JP2833661B2 - Optical communication equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical communication device that performs optical communication with another device via an optical communication medium.

[Prior Art] The conventional wavelength division multiplexing optical communication system multiplexes light waves ranging from tens to hundreds of waves by changing the wavelength little by little, thereby enabling large-capacity communication. . To increase the communication capacity, it is important to stabilize the oscillation wavelength.

For this reason, several methods for stabilizing the oscillation wavelength have been proposed.

For example, a method has been proposed in which an oscillation frequency is individually assigned to each light source for transmission, and each terminal station manages the oscillation frequency.

As another method, a central office for managing frequency is provided, and the central office sends light as a predetermined reference to all the subscribers, and based on the reference light, each subscriber sets a wavelength. A tuning method has been proposed.

As a method of managing the frequency by the central station, there is a method described in, for example, JP-A-63-52528.

FIG. 6 is a block diagram showing the principle of the conventional central office managing the frequency, and FIG. 7 shows an example of the system configuration.

In FIG. 6, reference numeral 7010 denotes a frequency reference light extraction unit that separates frequency reference light from light transmitted from the central office, 7011 denotes a heterodyne detection unit that performs heterodyne detection on the frequency reference light, and 7012 denotes a local oscillator or a transmitter. 7013 is a tuner for setting the frequency of the light source 7012, 7014 is a peak detector for detecting the peak value of the beat signal obtained by the heterodyne detector 7011, and 7015 is for comparing the peak values of adjacent beats. Represents a frequency position detection unit that detects a frequency position.

As the frequency reference light, for example, an optical signal obtained by modulating the oscillation light of the stabilized light source at a high speed is sent from the central station to each terminal station, and each terminal station uses the frequency reference light from the light sent from the central station. The extraction unit 7010 extracts the frequency reference light.

The oscillation frequency of the light source 7012 is moved by the tuner 7013, and the output of the frequency reference light extraction unit 7010 and the output of the light source 7012 are mixed by the heterodyne detection unit 7011 to perform heterodyne detection.

The peak detector 7014 detects a peak value of the beat signal obtained by the detection by the heterodyne detector 7011. By changing the frequency of the light source 7012 by the tuner 7012, a plurality of peak values can be obtained.
By comparing the peak values of the adjacent beats, the frequency position detection unit 7015 can detect the number of the FM sideband at which the current tuning frequency is located.

In Figure 7, 7020 star coupler 7021 central office, 7022-1,7022-4 the terminal station subscriber, R _X is transmitting unit,
T _X is a receiving unit.

Each of the terminal stations 702-1 to 7022-4 is connected by an optical fiber via a star coupler 7020. Central office 7021
Are also connected via a star coupler 7020.

Then, frequency multiplex transmission using coherent light is performed, and the criterion for setting the frequency is determined by each of the terminal stations 7022 to 7022.
1-7022-4 do not manage individually, but the central office 7021
Centrally manages and sends a frequency reference to each of the terminal stations 702-1 to 7022-4.

 FIG. 8 shows an example of the arrangement based on the frequency.

At the central office 7021, when high-speed modulation of the oscillation light from the stabilization source for example in 10GH _Z ~50GH _Z, as shown in FIG. 8, around the center frequency _{f o, {f o ± nf} m} that sideband Appears.

Therefore, if these sidebands can be detected at the terminal station and the position of the sideband with respect to the center frequency can be determined, the frequency of the light source used for transmission or reception can be set based on the position.

For example, it is possible between the frequency f _o and the frequency f _o + f _m, sets a number of frequency bands K _o, K _l ... K _i of each station. Accordance connexion, when determining the frequency band of the received or transmitted, by detecting the frequency f _o + f _m at frequency reference light each station sends out, sets the frequency shifted by a predetermined frequency from these reference frequency do it.

[Problems to be Solved by the Invention] However, in the above conventional example, since the frequency band used by each optical transmitter must be strictly managed and set in order to avoid interference, there are the following disadvantages. Was.

(1) When each optical transmitter individually has a reference wavelength light source, it is necessary to precisely control the light emitting element temperature and the like of each optical transmitter and maintain the same reference wavelength.

(2) Also, if a wavelength to be used is previously assigned to each optical transmitter, each optical transmitter cannot use the wavelength assigned to another optical transmitter, and the use efficiency of the wavelength decreases.

[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 means for solving the above problems.

