阅读说明：本技术 一种基于二维硒化亚锗的偏振相位调制器件及其设计方法 (Polarization phase modulation device based on two-dimensional germanium selenide and design method thereof ) 是由 魏钟鸣 谷洪刚 郭正峰 刘世元 于 2020-12-30 设计创作，主要内容包括：本发明属于新型偏振光学器件领域,更具体地,涉及一种基于二维硒化亚锗的偏振相位调制器件及其设计方法。其设计方法包括以下步骤：本发明首先制作若干不同厚度的二维GeSe并将其附着于衬底上,获取这些二维GeSe的平面内光学常数,结合相位延迟量计算公式,计算得到不同厚度对应的相位延迟量,根据目标偏振相位调制器件对相位延迟量要求,确定该目标偏振相位调制器件中二维GeSe的厚度,最后通过实验测量和计算拟合的比较来检验制作得到的偏振相位调制器件是否符合要求。本方法只需简单设计便能实现偏振相位调制器件的厚度纳米化,非常具有应用前景。(The invention belongs to the field of novel polarization optical devices, and particularly relates to a polarization phase modulation device based on two-dimensional germanium selenide and a design method thereof. The design method comprises the following steps: the method comprises the steps of firstly manufacturing a plurality of two-dimensional GeSe with different thicknesses, attaching the two-dimensional GeSe to a substrate, obtaining in-plane optical constants of the two-dimensional GeSe, calculating phase retardation corresponding to the different thicknesses by combining a phase retardation calculation formula, determining the thickness of the two-dimensional GeSe in a target polarization phase modulation device according to the requirement of the target polarization phase modulation device on the phase retardation, and finally checking whether the manufactured polarization phase modulation device meets the requirement or not through comparison of experimental measurement and calculation fitting. The method can realize the thickness nanocrystallization of the polarization phase modulation device only by simple design, and has a very good application prospect.)

1. The application of two-dimensional GeSe in preparing a polarization phase modulation device.

2. The use of claim 1, wherein the two-dimensional GeSe is applied at a thickness of 1 to 1000 nanometers, and wherein the two-dimensional GeSe is attached to a surface of a substrate.

3. The polarization phase modulation device based on two-dimensional GeSe is characterized by comprising a substrate and a two-dimensional GeSe layer positioned on the surface of the substrate, wherein the two-dimensional GeSe is taken as a functional material layer of the polarization phase modulation device, and the thickness of the two-dimensional GeSe layer is preferably 1-1000 nanometers.

4. A method for designing a polarization phase modulation device according to claim 3, comprising the steps of:

(1) attaching a plurality of two-dimensional GeSe layers with different thicknesses to a substrate to obtain a plurality of composite materials containing two-dimensional GeSe functional layers;

(2) obtaining the thickness d of the two-dimensional GeSe functional layer in the composite material in the step (1) and the corresponding in-plane optical constants under the thickness, wherein the in-plane optical constants comprise extinction coefficients k along the armchair direction and the zigzag direction of GeSe under different wavelength conditions_ACAnd k_ZZAnd a refractive index n_ACAnd n_ZZObtaining a relation curve of the change of the delta k and the delta n along with the wavelength, wherein the delta k is equal to k_AC-k_ZZ，Δn＝n_ZZ-n_AC；

(3) For any one of the composite materials containing the two-dimensional GeSe functional layer in the step (1), at a wavelength range or a single wavelength point lambda which satisfies that the Deltak is 0, obtaining a set of data sets which are composed of the thickness d of the two-dimensional GeSe functional layer in the composite material, the wavelength range or the single wavelength point lambda which satisfies that the Deltak is 0 under the thickness d, and delta n corresponding to the wavelength range or the single wavelength point lambda; for the plurality of composite materials containing the two-dimensional GeSe functional layer in the step (1), a plurality of data sets are obtained;

(4) substituting the data in the data set of the step (3) into a phase delay amount calculation formulaAnd calculating to obtain a phase delay amount set corresponding to different two-dimensional GeSe functional layer thicknesses, selecting data matched with the phase delay amount of the target polarization phase modulation device from the phase delay amount set according to the phase delay amount requirement of the target polarization phase modulation device, and obtaining the thickness of the two-dimensional GeSe functional layer corresponding to the phase delay amount data, thereby obtaining the target polarization phase modulation device.

5. The design method of claim 4, wherein the thickness of the two-dimensional GeSe functional layer in the composite material in the step (1) is at least between 1 and 10nm and at most not more than 1000 nm.

6. The design method as claimed in claim 4, wherein step (4) is to expand the thickness range of the two-dimensional GeSe functional layer in step (1) or reduce the thickness gradient if no data matching the phase retardation of the target polarization phase modulation device can be found from the phase retardation set, and then repeating steps (1) to (4) until the target polarization phase modulation device is manufactured.

