JP2839103B2 - Optical communication device, optical communication method, and optical communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical communication device, an optical communication method, and an optical communication system used in an optical communication system in which a plurality of optical communication devices are interconnected. is there.

[Prior Art] The conventional wavelength multiplexing optical communication system transmits optical signals of different wavelengths through one transmission line to improve the utilization efficiency of the transmission line. Usually, a plurality of terminals transmitting optical signals of different wavelengths, an optical superimposing means for putting these optical signals into one transmission line, one transmission line, and a wavelength multiplexed signal are necessary. And a plurality of terminals that receive this signal.

A semiconductor laser is mainly used as a light source for transmitting light from each terminal, and an optical fiber is often used for a transmission path. In addition, as a light superimposing means for putting light of a plurality of wavelengths into one optical fiber, an optical converging element composed of a half mirror, a beam splitter, or the like, an optical converging element using an optical waveguide, or the like is used.

On the other hand, conventionally, an optical wavelength filter, a prism, or the like has been used as a means for extracting a required optical wavelength from the wavelength-multiplexed optical signal.

As another means, an optical heterodyne method is also used. This is achieved by mixing a wavelength multiplexed optical signal with light having a wavelength very close to the optical wavelength of the desired signal, converting it into an electrical signal with a photodetector, and electrically filtering the difference frequency signal. It separates necessary signals. This method has attracted attention as a method for dramatically improving the wavelength multiplicity.

[Problem to be Solved by the Invention] However, usually, in optical communication, a semiconductor laser is used as a light source as described above, and the emission wavelength of the semiconductor laser is liable to fluctuate due to temperature and other factors. There were serious disadvantages.

(1) In a system in which a required optical wavelength is separated from an optical signal wavelength-division multiplexed using an optical wavelength filter or a prism or the like, even if such a semiconductor laser wavelength fluctuation occurs, light of each wavelength is received on the receiving side. In order to separate the signals so that no interference occurs, the bandwidth of each wavelength needs to be sufficiently wide. For this reason, the wavelength interval used for communication is widened, and it is difficult to increase the multiplicity.

(2) In the method of separating optical wavelengths using the optical heterodyne detection method, it is necessary to control so that the wavelength does not change. For this reason, it is necessary to strictly control the temperature of the light source portion, and when stricter wavelength stability is required, the emission wavelength is monitored by a spectrometer or the like so that the emission at a desired wavelength is performed. Need to give feedback.

These controls require a large-scale circuit and increase costs, so that it is difficult to use the control except for a specific optical communication system in the trunk system.

[Means for Solving the Problems] The present invention has been made for the purpose of solving the above problems, and has the following configuration as one means for solving the above problems.

That is, in an optical communication device used in an optical communication system in which a plurality of optical communication devices are interconnected, a wavelength-variable light source that transmits an optical signal at a set wavelength, an optical signal emitted from the wavelength-variable light source, An optical signal transmitted from another optical communication device of the communication system is received, interference detection means for detecting interference between these optical signals, and light emitted from the light source when interference is detected by the interference detection means. Control means for changing the wavelength of the signal.

And, for example, the control means is characterized in that the wavelength of the optical signal emitted by the wavelength variable light source is continuously changed so as to be away from the wavelength of the optical signal transmitted from another optical communication device.

Alternatively, in an optical communication device used in an optical communication system in which a plurality of optical communication devices are connected to each other, a wavelength tunable light source that transmits an optical signal at a set wavelength, and a setting wavelength of the wavelength tunable light source. A first tunable filter that transmits light in a narrow wavelength range, a second tunable filter that transmits light in a narrow wavelength range centered on a wavelength slightly shorter than the set wavelength, and a second tunable filter that transmits light in a narrow wavelength range. A third wavelength tunable filter that transmits light in a narrow wavelength range centered on a slightly longer wavelength, and an optical signal emitted from the wavelength tunable light source and an optical signal transmitted from another optical communication device. An optical element to be incident on each of the first, second and third wavelength tunable filters, and first, second and third lights respectively receiving light transmitted through the first, second and third wavelength tunable filters. A detector, Proximity detection means for detecting from the outputs of the second and third photodetectors that the wavelength of the optical signal emitted from the wavelength tunable light source has approached the wavelength of the optical signal transmitted from another optical communication device; And a control means for changing a set wavelength of the variable wavelength light source when an approach is detected by the approach detection means.