That is, a transmitting means for transmitting any one wavelength out of the entire wavelength range commonly used by all devices connected to the network, and an arbitrary one which is the same as or different from the transmitting wavelength of the transmitting means. An optical communication device having at least receiving means for receiving a wavelength and connected to an optical communication network connected to each other via an optical communication medium, wherein the optical communication device is used in common when transmission is desired. First wavelength finding means for finding an unused first wavelength from the entire wavelength range to be transmitted, and transmitting a call signal to a transmission destination using the first wavelength found by the first wavelength finding means. Call signal transmitting means for continuing, confirmation signal detecting means for detecting a confirmation signal from the other party to a call signal transmitted by the call signal transmitting means from a wavelength band other than the first wavelength, and not in a communication state, and Do not want to send Sometimes, a call signal detecting means for finding a call signal addressed to the own device from a device desired to be transmitted, and a second signal for finding a second wavelength not used in the entire wavelength band commonly used by all devices. And a acknowledgment signal transmitting means for transmitting an acknowledgment signal for a call signal addressed to the own device using the second wavelength found by the second wavelength finding means.

[Operation] In the above configuration, when performing communication, the terminal has a function of grasping the usage status of the wavelength over the entire wavelength band commonly used by all the terminals, and the terminal desiring to transmit,
According to the above function, a first unused wavelength can be found, and a call signal for specifying a receiving terminal can be transmitted using the unused wavelength.

When a terminal desiring to transmit is designated as a receiving terminal, it knows that the own station is designated as a receiving terminal by the above function, and then finds a second unused wavelength by using the function. By using the second unused wavelength, it is possible to transmit a signal for notifying the terminal desiring to transmit that the preparation for reception is completed.

Further, when transmission is desired, the signal is received by the above function, and thereafter, transmission of information is started from the terminal desiring transmission to the receiving terminal using the first unused wavelength or the second unused wavelength. be able to.

This solves the problem of the conventional example, and enables wavelength-division multiplexing communication with high wavelength use efficiency without requiring a strict reference wavelength control station or the like.

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

1 and 2 are diagrams showing an embodiment according to the present invention. FIG. 1 is a system configuration diagram showing the whole wavelength division multiplexing optical communication system constituted by the devices according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the optical transmitter / receiver of each terminal which is the optical communication device of the present embodiment.

In FIG. 1, 11-1n and 21-2m are optical communication terminals, and 40,411-41.
n, 421 to 42 m are optical fibers that are optical transmission lines, 31, 3
2 is an optical star cutlery.

In FIG. 2, reference numeral 51 denotes a control circuit for controlling the entire embodiment, 52 denotes a variable wavelength light source, 53 denotes an optical isolator,
54 is a photodetector, 55 is a tunable bandpass filter capable of changing the wavelength range of transmitted light, 56 is an optical branching / combining element composed of, for example, a half mirror or a beam splitter, and 57 is a terminal device Reference numerals 58 denote transmission lines formed of optical fibers for performing optical communication.

In the above configuration, the control circuit 51 transmits the information from the terminal device 57 to the transmission line 58, and outputs the information from the transmission line 58 to the terminal device 57 by using the semiconductor laser 52, the tunable filter 55, The operation of the detector 54 is controlled.

The tunable light source 52 has, for example, a DBR (Distributed Reflection Mirror) region in which a carrier is injected into a DBR (Distributed Reflection Mirror) region to change the Bragg wavelength.
It is composed of a BR semiconductor laser, and its oscillation wavelength can be continuously changed by adjusting the amount of carrier injected into the DBR region. This tunable light source
51, for example, K.KOTAKI, M.MATSUDA, M.YANO, H.IS
Electroniccs Letters 1987 by IKAWA, H.IMAI
Structures described in Vol. 23, No. 7, pp. 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 filter 55 is a tunable DBR (distributed reflection type Bragg mirror) (for example, the one described in Japanese Patent Application Laid-Open No. 60-175025) which changes its Bragg wavelength by the above-described carrier injection. Which can be used).

Next, the operation of the present embodiment having the above configuration will be described.

As shown in FIG. 3, each terminal transmits from the wavelength λ _A to the wavelength λ _B
And the width of the transmission spectrum of the bandpass filter is Δλ. When a plurality of communications are performed within the width of Δλ, interference occurs.
Only a single communication can be included in the width of λ.

Now, for example, consider a case where communication from the terminal 12 to the terminal 23 is started.

In this embodiment, this communication is started by the following procedure.

A terminal (including the terminal 23) that is not in a communication state and does not want to transmit always sweeps the wavelength from the wavelength λ _A to the wavelength λ _B by using the wavelength variable filter, and receives a signal to transmit the signal to its own station. It is checking whether a call signal has not been issued.

Desired transmission terminal 12, a photodetector 54 of its own terminal to the light receiving state, by sweeping the transmission wavelength of the tunable filter 55 from lambda _A to lambda _B, examines the use states of the wavelength in all wavelengths available , The first among the unused wavelengths
To select a wavelength λ _1.

Next, the transmission requesting terminal 12 uses this wavelength λ ₁ to
The transmission of a call signal including information for identifying the terminal 12 and the destination terminal 23 is started.

