System and method for measuring satellite ghost efficiency of diffractive lens

Abstract

A system for measuring satellite ghost efficiency of a diffractive lens is provided. The system includes: a light source configured to output a first probe beam; and the light beam fine tuning assembly is arranged between the light source and the diffraction lens and is configured to convert the first detection light beam into a second detection light beam, and the second detection light beam is a non-collimated light beam. The diffractive lens diffracts the second probe beam into a plurality of diffracted beams including a first diffracted beam of a main diffraction order and a second diffracted beam of a satellite ghost diffraction order. The beam fine tuning assembly includes one or more optical lenses and an adjustable optical power. The system also includes a detector configured to generate a beam spot pattern including a first beam spot corresponding to the first diffracted beam and a second beam spot corresponding to the second diffracted beam.

Description

Technical Field

[0001] The present disclosure generally relates to optical systems and methods, and more particularly, to systems and methods for measuring the satellite ghost efficiency of diffractive lenses. Background Art

[0002] Diffractive optical elements ("DOEs") are thin phase elements that generate a desired light distribution by means of interference and diffraction operations. Diffractive lenses are members of the DOE family. In addition to diffracting an incident light beam into several light beams propagating in different directions (i.e., different diffraction angles), diffractive lenses can also converge or diverge the incident light beam. Diffractive lenses include ruled diffractive lenses, holographic diffractive lenses, Fresnel lenses, liquid crystal diffractive lenses, metamaterial or metasurface lenses, Pancharatnam-Berry phase ("PBP") lenses, polarization volume hologram ("PVH") lenses, diffractive lenses based on surface relief structures, diffractive lenses based on volume Bragg gratings ("VBGs"), and the like. Diffractive lenses provide an aperture and focal length comparable to those of conventional lenses with continuous curved surfaces, with smaller thickness and lighter weight. Therefore, diffractive lenses are low-cost and lightweight alternatives to conventional lenses. Summary of the Invention

[0003] In accordance with one aspect of the present disclosure, there is provided a system for measuring the satellite ghost efficiency of a diffractive lens. The system includes: a light source configured to output a first probe beam; and a beam tweaking assembly disposed between the light source and the diffractive lens and configured to convert the first probe beam into a second probe beam, the second probe beam being a non-collimated beam. The diffractive lens diffracts the second probe beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of a parent diffraction order and a second diffracted beam of a satellite ghost diffraction order. The beam tweaking assembly includes one or more optical lenses, and the optical power of the beam tweaking assembly is adjustable. The system further includes a detector configured to generate a spot pattern, the spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam.

[0004] Optionally, the first detection beam has a first beam diameter at the light input surface of the beam fine-tuning component, the second detection beam has a second beam diameter at the light output surface of the beam fine-tuning component, and the first beam diameter is greater than the second beam diameter.

[0005] Optionally, the system may further include a controller configured to adjust the optical power of the beam fine-tuning component, thereby adjusting the spot size of each of the first spot and the second spot and the spacing between the first spot and the second spot until the controller determines that the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing is greater than a second predetermined value.

[0006] Optionally, the controller may further be configured to: analyze the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than a first predetermined value and whether the spacing between the first spot and the second spot is greater than a second predetermined value; and based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value, or the spacing is less than or equal to the second predetermined value, adjust the optical power provided to the first detection beam of the beam fine-tuning component until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing is greater than the second predetermined value.

[0007] Optionally, the controller may further be configured to: determine the optical power of the second diffracted beam and the optical power of the second detection beam when the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing is greater than a second predetermined value; and determine the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

[0008] Optionally, the first predetermined value and the second predetermined value may be equal to the size of the effective light receiving area of the detection unit in the detector.

[0009] Optionally, the satellite ghost line diffraction order corresponding to the second diffracted beam is the first satellite ghost line diffraction order, the plurality of diffracted beams further includes a third diffracted beam of a second satellite ghost line diffraction order, and the spot pattern further includes a third spot corresponding to the third diffracted beam.

[0010] Optionally, the system may further include a controller configured to adjust the optical power of the beam fine-tuning component, thereby adjusting the spot size of each of the first spot, the second spot, and the third spot, the first spacing between the first spot and the second spot, and the second spacing between the second spot and the third spot until the spot size of each of the first spot, the second spot, and the third spot is less than a first predetermined value and the first spacing and the second spacing are greater than a second predetermined value.

[0011] Optionally, one or more optical lenses included in the beam fine-tuning assembly may include a first optical lens and a second optical lens, and the distance between the first optical lens and the second optical lens may be adjustable.

[0012] Optionally, at least one of the one or more optical lenses included in the beam fine-tuning assembly may have an adjustable optical power.

[0013] Optionally, the beam fine-tuning assembly includes a spatial filter, a singlet lens, and a reverse beam expander arranged in an optical sequence, and the singlet lens is disposed between the spatial filter and the reverse beam expander.

[0014] In accordance with another aspect of the present disclosure, a method for measuring the satellite ghost line efficiency of a diffractive lens is provided. The method includes: outputting a first probe beam from a light source to a beam fine-tuning assembly disposed between the light source and the diffractive lens, the beam fine-tuning assembly including one or more optical lenses, and the optical power of the beam fine-tuning assembly being adjustable. The method further includes: converting, by the beam fine-tuning assembly, the first probe beam into a second probe beam propagating toward the diffractive lens, the second probe beam being a non-collimated beam, and the diffractive lens diffracting the second probe beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of a main diffraction order and a second diffracted beam of a satellite ghost line diffraction order. The method further includes: generating, by a detector, a spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam.

[0015] Optionally, the first probe beam has a first beam diameter at the light input surface of the beam fine-tuning assembly, the second probe beam has a second beam diameter at the light output surface of the beam fine-tuning assembly, and the first beam diameter is greater than the second beam diameter.

[0016] Optionally, the method may further include: controlling, by a controller, the optical power of the beam fine-tuning assembly to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value.

[0017] Optionally, the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value, including: the controller analyzes the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than the first predetermined value and whether the spacing distance between the first spot and the second spot is greater than the second predetermined value; and based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value, or the spacing distance is less than or equal to the second predetermined value, the controller adjusts the optical power of the beam fine-tuning component provided to the first detection beam until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value.

[0018] Optionally, the method may further include: when the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value, the controller determines the optical power of the second diffracted beam and the optical power of the second detection beam; and the controller determines the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

[0019] Optionally, the first predetermined value and the second predetermined value may be equal to the size of the effective light receiving area of the detection unit in the detector.

[0020] Optionally, one or more optical lenses included in the beam fine-tuning component include a first optical lens and a second optical lens, and the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot, including: the controller adjusts the distance between the first optical lens and the second optical lens to change the optical power of the beam fine-tuning component.

[0021] Optionally, the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot, including: the controller adjusts the optical power of at least one optical lens among one or more optical lenses included in the beam fine-tuning component.

[0022] Optionally, the spot pattern further includes a third spot corresponding to the third diffracted beam, and the method further includes: analyzing the spot pattern by a controller to determine whether a plurality of spot sizes of the first spot, the second spot, and the third spot are smaller than the size of the effective light receiving area of the detection unit of the detector, and whether a plurality of spacing distances between adjacent spots among the first spot, the second spot, and the third spot are greater than the size of the effective light receiving area of the detection unit of the detector; based on determining that at least one of the plurality of spot sizes is greater than or equal to the size of the effective light receiving area of the detection unit of the detector, or at least one of the plurality of spacing distances is less than or equal to the size of the effective light receiving area of the detection unit of the detector, continuously adjusting, by the controller, the optical power of the beam fine-tuning component to reduce the beam diameter of the second detection beam until the controller determines that the plurality of spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the plurality of spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector; and based on determining that the plurality of spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the plurality of spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector, obtaining, by the controller, a first optical power of one of the first diffracted beam, the second diffracted beam, and the third diffracted beam corresponding to the satellite ghost line diffraction order of the diffraction lens and a second optical power of the second detection beam, and calculating the satellite ghost line efficiency of the diffraction lens by dividing the first optical power by the second optical power.

[0023] It will be appreciated that any features described herein as being suitable for incorporation into one or more aspects or embodiments of the present disclosure are intended to be general across any and all aspects and embodiments of the present disclosure. Those skilled in the art can understand other aspects of the present disclosure based on the specification, claims, and drawings of the present disclosure. The above general description and the following detailed description are merely exemplary and illustrative, and are not limiting of the claims.

[0024] Those skilled in the art can understand other aspects of the present disclosure based on the specification, claims, and drawings of the present disclosure. The above general description and the following detailed description are merely exemplary and illustrative, and are not limiting of the claims. Description of the Drawings

[0025] The following drawings are provided for illustrative purposes in accordance with various disclosed embodiments, and these drawings are not intended to limit the scope of the present disclosure. In the drawings:

[0026] Figure 1A Shows a class I satellite ghost line diffraction order of a diffraction lens according to an embodiment of the present disclosure;

[0027] Figure 1B Shows a class I satellite ghost line diffraction order of a diffraction lens according to an embodiment of the present disclosure;

[0028] Figure 1C FIG. 1 shows a schematic diagram of a conventional system for measuring the diffraction efficiency of a diffraction grating using a collimated probe beam and a detector;

[0029] Figure 1D FIG. 2 shows the use of Figure 1C the conventional system shown in FIG. 1 to measure the diffraction efficiency of a diffractive lens;

[0030] Figure 2A FIG. 3 shows a schematic diagram of a system for measuring the satellite ghost line efficiency of a diffractive lens according to an embodiment of the present disclosure;

[0031] Figures 2B to 2D FIG. 4 shows various spot patterns formed by the beam diffracted by the diffractive lens at the measurement plane when adjusting the beam fine-tuning component included in the system shown in FIG. 3 according to various embodiments of the present disclosure to provide various optical powers; Figure 2A FIG. 5 shows a schematic diagram of a system according to an embodiment of the present disclosure, which shows an exemplary structure of the beam fine-tuning component shown in FIG. 4;

[0032] Figure 3A FIG. 6 shows a schematic diagram of a system according to an embodiment of the present disclosure, which shows an exemplary structure of the beam fine-tuning component shown in FIG. 4; Figure 2A FIG. 7 shows a spot pattern of a diffractive lens experimentally detected at the measurement plane using the system shown in FIG. 5 according to an embodiment of the present disclosure; Figure 2A FIG. 8 shows a spot pattern of the same diffractive lens experimentally detected at the same measurement plane using a conventional system;

[0033] Figure 3B FIG. 9 shows a flowchart of a method for measuring the satellite ghost line efficiency of a diffractive lens according to an embodiment of the present disclosure; Figure 2A FIG. 10 schematically shows a three-dimensional (3D) view of an optical film included in a diffractive lens according to an embodiment of the present disclosure, and the satellite ghost line efficiency of the diffractive lens can be measured by the disclosed system; and Figure 2A FIG. 11 shows a spot pattern of a diffractive lens experimentally detected at the measurement plane using the system shown in FIG. 5 according to an embodiment of the present disclosure;

[0034] Figure 4A FIG. 12 shows a spot pattern of a diffractive lens experimentally detected at the measurement plane using the system shown in FIG. 5 according to an embodiment of the present disclosure; Figure 3A FIG. 13 shows a spot pattern of the same diffractive lens experimentally detected at the same measurement plane using a conventional system;

[0035] Figure 4B FIG. 14 shows a spot pattern of the same diffractive lens experimentally detected at the same measurement plane using a conventional system; Figure 4A FIG. 15 shows a spot pattern of the same diffractive lens experimentally detected at the same measurement plane using a conventional system;

[0036] Figure 5 FIG. 16 is a flowchart showing a method for measuring the satellite ghost line efficiency of a diffractive lens according to an embodiment of the present disclosure;

[0037] Figure 6A FIG. 17 schematically shows a three-dimensional (three-dimensional, “3D”) view of an optical film included in a diffractive lens according to an embodiment of the present disclosure, and the satellite ghost line efficiency of the diffractive lens can be measured by the disclosed system; and

[0038] Figure 6B and 6CSchematically shows according to an embodiment of the present disclosure Figure 6A Various views of a part of the optical film shown in the figure, which show the in-plane orientation of the optically anisotropic molecules in the optical film. Detailed description

[0039] Embodiments consistent with the present disclosure will be described with reference to the accompanying drawings. These drawings are merely examples for illustrative purposes and are not intended to limit the scope of the present disclosure. Whenever possible, the same reference numerals are used in all the drawings to represent the same or similar components, and their detailed descriptions may be omitted.

[0040] In addition, in the present disclosure, the disclosed embodiments and the features of the disclosed embodiments may be combined. The described embodiments are some but not all of the embodiments of the present disclosure. Based on the disclosed embodiments, those of ordinary skill in the art can derive other embodiments according to the present disclosure. For example, modifications, adaptations, substitutions, additions, or other variations can be made based on the disclosed embodiments. Such variations of the disclosed embodiments are still within the scope of the present disclosure. Therefore, the present disclosure is not limited to the disclosed embodiments. Instead, the scope of the present disclosure is defined by the appended claims.

[0041] As used herein, terms such as "couple," "coupled," or "coupling" may include optical coupling, mechanical coupling, electrical coupling, electromagnetic coupling, or any combination thereof. "Optical coupling" between two optical elements refers to a configuration in which the two optical elements are arranged in an optical sequence, and the light output from one optical element can be directly or indirectly received by the other optical element. The optical sequence refers to the optical positioning of a plurality of optical elements in an optical path such that the light output from one optical element can be transmitted, reflected, diffracted, converted, modified, or otherwise processed or manipulated by one or more of the plurality of other optical elements. In some embodiments, the order in which the plurality of optical elements are arranged may or may not affect the overall output of the plurality of optical elements. The coupling can be direct coupling or indirect coupling (e.g., coupling through an intermediate element).

[0042] The phrase "at least one of A or B" can include all combinations of A and B, such as only A, only B, or A and B. Similarly, the phrase "at least one of A, B, or C" can include all combinations of A, B, and C, such as only A, only B, only C, A and B, A and C, B and C, or A and B and C. The phrase "A and / or B" can be interpreted in a manner similar to the phrase "at least one of A or B". For example, the phrase "A and / or B" can include all combinations of A and B, such as only A, only B, or A and B. Likewise, the meaning of the phrase "A, B, and / or C" is similar to the meaning of the phrase "at least one of A, B, or C". For example, the phrase "A, B, and / or C" can include all combinations of A, B, and C, such as only A, only B, only C, A and B, A and C, B and C, or A and B and C.

[0043] When a first element is described as being "attached", "provided", "formed", "affixed", "mounted", "fixed", "connected", "coupled", "recorded", or "disposed" to, on, at, or at least partially in a second element, the first element can be "attached", "provided", "formed", "affixed", "mounted", "fixed", "connected", "coupled", "recorded", or "disposed" to, on, at, or at least partially in the second element using any suitable mechanical or non-mechanical means (e.g., deposition, coating, etching, bonding, adhesion, threading, press fitting, snap fitting, clamping, etc.). Additionally, the first element can be in direct contact with the second element, or there can be an intermediate element between the first element and the second element. The first element can be disposed on any suitable side of the second element, such as left, right, front, back, top, or bottom.

