JPH08293855A - Optical wdm transmission system and method for synthesizing the system - Google Patents

Abstract

PURPOSE: To make best use of the number of potential branches at each system by being connected to the output port of a second optical branching means so as to allow the reception threshold values and the attenuation rates of first and second signal light to satisfy a specified condition. CONSTITUTION: A center equipment 21 outputs the signal light of a wavelength λ1 and power P1 and a center equipment 22 outputs the signal light of a wavelength λ2 and power P2 . On the other hand, it is assumed that attenuation rates caused by the branch loss of a 2-branch element 16 and 4-branch element 15-1 are respectively A1 and A2 and the minimal photodetecting levels of user's equipments 31-K and 32-K are respectively R1 and R2 . Then the attenuation rate A1 is determined by a value obtained by adding the branch loss of the element 16 with a propagation loss from the equipment 21 to the element 16, and the attenuation loss A2 is determined by adding the branch loss of the element 15-1 with a propagation loss from the element 16 to user's equipment 35-K. Then when P1 ×A1 >=R2 and P2 ×A2 >=R2 are valid, signal light from the equipments 21 and 22 reach the equipments 31-K and 32-K with the respective power of P1 ×A1 ×A2 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical WDM transmission system for performing communication using optical WDM (wavelength division multiplexing) between a center device and a user device, and particularly, a permissible loss up to the user device is different. The present invention relates to an optical WDM transmission system capable of accommodating a maximum number of user equipments within each allowable loss in a system including a plurality of center equipments, and a combining method of the system.

[0002]

2. Description of the Related Art Currently, FTTH (Fiber T
PD as an optical subscriber system that realizes "The Home"
Research and development of the S (Passive Double Star) optical subscriber system is being actively pursued.

FIG. 1 shows a conventional example of a PDS optical subscriber system, which is a partial modification of the system disclosed in Japanese Patent Laid-Open No. 62-290219. In the PDS system, an optical star coupler 7 which is a passive optical component is arranged at a branch point on the optical transmission line, and time division multiplexing is performed between each center device 5 installed in the station C and a plurality of user devices 6. It is intended for communication. In this system, since the plurality of user devices 6 share the center device 5 and the transmission path,
The cost of the system can be reduced.

The number of user devices 6 that can be connected to the optical star coupler 7 is not the same. For example, a user device in a subscriber area (for example, A ₄ ) having a short transmission distance is connected to the center device 5 via an optical star coupler 7 having a large number of branches, and the number of branches decreases as the transmission distance increases. An optical star coupler is used. For example, the farthest area A
₂ user devices via a two-branch star coupler 7,
It is connected to the center device 5. This is because the loss from the center device to the user device increases as the transmission distance increases, and the number of branches must be reduced.

Consider a configuration for providing different services using such a PDS system. Signals handled by transmission systems include low-speed narrow-band signals such as telephone signals to high-speed wide-band signals represented by image signals.
There are a wide variety. There are various data speeds, capacities, or modulation methods.

In such a case, various services can be collectively provided to all users by using the wideband signal. However, in such a system configuration, a high-speed transmission device is used even for a user who uses only a low-speed service such as a telephone, and the system becomes expensive.

There are also the following problems. For example,
When receiving a video signal, an economical system can be constructed by using a commercially available TV receiver. for that purpose,
It is necessary to use an AM modulation method or an FM modulation method which is an analog modulation method. In this case, the wideband analog signal and the digital signal cannot be sent as they are through the optical transmission line because they cannot be electrically multiplexed as they are.
Further, when such a system is constructed using a high-speed digital transmission line, a device for converting a digital signal into an analog signal or an analog signal into a digital signal is required, which is expensive.

Therefore, a system using WDM transmission has been proposed. For example, when providing a low-speed two-way communication service such as a telephone and a one-way wide band transmission service such as CATV, the low-speed communication is a two-way transmission of 1.3 μm band and the wide-band transmission is one-way of a 1.55 μm band. It is realized by transmission and these are combined by wavelength division multiplexing. WDM like this
According to the PDS system using, the transmission path can be shared by a plurality of systems that provide different services.

The advantage of the PDS system is that it is economical because many user devices share one center device. For example, among the center devices shown in FIG. 1, the center device accommodating each user device in the area A ₄ has the highest economic efficiency due to user multiplexing. Thus, the larger the number of branches, the more economical. However, an increase in the number of branches directly leads to an increase in optical loss. Since the permissible optical loss of the system that provides each service is finite, the number of branches within the permissible loss is actually suppressed. Such a permissible loss depends not only on the transmission distance but also on the type of service and the transmission rate and the modulation method that change accordingly. For example, in the case of using WDM to provide a broadband communication service such as video distribution in addition to an existing low-speed communication service such as a general telephone, from each center device that provides these services to a specific user device. The power dissipation has different values. Therefore, when providing different services using WDM, the following inconvenience occurs.

FIG. 2 shows two point-multipoint optical transmission systems that provide services independent of each other.
This is a system combined by an optical multiplexing / demultiplexing device.

