How to Extend Transmission length

[koll]

Hi I had the following system as attached.(figure 10) I would like to extend the transmission length and improve signal quality. How do I do that? Thank you for your help.

My attenuation of the the optical fibre is 0db/km

[alistu]

Hi koll,

Extending transmission length or increasing bit rate might actually exacerbate system performance. You may change some parameters (such as dispersion, nonlinearity, extinction ratio, …) in your design to more ideal values so that you would get better results, but then the results are not reliable. However, what you can do in your current system is to use DCF to compensate for dispersion. The use of DCF is not uncommon.

Regards

[koll]

Hi what is DFC? I attached the file for my system. Could you show me how? Thank you for your help.

[alistu]

Since dispersion has an accumulative effect, a dispersion compensating fiber can also be used in the line to compensate for the dispersion caused by the fiber. For example if you use a 5km SMF with dispersion=10, then you’ll have a total dispersion of 10×5=50. Now if you use 1km dcf with dispersion=-50, the total dispersion is 50+(-50)=0 and therefore, the dispersion is compensated.

I have attached the modified file, please check the second fiber’s dispersion characteristics and compare it to the first one. BTW, your fiber attenuation is 0.2 dB/km and not zero as you mentioned.

[koll]

Hi I couldn’t open the modified file. 🙁 I using the latest version of optics.

Thank you for your help.

[alistu]

Do you mean you are using the latest version of “Optisystem”? If you are using version 13.0.3 (the same as I do), then you should be able to open the file. Could you check your version by chooseing “about OptiSystem” option on “help” tab in menu bar and verify if you are using the same version?

[koll]

Hi I using this version. Please find attached photo.(captured)

The error.jpg is the error I got when I opened the modified file

Thank you.

[alistu]

As it can be seen in your image “Capture1”, you are using version 13.0.1 and not the latest version which is v. 13.0.3. So you cannot open my file unless you upgrade your version. In case you are using the trial, you can uninstall your current version, download the latest version from your profile and install it.

[kelly howard]

hi, i would like to ask if assumed the attenuation of the optical fiber is 0db/km, how do i extend the transmission length and avoid signal degradation?

[alistu]

Hi, in that case you would not need to use optical amplifiers for compensating the fiber attenuation, and since the optical amplifiers have a noise figure, your system would have better performance. Still, for a system with the same schemes (same modulation, same equalization, …) used, increasing bit rate or transmission length causes degradation of the signal to an extent depending on the system.

[koll]

Hi Alistu

why did you set to 100km and 20km for the optical fibre? But if I changed to 0dm/km my result worsen.

I got a nice result when I run your modified file.

[Sasha]

Hi Koll,

In alitsu file, he gave input power source = ‘0’dbm (i.e 1 milli watts) given to the modulator input and getting output = -3dbm approximately (by default), modulated input is given to the optical fiber with length = 100km,attenuation = 0.2db/km and you will get a attenuation of 20db/km, so totally till now you have a power value of = -23dbm. To make this zero, he has given value of = 24db(i.e gain = 20db, noise figure=4db, summing up gives= 24db). At the output of the optical amplifier, you will get 24-23 = 1db. Again this output is given to the next optical fiber with length of = 20km, attenuation = 0.2db/km,attenuation value = 4db, then output power from the second fiber= 5db(1db output from amplifier+4db). Finally given attenuator with value=10db, then output = 10+5=15db.

All I have given is approximate values, simulate your file and check it.

[alistu]

Hi koll,

Because of the dispersion values I have used used for the SMF and the DCF, in order to compensate the dispersion the length of SMF should be 5 times more than that that of DCF (please see my reply #25429 on this topic). Now if you put one of the equal to zero, the dispersion is not compensated anymore and that’s why you get worse results.

Regards

[gaganpreet Kaur]

hi is it feasible to design a system with attenuation of 0 db/km ? if yes do we need to amke any changes to non-linearilty, area or dispersion values or simply put attenuation as zero in fiber properties.

[alistu]

Hi Gaganpreet,

It is possible to do so in Optisystem, as Sasha has demostrated how, but I don’t think it would be realistic and the results obtained this way would be reliable, as there is always in optical fibers due to many contributing factors, some of which more dominant (if this is what you mean by “feasible”).

Regards

[Sasha]

Hi Gaganpreet,

You can design a Single mode fiber with zero attenuation. In Optical Fiber Properties, Main tab – select attenuation data type – constant, attenuation – 0 db/km, other factors like dispersion, non linearity doesn’t affect the attenuation. But in input source, even though if you are giving power = 0dbm (i.e 1 milli watts), when modulating the input signal you will get some power value at the output. When the signal travels in the fiber, it won’t get attenuated.

I have attached a picture. You can take a look at it.

The 1st optical power meter = output from source
The 2nd optical power meter = modulated output of the input signal
The 3rd optical power meter = output from Single mode fiber.

Note that modulated output and Optical fiber output are same (attenuation = 0 db/km in optical fiber).

[Sasha]

Hi Koll,

Here I have attached a file with ‘0’ attenuation. Check it. If you want to increase the length, just change in optical fiber length.

In this file,I have disabled all noise components. You will get the output as input.

[gaganpreet Kaur]

thank you alistu i too feel zero attenuation fiber based system would be accepted as good work or design for its results. because if take theoretical analysis or experimental verification both work on fiber with attenuation. lossless fibers are practically notfeasible.

[Sasha]

Hello Alitsu,

You said to compensate dispersion, DCF is used. But you used optical amplifier in that Opti2-with-DCF file. Can you please explain?

Thanks in advance.

[alistu]

Hi Sasha,

DCF and optical amplifier do completely different tasks in my simulation. DCF is used to compensate for the fiber dispersion and optical amplifier is used to compensate for the fiber attenuation, and I think I have used both of them in my implementation to improve performance as demanded by Koll.

Regards

[koll]

Hello Alistu

Do you know how to improve on the SNR using the same system?

Thank you

[alistu]

Hi Koll,

The use of optical amplifiers would add some noise to the signal due to the amplifier noise figure, so you would have to increase the system launch power by increasing the power of CW laser to get better SNR in the same system with the same components and the same modulation schemes being used.

Regards

[koll]

Hi Alistu

If now my optical fibre length attenuation is set to 0db/km. So I won’t need to use the optical amplifier. How do I improve SNR? I mean other than increasing the power?

[alistu]

You indeed won’t need optical amplifiers in that case, but it is not realistic. For the same system with the same components, I can only think of increasing launched power to boost SNR, unless you are OK with reducing the bitrate-length product of the system for this purpose (which I don’ think is what you are looking for).

[koll]

Hi Alistu

Thank you for your replies. Another question. If now I varies my optical attenuator to different value. And my optical fibre length is set to 30km and attenuation is 0.2db/km. My eye diagram worsen when my optical attenuator increased. Is it because attenuator affect power?

[alistu]

You’re welcome. Yes, the attenuation component attenuates the optical power entering it. So when the attenuation amount increases, the signal received at the receiver gets weaker. When this weakened signal is added with the receiver noise, the overall SNR becomes less than before. So the detected signal is more corrupted.

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