JPH053457A - Star coupler and optical communication network - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the number of terminals per node of a star coupler and to facilitate network expansion using a star coupler. [Structure] Three optical demultiplexers / multiplexers 2 are connected in a triangular shape, and terminals x ₁ , x ₂ , x ₃ are derived from each optical demultiplexer / multiplexer 2. Each optical demultiplexer / multiplexer 2 is, for example, one waveguide branched into two waveguides having different widths. The input signal v1 to one terminal x ₁ is divided into two other terminals x ₂ and x ₃ and output. Also, it does not substantially return to its own terminal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a star coupler which can be used by being interconnected and an optical communication network constructed by using the star coupler.

[0002]

2. Description of the Related Art Local Area Network (LAN)
Has recently become widespread as a data communication network between computers, workstations, etc., which are arranged in a relatively short distance. One of them is called "Ethernet (registered trademark)" developed by Xerox Co., Ltd. There is.

FIG. 30 is a diagram showing an Ethernet network. In FIG. 30, 20 is a coaxial cable, 21
Is a tap (branch point), and 22 is a node (terminal, station).

Each node 22 is connected to the coaxial cable 20 by a tap 21. When the number of nodes 22 to be connected increases, a tap 21 is newly provided and a new node 22 is connected to it.

On the other hand, in recent years, the development of optical communication using an optical fiber as a transmission medium has been remarkable. LAN has the excellent characteristics of optical fiber such as wide band, low loss and high noise resistance.
Suitable for However, since it is not possible to provide taps one after another with an optical fiber like a coaxial cable, it is difficult to construct a network similar to Ethernet.

Therefore, a network has been proposed in which transmission and reception of a node are divided into separate terminals and all nodes are distributed by a star coupler. For example,
E. G. Rawson, IEEE Transacti
on on Communications, VO
L, COM-26, NO. 7, July 1978,
"Fibernet: Multimode Optic
al Fibers for Local Compu
ter Networks ”, etc.

FIG. 31 shows an example of the above proposal of an optical communication network using a star coupler. In FIG. 31, 23
Reference numerals a and 23b are optical fibers, 22 is a node, 24 is a mixing rod type star coupler, and 25 is a terminal.

A signal from each node 22 is supplied to each light emitting element 2
It is converted into an optical signal by 2a and supplied to the star coupler 24 via each optical fiber 23a. These optical signals are mixed once by the star coupler 24, then distributed to the respective light receiving elements 22b via the respective optical fibers 23b and converted into electric signals again, and these electric signals are supplied to the respective nodes 22. It As a result, the signal transmitted from one node can be transmitted to all the nodes (multicast property), and a communication network similar to Ethernet can be constructed.

As an actual star coupler, as shown in FIG. 32, it is reported that an optical waveguide is formed on a glass substrate. See, for example, Wada, Okuda, Yamazaki, 1985 National Conference of the Institute of Electronics and Communication Engineers, 963. In FIG. 32, 23 is an optical fiber, 25 is a terminal, 26 is a mixing part, 27 is a waveguide, and 28 is a glass substrate. The waveguide 27 and the mixing portion 28 are formed by diffusing thallium (Tl) ions or the like into the glass substrate 28.

There is also an example in which one having the same function is realized on a plastic substrate such as polycarbonate by a manufacturing method different from that of the star coupler formed on the glass substrate. For example, Takato and Kurokawa, "Optical Waveguide Fabrication Technology in Polymer Materials," Oplus E, 1984 1
See p. 78-83, January.

However, the optical communication network using such a star coupler has a drawback in that even if an attempt is made to add a network to expand the network, only the number of terminals included in the star coupler can be added.

This is because, as described in the specification of Japanese Patent Application No. 2-98370 filed by the applicant of the present invention, when star couplers are connected to each other, a closed loop is formed in the transmission line, which causes oscillation and This is because a phenomenon such as damped vibration occurs.

For example, as shown in FIG. 33, one star coupler A has three input / output terminal pairs 5-6, 7-8, 9
-10 and the other star coupler B has three input / output terminal pairs 11-12, 13-14, 15-16, one star coupler is used to connect the star couplers. Since it is necessary to connect the input terminals 10 and 11 of the above to the output terminals 12 and 9 of the other star coupler, respectively, they must be cross-connected as shown in FIG. Note that the X _k, x _n in Fig input signal to the input terminals 10, 11, Y _k, is y _n is the output signal from the output terminal 9 and 12. The input signal X _k supplied to the input terminal 10 of the one star coupler A is X _k from the input terminal 10 to the output terminal 9.
_Is changed to a level determined by a transfer coefficient A _kk to the output terminal 9 and output from the output terminal 9 as an output signal Y _k . This output signal Y _k is supplied to the input terminal 11 of the other star coupler B as an input signal x _n . In the star coupler B as well, as in the star coupler A, the input signal x _n is changed to a level determined by the transfer coefficient B _nn from the input terminal 11 to the output terminal 12, and is output from the output terminal 12 as the output signal y _n. Is output. This output signal y _n is supplied to the input terminal 10 of one star coupler A as an input signal X _k . For this reason, a closed loop as shown in FIG. 34 is effectively formed, and a signal circulates, which causes inconvenience such as oscillation.

