  We demonstrate the efficient coupling (99.5%) of a silica whispering gallery
mode microresonator directly with a silicon chip by using a silicon photonic
crystal waveguide as a coupler. The efficient coupling is attributed to the
small effective refractive index difference between the two devices. The large
group index of the photonic crystal waveguide mode also contributes to the
efficient coupling. A coupling Q of 2.68*10^6 is obtained, which allows us to
achieve the critical coupling of a silica whispering gallery mode with an
intrinsic Q of close to 10^7 with a Si chip.
