Polarization-insensitive electro-optic modulator based on thin-film lithium niobate multimode waveguide

We demonstrate a polarization-insensitive electro-optic (EO) modulator based on x-cut thin-film lithium niobate (TFLN), employing capacitively loaded traveling-wave (CLTW) electrodes on an undercut-etched silicon substrate. By converting the TM0 mode into a higher-order TE1 mode via adiabatic mode converters and modulating both TE0 and TE1 modes simultaneously in a multimode Mach–Zehnder interferometer, polarization-insensitive modulation is achieved without duplicating modulators or control circuits. The fabricated device exhibits a polarization-dependent loss (PDL) of 2.2 dB, a modulation efficiency of VπL = 3.12 V cm, and a 3-dB EO bandwidth of 43 GHz for both modes. High-speed data transmission is experimentally verified with clear eye diagrams up to 100 Gb/s (OOK) and 112 Gb/s (PAM-4) for both polarizations. These results highlight the feasibility of dual-mode modulation for polarization-insensitive interconnects and support its potential for deployment in co-packaged optics (CPO) and remote external light sources related transmitter systems.