Fig. 1. (a) Experimental setup for measuring MZM transfer characteristics with different input light polarization states. The bold lines represent polarization-maintaining components. (b) The polarization state of the light traveling on the slow axis of a PMF into the modulator. (c) The polarization state of the light traveling on the fast axis of a PMF into the modulator.

Fig. 2. Slow-axis (solid) and fast-axis (dotted) light attenuation in a Mach–Zehnder modulator for different input DC voltages.

Fig. 3. Attenuation difference between the slow-axis and fast-axis light in a Mach–Zehnder modulator for different input DC voltages.

Fig. 4. Output spectrum of the MZM-based variable optical attenuator when two different-wavelength orthogonal linearly polarized light components enter the modulator. The DC voltage into the modulator is (a) 3.5 V and (b) 10.1 V.

Fig. 5. Dual-polarization MZM-based variable optical attenuator for independent control of the slow-axis (red arrow) and fast-axis (blue arrow) light amplitudes.

Fig. 6. Attenuation of the input fast-axis (solid) and slow-axis (dash) light for different DC voltages into (a) MZX and (b) MZY.