dispersion compensation

[aasif bashir dar]

hello all,
gennerally we use inline dispersion compensation , which can have three maping methods?
i want know which the three maping dispersion compensation technique is better and why?

and is that always soo or may vary with condition, if so what are those conditions?

[aasif bashir dar]

hi all
sorry i missed oout mentening the three maping schems for dispersion compensation.

pre-compensation(before fiber in simple terms)
post- compensation(after fiber……)
and hybrid or symmetrical compensation.

gennerally we say symmetrical is better , is it always like that.

with regards

[alistu]

Hi Aasif,

The performance of three three aformentioned compensation methods may depend on a lot of factors such as signal modulation format, system configuration, modulation scheme and so on. I read in a paper that for a system with 10 Gbps bit rate and NRZ signal format, symmetric compensation was reported to be better.

Regards

[aasif bashir dar]

hi alistu,
thanks for reply
i also read such a paper in which NRZ signal was used at 10 gbps data rate(by R S kaler).

you mentioned that it depends on the no. of factors such as signal modulation format, system configuration, modulation scheme .
therefore you think that symmetrical may not be always best?

with regards

[alistu]

Hi aasif,

You’re welcome. I believe being the best is different from giving the best performance for practical purposes. There may be times when use of the other two aforementioned compensation methods may be more beneficial to the system as they may reduce complexity. or in some cases may be the difference in performance may not be that remarkable.

Regards

[aasif bashir dar]

hi alistu,
thanks for for your valuable reply

thus for a network i have to select the maping technique which best fit in terms of the quality factor and BER,power budget ,cost,,etc.

i got you point

with regards

[alistu]

You’re welcome Aasif. That is exactly the point, and this should always be considered in all system designs. Otherwise there should have been a paper introducing the best scheme in a general sense, and not only for a specific system (which in the case of the aforementioned paper is NRZ for 10 Gbps).

Regards

[FAYIQA NAQSHBANDI]

Hi

I agree with alistu..Although symmetric technique is known to show the best compensation but that may not be the case always.
The worst effect of dispersion is seen in the fiber.Logicaly post compensation should be enough to remove the effect of dispersion.
But anyway it again depends on the system you are working on.

Thanks

Regards

[Karan Ahuja]

Hi

Dispersion limits the information capacity at high transmission speeds. Dispersion reduces the effective bandwidth and at same time it increases the BER due to an increasing inter symbol interference. In order to remove the spreading of optical pulses, dispersion compensation is required. In single-mode fiber, performance is primarily limited by chromatic dispersion (also called group velocity dispersion) which occurs because the index of the glass varies slightly depending on the wavelength of the light, and light from real optical transmitters necessarily has nonzero spectral width. Polarization mode dispersion is another source of limitation which occurs because, although the single-mode fiber can sustain only one transverse mode, it can carry this mode with two different polarizations, and slight imperfections or distortions in a fiber can alter the propagation velocities for the two polarizations. This phenomenon is called birefringence.

Here are few links you may refer to:
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5719

https://www.google.co.in/urlsa=t&rct=j&q=&esrc=s&source=web&cd=9&cad=rja&uact=8&ved=0ahUKEwiM9mWvs7NAhXEW5QKHdh4CW8QFghJMAg&url=http%3A%2F%2Fwww.itu.int%2Fitudoc%2Fitu-t%2Fworkshop%2Foptical%2Fs4am-p02_pp7.ppt&usg=AFQjCNFtHtuka6ZRWWVZPFHq5UfudWfO7A&bvm=bv.125801520,d.dGo

http://www.m2optics.com/fiber-test-boxes/dispersion-compensating
http://www.ijarcce.com/upload/2015/february-15/IJARCCE6E.pdf

thanks

[aasif bashir dar]

hi all
in that paper of which alistu was reffering to the capability of these schemes have following order.
symmetrical(top)
post(seconD)
pre-compensation(last)

but it is done for only one modulation scheme and at one data rate

with regrds

[alistu]

Hi Aasif,

I believe the reason for such issues being discussed in such ways (I mean, for a specific system architecture and even sometimes with some specific system configurations) like the discussed paper is the fact that it is not feasible to reliably analyze these issues theoretically, and therefore simulation should be used on a case-by-case basis.

Regards

[aasif bashir dar]

hi all,
thanks all for there valuable reply and i appreciate efforts of for the discussion.
with regards

[Karan Ahuja]

Hi

Amongst the various techniques proposed in the literature, the ones that appear to hold immediate promise for dispersion compensation and management could be broadly classified as: dispersion compensating fibers (DCF), chirped fiber bragg gratings (FBG) and high-order mode (HOM) fiber. The idea of using dispersion compensation fiber for dispersion compensation was proposed in 1980 but, until after the invention of optical amplifiers, DCF began to be widespread attention and study. As the products of DCF are more mature, stable, not easily affected by temperature, wide bandwidth, DCF has become a most suitable method of dispersion compensation. There is positive second-order and third-order dispersion value in SMF, while the DCF dispersion value is negative. So by inserting a DCF, the average dispersion is close to zero.
The use of dispersion compensating fibers is an efficient way to upgrade installed links of standard single mode fiber (SMF). Conventional dispersion compensating fibers have a high negative dispersion -70 to -90 ps/nm.km and can be used to compensate the positive dispersion of
transmission fiber in C-band. According to the relative position of DCF and single mode fiber, post-compensation, pre-compensation and
symmetrical/mix compensation, is proposed. DCF precompensation scheme achieve dispersion compensation by placing the DCF before a conventional single mode fiber or after the optical transmitter. Post-compensation scheme achieve dispersion compensation by placing the DCF after the single mode fiber. Symmetrical/mix compensation scheme is consist .

