Single-pixel point target automatic focusing system based on norm measurement

Abstract

The invention provides a single pixel point target automatic focusing system based on norm measurement, and belongs to the technical field of computational imaging, and the system comprises a programmable light field modulation module which is used for generating a structured illumination light field; the focusing module is used for adjusting the illumination light field, focusing the illumination light field to an imaging target and collecting a light signal generated by a target point in the imaging target; the single-pixel detection module is used for receiving an optical signal and converting the optical signal into an electric signal; the second photoelectric sensor is arranged on the imaging side of the focusing module and used for collecting light intensity measurement signals used for single-pixel imaging after automatic focusing is completed. According to the invention, the position of the optical path is adjusted by controlling the programmable micro-displacement actuator, so that the maximum value of the energy index is obtained, rapid and robust point target focusing is realized, and the method is suitable for application scenes such as optical fiber coupling, free space communication, single-pixel microscopy, weak light detection and the like.

Description

Technical Field

[0001] This invention relates to the field of computational imaging technology, and in particular, to a single-pixel point target autofocus system based on norm metric. Background Technology

[0002] The ability to quickly and accurately focus on spatial point targets in optical systems is crucial for fiber optic coupling, free-space communication, industrial inspection, optical field positioning, deep tissue imaging, and precision measurements under resource-constrained conditions. To improve focusing efficiency, existing autofocus technologies primarily focus on constructing and searching for focusing evaluation functions.

[0003] On the one hand, many autofocus methods still rely on area array camera imaging, evaluating sharpness by processing complete or partial two-dimensional images. For example, existing fast autofocus methods based on display panels use a combination of large and small step sizes to search across the entire focal length range, binarizing the acquired image, marking connected components, and calculating the brightness centroid. The brightness proportion of a local area is used as the focus evaluation index to determine the sharp focus position and make fine adjustments. Another example is the existing fiber-waveguide automatic alignment coupler based on image processing, which uses two-channel micro-CMOS imaging to acquire side and end views of the coupling area, respectively. Edge extraction and position deviation calculation drive a six-dimensional electric displacement stage to achieve automatic alignment and focusing of the fiber and waveguide. These solutions rely on two-dimensional image plane information and image sharpness evaluation functions, making them difficult to directly apply to single-pixel detection scenarios with only single-channel light intensity output and lacking pixel structure.

[0004] On the other hand, to adapt to "pixel-less" detection hardware such as optical power meters or single-channel detectors, some patents propose direct estimation strategies based on measurement domain signals. For example, existing methods for automatic alignment of optical waveguide devices and fiber arrays use wide-source illumination and power meter detection of each channel's output power. A hybrid automatic alignment algorithm is then used to progressively scan in multi-dimensional space, constructing a three-dimensional energy distribution and searching for the location of maximum energy, thus achieving precise automatic alignment of the fiber array and waveguide device. This type of technology uses single-channel power or multi-channel power difference as the evaluation function. Although it avoids the imaging stage, it still relies on large-scale, multi-step mechanical scanning, resulting in limited convergence speed. Furthermore, there is no clear physical correspondence between the evaluation function and the optical point spread function (PSF).

[0005] For example, existing autofocus devices construct a microscopic optical path through a light source, optical coupler, and objective lens. A photodiode converts the echo light into a one-dimensional light intensity signal, and a signal template is pre-stored in memory. A microprocessor performs cross-correlation calculations between the real-time light intensity sequence and the template, searches for relevant peak positions, and drives an adjustable microscope platform to move along the optical axis, thus automatically locking the focal point. This technical solution essentially utilizes the correlation characteristics of a single-channel signal for extreme value localization, enabling autofocus without imaging. However, its template is highly dependent on the sample being measured and the system structure, limiting its adaptability and generalization capabilities, and making it prone to deviations under complex three-dimensional targets or scattering media.

[0006] In recent years, some patents have introduced single-pixel detectors into the fields of target localization and scanning imaging. For example, the existing technology of a beam-shaping rapid target localization method based on a single-pixel detector uses a beam-shaping device to spatially shape the pulsed laser, combined with a temporal or spatial-angle scanning strategy, to achieve rapid target localization and 3D information acquisition using only a single-pixel detector. This patented technology is representative in the combination of light field modulation and single-pixel detection, but it is mainly aimed at long-range lidar and target tracking scenarios. The focus criterion is usually based on the overall echo energy or statistics, making it difficult to finely characterize the energy distribution characteristics of the point spread function as it defocuses in a microscopic or fiber-coupled system.

[0007] In summary, existing autofocus and single-pixel detection technologies suffer from the following main problems: some technologies rely on two-dimensional image information and cannot be directly used with single-channel detectors; others rely on empirical power evaluation functions or templates, which lack strong physical constraints under complex three-dimensional samples, low-light environments, and conditions involving scattering and scale changes, making it difficult to stably reflect the characteristics of the point spread function's evolution with defocus. Particularly in the scenario of precise three-dimensional positioning of single-pixel targets, existing technologies struggle to achieve fast, robust, and generalizable autofocus within a single-channel measurement domain without performing two-dimensional imaging or PSF reconstruction.