[0044] When a first element is shown or described as being “on” a second element, the term “on” is used only to indicate an exemplary relative orientation between the first element and the second element. This description may be based on the reference coordinate system shown in the figure, or may be based on the current view or exemplary configuration shown in the figure. For example, when describing the view shown in the figure, the first element may be described as being “on” the second element. It is understood that the term “on” does not necessarily mean that the first element is above the second element in the vertical gravitational direction. For example, when the assembly of the first element and the second element is rotated 180 degrees, the first element may be “under” the second element (or the second element may be “on” the first element). Therefore, it should be understood that when the first element is shown “on” the second element, this configuration is only an illustrative example. The first element may be arranged or disposed relative to the second element in any suitable orientation (e.g., on or above the second element, under or below the second element, to the left of the second element, to the right of the second element, behind the second element, in front of the second element, etc.).

[0045] When the first element is described as being on the second element, the first element may be directly or indirectly disposed on the second element. The first element is directly disposed on the second element means that no additional element is disposed between the first element and the second element. The first element is indirectly disposed on the second element means that one or more additional elements are disposed between the first element and the second element.

[0046] The term “processor” as used herein may include any suitable processor, such as a central processing unit (“CPU”), a graphics processing unit (“GPU”), an application-specific integrated circuit (“ASIC”), a programmable logic device (“PLD”), or any combination thereof. Other processors not listed above may also be used. The processor may be implemented as software, hardware, firmware, or any combination thereof.

[0047] The term “controller” may include any suitable circuit, software, or processor configured to generate control signals for controlling a device, a circuit, an optical element, etc. The “controller” may be implemented as software, hardware, firmware, or any combination thereof. For example, the controller may include a processor, or may be included as part of a processor.

[0048] The term "non-transitory computer-readable medium" can include any suitable medium for storing, transferring, transmitting, broadcasting, or transporting data, signals, or information. For example, non-transitory computer-readable media can include memories, hard disks, magnetic disks, optical disks, magnetic tapes, and the like. Memories can include read-only memory ("ROM"), random-access memory ("RAM"), flash memory, and the like.

[0049] The terms "film", "layer", "coating", or "plate" can include rigid or flexible, self-supporting or free-standing films, layers, coatings, or plates, which can be disposed on a supporting substrate or between substrates. The terms "film", "layer", "coating", and "plate" can be interchangeable. The term "film plane" refers to a plane perpendicular to the thickness direction in a film, layer, coating, or plate. The film plane can be a plane within the volume of the film, layer, coating, or plate, or can be the surface plane of the film, layer, coating, or plate. For example, the term "in-plane" in "in-plane orientation", "in-plane direction", "in-plane spacing", etc. refers to the orientation, direction, or spacing within the film plane. For example, the term "out-of-plane" in "out-of-plane direction", "out-of-plane orientation", or "out-of-plane pitch", etc. means that the orientation, direction, or spacing is not within the film plane (i.e., not parallel to the film plane). For example, the direction, orientation, or spacing can be along a line that is perpendicular to the film plane, or a line that forms an acute or obtuse angle with the film plane. For example, an "in-plane" direction or orientation can refer to a direction or orientation within the surface plane, and an "out-of-plane" direction or orientation can refer to a thickness direction or orientation that is not parallel to the surface plane (e.g., perpendicular).

[0050] The term "orthogonal" in "orthogonal polarization" or the term "orthogonal" in "orthogonally polarized" means that the inner product of two vectors representing two polarizations is substantially zero. For example, two lights or light beams with orthogonal polarizations (or two orthogonally polarized lights or light beams) can be two linearly polarized lights (or light beams) with two orthogonal polarization directions (e.g., the x-axis direction and the y-axis direction in a Cartesian coordinate system) or two circularly polarized lights with opposite circular polarizations (e.g., left-handed circularly polarized light and right-handed circularly polarized light).

[0051] The terms "substantially" or "primarily" used to modify optical response actions (such as transmission, reflection, diffraction, or blocking, etc.) describing light processing mean that most (including all) of the light is transmitted, reflected, diffracted, or blocked, etc. Most can be a predetermined percentage (greater than 50%) of the entire light, such as 100%, 98%, 90%, 85%, 80%, etc., which can be determined based on specific application requirements.

[0052] The wavelength ranges, spectra, or bands mentioned in this disclosure are for illustrative purposes. The disclosed optical devices, systems, components, assemblies, and methods can be applied to the visible band as well as other bands, such as the ultraviolet ("UV") band, the infrared ("IR") band, or combinations thereof.

[0053] The "optical power" of a light beam refers to the energy transmitted per unit time in the light beam (e.g., a laser beam). The "optical power" of an optical element / device / system refers to the degree to which the optical element / device / system converges or diverges a light beam. The optical element / device / system can include a lens or multiple lenses arranged in an optical sequence, etc.

[0054] The beam diameter or beam width of a light beam is the dimension (e.g., diameter, width) along a specified line perpendicular to and intersecting the beam axis. Since a light beam typically does not have sharp edges, the beam diameter or beam width of the light beam can be defined in various ways. There are five commonly used definitions of the beam diameter or beam width: D4σ, 10 / 90 or 20 / 80 knife-edge, 1 / e 2 , full width at half maximum ("FWHM"), and D86. The beam diameter or beam width of the light beam can be measured in units of length in a cross-sectional plane perpendicular to the beam axis. The beam diameter is typically used in applications where the light beam has a circular cross-section (or circular spot) in a cross-sectional plane perpendicular to the beam axis. The beam width is typically used in applications where the light beam does not have circular symmetry. When the light beam has an elliptical cross-section, the direction of the beam diameter or beam width can be specified relative to the major axis or minor axis of the elliptical cross-section. The beam angular width is the angle subtended by the light beam at the light source and is also called the beam divergence. For purposes of illustration and discussion, it is assumed that the light beams described herein have a circular cross-section with a beam diameter.

[0055] Diffractive optical elements (“DOEs”) exhibit a main diffractive order and satellite ghost diffractive orders (hereinafter referred to as satellites or satellite ghosts). There are two types of satellites: Class I satellites are diffractive orders that are multiples of a specific order (e.g., 1×, 2×, 3×, etc.); and Class II satellites are diffractive orders that are not multiples of a specific order. Class I satellites are typically observed in most, if not all, diffractive optical elements (“DOEs”) and are responsible for bright ghost images (e.g., having 1% to 15% of the energy of the incident beam). Class I satellites are similar to the Rowland ghosts in historical literature. Rowland ghosts are spurious spectral lines generated by diffraction gratings and are caused by periodic errors in the groove positions. Class II satellites are rarely observed but do exist in some cases (e.g., having 1% to 2% of the energy of the incident beam). Class II satellites are similar to the Lyman ghosts in historical literature. Lyman ghosts are spurious lines observed in a spectroscope due to the combined effects of the periodicity of the ruling. The history of these satellites dates back to 1893. Although new technologies (e.g., liquid crystals) are now used to obtain DOEs, and in the old days, blazed gratings were made using optical ruling engines, the physical nature of the satellites is the same.

[0056] Figure 1A Shows the Class I satellite ghost diffractive orders of a diffractive lens (e.g., a PBP lens) according to an embodiment of the present disclosure. Figure 1A Shows the spot of the beam of the +1 diffractive order (which is the main diffractive order) and the spots of the beams of a series of satellite ghost diffractive orders. The spots corresponding to the satellite ghost diffractive orders are distributed on both sides of the spot corresponding to the main diffractive order. The Class I satellite ghost diffractive orders are the dominant satellite ghosts, which can be classified according to the main diffractive order and can have a logical spatial distance of 1 / 2, 1 / 4, 1 / 8, etc. relative to the main diffractive order. The Class I satellite ghosts are similar to the Rowland ghosts in historical literature.

[0057] Figure 1B Shows the Class II satellite ghost diffractive orders of a diffractive lens (e.g., a PBP lens) according to an embodiment of the present disclosure. Figure 1B Shows the spot of the beam of the +1 diffractive order (which is the main diffractive order), the spot of the beam of the -1 diffractive order (which is another main diffractive order). Surrounding each main diffractive order are the spots of the beams of a series of satellite ghost diffractive orders (labeled “UFO”). The Class II satellite ghost diffractive orders do not have a logical spatial distance and are not classified according to adjacent diffractive orders. The Class II satellite ghost diffractive orders are rarely observed and generally have low energy efficiency. The Class II satellite ghost diffractive orders are similar to the Lyman ghosts.

[0058] When implementing a diffractive lens in an optical device or an optical system, satellite ghost lines with sufficiently high energy (e.g., class I satellite ghost lines) may produce bright ghost line patterns, thereby degrading the performance of the optical system. Therefore, it is desirable to measure or determine the diffraction efficiency of the satellite ghost lines of the diffractive lens within a relevant spectral range so as to maintain the satellite ghost line efficiency of the diffractive lens within a predetermined range, thereby enabling the diffractive lens to meet the design specifications.

[0059] Diffraction efficiency is the performance of a DOE in terms of optical power flux. When an incident beam is diffracted by a DOE into diffracted beams (or beams with diffraction orders), the diffraction efficiency can be defined as the ratio between the optical power of the diffracted beams output from the DOE and the optical power of the incident beam, i.e., P o / P i where P o is the optical power of the diffracted beams output from the DOE and P i is the optical power of the incident beam. The optical power of a beam can be measured by a dedicated optical power meter or can be measured from signals obtained from a detector configured to detect the beam.

[0060] Figure 1C FIG. shows a schematic diagram of a conventional system 100 for measuring the diffraction efficiency of a diffraction grating 105. The grating 105 is designed and fabricated for a collimated beam. For example, the grating 105 diffracts a substantially collimated incident beam with maximum diffraction efficiency, with minimum aberration and blur. As Figure 1C shown, the grating 105 is disposed between a light source (not shown) and a detector 111. A collimated probe beam 102 output from the light source propagates towards the grating 105. The grating 105 diffracts the collimated probe beam 102 into a plurality of beams 104-1, 104-2, and 104-3 that propagate towards the detector 111 in different directions (e.g., different diffraction angles). The wavelength of the collimated beam 102 is substantially the same as the design wavelength of the grating 105. The effective light receiving area of the detector 111 has a circular cross-section, and the beam diameter of the collimated probe beam 102 is smaller than the size (e.g., diameter or width) of the effective light receiving area of the detector 111.

[0061] The grating 105 provides zero optical power to the collimated probe beam 102. Therefore, the diffracted beams 104-1, 104-2, and 104-3 remain substantially collimated, and as the diffracted beams 104-1, 104-2, and 104-3 propagate in space, the spacing between adjacent diffracted beams can gradually increase. For example, Figure 1CIt is shown that at the near measurement plane 107 close to the grating 105, the beam spots of adjacent diffracted beams 104-1, 104-2, and 104-3 overlap with each other. In this case, the optical power of each beam cannot be measured individually. Therefore, the diffraction efficiency of the grating 105 for different diffraction orders cannot be calculated. For the grating 105 with zero optical power, this problem can be solved by increasing the distance from the measurement plane to the grating 105. For example, as Figure 1C shown, at the far measurement plane 109 that is farther from the grating 105 than the near measurement plane 107, the beam spots of adjacent diffracted beams 104-1, 104-2, and 104-3 are sufficiently separated from each other, so that the detector 111 arranged at the far measurement plane 109 can separately and individually identify the beam spots of each diffracted beam 104-1, 104-2, or 104-3, and obtain the corresponding optical power of each diffracted beam 104-1, 104-2, or 104-3.

[0062] Based on the optical power of the probe beam 102 and the optical power of each diffracted beam 104-1, 104-2, or 104-3, the diffraction efficiency of the grating 105 for each diffraction order is calculated by dividing the optical power of the diffracted beam (104-1, 104-2, or 104-3) by the optical power of the probe beam 102. When the diffracted beams 104-1, 104-2, and 104-3 include the beams of the main diffraction order and one or more beams of one or more satellite ghost line diffraction orders, the diffraction efficiency associated with each of the one or more satellite ghost line diffraction orders is determined by dividing the optical power of the diffracted beam corresponding to each satellite ghost line diffraction order by the optical power of the probe beam 102 incident on the grating 105.

[0063] Unlike Figure 1C the grating 105 with zero optical power shown in the conventional system 100, the diffractive lens is a diffractive grating with non-zero optical power, which can converge or diverge the beam when diffracting the beam. Due to the non-zero optical power provided by the diffractive lens to the incident beam, the diffracted beams associated with the main diffraction order and one or more satellite ghost line diffraction orders may be mixed together, so that the diffraction orders cannot be separated by simply increasing the distance from the measurement plane to the grating 105.

[0064] Figure 1D shows the measurement of the diffraction efficiency of the diffractive lens 155 using Figure 1C the conventional system 100 shown. The diffractive lens 155 is designed and manufactured for a collimated beam. That is, the diffractive lens 155 can diffract and converge or diverge a substantially collimated incident beam with the maximum diffraction efficiency, having the minimum aberration and blur. As Figure 1DAs shown, the collimated probe beam 102 is directed to the diffraction lens 155. The diffraction lens 155 diffracts the probe beam 102 into multiple beams 154-1, 154-2, and 154-3 of different orders propagating in different directions (e.g., different diffraction angles). Due to non-zero optical power, the diffraction lens 155 can converge or diverge the probe beam 102 while diffracting the probe beam 102, thereby modulating the plane wavefront of the collimated probe beam 102 into a non-plane wavefront (e.g., spherical wavefront) of the diffracted beams 154-1, 154-2, or 154-3. For example, Figure 1D It is shown that the diffraction lens 155 diverges and diffracts the probe beam 102, and the diffracted beams 154-1, 154-2, and 154-3 are diverging beams (i.e., non-collimated beams) rather than collimated beams. Figure 1D It is shown that the spots of adjacent diffracted beams 154-1, 154-2, and 154-3 overlap with each other at the near measurement plane 157 and the far measurement plane 159. That is, simply increasing the distance from the measurement plane to the diffraction lens 155 cannot separate the diffraction orders, and thus the diffraction efficiency of each diffraction order cannot be calculated.

[0065] When the diffracted beams 154-1, 154-2, and 154-3 include both the main diffraction order and the satellite ghost line diffraction order beams, the beams of the satellite ghost line diffraction order may be mixed (or overlapped) with the beams of the main diffraction order, and this overlapping problem cannot be solved by simply increasing the distance from the measurement plane to the diffraction lens 155. For example, in some cases, at the far measurement plane 159, the size of each spot may be larger than the size of the effective light receiving area of the detection unit of the detector 111. Therefore, the effective light receiving area of the detector 111 may only receive a part of a single spot, rather than the entire single spot. In some cases, at the far measurement plane 159, the size of each spot may be smaller than the size of the effective light receiving area of the detector 111. However, due to the overlapping spots not being sufficiently separated from each other, the effective light receiving area of the detector 111 may receive parts of two overlapping spots. Since the overlapping spots corresponding to the beams 154-1, 154-2, and 154-3 cannot be sufficiently separated, the optical power of each of the beams 154-1, 154-2, and 154-3 cannot be determined or measured separately and individually. Therefore, the conventional system 100 cannot determine the satellite ghost line efficiency of the diffraction lens 155 corresponding to each of one or more satellite ghost line diffraction orders.

