Enhanced bandwidth performance in Michelson interferometer modulator via a combination of micro-structured electrodes and Bragg grating reflector

The Michelson interferometer (MI) modulator is a folded-type modulator with significantly reduced dimensions because of the doubled effective interaction length between the transmitted light and modulation signal. However, the folded structure also exacerbates the velocity mismatch, which limits the bandwidth of the MI modulators. In addition, the relatively large footprint of the reflector also hinders further miniaturization of MI modulators. Herein, we propose a new type of modulator that incorporates both a microstructured electrode and a Bragg grating reflector. Based on the thin-film lithium niobate (TFLN) platform, the proposed MI modulator was successfully fabricated. Owing to the application of microstructured electrodes, the microwave loss is reduced to only 1 dB/cm at 50 GHz, indicating an enhanced modulation bandwidth. Meanwhile, the footprint of the reflection region was reduced to 36 μm using a Bragg grating reflector, which is one-tenth that of the loop mirror. Finally, the proposed MI modulator demonstrates a high 3 dB bandwidth (beyond 60 GHz), a low half-wave length product (1.45 V cm), and a significantly enhanced voltage-bandwidth performance (approximately 2.58 GHz V−1), indicating a great potential for applications in future optical interconnection modules, where lower microwave loss and higher integration are urgently needed.