7. The design method of claim 4, further comprising the steps of:

(5) measuring the light intensity of the polarization phase modulation device manufactured in the step (4) under different polarizer angles and analyzer rotation angles by using the built transmission type light path or reflection type light path; comparing the experimental test value with the light intensity at different polarizer angles and analyzer rotation angles obtained by fitting according to the in-plane optical constant obtained in the step (2), and if the deviation between the experimental measured value and the fitting value is not more than 5%, indicating that the manufactured polarization phase modulation device is the target polarization phase modulation device; and (3) conversely, the thickness range of the two-dimensional GeSe functional layer in the composite material in the step (1) is expanded, or the thickness gradient of the two-dimensional GeSe functional layer is reduced, and then the steps (1) to (4) are repeated until the target polarization phase modulation device is manufactured.

8. The design method according to claim 4, wherein a transmission-type optical path composed of the light source, the polarizer, the polarization phase modulation device manufactured in step (4), the rotation analyzer and the light intensity detector is used for detecting the performance of the two-dimensional GeSe polarization phase modulation device, wherein the substrate in the polarization phase modulation device is a transparent substrate, and the specific test method is as follows:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

and fixing an included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling the light to enter a polarization phase modulation device consisting of the two-dimensional GeSe layer and the transparent substrate after passing through the analyzer, fixing the crystal axis position of the two-dimensional GeSe layer to enable the armchair and the zigzag direction in the plane to be respectively parallel to the y axis and the x axis, and finally reaching the light intensity detector after passing through the rotary analyzer forming a beta between the transmission axis direction and the y axis, thereby obtaining a light intensity test value.

9. The design method of claim 4, wherein after the light source is incident on the polarizer along the z-axis, only the component of the electric field direction along the transmission axis is transmitted; let the amplitude of the electric field passing through the polarizer be E₀So that the electric field amplitude along the x-axis and y-axis is represented as:

E_0,y＝E₀cosα；E_0,x＝E₀sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

wherein when incident light passes through the two-dimensional GeSe layer and the transparent substrate, the transmission coefficient t of the crystal axis in the two directions of the armchair AC and the zigzag ZZ in the two-dimensional GeSe plane_AC、t_ZZRespectively as follows:

wherein E is_T,yAnd E_T,xThe amplitudes of the electric fields passing through the two-dimensional GeSe and the transparent substrate along the y axis and the x axis respectively;

because the included angle between the analyzer and the y-axis is beta, the electric field along the x-axis direction and the y-axis direction is projected to the electric field E along the direction of the rotating analyzer A_ACan be expressed as:

E_A＝E_T,ycosβ+E_T,xsinβ＝t_ACE_0,ycosβ+t_ZZE_0,xsinβ＝t_ACE₀cosαcosβ+t_ZZE₀sinαsinβ

thus the transmission coefficient t after passing through the analyzer_AComprises the following steps:

finally obtaining the fitted transmitted light intensity

I_A＝|t_A|²。

10. The design method according to claim 7, wherein in step (3), the optical constants and thicknesses in the AC and ZZ directions of the two-dimensional GeSe layer and the optical constants and thicknesses of the substrate are used as input, reflection coefficients in the two crystal axis directions are respectively obtained by a transmission matrix method, and a reflection type light path is constructed to realize the inspection of the polarization phase modulation device;

and (3) detecting the performance of the two-dimensional GeSe polarization phase modulation device by adopting a reflection type light path consisting of a light source, a polarizer, the polarization phase modulation device obtained in the step (4), a rotary analyzer and a light intensity detector, wherein the specific test method comprises the following steps:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

fixing an included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling light to enter a polarization phase modulation device consisting of a two-dimensional GeSe layer and a substrate after passing through a polarization analyzer, fixing the crystal axis position of the two-dimensional GeSe layer, enabling the armchair and the zigzag direction in the plane of the polarization phase modulation device to be parallel to the y axis and the x axis respectively, reflecting the light by the polarization phase modulation device, then passing through a rotary polarization analyzer forming a beta between the transmission axis direction and the y axis included angle, and finally reaching a light intensity detector to obtain a light intensity test value;

after the light source enters the polarizer along the z axis, only the component of the electric field direction along the light transmission axis can penetrate through the polarizer; let the amplitude E of the electric field after passing through the polarizer₀Thus, the electric field amplitude along the x-axis and y-axis can be expressed as:

E_0,y＝E₀cosα；E_0,x＝E₀sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

after incident light passes through the two-dimensional GeSe layer and the transparent substrate, the reflection coefficients of crystal axes in two directions of an Armchair (AC) and a zigzag (ZZ) in the two-dimensional GeSe plane are respectively as follows:

wherein E is_R,yAnd E_R,xThe amplitudes of the electric fields reflected by the two-dimensional GeSe and the substrate along the y axis and the x axis respectively;

since the included angle between the analyzer and the y-axis is β, the electric field projected from the x-axis direction and the y-axis direction to the direction of the rotating analyzer a can be expressed as:

E_A＝E_R,ycosβ+E_R,xsinβ＝r_ACE_0,ycosβ+r_ZZE_0,xsinβ＝r_ACE₀cosαcosβ+r_ZZE₀sinαsinβ

the reflection coefficient after passing through the analyzer is thus:

finally obtaining the fitted reflected light intensity

I_A’＝|r_A|²。

Technical Field

The invention belongs to the field of novel polarization optical devices, and particularly relates to a polarization phase modulation device based on two-dimensional germanium selenide (GeSe) and a design method thereof.