In order to solve such a problem, as described in the above-mentioned Japanese Patent Application No. 2-98370, a pair of star couplers are connected to be connected to the same node. The transmission coefficient between the input terminal and the output terminal may be set to 0. If you do this,
It is possible to connect star couplers one after another to expand the scale of the network. A star coupler in which the transfer coefficient between the input terminal and the output terminal forming a pair so as to be connected to the same node of the star coupler is zero is hereinafter referred to as an interconnectable star coupler. In addition, bidirectional communication is possible between two nodes connected to the network configured in this way,
Further, collision detection can be easily performed by utilizing this bidirectionality.

[0015]

However, in the above-proposed optical communication network using the star coupler, it is necessary to dispose two optical fibers for transmission and reception, and in Ethernet, There is a problem in that the number of optical fibers, connectors, and relay amplifiers required for constructing a network increases, compared to the case where one coaxial cable serves both transmission and reception. Especially when the network path is long, expensive fiber optics
This arrangement causes an increase in installation cost, and
There is also a problem that handling of the optical fiber becomes difficult.

The present invention has been devised in order to solve the above-mentioned problems, in which each star coupler is provided with one optical fiber by inputting and outputting an optical signal from the same terminal. The purpose is to enable easy expansion of network work by simply connecting to each other via. Another object of the present invention is to make it possible to construct an interconnectable star coupler having an arbitrary number of terminals.

[0017]

In order to achieve the above object, a star coupler of the present invention has a plurality of terminals, an optical signal is input / output from the same terminal, and an input signal to its own terminal is It is characterized in that it has a transfer characteristic that it is not distributed as an output signal from the own terminal and is distributed as an output signal to all terminals other than the own terminal.

The star coupler includes three terminals for inputting and outputting optical signals from the same terminal, three directional optical couplers, and each of the terminals and each directional optical coupler. And an optical waveguide formed between the directional optical couplers.

In order to achieve the above-mentioned object, the optical communication network of the present invention has a plurality of terminals, an optical signal is input / output from the same terminal, and the input signal to the own terminal is the own terminal. A plurality of star couplers having a transfer characteristic that is not distributed as an output signal from the device and is distributed as an output signal is provided at all terminals other than the self terminal, and each star coupler is connected via the terminal. It is characterized by being connected to each other.

[0020]

The operation of the present invention will be described with reference to specific examples.

The star coupler according to the present invention has a structure in which one node and one terminal are connected, and the structure is schematically shown in FIG.

The star coupler 1 has N terminals x ₁ , x ₂ ,.
.., x _N Input signals to these terminals are v ₁ , v
₂ , ..., V _N, and the output signals are w ₁ , w ₂ , ..., W
_When expressed as _N , the transfer characteristic of the signal of this star coupler is given by the matrix expression as the following expression.

[0023]

[Equation 1]

In the present invention, the input from the self-terminal is not distributed as the output from the self-terminal but is distributed to all the other terminals. Therefore, the diagonal components in the above equation are all 0. , And all other components are non-zero. Therefore, each element of the matrix of the above equation (1) can be expressed as follows.

[0025]

[Equation 2]

However, N is an integer such that N ≧ 3, and i is i ≦ N
Is a natural number of j, and j is a natural number such that j ≦ N

The delta function is a function that becomes 1 when i and j are equal and 0 when i and j are not equal, as shown in the following equation (3).

[0028]

[Equation 3]

When actually manufacturing a star coupler, the diagonal component of the equation (1) cannot be set to 0 at all, and some light is inevitably returned. This is similar to the inability to completely eliminate noise in electronic circuits. In the present invention, the fact that the input signal to the own terminal is not distributed as the output signal from the own terminal is merely a definition in principle, and even if the signal from the own terminal returns to the own terminal, they are It goes without saying that even a star coupler having a small amount of returning light falls within the scope of the present invention, except for the case of positively utilizing it for some purpose.

According to the star coupler having the above-described structure, the transmission line and the reception line can be shared by one optical fiber, and the node and the star coupler can be connected by one optical fiber. Also, even if you connect star couplers to increase the scale of the network,
Since the signal sent from one star coupler to the other star coupler does not flow back, the network can be expanded by connecting one terminal of each star coupler. In addition, it is possible to perform bidirectional communication between two nodes connected to this network, and further, by utilizing this bidirectionality, collision detection can be easily performed.

