FILTER

[ZULKARNAIN]

Hi all…
Can anyone tell me about the various filters used in optiwave like Low pass Bessel filter, Guassian filter etc.
I am using low pass bessel filter in my project. Does it have any preference over the other filters? If not, then what are the conditions for using a particular filter for better results?
Answer will be appreciated.

[Aabid Baba]

Hi zulkarnain,
As far as i am concerned there are many filters used and that too as per requirement of the design. You have mentioned about low pass bessel but there are lot of filters present in the filter library itself both in optical as well as electrical domain. Others include fabry parot , FBG can be used as filter, there are also bandpass. I would suggest you to choose one as per your requirement.
Can you tell me what for and where you have to use it??
regards

[Ubaid Bhat]

hi zulkarnain…
i agree with aabid baba that there are many filters which can be used in a design and that too as per requirement of the design.These include fabry parot , FBG can be used as filter, there are also bandpass. I would suggest you to choose one as per your requirement.
with regards
ubaid bhat

[Tanveer]

hi Zulkarnain…..
in order to understand about the filters in optiwave you should consult the link where it is already discussed…
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwiGyoqMvrHLAhXRCI4KHcUfDi8QFggpMAI&url=http%3A%2F%2Foptiwave.com%2Fforums%2Ftopic%2Foptical-filters%2F&usg=AFQjCNFUTFquKhAz5qpq0-jlOGd7MRbtHg&sig2=VDq57CqcgTNKd1KJpXDTgw

moreover if you want to understand their usage in optiwave consult this link
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiGyoqMvrHLAhXRCI4KHcUfDi8QFggbMAA&url=http%3A%2F%2Foptiwave.com%2Fresources%2Fapplications-resources%2Foptical-system-lesson-3-optical-systems-wdm-design%2F&usg=AFQjCNF57O1dfMJAajIUgzfWDvMftOtYkw&sig2=FDZzBWJr3E1ngpHYdpOFsA

best regards

[ZULKARNAIN]

thank you aabid for your informative reply.
Well i have to use a filter in the electrical domain after the Photo diode.Actually i am working on output spectrum of a laser and the effect of various modulations on the output spectrum.

[Aabid Baba]

Hi zulkarnain,
Talking about myself i usually use low pass bessel filter after photo detection because it gives a good response but i normally use 4th order bessel filter because it serves my purpose. You can use filter as per your requirement but low pass bessel will work fine for your design. you can increase the order of the filter if you want more smooth response. I hope it will help.
Regards

[ZULKARNAIN]

thank you aabid

[ZULKARNAIN]

Aabid baba will you please tell me the difference between extinction ratio and speed of operation.Actually i am unable to understand their inverse relationship.

[Aabid Baba]

hi zukarnain,
Optical transmitters used in high-speed digital communication systems are typically required to maintain a specific set of performance
levels. One parameter, extinction ratio, is used to describe optimal biasing conditions and how efficiently available laser transmitter power is converted to modulation power.Please visit the links for further:
http://cp.literature.agilent.com/litweb/pdf/5966-4316E.pdf
I hope it helps

[Aabid Baba]

Also small changes in extinction ratio can make a relatively large difference in the power required to maintain a constant bit error rate (BER). The purpose of this application note is to show how the optical extinction ratio is defined and to demonstrate how variations in extinction ratio affect the performance of digital optical communication systems.
Please follow this link also it clearly mentions things you require.
http://www.eetimes.com/document.asp?doc_id=1225421

regards

[ZULKARNAIN]

thank you tanveer for your reply.

[Aabid Baba]

Also i would like to mention that OptiSystem component library includes different types of components for WDM systems, the tunable optical filters include Fabry-Perot filters, Mach-Zehnder interferometers, and grating based filters. now it also depends on the design you are designing. I would recommend you to go through the tutorial. I am posting the link. Please refer to it.

