JP3229489B2 - Optical network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical network in which optical transmission and reception between a master station and a plurality of slave stations are performed by a single optical fiber, and more particularly, to uniform transmission loss between the master station and slave stations. Can,
The present invention relates to an optical network for facilitating the extension of slave stations.

[0002]

2. Description of the Related Art FIG. 8 shows an optical network in which a master station and a plurality of slave stations are connected by a single optical fiber, and optical signals transmitted from each slave station are collected in the master station. In this network,
The optical transmitters (slave station optical transmitters) 2c, 2b, and 2a in the slave station devices 4c, 4b, and 4a sequentially become optical splitters 1c, 1b, and 1a.
Is connected to one optical fiber, and an optical receiver (master optical receiver) 3 in the master station device 5 is connected to the optical fiber. Each of the slave station optical transmitters 2c, 2b, and 2a outputs signal light having the same intensity P1 = P2 =... = Pn. Each optical splitter optimizes the branching ratio so that the signal intensity transmitted from the slave station far away from the master station to the signal light transmitted from the slave station near the master station has the same intensity at the master station. Have been. Each branching ratio is determined by calculating the number n of the optical branching units, the branch loss and excess loss of the optical branching unit, the transmission loss between the optical branching units, and the like at the stage of designing the network. With such a network configuration, the transmission loss between the master station and each slave station becomes constant, and the master station receiver converts the signal light transmitted from each slave station transmitter to the same light intensity P1f = P2f = .. = Pnf.

[0003] The optical branching device is realized by a fiber type optical coupler formed by fusing and stretching two optical fibers or a planar type optical coupler having an optical waveguide formed on a glass substrate or the like.

FIG. 9 shows a two-way optical transmission optical network in which each slave station receives an optical signal transmitted from a master station using the same optical fiber. As in the network of FIG. 8, the branching ratios k1, k2, and kn of the optical branching units are optimized so that the transmission loss between the master station and each slave station is constant. In the bidirectional transmission optical network, an upstream (slave station → slave station) signal light and a downstream (master station → slave station) signal light are transmitted in the master station apparatus 5 and in each of the slave station apparatuses 4c, 4b and 4a. Optical splitters 22c, 22b, 22a for combining and separating are provided. With such a configuration, the transmission loss between all the slave stations and the master station becomes constant, and uniform transmission characteristics can be obtained.

[0005]

By the way, when a new slave station is newly added in the transmission line of the conventional network, the optical branching device between the slave station and the master station deviates from the optimized state. In addition, the transmission loss between the master station and each slave station is not constant. Therefore, for example, in the master station receiver, the light intensity of the signal light transmitted from each slave station transmitter varies.

In order to eliminate this variation, it is necessary to change the design of the branching ratio of the optical branching device between the slave station to be added and the master station. A fiber type optical coupler or a planar type optical coupler used as an optical splitter has a fixed split ratio, and in order to change the split ratio, the optical splitter must be replaced. Since a plurality of optical branching devices are replaced in order to add one slave station, the cost for the addition increases.
Also, if the network is spread over a wide area, the exchange takes a lot of time.

It is an object of the present invention to provide an optical network that solves the above-mentioned problems, makes transmission loss between a master station and a slave station uniform, and facilitates the addition of slave stations.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a light receiving device which collects signal lights transmitted from a plurality of slave stations into one optical fiber by an optical branching device and receives the signals at a master station. In the network, each of the optical splitters is a three-terminal optical circulator provided with three terminals A, B, and C;
A forward transmission characteristic is provided from terminal A to terminal B and from terminal B to terminal C, and an optical fiber on the master station side is connected to terminal C,
An optical fiber on the opposite side of the master station is connected to the terminal A, and a slave station is connected to the terminal B via a variable reflection type optical distributor for variably distributing the signal light to the passing light and the reflected light, In order to change the ratio of the light intensity at the terminal C between the signal light incident at the terminal A and emitted at the terminal C and the signal light transmitted from the slave station and emitted at the terminal C, the distribution ratio of the variable reflection type optical distributor is changed. Is provided with distribution ratio control means for controlling the distribution ratio.

