WO2018074289A1 - Optical transmission/reception device and optical communication system - Google Patents

Abstract

An optical transmission/reception device that comprises: a transmission unit that has a light source and a directional coupler; and a reception unit that is optically coupled to the directional coupler. The light source has a first light-emitting unit that emits a basic mode and/or a higher-order mode. The directional coupler has a first core and a second core. The first core is arranged to receive light from the first light-emitting unit. The second core is arranged such that at least one portion of one of the basic mode and the higher-order mode can be transitioned between the first core and the second core. The reception unit comprises a splitter and a reception unit main body that is optically coupled to the splitter. The splitter has: a main core that is optically coupled to the first core or the second core; and a first separation core that separates, from the main core, at least one portion of one of the basic mode and the higher-order mode. The reception unit main body has a first light-receiving unit that receives at least one portion of the basic mode or the higher-order mode as emitted from the first separation core.

Description

Optical transceiver and optical communication system

The present invention relates to an optical transceiver and an optical communication system.
This application claims priority on October 21, 2016 based on Japanese Patent Application No. 2016-207303 for which it applied to Japan, and uses the content here.

Conventionally, a single-core bidirectional optical module that can perform bidirectional communication with a single optical fiber has been used in Passive Optical Network (PON), which is subscriber-based communication. As shown in Patent Document 1, the single-core bidirectional optical module transmits and receives different wavelengths of laser light in the upstream (first direction) and downstream (second direction), and the long wavelength cut filter or the short wavelength cut. A filter is used to combine and demultiplex light. As the filter, a dielectric multilayer film is used by being incorporated in the optical path.

Japanese Unexamined Patent Publication No. 2006-119464

In the conventional optical communication system, it is necessary to use different wavelengths of light in the first direction and the second direction using a wavelength selection device such as a filter. For this reason, since an apparatus for wavelength selection such as a filter is provided between the laser or the light receiving element and the optical fiber, the apparatus configuration is complicated or increased in size.

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 reduced in size and price.

An optical transceiver according to a first aspect of the present invention includes a transmitter having a light source and a directional coupler, and a receiver optically coupled to the directional coupler. A first light-emitting unit that emits at least one of higher-order modes having a higher order than the basic mode, and the directional coupler includes a first core and a first core that are formed at an interval so as to be optically coupled to each other. The first core is disposed so that light from the first light emitting unit is incident thereon, and the second core is coupled to the first core with the fundamental mode and the higher order. At least a part of one of the modes is disposed so as to be capable of transition, and the receiving unit includes a duplexer and a receiver main body optically coupled to the duplexer, and the duplexer includes the first core Or a main core optically coupled to the second core, and the fundamental mode And a first separating core that separates at least a part of one of the higher-order modes from the main core, and the receiver main body is emitted from the first separating core. It has the 1st light-receiving part in which at least one part of higher order mode injects.
Here, the light source further includes a second light emitting unit that emits at least one of the fundamental mode and the higher-order mode, and the duplexer includes at least a part of the other of the fundamental mode and the higher-order mode. Is further separated from the main core, and at least a part of the fundamental mode or the higher-order mode emitted from the second separation core is incident on the receiver body. You may further have a 2nd light-receiving part.
The ratio of the higher order mode to the fundamental mode in the light emitted from the first light emitting unit may be lower than the ratio of the higher order mode to the fundamental mode in the light emitted from the second light emitting unit.
The light source may be a surface emitting laser.
The directional coupler may be a multi-core optical fiber.

An optical communication system according to a second aspect of the present invention includes a pair of the optical transmission / reception devices and an optical transmission path that connects the pair of optical transmission / reception devices to each other.
Here, the optical transmission line may be a graded index optical fiber.

According to the optical receiver of the above aspect, the second core of the directional coupler is arranged so that the fundamental mode or the higher order mode can transition between the first core. Moreover, the optical communication system of the said aspect can each provide a light emission part which can radiate | emit two different modes, a fundamental mode and a high-order mode, in a pair of optical transmission / reception apparatus. Thus, when light is emitted, the ratio of the fundamental mode can be set high for the light from one light emitting section, and the ratio of the higher mode can be set high for the light from the other light emitting section. it can. Therefore, communication using the basic mode and the higher-order mode can be performed in the first direction and the second direction, respectively.
Therefore, a device for wavelength selection such as a filter is not necessary as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths in the first direction and the second direction, thus simplifying the device structure. Therefore, it is possible to reduce the size and the price.
In addition, since light including transverse modes having different orders in the first direction and the second direction is used, two-way communication is possible with the same wavelength in the first direction and the second direction. Therefore, the device structure can be further simplified as compared with the conventional optical transceiver described above.

It is a block diagram of the optical communication system of 1st Embodiment. It is a block diagram of the 1st transmission / reception part of the optical communication system of FIG. It is sectional drawing of the light source used for the optical communication system of FIG. It is sectional drawing of the directional coupler used for the optical communication system of FIG. It is a block diagram of the 2nd transmission / reception part of the optical communication system of FIG. It is a figure which shows the example of the spectrum of light. 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 of 2nd Embodiment. It is sectional drawing of the light source used for the optical communication system of FIG. It is a top view of the transmission part of the optical communication system of FIG. It is sectional drawing of a part of transmission part. It is explanatory drawing of the optical path in the optical communication system of FIG. It is explanatory drawing of the optical path in the optical communication system of FIG.

