Phase measurement system and super lens detection method

Abstract

The invention discloses a phase measurement system and a super-lens detection method, and belongs to the technical field of super-lens wavefront detection method.The phase measurement system comprises a light source, a spectroscope, a beam compressor, a beam splitter, a detection optical assembly and an image acquisition device.The beam splitter is used for dividing detection light passing through the beam compressor into a reference light beam and a detection light beam; the detection optical assembly comprises an objective lens and a detection platform, the detection platform is used for supporting a to-be-detected optical element or a reference element, and the image acquisition device is used for generating a first aberration signal according to the first detection light beam and the reference light beam and generating a second aberration signal according to the second detection light beam and the reference light beam; the wavefront aberration of the super lens can be obtained through the difference between the first aberration signal and the second aberration signal, so that the interference problem of the objective lens aberration in the detection process can be effectively solved, the high-precision measurement of the wave aberration of the super lens is realized, and the performance evaluation of the imaging quality of the super lens can be carried out.

Description

Technical Field

[0001] The present invention relates to the field of phase detection technology, and in particular to a phase measurement system and a superlens detection method. Background Art

[0002] Lenses are widely used. For example, mobile phones, cameras, glasses, microscopes, projectors, photography drones, VR and AR virtual reality devices all require a lot of lenses. The working principle of the lens is to control the phase distribution of light waves to achieve the manipulation of the wavefront. Common lenses can have high focusing efficiency, but due to the limitations of the manufacturing process, it is difficult to reduce the size or thickness of the lens to achieve system integration and lightweight, and the inherent spherical aberration of the lens will seriously affect the performance of the lens.

[0003] With the development of micro-nano photonics, meta-lens, also known as super-structure lens, has emerged. Meta-lens is a new type of optical element composed of nano-antennas. It has attracted widespread attention due to its excellent optical performance and miniaturized size (it can be as thin as a few hundred nanometers and as small as tens of microns). The essence of meta-lens is to use nano-antennas to control the phase, including the propagation phase, resonance phase, and geometric phase caused by cross-polarization. The phase distribution actually controlled by the meta-lens will be limited by the material and manufacturing process. The deviation between the actual controlled phase distribution and the ideal phase distribution will affect the optical performance of the meta-lens.

[0004] Since the aperture of the superlens is too small, the phase of the superlens cannot be directly detected using traditional optical detection methods alone. Therefore, its imaging performance cannot be accurately judged, and it is impossible to optimize the wavefront error and phase during the design and manufacturing process.

[0005] In the related art, the metalens phase detection method is based on a phase measurement system based on interferometric imaging, which is based on off-axis digital holography and digital holographic microscopy. However, the static interference fringe processing method used for the metalens has the characteristics of low precision, low efficiency and poor repeatability. Moreover, the above-mentioned phase interference system based on interferometric imaging will be interfered by the objective lens aberration in the off-axis test optical path, and it is impossible to achieve high-precision measurement of the metalens aberration. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a phase measurement system that can achieve high-precision, high-efficiency and convenient metalens phase detection.

[0007] The present invention also provides a super lens detection method applicable to the above phase measurement system.

[0008] A phase measurement system according to a first aspect of an embodiment of the present invention comprises: a light source for emitting a detection light; a spectroscope for transmitting the detection light and being able to reflect light in the opposite direction of the light source; a beam reducer for reducing the diameter of a light beam transmitted through the spectroscope; a beam splitter for dividing the detection light through the spectroscope into a reference beam and a detection beam, wherein the reference beam is reflected by the beam splitter and transmitted to the spectroscope in the opposite direction of the detection light and reflected by the spectroscope to an image acquisition device, and the detection beam is transmitted through the beam splitter; and a detection optical component comprising an objective lens and a detection platform, wherein the detection platform is used to support an optical element to be detected or a reference element. , the objective lens focuses the detection beam onto the optical element to be detected or the reference element and receives the detection beam reflected by the optical element to be detected or the reference element; and the image acquisition device is used to respectively receive the detection beam transmitted by the objective lens to the beam splitter and transmitted through the propagation path of the detection light, the detection beam includes a first detection beam corresponding to the optical element to be detected, and a second detection beam corresponding to the reference element, and the image acquisition device is further used to generate a first aberration signal according to the first detection beam and the reference beam, and to generate a second aberration signal according to the second detection beam and the reference beam.

[0009] According to some embodiments of the present invention, the optical element to be detected includes a metalens and a plane reflector located on a side of the metalens away from the objective lens; and the reference element includes a spherical reflector.

[0010] According to some embodiments of the present invention, the numerical aperture of the objective lens is greater than the numerical aperture of the metalens.

[0011] According to some embodiments of the present invention, the image acquisition device includes a comparator, and the comparator is used to obtain a wavefront aberration corresponding to the metalens according to a difference between the first aberration signal and the second aberration signal.

[0012] According to some embodiments of the present invention, the detection platform is movably arranged relative to the objective lens.

