Optical terminal device for space satellite telescope

Abstract

Title: Optical Terminal Device for a Space Satellite Telescope The invention relates to an optical terminal device for a space satellite telescope, consisting of a first light beam (1) transmitted to Earth and a second light beam (2) received from Earth, comprising local (11d) and global (11e) pointing mirrors, a linking module (11ab), and a pupil imaging module (10). The local pointing mirror is configured to receive and orient one of the first and second light beams. The global pointing mirror (11e) is configured to receive and orient both the first and second light beams. The linking module comprises converging (11a) and diverging (11b) optical components configured together to increase the size of the first light beam and decrease that of the second light beam.The pupillary imaging module and the linking module are configured, with the local and global pointing mirrors so that they are the image of each other. Figure for the abbreviation: Fig. 3A.

Description

Title of the invention: Optical terminal device for space satellite telescope Technical field

[0001] The present invention relates to the field of optical terminal devices for space satellite telescopes. It finds a particularly advantageous application in the field of optical space telecommunications terminals, preferably for transatmospheric links and preferentially for links between the Earth and the GEO orbit or the LEO orbit. STATE OF THE ART

[0002] In the field of space optical telecommunications, there is equipment on board space optical telecommunications terminals for transporting a data stream to Earth (or from Earth) or to other satellites (or from other satellites) located in the same orbit or a different orbit. In particular, a distinction is made between LEO (low earth orbit), MEO (medium earth orbit) and GEO (geostationary orbit). In the case of a data stream sent from a satellite 31 to Earth 30, we speak of downlink signals, as illustrated by the arrow F1 in [Fig.l], as distinguished from uplink signals coming from Earth 30 (illustrated by the arrow F2).

[0003] In the case of a data flow circulating between satellites located in the same constellation (where the distances to be covered are of the order of a few thousand kilometers), the pointing and tracking of the transmitted beam and the received beam are generally carried out by means of technical solutions comprising a telescope making it possible to shape the transmission beam and to collect the reception beam. These solutions comprise a module, downstream of the telescope according to the propagation direction of the received beam, making it possible to process the switching between the transmission beam and the reception beam. The pointing of the beams is typically carried out upstream of the telescope using a tip-tilt mirror (or steerable mirror in French) or a dual-axis steerable head.

[0004] In the case of transatmospheric optical links (and in particular, in the case of data transmission between GEO orbit and Earth or between LEO orbit and Earth) the distances covered are typically longer. They can for example reach 36,000 km. In the case of transatmospheric optical links, due to the effects of turbulence, absorption and the greater distance covered, the beams implemented have a large diameter and carry a significant power, which implies the need to use large diameter telescopes.

[0005] The technical solutions implemented for pointing, tracking and routing data in the case of satellites located in the same constellation, such as tip-tilt mirrors or dual-axis orientable heads, are therefore difficult to transpose.

[0006] Indeed, these technical solutions are unsuitable for use on transatmospheric optical links (and in particular, in the case of links between the GEO orbit and the Earth or between the LEO orbit and the Earth) due to the volumes occupied by the light beams being too large and the tip-tilt mirror tilting speeds which are then insufficient.

[0007] Technical solutions for transatmospheric optical links (and in particular, in the case of links between the GEO orbit and the Earth or between the LEO orbit and the Earth) have therefore been developed. In this type of technical solution, the telescope, whose role is to shape the emission and reception of light beams, is fixed or mobile so as to allow a rough modification of its orientation to perform the coarse pointing function. The other functions, beam steering, fine pointing and connection with the fiber links are performed by means of a module located downstream of the telescope according to the direction of propagation of the received beam.The disadvantage of these technical solutions lies in the fact that downstream of the telescope, a large number of optical components in a limited space will be present in order to carry out a large number of functions (beam steering, fine pointing and connection with fiber links).

