Reflecting 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 at least one incident beam (20), and to transmit a portion of the at least one incident beam (20) to form a transmitted beam (22). The reflector device (1) further comprises at least one diffraction grating (14) attached to the mirror (10) and configured to diffract the transmitted beam (22) into at least one diffracted beam (23) of order m, m being non-zero. A detector module (11) is configured to measure a position of the at least one diffracted beam (23) of order m, and from the measurement of said position, to determine an angle (θi) between the mirror (10) and the incident beam (20), so as to determine an orientation state of the mirror (10). Figure for the abstract: Fig. 3A

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] For this purpose, an incident light beam is emitted by a source towards the reflecting device having an at least partially transparent mirror. 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. The micromirrors may therefore comprise an actuator module configured to rotate 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 disk-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 reflective 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. movement of the mirrors is typically induced by actuators. 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, induced by actuators, 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 the position of the reflected beam, in order to properly orient the reflected beam in the intended direction.

[0010] For this, the orientation of the mirror can be monitored. There are indirect measurement solutions implementing indirect monitoring of the orientation of the mirror by implementing piezo-resistive gauges in the actuator arms. These gauges measure the deformation of the actuator arms. With calibration, it is possible to go back to the angle of the mirror. These piezo-resistive gauges can however drift over time, which leads to a lack of reliability in determining the orientation of the mirror. These solutions also remain quite complex to implement at the level of the architecture of the reflector device.

[0011] An object of the present invention is therefore to propose a solution improving the determination of the orientation of a mirror of a reflecting device.

[0012] Other objects, features and advantages of the present invention will become apparent from a consideration of the following description and 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 comprising a partially transparent mirror having a front face arranged so as to receive at least one 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 at least one incident beam, and to transmit a portion of the at least one incident beam via the rear face to form a transmitted beam.

[0014] Advantageously, the reflector device further comprises: - at least one diffraction grating arranged opposite the rear face of the mirror and secured to the mirror, the grating being configured to diffract the beam transmitted in at least one diffracted beam of order m, m being non-zero, - a detector module configured for: • measure a position of at least one diffracted beam of order m, • from the measurement of said position, determine an angle between the mirror and the incident beam, so as to determine a state of orientation of the mirror.

[0015] For example, following an impact or when using the reflector device, if the orientation of the mirror is changed, the angle between the incident beam and the mirror will be changed. The propagation of the reflected beam will be impacted accordingly. The reflector device makes it possible to detect this by means of the diffracted beam.

[0016] The mirror reflects a portion of the incident beam to form the reflected beam. The mirror transmits another portion of the incident beam to form the transmitted beam. The diffraction grating diffracts the transmitted beam in order to follow the movement of the mirror. The direction of propagation of a diffracted beam is directly dependent on the orientation of the diffraction grating, which is integral with the movement of the mirror. Thus, the beam transmitted by the mirror, and diffracted by the diffraction grating, can be used to determine the orientation state of the mirror. The reflector device therefore makes it possible to know the orientation of the mirror, during the reflection of the reflected beam in a given direction, and in particular towards a target.

[0017] The reflector device therefore allows direct and real-time measurement of the orientation of the mirror. It is therefore possible to continuously ensure the orientation of the mirror, and therefore that the reflected beam is indeed going in the desired direction. The reflector device is therefore particularly advantageous for applications in which there is no return from the target, that is to say it is difficult or impossible to ensure that the reflected beam correctly reaches the target. This also makes it possible to overcome possible drifts linked to the tracking of the orientation by indirect means, such as the tracking associated with the elements responsible for the orientation of the mirror and for example with the actuators. The tracking of the orientation of the mirror is therefore made more reliable. The orientation of the reflected beam is consequently made more reliable.

[0018] A second aspect relates to a method for measuring the orientation of a mirror implementing a reflector device according to the first aspect. The method comprises: - the emission of at least one incident beam from a light source towards the reflecting device, - a reflection of a part of the at least one incident beam by the mirror to form the reflected beam, - a transmission of another part of the at least one incident beam by the mirror to form the transmitted beam, - a diffraction, by the diffraction grating, of the transmitted beam into at least one diffracted beam of order m, m being non-zero, - a so-called “orientation” measurement, by the detector module, of a position of at least one diffracted beam of order m, - from the measurement of said position, a determination of an angle between the mirror and the incident beam, so as to determine a state of orientation of the mirror.

[0019] It is therefore understood that the measuring method also allows a direct and real-time measurement of the orientation of the mirror, that is to say of the angular position of the mirror relative to the incident beam. The method allows a reliable determination of the orientation of the mirror and therefore of the direction of the reflected beam. BRIEF DESCRIPTION OF THE FIGURES

[0020] 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:

[0021] [Fig.lA]

[0022] [Fig. 1B] Figures 1A and 1B show two examples of state-of-the-art reflective devices.

[0023] [Fig.2A] [Fig.2A] represents a perspective view of an example of a mirror mounted pivoting about an axis of rotation.

[0024] [Fig.2B] [Fig.2B] represents a top view of an example of a mirror mounted to pivot about two axes of rotation.

[0025] [Fig.3A]

[0026] [Fig.3B] Figures 3A and 3B represent a cross-sectional view of the reflector device during a determination of an orientation state of the mirror, according to an exemplary embodiment.

[0027] [Fig.4] [Fig.4] schematically illustrates the formation of diffracted beams of order m from the transmitted part of the incident beam.

[0028] [Fig.5A]

[0029] [Fig.5B] Figures 5A and 5B schematically represent the deviation of the diffracted beams of order m as a function of the angle between the incident beam and the mirror.

[0030] [Fig.6] [Fig.6] represents a sectional view of a reflective device comprising a focusing lens, according to an exemplary embodiment.

[0031] [Fig.7A]

[0032] [Fig.7B]

[0033] [Fig.7C] Figures 7A to 7C illustrate the tracking of the position of a diffracted beam of order m.

[0034] [Fig. 8 A]

[0035] [Fig.8B] Figures 8A and 8B schematically represent the deviation of the interference fringes at the intersection of two diffracted beams of order m as a function of the angle between the incident beam and the mirror.

[0036] [Fig.9] [Fig.9] represents a sectional view of a reflective device comprising two detectors, according to an exemplary embodiment.

[0037] [Fig. 10] [Fig. 10] represents a sectional view of a reflector device receiving two incident beams of different wavelengths, according to an exemplary embodiment.

[0038] [Fig. 11]

[0039] [Fig. 12] Figures 11 and 12 show a sectional view of two variants of the reflector device.

