JPH10276129A - Light branching/inserting circuit and light transmitting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase communication capacity without exchanging a light branching/ inserting circuit by transmitting signal light transmitting a low pass filter from a transmission station when signal light outputted from the branching side of a light branching/inserting circuit is increased and transmitting signal light transmitting a high pass filter from a transmission station when signal light transmitting the light branching/inserting circuit it increased. SOLUTION: The four signal light beams whose wavelengths (b), (d), (e) and (f) (b<d<e<f) are multiplexed and transmitted from a station building A6. The four signal light beams are branched into two by a branching unit 4. One is inputted to the low pass filter and only the wavelength (b) transmits the low pass filter 3 and is sent to a station building C8a. Other signal light branched by the branching unit 4 is inputted to the high pass filter 2 and the wavelengths (d), (e) and (f) are transmitted. The light of the wavelength (b) is transmitted from the station building C8a and a multiplexes 5 multiplexes the signal light beams of the wavelengths (d), (e) and (f), which are transmitted from the high pass filter 2, and the light beam of the wavelength (b), which is transmitted from the station A8a, are multiplexed and transmitted a station building B7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical add / drop circuit which is used in a long-distance optical transmission system of a wavelength division multiplex system and has a function of dropping and inserting signal light.

[0002]

2. Description of the Related Art Conventionally, a long-distance optical transmission system using an optical add / drop circuit 1a has a basic configuration as shown in FIG. That is, the signal light of a plurality of wavelengths that has been wavelength-multiplexed and transmitted from the station 6 is input to the optical add / drop circuit 1a. Of these signal lights, the signal light of one or several wavelengths is transmitted to the station 8a by the splitter 4 as a branch output.
The station 8a sends out a signal having the same wavelength as the input signal to the optical add / drop circuit 1a. In the optical add / drop circuit 1a, the multiplexer 5 multiplexes the signal light transmitted through the demultiplexer 4 and the signal light input from the station 8a, and sends the multiplexed signal to the station 7.

[0003]

Generally, in a long-distance optical transmission system, it may be necessary to increase the communication capacity after the system is installed. The system shown in FIG. 9 is a case where the number of signal lights in a branch path branched from the optical add / drop circuit 1a and the number of signal lights in a main transmission path passing through the optical drop / add circuit 1a are increased. In such a case, the optical add / drop circuit 1a must be once removed from the system, and components such as fiber gratings and optical bandpass filters must be replaced with components having different characteristics. However, when the optical add / drop circuit 1a is applied to a submarine repeater system, replacing components or the optical add / drop circuit 1a requires a large amount of cost.

An object of the present invention is to provide a configuration of an optical add / drop circuit that can increase the communication capacity after installation of the system in an optical transmission system to which the optical add / drop circuit is applied, without replacing the optical drop / add circuit. And an optical transmission method using the circuit.

[0005]

According to the present invention, there is provided an optical add / drop circuit for splitting an input optical signal into first and second output lights, and a first output light. And a low-pass filter to which the second output light is input, and a multiplexer for multiplexing the signal light output from the high-pass filter with another input light. I have. When optical transmission is performed using this optical add / drop circuit, when increasing the signal light output from the branch side of the optical add / drop circuit, the signal light transmitted through the low-pass filter is transmitted from the transmitting station, and the optical drop is performed. When increasing the signal light transmitted through the insertion circuit, the signal light transmitted through the high-pass filter is transmitted from the transmitting station.

Next, in another configuration of the optical add / drop circuit of the present invention, an optical splitter for splitting an input optical signal into first and second output lights, and the first output light are input. A low-pass filter, a high-pass filter to which the second output light is input, and a multiplexer for multiplexing the signal light output from the low-pass filter with another input light. When optical transmission is performed using the optical add / drop circuit, when increasing the signal light output from the branch side of the optical add / drop circuit, the signal light transmitted through the high-pass filter is transmitted from the transmitting station, When increasing the signal light to the transmission side of the insertion circuit, the signal light transmitted through the low-pass filter is transmitted from the transmitting station.