[0009] Also, the signal lights transmitted from the plurality of slave stations are sequentially collected into one optical fiber by an optical splitter and received by the master station, and conversely, the signal lights sent from the master station are reflected by each slave station. In an optical network capable of bidirectional optical transmission for receiving light, each of the optical splitters is a four-terminal optical circulator provided with four terminals A, B, C, and D, and a terminal B is connected from terminal A to terminal B.
From the terminal C to the terminal C, from the terminal C to the terminal D, and from the terminal D to the terminal A, with the master station side optical fiber connected to the terminal C, and the terminal A opposite to the master station optical fiber. And a terminal B connected to an optical transmitter of a slave station via a first variable reflection type optical distributor for variably distributing signal light to passing light and reflected light, and to a terminal D. The optical receiver of the slave station is connected via the same second variable reflection type optical distributor, and the signal light which enters at the terminal A and emerges at the terminal C and the signal light which is transmitted from the optical transmitter of the slave station to the terminal C And the ratio of the light intensity at the terminal C to the signal light emitted at the terminal C and the signal light incident at the terminal C and emitted at the terminal A and the signal light incident at the terminal C and received by the optical receiver of the slave station Distribution ratio control means for controlling the distribution ratio of the first and second variable reflection type optical distributors in order to change the respective intensity ratios is provided. Than it is.

[0010] The distribution ratio of each of the variable reflection type optical distributors may be set from the master station.

[0011]

According to the above configuration, the signal light having the light intensity Pa incident from the terminal A of the three-terminal optical circulator exits from the terminal B due to the forward transmission characteristic, and enters the variable reflection type optical distributor 9. Here, the distribution ratio of the variable reflection type optical distributor 9 is R (≦
1), the signal light having the light intensity Pa is the light intensity Par = P
The reflected light is distributed into a × R reflected light and transmitted light having a light intensity Pat = Pa × (1−R). The reflected light of light intensity Par is the terminal B
And the passing light having the light intensity Pat goes to the slave station optical transmitter side. The reflected light having the light intensity Par incident on the terminal B exits from the terminal C due to the forward transmission characteristic.

On the other hand, the signal light of the light intensity Pb emitted from the slave station optical transmitter enters the variable reflection type optical distributor, and the reflected light of the light intensity Pbr = Pa × R and the light intensity Pbt = Pa ×
(1-R) and the transmitted light. The reflected light having the light intensity Pbr returns to the slave station optical transmitter, and the light having passed the light intensity Pbt enters the terminal B and exits from the terminal C due to the forward transmission characteristic.

In this manner, the light intensity P
ar = Pa × R signal light and light intensity Pbt = Pa × (1-
Although the signal light of R) is emitted, the ratio of the light intensity of the two signal lights can be changed by changing the distribution ratio R using the distribution ratio control means. For example, if the number of slave stations upstream of the slave station, that is, the number of slave stations on the opposite side of the master station is one, control is performed so that the ratio is 1 to 1, that is, Par = Pbt. If the number of slave stations on the opposite side of the master station is N, control is performed so that Par / N = Pbt.

A device that performs bidirectional transmission between a master station and a slave station performs the same operation as described above with respect to transmission from the slave station. Regarding the transmission from the master station, the signal light having the light intensity Pc that enters from the terminal C of the four-terminal optical circulator exits from the terminal D due to the forward transfer characteristic, and enters the second variable reflection type optical distributor. Here, assuming that the distribution ratio of the second variable reflection type optical distributor is R (≦ 1), the signal light of the light intensity Pc is the reflected light of the light intensity Pcr = Pc × R and the light intensity Pct =
Pc × (1-R) and the transmitted light. Light intensity Pc
The reflected light of r returns to the terminal D, and the transmitted light of the light intensity Pct is received by the slave station optical receiver. Light intensity Pc incident on terminal D
The reflected light of r exits from the terminal A due to the forward transfer characteristic,
Head to the slave station opposite the master station.

