Imaging system

Abstract

Title: Imaging system The invention relates to a catadioptric imaging system comprising an optical assembly (1) and a support (2), the optical assembly (1) being supported by the support (2), the optical assembly (1) comprising along an optical axis (X1): a concave mirror (13), a first lens (11) distant from the mirror (13), a second lens (12) positioned at the center of the first lens (11), the system being configured so that at least two connecting pieces (14) join the first lens (11) and the mirror (13), the at least two connecting pieces (14) being spaced apart on the contour of the mirror (13) and on the contour of the first lens (11), the mirror (13), the first lens (11), the second lens (12) and the at least connecting piece (14) each being made of a silica-based material. Figure for abstract: Fig.1

Description

Title of the invention: Imaging system Technical field

[0001] The present invention relates to the field of optical systems. The invention will find particular application in wide-field catadioptric imaging systems. STATE OF THE ART

[0002] In the field of astronomical space applications, but also for Earth observation or climate studies, the sensitivity aspects of optical devices are essential, particularly in the face of thermal variations. It is generally appropriate to integrate cryogenic systems to counter thermal stability defects. Indeed, during temperature variations, a non-athermalized optical device presents a higher risk of deformation of its parts, a risk linked to the phenomenon of thermal expansion. To maintain the performance of the system, the focal plane of the detector must be maintained on the image plane of the optical system. This maintenance generally requires a very precise, complex and generally expensive refocusing system.

[0003] Single-material optical systems such as those developed by the space industry, for example using silicon carbide, make it possible to avoid these problems by proposing homothetic expansions. But this only works with mirror systems. For mixed systems comprising mirrors and lenses, the variation in the optical index of the glasses also comes into play.

[0004] There are technical solutions such as those in the publication: "A full silica F / 0.95 compact, achromatic and athermalized camera compatible with 60 x 60 mm detector", Bernard Délabré, Emesto Olivia, Design and fabrication Congess 2017, IODC, Freeform OFTT, © OSA 2017. In this publication, a spectrograph-type optical device is disclosed comprising a mirror and a lens assembled via a quartz glass cylinder. The advantage of this type of assembly lies in the use of a silica-based material whose thermal expansion coefficient is very low and allows homothetic deformation of the optical assembly thus formed. In this disclosed system, however, there is no mention of a detector focal plane maintained at the focus of the optical system.

[0005] The optical assembly in this solution is carried out by respective fittings of the mirror and the first lens in the cylinder and requires a high level of finishing of the parts taking into account the precision of the assembly.

[0006] This type of device assembly has several disadvantages such as the fact that it is necessary to maintain the optical assembly with the focal plane of the detector by a dedicated mechanism. This results in the breaking of the athermalization principle. In addition, with this type of device it is necessary to adapt the dimensioning of the optical elements with the internal diameter of the cylinder. This leads to undesired spacings between the different elements and tends to make the device heavier.

[0007] An object of the present invention is therefore to propose a solution which makes it possible to eliminate or limit at least one of the aforementioned drawbacks.

[0008] There is therefore a need for a solution allowing the assembly of a spectrograph type device in such a way as to be able to adapt to different sizes of optical elements with a solution allowing clearances or spacings to be avoided.

[0009] Other objects, features, and advantages of the present invention will become apparent from the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0010] To achieve this objective, according to one embodiment, a catadioptric imaging system is provided comprising an optical assembly and a support, the optical assembly being supported by the support, the optical assembly comprising along an optical axis: - a concave mirror, - a first lens distant from the mirror, - a second lens positioned in the center of the first lens, - a connecting portion securing the mirror and the first lens,

[0011] The mirror, the first lens, the second lens and the connecting portion each being made of a silica-based material.

[0012] The system being configured such that the connecting portion comprises at least two connecting pieces made of a silica-based material and which join the first lens and the mirror, at least two connecting pieces being spaced on the contour of the mirror and on the contour of the first lens.

[0013] Without these provisions, it would be necessary to allow precise adjustment between the different optical elements by using, for example, a custom-made cylinder with a high level of finish.