The signal light input to the optical add / drop circuit is wavelength multiplexed light, and the signal light of each wavelength passes through only one of the high-pass filter and the low-pass filter of the optical add / drop circuit.

By using the above configuration and method, according to the present invention, after installing the optical transmission system, the transmission capacity of the main transmission line or the branch line can be easily increased without replacing the optical add / drop circuit and its components. be able to.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a basic configuration of an optical add / drop circuit 1a according to the present invention. First, signal light of a plurality of wavelengths is wavelength-multiplexed and transmitted from the station 6. The wavelength-multiplexed signal light is input to the demultiplexer 4 and split into two. One of the split signal lights is input to the low-pass filter 3, and
Only a predetermined number of optical signals on the short wavelength side of the signal light are transmitted. The transmitted light is sent from the branch of the optical add / drop circuit 1a to the office 8a. The other signal light demultiplexed by the demultiplexer 4 is input to the high-pass filter 2, and only a predetermined number of optical signals on the long wavelength side of the signal light are transmitted. Light having the same number and wavelength as the signal light input from the branch path is transmitted from the office 8a to the optical add / drop circuit 1a. The signal light transmitted through the high-pass filter 2 and the insertion light transmitted from the station 8a are multiplexed by the multiplexer 5 and sent to the station 7 as output light of the optical add / drop circuit 1a. 1 and the following embodiments, the low-pass filter is a filter that transmits signal light having a wavelength shorter than the predetermined wavelength c, and the high-pass filter is a filter that has a longer wavelength than the predetermined wavelength c. It is assumed that the filter transmits signal light.

FIG. 2 shows a basic operation of an optical transmission system using the optical add / drop circuit 1a of FIG. For example, office building 6
, Four signal lights having wavelengths b, d, e, and f (where b <d <e <f) are wavelength-multiplexed and transmitted. These four signal lights are split into two by the splitter 4. One of the branched lights is input to the low-pass filter 3, and only the wavelength b is transmitted through the filter 3 and sent to the office 8a. The other signal light branched by the demultiplexer 4 is input to the high-pass filter 2, and the wavelengths d, e, and f are transmitted. Wavelength b from the office 8a
Is emitted. The multiplexer 5 multiplexes the signal lights of the wavelengths d, e, and f transmitted from the high-pass filter 2 with the light of the wavelength b transmitted from the station 8a. As a result, the wavelengths b, d, e, and f transmitted from the station 6 from the optical add / drop circuit 1a.
Are transmitted to the station 7 with the same four wavelengths.

FIGS. 3A and 3B are schematic diagrams showing characteristics of a high-pass filter and a low-pass filter used in the present invention. The high-pass filter transmits signal light on the longer wavelength side than the specific wavelength c, and the low-pass filter transmits signal light on the shorter wavelength side than the same wavelength c. For example, there is a difference of about 20 to 30 dB between the transmission area and the stop area.

FIG. 4 shows an example in which the communication capacity (ie, the number of signal lights) from the optical add / drop circuit 1a to the station 8a is increased in the configuration shown in FIG. The station 6 multiplexes the wavelength a desired to be sent to the station 8a with the other wavelengths b, d, e, and f, and sends it to the optical add / drop multiplexer 1a. The wavelengths of these signal lights are longer in the order of a <b <c <d <f. Since the signal light having the wavelength a is shorter in wavelength than the signal light having the wavelength b, the signal light passes through the low-pass filter 3 and is sent to the station 8a. The station 8a sends out the signal lights of the wavelengths a and b to the optical add / drop multiplexer 1a. The signal lights of the wavelengths a and b are supplied to the optical add / drop circuit 1.
a, the wavelengths d, e, transmitted through the high-pass filter 2;
The light is combined with the light of f and transmitted to the station 7.

