Phase measurement system and superlens detection method

Abstract

This invention discloses a phase measurement system and a superlens detection method, belonging to the technical field of superlens wavefront detection methods. The phase measurement system includes a light source, a beam splitter, a beam reducer, a detection optical component, and an image acquisition device. The beam splitter divides the probe light after passing through the beam reducer into a reference beam and a detection beam. The detection optical component includes an objective lens and a detection platform. The detection platform supports the optical element to be detected or a reference element. The image acquisition device generates a first aberration signal based on the first detection beam and the reference beam, and a second aberration signal based on the second detection beam and the reference beam. The difference between the first and second aberration signals yields the wavefront aberration of the superlens. This effectively solves the interference problem of objective aberration during detection, achieving high-precision measurement of superlens wavefront aberrations and enabling performance evaluation of the superlens's imaging quality.

Description

Technical Field

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

[0002] Lenses have a wide range of applications; for example, mobile phones, cameras, eyeglasses, microscopes, projectors, drones, VR and AR virtual reality devices all require many lenses. The working principle of a lens is to modulate the phase distribution of light waves, thereby manipulating the wavefront. Common lenses can have high focusing efficiency, but due to manufacturing limitations, it is difficult to reduce their size or thickness to achieve system integration and lightweighting. Furthermore, the inherent spherical aberration of lenses can severely affect their performance.

[0003] With the development of micro-nano photonics, meta-lenses have emerged. Meta-lenses are novel optical elements composed of nanoantennas, attracting widespread attention due to their excellent optical performance and miniaturized size (ranging from hundreds of nanometers to tens of micrometers). The essence of a meta-lens is to utilize nanoantennas to control the phase, including the propagation phase, resonant phase, and geometric phase caused by cross-polarization. The actual phase distribution that a meta-lens can control is limited by materials and manufacturing processes; deviations between the actual controlled phase distribution and the ideal phase distribution will affect the meta-lens's optical performance.

[0004] Because the aperture of the superlens is too small, the phase of the superlens cannot be directly detected by traditional optical detection methods. 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 related technologies, the phase detection method for superlenses is based on the phase measurement system of interferometric imaging. This measurement system is based on off-axis digital holography and digital holographic microscopy. However, the static interference fringe processing method used for superlenses has the characteristics of low accuracy, low efficiency and poor repeatability. Moreover, the aforementioned phase interferometric system based on interferometric imaging will be interfered with by object image aberration in the off-axis test optical path, which makes it impossible to achieve high-precision measurement of superlens aberrations. Summary of the Invention

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

[0007] The present invention also provides a superlens detection method applicable to the above-described phase measurement system.

[0008] According to a first aspect of the present invention, a phase measurement system includes: a light source for emitting a probe ray; a beam splitter for transmitting the probe ray and reflecting light rays in the opposite direction to the light source; a beam reducer for reducing the diameter of the beam transmitted through the beam splitter; a beam splitter for splitting the probe ray 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 to the probe ray, and is reflected by the beam splitter to an image acquisition device, and the detection beam is transmitted through the beam splitter; and a detection optical assembly including an objective lens and a detection platform, wherein the detection platform supports an optical element to be detected or a reference element. The objective lens focuses the detection beam onto the optical element under test or the reference element and receives the detection beam reflected back from the optical element under test or the reference element; and the image acquisition device is used to receive the detection beam transmitted by the objective lens to the beam splitter and transmitted through the propagation path of the probe light, the detection beam including a first detection beam corresponding to the optical element under test and a second detection beam corresponding to the reference element, and the image acquisition device is further used to generate a first aberration signal based on the first detection beam and the reference beam, and to generate a second aberration signal based on the second detection beam and the reference beam.

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

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

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

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

[0013] According to some embodiments of the present invention, the detection platform includes a support base for supporting the plane mirror and a motion controller connected to the superlens for driving the superlens to move in order to adjust the relative position of its object-side focal point and the image-side focal point of the objective lens.

