Depth of field extension system and method

Abstract

The present invention relates to a system and method for extending a depth of field for an optical system, the system including a binary phase mask disposed between first and second lenses of the optical system, and a controller for controlling a binary phase structure formed on the phase shift mask.

Description

[Technical field]

[0001] The present invention relates to a depth of field extension system and method, and more particularly to a system and method for extending the depth of field (DOF) of an optical system using a binary phase structure. [Background technology]

[0002] Optical systems are used in various industrial fields including the medical field for the purpose of diagnosing the shape and condition of an object to be imaged, etc. In this case, the optical system must satisfy optical signal quality requirements in order to provide an optical signal having sufficient resolution and accuracy for use.

[0003] In particular, since defocus in an optical system is a factor that can damage the quality of an optical signal, a technology that expands (increases) the depth of field (DOF) is needed to solve the problem of defocus. In particular, in a non-interferometric optical system, a trade-off occurs between depth and resolution. That is, expanding (increasing) the depth causes a problem of decreasing the resolution.

[0004] Therefore, there is a need for an improved solution that can extend the depth of field while overcoming some of the trade-off between depth and resolution.

[0005] However, the above content is merely intended to provide background information for the present invention and is not intended to represent any publicly known technology. Summary of the Invention [Problem to be solved by the invention]

[0006] In order to address the problems of the prior art as described above, the present invention aims to provide a system and method for extending the depth of field (DOF) of an optical system using a binary phase structure.

[0007] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present invention pertains from the following description. [Means for solving the problem]

[0008] To solve the above problems, one embodiment of the present invention provides a system for extending a depth of field for an optical system, comprising: a binary phase mask disposed between a first and a second lens of the optical system; and a controller for controlling a binary phase structure formed in the phase shift mask.

[0009] The control unit may evaluate the binary phase structure of the phase shift mask using light output from the second lens, and then use or modify the binary phase structure depending on the results of the evaluation.

[0010] The phase shift mask may include first and second regions that provide different phase shift effects on light.

[0011] The first region may output incident light with a first phase delay, and the second region may output incident light with a second phase delay.

[0012] The first region may output incident light with a 0° phase delay, and the second region may output incident light with a 180° phase delay.

[0013] The first and second regions may be provided in a plurality and may be alternately formed.

[0014] The second region may be centrally located.

[0015] The binary phase mask may be embodied by a spatial light modulator or a grating light valve.

[0016] The controller can be modified to an optimal binary phase structure using particle swarm optimization.

[0017] According to one embodiment of the present invention, a method for extending a depth of field for an optical system includes the steps of placing a binary phase mask between first and second lenses of the optical system, and applying an optimal binary phase structure while controlling a binary phase structure formed in the phase shift mask.

[0018] The applying step may include a step of evaluating the binary phase structure using light output from the second lens according to a binary phase structure of the phase shift mask, and then using or modifying the binary phase structure depending on a result of the evaluation.

[0019] The applying step may include applying the optimal binary phase structure using a particle swarm optimization. Effect of the Invention

[0020] The present invention configured as described above has an advantage that the depth of field (DOF) of an optical system can be extended using a binary phase structure.

[0021] In addition, the present invention has the advantage that the parameters used for designing the binary phase mask can be significantly reduced and the performance can be optimized by generating the optimal binary phase structure based on particle swarm optimization (PSO).

