmission line 2 is preferably a step index (SI) type optical fiber.
The first end 2 a of the optical transmission line 2 is optically coupled to the other end 14 b of the relay unit 14 via the optical connector 45. The second end 2 b of the optical transmission line 2 is optically coupled to the other end 114 b of the relay unit 114 via the optical connector 145. The optical transmission line 2 connects the first transmission / reception unit 1 and the second transmission / reception unit 3.

FIG. 7A is a cross-sectional view schematically showing a schematic configuration of the second transmission / reception unit 3 of the optical communication system 10. FIG. 7B is a diagram illustrating a mode (LP01 mode) in the code F illustrated in FIG. 7A. FIG. 7C is a diagram illustrating modes (LP11 mode and LP12 mode) in the code G illustrated in FIG. 7A. FIG. 7D is a diagram showing a mode (LP01 mode) in the symbol H shown in FIG. 7A. FIG. 7E is a diagram showing the modes (LP01 mode, LP11 mode, and LP12 mode) in the symbol I shown in FIG. 7A.
FIG. 8 is a cross-sectional view taken along line VIII-VIII shown in FIG. 7A. FIG. 9 is a plan view schematically showing a schematic configuration of the second transmission / reception unit 3.
As illustrated in FIG. 7A, the second transmission / reception unit 3 includes a light source 111, a reception unit 112, a directional coupler 113, and a relay unit 114.
The light source 111 is, for example, a surface emitting laser (VCSEL). By using the VCSEL, the structure of the second transmission / reception unit 3 can be simplified.

As shown in FIG. 9, the light source 111 includes a base part 116, a light emitting part 117, a cathode electrode 118, and an anode electrode 119. The light emitting unit 117, the cathode electrode 118, and the anode electrode 119 are provided on the base unit 116. The cathode electrode 118 and the anode electrode 119 are connected to the driver 121 via the wire 120.
The base unit 116 and the driver 121 are provided on the substrate 131. The substrate 131 is connected to the card edge connector 133 via an FPC (flexible printed wiring board) 132.
The electric signal is amplified by the driver 121 and input from the electrodes 118 and 119 to the base unit 116, whereby the light emitting unit 117 emits the modulated second light L2 (see FIGS. 7A and 7E). .

FIG. 10 is a diagram illustrating an example of a spectrum of the second light L <b> 2 emitted from the light source 111 of the second transmission / reception unit 3.
As shown in FIG. 10, the light L2 includes at least a higher order mode (for example, LP11 mode, LP12 mode, etc.) having a higher order than the fundamental mode. The light L2 is, for example, multimode light including a basic mode (for example, LP01 mode) and a higher-order mode. When the ratio of the higher-order mode in the light L2 is large, it is possible to reduce the crosstalk noise between the upstream signal and the downstream signal during optical transmission on the optical transmission path 2.
The light L2 may have the same wavelength as the light L1.

As shown in FIG. 9, the receiving unit 112 is, for example, a photodiode (PD). Examples of PD include PIN-PD and APD. The receiving unit 112 includes a base unit 136, a light receiving unit 137, a cathode electrode 138, and an anode electrode 139.
At least a part of the fundamental mode emitted from the first core 128A is incident on the light receiving unit 137 at the first end 113a (see FIG. 7A) of the directional coupler 113.
The light receiving portion 137, the cathode electrode 138, and the anode electrode 139 are provided on the base portion 136. The cathode electrode 138 and the anode electrode 139 are connected to the TIA 141 via the wire 140.
The base portion 136 and the TIA 141 are provided on the substrate 131.

As shown in FIG. 7A, the directional coupler 113 includes first and second waveguide regions 126 and 127 and a clad 125 surrounding the first and second waveguide regions 126 and 127.
The first waveguide region 126 has a first core 128A. The first core 128 </ b> A extends along the longitudinal direction of the directional coupler 113.
The first waveguide region 126 is arranged so that the light L <b> 2 emitted from the first core 128 </ b> A is incident on the light receiving unit 137 of the receiving unit 112 at the first end 113 a of the directional coupler 113.
Specifically, since the first core 128A is located at a position where at least a part of the terminal end 128Ab at the first end 113a overlaps the light receiving unit 137 of the receiving unit 112 in plan view, the light L1 emitted from the first core 128A. Is incident on the light receiving unit 137. That is, the first core 128A is arranged so as to be optically coupled to the light receiving unit 137. In addition, planar view means seeing from the length direction of the directional coupler 113 or the relay part 114.
Since the first end 128Aa of the first core 128A is at a position at least partially overlapping the second end 23b of the transmission path core 23 of the optical transmission path 2 in plan view (see FIG. 1), the first core 128A is an optical transmission path. Two transmission path cores 23 are optically coupled.
In addition, although the 1st waveguide region 126 is the structure which has only the 1st core 128A, the 1st waveguide region may have two or more cores.