In the figure, n user devices 30-1 to 30-1
30-n is connected to two center devices 21 and 22 via an optical fiber transmission line 13, an n-branching element 12 and a WDM element (optical multiplexing / demultiplexing element) 17, respectively.
The downstream signal lights with wavelengths λ ₁ and λ ₂ output from the center devices 21 and 22 undergo time division multiplexing by each center device and wavelength multiplexing by the WDM element 17, and
Each of the user devices 30-1 to 30-3 is branched by the branching element 12.
0-n. Each user equipment extracts the signal light addressed to itself from the wavelength-multiplexed downlink signal light.

On the other hand, among the user equipments 30-1 to 30-n, the user equipment performing bidirectional communication transmits the signal light at a predetermined transmission timing assigned by time division multiplexing. The signal light transmitted from the user device is generated by modulating the light from the light source in the user device or the light supplied from the center device. These upstream signal lights are passively multiplexed on the time axis by the n-branching element 12, demultiplexed into signal lights having wavelengths λ ₁ and λ ₂ by the WDM element 17, and received by the center devices 21 and 22.

In such a configuration, each user device 30-
1 to 30-n can communicate with the respective center devices 21 and 22 by selecting the wavelength. Therefore, when the center device provides different services, different services can be received through the common transmission path.

By the way, the point-multipoint optical transmission system for providing services independent of each other is optimized independently and in consideration of factors such as the modulation system used, the device, the transmission signal band, the stability and the economical efficiency. Designed to. Therefore, the allowable loss in the optical fiber transmission line and the branching element has a value unique to each system, and the number of user devices accommodated in each system, that is, the number of branches also differs. Therefore, when trying to integrate two or more systems that provide different services into one system by wavelength-division multiplexing, the system has conventionally been adapted to the system with the minimum allowable loss.

For example, consider the case where the system 1 shown in FIG. 4A and the system 2 shown in FIG. 4B are integrated. The system 1 accommodates eight user devices 31-1 to 31-8 via the 8-branch element 14, and the system 2
Through the four-branch element 15, four user devices 32-
It houses 1-32-4. Such a system
The system configuration shown in FIG. 2 cannot be combined into one.

Therefore, it is necessary to divide the system 1 as shown in FIG. 4C and then integrate both systems 1 and 2 as shown in FIG. That is, it is necessary to divide the system 1 according to the system 2 having a smaller allowable loss (the number of branches), and then use the optical multiplexing / demultiplexing device 17 to unify the systems 1 and 2. It should be noted that the user devices 35-1 to 35-4 shown in FIG.
It has the configuration shown in FIG. In this way, multiple P
When the DS system is integrated using WDM elements and the transmission line including the star coupler is to be shared, the center device must be installed according to the minimum number of branches in each system. How to do it. Therefore, the maximum number of branches of each system could not be effectively utilized. This is an essential problem when trying to utilize the PDS transmission line architecture and the WDM element at the same time. If the permissible loss is almost the same in each system, such a problem does not occur, but the service to be provided determines the transmission method and the number of multiplexes independently. is there. In addition, designing each system to have the same allowable loss impairs the original purpose of the system using the WDM element, that is, the advantage that a new system can be designed independently of the existing system.

[0017]

Therefore, an object of the present invention is to provide a plurality of points having different allowable losses (the number of possible branches).
An object of the present invention is to provide an optical WDM transmission system and a method of combining the same, which can maximize the number of possible branches of each system when integrating a multipoint optical transmission system by wavelength multiplexing using WDM elements.

[0018]

In order to achieve the above object, the present invention according to claim 1 provides a first center device for outputting a _first signal light having a wavelength λ ₁ with an output power P _1. , A second center device that outputs a _second signal light having a wavelength of λ ₂ with an output power P ₂ and an output port of the first center device, and the first signal light is attenuated by an attenuation rate A ₁ Is connected to the output ports of the second center device and the first optical branching means, and the optical signal is multiplexed with the second signal light and the first signal light. A _second optical branching unit that is connected to the output port of the optical multiplexing unit and that splits the multiplexed first signal light and second signal light at an attenuation rate A 2; Which is connected to the output port of the optical branching means for receiving the first signal light,
A first user equipment having a reception threshold value R _{1 and} a second user equipment having a reception threshold value R ₂ connected to the output port of the second optical branching means and receiving the second signal light. It is characterized by comprising a user device and satisfying the conditions of P ₁ × A ₁ × A ₂ ≧ R ₁ and P ₂ × A ₂ ≧ R ₂ .

According to a second aspect of the present invention, there is provided third optical branching means for branching the second signal light at an attenuation rate A ₃ between the second center device and the optical multiplexing means. , P ₁ × A ₁ × A ₂ ≧ R ₁ and P ₂ × A ₃ × A ₂ ≧ R ₂ are satisfied.

According to a third aspect of the present invention, the first optical branching means and the second optical branching means branch the input signal light into 2 ^N (N is a positive integer). And

According to a fourth aspect of the present invention, at least one of the first light branching means and the third light branching means comprises a plurality of light branching elements configured in multiple stages.

According to a fifth aspect of the present invention, in the optical multiplexing means and the second optical branching means, the input ports are the output port of the second center device and the output port of the first optical branching means. An optical branching unit of a multi-input port, which is connected and whose output port is connected to the first user device and the second user device, and the first signal which is arranged at the output port of the first center device It is characterized by comprising a first wavelength filter that passes light and a second wavelength filter that is arranged at the output port of the second center device and that passes the second signal light.

