Method for suppressing zero-order spot of diffractive optical element and corresponding optical component

Abstract

The method for suppressing the zero-order spot of a diffractive optical element of the present invention includes: 1) removing the diffractive optical element from the optical path of the optical assembly; 2) adding a solid lens in the optical path of the optical assembly; 3) moving the lens along the optical axis so that the spot size of the outgoing beam of the lens projected on the working plane is larger than the size of the zero-order diffraction spot of the original optical assembly and smaller than the spot size of the first-order diffraction beam of the original optical assembly projected on the working plane; and 4) reinserting the diffractive optical element into the optical path. The present invention also provides a corresponding optical assembly for suppressing the zero-order spot of a diffractive optical element. The present invention can be well adapted to existing devices or equipment based on diffractive optical elements, and these existing devices or equipment can be upgraded by relatively simplified measures to suppress the zero-order spot and improve the quality of the output beam.

Description

Technical Field

[0001] The present invention relates to the fields of optical technology and diffractive optical technology. Specifically, the present invention relates to a method for suppressing the zero-order spot of a diffractive optical element and a corresponding optical component. Background Art

[0002] Diffractive Optical Elements (DOE) have become one of the indispensable optical elements for many manufacturers (such as laser manufacturers) and laser users. By designing the surface microstructure of the DOE, the phase of light can be adjusted so that when a specific light is input, light with any light intensity distribution that meets the design can be output, thereby helping to achieve many optical functions and operations that are difficult to achieve with traditional optical systems. In many application fields, diffractive optical technology has many advantages such as high efficiency, high precision, small size, and low weight, so it is increasingly favored by the market. Currently, diffractive optical elements have been widely used in many fields such as laser heat treatment, laser hardening, laser processing of semiconductor wafers, laser welding, laser drilling, laser marking, medical beauty, etc., and have good economic benefits.

[0003] One of the important functions of diffractive optical elements is to shape the light beam. The light beam directly output by a laser is usually a single-mode or multi-mode Gaussian beam, which is difficult to be directly used in some scenarios in the fields of industry, medical treatment, and consumer electronics (or it is difficult to be directly applied to some scenarios in the fields of industry, medical treatment, and consumer electronics). And a beam shaper can shape a single-mode or multi-mode Gaussian beam into a beam with a uniform distribution, a quasi-uniform distribution, or a power density distribution presenting an M-shaped distribution (that is, strong at the edge of the spot and weak in the center). Common beam shapers usually include a collimating mirror and a diffractive optical element. Among them, the collimating mirror is used to collimate the light beam so that the diffractive optical element can output the expected spot pattern. The spot pattern can be, for example, a circular, rectangular, square, linear, or other shaped spot with uniform intensity. And the spot has a high-quality sharp edge on a specific working plane, thereby providing high-quality laser processing capabilities for the industrial community.

[0004] However, despite its many advantages, diffraction optical elements still have some problems that need to be solved. For example, the output light beam of a diffraction optical element often has the problem of a central zero-order spot. For an incident light beam (usually a collimated light beam) pointing to a diffraction optical element, there is always a part of the light beam that is not diffracted, and these light beams pass directly from the center of the diffraction optical element into the working plane, forming a zero-order spot. The power density of the zero-order spot is usually several times the power density of the diffraction first-order spot, which often leads to a significant decrease in the uniformity of the diffraction optical element, and sometimes even causes the power density of a local area of the output light spot to exceed the threshold, seriously affecting the use of the diffraction optical element. Therefore, people are looking forward to a solution that can suppress the zero-order spot of a diffraction optical element.

[0005] In the prior art, there have been some solutions for suppressing the zero-order spot of diffractive optical elements. One solution is to suppress the zero-order spot by increasing the number of phase steps of the diffractive optical element. For example, a third phase step can be introduced into the original two-step grating profile, thereby significantly reducing the sensitivity of the diffractive optical element to the depth error of the microstructure profile, that is, reducing the power density of the zero-order spot caused by the spectral width. This solution of using a diffractive structure with three phase steps instead of a two-phase step diffractive structure can play a role in suppressing the zero-order spot. However, its processing difficulty and production cost also increase significantly. Another solution is the double diffractive surface solution applied to beam homogenizing elements. The double diffractive surface means that the diffractive optical element has two diffractive surfaces. The first diffractive surface reduces the coherence of the incident light beam, and the second diffractive surface changes the power density distribution of the light beam (i.e., the light beam shape). This solution will also significantly increase the processing difficulty and production cost of the diffractive optical element. There is also a class of solutions that integrate virtual optical elements (such as virtual Fresnel lenses, diffractive prisms) on the basis of the original diffractive optical element. For example, in some solutions, an attempt is made to integrate a virtual Fresnel lens into the diffractive optical element. The virtual Fresnel lens is actually a diffractive lens that is approximated by two steps or more steps in the height direction and is discrete in the lateral position. And the original diffractive lens itself is also a diffractive element used to achieve a certain or certain specific functions. There may sometimes be compatibility problems when the two are integrated together. And since the virtual Fresnel lens itself is also a diffractive lens and has a zero-order, the effect of reducing the zero-order by integrating a virtual Fresnel lens into the diffractive optical element is often not ideal. For another example, the desired output image can be laterally shifted relative to the zero-order by integrating a virtual diffractive prism into the original diffractive optical element so that their positions are staggered, thereby avoiding the interference of the output image by the zero-order spot. However, integrating a new virtual optical element on the basis of the original diffractive optical element requires changing the surface microstructure of the diffractive optical element, and the stability and reliability of the product are put to the test. On the other hand, the application scenarios of this solution of integrating a new virtual optical element on the basis of the original diffractive optical element are limited. For example, the solution of integrating a diffractive prism is not suitable for the case where the first-order diffraction angle is large. Because the zero-order energy is on the optical axis, it is necessary to move the first-order diffraction completely outside the optical axis to eliminate the influence of the zero-order on the first-order. That is to say, the angle of the first-order diffraction angle is at least twice that before the diffractive prism is added, so the requirement for the machine processing accuracy is at least increased to twice that before, which will greatly increase the investment cost. Finally, there is also a solution to reduce the zero-order through special diffractive design. Since most diffractive optical elements are designed using the iterative Fourier transform algorithm, the zero-order power can be made to occupy a greater weight than uniformity and diffraction efficiency in the overall merit function during the design, thereby reducing the zero-order. However, this special diffractive design will lead to a decrease in the uniformity and diffraction efficiency of the output power density distribution (output pattern) of the diffractive optical element.

