The gain spectrum that was ensured by the LRA with 590 mW 209.975 THz pumping radiation and 2.82 km long HNLF is shown in Fig.
Gain spectrum provided by the single-pump FOPA with 590 mW 192.929 THz pumping radiation.
Gain spectrum provided by the single-pump LRA with 590 mW 209.975 THz counter-propagating pumping radiation.
"I tried to stop doctors pumping radiation
and chemotherapy drugs into him that he doesn't need.
It was required to implement double filtering (optical band pass filter and AWG) because the extinction ratio of real life optical filters is not enough to filter out the powerful pumping radiation
--Scattering of pumping radiation in the backword direction that is caused by initiation of stimulated Brillouin scattering (SBS) nonlinearity in the gain medium;
As mismatch between the states of polarization of the input signal and the pumping radiation can directly impact FWM and, therefore, also the idler generation process, it was decided to analyse gain polarization dependence of parametric amplifiers before estimating the impact of FOPA pump-phase modulation on the idler spectral components.
While obtaining the dependence of idler generation efficiency on the mutual mismatch of the states of polarization between the signal and the pumping radiation, it was decided to simplify the simulation model as much as possible to avoid impact of other factors on the obtained results.
The pumping radiation of the FOPA (500 mW 192.93 THz) is phase modulated using four radio frequency tunes in order to broaden its spectrum and, therefore, supress SBS.
Phase modulation of the pump was required in order to broaden the spectrum of the pumping radiation, in such a way mitigating the impact of stimulated Brillouin scattering.
At the output of the FOPA the amplified signal passes through a 5 nm bandpass optical filter with center frequency of 196.78 THz, in order to suppress the pumping radiation and the idler spectral components that were produced in the HNLF during the process of amplification.
The same pump wavelength as mentioned above was used to find the most appropriate power of the pumping radiation. It is very important to note, that even though higher pumping powers can ensure higher level of amplification, excessive pumping of the FOPA may result in serious degradation of quality of the amplified signal and hence also will cause severe power penalty at the receiver.