[0008] Therefore, it is necessary to propose a single-pixel point target autofocus technology that does not require two-dimensional imaging, introduces physical constraints consistent with the evolution of the point spread function in the single-pixel measurement domain, and has high robustness and high generalization ability, so as to achieve fast and accurate three-dimensional point target focal plane estimation and positioning under limited hardware resources. Summary of the Invention

[0009] The purpose of this invention is to propose a single-pixel point target autofocus system based on norm metric, which is used to solve the problem of achieving fast and accurate three-dimensional point target focal plane estimation and positioning.

[0010] To achieve the above objectives, the present invention provides a single-pixel target autofocus system based on norm metric. The system includes: a programmable light field modulation module comprising a light source and a spatial light modulator for generating a structured illumination light field; a focusing module comprising an aperture, an objective lens, and a displacement stage connected to the objective lens for adjusting the illumination light field and focusing on the imaging target, and collecting light signals generated by target points within the imaging target; a single-pixel detection module comprising an optical fiber and a first photoelectric sensor for receiving the light signals and converting them into electrical signals; and a single-pixel imaging module comprising a second photoelectric sensor, the second light... An electrical sensor is disposed on the imaging side of the focusing module and is used to collect light intensity measurement signals for single-pixel imaging after autofocus is completed. The data processing terminal is used to control the pattern refresh of the spatial light modulator to perform spatial structured modulation of the incident light, drive the displacement stage to move the objective lens in the optical axis direction to traverse different defocus positions, control the collection of data from the first photoelectric sensor, and also to form a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable based on the one-dimensional single-channel detection signal of the current defocus position, and drive the movement of the displacement stage according to the norm energy curve for autofocus.

[0011] The beneficial effects of this invention are as follows:

[0012] This invention enables fast and robust point target focusing under conditions of no image, low sampling, weak light, and complex three-dimensional samples. It has the advantages of low computational cost, high accuracy, and strong adaptability. It does not require reconstruction of the target point's image or point spread function, does not depend on sample texture features, and completes automatic focusing directly based on the measurement domain. Specifically, it includes: (1) no imaging required, avoiding the problems of large reconstruction computation and noise sensitivity; (2) based on the physical energy concentration variation law, the focusing curve has unimodality and high robustness; (3) L1 norm (also known as the first norm or Manhattan norm) normalization eliminates the influence of light source fluctuations and system energy drift, and its stability is far superior to traditional statistical methods; (4) applicable to any target point, without depending on texture, structure, or high-frequency components; (5) suitable for weak light scenes, deep tissue imaging, fiber optic coupling, and free space optical communication. Attached Figure Description

[0013] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0014] Figure 1 This is the optical path diagram of the single-pixel target autofocus system provided by the present invention;

[0015] Figure 2This invention provides the point spread function and image acquisition effect;

[0016] Figure 3 These are the simulated peak curves under different norms provided by this invention;

[0017] Figure 4 This is the L4 norm focusing index change curve during objective lens scanning provided by the present invention;

[0018] Figure 5 This is a comparison result of the corresponding images before and after autofocus provided by the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0021] This invention provides a single-pixel target autofocus system based on norm metric, which includes a programmable light field modulation module, a focusing module, a single-pixel detection module, a single-pixel imaging module, and a data processing terminal.

[0022] The programmable light field modulation module includes a light source 101 and a spatial light modulator 102 for generating a structured illumination light field.

[0023] The focusing module includes an aperture 103, an objective lens 104, and a displacement stage 105 connected to the objective lens 104, for adjusting the illumination light field and focusing on the imaging target 106, and collecting the light signal generated by the target point in the imaging target 106.

[0024] The single-pixel detection module includes an optical fiber 108 and a first photoelectric sensor 109, which are used to receive optical signals and convert the optical signals into electrical signals;

[0025] The single-pixel imaging module includes a second photoelectric sensor 107, which is disposed on the imaging side of the focusing module and is used to collect light intensity measurement signals for single-pixel imaging after autofocus is completed.

[0026] The data processing terminal is used to control the pattern refresh of the spatial light modulator 102 to perform spatial structured modulation of the incident light, drive the displacement stage 105 to move the objective lens 104 along the optical axis to traverse different defocus positions, control the acquisition of data from the first photoelectric sensor 109, and also to form a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable based on the one-dimensional single-channel detection signal of the current defocus position, and drive the movement of the displacement stage 105 according to the norm energy curve to perform automatic focusing.

