Self-collimation photonic-crystal-based modulator and switching elements in silicon

We design and characterize a photonic crystal (PhC) based silicon electro-optic modulator. The device is composed of a planar photonic crystal with associated input and output dielectric waveguides and a p-i-n diode to inject free carriers for index modulation. The photonic crystal, which confines light using the self-collimation phenomenon, has two regions of varying air hole diameters forming a defect area in a host self-collimation lattice. At the interface of the defect with the host lattice, an impedance mismatch is formed which is modulated using free carrier injection. With sufficient index modulation the impedance mismatch is large enough to decrease the transmission through the defect region, thus, modulation the overall transmission of the device. Our analysis shows that with a doping concentration in the range of 1020/cm3, the injected free carrier concentration can exceed 2.5*1019 with a drive voltage of 2.6 V. This free carrier concentration is sufficient to modulate the refractive index, Δn, greater than .05, which in turn produces a modulation depth greater than 75%. A fabricated device produces a modulation depth of 80% with a drive current of 4mA.