According to a sixth aspect of the present invention, at least a part of the first optical branching means and the optical multiplexing means is housed in the first center device.

According to a seventh aspect of the present invention, a dual path from at least one of the first center apparatus and the second center apparatus to the second optical branching unit, and the dual path And selecting means for connecting the output port of the center device connected to the one of the dual paths.

According to an eighth aspect of the present invention, there is provided a dual path from one or more of the first and second user equipments to the second optical branching means, and a user equipment connected to the dual path. Selecting means for connecting the input port to one of the dual paths.

According to a ninth aspect of the present invention, the optical multiplexing means passes through the second optical branching means to the first and second optical branching means.
Is optical multiplexing / demultiplexing means for demultiplexing the signal light supplied from the user device into a signal light having a wavelength of λ _{1 and} a signal light having a wavelength of λ ₂ , the first center device and the first user device. At least one of the transmission path connecting the devices and the transmission path connecting the second center apparatus and the second user apparatus is a bidirectional transmission path.

According to a tenth aspect of the present invention, the first signal light having a wavelength of λ ₁ output from the first center device is branched so that the plurality of first user devices have a first allowable loss or less. Point-to-multipoint first optical transmission system and the wavelength output from the second center device is λ ₂
Point-multipoint type second optical transmission system that splits the second signal light of the above and supplies it to a plurality of second user equipments with a second allowable loss or less. Selecting a multi-service user equipment for receiving both the first signal light and the second signal light from the first user equipment and the second user equipment in a method of integrating into a transmission system; A step of branching a third signal light generated by optically multiplexing the first signal light and the second signal light to supply a path to the multi-service user equipment; The optical loss from the center device to the first user device is set to the first allowable loss or less, and the optical loss from the second center device to the second user device is set to the second allowable loss or less. Tosu The number of branches, characterized by comprising a process of setting the number of branches of the first signal light and at least one of the signal light of the second signal light.

The eleventh aspect of the present invention comprises the step of establishing a path for supplying the signal light output from the first user equipment to the first center equipment by time division multiplexing. To do.

According to the present invention, when a plurality of point-multipoint optical transmission systems are integrated into one optical transmission system sharing a transmission line including a star coupler by using wavelength division multiplexing, each optical transmission system is Even if the allowable losses (the number of possible branches) are different, the original allowable number of branches can be utilized without being limited by the allowable losses of other systems. That is, it is possible to accommodate user devices corresponding to the number of possible branches for each system. Therefore, the number of user devices accommodated in one center device can be increased more than ever before, and a system with high economic efficiency can be realized.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 5 is a block diagram showing a first embodiment of an optical WDM transmission system according to the present invention. The present embodiment is a system 1 using the first signal light of wavelength λ ₁ shown in FIG.
This is an example in which the system 2 using the second signal light of wavelength λ ₂ shown in FIG. 6B is integrated into one system by wavelength multiplexing. The system 1 includes eight user devices 31-
1 to 3-8 are connected to the center device 2 via the 8-branch element 14.
It is a configuration connected to 1. On the other hand, the system 2 has a configuration in which four user devices 32-1 to 32-4 are connected to the center device 22 via the four-branch element 15.

These systems 1 and 2 are integrated so that the corresponding user devices 31-k and 32-k (k =
Consider a case where (1, 2, 3, 4) are combined into a single user device 35-k as shown in FIG. 9 (A). User equipment that includes more than one user equipment, such as user equipment 35-k, is referred to as a multi-service user equipment. The multi-service user equipment includes an optical multiplexer / demultiplexer (WD).
(M element) 51, the received signal light is demultiplexed according to the wavelength, and the transmitted signal lights having different wavelengths are combined and transmitted to the center device.

When the systems 1 and 2 are integrated, the system 1 is modified as shown in FIG. That is,
Instead of the 8-branch element 14, two 4-branch elements 15-1 and 15-2 and a 2-branch element 16 are used, and the user apparatus 31 is combined with the user apparatuses 32-1 to 32-4 as a multi-service user apparatus. -1 to 31-4 are connected to the 4-branch element 15-1, and other user devices 31-5 to 31-5
31-8 is connected to the 4-branch element 15-2.

Next, the user devices 31-1 to 31-4 and 32-1 which are grouped as a multi-service user device.
4-branch elements 15-1 and 1 for accommodating 1-32-4
The WDM element 17 is inserted at the position of the input port A of 5-2. That is, the output port of the WDM element 17 is connected to the input port of the 4-branch element 15-1, the first input port of the WDM element 17 is connected to the input / output port of the center device 22 of the system 2, and the second input port is First of two-branch element 16
Connect to the output port. Thus, the four multi-service user equipments 35-1 to 35-4 have four branch elements 15-
1 and the WDM element 17 to be connected to the center device 22 of the system 2 and the 4-branch element 15-1, W
It is connected to the center device 21 of the system 1 via the DM element 17 and the two-branching element 16. Furthermore, system 1
User devices 31-5 to 31-8 connected only to
It is connected to the center device 21 of the system 1 via the branch element 15-2 and the two-branch element 16.

