A processing device for complex amplitude modulation polymer liquid crystal diffractive optical element

Abstract

The present invention discloses a processing device for a complex amplitude modulated polymer liquid crystal diffractive optical element, which is applied to the technical field of diffractive optical element processing. The present invention comprises a laser, a polarization state modulation device, an exposure angle modulation device, a liquid crystal diffractive optical element, and a two-dimensional displacement stage arranged in sequence along the optical path direction; the polarization state modulation device comprises a Pockels cell and a quarter wave plate; the exposure angle modulation device comprises an electrically controlled deflection mirror, a first convex lens, and a second convex lens. The polarization direction of the exposure light beam of the present invention is modulated by the Pockels cell and the quarter wave plate, and the exposure angle of the light beam is modulated by the electrically controlled deflection mirror, the first convex lens, and the second convex lens, so as to solve the problem that the existing diffractive optical element processing equipment cannot independently modulate the amplitude and phase of the diffractive optical element when processing each unit.

Description

Technical Field

[0001] The invention relates to the technical field of diffractive optical element processing, and more specifically to a processing device for a complex amplitude modulation polymer liquid crystal diffractive optical element. Background Art

[0002] According to the principle of diffraction, the amplitude or phase modulation of each small unit (pixel) on the flat material for a specific function is calculated by a computer, and then the flat material is processed by processing equipment to achieve the specified amplitude or phase modulation of each unit for the light beam. The resulting optical device is a diffractive optical element. Existing diffractive optical elements can only modulate the amplitude or phase of the light beam, and cannot achieve simultaneous independent modulation of amplitude and phase, which makes the design freedom of diffractive optical elements low and faces problems such as low diffraction efficiency.

[0003] Therefore, it is an urgent problem for those skilled in the art to propose a processing device for complex amplitude modulation polymer liquid crystal diffractive optical elements to solve the difficulties existing in the prior art. Summary of the invention

[0004] In view of this, the present invention provides a processing device for a complex amplitude modulated polymer liquid crystal diffractive optical element, which solves the problem that the existing diffractive optical element processing equipment cannot independently modulate the amplitude and phase of the diffractive optical element when processing each unit.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A processing device for a complex amplitude modulated polymer liquid crystal diffractive optical element comprises a laser, a polarization state modulating device, an exposure angle modulating device, a liquid crystal diffractive optical element and a two-dimensional displacement stage which are sequentially arranged along the optical path direction.

[0007] Optionally, the polarization state modulation device includes a Pockels cell and a quarter wave plate arranged along the optical path;

[0008] The Pockels cell and the quarter-wave plate are used to modulate the polarization direction of the exposure beam emitted by the laser.

[0009] Optionally, after the light beam passes through the Pockels cell, the polarization state S(t) of the light beam is described by the Stokes matrix:

[0010]

[0011] Where I(t) is the intensity of the light beam at that moment, and ψ(t) is the angle between the deflection direction of the light beam and the X-axis at that moment.

[0012] Optionally, the alignment direction of the liquid crystal diffractive optical element is determined by the average value of the Stowers matrix of the light beam within the alignment time τ, as shown in the following formula:

[0013]

[0014] The angle between the average polarization direction of the beam and the x-axis is described as:

[0015] α=2tan -1 (S2 / S1).

[0016] Optionally, the exposure angle modulation device includes an electrically controlled deflecting mirror, a first convex lens, and a second convex lens arranged along the optical path.

