Radial shearing interference plate based on metasurface structure

Abstract

The present invention proposes a radial shearing interferometer plate based on a metasurface structure, which relates to the field of optical detection technology. The radial shearing interferometer plate is composed of two metasurface optical lenses with different focal lengths integrated into one; the metasurface optical lens is based on a phase-controlled metasurface unit structure as a basic structural unit, and the phase-controlled metasurface unit structure is staggered into a concentric ring structure with a width less than or equal to λ / 2 according to two different phase control parameters. The two metasurface optical lenses occupy odd and even rings respectively to form the radial shearing interferometer plate. The present invention has the advantages of polarization independence, high energy utilization, simple structure, small size, high integration, high precision, high spatial resolution, high speed, not susceptible to environmental interference, no need for reference light setting, no leakage of wavefront information, easy adjustment of shear rate, and high dynamic range of detection, which can meet the requirements of real-time and accurate laser wavefront detection.

Description

Technical Field

[0001] The present invention relates to the field of optical detection technology, and more particularly to a radial shearing interference plate based on a metasurface structure. Background Art

[0002] Laser wavefront information is a crucial parameter in laser beam quality. It not only determines the beam's focusing characteristics, namely the size and energy distribution of the focal spot, but also influences the conversion efficiency of the frequency-doubled light. Therefore, beam wavefront detection is essential in applications such as laser star guidance, detection, machining, and adaptive optics. Real-time and accurate measurement of wavefront parameters, such as shape and distortion, is a prerequisite and key to implementing effective measures to control and improve beam quality.

[0003] Among the commonly used wavefront detection sensors, the Shack-Hartmann sensor has a fast detection speed and can be used for closed-loop real-time correction, but its resolution is low, it cannot detect high-frequency components, and its accuracy needs to be improved; the traditional interferometer has the highest resolution and accuracy, but due to its complex structure and sensitivity to the environment, it is only suitable for static characteristic measurement; the knife-edge method is extremely susceptible to environmental interference and still needs to be improved.

[0004] The wavefront testing method based on shearing interferometry is based on the principle of light interference and uses reference light to convert phase data into easily detectable intensity data. It has higher detection accuracy than other detection methods. In particular, radial shearing interferometry wavefront detection technology has more advantages than point diffraction interferometry and lateral shearing interferometry, and has been an important research direction for wavefront detection in recent years. Compared with point diffraction interferometry, it has the advantages of high energy utilization and no need for reference light setup; compared with lateral shearing interferometry, it has the advantage of no leakage of wavefront information. However, the current radial shearing interferometry wavefront detection device is large in size, has many components, low integration, low precision, slow speed, difficulty in adjusting the shear rate, and difficulty in achieving fast and high-precision wavefront measurement in complex working environments; the interference plate based on binary waveplate has problems such as low spatial resolution and poor light field control ability, making it difficult to achieve accurate recovery of the wavefront. The above problems are important factors restricting its practical application. Summary of the Invention

[0005] In response to the shortcomings of existing wavefront detection sensors, the present invention proposes a radial shearing interferometer based on a metasurface structure, which achieves high energy utilization, no need for reference light setting, no leakage of wavefront information, simple structure, easy adjustment of shear rate, and is not easily affected by environmental interference, meeting the purpose of real-time and accurate wavefront detection.

[0006] The technical solutions of the present invention are as follows:

[0007] The radial shearing interference plate based on the metasurface structure proposed by the present invention is composed of two metasurface optical lenses with different focal lengths integrated into one. The metasurface optical lens is based on a transmission-type (optical) phase-modulated metasurface unit structure as the basic structural unit, specifically a transmission-type phase-modulated metasurface unit structure. The phase-modulated metasurface unit structure is staggered into a concentric ring belt structure with a width less than or equal to λ / 2 according to two different phase control parameters. The two metasurface optical lenses occupy odd and even ring belts respectively to form the radial shearing interference plate. Here, staggered arrangement means that the phase control parameters of the same ring belt are the same, and the phase control parameters of adjacent ring belts are different. The transmission-type phase-modulated metasurface unit structure forms a positive lens and a negative lens based on the metasurface through different phase arrangements, and finally forms a shearing interference plate. The transmission-type phase-modulated metasurface unit structure is implemented by a PB phase control method. In fact, it can also be implemented by a transmission phase control method.

