JP3262475B2 - Wavelength control method used for wavelength multiplex communication and optical communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wavelength multiplex communication, and more particularly, to an optical transmitter and an optical transceiver used for wavelength multiplex communication, an optical communication system for wavelength multiplex communication, and wavelength multiplex communication. The present invention relates to a wavelength control method in an optical transmitter used for the present invention.

[0002]

2. Description of the Related Art Wavelength division multiplexing communication can have a large number of independent channels in one transmission line. Since multiplexing on the time axis such as frame synchronization is not required, it is not necessary to match the transmission speed of each channel, which is suitable for multimedia communication that requires network flexibility.

As an example of a wavelength division multiplex communication system, there is a system in which each terminal has a set of optical transmitters and optical receivers whose wavelengths are variable. The transmitting terminal tunes the wavelength of the wavelength variable light source of the optical transmitter to a wavelength not used for communication ("channel" of wavelength multiplex communication). On the other hand, the receiving terminal receives the signal after making the center wavelength of the transmission spectrum of the optical bandpass filter (hereinafter, referred to as an optical filter) of the optical receiver coincide with the wavelength to be received (hereinafter, referred to as the wavelength of the optical filter). The wavelength range that can be used in the system is determined by the wavelength tunable range of the optical transmitter and the optical receiver. Further, the wavelength interval of a channel (hereinafter, referred to as a channel interval) is determined by the width of the transmission spectrum of the optical filter of the optical receiver.

As a wavelength variable light source, a wavelength variable semiconductor laser (hereinafter, a semiconductor laser is called an LD) can be used. Research is underway to expand the wavelength tunable range, but at the current practical level, a multi-electrode DBR (distr
ibuted Bragg refrector) or DFB (distributed feedba
ck) type, and the wavelength variable width is several nm. An example is described in the publication OQE89-116 of the Institute of Electronics, Information and Communication Engineers, “Three-electrode long cavity λ / 4 shift MQW-DFB laser”. On the other hand, a Fabry-Perot resonator type filter can be used as the wavelength variable filter. A wavelength variable width of several tens of nm and a spectrum width of about 0.1 nm are at a practical level. An example is the publication ECOC'90-605, "A
field-worthy, high-performance, tunable fiber Fab
ry-Perot filter ".

[0005]

By narrowing the channel spacing, many channels can be obtained with the same wavelength variable width. In order to make the interval smaller than the fluctuation width due to the drift of the wavelength of the LD and the optical filter, the influence of the drift must be suppressed by control. In order to suppress the influence of drift, it is necessary to stabilize the wavelength absolutely or relatively. However, the absolute reference of the wavelength is not simple. Also, it is difficult to stabilize relatively in a communication system such as a LAN where the optical transmitter is located at a remote place.

[0006]

According to the present invention, in order to solve the above-mentioned problems, in an optical transmitter, one of the wavelengths adjacent to one of the wavelengths on the wavelength axis and the emission wavelength of the own station are compared. The positional relationship on the wavelength axis is detected, and control is performed so that the wavelength interval between the adjacent wavelength and the emission wavelength of the own station is maintained at a predetermined interval. As a result, the transmission wavelengths of the respective stations are multiplexed sequentially from the end of the wavelength region in the order of transmission start on the wavelength axis. At this time, there is no need to absolutely control the wavelength nor to provide an absolute reference wavelength. Further, in the present invention, it is determined which of the adjacent wavelengths on the wavelength axis should be kept at a predetermined interval according to the type of data to be transmitted (channel interval required for transmitting the data and priority of the data). I do. Specifically, the optical transmitter of the present invention has the following configuration.

[0007] 1. An optical transmitter used in an optical communication system for performing wavelength division multiplexing communication on an optical transmission line, comprising: a light emitting unit capable of changing a light emitting wavelength of output light; a wavelength detecting unit detecting a wavelength of input light; Means for inputting light on a transmission path to the wavelength detecting means, switch means for selecting whether or not to output light from the light emitting means to the optical transmission path, and based on a detection result by the wavelength detecting means,
The wavelength interval between the emission wavelength of the light emitting means and the wavelength of another light adjacent to at least one of the long wavelength side and the short wavelength side of the wavelength region in which the wavelength multiplex communication is performed is controlled to be a predetermined interval. And a means for selecting either the long wavelength side or the short wavelength side depending on the type of data to be transmitted.

Further, the optical transmitter may have the following configuration.

[0009] 2. The optical transmitter determines, based on the detection result by the wavelength detecting unit, whether there is an empty space capable of outputting light from the light emitting unit to the optical transmission line without causing interference with other light on the optical transmission line. Having means.

[0010] 3. The wavelength detecting means has a tunable bandpass filter capable of controlling a transmission wavelength.

4. The light emitting means is a wavelength tunable laser capable of controlling an oscillation wavelength.

An optical transceiver according to the present invention is configured as follows using the optical transmitter described above.

5. An optical transceiver for use in an optical communication system for performing wavelength division multiplexing communication on an optical transmission line, wherein
And an optical transmitter for selecting an optical signal to be received by its own optical transceiver from the input optical signal and receiving the received signal by following a variation in the wavelength of the optical signal. Having.

The optical communication system of the present invention is configured as follows.

