Beam shaping device with improved performance

Abstract

Liquid crystal (LC) beam control devices utilize dispersion-shaping (DS) half-wave plates (HWPs) with specific physical properties to allow broadened beams to maintain significantly better color cohesion. This paper describes the advantages of using HWPs with appropriate thickness and birefringence, which makes them inefficient in the blue wavelength spectrum, thus reducing blue photon loss at the center of the broadened beam. This paper also describes combinations of vertically aligned LC cells and DS HWP structures for reducing color separation, accelerating relaxation time, and reducing ground-state scattering.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority to U.S. Provisional Patent Applications No. 63 / 019,707, filed May 4, 2020, and No. 63 / 080,519, filed September 18, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This patent application relates to a liquid crystal beam control device, and in particular to reducing color separation in a broadened beam. Background Technology

[0004] Liquid crystal (LC) beam control devices are known in the art. Some such devices use patterned electrodes on an LC cell to arrange the alignment of LC molecules within the cell. By changing the alignment of the LC molecules to a desired orientation, the effective refractive index of the material is locally altered, and thus the beam passing through the cell can be controlled. While using such devices to control the beam can be advantageous, several problems exist that affect their use. These problems may include limited degree of angle control, poor quality of beam intensity distribution, excessive angular color separation, etc.

[0005] Many specific applications using “smart” lighting systems will benefit from the use of LC beam control devices. For example, light-emitting diode (LED) lighting sources are increasingly used in architectural lighting and the automotive industry. However, in most cases, the parameters of these lighting systems (diffuseness, divergence, glare, direction, etc.) are fixed. The ability to dynamically control some or all of these parameters without any mechanical or electromechanical systems offers significant advantages (e.g., reduced complexity, easier maintenance, etc.). An example of a device that significantly benefits from such LC beam control devices is an automotive lighting system that automatically controls divergence when it senses the car moving in the opposite direction to avoid disturbing other drivers. Further examples include residential and architectural lighting, as well as Li-Fi technologies, which may require the ability to steer light and focus / broaden the light source.

[0006] However, some fundamental problems need to be addressed before current LC beam control equipment can be optimally used for certain applications. One such problem is angular color separation caused by the beam broadening effect of LC equipment. This fundamental problem, set by standard multi-LC units acting in two different polarization directions, results in a non-uniform white color throughout the broadened beam. Typically, the center of the broadened beam will have fewer blue and red photons compared to the rest of the beam. This is usually due to the birefringence of typical LC materials, which is higher in the shorter wavelength (blue) spectrum. Therefore, this higher birefringence can lead to chromatic aberration: more blue photons will be affected by the operation of the LC unit compared to those experienced by green and red photons (i.e., more blue photons will be broadened compared to red and green).

[0007] This problem is particularly important in the case of architectural lighting because the broadened beam will have an undesirable color change between the center and the sides. This color change is often noticeable enough to be visually perceptible, and thus hinders the use of LC beam control devices (which could otherwise be beneficial) in some applications. Summary of the Invention

[0008] The applicant discovered that using a dispersion-shaping (DS) half-wave plate (HWP) with specific (unique) physical properties at the center of a multi-LC unit configuration allows the broadened beam to maintain significantly better color cohesion. The applicant found that selecting an HWP material with a specific thickness and birefringence (which makes it less efficient at polarization rotation in the blue wavelength spectrum) reduces blue photon loss at the center of the broadened beam when used with a standard LC beam broadening unit, which typically broadens blue light better than green and red light. This inevitably leads to a reduced color change at the beam center and thus better preservation of the so-called correlated color temperature (CCT) at the beam center. Furthermore, because fewer blue photons are scattered to the sides of the broadened beam, the perceived color separation between the center of the broadened beam and the rest of the broadened beam is reduced.

[0009] The applicant also discovered that by combining the DS HWP with a homeotropic oriented LC unit structure, the resulting LC device not only reduced color changes and separation, but also further reduced ground-state scattering of the beam.

[0010] Furthermore, the applicant found that further use of internal electrodes on both sides of each LC cell (with DS HWP and vertically aligned LC alignment) allows for the resolution of the slow relaxation time problem, while also ensuring better CCT cohesion and reduced ground state scattering.

[0011] LC-LC beam control devices using DS HWPs with specific physical properties allow broadened beams to maintain significantly better color cohesion. This paper describes the advantages of using HWPs with width and birefringence, which makes them inefficient in the blue wavelength spectrum, thus reducing blue photon loss at the center of the broadened beam. This paper also describes combinations of LC cells and DSHWP structures for reducing color separation, accelerating relaxation time, and reducing ground-state scattering.

