JP2685569B2 - Terminal - Google Patents

Description

The present invention relates to a terminal station used in an optical network communication system.

[Prior Art] In the wavelength multiplexing method used for communication by multiplexing lights of different wavelengths on the same communication path or the frequency multiplexing method in coherent optical communication, the wavelength of the signal light is kept constant or It is necessary to prevent crosstalk by controlling the wavelength of the signal light at a constant interval. For this purpose, a method of setting a light source having a reference wavelength and setting operating wavelengths of other optical elements based on the reference wavelength is adopted. In an optical multiplex communication system or the like of an optical network, it is difficult for each terminal station to have a light source of a reference wavelength so that the wavelengths of the light sources of the reference wavelengths match. In addition, since the cost of the terminal station increases, a center station is installed, a light source of the reference wavelength is placed there, and the reference wavelength is transmitted from the light source of the reference wavelength of the center to each terminal station on the network by the multiplex communication method. The method of doing is proposed.

FIG. 7 is a schematic diagram showing an optical network communication system. 101 is an optical transmission line, which is an optical fiber. 1
02 is a center station in which a reference wavelength light source is located. 103a
˜103d are optical couplers. Each of 104a to 104d is a connection line that connects each of the terminal stations 105a to 105d and the corresponding optical coupler, and is composed of an optical fiber or an optical waveguide.

In addition to the signal light, the reference wavelength light from the center station 102 propagates in the optical transmission line 101. Signal light or reference wavelength light in the optical transmission line 101 is connected from the optical couplers 103a to 103d to the connection line 104a.
... 104d, is taken in, is made incident on the terminal stations 105a ... 105d, and signal processing is performed in each terminal station.

Further, the signal lights transmitted from the terminal stations 105a to 105d pass through the connection lines 104a to 104d and are sent out into the optical transmission line 101 via the optical couplers 103a to 103d. The signal light multiplexed on the optical transmission line 101 is uniquely taken into the center station and processed. In the terminal stations 105a to 105d, using the reference wavelength A transmitted from the center station 102, control can be performed to keep the wavelengths of the optical elements in the terminal station, that is, the signal light source and the light source and the optical heterodyne detection station light source constant. Has been done.

[Problems to be Solved by the Invention] However, in the above conventional example, the reference wavelength light is transmitted from the center station to each terminal station by the multiplex communication system, and each terminal station determines the operating wavelength of each optical element to the reference wavelength light. It is based on. The processing for matching the wavelengths is performed between the centimeter station and the terminal station when the terminal stations of the optical network communication system are not communicating. Therefore, when the optical network communication system is used, there is a drawback that the network communication utilization efficiency decreases.

In addition, when performing continuous signal transmission for a long time using a transmission line of an optical network, for example, when transmitting a moving image, optical multiplex transmission between a center station and a terminal station becomes impossible, The reference wavelength light cannot be transmitted from the center station to the terminal station. Therefore, the wavelength control of the operating wavelength using the reference wavelength is not possible within the terminal station, so the wavelength of the signal light within the terminal station gradually deviates from the desired value, and the optical signal between the center station and the terminal station is lost. There was a problem that multiplex communication could not be performed.

The present invention has been made in view of the above-mentioned conventional example, and by setting the output wavelength according to the high level and low level of the transmission signal and performing wavelength control of the output wavelength, the time period for transmitting the transmission signal is It is an object of the present invention to provide a terminal station that can always send a transmission signal at an output wavelength for which wavelength control is performed, without the need to separately provide a time zone for performing wavelength control.

[Means for Solving the Problems] In order to achieve the above object, the terminal station of the present invention has the following configuration. That is, a terminal station used in an optical network communication system for communicating information by optical signals between a plurality of terminal stations via a transmission line, the light source capable of controlling an output wavelength, and the light source controlling the output wavelength. A wavelength control means for inputting a control signal for controlling the output wavelength, the first control signal for setting the output wavelength to a first wavelength, and the second control for setting the output wavelength to a second wavelength for wavelength control. A wavelength switching means for inputting a signal to the light source according to a high level and a low level of a transmission signal, and comparing the second wavelength with a reference wavelength, and the difference between the second wavelength and the reference wavelength is 0 to 0. The second control signal is controlled so as to have a constant value, and the first control signal is controlled so that the controlled second control signal and the first control signal have a predetermined relationship. Control means for controlling Sign.