[0008] Specifically, the two metasurface optical lenses can be positive and negative lenses with focal lengths of ±f, respectively. The positive and negative lens structures are concentric ring structures with a width less than or equal to λ / 2; the positive and negative lenses occupy odd and even rings respectively, and are staggered to form a radial shear interference plate.

[0009] The positive and negative lenses are formed by arranging the phase control metasurface unit structure in a specific manner according to the phase control parameters, and the even-numbered rings and odd-numbered rings respectively meet the phase conditions or

[0010] Specifically, the two metasurface optical lenses constituting the radial shearing interferometer plate can also be positive lenses with focal lengths of f1 and f2. The two lens structures are concentric ring band structures with a width of less than or equal to λ / 2; the two lenses with different focal lengths occupy odd and even ring bands respectively, and are staggered to form a radial shearing interferometer plate. Among them, the two positive lenses with focal lengths of f1 and f2 are arranged in a specific manner by a transmission-type phase-modulated metasurface unit structure according to the phase control parameters, and the even ring bands and the odd ring bands respectively meet the phase conditions or

[0011] Specifically, the two metasurface optical lenses constituting the radial shearing interferometer plate can also be negative lenses with focal lengths of -f1 and -f2. The two lens structures with different focal lengths are concentric ring band structures with a width less than or equal to λ / 2; the two lenses with different focal lengths occupy odd and even ring bands respectively, and are staggered to form a radial shearing interferometer plate. Among them, the negative lenses of -f1 and -f2 are composed of a transmission-type phase-modulated metasurface unit structure arranged in a specific manner according to the phase control parameters, and the even ring bands and odd ring bands respectively meet the phase conditions, or

[0012] The transmissive phase-modulating metasurface structure used in the various shear plates described above exhibits continuous phase control capabilities. It comprises a substrate and an all-dielectric cubic metasurface structure atop it. By rotating the all-dielectric cubic metasurface, the wavefront of the outgoing light can be manipulated on a subwavelength scale. The light control efficiency can be adjusted by varying the length, width, height, and period of the all-dielectric cubic metasurface structure.

[0013] The period of the transmission-type phase-modulation metasurface unit structure is less than or equal to half a wavelength, there is only zero-order diffraction, and the odd and even rings produce double-beam interference, with high energy utilization.

[0014] The ring-shaped structure formed by the two metasurface optical lenses above uses the polarization characteristics of the transmission-type phase-modulated metasurface unit structure. Any ring-shaped structure has opposite deflection directions for left-handed and right-handed circularly polarized light. Odd-numbered rings converge for left-handed circularly polarized light and diverge for right-handed circularly polarized light; the opposite is true for even-numbered rings. Because the spacing between odd and even rings is less than or equal to half a wavelength, the interference fringes produced on the detection surface after modulation of left-handed and right-handed circularly polarized light by the radial shearing interferometer are only offset by half a wavelength in the radial direction, far smaller than the detector pixels, and can be considered to be completely overlapping. Since any polarized light is a linear superposition of left-handed and right-handed circularly polarized light, the radial shearing interferometer is polarization-independent and has high light energy utilization.

[0015] The present invention has the following advantages:

[0016] 1. The present invention utilizes a metasurface structure to continuously control phase, amplitude, etc. At the same time, the unit size is small (can be less than 0.5 times the wavelength), and it has the characteristics of high spatial resolution, high optical efficiency, ultra-thin, ultra-light, easy integration, and broadband control. It has the advantages of polarization independence, high energy utilization, simple structure, small size, high integration, high precision, high spatial resolution, fast speed, and not susceptible to environmental interference, which can meet the requirements of real-time and accurate laser wavefront detection.

[0017] 2. The present invention integrates two lenses of different focal lengths in a half-wavelength ring structure to form a radial shearing interferometer plate, which has the advantages of no need for reference light setting, no leakage of wavefront information, simple structure, small size, high integration, easy adjustment of shear rate, and high dynamic range of detection.

[0018] 3. The present invention compresses the traditional shearing interference wavefront detection device into an integrated optical element, overcoming the defects of the traditional shearing interference wavefront detection device, such as large size, many components, low integration, low precision, slow speed, and difficulty in adjusting the shear rate. It has the advantages of small size, few components, easy integration, high precision, simple overall structure, fast speed, and easy adjustment of the shear rate.

[0019] The present invention can be widely used in the fields of laser guide star, laser detection, laser processing, adaptive optics, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the radial shearing interferometry principle.