[0014] According to some embodiments of the present invention, the support base is used to support the planar mirror or the spherical mirror, and can drive the spherical mirror 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 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 collimating lens 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] This invention also provides a superlens detection method using the above-described phase measurement system, comprising:

[0019] Signal detection steps: The optical element to be tested, including the superlens and the first reflecting mirror, is mounted on the detection platform, with the first reflecting mirror located on the side of the superlens away from the objective lens; the distance between the objective lens and the superlens is adjusted so that the image-side focal point of the objective lens coincides with the object-side focal point of the superlens, and the detection beam focused on the superlens is emitted parallel to the superlens; the detection beam emitted through the superlens is reflected by the first reflecting mirror and transmitted sequentially through the superlens and the objective lens to the beam splitter, and further transmitted along the propagation path of the reference beam to the image acquisition device; the image acquisition device generates a first aberration signal based on the reference beam and the detection beam;

[0020] The detection steps are as follows: The second reflecting mirror is installed on the detection platform; the distance between the objective lens and the second reflecting mirror is adjusted so that the detection beam is focused onto the second reflecting mirror and reflected back to the objective lens, then transmitted to the beam splitter and further transmitted along the propagation path of the reference beam to the image sensor; 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 superlens is obtained based on the difference between the first aberration signal and the second aberration signal. The wavefront aberration of the superlens is then processed to obtain the parameters of the superlens.

[0022] According to some embodiments of the present invention, the step of processing the wavelet aberration of the superlens to obtain the parameters of the superlens includes:

[0023] The pupil function is calculated based on the wavefront aberration of the superlens. The pupil function is the complex amplitude distribution of the spherical wave emitted by the light source after passing through the phase measurement system at the exit pupil position.

[0024] The point spread function and modulation transfer function of the superlens are obtained based on the pupil function.

[0025] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the phase measurement system in related technologies;

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

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

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

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

[0031] Figure 6 This is a detection wavefront image of the objective lens and superlens according to an embodiment of the present invention;

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

[0033] Figure 8 The detection wavefront image of the superlens is obtained by subtracting the first wave aberration and the second wave aberration according to an embodiment of the present invention.

[0034] Figure 9 This is the MTF of a superlens obtained through processing according to an embodiment of the present invention;

[0035] Figure 10 This is the PSF of a superlens obtained through processing according to an embodiment of the present invention.

[0036] Figure label:

[0037] Light source 100;

[0038] 200mm beam splitter;

[0039] 300-type beam reducer;

[0040] Beam splitter 400;

[0041] Detection optical component 500; Optical element to be tested 501; Reference element 502; Objective lens 510; Superlens 520; Plane mirror 530; Spherical mirror 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] 700mm optical path reflector;

[0044] Collimating lens 800. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0046] In the description of this invention, it should be understood that the terms "upper," "lower," "axial," etc., indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0047] In the description of this invention, "multiple" means two or more; "greater than" and "less than" are understood to exclude the stated number; and "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0048] In the description of this invention, it should be noted that terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

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

[0050] Reference Figure 1 As shown, Figure 1 The diagram illustrates a phase measurement system based on interferometric imaging, which utilizes off-axis digital holography and digital holographic microscopy. This system can obtain the phase distribution regulated by a superlens with just one photograph. A schematic diagram of the optical path is shown below. Figure 1As shown, this phase measurement system can be used to measure superlenses as small as tens of micrometers, with a phase measurement accuracy of 0.05 rad. Based on the measured phase distribution of the superlens, the optical field distribution of the superlens can be obtained. Furthermore, key indicators such as the pupil function, point spread function (PSF), modulation transfer function (MTF), Strehl ratio (SR), and depth of focus (DOF) of the superlens can be obtained, and a quantitative evaluation of the measured superlens can be performed.

