Multi-focus array light intensity regulation and control method for liquid crystal spatial light modulator

Abstract

The invention discloses a multi-focus array light intensity regulation and control method for a liquid crystal spatial light modulator, and relates to the technical field of light field regulation and control. Comprising the following steps: dividing an entrance pupil area into a plurality of fan-shaped areas by taking an entrance pupil center of an objective lens as a vertex, and endowing specific phase values for the fan-shaped areas to obtain a multi-focus phase diagram; the multi-focus phase diagram is loaded on a spatial light modulator for phase modulation, and after entrance pupil phase coding is carried out on an objective lens, a multi-focus array is obtained on a focal plane; calibrating the relationship between the central angle of the phase segmentation region and the light intensity distribution for the multi-focus array by using an image processing method; adjusting the central angle parameter of the phase segmentation region according to the relationship between the central angle of the phase segmentation region and the light intensity distribution, and controlling the light intensity distribution of the multi-focus array; and setting corresponding phase distribution to obtain a multi-focus array with light intensity distribution, focus position and morphology control. According to the method, the light intensity distribution control calculation of the multi-focus array is efficient, and the multi-focus array with controllable intensity, position and morphology can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of light field regulation, and more particularly to a multi-focal array light intensity regulation method for a liquid crystal spatial light modulator. Background Art

[0002] As a common light field control device, spatial light modulator can easily and quickly generate multi-focal light arrays. Multi-focal light arrays have important applications in laser micro-nano processing, optical imaging, laser communication, optical operation and capture, and multiple focal points working simultaneously greatly improve efficiency and accuracy. However, there is an uneven distribution of light field intensity in the generated multi-focal array, or there are some situations, such as when using special structured light fields for processing, the light field intensities required for parallel processing of light fields of different morphologies are different.

[0003] Obata et al. used an iterative two-dimensional Fourier transform algorithm to generate a series of computerized holograms, assigned different laser powers to each computerized hologram, and used the dynamic periodic loading of the SLM to produce a multi-focal laser spot whose position and laser intensity can be individually controlled. Shenglong Rao et al. filled some of the modulation areas in the computerized hologram with black, so that the black part directly reflected the incident light, and controlled the active area without superimposing any modulation to achieve real-time control of the light intensity between multiple foci. However, most traditional methods for controlling the intensity distribution of the light field between multiple foci rely on iterative optimization or indirect modulation, which is difficult to meet the needs of high-precision and high-efficiency energy distribution.

[0004] Therefore, it is an urgent problem for those skilled in the art to propose a multi-focal array light intensity control method for a liquid crystal spatial light modulator to solve the difficulties existing in the prior art. Summary of the invention

[0005] In view of this, the present invention provides a multi-focal array light intensity control method for a liquid crystal spatial light modulator, aiming to solve the problems of uneven light intensity distribution, high computational complexity, and inaccurate energy control in the prior art. The present invention generates a multi-focal array with controllable light intensity distribution, focal position, and morphology through an innovative non-iterative sectoral segmentation (SPS) method.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A multi-focal array light intensity control method for a liquid crystal spatial light modulator comprises the following steps:

[0008] S1. Taking the entrance pupil center of the objective lens as the vertex, the entrance pupil area is divided into several sector-shaped areas, and specific phase values ​​are assigned to the sector-shaped areas according to the vector diffraction integral theory to obtain a multi-focus phase map;

[0009] S2, loading the multi-focal phase image onto the spatial light modulator for phase modulation, and obtaining a multi-focal array on the focal plane after the entrance pupil phase is encoded by the 4f optical system;

[0010] S3, using the image processing method to calibrate the multi-focal array to determine the relationship between the central angle of the phase segmentation area and the light intensity distribution;

[0011] S4, adjusting the phase division area center angle parameter according to the relationship between the phase division area center angle and the light intensity distribution, and controlling the light intensity distribution of the multi-focus array;

[0012] S5. According to S1-S4, the corresponding phase distribution is set to obtain a multi-focus array with controlled light intensity distribution, focus position and morphology.

[0013] In the above method, optionally, the specific content of dividing the entrance pupil area into a plurality of sector-shaped areas in S1 is:

[0014] Taking the center of the objective lens entrance pupil as the vertex, the entrance pupil area is divided into N sector-shaped areas, that is, N main areas are generated;

[0015] Each main area is divided into M fan-shaped sub-areas, where M and N are both positive integers, and M corresponds to the number of foci expected to be generated.

