CN109581558B - Preparation method of multifocal diffraction element and multifocal diffraction element - Google Patents
Preparation method of multifocal diffraction element and multifocal diffraction element Download PDFInfo
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Abstract
The application relates to a preparation method of a multifocal diffraction element and the multifocal diffraction element, comprising the following steps: acquiring basic parameters of a multifocal diffraction element; calculating the step etching depth corresponding to each focal segment according to the basic parameters; and carrying out simulation experiment demonstration according to the step etching depth to obtain the multifocal diffraction element. The multifocal diffraction element provided by the application reduces the size of the multifocal diffraction element, avoids the alignment problem among a plurality of optical elements, and enables the use scene to be more flexible and wider. The multifocal diffraction element can generate equidistant multifocal, peak energy uniformity and point spread function consistency among focuses can obtain good results through optimization, can be used as an important light splitting element in a high-precision micro-nano processing system, and has an important function for increasing the focal depth in certain specific imaging optical systems.
Description
Technical Field
The present disclosure relates to the field of optical elements, and in particular, to a method for manufacturing a multifocal diffractive element and a multifocal diffractive element.
Background
The special optical property of the multi-focus optical element enables a beam of parallel light to be converged at a plurality of axial focuses simultaneously, so that the multi-focus optical element is widely applied to various modern optical processing and imaging systems. For example, when a femtosecond laser cuts a thick transparent material, because the cutting and separation of the transparent material by using a single laser focus is greatly influenced by the thickness of the material, the trend of thermal cracks induced at the laser focus in the thickness direction is not controlled along with the increase of the thickness of the transparent material, so that the surface shape of a cut section is irregular, even the surface is broken, and the like, the physical properties of the surface of the material are seriously influenced, and the application of the femtosecond laser cutting in the thick transparent material is limited. The laser beams are converged into a plurality of focuses in the axial direction by the multi-focus optical element and are uniformly distributed at different positions in the thickness direction of the transparent material, so that a cutting surface with high flatness is obtained; for example, the characteristics of the compound eye structure, such as high sensitivity to a moving object, are widely concerned and researched due to the special performance of a wide field of view, and in order to expand the focal depth of the bionic compound eye structure during imaging, the bionic compound eye structure can be realized by using a multifocal optical lens array.
Conventional multifocal optical elements generally have two implementations. One type is a fold-back optic, as shown in fig. 1. Common forms of such optical elements are: the multi-focus optical device has larger volume, is inconvenient for adjusting a light path and greatly limits the application scene; and the optical elements in the system are usually made into hollow structures, which is inconvenient to process. The second is to use diffractive optics to achieve multiple focal points, but such conventional multiple focal point diffractive elements have three major disadvantages: the conventional multifocal diffractive element is a diffractive-refractive hybrid optical device consisting of two parts: a conventional convex lens and diffractive optical element. This approach also limits the use of its functionality to some extent, for example, when used in a bionic compound eye structure, the alignment of two optical elements becomes an urgent problem to be solved. ② such conventional diffractive multifocal optical elements cannot form equidistant multifocal lenses due to problems inherent to the design. And thirdly, point spread functions of all the focuses are inconsistent, so that the peak energy intensity and the full width at half maximum of all the focuses are inconsistent, and the imaging quality of all the focal planes is influenced.
Disclosure of Invention
In view of the above, the present application provides a method for manufacturing a multifocal diffractive element and a multifocal diffractive element, so as to solve the above problems.
A first aspect of embodiments of the present application provides a method for manufacturing a multifocal diffractive element, the method comprising:
acquiring basic parameters of a multifocal diffraction element, wherein multifocal is a focus with equal step width;
calculating the step etching depth corresponding to each focal segment according to the basic parameters;
and carrying out simulation experiment demonstration according to the step etching depth to obtain the multifocal diffraction element.
Optionally, the calculating step etching depths corresponding to the focal segments according to the basic parameters includes:
planning and calculating the step etching position and the step etching depth to be etched according to the number of focuses of the multifocal diffraction element;
and integrating the step etching depths, and sequencing the step etching depths corresponding to the radial widths in sequence according to the focal sections so as to finally obtain the ordered step etching depths.
Optionally, the step etching depth is calculated by the following formula:
wherein HiTo etch depth, fiIn order to design the focal length, n is the refractive index of the material, r is the radial distance of each step of the diffraction element, lambda is the design wavelength, and m is the number of focuses.
Optionally, the performing simulation experiment demonstration according to the step etching depth to obtain the multifocal diffractive element includes:
after step etching is carried out according to the step etching depth, whether the peak energy of each focus is consistent with the half-width height of the corresponding energy peak is verified;
if the difference is not consistent, the difference between the peak value energy of each focus and the half width height of the corresponding energy peak is adjusted to be within a specified range by increasing or decreasing the number of steps corresponding to the focus section, and finally the multifocal diffraction element is obtained.