[0006] In summary, in the prior art, most of the methods for suppressing the zero-order spot of a diffractive optical element require substantial modifications to the structure of the diffractive optical element itself, which will increase the processing difficulty and production cost. There is a need for a solution that can suppress the zero-order spot of a diffractive optical element without changing the structure of the diffractive optical element itself. SUMMARY OF THE INVENTION

[0007] The object of the present invention is to overcome the deficiencies of the prior art and provide a solution that can suppress the zero-order spot of a diffractive optical element without changing the structure of the diffractive optical element itself.

[0008] To solve the above technical problems, the present invention provides a method for suppressing the zero-order spot of a diffractive optical element, which relates to an optical assembly based on a diffractive optical element. The method for suppressing the zero-order spot of a diffractive optical element includes: 1) removing the diffractive optical element from the optical path of the optical assembly; 2) adding a solid lens to the optical path of the optical assembly; 3) moving the lens along the optical axis so that the spot size of the outgoing beam of the lens projected on the working plane is larger than the size of the zero-order diffraction spot of the original optical assembly and smaller than the spot size of the first-order diffraction beam of the original optical assembly projected on the working plane; and 4) reinserting the diffractive optical element into the optical path.

[0009] Wherein, in step 2), the lens is a convex lens.

[0010] Wherein, in step 2), the lens is a concave lens.

[0011] Wherein, in step 2), the lens is a telescope.

[0012] Wherein, in step 2), the lens function of the lens is a quadratic function of a sphere, a paraboloid or an ellipsoid; or a sum of a quadratic function and higher-order terms.

[0013] Wherein, step 4) further includes: ensuring that the incident beam incident on the diffractive optical element does not fall outside the diffraction region of the diffractive optical element, and the beam incident on the inserted lens also does not fall outside the effective optical region of the lens.

[0014] Wherein, in steps 1) and 4), the diffraction full angle of the first-order diffraction beam of the diffractive optical element is greater than 5 degrees.

[0015] Wherein, in step 3), the position of the lens is such that ; wherein,

[0016] Position represents the position where the working plane is located;

[0017]

[0018]

[0019] wherein,

[0020] represents the spot size of the laser at the position d after adding the said lens, represents the spot size of the laser at the position (z + z' + d) without inserting the said lens, M 2 is the laser beam quality factor, is the laser wavelength, z is the distance between the waist of the incident beam and the said lens, d is the distance between the waist of the emerging beam after the laser passes through the said lens and the working plane, is the waist radius of the incident laser beam, is the waist radius of the emerging beam after the laser passes through the said lens, is the distance between the said lens and the waist of the output laser beam, is the focal length of the said lens.

[0021] Wherein, step 4) further includes: reducing the power density of the first-order spot in the coverage area of the zero-order spot diffused by the said lens, so that the power density of the superposition of the first-order spot and the zero-order spot diffused by adding the said lens is consistent with the power density of the first-order spot without adding the said lens.

[0022] According to another aspect of the present invention, there is also provided an optical assembly for suppressing the zero-order spot of a diffractive optical element, which includes a working plane, a diffractive optical element, and a beam expander. Wherein, the diffractive optical element is adapted to receive an incident collimated beam and project a diffracted beam onto the working plane, the diffracted beam includes a zero-order diffracted beam and a first-order diffracted beam, and the diffraction full angle of the first-order diffracted beam is greater than 5 degrees. The beam expander is adapted to be inserted into the optical path of the optical assembly, and the surface shape and insertion position of the beam expander satisfy: making the size of the expanded spot greater than the size of the original zero-order spot of the diffractive optical element, and the size of the expanded spot not exceeding the size of the spot of the first-order diffracted beam; wherein the expanded spot is the spot projected onto the working plane after the beam expander expands the collimated beam in the state of removing the diffractive optical element; the original zero-order spot is the spot projected onto the working plane by the zero-order diffracted beam in the state of not inserting the beam expander.

