WO2004088893A1

WO2004088893A1 - Optical branching device

Info

Publication number: WO2004088893A1
Application number: PCT/JP2003/004035
Authority: WO
Inventors: Izumi Yokota
Original assignee: Fujitsu Limited
Priority date: 2003-03-28
Filing date: 2003-03-28
Publication date: 2004-10-14
Also published as: JPWO2004088893A1

Abstract

An optical branching device for branching a trunk line of a wavelength multiplex signal optical communication system on wavelength multiplex signal light basis to branch lines. The device includes monitor means for monitoring power of signal light as a sum of input signal light from the trunk line and input signal light from the branch line and switching means for attenuating the input signal light from the trunk line and outputting the input signal light from the branch line when the signal light power obtained by the monitor means is above a threshold value and for releasing the attenuation of the input signal light from the trunk line and outputting it when the signal light power obtained by the monitor means is below the threshold value. Thus, it is possible to perform communication without requiring a guard band and reducing the number of wavelength multiplexes. When a branch line has failed, it is possible to use another branch line having no failure.

Description

Description Optical branching device Technical field

The present invention relates to an optical branching device, and more particularly to an optical branching device used in a wavelength division multiplexed signal optical communication system. Background art

Due to the spread of the Internet and other factors, the amount of information transmitted via networks has been rapidly increasing, and there is a need for a further increase in the capacity of transmission systems. Wavelength division multiplexing (WDM) has been put into practical use. In a wavelength multiplexed signal optical communication system, a plurality of terminal stations are connected by an optical transmission line, an optical branching device, and an optical repeater.

The function of an optical branching device applied to a wavelength division multiplexed signal optical communication system having at least three terminal stations can be roughly divided into two. One is to switch the power supply path to the repeater (optical amplifier), and the other is to separate the path through which the signal light is transmitted. There are two possible configurations for dividing the latter signal light transmission path. One is a configuration in which a path is divided for each optical fiber, which is a transmission path of signal light (hereinafter, referred to as “fibre branching”). The other is a transmission path for transmitting to a branch line for each signal light wavelength. This is the configuration of the wavelength selective branch that selects the power to be transmitted to the rank line (hereinafter referred to as “ad-drop drop”).

FIG. 1 shows a configuration diagram of an example of a fiber branch configuration. In the figure, a terminal station 10 is connected to an optical branching device 13 by optical fiber pairs 11 and 12 of a trunk line. The optical branching device 13 transmits all signal light wavelengths transmitted on the optical fiber pair 11 to the optical branching device 15 on the optical fiber pair 14 of the traffic line, and branches all signal light wavelengths transmitted on the optical fiber pair 12. The signal is transmitted to the terminal 17 via the optical fiber pair 16 of the line. In addition, all the signals transmitted from the terminal station 17 through the optical fiber pair 18 of the plantch line are The signal light wavelength is transmitted from the optical fiber pair 20 of the trunk line to the optical branching device 15 through the optical branching device 13.

In the optical branching device 15, all signal light wavelengths transmitted on the trunk line optical fiber pair 14 are transmitted to the terminal station 22 via the trunk line optical fiber pair 21, and the trunk line optical fiber pair 2 is transmitted. All the signal light wavelengths transmitted at 0 are transmitted to the terminal station 24 over the optical fiber pair 23 of the branch line. In addition, all signal light wavelengths transmitted from the terminal station 24 to the branch line optical fiber pair 25 are transmitted from the trunk line optical fiber pair 26 to the terminal station 22 through the optical branching device 15. . A repeater (optical amplifier) is inserted and connected to each of the above trunk lines and branch lines.

FIG. 2 shows a configuration diagram of an example of a done-drop branch configuration. In the figure, a terminal station 30 is connected to an optical branching device 33 by an optical fiber pair 31 and 32 of a trunk line. The optical branching device 33 has a fiber grating (FBG) and an optical circuit, and branches the specific wavelength B of the signal light wavelengths transmitted by the optical fiber pair 32 to form a branch line optical fiber pair. 3 4 transmits to the terminal station 3 5, and the specific wavelength B transmitted from the terminal station 3 5 through the optical fiber pair 36 of the branch line is multiplexed with a wavelength other than the above-mentioned specific wavelength to form a trunk line 3 7 Is transmitted to the optical branching device 38.

