JPH03214831A - Optical communication equipment - Google Patents

Abstract

PURPOSE:To eliminate the need for strict management of a reference wavelength and an absolute wavelength by providing a means to find out a wavelength not in use from an entire wavelength region and a means finding out a call signal or a confirmation signal to its own terminal equipment. CONSTITUTION:A transmission desiring terminal equipment 12 sweeps a transmission wavelengths lambdaA-lambdaB a wavelength variable filter 55 to check the operating state of a wavelength in the entire available wavelength area and to select a 1st wavelength lambda1 among wavelengths not in use. Then the terminal equipment 12 uses the wavelength lambda1 starts sending a call signal including information to identify its own terminal equipment 12 and a destination terminal equipment 23 by using the wavelength lambda1. The terminal equipment 23 recognizes a call signal to its own station to prepare the reception. At first, the wavelength area from lambdaA to lambdaB is checked to find out a 2nd wavelength lambda2 not in use. Then a confirmation signal including the information of starting reception of the call signal and of end of reception preparation is sent by using the wavelength lambda2. The terminal equipment 12 recognizes the finished preparation of the terminal equipment 23 by receiving the confirmation signal and uses the wavelength lambda1 to start the transmission of the information to the destination terminal equipment.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical communication device that performs optical communication with other devices via an optical communication medium.

[Prior Art] Conventional wavelength division multiplexing optical communication systems enable large-capacity communication by multiplexing dozens to hundreds of light waves by changing their wavelengths little by little and sending them. When increasing communication capacity, it is important to stabilize the oscillation wavelength.

For this reason, several methods have been proposed to stabilize the oscillation wavelength.

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.

Another method is to install a central station that manages frequencies, and the central station sends a predetermined reference light to all subscribers, and each subscriber uses the reference light to A method of tuning the wavelength has been proposed.

As a method for this central station to manage frequencies, there is, for example, the method described in Japanese Patent Laid-Open No. 63-52528.

FIG. 6 shows a block diagram of the principle of this conventional method for central station frequency management, and FIG. 7 shows an example of the system configuration.

In FIG. 6, 7.010 is a frequency reference light extraction unit that separates the frequency reference light from the light sent from the central station;
0l1 is a heterodyne detection unit that performs heterodyne detection on the frequency reference light, 7012 is a light source for local oscillation or transmission, 7013 is a tuner that sets the frequency of the light source 7012, and 7014 is a signal obtained by the heterodyne detection unit 7011. 7015 represents a frequency position detection unit that detects a frequency position by comparing peak values of adjacent beats.

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

A tuner 7013 moves the oscillation frequency of the light source 7012, and a heterodyne detection section 7011 mixes the output of the frequency reference light extraction section 7010 and the output of the light source 70l2 to perform heterodyne detection.

The peak detection section 7014 detects the peak value of the beat signal obtained by the detection by the heterolog detection section 7011. By the tuner 7012, the light source 701
By changing the frequency of 2, a plurality of peak values can be obtained. However, by comparing the peak values of each adjacent beat, the frequency position detection unit 7015 determines which FM the currently tuned frequency is. It is possible to detect whether it is a side band.

In FIG. 7, 7020 is a star coupler, 7021 is a central station, 7022-1.7022-4 is a terminal station of a subscriber system, Rx is a transmitter, and Tx is a receiver.

Each terminal station 7022-1 to 7'022-4 is connected by an optical fiber via a star coupler 7020. Further, the central office 7021 is also connected via a star coupler 7020.

Frequency multiplexing transmission using coherent light is performed, but the standard for frequency setting is set at each terminal 7022.
-1 to 7022-4 are not individually managed, but the central office 7o21 centrally manages each terminal station 7022-1 to 7022-4.
The frequency reference is sent to 7022-4.

FIG. 8 shows an example of the arrangement of the frequency standards.

