Build a Simple Fiber Optic Tester




About: I started taking things apart when I was 6 started putting them back together at 8 and they actually worked again when I was 10 or 11...

Intro: This instructable will show you how to make a simple fiber optic cable tester for any LC style fiber. I work in the medical industry for a company that builds integrated OR’s (Operating Rooms). We supply images to flat panel displays for minimally invasive surgery that includes laparoscopic cameras, MRI’s, and live C-arm images. All of these are delivered via DVI over fiber optic cables. We have to use fiber because of the distance between the image source and the space limitations of flat panel arms. Our DVI signal is carried over four fibers, one each for the red, green, blue and clock signals. We use LC connectors which are standard for IT infrastructure too. Our installers pull the fiber through conduit during the installation of the OR and need a quick way to verify that the fiber is good. Most testers I found were very expensive and measured db loss through the fiber. We just needed to know if it was intact or broken. I came up with this idea after looking at an LC fiber coupler and shoving a 5mm LED into it and finding out it was a perfect press fit! This tester works great for finding a broken fiber or if you have multiple fibers in an IT closet that no one has labeled (like that would ever happen…) identifying them.

Step 1: Materials and Tools

Parts List:
  1. Four high brightness RED LED’s
  2. Four 330-Ohm resistors for current limiting
  3. Two dual fiber couplers
  4. Nine volt battery clip
  5. Hot glue
  6. ¼” or 3/16” Heat Shrink Tubing
  1. Hot Glue Gun
  2. Soldering Iron
  3. Hot Air Gun
  4. Needle Nose Pliers, Cutters and other misc small tools

Step 2: Construction

  1. Glue the two fiber couplers  together.
  2. Pull out four of the white plastic hole protectors from one end
  3. Insert the LED’s into the holes keeping the short leads to one side the long leads to the other side. You will need to press them in using needle nose pliers
  4. Hot glue the LED’s into place and let coo
  5. Bend the Shorter lead (-) over to one side about a 45 degree angle
  6. Cut the longer leads to about ½” and using needle nose pliers make a loop to solder to the resistor.
  7. Cut one lead of the resistors to ½” and form a loop to connect to the LED’s
  8. Solder the four resistors to the LED’s
  9. Bend the left most (-) LED lead over touching the other three LED (-) leads. Cut the three remaining leads and bend them over the first LED lead. Solder as shown above.
  10. Slide short pieces of heat shrink tubing over the resistors and then twist two of the resistor leads together to form pairs.
  11. Shrink the tubing. 
  12. Solder the two resistor leads together then connect those two together to form one common positive connection. Solder the 9-Volt battery clip Red to the (+) and black to the (-) and you are finished!

Step 3: Use

Using this tester is very simple. Plug an LC terminated fiber optic cable into this and look at the end of the fiber to verify that Red Light is coming out. Each of the four fibers should be the same brightness. If one is noticeably dimmer or not lit, you have found your defective fiber. Much simpler than measuring db loss down a fiber, and... Much more intuitive to a human.

The picture doesn't really show how visible the red led light is. Word of Caution the transmitters that are normally used with fiber are near IR lasers. Even though they are <1mW DO NOT LOOK AT THE END OF THE FIBER WITH A LASER attached to it. Unless of course you do not like your vision.

This tool really helps trouble shoot fiber optic installations.

Enjoy and happy soldering!



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    14 Discussions


    2 years ago

    Superb Instructable!
    I connect f.o. for a living, and would like to add some thoughts....
    Fiest....preventing some mistake that could lead anybody to "take a look" on a really "laser connected" f.o.,
    Second, I will do this with blinking the LEDs (a 555 IC could do the trick) and, for added security I would use blue LEDs.....
    So, I used your device in some 30 ft MM cables and works really good, but, in fear of "live" lasers, I never looked directly to the fibers. I put a semitranslucent paper on te "output connector" to see the red glow through the paper.It works fine, adds security.And Its cost was 0$ !!

    1 reply

    3 years ago

    I just tried 5mm High Brightness Leds and yes, this technique works very well for *multimode*, but with diminished intensity on singlemode cables at the other end. But for the few bucks, USB powered, this is an instructable that saves costs. Fiber Identifiers from China are about $30-40 in Laser 5mW but there are inherent dangers . My question to viewers is: which color of ordinary high intensity Leds are the favorites and which colors illuminate best at the other end(s) in normal office lighting and with reasonable distances between riser cabinets? I used a single LC-LC coupler. I will modify mine to have two pairs of devices powered by 9V; one side shoots HighIntensity IR Led light pulsed by 555, and the other side has detector , perhaps IR detector and Transistor common collector to LEDs. IR is closer in wavelength to the business of 850nM transmission anyway. But I credit your Instructable to my test set pair. Yes, I made yours first and yes, even on SM (tiny core) short patch 15m , I did see a faint RED led light on the other end.

    1 reply

    Reply 3 years ago

    Thanks RadMan. My use case is carrying DVI over four fibers and we tried using different colors. We found using high brightness red is the easiest to see. This thing is really a go-nogo tester and works really well for that.


    4 years ago on Introduction

    Surely attaching a led as source for fiber optic and data transmission or light emission as your project was simple but great job.



    4 years ago on Introduction

    I wonder how far does it reach only with regular LED. I bought a cheap 5mW laser but so far it's not as bright at the other end as I expected.

    2 replies

    Reply 4 years ago on Introduction

    I use this with 75 ft fiber cables and they are very bright. We have a roll at work that is 1000ft long. Ill check to see how bright it is on that. I suspect it will be good!



    Reply 4 years ago on Introduction

    Thanks, i'll make one with LEDs, it will surely be enough for our local cabling.
    I'm hoping to reach 2km (1,2 miles) with laser. I tried without coupler on few ft cable, but i'm planning to attach coupler to laser pointer and try it out on a larger distance. I'll post my results.


    4 years ago on Introduction

    Hi Thanks a lot for this great information, I've successfully built it and it's working brilliantly, everyone should try this it will save a lot of money.

    1 reply

    6 years ago on Introduction

    just plug it in to the out output and see if you see the light on the other end is all you have too do