Wen-Tse Hsiao

Fabrication of a double-sided micro-lens array by a glass molding technique

In recent years, micro-lens arrays (MLAs) have become important elements of optical systems. One function of MLAs is to create a uniform intensity of light. Compared with one-sided MLAs, the uniformity of light intensity increases with double-sided MLAs. MLAs fabricated by glass can be used in higher temperature environments or in high-energy systems. Glass-based MLAs can be fabricated by laser machining, photolithography, precision diamond grinding process and precision glass molding (PGM) technologies, but laser machining, photolithography and precision diamond grinding process technologies are not the perfect approach for mass production. Therefore, this paper proposes a method to fabricate a mold by laser micro-machining and a double-sided MLA by a PGM process. First, a micro-hole array was fabricated on the surface of a silicon carbide mold. A double-sided MLA using two molds was then formed by a PGM process. In this paper, the PGM process parameters including molding temperature and molding force are discussed. Moreover, the profile of a double-sided MLA is discussed. Finally, a double-sided MLA with a diameter of 20 mm, and lenses with a height of 52 µm, a radius of 851 µm and a pitch of 700 µm were formed on glass.

The evaluation of blood flow velocity and heart rate by the frequency of oxygen saturation fluctuation in skin tissue

The oxygen in human body is transported by the hemoglobin and blood, and blood flow velocity (BFV) was related to the heart rate (HR); therefore, the oxygen saturation image of human skin can be used to evaluate the HR and BFV of human. When irradiating two different wavelengths light alternately and repeatedly, the frequency of oxygen saturation (SpO2) fluctuation (fc) can be obtained from the Fourier transformation of SpO2 images, and roughly applied to build the relationship between BFV and HR. In the experiment, a high speed light controller was employed to switch two LED light source (red-660 nm and NIR-890 nm). Due to the penetration depth of incident light increases with increasing wavelength, and the deoxy-hemoglobin (Hb) and oxy-hemoglobin (HbO2) has a relatively high absorptivity in visible and near-infrared (NIR) spectrum, respectively; the intensity of diffuse reflected images of skin can be used to compute the oxygen saturation images of skin tissue. The experiments show the SpO2 after 3 minutes exercise would decrease 3 % and recover in 100 seconds, and the SpO2 after 30 minutes exercise increased 1.5 % and became stable in 3 minutes. Simultaneously, the HR and BFV have the linear relationship to the frequency of SpO2 fluctuation (fc), so both two physiological indexes can be directly evaluated by SpO2 images.

Dynamic Behaviors Analysis of the Aerostatic Linear Guideway with a Passive Compensator for PCB Drilling Machine

Externally pressurized gas-lubricated linear guideway has been successfully used in the PCB drilling machine. In this paper, we analyze the performance of the grooved aerostatic thrust bearing with passive compensator and the dynamic behaviors of aerostatic linear guideway with compensating aerostatic thrust bearings. The Newmark integration method and the modified resistance network method (RNM), which consider the equilibrium of mass flow rate and the squeeze film effect, use to analyze the time-dependent dynamic behaviors. The results indicate that the passive compensator could maintain the thrust bearing in the suitable film gap. Therefore, the aerostatic linear guideway could achieve accurate straight motion and reduce vibration amplitude.

Surface Formation of Nano- / Micro- Structures on Titanium Alloy Composites using Picosecond Laser Scanning Technology

This study reports on the development of picosecond laser system to titanium alloy surface treatment applications. In the picosecond laser-scanning system, that is based on the fiber-optics laser source and integrated with a designed optics / optical machine design and control technology of scanning system. To analyze the laser material interaction, the laser fluence, pulse repetition frequency of laser source, position of focused points, scan speed and pulse duration were adjusted. After laser surface treatment, the surface roughness and surface morphologies of treated surface were evaluated by using a field emission scanning electron microscope. Moreover, the contact angle measurement was used to analyze the hydrophilic and hydrophobic properties of the treatment surface with micro/ nanostructures.

Laser Micro-Structuring on Glass Substrates with Compensation Function for Multi-wavelength Mixed Laser Diode Module

A glass substrate has excellent optical transmittance for the visible spectrum (400–700 nm). This study used three type glass (D263TTM, EAGLE XG○,R, and BK7) for laser micro-structuring in the light compensation technique applied to a multi-wavelength mixed light module. An ultraviolet laser system combined with a high-speed galvanometric scanner was used to fabricate microstructures on the specimen surface. The light compensation chromaticity properties of the microstructures on glass substrates depended on the laser machining conditions. The characteristics of the machined glass were systematically analyzed using a spectrophotometer and charge-coupled device camera. The experimental results demonstrate that the microstructures affected chromaticity under different laser micro-structuring pitches.

Inspection of Laser Ablated Transparent Conductive Oxide Thin Films by a Multifunction Optical Measurement System

In recent years, laser ablation method has been increasingly used in the touch panel industry. Touch panel devices are produced by applying laser ablation process on transparent conductive oxide (TCO) thin films coated on glass substrates. The pattern and the surface profile of the transparent conductive layer on glass substrates after laser ablation are crucial on the quality of the touch panel. Therefore, a self-assembled multifunction optical measurement system was employed to investigate the details of the surface of the test specimen of the TCO thin films after ablation. The system integrates both optical microscope and white-light scanning interferometer to inspect the specimen under the same field of view. The transparency of the test specimen was inspected by the optical microscope to examine the uniformity of the gray levels throughout the ablated region. The depth of the ablated thin films and whether the thin films are fully cut can be determined from the surface profile obtained from the white-light scanning interferometer. Based on the aforementioned experimental results, the self-assembled multifunction optical measurement system is full of potential to be used to determine the manufacturing parameters in laser ablation process.

