Photonic quantization and encoding scheme with improved bit resolution based on waveform folding.

Taylor's scheme for photonic quantization and encoding based on Mach-Zehnder modulators (MZMs) requires that the employed MZMs have geometrically scaled half-wave voltages (Vπ), which is impractical even with the state-of-art photonic fabrication techniques when the desired bit resolution is greater than 3 or 4 bits. The approaches based on the phase-shifting of modulation transfer functions eliminate the need of geometrically scaled Vπ, but they realize lower resolution than Taylor's scheme as the realized resolution is log2(2N), but not N as in Taylor's scheme, where N is the number of optical channels (or MZMs). In this paper, we propose a novel photonic quantization and encoding scheme based on waveform folding using rectifier circuits, which aims to realize higher resolution with less MZMs (and less Vπ). In our design, a 4-bit quantization can be achieved using 2 MZMs with identical Vπ with the help of two rectifiers. A proof-of-concept experiment is implemented, which fully verifies the correctness of the approach. The scheme is modular extendable, i. e. an 8-bit quantization can be realized by using 4 MZMs (with 2 different Vπ), and 12-bit can be realized by using 6 MZMs (with 3 different Vπ). The impact of the rectifiers' bandwidth on the system performance is also investigated. As less MZMs are employed and lower requirement on Vπ scaling, the proposed design provides a promising solution for high-performance photonic analog-to-digital conversion.

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