Furthermore, in an optical communication device used in an optical communication system in which a plurality of optical communication devices are interconnected, a wavelength-variable light source that transmits an optical signal at a set wavelength, and a light source that emits light from the wavelength-variable light source. A first modulator that modulates a part according to a signal to be transmitted, a second modulator that modulates another part of the light emitted from the tunable light source according to a signal of a predetermined first frequency, An optical element for mixing a part of an optical signal modulated by the first modulator, an optical signal transmitted from another optical communication device, and an optical signal modulated by a second optical modulator; A photodetector that detects an optical signal mixed by the element, and a mixing unit that mixes an output of the photodetector and an electric signal having a predetermined second frequency.
A filter that passes a low-frequency signal component distant from the vicinity of the second frequency among the electric signals mixed by the mixing unit, and a wavelength of light emitted by the light source from a signal component transmitted through the filter. And control means for detecting that the wavelength of the optical signal transmitted from another optical communication device has approached, and changing the set wavelength of the light source when the approach is detected.

Further, for example, the apparatus further comprises a comparing means for comparing the phase of the signal component transmitted through the filter with the phase of the signal of the first frequency. Alternatively, the second optical modulator includes: a sine wave generating unit that generates a sine wave signal of the first frequency; and an optical modulation element that is driven according to the sine wave signal generated by the sine wave generating unit. It is characterized by comprising.

Furthermore, a low-pass filter is provided which filters a part of the output of the photodetector without being mixed with an electric signal having a second frequency and inputs the filtered signal to a control circuit.

Alternatively, in an optical communication system in which a plurality of optical communication devices are connected to each other, each of the optical communication devices transmits a wavelength-variable light source at a set wavelength, and an optical signal emitted from the light source. An interference detection unit that receives optical signals transmitted from other optical communication devices of the communication system and detects interference of these optical signals, and when interference is detected by the interference detection unit, an optical signal generated by the light source is emitted. Control means for changing the wavelength.

[Operation] In the above configuration, it is possible to realize wavelength-division multiplexed optical communication with a large wavelength multiplicity without strictly stabilizing the emission wavelength.

Hereinafter, an embodiment according to the present invention will be described in detail with reference to the drawings.

First Embodiment FIGS. 1 and 2 show a first embodiment according to the present invention. FIG. 1 is a schematic diagram showing a system for achieving the wavelength division multiplexing optical communication system of this embodiment.

In the figure, 11-1n, 21-2m are optical communication terminals, 40,411-41n, 421
42 m is an optical fiber which is an optical transmission line, and 31 and 32 are optical star couplers.

FIG. 2 shows the terminals 11-1n and 21-2m shown in FIG.
FIG. 3 is a schematic view of an optical transceiver section of FIG. In FIG. 2, reference numeral 51 denotes a wavelength tunable light source such as a semiconductor laser capable of changing an oscillation wavelength by external control, for example, and 53 branches a signal light from the wavelength tunable light source 51 to a transmission line and an optical branch element 54, An optical branching / combining element for transmitting the wavelength multiplexed light from the transmission path to the optical branching element 54; an optical branching element 54 for distributing the light from the branching / combining element 53 to the wavelength tunable filters 551, 552, 553; 57 is a circuit for extracting necessary information from signals from the photodetectors 562 and 563, 58 is transmitting data from the terminal device, receiving data from the transmission line, and performing interference with other terminals. Control circuit for controlling the wavelength tunable light source 51 and the wavelength tunable filters 551 to 553 in order to avoid
Reference numeral 53 denotes a wavelength variable bandpass filter capable of changing the wavelength range of light transmitted by external control, and reference numerals 561 to 563 denote photodetectors.