[0022] The effects obtained from the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those having ordinary skill in the art to which the present invention pertains from the following description. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic block diagram of a system (100) according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram showing an example in which a system (100) according to an embodiment of the present invention is applied to an optical system (101). [Diagram 3] 1A-1C show various examples for binary phase structures in the plane of a phase shift mask (110). [Figure 4] 1 is a schematic block diagram of an electronic device (120). [Diagram 5] FIG. 13 is a diagram showing an example of the application and non-application of a phase shift mask (110) when a point light source is incident on an optical system. [Figure 6] FIG. 13 is a diagram showing examples of the case where light from an object at various distances is incident on an optical system with and without the application of a phase shift mask (110). [Figure 7] 4 is a flowchart illustrating a control method according to an embodiment of the present invention. [Figure 8] FIG. 2 is a diagram illustrating the concept of a control method according to an embodiment of the present invention. [Figure 9] FIG. 2 is a diagram illustrating the concept of a control method according to an embodiment of the present invention. [Figure 10] FIG. 2 is a diagram showing an overview of image acquisition using an optical system (101). [Figure 11]1 is a diagram showing the change in point spread function and image quality at different depths in the optical axis direction (u) of a general optical system. [Figure 12] FIG. 1 illustrates various continuous phase patterns and the results of binarizing each pattern. [Figure 13] FIG. 13 is a diagram showing a binarization result of a continuous phase pattern consisting of a quadratic expression in which a linear term and a quadratic term are combined. [Figure 14] 13 is a diagram showing a number of binary phase structures and their focus results obtained by generating a continuous function by adjusting the coefficients of the linear and quadratic terms and binarizing the generated function. FIG. [Figure 15] FIG. 1 shows a number of binary phase structures generated using second-order and fourth-order terms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The above objects, means and effects of the present invention will become more apparent from the following detailed description in conjunction with the accompanying drawings, so that those skilled in the art will be able to easily carry out the technical ideas of the present invention. Furthermore, in describing the present invention, if it is determined that a detailed description of the known art related to the present invention may obscure the gist of the present invention, the detailed description will be omitted.

[0025] The terms used in the present specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In the present specification, the singular form includes the plural form unless otherwise specified in the phrase. In the present specification, the terms "comprise", "include", "have" or "have" do not exclude the presence or addition of one or more other elements other than the elements mentioned.

[0026] As used herein, terms such as "or" and "at least one" can refer to one of the words listed together or a combination of two or more. For example, "A or B" and "at least one of A and B" may include only one of A or B, or may include both A and B.

[0027] In this specification, descriptions such as "for example" and "for example" should not be construed as limiting the embodiments of the invention according to various embodiments of the invention, including but not limited to the exact nature of the presented information, such as the recited characteristics, variables, or values, and variations therein, including but not limited to tolerances, measurement errors, limitations of measurement accuracy, and other factors commonly known in the art.

[0028] In this specification, when a component is described as being "coupled" or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but there may be other components in between. On the other hand, when a component is described as being "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0029] In this specification, when a component is described as being "on" or "in contact with" another component, it should be understood that it may be directly on top of or connected to the other component, but there may be other components in between. On the other hand, when a component is described as being "directly on" or "in contact with" another component, it may be understood that there are no other components in between. Other expressions describing the relationship between components, such as "between" and "directly between," can be interpreted in a similar manner.

[0030] In this specification, terms such as "first" and "second" may be used to describe various components, but the components should not be limited by the terms. In addition, the terms should not be construed as limiting the order of each component, but may be used to distinguish one component from another. For example, a "first component" can be named a "second component", and similarly, a "second component" can be named a "first component".

[0031] Unless otherwise specified, all terms used in this specification will be used in the sense that they can be commonly understood by those having ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries will not be interpreted ideally or excessively unless they are clearly and specifically defined.

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] FIG. 1 is a block diagram showing a schematic configuration of a system 100 according to an embodiment of the present invention, and FIG. 2 shows an example in which the system 100 according to the embodiment of the present invention is applied to an optical system 101.

[0034] A system 100 according to an embodiment of the present invention is a system for extending the depth of field (DOF) of an optical system 101. In this case, the optical system 101 includes a number of lenses and performs various optical functions on an incident light source (e.g., functions of collecting and refracting the light source and creating an optical image of an object, etc.). As an example, the optical system 101 may be, but is not limited to, a video capture device.

[0035] Such an optical system 101 includes a first lens 102 arranged adjacent to an input section where light from the light source is incident, and a second lens 103 arranged adjacent to an output section where the light is finally emitted by optical action. As an example, light from the light source may be incident from a front region of the first lens 102, and the light may be emitted from a rear region of the second lens 103 arranged behind the first lens 102, and a focal point of the light emitted from the rear region may be formed.

