JPH0683181B2 - Optical communication node device - Google Patents

Description

The present invention relates to an optical communication node device in a system for collecting transmission signals from nodes installed at a plurality of locations by using a single-core optical fiber.

[Conventional technology]

Conventionally, an optical communication node device of this type receives an optical signal transmitted from a preceding node through a one-core optical fiber 11 and demodulates and amplifies it into an electric signal as shown in FIG. Frequency different from circuit 6 and carrier of other node
A synthesizing circuit 7 for synthesizing a signal having a carrier wave of f _n and modulated by the transmission signal of its own node with the output signal of the optical receiving circuit 6.
And an optical transmission circuit 8 for transmitting the combined signal as a transmission optical signal to the next node through the one-core optical fiber.

In this device, the signal of its own node is sequentially frequency-division-multiplexed with the signal of the preceding node, and as a result, the signals of a plurality of nodes are collected.

[Problems to be Solved by the Invention]

In the conventional device described above, since the signal of the own node is combined with the signal of another node in the form of an electric signal, it is necessary to demodulate the received optical signal once into an electric signal. In demodulating the received optical signal, the transmission characteristics have to be changed due to noise and distortion of the optical receiving circuit 6, and there is a problem that a high-performance optical receiving circuit is required.

In addition, the input signal to the optical transmission circuit 8 has a problem that the number of multiplexed carrier waves increases toward the subsequent node, which makes it difficult to satisfactorily modulate an optical signal.

It is an object of the present invention to provide an optical communication node device that improves the deterioration of the transmission characteristics of the system.

[Means for Solving the Problems]

The optical communication node device of the present invention is a frequency division multiplexing system in which a plurality of nodes, each having a carrier wave of a different frequency and having the same degree of modulation of an optical signal by each carrier wave, are connected by a one-core optical fiber. An optical communication system that collects the transmission signal of each node by the method, an optical branching device that branches a part of the received optical signal from the preceding node, a level detection circuit that detects the level of the branched optical signal, An optical transmission circuit that modulates and outputs a carrier wave of its own node with an optical signal according to a preset modulation degree, and an output level control circuit that controls an optical signal output level from this optical transmission circuit according to the detected level. An optical combiner that combines the optical signal from the optical transmission circuit with the optical signal from the preceding node, and controls the optical signal level in the output level control circuit. Equal carrier level from De is the carrier level from the previous position node, or when the carrier level from the previous position nodes that do not exist are configured such that the prescribed level.

[Action]

With the configuration described above, the signal of the own node can be inserted into the transmission signal without demodulating the received optical signal into an electric signal.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of an optical communication node device according to the present invention. In the figure, reference numeral 1 is an optical branching device, which is connected to the preceding node by an optical fiber 11 of one core. A level detection circuit 2, an output level control circuit 3, an optical transmission circuit 4, and an optical combiner 5 are arranged in this branch path, and the branched signal is transmitted again through the 1-core optical fiber 11 in the optical combiner 5. Synthesized into a signal.

That is, a part of the received optical signal from the preceding node is branched by the optical branching device 1, and the level detection circuit 2 detects a detection signal corresponding to the level of the received optical signal. Then, the output level control circuit 3 controls the optical transmission circuit 4 based on this detection signal. The optical transmission circuit 4 modulates a signal of its own node with a carrier having a frequency f _n different from that of other nodes,
The output level of this optical signal is controlled by the output level control circuit 3. Here, since the degree of modulation by the carrier wave of the transmission optical signal in each node is set to be equal to each other, by controlling the level of the transmission optical signal combined in the optical combiner 5, the node of the own node after combination is controlled. The carrier level can be controlled to be substantially equal to the carrier level of the preceding node transmitted through the one-core optical fiber 11.

As a result, the transmission optical signal is a signal that is modulated by the frequency division multiplexed signal in which the carrier wave of each node up to the own node is inserted together with the carrier wave of the own node, and each carrier wave level is uniform.

Here, the level detection circuit 2 obtains the detection signal corresponding to the optical signal level as described above. For example, in the node at the forefront, only the level reference pilot signal previously inserted in the received optical signal is received. A detection signal can be obtained by the detection and can be easily realized. Further, since the optical transmission circuit 4 only needs to modulate the optical signal with one carrier wave of the frequency f _n , it can be realized more easily than the optical transmission circuit of the conventional device, and good modulation characteristics can be obtained. Becomes

Further, by appropriately setting the branching ratio of the optical branching device 1 and the combining ratio of the optical combiner 5, it is possible to reduce the loss between the received optical signal and the transmitted optical signal as much as possible.

When the output of the level detection circuit 2 is equal to or lower than a preset value, for example, when there is no carrier wave from the preceding node, the output level of the optical transmission circuit 4 is controlled to a preset specified level. The above-mentioned configuration should be naturally designed when constructing the optical communication system according to the present invention.

〔The invention's effect〕

As described above, the present invention is configured to detect the level of the received optical signal from the preceding node, control the optical signal output level from the optical transmission circuit based on this level, and combine it with the transmitted optical signal. As a result, the signal of its own node can be inserted into the transmission signal without demodulating the received optical signal into an electrical signal, and it has better transmission characteristics than conventional devices without requiring a high-performance optical receiving circuit. There is an effect that can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an optical communication node device according to the present invention, and FIG. 2 is a block diagram of a conventional device. 1 ... Optical branching device, 2 ... Level detection circuit, 3 ... Output level control circuit, 4 ... Optical transmission circuit, 5 ... Optical combiner, 6
...... Light receiving circuit, 7 …… Synthesis circuit, 8 …… Light transmitting circuit,
11 ... 1-core optical fiber.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location 7341-5K H04L 11/00 320

Claims (1)

[Claims] 1. A single-core optical fiber is used to connect a plurality of nodes each having a carrier wave of a different frequency and having the same degree of modulation of an optical signal by the carrier wave, and each node is connected by a frequency division multiplexing method. Configuring an optical communication system that collects the transmission signal of, the optical branching device that branches a part of the optical signal received from the preceding node, the level detection circuit that detects the level of the branched optical signal, and the carrier wave of the own node An optical transmission circuit that modulates and outputs an optical signal according to a preset modulation degree, an output level control circuit that controls the optical signal output level from the optical transmission circuit according to the detected level, and the optical transmission An optical combiner for combining an optical signal from a circuit with an optical signal from the preceding node, and a carrier wave from the own node by controlling an optical signal level in the output level control circuit. Bell equal to the carrier level from the previous position node, or optical communication node device characterized by being configured such that the prescribed level when the carrier level does not exist from the previous position node.