Compact device for performing imaging of a wavefront by interferometry

Abstract

The invention relates to an imaging module (Mod) designed to characterise a wavefront by interferometry, comprising: an imaging sensor (Sens) comprising a matrix (Mat) of photosensitive pixels formed on a planar substrate (Sub); and a phase and / or amplitude optical grating (Arr) formed by a support (Sprt), one face (StrctFac) of which is structured so as to introduce periodic variations in phase and / or amplitude into an incident light beam; wherein the grating (Arr) is attached to the imaging sensor (Sens) in such a way that at least one optical element (Sprt, OptE1) is interposed between the structured face (StrctFac) of the grating (Arr) and the matrix (Mat) of photosensitive pixels, and wherein the optical element comprises two opposite faces (StrctFac, nStrctFac, F1, F2), each parallel to the matrix (Mat) of photosensitive pixels and to the structured face (StrctFac) of the grating (Arr), wherein one of the faces is in mechanical contact with the imaging sensor (Sens).

Description

Compact device for imaging a wavefront by interferometry TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a device for analyzing the wavefront of incident light radiation. The light radiation passes through an optical device introducing periodic variations in phase and / or intensity. Such a device is based on an analysis by interferometry such as, for example, quadri-lateral shift interferometry, or QLSI for Quadriwave Lateral Shearing Interferometry in English terminology. TECHNOLOGICAL BACKGROUND

[0002] Wavefront imaging

[0003] Quadrilateral shift interferometry, or QLSI, is a quantitative phase imaging technique based on the use of a diffraction grating placed in front of an imager. This grating creates an image called an interferogram, from which the intensity and phase profiles of an incoming light beam can be derived. Invented in the 1990s, QLSI is used in many applications, such as laser beam characterization, optical lens metrology, topography measurements, adaptive optics, gas jet metrology, and more recently, the technique has been implemented in optical microscopes to characterize micro- and nano-objects for bioimaging and nanophotonics applications.

[0004] A diffraction grating used for wavefront analysis is designed to induce (i) phase and / or amplitude differences and (ii) a diffraction phenomenon in light radiation passing through the grating. A diffraction grating can thus be defined as an optical device introducing periodic variations in phase and / or intensity.

[0005] The network generates different beams which interfere to form an image whose deformations are linked to the gradients of the analyzed wave surface. Documents CN 115314626 A, US 2008 / 0144043 A1, US 019 / 257987 A1 and EP 1,411,321 A2 describe various devices implementing the principle of optical interference, possibly for the purpose of analyzing an incident beam.

[0006] A special case of wavefront analysis techniques, QLSI is based on so-called "four-wave" interference obtained using a diffraction grating comprising (i) opaque lines and columns delimiting transparent openings and (ii) periodic thickness differences in the form of a checkerboard at these openings. Such an optical device introduces periodic variations in phase and intensity. For example, reference may be made to patent FR 2 795 175 B1.

[0007] Other variants of these techniques are called "three-wave" and are based on the use of hexagonal geometry networks. Such networks can be designed to introduce only periodic phase variations or only periodic intensity variations. For example, we can refer to patent FR 2712978 B1.

[0008] Thus, in general, a diffraction grating used for the analysis of a wavefront by interferometry can be defined as an optical device introducing (i) periodic phase variations, (ii) periodic amplitude variations, or (iii) periodic phase variations and periodic amplitude variations.

[0009] In all cases, it is a characterization of the wavefront of an incident wave by interferometry.

[0010] The sensitivity of the wavefront characterization system, composed of the imager and the diffraction grating, is a function of the dimension p of the pixels of the imager used and the distance d separating the structured face of the diffraction grating from the image sensor. It is therefore understood that a good quality characterization of the wavefront requires a good knowledge of these two parameters, the only one possibly accessible to the user being the distance d once the imager has been chosen. The periodicity of the diffraction grating is precisely known and fixed since its manufacture. It is also adapted to the dimensions of the photosensitive pixels of the image sensor used. On the other hand, a precise knowledge of the distance d requires a precise positioning and parallelism of the diffraction grating with respect to the image sensor to ensure a homogeneous distance d over the entire surface of the sensor for a quantitative analysis of the wavefront.

