Reflective device comprising a detector, and associated method

Abstract

Reflector device comprising a detector, and associated method The invention relates to a reflector device (1) comprising a partially transparent mirror (10) configured to form a reflected beam (21) by reflection of a portion of the incident beam (20), and to transmit another portion of the incident beam (20) to form a transmitted beam (22); the reflector device (1) further comprises a detector module (11) configured to measure at least one parameter associated with the transmitted beam (22), the at least one parameter being chosen from: a presence or an absence of the transmitted beam (22), a position (220) of the transmitted beam (22), a shape (222) of the transmitted beam (22), and to determine a state of alignment of the incident beam (20) with the reflector device (1) and / or a deformation of the mirror (10). Figure for abstract: Fig.2B

Description

Title of the invention: Reflective device comprising a detector, and associated method Technical field

[0001] The present invention relates to the field of reflective devices intended to reflect an incident light beam towards a target. It finds a particularly advantageous application in the field of MEMS micromirrors (microelectromechanical systems), in particular for LIDAR (light detection and ranging) and laser pointing applications, for example for focusing a beam at a given point in a scene. STATE OF THE ART

[0002] Reflective devices are used in many applications in which an attempt is made to reflect an incident light beam towards a given target.

[0003] To do this, an incident light beam is emitted by a source towards the reflector device having a mirror that is at least partially transparent. The mirror has a front face arranged to receive the incident light beam. The mirror is oriented with the source so as to form a reflected beam in the direction of the target.

[0004] For example, MEMS micromirrors are commonly used for LIDAR or laser pointing applications. To this end, the micromirrors can comprise an actuator module configured to pivot the micromirror about at least one axis of rotation.

[0005] In LIDAR type devices, micromirrors are used to scan a surface or target with light radiation for detection or imaging purposes. Typically, the micromirrors are configured to oscillate along one or two rotation axes, at a predetermined scanning frequency, so as to reflect incident radiation in different directions.

[0006] The scanning frequency of the micromirrors can vary from a few Hz to several kHz, and their size can be of the order of a few tens of micrometers to several millimeters (for example a few millimeters in diameter for disc-shaped micromirrors), and can in particular be between 500 μm and 10 mm.

[0007] Figures 1A and 1B illustrate by way of example two architectures of reflector device 1'. In [Fig.1A], the device 1' may comprise a first micromirror 10 and a second micromirror 10', arranged to pivot respectively around a first axis of rotation X and a second axis of rotation Y which are not parallel to each other. In par In particular, these two micromirrors 10, 10' are arranged so that a light beam 20 emitted by a light source 2 is reflected by the first micromirror 10 towards the second micromirror 10' which in turn reflects it towards, for example, a screen or a target 3. The rotation of each of the micromirrors 10, 10' around their respective axis of rotation thus makes it possible to scan a surface with the reflected light beam 21, for example, for imaging or detection purposes.

[0008] In [Fig.lB], the device 1' may comprise a single micromirror 10 pivotally mounted around two axes of rotation X and Y that are not parallel to each other. The rotation of this micromirror 10 around one and the other of the two axes X, Y thus makes it possible to scan the surface of a screen or a target 3 by means of a reflected light beam 21 coming from a light source 2 and reflected by this micromirror 10.

[0009] In these devices, it is important to ensure good alignment between the beam source and the micromirror in order to properly orient the reflected beam. In addition, these devices are often exposed to thermal and mechanical stresses that can impact their operation, and in particular the properties of the reflected beam.

[0010] The document EP3726268A1 discloses in particular a reflector device comprising a partially transparent mirror and means for absorbing a beam transmitted through the rear face of the mirror to limit thermal heating. However, this solution remains limited to ensure the proper functioning of the reflector device.

[0011] An object of the present invention is therefore to provide a solution improving the reliability of reflection by a partially reflecting reflector device.

[0012] The other objects, features and advantages of the present invention will appear upon examination of the following description and the accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0013] To achieve this objective, according to a first aspect, a reflector device is provided, more particularly intended to reflect an incident light beam towards a target. The reflector device comprises a partially transparent mirror having a front face arranged to receive the incident light beam and a rear face opposite the front face, the mirror being configured to form a reflected beam by reflection of a portion of the incident beam, and to transmit another portion of the incident beam via the rear face to form a transmitted beam.

[0014] Advantageously, the reflector device further comprises a detector module arranged opposite the rear face of the mirror. The detector module is configured to measure at least one parameter associated with the transmitted beam, the at least one parameter being chosen from: - a presence or absence of the transmitted beam, - a position of the transmitted beam, - a shape of the transmitted beam,

[0015] and to determine a state of alignment of the incident beam with the reflector device and / or a deformation of the mirror.

[0016] Thus, the beam transmitted by the partially transparent mirror can be used to ensure the correct alignment of the incident beam with the mirror, and in particular the correct alignment between the source and the mirror, and / or to detect any deformation of the mirror, while allowing the reflection of the reflected beam towards the target.

[0017] If, following an impact for example, the mirror and / or the source are displaced, the incident beam may no longer be reflected by the mirror or its position may be changed. The reflector device makes it possible to detect this and possibly to consider corrective actions. When the reflector device is exposed to thermal stresses, the reflector device makes it possible to determine a deformation of the mirror, in particular resulting in a change in the focusing of the transmitted beam.

