Cascade liquid crystal geometric phase lens with adjustable focal intensity and achromatic function and preparation method thereof

Abstract

The application discloses a kind of cascade liquid crystal geometric phase lens and preparation method for realizing focal point intensity adjustable and achromatic function.The diffraction plane lens compared with traditional refractive optical lens can bring convenience for light weight, miniaturization optical system more.But its inherent characteristics lead to its chromatic aberration phenomenon is more serious.For double-layer cascade liquid crystal geometric phase lens structure to realize three-wavelength achromatic focusing, in this structure, the geometric phase distribution of two layers of liquid crystal lens can be focused on two wavelengths respectively, and simultaneously, the coupling of their geometric phase can also be focused on another specific wavelength.Based on the principle, in three-layer cascade liquid crystal geometric phase lens, due to layer and layer are coupled according to permutation and combination, achromatic can be realized for 7 different wavelengths.In addition, since amplitude coefficient is related to the phase retardation of liquid crystal, therefore focal point intensity can be adjusted by voltage.The method provides a solution for multifunctional multi-scene plane lens application.

Description

Technical Field

[0001] This invention belongs to the field of achromatic diffractive lenses, specifically a cascaded liquid crystal geometric phase lens that achieves adjustable focal intensity and achromatic function, and its preparation method. Background Technology

[0002] Since Newton discovered the phenomenon that white light can be decomposed into multiple colors using a prism, dispersion has been defined as the inherent property that the refractive index of most optical materials decreases with increasing wavelength. Chromatic aberration caused by dispersion can introduce perturbations into many imaging systems. Therefore, using achromatic lenses and other components to achieve broadband or multi-wavelength phase compensation helps obtain accurate, clear, and sharp imaging patterns. Currently, facing the urgent need for lightweight and compact optical systems, planar superlenses have been proposed. However, regardless of whether the phase shift of the element comes from the transmission phase, the detour phase, or the geometric phase, they still conform to the negative dispersion characteristics of diffractive lenses, only meeting the focusing requirements of a single wavelength and unable to meet the needs of broadband or multi-wavelength applications. Recent research in the field of metasurfaces has also provided novel solutions for achromatic superlenses. For example, by designing the parameters of the strip dielectric resonator on the superlens to compensate for the chromatic aberration caused by the propagation phase, a three-wavelength confocal superlens of 1300 nm, 1550 nm, and 1800 nm can be achieved. There are also dual-wavelength achromatic lenses based on spatial multiplexing design, as well as metasurface structures that use materials such as gallium nitride and silicon nitride as resonant resonators to achieve broadband achromatic functions. Alternatively, the dynamic phase modulation characteristics of liquid crystals can be combined with metasurfaces to achieve achromatic and zoom functions. Of course, there are also RGB achromatic functions achieved by vertically stacked three-layer metal superlenses.

[0003] However, these achromatic techniques only achieve three achromatic wavelengths, with a very small wavelength range and no adjustable range. To address this, we propose a method for achieving adjustable focus intensity and achromatic function using cascaded liquid crystal geometric phase lenses. In a similar three-layer cascade configuration, the number of achromatic wavelengths reaches seven, and the focus intensity can be adjusted. Summary of the Invention

[0004] To address the shortcomings of traditional diffractive lenses in achromatic correction, this invention proposes a method for achieving adjustable focal intensity and achromatic correction using cascaded liquid crystal geometric phase lenses. Traditional diffractive lenses exhibit a one-to-one correspondence between phase distribution and wavelength. This means that using stacked three layers of diffractive lenses, multiplexing three regions on a single lens, or using phase units with different structures can only achieve achromatic wavelengths of up to three, with a very small wavelength range. Cascaded liquid crystal geometric phase lenses, however, possess unique advantages in this regard.

