Direct modulation of laser

[muhammad jawad]

Dear colleagues
By direct modulation of a directly modulated laser by a sine signal, we get multiple coherent carriers as shown in upper spectrum analyzer. In the same, way on direct modulation of a VSCEL as shown in lower plot in attached figure, i do not get multiple carriers. Please tell me what is the issue and how to correct it.
I will be highy obliged
Regards

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[Ahmad Atieh]

Dear Muhammad,
you have to be careful when setting the VCSEL. The modulation peak current setting affects the relaxation oscillation of the VCSEL and the modulating signal frequency affects the VCSEL output signal. It can be distorted after 2.5Gbps.
Regards,
Ahmad

[muhammad jawad]

Please sir tell me, in order to operate VCSELs like DMLs, we have to find its LI characteristics curve and then bias it at the half of the middle point of the LI curve?

[muhammad jawad]

Sir i have drawn a LI curve at 1 Gbps data, Modulation peak current =10mA, Bias current sweeps from 0 to 25mA. I gets a circular type curve as shown in Fig attached. How to get a linear straight curve like DML laser so that VCSEL can be biased at middle of this linear region?

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   plot.png
   

[Ahmad Atieh]

Dear Muhammad,
you may use the measured VCSEL because it give more freedom to control the laser specs.
Regards,
Ahmad

[muhammad jawad]

ok sir thanks

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