[0040] [Fig. 13 A]

[0041] [Fig. 13B] Figures 13A and 13B represent a top view of the diffraction grating according to two exemplary embodiments.

[0042] [Fig.l4A]

[0043] [Fig.14B] Figures 14A and 14B represent a sectional view of the reflector device for determining a misalignment between the source and the mirror, according to an exemplary embodiment.

[0044] [Fig. 15 A]

[0045] [Fig. 15B] Figures 15A and 15B show a sectional view of two particular examples of reflective device.

[0046] 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 reflective device are not representative of reality. DETAILED DESCRIPTION

[0047] 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.

[0048] 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, and wherein the detector module is secured to the support. The reflector device is thus particularly suitable for mirror applications MEMS. Since the detector module is integral with the support, the mirror orientation can be determined independently of the actuator. A direct measurement of the mirror orientation is therefore made.

[0049] According to one example, the detector module has a time resolution greater than or equal to a quantity characteristic of the pivoting of the mirror by the actuator module. The response time of the detector may be less than or equal to, and preferably strictly less than, the rotation period of the mirror. In other words, the detector module may have an acquisition frequency greater than or equal to a scanning frequency of the mirror by the actuator module. Thus, the tracking of the orientation of the mirror is temporally more precise than the movement of the mirror. This makes the determination of the orientation of the mirror even more reliable.

[0050] According to one example, the mirror comprises: - a metallic reflective layer having a thickness chosen to transmit a portion of the incident beam to form the transmitted beam, or - a Bragg stack comprising at least one so-called “elementary” Bragg stack comprising two layers having distinct refractive indices.

[0051] 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.

[0052] According to one example, the elementary Bragg stack comprises two dielectric and / or semiconducting layers.

[0053] According to one example, the elementary Bragg stack comprises a layer of amorphous silicon and a layer of silicon oxide.

[0054] According to one example, the diffraction grating is configured to diffract the transmitted beam into a plurality of diffracted beams of orders m, m being distinct between the diffracted beams, and the detector module is configured to measure the position of a plurality of diffracted beams of orders m distinct from each other. The angular resolution of the determination of the orientation of the mirror can thus be improved.

[0055] According to one example, the diffraction grating is configured to diffract the transmitted beam into a plurality of diffracted beams of orders m, m being distinct between the diffracted beams, and the detector module is arranged at an intersection between at least two diffracted beams of orders m distinct so as to measure a position of interference fringes between said at least two diffracted beams. The use of the interference fringes further significantly improves the angular resolution of the determination of the orientation of the mirror.

[0056] According to one example, the incident beam having a wavelength X, the diffraction grating has a period a such that a is between 1.5X and 20X, preferably between 5X and 10X. A period a greater than or equal to 1.5X, and preferably greater than or equal to 5X, makes it possible to obtain several diffracted beams of distinct orders. A period a less than or equal to 20X avoids having an overly complex diffraction pattern, thus simplifying the determination of the orientation of the mirror.

[0057] According to one example, the diffraction grating comprises: - a network of a material opaque to the incident light beam, for example a metallic reflective layer, having openings of period a, or - a network of two materials transparent to the incident light beam, having between them a difference in refractive index, the two materials being alternated so as to form the period a.

[0058] According to one example, the diffraction grating is formed from the same materials as the Bragg stack. The manufacture of the reflector device is thus facilitated.

[0059] According to one example, the reflector device comprises a plurality of diffraction gratings, preferably juxtaposed, having distinct periods a between them. The period a influences the number of diffracted beams as a function of the incident wavelength. Diffraction gratings of different periods a make it possible to modulate the diffraction pattern obtained according to the period. The number of diffracted orders can thus be adapted, for example according to the rotation amplitude of the mirror. This also makes it possible to have gratings each more suited to a given wavelength. Thus, the same reflector device can be used in different applications, and in particular applications using different wavelengths. The reflector device is thus made more versatile.

[0060] According to one example, the detector module is arranged at a 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.

[0061] According to one example, the device comprises a mechanical support layer having a front face and a rear face opposite the front face.

[0062] According to one example, the mirror surmounts, by its rear face, the front face of the mechanical support layer.

[0063] According to one example, the diffraction grating is arranged between the mechanical support layer and the mirror.

[0064] According to one example, the detector module is arranged at a distance from the rear face of the mechanical support layer.

[0065] According to one example, the detector module is arranged on the rear face of the mechanical support layer.

[0066] According to one example, the mechanical support layer is based on silicon, preference for monocrystalline silicon.

[0067] According to one example, the detector module comprises a two-dimensional pixel matrix. Tracking the position of the m-order diffracted beam is thus facilitated. A two-dimensional pixel matrix allows tracking the orientation of the mirror by projection of the m-order diffracted beam into the plane defined by these two dimensions. This is particularly advantageous for mirrors pivoting along two axes of rotation.

[0068] According to one example, the reflector device comprises an optical element, for example a lens, configured to focus the at least one diffracted beam of order m onto the detector module, and where appropriate the non-diffracted transmitted beam 22. The focusing of the transmitted and diffracted beams onto the detector module can thus be modified, and in particular in synergy with the distance of the detector module relative to the lens. Thus, the size of the impact zones of the beams on the detector module can be modified, and in particular reduced. The measurement can thus be facilitated. The angular resolution of the determination of the orientation of the mirror can also be improved.

[0069] 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.

[0070] According to one example, the device comprises the light source configured to emit the at least one incident beam.

[0071] According to one example, the light source is an infrared source.

[0072] 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.

[0073] According to one example, the light source is a laser source.

[0074] According to one example, the device is a LIDAR reflector device.

[0075] According to another example, the device is a pointing system, and in particular a laser pointing system.

[0076] According to these two examples, the reflector device may further comprise 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.

[0077] According to one example, the diffraction grating lets through a portion of the transmitted beam so as to form a non-diffracted zero-order beam.

[0078] According to one example, the detector module is configured to measure at least one parameter associated with the beam of order 0, the at least one parameter being chosen from: - a presence or an absence of the beam of order 0, - a position of the beam of order 0.

[0079] and to determine a state of alignment of the incident beam with the reflector device.

[0080] Thus, the transmitted beam of order 0 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. This is furthermore possible independently of the orientation of the mirror, the transmitted and undiffracted beam not being substantially deflected when passing the mirror and the diffraction grating. This can for example be done when the mirror 10 is in a rest position, that is to say when it is not pivoted by the actuator module.

[0081] If, following an impact for example, the mirror and / or the source are moved, 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 consider corrective actions.

