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Conventional interference fringes counting methods often process two sinusoidal interference signals with a phase difference of π/2 to realize fringe-counting. But when the signals fluctuate in half a period of the signal, the conventional fringe-counting method sometimes produces direction-distinguishing mistakes, then resulting in counting errors. To address the problem, this paper presents a novel interference fringes counting method that uses software to distinguish the forward or backward direction of interference fringe and to count. This fringe-counting method can accurately distinguish the moving direction induced by the fluctuation of interference fringes, so it has the advantages of exact counting, intelligence and reliability. An experimental setup based on a Michelson interferometer is constructed to demonstrate the utility of this fringe-counting method for displacement measurement, and experimental results with a range of 1036mm is presented.

Near-field optical virtual probe is a kind of virtual probe based on evanescence wave interference and aperture diffraction, which has great potential in near-field optical data storage.

We propose a novel multi-pickup and multi-disk drive, in which multiple optical disks are mounted on a spindle at a equal spacing and multiple optical pickups, whose quantity is equal to that of the data surfaces of the optical disks, simultaneously read or write data in parallel. The key part of the drive is its servo-control system, which controls these optical pickups in parallel to implement the focusing servo-control and the tracking servo-control of each optical pickup in real-time in order to ensure the correct data read or write. The drive is important solution to offer super-large-capacity and quick-data-access information storage.

Near-field optical recording based on solid immersion lens (SIL) system has attracted great attention in the field of high-density data storage in recent years. The diffraction limited spot size in optical recording and lithography can be decreased by utilizing the SIL. The SIL near-field optical storage has advantages of high density, mass storage capacity and compatibility with many technologies well developed. We have set up a SIL near-field static recording system. The recording medium is placed on a 3-D scanning stage with the scanning range of 70×70×70μm and positioning accuracy of sub-nanometer, which will ensure the rigorous separation control in SIL system and the precision motion of the recording medium. The SIL is mounted on an inverted microscope. The focusing between long working distance objective and SIL can be monitored and observed by the CCD camera and eyes. Readout signal can be collected by a detector. Some experiments have been performed based on the SIL near-field recording system. The attempt of the near-field recording on photochromic medium has been made and the resolution improvement of the SIL has been presented. The influence factors in SIL near-field recording system are also discussed in the paper.

Near-field optical virtual probe (NFOVP) is a kind of immaterial tip based on evanescence wave interference and nano-aperture diffraction, which has great potential in near-field optical data storage, nano-lithography, near-field optical imaging and spectral detection, near-field optical manipulation and etc. . In this paper, the characteristics of NFOVP have been revealed through numerical simulation by the method of 3-D Finite-Difference Time-Domain (FDTD) and vector diffraction. The simulation results show that the transmission efficiency is higher than that of nanoaperture metal-coated fiber probe widely used in near-field optical systems. The FWHM of central peak, in other words, the size ofnear-field virtual probe is constant whatever the distance increases in a certain range so that the critical nanoseparation control in near-field optical system can be relaxed. A realization model of NFOVP in solid immersion lens system has been proposed. The influences of some factors of NFOVP, such as the shape and size of aperture, polarization and etc. have been analyzed. And the results also show that sidelobe suppression may depend on optimization ofaperture function and incident beams of NFOVP.

In this paper is introduced a new concept -- image point displacement (IPD), on the basis of which the principles and key tasks of light pattern projection profilometry are re- interpreted and evaluated. Two error sources that have not been addressed adequately are analyzed in detail. One is coordinate deviation, which comes from the different magnification at different depth. The other is the nonlinearity of the phase-IPD and phase-height relationship. These error sources will be more and more non-negligible as researchers make their ways to improve accuracy and increase measuring range. Some compensation approaches are also proposed, which have been verified by numerical simulations and experiments.

Grating projection 3D profilometry has three major problems that have to be handled with great care. They are local shadows, phase discontinuities and surface isolations. Carrying no information, shadow areas give us no clue about the profile there. Phase discontinuities often baffle phase unwrappers because they may be generated for several reasons difficult to distinguish. Spatial phase unwrapping will inevitably fail if the object under teste have surface isolations. In this paper, a complementary grating projection profilometry is reported, which attempts to tackle the three aforementioned problems simultaneously. This technique involves projecting two grating patterns form both sides of the CCD camera. Phase unwrapping is carried out pixel by pixel using the two phase maps based on the excess fraction method, which is immune to phase discontinuities or surface isolations. Complementary projection makes sure that no area in the visible volume of CCD is devoid of fringe information, although in some cases a small area of the reconstructed profile is of low accuracy compared with others. The system calibration procedures and measurement results are presented in detail, and possible improvement is discussed.

