What are fiber optic loopback modules?

The optical transport networks and the most of telecommunication networks have a series of techniques for troubleshooting the faults in communication. One of the most used methods is the loopback procedure.

The loopback is defined as the procedure either software or hardware that returns the received signal back to the sending end of the transmission system. The hardware procedure involves the optic loopback modules that physically connects receiving optical signal to the transmitting optical signal. The test is passed when the data pattern that is received, it passes the hardware loop - optical loopback modules - and is passed back to the sender withe the same data pattern. The pattern can be: all bits having value set to one. The best practice is to send a loopback test to network equipment, one at a time for isolating the problem.

Implementations of the Internet Protocol Suite include a virtual network interface through which network applications can communicate when executing on the same machine. It is implemented entirely within the operating systems networking software and passes no packets to any network interface controller. Any traffic that a computer program sends to a loopback IP address is simply and immediately passed back up the network software stack as if it had been received from another device. Fiber Optic Loopback Modules incorporate two fiber optic connectors. One fiber optic connector is plugged into the output port, while the other fiber optic connector is plugged into the input port of the equipment. Generally, fiber optic loopback cable and fiber optic loopback module are both fiber optic loopbacks. Fiber optic loopbacks are designed in a compact footprint. When sticking the connectors together, the cable will shape like a loop. As for fiber optic loopback module, the biggest difference is that it has a enclosure to protect the inside cable. And the looped space is reduced for an easier usage and economic package.

They are compliant with fast Ethernet, fiber channel, ATM and Gigabit Ethernet. Common fiber optic loopbacks types are: SC fiber optic loopback, FC fiber optic loopback, LC fiber optic loopback, MT-RJ fiber optic loopback.

Similar to other cables, it also has multiple classifications of fiber types, connector types for different needs. Just like fiber optic patch cables, fiber optic loopbacks can also be classified by fiber types: single-mode and multimode. The fiber types can be 9/125µm single-mode fiber, 50/125µm multimode fiber, or 62.5/125µm multimode fiber. Typically, single mode SC and LC loopbacks are blue, and typical multimode LC and SC loopbacks are beige. The color also goes with the practice of SC LC fiber patch cable. The deployment of fiber optic loopback components has greatly saved the trouble for device checking. There is no doubt that using fiber optic loopback is an effective method in fiber optic communication. Loopback test is the easiest way to ensure the transceiver is working faultlessly. On fiber optic transceiver manufacturing floors and in R&D labs, a fiber optic loopback is used to verify the transceiver whether it is working perfectly as designed. Basically what the loopback does is directly routing the laser signal from the transmitter port back to the receiver port. Then the transmitted pattern is compared with the received pattern to make sure they are identical and have no error.