[0036] Such a system 100 includes a phase shift mask 110 and electronics 120, as shown in FIGS.

[0037] 3 shows various examples for the binary phase structure in the plane of the phase shift mask 110. Here, the plane refers to the plane of the axes (x-axis and y-axis) perpendicular to the optical axis (z-axis).

[0038] The phase shift mask 110 is a mask that shifts incident light in a binary phase manner, and may be called a binary phase mask (BPM), and may be disposed between the first and second lenses 102 and 103 of the optical system 101. That is, referring to FIG. 2, the phase shift mask 110 includes a binary phase structure in a region through which light passes in its plane. At this time, the binary phase structure includes first and second regions 111 and 112 that perform different phase shift functions. As a result, the light passing between the first and second lenses 102 and 103 is delayed and output from the first and second regions 111 and 112 with different phases.

[0039] That is, in the light passing region of the plane of the phase shift mask 110, at least one of the first regions 111 can delay the incident light by a first phase (e.g., a phase of 0°) and emit the light, and at least one of the second regions (e.g., the remaining region) 112 can delay the incident light by a second phase (e.g., a phase of 180°) and emit the light. In this case, the first and second regions 111 and 112 may be formed alternately one by one.

[0040] 3, the light passing region may be a circular region on the plane of the phase shift mask 110, a circular second region 112 may be arranged in the center of the light passing region, and a circular band-shaped first region 111 may be arranged around the central second region 112. Of course, a circular band-shaped second region 112 may be further arranged around the first region 111, and a circular band-shaped first region 112 may be further arranged around the circular band-shaped second region 112, and the first and second regions 111 and 112 may be arranged alternately. Also, a third region 113 that blocks light may be arranged in the outermost region on the plane of the phase shift mask 110. Of course, the first and second regions 111 and 112 may be formed in the opposite pattern to that described above (i.e., a pattern in which the first region 111 is located in the center). The shapes, numbers, and sizes of the first and second regions 111 and 112 may be designed in various ways, and may be designed under the control of the electronic device 120, which will be described later.

[0041] The phase shift mask 110 is preferably a device capable of dynamically adjusting the shape, number, and size of each of the first and second regions 111 and 112. As an example, the phase shift mask 110 may be realized by a spatial light modulator (SLM) or a grating light valve (GLV). That is, in the case of an SLM, a space of the first and second regions 111 and 112 is formed by inputting an electrical or optical signal, and the phase of the incident light is changed in each of the first and second regions 111 and 112 and output. Such an SLM may be a MEMS (Micro-Electro-Mechanical System)-based SLM or a LC (Liquid Crystal)-based SLM. In addition, a GLV forms the first and second regions 111 and 112 by a dynamically adjustable diffraction grating, and changes the phase of the incident light in each of the first and second regions 111 and 112 and output.

[0042] Of course, in the case of a dynamically adjustable device such as an SLM or GLV, the phase shift mask 110 is connected to a phase structure controller (not shown) for implementing the binary phase structure of the phase shift mask 110. Such a phase structure controller may include a memory that stores information for implementing the binary phase structure of the phase shift mask 110, and a processor that processes the implementation of the binary phase structure using the information stored in the memory.

[0043] However, the present invention is not limited to this, and the phase shift mask 110 may be embodied in the above-mentioned first and second regions 111, 112 using physical steps through methods such as imprinting, thin film deposition, wet / dry etching, or a hologram film.

[0044] FIG. 4 is a schematic block diagram of the electronic device 120. As shown in FIG.

[0045] The electronic device 120 is an electronic device capable of computing and may have at least a first and a second function. That is, the first function is a function of generating a control signal for the binary phase structure of the phase shift mask 110 (i.e., the design of the shape, number, and width of each of the first and second regions 111 and 112). Also, the second function is a function of applying the current binary phase structure of the phase shift mask 110 to the optical system 101 and evaluating the current binary phase structure using the output final light. The first function may be performed at the time of initialization, and then the first function may be repeatedly performed so that a modified binary phase structure of the phase shift mask 110 is applied according to the evaluation result of the second function.