[0021] Figure 2 Schematic diagram of the working principle of the radial shearing interferometer based on the transmission-type BP phase-controlled metasurface structure.

[0022] Figure 3a PB phase optical metasurface unit structure diagram.

[0023] Figure 3b Phase and amplitude transmittance control curve of PB phase optical metasurface unit structure.

[0024] Figure 4 Schematic diagram of the metasurface structure unit array after partial enlargement of the radial shearing interferometer plate based on the transmission-type BP phase control metasurface structure.

[0025] Figure 5 It is the interference fringe pattern under different shear ratios when using ideal plane wave illumination. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to the accompanying drawings and examples:

[0027] like Figure 1 As shown in the figure, the principle of wavefront detection by the radial shearing interferometer device is as follows: the light to be measured 1 is split by the radial shearing interferometer device 2 to produce a radially reduced wavefront 3 (with a diameter of d1) and a radially expanded wavefront 4 (with a diameter of d2). The two wavefronts are the same in shape but with a different aperture from the wavefront to be measured. The reduced wavefront and the expanded wavefront interfere with each other in the overlapping area, and the phase information in the wavefront is converted into intensity information for subsequent detection. 5 in the figure is the shear amount, which is defined as the shear ratio d1 / d2. Proper adjustment of the shear ratio can change the density of the interference fringes. The common problems of the currently reported radial shearing interferometer wavefront detection devices are large size, many components, low integration, low precision, slow speed, and difficulty in adjusting the shear rate. Therefore, it is difficult to achieve fast and high-precision wavefront measurement in a complex working environment.

[0028] The radial shearing interferometer plate based on a metasurface structure proposed in the present invention is constructed by integrating two metasurface optical lenses of different focal lengths. The two metasurface optical lenses are based on a phase-modulated metasurface unit structure. For example, in this embodiment, a transmission-type BP phase-modulated metasurface unit structure is specifically adopted. The transmission-type BP phase-modulated metasurface unit structure is arranged into a concentric ring structure with a width less than or equal to λ / 2 according to different phase control parameters. The two metasurface optical lenses are staggered, occupying odd and even rings, respectively, to form the radial shearing interferometer plate.

[0029] Specifically, the radial shearing interference plate can be of at least three types, as follows:

[0030] The two metasurface optical lenses of the first radial shearing interferometer are positive and negative lenses with focal lengths of +f and -f, respectively. The even-numbered and odd-numbered ring zones satisfy the phase conditions respectively. or, Where r is the polar diameter of the spatial polar coordinate on the metasurface optical lens, and λ is the wavelength of light.

[0031] The two metasurface optical lenses of the second radial shearing interferometer are positive lenses with focal lengths of f1 and f2, and the even-numbered and odd-numbered rings respectively meet the phase conditions or

[0032]

[0033] The two metasurface optical lenses of the third radial shearing interferometer are negative lenses with focal lengths of -f1 and -f2, respectively. The even-numbered and odd-numbered rings satisfy the phase conditions respectively. or

[0034] The working principle of the radial shear interference plate proposed in this invention can be found in Figure 2 , this figure corresponds to the first of the three types of radial shearing interference plates mentioned above, and the principle is as follows:

[0035] After the light to be measured 1 is incident on the radial shearing interferometer plate 2, since this radial shearing interferometer plate integrates a positive lens and a negative lens, it generates a radially reduced wavefront 3 and a radially expanded wavefront 4. The two wavefronts differ from the wavefront to be measured only in aperture, but have the same surface shape. The reduced wavefront and the expanded wavefront interfere with each other in the overlapping area, converting the phase information in the wavefront into intensity information for subsequent detection. More specifically, the light to be measured 1 is focused by the metasurface integrated dual lenses on the radial shearing interferometer plate 2 into two beams converging at z = f1 (real focus) and z = f2 (virtual focus); at z = z dAt the intersection of the two beams, they partially overlap and interfere with each other, forming an interference pattern. The intensity distribution of the interference pattern is obtained by the detector array, and the wavefront distribution of the incident beam can be obtained through the reconstruction algorithm.

