en>Gadget850: /* Application */update gallery center, replaced: → , removed: perrow="5" using AWB

2014-12-27T22:48:26Z

Application: update gallery center, replaced: <center><gallery → <gallery class="center" , </gallery></center> → </gallery>, removed: perrow="5" using AWB

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	~~[[File:Modulateur d'intensité optique 3.jpg\|thumb\|An optical intensity modulator for optical telecommunications]]~~		Here are 10 exclusive methods to quit that you ought to attempt. They have success rates that are somewhat high and there is a probability that is very good that one or more of them will be the answer you have been trying to find.<br><br><br><br>Smokers enjoy their cigarettes. You understand what I am discussing if you smoke then. For a lot of smokers it is a love-hate relationship. You understand it is not good for you but you take pleasure in the feeling and also the precise routine of smoking. This is exactly why nicotine-delivery choices like the area along with gum don't cut it. They don't really simulate the specific smoking experience. That is where the [http://thewondersofsmoke.webs.com/ smokey bones] comes in. It claims to reproduce an actual smoking encounter but with no same health problems and other disadvantages of smoking tobacco. And guess what happens? It does a job that is pretty good. the parallels are fantastic enough to satisfy many smokers although it may not be a similar.<br><br>As a result of the cost, I chose to view if there was a way to try out the merchandise for a lower value. I discovered one e-cigarette which got rave reviews and only charge about $30.00 to begin with also it involved 5 cartridges (regarding the similar cost of 5 packages of cigarettes) and so I figured the cost would be a "wash" if I truly applied all 5 tubes. Naturally, I placed my order and got the plunge.<br><br>And so I never learned what she finished up performing, I lost touch along with her, but I have regarded those who have used cigarettes to prevent smoking. Many began by getting an e-cigarette reviews some Ejuice and starter kit. As time passes, they lowered the total amount of nicotine they were using. they extended to use the electric cigarettes, although some wound up employing no-nicotine, at all. They found the routine soothing.<br><br>Green Smoke will be a lot such as the additional e-cigarette in regards right down to tastes, opinions corporations outthere. They feature the traditional tobacco and menthol styles along with a couple of others (candy, vanilla, coffee). However the one thing that I truly appreciated about Inexperienced Smokes styles is the fact that chocolate is offered by them. I've not seen every other organization offer this flavor although most most of the others provide vanilla and coffee.
	~~'''Electro-optic modulator''' ('''EOM''') is an optical device in which a signal-controlled element exhibiting the [[electro-optic effect]] is used~~ to modulate a [[Light beam\|beam of light]]. The [[modulation]] may be imposed on the [[phase (waves)\|phase]], [[frequency]], [[amplitude]], or [[Polarization (waves)\|polarization]] of the beam. Modulation bandwidths extending into the [[gigahertz]] range are possible with the use of [[laser]]-controlled modulators.

	~~The [[electro-optic effect]] is the change in the refractive index of a material resulting from the application of a DC or low-frequency electric field. This is caused by forces~~ that ~~distort the position, orientation, or shape of the molecules constituting the material~~. ~~Generally, a [[nonlinear optics\|nonlinear optical]] material ([[organic polymer]]s~~ have ~~the fastest response~~ rates, and ~~thus are best for this application) with an incident static or low frequency [[optical field]] will see a modulation of its [[refractive index]].~~

	~~The simplest kind of EOM consists of a crystal, such as [[Lithium niobate]], whose refractive index~~ is a ~~function of the strength of the local [[electric field]]. That means~~ that ~~if lithium niobate~~ is ~~exposed to an electric field, light will travel~~ more ~~slowly through it. But the phase~~ of ~~the light leaving the crystal is directly proportional to the length of time it takes that light to pass through it. Therefore, the phase of the laser light exiting an EOM can~~ be ~~controlled by changing~~ the ~~electric field in the crystal.~~

	Note that the electric field can be created by placing a parallel plate [[capacitor]] across the crystal. Since the field inside a parallel plate capacitor depends [[linearly]] on the potential, the index of refraction depends linearly on the field (for crystals where [[Pockels effect]] dominates), and the phase depends linearly on the index of refraction, the phase modulation must depend linearly on the potential applied to ~~the EOM~~.

	~~The voltage required for inducing a phase change of~~ <~~math~~>~~\pi~~<~~/math~~> ~~is called the half-wave voltage (~~<~~math~~>~~V_{\pi}~~<~~/math~~>). For a ~~Pockels cell,~~ it is ~~usually hundreds or even thousands of volts, so that~~ a ~~high~~-~~voltage amplifier~~ is ~~required. Suitable electronic circuits can switch such large voltages within a few nanoseconds, allowing~~ the ~~use~~ of ~~EOMs as fast optical switches~~.

	~~[[LCD\|Liquid crystal devices]] are electro~~-~~optical phase modulators if no polarizers are used~~.

