FR3059156B1 - OPTICAL DETECTION MODULE - Google Patents

Abstract

An optical detection module (120) comprising a photodetection assembly (121) with a detection surface (140) having a first region (141) receiving a focused image of a scene, at least one aperture (122) positioned upstream of the photodetection assembly (121) and provided with an aperture (122b) which passes light beams useful for forming the focused image and which blocks parasitic light beams, and a defocus optical component (123) mounted on the diaphragm (122), at the opening (122b) thereof, and which forms on a second region (142) of the sensing surface (140) a first laterally offset and defocused image of a value predetermined with respect to a second image.

Description

OPTICAL DETECTION MODULE

TECHNICAL AREA

The present disclosure relates to an optical detection module and an optical instrument comprising such a module. Such an instrument can be used, in particular, for imaging in the space domain. It may be, in particular, a space telescope.

BACKGROUND

In the field of imaging and, more particularly, in the field of spatial imaging, it is known to use telescope-type optical instruments to produce, for example, images of the sun or planets. These optical instruments can be installed on the ground on Earth, or be embedded on a satellite. In the latter case, they can be used to make images (called satellite images) of the Earth.

Such optical instruments generally comprise an optical focusing assembly, provided with lenses, mirrors or other optical components, for focusing the light beams coming from the observed scene, a detection system for receiving and transforming these light beams into signals and a unit. process for producing an image from the signals. Such a system can constitute, in particular, a large-field, high-resolution imaging system, that is to say an imaging system having an image width greater than 10 km and a ground resolution of less than 10. m.

The detection system is itself formed of one or more photodetection modules each comprising a set of photodetection. A photodetection assembly typically comprises a plurality of photodetectors arranged in a matrix or in a line on a support. These photodetectors are also called elementary detectors or "pixels". For example, the photodetectors may be arranged along one or more lines in the same plane, thus forming a subset commonly known as a focal plane array.

In the case of a large-field, high-resolution imaging detection system comprising a plurality of photodetection modules, the photodetection modules may themselves be arranged end-to-end to form one or more major detection lines. The phase error of the wavefront of an optical instrument characterizes the quality of this instrument and, more particularly, the aberrations and misalignments of the optical focusing assembly of the instrument. The phase error of the wavefront is also called "WFE", for "Wave-Front Error". Knowing the WFE makes it possible to improve the quality of the image made, either by taking into account the WFE to correct by calculation, after detection, the signals emitted by the detection system, or taking into account the WFE to correct activates the shape or alignment of one or more mirrors of the optical instrument so that the detected image (ie the focused image) is as sharp as possible.

To determine the WFE, wavefront analyzers (or wavefront analyzers) using different techniques are used. One of these techniques consists in using a phase diversity algorithm that makes it possible to estimate the WFE from two images, one of which has a known aberration with respect to the other. This known aberration can be a defocus.

Especially in the field of spatial imaging, there is a constant need for improvement of optical instruments. In particular, the compactness and lightness of the instruments, with equivalent performances, are constant concerns.

SUMMARY OF THE INVENTION

In a first aspect, the present disclosure relates to an optical detection module. This module comprises a photodetection assembly comprising a detection surface of which a first zone receives a focused image of a scene. It also comprises at least one diaphragm positioned upstream of the photodetection assembly and provided with an opening that passes light beams useful for the formation of the focused image and blocks parasitic light beams. The module further includes a defocus optical component mounted on the diaphragm at the opening thereof. The defocus optical component forms on a second area of the detection surface of the photodetection assembly a first image laterally offset and defocused by a predetermined value with respect to a second image.

In the present description, the upstream and downstream are defined with respect to the normal propagation direction of the light beams from the observed scene. A first element disposed upstream of a second element therefore receives these light beams before the second element.

The function of sorting the useful and parasitic light beams provided by the diaphragm or diaphragms is also known as the baffling function. Each diaphragm may have, in addition to its baffling function, other functions. For example, the diaphragm may have a spectral filtering function.

Such an optical detection module has the advantage of integrating the defocus optical component into the relatively small volume of the module. The compactness of the module is thus preserved. The fact that the defocus optical component is mounted on the diaphragm also allows this component to be positioned closer to the photodetection assembly, thereby minimizing the impact of the defocus optical component on the grip width. from view, or mowed, the image using the least pixels possible on the module. In other words, this makes it possible to limit the number of photodetectors or pixels dedicated to the estimation of the WFE and, consequently, to dedicate as many photodetectors as possible to the imaging.