[0008] One of the disadvantages of these technical solutions therefore lies in the fact that these technical solutions remain complex. They are also not suitable for the incorporation of additional functions, in particular, such as isolation, circulation or wavelength division multiplexing (WDM) functions, because these would further complicate the architecture of these technical solutions. The development of a more optimized organization of these technical solutions is then necessary.

[0009] An object of the present invention is therefore to propose a technical solution improving the pointing, tracking, and preferably the routing, of optical beams by space satellite telescope, for use in particular on transatmospheric optical links (and in particular, in the case of links between the GEO orbit and the Earth or between the LEO orbit and the Earth), by making it possible to overcome at least in part the drawbacks of existing solutions.

[0010] Other objects, characteristics and advantages of the present invention will appear from consideration of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0011] To achieve this objective, according to one embodiment, an optical terminal device for a space satellite telescope is provided, with a first light beam transmitted to Earth and a second light beam received from Earth. Advantageously, the device comprises: • a first orientable mirror, called a “local pointing mirror”, configured to receive and orient one of the first light beam and the second light beam, and preferably only one of the first beam and the second light beam, • a second orientable mirror, called a “global pointing mirror”, configured to receive and orient the first light beam and the second light beam, • an optical module called a “linking module” comprising a first optical component and a second optical component, the linking module being configured to make a link between the global pointing mirror and the local pointing mirror by being arranged between the global pointing mirror and the local pointing mirror, the first optical component and the second optical component being configured together to increase a size of the first transmitted light beam and decrease a size of the second received light beam, during their propagation in the linking module, • an optical module called “pupillary imaging”, • the pupil imaging optical module and the link module being configured, with the local pointing mirror and the global pointing mirror such that the local pointing mirror and the global pointing mirror are the image of each other.

[0012] Thus, the optical terminal device for a space satellite telescope makes it possible to improve the pointing, tracking, and preferably the routing of optical beams of an optical telecommunications terminal, for intersatellite and transatmospheric telecommunications, in particular, and in particular between the GEO orbit and Earth. More particularly, this device allows an improvement in the architecture of the optical terminal between a stage dedicated to the pointing and tracking functions, and a stage dedicated to routing.

[0013] More specifically, the configuration of the optical terminal device for a space satellite telescope makes it possible to define a first stage, for example an upper stage, corresponding to the area of ​​space in which the first light beam and the second light beam have an increased size and a second stage, for example example a lower floor, connected to the first floor by the link module, corresponding to the area of ​​space in which the first light beam and the second light beam have a reduced size. The link module connects these two floors by modifying the size of the beams. By this modification of beam size, the link module therefore optically connects the floor dedicated to the pointing and tracking functions, and the floor dedicated to switching.

[0014] Due to the existence of these two stages configured to obtain different beam sizes, it is possible to integrate, according to their characteristics and in a way to simplify and make the device more versatile, technical functions allowing the correct operation of the optical terminal device either on the first stage or on the lower stage. Thus, more precisely, the beam pointing and tracking function (PAT function for "Pointing And Tracking" in English), that is to say to give the beams the desired direction, can be integrated on the first stage while the functions of switching and connection with the optical fibers can be integrated on the second stage.

[0015] The link module therefore has a beam enlarger function so that beams of a size compatible with transatmospheric links are handled for the pointing and tracking functions while beams of reduced size are handled during switching and connection with the optical fibers. It is in fact simpler to integrate the sensors making it possible to follow the direction of propagation of the transmission and reception beams on the upper stage where the beams can be quite wide, that is to say typically have a diameter of between 10 and 20 mm, in comparison to the lower stage where the beams have a smaller diameter, that is to say a diameter of less than 1 mm. On the other hand, on the upper stage, the switching functions will be complex to carry out because they will be sensitive to pointing errors.

[0016] The configuration of the optical terminal device for a space satellite telescope due to its configuration and therefore the presence of two stages corresponding to different beam sizes will simplify the integration of additional (potentially different) functions such as isolation, circulation, coupling or wavelength division multiplexing (WDM) functions while limiting stability constraints and reducing the sensitivity of the integrated optics and thus the complexity of the opto-mechanical structures.