The second waveguide region 127 has a second core 129A and a third core 129B. The second core 129 </ b> A and the third core 129 </ b> B extend along the longitudinal direction of the directional coupler 113.
The third core 129B is optically coupled to the first core 128A so that at least a part of the higher-order mode of the first core 128A can transition. As a result, in the second waveguide region 127, at least a part of the higher-order mode can transition between the first core 128A and the second waveguide region 127.
The third core 129B is formed in parallel with the second core 129A at an interval that enables optical coupling. The third core 129B is optically coupled to the second core 129A so that at least a part of the higher-order mode can transition.
The second waveguide region 127 has a second core 129A and a third core 129B, but the second waveguide region may have three or more cores.

In the third core 129B, the start end 129Ba at the first end portion 113a (one end portion 143a of the first coupling portion 143) is at a position away from the light receiving portion 137 of the receiving portion 112 in plan view. Therefore, the third core 129B is not optically coupled to the light receiving unit 137. The end 129Bb of the third core 129B is at the other end 144b of the second coupling portion 144.
In FIG. 7A, the starting end 129Ba of the third core 129B reaches the first end 113a, but it does not necessarily have to reach the first end 113a. In FIG. 7A, the end 129Bb of the third core 129B reaches the other end 144b of the second coupling portion 144, but it does not necessarily have to reach the other end 144b of the second coupling portion 144.

  The starting end 129Ba of the third core 129B is at a position away from the light emitting unit 117 of the light source 111 in plan view. For this reason, the third core 129 </ b> B is not optically coupled to the light emitting unit 117.

The second core 129A is in a position where at least a part of the start end 129Aa at the first end 113a (one end 143a of the first coupling portion 143) overlaps the light emitting portion 117 of the light source 111 in plan view. Therefore, the light L2 emitted from the light emitting unit 117 is incident on the starting end 129Aa. That is, the second core 129 </ b> A is disposed so as to be optically coupled to the light emitting unit 117. The end 129Ab of the second core 129A is at the other end 143b of the first coupling portion 143.
In FIG. 7A, the starting end 129Aa of the second core 129A has reached the first end 113a, but does not necessarily have to reach the first end 113a. In FIG. 7A, the end 129Ab of the second core 129A reaches the other end 143b of the first coupling portion 143, but it does not necessarily have to reach the other end 143b of the first coupling portion 143.

The directional coupler 113 includes a first coupling portion 143 and a second coupling portion 144. One end 143 a of the first coupling portion 143 is the first end 113 a of the directional coupler 113.
As shown in FIG. 8, the first coupling portion 143 includes a first core 128A, a third core 129B, a second core 129A, and a clad 125 surrounding the cores 128A, 129B, and 129A.
The first core 128A, the third core 129B, and the second core 129A are arranged in the radial direction of the directional coupler 113 in this order. The center distance D3 (distance between center axes) between the first core 128A and the third core 129B is greater than the center distance D4 (distance between center axes) between the third core 129B and the second core 129A. preferable. Thereby, in the first coupling portion 143, the return amount of the higher-order mode from the third core 129B to the first core 128A can be reduced.
As the first coupling portion 143, a 3-core multi-core optical fiber can be used. The multi-core optical fiber used for the first coupling unit 143 is, for example, a step index (SI) type.

As shown in FIG. 7A, the second coupling portion 144 includes a first core 128A, a third core 129B, and a cladding 128 surrounding the core 128A and the core 129B. As the second coupling portion 144, a two-core multicore optical fiber can be used. The multi-core optical fiber used for the second coupling unit 144 is, for example, a step index (SI) type.
One end portion 144 a of the second coupling portion 144 is connected to the other end portion 143 b of the first coupling portion 143.

