Systems and methods for optical imaging and measurement of objects

Abstract

Systems and methods are provided for imaging, measuring objects, and characterizing samples. The optical speckle-based imaging system includes an illumination unit including at least one coherent light source for illuminating a sample, a collection unit for collecting input light from the sample, the collection unit consisting of imaging optics and a wavefront imaging sensor, and a control unit coupled to the illumination unit and the collection unit to analyze the input light to generate a speckle wavefront image, wherein the at least one coherent light source generates primary speckles in or on the sample, and the imaging optics captures secondary speckle patterns in or on the sample caused by the illumination unit.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from U.S. Provisional Patent Application No. 62 / 960,716, filed January 14, 2020, which is incorporated herein by reference.

[0002] The present invention relates generally to optical imaging and measurement, and more particularly to optical imaging, measurement and characterization of objects and samples, and optical biometric measurement of people or animals. [Background technology]

[0003] Optical speckle-based metrology is a non-contact method for measuring objects and samples. Properties such as movement, orientation, vibration, and deformation can be measured. Various objects can be measured for a number of purposes. For example, mechanical components of objects can be measured for monitoring and characterization under stress in test or working conditions.

[0004] Another example is biometric measurements: heart rate, blood pressure, respiration, and other parameters can be measured by performing a series of measurements on relevant parts of the body. Furthermore, acoustic signals can be recovered by measuring the vibrations of a sound source, e.g., a speaker, the human neck area, or a nearby object vibrating with the acoustic signal.

[0005] There is a need in the art for improved sample coverage in various areas, There is a need in the art for enhanced sensitivity and robustness in imaging and measuring various objects. Summary of the Invention

[0006] According to embodiments of the present invention, systems and methods are provided for imaging objects, measuring objects, and characterizing samples.

[0007] According to one aspect of the present invention, an optical speckle-based imaging system is provided, comprising: an illumination unit including at least one coherent light source for illuminating a sample; a collection unit for collecting input light from the sample, the collection unit consisting of imaging optics and a wavefront imaging sensor; and a control unit coupled to the illumination unit and the collection unit for analyzing the input light and generating a speckle wavefront image, wherein the at least one coherent light source generates primary speckles in or on the sample, and the imaging optics captures secondary speckle patterns caused by the illumination unit in or on the sample.

[0008] According to an embodiment of the present invention, an optical speckle-based imaging system is provided, comprising: an illumination unit including at least one coherent light source for illuminating a sample; a collection unit for collecting input light from the sample, the collection unit consisting of an imaging optical system and a wavefront imaging sensor; and a control unit coupled to the illumination unit and the collection unit for analyzing the input light and generating a speckle wavefront image, wherein the size of the exit pupil of the illumination unit is smaller than the size of the entrance pupil of the imaging optical system, and the at least one coherent light source generates primary speckles in or on the sample, and the imaging optical system captures secondary speckle patterns in or on the sample caused by the illumination unit.

[0009] According to one embodiment of the present invention, the control unit further influences at least one of the size of the exit pupil and the size of the entrance pupil and the relationship therebetween.

[0010] The at least one coherent light source can have a temporal coherence length greater than at least one of: (1) the optical diffusion length of the sample; and (2) the surface roughness of the sample.

[0011] The coherent light source can have a spatial coherence length, and the collector can have a spatial coherence length of the point spread function, wherein the spatial coherence length of the coherent light source projected onto the sample, when projected onto the sample, is on the order of or greater than the spatial coherence length of the point spread function of the collector projected onto the sample via the imaging optics.

[0012] The optical properties of the illumination unit and the collection unit may be selected to form, for every point imaged on the sample, an angle subtended by the optical aperture of the collection unit as seen from any point on the sample that is greater than the angle subtended by the optical aperture of the illumination unit as seen from the same point on the sample.

[0013] The illumination unit can have an illumination aperture that determines an illumination angle, and the collection unit can have a collection aperture that determines a collection angle, and the control unit is further coupled to the illumination unit to affect the illumination conditions and further to affect the collection conditions to form a collection angle seen from any point on the sample, the collection angle being greater for all points imaged on the sample than the illumination angle seen from the same point on the sample.

[0014] The acquisition portion may further measure data indicative of at least one of speckle intensity, speckle wavefront, and speckle coherence.

[0015] The illumination unit may further include an incoherent light source, and the control unit may further generate the light field image in response to the incoherent illumination.

[0016] The control unit can operate the illumination unit to selectively provide coherent light and incoherent light.

[0017] The illumination unit may further include an incoherent light source, and the control unit may operate the aperture of the illumination unit so that the spatial coherence length of the incoherent illumination is shorter than the spatial coherence length of the imaging optics of the collection unit.

[0018] The wavefront imaging sensor may be one of the group consisting of a plenoptic camera, a light field camera, a Shack-Hartmann wavefront sensor, and a coherence camera wavefront sensor, comprising an encoder having a plurality of similar unit cells and an array of sensor cells located a distance downstream of the unit cell with respect to the overall direction of propagation of input light through the wavefront imaging sensor, wherein the array of sensor cells defines a plurality of sub-array unit cells, each sub-array corresponding to one of the plurality of unit cells of the encoder, each sub-array including a predetermined number M of sensor elements, wherein the encoder applies a predetermined modulation to the input light such that each unit cell of the encoder directs a portion of the input light incident thereon to its corresponding sub-array unit cell and one or more neighboring sub-array unit cells within a predetermined proximity region, wherein the predetermined number M is determined according to a predetermined number of sub-array unit cells within the predetermined proximity region.

[0019] The illuminator can provide at least one light from the group consisting of coherent light, partially coherent light, and incoherent light. The illuminator can further provide the light as a set of varying optical properties, the optical properties and conditions being from the group consisting of a selected wavelength range, a selected temporal coherence range, and a selected illumination direction, and the controller can generate one or more of the group consisting of an intensity map, a wavefront map, and a coherence map.

[0020] According to one aspect of the present invention, an imaging method is provided, including illuminating a sample with coherent light, capturing input light from the sample with a collection unit comprising imaging optics and a wavefront imaging sensor, and analyzing the input light to generate a speckle wavefront image with a controller coupled to the collection unit, wherein at least one coherent light source generates primary speckles in or on the sample, and the imaging optics captures secondary speckle patterns in or on the sample caused by the illumination unit. The size of the exit pupil of the illumination unit may be smaller than the size of the entrance pupil of the imaging optics. The controller may affect at least one of the size of the exit pupil and the size of the entrance pupil, and the relationship therebetween.

[0021] The method may include capturing and analyzing at least one additional input light from the sample to generate at least one additional speckle wavefront image, and calculating the sample deformation based on the speckle wavefront image and the at least one additional speckle wavefront image.

[0022] The operation of calculating the sample deformation may be performed by determining the change in local slope between one or more pairs of speckle wavefront images.

[0023] The method may include computing a time sequence of spatiotemporal deformation maps.

[0024] The method may include at least one step from the group consisting of analyzing the time sequence of spatiotemporal deformation maps and selecting a specific region of interest within the sample; analyzing the time sequence of spatiotemporal deformation maps and distinguishing between the sample and its surroundings; analyzing the time sequence of spatiotemporal deformation maps and distinguishing between global movement and local deformation or vibration of the sample; analyzing the time sequence of spatiotemporal deformation maps and performing spatial segmentation; analyzing the time sequence of spatiotemporal deformation maps and performing time segmentation; analyzing the time sequence of spatiotemporal deformation maps and extracting acoustic signals; analyzing the time sequence of spatiotemporal deformation maps and measuring biometric parameters; analyzing the time sequence of spatiotemporal deformation maps and mapping mechanical vibration modes.

[0025] The method may include illuminating a face or portion thereof with at least one of spatially incoherent light and ambient light, capturing an incoherent wavefront image, calculating a two-dimensional (2D) intensity image and a depth map, extracting unique three-dimensional (3D) facial recognition data, comparing the facial recognition data with stored unique three-dimensional (3D) facial recognition data, and determining a recognition approval or rejection decision.

[0026] The method may include analyzing a time sequence of spatiotemporal deformation maps to extract spatiotemporal biometric parameters, extracting unique biomarkers, comparing the unique biomarkers to stored unique biomarkers, and determining a recognition approval or rejection decision.

[0027] The method may include repeating the operations of illumination, capture, analysis, and generation for a sequence of wavelengths, performing multispectral phase unwrapping, and estimating the surface profile.

