Build a Simple Fiber Optic Tester

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.

Parts List:
 

1. Four high brightness RED LED’s
2. Four 330-Ohm resistors for current limiting
3. Two dual fiber couplers http://www.l-com.com/productfamily.aspx?id=528
4. Nine volt battery clip
5. Hot glue
6. ¼” or 3/16” Heat Shrink Tubing

Tools:

1. Hot Glue Gun
2. Soldering Iron
3. Hot Air Gun
4. Needle Nose Pliers, Cutters and other misc small tools

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!

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!