[0031]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 2 shows an embodiment of a concrete star coupler. Three optical demultiplexers / multiplexers 2 are connected in a triangular shape, and terminals x ₁ , x ₂ and x ₃ are derived from the respective optical demultiplexers / multiplexers 2. Each optical demultiplexer / multiplexer 2 has a structure as shown in FIG. 3, and has one waveguide 2a with a width d _0.
Is branched into two waveguides 2b and 2c. If the widths d ₁ and d _{2 of the} waveguides 2b and 2c after branching are equal, a branching ratio of 1: 1 is obtained, and if d ₁ > d ₂ , more light is branched to d ₁ . The branching ratio is approximately equal to the ratio of this waveguide.

In the embodiment shown in FIG. 2, each optical demultiplexer /
The branching ratio of the multiplexer 2 is set to 1: 1 and the input signal to one terminal is divided into two and output to the other two terminals. Also, it does not substantially return to its own terminal.
Therefore, relationship between the input signal v _1, v _2, v ₃ and the output signal w _1, w _2, w ₃ in the three terminals x _1, x _2, x ₃ is shown as equation (4).

[0034]

[Equation 4]

The optical demultiplexer / multiplexer 2 is described in, for example, Yamazaki, Okuda, "Manufacturing Technology in Glass Materials", O.
plus E, November 1984, p71-78.

The above is the embodiment in the case where the number of terminals N is 3 (N = 3), but next, the embodiment in the case of 6 terminals (N = 6), which is more terminals, is shown in FIG. 4 shows.

In the case of the embodiment shown in FIG. 4, an optical demultiplexer / multiplexer 3 having a branching ratio of 4: 1 and an optical demultiplexer / multiplexer 4 having a branching ratio of 1: 1.
By combining, v ₁ which is incident from the terminal x ₁
Is branched to the terminal x ₂ side by (1/5) v ₁ ,
The remaining (4/5) v ₁ is further branched as shown in the figure, and eventually (1) is applied to each terminal of x ₂ , x ₃ , x ₄ , x ₅ , x _6.
/ 5) It is distributed by v ₁ .

The same applies to the input signals from the terminals of x ₂ , x ₃ , x ₄ , x ₅ , and x ₆ , and when these are collectively expressed in a matrix, the equation (5) is obtained.

[0039]

[Equation 5]

FIG. 5 shows the structure shown in FIG.
4 is a plan view showing an example in which the 6-terminal star coupler shown in FIG.

When a substrate in which a methyl acrylate monomer is contained in polycarbonate is used as a substrate and a mask is laid on the substrate and exposed to ultraviolet rays, the monomer in the portions exposed to ultraviolet rays reacts to form a low refractive index portion and ultraviolet rays are exposed. The part not hit becomes the optical waveguide layer. In addition, this manufacturing method itself
It is known. For example, Takato and Kurokawa, "Optical Waveguide Making Technology in Polymer Materials," O plus E, 19
See pp. 78-83, November 1984.

In FIG. 5, three semicircular optical waveguides 32 are formed on a polycarbonate substrate 31 which is hexagonal as a whole, with their circumferences in contact with each other. Further, three arc-shaped optical waveguides 35 are formed so as to contact the circumferences of the two semicircular optical waveguides 32. An optical demultiplexer / multiplexer 33 having a branching ratio of 4: 1 is provided at a contact point between the optical waveguides 32 and 35. The optical demultiplexing / multiplexing circuit 33 is obtained by a width d _1, d ₂ the width d ₀ appropriate ratio of the waveguide 2a of the intersection of the optical demultiplexer / multiplexer 2 shown in FIG. Further, an optical branch path 34 for performing multiplexing and demultiplexing is provided at the contact point of each optical waveguide 32. As shown in FIG. 6, a part of the two optical waveguides is common to the optical branch path 34. For example, the optical component 36 is branched into two optical components 37 and 38. Furthermore, each optical waveguide 32
One end of an optical fiber 39 (only one is shown in FIG. 5) is connected to the end portion of the. A node (not shown) is connected to the other end of the optical fiber 39. The detailed structure of the node portion will be described later.

In FIG. 5, each of the optical waveguides 32 and 35 is
Six circles with the same radius are circumscribing each other. This is because the waveguide has a minimum bendable radius, and bending at a radius smaller than this minimum radius significantly increases radiation loss. This is because. The width of the optical waveguide 35 is narrower than that of the optical waveguide 32 in accordance with the relationship between the widths d ₁ and d ₂ of the optical demultiplexer / multiplexer shown in FIG.