[0013] According to some embodiments of the present invention, the detection platform includes a support base supporting the plane reflector, and a motion controller connected to the superlens for driving the superlens to move so as to adjust the relative position of its object focus and the image focus of the objective lens.

[0014] According to some embodiments of the present invention, the support seat is used to support the plane reflector or the spherical reflector, and can drive the spherical reflector to move relative to the objective lens.

[0015] According to some embodiments of the present invention, the phase measurement system further includes: an optical path reflector, disposed between the beam splitter and the objective lens, for reflecting the detection light beam to the objective lens.

[0016] According to some embodiments of the present invention, the light source is a monochromatic point light source, and the phase measurement system further includes a collimator, and the collimator is located between the beam splitter and the beam reducer.

[0017] According to some embodiments of the present invention, the beam splitter is a semi-transparent and semi-reflective mirror.

[0018] The present invention also provides a metalens detection method using the above phase measurement system, comprising:

[0019] Signal detection step: installing the optical element to be detected including the metalens and the first reflector to the detection platform, wherein the first reflector is located on the side of the metalens away from the objective lens; adjusting the distance between the objective lens and the metalens so that the image focus of the objective lens coincides with the object focus of the metalens, and the detection light beam focused on the metalens is emitted in parallel through the metalens; the detection light beam emitted through the metalens is reflected by the first reflector and sequentially transmitted through the metalens and the objective lens to the beam splitter and further transmitted along the propagation path of the reference light beam to the image acquisition device, wherein the image acquisition device generates a first aberration signal based on the reference light beam and the detection light beam;

[0020] A control detection step: installing a second reflector to the detection platform, adjusting the distance between the objective lens and the second reflector, so that the detection beam is focused on the second reflector and reflected by the second reflector to the objective lens and transmitted to the beam splitter and further transmitted to the image sensor along the propagation path of the reference beam, and the image acquisition device generates a second aberration signal based on the reference beam and the detection beam; and

[0021] The wavefront aberration of the metalens is obtained based on the difference between the first aberration signal and the second aberration signal, and the wavefront aberration of the metalens is data processed to obtain the parameters of the metalens.

[0022] According to some embodiments of the present invention, the step of performing data processing on the wave aberration of the metalens to obtain parameters of the metalens includes:

[0023] Calculating a pupil function according to the wave aberration of the metalens, wherein the pupil function is a complex amplitude distribution of a spherical wave emitted by the light source at an exit pupil position after passing through the phase measurement system;

[0024] The point spread function and the modulation transfer function of the metalens are obtained according to the pupil function.

[0025] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of a phase measurement system in the related art;

[0027] Figure 2 is a structural schematic diagram of a phase measurement system according to an embodiment of the present invention;

[0028] Figure 3 is a structural schematic diagram of a phase measurement system according to another embodiment of the present invention;

[0029] Figure 4 is a flow chart of a superlens detection method according to an embodiment of the present invention;

[0030] Figure 5 is a flow chart of processing the wave aberration data of a superlens according to an embodiment of the present invention;

[0031] Figure 6 1 is a detection wavefront diagram of an objective lens and a super lens according to an embodiment of the present invention;

[0032] Figure 7 is a detection wavefront diagram of an objective lens according to an embodiment of the present invention;

[0033] Figure 8 A detection wavefront image of a metalens obtained by subtracting the first wave aberration and the second wave aberration in one embodiment of the present invention;

[0034] Fig. 9 is the MTF of the processed superlens according to one embodiment of the present invention;

[0035] Fig.10 is the PSF of the processed superlens according to one embodiment of the present invention.

[0036] Reference numerals:

[0037] Light source 100;

[0038] Beam splitter 200;

[0039] A beam reducer 300;

[0040] Beam splitter 400;

[0041] Detection optical assembly 500; optical element to be detected 501; reference element 502; objective lens 510; super lens 520; plane reflector 530; spherical reflector 540; first motion controller 550; second motion controller 560; third motion controller 570;

[0042] Image acquisition device 600; imaging lens 610; CCD camera 620;

[0043] Light path reflector 700;

[0044] Collimating mirror 800. DETAILED DESCRIPTION

[0045] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0046] In the description of the present invention, it is necessary to understand that the orientation or positional relationship indicated by the terms upper, lower, axial, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0047] In the description of the present invention, the meaning of "above" and "below" is more than two, "greater than" and "less than" are understood to exclude the number itself, and "above", "below" and "within" are understood to include the number itself. If there is a description of "first" and "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0048] In the description of the present invention, it should be noted that the terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific content of the technical solution.

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, not all embodiments.