Moreover, the proposed configuration makes it possible to easily and accurately adjust the position of the optical defocusing component with respect to the photodetectors obtained by taking advantage, on the one hand, of the aperture of the diaphragm constitutes a good reference for the positioning of the optical component of defocusing with respect to the diaphragm and, secondly, the accuracy of the adjustment of the diaphragm relative to the entire photodetection.

Associating the optical defocusing component with the diaphragm makes it possible to take advantage of the function of baffling the diaphragm to automatically select the area of the component that is useful for defocusing and thus limit the stray light. The defocus optical component thus does not need a bafflage function of its own. In some embodiments, the optical detection module includes a housing enclosing the photodetection assembly, the diaphragm, and the defocus optical component. Of course, the housing can enclose other elements. This allows, for example, to protect the elements it contains dust or other environmental pollution. In particular, the housing can be hermetic or simply impervious to particles.

In some embodiments, the optical detection module comprises at least one passive optical component, typically a spectral filter, which passes light beams of a given spectral band. The passive optical component (s) may be enclosed within the housing of the detection module. On the other hand, the passive optical component and the diaphragm may form only one component. In other words, the diaphragm can provide spectral filtering functions.

In particular, to obtain more information through the acquisition of the images, multi-spectral images, that is to say images obtained in different spectral bands, are formed. For this purpose, a set of spectral filters is positioned in front of the detection assembly, each filter covering one or more elementary detectors. Typically, each filter may cover a line of elementary detectors. In this case, each line of detectors is associated with a passive optical component and a diaphragm. As indicated above, the passive optical component and the diaphragm may be one and the same component.

In some embodiments, the defocus optical component is positioned upstream of the diaphragm and, for example, between the diaphragm and the passive optical component. In other embodiments, the defocus optical component is positioned downstream of the diaphragm, i.e. between the diaphragm and the sensing surface. In the latter case, the optical defocus component being closer to the detection surface, its impact on the shooting width, or mowed, is more limited.

In some embodiments, the defocus optical component is attached to the diaphragm, for example by gluing or brazing. The defocus optical component and the diaphragm thus form a subset whose positioning relative to the photodetection assembly can be easily adjusted. When the defocus optical component has a defocus area surrounded by non-useful areas, the non-useful areas can be used for attachment of the component to the diaphragm.

According to another aspect, the present description relates to an optical instrument comprising an optical detection module as previously described and an optical focusing assembly for converging the light beams coming from the observed scene towards the photodetection assembly of the module and forming thus an image focused on this set of photodetection. The photodetection assembly emits signals characteristic of the detected focused image. These signals can be transmitted to a processing unit that makes an image from these signals. This processing unit can be integrated into the optical instrument or, on the contrary, be separated from it.

In some embodiments, the optical instrument is associated with a (ie, at least one) wavefront analyzer that implements a phase diversity algorithm to estimate a wavefront phase error of the optical instrument from the first and second images formed on the second area of the detection surface of the module by the defocus optical component and detected by the photodetection assembly. This wavefront analyzer can be integrated into the optical instrument or, on the contrary, be separated from it. The optical instrument can be used for spatial imaging and, in particular, for so-called "large field" and "high resolution" imaging. In particular, it may be a space telescope.

The above-mentioned characteristics and advantages, as well as others, will appear on reading the following detailed description of embodiments of the detection module and the optical instrument proposed. This detailed description refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are diagrammatic and are not to scale. They are primarily intended to illustrate the principles of the invention.

In these drawings, from one figure (FIG) to the other, identical or similar elements (or parts of element) are identified by the same reference signs.

FIG. 1 represents an example of an optical instrument associated with a wavefront analyzer.

FIG. 2 represents an example of an optical detection module.

FIG. 3 represents an exemplary defocus optical component mounted on a diaphragm.

FIG. 4 represents another example of a defocus optical component mounted on several diaphragms.

FIG. 5 is an optical diagram showing light rays defocused relative to each other by a predetermined value, using an example of a defocus optical component.

FIG. 6 is an optical diagram showing focused light rays used for imaging.

