DIY fiber coupling?

[Gryphon]

I just saw Alex2893 has an Jet Lasers Dazzler for sale that uses a fiber coupled multimode diode and produces a round spot, effectively neutralizing the naturally bad divergence of the laser diode. It got the gears turning in my head and now I'm wondering if it's possible to this with the new NUBM0G or JLD-470 diodes for 7W of ~470nm round laser dot goodness.

I was unsuccessful at finding a module that allows you to press in diode and get a fiber out the other side. I assume that the alignment between the laser die and the end of the fiber is something that needs to be done by hand with precise tools and simply pressing a diode into a module that has fiber output is not going to cut it, but thats just my guess at the mechanics. But in my searching I did come across this little contraption:

Multimode Combiners

Thorlabs specializes in the building blocks for laser and fiber optic systems. From optomechanical components to telecom test instrumentation, Thorlabs' extensive manufacturing capabilities allow us to ship high quality, well priced components and devices for next-day delivery. Optomechanics...

www.thorlabs.com

If I could somehow get three of these new 470nm diodes fiber coupled the resulting output would be a sight to behold! Is this a fools dream or something that could be feasible?

 

[RedCowboy]

Your divergence will be worse coming out of a fiber, I think what that pointer uses is a FAC type fiber which is really just a small FAC lens, the Chinese call the FAC lenses they mount under the window cans of diodes a " fiber " but it's really a FAC lens.

 

[Gryphon]

I thought about FAC as well but in the images of the dot that I've managed to find I'm not completely convinced.

The dot is so perfectly round like what I've seen from true fiber coupled lasers, where as a FAC diode would have some 'squareness' to it. Not to mention the spot appears to stay circular throughout its adjustable focusing range where I would imagine a corner clipped square diode output would reappear.

All of this is just speculation

 

[RedCowboy]

I have not had any visible fiber coupled lasers, only multi mode IR pump lasers coupled to fiber and the divergence out of the fiber is not good.

Only with active fiber such as a MOPA system where a seed laser is amplified in a double clad fiber do we see excellent beam quality straight out of the fiber at high power AFAIK.

For visible fiber I think there is single mode fiber and multi mode fiber with one being bigger than the other.

Maybe they use a FAC and then couple to the optical fiber, as I have been told it's not as simple as focusing a multi mode laser diode into a length of fiber and getting a Gaussian beam out and I expect it's not, but I would like to know/learn what they are doing in this " equity dazzler " because it advertises 700-1000mw of 520nm so you know it's a cheap MM diode.

I found some things:

Fiber Optic Coupling

www.newport.com

I am just now watching this so I don't know if it's any help or not.

EDIT: Ok that blue beam is a 488nm which is a single mode, but I think member Lazerer focused a MM blue into a fiber with a lens and some patience, but what he got out the other end IDK.

 

[Gryphon]

I’d be curious to know what’s going on inside of those as well. I think I’ll do a little experimenting with some cheap components

 

[RedCowboy]

Yep me too, I love learning and can never get enough.

Edit: I know we can focus the MM blues down pretty tight, but it's the entry angle into the fiber.
I have a couple of the 5W FAC blue diodes, that might be a better start than a normal one, then maybe a circularizing optic ?

This is a MM blue and you can see my beam waist is very small, but the angle is likely too steep to couple to a small dia. fiber.
I know I can do better with a FAC MM diode, I will try to get a pic after dinner.



EDIT AGAIN : Also that equity dazzler according to Alex makes a 2 inch wide spot at 30 feet or there about at it's very best focus. That's no Gaussian beam, warmed over rounded multi mode yes, but not a Gaussian green beam like a 532nm dpss.

The way I get a better beam from the 5-7W MM diodes is with cylindrical lenses, that and a beam expander lets me set cardboard alight at 75 feet or more.

This is one of my 1st builds, it's crude but was fun to learn to do.

 

[Gryphon]

Nice! I have some 6X corrective optics from OPT Laser on the way, gonna try them with one of the re-canned NUBM0G's.

 

[RedCowboy]

I have one of the NUBM0F's on the way, we will see how they perform.

This is a 5W MM with the square output FAC


Compared to the non FAC 05 or 08... pretty sure it was an 05 so similar base divergence.

Neither one has the right lens for fiber coupling, but the FAC has the longer throat or narrow portion of the beam waist, so with the right super short FL lens and a coupler to adjust the alignment all in close quarters I think the FAC diode has the best chance.

Here's my 6W FAC with line output and it has the best tightest far field spot when using a long FL lens, look at this beam waist.

 

[Gryphon]

I wonder if I could cut out the middle man entirely. Some of the fiber coupled IR lasers place the end of the fiber right up next to the end of the die. True a lot of them use an 'injection' method with a separate focusing lens before the fiber, but a larger multimode fiber placed right up to the die of a decanned laser diode might do something.

This one is using optics inside the diode package to steer and focus the laser into the fiber

This one just places the fiber right at the end of the die with FAC

I think for the simple home gamer like me, placing the fiber right up to the diode will be easier, albeit probably more wasteful in terms of light collected

 

[RedCowboy]

All those bond wires connect to emitters and those optics are reflecting the rows of beams around to shape the bundle, then that lens that sits a long way from the fiber incept/inject, the bottom one likely has a lens at the end of that row of emitters, also remember it's not just the dia. of your beam but it's angle, it needs to be within a narrow range..... even if it's a tiny beam it's angle entering the fiber matters.

I think the raw output from a MM blue spreads out way too fast to butt a fiber up to the facet, the angle is too steep, you will need a lens and probably a FAC lens then a fiber launch lens or your own compound set up.

