Need help identifying laser module

[RedCowboy]

IIRC, that amount of power loss at 30 watts would equal 4.75 watts at the splice in waste heat.

Starting with 30 watts before the splice with 0.2dB loss.

Should be 1.35 watts lost with 28.65 watts getting through.

0.2dB would be .955 remaining.

4.5 percent loss

That's still more heat in the splice than I would want, probably better to terminate the end and polish the tip of the fiber as it should be done.

 

[paul1598419]

I had to go back and look it up. I hate working in common log. Yeah, 1 dB would be a 20.6% loss. And 0.2 dB would be 4.5% loss, so at 30 watts in the loss would be 1.35 watts at the junction. I should never rely on my memory, but I still seem to do it all too often. That is a lot of heat in such a tiny spot.

 

[Buontinh]

Thank you for all the info, RedCowBoy. They really help.

So to recap, I need to terminate the fiber using this https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=6975
then polish with something like this https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1350
connect the terminated end to one of these https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=4353

But I'm confused about gradient index (GRIN) Lenses. Do I need it and could you provide a link? Also is it necessary to cleave the fiber before polishing? Shouldn't it be cleaved already at the factory?

 

[RedCowboy]

After you seat your fiber cable into the termination and crimp/secure it you score the glass fiber itself at the end of the termination and pull it away from the termination to break it as clean as possible at the end of the termination center stalk that countersinks into the ThorLabs lens end so you don't have to do a bunch of alignment.

Now after you score the fiber and pull it to break it clean you must polish it flat and clear, the face of the fiber should end up being perpendicular to that center pin that it's seated into. This is why they polish with the disc and flat plate under the abrasive, to be sure the polished face of the fiber is perpendicular to the termination stalk it's seated into.

If you feel there's any unevenness where it broke you can use a slightly coarse grit to get it flat then polish with the super fine and then ultra fine.

The termination should countersink into the lens ends ThorLabs sells, the grin lens if needed helps to collimate across any free space between the fiber and the lens. Ask ThorLabs what you need, tell them your multi mode fiber core dia. cladding dia. and wavelength.

I have not yet done this myself, I just bought a NV camera that doesn't have that IR blocking filter so I can set it up and work without having to hold a modified hand camera, I will be wearing attenuation safety glasses that absorb stray/diffuse and hopefully not any specular reflections while working with IR so that I can see the beam/spot on my monitor.

So what I am saying is the IR light coming out of your polished fiber will diverge based on the numerical aperture that's determined by your multi mode fibers core and cladding diameters and it will diverge pretty aggressively, so because you may have some small space between your fiber's polished end and lens of the adaptor you may need a gradient index lens that will collimate your beam and let it traverse any free space before your focusing lens, just what lens you will need I don't know, but Thorlabs can tell you based on your core diameter, cladding diameter and wavelength.

You may want an adjustable telescope end to expand and focus your beam or you may want a fixed lens for CNC.


Here's an example of installing a termination, you can see how he scores the extra fiber and polishes it flat with the disc.

Here's a different type of termination, but it works the same, see how he scores the glass and polishes it.

**Please note: The information I share is to the best of my knowledge correct, but although I intend to in the future I have not as yet done this procedure, I can see that you will want the correct termination for your fiber, so talk to ThorLabs and get the right termination and adaptor/lens that you need.

 

[Alaskan]

I sure missed these last posts in this thread before, just what I needed now, thanks.

 

[Buontinh]

So today I gave into temptation and just had to try and see if the laser works before wasting time and money. I set the current to 1amp and slowly raised the voltage...nothing at 3v, still nothing at 4, 5, 6, 7, 8.. then at 9 something volt, the fiber started to glow/burn from the tip down like slow burning fuse uses to set explosive. I turned the voltage down, but didn't turn it down fast enough to stop it so I just shut the power supply off. Anyway, it burned off about 2 inches of the outer fiber layer. Please see attached picture.

So what exactly happened here? Did it back fire or something like that because I didn't polish the fiber?

Thank you

 

[paul1598419]

These are IR arrays and if you were waiting to see some light, you just over drove your array. You likely damaged more than just the fiber optic cable. Might be a dead array now.

 

[Buontinh]

I know they are IR. I watched the current draw while raising the voltage and it was under 2 amp so it wasn't over driven as these arrays need something like 10amp or more at full power. So could a dirty/unpolished fiber caused the outer layer (cladding?) to burn?

Thank you

 

[paul1598419]

You misunderstood me. The forward voltage is ~2.4 volts. If you increased the forward voltage past that, you have over driven it.

 

[Buontinh]

The forward voltage must be 9 something volt. If it is 2.4v, the current observed should be much higher. It didn't draw any current until it got to 9v. I checked the spec for the current PLD 70 series before trying and they list the forward voltage at 9.57v so if what I have is similar then it might even be higher than that.