Background

The traditional optical instrument (such as an ellipsometer and the like) is limited by the volume of the instrument, and cannot meet the functional requirements of small volume and equal or even better for in-situ detection of living body life, in-situ deep detection of large-scale precise instruments and the like. Although the polarization phase modulation device made of the super surface and the super material can also realize larger birefringence effect, the high preparation cost and the optical loss make the practical application of the polarization phase modulation device still have great importance (Nature Photonics,2018,12(7): 392.).

The nano optical instrument constructed by the two-dimensional material has the advantage of small volume, and can realize accurate control on light through accurate regulation and control on the thickness of the nano material, so that the size of the instrument is greatly reduced, but the function of the instrument is not simplified or even enhanced. In addition, the two-dimensional material is convenient to integrate into the existing optical element (such as high-transmittance optical glass) or manufacture an integrated series optical element by utilizing the characteristics that the two-dimensional material is easy to attach to the substrate and van der Waals force is easy to form between the two-dimensional materials. The core of instrument miniaturization is the miniaturization of critical optical elements.

The polarization phase modulation device comprises an eighth wave plate, a quarter wave plate, a half wave plate, a full wave plate and the like, and is one of core optical elements of a large number of optical instruments (such as an ellipsometer). For example, the eighth wave plate can generate a phase retardation amount delta of 45 ° (pi/4) for two mutually perpendicular components of polarized light, so that linearly polarized light and elliptically polarized light are mutually converted or elliptically polarized light and circularly polarized light are mutually converted; the quarter-wave plate generates a phase retardation delta of 90 degrees (pi/2), and can convert a beam of linearly polarized light into circularly polarized light or convert the circularly polarized light into linearly polarized light; the half-wave plate makes the phase retardation delta generated by the polarized light be 180 degrees (pi), changes the rotation direction of circular (elliptical) polarized light (for example, changes right circularly polarized light into left circularly polarized light) or changes the vibration direction of linearly polarized light, and changes the included angle theta between the original vibration direction and the fast (slow) axis into 2 theta after passing through the half-wave plate; the full wave plate corresponds to a phase retardation of 360 ° (2 pi), and the polarization phase modulation device does not change the polarization state of light and is generally used for increasing the optical path length.

The phase delay delta is calculated by the formula

(in the formula, λ, Δ n, and d are the wavelength of incident light, the difference in refractive index of the material, and the thickness of the polarization phase modulation device, respectively).

The traditional wave plate made of birefringent crystals such as quartz and magnesium fluoride has huge volume and small birefringence effect (delta n) (generally about 0.1 or even lower). According to the formula (1), under the condition that the wavelength of the incident light is kept unchanged, for the same type of polarization phase modulation device, the lower birefringence effect tends to result in the thicker thickness of the polarization phase modulation device, which is not beneficial to the miniaturization of the polarization phase modulation device.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a polarization phase modulation device based on two-dimensional germanium selenide (GeSe) and a design method thereof.

In order to achieve the purpose, the invention provides application of two-dimensional GeSe in preparing a polarization phase modulation device.

Preferably, the thickness of the two-dimensional GeSe is 1-1000 nanometers when the two-dimensional GeSe is applied, and the two-dimensional GeSe is attached to the surface of the substrate.

Preferably, the thickness of the two-dimensional GeSe is 1-500 nm when applied.

According to another aspect of the present invention, there is provided a two-dimensional GeSe-based polarization phase modulation device, which includes a substrate and a two-dimensional GeSe layer on a surface of the substrate, and the polarization phase modulation device uses two-dimensional GeSe as a functional material layer.

Preferably, the thickness of the two-dimensional GeSe layer is 1-1000 nanometers.

According to another aspect of the present invention, there is provided a method for designing a polarization phase modulation device, comprising the steps of:

(1) attaching a plurality of two-dimensional GeSe layers with different thicknesses to a substrate to obtain a plurality of composite materials containing two-dimensional GeSe functional layers;

(2) obtaining the thickness d of the two-dimensional GeSe functional layer in the composite material in the step (1) and the corresponding in-plane optical constants under the thickness, wherein the in-plane optical constants comprise extinction coefficients k along the armchair direction and the zigzag direction of GeSe under different wavelength conditions_ACAnd k_ZZAnd a refractive index n_ACAnd n_ZZObtaining a relation curve of the change of the delta k and the delta n along with the wavelength, wherein the delta k is equal to k_AC-k_ZZ，Δn＝n_ZZ-n_AC；

(3) For any one of the composite materials containing the two-dimensional GeSe functional layer in the step (1), at a wavelength range or a single wavelength point lambda which satisfies that the Deltak is 0, obtaining a set of data sets which are composed of the thickness d of the two-dimensional GeSe functional layer in the composite material, the wavelength range or the single wavelength point lambda which satisfies that the Deltak is 0 under the thickness d, and delta n corresponding to the wavelength range or the single wavelength point lambda; for the plurality of composite materials containing the two-dimensional GeSe functional layer in the step (1), a plurality of data sets are obtained;

(4) substituting the data in the data set of the step (3) into a phase delay amount calculation formulaCalculating to obtain phase delay amount sets corresponding to different two-dimensional GeSe functional layer thicknessesAnd selecting data matched with the phase delay amount of the target polarization phase modulation device from the phase delay amount set according to the phase delay amount requirement of the target polarization phase modulation device, and acquiring the thickness of the two-dimensional GeSe functional layer corresponding to the phase delay amount data, thereby obtaining the target polarization phase modulation device.

