Compact device for imaging a wavefront by interferometry

Abstract

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 / or 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). Figure to be published with the abstract: Fig.4.

Description

Title of the invention: 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 an imaging technique Quantitative phase scaling is 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 nanoobjects for bioimaging and nanophotonics applications.

[0004] A diffraction grating used for the analysis of a wavefront is designed to induce (i) phase and / or amplitude differences and (ii) a diffraction phenomenon in light radiation passing through the grating. The 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.

[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 2795 175B1.

[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 for introduce only periodic phase variations or only periodic intensity variations. For example, we can refer to patent FR 2712978 Bl.

[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 of 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 positioning as well as a precise 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] [Fig. 1] 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 ImConv imager. 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 ImConv imagers are usually supplied by their manufacturers protected in protective housings 120, 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 conventional ImConv imagers.

[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 for manufacturing wavefront analysis devices according to QLSI.

[0015] A first approach is illustrated by the QLSI system 200 of [Fig. 2]. This approach makes it possible to place the diffraction grating 220 at an arbitrary distance from the imaging plane embodied 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 to be mounted capable of performing QLSI from a camera of any characteristics 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, or even frost, the latter point being critical when the camera is equipped with a sensor cooling system. Another advantage is the possibility of very finely adjusting 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 holding of several elements together: diffraction grating, lenses, camera and, inside the camera, the image sensor itself. Adjusting the parallelism can in particular be 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 [Fig. 3]. 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 sliding The relative adjustment of the two rings therefore makes it possible to adjust the distance d. This approach, detailed in 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 d, such as of the order of a millimeter or less, for example 500 μm, requires removing the glass isolating the image sensor from the environment of the camera, leading to a high risk of contamination by dust and ambient humidity. This latter problem is exacerbated when the image sensor used requires cooling, with a risk of freezing and deterioration of the sensor by the ice crystals thus formed.

[0020] The technical solutions considered so far only lead to wavefront characterization systems which 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. Statement of the invention

[0021] An object of the invention is to provide a wavefront imaging device which 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.

[0023] A first advantage of the device according to the invention is its ease of use, the 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 same, (ü) 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, particularly in the situation where the image sensor needs to be cooled.

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

[0027] - the optical network may comprise a structured face having (i) lines and opaque orthogonal 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;

[0028] - the at least one optical element can be in direct contact with the sensor imaging;

[0029] - the imaging sensor may comprise an array of microlenses covering the photosensitive pixel matrix;

[0030] - the at least one optical element can be attached to the imaging sensor by gluing to the by means of an adhesive;

[0031] - the adhesive may be formed continuously around a periphery of the network and in direct contact with the imaging sensor and network;

[0032] - the at least one optical element may consist of the network, a distance of separation between the structured face of the network and the matrix of photosensitive pixels being fixed by means of a thickness of the network;

[0033] - the imaging module may further comprise an additional optical element, the network being interposed between this additional optical element and the imaging sensor;

[0034] - the at least one optical element may consist of an additional optical element interposed between the imaging sensor and the array, a separation distance between the structured face of the array and the photosensitive pixel matrix can be set: (i) by means of a sum of a thickness of the grating and a thickness of the additional optical element if the grating support 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 grating support;

[0035] - the additional optical element can be chosen from a spectral filtering element, a spatial filtering element, and a polarization filtering element;

[0036] - the optical element can be structured on a scale of a group of pixels photosensitive of the matrix, or at a scale of one pixel of the matrix;

[0037] - the optical element may comprise a face structured so as to constitute a Fabry-Pérot filter matrix, the optical element being oriented in such a way that this structured face is immediately adjacent to the sensor.

[0038] Another aspect of the invention relates to an imager comprising a housing in which the imaging module according to the invention is placed.

[0039] The imager may include a protective glass closing the housing.

