JPH1065649A - Wavelength multiplex optical transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost and to improve reliability by keeping the respective wavelength of a light source, which are multiplexed in high density, to be constant with simple constitution and considerably reducing the number of spare light sources provided for the fault of the light source. SOLUTION: A part of the previous light of a final multiplex stage is branched and it is inputted to a collective wavelength sensor through an optical switch. Light beams inputted to the final multiplex stage are arranged so that the wavelength are alternately arranged, for example. Thus, the wavelength intervals of wavelength multiplex light beams which are inputted to the collective wavelength sensor at once are enlarged. In high density WDM (wavelength multiplex communication system) whose wavelength grid is sufficiently narrow against the variable wavelength range of LD(laser diode), a plurality of LD can correspond to one wavelength grid. When LDs of the prescribed wavelength break down, LDs with the oscillation wavelength of standby LDs are sequentially shifted and therefore the number of standby LDs can considerably be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength stabilization of a transmission light source and recovery of a failed light source in a wavelength division multiplexing optical communication system.

[0002]

2. Description of the Related Art A wavelength division multiplexing communication system (WDM: Wavelength Divis)
The term “ion multiplexing,” which is synonymous with the optical frequency multiplexing communication system, means that, on the transmission side, a plurality of lights having different wavelengths are subjected to data modulation of different channels, and then wavelength-multiplexed by a multiplexer to an optical fiber transmission line. The transmitting and receiving side converts the received wavelength multiplexed signal light into an optical band-pass filter (hereinafter referred to as OBPF: Optical BandP).
Assembler) and other wavelength selection means,
This is a method in which only light having a desired wavelength is demultiplexed, light is received, and the original data is demodulated.

In recent years, the wavelength multiplexing method has been actively researched and developed as a technique for dramatically increasing the transmission capacity per optical fiber transmission line. The wavelength band expected to be commercialized first is 1.53 to 1.56 μm, which is the amplification wavelength band of the erbium-doped optical fiber amplifier.

<Conventional Technique of Wavelength Stabilization> In the wavelength multiplexing method, each channel is identified by wavelength, and it is needless to say that the correspondence between wavelength and channel needs to be matched between the transmitting side and the receiving side. In addition, even if the fluctuation of the wavelength is slight, if optical interference occurs by overlapping with the wavelength of the adjacent signal light, the bit error rate characteristic is significantly deteriorated. Therefore, it is necessary to stabilize the wavelength of the light source. The typical prior art will be described with reference to the configuration diagram of FIG. FIG. Toba a
nd K. Nosu, "Optical Frequency
ncy Division Multiplexing
Systems ", IEICE TRANS.COM
MUN. , VolE-75-B. no. 4, pp. 24
This is a simplified version of what is shown in FIGS. 3-255, 1992.

The mechanism is as follows. LD (L
A plurality of light beams having different wavelengths output from an assembler diode are wavelength-multiplexed by a multiplexer. A part of the wavelength multiplexed light is guided to a wavelength sensor. The difference between the actual wavelength value obtained by the wavelength sensor and the set wavelength value is negatively fed back to the temperature and drive current of the LD to maintain the wavelength at the set value.
The wavelength sensor used here exhibits discrimination characteristics with respect to wavelength, and typically uses an optical resonator such as a Fabry-Perot resonator or a ring resonator, or a diffraction grating. These use not only a fixed type but also a sweep type. In addition to optical resonators, optical interference interferograms are measured using an optical interferometer equipped with a variable optical delay device or a device that detects beats with a wavelength-variable light source, and the result is subjected to inverse Fourier transform to obtain an optical spectrum. Some of them get information.

It is desired that the wavelength sensor be capable of inputting wavelength-multiplexed light and measuring individual wavelengths contained therein. A measuring instrument generally called an optical spectrum analyzer corresponds to this. If this is not possible,
Light before wavelength division multiplexing must be partially branched and input to a wavelength sensor while individually switching by an N-input / one-output optical switch to individually monitor the wavelength, resulting in a significantly complicated and expensive configuration. become. In order to detect an abnormality between the light source and the multiplexer, it is preferable to monitor the wavelength-multiplexed light.

