Fig. 1. (a) Proposed tunable MPF. LD, laser diode; VNA, vector network analyzer; DP-QPSK modulator, dual-polarization quadrature phase shift keying modulator; HC, hybrid coupler; OBPF, optical band-pass filter; TDGDE, tunable differential group delay element; PD, photodetector; 90° PR, 90° polarization rotator. (b) The detailed structure of the QPSK modulator. MZM, Mach–Zehnder modulator.

Fig. 2. (a) Measured optical spectra of the CS-DSB and $\mathrm{CS}-\mathrm{DSB}+\mathrm{OC}$ signal. (b) Measured optical spectra before and after the OBPF, as well as the transfer function of the OBPF.

Fig. 3. (a) Phase shift of the recovered RF signal over the frequency range of 10–32 GHz. (b) Relative power variation for different phase shifts.

Fig. 4. Measured (a) phase shift and (b) relative power variation of the RF signal at the frequency of 20 GHz over the sweeping time of 200 s.

Fig. 5. Measured frequency responses of the proposed MPF (a) with different bias voltages of X3 and (b) at different times with the same bias voltages.

Fig. 6. Measured notch positions of the proposed filter with different bias voltages.