Similarly, the optical branching device 38 also has a fiber grating and an optical circulator, and branches a specific wavelength A among the signal light wavelengths transmitted through the trunk line 37 to form an optical fiber pair 39 9 of the branch line. The specific wavelength A transmitted from the terminal station 40 to the branch line optical fiber pair 41 through the branch line optical fiber pair 41 is combined with a wavelength other than the above specific wavelength to transmit the trunk line optical fiber pair 4 to the terminal line 40. Transmit to terminal station 4 4 in 2, 4 3. A repeater (optical amplifier) is inserted and connected to each of the above trunk lines and branch lines.

Patent Document 1 discloses a conventional light splitter / input node device for preventing leakage of signal light to be branched when a failure occurs.

Patent Document 1

Unexamined Japanese Patent Publication No. 2000-3504 06

In the fiber branch configuration shown in Fig. 1, when the terminal stations 10 and 22 of two trunk lines and the terminal stations 17 and 24 of two or more branch lines are connected, One optical fiber pair 11 and 21 connects two terminal stations 10 and 22 of the trunk line without passing through terminal stations 17 and 24 of the branch line. The other optical fiber pairs 12 are branched into branch lines for each of the optical branching devices 13 and 15, and are configured to connect terminal stations 17 and 24 of the branch lines. Also, consider a configuration in which some of the signal light wavelengths A and B in the optical fiber pair are not communicated at the terminal stations 17 and 24 of the branch line, and are returned to the optical branching devices 13 and 15 as they are.

In this case, the signal light wavelength A within the optical fiber pair of the branch line connects the terminal station 10 to the terminal station 17 and the terminal station 17 to the terminal station 22 and the signal light wavelength B corresponds to the terminal station 10 Terminal station 24 and terminal station 24 are connected to terminal station 2 2.

Here, if a failure occurs in the optical fiber pair 16 and 18 of the branch line connected to the terminal station 17, all signal light transmitted on the optical fiber pair of the branch lines 16 and 18 stops. Resulting in. Although the signal light wavelength A transmitted on the optical fiber pair 16 and 18 of the branch line is not related to the communication with the terminal station 17, the terminal station 10 and the terminal station 2 based on the signal light wavelength A are used. There was a problem that transmission between 4 became impossible.

In the add / drop branch configuration shown in FIG. 2, only the wavelengths necessary for the terminal stations 35 and 40 in the optical branching devices 33 and 38 are selected, and the optical finopairs 34 and 3 of the branch line are selected. Transmit to 9. Such a configuration solves the above-described problem in the fiber branch configuration. Even if a failure occurs in the optical fiber pair 34, 36 of the branch line connected to the terminal station 35, the signal light wavelength A does not pass through the optical fiber pair 34, 36 of the branch line connected to the terminal station 35. However, communication between the terminal stations 30 and 35 is secured without being affected by the above-mentioned failure.

In recent years, in a wavelength division multiplexed signal optical communication system, the signal light wavelength interval has been narrowed in order to reduce the number of wavelength multiplexing. The fiber grating (FBG) 50 shown in Fig. 3, which performs wavelength selection in the optical branching devices 33 and 38, has a very steep light transmission characteristic. If the wavelength is about 0 nm, the wavelength can be selected sufficiently. However, if the wavelength interval of the signal light is reduced to 0.4 nm or less, it is not possible to sufficiently select adjacent signal light wavelengths by means of the fifty bug rating 50. Therefore, it is necessary to provide a guard band GB between adjacent signal light wavelengths. Figure 2 example In such a case, a guard pan KGB is required between the signal light wavelengths A and B, and if the number of multiplexed wavelengths is reduced within a predetermined signal band, a problem occurs. Disclosure of the invention

It is a general object of the present invention to provide an optical branching device capable of performing communication on another branch line having no failure at the time of failure of any branch line without reducing the number of wavelength multiplexing. And

In order to achieve this object, the present invention provides an optical branching device for branching a trunk line of a wavelength division multiplexed signal optical communication system into branch lines in units of wavelength division multiplexed signal light, wherein the input signal light from the trunk line and the branch line Monitoring means for monitoring the power of the signal light combined with the input signal light, and when the signal light power obtained by the monitoring means exceeds a threshold value, the input signal light from the trunk spring is attenuated and the branch line is attenuated. And switching means for outputting the input signal light from the trunk line and releasing the attenuation of the input signal light from the trunk line when the signal light power obtained by the monitor means falls below a threshold value and outputting the signal light.

