Photonic multi-threshold comparator based on Mach-Zehnder modulator

A new photonic approach of multi-threshold comparator based on Mach-Zehnder modulator is proposed and experimentally demonstrated. Unlike previous methods, we avoid the use of electronic comparators. The comparator consists of two modulators, one of which provides a sinusoidal transmission curve and the other modulator biased at quadrature point shapes the sinusoidal transmission curve to a square transmission curve. The theoretical analysis and simulation are developed. The comparator stands out for its simple structure, cost-effectiveness, and the flexibility to adjust the threshold. The transmission curve of the comparator exhibits flat tops and bottoms with a relatively steep slope between them, closely resembling the ideal comparator with a fitting degree of 0.82; thus may be used to construct multi-bit analog-to-digital convertors.