This lesson demonstrates the application of traveling wave SOA as a wavelength converter using cross-gain saturation effect.

The principle use of the cross-gain modulation in SOA is as an intensity-modulated input signal that modulates the gain in the SOA via gain saturation effect. A continuous wave signal at the selected output wavelength is modulated by the gain variation. After the SOA, the continuous wave signal carries the same information as the intensity modulated signal. The input signal and the CW signal can be launched either co-directionally or counter-directionally into the SOA. A co-propagation scheme is considered here.

To realize this idea, the intensity-modulated input signal and a CW signal are multiplexed and then launched into SOA, as shown in Figure 1.

Optical System - Figure 1 Multiplexed intensity-modulated input signal and CW signal

Figure 1: Multiplexed intensity-modulated input signal and CW signal

To demonstrate conversion at 10 Gb/s requires following global parameters (see Figure 2).

Optical System - Figure 2 Simulation parameters

Figure 2: Simulation parameters

The intensity-modulated input signal and a CW signal have carrier wavelengths of 1550 and 1540 nm (or frequency separation from 1.25 GHz) and powers of 0.316 mW and 0.158 mW (without line widths, initial phases, and polarizations). The signals are multiplexed with the help of WDM Mux 2×1 and launched in SOA.

Figure 3 shows the Optical Gaussian Pulse Generator parameters.

Optical System - Figure 3 Optical Gaussian Pulse Generator Main parameters

Figure 3: Optical Gaussian Pulse Generator Main parameters

Figure 4 shows the shape and spectrum of the intensity modulated signal.

Optical System - Figure 4 Shape and spectrum of the intensity modulated signal

Figure 4: Shape and spectrum of the intensity modulated signal

Figure 5 shows the multiplexer parameters and channels.

Optical System - Figure 5 WDM Mux 2x1 Main parameters and channels

Optical System - Figure 5 WDM Mux 2x1 Main parameters and channels

Figure 5: WDM Mux 2×1 Main parameters and channels

Figure 6 shows the shape of the WDM Mux 2×1 signal after multiplexing.

Optical System - Figure 6 Shape of WDM Mux signal

Figure 6: Shape of WDM Mux signal

Figure 7 shows the SOA Physical parameters.

Optical System - Figure 7 SOA Physical parameters

Figure 7: SOA Physical parameters

These amplifier parameters give the unsaturated single pass gain G0 ~ 30 dB.

Figure 8 shows the form of the amplified signal.

Optical System - Figure 8 Amplified signal

Figure 8: Amplified signal

The amplified signal passed through the demultiplexer, which has properties similar to the multiplexer. Figure 9 shows the signal shape and spectrum at λ = 1550 nm after the demultiplexer.

Optical System - Figure 9 Shape and spectrum of the signal at λ = 1550 nm

Figure 9: Shape and spectrum of the signal at λ = 1550 nm

Figure 10 shows the signal shape and spectrum at λ =1540 nm after the demultiplexer.

Optical System - Figure 10 Shape and spectrum of the signal at λ = 1540 nm

Figure 10: Shape and spectrum of the signal at λ = 1540 nm

The inversion of the signal can be clearly seen.

This lesson demonstrated the application of traveling wave SOA as a wavelength converter using cross-gain saturation effect.

References:

[1] Terji Durhuus, Benny Mikkelsen, Carsten Joergensen, Soergen Danielsen, and Kristian Stunkjaer, “All-optical wavelength conversion by semiconductor optical amplifier”, Journal of Lightwave Technology, Vol. 14, pp. 942-954,1996.

[2] G.P. Agrawal, “Fiber Optic Communication Systems”, 2nd Edition, John Wiley & Sons Inc., 1997.

[3] R. Sabella and P. Ludgi, “High speed optical communications”, Kluwer Academic Publishers, 1999.