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30 votes
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Why does an optical fibre employ total internal reflection instead of just reflection?

There are essentially two reasons: manufacturability and loss. Manufacturability Optical fibers can be mass produced very inexpensively (cents per meter) by putting preforms of different glass ...
user1850479's user avatar
19 votes
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How does an endoscope form the image?

Optical fibres can be accurately aligned in an array such that the order of the fibres at one end is identical to the order in the other end to form what is called a coherent bundle. If an image is ...
Farcher's user avatar
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9 votes
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How do non-mechanical solid-state optical switches work?

It looks like there are at least two ways to go about this: Bistable MEMS MEMS (Microelectromechanical systems) are very small structures, with features from $1-100\mu m$ in size, generally made with ...
Mark Omo's user avatar
  • 283
8 votes

Single mode fibre

Why do single-mode fibers have lower attenuation than multimode fibers? It's an engineering/economic reason, not physics. The extremely low absorption loss in single-mode fiber (SMF) is obtained by ...
The Photon's user avatar
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8 votes

Why does an optical fibre employ total internal reflection instead of just reflection?

Microwave waveguides above 10 GHz have an obvious problem. The resistive losses in the waveguide walls*, even if are made of the purest silver or the finest gold alloys, make them practically useless ...
hyportnex's user avatar
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7 votes

Intensity fluctuations at the output of a single mode fiber coupled to a He Ne laser

My bet is that your fiber is very short (something like one meter or so) and that the fluctuations you see on the output mode are due to cladding modes, i.e. a part of the injected light propagating ...
dolun's user avatar
  • 2,588
6 votes
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What causes the bright glow on the edge of fiber optics and translucent sheets?

The translucent sheets and optical fibers are being lit from below. Light enters one end with a relative small angle incidence. Once inside the sheet/fiber the light experiences total internal ...
M. Enns's user avatar
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6 votes
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Speed of Signals in a Wire vs Fiber Optic Cable

Let's state some basic facts. Whenever speed of light is given as $186,000~\rm mi/s$ or $300,000~\rm km/s$, that's its speed in a vacuum. In the real world we use copper cable or fibre optic (...
James Reilly's user avatar
6 votes
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Meaning of imaginary part of complex field amplitude for waveguide modes (e.g. TE, TM, HE, EH)

As usual, whenever you have a complex-valued amplitude $\tilde{\mathbf{E}}(\mathbf r)$, it's a stand-in for a physical field that's obtained as its real part, i.e. $$ \mathbf E(\mathbf r,t) = \mathrm{...
Emilio Pisanty's user avatar
5 votes

Intensity fluctuations at the output of a single mode fiber coupled to a He Ne laser

This sounds as though the aberration in the laser's output could be fluctuating owing to "mode hopping" (where several of the laser's cavity modes are active and playing a time varying role) so that, ...
Selene Routley's user avatar
5 votes

How does an endoscope form the image?

The objective lens forms an image of the object on the end of the fiber bundle. The fiber bundle is a bundle of very fine parallel fibers. Each fiber carries a pixel to the other end of the fiber ...
mmesser314's user avatar
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5 votes
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Why some laser diodes have angled window?

The angled optical window is also called a Brewster window and it has two functions: Virtually eliminating or greatly reducing the light being reflected back to the laser by utilizing Brewster's ...
Jimski's user avatar
  • 214
4 votes

Speed of Signals in a Wire vs Fiber Optic Cable

I test fibre and copper cables. The speed of a "signal" or a pulse of electricity ,or light ,through either is about 200,000 km/hr. the problem is copper carrying current creates a magnetic field. ...
James Reilly's user avatar
4 votes

What is the purpose of glass in common mirrors?

In a mirror the thin layer of metal at the back provides the reflection. If this metal is exposed to air it will 'tarnish' - ie become dull due to formation of oxides on the surface. It can also ...
sammy gerbil's user avatar
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4 votes

What is the problem if we use air as clad in fiber communication?