As described above, the signal light having the light intensity Pc incident from the terminal C is equal to the light intensity Pcr =
The signal light is divided into a signal light of Pa × R and a signal light of light intensity Pct = Pc × (1-R) received by the slave station optical receiver.
By changing the distribution ratio R using the distribution ratio control means, the ratio of the light intensities of the two signal lights can be changed. For example, if the number of slave stations upstream from the slave station is one, control is performed so that the ratio is 1: 1, that is, Pcr = Pct. If the number of slave stations on the opposite side of the master station is N, control is performed so that Pcr / N = Pct.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, the optical network according to the present invention comprises a master station at one end of an optical transmission line in which a plurality of optical branching devices composed of three-terminal optical circulators 6a, 6b, 6c are sequentially connected by optical fibers. Is provided. Each of the three-terminal optical circulators has a variable reflection type optical distributor 7a, 7b, 7c and a slave station device 4a, 4 constituting a slave station.
b, 4c are provided. In the optical network, signal light transmitted from a slave station is sequentially collected into one optical fiber by an optical splitter and received by a master station. For this purpose, the master station device 5 is provided with a master station optical receiver 3 composed of an optical / electrical converter (O / E), and the slave station devices 4a, 4b, 4c are respectively provided with electro-optical converters (E / O). ) Optical transmitter 2
a, 2b and 2c are provided. Here, the slave station device 4c
Is for the n-th slave station counted from the master station.

The details around the slave station will be described with reference to FIG.

The three-terminal optical circulator 10 has three terminals A, B, and C, and has forward transmission characteristics from the terminal A to the terminal B and from the terminal B to the terminal C. That is, light incident on the terminal A exits from the terminal B, and light incident on the terminal B exits from the terminal C. In the optical network of the present invention, the optical fiber on the master station side is connected to the terminal C, and the optical fiber on the opposite side of the master station is connected to the terminal A. The variable reflection type optical distributor 9 inserted between the terminal B of the three-terminal optical circulator 10 and the sub-station optical transmitter 8 allows a part of the light incident on one of them to pass to the other and the other to enter the other. The light is reflected and the light incident on the other is transmitted and reflected in the same manner. The signal light is distributed to the transmitted light and the reflected light, and the distribution ratio can be changed. The distribution ratio control means 11 controls the distribution ratio of the variable reflection type optical distributor 9.

FIG. 3 shows an example of the variable reflection type optical distributor.
As shown in FIG. 3 (b), the variable reflection type optical distributor
A semi-transmissive reflective plate 13 formed in a circular shape, and a pair of optical fibers 12 arranged on the outer periphery of the reflective plate 13 with the optical axis aligned with the reflective plate 13 with the reflective plate 13 interposed therebetween.
a and 12b, a pair of rod lenses 18a and 18b for converting signal light emitted from the end of the optical fiber into parallel light and condensing the parallel light on the end of the optical fiber, and a stepping motor 14 for rotating the reflection plate 13. Be composed. As shown in FIG. 3A, the distribution ratio of the transmitted light and the reflected light of the reflection plate 13 is gradually changed in the circumferential direction. here,
There are n types of distribution ratios of R1, R2,..., Rn, and a desired distribution ratio can be obtained from the n types by the distribution ratio control means 11 rotating the stepping motor 14 by an appropriate angle.

As shown in FIG. 3C, the semi-transmissive reflection plate 13 uses an ND filter which is a neutral density (achromatic) filter that does not exhibit spectral selective absorption.
The reflective film 15 is formed by depositing a metal on the surface of the glass disk 17. By changing the deposition density depending on the position, different distribution ratios can be obtained depending on the position. Here, the glass disk 17 is divided into n parts in the circumferential direction,
The reflector 13 having n kinds of distribution ratios is formed by changing the deposition density for each part. An anti-reflection film 16 is formed on the opposite side of the surface of the glass disk 17 on which the reflection film 15 is formed to prevent unnecessary reflection.

Next, the operation of the embodiment will be described.

In FIG. 2, a signal light having a light intensity Pa incident from a terminal A of a three-terminal optical circulator exits from a terminal B due to a forward transmission characteristic and enters a variable reflection type optical distributor 9. Here, the distribution ratio of the variable reflection type optical distributor 9 is R (≦
1), the signal light having the light intensity Pa is the light intensity Par = P
The reflected light is distributed into a × R reflected light and transmitted light having a light intensity Pat = Pa × (1−R). The reflected light of light intensity Par is the terminal B
And the passing light having the light intensity Pat goes to the slave station optical transmitter 8 side. The reflected light having the light intensity Par incident on the terminal B exits from the terminal C due to the forward transmission characteristic.

