[0040] See figure 1 as well as figure 2 , The present invention provides an imaging system based on wavefront coding with an ultra-large depth of field, which can simultaneously achieve a large relative aperture, an ultra-large depth of field and a larger field of view, including a wavefront encoding imaging lens, a 1/1.8-inch image detector, and a decoding processing unit The wavefront encoding imaging lens includes a first lens 21, a second lens 22, a phase mask 23, a third lens 24, a fourth lens 25, and a fifth lens 26; the first lens 21, the second lens 22, and the phase mask The diaphragm 23, the third lens 24, the fourth lens 25, the fifth lens 26, and the 1/1.8-inch image detector are sequentially arranged on the same optical path; the wavefront encoding imaging system adopts an asymmetric double Gaussian structure with a circular aperture , Where the radius of curvature of the front and rear surfaces of the first lens 21 and the radius of curvature of the front and rear surfaces of the fourth lens 25 are opposite to each other, the radius of curvature of the front, middle and rear surfaces of the second lens 22 and the radius of curvature of the front, middle and rear surfaces of the third lens 24 are opposite to each other, The fifth lens 26 is used to increase the field of view. In addition, except for the phase mask 23, all the other lenses are spherical lenses.
[0041] The radius of curvature of the front surface of the first lens 21 is 26.75mm, and the half-aperture of the front surface of the first lens 21 is 9.7553mm; the radius of curvature of the rear surface of the first lens 21 is 73.2mm, The clear half-aperture is 9.3811mm; the distance between the front surface of the first lens 21 and the rear surface of the first lens 21, that is, the center thickness of the first lens 21 is 2.5681mm;
[0042] The second lens 22 is a double cemented lens. Among them, the radius of curvature of the front surface is 14.689mm, and the half-aperture of the front surface is 7.0391mm; the radius of curvature of the middle surface is -101.62mm, and the half-aperture of the middle surface is 6.2167mm; the radius of curvature of the rear surface is 9.3760mm. The surface clear half aperture is 4.7580mm; the distance between the front surface and the middle surface is 3.8mm, and the distance between the middle surface and the back surface is 1.5562mm; the back surface of the first lens 21 and the front surface of the second lens 22 The distance between the first lens 21 and the second lens 22 is 4.7939mm;
[0043] The front surface of the phase mask 23 is the diaphragm surface, and the half-aperture of the front surface is 3.2057mm; the rear surface of the phase mask 23 is a plane, and the half-aperture of the rear surface is 4.0978mm; the phase mask 23 The distance between the front surface and the back surface of the phase mask 23, that is, the thickness of the phase mask 23 is 5mm; the distance between the back surface of the second lens 22 and the front surface of the phase mask 23, that is, the second lens 22 and the phase mask The distance between the mask plates 23 is 5.0169 mm;
[0044] The third lens 24 is also a double cemented lens. Among them, the radius of curvature of the front surface is -9.376mm, the half-aperture of the front surface is 4.2815mm; the radius of curvature of the middle surface is 101.62mm, and the half-aperture of the middle surface is 6.0116mm; the radius of curvature of the rear surface is -14.689mm, The clear half-aperture of the back surface is 6.4246mm; the distance between the front surface and the middle surface is 3.4384mm, and the distance between the middle surface and the back surface is 2.8661mm; the back surface of the phase mask 23 and the third lens 24 The distance between the front surfaces, that is, the distance between the phase mask 23 and the third lens 24 is 1.6762 mm;
[0045] The radius of curvature of the front surface of the fourth lens 25 is -73.2mm, and the semi-aperture of the front surface of the fourth lens 25 is 6.8136mm; the radius of curvature of the rear surface of the fourth lens 25 is -26.75mm, and the rear surface of the fourth lens 25 The clear half-aperture is 7.0273mm; the distance between the back surface of the third lens 24 and the front surface of the fourth lens 25, that is, the distance between the third lens 24 and the fourth lens 25 is 0.4629mm; the fourth lens 25 The distance between the front surface of the fourth lens 25 and the rear surface of the fourth lens 25, that is, the center thickness of the fourth lens 25 is 1.8261mm;
[0046] The radius of curvature of the front surface of the fifth lens 26 is 120.23mm, and the semi-aperture of the front surface of the fifth lens 26 is 7.1664mm; the radius of curvature of the rear surface of the fifth lens 26 is -66.37mm, and the rear surface of the fifth lens 26 is transparent. The optical half-aperture is 7.3062mm; the distance between the rear surface of the fourth lens 25 and the front surface of the fifth lens 26, that is, the distance between the fourth lens 25 and the fifth lens 26 is 0.1mm; The distance between the front surface and the rear surface of the fifth lens 26, that is, the center thickness of the fifth lens 26 is 3.8 mm;
[0047] The distance between the rear surface of the fifth lens 26 and the 1/1.8 inch image detector is 22.216 mm.
[0048] Among them, the phase mask 23 adopts the classic cubic encoding method, and the 2D mask function form can be expressed as:
[0049]
[0050] among them:
[0051] α represents the phase modulation intensity of the cubic phase mask 23, and the value of α is 0.01 mm;
[0052] Both x and y are normalized aperture coordinates, the unit is mm, and the range of values for x and y are both [-3.2057, 3.2057].