In the central station 702l, when the oscillation light from the stabilized light source is high-speed modulated at, for example, 10 GHz to 50 GHz, the center frequency f as shown in FIG. Around {
t'o±nf. } sideband appears.

Therefore, if the terminal station can detect these sidebands and determine the position of the sideband with respect to the center frequency, the frequency of the light source used for transmission or reception can be set using that position as a reference.

For example, the frequency f. and the frequency fo +fffl, the frequency bands Ko, K+...K. can be set multiple times. Therefore, when determining the frequency band for reception or transmission, the frequency f in the frequency reference light transmitted by each terminal station. By detecting +fm, a frequency shifted by a predetermined frequency from these reference frequencies may be set.

[Problems to be Solved by the Invention] However, in the conventional example described above, the frequency band used by each optical transmitter must be strictly managed and set in order to avoid interference, resulting in the following drawbacks. Ta.

(1) When each optical transmitter has an individual reference wavelength light source, the temperature of the light emitting element of each optical transmitter must be precisely controlled to maintain the same reference wavelength.

(2) Furthermore, if wavelengths to be used are assigned in advance to each optical transmitter, each optical transmitter cannot use the assigned wavelengths of other optical transmitters, resulting in a decrease in wavelength usage efficiency.

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

In other words, a transmitter that transmits any one wavelength out of the entire wavelength range that is commonly used by all devices connected to the network, and whether the wavelength transmitted by the transmitter is the same or if
is an optical communication device that is connected to an optical communication network that is connected to an optical communication network that is connected to each other via an optical communication medium, and that when a transmission is desired, the a first wavelength discovery means for discovering an unused first wavelength from all commonly used wavelength ranges; a call signal transmitting means for continuously transmitting a call signal; a confirmation signal detecting means for detecting a confirmation signal from a called party in response to a call signal transmitted by the call signal transmitting means from a wavelength range other than the first wavelength; If the device does not have a call signal and does not wish to transmit, there is a call signal inspection means that detects the call signal addressed to the device from the device that wishes to transmit, and a call signal detection means that detects the call signal addressed to the device itself from the device that wishes to transmit, and if it is not used in all wavelength ranges that are commonly used by all devices. a second wavelength finding means for finding a second wavelength;
and confirmation signal transmitting means for transmitting a confirmation signal for a call signal addressed to the device itself using the second wavelength discovered by the wavelength discovery means.

[Operation] In the above configuration, when performing communication, all terminals have a function to grasp the usage status of wavelengths over the entire wavelength range commonly used, and a terminal desiring to transmit can use the function to It is possible to find an unused wavelength of , and use the unused wavelength to transmit a call signal for identifying the receiving terminal.

When a terminal desiring to send transmits a message, it learns that it has been designated as a receiving terminal by the above function, and then uses the above function to transmit a second terminal.
It is possible to find an unused wavelength of the second unused wavelength, and to use the second unused wavelength, to transmit a signal to the terminal desiring to transmit that it is ready for reception.

Furthermore, when a transmission is desired, the function receives this signal and then starts transmitting information from the desired transmission terminal to the receiving terminal using the first unused wavelength or the second unused wavelength. be able to.

This solves the problems of the conventional example and enables wavelength multiplexing communication with high wavelength utilization efficiency without requiring strict reference wavelength management cycles.

[Example] Hereinafter, an example according to the present invention will be described in detail with reference to the drawings.

1 and 2 are diagrams showing one embodiment of the present invention, and FIG. Figure 2 shows the optical transmission and
FIG. 2 is a block diagram showing the configuration of a receiver.

In Fig. 1, 1 1 to 1 n, 21 to 2 m are optical communication terminals,
40, 41 1 to 41n, 421 to 42m are optical fibers which are optical transmission lines, and 31.32 is an optical star coupler.