[Operation] With the above configuration, the first control signal for setting the output wavelength to the first wavelength for the light source capable of controlling the output wavelength and the second control signal for setting the output wavelength to the second wavelength for wavelength control The control signal and the control signal are input to the light source according to the high level and the low level of the transmission signal, and the second wavelength thereof is compared with the reference wavelength,
The second control signal is controlled so that the difference between the second wavelength and the reference wavelength is 0 or a constant value, and the controlled second control signal and the first control signal have a predetermined relationship. So as to control the first control signal.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Description of the First Embodiment (FIGS. 1 and 2)] FIG. 1 is a block diagram showing the first embodiment of the present invention.
3 shows a transmission unit of a node of each terminal station in the communication network system.

In the figure, reference numeral 11 denotes received light, which is an optical signal sent from another terminal station or center station on the optical communication network. Reference numerals 12 and 13 are optical branching / combining devices, and for example, a Parc beam splitter or an optical waveguide type element is used.
Here, 12 operates as an optical branching device and 13 operates as an optical combiner. 14 is a photodetector. Reference numeral 15 is a wavelength tunable laser, and for example, as shown in FIG. 3, a semiconductor laser whose emission wavelength changes depending on the injection amount of the current input from the tuner 16 is used. Reference numeral 17 denotes emitted light output from the laser 15. 18 signal sources, which are sources of information output from this node. 16 is China.

19 is a modulator, in this absorption spectrum of the band in the semiconductor for applying an electric field to the semiconductor in the modulator 19 is changed element changing the transmittance of the optical or electrical-optical effects such as L _i NbO _3, It is possible to construct an interferometer such as a Mach-Zenda interferometer with a large material and use an element that changes the refractive index by applying an electric field to one arm and changes the optical path length to change the intensity of transmitted light. it can. Reference numeral 27 is the transmission light of this node that is sent out on the optical network, and is sent to the transmission line of the optical network via the connection line, the coupler and the like.

Explaining the configuration of the receiving system, 20 is a low pass filter (LPF) and 21 is an amplifier. A switch 22 is turned on / off by a control signal 42 from the signal source 18. twenty three
Is a frequency controller, and 24 is a wavelength designator that designates the output wavelength at this node. Reference numeral 25 denotes a memory, which stores the output current value of the tuner 16 with respect to the output wavelength of the laser 15 as shown in FIG. 26 is an interpolator described later.

FIG. 2 is a diagram showing the distribution of wavelengths used in this transmission line.

201 is the wavelength spectrum of the reference wavelength light, λ ₁ , λ ₂ ,
It is assumed that the four wavelengths λ ₃ and λ ₄ are set. 202 is a wavelength spectrum of the signal light, and its wavelength is λ. Here, the node of the terminal station shown in FIG. 1 uses it as the wavelength of the transmission light 27. Reference numeral 203 denotes a wavelength spectrum of signal light of another station, which is a wavelength used for signal transmission in another terminal station, like the wavelength spectrum of the signal light 27.

As shown in FIG. 2, the wavelength spectrum 201 of the reference wavelength light and the wavelength spectrum 20 of the signal light sent from the center station
2.The wavelength spectrum 203 of the other signal light is different from each other, and in this embodiment, the wavelength tracking of the signal light is based on the reference wavelength from the center station, and is interpolated using the data in the memory 25. Performed by interpolation processing according to 26.

In FIG. 1, the received light 11 passes through an optical branching / combining device 12 and enters a photodetector 14. On the other hand, a part of the emitted light 17 from the wavelength tunable laser 15 is reflected by the optical branching device 13, and is further reflected by the optical branching / combining device 12 again so that the photodetector
It is incident on 14. As a result, the output of the photodetector 14 is 2
A beat signal of two incident light beams is obtained.

The signal from the signal source 18 is sent to the tuner 16 and
Reference numeral 16 changes the wavelength of the emitted light 17 of the wavelength tunable laser 15 based on the signal. The emitted light of the wavelength tunable laser 15 is controlled as follows.

[Description of Semiconductor Laser (FIG. 3)] FIG. 3 is a front view of the wavelength tunable laser 15 used in this node.