[0023] Compared with the prior art, the present application has at least one of the following technical effects:

[0024] 1. Without changing the design of the diffractive optical element itself, that is, without changing the surface microstructure of the diffractive optical element, the present application can achieve the suppression of the zero-order spot of the diffractive optical element.

[0025] 2. The zero-order spot suppression method of the present application can be well adapted to existing devices or equipment based on diffractive optical elements. By relatively simple measures, these existing devices or equipment can be upgraded to suppress the zero-order spot and improve the quality of the output beam.

[0026] 3. The zero-order spot suppression scheme of the present application can improve the safety of the output beam.

[0027] 4. The zero-order spot suppression scheme of the present application does not require integrating an additional virtual diffractive lens into the diffractive optical element, avoiding overly high processing requirements for the diffractive optical element. In other words, the present application can avoid problems in many aspects such as tolerances, costs, and reliability caused by overly high process difficulties. For example, in some embodiments of the present application, the diffractive optical element can maintain a small number of step levels (for example, the surface microstructure of the diffractive optical element can be composed of two-level steps), which is beneficial to reducing the processing difficulty.

[0028] 5. The zero-order spot suppression scheme of the present application does not require integrating an additional virtual diffractive lens into the diffractive optical element, avoiding the zero-order spot brought by the additional virtual diffractive lens itself.

[0029] 6. The zero-order spot suppression scheme of the present application can effectively suppress the zero-order spot without affecting or basically not affecting the first-order spot. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Shows a flowchart of a method for suppressing the zero-order spot of a diffractive optical element in an embodiment of the present invention;

[0031] Figure 2 Shows an optical path schematic diagram of an optical component to be upgraded in an embodiment of the present application;

[0032] Figure 3 Shows an optical path schematic diagram of an optical component for suppressing the zero-order spot by inserting a lens in an embodiment of the present application;

[0033] Figure 4 Shows an optical path schematic diagram of an optical component for suppressing the zero-order spot by inserting a lens in another embodiment of the present application;

[0034] Figure 5The figure shows the optical path schematic diagram of the optical component with an inserted solid convex lens based on the Gaussian light propagation principle in an embodiment of the present application;

[0035] Figure 6 The figure shows the optical path schematic diagram of the optical component without an inserted solid convex lens based on the Gaussian light propagation principle;

[0036] Figure 7 The figure shows an example of the power density curve of the light spot at the working plane after inserting the convex lens and adjusting it to an appropriate position in an embodiment of the present invention;

[0037] Figure 8 The figure shows an example of the power density curve of the light spot at the working plane without inserting the convex lens. Detailed implementation manners

[0038] To better understand the present application, more detailed descriptions of various aspects of the present application will be made with reference to the accompanying drawings. It should be understood that these detailed descriptions are only descriptions of the exemplary embodiments of the present application and do not limit the scope of the present application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] It should be noted that in this specification, the expressions such as first, second, etc. are only used to distinguish one feature from another feature and do not represent any limitation on the feature. Therefore, without departing from the teachings of the present application, the first subject discussed below may also be referred to as the second subject.

[0040] In the drawings, for ease of illustration, the thickness, dimensions, and shape of the objects have been slightly exaggerated. The drawings are only examples and are not drawn to an exact scale.

[0041] It should also be understood that the terms "include", "include having", "have", "contain", and / or "contain having", when used in this specification, indicate the presence of the stated features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or their combinations. In addition, when an expression such as "at least one of..." appears after the list of listed features, it modifies the entire list of listed features rather than an individual element in the list. In addition, when describing the embodiments of the present application, using "may" means "one or more embodiments of the present application". And the term "exemplary" is intended to refer to an example or illustration.

[0042] As used herein, the terms "substantially", "about" and similar terms are used as terms of approximation and not of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by a person of ordinary skill in the art.

[0043] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this application belongs. It should also be understood that terms (such as those defined in a common dictionary) should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0044] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other.

[0045] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0046] According to an embodiment of the present invention, there is provided a method for suppressing the zero-order spot of a diffractive optical element. The method makes the zero-order spot of the diffractive optical element diverge by adding a solid lens to the optical path and reasonably designing its surface profile and its position in the optical path, so as to achieve the technical effect of suppressing the zero-order spot of the diffractive optical element. In this embodiment, the design scheme of the diffractive optical element itself may not be changed, that is, the surface microstructure of the diffractive optical element is not changed. Therefore, the method of this embodiment can be better adapted to existing devices or equipment based on diffractive optical elements, and these existing devices or equipment can be upgraded through relatively simple measures to suppress the zero-order spot and improve the quality of the output beam. For example, after upgrading using the method of this embodiment, devices or equipment based on diffractive optical elements can improve the uniformity of the output beam and enhance the safety of the output beam.

[0047] Figure 1 The flowchart of the method for suppressing the zero-order spot of a diffractive optical element in an embodiment of the present invention is shown. Referring to Figure 1 , in this embodiment, the method for suppressing the zero-order spot of a diffractive optical element may include the following steps.