[0046] For example, the electronic device may be a general-purpose computing device such as a desktop personal computer, a laptop personal computer, a tablet personal computer, a netbook computer, a workstation, a smart phone, a smart pad, or a mobile phone, or may be a dedicated embedded system implemented based on Embedded Linux®, but is not limited to this.

[0047] Referring to FIG. 4, the electronic device 120 may include an input unit 121, a communication unit 122, a display 123, a memory 124, and a control unit 125.

[0048] The input unit 121 generates input data in response to various user inputs and may include various input means, such as, but not limited to, a keyboard, a key pad, a dome switch, a touch panel, a touch key, a touch pad, a mouse, and a menu button.

[0049] The communication unit 122 is configured to communicate with other devices such as the phase shift mask 110 or the phase structure control unit. For example, the communication unit 122 can transmit control information of the binary phase structure of the phase shift mask 110 generated by the first function to the phase shift mask 110 or its phase structure control unit. In addition, the communication unit 122 can receive information required for executing the first and second functions from another terminal or a server. For example, the communication unit 122 can perform wireless communication such as 5G (5th generation communication), LTE-A (long term evolution-advanced), LTE (long term evolution), Bluetooth (registered trademark), BLE (Bluetooth (registered trademark) low energy), NFC (near field communication), and WiFi (WiFi) communication, or wired communication such as cable communication, but is not limited thereto.

[0050] The display 123 displays various image data as a screen and may be configured as a non-emissive panel or an emissive panel. For example, the display may display a screen for a process and a result of executing the first and second functions. For example, the display may include, but is not limited to, a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a micro electro mechanical systems (MEMS) display, or an electronic paper display. In addition, the display may be combined with the input unit 121 and embodied as a touch screen.

[0051] The memory 124 stores various information required for the operation of the electronic device 120. That is, the memory 124 may store control program information required for the execution of the first and second functions. For example, the memory 124 may include, but is not limited to, a hard disk type, a magnetic media type, a compact disc read only memory (CD-ROM), an optical media type, a magneto-optical media type, a multimedia card micro type, a flash memory type, a read only memory type (ROM type), or a random access memory type (RAM type) depending on its type. In addition, the memory 124 may be, but is not limited to, a cache, a buffer, a main memory device, or an auxiliary memory device, or a separately provided memory system depending on its purpose / location.

[0052] The control unit 125 can perform various control operations of the control device 120. That is, the control unit 125 can control the execution of the first and second functions, control the execution of a control program stored in the memory 124 and a control method described below, and control the operations of the remaining components of the electronic device 120, i.e., the input unit 121, the communication unit 122, the memory 124, the display, etc. For example, the control unit 125 may include at least one processor that is hardware and a process that is software executed by the processor, but is not limited thereto.

[0053] When the first function is executed, the control unit 125 can control the design of the binary phase structure of the phase transition mask 110. That is, the control unit 125 can derive the binary phase structure (initial binary phase structure) of the phase transition mask 110 at the time of initialization arbitrarily or according to a preset setting. Thereafter, the phase structure control unit can derive a modified binary phase structure of the phase transition mask 110 based on a particle swarm optimization (PSO) technique to be described later according to an evaluation result of the execution of the second function for the previous binary phase structure.

[0054] Of course, if necessary, the control unit 125 can transmit a control signal for the derived binary phase structure to the phase shift mask 110 or the phase structure control unit disposed in the optical system 101. In this case, the phase shift mask 110 or the phase structure control unit can reflect the corresponding binary phase structure according to the received control signal and realize the first region 111 and the second region 112.

[0055] Meanwhile, when the second function is executed, the control unit 125 controls the measurement unit 131 to derive a distance-specific focal shape and an image shape predicted by the current binary phase structure of the phase shift mask 110. Then, the control unit 125 derives image quality by depth (e.g., structural similarity, peak signal-to-noise ratio, mean squared error, etc.) based on the prediction result, and controls an evaluation as to whether a given image quality condition is satisfied in a target depth range.