[0050] Reference Figure 1 As shown, Figure 1 The phase measurement system based on interferometric imaging in the related art is shown in FIG. The phase measurement system is based on off-axis digital holography technology and digital holographic microscopy technology. Only one photo is needed to obtain the phase distribution regulated by the superlens. The specific optical path diagram is shown in FIG. Figure 1As shown. The phase measurement system can be used to measure metalenses as small as tens of microns, with a phase measurement accuracy of 0.05rad. Based on the measured phase distribution of the metalens, the light field distribution of the metalens can be obtained, and further the pupil function, point spread function (PSF), modulation transfer function (MTF), Strehl ratio (SR), depth of focus (DOF) and other key indicators of the metalens can be obtained, and the measured metalens is quantitatively evaluated.

[0051] like Figure 1 As shown, the laser light emitted by the laser 10 passes through the beam expander 20 to obtain a plane wavefront, which is then divided into two beams by the semi-transparent and semi-reflective mirror 30: a detection beam and a reference beam. In the optical path of the detection beam, an objective lens 70 and an achromatic double lens 80 are used to image the superlens 60 on the charge coupled device 90 (CCD). In the optical path of the reference beam, by changing the position of the lens in the vertical direction, the reference beam is incident on the CCD at a certain angle, thereby achieving off-axis interference. In order to make the interference patterns on the CCD overlap as much as possible, it is necessary to expand the reference beam through the first lens 40 and the second lens 50. This phase measurement system is suitable for superlenses of linearly polarized light.

[0052] You only need to take a picture to get the phase distribution of the superlens control (optical path diagram as shown in Figure 1 As shown). The system can be used to measure metalenses as small as tens of microns, with a phase measurement accuracy of 0.05rad. Based on the measured phase distribution of the metalens, the light field distribution of the metalens can be obtained, and further the pupil function, point spread function (PSF), optical modulation transfer function (MTF), Strehl rate (SR), depth of focus (DOF) and other key indicators of the metalens can be obtained, and the measured metalens is quantitatively evaluated. However, the above-mentioned phase measurement system based on interferometric imaging will be interfered by the objective lens aberration in the off-axis test optical path, and it is impossible to achieve high-precision measurement of the metalens aberration.

[0053] The phase measurement system of the embodiment of the present invention is based on the principle of phase-shift interference, and is also called a small-aperture interference imaging inspection system. Through the Fizeau interference principle of the common optical path, the wavefront detection of the superlens can be realized with high precision, high efficiency and convenience. In addition, the wavefront detection of superlenses with different fields of view can be realized to confirm the aberration difference between the 0° field of view and the near 0° field of view based on the superlens. According to the measured wavefront and phase distribution of the superlens, the optical modulation transfer function, point spread function and other parameters of the superlens can be calculated to realize the imaging quality analysis of the superlens.

[0054] refer to Figures 2 to 3 A phase measurement system according to an embodiment of the present invention is described. The phase measurement system is suitable for wavefront detection of a superlens 520. The phase measurement system is described below by taking a specific example.

[0055] Reference Figure 2 As shown, the phase measurement system of the embodiment of the present invention includes a light source 100 , a beam splitter 200 , a beam reducer 300 , a beam splitter 400 , a detection optical component 500 and an image acquisition device 600 .

[0056] Among them, the light source 100 is used to emit detection light, and the light source 100 is specifically a monochromatic point light source; the beam splitter 200 is located between the light source 100 and the beam reducer 300. The beam splitter 200 has the functions of a lens and a reflector, and can transmit the detection light of the light source 100 to the beam reducer 300. The diameter of the light beam is reduced by the beam reducer 300. The light beam emitted by the beam reducer 300 is a parallel light beam, and then the parallel light beam enters the beam splitter 400. The beam splitter 400 is used to divide the parallel light beam into a reference light beam and a detection light beam. The reference light beam and the detection light beam are emitted in different directions. The reference light beam is reflected by the beam splitter 400 and transmitted to the beam splitter 200 in the opposite direction of the detection light, and then reflected by the beam splitter 200 to the image acquisition device 600. That is, the reference light beam is turned back and reflected to the image acquisition device 600 by the beam splitter 200, and the detection light beam is transmitted by the beam splitter 400 and emitted to the detection optical component 500.

[0057] Specifically, the beam splitter 400 is a reference plane mirror. A parallel light beam is incident from one side of the reference plane mirror. The light beam reflected by the reference plane mirror is the reference light beam. The reference light beam returns along the original optical path, that is, the reference light beam passes through the beam reducer 300 and then is emitted to the beam splitter 200. Since the beam splitter 200 can reflect light from the opposite direction, the reference light beam can be reflected toward the image acquisition device 600 through the beam splitter 200.

[0058] Reference Figure 2 As shown, the light beam passing through the reference plane mirror is the detection light beam, which is a parallel light beam, and is emitted toward the detection optical component 500. In the embodiment, the detection optical component 500 includes an objective lens 510 and a detection platform, wherein the detection platform is used to support the optical element 501 to be detected or the reference element 502, and the optical element 501 to be detected or the reference element 502 can be selectively installed on the detection platform according to the measurement requirements; the objective lens 510 can focus the detection light beam to the optical element 501 to be detected or the reference element 502, and can receive the detection light beam reflected back by the optical element 501 to be detected or the reference element 502.