Phase unwrapping is an inevitable process in modern phase- evaluation based fringe analysis because the arctangent functions used in phase extraction only return phase modulo 2(pi) . In recent years, several temporal phase unwrapping methods have been proposed, which use a couple of phase maps with different sensitivities for the unique determination of the unwrapped phase on a pixel-by-pixel basis. We have found that, however, some of them are not effectively designed, probably due to the lack of proper philosophy for guidance. In this paper, we present a generalized mathematical excess fraction method, which is more compete and general in nature and can be used to re-interpret those temporal phase unwrapping algorithms in a unifying perspective. It is also demonstrated that more efficient and flexible algorithms can be designed based on the principle of the generalized excess fraction method.

A common-path heterodyne interferometer for on-line non- contact measurement of surface profile has been developed. A single-mode frequency-stabilized laser diode (780 nm) serves as the light source to make whole system compact (total volume 250L X 200W X 100Dmm). The optical common-path configuration remarkably minimizes the effects caused by vibration, air turbulence and other environmental variations. Multiperiodical phase measuring technique, which is based on the combination of fractional periodic phase measurement and integer periodic phase counting, is employed in signal processing, so the system features not only high vertical resolution but wide measuring range as well. In addition, the automatic focusing system greatly facilitates the measurement especially on-line profiling. This paper gives the brief principles, the arrangement of the interferometer and some test results. The system has vertical resolution of 0.39 nm and lateral resolution of 0.73 micrometer. The stability is 1.95 nm (3(sigma) ) during about 1 hour and the accuracy of automatic focusing system is 0.1 micrometer within plus or minus 25 micrometer of the focus.

A four-segmented piezoelectric tube performs XYZ spatial scanning in a SPM system. The measurement of characteristics including scanning range, accuracy, linearity and the lowest resonant frequency are essential to obtain a reliable image and get information about the scanning velocity. An optical fiber laser interferometer capable of vibration measurement is used to characterize the scanning tube with the inner diameter of 6mm, thickness 1mm and length 25mm is measured. We find that the lowest resonant frequency is much lower than the calculated result. The low resonant frequency will limit the scanning velocity and influence the quality of the obtained image greatly. In addition, the non-linearity curve can be obtained by driving the scanning tube with a triangle wave slowly. The measurement is easy, quick and continuous. In addition, we measure the non-linearity statically by inductive micrometer as well. The two results are compared. The result shows that there is difference between them.

Fourier transform technique for moire deflectogram is proposed to automatically map the phase object. The moire deflectogram is generate by conventional deflectometer and is analyzed by means of Fourier transform algorithm, in which the fringe phase is retrieved and phase object message is obtained automatically. Theoretical analysis, simulation calculation and application example are presented.

In this paper , an Atomic Force Microscope( AFM) with laser lever and it ' s application in specting microprofile of optical surface are presented. The nanometer-grade defects in optical and supersmooth surface can be tested byAFM. The microprofile drawings have the accuracy higher than (0 . 1 mm) in both vertical and lateral resolu-tion. Some testing results of optical and supersmooth surfaces are shown in the paper. Keywords : defect of optical surface; microprofile drawing; optical inspecting 1.. INTRODUCTION The roughness inspecting of optical surface use to be made by inteference method, as the double focus intefer-ence profile testing method[1 • The inteference method has the vertical resolution better than 0. 1 nm and the lateralone better than 2pm. But some researchs represents, these methods have a good vertical resolution but a poor lateral one. Without these , one developed some new methods for optical surface inspecting , as using a microdensitometer[21or CCD camera3 to analyzer electron micrographs of shadowed-surface replicas.