[0056] If the evaluation result of performing the second function indicates that the image quality condition is not satisfied, the control unit 125 can perform the first function again based on PSO to derive a modified binary phase structure of the phase transition mask 110.

[0057] Figure 5 shows an example of whether or not to apply the phase shift mask 110 when a point light source is incident on the optical system, and Figure 6 shows an example of whether or not to apply the phase shift mask 110 when light from subjects at various distances is incident on the optical system.

[0058] 5, it can be seen that when the phase shift mask 110 is applied to the optical system 101, it is possible to control the focal spot formation pattern for a point light source. That is, by applying the phase shift mask 110 to the optical system 101, it is possible to change the focal spot performance as shown in the lower diagram of FIG. 4, and in particular, it is possible to increase the focal spot depth while keeping the focal spot size small. That is, by applying the phase shift mask 110 to the optical system 101, it is possible to extend the depth of field.

[0059] Also, referring to Fig. 6, it can be seen that when the phase shift mask 110 is applied to the optical system 101, it is possible to control the depth of field. That is, by applying the phase shift mask 110 to the optical system 101, it is possible to change the resolution according to the object distance as shown in the lower diagram of Fig. 5, and in particular, it is possible to image all objects at different distances with good resolution. That is, by applying the phase shift mask 110 to the optical system 101, it is possible to extend the depth of field.

[0060] The control method according to the present invention will now be described in more detail.

[0061] FIG. 7 is a flowchart of a control method according to an embodiment of the present invention, and FIGS. 8 and 9 are conceptual diagrams showing a control method according to an embodiment of the present invention.

[0062] A control method according to an embodiment of the present invention (hereinafter referred to as "the control method") is performed by the above-mentioned system 100, i.e., the control unit 125 of the electronic device 120. The control method is a method for designing a binary phase structure having an optimal extended depth of field for the phase shift mask 110.

[0063] The control method may include a first step of disposing a binary phase shift mask 110 between the first and second lenses 102 and 103 of the optical system, and a second step of applying an optimal binary phase structure while controlling a binary phase structure formed on the phase shift mask 110. As an example, as shown in FIG 7, the control method may include S201 to S204 corresponding to detailed steps of the second step.

[0064] First, in S201, the control unit 125 executes a first function to derive a design of a binary phase structure of the phase shift mask 110. At this time, at the time of initialization, the design of an initial binary phase structure is derived arbitrarily or according to a preset setting.

[0065] As an example, referring to FIG. 3, FIG. 8 and FIG. 9, the phase shift mask 110 is set to a binary phase structure having n (n is a natural number of 2 or more) first regions 111 and second regions 112 arranged alternately. The distance ( A matrix with elements JPEG2025508150000002.jpg625) JPEG2025508150000003.jpg535. That is, the control unit 125 can design the phase transition mask 110 by making the binary phase structure of the phase transition mask 110 variable and processing it.

[0066] Thereafter, in S202, the control unit 125 performs a second function to evaluate the design of the binary phase structure derived in S201. At this time, the control unit 125 may evaluate the binary phase structure using light output from the second lens 103 according to the derived binary phase structure of the phase shift mask 110. That is, the control unit 125 derives the focal shape and image form according to distance that are predicted according to the current binary phase structure of the phase shift mask 110 by the measurement unit 131, and evaluates the image quality according to depth based on the prediction result.

[0067] Thereafter, in S203, the control unit 125 checks whether the derived image quality result satisfies the image quality condition given in the target depth section. If the condition is satisfied, the control unit 125 transmits a control signal for the current binary phase structure design to the phase transition mask 110 or the phase structure control unit (S204). As a result, the phase transition mask 110 or the phase structure control unit can implement the first region 111 and the second region 112 by reflecting the design of the corresponding binary phase structure according to the received control signal.

