fiber optic beam combining

[VDX]

... I don't use or mount fibers "across" the diodes - my previously linked image (here the direct link for clarity) where three 9Watt-diodes are combined into a 105µ fiber is from opening a 25Watt-diode from IPG.

They glued thin plano-convex cylinder lenses horizontal before the diode to collimate the vertical oriented fast axis and a bigger vertical plano-convex cylinder lens shortly before the 45°-mirrors to collimate the horizontal oriented slow axis.

The diodes and collimated beams are set to different heights, so the 'horizontal' beams combines to a quadrate and then are focussed together into the 105µ output fiber in the right lower edge.

Where I've seen a piece of glass rod "across" a laser beam is in line-lasers - but there the beam is collimated and the glass cylinder only refocus the beam, so it forms a line instead a spot ...

Viktor

PS: ... and yes, my 'working dimensions' were sometimes in the range of some ten microns, when I had to assemble, align and adjust micro-sensors with micro- and nano-wires

[VDX]

... to simulate the 'effect', I've filled a plastic tube with water and used it to collimate the fast axis of a 445nm-diode without optics.

Here the images of the test:

- the 'naked' diode with removed optics:





- the far-field beam in rougly 1,5m distance:





- and with the water-filled tube, placed horizontally in some 20mm distance from the diode output to get best focussing of the 'collimated' fast axis:





As you can see, I've influenced only the fast axis - the slow axis stays unchanged -- but could be collimated too with a bigger/weaker glass rod or cylinder lens to get a perfect (rectangular shaped) beam ...

Viktor

[VDX]

... and for the size relations - the cylinder with around 20mm diameter in 20mm distance can be replaced by a short piece of glass fiber with 2mm diameter in 2mm distance or 500 microns diameter in 500 microns distance from the laser output.

With different refractive indexes the numbers will change, but so you can get a 'roughly' estimate ...

Viktor

[mixedgas]

NO, No, no...
!
The diode is decanned, a small block of metal is laser welded to the back can of the diode, and a computer positions a piece of glass like a fiber onto the metal block for most circular beam. By some proprietary process, the fiber is spiked down (metalized and welded, solder, UV glue, who knows!) into position The assembly is a baked to remove water vapor, The new can with ar coated lens is welded on, and backfilled with a gas mixture that is mostly inert gas. For some strange reason, the dry gas mix matters, and is patented. The whole process is covered with multiple world patents, that are enforced.

Circularized Diodes... AKA VPSL...
!
Not all that easy to do as you really need a servo stage to position the fiber, and the correct fiber diameter.
!
http://www.blueskyresearch.com/c/b/posts/view/32
!
Before everybody calls Blue Sky, keep in mind the minimum order is around 3000-5000 pieces with NRE fees... I know, I tried, for something much more then a personal project, and 1000 pieces of ONE type of diode was not enough.
!
Transverse Optics for diode arrays or C mounts can be purchased, but I'm not going to name my source company, least they be bombarded with requests for single piece orders.
If your in the business, you know where to look.
!
Steve

[VDX]

... oh, this "glass fiber/cylinder"-hack is not meant to manufacture high precision modules (but can be used for this too with some serious gear).

I'm building and developing medium power (some Watts to some ten Watts) modules for material processing and laser sintering and had some success with simply 'adding' a bunch of diodes on an averaged spot to get 12 Watts @445nm on a spot 0f 0.3mm diameter with 6x 2Watt-diodes (single diode spot around 0.07mm).

For another company and project, maybe ten years ago, we developed the aligning/justage rig for a "ringfocus-laser", where 80 IR-diodes with 20Watts each were combined on a spot of roughly 2mm diamter and 1600 Watts averaged power to weld steel.

This was done with highly complex alignment, cylinder-lenses and conical mirror-cones and -rings to get all the beams on the spot.

With some much simpler handling and fiber-coupled diodes I could build a much smaller/cheaper module with the same power, but focussed on 0.5mm instead of 2mm -- so roughly 16x the energy density!

Actually I'm developing some drivers and modules for sintering and welding/hard-soldering with NIR- or VIS-diodes ... it should be interesting to combine some ten of the blue 6W-diodes to a spot of 0.3mm diameter and some hundred Watts of power ... or 0.1mm and 'only' 30 Watts

Viktor

[catalanjo]

Keep your hat on Steve...I am just contemplating mucking about on the kitchen table trying to UP the REDness a bit,.... not starting a ripoff corporation to get around the patent laws

We are not talking about "arrays" at all, just considering how close one can get to wide stripe diode and what bits to use.

I had hoped that Viktor had actually tried this but it seems he hasn't ........."yet"!

"Positioning" and "fixing"might well be a hassle but I think Victors new pics and posts demonstrate his idea better than a diagram, and it's nice to daydream about how to achieve something similar with say a 500micron fibre.

As for the gas ...I think maybe heat has something to do with it.

Reminds me a bit of Robin soldering his "grain of sand" to a stripped down transistor.

Cheers
PS. Thanks for the link !

[planters]

I do not understand the novelty of this approach. I do not disagree that it works, but how is this different than a FAC diode?

Using a fiber laterally as a small, cylinder shaped lens to FAC a diode output is interesting, but remember that these fibers are not AR coated on the surface that is designed to retain light by total internal reflection. That is a loss of 4-5%/surface times two surfaces.

The output from a multimode diode at any wavelength is a cluster of ray paths that is usually pretty symmetrical in each axis ie l ll l, but it is not a smooth and continuous transition like the Gaussian spread of a single mode beam. Trying to get the smallest focus which is the same as achieving the lowest divergence requires a complex lens shape. Even the main stripe is not the same as the single mode spot and has structure.

It should not matter what scale of the correction lens and spacing that you use, ie a 20mm lens at 10mm from the diode or 100um at 50um from the diode, the result should be the same. The rays will follow straight paths to each lens surface and the correction should be scale invariant. The larger lens will be less expensive and much easier to position. The divergence will be the same and so even if the FAC diode's small spot would seem to allow tighter knife edging (more beams/mm^2) the divergence will be proportionally higher and the far field brightness will be the same.

[kecked]

I find cyl len just fine. You got me thinking though why not pass the diodes through the first concave lens of the set to make the line and then knife the diodes(one concave per diode and then send the result together through the convex second lens after the knife edge. Saves one optic per diode. Seems you can align the stripes much tighter. Just need to have the distance between the optic large enough for the extra path length.
I have no plan to try this but if someone wants to let me know if it works. I doubt the trouble is worth it for two diodes but a stack of 4 might be worth the effort and eliminates the cubes and waveplates.

[kecked]

reading about fiber lasers the limit seems to be 6 diodes in a combiner before you overload the core.

[Nii]

Can anyone explain to someone far less experienced, are there any advantages to using fibres instead of good-ol knife edging when it comes to the quality (beam profile and diameter) of the beam which goes to the scanners?
If yes, why? (if possible to be explained in a nutshell)