A large-aperture thin-film imaging device and its fabrication method

Abstract

This invention discloses a large-aperture thin-film imaging device and its fabrication method. The thin-film imaging device includes a liquid crystal polymer layer. Liquid crystal molecules within the polymer layer impart a gradually varying parabolic phase distribution to the wavefront. Wavefront phase modulation is achieved through the principle of liquid crystal geometric phase, where the wavefront phase ψ = 2θ, and θ is the azimuth angle of the liquid crystal molecules in the plane. Arbitrary 0-2π phase manipulation is achieved by arranging the liquid crystal molecules in the 0-pi direction within the plane. Based on the principle of geometric phase, this invention changes the phase of incident polarized light through the arrangement of liquid crystal molecules to achieve positive or negative focal length effects. The liquid crystal material exhibits minimal absorption in the visible to near-infrared range, resulting in high light energy utilization. The fabrication of the thin-film imaging device is simple, requiring only the uniform coating of a light-polarizing sensitive material onto a substrate to form a light alignment layer, followed by light alignment, and finally the coating and curing of the liquid crystal material. Complex steps such as alignment, etching, and transfer are unnecessary, resulting in low processing errors and excellent image quality.

Description

Technical Field

[0001] This invention relates to the field of optical technology, specifically to a large-aperture thin-film imaging device and its fabrication method. Background Technology

[0002] Optical imaging technology has many advantages over other imaging technologies, such as high geometric resolution for target observation and the ability to acquire spectral information of targets. Based on these advantages, space optical imaging technology has become an important development direction in aerospace technology and is widely used in fields such as astronomical observation, Earth observation, and national defense.

[0003] Given the significant importance of developing space optical imaging technology, the demand for large-aperture, high-resolution optical imaging systems is constantly increasing across various application fields, especially for space telescopes. Increasing the aperture of the optical system can significantly enhance its application value. The development trend of astronomical observation is a process of continuously increasing telescope aperture. A large-aperture primary mirror can help space telescopes collect more light, thereby shortening observation time. At the same time, a larger numerical aperture can help improve resolution, enabling clearer resolution of celestial objects. In terms of Earth observation, imaging systems using the optical band, mounted on spacecraft, provide important data on the Earth's surface topography, agricultural conditions, land resources, meteorological information, etc. Increasing the aperture of the optical imaging system can greatly improve Earth observation capabilities, increase resolution, and extend observation distance.

[0004] Reflective optical systems are heavy and large in size, and large-aperture reflective space optical systems are too expensive, pushing the limits of engineering technology in all aspects of manufacturing, launch, use and maintenance.

[0005] Thin-film optical systems constructed using polyimide (PI) thin-film imaging devices can overcome the two major challenges of aperture and weight faced by reflective optical systems. Polyimide thin-film imaging devices are realized through relief micro / nano structures, and the fabrication process involves repeated exposure, development, etching, and transfer steps. On the one hand, the relief micro / nano structure needs to be transferred to the polyimide film through multiple such operations, which leads to a decrease in the precision of the micro / nano structure and affects the imaging effect. On the other hand, polyimide thin-film imaging devices require high-temperature curing at 300°C, and the thermal stress after the film cools further causes deformation of the micro / nano structure, degrading the imaging effect.

[0006] Polyimide material itself is pale yellow, and its transmittance in the visible light band is lower than that of quartz material and UV-cured adhesive, which reduces the system's light energy utilization. Furthermore, polyimide is highly sensitive to humidity; the humidity during ground processing is inevitably higher than the humidity during use in the ambient space, causing the lens to shrink during use. This places stringent requirements on the processing and usage environment. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a large-aperture thin-film imaging device and its fabrication method.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] This invention discloses a large-aperture thin-film imaging device, which includes a liquid crystal polymer layer. The liquid crystal molecules in the liquid crystal polymer layer add a gradually changing parabolic phase distribution to the wavefront. Wavefront phase modulation is achieved through the principle of liquid crystal geometric phase, where the wavefront phase ψ = 2θ, and θ is the azimuth angle of the liquid crystal molecules in the plane. Arbitrary 0-2pi phase manipulation is achieved by arranging the liquid crystal molecules in the plane in the 0-pi direction.

