JPH0458736B2 - - Google Patents

Abstract

PURPOSE:To propagate an optical signal without phase difference between plural optical signals by using the phase difference between monotoring optical signals having two kinds of wavelengths, calculating the optical transmission path length between two points, and causing delays different in plural optical signals in response to the optical transmission path length. CONSTITUTION:Three optical signals modulated by wavelengths lambda1, lambda2 and lambda3 are made incident to an optical fiber cable 100. The pulse of a prescribed period is generated in a pulse generator 101. Electrooptic converting circuits 102 and 103 have output wavelengths of lambda4 and lambda5. An optical synthesizer 104 inputs those signals and an optical fiber cable 105 is connected to the output terminal. The optical signals having the wavelengths lambda1, lambda2 and lambda3 from an optical branching filter 106 are inputted to variable light delay elements 107, 108 and 109. The optical signals having the wavelengths lambda4 and lambda5 is led to photoelectric converting circuits 110, 111 and a control circuit 12 decides the amount of delay of elements 107, 108 and 109 depending on the said signal. The output of the elements 107, 108 and 109 is led to an optical synthesizer 113.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention transmits a plurality of wavelength-multiplexed optical signals.
This paper relates to an optical dispersion compensation method in an optical communication network to be exchanged.

Today, optical fiber cable transmission systems that use optical fiber cable as a transmission route are small diameter, wideband,
Because it has many advantages such as low loss and resistance to electromagnetic induction, it has been introduced into various communication networks, both public and private, in place of conventional coaxial cable transmission systems. Switching equipment, which is another important component in such communication networks, converts optical signals sent through optical fiber cables into electrical signals and then connects them to the switch.
Currently, the signal is converted back into an optical signal and sent out over an optical fiber cable.

However, in recent years, as seen in the Institute of Electronics and Communication Engineers Technical Report vol. 78, pp. 73-79, "An Attempt at Space-Division Optical Switching", optical signals sent via optical fiber cables have been Research and development is progressing on optical switching equipment that exchanges and connects signals and sends them out again to optical fiber cables, and it is expected that in the near future an optical communication network that will be able to transmit and exchange optical signals as they are will emerge.

In such optical communication networks, multiple pieces of information that are temporally related to each other are modulated using multiple different wavelengths, and multiplexed transmission is performed on one optical transmission line to make the optical transmission line effective. It is possible to use it.

However, optical fiber cables generally have different propagation speeds for each wavelength due to structural dispersion, material dispersion, etc., so they have the disadvantage that a phase difference occurs between the plurality of pieces of information as they propagate through the optical fiber cable. Furthermore, since this phase difference depends on the distance of the transmission path, it exhibits a different value each time an optical transmission path is set up in an optical communication network.

An object of the present invention is to transmit and exchange a plurality of wavelength-multiplexed optical signals between any two points on which an optical transmission line is set up in an optical communication network, without causing a phase difference between the plurality of optical signals. The object of the present invention is to provide an optical dispersion compensation system that can propagate.

According to the present invention, optical signals obtained by modulating and combining multiple pieces of light having different wavelengths using multiple pieces of information can be transmitted and exchanged while maintaining the correspondence between information and wavelength. A monitoring optical signal modulated by first and second wavelengths different from those of the plurality of lights is transmitted from one end between any two points at which a route has been selected in an optical communication network, and calculating the optical transmission path length between the two points based on the phase difference between the monitoring optical signals having the first wavelength and the second wavelength obtained at the other end of the optical transmission path; As a result, an optical dispersion compensation system can be obtained which gives different delays to the plurality of optical signals.

Furthermore, according to the present invention, an optical signal obtained by modulating and combining a plurality of lights each having a different wavelength using a plurality of pieces of information can be transmitted and multiplexed while maintaining the correspondence between the information and the wavelength. Injecting a monitoring optical signal having a wavelength different from the plurality of lights from one end between any two points where a path has been selected in the optical communication network to be exchanged, and reflecting it at the other end between the two points. The optical transmission path length between the two points is calculated based on the phase difference between the reflected monitoring optical signal obtained at one end between the two points and the incident monitoring optical signal, and the optical transmission path length is calculated as the optical transmission path length. Accordingly, an optical dispersion compensation system can be obtained that provides different delays to the plurality of optical signals.

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

FIG. 1 is a diagram showing a first embodiment of the present invention.

