over comming fibre cromatic dispersion effects

[Dhananjay Patel]

Hi,

I am trying to simulate the paper of “overcoming chromatic dispersion effects in fiber wireless systems incorporating external modulators” by Graham H. Smith, Dalma Novak and Zaheer Ahmed, but my results are quite different than the one in the paper.

Please find attached my design for the same. Let me know if there is some error in the design.

I have also uploaded my design on the forum, but haven’t got any reply. Kindly check

[Damian Marek]

Hello,

I do not have access to that journal. What exactly are you having trouble matching?

[Ravil]

Hi Dhananjay,

Do you have a chance to attach the scheme from that paper or, at least, quickly describe the main goal which you are trying to implement (paper attachment would work better if it will not against the copyrights, of course)? Is this question about the usage of single side band (SSB) with external modulation (if I am not mistaken)?

[Dhananjay Patel]

I am trying to vary the chirp parameter of the MZM modulator so that the fiber link distance can be increased. Here in this scheme, I am changing the chirp of MZM (making it negative using the equation v= ((V1+V2)/(V1-V2))). The paper has stated that if the chirp is made negative then the signal can overcome chromatic dispersion and will be able to travel longer distance over the fiber without much dispersion.

I am using both the DSB as well as SSB modualtion schemes for the same.

In both the cases by making chirp parameter Negative (for eg =3), the signal is transmitted over the fiber through 80 Kms and back to back. Then photodetected. After detection, the RF power differences are measured between back to back and 80km transmission.

I am not getting the required results. Please help

[Damian Marek]

Thanks for the explanation! It actually seems like it is working to me. IF you look at your first sweep iteration at 5 GHz and you place an optical time domain visualizer before and after the fiber you can look at how the chirp changes across the intensity profile.

You’ll notice in the attached image that on the left there is the initial predistorted pulses with an almost linear negative chirp over the pulse. On the right you have the post fiber signal (I disabled nonlinearity, PMD, third order dispersion and attenuation). The pulses are very compresses and the chirp is still negative but much smaller.

There seems to still be a problem with the input signal as the chirp is not linear over the entire power of the pulses.

Regards

[Dhananjay Patel]

This is the abstract of the paper:

Overcoming chromatic-dispersion effects in fiber-wireless systems incorporating external modulators (Citations: 211)
Graham H. Smith, Dalma Novak, Zaheer Ahmed

Abstract:
We demonstrate two techniques to reduce the effects of fiber chromatic dispersion in fiber-wireless systems incorporating external modulators. We theoretically and experimentally show that the achievable link distance can be increased by varying the chirp parameter of the modulator to give large negative chirp using a dual-electrode Mach-Zehnder modulator (MZM) biased at quadrature. In addition, we show that dispersion can be almost totally overcome by implementing a simple method using the dual-electrode MZM to generate an optical carrier with single sideband (SSB) modulation. We demonstrate the transmission of a 51.8-Mb/s pseudorandom bit sequence (PRBS) at 12 GHz over 80 km of standard single-mode fiber using the SSB generator and measure a bit-error-rate (BER) power penalty due to fiber dispersion of less than 0.5 dB for a BER equal to 10-9

Journal: IEEE Transactions on Microwave Theory and Techniques – IEEE TRANS MICROWAVE THEORY , vol. 45, no. 8, pp. 1410-1415, 1997

[Alessandro Festa]

Hi Patel, how much power are you launching into the fibers?

[Dhananjay Patel]

Hi All,

I have tried all the possible scenarios as stated. But when i am transmitting my signal over different frequencies with negative chirp, at the receiver end the power level for all the frequency is remaining the same. It should vary with the change in RF frequency.

Alessandro: I am launching 0dbm.

[Dhananjay Patel]

IF you guys can download the paper stated above, then you can visualize the issue I am talking about. Kindly help?

[Alessandro Festa]

Hi Patel, unfortunately I cannot download that paper so I can’t help you on this topic.

Regards,

Alessandro

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