The digital Moiré interferometer technique (DMIT) based on partial compensation principle is an effective approach for aspheric and freeform measurement. Besides a real interferometer, virtual interferometer, as a part of DMIT, plays an important role in the phase-shifting and alignment. The virtual interferometer based on the ray tracing, by creating a light path which is exactly the same with the actual interferometer, can obtain a simulated virtual interferogram for the phaseshifting and alignment. Generally, the ray tracing is simulated by Zemax software. However, due to the limitation of software, a communication delay between Zemax and other modules will influence the efficiency and response time of the whole system. So, how to realize ray tracing in an efficient way is still worth exploring. In this paper, we present a method for tracing ray to improve the efficiency. By using the vector formula of ray tracing, we can improve the calculation accuracy and shorten the calculation time of ray tracing, which can be used in most optical systems. Furthermore, we implement the algorithm of virtual interferometer on the basis of Visual C++, which is the software development platform of DMIT. In this way, we can integrate the virtual interferometer into the software system of DMIT, and then reduce the calling time between modules. Several simulation results are present to validate the feasibility of our method.
Deformable mirror (DM) is a flexible wavefront modulator with a changeable surface. It is traditionally adopted in adaptive optical system for aberration correction. Recently applications in zoom imaging system and interferometer for freeform measurement have been proposed because the improvement in fabrication technique makes larger stroke amount and faster response possible. The order and accuracy of aberration correction are typical wavefront correction characteristics of DMs. Due to the non-linearity, hysteresis and creep characteristic of piezoelectric ceramics, accurate control of piezoelectric type DM remains a challenge. Generally, the surface shape of a DM is changed by altering the voltages applied to different actuators below the DM film. And the shape of the DM can be fitted with Zernike polynomial to better characterize the aberration. So accurate control of the DM surface shape requires a relationship between the control voltage vector and the Zernike coefficients of the surface shape. We adopt neural network for the foundation of the relationship. 3000 set of control-voltage-vector and Zernike-coefficient pairs are experimentally collected based on the data measured with an interferometer and fitted with Zernike polynomials. The neural network is constructed and trained, and the control voltage vectors of new surface shapes can be retrieved with the network. The accuracy of shape realization is finally demonstrated by comparison between measured and predicted voltages.
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