[0027] In the light source module: the light source 101 is used to generate illumination light and provide incident light to the spatial light modulator 102; the spatial light modulator 102 is disposed on the light-emitting side of the light source 101 and is used to perform spatial structured modulation of the incident light under the action of a control signal to form a time-varying illumination light field.

[0028] In the focusing module: the aperture 103 is disposed between the spatial light modulator 102 and the objective lens 104 to limit the beam range and suppress stray light; the objective lens 104 is disposed on the light-emitting side of the spatial light modulator 102 to focus the modulated light field onto the imaging target 106 and collect the light signal generated by the target point in the imaging target 106, the light signal including reflected light, scattered light or transmitted light; the displacement stage 105 is connected to the objective lens 104 to drive the objective lens 104 to move along the optical axis to change the axial position of the target point relative to the objective lens 104.

[0029] In the single-pixel detection module, one end of the optical fiber 108 is disposed on the imaging side of the objective lens 104 to receive the light signal returned from the target point and collected by the objective lens 104, and the other end is connected to the first photoelectric sensor 109. Furthermore, in the single-pixel detection module, the first photoelectric sensor 109 is used to convert the collected light signal into an electrical signal to form a one-dimensional single-channel detection signal for autofocus.

[0030] In the single-pixel imaging module, the second photoelectric sensor 107 is disposed on the imaging side of the objective lens 104 and is used to collect light intensity measurement signals for single-pixel imaging after autofocus is completed.

[0031] In the single-pixel detection module, the optical fiber 108 is configured as a probe and extends into the sample area or near-field area to collect the optical signal; wherein, the sample area is the spatial area where the target point to be measured is located, and is used to reflect, scatter or transmit with the illumination light field modulated by spatial light, and generate an optical signal.

[0032] Among them, the aperture 103 is a limiting aperture, which is set between the light source 101 and the spatial light modulator 102 or between the spatial light modulator 102 and the sample area, and is used to limit the field of view or filter out stray light.

[0033] The data processing terminal is used to drive the displacement stage 105 to move, control the pattern refresh of the spatial light modulator 102, and acquire data from the first photoelectric sensor 109. The data processing terminal performs the following steps:

[0034] Step S1: Control the micromirror unit inside the spatial light modulator 102 to switch between different tilt states to achieve spatial structured modulation of the incident light in order to obtain a structured illumination field.

[0035] In step S2, the control stage 105 moves the objective lens 104 along the optical axis to traverse different defocus positions. The spatial light modulator 102 sequentially illuminates and modulates the target point in the sample area at each defocus position. The light signal reflected or transmitted by the target is converged to the single-pixel detection module, and a one-dimensional single-channel detection signal corresponding to the current defocus position is obtained.

[0036] Step S3: Normalize the one-dimensional single-channel detection signal to obtain the normalized one-dimensional single-channel detection signal;

[0037] Step S4: Based on the normalized one-dimensional single-channel detection signal, construct a focusing evaluation function that can characterize the energy concentration of the target point. Calculate the norm energy index that characterizes the energy concentration of the target point at the corresponding defocus position according to the focusing evaluation function, and form a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable.

[0038] Step S5: Drive the displacement stage 105 to move to the corresponding axial position according to the norm energy curve, thereby automatically locking the optimal focus position of the target point.

[0039] The data processing terminal also performs the following steps:

[0040] In step S1, modulation matrix generation and loading: generating a spatially encoded mask pattern for autofocus; constructing an orthogonally complete Hadamard matrix (the Hadamard matrix is ​​an orthogonal encoded matrix), extracting the row vectors or column vectors of the Hadamard matrix and rearranging them to generate a series of binarized pattern sequences to obtain a Hadamard mask pattern sequence; loading the Hadamard mask pattern sequence sequentially onto the spatial light modulator 102 during autofocus scanning; during autofocus scanning, the spatial light modulator 102 loads the Hadamard mask pattern sequence frame by frame according to the control signal; by controlling the micromirror unit inside the spatial light modulator 102 to switch between different tilt states, spatially structured modulation of the incident light is achieved to obtain a structured illumination field;

[0041] In step S2, defocus sequence scanning and detection: A scanning and detection mechanism along the optical axis is constructed. The displacement stage 105 moves the objective lens 104 along the optical axis, thereby traversing different defocus positions. The defocus position is the axial offset of the objective lens 104's current position relative to the optimal focus position. At each defocus position, the spatial light modulator 102 rapidly projects a complete Hadamard mask pattern sequence to sequentially illuminate and modulate the target point within the sample area. The light signals reflected or transmitted by the target converge to the single-pixel detection module. The first photoelectric sensor 109 converts the light signal into an electrical signal and performs analog-to-digital conversion on the electrical signal to obtain a one-dimensional single-channel detection signal corresponding to the current defocus position. The one-dimensional single-channel detection signal is the Hadamard transform coefficient, which is a one-dimensional single-channel measurement sequence.