 

[RedCowboy]

Could be, I still want to get ahold of a still working de commissioned industrial active fiber laser.

I do wonder about waste heat, I know there are special scavengers to clean up unwanted radiation in some cases, but with the double clad ytterbium/erbium doped fiber with bragg gratings itself being the gain medium, I wonder if there is much waste heat and how it's managed, I get the idea that there's not all that much.

Has anyone owned one, taken on e apart, seen the insides of one ?

 

[Buontinh]

With the coating burned off, the uncoated part of the fiber is much more fragile and break easily. With most of the uncoated fiber broken off, but there is still 6mm or so intact, I tested it again today and the module still works fine. With just 1amp, it could smoke wood from a distance of 8mm or so without collimator. At 5amp, it could make charcoal glow from a distance of 60mm and beam diameter of almost 1inch based on the glow's diameter.

From watching this video about cleaving fiber https://www.youtube.com/watch?v=t0esDSqWS3s
I'm wondering if the layer that burned off isn't the cladding, but just some kind of silicone coating that needs to be stripped off before terminating? The fiber measures about .22mm with that coating and about .11mm without that coating. But without that coating, the fiber break easily though. I guess if the fiber is polished properly and with the coating still intact, it would allow light to pass out the fiber without heating up the tip causing the coating to burn?

Also how can you tell if this is a single mode or multimode laser? Is overcooling to the point of causing condensation on the module just as bad as under cooling?

Thank you

 

[Buontinh]

After further research, I learned that the coating on top of core/cladding is known as the primary buffer. This is the coating that got burned in my case and does needs to be removed for terminating. Also single mode fiber typically has a core diameter of 8 or 9 micron vs 50 micron or more for multimode fiber.

I finally went and bought a collimator from Thorlabs. This one here https://www.thorlabs.com/thorproduct.cfm?partnumber=F240FC-980
The diameter of the collimator is only 12mm. It can get quite hot running at just 3amp. I made a 17mmx51mm heatsink for it and it still get hot running at 7amp. I will need to make a bigger one if I want to run higher current without it getting uncomfortably hot.

I haven't crimped the terminator or polished the fiber yet. That would be next. To test it, I simply taped it to the terminator to prevent the fiber cable from slipping out.

Attached are pix of it lighting up concrete block and melting spring at about 7amp. I haven't tried pushing it above 7amp yet although it can burn hole in thin steel even at less than 7amp.

Thank you RedCowboy for all the info you provided. They helped me learn a great deal.

 

[RedCowboy]

Very nice, Alaskan and myself are working on the same. HERE >>> https://laserpointerforums.com/f44/...laser-diode-cnc-cutting-engraving-102792.html

I just burned off my buffer after attempting a hand polishing.

So you needed to remove the buffer you say ?

My core is 105um IINM what size is yours and where did you buy your connector/termination ?

I am going to jury rig this for my collimator >>> https://www.ebay.com/itm/Laser-Modu...997113?hash=item1eaf2d3fb9:g:qFEAAOSw3mpXGEHU

p.s. Not having your fiber end polished is likely a major factor in your collimator heat problem, you bought a high end lens so it shouldn't be getting that hot.

 

[paul1598419]

That is a nice lens for this purpose. I suspect once you terminate it properly, it will not run hot at all. This is becoming a very interesting thread. I use fiber optics, but at extremely low powers for spectroscopy. Much of this is new to me and I love learning anything new.

 

[Buontinh]

Yeah, all the info I read about terminating say the buffer does needs to be removed. There is a Youtube video showing how to remove it using a razor blade and that is what I did. I just removed enough for the core to fit through the terminator. I measured my core with a caliper and it says 110um, but calipers are usually only accurate down to 10um so it probably is same as yours. My collimator uses FC/PC connector so I bought the one that has 127um bore https://www.thorlabs.com/thorproduct.cfm?partnumber=30128C3 from Thorlabs. The fiber core seems to fit perfectly in it.

About the collimator heating up, that is what I thought too so hopefully it will run cool after polishing. For anyone looking for polishing film, I bought 5um and .3um from https://www.specialized.net/fiberxp-fiber-optic-lapping-film-5-um.html They seem to be a lot cheaper than other sources.

The collimator I bought have a focal length of about 8mm and beam width of 1.7mm which is kind of big for my liking. They have one with focal length of 4.5mm and beam diameter of .98mm, but the short focal length kind of turned me off. I might get it in the future as if the laser is focused down that small it would be even more intense. I also looked into making my own collimator using aspheric lens as it seems simple enough for single lens collimator, but the lens alone cost $80 and they don't have any with a designed AR wavelength of 980nm, though their datasheet shows very little loss when using at that wavelength.

I used spiral wrap coil to protect the fiber cable which also makes handling it so much easier. It has an OD of 3mm and 1mm something ID which is a perfect fit for the fiber cable. I also have a bigger version of the same wrap in case I need double protection.