6. An optical communication system for performing wavelength division multiplexing communication by connecting a plurality of terminal stations each having an optical transmitter, wherein the transmission wavelengths of the optical transmitters of the plurality of terminal stations are longer than the wavelength region in which the wavelength division multiplexing communication is performed. An optical communication system characterized in that wavelength multiplexing is sequentially performed from both the wavelength side and the short wavelength side in the transmission start order. In addition, this optical communication system can have the following configuration.

[7] The wavelength intervals at the time of wavelength multiplexing on the long wavelength side and the short wavelength side are different.

8. Only a transmission wavelength with a high priority is multiplexed on either the long wavelength side or the short wavelength side.

9. In the configuration described in the above item 8, a predetermined wavelength is set in the wavelength region, and only a transmission wavelength having a high priority is multiplexed on the long wavelength side of the predetermined wavelength or on the short wavelength side of the predetermined wavelength.

10. 10. In the optical communication system according to any one of the above items 6 to 9, each of the terminal stations selects an optical signal to be received by the own terminal station from the input optical signal, and causes the received wavelength to follow a fluctuation in the wavelength of the optical signal. It has a receiver for receiving.

The emission wavelength control method of the present invention is configured as follows.

11. An emission wavelength control method for a light emitting unit of an optical transmitter used in an optical communication system for performing wavelength division multiplexing communication on an optical transmission line, comprising detecting a wavelength of light other than output light of a self light emitting unit on the optical transmission line, and An empty space that does not interfere with other light even when the light from the light emitting means is output onto the optical transmission path is searched for, and the light emitting means is controlled to emit light at a wavelength in the empty space, and the emission wavelength of the light emitting means is controlled. When,
One of the long wavelength side and the short wavelength side of the wavelength region in which the wavelength multiplexing communication is performed is determined according to the type of data to be transmitted, and the wavelength interval with another adjacent light wavelength is maintained at a predetermined interval.

Further, in this emission wavelength control method, the following configuration can be adopted.

12. The predetermined interval is different between when the wavelength of the other adjacent light is on the long wavelength side and when it is on the short wavelength side.

Further, the second emission wavelength control method of the present invention comprises:
It is configured as follows.

13. An emission wavelength control method for a light emitting unit of an optical transmitter used in an optical communication system for performing wavelength division multiplexing communication on an optical transmission line, comprising detecting a wavelength of light other than output light of a self light emitting unit on the optical transmission line, and Even if the light from the light emitting means is output onto the optical transmission line, an empty space that does not interfere with other light is searched for, and the light emitting means is controlled to emit light at a wavelength within the empty space, and the emission wavelength of the light emitting means is controlled. A first wavelength which is longer or shorter than a predetermined wavelength in a wavelength region in which the wavelength multiplex communication is performed.
The emission wavelength is controlled so as to maintain a predetermined interval between the wavelength of the other light adjacent to the other wavelength on the wavelength side, and the predetermined wavelength interval between the wavelength of the other adjacent light on the first wavelength side. In the case where the emission wavelength exceeds the predetermined wavelength when the control is performed so as to keep the interval of the data and the type of data to be transmitted is a high priority type, the adjacent wavelength is adjacent on the second wavelength side. The wavelength interval from other light wavelengths is kept at a predetermined interval.

Further, this emission wavelength control method may have the following configuration.

14. If there is no other adjacent light to keep the predetermined interval, control is performed so as to emit light at the longest or shortest wavelength that the self-light emitting means can emit.

Further, in the emission wavelength control method described in the above items 11 to 14, the following configuration can be adopted.

15. The wavelength is detected by sweeping the detectable wavelength of the wavelength detecting means in the transmitter.

16. In the emission wavelength control method described in the above 15, the area including at least the wavelength variable range of the self-emission means is detected by sweeping.

17. In the emission wavelength control method according to any one of the above 15 and 16, the self-emission means is caused to emit light at the time of the sweep detection, and the wavelength detectable by the wavelength detection means is swept, so that the wavelength of the output light of the self-emission means is adjusted on the optical transmission line. At the same time as the wavelength of the other light.

18. 18. The emission wavelength control method according to the above 17, wherein the output light of the self-luminous means is input to the wavelength detecting means without being output to the optical transmission path, and the wavelength of the output light of the self-luminous means is changed to another light on the optical transmission path. At the same time as the wavelength.

19. In the emission wavelength control method according to any one of the above 11 to 18, the wavelength of the output light of the self-luminous means and the wavelength interval of the adjacent other light are detected as needed, so that the wavelength interval is not a predetermined interval. The self-luminous means is controlled so as to approach a predetermined interval. Further, the wavelength control method used in the wavelength division multiplexing communication according to the present invention is a self-luminous means, a branching means for branching light emitted from the self-luminous means,
An optical switch for controlling the output of the first light branched by the branching means to an optical transmission line, and a wavelength detection for detecting the wavelength of the second light branched by the branching means and the wavelength of the light on the optical transmission path Using an optical communication system configured including means,
A detecting step of detecting a wavelength of light other than the output light by the self-luminous means by sweeping a predetermined range by the wavelength detecting means on the optical transmission path; And a wavelength which does not interfere with the other light at a position separated by a predetermined distance from the wavelength of another light adjacent on the short wavelength side (long wavelength side) on the wavelength axis on the optical transmission line. A step of setting a wavelength, a step of sweeping the wavelength of the self-luminous means to coincide with the set wavelength in a state where the optical switch is turned off, a step of setting the optical switch to an output state, and Outputting the light, performing first wavelength control of the self-luminous means so as to maintain the predetermined interval with the wavelength of another light adjacent on the short wavelength side (long wavelength side),
Alternatively, the wavelength of the self-luminous means is shifted to a long wavelength side (short wavelength side) within a range that does not interfere with other light on the optical transmission line,
A step of selecting whether to perform the second wavelength control of the self-luminous means so as to maintain a predetermined interval with another light adjacent on the long wavelength side (short wavelength side), and the selected first or second selected It is characterized by having a step of performing wavelength control. Hereinafter, the present invention will be described with reference to examples.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic principle of the present invention will be described.
The basic principle of the present invention is to arrange the wavelengths of the respective optical transmitters in the network at regular intervals on the long wavelength side (or the short wavelength side) in the order in which transmission starts earlier. This scheme does not require an absolute or relative wavelength reference. The vicinity of the wavelength of the optical transmitter is swept by an optical filter (located in the optical transmitter) to maintain a wavelength interval between adjacent channels. The outline will be described below. In addition, although there are some differences in the configuration of a drawing used for description, and a component, the whole structure has the same function.