In the example of FIG. 5, the substrate 31 is a polycarbonate substrate, but the polycarbonate substrate may be changed to a glass substrate to form an optical waveguide by diffusing thallium (Tl) ions or the like. In this case, the portion corresponding to the optical demultiplexer / multiplexer 33 shown in FIG. 5 needs to be a directional optical coupler as shown in FIG. This is because it is difficult to form waveguides having different diameters on one substrate due to the restrictions in the manufacturing method. The branching ratio of the portion corresponding to the optical demultiplexer 33 of the star coupler shown in FIG. 5 is set to 2: 1 in order to make all the non-diagonal components in the transfer characteristic equal. In the directional optical coupler shown in FIG. 7, the optical component 40 incident from one optical waveguide 33a is branched into two optical components 41 and 42. Further, a part of the light component 43 incident from the other optical waveguide 33b is transmitted to the one optical waveguide 33a and becomes a light component 44, and the rest becomes a loss light component 45.

The transfer characteristic in this case is expressed by equation (6).

[0046]

[Equation 6]

In the equation (6), the loss generated at the time of distribution is larger than that in the equation (5) because there is a loss light component 45 as shown in FIG. If the branching ratio of the portion corresponding to the optical demultiplexer 33 is not 2: 1, the non-diagonal components cannot all have the same value, that is, 1/9.

From this viewpoint, it seems that there is no advantage in constructing the star coupler as shown in FIG. 5 on the glass substrate. However, in the above-mentioned optical waveguide formed on the polycarbonate substrate, due to the structural problem caused by the manufacturing process, return light of about -35 dB is generated at the branch portion, while the optical waveguide is formed on the glass substrate. When the waveguide is formed, there is an advantage that the return light is significantly reduced to about -50 dB. Further, the optical branching path as shown in FIG. 3 has a drawback that it can be applied to a multimode optical waveguide but is difficult to apply to a single mode optical waveguide.
On the other hand, the configuration shown in FIG. 7 has an advantage that it can be applied to a single-mode optical waveguide.

A structure similar to that of the star coupler shown in FIG.
It is also possible to use a fusion coupler. In FIG. 8, reference numeral 51 is a fusion coupler having a branching ratio of 1: 1 and 52 is a fusion coupler having a branching ratio of 2: 1. What is a fusion coupler?
The clads of two optical fibers are melted and adhered to each other, and the cores of the respective optical fibers are brought sufficiently close to each other, which functions as a directional optical coupler.

The branching ratio of the fusion coupler 52 functioning as a directional coupler is defined as shown in FIG. Two optical fibers or optical waveguides (hereinafter simply called optical paths)
Among them, if the light incident from one end of one optical path is I ₀ , the light emitted from the other end of the optical path is I ₁ , and the light emitted to the other optical paths is I ₂ , the branching ratio is I ₁ : It is represented by I ₂ . Therefore, a branching ratio of 2: 1 means that I ₁ =
(2/3) I ₀ , I ₂ = (1/3) I ₀ .

Further, a star coupler having a multi-terminal and a similar function can be constructed. As shown in FIG.
An optical branching path 62 having a branching ratio of 10: 1 and a branching ratio of 1: is provided to each of the terminals X ₁ , X ₂ , X ₃ , X ₄ , X ₅ , X ₆ of the six-terminal star coupler 61 having the configuration shown in FIG. This is a configuration in which one optical branch path 60 and one optical branch path 60 are connected in a triangular shape. With this configuration, a 12-terminal star coupler having a transfer characteristic matrix whose diagonal components are all 1/11 can be configured. It goes without saying that the same method can be repeatedly used to increase the number of terminals such as 24 terminals and 48 terminals.

FIG. 11 is a diagram showing an embodiment of an optical communication network constructed by using the above-mentioned 6-terminal star coupler. The node 72 is connected to four terminals of the six terminals of the star coupler 71, and the star couplers 71 are connected to each other using the remaining two terminals. In this case, each star coupler 71 is connected via a relay amplifier 73. The relay amplifier 73 is preferably a bidirectional optical amplifier, for example, a rare earth-doped fiber amplifier or a semiconductor laser amplifier, but it may be a normal regenerative relay amplifier. Regarding the rare earth-doped fiber amplifier, see Horiguchi, "Optical Fiber Amplifier," Optics, Vol. 19, No. 5, May 1990, pp. 276-282. Regarding semiconductor laser amplifiers, Shimada and Nakagawa “Research Status of Semiconductor Laser Amplifiers Used in Optical Communication Systems”, O plus
E, August 1989, pp 106-111.

In the configuration of FIG. 11, when a rare earth-doped fiber amplifier is used as the repeater amplifier 73, even if the pump light source goes down, a small amount of signal light is transmitted, so that one amplifier fails. Can be designed so as not to bring down the entire network, resulting in high reliability.

If a regenerative repeater amplifier is used, then FIG.
As shown in 2, it is necessary to prepare two systems of amplifiers. That is, it is necessary to dispose two optical demultiplexer / multiplexer 80, light receiver 81, light emitting source 82, and amplifier 83 for two-way amplification. In the case of this regenerative repeater amplifier, not only simple amplification but also so-called 2R (Reshaping, Retimin
g) and 3R (Reshaping, Retiming, Regenerating) functions can be added. The terminals 84 and 85 in FIG.
Each is connected to one terminal of another star coupler.

