Key Engineering Materials Vols. 364-366

Abstract: A novel design of triple-wavelength design for a compact optical pickup head is presented here. We propose the use of two rhomboid beam-splitter prisms for HD-DVD, DVD and CD devices to align signals with three different wavelengths on the same optical axis. The light is collimated by a collimating lens. The parallel beams are incident on the wavelength selector. The wavelength selector separates the wavelengths with different numerical apertures. The different wavelength signals are focused on the disc by an objective lens.

Abstract: This paper has partitioned the laser range-finder into two parts: one is the laser diode (LD) driver circuit and the other is the focusing lens. The LD’s surface temperature rise will affect the LD’s light-power simultaneously when an LD works in a steady current. For this reason, we designed a driver circuit to control the LD’s light power to be effective and so as to freely adjust the LD’s brightness. There are three parts in driver circuit: the regulated power circuits, the regulated current circuit, and the limited current circuit. This investigation used a power meter to measure the LD’s power which was relative to the surface temperature. Then the experimental results were compared with the PSpice simulation, and the differences between the result and the simulation were eventually analyzed. The limited current circuit is an important part in our systems because the LD is easily damaged when active current is unstable. Similarly, the surface temperature would be raised after the LD is working for a while which results in the circuit failure. If the LD has worked for a very long time, the heat generated in the circuit should be taken care of. Therefore, we added an automatic power control circuit (APC) into the LD driver circuit in order to reduce the impact of heat. The emitted distance of laser beam could be up to 10 meters with adjusted focusing lens. The laser spot was extended into an ellipse before focusing laser beams. Therefore, we had to put a focal lens to shape the the laser spot into a circular spot. During this experiment, the LD did not work directly without installing the heat sink. Otherwise, the high temperature would damage LD immediately.

Abstract: The optimization of the directly-under-light type backlight module structure for brightness uniformity is investigated. All structure parameters of the 32-inch LCD-TV backlight module are chosen by the ray-tracing method for the optimal brightness uniformity. It is shown that the brightness uniformity without optical sheets can be made as high as 87.3%.

Abstract: This study discusses optimization of the adiabatic optical directional coupler (AODC) based on sin-square weighting functions (SSF) for waveguide structure. The objective of the work includes the define coupler of theory ranges, low crosstalk and short coupler length, respectively. When the crosstalk is demanded to be smaller than -35 dB, the coupler length for SSF is 2 b0 λ (minimum local beat length). Definitely SSF which is proposed can obtain a better result after the structural design.

Abstract: V-grooved quartz substrates are manufactured by glass molding press and the pitch errors of the molded quartz fiber array blocks are statistically investigated. The V-grooved carbon molds of 8 and 16 channels and 250 μm in pitch are machined and then quartz substrates are molded on the V-grooved carbon molds by glass molding press. The pitch errors of X, Y and diagonal axis are measured and then statically analyzed. It is demonstrated that the V-grooved quartz fiber array blocks of 8 and 16 channels and 250 μm in pitch can be manufactured by glass molding technology without significant pitch errors.

Abstract: Vibration is the biggest problem for precise on-line surface measurement. In order to investigate the possibility for phase-shifting interference technique to be applied to precise on-line surface measurement, a synchronic phase-shifting technique is proposed. Its anti-vibration characteristics are analyzed and a vibration table to simulate different vibration conditions is set up, on which many experiments for surface measurement under different vibration conditions are conducted. The analysis and experimental testing verify the excellent anti-vibration characteristics of the interferometer for on-line precise surface measurement.

Abstract: Indentation tests and single-point scratch tests are probably the simplest methods of measuring the elastic, plastic and fracture behavior of brittle materials. In this paper, the nearsurface mechanical properties of KDP single crystal have been investigated including the elasticity like Young’s modulus E, and the plasticity like the hardness H. These material properties can be used to predict the material responses in optical manufacturing operations. Hardness and elastic modulus on different crystal plane of KDP single crystal have been examined under different loads by nanoindentation test, and the influence of the indentation load on hardness and elastic modulus have been also analyzed systematically. The results show the nanoindentation size effect, that is, the hardness and elastic modulus increase as the indentation load decreases. The hardness and elastic modulus have strong anisotropy in the different crystallographic orientation of the same crystal plane.

Abstract: This paper investigates that polarizations of a laser vary in the process of reflections after a linearly or circularly polarized beam is incident on a paraboloid of revolution-shaped cavity. This analysis is based on the viewpoint of geometry optics because the opening radius is about 100μm, which is ten times the size of the wavelength 10.6μm of an incident CO2 laser beam. Considering the profile of laser beam to be Gaussian distribution, the variation of polarization in the process of reflections is mathematically modeled. The result reveals that the state of polarization for an incoming ray with circular polarization is almost totally transformed into linear polarization perpendicular to the plane of incidence after the ray intervenes multiple reflections. The effects of cavity depth and absorptive index of material on the polarization variation are also discussed. The circularly polarized ray entering the deeper cavity is finally changed into the higher degree of linear polarization. The increase in absorptive index reduces the speed approaching the linear polarization.

Abstract: An optical measuring system for the ring test is proposed. In this approach, the machine vision inspection equipment is first built to record and capture the images of ring test from the digital camcorder.The image processing procedures to detect and locate the edge points of the inner and outer radii in ring convex forming are presented. Unlike the conventional sub-pixel estimation based on gray-level values, the quantity (8 bits) of color’s scale has been adopted. In image processing procedures, a clustering method called Adaptive Competitive Learning Network (ACLN) is first used to classify the image hues which represent the different heights of bulge profiles on the top of ring, and then the edge points can be searched by the interpolation step of subpixel accuracy. The calibration curves constructed by the mode of non-constant friction factor called F-value approach is designed to compare and check with the measurement data. The experimental results will be presented and discussed in this study.

Abstract: By focusing femtosecond laser pulses in the bulk of a quartz wafer, sub-surface waveguides were microexploded. The material around the femtosecond laser induced microexplosive zone was densified, which altered local refractive index. Changes in material density can take corresponding variations in nanomechanical properties, which were proved by the depth dependent modulus and hardness variations tested by nanoindentation in the area around the microexplosive zone. Changes in refractive index were correlated with residual strains along radial direction of the waveguide cross section. An equation of residual strain in such area that based on nanoindentation data was set up, so as to discover density and refractive index variations in the adjacent areas of femtosecond laser microexplosive zone indirectly.