Jinbang Chen

Frustrated total internal reflection evanescent switching

Abstract The mechanism of frustrated total internal reflection was analyzed according to the theory of optical film. The transmission and reflection functions were developed and the curves of transmission and reflection changing from the relative gap width d / λ , incident angle θ 0 , and refraction index n were shown in graphs. We proposed a scheme of experimental device to test the theoretical conclusion. A self-made electronic actuator drove the piezoelectric ceramics of FTIR. Experiments showed that the evanescent of transmission is 80% for He–Ne laser and smaller for YAG laser and Er:glass laser.

New algorithm on phase-shifting interferometry: the overlapping averaging 4-frame algorithm

Phase shifting interferometry (PSI) is a highly efficient and accurate phase measuring method. The accuracy of PSI is most seriously impaired by calibration error and nonlinearity in the phase shifter. This paper presents a new algorithm, the overlapping averaging 4-frame (OAF) algorithm, which can reduce the phase error due to phase shifter errors. The relationship between the accuracy of OAF algorithm and phase shifter errors is given. From this relationship, it is verified that the OAF algorithm can reduce the phase error due to phase shifter errors. The computer simulation providing the magnitude of a calibration error and nonlinearity in the phase shifter are shown for a number of different phase-measurement algorithms. From the analysis, the result is obtained that the OAF algorithm is more highly accurate than other phase-measurement algorithms.

Processing technique for interference pattern with step using phase-shift interferometry

Based on introducing the principle and method of processing technique for interference pattern with step using the characteristic of phase-shift interferometry. The paper has discussed a new phase-unwrapping algorithm for the phase map containing discontinuities. The correct phase values in the presence of discontinuities, especially those caused by the object with height steps, can be obtained. This algorithm is fast and accurate. The results of the measurement of three- dimensional object with height steps are presented. These techniques have been successfully applied to measure the surface and wave aberration of the system with step.

System for measurement of CCD parameters

This paper presents a system for measurement of CCD parameters that combines a photo-injection system and auto- focus systems. In the photo-injection system, a reverse microscope with plano-achromatic objective is used to produce a small light spot of (Phi) 2 micrometers . In the auto- focus system, astigmatic auto-focus method is applied. The auto-focus signal is detected by a simulation quadrate simulated by CCD. A piezoelectric transducer with high sensitivity and resolution is used to drive the focusing objective for a real-time control of the position of the small light spot which was required to be injected into one of pixels of CCD measured.

Ronchi test using overlapping averaging 4-frame algorithm

An automatic technique to process Ronchigrams is presented. The phase shifting error introduced by a phase shifter is reduced using overlapping averaging four-frame algorithm. A standard plano-convex lens is tested to verify the accuracy of this technique.

Realization of spherical absolute testing

Today, high quantities lens is more and more important to the optic-electric fields, and it brought about the demand of high accuracy testing of spherical surfaces. Absolute interferometric testing of spherical surfaces is a technical basis for establishing the spherical standard, and it is also an important application of computer aid interferometry. Partly work in the course of establishing the national spherical standard is introduced. A new method based on image processing has been developed instead of typical absolute testing which requires an eight-dimension mount whose cost is expensive and adjustment is very difficult. Interferograms sampled by phase-shifting interferometry can be processed to recognize the border of spherical surfaces. The key coefficients of position are in real time feedback to the operator to adjusting sphere precisely relative to the interferometer. This method can get more accuracy because of the high unison of three interferograms. This paper shows results of testing a 1/10 wave P-V sphere using two aplanats. It is easy to measure spherical surfaces to the accuracy better than 1/15 wave p- v.

Computer-aided testing for contact-type interferometer

Contact type interferometer is widely used equipment for testing relative length. It has been used to verify gauge block by metrology department because of its high accuracy. A computer-aided system based on it is introduced. There is a data acquisition system, including CCD and grabber etc., to detect and digitize interferograms instead of estimated by operator and avoids eyestrain. This system can analyze 2D interferogram automatically and quickly while both calibrate with monochromatic fringes and test with achromatic fringes. Many methods were used to analyze the 2D interferogram. It has been used by metrology department and its accuracy is better than 0.02 micrometers . Its resolution is better than the range per 1000 which is higher than the resolution estimated by operator. Different software has been developed to suit for different applications. One is the process-controlling software for verifying gauge block. The other is continuous- measuring software for testing tiny displacement about micron, such as measuring the responsive function of PZT.

Fiber geometry parameter measurement

An automatic method of measuring fiber geometry parameters is described. The parameters include core diameter, cladding diameter, core non-circularity, cladding non-circularity and core/cladding concentricity. The image of the fiber under test is received by a CCD camera and transferred to an image grabber plugged in a microcomputer for further analysis. Several digital image-processing methods are used to remove the noise in fiber image. The image segment algorithm is used to extract data points. The data is analyzed using different algorithms to give the geometry parameters of the fiber. Sophisticated software is programmed. An instrument is developed based on the hardware and software described above. All of the parameters and graphics can be obtained within 30 seconds. The repeatability of the instrument is as follows: core diameter, cladding diameter, core non- circularity, cladding non-circularity, core/cladding concentricity.

Using a long-wavelength (10.6-μm) interferometer to test a torus

A torus is a kind of aspherical surface, different from quadratic rotary surface. It plays an important role in special optical systems. However, up to now there is no effective method to test its wavefront. In this paper, a method is proposed using long wavelength (10.6 micrometers ) IR interferometry to test a torus, whose curvature radii is different from submillimeter deducing to micrometer, the principle is also given. Then a example torus is tested in self-developed IR spherical interferometer. When this torus is placed in typical positions along the optical axis, some interferograms are shown. According to these interferograms the wavefront error and the difference of two radii can be obtained and shown in this paper.

Infrared phase-shifting digital interferometer

This paper describes theory and performance of a self- developed IR phase-shifting digital interferometer which uses a CO2 laser as light source, this instrument comprises of a Fizeau interferometer whose aperture reaches (Phi) 250mm with accuracy better than (lambda) /50, and a Twyman spherical interferometer. Using piezoelectric transducer to shift reference mirror, phase measurement interferometry can be carried out as well as the temperature modulation of PEV target. A series of software packages used as wavefront fitting, image quality evaluation, are incorporated into the instrument. With the help of microcomputer, this interferometric system can measure refractive-index homogeneity of IR transmitting materials, wavefront error of IR optical system and surface quality of rough surface etc., which can all be shown by detailed data of optical path difference, vivid 2D contour and 3D surface.