[0036] Of course, the radial shearing interference plate can be composed of two positive lenses or two negative lenses, such as the second or third type above. As long as the focal lengths of the two lenses are different, radial shearing interference will occur. However, a reasonable setting of the shear rate can obtain interference fringes with better density and contrast. The process of adjusting the shear rate is very simple in the optical path of the radial shearing interference plate of the present invention. It only requires moving the distance between the detector and the interference plate to change the distance Z between the imaging surface 6. d This radial shearing interferometer plate, formed by integrating two lenses with different focal lengths, has the advantages of no need for reference light setting, no leakage of wavefront information, adjustable shear rate, simple structure, small size and high integration.

[0037] Figure 3a This is the unit structure diagram of the PB phase optical metasurface. Figure 3b This is the phase and amplitude transmittance control curve of the PB phase optical metasurface unit structure. Figure 2 The radial shearing interferometer plate adopts a continuous phase control metasurface design. Each metasurface optical lens is based on a transmission-type phase control metasurface unit structure. Here, the structure and principle of each control unit are illustrated by taking the PB phase optical metasurface unit as an example.

[0038] Existing research shows that the use of metasurface structures can achieve continuous wavefront control of incident light waves at a scale of less than half a wavelength in a plane, which provides a new way to flexibly realize various types of planar optical devices. The metasurface structure is a periodic subwavelength structure formed by micro-nano processing on a planar substrate. Its functional structural period can be less than half a wavelength and its thickness is about the wavelength scale. It can realize optical lenses with high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, and easy integration. The radial shearing interferometer plate involved in the present invention adopts a PB phase optical metasurface unit structure with continuous phase control function. Its structural units are as follows: Figure 3a As shown, for the wavelength working range [λ min ,λ max ] incident light, a full dielectric (e.g., TiO2, α-Si, etc.) cubic metasurface structure 8 is fabricated on a glass substrate 7. Within the plane of the glass substrate 7, the incident light wavefront (within the range of 0-2π) is continuously controlled by rotating the TiO2 cubic metasurface structure. The control efficiency mainly depends on the length L, width W, height t, and period T of the structure. Taking the TiO2 cubic structure as an example, when L = 120nm, W = 60nm, t = 320nm, and T = 260nm, as shown in FIG. Figure 3bAs shown in Figure 2, its amplitude transmittance can reach over 90%. Further improving the aspect ratio can achieve an amplitude transmittance close to 100%. By rotating the cubic unit structure, the wavefront of the output light can be controlled at a sub-wavelength scale. When the rotation angle is When , the corresponding phase shift is More importantly, the PB phase optical metasurface unit structure has excellent broadband characteristics, with a bandwidth of more than 400nm. It can be used to realize broadband metasurface radial shearing interferometers to meet the needs of broadband wavefront measurement.

[0039] Figure 4 The radial shearing interference metasurface proposed in this invention is a metasurface optical lens that integrates two different focal lengths. Its basic unit structure is as follows: Figure 3a The positive and negative lenses are arranged in a specific way by a transmissive phase-modulated metasurface structure according to the phase-modulation parameters, and the even-numbered and odd-numbered rings respectively meet the phase space distribution conditions:

[0040]

[0041]

[0042] or

[0043]

[0044]

[0045] Where r is the polar diameter of the spatial polar coordinates on the metasurface optical lens, f and -f are the focal lengths of the two lenses, λ is the wavelength of light, T is the period of the metasurface structure unit, and r i =i×T (i is an integer). The entire hypersurface is divided into several ring regions r with a width of T at the center of the circle. i ≤r <r i +T, where T≤λ / 2. In the two adjacent annular zones, the corresponding phases are described by the above two formulas respectively. Thus, two metasurface lenses with focal lengths of f and -f are integrated in the same plane structure. By optimizing f and -f, the required optimal shear rate can be obtained, thereby meeting the requirements of beam quality detection with a large dynamic range. Since the annular zone width is less than or equal to λ / 2, the sum of the annular zone widths of two lenses with different focal lengths is less than the wavelength of light λ. Therefore, its resolution of spatial wavefront control is better than one wavelength of light λ, thereby achieving high spatial resolution wavefront control. At the same time, since the annular zone width is less than the wavelength, there is only zero-order diffraction, and there is no higher-order diffraction beam, which achieves high energy utilization and avoids interference caused by higher-order diffraction.