[0018] The reflector device therefore allows real-time measurement of the alignment of the laser and the mirror and / or the deformation of the mirror, which cause a modification of the reflected beam. It is therefore possible to continuously ensure that the reflected beam is indeed going in the desired direction. The reliability of the reflection of the incident beam towards a target is therefore improved. The reflector device is therefore particularly advantageous for applications in which there is no return from the target, i.e. it is difficult or impossible to ensure that the reflected beam correctly reaches the target.

[0019] A second aspect relates to a method for measuring the alignment of an incident beam and / or a mirror deformation implementing the reflector device according to the first aspect, comprising: - an emission of the incident beam from a light source towards the reflecting device, - a measurement, by the detector module, of at least one parameter associated with the beam transmitted by the mirror, the at least one parameter being chosen from: • a presence or an absence of the transmitted beam, • a position of the transmitted beam, • a shape of the transmitted beam, - a determination of the alignment state of the incident beam with the reflecting device and / or the deformation of the mirror comprising: • if the parameter measured by the detector module is an absence of the transmitted beam and / or a position of the transmitted beam different from a defined position, a determination of a bad alignment of the incident beam, and / or • if the parameter measured by the detector module is a shape of the transmitted beam different from a defined shape, a determination of a deformation of the mirror.

[0020] It is therefore understood that the measuring method also allows real-time measurement of the alignment of the source and the mirror and / or the deformation of the mirror. The method therefore allows for reliability of the reflection of the incident beam. BRIEF DESCRIPTION OF THE FIGURES

[0021] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0022] [Fig.lA]

[0023] [Fig. 1B] Figures 1A and 1B show two examples of state-of-the-art reflective devices.

[0024] [Fig.2A]

[0025] [Fig.2B]

[0026] [Fig.2C] Figures 2A to 2C represent sectional views of three examples of reflective devices according to three exemplary embodiments of the invention.

[0027] [Fig.3] [Fig.3] represents a sectional view of the reflector device during a determination of a misalignment between the source and the mirror, according to an exemplary embodiment.

[0028] [Fig.4A]

[0029] [Fig.4B] Figures 4A and 4B represent a sectional view of the reflector device during a determination of a deformation of the mirror, according to an exemplary embodiment.

[0030] [Fig.5A] [Fig.5A] represents a perspective view of an example of a reflector device in which the mirror is pivotally mounted about an axis of rotation.

[0031] [Fig.5B] [Fig.5B] represents a top view of an example of a reflector device in which the mirror is pivotally mounted about two axes of rotation.

[0032] [Fig.6] [Fig.6] represents a sectional view of a reflective device comprising a focusing lens, according to an exemplary embodiment.

[0033] [Fig.7A]

[0034] [Fig.7B] Figures 7A and 7B show a sectional view of two particular examples of reflective device.

[0035] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular the relative dimensions of the layers and elements of the device reflector are not representative of reality. DETAILED DESCRIPTION

[0036] Before commencing a detailed review of embodiments of the invention, optional features are set out below which may optionally be used in combination or alternatively.

[0037] According to one example, the detector module is configured to determine the alignment state of the incident beam with the reflector device and / or a deformation of the mirror according to: - if the parameter measured by the detector module is an absence of the transmitted beam and / or a position of the transmitted beam different from a defined position, a misalignment of the incident beam is determined by the detector module, and / or - if the parameter measured by the detector module is a shape of the transmitted beam different from a defined shape, a deformation of the mirror is determined by the detector module.

[0038] Thus, the reflector device can make it possible to independently determine poor alignment of the incident beam and / or deformation of the mirror, depending on the nature of the information measured.

[0039] According to one example, the reflector device further comprises a support and an actuator module configured to pivot the mirror about at least one axis of rotation relative to the support, wherein the detector module is secured to the support. The reflector device is thus particularly suitable for MEMS mirror applications. Since the detector module is secured to the support, the determination of poor alignment of the incident beam and / or deformation of the mirror can be made independently of the angular position of the mirror. Indeed, the transmitted beam will not be impacted by the angular position of the mirror during its rotation.

[0040] According to one example, the detector module has a time resolution greater than or equal to a characteristic misalignment time of the incident beam. For this, for example, the detector module has an acquisition frequency greater than or equal to a vibration frequency of the source.

[0041] According to one example, the mirror comprises: - a metallic reflective layer comprising at least one opening and / or having a thickness chosen to transmit the other part of the incident beam to form the transmitted beam, and / or - a Bragg stack comprising at least one so-called “elementary” Bragg stack comprising two layers having distinct refractive indices.

[0042] The Bragg stack makes it possible to modulate the transmitted part and the reflected part of the beam according to the characteristics of the layers composing it and the number of elementary stacks. In addition, the reflection and transmission properties can be modulated according to the wavelength of the incident beam.

[0043] According to one example, the elementary Bragg stack comprises two dielectric and / or semiconducting layers.

[0044] According to one example, the elementary Bragg stack comprises a layer of amorphous silicon and a layer of silicon oxide.

[0045] According to one example, the detector module is arranged at a non-zero distance from the rear face of the mirror, said distance being between 1 μm and 15 cm, preferably between 0.5 cm and 15 cm.

[0046] According to one example, the device comprises a mechanical support layer having a front face and a rear face opposite the front face.

[0047] According to one example, the mirror surmounts, by its rear face, the front face of the mechanical support layer.

[0048] According to one example, the mechanical support layer is based on silicon, preferably monocrystalline silicon.

[0049] According to one example, the detector module comprises a single-element detector.