[0014] While current techniques direct those skilled in the art towards a solid optical assembly, a particular assembly is proposed here combining better mounting of the elements and improved accommodation of expansions. Thus, errors linked to the phenomenon of thermal expansion are avoided while allowing the use a lighter optical assembly that can adapt to any type of optical element. For example, it can adapt to different diameters of optical elements.

[0015] As a result, the proposed solution makes it possible to adapt to all types of optical elements by using a connecting part made of a silica-based material which allows easy connection between the peripheries of the optical elements so as to ensure homothetic deformation of the optical assembly relative to thermal expansion phenomena.

[0016] Preferably, the optical assembly 1 is made of a single material forming a monolithic assembly, so as to allow stability over a wide temperature range. The use of a monolithic optical assembly based on silica provides the system with very interesting optical and thermomechanical properties. Thus, the system becomes athermal and does not require any adjustment with regard to temperature.

[0017] Another preferred aspect of the imaging system is to facilitate the maintenance in position of a single-piece optical assembly on a support.

[0018] Another aspect relates to a method of mounting the system comprising the following steps: - alignment of the second lens relative to the first lens, - gluing of the second lens to the first lens, - adjustment of the first and second lens assembly relative to the mirror, - securing the first and second lens assembly relative to the mirror, using at least two connecting pieces, - alignment of the detector block relative to the first and second lens assembly, by mechanical wedging using bolting elements.

[0019] Preferably, the alignment of the detector block comprises passive maintenance of the detector focal plane in the image plane of the optical assembly. 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.l] [Fig.l] represents a perspective view of an example of a catadioptric imaging system according to the invention.

[0022] [Fig.2A] [Fig.2A] represents a perspective view of an example of an optical assembly forming a single-piece part based on silica.

[0023] [Fig.2B] [Fig.2B] shows a perspective view of an example of a support configured to support the optical assembly of [Fig.2A]. In this example, the support assembly is secured to a detector.

[0024] [Fig.3A] [Fig.3A] represents a top view of the system

[0025] [Fig.3B] [Fig.3B] represents a side view of the system

[0026] [Fig.4A] [Fig.4A] represents a rear perspective view of an example of system according to the present invention.

[0027] [Fig.4B] [Fig.4B] represents a zoomed view of the system of [Fig.4A].

[0028] [Fig.4C] [Fig.4C] shows a cross-sectional view of the rear of an example of catadioptric system according to the invention in which a detector block is positioned.

[0029] 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. DETAILED DESCRIPTION

[0030] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:

[0031] According to one example, at least two connecting pieces are identical.

[0032] This allows for optimized and preferably mass-produced silica-based elements with a shape that is simple to machine.

[0033] According to one example, at least two connecting pieces are arranged symmetrically relative to a plane comprising the optical axis.

[0034] According to one example, at least two connecting pieces are arranged symmetrically relative to a vertical plane which includes the optical axis.

[0035] According to one example, at least two connecting pieces are arranged symmetrically relative to a horizontal plane comprising the optical axis.

[0036] According to one example, the system comprises exactly four connecting pieces distributed equiradially relative to the contour of the mirror and the contour of the first lens.

[0037] This allows for reinforced retention of the first lens with the mirror. Preferably, the four connecting pieces are distributed at 90° relative to each other along the optical axis. Preferably, the four connecting pieces are distributed so that at least two connecting pieces are distributed symmetrically relative to a horizontal plane comprising the optical axis and / or the other two connecting pieces are symmetrical relative to a vertical plane.

[0038] According to one example, at least one connecting piece comprises a planar surface facing outwardly of the optical assembly, the planar surface being configured to cooperate with a distal connecting portion so that in a mounting configuration of the optical assembly on the support the flat surface is parallel to a vertical plane.

[0039] This allows the distal connecting portions to be positioned according to a planned surface.

[0040] According to one example, the support comprises at least one leg comprising a distal connection portion secured to the optical assembly.

[0041] Advantageously, the leg is made of metal, preferably titanium.

[0042] Preferably, the leg comprises at least one sheet metal portion configured to bend so as to prevent stresses on the optical assembly so as not to generate deformation of the optical elements.

[0043] Preferably, the leg is configured to have a preferred aptitude for bending in the direction oriented towards the optical assembly. It may be a portion of a rectangular bar whose section has a smaller dimension oriented along the normal to the support surface of the leg on the optical element.