[0046] The odd-numbered rings in the radial shearing interferometer plate converge the incident left-handed circularly polarized light and diverge for the right-handed circularly polarized light. Similarly, the even-numbered rings have the opposite effect on the left-handed and right-handed circularly polarized light. Thus, whether it is LCP light (left-handed circularly polarized light) or RCP light (right-handed circularly polarized light), the incident light will always be divided into a converging wavefront and a diverging wavefront, and then form the same interference pattern. Since any polarized light can be decomposed into the linear superposition of LCP light and RCP light, the radial shearing interferometer plate proposed by the present invention has polarization independence and can be applied to wavefront detection of any polarized light.

[0047] Figure 5 Figures a, b, c, and d show the simulated interference patterns for ideal plane wave illumination at shear rates of 0.9, 0.8, 0.7, and 0.6, respectively. The shear rate can be adjusted simply by adjusting the distance between the radial shearing interferometer and the camera.

[0048] As can be seen from the above embodiments, the present invention utilizes a metasurface structure to continuously control phase, amplitude, etc., and at the same time has the characteristics of high spatial resolution, high optical efficiency, ultra-thinness, ultra-lightness, easy integration, and broadband control, and proposes a radial shearing interferometer based on a metasurface structure. By integrating two metasurface optical lenses with different focal lengths, its basic unit structure is a transmission-type phase-control metasurface unit structure, which is arranged with annular bands less than or equal to half a wavelength according to specific phase requirements, achieving polarization independence, high energy utilization, no need for reference light setting, no leakage of wavefront information, simple structure, easy adjustment of shear rate, and not susceptible to environmental interference. The advantages of this technology's high degree of integration can overcome the weaknesses of existing radial shearing interferometer wavefront detection devices, such as large size, many components, low integration, low precision, slow speed, and difficulty in adjusting shear rate, and can meet the requirements of real-time and accurate laser wavefront detection.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention.

Claims

1. A radial shearing interference plate based on a metasurface structure, characterized by: The radial shearing interferometer plate is composed of two metasurface optical lenses with different focal lengths integrated into one; the metasurface optical lens is based on a phase-modulated metasurface unit structure, and the phase-modulated metasurface unit structure is staggered into a concentric ring structure with a width less than or equal to λ / 2 according to two different phase control parameters. The two metasurface optical lenses occupy odd and even rings respectively to form the radial shearing interferometer plate; There are three types of radial shearing interference plates, as follows: The two metasurface optical lenses of the first radial shearing interferometer are positive and negative lenses with focal lengths of +f and -f, respectively. The even-numbered and odd-numbered ring zones satisfy the phase conditions respectively. or, Where r is the polar diameter of the spatial polar coordinate on the metasurface optical lens, and λ is the wavelength of light; The two metasurface optical lenses of the second radial shearing interferometer are positive lenses with focal lengths of f1 and f2, and the even-numbered and odd-numbered rings respectively meet the phase conditions or The two metasurface optical lenses of the third radial shearing interferometer are negative lenses with focal lengths of -f1 and -f2, respectively. The even-numbered rings and odd-numbered rings satisfy the phase conditions respectively. or The polar radius r of the even-numbered and odd-numbered rings respectively satisfies: i ≤r<r i +T,r i+1 ≤r<r i+1 +T, where r is the polar diameter of the spatial polar coordinate on the metasurface optical lens, f and -f are the focal lengths of the two lenses, λ is the wavelength of light, T is the period of the metasurface structure unit, and r i =i×T, where i is an integer.

2. The radial shearing interference plate based on the metasurface structure according to claim 1, characterized in that: The phase-control metasurface unit structure has a continuous phase control function, including a substrate and an all-dielectric cubic metasurface structure thereon. By rotating the all-dielectric cubic metasurface structure, the wavefront of the outgoing light can be controlled on a subwavelength scale.

3. The radial shearing interference plate based on the metasurface structure according to claim 2, characterized in that: The period of the phase-controlled metasurface unit structure is less than or equal to half a wavelength, there is only zero-order diffraction, and the odd and even ring bands produce double-beam interference, thereby improving energy utilization.

4. The radial shearing interference plate based on a metasurface structure according to claim 2, characterized in that: The light regulation efficiency is changed by changing the length, width, height and period of the all-dielectric cubic metasurface structure.

5. The radial shearing interference plate based on a metasurface structure according to claim 1, 2, 3 or 4, characterized in that: Among the even-numbered and odd-numbered ring zones, any adjacent ring zones can focus and diverge left-handed circularly polarized light and right-handed polarized light respectively, so that the radial shearing interferometer plate has polarization independence.

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