According to FIG. 1, the first embodiment of the present invention comprises an optical fiber cable 100 having one end injected with three optical signals modulated by wavelengths λ ₁ , λ ₂ , and λ ₃ , and Pulse generation circuit 10 that generates a pulse train
1, electrical-to-optical conversion circuits 102 and 103 whose inputs are respectively connected to the output of this pulse generation circuit 101 and have output wavelengths of λ ₄ and λ ₅ , respectively; First,
The second input end is connected to the optical fiber cable 100.
An optical multiplexer 104 having a third input end led to the other end, an optical fiber cable 105 having one end in contact with the output end of the optical multiplexer 104, and an input end connected to the other end of the optical fiber cable 105. The adjacent optical demultiplexer 106 and the wavelength λ ₁ of this optical demultiplexer 106,
variable optical delay elements 107, 108, 109 each having one end guided to the first, second, and third output ends for outputting optical signals of λ ₂ and λ ₃ ; and the optical demultiplexer 106.
optical-to-electrical conversion circuits 110 and 111 whose input ends are respectively guided to fourth and fifth output ends that output optical signals with wavelengths λ ₄ and λ ₅ , and this optical-to-electrical conversion circuit 1
a control circuit 112 having first and second inputs connected to the outputs of the variable optical delay elements 10 and 111, respectively, and determining the amount of delay of the variable optical delay elements 107, 108, and 109 according to these two input signals; 10
It includes an optical multiplexer 113 whose first, second, and third input ends are in contact with the other ends of the optical multiplexers 7, 108, and 109, respectively, and an optical fiber cable 114 whose one end is in contact with the output end of the optical multiplexer 113.

In FIG. 1, the optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ incident on one end of the optical fiber cable 100 are as follows:
Optical fiber cable 105 via optical multiplexer 104
The light enters one end of the optical fiber cable 105, propagates within the optical fiber cable 105, and then reaches the other end of the optical fiber cable 105.

Generally, the optical fiber cable 105 has different propagation velocities for each wavelength due to structural dispersion, material dispersion, and the like. Therefore, the optical fiber cable 10
5, the line length l and the propagation speed at the wavelengths λ ₁ , λ ₂ , and λ ₃ of the optical fiber cable 105 are respectively v(λ ₁ ),
When v(λ ₂ ) and v(λ ₃ ), at the other end of the optical fiber cable 105, an optical signal having a wavelength λ ₁ and an optical signal having a wavelength λ ₂
A phase difference of T ₁₂ =l/v(λ ₁ )−v(λ ₂ ) (1) occurs between the optical signal and the optical signal having the following. Similarly, between an optical signal having wavelength λ ₁ and an optical signal having wavelength λ ₃ , a phase difference of T ₁₃ =l/v(λ ₁ )−v(λ ₃ ) ……(2) occurs. becomes.

The optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ thus obtained at the other end of the optical fiber cable 105 are demultiplexed by an optical demultiplexer 106 and then transferred to variable optical delay elements 107 and 108, respectively. , 109 and are applied to the first, second, and third input ends of the optical multiplexer 113. The optical signals having wavelengths λ ₁ , λ ₂ , and λ ₃ are further multiplexed by a multiplexer 113 and then sent to one end of an optical fiber cable 114 .

In the first embodiment of the present invention shown in FIG. 1, the output of the pulse generation circuit 101 is further converted into optical signals having wavelengths λ ₄ and λ ₅ by electro-optical conversion circuits 102 and 103, respectively. Later optical multiplexer 1
04 to one end of the optical fiber cable 105. In this way, the optical fiber cable 1
The optical signals having wavelengths λ ₄ and λ ₅ propagated through 05 are demultiplexed by the optical demultiplexer 106 and then converted into electrical signals by the optical-to-electrical conversion circuits 110 and 111, respectively. added to one input. Here, the wavelength λ ₄ of the optical fiber cable 105,
If the propagation velocities v(λ ₄ ) and v(λ ₅ ) at λ ₅ are known, the line length l of the optical fiber cable 105 can be determined by the phase difference T between the two electrical signals applied to the input of the control circuit 112. It can be calculated as shown in the following formula.

l={v( _λ4 )−v( _λ5 )}T...(3) The control circuit 112 uses equations (1) and (2) from the line length l obtained from equation (3). Phase differences T ₁₂ and T ₁₃ are calculated, and the delay amounts of variable delay elements 108 and 109 are set to T ₁₂ and T ₁₃ , respectively. In this way, the phases of the optical signals having wavelengths λ ₁ , λ ₂ , λ ₃ obtained at the other ends of the variable optical delay elements 107 , 108 , 109 can be matched.