Preferably, the thickness of the two-dimensional GeSe functional layer in the composite material in the step (1) is between 1 and 10nm at minimum and not more than 1000nm at maximum.

Preferably, if data matched with the phase retardation of the target polarization phase modulation device cannot be found in the phase retardation set in step (4), the thickness range of the two-dimensional GeSe functional layer in step (1) is expanded or the thickness gradient of the two-dimensional GeSe functional layer is reduced, and then steps (1) to (4) are repeated until the target polarization phase modulation device is manufactured.

Preferably, the design method further includes the steps of:

(5) measuring the light intensity of the polarization phase modulation device manufactured in the step (4) under different polarizer angles and analyzer rotation angles by using the built transmission type light path or reflection type light path; comparing the experimental test value with the light intensity at different polarizer angles and analyzer rotation angles obtained by fitting according to the in-plane optical constant obtained in the step (2), and if the deviation between the experimental measured value and the fitting value is not more than 5%, indicating that the manufactured polarization phase modulation device is the target polarization phase modulation device; and (3) conversely, the thickness range of the two-dimensional GeSe functional layer in the composite material in the step (1) is expanded, or the thickness gradient of the two-dimensional GeSe functional layer is reduced, and then the steps (1) to (4) are repeated until the target polarization phase modulation device is manufactured.

Preferably, a transmission-type light path composed of the light source, the polarizer, the polarization phase modulation device manufactured in the step (4), the rotation analyzer and the light intensity detector is adopted to detect the performance of the two-dimensional GeSe polarization phase modulation device, wherein the substrate in the polarization phase modulation device is a transparent substrate, and the specific test method is as follows:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

fixing the included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling the light to enter a polarization phase modulation device consisting of a two-dimensional GeSe layer and a transparent substrate after passing through a polarization Analyzer, fixing the crystal axis position of the two-dimensional GeSe layer, enabling the armchair and the zigzag direction in the plane to be respectively parallel to the y axis and the x axis, then passing through a rotary polarization Analyzer (Analyzer, recorded as A) which forms beta between the transmission axis direction and the y axis included angle, and finally reaching a light intensity detector to obtain a light intensity test value.

Preferably, after the light source is incident on the polarizer along the z-axis, only the component of the electric field direction along the transmission axis can transmit; let the amplitude of the electric field passing through the polarizer be E₀So that the electric field amplitude along the x-axis and y-axis is represented as:

E_0,y＝E₀ cosα；E_0,x＝E₀ sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

wherein when incident light passes through the two-dimensional GeSe layer and the transparent substrate, the transmission coefficient t of the crystal axis in the two directions of the armchair AC and the zigzag ZZ in the two-dimensional GeSe plane_AC、t_ZZRespectively as follows:

wherein E is_T,yAnd E_T,xThe amplitudes of the electric fields passing through the two-dimensional GeSe and the transparent substrate along the y axis and the x axis respectively;

because the included angle between the analyzer and the y-axis is beta, the electric field along the x-axis direction and the y-axis direction is projected to the electric field E along the direction of the rotating analyzer A_ACan be expressed as:

E_A＝E_T,y cosβ+E_T,x sinβ＝t_ACE_0,y cosβ+t_ZZE_0,x sinβ＝t_ACE₀ cosαcosβ+t_ZZE₀ sinαsinβ

thus the transmission coefficient t after passing through the analyzer_AComprises the following steps:

finally obtaining the fitted transmitted light intensity

I_A＝|t_A|²。

Preferably, the step (2) further measures the thickness d of the substrate and the optical constants of the substrate in the polarization phase modulation device in the step (1), and the transmission coefficients of the incident light along the crystal axes in the directions of the armchair and the zigzag in the GeSe plane are obtained as follows after the incident light passes through the two-dimensional GeSe layer and the transparent substrate:

after incident light vertically enters the two-dimensional GeSe and the transparent substrate, the optical constants and the thicknesses of the two-dimensional GeSe layer in the AC and ZZ directions and the optical constants and the thicknesses of the substrate are used as input, and the transmission coefficients of the incident light along crystal axes in the two directions of the armchair and the zigzag in the GeSe plane are respectively obtained by using a transmission matrix method after the incident light passes through the two-dimensional GeSe layer and the transparent substrate.