[0050] According to one example, the detector module comprises a pixelated matrix, of pixelated preference in two dimensions. This facilitates the detection of a shift in the position of the transmitted beam as well as the deformation of the transmitted beam. In addition, a quantitative measurement can be obtained, improving the measurement of the alignment of the incident beam and / or the deformation of the mirror. This further facilitates the implementation of subsequent corrective action.

[0051] According to one example, the reflector device further comprises an optical element, for example a lens, configured to focus the transmitted beam onto the detector module. The focusing of the transmitted beam onto the detector can thus be modulated, and in particular in synergy with the distance of the detector module relative to the lens. The resolution of the detection of the alignment state and / or the deformation of the mirror can thus be improved.

[0052] According to one example, the mirror extends in a main extension plane, over at least one millimetric dimension, for example a diameter, preferably between 500 μm and 10 mm, preferably between 500 μm and 5 mm.

[0053] According to one example, the device is a LIDAR reflector device.

[0054] According to another example, the device is a laser pointing system.

[0055] According to these two examples, the reflector device further comprises in particular a support and an actuator module configured to pivot the mirror around at least one axis of rotation relative to the support, the detector module being integral with the support.

[0056] According to one example, the device comprises the light source configured to emit the incident beam.

[0057] According to one example, the light source is an infrared source.

[0058] According to one example, the light source is configured to emit the beam incident with a wavelength greater than or equal to 900 nm, for example 905 nm or 1550 nm.

[0059] According to one example, the light source is a laser source.

[0060] According to one example, the incident beam and the reflected beam propagate according to distinct propagation directions between them.

[0061] According to one example, the method comprises reflecting a portion of the incident beam by the mirror to form the reflected beam, in particular towards a target.

[0062] According to one example, the method comprises transmitting another portion of the incident beam by the mirror, to form the transmitted beam.

[0063] According to one example, the reflection of the incident beam by the mirror to form the reflected beam is at least partly simultaneous with the measurement by the detector module of the at least one parameter associated with the transmitted beam.

[0064] According to one example, the method further comprises correcting at least one of the position of the light source and the position of the mirror if, when determining an alignment state of the incident beam with the reflector device and / or a deformation of the mirror, a misalignment of the incident beam is determined. The reliability of the reflector device can thus be improved by correcting the misalignment of the source or by compensating for this misalignment with the position of the mirror.

[0065] According to one example, the reflector device comprising an actuator module configured to pivot the mirror around at least one axis of rotation, and the detector module secured to the mirror comprising a two-dimensional pixelated matrix: - the determination of a state of alignment of the incident beam with the reflector device and / or of a deformation of the mirror comprises a determination of an offset between the position of the transmitted beam and the defined position, and - the correction of the position of the mirror comprises a modification of the angular range of pivoting of the mirror as a function of said offset.

[0066] The misalignment of the source can thus be determined quantitatively. Depending on this data, the modification of the angular range of pivoting of the mirror makes it possible to compensate for this misalignment in a simplified manner, and without having to review the alignment of the source. This is particularly advantageous for correction during use of the reflector device, without requiring disassembly and / or complex realignment.

[0067] According to one example, the method comprises issuing an alert and / or an action heat dissipation at the mirror if, when determining a state of alignment of the incident beam with the reflecting device and / or a deformation of the mirror, a deformation of the mirror is determined. The reliability of the reflection is thus improved either by issuing an alert to the user, or by acting on a cause of the deformation by limiting thermal heating of the mirror.

[0068] A substrate is understood to mean a layer based on a species A, a substrate, a layer comprising this species A only or this species A and possibly other species.

[0069] By microelectronic device is meant any type of device produced using microelectronic means. These devices include, in particular, in addition to devices for purely electronic purposes, micromechanical or electromechanical devices (MEMS, NEMS, etc.) as well as optical or optoelectronic devices (MOEMS, LEDs, etc.).

[0070] It is specified that in the context of the present invention, the thickness of a layer or a substrate is measured in a direction perpendicular to the surface along which this layer or this substrate has its maximum extension. The thickness is thus taken in a direction perpendicular to the main faces of the substrate on which the different layers rest.

[0071] It is specified that, in the context of the present invention, the terms "on", "overcomes", "covers", "underlying", "facing" and their equivalents do not necessarily mean "in contact with". Thus, for example, the arrangement of a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0072] A parameter “substantially equal / greater / less than” a given value means that this parameter is equal / greater / less than the given value, within plus or minus 10% of this value. A parameter “substantially between” two given values ​​means that this parameter is at least equal to the smallest given value, within plus or minus 10% of this value, and at most equal to the largest given value, within plus or minus 10% of this value.

[0073] In the present patent application, the term "secured" used to qualify the connection between two parts means that the two parts are linked / fixed to each other in all degrees of freedom, unless otherwise explicitly specified. For example, if it is indicated that two parts are secured in translation in the X direction, this means that the parts can be movable relative to each other, possibly in several degrees of freedom, excluding the degree of freedom in translation in the X direction. In other words, if one part is displaced in the X direction, the other part undergoes the same displacement.

[0074] In the following detailed description, use may be made of terms such as "horizontal", "vertical", "longitudinal", "transverse", "upper", "lower", "top", "bottom", "front", "rear", "inner", "outer". These terms must be interpreted relatively in relation to the normal position of the reflecting device and the propagation of the light beams, and in particular the incident light beam, relative to the reflecting device.

[0075] A reference will also be used whose longitudinal direction corresponds to the X axis, the transverse or right / left direction corresponds to the Y axis and the vertical or down / up or front / back direction corresponds to the Z axis.