[0012] A half-wave plate (HWP) can take the form of a single thin film, such as a polycarbonate-based polymer film known in the art. It can also be made in the form of two quarter-wave plates, which may be slightly tilted relative to each other to manage the dispersion characteristics of the component. The function of the HWP can also be accomplished by a liquid crystal layer twisted at 90 degrees to ensure broadband polarization rotation. Using a liquid crystal-based HWP, it can be electrically controlled to allow the polarization rotation to be switched ON and OFF for additional control. In all cases, the HWP is chosen for its efficiency in polarization rotation, which complements the color separation of the beam-broadening LC modulation device to provide better preservation of the so-called correlated color temperature (CCT) at the beam center.

[0013] In some embodiments, an LC beam modulation apparatus is provided having at least one tunable LC unit having an anisotropic (polarization-sensitive) LC material whose refractive index is variable in the visible spectrum, such that beam modulation has a first wavelength dependence, and the LC beam modulation apparatus having a polarization rotation element having a second wavelength dependence of rotation efficiency, the second wavelength dependence being the opposite of the first wavelength dependence. The polarization rotation element may be an HWP, and the LC beam modulation apparatus may include at least two tunable LC units arranged on opposite sides (before and after) of the HWP.

[0014] In some embodiments, at least one tunable LC cell includes a vertically aligned LC material and an electrode arrangement that causes the LC molecules to be reoriented when energized to change the effective refractive index distribution in the cell.

[0015] In other embodiments, the polarization rotation element is a quarter-wave plate, and the device also includes a reflector for reflecting light passing through the quarter-wave plate back through the quarter-wave plate and then back through at least one tunable LC unit.

[0016] In some embodiments, the device is configured to broaden the beam, while in other embodiments, it can perform beam steering or focusing. The device can be configured to broaden the beam in all directions, in a specific direction, or simultaneously in two vertical directions, or in a selected direction of two directions. Attached Figure Description

[0017] The invention will be better understood through the following detailed description of embodiments thereof with reference to the accompanying drawings, in which:

[0018] Figure 1A is a schematic diagram of a prior art LC beam control device, which includes four LC units whose molecules are locally averaged to be in-plane ground state oriented (the so-called guide n is parallel to the surface of the unit substrate).

[0019] Figure 1B is a schematic diagram of a prior art LC beam control device, which includes four LC units and a dynamic (electrically controllable) polarization rotator between each group of two LC units.

[0020] Figure 1C is a schematic diagram of an exemplary prior art setup of an LC beam control device having a light source, a reflector / collimator, and a dynamic LC beam shaper;

[0021] Figure 1D is a graph showing the CCT loss at the center of the broadened beam for different degrees of beam broadening (corresponding to different excitation levels of the LC unit);

[0022] Figure 2 This is a view of an exemplary HWP with a birefringence constant (Δn) and a given thickness (L);

[0023] Figure 3A This is a graph showing numerical examples of HWPs that work effectively in the blue light spectrum;

[0024] Figure 3B This is a graph showing numerical examples of HWPs that work effectively in the green light spectrum;

[0025] Figure 3C This is a graph showing numerical examples of HWPs that work effectively in the red light spectrum;

[0026] Figure 4 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having a "finger-like" (linear, interdigitated) electrode on only one of its inner surfaces, and these electrodes having a vertical orientation for the different units, and the LC beam control device includes an HWP placed between the two units;

[0027] Figure 5This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having a "finger-like" (linear, interdigitated) electrode on only one of its inner surfaces, and these electrodes having a parallel orientation for the different units, and the LC beam control device includes an HWP placed between the two units;

[0028] Figure 6 This is a schematic diagram of an exemplary LC beam control device, which includes four vertically aligned LC units (two groups of two units each), each group of two units having a vertical electrode direction, and the LC beam control device includes a central HWP.

[0029] Figure 7 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having a finger-like (linear, interdigitated) electrode on a substrate and a uniformly transparent electrode on a substrate on opposite sides of the same LC unit, and the LC beam control device includes a central HWP.

[0030] Figure 8 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having finger-like (linear, interdigitated) electrodes on two substrates on opposite sides of the same LC unit, and the LC beam control device includes a central HWP.

