Optical-gradient-force–induced nonlinearity in coupled microcavities

The nanosuspension is a stable solid-liquid hybrid fluid formed by suspending solid nanoparticles in a liquid. Based on nanosuspension, an optical-gradient-force–induced optical nonlinear characteristics in a coupled microcavities is theoretically investigated. Under high incident power, the nanoparticles that are in one of the cavities redistribute themselves leading to a significant change of the effective refractive index. The consequence of the redistribution is investigated by solving the nonlinear coupled mode theory equations. Both nonreciprocal transmission and bistability are observed due to disparate forward and backward incident field intensities in the coupled microcavities. Furthermore, the numerical simulation shows details of the mode interaction within the coupled microcavities, and agrees well with the theoretical modeling. This work demonstrates the viability of nanoparticle-mediated nonlinearity in microscale optical systems. The findings open more possibilities for light manipulation in sophisticated microfluidic systems and beyond.