[0076] For the purposes of this disclosure, the expression "A and / or B" means (A), (B), or (A and B). For the purposes of this disclosure, the expression "A, B and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0077] The reflector device 1 and the method for measuring the alignment of an incident beam 20 and / or a deformation of a mirror 10 are now described according to several exemplary embodiments.

[0078] As illustrated for example in Figures 2A to 2C, the reflector device 1 is intended to reflect an incident light beam 20 to form a reflected beam 21 propagating in a determined direction, typically towards a target 3. For this, the incident light beam 20 can be emitted by a source 2. The source 2 is more particularly aligned with the reflector device 1 so that, after reflection on the reflector device 1, the reflected beam 21 reaches the target 3.

[0079] The light source 2 may be an infrared source. According to one example, the light source 2 is configured to emit the incident beam with a wavelength greater than or equal to 900 nm, for example 905 nm or 1550 nm, propagating in air. Preferably, the light source 2 is a laser source.

[0080] The reflector device 1 comprises a mirror 10 having a front face 10a and a rear face 10b opposite the front face 10a. The incident beam 20 propagates from the source 2 to the mirror 10, and more particularly to its front face 10a. The reflected beam 21 then propagates from the front face 10a of the mirror 10 to the target 3. The mirror 10 is more particularly a plane mirror. Note that the size of the incident beam 20 on the mirror 10 may be larger than the size of the mirror 10, or smaller.

[0081] When the source 2 and the mirror 10 become misaligned, it is understood that the incident beam 20 may no longer be reflected on the mirror 10, or the reflected beam 21 may be deflected from its initially planned path and miss the target 3. This may occur, for example, in the event of an impact. Furthermore, a modification of the flatness of the mirror 10 may cause a change in the focusing of the reflected beam 21. The reflected beam 21 may then not correctly reach the target 3. This may occur for example during thermal stress following heating of the mirror 10 or a shock or mechanical stress on the structure, for example during vibration. The incident beam 20 may in fact heat the mirror 10, which will impact its reflection properties. This can be observed in particular when the incident beam is an infrared beam, and / or when the source 2 is a laser source.

[0082] In order to make the reflection by the reflector device 1 more reliable, the mirror 10 is configured to reflect a portion of the incident beam 20 to form the reflected beam 21, and to transmit another portion of the incident beam 20 via the rear face 10b of the mirror to form a transmitted beam 22. The mirror 10 is therefore partially transparent. It has a reflection component and a transmission component. Preferably, the mirror 10 is configured to reflect between 75% and 99.9% of the incident beam 20. The mirror 10 may be configured to transmit between 24.5% and 0.03% of the incident beam 20.

[0083] The reflector device 1 uses the transmitted beam 22 in order to determine a state of alignment of the incident beam 20 with the reflector device 1 and / or a deformation of the mirror 10. For this, the reflector device 1 comprises a detector module 11 arranged opposite the rear face 10b of the mirror 10. The detector module 11 is therefore placed below the mirror 10 in the reflector device 1, relative to the propagation of the incident beam 20. The detector module 11 is arranged so as to receive the transmitted beam 22 at least when the incident beam 20 is correctly aligned with the reflector device 1, and in particular the mirror 10.

[0084] The detector module 11 is configured to measure at least one parameter associated with the transmitted beam 22. This or these parameter(s) is / are chosen from: - a presence or an absence of the transmitted beam 22, - a position 220 of the transmitted beam 22, - a shape 222 of the transmitted beam 22.

[0085] Depending on this(these) parameter(s), the detector module 11 can determine a state of alignment of the incident beam 20 with the reflector device 1 and / or a deformation of the mirror 10. The reflector device 1 thus makes it possible to determine these states independently, and this, continuously during its use.

[0086] The detector module 11 may comprise a detector 110, 111. The detector module may further comprise analysis means 112, for example by at least one processor. The analysis means 112 may comprise instructions making it possible to carry out the steps of analyzing data and / or determining a state of alignment of the incident beam with the reflector device and / or a deformation of the mirror. These instructions may make it possible for the state of alignment of the incident beam 20 with the reflector device 1 and / or the deformation of the mirror 10 are determined from the measured parameter. These analysis means 112 may further comprise instructions for carrying out the prior analysis of data acquired by a detector to determine the parameter associated with the transmitted beam 22.

[0087] According to one example, the detector module 11 may comprise a single-element detector 110 and / or a detector comprising a pixelated matrix 111, for example along the two dimensions X, Y. In the figures, note that this pixelated matrix 111 is presented in a non-limiting manner in perspective, in particular for the purposes of readability and explanation. By single-element detector 110, it is meant that the detector is configured to measure the light intensity of the transmitted beam 22 without dedicated means for knowing its position on the detector 110. It is therefore not a pixelated detector. For example, the single-element detector is a single-detector, or even a single-pixel, of InGaAs or CMOS detector based on or made of silicon.

[0088] For radiation at 1550 nm, a detector 110, 111 based on or made of InGaAs will be preferred. For radiation at 905 pm, a detector 110, 111 based on or made of silicon may be considered, for example a CMOS detector. A CMOS detector is nevertheless generally limited in terms of acquisition frequency of the order of 1 kHz to 10 kHz. This may be limiting in relation to the pivoting speed of the mirror 10, as discussed in more detail later. There are scientific cameras with acquisition frequencies of several tens of kHz, however, they are expensive. The detector 110, 111 may be of a size smaller than or equal to that of the mirror 10 in the (X,Y) plane. For example, the detector 110, 111 may extend in projection in the (X,Y) plane over only a fraction of the surface of the mirror taken in the same plane.The detector 110, 111 may extend in a main extension plane substantially parallel to the main extension plane of the mirror 10. Alternatively, it may be provided that the detector 110, 111 is positioned obliquely relative to the mirror 10.