In the above configuration, the light branching / merging element 53 and the light branching molecule 54
Is composed of, for example, a half mirror or a beam splitter.
The variable wavelength light source 51 is, for example, a DBR (distributed reflection type mirror).
It consists of a wavelength tunable DBR semiconductor laser that has a DBR mirror with a structure that can change the Bragg wavelength by injecting carriers into the region.By adjusting the amount of carriers injected into the DBR region, the oscillation wavelength can be made continuous. It can be changed dynamically. As the wavelength variable light source 51, for example, K.KOTAKI, M.MATSUDA, M.YANO, H.ISIKAWA,
By H.IMAI, Electoronics Letters, 1987, Volume 23, 7
No. 325 to 327 can be used.

Here, it is assumed that the variable wavelength light source 51 includes a wavelength adjustment unit that changes the oscillation wavelength and an output light modulation unit that performs intensity modulation of the output light.

In the case of a wavelength tunable DBR semiconductor laser, the DBR section corresponds to a wavelength adjustment section, and the active region corresponds to an output light modulation section.

Further, the tunable band-pass filters 561 to 563 are, for example, tunable DBRs (distributed reflection type Bragg mirrors) for changing the Bragg wavelength by the above-described carrier injection (for example, those described in JP-A-60-175025). Which can be used).

FIG. 3 is a tunable bandpass filter shown in FIG.
It is a diagram showing the relative relationship between the transmission wavelength of 561 ~ 563,
In the figure, reference numerals 591 to 593 denote tunable bandpass filters 56, respectively.
The wavelength transmission characteristics of 1 to 563 are shown.

These tunable filters are set so that, when the transmission wavelength is changed by external control, the three transmission characteristics simultaneously change in the same direction by the same wavelength, while maintaining the relative relationship between these transmission characteristics. Have been.

Next, the operation of this embodiment having the above configuration will be described with reference to FIGS.

In the following description, the wavelength λ1 is transmitted from the terminal 11 to the terminal 23 in FIG.
In this example, the communication is performed from the terminal 12 to the terminal 22 using the light having the wavelength λ2. However, the present embodiment is not limited to the above example, and it goes without saying that exactly the same control is performed in communication between arbitrary terminals.

It is assumed that the wavelengths λ1 and λ2 are close to each other, but are separated from each other by more than the bandwidth required for communication, and that no interference has occurred.

At this time, in the optical transceiver of the terminal 11 shown in FIG. 2, the signal light of the wavelength λ1 emitted from the wavelength tunable light source 51 is partially transmitted to the transmission line by the branching / combining element 53 and
Transmitted to The rest is transmitted to the optical branching element 54. The split light from the splitting / merging element 53 is converted into an optical splitting element 54.
And the wavelength-available filters # 1 (551) and # 2
(552) and # 3 (553). Tunable filter #
1 (551) is controlled by a control signal from the control circuit 58 so that the center of the transmission wavelength coincides with the wavelength λ1, and a large output is output from the photodetector # 1 (561). From the detectors # 2 (562) and # 3 (563), the variable wavelength filters # 2 (552) and # 3 (55) as shown in FIG.
Only an output corresponding to the response amplitude for the wavelength λ1 of 3) is output.

On the other hand, in the optical transceiver of the terminal 23, the wavelength λ1 enters from the transmission line, light lambda ₂ passes through the branching / combining device 53, the light branching element 54, a wavelength tunable filter # 1 (551), # 2 (55
2), reaches # 3 (553). However, since the wavelength tunable filter # 1 (551) is centered on the transmission wavelength to the wavelength λ1, the light of the wavelength λ2 is blocked, and only the light of the wavelength λ1 is converted into an electric signal by the photodetector # 1 (561). Converted,
It is transmitted to the terminal device via the control circuit 58.