[0031] Figure 9 It is a graph showing the reduction in scattering across the entire visible light spectrum between a prior art "classic" device (with a planar oriented LC) and the design proposed in this application;

[0032] Figure 10 This is a schematic diagram of an exemplary LC beam control device for operation in reflection mode, which includes two vertically aligned LC units having vertical finger-like (linear, interdigitated) electrode directions, a quarter-wave plate, and a reflector;

[0033] Figure 11 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having two substrates with vertical finger (linear, interdigitated) electrode directions, and the LC beam control device includes a half-wave plate between the two vertically aligned LC units and rotation during alignment of the second vertically aligned LC unit.

[0034] Figures 12A to 12F It is a view of beam broadening in different directions as produced by an exemplary LC beam control device; and

[0035] Figure 13 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having two substrates with dual vertical electrode regions. Detailed Implementation

[0036] As described in the prior art, a beam control device is an optical device that controls the refracted output beam relative to beam divergence or beam direction. Controlled beam divergence is a special case of beam control that provides beam focusing and defocusing. Beam direction control can be used for beam steering purposes. Beam control devices that provide a combination of beam diffusion, beam divergence / convergence, or beam direction control are generally referred to herein as beam shaping devices.

[0037] In liquid crystal (LC) beam control devices, an electric field is typically used to control the molecular orientation within the LC cell. The electric field can be modulated (temporally and spatially) by preferably supplying power to transparent electrodes on one or both sides of the LC cell, such that the resulting electric field modulates the orientation of the LC molecules as needed. Changes in molecular orientation affect the local refractive index of the LC and may generate refractive index gradients throughout the entire LC volume (in the lateral / transverse and longitudinal directions).

[0038] Nematic LC layers can typically influence a single polarization component of incident unpolarized light. Therefore, to modulate unpolarized light, two or more orthogonally oriented LC layers are often used. Natural or unpolarized light can be considered as consisting of two orthogonally polarized beams, one of which will be modulated by a first LC layer, and the second (perpendicular) polarization by a second LC layer. Additional LC layers can be used when a portion of an LC device (e.g., a half-wave plate (HWP)) provides rotation of the plane of linear polarization, allowing the additional LC layers to act on different polarization planes.

[0039] Referring now to Figure 1A, which is a schematic diagram of a prior art LC beam control device comprising four LC units having in-plane orientation of their guides n. This embodiment consists of four units (each unit comprising two substrates and internal LC material). The guides n of the LC material in each unit are in-plane of the substrate (indicated by the slanted bold black arrows in each unit). Also shown are units with so-called "in-plane switching" parallel (or finger-like or interdigitated) linear electrodes (represented by blue and empty rectangles) on different substrates, aligned relative to the "plane" of the molecules (at +45 or -45 degrees relative to the in-plane electrodes). In this particular case, electrodes are only present on the first substrate of each unit, and no electrodes are present on the second substrate.

[0040] In this configuration, light propagates from left to right along the +x axis. Therefore, the two perpendicular polarizations of the beam along the y and z axes can be transformed by a combination of multiple units. Depending on the type of transformation desired, the electrodes of selected LC units can be activated (i.e., not all units need to be activated to broaden the beam in a plane).

[0041] As described in this paper, using this configuration of LC devices leads to several problems (color separation and color alteration, slow relaxation of light, and high ground-state scattering). These may all be related to the same factor: the fact that the guide n is aligned in the plane of the substrate. This results in very high dispersion of the LC material (perceived by incident light) and light scattering. Furthermore, natural relaxation of molecular reorientation is required to return to an unperturbed state (in the plane of the substrate).

[0042] Figure 1B illustrates another embodiment of a prior art LC beam control device using a configuration of four LC units and a polarization rotator at a set center. In this prior art embodiment, the rotator (e.g., HWP) can be dynamically controlled or can be a passive element. This configuration allows the LC device to broaden the beam in either a vertical or horizontal line if only one pair of LC units is powered. It can also broaden the beam in both directions when all units are powered. In these applications, the polarization rotator is typically chosen to rotate the light wave by 90 degrees, and it must be as wide as possible in bandwidth so that the second pair of LC units can broaden the polarization of light not broadened by the first pair of LC units.

[0043] Compared to the in-plane average molecular arrangement of Figure 1A, the embodiment of Figure 1B has also been described in the prior art as an alternative for LC cells employing vertical alignment. However, this configuration of the LC cell with a rotator does not solve the problems of color separation and color change in the broadened beam.

[0044] Figure 1C is a schematic diagram of an exemplary prior art setup of an LC beam control device, which includes a light source (typically a diode laser or an LED pumping a phosphor layer), a reflector (or base lens) for light collimation, and a dynamic LC beam shaper for beam broadening. As described above, and without any variable control over the light source (e.g., controlling the ratio of blue / green / red photons), the resulting beam typically exhibits noticeable color separation. Figure 1D illustrates the color change (at the beam center) of such a prior art device as a function of the broadening level.

