Photonic integrated circuit (or chip) is the foundation of the ultra-high speed and large capacity information network in the future. This leads to a hot point of optical research in recent years that is how to excite the nonlinear optical effect in the case of low threshold (mW or pJ order) and small scale (μm or less). As is known to all, the nonlinear optical ef-fect is too weak to be excited under normal conditions. That is why the nonlinear optics failed to develop before the appearance of laser. In other words, how to excite the nonlinear optical effect in the case of low threshold and small scale is difficult. In recent years, researchers found that the nonlinear optical effect could be greatly enhanced in the photonic crystals (PCs) which are expected to solve this problem.