[0028] The method may include repeating the illumination, capture, analysis, and generation operations for a sequence of wavelengths for various angles, performing multispectral phase unwrapping, and calculating the refractive index distribution of the three-dimensional diffraction tomography. [Brief explanation of the drawings]

[0029] For a better understanding of the present invention with respect to embodiments thereof, reference is now made to the accompanying drawings, in which like reference numerals indicate corresponding entities throughout.

[0030] [Figure 1] 1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 2a-2b] FIG. 2 is a block diagram showing in schematic detail the system shown in FIG. 1. [Figure 3] FIG. 1 is a flow diagram illustrating a method according to one embodiment of the present invention. [Figure 4] FIG. 4 is another flow diagram illustrating a method according to an embodiment of the present invention. [Figure 5a-5b] 1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 6a-6b] 1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 7a-7c] FIG. 1 is a flow diagram illustrating a method according to one embodiment of the present invention. [Figure 8a-8b] 1 illustrates a schematic diagram of coherent illumination at normal incidence according to an embodiment of the present invention; [Figure 9a-9b] 1 illustrates a schematic representation of a multispectral phase unwrapping technique according to an embodiment of the present invention; [Figure 10] FIG. 1 is a flow diagram illustrating a method according to one embodiment of the present invention. [Figures 11a-11c] 1 illustrates a schematic diagram of a multispectral diffraction tomography method according to an embodiment of the present invention; [Figure 12] 1A-1C illustrate schematic diagrams of multispectral speckle wavefront imaging from several illumination angles according to an aspect of the present invention. [Figure 13]1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 14] 1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 15] FIG. 1 is a flow diagram illustrating a method according to one embodiment of the present invention. [Figure 16] 1 is a block diagram that schematically illustrates a system according to an embodiment of the present invention. [Figure 17] 1 is a block diagram that schematically illustrates a wavefront imaging sensor and system according to an embodiment of the present invention; [Figure 18] 1 illustrates an aspect of a wavefront imaging sensor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Optical measurement and characterization of objects and samples is used to determine and evaluate parameters such as transmittance, reflectance, shape, depth, 3D structure, and texture. Changes in parameters over time can be measured to detect changes in sample movement, orientation, deformation, and vibration. In some applications, these data can be used to characterize samples for inspection and monitoring purposes. In other applications, these data may be used for biometric sampling, monitoring, or authentication, and for acquiring acoustic signals from samples, such as voice.

[0032] Several optical measurements and techniques for sample characterization are speckle-based.

[0033] Current optical methods for speckle-based measurement of sample motion, orientation, vibration, and deformation are based on illuminating the sample with a coherent light source and collecting the scattered light. Speckle-based measurements can be performed, for example, by (1) measuring the overall time-varying intensity distribution of light impinging on a photodetector, (2) directly imaging the speckle intensity pattern, or (3) imaging the speckle pattern on a focal plane displaced from the object.

[0034] Typically, speckle-based measurements involve illuminating a sample with a single, substantially coherent spot or with multiple, distinct, coherent spots. Single-spot and multi-spot illumination do not completely cover the sample's surface. Therefore, a complete map of the sample's deformation or vibration cannot be measured. Object movement, deformation, and vibration are typically measured only in specific regions of the sample.

[0035] Single-spot and multi-spot illumination measurements may not be able to distinguish between non-uniform deformations or vibrations within each such separate illumination spot. Instead, the deformations or vibrations within each separate illumination spot are treated as a whole. As such, single-spot and multi-spot illumination measurements can only provide data that indicate the spatial average of the deformations or vibrations within each separate illumination spot. In other words, there is no spatial resolution of the vibration or deformation map within each individual illumination spot. This is particularly true when imaging speckle patterns on a focal plane displaced from the sample, where the speckle pattern is imaged with strong defocus, resulting in a loss of spatial resolution of the vibrations or deformations and a far-field (Fourier plane) map of the speckle pattern.

[0036] Other measurement methods with wider sample coverage are based on the use of an interferometer setup with an additional reference beam or multiple beams illuminating the same area. These methods are commonly known as electronic speckle pattern interferometry. The interferometer setup and the multiple beams and optical paths can result in a measurement system that is very sensitive to vibrations of its components and external vibrations of the sample, and is therefore less robust and more susceptible to external environmental factors.

[0037] Other measurement methods may use special targets and reflectors attached to the sample. In such methods, data may be collected only from the area of ​​the sample where the target or reflector is attached. In many practical applications, the requirement to attach a target or reflector to the sample is prohibitive. For example, attaching targets and reflectors to people or animals may cause discomfort, and the sample may not otherwise be disturbed. Also, for very sensitive measurements, sample movement may not be fully transmitted to the target, resulting in less than optimal results.

[0038] Furthermore, speckle-based measurements provide limited data about the sample's microscopic surface profile for opaque samples and little information about the interior of translucent samples. This is primarily due to the large degree of roughness / diffusivity of the sample medium, which causes random speckle formation.

[0039] Furthermore, the above methods typically perform non-imaging measurements and utilize specialized optical configurations that are not easily adapted to provide standard 2D (2D, two-dimensional) images or to perform 3D (3D, three-dimensional) optical measurements. To obtain other information about the sample, such as overall reflectance / transmittance and sample shape, a separate imaging setup is typically required to perform traditional 2D imaging. Furthermore, 3D measurements require specialized equipment using a variety of techniques, such as stereo imaging, structured light, laser triangulation, time-of-flight measurements, active stereo, and light-field imaging, to name a few.

[0040] Prior art systems known as "quantitative phase imaging" typically use an interferometer setup to acquire quantitative phase images of a microscopic sample. Under conditions in which the sample induces relatively small phase variations, the resulting phase map has regular features related to the sample's microscopic structure. When used to image rough, diffuse, or macroscopic samples with large phase variations, quantitative phase imaging systems may provide random speckle phase maps. Therefore, a single speckle phase map provides little information about the sample, except perhaps for a rough overall intensity distribution given by the local average speckle intensity.

[0041] Also, quantitative phase imaging typically requires that the illumination angle be consistent with the orientation of the sample and imaging optics. This consistency is necessary to capture so-called "zero-order" transmission or specular reflection, i.e., "bright-field" setups. On the other hand, the present invention can be used in the speckle regime for macroscopic samples or samples with significant surface roughness or diffusivity, where the illumination angle is less critical because the speckle is scattered over a wide range of angles.

[0042] Embodiments of the present invention provide systems and methods for optical speckle-based measurement and characterization of objects and samples.

[0043] Embodiments of the present invention may be used to perform speckle-based motion, orientation, vibration, and deformation measurements with complete sample coverage. Thus, embodiments of the present invention facilitate the ability to map motion, orientation, vibration, and deformation data with high spatial resolution to distinguish different portions of a sample, while eliminating the need for complex setups involving multiple interfering beams. Embodiments of the present invention enable various types of measurements to be performed with the same basic system to obtain more information about the sample, such as its shape, reflectivity / transparency, and detailed surface profilometry, texture, or internal / external 3D structure.

[0044] The system comprises an illumination unit having one or more light sources (also referred to as illumination sources) and operable to illuminate the sample with coherent and / or incoherent light under variable illumination conditions; a collection unit having imaging optics and an imaging sensor for collecting light returned from and / or passing through the sample; and a control unit coupled to the collection unit to receive data indicative of at least one of speckle intensity, speckle wavefront, and speckle coherence and generate a speckle wavefront image, the control unit further coupled to the illumination unit to affect the illumination conditions or other optical properties.

[0045] The controller may further affect the optical properties of the system and various components. The controller may affect the illumination conditions, the collection conditions, or both. The controller may affect the optical properties of the illuminator and the optical properties of the collector. The controller may maintain a predetermined relationship between the optical properties of the illuminator and the optical properties of the collector. The variable illumination conditions may be selected from the group consisting of coherent illumination, incoherent illumination, partially coherent, degree of spatial coherence, degree of temporal coherence, wavelength range, illumination direction, and illumination angle.

[0046] The system may further comprise a beam splitting device located upstream of the imaging optics to project light onto the sample and collect light returned from the sample through the imaging optics.

[0047] The control unit further processes data snapshots or sequences received from the collection unit under single or multiple lighting conditions (or other optical characteristics) to determine data indicative of one or more properties of the sample (or surface of the sample), the one or more properties of the sample (or surface of the sample) being from the group consisting of reflectance of the sample, transmittance of the sample, shape of the sample, depth of the sample, three-dimensional structure of the sample, deformation of the surface of the sample, movement of the surface of the sample, vibration of the sample, orientation of the sample, and texture of the sample.