Hereinafter, an optical communication system according to an embodiment 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.

<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. FIG. 2 is a configuration diagram of the first transmission / reception unit 1. FIG. 3 is a cross-sectional view of the light source 11 along the thickness direction of the substrate 14 described later. FIG. 4 is a cross-sectional view orthogonal to the longitudinal direction in which the directional coupler 12 extends. FIG. 5 is a configuration diagram of the second transmission / reception unit 3.

As shown in FIGS. 1, 2, and 5, 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) optically coupled to each other. That is, the optical communication system 10 is a bidirectional optical communication system including a pair of transmission / reception units 1 and 3 and an optical transmission line 2 that connects them to each other.

(Definition)
Here, in the present embodiment, the light source (the light emitting unit, the first light emitting unit, or the second light emitting unit) and the first core or the second core are optically coupled. The light from the light source is the first core or the second core. Saying incident on the core.
For example, in the following cases (i) to (iii), it is said that the light source and the first core or the second core are optically coupled. (I) The light source and the first core or the second core are separated from each other, and the light emitted from the light source is incident on the first core or the second core. (Ii) The light source and the first core or the second core are separated from each other, are connected to each other through a relay optical transmission path such as an optical fiber, and the light emitted from the light source passes through the relay optical transmission path to the first core. Or when entering the second core. (Iii) The light source and the first core or the second core are installed in contact with each other, and the light emitted from the light source is incident on the first core or the second core.
In addition, two cores (the first core and the second core) are optically coupled so that at least part of the light can transition, for example, at least part of the light propagating through one of the two cores is the other. Say that you can transition to the core.
Further, the optical coupling between the first core or the second core and the main core of the duplexer means, for example, that light emitted from the first core or the second core enters the main core of the duplexer, Or it says that the light radiate | emitted from the main core of a splitter enters into a 1st core or a 2nd core.
Further, the optical coupling between the main core of the duplexer and the core of the optical transmission path means, for example, that light emitted from the first core or the second core enters the core of the optical transmission path, or It means that light emitted from the core of the transmission path enters the first core or the second core.
In addition, the fact that the separation core of the mode separator is optically coupled to the light receiving unit (the first light receiving unit or the second light receiving unit) means, for example, that light emitted from the separation core enters the light receiving unit.
In the light traveling direction, the side on which the light travels is called the downstream side, and the opposite side is called the upstream side.
Further, when the optical communication system 10 performs bidirectional communication, the communication direction from the first transmission / reception unit 1 to the second transmission / reception unit 3 is referred to as a first direction, and the second transmission / reception unit 3 changes to the first transmission / reception unit 1. The directed communication direction is referred to as the second direction.

As shown in FIGS. 1 and 2, the first transmission / reception unit 1 includes a transmission unit 4 and a reception unit 5.
The transmission unit 4 includes a light source 11 and a directional coupler 12.
As shown in FIG. 3, the light source 11 is, for example, a surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser). By using a VCSEL, communication using a basic mode and a higher-order mode can be realized with a simple structure.

The light source 11 includes a base unit 6 and a first light emitting unit 7 provided on the base unit 6.
The base portion 6 is configured by laminating a cathode electrode 13, a substrate 14, and a first mirror layer 15 in this order.
The cathode electrode 13 is provided on the outer surface of the substrate 14 (the lower surface in FIG. 3).
For example, an n-type GaAs substrate can be used as the substrate 14. In the present embodiment, the plan view means viewing from the thickness direction of the substrate 14.
The first mirror layer 15 is, for example, an n-type semiconductor layer, and is a distributed Bragg reflection type (DBR mirror) in which low refractive index layers and high refractive index layers are alternately stacked.

The first light emitting unit 7 is provided on the base unit 6.
The first light emitting unit 7 is configured by laminating an active layer 16, a current confinement layer 17, a second mirror layer 18, a passivation layer 19, and an anode electrode 20 in this order from the base unit 6. .
The active layer 16 has a multiple quantum well structure including a plurality of quantum well structures composed of, for example, a quantum well layer and a barrier layer.
The current confinement layer 17 is obtained, for example, by oxidizing an AlAs layer and has an opening 17a.
The second mirror layer 18 is, for example, a p-type semiconductor layer, and is a distributed Bragg reflection type (DBR mirror) in which low refractive index layers and high refractive index layers are alternately stacked.

The passivation layer 19 is formed, for example, surrounding the second mirror layer 18. The passivation layer 19 has an opening 19a surrounding at least the opening 17a of the current confinement layer 17 in plan view.
The anode electrode 20 is provided so as to surround the passivation layer 19 and the second mirror layer 18. The anode electrode 20 has an opening 20a surrounding the opening 17a of the current confinement layer 17 in plan view.
In the 1st light emission part 7, the light L1 is radiate | emitted through the opening part 20a of the anode electrode 20 (refer FIG. 2).

FIG. 6 is a diagram illustrating an example of a spectrum of light emitted from the first light emitting unit 7. As shown in FIG. 6, this light includes a plurality of transverse modes having different orders. The light includes a fundamental mode (LP01 mode) having the longest wavelength and a higher-order mode (LP11 mode and LP12 mode) having a higher order than the fundamental mode. Here, generally, when expressing the order of the transverse mode, the LP mode (linearly polarized polarized propagation mode) is used. Hereinafter, the LP mode may be used when expressing the order of the horizontal mode. The peak wavelength of the LP11 mode is shorter than the peak wavelength of the LP01 mode. The peak wavelength of the LP12 mode is shorter than the peak wavelength of the LP11 mode.

