WO2021184624A1

WO2021184624A1 - Method for controlling coherence of light beams by using artificial microstructure

Info

Publication number: WO2021184624A1
Application number: PCT/CN2020/103403
Authority: WO
Inventors: 刘磊鑫; 刘文玮; 王飞; 赵承良; 陈树琪; 蔡阳健
Original assignee: 苏州大学
Priority date: 2020-03-16
Filing date: 2020-07-22
Publication date: 2021-09-23
Also published as: CN111190278B; CN111190278A

Abstract

Disclosed is a method for controlling the coherence of light beams by using an artificial microstructure. The method comprises the steps of: S10, determining, according to the coherence of partially coherent light to be generated, the phase of said partially coherent light at each corresponding cell position in an artificial microstructure area; S20, calculating rotation angles of nanocells arranged at the cell positions; S30, arranging the nanocells having different rotation angles at corresponding cell positions to construct an artificial microstructure for light beam coherence control; and S40, enabling a focused light beam to reach the surface of the constructed artificial microstructure, selecting an incident area of the artificial microstructure according to requirements, and obtaining a partially coherent light beam having a corresponding degree of coherence. The present invention can avoid the noise of light field regulation, improve the utilization rate of energy, and achieve the precise modulation of the coherence of the light field. The use of nanocells to construct the structure can greatly reduce the size of the structure, thereby facilitating the miniaturization design of an optical system.

Description

A method for adjusting the coherence of light beams by using artificial microstructures

Technical field

The invention relates to the technical field of coherent optics, in particular to a method for adjusting the coherence of light beams by using artificial microstructures.

Background technique

As an important branch of modern optics, coherent optics has attracted the attention of a large number of researchers at home and abroad. Coherence actually represents the result of the correlation between certain quantities of two points in the fluctuating light field. This correlation can be measured by the fringe contrast of Young's double-slit interference. Coherence is an important characteristic of the light field, and the research on the control of the coherence of the light field is of great significance. Research has found that the control of the coherence of the light field is used in free-space optical communications, lidar, laser fusion, special optical imaging, quantum optics, etc. It has important application value in the field. In the past, the adjustment of the degree of coherence of the light field mainly used rotating ground glass to generate partially coherent light, and the coherence of the light field was adjusted by adjusting the distance between the ground glass and the focusing lens. However, the existing methods are mostly based on centimeter-level systems, which are not conducive to integrated and miniaturized designs. In addition, the existing method cannot know the coherence of the generated beam without measurement, and the energy utilization rate is low, which limits its further application.

Artificial microstructures are artificial optical materials with sub-wavelength scale structural units. The proposal of artificial microstructures provides a new way to achieve the enhancement and effective control of the interaction between light and matter, and is for the miniaturization, lightweight and integration of optical devices. It provides a brand-new approach. At present, artificial microstructures have been able to achieve effective control of the amplitude, phase and polarization state of the light field at the sub-wavelength scale, and have high application value, such as the realization of polarized optical anti-counterfeiting, achromatic lenses, high saturation structural colors, etc. However, so far, artificial microstructures have rarely been involved in the regulation of the coherence dimension of the light field.

Summary of the invention

In view of the shortcomings of the prior art, one of the objectives of the present invention is to provide a method for adjusting the coherence of light beams by using artificial microstructures with high energy utilization rate and high control precision. It adopts the following technical solutions:

A method for adjusting the coherence of light beams by using artificial microstructures, which includes the following steps:

S10: Determine the phase of each cell position in the corresponding artificial microstructure area according to the coherence of the partial coherent light to be generated;

S20. Calculate the rotation angle of the nanocells arranged at each cell position;

S30. Arrange nano cells with different rotation angles at corresponding cell positions to construct an artificial microstructure for realizing beam coherence control;

S40. Incident the focused light beam to the constructed artificial microstructure surface, select the incident area of the artificial microstructure according to requirements, and obtain a partially coherent light beam with a corresponding degree of coherence.