[0089] The transmitted beam 22 typically propagates substantially in the same direction relative to the incident beam 20. Equivalently, the transmitted beam 22 is substantially not deflected by the mirror 10. Equivalently, it is considered that the deviation of the beam 22 during its transmission by the mirror 10 is negligible with regard to the effects of the misalignment of the source 2 and / or the deformation of the mirror 10. In any event, a possible deviation of the transmitted beam 22 by the mirror (for example in the event of a lack of parallelism between the two surfaces of the mirror 10 or to a lesser extent due to the thickness of the mirror), can form a lower limit of deviation of the measurable incident beam 20. As illustrated in [Fig. 3], if the incident beam 20 is misaligned relative to its intended position (illustrated for comparison in FIGS. 2A to 2C), then the direction of propagation of the beam transmitted 22 is modified accordingly. The misalignment of the incident beam 20, and in particular the misalignment between the source 2 and the mirror 10, may be a rotation (which modifies the angle of incidence of the incident beam 20 on the mirror 10) or a translation (which does not modify the angle of incidence of the incident beam 20 on the mirror), or a combination of the two.

[0090] The transmitted beam 22 may no longer be detected by the detector module 11, or as illustrated the position 220 of the transmitted beam on the detector module may be modified. A poor alignment of the incident beam 20 and therefore a poor alignment of the source and the reflector device 1 may be determined.

[0091] When the detector module 11 comprises a single-element detector, the measured parameter will preferably be a presence or absence of the transmitted beam 22. When the detector module 11 comprises a pixelated matrix 111, a more quantitative measurement of the position 220 of the transmitted beam can further be obtained. For example, as illustrated in [Fig.3], an offset A22 of the position 220 of the transmitted beam can be measured relative to a defined position 221, for example its initial position.

[0092] When a poor alignment of the incident beam 20 is detected, a corrective action 4 can then be implemented. The reflector device 1, for example the mirror 10, and / or the source 2 can be realigned until the detection of a transmitted beam 22 on the detector module 11 is again obtained. As a complementary alternative, the reflector device 1, for example the mirror 10, and / or the source 2 can be realigned so as to compensate for the offset A22 of the position 220 of the transmitted beam. A more particular example is described later in relation to a mirror that can pivot in rotation.

[0093] During a deformation of the mirror 10, the focusing state of the reflected 21 and transmitted 22 beams can be modified. These beams 21, 22 can for example become more convergent or more divergent than the incident beam 20, which is generally focused at infinity. The shape 222 of the transmitted beam 22 on the detector module 11 can be modified, as illustrated for example in FIGS. 4A and 4B.

[0094] When the detector module 11 comprises a single-element detector, a deformation of the mirror 10 can be determined as a function of the measured light intensity. The shape of the transmitted beam 22 on the detector module 11 being modified, a variation in intensity can in fact be measured. Preferably, to determine a deformation of the mirror 10, the detector module 11 comprises a pixelated matrix 111. The area of ​​the spot formed by the transmitted beam 22 on the pixelated matrix 111 can be modified as a function of the focusing of the transmitted beam 22. For example, as illustrated in FIGS. 4A and 4B, an evolution of the shape 222 of the transmitted beam 22 can be determined with respect to a defined shape 223, for example its shape initial.

[0095] When a deformation of their mirror 10 is detected, an alert 5 can be issued, for example to the user. Thus the user is warned of a decreased reliability of the reflection of the incident beam 20 towards the target 3. Alternatively or complementarily, a heat dissipation action 6 can be carried out at the level of the mirror 10. For example, the source 2 can be turned off in order to dissipate the heating of the mirror 10. A person skilled in the art can quite envisage other actions for compensating and / or limiting the deformation of the mirror 10.

[0096] The defined position 221 and / or the defined shape 223 can be defined during a calibration step, for example before the reflection towards the target 3.

[0097] According to a particular example, illustrated by FIGS. 5A and 5B, the mirror 10 is configured to pivot about at least one axis of rotation X, and preferably about the axes of rotation X and Y, for example over an angular interval a, a1, a2. The axes X, Y are then non-parallel to each other, and preferably perpendicular. Preferably, at least one axis of rotation is parallel to, and preferably located in, a plane of the front reflection face 10a of the mirror 10. The mirror 10 may in particular be a MEMS type micromirror. The reflector device 1 is thus particularly suitable for LIDAR or laser pointing applications. Preferably, the mirror 10 is configured to pivot about the two axes of rotation X and Y.

[0098] When the mirror is in angular movement (in X and / or in Y), the position of the transmitted beam 22 does not move significantly except for misalignment of the source and the mirror 10 or modification of the shape of the mirror 10.

[0099] Since the mirror 10 is pivotable, it is possible to play on the angular position of the mirror 10 to compensate for the misalignment of the incident beam 20. For example, the angular rotation interval can be adapted to compensate for this misalignment. The angular rotation interval a, a1 and / or a2 can in particular be adapted according to the measured offset A22.

[0100] According to one example, the mirror 10 may be arranged on a support 108 configured to remain fixed during the movement of the mirror 10. This support is shown by way of example in FIGS. 5A and 7A, 7B. The detector module 11 is preferably secured to the support 108, preferably at least in rotation in the X and Y directions. The detector module 11 may be secured to the support 108 according to all degrees of freedom. It may be provided that the detector module 11 is free in translation relative to the support 108, in the Z direction. Thus the detector module 11 is independent of the movement of the mirror 10. The propagation of the transmitted beam 22 will therefore not be substantially impacted by the rotational position of the mirror 10.