[0051] like Figure 1 As shown, the laser emitted by laser 10 passes through a plane wavefront obtained by beam expander 20, and is then split into two beams by semi-transparent 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. To make the interference patterns on the CCD overlap as much as possible, the reference beam needs to be expanded by a first lens 40 and a second lens 50. This phase measurement system is suitable for superlenses of linearly polarized light.

[0052] The phase distribution controlled by the superlens can be obtained by taking just one photo (as shown in the optical path diagram). Figure 1 (As shown). This system can be used to measure superlenses as small as tens of micrometers, with a phase measurement accuracy of 0.05 rad. Based on the measured phase distribution of the superlens, the optical field distribution of the superlens can be obtained, and further key indicators such as the pupil function, point spread function (PSF), optical modulation transfer function (MTF), Strell rate (SR), and depth of focus (DOF) can be obtained, and the measured superlens can be quantitatively evaluated. However, the above-mentioned phase measurement system based on interferometric imaging is subject to object image aberration interference in the off-axis test optical path, making it impossible to achieve high-precision measurement of superlens aberrations.

[0053] The phase measurement system of this invention is based on the phase-shifting interferometry principle and is also known as a small-aperture interferometric imaging verification system. Through the Fizeau interferometry principle with a common optical path, wavefront detection of a superlens can be achieved with high precision, high efficiency, and convenience. Furthermore, wavefront detection of superlenses with different fields of view can be achieved to verify the aberration difference based on the superlens in the 0° and near-0° fields of view. Based on the measured wavefront and phase distribution of the superlens, parameters such as the optical modulation transfer function and point spread function of the superlens can be calculated to achieve 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, which is suitable for wavefront detection of a superlens 520. The phase measurement system is described below with specific examples.

[0055] Reference Figure 2 As shown, the phase measurement system of this embodiment 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] The light source 100 is used to emit a detection light beam, 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 beam from the light source 100 to the beam reducer 300. The beam reducer 300 reduces the diameter of the beam beam, and the beam emitted by the beam reducer 300 is a parallel beam. Then the parallel beam enters the beam splitter 400, which is used to split the parallel beam into a reference beam and a detection beam. The reference beam and the detection beam are emitted in different directions. The reference beam is reflected by the beam splitter 400 and transmitted to the beam splitter 200 in the opposite direction of the detection light beam. Then it is reflected by the beam splitter 200 to the image acquisition device 600. That is, the reference beam is folded back and reflected by the beam splitter 200 to the image acquisition device 600. The detection beam is transmitted through the beam splitter 400 and is directed towards the detection optical component 500.

[0057] Specifically, the beam splitter 400 is a reference plane mirror. The parallel beam is incident from one side of the reference plane mirror. The beam reflected by the reference plane mirror is the reference beam. The reference beam returns along the original optical path. That is, the reference beam is shot towards the beam splitter 200 after passing through the beam reducer 300. Since the beam splitter 200 can reflect light from the opposite direction, the reference beam can be reflected towards 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 beam, which is a parallel beam and is directed toward the detection optical assembly 500. In this embodiment, the detection optical assembly 500 includes an objective lens 510 and a detection platform. The detection platform is used to support the optical element 501 to be tested or the reference element 502, and the optical element 501 to be tested 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 beam onto the optical element 501 to be tested or the reference element 502, and can receive the detection beam reflected back from the optical element 501 to be tested or the reference element 502.

[0059] In some embodiments, the optical element 501 to be tested includes a superlens 520 and a first reflecting mirror. Specifically, the first reflecting mirror is located on the side of the superlens 520 away from the objective lens 510. In this embodiment, the first reflecting mirror is a plane reflecting mirror 530, and the superlens 520 is located between the objective lens 510 and the plane reflecting mirror 530. The objective lens 510 is used to focus the detection beam. After passing through the objective lens 510, the parallel beam will converge to the focal point. By adjusting the relative position of the superlens 520 and the objective lens 510, the object-side focal point of the superlens 520 coincides with the image-side focal point of the objective lens 510. In this way, the detection beam exits as a parallel beam after passing through the object-side focal point of the superlens 520.

