Photonic crystal has attracted extensive interest in the past 25 years due to its great power to mold the flow of light in micrometer/nanometer scale and promising aspects in building all-optical integrated devices and circuits. In this talk we present our recent efforts of design, fabrication, and characterization of integrated optical elements and devices in infrared silicon two-dimensional photonic crystal slabs. These devices operate either on band gap confinement or on band dispersion control. We focus on topics such as the broad-band wide-angle self-collimation effect, on-chip optical diodes and isolators, new cavities without apparent confinement barriers, and polymer-silicon hybrid nonlinear photonic crystal.