[0011] Illustrates a conventional imaging camera, not equipped for QLSI, comprising, within a camera housing 150, an electronic card 140 mechanically supporting and electronically controlling a conventional imager Im Conv . This imager comprises a photosensitive element 110, a protective housing 120 accommodating the photosensitive element 110, and a protective window 130. The photosensitive element 110 may be formed from a two-dimensional array of photosensitive pixels. The protective housing 120 is sealed by the window 130, located in front of the photosensitive element 110. The internal volume of the housing 120 may have a controlled atmosphere or a vacuum. During use, incident radiation Inc passes through the window 130 and strikes the photosensitive element 110.

[0012] Conventional Im imagers Convare usually supplied by their manufacturers protected in 120 protective boxes, with companies providing technical image analysis solutions having to integrate this element into cameras. However, QLSI practice requires the diffraction grating to be located at a distance d of between 0.5 and 10 mm from the imaging plane represented by the photosensitive pixels. Such a requirement is not very compatible with Im imagers Conv conventional.

[0013] Conventional QLSI approaches

[0014] As mentioned above, the distance d determines the sensitivity of the optical system and must therefore be adjusted according to the intended application. Parallelism between the diffraction grating and the image sensor must also be ensured. There are two approaches to manufacturing wavefront analysis devices according to QLSI.

[0015] A first approach is illustrated by the QLSI system 200 of the. This approach makes it possible to place the diffraction grating 220 at an arbitrary distance from the imaging plane materialized by the photosensitive element 210 which is integrated in a camera housing 250. Such an assembly is possible by means of an optical coupling system consisting here of the two lenses 230 and 240 of the same focal length f. The diffraction grating 220 is then placed at a distance 4f+d from the imaging plane, instead of the distance d in the absence of the optical coupling system. Reference may be made to the publication by Guillaume Baffou, “Quantitative phase microscopy using quadriwave lateral shearing interferometry (QLSI): principle, terminology, algorithm and grating shadow description”, J. Phys. D: Appl. Phys. 54 (2021) 294002 (13pp).

[0016] This system has several advantages. In particular, it allows a system capable of performing QLSI from a camera of any characteristics to be set up without compromising the integrity of a protective housing for the camera's photosensitive sensors. The protective housing keeps them in a controlled atmosphere, and therefore protected from dust, humidity, condensation, and even frost, the latter point being critical when the camera is equipped with a sensor cooling system. Another advantage is the ability to very finely adjust the distance d separating the diffraction grating from the imaging plane.

[0017] On the other hand, the assembly of the entire system is complex, with the mechanical maintenance of several elements together: diffraction grating, lenses, camera and, inside the camera, the image sensor itself. The adjustment of parallelism can be particularly tricky. The assembly can also become bulky and inconvenient to use, and the use of lenses intrinsically introduces chromatic aberrations which must be taken into account for quantitative measurements.

[0018] A second approach is illustrated by the system 300 of the. Here, the diffraction grating 320 is mounted close to the photosensitive element 310 located in the camera housing 350 by means of a mechanical assembly making it possible to modulate the distance d separating the diffraction grating 320 from the photosensitive element 310 constituting the image sensor of the system. Without going into details, the mechanical assembly is composed of two rings 330A and 330B capable of sliding relative to each other in a controlled manner. The ring 330A is secured to the camera housing while the ring 330 is secured to the diffraction grating. The relative sliding of the two rings therefore makes it possible to adjust the distance d. This approach, detailed in the patent document FR 2 879 288, has the main advantages of allowing very fine adjustment of the distance d and great simplicity of this adjustment.

[0019] On the other hand, the adjustment of the parallelism appears delicate, and the assembly, integrating the camera and the mechanical assembly for controlling the sliding, is bulky. In addition, approaching the diffraction grating at small distances, such as of the order of a millimeter or less, for example 500 µm, requires removing the glass isolating the image sensor from the camera environment, leading to a high risk of contamination by dust and ambient humidity. This last problem is exacerbated when the image sensor used requires cooling, with a risk of freezing and damage to the sensor by the ice crystals thus formed.

[0020] The technical solutions considered so far only lead to wavefront characterization systems that are bulky, require delicate adjustments due to the number of mechanical elements involved, and do not always effectively protect the image sensor, which is nevertheless a central element of these systems.

[0021] An object of the invention is to provide a wavefront imaging device that is easy to use, robust and compact.