3, the inner diameter D1 of the opening 17a of the current confinement layer 17 affects the ratio between the fundamental mode and the higher-order mode included in the light emitted from the first light emitting unit 7. For example, the smaller the inner diameter D1 of the opening 17a, the larger the ratio of the fundamental mode that occupies the whole. Further, the larger the inner diameter D1 of the opening 17a, the smaller the proportion of the fundamental mode in the whole. Therefore, the ratio between the basic mode and the higher order mode can be adjusted by selecting the inner diameter D1 of the opening 17a.

The bias current in the light source 11 affects the ratio between the fundamental mode and the higher order mode of the emitted light. For example, the basic mode ratio is large at a low current value of about 3 mA from the threshold value Ith, and the high-order mode ratio is large at a high current value of about 9 mA. That is, as the current value of the bias current in the light source 11 is increased, the higher-order mode ratio increases. Therefore, the ratio between the fundamental mode and the higher order mode can be adjusted by the bias current.

The first light emitting unit 7 emits light L1 including at least a basic mode (LP01 mode). The light L1 includes, for example, a basic mode and higher-order modes (for example, LP11 mode and LP12 mode).
Most of the light L1 is preferably in the fundamental mode. If most of the light L1 is in the fundamental mode, noise during optical transmission on the optical transmission line 2 can be reduced. The power ratio between the fundamental mode and the higher order mode of the light L1 may be 50:50, for example.

As shown in FIGS. 2 and 4, the directional coupler 12 includes a first core 23, a second core 24, and a cladding 25 that surrounds the cores 23 and 24.
The first core 23 and the second core 24 extend along the longitudinal direction of the directional coupler 12. The first core 23 and the second core 24 are formed in parallel at a distance so as to enable optical coupling to each other. The 1st core 23 and the 2nd core 24 are formed in the space | interval which optically couples at least one part of a higher mode so that transition is possible.
As the directional coupler 12, a multi-core optical fiber can be used. The multi-core optical fiber is preferably a step index (SI) type.

7 shows a directional coupler 12 having a pair of cores (a first core 23 and a second core 24). A center distance d (horizontal axis) between the first core 23 and the second core 24 and a coupling length (vertical). It is a figure which shows the example of a relationship with an axis | shaft.
FIG. 8 is a diagram illustrating an example of a relationship between the center distance d (horizontal axis) and the remaining power (vertical axis) of the LP01 mode in the first core. The first core 23 and the second core 24 have a diameter of 8 μm and a relative refractive index difference of 0.3%. The wavelength of the incident light was 850 nm.

As shown in FIG. 7 and FIG. 8, the coupling length of the cores changes according to the center distance d. When the center distance d is 14 μm, if the length of the core is 100 mm or more, the LP01 mode of 95% or more remains in the first core 23, and most of the LP11 mode is transferred from the first core 23 to the second core. Transition to 24.
Therefore, in the directional coupler 12 shown in FIGS. 2 and 4, for example, the center-to-center distance d between the first core 23 and the second core 24 is 13 to 15 μm and the length is 100 mm or more (for example, 100 to 150 mm). Is preferred.

As shown in FIG. 2, the first core 23 is in a position where at least a part of the first end 23a overlaps the first light emitting unit 7 of the light source 11 in a plan view. The second end 23b of the first core 23 is at a position where at least a part thereof overlaps the first end 33a of the main core 33 of the duplexer 31 in plan view. Therefore, the first core 23 is disposed so that the light L1 from the light source 11 is incident from the first end 23 a and is optically coupled to the main core 33 of the duplexer 31.

The first end 24a of the second core 24 is located away from the first light emitting unit 7 in plan view. Therefore, the second core 24 is not optically coupled to the first light emitting unit 7.
The second end 24b is located away from the first end 33a of the main core 33 of the receiving unit 5 in plan view. For this reason, the second core 24 is not optically coupled to the main core 33 of the duplexer 31.

The receiving unit 5 includes a duplexer 31 (demultiplexing unit) and a receiving unit main body 32 that is optically coupled to the duplexer 31.
The duplexer 31 includes, for example, a main core 33 (first main core), a separation core 34 (first separation core), and a clad 40 surrounding the cores 33 and 34. The main core 33 is linearly formed from the first end 33a to the second end 33b.

The separation core 34 has an upstream portion 35, a coupling portion 36, a downstream portion 37, and an extending portion 38 in this order from the connection optical transmission path 27 toward the receiver main body 32.
As will be described later, the upstream portion 35 is a portion that gradually approaches the main core 33 toward the downstream side in the light transmission direction when the receiving unit 5 receives light. The coupling portion 36 is a portion that is generally formed in parallel with the main core 33 at an interval that enables optical coupling. The downstream portion 37 is a portion that gradually moves away from the main core 33 toward the downstream side in the light transmission direction at the time of reception. The extending portion 38 is a portion that extends from the downstream portion 37 and reaches the first end 34 a of the separating core 34.