[0045] Figure 1D illustrates the loss of correlated color temperature (CCT) at the center of the broadened beam for different degrees of broadening. CCT is a well-known method for representing the perceived color that best approximates a given stimulus under the same brightness and specified viewing conditions. In the visible light spectrum, typical color temperatures exceed 5000K for bluish ("cool") colors, are in the range of 2700–3000K for yellowish colors, and are below 1500K for reddish ("warm") colors.

[0046] Therefore, the CCT loss shown in Figure 1D is significant, varying from 0K when the LC broadening device is not powered to 300K for broadening more than 20 degrees. In architectural lighting applications, lower color temperature light (i.e., “warm light”) is typically used to promote relaxation in a space, while higher color temperature light (i.e., “cool light”) is typically used to enhance attention. Therefore, it is important to select specific color temperature lighting for the designed space, and the device providing beam control for the lighting system should not significantly alter the color of the light (ideally, this alteration should be small or around 50K). This problem can be exacerbated by the fact that prior art LC broadening devices typically exhibit this color change primarily in the center of the broadened beam rather than in the surrounding light. Therefore, the color change may be more visually perceptible because the color of the beam is not constant for each light source.

[0047] The applicant discovered that in dynamic lighting applications (such as the prior art embodiment in Figure 1B), shorter wavelengths (blue light) are more affected than longer wavelengths (red light) (by broadening through the LC device). This is why blue light “loss” is observed at the center of the broadened beam, and therefore, it is the primary cause of color change. The applicant also discovered that using an HWP designed primarily for green and / or red light can significantly reduce the aforementioned CCT variation problem compared to a standard broadband HWP. In this case, the HWP may not function as a “good HWP” for blue light (short wavelengths). In other words, the polarization of these short wavelengths will not be fully rotated (it will be partially rotated and partially transformed from linear polarization to elliptic polarization), and therefore, it will not be effectively further broadened by the following HWP LC unit (in an extreme example, if the HWP does not rotate polarization at all, then the following unit will not broaden further). Therefore, these short wavelengths will be broadened less, and there will be less blue light loss at the center of the beam. Therefore, if this process is balanced with the broadening process of the LC device (dispersion due to the birefringence of the LC), the CCT will not be strongly affected.

[0048] Figure 2This is a view of an exemplary thin film of an HWP having optical birefringence (Δn) of its material and a given thickness (L). It is important to note that the material of an HWP typically also has its own dispersion. As described herein, using an HWP material with an appropriately chosen thickness and birefringence (and its dispersion) makes the HWP inefficient at blue light wavelengths, thus allowing for reduced CCT variations in broadened LC devices. The thin film of the HWP has birefringence (Δn) for light propagation and two polarization modes (ordinary and special) with a relative phase retardation G = 2πLΔn / λ; where λ is the wavelength of light in vacuum, L is the thickness of the birefringent film, and Δn is its birefringence value, which depends on λ due to the material's natural dispersion.

[0049] If the value of G equals π (≈3.14 rad) or π + 2π*m (where m = 0; 1, 2, 3, ...), then the HWP rotates the linear polarization plane of the input light (while maintaining the linear polarization state). Therefore, if the input polarization plane is oriented at 45 degrees (relative to the birefringence axis of the HWP), the linear polarization plane of the output beam will be oriented at -45 degrees (thus, we have a 90-degree flip). Otherwise, when G ≠ π, the film will not function like the HWP, and it will deform the polarization state (e.g., from linear to elliptical) instead of rotating it.

[0050] In all known applications of HWP, scientists and engineers have sought to obtain a curve of G versus light wavelength λ that is as flat as possible across the spectrum (see [link to HWP]). Figures 3A to 3C ), to maintain the condition G≈π for all λ. This means that the so-called ideal "wideband" operation (the flatter the HWP, the more expensive it is; there are "low-order" and "high-order" HWPs with different λ dependencies) is possible.

[0051] Figure 3A , Figure 3B and Figure 3C The graph presents three cases of simulated material selection (birefringence and wavelength) to illustrate HWP, showing the curve of a typical HWP. Figure 3A It works as a good HWP for blue light (wavelengths between 0.35μm and 0.45μm, indicated by dashed rectangles). Figure 3B It works as a good HWP for green light (wavelengths between 0.45 μm and 0.55 μm), and Figure 3C It works as a good HWP for red light (wavelengths between 0.56 μm and 0.7 μm).

