JP2018066962A - Light transmission/reception device and light communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light transmission/reception device and a light communication system which has a simple structure, and can be made small in size and low in cost.SOLUTION: A first transmission/reception part 1 comprises a transmission part 4 and a reception part 5 having a light source 11 and a directional coupler 12. The light source 11 has a light emission part 7 which emits at least one of a basic mode and a high order mode. The directional coupler 12 has a first core 23 and a second core 24 formed apart from each other in a manner making light coupling possible. The first core 23 is configured such that light L1 from the light emission part 7 is made incident. The second core 24 is configured such that one of the basic mode and the high order mode is shiftable between the first core 23 and itself. The reception part 5 has a splitter 31 and a reception part main body 32. The splitter 31 has a main core 33 and a core 34 for separation which separates one of the basic mode and the high order mode from the main core 33. The reception part main body 32 has a light reception part to which the basic mode or the high order mode emitted from the core 34 for separation is made incident.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical transceiver and an optical communication system.

  Conventionally, a bidirectional optical module capable of performing 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 bi-directional optical module transmits and receives different wavelengths of laser light in upstream and downstream, and uses a long wavelength cut filter or a short wavelength cut filter to combine and demultiplex light. Is going. As the filter, a dielectric multilayer film is used by being incorporated in the optical path.

JP 2006-119464 A

  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. For this reason, since a device for wavelength selection such as a filter is inserted between the laser or 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 transceiver and an optical communication system that have a simple structure and can be reduced in size and price.

One 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, and the light source has a higher order than the fundamental mode and the fundamental mode. A light emitting unit that emits at least one of the following modes; and the directional coupler includes a first core and a second core that are formed to be optically coupled to each other, and the first core includes: 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 second core and the first core. The receiving unit includes a duplexer and a receiver main body optically coupled to the duplexer, and the duplexer includes a main core optically coupled to the first core or the second core; , At least one of the fundamental mode and the higher order mode A separation core that separates the main portion from the main core, and the receiver main body includes a light receiving portion that is emitted from the separation core and into which at least a part of the fundamental mode or the higher-order mode is incident. An optical transmission / reception device is provided.
In the optical transmission / reception apparatus, the light emitting unit is a first light emitting unit, and the light source further includes a second light emitting unit that emits at least the other of the basic mode and the higher mode, The core is a first separation core, and 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, The receiving unit body may further include 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.
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 is preferably a surface emitting laser.
The optical transmission line is preferably a graded index optical fiber.
The directional coupler is preferably a multi-core optical fiber.

  One embodiment of the present invention provides an optical communication system including 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.

According to one aspect of the present invention, the second core of the directional coupler is disposed so that the fundamental mode or the higher-order mode can transition between the first core. In the optical communication system, light emitting units capable of emitting two different modes of the basic mode and the higher order mode are provided at two locations in the upstream direction and the downstream direction. 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 uplink direction and the downlink direction, respectively.
Therefore, a device for wavelength selection such as a filter is not required as compared with a conventional optical transmission / reception device that transmits and receives light with different wavelengths for upstream and downstream, thus simplifying the device structure, miniaturization, and lower cost. Can be achieved.
In addition, since light including transverse modes having different orders in the uplink direction and the downlink direction is used, two-way 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.

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 a previous figure. FIG. 10A is a plan view of a transmission unit of the optical communication system in FIG. (B) 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. FIG. 4 is a cross-sectional view of the directional coupler 12. 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 includes a pair of transmission / reception units 1 and 3 and an optical transmission path 2 that connects them to each other.

Here, in the present invention, the light source (light emitting unit, first light emitting unit, or 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. To be incident on.
For example, (i) the light source and the first core or 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 or the second core Are mutually connected 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, or (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.

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 part 6 and a light emitting part 7 provided on the base part 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. Note that 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 light emitting unit 7 is provided on the base unit 6.
The 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.
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 light emission part 7, the light L1 is radiate | emitted through the opening part 20a (refer FIG. 2).

  FIG. 6 is a diagram illustrating an example of a light spectrum. 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. The LP11 mode has a peak on the shorter wavelength side than the LP01 mode, and the LP12 mode has a peak on the shorter wavelength side than the LP11 mode.

