## 5 Experimental Setup
Figure 15: Object diagram include (**a**) optical transceiver monitoring module; (**b**) optical fiber; (**c**) CD regulator and (**d**) analog photodetector of main experiments of the dispersion monitoring system for the OOK signal. to realize the photoelectric conversion of the signal. The transmitting end carries the bit information on the optical pulse to generate the optical signal, and then, after passing through a section of optical fiber link, the receiving end converts the optical signal to be measured into an electrical signal and restores the electrical signal into the required digital signal. The optical receiving module mainly includes a photoelectric detector, a transimpedance amplifier, and a limiting amplifier. The control end of SFP is also called a digital diagnosis module. Its main function is to monitor the working voltage, temperature, bias current, receiving and emitting power, and other parameters of the optical module in real time. The maximum speed of the SFP optical module can reach 10.3 G, so the OOK signal rate designed in this paper is 10 G, and the wavelength is 1550 nm. Figure 15b shows the SSMF used in the experiment, which realizes the transmission function of the optical fiber link near 1550 nm. Figure 15c shows the CD regulator, which can be connected to the upper computer to change the CD value in the range of \(-1200\) ps/nm to 1200 ps/nm. Figure 15d shows the analog photodetector. Its main function is to realize the acquisition and storage of docking receiving signals, input the obtained data to the offline processing module, and complete the verification of the CD estimation of the experimental signals based on FrFT. In the CD estimation stage of the off-line digital signal processing, according to the above content, the estimation effect will be measured by the estimation results after changing different CD sizes in the optical fiber link. Figure 16 shows the calculated FrFT value of the OOK signal after transmission with different CD sizes. In order to simplify the calculation, the signal sampling point in this estimation process is 4096, and the search interval of FrFT order is 0.001. It can be seen from the figure that the OOK signal generated by the experiment can see that each datum has an obvious downward peak after different CD transmission and FrFT operations. In this way, the corresponding CD value can be calculated according to the transformation order of the peak position. Similarly, the correctness of the above method based on FrFT is verified, and it is also proved that this method can work well in the actual transmission system. For the OOK signal, we estimate the CD within the range of \(-1200\) ps/nm to 1200 ps/nm set in the experiment and obtain the estimation error value and error rate results within this range, as shown in Figure 17. It can be seen from the figure that for the OOK signal, the estimated CD error value changes with the set real cumulative range. It can be seen from the figure that both fluctuate within a fixed range, and the average value of CD error is 80 ps/nm, the maximum value is 103 ps/nm, and the average value of error rate is only 0.17. It is worth noting that the estimation error is still within the tolerance range of the estimation error mentioned above and will not affect the BER performance of the final  
Figure 16: FRFT results of the OOK signal after different dispersion transmissions. transmission system. It is proved that the estimation method based on FrFT has a good estimation effect in the actual transmission link. In order to evaluate the influence of different input powers on the CD estimation performance in the experimental environment, we choose to estimate the CD of the OOK signal under different input powers (respectively, \(-2\) dBm, \(0\) dBm, \(2\) dBm).