However, in such a collective wavelength sensor, each wavelength value can be obtained only discretely in time. This can be dealt with by providing a mechanism for holding the negative feedback signal once obtained until the next negative feedback signal is obtained. A general variable wavelength light source including an LD with a temperature adjustment mechanism usually has a mechanism for holding an input wavelength setting value. In other words, a mechanism for stabilizing a relatively fast wavelength fluctuation is provided in each of the wavelength tunable light sources, and by giving a wavelength setting value to them,
It is the role of this wavelength stabilization system to suppress slow wavelength fluctuations.

<Problems of Conventional Wavelength Stabilization Method> A wavelength sensor that can collectively measure multiple wavelengths is effective for simplifying the configuration, but has a problem of a resolution limit. For example, in a general optical spectrum analyzer using a diffraction grating, about 0.1 n
m (about 12.5 GHz at 1.55 μm) or less cannot be distinguished. Further, since the spectrum of each light is broadened by data modulation, it becomes more difficult to determine. For these reasons, there is a problem that it is impossible to discriminate each wavelength in high-density wavelength multiplexing in which the wavelength interval is narrowed to the minimum in the conventional method.

<Prior art of a method for recovering a failed light source> In a backbone large-capacity optical communication system or the like, it is necessary to prepare a spare in case of a failure. Since a LD which is a light source for optical communication rarely deteriorates particularly quickly compared with other electronic components, a backup light source is indispensable. However, since the light source accounts for a significant portion of the cost of an optical transmitter, the provision of a spare light source, particularly for a wavelength multiplexed optical transmitter, is an important issue. If the number of the spare light sources is equal to the number of the wavelengths, the cost becomes high.

On the other hand, a technique using a wavelength-variable light source as a standby light source is described in Japanese Patent Application No. 0538708 (Application No. 58-131370), "Wavelength Multiplexing Optical Transmitter". Here, a general light source, LD (La
A technique has been disclosed that utilizes the fact that the wavelength of the laser diode (ser diode) changes depending on the element temperature, and restores the wavelength of the backup LD by matching it with the wavelength of the failed LD.

By the way, depending on the temperature and the drive current value, the LD
The control of the oscillation wavelength of the laser itself is described in, for example, “Coherent Optical Communication Engineering” (Ogoshi and Kikuchi, Ohmsha, 1989).
As described on page 116 (Chapter 4, Section 1, [2] Frequency Stabilization), the above-mentioned technique is well-known prior to the filing of the patent.

<Problems of Conventional Recovery Method of Faulty Light Source> A common measure for sharing a backup light source by changing the oscillation wavelength of an LD according to a temperature or a drive current value as described in Japanese Patent No. 0153708 is effective. However, the disadvantage is that the variable wavelength range is narrow. At present, DFB (Distributed) which is generally used as a light source
In a Feedback LD, the rate of change of wavelength with temperature is about 0.07 nm / ° C., and the practical variable range is about 2.5 nm. The change due to the drive current is several steps smaller than this, and the current value is generally controlled so that the output is constant.

For this reason, in this method, at least 2.
It is necessary to prepare spare light sources at 5 nm intervals. This will be described with reference to FIG. The horizontal axis is the wavelength. The wavelength grid, which is indicated by a black circle (●) at the top, is a wavelength channel that has been negotiated between the transmitting side and the receiving side. The optical transmitter adjusts the transmission light wavelength so as to match this grid. on the other hand,
Open circles (○) indicate the oscillation wavelength of the LD at room temperature. Generally L
The oscillation wavelength of D shifts to the long-wave side when warmed and shifts to the short-wave side when cooled. The variable wavelength range obtained in this way is indicated by a horizontal bar. Since the LD is vulnerable to heat, the load in the cooling direction is less and the variable range can be widened.

As can be seen from FIG. 9, the backup light source must be prepared so that its variable wavelength range continues without interruption. If the used band is wider than the variable range, a large number of backup light sources are required. Requires LD.
For example, in the above-mentioned DFB LD, at least 12 backup LDs are required for a used band of 30 nm.

