# Integrated Fiber-FSO WDM Access System with Fiber Fault Protection
## 3 Experiment and Results
The detected power sensitivities of \(\lambda_{\text{1C}}\) to \(\lambda_{\text{8C}}\) are \(-30.5\), \(-29\)  
Figure 5: Experimental setup of (**a**) fiber and (**b**) FSO transmissions, respectively. The photos of insets are the corresponding active and passive components. \(-28\), \(-27.5\), \(-27\), \(-26.5\), \(-26.5\) and \(-26.5\) dBm at the FEC target, respectively. In addition, the obtained power sensitivity at the FEC can be improved from 1 to 1.5 dB after through 25 km SMF link, as seen in Figure 6a,b. This is because we exploit the \(-0.7\) chirp parameter MZM in the proposed PON to pre-compensate the fiber dispersion. The power budget of 35 to 38 dB can be achieved after 25 km SMF link. The insets (i) to (iv) of Figure 6a,b are the corresponding eye diagrams of 1535.04 nm (\(\lambda_{\text{IC}}\)) at the received powers of \(-29.5\), \(-23\), \(-30.5\) and \(-24\) dBm, respectively. The measured eyes of insets (ii) and (iv) are open and clear. In addition, the insets (i) and (iii) also can be distinguished for observation. Based on the presented PON architecture of Figure 2 and experimental setup of Figure 5a, the downstream signal will pass through the AWG\({}_{3}\) (6 dB), SW (1 dB), 25 km fiber (0.2 \(\times\) 25 = 5 dB) and OC\({}_{2}\) (0.5 dB) after leaving the CO\({}_{1}\) in normal state, respectively. Thus, 17 dB total insertion loss of each downstream traffic is produced by the proposed PON system. The upstream traffic also passes through the SW, AWG\({}_{3}\), and 25 km SMF. The upstream signal also results in the same insertion loss of 17 dB. Commonly, an optical amplifier is applied in the CO to compensate the insertion loss of upstream signal. Therefore, the insertion loss induced by the AWG\({}_{1}\), AWG\({}_{2}\), CP and WCP can be ignored in the CO site. Once the fault is happened at the \"F1\" or \"F2\" points of Figure 3a or Figure 3b, respectively, the downstream and upstream traffics will transmit through the SW (1 dB), WCP (1 dB), AWG\({}_{4}\) (6 dB), 25 km SMF (0.2 \(\times\) 25 = 5 dB) and OC (0.5 dB), when the SW switches to the point \"2\". Thus, the total insertion loss of downstream and upstream signals is both 13.5 dB, while the protection mechanism of PON system is operated. Moreover, as mentioned above, through 25 km fiber connection, the corresponding power budgets of downstream and upstream traffics can be achieved between 35 and 38 dB and 34 and 34.5 dB, respectively. As a result, the achieved power budgets can meet with the total insertion loss induced by the fiber access network under the normal and fault protection states. In the FSO measurement, the selected L-band wavelengths of 1560.61 (\(\lambda_{\text{1L}}\)), 1561.42 (\(\lambda_{\text{2L}}\)), 1562.23 (\(\lambda_{\text{3L}}\)) and 1563.05 nm (\(\lambda_{\text{4L}}\)); and 1563.86 (\(\lambda_{\text{5L}}\)), 1564.68 (\(\lambda_{\text{6L}}\)), 1565.50 (\(\lambda_{\text{7L}}\)) and 1566.31 nm (\(\lambda_{\text{8L}}\)) are served as the downstream and upstream traffics, respectively. Here, the  
Figure 6: Measured BER performances of \(\lambda_{\text{IC}}\) to \(\lambda_{\text{SC}}\) (**a**) at the BTB state and (**b**) through 25 km SMF, respectively. Insets (i) to (iv) are the observed corresponding eye diagrams under different received powers. output power of TLS at the port \"2\" of OC\({}_{1}\) and OC\({}_{2}\) is 7.5 dBm, as illustrated in Figure 5b. We also apply 10 Gb/s OOK format on MZM to generate the symmetric downstream and upstream FSO signals in the presented PON system. Figure 7a,b exhibit the measured 10 Gb/s OOK FSO BERs of downstream (\(\lambda_{\text{IL}}\) to \(\lambda_{\text{4L}}\)) and upstream transmissions (\(\lambda_{\text{5L}}\) to \(\lambda_{\text{8L}}\)) after 25 km SMF link and 2 m free space connection, respectively. The observed power sensitivities of eight wavelengths (\(\lambda_{\text{1L}}\) to \(\lambda_{\text{8L}}\)) are \(-21.5\), \(-21.5\), \(-21.5\) and \(-21.5\) dBm and \(-22\), \(-22\), \(-22\) and \(-22\) dBm below the FEC threshold, respectively.