[0048] The imaging sensor may be a wavefront sensor or a light field sensor. The imaging sensor may be one of a plenoptic camera (light field camera), a Shack-Hartmann wavefront sensor, or a coherence camera wavefront sensor, as described in WIPO Patent Application WO / 2018 / 185740, which is incorporated herein by reference.

[0049] The wavefront imaging sensor may include an encoder having a plurality of similar unit cells and an array of sensor cells located a distance downstream of the unit cells with respect to the overall direction of propagation of input light through the wavefront imaging sensor 108. The array of sensor cells defines a plurality of subarray unit cells, each subarray corresponding to one unit cell of the plurality of unit cells of the encoder, and each subarray including a predetermined number M of sensor elements. The encoder is configured to apply a predetermined modulation to the input light such that each unit cell of the encoder directs a portion of the input light incident thereon to its corresponding subarray unit cell and one or more neighboring subarray unit cells within a predetermined proximity region (PR). The predetermined number M is determined according to a predetermined number of subarray unit cells within the predetermined proximity region.

[0050] The illumination source can be a coherent light source to induce speckle on or in the sample, also called "primary speckle," which can be obtained by a light source with a temporal coherence length greater than the optical diffusion length or surface roughness of the sample.

[0051] The imaging optics of the collector are configured to have sufficient spatial resolution to resolve speckle patterns induced on or within the sample, thereby obtaining a "secondary speckle" image. The system may further be arranged such that the exit pupil of the illuminator is smaller than the entrance pupil of the collector. This arrangement ensures that the imaging system has sufficient spatial resolution to obtain "secondary speckle" at the image plane.

[0052] If a coherent light source, when projected onto the sample, has a spatial coherence length greater than the spatial coherence length of the collecting point spread function projected onto the sample via the imaging optics, sufficient spatial resolution can be obtained to resolve the speckle pattern.

[0053] According to embodiments of the present invention, the spatial coherence length of the coherent light source is 1.1, 1.2, 1.5, or more times greater than the spatial coherence length of the point spread function of the collector projected onto the sample through the imaging optics.

[0054] The system may further be arranged so that for all points imaged on the sample (also referred to as all points in the field of view of the collector), the collection angle defined by the optical aperture of the collector as seen from any point on the sample is greater than the illumination angle defined by the optical aperture of the illumination unit as seen from the same point on the sample.

[0055] The illumination unit may include a coherent illumination source and an incoherent illumination source. The coherent source is used to perform speckle wavefront imaging as described above, and the ambient light or incoherent source is used to perform light field imaging to estimate the luminous intensity and 3D shape of the sample. The illumination source may be selectively operable to provide coherent light and incoherent light. The incoherent light may be provided through a large aperture so that the spatial coherence length of the resulting illumination is less than or equal to the spatial coherence length of the imaging optics of the collection unit. The control unit may be capable of switching between the coherent light and the incoherent light.

[0056] According to an aspect of the present invention, a system for use in optical imaging and measurement of a sample is described, comprising: an illuminator configured to provide coherent, partially coherent, or incoherent illumination in one or more selected wavelength ranges and / or temporal coherence ranges, and / or to provide illumination of the sample from various directions and direct it toward the sample or a portion thereof; a collector configured to collect light returning from and / or passing through the sample and image the sample using a wavefront imaging or lightfield imaging sensor to provide data indicative of the intensity, wavefront, and coherence of the light interacting with the sample; and a controller for analyzing a single snapshot or sequence of intensity, wavefront, and coherence maps, wherein the controller also influences the illuminator to provide different degrees of spatial and temporal coherence, as well as wavelength ranges and illumination directions, and the controller processes the data snapshots or sequences from the collector under single or multiple illumination conditions (or other optical properties) to determine data indicative of the reflectance and / or transmittance, shape, depth, 3D structure, deformation, movement, vibration, orientation, and / or texture of the sample.

[0057] According to an embodiment of the present invention, a versatile optical imaging and measurement system based on a wavefront imaging sensor is used with a coherent light source to perform speckle-based imaging and measurement. Furthermore, by using ambient or incoherent flood illumination, the same wavefront imaging sensor can be used to perform 2D imaging as well as 3D measurements. By controlling the light source in either wavelength or illumination direction (or both), the system can be used to perform high-dynamic-range optical profilometry, quantitative phase imaging, or diffraction tomography.

[0058] Such a versatile optical system can provide improved sample coverage, system sensitivity, and robustness. Furthermore, it uses a simple and robust single-line-of-sight wavefront imaging optical module and simple illumination requirements. By simply changing the illumination parameters, excellent flexibility and scope are provided while maintaining the same basic configuration and using the same wavefront imaging optical system.

[0059] 1 illustrates a schematic diagram of a system 10 according to one embodiment of the present invention. The system 10 includes an illumination unit 102 having a coherent light source (not shown) and an exit pupil 102.1, a collection unit 104 that collects light returned from and / or passing through the sample, and a control unit 110 coupled to the collection unit 104 to generate a speckle wavefront image and further coupled to the illumination unit to affect illumination conditions or other optical properties. The collection unit 104 may consist of imaging optics 106 having an entrance pupil 106.1 and a wavefront imaging sensor 108.

[0060] The sample 100 is illuminated with coherent light IL, which causes speckle formation on the sample 100 due to the sample's microscopic light scattering properties. The resulting speckle field (also referred to as a speckle pattern, or "primary" or "objective" speckle) CL is imaged through a collector 104. Imaging optics 106 projects an image of the speckle field PL onto a wavefront imaging sensor 108. A speckle wavefront SW is thus formed.

[0061] "First order" speckle may be obtained under the following conditions: The illumination unit 102 may include a coherent light source with a temporal coherence length greater than the optical diffusion length or surface roughness of the sample 100.

[0062] The imaging optics 106 of the collection section 104 are configured so that a "secondary" speckle image is formed at the image plane. This requires an imaging system with sufficient optical resolution to resolve the "secondary" or "subjective" speckle pattern generated on or within the sample. There are several ways to achieve this.

[0063] The relationship between the optical properties of the illumination unit 102 and the collection unit 104 is selected so that "secondary" speckle patterns can be resolved with sufficient resolution. According to one embodiment of the present invention, the illumination unit exit pupil 102.1 is smaller than the collection unit entrance pupil 106.1. "Smaller" in this context may mean that the size of the exit pupil 102.1 is smaller than the size of the entrance pupil 106.1.

[0064] According to embodiments of the present invention, the size of the exit pupil 102.1 and the size of the entrance pupil 106.1 of the same order of magnitude may differ by a factor of, for example, 1.1, 1.2, 1.5, and more.

[0065] According to an embodiment of the present invention, the size of the exit pupil 102.1 and the size of the entrance pupil 106.1, and the relationship therebetween, are preset. According to another embodiment of the present invention, the size of the exit pupil 102.1 and the size of the entrance pupil 106.1, and the relationship therebetween, are dynamically and adaptively set. The control unit 110 is coupled to the illumination unit 102 and the collection unit 104 and can affect the optical properties of the illumination unit 102 and the collection unit 104. According to an embodiment of the present invention, the control unit 110 can affect the size of the exit pupil 102.1, the size of the entrance pupil 106.1, or both, and thus can control the relationship therebetween.

[0066] The relationship between the optical properties of the illumination section 102 and the collection section 104 can be described as follows: the coherent light source of the illumination section 102, when projected onto the sample 100, may have a spatial coherence length that is greater than the spatial coherence length of the point spread function of the collection section 104 projected onto the sample through the imaging optics 106.

[0067] Another way of expressing the relationship between the optical properties of the illumination portion 102 and the collection portion 104 is shown in Figure 5b. For every point imaged on the sample, the angle A subtended by the optical aperture of the collection portion 104 as seen from any point on the sample 100 is c is the angle A subtended by the optical aperture of the illumination unit 102 as seen from the same point on the sample 100. I must be greater than

[0068] The wavefront imaging sensor 108 may be a plenoptic camera or a Shack-Hartmann wavefront sensor, or other type of coherence camera capable of performing wavefront imaging up to optical diffraction-limited resolution. Such coherence cameras are referred to herein as wavefront imaging sensors.

[0069] The control unit 110 analyzes the speckle wavefront SW data to generate a speckle wavefront image. The speckle wavefront SW data may indicate speckle intensity, wavefront, and coherence. This data is used to measure and characterize various properties of the sample 100.

[0070] The control unit 110 typically includes a processing utility 111 and a storage utility 113, as well as a communication utility that allows input and output communications and a possible user interface, not specifically shown.