On the other hand, if a special laser such as an external mirror resonator laser or an LD having a mechanism for largely changing the wavelength is used, a wide wavelength tunable range can be obtained. However, such a wavelength tunable laser is generally expensive. In addition, there is a problem that the stability and reliability of the wavelength are often lacked because the wavelength variable range is wide.

[0016]

Means for Solving the Problems A first invention of the present invention is:
A wavelength tunable light source provided with a control means for the wavelength of the output light,
A plurality of wavelength tunable light sources whose wavelengths are set to mutually different values, and a multiplexing unit that multiplexes the plurality of modulated lights in a stepwise manner,
An optical transmitter using a wavelength division multiplexing technology, comprising: a demultiplexer that branches a part of the wavelength multiplexed light output from the multiplexing means, the output light of the demultiplexer being input, and Outputting a signal corresponding to the plurality of wavelengths included in the multiplexed light, a wavelength measuring unit, and calculating an error of each of the plurality of wavelength measurement values with respect to a wavelength setting value of each of the plurality of light sources; A wavelength-division multiplexing optical transmission device comprising at least means for negative feedback to the wavelength control means of the light source, and capable of performing wavelength stabilization. A wavelength-division multiplexing optical transmission device characterized in that the minimum value of the wavelength interval included in the partially branched light is set to be wider than the minimum wavelength resolution of the wavelength measuring means.

According to a second aspect of the present invention, in the partially branched light of the first aspect, the light from the plurality of light sources is set to be included in any of the plurality of partially branched lights. It is a wavelength division multiplexing optical transmitter.

According to a third aspect of the present invention, a plurality of wavelength division multiplexed lights are inputted to an optical switch means, and one of the plurality of wavelength division multiplexed lights is inputted to the wavelength measurement means in a time division manner to measure a wavelength. A wavelength division multiplexing optical transmitter according to a second aspect of the present invention.

According to a fourth aspect of the present invention, there is provided a wavelength tunable light source provided with control means for controlling the wavelength of output light, wherein a plurality of tunable light sources having wavelengths set to different values are provided. Multiplexing means for multiplexing, and an optical transmitter using a wavelength multiplexing technique, wherein each of the plurality of wavelength setting values falls within a range of tunable wavelengths of a plurality of tunable light sources. In a wavelength multiplexed optical transmitter, when a light source of a certain wavelength fails, the wavelength of the light source existing between the wavelength of the failed light source and the wavelength of the spare light source is sequentially shifted, so that the original wavelength setting value is obtained. Characterized by having a function to recover from a light source failure by returning to
This is a wavelength division multiplexing optical transmission device.

(Operation) <Wavelength stabilizing system> Light before the final wavelength multiplexing stage is partially branched and input to a wavelength sensor through an optical switch. The wavelength multiplexed light input to the final multiplexing stage is arranged such that the wavelengths contained therein are arranged, for example, alternately. Thus, for example, in the case of an optical transmitter that finally multiplexes at equal wavelength intervals, if the number of multiplexes in the final stage is 4, the wavelength interval of light input to the final multiplex stage is four times the final wavelength interval, The array is shifted only by the wavelength offset value. By doing so, the wavelength sensor can easily resolve and recognize each wavelength and measure the wavelength.

<Method of Recovering from Light Source Failure> In a high-density WDM in which the wavelength grid is sufficiently narrow with respect to the variable wavelength range of the LD, a plurality of LDs can cope with one wavelength grid. In case of failure, by shifting the LD between the oscillation wavelength of the spare LD and the LD in order,
The number of spare LDs can be greatly reduced.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment of the Invention of Claims 1 to 3> A first embodiment for describing a wavelength stabilizing system to which the invention of claims 1 to 3 is applied will be described below.

FIG. 1 is a diagram showing the configuration. Wavelength multiplexing is performed stepwise without performing all at once. Immediately before finally multiplexing into one, a part of them is branched and input to a wavelength sensor through an optical switch. The light input to the final multiplex stage is shown in FIG.
Are arranged such that the wavelengths alternate. In this example, the number of wavelengths entering the wavelength sensor is halved, and the wavelength interval is doubled. Therefore, even in high-density wavelength multiplexing in which the wavelength interval is narrowed to the limit, each wavelength can be determined, and wavelength stabilization can be stably performed.