[0066] The present disclosure provides systems and methods for determining (e.g., measuring or calculating) the satellite ghost line efficiency of a diffraction lens based on beam fine-tuning techniques. The disclosed systems and methods for measuring the satellite ghost line efficiency are characterized by low cost, high detection sensitivity, high detection efficiency, and high detection accuracy. The disclosed systems and methods can be used in the quality control process of mass production of diffraction lenses.

[0067] Figure 2A FIG. 2 shows a schematic diagram of a system 200 for measuring the satellite ghost line efficiency of a sample diffractive lens 205 according to an embodiment of the present disclosure. The sample diffractive lens 205 is a sample to be tested for satellite ghost line efficiency. As Figure 2A shown, the system 200 may include a light source 210, a beam fine-tuning assembly 215, a detector 220, and a controller 230. The system 200 may also include Figure 2A additional elements not shown in FIG. 2. The sample diffractive lens 205 (also referred to as the diffractive lens 205 for convenience of description) may be disposed between the beam fine-tuning assembly 215 and the detector 220. The diffractive lens 205 may be designed and manufactured for a collimated incident beam. For example, the diffractive lens 205 may diffract and simultaneously converge or diverge a collimated incident beam with maximum diffraction efficiency, with minimum aberration and blur. The beam fine-tuning assembly 215 may be disposed between the light source 210 and the diffractive lens 205. The detector 220 may be arranged at a measurement plane 235 at a predetermined distance from the diffractive lens 205.

[0068] The light source 210 may output a first probe beam 202 toward the light input surface 215-1 of the beam fine-tuning assembly 215. The first probe beam 202 may have a first beam divergence and may have a first beam diameter at the light input surface 215-1 of the beam fine-tuning assembly 215. The beam divergence defines the diffusion range of the beam over the propagation distance. The beam fine-tuning assembly 215 may be configured to fine-tune (or adjust) the first probe beam 202 and output an adjusted second probe beam 204. The second probe beam 204 may propagate from the light output surface 215-2 of the beam fine-tuning assembly 215 toward the diffractive lens 205.

[0069] The optical power of the beam fine-tuning assembly 215 may be configured or controlled such that the second probe beam 204 output from the beam fine-tuning assembly 215 may be a non-collimated probe beam having a second beam diameter at the light output surface 215-2 of the beam fine-tuning assembly 215, and the second probe beam 204 may have a second beam divergence. Thus, when the second probe beam 204 reaches the light input surface 205-1 of the diffractive lens 205, the second probe beam 204 may have a third beam diameter at the light input surface 205-1 of the diffractive lens 205.

[0070] The diffractive lens 205 can diffract the second detection beam 204 into a plurality of diffracted beams 206-1, 206-2, and 206-3, which propagate toward the detector 220 at different diffraction angles (relative to the surface normal of the light output side of the diffractive lens 205). The diffracted beams 206-1, 206-2, and 206-3 can correspond to different diffraction orders, including, for example, the main diffraction order (e.g., 206-1) and one or more satellite ghost line diffraction orders (e.g., Figure 2A 206-2 and 206-3 in the example shown). For discussion purposes, Figure 2A Three diffracted beams 206-1, 206-2, and 206-3 are shown. In some embodiments, the diffractive lens 205 can diffract the second detection beam 204 into any suitable number of diffracted beams, which can include one or more main diffraction orders and one or more satellite ghost line diffraction orders.

[0071] At the measurement plane 235, the diffracted beams 206-1, 206-2, and 206-3 can be detected by the detector 220 as beam spots (or diffraction order spots) 208-1, 208-2, and 208-3. The beam fine-tuning assembly 215 can be configured or adjusted by the controller 230 to reduce the size of each of the beam spots 208-1, 208-2, and 208-3 (hereinafter referred to as "beam spot size") to be small enough and increase the distance between any two adjacent beam spots 208-1, 208-2, and 208-3 to be large enough. For illustrative purposes and for the convenience of description, Figure 2A the beam spots 208-1, 208-2, and 208-3 in Figure 2A are shown and described as having the same beam spot size. It should be understood that the beam spots 208-1, 208-2, 208-3 can have different beam spot sizes. Similarly, for illustrative purposes and for the convenience of description, Figure 2A any two adjacent beam spots in Figure 2A are shown as being separated by the same distance. It can be understood that the distance between different adjacent beam spots can be different. The distance between any two adjacent beam spots 208-1, 208-2, and 208-3 can refer to the distance between the geometric centers of two adjacent beam spots, or can be defined in another suitable way.

[0072] For discussion purposes, in Figure 2A each of the beam spots 208-1, 208-2, and 208-3 is assumed to have a circular shape with the same diameter. Therefore, the size of the beam spot 208-1, 208-2, or 208-3 can be represented by the diameter of the beam spot, and the distance between two adjacent beam spots 208-1, 208-2, and 208-3 can be the distance between the centers of the two beam spots.

[0073] In some embodiments, detector 220 may include a single detection unit (e.g., a single photodiode). In some embodiments, detector 220 may include a plurality of detection units arranged in an array (e.g., a photodiode array). Each detection unit (e.g., a single detection unit or each detection unit in the array) may have an effective light receiving area configured to receive light and generate a signal based on the received light. The effective light receiving area may have a suitable shape, such as a circle with a diameter or a square with a width, etc. For the purpose of discussion, the effective light receiving area of each detection unit is assumed to have a circular shape or a square shape, and the size of the effective light receiving area of each detection unit may be represented by the diameter of the circular shape or the width of the square shape. For detector 220 including a single detection unit, the entire effective light receiving area of detector 220 may be the same as the effective light receiving area of the single detection unit. For detector 220 including an array of detection units, the entire effective light receiving area of detector 220 may be the sum of the effective light receiving areas of the individual detection units.

[0074] In some embodiments, the beam fine-tuning assembly 215 may be adjusted by the controller 230 to reduce the beam spot size (e.g., diameter) of each beam spot at the measurement plane 235 to less than the size (e.g., diameter or width) of the effective light receiving area of detector 220, and to increase the spacing distance between any two adjacent beam spots to greater than the size of the effective light receiving area of detector 220. Thus, the beam spots 208-1, 208-2, and 208-3 may be sufficiently separated from each other at the measurement plane 235, and each beam spot may be completely and individually captured by the effective light receiving area of detector 220.

[0075] Since the detector 220 captures each beam spot completely and individually, the optical power of each diffracted beam 206-1, 206-2, 206-3 can be determined (e.g., measured or calculated). Accordingly, the satellite ghost line efficiency of the diffractive lens 205 for each satellite ghost line diffraction order (e.g., 206-2 or 206-3) can be determined. The satellite ghost line efficiency can be calculated by dividing the optical power of the beam corresponding to the satellite ghost line diffraction order (e.g., 206-2 or 206-3) output from the diffractive lens 205 by the optical power of the second probe beam 204 incident on the diffractive lens 205. Various methods can be used to measure the optical power of the diffracted beams 206-1, 206-2, 206-3 (or beam spots 208-1, 208-2, 208-3). In some embodiments, the system 200 can include a powermeter 222 that can be moved to different positions within the measurement plane 235 to measure the optical power of each beam (or beam spot). In some embodiments, the powermeter 222 can be omitted, and the optical power of each beam can be determined by the controller 230 based on the signals received from the detector 220. Other suitable methods can also be used to measure the optical power of the beams 206-1, 206-2, 206-3.

[0076] The controller 230 can be communicatively coupled to the light source 210, the beam fine tuning assembly 215, the detector 220, and / or the diffractive lens 205 to control their operations. The controller 230 can include a processor or processing unit 231. The processor 231 can be any suitable processor, such as a central processing unit (“CPU”), a graphic processing unit (“GPU”), etc. The controller 230 can include a storage device 232. The storage device 232 can be a non-transitory computer-readable medium, such as a memory, a hard disk, etc. The storage device 232 can be configured to store data or information, including computer-executable program instructions or code, which can be executed by the processor 231 to perform various controls or functions described in the methods or processes disclosed herein. For example, the storage device 232 can store the data or signals acquired by the detector 220, which can be retrieved by the processor 231 for analysis.

[0077] Refer to Figure 2A, the first detection beam 202 output from the light source 210 may have a predetermined wavelength range, for example, a wavelength range within the operating wavelength range of the diffraction lens 205 (e.g., the visible spectrum). In some embodiments, the first detection beam 202 may be a collimated detection beam propagating along the optical axis 225 of the system 200. In some embodiments, the light source 210 may be a laser source configured to emit a laser beam, such as a laser diode. The laser beam output from the laser source is assumed to be collimated. For discussion purposes, the term "collimated detection beam" refers to a substantially collimated detection beam that has zero beam divergence or a very small divergence that can be neglected (e.g., the beam divergence is less than a predetermined value).

[0078] In some embodiments, the light source 210 may include a single laser source associated with a single laser wavelength. In some embodiments, the wavelength of the laser beam may be substantially the same as the design or operating wavelength of the diffraction lens 205. In some embodiments, the light source 210 may include multiple laser sources associated with multiple different laser wavelengths, and these different laser wavelengths are substantially the same as the corresponding design wavelengths of the diffraction lens 205, and the system 200 can be used to measure the satellite ghost line efficiency of the diffraction lens 205 at different design or operating wavelengths.

[0079] The first detection beam 202 may propagate toward the beam fine-tuning assembly 215 before reaching the diffraction lens 205. The first detection beam 202 may have a first beam diameter at the light input surface 215-1 of the beam fine-tuning assembly 215. The beam fine-tuning assembly 215 may convert the first detection beam 202 into a second detection beam 204 when transmitting the first detection beam 202. For discussion purposes, it is assumed that the first detection beam 202 and the second detection beam (or non-collimated beam) 204 have the same optical power.

[0080] In some embodiments, the second detection beam 204 may be a non-collimated detection beam having a second beam diameter at the light output surface 215-2 of the beam fine-tuning assembly 215. The second detection beam 204 may have a second beam divergence. In some embodiments, the second beam divergence of the second detection beam 204 may be greater than the first beam divergence of the first detection beam 202.

[0081] In some embodiments, the beam fine-tuning assembly 215 can be configured or adjusted by the controller 230 such that the second beam diameter of the second detection beam 204 at the light output surface 215-2 of the beam fine-tuning assembly 215 is smaller than the first beam diameter of the first detection beam 202 at the light input surface 215-1 of the beam fine-tuning assembly 215. In some embodiments, the second beam diameter can be reduced by the beam fine-tuning assembly 215 to be equal to or less than about 50%, about 45%, about 40%, about 35%, about 30%, about 25%, or about 20% of the first beam diameter. The percentage can be any other suitable value selected from the following ranges: 10% to 50%; 20% to 50%; 30% to 50%; 40% to 50%; 10% to 20%; 20% to 30%; 30% to 40%; 10% to 30%; 10% to 40%; 20% to 40%; 20% to 50%; 30% to 50%; or any other suitable range.

[0082] The second detection beam (e.g., non-collimated detection beam) 204 can propagate from the beam fine-tuning assembly 215 towards the diffractive lens 205. The diffractive lens 205 can provide optical power to the second detection beam 204, thereby converging or diverging the second detection beam 204 when diffracting the second detection beam 204. In Figure 2A the illustrated embodiment, the beam fine-tuning assembly 215 and the diffractive lens 205 are shown spaced apart from each other by a gap. In some embodiments, the beam fine-tuning assembly 215 and the diffractive lens 205 can be stacked without a gap (e.g., by direct contact).

[0083] The second detection beam (e.g., non-collimated detection beam) 204 can be incident on the diffractive lens 205. In some embodiments, as Figure 2A shown, the diffractive lens 205 can have a light input surface 205-1 facing the beam fine-tuning assembly 215 and a light output surface 205-2 facing the detector 220. The second detection beam (e.g., non-collimated detection beam) 204 can have a third beam diameter at the light input surface 205-1 of the diffractive lens 205. In some embodiments, the third beam diameter of the second detection beam 204 at the light input surface 205-1 of the diffractive lens 205 can be smaller than the second beam diameter of the second detection beam 204 at the light output surface 215-2 of the beam fine-tuning assembly 215. When the diffracted beams 206-1, 206-2, and 206-3 propagate from the light output surface 205-2 towards the measurement plane 235, the diffractive lens 205 can diffract the second detection beam (e.g., non-collimated detection beam) 204. For discussion purposes, Figure 2A each of the diffracted beams 206-1, 206-2, or 206-3 in is shown to have a third beam diameter at the light output surface 205-2 of the diffractive lens 205.

[0084] In some embodiments, the beam fine-tuning assembly 215 may include one or more suitable lenses arranged in an optical sequence, such as one or more lenses with a fixed optical power (e.g., glass lenses or polymer lenses, etc.), one or more lenses with a variable optical power (e.g., liquid crystal lenses or liquid lenses, etc.), or a combination thereof. Parameters of the one or more lenses (e.g., aperture, focal length, or optical power, etc.) and one or more distances between the multiple lenses (if multiple lenses are included) may be configured or adjusted, for example, by the controller 230, such that the beam fine-tuning assembly 215 can convert the first detection beam 202 into a second detection beam (e.g., a non-collimated detection beam) 204 with a reduced beam diameter (e.g., the second beam diameter) at the light output surface 215-2 of the beam fine-tuning assembly 215.

[0085] In some embodiments, the beam fine-tuning assembly 215 may be configured or adjusted by the controller 230 to provide an optical power opposite to that of the diffractive lens 205. In some embodiments, the absolute value of the total optical power provided by the combination of the beam fine-tuning assembly 215 and the diffractive lens 205 may be less than a predetermined value (e.g., a value close to zero). In some embodiments, the predetermined value may be determined in part by: the distance between the beam fine-tuning assembly 215 and the diffractive lens 205; the distance between the measurement plane 235 and the diffractive lens 205; the size of the effective light receiving area of the detector 220; or the size of the effective light receiving area of a single detection unit in the detector 220 (if the detector 220 includes multiple single detection units); and / or the distance between adjacent detection units in the detector 220 (if the detector 220 includes multiple detection units), etc.

[0086] In some embodiments, the beam fine-tuning assembly 215 may be configured or adjusted by the controller 230 to provide a variable optical power to the first detection beam 202. The controller 230 may control one or more components included in the beam fine-tuning assembly 215 to change the optical power of the beam fine-tuning assembly 215, thereby adjusting the second beam diameter and / or the second beam divergence of the second detection beam (e.g., a non-collimated detection beam) 204 at the light output surface 215-2 of the beam fine-tuning assembly 215.