[0071] The control system 110 may be integral with the collection unit 104, the wavefront imaging sensor 108, the illumination unit 102, or a separate unit. In some embodiments, the control unit 110 may be separate from other elements of the imaging system 10 or may be based on remote or cloud processing of data. In such a configuration, the imaging system 10 may include a communications module configured to transmit data to the control unit 110 for processing.

[0072] The operation of the system 100 of FIG. 1 will be further discussed with reference to FIG. 2a. The same reference numerals are used to refer to the same elements as in FIG. 1. The system 10 measures a slightly perturbed sample 101, for example, subjected to a slight rotation or deformation. The rotation or deformation of the sample 101 is marked by a dashed line in FIG. 2a. The perturbation of the sample can be caused by mechanical or thermal stress, external shock, vibration, acoustic waves passing through the sample, pulses, or biological functions such as breathing, sound, or muscle movement.

[0073] 2b zooms in on a particular patch of the perturbed sample and shows some elements of system 10, namely imaging optics 106 and wavefront imaging sensor 108. The perturbation of sample 101 corresponds to a local rigid shift and tilt of the patch, which is shown with reference to the solid line representing the unperturbed sample 101 and the dashed line representing the perturbed sample 101.

[0074] For simplicity, for small patches, θ z Possible rotations θ because rotations can be treated as rigid shifts of (x, y) z is ignored.

[0075] For the speckle pattern generated in the sample (also known as "primary" or "objective" speckle), the perturbation is expressed as a rigid shift (x, y, z) and tilt (θx, θy) of the speckle wavefront.

[0076] The speckle wavefront SW is imaged on the wavefront imaging sensor via the imaging optical system of the collecting unit.o denotes the speckle wavefront resulting from the illumination of an undisturbed sample, and the speckle wavefront SW d denotes the speckle wavefront resulting from the illumination of the perturbed sample. The imaged speckle wavefront SW o and S.W. d The corresponding changes in are the rigid shift (x', y', z') and the local tilt (θ'x, θ'y), which are related to the original patch volume by the imaging magnification of the optical system.

[0077] Due to the limited optical resolution of the imaging system, in most practical macroscopic scenarios, the imaged speckle wavefront will have a much lower resolution (also known as "second-order" or "subjective" speckle). In practice, this reduction in resolution erases all information about the rigid shift (x', y', z') in the imaged speckle wavefront, while information about the local tilt (θ'x, θ'y) is typically well preserved.

[0078] According to one aspect of the present invention, a wavefront image of perturbed speckle is captured. It appears to have a random wavefront. However, when compared to the original speckle wavefront image of an unperturbed sample, it is found that the speckle wavefront differs in local tilt (θ'x, θ'y). Therefore, by comparing the original speckle wavefront image with the perturbed speckle wavefront image, the local tilt across the sample can be inferred and mapped, providing an accurate indication of the sample's deformation.

[0079] The inventors have found that local tilt maps have spatial resolution that allows them to distinguish between different values ​​of local tilt (θ'x, θ'y) at different locations on the sample. According to embodiments of the present invention, a continuous local tilt map is provided. The continuous local tilt map is spatially dependent and can provide full coverage of the sample. This new capability improves upon prior art speckle-based measurements, which provide uniform tilt values ​​for each distinct, spatially separated illumination spot impinging on the sample.

[0080] According to one embodiment of the present invention, a series of speckle wavefront images are captured, for example, before and after deformation of a sample. This is shown in FIG. 3 as flow diagram 30. Flow 30 begins with operation 300, in which a sample is illuminated with coherent illumination. In operation 302, a first speckle wavefront image is captured. In operation 306, the first speckle wavefront image is stored for further processing. In operation 304, a second speckle wavefront image is captured at a different time than the first speckle wavefront image. The sample may undergo sample deformation between the capture of the first speckle wavefront image in operation 302 and the capture of the second speckle wavefront image in operation 304. In operation 308, the second speckle wavefront image is stored for further processing. The first and second speckle wavefront images may differ due to local wavefront tilt caused by the deformation. In operation 310, the deformation of the sample is calculated, for example, by comparing the first and second speckle wavefront images and generating a local wavefront slope map calculated across the sample.

[0081] FIG. 4 illustrates a flow 40 of a series of several speckle wavefronts. In operation 400, a sample is illuminated using coherent illumination. In the loop of operation 402, a time series of speckle wavefront images are captured (operations 404, 406) and stored (operations 408, 410). In operation 412, a local tilt change is determined between pairs of speckle wavefront images. For example, the local tilt change is determined between adjacent pairs of speckle wavefront images. Based on the local tilt change, a time-dependent spatial mapping of the deformation of the sample can be estimated. In operation 414, a spatiotemporal deformation map sequence is calculated. This is a time sequence of spatial deformation maps. Each time step corresponds to a spatial deformation map measured between the capture of speckle wavefront image 404 and the next captured speckle wavefront image 406. The spatiotemporal deformation map sequence can be further analyzed to select specific regions of interest within the sample, distinguish between the sample and its surroundings, distinguish between global motion and local deformations and vibrations of the sample, or perform other spatial or temporal segmentation. For example, depending on the application, the time-dependent deformation of the region of interest can be analyzed to extract acoustic signals such as speech in operation 416, measure biometric parameters such as pulse and respiration in operation 418, track muscle movement, and map mechanical vibration modes in operation 420. This system can also be used to perform standard 2D and / or 3D imaging using incoherent or ambient light. By using the control unit 110 to affect the illumination unit 102 to synchronously alternate between coherent and incoherent illumination for each frame captured by the wavefront imaging sensor 108, the above-described temporal speckle image sequences 404 and 406 can be interlaced with incoherent 2D / 3D imaging sequences to provide additional data indicative of the sample's reflectance and / or transmittance, shape, depth, and 3D structure. These data streams are inherently fused because they are acquired using the same acquisition unit, which utilizes the same viewpoint, the same imaging optics, and the same wavefront imaging sensor. A more detailed description can be found below.According to embodiments of the present invention, it is also possible to fuse the spatiotemporal deformation map with external data sources, such as conventional 2D cameras, as well as other types of 3D sensors, in which case the data fusion operation must take into account the different viewpoints, imaging optics, and imaging sensors of the external data sources.

[0082] 4, the information generated by embodiments of the present invention is useful for a variety of implementations. For example, the spatial information generated in operations 414, 416, 418, or 420 can be used to distinguish between vibrations of a sample due to its external environment and the sample's own vibrations. In this way, it is possible to pick up sounds in noisy environments, monitor biometric parameters of occupants of a moving vehicle, and monitor specific machine parts in vibrating environments.

[0083] The operation of the system 100 of Figure 1 and its configuration will be further discussed with reference to Figure 5a. The same reference numerals are used to refer to the same elements as in Figure 1. According to one embodiment of the present invention, the optical properties of the illumination unit 102 are set or selected in relation to the optical properties of the sample to be measured. The optical properties of the illumination unit 102 can be set by pre-selecting an appropriate coherent illumination source or can be selectively set under the control of the control unit 110.

[0084] System 10 is designed to measure speckle wavefront deformation of a sample. Two conditions must be met: 1) "primary" speckle generation on or within the sample, and 2) the imaging optics 106 of the collection section 104 must have sufficient optical imaging resolution (also referred to as "spatial resolution") so that "secondary" speckle SW is formed in the image plane of the wavefront imaging sensor 108.

[0085] According to embodiments of the present invention, optical properties such as temporal coherence length, spatial coherence length, illumination aperture, illuminator exit pupil size, collection aperture, collector entrance pupil size, wavelength, direction of illumination, and collection relative to the sample are preselected. According to other embodiments of the present invention, some or all of the optical properties of illuminator 102 and collector 104 are adjustable and controllable by controller 110.

[0086] The first condition can be obtained when the system 10 measures a sample 100 characterized by a particular light diffusion length or a particular sample surface roughness (not shown in FIG. 5a). The coherence illumination source of the illumination unit 102 is set to a value that is equal to the light diffusion length or surface roughness L of the sample 100. S Longitudinal coherence length L of the order of or greater than L (also known as the temporal coherence length).

[0087] The coherent wave has a temporal coherence length L L Maintain a specified level of coherence over a propagation distance, denoted by L L The value of is usually 2 / The coherence length is given by Δλ, where λ denotes the central wavelength of the illumination source and Δλ denotes the spectral width of the illumination source. For example, a single-mode laser with a very narrow spectrum can have a coherence length on the order of meters to kilometers. Multimode lasers with wider spectral widths have coherence lengths on the order of centimeters to decimeters, while simple diode lasers typically have coherence lengths on the order of a millimeter or less. Even light-emitting diodes (LEDs) with sufficiently narrow spectra (about 10 nm) can have significant coherence lengths on the order of tens of microns.

