Coupling Laser beams into Fiber Optic Cable!

in this episode we're going to take a look at coupling lasers into Fiber Optic Cables so let's go So lately I've been experimenting with fiber optic cable this is actually a really really interesting stuff with applications that go far beyond telecommunications in fact you can use fiber optic cable for all sorts of weird and wonderful stuff like you can use it for remote sensing you can actually use the cable itself as a sensor you can measure temperature with it you can measure high voltage with it you can probably measure magnetic fields with it all sorts of really really interesting stuff at the moment I've actually got a couple of really cool projects in the works involving fiber optic cable and so I would say to you if you're not subscribed to this channel already you should absolutely do so because there's some really really cool stuff coming up in the future from most of my projects I'm actually going to be using standard telecommunications cable this stuff is dirt cheap because it's everywhere I picked this up there's about 35 meters picked it up from Amazon for about 15 bucks and so very very cheap I do have a collection of non-standard fibers that I've picked up off eBay for various other projects this is a 100 Micron silica fiber it's a particularly large diameter fiber for a certain specialist applications but yeah for the most part telecoms fiber all the way this has standard connectors on the end we've got an st connector on here it's like a little bayonet connector and we can connect it up to you know whatever patch panels or whatever normally um with our little bayonet connector on the end there what I'm really interested in in the topic of this video is how to couple laser light into these things um in a sort of sensible fashion get get the maximum light traveling through the fiber that we can if I take this piece of multi-mold fiber and a laser pointer we'll see if we can get some light coupled into it just by shining a laser in the end so just pop off the ends real quick there we are pointing towards the camera and we'll try and get some laser light coupled in there and we might see a little Flash not very much light is being coupled in at all and so we need a method of efficiently coupling our lasers into the fiber fortunately it's possible to buy a fiber optic collimators and this is an example of one this is an FC connector and the FC connector seem to be the most common for fiber optic cable but very very simply it's just a little Barrel assembly with a lens mounted on the front that we couple our light into the fiber with I'll just unscrew this and we'll have a look don't anything too exciting in there that's it it's just a threaded barrel with a lens that's all there is to it and I suppose we could attempt to try and couple some light in with a laser pointer uh we'll give this a go it won't work out very well uh we'll we'll talk about why that is shortly but let's screw on our collimator and we'll see if we can couple any more lighting now this will be junky as right it's not likely to work very well but and we'll give it a go and we maybe get one or two very very tiny flashes at the end of the cable we don't seem to be doing very well at all right um so yeah let's let's look at how we might effectively couple light into these cables so as we saw just simply pointing a laser pointer in the end of a fiber cable can't really be expected to work very well at all I mean the beam damage of this is about four or five millimeters and the fiber core diameter on the end of our cable is about nine microns so I mean we're only going to couple in a very very small amount of light even when we have the fiber optic coupler hooked up to the end of the cable we're still not effectively coupling in the light and the light will only get coupled into the core of the cable if everything is perfectly aligned so I have a diagram here where we have a fiber tip and in the middle the line represents our nine Micron spot and if we can get light to go into the end of the coupler very very straight and very very precisely and then it's not beyond the balance of possibility that we could focus our light into the very end of the fiber if uh if we're off uh we're off center or off axis by even you know fractions of a degree and I'll draw an exaggerated diagram here but if we're off by fractions of a degree then we're probably going to focus light that's going to end up you know significantly away from our Target 9 Micron Center uh it's nothing to do with the accuracy of this cheap collimator this came off of AliExpress and cost about 15 bucks and so they're relatively you know they're relatively inexpensive but there's nothing mechanically on sound about this uh we need a sensible way of coupling uh coupling light in there on axis um about fiber collimators I thought that 15 bucks for this was quite expensive and so and since I have such a variety of fiber connectors on the selection of cable that I have I've actually made a bunch of my own so here's one for St connectors that I've put together and I've got another one here for the Nano the SMA 905 connector and this is just a standard SMA connector that I've punched out the uh the the electrical pin that was normally in there and then silver sold it on a uh a collimator assembly from a lasered out uh I laid it out like this um these these lens assemblies for inexpensive laser dials can be harder for like you know you can get for like 10 in a bag for a couple of bucks right and so very very inexpensive indeed and so I've got a whole selection of these things here's another one that couples to FC cable this is another homemade connector and to get the FC style coupling I've just used standard FC coupler and turned one end off in the lathe and then silver soldered my uh my lizard out collimator onto the end of it and so yeah we've got effective means of focusing the light we just need an effective means of directing the light in there and getting it absolutely Square in order to do super simple fiber coupling we actually need a laser light source that's already coupled into one end of the fiber and so to accomplish this I've picked up a visual fault locator off of Amazon this was 15 bucks delivered and not affiliated with Amazon or the manufacturer of these things but let's have a look um looks a little bit like a torch um it's basically a laser pointer nothing more exciting than that except at the end we've got a special coupling that allows us to couple this into the end of our fiber the idea behind these things is if you're working on fibers in the field and you want to identify you know if you've got a fiber bundle of like 100 fibers or whatever and you want to know which connectors which you can just couple this up to one connector at one end and you can see the light output from the other it's as simple as that and this thing made me chuckle when I took it out of its case the warning label on there actually says this is an XML laser if you could buy an XML laser for 15 I would be like super happy and but it is just the standard red laser so a laser diode and if we're shining on the work surface there