The relay unit 114 includes a first core 128A and a clad 125 surrounding the first core 128A. As the relay unit 114, a single core optical fiber can be used. The optical fiber used for the relay unit 114 is, for example, a step index (SI) type.
One end portion 114 a of the relay portion 114 is connected to the other end portion 144 b of the second coupling portion 144.

FIG. 11 is a diagram showing an example of the relationship between the center-to-center distance d (horizontal axis) and the coupling length (vertical axis) of the pair of cores in the directional coupler having a pair of cores.
FIG. 12 is a diagram illustrating an example of the relationship between the core center-to-center distance d (horizontal axis) and the LP01 mode remaining power (vertical axis) in one core. The core diameter was 8 μm, the wavelength was 850 nm, and the relative refractive index difference of the core was 0.3%.

As shown in FIG. 11 and FIG. 12, the coupling length of the cores changes according to the center distance d. When the center-to-center distance d is 14 μm, if the length of the core is 100 mm or more, the LP11 mode of 95% or more remains in the first core, and most of the LP11 mode transitions from the first core to the second core. Can be made.
Therefore, in the directional couplers 13 and 113 shown in FIGS. 1, 3A and 7A, for example, the distance between the centers of two adjacent cores is 13 to 15 μm and the length is 100 mm or more (for example, 100 to 150 mm). Can do.

Next, an example of a communication method using the optical communication system 10 will be described.
First, communication in the direction from the first transmission / reception unit 1 to the second transmission / reception unit 3 (hereinafter referred to as the uplink direction) will be described.
As shown in FIGS. 1 and 3A, the light L1 emitted from the light emitting unit 17 of the light source 11 of the first transmitting / receiving unit 1 is incident on the first core 28A from the starting end 28Aa. The light L1 includes at least a fundamental mode (LP01 mode). The light L1 may be mostly in the fundamental mode.
When the light L1 includes a higher order mode, a part of the higher order mode transitions from the first core 28A to the third core 29B. Part of the higher order mode of the third core 29B transitions to the first core 28A.

The light L <b> 1 is emitted from the first core 28 </ b> A, is incident on the transmission path core 23 of the optical transmission path 2, and travels toward the second transmission / reception unit 3.
As shown in FIGS. 1 and 7A, the light L1 is incident on the first core 128A of the second transceiver 3 and is incident on the light receiver 137 of the receiver 112. The optical signal incident on the light receiving unit 137 is photoelectrically converted to obtain an electrical signal.
Even when the light L1 incident on the light receiving unit 137 of the receiving unit 112 includes a high-order mode, communication is not adversely affected if the high-order mode is at a low level.

When the higher-order mode is included in the light L1, a part of the higher-order mode mainly transits from the first core 128A to the third core 129B mainly in the region of the second coupling portion 144, and then Most of the transition from the third core 129B to the second core 129A mainly in the region of the first coupling portion 143.
Part of the higher-order mode that has transitioned to the second core 129A is emitted into the space from the first end 113a (starting end 129Aa), is reflected by the light source 111, becomes stray light, and is repeatedly reflected inside the components of the optical communication system 10. Attenuates. Part of the higher-order mode that has been transitioned to the third core 129B is emitted into the space from the first end 113a (starting end 129Ba) and becomes stray light, and the reflection is repeatedly attenuated inside the components of the optical communication system 10.

Next, communication in the direction from the second transmission / reception unit 3 to the first transmission / reception unit 1 (hereinafter referred to as the downlink direction) will be described.
As shown in FIGS. 1 and 7A, the light L2 emitted from the light emitting unit 117 of the light source 111 of the second transmitting / receiving unit 3 enters the second core 129A from the start end 129Aa.
Since the second core 129A and the third core 129B can be optically coupled, at least a part of the higher-order mode (for example, most of the higher-order mode) is transmitted in the second core 129A in the process of being transmitted. Transition from the core 129A to the third core 129B. Most of the fundamental mode of the light L2 incident on the second core 129A remains in the second core 129A and disappears.

Since the third core 129B and the first core 128A can be optically coupled, at least a part of the higher-order mode of the light L2 of the third core 129B (for example, most of the higher-order mode) is the third core 129B. Is transferred from the third core 129B to the first core 128A.
The light L <b> 2 including the higher order mode is emitted from the first core 128 </ b> A, enters the transmission path core 23 of the optical transmission path 2, and travels toward the first transmission / reception unit 1.