[0017] More generally, the link module makes it possible to decouple the beam size between two stages generally equipped by different equipment manufacturers. The pointing and tracking part on the upper stage, traditionally handled by the satellite designer, and the beam routing and connection with the fibers part on the upper stage lower, traditionally handled by the terminal manufacturer. The optical train of the upper stage is generally different from one satellite designer to another and can be quite complex. Here, the link module makes it possible to overcome these specificities depending on the telescopes by coupling in a simplified way equipment that can come from different designers.

[0018] Furthermore, the pupil imaging optical module makes it possible, at the level of the orientable mirrors, to maintain the transverse position of the beams and in particular to prevent a movement of the global pointing mirror or the local pointing mirror from generating a displacement of the beam. Thus, at the level of the local and global pointing mirrors, whatever their positioning, the pupil imaging optical module maintains the transverse position of the first and second light beams. It is therefore understood that the coupling losses can be reduced.

[0019] Another aspect relates to a space satellite telescope optical terminal assembly comprising the space satellite telescope optical terminal device and a satellite telescope, preferably a geostationary space satellite.

[0020] Another aspect relates to a method for transmitting and receiving optical beams by a space satellite telescope, a first light beam transmitted to Earth and a second light beam received from Earth, implementing the optical terminal device for space satellite telescope or the optical terminal assembly for space satellite telescope, comprising: • A support and an increase in the size of the first light beam by the link module, comprising a propagation of the first light beam from the second optical component to the first optical component, • A support and a reduction of the size of the second light beam by the link module, comprising a propagation of the second light beam from the first optical component to the second optical component, • After the first light beam has been taken over and increased in size by the linking module, and before the second light beam has been taken over and decreased in size by the linking module, an orientation of the first and second light beams by the global pointing mirror, • After the connection module has taken over and reduced the size of the second light beam, an orientation of the second light beam by the local pointing mirror, or before the connection module has taken over and increased the size of the first light beam, an orientation of the first light beam by the pointing mirror local.

[0021] Thus, this method of transmitting and receiving optical beams by a space satellite telescope makes it possible, like the optical terminal device previously presented, to create two stages, the first stage and the second stage, in order to obtain a displacement of the beams from one stage to another associated with a modification of the diameter of the beams. More precisely, on the first stage, the light beams have a larger size than on the lower stage. For example, the light beams of the first stage have a diameter of between 5 and 10 mm while on the second stage, the light beams have a diameter having a reduced value, that is to say a value less than 1 mm, preferably a value of between 300 pm and 500 pm. It is important to note that the typical dimensions of the beams in the optical telecom components of the fiber network are between 250 pm and 500 pm.It is therefore sought to approach these values ​​so that the pointing errors are not too severe. This configuration makes it possible in particular to simplify the integration of functions at each stage and thus to simplify the emission and reception of optical beams, in particular for transatmospheric links (and in particular, in the case of links between the GEO orbit and the Earth or between the LEO orbit and the Earth). BRIEF DESCRIPTION OF THE FIGURES

[0022] 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:

[0023] [Fig. 1] [Fig. 1] represents the positioning of the space satellite relative to the Earth where the beams sent and received can be viewed, according to an exemplary embodiment.

[0024] [Fig.2A] [Fig.2A] represents the reflection of a light beam on an optical part, depending on whether an error in angle or in position of the optical part is configured.

[0025] [Fig.2B] [Fig.2B] represents a graph showing the curve of the value of the uncertainty on the position of a light beam and that on the angle of a light beam (following its reflection (illustrated in [Fig.2A]) on an optical part on which an error on the position and on the angle with respect to a normal has been configured) as a function of the size of the beam.

[0026] [Fig.3A] [Fig.3A] represents the device according to an exemplary embodiment, in which the focusing function is performed by the connection module and the telescope.

