## 4 25 km Fiber Transmission Experiment  
The performance of the BMWC was finally evaluated in a 25 km fiber transmission experiment without employing any dispersion compensation. The experimental setup used is shown in Figure 4. Two separate signals at \(\lambda_{1}\) = 1550.4 nm and \(\lambda_{5}\) = 1551.1 nm were combined in a 50:50 coupler and injected into a PPG-driven LiNbO\({}_{3}\) modulator to produce a 284 bit pattern including one repetition of 10 Gb/s 2\({}^{7}\)-1 PRBS. The two wavelength streams were then demultiplexed through an Arrayed Waveguide Grating (AWG), and transmitted through two different optical paths with 25 km difference, with one of the branches featuring an ODL for controlling the time synchronization of the data. The two optical wavelength streams were then combined through a 50:50 coupler into a single data stream comprising  
\begin{table}
\begin{tabular}{l l} \hline
**Parameter** & **Value** \\ \hline SOA length & 1.7 mm \\ Output saturation power of SOA & 18 dBm \\ Typical recovery time of the SOA & 80 ps \\ Small signal gain of the SOA & 30 dB \\ Current SOA1 & 268 mA \\ Current SOA2 & 330 mA \\ Power of Nas1 & 7.13 dBm \\ Power of Nas2 & \(-\)11.93 dBm \\ Input power & 6.96 dBm \\ Control 1 power (Port A) & \(-\)1.5 dBm \\ Control 2 power (Port H) & 9.8 dBm \\ \hline \end{tabular}
\end{table}
Table 1: Operational conditions of the BMWC.  
Figure 3: Experimental results for 20 Gb/s for 3 dB loud/soft ratio (**a**) input trace (2.5 \(\upmu\)s/div), (**d**) output trace (1 \(\upmu\)s/div), (**g**) output eye diagram (20 ps/div). For 4 dB (**b**) input trace, (**e**) output trace, (**h**) output eye diagram. For 5 dB (**c**) input trace, (**f**) output trace, (**i**) output eye diagram, (**j**) BER measurements for input and output signals and (**k**) BER improvement of input-output signals at different loud/soft ratios. All traces and eyes are in 4 mV/div.  
two sequential loud/soft PRBS7 packets of 127 bits, with an intermediate guardband of 15 bits, towards an overall 284 bit long multi-wavelength pattern that emulates the aggregated non-compensated traffic of two PON clients reaching the BMWC. At various stages of the setup, Isolators (ISO), Polarization Controllers (PC), Variable Optical Attenuators (VOA), ODLs and 99:1 monitoring couplers were used to control and optimize the operational settings of the experiment, while the BMWC was operated at the same conditions found at the loud/soft characterization experiments of the previous section.  
The results obtained for the 25 km long fiber transmission experiment are illustrated in Figure 5. More specifically, Figure 5a,b show the time traces and eye diagrams of the incoming packet bursts exhibiting 5.2 dB loud/soft ratio due to the propagation losses of the 25 km long fiber, and broadened pulses for the soft burst stemming from the chromatic dispersion effect. The BMWC's output signal is illustrated in Figure 5c,d, exhibiting equalized peak power levels and an eye diagram with an ER of 6.5 dB. Figure 5e depicts the BER measurements for the 25 km fiber transmission with and without the BMWC, revealing error free operation with 1.43 dB BER improvement for the case of the BMWC.  
Finally, it is worth mentioning, that the BMWC could potentially support higher data rates up to 40 Gb/s and fiber spans up to 40 km, as the differentially-biased scheme has already been demonstrated at this speed [21], and the loud/soft ratio has been shown at up to 9 dB.