FIG. 4 is a configuration diagram of an example of an optical communication system using an optical transmitter to which the wavelength control method is applied. Number of terminal stations n
Is a star network. As shown in the figure, terminal stations 4-1-1 to n, optical nodes 4-2-1 to n, and n × n star coupler 4-
3, composed of optical fibers 4-4-1 to 4-n and 4-5-1 to n. Also,
Each of the optical nodes 4-2-1 to 4-n includes an optical transmitter 4-6, an optical receiver 4-7, and an optical splitter 4-8.

The terminal stations 4-1-1 to n are connected to the network by optical nodes 4-2-1 to n. Each of the optical nodes 4-2-1 to n has an optical fiber for transmission 4-4-1 to n and an optical fiber for reception 4-5-1 to n
To connect to the n × n star coupler 4-3. The transmission light from the optical transmitter is sent to the n × n star coupler 4-3 via the transmission optical fibers 4-4-1 to 4-n. The nxn star coupler 4-3 distributes the transmission light equally to the receiving optical fibers 4-5-1 to 4-n and sends the same to the optical nodes 4-2-1 to n. The incident light from the receiving optical fibers 4-5-1 to 4-n is split into two by an optical splitter 4-8 and input to an optical receiver 4-7 and an optical transmitter 4-6. With this configuration, the transmission light of the own station enters the optical filter of the optical transmitter together with the transmission light of the other station.

FIG. 8 is a configuration diagram of an optical transmitter to which the present basic principle is applied. As shown, the wavelength control systems 2-1, LD2-2,
Optical filter 2-3, LD drive circuit 2-4, Optical filter drive circuit 2-
5, light receiving element 2-6, amplifier 2-7, discriminator 2-8, optical modulator 2-9
It consists of.

The wavelength control system 2-1 controls the LD drive circuit 2-4 and the optical filter control circuit 2-5 based on the output signal of the discriminator 2-8 to perform a tuning operation. The start of tuning and the like is controlled from the terminal station. It is composed of an arithmetic processing circuit, a storage element, an A / D converter, a D / A converter, and the like. The parameters and operation procedures required for the tuning operation are stored.

As the LD 2-2 and the optical filter 2-3, the elements described in the above conventional example are used. The bandwidth (half-width, hereinafter referred to as λfb) of the transmission spectrum of the optical filter 2-3 is a main factor for determining the channel interval Δλ. Set to an appropriate value of Δλ or less. The wavelength tunable range of the optical filter 2-3 is larger than the wavelength tunable range of all LDs in the system.

The optical modulator 2-9 modulates the intensity of the output light of the LD 2-2 with the transmission signal. In the case of direct modulation with the current injected into the LD 2-2, a wavelength fluctuation of about 0.1 nm occurs. Therefore, in this example, an external intensity modulation method using an optical modulator is adopted.

The LD drive circuit 2-4 is provided with an LD from the wavelength control system 2-1.
The LD 2-2 is driven (current is injected) so as to have a wavelength corresponding to a control voltage (hereinafter, referred to as Ve). When the above-described three-electrode long-cavity λ / 4 shift MQW-DFB laser is used, its output becomes three. The amount of change in Ve is proportional to the amount of change in the wavelength of LD2-2. The amount of change of Ve corresponding to Δλ is defined as ΔVe. LD
Ve corresponding to the shortest wavelength in the variable wavelength range of 2-2 is Vemin, and Ve corresponding to the longest wavelength is Vemax. Step Ves when changing the value by controlling Ve during wavelength control is Δ
Set based on λ, λfb, etc. A value of 1/20 from the number of ΔVe is appropriate.

The optical filter driving circuit 2-5 includes a wavelength control system 2-1.
The optical filter 2-3 is driven so as to have a wavelength corresponding to the optical filter control voltage (hereinafter, referred to as Vf). The amount of change in Ve is proportional to the amount of change in the wavelength of LD2-2. The amount of change of Vf corresponding to Δλ is defined as ΔVf. It is assumed that Vf corresponding to the shortest wavelength in the wavelength variable range of the optical filter 2-3 is Vfmin, and Vf corresponding to the longest wavelength is Vfmax. The step Vfs of Vf at the time of wavelength control is set to a value corresponding to Ves. The response here is
This means that the amount of change in the wavelength of the LD when Ve is changed by Ves is equal to the amount of change in the wavelength of the optical filter when Vf is changed by Vfs.