In the figure, 31 is a substrate, 32 is an optical waveguide layer, and 33 is a cladding layer. A grating is formed on a part of the interface between the substrate 31 and the optical waveguide layer 32 to form a DBR region. 34 is an active layer. 35a, 35b and 35c are a signal electrode, a phase control electrode and a DBR region control electrode, respectively. 36 is a common electrode. 37a, 37b, and 37c are a signal line, a phase control line, and a DBR region control line, which are connected to the signal electrode 35a, the phase control electrode 35b, and the DBR region control electrode 35c, respectively. 38 is emitted light. This wavelength tunable laser 15 is composed of G _a A _s / G _a AlA _s , I _n
It can be produced using the P / I _n G _{a A s} material such as P.

The substrate 31, the optical waveguide layer 32, and the cladding layer 33 form an optical waveguide in which light can propagate. Light is generated by current injection in the active layer 34, and laser oscillation is generated by reciprocating in a cavity formed by a grating and a cleavage plane. A current injected between the signal electrode 35a and the common electrode 36 and flowing from the signal line 37a controls laser oscillation to turn on / off the emitted light 38, and a signal can be placed on the output signal light. However, in this embodiment, CW oscillation is kept on.

On the other hand, the current injected from the DBR region control line 37c and flowing between the DBR region control electrode 35c and the common electrode 36 changes the refractive index of this region by carrier injection and changes the optical path length. Then, the wavelength of the emitted light 38 is changed. The amount of change in wavelength caused by the change in current injection of the DBR region control line 37c is relatively large. Also,
Control means for finely adjusting the wavelength is provided by the phase control electrode 35b and the phase control line 37b. This is because when a current is passed between the phase control electrode 35b and the common electrode 36 through the phase control line 37b, the refractive index changes due to the effect of carrier injection,
Optical path length change occurs. The wavelength change of the emitted light 38 caused by this is small, and when combined with the wavelength change using the DBR region control line 37c, a semiconductor laser capable of smoothly changing the wavelength can be obtained.

[Description of Transmission Wavelength Control (FIG. 4)] FIG. 4 is a timing chart of transmission and wavelength control in this node.

In FIG. 4, 41 is a wavelength designation signal, which is a signal sent from the wavelength designator 24 of FIG. 1 to the frequency controller 23. The wavelength designation signal 41 is a signal indicating which wavelength of the wavelength reference signal the wavelength should be controlled at present. Reference numeral 42 is a transmission signal output from the signal source 18. The transmission signal 42 is an encoded version of the data to be transmitted. For this code, for example, the Mantiester code is used. Here, the transmitted signal
42 represents the case where the Mantiester code is used. Reference numeral 43 indicates an oscillation wavelength output from the wavelength tunable laser 15.

With the wavelength designation signal 41, the wavelength control for the reference wavelength light from the center station changes from λ ₁ to λ _{4 in} order, and again λ 4
It is specified to be performed in the order of returning to ₁ . Source 18
When the transmission signal 42 is sent from the tuner 16 to the tuner 16,
Changes the oscillation wavelength of the wavelength tunable laser 15 based on the transmission signal 42.

The output current of the tuner 16 is the phase control line 37b and the DBR region control line 37c of the wavelength tunable semiconductor laser 15 shown in FIG.
Connected to flow. Tunable semiconductor laser
The oscillation wavelength 43 output from 15 is the wavelength λ of the signal light when the transmission signal 42 is at a high level, and the wavelength designated by the wavelength designation signal 41 when the transmission signal 42 is at a low level, that is, λ.
It becomes one of ₁ ... λ ₄ . Therefore, the wavelength tunable laser 15 oscillates in CW, and the emitted light 17 also continuously exists.

Here, a part of the emitted light 17 is transmitted through the optical branching device 13 and is incident on the modulator 19. The transmission signal 42 from the signal source 18 is input to the modulator 19, and the modulator 19 turns on / off the light according to the high level and the low level of the transmission signal 42. Therefore, the transmitted light 27 has only the component of the wavelength λ, and becomes an intensity-modulated light flux with the frequency corresponding to λ as the center frequency.

The oscillation wavelength control of the wavelength tunable laser 15 is performed as follows.