In FIG. 1, only the optical fiber cable 105 is shown as an optical transmission path from the output end of the optical multiplexer 104 to the optical demultiplexer 106. Even in cases where the system is configured with multiple optical switches or several links of optical fiber cables, and different connection routes are selected depending on the traffic at the time, as seen in "An Attempt at a Split Optical Switch," optical dispersion is always used. It is possible to compensate for the phase difference that occurs between a plurality of wavelength-multiplexed optical signals.

FIG. 2 shows the variable optical delay element 10 shown in FIG.
7, 108, and 109 are diagrams showing specific examples. According to FIG. 2, the variable optical delay element includes a waveguide optical switch 202 having a first input connected to one end of an optical fiber cable 200 and a first output connected to one end of an optical fiber cable 201, and a waveguide optical switch 202 connected to the optical fiber cable 201. an optical fiber cable 2 having one end connected to a second input and a second output of the waveform optical switch 202;
03,204 and this optical fiber cable 20
A waveguide optical switch 205 having a first output and a first input respectively connected to the other end of 3,204.
, optical fiber cables 206 and 207 each have one end connected to the second input and second output of this waveguide optical switch 205, and a first end connected to the other end of this optical fiber cable 206 and 207, respectively.
a waveguide optical switch 208 connected to the output and a first input of the waveguide optical switch 208; and optical fiber cables 209 and 210 each having one end connected to a second input and a second output of the waveguide optical switch 208,
A waveguide optical switch 211 has a first output and a first input connected to the other ends of the optical fiber cables 209 and 210, respectively, and a second input and a second output of the waveguide optical switch 211, respectively. Optical fiber cable 21 connected at one end
2,213 and this optical fiber cable 212,
A waveguide optical switch 214 has a first output and a first input connected to the other end of the waveguide optical switch 213, and one end is connected to the second input and the other end is connected to the second output of the waveguide optical switch 214. and a connected fiber optic cable 215.

Waveguide optical switches 202, 20 shown in FIG.
5, 208, 211, and 214 are connected to the first input and the first
The state in which the output, the second input, and the second output are connected (hereinafter referred to as the bar state), the first input and the second output, and the second input and the first
Switching is performed between a state in which the outputs of the two terminals are connected to each other (hereinafter referred to as a cross state).
Such a waveguide type optical switch is described in, for example, IEICE technical research report OEQ81-79 "1.3 .mu.m L; NbO ₃ 4.times.4 optical switch with single mode optical fiber array".

When the waveguide optical switch 202 is in the bar state in the variable optical delay element shown in FIG. 1 to the optical fiber cable 201. Next, waveguide optical switches 202 and 205
When set to cross state and bar state respectively,
The optical signal input from the optical fiber cable 200 to the first input of the waveguide optical switch is transmitted to the waveguide optical switch 2 via the optical fiber cable 204 - waveguide optical switch 205 - optical fiber cable 203.
fiber optic cable 201 from the first output of 02
will be sent to. Therefore, in this case, the optical signal input from the optical fiber cable 200 to the waveguide optical switch 202 is transmitted to the optical fiber cables 203 and 204.
fiber optic cable 201 after a propagation delay of
will be sent to. Further, waveguide optical switches 202,2
When 05 and 208 are set to a cross state, a cross state, and a bar state, respectively, the optical signal incident from the optical fiber cable 200 is transmitted to the waveguide optical switch 2.
02 - Optical fiber cable 204 - Waveguide optical switch 205 - Optical fiber cable 207 - Waveguide optical switch 208 - Optical fiber cable 206 -
Waveguide optical switch 205-optical fiber cable 2
03-Sent to optical fiber cable 201 via waveguide optical switch 202. In this case, the delay time from the first input to the first output of the waveguide optical switch 202 is
This is the sum of propagation delays of 7, 206, and 203. Similarly, the variable optical delay element shown in FIG. can be set to a value of

FIG. 3 is a diagram showing a second embodiment of the present invention.

In FIG. 3, the same numbers as in FIG. 1 indicate the same components as in FIG.