The threshold value of the discriminator 2-8 depends on the wavelength of each channel incident on the optical filter 2-3 from the transmission line and the optical filter 2
The value is set to a value (for example, a half value) equal to or less than the output of the amplifier 2-8 when the wavelength of -3 matches. H if the input signal is above the threshold, L otherwise (H is 1, L of the digital signal
Indicates a digital signal 0).

FIG. 7 is an explanatory diagram of the operation of the present basic principle. There are “operation 1” to “operation 2”, which show the positional relationship between the LD and the wavelength of the optical filter in each operation. In the figure, λn (n = 1 to 4) is the wavelength of the optical transmitter performing transmission when the optical transmitter for explaining the operation starts tuning. λe is the LD wavelength of the optical transmitter for explaining the operation. λfs1 is the sweep start wavelength of the optical filter, and λfs2 is the sweep end wavelength of the optical filter.

In this wavelength control method, the wavelengths are relatively related by the control voltages Ve and Vf when the wavelength of the LD 2-2 (own station or another station) and the wavelength of the optical filter 2-3 coincide, and the wavelength is controlled. To keep the channel interval Δλ constant. Wavelength control system 2-
ΔVe and ΔVf stored in 1 have an error with respect to Δλ. For this reason, the range of the wavelength sweep for the relative correlation of the wavelengths is made large on both sides to allow the error. In this method, Vf is used as a reference for wavelength control. In the following explanation,
Let the enlarged value of Vf be dVf. As dVf, 1/10 from the number of ΔVf is appropriate.

The tuning is performed by setting the wavelength control system 2-1 to Ve and V
This is performed based on f and the output (H or L) of the classifier 2-8. Only when the wavelength of the LD of the other station or the own station matches the wavelength of the optical filter, the output of the discriminator 2-8 becomes H. Wavelength control system 2-
1 stores a control voltage (Ve for an LD, Vf for an optical filter) at which the output of the discriminator 2-8 becomes H when the wavelength of the LD 2-2 or the optical filter 2-3 is swept. However, when the sweep step of the wavelength is smaller than the transmission spectrum width of the optical filter, the control voltage which becomes H may be continuous. In that case, the average of those voltages is taken.

The tuning operation will be described with reference to FIG.

"Operation 1". With Ve as Vemin, LD2-2 is oscillated at the shortest wavelength, and Vf is swept from Vfmin to Vfmin + 2ΔVf + dVf (corresponding to λfmin to λfmin + 2Δλ + dλ in wavelength). By this operation, the wavelength of LD2-2 and the presence or absence of an empty channel can be determined. Vf at which the output of the discriminator 2-8 becomes H during the sweep corresponds to the wavelength of LD2-2. This value of Vf is stored as Vfm. Once the output of the discriminator 2-8 goes low, it goes high again.
, It is determined that there is no empty channel, and the tuning operation is stopped. Otherwise, it is determined that there is an empty channel, and "operation 2" is performed.

"Operation 2". Set Vem to the value from the previous operation (V
em is a value that is updated and stored in the control system for each operation or for each operation repetition so that it becomes a reference value when updating Ve when moving to the next operation or when repeating the same operation . ), Ve = Vem, and Vf from Vfm−dVf to Vfm +
Sweep to ΔVf + dVf (wavelength λe−dλ to λe + Δ
λ + dλ). During the sweep, the Vf at which the output of the discriminator 2-8 first becomes H is stored as Vfm1, and the Vf which once becomes L and becomes H again is stored as Vfm2 (however, if it does not become H again, Vfm2 is stored). = Vfm1 + ΔVf + dVf). If | Vfm2−Vfm1−ΔVf | ≦ Vfs: Vem = Vem Vfm2−Vfm1−ΔVf <−Vfs: Vem = Vem−Ves Vfm2−Vfm1−ΔVf>Vfs> Vem = Vem + Ves, and Operation 2 ″ is repeated. By this operation, λ
e shifts to the longer wavelength side, and the channel spacing of Δλ and the adjacent channel (λ4 in FIG. 7) on the longer wavelength side is maintained within the error range. When the transmission of a certain terminal station ends and the light of that wavelength disappears, the channel spacing on the long wavelength side of the short wavelength side becomes 2Δλ.
The wavelength shifts to the longer wavelength side, and the channel spacing becomes Δλ again. Thus, in the steady state, the wavelengths are arranged at a channel interval of Δλ from the long wavelength side. In the figure, (1) shows a state at the start of the shift, and (2) shows a state in which the shift is completed and Δλ is maintained. During the repetition of this operation, if Vem ≧ Vemax (when there is no terminal station transmitting before this terminal station starts transmission), the tuning operation ends.
The state of Ve = Vemax is maintained.

The present invention is a further improvement based on the above basic principle. In the above method, the LD oscillates at one end of the wavelength range and shifts to the other end. as a result,
The wavelengths are arranged in the order of starting transmission. Since channels of different types of signals (for example, signals having different transmission rates) may be adjacent to each other, the channel interval is set to be the widest. For this reason, when channels having narrow wavelength intervals are arranged, a wavelength wider than necessary is used, and the multiplicity of the system cannot be maximized. Further, the priority of communication cannot be set, and when the entire wavelength range of the LD is used, communication cannot be performed even with communication having high priority.

Therefore, in the present invention, as shown in the following embodiments, channels are divided into two wavelength regions as necessary.