[0017] Optionally, the exposure angle of the light beam is modulated by an electrically controlled deflection mirror, a first convex lens and a second convex lens, wherein the first convex lens and the second convex lens are parallel to each other; after the light beam passes through a Pockels cell and a quarter-wave plate to modulate the polarization state, it is incident on the electrically controlled deflection mirror for light beam deflection; the focus of the first convex lens coincides with the position where the light beam is incident on the electrically controlled deflection mirror, and no matter how the electrically controlled deflection mirror is deflected, the first convex lens collimates the reflected light beam, and the light beam deflection direction modulation is perpendicular to the first convex lens;

[0018] The focal position of the second convex lens coincides with the exposure position of the liquid crystal diffractive optical element on the two-dimensional displacement stage. The light beam passing through the first convex lens will be focused on the position to be exposed of the liquid crystal diffractive optical element after passing through the second convex lens, no matter how the electrically-controlled rotating mirror rotates.

[0019] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a processing device for a complex amplitude modulation polymer liquid crystal diffractive optical element, which has the following beneficial effects:

[0020] The present invention solves the problem that the existing diffractive optical element processing equipment cannot independently modulate the amplitude and phase of the diffractive optical element when processing each unit through the common arrangement of a laser, a polarization state modulation device, an exposure angle modulation device, a liquid crystal diffractive optical element, and a two-dimensional translation stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] Figure 1 is the optical axis direction diagram of the liquid crystal material of the present invention;

[0023] Figure 2 is the rotation angle of the optical axis of the polymer liquid crystal material of the present invention;

[0024] Figure 3 A diagram of a processing device for a complex amplitude modulation polymer liquid crystal diffractive optical element provided by the present invention;

[0025] Figure 4 It is the working principle diagram of the Pockels cell of the present invention;

[0026] Figure 5 The refractive index ellipsoid after an electric field is applied to the electro-optical crystal of the present invention;

[0027] Figure 6 The working principle diagram of the electrically controlled deflecting mirror of the present invention;

[0028] Among them, 1-laser, 2-polarization state modulation device, 2-1-Pockels cell, 2-2-quarter wave plate, 3-exposure angle modulation device, 3-1-electrically controlled deflection mirror, 3-2-first convex lens, 3-3-second convex lens, 4-liquid crystal diffraction optical element, 5-two-dimensional position station, 6-mirror, 7-piezoelectric actuator, 8-substrate. DETAILED DESCRIPTION

[0029] 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.

[0030] The present invention uses polymer liquid crystal with a thickness equivalent to that of a half-wave plate as a processing material. The polymer liquid crystal is a birefringent material, and the direction of its optical axis can be determined by optical alignment. When working, the liquid crystal diffraction optical element is Figure 1 The structure shown in the figure is used to work. The amplitude A of the left-handed polarized light after passing through each unit is only related to Figure 2 The vertical rotation angle θ of the liquid crystal director of the unit is related to the phase φ. Figure 2 The horizontal rotation angle α of the liquid crystal director of the cell is shown.

[0031] The relationship is:

[0032] A=sin(θ)

[0033] φ=2α

[0034] Therefore, the purpose of manufacturing a liquid crystal diffractive optical element capable of complex amplitude modulation can be achieved by only realizing independent control of the vertical rotation angle and the horizontal rotation angle of the liquid crystal optical axis in each unit of the liquid crystal diffractive optical element.

[0035] In the process of photo-alignment of polymer liquid crystal, the vertical rotation angle in each unit is determined by the incident angle of the light beam, and the horizontal rotation angle is determined by the polarization direction of the light beam. Therefore, the present method proposes the following device to process the liquid crystal diffractive optical element by photo-alignment, such as Figure 3 As shown, the present invention discloses a processing device for a complex amplitude modulated polymer liquid crystal diffractive optical element, comprising a laser 1, a polarization state modulation device 2, an exposure angle modulation device 3, a liquid crystal diffractive optical element 4, and a two-dimensional displacement stage 5 which are sequentially arranged along the optical path direction.