[0016] In the above method, optionally, the mth sub-area in the Nth main area is assumed to be Nm, and the value range of m is 1-M. Then the phase area corresponding to the mth focus in the optical array is 1-m, 2-m, 3-m...Nm, that is, the mth sub-area of ​​each main area together constitutes the phase area of ​​the mth focus.

[0017] In the above method, optionally, the specific content of obtaining the multi-focus phase map by assigning a specific phase value to the sector area according to the vector diffraction integral theory in S1 is:

[0018] The phase shift expression is derived based on the vector diffraction integral theory;

[0019] The phase shift expression is sequentially filled into the phase segmentation area of ​​focus m to obtain the phase diagram of focus m, and so on to obtain the multi-focus phase diagram.

[0020] The above method can optionally derive the phase shift expression based on the vector diffraction integral theory, and the formula is as follows:

[0021]

[0022] Among them, (x1, y1, z1) is the rectangular coordinate of the back stop, λ is the laser wavelength, NA is the numerical aperture of the objective lens, N t is the refractive index of the lens immersion medium, (Δx, Δy, Δz) are the position coordinates of a single focus in three-dimensional space, and R is the radius of the aperture stop.

[0023] In the above method, optionally, the specific content of calibrating the multi-focal array using the image processing method in S3 is:

[0024] The normalized light intensity distribution of the multi-focal array is obtained by image processing method. The relationship between the light intensity distribution of the multi-focal Gaussian light array and the multi-focal vortex light array structured light array and the central angle of the phase division area is calibrated, and the corresponding relationship between the light intensity distribution of the multi-focal light array and the area of ​​the phase division area is obtained.

[0025] In the above method, optionally, the specific content of the relationship between the central angle of the phase division area and the light intensity distribution in S3 is:

[0026] I m =A·Nθ m

[0027] Among them, A is a constant, θ m is the central angle of sub-area Nm, used for multi-focus light arrays with the same focus morphology, and N is the number of main areas.

[0028] In the above method, optionally, in S4, the parameters of the central angle of the phase division area are adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution, and the specific content of controlling the light intensity distribution of the multi-focus array is:

[0029] According to the relationship between the central angle of the phase division area and the light intensity distribution, the parameters of the central angle of the phase division area are adjusted to control the area of ​​the phase division area at the entrance pupil. That is, by unevenly dividing the phase area at the entrance pupil, the parameters of the central angle of the phase division area are adjusted to control the light intensity distribution of the multi-focal array.

[0030] In the above method, optionally, in S4, the parameters of the central angle of the phase division area are adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution, and the specific contents of controlling the light intensity distribution of the multi-focal array further include:

[0031] A phase area that does not contain phase information is reserved. The phase area is activated only when the light intensity of a certain focus needs to be independently adjusted. Independent control of the light intensity of a single focus is achieved by locally calling or releasing the area of ​​the phase area.

[0032] In the above method, optionally, the specific contents of setting the corresponding phase distribution in S5 to obtain the multi-focus array with light intensity distribution, focus position and morphology control are as follows:

[0033] By changing the position parameters (Δx, Δy, Δz) of the phase shift expression, the free movement of the focus in three-dimensional space can be controlled;

[0034] By bringing the phase factor of the special light field into the phase shift expression, the morphological information of the focus can be controlled;

[0035] The parameters of the central angle of the phase division area are adjusted according to the relationship to control the light intensity distribution of the multi-focal array.

[0036] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a multi-focal array light intensity control method for a liquid crystal spatial light modulator, which has the following beneficial effects:

[0037] Compared with the traditional method of controlling the light field intensity distribution between multiple focal points, the method of the present invention is computationally efficient and has precise light intensity control. The generated multi-focal light array has the characteristics of controllable light intensity distribution, focal position and morphology. It has great application prospects in laser micro-nano processing, light field imaging, laser communication, optical operation and capture, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0039] Figure 1 A flow chart of a multi-focal array light intensity control method for a liquid crystal spatial light modulator provided by the present invention;

[0040] Figure 2 A schematic diagram of the entrance pupil area division method provided by the present invention;

[0041] Figure 3 A light path setting diagram provided by the present invention;