WDM Components – Tunable Filters

regards

[Tanveer]

hi zulkarnain…
as far Bessel filter is concerned it has flat group delay in the pass-band that is all the frequencies that are allowed to pass experience a constant delay and hence the fidelity of the signal at the output is maintained,…..
so it is up to your requirements which filter you will use in your work…

best regards

[ZULKARNAIN]

Thank you aabid baba and tanveer for your answers.
I understood that the use of a particular filter depend on the design at hand.

[Aabid Baba]

you are welcome zulkarnain. I hope the information is somehow useful to you.
Regards

[Tanveer]

Hi Zulkarnain…
As far as speed is concerned, it is one of the important parameter to be considered about the laser to be used. The speed of operation is required to be high as input data frequency is high, so the laser should be able to switch between states immediately.
No the extinction ratio is the ration of the power level corresponding to “MARK” to the power level corresponding to “SPACE”.
ER=P1/P0…………P1 is for MARK and P2 for SPACE,,,
The value of ER should be high for easy recognition of MARK and SPACE,,,,

Hope it helps you to some extent

best regards.,

[aasif bashir dar]

hi zulkarnain,
good replies by all, but i would like to add up a bit,
extinction ratio is the ratio of power at the on to off mode of the modulator or laser(DMLs). it should be high.BUT>>>>we have to look for the other things also

only high ratio does not imply that system response is good;
e.g Pon=5mW, and Poff=1mW then ext. ratio=Pon/Poff=5;
Pon=1mW, and Poff=0.2mW then ext. ratio=Pon/Poff=5;

which of two is better?????
ofcourse the second one, because poweer at off stage should ideal be zero…because lower power at off stage makes the laser power efficient, brings thermal stability(because laser or modulator cools a bit in this mode, if power is less).
thus high extinction ratio along with lower power value at the off mode of laser or modulator is better than only the system having the better extinction ratio.

with regards

[ZULKARNAIN]

thank you aasif bashir dar for this reply. Your reply was very satisfactory and i understand that it is better that the Poff should be as much less as possible for the thermal stability.

[ZULKARNAIN]

Hi all…
When the state at the output changes from marks to space or space to marks oscillations occur at the output known as the relaxation oscillations.
Can anybody tell me the reason for these oscillations at the output?
Answers will be appreciated.

[Aabid Baba]

Hi zulkarnain,
I agree with asif. If the laser can be pumped strong enough, i.e. r can be made large enough so that the stimulated lifetime becomes as short as the cavity decay time, relaxation oscillations vanish. The physical reason for relaxation oscillations and later instabilities is, that the gain reacts to slow on the light field, i.e. the stimulated lifetime is long in comparison with the cavity decay time.
Regards

[ZULKARNAIN]

thank you aabid baba for your reply.
i understood that the physical reason for relaxation oscillations and later instabilities is, that the gain reacts to slow on the light field, i.e. the stimulated lifetime is long in comparison with the cavity decay time.
Indeed it helped a lot.
regards

[Aabid Baba]

Hello asif,
Thank you so much asif for sharing some valuable information which is quite helpful. It was an important and useful add up to the extinction ratio topic. It is clear now that high extinction ratio along with lower power value at the off mode of laser or modulator is better than only the system having the better extinction ratio. I hope zulkarnain would find it helpful.

Regards

[Yosra Bouchoucha]

Hello Mr,
I want to make rf filter using ring resonator using fdtd .Can you help me .

[aasif bashir dar]

hi zulkarnain
A desirable feature of a laser is the constant amplitude. Right after the laser turns on, the amplitude varies for a while and then gets stabilized to a constant. We call the frequency before the laser gets stabilized the relaxation oscillation frequency.

for your explanation, plese visit;
http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-977-ultrafast-optics-spring-2005/lecture-notes/chapter4.pdf

with regards

[aasif bashir dar]

hi zulkarnain and aabid baba

you are welcome

[ZULKARNAIN]

thank you aasif bashir dar…
i understood the concept of these damping oscillations and that it is due to interplay between injected charge and emitted photons.

