| Popis: |
We have recently shown theoretically that a two-pump fiber optical parametric amplifier (OPA), operated near the fiber zero-dispersion wavelength, λ0, can exhibit very uniform gain over a wide wavelength range [1]. For example, a standard dispersion-shifted fiber operated near λ0 = 1550 nm can exhibit 20 dB of gain over a 45 nm bandwidth, with a gain ripple not exceeding 0.1 dB. The fact that the predicted ripple is so small raises the question of whether it might not be substantially increased by incorporating into the model some features left out of the original model as a first approximation. Of particular concern are the facts that we assumed: (i) a single nonlinearity coefficient γ to describe interactions between different waves; (ii) that this γ did not change with frequency. Even if (i) were correct, (ii) clearly is questionable because: 1) we are interested in large frequency ranges (say up to 50 nm bandwidth); 2) γ has both explicit and implicit wavelength dependences. Specifically, γ is given by γ = 2πn2/λA eff , where n2 is the nonlinear-index coefficient, λ is the vacuum wavelength, and A eff is the effective core area. Ae ff generally increases with λ, and thus the denominator of γ can exhibit a fairly strong λ-dependence. In addition n2, which is determined by the materials making up the core and cladding, may also be wavelength dependent. In this paper we study the influence of the dispersion of λAe ff on the OPA gain characteristics. We also assume a priori that the various interactions are governed by different γ’s, and we keep these throughout the entire calculation. We will show that, because of symmetries governing the interacting frequencies, the gain spectrum uniformity of the fiber OPA will not be greatly affected by the inclusion of these additional effects. |