[0082] The reflector device therefore allows real-time measurement of the alignment of the laser and the mirror, which results in a modification of the reflected beam. It is therefore possible to continuously ensure that the reflected beam is indeed going in the desired direction, in synergy with the determination of the orientation of the mirror. The reliability of the reflection of the incident beam towards a target is further improved.

[0083] According to one example, the detector module is configured to determine the alignment state of the incident beam with the reflector device such that, if the parameter measured by the detector module is an absence of the 0th order beam and / or a position of the 0th order beam different from a defined position, a bad alignment of the incident beam is determined by the detector module.

[0084] Thus, the reflector device can make it possible to independently determine poor alignment of the incident beam, depending on the nature of the information measured.

[0085] According to one example, the incident beam and the reflected beam propagate along propagation directions that are distinct from each other.

[0086] According to one example, the transmitted beam is diffracted into a plurality of diffracted beams of orders m, m being distinct between the diffracted beams, and in which, during the orientation measurement.

[0087] According to one example, the position of at least two diffracted beams of distinct orders m is measured. The robustness of the determination of the orientation of the mirror can thus be improved.

[0088] According to one example, the detector module is arranged at an intersection between the at least two diffracted beams of distinct orders m, and in which, during the orientation measurement, a position of interference fringes between said diffracted beams is measured. The use of the interference fringes further significantly improves the angular resolution of the determination of the orientation of the mirror.

[0089] According to one example, the emission of the at least one incident beam comprises the emission of a first incident beam and a second incident beam from the light source towards the reflector device, the method implementing at least the steps of transmission, diffraction, orientation measurement and angle determination from the first incident beam, the method further comprising a reflection of the second incident beam by the mirror to form the beam reflected towards a target. One incident beam can thus be dedicated to reflection, while the other incident beam can be dedicated to tracking the orientation of the mirror. It is thus possible to play on the parameters of the reflector device to adapt the diffraction and / or the reflection for example according to the period a, the nature of the mirror, and more particularly of the Bragg stack.It is thus possible to maximize the reflected part of the second incident beam dedicated to reflection, while following the orientation of the mirror with the first incident beam.

[0090] According to one example, a portion of the transmitted beam is not diffracted and forms a non-diffracted zero-order beam, the method further comprising, preferably prior to determining an angle between the mirror and the incident beam: - a so-called “verification” measurement, by the detector module, of at least one parameter associated with the zero-order beam by the mirror, the at least one parameter being chosen from: • a presence or absence of the beam of order 0, • a position of the beam of order 0. - a determination of a state of alignment of the at least one incident beam with the reflector device comprising • if the parameter measured by the detector module is an absence of the 0th order beam and / or a position of the 0th order beam different from a defined position, a determination of poor alignment of the incident beam.

[0091] As previously stated with respect to the reflector device, the method therefore allows real-time measurement of the alignment of the laser and the mirror, which results in a modification of the reflected beam. It is therefore possible to continuously ensure that the reflected beam is indeed going in the desired direction, in synergy with the determination of the orientation of the mirror. The reliability of the reflection of the incident beam towards a target is further improved.

[0092] According to one example, the reflection of the at least one incident beam by the mirror to form the reflected beam is at least partly simultaneous with the orientation measurement by the detector module.

[0093] According to one example, the reflection of the at least one incident beam by the mirror to form the reflected beam is at least partly simultaneous with the verification measurement. by the detector module.

[0094] 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, 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.

[0095] 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 comprises a determination of an offset between the position of the beam of order 0 and the defined position, and - the correction of the mirror position includes a modification of the angular range of pivoting of the mirror as a function of said offset.

[0096] 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.

[0097] 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.

[0098] 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.).

[0099] 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.

[0100] 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 in direct 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.

[0101] 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.

[0102] In the present patent application, the term "integral" used to qualify the connection between two parts means that the two parts are linked / fixed relative to each other, according to all degrees of freedom, unless explicitly specified differently. For example, if it is indicated that two parts are integral in translation according to a direction X, this means that the parts can be movable relative to each other, possibly according to several degrees of freedom, excluding the freedom in translation according to the direction X. In other words, if one part is moved according to the direction X, the other part performs the same movement.

[0103] 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.

[0104] We will also use a reference 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.

[0105] 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).

[0106] The reflector device 1 and the method for measuring the orientation of the mirror 10 are now described according to several exemplary embodiments.

[0107] As illustrated for example in Figures 2A to 3B, 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.

[0108] 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.

[0109] 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, the size of the mirror 10, or smaller.

[0110] According to an example, illustrated by FIGS. 2A and 2B, the mirror 10 is configured to pivot about at least one rotation axis X, and preferably about the rotation axes 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 rotation axis 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 rotation axes X and Y.

[0111] The reflector device 1 may comprise for this purpose 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, preferably 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.

[0112] When the incident beam 20 is reflected 21 towards a target 3, it is important to know the orientation of the mirror 10, in particular with respect to the incident beam 20. This is particularly advantageous when the mirror 10 pivots along at least one axis of rotation. Note that the orientation of the mirror 10 with respect to the incident beam 20 can be sought even for a fixed mirror.

[0113] For this, the mirror 10 is configured to reflect a part of an incident beam 20 to form the reflected beam 21, and to transmit another part of the incident beam 20 through 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, mirror 10 is configured to reflect between 75% and 99.9% of the incident beam 20. Mirror 10 may be configured to transmit between 24.5% and 0.03% of the incident beam 20.

[0114] The reflector device 1 further comprises a diffraction grating 14 secured to the mirror 10 and arranged below the mirror 10 relative to the direction of propagation of the incident beam 20. The diffraction grating 14 is configured to receive the transmitted portion 22 of the incident beam 20 and diffract this transmitted beam 22. As illustrated by FIGS. 3A and 3B, the diffraction results in the formation of several beams. The transmitted beam 22 is therefore separated into several beams. A first beam will not be deflected by the diffraction grating 14 and forms the transmitted beam 22, also referred to as the 0th order beam. The 0th order beam 22 typically propagates substantially in the same direction relative to the incident beam 20. Equivalently, the 0th order beam 22 is substantially not deflected by the mirror 10.Equivalently, it is considered that the deviation or shift of the beam 22 of order 0, during its transmission by the mirror 10, is negligible with respect to the deviation of the other beams linked to the orientation of the mirror. In any event, a possible deviation or a possible shift of the beam transmitted 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 for determining the orientation of the mirror.