The reference wavelength light from the center station and a part of the emitted light 17 of the wavelength tunable laser 15 are incident on the photodetector 14 to obtain a beat signal of two light fluxes. The beat signal generated by the wavelength light is extracted. LPF2
The output signal of 0 is amplified by the amplifier 21 and sent to the switch 22. Switch 22 is an analog switch and
It is opened and closed by switching with the transmission signal 42 from. The switch 22 is adapted to open when the transmission signal 42 is at a low level. That is, when the oscillation wavelength of the wavelength tunable laser 15 is _one of the wavelength spectra λ ₁ ... λ ₄ of the reference wavelength light, only the beat signal obtained by the photodetector 14 is passed to the next stage (frequency controller 23). have. The switch 22 is for improving the detection accuracy of the control signal for wavelength control, and may be omitted depending on the specifications of the control system.

The output of the amplifier 21 that has passed through the switch 22 is the frequency controller.
Sent to 23. The frequency controller 23 detects the frequency of the output and outputs a control output to the memory 25 so that the value becomes 0 or a constant value. That is, control by homodyne or heterodyne detection is performed. Alternatively, when the wavelength control is not so strict, a method may be adopted in which the output signal values of the amplifier 21 that have passed through the switch 22 are time-averaged and the value is controlled to increase. In this case, the magnitude of the time-averaged signal depends on the content of the transmission signal 42, but the ratio of the time of high level and the time of low level of many codes including the Mantiester code is almost one to one, which is not so much. It doesn't matter.

As described above, the wavelength designating signal 24 is sent from the wavelength designating device 24 to the frequency controller 23. The frequency controller 23 outputs a control signal 43 so that the tuner 16 outputs an output current so that the wavelength tunable laser 15 oscillates the wavelength designated by the wavelength designation signal 41 when the transmission signal 42 is at a low level. This control signal 43 is stored in the memory 16 and then sent to the tuner 16, and according to this control signal 43, the wavelength tunable laser is
15 are controlled.

The oscillation wavelength of the laser 15 whose wavelength is controlled in this way is detected again by the photodetector 14 and the like, and is repeatedly controlled.
The wavelength tunable laser 15 is thus feedback controlled. The output wavelength of the wavelength tunable laser 15 is controlled by λ ₁ , λ ₂ ,
λ ₃ and λ ₄ are sequentially performed, and then the process returns to λ ₁ . Since this wavelength variation occurs relatively slowly, the change of the wavelength designation signal 41 is slower than the change of the transmission signal 42.

The memory 16 has the oscillation wavelength λ ₁ ... λ of the wavelength tunable laser 15.
₄ is stored, and the interpolator 26 calculates the control data for the wavelength of the signal light from the control data in these memories. That is, in FIG. 2, since the control data for the spectrum 201 of the reference wavelength light or the wavelength in the vicinity thereof is actually obtained, the control data corresponding to the wavelength spectrum λ202 of the signal light or the wavelength spectrum 203 of the other signal light is obtained. Is obtained by interpolation.

FIG. 5 is a graph showing the relationship between the output current of the tuner 16 and the oscillation wavelength of the wavelength tunable laser 15.

Reference numeral 51 is a characteristic curve of the output current of the tuner 16 and the oscillation wavelength of the wavelength tunable laser 15. Reference numeral 52 is a plot for the reference wavelength light, 53 is a plot for the signal light, and 54 is a plot for the other signal light.

The output current from the tuner 16 is appropriately divided and output to the phase control line 37b and the DBR region control line 37c. The characteristic curve 51 of the output current and the oscillation wavelength of the tuner 16 fluctuates due to the effects of temperature, changes over time, changes in the external environment, etc.
The plot 52 is obtained by controlling the wavelength tunable laser 15 with respect to the reference wavelength light. That is, the current value I ₁ ... I ₄ for oscillating at a wavelength λ _{1 ...} λ ₄ are required. The current value required to oscillate at the wavelength of the signal light determined from this,
The interpolator 26 performs interpolation processing to obtain the value. The plot 53 for the signal light and the plot 54 for the other signal lights come to the positions shown in FIG.

The simplest way to obtain the current I for oscillating at the wavelength λ is by connecting between (I, λ ₁ ) and (I, λ ₂ ) and performing linear interpolation, where λ is λ ₁ If it is an intermediate position between λ ₂ and λ _2, the current value I is of course the intermediate value between I ₁ and I ₂ . Alternatively, in addition to this, the characteristic curve 51 of the output current of the tuner 16 and the oscillation wavelength is obtained in advance, the values are stored in the memory, and the curve drawn based on these values is referenced to interpolate. May be. Also, by performing curve fitting based on theoretical curves, polynomial approximation, etc., the tuner 16
The current value I to be input to may be obtained. The current values for the other wavelengths of the signal light can be similarly obtained.

