DIY: How to do a fiber optic mechanical splicing: steps and tips

Mechanical splicing is the process of precisely aligning two fiber optics together using an alignment device and index matching gel that has a similar refractive index and covers the possible air gaps, helping light travel from one fiber to another with minimal loss and little back reflection.

However, they are still two separate optical fibers, which is why this method is considered temporary and is mostly use to rapidly restore short-haul single mode or multimode cables in FTTH installations.

How to do it?

Mechanical splicing is easy to do if you have all the tools you need, as it only takes three steps to be done. It requires:

A fiber optic stripper.
A cleaver.
Isopropyl alcohol
A mechanical splice device of your need.
Step 1: The first thing you have to do is strip the cables, taking away the coats, buffers and any other protective layers, leaving the optical fibers naked. Then clean the fibers using an optic clean wipe soaked with isopropyl alcohol.

Step 2: Now it’s time to cleave the fibers. You have to do this following the instructions of the cleaver you are using.

Step 3: Place the cleaved ends of the fibers together into the mechanical splice device. Now light will travel from one fiber to another thanks to the index matching gel. And your fiber splicing is ready!

If you want to check the signal loss, you could use a Visual Fault Locator, an inexpensive small device that shoots red laser light into the patch cords and makes high loss points visible. This method works great with yellow coated single mode and orange coated multimode fibers. If you want to learn more about the difference between singlemode and multimode, click here.

Get better splices

Constantly clean your tools: Particles that you might consider invisible can cause great damages on fiber optics. So getting obsessed with cleaning is never a problem.

Buy an expensive cleaver: Cleaving is the most important step when splicing because a bad cleave can increase signal loss. Economic cleavers generally need more practice and skills to achieve the appropriate cleave angle, so if you regularly do mechanical splices buy a cleaver that is generally used in fusion splices.

But what happens if you need to do an emergency restoration and don’t have a cleaver with you? Jim Hayes, president of the Fiber Optic Association (FOA) advises to use a scriber and an inexpensive cleave fixture that consists on a small piece of flexible plastic. Place the fiber on the plastic, scratch it with the scriber and it’s done.

The best tools

The FOA suggest using the ULTRA splice device since it is easy to install, inexpensive and high performance. Its biggest advantage is that it has visible glass on top with pre-loaded index matching gel that allows you to see the optical fibers during the installation. The 3M Fibrlok is one of the most popular mechanical splices too due to its elegant design and good throughput.

When it comes to cleavers, the Fujikura AFL CT-06 is highly recommended because it provides high quality cleaving at an economical price. Designed for cleaving single fibers,this cleaver’s blade can make over 48 thousand cleaves. The Sumitomo FC-7 Cleaver is highly recommended because it fits in the palm of your hand which makes it easy to take to any location.

Choosing the proper stripper according to the coding sizes of the fiber is also really important because you need to be careful not to scratch the fiber while removing the buffer. No-Nik, Micro-Strip and Miller stripper are the most commonly used by technicians due to their quality.

4 thoughts on “DIY: How to do a fiber optic mechanical splicing: steps and tips”

  1. Nice write up.
    I have to do similar repairs on automotive MOST BUS systems when a fiber line gets a crack in it.
    Pain in the butt to find the fracture, let me tell you! Wait, probably don't have to.

  2. You can use the diagnostic computer to execute a ring break test.
    This gives a you a general idea where your issue lies.
    From there it is a matter of chasing the light.
    Sometimes I will dim the shop lights and use my LED flashlight to send light down a line. Typically if there is a crack it comes beaming out.
    If the “leak” is too minute to be found I will just run a new line, but this rarely happens.
    This is a very short summary of how I would diagnose a break, but I also have special tools to bridge modules over etc…
    Usually when there is a MOST issue in a vehicle it is because a module/controller went down and it is not sending the light/signal to the next module in the “ring”.
    Do a lot of MOST diagnosis for the local body shops as you can imagine, lol.

    So are you in telecommunications or…?

    For those that do not know an automotive MOST(Media Oriented System Transport) BUS is a “ring style” fiber optic BUS network typically used for infotainment purposes. If the light/signal is dropped/not transmitted on to the next module in X amount of time the entire BUS becomes inoperative/goes dark.
    Usually the customer will Identify it as “I have no sound and the screen is black.”

  3. I was doing a search for another topic and found this article on MOST bus fiber splicing. I know it's a bit old and sorry for jumping in here, but I find DIY repairs to be irresistible brain candy. I happen to work with Infotainment OEM part testing and would like to learn more about fiber cable troubleshooting and repair. Can you direct me to some links on the topic. Thank you.

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