Further, in FIG. 2, 51 is a control circuit that controls the entire embodiment, 52 is a variable wavelength light source, 53 is an optical isolator, 54 is a photodetector, and 55 is a control circuit that controls the entire wavelength range of transmitted light. A variable wavelength band pass filter 56 is an optical branching/combining element composed of, for example, a half mirror or a beam splinter, 57 is a terminal device, and 58 is a transmission line made of an optical fiber for optical communication.

In the above configuration, the control circuit 5l transmits information from the terminal device 57 to the transmission path 58, and outputs information from the transmission path 58 to the terminal isoki 57 by using the semiconductor laser 52, the wavelength variable filter 55, The operation of the photodetector 54 is controlled.

Further, the wavelength variable light source 52 is a DBR (distributed reflection mirror) having a structure that can change the Bragg wavelength by injecting carriers into a DBR (distributed reflection mirror) region, for example. It is composed of a wavelength tunable DBR semiconductor laser having an R mirror, and its oscillation wavelength can be continuously changed by adjusting the amount of carriers injected into the DBR region. As this wavelength variable light source 51, for example. K. KOT
AKI, M. MA: rSUDA, M.A. YANO,H
．． ISIKAWA, l{. The structure described by IMAI in Electronics Letters, Vol. 23, No. 7, pp. 325-327, published in 1987 can be used.

Here, it is assumed that the variable wavelength light source 51 is composed of a wavelength adjustment section that changes the oscillation wavelength thereof and an output light modulation section that modulates the intensity of output light.

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

Furthermore, the wavelength tunable bandpass filter 55 may be a wavelength tunable DBR (distributed reflection type Bragg mirror) (for example, the one described in Japanese Patent Laid-Open No. 175025/1983) that changes its Bragg wavelength by carrier injection as described above. This can be achieved by using

Next, the operation of this embodiment having the above configuration will be explained.

As shown in Figure 3, each terminal has a different wavelength. It is assumed that a wavelength range from λB to λB can be used, and the width of the transmission spectrum of the bandpass filter is Δλ. If multiple communications occur within this △ range, interference will occur, so △λ
Only a single communication can fit within the width of .

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.

■Terminals that are not in communication status and do not wish to transmit (including terminal 23) always sweep the range from wavelength λ8 to wavelength λ8 using a variable wavelength filter, and receive signals to send signals to their own station. Checking to see if a call signal is being issued.

(2) The terminal 12 desiring transmission puts its own photodetector 54 into a light receiving state, and sets the transmission wavelength of the variable wavelength filter 55 to λ. from λ
, to check the usage status of wavelengths in the entire usable wavelength range, and select the first wavelength λ1 from the unused wavelengths.

Next, the terminal 12 desiring to transmit starts transmitting a call signal containing information for identifying its own terminal 12 and the destination terminal 23 using this wavelength λ.

At the same time, the variable wavelength filter 55 sweeps between wavelengths λ1 and λ, receives signals, and begins checking whether or not a confirmation signal for the call signal being transmitted has been returned.

(2) The terminal 23 recognizes that a call signal is being sent to its own station through the process (2) above, and prepares for reception.

First, the wavelength range from λ^ to λ8 is examined to find an unused second wavelength λ2. After that, it starts transmitting a confirmation signal containing information that the call signal has been received and that reception preparations have been completed, using the unused second wavelength λ3.

(2) The terminal 12 can know that the other party's terminal 23 is ready by receiving the confirmation signal sent from the other party's terminal in the process (2).

Now that the communication preparations are complete, the terminal starts transmitting information to the other party's terminal using the wavelength λ.

In this embodiment, through the procedure described above, it is possible to select an unused wavelength from the entire available wavelength range and start communication.

In the above procedure, for example, if the terminal 23 is in a communication state and cannot receive a call signal from the terminal 12, or if there is no unused second wavelength, or if the terminal Communication may not be able to start between terminal 12 and terminal 230, such as when terminals other than terminal 12 that wish to transmit call signals are issued at the same time.