[0087] Under the control of the controller 230, the optical power of the beam fine-tuning assembly 215 can be adjusted by a suitable external field. For example, in some embodiments, the beam fine-tuning assembly 215 can include two lenses with an adjustable distance therebetween. The two lenses can be lenses with a fixed optical power, lenses with a variable optical power, or a combination of a lens with a fixed optical power and a lens with a variable optical power. In some embodiments, at least one of the two lenses can be mounted on a movable support structure, which can be controlled by the controller 230. When the controller 230 controls the movable support structure to move to different positions, the distance between the two lenses can be adjusted.

[0088] In some embodiments, the optical power of the beam fine-tuning assembly 215 can be adjusted by adjusting the optical power of a variable lens (which can be controlled by the controller 230) included in the beam fine-tuning assembly 215. For example, the optical power of a liquid crystal lens included in the beam fine-tuning assembly 215 can be adjusted by the controller 230 by adjusting the voltage supplied from a power source ( Figure 2A not shown) to the electrodes included in the liquid crystal lens. The optical power of a liquid lens (which can include any suitable liquid) can be adjusted by the controller 230 by adjusting the current or voltage applied to the electrodes of the liquid lens, or by controlling an actuator coupled to the liquid lens to change the curvature of the liquid lens. The actuator can be a mechanical actuator, a piezoelectric actuator, a voice coil actuator, etc. In some embodiments, the beam fine-tuning assembly 215 can include Figure 2A additional elements not shown, such as a spatial filter assembly, an aperture, and / or a polarizer, etc.

[0089] The diffractive lens 205 can be used as a transmissive diffractive lens or a reflective diffractive lens. A transmissive diffractive lens can diverge or converge an incident beam when diffracting the incident beam substantially forward. A reflective diffractive lens can diverge or converge an incident beam when diffracting the incident beam substantially backward. For illustrative purposes, Figure 2A the diffractive lens 205 is shown as a transmissive diffractive lens that diffracts the second probe beam 204 substantially forward. In some embodiments, the diffractive lens 205 can have a fixed (constant) optical power. In some embodiments, the diffractive lens 205 can have a variable or adjustable optical power, which can be adjusted by an external field.

[0090] The detector 220 may be disposed at the measurement plane 235 and may be aimed at the diffractive lens 205 to receive the diffracted light beams 206-1, 206-2, and 206-3 (or beam spots 208-1, 208-2, 208-3). In some embodiments, the detector 220 may include an optical sensor configured to generate a signal based on the received light, such as a photodiode, a charge-coupled device (“CCD”) sensor, a complementary metal-oxide-semiconductor (“CMOS”) sensor, an N-type metal-oxide-semiconductor (“NMOS”) sensor, a pixelated polarization camera, or any other optical sensor. In some embodiments, the detector 220 may include a single detection unit (or pixel). For example, the detector 220 may be a single photodiode for photon detection having an effective light receiving area. In some embodiments, the detector 220 may include a 2D array of detection units (or pixels), and each of the plurality of detection units (or pixels) may be a photodiode for photon detection having an effective light receiving area. For example, the detector 220 may be a camera including a 2D array of pixels. In some embodiments, the detector 220 may also be referred to as an imaging device.

[0091] In some embodiments, the detector 220 may be mounted to a movable support structure (not shown). The movable support structure may be a platform, a frame, or an arm. The movable support structure may be configured to be translatable in the x-axis and y-axis directions and / or rotatable about the z-axis, such that the detector 220 may be translated and / or rotated within the measurement plane 235. In some embodiments, the movable support structure may also be translated along the z-axis to adjust the distance between the measurement plane 235 and the diffractive lens 205 that is the sample under test. In some embodiments, the controller 230 may be communicatively coupled to the movable support structure and may control the rotational and / or translational movement of the movable support structure. In some embodiments, the movable support structure may be translated in one or more linear directions, thereby translating or moving the detector 220 in one or more linear directions (e.g., Figure 2A the x-axis direction and / or the y-axis direction as shown) within the measurement plane 235. Accordingly, the detector 220 may be moved to multiple measurement positions within the measurement plane 235 to detect the diffracted beam spots 208-1, 208-2, and 208-3.

[0092] Note that when the diffractive lens 205 is a reflective diffractive lens instead of a transmissive diffractive lens, the configuration of the system 200 can be modified by changing the position of the measurement plane 235 to receive the backward diffracted light beam output from the diffractive lens 205. The working principle described herein using a transmissive diffractive lens as an example can be similarly applied to a reflective diffractive lens, which will not be repeated here.

[0093] In some embodiments, the measurement plane 235 can be at a predetermined distance from the diffractive lens 205. In the disclosed embodiments, the predetermined distance between the measurement plane 235 and the diffractive lens 205 can be configured to be about 0.5 m to 1.0 m, 0.6 m to 1.0 m, 0.7 m to 1.0 m, 0.8 m to 1.0 m, 0.9 m to 1.0 m, 1.0 m to 1.5 m, or 1.5 m to 2.0 m, etc.

[0094] During the process of measuring the satellite ghost line efficiency of the diffractive lens 205, the detector 220 can detect (or generate, record) the spot pattern 237 of the diffracted light beams 206-1, 206-2, and 206-3 (or spots 208-1, 208-2, and 208-3) at the measurement plane 235. The spot pattern 237 can be represented by the signal or image data generated by the detector 220. In the spot pattern 237, the spots 208-1, 208-2, and 208-3 can be distributed in a predetermined direction (e.g., the y-axis direction). In some embodiments, the controller 230 can control the detector 220 to move to multiple measurement positions within the measurement plane 235 to detect each of the spots 208-1, 208-2, and 208-3, so as to detect (or generate, record) the spot pattern 237. The controller 230 can analyze the spot pattern 237 to obtain information about the following: the size (e.g., diameter) of the spots 208-1, 208-2, and 208-3; the positions of the spots 208-1, 208-2, and 208-3; the spacing distance between adjacent spots 208-1, 208-2, and 208-3; and / or the optical power of the diffracted light beams 206-1, 206-2, and 206-3, etc. In some embodiments, the optical power of the diffracted light beams 206-1, 206-2, and 206-3 can be measured by a separate optical power meter 222.

[0095] The controller 230 may receive a signal or image data representing the beam spot pattern 237 from the detector 220, and may analyze the beam spot pattern 237 to determine whether the beam spots 208-1, 208-2, and 208-3 can be individually and separately identified. The term "individually" means that the entire beam spot is identified. That is, the size of the beam spot is smaller than the size of the effective light receiving area of the detection unit of the detector 220. The term "separately" means that adjacent beam spots do not overlap. For example, in some embodiments, the controller 230 may measure each spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3, and each beam spot size of each beam spot 208-1, 208-2, or 208-3. The controller 230 may determine whether each spacing distance is greater than a first predetermined value. The controller 230 may also determine whether the beam spot size of each beam spot 208-1, 208-2, or 208-3 is smaller than a second predetermined value. In some embodiments, the first predetermined value may be different from the second predetermined value. In some embodiments, the first predetermined value and the second predetermined value may be the same. For example, both the first predetermined value and the second predetermined value may be the size (e.g., diameter or width) of the effective light receiving area of the detection unit in the detector 220.

[0096] Based on the result of analyzing the beam spot pattern 237, the controller 230 may send a control command or signal for adjusting or maintaining the optical power of the beam fine-tuning assembly 215 to the beam fine-tuning assembly 215. For example, when the controller 230 determines, according to the analysis of the beam spot pattern 237, that at least one spacing distance is less than or equal to the size of the effective light receiving area of the detection unit in the detector 220 and / or at least one beam spot size is greater than or equal to the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may continuously adjust the optical power provided to the first detection beam 202 by the beam fine-tuning assembly 215 until each spacing distance is greater than the size of the effective light receiving area of the detection unit in the detector 220, and each beam spot size is smaller than the size of the effective light receiving area of the detection unit in the detector 220. In some embodiments, when the controller 230 determines that each spacing distance is greater than the size of the effective light receiving area of the detection unit in the detector 220, and each beam spot size is smaller than the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may stop adjusting the optical power of the beam fine-tuning assembly 215, or may send a control command or signal for maintaining the optical power of the beam fine-tuning assembly 215 to the beam fine-tuning assembly 215.

[0097] In some embodiments, the controller 230 may measure the spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3 based on the analysis of the beam spot pattern 237, and determine whether each spacing distance is greater than the size of the effective light receiving area of the detection unit in the detector 220. When each spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3 is greater than the size of the effective light receiving area of the detection unit in the detector 220, the beam spot size of each beam spot 208-1, 208-2, or 208-3 may automatically become smaller than the size of the effective light receiving area of the detection unit in the detector 220. Thus, when the controller 230 determines that at least one spacing distance is less than or equal to the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may send the following control command or signal to the beam fine-tuning assembly 215: The control command or signal is used to continuously adjust the optical power of the beam fine-tuning assembly 215 until the controller 230 determines that each spacing distance is greater than the size of the effective light receiving area of the detection unit in the detector 220. Based on determining that each spacing distance is greater than the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may stop adjusting the optical power of the beam fine-tuning assembly 215, or may send a signal or control command to the beam fine-tuning assembly 215 for maintaining the optical power of the beam fine-tuning assembly 215.

[0098] In some embodiments, the controller 230 may measure the beam spot size of each beam spot 208-1, 208-2, or 208-3, and determine whether each beam spot size is less than the size of the effective light receiving area of the detection unit in the detector 220. When the beam spot size of each beam spot 208-1, 208-2, or 208-3 is less than the size of the effective light receiving area of the detection unit in the detector 220, each spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3 may automatically become greater than the size of the effective light receiving area of the detection unit in the detector 220. Thus, when the controller 230 determines that the beam spot size of at least one of the beam spots 208-1, 208-2, and 208-3 is greater than or equal to the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may send the following control command or signal to the beam fine-tuning assembly 215: The control command or signal is used to continuously adjust the optical power of the beam fine-tuning assembly 215 until the controller 230 determines that each beam spot size is less than the size of the effective light receiving area of the detection unit in the detector 220. Based on determining that each beam spot size is less than the size of the effective light receiving area of the detection unit in the detector 220, the controller 230 may stop adjusting the optical power of the beam fine-tuning assembly 215, or may send a signal or control command to the beam fine-tuning assembly 215 for maintaining the optical power of the beam fine-tuning assembly 215.

[0099] In some embodiments, to reduce the sizes of beam spots 208-1, 208-2, and 208-3 and increase the spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3, the controller 230 can adjust the optical power of the beam fine-tuning assembly 215, thereby reducing the beam diameter of the diffracted beam 204, which in turn can cause the sizes of beam spots 208-1, 208-2, and 208-3 to decrease and the spacing distance between any two adjacent beam spots 208-1, 208-2, and 208-3 to increase. Thus, the third beam diameter of the second detection beam 204 at the light input surface 205-1 of the diffraction lens 205 can be adjusted. Thus, the parameters (such as beam divergence, diffraction angle, etc.) of the diffracted beams 208-1, 208-2, or 208-3 output from the diffraction lens 205 can be adjusted. In other words, the beam spot pattern 237 formed by the diffracted beam spots 208-1, 208-2, and 208-3 at the measurement plane 235 can be adjusted such that each beam spot 208-1, 208-2, or 208-3 can be separated and individually captured by the detector 220. Thus, the optical power of each diffracted beam 206-1, 206-2, 206-3 can be determined (such as measured or calculated) separately and individually.

[0100] For example, the beam spots 208-1, 208-2, or 208-3 can be circular beam spots, and the detector 220 can be a single photodiode having a circular effective light receiving area with a diameter of 10 mm. When the beam spot size (or diameter) of each beam spot (or diffraction order spot) 208-1, 208-2, or 208-3 is less than a first predetermined value (such as the diameter of the effective light receiving area, 10 mm), and any two adjacent beam spots 208-1, 208-2, and 208-3 are separated by a spacing distance greater than a second predetermined value (such as the diameter of the effective light receiving area, 10 mm), the controller 230 can determine that each beam spot 208-1, 208-2, or 208-3 in the beam spot pattern 237 is separable and individually identifiable. The controller 230 can separately and individually identify each beam spot 208-1, 208-2, and 208-3. The optical power of each diffracted beam 206-1, 206-2, or 206-3 can be determined (such as measured or calculated), for example, based on data from the beam spot pattern 237 or based on measurements from the independent optical power meter 222. Thus, the diffraction efficiency of the diffraction lens 205 for each diffracted beam 206-1, 206-2, or 206-3 can be determined as described above.

[0101] For illustrative purposes, Figure 2AShows that when the diffracted light beams 206-1, 206-2, and 206-3 form a spot pattern 237 at the far measurement plane 235 (where each spot 208-1, 208-2, or 208-3 can be separated and individually identified), the diffracted light beams 206-1, 206-2, and 206-3 can also form a spot pattern 242 at the near measurement plane 240. The far measurement plane 235 is farther from the diffraction lens 205 than the near measurement plane 240. Due to the overlapping spots and the relatively large spot size (e.g., larger than the size of the effective light receiving area of the detection units of the detector 220), each spot in the spot pattern 242 may not be separated and individually identified.

[0102] Any suitable control algorithm (e.g., a closed-loop feedback control algorithm) can be encoded in the controller 230 to continuously adjust the optical power provided by the beam fine-tuning assembly 215 to the first probe beam 202 until each spot 208-1, 208-2, or 208-3 in the spot pattern 237 can be separated and individually identified (e.g., until each spot size is smaller than the size of the effective light receiving area of the detection units included in the detector 220, and each spacing distance between any two adjacent spots is greater than the size of the effective light receiving area of the detection units included in the detector 220). The controller 230 can continuously receive signals (or image data or feedback) from the detector 220 and analyze these signals to determine whether each spot can be separated and individually identified.

[0103] If each spot is not separated and individually identifiable (e.g., if at least one spot size is greater than or equal to the size of the effective light receiving area of the detection units included in the detector 220, or at least one spacing distance between any two adjacent spots is less than or equal to the size of the effective light receiving area of the detection units included in the detector 220), then the controller 230 can continuously and in real time adjust the optical power of the beam fine-tuning assembly 215, thereby adjusting in real time each spot size and each spacing distance in the spot pattern 237 until the controller 230 determines that each spot size is smaller than the size of the effective light receiving area of the detection units in the detector 220, and each spacing distance is greater than the size of the effective light receiving area of the detection units in the detector 220, i.e., until the spots can be separated and individually identified. It should be understood that the spots to be separated and individually identified are the spots of interest, and the present disclosure does not require that all spots detected by the detector 220 at the measurement plane 235 be separated and individually identified.