[0040] 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

[0041] 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:

[0042] [Fig.l] [Fig.l] illustrates a conventional camera;

[0043] [Fig.2] [Fig.2] illustrates a first conventional approach for a QLSI optical system;

[0044] [Fig.3] [Fig.3] illustrates a second conventional approach for a QLSI optical system;

[0045] [Fig.4] [Fig.4] illustrates an imaging module for characterizing a wavefront by interferometry;

[0046] [Fig.5] [Fig.5] illustrates a first variant for the module of [Fig.4];

[0047] [Fig.6] [Fig.6] illustrates a second variant for the module of [Fig.4];

[0048] [Fig.7] [Fig.7] illustrates a third variant for the module of [Fig.4];

[0049] [Fig.8] [Fig.8] illustrates a fourth variant for the module of [Fig.4];

[0050] [Fig.9] [Fig.9] illustrates a fifth variant for the module of [Fig.4];

[0051] [Fig. 10] [Fig. 10] illustrates a first imager integrating an imaging module for characterizing a wavefront by interferometry;

[0052] [Fig. 11] [Fig. 11] illustrates a second imager integrating an imaging module for characterizing a wavefront by interferometry;

[0053] [Fig. 12] [Fig. 12] illustrates the attachment of a diffraction grating for characterizing a wavefront by interferometry to an imaging sensor;

[0054] [Fig. 13] [Fig. 13] illustrates a camera incorporating an imager such as that of Figures 10 and 11; and

[0055] [Fig. 14] [Fig. 14] illustrates a diffraction grating used in QLSI. DETAILED DESCRIPTION OF THE INVENTION Method of carrying out the invention

[0056] An embodiment of the invention is detailed using figures 4 to 13.

[0057] Figures 4 to 6 illustrate three variants of an imaging Mod module in 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 the analysis of incident radiation: it can be a spectral filtering element, a spatial filtering element, or a polarization element, for example.

[0058] [Fig.4] is a cross-sectional view of a first variant of an imaging module designed to characterize a wavefront, with an imaging module Mod 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.

[0059] The imaging 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 fields such as InGaAs technology for example.

[0060] The diffraction grating Arr is formed from an optically transparent Sprt support, one face of which StrcFac is structured so as to introduce periodic variations in phase and / or amplitude (and therefore intensity) into 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 zones. The transparent zones are etched so as to form an achromatic phase shifter in a checkerboard pattern: for every other opening according to a checkerboard geometry, the surface of the support is etched to a certain depth e, so that this thickness is made up of the material of the support for every other opening and air for the other openings, which generates phase shifts of the incident radiation.The periodic bands and structured transparent areas are responsible for amplitude and phase modulation. of radiation passing through the network. Reference may be made to patent document FR 2 795 175.

[0061] 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.

[0062] In this variant, the Arr network is in direct mechanical contact with the surface of the imaging Direction sensor receiving the Mat matrix. Thus, parallelism between the active face of the Arr network and the imaging plane, materialized by the Mat matrix, is ensured.

[0063] The structured face StrctFac of the network Arr is located on the opposite side to the matrix Mat, that is to say that the support Sprt is interposed between the matrix Mat and the structured face StrctFac of the network Arr.

[0064] The distance d separating the structured face StrctFac from the network Arr and the matrix Mat of photosensitive pixels is naturally determined and fixed by the thickness t^ of the network Arr. In this configuration, the distance d is even equal to the thickness t^. It is therefore appropriate to choose the thickness of the support Sprt on which the structured face StrctFac is formed according to the intended use for the imaging module Mod.

[0065] In determining the distance d, the refractive index of the material forming the Sprt support should be taken into account. In the situation of [Fig. 4], 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 distance of positioning of the grating relative to 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.

[0066] The Arr network is here fixed to the Sens sensor by means of an adhesive Ad. Fixing by a mechanical device is conceivable, the adhesive fixing having the advantage of simplicity and compactness. As illustrated in (A) of [Fig. 12], the adhesive Ad can be formed of glue dots at the Cire periphery of the Arr network. Alternatively, as illustrated in (B) of [Fig. 12], the adhesive can be formed continuously around the Cire periphery of the Arr network and in direct contact with the imaging Sens sensor and the Arr network, forming a barrier impervious to dust and moisture and thus protecting the Mat matrix from environmental aggressions. In this second case, a window hermetically closing a housing accommodating the Sens sensor is not a necessity, even if it provides appreciable additional protection and sealing.