  As shown in FIG. 3, the inner diameter D <b> 1 of the opening 17 a 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 light emitting unit 7. For example, as for the opening part 17a, there exists a tendency for the ratio of the fundamental mode to occupy the whole to become large, so that the internal diameter D1 is small. Moreover, the ratio of the fundamental mode which occupies for the opening part 17a tends to become small, so that the internal diameter D1 is large. 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 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. When most of the first light L1 is in the fundamental mode, noise during optical transmission on the optical transmission path 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 with each other at an interval that enables optical coupling. 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.

  FIG. 7 shows the relationship between the center-to-center distance d (horizontal axis) and the coupling length (vertical axis) between the first core and the second core in a directional coupler having a pair of cores (first core and second core). It is a figure which shows the example of. FIG. 8 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 the first 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. 7 and FIG. 8, 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 coupler 12 shown in FIGS. 2 and 4, for example, the distance between the centers of 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). .

  As shown in FIG. 2, the first core 23 is in a position where at least a part of the first end 23 a overlaps the light emitting unit 7 of the light source 11 in 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 light emitting unit 7 in plan view. Therefore, the second core 24 is not optically coupled to the light emitting unit 7.
The second end 24b is at a position 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 separating core 34 has a front part 35, a coupling part 36, a rear part 37, and an extending part 38 in this order toward the first end 34a optically coupled to the receiving unit main body 32.
The front portion 35 is a portion that gradually approaches the main core 33 in the light transmission direction at the time of reception, which will be described later. 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 rear stage portion 37 is a portion that is gradually separated from the main core 33 in the light transmission direction. The extending portion 38 is a portion that extends from the rear portion 37 and reaches the first end 34a.

The separation core 34 is in a position where at least a part of the first end 34a overlaps the light receiving part 39 of the receiving part 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.
The first end 31a of the duplexer 31 is fixed with, for example, an adhesive so that the optical axis does not shift from the second end 12b 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.
In the light emission part 57 of the light source 51, the light L2 is emitted.
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 third core 73, a fourth core 74, and a clad 25 that surrounds the cores 73 and 74.
The third core 73 and the fourth core 74 extend along the longitudinal direction of the directional coupler 52. The third core 73 and the fourth core 74 are formed in parallel with each other at an interval that enables optical coupling. The third core 73 and the fourth core 74 are formed with an interval at which at least a part of the higher order mode is optically coupled so as to be capable of transition.
The third core 73 is a first core of the directional coupler 52. The fourth core 74 is a second core of the directional coupler 52.

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

The first end 74a of the fourth core 74 is at a position away from the light emitting unit 57 in plan view. Therefore, the fourth core 74 is not optically coupled to the light emitting unit 57.
The second end 74b of the fourth core 74 is at a position where at least a part thereof overlaps the first end 83a of the main core 83 of the receiving unit 45 in plan view. Therefore, the fourth core 74 is arranged 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 third core 73, and the fourth 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 a front part 85, a coupling part 86, a rear part 87, and an extension part 88 in this order toward the first end 84a optically coupled to the receiver main body 82.
The pre-stage portion 85 is a portion that gradually approaches the main core 83 in the light transmission direction at the time of reception 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 rear portion 87 is a portion that is gradually separated from the main core 83 in the light transmission direction. The extending portion 88 is a portion that extends from the rear portion 87 and reaches the first end 84a.

The separation core 84 is at a position where at least a part of the first end 84a 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.
The first end 81a of the duplexer 81 can be fixed to the second end 52b of the directional coupler 52 with an adhesive. Thereby, it is possible to prevent the optical axes of the fourth core 74 and the main core 83 from shifting.
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 (hereinafter referred to as the uplink 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 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 33 of the duplexer 81 of the second transmission / reception unit 3 through the connection optical transmission line 77 (see FIG. 1).
As shown in FIG. 5, at least a part of the fundamental mode incident on the main core 33 transitions to the separation core 84 at the coupling portion 86, passes through the rear portion 87 and the extension portion 88, and The light enters the light receiving unit 89. 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 to the first transmission / reception unit 1 (hereinafter referred to as the downlink 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 light emitting unit 57 and is incident on the third core 73 of the directional coupler 52.