The second embodiment of the present invention shown in FIG. 3 differs from the first embodiment in that a pulse generating circuit 101 is provided at the receiving end of the optical fiber cable. In FIG. 3, the output of the pulse generation circuit 101 is converted into an optical signal having a wavelength λ ₄ by an electrical-optical conversion circuit 300, and then a half mirror 301 and an optical demultiplexer 10
6 to one end of the optical fiber cable 105. This optical signal having the wavelength λ ₄ propagates through the optical fiber cable 105, passes through the optical multiplexer 104, and enters one end of the optical fiber cable 302.
This optical signal having the wavelength λ ₄ is further reflected by a mirror 303 provided at the other end of the optical fiber cable 302, and then returned to the optical fiber cable 302.
2-Optical multiplexer 104-Optical fiber cable 105
It reaches the input end of the optical-to-electrical conversion circuit 304 via the optical demultiplexer 106 and the half mirror 301. The optical signal having the wavelength λ ₄ thus obtained at the input end of the optical-to-electrical conversion circuit 304 is converted into an electrical signal by the optical-to-electrical conversion circuit 304 and then input to one input of the control circuit 112. Added. The control circuit 112 sets the delay times of the variable optical delay elements 107, 108, and 109 according to the phase difference T between the electrical signal obtained in this way and the output of the pulse generation circuit 101. In this case, the optical fiber cable 105
Let v(λ ₄ ) be the propagation velocity at the wavelength λ ₄ of
The line length l of the optical fiber cable 105 can be calculated using the following equation.

l=1/2v(λ ₄ )T...(4) The second embodiment of the present invention shown in FIG. This has the advantage that it can be constructed more economically.

Note that the first aspect of the present invention shown in FIGS. 1 and 3
In both the second embodiment and the second embodiment, variable optical delay elements 107, 108, and 109 for compensating for optical dispersion are provided at the receiving end of the optical fiber cable 105. In the embodiment 1, the pulse generation circuit 101 and the electrical-to-optical conversion circuits 102 and 103 are connected to an optical fiber cable 105.
variable optical delay elements 107, 108, 1 at the receiving end of
09 etc. at the transmitting end of the optical fiber cable 105, the wavelength λ ₁ ,
A similar effect can be obtained by giving optical signals having λ ₂ and λ ₃ a phase difference corresponding to the optical dispersion occurring in the optical fiber cable 105 and sending them to the optical fiber cable 105.

Similarly, in the second embodiment of the present invention shown in FIG.
At the receiving end of 05, variable optical delay elements 107, 10
It is clear that the same effect can be obtained by providing the pulse generating circuit 101, 8, 109, etc. at the transmitting end of the optical fiber cable 105, respectively.

As described above, according to the present invention, in an optical communication network that transmits and exchanges a plurality of wavelength-multiplexed optical signals, the phase difference between the plurality of optical signals can be It can be propagated without causing any problems.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG.
The figure shows variable optical delay elements 107 and 10 shown in FIG.
8 and 109, and FIG. 3 is a diagram showing a second embodiment of the present invention. In the figure, 101 is a pulse generation circuit, 102,
103,300 is an electric-optical conversion circuit, 104,1
13 is a multiplexer, 106 is a demultiplexer, 107, 10
8, 109 are variable optical delay elements, 110, 111,
304 is a photo-electric conversion circuit, 112 is a control circuit,
301 represents a half mirror, and 303 represents a mirror.

Claims (1)

[Claims] 1. Transmitting and combining an optical signal obtained by modulating and combining a plurality of lights each having a different wavelength using a plurality of pieces of information while maintaining the correspondence between the information and the wavelength. Sending out a monitoring optical signal modulated by first and second wavelengths different from the plurality of lights from one end between any two points where a route has been selected in an optical communication network for exchanging, The length of the optical transmission path between the two points is calculated based on the phase difference between the monitoring optical signals having the first wavelength and the second wavelength obtained at the other end between the two points, and the length of the optical transmission path is calculated between the two points. An optical dispersion compensation system characterized in that a different delay is given to each of the plurality of optical signals depending on the optical signals. 2. An optical communication network that transmits and exchanges optical signals obtained by modulating and combining multiple pieces of light with different wavelengths using multiple pieces of information while maintaining the correspondence between information and wavelength. A monitoring optical signal having a wavelength different from that of the plurality of lights is inputted from one end between any two points where the path selection has been performed in , and is reflected at the other end between the two points. The length of the optical transmission path between the two points is calculated based on the phase difference between the reflection monitoring optical signal obtained at one end between the points and the incident monitoring optical signal, and the length of the optical transmission path between the two points is calculated according to the optical transmission path length. An optical dispersion compensation method that is characterized by giving different delays to optical signals.