As a further improvement of the present invention, the step S10 specifically includes:

According to the generation conditions of the partially coherent light, the range of the random phase corresponding to the partially coherent light to be generated determines its coherence. Among them, the coherence degree of the partially coherent light generated by the artificial microstructure with a specific phase distribution is:

Where μ(r ₁ , r ₂ ) is the degree of coherence of the coherent light to be generated,

Is the phase distribution at each cell position of the artificial microstructure area corresponding to the partial coherent light to be generated, and "<>" represents the time average.

As a further improvement of the present invention, the phase distribution formula of the artificial microstructure in step S10 is:

in,

Is the phase of the partially coherent light to be generated at its different cell positions, a is the size parameter for adjusting the coherence of the partially coherent light generated in different regions of the artificial microstructure, and rand is a random function, representing each cell of the artificial microstructure The phase corresponding to is a random phase in a fixed interval.

As a further improvement of the present invention, the step S20 specifically includes:

According to the phase relationship formula and the phase of the partial coherent light to be generated at each cell position, the rotation angle of the nanocells arranged at each cell position is calculated.

As a further improvement of the present invention, the step S40 selects the incident area of the artificial microstructure according to requirements, and obtains a partially coherent beam with a corresponding degree of coherence, which specifically includes:

Determine the phase distribution at each cell position of the artificial microstructure according to the required degree of coherence. The phase distribution at each cell position is controlled by the parameter a. The parameter a can take any non-negative real value, that is, the coherence degree can be generated as Partially coherent light with an arbitrary value from 0 to 1, where, when the degree of coherence is 0, the generated beam is completely incoherent light, when the degree of coherence is 1, the generated beam is completely coherent light, and when the degree of coherence is between 0 and 1. , The generated light beam is partially coherent light.

As a further improvement of the present invention, a=0, 0.2, 0.4, 0.6, 0.8, 1 is selected, and the phase difference corresponding to the random phase interval is used to determine the phase at each cell position corresponding to the artificial microstructure area of the partially coherent light to be generated Basis of distribution.

As a further improvement of the present invention, the artificial microstructure constructed in the step S30 is an array structure composed of nanocells.

As a further improvement of the present invention, the shown nano cell is a titanium dioxide rectangular column cell, which includes a silicon dioxide substrate and a rectangular column on the silicon dioxide substrate.

As a further improvement of the present invention, the silicon dioxide substrate is square, side length p=330nm, and the dimensions of the rectangular column are: length a=260nm, width b=90nm, and height h=450nm.

The beneficial effects of the present invention:

The method of using artificial microstructures to control the coherence of beams calculates the phase distribution corresponding to the partially coherent beams and determines the nanocells with different rotation angles at different cell positions, so that different nanocells can achieve different light field coherence. The coherence of the beam can be controlled quantitatively; the utilization of the beam energy is greatly improved, and the light intensity of the partially coherent beam is increased; the artificial microstructure that realizes the coherence control can be constructed by using nano-cells. The size of the device is reduced to a large extent, which in turn can facilitate the realization of the miniaturized design of the optical system to which the device is applied.

The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly, it can be implemented in accordance with the content of the specification, and in order to make the above and other objectives, features and advantages of the present invention more obvious and understandable. In the following, the preferred embodiments are cited in conjunction with the drawings, and the detailed description is as follows.

Description of the drawings

Fig. 1 is a schematic diagram of a method for adjusting the coherence of light beams by using artificial microstructures in a preferred embodiment of the present invention;

Figure 2 is a schematic diagram of the structure of a single nanocell in a preferred embodiment of the present invention;

3 is a schematic diagram of a square phase distribution gradient of artificial microstructures that generate partially coherent beams with different degrees of coherence in a preferred embodiment of the present invention;

Fig. 4 is a schematic diagram of a system for adjusting the coherence of light beams by using artificial microstructures in a preferred embodiment of the present invention.

Marking description: 1. Laser; 2. Beam expander; 3. Focusing lens; 4. Artificial microstructure; 5. Objective; 6. Charge coupled element; 7. First computer; 8. Motorized translation stage; 9. Second computer.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the examples cited are not intended to limit the present invention.