DETAILED DESCRIPTION

Exemplary embodiments are described in detail below, with reference to the accompanying drawings. These examples illustrate the features and advantages of the invention. However, it is recalled that the invention is not limited to these examples.

An example of an optical instrument 100 is shown in FIG. 2. The instrument 100 comprises focusing optics 110 and an optical detection module 120. A processing unit 130 is also shown in FIG. 2. This unit 130 may be integrated, in whole or in part, with the optical instrument 100 or, on the contrary, be separated therefrom. The focusing optics 110 comprise one or more optical components, of the lens or mirror type, which form an optical focusing assembly ensuring the convergence of the light beams coming from the observed scene towards the detection module 120.

The detection module 120 comprises a photodetection assembly 121 comprising itself photodetectors, or elementary detectors, arranged in a matrix or along one or more lines. When the photodetection assembly 121 comprises photodetector arrays, the assembly 121 is driven by a relative displacement with respect to the observed scene. This relative movement can be obtained by an opto-mechanical device to ensure a scanning of the scene. Relative motion can also be achieved by moving the optical instrument itself. For example, when the optical instrument is embarked on a satellite to make a satellite image of the Earth, the relative motion is obtained by moving the satellite relative to the Earth. Whatever the configuration of the photodetectors chosen, these photodetectors are arranged in a detection plane 121a, often called the focal plane. The focal plane is defined to coincide with the best-developed plan of the optical instrument. In the example of Figure 2, the photodetectors are arranged along a line.

The optical detection module 120 further comprises a diaphragm 122 positioned upstream of the photodetection assembly 121 in the direction X of propagation of the light beams transmitted by the focusing optics 110. The diaphragm 122 makes it possible to sort the beams light beam propagating within the detection module 120 so that only the beams useful for the formation of the focused image reach the detection surface 140. For this, the diaphragm 122 is provided with an opening 122b blocking the parasitic light beams (or "stray light" in English, resulting, for example, from reflections on the different internal surfaces of the optical instrument) and letting through the light beams useful for imaging. In some embodiments, the diaphragm 122 may be a plate, for example a metal plate or a glass plate, in which an opening 122b is formed. An opaque coating, possibly black, may be deposited locally on the plate around the opening 122b to absorb parasitic light beams. Typically the stray light beams are / come from multiple internal reflections on surfaces of the optical instrument or scattering across surfaces in the instrument, including at the level of the detection module.

The detection surface 140, as used herein, is the total detection area of the photodetection assembly 121 and corresponds to the sum of the detection surfaces of the photodetectors, or "pixels". A first zone 141 of the surface 140 receives a focused image of the observed scene, as illustrated in FIG. 6. In this figure, light rays 50 and 60 coming from the observed scene pass through the focusing optics 110 which makes them converge. towards a focal point F of the detection plane 121a. The light rays 50 and 60 after convergence are respectively referenced 53 and 63. They pass through the opening 122b of the diaphragm 122, described below, and reach the first zone 141 of the detection surface 140. These rays 53, 63 participate in the formation of the image of the scene.

The optical detection module 100 also includes a defocus optical component 123 mounted on the diaphragm 122 at the aperture 122b. The defocus optical component 123 provides for the formation, on the detection plane 121a of the photodetection assembly 121, of a first image laterally offset and defocused by a predetermined defocusing value with respect to a second image. As described below, with reference to FIG. 5, the first and second images are each obtained from at least two defocused light beams. The defocus optical component 123 may, for example, be a prism, an optical plate with flat faces, parallel or otherwise, an assembly of prisms, or any other optical component making it possible to form from incident beams focused on the set of photodetection 121 two images defocused together with a known defocus value.

Whatever the defocus optical component 123 retained, it can be fixed, for example by gluing or brazing, on one of the main faces 122c, 122d of the diaphragm 122. The defocusing optical component 123 and the diaphragm 122 thus form a sub-surface. together, the relative positioning of the defocus optical component 123 and the diaphragm 122 being fixed. The positioning of this subassembly with respect to the photodetection assembly 121 can then be precisely adjusted. Indeed, unlike the edges of the defocus optical component 123 which are not necessarily manufactured or shaped with great precision, the edges of the diaphragm 122 are generally precisely defined and can therefore serve as a reliable reference for the positioning of said subassembly relative to the photodetection assembly 121.