[0044] According to one example, the distal connecting portion of each leg is secured to the optical assembly by gluing.

[0045] Preferably, a glue of the thermosetting liquid polymer resin or polyepoxide type is used.

[0046] According to one example, the support comprises exactly three legs whose respective distal connection portions are distributed at 120° around the optical assembly.

[0047] This allows quasi-isostatic maintenance of the optical assembly on the support.

[0048] According to one example, the distal connecting portion of a first of the legs has a bearing surface on the optical element extending along a plane whose direction normal to the center of this plane is parallel to the optical axis.

[0049] According to one example, the distal connecting portions of a second and a third of the legs each have a bearing surface on the optical element extending along a plane on the optical assembly whose normal direction at the center of this plane intersects the optical axis non-perpendicularly, said normal directions intersecting the optical axis at the same point. Thus, the three normals also form a set with three sectors of 120°.

[0050] According to one embodiment, the optical unit is configured to deform homothetically and the detector unit can thus follow its movement.

[0051] According to one example, the optical assembly moves in translation along the optical axis.

[0052] According to one example, the elements of the optical assembly are made of the same material.

[0053] According to one example, the system comprises a detector positioned flexibly relative to the support and held securely to the first lens so as to capture the rays exiting the second lens.

[0054] According to the example, the system comprises proximity electronics adapted to the detector block. The detector block comprises an active or passive cold source.

[0055] According to one example, at least one of the mirror and the first lens comprises a planar peripheral surface configured to allow plane-to-plane bonding of the part at least one of the at least two connecting parts. Preferably, the mirror and the first lens are aligned along a plane normal to the optical axis.

[0056] It is specified that in the context of the present invention, the term “silica-based material” is understood as any solid material comprising silica.

[0057] It will be noted that the light passing through the system can be interpreted as a set of light beams.

[0058] A catadioptric imaging system will be understood to mean a system comprising at least one mirror and at least one wide-field lens, preferably greater than 1° of total field and widely open, preferably with an aperture greater than F / 2, i.e. with an aperture of F / N and N<2. This type of architecture allows the positioning of a capture portion of the detector block, passively, on the image plane for a wide range of wavelengths.

[0059] It is specified that, in the context of the present invention, the terms “on”, “overcomes”, “covers”, “underlying”, “opposite” and their equivalents do not necessarily mean “in contact with”.

[0060] In the following description, unless otherwise indicated, when reference is made to absolute position qualifiers, such as the terms "front", "rear", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", "lateral", etc., reference is made to the orientation of the corresponding figures, it being understood that, in practice, the devices and assemblies described may be oriented differently.

[0061] The terms “substantially”, “approximately”, “of the order of” mean “to within 10%, preferably to within 5%” or, when it is an angular orientation, “to within 10°”. Thus, a direction substantially normal to a plane means a direction having an angle of 90+10° relative to the plane.

[0062] In the remainder of the description, the term “on” does not necessarily mean “directly on”. Thus, when it is indicated that a part or member A is supported “on” a part or member B, this does not mean that the parts or members A and B are necessarily in direct contact with each other. These parts or members A and B may be either in direct contact or be supported on each other. through one or more other parts. The same applies to other expressions such as, for example, the expression "A acts on B" which can mean "A acts directly on B" or "A acts on B through one or more other parts".

[0063] In the context of the present patent application, the expression "kinematically interposed between" does not necessarily mean not in "contact with". Thus, if a part A is kinematically interposed between a part B and a part C, this does not mean that A and B are necessarily in direct contact or that A and C are necessarily in direct contact. This means that a movement or a force of the part B, respectively of the part C, can be at least partly transmitted to the part C, respectively to the part B, via the part A.

[0064] In this patent application, when it is indicated that two parts are distinct, this means that these parts are separate. They are: - positioned at a distance from each other, and / or - mobile relative to each other and / or - integral with each other by being fixed by added elements, this fixing being removable or not.

[0065] A single-piece unit cannot therefore be made up of two separate parts.

[0066] 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 in a direction X, this means that the parts can be movable relative to each other except in the direction X. In other words, if one part is moved in the direction X, the other part performs the same movement.