[0010] Based on the above technical solution, the following improvements can be made:

[0011] As a preferred embodiment, the liquid crystal polymer layer is prepared by permanently fixing the liquid crystal phase into a liquid crystal material through cross-linking polymerization.

[0012] As a preferred embodiment, the birefringence Δn of the liquid crystal polymer layer is between 0.05 and 0.25.

[0013] As a preferred option, the imaging aperture of the thin-film imaging device is greater than 0.5m.

[0014] As a preferred option, the phase distribution of the wavefront is one or more of the following phase distribution structures: Fresnel ring, achromatic imaging, and multiplexing imaging.

[0015] As a preferred embodiment, when the phase distribution of the wavefront is a Fresnel ring, the edge structure linewidth of the thin-film imaging device is Δr = λF, where: λ is the operating wavelength, F = f / d, f is the focal length, and d is the thickness of the liquid crystal polymer layer.

[0016] As a preferred embodiment, the thickness d of the liquid crystal polymer layer is obtained by the following formula:

[0017] 2△nd=(2k+1)λ;

[0018] in:

[0019] Δn is the birefringence coefficient of the liquid crystal;

[0020] λ is the operating wavelength;

[0021] k is a coefficient, and k is an integer.

[0022] As a preferred embodiment, the thin-film imaging device further includes a flexible substrate layer for supporting the liquid crystal polymer layer.

[0023] On the other hand, the present invention also discloses a method for fabricating a large-aperture thin-film imaging device, used to fabricate any of the above-mentioned thin-film imaging devices, specifically including the following steps:

[0024] S1: Coat the surface of the substrate with a light polarization-sensitive material;

[0025] S2: Orienting light in a specific polarization direction to a light polarization-sensitive material;

[0026] S3: Coating liquid crystal material to form a liquid crystal polymer layer;

[0027] S4: UV curing, peeling.

[0028] As a preferred embodiment, in S3, the liquid crystal polymer layer reaches a predetermined thickness d by adjusting the concentration of the liquid crystal material, the spin coating speed, and the number of spin coating layers.

[0029] The large-aperture thin-film imaging device and its fabrication method of the present invention have the following beneficial effects:

[0030] First, thin-film imaging devices are based on the principle of geometric phase, which changes the phase of incident polarized light by arranging liquid crystal molecules to achieve the effect of positive or negative focal length.

[0031] Second, liquid crystal materials have virtually no absorption in the visible to near-infrared range, resulting in high light energy utilization.

[0032] Third, the liquid crystal polymer layer has a high degree of cross-linking, thus it is resistant to high temperature, radiation and humidity, meeting the stringent requirements of space imaging.

[0033] Fourth, the thickness of thin-film imaging devices is on the order of micrometers, and the weight of optical elements is orders of magnitude smaller compared to reflective and refractive elements of the same aperture.

[0034] Fifth, the imaging quality of large-aperture transmission optical elements is not sensitive to surface shape errors, and has a high tolerance for manufacturing and processing errors, which is more conducive to maintaining a stable surface shape of the optical system in space.

[0035] Sixth, the fabrication of thin-film imaging devices is simple. It only requires uniformly coating a light polarization-sensitive material on a substrate to form a light alignment layer, then performing light alignment, and finally coating a liquid crystal material for curing. There is no need for complex steps such as alignment, etching, and transfer. Therefore, the processing error is low and the imaging quality is good.

[0036] Seventh, liquid crystal materials can be self-supported and peeled off from the substrate, which facilitates the processing of large-aperture thin-film imaging devices. Moreover, all the above steps are carried out on the same substrate at room temperature, so there is no need to worry about the film being deformed by temperature, humidity or mechanical stretching. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 The optical axis distribution diagram of liquid crystal molecules in the thin-film imaging device provided in the embodiment of the present invention.

[0039] Figure 2 A cross-sectional view of a thin-film imaging device provided in an embodiment of the present invention (with a flexible substrate layer).

[0040] Figure 3 This is a flowchart illustrating the fabrication method of a thin-film imaging device provided in an embodiment of the present invention.

[0041] Wherein: 1-Thin film imaging device; 11-Liquid crystal polymer layer; 12-Flexible substrate layer. Detailed Implementation

[0042] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Using ordinal numbers such as “first,” “second,” “third,” etc. to describe ordinary objects merely indicates different instances of similar objects and is not intended to imply that the objects being described must have a given order in time, space, sequence, or any other way.

