While working to protect our extremely thin optical fiber, we experienced many delays and inconsistencies in attenuation and light performance. This indicated that our fiber was being damaged through some settings in the over jacketing process. Our initial method for testing the fiber took over an hour to measure around 10m of fiber in a destructive, non-repeatable manner.

The pictured design shows our working test fixture, which, in its current version, allowed us to measure around 30m of fiber in less than a minute (an 180x increase in speed over the cutback method and 9x increase in speed over the camera method). Additionally, we are able to test the fiber over and over again as well as use the fiber in our products. This test fixture is a novel solution to test side-emitting optical fiber in a fast, repeatable, and non-destructive manner.

The PCBA, pulley system, firmware, and panel mount system were fully designed by me to eventually be used for our team in China. The initial pulleys and light chamber were machined and fabricated by me, but were eventually swapped for parts fabricated abroad but designed by me. The design utilized several machined and laser-cut custom parts, a custom PCBA which mounted peripherals like the screen, button, and power inputs as well as an Arduino Mega, and a calibrated ThorLabs photodiode and transimpedance amplifier.

Additionally, to keep the high power laser diode (~500 mW) output stable, I built a PID controller using a fiber power splitter and optical power meter that constantly read and fed back power to the laser driver based on a 10% power split. This was an unforeseen but critical portion of the fixture’s design, that allowed us to start taking readings within 2 seconds of turning the device on as opposed to the usual 2-5 minutes the laser would take to reach its actively cooled temperature.

This test fixture was the final step in our efforts to develop a fast, repeatable, and non-destructive method to measure our optical fiber’s attenuation on the line before it was added to our final products. It was extremely effective and repeatable, with results usually varying less than 2% between several sets of tests of the same fiber strand. Additionally, the fixture worked well for both wavelengths of light we planned on launching in the fiber. Further improvements would have allowed us to measure longer lengths of fiber (likely over 100m) and fully automated pull through and testing.