[0048] Step S10, for a device or equipment based on a diffractive optical element to be upgraded, remove the diffractive optical element from its optical path. A device or equipment based on a diffractive optical element can be understood as an optical component based on a diffractive optical element. For ease of description, it will sometimes be simply referred to as an optical component hereinafter.

[0049] Step S20: Add a lens to the optical path of the optical component. After adding the lens, the spot size on the original working plane (i.e., the working plane of the original device or equipment) can be observed. If the spot size after adding the lens is larger than the spot size without adding the lens, it indicates that the current position of the lens can reduce the influence of the zero-order spot.

[0050] In this embodiment, the lens can be a convex lens or a concave lens. The surface type of the lens can be a spherical surface, a parabolic surface, an ellipsoidal surface, etc. In other words, the lens function of the lens can be a quadratic function such as a spherical surface, a parabolic surface, or an ellipsoidal surface. Further, the lens function can also be the sum of a quadratic function such as a spherical surface, a parabolic surface, or an ellipsoidal surface and higher-order terms. For lenses with different surface types and different parameters, their setting positions may be different. Continuing to execute the following step S30 can help find a suitable setting position.

[0051] Step S30: Move the lens to adjust its position in the optical path and find a setting position that meets the set conditions. The set conditions can be: after adjusting the position of the lens, the spot size of the light beam emitted by the lens projected on the working plane is larger than the size of the zero-order diffraction spot of the original optical component, and at the same time, this spot size (the spot size of the light beam emitted by the lens projected on the working plane) is smaller than the spot size required by the original device or equipment (i.e., smaller than the spot size of the first-order diffraction beam output by the original device or equipment on its working plane). The position that meets the above set conditions can be regarded as the optimal setting position of the lens for the optical component to be upgraded.

[0052] Step S40: Re-insert the diffractive optical element into the optical path. Note that ensure that the incident light beam of the diffractive optical element does not fall outside the diffraction region of the diffractive optical element, and at the same time, the light beam incident on the inserted lens does not fall outside the effective optical region of the lens. In this step, the inserted diffractive optical element can be exactly the same as the diffractive optical element taken out in step S10. That is, the two can be the same diffractive optical element with exactly the same optical parameters.

[0053] Further, Figure 2 shows the schematic optical path diagram of the optical component to be upgraded in an embodiment of the present application. Figure 3 shows the schematic optical path diagram of the optical component that suppresses the zero-order spot by inserting a lens in an embodiment of the present application. Refer to Fig. Figure 2 and Figure 3 , in this embodiment, before performing step S10, the collimated laser a irradiates the diffractive optical element 1, and the first-order spot output by the diffractive optical element 1 is used as the working spot (or called the working beam) on the working plane. In this embodiment, the first-order spot covers the ±1-order diffraction angles. Figure 2The light rays c1 and c2 correspond to the ±1 order diffraction angles respectively. On the other hand, based on the diffraction principle, the center of the diffractive optical element 1 has a zero-order light spot formed by the zero-order beam b, and the power density of this zero-order light spot is relatively high, which easily causes the non-uniformity of the working light spot (or called the working beam). Figure 3 It shows the optical path of the optical component after step S40 is completed. In this embodiment, the position where the lens 2 is inserted is such that the diffractive optical element 1 is located in front of the focal plane of the lens 2. The lens 2 can diverge the zero-order beam b, thereby suppressing the power density of the zero-order light spot and improving the uniformity of the working beam. On the other hand, the ±1 order diffraction angles of the diffracted beam (i.e., the output beam of the diffractive optical element 1) can remain basically unchanged. In particular, when both the ±1 order diffraction angles are greater than 2.5 degrees (i.e., the first-order diffraction full angle is greater than 5.0 degrees), the influence of the inserted diffractive optical element on the ±1 order diffraction angles can be negligible (here, negligible can be understood as adding the lens will not affect the realization of the original functions of the output light spot). When both the ±1 order diffraction angles are greater than 12.5 degrees (i.e., the first-order diffraction full angle is greater than 25.0 degrees), the solution of suppressing the zero-order light spot by inserting a lens in this embodiment will have more obvious advantages compared with the prior art. For example, the solution of suppressing the zero-order light spot by inserting a lens in this embodiment can significantly reduce the processing difficulty and cost. When the first-order diffraction full angle is greater than 25.0 degrees, if a virtual diffraction prism is integrated in the diffractive optical element, the requirement for manufacturing accuracy will be greatly increased. For the solution of integrating a virtual diffraction prism to suppress the zero-order light spot, its diffractive optical element generally requires at least 4 steps, which not only greatly increases the processing difficulty but also causes problems such as excessive cost. And the solution of this embodiment can avoid these problems.

[0054] Furthermore, Figure 4 It shows a schematic diagram of the optical path of the optical component for suppressing the zero-order light spot by inserting a lens in another embodiment of the present application. In this embodiment, the position where the lens 2 is inserted is such that the diffractive optical element 1 is located behind the focal plane of the lens 2. After the incident collimated beam a passes through the lens 2, it converges first and then diverges, thereby diverging the zero-order beam b of the diffractive optical element 1 and reducing the power density. At the same time, the ±1 order diffraction angles of the diffracted beam (i.e., the output beam of the diffractive optical element 1) can remain basically unchanged.