FIG. 5 shows a configuration of the station 6 in the configuration shown in FIG.
An example is shown in which the capacity of the main transmission path from the station to the station 7 is increased. In the station 6, the wavelength g to be transmitted to the station 7 via the main transmission path is added to the other wavelengths b, d, e, and f, and the wavelength is multiplexed and transmitted to the optical add / drop multiplexer 1a. The wavelengths of these signal lights are longer in the order of b <d <e <f <g. Wavelength g
Is longer than the signal light of wavelength f, so that the wavelength d,
The light passes through the high-pass filter 2 together with the signal lights of the wavelengths e and f. The signal light having the wavelengths d, e, f, and g is transmitted to the station building 8a.
The signal is multiplexed by the multiplexer 5 together with the signal light of the wavelength b transmitted from the optical network and is transmitted to the station 7.

FIG. 6 shows a configuration in which two optical add / drop circuits of the present invention are arranged in a series on a main transmission line between a station 6 and a station 7. An optical add / drop circuit 1a between the office 6 and the office 7,
1b, and offices 8a and 8b are connected to the optical add / drop circuits 1a and 1b, respectively.

FIG. 7 shows a case where the signal light to the stations 8a and 8b is further increased by one wavelength in the configuration of FIG. At the station 6, a signal light having a shorter wavelength a than the signal light having the shortest wavelength b is added and transmitted.
The signal light having the wavelength a and the signal light having the wavelength b are transmitted through the low-pass filter and sent to the stations 8a and 8b. From the offices 8a and 8b, signal lights of wavelengths a and b are transmitted to the optical add / drop circuit. Therefore, the signal light of the wavelengths a, b, d, e, and f transmitted from the station 6 is sent to the station 7. In FIG. 7, two signal lights of the same wavelengths a and b are transmitted to the stations 8a and 8b, respectively. In this case, it is conceivable that the station 8a uses only the signal light of the wavelength a and the station 8b uses the signal light of the wavelength b. First, the signal light is split into as many as the number of stations that send the split signal light,
Further, a method is possible in which a branch signal light is added, and the added signal light is used by a station that wants to increase the communication capacity. The characteristics of the low-pass filter 3 arranged in the optical add / drop circuit 1a closest to the station 6 which is the transmitting station are changed in order, and one signal light is split for each station sequentially from the shortest wavelength. Many configurations are possible. In such a case, it is desirable to make the wavelength interval of the signal light larger than 0.8 nm. Further, among the stations that receive the branched signal light, those that are distant from the transmitting station may be provided with band-pass filters that transmit signal light in a predetermined wavelength range instead of low-pass filters.

FIG. 8 shows another configuration of the optical add / drop circuit of the present invention. In this configuration, the positions at which the low-pass transmission filter 3 and the high-pass transmission filter 2 are installed are reversed with respect to the configuration of FIG. Accordingly, when increasing the communication capacity of the branch path to the station 8a, the station 6 wavelength-multiplexes and transmits an optical signal having a longer wavelength than the wavelength of the signal light already used. On the other hand, when increasing the communication capacity of the main transmission path from the station 6 to the station 7, an optical signal on the short wavelength side is added.

In the optical add / drop circuit of the present invention as described above, depending on the configuration of the optical add / drop circuit used, only the signal light that passes through only the low-pass filter or the high-pass filter is added. Even after installing the optical transmission system,
There is an excellent effect that the communication capacity (the number of signal lights) of the main transmission path or the branch path can be increased without replacing the optical add / drop circuit.