[0042] Figure 4 A schematic diagram of phase division of the entrance pupil area provided by the present invention;

[0043] Figure 5 A schematic diagram of phase region division without phase information provided by the present invention;

[0044] Figure 6 A diagram of a 9-focus light array with decreasing light intensity distribution provided by the present invention;

[0045] Figure 7A diagram of a 4-vortex focus light array with different topological charges that produces consistent light intensity distribution provided by the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] See also Figure 1 As shown, the present invention discloses a multi-focal array light intensity control method for a liquid crystal spatial light modulator, which is called a non-iterative sector segmentation (SPS) method, comprising the following steps:

[0048] S1. Taking the entrance pupil center of the objective lens as the vertex, the entrance pupil area is divided into several sector-shaped areas, and specific phase values ​​are assigned to the sector-shaped areas according to the vector diffraction integral theory to obtain a multi-focus phase map;

[0049] S2, loading the multi-focal phase image onto the spatial light modulator for phase modulation, and obtaining a multi-focal array on the focal plane after the entrance pupil phase is encoded by the 4f optical system;

[0050] Specifically, in this embodiment, the multi-focus array light intensity control method for liquid crystal spatial light modulator is verified by experiment. The optical path setting adopted by the present invention is as follows: Figure 3 As shown in the figure, the laser used in the experiment is an 800nm ​​femtosecond laser with a repetition rate of 80MHz. The incident light beam enters the spatial light modulator SLM at a certain angle, and the calculated multi-focus phase map is loaded onto the spatial light modulator SLM in the form of a grayscale map. The grayscale value varies from 0 to 255, and the corresponding phase modulation varies from 0 to 2π. The incident light beam is modulated by the electrically controlled birefringence effect and twisted nematic effect of the liquid crystal molecules in the liquid crystal panel on the spatial light modulator. After the light beam modulated by the spatial light modulator is phase-encoded by the 4f optical system for the high numerical aperture objective lens, a multi-focus array is obtained on the focal plane.

[0051] S3, using the image processing method to calibrate the multi-focal array to determine the relationship between the central angle of the phase segmentation area and the light intensity distribution;

[0052] S4, adjusting the phase division area center angle parameter according to the relationship between the phase division area center angle and the light intensity distribution, and controlling the light intensity distribution of the multi-focus array;

[0053] S5. According to S1-S4, the corresponding phase distribution is set to obtain a multi-focus array with controlled light intensity distribution, focus position and morphology.

[0054] Furthermore, the entrance pupil area division method is as follows Figure 2 As shown, the specific content of dividing the entrance pupil area into several sector-shaped areas in S1 is:

[0055] Taking the center of the objective lens entrance pupil as the vertex, the entrance pupil area is divided into N sector-shaped areas, that is, N main areas are generated;

[0056] Each main area is divided into M fan-shaped sub-areas, where M and N are both positive integers, and M corresponds to the number of foci expected to be generated.

[0057] Furthermore, assuming that the mth sub-region in the Nth main region is Nm, and the value range of m is 1-M, then the phase region corresponding to the mth focus in the optical array is 1-m, 2-m, 3-m...Nm, that is, the mth sub-region of each main region together constitutes the phase region of the mth focus.

[0058] Furthermore, in S1, specific phase values ​​are assigned to the fan-shaped areas according to the vector diffraction integral theory to obtain the multi-focus phase map as follows:

[0059] The phase shift expression is derived based on the vector diffraction integral theory;

[0060] The phase shift expression is sequentially filled into the phase segmentation area of ​​focus m to obtain the phase diagram of focus m, and so on to obtain the multi-focus phase diagram.

[0061] Specifically, this method avoids the complex calculation process of the traditional iterative algorithm, significantly improves the calculation efficiency, and can accurately control the light intensity distribution of the multi-focal array.

[0062] Furthermore, the phase shift expression is derived based on the vector diffraction integral theory, and the formula is as follows:

[0063]

[0064] Among them, (x1, y1, z1) is the rectangular coordinate of the back stop, λ is the laser wavelength, NA is the numerical aperture of the objective lens, N t is the refractive index of the lens immersion medium, (Δx, Δy, Δz) are the position coordinates of a single focus in three-dimensional space, and R is the radius of the aperture stop.

