Differential Group Delay

[Mohamed Ben zegalamParticipant]

Hi All,

What is the different between the Differential Group Delay and the signal time delay. there is parameter in the optical fiber called Differential group delay (ps/km). if I set the length of the fiber to 100km and the differential group delay to 0.2. is that mean the optical signal will be delay or advance by 20ps.

[alistuParticipant]

Hi Mohammad,

The word “differential” in differential group delay refers to the difference in propagation time between the x polarization axis and y polarization axis. So in 100 km, you’ll have 20ps time difference between x-pol. and y-pol. signals.

Signal time delay means that the determined delay is applied to the whole signal.

Regards

[Mohamed Ben zegalamParticipant]

Hi Alistu,

Thanks for your reply, do you know how can I calculate the time delay for the signal.

I tried to check the optical signal before and after the optical fiber using optical time vir. and I found the time different between them is half of the differential group delay.

[alistuParticipant]

Hi Mohamed,

The time delay of the signal is dependent on the dispersion parameter, and the dispersion parameter is wavelength dependent, which causes a pulse broadening (as for different wavelengths, the delay is different). I don’t know if it can be calculated using some formula, but maybe it can be done using dispersion of elements with least delay (I have never tried it though).