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

[0061] Understandably, the plane mirror 530 is used to reflect the detection beam after passing through the superlens 520, so that the detection beam is folded back and reflected by the beam splitter 200 to the image acquisition device 600; that is, the detection beam after passing through the plane mirror 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 beam toward the image acquisition device 600, so that the reference beam and the detection beam form interference, and the image acquisition device 600 can acquire the interference pattern.

[0062] 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 beam splitter 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 superlens 520 can be observed. The structure composed of the imaging lens 610 and the CCD camera 620 is also called an interferometer.

[0063] It is understood that a CCD is a semiconductor device that can convert optical images into digital signals. The more pixels a CCD contains, the higher the resolution of the image it provides. This invention is based on the Fizeau interferometry principle; the interferometer is also called a Fizeau interferometer. Adding a beam reducer 300 to the Fizeau interferometer can significantly improve the resolution of detecting the small-aperture superlens 520, thereby improving detection accuracy and efficiency. Specifically, without the beam reducer 300, the beam size is 4 inches, and the number of pixels that can be collected on a 1mm aperture is approximately 70*70. With the beam reducer 300, the beam size is 1 inch, and the number of pixels that can be collected on a 1mm aperture is approximately 280*280. This is equivalent to an increase in the number of pixels per unit area in the interferometer, thus improving resolution and achieving the goal of improving detection accuracy and efficiency.

[0064] Considering the interference of objective lens 510 aberration in the off-axis test optical path of the phase measurement system, high-precision measurement of metalens aberration cannot be achieved. To solve the above technical problem, a reference element 502 is introduced in this embodiment of the invention. The reference element 502 can be optionally installed on the detection platform. The reference element 502 includes a second reflecting mirror, specifically a spherical reflecting mirror 540. The detection optical assembly 500 is configured to replace the plane reflecting mirror 530 with the spherical reflecting mirror 540 and remove the metalens 520. The spherical reflecting mirror 540 is used to reflect the detection beam passing through the objective lens 510, so that the detection beam is refracted and reflected to the image acquisition device 600 through the beam splitter 200. That is, after the metalens 520 is removed, the detection beam can be returned along the original optical path through the spherical reflecting mirror 540.

[0065] Reference Figure 2 and Figure 3 As shown, Figure 2 This illustrates a phase measurement system consisting of an objective lens 510, a superlens 520, and a plane mirror 530. Figure 3 A phase measurement system is shown, consisting of an adjusted objective lens 510 and a spherical mirror 540.

[0066] Specifically, the phase measurement system first detects the overall wavefront of the objective lens 510, the superlens 520, and the plane mirror 530. At this point, the detection beam is the first detection beam corresponding to the superlens 520 and the plane mirror 530. The image acquisition device 600 generates 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 superlens 520 is removed. The wavefronts of the objective lens 510 and the spherical mirror 540 are detected. At this point, the detection beam is the second detection beam corresponding to the spherical mirror 540. The image acquisition device 600 generates a second aberration signal based on the second detection beam and the reference beam. Since the wavefronts of the plane mirror 530 and the spherical mirror 540 differ only slightly, they can be considered approximately equal. The wavefront of the superlens 520 can be obtained by taking the difference between the two detected wavefronts. That is, the wavefront aberration of the superlens 520 can be obtained based on the difference between the first aberration signal and the second aberration signal. This can effectively solve the interference problem of the objective lens 510 aberration during the detection process, realize the high-precision measurement of the wavefront aberration of the superlens 520, and thus realize the high-precision and fast phase and wavefront distribution detection of the superlens 520, enabling the performance evaluation of the imaging quality of the superlens 520.