[0059] In some embodiments, the optical element 501 to be detected includes a metalens 520 and a first reflector. Specifically, the first reflector is located on the side of the metalens 520 away from the objective lens 510. In the embodiment, the first reflector is a plane reflector 530, and the metalens 520 is located between the objective lens 510 and the plane reflector 530. The objective lens 510 is used to focus the detection beam. After passing through the objective lens 510, the parallel beam will be focused on the focus. By adjusting the relative position of the metalens 520 and the objective lens 510, the object focus of the metalens 520 and the image focus of the objective lens 510 are overlapped, so that the detection beam passes through the object focus of the metalens 520 and is emitted as a parallel beam.

[0060] The objective lens 510 is a lens group composed of a plurality of lenses, which can overcome the imaging defects of a single lens and improve the optical quality of the objective lens 510. The numerical aperture characterizes the light-gathering ability of the objective lens 510 and is one of the important properties of the objective lens 510, usually represented by "NA". The numerical aperture of the objective lens 510 determines the resolution and effective magnification of the objective lens 510. In some embodiments, the NA of the objective lens 510 needs to be greater than the NA of the metalens 520 to meet the resolution requirements.

[0061] It can be understood that the plane reflector 530 is used to reflect the detection light beam passing through the superlens 520, so that the detection light beam is folded back and reflected to the image acquisition device 600 through the beam splitter 200; that is, the detection light beam passing through the plane reflector 530 is transmitted to the beam splitter 400 through the objective lens 510, and then returns to the beam splitter 200 along the propagation path of the detection light. The beam splitter 200 can reflect the folded detection light beam toward the image acquisition device 600, so that the reference light beam and the detection light beam form interference, and the interference pattern can be obtained through the image acquisition device 600.

[0062] Among them, the image acquisition device 600 includes an imaging lens 610 and a CCD camera 620. The imaging lens 610 can image the reference beam and the detection beam reflected by the spectroscope 200 onto the CCD camera 620, so that the reference beam and the detection beam form interference. At this time, the interference pattern of the super lens 520 can be observed. The structure composed of the imaging lens 610 and the CCD camera 620 is also called an interferometer.

[0063] It can be understood that CCD is a semiconductor device that can convert optical images into digital signals. The more pixels contained on the CCD, the higher the picture resolution it provides. The embodiment of the present invention is based on the Fizeau interference principle. The interferometer is also called the Fizeau interferometer. The addition of the beam reducer 300 in the Fizeau interferometer can greatly improve the resolution of detecting the small-aperture metalens 520, and improve the detection accuracy and efficiency. Specifically, the beam size without adding the beam reducer 300 is 4 inches, and the pixels that can be collected on the 1mm caliber are approximately 70*70; the beam size after adding the beam reducer 300 is 1 inch, and the pixels that can be collected on the 1mm caliber are approximately 280*280, which is equivalent to an increase in the number of pixels per unit area in the interferometer corresponding to the unit area, and the resolution is improved, thereby achieving the purpose of improving the detection accuracy and efficiency.

[0064] Considering the interference of the aberration of the objective lens 510 in the off-axis test optical path of the phase measurement system, it is impossible to achieve high-precision measurement of the aberration of the meta-lens. In order to solve the above technical problems, a reference element 502 is introduced in the embodiment of the present invention, and the reference element 502 can be optionally installed on the detection platform. The reference element 502 includes a second reflector, which is specifically a spherical reflector 540; the detection optical component 500 is configured to replace the plane reflector 530 with a spherical reflector 540, and remove the super lens 520. The spherical reflector 540 is used to reflect the detection light beam passing through the objective lens 510, so that the detection light beam is folded back and reflected to the image acquisition device 600 through the beam splitter 200. That is to say, after removing the super lens 520, the detection light beam can be returned along the original light path through the spherical reflector 540.

[0065] Reference Figure 2 and Figure 3 As shown, Figure 2 A phase measurement system is shown which includes an objective lens 510, a metalens 520 and a plane mirror 530. Figure 3 A phase measurement system in which an adjusted objective lens 510 is combined with a spherical mirror 540 is shown.

[0066] Specifically, the phase measurement system is used to first detect the overall wavefront of the objective lens 510, the metalens 520 and the plane mirror 530. At this time, the detection beam is a first detection beam corresponding to the metalens 520 and the plane mirror 530. The image acquisition device 600 can generate a first aberration signal based on the first detection beam and the reference beam; then the plane mirror 530 is replaced with a spherical mirror 540, and the metalens 520 is removed, and the wavefront of the objective lens 510 and the spherical mirror 540 is detected. At this time, the detection beam is a second detection beam corresponding to the spherical mirror 540. The image acquisition device 600 can generate a second aberration signal based on the second detection beam and the reference beam. Since the wavefront of the plane mirror 530 and the wavefront of the spherical mirror 540 differ slightly, they can be considered to be approximately equal. The wavefront of the metalens 520 can be obtained by taking the difference between the two detected wavefronts, that is, the wavefront aberration of the metalens 520 can be obtained according to the difference between the first aberration signal and the second aberration signal. This can effectively solve the interference problem of the aberration of the objective lens 510 during the detection process, and realize high-precision measurement of the wave aberration of the metalens 520, thereby realizing high-precision and fast phase and wavefront distribution detection of the metalens 520, and can perform performance evaluation on the imaging quality of the metalens 520.