According to the present embodiment, the loss from the center device 21 to the user devices 31-1 to 31-8 of the system 1 is the same as when the 8-branch element 14 is used. Also,
From the center device 22 of the system 2 to the user devices 32-1
The loss up to 32-4 is the same as when the 4-branch element 15 is used. In other words, the maximum number of branches (loss) can be secured within the allowable loss of each system 1 and 2.

This point will be described using an equation. The center device 21 outputs a signal light having a wavelength of λ ₁ and a power of P ₁ ,
The center device 22 outputs signal light having a wavelength of λ ₂ and power of P ₂ . In addition, the two-branch elements 16 and 4
The attenuation factors due to the branch loss (including the propagation loss) of the branch element 15-1 are A ₁ and A ₂ , respectively, and the user device 31
The minimum received light levels of −k and 32-k are R ₁ respectively.
And R ₂ . Here, the attenuation rate A ₁ is determined by a value obtained by adding the propagation loss from the center device 21 to the two-branch element 16 to the branch loss of the two-branch element 16, and the attenuation rate A ₂
Is determined by the sum of the branch loss of the 4-branch element 15-1 and the propagation loss from the 2-branch element 16 to the user apparatus 35-k. In this case, the signal light with the wavelength λ ₁ output from the center device 21 of the system 1 is transmitted to the user device 31-
k is reached with a power of P ₁ × A ₁ × A ₂ . Further, the signal light having the wavelength λ ₂ output from the center device 22 of the system 2 is transmitted to the user device 32-k by P ₂ × A ₂
Reach with the power. Therefore, the following formula must hold.

P ₁ × A ₁ × A ₂ ≧ R ₁ P ₂ × A ₂ ≧ R ₂ Here, the loss (attenuation rate A ₁ × A ₂ ) due to the two-branch element 16 and the four-branch element 15-1 is the system 8-branch element 1 of 1
4 is the same as the loss due to the 4-branch element 15-1 and the loss due to the 4-branch element 15-1 (attenuation rate A ₂ ) is the same as the loss due to the 4-branch element 15 of the system 2, so the above equation is satisfied. Therefore, the maximum number of branches is secured within the allowable loss of each system.

Second Embodiment FIG. 7 is a block diagram showing a second embodiment of the optical WDM transmission system according to the present invention. In the present embodiment, the system 1 (used wavelength λ ₁ ) shown in FIG. 8A, the system 2 (used wavelength λ ₂ ) shown in FIG. 8B, and the system 3 (used wavelength) used in FIG. 8C. In this example, wavelength λ3) and wavelength λ3) are integrated into one system by wavelength multiplexing. The system 1 has a configuration in which 16 user devices 31-1 to 31-16 are connected to a center device 21 via a 16-branch element 19. The system 2 includes 16 user devices 32-1 to 32-8 and 32 user devices.
-9 to 32-12 and 32-17 to 32-20,
The configuration is such that it is connected to the center devices 22-1 and 22-2 via two eight-branch elements 14-1 and 14-2, respectively. Further, the system 3 includes four user devices 3
3-1 to 33-4 are connected to the center device 23 via the 4-branch element 15.

When these systems 1, 2 and 3 are integrated, the corresponding user devices 31-k, 32-k and 33-k of the three systems 1, 2 and 3 (k = 1-4)
Are integrated into one multi-service user device 37-k as shown in FIG. 9 (B). In addition, the corresponding user devices 31-k and 32-k of the systems 1 and 2 (k = 5
-12) is integrated into the multi-service user equipment 35-k as shown in FIG. 9 (A). Of course, it is also possible to use them as separate user devices without integration.

The integration procedure is as follows. First, the system 1 is modified as shown in FIG. That is, 1
The six user devices 31-1 to 31-16 are divided into four, and each is connected to the 4-branch elements 15-1 to 15-4. Also, two 4-branch elements 15-1 and 15-2
Is connected to the center device 21 via the two-branch elements 16-2 and 16-1, and the other two four-branch elements 15-3 and 15-4 are connected to the two-branch elements 16-3 and 16-1. It connects to the center apparatus 21 via the.

On the other hand, the system 2 is modified as shown in FIG. That is, 12 user devices 32-1 to 32
-12 is divided into four pieces, and each of them is divided into four branch elements 15
−1 to 15-3 and the remaining four user devices 32
-17 to 32-20 are connected to the 4-branch element 15-5.
In addition, two 4-branch elements 15-1 and 15-2 are connected to 2
The other two 4-branch elements 15-3 and 15-5 are connected to the center device 22-1 via the branch element 16-2.
It is connected to the center device 22-2 via the two-branch element 16-4. The system 3 does not change.

