Liquid crystal micro-optical structure and liquid crystal-based electrically adjustable light field imaging detection chip

Abstract

The invention discloses a liquid crystal micro-optical structure and a liquid crystal-based electrically adjustable light field imaging detection chip, which belongs to the field of optical imaging detection. The liquid crystal micro-optical structure includes a liquid crystal material layer and a patterned electrode layer and a common electrode layer respectively arranged on both sides thereof; the patterned electrode layer is composed of a conductive film, and an array-distributed electrode micropore is arranged in the conductive film, and the electrode micropores of different apertures are arranged alternately, and the electrode micropores of the same aperture are arranged periodically; when the mean square amplitude of the signal voltage applied between the patterned electrode layer and the common electrode layer is higher than the mean square amplitude threshold, the liquid crystal molecules in the liquid crystal material layer under the electrode micropores of different apertures are arranged in different spatial forms, so as to form a gradient refractive index distribution corresponding to the periodic alternating array distribution in the liquid crystal material layer, so that the liquid crystal micro-optical structure has multiple focal lengths at the same time. Multiple focal lengths can extend the depth of field range twice, so as to clearly image objects within a wider depth range in the field of view.

Description

Technical Field

[0001] The present invention belongs to the field of optical imaging detection, and more specifically, relates to a liquid crystal micro-optical structure and a liquid crystal-based electrically adjustable light field imaging detection chip. Background Art

[0002] Conventional imaging methods use a main lens to project a three-dimensional scene onto a two-dimensional detector plane, which directly causes the loss of original depth information. Light field imaging can obtain four-dimensional space and angle information of a three-dimensional object space scene by adding a layer of microlens array between the main lens and the detector. Light field imaging has the unique advantage of "shooting first, focusing later", and can realize a variety of imaging applications such as multi-view imaging, digital refocusing, full focus imaging, depth estimation, and three-dimensional reconstruction through computational imaging. Although the imaging modes are different, the realization of these applications is inevitably still limited by the depth of field range of the light field imaging system. If the depth of field range of the light field imaging system can be expanded, the competitiveness of light field imaging technology can be greatly enhanced.

[0003] At present, as representatives of mainstream commercial light field cameras on the market, the microlens arrays used in the commercial light field cameras of Lytro Corporation in the United States and Raytrix Corporation in Germany are both fixed profile microlens arrays with fixed focal lengths. When other geometric parameters remain unchanged, these two types of light field cameras can only perform light field imaging on targets within a specific depth range in the object space, which limits its application to a certain extent. Liquid crystal microlenses have the excellent performance of electrically tunable focal length, which enables them to perform light field imaging on targets within a variety of depth ranges in the object space. However, existing liquid crystal microlenses can only achieve one focal length in one optical imaging process, and the depth of field extension capability is relatively low. Summary of the invention

[0004] In view of the defects of the prior art and the need for improvement, the present invention provides a liquid crystal micro-optical structure and a liquid crystal-based electrically adjustable light field imaging detection chip, the purpose of which is to form a gradient refractive index distribution to realize a multi-focal length microlens array, and to secondarily expand the depth of field to clearly image objects within a wider depth range in the field of view.

[0005] To achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a liquid crystal micro-optical structure, comprising a liquid crystal material layer and a patterned electrode layer and a common electrode layer respectively arranged on both sides of the liquid crystal material layer; the patterned electrode layer is composed of a conductive film, and an array-distributed electrode micropore is arranged in the conductive film, and the electrode micropores with different apertures are arranged alternately, and the electrode micropores with the same aperture are arranged periodically; when the mean square amplitude of the signal voltage applied between the patterned electrode layer and the common electrode layer is higher than the mean square amplitude threshold, the liquid crystal molecules in the liquid crystal material layer are arranged in different spatial forms under the electrode micropores with different apertures, so as to form a gradient refractive index distribution corresponding to the periodic alternating array distribution in the liquid crystal material layer, so that the liquid crystal micro-optical structure has multiple focal lengths at the same time.

