Variable Optic Attenuator

Variable Optic Attenuator

Variable Optic Attenuator

Optical sources (lasers and LEDs) are crazy powerful! They seem to be getting ever more powerful. This isn’t required for optogenetics. In fact, delivering light to tissue, even in the absence of any opsin, will increase neural activity. Optic power delivery results in tissue heating, thereby increasing the general activity of the neurons. But you’re testing this with your controls, right? Right??

We live in the real world (sigh) and therefore when we ask our lasers to turn on and off with very specific TTL pulses, they do not do so instantaneously. Some lasers are slow to ramp up to their set power, and others will in fact overshoot their power and take some time to settle down to a power you can accurately measure with a power meter. The timing characteristics of optical sources can be tested with a photodetector. Typically, optical sources have their best timing characteristics when their power is at their maximum. But, again, that is probably WAY to high for optogenetic stimulation.

Here are two parts that can be 3D printed (high resolution printing is recommended, i.e. SLA). Rosenberg Industries has proven success in printing these parts. Each part has an FC/PC connector (typical for laser patch cords). Connect one patch cord to each part, then you can thread the two parts together. This allows you to set the power high on the optic source and easily vary the optic power in a controlled and safe manner.


The threading of the parts may wear, so it is recommended to apply a little oil to all threads prior to assembly. The inner part has two tabs to hold onto during threading, but also to glue in two M3 nuts. You can then thread two M3 screws through to butt against the outer part, thereby fixing the set position. The printed parts may not be perfect (100 μm diameter cores), so it is recommended that the two patch cords be connected with a Ø2.5 mm sleeve. This ensures X-Y alignment. The Z alignment is controlled with the threading between the two parts.




File Description
VarAttenOutter.sldprt The outer part
VarAttenOutter.stl The outer part
VarAttenInner.sldprt The inner part
VarAttenInner.stl The inner part

Click on the .stl parts to see the parts in your browser. From there you can download the part with the cloud down arrow button.

ONE Core acknowledgement

Please acknowledge the ONE Core facility in your publications. An appropriate wording would be:

“The Optogenetics and Neural Engineering (ONE) Core at the University of Colorado School of Medicine provided engineering support for this research. The ONE Core is part of the NeuroTechnology Center, funded in part by the School of Medicine and by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under award number P30NS048154.”