The first end 34a of the separation core 34 is at a position where at least a part thereof overlaps the light receiving unit 39 of the receiving unit main body 32 in plan view. Therefore, the separation core 34 is arranged so that light emitted from the separation core 34 enters the light receiving unit 39. That is, at the first end 34 a of the separation core 34, the separation core 34 and the light receiving unit 39 are optically coupled.
The first end 31 a of the duplexer 31 is fixed to the second end 12 b of the directional coupler 12 with, for example, an adhesive. Thereby, it is possible to prevent the optical axis from being shifted between the main core 33 of the duplexer 31 and the first core 23 of the directional coupler 12.
Connected to the second end 33b of the main core 33 of the duplexer 31 is a connection optical transmission line 27 (see FIG. 1) having an optical connector 26 at the tip.

The receiving unit main body 32 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 body 32 has a light receiving unit 39 into which light from the separating core 34 is incident.

As shown in FIG. 1, the optical transmission line 2 is, for example, an optical fiber. The optical transmission line 2 is preferably a graded index (GI) optical fiber. A stable signal can be obtained by using a GI type optical fiber.
The first end 2 a of the optical transmission line 2 is optically coupled to the duplexer 31 of the reception unit 5 of the first transmission / reception unit 1 via the optical connector 26 and the connection optical transmission line 27. The second end 2 b of the optical transmission line 2 is optically coupled to the duplexer 81 of the reception unit 45 of the second transmission / reception unit 3 via the optical connector 76 and the connection optical transmission line 77. The optical transmission line 2 connects the first transmission / reception unit 1 and the second transmission / reception unit 3.

As shown in FIG. 5, the second transmission / reception unit 3 includes a transmission unit 44 and a reception unit 45. Hereinafter, the same components as those of the first transmission / reception unit 1 are denoted by the same reference numerals and description thereof is omitted.
The transmission unit 44 includes a light source 51 and a directional coupler 52 optically coupled to the light source 51. The light source 51 can employ the same configuration as the light source 11 of the first transmission / reception unit 1 shown in FIG.
The first light emitting unit 57 of the light source 51 emits light L2.
The light L2 includes at least a higher-order mode (for example, LP11 mode and LP12 mode). The light L2 includes, for example, 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, noise during optical transmission in the optical transmission path 2 can be reduced.
The light L2 may have the same wavelength as the light L1.

The directional coupler 52 includes a first core 73, a second core 74, and a clad 25 that surrounds the cores 73 and 74.
The first core 73 and the second core 74 extend along the longitudinal direction in which the directional coupler 52 extends. The first core 73 and the second core 74 are formed in parallel at a distance so as to enable optical coupling to each other. The first core 73 and the second core 74 are formed at an interval at which at least a part of the higher-order mode is optically coupled so that transition is possible.

The first core 73 is in a position where at least a part of the first end 73a overlaps the first light emitting unit 57 of the light source 51 in plan view. Therefore, the first core 73 is arranged so that the light L2 from the light source 51 is incident from the first end 73a. That is, the first core 73 is optically coupled to the light source 51.
The second end 73b of the first core 73 is located away from the first end 83a of the main core 83 of the receiving unit 45 in plan view. Therefore, the first core 73 is not optically coupled to the main core 83 of the receiving unit 45.

The first end 74a of the second core 74 is located away from the first light emitting unit 57 in plan view. For this reason, the second core 74 is not optically coupled to the first light emitting unit 57.
The second end 74b of the second core 74 is at a position where at least a portion thereof overlaps the first end 83a of the main core 83 of the receiving unit 45 in plan view. Therefore, the second core 74 is disposed so as to be optically coupled to the main core 83 of the receiving unit 45.

Two or more of the first core 23, the second core 24, the first core 73, and the second core 74 may have the same configuration (for example, material, outer diameter, etc.), or may have different configurations. Good.
The main core 33 and the main core 83 may have the same configuration (for example, material, outer diameter, etc.), or may have different configurations.

The receiving unit 45 includes a duplexer 81 and a receiver main body 82 optically coupled to the duplexer 81.
The duplexer 81 includes, for example, a main core 83 (second main core), a separation core 84 (second separation core), and a clad 40 surrounding the cores 83 and 84.
The separation core 84 has an upstream portion 85, a coupling portion 86, a downstream portion 87, and an extending portion 88 in this order from the connection optical transmission path 77 toward the receiver main body 82.
The upstream portion 85 is a portion that gradually approaches the main core 83 toward the downstream side in the light transmission direction when the receiving unit 45 receives light, as will be described later. The coupling portion 86 is a portion that is generally formed in parallel to the main core 83 at an interval that enables optical coupling. The downstream portion 87 is a portion that gradually separates from the main core 83 toward the downstream side in the light transmission direction at the time of reception. The extending portion 88 is a portion that extends from the downstream portion 87 and reaches the first end 84 a of the separating core 84.

The first end 84a of the separation core 84 is at a position where at least a part thereof overlaps the light receiving portion 89 of the receiving portion main body 82 in plan view. Therefore, the separation core 84 is arranged so that the light emitted from the separation core 84 enters the light receiving unit 89. In other words, at the first end 84 a of the separation core 84, the separation core 84 and the light receiving unit 89 are optically coupled.
The first end 81 a of the duplexer 81 can be fixed to the second end 52 b of the directional coupler 52 with an adhesive. As a result, the optical axis can be prevented from shifting between the second core 74 of the directional coupler 52 and the main core 83 of the duplexer 81.
A connection optical transmission line 77 (see FIG. 1) having an optical connector 76 at the tip is connected to the second end 83b of the main core 83 of the duplexer 81 of the receiver 45.
The receiving unit main body 82 includes a light receiving unit 89 into which light from the separation core 84 is incident.