Embodiment 1 Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a wavelength arrangement diagram of a first embodiment of the wavelength control system of the present invention. In this embodiment, there are two types of channels in the communication system. Channel A has a low transmission speed (for example, several tens to 100 Mb / s), and channel B has a high transmission speed (for example, about 1 Gb / s). In the figure, λan (n = 1 to 7)
Indicates the wavelength of the A channel, and λbn (n = 1 to 3) indicates the wavelength of the B channel (the smaller the n, the earlier the transmission start time). Δλa indicates a channel interval required for A channel transmission, and Δλb indicates a channel interval required for B channel transmission. Channel A is arranged at intervals of Δλa from the short wavelength side in ascending order of transmission start time, and channel B is arranged at intervals of Δλb from the long wavelength side in ascending order of transmission start time.

FIG. 2 is a configuration diagram of an optical transmitter to which the wavelength control method of the present invention is applied. Optical splitter 2-10, optical combiner 2-11,
The components other than the optical switch 2-12 are the same as those of the optical transmitter to which the above basic principle shown in FIG. 8 is applied, and therefore the description thereof is omitted here. Optical splitter 2-10 outputs the output light of LD to 2
And input to the optical switch 2-12 and optical combiner 2-11.
The optical combiner 2-12 combines the light and the light from the transmission line and inputs the combined light to the optical filter 2-3. Optical switch 2-11 is optical splitter 2-10
Is output to the transmission line when the ON / OFF signal is H, and is not output to the transmission line when the ON / OFF signal is L. With this configuration, the LD of LD2-2
Calibration of the control voltage Ve and the optical filter control voltage Vf of the optical filter 2-3 can be performed without emitting light to the transmission line.

FIG. 3 is an explanatory diagram of the operation of the first embodiment of the wavelength control system of the present invention. There are “operation 1” to “operation 3”, and the positional relationship between the wavelength of the LD 2-2 and the wavelength of the optical filter 2-3 in each operation is shown. In the figure, λan (n = 1 to 4) and λb
n (n = 1 to 2) is the wavelength of the optical transmitter that is transmitting when the optical transmitter explaining the operation starts tuning. λe is the LD wavelength of the optical transmitter for explaining the operation.
Λes1 and λes2 are the start wavelength and end wavelength of the sweep of the LD 2-2, respectively, and λfs1 and λfs2 are the start wavelength and end wavelength of the sweep of the optical filter 2-3, respectively. As in FIG. 1, the wavelengths λan (n = 1 to 4) of the A channel are arranged at intervals of Δλa from the short wavelength side in ascending order of the transmission start time, and the wavelength λbn (n = 1 to 2) of the B channel is the transmission start time Are arranged from the long wavelength side at an interval of Δλb in ascending order.

FIG. 4 is a configuration diagram of an example of an optical communication system using an optical transmitter to which the wavelength control method is applied. Since the description of this figure is as described above, it is omitted here.

In this embodiment, the optical transmitter searches for an empty space in the entire wavelength variable range of the built-in LD, starts tuning on the short wavelength side of the empty space, and shifts the wavelength to the long wavelength side. . In order to search for an empty space within the variable wavelength range of the LD, it is necessary to check the relative positional relationship between the LD and the wavelength on the transmission line. In order to avoid interference with other light on the transmission line, this operation is performed by cutting off the output to the transmission line by the optical switch 2-11.

The tuning operation is performed by the wavelength control system 2-1. Basic operation of wavelength control for tuning (sweep,
The relation between Ve and Vf, etc.) is the same as the basic principle described above, and the description thereof is omitted here. Hereinafter, the overall operation of tuning will be described (FIG. 3).

The LD control voltage steps Vesa, Vesb (Ve
sa is A channel, Vesb is B channel), optical filter control voltage steps Vfsa, Vfsb (Vfsa is A channel, Vfs
The setting of the half-width λfb of the transmission spectrum of the optical filter, the enlarged value dVf of the optical filter control voltage to allow an error in the system, and the like are the same as those of the above basic principle. An example is given below.

Vesa = 0.05ΔVea, Vesb = 0.05ΔVeb Vfsa = 0.05ΔVfa, Vfsb = 0.05ΔVfb λfb = 0.1Δλa dVf = 0.2ΔVfa where ΔVea is the change amount of Ve corresponding to Δλa, and ΔVeb is Ve corresponding to Δλb. ΔVfa is V corresponding to Δλa.
The change amount of f, ΔVfb, is the change amount of Vf corresponding to Δλb.

"Operation 1". Here, the wavelength of the optical filter 2-3 is set to an empty channel. In this behavior,
The LD may be in the OFF state, and the optical switch may be in either the ON / OFF state.

Vf is swept so that the wavelength of the optical filter 2-3 changes from the shortest wavelength to the long wavelength side. Vf sweep is Vfmin
(Vf at which the wavelength of the optical filter becomes the shortest wavelength).
During the sweep, the value of Vf when the output of
To be stored. Sweep to Vf = Vfm + ΔVfa + ΔVfb + 2dVf. Once the Vfm is stored, the output of the discriminator 2-8 becomes H
If it becomes, change Vfm to the value of Vf at that time, and Vf = Vfm
Sweep to + ΔVfa + ΔVfb + 2dVf. After this sweep, Vf
Vfm + ΔVfa + dVf is set. In the example of FIG. 3, by this operation, the wavelength of the optical filter is set to the longer wavelength side of λa4 by Δλa + dλ. At this time, the sweep of the optical filter is Vfm + ΔVfa
Since the operation is performed up to + ΔVfb + 2dVf, there is no other light wavelength at least between ΔVfb + dVf on the long wavelength side of the set optical filter.