[0036] Furthermore, the polarization state modulation device 2 includes a Pockels cell 2-1 and a quarter wave plate 2-2 arranged along the optical path; the Pockels cell 2-1 is an electrically controlled electro-optical crystal, the laser 1 applies an electric field along the Z direction to the electro-optical crystal, and the electro-optical effect changes the refractive index ellipsoid of the electro-optical crystal, thereby realizing the modulation of the phase delay amount such as Figure 5 As shown; the entire Pockels cell is equivalent to an electrically controlled phase delay plate, the phase delay amount ranges from -Π to Π, and its response speed can usually reach 1KHZ, which is much lower than the time required for liquid crystal alignment; the quarter-wave plate 2-2 introduces a fixed optical path difference to prevent the output light signal from being distorted when a low voltage is applied across the KDP crystal.

[0037] Specifically, in the device, the polarization direction of the exposure beam is modulated by the Pockels cell 2-1 and the quarter wave plate 2-2. The Pockels cell 2-1 is an electrically controlled electro-optical crystal that can modulate the phase delay by changing the applied voltage. Its working principle is as follows: Figure 4 shown.

[0038] Furthermore, after the light beam passes through the Pockels cell 2-1, the polarization state S(t) of the light beam is described by the Stokes matrix as follows:

[0039]

[0040] Where I(t) is the intensity of the light beam at that moment, and ψ(t) is the angle between the deflection direction of the light beam and the X-axis at that moment.

[0041] Furthermore, since the alignment time of the liquid crystal diffractive optical element is much longer than the response time of the Pockels cell, the alignment direction of the liquid crystal diffractive optical element is determined by the average value of the Stowers matrix of the light beam within the alignment time τ, as shown in the following formula:

[0042]

[0043] The angle between the average polarization direction of the beam and the x-axis is described as:

[0044] α=2tan -1 (S2 / S1)

[0045] Specifically, the angle between the average polarization direction of the light beam and the x-axis is the final horizontal rotation angle of the liquid crystal alignment. Since the response time of the Pockels cell is much lower than the liquid crystal alignment time, the average deflection angle of the light beam can be controlled by controlling the power-on voltage and time of the Pockels cell, thereby accurately controlling the horizontal alignment angle α of the liquid crystal.

[0046] Furthermore, the exposure angle modulation device 3 includes an electrically controlled deflection mirror 3-1, a first convex lens 3-2, and a second convex lens 3-3 arranged along the optical path.

[0047] Furthermore, the exposure angle of the light beam is modulated by the electrically controlled deflection mirror 3-1, the first convex lens 3-2 and the second convex lens 3-3, wherein the first convex lens 3-2 and the second convex lens 3-3 are parallel to each other; after the light beam passes through the Pockels cell 2-1 and the quarter wave plate 2-2 for polarization state modulation, it is incident on the electrically controlled deflection mirror 3-1 for light beam deflection; the focus of the first convex lens 3-2 coincides with the position where the light beam is incident on the electrically controlled deflection mirror 3-1, and no matter how the electrically controlled deflection mirror 3-1 is deflected, the first convex lens 3-2 will collimate the reflected light beam, and the light beam deflection direction modulation is perpendicular to the first convex lens 3-2;

[0048] The focal position of the second convex lens 3-3 coincides with the exposure position of the liquid crystal diffraction optical element on the two-dimensional displacement stage 5. The light beam after passing through the first convex lens 3-2 will be focused on the position to be exposed of the liquid crystal diffraction optical element 4 after passing through the second convex lens 3-3, no matter how the electrically-controlled rotating mirror 3-1 rotates.

[0049] Specifically, the rotation angle of the electrically controlled rotating mirror is different, the incident angle of the light beam during exposure is also different, and the vertical alignment angle of the liquid crystal diffraction optics is also different.

[0050] The electrically controlled deflection mirror 3-1 used in the device is a piezoelectric deflection mirror, and its working principle is as follows: Figure 6 As shown. The two groups of piezoelectric actuators 7 are connected to the substrate 8 at the bottom and to the mirror 6 at the top. When voltage is applied, the piezoelectric actuator 7 drives the mirror 6 to deflect by massaging motion. The advantage of using a piezoelectric deflection mirror is that the response time of the piezoelectric deflection mirror is extremely fast, usually up to 1KHz, which is much shorter than the time required for a certain unit liquid crystal alignment.