[0045] Furthermore, the expression "includes" is an "open-ended" expression, which means only that there is a corresponding component or step, and should not be interpreted as excluding additional components or steps.

[0046] To achieve the objectives of this invention, some embodiments of a large-aperture thin-film imaging device and its fabrication method are provided, such as... Figure 1As shown, the thin-film imaging device 1 includes: a liquid crystal polymer layer 11, in which liquid crystal molecules in the liquid crystal polymer layer add a gradually changing parabolic phase distribution to the wavefront, and wavefront phase modulation is achieved through the principle of liquid crystal geometric phase, the wavefront phase ψ = 2θ, where θ is the azimuth angle of the liquid crystal molecules in the plane, and arbitrary 0-2pi phase manipulation is achieved by arranging the liquid crystal molecules in the plane in the 0-pi direction.

[0047] This invention discloses a large-aperture thin-film imaging device, wherein the thin-film imaging device 1 is a diffractive liquid crystal lens. Based on the geometric phase principle, the wavefront 0-2pi phase is controlled by the change in the molecular mass of liquid crystal molecules in the 0-pi plane. Therefore, the crystal axis orientation of the liquid crystal molecules flexibly manipulates the phase of the incident light. When specific rotationally polarized light is incident, a continuously gradually changing parabolic phase distribution is added to the outgoing wavefront to achieve the effect of positive or negative focal length.

[0048] It is worth noting that the crystal axis orientation of liquid crystal molecules in the large-aperture thin-film imaging device of the present invention can be achieved not only by optical orientation, but also by means of atomic force probe relief orientation and other methods.

[0049] During operation, the thin-film imaging device 1 can work independently or in conjunction with waveplates and polarizers.

[0050] The thin-film imaging device 1 of the present invention is a diffractive liquid crystal lens, in which liquid crystal molecules undergo continuous gradient orientation to achieve continuous alignment of liquid crystal molecule pointing vectors, which greatly improves the lens diffraction efficiency to 95%.

[0051] To further optimize the implementation effect of the present invention, in some other embodiments, the remaining features are the same, except that the liquid crystal polymer layer is prepared by permanently fixing the liquid crystal phase into a liquid crystal material through cross-linking polymerization.

[0052] This liquid crystal material is composed of liquid crystal polymer elements (RM), and has the advantages of high cross-linking density, high light transmittance, and good stability.

[0053] To further optimize the implementation effect of the present invention, in some other embodiments, the remaining features are the same, except that the birefringence Δn of the liquid crystal polymer layer is between 0.05 and 0.25.

[0054] To further optimize the implementation effect of the present invention, in some other embodiments, the remaining features are the same, except that the imaging aperture of the thin film imaging device 1 is greater than 0.5m.

[0055] The imaging aperture of the thin-film imaging device is set according to the actual application requirements of space imaging.

[0056] In some specific embodiments, the imaging aperture of the thin-film imaging device 1 is 0.5m to 20m, or greater than 20m.

[0057] To further optimize the implementation effect of the present invention, in some other embodiments, the remaining technical features are the same, the difference being that, for example... Figure 1 As shown, the phase distribution of the wavefront exhibits a Fresnel ring structure. Figure 1 The short and medium lines represent the directional arrangement of liquid crystal molecules.

[0058] Furthermore, when the phase distribution of the wavefront is a Fresnel ring, the edge structure linewidth of the thin-film imaging device 1 is Δr = λF;

[0059] Where: λ is the working wavelength, F = f / d, f is the focal length, and d is the thickness of the liquid crystal polymer layer.

[0060] This allows for a much lower processing tolerance than refractive or reflective lenses, making it easy to fabricate large-aperture thin-film imaging devices.

[0061] A larger F-number requires lower processing capabilities, but correspondingly, the system's working length is longer. Generally, an appropriate F-number is set according to the working mode. For example, a smaller F-number can be set when using a single-satellite imaging system in space to shorten the working distance; while a larger F-number can be used when using a dual-satellite imaging system to increase the imaging lens aperture and obtain a larger imaging field of view and resolution.