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, that is, the first direction will be described.
As shown in FIG. 2, the light L <b> 1 modulated by the light source 11 of the first transmission / reception unit 1 and given a signal is emitted from the first light emitting unit 7 and is incident on the first core 23 of the directional coupler 12. .

Most of the fundamental mode of the light L1 incident on the first core 23 remains in the first core 23, and at least a part of the higher-order mode (for example, most of the higher-order mode) transitions to the second core 24.
The light L1 including the fundamental mode remaining in the first core 23 is emitted from the second end 23b and is incident on the main core 33 of the duplexer 31 of the receiving unit 5.
Since the second core 24 is not optically coupled to the main core 33 of the duplexer 31, the higher-order mode transferred to the second core 24 is not incident on the main core 33. Even if the higher-order mode is incident on the part other than the main core 33 of the duplexer 31, it disappears due to leakage.

The light L1 including the fundamental mode incident on the main core 33 of the duplexer 31 is emitted from the second end 33b, is emitted to the optical transmission line 2 through the connection optical transmission line 27, and is transmitted through the optical transmission line 2 to the first optical transmission line 2. 2 Go to the transceiver 3. The light L1 is incident on the main core 83 of the duplexer 81 of the second transmission / reception unit 3 through the connection optical transmission line 77 (see FIG. 1).
At least a part of the fundamental mode incident on the main core 83 transitions to the separation core 84 at the coupling portion 86 and enters the light receiving portion 89 of the receiver main body 82 via the downstream portion 87 and the extending portion 88. (See FIG. 5). The optical signal incident on the light receiving unit 89 is photoelectrically converted to obtain an electrical signal.

Next, communication in the direction from the second transmission / reception unit 3 toward the first transmission / reception unit 1, that is, the second direction will be described.
As shown in FIG. 5, the light L <b> 2 modulated by the light source 51 of the second transmission / reception unit 3 and given a signal is emitted from the first light emitting unit 57 and is incident on the first core 73 of the directional coupler 52. .

Most of the fundamental mode of the light L2 incident on the first core 73 remains in the first core 73, and at least a part of the higher-order mode (for example, most of the higher-order mode) transitions to the second core 74.
The light L <b> 2 including the higher order mode transferred to the second core 74 is emitted from the second end 74 b and is incident on the main core 83 of the duplexer 81 of the receiving unit 45.
Since the first core 73 is not optically coupled to the main core 83 of the duplexer 81, the fundamental mode remaining in the first core 73 is not incident on the main core 83. Even if the fundamental mode is incident on a part other than the main core 83 of the duplexer 81, it disappears due to leakage.

The light L2 including the higher-order mode incident on the main core 83 of the duplexer 81 is emitted from the second end 83b, is emitted to the optical transmission line 2 through the connection optical transmission line 77, and passes through the optical transmission line 2 to 1 Head to the transceiver 1. The light L2 is incident on the main core 33 of the duplexer 31 of the first transmitting / receiving unit 1 through the connection optical transmission path 27 (see FIG. 1).
At least a part of the higher-order mode incident on the main core 33 transits to the separation core 34 at the coupling portion 36, enters the light receiving portion 39 of the receiving portion main body 32 through the downstream portion 37 and the extending portion 38. (See FIG. 2). The optical signal incident on the light receiving unit 39 is photoelectrically converted to obtain an electrical signal.

As described above, in the first transmission / reception unit 1 and the second transmission / reception unit 3 shown in FIGS. 1 to 5, the second cores 24 and 74 of the directional couplers 12 and 52 are the first cores 23 and 73, respectively. Are arranged so that the higher order modes can transition between the two. In addition, the optical communication system 10 includes light emitting units 7 and 57 that can emit two different modes of a basic mode and a higher-order mode in a pair of transmission / reception units 1 and 3, respectively. Thus, when light is emitted, the ratio of the fundamental mode can be set high for the light from one light emitting section, and the ratio of the higher mode can be set high for the light from the other light emitting section. it can. Therefore, communication using the basic mode and the higher-order mode can be performed in the first direction and the second direction, respectively.
The first transmission / reception unit 1 and the second transmission / reception unit 3 are devices for wavelength selection such as filters, etc., compared to a conventional optical transmission / reception device that transmits and receives light with different wavelengths in the first direction and the second direction. Therefore, the apparatus configuration can be simplified, and the size and price can be reduced.
In addition, since light including transverse modes having different orders in the first direction and the second direction is used, two-way communication is possible with the same wavelength in the first direction and the second direction. Therefore, the device structure can be further simplified as compared with the conventional optical transceiver described above.

Further, in the first transmission / reception unit 1, the directional coupler 12 has the second core 24, and at least a part of the higher-order mode can be transitioned from the first core 23 to the second core 24. Yes. Thereby, the higher mode of the light L1 in the first core 23 can be reduced. Therefore, it is possible to further reduce noise and realize high quality communication.

