Achromatic weak measurement wavefront sensor

Abstract

The application discloses an achromatic weak measurement wavefront sensor, which divides light into positive diagonal and negative diagonal components, and ensures that the relative positions of the light of the two components after displacement are horizontal and vertical. After the light of the positive diagonal and negative diagonal components passes through a Savart plate, the light of the two components experiences displacement and non-displacement once, so that there is no optical path difference between the light of the two components in theory. In cooperation with an achromatic phase retarder, the weak measurement wavefront sensor provided by the application can be applied to monochromatic light of a certain range of wavelengths, and during use, only l corresponding to the wavelength can be inquired according to a dispersion relation. The applicable wavelength range is mainly determined by the applicable range of the achromatic wave plate.

Description

Technical Field

[0001] This invention relates to the field of optical information measurement technology, and in particular to an achromatic weak measurement wavefront sensor. Background Technology

[0002] A wavefront sensor is a modern optical measurement instrument that can measure phase information that is not easily measured by light. It is mainly used for wavefront distortion correction in adaptive optics.

[0003] The most common type of wavefront sensing, the Hartmann wavefront sensor, uses a lens array and is suitable for light of a certain wavelength range. The size of a single lens limits the spatial resolution of the wavefront sensor.

[0004] The wavefront sensor based on quantum weak measurement invented by the University of Science and Technology of China (see application number CN201910019845.8, publication number CN109520625A) uses a quarter-wave plate and requires tilting a thin birefringent crystal to compensate for the optical path difference between the horizontal and vertical polarization components, up to an integer multiple of the wavelength. However, after correcting the device for a certain wavelength, the phase difference between the horizontal and vertical polarization components is no longer an integer multiple of 2π for other wavelengths. Therefore, when changing to other wavelengths, the device needs to be recalibrated; otherwise, it cannot be used. Summary of the Invention

[0005] The purpose of this invention is to provide an achromatic weak measurement wavefront sensor, which is a weak measurement wavefront sensor applicable to light within a certain wavelength range, and has a higher spatial resolution than the traditional Hartmann wavefront sensor.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A wavefront sensor for achromatic weak measurement includes: a polarizer, a Savart plate, an achromatic phase delayer, and a polarization separation and light intensity acquisition device; wherein: the polarizer prepares the polarization of the incident monochromatic light to be measured into a horizontal polarization state and directs it into the Savart plate; depending on the measurement direction, the Savart plate is rotated around the light propagation direction; the light beam emitted from the Savart plate passes through the achromatic phase delayer and enters the polarization separation and light intensity acquisition device; the achromatic phase delayer and the polarization separation and light intensity acquisition device separate left-handed and right-handed circularly polarized light and detect the light intensity.

[0008] As can be seen from the technical solution provided by the present invention, light is divided into diagonal and anti-diagonal components according to polarization, ensuring that the relative positions l of the two components after displacement are horizontal and vertical. After passing through the Savart plate, both diagonal and anti-diagonal components undergo one displacement and one non-displacement perpendicular to the propagation direction, theoretically resulting in no optical path difference between them. Combined with an achromatic phase retarder, the weak measurement wavefront sensor provided by the present invention can be applied to monochromatic light within a certain wavelength range. In use, it is only necessary to look up the corresponding l for that wavelength based on the dispersion relation. The applicable wavelength range is mainly determined by the applicable range of the achromatic phase retarder. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of an achromatic difference weak measurement wavefront sensor provided in an embodiment of the present invention. Detailed Implementation

[0011] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0012] First, the following explanations are provided for the terms that may be used in this article:

[0013] The terms “including,” “comprising,” “containing,” “having,” or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, “including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.)” should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0014] The terms “thickness,” “upper,” “lower,” “left,” “right,” “horizontal,” “clockwise,” and “counterclockwise” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience and simplification of description and do not imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this document.