In an example (not shown), the defocus optical component 123 is fixed on the face 122d of the diaphragm located opposite the detection plane 121a, or downstream face of the diaphragm. The defocus optical component 123 is then positioned between the diaphragm 122 and the photodetection assembly 121. In this example, only useful light beams having passed through the aperture 122b of the diaphragm 122 enter the defocus optical component 123. configurations of FIG 2 to 5 where the optical defocus component 123 is located upstream of the diaphragm 122 (ie above the diaphragm 122 in the figures), such a configuration has the advantage of reducing the impact of the defocus optical component 123 on the field of view width or mowed.

In the example of FIGS. 2 to 5, the defocusing optical component 123 is fixed on the face 122c of the diaphragm turned towards the focusing optic 110, or upstream face of the diaphragm. The defocus optical component 123 is positioned at the aperture 122b of the diaphragm 122 so that the usable area 123u at the defocusing of the component 123 is located opposite the aperture 122b (see FIGS. 3 and 5). In other words, the useful area 123u is located opposite the opening 122b in the X direction of propagation of the light beams. On the contrary, the non-useful areas for defocusing and, in particular, the areas that do not have (or may not present) the qualities required for the desired defocusing, eg, the areas having (or likely to present) optical defects. , are not located opposite but around the opening 122b. In this way, the light beams passing through the non-useful areas do not pass through the aperture 122b of the diaphragm 122 and do not reach the photodetection assembly 121. The diaphragm 122 thus makes it possible to sort between the light beams that we know correctly defocused (by the useful area 123u) and the other light beams. In addition, the diaphragm 122 blocks the parasitic light beams resulting, for example, from reflections and diffusions on the different surfaces of the defocus optical component 123. This makes it possible to limit the beams to the beams that are useful for imaging.

The defective zone 123u of the optical component 123 is, for example, a zone having undergone quality controls ensuring that this zone is capable of achieving the desired defocusing. On the contrary, the non-useful areas of the optical component 123 are areas that are not considered as capable of achieving the desired defocusing, or areas which, by themselves, are capable of producing stray light (edge of the optical treatment , chamfers, or component edges, for example).

In the example of FIG. 4, the defocusing optical component 123 is fixed on the upstream faces 122c of three diaphragms 122-1, 122-2, 122-3 arranged side by side. In particular, the defocus optical component 123 is positioned astride the three diaphragms. In such a three-diaphragm configuration, the detection surface 140 of the photodetection assembly 121 is defined by three lines of photodetectors (not shown) located respectively downstream and in front of the openings 122b of the diaphragms 122-1, 122-2. , 122-3. In this case, the defocus optical component 123 may have one or more useful zones 123u each disposed in front of an opening 122b of one of the diaphragms. Several detection zones (together forming the second area 142 of the detection surface, as defined herein) are then provided and associated, respectively, to the useful areas 123u. The number of useful areas 123u depends on the number of defocus measurements desired for estimating the phase error of the wavefront of the instrument. For example, by multiplying the defocusing measures, it becomes possible to make an average of these measurements.

In general, the diaphragm 122 is located at a small distance from the photodetection assembly 121 so as to be positioned very precisely with respect to the detection surface 140. By mounting the defocus optical component 123 on the diaphragm 122, the distance between the defocus optical component 123 and the detection surface is therefore also weak. This makes it possible to limit the second zone 142 of the detection surface allocated to the measurement of the two beams 51, 52, 61, 62 defocused together by a known value, in favor of the first zone 141 of the dedicated detection surface 140. the detection of the focused image used for imaging. Thus, the area of the second zone 142 may be about 10% or less than 10% and, more particularly, less than 8% of the total detection area 140 of the photodetection assembly 120. In this case, the area of the first area 141 dedicated to imaging may measure about 90% or more than 90% of the total detection area 140.

The optical detection module 100 may also comprise a passive optical component 125, in particular a spectral filter, which passes light beams of a given spectral band. In the example of FIG. 2, the defocus optical component 123 and the diaphragm 122 are positioned between the photodetection assembly 121 and the passive optical component 125.