As shown in FIG. 1 and FIG. 3A, the light L <b> 2 enters the first core 28 </ b> A of the first transmission / reception unit 1 from the optical transmission path 2.
Since the first core 28A and the third core 29B can be optically coupled, at least a part of the higher-order modes of the first core 28A (for example, most of the higher-order modes) is transmitted through the first core 28A. In the process (mainly in the region of the second coupling portion 44), the transition is made to the third core 29B.
Since the third core 29B and the second core 29A can be optically coupled, at least a part of the higher-order modes of the light L2 of the third core 29B (for example, most of the higher-order modes) is the third core 29B. Is transferred to the second core 29A in the process of being transmitted (mainly in the region of the first coupling portion 43).
The light L2 of the second core 29A enters the light receiving unit 37 of the receiving unit 12 from the terminal end 29Ab. The optical signal incident on the light receiving unit 37 is photoelectrically converted to obtain an electrical signal.
Even when the basic mode is included in the light L2 incident on the light receiving unit 37 of the receiving unit 12, communication is not adversely affected if the basic mode is at a low level.

  A part of the fundamental mode of the light L2 remaining in the first core 28A is emitted into the space from the first end portion 13a (starting end 28Aa) and becomes stray light, and the reflection is repeatedly attenuated inside the components of the optical communication system 10. Part of the higher-order mode that has been shifted to the third core 29B is emitted from the first end portion 13a (terminal 29Bb) into the space and becomes stray light, and the reflection is repeatedly attenuated inside the components of the optical communication system 10.

1 and 3A includes a first waveguide region 26 in which light L1 including a fundamental mode is incident on the first core 28A, and at least a part of a higher-order mode is the first core 28A. And a second waveguide region 27 capable of transitioning between. For this reason, communication using the basic mode and the higher-order mode is possible with the second transmission / reception unit 3.
Since the first transmission / reception unit 1 does not require a device for wavelength selection such as a filter compared to a conventional optical transmission / reception device that transmits and receives light with different wavelengths for uplink and downlink, the device configuration is simplified, Miniaturization can be achieved. In addition, since the apparatus configuration can be simplified, the cost can be reduced.

In the first transmission / reception unit 1 and the second transmission / reception unit 3, the second cores 29 </ b> A and 129 </ b> A of the directional couplers 13 and 113 are arranged so that the higher-order mode can transition between the first cores 28 </ b> A and 128 </ b> A. ing. The first transmitter / receiver 1 includes a light source 11 that emits light L1 including the fundamental mode, and the second transmitter / receiver 3 includes a light source 111 that emits light L2 including the higher-order mode. Therefore, communication using the basic mode and the higher-order mode can be performed in the uplink direction and the downlink direction, respectively.
Further, in the first transmitter / receiver 1, when the directional coupler 13 includes the second core 29A and the third core 29B, a part of the higher-order mode of the light L1 transitions from the first core 28A to the third core 29B. Therefore, the higher order mode of the light L1 in the first core 28A can be reduced as compared with the case where the third core 29B is not provided. Therefore, it is possible to further reduce noise and realize high quality communication.
In addition, when the directional coupler 113 includes the first core 128A and the third core 129B, the second transmitting / receiving unit 3 transitions a part of the higher-order mode of the light L1 from the first core 128A to the third core 129B. Therefore, the higher-order mode of the light L1 in the first core 128A can be further reduced as compared with the case where the third core 129B is not provided. Therefore, it is possible to further reduce noise and realize high quality communication.

  In the first transmitter / receiver 1, since the directional coupler 13 has the third core 29B, the higher-order mode of the light L2 transitions from the first core 28A to the second core 29A via the third core 29B. For this reason, a sufficient distance between the first core 28A and the second core 29A can be secured. Therefore, the distance between the light emitting unit 17 of the light source 11 and the light receiving unit 37 of the receiving unit 12 can be increased, and design restrictions can be reduced.

