What is Chromatic Dispersion in Optical Fibers

In this video, I will explain what is Chromatic Dispersion.
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In an optical fiber, different colors of light travels at different speed. The blue light may run faster, and the red light may run slower. As represented by the blue color car and red color car in this picture. Even though they start at the same time in the beginning, they arrive at the destination at different times. This time delay is called chromatic dispersion. Here, "chromatic" stresses the fact that the time delay depends on the color difference, or wavelength difference between the lights.
So what effect does chromatic dispersion have on fiber optic communication systems?
The direct effect is light pulse broadening. A perfect pulse starts at the beginning. After it travels a length of fiber, may it be 100 meters, or 20000 meters, the light pulse becomes wider than the original signal. This is caused by chromatic dispersion. Because in the same pulse, the blue light travels faster, and the red light travels slower, so the total width of the pulse gets stretched wider.
Now let's look at the bottom part of the picture. Two perfect signals start at the beginning, but at the end, since both pulses get wider because of chromatic dispersion, they get overlapped to each other. If the overlap is too big, the detector may not be able to recognize these two signals and you get an error.
So chromatic dispersion causes pulse broadening and bit error.
Chromatic dispersion is actually the sum of two different dispersion types.
The first type is called material dispersion. This is because that the refractive index of silica, the material used to make optical fiber, is frequency dependent. So different frequency components, which means different wavelengths of light, travel at different speeds in silica. This is called material dispersion.
Material Dispersion depends on the material's built-in refractive index and we cannot change that.
The second type is called waveguide dispersion.
To understand waveguide dispersion, we need to know that light pulse travels partly in the core and partly in the cladding of the fiber. Light travels slower at the core, and faster at the cladding. The overall speed depends on the proportion of power that is distributed in the core and cladding.
However, the power distribution itself is a function of the wavelength. The longer the wavelength, the more power in the cladding. So different colors of light travels at different speed because of different power distribution in the core and cladding.
This phenomenon is called waveguide dispersion.
Since we can change the fiber's refractive index profile, we can engineer the waveguide dispersion to make specialty fibers.
The total chromatic dispersion is the sum of material dispersion and waveguide dispersion.
In this figure, we can see the dispersion versus wavelength curves of the material dispersion, shown as the red line, the waveguide dispersion, shown as the blue line, and the total chromatic dispersion, sown as the pink line.
Even though we cannot change material dispersion since it only depends on the optical fiber material itself, we can change the fiber's refractive index profile design to make the waveguide dispersion compensate for the material dispersion so we can get zero chromatic dispersion at a specific wavelength. As shown in this figure, the zero chromatic dispersion point is at 1300nm. This is the chromatic dispersion profile of a standard single mode fiber.
So there you have it. Please leave your comment below if you'd like to see other topics.
Don't forget to visit
www.fiberoptics4sale.com
for more free fiber optic tutorials. I will see you in the next video!
Colin Yao
Sales Manager
Fiber Optics For Sale Co.

[@abdallah13th]

By the way Colin, at 2:50 you said that the pulse travel slower in the core which is true. However, on the slide you wrote the opposite. I think the slide needs to be corrected.

[@user-kj1xl7jq1x]

Because the speed is in inverse proportion to the refractive index, and the rf of the core is higher than that of the cladding, so the statement of the slide is wrong.

[@MasterPeaC1]

In presentation stands this sentence: "Light travels slower at the core, and faster at the cladding", but you sad at 2:52 "Light travels faster at the core, and slower at the cladding". Despite this small lapse this is good explanation of CD.

[@brennanaidan]

I'm currently studying for the Certified Fiber to the Home Professional (CFHP) exam, these videos are excellent. Keep up the good work.

[@chintanchavda5218]

i would like to thank for both and the vedio,as well as the fore comment makers for crystalizing the facts & information about Fiber optics........
thanks again..........

[@Dawoudkhalifa]

such great and creative way of explanations, I really understand it now. Thanks :D

[@abdallah13th]

Well explained Colin !

[@dtibbs23]

Thanks for the explanation, awesome video

[@SunilRajaretnam]

Awesome video..!!Helped me a lot in understanding the concept.

[@tfHimanshu]

good for last Min revision thanks Colin :)

[@javidshakira4554]

Kumaran Anna well explained. It is very useful for us

[@chloembe5403]

thanks mister yao, c'était très instructif, merci à vous

[@igorpaz2710]

Thank you for this class.

[@aaa039811]

thank you so much! clear explanation!