[0042] In step S3, signal interference immunity and norm normalization: In order to eliminate the effects of light source power fluctuation, environmental noise interference and drift caused by long-term system operation, the one-dimensional single-channel detection signal collected at each defocus position is normalized. For the one-dimensional single-channel detection signal obtained at the current defocus position, the sum of the absolute values ​​of the amplitudes of each measured value in the one-dimensional single-channel detection signal is calculated. Each measured value in the one-dimensional single-channel detection signal is divided by the sum of the absolute values ​​to obtain the normalized one-dimensional single-channel detection signal.

[0043] In step S4, the norm energy index is calculated as follows: Based on the normalized one-dimensional single-channel detection signal, a focusing evaluation function that can characterize the energy concentration of the target point is constructed. The p-order norm is selected as the calculation form of the focusing evaluation function, where p is a positive integer greater than or equal to 2. At each defocus position, the p-order norm is calculated for the amplitude of each measured value in the normalized one-dimensional single-channel detection signal corresponding to the defocus position. The norm energy index that characterizes the energy concentration of the target point at the corresponding defocus position is obtained according to the focusing evaluation function. A one-to-one correspondence is established between the norm energy index obtained at different defocus positions and the corresponding defocus positions, thereby forming a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable.

[0044] In step S5, optimal focal plane positioning: peak search or Gaussian fitting is performed on the norm energy curve. Based on the extreme value characteristics of the norm energy curve, the axial position corresponding to the maximum value of the norm energy index in the norm energy curve is determined to be the actual focal plane of the system. At the position where the norm energy index reaches the maximum value in the norm energy curve, the displacement stage 105 is driven to move to the corresponding axial position, thereby automatically locking the optimal focus position of the target point.

[0045] The technical solution provided by this invention obtains a one-dimensional single-channel detection signal through programmable light field modulation, calculates the norm energy concentration measure after L1 normalization, and directly locates the focus by utilizing its monotonic change with defocus, without the need for two-dimensional image reconstruction. Furthermore, a digital micromirror device (DMD) projects a Hadamard or other orthogonal modulation mode to sequentially illuminate the target area, and a single-pixel detection module records the corresponding one-dimensional single-channel detection signal to obtain the measurement value of a spatial point under different modulation modes. Furthermore, the total energy of the PSF remains consistent under different defocus levels after normalization, eliminating the influence of light source fluctuations, system drift, and geometric scale changes. Furthermore, the norm is used to quantify the energy concentration of the PSF, and its monotonicity, which gradually decreases with increasing defocus, is used to determine the focus position. Furthermore, the norm reaches its maximum value at the focal plane; as defocus increases, the curve shows a symmetrical downward trend, and the peak value is the optimal focus position of the target point.

[0046] The execution process of the present invention includes: (1) constructing a single-pixel modulation measurement model; (2) acquiring one-dimensional single-channel detection signals at different defocus positions; (3) performing L1 normalization on the one-dimensional single-channel detection signals to eliminate the influence of light intensity and total energy changes; (4) calculating the norm energy concentration index and establishing the defocus response curve; (5) determining the focal plane according to the norm peak position to achieve automatic focusing.

[0047] The present invention will be described in more detail below through specific embodiments.

[0048] The point spread function in this invention serves as a focusing criterion and explains the principle of Hadamard single-pixel imaging:

[0049] Point spread function (PSF) focusing principle: The response of an optical system to a point in space is determined by its point spread function. When the objective lens is at the focal plane, the PSF energy is highly concentrated and the main lobe is narrowest. Defocusing causes the PSF to broaden, the peak value to decrease, and the spatial frequency components to decrease.

[0050] Hadamard single-pixel modulation principle: Hadamard coding is a set of orthogonal ±1 modulation modes loaded onto a spatial light modulator. Each modulation mode corresponds to a single-pixel intensity measurement. For the PSF of a target spatial point, the single-pixel measurement value obtained under different Hadamard modulation modes can be expressed as the weighted response of the spread function at that point under the corresponding modulation mode.

[0051] It is evident that the one-dimensional single-channel detection signal is essentially a projection representation of the PSF onto the Hadamard orthogonal basis. As the PSF broadens due to defocusing, the measured amplitude in the Hadamard modulation mode corresponding to high spatial frequencies decreases rapidly, thereby affecting the overall energy distribution of the one-dimensional single-channel detection signal.

[0052] The following is combined with Figure 1The diagram illustrates the optical path of a single-pixel point target autofocus system, providing a detailed description of the overall structure, optical path, and functions of each component. The system includes a programmable light field modulation module, a focusing module, a single-pixel detection module, and a single-pixel imaging module. These modules work collaboratively to achieve fast, stable, and image-free point target autofocus.