Most of the fundamental mode of the light L2 incident on the third core 73 remains in the third core 73, and at least a part of the higher-order mode (for example, most of the higher-order mode) transitions to the fourth core 74.
The light L2 including the higher order mode transferred to the fourth core 74 is emitted from the second end 74b and is incident on the main core 83 of the duplexer 81 of the receiving unit 45.
Since the third core 73 is not optically coupled to the main core 83 of the duplexer 81, the fundamental mode remaining in the third 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).
As shown in FIG. 2, at least a part of the higher-order mode incident on the main core 33 makes a transition to the separation core 34 in the coupling portion 36, passes through the rear-stage portion 37 and the extension portion 38, and The light enters the light receiving unit 39. The optical signal incident on the light receiving unit 39 is photoelectrically converted to obtain an electrical signal.

1-5, the 1st transmission / reception part 1 and the 2nd transmission / reception part 3 are the 2nd core 24 and the 4th core 74 of the directional couplers 12 and 52, and the 1st core 23 and the 3rd core 73, respectively. Are arranged so that higher order modes can transition between the two. Further, the optical fiber reinforcing structure 10 is provided with light emitting portions 7 and 57 capable of emitting two different modes, a basic mode and a higher-order mode, at two locations in the upward direction and the downward direction. 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 uplink direction and the downlink direction, respectively.
Since the first transmission / reception unit 1 and the second transmission / reception unit 3 do not require a device for wavelength selection such as a filter as compared with a conventional optical transmission / reception device that performs transmission / reception with different wavelengths of uplink and downlink, The apparatus configuration can be simplified, and the size and cost can be reduced.
In addition, since light including transverse modes having different orders in the uplink direction and the downlink direction is used, two-way 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.

  Since the directional coupler 12 has the second core 24, the first transmission / reception unit 1 can reduce the higher-order mode of the light L1 in the first core 23. 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 part of the transmission unit 104. 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).
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 two light emitting portions 7 and 8 provided on the base portion 6. The light emitting units 7 and 8 are referred to as a first light emitting unit 7 and a second light emitting unit 8, respectively.
The first light emitting unit 7 and the second light emitting unit 8 are provided on the base unit 6 at different positions in plan view.

  The first light emitting section 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. 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. 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. In the second light emitting unit 8, the second light L12 is emitted through the opening 20Ba.
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 basic mode is used for upstream communication and the higher order mode is used for downstream communication, 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 is compared. Therefore, the 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.
Reference numeral 21 shown in FIG. 11A denotes an anode electrode terminal connected to the anode electrodes 20A and 20B. Reference numeral 22 denotes a cathode electrode terminal connected to the cathode electrode 13.

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 are formed at different positions in the length direction of the main core 33. Reference numerals 36A and 36B are joint portions of the separation cores 34A and 34B.
The separation cores 34A and 34B are arranged such that at least a part of the light emitted from the separation cores 34A and 34B is incident on the light receiving portions 39A and 39B of the receiving portion main body 132, respectively.
The receiving unit main body 132 includes a first light receiving unit 39A and a second light receiving unit 39B provided 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 first core 23 and the second core 24 in the second transceiver 103 are also referred to as a third core and a fourth core, respectively. 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.

