# Fast Reconfigurable SOA-Based Wavelength Conversion of Advanced Modulation Format Data +
## 5 Results and Discussion  
The wavelength of the fast-tuning SGDBR pump laser is switched between two operating modes by applying a switching signal to the wavelength tuning sections. In order to benchmark the system performance, we first present the BER performances when pump2 is tuned and fixed to the two wavelengths that pump2 will later be dynamically switched between. The wavelength and power of the signal and pump1 (ECL) are kept constant throughout. The input and output spectra of the SOA when the SGDBR laser is set at 1548.68 nm and 1553.70 nm are shown in Figure 6a,b, respectively, and it can be observed that the indicated idler of interest has changed wavelength position from Ch1 (1541.395 nm) to Ch2 (1538.684 nm). BER performance as a function of OSNR at the receiver for the original signal; the signal after SOA and converted signals (idlers) for the QPSK and PM-QPSK signals at 12.5 GBaud are displayed in Figure 7a,b, respectively. It can be observed that the penalty between the original signal, the signal after SOA, and wavelength converted idler is under 0.5 dB for both cases, indicating the quality  
Figure 6: Input and output spectra of SOA showing the spectral locations of the signal of the external cavity laser (ECL), pump1 (ECL), pump2 (SGDBR), and converted idlers. (**a**) SOA input and output spectra when SGDBR is set at 1548.68 nm. (**b**) SOA input and output spectra when SGDBR is set at 1553.70 nm. The detected idlers are indicated. of the wavelength conversion scheme and potential usefulness. The constellation diagrams of the wavelength converted idler for a received OSNR of 12 dB and 14.5 dB are also given in Figure 7a,b, respectively. The phase noise of the FWM components is studied by using a coherent phase noise measurement technique [37; 46]. The ECL's employed for the signal and pump1 have a linewidth of around 40 kHz and the linewidth of the 1548.68 nm and 1553.70 nm wavelengths of the SGDBR laser (employed as the second pump for FWM scheme) are 260 kHz and 230 kHz, respectively. The linewidth (from the high frequency phase noise region) of the idlers is measured to be around 370 kHz and 300 kHz, as expected when the SGDBR is set to the two operating modes, since the idler linewidth is the sum of the linewidths of the pumps and signal, and in this case the linewidth of the SGDBR pump laser dominates. To calculate the limitations of the wavelength conversion scheme, we study the OSNR of the idler as a function of the detuning between the two pumps. The different wavelength converted idlers are filtered out by using an optical tunable band-pass filter. The OSNR measurement is then undertaken by using the OSA. In order to estimate the signal power and the noise floor correctly, the solution is to take two consecutive sweeps of the OSA with different resolution bandwidth (RBW) settings [56]. For the first sweep, OSA 0.2 nm RBW is used for the measurement of the signal power,  
Figure 7: (**a**) Bit error rate (BER) versus optical signal to noise ratio (OSNR) curves for the input original signal, the signal after SOA, and the converted idlers for 12.5 GBaud QPSK signal. (**b**) BER versus OSNR curves for the input original signal, the signal after SOA, and the converted idlers for 12.5 GBaud PM-QPSK signal. and the second sweep measures the noise power by using 0.1 nm RBW setting. The output OSNR of the idler wavelength for the case with signal fixed at 1542.5 nm, pump1 fixed at 1549.8 nm, and the pump2 (SGDBR) tuned from 1548.7 nm to 1564.7 nm is displayed in Figure 8, which shows a tuning range of around 14 nm can be achieved with more than 9 dB OSNR, which is enough for the wavelength conversion of the QPSK data at 12.5 Gbaud to get a BER value below the 7% FEC limit (3.8 \(\times\) 10\({}^{-3}\)). Around 11 nm tuning range can be achieved for the wavelength conversion of PM-QPSK data to get a BER value below the 7% FEC limit.