Fig. 1. (a) Schematic of the integrated DPMZM in the LNOI platform; (b) microscope image of the fabricated device (spliced and colored).

Fig. 2. (a) Detail view of the 3 dB MMI; (b) detail view of the heating electrode; (c) detail view of the TWEs straddling the optical waveguides.

Fig. 3. (a) Cross-sectional view of the material stack and dimension definitions; (b) simulated fundamental TE optical mode profile distribution; (c) effective indices of the first few modes supported by the LNOI ridge waveguide dependent on the waveguide width at 1550 nm wavelength; (d) calculated electric field distribution with a 1 V DC voltage.

Fig. 4. (a) Aerial view of the mode profile within the MMI; (b) simulated output power for each MMI port and total output power as the input wavelength swept from 1.5 to 1.6 µm.

Fig. 5. Fabrication flow chart of the proposed x-cut DPMZM.

Fig. 6. Schematic diagram of the proposed DFS measurement scheme. (a)–(c) are the diagrams of the optical spectra at different locations. LD: laser diode; PC: polarization controller; MZM: Mach–Zehnder modulator; EDFA: erbium-doped fiber amplifier; PD: photodiode; ESA: electrical spectrum analyzer.

Fig. 7. Photo of the packaged chip.

Fig. 8. (a) Measured EE S-parameters of the 6 mm DPMZM; (b) measured V_π of the 6 mm sub-MZM. The measurement is taken at 100 kHz, and the V_π is roughly 6 V.

Fig. 9. Output optical spectra of the two sub-MZMs (only the corresponding RF port is fed with a signal).

Fig. 10. Measured electrical spectra for (a) a −0.2 MHz DFS and (b) a +0.2 MHz DFS.

Fig. 11. (a) Measured DFS (green square) and corresponding error (blue dots) for the echo signal frequency changes from 15 GHz − 100 kHz to 15 GHz + 100 kHz; (b) measurement errors when the transmit signal frequency changes from 5 to 30 GHz.