[0104] In some embodiments, the controller 230 can determine the optical power of each diffracted beam 206-1, 206-2, or 206-3 at the measurement plane 235 (i.e., the optical power of the beam spots 208-1, 208-2, or 208-3) based on the received signal from the optical power meter 222 or based on the received signal from the detector 220. Based on the optical power of the second probe beam (e.g., non-collimated probe beam) 204 and the optical power of each diffracted beam 206-1, 206-2, or 206-3 determined at the measurement plane 235, the controller 230 can determine the diffraction efficiency of the diffraction lens 205 for each diffracted beam by dividing the optical power of each diffracted beam 206-1, 206-2, or 206-3 by the optical power of the second probe beam 204. For example, the satellite ghost line efficiency of the diffraction lens 205 for each satellite ghost line diffraction order (e.g., 206-2 or 206-3) can be determined by dividing the optical power of the beam 206-2 or 206-3 by the optical power of the second probe beam 204. In some embodiments, based on the positions of the beam spots 208-1, 208-2, and 208-3 and the distance between the measurement plane 235 and the diffraction lens 205, the controller 230 can determine the diffraction angles of the diffracted beams 206-1, 206-2, and 206-3, and the angular separation between two adjacent diffracted beams among the beams 206-1, 206-2, and 206-3.

[0105] In some embodiments, based on the determined satellite ghost line efficiency of the diffraction lens 205 for each satellite ghost line diffraction order (e.g., 206-2 or 206-3) and the diffraction angles of each diffraction order 206-1, 206-2, and 206-3, the controller 230 can determine whether the satellite ghost line efficiency of the diffraction lens 205 meets the satellite ghost line efficiency standard, or whether there are any irregularities in the diffraction angles. For example, the satellite ghost line efficiency standard can be a satellite ghost line efficiency less than a predetermined value (e.g., 1%, 0.5%, etc.). Such information can be used to improve quality control in the mass production of the diffraction lens 205. In some embodiments, the controller 230 can analyze the satellite diffraction efficiency measurement values to determine and provide guidance for the product quality control of the diffraction lens 205 in mass production. For example, the guidance can include adjusting the composition of the material used to manufacture the diffraction lens 205 and adjusting the structure of the diffraction lens 205 to achieve a low satellite ghost line efficiency.

[0106] In some embodiments, the diffractive lens 205 can operate in multiple optical states associated with different optical powers. That is, the diffractive lens 205 itself can have an adjustable optical power, which can be controlled by the controller 230 or a separate controller. When the diffractive lens 205 is adjusted in real time to operate in different optical states, the controller 230 can correspondingly adjust the optical power of the beam fine-tuning component 215 in real time, such that the size of each beam spot 208-1, 208-2, or 208-3 is smaller than the size of the effective light-receiving area of the detection unit in the detector 220 and the spacing distance between any two adjacent beam spots is greater than the size of the effective light-receiving area of the detection unit in the detector 220, thereby enabling real-time measurement of the satellite ghost line efficiency.

[0107] Compared with conventional systems (e.g., Figure 1C the system 100 shown in ) that use a collimated beam as the probing beam for measuring the satellite ghost line efficiency of a diffractive lens, the system 200 of the present disclosure can use a specially designed or configured non-collimated beam (e.g., 204) as the probing beam for measuring the satellite ghost line efficiency of the diffractive lens 205, and the specially designed or configured non-collimated beam (e.g., 204) has a suitable beam divergence and a suitable beam diameter at the light input surface 205-1 of the diffractive lens 205. Although a certain amount of collimation of the probing beam is sacrificed (the amount can be specifically determined based on specific application requirements), the disclosed system 200 achieves flexible measurement of the satellite ghost line efficiency of the diffractive lens 205 through the beam fine-tuning component 215. The disclosed system and method for measuring the satellite ghost line efficiency of a diffractive lens 205 feature low cost, high detection sensitivity, high detection accuracy, and high detection reliability.

[0108] In addition, in some embodiments, the beam fine-tuning component 215 can be disposed in front of the diffractive lens 205 and between the light source 210 and the diffractive lens 205. The beam fine-tuning component 215 can be controlled to provide optical power to the first probing beam 202. Thus, the beam fine-tuning component 215 can provide the same optical power to all diffraction orders of interest of the diffractive lens 205. In a conventional system, a single lens is disposed behind the test sample and between the test sample and the detector. In such a conventional configuration, it is necessary to separately adjust the position or optical power of the single lens for each diffraction order to refocus each diffraction order onto the measurement plane, which is time-consuming and inefficient. Since the disclosed system 200 has the beam fine-tuning component 215 disposed in front of the diffractive lens 205, the measurement complexity of the system 200 is reduced, the operation is simplified, and the detection efficiency is improved.

[0109] In some embodiments, the diffractive lens 205 can be polarization-independent (or polarization-nonselective), and thus can provide the same optical power to the second probe beam (e.g., a non-collimated probe beam) 204 regardless of the polarization of the second probe beam 204. For example, the diffractive lens 205 with negative optical power can diverge the second probe beam 204, while the diffractive lens 205 with positive optical power can converge the second probe beam 204. In either case, the beam fine-tuning component 215 can be configured to reduce the beam diameter of the probe beam 204 to a certain extent until the beam spots 208-1, 208-2, and 208-3 can be separated and individually identified, so that the optical power of the diffracted beams 206-1, 206-2, and 206-3 can be determined, and the satellite ghost line efficiency for each satellite ghost line level can be determined.

[0110] In some embodiments, the diffractive lens 205 can be polarization-dependent (or polarization-selective), so as to provide different optical powers to the second probe beam 204 when the second probe beam 204 has different polarizations. For example, the diffractive lens 205 can be a PBP lens, which provides positive optical power (i.e., converges the second probe beam 204) to the second probe beam 204 when the second probe beam 204 has a predetermined polarization, and provides negative optical power (i.e., diverges the second probe beam 204) to the second probe beam 204 when the second probe beam 204 has a polarization orthogonal to the predetermined polarization. In some embodiments, when the second probe beam 204 includes a first part with a predetermined polarization and a second part with an orthogonal polarization, the diffractive lens 205 can provide positive optical power (i.e., converge the first part) to the first part and provide negative optical power (i.e., diverge the second part) to the second part. In some embodiments, the diffractive lens 205 can be a PVH lens, which provides optical power to the second probe beam 204 when the second probe beam 204 has a predetermined polarization, and can transmit the second probe beam 204 (without providing optical power) when the second probe beam 204 has an orthogonal polarization.

[0111] Figures 2B to 2D Illustrated are various embodiments according to the present disclosure in controlling Figure 2AWhen the beam fine-tuning component 215 included in the illustrated system 200 provides various optical powers, various spot patterns are formed by the beam diffracted by the diffraction lens 205 at the measurement plane 235. The diffraction lens 205 may be polarization-dependent. For discussion purposes, the second probe beam (e.g., non-collimated probe beam) 204 may include a first part with right-handed (“RH”) circular polarization and a second part with left-handed (“LH”) circular polarization. For discussion purposes, the diffraction lens 205 may be a PBP lens configured to provide positive optical power (i.e., converging) to the first part with RH circular polarization and negative optical power (i.e., diverging) to the second part with LH circular polarization.

[0112] Referring Figures 2B to 2D , the diffraction lens 205 can diffract the second probe beam (e.g., non-collimated probe beam) 204 into a main diffraction order that forms a spot 258, a first series of satellite ghost line diffraction orders that form a first series of spots 259a, 259b, 259c located to the right of the spot 258, and a second series of satellite ghost line diffraction orders that form a second series of spots 259d, 259e, 259f located to the left of the spot 258. The first series of satellite ghost line diffraction orders may be diffracted beams of the first part (e.g., RH circular polarization part) of the second probe beam 204, and the second series of satellite ghost line diffraction orders may be diffracted beams of the second part (e.g., LH circular polarization part) of the second probe beam 204.

[0113] Figure 2B The spot pattern 257 at the measurement plane 235 is shown when the controller 230 controls the beam fine-tuning component 215 to provide a first optical power. Figure 2B It is shown that the spots 259a to 259f have substantially the same spot size, which is relatively large compared to the spot 258. The spacing distance between any two adjacent spots in the first series of spots 259a to 259c is small, and the spacing distance between any two adjacent spots in the second series of spots 259d to 259f is also small.

[0114] Figure 2C The spot pattern 267 at the measurement plane 235 is shown when the controller 230 controls the beam fine-tuning component 215 to provide a second optical power to reduce the size of the spots in the first series and the second series. Figure 2C It is shown that the spots 259a to 259f have substantially the same spot size, which is reduced compared to the spot size of the spots 259a to 259f in the Figure 2B shown spot pattern 257. At least partly due to the reduction in the spot size, the spacing distance between two adjacent spots in the first series of spots 259a to 259c is compared with Figure 2BThe spacing distance shown in [reference] is relatively large compared to. The spacing distance between any two adjacent beam spots in the second series of beam spots 259d to 259f is also relatively large compared to Figure 2B the spacing distance shown in [reference]. That is, when the controller 230 controls the beam fine-tuning component 215 to provide a second optical power (changed from the first optical power), in each of the first series of beam spots 259a to 259c and the second series of beam spots 259d to 259f, compared to Figure 2B the beam spot size in the beam spot pattern 257 shown in [reference], the beam spot size of a single beam spot can be reduced. Therefore, the spacing distance between two adjacent beam spots can be increased.

[0115] Figure 2D FIG. [reference number] shows the beam spot pattern 287 at the measurement plane 235 when the controller 230 controls the beam fine-tuning component 215 to provide a third optical power, which can be an increase or decrease of the second optical power. Changing from the second optical power to the third optical power can be in the same trend direction as changing from the first optical power to the second optical power. With the third optical power, the beam fine-tuning component can further focus the first part (e.g., the RH circularly polarized part) of the second detection beam 204. The beam spot size of the beam spots 259a, 259b, or 259c in the first series can be further reduced, while the beam spot size of the beam spots 259d, 259e, or 259f in the second series can be increased. For example, if the change from the first optical power to the second optical power is an increase in optical power, the third optical power is an increase from the second optical power. In other words, Figure 2C and Figure 2D FIG. [reference number] shows that in some embodiments, further increasing the optical power of the beam fine-tuning component 215 can cause one of the first series of beam spots and the second series of beam spots to not be separable and individually identifiable due to the mixing (or overlapping) of the beam spots and the increase in beam spot size. Compared to Figure 2C in Figure 2D the beam spot pattern 287 shown in [reference], the beam spot size of the first series of beam spots 259a to 259c does not change significantly (remains basically the same), but the beam spot size of the second series of beam spots 259d to 259f increases significantly, which results in the beam spots 259d to 259f being mixed (or overlapping) together. Therefore, the beam spots 259d to 259f may not be separable and individually identifiable by the detector 220, but the beam spots 259a to 259c can still be separable and individually identifiable by the detector 220. In some cases, when the quality of the sample is low, the beam spot pattern may be similar to Figure 2D that shown in [reference], that is, the satellite levels on one side of the primary level may have a much larger beam spot size than the satellite levels on the other side of the primary level. In this case, adjusting the optical power of the beam fine-tuning component 215 to the optimal value can obtain a pattern similar to Figure 2CThe shown spot pattern, in which the spot sizes of the satellite levels on both sides of the main level are substantially equal. Then the satellite ghost line efficiency of the satellite levels can be measured.

[0116] Figures 2B to 2D It is shown that in order for most of the satellite ghost lines in the first series of spots 259a to 259c and the second series of spots 259d to 259f to be separated and individually identified, the optimal optical power of the beam fine-tuning component 215 can occur at a certain value (e.g., the second optical power). In the case of the optimal optical power, the spot sizes of the first series of spots 259a to 259c and the spot sizes of the second series of spots 259d to 259f can be substantially equal.

[0117] Figure 3A It is shown according to an embodiment of the present disclosure Figure 2A The X-Z cross-sectional view of the system 200 shown in, which shows exemplary components of the beam fine-tuning component 215. As Figure 3A shown, in some embodiments, the beam fine-tuning component 215 may include a first lens 305, a pinhole 307, a diaphragm (or aperture) 309, a second lens 311, and a reverse beam expander (or beam reducer) 359 arranged in an optical sequence. The first lens 305 may be disposed between the light source 210 and the pinhole 307. The pinhole 307 may be disposed between the first lens 305 and the diaphragm 309. The diaphragm 309 may be disposed between the pinhole 307 and the second lens 311. The second lens 311 may be disposed between the diaphragm 309 and the reverse beam expander 359. The reverse beam expander 359 may be disposed between the second lens 311 and the diffraction lens 205 to be tested. In some embodiments, the beam fine-tuning component 215 may include Figure 3A Additional elements not shown in. In some embodiments, some elements of the multiple elements included in the Figure 3A beam fine-tuning component 215 shown in may be omitted.

[0118] In some embodiments, the first lens 305 and the pinhole 307 may be used as a spatial filter 313, which is configured to "clean" the laser beam when the light source 210 includes a laser light source. The laser beam generated by the laser light source may not have a smooth intensity distribution. In order to generate a "clean" Gaussian beam with a relatively smooth intensity distribution, the spatial filter 313 can be used to remove unwanted multi-level energy peaks and only allow the central maximum of the diffraction pattern to pass through. In addition, the spatial filter 313 can also remove additional spatial noise from the environment in which the laser beam propagates.

[0119] In some embodiments, the first lens 305 may include an objective lens (e.g., a microscope objective lens). The first lens 305 may focus the first detection beam 202 onto a point 336 on the optical axis 225. For example, the first lens 305 may convert the first detection beam 202 into a detection beam 304 focused on the point 336 when transmitting the first detection beam 202. The aperture 307 may be centered at the point 336 and may block unwanted noise rings while allowing most of the energy of the detection beam 304 to pass through. Thus, the aperture 307 may output the detection beam 306, e.g., a "clean" Gaussian beam, towards the diaphragm 309. The diaphragm 309 may further filter the detection beam 306 output from the spatial filter 313, and / or define the beam diameter of the detection beam 306 at the light input surface of the second lens 311.

[0120] In some embodiments, the point 336 onto which the first detection beam 202 is focused may be offset from the focal point of the first lens 305 along the optical axis 225. Thus, the second lens 311 may convert the detection beam 306 into a detection beam 308, which is a non-collimated beam. In Figure 3A the illustrated embodiment, the second lens 311 may have a longer effective focal length ("EFL") than the first lens (e.g., the objective lens) 305. The detection beam 308 may be incident on the light input surface of the reverse beam expander 359. The reverse beam expander 359 may be configured to further reduce the beam diameter of the detection beam 308 when transmitting the detection beam 308. For example, as Figure 3A illustrated, the reverse beam expander 359 may convert the detection beam 308 into a second (e.g., non-collimated) detection beam 204, which may be output from the light output surface of the reverse beam expander 359. The second beam diameter of the second detection beam 204 at the light output surface of the reverse beam expander 359 may be smaller than the beam diameter of the detection beam 308 at the light input surface of the reverse beam expander 359.

