Testing a fiber link in a communication system without interrupting service

1. Field of the Invention

The present invention relates to testing a fiber link, and more particularly, to a technique for testing a fiber link in a communication system without interrupting service in the communication system.

2. Description of the Related Art

For a high capacity fiber optic transport system such as a synchronous optical network (SONET) or a dense wave division multiplexing (DWDM) system, quality or condition of all elements of a fiber link between terminals is very important. These elements may include optical fiber, connectors, splices, attenuators and other optical components. Fiber link degradation due to poor performance of one or more elements could cause service interruption. The condition of the fiber link in service is also important when service is being upgraded to a higher speed, for example, by utilizing additional wavelengths, and it is also desired to make such an upgrade without service interruption.

Current methods for testing a fiber link are not performed while normal communication signals are routed through the fiber link. To test a fiber link that is being used for normal communication, the communication signal may be switched to another fiber link, designated as a protection path, but such switching causes at least a short service interruption. If there is no protection path, and therefore no fiber link to which the communication signal can be switched, then there will be a relatively long service interruption. The service interruption is necessary in order to access one or both ends of the fiber link under test.

An alarm is an indication that a signal has failed, or that an optical power level is below an acceptable threshold. Conventional optical transport systems provide information and alarms by monitoring the optical signal power level. However, in a case of signal degradation, monitoring of received optical signal power cannot identify a cause or a location of the signal degradation. Consequently, further analysis of the problem or sectionalization of the system would typically require service interruption. A service interruption is also typically required in order to definitively determine whether a fiber can handle a particular set of wavelengths.

Consequently, there is a need for a technique for testing a fiber link in a communication system without interrupting service in the system.

It is an object of the present invention to provide a technique for fiber link testing in a fiber optic transport system in which the testing does not interrupt service in the system.

It is another object of the present invention to provide such a technique in which the testing does not interfere with, or attenuate, normal communication signals on the fiber link.

It is a further object of the present invention to provide such a technique in which the testing can be performed bi-directionally on the fiber link.

These and other objects of the present invention are achieved by a method for testing an optical fiber link that includes employing a WDM to receive a signal via a port of the WDM and multiplex the signal onto the optical fiber link. The signal is used in a test of the optical fiber link.

Another method for testing an optical fiber link includes employing a WDM to couple a test signal between a first port of the WDM and the optical fiber link, and couple a communication signal between a second port of the WDM and the optical fiber link. The test signal is used in a test of the optical fiber link.

An arrangement for testing an optical fiber link includes a wavelength division multiplexer (WDM) for receiving a signal via a port of the WDM and multiplexing the signal onto the optical fiber link. The signal is used in a test of the optical fiber link.

Another arrangement for testing an optical fiber link includes a wavelength division multiplexer (WDM) for coupling a test signal between a first port of the WDM and the optical fiber link, and coupling a communication signal between a second port of the WDM and the optical fiber link. The test signal is used in a test of the optical fiber link.