[0005] Liquid crystal is a birefringent element with a phase retardation amount It can be represented as ,in d represents the birefringence of the liquid crystal, while d represents the thickness of the liquid crystal layer or cell. The wavelength of the incident light is given. Phase control can be achieved in two ways: first, by applying a voltage to the liquid crystal cell, the tilt angle of the liquid crystal molecules is controlled, thus achieving dynamic phase control; second, the azimuth angle of the liquid crystal molecules can be controlled through optical orientation, achieving geometric phase control. The Jones matrix can be used to calculate the path of linearly polarized light through the liquid crystal cell.

[0006] Firstly, for a single-layer liquid crystal, the incident light matrix is ​​defined. Then, the emitted light matrix of a certain pixel in the first liquid crystal layer It satisfies the following formula:

[0007] =

[0008] Assume the polarization components in the x and y directions are respectively , Linearly polarized monochromatic wave incident by a matrix is ​​represented as follows .

[0009] Then, the matrix after emission is decomposed into a combination of left and right circular polarizations.

[0010]

[0011] when For dextrorotatory and levorotatory light, respectively, [the following was assigned] , The geometric phase. With Variations in angle can achieve different phase distributions. Based on existing technologies, the same phase distribution can be achieved using light orientation. The pixel orientation region size at the corner can be as small as 100nm, easily meeting the design requirements of a diffractive lens. Specifically, after a plane wave is incident, different angles at different positions produce different geometric phases. These geometric phases satisfy a gradient phase shift, causing the wavefront to converge to a focal point. The formula is as follows:

[0012] (4)

[0013] Where f is the focal length of the lens.

[0014] Obviously, a single-layer lens cannot be adjusted, and its function is relatively limited. Therefore, a liquid crystal lens 2 is introduced. When pixel-to-pixel alignment is achieved, the phase retardation of a certain pixel in the liquid crystal lens 1 is... azimuth angle is The phase retardation of liquid crystal lens 2 is azimuth The phase delay of the two lenses can be changed by voltage.

[0015] After the beam enters, it passes through two pixels and finally exits. This can be represented by the following formula from the perspective of the Jones matrix.

[0016]

[0017]

[0018] The above equation has three phase components, namely: , , - Therefore, they can correspond to the phases of the three wavelengths respectively. Let

[0019]

[0020]

[0021] The three wavelengths can then be focused. Since the amplitude factor before different phase terms is related to the phase retardation of different liquid crystal layers, the focal intensity can be controlled by adjusting the voltage applied to the lens.

[0022] Furthermore, extending the cascaded lens to three layers results in three initial write phase distributions, three pairwise coupled phase distributions, and one phase distribution where all three layers are coupled together. Theoretically, these seven phase distributions can enable confocal focusing of seven wavelengths. For example, if we set the three initial design wavelengths of the three-layer cascaded liquid crystal lens to 396.8nm, 1064nm, and 1550nm, then the coupling geometric phase can focus light of four different wavelengths—632.8nm, 532.8nm, 3383nm, and 450nm—at the same location.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention utilizes the principle of phase coupling between cascaded liquid crystal geometric phase lenses to achieve focusing of a specific wavelength using coupled geometric phase, with the focal point position consistent with the initially designed wavelength. This effect lies in the fact that cascaded liquid crystal geometric phase lenses overcome the traditional rule that the number of diffractive lens layers must correspond one-to-one with the number of achromatic wavelengths. Specifically, cascaded liquid crystal geometric phase lenses overcome the limitation that two-layer diffractive lenses can only satisfy two wavelengths of achromatic aberration, and three-layer diffractive lenses can only satisfy three wavelengths of achromatic aberration, with a very small span between achromatic wavelengths. Through different interlayer couplings of cascaded liquid crystal lenses, two layers can achieve three wavelengths of achromatic aberration, and three layers can achieve seven wavelengths of achromatic aberration, with a large span between achromatic wavelengths. Within a limited space, this greatly enriches the application scenarios of diffractive lenses, providing a solution for lightweight and compact optical systems.