In the above description, the case where the wavelength spectrum of the signal light is included in each of the two spectra of the reference wavelength has been described. However, a plurality of wavelength spectra may be provided between the spectra of the two reference wavelengths. It is possible to allocate the signal wavelength by dividing into several parts, and to execute the interpolation processing accordingly. The interpolation data calculated by the interpolator 26 here is stored in the memory 16 and used for the subsequent wavelength control.

Next, the processing of the received light 11 will be described. The signal light is received by the receiving unit of the node of each terminal station. In the receiving section, the received light 11 is passed through a wavelength tunable filter to a photodetector.
It is structured to lead to 14. A wavelength tunable filter is an element capable of varying the transmission wavelength range, and various elements are known. This includes mechanical rotation of the grating type spectroscope, and construction of an interference system using a material having an electro-optic effect to change the optical path length by applying an electric field to change the transmission wavelength. . Also, there is a structure having a structure similar to that of the wavelength tunable semiconductor laser 15 shown in FIG. 3, in which the active layer is eliminated and the transmission wavelength is changed by a DBR or DFB type grating structure element.

Since the reference wavelength light and the signal light from the terminal station have different wavelengths, only the desired signal light can be easily transmitted by the wavelength tunable filter and uniquely identified. Since the wavelength of the signal light is stabilized, there is almost no fluctuation, and the control of the wavelength tunable filter may be small. Further, the feedback control by the output may be controlled so that the output becomes large.

The optical branching device 13 and the modulator 19 can be replaced with an optical branching switch. The optical branch switch is, for example, an optical waveguide type directional coupler or a total reflection type switch, and distributes a propagating light beam in two directions according to a control signal.
That is, when the transmission signal 42 is at the high level, it is directed toward the transmission line of the optical network, and when it is at the low level, it is directed toward the optical branching / combining device 12 and further toward the photodetector 14.
In this case, the utilization efficiency of the emitted light 17 is improved.

Further, it is also possible to use an element in which the optical branching / combining device 13 has a wavelength-dependent characteristic and can further change the transmission wavelength range. That is, a variable optical filter that transmits only wavelengths in an arbitrary band and blocks other wavelengths may be used.
When such an element is realized by an optical lens system, the wavelength tunable filter described above can be realized by setting the incident angle of incident light at 45 °. For example, the transmission wavelength is set in the vicinity of λ, and the light of other wavelengths λ ₁ , λ ₂ , λ ₃ and λ ₄ is used by being reflected. At this time, the modulator 19 is unnecessary.

[Reference Example] FIG. 6 is a view showing a reference example of the present invention, and this figure shows a transmitting section of a node of a terminal station of an optical network communication system.

61 is the received light. Reference numeral 62 denotes an optical switch which uses the optical branching switch described in the first embodiment in the opposite direction and utilizes the optical characteristics of the two optical inputs to transmit the light of one wavelength and output it. 63 is a variable wavelength filter,
64 is a photodetector. Reference numeral 65 is a wavelength tunable laser similar to that described in the first embodiment, and 66 is the emitted light of the wavelength tunable laser 65. 67 is an optical branching / combining device, 68 is a wavelength control light, which is a part of the emitted light 66. 69 is a destination, which is sent into the transmission line through the connecting line and the coupler. Further, 70 is an amplifier, 71 is a wavelength controller, 72 is a tuner, 73 is a memory, and 74 is an interpolator. 75 is a tuner, 76 is a signal source,
77 is a driver.

As shown in FIG. 2, the received light 61 includes a reference wavelength signal from the center station and a signal light for communication between the terminal stations. The received light 61 first enters the optical switch 62. The optical switch 62 is initially in a state of transmitting the received light 61. Therefore, the received light 61 is incident on the wavelength tunable filter 63, and the light transmitted through the wavelength tunable filter 63 is detected by the photodetector 64.

