Which Fiber Loopback Should I Use for My Transceiver?

In telecommunication, fiber loopback is a hardware designed to provide a media of return patch for a fiber optic signal, which is typically used for fiber optic testing or network restorations. When we need to know whether our fiber optic transceiver is working perfectly, we can use a fiber loopback cable as an economic way to check and ensure it. Basically, the loopback aids in debugging the physical connection problem of the transceiver by directly routing the laser signal from the transmitter port back to the receiver port. Since fiber optic transceivers have different interface types and connect different types of cables, it is not that simple to choose a right loopback for our transceiver. This post will be a guide on how to choose a right loopback cable for specific transceiver module.

Fiber Loopback Types and Configurations

Before deciding which loopback cable to use, we should firstly know the structure and classification of fiber loopback cable. Generally, a fiber loopback is a simplex fiber optic cable terminated with two connectors on each end, forming a loop. Some vendors provide improved structure with a black enclosure to protect the optical cable. This designing is more compact in size and stronger in use. Based on the fiber type used, there is single-mode loopback and multimode loopback, available for different polishing types. According to the optical connector type of the loopback, fiber loopback cables can be divided to LC, SC, FC, ST, MTP/MPO, E2000, etc. In testing fiber optic transceiver modules, the most commonly used are LC, SC and MTP/MPO loopback cables.

lc&sc loopback cable
Figure 1: LC & SC Loopback Cable

The LC and SC loopbacks are made with simplex fiber cable and common connectors; it’s not difficult to understand their configurations. As for the MTP/MPO loopback, it is mainly used for testing parallel optics, such as 40G and 100G transceivers. Its configuration varies since the fiber count is not always the same in different applications.

8 Fibers MTP/MPO Loopback Cable Configuration

In a 8 fibers MTP/MPO loopback, eight fibers are aligned on two sides of the connector, leaving the central four channels empty. And the fibers adopt a straight configuration of 1-12, 2-11, 5-8, 6-7. The polarity channel alignment is illustrated in the following figure.

8 Fibers Loopback Polarity Channel Alignment
Figure 2: 8 Fibers Loopback Polarity Channel Alignment
12 Fibers MTP/MPO Loopback Cable Configuration

The only difference between the 12-fiber MTP loopback and the 8-fiber loopback is that the central four channels are not empty. Its alignment is 1-12, 2-11, 3-10, 4-9, 5-8, 6-7.

12 Fibers Loopback Polarity Channel Alignment
Figure 3: 12 Fibers Loopback Polarity Channel Alignment
24 Fibers MTP/MPO Loopback Cable Configuration

The 24 fibers MTP loopback also adopts type 1 polarity. Its alignment design is shown below.

24 Fibers Loopback Polarity Channel Alignment
Figure 4: 24 Fibers Loopback Polarity Channel Alignment
Which to Choose for a Specific Transceiver?

Considering the common features of the transceiver and the loopback, we should think about the connector type, polish type, and cable type when selecting a loopback for the transceiver. The selection guide for some mostly used transceiver modules is summarized in the following tables.

Table 1: Loopback choices for 10G SFP+ transceivers

Model Interface type Cable Type Suited Loopback

LC/UPC Duplex Multimode Fiber Loopback


LC/UPC Duplex Single-mode Fiber Loopback


Table 2: Loopback choices for 40G QSFP+ transceivers

Model Interface type Cable Type Suited Loopback

8/12 Fibers MTP/UPC Multimode Fiber Loopback


8/12 Fibers MTP/APC Single-mode Fiber Loopback

40GBASE-LR4 LC Duplex (PC) SMF

LC/UPC Duplex Single-mode Fiber Loopback


LC/UPC Duplex Multimode/Single-mode Fiber Loopback

Table 3: Loopback choices for 100G QSFP28 transceivers

Model Interface type Cable Type Suited Loopback

8/12 Fibers MTP/UPC Multimode Fiber Loopback


8/12 Fibers MTP/APC Single-mode Fiber Loopback

100GBASE-LR4 LC Duplex (UPC) SMF

LC/UPC Duplex Single-mode Fiber Loopback

Table 4: Loopback choices for CFP transceivers

Model Interface type Cable Type Suited Loopback

8/12 Fibers MTP/UPC Multimode Fiber Loopback


SC/UPC Duplex Single-mode Fiber Loopback


24 Fibers MTP/UPC Multimode Fiber Loopback


This post discusses specific fiber loopback choices for some most commonly used fiber optic transceivers. For other transceiver modules that are not mentioned in this post, we can also know how to choose a suitable loopback for it by getting details about its interface type, physical contact and cable type.

