# Fast Reconfigurable SOA-Based Wavelength Conversion of Advanced Modulation Format Data +
## 4 Experimental Setup for Reconfigurable Wavelength Converter  
Figure 5 depicts the schematic diagram of the experimental setup of the SOA-based wavelength conversion of QPSK and PM-QPSK (blue dashed) signals using a SGDBR laser as one of the pump sources. A narrow linewidth external cavity laser (ECL) tuned to 1542.5 nm for all experiments is used as the signal source and was modulated with QPSK data at 12.5-Gbaud using an optical IQ modulator. The optical modulator is driven by electrical signals generated by the arbitrary waveform  
Figure 4: Measured high frequency linewidth (green triangles), low frequency linewidth (red dots), and output wavelength (blue squares) with different currents on the front section of the SGDBR laser, with 90 mA current on the gain section, 0 mA current on the phase and back section. Figure 3: (**a**) Structure of the sampled, grating-distributed Bragg reflector (SGDBR) laser; (**b**) frequency modulation (FM) noise spectrum of the SGDBR laser. generator (AWG) with two uncorrelated pseudo-random bit sequences (PRBS) of 2\({}^{7}\)-1 bits periodicity. The AWG operated at 25 GSa/s, which gives 2 samples per symbol for the 12.5-Gbaud QPSK signal. The two QPSK signals are amplified by using the radio frequency (RF) amplifiers. To implement the PM-QPSK signal scheme, the PM-QPSK signal is generated by using a Pol-Mux emulator, consisting of a polarization beam splitter (PBS) at its input, a passive stage with a delay of 4.88 ns (61 symbols), two polarization controllers, and a polarization beam combiner (PBC) to combine the polarization tributaries. The output of the two pumps are passed through polarization controllers, combined, and polarization-aligned using a 3 dB coupler and a PBS. For the wavelength conversion of the QPSK signal data, the generated optical QPSK signal is then coupled with two pumps (one SGDBR laser and one narrow linewidth ECL) and sent into the SOA-based wavelength converter. For both QPSK and PM-QPSK schemes, the power of the signal and the pumps at the input of the SOA are set at \(-10\) dBm and 0 dBm, respectively, for optimum conversion efficiency [48]. The signal wavelength undergoes wavelength conversion through non-degenerate FWM in the SOA operating at 500 mA bias current. The SOA device used in the experiment is a nonlinear SOA with a very fast gain recovery time less than 25 ps. It operates over C-band with a typical small gain of 25 dB, a saturation power of +13 dBm, and less than 0.5 dB polarization-dependent saturated gain. After the FWM process in the SOA, the converted idler is then filtered out by using a tunable optical bandpass filter (OBPF). For system performance evaluation purposes, the optical signal to noise ratio (OSNR) of the idler is changed by adding amplified spontaneous emission (ASE) from an Erbium-doped fiber amplifier (EDFA) that is passed through a 2 nm bandwidth tunable optical bandpass filter. The filtered idler is then passed through a 3 dB splitter with one arm sent to the optical spectrum analyzer (OSA)for the OSNR measurement, and the other arm is passed into the polarization diversity coherent optical receiver and captured by a real-time oscilloscope sampling at 50 GSa/s for offline DSP processing. The received idler power at the input of the coherent receiver is maintained at \(-19\) dBm. The data captured from the real-time oscilloscope is first resampled to 2 samples per symbol using a priori knowledge of the clock frequency. Then the constant modulus algorithm (CMA) [49; 50; 51] is utilized to enable polarization de-multiplexing for PM-QPSK signal.