In preparation for such a case, if the terminal 12 does not receive a confirmation signal within a preset time after starting to emit a call signal, the terminal 12 has a function to stop transmitting the call signal and start the above procedure again. It is good if you add .

As is clear from the above description, in this embodiment, wavelength division multiplexing optical communication can be realized without strictly managing the reference wavelength or controlling the absolute value of the wavelength.

Further, the multiplicity can be approximately the number of channels equal to the entire usable wavelength range divided by the width of the transmission spectrum of the bandpass filter.

This makes it possible to perform wavelength multiplexing with very high efficiency.

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

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

In FIG. 4, 43 is an optical fiber transmission line, 61 to 6n
71 to 7n are terminals, 71 to 7n are optical nodes that send optical signals from terminals 61 to 6n to optical fiber transmission lines, and part of the optical signals on the optical fiber transmission lines to the terminals, and 81.82 is optical fiber transmission. This is a termination device that prevents optical signals from being reflected at the roadside.

FIG. 5 is a block diagram showing the configuration of an optical transceiver of a terminal used in the second embodiment system shown in FIG. 4.

In the figure, 5l is a control circuit, 52 is a first wavelength variable light source, 5
3 is an optical isolator, 56 is an optical branching/combining element, and 57 is a terminal device, and each of these components can be the same as those described in the first embodiment.

Further, 7 is an optical node, 43 is an optical fiber transmission line,
By using these, a bus type network shown in FIG. 4 can be formed.

Furthermore, in FIG. 5, 91 is a low-pass filter for electric signals, 92 is a photodetector, 93 is a light combining element, and 94
is the second wavelength tunable light source.

In this embodiment as well, the procedure for starting communication is basically the same as in the first embodiment. The difference from the first embodiment is that the received signal is swept over the entire usable wavelength range,
This involves finding unused first and second wavelengths, and searching for a call signal or confirmation signal to the own terminal.

These means in this embodiment are called optical heterogeneous detection, and will be explained in detail below.

The wavelength multiplexed signal transmitted through the optical fiber transmission line 43 is sent to the optical merging element 93 via the node 7 and the branching/merging element 56.
, where it is mixed with the light from the second wavelength tunable light source 94 and input to the photodetector 92! By performing square law detection, the electrical signals obtained by heterodyne detection of the two lights are output to the low-pass filter 9l.

When there is no light on the line, the signal output from the photovoltaic detector 92 is only direct current.

Further, when there is an optical signal on the line, an electric signal (beat signal) having a frequency that is the difference between the frequency of the light on the line and the frequency of the light from the second wavelength tunable light source 94 is output. For example, the wavelength of the light from the wavelength tunable light source 94 is 880 nm.
If the light on the line is 881 nm, it is about 386 GH
The Z beat signal will be output.

This beat signal is filtered by a low-pass filter 91 for electrical signals and input to the control circuit 5l. Suppose that the cutoff frequency of this low-pass filter 91 is set to 2G.
Hz and the wavelength of the wavelength tunable light source 94 is 880 nm, it will have the same effect as providing an optical filter having a half width of 0.011 nm around the wavelength of 880 nm.

The wavelength of the wavelength tunable light source 94 is swept over the entire usable wavelength range from λ to λ8 shown in FIG.
By detecting the output from the station, it is possible to find unused wavelengths and call signals and confirmation signals for the own station.

As is clear from the above explanation, the wavelength bandwidth used for one communication in this example is comparable to the bandwidth of the low-pass filter, and is comparable to the wavelength tunable band-pass filter used in the first example. It can be made much narrower.

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

Although the content of the present invention has been explained above using the first and second embodiments, the scope of application of the present invention is not limited to these two examples. For example, it is possible to use the optical heterogeneous detection method described in the second embodiment in the network configuration shown in the first embodiment, and the opposite application mode can also be realized.