The second transmitting / receiving unit 3 illustrated in FIGS. 1 and 7A includes a second waveguide region 127 in which light L2 including a higher order mode is incident on the second core 129A, and at least a part of the higher order mode is the second core 129A. And a first waveguide region 126 capable of transitioning between. For this reason, communication using the basic mode and the higher-order mode is possible between the first transmission / reception unit 1 and the second transmission / reception unit 3.
Since the second transmitter / receiver 3 does not require a device for wavelength selection such as a filter as compared with a conventional optical transmitter / receiver that transmits and receives light with different wavelengths for uplink and downlink, the device configuration is simplified, Miniaturization can be achieved. In addition, since the apparatus configuration can be simplified, the cost can be reduced.

  In the second transmitter / receiver 3, since the directional coupler 113 has the third core 129B, the higher-order mode of the light L2 transitions from the second core 129A to the first core 128A via the third core 129B. Therefore, a sufficient distance between the first core 128A and the second core 129A can be ensured. Therefore, the distance between the light emitting unit 117 of the light source 111 and the light receiving unit 137 of the receiving unit 112 can be increased, and design restrictions can be reduced.

The optical communication system 10 shown in FIG. 1 can perform communication using the basic mode and the higher-order mode in the upstream direction and the downstream direction, respectively. Since the optical communication system 10 does not require a device for wavelength selection such as a filter as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths in upstream and downstream, the device configuration is simplified, Miniaturization can be achieved. In addition, since the apparatus configuration can be simplified, the cost can be reduced.
Since the optical communication system 10 uses light including transverse modes having different orders in the uplink direction and the downlink direction, bidirectional communication is possible at the same wavelength in the uplink direction and the downlink direction. Therefore, the device structure can be further simplified as compared with the conventional optical transceiver described above.

  In the optical communication system 10, since the directional couplers 13 and 113 have the third cores 29B and 129B, as described above, the distance between the light emitting units 17 and 117 and the light receiving units 37 and 137 can be increased, and design restrictions are imposed. Can be reduced.

<Optical Transceiver and Optical Communication System (Second Embodiment)>
FIG. 13 is a configuration diagram of an optical communication system 210 according to the second embodiment. In addition, about the structure which is common in 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 13, the optical communication system 210 includes a first transmission / reception unit 201 (optical transmission / reception device), an optical transmission path 2 optically coupled to the first transmission / reception unit 201, and an optical transmission path 2. A second transceiver 203 (optical transceiver). That is, the optical communication system 210 includes a pair of transmission / reception units 201 and 203 and an optical transmission path 2 that connects them.

The first transmission / reception unit 201 is different from the first transmission / reception unit 1 of the first embodiment in that the third core 29B is not provided.
The second core 29A is formed in parallel with the first core 28A at an interval that enables optical coupling. The second core 29A is optically coupled to the first core 28A so that at least a part of the higher-order mode can transition.

The second transmission / reception unit 203 is different from the second transmission / reception unit 3 of the first embodiment in that it does not include the third core 129B.
The second core 129A is formed in parallel with the first core 128A at an interval that enables optical coupling. The second core 129A is optically coupled to the first core 128A so that at least a part of the higher-order mode can transition.

Next, an example of a communication method using the optical communication system 210 will be described.
First, communication in a direction from the first transmission / reception unit 201 toward the second transmission / reception unit 203 (hereinafter referred to as an uplink direction) will be described.
The light L1 emitted from the light source 11 of the first transmitting / receiving unit 201 is emitted from the light emitting unit 17 and is incident on the first core 28A. The light L1 travels to the second transmission / reception unit 203 through the transmission path core 23 of the optical transmission path 2.
The light L1 is incident on the first core 128A of the second transmission / reception unit 203 and is incident on the light receiving unit 137 of the reception unit 112. The optical signal incident on the light receiving unit 137 is photoelectrically converted to obtain an electrical signal.

  When the higher-order mode is included in the light L1, a part of this higher-order mode transitions to the second core 129A. Part of the higher-order mode that has transitioned to the second core 129 </ b> A is emitted into the space from the first end portion 113 a and becomes stray light, and the reflection is repeatedly attenuated inside the components of the optical communication system 210.

Next, communication in a direction from the second transmission / reception unit 203 toward the first transmission / reception unit 201 (hereinafter referred to as a downlink direction) will be described.
Light L2 emitted from the light source 111 of the second transmission / reception unit 203 is emitted from the light emitting unit 117 and is incident on the second core 129A.
Since the second core 129A and the first core 128A can be optically coupled, at least a part of the higher-order mode (for example, most of the higher-order mode) transitions to the first core 128A. Most of the fundamental mode of the light L2 incident on the second core 129A remains in the second core 129A and disappears.