Preferably, in the step (3), the optical constants and thicknesses of the two-dimensional GeSe layer in the AC and ZZ directions and the optical constant and thickness of the substrate are used as input, reflection coefficients along the two crystal axis directions are respectively obtained by a transmission matrix method, and a reflection-type light path is built to realize the inspection of the polarization phase modulation device;

and (3) detecting the performance of the two-dimensional GeSe polarization phase modulation device by adopting a reflection type light path consisting of a light source, a polarizer, the polarization phase modulation device obtained in the step (4), a rotary analyzer and a light intensity detector, wherein the specific test method comprises the following steps:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

fixing an included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling light to enter a polarization phase modulation device consisting of a two-dimensional GeSe layer and a substrate after passing through a polarization analyzer, fixing the crystal axis position of the two-dimensional GeSe layer, enabling the armchair and the zigzag direction in the plane of the polarization phase modulation device to be parallel to the y axis and the x axis respectively, reflecting the light by the polarization phase modulation device, then passing through a rotary polarization analyzer forming a beta between the transmission axis direction and the y axis included angle, and finally reaching a light intensity detector to obtain a light intensity test value;

after the light source enters the polarizer along the z axis, only the component of the electric field direction along the light transmission axis can penetrate through the polarizer; let the amplitude E of the electric field after passing through the polarizer₀Thus, the electric field amplitude along the x-axis and y-axis can be expressed as:

E_0,y＝E₀ cosα；E_0,x＝E₀ sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

after incident light passes through the two-dimensional GeSe layer and the transparent substrate, the reflection coefficients of crystal axes in two directions of an Armchair (AC) and a zigzag (ZZ) in the two-dimensional GeSe plane are respectively as follows:

wherein E is_R,yAnd E_R,xThe amplitudes of the electric fields reflected by the two-dimensional GeSe and the substrate along the y axis and the x axis respectively;

since the included angle between the analyzer and the y-axis is β, the electric field projected from the x-axis direction and the y-axis direction to the direction of the rotating analyzer a can be expressed as:

E_A＝E_R,y cosβ+E_R,x sinβ＝r_ACE_0,y cosβ+r_ZZE_0,x sinβ＝r_ACE₀ cosαcosβ+r_ZZE₀ sinαsinβ

the reflection coefficient after passing through the analyzer is thus:

finally obtaining the fitted reflected light intensity

I_A’＝|r_A|²。

Through the technical scheme, compared with the prior art, the invention can obtain the following beneficial effects:

(1) the invention provides that two-dimensional GeSe is applied to preparing a polarization phase modulation device, the two-dimensional GeSe has a higher birefringence effect delta n in a plane, the two-dimensional material is easy to adhere to a substrate, the characteristics of the two-dimensional GeSe are utilized to design and realize a novel polarization phase modulation device based on the two-dimensional GeSe, and the polarization phase modulation device prepared by the GeSe is more favorable for the nano-crystallization of an optical element due to the nanoscale thickness, so that a foundation is laid for the micro-nano and integration of an optical instrument.

(2) Firstly, accurately and efficiently measuring in-plane optical constants of polarization phase modulation devices based on two-dimensional GeSe layers with different thicknesses by adopting advanced measurement and characterization means, and realizing in-plane optical constant measurement in a continuous spectrum range; and then calculating according to the measured optical constant data and the thickness data of the two-dimensional GeSe according to a phase delay delta calculation formula to obtain a corresponding phase delay, and determining the thickness of the appropriate two-dimensional GeSe layer according to the requirement of the target polarization phase modulation device on the phase delay so as to realize the manufacture of the target polarization phase modulation device. The method is simple and efficient, and complex calculation and simulation are not needed.

(3) The invention adopts a simple optical path to realize the direct measurement of the light intensity, then deduces a light intensity expression by a vector method, and then compares an experimental measured value with a vector method deduced value, thereby identifying and checking whether the manufactured polarization phase modulation device is the type of a target polarization phase modulation device. The derivation process is simple and clear, and the efficient and quick identification and detection of the polarization phase modulation device are realized.

Drawings

FIG. 1 is a crystal structure diagram of GeSe;

FIG. 2 is a thickness measured by a two-dimensional GeSe optical microscope and an atomic force microscope;

FIG. 3 shows the birefringence Δ n and the dichroic Δ k in the GeSe plane for ellipsometry;

FIG. 4 is a two-dimensional GeSe polarization absorption; the left graph shows the change of the absorption rate along with the angle of the incident polarized light electric field when the two-dimensional GeSe is in the wavelength range of 600-850 nanometers, and the right graph shows the change of the two-dimensional GeSe absorption rate along with the polarized light electric field at 750 nanometers;

fig. 5 is a diagram for examining an actual optical path of a two-dimensional GeSe polarization-based phase modulation device.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Since the thickness is often only on the order of nanometers or even thinner, birefringence phenomena in two-dimensional materials are mainly due to the difference in refractive indices along the two crystallographic axes in the plane. It has been found that two-dimensional materials with a crystal structure with low symmetry tend to have a high in-plane birefringence effect. GeSe is a typical biaxial crystalline material (space group is) The symmetry is lower than that of a uniaxial crystal traditional wave plate material, and theoretical calculation shows that (adv. optical Mater.2018,1801311), the two-dimensional GeSe in-plane birefringence effect delta n is as high as 0.8 and is far higher than that of the traditional wave plate material. The invention designs and realizes a novel polarization phase modulation device based on two-dimensional GeSe by utilizing the higher birefringence effect delta n in a two-dimensional GeSe plane and simultaneously utilizing the characteristic that a two-dimensional material is easy to adhere to a substrate, and lays a foundation for the nanocrystallization of an instrument.