[0022] For the purpose of achieving these objects, one aspect of the invention is an imaging module designed to characterize a wavefront by interferometry, comprising: an imaging sensor comprising a matrix of photosensitive pixels formed on a planar substrate, and an optical phase and / or amplitude grating formed of a support, one face of which is structured so as to introduce periodic phase and / or amplitude variations into an incident light beam, in which the grating is fixed to the imaging sensor in such a way that at least one optical element is interposed between the structured face of the grating and the matrix of photosensitive pixels, the optical element comprising two opposite faces each parallel to the matrix of photosensitive pixels and to the structured face of the grating, and one of them being in mechanical contact with the imaging sensor,the optical network comprising a structured face having (i) opaque orthogonal lines and columns delimiting transparent openings and (ii) half of the transparent openings, distributed in a checkerboard pattern, having an etching of a given depth so as to form a phase checkerboard.,

[0023] A first advantage of the device according to the invention is its ease of use, parallelism being ensured in a simple and definitive manner by the use of the optical element which, with its parallel faces, makes it possible to rigorously orient the structured face of the diffraction grating parallel to the imaging plane materialized by the matrix of photosensitive pixels.

[0024] A second advantage of the device is that the distance d separating the active face of the diffraction grating from the imaging plane can be perfectly defined (i) by the thickness of the optical element, which can be made up of the diffraction grating itself, (ii) by the thickness of an additional optical element mounted on the imaging sensor, or (iii) by the thickness of a combination of the diffraction grating and this additional optical element. Thus, the sensitivity of the device is also very precisely known, allowing optimal exploitation of the images acquired during the analysis of incident radiation. It should be noted that the sensitivity is not simply dependent on the geometric distance separating the grating from the matrix of photosensitive pixels, but is also a function of the refractive index of each of the media traveled by the incident radiation after its diffraction by the grating.It is therefore necessary to take into account the optical index of the material(s) forming these elements when determining the distance d.

[0025] A third advantage of the device is its compactness, such that it can be integrated into conventional imaging housings, and therefore into any type of camera, benefiting from all their functionalities. Thanks to its compactness, the device can be effectively protected from its environment, preventing the harmful effects of dust, humidity, and frost, especially in the situation where the image sensor requires cooling.

[0026] According to additional non-limiting characteristics of the invention, considered individually or in any technically feasible combination:

[0027] - the at least one optical element may be in direct contact with the imaging sensor;

[0028] - the imaging sensor may comprise an array of microlenses covering the matrix of photosensitive pixels;

[0029] - the at least one optical element can be attached to the imaging sensor by gluing using an adhesive;

[0030] - the adhesive can be continuously formed around a periphery of the array and in direct contact with the imaging sensor and the array;

[0031] - the at least one optical element may consist of the grating, a separation distance between the structured face of the grating and the matrix of photosensitive pixels being fixed by means of a thickness of the grating;

[0032] - the imaging module may further comprise an additional optical element, the network being interposed between this additional optical element and the imaging sensor;

[0033] - the at least one optical element may consist of an additional optical element interposed between the imaging sensor and the grating, a separation distance between the structured face of the grating and the matrix of photosensitive pixels being able to be fixed: (i) by means of a sum of a thickness of the grating and a thickness of the additional optical element if the support of the grating is interposed between the imaging sensor and the structured face of the grating, or (ii) by means of the thickness of the optical element if the structured face of the grating is interposed between the optical element and the support of the grating;

[0034] - the additional optical element can be chosen from a spectral filtering element, a spatial filtering element, and a polarization filtering element;

[0035] - the optical element can be structured on a scale of a group of photosensitive pixels of the matrix, or on a scale of a pixel of the matrix;

[0036] - the optical element may comprise a face structured so as to constitute a matrix of Fabry-Pérot filters, the optical element being oriented in such a way that this structured face is immediately adjacent to the sensor.

[0037] Another aspect of the invention relates to an imager comprising a housing in which the imaging module according to the invention is placed.

[0038] The imager may include a protective glass covering the housing.

