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Thread: Focus mixed RGB beam into fiber...

  1. #1
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    Lightbulb Focus mixed RGB beam into fiber...

    How hard, and what might a list of materials be to take a mixed RGB beam from before a set of scanners, in the "normal" projector, and put it into a fiber optic cable?

    I'd like a cleaner and prettier way to split my white beam before it gets to my scanner. I've gotten find of splitting my beam with microscope slides and using the beams for different effects. Astroguy gave me a cool little set up with two motors with mirrors and a driver board, I have a motorized first surface mirror that makes a fan, and I have two open loop galvos that are hooked up to sound. Right now I'm at the mercy of where I can get the slides to point the beams. I'd like to have more control of the beams and a nicer distrabution. I have about 50 feet of 6 strand fiber, but it's not terminated. That's not too much of a problem but I'm not sure if it'll be to hard to get the beam into the fiber and then split it... Or is this too far out there and just a pipe dream?
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

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    Unhappy

    Nothin huh?

  3. #3
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    Hey Allthat,

    I would reply if I knew anything about fiber coupling, hell, I reply anyway
    I have two optical patch cables that I salvaged a few year ago from an old library that they were turning into appartments (legally). Looking at how tiny the fiber is, I'm happy just to get a few milliwats in there! Maybe yours are a little thicker.
    Sometimes on ebay there are positioning devices to get the beam into the fiber, the way I see it is that it takes a lot of precision to focus the beam into the fiber. This might be practically impossible with an RGB beam where each laser has it's own beam characteristics. The focal point may not be the same and line misalignments in terms of graphics might be huge misalignments in terms of focal point. When the beam exits the fiber you'll need to colimate it again..... not sure how that will effect the beam.

    just my 2p, but hey give it a try and let us know

  4. #4
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    No, that's what I'm looking for... If it is not possible, well, for me atleast I want to know so I can stop imagining it... You bring up points I am worried about but have no experience with. The fiber I have is for data and really tiny, and I didn't think of collminating it after the fiber... I was just throwing feelers out there to see if it is possible and... economical money and mWattage wise.

  5. #5
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    coupling to fibre isn't as easy as you would hope.

    You wont be able to do it on the cheap.
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  6. #6
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    Thanks dave! I kinda figured, or "We'd all be doing it..." What's the most expensive part? Components or cable?

  7. #7
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    We actually run fiber to most of our heads. It's much easier aligning gas lasers but if you have each mirror/dichro from a diode laser off a MM1 then after you set the focal length then you can dial each color line in seperately.

    The big advantage to fiber is that the colors come out very well blended, so for example, it can actually look like a true yellow beam if you dial it in right.

    The drawback is that you will see power loss even if everything is aligned perfect, and if it isn't perfect you can see dramatic power loss. Basically attention to detail wins the game. Alignment of fiber from scratch is a tad easier than a PCAOMs from scratch, but harder than a 3 diode whitelight for some reference

    I'd say a DIY fiber system is very much doable except for the gradient index multi-mode fiber, which you'll have to buy. If you don't have access to a fiber polishing machine, then you'll have to get them pre-polished which would add to the cost. The metal SMA style fiber end caps are not expensive and are necessary at any real power level. I would strongly recommend buying fiber with the ends premade and polished if you don't have experience with it.

    The fiber input can be as simple as a single convex lens on a fine pitch thread attached to the input holder. Attached the entire unit to an MM1 for quick realignment. Other designs have seperate focusing lens and fiber holder, this makes it easier to align, but has more moving parts that will require constant maintenance if your gear is on the road.

    The output can be as simple as a laser diode collimation housing with the fiber output where the laser diode would normally be.

    The thickness of the fiber will determine the beam width and how tightly you can collimate the beam. The smaller the better, but you'll also find that fiber alignment is much easier with a larger fiber... It's all about finding the right balance for your application.

    In terms of what I use, I just buy premade fiber input and launchers and buy my fiber premade. I don't buy in large quantities so the cost of a well designed commercial system runs us a bit over a couple grand per system.

    I'll also add that coupling an arctos red into fiber is an exercise in hairpulling and screaming.

    Fiber alignment is where I miss the nice beams of the big gas lasers...
    Last edited by yaddatrance; 02-12-2007 at 17:54.

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    P.S. I forgot to add... If your power is <1W then you can get away with quite a bit! The comments above are for "serious use"...

    It wouldn't be necessarily trivial to split the beam IN fiber, though I have seen really creepy fiber tricks doing things like inducing modes, etc. Most of the units you sometimes see on ebay are very specialized miniscule prism-like devices with the ends of the fiber optically bonded to the faces.

    For a low power <1W system, you could get away with removing the cladding from multiple fiber strands and joining them and then focusing the laser evenly across the multiple strands. At higher powers, the clear sheathing ablates and you'll end up with low power output from the now opaque inputs.

    To get a usable beam out of fiber, you need to recollimate it just like a raw laser pointer diode. So in the multiple fiber idea, just replace the diodes from the red gas station pointers with the fiber strand.

    Oh yeah, at <1W you could get away with plastic fiber! This will reduce costs dramatically... The only thing to make sure is that the fiber is multi-mode... you'll be very disappointed with the behavior of single-mode fiber unless you're running at only one frequency.

    [added]
    While I'm thinking about it...

    Use f=20mm/0.75" acromats for the input and f=25mm/1" acromats on the output collimator for the best results. The industry standard uses SMA905 connectors on the fiber...
    Last edited by yaddatrance; 02-12-2007 at 18:20.

  9. #9
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    Thanks yadda!!! I think...

    I think the fiber I have is multimode. I'll have to look at it and do some research... It's not terminated but I have a lil experience with that. I do think this may be way beyond my current projector, , but definatly something I'd like to look into for the future. I can get some of the cabling parts from some friends I have in Telcom, so hopefully that'll get rid of some of the costs. This'll definatly have to go on the back burner... Pangolin is my next goal. Talk about costs.

  10. #10
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    No problem, Often fiber can take away some of the headaches.

    Here's a ghetto cutaway of the input side to give a clearer illustration.


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