At each node 71 of the optical communication network shown in FIG. 11, a light receiver 81 such as a photodiode and a light emitting source 82 such as a laser diode are provided one by one as shown in FIG. The multiplexer 80 performs demultiplexing and multiplexing. The terminal 87 derived from the optical demultiplexer / multiplexer 80 is
It is connected to one terminal of the star coupler 71 shown in FIG. Reference numeral 86 is a terminal device such as a workstation.

The star coupler shown in the embodiment of the present invention is
The transfer matrix is set so that the non-diagonal components are equal. This is to allow a new star coupler to be connected from any terminal of the star coupler through the relay amplifier when the network is expanded. That is, by equalizing the non-diagonal components of the transfer matrix, the gains required for the relay amplifiers become substantially equal, and the communication network is formed by combining the standardized star couplers with the same number of terminals and the relay amplifiers with the same gain. Can be built.

The star coupler is not limited to a polycarbonate substrate or a glass substrate, but may be a sapphire or a lithium niobate single crystal dielectric, or GaAs or In.
It can be constructed on a semiconductor such as P or Si by a similar method. As a result, the star coupler having the above characteristics can be realized as an optical integrated circuit. This is
This is because the circuit configurations shown in FIGS. 5 and 10 are both planar and the optical waveguides do not intersect.

In the above-mentioned embodiments, the star couplers having three terminals, six terminals and twelve terminals have been described as examples, but the present invention can be applied to star couplers having an arbitrary number of terminals.

An embodiment for realizing an interconnectable star coupler having an arbitrary number of terminals will be described below.

FIG. 14 shows a star coupler used as a component for realizing a star coupler having an arbitrary number of terminals which can be connected to each other.
And two optical unequal branch paths 101 having substantially the same distribution ratio are connected in a triangular shape.

The structure of the optical unequal branch path 101 is shown in FIG.
Shown in. In the figure, the optical signal S incident from the terminal 101a is distributed so as to be αS to the terminal 101c and βS to the terminal 101b. Assuming no loss, α +
β = 1. Further, it is assumed that α> β. The optical signal incident from the terminal 101b is distributed only to the terminal 101a, and the optical signal incident from the terminal 101c is distributed to the terminal 101a.
Will only be distributed to. In FIG. 14, the terminals 101b of the two optical unequal branches 101 are connected to each other, and
01c is connected to the terminal 102b of the optical branch path 102.

According to the star coupler shown in FIG. 14, the optical signal incident on one terminal 101a is transmitted to the other terminal 1a.
More is distributed to the terminals 102a than is distributed to the terminals 01a. The optical signal incident on the terminal 102a is equally distributed to the two terminals 101a.

The structure of the optical branch path 102 is shown in FIG. The optical signal S incident from the terminal 102a is distributed to both terminals 102b by S / 2.

FIG. 16A shows the above-mentioned optical unequal branch path 10.
1 shows a schematic configuration of a three-terminal star coupler configured by combining 1 and optical iso-branching paths 102. FIG. 2B is a schematic diagram of a 3-terminal star coupler configured by connecting three optical iso-branching paths 102 in a triangular shape. The configuration is shown.

Further, FIGS. 17A to 17F are similar to FIG.
A combination of only the three-terminal star coupler 103 shown in FIG.
FIG. 18A to FIG. 18C show a schematic configuration of a star coupler that can be interconnected from 4 terminals to 9 terminals, which is configured by combining the 3-terminal star coupler 104 shown in FIG. The schematic structure of the star coupler which can be mutually connected to a terminal is shown. However, the distribution ratios α: β of the optical unequal branch paths 101 are not necessarily the same. This distribution ratio will be described later. 16 to 18, the black circles indicate the light unequal branch paths 101, and the white circles indicate the light unequal branch paths 102.

Each of the star couplers described above can be realized as an optical integrated circuit by using an optical waveguide formed on an appropriate substrate.

FIG. 19 shows a structure of an optical integrated circuit 3
The example of the star coupler of a terminal is shown. The optical waveguides 107a to 107c formed on the substrate 105 have the same shape as the arcs of the circles 108a to 108c having the curvature R, respectively. The optical fiber 106 is connected to the ends of the optical waveguides 107a to 107c. The star coupler shown in FIG. 19 is
The optical nonuniform branch path 101 or the optical equal branch path 102 is arranged at the outer contact points of the circular arc optical waveguides 107a to 107c. The configuration of FIG. 19 is shown in FIG.
It corresponds to the star coupler 103 shown in FIG.