[0053] like Figure 1 As shown, the optical path of the single-pixel target autofocus system provided by the present invention includes a light source 101, a spatial light modulator 102, an aperture 103, an objective lens 104, a displacement stage 105, an imaging target 106, a second photoelectric sensor 107, an optical fiber 108, and a first photoelectric sensor 109. The optical path includes two parts: a non-imaging focusing optical path and a single-pixel microscopic imaging optical path. These two parts share the following components:

[0054] Light source 101 is used to illuminate the spatial area in front of objective lens 104. In this embodiment, an LED light source is selected to ensure stable illumination and sufficient luminous flux. The light source illuminates the spatial light modulator 102 at an appropriate angle, so that the spatial light modulator 102 can perform structured modulation of the incident light.

[0055] Spatial light modulator 102, such as a digital micromirror device (DMD), is used to perform structured light modulation on the incident light to obtain a modulation pattern. The spatial light modulator 102 loads different Hadamard mask patterns or other coded structures according to control signals from the data processing terminal, causing the outgoing light to carry corresponding spatial frequency characteristics. Each modulation pattern corresponds to one single-pixel measurement; that is, under the action of the modulation pattern, the first photoelectric sensor 109 collects the light signal generated by the target point and forms a measurement value, which characterizes the optical response of the target point under this modulation mode, thus constituting the one-dimensional single-channel detection signal required for subsequent normalization processing and norm energy index calculation.

[0056] Aperture 103 is used to limit the beam range, improve the quality of the modulated light field, and suppress stray light. Its function is similar to "spatial filtering / beam shaping", but it does not perform imaging.

[0057] Objective lens 104 is used to focus the modulated structured light onto the imaging target 106, and at the same time collect reflected or scattered light from the target point. The target point is a spatial point located within the sample area for autofocus and measurement. It is used to optically interact with the modulated structured light and generate an optical signal that can be received by the single-pixel detection module. The axial position of objective lens 104 is controlled by displacement stage 105 to change the focal length, which is used to generate the scanning data required for autofocus.

[0058] The displacement stage 105 is a precision moving device responsible for moving the objective lens 104 along the optical axis. In this embodiment, the position of the objective lens 104 can be continuously adjusted according to a preset step distance through the displacement stage 105, which is used to construct a curve of light intensity index changing with focal length;

[0059] The imaging target 106, used as a sample for focus evaluation or imaging verification, can be a standard resolution plate, a point target, a scatterer, or any target to be tested.

[0060] The non-imaging focusing optical path is the foundation for realizing the single-pixel non-imaging focusing method. In addition to the common components mentioned above, it also includes:

[0061] Fiber 108 is used to couple the return light collected by objective lens 104 to first photoelectric sensor 109. Fiber 108 has advantages such as strong anti-interference ability and stable optical coupling, which enables it to accurately reflect the energy change of point spread function (PSF) after being affected by defocus.

[0062] The first photoelectric sensor 109 (dedicated to focusing) is used to receive a single-channel optical signal from the optical fiber 108. The modulated structured light acts on the target point at different focal lengths, and its reflected light is collected by the objective lens 104 and enters the optical fiber 108, so that the first photoelectric sensor 109 obtains a series of light intensity values ​​that change with the modulation pattern and forms a one-dimensional single-channel detection signal. This one-dimensional single-channel detection signal reflects the width change of the PSF and can be used as a physical basis for focusing judgment.

[0063] The single-pixel imaging optical path is the foundation for subsequent single-pixel observation and focus confirmation. In addition to the shared components mentioned above, it also includes:

[0064] The second photoelectric sensor 107 (dedicated to imaging) is used to perform the single-pixel imaging process after focusing is completed. This optical path directly receives signals from the objective lens 104 without transmission through the optical fiber 108, resulting in a high signal-to-noise ratio and enabling high-quality single-pixel reconstruction.

[0065] Based on the single-pixel target autofocus system provided by this invention, this invention achieves single-pixel target autofocus without imaging through a data processing terminal, and performs single-pixel imaging verification after focusing is completed. The operation steps of this embodiment include two parts: point spread function information acquisition and autofocus, and single-pixel imaging verification.

[0066] from Figure 2 As can be seen, the results include the distribution of the point spread function at different focal plane positions and the single-pixel reconstructed image effect under the corresponding conditions.

[0067] Near the focal point, the point spread function exhibits a highly concentrated energy distribution, with a small main lobe, a prominent central peak, and weaker energy in the surrounding side lobes, indicating that the system is in good focus. In this state, the reconstructed single-pixel image has high sharpness and contrast, and the detailed contours of the target can be effectively identified.

[0068] When the system is out of focus, the point spread function gradually widens, energy diffuses from the center outwards, the main lobe size increases significantly, and the side lobe structure strengthens, resulting in a more dispersed overall energy distribution. The corresponding single-pixel reconstructed image appears blurred, with significant attenuation of target edges and details, and a decrease in spatial resolution.