[0088] The optical diffusion length of a sample corresponds to the average path difference of light as it leaves the sample and propagates through the sample before being subsequently captured by a collection system. Light propagating through a sample consisting of many random scatterers passes through many propagation paths, each with a different random optical path length. The standard deviation of the different propagation path lengths is the sample L S The diffusion length L S Such a sample has a coherence length L L >L S When illuminated with coherent light, a primary speckle pattern is produced.

[0089] For samples with surface roughness, the typical length L S corresponds to the surface roughness statistics, usually the standard deviation of the surface roughness. Again, if the sample is L >L S When illuminated with coherent light, first-order speckles are obtained.

[0090] Finally, in most situations where primary speckles are formed, L L >L S Note that >λ, however, if the optical system is configured such that "zero-order" bright-field specular reflection (or direct transmission in the case of semi-transparent samples) is not captured by the collector, then requirement L S >λ can be relaxed. In microscopy, such a configuration is commonly referred to as a "dark field" illumination condition.

[0091] By selecting a coherent illumination source that meets the specified coherence length requirement, high-contrast speckle images can be obtained. The requirement that the temporal coherence length be on the order of the optical diffusion length or surface roughness of the sample ensures a strong speckle response while the coherent illumination impinges on or passes through the surface.

[0092] According to one embodiment of the present invention, the optical properties of the illumination unit 102 are further set in relation to the optical properties of the collection unit 104. The optical properties of the illumination unit 102 may be set by pre-selecting an appropriate coherent illumination source or may be selectively set under the control of the control unit 110. The optical properties of the collection unit 104 may also be controlled by the control unit 110. These settings are necessary to ensure that secondary speckles are obtained at the image plane of the system when primary speckles are generated at the sample.

[0093] The illumination unit 102 has a spatial coherence length L of the illumination source when projected onto the sample. I (also known as the transverse coherence length and denoted by I-SCL in Figure 5a). The spatial coherence length describes the relationship between illuminated waves at various points in space and is a measure of the transverse distance between pairs of points on the sample that are still mutually coherent to some degree.

[0094] The collection unit 104 calculates the value L C It is characterized by the spatial coherence length of the point spread function of the imaging optics of the collector projected onto the sample through the imaging optics, denoted by (C-SCL in Figure 5a).

[0095] To obtain speckle wavefront imaging, i.e., to generate secondary speckles on the image plane of the system, the spatial coherence length L of the illumination source of the illumination unit 102 projected onto the sample is I is the spatial coherence length L of the point spread function of the imaging optics 106 of the collection section 104 projected onto the sample 100 through the imaging optics 106. C Mathematically, this relationship is expressed as L I >L C This is shown schematically in Figure 5a.

[0096] The relationship between the optical properties of the illumination portion 102 and the collection portion 104 is such that for every point on the sample that is imaged, the angle A subtended by the optical aperture of the collection portion 104 as seen from any point on the sample 100 isc is the angle A subtended by the optical aperture of the illumination unit 102 as viewed from the same point on the sample 100. I This can also be expressed as a condition that is greater than . This is shown in Figure 5b. Statement A I C is the previous relation L I> L C is equivalent in Fourier optics to

[0097] The relationship between the optical properties of the illuminator 102 and collector 104 can also be expressed as a requirement that the exit pupil of the illuminator (element 102.1 shown in FIG. 1) is smaller than the entrance pupil of the collector (element 106.1 shown in FIG. 1). This can be expressed as Statement A I C and is geometrically equivalent to the relation L I >L C is equivalent in Fourier optics to

[0098] 6a and 6b are schematic diagrams of systems 60, 62 capable of incoherent wavefront imaging for two-dimensional (2D) and three-dimensional (3D) imaging. Like elements of systems 60, 62 and system 10 of FIG. 1 are referenced with like numerals.

[0099] As shown in Figure 6a, the illumination section 120 of the system 60 comprises a coherent illuminator 122 and an incoherent illuminator 124. The incoherent illuminator 124 can be implemented as an ambient light source or as an incoherent flood illuminator.

[0100] ​​As shown in FIG. 6b, the illumination portion 130 of the system 62 can provide both coherent and incoherent illumination. The coherent illumination (shown in FIG. 6b by a solid line) is projected from a small aperture, while the incoherent illumination (shown in FIG. 6b by a dashed line) uses a large aperture. Because a large aperture is used, the spatial coherence length of the resulting illumination is less than or equal to the spatial coherence length of the collection portion's imaging optics. According to embodiments of the present invention, the spatial coherence length of the collection portion's imaging optics may be 1.0 times or more greater than the spatial coherence length of the illumination.

[0101] An incoherent wavefront image (also known as a "light field image") is captured under incoherent illumination and analyzed to extract a 2D intensity image and depth data, according to known techniques.

[0102] Thus, embodiments of the present invention facilitate versatile, cost-effective imaging systems and methods that can be used for a variety of use cases. For example, highly secure biometric authentication can be efficiently performed. Using incoherent illumination modes (as described with reference to FIGS. 6a-6b), 2D and 3D imaging of a person's face can be performed for authentication purposes. Using coherent speckle-based imaging sequences (as described with reference to FIGS. 1-5b), authentication can be performed by acquiring a person's biometric markers, such as facial pulse patterns, breathing, muscle movements, and voice. By switching between illumination methods, both authentication methods can be combined using the same system.

[0103] FIG. 7a illustrates a flow 70 for performing 2D / 3D imaging, for example, for facial biometric authentication. In operation 700, a person's face is illuminated by ambient lighting or incoherent flood lighting. In operation 702, an incoherent wavefront image snapshot of the person's face is captured. In operation 704, the wavefront image is analyzed to calculate a 2D intensity image and a corresponding 3D depth map. In operation 706, the 2D intensity image and the corresponding 3D depth map are further analyzed to extract unique 3D facial recognition data, for example, by using an artificial neural network. In operation 708, stored 3D facial recognition data, captured during enrollment in the system, for example, is retrieved (or received from an external source). In operation 710, the extracted unique 3D facial recognition data is compared to the stored 3D facial recognition data. A decision is made to approve the person (in operation 714) or reject the person (in operation 712).

[0104] FIG. 7b illustrates a flow 72 for speckle wavefront imaging, for example, to perform biometric authentication. In operation 720, a subject is illuminated using coherent illumination. In operation 722, a time series of speckle wavefront images are captured, and a localized spatiotemporal deformation map sequence is calculated. In operation 724, the deformation map is analyzed to obtain specific biometric parameters (biomarkers), such as facial pulse patterns, respiration, voice, coordinated muscle movements, and twitches. The biometric parameter data can be further analyzed in operation 726, for example, by using an artificial neural network, to extract unique biomarker recognition data. In operation 728, stored biomarker data, for example, acquired during enrollment in the system, is retrieved (or received from an external source). In operation 730, the extracted unique biomarkers are compared to the stored biomarkers, and a decision is made to approve (in operation 734) or reject (in operation 732) the person.

[0105] Figure 7c illustrates a combined authentication flow 74 that uses both the coherent and incoherent wavefront imaging flows 70 and 72 described in Figures 7a and 7b. Flows 70 and 72 can be performed sequentially by switching lighting conditions. For example, the incoherent wavefront imaging authentication sequence described in Figure 7a can be first performed under ambient or incoherent illumination, and then the speckle-based wavefront imaging authentication described in Figure 7b can be performed using coherent illumination, or vice versa. In operation 740, the combined authentication data from both methods is analyzed and used to determine whether to approve the person (in operation 744) or reject the person (in operation 742).

[0106] For ease of explanation, Figure 7c illustrates the performance of flows 70 and 72 as separate flows as a whole, up to multi-parameter authentication operation 740. It will be apparent that the various operations of flows 70 and 72 can be performed simultaneously or sequentially.

