1.1-cm-long-thin-film lithium niobate Mach-Zehnder modulator with low driving voltage integrated by micro-transfer printing

The heterogeneous integration of thin-film lithium niobate (TFLN) provides energy-efficient broadband optical modulation of photonic platforms. Micro-transfer printing (µ-TP) yields dense integration of heterogeneous materials and cost-effective photonic integrated circuits. However, the reports so far have considered unpatterned slab membranes for the structure of the µ-TP integrated TFLN, and the short interaction length increases the driving voltage. In this study, the µ-TP of pre-structure-defined TFLN Mach-Zehender (MZ) interferometer was demonstrated for up to 1.1 cm with propagation loss of 0.7 dB/cm. The TFLN MZ modulator integrated on a silicon substrate using µ-TP exhibited the lowest driving voltage Vπ of 2.7 V and a modulation bandwidth of 28 GHz with a low insertion loss of 0.97 dB. In addition, modulation frequencies exceeding 50 GHz and Vπ of 8.9 V were demonstrated in a device with 3-mm-long electrodes.