OPTICAL FILTERS

[sindhu kadirvel]

Hi all,

I need to know the difference between optical band pass filter
,guassian optical filter
and rectangular optical filter.Under which conditions each will be useful.Pls help

[Ravil]

Hi sindhu,

If I am not mistaken, we have discussed similar question about Gaussian and band-pass filters in one of the previous forums. The main difference between these to filters is their filtering shape (which follows from their names). This shape (Gaussian and rectangular) is defined by the impulse response of each of these filters. The main condition of their application is matching their impulse response shape with the shape of received pulse.

[Ravil]

This “shape-matching” condition for filters calls optimal filtering, and it is widely used for communication channels for minimization of BER by improving signal-to-noise ratio.

[sindhu kadirvel]

Yes ravil,can we use guassian optical filter for nrz or rz input pulses?

[Ravil]

Hi Sindhu!

Just want to confirm one thing first: what types/shapes of NRZ/RZ and pulses are you considering in your question for choosing filter? In general, it is known that pulses generated by optical source (e.g. laser) have Gaussian shape. It is also known, that after distortion and attenuation during propagation through the medium, the shape of this pulses remains Gaussian. Therefore, we have Gaussian pulses at the receiver in this case.

[gaganpreet Kaur]

Thank u Ravil ur post was gr8 help to me it cleared a very big problem i was facing for low Q factor around 3 only whereas min required is 6 in my WDM system may b because i was not using right filter. i will try and get back to u for further help.
Regards

[Ravil]

You are welcome, gaganpreet. As a forum member, I am always very glad to give you my advice and/or explanations. I am also happy that it helped with the particular problem in your research! Best of luck with your future work and research and with OptiSystem experience, of course!

[Chhayou Te]

Hi Ravil,

In a system design bitrate 2.5 Gbps for Gaussian optical bandpass filter do we need to change any default parameters or we just only change the Bandwidth and how those parameters affect the system?

Regards

[Ravil]

Hence, according to the explanation of my point of view given above, you can and should use Gaussian filter for these pulses. In this scenario, your filter will be matched and you will have less noise. The duration format of your pulses (RZ or NRZ) won’t make a difference on your pulses shape. On the other hand, if your pulses have other shape (e.g. pre-shaped) the corresponding matched filter should be used for them…

[Ashu verma]

hello, sindhu kadirvel
Ravil gave you very good points and explanation regarding the filters you have mentioned in your post. We have discussed similar topic in your previous post also. However, Ravil explained about the filters for different pulse shapes. I suggest you to go through the links i have given below ↓ . These papers may help you to understand the working of different filters

https://en.wikipedia.org/wiki/Gaussian_filter
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6887190&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F6878060%2F6886510%2F06887190.pdf%3Farnumber%3D6887190
https://en.wikipedia.org/wiki/Optical_filter

[Ashu verma]

You can analyze the performance of optical bessel filter and gaussian filter in your system. Sometimes bessel filter performs better than gaussian filter ( just for checking ) because it did happen to me that gaussian filter performed better than bessel in one of my systems using MDRZ and CSRZ while bessel filter in the case of NRZ performed better. The example i have given is just my experience. You can try and get to know which filter provides you better results.

[Ravil]

Hi Sam Sung! Did you have any chance to check/confirm the reason of the results that you have obtained in your experiment? (just a question of my general knowledge interest, in case you know) I am talking about the application of Gaussian and Bessel filters for different types of coding that you have described above. In my opinion, the second main filtering factor (after shape matching) is the rise/drop factor of certain type of filter…

[Ashu verma]

Hello Ravil,in one of my system Dwdm at ultra narrow spacing,i have checked the performance if bessel and gaussian filter for nrz rz and mdrz.I have found that bessel worked good for rz nrz and gaussian for mdrz.i have checked the paper to varify my results with the the i have given below

1.6 Tbps High Speed Long Reach DWDM System by … – Inpressco

[windy herlin]

hi all
I want to know about the loss comes from Bessel Bandpass Optical Filter which filter the specified lamda and rejact the others.
I already test it when the input power to the Filter is about -20 dbm, the output is abut -26.02 dBm. whre does the loss come from?
with regrads

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