[0055] The method for suppressing the zero-order spot of a diffractive optical element in the above embodiments can avoid complex optical designs, without the need to change the surface microstructure of the original diffractive optical element. Through relatively simple and feasible measures, these existing devices or equipment can be upgraded to eliminate or suppress the negative impact of the zero-order spot, with good economic benefits. Moreover, the method of this embodiment has a wide range of applicable scenarios. For example, the method of this embodiment can be applied to various Gaussian beam shaping components to eliminate or suppress the negative impact of the zero-order spot. The Gaussian beam shaping components can be used in various types of laser devices to shape the Gaussian beam of common lasers into a beam with a uniform distribution, a quasi-uniform distribution, or a power density distribution presenting an M-shaped distribution (i.e., strong at the edge and weak at the center of the spot). The above Gaussian beam shaping components can be applied to many fields such as laser heat treatment, laser hardening, laser processing of semiconductor wafers, laser welding, laser drilling, laser marking, and medical beauty. Therefore, the method of this embodiment has a wide scope of application and excellent portability, and is particularly suitable for upgrading existing laser processing equipment or laser treatment equipment that has been applied in various industrial or medical fields. In addition, this embodiment also has application value in the field of laser photography. For example, the time-of-flight (TOF) measurement technology in the three-dimensional sensing field requires a laser beam with a uniform power density distribution. Therefore, the method of this embodiment can be used to suppress the zero-order spot of the projected laser of the TOF module or TOF equipment. Another example is that in the application scenario of laser illumination (some high-end photography may use laser illumination), the method of this embodiment can be used to suppress the zero-order spot of the laser illumination source.

[0056] Further, still referring to Figure 3 , in the method for suppressing the zero-order spot of a diffractive optical element according to an embodiment of the present invention, the lens inserted into the optical path is a solid convex lens. Here, "solid" is relative to "virtual", that is, the lens is an actual optical element. When the solid lens is a convex lens, the position of the convex lens can be set so that the waist position of the incident laser and the focal length of the convex lens satisfy a certain relationship to meet the set conditions described above. Although when the waist position of the incident laser is outside the focal plane of the convex lens, the convex lens focuses the incident laser, the incident laser will diverge again after focusing. If the position of the required uniform spot or quasi-uniform spot is far from the lens, so that the incident laser has diverged at the use position and the divergence is greater than the spot size without using the lens, then the zero-order power density can also be reduced at this time. That is, the effect of suppressing the zero-order spot is achieved. The following further describes this embodiment in combination with the principle and the drawings.

[0057] When no lens is inserted, the size of the zero-order spot follows the propagation equation of single-mode Gaussian light or multi-mode Gaussian light. For single-mode Gaussian light, the spot radius satisfies the following formula (1).

[0058] (1)

[0059] For multimode Gaussian light, the spot radius of the laser after propagating a distance z satisfies the following formula (2).

[0060] (2)

[0061] In formulas (1) and (2), is the waist radius of the single-mode Gaussian light, is the beam quality factor of the multimode Gaussian light. is the laser wavelength.

[0062] Furthermore, Figure 5 shows the optical path schematic diagram of the optical component with an inserted solid convex lens based on the Gaussian light propagation principle in an embodiment of the present application. Figure 6 shows the optical path schematic diagram of the optical component without inserting a solid convex lens based on the Gaussian light propagation principle. Taking to represent the spot size of the laser at the position d after adding the lens, represents the spot size of the laser at the position (z + z' + d) without inserting the lens. Figure 5 The position d in Figure 6 and the position (z + z' + d) in M 2 is the laser beam quality factor, is the laser wavelength, z is the distance between the waist of the incident beam and the lens, d is the distance between the waist of the emergent beam of the laser passing through the lens and the working plane, is the waist radius of the original laser (or incident laser), is the waist radius of the emergent beam of the laser after passing through the lens, then

[0063] (3)

[0064] (4)

[0065] Wherein, (5)

[0066] is the focal length of the inserted solid lens. When f is positive, the inserted solid lens is a convex lens; when f is negative, the inserted solid lens is a concave lens.

[0067] To meet the set conditions described above, it is necessary to ensure that the spot size after adding the lens is larger than the spot size before adding the lens, that is , where the position represents the position where the working plane is located. Based on the above formula, the lens setting position or position range that meets the set conditions described above can be calculated. Among them, the set conditions can be that the spot size after adding the lens is larger than the spot size before adding the lens, and the size of the diffraction zero-order spot after adding the lens is not larger than the size of the diffraction first-order spot.

[0068] Furthermore, in an embodiment of the present application, the step S30 may include: first calculate the lens setting position range or the preferred position that can meet the set conditions according to the above formulas (3), (4) and (5), then adjust the solid lens to the lens setting position range or the preferred position, and then observe or measure the spot size on the working plane, and then finely adjust the position of the solid lens according to the measured spot size to determine the final position of the solid lens.

[0069] Furthermore, in another embodiment of the present application, the step S30 may include: first determine the magnification of the zero-order spot size, then calculate the lens setting position corresponding to the set magnification that can meet the set conditions according to the above formulas (3), (4) and (5), then adjust the solid lens to the calculated lens setting position, and then observe or measure the spot size on the working plane, and then finely adjust the position of the solid lens according to the measured spot size to determine the final position of the solid lens.