[0107] For example, operation 700 (of flow 70) and operation 720 (of flow 72) can be performed sequentially using system 60 of FIG. 6a or system 62 of FIG. 6b. In system 60, the operation of coherent illuminator 122 and incoherent illuminator 124 are switched sequentially. In system 62, illuminator 130 can be controlled to change between its coherent and incoherent illumination modes. As a result, operation 702 (of flow 70) and operation 722 (of flow 72) can be performed sequentially by the same system element (e.g., collector 104 and controller 110 of FIG. 1). Similarly, operations 704, 706, and 708 (of flow 70) and operations 724, 726, and 728 (of flow 72) can be performed simultaneously or sequentially by the controller. Operation 710 (of flow 70) and operation 730 (of flow 72) may be performed simultaneously or sequentially to provide a rejection or approval decision as input to operation 740 of flow 74. Alternatively, the performance of operation 710 (of flow 70) and operation 730 (of flow 72) may be integrated to comprise operation 740 of flow 74. Other modifications and variations can be made to this flow without departing from the scope or spirit of various embodiments.

[0108] The versatility of imaging systems according to embodiments of the present invention can also be used to perform combined monitoring of people or inanimate objects by alternating between coherent and incoherent imaging. For example, biometric monitoring of people can be performed for, e.g., vital signs, pulse, respiration, eye tracking, and facial expression recognition. Another application is performing combined monitoring of machine vibrations and overall 2D and 3D image monitoring.

[0109] In combined coherent and incoherent monitoring, a series of wavefront images are captured under lighting conditions that alternate between coherent and ambient or incoherent illumination, as influenced by the control unit. The images can then be separated into two sequences: one incoherent image and one coherent image. The set of coherent images is used to calculate a spatiotemporal distortion map and extract specific vibration patterns or biometric parameters, as previously described. The set of 2D and 3D images can be used to monitor overall shape, geometry, reflectivity changes, and other imaging parameters of interest.

[0110] In general, the sequence of wavefront images does not need to be split 1:1 between coherent and incoherent illumination: in some applications, it may be beneficial to acquire several coherent wavefront images for each incoherent wavefront image, or vice versa.

[0111] As mentioned above, under coherent illumination conditions, a single speckle wavefront image provides little information about the sample due to its random phase wavefront. The randomness is caused by the interaction between the illumination and the sample, where the optical diffusion length or surface roughness of the sample is smaller than the temporal coherence length of the light used to illuminate the sample. A random phase wavefront is not suitable for standard phase unwrapping techniques, such as those used in the Rytov approximation. However, by acquiring speckle wavefront images at several wavelengths, multispectral phase unwrapping can be performed to recover the sample's surface profile relative to the internal structure of opaque or semitransparent samples.

[0112] Without loss of generality, we will deal with large surface profile steps with conventional coherent illumination. The meaning of a "large" step profile will become clear shortly. Furthermore, the principles described here are valid for transmission and / or reflection through or from semitransparent samples, as well as random roughness. In the case of reflection off a surface with random roughness, the random surface profile induces random optical path lengths for light impinging on the surface. In the case of transmission or reflection through a semitransparent sample, random scattering by the sample's internal structure also induces random optical path lengths for light interacting with the sample. Furthermore, semitransparent samples with surface roughness induce random optical path lengths due to both effects. In all cases, the following example of reflection off a large surface profile step provides an excellent proxy for illustrating how the optical path length difference between two points on a sample is measured.

[0113] According to one embodiment of the present invention, FIG. 8a illustrates coherent illumination 800 having a wavelength λ impinging at normal incidence on a step profile 810 of height h. As shown in FIG. 8b, light 820 is reflected from either side of step 810. Note that while the incident light has a uniform wavefront as shown in FIG. 8a, the wavefront of the reflected light has a phase shift, indicated by dashed line D in FIG. 8b. The phase difference between the left and right halves of the step profile is the result of an optical path difference of ΔL = 2h accumulated during the round trip the light underwent upon reflection from both sides of step profile 810. This results in a phase difference of 2πΔL / λ radians on each side of the reflected wavefront. However, the imaging wavefront sensor (e.g., element 108 in FIG. 1) can only measure fractional parts of this phase difference up to 2π, meaning it is not affected by phase differences that are integer wavelengths. Therefore, the measured phase difference is an accurate estimate of the step height only for "small" step heights where ΔL < λ. For larger step heights, the integer part of the phase shift introduces ambiguity into the estimation of the step height.

[0114] The height ambiguity can be resolved by measuring the phase difference at several wavelengths. For example, for two close wavelengths λ, λ' = λ + Δλ, we measure the phase difference at φ = 2πΔL / λ and φ' = 2πΔL / (λ + Δλ), which, under the assumption of Δλ"λ, gives φ' = φ - 2πΔLΔλ / λ 2 Therefore, the variation in the phase difference between both wavelengths is approximately Δφ=-2πΔLΔλ / λ 2 Again, this phase difference is measured only to an integer number of wavelengths, i.e., there is a phase ambiguity of 2π. However, the effective range over which the actual difference is unambiguous is much larger than ΔL<λ λ / Δλ, which is λ / Δλ larger than for small step heights. The quantity λ 2 / Δλ is sometimes referred to as the "synthetic wavelength" because it defines a virtual wavelength at which the phase ambiguity is resolved.

[0115] The above principles are easily extended to multispectral phase unwrapping techniques, as shown in Figures 10a-10b.

[0116] Figure 10a shows the wavelengths λ1, λ2...λ n A series of 900 2D phase maps (phase images) φ1(x,y), φ2(x,y), …, φ n (x, y) is shown schematically. In this case, additional wavelengths help to more reliably resolve height ambiguities over a wider range of optical path length differences. For each point (x, y) in the set of 2D phase maps (marked with an "X" label in each map φ in Figure 10a), the optical path length ΔL is calculated as follows: We start by selecting a phase at a particular wavelength. Next, for each pair of adjacent wavelengths, we calculate the phase difference Δφ at the point under consideration. We can then accumulate the phase difference as a function of wavenumber k = 2π / λ. This is similar to performing a discrete approximation to the integral in Equation 1.

number

[0117] The resulting cumulative phase difference as a function of wavenumber produces the linear plot 910 shown in Figure 9b. The slope of plot 920 is directly related to the optical path difference ΔL through the relationship φ = 2π / λ ΔL. When repeated for each point in the set of phase maps 900, an optical path length map ΔL(x,y) is obtained.

[0118] The multispectral phase unwrapping technique described above is directly applicable to speckle wavefront images obtained by systems according to embodiments of the present invention. The random nature of speckle wavefronts obtained at a single wavelength is the result of the random distribution of the large optical path difference ΔL caused by the interaction of coherent light with the sample itself. As explained above, the optical path difference can be the result of surface roughness in the case of reflective, opaque samples, light diffusion in translucent objects, or a combination of both. Because the typical optical path difference is much larger than the wavelength ΔL > λ, there is a phase ambiguity for a single wavelength, and it cannot be used alone to determine the optical path difference. The structure of the sample is directly related to the optical path difference, and because the optical path difference is ambiguous, it is virtually impossible to reconstruct the structure of the sample from a single-wavelength phase image.

[0119] However, wavelengths λ1, λ2, ..., λ n By acquiring a series of speckle wavefront images at a set of λ (as shown in Figures 9a-9b), it is possible to perform multispectral phase unwinding as described above and thus obtain an operational and practical estimate of the spatial distribution of ΔL. For reflective samples, ΔL is exactly twice the surface profile due to the relationship ΔL = 2h. For transmissive samples, the optical path difference is directly related to the change in refractive index distribution by ΔL = t Δn, where t is the sample thickness and Δn is the deviation of the refractive index from some reference nominal value.

[0120] 10 is a flow diagram illustrating a measurement flow 12 according to an embodiment of the present invention. In this embodiment, an illumination source is required to provide coherent illumination at several wavelengths. This can be achieved, for example, by using a filter wheel or a broadband light source with a tunable filter, for example, a supercontinuum laser with a tunable acoustic filter. In another example, a tunable laser light source can be used. By yet another example, an illumination module can include several light sources, each at several wavelengths, each used separately in turn.

[0121] Flow 12 begins at operation 1002, where a sample is illuminated with coherent illumination at a first wavelength. A respective speckle wavefront image is captured in operation 1004 and stored in operation 1006. In operation 1008, the sample is coherently illuminated at a second wavelength, and again a speckle wavefront image is captured (operation 1010) and stored (operation 1012). This is repeated for all remaining wavelengths (denoted by three dots in FIG. 10 , followed by operations 1014, 1016, and 1018. In operation 1020, for each spatial point in the series of speckle wavefront images, the phase ambiguity is determined according to the multispectral phase unwrapping procedure described. This results in a spatial distribution of the optical path difference ΔL. Depending on the sample type and application, the spatial mapping of the optical path difference ΔL can be used to estimate the surface profile (operation 1022), the refractive index distribution, or a combination of both. For example, a large-scale surface profile can be calculated (in operation 1022), a virtual optical coherence tomography (OCT) 3D depth profile can be obtained (calculated in operation 1024), and a large-scale quantitative phase image can be generated (calculated in operation 1026).