The problem is that if you have air as clad, then nothing may touch your fiber. This means that you have to suspend the fiber in air - at any point where you touch it, you would change the reflective ...
Floris's user avatar
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4 votes
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Understanding of a" Mode" in Optical Fibers

I have in my understanding that "Mode" is just a path of light propagation in a fiber. That's a very rough way of understanding it. A better way to describe it is that a mode is a way for the EM ...
The Photon's user avatar
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4 votes

How is metadata transmitted alongside data, through light pulses (e.g. fibre optic)?

As mentioned by Jon Custer in the comment, there are many layers with different protocols in computer network communication. The protocol is for example WWW for web browser which is acting on the ...
Martin Vesely's user avatar
4 votes
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Why is fiber optic not affected by EMI?

Free-air laser communications can be affected by EMI if that EMI matches the of the detector (i.e. is some other matching light). This is just another way of saying stray light will interfere with ...
DKNguyen's user avatar
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4 votes
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Can a fibre preserve the shape of the light being transported through it?

A conventional fiber cannot do this because the modes inside the fiber determine the distribution of energy of transported light. Thus the output distribution is entirely independent of the input ...
user1850479's user avatar
4 votes

Why does an optical fibre employ total internal reflection instead of just reflection?

First, at some wavelengths metal mirrors are used instead of total internal reflection. For example, see this microwave band component: Microwave waveguide E&H-Bend. But, for visible light, we ...
Dast's user avatar
  • 1,816
3 votes

Intensity fluctuations at the output of a single mode fiber coupled to a He Ne laser

Some other effects that might be at play: 1. Reflections from the end-faces of the fiber causing interference 2. Brillion Scattering 3. Check to see if in fact the fiber you're using has a cut-off ...
JQK's user avatar
  • 1,785
3 votes
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Calculating reflection of light when the refractive index changes continuously

Suppose we define the following $\zeta = \ln{\varepsilon}$ and $\xi = \ln{\mu}$, where $\varepsilon$ and $\mu$ are the permittivity and permeability, respectively. In a system with no sources (i.e., $...
honeste_vivere's user avatar
3 votes
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Single-moded optical fiber and frequency

No, a mode does not have a specific frequency, but a specific field distribution. For each mode there is a minimum frequency that can be propagated (cut-off frequency) but above the cut-off frequency ...
Massimo Ortolano's user avatar
3 votes
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What degenerates mode in a fiber have in common? Do they have the same eigenvalues?

Emilio Pisanty answers this most succinctly with: "Who says that modes can't share eigenvalues?" So yes, degenerate modes share the same eigenvalue. This is the fundamental definition of "...
Selene Routley's user avatar
3 votes
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The core diameter of the optical fiber is equal to the wavelength of light?

Probably nothing too unusual. The modal field will tend to be a little larger than the core. If the core cladding index difference is small, then the modal field spreads out a long way into the ...
Selene Routley's user avatar
3 votes
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Self-phase modulation induced spectral broadening

As you point out, self-phase modulation can be thought of as an added chirp, but the crucial point is that this is a local chirp that changes from the front to the back of the pulse, in essence ...
Emilio Pisanty's user avatar
3 votes

Solar Sailing with Optical Amplification

If you could get this to work, then yes, this would increase the thrust provided by the solar sail. However, the core problem with the idea is the energy source that would power this amplification; ...
Emilio Pisanty's user avatar
3 votes
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Data in Optical Fiber Communication?

optical fiber can communicate 1 bit of data at a time ? Let's consider the simplest kind of encoding in fiber optics, on-off keying (OOK). This means you send some light down the fiber to represent a ...
The Photon's user avatar
  • 27.9k
3 votes

Modes in optical fibers

"TE" means "Transverse Electrical". That means these modes have E-field perpendicular to the axis of the fiber. Because the fiber is circularly symmetric, the E field could point in any direction ...
The Photon's user avatar
  • 27.9k
3 votes
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Is it possible to have an optical version of a greenhouse? With optical fibers?

Non-absorbing waveguides, such as optical fibers, are reciprocal optical elements, which means that as easily as light can get in, it can also get out. (This is also true for greenhouses, which work ...
Gilbert's user avatar
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