At the same time, the signal is received by sweeping between the wavelengths λ _A and λ _B by the wavelength tunable filter 55, and it starts to check whether or not a confirmation signal for the transmitted call signal has been returned.

The terminal 23 recognizes that a call signal to its own station has been issued by the above process, and prepares for reception.

First, the wavelength range from λ _A to λ _B is examined to find a _second wavelength λ ₂ that is not used. Thereafter, a confirmation signal including the information indicating the completion of reception preparation and that it has received the call signal begins transmitting using the second wavelength lambda ₂ which are not used.

The terminal 12 can know that the preparation of the destination terminal 23 is completed by receiving the confirmation signal sent from the destination terminal in the process.

Since communication preparation in this is complete, the after using the wavelength lambda _1, it starts to transmit the information to the counterpart terminal.

In the present embodiment, it is possible to start communication by selecting an unused wavelength from the entire available wavelength range by the above procedure.

In the above procedure, for example, when the terminal 23 is in a communication state and cannot receive a call signal from the terminal 12, when there is no second wavelength that is not used, or when the terminal 23 In some cases, communication between the terminals 12 and 23 cannot be started, for example, when terminals other than 12 that desire to transmit transmit a call signal at the same time.

In preparation for such a case, when the terminal 12 does not receive the confirmation signal within a preset time from the start of oscillating the call signal, the terminal 12 stops transmitting the call signal and starts the procedure again. It is good if you put on.

As is clear from the above description, in this embodiment,
Wavelength multiplexing optical communication can be realized without strict management of the reference wavelength and control of the absolute value of the wavelength.

Further, the multiplicity can be set to the number of channels obtained by dividing substantially the entire usable wavelength range by the width of the transmission spectrum of the bandpass filter.

Therefore, wavelength multiplexing with very high efficiency can be performed.

[Other Embodiments] A second embodiment according to the present invention will be described below with reference to FIGS. 4 and 5. FIG.

FIG. 4 is an overall system diagram of the wavelength division multiplexing communication system of the second embodiment according to the present invention.

In FIG. 4, 43 is an optical fiber transmission line, 61 to 6n are terminals, 71 to 7n are transmitting optical signals from the terminals 61 to 6n to the optical fiber transmission line, and are one of the optical signals on the optical fiber transmission line. Optical nodes 81 and 82, which send out the units to the terminals, are terminating devices that prevent optical signals from being reflected at the end of the optical fiber transmission line.

FIG. 5 is a block diagram showing a configuration of an optical transceiver of a terminal used in the system of the second embodiment shown in FIG.

In the figure, 51 is a control circuit, 52 is a first variable wavelength light source, 53 is an optical isolator, 56 is an optical branching / combining element, and 57 is a terminal device. These components are described in the above-described first embodiment. The same one as described above can be used.

7 is an optical node, 43 is an optical fiber transmission line,
By using these, it is possible to take the form of a bus-type network shown in FIG.

Further, in FIG. 5, reference numeral 91 denotes a low-pass filter for electric signals, 92 denotes a photodetector, 93 denotes an optical converging element, and 94 denotes a second
Wavelength tunable light source.

In this embodiment, the procedure for starting communication is basically the same as that in the first embodiment. The difference from the first embodiment is that the received signal is swept over the entire usable wavelength range to find unused first and second wavelengths, a call signal to the terminal itself, and a confirmation signal. Is in the part that seeks out.

These means in the present embodiment are called optical heterodyne detection, and will be described in detail below.

The wavelength multiplexed signal transmitted through the optical fiber transmission line 43 reaches the optical multiplexing device 93 via the node 7 and the branching / combining device 56, where it is mixed with the light from the second tunable light source 94 to detect light. The input signal is input to the detector 92 and square-detected, whereby an electric signal obtained by heterodyne detection of the two lights is output to the low-pass filter 91.

When there is no light on the line, the signal output from the photodetector 92 is only DC.

When an optical signal is present on the line, an electric signal (beat signal) having a frequency equal to the difference between the frequency of the light on the line and the frequency of the light of the second variable wavelength light source 94 is output. For example, when the wavelength of the light of the wavelength variable light source 94 is 880 nm and the light on the line is 881 nm, a beat signal of about 386 GHz is output.

This beat signal is filtered by a low-pass filter 91 for the electric signal and input to the control circuit 51. Assuming that the cut-off frequency of the low-pass filter 91 is 2 GHz and the wavelength of the wavelength variable light source 94 is 880 nm, it has the same effect as providing an optical filter having a half width of 0.011 nm width centered on the wavelength 880 nm. Become.

The wavelength of the wavelength tunable light source 94 is swept from the entire usable wavelength range λ _A to λ _B shown in FIG. 3 and the output from the low-pass filter 91 is detected, so that unused wavelengths and calls to the own station are detected. Signals and confirmation signals can be found.