In the first embodiment, from 1530 nm to 156 nm
Wavelength multiplexing of 94 waves is performed at equal intervals of 0.32 nm over 0 nm. The light source was the DFB LD described in the related art, and the wavelength tunable range was about 2 nm. Each LD
Has a constant temperature controller and a constant output controller.
In the optical modulator, light intensity modulation was performed in a pseudo random pattern of 10 Gb / s. The wavelengths λi are arranged in order from the short wavelength, and λ1, λ3, λ5,.
λ2, λ4, λ6,... are wavelength-multiplexed to the wavelength-division multiplexed light 2. A mechanical switch having two inputs and one output was used as the optical switch. Since the optical path is physically switched, it has excellent wavelength dependence, polarization dependence, reproducibility, stability, and the like. This optical switch operates by switching with a TTL level voltage signal.
The wavelength sensor measures the optical interference interferogram with a Michelson interferometer equipped with a variable optical delay line and
A wavelength meter having a mechanism of obtaining an optical spectrum by performing T (fast Fourier transform) was used. Its resolution is about 40 GHz.
The absolute wavelength is based on an internal HeNe laser, and its absolute accuracy is about 1 GHz. Since the wavelength interval of the final wavelength multiplexed output light 3 is about 40 GHz, there is no margin at all as compared with the resolution of the wavelength meter, and the optical spectrum is wide due to data modulation. The wavelength cannot be separated due to the deviation, and the device does not operate stably. However, the wavelength interval of the wavelength multiplexed light 1.2 was about 80 GHz, and the wavelength could be identified and measured with a margin.

As the controller, a personal computer (PC) was used. The switching of the optical switch and the sweep of the wavelength meter were synchronized, and the wavelength multiplexed light 1 and 2 were measured alternately. Wavelength meter 1
It took about 2 seconds for the sweep and about 0.5 seconds for the data transfer, and one cycle of measuring two input lights including the other processing time was performed in less than 10 seconds. This speed was too fast for a device that reached thermal parallelism in a room where the temperature was kept constant, so a timer operation was performed and this operation was performed once every 180 seconds, and sufficient wavelength stability was obtained. .

In this example, multiplexing is performed at equal wavelength intervals, but it is needless to say that the present invention can be applied to unequal wavelength intervals. That is, the wavelength of each light source may be set so that the wavelength interval of each wavelength multiplexed light input to the final multiplex stage is wider than the resolution of the wavelength sensor. If the wavelength interval is already lower than the resolution of the wavelength sensor before the final multiplexing stage, the light that has been traced back to the wavelength interval may be monitored, and the input light to the optical switch may be increased as appropriate.

The wavelength variable light source is, for example, 1552.12.
There are those in which the set wavelength value can be specified by an absolute wavelength value, such as 3 nm, and those in which a signal which is not related to the absolute wavelength but has a unique relationship with the wavelength is specified. A general LD with a temperature adjusting mechanism as used in the first embodiment belongs to the latter.

When the latter light source is used in the present invention, it is necessary to individually measure the wavelength of each light source at the start of operation of the apparatus. This is because, during normal operation, wavelength-multiplexed light is measured by a wavelength sensor, and therefore, it is impossible to know the negative feedback control destination without knowing which wavelength is emitted from which light source. Further, when the initial values of the wavelengths of a plurality of light sources overlap, there is also a problem that the wavelength sensor discriminates them as one light source. However, since the latter problem can be avoided once the correspondence between the light source and the wavelength is grasped, it is not an operational problem.

When the apparatus is started up, or when a plurality of light sources overlap with one wavelength and cannot be determined by the wavelength sensor, a method of obtaining the correspondence between the light source and the wavelength is as follows. There is something. First, the inputs to the wavelength controllers of all the tunable light sources are set to initial values. One example of the initial wavelength setting value is the center of each wavelength variable range. Next, only one light source is turned on in order, and the respective wavelengths may be measured and sequentially stored in a microcomputer or the like. In the configuration shown in FIG. 1, when the optical modulator is an intensity modulator, all the light sources may be turned on and the intensity modulator may output only light from one light source.