The light L2 including the higher mode is directed to the first transmitting / receiving unit 201 through the transmission line core 23 of the optical transmission line 2 and is incident on the first core 28A.
Since the first core 28A and the second core 29A can be optically coupled, at least a part of the higher order modes of the first core 28A (for example, most of the higher order modes) transition to the second core 29A. .
The light L2 from the second core 29A is incident on the light receiving unit 37 of the receiving unit 12. The optical signal incident on the light receiving unit 37 is photoelectrically converted to obtain an electrical signal.

  A part of the fundamental mode of the light L2 remaining in the first core 28A is emitted into the space from the first end portion 13a to become stray light, and the reflection is repeatedly attenuated inside the components of the optical communication system 210.

The first transmission / reception unit 201 can perform communication using the basic mode and the higher-order mode, and has a wavelength selection function such as a filter as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths for uplink and downlink. For this purpose is not necessary. For this reason, the apparatus configuration can be simplified and the size can be reduced. In addition, since the apparatus configuration can be simplified, the cost can be reduced.
The second transmission / reception unit 203 can perform communication using the basic mode and the higher-order mode, and has a wavelength selection function such as a filter as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths for uplink and downlink. For this purpose is not necessary. For this reason, the apparatus configuration can be simplified and the size can be reduced. In addition, since the apparatus configuration can be simplified, the cost can be reduced.
The optical communication system 210 can perform communication using the basic mode and the higher-order mode in the upstream direction and the downstream direction, respectively. The optical communication system 210 does not require a wavelength selection device such as a filter, as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths for uplink and downlink. For this reason, the apparatus configuration can be simplified and the size can be reduced. In addition, since the apparatus configuration can be simplified, the cost can be reduced.

The first transmission / reception unit 201 is arranged so that the higher-order mode can transition between the second core 29A and the first core 28A. The second transmission / reception unit 203 is arranged so that the higher-order mode can transition between the second core 129A and the first core 128A.
Therefore, communication using the basic mode and the higher-order mode can be performed in the uplink direction and the downlink direction, respectively.
In addition, since the first transmitting / receiving unit 201 includes the second core 29A, a part of the higher-order mode of the light L1 transitions from the first core 28A to the second core 29A, and thus the light L1 in the first core 28A. Higher order modes can be reduced. Therefore, it is possible to further reduce noise and realize high quality communication.
In addition, since the second transmitting / receiving unit 203 includes the second core 129A, a part of the higher-order mode of the light L1 transitions from the first core 128A to the third core 129B, and thus the light L1 in the first core 128A. Higher order modes can be reduced. Therefore, it is possible to further reduce noise and realize high quality communication.

The embodiment of the present invention has been described above. However, the configuration in the embodiment is an example, and the addition, omission, replacement, and other modifications of the configuration can be made without departing from the spirit of the present invention.
In the optical communication system 10 shown in FIG. 1 and the like, the VCSEL is exemplified as the light source 11. However, the light source 11 is not limited to the VCSEL, and may be an edge emitting laser that oscillates in a multimode transverse mode.

In the optical communication system 10 according to the first embodiment illustrated in FIG. 1, the third core is used to easily secure the distance between the first core and the second core. However, the optical communication system has this configuration. Not exclusively. For example, the distance between the light emitting part and the light receiving part may be further increased by providing a plurality of cores between the first core and the second core. The number of cores arranged between the first core and the second core may be an arbitrary number of 2 or more.
In the optical communication systems 10 and 210, the light source 11 of the first transmission / reception unit 1 emits light L1 including the basic mode (first mode), and the light source 111 of the second transmission / reception unit 3 has a higher order mode (order higher than the basic mode). In the optical communication system, the light source of the first transmission / reception unit emits light including a higher order mode higher than the basic mode, and the light source of the second transmission / reception unit includes the basic mode. The structure which emits light may be sufficient. In the optical communication system having this configuration, the first mode is a higher-order mode, and the second mode is a basic mode. Further, in the optical communication system having this configuration, at least a part of the fundamental mode emitted from the light source of the second transmission / reception unit is incident on the reception unit of the first transmission / reception unit and is emitted from the light source of the first transmission / reception unit. At least a part of the mode is incident on the receiving unit of the second transmitting / receiving unit. In the optical communication system having this configuration, the light L1 or the light is transmitted between the cores such as the first core, the second core, and the third core so that the above-described configuration (light source, reception unit) can obtain the above-described functions. Each core such as the first core, the second core, and the third core is provided so that L2 transitions. The configuration of the optical communication system described above (light source, receiver, first core, second core, third core, etc.) can be similarly applied to the configuration of the optical transmission / reception apparatus of the present invention.