[0121] In some embodiments, the reverse beam expander 359 may include a plurality of lenses arranged in an optical sequence. For example, the reverse beam expander 359 may include a third lens 355 having a positive focal length and a fourth lens 357 having a negative focal length. The third lens 355 and the fourth lens 357 may be arranged in an optical sequence, where the third lens 355 is disposed upstream of the fourth lens 357 in the propagation direction of the detection beam. That is, the detection beam 308 may propagate through the third lens 355 before reaching the fourth lens 357. In some embodiments, the third lens 355 may be disposed between the second lens 311 and the fourth lens 357, and the fourth lens 357 may be disposed between the third lens 355 and the diffraction lens 205. For discussion purposes, Figure 3AThe third lens 355 is shown as a biconvex lens, and the fourth lens 357 is shown as a biconcave lens. In some embodiments, the third lens 355 may be a suitable lens with a positive focal length, and the fourth lens 357 may be a suitable lens with a negative focal length.

[0122] The distance between the third lens 355 and the fourth lens 357 may be adjustable. For example, at least one of the third lens 355 or the fourth lens 357 may be mounted on a movable support structure (not shown), and the controller 230 may control the movable support structure to adjust the distance between the third lens 355 and the fourth lens 357. When the controller 230 adjusts the distance between the third lens 355 and the fourth lens 357, the beam reduction ratio provided by the beam expander 359 may be adjusted. The beam reduction ratio may be the ratio between the second beam diameter of the second (e.g., non-collimated) probe beam 204 at the light output surface of the beam expander 359 and the beam diameter of the probe beam 308 at the light input surface of the beam expander 359. The light input surface of the beam expander 359 may be the light input surface of the third lens 355, and the light output surface of the beam expander 359 may be the light output surface of the fourth lens 357. The light output surface of the beam expander 359 may also be the light output surface 215-2 of the beam fine-tuning assembly 215.

[0123] In Figure 3A the illustrated embodiment, by adjusting the distance between the third lens 355 and the fourth lens 357 included in the beam expander 359, the second probe beam (e.g., non-collimated probe beam) 204 may be adjusted to have a second beam diameter at the light output surface 215-2 of the beam fine-tuning assembly 215. Thus, when the second probe beam 204 reaches the light input surface 205-1 of the diffraction lens 205, the second probe beam 204 may have a third beam diameter at the light input surface 205-1 of the diffraction lens 205. The controller 230 may continuously adjust the distance between the third lens 355 and the fourth lens 357 to different distance values, thereby continuously adjusting the beam reduction ratio. Further, the optical power provided by the beam fine-tuning assembly 215 to the first probe beam 202 may be continuously adjusted. Therefore, in the spot pattern formed by the diffracted beam of the diffraction lens 205 at the measurement plane 235, each spot size and each spacing distance may be continuously adjusted to achieve a desired value. The distance between the third lens 355 and the fourth lens 357 may be continuously adjusted until each spot (e.g., Figure 2A the spots 208-1, 208-2, or 208-3 shown in ) formed by each diffracted beam (e.g., 206-1, 206-2, 206-3) at the measurement plane 235 is separated and individually identified by the controller 230. Thus, the satellite ghost line efficiency of the diffraction lens 205 may be determined.

[0124] Based on Figure 3A An experiment was set up based on the system 200 shown, and the beam spot pattern of the sample diffractive lens on the measurement plane was captured. In this experiment, the first probe beam 202 emitted from the light source 210 is a laser beam with a wavelength of 532 nm. The first lens 305 is a 10 - fold (10X) microscope objective, and the diameter of the aperture 307 is 15 μm. The effective focal length (“EFL”) of the second lens 311 is 35 mm. The distance between the measurement plane 235 and the diffractive lens 205 is approximately 1 meter (m). In this experiment, the reverse beam expander 359 is realized by reversing a commercial beam expander. The detector 220 is a photodiode with a circular effective light - receiving area having a diameter of 10 mm. By adjusting the distance between the third lens 355 and the fourth lens 357 included in the reverse beam expander 359 via the focusing ring, the size of the beam spots (or diffractive - order spots) 208 - 1, 208 - 2, or 208 - 3 formed by the diffracted beam at the measurement plane 235 is reduced to a range of approximately 1.5 mm to 5 mm (FWHM of 1 mm to 2.5 mm).

[0125] Figure 4A Shows the use of Figure 3A The beam spot pattern 407 of the diffractive lens 205 detected experimentally at the measurement plane 235 for the experimental setup using the system 200 shown. The beam spot pattern 407 is detected or captured by the detector 220. The diffractive lens 205 used in the experiment is a PBP lens. As Figure 4A shown, the experimentally detected beam spot pattern 407 includes a first series of diffractive - order spots (or beam spots) 401, 403, and 405, a second series of diffractive - order spots (or beam spots) 402a to 402e, and a third series of diffractive - order spots (or beam spots) 404a to 404e. The diffractive orders corresponding to the first series of diffractive - order spots 401, 403, and 405 are the main diffractive orders (also referred to as 401, 403, and 405 for discussion purposes), such as the 0th order, the - 1st order, and the + 1st order.

[0126] The diffraction orders corresponding to the second series of diffraction order spots 402a to 402e are satellite ghost line diffraction orders of the main diffraction order 403 (also referred to as 402a to 402e for discussion purposes). The satellite ghost line diffraction orders 402a to 402e are sufficiently separated from the main diffraction order 403 (for example, each separation distance is greater than the diameter of the effective light receiving area, 10 mm), and the beam spot size of each of the diffraction order spots 402a to 402e is small enough (for example, each beam spot size is less than the diameter of the effective light receiving area, 10 mm). The diffraction orders corresponding to the second series of diffraction order spots 404a to 404e are satellite ghost line diffraction orders of the main diffraction order 405 (also referred to as 404a to 404e for discussion purposes). The satellite ghost line diffraction orders 404a to 404e are sufficiently separated from the main diffraction order 405 (for example, each separation distance is greater than the diameter of the effective light receiving area, 10 mm), and the beam spot size of each of 404a to 404e is small enough (for example, each beam spot size is less than the diameter of the effective light receiving area, 10 mm). Therefore, the diffraction order spots 401, 403, 405, 402a to 402e, 404a to 404e formed by the corresponding diffraction beams at the measurement plane 235 can be individually and separately identified by the controller 230. Therefore, the satellite ghost line efficiency of the diffraction lens 205 for each satellite ghost line diffraction order can be determined.

[0127] For comparison, Figure 4B FIG. shows the beam spot pattern 457 of the diffraction lens 205 experimentally detected at the measurement plane 235 using a conventional system that does not include the beam fine-tuning assembly 215 (for example, Figure 1A the system 100 shown in ). As Figure 4B shown, in the absence of the beam fine-tuning assembly 215, the experimentally detected beam spot pattern 457 includes a small spot 451 located at the center, and two relatively large spots 460 and 470 located on both sides of the small spot 451. The small spot 451 may be a diffraction order spot of the main diffraction order (also referred to as 451 for discussion purposes), and the main diffraction order is, for example, the 0th order. The relatively large spot 460 or 470 may include a diffraction order spot of the main diffraction order, and diffraction order spots of a series of satellite ghost line diffraction orders that are clustered together. This series of satellite ghost line diffraction orders is mixed with the main diffraction order, generating a relatively large and bright spot 460 or 470 at the measurement plane 235. That is, using a conventional system that does not include the beam fine-tuning assembly 215 (for example, Figure 1A the system 100 shown in ), it is impossible to separately and individually identify the satellite ghost line diffraction orders from the main diffraction order at the measurement plane 235.

[0128] Returning to refer to Figure 3A, the second lens 311 and the inverse beam expander 359 may be disposed in front of the diffractive lens 205 and between the light source 210 and the diffractive lens 205. The combination of the second lens 311 and the inverse beam expander 359 may provide optical power to the probe beam 306. The combination of the second lens 311 and the inverse beam expander 359 may provide the same optical power to all diffractive orders of interest output from the diffractive lens 205. In a conventional system, a single lens is disposed after the test sample and between the test sample and the detector. In such a conventional configuration, it is necessary to individually adjust the position or optical power of the single lens for each diffractive order to refocus each diffractive order onto the measurement plane, which is time-consuming and inefficient. Since the disclosed system 200 has a combination of the second lens 311 and the inverse beam expander 359 disposed in front of the diffractive lens 205 for testing, the measurement complexity of the system 200 is reduced, the operation is simplified, and the detection efficiency is improved.

[0129] Figure 3B FIG. 4 shows an x-z cross-sectional view of the system 200 according to another embodiment of the present disclosure, in which exemplary components of the beam fine-tuning assembly 215 are shown. As Figure 3B shown, the beam fine-tuning assembly 215 may include elements similar to Figure 3A the beam fine-tuning assembly 215 shown. Figure 3A For a detailed description of the same or similar elements included in the beam fine-tuning assembly 215 shown in Figure 3A reference may be made to the above description presented in conjunction with

[0130] In Figure 3B the embodiment shown, the beam fine-tuning assembly 215 may include a first lens 375, a hole 307, a diaphragm 309, and a second lens 371 arranged in an optical sequence. The first lens 375 may be disposed between the light source 210 and the hole 307. The hole 307 may be disposed between the first lens 375 and the diaphragm 309. The diaphragm 309 may be disposed between the hole 307 and the second lens 371. The second lens 371 may be disposed between the diaphragm 309 and the diffractive lens 205. In some embodiments, the beam fine-tuning assembly 215 may include Figure 3B additional elements not shown in Figure 3B the beam fine-tuning assembly 215 shown. In some embodiments, some elements included in

[0131] the beam fine-tuning assembly 215 shown may be omitted. Figure 3AThe spatial filter 313 shown in [Figure 0]. The spatial filter 373 can be configured to "clean up" the first detection beam 202 output from the light source 210. The first lens 375 can convert the first detection beam 202 into a detection beam 364 focused on the point 386 on the optical axis 225 when transmitting the first detection beam 202. The aperture 307 can be centered on the point 386 and can block the unwanted noise ring while allowing most of the energy of the detection beam 364 to pass through. The aperture 307 can output the detection beam 366 towards the diaphragm 309, for example, a "clean" Gaussian beam. The diaphragm 309 can further filter the detection beam 366 output from the spatial filter 313 and / or define the beam diameter of the detection beam 366 at the light input surface of the second lens 371.

[0132] In some embodiments, the point 386 to which the detection beam 364 is focused can be offset from the focal point of the first lens 375 along the optical axis 225. Thus, the second lens 371 can convert the detection beam 366 into a second detection beam 204, which is a non-collimated beam propagating towards the diffraction lens 205. In some embodiments, the beam waist ratio between the output beam and the input beam of the beam fine-tuning assembly 215 (e.g., the ratio between the second beam diameter of the second detection beam 204 at the light output surface 215-2 and the first beam diameter of the first detection beam 202 at the light input surface 215-1) can be determined by the focal length ratio of the second lens 371 to the first lens 375. That is, when the second lens 371 has a shorter EFL than the first lens 375, the second beam diameter of the second detection beam 204 at the light output surface 215-2 can be smaller than the first beam diameter of the first detection beam 202 at the light input surface 215-1. By configuring the corresponding EFLs of the first lens 375 and the second lens 371, the second beam diameter of the second detection beam 204 at the light output surface 215-2 can be small enough. Thus, in the spot pattern formed by the diffracted beam of the diffraction lens 205 at the measurement plane 235, each spot size and each spacing distance can reach the desired value. Thus, the Figure 3A shown inverse beam expander 359 can be omitted.

[0133] In some embodiments, the second lens 371 may have a fixed (or constant) optical power, and the controller 230 may control (or adjust) the optical power of the beam fine-tuning assembly 215 by adjusting the distance between the second lens 371 and the first lens 375. In some embodiments, the second lens 371 may have a variable optical power, and the controller 230 may control (or adjust) the optical power of the beam fine-tuning assembly 215 by adjusting at least one of the distance between the second lens 371 and the first lens 375 or the optical power of the second lens 371. The controller 230 may control (or adjust) the optical power of the beam fine-tuning assembly 215 such that the second detection beam (e.g., non-collimated detection beam) 204 output from the second lens 371 may have a second beam divergence and a second beam diameter at the light output surface 215-2 of the beam fine-tuning assembly 215. Therefore, when the second detection beam (e.g., non-collimated detection beam) 204 reaches the light input surface 205-1 of the diffraction lens 205, the second detection beam 204 may have a predetermined third beam diameter at the light input surface 205-1 of the diffraction lens 205. Therefore, each spot (or diffraction order spot) 208-1, 208-2, or 208-3 formed by the diffracted beam at the measurement plane 235 may be individually and separately identified by the controller 230. Therefore, the satellite ghost line efficiency of the diffraction lens 205 can be determined.

[0134] In Figure 3B it, the second lens 371 may be disposed in front of the diffraction lens 205 and between the light source 210 and the diffraction lens 205. The second lens 371 may be controlled to provide optical power to the detection beam 366. The second lens 371 may provide the same optical power to all diffraction orders of interest output from the diffraction lens 205. In a conventional system, a single lens is disposed after the test sample and between the test sample and the detector. In a conventional configuration, it is necessary to separately adjust the position or optical power of the single lens for each of the multiple diffraction orders to refocus each diffraction order onto the measurement plane, which is time-consuming and inefficient. Since the disclosed system 200 has the second lens 371 disposed in front of the diffraction lens 205, the measurement complexity of the system 200 is reduced, the operation is simplified, and the detection efficiency is improved.

[0135] In some embodiments, Figure 3A the second lens 311 shown in it may have a fixed (or constant) optical power, and the controller 230 may control (or adjust) the optical power of the beam fine-tuning assembly 215 by adjusting the distance between the second lens 311 and the first lens 305. In some embodiments, Figure 3AThe second lens 311 shown in [the figure] may have a variable optical power, and the controller 230 may control (or adjust) the optical power of the beam fine-tuning assembly 215 by adjusting at least one of the distance between the second lens 311 and the first lens 305 or the optical power of the second lens 311. In some embodiments, Figure 3A the first lens 305 shown in [the figure] and / or Figure 3B the first lens 375 shown in [the figure] may have a variable optical power. In some embodiments, Figure 3A the third lens 355 and / or the fourth lens 357 shown in [the figure] may have a variable optical power.

[0136] The present disclosure also provides a method for measuring the satellite ghost line efficiency of a diffractive lens. This method may be performed by one or more components included in the disclosed system. Descriptions of the same or similar components, structures, and / or functions may refer to the descriptions presented above in conjunction with Figure 2A , Figure 3A and Figure 3B presented. Figure 5 is a flowchart showing a method 500 for measuring the satellite ghost line efficiency of a diffractive lens according to an embodiment of the present disclosure.

[0137] As Figure 5 shown, the method 500 may include: outputting a first detection beam from a light source to a beam fine-tuning assembly disposed between the light source and the diffractive lens, the beam fine-tuning assembly including one or more optical lenses, and the optical power of the beam fine-tuning assembly being adjustable (step 510). The first detection beam may have a first beam divergence and a first beam diameter at the light input surface of the beam fine-tuning assembly. In some embodiments, the first detection beam may be a substantially collimated beam.