The passive optical component 125 may comprise a substrate with optical faces. The substrate may be a transparent material in a selected detection spectral band. One or both optical faces of the substrate may be wholly or partially structured or coated with one or more optical coatings so that the passive optical component 125 performs one or more optical functions. An optical coating may be, for example, a spectral processing adapted to the transmission of light in a sub-band of the detection spectral band or a polarization treatment. Thus, the optical functions of the component 125 may be, for example, spectral filtering functions, possibly according to several different spectral bands, and / or polarization functions, etc.

Note that the passive optical component 125 is optional, especially when the spectral filter function is provided by the diaphragm 122. In this case, the diaphragm 122 is made of a filter material or covered with a filter coating. In particular, in the example of FIG 4 the diaphragms 122-1, 122-2, 122-3 can pass, respectively, the light beams in separate spectral bands.

The optical detection module 120 may comprise a housing 124 enclosing the diaphragm 122 and the defocus optical component 123 so as to protect these elements, for example against dust or other types of pollution. The housing 124 can also enclose other elements such as the passive optical component 125 and the photodetection assembly 121. The housing 124 can be hermetic and allow, in particular, the confinement of the detection module 120 in a clean environment. The housing 124 has a window 126 allowing the light beams to enter the housing 124. The optical instrument 100 may further comprise one or more processing units 130 each connected to the optical detection module 120. The unit or units processors 130 process the data from the photodetection assembly 121. Each processing unit 130 may be connected to the optical detection module 120 by a connection-type electrical connection device 127 or any other suitable connection system, wired or not.

The at least one processing unit 130 has at least the following two functions.

The first function is to produce images from the signals coming from the photodetection assembly 121. These signals characterize the focused light beams (ie the focused image) coming from the observed scene which are detected by the first zone 141. of the detection surface 140.

The second function is to implement a phase diversity algorithm for estimating a phase error of the wavefront of the optical instrument from two images defocused together, detected by the second zone 142 of the detection surface. .

These two functions can be provided by the same processing unit (s) 130 or by different processing units 130.

With regard to the second function, FIG 5 represents the optical path traversed by two light rays 50 and 60, in an exemplary optical detection module 120. For the sake of simplification, only the focusing optics 110, the optical defocusing component 123 the diaphragm 122 to which it is attached and the photodetection assembly 121 are shown. The dimensions of these elements or the distances between these elements are not respected, FIG 5 aiming above all to illustrate the defocusing performed. The light rays 50 and 60 are useful light rays which pass through the opening 122b of the diaphragm 122. These light rays 50, 60 from the observed scene pass through the focusing optics 110 which makes them converge. The light rays 50 and 60 after convergence are referenced 51 and 61, respectively.

In the example shown, the defocus optical component 123 is an optical plate with plane faces 123a, 123b, parallel to each other. The defocus optical component 123 could, however, be in another form.

By passing through the defocus optical component 123, the light beam 51 is first reflected by the face 123b with a first deflection angle, then by the opposite face 123a with a second deflection angle. After this double reflection within the optical defocus component 123, the light beam is defocused. It is referenced 52. In the same way, the light ray 61 undergoes a double reflection, with deflection, on the face 123b and then on the face 123a of the defocus optical component 123. After the double reflection within the defocus optical component 123 , the light beam is defocused. It is referenced 62. The defocused light rays 52 and 62 form a first defocused image with respect to the second image formed by the rays 51 and 61. This first defocused image is also offset laterally with respect to the second image formed by the light rays. 51 and 61.

In the present disclosure, by lateral shift, is meant the offset in the detection plane (in the example of the figures, the plane 121a) for separating the first and the second image inside the second zone of the surface detection (in the example of the figures, the area 142).

The offset and defocus values depend on several characteristics of the defocus optical component 123 such as, for example, the thickness of the defocus optical component, its optical index, the angle between the faces 123a and 123b. These characteristics being known or easily calculable, the values of the defocusing and of the offset with respect to the focused image are known.

A phase diversity algorithm is implemented by a processing unit 130 to estimate the wavefront phase error, or WFE, seen by the optical instrument. To estimate the WFE, this algorithm uses data from the two defocused and laterally offset images and the known defocus and offset values. Since phase diversity algorithms are well known in the art, they will not be described in more detail.

Once the WFE has been estimated, it can be taken into account, either to correct by calculation the signals emitted by the photodetection assembly 121, or to actively correct the shape or configuration of certain elements of the optical instrument 100 ( in particular focusing optics 110) so that the detected image is as sharp as possible. An example of active correction is given below, with reference to FIG.