[0053] The focal length of the wavefront encoding imaging lens is 35mm, the relative aperture is 1/3.5, the full field angle is 30°, the working spectrum is 480um~680um, it can image 2m to infinity clearly, and the focal depth can reach 0.62mm. Compared with a conventional optical imaging system with the same specifications but not using wavefront coding technology, the focal depth is expanded by more than 40 times. The ultra-large depth-of-field wavefront coding imaging system has a depth of focus expansion factor of more than 40 times, and the image quality after filtering and decoding is still close to diffraction limited.
[0054] reference figure 1 In the system proposed by the present invention, after the imaging target 1 passes through the wavefront encoding imaging lens 2, a blurred intermediate image is formed on the 1/1.8 inch image detector 3, and then the decoding processing unit 4 performs deconvolution processing, and finally Obtain a clear image with clear focus and large depth of field.
[0055] The structure of the wavefront coding imaging lens 2 is as figure 2 As shown, the starting point of the present invention is a symmetrical double Gaussian structure with double glued lenses, and the expansion of the design field of view is achieved by adding another lens in front of the detector. Wherein, the phase mask 23 is located at the aperture stop, and the requirement of defocus insensitive depth of field expansion is achieved by adopting a cubic phase encoding on its front surface. Such as image 3 As shown, the phase distribution of the cubic phase mask 23 used in the present invention is given.
[0056] As mentioned earlier, if the wavefront coding technology is not used, in order to achieve a larger relative aperture and a larger field of view, more components or even aspheric optical components have to be used for aberration balance. Increase the cost of lens development and testing. Fortunately, the wavefront coding technology has two major characteristics that allow it to be designed with a larger relative aperture and a larger field of view. First, since the depth of field of the optical imaging system is inversely proportional to the square of the relative aperture, wavefront encoding allows the optical system to have a larger relative aperture by suppressing defocus. Secondly, the wavefront coding technology can simultaneously suppress defocus-related aberrations while achieving constant defocus. Some of these aberrations are related to the aperture, while others are related to the field of view. Therefore, the defocusing Suppression also means allowing the optical system to have a larger field of view. The present invention is based on the above characteristics of the wavefront coding imaging technology, and proposes such as figure 1 with figure 2 The ultra-large depth-of-field imaging system shown. In this system, except for the encoding surface of the phase mask 23 which needs to be processed by a five-degree-of-freedom surface processing equipment, all other lenses are spherical lenses, and the conventional process can be completed at a very low cost.
[0057] reference figure 2 After the imaging light emitted by the target scene passes through the wavefront-encoded imaging lens, the depth information of different positions of the scene carried by it is encoded, and consequently the system is not sensitive to defocus, such as Figure 4 As shown, the corresponding MTF of the ultra-large depth-of-field imaging system proposed by the present invention at imaging distances of 2m (a), 10m (b) and infinity (c) is given (where the abscissa represents the number of lines per millimeter The ordinate represents the normalized MTF amplitude). It can be seen that the MTF corresponding to different defocus amounts, different fields of view, and different wavelengths all have excellent consistency. This proves the effect of depth of field extension. corresponding, Figure 5 The change of MTF with the imaging distance when the wavefront coding technology is not used for the same specification parameters is given. Obviously, if the wavefront coding technology is not used, conventional optical systems cannot achieve imaging from 2m to infinity. As mentioned above, the relative aperture of the ultra-large depth-of-field imaging system proposed by the present invention is 1/3.5, so according to the calculation formula of the focal depth, the focal depth of the system is approximately 14.4um. However, according to the Gaussian formula, when the focal length is 35mm and the imaging distance changes from 2m to infinity, the focal plane will shift by 0.623mm, which is about 43.26 times the focal depth. In other words, wavefront encoding technology can extend the focal depth of conventional optical systems by 43.26 times. by Figure 4 It can be seen that although the MTF value after encoding is smaller than the value before encoding, it will not have a zero value in the presence of defocus, so it will not cause the loss of image detail information. The image detector is a uniformly blurred image, which is decoded by the decoding processing unit, and the MTF value of the system is increased to close to the diffraction limit, thereby recovering a sharp and clear image.
[0058] Image 6 A simulation comparison of imaging effects between the ultra-large depth-of-field imaging system proposed by the present invention and a conventional optical system with the same parameters is given. Among them, (a) represents the simulation imaging effect of conventional optical systems with the same specifications but without wavefront coding imaging technology at different imaging distances; (b) represents the super-large depth of field wavefront coding imaging system proposed by the present invention in different imaging Simulation imaging effect at distance. It can be seen that when the imaging distance of the conventional optical imaging system changes greatly, due to the rapid decline of the MTF amplitude, the image becomes more and more blurred, so that the details cannot be distinguished. For the ultra-large depth-of-field imaging system using wavefront coding technology, no matter what the imaging distance is, the blur degree of the intermediate image is almost the same, and it can be restored to the diffraction limited state after decoding. Especially when the focus is severely defocused, the image obtained by the conventional optical system is very blurry, and the image quality can still be close to the diffraction limited state after the application of encoding imaging technology, which proves the ability of the ultra-large depth of field imaging system based on wavefront encoding technology .
[0059] In summary, the ultra-large depth-of-field imaging system adopting wavefront coding technology proposed by the present invention allows focusing-free fast imaging, which is very suitable for moving target imaging, and a larger relative aperture with a high-sensitivity CMOS detector can achieve low The purpose of illuminating the scene for clear imaging.
