A Mode scrambler
Today I decided to take a look at a mode scrambler. The mode scrambler shown here takes multimode fiber as the input and output. It then “scrambles” the illumination evening it out. In my experiments I’ve found it significantly cleans up the illumination profile when used in microscopy.
I picked this one up on eBay, but they likely cost $1000+ new. Inside, they are surprisingly simple:
It takes a 5V input and has a PIC microcontroller and a couple of inductors. Feeding the central disc-like structure. The mode-scrambler basically just wiggles the fiber around. It’s a bit like a AOM (Acousto-optic modulator) These generally use piezo actuators (basically piezo buzzers) to vibrate an optical median and shift the wavelength.
So, I figured this would likely be using a piezo transducer of some kind. However, if you take a peak under this disc you can see they’re using essentially a modified speaker:
This is likely due to the lower frequencies being used here. You can see how the bare fiber is coupled to the speaker in the image below:
The PIC like just generates a fixed frequency I assume a microcontroller is so that the frequency can easy be changed at the factory, but there’s no control input to allow parameters to be set during operation.
The inductors likely step up the voltage/provide enough current to drive the speaker.
The mode scrambler is pretty noisy and produces quite of lot of vibrational noise too (so in microscopy applications needs vibrational isolation). You can hear its low hum in the video below, as well as see the fiber wiggling around:
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