[0138] The method may further include: converting, by the beam fine-tuning assembly, the first detection beam into a second detection beam propagating toward the diffractive lens, the second detection beam being a non-collimated beam, and the diffractive lens diffracting the second detection beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of the main diffraction order and a second diffracted beam of the satellite ghost line diffraction order (step 520). The second detection beam may have a second beam divergence and a second beam diameter at the light output surface of the beam fine-tuning assembly. In some embodiments, the first beam divergence may be less than the second beam divergence. In some embodiments, the first beam diameter may be greater than the second beam diameter.

[0139] The method may further include: generating, by a detector, a beam spot pattern that includes a first beam spot corresponding to a first diffracted beam and a second beam spot corresponding to a second diffracted beam (step 530). The beam spot pattern may include a plurality of beam spots corresponding to a plurality of diffracted beams output from a diffractive lens. In some embodiments, the satellite ghost diffraction order corresponding to the second diffracted beam may be a first satellite ghost diffraction order, and the plurality of diffracted beams may further include a third diffracted beam of a second satellite ghost diffraction order. The beam spot pattern may include a third beam spot corresponding to the third diffracted beam.

[0140] Method 500 may include: controlling, by a controller, a beam fine-tuning component to adjust the beam spot size of each of the first beam spot and the second beam spot and the spacing distance between the first beam spot and the second beam spot until the beam spot size of each of the first beam spot and the second beam spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value (step 540). In some embodiments, the first predetermined value may be substantially the same as the second predetermined value, and the first predetermined value and the second predetermined value may be equal to the size of the effective light receiving area of a detection unit included in the detector.

[0141] In some embodiments, step 540 may include: analyzing, by the controller, the beam spot pattern to determine whether the beam spot size of each of the first beam spot and the second beam spot is less than the first predetermined value and whether the spacing distance between the first beam spot and the second beam spot is greater than the second predetermined value. In some embodiments, step 540 may further include: based on determining that the beam spot size of at least one of the first beam spot or the second beam spot is greater than or equal to the first predetermined value, or the spacing distance is less than or equal to the second predetermined value, adjusting, by the controller, the optical power provided to the first detection beam by the beam fine-tuning component until the beam spot size of each of the first beam spot and the second beam spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value.

[0142] Method 500 may include Figure 5. For example, the method 500 may further include: controlling the detector to move to a plurality of measurement positions within the measurement plane by a controller (e.g., the controller 230) to detect a plurality of beam spots forming a beam spot pattern. Controlling the beam fine-tuning assembly to adjust the corresponding beam spot sizes of the plurality of beam spots included in the beam spot pattern and the corresponding spacing distances between any two adjacent beam spots may include: adjusting the optical power provided by the beam fine-tuning assembly to the first detection beam to adjust the corresponding beam spot sizes of the plurality of beam spots included in the beam spot pattern and the corresponding spacing distances between any two adjacent beam spots. The method 500 may include: analyzing the beam spot pattern by the controller to obtain the corresponding beam spot sizes of the plurality of beam spots, the corresponding positions of the plurality of beam spots, and the corresponding spacing distances between any two adjacent beam spots. The controller 230 may compare each beam spot size with a first predetermined value to determine whether each beam spot size is less than the first predetermined value. If one of the plurality of beam spot sizes is greater than or equal to the first predetermined value, the controller 230 may continue to adjust the optical power provided by the beam fine-tuning assembly to the first detection beam until each beam spot size is less than the first predetermined value.

[0143] The controller 230 may compare each spacing distance between any two adjacent beam spots with a second predetermined value. If there are beam spots of different series or clusters, there may be multiple spacing distances for the different series or clusters, and the controller 230 may compare all the spacing distances with the second predetermined value. The controller 230 may determine whether each spacing distance is greater than the second predetermined value. If one of the multiple spacing distances is less than or equal to the second predetermined value, the controller 230 may continue to adjust the optical power of the beam fine-tuning assembly until all spacing distances are greater than the second predetermined value.

[0144] When the controller 230 determines that each beam spot size is less than the first predetermined value and each separation distance is greater than the second predetermined value, the controller 230 may determine that each beam spot can be separated and individually identified, and the controller 230 may determine the optical power of each beam spot, or the optical power of those beam spots of interest, such as the optical power of the beam spots corresponding to the satellite ghost line order. The controller 230 may determine (e.g., calculate) the satellite ghost line efficiency based on the optical power of one second diffraction beam of the plurality of second diffraction beams corresponding to the satellite ghost line diffraction order and the optical power of the second detection beam (or the first detection beam).

[0145] Figure 2A , Figure 3A and Figure 3BIt is shown that the diffractive lens 205 is disposed perpendicular to the optical axis 225, or the thickness direction of the diffractive lens 205 is arranged parallel to the optical axis 225. In some embodiments, the diffractive lens 205 may not be disposed perpendicular to the optical axis 225 and may be tilted to form an acute angle with respect to the optical axis 225. The principles of the disclosed systems and methods for measuring the satellite ghost line efficiency of the diffractive lens 205 are also applicable to the case where the diffractive lens 205 is tilted at an acute angle with respect to the optical axis 225.

[0146] In Figure 2A , Figure 3A and Figure 3B the illustrated embodiments, the diffractive lens 205 can be any suitable diffractive lens, such as a ruled diffractive lens, a holographic diffractive lens, a Fresnel lens, a liquid crystal-based diffractive lens, a metasurface lens, a Pancharatnam-Berry phase (“PBP”) lens, a polarization volume hologram (“PVH”) lens, a diffractive lens based on a surface relief structure, a diffractive lens based on a volume Bragg grating (“VBG”), etc. The diffractive lens 205 can be a single-layer diffractive lens or a multi-layer diffractive lens. For illustrative purposes, Figure 2A , Figure 3A and Figure 3B the diffractive lens 205 is shown as a single-layer diffractive lens. In some embodiments, the diffractive lens 205 can have a multi-layer structure having two or more layers of optical films, plates, or elements. For example, the diffractive lens 205 can include a first layer and a second layer, at least one of which can be a lens. In some embodiments, the first layer can be a substrate that provides support and protection to other layers, films, and / or structures formed thereon, and the second layer can be an optical film that converges or diverges the incident light beam when diffracting the incident light beam. In some embodiments, the optical film can be a liquid crystal polymer (“LCP”) layer. In some embodiments, the LCP layer can include polymerized (or crosslinked) liquid crystal (“LC”), polymer-stabilized LC, photosensitive C polymer, or any combination thereof. The LC can include nematic LC, twist-bend LC, chiral nematic LC, smectic LC, or any combination thereof. In some embodiments, the optical film can be a photosensitive polymer layer that includes a birefringent photorefractive holographic material other than LC, such as an amorphous polymer.

[0147] In some embodiments, the diffractive lens 205 may include one or more protective films and one or more layers that provide optical functions. In some embodiments, the diffractive lens 205 may include an alignment structure or layer disposed between other layers (e.g., between a substrate and an optical film). The alignment structure may provide a predetermined alignment pattern to align molecules in the optical film. In some embodiments, the diffractive lens 205 may include two substrates, two alignment layers, and an LC layer disposed between the two alignment layers. The LC layer may include active LC, and the diffraction efficiency of the diffractive lens 205 may be adjusted by adjusting the orientation of the LC.

[0148] Figure 6A A schematic three-dimensional (3D) view of an optical film 600 that may be included in the diffractive lens 205 shown in Figure 2A , Figure 3A or Figure 3B is shown. The non-collimated beam 604 may be incident on the optical film 600 as a probe beam for the satellite ghost line diffraction efficiency measurement described above. Figures 6B to 6C Schematically shown are various views of a portion of the optical film 600 shown in Figure 6A , which show the in-plane orientation of the optically anisotropic molecules in the optical film 600.

[0149] For illustrative purposes, the optical film 600 is shown in Figure 6A as having a flat rectangular plate shape. It should be understood that the optical film 600 may have any suitable shape, such as a circular shape. In some embodiments, one or both surfaces along the light propagation path of the non-collimated beam 604 may have a curved shape. In some embodiments, the optical film 600 may include a layer of birefringent medium 615 that has an intrinsic or induced (e.g., photo-induced) optical anisotropy. For example, the birefringent medium 615 may include liquid crystal, liquid crystal polymer, and / or amorphous polymer, etc. The optical film 600 may also be referred to as the birefringent medium layer 600.

[0150] In some embodiments, the optical film 600 may be a polymer layer (or film). For example, in some embodiments, the optical film 600 may be a liquid crystal polymer (“LCP”) layer. In some embodiments, the LCP layer may include polymerized (or cross-linked) LC, polymer-stabilized LC, photosensitive LC polymer, or any combination thereof. In some embodiments, the optical film 600 may include active LC. The LC may include nematic LC, twist-bend LC, chiral nematic LC, smectic LC, or any combination thereof. In some embodiments, the optical film 600 may be a polymer layer that includes a birefringent photorefractive holographic material other than LC, such as amorphous polymer.

[0151] The optical film 600 may have a first surface 615-1 (or light input surface) and a second surface 615-2 (or light output surface). The first surface 615-1 and the second surface 615-2 may be surfaces along the light propagation path of the incident light beam 604. In some embodiments, the first surface 615-1 may be an interface between the optical film 600 and a substrate (or alignment structure, not shown) on which the optical film 600 is formed, and the second surface 615-2 may be an interface between the optical film 600 and a protective film (e.g., a triacetyl cellulose (TAC) film, not shown) or the external environment (e.g., air), or an interface between the optical film 600 and another substrate (or another alignment structure, not shown).

[0152] The optical film 600 (or the birefringent medium 615 in the optical film 600) may include optically anisotropic molecules (e.g., LC molecules) configured with a three-dimensional (3D) orientation pattern. In some embodiments, the optical axis of the birefringent medium 615 or the optical film 600 may be configured to have a spatially varying orientation in at least one in-plane direction. For example, the optical axis of the LC material may vary periodically or aperiodically in at least one in-plane linear direction, in at least one in-plane radial direction, in at least one in-plane circumferential (e.g., azimuthal) direction, or a combination thereof. The LC molecules may be configured with an in-plane orientation pattern, wherein the director of the LC molecules may vary periodically or aperiodically in at least one in-plane direction. In some embodiments, the optical axis of the LC material may also be configured to have a spatially varying orientation in the out-of-plane direction. The director of the LC molecules may also be configured to have a spatially varying orientation in the out-of-plane direction. For example, the optical axis (or the director of the LC molecules) of the LC material may twist in a helical manner in the out-of-plane direction.

[0153] Figure 6B and Figure 6C Schematically shows according to various embodiments of the present disclosure Figure 6A An x-y cross-sectional view of a portion of the optical film 600 shown in, which shows the in-plane orientation of the optically anisotropic molecules 612 in the optical film 600. Figures 6B to 6CThe in-plane orientation of the optically anisotropic molecules 612 in the optical film 600 shown is for illustrative purposes. In some embodiments, the optically anisotropic molecules 612 in the optical film 600 may have other in-plane orientation patterns. For discussion purposes, rod-shaped LC molecules 612 are used as an example of the optically anisotropic molecules 612 of the optical film 600. The rod-shaped LC molecules 612 may have a longitudinal axis (or an axis in the length direction) and a transverse axis (or an axis in the width direction). The longitudinal axis of the LC molecule 612 may be referred to as the director of the LC molecule 612 or the LC director. The orientation of the LC director may determine the orientation of the local optical axis of the optical film 600 or the optical axis at a local point. The term "optical axis" may refer to a direction in a crystal. Light propagating in the direction of the optical axis may not undergo birefringence (or double refraction). The optical axis may be a direction rather than a single line: light parallel to this direction may not undergo birefringence. The local optical axis may refer to the optical axis within a predetermined region of the crystal. For illustrative purposes, Figures 6B to 6C the LC director of the LC molecules 612 shown in is assumed to be in the film plane of the birefringent medium layer 615, and this film plane has a very small tilt angle relative to the surface.

[0154] Figure 6B An x-y cross-sectional view schematically showing a part of the optical film 600 is shown, which shows the in-plane orientation pattern of the radial variation of the LC directors of the LC molecules 612 located in Figure 6A the film plane of the optical film 600 shown. Figure 6C Shows a cross-section of the in-plane orientation pattern taken along the Figure 6B x-axis in the optical film 600 shown in accordance with an embodiment of the present disclosure. In the film plane of the birefringent medium layer 615 of the optical film 600, the orientation of the optical axis of the optical film 600 may exhibit a continuous rotation at varying spacings in at least two opposite in-plane directions from the center of the optical film 600 to the relative periphery of the optical film 600. In some embodiments, Figure 6B the in-plane orientation pattern of the orientation of the LC directors shown in may also be referred to as a lens pattern. Therefore, Figure 6B the optical film 600 having the LC director orientation shown in may be used as a polarization-selective diffractive lens, such as a PBP lens or a PVH lens, etc.

[0155] As Figure 6BAs shown, the orientation of the LC molecules 612 in the film plane of the birefringent medium layer 615 can be configured with an in-plane orientation pattern that has a varying pitch in at least two opposite in-plane directions from the lens center 650 to the opposite lens periphery 655. For example, the orientation of the LC director of the LC molecules 612 in the film plane of the birefringent medium layer 615 can exhibit a continuous rotation in at least two opposite in-plane directions (e.g., multiple opposite radial directions) with a varying pitch from the lens center 650 to the opposite lens periphery 655. The orientation of the LC director from the lens center 650 to the opposite lens periphery 655 can exhibit a rotation in the same (e.g., clockwise or counterclockwise) rotation direction. The pitch Λ of the in-plane orientation pattern can be defined as the distance in the in-plane direction (e.g., the radial direction) at which the orientation of the LC director (or the azimuthal angle φ of the LC molecules 612) changes by a predetermined angle (e.g., 180°) from a predetermined initial state.

[0156] As Figure 6C shown, according to the LC director field along the x-axis direction, the pitch Λ can be a function of the distance from the lens center 650. In at least two opposite in-plane directions (e.g., two opposite radial directions) in the x-y plane, the pitch Λ can monotonically decrease from the lens center 650 to the lens periphery 655, e.g., Λ0 > Λ1 >... > Λ r . Λ0 is the pitch at the central region of the lens pattern, which can be the largest. The pitch Λ r is the pitch at the peripheral region (e.g., the periphery 655) of the lens pattern, which can be the smallest. In some embodiments, the azimuthal angle φ of the LC molecules 612 can change in proportion to the distance from the lens center 650 to the local point of the optical film 600 where the LC molecules 612 are located.

[0157] For illustrative purposes, Figure 6B and Figure 6C show the in-plane orientation pattern of the LC director when the optical film 600 is a PBP or PVH lens that is an on-axis spherical lens. In some embodiments, the optical film 600 can be a PBP or PVH lens that is an off-axis spherical lens, a cylindrical lens, an aspherical lens, or a freeform lens, etc.

