Application of optical forces in microphotonic systems

Optical forces represent an exciting new approach for manipulating microphotonic devices. In this thesis, the overall goal is to invent and demonstrate novel microphotonic device functionalities based on optical forces. There are two major tasks. One is to explore how optical forces can be used to achieve highly tunable, on-chip photonic devices. The other task is to utilize optical forces for light-assisted, template self-assembly of nanoparticles.;Optical forces are numerically investigated in different configurations. Attractive forces exist between a suspended one-dimensional periodic photonic crystal waveguide and underlying substrate in a silicon-on-insulator platform. It is shown that the optical force can be enhanced by designing the waveguide cross section to make the mode approach the band edge or substrate light line. For periodic waveguides, the optical force is non-monotonic with waveguide-substrate separation. This effect may enable the design of compact, integrated optical power limiters.;An analytical method is proposed to calculate optical forces between silicon waveguides based on the perturbation of effective index at fixed frequency. The method is used to investigate the mechanical Kerr effect in a coupled-waveguide system with bipolar forces. It is shown that positive mechanical Kerr coefficient results from either an attractive or repulsive force. An enhanced mechanical Kerr coefficient several orders of magnitude larger than the intrinsic Kerr coefficient is obtained in waveguides for which the optical mode approaches the air light line, given appropriate design of the waveguide dimensions.;Optical forces are proposed to tune phase and group birefringence in parallel silicon strip waveguides. Widely tunable phase and group birefringence can be achieved by varying the pump power, with maximum values of 0.026 and 0.13, respectively. The giant phase birefringence allows linear to circular polarization conversion within 30 microm for a pump power of 67 mW. The group birefringence gives a tunable differential group delay of 6 fs between orthogonal polarizations.;A novel photonic crystal lattice is proposed for assembling a two-dimensional array of particles by optical forces with low power. The lattice is created by introducing a rectangular slot in each unit cell of the Suzuki-Phase lattice to enhance the light confinement of guided resonance modes. Large quality factors on the order of 105 are predicted in the lattice. A significant decrease of the optical power required for optical trapping can be achieved compared to the previous design based on square lattice. Experiments are carried out to optically characterize the high-Q guided resonance modes with slot confinement. The evolution of the measured wavelengths and quality factors follows the trend predicted by the simulations.;The intrinsic, radiation loss of a coupled resonator optical waveguide (CROW) is studied by the tight binding approximation (TBA). The TBA predicts that the quality factor of the CROW increases with that of the isolated cavity. The results provide a method to design CROWs with low intrinsic loss across the entire waveguide band. The method may facilitate the design of large-area, coupled-cavity modes with high quality factor that nevertheless couple to normally-incident radiation for assembly.