Introduction of Fiber Splice Tray

Fiber splice tray is designed to provide a place to store the fiber cables and splices and prevent them from becoming damaged or being misplaced. It is also called as splice enclosure or splice organizer. This device does not contain any technical functions, and the design is simple. Also, it has a very low price for people to afford. However, the importance of fiber splice tray for protecting fibers is significant. And the skills needed for using fiber splice tray is not as simple as you think.

Function of Fiber Splice Tray

With such a simple structure, you may wonder how the fiber splice tray actually works. Here is the brief introduction of its working function: The incoming cable is brought into the splicing center where the outside jacket of the cable is stripped away. The fibers are then looped completely around the tray and into a splice holder. Different holders are available for different types of splices. The fibers are then spliced onto the outgoing cable if it is an intermediate point or on to pigtails if it is a termination point. These are also looped completely around the tray and then fed out of the tray.

Installation Procedures

The installation procedures can be divided into five steps:

Step one, route fibers into splice tray using spiral transportation or fiber furcation tubes and secure with cable ties.


Step two, splice fibers per local practice.


Step three, place spliced fibers into the sleeve holders arranged by color code.


Step four, carefully coil the outgoing fiber slack into the tray (coil 1).


Step five, carefully coil incoming fiber slack into the tray (coil 2).



Fiber splice trays are usually placed in the middle of a route where cables are required to be joined or at the termination and patch panel points at the end of the cable runs. Also, splices can be placed in a splice tray which is then placed inside a splice closure for OSP (outside plant) installations or a patch panel box for premises applications. As for indoor application, fiber splice trays are often integrated into patch panels to provide for connections to the fibers.


As a protection for fiber splices, fiber splice tray is no doubt the most cost-effective device. This simple design solves a lot of problems during fiber cables installation. Fiberstore provides different shaped splice trays with different fiber capacities in a competitive price. If you are interested, FS.COM is a good place to go.

How to Terminate Fiber Optic Cables?

Since the late 1970s, various connectors and termination methods have been brought to market. Now in the common case, cables are terminated in two ways: use connectors to make two fibers jointed or to connect the fiber to other network gears; use splices to make a permanent joint between two fibers. And for the former method, you may have little confusions to deal with it. So today this paper will teach you how to terminate by taking an example of fiber optic cable using epoxy.

First and foremost, use a proper fiber stripper to carefully slide the jacket off of the fiber to a bare fiber. When you are doing this, be careful that try to avoid breaking the fragile glass fiber. After that, mix the epoxy resin and hardener together and load it into a syringe (If you use the pre-loaded epoxy syringes that are premixed and kept frozen until use, then you don’t do that). And next you must inject the epoxy from the syringe directly into the connector ferrule.

Fiber Stripping Tool

Once you have well prepared the epoxy for your connector, you can insert the fiber cable gently into the terminus inside the connector wall and make the bare fiber core stick out about a half an inch from the front of the ferrule. In the case that your cable is jacketed, you may need a crimping tool, such as Sunkit Modular Crimping Tool, to secure the connector to the jacket and strength the cables. Usually two crimp tools would be perfect to this operation.

Next, you can just wait the epoxy to cure. During this process, in order to make sure the end of the fiber is not damaged while curing, you should place the connected end in a curing holder. And when this is done, just place the cable and curing holder into a curing oven. But you may worry about “wicking” while curing with a conventional oven. All you have to do to avoid that is to make the end face down, which can ensure the epoxy does not come out of the back side of the connector and compromise the strength member of the cable. Remember: your epoxy curing must in accurate times and temperatures.

After the epoxy cured sufficiently, fiber cleaver tools will be in use to cleave the excess protruding fiber core so that it could make the fiber close as much as possible to the ferrule tip in case of fiber twisting. Once cleaved, you have to dispose of the fiber clipping. There is a point you should think highly of that you must use a regular piece of tape to retain your fiber debris, or they will easily end up in your skin or even in your eyes or respiratory system.

High Precision Fiber Optic Cleaver

When you finished the fiber cleaved work, you could need fiber polishing tool to remove the excess epoxy from the ferrule tip and buff out any imperfections on the surface of the fiber. A smooth fiber surface can help to reduce the loss of the light. Last, if you have done all the above work, you may move on to the cleaning of the ferrule and fiber tip. After that, the whole termination procedure is done.

If you want to terminate your fiber optic cables by hands, you can follow the above steps. But before you get down to it, you must prepare the tools first that I have mentioned in this paper. All these tools can be found in Fiberstore with good quality and low price. In addition, Fiberstore also can provide the termination tool kits that may be helpful to you. For more details, you could visit www.fs.com.