According to such an optical branching device, a guard band is not required, and communication can be performed at another branch line without failure in the event of a failure in any branch line without reducing the number of wavelength multiplexing. it can. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a configuration diagram of an example of a fiber branch configuration.

FIG. 2 is a configuration diagram of an example of an add-drop branch configuration.

FIG. 3 is a diagram for explaining a problem of the ad Z-drop branch configuration. FIG. 4 is a block diagram of a first embodiment of the optical branching device of the present invention.

FIG. 5 is a block diagram of a modification of the optical branching device of the present invention.

FIG. 6 is a flowchart of the operation at startup.

FIG. 7 is a characteristic diagram of a hysteresis comparator for explaining an operation at the time of startup.

Figure 8 is a flowchart of the operation when a branch line failure occurs. Figure 9 is a flowchart of the operation at the time of branch line failure recovery.

FIG. 10 is a characteristic diagram of the hysteresis comparator for explaining the operation at the time of branch line failure and recovery from the branch line failure.

FIG. 11 is an output waveform diagram when the number of signal light wavelengths in the optical branching device of the present invention is reduced from 40 waves to one wave.

FIG. 12 is a block diagram of another modification of the optical branching device of the present invention.

FIG. 13 is a characteristic diagram of the comparator. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 4 shows a block diagram of a first embodiment of the optical branching device of the present invention. The optical branching device 60 has a fiber branch configuration in which optical path switching is performed in units of wavelength multiplexed signal light.

In the figure, an optical splitter 62 for splitting an input signal light (wavelength multiplexed signal light) from a trunk line 61 into two is provided in an optical splitter 60. One output of the optical splitter 62 is supplied to the optical power controller 63, and the other output is transmitted to the branch line 64. Also, the input signal light from the branch line 65 and the output of the optical power controller 63 are supplied to the optical branch device 66, and one output of the optical branch device 66 is connected to the trunk line.

The other output is supplied to a monitor photoelectric converter 68. The signal photoelectrically converted by the photoelectric conversion 68 is amplified by the amplifier 69 and supplied to the hysteresis comparator 70. Hysteresis comparator 70 is supplied with terminals 71 and 72 and thresholds a and b. Hysteresis comparator 70 compares the photoelectric conversion signal with thresholds a and b to generate a control signal. The control signal controls the optical power controller 63 described above.

FIG. 5 is a block diagram showing a modification of the optical branching device of the present invention. The optical branching device 74 shown in FIG. 5 differs from the optical branching device shown in FIG.

76, an optical switch 77 as an optical power controller 63, and a monitor PD (photodiode) 78 as an optical-electrical converter 68, between the optical power plug 76 and the photodiode 78. The point is that a light transmitter 79 is provided. The light transmitter 79 Only the signal light wavelength La band returned at the terminal station 80 connected to the branching device 74 via the branch lines 64 and 65 is transmitted. As a result, the signal light supplied to the monitor PD 78 is only a signal turned back at the terminal station 80.

The startup operation of the optical branching device 74 of FIG. 5 will be described with reference to the flowchart of FIG. FIG. 7 shows the signal levels supplied from the amplifier 69 to the hysteresis comparator 70, and the step numbers in the rough chart are indicated by circled numbers. At the time of starting the thread combination, the optical switch 77 is on (step S l), and the signal light input from the trunk line 61 is supplied to the monitor PD 78 through the optical switch 77. The signal light from the branch line 65 is also supplied to the monitor PD 78 (steps S2 and S3). As a result, the signal level supplied from the amplifier 69 to the hysteresis comparator 70 increases as shown in FIG.

When the signal level supplied from the amplifier 69 to the hysteresis comparator 70 exceeds the threshold value a, the optical switch 77 is controlled to be turned off (step S5), and the monitor PD 78 receives the signal light from the branch line 65. Only will be supplied. This state becomes a steady state (step S6).

Next, the operation of the optical branching device 74 in FIG. 5 when a branch line failure occurs and when the branch line failure is recovered will be described with reference to the flowcharts in FIGS. FIG. 10 shows the signal levels supplied from the amplifier 69 to the hysteresis comparator 70, and the step numbers of the flowchart are indicated by circled numbers.

If a failure occurs in the branch lines 64 and 65, the signal light from the branch line 65 disappears (step S11), and the signal level supplied from the amplifier 69 to the hysteresis comparator 70 is reduced. When it falls below the threshold value b of 0 (step S1 2), the optical switch 77 is controlled to be ON (step S1 3). Then, the signal light is input to the monitor PD 78 through the trunk line 61 and the optical switch 77 to be in a steady state (step S 14). The signal light branched to the branch line 64 is transmitted to the trunk line 67 through the optical branching device without passing through the terminal station 80 of the branch lines 64 and 65 due to the failure of the branch line. Therefore, it does not affect other stations.

