Dong-Po Cai

High Q-factor microring resonator wrapped by the curved waveguide.

In this work, we study the performances of ring resonators of different type by analyzing the bending loss and the condition of the critical coupling. We propose that the bending loss of microring can be reduced by wrapping a concentrically curved waveguide. The difference of propagation constant between two concentrically curved waveguides can be tuned by adjusting the bus waveguide width to optimize the critical coupling. Furthermore, we propose to enlarge the difference of the propagation constant between two concentrically curved waveguides to maintain the circulating light in the ring to obtain higher quality factor. In this study, the highest quality factor that we measured is 7 × 105.

Electrically tunable liquid crystal waveguide attenuators

The attenuator is fabricated by infiltrating liquid crystal (LC) E7 into hollow waveguides (HWGs). The attenuation of device is over 30 dB. The performance of device is independent of the polarization states of input light.

Liquid crystal infiltrated waveguide with distributed Bragg reflectors

The optimal design of liquid crystal infiltrated waveguide with distributed Bragger reflector is realized to confine the optical waves. The bandgap structure and propagation behavior of visible light is calculated to investigate propagation loss, polarization dependence transmission and wavelength tuning property.

Study of Coupling Length of Concentrically Curved Waveguides

In this paper, we propose a method based on Helmholtz equation to determine the coupling length of the light propagating in concentrically curved waveguides by the conformal transformation. After the transformation, the concentrically curved waveguides are regarded as straight directional couplers, and the coupling length can be obtained rapidly by using this method. We also calculate the coupling length by the finite-difference time-domain (FDTD) method to compare with the result obtained by our method. The results show a good agreement between the coupling length obtained by the conformal transformation and the FDTD method.

Compact pulley-type microring resonator with high quality factor

A pulley-type microring resonator with ultra-small dimensions and ultra-high quality factor on a silicon-on-insulator wafer is fabricated and characterized. Simulation results show that the bending loss of the pulley-type microring resonator can be diminished by wrapping the curved waveguide around the microring, and that the energy loss from the output port can be decreased by tuning the width of the bus waveguide to achieve destructive interference. A quality factor of 1.73 × 105 is obtained in this experiment. The compact size of the pulley-type microring resonator with low bending loss is suitable for an integrated optical circuit.

Photonic Crystal Cavity With Double Heterostructure in GaN Bulk

In this study, the photonic crystal cavity has been designed, fabricated, and characterized in GaN bulk materials with the double heterostructure, which can provide high Q-factor. The cavity is characterized by optical pumping. The resonant mode is observed at the wavelength of 362 nm. The threshold of excitation power is found to be 0.9 mW, corresponding to the power density of 12.7 kW/ cm2 . The Q-factor of the cavity is measured to be as high as 104.

Nano-magnetic-field generator using surface plasmon polaritons

We propose a magnetic field generator using surface plasmon on a metallic microring. The positive charge is excited on the metallic microring. The propagating surface plasmon drives the charge flow to generate the magnetic field.

Pulley-type ring resonator and optimization

In this work, we propose a guideline to design the high Q-factor ring resonators. To keep the optical energy in the ring, the radiation loss of the ring should be reduced. The difference of the propagation constant between the bus waveguide and the ring should be enlarged to prevent from the light in ring to be coupled back to the bus waveguide. The phase difference of the light between the bus waveguide and ring should be adjusted to obtain the destructive interference at the output port (critical coupling). From these points mentioned above, we compare the 6 types of ring resonators. We conclude that the high Q-factor pulleytype ring resonator can be more easily designed. The experimental Q-factor of the pulley-type ring resonators with ring radius of only 4.43µm can be obtained up to 1.73×105.

Genetic algorithms optimization of photonic crystal fibers for half diffraction angle reduction of output beam

In this work, we optimize the structure of the photonic crystal fibers by using genetic algorithms to provide strong light confinement in fiber and small half diffraction angle of output beam. Furthermore, this article shows the potentials of this study, such as optimizing three purposes at the same time and the arbitrary structure design is achieved. We report two optimized results obtained by different optimization conditions. The results show that the half diffraction angle of the output beam of the photonic crystal fibers can be reduced.

Hollow waveguide modulators by infiltrating liquid crystal

In this work, we fabricate the liquid crystal waveguides by infiltrating liquid crystal E7 into hollow waveguides (HWGs) with SiO2 cladding layer. The reorientation of the high susceptibility of liquid crystals molecular is achieved by applying the external fields to change the optical characterization of the liquid crystal waveguides. By applying external voltage to SiO2-cladded HWGs, the output intensity decreases with the voltage. The devices can serve as an electrically tunable liquid crystal switch with over 30dB attenuation at 4∼5 Vpp