A four-segment scanning PZT tube is characterized using a laser vibration measurement system. Several periods of quasi-decay mechanical oscillation are observed in the experiments when the scanning tube is driven by series of step signals. The oscillation frequency is much lower than the lowest resonant frequency calculated base on the reported formula. The mechanism of the oscillation is analyzed. The possible reasons include mechanical inertial or damping, driving power supply impedance properties and the base vibration are discussed. The low resonant frequency of the scanning tube may be the result of its own complicated boundary conditions based on the experimental result of amplitude and frequency properties although there is a considerable difference between theoretical and experimental results. Some possible approaches to reduce or eliminate oscillation are proposed.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In modern semiconductor and optics industries, there is a strong demand for a highly sensitive and non-contact surface profilometer. This paper describes an optical heterodyne surface profiling interferometer with automatic focusing which has been developed recently. The essential feature of the profilometer is a newly designed common-path method to minimize the effects of environmental conditions. A powerful signal processing scheme is also developed, which includes three parts: automatic voltage control, phase measurement and automatic focusing control. All these make the repeatability and stability of the profiling interferometer greatly improved. The height resolution is 3.5 nm and lateral resolution is 0.4 micrometers . Experiments show that the profiling interferometer is suitable for on-line use.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A research on using linear array CCD detecting technique in measuring form and position errors of large scale dimension is described in this paper. The basic idea of this kind of measurement is that using a stable aligned laser beam incident on a 1D asymmetrical phase plate to form a black line as the reference of the beam, form and position datum lines and planes can be established through a scanner. A linear array CCD is used to measure deviation between the datum and the quantity be measured directly and absolutely. In the paper, we also discuss the reading error of the CCD probe caused by various factors in detail and introduce the CCD probe and its signal processing circuit. Some of experiment results and its application are shown.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper a novel method of measuring coaxiality and perpendicularity using laser alignment, diffraction imaging and CCD image detecting is proposed. In this method, we use a laser diode fiber alignment beam as the datum reference of straightness, deviation of the center of the hole from this datum, coaxiality, can be detected by a CCD camera. By rotating a penta-prism that makes this alignment beam bend a right angle a scanning datum plane is generated which can be used to detect the perpendicularity of the axis to an end plane. In the paper the factors that affect the accuracy of the system are analyzed. The experiment result shows that the measurement accuracy of the system is 3 + 2.3 X 10+6.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, an instrument for measuring flatness derivation by using an aligned laser beam and CCD detector is described. A stable aligned laser beam is used to form a datum plane in the instrument by rotating shaft and a pentagonal prism. Using a linear array CCD detector as the sensing probe, the system can detect the deviation of height related to the datum plane directly and absolutely. The experiment result shows that the measurement accuracy ofthe instrument is 2.3x r6. Keyword: Flatness, Laser beam, CCD detector

An improved signal processing method for laser interferometer is investigated to measure the radius of large precision centrifuge. Based on phase and integer periodic phase measurement, it not only makes the resolution up to 1 in 2000 of a wavelength, but also enlarges the range of the interferometer. The absolute radius measurement of the 5m centrifuge with the accuracy of +/- 3.4micrometers is achieved.

In this paper, a system for measuring perpendicularity and parallelism derivation using a laser diode fiber aligned beam and CCD detector is described. A stable aligned laser diode beam is used to form datum planes by rotating scanner equipped with pentagonal prism. Using a linear array CCD detector as the sensing probe, the system can detect the deviation of height related to the datum plane directly and absolutely. The experiment result is shown in the paper.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper describes an high precision in-process optical surface profilometer system. The measurement principle of the profilometer is based on phase comparison of optical heterodyne signals. Disturbance from environment vibration and mechanical instability of the interferometer was effectively eliminated by using optical and electronic common-mode rejection techniques. Measuring light can be automatically focused on the surface by a moving-coil lens during the sample scanning process. The size of the profilometer is small since a laser diode is used instead of a big He-Ne laser. This profilometer is suitable for use on machine. The height sensitivity is of the order of 1 nm and lateral resolution is 0.8 micrometers .© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The paper discusses some optical methods of measuring the profile of disk non-contacting. Grazing incident interferometer, Color schieren, and Moire deflectometer. Especially in the paper a new measuring method and instrument is introduced which is a pointwise instrument with an optical probe. It can measure a global and local profile of a disk in tangential and radial direction at the same time, without sacrificing the measurement accuracy. The resolution of the probe is 0.3 nm, the instrument accuracy better than 0.04 micrometers , the dynamic range larger than 5 mm.