According to the star coupler shown in FIG. 19, the substrate area required for the optical integrated circuit substrate can be reduced. The minimum radius that can be bent for an optical fiber or an optical waveguide is set assuming a certain radiation loss. If the structure of the star coupler shown in FIG. 14 is realized under the condition that the optical waveguide is not bent with a radius of curvature smaller than this minimum radius, it becomes as shown in FIG.

When an interconnected star coupler is realized as an optical integrated circuit by using an optical waveguide formed on a glass or plastic substrate, it is possible to carry out batch production using photolithography, which facilitates production. There are advantages. Further, in this case, if the optical waveguide is formed in an arc shape and the optical branch path is arranged at the outer contact, the area of the substrate required for the optical integrated circuit can be reduced under the assumption of a constant radiation loss. Therefore, there is an advantage that the optical waveguide can be easily manufactured and the cost can be reduced.

FIG. 20 shows a structure of an optical integrated circuit 4
The example of the star coupler of a terminal is shown. This is shown in FIG.
This corresponds to the configuration of (a). The light unequal branch path 101 and the light unequal branch path 102 are specifically structured as shown in FIGS. 21 and 22, respectively. In FIG. 21 (a), the optical unequal branch paths 101 are provided with optical waveguides 111b (corresponding to terminals 101b) and 111c (corresponding to terminals 101c) having different widths.
And is suitable for forming the optical unequal branch path 101 mainly by using a multimode optical waveguide. Incidentally, 111a is an optical waveguide corresponding to the terminal 101a.

In addition, FIG. 21B shows the optical unequal branch path 10.
1 is realized by a directional coupler, and is suitable for forming an optical unequal branch path mainly by using a single mode optical waveguide. When the unequal optical branch path is formed by a directional coupler, there is no problem when the optical signal is branched, but when the optical signal joins from the optical waveguides 111b and 111c side to the optical waveguide 111a side, 21 (a) has a loss which is not present in the configuration. This is because, for example, the optical signal 108 from the optical waveguide 111c side of FIG.
This is because a part 108b of the optical signal 108 is distributed to the optical waveguide 111b side when it is incident on the optical waveguide 111b, and the distributed optical signal is radiated from the optical waveguide 111c into the substrate as a loss component 109.

Further, FIG. 22 shows the structure of the optical isolating path 102, which is an optical waveguide 112a (corresponding to the terminal 102a).
The optical signal from is equally divided into two optical waveguides 112b (corresponding to the terminal 102b) having the same width.

FIG. 23 is a plan view of a 5-terminal interconnectable star coupler. This corresponds to the configuration of FIG.

Hereinafter, FIG. 24 (corresponding to FIG. 17C) is 6
FIG. 25 (corresponding to FIG. 17D) has 7 terminals, FIG. 26 (corresponding to FIG. 17E) has 8 terminals, and FIG.
8 (c) corresponds to a plan view of a 12-terminal interconnectable star coupler. The 5-terminal star coupler of FIG. 23 is vertically symmetrical, the 6-terminal star coupler of FIG. 24 is symmetrical, and FIG.
The 8-terminal star coupler of 6 is vertically and horizontally symmetrical, 12 of FIG.
The terminal star coupler is for left and right. In addition, 6 in FIG.
In the terminal star coupler, only two optical fibers 106 are shown and the other four are omitted, and in the 12-terminal star coupler of FIG. 27, only the four optical fibers 106 are shown and the other eight are omitted. There is.

As described above, the above-mentioned structure is specifically formed by a method of forming an optical waveguide by diffusing thallium (Tl) ions or the like into a glass substrate or by irradiating polycarbonate with ultraviolet rays. It can be prepared by a method of forming an optical waveguide by selectively polymerizing a refractive index distribution.

Next, the design of the distribution ratio of the star coupler having the above structure will be described.

Now, in the four-terminal star coupler shown in FIG. 17A, it is assumed that the distribution ratios of the two three-terminal star couplers 103 constituting the same are both K ₁ .
However, K ₁ is K ₁ = α / β with respect to α and β described above (see FIG. 15). This relationship is illustrated in FIG.
It becomes like (a). In FIG. 28, the black circles indicate the light unequal branch paths 101, and the open circles indicate the light unequal branch paths 10.
2 is shown. The input signals to the terminals Q _{1 to} Q _{4 in} the figure are referred to as v _{1 to} v ₄ , respectively. The output signals from Q _{1 to} Q ₄ are w ₁ to w ₄ , respectively. At this time, if K ₁ = 2, the following relationship holds between v _{1 to} v ₄ and w _{1 to} w ₄ .

[0078]

[Equation 7]

In the case of the 5-terminal star coupler configuration shown in FIG. 17B, the distribution ratios of the star couplers 103b and 103c are respectively K ₂ =, as shown in FIG. 28B.
3, and K ₃ = 2, the following relationship holds.

