Photonic crystal all-optical diode is an important mesoscopic photonic device, and has potential applications in fields of optical computing, optical interconnection systems, and integrated photonic circuits. Low operating power and high transmission contrast are the two key characteristics for photonic crystal all-optical diodes. Owing to the relatively small nonlinear optical coefficients of the conventional optical materials, the operating threshold power is rather high with the threshold intensity of several hundreds GW/cm². Moreover, the transmission contrast was achieved as less than 100. This has greatly restricted the practical applications of photonic crystal all-optical diodes.

Gong’s group has used a new mechanism for constructing photonic materials with large nonlinear optical coefficients: combining the strong plasmonic response of metal nanoparticles and the strong photon confinement effect of photonic crystal microcavity to achieving a large nonlinear susceptibility. The nano-Au:MEH-PPV nanocomposite photonic crystal microcavity with a very large third-order nonlinear susceptibilities are fabricated based on this mechanism. The prototype device of photonic crystal all-optical diode is realized based on the effect of surface-plasmon resonance enhancing optical nonlinearity and dynamic coupling of asymmetrical microcavity modes. An ultralow threshold photon intensity of 2.1 MW/cm²and an ultrahigh transmission contrast over 104 are realized simultaneously. Compared with previously reported all-optical diodes, the operating threshold power is reduced by five orders of magnitude, while the transmission contrast is enlarged by three orders of magnitude.

This work can not only improves the process of the practical applications of mesoscopic photonic devices including all-optical diode, but also provides a new approach for the study of nonlinear photonic materials.

The work was supported by the Creative Research Group Project of the National Natural Science Foundation of China, and the National Basic Research Program of China.

Figure: (Left) SEM image of nano-Au:MEH-PPV nanocomposite photonic crystal microcavity; (Right) All-optical diode effect.