[SAHIL SINGH]

hi all.
which filter should i use to get good results for my system. i am designing a simple transmitter receiver system for which i used bessel filter as shown in the examples given on the optiwave website. can anybody tell me which filter is best to use and gives better performance.
i hope u will reply. thanks in advance to all

[ZULKARNAIN]

Hi Sahil SIngh…
as already explained by aabid baba in the previous post that there are lot of filters present in the filter library itself both in optical as well as electrical domain including fabry parot , FBG can be used as filter, there are also bandpass. I would suggest you to choose one as per your requirement.As far Bessel filter is concerned it has flat group delay in the pass-band that is all the frequencies that are allowed to pass experience a constant delay and hence the fidelity of the signal at the output is maintained.
I hope that it will help you.

[Aabid Baba]

hello sahil,
As far as your system is concerned a simple 4th order low pass bessel filter will work fine. Since you do not have to go for optimization , low pass bessel filter is perfectly fine with your system. In case you want much better performance try using other filters in the library like butterworth , bandpass and etc.
Hope it would help you..
Regards

[umer syed]

hi zulkarnain,
thanks for reply
usually the emitttion of light is due to cavity action, hence some times the ouput power fluctuates.
you might have heard of resonace cavities in which coherence action takes place. same idea may aplly here

with regrads

[Aabid Baba]

Hello umer syed,
Can you please little bit about these cavities. Where in optisystem do these cavities come into play.. Please can you suggest some links which mention so. Because it is for the first time i am hearing about cavities emitting light due to which power fluctuates in the system.
Can you please explain it in detail so that we could understand.

Regards

[ZULKARNAIN]

thank you umer syed for your reply…
ya i got the point of resonance cavities in which coherence occurs.

[umer syed]

hi all,

the use of filter depends on the type of aplplication,
e.g low pass bessel filter is used at reciver end for removing the noise,
FBG can be used for reflecting perticular band of frequencies, or form band stop filter
fabry parrot at transmitter end for making finer optical spectrum of laser source

with regards

[aasif bashir dar]

hi zulkarnain,

taking about theory of filters, it is never ending question then.
i suggest you to put forward your real quary or application in which you want the use of the filters.
then you may take suggestion and it will be fruit full discussion.

with regards

[ZULKARNAIN]

As for as my work is concerned i am studying the output spectrum of a laser. well it is a basic problem and i had previously discussed it over forum to clear my misconceptions regarding the same design.Indeed it helped a lot in selecting the various components and their use.
Regarding filter i am now using a low pass bessel filter in my design being flat in response and i think it will be sufficient for the current design.
Can i use other filters in this design?
Also i would to know that by increasing my fiber length why my results got varied and also the quality factor got reduced?
is their some provision of increasing the length of the fiber variably so that i can know that upto which distance my design is working satisfactorily.
Answer will be appreciated.
regards

[Ubaid Bhat]

hi zulkarnain…..
well it is good to know that you got help from the forum masters for your project.
talking about the filter which you have used in your design is sufficient for your current design as it will give you good results.yes you can also use other filters as well like guassian etc…
with regards
ubaid bhat

[Ubaid Bhat]

well regarding your result variation due to increase in fiber length,it is because of the losses which increase due length of the fiber.Dispersion and attenuation result because of the increase in length.
You should try to use amplifiers in your design to amplify your signal so that you can get good results. you can also use dispersion mode fibers to decrease the losses.
hope you got your query answered.
with regards
ubaid bhat

[ZULKARNAIN]

thankyou aasif bashir dar for giving an opportunity for starting a discussion on filters.Indeed it will help a lot in understanding the queries related to the filters.

[aasif bashir dar]

hi aabid baba,

i think umar is reffering to the laser action fluctuation (population inversion fluctuations)in the laser.
espaccially that of the distributed feedback laser , fabri parot laser ,… in these lasers the resonance action (interference of photons of same nature are constructively intereferet)also takes place..

in that case i think he valid on his point.
i hope he will back his point soon

with regards

[Aabid Baba]

hello asif,
yeah i guess so. Actually i was confused about the analogy umer had given because i was not able to relate it somehow. Anyways confusions happen and discussion is the way out how you clear all your doubts and confusions. Anyways thanks for explaining and sharing this valuable information.
Regards

[SAHIL SINGH]

Hi Aabid baba,
Indeed i will try with the 4th order low pass bessel filter..
Thanikng you for your valuable time..

