Hua-Kung Chiu

Output power enhancement of light-emitting diodes via two-dimensional hole arrays generated by a monolayer of microspheres

The output power enhancement of the GaN-based light-emitting diodes (LEDs) featuring two-dimensional (2D) hole arrays is demonstrated. The 2D air hole arrays were first generated in the photoresist by utilizing the focusing nature of microspheres, and then transferred onto the GaN surface through dry etching. The maximum output power of the surface-textured LEDs was enhanced by 45% compared with the LEDs without surface texturing. The finite-difference time-domain calculation was performed and revealed that the light extraction efficiency of the textured LEDs increased with increasing etching depth.

The Comparison Between the Graded Photonic Crystal Coupler and Various Couplers

The coupling between a dielectric waveguide and a photonic crystal waveguide is studied theoretically and experimentally. The coupling methods studied in this work include graded photonic crystal coupler, photonic crystal taper, waveguide taper, and parabolic mirror coupler. The properties of each coupler are discussed and compared.

Compact and low-loss bent hollow waveguides with distributed Bragg reflector

In this study, a hollow bent waveguide with distributed Bragg reflectors (DBR) in silicon substrate was presented theoretically and experimentally. We used the two-dimensional finite-difference time-domain method to simulate bending transmission efficiencies for arc- and cut-type 90 degrees -bent waveguides. The air core was embedded by Si(3)N(4)/SiO(2) multilayer. The multilayer stacks were deposited by using plasma-enhanced chemical vapor deposition on the top and bottom of air core. The lowest 90 degree bending loss is around 3.9dB for the arc-type bending waveguides and 0.8dB for cut-type bending waveguides, respectively. This waveguide demonstrates a possibility for higher density of integration in planar light wave circuits.

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.

Wavelength-selective filter based on a hollow optical waveguide.

In this paper, we describe a theoretical and experimental study of a wavelength-selective filter derived from hollow optical waveguides composed of Bragg reflectors with defect layers on a silicon substrate. The defect states of the transmission filter at wavelengths of 1519 and 1571 nm were realized using one-dimensional photonic crystals (1D PCs) formed from a-Si and SiO(2). The transmission spectra of the filter waveguides and the band structure of the defect 1D PCs were calculated using the two-dimensional finite-difference time-domain and transfer matrix methods, respectively. The device exhibited the narrow bandwidths of 0.5 and 1.1 nm for wavelengths of 1571 and 1519 nm, respectively.

Sharply bent hollow optical waveguides formed by an omni-directional reflector

In this work, we demonstrate theoretically and experimentally the air core bent optical waveguide composed of omni-directional reflectors on a silicon substrate. Amorphous silicon and silicon oxide are used for high index-contrast Bragg reflectors. The transmission efficiency of power for the bent optical waveguide with various bending angles of 1??90? is calculated by the two-dimensional finite-difference time-domain method and the three-dimensional beam propagation method. The sample is measured using the end-butt method. The device exhibits a lower polarization dependent loss at the operation wavelength of 1550?nm.

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