As is clear from the above description, the bandwidth of the wavelength used for one communication in the present embodiment is almost the same as the bandwidth of the low-pass filter, and compared with the wavelength-tunable band-pass filter used in the first embodiment. Can be significantly reduced.

As a result, in this embodiment, it is possible to further increase the wavelength multiplicity than in the first embodiment.

Although the contents of the present invention have been described using the first and second embodiments, the scope of the present invention is not limited to these two examples. For example, the optical heterodyne detection system described in the second embodiment can be used for the network configuration shown in the first embodiment, and the reverse application configuration can be realized.

In the first embodiment, an example is described in which the first wavelength λ ₁ not used for transmitting information is used. However, it is also possible to use λ ₂ of the second wavelength which is not used for this. ,
Simultaneous two-way communication can be performed using both wavelengths λ ₁ and λ ₂ .

Further, in the above embodiment, a semiconductor laser is used as a light source as a basic light source. However, the present invention is not limited to the above example, and any light source that emits light corresponding to an input electric signal, such as a gas laser, a solid laser, and a dye laser, may be used. Of course, it is possible to use those.

Furthermore, these light sources do not emit light in response to an input signal, but may continuously emit light, and may modulate the laser light using a modulator provided outside.

In the above embodiments, each optical transmitter, optical receiver, and optical transceiver are configured using semiconductor elements. However, it is needless to say that other optical components having the same effect are used. It is clear that this is good.

[Effects of the Invention] As described above, according to the present invention, a means for finding an unused wavelength from the entire wavelength range usable for each terminal performing wavelength division multiplexing optical communication, a call signal for the own terminal, Alternatively, by providing means for finding a confirmation signal, wavelength multiplexing optical communication with high multiplicity and high wavelength use efficiency can be performed without strict reference wavelength or absolute wavelength management. Natsuta

[Brief description of the drawings]

FIG. 1 is an overall system diagram of a first embodiment according to the present invention, FIG. 2 is a block diagram of an optical transceiver of the first embodiment, and FIG. 3 is a diagram of wavelengths used for communication in the first embodiment. FIG. 4 is a diagram showing an assignment state, FIG. 4 is an overall view of a system according to a second embodiment of the present invention, FIG. 5 is a block diagram of an optical transceiver according to the second embodiment, and FIGS. FIG. 4 is a diagram illustrating an example of an optical communication device. In the figure, 11-1n, 21-2n, 61-6n ... Terminal, 40-43, 411-41
n, 421-42n ... optical fiber, 31,32 ... star cutler, 71-71n ... optical node, 51 ... control circuit, 52,94 ...
Tunable light source, 53… isolator, 54, 92… photodetector, 55… tunable bandpass filter, 56… optical branching / combining element, 57… terminal equipment, 58… optical transmission line, 91 ......
An electric low-pass filter 93 is a merging element.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 10/08 H04B 10/12-10/158 H04B 10/20-10/213

Claims (4)

(57) [Claims] 1. A transmitting means for transmitting an arbitrary wavelength in an entire wavelength range commonly used by all devices connected to a network, and a transmitting wavelength equal to the transmitting wavelength of the transmitting means.
Or an optical communication device having at least receiving means for receiving a different arbitrary one wavelength and connected to an optical communication network connected to each other via an optical communication medium, and A first wavelength finding means for finding an unused first wavelength from the common wavelength range, and a transmission destination using the first wavelength found by the first wavelength finding means. A call signal transmitting unit for continuously transmitting a call signal to the communication device; a confirmation signal detecting unit for detecting a confirmation signal from the other party to the call signal transmitted by the call signal transmission unit from a wavelength band other than the first wavelength; When it is not in a state and does not want to transmit, it is used in a call signal detecting means for finding a call signal addressed to its own device from a device that wants to transmit, and is used in all wavelength bands commonly used by all devices. Not first A second wavelength discovering means for finding the wavelength of the second signal, and a confirmation signal transmitting means for transmitting a confirmation signal for the call signal addressed to the own device using the second wavelength found by the second wavelength finding means. An optical communication device, comprising: 2. The method according to claim 1, wherein the first wavelength finding means or the second wavelength finding means changes the transmission band of the tunable bandpass filter over the common wavelength band. 2. The optical communication device according to claim 1, wherein a wavelength that is not used is detected. 3. A method according to claim 2, wherein said call signal detecting means or said acknowledgment signal detecting means detects a desired signal by receiving a signal while changing a transmission band of the variable bandpass filter. 2. The optical communication device according to claim 1. 4. The apparatus according to claim 1, wherein said first and second wavelength finding means, call signal detecting means, and acknowledgment signal detecting means find a desired signal using an optical heterodyne detection method. Equipment.