When the failure in the branch lines 64 and 65 is restored, When the signal light supplied from the amplifier 69 to the hysteresis comparator 70 rises above the threshold a of the hysteresis comparator 70 (step S16), the optical switch 77 is turned off. (Step S17). Then, the signal light is input from the branch line 65 to the monitor PD 78 through the optical switch 77, and a steady state is set (step S18).

As described above, since the basic configuration of the optical branching device of the present invention is a fiber branching configuration in which optical path switching is performed in units of wavelength multiplexed signal light, it is necessary to provide a guard band which has been a problem in an add-drop configuration. It can be solved that the number of multiplexed wavelengths is reduced _(and the branch line 64, in order to eliminate the influence of the 65 other lines at the time of failure of the branch line 64 by monitoring the signal light power in branch unit within 60, It determines whether there is a failure in 65. If there is a failure in the branch lines 64 and 65, the signal light is switched from the planned line to the trunk line and output, and if there is no failure in the branch line, the reverse optical path switching is performed. By applying the above-mentioned optical branching device to a wavelength division multiplexed signal optical communication system, it is possible to reduce the number of wavelength division multiplexing and to reduce branch line failures. The effect on other lines can be eliminated.

Although the optical switch 77 is used as the optical power controller 63 in the optical branching device 74 of FIG. 5, an optical attenuator may be used. Further, the light transmitter 79 immediately before the monitor PD 78 may be a fiber grating (FBG) or an optical film.

FIG. 11 is a block diagram showing another modification of the optical branching device of the present invention. The optical branching device 82 shown in FIG. 11 differs from FIG. 5 in that the wavelength division multiplexed signal light supplied from the trunk line 61 is the signal light wavelength that is looped back at the terminal 80; This is a point that a small signal (of several kHz) is frozen (for example, amplitude modulation), and is supplied to the amplifier 69 through a band-pass filter (BPF) 83 that allows the output signal of the monitor PD 78 to pass only the frequency fa. In this case, the light transmitter 79 is unnecessary.

FIG. 12 shows a block diagram of a second embodiment of the optical branching device of the present invention. The optical branching device 85 has a fiber branching configuration that performs optical path switching in units of wavelength multiplexed signal light.

In the figure, the same parts as those in FIG. In Fig. 12, inside the optical branching device 85 The input signal light (wavelength multiplexed signal light) from trunk line 61 is split into two by optical power plug 75, one output is supplied to optical switch 77, and the other output is transmitted to branch line 64. Is done.

The input signal light from the branch line 65 is split into two by an optical power switch 86, one output is supplied to an optical switch 87, and the other output is supplied to a light transmitter 79. The optical transmitter 79 transmits only the signal light wavelength λa band returned at the terminal station 80 connected to the optical branching device 74 by the branch lines 64 and 65, and the monitor PD 78 transmits the terminal station 8. Only the signal turned back at 0 is photoelectrically converted and supplied to the comparator 88 through the amplifier 69.

The threshold value c is supplied to the comparator 88 from the terminal 89. As shown in FIG. 13, the comparator 88 compares the photoelectric conversion signal with the threshold value c to generate a binary control signal, and controls the optical switches 77 and 87 with the control signal. The optical switch 77 is turned on when the control signal is at the mouth level and turned off when the control signal is at the high level, and the optical switch 87 is turned off when the control signal is at the low level and turned on when the control signal is at the high level. The signal lights output from the optical switches 77 and 87 are combined by the optical combiner 90 and output to the trunk line 67.

In this embodiment, when a failure occurs in the branch lines 64 and 65, the optical switch 87 is turned off, so that the noise generated by the optical amplifier 91 provided as a middle or a relay in the branch line 65 becomes a trunk. It can be prevented from being sent to the line 67.

Also in this embodiment, of the wavelength multiplexed signal light supplied from the trunk line 61, only the signal light wavelength λa returned by the terminal station 80 has the frequency fa (several kHz to kHz ) Is superimposed (for example, amplitude modulation), the output signal of the monitor PD 78 is supplied to the amplifier 69 through a bandpass filter 83 that passes only the frequency fa, and the optical transmitter 79 is removed. It can also be.