[0067] A wavefront is the surface formed by particles that have just begun to displace during a wave's propagation in a medium. It represents the spatial position where the wave energy has reached at a given moment, indicating that the wave is in motion. Based on the shape of the wavefront, waves can generally be classified as spherical waves, plane waves, cylindrical waves, etc. In this embodiment, the wavefront is the surface formed by points in phase during the propagation of a light wave. A light wave is a transverse wave with its vibration surface perpendicular to the direction of propagation, and the wavefront is a plane formed by electromagnetic vibration. The wavefront of the entire light wave is formed by points in phase within different wavefronts. The propagation of a light wave is actually a process of continuous wavefront reproduction; a point light source forms a spherical wavefront, and a 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 them. In this way, the wavefront aberration of the superlens 520 is obtained based on the difference between the first aberration signal and the second aberration signal.

[0069] Of course, this is just an example. The first reflecting mirror is not limited to the plane reflecting mirror 530. The first reflecting mirror can reflect the detection beam after passing through the superlens 520. The second reflecting mirror is not limited to the spherical reflecting mirror 540. The second reflecting mirror can reflect the detection beam after passing through the objective lens 510.

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

[0071] Reference Figure 2 and Figure 3 As shown, in some embodiments, the beam splitter 200 is a semi-transparent, semi-reflective mirror. Specifically, it is an optical element in which a semi-reflective film is deposited on optical glass to change the original ratio of transmission and reflection of the incident light beam. By depositing the film layer, transmission can be increased, thereby increasing light intensity; conversely, reflection can be increased, thereby decreasing light intensity. A 50% transmittance and 50% reflectance can be achieved. When the probe light passes through this film, the transmitted light intensity and the reflected light intensity each account for 50%. The specific reflectance can be selected according to actual needs.

[0072] Understandably, the phase measurement system also includes a collimating mirror 800, which is located between the beam splitter 200 and the beam reducer 300. The function of the collimating mirror 800 is to ensure that the probe light rays propagate parallel to each other. The monochromatic light source 100 generates diverging light, which is collimated into a parallel beam by the collimating mirror 800 after passing through the beam splitter 200. Then, the parallel beam is incident on the beam reducer 300 to ensure that the probe light rays propagate to the beam reducer 300 in the form of parallel light.

[0073] In order to adjust the relative position of the optical element 501 under test and the objective lens 510, in some embodiments, the testing platform is movable relative to the objective lens 510. By moving the testing platform, the relative position of the superlens 520 and the objective lens 510, or the relative position of the plane mirror 530 and the objective lens 510, can be adjusted. For example, a driving mechanism can drive the testing platform to move along the x, y, and z axes, so that the testing platform can move 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 superlens 520. By driving the superlens 520 to move through the first motion controller 550, the relative position of the object-side focal point of the superlens 520 and the image-side focal point of the objective lens 510 can be adjusted. The purpose is to make the object-side focal point of the superlens 520 coincide with the image-side focal point of the objective lens 510, so that the detection beam is emitted in parallel after passing through the superlens 520, ensuring that the detection beam is incident on the plane mirror 530 in the form of parallel light and is reflected back along the original optical path.

[0075] The detection platform includes a support base for supporting the plane mirror 530. The support base is equipped with a second motion controller 560, which is connected to the plane mirror 530. The second motion controller 560 drives the plane mirror 530 to move, thereby adjusting the relative position of the plane mirror 530 and the superlens 520 to ensure that the detection beam is perpendicular to the incident surface of the plane mirror 530.