Optionally, the adjusting the difference of the peak energy of each focus to the half width height of the energy peak corresponding to the peak energy by increasing or decreasing the number of steps of the corresponding focus segment to a specified range includes:
changing the utilization rate of each focus by increasing or decreasing the number of steps corresponding to the focus section;
and adjusting the consistency of point spread function areas at each focus by changing the step width corresponding to each focus section, so that the difference between the peak energy of each focus and the half width height of the energy peak corresponding to the peak energy is within a specified range.
A second aspect of embodiments of the present application provides a multifocal diffractive element produced by a method described in any one of the above methods for producing a multifocal diffractive element.
The invention has the beneficial effects that: in the method for manufacturing the multifocal diffraction element, the multifocal diffraction element is provided with a plurality of focuses, so that multifocal distribution can be realized by using only one diffraction element without a focusing lens. Compared with the traditional multifocal diffraction element, the multifocal diffraction element provided by the application further reduces the size of the multifocal diffraction element, and avoids the alignment problem among a plurality of optical elements, so that the use scene is more flexible and wide; secondly, the multifocal diffraction element provided by the application can generate equidistant multifocal, and peak energy uniformity and point spread function consistency among focuses can obtain good results through optimization, so that the multifocal diffraction element can be used as an important light splitting element in a high-precision micro-nano processing system and has an important function of increasing the focal depth in some specific imaging optical systems.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
FIG. 1 is a multifocal diffractive element provided in the prior art;
FIG. 2 is a schematic flow chart illustrating a method for fabricating a multifocal diffractive element according to an embodiment of the present invention;
FIG. 3 is a schematic view of a step etch depth design according to an embodiment of the present disclosure;
FIG. 4 is a diagram illustrating a difference between peak energy distributions of a multifocal diffractive element and a diffractive element fabricated by a conventional method according to an embodiment of the present invention;
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth, such as particular system structures, techniques, etc. in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.
Fig. 2 illustrates a method for manufacturing a multifocal diffractive element provided herein, which is detailed below: the preparation method comprises the following steps:
step S21, obtaining basic parameters of a multifocal diffractive element, wherein the multifocal is a focus with an equal step width.
In the embodiments provided in the present application, when manufacturing the multifocal diffractive element, basic parameters of the multifocal diffractive element, such as the number of focuses, the focal length of each focus, the initial step width, the number of step cycles, and the like, are first determined. The plurality of focuses in the multifocal diffractive element provided by the present application are focuses of equal step width.
And step S22, calculating the step etching depth corresponding to each focal segment according to the basic parameters.
Optionally, the calculating step etching depths corresponding to the focal segments according to the basic parameters includes:
planning and calculating the step etching position and the step etching depth to be etched according to the number of focuses of the multifocal diffraction element;
and integrating the step etching depths, and sequencing the step etching depths corresponding to the radial widths in sequence according to the focal sections so as to finally obtain the ordered step etching depths.
Optionally, the step etching depth is calculated by the following formula:
wherein HiTo etch depth, fiIn order to design the focal length, n is the refractive index of the material, r is the radial distance of each step of the diffraction element, lambda is the design wavelength, and m is the number of focuses.
The design of the diffraction element with the equal step width is carried out on each focus, and the step height required to be etched is calculated. As shown in fig. 2.
The calculation formula is as follows:
wherein HiTo etch depth, fiIn order to design the focal length, n is the refractive index of the material, r is the radial distance of each step of the diffraction element, lambda is the design wavelength, and m is the number of focuses. Therefore, the step etching depth corresponding to each focal segment is obtained.
And then integrating the step etching depth, and sequentially arranging the etching depths corresponding to the radial widths according to the focal segments, wherein the final etching depth is as shown in figure 2.
H＝[h1 h2 ... hi h1 h2 ... hi ... h1 h2 ... hi]
And step S23, performing simulation experiment demonstration according to the step etching depth to obtain the multifocal diffraction element.
Optionally, the performing simulation experiment demonstration according to the step etching depth to obtain the multifocal diffractive element includes: and verifying whether the peak energy of each focus is consistent with the half-width height of the corresponding energy peak after step etching is carried out according to the step etching depth.
If the difference is not consistent, the difference between the peak value energy of each focus and the half width height of the corresponding energy peak is adjusted to be within a specified range by increasing or decreasing the number of steps corresponding to the focus section, and finally the multifocal diffraction element is obtained.