[0052] Therefore, the HWP can be shaped in a way that compensates for blue light loss. For example, in an extreme case, if the HWP only rotates the green and red light (but not the blue light), only half of the incident (original) natural unpolarized blue light will be broadened (through the first LC unit), while the other half will travel through the system without broadening. This results in significantly more blue light remaining at the beam center, while the green and red light will undergo 100% broadening (both their polarization components are broadened). Thus, the DS HWP allows control of the device's CCT by selecting the dispersion characteristics of the two LC units and the birefringence and thickness of the HWP material used.

[0053] Now for reference Figure 4 , Figure 4 An exemplary LC beam control device is shown, comprising a central HWP39 and two vertically aligned LC units having vertical electrodes 35, 37. As described herein, the performance of the LC beam control device is improved by using vertically aligned LC units (guides n are perpendicular to unit substrates 31, 33, as indicated by thick arrow n), such as the embodiment described in FIG1A.

[0054] In the device's ground state, using vertical alignment, incident light traveling through the LC device will have a "normal" polarization mode and will therefore suffer less dispersion and less light scattering (see [reference]). Figure 9 ).

[0055] like Figure 4 As shown, the basic unit of the vertically aligned LC device consists of two LC units and a “specific” DS HWP 39 with an anisotropic axis oriented at 45° (relative to the in-plane switching electrode pair). In this embodiment, the electrode pairs 35, 37 of the different units are vertical (“vertical” in the input unit and “horizontal” in the output unit), but they can also be parallel, depending on the desired function of the device.

[0056] exist Figure 4 In this embodiment, the y-polarization component of the input light (propagating in the +x direction) will not be affected by the first unit (LC unit 1). However, the z-polarization component of the input light will be affected. In fact, the LC unit 1 of this device ( Figure 4 This will focus the z-component of the input light polarization (because a pair of electrodes 35 and 37 are oriented parallel to the y-axis). This will further broaden the z-component in the "horizontal" plane xz.

[0057] Then, after passing through HWP 39, the two input polarization components (z and y) are rotated 90° (through HWP 39), and the original z-polarization component is again affected by LC unit 2 (focused and broadened in the "vertical" xy plane). The original y-polarization component will also be unaffected by the second LC unit. Therefore, this device can be used to broaden linearly polarized (in the z direction) light in two planes (xz and xy). Furthermore, compared to prior art LC devices, when the DS HWP 39 has poor HWP characteristics in the blue light spectrum (as described in this paper), Figure 2 and Figures 3A to 3C As described, color separation may be significantly reduced. However, the original y-component of light will not be affected, and therefore we will observe a "hot spot at the center of the beam," which is generally undesirable.

[0058] It should be understood that if the LC beam broadening device has an LC material that broadens red light more than blue and green light, the HWP can be designed to favor polarization rotation of blue and green light while reducing rotation of red light, resulting in the same CCT stabilization effect.

[0059] Figure 5 This is another embodiment of an exemplary LC beam control device including a central DS HWP 39 and two vertically aligned liquid crystal cells. This embodiment is... Figure 4 The alternative assembly of the embodiment presented herein, wherein electrodes 35 and 37 are in the same orientation for both LC cells.

[0060] In this embodiment, the original y-polarization of light (propagating in the +x direction) will not be affected by the first LC unit. However, the z-polarization of light will be affected by the first LC unit (focused and broadened on the "horizontal" plane xz). Then, after passing through HWP 39, both polarizations will be rotated 90° by HWP 39. Therefore, the original z-polarization will now be vertically oriented and will not be affected by the second LC unit, while the original y-polarization component will become parallel to the z-axis and will therefore be focused and broadened by the second LC unit in the same "horizontal" plane xz. Thus, the LC device of this embodiment can be used to stretch (broaden) two polarized lights in a plane (xz) (allowing operation with unpolarized light sources). Furthermore, compared to prior art LC devices, color separation can be significantly reduced when the DS HWP39 has poor HWP characteristics in the blue light spectrum.

[0061] Those skilled in the art will understand that Figure 4 and Figure 5 The embodiments presented describe beam broadening for one or two polarization components, and different electrode arrangements on the LC unit substrate can be used to broaden one or more polarizations of the beam on one or more desired planes.

[0062] Figure 6 Another embodiment of an exemplary LC beam control device is shown, comprising four vertically aligned LC units and a central DS HWP39. This LC beam control device is configured to operate in conjunction with... Figure 4 and Figure 5 Similar to what is described in [the text], but allows for the broadening of unpolarized light in two planes.