<Optical Transceiver and Optical Communication System (Second Embodiment)>
FIG. 9 is a configuration diagram of the optical communication system 60 of the second embodiment. FIG. 10 is a cross-sectional view of the light source 111 used in the optical communication system 60. FIG. 11A is a plan view of the transmission unit 104 of the optical communication system 60. FIG. 11B is a cross-sectional view of a part of the transmission unit 104 along the thickness direction of the substrate 14 described later. 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. 9, the optical communication system 60 includes a first transmission / reception unit 101 (optical transmission / reception device), an optical transmission line 2 optically coupled to the first transmission / reception unit 101, and an optical transmission line 2. A second transceiver 103 (optical transceiver). That is, the optical communication system 60 is a bidirectional optical communication system including a pair of transmission / reception units 101 and 103 and an optical transmission line 2 that connects them to each other.
In the optical communication system 60, the transmission unit 104 having the light source 111 is used instead of the transmission units 4 and 44 having the light sources 11 and 51, and the reception units 5 and 45 having the separation cores 34 and 84 are used. 1 is different from the optical communication system 10 shown in FIG. 1 in that a receiving unit 105 having separation cores 34A and 34B is used.

The first transmission / reception unit 101 includes a transmission unit 104 and a reception unit 105.
The transmission unit 104 includes a light source 111 and a directional coupler 12 that is optically coupled to the light source 111. The light source 111 is, for example, a VCSEL.
As shown in FIG. 10, the light source 111 includes a base portion 6, and a first light emitting portion 7 and a second light emitting portion 8 provided on the base portion 6.
The 1st light emission part 7 and the 2nd light emission part 8 are arrange | positioned on the base part 6 in a mutually different position in planar view.

The first light emitting unit 7 is configured by laminating an active layer 16A, a current confinement layer 17A, a second mirror layer 18A, a passivation layer 19A, and an anode electrode 20A in this order from the base unit 6. . The second light emitting unit 8 is configured by laminating an active layer 16B, a current confinement layer 17B, a second mirror layer 18B, a passivation layer 19B, and an anode electrode 20B in this order from the base unit 6. . The current confinement layers 17A and 17B have openings 17Aa and 17Ba, respectively. The passivation layers 19A and 19B have openings 19Aa and 19Ba, respectively. The anode electrodes 20A and 20B have openings 20Aa and 20Ba, respectively.

As shown in FIGS. 10 and 11B, in the first light emitting unit 7, the first light L11 is emitted through the opening 20Aa of the anode electrode 20A. In the second light emitting unit 8, the second light L12 is emitted through the opening 20Ba of the anode electrode 20B.
The first light L11 includes at least a fundamental mode. The first light L11 includes, for example, a fundamental mode and a higher-order mode. The second light L12 includes at least a higher-order mode. The second light L12 includes, for example, a basic mode and a higher-order mode.

The ratio of the higher order mode to the fundamental mode in the first light L11 (higher order mode / fundamental mode) (hereinafter referred to as higher order mode ratio) may be different from the higher order mode ratio in the second light L12. Good.
For example, the higher order mode ratio in the first light L11 can be made lower than the higher order mode ratio in the second light L12. When the fundamental mode is used for communication in the first direction and the higher order mode is used for communication in the second direction, the ratio of the fundamental mode of the first light L11 is relatively high, and the ratio of the higher order mode of the second light L12. Due to the relatively high value, noise can be reduced.

Since the first core 23 is at a position where at least a part of the first end overlaps the first light emitting unit 7 of the light source 111 in plan view, the first core 23 is arranged so that the light L11 from the first light emitting unit 7 is incident thereon. Yes. Since the first core 23 is at a position where at least a part of the second end overlaps the first end of the main core 33 of the duplexer 131 in plan view, the first core 23 is optically coupled to the main core 33 of the duplexer 131. Is arranged.
Since the second core 24 is at a position where at least a part of the first end overlaps the second light emitting unit 8 of the light source 111 in plan view, the second core 24 is arranged so that the light L12 from the second light emitting unit 8 is incident thereon. Yes. The second core 24 is not optically coupled to the main core 33 of the duplexer 131.
A pair of anode electrode terminals 21 shown in FIG. 11A is connected to anode electrodes 20A and 20B shown in FIG. The pair of cathode electrode terminals 22 shown in FIG. 11A is connected to the cathode electrode 13 shown in FIG.

As illustrated in FIG. 9, the reception unit 105 includes a duplexer 131 (demultiplexing unit) and a reception unit main body 132 that is optically coupled to the duplexer 131.
The duplexer 131 includes, for example, a main core 33, a first separation core 34A, a second separation core 34B, and a clad 40 surrounding the cores 33, 34A, and 34B.
The first separation core 34 </ b> A and the second separation core 34 </ b> B extend in the length direction of the main core 33. The first separation core 34A and the second separation core 34B are formed at different positions. The first separation core 34A is coupled to the main core 33 at the coupling portion 36A. The second separation core 34B is coupled to the main core 33 at the coupling portion 36B. The coupling portion 36A of the first separation core 34A is disposed at a position farther from the connection optical transmission line 27 than the coupling portion 36B of the second separation core 34B.
The first separation core 34A is arranged such that at least a part of the light emitted from the first separation core 34A is incident on the first light receiving unit 39A of the reception unit main body 132. The second separation core 34B is arranged such that at least a part of the light emitted from the second separation core 34B is incident on the second light receiving unit 39B of the reception unit main body 132.
The receiving unit main body 132 includes a first light receiving unit 39A and a second light receiving unit 39B arranged at different positions in plan view.