Optionally, the adjusting the difference of the peak energy of each focus to the half width height of the energy peak corresponding to the peak energy by increasing or decreasing the number of steps of the corresponding focus segment to a specified range includes:
changing the utilization rate of each focus by increasing or decreasing the number of steps corresponding to the focus section;
and adjusting the consistency of point spread function areas at each focus by changing the step width corresponding to each focus section, so that the difference between the peak energy of each focus and the half width height of the energy peak corresponding to the peak energy is within a specified range.
Specifically, the peak energy and the half-width height of each focus of the multifocal diffractive element prepared by the above process are not uniform, which is caused by the fact that the effective R/# of each focus is not the same. The peak energy intensity and the half-width height of each focus are required to be consistent through a subsequent optimization step.
The specific optimization method comprises the following steps:
according to the formula
The number of steps corresponding to each focal section is increased or decreased to ensure that the R/# corresponding to each focal point is equal, so that the energy utilization rate of each focal point is changed, then the width of the step corresponding to each focal section is changed to enable the point spread functions at each focal point to be consistent, finally the peak energy and the full width at half maximum of each focal point are kept similar, and the process needs to be iterated for multiple times. The specific flow of design and optimization is shown in fig. 3.
As shown in fig. 4, the bifocal diffractive element was designed for focal lengths of 40mm and 50mm, respectively, both 2.2mm in diameter using the conventional multifocal diffractive element design method and the design method of the present invention. The peak energy (normalization) of the bifocal optical element designed by the traditional design method at two focuses is 1/0.64 respectively, and the full width at half maximum (normalization) is 0.63/1 respectively; the peak energy (normalization) at the two focuses of the bifocal diffractive element of the present invention is 1/0.97, and the full width at half maximum (normalization) is 0.89/1. The uniformity of the peak energy is improved by 51 percent, and the uniformity of the full width at half maximum is improved by 41 percent. It can be seen that the advantages of the multifocal diffractive element design method of the present invention are significant.
In the method for manufacturing the multifocal diffraction element, the multifocal diffraction element is provided with a plurality of focuses, so that multifocal distribution can be realized by using only one diffraction element without a focusing lens. Compared with the traditional multifocal diffraction element, the multifocal diffraction element provided by the application further reduces the size of the multifocal diffraction element, and avoids the alignment problem among a plurality of optical elements, so that the use scene is more flexible and wide; secondly, the multifocal diffraction element provided by the application can generate equidistant multifocal, and peak energy uniformity and point spread function consistency among focuses can obtain good results through optimization, so that the multifocal diffraction element can be used as an important light splitting element in a high-precision micro-nano processing system and has an important function of increasing the focal depth in some specific imaging optical systems.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes performed by the present specification and drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (4)
1. A method of manufacturing a multifocal diffractive element, said method comprising:
acquiring basic parameters of a multifocal diffraction element, wherein multifocal is a focus with equal step width;
calculating the step etching depth corresponding to each focal segment according to the basic parameters;
performing simulation experiment demonstration according to the step etching depth to obtain the multifocal diffraction element;
the step etching depth corresponding to each focal segment is calculated according to the basic parameters, and the step etching depth comprises the following steps:
planning and calculating the step etching position and the step etching depth to be etched according to the number of focuses of the multifocal diffraction element;
integrating the step etching depths, and sequencing the step etching depths corresponding to the radial widths in sequence according to the focal sections to finally obtain the ordered step etching depths;
the step etching depth is calculated by the following formula:
where λ is the design wavelength, fiAnd the designed focal length is the ith focal point, r is the radial distance of the diffraction element step, n is the refractive index of the material, and m is the number of focal points of the multifocal diffraction element.
2. The method of claim 1, wherein the performing experimental demonstration of a simulation according to the step etching depth to obtain the multifocal diffractive element comprises:
after step etching is carried out according to the step etching depth, whether the peak energy of each focus is consistent with the half-width height of the corresponding energy peak is verified;
if the difference is not consistent, the difference between the peak value energy of each focus and the half width height of the corresponding energy peak is adjusted to be within a specified range by increasing or decreasing the number of steps corresponding to the focus section, and finally the multifocal diffraction element is obtained.
3. The method of claim 2, wherein adjusting the difference between the peak energy of each focal point and the half width height of the corresponding energy peak by increasing or decreasing the number of steps of the corresponding focal segment to a predetermined range comprises:
changing the utilization rate of each focus by increasing or decreasing the number of steps corresponding to the focus section;
and adjusting the consistency of point spread function areas at each focus by changing the step width corresponding to each focus section, so that the difference between the peak energy of each focus and the half width height of the energy peak corresponding to the peak energy is within a specified range.
4. A multifocal diffractive element characterized in that it is produced by the process of any one of claims 1 to 3.
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