All-optical analog-to-digital converters based on a thin-film lithium niobate modulator and a star coupler

In this paper, a phase-quantization all-optical analog-to-digital converter (ADC) scheme is proposed and experimentally demonstrated using a thin-film lithium niobate (TFLN) Mach–Zehnder modulator (MZM) and a star coupler, overcoming the limitations of traditional phase-shift quantization approaches where increasing output ports leads to significantly higher design complexity. With the TFLN MZM integrated, the fabricated device supports up to 40 GHz analog input at 100 GS/s sampling rate. Specifically, within the dynamic range, the demonstrated all-optical ADC device achieves an effective number of bits (ENOB) of 5.07 bits for triangular waves and 4.4 bits for sinusoidal waves at low-speed testing (1 MHz). For high-speed testing, 1.25 GHz triangular and arbitrary analog input waveforms are successfully recovered and the corresponding ENOBs are 4.2 bits and 3.9 bits. Moreover, the proposed all-optical ADC scheme demonstrates strong scalability—when the input voltage exceeds the dynamic range, additional quantization levels can be algorithmically recovered and an ENOB of 5.8 is experimentally observed.