Effects of UV laser milling parameters on the profile cutting of Gorilla glass substrates

The purposes of this study were to develop a high-speed milling system combined with an ablation path of the parallel lines and to investigate the cut quality on the glass substrates conducted by a nanosecond pulsed Nd:YVO4 laser (λ:355 nm). Experimental specimens were commercial Corning Gorilla glass with a thickness of 800 μm. Laser milling parameters including the laser fluence, number of milling pass, and scan speed of galvanometers along the processing path were adjusted for the profile cutting of the glass substrates. The laser milled depth, surface morphology, and surface roughness of the glass substrates after laser milling were measured by a 3D confocal laser scanning microscope. Experimental results showed that the milled depth outstandingly increased as increasing the laser fluence and the number of milling pass or decreasing the scan speed of galvanometers. The milled depths averagely increased from 38 μm to 107 μm when the scan speed of galvanometers decreased from 1500 mm/s to 300 mm/s with the laser fluence of 52 J/cm2 in a one-cycle milling process. Moreover, the milled depths averagely increased from 107 μm to 185 μm when the laser fluence decreased from 54 J/cm2 to 95 J/cm2 with the scan speed of galvanometers of 300 mm/s. When the number of milling pass increased to 5 with the laser fluences of 95 J/cm2 and scan speed of 300 mm/s, the Gorilla glass substrate was cut through a square hole. The edge of milled hollow square structures on the glass substrate had few of micro cracks, square angles, and steep and oblique walls around the milled boundaries as increasing the number of milling pass. In addition, the value of surface roughness increased with increasing the numbers of milling pass.

Parameters optimization of laser electrode patterning on ITO/glass using multi-performance characteristics analysis

The objective of this study was to obtain the optimal parameters for laser electrode patterning of indium-tinoxide (ITO) films coated on soda lime glass substrates; the parameters were determined through grey relational analysis. The electrode patterning parameters affecting the sheet resistance and optical transmittance of the film include the laser power, pulse repetition frequency, pulse duration, and focus point position. Multiple performance characteristics associated with the sheet resistance and optical transmittance were investigated by conducting experiments. An infrared (1064 nm) laser system was used to directly fabricate electrode patterns on ITO films, and the characteristics of the patterned films were systematically analyzed using an ultraviolet-visible-near-infrared spectrophotometer and a four-point probe instrument. The data obtained from the experiments were analyzed to optimize the laser patterning parameters correlated with multiple performance characteristics.

Dual photoresist complimentary lithography technique produces sub-micro patterns on sapphire substrates

Dual photoresist complimentary lithography technique consisting of inorganic oxide photoresist and organic photoresist is applied to produce the sub-micro pit patterns on a sapphire surface. The oxide photoresist is patterned by the direct laser writing and the developed mark size decreases to a smaller value than the laser spot size due to the thermal lithography. The small developed pit diameter is one of the advantages using oxide photoresist. The oxide photoresist possesses strong etching resistance against the oxygen plasma but shows no resistance against the chlorine plasma. The chlorine plasma is a necessary component to etch the sapphire during the ion-coupled-plasma reactive-ion-etching process because of sapphire’s mechanical hardness and chemical stability. However, the characteristics of organic resist SU8 are opposite to that of oxide photoresist and possess moderate resistance against chlorine plasma but show no resistance to oxygen plasma. The thermal and developing characteristics of oxide photoresist are reported here. The dependence of the laser power on the developed mark sizes and morphologies is illustrated by atomic force microscopy. The temperature distribution on the photoresist structure during the laser writing is simulated. Images of patterned pits on the large commercial sapphire substrates are also shown.

Dual-photoresist complementary lithography technique for the formation of submicron patterns on sapphire substrates

Abstract. Dual-photoresist complementary lithography technique consisting of inorganic oxide photoresist and organic photoresist is applied to produce the submicron pit array patterns on a sapphire surface. The oxide photoresist is patterned by direct laser writing, and the developed pit size decreases to a smaller value than the laser spot size due to the thermal lithography. The oxide photoresist possesses strong etching resistance against oxygen plasma but shows no resistance against chlorine plasma. During the ion-coupled-plasma reactive-ion-etching process, chlorine plasma is a necessary component to etch the sapphire. Moreover, the characteristics of organic resist are opposite those of oxide photoresist and possess moderate resistance against chlorine plasma but no resistance against oxygen plasma. The thermal and developing characteristics of oxide photoresist are reported in this study. The dependence of laser power on the developed mark sizes and morphologies is examined by atomic force microscopy. The temperature distribution on the photoresist structure during the laser writing is simulated, and the thermal lithography concept is introduced to explain the effect of power on the developed oxide mark width. Images of patterned pit array on a commercial 4-inch-diameter sapphire substrate are also shown.