[0080]

[Equation 8]

However, the terminals P _{0a to} P _{4a of} FIG.
The input signal to, and v ₀ to v _4, respectively. Also, P
The output signal from _0a to P _4a, respectively, and w ₀ to w _4.

As described above, by appropriately designing the distribution ratio of the star coupler 103, it is possible to make a multi-terminal star coupler in which the diagonal components of the transfer matrix are all zero and the non-diagonal components are all equal in value. it can. As described above, such a multi-terminal star coupler is suitable for constructing an optical communication network. In the above embodiment, the structure of the optical unequal branch path 101 is as shown in FIG.
The configuration shown in is used. In addition, the absorption loss of the optical waveguide and the radiation loss due to the bending of the optical waveguide are ignored in the design.

Furthermore, by changing the distribution ratio of the star coupler 103, the transfer matrix of the multi-terminal star coupler can be changed to a different one as shown below.

As shown in FIG. 28 (c), the distribution ratios of the star couplers 103d and 103e are K ₄ = 14 and K ₄ , respectively.
_{If 5} = 6, the following relation holds.

[0085]

[Equation 9]

Such a star coupler is used as shown in FIG. That is, the terminals P ₀ of the four 5-terminal star couplers 114 are connected to the terminals of the star coupler 113 so that they function as a whole as a 16-terminal interconnectable star coupler. In FIG. 29, a 4-terminal star coupler 113 is a star coupler whose distribution ratio is designed as shown in FIG. 4-terminal star coupler 113
Each terminal Q ₁ to Q ₄ are the terminals Q ₁ to Q ₄ of FIG. 28 (a) of
Respectively correspond to. 5-terminal star coupler 114
Has a distribution ratio designed as shown in FIG.
The terminals P _{0 to} P ₄ of the 5-terminal star coupler 114 are shown in FIG.
These correspond to P _{0 to} P ₄ in (c), respectively.

In this way, in the network shown in FIG. 29, the diagonal components of the 16-terminal transfer matrix are all zero,
The values of the off-diagonal components are equivalent to star couplers that are all equal. In an actual network configuration, it is practical that the skeletal part of the network is configured by connecting the star coupler 113 via a relay amplifier, and the optical signal is distributed to the end node via the star coupler 14. is there.
This is because such a configuration requires less laying amount of the optical fiber cable than a network configured by arranging a multi-terminal (for example, 16 terminals) star coupler in the center.

By applying the idea of the above embodiment, it is possible to realize a star coupler in which the number of terminals other than the above number is connectable. Therefore, it goes without saying that all such interconnectable star couplers are within the scope of the present invention.

The directional optical coupler referred to in the present specification means a passive element for demultiplexing and multiplexing light, and the optical branch path and the optical demultiplexing / multiplexing device are the directional optical couplers. It is a kind of bowl.

[0090]

As described above, according to the present invention,
Nodes can be connected by one terminal, and the network can be easily expanded by connecting star couplers. In addition, a bidirectional communication function can be realized and collision detection can be performed. Further, since the connection between the node and the star coupler and the connection between the star couplers can be made by one terminal, the number of optical fibers, connectors, and relay amplifiers required for constructing the network can be reduced by about half. Furthermore, by designing the off-diagonal components of the transfer matrix of the star coupler equal,
The gain of the relay amplifier can be the same.

Further, according to the present invention, it is possible to realize an interconnectable star coupler having an arbitrary number of terminals, and it is possible to freely change the values of the non-diagonal components of the transfer matrix to some extent.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a star coupler according to the present invention.

FIG. 2 is a schematic diagram of a three-terminal star coupler that is an embodiment of the present invention.

FIG. 3 is a plan view of an optical demultiplexer / multiplexer used in the star coupler shown in FIG.

FIG. 4 is a schematic diagram of a 6-terminal star coupler that is an embodiment of the present invention.

5 is a plan view of a case where the star coupler shown in FIG. 4 is realized as an optical integrated circuit on a substrate.

FIG. 6 is a plan view of an optical branch path used in the star coupler shown in FIG.

7 is a plan view showing a directional coupler using an optical waveguide used in the star coupler shown in FIG.

FIG. 8 is a schematic diagram of a 6-terminal star coupler according to the present invention configured with a fusion coupler.

FIG. 9 is a diagram for explaining a distribution ratio in the fusion coupler.

FIG. 10 is a diagram showing a connection method for expanding a 6-terminal star coupler to a 12-terminal star coupler.

FIG. 11 is a diagram showing an optical communication network configured by multiple connection of star couplers of the present invention.

12 is a diagram showing the internal structure of a bidirectional regenerative repeater amplifier used in the optical communication network shown in FIG.

FIG. 13 is a diagram showing a structure inside a node.

FIG. 14 is a diagram showing a schematic configuration of a three-terminal star coupler as a constituent element for configuring a star coupler having an arbitrary number of terminals.