[0065] Specifically, through the vector diffraction integral theory, the light field intensity when the light beam is focused through a high numerical aperture objective lens can be expressed in the form of a vector diffraction integral formula. Combined with the Fourier shift theorem and Fourier transform, the phase shift expression is derived.

[0066] Furthermore, the specific content of calibrating the multi-focal array using the image processing method in S3 is:

[0067] The normalized light intensity distribution of the multi-focal array is obtained by image processing method. The relationship between the light intensity distribution of the multi-focal Gaussian light array and the multi-focal vortex light array structured light array and the central angle of the phase division area is calibrated, and the corresponding relationship between the light intensity distribution of the multi-focal light array and the area of ​​the phase division area is obtained.

[0068] Furthermore, the specific content of the relationship between the central angle of the phase division area and the light intensity distribution in S3 is:

[0069] I m =A·Nθ m

[0070] Among them, A is a constant, θ m is the central angle of sub-area Nm, used for multi-focus light arrays with the same focus morphology, and N is the number of main areas.

[0071] For further information, see Figure 4 As shown, Figure 4 The left side of the figure is the phase division area of ​​focus 1, and the right side of the figure is the phase division area of ​​focus 2. In S4, the central angle parameter of the phase division area is adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution. The specific content of controlling the light intensity distribution of the multi-focus array is:

[0072] According to the relationship between the central angle of the phase division area and the light intensity distribution, the parameters of the central angle of the phase division area are adjusted to control the area of ​​the phase division area at the entrance pupil. That is, by unevenly dividing the phase area at the entrance pupil, the parameters of the central angle of the phase division area are adjusted to control the light intensity distribution of the multi-focal array.

[0073] Specifically, in practical applications, for deviations caused by external factors such as optical path alignment, light intensity collection can be used to obtain real-time light intensity distribution, and the parameters of the central angle of the phase division area can be further adjusted until the expected light intensity distribution is obtained.

[0074] Furthermore, in S4, the parameters of the central angle of the phase division area are adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution, and the specific contents of controlling the light intensity distribution of the multi-focus array also include:

[0075] A phase area that does not contain phase information is reserved. The phase area is activated only when the light intensity of a certain focus needs to be independently adjusted. Independent control of the light intensity of a single focus is achieved by locally calling or releasing the area of ​​the phase area.

[0076] For a specific diagram of phase region division without phase information, see Figure 5 As shown, the P area in the figure is locally called to achieve independent control of the light intensity of a single focus.

[0077] Furthermore, the specific contents of setting the corresponding phase distribution in S5 to obtain the multi-focus array for controlling the light intensity distribution, focus position and morphology are as follows:

[0078] By changing the position parameters (Δx, Δy, Δz) of the phase shift expression, the free movement of the focus in three-dimensional space can be controlled;

[0079] By bringing the phase factor of the special light field into the phase shift expression, the morphological information of the focus can be controlled;

[0080] The parameters of the central angle of the phase division area are adjusted according to the relationship to control the light intensity distribution of the multi-focal array.

[0081] Specifically, for example, by substituting the phase factor exp(ilφ) of the vortex light field into the phase displacement expression, the phase displacement expression of the vortex light can be obtained:

[0082]

[0083] See also Figure 6 As shown, a 9-focus light array with decreasing light intensity distribution based on the present invention is shown. The average error between the 9 focuses and the desired light intensity distribution is E=0.0593. Figure 7 The figure shows a 4-vortex focus light array with different topological charges (L=0, 2, 3, 4) that produces consistent light intensity distribution based on the present invention, and the average error from the expected light intensity distribution is E=0.0375.

[0084] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0085] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multi-focal array light intensity control method for a liquid crystal spatial light modulator, characterized in that: The following steps are involved: S1. Taking the entrance pupil center of the objective lens as the vertex, the entrance pupil area is divided into several sector-shaped areas, and specific phase values ​​are assigned to the sector-shaped areas according to the vector diffraction integral theory to obtain a multi-focus phase map; S2, loading the multi-focal phase image onto the spatial light modulator for phase modulation, and obtaining a multi-focal array on the focal plane after the entrance pupil phase is encoded by the 4f optical system; S3, using the image processing method to calibrate the multi-focal array to determine the relationship between the central angle of the phase segmentation area and the light intensity distribution; S4, adjusting the phase division area center angle parameter according to the relationship between the phase division area center angle and the light intensity distribution, and controlling the light intensity distribution of the multi-focus array; S5. According to S1-S4, the corresponding phase distribution is set to obtain a multi-focus array with controlled light intensity distribution, focus position and morphology.

2. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 1, characterized in that: The specific content of dividing the entrance pupil area into several sector-shaped areas in S1 is: Taking the center of the objective lens entrance pupil as the vertex, the entrance pupil area is divided into N sector-shaped areas, that is, N main areas are generated; Each main area is divided into M fan-shaped sub-areas, where M and N are both positive integers, and M corresponds to the number of foci expected to be generated.

3. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 2, characterized in that: Assume that the mth sub-region in the Nth main region is Nm, and the value range of m is 1-M. Then the phase region corresponding to the mth focus in the optical array is 1-m, 2-m, 3-m...Nm, that is, the mth sub-region of each main region together constitutes the phase region of the mth focus.

4. The multi-focal array light intensity control method for a liquid crystal spatial light modulator according to claim 1, characterized in that: In S1, according to the vector diffraction integral theory, a specific phase value is assigned to the fan-shaped area to obtain the multi-focus phase map. The specific content is: The phase shift expression is derived based on the vector diffraction integral theory; The phase shift expression is sequentially filled into the phase segmentation area of ​​focus m to obtain the phase diagram of focus m, and so on to obtain the multi-focus phase diagram.

5. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 4, characterized in that: The phase shift expression is derived based on the vector diffraction integral theory, and the formula is as follows: Among them, (x1, y1, z1) is the rectangular coordinate of the back stop, λ is the laser wavelength, NA is the numerical aperture of the objective lens, N t is the refractive index of the lens immersion medium, (Δx, Δy, Δz) are the position coordinates of a single focus in three-dimensional space, and R is the radius of the aperture stop.

6. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 1, characterized in that: The specific contents of calibrating the multi-focal array using the image processing method in S3 are as follows: The normalized light intensity distribution of the multi-focal array is obtained by image processing method. The relationship between the light intensity distribution of the multi-focal Gaussian light array and the multi-focal vortex light array structured light array and the central angle of the phase division area is calibrated, and the corresponding relationship between the light intensity distribution of the multi-focal light array and the area of ​​the phase division area is obtained.

7. A multi-focal array light intensity control method for a liquid crystal spatial light modulator according to claim 1 or 3, characterized in that: The specific content of the relationship between the central angle of the phase division area and the light intensity distribution in S3 is: I m =A·Nθ m Among them, A is a constant, θ m is the central angle of sub-area Nm, used for multi-focus light arrays with the same focus morphology, and N is the number of main areas.

8. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 1, characterized in that: In S4, the parameters of the central angle of the phase division area are adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution, and the specific contents of controlling the light intensity distribution of the multi-focus array are as follows: According to the relationship between the central angle of the phase division area and the light intensity distribution, the parameters of the central angle of the phase division area are adjusted to control the area of ​​the phase division area at the entrance pupil. That is, by unevenly dividing the phase area at the entrance pupil, the parameters of the central angle of the phase division area are adjusted to control the light intensity distribution of the multi-focal array.

9. The method for controlling light intensity of a multi-focal array for a liquid crystal spatial light modulator according to claim 1, characterized in that: In S4, the parameters of the central angle of the phase division area are adjusted according to the relationship between the central angle of the phase division area and the light intensity distribution, and the specific contents of controlling the light intensity distribution of the multi-focus array also include: A phase area that does not contain phase information is reserved. The phase area is activated only when the light intensity of a certain focus needs to be independently adjusted. Independent control of the light intensity of a single focus is achieved by locally calling or releasing the area of ​​the phase area.

10. The multi-focal array light intensity control method for a liquid crystal spatial light modulator according to claim 5, characterized in that: The specific contents of setting the corresponding phase distribution in S5 to obtain the multi-focus array with light intensity distribution, focus position and morphology control are as follows: By changing the position parameters (Δx, Δy, Δz) of the phase shift expression, the free movement of the focus in three-dimensional space can be controlled; By bringing the phase factor of the special light field into the phase shift expression, the morphological information of the focus can be controlled; The parameters of the central angle of the phase division area are adjusted according to the relationship to control the light intensity distribution of the multi-focal array.

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