[0063] In this embodiment, the original z-polarization of light (propagating in the +x direction) will be affected by unit 1 (focused and broadened in the xz plane), while the original y-polarization of light will be affected by unit 2 (focused and broadened in the xy plane). Therefore, each polarization component will be broadened in a specific plane (defined by the orientation of the finger electrodes).

[0064] Then, after passing through HWP 39, the two polarizations will be rotated by 90° by HWP 39, and the original z-polarized component of the light will become parallel to the y-axis and will therefore be affected by unit 4 (focused and broadened in the xy plane). At the same time, the original y-polarized component is now parallel to the z-axis and will therefore be affected by unit 3 (focused and broadened in the xz plane).

[0065] Therefore, this device can be used to stretch (broaden) the two polarizations of light in two planes (xz and / or xy) (i.e., operate with an unpolarized light source). Clearly, different electrode pairs can be activated individually in different cells, thus allowing the LC device to perform more complex functions.

[0066] That is, if only the electrode of unit 1 is activated, only the input z polarization will be affected and broadened in the xz plane. Similarly, activating the electrodes of both units 1 and 3 will cause the two input polarization components (along the y and z axes) to broaden in the same xz plane.

[0067] Alternatively, the broadening of light in the xy plane can be accomplished by powering the electrodes of units 2 and 4. These electrodes are the only working electrodes in each LC unit and can be individually controlled using the device, which can start from a circular beam and produce various shapes (larger circles, linear, rectangular, etc.).

[0068] Compared to planar alignment in existing technologies (e.g., Figure 1A), using vertically aligned LC cells in a device can improve dispersion and scattering because the incident light has ordinary polarization, thus reducing dispersion characteristics and scattering. However, if appropriate electrode and driving techniques are used, the vertically aligned LC cell structure can also help reduce the time required to return to the original orientation compared to natural relaxation (i.e., the time it takes for LC molecules to return to their initial alignment after the electrode cycle returns to a non-powered state).

[0069] Right now, Figure 7 This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each having interdigitated finger electrodes on a substrate and uniformly transparent electrodes 41 on the substrate on opposite sides of the same LC unit, and the LC beam control device includes a central HWP.

[0070] Therefore, in order to accelerate the relaxation process and thus reduce the operating time of the device, a uniform transparent electrode 41 can be added to the second substrate of each LC unit, such as... Figure 7 As illustrated in the embodiment, in this case, the same (e.g., high U) potential is applied to the electrodes 35, 37 (U1 = U2 = Uh) of the first substrate, while a different potential (e.g., U = Ul0) is applied to the uniform transparent electrode 41 of the second substrate, allowing the LC cell to quickly return to its original vertical alignment. Although the resulting field may not be perfectly uniform, this still helps to force the LC's guides back to the orientation of the vertical alignment. This results in "forced relaxation" rather than natural relaxation and provides a significant transition time advantage.

[0071] The applicant characterized this difference in transition time between natural relaxation and forced relaxation, and found that forced relaxation can reduce the transition time by up to 50% for a relatively moderate voltage V = Uh - Ul = 10 Volts. For example, using exemplary LC beam control devices (such as...) Figure 7 As shown, the test results showed a natural relaxation time of 0.46 seconds (i.e., when the uniform transparent electrode 41 is not used and the voltage between electrodes 35 and 37 is simply removed). In contrast, applying a voltage between electrodes 35 and 37 (with the same potential) and the uniform transparent electrode 41 resulted in a transition time of 0.24 seconds. Those skilled in the art will understand that a lower transition time can be achieved by using a higher voltage.

[0072] Therefore, in a vertically aligned LC beam control device, in addition to the DS HWP 39, using a uniform transparent electrode 41 as electrodes 35 and 37 on opposite substrates can significantly reduce the transition time of the LC unit.

[0073] Figure 8 Is with Figure 7 The embodiment is a schematic diagram of an exemplary LC beam control device similar to that described in the embodiment. This embodiment includes two vertically aligned LC units, each having reciprocating electrodes 35, 37 on two substrates (instead of uniform transparent electrodes on a single substrate), and also includes a central HWP 39.

[0074] In this embodiment, to accelerate relaxation, the same (e.g., high) potential can be applied to the electrodes 35 and 37 (U1 = U2 = Uh) on the first substrate of the cell, while different potentials (e.g., low, U = 0) are applied to the two electrodes 35' and 37' on the opposite substrate (U3 = U4 = 0). Therefore, the resulting electric field will be more non-uniform within the cell, but even so, it helps reduce the time required to return to the original vertical alignment. Once the main portion of relaxation is obtained, the electric field can be completely removed to obtain the true ground state.

