Thin-film lithium niobate dual-parallel Mach-Zehnder modulator for a simple photonic system measuring Doppler frequency shift

In recent years, thin-film lithium niobate (TFLN) electro-optic (EO) modulators have developed rapidly and are the core solution for the next generation of microwave photonics (MWP) problems. We designed and fabricated a dual-parallel Mach-Zehnder modulator (DPMZM) based on TFLN, achieving a 3 dB electro-electro (EE) bandwidth of 29 GHz and a low drive voltage (V pi = 6 V). The device we manufactured is metal-encapsulated. It is noteworthy that we proposed a single-channel Doppler frequency shift (DFS) measurement system based on this device and conducted verification experiments. We coupled light from an external laser into the chip and passed it through each of the two sub-MZMs of the DPMZM. These lights were modulated by echo signals and reference signals. By measuring the frequency of the output signal, we can obtain a DFS value without directional ambiguity. The success of this experiment marks a key step in the practical application of TFLN modulators in MWP.