JPH06209292A - Optical communication network - Google Patents

Abstract

PURPOSE:To enable the optical communication between arbitrary optical terminal stations by adjusting the signal which is transmitted by its own station and transmits one round of a loop state optical communication network so that the C/N of this received signal may be within a certain range at an optical terminal station. CONSTITUTION:A carrier wave modulation into the carrier wave signal of its own station performed for a signal to be transmitted in a loop from an input/output device 24 via a carrier wave modulation circuit 33. This carrier wave signal is transmitted in the loop from an optical transmitter 22 via an amplitude adjusting circuit 44 and a signal synthetic circuit 34. An optical receiver 23 receives the carrier wave signal from other optical terminal station and the carrier wave signal of the own station which made one round of the loop and returns. A C/N detection circuit 40 detects the carrier wave frequency and noise components of its own station from among the signals of the optical receiver 23 and a C/N detection value 45 is obtained. A comparator circuit 41 outputs a control signal 46 for increasing the amplitude of the output signal 48 of the circuit 44 when the detection value 45 is lower than a reference value 42 and outputs a control signal 47 for decreasing the amplitude of the signal 48 when the value is higher than a reference value 43.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication network in which a plurality of optical terminals are connected in a loop with an optical fiber,
In particular, the present invention relates to an optical communication network that automatically adjusts the C / N of a carrier signal transmitted from each optical terminal within a fixed range.

[0002]

2. Description of the Related Art A loop type optical communication network is formed by connecting a plurality of optical terminal stations with an optical fiber in a loop shape.
FIG. 3 also shows a configuration example of a loop type optical communication network having four optical terminal stations. 4 optical terminal stations 1, 2,
3 and 4 are sequentially connected by the optical fibers 5a, 5b, 5c and 5d to form a loop. FIG. 4 shows a configuration example of the optical terminal station.

The optical terminal station 1 includes a signal processing section 11 and an optical transmitter 1.
2. The optical receiver 13 includes optical fibers 5a and 5b for connecting to other optical terminal stations. Further, the signal processing unit 11 is connected to the signal input / output device 14 connected to the optical terminal 1. The four optical terminal stations 1 of FIG.
2, 3, and 4 have the same configuration.

In the optical terminal station 1, the optical signal input from the optical fiber 5a is received by the optical receiver 13, and the signal processing section 11 extracts the information transmitted to the optical terminal station 1 from the received signal. Then, the output information signal 15 is output to the signal input / output device 14.

The information signal 16 input from the signal input / output device 14 is converted into an optical communication format by the signal processing unit 11, further converted into an optical signal by the optical transmitter 12, and sent to the optical fiber 5b. It

An optical modulation method for transmitting an optical signal from an optical transmitter is a digital intensity modulation method for switching on / off the optical signal according to an information signal converted into a digital signal,
There is a carrier intensity modulation method in which light intensity is modulated by a signal obtained by modulating a specific carrier frequency from a digital signal or an analog signal.

In the carrier intensity modulation method, there are cases where only one carrier frequency is used in the optical communication network and cases where different carrier frequencies are assigned to the respective optical terminal stations.

FIG. 5 shows a configuration example of the optical terminal station in the case of. The optical terminal 20 shown in FIG. 5 corresponds to the optical terminals 1, 2, 3, 4 shown in FIG.
Is shown.

The information signal to be transmitted is input from the input / output device 24 through the signal processing section 21 to the carrier modulation circuit 33, and information is transmitted using the carrier frequency individually assigned to each optical terminal station 20. The signal is modulated.

On the other hand, in the optical terminal 20, the optical fiber 6a
The optical signal input from the optical receiver 23 is received by the optical receiver 23, and in the channel selection demodulation circuit 31, the carrier signal of the partner station with which communication is to be performed is selected from the received signal and demodulated. The demodulated information signal 36 is output to the signal processing unit 21,
Further, it is output to the input / output device 24 as the information signal output 25.

At the same time, a signal 37 is extracted from the output signal 35 of the optical receiver 23 by the band elimination filter 32, in which only the carrier wave transmitted from the own station and having gone around the loop is eliminated. The signal combining circuit 34 combines the signal 37 and the output of the carrier modulation circuit 33 to obtain a combined signal 39,
The optical transmitter 22 converts this signal 39 into an optical signal and sends it to the optical fiber 6b.

There are various modulation methods in the carrier modulation circuit 33 depending on the application. When the information signal input from the signal processing unit 21 is digital data, FSK, MS
K, QPSK, etc. When the information signal is an analog signal, it is AM, FM or the like.

