Fig. 1. (a) Schematic diagram of the sampling and quantization process based on our proposed phase-shifted optical quantizer. (b) The initial and (c) optimized structures of MMI. The y-coordinates of the green points on the boundary are parameters for shape optimization. (d) Quantization curves and (e) quantization codes of the ideal optical quantizer. (f) FOM/Target convergence curve. The inset is the boundary curve of the optimized MMI.

Fig. 2. Initial electric field profiles at 1550 nm for (a) one input light and (b) two input lights. The optimized electric field profiles at 1550 nm for (c) one input light and (d) two input lights.

Fig. 3. (a) Simulated transmittance curves of the 5 output ports at 1550 nm. (b) IL, (c) uniformity, and (d) ENOB of the initial and optimized optical quantizers.

Fig. 4. (a) IL, (b) uniformity, and (c) ENOB of the optimized optical quantizer for various values of width (ΔW = −40, 0, and 40 nm). The changes in width cause small shifts of the center wavelength.

Fig. 5. Microscopic images of the fabricated devices. (a) The system structures of the optical quantizers with (b) the initial and (c) the optimized MMIs.

Fig. 6. (a) Measured transmittance curves of the initial and optimized optical quantizers at 1550 nm. Transfer functions and ideal values for (b) the initial and (c) the optimized optical quantizers at 1550 nm. (d) IL, (e) uniformity, and (f) ENOB of the initial and optimized optical quantizers.