This method is used in the first embodiment. The program was designed to always check whether the total number of wavelengths, which is the number of wavelength grids, and the number of wavelengths reported by the wavelength meter match, and if they do not match, re-examine the correspondence between the light source and the wavelength. . If the number of wavelengths differs from the set number of wavelengths even after this investigation, a failure of the light source is suspected, and an alarm is output.

Next, a second embodiment of the present invention will be described below.

In the first embodiment, the light from all the light sources to be wavelength-multiplexed is guided to the wavelength measuring means. However, the wavelengths of all the light sources need not necessarily be guided to the wavelength measuring means. For example, by using the technology disclosed in Japanese Patent Laid-Open No. 60-242739, "Frequency multiplexing optical transmitter",
Based on the wavelength of one light source, it is possible to obtain a set of a plurality of light sources that maintain a constant wavelength interval therefrom. Fig. 3
The wavelength setting will be described with reference to FIG.

A part of the output light of the light sources 1, 2, 3 is branched,
These branched lights are combined, guided to a photodetector, and caused to interfere.
Then, the beat frequencies according to the wavelength difference between the light sources are detected, and the temperatures of the light sources 2 and 3 are set so that the beat frequency of the light source 1 and the light source 2 becomes Δfa = 13 GHz and the beat frequency of the light source 1 and the light source 3 becomes Δfb = 14 GHz. Negative feedback to. This is called a local wavelength lock mechanism. Similarly, based on the light sources 4, 7, and 10, the output light wavelengths of the light sources 5, 6, 8, 9, 11, and 12 are locked. These beat frequencies were also 13 GHz and 14 GHz, respectively, as shown in FIG.

On the other hand, the output wavelengths of the light sources 1, 4, 7, and 10 are stabilized in the same manner as in the first embodiment. as a result,
The wavelengths of all light sources are stabilized.

In this embodiment, as in the first embodiment, wavelength multiplexed light having a wavelength interval wider than the actual wavelength multiplexing interval is guided to the wavelength sensor and the wavelength is measured. Some features are mitigated.

In the above embodiment, the wavelength meter is used as the wavelength measuring means, but other wavelength measuring means as described in the prior art may be used. It is needless to say that a light source which does not need to be wavelength-stabilized among the wavelength-multiplexed light does not need to be incorporated in the wavelength stabilization system as described above.

<Embodiment of the Fourth Invention> A third embodiment of the invention of the fourth invention for explaining a method of recovering a failed light source will be described below.

This will be described with reference to FIGS. As described above, the horizontal axis is wavelength, and the top black circle (●) is WDM gr.
The lower part shows the wavelength (波長) at room temperature of the working LD and the variable wavelength range thereof at the room temperature. In a high-density WDM that has been actively studied in recent years, a plurality of grids can exist in the variable wavelength range of one LD. Conversely, a plurality of LDs can correspond to one grid. Therefore, a new backup method becomes possible.

In FIG. 5a), two or more LDs can correspond to one grid. Wavelength sections in which this relationship continues are defined as one group. In the figure, (1 to
3), (4 to 7), and (8 to 9) are groups. A backup LD is prepared only in a portion where the relationship is broken.

In the experiment of the third embodiment, the wavelength grid was set at an interval of 1 nm between 1530 nm and 1540 nm. That is, λi = 1530 + i [nm]. This experiment was performed using the same apparatus as the experiment of the first embodiment. The light source was a DFB LD, and the variable wavelength range was about 2 nm, including about 1.3 nm on the short wavelength side and about 0.7 nm on the long wavelength side from room temperature wavelengths. The data of the wavelength of each LD at room temperature (25 ° C.) is all stored in the PC. In addition, from a preliminary experiment, the rate of change in wavelength with respect to temperature was uniformly 0.067 nm.
/ ° C., and the variable range of temperature is 5 to 35 ° C., so that the above-described wavelength variable range of about 2 nm can be obtained.

First, the wavelength g is adjusted so that the state shown in FIG.
The lid and the LD were made to correspond. An LD that outputs λi is referred to as LDi for convenience of explanation. The backup LDs BLDi are 1532.5 nm, 1535.6 nm and 153 nm.
Each was arranged at 9.5 nm. This is the wavelength at the boundary between groups as described above.