[0076] It is understandable that, since the motion control of the superlens 520 and the plane mirror 530 requires high-precision displacement adjustment to achieve high-precision measurement of the superlens 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 superlens 520 are located is completely perpendicular to the optical path. In this 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, taking the first motion controller 550 as an example, the embodiment uses a six-axis controller to adjust the superlens 520. The directional axes include six dimensions: x-axis, y-axis, z-axis, u-axis (rotation around the x-axis), v-axis (rotation around the y-axis), and w-axis (rotation around the z-axis). In other words, 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 also equipped with a third motion controller 570. When the plane mirror 530 is replaced with a spherical mirror 540, the third motion controller 570 is connected to the spherical mirror 540 and is used to drive the spherical mirror 540 to move, thereby adjusting the relative position of the spherical mirror 540 and the objective lens 510. In this embodiment, the spherical mirror 540 is specifically a concave mirror. By adjusting the spherical mirror 540 through the third motion controller 570, the focal point of the spherical mirror 540 can be made to coincide with the focal point of the objective lens 510, ensuring that the light beam can be reflected back along the original optical path after being reflected by the spherical mirror 540.

[0079] It is understood that the third motion controller 570 can also be a six-axis controller to achieve high-precision adjustment of the spherical reflector 540, as can be seen from the control method of the second motion controller 560 described above. In some embodiments, the second motion controller 560 and the third motion controller 570 can be the same drive mechanism or different drive mechanisms.

[0080] This invention proposes a small-aperture interferometric imaging detection system for wavefront and phase detection of metalenses. This system offers high accuracy, low error, and convenient operation. This invention is also applicable to aberration detection of other small-aperture optical elements, with a minimum detection aperture of hundreds of micrometers.

[0081] refer to Figures 4 to 5 The superlens 520 detection method according to an embodiment of the present invention is described. This 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 [reference needed]. Figure 2 and Figure 3 The embodiments shown will not be described in detail here. The detection method of the superlens 520 will be explained below with specific examples.

[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: Install the optical element 501 to be tested onto the testing platform;

[0084] Step S200: Adjust the distance between objective lens 510 and superlens 520 so that the image-side focal point of objective lens 510 coincides with the object-side focal point of superlens 520, and the first detection beam focused on superlens 520 is emitted parallel through superlens 520.

[0085] In step S300, the first detection beam emitted from the superlens 520 is reflected by the first reflecting mirror and transmitted sequentially through the superlens 520 and the objective lens 510 to the beam splitter 400, and further transmitted to the image acquisition device 600 along the propagation path of the reference beam.

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

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

[0088] It should be noted that, since the phase measurement system requires the selection and installation of the optical element to be tested 501 and the reference element 502 for testing, the superlens testing method includes two parts: a signal detection step and a comparison detection step. Steps S100 to S400 above illustrate the signal detection step in the superlens testing 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: Install the second reflector onto the testing platform;

[0091] In step S600, the distance between the objective lens 510 and the second reflector is adjusted so that the second detection beam is focused onto 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. The image acquisition device 600 generates a second aberration signal based on the reference beam and the second detection beam.

[0092] Step S700: The wavefront aberration of the superlens 520 is obtained based on the difference between the first aberration signal and the second aberration signal. The wavefront aberration of the superlens 520 is processed to obtain the parameters of the superlens 520.

[0093] Among them, steps S500 to S600 above illustrate the control detection step in the superlens 520 detection method.

[0094] It is understandable that, such as Figure 2 As shown, the optical path of the phase measurement system is calibrated before the test. The interferometer is calibrated with the plane mirror 530 at the farthest distance to ensure that the interferometer can receive the reflected light beam. Since the interferometer and the plane mirror 530 at the farthest distance return the reflected light directly to the interferometer through the surface of the optical path mirror 700, interference fringes are formed. By adjusting the plane mirror 530, zero interference fringes are obtained, which means that the interferometer can receive the reflected light beam.

[0095] After calibration, using Figure 2 The phase measurement system shown can detect the overall wavefront aberration of the combination of objective lens 510, superlens 520, and plane mirror 530. This overall wavefront aberration is the first wavefront aberration, i.e., the first aberration signal. Then, the plane mirror 530 is replaced with a spherical mirror 540, and the superlens 520 is removed. The system is then recalibrated. Figure 3 The phase measurement system shown measures the wavefront aberration between the objective lens 510 and the spherical mirror 540. This wavefront aberration is the second wavefront aberration, which is the second aberration signal. Then, the difference between the first wavefront aberration and the second wavefront aberration is calculated to obtain the wavefront aberration of the superlens 520. Finally, the wavefront aberration of the superlens 520 is processed to obtain the parameters of the superlens 520.

