3. Experimental Demonstration
In the experiment, we implement a two-tap microwave photonic filter in an RoF system, and the
experimental setup is shown in Fig. 4. A tunable laser (TL, Agilent 81940A) and a commercial
distributed feedback (DFB) laser (Lightcomm OS-D-155) are used as the optical sources, which are
combined by an optical coupler (OC). The optical carrier is launched to a Mach–Zehnder modulator
(MZM) after a polarization controller (PC). The subcarrier from a microwave signal generator (MSG,Agilent E8257D) with the frequency of 2.5 GHz is mixed with the 150-Mb/s OOK data from a
pseudo-pattern generator (PPG-SQA, Anritsu MP1800) and modulates the optical carrier via the
MZM. Then, the modulated optical signal is amplified by an EDFA and transmitted through a 25-km
fiber link. In the RAU, the microwave signal is recovered by a photodiode (PD) with 10-GHz
bandwidth and then mixed with the local oscillator (LO) to get the baseband signal, which is then
tested by the oscilloscope (Agilent 86100A).
By employing the embedded microwave photonic filter, the desired signal located at the peak
frequency of the filter is filtered out, and the undesirable signal located at the valley frequency is
suppressed. In the experiment, we do not employ the tunable dispersive medium in the RAU;
instead, a tunable laser is used. By changing the wavelength spacing of the two optical sources, the
time delay between the two taps of the filter can be tuned consequently. When the wavelengths of
the TL and LD are 1552.89 nm and 1554.75 nm, respectively, the FSR of the embedded microwave