[0039] The invention extends to a camera comprising a camera housing containing the imaging module according to the invention or the imager according to the invention. BRIEF DESCRIPTION OF THE FIGURES

[0040] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0041] Illustrates a conventional camera;

[0042] Illustrates a first conventional approach for a QLSI optical system;

[0043] Illustrates a second conventional approach for a QLSI optical system;

[0044] Illustrates an imaging module for characterizing a wavefront by interferometry;

[0045] Illustrates a first variant for the module of the;

[0046] Illustrates a second variant for the module of the;

[0047] Illustrates a third variant for the module of the;

[0048] Illustrates a fourth variant for the module of the;

[0049] Illustrates a fifth variant for the module of the;

[0050] Illustrates a first imager integrating an imaging module for characterizing a wavefront by interferometry;

[0051] Illustrates a second imager integrating an imaging module for characterizing a wavefront by interferometry;

[0052] Illustrates the attachment of a diffraction grating for characterizing a wavefront by interferometry to an imaging sensor;

[0053] Illustrates a camera incorporating an imager such as that of Figures 10 and 11; and

[0054] Illustrates a diffraction grating used in QLSI. DETAILED DESCRIPTION OF THE INVENTION Method of carrying out the invention

[0055] An embodiment of the invention is detailed using figures 4 to 13.

[0056] Figures 4 to 6 illustrate three variants of an imaging module Mod in which a diffraction grating Arr is in direct contact with an imaging Sens sensor. Figures 7 to 9 illustrate three variants of the imaging module, in which an optical element OptEl is interposed between the imaging Sens sensor and the grating Arr. This optical element is chosen to have an optical function useful for analyzing incident radiation: it may be a spectral filtering, spatial filtering, or polarization element, for example.

[0057] This is a cross-sectional view of a first variant of an imaging module designed to characterize a wavefront, with an imaging Mod module comprising an imaging Sens sensor and the diffraction grating Arr. The grating Arr can more specifically be described as an optical phase and / or amplitude grating, due to its functions of modulating the phase and / or amplitude of radiation passing through it.

[0058] The Sens d'imagerie sensor comprises a Mat matrix of photosensitive pixels formed on a planar substrate Sub. The Mat matrix can be formed according to known principles, for example by using CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor) type sensors or other detection technologies in the infrared domains such as InGaAs technology for example.

[0059] The diffraction grating Arr is formed from an optically transparent Sprt support, one face of which StrcFac is structured to introduce periodic phase and / or amplitude (and therefore intensity) variations in an incident light beam. In the case of QLSI, it may be a Sprt support on which a pattern of periodic horizontal H-Str and vertical V-Str bands of zero transmission are formed, delimiting transparent areas. The transparent areas are etched to form an achromatic phase shifter in a checkerboard pattern: for every other aperture in a checkerboard geometry, the surface of the support is etched to a certain depth e, so that this thickness is made of the support material for every other aperture and air for the other apertures, which generates phase shifts of the incident radiation.The periodic bands and structured transparent areas are responsible for the amplitude and phase modulation of radiation passing through the grating. Reference may be made to patent document FR 2 795 175.

[0060] The face of the Arr network opposite the structured face is designated by nStrctFac. The two faces StrctFac and nStrctFac are parallel to each other.

[0061] In this variant, the Arr network is in direct mechanical contact with the surface of the Imaging Direction sensor hosting the Mat matrix. Thus, parallelism between the active face of the Arr network and the imaging plane, materialized by the Mat matrix, is ensured.

[0062] The StrctFac structured face of the Arr network is located on the opposite side to the Mat matrix, i.e. the Sprt support is interposed between the Mat matrix and the StrctFac structured face of the Arr network.

[0063] The distance d separating the structured face StrctFac of the network Arr and the matrix Mat of photosensitive pixels is naturally determined and fixed by the thickness t Arr of the Arr network. In this configuration, the distance d is even equal to the thickness t Arr . It is therefore advisable to choose the thickness of the Sprt support on which the StrctFac structured face is formed according to the intended use for the Imaging Mod module.

[0064] In determining the distance d, the refractive index of the material forming the Sprt support should be taken into account. In the situation of, where the space separating the structured face StructFac from the photosensitive pixels is essentially filled with the material forming the Sprt support, the distance d is d0 / n, where n represents the refractive index of the material forming the Sprt support and d0 represents the geometric positioning distance of the grating from the photosensitive pixels in a conventional situation where the propagation medium of the radiation emerging from the structured face StructFac of the grating is air.

