Che-Lung Hsu

Laser emission from GaN photonic crystals

In this study, photonic crystals have been designed, fabricated, and characterized in GaN bulk materials. The energy dependent measurement showed that the emission peak width can be significantly reduced as the pumping pulse energy was larger than 0.7μJ at room temperature. The mode at the wavelength of 371nm emitted from the defect due to the structure disorder unintentionally introduced during the fabrication process of the GaN photonic crystals can be obtained.

Bulk-micromachined optical filter based on guided-mode resonance in silicon-nitride membrane

In this paper, a single-layer guided-mode resonance (GMR) filter based on a free-standing silicon-nitride membrane suspended on a silicon substrate is achieved by using bulk-micromachining technology. Both of grating and waveguide structures without a lower-cladding layer, i.e., substrate, are fabricated simultaneously on a silicon-nitride membrane. The device can be used as a transmission bandstop filter with the advantages of simple structure, high efficiency, and feasibility to integrate with other optoelectronic elements into a microsystem chip. The design consideration, fabrication procedures, and measured spectral response are shown in this paper. Moreover, by stacking two proposed devices, /spl Delta//spl lambda/ of the stopband at a transmission below 10% is 5.06 nm.

Enhancing the resonance quality factor in membrane-type resonant grating waveguides

In this Letter, we present a method of reducing the spectral width of guided-mode resonance (GMR) in air-bridged resonant grating-waveguide structures to enhance the Q factor. The posttreatment of adding a dielectric film to the bottom of the membrane to manipulate the resonance behavior is practicable. The introduced underlayer is shown to be capable of effectively reducing the coupling and enhancing the resonant Q factor. The proposed method provides an effective means of adjusting the resonance property without varying the original GMR structure. The results also imply that TM resonance is more feasible for achieving narrow resonance and potentially in sensing applications, because it has higher sensitivity than TE resonance.

Authentication labels based on guided-mode resonant filters

A guided-mode resonance (GMR) filter with wide angular tolerances is experimentally demonstrated as an authentication label illuminated with unpolarized white light. The proposed filter, based on a free-standing silicon nitride membrane suspended on a silicon substrate, is fabricated by using anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both grating and waveguide structures without a lower cladding layer, i.e., a substrate, are fabricated simultaneously on a silicon nitride membrane. Since the silicon nitride is transparent within the spectra of visible and infrared light, such suspended-membrane-type GMR filters are well suited for applications within the visible spectrum. Moreover, the high refractive index of silicon nitride allows the proposed filters to have strongly modulated gratings and an immunity to high angular deviation. The measured reflection resonance has an angular tolerance up to +/-5 degrees under normal incidence for the wavelength of 629.5 nm.

Silicon-based and suspended-membrane-type guided-mode resonance filters with a spectrum-modifying layer design

The concept of a spectrum-modifying layer is proposed for the design of a silicon-based guided-mode resonance filter. To realize such a novel device, a grating and waveguide structures are fabricated simultaneously in a suspended silicon nitride membrane. The cladding layer of the silicon substrate is replaced by the silicon dioxide membrane to reduce the absorption loss of the bulky substrate. Moreover, the silicon dioxide membrane plays a role in modifying the spectral response. According to the experimental results of the proposed structures, symmetrical line shapes and improved sidebands of nonresonance are demonstrated.

Flattened Broadband Notch Filters Using Guided-Mode Resonance Associated With Asymmetric Binary Gratings

In this letter, the broadband notch filter exhibiting a flattened bandstop spectral response is experimentally demonstrated for the first time by using the guided-mode resonance associated with the periodic subwavelength structure possessing asymmetric binary grating profiles. The proposed filter consisting of grating and waveguide structures is realized by utilizing a single-layer poly-silicon film deposited on a quartz substrate. The asymmetric grating profile is carried out by dividing the one-filling-factor binary structure into the one with two distinct filling factors within one identical period. A flat bandstop spectral response at the central wavelength of 1.22 mum is obtained under normal incidence for transverse-electric polarization. Its transmittance of bandstop spectrum can be suppressed as low as -20dB within a broad spectral range of 85 nm and its corresponding Deltalambda/lambda is larger than 6%. The spectra under oblique incidence are demonstrated to verify the proposed filter has a high immunity for the angular deviation up to 20deg

Propagation loss reduction of photonic crystal slab waveguides by microspheres.

Dielectric microspheres are theoretically studied to reduce the propagation loss of Si-based photonic crystal slab waveguides. Two-dimensional photonic crystal formed by etched air hole can act as a template for microsphere sedimentation. The analytical results show that the transmission of the photonic crystal slab waveguides with microspheres can be enhanced to be around twice that without microspheres.

Experimental and Theoretical Demonstration of Resonant Leaky-Mode in Grating Waveguide Structure with A Flattened Passband

In this study, the first experimental demonstration of the strongly modulated refractive index of gratings with two distinct filling factors within one period is carried out for broadband guided mode resonance (GMR) filters. The proposed filters are realized by utilizing a single-layer poly-silicon film deposited on a quartz substrate. In order to clarify the unique features of strongly modulated gratings caused by subwavelength profiles with two filling factors in the lateral direction, dispersion relations and spectral responses are analyzed. A flattened bandstop spectral response of 85 nm with a transmittance of lower than -20 dB at a central wavelength of 1.22 µm and a high immunity to the angular deviation of incident wave up to 20° are experimentally obtained. Compared with the strongly modulated gratings achieved using longitudinal cascaded GMR filters, the proposed two-filling-factor gratings have a more compact design and are more suitable for further integration with other optoelectronic components.

Real-time monitoring DNA hybridization by guided resonant mode biosensor

In this paper, a label free approach of the DNA hybridization detection by the guided-mode resonance (GMR) spectroscopy sensor is presented. The GMR biosensor can easily detect any slight variation of the DNA hybridization by the resonant wavelength peak shift. The corresponding peak wavelength shifts of the capture DNA, the target DNA and the probe DNA serially hybridized reactions from GMR are measured, respectively. Furthermore, the stability and reliability of the GMR biosensor for nucleic acid hybridization have also been examined. The result obviously reveals the feasibility of implementation of the GMR-based DNA microarray for detecting on the dynamics of DNA hybridization.

Novel GMR-based biochip

For the detection of molecular interaction, a novel approach of the guided-mode resonance (GMR) spectroscopy identifies molecules via specific bindings with their ligands immobilized on the grating surface is presented. The structure of GMR device generally consists of two stages -- upper grating layer and waveguide layer. When the wide-band light illuminating, the GMR device inhibits on a specific resonant narrow-band of wavelength, and allows for other wavelength to transmit. The specific resonant narrow-band of wavelength results in the diffraction of the incident wide-band wave and the selection in the waveguide layer. This is very useful in highly sensitive measurement, especially for the variations in the refractive index of bulk media, and for the monitoring of variations in the thickness of thin film. In the simulation, one Si3N4 (n=2) GMR device is designed. When the wavelength of the illumination ranges from 1520nm to 1620nm, the resonant peak wavelength will shift 0.03nm as per 1nm bio-layer (nbio 1.3) has been attached on. Finally, on the basis of the theoretical analysis, the optimization of a spectral GMR sensor in terms of the operation wavelength has been carried out.