Coupling LEDs to a fiber and merging the light from 2 fibers with low optical loss

  • Thread starter Octo
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  • #1
Octo
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Hi,

I am looking for a suitable method to couple light from 2 LEDs into a fiber and then join both fibers, so that I only have one fiber at the end so that both wavelengths can be emitted from a single fiber.
The first coupling step from LED into fiber seems to be more easy, I already heard some just put the fiber in front of the LED and hope for the best. This seems to work kinda well for them.
The more complex step is to couple light from two individual fibers into a single fiber afterwards. I know there are some fiber couplers, but unfortunately not in the wavelength range I want to use as far as I know (UV light decomposes glue).

Therefore, I think about using several ball lenses to achieve my goal, but my understandings of optics is not good enough to really know if it would work this way (or maybe is there a programm to calculate such things?). You can see my plan attached.

The scheme is somewhat size accurate, the light path is drawn from my hopes. :)

Here are my specs:
LED1: 365 nm, 120 ° angle
LED2: 465 nm, 130 ° angle
fiber: 1000 µm core, 300 - 800 nm, 0.39 NA or 0.22 NA
ball lenses: d = 8 mm or 4 mm, n = 1,458, 200 - 2200 nm

Can someone confirm, that this would work or tell me problems with this? I have in mind that I would need to adjust the lens fiber distances so that the focal length is correct.

Thanks
Octo
 

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  • #2
Andy Resnick
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Summary:: A suitable method for coupling light from LEDs into fibers and then fuse 2 fibers into one.

Hi,

I am looking for a suitable method to couple light from 2 LEDs into a fiber and then join both fibers, so that I only have one fiber at the end so that both wavelengths can be emitted from a single fiber.
The first coupling step from LED into fiber seems to be more easy, I already heard some just put the fiber in front of the LED and hope for the best. This seems to work kinda well for them.
The more complex step is to couple light from two individual fibers into a single fiber afterwards. I know there are some fiber couplers, but unfortunately not in the wavelength range I want to use as far as I know (UV light decomposes glue).

Therefore, I think about using several ball lenses to achieve my goal, but my understandings of optics is not good enough to really know if it would work this way (or maybe is there a programm to calculate such things?). You can see my plan attached.

The scheme is somewhat size accurate, the light path is drawn from my hopes. :)

Here are my specs:
LED1: 365 nm, 120 ° angle
LED2: 465 nm, 130 ° angle
fiber: 1000 µm core, 300 - 800 nm, 0.39 NA or 0.22 NA
ball lenses: d = 8 mm or 4 mm, n = 1,458, 200 - 2200 nm

Can someone confirm, that this would work or tell me problems with this? I have in mind that I would need to adjust the lens fiber distances so that the focal length is correct.

Thanks
Octo
What you are trying to do seems to require an excessive amount of alignment headaches. If the LEDs aren't already pigtailed to fibers, why can't you directly couple both LEDs into a single fiber by, for example, using a dichroic mirror?

PS-"just put the fiber in front of the LED and hope for the best" is a bad strategy for a variety of reasons: not just poor coupling efficiency, but also high susceptibility to misalignment/vibration/dust/ etc.
 
  • #3
Octo
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Yeah, that's why I originally intended to use a fiber coupler. But you are right, getting the light of both LEDs into one fiber directly at the start seems to be way better. I kinda blocked my mind with the idea of coupling two fibers. Thanks!

So from my understanding now, I would have to focus the light of both LEDs on the fiber tip. So I would think I need condenser lenses for both LEDs and send one beam from behind a dichroic mirror and one mirroring from one side, right?
I will look for a suitable dichroic mirror then, I hope I can find one separating UV and vis light.
 

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