As described above, since the semiconductor laser is used as the variable wavelength light source 51, the oscillation wavelength tends to change depending on the temperature. Therefore, the wavelength λ currently transmitted from the terminal 12 is
The operation of the present embodiment when the wavelength of the second signal fluctuates so as to approach the wavelength λ1 will be described.

At this time, the light having the wavelength λ2 is transmitted to the wavelength tunable filter # 2 (56
When it enters the pass band of 2), photodetector # 2 (562)
Output increases. In contrast, photodetector # 3 (56
The output of 3) does not change. Therefore, the adjacent channel approach detection circuit 57 can detect that light having a wavelength shorter than the wavelength λ1 is approaching by checking the outputs of the two photodetectors. Adjacent channel approach detection circuit 57
Transmits this detection information to the control circuit 58.

The control circuit 58 uses the wavelength control signal in accordance with the detection information to continuously move the wavelength of the wavelength variable light source 51 to a longer wavelength than λ1 to control interference with a signal with the approaching wavelength λ2. . At the same time, the control circuit 58 uses the transmission wavelength control signals of the tunable filters # 1 (551), # 2 (552), and # 3 (553) to transmit the wavelength λ1 and the transmission center of the tunable filter # 1 (551). Control is performed so that the wavelengths match.

On the other hand, in the terminal 23 receiving the wavelength λ1, the output signal of the photodetector # 1 (561) becomes smaller in response to the terminal 11 moving the wavelength λ1 to avoid interference. However, the control circuit 58 of the terminal 23 always uses the transmission wavelength control signal to set the center of the transmission wavelength of the wavelength tunable filter # 1 (551) such that the output signal from the photodetector # 1 (561) is maximized. If it is moved, such a decrease in output can be avoided, and the terminal 23 can always receive the signal from the terminal 11 following the fluctuation of the wavelength.

With the operation described above, the terminal 11 can prevent interference even when the output wavelength of the terminal 12 fluctuates and approaches the output wavelength of the terminal itself, and the terminal 23 can be disconnected from the terminal 11 without being detuned. Can be continuously received.

Further, when the wavelength λ2 approaches from a wavelength range longer than the wavelength λ1, the output of the photodetector # 3 (563) increases, and this can be transmitted to the adjacent channel approach detection circuit 57.

Furthermore, when λ2 does not change and only λ1 changes, λ1,
Even when both λ2 fluctuate, the above-described function can maintain communication while avoiding interference.

Second Embodiment FIG. 4 is a schematic diagram of an optical transceiver part of a terminal according to a second embodiment of the present invention. The configuration of the optical transceiver section of the second embodiment is also suitably used in the wavelength division multiplexing optical communication system of the first embodiment shown in FIG.

In FIG. 4, reference numeral 58 denotes a control circuit for controlling the overall operation of this embodiment similar to that of FIG. 2, reference numeral 61 denotes a branching / junction element, and reference numeral 62 denotes light from the second external modulation element 75 and the branching / junction element 61. An optical converging element for mixing light, 63 is a photodetector, 64 is a low-pass filter having a cutoff frequency of 5 GHz, for example, 65 is a local oscillator having an oscillation frequency of 3 GHz, and 67 is a local oscillator having a cutoff frequency of about 1 GHz, for example. A low-pass filter, 68 is a phase comparison circuit for detecting a phase difference between a signal from the sine wave generation circuit 74 and a signal from the low-pass filter 67, 71 is a wavelength tunable light source, 72 is frequency modulation or phase of light from the wavelength tunable light source 71. A first external modulating element for modulating, 73 an optical switch, 74 a sine wave generating circuit for generating a 100 kHz sine wave signal,
75 is a second external modulation element.

In this embodiment, it is assumed that the signal from each terminal has a bandwidth of 1 MHz to 1 GHz.

