Ming-Chang M. Lee

Thermal annealing in hydrogen for 3-D profile transformation on silicon-on-insulator and sidewall roughness reduction

A fast, effective process using hydrogen annealing is introduced to perform profile transformation on silicon-on-insulator (SOI) and to reduce sidewall roughness on silicon surfaces. By controlling the dimensions of as-etched structures, microspheres with 1 /spl mu/m radii, submicron wires with 0.5 /spl mu/m radii, and a microdisk toroid with 0.2 /spl mu/m toroidal radius have been successfully demonstrated on SOI substrates. Utilizing this technique, we also observe the root-mean-square (rms) sidewall roughness dramatically reduced from 20 to 0.26 nm. A theoretical model is presented to analyze the profile transformation, and experimental results show this process can be engineered by several parameters including temperature, pressure, and time.

MEMS-actuated microdisk resonators with variable power coupling ratios

A novel tunable microdisk resonator with microelectromechanical-system (MEMS)-actuated deformable waveguides is demonstrated for the first time. The deformable waveguide enables us to continuously vary the power coupling ratio of the microdisks. A laterally coupled device with a quality factor of 7700 is fabricated on silicon-on-insulator substrate. An optical notch filter with variable attenuation at the resonant wavelength is successfully demonstrated, with an extinction ratio of 9 dB. The MEMS-actuated tunable microdisk is a basic building block for many dynamic wavelength-division-multiplexing circuits.

Enhanced light outcoupling in a thin film by texturing meshed surfaces

The authors demonstrate a method of texturing a meshed surface on a poly(dimethyl siloxane) (PDMS) film for improving light extraction. This meshed surface is fabricated through a casting process by using a self-organized porous film as a template. Experimental results show that the light outcoupling efficiency increases on the meshed surface of a freestanding PDMS film with large incident angles. The external quantum efficiency of an organic light-emitting diode with the textured PDMS film was also demonstrated to have an enhancement of 46%.

Tunable coupling regimes of silicon microdisk resonators using MEMS actuators

Tunable coupling regimes of a silicon microdisk resonator controlled by MEMS (microelectromechanical system) actuation are demonstrated for the first time. By varying the gap spacing between the waveguide and the disk, this microresonator can dynamically operate in either under-, ciritcal or over-coupling regime. The waveguide transmittance is suppressed by 30 dB in critical coupling, and the quality factor of the microdisk is measured to be as high as 10(5). Additionally, the microdisk presents tunable group delay from 27 ps to 65 ps, and tunable group velocity dispersion from 185 ps/nm to 1200 ps/nm. Waveguides, microdisks and actuators are all integrated on a silicon-on-insulator (SOI) substrate. This compact device exhibits the promise to construct resonator-based reconfigurable photonic integrated circuits.

Silicon Microtoroidal Resonators With Integrated MEMS Tunable Coupler

A single crystalline silicon microtoroidal resonator with integrated MEMS-actuated tunable optical coupler is demonstrated for the first time. It is fabricated by combining hydrogen annealing and wafer bonding processes. The device operates in all three coupling regimes: under-, critical, and over-coupling. We have also developed a comprehensive model based on time-domain coupling theory. The experimental and theoretical results agree very well. The quality factor (Q) is extracted by fitting the experimental curve with the model. The unloaded Q is as high as 110 000, and the loaded Q is continuously tunable from 110 000 to 5400. The extinction ratio of the transmittance is 22.4 dB. This device can be used as a building block of resonator-based reconfigurable photonic integrated circuits

Extraction enhancement in organic light emitting devices by using metallic nanowire arrays

The extraction efficiency of organic light emitting devices is enhanced by depositing metallic nanowires on the glass surface and indium tin oxide (ITO) anode. For the aluminum tris-(8-hydroxyquinoline) (Alq3) based devices, a 100nm-width and 450nm-period gold nanowire array increases light extraction up to 46% from glass substrate and 80% from the organic layer. Such metallic nanowire arrays double the brightness with small absorption, only 10% lower than ITO glass. In addition, colors of the devices can be selected by the period of nanowire array. We demonstrated blue to red light emission by using single Alq3-based device.

Giant birefringence induced by plasmonic nanoslit arrays

Large phase differences between transverse electric (TE) and transverse magnetic (TM) waves were investigated in plasmonic nanoslit arrays. The phase of the TE wave shifts ahead because of its low propagation constant. On the other hand, the phase of the TM wave is retarded due to the propagation of surface plasmons. The opposite phase shift forms a giant birefringence. Its magnitude was dependent on the width of nanoslits. The birefringence magnitude was ∼1 for 300-nm-wide nanoslits and up to ∼2.7 for 100 nm ones. The spectroscopic measurements indicate that waveplates made of gold nanoslits have large bandwidths.

Study of anode work function modified by self-assembled monolayers on pentacene/fullerene organic solar cells

The authors investigated the anode work function modified by series of self-assembled monolayers comprising alkanethiols and perfluorinated alkanethiols with different alkyl lengths on pentacene/fullerene thin-film organic solar cells. Via selecting different types of self-assembled molecules, the anode work function can be tailored for modifying the interfacial barrier. The measured open-circuit voltages indicated reduced anode work function that tends to form Schottky contact. The maximal open-circuit voltage and short-circuit current were measured to be 0.4V and 17.7mA∕cm2, respectively, in the case of anode work function modified by perfluorinated alkanethiols. The power conversion efficiency is 2.24%.

MEMS-actuated photonic crystal switches

A compact guided-wave optical switch is realized by integrating one-dimensional photonic crystals with microelectromechanical systems (MEMS) actuators. The ON-OFF switching is achieved by physically moving a photonic crystal defect. Experimental results show an extinction ratio of 11 dB at 1.56-/spl mu/m wavelength and a 0.5-ms time constant of the step response.

Variable bandwidth of dynamic add-drop filters based on coupling-controlled microdisk resonators

Dynamic add-drop filters with variable bandwidth are demonstrated on microelectromechanical-system (MEMS)-actuated microdisk resonators for what is believed to be the first time. The tuning mechanism is based on a variable power coupling ratio that is controlled by varying the gap spacing between the waveguide and the microdisk through MEMS actuators. The results show wavelength switching with an extinction ratio of 20 dB and a tunable bandwidth ranging from 12 to 27 GHz. These dual functions were realized using the device with the operation voltage varying between 0 and 35 V.