The invention provides application of two-dimensional GeSe in preparation of a polarization phase modulation device. The thickness of the two-dimensional GeSe is 1-1000 nanometers, preferably 1-500 nanometers when in application. Attaching the two-dimensional GeSe to a surface of a substrate. In some embodiments, it is used to prepare an eighth wave plate, a quarter wave plate, a half wave plate, or a full wave plate.

The invention also provides a two-dimensional GeSe-based polarization phase modulation device, which comprises a substrate and a two-dimensional GeSe layer positioned on the surface of the substrate, wherein the two-dimensional GeSe is taken as a functional material layer of the polarization phase modulation device, and the thickness of the two-dimensional GeSe layer is preferably 1-1000 nanometers.

The invention also provides a design method of the polarization phase modulation device, which comprises the following steps:

(1) attaching a plurality of two-dimensional GeSe layers with different thicknesses to a substrate to obtain a plurality of composite materials containing two-dimensional GeSe functional layers;

(2) obtaining the thickness d of the two-dimensional GeSe functional layer in the composite material obtained in the step (1) and the corresponding in-plane optical constants under the thickness, wherein the in-plane optical constants comprise extinction coefficients k along the Armchair direction (Armchair, recorded as the c-axis direction in the AC and GeSe crystal structure) and the Zigzag direction (Zigzag, recorded as the ZZ and b-axis direction in the GeSe crystal structure) of GeSe under different wavelength conditions_ACAnd k_ZZAnd a refractive index n_ACAnd n_ZZObtaining a relation curve of the change of the delta k and the delta n along with the wavelength, wherein the delta k is equal to k_AC-k_ZZ，Δn＝n_ZZ-n_AC；

(3) For the two-dimensional GeSe functional material layer of the polarization phase modulation device, it is necessary to satisfy the condition that Δ k of GeSe is 0, and therefore, for the plurality of composite materials including the two-dimensional GeSe functional layer in step (1), a data set is obtained which is composed of the thickness d of the two-dimensional GeSe functional layer in the composite material, the wavelength range or the single wavelength point λ satisfying Δ k of 0 at the thickness d, and Δ n corresponding to the wavelength range or the single wavelength point λ, at the wavelength range or the single wavelength point λ satisfying Δ k of 0; (ii) a For the plurality of composite materials containing the two-dimensional GeSe functional layer in the step (1), a plurality of data sets are obtained;

(4) substituting the data in the data set of the step (3) into a phase delay amount calculation formulaCalculating to obtain a phase delay amount set corresponding to different two-dimensional GeSe functional layer thicknesses, selecting data matched with the phase delay amount of the target polarization phase modulation device from the phase delay amount set according to the phase delay amount requirement of the target polarization phase modulation device, obtaining the thickness of the two-dimensional GeSe functional layer corresponding to the phase delay amount data, attaching the two-dimensional GeSe with the thickness to the substrate, and finally manufacturing the target polarization phase modulation device.

In some embodiments, step (1) measures the thickness of the two-dimensional GeSe layer in the device by using an atomic force microscope, a stage profiler, or an ellipsometer.

In some embodiments, the step (1) obtains the in-plane anisotropic optical constants of the two-dimensional GeSe layer through a spectral Mohler ellipsometer measurement; or by measuring the reflectivity and transmissivity of the device and extracting the optical constants reversely by a transmission matrix method.

When the optical constants are inversely extracted by measuring the reflectivity and the transmissivity of the device and by a transmission matrix method, the crystal axis orientation of the two-dimensional GeSe layer in the device needs to be determined.

In some embodiments, step (1) determines the crystallographic axis orientation of the two-dimensional GeSe layer by transmission electron microscopy, scanning tunneling microscopy, polarized raman, or polarized absorption.

In some embodiments, the thickness of the two-dimensional GeSe functional layer in the composite material obtained in step (1) is at least 1-10nm and at most 1000 nm.

In some embodiments, if the step (4) cannot find data matching the phase retardation of the target polarization phase modulation device from the set of phase retardations, the step (1) is repeated to the step (4) by expanding the thickness range of the two-dimensional GeSe functional layer in the step (1) or reducing the thickness gradient thereof until the target polarization phase modulation device is manufactured.

In some embodiments, the design method further includes the steps of:

(5) measuring the light intensity of the polarization phase modulation device manufactured in the step (4) under different polarizer angles and analyzer rotation angles by using the built transmission type light path or reflection type light path; comparing the experimental test value with the light intensity at different polarizer angles and analyzer rotation angles obtained by fitting according to the in-plane optical constant obtained in the step (2), and if the deviation between the experimental measured value and the fitting value is not more than 5%, indicating that the manufactured polarization phase modulation device is the target polarization phase modulation device; and (3) conversely, the thickness range of the two-dimensional GeSe functional layer in the composite material in the step (1) is expanded, or the thickness gradient of the two-dimensional GeSe functional layer is reduced, and then the steps (1) to (4) are repeated until the target polarization phase modulation device is manufactured.