On the other hand, the signal light of the light intensity Pb emitted from the slave station optical transmitter 8 enters the variable reflection type optical distributor 9, and the reflected light of the light intensity Pbr = Pa × R and the light intensity Pbt = Pa
× (1-R) passing light. The reflected light having the light intensity Pbr returns to the slave station optical transmitter 8, and the light having the light intensity Pbt enters the terminal B and exits from the terminal C due to the forward transmission characteristic.

In this way, the light intensity P
ar = Pa × R signal light and light intensity Pbt = Pa × (1-
Although the signal light of R) is emitted, the ratio of the light intensity of the two signal lights can be changed by changing the distribution ratio R using the distribution ratio control means 11. For example, if the number of slave stations upstream of the slave station, that is, the number of slave stations on the opposite side of the master station is one, control is performed so that the ratio is 1 to 1, that is, Par = Pbt. If the number of slave stations on the opposite side of the master station is N, control is performed so that Par / N = Pbt.
With such a network configuration, the transmission loss between the master station and each slave station becomes constant, and the master station receiver converts the signal light transmitted from each slave station transmitter to the same light intensity P1.
f = P2f =... = Pnf.

In the conventional network, when adding a new slave station, all the optical branching devices between the slave station to be added and the master station are exchanged. According to the present invention, the branching ratio of all the optical branching devices on the network can be easily changed, so that there is no need for replacement when adding. Therefore, the expandability of the network is greatly improved.

The operation of the variable reflection type optical distributor will be described. Now, in FIG. 3C, the optical fiber 12 on the port E side
When the signal light having the light intensity Pe is made incident through a, the light is converted into parallel light by the rod lens 18a and enters the reflector 13. In the reflection plate 13, the light intensity Per =
Reflected light of Pe × R and light intensity Pet = Pe × (1-R)
And the light passing therethrough. The reflected light is focused on the port E-side optical fiber 12a by the rod lens 18a on the port E side. The passing light is focused on the optical fiber 12b on the port F side by the rod lens 18b on the port F side.

Similarly, the optical fiber 12 on the port F side
When the signal light having the light intensity Pf is incident through b, the light is converted into parallel light by the rod lens 18 b and is incident on the reflection plate 13. In the reflector 13, the light intensity Pfr =
The reflected light of Pf × R and the light intensity Pft = Pe × (1-R)
And the light passing therethrough. The reflected light is focused on the optical fiber 12b on the port F side by the rod lens 18b on the port F side. The passing light is the rod lens 18a on the port E side.
Is focused on the optical fiber 12a on the port E side.

Another embodiment will be described.

The optical network shown in FIG. 4 is a master station device which forms a master station at one end of an optical transmission line in which a plurality of optical branching devices consisting of four terminal optical circulators 24a, 24b and 24c are sequentially connected by optical fibers. 5 are provided. Each of the four-terminal optical circulators 24a, 24b, 24c has a variable reflection type optical distributor 7a, 7b, 7c, 25a, 25b, 25.
c and slave station devices 2a, 2b, and 2c that constitute slave stations. In this optical network, signal light transmitted from slave stations is sequentially collected by an optical splitter into one optical fiber and received by a master station, and conversely, signal light sent from the master station is received by each slave station. Thereby, bidirectional transmission is performed between the master station and the slave station.

The master station device 5 is provided with a master station optical receiver 3 comprising an optical-electrical converter (O / E) and a master station optical transmitter 19 comprising an electro-optical converter (E / O). The master station optical transmitter 19 is connected to the terminal A of the optical circulator 23, and the master station optical receiver 3 is connected to the terminal C. Slave station devices 4a, 4b, 4
c, slave station optical transmitters 2a, 2b, 2c each comprising an electro-optical converter (E / O) and an opto-electric converter (O / E)
The sub-station optical receivers 21a, 21b and 21c are provided. Here, the slave station device 4c is of the n-th slave station counted from the master station.

The details around the slave station will be described with reference to FIG.