[0115] As the diffraction grating 14 passes, at least one and preferably a plurality of diffracted beams 23 are also formed. As illustrated in [Fig.4], as a diffraction grating 14 of period a passes, the transmitted portion 22 of the incident beam 20 is diffracted to form at least one diffracted beam 23 propagating in a direction distinct from the direction of propagation of the incident beam 20. One or more diffracted beams 23 may be formed. In the following, it is considered, without limitation, that several diffracted beams 23 are formed. Each diffracted beam 23 will have a direction of propagation angularly spaced from the transmitted beam 22 by an angle 0t. We can also consider the angle 0m with respect to the normal to the diffraction grating 14, or equivalently with respect to the normal to the mirror 10, the diffraction grating being integral with the mirror 10.

[0116] In a known manner, the more the period a of the diffraction grating 14 increases, the more the number of diffracted beams 23 increases. These diffracted beams 23 each propagate in different propagation directions. Thus, the angles 0m and 0t are specific to each diffracted beam 23. It is therefore considered that the diffracted beams 23 are diffracted according to different orders m, each order m propagating in a given direction. Distinct diffracted beams 23 of order m cor therefore correspond to diffracted beams 23 propagating according to directions of propagation distinct from each other. The transmitted beam 22 is therefore the beam of order 0, it is not deflected. The diffracted beams 23 are numbered progressively according to their order m, the more their direction of propagation deviates from the transmitted beam 22. The order m can be positive, when the angles 0m and 0t are inscribed in a given direction of deviation relative to the direction of propagation of the transmitted beam 22. The order m can be negative, when the angles 0m and 0t are inscribed in the opposite direction of deviation.

[0117] As illustrated by Figures 3A to 5B, the direction of propagation of the incident beam 20 has an angle 0i 1 with the mirror 10, and more particularly with respect to the normal to the mirror 10. The diffracted beams 23 will each have an angle 0t 1 with respect to the transmitted beam 22 propagating in the same direction as the incident beam 20.

[0118] When the orientation of the mirror 10 is modified, for example following an impact and / or according to the rotational position of the mirror 10 by an actuator 12, the angle 0i2 between the mirror 10 and the incident beam 20 is modified. The direction of propagation of the transmitted beam 22 is substantially unchanged with the rotation of the mirror 10. On the other hand, the diffracted beams 23 will then each have an angle 0t2 relative to the transmitted beam, this angle being modified relative to the angle 0tl.

[0119] It is therefore possible to determine the change in orientation of the mirror 10 as a function of the position of the diffracted beams 23. For this, the reflector device 1 comprises a detector module 11 arranged opposite the rear face 10b of the mirror 10 and a rear face of the diffraction grating 14. The detector module 11 is therefore placed below the mirror 10 and the diffraction grating 14 in the reflector device 1, relative to the propagation of the incident beam 20. The detector module 11 is arranged so as to receive at least one diffracted beam 23, preferably several diffracted beams 23. According to one example, the detector module 11 is arranged so as to receive the transmitted beam 22 and at least one diffracted beam 23, and preferably several diffracted beams 23.

[0120] The diffracted beam(s) 23 form a diffraction pattern on the detector. Depending on the orientation of the mirror 10, the position of the diffraction pattern will be modified. As an example, and with reference to [Fig.4], the grating law in fact gives:

[0121] [Math.l] a [ sin6 m - sindi ] = mX

[0122] [Math.2] 0 m = asin^sindi+m~ )

[0123] The angle between a diffracted beam 23 of order m and the incident beam 20 can therefore be given by:

[0124] [Math.3] B t = 0 m - 0j = asin ( sin + m~ ) - 3 t

[0125] When the grating rotates by an angle A0i, the angle of the diffracted orders changes. Order 0 remains in the direction of incidence. The angle variation between a diffracted beam of order m and the direction of the incident beam can be given by:

[0126] [Math.4] A3t = asin (sin (3S+A3; ) + ) - asin (sin (6; ) +

[0127] Note that the smaller the angles, the closer AOt is to 0. The deviation of the diffracted beams 23 of order m becomes more significant with large angles and is based on the non-linearity of the sine and arcsine functions.

[0128] The detector module 11 is more particularly configured to measure the position of at least one diffracted beam 23. Depending on this position, the detector module is configured to determine the orientation of the mirror 10. Preferably, the position of several diffracted beams 23 is measured. The measurement is thus more robust. In the following, we speak, without limitation, of the position of a diffracted beam 23 of order m.

[0129] According to one example, the detector module 11 can be configured to measure the relative position of the beam 22 of order 0 and at least one diffracted beam 23 of order m. The beam 22 of order 0 not being deflected, it is thus possible with a single measurement to know the orientation of the mirror 10. According to another example, the detector module 11 can be configured to make a first measurement of the position of the diffracted beam 23 of order m in a first position of the mirror 10, and to make a second measurement of the position of this diffracted beam 23 in a second position of the mirror 10. When the second position of the mirror 10 is distinct from its first position, the position of the diffracted beam 23 on the detector will be modified. The detector module 11 can then be configured to determine the variation in orientation of the mirror 10 between its first position and its second position.

[0130] 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. 2A and 15A and 15B. The detector module 11, and in particular a detector 111, is preferably integral with the support 108, preferably at least in rotation in the X and Y directions. The detector module 11 may be integral with 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. When the mirror is in angular movement (in X and / or in Y), the position of the transmitted beam 22 does not move appreciably except for misalignment of the source and the mirror 10 or modification of the shape of mirror 10.

[0131] The detector module 11 and the support 108 can be separated from each other, as for example illustrated in [Fig.l5A]. 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.l5B].

[0132] According to one example, the detector module 11 may comprise a detector 111. This detector may comprise a pixelated matrix 111 along at least one dimension, and preferably 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.

[0133] For radiation at 1550 nm, a detector 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 can be considered, for example a CMOS detector. A CMOS detector is nevertheless limited in terms of acquisition frequency of the order of 1 kHz to 10 kHz. This can be limiting compared 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 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 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 111 can extend in a main extension plane substantially parallel to the main extension plane of the mirror 10.Alternatively, it is possible to provide for the detector 111 to be positioned obliquely relative to the mirror 10, for example by being arranged perpendicular to the direction of propagation of a diffracted beam 23 of order m.

[0134] 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 focus the diffracted beams 23, and preferably also the transmitted beam 22, onto the detector 111. Thus the resolution of the measurement of the position of the beams on the detector 111 can be improved. For this, the distance dl between the lens 13 and the detector 111 can for example be adapted.