[0006] Furthermore, it also includes: a first liquid crystal alignment layer, a first substrate, a protective anti-reflection film, a second liquid crystal alignment layer and a second substrate; the first liquid crystal alignment layer, the patterned electrode layer, the first substrate and the protective anti-reflection film are arranged in sequence on the upper surface side of the liquid crystal material layer; the second liquid crystal alignment layer, the common electrode layer and the second substrate are arranged in sequence on the lower surface side of the liquid crystal material layer.

[0007] Furthermore, the thickness of the first liquid crystal alignment layer and the second liquid crystal alignment layer is nanometer level, and the first substrate and the second substrate are quartz wafers with a thickness of hundreds of micrometers.

[0008] Furthermore, the thickness of the liquid crystal material layer is in micrometer level.

[0009] According to one aspect of the present invention, there is provided a liquid crystal-based electrically adjustable light field imaging detection chip, comprising the liquid crystal micro-optical structure, a planar array photodetector and a drive control preprocessing module as described above; the liquid crystal micro-optical structure is divided into a plurality of unit electrically controlled liquid crystal microlenses by electrode micropores, each of the electrode micropores being located at the center of a corresponding unit electrically controlled liquid crystal microlens; the planar array photodetector comprises a plurality of sub-planar array photodetectors, the sub-planar array photodetectors are matched and coupled with the unit electrically controlled liquid crystal microlenses in a one-to-one correspondence to form a corresponding imaging monocular; each of the unit electrically controlled liquid crystal microlenses is used to direct a light beam into a corresponding sub-planar array photodetector; each of the sub-planar array photodetectors is used to convert a received light beam into an electrical signal; the drive control preprocessing module is used to perform monocular imaging on each of the electrical signals to obtain corresponding sequence sub-image data.

[0010] Furthermore, the sub-array photoelectric detector includes a plurality of photosensitive elements distributed in an array.

[0011] Furthermore, the drive control pre-processing module is also used to provide a drive signal and an adjustable control signal for the liquid crystal micro-optical structure.

[0012] Furthermore, it also includes a ceramic shell, in which the liquid crystal micro-optical structure and the area array photodetector are coaxially packaged in sequence; an incident window is provided on a side of the ceramic shell that contacts the liquid crystal micro-optical structure, for transmitting an external incident light beam to the liquid crystal micro-optical structure.

[0013] In general, the above technical scheme conceived by the present invention can achieve the following beneficial effects: by designing a patterned electrode layer with a periodically overlapping electrode micropore structure, when the mean square amplitude of the signal voltage loaded between the patterned electrode layer and the common electrode layer is higher than the mean square amplitude threshold, the liquid crystal molecules in the liquid crystal material layer form a specific spatial arrangement morphology under the control of the electric field, and the liquid crystal molecules under the electrode micropores with different apertures will produce different spatial arrangement morphologies, which can form a gradient refractive index distribution on a macro scale, and one gradient refractive index corresponds to one equivalent focal length, thereby producing different macro focal lengths. At this time, the liquid crystal micro-optical structure is equivalent to a planar multi-focal length liquid crystal microlens array, which is equivalent to a secondary expansion of the depth of field range, and a larger depth of field range can be obtained, so that the light field camera can clearly image the three-dimensional object space scene within a wider depth range in the field of view. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the structure of a liquid crystal micro-optical structure provided by an embodiment of the present invention;

[0015] Figure 2 for Figure 1 Schematic diagram of electrode micropores of the patterned electrode layer in the liquid crystal micro-optical structure shown;

[0016] Figure 3 A schematic diagram of the structure of a liquid crystal based electrically modulated light field imaging detection chip provided by an embodiment of the present invention;

[0017] Figure 4 for Figure 3 The schematic diagram of the combination of the liquid crystal micro-optical structure and the area array photodetector in the liquid crystal-based electrically modulated light field imaging detection chip shown;

[0018] Figure 5 for Figure 3 The diagram shown is a schematic diagram of the optical imaging application configuration of the liquid crystal based electrically tunable light field imaging detection chip.

