Photonic analog-to-digital converter based on the robust symmetrical number system

A novel approach to realizing photonic analog-to-digital conversion with Gray-code-like property is proposed and demonstrated. Instead of using Mach-Zehnder modulators (MZMs) with different half-wave voltages, an array of MZMs with identical half-wave voltages are applied to realize quantization and encoding, which greatly simplifies the implementation. Multiple comparators with preset thresholds are applied at the output of each MZM to improve the number of bits. Through properly setting the bias voltages of the MZMs, a photonic analog to digital converter (ADC) based on the robust symmetrical number system (RSNS) coding method is realized. As an example, a 3-channel structure with maximum quantization level of 17 (corresponding to 4.09 bits) is investigated in detail. We show that the differential encoding technique can be applied in the proposed structure, which increases the equivalent number of bits of the ADC system.