[0135] According to an example illustrated by FIGS. 7A to 7C, the lens 13 can be placed at a distance d from the diffraction grating 14. The lens 13 can be arranged at a distance f from the detector 111, f being the focal length of the lens 13. Thus, the image of the diffracted beam 23 of order m can be punctual on the detector 111. This improves the resolution of the tracking of the position 232 of the diffracted beam 23 of order m on the detector 111, and therefore the angular resolution of the determination of the orientation of the mirror 10. It can be provided that the distance between the lens 13 and the detector 111 is not equal at the focal length f, and in particular to play on the focusing of the diffracted beam 23 on the detector 111. For example, one can seek to ensure that the image of the diffracted beam 23 on the detector 111 covers several pixels. In order to improve the resolution of the tracking of the position 232 of the diffracted beam 23, the barycenter of the image of the diffracted beam 23 can then be tracked.

[0136] The method for measuring the orientation of the mirror 10 may comprise a determination of the direction of rotation of the mirror 10 according to the position of the diffracted beam 23. Whether the reflector device 1 comprises a lens 13 or not, depending on the direction of change of the position 232 of the diffracted beam 23 on the detector 111 the direction of change of orientation of the mirror 10 may be determined. For example and as illustrated by FIGS. 7A to 7C, when the mirror 10 is rotated in a first direction of rotation, the position 232 of the diffracted beam 23 may have an offset A232 relative to an initial position 232', in a first direction. When the mirror 10 is rotated in a second direction of rotation opposite to the first direction, the position 232 of the diffracted beam 23 may have an offset -A232 relative to an initial position 232' in the same direction.Note that this can be done between two successive measurements by the detector 11 and / or by the relative position between the diffracted beam 23 and the transmitted beam 22.

[0137] The method for measuring the orientation of the mirror 10 may further comprise a selection of the diffracted beam 23 of order m whose position will be measured. This selection may be configured so as to select the diffracted beam(s) 23 of order m having a maximum position shift for a given change in orientation of the mirror 10. Thus, for the same rotation of the mirror 10, the position shift of the diffracted beam of order m will be greater. The angular resolution of the determination of the orientation of the mirror 10 is thus improved. When measuring the position of the diffracted beam 23 of order m, the position of the selected diffracted beam 23 may be tracked, possibly in addition to the position of other diffracted beams 23 of different orders m.

[0138] According to a first example, the angles 0m and 0t were calculated for a diffraction grating 14 with a period a equal to 10 pm and a wavelength / . of the incident beam of 1550 nm. These data are presented in the table below.

[0139] [Tables 1] m 0i 0i AOt 35° 40° 0m 0t 0m 0t 2 62.08 27.08 72.32 32.32 5.25 1 46.77 11.77 52.92 12.92 1.15 0 35.00 0.00 40.00 0.00 0.00 -1 27.74 -10.80 29.20 -10.80 -0.55 -2 15.28 -19.72 19.44 -20.56 -.084 -3 6.23 -28.77 10.24 -29.76 -0.99 -4 -2.66 -37.66 1.31 -38.69 -1.03 -5 -11.62 -46.62 -7.60 -47.60 -0.98 -6 -20.88 -55.88 -16.69 -56.69 -0.81 -7 -30.76 -65.76 -26.25 -66.25 -0.49 -8 -41.79 -76.79 -36.67 -76.67 0.12 -9 -55.23 -90.23 -48.78 -88.78 1.45 -10 -77.53 -112.53 -65.12 -105.12 7.41

[0140] In this particular example, it is considered that the diffracted beams 23 that can be detected by the detector 111 are located in an output cone of approximately 76°. This output cone can typically be linked to mechanical limitations of the reflector device 1. For example, a mirror 10 is considered extending in the direction y over a length L of 2 mm, and distant in the plane (X,Y) from the support 108 by a distance of 2.9 mm, the support 108 having a height of 0.7 mm. The angle a of the diffracted beam 23 propagating from the edge of the mirror 10 to a lower limit of the support 108 is equal to ir / 2-[3= jr / 2-[3=90o-13o=76°. For example, it is considered here that excessively deflected diffracted beams 23 will be incident on edges of the structure of the reflector device 1, for example the support 108 described in more detail internally. They are preferably not tracked by the detector module 11.

[0141] The diffracted beams 23 of order m = -1 to m = -7 are considered here. Among these beams, we observe that the order presenting a rotation AOt is the largest and the order m=-4. For a change in orientation of the mirror of approximately 5°, we obtain an AOt approximately equal to 1°.

[0142] According to an example illustrated by figures 8A and 8B, the detector module 11, and more particularly the detector 111, is arranged at an intersection 230 between at least two distinct diffracted beams 23 of order m. In this intersection zone 230, when the light source is coherent, the diffracted beams 23 will form interference fringes 231. For example, considering an intersection 230 where two orders are superimposed, the two distinct beams of orders m interfere and the interference fringes are planes oriented along the bisector between the two distinct beams of orders m.

[0143] When the orientation of the mirror 10 changes, the position of these interference fringes 231 is modified. The detector can therefore be configured to measure the position of the interference fringes 231. The position of the interference fringes 231 can be determined relative to the position of the beam 22 of order 0, in the same measurement. The resolution of the determination of the orientation of the mirror 10 is then further improved, as will be described later with reference to a particular example. An offset in the position of the interference fringes 231 can further be determined between two successive measurements of the position of these interference fringes 231 by the detector 111. This has the advantage of not having to know the position of the beam 22 of order 0 to determine the orientation of the mirror. A smaller detector module 11 can therefore be used.Preferably, the detector 111 has a spatial resolution, for example a pitch between these pixels, at least twice smaller than the pitch between the interference fringes 231.

[0144] Several variants of the reflector device 1 are now described. As illustrated by [Fig.9], the reflector device 1 may comprise a plurality of detectors 111, arranged so as to receive different beams from among the transmitted beam 22 of order 0 and the diffracted beams 23 of order m. The plurality of detectors 111 may be arranged in the same plane (X, Y), for example substantially parallel to the main extension plane of the mirror 10. The plurality of detectors 111 may be arranged obliquely relative to the main extension plane of the mirror 10, as detailed previously. It may further be provided that one or more detectors 111 are parallel to the mirror 10 and that one or more other detectors are arranged obliquely relative to the mirror 10. The detectors 111 may be juxtaposed.

[0145] Preferably, the detector module 11 acquires images more quickly than the rotation of the mirror 10. For this, the response time of the detector may be less than or equal to, and preferably significantly less than, the rotation period of the mirror. The acquisition frequency of the detector module 11 may more particularly be greater than or equal to, and preferably significantly greater than, the scanning frequency of the mirror 10.