On the other hand, the emitted light 66 output from the wavelength tunable laser 65 is
A part of the light is branched by the optical branching / combining device 67 to become the wavelength control light 68. This wavelength control light 68 is incident on the optical switch 62, and depending on the state of the optical switch 62, it goes to the variable wavelength filter 63 and is detected by the photodetector 64. Light splitting / combining of the emitted light 66
The component transmitted through 67 becomes transmitted light 69.

The output of the photodetector 64 is amplified by the amplifier 70 and sent to the wavelength controller 71. Tunable filter 63 is a tuner
It is controlled by 72, and its transmission wavelength is changed by changes in the applied electric field, the injection current, and the like.

The wavelength controller 71 tunes the variable wavelength filter 63 according to the wavelength of the reference wavelength light in the received light 61. Data for performing wavelength control is stored in the memory 73. The tuner is selected according to the data read from the memory 73.
72 changes the transmission spectrum of the variable wavelength filter 63, and the controller 71 monitors the output from the variable wavelength filter 63. The wavelength sweep of the wavelength tunable filter 63 is performed so as to gradually shift from the shortest wavelength side to the long wavelength side. At that time, not only the reference wavelength light but also the signal is detected. However, since the wavelength of the reference wavelength light and the mutual wavelength interval are known, the signal can be identified.

The memory 73 stores data for setting the wavelength of the wavelength tunable filter 63 for the wavelength of the reference wavelength light, for example, λ ₁ ... λ ₄ , and the interpolator 74 performs interpolation processing or data generation based on the data. By performing processing, the wavelength tunable laser 65 calculates data corresponding to the wavelength of the signal light used for transmission, for example, λ. This data is stored again in the memory 73 and sent to the tuner 72. As a result, the tuner 72 sets the transmission wavelength of the variable wavelength filter 63 to be λ.

Here, the optical switch 62 is switched so that the wavelength control light 68 enters the wavelength tunable filter 63. The switching of the optical switch 62 is performed based on the control signal 75 from the wavelength controller 71. All control lines from the wavelength controller 71 are not shown for simplicity.

The wavelength control light 68 that has passed through the wavelength tunable filter 63 is detected by the photodetector 64, amplified by the amplifier 70, and then sent to the wavelength controller 71. The wavelength controller 71 is
A tuner is used to increase the output of this wavelength control light 68.
75 is controlled to change the oscillation wavelength of the wavelength tunable laser 65. The output of the tuner 75 is connected to, for example, the phase control line 37b and the DBR region control line 37c of the wavelength tunable semiconductor laser of FIG.

On the other hand, the signal from the signal source 76 is sent to the driver 77, and the driver 77 drives the wavelength tunable laser 65 based on the signal. The output of the driver 77 is connected to the signal line 37a of the wavelength tunable semiconductor laser shown in FIG. Tunable semiconductor laser 6
The wavelength of the emitted light 66 from 5 has a wavelength of the signal light, for example, λ, and becomes a light flux whose intensity is modulated by a transmission signal from the signal source 76, for example, a signal encoded by the Mantiester code. Such oscillation wavelength control of the wavelength tunable laser 65 can be performed in parallel with signal transmission. Generally, the oscillation wavelength of the wavelength tunable laser 65 varies relatively slowly due to changes in the external environment such as changes in temperature and changes with time. Therefore, wavelength control involving interpolation processing can be sufficiently followed.

With respect to the receiving section of a certain terminal station node of the optical network communication system, reception can be performed by the same method as described in the first embodiment.

In the reference example, the wavelength tunable filter 63 is tuned with the reference wavelength light by combining the wavelength tunable filter and the 63 photodetector 64. Then, after that, the method of setting the wavelength of the wavelength tunable laser 65, which is the transmission light source, to a desired value is used, but a method of placing a local oscillator and adjusting the oscillation wavelength first is also possible. A wavelength tunable laser is used for this local oscillator, and its emitted light is made incident on a photodetector together with the reference wavelength light to detect a beat signal. Since data for local oscillator tuning according to each reference wavelength light is obtained from this beat signal, interpolation processing is performed next to control the oscillation wavelength of the local oscillator so as to correspond to the wavelength of the transmission signal destination. Finally, the wavelength of the wavelength tunable laser that is the transmission light source may be controlled with respect to the wavelength of the local oscillator by a beat signal detection method.