[0068] If the condition is not satisfied in S203, S201 is performed again. In this case, the control unit 125 executes a first function based on particle swarm optimization (PSO) to derive a design of a modified binary phase structure (i.e., an optimal previous phase structure) of the phase transition mask 110. To this end, S202 and S203 may be repeatedly performed to evaluate the design of the modified binary phase structure and check whether the condition is satisfied.

[0069] The above process is repeated until the design of the binary phase structure satisfies the requirements. As an example, the initial binary phase structure is JPEG2025508150000004.jpg89, and the binary phase structure of the t-th iteration is JPEG2025508150000005.jpg89. That is, at the tth time, If the condition is not met as a result of the evaluation of JPEG2025508150000006.jpg89, A modified binary phase structure for JPEG2025508150000007.jpg813 was derived and The evaluation for JPEG2025508150000008.jpg813 may be performed again.

[0070] The theory and principles applied to the control method according to one embodiment of the present invention will now be described.

[0071] <Method and optical system for predicting focal shape and image shape according to distance>

[0072] FIG. 10 shows an overview of image acquisition using an optical system 101.

[0073] Referring to FIG. 10, the function of an optical device is generally to obtain a portion of light emitted or scattered from an object to create an image of the object. However, an actual optical system cannot obtain all light rays from an object, and experiences aberration due to the diffraction phenomenon of light and the refraction and distortion of light by a lens. The transfer function of such an optical system is known as a point spread function (PSF). The imaging method of an optical system using such a point spread function can be expressed as the following equation (1), and the convolution of the object and the point spread function represents the image.

[0074]

number

[0075] Resolution (angular resolution, spatial resolution) is an index of the imaging capability of an imaging device, and refers to the ability to distinguish two objects that are far from each other, and can be expressed by the shape of the point spread function.

[0076] FIG. 11 shows the change in image quality and point spread function at different depths in the optical axis direction (u) of a general optical system.

[0077] 11, as light propagates from position aa to position cc, the point spread function changes due to diffraction of light, and image distortion is unavoidable. The depth of focus is defined as the section in the optical axis direction in which focus is maintained, and the depth of field is defined as the section of the field in which an acceptable level of resolution can be maintained.

[0078] <Details of Applying PSO>

[0079] The optical system 101 includes lens information of the optical system to which BPM is to be applied. Current optical design programs include Zemax, CodeV, LightTools, ASAP, TracePro, etc., and are based on "ray tracing" based on geometric optics. "Ray tracing" is performed by refraction by media having different refractive indices from each other and transmission occurring in one medium, and can be calculated from the geometric information of the boundary of the medium and the optical physical properties of the medium. The calculated rays are analyzed using defined diffraction and physical optics calculation formulas, such as the modulation transfer function (MTF) and the point spread function (PSF).

[0080] In the present invention, the optical system 101 includes the geometric information and optical physical properties of the same lens as the video system that attempts to acquire an actual video, and calculates the optical transfer function according to the depth of the subject.

[0081] - Video reproduction

[0082] Video reproduction is performed by convolving the point spread function calculated by the optical system 101 and a test target. "USAF 1951", "Ronchi Ruling", "Star", etc., which are devised to be useful for evaluating and correcting the performance of the video system, may be used.

[0083] - Performance evaluation

[0084] Performance evaluation is performed by image quality assessment according to the depth of the subject. Referring to Table 1, as the image quality evaluation method, a full-reference evaluation method that refers to a distortion-free video and a no-reference evaluation method that does not refer to a distortion-free video can be used.

[0085] [Table 1]

[0086]

number

[0087] Equation (2) is the equation for the cost (y) of this algorithm, and in the present invention, we can derive a binary phase structure that minimizes this. In this case, f is the image quality evaluation result, f0 is the target image quality, JPEG2025508150000012.jpg89 is the binary phase structure matrix at the t-th iteration, JPEG2025508150000013.jpg917 represents the target depth extension interval, and λ is the regularization coefficient.