[0146] 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 application. sight. For example, for a 2 mm diameter mirror, the slow and fast frequencies will be 10 Hz to 40 Hz and 200 Hz to 1000 Hz respectively. For smaller mirrors (for example around 0.5 mm in diameter) the fast frequencies can go up to 20 kHz for example.

[0147] The reflector device 1 can further receive several incident beams 20a, 20b, as illustrated for example in [Fig. 10]. Thus the reflector device 1 can be configured to use an incident beam 20a for tracking the orientation of the mirror 10 and to reflect the second incident beam 20b towards a given target 3. For this, the mirror 10 can be more particularly configured to reflect the incident beam 20b, for example by minimizing the transmitted component 22b. The mirror 10 can be configured to increase, and preferably maximize, the transmitted portion 22a of the incident beam 20a relative to that of the beam 20b. The diffraction grating 14 can be configured to diffract the transmitted portion 22a of the incident beam 20a. For example, the period of the diffraction grating 14 can be adapted to the incident beam 20a, and in particular to its wavelength.The incident beams 20a and 20b preferably have different wavelengths X1, X2.

[0148] The diffraction grating 14 is now described according to several exemplary embodiments with reference to FIGS. 10 to 13B. The diffraction grating 14 may be formed of materials alternating along at least one direction of the plane (X;Y), for example two solid materials or a solid material and gas or air. The alternating materials more particularly have refractive indices that are distinct from each other. The index difference may be greater than or equal to 0.05 for example, and preferably greater than or equal to 0.1. The greater the index difference, the greater the intensity of the diffracted beams. These beams are therefore more easily detectable. One material may be opaque to the incident beam 20, while the other material is at least partially transparent. The pitch formed by the alternation of these two materials defines the period a of the diffraction grating 14.The period a is preferably inscribed in a plane parallel to the main extension plane of the mirror 10. .

[0149] The number of diffracted beams 23 of orders m is a function of the period a. The period a is strictly greater than the wavelength X of the incident beam 20 so as to obtain a diffraction. A and preferably between 1.5X and 20X, preferably between 5X and 10X. This makes it possible to obtain several diffracted beams 23 of distinct orders while limiting the complexity of the diffraction pattern, thus simplifying the determination of the orientation of the mirror 10. It is therefore understood that the period a can be chosen as a function of the wavelength of the incident beam 20. For example, for an incident wavelength of 1.55 pm, the period a of the grating can be between 1 excluded and 20 times the wavelength, for example between 1.55 pm excluded and 30 pm (for example 10 pm).

[0150] The reflector device 1 may comprise a plurality of diffraction gratings 14 having periods a that are distinct from each other. As illustrated in [Fig. 11], a first diffraction grating 14 may have a period a that is less than the period a of a second diffraction grating 14. Diffraction gratings with different periods a make it possible to modulate the diffraction pattern obtained according to the period a. The number of diffracted orders may thus be adapted, for example according to the rotation amplitude of the mirror. In particular, for a mirror pivoting along two rotation axes X and Y with a slow axis and a fast axis, a period a may be more suited to tracking the orientation of the mirror 10 along the slow axis, and another period a may be more suited to tracking the orientation of the mirror 10 along the fast axis. This also makes it possible to have gratings that are each more suited to a given wavelength.Multiple networks 14 may have different shapes and / or sizes.

[0151] As illustrated in [Fig. 12], the grating 14 may comprise a material 140 opaque to the incident light beam 20, for example a metallic reflective layer, having openings 141 of period a. The openings may be empty or filled with a gas or filled with a different material. As illustrated in the other figures, the grating 14 may comprise two materials 142, 143 transparent to the incident light beam, having between them a difference in refractive index, the two materials 142, 143 being alternated so as to form the period a.

[0152] As illustrated by Figures 13A to 13B, the grating 14 can form the period a in a single direction of the (X,Y) plane. Preferably, the period a is formed in two distinct non-parallel directions of the (X,Y) plane, these directions preferably being perpendicular to each other.

[0153] According to one example, the grating 14 comprises amorphous silicon and SiO2. For example, for an incident wavelength of 1.55 pm, the period a of the grating may be between one time excluded and 20 times the wavelength, and therefore between 1.55 pm excluded and 30 pm (for example 10 pm). The thickness of the amorphous silicon and SiO2 grating is, for example, between 0.1 and 10 pm (for example 300 nm). The grating may comprise SiO2 pads to form the period a. The width of the SiO2 pads may be between 1 pm and the value of the period a reduced by 1 pm (for example 5 pm). For an incident wavelength of 905 nm, it may be envisaged to use TiO2 and SiO2.

[0154] According to one example, it is possible to provide outside the network 14, for example in the same plane as the network 14, an absorbent layer making it possible to spatially limit the diameter of the transmitted beam 22.

[0155] 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. 12], the metallic reflective layer 100 may have a thickness elOO 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. For example, the metallic reflective layer 100 has a thickness elOO substantially less than or equal to 50 nm

[0156] Alternatively or additionally, 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 el00 of the metallic reflective layer 100 may then be greater than the above range.

[0157] According to a preferred example, for example illustrated in figures 3A, 3B, 6 and 9 to 11, 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.

[0158] 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 ten, preferably between one and five, elementary Bragg stacks 102.

[0159] Preferably, the thickness of the layers 103, 104 is chosen so that these layers, and preferably each of the layers, 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.

[0160] 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 el04 of approximately 268 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 el03 of 113 nm (whose refractive index at 1550 nm is 3.42). These thicknesses are illustrated as an example in [Fig. 11].

[0161] 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.

[0162] 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.

[0163] 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.

[0164] 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.

[0165] The distance between the detector module 11 and the mirror 10 can be modified to optimize the measurement. As illustrated for example in FIGS. 15A and 15B, 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 11 is arranged on the rear face of the mechanical support layer 105.

[0166] 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 [Fig. 11], 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 el06 sen possibly 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 el07 substantially between 0.2 pm and 2 pm.

[0167] Furthermore, during a misalignment of the source 2 and the mirror 10, 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. The incident beam 20 may indeed 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.

[0168] 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.

[0169] 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. This can be done before or at least partly simultaneously with the diffraction of the transmitted part 22 of the incident beam 20. The reflector device 1 thus makes it possible to determine these states independently, and this, continuously during its use.

[0170] The transmitted beam 22 typically propagates in substantially the same direction relative to the incident beam 20. As illustrated in FIGS. 14A and 14B, if the incident beam 20 is misaligned from its intended position, then the propagation direction of the transmitted beam 22 is modified accordingly. 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 misalignment of the incident beam 20 and therefore a misalignment of the source and the reflector device 1 may be determined.