The four-terminal optical circulator 26 has four terminals A, B, C, and D.
From terminal C to terminal C, and from terminal D to terminal A. That is, light incident on terminal A exits from terminal B, light incident on terminal B exits from terminal C, light incident on terminal C exits from terminal D, and light incident on terminal D exits on terminal A Emitted from In this optical network, a terminal C is connected to an optical fiber on the master station side, and a terminal A is connected to an optical fiber on the opposite side of the master station. First variable reflection type optical distributor 9 similar to the above embodiment
Is inserted between the terminal B of the four-terminal optical circulator 26 and the local station optical transmitter 8, and a similar second variable reflection type optical distributor 27 is inserted between the terminal D and the local station optical receiver 28. ing. The distribution ratio control means 29 controls the distribution ratio of the two variable reflection type optical distributors 9 and 27.

In the uplink (slave station → master station), FIG.
In the same manner as the network of FIG. 1, the signal light having the light intensity Pa incident from the terminal A is distributed by the variable reflection type optical distributor 9 to the distribution ratio R.
(≦ 1), the light is distributed into reflected light having a light intensity Par = Pa × R and transmitted light having a light intensity Pat = Pa × (1-R),
The reflected light having the light intensity Par exits from the terminal C. On the other hand, the signal light of the light intensity Pb emitted from the slave station optical transmitter 8 is reflected by the variable reflection type optical distributor 9 at the light intensity Pbr = Pa × R and the light intensity Pbt = Pa × (1-R ), And the transmitted light having the light intensity Pbt is emitted from the terminal C. By changing the distribution ratio R using the distribution ratio control means 29, the ratio of the light intensity of the two signal lights emitted from the terminal C can be changed. For example, if the number of slave stations upstream from the slave station is 1, the control is performed so that Par = Pbt. If the number of slave stations upstream is N, Par = Pbt.
/ N = Pbt.

In the downstream line (from the master station to the slave station), the signal light having the light intensity Pc transmitted from the terminal C of the four-terminal optical circulator 26 is emitted from the terminal D due to the forward transmission characteristic, and is output from the variable reflection type. The light enters the light distributor 27. Here, assuming that the distribution ratio of the variable reflection type optical distributor 27 is R (≦ 1), the signal light having the light intensity Pc is the reflected light having the light intensity Pcr = Pc × R and the light intensity Pct = Pc × (1-R ) And the transmitted light. The reflected light having the light intensity Pcr returns to the terminal D, and the light having passed the light intensity Pct is received by the slave station optical receiver 28.
The reflected light having the light intensity Pcr incident on the terminal D exits from the terminal A due to the forward transmission characteristic, and travels toward the upstream slave station.

As described above, the signal light having the light intensity Pc incident from the terminal C becomes the light intensity Pcr =
The signal light is distributed to the signal light of Pa × R and the signal light of the light intensity Pct = Pc × (1-R) received by the slave station optical receiver 28. , The ratio of the light intensity of the two signal lights can be changed. For example, if the number of slave stations upstream from the slave station is 1
If it is a station, control is performed so that the ratio is 1: 1, that is, Pcr = Pct. If the number of slave stations on the opposite side of the master station is N, control is performed so that Pcr / N = Pct.

Conventionally, in a bidirectional transmission system using optical signals of the same wavelength band in the upper and lower lines, a 3 dB optical coupler for separating the optical signals in the upper and lower lines on a one-to-one basis was required in the slave station and the master station. Branch loss occurred. In this configuration, since the optical circulator is used for combining and separating the optical signals of the uplink and the downlink, no branch loss occurs. As a result, the reception sensitivity is improved by 6 dB in both the upper and lower lines, and the maximum transmission distance can be increased, the number of accommodated slave stations can be increased, and the transmission characteristics can be improved.

Variable reflection type optical distributors 9 and 27 of optical branching devices
Can be shared because the distribution ratio R has the same value when the number of optical transmitters and the number of optical receivers in the uplink and downlink are the same.

The variable reflection type optical distributor shown in FIG. 6 has two pairs of a reflector 13 and an outer periphery of the reflector 13 which is disposed so as to be perpendicular to the reflector 13 and have the optical axis aligned with the reflector 13 interposed therebetween. Optical fibers 12a, 12b, 12c, and 12d;
It comprises two pairs of rod lenses 18a, 18b, 18c, 18d for converting signal light emitted from the end of the optical fiber into parallel light and condensing the parallel light at the end of the optical fiber, and a stepping motor 14. The reflection plate 13 and the stepping motor 14 are the same as those in FIG. 3 and are commonly used.

