Trapping a Beam of Light In a Loop Of Fiber Optic Cable

in my previous video I showed you the most reflective surface on Earth it's about 99.5 reflective but is it possible for something to be a hundred percent reflective well actually it is and it's not that hard to do this water can actually become a hundred percent reflective when viewed from the right angle for example if we look at the surface of the water from below at this angle we can see right through it but suddenly when we hit a certain angle called the critical angle it becomes a perfect mirror and it truly isn't letting any light through so it's really weird we can see into it but the light can escape from it so at this angle you can see the laser coming up here and it's exiting the water and shining on the background here some of it's being reflected but not a lot of it so watch how bright this part of the laser gets after I reach the critical angle so this isn't the critical angle but then bend a little bit more and now this beam here is just as bright as this beam which means the reflection is just as bright so it's perfect reflection this is called total internal reflection it happens when light's going from a denser material with a high refractive index to a less dense material with a lower refractive index but only past a certain shallow angle will it occur in fact this is how they make diamonds look so bright and shiny if you angle the cuts at the right way the light doesn't just exit the bottom of the clear Diamond but it gets reflected off the bottom Cuts as though they were mirrors and it makes it easy to do with diamonds because they have such a high refractive index so the angle doesn't have to be as shallow for the light to reflect off it like it's a mirror so we know that we can make total internal reflection occur with all sorts of different materials even glass so if I have this long sheet of glass and look at this laser light inside you can see that the laser gets trapped inside of the sheet of glass so what if we had hundreds of feet of a small rod of glass well then we could trap light inside the rod of glass if it's hitting at the right angle and that's exactly what I have here this is a tiny Rod of glass inside a sheath of plastic to stabilize it the glass inside has a tiny diameter about a tenth the size of a human hair so in order to get my laser light into this tube I need to focus this laser light see how big that is way bigger than a tenth the size of a human hair so I need to focus that all down into a very small diameter so I have a lens on this one that focus is the laser light down so it's spread out here but that's because it's past its focal point the focal point is right to where it exits the laser right there a very small focal point so if I plug this into my long glass tube Watch What Happens I get a laser light coming out the end of it look at that think about how many Reflections it's going through through this entire cable it's bouncing off that tiny little hair of glass all the way through this and because it's almost perfect reflection through this entire thing I get about the same brightness of light coming out of it that I'm putting into it once it's inside the lights locked in there it can't escape because inside is coming at such a shallow angle total internal reflection occurs and keeps the laser light locked inside of it as if we're a perfect mirror that's hitting on the outside now for some of you this might not be that surprising to learn and you might even recognize what I have here this is simply a fiber optic cable these are used all over the place in place of electric wires you can send light through the cable instead of electricity and then you can convert that light signal back into electricity to be used by computers so I'm going to use this to convert this light signal into an electrical signal so I turn on my laser here you can see I have it coming out the end and I'm just going to plug this into hair and I'm going to measure the voltage on here so I get .39 volts so you can see I'm turning this light signal into a voltage on 0.39 Volts off zero one of the downsides of fiber optic cables is that since the light has to bounce off the cord at a certain angle they can't bend too much so it can easily curve around inside of this cable but not if I bend it too much see the light escapes from it now because we're not past its critical Angle now so it can just exit the glass there's no longer perfect internal reflection you can see it very clear if I just show the center plastic part directly around the core so now I've Stripped Away the outer coating so now I just have the plastic sheath with the glass core right inside of it look how weird this looks it suddenly just lights up when we give it any significant band this is so cool so as long as you don't bend your Fiber Optic Cables too much then you can basically have a perfect surface to continually reflect the light through it but then that leads me to my next question what if you just shine some light in a long Loop of cable and then remove the light and connected the two ends together with the light just continually go around in a circle forever so you essentially trapped light inside of the cable so I can connect both ends of these so that I have a complete Loop now so what if we were to trap all the light inside