Similar to the first transmission / reception unit 101, the second transmission / reception unit 103 includes a transmission unit 104 and a reception unit 105.
The main core 33 in the first transmission / reception unit 101 is also referred to as a first main core. The main core 33 in the second transceiver 103 is also referred to as a second main core. The first separation core 34A and the second separation core 34B in the second transceiver 103 are also referred to as a third separation core and a fourth separation core, respectively. The light source 111 in the first transmission / reception unit 101 is also referred to as a first light source, and the light source 111 in the second transmission / reception unit 103 is also referred to as a second light source. The first light emitting unit 7 and the second light emitting unit 8 in the second transmitting / receiving unit 103 are also referred to as a third light emitting unit and a fourth light emitting unit, respectively.

In both the first transmission / reception unit 101 and the second transmission / reception unit 103, when the first light L 11 is emitted from the first light emitting unit 7 of the light source 111, the first light L 11 is output from the first directional coupler 12. It is incident on the core 23 (see FIG. 12). Most of the fundamental modes of the first light L11 remain in the first core 23, and most of the higher-order modes transition to the second core 24.
In both the first transmission / reception unit 101 and the second transmission / reception unit 103, when the second light L 12 is emitted from the second light emitting unit 8 of the light source 111, the second light L 12 is emitted from the second directional coupler 12. It is incident on the core 24 (see FIG. 13). Most of the fundamental modes of the second light L12 remain in the second core 24, and most of the higher-order modes transition to the first core 23.

Next, an example of a communication method using the optical communication system 60 will be described.
(First communication method)
First, as a first communication method, a method using a basic mode for communication in the first direction and using a higher-order mode for communication in the second direction will be described.
As shown in FIG. 9, in the communication in the direction (first direction) from the first transmission / reception unit 101 to the second transmission / reception unit 103, the first light from the first light emitting unit 7 alone in the light source 111 of the first transmission / reception unit 101. L11 is emitted (see FIG. 12).
The first light L11 is incident on the first core 23 of the directional coupler 12. Most of the fundamental modes of the first light L11 remain in the first core 23, and most of the higher-order modes transition to the second core 24.
The fundamental mode remaining in the first core 23 is incident on the main core 33 of the duplexer 131 of the second transceiver 103 via the main core 33 of the duplexer 131 of the receiver 105 and the optical transmission path 2 ( (See FIG. 9).
Most of the fundamental mode incident on the main core 33 of the second transmitting / receiving unit 103 transitions to the first separation core 34A at the coupling portion 36A and is incident on the first light receiving unit 39A of the receiver main body 132. The optical signal incident on the first light receiving unit 39A is photoelectrically converted.

In communication in the direction (second direction) from the second transmission / reception unit 103 to the first transmission / reception unit 101, the light source 111 of the second transmission / reception unit 103 emits the second light L12 only from the second light emitting unit 8 (FIG. 13). reference).
The second light L12 is incident on the second core 24 of the directional coupler 12. Most of the fundamental modes of the second light L12 remain in the second core 24, and most of the higher-order modes transition to the first core 23.
The higher-order mode transferred to the first core 23 is incident on the main core 33 of the duplexer 131 of the first transmitting / receiving unit 101 via the main core 33 of the duplexer 131 of the receiving unit 105 and the optical transmission path 2. .
Most of the higher-order mode incident on the main core 33 of the first transmitting / receiving unit 101 transitions to the second separation core 34B in the coupling portion 36B and is incident on the second light receiving unit 39B of the receiving unit main body 132. The optical signal incident on the second light receiving unit 39B is photoelectrically converted.

(Second communication method)
Next, as a second communication method, a method in which a higher-order mode is used for communication in the first direction and a basic mode is used for communication in the second direction will be described.
In communication in the direction (first direction) from the first transmitter / receiver 101 to the second transmitter / receiver 103, the light source 111 of the first transmitter / receiver 101 emits the second light L12 only from the second light emitter 8 (FIG. 13). reference).
The second light L12 is incident on the second core 24 of the directional coupler 12. Most of the fundamental modes of the second light L12 remain in the second core 24, and most of the higher-order modes transition to the first core 23.
The higher order mode transferred to the first core 23 is incident on the main core 33 of the duplexer 131 of the second transceiver 103 via the main core 33 of the duplexer 131 of the receiver 105 and the optical transmission path 2. .
Most of the higher-order mode incident on the main core 33 of the second transceiver 103 is transferred to the second separation core 34B at the coupling portion 36B and incident on the second light receiving portion 39B of the receiver main body 132. The optical signal incident on the second light receiving unit 39B is photoelectrically converted.

In communication in the direction (second direction) from the second transmission / reception unit 103 toward the first transmission / reception unit 101, the light source 111 of the second transmission / reception unit 103 causes the first light L11 to be emitted only from the first light emitting unit 7 (FIG. 12). reference).
The first light L11 is incident on the first core 23 of the directional coupler 12. Most of the fundamental modes of the first light L11 remain in the first core 23, and most of the higher-order modes transition to the second core 24.
The fundamental mode remaining in the first core 23 is incident on the main core 33 of the duplexer 131 of the first transceiver 101 through the main core 33 of the duplexer 131 of the receiver 105 and the optical transmission path 2.
Most of the fundamental mode incident on the main core 33 of the first transmission / reception unit 101 transitions to the first separation core 34A at the coupling portion 36A and enters the first light receiving unit 39A of the reception unit main body 132. The optical signal incident on the first light receiving unit 39A is photoelectrically converted.