In the second embodiment, similarly to the first embodiment, the terminal 11 in FIG.
The operation of the optical communication apparatus shown in FIG. 4 will be described below in detail with reference to FIGS.

FIG. 5 and FIG. 6 are diagrams showing the spectrum of the signal at the points indicated by and in FIG. 4. FIG. 5 shows the case where the wavelengths of the adjacent channels are not approaching. Indicates the case where the wavelengths of adjacent channels are approaching.

First, the operation of the terminal in the transmission state will be described with reference to FIG. 4 and FIG. The following description is for the case where the wavelengths of adjacent channels are not approaching.

The signal output from the terminal 11 in the transmission state has a bandwidth of 1 MHz to 1 GHz as described above. The light signal of the wavelength λ1 from the tunable light source 71 within the bandwidth is supplied to the first external modulation element 72 according to the control signal from the control circuit 58.
And is output to the optical switch 73. In the terminal in the transmission state, the optical switch 73 is always "ON", and the input light can pass through as it is. For this reason, the light that has passed through the optical switch 73 is sent out to the transmission line via the branching / joining element 61.

A part of the output light is branched by the branch / merge element 61 and reaches the optical merge element 62.

On the other hand, part of the light from the wavelength variable light source 71 is sent to the second external modulation element 75, where it undergoes frequency modulation or phase modulation with the frequency of 100 KHz output from the sine wave generation circuit 74, and Element 62 is reached.

The light converging element 62 mixes the light from the branching / converging element 61 and the light from the second external modulating element 75 and sends the light to the photodetector 63. The photodetector 63 square-detects the mixed light,
Convert to electrical signals. Therefore, the photodetector 63 outputs a difference frequency signal (beat signal) of the input optical signal. The signal from the photodetector 63 is applied to a low-pass filter 64.
Is output to The signal output to the low-pass filter 64 is a signal having the same light source but modulated by different electric signals, so that the signal is output to the low-pass filter 64 and homodyne detection is performed.

Therefore, the low-pass filter 64 at the point in FIG.
The output signal has the same spectrum as the signal from the terminal except for the sine wave component of 100 KHz.
A signal as shown by 101 is obtained. The signal 101 is input to the control circuit 58.

This signal is a local oscillator circuit that outputs a frequency of 3 GHz.
The signal is mixed with the signal from 65 and input to the low-pass filter 67. The signal at this point in FIG. 4 is a signal having a frequency spectrum indicated by 101 in FIG.
Since it becomes a sum / difference signal of the signal having the center frequency of z, as shown by 102 and 103 in FIG. 5B, the frequency spectrum has a double-sideband of 1 GHz on both sides around 3 GHz.

The low-pass filter 67 is a filter having a cut-off frequency of 1 GHz. The input signals 102 and 103 having the frequency spectrum shown in FIG.
And nothing is output to the filter output.

With the above configuration, when the wavelengths of the approaching channels are not approaching, there is no output from the low-pass filter 67, and no approach detection signal is output to the control circuit 58.

Next, referring to FIG. 4 and FIG.
A case will be described in which the light of the wavelength λ2 transmitted from the terminal 22 to the terminal 22 causes a wavelength fluctuation, and the wavelength approaches λ1.

The optical convergence element 62 has a wavelength λ1
The light of the wavelength λ2 is input together with the light of the above. here,
For example, it is assumed that the wavelength λ1 and the wavelength λ2 approach each other up to a frequency difference of about 4 GHz. In this case, the output from the photodetector 63, together with the homodyne detection signal of wavelength λ1 modulated by two different signals as described above, together with the light of wavelength λ2 and the second
Also, a beat frequency signal (heterodyne detection signal) with light guided from the external modulation element 75 is output. Therefore,
As shown in FIG. 6A, the signal spectrum at the point is a mixture of the signal 110 based on homodyne detection and the signal 111 based on heterodyne detection.