Next, as shown in FIG. 7, a two-branch element 16- that accommodates eight multi-service user equipments 37-1 to 35-8 which are serviced by two or more systems.
2 at the position of the input port A (FIG. 10) of the WDM element 17-
1 is inserted, and the center device 22-1 of the system 2 and the first of the two-branch element 16-1 are connected to the input port of the WDM element 17-1.
Connect the output port. Similarly, WDM element 17-2 is located at the input port B of 4-branch element 15-3, which accommodates the remaining four multi-service user equipments 35-9 to 35-12, which are serviced by both systems 1 and 2.
And connect the first output ports of the bifurcating elements 16-3 and 16-4 to the input port of the WDM element 17-2. Also, multi-service user devices 37-1 to 37- that receive services from the three systems 1, 2 and 3
The WDM element 17-3 is inserted at the position of the input port C of the 4-branch element 15-1 to which 4 is connected,
The center device 23 of the system 3 and the first output port of the bifurcating element 16-2 are connected to the input port of the. This forms the system shown in FIG. Note that the user devices 31-13 to 31-16 connected only to the system 1
Is a 4-branch element 15-4, a 2-branch element 16-3 and 1
It is connected to the center device 21 of the system 1 via 6-1. Also, the user device 3 connected only to the system 2
2-17 to 32-20 are 4-branch elements 15-5 and 2
The center device 2 of the system 2 via the branching element 16-4.
2-2 is connected.

According to this embodiment, the loss from the center device 21 to the user devices 31-1 to 31-16 of the system 1 is the same as that when the 16-branch element 19 is used. Further, from the center devices 22-1 and 22-2 of the system 2 to the user devices 32-1 to 32-12 and 32-17 to.
The loss up to 32-20 is the same as when using an 8-branch element. Furthermore, the loss from the center device 23 to the user devices 33-1 to 33-4 of the system 3 is the same as that when the 4-branch element 15 is used. In other words, the maximum number of branches can be secured within the allowable loss of each system.

Third Embodiment FIG. 12 is a block diagram showing a third embodiment of the optical WDM transmission system according to the present invention. This embodiment is shown in FIG.
System 1 (used wavelength λ ₁ ) shown in FIG.
This is an example in which the system 2 (used wavelength λ ₂ ) shown in (B) is integrated into one system by wavelength multiplexing. The system 1 connects four user devices 31-1 to 31-4 to the 4-branch element 15 and connects the 4-branch element 15 with an input port.
The configuration is such that the three user devices 31-5 to 31-7 are connected to the center device 21 via the 4-branch element 16. On the other hand, the system 2 has four user devices 32-1 to 32-
4 is connected to the 4-branch element 15, and the input port of the 4-branch element 15 and the user device 32-5 are connected to the 2-branch element 16-1.
The two user devices 32-6 and 32-7 are connected to the center device 22-1 via the two-branch element 1
The configuration is such that it is connected to the center device 22-2 via 6-2.

In the present embodiment, the corresponding user devices 31-k and 32-k (k = 1-7) are combined into a multi-service user device 35-k, and these systems 1 and 2 are integrated. That is, the user device 31-1 of the system 1
~ 31-5 and user devices 32-1 to 32 of system 2
5, and multi-service user devices 35-1 to 35-35 that receive the services of both the center device 21 of the system 1 and the center device 22-1 of the system 2.
5, the user devices 31-6 to 31-7 of the system 1 and the user devices 32-6 to 32-7 of the system 2 are combined, and the center device 21 of the system 1 and the center device 22-2 of the system 2 are combined. It is assumed that the multi-service user devices 35-6 and 35-7 receive both services.

In this case, the 4-branch element 16 of the system 1
As shown in FIG. 13 (C),
, 16-2 and 16-3. Next, as shown in FIG. 12, the multi-service user equipment 35-1
The WDM element 17-1 is inserted into the position of the input port A of the two-branching element 16-1 which accommodates ~ 35-5. That is,
The center device 22-1 of the system 2 is connected to the first input port of the WDM element 17-1, and the first output port of the two-branch element 16-3 is connected to the second input port. Also WDM
The output port of the element 17-1 is connected to the input port of the bifurcating element 16-1. Furthermore, the two-branch element 16 to which the multi-service user equipments 35-6 and 35-7 are connected
The WDM element 17-2 is inserted into the position of the input port B of -2. That is, the input / output port of the center device 22-2 of the system 2 and the second output port of the bifurcating element 16-3 are connected to the input port of the WDM element 17-2, respectively, and W
The output port of the DM element 17-2 is connected to the input port of the bifurcating element 16-2. Thus, the system shown in FIG. 12 is formed.

According to this embodiment, the loss from the center device 21 of the system 1 to the user devices 31-1 to 31-4 is the same as that when the 16-branch element is used. In addition, from the center device 21 of the system 1 to the user devices 31-5 to 3-3.
The loss up to 1-7 is the same as when the 4-branch element 16 is used. Further, the loss from the center device 22-1 to the user devices 32-1 to 32-4 of the system 2 is the same as that when using the 8-branch element, and the center device 22-2 to the user devices 32-5 to 32. The loss up to −7 is the same as when the two-branch element is used. In other words, the maximum number of branches can be secured within the allowable loss of each system.

14 (A) and 14 (B) are graphs showing the relationship between the subscriber distribution and the number of possible branches in the systems 1 and 2. The horizontal axis of this graph is
The loss between the center device and the user device is shown, and the vertical axis shows the number of users. In FIG. 14A, the number of branchable user devices 31-1 to 31-4 is 16, and the number of branchable user devices 31-5 to 31-7 is 4. In addition, in FIG. 14B, the number of branchable user devices 32-1 to 32-4 is eight, and the user devices 32-5 to 32-7.
The number of branches of is 2. The system of FIG. 12 satisfies these branchable numbers.

