The Loopback Test Ensure Your Optical Transceiver Working Perfect

The Loopback Test Ensure Your Optical Transceiver Working Perfect

Posted on by FS.COM

Optical transceiver is the fundamental part in any fiber optic communication network equipment. Its function is exactly the same as your computer’s Ethernet Card. There are two ports of fiber optic transceiver, a transmitter port and a receriver port. The transmitter port sends out laser signal to a linked transceiver and the receiver port receives laser signal from the other transceiver.

On fiber optic transceiver manufacturing floors and in R&D labs, we usually use a fiber optic loopback module to verify the transceiver is working perfectly as designed instead of using another transceiver as its partner.

What is a loopback test? A loopback test is a hardware or software method which feeds a received signal or data back to the sender. It is used as an aid in debugging physical connection problems.

What types of Fiber loopback modules are available?

The most popular types of fiber optic loopback modules are SC, LC, FC and MTRJ connector types. But each connector type is divided again by fiber type, connector polish type and attenuation.

>>Fiber Types

Each connector type is available for three fiber types. They are 10G OM3 50/125um multimode, OM2 50/125um multimode, OM1 62.5/125um multimode and 9/125um single mode.

>>Connector Polish Types

Only PC polish is available for multimode type fibers. But for single mode fiber, two connector polish types are available: UPC polish and APC polish.

>>Working Wavelength

In addition to fiber type, working wavelength is the other important factor for choosing the correct fiber optic loopback module for your specific application. Available wavelengths are 850nm, 1310nm and 1550nm. 850nm and 1310nm are for multimode applications and 1550nm is for single mode applications.


You can appoint how the signal power level should be reduced in the loopback path. This is because the receiver port cannot handle very high power. And in real life fiber optic network, there are always attenuation introduced by fibers, equipment and physical environment. So the transmitter power is attenuated to a safe level through the network before reaching the other receiver.

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