[0019] In all drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0020] 1 is a liquid crystal micro-optical structure, 11 is a second substrate, 12 is a common electrode layer, 13 is a second liquid crystal alignment layer, 14 is a liquid crystal material layer, 15 is a first liquid crystal alignment layer, 16 is a patterned electrode layer, 161 is an electrode micropore, 162 is a conductive film, 17 is a first substrate, 18 is a protective anti-reflection film, 2 is a planar array photodetector, 3 is a ceramic housing, 31 is an incident window, 32 is a port, and 33 is an indicator light. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0023] Figure 1 A schematic diagram of a liquid crystal micro-optical structure provided by an embodiment of the present invention. Figure 1 , combined with Figure 2 , the liquid crystal micro-optical structure in this embodiment is described in detail.

[0024] The liquid crystal micro-optical structure 1 includes a liquid crystal material layer 14 and a patterned electrode layer 16 and a common electrode layer 12 respectively arranged on both sides of the liquid crystal material layer 14. The patterned electrode layer 16 is composed of a conductive film 162, in which an array of electrode micropores 161 are arranged, and electrode micropores with different apertures are arranged alternately, and electrode micropores with the same aperture are arranged periodically. The conductive film is provided with electrode micropores with two or more apertures, such as Figure 2 The patterned electrode layer 16 is formed by periodically alternating the electrode micropores of two different apertures. It should be noted that the periodically alternating electrode micropores in this embodiment can be composed of two or more micropores of different apertures; in addition, the micropores can be circular holes, triangular holes, square holes, regular pentagonal holes, regular hexagonal holes, etc.

[0025] When the mean square amplitude of the signal voltage applied between the patterned electrode layer 16 and the common electrode layer 12 is higher than the mean square amplitude threshold, the liquid crystal molecules in the liquid crystal material layer 14 under the micropores of the electrodes with different apertures are arranged in different spatial configurations, so that the macroscopic focal lengths produced are different, so as to form a gradient refractive index distribution corresponding to the periodic alternating array distribution in the liquid crystal material layer 14, and one gradient refractive index corresponds to one equivalent focal length, so that the liquid crystal micro-optical structure has multiple focal lengths at the same time, and the multi-focal length can expand the depth of field twice, so as to clearly image objects within a wider depth range in the field of view. The spatial resolution of the clear imaging of the electrically controlled liquid crystal micro-optical structure is determined by its scale, and the spatial arrangement of the liquid crystal molecules can be changed by adjusting the mean square amplitude of the signal voltage, thereby adjusting the focusing ability of the unit electrically controlled liquid crystal micro-lenses of the planar array multi-focal length liquid crystal micro-lens array, so that this three-dimensional light field imaging has the effect of electrically controlled modulation.

[0026] The liquid crystal micro-optical structure 1 further includes a first liquid crystal alignment layer 15, a first substrate 17, a protective anti-reflection film 18, a second liquid crystal alignment layer 13 and a second substrate 11. Figure 1 As shown. The first liquid crystal alignment layer 15, the patterned electrode layer 16, the first substrate 17 and the protective anti-reflection film 18 are sequentially arranged on the upper surface side of the liquid crystal material layer 14. The second liquid crystal alignment layer 13, the common electrode layer 12 and the second substrate 11 are sequentially arranged on the lower surface side of the liquid crystal material layer 14. The thickness of the first liquid crystal alignment layer 15 and the second liquid crystal alignment layer 13 is nanometer level. The first substrate 17 and the second substrate 11 are quartz wafers with a thickness of hundreds of micrometers. The thickness of the liquid crystal material layer 14 is micrometer level.