An optical heterodyne system for the measurement of profile and roughness has been developed. Several improved techniques are employed. The optical system was designed with entire common path. The effect of sample vibration and the thermal drift could be eliminated. A modified objective was used to perform respectively the measurement beam and the reference beam. The detected signals were processed with phase comparison technique to give a high accuracy. The optical system can be developed to an accessory of the Zeeman laser interferometers.

A frequency-modulation absolute distance measurement techniques using a external-cavity semiconductor laser is proposed. A reference interferometer was adopted in order to reduce the effect of the central frequency drift of the laser on the measurement accuracy. The principle of the measurement is described and the experimental setup is introduced. The measurable range is as large as ten meters.

A fiber displacement sensor with a Linear Frequency Modulation (LFM) laser diode and its optical electric signal processing method are described in the paper. It operates on the principle of a non-balance optical fiber Michelson interferometer to realize heterodyne detecting. During processing the heterodyne signal, phase locked loops (PLL) are used to extend the resolution. The resolution of the sensor can reach to π/40. In the paper the experiment result is being showed also.

A new method for measuring absolute distance is described which is based on the frequency modulated continuous wave (FMCV technique. The preliminary experiment results show that the accuracy can reach 0. 3mx at a distance of 7 meters and the measuring range can exceed 10 meters by using an external cavity laser diode

The paper introduces a new method to measure the flatness of the disk with the laser heterodyne interferometer. Its most important advantage is that it can measure the large and intermediate scale disk profile at the same time, without sacrificing the measurement accuracy. The resolution of the interferometer is 0.3 nm, the accuracy better than 0.04 jim, the dynamic range larger than 5 mm. Otherwise the interferometer can nieasure the disk global and local profile in tangential and radial direction.

An heterodyne interferoaeter is constructed with a sodulated laser diode (LD) in a Michelson interferoaeter. Phase drift of beat frequency with teiperature and its affection aechanis is discussed and a method elisinating the affection aentioned above is proposed. 1 . OPTICAL HETERODYNE INTERFEROMETER Optical frequency of laser diode can be linearly aodulated by an injection current. An optical heterodyne interferoseter is constructed with a modulated laser diode in a Michelson interferoseter. If a difference exists between two arms in the interferometer a optical beat frequency phenoaenon will be forRed. The beatfrequency signal can be detected with a photoelectric device. The output signal can be described by the following equation: 1g10[1+cos(2xfbt+t)J (1) and fb is given by fb 6f''8Lf. I C (2) Where f is the aaxiRua optical frequency variation value of wxiulated laser fb the beat frequency value fa the odulated signal frequency L the optical path difference between two aras in the interferoaeter C optical wave speed. 2. VARIATION OF BEAT FREQUENCY PHASE WITh TEMPERATURE It is well known that the optical frequency of a laser diode is affected by the tesperature (in the equation (1)) ay be changed with the variation of central wavelength of . odulated optical frequency. t aay be expressed in the for. : Li A242Ai t 2ir( ) (3) AiA2 The plus and ainus . arks in the equation above are corresponding to the upward

A method for non-contact on-line measuring large shaft diaseter using laser beas scanning technique is presented in this paper. Diaaeter froa 500 to 2000 s can be Measured by the aethod over large seasuring range resolution is 0. 005 ii accuracy of variation over 700 0. 02 s. 1 .

Many Methods have been developed to .easure displace.ent with high accuracy, for exap1e, with a dual frequency laser interferometer (AC interferometer) and an classic interferoseter (DC interferoeter) which use a stabilized laser and fringe counter, and an AC interfero.eter has ore advantage over the DC one. An AC interfero.eter with a Zee.an laser can get a high resolution, in the order of nanoMeters, but its resolution extension liRited by nonlinear relation between phase and displace.ent which caused by the two-frequency coRponents in interferoaeter[1]. Because the fundaaental length scale of the interferometer is the wavelength of the light source in the air. The accuracy of an interferoeter is li.ited by the operating envireaent, teRperature, husidity, pressure, etc. because the aiRs of interferoseters expose in the air. A high resolution optical fiber heterodyne interfermeter is described in the paper.