As shown in FIG. 1, it is a method for adjusting the coherence of light beams by using artificial microstructures in a preferred embodiment of the present invention, and the method includes the following steps:

S10: Determine the phase of each cell position of the corresponding artificial microstructure area according to the coherence of the partial coherent light to be generated.

Wherein, the cell position is the spatial arrangement position of each nanocell constructing the artificial microstructure.

According to the generation conditions of the partially coherent light, the range of the random phase corresponding to the partially coherent light to be generated determines the magnitude of its coherence. Among them, the coherence degree of the partially coherent light generated by the micro-nano structure with a specific phase distribution is:

Among them, the phase distribution formula of the artificial microstructure is:

in,

Is the phase of the partially coherent light to be generated at its different cell positions, a is the size parameter for adjusting the coherence of the partially coherent light generated in different regions of the artificial microstructure, and rand is a random function, representing each cell of the artificial microstructure The phase corresponding to is a random phase in a fixed interval. The above-mentioned optical parameters are preset by the user based on the actual requirements of the coherence degree of the partially coherent beam. In this embodiment, the partially coherent beam is a partially coherent vortex beam at a focal field.

In this embodiment, the artificial microstructure used to realize the partially coherent beam to be generated is an array structure composed of nanocells. Therefore, each cell position of the artificial microstructure has a corresponding phase. The phase can be determined according to preset optical parameters.

Specifically, it includes: calculating the rotation angle of the nano cells arranged at each cell position according to the phase relation formula and the phase of the partial coherent light to be generated at each cell position.

The phase relationship formula is:

in,

In order to regulate the phase of the coherence artificial microstructure of the beam at the position of the i-th cell, θ _i is the rotation angle of the arranged nano-cells at the position of the i-th cell.

In one of the embodiments, the nanocell may be a titanium dioxide rectangular column cell with a nanometer size, and different phases can be realized by setting different rotation angles, thereby realizing the generation of partially coherent beams with different coherence degrees.

S30: Arranging nanocells with different rotation angles at corresponding cell positions to construct an artificial microstructure for realizing light beam coherence control.

The selecting the incident area of the artificial microstructure according to requirements and obtaining a partially coherent beam with a corresponding degree of coherence specifically includes: determining the phase distribution at each cell position of the artificial microstructure according to the required degree of coherence, and each element The phase distribution at the cell position is regulated by the parameter a. The parameter a can take any non-negative real value, that is, it can produce a partial coherent light with a coherence degree of 0 to 1 with any value. When the coherence degree is 0, the generated light beam is For completely incoherent light, when the degree of coherence is 1, the generated light beam is completely coherent light, and when the degree of coherence is between 0 and 1, the generated light beam is partially coherent light.

In one of the embodiments, a=0, 0.2, 0.4, 0.6, 0.8, 1 is selected, and the phase difference corresponding to the random phase interval is used to determine the phase at each cell position corresponding to the artificial microstructure area of the partially coherent light to be generated Basis of distribution.

There are many ways to construct optical artificial microstructures by using nanocells. For example, nanocells with corresponding rotation angles can be prepared at each cell position of the artificial microstructure, or they can be selected from the existing nanocells. And arrange the selected nanocells to the matching cell position of the surface array. Of course, the above two methods are only exemplary instructions for constructing an area array, and should not be construed as limitations.

Specifically, as shown in FIG. 2, it is a schematic diagram of the structure of a single nano-cell in one of the embodiments. The nano-cell is a rectangular column cell of titanium dioxide, which includes a silicon dioxide substrate (SiO ₂ ) and a silicon dioxide substrate. The rectangular column (TiO ₂ ) on the bottom. More specifically, the silicon dioxide substrate may have a side length p=330 nm, and the dimensions of the rectangular column include: length a=260 nm, width b=90 nm, and height h=450 nm. All nanocells in the artificial microstructure have the same length, width, and height. Different phase distributions can be achieved by setting different rotation angles θ, thereby realizing the control of optical field coherence; among them, the rotation angle θ can be a rectangular column The angle of rotation about the y axis in the xy plane.