The operation of the present invention will be described in the case where the LD 5 in the group (4-7) has failed. First, the BLD 2 is made active and assigned to λ7. LD7 is λ6, LD6
Is sequentially shifted to λ5, and finally, as shown in FIG. 5B), the light sources of all the wavelengths are aligned again, and it is possible to recover from the failure state. All of these operations are automatically performed by the PC. Actually, when the output optical fiber connector of the LD 5 was intentionally removed, the apparatus recovered from the failure state by the above procedure. LD
If an LD having a wavelength corresponding to 5 can be obtained, the reverse shift is performed and the BLD 2 may be brought into the backup state again.

With such a backup method, the number of standby light sources can be significantly reduced. In this example, the wavelength interval is 1 nm, which is not so remarkable. Nevertheless, the conventional method requires at least five backup LDs, whereas the present embodiment requires only three backup LDs. By devising so that all 10 wavelengths belong to one group, the number can be reduced to one.

During the shift of the wavelength, it is necessary to frequently obtain the information on the wavelength of the light source. For this purpose, the measurement range of the wavelength sensor is set within the wavelength range of interest only during the wavelength shift. What is necessary is to concentrate and reduce the frequency of measuring other wavelengths. If a certain period of time has elapsed after the operation of the device, the entire device reaches thermal equilibrium, so that the wavelength accuracy can be maintained even if the frequency of the negative feedback is reduced. In fact, in the present embodiment, such a mechanism is incorporated in the program. In the recovery experiment of the LD5 described above, one cycle is usually 180 seconds by the timer operation, but when the wavelength shift starts for failure recovery, only the wavelength range is swept without the timer operation and the temperature is negatively feedback-controlled. . One cycle was about 3 seconds, and the time until all the wavelengths were restored was about 90 seconds.

In this embodiment, two light sources can correspond to one wavelength grid.
The present invention is more effective when three or more light sources can correspond to the lid. In this case, since the light source can be shifted on both the short wavelength side and the long wavelength side, it is preferable to shift between the failed light source and the backup light source having a small wavelength difference. For example, in FIG.
In case of failure, BLD1 has the smallest wavelength difference, so if LD4 can also output λ5,
When shifting from LD4 to λ5, BLD1 to λ4, the number of LDs to be shifted can be reduced.

In the third embodiment, all channels in the wavelength range from the failed LD to the backup LD must be once avoided by another channel. Therefore, the fourth and fifth embodiments are designed to minimize the number of channels that must be avoided.

The fourth embodiment is a method for automatically tracking the wavelength on the receiving side. When the transmitting side performs wavelength shift,
If the wavelength is tracked on the receiving side, the shift can be performed without data loss. For example, the transition from a) to b) in FIG. 5 is as follows. First, the wavelength of the LD 6 shifts to λ5, and the wavelength of the LD 7 shifts to λ6. In synchronization with that, the OBPF that has selected λ6 on the receiving side becomes λ5
The OBPF that has selected λ7 continuously shifts the selected wavelength to λ6. As a result of such a procedure, the temporary loss of data occurs only in the λ7-LD7 channel except for the failed λ5-LD5 channel.

The automatic tracking method on the receiving side uses a variable transmission wavelength O
A method of dithering the center wavelength of the BPF, synchronously detecting the average power of the transmitted light, detecting the difference between the center transmission wavelength of the OBPF and the signal wavelength, and performing negative feedback on the center transmission wavelength of the OBPF to track the OBPF. It is commonly used.

The fifth embodiment is a method using a spare channel. This will be described with reference to FIGS. Figure 6 shows the initial state.
a). Here, the light source of λ1 is changed from LD1 to LDs.
The operation for switching to tby will be described. First, as shown in FIG. 6B), a channel for temporary avoidance is prepared in λtmp, and channel A (ch. A in the figure) is temporarily avoided. Next, FIG.
As shown in c), LD1 is turned off and L for backup is turned off.
Turn on Sstby to adjust the wavelength to λ1. Finally, as shown in FIG. 6D), the channel A temporarily avoided is restored. Since LD1 is now in the backup state, LD2 and LD1 can be switched by repeating the same operation. In this way, it is possible to change the order.