After the mixed signal and the 3 GHz signal from the local oscillation circuit 65 are interfered with each other, as shown in FIG.
Signals 116 and 117 frequency-converted around the
A difference signal 115 between the signal and the signal of 3 GHz is also generated. The difference signal 115 is a signal having a frequency component lower than the cutoff frequency of the low-pass filter 67. The difference signal 115 passes through the low-pass filter 67 and is output to the control circuit 58 as an approach detection signal. Accordingly, by detecting the output of the low-pass filter 67, the control circuit 58 can know that the wavelength λ2 is approaching the wavelength λ1.

Further, in this state, the light guided from the external modulation element 75 is modulated by a sine wave of 100 KHz, and when the light of the wavelength λ2 has a shorter wavelength than the light of the wavelength λ1, that is, when approaching from the higher frequency side. At this time, the output signal from the low-pass filter 67 is modulated by the sine wave signal generated from the sine wave generation circuit 74 so that the sine signal has a phase opposite to that of the sine signal.

On the other hand, when the light having the wavelength λ2 has a longer wavelength than the light having the wavelength λ1, that is, when approaching from the lower frequency side, the sine wave signal generated from the sine wave generation circuit 74 causes the sine wave signal to be in phase. Modulated.

Therefore, these signals are compared by the phase comparison circuit 68, and the comparison result is output to the control circuit 58, so that the control circuit 58 can know from which light the wavelength λ2 is approaching.

As a result, the wavelength of the output light from the tunable light source 71 is set to λ1 in a direction away from the approach wavelength so as not to interfere with the approach signal.
Can be moved continuously.

Next, the operation of the terminal 23 on the receiving side receiving the light of the wavelength λ1 will be described.

Similarly to the terminal 11, the terminal 23 includes an optical transceiver having the configuration shown in FIG. 4, and when in the receiving state, the light having the wavelength λ1 and the light having the wavelength λ2 which are incident from the transmission line are split / combined by the element 61. In a state where light is received. Here, in the terminal in the receiving state, the optical switch 73 is always in the “OFF” state, and light from the first external modulation element 72 cannot pass therethrough. For this reason, only the light from the transmission path received by the branching / joining element 61 reaches the optical joining element 61.

On the other hand, the control circuit 58 controls the wavelength variable light source 71 to output light having a wavelength substantially equal to the reception wavelength λ1. This light is modulated by the second external modulation element 75 and then reaches the optical convergence element 62.

In the optical convergence element 62, the signal light transmitted from the transmission path and received and branched by the branch / merge element 61 and the light from the second external modulation element 75 are mixed and sent to the photodetector 63. Heterodyne detection is performed by the photodetector 63, and a low-pass filter
Output to 64.

Since the wavelength difference between the signal light from the terminal 11 and the light from the tunable light source 71 is substantially “0”, the signal output from the photodetector 63 has the same frequency spectrum as the signal from the terminal 11, That is, the signal has a band of 1 MHz to 1 GHz. For this reason, a low-pass filter 64 with a cut-off frequency of 5 GHz
Can pass through.

Meanwhile, the light from the terminal 12 is the wavelength lambda _2, the light of the wavelength lambda ₁ and the wavelength λ2 is controlled so as not approach than 5GHz by the above-mentioned function of the terminal 11, and light from the wavelength light source 71 Beat signal low-pass filter 6 with light of wavelength λ ₂
4 can not pass.

The light that has passed through the second external modulation element 75 is
Because it is modulated at 100 KHz, the frequency spectrum at the point has a line spectrum at 100 KHzk frequency. For this reason,
Although the frequency spectrum of the point has a sideband at 100 KHz detuning from the 3 GHz signal, the signal from the terminal only occupies the 1 MHz to 1 GHz band as described above.
The information from the terminal 11 is not affected by the 100 KHz signal. Therefore, by passing the output signal from the low-pass filter 64 through a band-pass filter having a pass band of 1 MHz to 1 GHz, the signal from the terminal 11 can be received, and the control circuit 58 is connected to this signal. To the terminal device that received the signal.