Regarding the partial coherent light to be generated with different degrees of coherence, in this embodiment, you can use

Indicates the phase distribution corresponding to the partially coherent beam to be generated. In this embodiment, a total of 6 partial coherent beams with different degrees of coherence are generated. The artificial microstructure corresponds to 6 phase distributions, and the phase distribution is:

in,

Is the phase distribution of the artificial microstructure corresponding to the i-th coherence degree of the partially coherent beam, and a _i is the corresponding optical parameter. In this embodiment, a ₁ =0, a ₂ =0.2, a ₃ =0.4, a ₄ = 0.6, a ₅ = 0.8, and a ₆ =1. The six phase distributions are arranged according to the phase gradient distribution shown in FIG. 3.

Based on the above description of the nanocell and the partial coherent beam to be generated, the nanocell distribution diagram shown in Figure 3 can be used to represent the artificial microstructure that realizes the control of the light field coherence. It is assumed that the artificial microstructure includes X×Y Nanocells, for ease of description, the two-dimensional coordinates (m, n) of each cell position in the artificial microstructure (the two-dimensional coordinates are any coordinate value in the free space coordinates) can be converted to nanometers according to the number conversion formula. The sequence number i of the cell; among them, the number conversion formula is as follows:

i=(m-1)×Y+n

Among them, i is the sequence number of the nanocell, m and n are the horizontal and vertical coordinate parameters of the i-th nanocell in the artificial microstructure respectively, and Y is the total number of nanocells arranged in the longitudinal direction in the array. . Based on this, the nanocell arranged at the i-th cell position can be referred to as the i-th nanocell for short.

As shown in FIG. 4, this embodiment uses an artificial microstructure to control the coherence of the beam, which includes the artificial microstructure 4 constructed by the method in the above embodiment, and the system further includes a laser 1, a beam expander 2, Focusing lens 3, objective lens 5, charge-coupled element 6, displacement mechanism, second computer 9. The displacement mechanism is used to drive the displacement of the artificial microstructure 4, and the second computer 9 is used to control the charge-coupled element 6 to collect and record the partially coherent beam generated ；

The beam generated by the laser 1 is expanded by the beam expander 2, and the expanded laser beam is focused by the focusing lens 3. In this embodiment, the beam waist is about 40um (as shown in Figure 4 for each phase gradient of the artificial microstructure Width), then incident on the surface of the artificial microstructure 4 and transmitted, and then the light beam is amplified by the objective lens 5 and then collected and recorded by the charge-coupled element 6.

Specifically, the displacement mechanism includes a first computer 7 and an electric stage 8. The electric stage 8 is used to carry the artificial microstructure 4, and the first computer 7 is used to control the movement of the electric stage 8. The first computer 7 controls the electric stage 8 to move along the same phase distribution direction of the artificial microstructure 4 at a predetermined frequency, so that the random phase imparted to the incident light beam changes with time, thereby generating a smooth and uniform partially coherent light beam.

As shown in Fig. 3, the partial coherent beam generated by the laser beam passing through the artificial microstructures with the above six phase distributions is basically consistent with the predicted coherence degree using the method of calculating the beam coherence degree by using multiple speckles.

It can be seen that by setting the optical parameters a=0, 0.2, 0.4, 0.6, 0.8, 1 to control the coherence of the incident beam, a partially coherent beam with a degree of coherence from high to low can be generated, and when a=0, The generated beam is a completely coherent beam, and its coherence degree can be regarded as 1, when a=0, the coherence degree of the generated beam is 0.08, which can be approximately regarded as a completely incoherent beam (coherence degree is 0). The degree of coherence here is the degree of global coherence, that is, the experimentally measured coherence length/beam waist.