[0065] The Arr array is here attached to the Sens sensor by means of an adhesive Ad. Attachment by a mechanical device is possible, the adhesive attachment having the advantage of simplicity and compactness. As illustrated in (A) of the, the adhesive Ad can be formed by glue dots at the periphery Circ of the Arr array. Alternatively, as illustrated in (B) of the, the adhesive can be formed continuously around the periphery Circ of the Arr array and in direct contact with the imaging Sens sensor and the Arr array, forming a dust- and moisture-tight barrier and thus protecting the Mat matrix from environmental aggressions. In this second case, a window hermetically closing a housing housing the Sens sensor is not a necessity, even if it provides appreciable additional protection and sealing.

[0066] Illustrates a first variant of the imaging module Mod. In this variant, the imaging sensor Sens is equipped with a LensAr array of microlenses covering the Mat matrix of photosensitive pixels. The microlenses can be designed to focus the incident radiation onto the photosensitive surface of the pixels constituting the Mat matrix. In this case, the microlens array constitutes the part of the Sens sensor in mechanical contact with the Arr array. The distance d is no longer identical to the thickness t Arr of the network, so that the integrator of the Arr network on the Sens sensor could have to take into account the height of the microlenses if this is not negligible in view of the intended uses. That being said, the module continues to benefit from the fixing of the distance d and the parallelism ensured by the support of the network itself, as for the situation of the.

[0067] The is similar to the, the imaging module being further equipped with an additional OptEl optical element stacked on the Arr array. The Arr array is therefore interposed between this additional OptEl optical element and the Imaging Direction sensor.

[0068] The OptEl element may be selected from a filtering element, optionally spatial filtering, and a polarization element, among other examples.

[0069] Figures 7 to 9 illustrate three variants of the imaging module Mod, in which an additional optical element OptEl is interposed between the imaging sensor Sens and the Arr network, unlike the variants of Figures 4 to 6. The separation distance d between the structured face StrctFac of the Arr network and the matrix Mat is therefore at least conditioned by the thickness t OptElof the optical element OptEl. Both the Arr array and the optical element can be attached to the Sens sensor by gluing using the Ad adhesive as described above and illustrated in Figures 4 to 12.

[0070] Illustrates a variant of the imaging module Mod, which comprises the optical element OptEl interposed between the imaging sensor Sens and the Arr array. The element OptEl comprises two opposite faces F1 and F2 parallel to each other, one of these faces being in direct contact with the sensor Sens and the other of these faces being in direct contact with the structured face StrctFac of the Arr array. Thus, parallelism between the active face of the Arr array and the imaging plane, materialized by the matrix Mat, is ensured.

[0071] The distance d separating the structured face StrctFac of the network Arr and the matrix Mat of photosensitive pixels is naturally determined and fixed by the thickness t OptElof the OptEl element. In this configuration, the distance d is even equal to the thickness t OptEl . It is therefore appropriate to choose the thickness t OptEl of the OptEl element depending on the intended use for the Mod module in the same way as the thickness t Arr of the Arr network in the situation of the.

[0072] The optical element OptEl may comprise a structured face on a scale of a group of photosensitive pixels of the matrix Mat, or on a scale of a pixel of the matrix Mat, which means that the smallest structural element of the OptEl element may have a lateral extension dimension of the order of a lateral dimension of the matrix, of the order of a lateral dimension of a set of pixels such as a two-dimensional matrix of 2x2, 3x3, 4x4 or 5x5 pixels, or of the order of the lateral dimension of a single pixel, respectively. The expression "a dimension of the order of" here means "a dimension between 50% and 150% of". In such a case, the structured face must be as close as possible to the photosensitive pixels, the additional optical element OptEl must therefore be placed directly against the sensor Sens, interposed between the latter and the array Arr.Furthermore, the structured face must be on the Sens sensor side, i.e. immediately adjacent to the Sens sensor, this structured face (F2 in Figures 7 and 8) being interposed between the Sens sensor and the opposite face of the optical element OptEl (F1 in Figures 7 and 8). Figures 7 and 8 illustrate such a case, in which the structured face is the face F2 of the optical element OptEl. Such a spectral filtering optical element may comprise an array of spectral filters such as Fabry-Pérot filters or resin filters designed to each cover a pixel or a group of pixels, with applications in the field of multispectral imaging.