[0067] 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 system and / or the optical assembly and / or the support.

[0068] “Vertical” or “horizontal” means directions relative to the surface on which the support is positioned. For example, if the support is positioned on the ground so as to support the optical assembly off the ground, the vertical direction will be understood as the direction normal to the ground. In other words, the terms “vertical” and “horizontal” are understood in a usage situation in which the system is on a support surface.

[0069] We will also use a reference whose longitudinal or rear / front direction corresponds to the optical axis Xb

[0070] As illustrated in [Fig.l] and according to one example, the imaging system comprises an optical assembly 1 and a support 2. The support 2 is configured to carry the optical assembly 2. Preferably, the support 2 is configured to carry the optical assembly 1 above ground level so that the optical assembly 1 is suspended.

[0071] OPTICAL ASSEMBLY

[0072] According to a preferred embodiment of the present invention, the optical assembly 1 comprises several optical elements including at least one mirror 13, a first lens 11 and a second lens 12.

[0073] According to one example, the mirror 13 extends mainly along a third plane located opposite the first lens 11 and the second lens 12, preferably, the optical axis Xi extends normally to the third plane.

[0074] According to a preferred embodiment of the present invention, the first lens 11 has a diameter greater than that of the second lens 12. The second lens 12 is advantageously secured to the first lens 11. The first lens 11 and the second lens 12 are advantageously secured by gluing. Preferably, the first lens 11 comprises an opening in its center configured to allow the fixing of the second lens 12. Preferably, the second lens 12 comprises a flat surface machined along a plane normal to the optical axis and configured to generate a shoulder in order to allow the gluing of the second lens 12 on the first lens 11. Alternatively or in combination, a mechanical means other than gluing can be used to allow the connection parts to be secured to the mirror and / or to the first lens.This will preferably be a means of holding in position without bolting elements.

[0075] According to one embodiment, the mirror 13 is concave. The mirror 13 is advantageously configured to reflect the rays coming from the first lens 11 onto the second lens 12. The mirror 13 is made of a silica-based material.

[0076] Preferably, the mirror 13 and / or the first lens 11 have a diameter of approximately 400 mm.

[0077] As illustrated in [Fig.2A] and according to the same example, the mirror 13 and the first lens 11 are distant from each other and connected by at least two connecting pieces 14.

[0078] According to a very particular example, the optical assembly 1 is made up of a first silica lens 11 with a diameter of 320 mm, a silica mirror 13 with a diameter of 380 mm, a second silica lens 12, and rectangular with a diameter of 90 mm by 90 mm. The second lens 12 is glued onto the first lens 11, preferably in the center of the first lens 11. The first and second lens assembly 11, 12 is assembled to the mirror 13 by means of connecting pieces 14, such as silica bars glued to each of the optics. In fact, a single-material silica optical block is thus formed.

[0079] CONNECTING PARTS

[0080] According to one embodiment, the joining of the mirror 13 and the first lens 11 is carried out using at least two connecting pieces 14. The connecting piece 14 is made of a silica-based material. The connecting pieces 14 may be made of quartz glass. The connecting pieces 14 may comprise, in section along a plane normal to the main axis Xb, trapezoidal sections, preferably rectangular sections. The connecting pieces 14 are distant and distinct from each other so that the connection between the mirror and the first lens leaves passage openings between the connecting pieces 14. This allows, for example, access between the mirror 13 and the lenses 11, 12, for example for maintenance operations, such as cleaning.

[0081] Preferably, the optical assembly comprises a second lens 12. The second lens 12 is advantageously located at the center of the first lens 11.

[0082] THE SUPPORT

[0083] The support 1 comprises a support surface directed along a support plane and configured to be applied to the ground. At least two connecting pieces 14 are arranged symmetrically relative to a plane containing the optical axis Xi and perpendicular or parallel to the support plane.

[0084] [Fig.2B] - ARCHITECTURE OF THE SUPPORT

[0085] According to one embodiment, the support comprises a base 22 and at least one leg 21. Preferably, at least one leg 21 extends vertically from the base 22.