To sum up, the present invention uses artificial microstructures to control the coherence of light beams. By determining the phases of nanocells with different rotation angles at different cell positions, different nanocells can achieve light field control, and the nanocells are combined. Compared with the existing method of using rotating ground glass to generate a partially coherent beam, the method of calculating the phase-control coherence can predict the degree of coherence of the partially coherent beam to be generated in advance. Realize quantitative control of the coherence of the light beam; by adopting the artificial microstructure constructed by nano-cells with a transmittance of more than 90%, compared with the existing method of adjusting the coherence through ground glass, the utilization rate of the light beam is greatly improved, resulting in The light intensity of part of the coherent beam is increased; by using nano-cells to construct artificial microstructures that achieve coherence control, the size of the device can be reduced to a large extent, which can be beneficial to realize the miniaturization of the optical system using the device design.

The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or alterations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention is subject to the claims.

Claims

A method for adjusting the coherence of light beams by using artificial microstructures, which is characterized in that it comprises the following steps:

S10: Determine the phase of each cell position in the corresponding artificial microstructure area according to the coherence of the partial coherent light to be generated;

S20. Calculate the rotation angle of the nanocells arranged at each cell position;

S30. Arrange nano cells with different rotation angles at corresponding cell positions to construct an artificial microstructure for realizing beam coherence control;

S40. Incident the focused light beam to the constructed artificial microstructure surface, select the incident area of the artificial microstructure according to requirements, and obtain a partially coherent light beam with a corresponding degree of coherence.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 1, wherein the step S10 specifically includes:

According to the generation conditions of the partially coherent light, the range of the random phase corresponding to the partially coherent light to be generated determines its coherence. Among them, the coherence degree of the partially coherent light generated by the artificial microstructure with a specific phase distribution is:

Where μ(r 1 , r 2 ) is the degree of coherence of the coherent light to be generated,
Is the phase distribution at each cell position of the artificial microstructure area corresponding to the partial coherent light to be generated, and "<>" represents the time average.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 1, wherein the phase distribution formula of the artificial microstructures in step S10 is:

in,
Is the phase of the partially coherent light to be generated at its different cell positions, a is the size parameter for adjusting the coherence of the partially coherent light generated in different regions of the artificial microstructure, and rand is a random function, representing each cell of the artificial microstructure The phase corresponding to is a random phase in a fixed interval.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 1, wherein the step S20 specifically includes:

According to the phase relationship formula and the phase of the partial coherent light to be generated at each cell position, the rotation angle of the nanocells arranged at each cell position is calculated.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 4, wherein the phase relationship formula is:

in,
In order to regulate the phase of the coherence artificial microstructure of the beam at the position of the i-th cell, θ i is the rotation angle of the arranged nano-cells at the position of the i-th cell.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 1, wherein in step S40, the incident area of the artificial microstructures is selected according to requirements, and a partially coherent light beam with a corresponding degree of coherence is obtained. Specifically:

Determine the phase distribution at each cell position of the artificial microstructure according to the required degree of coherence. The phase distribution at each cell position is controlled by the parameter a. The parameter a can take any non-negative real value, that is, the coherence degree can be generated as Partially coherent light with an arbitrary value from 0 to 1, where, when the degree of coherence is 0, the generated beam is completely incoherent light, when the degree of coherence is 1, the generated beam is completely coherent light, and when the degree of coherence is between 0 and 1. , The generated light beam is partially coherent light.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 6, characterized in that a=0, 0.2, 0.4, 0.6, 0.8, 1 is selected, and the phase difference corresponding to the random phase interval is used to determine the part to be generated. Coherent light corresponds to the basis of the phase distribution at each cell position in the artificial microstructure area.
The method for adjusting the coherence of light beams using artificial microstructures according to claim 1, wherein the artificial microstructure constructed in step S30 is an array structure composed of nanocells.
The method for adjusting the coherence of light beams by using artificial microstructures according to claim 8, wherein the nano-cell is a rectangular column cell of titanium dioxide, which includes a silicon dioxide substrate and a rectangular column on the silicon dioxide substrate. column.
9. The method for adjusting the coherence of light beams using artificial microstructures according to claim 9, wherein the silicon dioxide substrate is square with side length p=330nm, and the size of the rectangular column is: length a=260nm, Width b=90nm, height h=450nm.