## 5 Experimental Setup  
Based on the theoretical research and simulation environment, an adjustable CD estimation system based on FrFT is established. Limited to the experimental environment and conditions, this section only carries out the estimation experiment of the OOK signal at a 10 Gbit/s transmission rate. Figure 14 shows the schematic diagram of the OOK optical signal transmission. As shown in the figure, the experimental platform is composed of a continuous light source, modulator, PRBS generator, transmission fiber, CD regulator, detector, and off-line processing module. At the transmitting end, the central wavelength of the light source is 1550 nm, the optical signal symbol rate is 10 Gbit/s, the emission power of the light source is \(-2\) dBm, and the linewidth is set to 100 kHz. The power spectrum diagram of the transmitted signal is shown on the left side of the figure. Then, the optical signal passes through the optical fiber transmission link and the CD regulator to control the CD range from \(-1200\) ps/nm to 1200 ps/nm. The schematic diagram of the optical signal power spectrum affected by the transmission link is shown on the right side of the figure. It can be found that after the influence of the transmission link and CD, the power spectrum effect of the optical signal becomes worse, obviously. Finally, we receive the optical signal through a detector and input the data into the off-line processing module for a CD estimation based on FrFT. It is worth noting that it is obvious from the eye diagram that the transmission link and CD will affect the quality of the optical signal. Accordingly, it can be shown that the experimental platform can fully prove the correctness of the CD estimation method based on FrFT. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **CD Estiamtion of FrFT** & **Best Match Search [24]** & \begin{tabular}{c} **Time Frequency Autocorrelation** \\ **Method [25]** \\ \end{tabular} \\ \hline Sampling Point & 4096 & 6144 & 4096 \\ \hline Main Calculation & FrFT & \begin{tabular}{c} FFT, Differential \\ compensation, IFFT \\ \end{tabular} & \begin{tabular}{c} FFT, Spectrum superposition, \\ Autocorrelation \\ \end{tabular} \\ \hline Standard Deviation & 54 & 76 & 74 \\ \hline Error Range & \(-137\)–\(204\) & \(-300\)–\(300\) & \(-210\)–\(210\) \\ \hline CD Range & 0–\(32\),\(000\) & \(-32\),\(000\)–\(32\),\(000\) & \(1280\)–\(29\),\(440\) \\ \hline \begin{tabular}{c} Influence of OSNR and \\ PMD on CD Estimation \\ \end{tabular} & \begin{tabular}{c} Good robustness to \\ OSNR and PMD \\ \end{tabular} & \
\begin{tabular}{c} Only the CD estimation effect with \\ OSNR of 14 dB and PMD of 25 ps \\ is discussed \\ \end{tabular} &
\begin{tabular}{c} Only the CD estimation effect with \\ OSNR of 12 dB and PMD of 25 ps \\ is discussed \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: CD estimation performance under different sampling points and search interval. According to the OOK signal dispersion monitoring scheme in Figure 14, the experimental environment and platform are constructed, and the corresponding physical objects of the main experimental system are shown in Figure 15.  
Figure 15a shows the optical transceiver monitoring module used in the experiment. The optical transceiver module is equipped with an optical module. The optical fiber is connected to the optical module through the interface, and when the light passes through the dispersion adjustment module, it is connected back to the receiving end of the optical transceiver module. The optical module carried in this experiment is a small form-factor pluggable (SFP) optical module with a digital diagnosis function. Its structure mainly includes a transmitter, a controller, and a receiver. The function of the optical module is  
Figure 14: Scheme of dispersion monitoring system for OOK signal.