[@yichizhang795]

You're way better than my Spanish lecturer..

[@momchilmilev5472]

Good video, good explanation, the only suggestion: change the colors of the cars! The red color has longer wavelength hence travels faster ;)... the example where the blue car travels faster is a bit counter-intuitive in the context of wavelengths :) (not joking!)

[@annyni6640]

taking a laser and photonics class. I am so lost but this helped a lot

[@aRtaBxaR]

Would you have tutorial on TDC sweep which enables transponders and muxponders compensate chromatic dispersion ?

[@chuanbowensun7982]

I like your videos very much!! Could you explain some OFDM related topics if you got some time?

[@user-rp1ng2on5u]

It's the excellent Video. I just want to point out one minor mistake in video. In the slide said the light travels faster in core, slower in cladding but you presented the opposite. Thanks

[@humanimal1]

I would like to see something about any differences required in fusion splicers to splice Rare-Earth doped fibers as opposed to silica based fibers. What handling differences, prep, etc. Also explain the nuances of end caps. Are the larger diameter fibers more difficult or the smaller? Likewise the same questions with Photonic Crystal fibers.

[@ambirf]

Well explained!

[@ABHISHEKKUMAR-vl4ey]

nice video for brief understanding

[@gototots]

I have read that strain shifts the Bragg wavelenght throug compressing the grating and changing the effective index. Is this the way FBG is used to measure pressure?

[@derekhardison]

That was very good. What about intermodal dispersion and how it compare to chromatic dispersion?
Thanks again!

[@nelsonlungu2617]

Excellent explanation

[@princesharma1751]

Thanx for nice video but what is the application/ use of zero cromatic dispersion pls explain

[@tanoojamishra511]

very good explaination SIR

[@omkkad6302]

Thank you, you are the best :))))

[@phanicharan7580]

good explanation.

[@khonaa1]

Thanks for the video and explanation
There a mistake on 2:52 when you say: light travel slower in the core and faster in the cladding it should be the opposite
Light travel faster at the core and slower at the cladding
Thanks

[@rafaqatali19800]

Well explained ...

[@mohamedyousuf8515]

what is difference between frequency in rf and frequency in optical fibre..can u explain the term spectral width in opticalfibre

[@mnoneleligovuzela]

excellent ,on point .

[@monarahatkhah9479]

so usefull.thanks.

[@ChrisSmith176-v6p]

very good video

[@TheEtbetween]

Thank Excellent job

[@tazmaniac1991]

Hello, would you have any videos on anomalous dispersion by any chance?
Thanks

[@atsul.7943]

I thought the core should rather have light traveling slower in it than the cladding since its refractive index is higher than the cladding.

[@mohankrish6515]

Actually sir pravin is in love with vellapi😍

[@soorajsundaran3710]

thanks for saving me in my exams

[@prachifrombasti]

good knowledge

[@rmkjain]

I hope the video is corrected now.
By the way Colin, at 2:50 you said that the pulse travels slower in the core which is true. However, on the slide, you wrote the opposite. I think the slide needs to be corrected.

[@arepallisathibabu3464]

it helps me a lot
tanq

[@mayayoel]

Thank You ! :)

[@engineeringfuture1]

thank you

[@kichigan1]

I'm I correct in thinking that the difference between Chromatic Dispersion (CD) and Polarization Mode Dispersion (PMD) is that in DC there are different laser colors?

[@FerchoSalazar]

Since the core is made of a higher index of refraction glass than the cladding, the light in the cladding travels faster than the light in the core?

[@timmitimmi-fy6gh]

yes

[@muhanadsarem7379]

fantastic

[@michaelhill216]

Colin,You state that the light travels faster in the cladding and slower In the core. The diagram shows the opposite. I was always taught faster in the core?

[@nihirgulati6971]

you were taught wrong, it is always faster in the cladding

[@thewinner4424]

Can we calculate dispersion chromatic analytic??

[@yahiataibi6160]

S.V.P Monsieur si vous ouvez me donner un ficheir pdf sur la dispersion
thanks

[@mohankrish6515]

Nitish kumar pandurangan😍

[@ChamithDulshan]

Thanx

[@helalhassanalbarho8593]

Great

[@halakamal5478]

Thanks from iraq

[@palminator73]

Blue light is slower than red due to the high n value!!! Not the way that you said in the video

[@TumulKhan]

That's the normal case. In case of anomalous dispersion, blue travels faster

[@javidshakira4554]

P oll jagan 💯

[@mohammedazar9798]

kumaran anna⚠️