FIG. 15 is a diagram showing the transmission loss from the two systems 1 and 2 to the user equipment and the distribution of the number of user equipments. The range divided by the vertical solid line indicates the number of possible branches of the system 1, and the range divided by the vertical broken line indicates the number of possible branches of the system 2. As shown in the figure,
Even with the same user device, the number of possible branches may vary depending on the system. An example will be described in which such systems 1 and 2 are integrated into one system using wavelength multiplexing.

The number of possible branches of both systems is in the range [1],
It is the same in [3] and [5]. In this case, the optimum system configuration can be realized by disposing the WDM element between the center device and the branch element as in each of the above embodiments.

On the other hand, in the ranges [2], [4] and [6], the number of possible branches of the system 1 is twice the number of possible branches of the system 2. In this case, as in Example 1 shown in FIGS. 5 to 6C, one branching element to which the user device of the system 1 is connected is disassembled into two branching elements, and a new branching element after disassembly is used. It is connected to the center device via a two-branch element. Then, by arranging the WDM element between this two-branch element and one of the new branch elements, the optimum system configuration can be realized.

When the allowable loss is greatly different between the system 1 and the system 2, there may be a case where the same number of possible branches does not exist. Similarly in this case, the second embodiment shown in FIG.
As described above, it is possible to perform optimization by sequentially arranging branch elements of a power of 2 in multiple stages and arranging the WDM element at a point where the number of branches to the user apparatus is the same.

16 (A) to 16 (D) are diagrams for explaining the effect of the present invention. 16A and FIG.
(B) shows the relationship between the transmission path loss and the number of branches that can be branched. As for the system 1, N ₁ user equipments exist in the area of 16 possible diversions, and N ₂ user equipments exist in the area of 8 divisible possible areas. Further, regarding the system 2, N ₁ user apparatuses exist in the area of the number of dividable 8 and N ₂ user apparatuses exist in the area of the number of 4 divisible.

When the two systems 1 and 2 are integrated into one system by wavelength division multiplexing, in the conventional method, four-branch elements are used in accordance with the system 2 having a small number of branches. As a result, as shown in FIG. 16C, the number of center devices is (N ₁ + N ₂ ) /
It becomes 4.

On the other hand, in the present invention, the largest possible branch number is used. That is, as shown in FIG. 16 (D), the center device number, system 1 in N _1/16 + N ₂ /
Next 8, the _{N 1/8 + N 2/} 4 in the system 2. As a result, the number of accommodated user devices per center device increases, the required number of center devices decreases, and an economical system can be configured. For example, when N ₁ = 80 and N ₂ = 32, the number of center devices in the conventional system is 1
Both are 28. On the other hand, in the present invention, system 1 has 9 and system 2 has 18. That is, according to the present invention, the center device is about 1/3 in the system 1 and about 2/3 in the system 2.

Fourth Embodiment FIG. 17 is a block diagram showing a fourth embodiment of the optical WDM transmission system according to the present invention. This is the first shown in FIG.
It is a system corresponding to the embodiment. This embodiment is different from the first embodiment in the following points.

(1) The WDM element 17 and the 4-branch element 15-1 of the first embodiment are replaced with a 2 × 4 optical coupler 18.

(2) The wavelength filters 41 and 42 are arranged at the input / output ports of the center devices 21 and 22.

As the 2 × 4 optical coupler 18, it is possible to use a fiber coupler or an optical waveguide having a wide operating wavelength range. The wavelength filter 41 passes only the wavelength λ ₁ , and the wavelength filter 42 passes only the wavelength λ ₂ . These wavelength filters are provided because the 2 × 4 coupler 18 does not have a demultiplexing function, and may be provided in the center device.

With such a structure, the same effect as that of the first embodiment can be obtained.

Embodiment 5 FIG. 18 is a block diagram showing a fifth embodiment of the optical WDM transmission system according to the present invention. This is the second shown in FIG.
It is a system corresponding to the embodiment. The present embodiment is different from the second embodiment in the following points.

(1) The WDM element 17-1 and the two-branching element 16-2 of the second embodiment are replaced with a 2 × 2 optical coupler 18-1.

(2) The WDM element 17-2 and the 4-branch element 15-3 are replaced with a 2 × 4 optical coupler 18-2.

(3) The WDM element 17-3 and the 4-branch element 15-1 are replaced with a 2 × 4 optical coupler 18-3.

(4) Center devices 21, 22-1, 22-
Wavelength filters 41, 4 at the input and output ports of 2 and 23
The point where 2, 42 and 43 are placed. Wavelength filter 43
Is a filter that passes only the signal light of wavelength λ3.

With such a structure, the same effect as that of the second embodiment can be obtained.

Example 6 FIGS. 19A to 19C show an optical WDM according to the present invention.
It is a block diagram which shows the structure of the principal part of 6th Example of a transmission system.

FIG. 19A shows a new center device 21 by combining the center device 21 of FIG. 5 and the bifurcating element 16.

