Dear RG-community,
in our lab, we currently use silica fibers (1 mm core, NA=0.22, multimode, 1 m) coupled to LEDs (470 or 630 nm) for in vivo optogenetics in behaving head-fixed mice. In search of fibers that increase optical power transmission, I have come across high NA plastic/polymer fibers (NA=0.68), which should obviously increase light power.
Besides this advantage for plastic fibers, are there any disadvantages to using plastic fibers instead of silica ones for our application?
Many thanks in advance!
Image source:
http://doriclenses.com/life-sciences/mono-fiber-optic/855-mono-fiber-optic-patch-cords-plastic.html#/jacket_glass-standard/connector_code_mfp_2-sma/connector_code_1_mfp_dfp-sma/fiber_optic_code_plastic-480_500_0_63
Your fiber core and area are bigger than some LEDs and smaller than others. The NA of your current fiber is bigger than some LEDs and smaller than others. It matters.
You probably should consider the whole optical train before you go swapping out components. This is because the LEDs will emit over a certain NA and area, the optical systems that couples light into your fiber (if there is one) alters it, the fiber transfers it and the optical system that couples light from your fiber to your sample alters it yet again. So what intensity are you trying to achieve and can you tolerate at the sample?
You have to analyze the whole optical train.
Or you just use the old method of buy and try. And then wonder... Why?
Hi Yannik,
There's a lot to unpack here. Just to clarify, are you talking about the fibre optic patch cables (connecting the LED to the mouse) or are you talking about the optic cannula (that's going in the mouse's brain)? From your screenshot, I'm assuming you mean the patch cords. Doric do have some further info summarising the different types of fibre cores: https://neuro.doriclenses.com/collections/fiber-optic-cannulas/products/mono-fiber-optic-cannulas?productoption%5BFiber-optic%20Material%5D=Silica%20%2F%20Silica&productoption%5BReceptacle%5D=ZF1.25&productoption%5BFiber%20Tip%5D=FLT
Firstly, what optic cannula are you using? For optogenetics, I always recommend 200 um core 0.22 NA fibres, even when using LED sources. Reason being, as soon as you increase the NA of you fibre, you can get a marginal increase in light entering the mouse's brain, but it scatters far more widely, so it's actually less effective. For further info, check out my Optogenetics Power Calculator: https://nicneuro.net/power-calculator/
Next, about the patch cords. As Norman said, the optimal patch cord will depend on your LED. However, assuming that you are using a 200 um optic cannula, you do not need the full 1 mm diameter core. So, my suggestion would to drop the diameter of your patch fibre (maybe to 400 um), to maximise irradiance capture from the LED. In this case, the NA of the fibre shouldn't matter too much, so long as you do use the 0.22 NA fibre cannula.
Lastly, does your patch cable have a rotary joint? If the mouse is head-fixed that isn't necessary, and will lead to an avoidable loss of light power.
Unfortunately, many of the LED's sold for in vivo optogenetics are simply not bright enough. In particular, I'm not sure I've seen any outside of the blue 450-470 nm range that are really bright enough for normal optogenetic tools.