[0015] The following is a detailed description of an achromatic weak measurement wavefront sensor provided by the present invention. Contents not described in detail in the embodiments of the present invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of the present invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Instruments used in the embodiments of the present invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] like Figure 1 As shown, an achromatic weak measurement wavefront sensor mainly includes: a polarizer, a Savart plate, an achromatic phase retarder, and a polarization separation and intensity acquisition device. The polarizer prepares the incident monochromatic light to be measured into a horizontal polarization state and directs it into the Savart plate. Depending on the measurement direction, the Savart plate rotates around the light propagation direction. The light beam emitted from the Savart plate passes through the achromatic phase retarder and enters the polarization camera. The achromatic phase retarder and the polarization separation and intensity acquisition device separate left-handed and right-handed circularly polarized light and detect the light intensity. The polarization separation and intensity acquisition device can be implemented using a polarization camera or a thick birefringent crystal and camera, which will be described in detail later. Figure 1 As shown, an example of using a thick birefringent crystal and a camera as a polarization separation and light intensity acquisition device is provided.

[0017] To facilitate understanding, the structure and working principle of each part of the achromatic weak measurement wavefront sensor will be introduced below.

[0018] I. Structure of a wavefront sensor for achromatic weak measurement.

[0019] 1. Polarizer.

[0020] In this embodiment of the invention, the polarizer can be a PBS (polarizing beam splitter) or other types of polarizers. The polarizer is mainly used to prepare the polarization of the incident monochromatic light to be measured into a horizontal polarization state. This horizontal polarization state is taken as the initial state, which is described in quantum mechanical terms as |H>|ψ(x,y)>. H refers to horizontal polarization, |ψ(x,y)> is the spatial mode of the photon, and (x,y) are the coordinates.

[0021] Those skilled in the art will understand that in linearly polarized light, both horizontally and vertically polarized light can be considered as a superposition of diagonally and anti-diagonally polarized light. Linearly polarized light at all angles can be considered as a superposition of left-handed and right-handed circularly polarized light.

[0022] 2. Savart film.

[0023] In this embodiment of the invention, the Savart sheet is composed of two thin birefringent crystals (such as calcite) of the same thickness (processed on the same disc) with the same angle between their optical axes and the incident plane (usually 45°). The optical axes of the two thin birefringent crystals are in different directions. The thin birefringent crystal near the polarizer is called the first thin birefringent crystal, and the thin birefringent crystal near the phase retarder is called the second thin birefringent crystal.

[0024] In this embodiment of the invention, a thin birefringent crystal refers to a crystal whose displacement of light is much smaller than the size of the light spot.

[0025] Depending on the measurement direction, the preferred method for rotating the Savart plate around the light propagation direction is as follows:

[0026] When measuring the partial derivative k of the wavefront phase in the x-direction x At that time, the first thin birefringent crystal moves the diagonally (45°) polarized light in the horizontal polarization state to the upper right, and the second thin birefringent crystal moves the anti-diagonally polarized light (135°) in the horizontal polarization state to the upper left.

[0027] When measuring the partial derivative k of the wavefront phase in the y-direction y At this time, the optical axes of the two thin birefringent crystals rotate 90° counterclockwise. The first thin birefringent crystal moves the anti-angle polarized light in the horizontal polarization state to the upper left, and the second thin birefringent crystal moves the diagonally polarized light in the horizontal polarization state to the lower left.

[0028] In this embodiment of the invention, upper right, upper left, and lower left all refer to the direction relative to the light beam when looking towards the light.

[0029] By using Savart chips, the weak measurement wavefront sensor provided by this invention can be applied to monochromatic light within a certain wavelength range.

[0030] Of course, other adjustment schemes can be used depending on the situation, for example, measuring k. y At that time, only the second thin birefringent crystal was rotated 180°.

[0031] 3. Achromatic phase delay unit.

[0032] In this embodiment of the invention, the achromatic phase delayer can be an achromatic quarter-wave plate or a Fresnel rhombus prism, etc.

[0033] By using an achromatic phase delayer, left-handed and right-handed circularly polarized light within a certain wavelength range can be converted into horizontally and vertically polarized light, respectively. For example... Figure 1 As shown, an example of using an achromatic quarter-wave plate as a phase delayer is provided. The wavelength range applicable to this invention can be determined by the applicable range of the achromatic quarter-wave plate.

[0034] 4. Polarization separation and light intensity acquisition equipment.

[0035] In this embodiment of the invention, the polarization separation and light intensity acquisition device can be implemented by a polarization camera, or by a thick birefringent crystal and a camera (the camera is used to detect light intensity, and the camera can be a CCD or a CMOS camera).

