  We demonstrate parametric all-optical modulation in a periodically-poled
lithium niobate microring resonator on chip. It employs quantum Zeno blockade
between two distinct waves, a signal and a pump, through their sum-frequency
generation at a large per-photon efficiency of 8.2 MHz. With nanosecond pump
pulses at 6 mW peak power, 85.7% modulation extinction is observed, marking
over 30~times efficiency improvement across various previous implementations.
With only 2 mW pump peak power, 43.0% modulation extinction is observed for a
doubly-stronger signal at 4 mW. This demonstrates, for the first time, that
optical transistors with cascadability and fan-out are possible with just
parametric nonlinear optics. These results, together with inherent advantages
in such photonic integrated circuits, open the door to scalable technology for
all-optical and quantum information processing.