of this Loop okay I've got light coming out of the end now I'm going to hurry and take it off and plug it in I get it well the first problem with doing this is in the instant that I disconnect the light from this end of the cable to connect the other end then the lights already exited the other end because I don't know if you've heard this already but light moves really fast so there's no way I can move fast enough to connect the other end so if we want to trap light in this Loop then we would need to somehow inject the light into the cable while it's already in a closed loop but how could we do that so basically you saw that when I bend the cable too much light can escape but if light can escape that means the light can also enter it as well so if I just open this cord up so we have access to the sheath core here then I can inject the light into the cable so that it comes out both ends so I'm going to put this bent piece right in front of the bright flashlight and I'm going to show you on my cell phone camera here how it lights up the center here so you can see the light is entering from here [Music] you can see that I can see the white light coming out both ends so let's try to store some light in the loop of cable by injecting it in the middle here now before we try this I'd like to thank the sponsor for this video foreo they have a device called the bear device that's been shown to reduce wrinkles and fine lines in the skin and also increase the Skin's firmness and elasticity but how could it do this well what you do is you apply a serum to the areas you want to treat and then you massage with the bare device now this device actually delivers painless microcurrents or mini shocks to your skin it sounds surprising that running small amounts of electricity through your skin could do anything but decades ago it was discovered that when the Skins damaged there's a measurable voltage near the wound this happens due to the interrupted ion transport of Na plus and cl minus and other ions so the wound site acts like a cathode so wound healing cells know to migrate to the areas of the skin that act like a cathode or an anode so basically by applying voltages to the skin you can send wound healing cells to those areas so wound healing techniques like this have been used for decades but foreo made a device that's much more manageable for everyday uses and combined it with their skin serums to try to reduce the signs of aging from the studies I've seen with their device and the reviews online it's pretty clear that the device does a good job so if you want to try it out yourself you can click the link in the description to get 21 off your bare device and now let's get back to our experiment so let's try to inject some light into our cable here okay we've got it connected on both ends so it's a continuous loop now let's turn on our hundred thousand Lumen flashlight and light up this band to send some light into the loop oh yeah it's really hot in my hand that has a lot of light okay release the band so it's straight now now that we are at the critical angle anymore no more light can escape from the cable so we've stored it inside the cable okay we've got this continuous loop now so let's open it up and see if we see any light shining one two three nothing or we can also charge it up again than to let the light out we could just bend this but no light so do we actually have light going around in loops around and around in a circle here even the best fiber optic cables lose about 0.1 decibels per kilometer of cable now that doesn't sound like a lot but since light travels so fast that means that in this cable after only one second we only have about 10 to the negative 2 000 as much light as we've started with so it quickly gets absorbed into the cable and decays to nothing but it did travel around the cable many thousands and hundreds of thousands of times so when we open it up we can't see any light come out of it still but that doesn't mean a loop of fiber optic cables can't be useful sometimes you need to delay the signal in a cable for a few nanoseconds to match up with the RF signals in two fibers so you can put a delay in the line that holds up the light for a split second you can also use Loops of optical fiber for ring resonators for interferometers so in our case although we did technically trap light it quickly got absorbed this is similar to what happens when you trap Light Between Two mirrors it quickly gets absorbed as well but in the case with Optical fibers it stayed alive in there much longer than the mirrors since the reflection of mirrors absorbs almost 10 percent of lye even with very good mirrors with each hit so even our most reflective mirror would have almost completely absorbed the light with only about a thousand bumps which is only a few inches If This Were a small cable so what are your ideas to store light as long as possible in a confined space and thanks for watching another episode of the action lab I hope you enjoyed it if you did don't forget to subscribe to my channel if you haven't yet and we'll see you next time foreign

Channel: The Action Lab

Views: 479,162

Keywords: fiber optic, optical trapping, fiber optics, optical fiber, total internal reflection, refraction of light

Id: -lYAYtDx27I

Length: 10min 31sec (631 seconds)

Published: Fri Aug 25 2023