[0067] [Fig.5] illustrates a first variant of the imaging module Mod of [Fig.4]. In this variant, the imaging sensor Sens is provided with a LensAr array of microlenses covering the Mat matrix of photosensitive pixels. The microlenses can be provided 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^ of the array, so that the integrator of the Arr array 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 array itself, as for the situation in [Fig.4],

[0068] [Fig.6] is similar to [Fig.5], the imaging module being further equipped with an additional optical element OptEl stacked on the Arr array. The Arr array is therefore interposed between this additional optical element OptEl and the imaging Direction sensor.

[0069] The OptEl element can be chosen from a filtering element, optionally spatial filtering, and a polarization element, among other examples.

[0070] Figures 7 to 9 illustrate three variants of the imaging module Mod of [Fig.4], in which an additional optical element OptEl is interposed between the imaging sensor Sens and the grating Arr, unlike the variants of Figures 4 to 6. The separation distance d between the structured face StrctFac of the grating Arr and the matrix Mat is therefore at least conditioned by the thickness tOptEi of the optical element OptEl. The grating Arr and the optical element can both be fixed to the sensor Sens by gluing using the adhesive Ad as described above and illustrated by Figures 4 to 12.

[0071] [Fig.7] illustrates a variant of the imaging module Mod, which comprises the optical element OptEl interposed between the imaging sensor Sens and the network Arr. The element OptEl comprises two opposite faces Fl 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 network Arr. Thus, the parallelism between the active face of the network Arr and the imaging plane, materialized by the matrix Mat, is ensured.

[0072] 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 tOptEi of the element OptEl. In this configuration, the distance d is even equal to the thickness top®. It is therefore appropriate to choose the thickness toptEi of the element OptEl according to the intended use for the module Mod in the same way as the thickness t^ of the network Arr in the situation of [Fig. 1].

[0073] The optical element OptEl may comprise a face 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, which means that the smallest structural element of the element OptEl may have a lateral extension dimension of the order of one lateral dimension of the array, of the order of one lateral dimension of a pixel array such as a two-dimensional array 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 (Fl in Figures 7 and 8).Figures 7 and 8 illustrate such a case, in which the structured face is the F2 face 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.

[0074] [Fig.8] shows a variant of the imaging module Mod, which differs from that of [Fig.7] on the following two points: (i) the imaging Sens sensor is provided with a microlens array LensAr which is similar to that of [Fig.5], and (ii) one of the two opposite faces Fl 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.

[0075] In such a case, the support Sprt of the grating Arr is interposed between the imaging sensor Sens and the structured face StrctFac of the grating Arr, and the distance d is fixed by the sum tOptEi+tAir of the thickness t^ of the grating Arr and the thickness of the optical element OptEl. The distance d is not strictly equal to the sum tOptEi+tAn-, so that the integrator of the grating Arr on the sensor Sens could have to take into account the height of the microlenses if this is not negligible with regard to 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 grating Arr and the element OptEl. It is therefore appropriate to choose the thicknesses toptEi and t^ according to the intended use for the module Mod.

[0076] In a configuration like that of [Fig.8], the Arr network 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 with regard to the intended uses. It can also be measured and compensated for if necessary. Parallelism is ensured by self-leveling of the glue before crosslinking. The facing faces of the grating and the optical element are chosen so that the glue does not interfere with the optical functionality of these elements.

[0077] [Fig.9] illustrates 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 [Fig.8] and (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 [Fig.7].

[0078] 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 tAn- of the array, so that the integrator of the array Arr 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 OptEl element, as for the situation in [Fig.7].

[0079] Of course, other variants than those described in figures 4 to 9 are conceivable, 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 relative to the diffraction filter, or even the orientation of the diffraction filter.