15 is a diagram showing a schematic configuration of an unequal optical branch path and an equal optical branch path that constitute the three-terminal star coupler shown in FIG.

16 is a diagram showing a configuration of 3 using the components shown in FIG.
It is a figure which shows the schematic structure of the star coupler of 3 terminals comprised only from the star coupler of a terminal, and optical branch paths.

FIG. 17 is a diagram showing a configuration of 4 using the components shown in FIG.
It is a figure which shows the schematic structure of the star coupler which can be mutually connected from a terminal to 9 terminals.

FIG. 18 is a block diagram of the configuration shown in FIG.
It is a figure which shows schematic structure of the star coupler which can be mutually connected from 0 terminal to 12 terminals.

FIG. 19 is a plan view showing a schematic configuration when the configuration shown in FIG. 14 is realized as an integrated circuit.

FIG. 20 is a plan view of a 4-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 21 is a plan view showing a case where an optical unequal branch path is configured by using an optical waveguide.

FIG. 22 is a plan view showing a case where a branch path for light and the like is formed by using an optical waveguide.

FIG. 23 is a plan view of a five-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 24 is a plan view of a 6-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 25 is a plan view of a 7-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 26 is a plan view of an 8-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 27 is a plan view of a 12-terminal interconnectable star coupler realized as an integrated circuit.

FIG. 28 is a diagram showing distribution of distribution ratios inside a star coupler capable of interconnecting multiple terminals.

FIG. 29 is a diagram showing a network in which the terminals of the four-terminal interconnectable star coupler are connected to the terminals of the star coupler based on the internal distribution ratio of FIG. 28 (c).

FIG. 30 is a diagram showing an Ethernet network.

FIG. 31 is a diagram showing a network of star couplers using a mixing rod.

FIG. 32 is a plan view showing a star coupler realized on a glass substrate.

FIG. 33 is a diagram in which two star couplers are connected.

FIG. 34 is a diagram for explaining signal circulation when two star couplers are connected.

[Explanation of symbols]

1 Star coupler, 2 Optical demultiplexer / multiplexer, 2a, 2b,
2c waveguide, 3,4 optical demultiplexer / multiplexer, 5-16 terminals, 20 coaxial cables, 21 taps, 22 nodes,
22a light emitting element, 22b light receiving element, 23, 23a,
23b optical fiber, 24 star coupler, 25 terminal, 26 mixing section, 27 waveguide, 28 glass substrate, 31 polycarbonate substrate, 32 optical waveguide,
33 optical demultiplexer / multiplexer, 33a, 33b optical waveguide, 3
4 optical branch paths, 35 optical waveguides, 36 to 38 optical components,
39 optical fiber, 40-44 optical component, 45 loss light component, 51 fusion coupler, 52 fusion coupler, 60 optical branch path, 61 star coupler, 62 optical branch path, 71
Star coupler, 72 nodes, 73 relay amplifier, 80
Optical branch, 81 light receiver, 82 light source, 83 amplifier, 84, 85 terminal, 86 terminal device, 87 terminal,
101 light unequal branch paths, 101a to 101c each terminal of light unequal branch paths, 102 light unequal branch paths, 102a to 102c
Each terminal of the branch path such as light, 103, 103a to 103e,
104 3-terminal star coupler, 105 substrate, 106
Optical fiber, 107 optical waveguide, 108 optical signal, 10
8a, 108b optical signal, 109 loss component, 111
Optical unequal branch paths, 111a to 111c optical waveguides, 11
2, 112a optical waveguide, 113 4-terminal interconnectable star coupler, 114 5-terminal interconnectable star coupler, R, R ₁ , R ₂ optical waveguide curvature radii, S
Optical signal

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 19, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Fig. 16

[Correction method] Change

[Correction content]

16 is a diagram showing a configuration of 3 using the components shown in FIG.
It is a figure which shows the schematic structure of the star coupler of a terminal.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G02B 6/28 U 7820-2K H04L 12/44 7928-5K H04L 11/00 340

Claims (3)

[Claims] 1. A plurality of terminals, wherein an optical signal is input / output from the same terminal, an input signal to the own terminal is not distributed as an output signal from the own terminal, and the own terminal is provided. A star coupler having transfer characteristics that are distributed as output signals to all terminals other than the above. 2. An optical signal formed between three terminals for inputting and outputting an optical signal from the same terminal, three directional optical couplers, and each of the terminals and each directional optical coupler. The star coupler according to claim 1, comprising a waveguide and an optical waveguide formed between each of the directional optical couplers. 3. A plurality of terminals, wherein an optical signal is input / output from the same terminal, an input signal to the own terminal is not distributed as an output signal from the own terminal, and the own terminal is used. An optical communication network characterized in that a plurality of star couplers having transfer characteristics that are distributed as output signals are provided at all terminals other than the terminals, and the star couplers are connected to each other through the terminals.