[0069] Furthermore, although the morphology of the point spread function differs in its specific distribution under different defocus directions and degrees, they all exhibit the common characteristics of decreased energy concentration and enhanced spatial expansion. This trend is consistent with the changes in the sharpness of the single-pixel reconstructed image. Therefore, the energy concentration of the point spread function can effectively reflect the focusing state of the system, providing a physical basis for the subsequent construction of norm energy indices based on one-dimensional single-channel detection signals and the determination of the optimal focal plane.

[0070] The spatial light modulator 102 sequentially loads multiple Hadamard structured light modulation patterns, causing the illumination light field to produce different known structures in space. Each modulation pattern corresponds to one measurement. After being constrained by the aperture 103, the modulated light directly enters the objective lens 104 and acts on the imaging target 106.

[0071] The reflected or scattered light from the imaging target 106 is collected by the objective lens 104 and then enters the optical fiber 108, before being transmitted to the first photoelectric sensor 109. The first photoelectric sensor 109 measures the light intensity value corresponding to each modulation pattern, forming a one-dimensional single-channel detection signal. This one-dimensional single-channel detection signal reflects the optical response of the target point under different spatial modulation conditions and is highly correlated with the width and shape of the PSF.

[0072] To eliminate the influence of factors such as light source fluctuations and changes in fiber coupling efficiency, this embodiment normalizes the one-dimensional single-channel detection signal, making the measurement results obtained under different modulation conditions comparable. The normalized one-dimensional single-channel detection signal can more stably reflect the trend of PSF variation with focal length.

[0073] This embodiment uses the norm as a quantitative indicator of focus level. By calculating the energy concentration of the normalized one-dimensional single-channel detection signal, an evaluation value characterizing the current focus state can be obtained. When the system is at the accurate focus position, the PSF energy is most concentrated, and the corresponding evaluation value reaches its maximum; when the system defocuses, the PSF widens, and the evaluation value decreases accordingly.

[0074] Figure 3 These are the simulated peak curves for different norms provided by this invention. The different colored curves in the figure correspond to the norm calculation results of different orders. Figure 3 In the diagram, L2 represents the L2 norm evaluation result, L4 represents the L4 norm evaluation result, L6 represents the L6 norm evaluation result, and L∞ represents the infinity norm evaluation result. The horizontal axis represents the defocus position of the system along the optical axis, and the vertical axis represents the norm energy index calculated at the corresponding defocus position. Figure 3 As can be seen, all the norms used exhibit obvious peak characteristics at the focal position, with the peak differentiation of the L2 norm being the most prominent.

[0075] The displacement stage 105 moves the objective lens 104 along the optical axis at a preset step distance, allowing the system to experience a complete process from defocusing to focusing and then back to defocusing. At each position moved, the aforementioned light intensity acquisition and evaluation index calculation process is executed.

[0076] Figure 4 This is the L4 norm focusing index change curve during objective lens scanning provided by the present invention, such as... Figure 4 As shown, the actual measurement curves of the evaluation index as the objective lens 104 changes with its position during the scanning process are illustrated. The curve exhibits a typical single-peak structure, with the peak position corresponding to the optimal focusing state of the objective lens 104 along the optical axis, i.e., the optimal relative focusing position between the objective lens 104 and the target point in the sample area. To improve the stability of peak positioning and suppress the influence of measurement noise on the curve shape, the control system first smooths the L4 norm energy index sequence calculated at each scanning position. Smoothing can be achieved using sliding window averaging or Gaussian smoothing. The smoothing parameters include at least the smoothing window length or the smoothing kernel width, which are preset or adaptively set according to the scanning step size and measurement noise level, thereby obtaining the smoothed norm energy curve. Subsequently, the control system performs a peak-finding operation on the smoothed norm energy curve. This peak-finding operation involves searching for the maximum value point of the norm energy index within a preset scanning range and determining the axial position of the objective lens corresponding to this maximum value point as the candidate focus position. Furthermore, to achieve sub-step level focus positioning accuracy, the control system can select local data near the candidate focus position, including the peak point and several adjacent sampling points. This local data is then subjected to curve fitting, with the fitting model being a Gaussian function or a polynomial function. The control system calculates the optimal focus position based on the maximum value of the fitted curve and controls the displacement stage to move the objective lens 104 to this optimal focus position, thereby achieving automatic locking and focusing on the target point.

[0077] Once the optimal focus position is detected, the control system instructs the stage 105 to move the objective lens 104 to that position, thus completing the entire autofocus process. The entire focusing process relies solely on single-pixel measurements, eliminating the need for two-dimensional image reconstruction, resulting in fast focusing speed and strong system robustness.

[0078] After focusing is complete, the system switches to the imaging optical path, where the second photoelectric sensor 107 receives the light intensity signal collected by the objective lens 104 and modulated by the spatial light modulator 102 with structured light. The spatial light modulator 102 loads a complete Hadamard mask pattern sequence, and the second photoelectric sensor 107 records the light intensity measurement signals (i.e., light intensity measurement sequences) corresponding to all modulation patterns.