Article source: http://www.chinacablesbuy.com/how-to-terminate-fiber-optic-cables.html

Some Special Tools for Fiber Optics From Fiberstore

As we know, splicers will need much the same tools to open and set up a fiber splice as they want a copper splice. The usual cable knife, tabbing shears, etc, are required, along with a few specially tools used only for fiber splicing.

Once the sheath has been opened and the field bonded in the standard fashion, a buffer tube cutter is required to score the hard, gel-filled buffer tubes. Caution should be exercised when performing this operation, because the buffer tubes contain fibers that are protected only by their primary coating. Use this tool only to score the tube and not to cut it. After opening up an express run (straight through cable), the splicer will have to use a tube splitter tool to remove the buffer tube bu running it along the tube, which then splits. Other handy tools include ceramic scissors for cutting the Kevlar in many cables, a magnifier for close-up examination of the fiber end face, and masking tapes for scarp containment. Alcohol with lint-free pads and a Fiber Optic Stripper are also requirement.

Fiber Optic Stripper

Most critical of all, however, is the choice of splitter. With the exception of the AMP Optimal splice/workstation (the splitter is built in), every fiber optic splice requires the use of a separate splitter. This tool, carrying in price 150 dollars to 2,500 dollars, can make or break a splicer’s day. The Fiber splitter on the end of a fiber is the most critical part of a successful splice, so it is advised to purchase and use a high-quality splitter. In my experience, at least half of all failed fiber splices are a direct result of a bad cleave from a cheap splitter. This is not the place to save money.

Unlike testing copper cable, testing fiber cable is easy and fun, Only two tests are specified by the EIA/TIA and most firms don’t even require those. The four basic tests that can be performed on fiber are the continuity test, received power test, single-ended test, and double-ended test, the continuity test can be performed quickly and easily with as little equipment as a 10 dollars flashlight, while the received power test requires the use of a power meter, which can be purchased for as little as 500 dollars. The other two EIA/TIA test procedures require the use of a light source, power meter, and several good jumper cords. Kits containing this equipment are available for as little as 1,000 dollars.

The optical time domain reflectometer (OTDR) is an expensive instrument used primarily for acceptance testing and fault locating on long-haul single-mode fiber systems. This is called the “blind spot” or “dead zone.” However, once outside the dead zone, the OTDR is used primarily for reading insertion loss and back reflection at splice points. This instrument is not designed to give accurate end-to-end loss measurements on a fiber system. Use the standard for this test. OTDRs may be purchased for one or two wavelengths and may be single mode, multimode, or contain launch modules for both modes of operation. Prices vary from slightly less than 10000 dollars to as much as 45,000 dollars, depending on features desired.

Fiber optic cables are becoming the predominant medium of the ’90s and on into the 21st century. The necessary equipment, tools, and materials are more sophisticated than those used for copper splicing and trouble-shooting, but they are coming down in price as competition increase in this field. The wide bandwidth of fiber transmission will continue to drive improvements in fiber optics as voice, video, and data find their way into homes.

Fiberstore, as you know, it provides all kinds of fiber optical products include what you need, and it can supply custom service, we can according to your needs to make up it, I think it is the feature that many store can not do like this. Except this, the price is also exciting, almost products are doing 30% discount on the price, I really recommend you to have a try, it must bring you big surprise…

Fiber Optic Visual Light Testers from FiberStore

Visual fault locators can be part of OTDR, which is able to locate the breakpoint, bending or cracking of the fiber glass. It can also locate the fault of OTDR dead zone and make fiber identification from one end to the other end. Fiber optic visual fault locators include the pen type, the handheld type and portable visual fault locator. FiberStore also supply a new kind of fiber optic laser tester that can locates fault up to 30km in fiber optic cable.fiber testing red light

The new visual fault locator fiber optic laser tester 30km is especially designed for field personnel who need an efficient and economical tool for fiber tracking, fiber routing and continuity checking in an optical network during and after installation. It can send fiber testing red light through fiber optic cables, then the breaks or faults in the fiber will refract the light, creating a bright glow around the faulty area. Its pen shape made it very easy to carry, and its Cu-alloy material shell made it sturdy and durable, 2.5nm universal interface make it more attractive. The inspection distance various according to different mode.

Easy to check fiber faults with visual red laser light
FC, SC, ST General interface
Sturdy and durable shell
Constant output power
Long inspection distance
Operates in either CW (Continuous wave) or pulse (Both modes are available)
Pen pattern design, convenient for use and carry
Dust-proof design keeps fiber connectors clean

Compact in size, light in weight, red laser output, both SM and MM available

FiberStore provides enough stock of fiber optic visual light testers which usually be shipped out in a short time, and can be shipped out in 2-4 business days. We offer 1 years warranty for the quality of these products, so customers can place the order with 100% confidence!