Investigation of Semiconductor Quantum Dots for Waveguide Electroabsorption Modulator.

In this work, we investigated the use of 10-layer InAs quantum dot (QD) as active region of an electroabsorption modulator (EAM). The QD-EAM is a p-i-n ridge waveguide structure with intrinsic layer thickness of 0.4 mum, width of 10 mum, and length of 1.0 mm. Photocurrent measurement reveals a Stark shift of ~5 meV (~7 nm) at reverse bias of 3 V (75 kV/cm) and broadening of the resonance peak due to field ionization of electrons and holes was observed for E-field larger than 25 kV/cm. Investigation at wavelength range of 1,300-1320 nm reveals that the largest absorption change occurs at 1317 nm. Optical transmission measurement at this wavelength shows insertion loss of ~8 dB, and extinction ratio of ~5 dB at reverse bias of 5 V. Consequently, methods to improve the performance of the QD-EAM are proposed. We believe that QDs are promising for EAM and the performance of QD-EAM will improve with increasing research efforts.

Fabrication of ultralow-loss Si/SiO(2) waveguides by roughness reduction.

We demonstrate 0.8-dB/cm transmission loss for a single-mode, strip Si/SiO(2) waveguide with submicrometer cross-sectional dimensions. We compare the conventional waveguide-fabrication method with two smoothing technologies that we have developed, oxidation smoothing and anisotropic etching. We observe significant reduction of sidewall roughness with our smoothing technologies, which directly results in reduced scattering losses. The rapid increase in the scattering losses as the waveguide dimension is miniaturized, as seen in conventionally fabricated waveguides, is effectively suppressed in the waveguides made with our smoothing technologies. In the oxidation smoothing case, the loss is reduced from 32 dB/cm for the conventional fabrication method to 0.8 dB/cm for the single-mode waveguide width of 0.5 microm . This is to our knowledge the smallest reported loss for a high-index-difference system such as a Si/SiO(2) strip waveguide.

Pedestal antiresonant reflecting waveguides for robust coupling to microsphere resonators and for microphotonic circuits.

Strip-line pedestal antiresonant reflecting waveguides are high-confinement, silica integrated optical waveguides in which the optical modes are completely isolated from the substrate by thin high-index layers. These waveguides are particularly well suited for whispering-gallery mode excitation in high-Q microspheres. They can also be used in microphotonic circuits, such as for microring resonators. The theory and design of these structures are highlighted. Experiments that show high coupling efficiency to microspheres are also demonstrated.

Planar integrated wavelength-drop device based on pedestal antiresonant reflecting waveguides and high-Q silica microspheres.

Whispering-gallery modes in silica microspheres can be accessed very efficiently with the recently introduced stripline pedestal antiresonant reflecting optical waveguide (SPARROW) structure. This integrated-optics coupling technique creates novel application opportunities for the high-Q spherical cavities. We report the demonstration of a narrow-band wavelength-drop configuration utilizing SPARROW waveguides and a silica microsphere.