[0073] Lapresents a variant of the imaging Mod module, which differs from that of theon the following two points: (i) the imaging Sens sensor is provided with a LensAr array of microlenses which is similar to that of the, and (ii) one of the two opposite faces F1 and F2 is in direct contact with the Sens sensor and the other of these faces is in direct contact with the unstructured face nStructFac of the Arr array. The microlens array constitutes the part of the Sens sensor in direct mechanical contact with the Sens sensor.

[0074] In such a case, the support Sprt of the network Arr is interposed between the imaging sensor Sens and the structured face StrctFac of the network Arr, and the distance d is fixed by the sum t OptEl +t Arr of thickness t Arr of the network Arr and the thickness of the optical element OptEl. The distance d is not strictly equal to the sum t OptEl +t Arr, so that the integrator of the Arr network on the Sens sensor could have to take into account the height of the microlenses if this is not negligible in view of the intended uses. That being said, the device continues to benefit from the fixing of the distance d and the parallelism ensured by the thickness and parallelism characteristics of the faces of the Arr network and the OptEl element. It is therefore appropriate to choose the thickness t OptEl and t Arr depending on the intended use for the Mod module.

[0075] In a configuration like that of the, the Arr grating and the additional OptEl optical element can be bonded by their respective facing surfaces. The excess thickness of optical glue is low (usually less than 20 micrometers) and possibly negligible given the intended uses. It can also be measured and compensated for if necessary. Parallelism is ensured by self-leveling of the glue before its crosslinking. The facing faces of the grating and the optical element are chosen so that the glue does not interfere with the optical functionalities of these elements.

[0076] Laillustrates a combination of the variants illustrated by Figures 7 and 8. More specifically, (i) the imaging Sens sensor is provided with a LensAr array of microlenses as illustrated by laand (ii) one of the two faces of the Sens sensor is in direct contact with the structured face StrctFac of the Arr array as illustrated by la.

[0077] In this case, the microlens array constitutes the part of the Sens sensor in direct mechanical contact with the OptEl element. The distance d is not identical to the thickness t Arr of the network, so that the integrator of the Arr network on the Sens sensor could have to take into account the height of the microlenses if this is not negligible given the intended uses. That being said, the device continues to benefit from the fixing of the distance d and the parallelism ensured by the OptEl element, as for the situation of the.

[0078] Of course, other variants than those described in figures 4 to 9 are possible, by playing on the parameters which are the presence or absence of a microlens array, the presence or absence of an additional optical element and the positioning of the latter in relation to the diffraction filter, or even the orientation of the diffraction filter.

[0079] Imaging Module Integration

[0080] The imaging module Mod is intended to be integrated into equipment enabling an end user to study and characterize incident radiation wavefronts. For this purpose, for convenience and protection, the module Mod may be placed in a supporting and protective box, as illustrated in Figures 10 and 11, to form an Im imager. This box may be closed by a window Gl, preferably hermetically, in order to add protection to the module Mod.

[0081] In practice, a Mod module can be manufactured by adding the Arr network and, if necessary, an additional OptEl optical element to a commercially available and distributed Sens image sensor integrated into the Box housing.

[0082] When the total height of the elements added to the Sens sensor is sufficiently low compared to the depth of the Box housing, simply remove the window, fix the elements to be added to the sensor on it and close the window.

[0083] When the total height of the elements added to the Sens sensor is too high to be able to directly replace the window, then an H+ riser allowing the height of the edges of the housing to be increased can be used, as illustrated by the.

[0084] Illustrates a Cam camera incorporating a Mod module of any of the variants illustrated in Figures 4 to 9. This can further be integrated into an Im imager such as those illustrated in Figures 10 and 11, itself integrated into a camera housing 150.

[0085] The present description takes QLSI as representative of wavefront analysis techniques, with a particular geometry of the diffraction grating, but it is understood that the principles detailed above are not limited to QLSI, and arbitrary geometries of diffraction filters can be employed, as long as they allow the generation of different emergent beams which interfere to form an image whose deformations are related to the gradients of the analyzed wave surface.

[0086] The figures in this document are not necessarily to scale. Some features and components may be shown exaggerated in relation to other components or in a somewhat schematic form, and some details of conventional items may not be shown in the interest of clarity and conciseness.