[0171] When the detector module 11 comprises a pixelated matrix 111, a quantitative measurement of the position 220 of the transmitted beam can be obtained. For example, as illustrated in [Fig.l4B], 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.

[0172] When a misalignment of the incident beam 20 is detected, a cor action rectrice 4 can then be put in place. 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 obtained again. 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. When the mirror 10 is pivotable, it is possible to adjust 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, al and / or a2 can in particular be adapted according to the measured offset A22.

[0173] The defined position 221 and / or the defined shape 223 may be defined during a calibration step, for example before reflection towards the intended target 3.

[0174] The detector module 11 may further comprise analysis means 112, for example by at least one processor. The analysis means 112 may comprise instructions for carrying out the steps of data analysis and / or determination of an orientation state of the mirror 10 and / or determination of an alignment state of the incident beam with the reflector device. These instructions may allow the orientation state of the mirror 10 to be determined from the measurement of the position of the diffracted beam 23. These instructions may allow the alignment state of the incident beam 20 with the reflector device 1 to be 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 111 to determine the position of the transmitted beam 23. the parameter associated with the transmitted beam 22.

[0175] An example of architecture of the reflector device 1 is now described with reference to FIGS. 15A and 15B. 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 layer of monocrystalline silicon 106 covering a layer of silicon dioxide 107 formed on a monocrystalline silicon substrate 108.

[0176] 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.

[0177] 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. silicon. The reflective device 1 may further comprise contact connections 125, for example based on or made of gold.

[0178] 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.

[0179] The mirror 109 may be partially surrounded by trenches, passing through 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 with the support 108, in particular due to the release of the mirror 10 and the trenches 129.

[0180] 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.

[0181] Particular examples of dimensioning and corresponding resolutions

[0182] Three particular examples of reflector device 1 are now described.

[0183] According to the first example, with: - Incident beam 20: X=1550 nm; 0i equal to 35°, - Diffraction grating 14: period a=10 pm, length in the x and y direction L = 2 mm, - Distance dl between the network 14 and the lens 13: dl = 1 cm

[0184] Following the order m = -4, as described previously, we have A0i = 5° and therefore AOt approximately equal to 1°.

[0185] To collect the transmitted beam over a range ±A0t, the diameter <e>of the lens is in this example is greater than <e>lens>2dtan AOt + L / cos(0m), and therefore Olens is greater than 2.8 mm. L and dl only intervene in these examples to size the diameter of the focusing lens 13.

[0186] With for example a focal length of 5 mm, the ratio f# between the focal length and the diameter of the lens 13 can be less than or equal to 1.8. The diameter OAiry of the image of the diffracted beam 23 on the detector 111 is at best equal to OAiry = 1.22Xf# = 3.4 pm.

[0187] By choosing a detector 111 with a pixel size greater than the size of the beam image on the detector 111, for example a pixel size p of 5 pm, the smallest measurable displacement on the sensor is 1 pixel, which corresponds to a rotation of the diffracted beam 23 of order m of ô0t=p / f = 0.06° or 3.5'. The angular resolution of the reflector device 1 is therefore ô0i«5ô0t = 5p / f = 17' or 0.3°.

[0188] A second example of a reflector device 1 according to the configuration of figures 15A and 15B is used with the following parameters: - Incident beam 20: X=1550 nm; 0i equal to 35°, - Diffraction grating 14: period a=10 pm, length in the x and y direction L = 2 mm, - Distance dl between network 14 and lens 13: dl = 10 cm

[0189] To collect the transmitted beam over a range ±A0t, the diameter <e>of the lens is in this example greater than <e>lens>2dtan A0t + L / cos(0m), and therefore Olens is greater than 5.9 mm.

[0190] With for example a focal length of 10 mm, the ratio f# between the focal length and the diameter of the lens 13 can be less than or equal to 1.7. The diameter OAiry of the image of the diffracted beam 23 on the detector 111 is at best equal to OAiry = 1.22Xf# = 3.2 pm.

[0191] By choosing a detector 111 with a pixel size greater than the size of the beam image on the detector 111, for example a pixel size p of 5 pm, the smallest measurable displacement on the sensor is 1 pixel, which corresponds to a rotation of the diffracted beam 23 of order m of ô0t=p / f = 0.03° or 1.7'. The angular resolution of the reflector device 1 is therefore ô0i«5ô0t = 5p / f = 8' or 0.15°, an improvement of a factor of 2 compared to the first example.

[0192] A third example of a reflector device 1 according to the configuration of FIGS. 15A and 15B is used with the following parameters: - Incident beam 20: / .=905 nm; 0i varying between 35° and 40° - Diffraction grating 14: period a=10 pm, length in the x and y direction L = 2 mm, - Distance dl between network 14 and lens 13: dl = 10 cm

[0193] In this example, the size of the detector pixels is smaller than the previous examples (3 pm), because the Airy task is smaller.

[0194] [Tables2] m 0i 0i AOt 35° 40° 0m 0t 0m 0t 2 48.99 13.99 55.47 15.47 1.48 1 41.61 6.61 47.16 7.16 0.55 0 35.00 0.00 40.00 0.00 0.00 -1 28.89 -6.11 33.52 -6.78 -.06 -2 23.11 -11.89 27.50 -12.50 -0.61 -3 17.58 -17.42 21.80 -18.20 -0.79 -4 12.21 -22.79 16.31 -23.69 -0.91 -5 6.95 -28.05 10.97 -29.03 -0.98 -6 1.75 -33.25 5.73 -34.27 -1.03 -7 -3.44 -38.44 0.53 -39.47 -1.03 -8 -8.65 -43.65 -4.66 -44.66 -1.01 -9 -13.94 -48.94 -9.89 -49.89 -0.95 -10 -19.36 -54.36 -15.20 -55.20 -0.85 -11 -24.96 -59.96 -20.65 -60.65 -0.70 -12 -30.83 -65.83 -26.31 -66.31 -0.48 -13 -37.08 -72.08 -32.26 -72.26 -0.18 -14 -43.90 -78.90 -38.62 -78.62 0.28 -15 -51.62 -86.62 -45.62 -85.62 1.00 -16 -60.98 -95.98 -53.63 -93.63 2.35

[0195] Between the orders m=-l and m=-12, the order m=-7 presenting the largest rotation AOt is selected.