[0070] Furthermore, in yet another embodiment of the present invention, in the method for suppressing the zero-order spot of a diffractive optical element, the lens inserted into the optical path is a solid concave lens. A concave lens generally can play a role in beam expansion, so using a concave lens generally can reduce the influence of the zero order. The setting position of the concave lens can be adjusted according to the actual spot size on the working plane after inserting the concave lens. In another embodiment, the setting position of the concave lens can also be calculated or estimated according to the above formulas (3), (4) and (5). When the focal length f is negative, the inserted solid lens is a concave lens; or first calculate or estimate the setting position of the concave lens, and then adjust the setting position of the concave lens according to the actual spot size on the working plane after inserting the concave lens.

[0071] Furthermore, in still another embodiment of the present invention, in the method for suppressing the zero-order spot of a diffractive optical element, the lens inserted into the optical path is a solid telescope (including Newton telescope and Galileo telescope). While collimating the laser, the telescope also expands the laser beam, so the telescope can reduce the power density of the zero order.

[0072] Adding a solid lens to the optical path theoretically changes the diffraction angle of the first-order diffraction. However, if the angle of the first-order diffraction is large, this change can usually be ignored, that is, it will not affect the use of the laser device. In a set of experimental cases, the full diffraction angles of the first-order diffraction are 30.0 degrees and 40.0 degrees respectively. The full diffraction angle of the first-order diffraction refers to the angle after combining the diffraction angles of ±1 order. Referring to Figure 2 , the full diffraction angle of the first-order diffraction is the included angle between the light ray c1 and the light ray c2. In the experiment, when the original full diffraction angle of ±1 order is 30.0 degrees, at a working distance of 2 meters (that is, the working plane is located 2 meters from the diffractive optical element), after inserting the solid lens, the diameter of the 0th-order light spot increases from 2 mm to about 10 mm, which is equivalent to the full angle of the 0th order increasing from 0.06 degrees to 0.29 degrees, an increase of 0.23 degrees (an increase of about 383%), and the full angle of the ±1 order diffraction is 30.2 degrees. When the original full diffraction angle of ±1 order is 40.0 degrees, at a working distance of 2 meters (that is, the working plane is located 2 meters from the diffractive optical element), after inserting the solid lens, the diameter of the 0th-order light spot increases from 2 mm to about 10 mm, which is equivalent to the full angle of the 0th order increasing from 0.06 degrees to 0.29 degrees, an increase of 0.23 degrees. And the full angle of the ±1 order diffraction is 40.2 degrees. It can be seen that after inserting the solid lens, the influence on the full diffraction angle of the ±1 order can be ignored. In this experimental case, for the zero order, since the diameter of the zero-order light spot increases from 2 mm to about 10 mm, the power density of the 0th order drops to 4% of the original 0th-order power density (that is, the 0th-order power density in the case of not using the method of the present invention). In other words, inserting a solid lens can effectively reduce the power density of the zero-order light spot. In fact, when the full diffraction angle of the first-order diffraction is greater than 5.0 degrees, the influence of inserting the lens on the ±1 order diffraction light spot is very small. For the original device or equipment (that is, the original un-upgraded device or equipment based on the diffractive optical element), when the full diffraction angle of the first-order diffraction is greater than 5.0 degrees, then after inserting the solid lens according to the method of the present invention, the output laser light spot can still achieve its original function. At the same time, due to the insertion of the solid lens, the zero-order light spot in the output light spot can be effectively suppressed. When the full diffraction angle of the first-order diffraction is greater than 25.0 degrees, compared with the prior art, the solution provided by the present invention for suppressing the zero-order light spot by inserting a solid lens will have more obvious advantages.

[0073] Furthermore, Figure 7 shows an example of the spot power density curve at the working plane after inserting a convex lens and adjusting it to an appropriate position in an embodiment of the present invention, Figure 8 shows an example of the spot power density curve at the working plane without inserting a convex lens. Comparing Figure 7 and Figure 8It can be seen that after inserting the solid convex lens, the zero-order light spot located near the optical axis is eliminated or significantly weakened. In other words, inserting the solid convex lens according to the method of the present invention can effectively suppress the zero-order diffraction light spot. Figure 7 and Figure 8 In [references], the abscissa represents the field of view (abbreviated as FOV) corresponding to the measurement position points on the working plane, and its unit is degree. Specifically, the measurement position point refers to the position point where the power density is measured. The field of view of the measurement position point is the angle between the line connecting the measurement position point and the center of the DOE (diffractive optical element) and the optical axis. The center of the DOE refers to the intersection point of the DOE and the optical axis. The ordinate represents the power density, that is, the power density measured at the measurement position point. In this embodiment, the power density is the normalized power density. Refer to Figure 7 and Figure 8 In [references], during the test, the diffraction full angle of the first-order diffraction is about 40 degrees. When the convex lens is not inserted (refer to Figure 8 ), the central peak of the power density curve caused by the zero-order light spot is very obvious. After inserting the convex lens (refer to Figure 7 ), the power density curve is smooth and the zero-order light spot is effectively suppressed.