[0075] Furthermore, this embodiment ( Figure 8 The LC unit allows for individual control of the electrodes on each substrate to perform specific additional functions (e.g., generating various forms of broadened beams). For example, broadening of light in only one (e.g., xz or horizontal) plane can be accomplished by activating only the electrode pairs 35', 37' on the second (or exit) substrate of each LC unit. In this case, the input light with the original z-polarized component will be broadened in the xz plane by unit 1, then rotated 90 degrees by HWP 39, and will not be affected by unit 2. Simultaneously, the original y-polarized component will not be affected by unit 1, will be rotated 90 degrees by HWP 39, and will then be broadened in the same xz plane by the action of electrodes 35', 37' on the second substrate of unit 2. Therefore, both polarization components of the input light will be broadened (or angularly stretched) in the horizontal (xz) plane.

[0076] Alternatively, electrodes 35, 37 (on the first (or inlet) substrate of both units can be used only. Figure 8 This allows for similar single-plane broadening of unpolarized light in the vertical direction (in the vertical or xy plane).

[0077] It is worth noting that the situation is different if we activate all the electrodes simultaneously or with phase shifting, such as 0 and 180 degrees at the inlet substrate and 90 and 270 degrees at the outlet substrate. In this case, the original y (vertical) polarization component of the input beam will be broadened in the vertical xy plane by the lens structure generated by the LC inlet plate of unit 1 (due to electrodes 35, 37), and then gradually rotated (approximately 90 degrees) while propagating within unit 1. Before reaching the outlet substrate (with electrodes 35', 37'), it will then be broadened in the horizontal xz plane by the outlet plate of the same unit 1. Therefore, unit 1 will broaden the original y polarization component in both planes. Furthermore, this polarization component (original y) will be rotated by 90 degrees by HWP 39, and the same broadening process will be performed by unit 2. Therefore, the original y polarization component will be broadened twice in both planes. Conversely, the original horizontal (or z) polarization component will not be significantly affected by the overall device. Therefore, we will observe an intensity hotspot at the center of the transmitted beam.

[0078] Therefore, in vertically aligned LC beam control devices, in addition to DS HWP 39, using electrodes on each (inlet and outlet) substrate of the LC cell can not only significantly reduce color separation, but also further reduce the ground state light scattering and transition time of the LC cell.

[0079] As described in this paper, the use of vertically aligned LC unit cell structures helps to reduce ground-state scattering of the beam. Figure 9 This is an experimental graph showing the reduction in scattering between prior art devices and the design proposed in this application across the entire visible light spectrum. Figure 9 The curves for "Prior Art (Classic S1)" and "Proposed Design (Fast S1)" are shown. The prior art curve illustrates the scattering of a prior art LC beam control device in the configuration described in Figure 1A, while the curve for the proposed design curve shows the scattering of a device using a vertically aligned LC unit structure. It can be clearly observed from the figures that the new design significantly reduces scattering (by up to 10% in the blue light wavelength spectrum). Furthermore, a further reduction in dispersion (the scattering difference between blue and red light) can be seen, which is significantly reduced in the new design.

[0080] Although the embodiments described above operate in transmission mode, it is understood that a suitable quarter-wave plate 39' can be used instead of the HWP, and a reflector can be used instead of the second LC unit to provide beam broadening in reflection mode. Figure 10 An embodiment of the reflection mode is illustrated. This reflection mode device can be used to redirect a source beam toward a desired target area while providing beam broadening. During reflection, the beam propagates twice through the quarter-wave plate, thus achieving the HWP function with the results described above.

[0081] Now for reference Figure 11 , Figure 11This is a schematic diagram of an exemplary LC beam control device, comprising two vertically aligned LC units, each having two substrates having perpendicular finger (linear, interdigitated) electrode orientations. The LC beam control device includes a half-wave plate 39 between the two vertically aligned LC units and rotation during alignment of a second vertically aligned LC unit. In such an embodiment, the second LC unit can be rotated more than 90° compared to the first LC unit. An additional rotation can be approximately + / - 2.5°, such that the second LC unit can have approximately 92.5° of rotation compared to the first LC unit. Similar to other embodiments described herein, each LC unit substrate can have interdigitated linear electrodes and different vertical orientations. For example, the first substrate of the first LC unit can have generally vertical interdigitated electrodes 35, 37, while the second substrate of the first LC unit can have generally horizontal (i.e., perpendicular to the electrodes on the first substrate) interdigitated electrodes 35', 37'. Doubling the number of elements increases beam modulation, and a rotational offset of approximately 2.5 degrees reduces beam artifacts, i.e., improves the smoothness of the beam intensity curve.

