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Optics: Propagation in Optical Fibers

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Optics: Propagation in Optical Fibers
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Single mode fiber
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49
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CC Attribution - NonCommercial - ShareAlike 4.0 International:
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This resource contains demonstrations used to illustrate the theory and applications of lasers and optics. A detailed listing of the topics can be found below. Lasers today are being used in an ever-increasing number of applications. In fact, there is hardly a field that has not been touched by the laser. Lasers are playing key roles in the home, office, hospital, factory, outdoors, and theater, as well as in the laboratory. To learn about lasers and related optics, one usually takes a course or two, or acquires the necessary information from books and journal articles. To make this learning more vivid and more exciting, and, one hopes, more understandable, one needs to see some of the basic phenomena involved. To fill this need, Professor Ezekiel has videotaped 48 demonstrations that illustrate most of the fundamental phenomena relating to lasers and physical optics. By using split-screen inserts and a wide range of video-recording capabilities, it is possible to show real-time effects in lasers and optics with the simultaneous manipulation of the components that cause these effects. In this way, one can see effects in close up that would be difficult, if not impossible, to display in front of an audience or in the classroom. These video demonstrations are designed for: The individual student of lasers and optics who wants to observe the various phenomena covered in theoretical treatments in courses, books, and technical papers. The Instructor in lasers and optics in a company, university, college, or high school who wants to illustrate, in class, many of the fundamental phenomena in optics and lasers.
LaserVideoOpticsMonomodefaserFiberQuality (business)Ground stationMaterial
GlasfaserkabelGlasfaserLaserOrder and disorder (physics)SensorLightFernsehsatellitCommunications satelliteTiefdruckgebietLecture/Conference
Camera lensGlasfaserkabelRear-view mirrorKopfstützeLight
GlasfaserkabelFACTS (newspaper)Lecture/Conference
GlasfaserkabelKopfstützeNuclear fuelMagnetic coreLecture/Conference
DreibackenfutterGlasfaserkabelLocherLecture/Conference
GlasfaserkabelLocherScreen printing
Glasfaserkabel
GlasfaserkabelNuclear fuelFACTS (newspaper)
GlasfaserkabelNuclear fuelLecture/Conference
Nuclear fuelWavelengthHose couplingMagnetic coreLightGlasfaserkabelMode of transportTransverse modeIntensity (physics)Video
Spare partMagnetic coreRefractive indexTransverse modeGlasfaserkabel
LightGlasfaserkabelAngle of attackSharpeningIntensity (physics)Bending (metalworking)RulerRegentropfenTransverse modeTotalreflexionFACTS (newspaper)Band gap
GlasfaserkabelSizingTransverse modeMagnetic coreLecture/Conference
Transcript: English(auto-generated)
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In this demonstration, we're going to illustrate the propagation of light in a fiber, a glass fiber. As we know today, optical fibers have very low loss of the order of one or two dBs per kilometer. And of course, they're being used for communication as well
as other applications like sensors. So the setup we have is a helium-neon laser over here. Here's the output from the laser. We're going to reflect it by this mirror and this mirror, and then pass it through a lens.
This lens over here focuses the light into the fiber end. And if we can take a close-up of what's going on over here, what you would see is then a lens, this lens then focusing the light and fiber. And the fiber is very close to the lens. And then the rest of the fiber is here.
All right, so here is the rest of the fiber. Now this fiber, in fact, what you're seeing over here is essentially the plastic jacket. The fiber core is about four microns in diameter. And the cladding is 125 microns.
And the rest that you see here is the plastic jacket. That's why it looks so visible because it's so thick. The other end of the fiber then goes into this holder and the chuck here. It's in a fiber hole in a chuck. And the output of the fiber then is over here
onto this little screen. Now, if we can, maybe we can take a close look at the fiber end here, which shows that what you see over here, in fact, let me point to it.
What you see over here is the cladding. Essentially, we strip the jacket. And what you see here is just the cladding. And this is the 125 microns. While over here, over here is the fiber with the plastic, with the plastic jacket.
So when you remove the plastic jacket, then you have, essentially what you're seeing is just the 125 micron cladding. All right, so this is then the fiber. And there's the output of the fiber. Now, what we see, if we can then enhance this and bring it in, what we see is the single mode
behavior of a fiber. And it looks almost like a Gaussian kind of spot. Not quite Gaussian, but it looks like a Gaussian kind of spot. Now, what I'm doing now is just adjusting the coupling
into the fiber. And it's very touchy because, as I said, the core is only about four microns. All right, so this is what then a single mode fiber, the output from a single mode fiber looks like.
And as I misalign here, it doesn't make any difference. All you get is just a loss in intensity. The shape of the mode stays the same. So remember, the core is four microns. Cladding is 125. The wavelength of the light is 6328 angstroms. And the core to index difference
is about one part in 10 to the 3. So this way, you can show that, indeed, you get single mode propagation. Now, I would like to illustrate some interesting phenomena about fiber. So if we get the camera to look over here, I want to illustrate how touchy is
the propagation of light in a single mode fiber. Now, here is a piece of fiber. And you can see that there's no light scattered from the fiber. Now, all I have to do is bend the fiber. Bend the fiber, and you're beginning to see light
that gets transmitted out of the fiber, gets essentially kicked out the fiber because of the bend. And the reason for that, because you start going against the rules of propagation of light in a fiber.
For example, if you take the ray explanation, is that what you're doing, you are exceeding or you're changing the angle of light with respect to the fiber, which means that if you're
below the critical angle, then the light is no longer totally internally reflected and therefore gets kicked out. So here it is. It's very dramatic. As soon as you put a little bend in this fiber, you can kick out a lot of light. In fact, this is the glow right here. Now, if we can bring in the output of the fiber
into the inset over here, now you can see that as I increase the bend, you can see that the intensity drops quite a bit, which means I've kicked out almost all the light by simply putting a bend into the fiber.
So the illustration here then shows that if you leave the fiber alone without sharp bends, everything is fine. If you put in a bend, then you can kick out a lot of light, and then not much will be transmitted.
So you have to be careful. You don't put it too tight a bend. Otherwise, your fiber is brittle and you break the fiber. So you have to be careful how you do this. All right? So in this demonstration, we've seen how single-mode fiber behaves. In the next demonstration, we're going to bring another fiber with a different size core,
and we're going to see what comes out from that fiber.