In addition, in the first embodiment, an example was written in which the first wavelength λ1, which is not used for information transmission, is used, but it is also possible to use the second wavelength λ2, which is not used. It is also possible to perform simultaneous bidirectional communication using both wavelengths λ2 and λ2.

Furthermore, in the above embodiments, a semiconductor laser was used as the light source, but the light source is not limited to the above examples. Of course, any one can be used.

Further, these light sources do not emit light in response to an input signal, but may be configured to continue emitting light constantly and modulating this laser light using an external modulator.

Furthermore, in the above embodiments, each optical transmitter, optical receiver, and optical transceiver are configured using semiconductor elements, but
Of course, it is obvious that other optical components having similar effects may be used.

[Effects of the Invention] As explained above, according to the present invention, each terminal that performs wavelength division multiplexing optical communication has a means for finding an unused wavelength from among the entire wavelength range available to the terminal, and a method for making calls to the own terminal. By providing a means to find a signal or confirmation signal, it is possible to perform wavelength division multiplexing optical communication with high multiplicity (wavelength division multiplexing) with high wavelength usage efficiency without strict reference wavelength or absolute wavelength management. Became.

Fig. 1 is an overall system diagram of the first embodiment of the present invention, Fig. 2 is a block diagram of the optical transceiver of the first embodiment, and Fig. 3 is a diagram of the wavelength used for communication in the first embodiment. A diagram showing the allocation state, FIG. 4 is an overall system diagram of the second embodiment of the present invention, FIG. 5 is a block diagram of the optical transceiver of the second embodiment, and FIGS. 6 to 8 are conventional diagrams. FIG. 2 is a diagram illustrating an example optical communication device.

In the figure, 1 1 - l n, 2 1 - 2 n, 6 1 - 6 terminals, 40 - 43, 4 1 1 - 4 1 n, 4 2 1 - 4 2 n... optical fiber, 3 1 3 2...・Star cup, 7 1 to 7 1 n... Optical node, 5 l... Control circuit, 5 2 9 4... Tunable wavelength light source, 5 3... Isolator, 54.92... Optical detector, 55... Variable wavelength band pass filter, S6... Optical branching/merging element, 57
Terminal equipment, 58 Optical transmission line, 9l Electrical low-pass filter, 93 Merging element.

Patent applicant

Claims (4)

[Claims] (1) A transmission means that transmits any one wavelength out of the entire wavelength range commonly used by all devices connected to the network, and any one wavelength that is the same as or different from the transmission wavelength of the transmission means. An optical communication device that is connected to an optical communication network that is connected to each other via an optical communication medium, and that is used in common when transmission is desired. A first wavelength discovery means for discovering a first wavelength that is not used from the entire wavelength range, and a call signal to a transmission destination using the first wavelength discovered by the first wavelength discovery means. and confirmation signal detection means for detecting a confirmation signal from the other party in response to the call signal transmitted by the call signal transmission means from a wavelength range other than the first wavelength, and is not in a communication state, and When transmission is not desired, there is a call signal detecting means for detecting a call signal addressed to the device from the device desiring to transmit, and a second wavelength that is not used in the entire wavelength range that is commonly used by all devices. It is characterized by comprising a second wavelength discovering means for discovering a wavelength, and a confirmation signal transmitting means for transmitting a confirmation signal for a call signal addressed to the own device using the second wavelength discovered by the second wavelength discovering means. optical communication equipment. (2) The first wavelength finding means or the second wavelength finding means is used by changing the transmission band of the variable bandpass filter over the entire commonly used wavelength range. 2. The optical communication device according to claim 1, wherein the optical communication device detects a wavelength that is not detected. (3) The call signal detection means or the confirmation signal detection means finds a desired signal by receiving the signal while changing the transmission band of a variable bandpass filter. Optical communication equipment described in section. (4) The device according to claim 1, wherein the first and second wavelength discovery means, call signal detection means, and confirmation signal detection means discover the desired signal using an optical heterodyne detection method. .