[0082] The second LC unit can have a substrate structure similar to the substrate structure described for the first LC unit. Figure 11 In one embodiment, an HWP 39 may be included between the first LC unit and the second LC unit. Therefore, the beam can be steered and / or broadened in any direction by activating some or all of the electrodes.

[0083] Figure 12 is from Figure 11 A comprehensive view of the beam broadening in different directions produced by an exemplary LC beam control device. Figure 12A It shows equally strong (i.e., 10V) broadening in both directions. Figure 12B The diagram shows broadening in the Y direction (i.e., 10V) and no broadening in the X direction. Figure 12C This illustrates applying 5V in the X direction while simultaneously applying 2.5V in the Y direction. Figure 12D This illustrates applying 10V in the X direction and 0V in the Y direction. Figure 12E It shows equally weak broadening in both directions (i.e., 3V), and Figure 12F It shows that 2.5V is applied in the X direction and 5V is applied in the Y direction.

[0084] Now for reference Figure 13 , Figure 13This is a schematic diagram of an exemplary LC beam control device, which includes two vertically aligned LC units, each LC unit having two substrates with dual vertical electrode regions, and the LC beam control device including an HWP between the first and second LC units. To improve the symmetry of beam broadening or steering, substrates with more than one active region can be used. Figure 13 The embodiments illustrate a contiguous dual-region substrate with electrodes vertically arranged between these regions. Furthermore, the second substrate of the LC cell may also have spatially matched dual regions, with a vertical electrode orientation compared to the matched regions on the first substrate (e.g., the first region in the first substrate may have horizontal electrodes, and its matched first region in the second substrate may have vertical electrodes). As described herein, the electrodes may be interdigitated, and the second LC cell may be rotated more than 90° compared to the first LC cell (e.g., it may be rotated about 92.5° or 87.5°).

[0085] Those skilled in the art will understand that, without departing from the teachings of this disclosure, the substrate may have any number of regions.

Claims

1. A liquid crystal (LC) beam modulation device comprising: At least one tunable LC unit component, the at least one tunable LC unit component having an LC material whose refractive index is variable in the visible spectrum, such that beam modulation has a first wavelength dependence, thereby short-wavelength photons are more affected by beam modulation than green photons and long-wavelength photons. as well as A polarization rotation element having a second wavelength dependence of rotation efficiency, which is opposite to the first wavelength dependence, resulting in lower polarization rotation efficiency of the polarization rotation element in the short wavelength spectrum.

2. The apparatus of claim 1, wherein, The polarization rotation element is a half-wave plate (HWP), and the at least one tunable LC unit assembly includes at least two tunable LC units arranged on opposite sides of the half-wave plate (HWP).

3. The apparatus of claim 2, wherein, Two tunable LC units are arranged on each side of the half-wave plate (HWP).

4. The apparatus of any one of claims 1, 2, or 3, wherein, The at least one tunable LC unit assembly includes vertically aligned LC material and an electrode arrangement that causes the LC material to change its refractive index when energized.

5. The device according to claim 1, wherein, The polarization rotation element is a quarter-wave plate and also includes a reflector for reflecting light passing through the quarter-wave plate back through the quarter-wave plate and then back through the at least one tunable LC unit assembly.

6. The apparatus of any one of claims 2 to 5, wherein, The electrode orientations of two of the at least two tunable LC units are oriented at 92.5 or 87.5 degrees relative to each other.

7. The apparatus of any one of claims 1 to 6, wherein, The at least one tunable LC unit component includes at least two interconnected regions, which are operable to act on at least two different optical poles.

8. The apparatus of any one of claims 1 to 7, wherein, The device is configured to broaden the beam.

9. The apparatus of claim 8, wherein, The device is configured to broaden the light beam in one direction.

10. The apparatus of claim 8, wherein, The device is configured to broaden the beam in two directions simultaneously.

11. The apparatus of claim 8, wherein, The device is configured to broaden the beam in one of two selected directions.

12. The apparatus of claim 8, wherein, The device is configured to broaden only one optical polarization.

13. The device according to claim 8, wherein, The device is configured to broaden two optical polarizations.

14. The apparatus of claim 8, wherein, The device is configured to dynamically switch the potential on each of multiple electrode pairs and accelerate the return transition time by applying a potential difference between two substrates in the same LC cell.

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