[0027] [Fig.3B] [Fig.3B] represents the device according to another exemplary embodiment, in which the focusing function is performed in particular by a lens.

[0028] [Fig.3C] [Fig.3C] represents the device according to the invention according to an example of realization, in which the first set and the second set can be observed.

[0029] [Fig.4] [Fig.4] represents an example of the device, according to a view where the path of the second light beam can be observed from the first optical component to the local pointing mirror, and in which the focusing function is performed by the link module and the telescope.

[0030] [Fig.5] [Fig.5] shows the beams sent to Earth and received from Earth where the forward pointing angle can be observed.

[0031] [Fig.6] [Fig.6] shows an example of the device, according to a view where the path of the first light beam and the path of the second light beam can be observed from the overall pointing mirror to the second optical component of the link module.

[0032] [Fig.7] [Fig.7] represents the slope of the optical zone of the first optical component and of the second optical component seen by the beams when the first optical component and the second optical component are mirrors having a free shape, according to an exemplary embodiment.

[0033] [Fig.8A] [Fig.8A] represents the connection module according to a first example, in which the beams are only moved and their size is modified.

[0034] [Fig.8B] [Fig.8B] represents the linking module according to a second example, in which the linking module is further configured to modify the irradiance distribution of the beams.

[0035] [Fig.9A] [Fig.9A] represents a diagram showing the values ​​of the power Pr, the PRIB (for “Power Ratio In the Bucket” in English translated into French as “power ratio in the bucket”) and the irradiance Imax in the ideal case of an emission from a full and uniform pupil with a diameter of 500 mm, without central obscuration.

[0036] [Fig.9B] [Fig.9B] represents a diagram showing the values ​​of the power Pr, the PRIB (for “Power Ratio In the Bucket” in English translated into French as “power ratio in the bucket”) and the irradiance Imax in the classic case of a Gaussian emission with a central obscuration on the telescope.

[0037] [Fig.9C] [Fig.9C] represents a diagram showing the values ​​of the power Pr, the PRIB (for “Power Ratio In the Bucket” in English translated into French as “power ratio in the bucket”) and the irradiance Imax in the case of a link module capable of transforming a Gaussian profile into a uniform profile.

[0038] [Fig. 10] [Fig. 10] represents a view of [Fig.5] optically reproduced at the level of the optical beam splitting module.

[0039] [Fig. 11] [Fig. 11] represents a schematic perspective view of the optical beam splitting module according to an exemplary embodiment.

[0040] [Fig. 12] [Fig. 12] represents a schematic front view of the optical beam splitting module according to the embodiment illustrated in [Fig. 11] on which the impact of the beams on the optical beam splitting module can be observed.

[0041] [Fig. 13] [Fig. 13] represents the separation module according to an exemplary embodiment in which the separation module has a U-shape.

[0042] [Fig. 14] [Fig. 14] represents the separation module according to an exemplary embodiment in which the separation module is a thin-edged mirror having a rectangular shape.

[0043] 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

[0044] 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.

[0045] According to one example, the pupil imaging optical module comprises at least one lens.

[0046] According to one example, the pupil imaging module and the connecting module are made by the same optical components. More particularly, according to one example, the pupil imaging module and the connecting module are made by the first optical component and the second optical component, possibly supplemented by at least one lens.

[0047] Additionally, according to one example, the pupil imaging module is distinct from the linking module and the pupil imaging module preferably comprises at least one lens.

[0048] According to an example: • the first optical component is convergent and the second optical component is divergent, the pupil imaging optical module preferably comprising at least one lens, or • wherein the first optical component is convergent and the second optical component is convergent.

[0049] According to an example, the linking module is configured so that the ratio between the size of the first light beam, after its propagation in the linking module and the size of the first light beam before its propagation in the linking module and the ratio between the size of the second light beam, before its propagation in the linking module and the size of the second light beam after its propagation in the linking module are between 5 and 10, preferably are equal to 6.5.