[0086] As illustrated in [Fig.2B] and according to one example, the support 2 comprises a base 22 having a surface allowing the legs 21 to be fixed. Preferably, the support 2 comprises at least one leg 21, preferably at least two legs 21, preferably exactly three legs distributed circularly at 120°.

[0087] Preferably, the legs 21 are configured to support the optical assembly 1.

[0088] According to one example, a leg 21 comprises at a first end a fixing zone allowing a connection to the base 22. The leg 21 can be held in position on the base 22 by means of a screw-nut connection and / or by means of glue or welding.

[0089] Preferably, the leg 21 comprises at a second end opposite the first end, a distal connection portion 211.

[0090] Preferably, the leg 21 is made of a base of a metal-based material. According to one example, the leg 21 comprises a triangulated base. According to one example, the leg 21 is configured to have a preferred ability to bend in a direction oriented towards the optical assembly 1.

[0091] THE LEGS

[0092] Preferably, the support 2 comprises a leg 21, preferably a plurality of legs 21, preferably three legs 21 distributed at 120°.

[0093] The distal connection portion 211 is located at the upper end of the leg 21. According to a particular embodiment, the distal connection portion 211 comprises an intermediate piece such as a pad so that in a configuration for mounting the optical assembly on the support 2, the intermediate piece will be positioned between the leg 21 and the optical assembly 1. Thus, the contact between the support 2 and the optical assembly 1 is optimized. In fact, the holding in position by gluing of the optical assembly 1 is improved and eliminates play. The pad may be, for example, made of a low-expansion nickel-iron alloy such as Invar 36®.

[0094] Preferably, the connection between the support 2 and the optical assembly 1 is made by means of at least one plane-to-plane contact. Preferably, this is a contact between a first plane surface 14a carried by the connecting piece 14 and a second plane surface carried by the leg 21.

[0095] BENDING ARROW

[0096] Each leg 21 is configured so as to flex in a direction having a non-zero component along an axis parallel to the resultant normal to the main surface 211a of the distal connection portion 211.

[0097] SUPPORT POINT ON THE OPTICAL AXIS

[0098] Advantageously, a leg 21 has on its main surface 211a, a contact zone with the optical assembly 1 intersecting with the optical axis Xb. Preferably, the contact zone is located between the distal connection portion 211 of the leg 21 and the rear of the mirror 13.

[0099] In accordance with this embodiment, the support 2 comprises two other legs 21 distributed symmetrically relative to the optical axis and / or so as to allow optimized balancing of the optical assembly 1 on the support 2. Advantageously, the optical assembly 1 is supported by three distal connection portions 211, three legs 21 distributed at 120°. The distal connection portions 211 are advantageously glued to the optical assembly along a vertical surface.

[0100] FUNCTIONAL APPROACH - THE OPTICAL PATH

[0101] As illustrated in [Fig.3A] and according to a preferred embodiment of the present invention, the system is structurally configured so that the beams light entering through the first lens 11 are directed towards the detector block 25 at the output of the second lens 12. An example of optical paths of light rays collimated at the input on the first lens 11 is thus represented in [Fig.3A].

[0102] The optical assembly 1 is configured so that the light rays entering through the first lens 11 pass through the latter and then converge towards the mirror 13 to be reflected and redirected onto the second lens 12.

[0103] The light beam entering through the first lens 11 is directed out of the optical assembly at the detector block 25.

[0104] According to one example, the mirror 13 is concave so as to reflect the incident rays onto the second lens 12 located at the center of the first lens 11. In other words, the incident rays reflected on the mirror 13 and coming from the first lens 11 are directed into a zone close to the center of the first lens 11. In this zone, the bonding of the second lens 12 onto the first lens 11 takes place.

[0105] According to one example, the mirror 13, the first lens 11 and the second lens 12 are aligned along the same optical axis Xb

[0106] According to one example, the focal plane of the detector 25 is positioned on the image plane of the optical assembly 1.

[0107] According to one example, the detector 25 is held on the first lens 11.

[0108] [Fig.3B] - DETECTION CONFIGURATION

[0109] As illustrated in [Fig.3B], the system is configured so as to comprise a detector block 25 supported by the support 2 via an additional support 27. The detector block 25 is thus configured so as to capture the light rays coming from the second lens 12.

