Method For Measuring Modulation Transfer Function Of Optical System Using Laser Speckle

The polarization sensitive response of optical modulation transfer function MTF in laser speckle measurement is a combination of optical measurement and polarization technology,which opens a new situation for MTF characterization of polarization imaging system.Optical modulation transfer function is a common method to evaluate the image quality of optical imaging system.It is applicable to all kinds of optical systems and has the advantages of comprehensive,objective and reliable evaluation of image quality.It has been widely used.With the continuous development of science and technology,there have been many methods to measure the modulation transfer function of optical system.But for polarization optical system,the traditional measurement method has many limitations.Therefore,this paper proposes a new measurement method,taking CMOS optical imaging system as the research object.The CMOS is generally regarded as scalar systems,but due to the coating medium of optical system,the polarization of CMOS camera may be slightly affected.Therefore,we introduce different linearly polarized light and use laser speckle as information carrier to measure,so as to explore the sensitive response of modulation transfer function of laser speckle under different polarization states.The polarization sensitive response of optical imaging system is helpful to promote the development of polarization imaging technology.At the same time,this method does not need to use high-quality optical components and mechanical components,and its high cost performance,for the engineering field MTF test provides a simple and fast method.In this paper,analyzing methods of optical system modulation transfer function measured by laser speckle are will be from the following aspects:(1)The advantages and disadvantages of traditional methods for measuring modulation transfer function such as contrast method,pinhole method and point source method are compared and analyzed.On this basis,the necessity of speckle measurement method is put forward.(2)Establishing mathematical modeling based on Laser speckle and its statistical characteristics.Based on the mathematical description of polarization,the basic theory of electromagnetic vector field and the characteristics of laser speckle,the relationship between the autocorrelation function of light intensity and power spectrum of different linearly polarized speckle is deduced,OTF under circular pupil is calculated,and calculating the speckle size.In order to obtain a feasible speckle pattern,based on Nyquist sampling theorem and limit diffraction theorem,the relationship between speckle and pupil position,size and diffraction distance was deduced.Finally,a mathematical model is established to characterize the modulation transfer function of optical systems with different polarization states by laser speckle method.(3)On the basis of the established mathematical model,the measurement system of the modulation transfer function represented by the laser speckle method is constructed,which includes the incident light modulation module,the laser speckle module,and the receiving and processing module of the photometry system.Calculating the position and parameters of each optical component,introducing the specific operation process,and giving a complete measurement method.Finally,the MTF of the optical system under different linear polarization states is measured by four groups of experiments,and the three-dimensional MTF curve and the MTF curve along the meridian and Sagittal direction under different linear polarization states are fitted respectively.In this paper,the modulation transfer function response of CMOS optical imaging system with laser speckle in different polarization states is studied.Through the establishment of mathematical model,experimental measurement system and algorithm design,the sensitive response of optical modulation transfer function of optical system under different polarization states is obtained.These results will help to intuitive understanding and evaluation the MTF of polarization optical system,thus promote the innovation of the related theory,motivate the development of industry,military equipment,medical imaging.