combining lasers with fibers?

[Krutz]

hi everyone!

i was thinking about coupling laserdiodes.
i know about dichros and polarising filters/cubes, but am talking about combining many more of them.
there seem to be quite many (well, relatively) people using mirrors, like having a final beam made of "pieces" like a mosaik. great example:
http://www.photonlexicon.com/forums/showthread.php?t=3083 photonlexicon's "project red"
sorry, pics only with login. dont have a login neither..

the pro with mirrors is you keep the (good) collimation from your individual lasermodules. con is the large diameter in the end, its just many beams side by side. use a telescope to make a slimmer beam with higher divergence.

so i was thinking.. use individual laserdies or mounted ones, without any optics. put fibers in front of them. this will work reasonably well, if the distance is really close. fibercoupled diodes you buy often have nothing between the die and the fiber too.
out of the fiber comes a "nice" beam, without astigmatism, round. so lets see. you would have a lightsource the diameter of the fiber, which could for example be 200 microns for the active core. thats 0.2mm if i still am awake enough..
thats *much* larger than the bacteria-sized quantumwell the diode had originally, so the divergence after a collimator would be much worse. but then you could put many fibers side-by-side, and use only one lens to collimate everything to one nice round beam. in the end the beam should be slimmer but more divergent than the mirror approach. use a telescope to enlarge the beam and enhance its divergence.
so, nothing gained?
au contraire!

-only one lens, instead of *many*
-very compact size
-no adjustments later

anyone cares to play with numbers?
i wouldnt believe my own numbers, i have absolutely no "feeling" about what would sound reasonable..

what do you think? obviously, that big manufactor uses mirrors instead of fibers, so there must be something..

manuel

 

[wooooooolazer]

If you want to see the pictures log in with this..

Username: asdffdsa
Password: asdffdsa

...laazer.... ;D ;D ;D

 

[tripper]

not allowed to talk about other forums.


anyway i would go with the mirrors way, they seem to work much better for collimating ect. IMO.

 

[wooooooolazer]

You can as long as your not advertising, heres what c0ldshadow said..

"links to other laser forums are ok as long as the sole purpose of the link is not to advertise."

....lazer... ;D ;D ;D

 

[Da_Dude]

Do you mean like this?
http://www.photonic-products.com/products/pigtailed_laser_diodes/pig_visible.html
But a bunch put togeter?

 

[disma]

I wouldnt bother, I found out the hard way that you wont be able to collimate it! :-/ look at my post about the 17watt Totaly Uncollimatable Really Divergent laser! the best Ive been able to do is get a 6 inch wide beam at 30 feet. This laser diode has a 600 micron wide fiber, so, maybe you could do better with a smaller fiber, but I still dont think its worth the trouble. I was able to get a decent beam from a to-3 multimode diode though. it will burn at 20 foot, the 17w only heats things up at that distance...

Max

 

[Archane]

in theory it would work, but you are still going to run into adjustment problems. some of the limitations to take into consideration

1) fiber cut, if the end of the fiber is not a clean cut beam = crap
2) getting all of the fibers to point at the same spot in the same direction. You cant just bunch them all up with a rubber band at the end, they won't all hit the same spot.
3) collimating it, the problem here is you don't know if the lens needs to be millimeters away or a foot away for the beam to hit the ideal size. The reason for the unknown is we don't know how the beam is going to act exiting the fiber.

These are just my first thoughts on the idea, whoever I like the idea since it would allow you to make a more compact laser in the end as you wouldn't need soo much space for mirrors and such.


Archane

 

[Krutz]

thanks for the comments.

i didnt calculate divergence vs diameter for both systems (mirror and fiber) yet, but read at sam's laserfaq about some commercial fiberlasers. read about numbers in the 40 to 60% area for efficiency, only for the coupling of one diode into one fiber! was multimode though, singlemode is better. but since we are going to use multimode diodes anyway..?
so far, we have 2x powerdensity for mirrors (because we can mix with a polarizer without real losses), and up to 50% losses with coupling into the fiber. surfacemirrors are quite efficient, and collimation for the mirrors would be in the 10% region.
all in all, it looks like no use. even if the collimation would be comparable or better, the fibersystem would need more input, and would potentially have larger diameter.

nevertheless, one day i will play with some fibers i still have, and see what happens. by the way, they use the core of fibers as microlenses too. anyone with a mediocre opencan to give it a try?

manuel

 

[Archane]

here is an idea for you, use one large fibler cable, see fiber has this great ability most people aren't aware of that it can handle multiple streams of data(ie light) in one cable be changing the angle in which the light enters the cable. so if you had a cable say an inch thick and hit it with more diodes you could collimate the final output. This might give you the same result you wanted with alot less work.

The reason this works is light entering the fiber cable won't escape out the sides unless the cable is damaged or unless the angle of entry it too steap. It's something i've been thinking about but haven't had time to throw any money at yet.

Granted if you put in 500mw of power (say 5x 100mw diodes for math sake) you arne't going to get 500mw out the other end. there will be some loss in the form of distance travled and clarity of the fiber and optics. But the loss should be less than 10%. The reason distance in this case matters is if you change the angle of entry you in turn change the distance traveled because of it bouncing inside the fiber cable. so the shorter the fiber the better.

Just my thoughts, let me know what you think.