[0122] It is noted that, without loss of generality, the processing and phase unwrapping of speckle wavefront images can proceed in combination with the spectral image acquisition sequence described above.

[0123] According to embodiments of the present invention, multispectral diffraction tomography can be performed, which is similar to performing multispectral speckle wavefront imaging for a series of different illumination angles.

[0124] Figure 11a shows an L-shaped semi-transparent object S illuminated from above by coherent illumination 1100. A step refractive index profile Δn 1130 is obtained by performing multispectral speckle wavefront imaging, as described with reference to Figure 10. However, this profile Δn 1130 is not sufficient to estimate the 3D refractive index distribution of object S. Figures 11b and 11c show objects S1 and S2, which obtain refractive index profiles Δn 1140 and 1150 similar to refractive index profile Δn 1130. The refractive index profiles are similar because multispectral speckle wavefront imaging estimates the total cumulative refractive index throughout the thickness of the sample, as shown in Equation 2.

[0125] Equation 2ΔL=t·Δn.

[0126] The ambiguity in the refractive index profile can be resolved by performing multispectral speckle wavefront imaging from several illumination angles, as shown in Figure 12. For each illumination angle θ i 1200, 1210, 1220 (i=1, 2, 3) respectively generate different refractive index profiles Δn i 1230, 1240, 1250. The correct 3D refractive index profile of the object can then be estimated using known tomographic techniques such as the inverse Radon transform.

[0127] FIG. 13 is a block diagram illustrating a system 13 according to an embodiment of the present invention. The same reference numerals are used to denote the same elements as in FIGS. 1, 2a-2b, 5a-5b, and 6a-6b. The system 13 includes multiple multispectral illuminators 103, 105, and 107 that can be used to perform multispectral diffraction tomography. According to another implementation (not shown in FIG. 13), the sample 100 is illuminated from different angles using movable illuminators. Another implementation is shown schematically in FIG. 14: the illuminator 102 can be adapted to illuminate the sample 100 with variable illumination angles, represented by dashed lines. According to yet another embodiment (not shown in FIGS. 13 and 14), a single illuminator is moved along with the collector 104. According to another embodiment, the sample is moved, thereby creating relative motion with respect to the illuminator, collector, or both. The present invention is not limited by the method for creating multi-angle spectral imaging.

[0128] FIG. 15 is a flow diagram illustrating a flow 51 for performing multispectral diffraction tomography. Multispectral speckle wavefront imaging is performed at a first illumination angle (operation 1500), and the corresponding spatial path length mapping is calculated and stored (operation 1510). The same operations are repeated for all other illumination angles. This is represented by operations 1520, 1530, and three dots followed by operations 1540 and 1550 in FIG. 15. As a result, a set of spatial path length mappings is obtained. In operation 1560, the set of spatial path length mappings is used to estimate the 3D structure of the sample using a tomographic technique such as the inverse Radon transform. Note that this technique is applicable to both transmission and reflection of the sample.

[0129] In all of the above descriptions of various embodiments of the present invention, the illumination unit is treated as separate from the collection optics. However, in some cases, it may be advantageous to use an illumination unit that projects light onto the sample through imaging optics. This can be achieved, for example, as shown schematically in FIG. 16. For ease of explanation, the embodiment of FIG. 16 will be described in comparison to the embodiment of FIG. 1. The system 80 of FIG. 16 differs from the system 10 of FIG. 1 by including a beam splitter arrangement 112. The beam splitter arrangement 112 is positioned in the illumination path between the illumination unit 102 and the imaging optics 106. Illumination IL (dashed line) emerges from the illumination unit 102, passes through the beam splitter arrangement 112 and the imaging optics 106, and impinges on the sample 100. In the collection path, the beam splitter arrangement 112 is positioned between the imaging optics 106 and the wavefront imaging sensor 108. Light CL reflected from or transmitted through sample 100 passes through imaging optics 106 and beam splitter arrangement 112 to reach wavefront imaging sensor 108. Without loss of generality, in other embodiments of the present invention, beam splitter arrangement 112 may be positioned before imaging optics 106 (not shown). Finally, with any beam splitter arrangement, care must be taken to ensure that the conditions for primary and secondary speckle formation are maintained, as discussed above in the relationships regarding longitudinal and spatial coherence. The latter aforementioned relationship between the spatial coherence of the illumination and the collection path (shown in FIGS. 1, 5a, and 5b) should also be maintained with any type of beam splitter arrangement.

[0130] The beam splitter arrangements may be integrated with other embodiments of the present invention, for example, as shown in Figures 2a-2b, 5a-5b, 6a-6b, 13, and 14, with appropriate modifications and alterations, without departing from the scope or spirit of the invention.

[0131] The wavefront imaging sensor can be spectrally sensitive. Spectral sensitivity can be achieved in several ways, for example, (1) by using a color filter array on the sensor pixels, such as an RGB (red-green-blue) Bayer filter or other type of pattern, (2) by using a spectral filter, or (3) by using a dichroic prism with a separate sensor pixel array for each spectral channel. The present invention is not limited by the method for achieving spectral sensitivity.

[0132] The spectral sensitivity of wavefront imaging sensors, when used under incoherent illumination conditions, may be used to acquire color or hyperspectral 2D images. Note that such spectrally sensitive wavefront imaging sensors can still be used to capture speckle wavefronts under coherent illumination, as long as it is ensured that the illuminator wavelength falls within one of the sensor's spectral sensitivity ranges.

[0133] Furthermore, the above-described spectral sensitivity of the sensor may be used to simultaneously capture multispectral speckle wavefront images for several wavelength ranges. This simultaneous capture may replace the sequential capture of multispectral speckle wavefront images at different illumination wavelengths, as described above. This type of simultaneous multispectral image capture can reduce image acquisition time, which may be beneficial in terms of increasing system throughput or reducing sensitivity to sample motion during a multispectral wavefront image capture sequence.

[0134] Without loss of generality, simultaneous capture of multispectral speckle wavefront images using a spectrally sensitive wavefront imaging sensor can also be used in combination with sequential capture of spectral wavefront images. An illumination source with a selective wavelength range can be used. For example, a sample can be illuminated simultaneously with several wavelengths, each of which is spectrally separated by the wavefront imaging sensor. The sample may be illuminated with several different wavelengths, each of which is spectrally separated by the wavefront imaging sensor.

[0135] According to an embodiment of the present invention, the wavefront imaging sensor 108 is configured as an optical detection system as described in PCT Patent Application Publication No. WO2018 / 185740, which is incorporated herein by reference.

[0136] 17 shows a schematic representation of a portion of a system according to an embodiment of the present invention, in which a wavefront imaging sensor 17 includes an encoder 1700 and a detector array 1710 positioned a predetermined distance L downstream of the encoder 1700 relative to the general direction of radiation propagation. For ease of illustration, the wavefront imaging sensor 17 is shown together with other parts of the collection portion 104, the imaging optics 106 are shown, and the sample 100 and its image Img on the encoder 1700 are shown. The wavefront imaging sensor 17 is further coupled to a control portion 110.

[0137] The encoder 1700 may be realized (1) as a separate unit from the detector array 1710, (2) monolithically integrated with the detector array 1710, or (3) as part of the process stack used to fabricate the sensor array, e.g., using metallization process steps and / or process steps similar to those used to fabricate microlens arrays typically used to improve the pixel fill factor of the sensor array.

[0138] The wavefront imaging sensor 17 may comprise an encoder 1700 (not shown in FIG. 17) having a periodic pattern defining a plurality of unit cells, with an array of sensor cells 1710 (not shown in FIG. 17) located a distance downstream of the unit cells with respect to the general direction of propagation of the input light through the system. The wavefront imaging sensor 17 is coupled to a controller 110 configured to receive input data collected by the array of sensor cells 1710 and process the input data in accordance with data related to the modulation function of the encoder 1700 to determine data indicative of the mutual coherence of the input light collected by the encoder 1700.

[0139] The array of sensor cells 1710 can define a plurality of sub-array unit cells (not shown in FIG. 17), each of which corresponds to a unit cell among the plurality of unit cells of the encoder 1700, and each of which includes a predetermined number M of sensor elements (not shown in FIG. 17).