In some embodiments, a transmission-type optical path formed by the light source, the polarizer, the polarization phase modulation device manufactured in step (4), the rotation analyzer, and the light intensity detector is used for detecting the performance of the two-dimensional GeSe polarization phase modulation device, wherein a substrate in the polarization phase modulation device is a transparent substrate, and the specific test method is as follows:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

fixing the included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling the light to enter a polarization phase modulation device consisting of a two-dimensional GeSe layer and a transparent substrate after passing through a polarization Analyzer, fixing the crystal axis position of the two-dimensional GeSe layer, enabling the armchair and the zigzag direction in the plane to be respectively parallel to the y axis and the x axis, then passing through a rotary polarization Analyzer (Analyzer, recorded as A) which forms beta between the transmission axis direction and the y axis included angle, and finally reaching a light intensity detector to obtain a light intensity test value.

In some embodiments, after the light source is incident on the polarizer along the z-axis, only the component of the electric field direction along the pass axis is transmitted; let the amplitude of the electric field passing through the polarizer be E₀Thus, the electric field amplitude along the x-axis and y-axis can be expressed as:

E_0,y＝E₀ cosα；E_0,x＝E₀ sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

wherein when incident light passes through the two-dimensional GeSe layer and the transparent substrate, the transmission coefficient t of crystal axis in two directions of Armchair (AC) and zigzag (ZZ) in the two-dimensional GeSe plane_AC、t_ZZRespectively as follows:

wherein E is_T,yAnd E_T,xThe amplitudes of the electric fields passing through the two-dimensional GeSe and the transparent substrate along the y axis and the x axis respectively;

since the included angle between the analyzer and the y-axis is β, the electric field projected from the x-axis direction and the y-axis direction to the direction of the rotating analyzer a can be expressed as:

E_A＝E_T,y cosβ+E_T,x sinβ＝t_ACE_0,y cosβ+t_ZZE_0,x sinβ＝t_ACE₀ cosαcosβ+t_ZZE₀ sinαsinβ

the transmission coefficient after passing through the analyzer is thus:

finally obtaining the fitted transmitted light intensity

I_A＝|t_A|²。

In some embodiments, the thickness d of the substrate and the optical constants of the substrate in the polarization phase modulation device in the step (1) are measured in the step (2), and after the incident light passes through the two-dimensional GeSe layer and the transparent substrate, the transmission coefficients along the crystal axes in the directions of the armchair and the zigzag in the GeSe plane are obtained as follows:

after incident light vertically enters the two-dimensional GeSe and the transparent substrate, the optical constants and the thicknesses of the two-dimensional GeSe layer in the AC and ZZ directions and the optical constants and the thicknesses of the substrate are used as input, and the transmission coefficients of the incident light along crystal axes in the two directions of the armchair and the zigzag in the GeSe plane are respectively obtained by using a transmission matrix method after the incident light passes through the two-dimensional GeSe layer and the transparent substrate.

In some embodiments, the transparent substrate is a crystalline or amorphous material that is transparent at a wavelength or a single wavelength point λ in a wavelength range satisfying Δ k ═ 0 corresponding to a thickness d satisfying a phase retardation requirement of the target polarization phase modulation device, that is, does not generate absorption (the extinction coefficient of the substrate is 0), and does not generate birefringence in the x-y plane.

In some embodiments, in the step (3), the optical constants and thicknesses of the two-dimensional GeSe layer in the AC and ZZ directions and the optical constant and thickness of the substrate are used as input, reflection coefficients in the two crystal axis directions are respectively obtained by using a transmission matrix method, and a reflection-type light path is built to realize the inspection of the polarization phase modulation device;

and (3) detecting the performance of the two-dimensional GeSe polarization phase modulation device by adopting a reflection type light path consisting of a light source, a polarizer, the polarization phase modulation device manufactured in the step (4), a rotary analyzer and a light intensity detector, wherein the specific test method comprises the following steps:

keeping incident light vertically incident, namely incident along the negative direction of the z axis, wherein the wavelength of the incident light is the wavelength or a single wavelength point λ in the wavelength range satisfying Δ k ═ 0 corresponding to the thickness d satisfying the phase retardation requirement of the target polarization phase modulation device in the step (4);

and fixing an included angle alpha between the transmission axis direction of the polarizer and the y axis in the vertical direction, enabling light to enter a polarization phase modulation device consisting of the two-dimensional GeSe layer and the substrate after passing through the analyzer, fixing the crystal axis position of the two-dimensional GeSe layer, enabling the armchair and the zigzag direction in the plane to be respectively parallel to the y axis and the x axis, reflecting the light by the polarization phase modulation device, then passing through a rotary analyzer forming a beta between the transmission axis direction and the y axis included angle, and finally reaching the light intensity detector to obtain a light intensity test value.