[Aabid Baba]

hello sahil singh,
you are welcome and yeah please do use it because it will serve your purpose here.
Regards

[umer syed]

hi zulkarnain…
Butterworth filters are used in applications where maximum pass band flatness is required
on the other hand Bessel filter is a linear form of filter that provides a maximally flat group delay or propagation delay
across the frequency spectrum, but offers a slower transition from pass-band to stop-band than for other forms of filter of the
same order.
Bessel filter is not used as widely as the Butterworth of Chebyshev filters for RF applications, although the fact that it has a maximally flat group delay means that Bessel filters are often used in audio applications such as audio cross-over networks.

with regards

[aasif bashir dar]

you are welcome aabid
discussion s are always welcomed

[ZULKARNAIN]

thank you umer syed for your reply..
it is indeed a good explanation of filters and i understood the use of filters based on their applications.

[ZULKARNAIN]

Hi jojo mathew….
i am able to see your replies as it is showing Awaiting moderation. Hope you will sort out this issue so that i am able to see your answers…
with regards

[Aabid Baba]

Hello zulkarnain,
it suggests that Mr jojo has just joined is his posts and replies are in monitoring mode. It is an admin thing and all moderation are must for allowing someone to join. You can think of it as verification scene.
regards

[Tanveer]

hi zulkarnain…
As already mentioned in my post about basic filters available in optiwave,,,,,u can find a brief comparison about them for your project in the below given links…
http://www.genuineholographics.com/designlibrary.html

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&cad=rja&uact=8&ved=0ahUKEwidm_6g57bLAhVHBI4KHX24BAw4ChAWCBowAA&url=http%3A%2F%2Foptiwave.com%2F%3Fwpdmdl%3D157&usg=AFQjCNHVqUFINDfAdEMP9uBIpBlVOomdBw&sig2=ucmCGHODkZaa3e_5I0SGfA&bvm=bv.116573086,d.c2E

hope it helps
with regards

[Jojo Mathew]

Hi Abid, Its a reply to your comment ”
As far as i am concerned there are many filters used and that too as per requirement of the design. You have mentioned about low pass bessel but there are lot of filters present in the filter library itself both in optical as well as electrical domain. Others include fabry parot , FBG can be used as filter, there are also bandpass. I would suggest you to choose one as per your requirement.”

You are right in saying that one has to use the filter as per one’s requirements and specifications. Next you talked about the bessel’s functions….. Bessels function is just a mathematical trignometric function. It is used for solving the equations that contain trignometric functions with in a function…It is frequently used in electronics and signal processing .
It is a type of analog linear filter with a maximally flat group/phase delay (maximally linear phase response), which preserves the wave shape of filtered signals in the passband. Bessel filters are often used in audio crossover systems.
In all these applications if the mathematical equation generated have trignometic functions as a function of trignometric function then Bessels function can be used in solving them.
Hope you query has been answered.
Regards.

[Jojo Mathew]

Hi Abid,

You are right in saying that one has to use the filter as per one’s requirements and specifications. Next you talked about the bessel’s functions….. Bessels function is just a mathematical trignometric function. It is used for solving the equations that contain trignometric functions with in a function…It is frequently used in electronics and signal processing .
It is a type of analog linear filter with a maximally flat group/phase delay (maximally linear phase response), which preserves the wave shape of filtered signals in the passband. Bessel filters are often used in audio crossover systems.
In all these applications if the mathematical equation generated have trignometic functions as a function of trignometric function then Bessels function can be used in solving them.
Hope you query has been answered.
Regards.