[0110] According to a particular embodiment, a leg 3 is located so as to bear plane on plane with the rear of the mirror 13. According to this same example, the detector block is configured so as to be positioned at the output of the second lens 12.

[0111] According to a particular embodiment, the detector block can be integral with the optical assembly 1.

[0112] [Fig.4B] - DETECTOR BLOCK

[0113] As illustrated in [Fig.4B] and according to one example, the detector block 25 is positioned on a platform. The platform is advantageously securely connected to an additional support 27. According to an embodiment preferred by the present invention, the first lens 11 is flexibly connected to the detector block 25.

[0114] According to one embodiment, the electronics are remote from the detector block 25, in fact, they are for example directly fixed on the additional support 27. Preferably, the connection between the detector block 25 and the electronics is flexible. The detector block 25 preferably comprises an infrared detector. According to one embodiment, the detector block 25 comprises a capture portion such as a camera.

[0115] According to a preferred embodiment of the present invention, the detector block 25 comprises a capture portion which has a photosensitive part at its end. This photosensitive part is preferably attached to one of the optical elements of the system to be positioned and held precisely on the image plane.

[0116] BAFFLING SYSTEM

[0117] According to a particular embodiment, the detector block 25 comprises a baffling element 28 so as to avoid the effects of stray light. The baffling element 28 is preferably glued directly onto the first lens 11 so as to perfect the connection of the detector block 25 with the optical assembly 1.

[0118] According to a particular embodiment, the detector block 25 is fixed to the baffle element 28 by means of bolting elements. In fact, these bolting elements, preferably three in number, allow precise adjustment of the position of the detector block 25 relative to the optical assembly 1.

[0119] ALIGNMENT

[0120] The alignment of the optical elements can be carried out according to a method comprising three main steps: - the first step consists of aligning the second lens 12 relative to the first lens 11 at the time of its bonding to the latter, - the second step is an adjustment of the assembly of the two lenses in relation to the mirror 13 which will be the optical and mechanical reference for this operation. The assembly thus formed is then glued in position by means of the connecting pieces 14, - the third step allows the alignment of the detector block 25, by mechanical wedging using bolting elements.

[0121] MOUNTING ON THE SUPPORT

[0122] According to one example, the optical assembly 1 and detector block 25 are mounted on the support 2 by means of quasi-isostatic legs 21 of the bipod type. The support 2 thus ensures great stiffness during potential vibrations due to earthquakes as well as thermoelastic decoupling during the cold descent of the capture system. Indeed, the optical assembly 1 is almost indilatable while its metal support 2 will contract. The difference in expansion will be absorbed by the legs 21.

[0123] COOLING SYSTEM

[0124] According to one embodiment, the system comprises a cooling device. The cooling system is preferably positioned under the platform. Indeed, in order to limit thermal noise, it is necessary for the detector block 25 to work in a cryogenic environment. According to one embodiment, the cooling system is configured to generate cold on the detector via an aluminum interface comprising thermal braids mounted on the additional support 27.

[0125] In fact, the cooling device is configured to allow the use of the detector at around 90 K (Kelvin). Preferably the camera is selectively maintained at around 130 K.

[0126] Thus, a thermoelastic decoupling takes place in the system between the detector and its cooling system because there is no 'rigid' connection between the detector block and 27. Thanks to this system, the malfunctions of the detector in operation are limited.

[0127] According to one example, this is a braid cooling system.

[0128] MATERIALS

[0129] The optical assembly 1 comprises elements made from silica. These may be optical glass or quartz glass.

[0130] Preferably, all the elements are made from identical materials and / or are made from materials in identical proportions. Advantageously, the mirror is covered with a reflective film. This may in particular be a concave mirror. Preferably, an adhesive or an epoxy resin is used to secure the elements of the optical assembly. In fact, the optical elements glued together form a unitary block.

[0131] The support may be made from a metal base, such as steel or aluminum, titanium or nickel.

[0132] The invention is not limited to the embodiments previously described.

