Fibre Optic Loopback Cables

Fibre Optic Loopback Cables are also known as Fibre Optic Loopback modules or adaptors. It is basically a simplex cable that has been looped, typically housed in a protective case (Loopback module or adaptor), or simply clipped together (Loopback cable).

The traditional Loopback Cable has a visible fibre part on the body, with two fibre optic connectors on each end of the cable. When this cable is clipped together you will notice the cable will naturally loop.

The Fibre Optic Loopback Module has a protective enclosure, is more compact and the cable is inside the cover for better shelter. This allows for easy handling and is slightly reduced in size.

Loopback cables are used to send data back to the source without any processing or modification as a means of testing and locating connection issues.

An optical loopback cable offers technicians a very simple, but effective way of testing the transmission ability and the receiver sensitivity of their network equipment. Checking that the data sent is identical to the data received from the loopback cable means the basic functions of the ports are operating correctly.

They are mostly used for testing fibre optic applications or for applications where network restorations are required. They are a very useful component to have in your toolkit when you are in the field.

Types of loopback cables.

As previously mentioned these fibre optic loopback modules incorporate two fibre optic connectors in one cable.

Depending upon the connector and fibre type there could be any number of loopback modules that you may need to fit the testing criteria. Some of the most popular ones are;

·        LCA Singlemode loopback modules

·        LC Multimode or Singlemode loopback modules

·        SCA Singlemode loopback modules

·        SC Multimode or Singlemode loopback modules,

      Just to name a few.

     As you can see each connector type is separated again by the type of fibre being used.

     Making the number of Loopback cables available, not much different to say a patch cable range, where you have OM1 62.5/125um, OM3, OM4, OM5 50/125um for Multimode applications and 9/125um for Singlemode applications.

Identification colours

Just like fibre optic patch cables, the loop-backs are made up of different kinds of cable and connector colours.


  • ·     Multimode OM1 LC and SC type fibre loopbacks are Beige,
  •       Multimode OM3 LC and SC type fibre loopbacks are Aqua,
  •   Multimode OM4 LC and SC type fibre loopbacks are Erika Violet,
  • ·     Singlemode SCA and LCA type fibre optic loopback cable are green,
  • ·     Singlemode SC type and LC type fibre optic loopback cable are blue.

Connector Polish Types

When looking for loopback modules for Singlemode fibre, Ultra Physical Contact polish and Angled Physical Contact polish types modules are available.

APC= Angled Physical Contact

UPC= Ultra Physical Contact

How do you use a fibre optic loopback cable?

If testing a transceiver you simply plug one of the fibre optic connectors into the transmit port (Tx), and the other fibre optic connector is plugged into the receive port (Rx) of the same equipment being tested.

If you are testing from a patch panel you would plug the loopback cable into the adaptor ports being tested.

If you are testing using an OTDR that does not have bi-directional capabilities, you would have the loopback at one end of the cable run allowing you to test both directions (if needed) using an OTDR at the other end.

By using the loopback method you eliminate the need for 2 OTDR’s (one each end) and you can reduce the time it takes to test by half.


They are made from low smoke halogen material which is tough, doesn’t fade, and is not easily broken. 

The high precision ceramic ferrule ensures, low insertion loss, low back reflection, and high precision alignment.

Temperature Range ≤ 0.2 dB (- 40 to +80 degree)

Exchangeability ≤ 0.2 (500 cycles passed)

Optical fibre mode: Singlemode 9/125 um  Multimode 50/125 um, Multimode 62.5/125 um,

Connector types: SC, SCA, LC, LCA, and more available

Insertion Loss (dB) ≤ 0.2

All our Loopback cables come with test results printed on the bag and serial numbers.

Available Wavelengths

Available working wavelengths are 850nm and 1300nm for multimode applications, and 1310 and 1550nm for Singlemode applications.


The Fibre Optic Loopback cables available are either single mode (9/125µm) or multimode (50µm/125 or 62.5/125µm).

They are specifically designed for equipment testing, self-testing, engineering, network diagnostics, and measurement applications.

Known also as loopback adapters, loopback cables, or fibre optic loopback modules, these devices are invaluable to have as part of your testing tool kit.