[0013]

By the way, in the above method, the optical transmitter 22 and the optical receiver 2 of each optical terminal 20 are used.
When the optical modulation degree of each carrier signal varies due to the amplitude frequency characteristic such as 3, the C / N of the carrier signal transmitted from each optical terminal 20 becomes different.
In the worst case, the C / N of these carrier signals is lower than the C / N required for some carriers, and the optical terminal 2
The signal of 0 cannot be received by the other optical terminal 20. As a result, the other optical terminal 20 cannot communicate with the optical terminal 20.

Therefore, an object of the present invention is to solve the above problems and provide an optical communication network for automatically adjusting the C / N of a carrier signal transmitted from each optical terminal within a certain range.

[0015]

In order to achieve the above object, the present invention provides a carrier modulation circuit for modulating a signal to be transmitted to each optical terminal station at a carrier frequency different for each optical terminal station. And a removal filter that removes only the carrier signal of the own station that has returned from the received signal of the optical receiver after going around the loop, and the carrier signal of the other station obtained by this removal filter from the carrier modulation circuit. A signal synthesizing circuit for synthesizing a carrier wave signal transmitted from its own station and outputting it to the optical transmitter, and a C for detecting C / N of the carrier wave signal of its own station in the received signal
/ N detection circuit.

A comparing circuit for detecting whether the C / N detected by the C / N detecting circuit exceeds a reference value that defines an upper limit and a lower limit, and the own terminal according to the comparison result. And an amplitude adjusting circuit for adjusting the amplitude of the carrier wave signal transmitted from.

[0017]

With the above structure, the C / N detection circuit detects the C / N of the carrier signal of its own station which has returned after making a round of the loop, and the comparison circuit detects the C / N and an upper limit predetermined as C / N. Compare with the lower reference value. If the C / N detection value exceeds the upper limit reference value, the amplitude adjusting circuit decreases the amplitude of the carrier signal, and if it does not reach the lower limit reference value, the amplitude adjusting circuit increases the amplitude of the carrier signal. To do. When the amplitude of the carrier signal is adjusted, C /
N is controlled within a range of upper and lower reference values.

[0018]

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

The optical communication network according to the present invention is shown in FIG.
, An optical communication network in which a plurality of optical terminal stations 1, 2, ... Are connected in a loop with a plurality of optical fibers 5a, 5b ,. The internal configuration of the optical terminal station is shown in FIG.

As shown in FIG. 1, this optical terminal station has a signal processing unit 21 connected to an input / output device 24 and an optical signal to an optical fiber 6b which is an optical fiber 5b forming a loop of the optical communication network. And an optical receiver 23 for receiving an optical signal from the optical fiber 6a which is also the optical fiber 5a.
Also, between the optical receiver 23 and the signal processing unit 21, a channel selection demodulation circuit 31 for selecting and demodulating a carrier signal of a partner station with which communication is to be performed, and transmitting from the own station at carrier frequencies different for each optical terminal station. Carrier modulation circuit 33 that modulates a signal for performing the operation, a removal filter 32 that removes only the carrier signal of the own station that has returned from the received signal of the optical receiver 23 through the loop, and the other station obtained by the removal filter 32. Signal combining circuit 34 for combining the carrier signal of the own station transmitted from the carrier modulation circuit 33 with the carrier signal of the above and outputting to the optical transmitter 22, C / N for detecting the C / N of the carrier signal of the own station in the received signal N detection circuit 40, a comparison circuit 41 for detecting whether C / N detected by the C / N detection circuit 40 exceeds a reference value defining an upper limit and a lower limit, and a carrier wave transmitted from the own station according to the comparison result. Signal And it includes the amplitude adjusting circuit 44 for width adjustment.

As shown in the figure, the output of the optical receiver 23 is input to each of the channel selection demodulation circuit 31, the C / N detection circuit 40, and the removal filter 32, and the output of the channel selection demodulation circuit 31 is a signal processing unit. 21, the output of the C / N detection circuit 40 is input to the comparison circuit 41, and the output of the removal filter 32 is input to the signal synthesis circuit 34. Further, predetermined reference values 42 and 43 are input to the comparison circuit 41. Comparison circuit 4
1 has two outputs, all of which are input to the amplitude adjusting circuit 44. The output of the signal processing unit 21 is input to the carrier modulation circuit 33, and the output of the carrier modulation circuit 33 is input to the amplitude adjustment circuit 44. The output of the amplitude adjusting circuit 44 is input to the optical transmitter 22 together with the output of the removal filter 32.

A configuration example of the C / N detection circuit 40 is shown in FIG.
Is shown in. The C / N detection circuit 40 includes a bandpass filter 51 that passes the carrier frequency of the own station, a bandpass filter 52 that does not include the carrier frequency of the own station and other stations, and passes a part of frequencies in the vicinity thereof, and respective band filter outputs. It is composed of amplitude detection circuits 53, 54 for detecting the amplitude of the signal and a ratio detection circuit 55 for detecting the C / N of the carrier signal of the own station from these amplitudes.