[0140] The encoder 1700 may define a detection surface and is configured to apply a predetermined modulation to input light collected by the optical imaging system, the predetermined modulation providing that each unit cell of the encoder 1700 directs a portion of the collected input light incident thereon to its corresponding sub-array unit cell of the array 1710 and to one or more neighboring sub-array unit cells within a predetermined proximity region.

[0141] The predetermined number M may be determined according to a predetermined number of sub-array unit cells of the array 1710 within a predetermined proximity area.

[0142] A given number M of sensor elements in a sub-array unit cell of array 1710 are (M≧2n R +1), where n R is a predetermined number of neighboring subarray unit cells in a predetermined proximity region.

[0143] A predetermined number M of sensor elements of the subarray unit cells of array 1710 may be selected according to a predetermined number of coherence matrix basis functions selected for use in reconstructing mutual coherence information of the collected input fields.

[0144] The arrangement of unit cells of the encoder 1700 may define a discretized unit measurement of the collected light such that each unit cell of the encoder 1700 is associated with a pixel of the image data generated by the wavefront imaging sensor 17.

[0145] The physical dimensions of a unit cell of encoder 1700 may correspond to a diffraction-limited spot of collected light incident on the encoder. For example, the physical dimensions of a unit cell of encoder 1700 may be within 0.1 to 0.25 of the diffraction-limited spot.

[0146] The encoder 1700 may be configured to collect and encode light in one or more selected wavelength ranges.

[0147] The encoder 1700 may be configured to apply a predetermined modulation to input light within a predetermined wavelength range.

[0148] The array of sensor cells 1710 may include sensor cells configured to separately detect light intensity in two or more wavelength ranges.

[0149] Figure 18 illustrates an embodiment of the wavefront imaging sensor 17 of Figure 17. Figure 18 illustrates an encoder 1700 and a detector array 1710. Figure 18 further illustrates input light S i passing through a single unit cell 1822 of the encoder 1700 at pitch p and propagating a distance L towards the detector array 1710.

[0150] A fundamental response function F R is formed that can be detected (in intensity detection) by the detector array 1710. For ease of explanation, a two-dimensional configuration of the fundamental response function F R is shown. The fundamental response function F R propagates downstream of the encoder 1700 and relates to the complex data (amplitude and phase) of the light field resulting from an impulse light field (e.g., a diffraction-limited spot excitation of the imaging system 106, or a shape such as a Gaussian, rectangular, or delta function) impinging on a unit cell of the encoder 1700.

[0151] In general, light passing through a region of the encoder 1700 associated with a single unit cell 1822, and its fundamental response, can be used to process intensity distribution data collected by the wavefront imaging sensor 18. As shown, an input light field S I directed at a single unit cell 1822 of the encoder undergoes a predetermined optical modulation and propagates through a sub-channel 1830 towards the detector array 1710.

[0152] Generally, the modulation provided by a single unit cell 1822 is continuous, providing a substantially continuous fundamental response function FR. However, for completeness, arrows are shown indicating five subchannels (D-2 through D+2). As noted above, these subchannels can be treated as discrete diffraction orders, which is typically due to the periodicity of the encoder 1700. As previously mentioned, a particular encoder unit cell 1822 transmits light via subchannels 1830 to several detector subarrays within a proximity region PR. This relationship is equivalent to the dual statement that a single subarray 1842 associated with a single unit cell 1822 receives light impinging on it via the appropriate subchannels 1830 from neighboring encoder unit cells defined in a similar proximity region.

[0153] As indicated above, the number of subarrays 1842 or sensor cells M in the detector array 1840 associated with different unit cells of the encoder 1700 can be selected according to the patterning of the encoder and the number of subchannels that transmit light components from the unit cell 1822 to the subarray 1842 in a particular proximity region PR.

[0154] Furthermore, the number of sensor cells M may be selected according to the selected basis reconstruction, reducing the number of sensor cells to enable effective reconstruction of the phase or coherence mapping of the collected light.

[0155] Generally, the fundamental response function FR drops to a negligible value outside the proximity region PR. For example, the pattern of the encoder 1700 may be configured to provide for interaction of the collected light with light components associated with one, two, or more neighboring unit cells, e.g., defining nearest neighbor interactions, next nearest neighbors, etc. Furthermore, the level of neighbor interactions may be different for different horizontal axes (x and y) of the wavefront imaging sensor 17.

[0156] Generally, the number M of sensor cells associated with each unit cell 1822 is M≧2n R +1, where n R is the total number of neighboring unit cells in the proximity region PR. R is the number of interactions of all neighboring unit cells with respect to a given unit cell, but each interaction is counted only once. However, as noted above, in some configurations, the number of sensor cells M may be reduced according to some basis functions used to reconstruct the collection field. For example, if optical encoder 1700 is configured to create interactions between a unit cell and its nearest neighbor to its right and its nearest neighbor above it, then n R = 2. This particular unit cell also interacts with the unit cells to its left and below. However, these interactions are counted as belonging to the neighboring unit cells to the left and below, respectively, to avoid counting interactions twice. If the neighborhood is separable into interactions along the x and y axes, then M ≥ (2n xR +1)(2n yR +1), where n xR is the number of interactions between neighboring unit cells along the x-axis, and n yR is the number of interactions of neighboring unit cells along the y-axis. As mentioned before, the number of interactions, n xR and n yR is counted on one side.

[0157] SUMMARY OF THE INVENTION Embodiments of the invention described herein provide optical speckle-based imaging systems and corresponding methods for determining data indicative of the intensity, phase, and coherence of collected light.

[0158] Accordingly, it will be understood that the above-described embodiments are cited by way of example, and that the present invention is not limited to what has been particularly shown and described above. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described above, as well as variations and modifications thereof which would occur to those skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

[0159] Those skilled in the art will readily appreciate that various modifications and changes can be made to the embodiments of the present invention, as described above, without departing from the scope thereof as defined in and by the appended claims.

Claims

1. 1. An optical speckle-based imaging system, comprising: an illumination unit including at least one coherent light source for illuminating the sample; a collector for collecting input light from the sample, the collector comprising imaging optics and a wavefront imaging sensor; a controller coupled to the illumination unit and the collection unit for analyzing the input light and generating a speckle wavefront image; the at least one coherent light source generates primary speckle in or on the sample, and the imaging optics captures a secondary speckle pattern caused by the illuminator in or on the sample; the wavefront imaging sensor provides data indicative of the intensity, wavefront, and coherence of light interacting with the sample; an exit pupil of the illumination unit is smaller than an entrance pupil of the imaging optical system; The system, wherein the control unit is adapted to affect at least one of the size of the exit pupil, the size of the entrance pupil, and a relationship therebetween.

2. 10. The system of claim 1, wherein the at least one coherent light source has a temporal coherence length greater than at least one of: (1) an optical diffusion length of the sample; and (2) a surface roughness of the sample.

3. 2. The system of claim 1, wherein the coherent light source has a spatial coherence length and the collector has a point spread function spatial coherence length, the spatial coherence length of the coherent light source projected onto the sample being greater than the spatial coherence length of the point spread function of the collector projected onto the sample via the imaging optics.

4. 2. The system of claim 1, wherein the optical properties of the illuminator and the collector are selected to form, for every point imaged on the sample, an angle subtended by the collector's optical aperture as seen from any point on the sample that is greater than the angle subtended by the illuminator's optical aperture as seen from the same point on the sample.

5. 2. The system of claim 1, wherein the illumination unit has an illumination aperture that defines an illumination angle, the collection unit has a collection aperture that defines a collection angle, and the control unit is further coupled to the illumination unit to affect illumination optical properties and further affect collection optical properties to form a collection angle seen from any point on the sample, the collection angle being greater than the illumination angle seen from the same point on the sample for all points imaged on the sample.

6. The system of claim 1 , wherein the collector measures data indicative of at least one of speckle intensity, speckle wavefront, and speckle coherence.

7. An imaging method, comprising: illuminating the sample with coherent light; capturing input light from the sample with a collection unit consisting of imaging optics and a wavefront imaging sensor; analyzing the input light with a controller coupled to the collector to generate a speckle wavefront image; at least one coherent light source generates primary speckle in or on the sample, and the imaging optics captures a secondary speckle pattern caused by an illuminator in or on the sample; the wavefront imaging sensor provides data indicative of the intensity, wavefront, and coherence of light interacting with the sample; an exit pupil of the illumination unit is smaller than an entrance pupil of the imaging optical system; The method, wherein the control unit is adapted to affect at least one of the size of the exit pupil, the size of the entrance pupil, and the relationship therebetween.

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