[0027] The liquid crystal micro-optical structure in this embodiment is an electrically controlled structure, which can be expressed as a planar multi-focal length liquid crystal micro-lens array depending on the voltage signal applied. Its main functional structures include: a top substrate structure with a protective film / light-enhancing film and a pattern electrode on the two outer surfaces respectively; a bottom substrate structure with a common electrode on the outer surface on one side; and a micron-thick liquid crystal material filled between the two substrates. When the mean square amplitude of the signal voltage loaded between the patterned electrode layer 16 and the common electrode layer 12 is higher than the mean square amplitude threshold, the spatial electric field stimulated by the signal voltage can exert a steering effect on the liquid crystal molecules. The degree of steering of the liquid crystal molecules is affected by the strength of the electric field and its spatial orientation. The electrically controlled liquid crystal micro-optical structure will be expressed as a planar multi-focal length liquid crystal micro-lens array. Figure 2In the figure, a refractive microlens array with a convex profile is used to vividly display the refractive index distribution characteristics of the liquid crystal convergence microlens. The surface array multi-focal length liquid crystal microlens array is composed of unit electrically controlled liquid crystal microlenses distributed in an m×n element array, where m×n is the size of the array distribution composed of electrode micropores. The unit electrically controlled liquid crystal microlenses correspond to the electrode micropores one by one, and each electrode micropore is located at the center of the corresponding unit electrically controlled liquid crystal microlens, forming the upper electrode of the unit electrically controlled liquid crystal microlens, and the lower electrodes of all unit electrically controlled liquid crystal microlenses are provided by the common electrode layer 12.

[0028] Figure 3 A schematic diagram of the structure of a liquid crystal based electrically adjustable light field imaging detection chip provided by an embodiment of the present invention. Figure 3 , combined with Figure 4-Figure 5 , the liquid crystal based electrically modulated light field imaging detection chip in this embodiment is described in detail.

[0029] Liquid crystal based electrically modulated light field imaging detection chips include: Figure 1-Figure 2 The liquid crystal micro-optical structure 1, the area array photodetector 2 and the drive control pre-processing module in the illustrated embodiment. The liquid crystal micro-optical structure 1 is divided into a plurality of unit electrically controlled liquid crystal microlenses by electrode micropores, and each electrode micropore is located at the center of the corresponding unit electrically controlled liquid crystal microlens. The area array photodetector includes a plurality of sub-area array photodetectors, and the sub-area array photodetectors are matched and coupled with the unit electrically controlled liquid crystal microlenses one-to-one to form a corresponding imaging single eye in the electrically controlled compound eye imaging detection mode. The area array photodetector is divided into sub-area array photodetectors distributed in an m×n element array, and the sub-area array photodetectors are matched with the unit electrically controlled liquid crystal microlenses one-to-one. The structural configuration between the electrically controlled liquid crystal micro-optical structure and the area array photodetector is as shown in FIG. Figure 4 and Figure 5 shown.

[0030] The sub-array photodetector includes a plurality of photosensitive elements distributed in an array, and each unit electrically controlled liquid crystal microlens is used to direct the light beam to the photosensitive element of the corresponding sub-array photodetector. Specifically, the liquid crystal micro-optical structure arranges the target light beams in different directions in a discrete manner, and directionally converges them onto the corresponding photosensitive elements of the sub-array photodetector corresponding to each unit electrically controlled liquid crystal microlens. Each sub-array photodetector is used to convert the received light beam into an electrical signal. The drive control preprocessing module is used to perform monocular imaging on each electrical signal to obtain corresponding sequence sub-image data containing three-dimensional spatial information. The drive control preprocessing module is also used to provide a drive signal and an adjustable control signal to the liquid crystal micro-optical structure to drive the liquid crystal micro-optical structure to work. The control signal is Figure 1-Figure 2 The signal voltage in the illustrated embodiment is used to perform amplitude- and frequency-dependent signal control on the liquid crystal micro-optical structure.