[0101] The alignment state of the incident beam 20 and / or the deformation of the mirror 10 can therefore be determined independently of the rotational position of the mirror 10. It is thus not necessary to carry out the measurement, to return the mirror 10 to a set position to make the measurement. The measurement of the alignment of an incident beam 20 and / or of a deformation of the mirror 10 can therefore be carried out continuously when using the reflector device 1, including for a rotating mirror 10.

[0102] The detector module 11 and the support 108 can be separated from each other, as for example illustrated in [Fig.7A]. The detector module 11 and the support 108 can be secured to each other by means of a support 113, as for example illustrated in [Fig.7B].

[0103] The reflector device 1 may further comprise an actuator module 12 configured to pivot the mirror around the rotation axis(es) X, Y, for example by actuator arms 120. The actuator module 12 may comprise at least one actuator chosen from: an electrostatic actuator, a magnetic actuator, a piezoelectric actuator, a thermal actuator. Preferably, the actuator module 12 comprises at least one piezoelectric actuator 120. The actuator module 12 has for example two actuators 120, one on a so-called “fast” rotation axis and one on a so-called “slow” rotation axis. The actuator module 12 may have movement frequencies of substantially 10 Hz on the slow axis and substantially 1 kHz on the fast axis.

[0104] Preferably, the detector module 11 has a time resolution greater than or equal to a characteristic misalignment time of the incident beam. For example, it is possible to provide that a source 2, for example a laser source, vibrates at a given frequency (for example linked to poorly compensated vibrations of the structure). This movement can thus be followed on the detector module 11. The transmitted beam 22 can move relative to the assembly formed by the mirror 10 and the detector module 11. The detector module 11 can detect this movement in real time when its acquisition frequency is greater than or equal to the movement of the point of impact of the transmitted beam 22 on the detector module 11.

[0105] According to one example, the pivoting speed of the mirror 10 is typically between 1 Hz and 50 kHz. This value may in particular be a function of the size of the mirror and the intended application. For example, for a mirror with a diameter of 2 mm, the slow and fast frequencies will be respectively from 10 Hz to 40 Hz and from 200 Hz to 1000 Hz. For smaller mirrors (for example around 0.5 mm in diameter) the fast frequencies may go up to 20 kHz for example.

[0106] According to an example illustrated in [Fig.6], the reflector device 1 may comprise an optical element 13, for example a lens 13, configured to modulate the focusing of the transmitted beam 22 on the detector module 11. Thus the resolution of the measurement of position 220 and / or of the shape 222 of the transmitted beam 22 may be improved, in particular when the detector module comprises a pixelated matrix 111. For In this case, the distance di between the lens 13 and the detector 110, 111 can, for example, be adapted.

[0107] The reflector device 1 is now described in more detail element by element, according to several exemplary embodiments.

[0108] The mirror 10 is partially transparent. For this, the mirror 10 may comprise at least one metallic reflective layer 100 configured to allow a portion of the incident beam 20 to pass through to form the transmitted beam 22. For this, and as illustrated in [Fig.2A], the metallic reflective layer 100 may have a thickness eiOo configured to allow a portion of the incident beam 20 to pass through. It is understood that this thickness may vary depending on the nature of the metal used. For example, the metallic reflective layer 100 is gold-based. According to one example, the metallic reflective layer 100 has a thickness eiOo substantially less than or equal to 100 nm.

[0109] Alternatively, and as illustrated in [Fig.2C], the mirror 10 may comprise an aperture 1000 configured to transmit a portion of the incident beam 20 to form the transmitted beam 22. The thickness e»» of the metallic reflective layer 100 may then be greater than the above range. The analysis of the deformation of the mirror 10 may however be limited in the case of a simple aperture 1000, without a component transmitted through the reflective material of the mirror 10.

[0110] According to a preferred example, for example illustrated in figures 2B, 3 to 4B, 6 and 7A and 7B, the mirror 10 comprises a Bragg stack 101, the Bragg stack comprising at least one elementary Bragg stack 102. By "Bragg stack" is meant a periodic succession of transparent, or partially transparent, layers with different refractive indices. An elementary Bragg stack comprises a stack of two dielectric and / or semiconducting layers 103, 104. In the Bragg stack, in a known manner, the difference in optical index between these layers is used to reflect the desired wavelength.

[0111] The nature of the layers 103, 104 can be chosen as a function of the wavelength of the incident beam 20, to modulate the transmitted portion and the reflected portion of the beam. The number of elementary Bragg stacks can further be chosen to modulate the transmitted portion and the reflected portion of the incident beam 20. For example, the number of elementary Bragg stacks 102 can make it possible to modulate the quantity of transmitted light so as not to dazzle the detector module 11 while ensuring a sufficient threshold for detection. Limiting the number of elementary Bragg stacks also makes it possible to reduce the mechanical stresses imposed on the mirror, and thus limit the risk of mechanical deformation of the mirror. According to one example, the Bragg stack 101 comprises between one and five, preferably between one and three, elementary Bragg stacks 102.

[0112] Preferably, the thickness of the layers 103, 104 is chosen so that they are so-called “X / 4” layers, that is to say that the product of the thickness of a layer by the optical index of the layer is substantially equal to a quarter of the wavelength in a vacuum. This makes it possible to obtain constructive interference in reflection and therefore to maximize the reflection of the incident beam 20, with a given number of layers, the remainder going into transmission.

