Commit | Line | Data |
---|---|---|
f9a73e9e AIL |
1 | distance = input('Enter fiber length in L_D '); |
2 | beta2 = input('dispersion: 1 for normal, -1 for anomalous '); | |
3 | N = input('Nonlinear parameter N = '); % Soliton order | |
4 | mshape = input('m = 0 for sech, m > 0 for super-Gaussian '); | |
5 | chirp0 = 0; | |
6 | ||
7 | % set simulation parameters | |
8 | nt = 1024; Tmax = 32; % FFT points and window size | |
9 | step_num = round(20 * distance * N^2); % No. of z steps | |
10 | deltaz = distance/step_num; % step size in z | |
11 | dtau = (2*Tmax) / nt; % step size in tau | |
12 | ||
13 | %% tau and omega arrays | |
14 | tau = (-nt/2 : nt/2-1) * dtau; % temporal grid | |
15 | omega = (pi/Tmax) * [(0:nt/2-1) (-nt/2:-1)]; % freq grid | |
16 | ||
17 | if mshape == 0 | |
18 | uu = sech(tau) .* exp(-0.5j * chirp0 * tau.^2); | |
19 | else | |
20 | uu = exp(-0.5 * (1 + 1j * chirp0) .* tau.^(2 * mshape)); | |
21 | end | |
22 | ||
23 | %% plot input pulse shape and spectrum | |
24 | temp = fftshift(ifft(uu)) .* (nt * dtau) / sqrt(2 * pi); % spectrum | |
25 | figure(1); clf; subplot(2,1,1); | |
26 | plot(tau, abs(uu).^2, '--k'); hold on; | |
27 | axis([-5 5 0 inf]); | |
28 | xlabel('Normalized Time'); | |
29 | ylabel('Normalized Power'); | |
30 | title('Input and Output pulse shape and spectrum'); | |
31 | ||
32 | subplot(2, 1, 2); | |
33 | plot(fftshift(omega)/(2*pi), abs(temp) .^ 2, '--k'); hold on; | |
34 | axis([-.5 .5 0 inf]); | |
35 | xlabel('Normaized freq'); | |
36 | ylabel('spectral power'); | |
37 | ||
38 | %% store dispersive phase shifts to speed up code | |
39 | dispersion = exp(0.5j * beta2 * omega.^2 * deltaz); % [hase factor | |
40 | hhz = 1j * N^2 * deltaz; | |
41 | ||
42 | %% begin main loop | |
43 | %% N/2 -> D -> N/2 first half step nonlinear | |
44 | temp = uu .* exp(abs(uu) .^ 2 .* hhz / 2); | |
45 | for n = 1 : step_num | |
46 | f_temp = ifft(temp) .* dispersion; | |
47 | uu = fft(f_temp); | |
48 | temp = uu .* exp(abs(uu) .^ 2 .* hhz); | |
49 | end | |
50 | uu = temp .* exp(-abs(uu) .^ 2 .* hhz); % final field | |
51 | temp = fftshift(ifft(uu)) .* (nt*dtau) / sqrt(2 * pi); % final spectrum | |
52 | %% end of main loop | |
53 | ||
54 | %% plot output pulse shape and spectrum | |
55 | subplot(2,1,1); | |
56 | plot(tau, abs(uu).^2, '-k'); | |
57 | subplot(2,1,2); | |
58 | plot(fftshift(omega) / (2*pi), abs(temp).^2, '-k'); |