As shown in FIG. 12, in both the first transmission / reception unit 101 and the second transmission / reception unit 103, when the light L11 is emitted from the first light emission unit 7 among the light emission units 7 and 8 of the light source 111, the light L11 is The light enters the first core 23 of the directional coupler 12. Most of the fundamental modes of the light L11 remain in the first core 23, and most of the higher-order modes transition to the second core 24.
As shown in FIG. 13, in both the first transmission / reception unit 101 and the second transmission / reception unit 103, when the light L12 is emitted from the second light emission unit 8 of the light emission units 7 and 8, the light L12 is directionally coupled. The light enters the second core 24 of the container 12. Most of the fundamental modes of the 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 uplink communication and using a higher-order mode for downlink communication will be described.
As shown in FIG. 9, in communication in the direction (upward direction) from the first transmission / reception unit 101 to the second transmission / reception unit 103, the light L <b> 11 is emitted only from the first light emission unit 7 in the light source 111 of the first transmission / reception unit 101. (See FIG. 12).
The light L11 is incident on the first core 23 of the directional coupler 12. Most of the fundamental modes of the light L11 remain in the first core 23, and most of the higher-order modes transition to the second core 24.
The basic mode remaining in the first core 23 is incident on the main core 33 of the duplexer 131 of the second transceiver 103 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 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 the communication in the direction (downward 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 light L12 to be emitted only from the second light emitting unit 8 (see FIG. 13).
The light L12 is incident on the second core 24 of the directional coupler 12. Most of the fundamental modes of the 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 of using a higher-order mode for uplink communication and using a basic mode for downlink communication will be described.
In communication in the direction (upward direction) from the first transmission / reception unit 101 to the second transmission / reception unit 103, the light source 111 of the first transmission / reception unit 101 emits light L12 only from the second light emitting unit 8 (see FIG. 13).
The light L12 is incident on the second core 24 of the directional coupler 12. Most of the fundamental modes of the 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 (downward 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 causes the light L11 to be emitted only from the first light emitting unit 7 (see FIG. 12).
The light L11 is incident on the first core 23 of the directional coupler 12. Most of the fundamental modes of the 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.

  The first transmission / reception unit 101 and the second transmission / reception unit 103 of the optical communication system 60 illustrated in FIG. 9 can perform communication using one and the other of the basic mode and the higher-order mode in the upstream direction and the downstream direction, respectively. 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, since the same configuration can be used for the first transmission / reception unit 101 and the second transmission / reception unit 103, bidirectional communication is possible with the same wavelength in the upstream and downstream directions with a relatively simple configuration. is there. 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.
The duplexer 31 shown in FIG. 1 and 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 of the first embodiment shown in FIG. 1, in the first transmitting / receiving unit 1, the second core 24 of the directional coupler 12 is optically coupled to the main core 33 of the duplexer 31. 2 In the transceiver 3, the first core 23 of the directional coupler 52 may 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 uplink communication and a basic mode can be used for downlink communication.
In that case, the light from the second transmission / reception unit 3 is incident on the demultiplexer 81 via the optical transmission path 2, and at least a part of the fundamental mode is separated by the demultiplexer 31 and incident on the receiver main body 32. . The light from the first transmission / reception unit 1 is incident on the demultiplexer 31 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.

  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 (1st light emission part), 8 ... 2nd light emission part (2nd light emission part), 10, 60 ... Optical communication system, 11, 41, 111, 141 ... Light source, 12, 52 ... Directional coupler, 23 ... First core, 24 ... Second core, 31, 131 ... Demultiplexer, 33, 83 ... Main core, 34, 84 ... Separation core, 34A ... First separation core ( First separating core), 34B... Second separating core (second separating core), 39... Light receiving portion, 39 A... First light receiving portion, 39 B. ... 4th core, L1 ... light, L2 ... light, L11 ... 1st light, L12 ... 2nd light.

Claims (7)

A transmitter having a light source and a directional coupler; and a receiver optically coupled to the directional coupler;
The light source has a 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 that are formed to be spaced apart from each other so as to be optically coupled.
The first core is disposed so that light from the 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 separation core that separates at least a part of one of the fundamental mode and the higher-order mode from the main core. Have
The optical transmission / reception apparatus, wherein the receiving unit main body includes a light receiving unit that is emitted from the separation core and into which at least a part of the basic mode or the higher-order mode is incident. The light emitting unit is a first light emitting unit,
The light source further includes a second light emitting unit that emits at least the other of the fundamental mode and the higher-order mode,
The separation core is a first separation core;
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 light according to claim 1, wherein the receiving 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. Transmitter / receiver.   3. The optical transceiver 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 the fundamental mode in light emitted from the second light emitting unit. .   The optical transmission / reception apparatus according to claim 1, wherein the light source is a surface emitting laser.   The optical transmission / reception apparatus according to claim 1, wherein the optical transmission line is a graded index optical fiber.   The optical transmission / reception apparatus according to claim 1, wherein the directional coupler is a multi-core optical fiber.   An optical communication system comprising a pair of the optical transmission / reception device according to claim 1 and an optical transmission path that connects the pair of optical transmission / reception devices to each other.