Due to the interference avoidance function in the terminal 11, the wavelength λ1
Is changed, a wavelength difference occurs between the light generated from the wavelength variable light source 71 and the light transmitted from the terminal 11, and a beat signal is generated at the output of the photodetector 63. Control circuit 58
By controlling the oscillation wavelength of the tunable light source 71 so that the beat signal is not always generated, the signal can be continuously received following the fluctuation of the optical wavelength from the terminal 11. These controls are the same as those described above.

As described above, according to the present embodiment, a terminal in a transmission state can constantly detect and monitor the transmission light from the own terminal and the light from another terminal by homodyne / heterodyne detection. It is possible to reduce the wave difference between adjacent stations to a minimum of about 5 GHz in frequency conversion.

As a result, the wavelength multiplicity can be significantly increased.

Although the outline of the present invention has been described using the two embodiments, the application of the present invention is not limited to these embodiments.

First, in the above embodiment, the communication system using the star coupler shown in FIG. 1 has been described as an example. However, the present invention can be applied to any type of communication system such as a bus type, a star type, and a loop type. Can be implemented as long as the operation is performed.

Further, the present invention can be applied not only to an optical fiber as a transmission medium but also to a case using space propagation.

Further, the wavelength tunable light source and the wavelength tunable filter are not limited to those having the configuration exemplified in the embodiment, but may be any element having the same function.

Further, in the second embodiment, the oscillation frequency of the sine wave generation circuit, the low-pass filter, the local oscillation circuit and the like and the cutoff frequency will be described with specific figures, and the frequency band of the signal to be transmitted will be explicitly described. However, these are specific examples for the sake of simplicity of explanation, and any configuration of numerical values may be used as long as the configuration is based on the same principle. Clearly there is.

[Effects of the Invention] As described above, according to the present invention, it is possible to perform wavelength-division multiplexed optical communication having a large wavelength multiplicity without strictly stabilizing the emission wavelength. Even in this case,
With a simple configuration and operation, communication can be maintained while avoiding interference.

Also, when in the transmission state, by receiving the transmitted light from itself and the other light and comparing the wavelengths, it is possible to reduce the wavelength difference between adjacent optical communication devices on the wavelength. It is possible to dramatically increase the wavelength multiplicity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an optical communication system according to one embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of an optical transceiver of a terminal in the first embodiment of the present invention, and FIG. FIG. 4 is a diagram showing a relationship between transmission wavelengths of the wavelength tunable filter shown in FIG. 4, FIG. 4 is a block diagram showing a configuration of an optical transceiver of a terminal according to a second embodiment of the present invention, and FIGS. 6 (A) and 6 (B) are diagrams for explaining the frequency spectrum at the points shown in FIG. 4, and FIG. 5 is a diagram showing the frequency spectrum when the wavelength of the adjacent channel is not close. FIG. 6 is a diagram showing an example of a frequency spectrum when the wavelength of an adjacent channel approaches. In the figure, 11-1n, 21-2m ... terminal, 40,411-41n, 421-42m ...
Optical fiber, 31, 32 ... star coupler, 51, 71 ... variable wavelength light source, 53, 61 ... branching / combining element, 57 ... adjacent channel proximity detection circuit, 58 ... control circuit, 64, 67 ... low pass filter, 6
8: phase comparison circuit, 72, 75: external modulation element, 73: optical switch, 551 to 553: tunable filter, 63, 561 to 563: photodetector.