[0062] Since the imaging resolution, aperture, and focal length of thin-film imaging devices are affected by the width of the edge structure, the edge structure width of small F-number thin-film imaging devices is generally on the order of micrometers, which can be achieved through existing optical orientation methods.

[0063] Furthermore, the thickness d of the liquid crystal polymer layer 11 is obtained by the following formula:

[0064] 2△nd=(2k+1)λ;

[0065] in:

[0066] Δn is the birefringence coefficient of the liquid crystal;

[0067] λ is the operating wavelength;

[0068] k is a coefficient, and k is an integer.

[0069] It is worth noting that in other embodiments, the phase distribution of the wavefront can also be other distribution structures such as achromatic imaging and multiplexing imaging.

[0070] To further optimize the implementation effect of the present invention, in some other embodiments, the remaining technical features are the same, the difference being that, for example... Figure 2As shown, the thin-film imaging device also includes a flexible substrate layer 12 for supporting the liquid crystal polymer layer 11.

[0071] The flexible substrate layer 12 does not allow for phase modulation of light waves, and therefore requires good physical properties, good stability, and high transmittance. Materials such as polyimide can be used.

[0072] When using a thin-film imaging device with a flexible substrate layer 12, it can be folded or rolled up before use to reduce the area, and then unfolded when in use.

[0073] On the other hand, embodiments of the present invention also disclose a method for fabricating a large-aperture thin-film imaging device, used to fabricate the thin-film imaging device disclosed in any of the above embodiments, such as... Figure 3 As shown, the specific steps include:

[0074] S1: Coat the surface of the substrate with a light polarization-sensitive material;

[0075] S2: Orienting light in a specific polarization direction to a light polarization-sensitive material;

[0076] S3: Coating liquid crystal material to form a liquid crystal polymer layer;

[0077] S4: UV curing, peeling.

[0078] Furthermore, in S3, the thickness d of the liquid crystal polymer is obtained by the following formula:

[0079] 2△nd=(2k+1)λ;

[0080] in:

[0081] Δn is the birefringence coefficient of the liquid crystal;

[0082] λ is the operating wavelength;

[0083] k is a coefficient, k = 1, 2, 3, ..., k is an integer.

[0084] Furthermore, in S3, by adjusting the concentration of the liquid crystal material, the spin coating speed, and the number of spin coating layers, the liquid crystal polymer layer 11 reaches a predetermined thickness d, so that the diffraction efficiency of the thin film imaging device 1 in the working band reaches its maximum.

[0085] Furthermore, the light polarization-sensitive material is one or more of azo materials, photocrosslinking materials, and photodegradable materials.

[0086] Furthermore, in S1, the substrate is glass or polyethylene terephthalate.

[0087] After being coated with liquid crystal material, the photo-aligning agent, guided by specific polarized light, will align the liquid crystal molecules to form a Fresnel ring structure. When polarized light is incident, it adds a continuously gradually changing parabolic phase distribution to the outgoing wavefront, thereby achieving a positive or negative focal length.

[0088] To facilitate understanding of the present invention, a specific embodiment is described below.

[0089] A thin-film imaging device with an aperture of 5m and a focal length of 10m for a working wavelength of 600nm was fabricated, with a Fresnel imaging lens distribution in phase.

[0090] The relationship between focal length and incident light wavelength is as follows:

[0091]

[0092] Where: r n Let be the radius from the k-th ring to the center of the circle, where k = 1, 2, 3…;

[0093] f is the focal length;

[0094] λ is the incident wavelength.

[0095] The preparation process specifically includes the following steps:

[0096] S1: A light polarization-sensitive material SD1 is spin-coated onto a glass surface, with a thickness of approximately 20 nm.

[0097] S2: The light polarization sensitive material is oriented in a specific polarization direction. Four polarization gray values ​​are taken, which correspond to liquid crystal molecule alignment of 0 degrees, 45 degrees, 90 degrees and 135 degrees respectively. The edge linewidth of this lens is 1.2μm, and the liquid crystal alignment area corresponding to a single gray value is 0.3μm.

[0098] S3: Coating liquid crystal material. For liquid crystal material with Δn = 0.155, according to the half-wave condition, the thickness d of the coated liquid crystal polymer layer is controlled to be approximately 1.935 μm.