[0088] - PSO algorithm

[0089] In the present invention, the PSO (particle swarm optimization) algorithm is a binary phase structure for every t-th The PSO algorithm is proposed to improve the quality of the image by minimizing the cost (y) calculated by Eq. (2). JPEG2025508150000015.jpg76( It is an optimization algorithm that searches for the optimal pixel size (JPEG2025508150000016.jpg714).

[0090] In the present invention, a binary phase structure Since the cost (y) from JPEG2025508150000017.jpg76 is not a differentiable function, minimum-cost search using differentiation such as gradient descent is not possible. PSO is a mathematical optimization methodology in which multiple particles (agents) exchange information with each other and simultaneously combine the stored information to search for the optimal solution. This type of swarm-based optimization has the advantage that since each agent performs optimization while exchanging information with each other, even if one agent converges to a local optimum solution, the swarm can converge to a global optimum solution.

[0091]

number

[0092]

number

[0093] Using multiple agents of the PSO algorithm, an optimization algorithm is performed in one or more variable spaces. Equations (3) and (4) respectively represent the velocity vector and position vector of the jth agent with respect to the ith variable in the t+1th iteration. Here, r1 and r2 are random numbers between 0 and 1, and c1 and c2 are the cognitive and social coefficients, respectively. The agent best solution for information exchange between agents is a ij and the swarm-minimum-cost (global best solution) is JPEG2025508150000020.jpg812. The PSO algorithm uses a binary phase structure JPEG2025508150000021.jpg89To modify the design, the initial jth agent may be expressed as an initial binary phase structure and equation (5).

[0094]

number

[0095] - PSO Algorithm Example

[0096] As an example, a binary phase filter for the i components can be written as the matrix The N binary phase filters processed in parallel by the agents can be expressed as the matrix The initial N binary phase filters can be expressed as the matrix It may be expressed as JPEG2025508150000025.jpg741.

[0097] After t iterations, the binary phase filter of the jth agent is The agent can have solutions such as JPEG2025508150000026.jpg652, and the solution with the lowest cost among them is called the agent best solution, a ij It can be defined as follows.

[0098] global best solution, JPEG2025508150000027.jpg813 is the best solution in history that showed the best result after t iterations. After t iterations, the binary phase filter is JPEG2025508150000028.jpg741; JPEG2025508150000029.jpg641;...; Among them, the solution with the lowest cost is called the global best solution. It may be defined as JPEG2025508150000031.jpg813.

[0099] <Continuous Phase Pattern Binary Generation>

[0100] In the present invention, the binary phase structure of the phase shift mask 110 may have a binary coded continuous phase pattern, and the specific patterning method thereof is as follows.

[0101] When there is a continuous phase pattern P(ρ) which is a function of the distance ρ from the center, its binarized function can be expressed as shown in equation (6).

[0102]

number

[0103] FIG. 12 shows various continuous phase patterns and the results of binarizing each pattern.

[0104] That is, in FIG. 12, (a1) is a continuous pattern expressed by defocus aberration, JPEG2025508150000033.jpg743, which is expressed as a quadratic function of ρ with respect to the defocus parameter ψ. Also, in FIG. 12, (a2) is the focal aspect that appears when (a1) is placed in front of the lens, and in each focal aspect diagram, the vertical direction is the light traveling direction, and the u=0 point is the focal plane corresponding to the focal length. In this case, (a1) has the effect of moving the focal point directly along the light traveling direction on the focal plane in proportion to the value of ψ. (b1) expresses spherical aberration (SA), It is expressed as JPEG2025508150000034.jpg636. Spherical aberration has the effect of spreading the focus long and wide along the direction of travel, as shown in (b2), and the degree of this effect increases with the γ value.

[0105] In FIG. 12, (c1) is an example of a linear function. JPEG2025508150000035.jpg740, which shows the effect of moving the focal point on the focal plane while simultaneously increasing the length itself, as in (c2). The amount of movement and the degree of extension increase in proportion to the α value. The lower part of FIG. 12 shows the result of binarizing each function in the upper part of FIG. 12 according to equation (6). The focal points for each binarized function are similar in form to the focal points generated by the continuous pattern, but generate additional shapes symmetrical about the focal plane. Using this phenomenon, polynomials for ρ having different orders can be considered when generating continuous functions.