[0031] According to an embodiment of the present invention, the liquid crystal based electrically adjustable light field imaging detection chip further comprises a ceramic housing 3, such as Figure 3 As shown. The liquid crystal micro-optical structure and the array photodetector are coaxially packaged in a ceramic housing. An incident window 31 is provided on one side of the ceramic housing that contacts the liquid crystal micro-optical structure, through which the protective anti-reflection film of the liquid crystal micro-optical structure is exposed to the outside, and is used to transmit the external incident light field to the liquid crystal micro-optical structure and perform light control operations.

[0032] The surface of the ceramic housing is also provided with a port 32. The parallel lines for providing driving signals and regulating signals in the drive control preprocessing module are connected to the inside of the ceramic housing through port 2, and are further connected to the liquid crystal micro-optical structure and the array photodetector. An indicator light 33 may also be provided on the surface of the ceramic housing to indicate the working state of the liquid crystal-based electrically modulated light field imaging detection chip. When the liquid crystal-based electrically modulated light field imaging detection chip is in a normal working state, the indicator light flashes.

[0033] See also Figure 5 , shows the optical imaging application configuration of the liquid crystal-based electrically modulated light field imaging detection chip. The main lens is located between the object and the liquid crystal-based electrically modulated light field imaging detection chip, and the micro-optical structure in the liquid crystal-based electrically modulated light field imaging detection chip is located between the cylindrical lens and the array photodetector. The external incident light field compressed by the main lens is further converged by the liquid crystal micro-optical structure and transmitted to the corresponding sub-array photodetector.

[0034] The working process of the liquid crystal-based electrically modulated light field imaging detection chip is as follows: first, a group of parallel lines that can provide drive control signals, regulation signals and data transmission are connected to the port; then the electronic signals for driving the array photodetector and the timing voltage signals with characteristic frequency, amplitude and duty cycle for driving the liquid crystal micro-optical structure are input respectively. At this time, the liquid crystal-based electrically modulated light field imaging detection chip works in the three-dimensional light field imaging mode, and the image data collected is output through the parallel lines connected to the port. During the above working process, the indicator light flashes continuously.

[0035] In addition, the liquid crystal-based electrically modulated light field imaging detection chip provided in this embodiment can also be used to measure the depth of the target object. Before the measurement, the relationship between the mean square amplitude of the electrical signal of the liquid crystal-based electrically modulated light field imaging detection chip and the optimal object plane depth should be obtained through experiments. Specifically, by building an optical test system, the relationship between the focal length of the liquid crystal microlens array and the mean square amplitude of the driving voltage signal can be effectively obtained; when the focusing ability of the unit liquid crystal microlens changes, it can be known from the knowledge of geometric optics that the optimal object plane corresponding to the imaging system will also change. Therefore, the relationship between the mean square amplitude of the driving voltage signal and the optimal object plane depth can be obtained accordingly, thereby establishing a mathematical relationship between the mean square amplitude of the electrical signal and the optimal object plane depth. Measure the depth of the target object, determine the plane depth of each layer of the target object according to the mean square amplitude of the electrical signal required to be applied when imaging the target object, calculate the difference between the maximum plane depth and the minimum plane depth, and thus obtain the depth of the target object.

[0036] In summary, the liquid crystal micro-optical structure and the liquid crystal-based electrically adjustable light field imaging detection chip provided in the embodiments of the present invention have the following advantages: depth of field expansion based on a multi-focal length microlens array and electrically controlled focusing can significantly expand the depth of field range; the focal length is controlled by constraining, intervening or guiding an external voltage, so that it has the characteristics of intelligent drive and control; it has extremely high stability of structural, electrical and electro-optical parameters and high control accuracy; the liquid crystal molecules are driven by an electric field to form a specific arrangement to achieve the convergence of incident light, and the liquid crystal molecules have birefringence characteristics in a wide spectrum (such as visible, near-infrared and even mid-infrared bands), and thus have the characteristics of wide-spectrum imaging detection; the main body of the chip is a liquid crystal microlens array encapsulated in a chip housing, and its functional thickness is only in the micron order, which is convenient for plugging in the optical path, easy to match and couple with conventional optical optoelectronic mechanical structures, and easy to use.