Continuation of front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H04B 10/00-10/28

Claims (10)

(57) [Claims] An optical communication device used in an optical communication system in which a plurality of optical communication devices are connected to each other, comprising: a wavelength-variable light source for transmitting an optical signal at a set wavelength; An optical signal and an optical signal transmitted from another optical communication device of the communication system, and an interference detection unit for detecting interference between these optical signals; and if the interference is detected by the interference detection unit, the light source Control means for changing the wavelength of the optical signal emitted by the optical communication device. 2. The apparatus according to claim 1, wherein said control means continuously changes the wavelength of the optical signal emitted from said wavelength tunable light source so as to keep away from the wavelength of the optical signal transmitted from another optical communication device. Item 2. The optical communication device according to item 1. 3. An optical communication device used in an optical communication system in which a plurality of optical communication devices are connected to each other, a wavelength tunable light source for transmitting an optical signal at a set wavelength, and a setting wavelength of the wavelength tunable light source. A first wavelength tunable filter that transmits light in a narrow wavelength range centered on a second wavelength tunable filter that transmits light in a narrow wavelength range centered on a wavelength slightly shorter than the set wavelength; A third wavelength tunable filter that transmits light in a narrow wavelength range centered on a wavelength slightly longer than the set wavelength, an optical signal emitted from the wavelength tunable light source, and an optical signal transmitted from another optical communication device And an optical element that causes the light to enter the first, second, and third wavelength tunable filters, respectively, and first, second, and second light that receive light transmitted through the first, second, and third wavelength tunable filters, respectively. Photodetection of 3 And detecting from the outputs of the second and third photodetectors that the wavelength of the optical signal emitted from the wavelength tunable light source and the wavelength of the optical signal transmitted from another optical communication device are close to each other. An optical communication apparatus, comprising: an approach detecting unit; and a control unit that changes a set wavelength of the variable wavelength light source when an approach is detected by the approach detecting unit. 4. An optical communication device used in an optical communication system in which a plurality of optical communication devices are connected to each other, comprising: a wavelength variable light source for transmitting an optical signal at a set wavelength; A first modulator that modulates a part of light according to a signal to be transmitted; and a first modulator that modulates another part of light emitted from the tunable light source.
A second modulator that modulates according to a signal having a frequency of: a part of an optical signal modulated by the first modulator, an optical signal transmitted from another optical communication device, and a second optical modulator An optical element that mixes the optical signals modulated by the optical element; a photodetector that detects the optical signal mixed by the optical element; and an output of the photodetector and an electric signal having a predetermined second frequency. A mixing unit, a filter that passes a low-frequency signal component distant from the vicinity of the second frequency in the electric signal mixed by the mixing unit, and a signal component that has passed through the filter. Control means for detecting that the wavelength of the emitted light and the wavelength of the optical signal transmitted from another optical communication device have approached, and changing the set wavelength of the light source when the approach is detected. Characteristic optical communication equipment. 5. The optical communication device according to claim 4, further comprising comparison means for comparing the phase of the signal component transmitted through the filter with the phase of the signal of the first frequency. 6. A sine wave generating means for generating a sine wave signal of the first frequency, and an optical modulator driven in accordance with a sine wave signal generated by the sine wave generating means. The optical communication device according to claim 4, comprising an element. 7. A low-pass filter for filtering a part of the output of the photodetector without mixing with an electric signal having a second frequency, and inputting the filtered signal to a control circuit. The optical communication device according to claim 4, wherein: 8. An optical communication method for performing communication using an optical communication system in which a plurality of optical communication devices are connected to each other, wherein a set is set between one set of the optical communication devices. A step of performing communication using light of a wavelength; a step of detecting interference between the communication between the pair of optical communication devices and the communication between the other optical communication devices; A step of avoiding interference by changing the wavelength of the optical signal. 9. The method according to claim 8, wherein in the process of avoiding the interference, the set wavelength is continuously changed so as to be away from a wavelength used for communication between other optical communication devices. Optical communication method. 10. An optical communication system in which a plurality of optical communication devices are connected to each other, wherein each of the optical communication devices emits an optical signal at a set wavelength and emits light from the light source. An interference detection unit that receives an optical signal and an optical signal transmitted from another optical communication device of the communication system and detects interference of these optical signals; and if the interference detection unit detects interference, the light source emits light. An optical communication system comprising: a control unit that changes a wavelength of an optical signal.