[0079] By performing an inverse Hadamard transform on the light intensity measurement signal, the two-dimensional intensity distribution of the imaged target can be reconstructed. The resulting reconstructed image is used not only to verify the accuracy of the autofocus results but also for subsequent target observation and detection.

[0080] Figure 5 This is a comparison of the reconstructed images before and after autofocus provided by the present invention, such as... Figure 5 As shown, the comparison demonstrates the single-pixel reconstructed image quality obtained under out-of-focus and focused conditions. Under out-of-focus conditions, the reconstructed image is generally blurry, with significant attenuation of target details and edge information, resulting in low spatial resolution. When the system automatically focuses on the focused surface, the reconstructed image sharpness is significantly improved, the target contour and detailed structure are effectively restored, and the resolution is significantly improved. The above comparison results show that the single-pixel autofocus method based on norm metric proposed in this invention can accurately locate the system's focused surface without the need for two-dimensional imaging to participate in the focusing process, thereby significantly improving the quality of subsequent single-pixel imaging.

[0081] In summary, existing methods (such as Fourier modulation and differential detection) all rely on specific frequency domain priors, sample structures, or indirect statistics, failing to directly establish themselves on the characterization of the core physical model of the point spread function (PSF). Therefore, they lack stability under complex conditions. In contrast, this invention directly addresses the physical laws governing the change of PSF with defocus, thereby achieving robust focusing without relying on sample priors.

[0082] The parts of this invention not described in detail are well-known to those skilled in the art. The embodiments described above are merely preferred embodiments of the invention, and do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Various modifications and improvements to the technical solutions of this invention made by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims of this invention.

[0083] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0084] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0085] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A single-pixel target autofocus system based on norm metric, characterized in that, The system includes: A programmable light field modulation module, comprising a light source (101) and a spatial light modulator (102), is used to generate a structured illumination light field; The focusing module includes an aperture stop (103), an objective lens (104), and a displacement stage (105) connected to the objective lens (104), for adjusting the illumination light field and focusing on the imaging target (106), and collecting the light signal generated by the target point in the imaging target (106); A single-pixel detection module includes an optical fiber (108) and a first photoelectric sensor (109) for receiving the optical signal and converting the optical signal into an electrical signal; The single-pixel imaging module includes a second photoelectric sensor (107), which is disposed on the imaging side of the focusing module and is used to collect light intensity measurement signals for single-pixel imaging after autofocus is completed. The data processing terminal is used to control the pattern refresh of the spatial light modulator (102) to perform spatial structured modulation of the incident light, drive the displacement stage (105) with the objective lens (104) to move in the optical axis direction to traverse different defocus positions, control the acquisition of data from the first photoelectric sensor (109), and also to form a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable based on the one-dimensional single-channel detection signal of the current defocus position, and drive the movement of the displacement stage (105) according to the norm energy curve to perform automatic focusing.

2. The single-pixel target autofocus system based on norm metric according to claim 1, characterized in that, In the light source module: The light source (101) is used to generate illumination light and provide incident light to the spatial light modulator (102); The spatial light modulator (102) is disposed on the light-emitting side of the light source (101) and is used to perform spatial structured modulation of the incident light under the action of a control signal to form a time-varying illumination light field.

3. The single-pixel target autofocus system based on norm metric according to claim 2, characterized in that, In the focusing module: The aperture (103) is disposed between the spatial light modulator (102) and the objective lens (104) to limit the beam range and suppress stray light; The objective lens (104) is disposed on the light-emitting side of the spatial light modulator (102) and is used to focus the modulated light field onto the imaging target (106) and collect the light signal generated by the target point in the imaging target (106), the light signal including reflected light, scattered light or transmitted light; The displacement stage (105) is connected to the objective lens (104) and is used to drive the objective lens (104) to move along the optical axis to change the axial position of the target point relative to the objective lens (104).

4. The single-pixel target autofocus system based on norm metric according to claim 3, characterized in that, In the single-pixel detection module, one end of the optical fiber (108) is disposed on the imaging side of the objective lens (104) to receive the light signal returned from the target point and collected by the objective lens (104), and the other end is connected to the first photoelectric sensor (109).

5. The single-pixel target autofocus system based on norm metric according to claim 4, characterized in that, In the single-pixel detection module, the first photoelectric sensor (109) is used to convert the collected light signal into an electrical signal to form a one-dimensional single-channel detection signal for autofocus.

6. The single-pixel target autofocus system based on norm metric according to claim 5, characterized in that, In the single-pixel imaging module, the second photoelectric sensor (107) is disposed on the imaging side of the objective lens (104) and is used to collect light intensity measurement signals for single-pixel imaging after autofocus is completed.