[0067] The wavefront refers to the surface formed by the particles that have just started to displace at a certain moment when the wave propagates in the medium. It represents the spatial position where the wave energy reaches at a certain moment and is moving. According to the shape of the wavefront, the wave can generally be divided into spherical waves, plane waves, cylindrical waves, etc. In the embodiment, the wavefront is the surface formed by the points with the same phase in the propagation of the light wave. The light wave is a transverse wave with a vibration plane perpendicular to the propagation direction. The wavefront is a plane formed by electromagnetic vibrations. The wavefront of the entire light wave is composed of the same-phase points in different wavefronts. The propagation of the light wave is actually a process of continuous reproduction of the wavefront. The point light source forms a spherical wavefront, and the parallel light source forms a plane wavefront.

[0068] It should be noted that the image acquisition device 600 includes a comparator, which can compare the first aberration signal and the second aberration signal to determine the difference between the two, so that the wavefront aberration with the super lens 520 is obtained according to the difference between the first aberration signal and the second aberration signal.

[0069] Of course, this is only an example. The first reflector is not limited to the plane reflector 530. The first reflector can reflect the detection light beam passing through the super lens 520. The second reflector is not limited to the spherical reflector 540. The second reflector can reflect the detection light beam passing through the objective lens 510.

[0070] Reference Figure 2 and Figure 3As shown, in some embodiments, a light path reflector 700 is arranged between the beam splitter 400 and the objective lens 510. The light path reflector 700 is arranged at an angle of 45° to the light path, and is also called a 45° reflector. The light path reflector 700 can reflect the detection light beam emitted from the reference plane mirror to the objective lens 510, thereby changing the direction of the light path.

[0071] Reference Figure 2 and Figure 3 As shown, in some embodiments, the beam splitter 200 used is a semi-transparent and semi-reflective mirror, which is specifically an optical element that coats a semi-reflective film on optical glass to change the original transmission and reflection ratio of the incident light beam. The coating layer can increase the transmittance and increase the light intensity, and can also increase the reflection and reduce the light intensity, so that the transmittance and reflectivity can be 50% each. When the detection light passes through this film, the intensity of the light transmitted and the intensity of the light reflected back each account for 50%. The required reflectivity can be selected according to actual needs.

[0072] It can be understood that the phase measurement system also includes a collimator 800, which is located between the beam splitter 200 and the beam reducer 300. The function of the collimator 800 is to ensure that the detection light propagates parallel to each other. The monochromatic light source 100 generates divergent light, which is collimated into a parallel light beam by the collimator 800 after passing through the beam splitter 200, and then the parallel light beam is incident on the beam reducer 300, ensuring that the detection light propagates to the beam reducer 300 in the form of parallel light.

[0073] In order to adjust the relative position of the optical element 501 to be detected and the objective lens 510, in some embodiments, the detection platform is movably arranged relative to the objective lens 510, and the relative position of the metalens 520 and the objective lens 510 can be adjusted by moving the detection platform, or the relative position of the plane reflector 530 and the objective lens 510 can be adjusted. For example, the detection platform can be driven to move along the x-axis, y-axis, and z-axis directions through the driving mechanism, so that the detection platform can be moved in three directions.

[0074] Reference Figure 2 As shown, the detection platform also includes a first motion controller 550 and a second motion controller 560. The first motion controller 550 is connected to the super lens 520. The super lens 520 is driven to move by the first motion controller 550, and the relative position of the object focus of the super lens 520 and the image focus of the objective lens 510 can be adjusted. The purpose is to achieve the coincidence of the object focus of the super lens 520 and the image focus of the objective lens 510, so that the detection light beam is emitted in parallel after passing through the super lens 520, ensuring that the detection light beam is incident on the plane reflector 530 in the form of parallel light and returns along the original light path.

[0075] Among them, the detection platform includes a support base supporting the plane reflector 530, and the support base is provided with a second motion controller 560. The second motion controller 560 is connected to the plane reflector 530, and the plane reflector 530 is driven to move by the second motion controller 560 to adjust the relative position of the plane reflector 530 and the super lens 520 to ensure that the detection light beam can be perpendicular to the incident surface of the plane reflector 530.

[0076] It can be understood that since the motion control of the metalens 520 and the plane reflector 530 needs to be adjusted using high-precision displacement to achieve high-precision measurement of the metalens 520, the first motion controller 550 and the second motion controller 560 need to calibrate whether the plane where the objective lens 510 and the metalens 520 are located is completely perpendicular to the optical path. In the embodiment, the first motion controller 550 and the second motion controller 560 use a multi-axis controller to achieve adjustment in multiple dimensions to meet the high-precision measurement requirements.