FIG. 19B shows the center device 21 of FIG.
The two-branch element 16-1 and the WDM element 17-1 are combined to form a new center device 21.

FIG. 19C shows the center device 22- of FIG.
1, a WDM element 17-1 and a bifurcating element 16-2 are combined to form a new center device 22-1.

The system according to the present invention can be easily constructed by using such a center device.

Seventh Embodiment FIG. 20 is a block diagram showing the configuration of the seventh embodiment of the optical WDM transmission system according to the present invention.

In this figure, the signal light of the wavelength λ ₁ output from the center device 21-1 of the system 1 passes through the WDM element 17-1 and the 4-branching element 15-5 and two multi-service user equipments 35. -1 to 35-2. Similarly, another center device 21 of the system 1
-2, the signal light of wavelength λ ₁ is output from the WDM element 1
It is supplied to two multi-service user equipments 35-3 to 35-4 through 7-2 and 4-branch element 15-6. The signal light of wavelength λ ₂ output from the center device 22 of the system 2 passes through the 2-branch element 16-1, the WDM elements 17-1 and 17-2, and the 4-branch elements 15-5 and 15-6. Are supplied to four multi-service user equipments 35-1 to 35-4. As described above, each multi-service user equipment 35-k (k = 1-4) includes two types of user equipment 31-k and 32-k for transmitting and receiving the signal lights of wavelengths λ ₁ and λ ₂ . .

The feature of this embodiment is that the user equipment 35-1
35-4 and the WDM elements 17-1 and 17-2 are duplicated, and one of the transmission paths is selected by the changeover switch 61 provided in the user apparatus. With such a configuration, the reliability of the system can be improved.

Eighth Embodiment FIG. 21 is a block diagram showing the configuration of an eighth embodiment of the optical WDM transmission system according to the present invention.

This embodiment is a system similar to that shown in FIG. 20 in which the center device and the WDM element are duplicated. The center devices 21-1, 21-2, and 22 have changeover switches 63 to 65, respectively, and select one of the dual transmission paths. This can increase the reliability of the system.

[0077]

As described above, according to the present invention,
When a plurality of point-multipoint optical transmission systems are integrated into one optical transmission system that shares a transmission line including a star coupler by using wavelength division multiplexing, each optical transmission system has its allowable loss (possible number of branches). Even if the
The original number of possible branches can be utilized without being limited by the allowable loss of other systems. That is, it is possible to accommodate user devices corresponding to the number of possible branches for each system. Therefore, the number of user devices accommodated in one center device can be increased more than ever before, and a system with high economic efficiency can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a conventional PDS optical transmission system.

FIG. 2 is a block diagram showing a configuration example of a conventional PDS optical transmission system using a wavelength multiplexing system.

FIG. 3 is a block diagram showing a conventional configuration method of a PDS optical transmission system using a wavelength multiplexing system.

4A to 4C are PDs using a wavelength multiplexing method.
It is a block diagram which shows the conventional structural method of the S optical transmission system.

FIG. 5 is a block diagram showing a first embodiment of an optical WDM transmission system according to the present invention.

6 (A) to (C) are block diagrams showing a configuration method of the first embodiment, (A) and (B) respectively showing two systems to be integrated, and (C). Indicates a state in which the system 1 is disassembled.

FIG. 7 is a block diagram showing a second embodiment of the optical WDM transmission system according to the present invention.

8A to 8C are block diagrams showing three systems to be integrated in the second embodiment.

9A and 9B are block diagrams respectively showing a configuration of a multi-service user apparatus.

FIG. 10 is a block diagram showing a state in which the systems 1 and 2 of the second embodiment are disassembled.

FIG. 11 is a block diagram showing a state where the systems 1 and 2 of the second embodiment are disassembled.

FIG. 12 is a block diagram showing a third embodiment of the optical WDM transmission system according to the present invention.

13 (A) to (C) are block diagrams showing a configuration method of a third embodiment, (A) and (B) respectively showing two systems to be integrated, and (C). Indicates a state in which the system 1 is disassembled.

14A and 14B are graphs showing the relationship between the subscriber distribution and the number of possible branches of the systems 1 and 2 integrated in the third embodiment.

FIG. 15 of system 1 and system 2 to be integrated,
It is a graph for explaining a system configuration method when the range of the number of possible branches is different.

16A to 16D are graphs showing effects of the present invention, FIGS. 16A and 16B are graphs showing subscriber distributions of the system 1 and the system 2, and FIG. A graph (D) showing the number of center devices required when the systems 1 and 2 are integrated by the conventional method shows the number of center devices required when the systems 1 and 2 are integrated by the method according to the present invention. It is a graph shown.

FIG. 17 is a block diagram showing a fourth embodiment of the optical WDM transmission system according to the present invention.

FIG. 18 is a block diagram showing a fifth embodiment of the optical WDM transmission system according to the present invention.

19A to 19C are block diagrams showing a configuration of a main part of a sixth embodiment of the optical WDM transmission system according to the present invention.

FIG. 20 is a block diagram showing a seventh embodiment of the optical WDM transmission system according to the present invention.

FIG. 21 is a block diagram showing an eighth embodiment of the optical WDM transmission system according to the present invention.