The wavelength of the optical signal used in the optical add / drop circuit of the present invention is set to be approximately 1.5 times the intermediate wavelength among a plurality of wavelengths.
It is possible to use a plurality of wavelengths having a wavelength difference of 585 μm and a wavelength difference of 0.8n around this wavelength. In the optical transmission system in which the optical add / drop circuit is arranged, when an erbium-doped optical direct amplifier is used, the wavelength of the optical signal to be used and the wavelength of the optical signal to be added later are within a range that can be amplified by the amplifier. It is necessary to be. Each signal light transmitted from the station 6 always passes through either the low-pass filter or the high-pass filter, and does not pass through both filters. Specifically, as in the above-described embodiment, the transmission upper-limit wavelength of the low-pass filter and the transmission lower-limit wavelength of the high-pass filter are set to the wavelength c.
(For example, 1.5585 μ), each signal light transmitted from the station 6 can be constituted by signal light having a shorter wavelength and a longer wavelength except for the wavelength c.

It is desirable to use a 3 dB coupler for the demultiplexer and the multiplexer. Further, the low-pass filter and the high-pass filter can be configured by a multilayer structure.

[0020]

As described above, when the optical add / drop circuit of the present invention is applied to an optical transmission system, it is not necessary to replace the optical add / drop circuit when increasing the capacity of the transmission line after the installation of the system. Thus, it is possible to increase the communication capacity of an optical transmission line without incurring a large cost in a submarine repeater system or the like.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an optical transmission system using an optical add / drop multiplexer of the present invention.

FIG. 2 is a block diagram showing an optical transmission method using the optical add / drop multiplexer of FIG.

FIG. 3 is a diagram showing characteristics of a high-pass filter and a low-pass filter used in the optical add / drop multiplexer of the present invention.

FIG. 4 is a block diagram showing a case where the number of signal lights in a branch path is increased.

FIG. 5 is a block diagram showing a case where the number of signal lights in a main transmission path is increased.

FIG. 6 is a block diagram showing a configuration example in which two optical add / drop devices are arranged.

FIG. 7 is a block diagram showing an optical transmission method in the configuration of FIG. 6;

FIG. 8 is a block diagram showing another configuration example of the optical add / drop multiplexer of the present invention.

FIG. 9 is a block diagram showing a configuration example of an optical transmission system using a conventional optical add / drop device.

[Explanation of symbols]

 1a, 1b, 1c Optical add / drop circuit 2 High-pass transmission filter 3 Low-pass transmission filter 4 Demultiplexer 5 Combiner 6, 7, 8a, 8a

Claims (7)

[Claims] An optical splitter for splitting an input optical signal into first and second output lights; a high-pass filter inputting the first output light; and a second output light. An optical add / drop circuit comprising: a low-pass filter to be input; and a multiplexer that multiplexes output light from the high-pass filter with another input light. 2. An optical splitter for splitting an input optical signal into first and second output lights, a low-pass filter to which the first output light is input, and a second output light. An optical add / drop circuit comprising: a high-pass filter for input; and a multiplexer for multiplexing output light from the low-pass filter with another input light. 3. The optical add / drop circuit according to claim 1, wherein the signal light input to the optical demultiplexer is a wavelength multiplexed light in which a plurality of lights having different wavelengths are multiplexed. 4. The optical add / drop circuit according to claim 3, wherein each signal light passes through only one of the high-pass filter and the low-pass filter. 5. The optical add / drop circuit according to claim 1, wherein each of the demultiplexer and the multiplexer has a 3 dB coupler. 6. An optical transmission method using an optical add / drop circuit according to claim 1, wherein when increasing the amount of signal light output from the branch side of the optical add / drop circuit, the signal light transmitted through the low-pass filter. Is transmitted from the transmitting station, and when increasing the amount of signal light transmitted through the optical add / drop circuit, the signal light transmitted through the high-pass filter is transmitted from the transmitting station. 7. An optical transmission method using an optical add / drop circuit according to claim 2, wherein when increasing the amount of signal light output from the branch side of the optical add / drop circuit, the signal light transmitted through the high-pass filter. Is transmitted from the transmitting station, and when increasing the amount of signal light transmitted through the optical add / drop circuit, the signal light transmitted through the low-pass filter is transmitted from the transmitting station.