	~~==Phase Modulation==~~

	~~A very common application of EOMs~~ is ~~for creating [[sideband]]s in a [[monochromatic]] laser beam. To see how this works, first imagine that~~ the ~~strength of a laser beam with~~ [~~[frequency]] <math>\omega<~~/~~math> entering the EOM is given by~~

	~~:<math>Ae^{i\omega t}~~.</~~math>~~

	~~Now suppose we apply a sinusoidally varying potential voltage~~ to ~~the EOM~~ with ~~frequency <math>\Omega</math>~~ and ~~small amplitude <math>\beta</math>~~. ~~This adds~~ a ~~time dependent phase~~ to ~~the above expression,~~

	~~:<math>Ae^{i\omega t + i\beta\sin(\Omega t)}~~.<~~/math>~~

	~~Since <math~~>~~\beta~~<~~/math~~> ~~is small, we can use~~ the ~~[[Taylor expansion]] for the exponential~~

	~~:<math>Ae^{i\omega t}\left( 1+i\beta\sin(\Omega t)\right)~~ ,~~</math>~~

	to ~~which we apply~~ a ~~simple identity~~ for ~~[[sine]],~~

	~~:<math>Ae^{i\omega t}\left( 1+\frac{\beta}{2}(e^{i\Omega t} -~~ e^{-~~i\Omega t})\right) = A\left( e^{i\omega t}+\frac{\beta}{2}e^{i(\omega+\Omega) t}-\frac{\beta}{2}e^{i(\omega-\Omega) t}\right) .</math>~~

	~~This expression we interpret to mean that we have the original [[Carrier wave\|carrier frequency]] plus two small sidebands, one at <math>\omega+\Omega</math>~~ and ~~another at <math>\omega-\Omega</math>. Notice however that we~~ only ~~used the first term in the Taylor expansion - in truth there are an infinite number of sidebands~~. ~~There is a useful identity involving [[Bessel functions]] called the [[Jacobi-Anger expansion]] which can be used~~ to ~~derive~~

	~~:<math>Ae^{i\omega t + i\beta\sin~~(~~\Omega t~~)~~} = Ae^{i\omega t}\left( J_0(\beta) + \sum_{k=1}^{\infty}J_k(\beta)e^{ik\Omega t} + \sum_{k=1}^{\infty}(-1)^k J_k(\beta)e^{-ik\Omega t}\right) , </math>~~

	~~which gives~~ the ~~amplitudes of~~ all ~~the sidebands~~. ~~Notice that if one modulates the amplitude instead of the phase~~, ~~one gets only~~ the ~~first set of sidebands,~~

	:<~~math~~>~~\left( 1 + \beta\sin(\Omega t)\right) Ae^{i\omega t} = Ae^{i\omega t} + \frac{A\beta}{2i}\left( e^{i(\omega+\Omega) t} - e^{i(\omega-\Omega)t} \right) .~~ <~~/math~~>

	~~==Amplitude modulation==~~

	~~A phase modulating EOM can also be~~ used as an ~~amplitude modulator by using a [[Mach~~-~~Zehnder interferometer]]~~. ~~A beam splitter divides~~ the ~~laser light into two paths, one~~ of ~~which has a phase modulator as described above~~. ~~The beams are then recombined. Changing~~ the electric ~~field on the phase modulating path will then determine whether the two beams interfere constructively or destructively at the output~~, ~~and thereby control the amplitude or intensity of the exiting light. This device is called a [[Mach~~-~~Zehnder modulator]]~~.


	~~==Polarization modulation==~~

	~~Depending on the type and orientation of the nonlinear crystal, and on the direction of~~ the ~~applied electric field, the phase delay can depend on the polarization direction~~. ~~A Pockels cell can thus~~ be ~~seen~~ as ~~a voltage~~-~~controlled waveplate~~, ~~and it can be used for modulating the polarization state~~. ~~For a linear input polarization (often oriented at 45° to~~ the ~~crystal axes), the output polarization will in general be elliptical, rather than simply a linear polarization state~~ with a ~~rotated direction.~~

	~~==See also==~~
	*[[Pockels effect]]
	*[[Acousto-optic modulator]]
	*[[Phase modulation]]
	*[[Dielectric wireless receiver]]

	~~==References==~~
	*{{cite book \| author=Karna, Shashi and Yeates, Alan (~~ed.) \| year=1996 \| title= Nonlinear Optical Materials: Theory and Modeling\| pages=2–3 \| location=Washington~~, ~~DC \| publisher=American Chemical Society \| isbn=0-8412-3401-9}}~~
	*{{cite book \| author=Saleh, ~~Teich (first ed.~~) ~~\| year=1991 \| title=Fundamentals of Photonics \| pages=697 \| location=New York \| publisher=Wiley-Interscience Publications \| isbn=0-471-83965-5}}~~
	*{{FS1037C MS188}}

	~~==External links==~~
	* [http://www.~~advr-inc~~.~~com/modulators.html AdvR - Research~~ and ~~custom EO phase and amplitude modulators]~~
	* [http://www.rp-photonics.com/electro_optic_modulators.~~html Encyclopedia of Laser Physics and Technology]~~

	~~[[Category:Optical devices]]~~
	~~[[Category:Nonlinear optics]]~~

en>Mogism: /* Lengthening antennas */Cleanup/Typo fixing, typo(s) fixed: a integer → an integer using AWB

2013-12-21T20:45:57Z

Lengthening antennas: Cleanup/Typo fixing, typo(s) fixed: a integer → an integer using AWB

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en>Srleffler: Category:Telecommunication theory

2012-07-23T01:13:10Z

Category:Telecommunication theory

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Electrical length - Revision history

en>Gadget850: /* Application */update gallery center, replaced: → , removed: perrow="5" using AWB

en>Mogism: /* Lengthening antennas */Cleanup/Typo fixing, typo(s) fixed: a integer → an integer using AWB

en>Srleffler: Category:Telecommunication theory