Fig. 1. (a) Cross section of a single-drive push–pull carrier-depletion-based optical modulator. Inset shows the zoom-in of the PN junction. (b) Microwave electrical field distribution in the modulation arms.

Fig. 2. (a) Electrical components contributed by each layer. (b) Two-port network and the equivalent circuit model of the modulator.

Fig. 3. (a) Calculated L and R as a function of frequency. Comparison between calculation and simulation results for (b) characteristic impedance (Z), (c) propagation constant (β) and microwave attenuation (α), and (d) EE S-parameters (S21 and S11).

Fig. 4. (a) Calculated EO 3 dB bandwidth as a function of metal line width Wmt and gap separation Gmt. (b) Effect of BOX layer thickness HBOX on the TWE characteristics. (c) Effect of doping separation Sdop on the TWE characteristics. (d) Microwave attenuation of the MZMs designed with a single or a segmented PN junction.

Fig. 5. (a) Modulation efficiency VπL and (b) optical loss versus PN junction doping concentrations at Vb=0  V.

Fig. 6. (a) Measurement setup to characterize the modulators. (b) Optical microscope image of the MZMs.

Fig. 7. (a) Optical transmission spectra of MZM-2 at 0 and 4 V reverse biases. (b) Modulation efficiency VπL of MZM-2. (c) Real part of the characteristic impedance. (d) Imaginary part of the characteristic impedance. (e) Microwave transmission response EE S21. (f) Microwave reflection response EE S11. (g) Modulator frequency response EO S21.

Fig. 8. Measured 56 Gb/s OOK modulation eye diagrams for (a) MZM-1, (b) MZM-2, and (c) MZM-3.

Fig. 9. 40 Gb/s BPSK modulation eye diagrams for (a) MZM-1, (b) MZM-2, and (c) MZM-3.

Fig. 10. Measured 40 Gb/s BPSK modulation BER curves for (a) MZM-2 and (b) MZM-3. Inset shows the constellation diagram.

Table 1. Design Parameters for Three MZMs