Home Forums SYSTEM laser linewidth

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• #29349
mohammed hosni
Participant

if i have laser source with linewidth=0.4nm ,what is the value of linewidth in MHZ?????

• #29350
Alessandro Festa
Participant

It depends on the central wavelength. The formula is LINE(Hz)=c/lambda^2 * LINE(m)

• #29352
alistu
Participant

I believe the linewidth in Hz very much depends on the central frequency of the laser whose linewidth you are calculating. I sort of had more or less the same question and here is the answer I got the following answer which explains it:

Converting wavelength to frequency

Regards

• #29358
mohammed hosni
Participant

the central wavelength is 1550 nm and linewidth is 0.4 nm

• #29359
mohammed hosni
Participant

if i have cw laser source at wavelength 1550 nm with linewidth 0.4 nm ,how can i enter the value of this linewidth in CW laser component??
the linewidth in optisystem is given in MHZ??

• #29360
alistu
Participant

According to the formula given by Alessandro in his comment (which is the formula for the explanation given to me in the addressed forum page) the linewidth of the laser is 49.948 GHz, which is a really large value for the CW laser linewidth especially for low power commercial lasers.

• #29364
mohammed hosni
Participant

What do you think about the appropriate value for the linewidth

• #29365
alistu
Participant

The laser linewidth can be from 1 kHz to 1 GHz depending on the laser. For low-power commercial CW lasers, values of a few kiloHz can be found. I have seen laser power being set as 100kHz in some of OptiSystem samples, which I think is a very realistic value with regard to commercial lasers.

• #29367
mohammed hosni
Participant

dr alistu :but i have a paper ,the author has done experiment with laser source with o/p power 6.8 dbm and with linewidth 0.4 nm at wavelength 645 nm using plastic fiber with length 200 m.
i need your help to know how can i enter the 0.4 nm at the linewidth of the laser source component in optisystem?

• #29368
alistu
Participant

I know it is a large value for the linewidth, butI have merely used the formula that Alessandro has suggested in his comment which I believe is definitely correct for calculation of the parameter. Can you please address the paper in which such a value has been assigned to the linewidth?

• #29384
Alessandro Festa
Participant

Dear Alitsu, thanks for using me as a reference ðŸ™‚

Dear Mihammed, 0.4nm at 645nm center is a linewidth of 288Ghz, which really seems a lot as Alitsu says! Can you send any reference?

Regards,

Alessandro

• #29404
alistu
Participant

You’re welcome Alessandro! The relation and your answer was really useful to me in the other forum, when I hadn’t noticed the point of central frequency being a factor in the process of calculation.

• #29398
mohammed hosni
Participant

ok

• #29399
mohammed hosni
Participant
• #29405
alistu
Participant

You are right Mohammed. And figure 11 where the spectrum of the laser is shown clearly states this rather great linewidth being used in the design. Therefore, I suggest you go on with your simulation and see if you find any trouble getting the proper results, which apparently you shouldn’t encounter.

• #29411
Alessandro Festa
Participant

Hi Mohammed, unfortunately I do not have access to IEEE articles. Anyway, good luck with your research and I hope I have been helpful!

Best Regards,

Alessandro