In the above description of the embodiments, the wavelength division multiplexing communication has been described, but the same can be applied to the frequency division multiplexing communication using the coherent optical communication.

As described above, according to the present embodiment, the signal light used for the signal transmission between the terminal stations of the optical network communication system and the reference wavelength light having a different wavelength are superimposed, and the element of each terminal station is applied to the reference wavelength light. Wavelength control. Then, the memory is used to store the control data in the memory, the control data for the signal light is calculated from the control data by the interpolation process, and the wavelength is controlled.

Therefore, continuous wavelength control is possible, and the reference wavelength in the terminal station is stabilized even when transmitting a continuous signal for a long time, and there is an effect that stable network communication transmission is always possible.

Further, since the wavelength control is used, it is not necessary to temporarily stop other communication, and there is an effect that the utilization efficiency of the network communication system is improved.

Furthermore, since it is a wavelength division multiplexing communication system, there is no need to draw a dedicated transmission line for transmitting the reference wavelength light, so that there is an effect that a more economical network communication system can be realized.

Also, by introducing the reference wavelength signal when the transmission signal is at the low level, it is possible to avoid wavelength tracking of the transmission signal directly on the reference wavelength signal.

[Effects of the Invention] As described above, according to the present invention, by setting the output wavelength and controlling the wavelength of the output wavelength according to the high level and the low level of the transmission signal, the time period for transmitting the transmission signal In addition to the above, there is an effect that it is not necessary to provide a time zone for performing wavelength control separately, and a transmission signal can always be transmitted at an output wavelength for which wavelength control has been performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical network communication system according to a first embodiment of the present invention, FIG. 2 is a diagram showing a wavelength distribution of an optical signal used in this system, and FIG. FIG. 4 is a front view of the tunable laser, FIG. 4 is a timing chart showing the transmission and wavelength control in the first embodiment, FIG. 5 is a view showing the relationship between the output current of the tuner and the oscillation wavelength of the tunable laser, and FIG. Is a block diagram showing the configuration of the optical network communication system of the second embodiment of the present invention, and FIG. 7 is a schematic diagram showing the optical network. In the figure, 12,13,67 ... Optical branching / combining device, 14,64 ... Photodetector, 15,65 ... Tunable laser, 16,75 ... Tuner, 1
8,76 …… Signal source, 19 …… Modulator, 20 …… LPF, 21,70 ……
Amplifier, 22 …… Switch, 23 …… Frequency controller, 24 ……
Wavelength specifier, 25,73 ... Memory, 26,74 ... Interpolator, 31 ...
… Substrate, 32 …… Optical waveguide layer, 33 …… Cladding layer, 34 …… Active layer, 41 …… Wavelength designation signal, 42 …… Transmission signal, 43 …… Oscillation wavelength, 62 …… Optical switch, 63 …… Wavelength tunable filter,
71: wavelength controller, 201: frequency spectrum of reference wavelength light, 202: wavelength spectrum of signal light.

Claims (5)

(57) [Claims] 1. A terminal station used in an optical network communication system for communicating information by optical signals between a plurality of terminal stations via a transmission line, the light source having a controllable output wavelength, and the output to the light source. A wavelength switching means for inputting a control signal for controlling a wavelength, comprising a first control signal for setting the output wavelength to a first wavelength and a second control signal for setting the output wavelength to a second wavelength for wavelength control. A wavelength switching means for inputting two control signals to the light source according to a high level and a low level of a transmission signal, and comparing the second wavelength with a reference wavelength, and calculating a difference between the second wavelength and the reference wavelength. Control the second control signal so that is 0 or a constant value, and the first control is performed so that the controlled second control signal and the first control signal have a predetermined relationship. Control means for controlling the signal, and A terminal station characterized by that. 2. The terminal station according to claim 1, wherein the reference wavelength is a wavelength of reference wavelength light. 3. The control means includes means for generating a beat signal of the light of the second wavelength and the reference wavelength light, and the beat signal has a frequency of 0 or a constant value. The terminal station according to claim 1 or 2, which controls the control signal of 2. 4. The terminal station according to claim 1, wherein the reference wavelength light is output by a transmitting means provided in the optical network communication system. 5. An optical network communication system for communicating information by optical signals between a plurality of terminal stations via a transmission path, wherein the terminal station according to claim 1 is used as the terminal station. An optical network communication system characterized by using a station.