[Show abstract][Hide abstract] ABSTRACT: A grating-based interferometer for 6-DOF displacement and angle measurement is proposed in this study. The proposed interferometer is composed of three identical detection parts sharing the same light source. Each detection part utilizes three techniques: heterodyne, grating shearing, and Michelson interferometries. Displacement information in the three perpendicular directions (X, Y, Z) can be sensed simultaneously by each detection part. Furthermore, angle information (θX, θY, θZ) can be obtained by comparing the displacement measurement results between two corresponding detection parts. The feasibility and performance of the proposed grating-based interferometer are evaluated in displacement and angle measurement experiments. In comparison with the internal capacitance sensor built into the commercial piezo-stage, the measurement resolutions of the displacement and angle of our proposed interferometer are about 2 nm and 0.05 μrad.
[Show abstract][Hide abstract] ABSTRACT: A wavelength-modulated heterodyne grating shearing interferometry using a birefringent crystal is proposed for two-dimensional displacement measurement. There is a difference in the optical path lengths of the p- and s- polarizations of the light beam in the birefringent crystal because of the double refraction caused by the birefringence. By passing through the unequal-pathlength optical configuration, the wavelength-modulated light beam is converted into a heterodyne light beam having two frequencies. The modulated heterodyne light beam is further combined with grating-shearing interferometry based on the quasi-common-optical-path (QCOP) design concept. According to the working principle and the Jones calculation, the displacement information of a moving grating can be obtained by means of the optical phase variation resulting from the grating. Theoretical analysis shows that the measurement sensitivity of the proposed method is about 0.134°/nm. The experimental results indicate that the resolution is about 10 nm for the centimetric-level measurement range.
[Show abstract][Hide abstract] ABSTRACT: A heterodyne grating-based interferometer for three-degree-of-freedom (3-DOF) displacement measurement is proposed. This technique has the merits of both heterodyne interferometry and grating interferometry. A heterodyne light beam is obtained using an electro-optic modulating technique for amplitude modulation. While the heterodyne light beam is normally incident into a transmission-type 2D grating, two detection parts for in-plane and out-of-plane displacement measurements will be obtained. The heterodyne light beam is utilized to carry the optical phase variation that results from grating displacement in three directions. The experimental results demonstrate that the proposed interferometer is capable of sensing the displacement of a motion stage in 3-DOF. The resolution and range of the measurement can achieve up to nanometric and millimetric levels.
[Show abstract][Hide abstract] ABSTRACT: In this research, a novel heterodyne laser encoder for 6-DOF displacement and angle measurements is proposed. The technique combines the advantages of heterodyne interferometry, grating shearing interferometry, and Michelson interferometry. When a heterodyne light beam with two orthogonally polarized directions is used to focus on a semi-transmission grating, two detection configurations for in-plane and out-of-plane will be obtained. By means of measuring the phase variations of the interfering signals from the moving grating, the in-plane displacement can be acquired. Besides, the out-of-plane displacement can be obtained by detecting the optical path difference between the reference beam and the reflection beam. Furthermore, 6-DOF displacement and angle information can be measured simultaneously by using the beam dividing method. According to the experimental results, the measurement resolution is about 2 nm. The experimental results show that our proposed method has the ability to measure 6-DOF displacement and angle information with high system stability. Comparing with other commercial measurement instructions, this laser encoder has the advantages of high resolution, high stability, and high flexibility.
[Show abstract][Hide abstract] ABSTRACT: The thermal characteristics of an alternating current light-emitting diode (AC LED) chip based on a three-dimensional unsteady numerical simulation are discussed. In this model, the difficulties due to the tiny scale and extra-low aspect ratio of the AC LED microchip geometry are resolved. A time lag between the maximum forward voltage and the highest mean junction temperature is observed. The influence of different input power frequencies on the thermal fields is also investigated for AC LEDs with 600 μm
× 600 μm area. A numerical simulation of the junction temperature distributions shows that the AC LED has a better performance under a higher frequency than under a lower frequency.
No preview · Article · May 2013 · Advances in Mechanical Engineering
[Show abstract][Hide abstract] ABSTRACT: A method of straightness measurement utilizing two corner cubes is proposed. The architectural design of the system leads to the magnification of the displacement of a light spot on the detector with the same offset of the determinand. This method enhances the sensitivity of the system and raises the precision to about 5 μm.
[Show abstract][Hide abstract] ABSTRACT: A method based on a specific quasi-common-optical-path (QCOP) configuration for two-dimensional displacement measurement is presented. The measurement system consists of a heterodyne light source, two-dimensional holographic grating, specially designed set of half wave plates, and lock-in amplifiers. Two measurement configurations, for single and differential detection, are designed. The sensitivity, resolution and nonlinear phase error of the differential detection type are better than those of the single detection type. The experimental results demonstrate that the QCOP interferometer has the ability to measure two-dimensional displacement while maintaining high system stability.
[Show abstract][Hide abstract] ABSTRACT: We present a heterodyne grating interferometer based on a quasi-common-optical-path (QCOP) design for a two-degrees-of-freedom (DOF) straightness measurement. Two half-wave plates are utilized to rotate the polarizations of two orthogonally polarized beams. The grating movement can be calculated by measuring the phase difference variation in each axis. The experimental results demonstrate that our method has the ability to measure two-DOF straightness and still maintain high system stability. The proposed and demonstrated method, which relies on heterodyne interferometric phase measurement combined with the QCOP configuration, has the advantages of high measurement resolution, relatively straightforward operation, and high system stability.
[Show abstract][Hide abstract] ABSTRACT: In this work, the pits were successfully etched onto (0001) or (112¯0) sapphire single crystal surfaces by using a Na2B4O7 solution. The difference in the morphology of etch pits on different planes of the sapphire was examined by atomic force microscopy measurements. It was found that the size of the etch pits was affected by the etching duration. The results of X-ray diffraction analysis also indicated the particular in-plane orientation of the etch pits on the sapphire surface. The relationship between the morphology of etch pit and the sapphire structure will be explained in the paper. In addition, the etching rates for the (0001) and (112¯0) types of sapphire will be compared.
No preview · Article · Feb 2008 · Journal of Physics and Chemistry of Solids
[Show abstract][Hide abstract] ABSTRACT: In present study, we applied the interferometric lithography with an exposure mathematical model, and set up an experimental system to verify the validity of this model. A simple and convenient interferometric lithography system for patterning large-area with nano-scaled dimensions gratings was built. Due to the position for patterning large-area grating, a two-axis servo-motion system will be added to the original interferometric lithography system. Based on the characters of the interference, we modified an exposure model to predict the exposure condition, and then calculate the step for the next movement. From the simulation results, the best moving distance can be suggested. The different situations at the overlapping region and the interference are also simulated. The gratings at the overlapping region will be shown as three types due to different moving conditions. The experiment results can clearly be illustrated from the simulations. Finally, the results show that our interferometric lithography system and exposure model can be potentially used for fabricating uniform periodic structures.