  DESCRIPTION OF SYMBOLS 1,201 ... 1st transmission / reception part (optical transmission / reception apparatus), 2 ... Optical transmission path, 3,203 ... 2nd transmission / reception part (optical transmission / reception apparatus), 12, 112 ... Reception part, 17,117 ... Light emission part, 10, 210: optical communication system, 11, 111: light source, 13, 113: directional coupler, 26, 126 ... first waveguide region, 27, 127 ... second waveguide region, 28A, 128A ... first core, 29A , 129A ... second core, 29B, 129B ... third core, 37, 137 ... light receiving part, L1 ... first light, L2 ... second light.

Claims (9)

At least a light source having a light emitting unit that emits a first mode that is a spatial mode or a transverse mode, a receiving unit, and a directional coupler optically coupled to the light source and the receiving unit,
The directional coupler includes at least a first waveguide region having a first core and a second waveguide region having a second core;
The first waveguide region is disposed so that light emitted from the light emitting unit is incident on the first core at a first end of the directional coupler,
The second waveguide region is disposed such that at least a part of a second mode having a different order from the first mode can be transitioned between the first core and the second waveguide region,
The optical transmission / reception apparatus, wherein the reception unit includes a light receiving unit into which at least a part of the second mode emitted from the second core is incident at a first end of the directional coupler. The second waveguide region has a third core that is optically coupled to the first core so that at least a part of the second mode of the first core can transition,
The optical transceiver according to claim 1, wherein the third core is optically coupled to the second core so that at least a part of the second mode can transition. The directional coupler includes a first coupling portion whose one end portion is the first end portion, and a second coupling portion connected to the other end portion of the first coupling portion,
The first coupling portion includes the first core, the second core, and the third core,
The optical transceiver according to claim 2, wherein the second coupling unit includes the first core and the third core.   4. The optical transmission / reception apparatus according to claim 2, wherein a center-to-center distance between the first core and the third core is greater than a center-to-center distance between the third core and the second core. At least a light source having a light emitting unit that emits a second mode having a different order from the first mode which is a spatial mode or a transverse mode, a receiving unit, and a directional coupler optically coupled to the light source and the receiving unit. Prepared,
The directional coupler includes at least a first waveguide region having a first core and a second waveguide region having a second core;
The second waveguide region is arranged such that light emitted from the light emitting unit is incident on the second core at a first end of the directional coupler,
The first waveguide region is disposed such that at least a part of the second mode can transition between the second core and the first waveguide region;
The optical transmission / reception apparatus, wherein the reception unit includes a light receiving unit into which at least a part of the first mode emitted from the first core is incident at a first end of the directional coupler. The second waveguide region has a third core that is optically coupled to the second core so that at least a part of the second mode of the second core can transition,
The optical transceiver according to claim 5, wherein the third core is optically coupled to the first core so that at least a part of the second mode can transition. The directional coupler includes a first coupling portion whose one end portion is the first end portion, and a second coupling portion connected to the other end portion of the first coupling portion,
The first coupling portion includes the first core, the second core, and the third core,
The optical transceiver according to claim 6, wherein the second coupling unit includes the first core and the third core.   The optical transmission / reception apparatus according to claim 6 or 7, wherein a center-to-center distance between the first core and the third core is greater than a center-to-center distance between the third core and the second core.   The first optical transmission / reception device, which is an optical transmission / reception device according to any one of claims 1 to 4, and the second optical, which is an optical transmission / reception device according to any one of claims 5 to 8. An optical communication system comprising: a transmission / reception device; and an optical transmission path that connects the first optical transmission / reception device and the second optical transmission / reception device.