%function [rOpt,state] = nl_step(state,aOpt,aDz)

function [rOpt_x,rOpt_y] = nl_step(opt_x,opt_y, dz, gamma, chi, use_manakov, beatlength, alpha_lin_x, alpha_lin_y)

    if ~use_manakov % CNLSE
        
        rOpt_x = opt_x .* exp( (-1j*(1/3)*gamma*dz).* ...
                           ( (2 + cos(2*chi)^2)*(abs(opt_x).^2) + ...
                             (2+2*sin(2*chi)^2)*(abs(opt_y).^2) ) );

        rOpt_y = opt_y .* exp( (-1j*(1/3)*gamma*dz).* ...
                           ( (2 + cos(2*chi)^2)*(abs(opt_y).^2) + ...
                             (2+2*sin(2*chi)^2)*(abs(opt_x).^2) ) );

%         A_x = opt_x;
%         A_y = opt_y;
% 
%         rOpt_x = 1i* gamma * (abs(A_x).^2 + (2/3 .* abs(A_y).^2) ) .* A_x + ((1i * gamma / 3) * conj(A_x).*(A_y.^2) * exp(-2i * dz * 2*pi / beatlength ));
%         rOpt_y = 1i* gamma * (abs(A_y).^2 + (2/3 .* abs(A_x).^2) ) .* A_y + ((1i * gamma / 3) * conj(A_y).*(A_x.^2) * exp(-2i * dz * 2*pi / beatlength ));

                         
    else
        % estimate effective length of dz (ref?)
        if (alpha_lin_x == 0) && (alpha_lin_y == 0)
            Leff = dz;
        else
            Leff = (1-exp(-alpha_lin_x*dz))/alpha_lin_x;
        end
        
        %compute power
        power = real(opt_x).^2+imag(opt_x).^2+real(opt_y).^2+imag(opt_y).^2;
%         power= abs(opt_x).^2+abs(opt_y).^2;
%         powers = [powers;power];
        Hnl = exp( -1j*8/9*gamma*power*Leff);
        rOpt_x = opt_x .* Hnl;
        rOpt_y = opt_y .* Hnl;
    end   
end