Qingxiang Li

Autofocus system for microscope

A technique is developed for microscope autofocusing, which is called the eccentric light beam approach with high resolution, wide focusing range, and compact construction. The principle is described. The theoretical formula of the eccentric light beam approach deduced can be applied not only to an object lens whose objective plane is just at the focal plane, but also to an object lens whose objective plane is not at the focal plane. The experimental setup uses a semiconductor laser device as the light source. The laser beam that enters into the microscope is eccentric with the main light axis. A defocused signal is acquired by a symmetrical silicon photocell for the change of the reflected light position caused by differential amplification and processed by a microprocessor. Then the electric signal is power-amplified and drives a dc motor, which moves a fine working platform to an automatic focus of the microscope. The result of the experiments shows a ±0.1-?m precision of autofocusing for a range of ±500-?m defocusing. The system has high reliability and can meet the requirements of various accurate micro measurement systems.

Optical profilometer based on the principle of differential interference

An optical profilometer based on the principle of differential interference has been developed. Using a common-light-path interfer- ence scheme, the instrument is insensitive to vibration, air turbulence, and temperature variation. Experimental results demonstrate that the vertical resolution and the repeatability of the instrument are both better than 1 nm in an ordinary environment.

Interferometer distance measurement system using a linear detector array

The principle and structure of a new self-scanning laser interferometer are introduced. The output of a self-scanning photodiode array is modulated to generate an ac measurement signal, thereby avoiding dc drift and low-frequency disturbances. Experiments show that the device can be used in the range of 100 mm and with a resolution of less than 0.02µm.

Experimental study on the measurement of the curvature radius of a spherical grid

To ensure the manufacturing accuracy of a spherical grid, it is necessary to accurately measure the curvature radius, which is one of its important parameters. A measurement system consisting of precision machinery, a microscope, CCD camera, an image processing unit, a grating measurement system, and a computer control is described. By using image processing, noncontact alignment with high speed and accuracy is achieved. The curvature radius of the grid is obtained accurately through applying least-square fitting for multiple points of the grid. The measuring principle and experiments based on the principle are described. The results show that the repeatability of the measurement is up to ±3 ?m.

Non-contact surface roughness measurement

A noncontact optical profiler for measuring surface roughness is described. The system consists of a differential interference microscope with a polarization phase shifter CCD detector array video frame grabber and computer. Interferometric phaseshifting techniques are used to obtain surface slope information. The slope data is then integrated to yield a surface profile. Vibration insensitivity has been achieved by adopting a differential interferometric scheme. The profiler has measured surface features with a vertical resolution of 1 nm and a lateral resolution of less than 0. 5 m in an ordinary laboratory environment without vibration isolation.

Experimental study on the measurement of micro structures

Measurement of micro structures is a key issue in microtechnology, and it will influence the production efficiency and quality of large-scale integrated circuits. An experimental study on the factors affecting the accuracy of measurement of micro structures has been carried out with a laboratory-built DXY-1 type linewidth measuring system. The experiment results show that the repeatability of the system is better than ±0.005 µm, and the difference between the nominal and measured values is less than ±0.02 µm.

Design and fabrication of an integrated optical flying head for near-field recording system

To achieve 50nm flying height and accuracy tracking motion, it is essential to reduce the whole size of optical flying head (OFH) to improve mechanical and optical performance. With a view to the practical applicability, a novel integrated OFH based on the combination of SIL and objective lens (OL) is proposed, which possesses both high optical performance and reasonable tolerance in assembly. In addition, the fabrication process of this OFH is illustrated in detail. Finally, the main parameters of ABS for OFH slider are presented by means of numerical simulation. The simulation result demonstrates that the flying height of the integrated OFH slider can keep stable from 43nm to 44nm at different radium of optical disk, which can yield high signal/noise ratio optical signal during the read/write motion in near field recording (NFR) system.

Research on control scheme in high-density multiwavelength optical disc mastering

In order to meet the development requirements of high density optical disc mastering, a control scheme of high-density multi-wavelength optical disc mastering by using the embedded architecture with the DSP as processor and CPLD as the logic path was supplied. A initial study on next generation ultra-high density mastering system was conducted and two level positioning technique and air-floating plus PZT aided focus technique are applied into the control system. The results of experiments show that the scheme is feasible, and the setups for optical disc mastering can meet the requirements.

Singularity recognization of vibration signal based on Hermitian wavelet for diagnosis

The vibration signal in the nature of singularity is always caused by mechanical fault of equipment. It is important to recognize the signal singularity correctly for mechanical fault diagnosis. The complex Hermitian wavelet is constructed by means of the first and the second derivatives of the Gaussian function to detect signal signularities. The Hermitian wavelet has a real Fourier transform that will not mix the signal phase with its filter phase, and its real part and imginary part have less oscillation than Morlet wavelet, so that the convolution operation can be process with fewer number of data points and the signal singularity will not be smeared. The time-scale amplitude plot and phase plot based on Hermitian wavelet are presented to detect signal singularities. A successful application has been obtained in diagnosis of large air compressor gearbox. According to the singularities extracted from amplitude plot and phase plot of gearbox vibration signals, it is obvious that there existed impact rub fault that caused intense vibration in the gearbox. After justified maintenance the compressor gearbox runs smoothly in a good condition.

Study on lateral dual-element electron tunneling accelerometer

Electron tunneling accelerometer has the advantages of high precision, small volume, low consumption and so on. This paper introduces the design on a lateral dual-element Electron Tunneling Accelerometer. The model, structure design, parameters test and fabrication process are provided in detail. The results of analysis and simulation show that the working frequency of sensor could be up to 2 kHz.