[Jojo Mathew]

Hi Sahil SIngh…Its my reply to your comment ”
as already explained by aabid baba in the previous post that there are lot of filters present in the filter library itself both in optical as well as electrical domain including fabry parot , FBG can be used as filter, there are also bandpass. I would suggest you to choose one as per your requirement.As far Bessel filter is concerned it has flat group delay in the pass-band that is all the frequencies that are allowed to pass experience a constant delay and hence the fidelity of the signal at the output is maintained.”
You are right in saying that one has to use the filter as per one’s requirements and specifications. Next you talked about the bessel’s functions….. Bessels function is just a mathematical trignometric function. It is used for solving the equations that contain trignometric functions with in a function…It is frequently used in electronics and signal processing .
It is a type of analog linear filter with a maximally flat group/phase delay (maximally linear phase response), which preserves the wave shape of filtered signals in the passband. Bessel filters are often used in audio crossover systems.
In all these applications if the mathematical equation generated have trignometic functions as a function of trignometric function then Bessels function can be used in solving them.
Hope you query has been answered.
Regards.

[varinder singh]

hi Zulkarnain…..
in order to understand about the filters in optiwave you should consult the link where it is already discussed…http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-977-ultrafast-optics-spring-2005/lecture-notes/chapter4.pdf
with regards

[Ranjeet Kumar]

Hi ZULKARNAIN,
To get basic understanding of different types of filters used in optisystem like Optical Digital Filter
Optical IIR Filter (Obsolete), Rectangle Optical Filter, Butterworth Optical Filter, Bessel Optical Filter, Fabry Perot Optical Filter, Raised Cosine Optical Filter, Inverse Gaussian Optical Filter, Inverse Sinc Optical Filter, Gain Flattening Filter, Transmission Filter Bidirectional
,Reflective Filter Bidirectional and other various filters .
I would suggest you to study the pdf file which i am uploading here.

Actually it is the file which contains the detail information about optisystem component library.
Hope this may help you.

[Ranjeet Kumar]

Unfortunately, i am unable to upload it.
Due to bad internet connectivity my file failed to being uploaded.

[Dr. Dhiman Kakati]

Hello everyone,
I have a query regarding Low pass bessel, It has 4 parameters such as Cutoff frequency, Insertion loss, Depth and order so as we know from basic principle of low pass filter that it has a cut of frequency and below this all the frequency will be passed so In one of the sample I found the cut of frequency is 50 GHz, so how it is going to filter the frequency. at the transmitter side the system use a electrical sine wave generator having a frequency of 20 GHz. The LPF is in electrical domain. looking for your response. Thanking you.

Regards,
Dhiman

[Ubaid Bhat]

hi dhiman kakati…
well indeed a very good question …
well you have already mentioned in the question that the low pass filter will pass only those frequencies which lie in it’s pass band and will reject those which lie outside of the passband. Since the input frequency is only 20Ghz which is well in the passband of the filter,so it will be passed as it is.
with regards
ubaid bhat

[SAHIL SINGH]

Hi Ubaid bhat,

No doubt a good question posted and infact very well explained by you as well..

Regards
Sahil Singh

[Ubaid Bhat]

hi dhiman kakati..
So if you want to filter some of the frequencies from the input frequecy then you have to use a filter with less cutoff and in this case below 20Ghz. But i think usually the information is available only for few Ghz so we need lpf with cutoff only for few Ghz. i hope you got my point.
with regards
ubaid bhat

[Manoj Kumar]

hi Zulkarnain…..
in order to understand about the filters in optiwave you should consult the link where it is already discussed…
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwiGyoqMvrHLAhXRCI4KHcUfDi8QFggpMAI&url=http%3A%2F%2Foptiwave.com%2Fforums%2Ftopic%2Foptical-filters%2F&usg=AFQjCNFUTFquKhAz5qpq0-jlOGd7MRbtHg&sig2=VDq57CqcgTNKd1KJpXDTgw

moreover if you want to understand their usage in optiwave consult this link
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiGyoqMvrHLAhXRCI4KHcUfDi8QFggbMAA&url=http%3A%2F%2Foptiwave.com%2Fresources%2Fapplications-resources%2Foptical-system-lesson-3-optical-systems-wdm-design%2F&usg=AFQjCNF57O1dfMJAajIUgzfWDvMftOtYkw&sig2=FDZzBWJr3E1ngpHYdpOFsA

best regards

[Author]

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