[0113] By way of example, when the radiation is in the infrared range, and more particularly of wavelength equal to 1550 nm, the elementary Bragg stack 102 may comprise a layer 104 based on or made of silicon dioxide with a thickness of substantially 305 nm (whose refractive index at 1550 nm is 1.45) topped with a layer 103 based on or made of amorphous silicon with a thickness of 110 nm (whose refractive index at 1550 nm is 3.42).

[0114] According to this configuration, a Bragg stack 101 comprising only a single elementary Bragg stack 102 will have, for an incidence of 20°, a reflection coefficient equal to 82.4% and a transmission coefficient equal to 17.6% when faced with light radiation of wavelength equal to 1550 nm. For an incidence of 45°, the reflection coefficient is 80.9% and the transmission coefficient is 19.1%. This stack will also not be absorbent and will have almost zero heating. The risk of heating of the mirror 10 is therefore limited.

[0115] Still according to this configuration, a Bragg stack 101 comprising two elementary Bragg stacks 102 will have, for a radiation incidence of 45°, a reflection coefficient equal to 96.4% and a transmission coefficient equal to 3.6% when faced with light radiation of wavelength equal to 1550 nm. This stack will also be only slightly or not absorbent and will have almost no heating.

[0116] According to one example, the mirror 10 extends in a main extension plane (X, Y), over at least one millimetric dimension, for example a diameter, preferably between 500 pm and 10 mm, preferably between 500 pm and 5 mm.

[0117] According to one example, the mirror 10 may be formed on a mechanical support layer 105 based on or made, for example, of a semiconductor or dielectric material.

[0118] The distance between the detector module 11 and the mirror 10 can be modified to optimize the measurement. As illustrated for example in FIGS. 7A and 7B, the detector module 11, and in particular the detector 110, 111, can be arranged at a non-zero distance d from the rear face 10b of the mirror 10. This distance d can be between 1 μm and 15 cm, preferably between 0.5 cm and 15 cm. According to one example, the detector module 11 is arranged at a distance from the rear face of the mechanical support layer 105. According to an alternative example, the detector module 1 is arranged on the rear face of the mechanical support layer 105.

[0119] The choice of the material of the mechanical support layer 105 may, for example, be a function of the wavelength X. For example, the absorption coefficient of a mechanical support layer 105 is negligible, or even zero, for wavelengths greater than 1250 nm. The mechanical support layer 105 may comprise one or more layers 106, 107. As for example illustrated in FIGS. 2A to 2C, the mechanical support layer 105 may comprise a layer 106 based on or made of silicon, for example monocrystalline silicon, for example with a thickness e^ substantially between 1 pm and 100 pm, and preferably equal to 20 pm. The mechanical support layer 105 may further comprise a layer 107 based on or made of silicon oxide, for example derived from a buried oxide layer. The layer 107, for example silicon oxide, may have a thickness substantially between 0.2 pm and 2 pm.

[0120] An example of architecture of the reflector device 1 is now described with reference to FIGS. 7A and 7B. The mechanical support layer 105 may be derived from a semiconductor-on-insulator substrate, and more particularly from silicon-on-insulator. This substrate may comprise, for example, a monocrystalline silicon layer 106 covering a silicon dioxide layer 107 formed on a monocrystalline silicon substrate 108.

[0121] The Bragg stack 101 can overcome the mechanical support layer 105. The Bragg stack shown in this figure notably comprises two elementary Bragg stacks 102 each comprising a layer of silicon dioxide 305 nm thick, and amorphous silicon 110 nm thick.

[0122] The reflective device further comprises a first protective layer 127, for example based on or made of silicon oxide, a lower electrode 124, a piezoelectric layer 123 (for example a PZT), an upper electrode 126, and a second protective layer 128, for example based on or made of silicon oxide. The reflective device 1 may further comprise contact connections 125, for example based on or made of gold.

[0123] The reflector device 1 may further comprise a mask 109, for example a hard mask. This mask 109, which may in particular be based on or made of silicon dioxide, may be produced during the manufacture of the reflector device to allow the release of the mirror 10 by etching from a rear face of the substrate SOL.

[0124] The mirror 109 may be partially surrounded by trenches, crossing the mechanical support layer 105. It is therefore understood that the mechanical support layer 105 of the mirror 10 may come from the same substrate as the support 108. It is considered that the mechanical support layer 105 of the mirror 10 may not be integral in rotation of the support 108, in particular due to the release of the mirror 10 and the trenches 129.

[0125] An example of the method of manufacturing the reflector device is for example given in the document EP3726268A1. The detector module 11 can be positioned opposite the rear face 10b of the mirror 10 by packaging methods known to those skilled in the art.

[0126] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. The present invention is not limited to the examples previously described. Many other variant embodiments are possible, for example by combining features previously described, without departing from the scope of the invention. For example, the illustrated examples implementing a Bragg stack can be transposed to a mirror having a partially reflective metal layer. A particular architecture of reflector device 11 is given as an example. The reflector device can be implemented on any other type of reflector device having a partially transparent mirror. Furthermore, the features described in relation to one aspect of the invention can be combined with another aspect of the invention.

Claims

Claims

1.

2.