When there is no other optical transmitter transmitting on the A channel, Vf is swept without storing Vfm. In this case, the sweep is stopped when Vf becomes equal to or more than a certain value (for example, 2ΔVfb + dVf), and “operation 2” is performed.

When Vf reaches the value Vfmax corresponding to the longest wavelength of the optical filter during the sweep, the tuning operation is stopped without any empty channel.

"Operation 2". Here, the wavelength of the LD 2-2 is matched with the wavelength of the optical filter 2-3. In this operation, the optical switch 2-12 is turned off.

Vf is set to the value in “operation 1” (Vfm + ΔVfa + dV
Set to f) and sweep the LD wavelength from the short wavelength side to the long wavelength side. Ve is swept from Vemin, the sweep is stopped when the output of the discriminator 2-8 becomes H, and Ve at that time is stored as Vem. With this operation, the wavelength of LD2-2 is set to the longer wavelength side of λa4, Δλa + dλ, and within the wavelength region where wavelength multiplex communication is performed,
LD2- in an empty space that does not cause interference with other light wavelengths
The wavelength of 2 is set.

"Operation 3". In this operation, the wavelength is shifted and the channel interval is maintained. This operation depends on the type of the channel and the control state. "Operation 3-
“A” transmits on the A channel, and “operation 3 -B” transmits on the B channel.The optical switch is ON in any operation.

"Operation 3-A". Ve is set to the value in the previous operation, and Vf is swept from Vfm + dVf to Vfm−ΔVfa−dVf (corresponding to λe + dλ to λe−Δλa−dλ in wavelength). Vf when the output of the discriminator 2-8 first became H during the sweep
Vfm1, and then Vf, which once goes low and goes high again, is stored as Vfm2. As a result, the wavelength interval between the wavelength of LD2-2 and the adjacent wavelength (λa4) on the A channel side becomes Vfm1 (the control voltage of the optical filter when the wavelength of LD2-2 is detected) and Vfm2 (λa4
Is detected as the difference between the control voltages of the optical filters at the time of detection. (However, if it does not become H again, LD2
The wavelength of −2 and λa4 are at least Δλa + dλ apart from each other, so provisionally, Vfm2 = Vfm1−ΔVfa−dVf). If | Vfm1−Vfm2−ΔVfa | ≦ Vfsa: Vem = Vem Vfm1−Vfm2−ΔVfa <−Vfsa: Vem = Vem + Vesa If Vfm1−Vfm2−ΔVfa> Vfsa: Vem = Vem−Vesa. Operation 3-A "is repeated. By this operation, λe becomes an adjacent channel on the short wavelength side (λa4 in FIG. 3).
And Δλa are maintained within the error range. In the figure, (1) indicates the start of the shift, and (2) indicates the end of the shift and Δλa
Is maintained. During the repetition of this operation, when Vem ≦ Vemin (when there is no node transmitting on the A channel before this node starts transmission), the tuning operation is terminated and Ve
= Vemin is maintained.

"Operation 3-B". In this operation, Ve is set to the value in the previous operation, and Vf is changed from Vfm−dVf to Vfm + ΔVfb + dV
Sweep to f (λe-dλ to λe + Δλb + dλ in wavelength)
Equivalent). During the sweep, the Vf whose output of the discriminator 2-8 first became H is Vfm1, and then the Vf which once became L and became H again is Vf
Store as m2. As a result, the wavelength interval between the wavelength of LD2-2 and the adjacent wavelength (λb2) on the B channel side becomes Vfm1 (LD2-
Control voltage of the optical filter when the wavelength of 2 is detected) and Vfm
2 (the control voltage of the optical filter when λb2 is detected). (However, if it does not become H again, the wavelength of LD2-2 and λb2 will be at least Δλb + dλ apart from each other. Therefore, provisionally, Vfm2 = Vfm1 + ΔVf
b + dVf). If | Vfm2−Vfm1−ΔVfb | ≦ Vfsb: Vem = Vem Vfm2−Vfm1−ΔVfb <−Vfsb: Vem = Vem−Vesb Vfm2−Vfm1−ΔVfb> Vfsb: Vem = Vem + Vesb. Operation 3-B "is repeated. By this operation, λe shifts to the long wavelength side, and the channel interval between the adjacent channel on the long wavelength side (λb2 in FIG. 3) and Δλb is maintained within the error range. In the figure, (1) is at the start of the shift,
(2) shows a state in which the shift is completed and Δλb is maintained. While repeating this operation, Vem ≧ V
emax (before this node starts transmitting, B
If there is no node transmitting on the channel), the tuning operation ends, and the state of Ve = Vemax is maintained.

The tuning of the LD of the optical transmitter, which is a feature of the present invention, has been described above. Next, an example of transmission and reception when this method is used will be described.

Transmission of communication data is started after a certain period of time after "operation 3" in FIG. Until then, an idle signal is transmitted. This is to wait for the time required for the wavelength of the optical filter in the optical receiver on the receiving side to match the channel and to identify the destination address. A destination address is attached to the idling signal, and is used to identify a receiving channel on the receiving side.