[0051] During the operation of the device, when the first unit of the liquid crystal diffractive optical element 4 is optically aligned, the two-dimensional displacement stage 5 is first adjusted so that the spatial position of the unit of the liquid crystal diffractive optical element 4 is located above the focus of the second convex lens 3-3. At this time, no matter how the reflector rotates, the light beam will only change the exposure direction, and will not change the exposure position in the liquid crystal diffractive optical element 4. Subsequently, the incident angle and polarization state of the alignment light beam are modulated to the values ​​corresponding to the designed amplitude and phase modulation capabilities of the unit by modulating the Pockels cell 2-1 and the electrically controlled deflection mirror 3-1, and optical alignment is performed, thus completing the optical alignment of the first unit of the liquid crystal diffractive optical element 4. Subsequently, the two-dimensional displacement stage 5 is adjusted so that the next unit of the liquid crystal diffractive optical element 4 is located at the focus of the convex lens, and the polarization state and incident direction are modulated to the values ​​corresponding to the designed amplitude and phase modulation capabilities of the unit, and optical alignment is performed. According to this process, each unit of the liquid crystal diffractive optical element 4 is processed, and the processing of the liquid crystal diffractive optical element 4 is completed.

[0052] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0053] 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 processing device for complex amplitude modulation polymer liquid crystal diffractive optical element, characterized in that: It includes a laser, a polarization state modulation device, an exposure angle modulation device, a liquid crystal diffraction optical element, and a two-dimensional displacement stage which are sequentially arranged along the optical path direction; The polarization state modulation device includes a Pockels cell and a quarter wave plate arranged along the optical path; The Pockels cell and the quarter-wave plate are used to modulate the polarization direction of the exposure beam emitted by the laser; The exposure angle modulation device comprises an electrically controlled deflection mirror, a first convex lens, and a second convex lens arranged along the optical path; The exposure angle of the light beam is modulated by the electric-controlled deflection mirror, the first convex lens and the second convex lens, wherein the first convex lens and the second convex lens are parallel to each other; after the light beam passes through the Pockels cell and the quarter-wave plate for polarization state modulation, it is incident on the electric-controlled deflection mirror for light beam deflection; the focus of the first convex lens coincides with the position where the light beam enters the electric-controlled deflection mirror, and no matter how the electric-controlled deflection mirror is deflected, the first convex lens will collimate the reflected light beam, and the light beam deflection direction modulation is perpendicular to the first convex lens; The focal position of the second convex lens coincides with the exposure position of the liquid crystal diffractive optical element on the two-dimensional displacement stage. The light beam passing through the first convex lens will be focused on the position to be exposed of the liquid crystal diffractive optical element after passing through the second convex lens, no matter how the electrically-controlled rotating mirror rotates.

2. The processing device of a complex amplitude modulation polymer liquid crystal diffractive optical element according to claim 1, characterized in that: When the light beam passes through the Pockels cell, the polarization state S(t) of the light beam is described by the Stokes matrix: Among them, I(t) is the intensity of the light beam at that moment, ψ(t) is the angle between the deflection direction of the light beam and the X-axis at that moment, and t is the time.

3. The processing device of a complex amplitude modulation polymer liquid crystal diffractive optical element according to claim 2, characterized in that: The alignment direction of the liquid crystal diffractive optical element is determined by the average value of the Stoles matrix of the light beam within the alignment time τ, as shown in the following formula: The angle between the average polarization direction of the beam and the x-axis is described as: <h2 style=";text-align:left;direction:ltr">α = 2tan<h2 style=";text-align:left;direction:ltr"> -1 <h2 style=";text-align:left;direction:ltr"> (S2 / S1) Wherein, α is the horizontal alignment angle of the liquid crystal.

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