As described above, the first transmission / reception unit 101 and the second transmission / reception unit 103 of the optical communication system 60 shown in FIG. 9 use one and the other of the fundamental mode and the higher-order mode in the first direction and the second direction, respectively. Communication was possible. Since either a basic mode or a higher-order mode can be used as a transmission mode, an optimal communication method can be selected in accordance with the characteristics of each mode.

In the optical communication system 60, the same configuration can be used for the first transmission / reception unit 101 and the second transmission / reception unit 103. For example, the first core 23 in the first transmission / reception unit 101 and the first core 23 in the second transmission / reception unit 103 can have the same material and configuration. Moreover, the 2nd core 24 in the 1st transmission / reception part 101 and the 2nd core 24 in the 2nd transmission / reception part 103 can be made into the mutually same material and structure. For this reason, bidirectional communication is possible with the same wavelength in the first direction and the second direction with a relatively simple configuration. Moreover, since it is not necessary to produce two different types of transmission / reception units, the cost can be reduced.

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.
For example, the duplexer 31 shown in FIG. 1 or the like is a waveguide type mode separator, but an optical fiber coupler type mode separator may be used instead.
In the optical communication system according to the embodiment, the VCSEL is exemplified as the light source 11. However, the light source 11 is not limited to this, and may be an edge-emitting laser that oscillates in multimode in the transverse mode.

In the optical communication system 10 according to the first embodiment shown in FIG. 1, the second core 24 of the directional coupler 12 is optically coupled to the main core 33 of the duplexer 31 in the first transmitting / receiving unit 1. In the second transmitting / receiving unit 3, the first core 73 of the directional coupler 52 can be optically coupled to the main core 33 of the duplexer 81.
In the optical communication system having such a configuration, a higher-order mode can be used for communication in the first direction, and a basic mode can be used for communication in the second direction.
In that case, the light from the second transmission / reception unit 3 is incident on the demultiplexer 31 via the optical transmission line 2, and at least a part of the fundamental mode is separated by the demultiplexer 31 and is incident on the receiving unit main body 32. . The light from the first transmission / reception unit 1 is incident on the demultiplexer 81 through the optical transmission line 2, and at least a part of the higher-order mode is separated by the demultiplexer 81 and is incident on the reception unit main body 82.
In the embodiment, the higher-order mode transitions between the first core and the second core, but at least a part of the fundamental mode transitions between the first core and the second core. May be.

DESCRIPTION OF SYMBOLS 1,101 ... 1st transmission / reception part (optical transmission / reception apparatus), 2 ... Optical transmission line, 3,103 ... 2nd transmission / reception part (optical transmission / reception apparatus), 4,44,104,144 ... Transmission part, 5,105 ... Reception , 7 ... 1st light emission part, 8 ... 2nd light emission part, 10, 60 ... Optical communication system, 11, 41, 111, 141 ... Light source, 12, 52 ... Directional coupler, 23, 73 ... 1st core 24, 74 ... second core, 31, 131 ... duplexer, 33, 83 ... main core, 34, 84 ... separation core, 34A ... first separation core, 34B ... second separation core, 39 ... Light receiving unit, 39A ... first light receiving unit, 39B ... second light receiving unit, L1 ... light, L2 ... light, L11 ... first light, L12 ... second light.

Claims (7)

1. A transmitter having a light source and a directional coupler; and a receiver optically coupled to the directional coupler;
   The light source includes a first light emitting unit that emits at least one of a fundamental mode and a higher-order mode having a higher order than the fundamental mode,
   The directional coupler has a first core and a second core formed at intervals so as to be optically coupled to each other,
   The first core is disposed so that light from the first light emitting unit is incident thereon,
   The second core is arranged so that at least a part of one of the fundamental mode and the higher order mode can transition between the first core and the first core,
   The receiver includes a duplexer, and a receiver main body optically coupled to the duplexer,
   The duplexer includes a main core optically coupled to the first core or the second core, and a first separation core that separates at least a part of one of the fundamental mode and the higher-order mode from the main core. And
   The optical receiver and receiver, wherein the receiver main body includes a first light receiving unit that is emitted from the first separation core and into which at least a part of the fundamental mode or the higher-order mode is incident.
2. The light source further includes a second light emitting unit that emits at least one of the fundamental mode and the higher-order mode,
   The duplexer further includes a second separation core that separates at least a part of the other of the fundamental mode and the higher-order mode from the main core;
   2. The optical transmission / reception apparatus according to claim 1, wherein the reception unit main body further includes a second light receiving unit that is emitted from the second separation core and into which at least a part of the fundamental mode or the higher-order mode is incident. .
3. The optical transmission / reception apparatus according to claim 2, wherein a ratio of a higher order mode to a fundamental mode in light emitted from the first light emitting unit is lower than a ratio of a higher order mode to a fundamental mode in light emitted from the second light emitting unit.
4. The optical transmission / reception apparatus according to any one of claims 1 to 3, wherein the light source is a surface emitting laser.
5. The optical transmission / reception apparatus according to any one of claims 1 to 4, wherein the directional coupler is a multi-core optical fiber.
6. An optical communication system comprising a pair of the optical transmission / reception apparatus according to any one of claims 1 to 5 and an optical transmission path that connects the pair of optical transmission / reception apparatuses to each other.
7. The optical communication system according to claim 6, wherein the optical transmission line is a graded index optical fiber.

Images