[0037] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A liquid crystal micro-optical structure, characterized in that: It includes a liquid crystal material layer and a patterned electrode layer and a common electrode layer respectively arranged on both sides of the liquid crystal material layer; The patterned electrode layer is composed of a conductive film, in which electrode micropores distributed in an array are arranged, and electrode micropores with different apertures are arranged alternately, and electrode micropores with the same aperture are arranged periodically; When the mean square amplitude of the signal voltage applied between the patterned electrode layer and the common electrode layer is higher than the mean square amplitude threshold, the liquid crystal molecules in the liquid crystal material layer are arranged in different spatial patterns under electrode micropores of different apertures, so as to form a gradient refractive index distribution corresponding to a periodic alternating array distribution in the liquid crystal material layer, so that the liquid crystal micro-optical structure has multiple focal lengths at the same time.

2. The liquid crystal micro-optical structure according to claim 1, characterized in that: Also includes: A first liquid crystal alignment layer, a first substrate, a protective anti-reflection film, a second liquid crystal alignment layer, and a second substrate; The first liquid crystal alignment layer, patterned electrode layer, first substrate and protective anti-reflection film are sequentially arranged on the upper surface side of the liquid crystal material layer; the second liquid crystal alignment layer, common electrode layer and second substrate are sequentially arranged on the lower surface side of the liquid crystal material layer.

3. The liquid crystal micro-optical structure according to claim 2, characterized in that: The thickness of the first liquid crystal alignment layer and the second liquid crystal alignment layer is nanometer level, and the first substrate and the second substrate are quartz wafers with a thickness of hundreds of micrometers.

4. The liquid crystal micro-optical structure according to any one of claims 1 to 3, characterized in that: The thickness of the liquid crystal material layer is in micrometer order.

5. A liquid crystal based electrically adjustable light field imaging detection chip, characterized in that: It comprises the liquid crystal micro-optical structure, the area array photoelectric detector and the drive control pre-processing module as described in any one of claims 1 to 4; The liquid crystal micro-optical structure is divided into a plurality of unit electrically controlled liquid crystal micro-lenses by electrode micro-holes, and each of the electrode micro-holes is located at the center of the corresponding unit electrically controlled liquid crystal micro-lens; The planar array photoelectric detector comprises a plurality of sub-planar array photoelectric detectors, and the sub-planar array photoelectric detectors are matched and coupled with the unit electrically controlled liquid crystal microlenses in a one-to-one correspondence to form a corresponding imaging monocular; Each of the unit electrically controlled liquid crystal microlenses is used to direct the light beam into the corresponding sub-array photoelectric detector; each of the sub-array photoelectric detectors is used to convert the received light beam into an electrical signal; and the drive control preprocessing module is used to perform monocular imaging on each of the electrical signals to obtain corresponding sequence sub-image data.

6. The liquid crystal based electrically modulated light field imaging detection chip according to claim 5, characterized in that: The sub-array photoelectric detector includes a plurality of photosensitive elements distributed in an array.

7. The liquid crystal based electrically modulated light field imaging detection chip according to claim 5, characterized in that: The drive control pre-processing module is also used to provide a drive signal and an adjustable control signal for the liquid crystal micro-optical structure.

8. The liquid crystal based electrically modulated light field imaging detection chip according to any one of claims 5 to 7, characterized in that: It also includes a ceramic housing, in which the liquid crystal micro-optical structure and the area array photodetector are coaxially and sequentially packaged; An incident window is provided on a side of the ceramic housing that contacts the liquid crystal micro-optical structure, and is used to transmit an external incident light beam to the liquid crystal micro-optical structure.

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