The reception is performed by transmitting only the wavelength of the channel to be received from the wavelength division multiplexed signal through the optical filter in the optical receiver. The optical receiver sequentially matches the wavelength of the optical filter in the optical receiver with the wavelength of the light on the transmission line, and checks whether or not the destination address exists and whether the address is addressed to the own station. If the destination address is the address of the own station, the wavelength of the optical filter is locked to the wavelength of the light and reception is started. At this time, the receiving station's LD2-2
Therefore, the shift step of the LD 2-2 and the bandwidth of the optical filter on the receiving side are set in association with each other.

As described above, in this embodiment,
Since the A channel and the B channel are arranged separately, the channel interval can be minimized, and the number of channels in the wavelength range of the wavelength division multiplex system can be increased.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 5 is a wavelength arrangement diagram of a second embodiment of the wavelength control system according to the present invention. In the figure, λan (n = 1 to 7) indicates the wavelength of the A channel, and λbn (n = 1 to 4) indicates the wavelength of the B channel (the smaller the n, the earlier the transmission start time). Δλ indicates a channel interval. The wavelength range for the priority channel is set on the long wavelength side of the wavelength range of the wavelength multiplexing system. λt is the shorter wavelength end of the wavelength range for the priority channel. Some of the A and B channels are arranged at intervals of Δλ from the short wavelength side in ascending order of the transmission start time, and the rest of the B channels are arranged at intervals of Δλ from the long wavelength side in ascending order of the transmission start time.

The configuration of the optical transmitter used in the present embodiment and the applicable communication system are the same as those in the first embodiment, and a description thereof will be omitted.

In the second embodiment, an area dedicated to the priority channel is set on the long wavelength side of the wavelength multiplexing range, and the channels of the communication system are given priority. There are two types of channels (A, B) with equal channel spacing, with the B channel having priority over the A channel.

The operation is basically the same as that of the first embodiment. The different parts will be described with reference to FIGS. The wavelength control system 2-1 stores Vf: Vft at which the wavelength of the optical filter 2-3 becomes λt. The "operation" in the following description refers to the operation in the first embodiment. In addition, since the channel interval between the A channel and the B channel is equal, Δλa,
There is no difference in the control amount between channels such as Δλb, ΔVsa, and ΔVsb.

At the time of sweeping the optical filter 2-3 in “operation 1”, Vf
Until Vft reaches Vft, tuning is performed on both the A channel and the B channel by the same operation as the A channel of the first embodiment. As a result, each wavelength becomes Δλ from the short wavelength side in the order of early transmission (regardless of A channel or B channel).
Lined up at intervals. In FIG. 5, λa1, λa2, λa3, λb1, λa
4, λa5, λa6, λa7.

When sweeping the optical filter 2-3 in “operation 1”, Vf
If V reaches Vft, transmission cannot be performed on the A channel, and the tuning operation stops here. Thereafter, the tuning operation is restarted after waiting (repeating the sweep of the optical filter 2-3 and waiting until Vf does not reach Vft).

On the other hand, in the B channel, regardless of Vft,
The operation of the B channel of the first embodiment is continued. As a result, even after transmission becomes impossible in the A channel, transmission can be performed in the B channel, and the wavelength used for the communication is Δλ from the longer wavelength side in the order of transmission start earlier.
Lined up at intervals. In FIG. 5, they are arranged in the order of λb2, λb3, λb4.

As described above, in this embodiment, the priority of communication can be realized by giving the right to use the B channel to some terminal stations in the communication system.

(Embodiment 3) Hereinafter, a third embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 6 is an explanatory diagram of the operation of the third embodiment of the wavelength control system according to the present invention. The symbols in the figure are the same as in FIG.

The third embodiment differs from the first embodiment in the "operation 1" and the "operation 2" in the tuning operation of the B channel. Specifically, if you want to send on the B channel,
In operation 1, the wavelength of the optical filter is set on the B channel side (at a distance of Δλb + dλ from the wavelength at the end of the B channel), and in operation 2, the wavelength of the LD 2-2 is similarly set. This is shown in FIG. The difference from the first embodiment (FIG. 3) will be described below.

The sweep of the optical filter 2-3 in “operation 1” is changed from Vfmax to Vfm−ΔVfa−ΔVfb−2dVf. Also,
The set value of Vf after the sweep is set to Vfm−ΔVfb−dVf. Thereby, the wavelength of the optical filter is set with an interval of λb2 and Δλb + dλ.

In the “operation 2”, the wavelength of the LD 2-2 is swept from the long wavelength side to the short wavelength side until it matches the transmission wavelength of the optical filter. Sweep of Ve is performed in the decreasing direction from Vemax.

The other parts are the same as in the first embodiment.

In the present embodiment, the operation of gradually shifting the wavelength of LD2-2 in the B channel from the short wavelength end of the empty space to the long wavelength side ((1) of "operation 3-B" in FIG. 3). Since there is no tuning, the tuning time of the B channel can be reduced.

(Other Embodiments) The short wavelength side and the long wavelength side are determined in the description of each embodiment in order to make the arrangement of channels and the direction of shift concrete.

[0091] The types of channels having different channel intervals, one having priority over the other, have been described. However, the present invention can be applied to other types of channels.

The LD of the own station is oscillated at a wavelength that does not interfere with the wavelength of the other transmitting terminal, shifted to one end of the wavelength range, and a wavelength interval that does not interfere with the adjacent wavelength is maintained. It is also possible to use the tuning operation of.

The components are not limited to those described in the embodiments as long as they have the same function (the same applies to a system composed of several components). Further, the numerical values are not limited to the described values as long as they are within the allowable range of the operation.