we can see we actually have a very large Divergent beam because this is designed to be coupled straight into the end of a fiber so let's see that so I'll just hook this up to a short piece of telecoms cable real quick and we can see what it does just pop the cap off and couple it in and if I turn the thing on we can see that the end is really quite well illuminated already so it's you know this thing's obviously coupling a decent amount of light into the end of the fiber and if we pop the cap off we can see our quite Divergent beam emerging there and if I take my homemade St connector collimator we can plug that in and we can collimate the beam into a nice tight spot again which is very very useful indeed um yeah so we're gonna we're gonna get the optical bench out I'm going to show you how to use this in order to quickly and easily couple any laser into the end of a fiber cable so let's take a look so I have the optical bench set up here if we're going to couple laser light into the end of a fiber we need some kind of mechanical stability and this Optical bench is perfect for that if you don't have one a slab of aluminum will do as long as things are bolted down and not held down with Huts nut and gravity you'll do just fine and we need two degrees of freedom in order to steer the beam into the end of the fiber and so I've got two adjustable mirror mounts with what looked like one a one a quarter inch mirrors mounted on them um I've got my 488 nanometer lasered out at the back there that one's a couple in and so we're about ready um the first thing that we need to consider before doing this is laser Powers so this laser is about 30 milliwatts and it's so high that I can feel the heat on the tip of my finger and so we need to turn this down because at some point we're going to have two laser beams pointing at each other and if 30 milliwatts of 488 nanometer light manages to reach the facet of the lasered out and the fault locator it will damage the lizard out and then that'll be that so I have the power turned down on the laser now to just above threshold we can see a spot on a piece of card there and that'll be just perfect for alignment purposes we may be looking at about I don't know maybe a half a milliwatt a milliwatt or so perfect um so we will put a collimator on one end of the fiber and put that in our mount once again all secret mounts good and if we take a look there'll be no light next in the fiber at this point because we're well off alignment if we take our fault locator and plug it into the other end and turn it on what we will have is the spot from the fault locator it's been projected out of the collimator and onto the card there the thing about the spot from the fault locator is is guaranteed to be on axis right so all that we need to do is line up the two laser beams until they're perfectly aligned end to end in this Optical path so I'll first of all line them up over here and then we'll come back to this side and line it up so what we're doing here is we're making sure that the beams are on access at each end of the optical setup and if they're on axis at each end of the optical setup then that means that there will be on axis when they're coupled into the fiber so we'll just go from end to end to end until we're happy that those things are perfectly on top of each other and that is more or less it at this point we should be able to uncouple The Fault locator and we will have light X in the end of the fiber so we're almost there the very last job is to really walk in the beam until we're happy with the amount of power that we're coupling in ideally we would do this with a laser power meter I don't have one handed just at the moment um but my eye will be good enough perfect so I'm reasonably happy with that I think there's a fair bit of tweaking to be done there oh that's pretty good I'll just keep going just a bit yeah I think I'd be happy enough with that there's a fair amount of light being coupled through and I'll put a collimator on this end and we'll be able to see our collimated beam excellent at this point we'll turn up the power Fantastic look at that beautifully collimated beam out at the end of the fiber excellent everybody loves laser beams in smoke so let's do an obligatory smoke shot absolutely fantastic beautiful excellent when we want to couple light into a single mold cable like this 35 meter length of telecoms cable we need to make sure that the laser we're using has exceptional beam quality this particular telecoms cable is core diameter is only 9 microns and so we need to focus our laser light into a nine Micron spot on the end of the cable and this is not very trivial even with this setup it's the same setup as before we've still got the two mirrors to steer the beam into the end of the coupler it just takes a little bit more time to finesse the beam and get the maximum output power from it that being said let's turn this on it's only roughly coupled but we'll take a look so we can see our beam being injected into the end of the fiber we can see already here there's a considerable amount of light leaking out of the first 12 inches of fiber or so and this is because some of that light is being coupled down the actual cladding layer in the fiber so we're losing quite a bit of light that way that said we've got a very nice collimated beam coming out of the end of the fiber and for some of the things I have lined up this should be just fine excellent I've got a nice nice you know tightly collimated spot on the subject of light leaking out of fibers if we take this fiber and bend it past its Bend radius green light will start to leak out of the edges of the fiber and it'll it'll bounce out through the core and out of the cladding and we can see it Illuminating the edge of the fiber there I mean we shouldn't really abuse fibers in this way but we can actually use this for sensing and you can actually you know mount a detector at the at the end of the fiber there and detect well how much light is passing through it and if we bend the fiber it will make the spot dimmer and so we can sort of infer how much the fiber has been bent or stretched and there are other things we can do as well mentioned earlier on that you can measure voltages with the fiber optic cable we can measure magnetic fields and all sorts of cool stuff um so yeah we'll have a look at some of these things in future videos thanks for watching this episode of Leslie's lab if you want to see more content like this don't forget to hit like And subscribe down below and I'll see you guys next time

Channel: Les' Lab

Views: 13,598

Keywords: fiber optic, fibre optic, fiber collimator, fibre collimator, multimode, multi-mode, singlemode, single-mode, fiber fault locator, fibre fault locator, laser mirror, blue laser, green laser, 488nm, fiber bend radius, fibre bend radius, fiber bend-radius, fibre bend-radius, laser coupling, fiber optics, fibre optics, telecoms, telecommunications, SMA904, ST connector, FC connector

Id: oA-nNeQ1zyA

Length: 14min 3sec (843 seconds)

Published: Sat Dec 03 2022

Reddit Comments

[u/Petersilius]

Pretty cool.

[u/JerryGarcia47]

Awesome video I'm tripping baaalllzzz mane