3. Reflecting device (1) intended to reflect an incident light beam (20) towards a target (3), the reflector device (1) comprising a partially transparent mirror (10) having a front face (10a) arranged to receive the incident light beam (20) and a rear face (10b) opposite the front face (10a), the mirror (10) being configured to form a reflected beam (21) by reflection of a portion of the incident beam (20), and to transmit another portion of the incident beam (20) via the rear face (10b) to form a transmitted beam (22), the reflector device (1) being characterized in that it further comprises a detector module (11) arranged opposite the rear face (10b) of the mirror (10), the detector module (11) being configured to measure at least one parameter associated with the transmitted beam (22), the at least one parameter being chosen from: a presence or absence of the transmitted beam (22), a position (220) of the transmitted beam (22), a shape (222) of the transmitted beam (22), and to determine a state of alignment of the incident beam (20) with the reflector device (1) and / or a deformation of the mirror (10). Reflective device (1) according to the preceding claim, in which the detector module (11) is configured to determine the alignment state of the incident beam (20) with the reflector device (1) and / or a deformation of the mirror (10) according to: if the parameter measured by the detector module (11) is an absence of the transmitted beam (22) and / or a position (220) of the transmitted beam (22) different from a defined position (221), a bad alignment of the incident beam (20) is determined by the detector module (11), and / or if the parameter measured by the detector module (11) is a shape (222) of the transmitted beam (22) different from a defined shape (223), a deformation of the mirror (10) is determined by the detector module (11). A reflective device (1) according to any preceding claim, further comprising a support (108) and an actuator module (12) configured to pivot the mirror (10) around at least one axis of rotation (X, Y) relative to the support (108), and in which the detector module (11) is integral with the support (108).

4. Reflector device (1) according to the preceding claim, in which the detector module (11) has a time resolution greater than or equal to a characteristic misalignment time of the incident beam (20), for example the detector module (11) has an acquisition frequency greater than or equal to a vibration frequency of a source emitting the incident beam (20).

5. Reflective device (1) according to any one of the preceding claims, in which the mirror (10) comprises: • a metallic reflective layer (100) comprising at least one opening (1000) and / or having a thickness (eiOo) chosen to transmit the other part of the incident beam (20) to form the transmitted beam (22), or • a Bragg stack (101) comprising at least one so-called “elementary” Bragg stack (102) comprising two layers (103, 104) having distinct refractive indices.

6. Reflector device (1) according to any one of the preceding claims, in which the detector module (11) is arranged at a non-zero distance (d) from the rear face (10b) of the mirror (10), said distance (d) being between 1 μm and 15 cm, preferably between 0.5 cm and 15

7. VIII. A reflective device (1) according to any preceding claim, wherein the detector module (11) comprises a single-element detector (110).

8. A reflective device (1) according to any one of claims 1 to 6, wherein the detector module (11) comprises a two-dimensional pixelated matrix (111).

9. A reflective device (1) according to any preceding claim, further comprising an optical element (13), for example a lens (13), configured to focus the transmitted beam (22) onto the detector module (11).

10. A reflective device (1) according to any preceding claim, further comprising a support (108) and an actuator module (12) configured to pivot the mirror (10) around at least one axis of rotation (X, Y) relative to the support (108), the detector module (11) being integral with the support (108), the device being a LIDAR reflector device.

11. A reflector device (1) according to any one of claims 1 to 9, further comprising a support (108) and an actuator module (12) configured to pivot the mirror (10) around at least one axis of rotation (X, Y) relative to the support (108), the detector module (11) being integral with the support (108), the device being a laser pointing system.

12. Method for measuring the alignment of an incident beam (20) and / or a deformation of a mirror (10) implementing the reflector device (1) according to any one of the preceding claims, comprising: • an emission of the incident beam (20) from a light source (2) towards the reflector device (1), • a measurement, by the detector module (11), of the at least one parameter associated with the beam transmitted (22) by the mirror (10), the at least one parameter being chosen from: - a presence or an absence of the transmitted beam (22), - a position (220) of the transmitted beam (22), - a shape (222) of the transmitted beam (22),• a determination of the alignment state of the incident beam (20) with the reflector device (1) and / or of the deformation of the mirror (10) comprising: - if the parameter measured by the detector module (11) is an absence of the transmitted beam (22) and / or a position (220) of the transmitted beam (22) different from a defined position (221), a determination of a bad alignment of the incident beam (20), and / or - if the parameter measured by the detector module (11) is a shape (222) of the transmitted beam (22) different from a defined shape (223), a determination of a deformation of the mirror (10).,

13. A method according to the preceding claim, further comprising a correction (4) of at least one of the position of the light source (2) and the position of the mirror (10) if, when determining a state of alignment of the incident beam (20) with the reflector device (1) and / or a deformation of the mirror (10), a misalignment of the incident beam (20) is determined.

14. Method according to the preceding claim, in which, the reflector device (1) comprising an actuator module (12) configured to pivot the mirror (10) around at least one axis of rotation (X, Y), and the detector module (11) secured to the mirror (10) comprising a two-dimensional pixelated matrix: • the determination of a state of alignment of the incident beam (20) with the reflector device (1) and / or of a deformation of the mirror (10) comprises a determination of an offset (A22) between the position (220) of the transmitted beam (22) and the defined position (221), and • the correction (4) of the position of the mirror (10) comprises a modification of the angular range (a) of pivoting of the mirror (10) as a function of said offset (A22).

15. Method according to any one of the three preceding claims, comprising an emission (5) of an alert and / or an action (6) of heat dissipation at the mirror (10) if, when determining a state of alignment of the incident beam (20) with the reflector device (1) and / or a deformation of the mirror (10), a deformation of the mirror (10) is determined.

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