Progress in the Research on the Calibration of the Spatial Light Modulator of Shanghai Institute of Optics

[ Instrument R & D of Instrumentation Network ] Recently, Zhang Junyong ’s research group of the High Power Laser Physics Joint Laboratory of Shanghai Institute of Optics and Precision Mechanics, Chinese Academy of Sciences and Shanghai Rui Li Ke Information Technology Co., Ltd. adopted a new concept of turning the zero-level background into signal light, targeting The optical modulator proposes a new type of single optical path absolute calibration method. The method is simple, effective, and has high accuracy. The adopted concept can also be extended to other measurement schemes.

The spatial light modulator means that under active control, it can modulate a certain parameter of the light field by liquid crystal molecules, for example, by modulating the amplitude of the light field, modulating the phase by the refractive index, modulating the polarization state by the rotation of the polarization plane, or Non-coherent-the conversion of coherent light, so that certain information is written into the light wave to achieve the purpose of light wave modulation. It can conveniently load information into one-dimensional or two-dimensional light field, and utilize the advantages of wide bandwidth of light and multi-channel parallel processing to quickly process the loaded information. It is the core device of real-time optical information processing, optical interconnection, optical computing and other systems.

The calibration of the spatial light modulator usually uses the fringe movement of the interference field to quantify the relationship between the driving voltage and the phase modulation capability, but interference requires multiple optical paths to achieve recording. The ability of the multi-optical interference system to resist interference from the external environment is poor, and it is easy to cause large measurement errors. The low calibration accuracy restricts the function of the spatial light modulator in high-end application scenarios. Another solution to avoid the interference of multiple light paths is the self-interference structure of the common light path, that is, the self-interference record on the detection surface is realized by loading multiple wavefronts, while retaining the processing algorithm of fringe pattern in the traditional calibration. However, the spatial light modulator as a type of diffractive element, the naturally occurring zero-order background light will reduce the signal-to-noise ratio of the self-interferogram and reduce the calibration accuracy of the spatial light modulator.

Optical measurement is a high-tech combination of photoelectric technology and mechanical measurement. Borrowing computer technology can realize fast and accurate measurement. Convenient recording, storage, printing, query and other functions.

According to reports, optical measurement is mainly used in modern industrial inspection, mainly to check whether the product's shape and position tolerance and numerical aperture are qualified. The main application areas are: metal products processing industry, mold, plastic, hardware, gear, mobile phone and other industries. Inspection, as well as industrial product development, mold design, wrench production, original engraving, RP rapid prototyping, circuit inspection and other fields. The main instruments are: two-dimensional, tool microscope, optical image measuring instrument, optical image projector, three-dimensional, three-coordinate measuring machine, three-dimensional laser reading machine, etc. In addition, the application of non-contact detection technology in the machinery manufacturing industry In order to make the machined products meet the design accuracy and quality requirements.

In response to the above problems, this study converts zero-level background light into signal light for use. This new concept not only retains the advantages of the standard fringe method, but also realizes the optical function of the self-interference single optical path structure. The review experts believe that this method is simple and easy to implement. On the one hand, the calibration scheme makes use of the difference in diffraction spots of large and small circles, on the other hand, it avoids the shortcomings of low signal-to-noise ratio of the self-interference optical path. Based on this method, the researchers performed calibration operations on the phase-type spatial light modulators provided by related companies, and conducted multiple rounds of verification verification with other conventional calibration methods. The results show that the spatial light modulator calibration scheme is simpler and more effective than the existing methods, and has higher accuracy. In addition, the concept can be applied to other measurement solutions, which expands new ideas for related research in the field of optical measurement.