We experimentally demonstrated an optical phase shifted quantizer using a cascade step-size MMI (CS-MMI), which was fabricated on a commercially available 220-nm SOI platform via multi-project wafer (MPW) process. An experimental setup was built to test the ability of the CS-MMI acting as a quantizer. The experimental results show that the proposed CS-MMI-based quantizer has an effective number of bit (ENOB) of 3.31bit, which is a little slighter than the ideal ENOB of 3.32bit. The operation range is 12 nm for ENOB≥3 bit. Moreover, the insertion loss of the CS-MMI is −1.26 dB at 1560 nm, the performance of the fabricated device agrees well with simulation results.

An optical analog-to-digital converter (OADC) scheme with enhanced bit resolution by using a multimode interference (MMI) coupler as optical quantization is proposed. The mathematical simulation model was established to verify the feasibility and to investigate the robustness of the scheme. Simulation results show that 20 quantization levels (corresponding to 4.32 of effective number of bits (ENOB)) are realized by using only 6 channels, which indicates that the scheme requires much fewer quantization channels or modulators to realize the same amount of ENOB. The scheme is robust and potential for integration.