[0077] Specifically, the first motion controller 550 is taken as an example for explanation. In the embodiment, a six-axis controller is used to adjust the superlens 520. The direction axes include six dimensions: x-axis, y-axis, z-axis, u-axis (rotation around x-axis), v-axis (rotation around y-axis), and w-axis (rotation around z-axis). That is to say, the superlens 520 can be adjusted in the above six dimensions with higher adjustment accuracy, ensuring that the optical path meets the high-precision measurement requirements.

[0078] Reference Figure 3 As shown, the support base is further provided with a third motion controller 570. When the plane reflector 530 is replaced by the spherical reflector 540, the third motion controller 570 is connected to the spherical reflector 540 to drive the spherical reflector 540 to move, and the relative position of the spherical reflector 540 and the objective lens 510 can be adjusted. In the embodiment, the spherical reflector 540 is specifically a concave mirror. By adjusting the spherical reflector 540 through the third motion controller 570, the focus of the spherical reflector 540 can be made to coincide with the focus of the objective lens 510, ensuring that the light beam can be reflected by the spherical reflector 540 and returned along the original light path.

[0079] It is understandable that the third motion controller 570 may also use a six-axis controller to achieve high-precision adjustment of the spherical reflector 540. For details, see the control method of the second motion controller 560. In some embodiments, the second motion controller 560 and the third motion controller 570 may be the same drive mechanism or different drive mechanisms.

[0080] The embodiment of the present invention proposes a small-aperture interferometric imaging detection system for the wavefront and phase detection of meta-lenses, which has high precision, small error, and is convenient and fast. The embodiment of the present invention is also applicable to the aberration detection of other small-aperture optical elements, and the minimum detection aperture can reach 100 microns.

[0081] refer to Figures 4 to 5 The metalens 520 detection method of the embodiment of the present invention is described. The method is applied to the phase measurement system shown in the above embodiment. The specific structure of the phase measurement system can be found in Figure 2 and Figure 3 The embodiments shown will not be described in detail here, and the detection method of the super lens 520 will be described below with a specific example.

[0082] Reference Figure 4 As shown, in some embodiments, the superlens 520 detection method includes but is not limited to the following steps:

[0083] Step S100, installing the optical element 501 to be inspected on the inspection platform;

[0084] Step S200, adjusting the distance between the objective lens 510 and the super lens 520 so that the image focus of the objective lens 510 coincides with the object focus of the super lens 520, and the first detection light beam focused on the super lens 520 is emitted in parallel through the super lens 520;

[0085] Step S300, the first detection light beam emitted by the super lens 520 is reflected by the first reflector and sequentially transmitted to the beam splitter 400 through the super lens 520 and the objective lens 510, and further transmitted to the image acquisition device 600 along the propagation path of the reference light beam;

[0086] In step S400 , the image acquisition device 600 generates a first aberration signal based on a reference beam and a first detection beam.

[0087] Combination Figure 2 and Figure 3 It can be understood that the metalens 520 detection method of the embodiment uses the phase measurement system of the above-mentioned embodiment, and aims to calculate the optical modulation transfer function, point spread function and other parameters of the metalens 520 based on the measured wavefront and phase distribution of the metalens 520, so as to realize the imaging quality analysis of the metalens 520.

[0088] It should be noted that, since the phase measurement system needs to select and install the optical element to be detected 501 and the reference element 502 for detection, the superlens detection method includes two parts: a signal detection step and a control detection step. The above steps S100 to S400 show the signal detection step in the superlens detection method.

[0089] Reference Figure 4 As shown, in some embodiments, the superlens detection method includes but is not limited to the following steps:

[0090] Step S500, installing the second reflector on the detection platform;

[0091] Step S600, adjusting the distance between the objective lens 510 and the second reflector, so that the second detection beam is focused on the second reflector and reflected by the second reflector to the objective lens 510 and transmitted to the beam splitter 400, and further transmitted to the image acquisition device 600 along the propagation path of the reference beam, and the image acquisition device 600 generates a second aberration signal based on the reference beam and the second detection beam;

[0092] Step S700, obtaining the wavefront aberration of the metalens 520 based on the difference between the first aberration signal and the second aberration signal, performing data processing on the wavefront aberration of the metalens 520, and obtaining the parameters of the metalens 520.

[0093] Among them, the above steps S500 to S600 show the control detection steps in the super lens 520 detection method.

[0094] It is understandable that if Figure 2 As shown, before the test, the optical path of the phase measurement system is calibrated, and the interferometer is calibrated with the farthest plane mirror 530 to ensure that the interferometer can receive the returned light beam. Since the light reflected by the surface of the optical path mirror 700 between the interferometer and the farthest plane mirror 530 directly returns to the interferometer, interference fringes are formed. By adjusting the plane mirror 530, interference zero fringes are adjusted, which indicates that the interferometer can receive the returned light beam.

