We theoretically investigate the quantum-noise properties of a pulse-pumped high-gain-fiber optical parametric amplifiers (FOPAs) by using the Bogoliubov transformation in multiple frequency modes to describe the evolution of the nondegenerate signal and idler twin beams. The results show that the noise figure of the FOPA is generally greater than the 3 dB quantum limit unless the joint spectral function is factorable and the spectrum of the input signal well matches the gain spectrum in the signal band. However, the intensity-difference noise 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 of the pump and the input signal are properly matched. Moreover, to closely resemble real experimental conditions, the quantum noise of twin beams generated from a broadband FOPA is numerically studied by taking the various kinds of experimental imperfections into account. Our study is not only useful for developing a compact fiber source of twin beams, but also helpful for understanding the quantum-noise limit of a pulse-pumped FOPA in the fiber communication system.
We experimentally demonstrate an improvement of
0.7±0.1 dB in the noise figure in a low noise fiber-optical parametric amplifier (FOPA) with the injection of correlated quantum fields generated from spontaneous four-wave mixing in fibers. The noise performance of the amplifier is characterized with homodyne detectors. The experimental result shows that the noise levels in the two output ports (signal and idler) of the amplifier are both
1.0±0.1 dB lower than a regular FOPA with vacuum at the unused input port. In addition, we demonstrate the scheme can be used as a quantum information tap with a combined information transfer efficiency (signal and tap) as
Tsig+Ttap=1.47±0.2, which is larger than the classical limit of 1. This low noise FOPA can be applied to the low noise amplification in the measurement of weak signals.