[0074] Furthermore, the added lens has a diverging effect on the zero-order light spot, and the diffused zero-order light spot may overlap with the first-order light spot. In the design, if the required first-order light spot is a relatively large uniform and strong light spot, usually the power density of the diffused zero-order light spot can be made much smaller than that of the first-order light spot, so as to prevent the interference caused by the superimposed zero-order light spot or minimize the negative impact caused by the zero-order light spot. For example, assuming that the power density of the first-order light spot is 1 and the power density of the zero-order light spot is 10, then the radius of the zero-order light spot can be diffused to 5 times or 10 times that of the zero-order light spot without the lens, that is, the area of the zero-order light spot is diffused to 25 times or 100 times that of the zero-order light spot without the lens. In this way, the power density of the zero-order light spot is reduced to 4% or 1% of the zero-order light spot without the lens. At this time, the non-uniformity error of the first-order light spot increases by at most 4% or 1%.

[0075] Furthermore, in an embodiment of the present invention, the influence of the diffusion of the zero-order light spot on the uniformity can also be overcome by the idea of power density compensation. For example, the power density of the first-order light spot in the area covered by the diffused zero-order light spot can be correspondingly adjusted downwards (for example, the power density is reduced by 4% or 1%). In this way, after adding the lens, the first-order light spot is superimposed with the diffused zero-order light spot due to the addition of the lens, which can make the power density of the actually output light spot closer to the required power density (the required power density can be understood as the designed power density of the laser device).

[0076] Numerous embodiments were introduced in the foregoing to describe the method provided by the present application for suppressing the zero-order spot of a diffractive optical element. Further, according to some other embodiments of the present application, an optical assembly for suppressing the zero-order spot of a diffractive optical element is also provided.

[0077] According to an embodiment of the present application, an optical assembly for suppressing the zero-order spot of a diffractive optical element is provided. In this embodiment, the optical assembly may be a device or equipment based on a diffractive optical element that needs to be upgraded, such as a beam shaper. Referring to Figure 3 , the optical assembly may include a working plane 3, a diffractive optical element 1, and a beam-expanding optical element. The diffractive optical element 1 is adapted to receive an incident collimated beam and project a diffracted beam onto the working plane 3, and the diffraction angle of the first-order diffracted beam of the diffractive optical element 1 is greater than 25 degrees. The beam-expanding optical element may be a lens 2, and the surface shape and installation position of the lens 2 are adapted to: expand the spot size at the working plane 3 of the optical assembly in the state without the diffractive optical element (relative to the size of the zero-order diffracted spot of the original optical assembly), and the spot size obtained after beam expansion does not exceed the spot size of the first-order diffracted beam. In this embodiment, the lens is a solid convex lens, which is arranged at the front end (i.e., the incident end) of the diffractive optical element. In this embodiment, the diffractive optical element 1 is located in front of the focal plane of the lens 2. Further, in one embodiment, the optical assembly may further include a collimating mirror, which is located at the front end of the beam-expanding optical element to provide an incident collimated beam.

[0078] Figure 4 An optical assembly for suppressing the zero-order spot of a diffractive optical element in another embodiment of the present application is shown. The difference between this embodiment and the Figure 3 embodiment shown is that in this embodiment, the diffractive optical element 1 is located behind the focal plane of the lens 2.

[0079] Further, in yet another embodiment of the present invention, in the optical assembly for suppressing the zero-order spot of a diffractive optical element, the beam-expanding optical element is a solid concave lens. A concave lens generally can play a role in beam expansion, so using a concave lens generally can reduce the influence of the zero order.

[0080] Further, in still another embodiment of the present invention, in the optical assembly for suppressing the zero-order spot of a diffractive optical element, the beam-expanding optical element is a solid telescope (including a Newtonian telescope and a Galilean telescope). A telescope collimates and expands the laser at the same time, so the telescope can reduce the power density of the zero order.

[0081] In the above embodiments, the diffractive optical element is adapted to receive an incident collimated beam and project a diffracted beam onto the working plane. The diffracted beam includes a zero-order diffracted beam and a first-order diffracted beam, and the total diffraction angle of the first-order diffracted beam is greater than 5 degrees. The beam expander is adapted to be inserted into the optical path of the optical assembly, and the surface shape and insertion position of the beam expander satisfy the following conditions: the size of the expanded beam spot is greater than the size of the original zero-order beam spot of the diffractive optical element, and the size of the expanded beam spot does not exceed the size of the beam spot of the first-order diffracted beam. Wherein the expanded beam spot is the beam spot projected onto the working plane after the beam expander expands the collimated beam in the state where the diffractive optical element is removed; the original zero-order beam spot is the beam spot projected onto the working plane by the zero-order diffracted beam in the state where the beam expander is not inserted.

[0082] Further, in yet another embodiment of the present invention, the position of the lens is such that ; wherein,

[0083] represents the position where the working plane is located;

[0084]

[0085]

[0086] Wherein,

[0087] represents the spot size of the laser at the position d after adding the lens, represents the spot size of the laser at the position (z + z' + d) when the lens is not inserted, M 2 is the laser beam quality factor, is the laser wavelength, d is the distance between the beam waist of the output beam of the laser passing through the lens and the lens, is the beam waist radius of the incident laser, is the beam waist radius of the output beam of the laser passing through the lens, is the distance between the lens and the output laser beam waist, is the focal length of the lens.

