optiwave

[Hager]

when i want to predict the system performance say sweep fiber length Vs BER , i can take the BER from any users BER analyzer and system performance is accurate?

when i want to compare at different cases i should take the BER from the same user in every case or not ?

how can i make sweep for received power and bitrate (i can not change it from global mode) ?

[Damian Marek]

Hi Hager,

I’m going to assume that you are designing some sort of WDM system with multiple channels/users.

1) I think as a first approximation the BER results of a single channel/user can be used. However, many effects are wavelength dependent (loss/dispersion) so to be sure you will want to measure the BER of each individual channel.

2) In different cases (received power) you should monitor the BER of the same user. Keep in mind the BER may change differently for different users.

3) The following tutorial should help you out with your sweep question:

Lesson 4: Parameter Sweeps — BER x Input Power

Regards

[Hager]

hi domian

when i change the bitrate from say 622Mbps to 2.5Gbps and i used bandwidth of 1.5THz for the optical source at 622Mbps. the bandwidth of optical source need to change or not when i increase bitrate ?

for my previous question if for example my system consists of 3 users, you say i can take the individual channle BER as a first aproximation, if i take the BER from the 3 users and calculate the average value of the 3 BER is the results became more accurate ?

[Damian Marek]

1) For a laser the bandwidth (linewidth) is a physical characteristic of the device. Generally a single mode very narrow linewidth is desired but not always possible. This parameter does not depend on the bit rate though. However, modulating a laser source changes the frequency spectrum by generally broadening it which is proportional to the bit rate. This is more important for designing filters and WDM mux’s later though.

2) Yes averaging between the 3 users will give a more accurate value for BER.

Regards

[Hager]

say, i have 4 users in system , when i setup the light source bandwidth , i should try different value until the BER of 4 users is almost the same ? to obtain accurate system design

[Damian Marek]

I don’t think I completely understand your project. Are you looking at SAC-OCDMA? The linewidth of the optical source will have an impact on your system, but it shouldn’t have an impact on the accuracy of the simulation.

Could you describe your project a little more?

Thanks

[Hager]

Hi Damian

my project represent one of SAC-OCDMA codes say i have 4 users with code length 12 wavelength range ( 1550-1558.8 ) to represent code with .8nm spectral width. i can’t determine the exact sample rate of white light source . i tried different value but when i increase the sample rate the performance improve. i put it 1.5 THZ and increase it to 2 THZ the performance improve to 10^-40 . i want to know how can determine the exact sample rate to every system ?? because i want to compare its performance with other codes so i want may result be logic and accurate.

also i try another code (construction of code is different )but has the same code length but i needed to increase the sample rate more than 1.5THZ for system to make results for all users although it has the same code length as the first code but it need more sample rate
this makes me little confused what the sample rate depend on in the system ?
also if i want to use LED haw can i determine the bandwidth value?
Thanks in advance

[Damian Marek]

Ok thanks for clarifying! The answer to your question is that you need to have a White Light bandwidth that covers the range from 1550 nm to 1558.8 nm. So you can set the center wavelength of the source to 1554.4 nm and a bandwidth of 8.8 nm. I believe I showed you how to change this from nm to Hz in another forum post. This is what determines the sample rate for your white light source. You can verify that the entire spectrum is covered by using a Spectrum Analyzer. For the LED it is the same answer.

One more very important point! The signals in OptiSystem are represented as time sampled signals, so think 2xN matrix with one column represents time and the other the complex field (there is also actually polarization info too). There is a strict relationship between the sample rate (inverse of time increment) and the bandwidth that can be represented in the frequency domain. A smaller time increment (larger sample rate) means that a larger bandwidth can be represented. The sample rate can be directly modified in the white light source, however in the LED only the bandwidth can be modified, so you need to make sure that in the global properties that the sample rate is sufficiently large.

Hope this clears it up!

[Damian Marek]

Here is an example file (OptiSystem 13.0) with the correct sample rate, bandwidth parameters that you are looking for.

[Hager]

Thanks Damian very much . your answers always very helpful.

[LALIT VERMA]

Sir how to write an MDW code on the SAC ocdma system in the papers only WDM is being used for slicing then PRBS & NRZ MZM are given for an sac ocdma sysytem.

[alistu]

Hi Lalit, OCDMA and MDW are two separate multi-access techniques which can be used together as a way to increase the number of network subscribers. You are right, WDM is only used to slice the signal (the way you put it) and then each sliced part has a number of users and uses OCDMA to code the data corresponding to each user.

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