Dual-wavelength Optical Interference Optical System Design And Simulation Research Phase Shift

Optical interferometry can be applied for measuring the figure of optical elements, characteristics of optical materials and properties of optical systems with high accuracy. Phase-shifting interferometry (PSI) which combines optical interferometry with opto-mechanical, electronic and computer techniques further improves the accuracy and degree of automation. However, the measurement range of conventional single-wavelength phase-shifting interferometer of visible light is restricted by its working wavelength. It can’t be used to test surface figures with large deviation, such as contours and steep aspheric surfaces. Two-wavelength phase-shifting interferometry utilizes two different wavelengths as working wavelength to measure surfaces. The surface information is retrieved by the phase information of equivalent wavelength. In this way, the measurement range of single-wavelength interferometry can be extended tremendously.In this paper, the basic principle of two-wavelength interferometry is studied. A two-wavelength interferometry system is designed by Zemax optical design software, including collimating beam expanding system, interfering optical path, and imaging system. As the result shown, the design meets the technical request and the tolerance range of optical manufacture and alignment. On the other hand, the equivalent wavelength phase extraction algorithm is researched. Combining with high-order phase-shifting algorithm and Carre algorithm, the conventional two-wavelength algorithm is improved.The two wavelength used in the simulation are632.8nm and543nm respectively. Based on the numerical experiments, the improved algorithms have a high accuracy and can suppress the phase-shifting error and the calibration error of PZT effectively. Finally, the two-wavelength phase-shifting interferometry system is constructed. The CGH element surface with deep etching contours is measured with the constructed system. The depth of the contours reached600nm. Experimental results demonstrate the usability of two-wavelength phase-shifting interferometry in measuring surfaces with large deviation and the accuracy of the improved two-wavelength algorithm.