In this case, it is necessary to simultaneously switch the correspondence between the channel and the wavelength grid on both the transmitting and receiving sides. For this purpose, a configuration as disclosed in Japanese Patent Application Laid-Open No. Sho 59-086929, "Optical Transmission System" may be used. FIG. 7 shows an example of the configuration. Each channel for transmission and reception is λtmp
It is only necessary to provide a switch that replaces only the channel, and a large-scale switch network is not required.

The channel used for the temporary avoidance is not limited to the λtmp channel multiplexed on the same fiber, and it goes without saying that the type is not limited as long as it is a channel connecting the transmitter and the receiver. For example, a channel via another optical fiber may be used.

In order to prevent data loss of channels other than the failed channel, a non-instantaneous interruption switch may be used.

[0053]

According to the first to third aspects of the present invention, wavelength stabilization can be realized easily and inexpensively even in a high-density wavelength multiplex transmitter.

According to the fourth aspect of the present invention, the number of spare light sources in preparation for a light source failure can be significantly reduced, and both low cost and high reliability can be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment for explaining the inventions of claims 1 to 3;

FIG. 2 is an explanatory diagram of a wavelength arrangement according to the first embodiment for describing the inventions of claims 1 to 3;

FIG. 3 is a configuration diagram of a second embodiment for explaining the invention of claim 1;

FIG. 4 is an explanatory diagram of a wavelength arrangement according to a second embodiment for explaining the invention of claim 1;

FIG. 5 is an explanatory view of a wavelength arrangement according to a third embodiment for explaining the invention of claim 4;

FIG. 6 is an operation explanatory view of a fifth embodiment for explaining the invention of claim 4;

FIG. 7 is a block diagram of a fifth embodiment for explaining the invention of claim 4;

FIG. 8 is a configuration diagram of a conventional wavelength stabilization system.

FIG. 9 is an explanatory view of a conventional method of recovering a failed light source.

Claims (4)

[Claims] 1. A wavelength tunable light source provided with a means for controlling the wavelength of output light, comprising: a plurality of tunable light sources whose wavelengths are set to different values from each other; A wavelength division multiplexing technique, comprising: a demultiplexer that branches a part of the wavelength multiplexed light output from the multiplexing means; And a wavelength measuring means for outputting signals corresponding to the plurality of wavelengths included in the wavelength multiplexed light, and calculating an error of the plurality of wavelength measured values with respect to respective wavelength set values of the plurality of light sources. A wavelength multiplexing optical transmission device having a wavelength stabilizing function by having a means for negatively feeding back to each of the wavelength control means of the plurality of light sources, wherein a partially branched light of the wavelength multiplexing light to be input to the wavelength measuring means. In this partly branched light Minimum value of Murrell wavelength and wavelength intervals, characterized in that it is set to be wider than the minimum wavelength resolution of the wavelength measuring device, the wavelength-multiplexed optical transmission system. 2. The partially branched light according to claim 1, wherein the light from the plurality of light sources is set to be included in any one of the plurality of partially branched lights. WDM optical transmitter. 3. The wavelength measuring device according to claim 1, wherein a part of the plurality of wavelength division multiplexed lights is inputted to an optical switch means, and one of the partially branched lights is inputted to the wavelength measuring means in a time division manner to measure the wavelength. Claim 2.
The wavelength-division multiplexing optical transmission device as described in the above. 4. A wavelength tunable light source provided with means for controlling the wavelength of output light, comprising: a plurality of tunable light sources whose wavelengths are set to values different from each other; A wavelength division multiplexing device, wherein each of the plurality of wavelength setting values is within a wavelength tunable range of a plurality of wavelength tunable light sources. In the transmitter, when a light source of a certain wavelength fails, the original wavelength setting value is restored by sequentially shifting the wavelength of the light source existing between the wavelength of the failed light source and the wavelength of the spare light source. A wavelength multiplexing optical transmission device characterized by having a function of recovering from a light source failure.