7. The single-pixel target autofocus system based on norm metric according to claim 1, characterized in that, In the single-pixel detection module, the optical fiber (108) is configured as a probe and extends into the sample area or near-field area to collect the optical signal; wherein, the sample area is the spatial area where the target point to be measured is located, and is used to reflect, scatter or transmit with the illumination light field modulated by spatial light, and generate the optical signal.

8. The single-pixel target autofocus system based on norm metric according to claim 7, characterized in that, The aperture stop (103) is a limiting aperture stop, which is disposed between the light source (101) and the spatial light modulator (102) or between the spatial light modulator (102) and the sample area, and is used to limit the field of view or filter out stray light.

9. The single-pixel target autofocus system based on norm metric according to claim 1, characterized in that, The data processing terminal performs the following steps: Step S1: Control the micromirror unit inside the spatial light modulator (102) to switch between different tilt states to achieve spatial structured modulation of the incident light, so as to obtain a structured illumination light field. Step S2: Control the displacement stage (105) to move the objective lens (104) along the optical axis direction, thereby traversing different defocus positions. The spatial light modulator (102) performs sequential illumination modulation on the target point located in the sample area at each defocus position. The light signal reflected or transmitted by the target is converged to the single pixel detection module, and a one-dimensional single-channel detection signal corresponding to the current defocus position is obtained. Step S3: Normalize the one-dimensional single-channel detection signal to obtain the normalized one-dimensional single-channel detection signal; Step S4: Based on the normalized one-dimensional single-channel detection signal, construct a focusing evaluation function that can characterize the energy concentration of the target point. Calculate the norm energy index that characterizes the energy concentration of the target point at the corresponding defocus position according to the focusing evaluation function, and form a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable. Step S5: Drive the displacement stage (105) to move to the corresponding axial position according to the norm energy curve, thereby automatically locking the optimal focus position of the target point.

10. The single-pixel target autofocus system based on norm metric according to claim 9, characterized in that, The data processing terminal also performs the following steps: In step S1, modulation matrix generation and loading: generating a spatially encoded mask pattern for autofocus; constructing an orthogonally complete Hadamard matrix, extracting the row vectors or column vectors of the Hadamard matrix and rearranging them to generate a series of binarized pattern sequences to obtain a Hadamard mask pattern sequence; loading the Hadamard mask pattern sequence sequentially onto the spatial light modulator (102) during autofocus, and loading the Hadamard mask pattern sequence frame by frame according to the control signal during the autofocus scanning process of the spatial light modulator (102); In step S2, defocus sequence scanning and detection: a scanning and detection mechanism along the optical axis is constructed, and the displacement stage (105) is controlled to move the objective lens (104) along the optical axis to traverse different defocus positions. The defocus position is the axial offset position of the objective lens (104) relative to the optimal focus position. At each defocus position, the spatial light modulator (102) quickly projects a complete Hadamard mask pattern sequence to sequentially illuminate and modulate the target point located in the sample area. The light signal reflected or transmitted by the target converges to the single-pixel detection module. The first photoelectric sensor (109) converts the light signal into an electrical signal and performs analog-to-digital conversion on the electrical signal to obtain a one-dimensional single-channel detection signal corresponding to the current defocus position. In step S3, signal interference immunity and norm normalization: the one-dimensional single-channel detection signal acquired at each defocus position is normalized. For the one-dimensional single-channel detection signal obtained at the current defocus position, the sum of the absolute values ​​of the amplitudes of each measured value in the one-dimensional single-channel detection signal is calculated. Each measured value in the one-dimensional single-channel detection signal is divided by the sum of the absolute values ​​to obtain the normalized one-dimensional single-channel detection signal. In step S4, the norm energy index is calculated as follows: Based on the normalized one-dimensional single-channel detection signal, a focusing evaluation function that can characterize the energy concentration of the target point is constructed. The p-order norm is selected as the calculation form of the focusing evaluation function, where p is a positive integer greater than or equal to 2. At each defocus position, the p-order norm is calculated for the amplitude of each measured value in the normalized one-dimensional single-channel detection signal corresponding to the defocus position. The norm energy index that characterizes the energy concentration of the target point at the corresponding defocus position is obtained according to the focusing evaluation function. A one-to-one correspondence is established between the norm energy index obtained at different defocus positions and the corresponding defocus positions, thereby forming a norm energy curve with the defocus position as the independent variable and the norm energy index as the dependent variable. In step S5, the optimal focal plane is located by performing peak search or Gaussian fitting on the norm energy curve. Based on the extreme value characteristics of the norm energy curve, the axial position corresponding to the maximum value of the norm energy index in the norm energy curve is determined to be the actual focal plane of the system. At the position where the norm energy index reaches the maximum value in the norm energy curve, the displacement stage (105) is driven to move to the corresponding axial position, thereby automatically locking the optimal focus position of the target point.

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