function [P_fwm, eta, deltaBeta, Leff] = calcFwmPower( ...
    f_i, f_j, f_k, f_0, Ds, alphaDbPerKm, Lkm, ...
    P_i, P_j, P_k, gammaWInvKmInv, degeneracyFactor)
% Calculate FWM power for a fiber with attenuation and phase mismatch.
%
% Inputs:
%   f_i, f_j, f_k, f_0 : frequencies in Hz
%   Ds                 : dispersion slope in ps / (nm^2 km)
%   alphaDbPerKm       : attenuation in dB/km
%   Lkm                : fiber length in km
%   P_i, P_j, P_k      : launch powers in W
%   gammaWInvKmInv     : nonlinear coefficient in 1/(W km)
%   degeneracyFactor   : typically 3 for degenerate FWM, 6 for non-degenerate

if nargin < 8 || isempty(P_i)
    P_i = 1;
end
if nargin < 9 || isempty(P_j)
    P_j = P_i;
end
if nargin < 10 || isempty(P_k)
    P_k = 1;
end
if nargin < 11 || isempty(gammaWInvKmInv)
    gammaWInvKmInv = 1;
end
if nargin < 12 || isempty(degeneracyFactor)
    degeneracyFactor = 1;
end

[eta, deltaBeta] = calcFwmEfficiency(f_i, f_j, f_k, f_0, Ds, alphaDbPerKm, Lkm);

alphaNpPerM = alphaDbPerKm .* log(10) ./ 10 ./ 1e3;
Lm = Lkm .* 1e3;
gammaWInvMInv = gammaWInvKmInv ./ 1e3;

if abs(alphaNpPerM) < eps
    Leff = Lm;
else
    Leff = (1 - exp(-alphaNpPerM .* Lm)) ./ alphaNpPerM;
end

P_fwm = degeneracyFactor .* eta .* ...
    (gammaWInvMInv .* Leff).^2 .* ...
    P_i .* P_j .* P_k .* ...
    exp(-alphaNpPerM .* Lm);

end