# Fast Reconfigurable SOA-Based Wavelength Conversion of Advanced Modulation Format Data +
## 5 Results and Discussion
In order to investigate the time-resolved BER [57; 58] performance of the fast-reconfigurable wavelength converter, we apply a square wave current with 500 kHz repetition rate to the front section of the SGDBR to switch the wavelength converted idler between Ch1 (1541.395 nm) and Ch2 (1538.684 nm), with the other currents applied to the SGDBR laser held constant and the received OSNR set at 12 dB for the QPSK signal and 14.5 dB for the PM-QPSK signal. The time-resolved BER measurement is characterized for Ch1 by fixing the center frequency of the OBPF to Ch1 and adjusting the LO to the wavelength of Ch1. The process is then repeated for Ch2. We now present results of wavelength conversion when pump2 is dynamically tuned between 1547.68 nm and 1553.7 nm. In order to accurately estimate the time-resolved BER performance after a switching event, a number of switching events are captured via multiple acquisitions using the real-time scope. Each data point in the time-resolved BER curves corresponds to the probability of receiving an error in a 10 ns period. This means the BER is averaged over a block length of 125 symbols (10 ns), and data captured from 200 switching events is used for the calculation, with a total of \(5\times 10^{4}\) bits and \(10^{5}\) bits used for calculating each BER point in the time-resolved BER curves for QPSK and PM-QPSK signal at 12.5 GBaud, respectively. It can be seen from Figure 9a,b that the reconfiguration time (time to have a BER better than the 7% FEC limit) after a switch is approximately 50 ns and 160 ns for QPSK and PM-QPSK signal, respectively. The red curves in Figure 9a,b show the temporal frequency offset between the idler and the local oscillator in the coherent receiver after a switching event. It takes around 70 ns for the frequency of the wavelength converted idler for QPSK signal to fully stabilize after a switch, and 100 ns for PM-QPSK signal. Figure 10 shows the BER measurement as a function of OSNR in a switching environment with different waiting time after the idler is switched to Ch1 and Ch2 when using QPSK and PM-QPSK decoding. The blue and red curves show the results for the data with a waiting time of 50 ns after switching when using QPSK decoding for Ch1 and Ch2, respectively. The brown and green curves are for a 160 ns waiting time when using PM-QPSK decoding for Ch1 and Ch2, respectively. The pink and black curves show the bad performance with a 50 ns waiting time using PM-QPSK decoding for Ch1 and Ch2, respectively. The required waiting time when using PM-QPSK decoding is longer than QPSK decoding mainly due to the longer convergence time associated with the CMA method used for de-multiplexing the dual-polarization packets. Figure 8: OSNR as a function of the wavelength of the converted idler. It also can be seen that the BER versus OSNR performance in a switching scenario corresponds with the static performance shown in Figure 7a,b, which indicates that the incoming signal can be precisely and quickly converted to the required channel on a timescale of around 50 ns and 160 ns for the 12.5-GBaud QPSK and PM-QPSK signal by using the wavelength converter we present. Figure 10: BER measurement as a function of OSNR in a switching environment with different waiting time after wavelength conversion when using QPSK and PM-QPSK decoding. Figure 9: Time-resolved BER and frequency offset curves for: (**a**) QPSK signal; and (**b**) PM-QPSK signal at 12.5-GBaud, when the wavelength of the received signal (idler) is set at Ch1.