[0080] Integration of the imaging module

[0081] The imaging module Mod is intended to be integrated within equipment allowing an end user to study and characterize the incident radiation wavefronts. For this purpose, for convenience and to protect it, the module Mod can be placed in a support and protection box, as illustrated in Figures 10 and 11 in order to form an imager Im. This box can be closed by a window Gl, preferably in a hermetic manner in order to add protection to the module Mod.

[0082] 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.

[0083] When the total height of the elements added to the Sens sensor is sufficiently low compared to the depth of the Box housing, it is sufficient to remove the window, fix the elements to be added to the sensor on it and close the window.

[0084] 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 in [Fig.11].

[0085] [Fig. 13] illustrates a camera Cam integrating a module Mod of any one of the variants illustrated by figures 4 to 9. This can further be integrated into an imager Im such as those illustrated by figures 10 and 11, itself integrated into a camera housing 150.

[0086] 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, insofar as they allow the generation of different emergent beams which interfere by forming an image whose deformations are linked to the gradients of the analyzed wave surface.

[0087] In this document, the figures are not necessarily to scale. Some features and components may be shown exaggerated relative to other components or in a somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness.

[0088] Of course, the invention is not limited to the embodiment described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. 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 / or 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, Fl, 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).

2. The imaging module (Mod) according to claim 1, the optical network (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.

3. The imaging module (Mod) according to any one of claims 1 to 2, wherein the at least one optical element (Sprt, OptEl) is in direct contact with the imaging sensor (Sens).

4. The imaging module (Mod) according to any one of claims 1 to 3, wherein the imaging sensor (Sens) comprises an array (LensAr) of microlenses covering the matrix (Mat) of photosensitive pixels.

5. The imaging module (Mod) according to any one of claims 1 to 4, wherein the at least one optical element (Sprt, OptEl) is fixed to the imaging sensor (Sens) by gluing using an adhesive (Ad).

6. The imaging module (Mod) according to claim 5, wherein the adhesive (Ad) is continuously formed around a periphery (Cire) of the network (Arr) and in direct contact with the imaging sensor (Sens) and the network (Arr).

7. The imaging module (Mod) according to any one of claims 1 to 6, wherein the at least one optical element consists of the grating (Arr), a separation distance (d) between the structured face (StrctFac) of the grating (Arr) and the matrix (Mat) of photosensitive pixels being fixed by means of a thickness (1^) of the grating (Arr).

8. The imaging module (Mod) according to claim 7, further comprising an additional optical element (OptEl), the network (Arr) being interposed between this additional optical element (OptEl) and the imaging sensor (Sens).

9. The imaging module (Mod) according to any one of claims 1 to 6, wherein the at least one optical element consists of an additional optical element (OptEl) interposed between the imaging sensor (Sens) and the array (Arr), a separation distance (d) between the structured face (StrcFac) of the array (Arr) and the matrix (Mat) of photosensitive pixels being fixed: - (i) by means of a sum (tOptEi+tAn-) of a thickness (^) of the array (Arr) and a thickness of the additional optical element (OptEl) if the support (Sprt) of the array (Arr) is interposed between the imaging sensor (Sens) and the structured face (StrctFac) of the array (Arr), or - (ii) by means of the thickness (tOptEi) 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).

10. The imaging module (Mod) according to claim 9, wherein the additional optical element (OptEl) is chosen from a spectral filtering element, a spatial filtering element, and a polarization filtering element.

11. The imaging module (Mod) according to claim 10, 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).

12. The imaging module (Mod) according to claim 10, 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).

13. Imager (Im) comprising a housing (Box) in which the imaging module (Mod) according to any one of claims 1 to 12 is placed.

14. The imager (Im) according to claim 13, comprising a protective window (Gl) closing the housing (Box).

15. Camera (Cam) comprising a camera housing (150) containing the imaging module (Mod) according to any one of claims 1 to 12 or the imager (Im) according to claim 13 or 14.

Images