[0025] More importantly, the liquid crystal in this invention has an electrically controlled birefringence effect, which can be adjusted for different wavelengths to obtain different intensity focal outputs. This electrically controlled intensity adjustment function is not available in traditional diffractive lenses. This invention utilizes this adjustable focal intensity characteristic to achieve energy distribution of focal points at different wavelengths, which has important value for optical communication and near-eye display fields. Attached Figure Description

[0026] The above and other objects, features and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings.

[0027] Figure 1 Flowchart of the fabrication process for achromatic cascaded liquid crystal geometric phase lenses.

[0028] Figure 2 (a) is a schematic diagram of a dual-layer achromatic cascaded liquid crystal geometric phase lens.

[0029] Figure 2 (b) is a schematic diagram of the azimuth angle of the liquid crystal molecules in the xy plane of the aligned pixel unit and the tilt angle of the long axis of the molecule to the xy plane.

[0030] Figure 3 Simulation diagram of three-wavelength incident light from a double-layer achromatic cascaded liquid crystal geometric phase lens Detailed Implementation

[0031] The invention will now be described in more detail with reference to the accompanying drawings. For clarity, the various parts in the drawings are not drawn to scale. Furthermore, some well-known parts may not be shown in the drawings.

[0032] Many specific details of the invention, such as the structure, materials, dimensions, processing methods, and techniques of the components, are described below to provide a clearer understanding of the invention. However, as those skilled in the art will understand, the invention may be implemented without following these specific details.

[0033] Figure 1 The process flow diagram for fabricating achromatic cascaded liquid crystal geometric phase lenses is shown. The main materials include glass substrate, ITO, optical alignment, liquid crystal, and curing adhesive.

[0034] Specifically, an ITO thin film is deposited on a glass substrate, and a photoalignment layer is spin-coated onto the ITO film. Two such structures are bonded together to form a cavity using a frame adhesive. After exposing the photoalignment layer according to the superlens design principle, liquid crystal is injected, and the cavity is sealed with a curing adhesive. This produces the first liquid crystal geometric phase lens. Then, another blank cell is stacked with the first liquid crystal geometric phase lens to ensure pixel-to-pixel alignment. A second exposure, a second injection, and a second sealing are performed sequentially to obtain a double-layer cascaded liquid crystal geometric phase lens. This double-layer structure can already achieve three-wavelength achromatic aberration. If a similar process is repeated to produce a three-layer cascaded structure, seven-wavelength achromatic aberration can be achieved.

[0035] Figure 2 (a) Further illustrates the structural schematic of a double-layer achromatic cascaded liquid crystal geometric phase lens. When the azimuth angle of the liquid crystal molecules satisfies the distribution conditions of the geometric phase lens, Figure 2 (b) A schematic diagram of a physical model showing two layers of liquid crystal pixels with different azimuth and tilt angles after alignment. The tilt angle of the liquid crystal molecules can be adjusted by applying voltage to achieve the focus intensity modulation function.

[0036] Figure 3 Simulations were performed on a dual-layer cascaded liquid crystal geometric phase lens with linearly polarized light incident at wavelengths of 396.8 nm, 1064 nm, and 632.8 nm. The results show that while the two-layer structure was originally designed for wavelengths of 396.8 nm and 1064 nm, the coupled geometric phase allows a beam of light at a wavelength of 632.8 nm to be focused at the same location. This demonstrates the effectiveness of the method described in this invention.