[0087] Of course, the invention is not limited to the method of implementation described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Imaging module (Mod) designed to characterize a wavefront by interferometry, comprising:- an imaging sensor (Sens) comprising a matrix (Mat) of photosensitive pixels formed on a flat substrate (Sub); and- an optical phase and amplitude grating (Arr) formed of a support (Sprt) one face (StrctFac) of which is structured so as to introduce periodic phase and / or amplitude variations into an incident light beam;wherein the array (Arr) is attached to the imaging sensor (Sens) in such a way that at least one optical element (Sprt, OptEl) is interposed between the structured face (StrctFac) of the array (Arr) and the matrix (Mat) of photosensitive pixels, the optical element comprising two opposite faces (StrctFac, nStrctFac, F1, F2) each parallel to the matrix (Mat) of photosensitive pixels and to the structured face (StrctFac) of the array (Arr), and one of them being in mechanical contact with the imaging sensor (Sens), the optical array (Arr) comprising a structured face (StrctFac) having (i) opaque orthogonal lines (H-Str) and columns (V-Str) delimiting transparent openings (Ap) and (ii) half of the transparent openings, distributed in a checkerboard pattern, having an etching of a given depth (e) so as to form a phase checkerboard.; The imaging module (Mod) according to claim 1, wherein the at least one optical element (Sprt, OptEl) is in direct contact with the imaging sensor (Sens). The imaging module (Mod) according to any one of claims 1 to 2, in which the imaging sensor (Sens) comprises an array (LensAr) of microlenses covering the matrix (Mat) of photosensitive pixels. The imaging module (Mod) according to any one of claims 1 to 3, wherein the at least one optical element (Sprt, OptEl) is fixed to the imaging sensor (Sens) by gluing using an adhesive (Ad). The imaging module (Mod) according to claim 4, wherein the adhesive (Ad) is formed continuously around a periphery (Circ) of the array (Arr) and in direct contact with the imaging sensor (Sens) and the array (Arr). The imaging module (Mod) according to any one of claims 1 to 5, wherein the at least one optical element consists of the array (Arr), a separation distance (d) between the structured face (StrctFac) of the array (Arr) and the matrix (Mat) of photosensitive pixels being fixed by means of a thickness (t Arr ) of the network (Arr). The imaging module (Mod) according to claim 6, further comprising an additional optical element (OptEl), the network (Arr) being interposed between this additional optical element (OptEl) and the imaging sensor (Sens). The imaging module (Mod) according to any one of claims 1 to 7, in which the at least one optical element consists of an additional optical element (OptEl) interposed between the imaging sensor (Sens) and the network (Arr), a separation distance (d) between the structured face (StrcFac) of the network (Arr) and the matrix (Mat) of photosensitive pixels being fixed: - (i) by means of a sum (t OptEl +t Arr ) of a thickness (t Arr ) of the network (Arr) and a thickness of the additional optical element (OptEl) if the support (Sprt) of the network (Arr) is interposed between the imaging sensor (Sens) and the structured face (StrctFac) of the network (Arr), or- (ii) by means of the thickness (t OptEl ) of the optical element (OptEl) if the structured face (StrctFac) of the network (Arr) is interposed between the optical element (OptEl) and the support (Sprt) of the network (Arr). The imaging module (Mod) according to claim 8, wherein the additional optical element (OptEl) is chosen from a spectral filtering element, a spatial filtering element, and a polarization filtering element. The imaging module (Mod) according to claim 9, wherein the optical element (OptEl) is structured on a scale of a group of photosensitive pixels of the matrix (Mat), or on a scale of a pixel of the matrix (Mat). The imaging module (Mod) according to claim 9, in which the optical element (OptEl) comprises a structured face (F2) so as to constitute a matrix of Fabry-Pérot filters, the optical element (Sens) being oriented in such a way that this structured face (F2) is immediately adjacent to the sensor (Sens). Imager (Im) comprising a housing (Box) in which the imaging module (Mod) according to any one of claims 1 to 11 is placed. The imager (Im) according to claim 12, comprising a protective window (Gl) closing the housing (Box). Camera (Cam) comprising a camera housing (150) containing the imaging module (Mod) according to any one of claims 1 to 11 or the imager (Im) according to claim 12 or 13.

Images