[0158] In some embodiments, the present disclosure provides a system for measuring the satellite ghost line efficiency of a diffractive lens. The system includes: a light source configured to output a first detection beam; and a beam fine-tuning component disposed between the light source and the diffractive lens and configured to convert the first detection beam into a second detection beam, which is a non-collimated beam. The diffractive lens diffracts the second detection beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of the main diffraction order and a second diffracted beam of the satellite ghost line diffraction order. The beam fine-tuning component includes one or more optical lenses, and the optical power of the beam adjustment component is adjustable. The system further includes a detector configured to generate a spot pattern, the spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam.

[0159] In some embodiments, the first detection beam has a first beam diameter at the light input surface of the beam fine-tuning component, the second detection beam has a second beam diameter at the light output surface of the beam fine-tuning component, and the first beam diameter is greater than the second beam diameter.

[0160] In some embodiments, the system further includes a controller configured to adjust the optical power of the beam fine-tuning component so as to adjust the spot size of each of the first spot and the second spot, and the spacing distance between the first spot and the second spot, until the controller determines that the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value.

[0161] In some embodiments, the controller may further be configured to analyze the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than the first predetermined value and whether the spacing distance between the first spot and the second spot is greater than the second predetermined value; and based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value, or the spacing distance is less than or equal to the second predetermined value, adjust the optical power provided to the first detection beam by the beam fine-tuning component until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value.

[0162] In some embodiments, the controller may further be configured to: when the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value, determine the optical power of the second diffracted beam and the optical power of the second detection beam; and determine the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

[0163] In some embodiments, the first predetermined value and the second predetermined value are equal to the size of the effective light receiving area of the detection unit in the detector.

[0164] In some embodiments, the satellite ghost line diffraction order corresponding to the second diffracted beam is the first satellite ghost line diffraction order. In some embodiments, the plurality of diffracted beams further includes a third diffracted beam of a second satellite ghost line diffraction order. In some embodiments, the spot pattern further includes a third spot corresponding to the third diffracted beam. In some embodiments, the system further includes a controller configured to adjust the optical power of the beam fine-tuning component, thereby adjusting the spot size of each of the first spot, the second spot, and the third spot, the first spacing distance between the first spot and the second spot, and the second spacing distance between the second spot and the third spot until the spot size of each of the first spot, the second spot, and the third spot is less than a first predetermined value and the first spacing distance and the second spacing distance are greater than a second predetermined value.

[0165] In some embodiments, one or more optical lenses included in the beam fine-tuning component include two optical lenses, and the distance between the two optical lenses is adjustable. In some embodiments, at least one of the one or more optical lenses included in the beam fine-tuning component has an adjustable optical power. In some embodiments, the beam fine-tuning component includes a spatial filter, a single lens, and a reverse beam expander arranged in an optical sequence, and the single lens is disposed between the spatial filter and the reverse beam expander.

[0166] In some embodiments, the present disclosure provides a method for measuring the satellite ghost line efficiency of a diffractive lens. The method includes: outputting a first probe beam from a light source to a beam fine-tuning component disposed between the light source and the diffractive lens, the beam fine-tuning component including one or more optical lenses and the optical power of the beam fine-tuning component being adjustable. The method further includes: converting, by the beam fine-tuning component, the first probe beam into a second probe beam propagating toward the diffractive lens, the second probe beam being a non-collimated beam, and the diffractive lens diffracting the second probe beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of a main diffraction order and a second diffracted beam of a satellite ghost line diffraction order. The method further includes: generating, by a detector, a spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam. In some embodiments, the first probe beam has a first beam diameter at the light input surface of the beam fine-tuning component, the second probe beam has a second beam diameter at the light output surface of the beam fine-tuning component, and the first beam diameter is greater than the second beam diameter.

[0167] In some embodiments, the method further includes: controlling, by a controller, the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value.

[0168] In some embodiments, the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value, including: the controller analyzes the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than the first predetermined value, and whether the spacing distance between the first spot and the second spot is greater than the second predetermined value; and based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value, or the spacing distance is less than or equal to the second predetermined value, the controller adjusts the optical power of the beam fine-tuning component supplied to the first detection beam until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value.

[0169] In some embodiments, the method further includes: when the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value, the controller determines the optical power of the second diffracted light and the optical power of the second detection beam; and the controller determines the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

[0170] In some embodiments, the first predetermined value and the second predetermined value are equal to the size of the effective light receiving area of the detection unit in the detector.

[0171] In some embodiments, one or more optical lenses included in the beam fine-tuning component include two optical lenses, wherein the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot, including: the controller adjusts the distance between the two optical lenses to change the optical power of the beam fine-tuning component.

[0172] In some embodiments, the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot, including: the controller adjusts the optical power of at least one optical lens included in one or more optical lenses included in the beam fine-tuning component.

[0173] In some embodiments, the spot pattern further includes a third spot corresponding to the third diffracted beam, and the method further includes: analyzing, by a controller, the spot pattern to determine whether a plurality of spot sizes of the first spot, the second spot, and the third spot are smaller than the size of the effective light receiving area of the detection unit of the detector, and whether a plurality of spacing distances between adjacent spots among the first spot, the second spot, and the third spot are greater than the size of the effective light receiving area of the detection unit of the detector; based on determining that at least one of the plurality of spot sizes is greater than or equal to the size of the effective light receiving area of the detection unit of the detector, or at least one of the plurality of spacing distances is less than or equal to the size of the effective light receiving area of the detection unit of the detector, continuously adjusting, by the controller, the optical power of the beam fine-tuning component to reduce the beam diameter of the second detection beam until the controller determines that the plurality of spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the plurality of spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector; and based on determining that the plurality of spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the plurality of spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector, obtaining, by the controller, a first optical power of one of the first diffracted beam, the second diffracted beam, and the third diffracted beam corresponding to the satellite ghost line diffraction order and a second optical power of the second detection beam, and calculating the satellite ghost line efficiency of the diffractive lens by dividing the first optical power by the second optical power.

[0174] Any step, operation, or process described herein can be performed or implemented alone or in combination with other devices using one or more hardware and / or software modules. In one embodiment, the software module is implemented using a computer program product including a computer-readable medium, the computer-readable medium including computer program code that can be executed by a computer processor to perform any or all of the described multiple steps, operations, or processes. In some embodiments, the hardware module can include hardware components such as devices, systems, optical elements, controllers, circuits, logic gates, etc.

[0175] In addition, when an embodiment shown in the drawings shows a single element, it is understood that the embodiment or an embodiment not shown in the drawings but within the scope of the present disclosure may include a plurality of such elements. Similarly, when an embodiment shown in the drawings shows a plurality of such elements, it is understood that the embodiment or an embodiment not shown in the drawings but within the scope of the present disclosure may include only one such element. The number of elements shown in the drawings is for illustrative purposes only and should not be construed as limiting the scope of the embodiments. In addition, unless otherwise stated, the embodiments shown in the drawings are not mutually exclusive and they can be combined in any suitable manner. For example, an element shown in one drawing / embodiment but not shown in another drawing / embodiment can still be included in that other drawing / embodiment. In any optical device disclosed herein that includes one or more optical layers, films, plates or elements, the number of layers, films, plates or elements shown in the drawings is for illustrative purposes only. In other embodiments not shown in the drawings but still within the scope of the present disclosure, the same or different layers, films, plates or elements shown in the same or different drawings / embodiments can be combined or repeated in various ways to form a stack.

[0176] Various embodiments have been described to illustrate exemplary implementations. Based on the disclosed embodiments, those of ordinary skill in the art can make various other changes, modifications, rearrangements and substitutions without departing from the scope of the present disclosure. Therefore, although the present disclosure has been described in detail with reference to the above embodiments, the present disclosure is not limited to the above embodiments. Without departing from the scope of the present disclosure, the present disclosure can be implemented in other equivalent forms. The scope of the present disclosure is defined in the appended claims.

Claims

1. A system for measuring the satellite ghost line efficiency of a diffractive lens, comprising: A light source configured to output a first detection beam; A beam fine-tuning component disposed between the light source and the diffractive lens and configured to convert the first detection beam into a second detection beam, the second detection beam being a non-collimated beam, and the diffractive lens diffracting the second detection beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of the main diffraction order and a second diffracted beam of the satellite ghost line diffraction order, wherein the beam fine-tuning component includes one or more optical lenses and the optical power of the beam fine-tuning component is adjustable; And A detector configured to generate a spot pattern, the spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam.

2. The system according to claim 1, wherein The first detection beam has a first beam diameter at the light input surface of the beam fine-tuning component, the second detection beam has a second beam diameter at the light output surface of the beam fine-tuning component, and the first beam diameter is greater than the second beam diameter.

3. The system according to claim 1 or 2, further comprising: A controller configured to adjust the optical power of the beam fine-tuning component so as to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot until the controller determines that the spot size of each of the first spot and the second spot is less than a first predetermined value and the spacing distance is greater than a second predetermined value.

4. The system according to claim 3, wherein, The controller is further configured to: Analyze the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than the first predetermined value and whether the spacing distance between the first spot and the second spot is greater than the second predetermined value; And Based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value or the spacing distance is less than or equal to the second predetermined value, adjust the optical power of the beam fine-tuning component provided to the first detection beam until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value; and / or Wherein the controller is further configured to: When the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value, determine the optical power of the second diffracted beam and the optical power of the second detection beam; And Determine the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

5. The system according to claim 3 or 4, wherein The first predetermined value and the second predetermined value are equal to the size of the effective light receiving area of the detection unit in the detector.

6. The system according to claim 1, wherein, The satellite ghost line diffraction order corresponding to the second diffracted beam is the first satellite ghost line diffraction order, the plurality of diffracted beams further includes a third diffracted beam of the second satellite ghost line diffraction order, and the spot pattern further includes a third spot corresponding to the third diffracted beam; and Optionally, wherein the system further includes: a controller configured to adjust the optical power of the beam fine-tuning component, thereby adjusting the spot size of each of the first spot, the second spot, and the third spot, the first spacing between the first spot and the second spot, and the second spacing between the second spot and the third spot until the spot size of each of the first spot, the second spot, and the third spot is less than a first predetermined value, and the first spacing and the second spacing are greater than a second predetermined value.

7. The system according to any one of the preceding claims, wherein, The one or more optical lenses included in the beam fine-tuning component include a first optical lens and a second optical lens, and the distance between the first optical lens and the second optical lens is adjustable; and / or wherein at least one of the one or more optical lenses included in the beam fine-tuning component has an adjustable optical power; and / or wherein the beam fine-tuning component includes a spatial filter, a single lens, and a reverse beam expander arranged in an optical sequence, and the single lens is disposed between the spatial filter and the reverse beam expander.

8. A method for measuring the satellite ghost line efficiency of a diffractive lens, comprising: outputting a first detection beam from a light source to a beam fine-tuning component disposed between the light source and the diffractive lens, the beam fine-tuning component including one or more optical lenses, and the optical power of the beam fine-tuning component being adjustable; converting, by the beam fine-tuning component, the first detection beam into a second detection beam propagating toward the diffractive lens, the second detection beam being a non-collimated beam, and the diffractive lens diffracting the second detection beam into a plurality of diffracted beams, the plurality of diffracted beams including a first diffracted beam of the main diffraction order and a second diffracted beam of the satellite ghost line diffraction order; and generating, by a detector, a spot pattern including a first spot corresponding to the first diffracted beam and a second spot corresponding to the second diffracted beam.

9. The method according to claim 8, wherein The first detection beam has a first beam diameter at the light input surface of the beam fine-tuning component, the second detection beam has a second beam diameter at the light output surface of the beam fine-tuning component, and the first beam diameter is greater than the second beam diameter.

10. The method according to claim 8 or 9, further comprising: controlling, by a controller, the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot, and the spacing between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than a first predetermined value, and the spacing is greater than a second predetermined value; and Optionally, the controller controls the optical power of the beam fine-tuning component to adjust the spot size of each of the first spot and the second spot, and the spacing distance between the first spot and the second spot until the spot size of each of the first spot and the second spot is less than the first predetermined value, and the spacing distance is greater than the second predetermined value, including: The controller analyzes the spot pattern to determine whether the spot size of each of the first spot and the second spot is less than the first predetermined value, and whether the spacing distance between the first spot and the second spot is greater than the second predetermined value; and Based on determining that the spot size of at least one of the first spot or the second spot is greater than or equal to the first predetermined value, or the spacing distance is less than or equal to the second predetermined value, the controller adjusts the optical power of the beam fine-tuning component provided to the first detection beam until the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value.

11. The method according to claim 10, further comprising: When the spot size of each of the first spot and the second spot is less than the first predetermined value and the spacing distance is greater than the second predetermined value, the controller determines the optical power of the second diffracted beam and the optical power of the second detection beam; And The controller determines the satellite ghost line efficiency based on the optical power of the second diffracted beam and the optical power of the second detection beam.

12. The method according to claim 10 or 11, wherein The first predetermined value and the second predetermined value are equal to the size of the effective light receiving area of the detection unit in the detector.

13. The method according to any one of claims 10 to 12, wherein, The one or more optical lenses included in the beam fine-tuning component include a first optical lens and a second optical lens, and wherein the controller controls the optical power of the control beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot includes: The controller adjusts the distance between the first optical lens and the second optical lens to change the optical power of the beam fine-tuning component.

14. The method according to claim 10, wherein The controller controls the optical power of the control beam fine-tuning component to adjust the spot size of each of the first spot and the second spot and the spacing distance between the first spot and the second spot includes: The controller adjusts the optical power of at least one of the one or more optical lenses included in the beam fine-tuning component.

15. The method according to claim 8, wherein, The spot pattern further includes a third spot corresponding to a third diffracted beam, and the method further includes: The controller analyzes the spot pattern to determine whether the multiple spot sizes of the first spot, the second spot, and the third spot are smaller than the size of the effective light receiving area of the detection unit of the detector, and whether the multiple spacing distances between adjacent spots among the first spot, the second spot, and the third spot are greater than the size of the effective light receiving area of the detection unit of the detector; Based on determining that at least one of the multiple spot sizes is greater than or equal to the size of the effective light receiving area of the detection unit of the detector, or at least one of the multiple spacing distances is less than or equal to the size of the effective light receiving area of the detection unit of the detector, the controller continuously adjusts the optical power of the beam fine-tuning component to reduce the beam diameter of the second detection beam until the controller determines that the multiple spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the multiple spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector; and Based on determining that the multiple spot sizes are smaller than the size of the effective light receiving area of the detection unit of the detector, and the multiple spacing distances are greater than the size of the effective light receiving area of the detection unit of the detector, the controller obtains the first optical power of one of the first diffracted beam, the second diffracted beam, and the third diffracted beam corresponding to the satellite ghost line diffraction order and the second optical power of the second detection beam, and calculates the satellite ghost line efficiency of the diffractive lens by dividing the first optical power by the second optical power.

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