Q penalties due to pump phase modulation and pump RIN in fiber optic parametric amplifiers with non-uniform dispersion
We present an experimental and numerical investigation of the quality factor degradation ($ΔQ$) due to pump phase modulation and pump relative intensity noise (RIN) in single- and double-pumped fiber optical parametric amplifiers (FOPAs). These penalties are investigated in FOPAs constructed with fibers having constant and randomly varying zero-dispersion wavelength ($λ_0$) along the fiber. We show that pump phase modulation in uniform fibers (constant $λ_0$) produces large $Q$ penalties, while in fibers with variations of $λ_0$, these penalties can be strongly reduced in both single- and double-pumped FOPAs. We also show that $Q$ penalties due to pump phase modulation tend to disappear in FOPAs made with very short fibers ($L<0.1~\mathrm{km}$) and very low dispersion slope $ S_0 < 0.002~ \mathrm{ps}\, \mathrm{nm}^{-2}\, \mathrm{km}^{-1}. $ The $Q$ penalties due to pump RIN, which for typical FOPA parameters are much smaller than those due to pump phase modulation, are also reduced in non-uniform fibers (varying $λ_0$), but do not depend on fiber length nor on fiber dispersion slope.