An example of an optical instrument 100 associated with a wavefront analyzer 220 is shown diagrammatically in FIG. 1. The optical instrument 100 comprises focusing optics 110 and an optical detection module 120 of the aforementioned type. The optical instrument 100, the wavefront analyzer 220 and control limit 230 are connected in series in a closed loop. The wavefront analyzer 220 implements a phase diversity algorithm. The wavefront analyzer 220 receives signals from the detection module 120. On the basis of these signals 10, the wavefront analyzer 220 determines, by the implementation of the diversity algorithm of phase, phase information 20 which is transmitted to the control unit 230. The control unit 230 analyzes the phase information 20 and transmits to the optical instrument 100 correction commands 30. for example, mirror deformation controls for correcting the distortion of one of the optical components of the instrument 100. The wavefront analyzer 220 and the control unit 230 may be integrated, in whole or in part, to the processing unit 130 of FIG.

The modes or examples of embodiment described in the present description are given for illustrative and not limiting, a person skilled in the art can easily, in view of this presentation, modify these modes or embodiments, or consider others, while remaining within the scope of the invention as defined in the appended claims.

Furthermore, when the terms "includes", "include", "including" and their derivatives are used in this specification (including the appended claims), they must be interpreted as indicating the presence of the characteristic (s), data, steps and / or components, without excluding the presence of other characteristics, data, steps and / or components.

Finally, the various features of the embodiments or examples of embodiments described in the present disclosure may be considered in isolation or may be combined with one another. When combined, these characteristics can be as described above or differently, the invention is not limited to the specific combinations described above. In particular, unless otherwise specified or technical incompatibility, a feature described in connection with a mode or an embodiment may be applied in a similar manner to another embodiment or embodiment.

Claims (10)

An optical sensing module (120) comprising: - a photodetection assembly (121) including a sensing surface (140) having a first region (141) receiving a focused image of a scene; ~ at least one diaphragm (122) positioned upstream of the photodetection assembly (121) and provided with an opening (122b) which passes light beams useful for the formation of the focused image of the scene on the first zone (141) and which blocks parasitic light seals; and a defocus optical component (123) mounted on the diaphragm (122) at the aperture (122b) thereof, the defocus optical component (123) covering only a portion of the aperture (122); 122b) and forming a first and a second image of the scene on a second area (142) of the detection surface (140), the first image being offset laterally and defocused by a predetermined value with respect to the second image. An optical detection module according to claim 1, wherein the defocus optical component (123) is positioned upstream of the diaphragm (122). An optical detection module according to claim 1, wherein the defocus optical component (123) is positioned between the diaphragm (122) and the detection surface (140). An optical detection module according to any one of claims 1 to 3, comprising a housing (124) enclosing the photodetection assembly (121), the diaphragm (122) and the defocus optical component (123). 5. Optical detection module according to any one of claims 1 to 4, comprising at least one passive optical component (125), in particular a spectral filter, which passes light beams of a given spectral band. An optical detection module according to claim 5, wherein the defocus optical component (123) is positioned between the diaphragm (122) and the passive optical component (125). 7. Optical detection module according to any one of claims 1 to 6, wherein the optical de-modeling component (123) is fixed, in particular by gluing or brazing, on the diaphragm (122). An optical sensing module as claimed in any one of claims 1 to 7, wherein the area of the second area (142) is about or less than 10%, particularly less than 8%, of the sensing surface (140). . An optical instrument comprising: at least one optical detection module (120) according to any one of claims 1 to 8; and an optical focusing assembly (110) for converging the light beams from the observed scene to the photodetection assembly (121) of the detection module (120) so that a portion of the converging light beams to the photodetection assembly (121) pass through the opening (122b) of the diaphragm (122), without passing through the defocus optical component (123), to form the focused image of the scene on the first region (141) of the detection surface (140), and a portion of the light beams converging towards the photodetection assembly (121) pass through the aperture (122b) of the diaphragm (122) and the optical de-modeling component (123) to form the first and second image of the scene on the second area (142) of the detection surface (140). An optical instrument according to claim 9 associated with a wavefront analyzer which implements a phase diversity algorithm for estimating a phase error of the optical instrument-edge of the first and second images formed. by the defocus optical component (123) and detected by the photodetection assembly (121).