Fig. 1. (a) Schematic of the DTCF coupler. (b) The cross-section of the DTCF.

Fig. 2. Δn1 versus (a) the etching depth, (b) the thickness of the electrodes, and (c) the thickness of the EO polymer.

Fig. 3. Δn2 versus the etching depth at ΔVa=5  V and ΔVa=10  V (black). Propagation loss versus the etching depth at Va=0, Va=5  V, and Va=10  V (red).

Fig. 4. Δn2 versus the thickness of the electrodes at ΔVa=5  V and ΔVa=10  V (black). Propagation loss versus the thickness of the electrodes at Va=0, Va=5  V, and Va=10  V (red).

Fig. 5. Δn2 versus the thickness of the polymer at ΔVa=5  V and ΔVa=10  V (black). Propagation loss versus the thickness of the polymer at Va=0, Va=5  V, and Va=10  V (red).

Fig. 6. Normalized optical power versus the applied voltages at L=Lc=1.36  cm.

Fig. 7. neff1 and neff2 versus the radius of core 1 at Va=0.

Fig. 8. Normalized optical power versus the applied voltages at L=Lc=1.54  cm.

Fig. 9. Normalized optical power versus applied voltages at r2=3.4  μm, r2=3  μm, r2=2.5  μm, and r2=2  μm.

Fig. 10. Transmission spectrum of the modulator versus the applied voltages of 0, 1.26, 2.5, 2.65, and 2.7 V.