[0096] Since the wavefronts of the plane mirror 530 and the spherical mirror 540 are very similar, they can be considered approximately equal. The wavefront of the superlens 520 can be obtained by taking the difference between the two detected wavefronts. This effectively solves the problem that the phase interferometer system cannot achieve high-precision aberration detection of the superlens 520 in the off-axis test optical path due to the aberration of the objective lens 510. It enables high-precision measurement of the wavefront aberration of the superlens 520, thereby achieving high-precision and rapid phase and wavefront distribution detection of the superlens 520, which facilitates the evaluation of the imaging quality of the superlens 520.

[0097] Reference Figure 6 , Figure 7 and Figure 8 As shown, Figure 6 The detection wavefront diagrams of objective lens 510 and superlens 520 are shown. Figure 7 The detection wavefront diagram of objective lens 510 is shown; Figure 8 The detection wavefront map of the superlens 520 is shown by subtracting two wave aberrations.

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

[0099] In step S210, adjust the objective lens 510 and the superlens 520 so that the planes containing the objective lens 510 and the superlens 520 are perpendicular to the optical path, and the numerical aperture of the objective lens 510 is greater than the numerical aperture of the superlens 520.

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

[0101] It is understandable that the movement of the superlens 520 can be adjusted by the first motion controller 550, and the movement of the plane mirror 530 can be adjusted by the second motion controller 560. The objective lens 510 is a microscope objective lens that can move relative to the optical path. In this way, by adjustment, the planes where the objective lens 510 and the superlens 520 are located can be made perpendicular to the optical path, respectively. The numerical aperture of the objective lens 510 is larger than that 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, adjust the superlens 520 or the objective lens 510, or adjust the superlens 520 and the objective lens 510 simultaneously, so that the image-side focal point of the objective lens 510 coincides with the object-side focal point of the superlens 520. In this way, the overall wavefront aberration of the objective lens 510 and the superlens 520 can be measured.

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

[0104] Step S710: Calculate the pupil function based on the wavelet aberration of the superlens 520. The pupil function is the complex amplitude distribution of the spherical wave emitted by the light source 100 after passing through the phase measurement system at the exit pupil position.

[0105] Step S720: Obtain the point spread function and modulation transfer function of the superlens 520 based on the pupil function.

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

[0107]

[0108] In the above formula, (Y,Z) are the coordinates of the exit pupil plane, A(Y,Z) is the amplitude distribution of the light emitted from the point source at the exit pupil plane, W(Y,Z) is the wavefront aberration introduced by the system for monochromatic light waves, λ represents the wavelength, and j is the imaginary unit. Under the condition 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, i.e.:

[0109]

[0110] (y′,z′) represent 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 the point spread form is expressed as:

[0111]

[0112] (μ,ν) is the displacement of the autocorrelation integral of the exit pupil function, known as the reduced 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 the OTF, MTF = |OTF|. 2 This allows us to obtain the pupil function from the system wave aberration, and then the point spread function and modulation transfer function. Based on these, the quality of the superlens 520 can be evaluated. (Refer to...) Figure 9 and Figure 10 As shown, Figure 9 The MTF of the superlens 520 is shown. Figure 10 The PSF of the superlens 520 is shown.

