Validation of FWM Effect

Compatibility:

This tutorial demonstrates the validity of the FWM algorithm, as well as providing the user with some useful designing tips for optimizing simulation time and accuracy.

The layout in was used to obtain results, and can be found in the sample file FWM Validation.osd

Optical System - Figure 1 - FWM project layout

Figure 1: FWM project layout

In the two CW Lasers, the frequencies are set to 1540 and 1540.5 nm, power set to 0 dBm, and the linewidth set to 0 (see Figure 2). The linewidth is set to 0 is because we are only interested in measuring the total power of the sideband frequencies, so the shape of the spectrum is not required.

The channels were then multiplexed together using a 2×1 Mux.

After the Mux, the signals are propagated through 75 km of nonlinear fiber, where they experience the effects of Attenuation, Group Velocity Dispersion (GVD), and FWM.

The setup for the SMF-28 fiber component can be see from Figure 3 through to Figure 6.

Optical System - Figure 2 - CW Laser properties dialog box

Figure 2: CW Laser properties dialog box

You can see in Figure 3 that the input and output coupling efficiencies are set to 0.

Optical System - Figure 3 - SMF-28 fiber properties dialog box—Main tab

Figure 3: SMF-28 fiber properties dialog box—Main tab

In Figure 4, the GVD parameter was set to 1 ps/nm/km, so that it follows the example in [1].

Optical System - Figure 4 - SMF-28 fiber properties dialog box—Dispersion tab

Figure 4: SMF-28 fiber properties dialog box—Dispersion tab

In Figure 5, you will see that the Effective Area was set to 64μ2, and the n2 constant to 4.3286e-21.

The n2 constant was calculated using the following equation:

Optical System Equation 1

where X1111 is the third-order nonlinear susceptibility, n is the refractive index, and
is the speed of light.

Now, X1111 = 6e – 15m3 / W / s, n = 1.48, c = 3e8m / s .

Therefore,

Optical System Equation

Optical System - Figure 5 - SMF-28 fiber properties dialog box—Nonlinear tab

Figure 5: SMF-28 fiber properties dialog box—Nonlinear tab

Optical System - Figure 6 - SMF-28 fiber properties dialog box—Numerical tab

Figure 6: SMF-28 fiber properties dialog box—Numerical tab

If you calculate the project, you will obtain the results see in Figure 7 and Figure 8.

Optical System - Figure 7 -  Input optical spectrum

Figure 7: Input optical spectrum

Optical System - Figure 8 - Output optical spectrum

Figure 8: Output optical spectrum

If you zoom in on the FWM sidebands, you will find that the power is approximately -72.7 dBm, compared to -72.3 as predicted by [1].

Reference:
[1]G. Keiser, Optical Fiber Communications 3rd Edition, Example 12-8. pp. 499, (2000)