High NA Fiber Optics and Collimators; Don’t Shoot Yourself in the Foot

A customer recently complained that the power output of her Prizmatix fiber coupled LED was too low. The LED system was 5 years old and she suspected that the power loss was due to age.

She wrote:

I'm using a  Prizmatix FC8-LED fiber coupled multi-channel LED source, along with a fiber that we purchased from you. This fiber is attached to a custom-made air-spaced doublet collimator focal length: 33.88mm, NA: 0.26

When my sample is placed only a couple of inches from the output of the collimating lens, the output power is very low, and I was hoping you could help me figure out why that is.

Is it possible that the bulbs have become dimmer over the past few years? What output power should I expect from each of those LEDs?….

The answer to her question is at the end of the first paragraph. A collimator with a NA=0.26 is not a good match for a fiber optic with NA of 0.5.  The lower NA optics will not accept 73% of the light emitted from the fiber. (Here is the math – (0.26/0.5)^2=0.27)

Switching to a collimator with a high NA will solve the problem. Prizmatix offers 3 High NA collimators:

½ inch collimator with NA=0.5

1 inch collimator with NA=0.5

1 inch collimator with NA=0.63

The performance of the three collimators with various fiber optics can be seen on the tables on  Prizmatix’s collimator product page.

Available on  Goldstone Scientific and Amazon.com

Of course checking the fiber for damage and wiping with a wet lab wipe is a good idea too.