[0113] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A phase measurement system, characterized in that, include: A light source, used to emit detection light; A beam splitter is used to transmit the probe light and to reflect light that is opposite to the light source. A beam reducer is used to reduce the diameter of the beam transmitted through the beam splitter. A beam splitter is used to split the probe light that has passed through the beam reducer into a reference beam and a detection beam. The reference beam is reflected by the beam splitter and transmitted to the beam splitter in the opposite direction of the probe light. The beam splitter then reflects the beam splitter to the image acquisition device. The detection beam is transmitted through the beam splitter. An optical component for testing includes an objective lens and a testing platform. The testing platform supports an optical element to be tested or a reference element. The objective lens focuses the test beam onto the optical element to be tested or the reference element and receives the test beam reflected back from the optical element to be tested or the reference element. The image acquisition device is configured to receive the detection beams transmitted from the objective lens to the beam splitter and through the propagation path of the probe light, the detection beams including a first detection beam corresponding to the optical element to be tested and a second detection beam corresponding to the reference element, the image acquisition device being further configured to generate a first aberration signal based on the first detection beam and the reference beam, and to generate a second aberration signal based on the second detection beam and the reference beam.

2. The phase measurement system as described in claim 1, characterized in that, The optical element to be tested includes a superlens and a plane mirror located on the side of the superlens away from the objective lens; the reference element includes a spherical mirror.

3. The phase measurement system as described in claim 2, characterized in that, The numerical aperture of the objective lens is larger than that of the superlens.

4. The phase measurement system as described in claim 3, characterized in that, The image acquisition device includes a comparator, which is used to obtain the wavefront aberration corresponding to the superlens based on the difference between the first aberration signal and the second aberration signal.

5. The phase measurement system as described in claim 2, characterized in that, The detection platform is movable relative to the objective lens.

6. The phase measurement system as described in claim 5, characterized in that, The detection platform includes a support base for supporting the plane mirror and a motion controller connected to the superlens for driving the superlens to move and adjust the relative position of its object-side focal point and the image-side focal point of the objective lens.

7. The phase measurement system as described in claim 6, characterized in that, The support base is used to support the plane mirror or the spherical mirror, and can drive the spherical mirror to move relative to the objective lens.

8. The phase measurement system as described in claim 1, characterized in that, The phase measurement system also includes: An optical path reflector is disposed between the beam splitter and the objective lens to reflect the detection beam to the objective lens.

9. The phase measurement system as described in claim 1, characterized in that, The light source is a monochromatic point light source, and the phase measurement system further includes a collimating mirror, which is located between the beam splitter and the beam reducer.

10. The phase measurement system as claimed in claim 1, characterized in that, The beam splitter is a semi-transparent, semi-reflective mirror.

11. A method for superlens detection using the phase measurement system as described in any one of claims 1-10, comprising: Signal detection steps: The optical element to be tested, including a superlens and a first reflecting mirror, is mounted on the detection platform, with the first reflecting mirror located on the side of the superlens away from the objective lens; the distance between the objective lens and the superlens is adjusted so that the image-side focal point of the objective lens coincides with the object-side focal point of the superlens, and the detection beam focused on the superlens is emitted parallel to the superlens; the detection beam emitted through the superlens is reflected by the first reflecting mirror and transmitted sequentially through the superlens and the objective lens to the beam splitter, and further transmitted along the propagation path of the reference beam to the image acquisition device; the image acquisition device generates a first aberration signal based on the reference beam and the detection beam; The detection procedure is as follows: The second reflector is installed on the detection platform, and the distance between the objective lens and the second reflector is adjusted 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. The beam is then transmitted to the image acquisition device along the propagation path of the reference beam. 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 superlens is obtained based on the difference between the first aberration signal and the second aberration signal. The wavefront aberration of the superlens is then processed to obtain the parameters of the superlens.

12. The superlens detection method as described in claim 11, characterized in that, The process of processing the wavefront aberration of the superlens to obtain the parameters of the superlens includes: The pupil function is calculated based on the wavefront aberration of the superlens. The pupil function is the complex amplitude distribution of the spherical wave emitted by the light source after passing through the phase measurement system at the exit pupil position. The point spread function and modulation transfer function of the superlens are obtained based on the pupil function.

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