[0095] After calibration is complete, use Figure 2 The phase measurement system shown in the figure can be used to measure the overall wave aberration of the combination of the objective lens 510, the metalens 520 and the plane reflector 530, and the overall wave aberration is the first wave aberration, that is, the first aberration signal; then the plane reflector 530 is replaced by the spherical reflector 540 in the system, and the metalens 520 is removed, and then the system is recalibrated, using Figure 3 The phase measurement system shown is used to measure the wave aberration of the objective lens 510 and the spherical reflector 540, and the wave aberration is the second wave aberration, that is, the second aberration signal. Then, the difference between the first wave aberration and the second wave aberration is calculated to obtain the wave aberration of the super lens 520. Finally, the wave aberration of the super lens 520 is processed to obtain the parameters of the super lens 520.

[0096] Since the difference between the wavefront of the plane reflector 530 and the wavefront of the spherical reflector 540 is very small, they can be considered to be approximately equal. The wavefront of the superlens 520 can be obtained by taking the difference between the two detected wavefronts. This can effectively solve the problem that the phase interferometer system cannot achieve high-precision aberration detection of the superlens 520 due to the aberration of the objective lens 510 in the off-axis test optical path. High-precision measurement of the wave aberration of the superlens 520 can be achieved, thereby realizing high-precision and fast phase and wavefront distribution detection of the superlens 520, which is convenient for evaluating the imaging quality of the superlens 520.

[0097] Reference Figure 6 , Figure 7 and Figure 8 As shown, Figure 6 5 shows the detected wavefront diagram of the objective lens 510 and the super lens 520, Figure 7 Detection wavefront diagram of objective lens 510 is shown; Figure 8 The detected wavefront image of the metalens 520 is shown by subtracting the two wave aberrations.

[0098] In some embodiments, the calibration process of step S200 specifically includes but is not limited to the following steps:

[0099] Step S210, adjusting the objective lens 510 and the super lens 520 so that the planes where the objective lens 510 and the super lens 520 are located are respectively perpendicular to the optical path, and the numerical aperture of the objective lens 510 is larger than the numerical aperture of the super lens 520.

[0100] Combination Figure 2 It can be understood that the second motion controller 560 is connected to the plane mirror 530, and the second motion controller 560 drives the plane mirror 530 to move, so as to adjust the relative position of the plane mirror 530 and the super lens 520, and ensure that the first detection light beam can be perpendicular to the incident surface of the plane mirror 530.

[0101] It can be understood that the movement of the superlens 520 can be adjusted by the first motion controller 550, and the movement of the plane reflector 530 can be adjusted by the second motion controller 560. The objective lens 510 is a microscope objective lens and can be moved relative to the optical path. In this way, the planes where the objective lens 510 and the superlens 520 are located can be adjusted to be perpendicular to the optical path respectively. The numerical aperture of the objective lens 510 is larger than the numerical aperture of the superlens 520, which meets the resolution requirements and is conducive to achieving high-precision measurement.

[0102] It should be noted that after the optical path is calibrated, the metalens 520 or the objective lens 510 is adjusted, or the metalens 520 and the objective lens 510 are adjusted simultaneously, so that the image focus of the objective lens 510 coincides with the object focus of the metalens 520, so that the overall wave aberration of the objective lens 510 and the metalens 520 is measured.

[0103] Reference Figure 5 As shown, in some embodiments, the above step S700 specifically includes but is not limited to the following steps:

[0104] Step S710, calculating the pupil function according to the wave aberration of the metalens 520, where the pupil function is the complex amplitude distribution of the spherical wave emitted by the light source 100 at the exit pupil position after passing through the phase measurement system;

[0105] Step S720, obtaining the point spread function and modulation transfer function of the metalens 520 according to the pupil function.

[0106] It can be understood that in order to calculate the point spread function of the optical system, the concept of pupil function is introduced. The pupil function is defined as the complex amplitude distribution g(Y,Z) of the spherical wave emitted by a point light source at the exit pupil position after passing through the optical system, which can be expressed as:

[0107]

[0108] In the above formula, (Y, Z) is the coordinate of the exit pupil plane, A(Y, Z) is the amplitude distribution of the light emitted by the point light source at the exit pupil plane, W(Y, Z) is the wave aberration introduced by the system to the monochromatic light wave, λ represents the wavelength, and j is the imaginary unit. In the case of uniform light energy distribution, A(Y, Z) is a constant. Under this condition, the point spread function P(y′, z′) is the square of the modulus of the Fourier transform of the pupil function, that is:

[0109]

[0110] (y′,z′) represents the coordinates of the image plane, and R represents the distance from the exit pupil to the image plane. The optical transfer function OTF (μ, ν) in point spread form is expressed as:

[0111]

[0112] (μ, ν) is the displacement of the exit pupil function autocorrelation integral, which is called the simplified spatial frequency. Therefore, the optical transfer function can also be defined as the Fourier transform of the point spread function. The modulation transfer function MTF is the square of the modulus of OTF, MTF = |OTF| 2 In this way, the point spread function and the modulation transfer function can be obtained from the pupil function obtained by the system wave aberration, and the quality of the metalens 520 can be evaluated based on the point spread function and the modulation transfer function. Fig. 9 and Fig.10 As shown, Fig. 9 shows the MTF of the metalens 520, Fig.10 The PSF of metalens 520 is shown.