[Rajguru M. Mohan]

Hi AAsif,
Although we have three dispersion compensation techniques namely pre, post and symmetrical.
I like to add basic elements and parameters of dispersion compensation :
Fiber Bragg gratings (FBG) are one of the important methods of
dispersion compensation. They reflect different frequencies from
different length, at the end, different frequency components of the
signal will see different phase delays. They have short length (~10-
15cm). They are not very suitable for WDM applications because
of their narrow bandwidth (~0.1-5nm). They have very low loss
like 1dB in 80km. Their short length provides less nonlinear
operation.
Dispersion-compensating fibers (DCF) are another important
method of dispersion compensation. They operate by insertion of
fibers with dispersion of negative slope, high absolute value. Their
lengths can be 17-20km. Lengths are too high that nonlinear
effects cause a problem. They have wide bandwidth suitable for
WDM applications (~20nm).

Thanks,

[Rajguru M. Mohan]

Hi,
Here i am adding a link of a research work by R.S. Kaler, Ajay K.Sharma, T.S. Kamal namely: Comparison of pre-, post- and
symmetrical-dispersion compensation schemes for 10 Gb/s NRZ links using standard and dispersion compensated fibers.
In this paper they compared all three techniques of dispersion compensation.
The results of three compensation methods have been compared and it is found that the symmetrical compensation method is superior to
pre- and post-compensation methods.On comparing pre- and post-compensation methods, it is found that the later is superior to the former.
I also agree to his points of The symmetrical compensation has the best performance followed by post- and pre-compensation”.
Also, the influence of transmission
distance on the three compensation methods has
been discussed by simultaneously increasing the
lengths of fibers and keeping the EDFA power
constant.As the lengths of the fibers are increased,
the bit error rate increases.The bit error rate for
symmetrical compensation method is again minimum
but for pre- and post-compensation methods,
the situation is not so good.

Thanks,

[Aabid Baba]

Hello Everyone,
Talking about dispersion compensation techniques i have come across many papers which suggest that using Fiber Bragg gratings for compensating dispersion is most effective method and is being widely used at the moment.
Regards

[Alok Kumar]

HI ASIF

what method are you using?
Pre or post? Can you give me your email id.
Thank u

[Karan Ahuja]

Hello

I am providing link of one paper that may help.
https://www.osapublishing.org/jlt/abstract.cfm?uri=jlt-23-11-3566
This paper reviews properties and use of conventional single-mode dispersion-compensating fibers (DCFs). The quality of the dispersion compensation expressed as residual dispersion after compensation is treated. Properties of actual DCFs for discrete compensation including loss and nonlinear effects are discussed. Fiber design with special emphasis on design tradeoffs is considered. The Raman properties of DCFs and their use as a discrete Raman amplifier are also discussed. Finally, DCF for use in dispersion-managed cables (DMCs) is addressed, including optimum fiber design and comparison of different configurations.

Thanks

[Karan Ahuja]

I want to add that When optical signals are transmitted over the optical links, different wavelength components of the signals will generally experience different propagation time due to the fact that the transport medium has different effective refractive indices for different wavelengths. In the recent years, with the rapid growth internet business needs, people urgently need more capacity and network systems. So the demand for the transmission capacity and bandwidth are becoming more and more challenging to the carriers and service suppliers. Under this situation, optical fiber is becoming the most favourable delivering media and laying more and more important role in information industry, with its huge bandwidth and excellent transmission performance. Therefore, it is necessary to investigate the transmission characteristics of optical fiber. The main goal of any communication system is to increase the transmission distance. Loss and dispersion are the major factors that affect the fiber optic communication system. The EDFA (Erbium doped fiber amplifier) is the gigantic change that happened in the optical fiber communication systems; the loss is no longer major factor to restrict the fiber optic transmission. Since EDFA works in 1550 nm wave band, the average Single Mode Fiber (SMF) dispersion value in this wave band is very big, about 15-20ps / (nm.km-1). So, it is easy to see that the dispersion become the major factor that restricts the long distance fiber optic system.

I hope it helpd

Thanks

[Aabid Baba]

Hello all,
Thank you for sharing such valuable information regarding different dispersion compensation r techniques that are being used for optical networks. As I had mentioned earlier most of the techniques use fiber Bragg grating for compensating dispersion effects and these finer Bragg gratings are being widely used. So I think Karan ha s shared some good points regarding these finer Bragg gratings. I hope these prove to be helpful. Thanking you.

Regards

[Author]

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