# Blind Phase Search with Angular Quantization Noise Mitigation for Efficient Carrier Phase Recovery
## 4 Experimental Setup and Results Validation  
The experimental setup for the validation of the proposed F-BPS scheme is shown in Figure 5. The transmitter consists of two synchronized 50 GSa/s arbitrary waveform generators (AWG), an optical IQ modulator, and an external cavity laser (ECL) with less than 100 kHz linewidth. A pseudo-random bit sequence (PRBS15) is mapped to a 28-Gbaud 64 QAM signal followed by Nyquist pulse shaping with a 0.15 roll off factor. The sequence is then re-sampled to match the sampling rate of the AWGs. A number of phase noise sequences are generated in order to emulate the phase noise of a semiconductor laser with different linewidths [17; 18]. The generated phase noise sequences are then multiplied with the resampled signal and its I and Q components are loaded into each of the AWGs. The electrical output of the synchronized AWGs is fed into an optical IQ modulator which linearly modulates the incoming electrical signal onto the transmitting ECL. The 28-Gbaud 64 QAM output of the IQ modulator is then amplified using an erbium doped amplifier (EDFA). An optical signal to noise ratio (OSNR) adjusting module consisting of an optical attenuator and an EDFA with constant output power is used to adjust the OSNR of the signal. The 64 QAM signal is then fed in the receiver consisting of a balanced coherent receiver front end, an 80 GSa/s and 33 GHz bandwidth digital sampling oscilloscope (DSO), and an integrated LO laser with <100 kHz linewidth. Data demodulation is performed offline using DSP routines where the proposed F-BPS and C-BPS CPR schemes are applied for their performance comparison. Figure 4: Tolerable combined linewidth symbol duration product comparative between the proposed F-BPS and C-BPS for 16 QAM and 64 QAM employing different number of test phases at BER levels of 3.8 \(\times\) 10\({}^{-3}\) and 2 \(\times\) 10\({}^{-2}\), respectively, and for 1 dB OSNR penalty. Figure 3: OSNR sensitivity penalty versus combined linewidth symbol duration product comparative between the proposed F-BPS and C-BPS for 16 QAM and 64 QAM employing different number of test phases at BER levels of 3.8 \(\times\) 10\({}^{-3}\) and 2 \(\times\) 10\({}^{-2}\), respectively. Figure 6 shows the experimental performance validation of the proposed F-BPS and its comparison with the C-BPS algorithm in a 28-Gbaud 64 QAM. Figure 6a shows the BER against the number of test phases at 31.8 dB of OSNR for three different emulated linewidths for the F-BPS and C-BPS schemes. For the C-BPS case, its block filter length was optimized to show the best performance for all points in the curves. For the F-BPS case, the C-BPS block filter length and the proposed angular quantization noise filter length were swept together, with the same value, to obtain the best performance for all the points in the curves. It is observed that the proposed filtering operation provides a phase noise tolerance improvement for all the three emulated linewidth cases compared to the C-BPS algorithm. It is also observed that the relative phase noise tolerance improvement increases for higher values of emulated linewidth. A significantly lower number of test phases for the F-BPS case is shown to be sufficient to achieve the C-BPS algorithm performance. Hence, showing a potential low complexity implementation of the algorithm as similar filter block lengths was required when optimizing the C-BPS and the F-BPS filter block lengths, for the same emulated linewidth cases, even when employing different number of test phases. Figure 6b illustrates the BER against OSNR curves for the proposed F-BPS (\(\beta\) = 16) and C-BPS (\(\beta\) = 16, 64) schemes for three different emulated linewidth levels. It is observed that similar or improved performance is achieved with the proposed F-BPS (\(\beta\) = 16) compared to that of the C-BPS (\(\beta\) = 64). If the same low number of test phases (\(\beta\) = 16) is used, a drastic performance improvement is achieved with the proposed F-BPS scheme.