[0196] We obtain ôOi ~ 5ô0t = 5p / f = 0.09. The angular resolution is improved by a factor of 3.4 compared to the first example and by a factor of 1.7 compared to the second example.

[0197] For comparison, the case where the interference fringes 231 are followed is studied. In this fourth example, a reflector device 1 without a focusing lens 13 is used. Indeed, at the image focal plane, the orders are separated and therefore do not interfere.

[0198] If the mirror rotates by AOi, the fringes on the sensor will translate by an amount ôy close to dA0t where d is the mirror / detector distance and A0t the average rotation of the two intersecting diffracted beams 23. For example, we have d = 10 cm, A0t = 1° and ôy = 1.7 mm).

[0199] The angular resolution of the device thus used is ô0i ~ 5ô0t ~ 5p / d. Since d > f (f being the focal length in the variant without interferences, the angular resolution is better than that obtained by following the displacement of diffracted beam 23 having a maximum rotation, as described previously. For example, with d=10 cm, p=5 pm, ô0i = 0.014°. This represents a gain of a factor of 10 in this case.

[0200] The rotation of the mirror 10 can also slightly vary the pitch of the fringes which is equal to:

[0201] [Math.5] Â Znn(^)

[0202] A0m is the angle between the two intersecting diffracted beams 23. This effect is negligible compared to the displacement of the interference fringes 231.

[0203] 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. 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.< / e> < / e> < / e> < / e>

Claims

Claims

1. A reflector device (1) comprising: • a partially transparent mirror (10) having a front face (10a) arranged to receive at least one 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 at least one incident beam (20), and to transmit a portion of the at least one incident beam (20) via the rear face (10b) to form a transmitted beam (22), characterized in that the reflector device (1) further comprises: • at least one diffraction grating (14) arranged opposite the rear face (10b) of the mirror (10) and secured to the mirror (10), the diffraction grating (14) being configured to diffract the transmitted beam (22) into at least one diffracted beam (23) of order m, m being not null,• a detector module (11) configured to: - measure a position of at least one diffracted beam (23) of order m, - from the measurement of said position, determine an angle (0i) between the mirror (10) and the incident beam (20), so as to determine an orientation state of the mirror (10).,

2. Reflector device (1) according to the 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).

3. A reflective device (1) according to any preceding claim, wherein the mirror (10) comprises: • a metallic reflective layer (100) having a thickness (eioo) chosen to transmit a portion of the incident beam (20) to form the transmitted beam (22), or • a Bragg stack (101) comprising at least one em- so-called “elementary” Bragg stack (102) comprising two layers (103, 104) having distinct refractive indices.

4. A reflector device (1) according to any preceding claim, wherein the diffraction grating (14) is configured to diffract the transmitted beam (22) into a plurality of diffracted beams (23) of orders m, m being distinct between the diffracted beams (23), and the detector module (11) is arranged at an intersection (230) between at least two diffracted beams (23) of orders m distinct so as to measure a position of interference fringes (231) between said at least two diffracted beams (23).

5. Reflector device (1) according to any one of the preceding claims, in which, the incident beam (20) having a wavelength X, the diffraction grating (14) has a period a such that a is between 1.5X and 20 / ..

6. Reflective device (1) according to the preceding claim, in which the diffraction grating (14) comprises: • a grating of a material (140) opaque to the incident light beam, for example a metallic reflective layer, having openings (141) of period a, or • a grating of two materials (142, 143) transparent to the incident light beam, having between them a difference in refractive index, the two materials (142, 143) being alternated so as to form the period a.

7. Reflective device (1) according to any one of the two preceding claims, comprising a plurality of diffraction gratings (14), preferably juxtaposed, having distinct periods a between them.

8. Reflector device (1) according to any one of the preceding claims, wherein the detector module (11) is arranged at a distance from the rear face (10b) of the mirror (10), said distance being between 1 pm and 15 cm, preferably between 0.5 cm and 15 cm.

9. A reflective device (1) according to any preceding claim, wherein the detector module (11) comprises a two-dimensional pixel array (111).

10. A reflector device (1) according to any preceding claim, further comprising an optical element (13), for example a lens (13), configured to focus the at least one diffracted beam (23) of order m onto the detector module (11).

11. Method for measuring the orientation of a mirror (10) implementing a reflector device (1) according to any one of the preceding claims, the method comprising: • the emission of at least one incident beam (20) from a light source (2) towards the reflector device (1), • a reflection of a part of the at least one incident beam (20) by the mirror (10) to form the reflected beam (21), • a transmission of another part of the at least one incident beam (22) by the mirror (10) to form the transmitted beam (22), • a diffraction, by the diffraction grating (14), of the transmitted beam (22) into at least one diffracted beam (23) of order m, m being non-zero, • a so-called “orientation” measurement, by the detector module (11), of a position of at least one diffracted beam (23) of order m, • from the measurement from the said position,a determination of an angle (0i) between the mirror (10) and the incident beam (20), so as to determine an orientation state of the mirror (10).,

12. Method according to the preceding claim, in which the transmitted beam (22) is diffracted into a plurality of diffracted beams (23) of orders m, m being distinct between the diffracted beams, and in which, during the orientation measurement, the position of at least two diffracted beams (23) of distinct orders m is measured.

13. Method according to the preceding claim, in which the detector module (11) is arranged at an intersection (230) between the at least two diffracted beams (23) of distinct orders m, and in which, during the orientation measurement, a position of interference fringes (231) between said diffracted beams (23) is measured.

14. A method according to any one of the three preceding claims, wherein the emission of the at least one incident beam (20) comprises the emission of a first incident beam (20a) and a second incident beam (20b) from the light source (2) to the reflector device (1), the method implementing at least the steps of transmission, diffraction, orientation measurement and determination of the angle (0i) from the first incident beam (20a), the method further comprising a reflection of the second incident beam (20b) by the mirror (10) to form the reflected beam (21b) towards a target (3).

15. A method according to any one of the four preceding claims, wherein a portion of the transmitted beam (22) is not diffracted and forms an undiffracted zero-order beam (22), the method further comprising: a so-called “verification” measurement, by the detector module (11), of at least one parameter associated with the 0th order beam (22) by the mirror (10), the at least one parameter being chosen from: - a presence or absence of the beam of order 0 (22), - a position (220) of the zero-order beam (22), a determination of a state of alignment of the at least one incident beam (20) with the reflector device (1) comprising: - if the parameter measured by the detector module (11) is an absence of the 0th order beam (22) and / or a position (220) of the 0th order beam (22) different from a defined position (221), a determination of a bad alignment of the incident beam (20).

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