[0113] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A phase measurement system, characterized in that: include: A light source, for emitting a detection light; A spectroscope, used for transmitting the detection light and reflecting the light in the opposite direction of the light source; A beam reducer, used to reduce the diameter of the light beam transmitted through the beam splitter; A beam splitter, used for splitting the detection light passing through the beam reducer into a reference beam and a detection beam, wherein the reference beam is reflected by the beam splitter and transmitted to the beam splitter in the opposite direction of the detection light and reflected by the beam splitter to the image acquisition device, and the detection beam is transmitted through the beam splitter; A detection optical assembly, comprising an objective lens and a detection platform, wherein the detection platform is used to support the optical element to be detected or the reference element, and the objective lens focuses the detection beam onto the optical element to be detected or the reference element and receives the detection beam reflected back by the optical element to be detected or the reference element; And the image acquisition device is used to respectively receive the detection light beams transmitted by the objective lens to the beam splitter and transmitted through the propagation path of the detection light, the detection light beams include a first detection light beam corresponding to the optical element to be detected, and a second detection light beam corresponding to the reference element, and the image acquisition device is further used to generate a first aberration signal according to the first detection light beam and the reference light beam, and generate a second aberration signal according to the second detection light beam and the reference light beam.

2. The phase measurement system according to claim 1, characterized in that The optical element to be detected includes a metalens and a plane reflector located on a side of the metalens away from the objective lens; the reference element includes a spherical reflector.

3. The phase measurement system according to claim 2, characterized in that: The numerical aperture of the objective lens is greater than the numerical aperture of the super lens.

4. The phase measurement system according to claim 3, characterized in that: The image acquisition device includes a comparator, and the comparator is used to obtain a wavefront aberration corresponding to the metalens according to a difference between the first aberration signal and the second aberration signal.

5. The phase measurement system according to claim 2, characterized in that: The detection platform is movably arranged relative to the objective lens.

6. The phase measurement system according to claim 5, characterized in that: The detection platform includes a support base for supporting the plane reflector, and a motion controller connected to the super lens for driving the super lens to move so as to adjust the relative position of its object focus and the image focus of the objective lens.

7. The phase measurement system according to claim 6, characterized in that: The support seat is used to support the plane reflector or the spherical reflector, and can drive the spherical reflector to move relative to the objective lens.

8. The phase measurement system according to claim 1, characterized in that: The phase measurement system further comprises: The optical path reflector is arranged between the beam splitter and the objective lens, and is used for reflecting the detection light beam to the objective lens.

9. The phase measurement system according to claim 1, characterized in that: The light source is a monochromatic point light source, and the phase measurement system further comprises a collimator, which is located between the beam splitter and the beam reducer.

10. The phase measurement system according to claim 1, characterized in that: The beam splitter is a semi-transparent and semi-reflective mirror.

11. A method for detecting a metalens using the phase measurement system according to any one of claims 1 to 10, comprising: Signal detection step: installing the optical element to be detected including a metalens and a first reflector to the detection platform, wherein the first reflector is located on the side of the metalens away from the objective lens; adjusting the distance between the objective lens and the metalens so that the image focus of the objective lens coincides with the object focus of the metalens, and the detection light beam focused on the metalens is emitted in parallel through the metalens; the detection light beam emitted through the metalens is reflected by the first reflector and sequentially transmitted through the metalens and the objective lens to the beam splitter and further transmitted along the propagation path of the reference light beam to the image acquisition device, and the image acquisition device generates a first aberration signal based on the reference light beam and the detection light beam; A control detection step: installing a second reflector to the detection platform, adjusting the distance between the objective lens and the second reflector, so that the detection beam is focused on the second reflector and reflected by the second reflector to the objective lens and transmitted to the beam splitter, and further transmitted to the image acquisition device along the propagation path of the reference beam, and the image acquisition device generates a second aberration signal based on the reference beam and the detection beam; as well as The wavefront aberration of the metalens is obtained based on the difference between the first aberration signal and the second aberration signal, and the wavefront aberration of the metalens is processed to obtain the parameters of the metalens.

12. The superlens detection method according to claim 11, characterized in that: The step of performing data processing on the wave aberration of the metalens to obtain parameters of the metalens includes: Calculating a pupil function according to the wave aberration of the metalens, wherein the pupil function is a complex amplitude distribution of a spherical wave emitted by the light source at an exit pupil position after passing through the phase measurement system; The point spread function and the modulation transfer function of the metalens are obtained according to the pupil function.

Images