[0099] S4: UV curing, peeling.

[0100] The large-aperture thin-film imaging device and its fabrication method of the present invention have the following beneficial effects:

[0101] First, thin-film imaging devices are based on the principle of geometric phase, which changes the phase of incident polarized light by arranging liquid crystal molecules to achieve the effect of positive or negative focal length.

[0102] Second, liquid crystal materials have virtually no absorption in the visible to near-infrared range, resulting in high light energy utilization.

[0103] Third, the liquid crystal polymer layer has a high degree of cross-linking, thus it is resistant to high temperature, radiation and humidity, meeting the stringent requirements of space imaging.

[0104] Fourth, the thickness of thin-film imaging devices is on the order of micrometers, and the weight of optical elements is orders of magnitude smaller compared to reflective and refractive elements of the same aperture.

[0105] Fifth, the imaging quality of large-aperture transmission optical elements is not sensitive to surface shape errors, and has a high tolerance for manufacturing and processing errors, which is more conducive to maintaining a stable surface shape of the optical system in space.

[0106] Sixth, the fabrication of thin-film imaging devices is simple. It only requires uniformly coating a light polarization-sensitive material on a substrate to form a light alignment layer, then performing light alignment, and finally coating a liquid crystal material for curing. There is no need for complex steps such as alignment, etching, and transfer. Therefore, the processing error is low and the imaging quality is good.

[0107] Seventh, liquid crystal materials can be self-supported and peeled off from the substrate, which facilitates the processing of large-aperture thin-film imaging devices. Moreover, all the above steps are carried out on the same substrate at room temperature, so there is no need to worry about the film being deformed by temperature, humidity or mechanical stretching.

[0108] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0109] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "screw connection," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0110] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

[0111] The control method of this invention is to control the device by manually starting and stopping the switch. The wiring diagram of the power element and the supply of power are common knowledge in the field. Since this invention is mainly used to protect mechanical devices, the control method and wiring layout will not be explained in detail.

Claims

1. A large-aperture thin-film imaging device, characterized in that, The thin-film imaging device includes: a liquid crystal polymer layer, wherein the liquid crystal molecules in the liquid crystal polymer layer add a gradually changing parabolic phase distribution to the wavefront, and wavefront phase modulation is achieved through the principle of liquid crystal geometric phase, the wavefront phase ψ=2θ, where θ is the azimuth angle of the liquid crystal molecules in the plane, and arbitrary 0-2pi phase manipulation is achieved by arranging the liquid crystal molecules in the plane in the 0-pi direction. When the phase distribution of the wavefront is a Fresnel ring, the edge structure linewidth of the thin-film imaging device ,in: For the operating wavelength, , d is the focal length, and d is the thickness of the liquid crystal polymer layer.

2. The thin-film imaging device according to claim 1, characterized in that, The liquid crystal polymer layer is prepared by permanently fixing the liquid crystal phase into a liquid crystal material through cross-linking polymerization.

3. The thin-film imaging device according to claim 1, characterized in that, The birefringence Δn of the liquid crystal polymer layer is between 0.05 and 0.

25.

4. The thin-film imaging device according to claim 1, characterized in that, The imaging aperture of the thin-film imaging device is greater than 0.5m.

5. The thin-film imaging device according to claim 1, characterized in that, The thickness d of the liquid crystal polymer layer is obtained by the following formula: ； in: is the birefringence coefficient of the liquid crystal; The operating wavelength; For coefficients, It is an integer.

6. The thin-film imaging device according to claim 1, characterized in that, The thin-film imaging device further includes a flexible substrate layer for supporting the liquid crystal polymer layer.

7. A method for fabricating a large-aperture thin-film imaging device, characterized in that, The method for preparing the thin-film imaging device according to any one of claims 1-6 specifically includes the following steps: S1: Coat the surface of the substrate with a light polarization-sensitive material; S2: Orienting light in a specific polarization direction to a light polarization-sensitive material; S3: Coating liquid crystal material to form a liquid crystal polymer layer; S4: UV curing, peeling.

8. The preparation method according to claim 7, characterized in that, In S3, the liquid crystal polymer layer reaches a predetermined thickness d by adjusting the concentration of liquid crystal material, spin coating speed, and number of spin coating layers.

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