How to find exact Bias Point in Direct Modulation

[Ibn Aziz]

Hi every one !
I am trying to find Bias point in Direct Modulation of Rf signal (as Input).

I have used “Directly Modulated Laser measured” component to do direct modulation in one scenario and “Laser measured” component (instead of Directly Modulated Laser measured) to do direct modulation in other scenario.

i tried to find bias point by making 2-d graph between DC input on x-axis and output power from modulator at y-axis.

But problem is that whenever i measure output power Vs all sweep values of input DC, the output power always remain constant. So i am not being able to find proper Bias point due to not getting non-linear graph (as getting constant value of output power).

Can some body help me finding Exact Bias point in Direct Modulation or any other alternative way of finding Bias point in direcct modulation.

I am attaching Fig and Opti sys file of both scenarios as follows.
I am using Opti sys version 7.

P.S the Bias values Shown in both fig r not the only values for which i have check BIAS point.

I wil be thankful to ur kind response.

Best Regards

[Damian Marek]

Hi Bilal,

There are a couple problems that I can see from the project files. (I can’t attach the working project files because they will not work with OptiSystem 7).

One problem is that the threshold current is in the 20 mA range, but your input current has an amplitude of 1 A.U. which in this context means 1 Amp. The amplitude is much too high for a physical device. The bias points are also too high since you start with 0.5 A.U. which converts to 500 mA.

The second problem is that in the Laser Measured project the bias current and modulation peak current of the Laser Measured Component need to be set to 0 to use the external source.

Regards

[Joseph Jiang]

hi,damian,i use the default setting in my directly modulation system.is it OK?

[Ibn Aziz]

Hi Damian,
u have shared gud point in ur above comments. But there are some ambiguities as follow.

1. in Laser Measured project i have used default values of bias current and modulation peak current that are 23mA and 28mA respectively while threshold current and refrence current were 18mA and 23mA respectively (all were default values). So is that wrong ?

2. Damien, problem is that if i get proper Bias point still i am not sure wether it is exact point or not because i have no non linear graph from which i can verify exact bias point.

a. Further, I always get number of side bands at almost all values of Bias point during modulation but still lacks confidence on weather it is ture bias point or not.
And that is what i need here in this scenario of direct modulation for getting totl 7 bands (three on both side of center band).

b. Kindly share any method from which i can verify proper bias point, if u know …??

3. Damien can u share ur settings of getting proper Bias point of direct Modulation using either laser measured component or directly modulated laser in Figures so that we i can understand it and become able to get proper bias point and 7 bands output ??

It wil be so nice of u if u share figures of ur setting for proper biase point. kindly keep 128Mbit/sec bit rate for this scenario.

I will be very thakful to u for ur this kindness.

Best Regards

[Ibn Aziz]

I have done it. Thanks Daimen ur above points really made my work.

Regrads

[Aadil Raza]

Hi All. Please share with me the exact bias point determining method as discussed in above posts.

[umer ashraf wani]

https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjRuYv1h8fMAhXNcI4KHZg6BngQFggjMAE&url=http%3A%2F%2Fwww.cpeu.dk%2Fdata%2Fuploads%2Fteaching%2F34129_e2009_cpeu_dml_eml.pdf&usg=AFQjCNGs6q4cbyQUPD1XVQ7gizRQMuCQdw
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjRuYv1h8fMAhXNcI4KHZg6BngQFggtMAI&url=http%3A%2F%2Fwww.ece.ucy.ac.cy%2Fcourses%2Fece645%2Fdocs%2F08_modulators_2015.pdf&usg=AFQjCNFjpyqjOePDxYuu4M_mUssfBaJtSA
https://books.google.co.in/books?id=FuzpPQN7HbQC&pg=PA356&lpg=PA356&dq=Bias+Point+in+Direct+Modulation&source=bl&ots=ILY8Rm88I6&sig=mJLD3ROKup1WimEf75P4VCpPFjM&hl=en&sa=X&ved=0ahUKEwjJwZyFiMfMAhVQ1I4KHbqZAnI4ChDoAQgdMAE
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=19&cad=rja&uact=8&ved=0ahUKEwjJwZyFiMfMAhVQ1I4KHbqZAnI4ChAWCEkwCA&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2F216526266_fig3_Fig-3-Direct-Modulation-Scheme&usg=AFQjCNFbOLWGFr9pJsMF3CE7CWviKJnmgA&bvm=bv.121421273,d.c2E
https://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=21&cad=rja&uact=8&ved=0ahUKEwjq07-RiMfMAhWLVI4KHdNFCHo4FBAWCBowAA&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.116.406%26rep%3Drep1%26type%3Dpdf&usg=AFQjCNGkmMyJFZB8BPYHWbZ1CoNquY0Gew&bvm=bv.121421273,d.c2E

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