Using the Bogoliubov transformation in multi-frequency modes to describe theevolution of the non-degenerate signal and idler twin beams, we theoreticallyinvestigate the quantum noise properties of the pulse pumped high gain fiberoptical parametric amplifiers (FOPA). The results show that the noise figure ofthe FOPA is generally greater than the 3 dB quantum limit unless the jointspectral function is factorable and the spectrum of the input signal wellmatches the gain spectrum in the signal band. However, the intensity differencenoise of the twin beams, which weakly depends on the joint spectral function,can be significantly less than the shot-noise limit when the temporal modes ofthe pump and the input signal are properly matched. Moreover, to closelyresemble the real experimental condition, the quantum noise of twin beamsgenerated from a broadband FOPA is numerically studied by taking the variouskinds of experimental imperfections into account. Our study is not only usefulfor developing a compact fiber source of twin beams, but also helpful forunderstanding the quantum noise limit of a pulse pumped FOPA in the fibercommunication system.
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