In this way, by applying the optical branching device of the present invention to a wavelength-division multiplexed signal optical communication system, it is possible to reduce the number of wavelength multiplexes and reduce the influence on other lines in the event of a failure in any branch line. Can be eliminated.

Incidentally, the optical-electrical converter 68 corresponds to the monitor means described in the claims, and the optical power controller 63 and the hysteresis comparator 70 correspond to the switching means and the first switching means. The light transmitting device 79 corresponds to the filter means, the bandpass filter 83 corresponds to the frequency extracting means, the comparator 88 and the optical switch 77 correspond to the first switching means and the first switching means, The comparator 88 and the optical switch 87 correspond to the second switching means, the optical switch 77 corresponds to the first optical switch, and the optical switch 87 corresponds to the second optical switch.

Claims

The scope of the claims

1. In an optical branching device that branches a trunk line of a wavelength division multiplexed signal optical communication system into branch lines in units of wavelength division multiplexed signal light,

Monitoring means for monitoring the power of the signal light obtained by combining the input signal light from the trunk line and the input signal light from the branch line;

When the signal light power obtained by the monitoring means exceeds a threshold value, the input signal light from the trunk circuit is attenuated to output the input signal light from the branch line, and the signal obtained by the monitoring means is output. An optical branching device having switching means for releasing attenuation of an input signal light from the trunk line and outputting the signal light when the optical power falls below a threshold value.

2. The optical branching device according to claim 1,

A filter that supplies a signal supplied to the monitor unit from a signal light obtained by combining the input signal light from the trunk line and the input signal light from the branch line, passing the signal light wavelength turned back at the terminal station connected to the branch line. An optical branching device having means.

3. The optical branching device according to claim 1 or 2,

A comparator having a hysteresis characteristic for generating a control signal by comparing the signal light power obtained by the monitor with a first threshold and a second threshold smaller than the first threshold,

An optical branching device that is supplied with an input signal light from the trunk line, has an optical switch that conducts / blocks according to the control signal, and outputs the input signal light from the trunk line when the conduction occurs.

4. The optical branching device according to claim 3,

An optical branching device having an optical attenuator that attenuates / releases an input signal light from the trunk line according to the control signal and outputs the signal instead of the optical switch.

5. The optical branching device according to claim 1, A signal of a predetermined frequency is superimposed only on a signal light wavelength that is turned back at a terminal station connected to the branch line in the input signal light from the trunk line,

An optical branching device having a frequency extracting unit that extracts the component of the predetermined frequency from the output signal of the monitoring unit and supplies the component to the switching unit.

6. An optical branching device for branching a trunk line of a wavelength division multiplexed signal optical communication system into branch lines in units of wavelength division multiplexed signal light, comprising: a monitoring unit for monitoring the power of the input signal light from the branch line; Attenuates the input signal light from the trunk line when the signal light power obtained in step 2 exceeds a threshold, and attenuates the input signal light from the trunk line when the signal light power obtained by the monitor means falls below the threshold. First switching means for canceling, and when the signal light power obtained by the monitoring means exceeds a threshold, cancels the attenuation of the input signal light from the branch line, and the signal light power obtained by the monitoring means becomes a threshold. A second switching means for attenuating the input signal light from the branch line when the signal light falls below the threshold value, the signal light output from the first switching means and the output from the second switching means. Optical branching device having a multiplexing means for a signal light multiplexed by output.

7. The optical branching device according to claim 6,

An optical branching device having a filter means for supplying, from input signal light from the branch line, a signal light wavelength turned back at a terminal station connected to the branch line to the monitor means.

8. The optical branching device according to claim 6 or 7,

A comparator for generating a control signal by comparing the signal light power obtained by the monitoring means with a threshold;

A first optical switch that is supplied with an input signal light from the trunk line, conducts / blocks according to the control signal, and supplies the input signal light from the trunk line to the multiplexing unit during the conduction.

An input signal light is supplied from the trunk line, and according to the control signal An optical branching device having a second optical switch which conducts when the first optical switch is cut off and outputs the input signal light from the trunk line to the multiplexing means.

9. The optical branching device according to claim 6,

A signal of a predetermined frequency is superimposed only on a signal light wavelength that is turned back at a terminal station connected to the branch line in the input signal light from the trunk line,

An optical branching device having frequency extracting means for extracting the component of the predetermined frequency from the output signal of the monitoring means and supplying the component to the first and second switching means.