• Loopback Information and Uses:
A fiber optic loopback device is also known as a loopback cable, a loopback adapter, a loopback plug, or a loopback module. Some will look like a small polymer block with two connectors and some will look like a fiber optic cable with the connectors clipped together. The fiber will be either singlemode 9/125um or multimode 50/125, 62.5/125 to match the transmit and receive ports.
The loopback cable style or loopback block style are both used by plugging it into a related pair of transmit and receive ports. This allows the test data to travel out of the transmit port and directly back into receive port. If the test data is identical, then the equipment is working as intended.


  • Uses of a loopback device:
- To test the physical ports of network equipment
- To identify network issues
- To identify the network device because the loopback address never changes
- To test the transmission capability and the receiver sensitivity of network equipment


Part Number Description Dimension
73500 LC/UPC Block Style .25" High x 2" Long x .5" Wide
73100 SC/UPC Block Style .5" High x 2.5" Long x 1 1/8" Wide
FDL-LOOP-LCU-4i LC/UPC Cable Style 4" +/-1" Long
FDL-LOOP-SCA-4i SC/APC Cable Style 4" +/-1" Long
Custom Labeling Available
Other Styles Available


New York
Fiberdyne Labs, Inc. carries a complete line of Loopbacks at our Frankfort, New York, facility.
Call your Fiberdyne Sales Representative at 800-894-9694 or email us at