Next, the operation of the embodiment will be described.

A signal to be transmitted from the input / output device 24 to the loop is modulated into a carrier signal of its own station through the signal processing unit 21 and the carrier modulation circuit 33. The carrier wave signal has an amplitude adjusting circuit 44 and a signal synthesizing circuit 3 as described later.
4 is sent to the optical transmitter 22 and is sent to the loop.
This signal returns around the loop via another optical terminal. The optical receiver 23 receives the carrier signal of its own station which has returned around the loop together with the carrier signals from other optical terminal stations.

The C / N detection circuit 40 extracts the carrier frequency of its own station from the carrier signal from the optical receiver 23 by the band filter 51, and part of the frequency in the vicinity thereof, that is, the noise component, by the band filter 52. Extract with. The amplitude detection circuits 53 and 54 detect the amplitudes 58 and 59 of the carrier frequency component 56 of its own station and its noise component 57. Ratio detection circuit 55
Obtains a C / N detection value 45.

In the comparison circuit 41, the reference values 42 and 43 are preset so that the reference value 42 <the reference value 43. The comparison circuit 41 uses the C / N detection value 45 (6 in FIG. 2).
0) is less than the reference value 42, the amplitude adjustment circuit 44
Control signal 46 for increasing the amplitude of the output signal 48 of
Is output. Further, the comparison circuit 41 determines that the C / N detection value 45
When (60) exceeds the reference value 43, the amplitude adjusting circuit 4
Control signal 4 for reducing the amplitude of the output signal 48 of FIG.
7 is output. Therefore, the amplitude adjusting circuit 44 adjusts the amplitude of the output signal 48 so that the C / N of the carrier signal of the station falls within the range of both reference values 42 and 43.
The output signal 48 is combined by the signal combining circuit 34 with the carrier signal 37 of the other station obtained by the removal filter 32 and sent to the optical transmitter 22.

As another embodiment of the present invention, in the optical terminal station of FIG. 1, when the signal 37 from which the carrier signal of the local station is removed by the removal filter 32 is taken out from the output of the optical receiver 23, each optical terminal station Add a bandpass filter that passes only all the bands of the carrier signal. By removing noise and distortion components other than the required band with this band filter, the modulation degree of the signal modulated in the optical transmitter 22 can be increased.

The system of the present invention can be applied not only to optical communication but also to a network using a coaxial cable or the like.

[0029]

The present invention exhibits the following excellent effects.

In the optical communication network of the present invention,
At the optical terminal station, the signal transmitted by itself is transmitted around the loop optical communication network,
Since / N is adjusted so as to be within a certain range, C / N at an optical terminal station on the way is also kept within a certain range. Since each optical terminal similarly adjusts the C / N of the carrier signal of its own station, a constant reception characteristic is ensured for all carrier signals anywhere in the optical communication network, and an arbitrary optical terminal always operates. Optical communication between them becomes possible.

[Brief description of drawings]

FIG. 1 is an internal configuration diagram of an optical terminal station showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a C / N detection circuit showing an embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical communication network.

FIG. 4 is a basic configuration diagram of an optical terminal station.

FIG. 5 is an internal configuration diagram of an optical terminal station showing a conventional example.

[Explanation of symbols]

 22 optical transmitter 23 optical receiver 32 removal filter 33 carrier modulation circuit 34 signal combining circuit 40 C / N detection circuit 41 comparison circuit 42 upper reference value 43 lower reference value 44 amplitude adjustment circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 10/06 8523-5K H04B 9/00 L

Claims (2)

[Claims] 1. An optical communication network in which a plurality of optical terminal stations each having an optical transmitter and an optical receiver are provided, and these optical terminal stations are connected in a loop by an optical fiber to form a loop,
To each optical terminal station, a carrier modulation circuit that modulates a signal to be transmitted from the local station at a carrier frequency different for each optical terminal station, and the local station that returns from the received signal of the optical receiver after looping around the loop. A removal filter that removes only the carrier signal of, and a signal combining circuit that combines the carrier signal of the other station obtained by this removal signal with the own-station transmitted carrier signal from the carrier modulation circuit and outputs the combined signal to the optical transmitter. An optical communication network comprising: a C / N detection circuit for detecting the C / N of the carrier signal of its own station in the received signal. 2. A comparison circuit for detecting in the optical terminal station whether or not the C / N detected by the C / N detection circuit exceeds a reference value defining an upper limit and a lower limit, and in accordance with a result of the comparison, a comparison circuit is provided. The optical communication network according to claim 1, further comprising an amplitude adjusting circuit that adjusts an amplitude of a carrier signal transmitted from the own station.