[0094]

As described above, according to the present invention, it is not necessary to stabilize the emission wavelength absolutely, and it is not necessary to provide a reference wavelength for stabilizing the emission wavelength. Also, wavelength multiplexing can be performed efficiently.

Further, according to the present invention, the channels can be divided into two wavelength regions as required. Thereby, flexible channel management can be realized.

According to the present invention, when there are two or more types of channels having different wavelength intervals in a wavelength division multiplexing communication system, a channel having a wide channel interval and a channel having a narrow channel interval can be arranged separately in a wavelength region. The number of channels that can be multiplexed can be increased,
The wavelength region can be used efficiently.

Further, according to the present invention, it is possible to give priority to some channels of the wavelength division multiplexing communication system.

[Brief description of the drawings]

FIG. 1 is a wavelength arrangement diagram of a first embodiment of a wavelength control system according to the present invention.

FIG. 2 is a configuration diagram of an optical transmitter to which the wavelength control method of the present invention is applied.

FIG. 3 is an explanatory diagram of the operation of the first embodiment of the wavelength control system of the present invention.

FIG. 4 is a configuration diagram of an optical communication system.

FIG. 5 is a wavelength arrangement diagram of a second embodiment of the wavelength control system according to the present invention.

FIG. 6 is an explanatory diagram of an operation of a third embodiment of the wavelength control system of the present invention.

FIG. 7 is an explanatory diagram of an operation of a wavelength control method serving as a basic principle of the present invention.

FIG. 8 is a configuration diagram of an optical transmitter to which the basic principle of the present invention is applied.

FIG. 9 is a wavelength arrangement diagram of the operation of the basic principle of the present invention.

[Explanation of symbols]

 2-1 Wavelength control system 2-2 LD 2-3 Optical filter 2-4 LD drive circuit 2-5 Optical filter drive circuit 2-6 Light receiving element 2-7 Amplifier 2-8 Discriminator 2-9 Optical modulator 2- Reference Signs List 10 optical splitter 2-11 optical coupler 2-12 optical switch 4-1 terminal station 4-2 optical node 4-3 nxn star coupler 4-4,5 optical fiber 4-6 optical transmitter 4-7 light Receiver 4-8 Optical splitter

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04B 10/20 10/26 10/28 H04J 14/02 (56) References JP-A-4-318713 (JP, A) JP JP-A-4-37225 (JP, A) JP-A-3-214830 (JP, A) JP-A-6-120896 (JP, A) JP-A-59-182638 (JP, A) (58) .Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H01S 5/06

Claims (3)

(57) [Claims] 1. A wavelength control method used for wavelength-division multiplexing communication on an optical transmission line, comprising: a self-luminous unit; a branch unit for branching light emitted from the self-luminous unit; An optical communication system configured to include an optical switch that controls output of light to an optical transmission line, a second light branched by the branching unit, and a wavelength detection unit that detects a wavelength of light on the optical transmission line. A detecting step of detecting a wavelength of light other than the output light by the self-luminous means by sweeping a predetermined range by the wavelength detecting means on the optical transmission line; and an empty space recognized based on the detecting step. The wavelength of the wavelength detection means is set to a wavelength that is not within the region and at a predetermined distance from the wavelength of another light adjacent to the short wavelength side on the wavelength axis on the optical transmission path and does not interfere with other light. Performing the optical switch Sweeping the wavelength of the self-luminous means to coincide with the set wavelength in a state where no light is output, setting the optical switch in an output state, and outputting light by the self-luminous means, the short wavelength The first wavelength control of the self light emitting means is performed so as to maintain the predetermined interval with the wavelength of another light adjacent on the side, or the wavelength of the self light emitting means is not interfered with other light on the optical transmission line. Selecting whether to perform the second wavelength control of the self-luminous means so as to shift to a longer wavelength side in the range and maintain a predetermined interval with other light adjacent to the longer wavelength side; and Alternatively, a wavelength control method comprising a step of performing a second wavelength control. 2. A wavelength control method used for wavelength-division multiplexing communication on an optical transmission line, comprising: a self-luminous unit; a branch unit for branching light emitted from the self-luminous unit; An optical communication system configured to include an optical switch that controls output of light to an optical transmission line, a second light branched by the branching unit, and a wavelength detection unit that detects a wavelength of light on the optical transmission line. A detecting step of detecting a wavelength of light other than the output light by the self-luminous means by sweeping a predetermined range by the wavelength detecting means on the optical transmission line; and an empty space recognized based on the detecting step. The wavelength of the wavelength detecting means is set to a wavelength that does not interfere with other light at a position that is within a range and at a predetermined distance from the wavelength of other light adjacent on the long wavelength side on the wavelength axis on the optical transmission line. Performing the optical switch Sweeping the wavelength of the self-luminous means to match the set wavelength in a state in which the light is not output; setting the optical switch to an output state; and outputting light by the self-luminous means; The first wavelength control of the self light emitting means is performed so as to maintain the predetermined interval with the wavelength of another light adjacent on the side, or the wavelength of the self light emitting means is not interfered with other light on the optical transmission line. Selecting whether to perform the second wavelength control of the self-luminous means so as to maintain a predetermined distance from other light adjacent on the short wavelength side by shifting to the short wavelength side in the range, and Alternatively, a wavelength control method comprising a step of performing a second wavelength control. 3. An optical communication system comprising the self-luminous means, the branching means, the optical switch, and the wavelength detecting means for performing the wavelength control method according to claim 1 or 2.