Like this, a low angle of entry.

So if you use a FAC diode like this one and a fiber coupler, then you use a LPM to adjust by hand until you get the highest output then cement everything in place.

fiber launch systems

Particularly with single-mode fibers, launching light into a fiber is not easy. Special fiber launch systems are available for that purpose.

www.rp-photonics.com

 

[Gryphon]

I quicky rigged up a little adjustable mount for a fiber to be slowly moved into position in front of a low powered single mode red. Before the fiber its 110mW and after the fiber its 60mW. I tried a couple of different times and that was the best I could get. The left and right adjustment for the fiber works pretty well, but I need to come up with a better solution for adjusting the 'depth' of the beam waist as I'm just doing that by eye, which is not super accurate

It should be said this cable probably isn't meant for a laser this strong, it was the cheapest fiber I could find on amazon and its quite noodly. The ad says it can be bent to a radius of 15mm which probably means it doesn't have a super nice fiber in it.

 

[RedCowboy]

I guess you also checked your rotation to alleviate any polarization issues ?

How well can you focus your beam out of the fiber, can you make a dot on the wall at the same distance of the same dia. as without the fiber coupled ?

 

[Shmackitup]

I'd say the easiest way to get a round beam is to shine the rectangular beam through a small enough round hole or tube. It will just cut off the excess. However, this will create a lot of internal reflection and heat which could wreak havoc on the diode and/or housing.

 

[RedCowboy]

I played with a little 50W ir pump array and it would burn the fiber from the tip backwards until I cleaved and polished the end, because the end/tip is an optical instrument.

Anyway the array has dozens of .5 - 1w emitters that are knife edged and fiber coupled, I would like to see some visible pump arrays like this and from what I read there are some 450nm units being produced or I could build my own as I have hundreds of m-140's

But I wonder if there's any advantage to fiber coupling them rather than aligning the knife edge array to infinity....... will fiber coupling circularize the combined output while alleviating the uneven divergence ? I can't see the fiber improving the divergence.

I expect I would need to use multi mode fiber and a reverse telescope or big beam expander to collimate the output.

Here's the little pump array I was playng with.



Raw output after I cleaved and polished the fiber end.

Then with a G2 lens after I installed a termination. But the divergence was still aggressive over any distance.

------------------------------

I wonder how well this could be focused with our common G2, G8 lenses ? It says 100um which is 100,000nm wide or about 4/1000 of an inch.
Anyway a single mode laser diodes emitter is about 5um x 1um ... well according to the web 3-7um x 1um
Multi mode laser diodes have emitters that are 30-300um x 1um

LASER TREE MultiMode 637nm 1000mW Fiber Coupled Laser Diode 100um | eBay

637nm RED Diode Laser. Fiber Coupled Laser Diode/ Mu ltimode. Applicati o ns.

www.ebay.com

Huh Here's a 15W 450nm with a 60um fiber, I wonder what the beam quality is like ?

Multi Mode Fiber Coupled Laser 450nm 15W Diode Laser Blue , Laser Light Source | eBay

450nm Blue Diode Las er. Note: Fiber Connectorï¼ SMA905,FC selectable ï¼ Leave a m essage when ordering ï¼. Special Light Source. (The video is for reference only ). We are always here if you need any help.

www.ebay.com

5W of 525nm with 60um fiber.

525nm 2W 3W 4W 5W Green Diode Laser Fiber Coupled Laser Built-in TEC Cooling | eBay

525nm Green Diode Las er. Built-in TEC Cooling. Note: Fiber Connectorï¼ SMA905,FC selectable ï¼ Leave a m essage when ordering ï¼. (The video is for reference only ). We are always here if you need any help.

www.ebay.com

 

[Gryphon]

I guess you also checked your rotation to alleviate any polarization issues ?

How well can you focus your beam out of the fiber, can you make a dot on the wall at the same distance of the same dia. as without the fiber coupled ?

Its a $4 fiber so I'm doubt it's a polarization maintaining fiber lol. The laser doesn't focus down as well as it would without the fiber. I tried a stock plastic, G2 and G8, not much of a difference between them with a ~1'" spot at 10'.

 

[RedCowboy]

Ok, and the " equity dazzler " according to Alex can make a 2 inch wide spot at 30 feet at it's best focus, so there's no magic there as per divergence, it's just now a round spot that has equally bad divergence all the way around..... i.e. a 1W 520nm MM laser with a 2E or G8 will make a bar that's about 1.5 inches wide on the wide axis at 30 feet.

Now the NUBM44 has even more aggressive divergence and makes about a 1 inch wide spot at 15 feet, 2 inches wide at 30 feet with a 3E lens...... but with a short FL lens the G2 it makes just under a 2 inch wide bar at 15 feet, but with a 6X c-lens pair after that G2 it's now 5/16 or about 1/3 of an inch or about 7.5mm wide. Add a 3X beam expander which is really 3.3X and the little thin bar is 2.5mm wide on the long side and makes fire on wood with an audible " pop ". ( Note there are 25.4 mm per inch. )

Now my better NUBM35 array makes 14 bars about 1 inch long each at 15 feet in about a 2 x 2.5 inch cluster which will light cardboard, but just imagine if each beam was corrected via. 6X c-lens pairs and then knife edged and focused through just a 3X beam expander, we would have a 75W spot/bundle just a few mm wide depending on how well we aligned it.

Edit: Just a note for any readers, a longer FL lens will make a wider starting beam but a tighter far field beam while a shorter FL lens will make a tighter starting beam but a wider far field beam.