A Ball Lens For Optical Fiber Coupling On The Cheap

It's fair to say that for most of us, using a fiber optic cable for digital audio or maybe networking will involve the use of an off-the-shelf termination. We snap the cable into the receptacle, and off we go. We know that inside there will be an LED and some lenses, but that's it. [TedYapo] though has gone a little further into the realm of fibers, by building his own termination. Faced with the relatively high cost of the ball lenses used to focus light from an LED into the end of the fiber he started looking outside the box. He discovered that spherical glass anti-bumping balls used when boiling fluids in laboratories make an acceptable and much cheaper alternative.

A ball lens has an extremely short focal length, meaning that this same property which allowed Antonie van Leeuwenhoek to use them in his microscopes is ideal for LED focusing in a small space at the end of a fiber. Chromatic aberrations are of no consequence for light of a single wavelength. It seems that the glass balls are uniformly spherical enough to do the job. Fitted with the LED and fiber termination in a 3D-printed block, the relative position of the ball can be controlled for optimum light transfer. It's a relatively simple hack mentioned in passing in a Twitter thread, but we like it because of its cheapness and also for an insight into the world of optical fiber termination.

Curious to know more about optical fibers? We covered just the video for you back in 2011.