[Explanation of symbols]

12 n branch element 13 optical fiber transmission line 15, 15-1 to 15-5 4 branch element 16, 16-1 to 16-4 2 branch element 17, 17-1 to 17-3 WDM element 18, 18-1 18-3 2 × 4 optical coupler 21,21-1,21-2 center device 22,22-1,22-2 center device 23 center device 30,30-1 to 30-n user device 31,31-1 to 31-8 User Equipment 32, 32-1 to 32-9, 32-12 to 32-20
User equipment 33,33-1 to 33-4 User equipment 35-1 to 35-12 Multi-service user equipment 37-1 to 37-4 Multi-service user equipment 41 to 43 Wavelength filter 51,52 WDM element 63 to 65 Changeover switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Watanabe 3-19-3 Nishishinjuku, Shinjuku-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation

Claims (11)

[Claims] 1. A second outputting a first center device that wavelength to output a first signal light lambda ₁ at the output power P _1, the second signal light wavelength of lambda ₂ at output power P ₂ Center device, a first optical branching unit that is connected to the output port of the first center device, and branches the first signal light at an attenuation rate A ₁ , the second center device, and the first optical branching unit. Of the second signal light and the first signal light
Of the optical multiplexing means for multiplexing the signal light, it is connected to the output port of said optical multiplexing means, which have been multiplexed second branching said first signal light and second signal light attenuation factor A ₂ An optical branching unit, a first user device connected to an output port of the second optical branching unit, for receiving the first signal light, and having a reception threshold value of R ₁ , and the second optical branching unit A second user equipment connected to the output port of the means for receiving the second signal light and having a reception threshold value of R ₂ , P ₁ × A ₁ × A ₂ ≧ R ₁ , and P An optical WDM transmission system characterized by satisfying a condition of ₂ × A ₂ ≧ R ₂ . 2. A _third optical branching means for branching the second signal light at an attenuation rate A ₃ is provided between the second center device and the optical multiplexing means, and P ₁ × A ₁ × The optical WDM transmission system according to claim 1, wherein the conditions of A ₂ ≧ R ₁ and P ₂ × A ₃ × A ₂ ≧ R ₂ are satisfied. 3. The first optical branching means and the second optical branching means branch the input signal light into 2 ^N (N is a positive integer). The optical WDM transmission system described in 1. 4. The optical WDM transmission according to claim 2, wherein at least one of the first optical branching means and the third optical branching means is composed of a plurality of optical branching elements configured in multiple stages. system. 5. The optical multiplexing means and the second optical branching means have an input port connected to an output port of the second center device and an output port of the first optical branching means, and an output port An optical branching means of a multi-input port connected to the first user equipment and the second user equipment;
The first center device is arranged at an output port of the first center device, and
A first wavelength filter that passes the signal light of
5. The optical WD according to claim 1, further comprising a second wavelength filter arranged at the output port of the center device for transmitting the second signal light.
M transmission system. 6. The method according to claim 1, wherein at least a part of the first optical branching means and the optical multiplexing means are housed in the first center device. Optical WDM transmission system. 7. The center device of at least one of the first center device and the second center device to the second center device.
7. A dual path to the optical branching means, and a selecting means for connecting an output port of the center device connected to the dual path to one of the dual paths. The optical WDM transmission system according to any one of 1. 8. A dual path from one or more of the first and second user equipments to the second optical branching means, and an input port of the user equipment connected to the dual path. 7. The optical WDM transmission system according to claim 1, further comprising a selection unit connected to one of the two. 9. The optical combining means converts the signal light supplied from the first and second user equipments through the second optical branching means into a signal light having a wavelength λ _{1 and} a signal light having a wavelength λ ₂ . An optical multiplexing / demultiplexing means for demultiplexing into light, a transmission path connecting the first center apparatus and the first user apparatus, and a transmission connecting the second center apparatus and the second user apparatus The optical WDM transmission system according to claim 5, wherein at least one of the paths is a bidirectional transmission path. 10. A point-multipoint system in which a first signal light having a wavelength of λ ₁ output from a first center device is split and supplied to a plurality of first user devices at a first allowable loss or less. Form of the first optical transmission system, and a second signal light having a wavelength of λ ₂ output from the second center device is branched and supplied to a plurality of second user devices with a second allowable loss or less. A point-multipoint type second optical transmission system for integrating the point-multipoint type optical transmission system into a point-multipoint type optical transmission system, the method comprising the steps of receiving both the first signal light and the second signal light. A process of selecting a service user equipment from the first user equipment and the second user equipment; and a third signal light generated by optically multiplexing the first signal light and the second signal light. Branch and A process of establishing a path to be supplied to a service user apparatus, and an optical loss from the first center apparatus to the first user apparatus is set to be equal to or less than the first allowable loss and the second center apparatus to the second And a step of setting the number of branches of at least one of the first signal light and the second signal light to the number of branches that makes the optical loss up to the second user equipment less than or equal to the second allowable loss. Optical WD characterized by having
A method of combining M (wavelength division multiplexing) transmission systems. 11. The method according to claim 10, further comprising the step of establishing a path for supplying the signal light output from the first user equipment to the first center equipment by time division multiplexing. A method for synthesizing an optical WDM transmission system.