[0088] Further, in another embodiment of the present invention, the optical component further includes a laser output module for providing the collimated beam, and the power density of the laser output module is adjustable. After inserting the beam expander, the power density of the laser output module can be reduced so that the power density after the superposition of the first-order spot output by the diffractive optical element and the zero-order spot diffused by inserting the beam expander is equal to the power density of the first-order spot when the beam expander is not inserted.

[0089] Further, in another embodiment of the present invention, for the optical component, after inserting the beam expander, the first-order spot output by the diffractive optical element and the zero-order spot diffused by inserting the beam expander are superposed to jointly form a spot with a preset function on the working plane.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for suppressing the zero-order spot of a diffractive optical element, which relates to an optical assembly based on a diffractive optical element. The diffractive optical element is adapted to receive an incident collimated beam and project a diffracted beam onto a working plane. The diffraction full angle of the first-order diffracted beam of the diffractive optical element is greater than 5 degrees, and it is characterized in that, The method for suppressing the zero-order spot of a diffractive optical element includes: 1) Removing the diffractive optical element from the optical path of the optical assembly; 2) Adding a solid lens to the optical path of the optical assembly; the lens function of the lens is a quadratic function of a spherical surface, a parabolic surface or an ellipsoidal surface, or the sum of a quadratic function and higher-order terms; 3) Moving the lens along the optical axis so that the spot size of the outgoing beam of the lens projected on the working plane is larger than the size of the zero-order diffraction spot of the original optical assembly and smaller than the spot size of the first-order diffraction beam of the original optical assembly projected on the working plane; and 4) Re-inserting the diffractive optical element into the optical path; Among them, in the said step 3), the position of the lens is such that ; among them, Represents the position where the working plane is located; ； ； Among them, ; Indicates the spot size of the laser at the position d after adding the lens, and represents the spot size of the laser at the position (z + z' + d) without inserting the lens, M 2 is the laser beam quality factor, is the laser wavelength, z is the distance between the waist of the incident beam and the lens, d is the distance between the waist of the output beam after the laser passes through the lens and the working plane, is the waist radius of the incident laser, is the waist radius of the output beam after the laser passes through the lens, is the distance between the lens and the waist of the output laser beam, is the focal length of the lens.

2. The method for suppressing the zero-order spot of a diffractive optical element according to claim 1, characterized in that, In step 2), the lens is a convex lens.

3. The method for suppressing the zero-order spot of a diffractive optical element according to claim 1, wherein In step 2), the lens is a concave lens.

4. The method for suppressing the zero-order spot of a diffractive optical element according to claim 1, wherein In step 2), the lens is a telescope.

5. The method for suppressing the zero-order spot of a diffractive optical element according to claim 1, characterized in that, Step 4) further includes: ensuring that the incident beam incident on the diffractive optical element does not fall outside the diffraction region of the diffractive optical element, and the beam incident on the inserted lens also does not fall outside the effective optical region of the lens.

6. The method for suppressing the zero-order spot of a diffractive optical element according to claim 1, wherein Step 4) further includes: reducing the power density of the first-order spot in the coverage area of the zero-order spot diffused by the lens so that the power density of the superposition of the first-order spot and the zero-order spot diffused by adding the lens is the same as the power density of the first-order spot without adding the lens.

7. An optical component for suppressing the zero-order spot of a diffractive optical element, characterized in that, Including: Working plane; A diffractive optical element adapted to receive an incident collimated beam and project a diffracted beam onto the working plane, the diffracted beam including a zero-order diffracted beam and a first-order diffracted beam, and the diffraction full angle of the first-order diffracted beam being greater than 25 degrees; And A beam expander optical element adapted to be inserted into the optical path of the optical assembly, and the surface shape and insertion position of the beam expander optical element satisfy: the size of the beam-expanded spot is larger than the size of the original zero-order spot of the diffractive optical element, and the size of the beam-expanded spot does not exceed the spot size of the first-order diffracted beam; wherein the beam-expanded spot is the spot projected on the working plane after the beam expander optical element expands the collimated beam in the state where the diffractive optical element is removed; the original zero-order spot is the spot projected on the working plane by the zero-order diffracted beam in the state where the beam expander optical element is not inserted. Among them, the beam expanding optical element is a solid lens; the lens function of the lens is a quadratic function of a spherical surface, a parabolic surface or an ellipsoidal surface, or the sum of a quadratic function and higher-order terms, and the position of the lens is such that ; among them, Represents the position where the working plane is located; ； ； Among them, ; Indicates the spot size of the laser at the position d after adding the lens, and indicates the spot size of the laser at the position (z + z' + d) without inserting the lens, M 2 is the laser beam quality factor, is the laser wavelength, z is the distance between the waist of the incident beam and the lens, d is the distance between the waist of the output beam after the laser passes through the lens and the working plane, is the waist radius of the incident laser, is the waist radius of the output beam after the laser passes through the lens, is the distance between the lens and the waist of the output laser beam, is the focal length of the lens.

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