| Nanoscale optical waveguides and resonators are the building blocks of integrated optical network systems. With nano-fabrication technologies we are able to realize such devices that are strongly confined in sub-micron dimensions. For the optical design, we have developed an iterative effective index method since conventional optical waveguide theories cannot give satisfactory results in this case. We also obtained a general formalism for the wave reflection and transmission at dielectric interface without any approximation. The iterative effective index method combining with this general formalism can give more accurate results near mode cut-off region.; Experimentally, we have developed several nano-fabrication processes to achieve strong mode confinement in devices based on InGaAsP/InP material system. One is polymer wafer bonding. Another is deep dry etching. Based on the nano-fabrication processes, we have successfully fabricated microdisk lasers and MMI 3-dB couplers. We achieve lasing in both InNAsP/InGaAsP quantum well and InAs/GaAs quantum dot microdisk lasers. By using deep dry etching, we fabricated MMI 3-dB couplers with coupling length as short as 20 μ m with well-balanced outputs and very small polarization-dependence loss.; Waveguide-coupled microdisk resonators are also fabricated. We measure the propagation loss in the coupling waveguides. Single microdisk resonators fabricated by polymer wafer bonding process show large free spectral ranges and narrow linewidths. Deeply etched microdisk resonators show similar results but have higher scattering loss. Higher-order optical filters are designed by using cascaded microdisk resonators. We study their optical spectral responses both theoretically and experimentally. The results show that higher-order filters have much flatter passbands and faster rolloffs than the single microdisk resonators. These devices can potentially function as optical add-drop filters. |