[0036] In this embodiment of the invention, horizontal and vertical polarized light are separated by a polarization separation and light intensity acquisition device, and the light intensity is detected.

[0037] During implementation, the achromatic phase retarder and the thick birefringent crystal (whose displacement of light should be much larger than the spot size) work together to separate left-handed and right-handed circularly polarized light, and the light intensity is detected by a camera; or the achromatic phase retarder and the polarizer in the polarization camera work together to separate left-handed and right-handed circularly polarized light, and the light intensity is detected.

[0038] The steps for separating left-handed and right-handed circularly polarized light and detecting its intensity can be described as follows:

[0039] 1) Convert left-handed and right-handed circularly polarized light into linearly polarized light: Use an achromatic quarter-wave plate or a Fresnel rhombus prism (i.e., an achromatic phase delayer) to convert left-handed circularly polarized light into horizontally polarized light and right-handed circularly polarized light into vertically polarized light; of course, it is also possible to convert left-handed circularly polarized light into vertically polarized light and right-handed circularly polarized light into horizontally polarized light.

[0040] 2) Separate horizontally and vertically polarized light and measure their intensity distribution using a camera: A polarization camera can be used to polarize the light at different pixel positions and detect the light intensity; alternatively, a thick birefringent crystal can be used to shift one type of polarized light (horizontally or vertically polarized light), with the displacement distance being much larger than the spot size. Then, the camera is used to detect the light intensity of the two spots (the spots of horizontally and vertically polarized light). The detected light intensities of the horizontally and vertically polarized light are the corresponding left-handed and right-handed circularly polarized light intensities, corresponding to the four light intensities I in the calculation formula below.

[0041] Combining the light intensity detected by the camera, the partial derivative k of the wavefront phase in the x-direction x The partial derivative k in the y-direction y It can be calculated using the following formula:

[0042]

[0043] Among them, I x,L with I x,R Let k represent the partial derivatives of the wavefront phase in the x-direction. x At that time, the intensity of the detected left-handed and right-handed circularly polarized light; I y,L with I y,R Let k represent the partial derivatives of the wavefront phase in the y-direction. y At that time, the intensity of the detected left-handed and right-handed circularly polarized light is denoted by l; l represents the distance the single thin birefringent crystal moves, which is equivalent to its wavelength corresponding to the wavelength of the monochromatic light being measured, and can be determined by referring to a table. In the above formula, the arcsine operation used is a correction method to make the measured value closer to the true value.

[0044] II. Measurement Principle.

[0045] In the following text, H, V, D, A, L, and R represent horizontal, vertical, diagonal, anti-diagonal, left-handed, and right-handed polarization, respectively; i is the imaginary unit; Re represents the real part; Im represents the imaginary part; and the asterisk * represents the complex conjugate. The magnitude of a quantity is equal to the square root of the product of itself and its conjugate. As mentioned earlier, the initial state is described in quantum mechanical terms as |H>|ψ(x,y)>. The partial derivative k of the wavefront phase in the x-direction is measured. x For example, after light passes through the Savart plate, its polarization state changes to:

[0046]

[0047] By separating left- and right-hand circularly polarized light, the wave functions of the left-hand and right-hand components are obtained:

[0048]

[0049] Its modulus squared is proportional to the light intensity:

[0050]

[0051] The partial derivative of the wavefront phase in the x-direction, k x It can be approximately obtained from the light intensity measured by the camera:

[0052]

[0053] Using a similar principle, we can obtain k. y :

[0054]

[0055] The above solution for partial derivative k x With k y The formula has some error; using the arcsine operation can reduce the error. This yields k.x With k y Then, the phase diagram of the wavefront of the monochromatic light under test can be reconstructed using the wavefront restoration algorithm. This part can be implemented with reference to conventional techniques, and will not be elaborated upon in this invention.

[0056] In the above-described embodiment of the present invention, light is divided into diagonally opposite and anti-diagonally opposite components based on polarization, ensuring that the relative positions of the two components are horizontal and vertical after displacement. After passing through the Savart plate, both components undergo one displacement and one non-displacement perpendicular to the propagation direction, theoretically eliminating any optical path difference between them. Combined with an achromatic phase retarder, this invention is applicable to monochromatic light within a certain wavelength range. When using it, it is only necessary to look up the corresponding wavelength (l) based on the dispersion relation. The applicable wavelength range is mainly determined by the applicable range of the achromatic phase retarder.