FIG. 7 is a diagram in which the variable reflection type optical distributor 30 of FIG. 6 is introduced in FIG. 5, and the same operation as in FIG. 5 can be obtained.

The distribution ratio control means 11 and 29 can be remotely controlled from the master station. In this case, the master station sets the branching ratio of each optical splitter so that the intensity of the signal light transmitted from each slave station and arriving at the master station becomes uniform. Can be easily reorganized.

[0042]

The present invention exhibits the following excellent effects.

(1) Since the transmission loss between the master station and the slave station can be easily made uniform, the expansion of the slave station is facilitated, and the expandability of the network is greatly improved.

(2) When adding a slave station, it is not necessary to replace an optical branching device, so that equipment costs and labor are not required.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical network showing one embodiment of the present invention.

FIG. 2 is a detailed configuration diagram around a slave station of the optical network of the present invention.

FIG. 3 is a diagram showing the structure and operation principle of a variable reflection type optical distributor used in the present invention.

FIG. 4 is a configuration diagram of an optical network showing another embodiment of the present invention.

FIG. 5 is a detailed configuration diagram around a slave station of the optical network of the present invention.

FIG. 6 is a structural diagram of a variable reflection type optical distributor used in the present invention.

FIG. 7 is a detailed configuration diagram around a slave station of the optical network of the present invention.

FIG. 8 is a configuration diagram of an optical network showing a conventional example.

FIG. 9 is a configuration diagram of an optical network showing a conventional example.

[Description of Signs] 2a, 2b, 2c, 8 Sub-station optical transmitter 3 Master-station optical receiver 4a, 4b, 4c Sub-station device 5 Master-station device 6a, 6b, 6c, 10 Three-terminal optical circulator 7a, 7b, 10 7c, 9 Variable reflection type optical distributor 11 Distribution ratio control means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-177627 (JP, A) JP-A-63-1223 (JP, A) JP-A-5-136745 (JP, A) JP-A-3-3 125101 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 G08C 13/00-25/00

Claims (3)

(57) [Claims] 1. In an optical network in which signal lights transmitted from a plurality of slave stations are sequentially collected into one optical fiber by an optical splitter and received by a master station, each optical splitter is connected to three terminals A and B. , C provided with forward transmission characteristics from terminal A to terminal B and from terminal B to terminal C, an optical fiber on the master station side being connected to terminal C, and a parent terminal being connected to terminal A. An optical fiber on the opposite side of the station is connected. A terminal B is connected to a slave station via a variable reflection type optical distributor which variably distributes signal light into passing light and reflected light at a distribution ratio. And a distribution controlling the variable reflection type optical distributor in order to change the ratio of the light intensity at the terminal C between the signal light emitted from the terminal C and the signal light transmitted from the slave station and emitted from the terminal C. An optical network comprising ratio control means. 2. The signal lights transmitted from a plurality of slave stations are sequentially collected into one optical fiber by an optical splitter and received by a master station. Conversely, the signal lights sent from the master station are received by each slave station. In the optical network capable of bidirectional optical transmission for receiving light, each of the optical splitters is a four-terminal optical circulator provided with four terminals A, B, C, and D, from terminal A to terminal B, and from terminal B to terminal C. From terminal C to terminal D and from terminal D to terminal A
To the terminal C, the optical fiber on the master station side is connected to the terminal C, the optical fiber on the opposite side of the master station is connected to the terminal A, and the signal light passes through the terminal B and the reflected light to the terminal B. The optical transmitter of the slave station is connected through a first variable reflection type optical splitter that variably distributes the signal to the terminal, and the terminal D is connected to the terminal D through a similar second variable reflection type optical splitter. The optical receiver is connected, the ratio of the light intensity at the terminal C between the signal light incident at the terminal A and emitted at the terminal C and the signal light emitted from the optical transmitter of the slave station and emitted at the terminal C, and the terminal C The first and second variable reflections are used to change the ratio of the light intensity between the signal light incident at the terminal A and emitted at the terminal A and the signal light incident at the terminal C and received by the optical receiver of the slave station. An optical network comprising a distribution ratio control means for controlling a distribution ratio of a type optical distributor. 3. The optical network according to claim 1, wherein a distribution ratio of each of the variable reflection type optical distributors is set from a master station.