Laser Power Requirement

[Hermawan Widiyanto]

hello, i want to ask again. In my project, i made a DWDM-ROF (Radio Over Fiber) scheme with 20 channels with bitrate each channels it’s about 25Gbps and 65 km fiber length. The problems is still difficult for me to set or to define the best output power of CW laser with these spesification so i can reach the minimum value of Q factor. So, is there any formula or some technical spesification to calculate the appropriate output power for CW laser?

thanks and regards
hermawan.w

[Dr. Dhiman Kakati]

Hello Hermawan Widiyanto,
First of all put the CW laser array power in sweep mode and try to increase the power from around -7dBm to 4dBm in 7 iteration as I have seen in many examples of WDM systems, his is one way tou can modify and further keep the power along the fiber below a certain limit, because High intensity light waves causes nonlinear effects in the fiber and the system performance degrades. try using Optical amplifier wherever necessary and dispersion compensating fiber to increase the bit rate of the system. Thanking you.

please refer to the following link

Sweep power in WDM system

hope to get some more reply in that link.

Regards,
Dhiman

[Hermawan Widiyanto]

thanks for your suggestion, mr.Dhiman i’m very appreciate it. So i have to try sweep mode in 7 iterations? sorry, i’m still bit unclear about “increase the power around -7 dBm to 4 dBm” . In the end, whether the results will be displayed for each power value in later or not

[SAHIL SINGH]

Hello Hermawan Widiyanto,

Well very nice points suggested by Dhiman kakati…. Also try to go through the links as posted by Dhiman kakati.. Hope your query gets resolved…

Regards
Sahil Singh

[Ubaid Bhat]

hi Hermawan Widiyanto,
well i think you should try to iterate your power as already told by dhiman and then look for the best results.for decreasing the losses you should try to use dispersion mode fibers or amplifiers. hope you got my point.
with regards
ubaid bhat

[–]

Hi Hermawan Widiyanto,
Once I went through a paper where it was written that the laser power that could be used is 6dB, so as to avoid non-linearity. May be this helps you to some extent.
Regards

[Atul Sharma]

Hello Hermawan Widiyanto. Greetings.

I agree to Dhiman Kakati to some extent but it is not necessary that you have to sweep power levels. Are you using array of CW lasers?
First try using same power level for each of the CW laser and try going through the standards for allowable power in radio over fiber systems.

With regards
Atul Sharma

[Ranjeet Kumar]

Hi Hermawan Widiyanto,
Fist i suggest you to always use the symmetrical number of channels more precisely ..2, 4, 8, 16, 32, 64…. 2^n where n is positive integers.
Because in almost all the research work you would find these types of number of channels, i am quite sure why we should use such type.
I will try to find out and will share.
I suggest you to read some basic research works of DWDM system.
Please read the article :
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5549128
http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1216189

[Rajguru M. Mohan]

Hello Hermawan Widiyanto,
Usually when we increase the input power of laser, our system performance will enhance.
But after a certain optimum value the system performance will remains the same.
In most of the cases of WDM system we varies the laser power in the range of -5dbm to 5dbm.
So, you should also check for the application of laser to decide the range of power input.
I think it also varies for different applications.

seeking your response.

[umer ashraf wani]

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[Rajguru M. Mohan]

Hi,
The power of laser can be calculated by:
E = n*e
where E is energy, n is the number of photons and e is the energy of a photon

E = nhf where h is Planck’s constant and f is frequency

Since P = E/t, P = nhf/t where t is time

For a time of 1s t =1 and disappears from the equation:

P = nhf = nhc/l where c is speed of light and l is wavelength.

Please also refer to following link
http://www.optique-ingenieur.org/en/courses/OPI_ang_M01_C01/co/Contenu_31.html

Thanks,

[Karan Ahuja]

Hi
Beyond the oscillation threshold, the power at 1064 nm is no longer negligible. To simplify the process, each pump photon beyond the oscillation threshold is assumed to become a laser photon and leave the cavity. To do this, the photons must either go through the output mirror or experience passive losses in the cavity. Figure E11 shows where the different laser outputs are situated. There are losses by diffusion on the mirrors and globally over all the interfaces. These losses, as well as the residue of the transmission through the mirror M2, cannot be used: they are the so-called passive losses. The only useful part of the beam is that which leaves via M1. The intensity of this beam is called the output power or Port.
I am attaching the photo. I hope this will help.
Regards

[Author]

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