[0037] As described above, these embodiments of the present invention do not exhaustively cover all details, nor do they limit the invention to the specific embodiments described. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic correction, characterized in that, For wavelength With design wavelength The common focal length f is used to design the orientation of liquid crystal molecules in the first liquid crystal geometric phase lens. The orientation of liquid crystal molecules with the second liquid crystal geometric phase lens The formula is as follows: In the formula, x and y are the center coordinates of each orientation unit on the liquid crystal lens plane, respectively; Two layers of geometric phase lenses are aligned unit-to-unit in a direction perpendicular to their stacking. This aligns the linearly polarized light in the y-direction. The emitted light matrix passes through any aligned liquid crystal alignment cell. It satisfies the following formula in, This is the phase delay. , d is the birefringence of the liquid crystal, and d is the thickness of the liquid crystal layer. Let be a rotation matrix. This represents the phase modulation of light propagating along the fast and slow axes by the liquid crystal; Similarly; This result can be expressed as a combination of levorotatory and dextrorotatory light. Besides the original and The geometric phase distribution also exists The geometric phase distribution, and has Therefore, this coupled geometric phase distribution can... It also produces the same focusing effect; the dual-layer cascaded liquid crystal lens achieves three-wavelength achromatic aberration.

2. The cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic correction as described in claim 1, characterized in that, In addition to the three inherent geometric phase distributions, the three-layer cascaded liquid crystal geometric lens also has three geometric phase distributions due to the pairwise coupling of two lenses and one geometric phase distribution due to the coupling of all three lenses together, for a total of seven different phase distributions, which can achieve seven-wavelength achromatic aberration.

3. The cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic correction as described in claim 1, characterized in that, The amplitude coefficients before different geometric phase terms are respectively Based on the characteristic of liquid crystal molecules to electrically control the birefringence, focal points of different intensities can be obtained by applying different voltages.

4. The cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic aberration function according to claim 1, characterized in that, Other materials that also possess geometric phase modulation capabilities can be applied to cascaded achromatic geometric phase lenses.

5. The cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic aberration function according to claim 1, characterized in that, The cascaded liquid crystal geometric phase lens can also be applied to information steganography. By using a holographic algorithm, the first layer orientation angle distribution can be designed to form an image by calculating the first hologram, the second layer orientation angle distribution can be designed to form an image by calculating the second hologram, and the coupled geometric phase can be designed to form an image by calculating the third hologram, thus realizing different information storage.

6. The cascaded liquid crystal geometric phase lens that achieves adjustable focus intensity and achromatic aberration function according to claim 1, characterized in that, when For monochromatic light incident, the focusing term is ， Therefore, arbitrary elliptic polarization output can be achieved.

7. A method for fabricating a cascaded liquid crystal geometric phase lens that achieves adjustable focal intensity and achromatic function, characterized in that, The cascaded liquid crystal geometric phase lens is the cascaded liquid crystal geometric phase lens as described in any one of claims 1-6, and the method is as follows: S1. Photoalignment layers are prepared on two ITO transparent substrates respectively, and the first liquid crystal cell is obtained by using the traditional liquid crystal cell preparation method. S2. Design the orientation angles of different pixel regions on the light alignment layer to form the geometric phase distribution of the first liquid crystal geometric phase lens, and write the geometric phase using light alignment technology. The pixel size range can be [missing information]. ; S3. Inject liquid crystal into the empty liquid crystal cell and seal it to obtain the first liquid crystal geometric phase lens. S4. Prepare a second liquid crystal cell, and stack and bond the second liquid crystal cell to the first liquid crystal geometric phase lens in the vertical direction using a curing adhesive to form a cascaded structure. Then, follow the same steps as S1-S3 to prepare the second liquid crystal geometric phase lens. S5. Repeating steps 1-3 above can produce a third liquid crystal geometric phase lens, and the first liquid crystal geometric phase lens, the second liquid crystal geometric phase lens, and the third liquid crystal geometric phase lens achieve pixel-to-pixel alignment.

8. The method for fabricating a cascaded liquid crystal geometric phase lens with adjustable focal intensity and achromatic function according to claim 1, characterized in that, When used with a single wavelength, the control voltage adjusts the phase delay of the liquid crystal in different cascaded layers to maximize its amplitude coefficient, thus maximizing the focal intensity, and the beam of that wavelength will be focused at the set focal point. When used with multiple wavelengths, the phase delay is adjusted to have a suitable amplitude coefficient for each wavelength, so that beams of multiple wavelengths can be confocalized.

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