## 2 Experimental Setup and Results
The broadband light source is launched to port 1 of OC and then routed to the TDLI for first filtering. The filtered broadband light source is reflected by the OFR and inserted back to the TDLI again for second filtering. After, the lightwave output from port 3 of OC is measured by the OSA, as the red line shows in Figure 4.  
Compared to single filtering, the double filtering structure, whose SNR is 16 dB, exhibits better performance. A round trip through the same tunable delay interferometer reduces the linewidth of the transmission peaks and is effective in suppressing spontaneous noise. The optical spectra of the self-start multi-wavelength laser, with and without the double filtering technique, are demonstrated in Figure 5. Without double filtering, the power fluctuation is about 7.5 dB and the TNR is 7 dB. By employing double filtering, the TNR has been improved to 18 dB. As the stability of the self-start multi-wavelength laser is another important factor, the optical power of 1537.768 nm, 1537.848 nm, 1537.928 nm, 1538.004 nm, 1538.084 nm, 1538.16 nm, 1538.24 nm, 1538.32 nm, 1538.396 nm, and 1538.476 nm are chosen to be monitored every 2 min as illustrated in Figure 6. Among all wavelengths, the power fluctuation is less than 0.18 dB, showing good stability of the proposed scheme. The experimental configuration of the RoF transport system based on the proposed self-start multi-wavelength laser is illustrated in Figure 2.0 In the central office, the multi-wavelength laser is externally modulated by the data via RSOA. At the transmission end, we use semiconductor optical amplifiers as modulators, in the output spectrum current region of RSOA is between 60-80 mA; we also fixed the RSOA bias current at 70 mA as an application. Subsequently, the modulated lightwave is amplified by an EDFA before the OTF. The OTF is utilized to select the specific wavelength to allocate the RF frequency. After 25 km SMF transmission, the PD converts optical components into an electrical signal and up-converts the signal to a higher frequency band based on the wavelength spacing of  
Figure 2.1 The broadband source with single-pass and double-pass filters. the selected wavelength at the BS. The optical signals displayed on OSA and the electrical signal were transmitted to the electrical spectrum analyzer and bit error tester. The bit error rate (BER) curve and eye diagram of 155 Mbps and 622 Mbps signals after back-to-back (BTB) within 25 km SMF distance data transmissions are illustrated in Figure 8, where we selected only one wavelength optical spectrum of the multi-wavelength laser. Figure 8 shows a BER and eye diagram with different modulation data. As demonstrated in Figure 8, the eye diagrams are clear and open. The eye diagrams of 155 Mbps and 622 Mbps signals were captured at \(-\)22.5 dBm and \(-\)21.5 dBm, respectively. The received optical power is measured using power monitor-attenuators (EigenLight Corporation). The measured point is before the PD. The table in Figure 8 shows the power penalty in different data rates. The power penalty of 155 Mbps and 622 Mbps signals were 0.1 dB and 0.2 dB, respectively. The power penalty for 622 Mbps signal transmission was relatively higher due to the effect of fiber dispersion. Figure 2.2 Output optical and TNR spectrum with and without a double-pass filter. Figure 2.3 _Cont._  
The optical spectra of the multi-wavelength laser and the selected two wavelengths are illustrated in the top inset of Figure 2.4 The wavelength spacing of the two selected wavelengths is about 0.08 nm, and thus the 155 Mbps data carried by these two optical tones is upconverted to 9.953 GHz. The bottom inset of Figure 9 demonstrates the measured electrical spectrum of the 155 Mbps data. The center frequency of the signal is located at 9.953 GHz and the eye diagram is also clear. The RF signal is generated by the two-tone interference method [17]. The SNR is over 20 dB, which may support future wireless broadband access applications. Moreover, the eye diagram was captured at \(-\)16.5 dBm.