[0106] FIG. 13 shows the binarization result of a continuous phase pattern consisting of a quadratic expression in which a linear term and a quadratic term are combined.

[0107] In FIG. 13, (a) shows a continuous phase pattern consisting of only linear expressions ( The result of binarizing the image (JPEG2025508150000036.jpg740) was assumed to be an α value of 5. The result of the focus formation is two extended foci that are symmetrically separated with respect to the focal plane, as shown in FIG. 13(b). FIG. 13(c) shows the continuous phase pattern ( The focus changed by this function shows an extended form compared to the existing focus, as shown in (d) of Figure 13, in which two focus points that were separated from each other are combined.

[0108] FIG. 13(e) is an intensity graph at v=0 in FIG. 13(b) and (d). It can be seen that the two foci that were separated from each other are combined to form one extended focus as the ψ value increases. In FIG. 13, only the case where the focus is extended using only the first and second order terms is considered, but by using terms of various orders, it is possible to form foci with various shapes, and it is possible to find many designs by adjusting the coefficient value of each term.

[0109] Figure 14 shows the results of adjusting the coefficients of the first and second terms ( JPEG2025508150000038.jpg965) A continuous function is generated, and the generated function is binarized to obtain a number of binary phase structures and their focus results. Figure 15 shows the results of the binarization using quadratic and quartic terms ( JPEG2025508150000039.jpg868) shows a number of the binary phase structures that were generated.

[0110] As shown in Figures 14 and 15, the focus generation state is predicted while adjusting the coefficient value of each term, and a number of binary phase structures can be found. In this embodiment, only linear, quadratic, and quartic terms are used, but various binary phase structures can be found when binarization is performed on polynomials including terms with orders other than these.

[0111] The present invention configured as described above has an advantage that the depth of field (DOF) of an optical system can be extended using a binary phase structure. In addition, the present invention has an advantage that the parameters used for designing a binary phase mask can be significantly reduced and performance can be optimized by generating an optimal binary phase structure based on particle swarm optimization (PSO).

[0112] Although the detailed description of the present invention has been given with reference to specific embodiments, it is to be understood that various modifications can be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the following claims and equivalents to these claims.

Claims

1. 1. A system for extending a depth of field for an optical system, the system comprising: a binary phase mask disposed between first and second lenses of the optical system; a controller for controlling a binary phase structure formed in the phase shift mask.

2. The system of claim 1 , wherein the control unit evaluates the binary phase structure of the phase shift mask using light output from the second lens, and then uses or modifies the binary phase structure based on the result of the evaluation.

3. 10. The system of claim 1, wherein the phase shift mask includes first and second regions that provide different phase shift effects on light.

4. 4. The system of claim 3, wherein the first region outputs light incident thereon with a first phase delay, and the second region outputs light incident thereon with a second phase delay.

5. 4. The system of claim 3, wherein the first region outputs light incident thereon with a 0 degree phase delay, and the second region outputs light incident thereon with a 180 degree phase delay.

6. The system of claim 5 , wherein the first and second regions are provided in a plurality of alternating fashions.

7. The system of claim 6 , wherein the second region is centrally located.

8. 10. The system of claim 1, wherein the binary phase mask is embodied by a spatial light modulator or a Grating light valve.

9. The system of claim 2 , wherein the controller modifies the optimal binary phase structure using particle swarm optimization.

10. 1. A method for extending a depth of field for an optical system, comprising: disposing a binary phase mask between first and second lenses of the optical system; applying an optimal binary phase structure while controlling the binary phase structure formed in the phase shift mask; The method includes:

11. The method of claim 10, wherein the applying step includes a step of evaluating the binary phase structure of the phase shift mask using light output from the second lens, and then using or modifying the binary phase structure based on the result of the evaluation.

12. The method of claim 10 , wherein the applying step comprises applying the optimal binary phase structure using particle swarm optimization.

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