[0133] Digital References • 1 / optical assembly • 11 / first lens • lia / flat peripheral surface • 12 / second lens • 13 / mirror • 13a / flat peripheral surface • 14 / connecting piece • 14a / flat surface • 2 / support • 21 / leg • 211 / distal connecting portions • 211a main surface • 22 / base • 25 / detector 26 / cooler 27 / additional support 28 / baffle element XI / optical axis

Claims

Claims

1. Catadioptric imaging system comprising an optical assembly (1), a support (2), and a detector (25) configured to capture the rays exiting the second lens (12), the optical assembly (1) being supported by the support (2), the optical assembly (1) comprising along an optical axis (XI): - a concave mirror (13), - a first lens (11) distant from the mirror (13), - a second lens (12) positioned at the center of the first lens (11), - a connecting portion securing the mirror (13) and the first lens (12), the mirror (13), the first lens (11), the second lens (12) and the connecting portion each being made of a silica-based material, the system being characterized in that the connecting portion comprises at least two connecting pieces (14) made of a silica-based material and which join the first lens (11) and the mirror (13) by their peripheries,the at least two connecting pieces (14) being spaced on the contour of the mirror (13) and on the contour (13c) of the first lens (11) and in that the detector block (25) is positioned integrally with the optical assembly (1), the detector block (25) comprising a baffling element glued directly onto the first lens (11), the detector block (25) being fixed to the baffling element by means of bolting elements.,

2. System according to the preceding claim in which at least two connecting pieces (14) are identical.

3. System according to any one of the preceding claims in which at least two connecting pieces (14) are arranged symmetrically relative to a plane comprising the optical axis (XI).

4. System according to any one of the preceding claims in which at least two connecting pieces (14) are arranged symmetrically relative to a vertical plane which comprises the optical axis (XI).

5. System according to any one of the preceding claims in which at least two connecting pieces (14) are arranged symmetrically relative to a horizontal plane comprising the optical axis (XI).

6. A system according to any preceding claim comprising exactly four connecting pieces (14) distributed equiradially relative to the contour of the mirror (13) and the contour of the first lens (11).

7. System according to any one of the preceding claims in which at least one connecting part (14) comprises a flat surface (14a) facing towards the outside of the optical assembly (1), the flat surface (14a) being configured to cooperate with a distal connecting portion (211) so that in a mounting configuration of the optical assembly (1) on the support (2) the flat surface (14a) is parallel to a vertical plane.

8. System according to any one of the preceding claims in which the support (2) comprises at least one leg (21) comprising a distal connection portion (211) integral with the optical assembly (1).

9. System according to the preceding claim in which the distal connection portion (211) of each leg (21) is secured to the optical assembly (1) by gluing.

10. System according to any one of the two preceding claims, in which the support (2) comprises exactly three legs (21) whose respective distal connection portions (211) are distributed at 120° around the optical assembly (1).

11. System according to any one of the three preceding claims in which the distal connection portion (211) of a first of the legs (21) has a bearing surface on the optical element (1) extending along a plane whose normal direction at the center of this plane is parallel to the optical axis (XI).

12. System according to the two preceding claims in combination, in which the distal connection portions (211) of a second and a third of the legs (21) each have a bearing surface on the optical element (1) extending along a plane on the optical assembly (1) whose normal direction at the center of this plane intersects the optical axis (XI) non-perpendicularly, said normal directions intersecting the optical axis at the same point.

13. System according to any one of the preceding claims, in which the elements of the optical assembly (1) are made of the same material.

14. System according to any one of the preceding claims in which at least one of the mirror (13) and the first lens (11) comprises a planar peripheral surface (11a, 13a) configured to allow plane-to-plane bonding of the part at least one of the at least two connecting parts (14).

15. Method for mounting the system according to any one of the preceding claims comprising the following steps: - alignment of the second lens (12) relative to the first lens (11) - bonding of the second lens (12) to the first lens (H) - adjustment of the first and second lens assembly (11, 12) relative to the mirror (13), - securing the first and second lens assembly (11, 12) relative to the mirror (13), using at least two connecting pieces (14), - alignment of the detector block (25) relative to the first and second lens assembly (11, 12), comprising bonding of the baffling element of the detector block (25) directly to the first lens (11) and mechanical wedging of the detector block (25) by means of bolting elements.

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