1. Field of the Invention
The present invention relates to a wavelength division multiplexing (WDM) apparatus, and more specifically to an optical protection apparatus in the WDM apparatus.
2. Description of the Related Art
The wavelength division multiplexing (WDM) is a system for multiplexing an optical signal having different wavelengths into one optical fiber and transmitting the signal. Recently, there has been a system realized for optical wavelength multiplexing 100 wavelengths or more at a transmission speed of 10 Gbps.
Normally, in a communications circuit, a signal path (a transmission line, a transmission device, an intra-device configuration package) has redundancy. In the conventional network including a wavelength division multiplexing system, there often is a redundant system configured by an electric process in a time division multiplexing (TDM) device, etc. connected under the wavelength multiplexing apparatus. However, with a higher multiplexing level of a wavelength multiplexing apparatus, there has been a strong demand of configuring a redundant system of a signal at an optical signal level.
In
RXPs 20-1 and 20-2 perform detection of input disconnection (LOL: loss of light), detection of displaced frame (LOF: loss of frame), and monitor of error performance (BER: bit error rate, SD: signal degradation). For example, assume that the system 0 is a foreground system, the system 1 is a background system, and the system 0 is selected for a SW. In the initial status, both systems 0 and 1 are free of the LOL, LOF, or error status in the RXPs 20-1 and 20-2 and the SW unit 14. From this status, if a switch trigger (the LOL, LOF, and exceeding an error threshold in the RXP, and the LOL in the SW unit 14) occurs in the foreground system, then a control unit 21 of the SW unit 14 which receives the information switches the SW selection to the background system on condition that there is no warning status (LOL, LOF, exceeding an error threshold, and LOL of the SW unit 14) in the background system. The system 1 which is a background system is switched on, the optical output of the SW unit 14 is the optical output of the system 1, the passage of a signal to a lower device is recovered after a switch trigger is detected and the SW control is delayed.
In
The prior art is disclosed by the patent literature 1 and 2. In the patent literature 1, the technology of superposing a monitor control signal on the main signal and then transmitting the resultant signal is disclosed. In the patent literature 2, an optical path switch monitor system using monitor light is disclosed.
In the system described above by referring to the conventional technology, an optical switch element is used as a signal switch unit. The system for the switch element can be a system of mechanically switching an optical path, a system for switching an optical path using an opto-magnetic effect (Kerr effect, etc.), etc. These switches have no monitoring function for generally confirming the operation status through feedback. Therefore, when the switches are used in switching an optical signal, the status to be controlled (what control signal is input) can be checked, but a selected system cannot be detected. In a transmission system having a redundant system, it is essential to confirm the currently selected system in the operation of transferring a fault of a transmission line. However, from the above-mentioned characteristic of the optical SW, the final selection of the system cannot be confirmed, thereby causing a serious problem in operating a network.
As shown in
The present invention aims at providing a device for correctly determining which is actually used, the foreground system or the background system, in the optical protection apparatus.
The optical protection apparatus according to the present invention enables correct communications even though there occurs a fault by switching between an optical signal of a foreground system and a background system, and includes: a switch unit for receiving an optical signal of a foreground system and an optical signal of a background system, and selecting the optical signal of the foreground system or the optical signal of the background system; a pilot signal multiplexing unit for multiplexing a pilot light having a wavelength different from those of the optical signal of the foreground system and the optical signal of the background system with the optical signal of the foreground system or the optical signal of the background system; and a pilot light detection unit for detecting on the output side of the switch unit whether or not a pilot light is contained in the optical signal output by the switch unit on the output side of the switch unit.
According to the present invention, even if the switch unit becomes faulty and does not operate according to the input control signal, it is correctly determined which system is actually used, the foreground system or the background system.
The following methods are used in the embodiment of the present invention.
(1) On the input side of the optical SW, either the system 0 or one of the system 1 of the main signal output from the RXP (reception transponder) is multiplexed with a wavelength light different from the main signal as a pilot light, and input to the optical SW.
(2) On the input side of the optical SW, the main signal is demultiplexed from the pilot light, and it is detected whether or not the pilot light has passed through the optical SW.
(3) Depending on the current selection system and the presence/absence of the pilot light after passing through the optical SW, the final system selection in which the optical SW is operating is monitored.
The embodiments of the present invention are described below by referring to the attached drawings. In each drawing, a similar component is assigned the same reference numeral.
The characteristics of the WDM coupler 35 connected to the output terminal of the optical SW 33 are set as shown in
The WDM coupler 34 connected to the input terminal of the optical SW 33 couples the 1550 nm optical signal as a main signal with the 1310 nm optical signal as a pilot light, and transmits the result to the optical SW 33. The WDM coupler 35 connected to the output terminal of the optical SW 33 demultiplexes the 1550 nm band main signal which has passed the optical SW 33 from the 1310 nm pilot light, transmits the 1550 nm main signal to the TDM device 15 connected to a device, and transmits the 1310 nm pilot light to the 1310 nm pilot light detection unit 31.
In an example of the system in the present embodiment, a 1550 nm band main signal and a 1310 nm pilot light are used. However, a main signal of any wavelength band can be monitored by changing the pilot light depending on the wavelength band of the main signal. For example, by using a 980 nm band pilot light for a 1310 nm main signal, system selection can be similarly monitored.
For example, when the system 0 is selected as a device, and the SW is normally operated, a 1310 nm pilot light does not pass through the optical SW 33, and the pilot light cannot be detected by the 1310 nm pilot light detection unit 31. As a result, it is determined that the optical SW 33 normally selects the system 0.
On the other hand, if the SW abnormally works and the optical signal of the system 1 is output even though the system 0 is selected as a device, then the 1310 nm pilot light passes through the optical SW 33. As a result, the 1310 nm pilot light detection unit 31 detects the pilot light, thereby determining that the system 1 has been mistakenly selected due to the abnormal operation of the optical SW 33.
If the system 1 is selected as a device and the optical SW 33 normally operates, the 1310 nm pilot light passes through the optical SW 33 and is detected by the 1310 nm pilot light detection unit 31. When the optical SW 33 abnormally operates and has selected the system 0, the 1310 nm pilot light detection unit 31 does not detect pilot light, thereby determining the abnormal operation of the optical SW 33.
The above-mentioned determination is made by the comparison unit 30 shown in
In the second embodiment of the present invention, the optical signals of the 1310 nm band and the 1550 nm band are multiplexed by a normal 2 branch optical coupler, which is realized by the WDM coupler in the first embodiment, and the demultiplexing process is performed by the 2 branch coupler and wavelength differentiating filter. A coupler 41 and a filter 43 have the characteristics as shown in
According to the embodiments of the present invention, the abnormal conditions of the optical SW unit or the optical paths in the process can be detected without an influence on the main signal during the operation. Furthermore, a signal disconnection due to an incorrect system switch can be avoided. When a device recognized system does not match an actually selected system, a signal disconnection due to an inoperable automatic system switch can be avoided.
In the above-mentioned embodiments of the present invention, only pilot light inserted into an optical signal of a background system is described, but the pilot light can also be inserted into the foreground system.
Number | Date | Country | Kind |
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2004-077203 | Mar 2004 | JP | national |