Light source polarizing by incident along z-axisAfter the device, only the component of the electric field direction along the light transmission axis direction can penetrate; let the amplitude E of the electric field after passing through the polarizer₀Thus, the electric field amplitude along the x-axis and y-axis can be expressed as:

E_0,y＝E₀ cosα；E_0,x＝E₀ sinα

wherein E is_0,xAnd E_0,yThe amplitudes of the electric fields passing through the polarizer along the x axis and the y axis respectively; alpha is the included angle between the transmission axis direction of the polarizer and the y axis in the vertical direction;

after incident light passes through the two-dimensional GeSe layer and the transparent substrate, the reflection coefficients of crystal axes in two directions of an Armchair (AC) and a zigzag (ZZ) in the two-dimensional GeSe plane are respectively as follows:

wherein E is_R,yAnd E_R,xThe amplitudes of the electric fields reflected by the two-dimensional GeSe and the substrate along the y axis and the x axis respectively;

since the included angle between the analyzer and the y-axis is β, the electric field projected from the x-axis direction and the y-axis direction to the direction of the rotating analyzer a can be expressed as:

E_A＝E_R,y cosβ+E_R,x sinβ＝r_ACE_0,y cosβ+r_ZZE_0,x sinβ＝r_ACE₀ cosαcosβ+r_ZZE₀ sinαsinβ

the reflection coefficient after passing through the analyzer is thus:

finally obtaining the fitted reflected light intensity

I_A’＝|r_A|²。

In the reflective optical path, the substrate can be made of a crystal material or an amorphous material which is transparent or opaque in a wavelength range satisfying Δ k 0 corresponding to a thickness d satisfying the phase retardation requirement of the target polarization phase modulation device or a single wavelength point λ and does not cause birefringence in the x-y plane.

The method comprises the steps of firstly making two-dimensional GeSe with a certain thickness gradient, obtaining in-plane optical constants of the two-dimensional GeSe, calculating to obtain phase delay amounts corresponding to different thickness gradients by combining a phase delay amount calculation formula, determining the thickness of the two-dimensional GeSe in a target polarization phase modulation device according to the phase delay amount requirement of the target polarization phase modulation device, attaching the two-dimensional GeSe to a substrate to make the target polarization phase modulation device, and finally checking whether the made polarization phase modulation device meets the requirement or not by comparing experimental measurement and calculation fitting.

As shown in fig. 1, GeSe is a typical layered material, and van der waals force is present in each layer of atoms along the a-axis direction (out-of-plane direction), while atoms in a plane perpendicular to the a-axis direction (in-plane direction) are bonded in the form of covalent bonds, and there is a large difference in the arrangement of atoms along the Armchair (Armchair, written as AC, c-axis direction in GeSe crystal structure) and the Zigzag (Zigzag, written as ZZ, b-axis direction in GeSe crystal structure), which is also a cause of GeSe having in-plane optical anisotropy.

FIG. 2 shows two-dimensional GeSe having a thickness of 102 nm as measured by atomic force microscopy; the difference between the in-plane anisotropic optical constants (birefringence Δ n and dichroism Δ k) measured by the ellipsometer is shown in FIG. 3; fig. 4 shows the measured absorption rate of GeSe sample with a thickness of 102 nm in the left graph, and the absorption rate at 750 nm along with the polarization angle of the electric field, and it can be seen that the absorption rate is the maximum when the polarization direction is 30 degrees, and the polarization direction is parallel to the AC crystal axis direction, so as to determine the crystal axis direction.

To fabricate the two-dimensional GeSe-based quarter-wave plate of this embodiment, the following steps are required:

s1: the method comprises the steps of manufacturing a set of GeSe nano sheets with the thickness of 100-500nm and the thickness gradient of 50nm, attaching the GeSe nano sheets to a transparent substrate, accurately measuring the GeSe nano sheets through an atomic force microscope, and measuring optical constants of the GeSe nano sheets by using a spectral Muller ellipsometer under the conditions of different wavelengthsExtinction coefficient k in the in-plane AC and ZZ directions_ACAnd k_ZZAnd a refractive index n_ACAnd n_ZZObtaining the relation curve of the change of the delta k and the delta n along with the wavelength, and determining the AC and ZZ axis orientation of the sample through a transmission electron microscope; curves of Δ k and Δ n as a function of wavelength were obtained.

S2: for manufacturing the quarter-wave plate, Δ k of GeSe needs to be 0, and a proper Δ n needs to be found in a wavelength range or a wavelength point where Δ k is 0, so that the phase retardation satisfies pi/2; according to the phase delay amount calculation formulaCalculating the phase retardation of all GeSe nanosheet sets in the wavelength range or wavelength points meeting the condition that delta k is 0 in S1, determining the thickness of the two-dimensional GeSe nanosheets when the phase retardation is pi/2, attaching the two-dimensional GeSe nanosheets to a glass substrate, and manufacturing a quarter-wave plate based on two-dimensional GeSe;

s3: according to the transmission-type optical path shown in fig. 5, a light source passes through a polarizer with an included angle of 45 degrees between the transmission axis direction and the y axis along the negative direction of the z axis, then passes through a quarter-wave plate based on two-dimensional GeSe (the ZZ direction is kept parallel to the x axis), then enters a rotary analyzer (the transmission axis direction of the analyzer and the included angle of the y axis are set to be beta), and finally enters a light intensity detector.

S4: and comparing the light intensity calculated by the transmission matrix and the vector method with the actually measured light intensity, wherein if the error is less than 5%, the quarter-wave plate based on the two-dimensional GeSe meets the requirement.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.