[0057] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An achromatic weak measurement wavefront sensor, characterized in that, The application relates to a device for measuring the spatial derivative of the refractive index of a material, which comprises: a polarizer, a Savart plate, an achromatic phase retarder, and a polarization separation and light intensity collection device; wherein: the polarizer prepares the polarization of the incident monochromatic light to be measured into a horizontal polarization state and the light is incident into the Savart plate; the Savart plate is rotated around the light propagation direction according to different measurement directions; the light emitted by the Savart plate is incident into the polarization separation and light intensity collection device through the achromatic phase retarder; and the left-handed and right-handed circularly polarized light is separated by the achromatic phase retarder and the polarization separation and light intensity collection device and the light intensity is detected. The Savart plate is composed of two thin birefringent crystals with the same thickness and the same angle between the optical axis and the incident surface, and the directions of the optical axes of the two thin birefringent crystals are different; the thin birefringent crystal close to the polarizer is called the first thin birefringent crystal, and the thin birefringent crystal close to the phase retarder is called the second thin birefringent crystal; wherein the thin birefringent crystal refers to the displacement of the light being far less than the size of the light spot. When measuring the partial derivative k of the wavefront phase in the x direction x The first thin birefringent crystal moves the right diagonal polarization light in the horizontal polarization state to the upper right, and the second thin birefringent crystal moves the left diagonal polarization light in the horizontal polarization state to the upper left; When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction y When measuring the partial derivative k of the wavefront phase in the y direction 2. An achromatic weak measurement wavefront sensor according to claim 1, wherein, The horizontal polarization state is used as the initial state, which is described as |H>|psi(x, y)> in the language of quantum mechanics, wherein H represents the horizontal polarization, |psi(x, y)> represents the spatial mode of the photon, and (x, y) is the coordinate.

3. An achromatic weak measurement wavefront sensor according to claim 1, wherein, The partial derivative in each measurement direction is calculated according to the detected light intensity, and the calculation process is represented as: Among them, I x,L with I x,R Let k represent the partial derivatives of the wavefront phase in the x-direction. x At that time, the intensity of the detected left-handed and right-handed circularly polarized light; I y,L with I y,R Let k represent the partial derivatives of the wavefront phase in the y-direction. y At that time, the intensity of the detected left-handed and right-handed circularly polarized light; l represents the displacement distance of a single thin birefringent crystal.

4. An achromatic weak measurement wavefront sensor according to claim 1, wherein, The achromatic phase retarder is realized by using an achromatic 1 / 4 wave plate or a Fresnel rhombic prism.

5. An achromatic weak measurement wavefront sensor according to claim 1, wherein, The polarization separation and light intensity collection device is realized by using a polarization camera or a thick birefringent crystal and a camera; wherein the thick birefringent crystal refers to the displacement of the light being far greater than the size of the light spot.

6. An achromatic weak measurement wavefront sensor according to claim 5, wherein, The left-handed and right-handed circularly polarized light is separated by the achromatic phase retarder and the polarization separation and light intensity collection device, and the light intensity is detected. The left-handed and right-handed circularly polarized light is separated by the achromatic phase retarder and the polarization separation and light intensity collection device, and the light intensity is detected.

7. An achromatic weak measurement wavefront sensor according to claim 6, wherein, The steps of separating the left-handed and right-handed circularly polarized light and detecting the light intensity include: Converting the left-handed and right-handed circularly polarized light into linearly polarized light: the left-handed circularly polarized light is changed into horizontal polarized light and the right-handed circularly polarized light is changed into vertical polarized light by the achromatic phase retarder; or the left-handed circularly polarized light is changed into vertical polarized light and the right-handed circularly polarized light is changed into horizontal polarized light; Separating the horizontal polarized light and the vertical polarized light and detecting the light intensity: the polarization camera is used to polarize and detect the light intensity at different pixel positions; or the thick birefringent crystal is used to displace the horizontal polarized light or the vertical polarized light, and then the light intensity of the two light spots is detected by the camera.

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