[0050] Thus, thanks to this configuration, the optical terminal device for a space satellite telescope makes it possible to obtain light beams having the desired size depending on whether they are used for the tracking and pointing functions or for the switching functions.

[0051] According to one example, the device comprises a first assembly configured to interface between the link module and the telescope.

[0052] According to one example, the device comprises a second assembly configured to direct the beams between the connection module and the optical fibers.

[0053] According to one example, the first set comprises the global pointing mirror.

[0054] According to one example, the second assembly comprises at least the pointing mirror local. According to one example, the second assembly comprises the third mirror, the second lens, the first lens and the beam splitting optical module.

[0055] According to an example, the second assembly comprises the local pointing mirror, the third mirror, the second lens, the first lens, the beam splitting optical module, the collimator and the connection zone with the optical fibers.

[0056] According to one example, in the first set, the beams have a diameter having a value between 10 mm and 20 mm.

[0057] According to one example, in the second set, the beams have a diameter having a value less than 1 mm.

[0058] According to one example, the link module is configured so that: • upstream of the first optical component, the first and second beams propagate in a first zone, • downstream of the second optical component, the first and second beams propagate in a second zone, the first zone and the second zone being distinct and at least partly superimposed on each other.

[0059] According to one example, the first assembly is arranged in the first zone.

[0060] According to one example, the second assembly is arranged in the second zone.

[0061] According to one example, at least one, and preferably each, of the first optical component and the second optical component is a mirror.

[0062] According to one example, the device comprises a so-called “transformation” optical module configured so that: • after the connecting module, the first light beam has a uniform irradiance distribution, and, before the connecting module, the first light beam has a Gaussian irradiance distribution, and • after the connection module, the second light beam has a dis Gaussian irradiance distribution, and, before the link module, the second light beam has a uniform irradiance distribution.

[0063] According to one example, the first optical component and the second optical component being mirrors, the transformation module comprises the connection module.

[0064] According to one example, the link module is configured such that • after the connecting module, the first light beam has a uniform irradiance distribution, and before the connecting module the first light beam has a Gaussian irradiance distribution, and • after the connecting module, the second light beam has a Gaussian irradiance distribution, and before the connecting module, the second light beam has a uniform irradiance distribution.

[0065] It is therefore understood that the role of the transformation module is then to be implemented by the connection module. Thus, the two previous configurations of the device make it possible to obtain the desired irradiance distribution depending on whether one is at the telescope interface or at the positioning of the optical fibers. Indeed, at the location where the telescope interface is located, that is to say after the global pointing mirror according to the propagation of the first light beam, due to the configuration of the telescope interface, it is desirable, for better performance of the telescope, that the light beams have a uniform irradiance distribution.More specifically, the telescope interface naturally exhibits beam profiles having a uniform irradiance distribution, this being due to the transfer function of the telescope which is formed by an entrance pupil having a uniform disk with a central shutter. On the other hand, at the terminal level and more precisely where the optical fibers are located, due to the configuration of the optical fibers, it is desirable that the light beams have a Gaussian irradiance profile. Indeed, generally speaking, for better performance of the optical fibers, the irradiance profile of the beams propagating in the optical fibers are essentially Gaussian, which is particularly the case for the emission beams emerging from optical fibers. According to this example, the first optical component and the second optical component are preferably mirrors.

[0066] According to one example, the optical terminal device for a space satellite telescope comprises: • an optical component called a focusing component configured to form, at a plane, an image of the first light beam and an image of the second light beam, the image of the first light beam being distinct from the image of the second light beam, • an optical beam splitting module configured to allow one of the first light beam and the second beam to pass through light, and to deflect the other among the first light beam and second light beam.

[0067] In the case of data transmission from GEO orbit to Earth and from Earth to GEO orbit, the distance between Earth and GEO orbit is significant. Because of this distance, the rotation of the Earth between the emission of a beam and its reception on Earth is not negligible compared to the intrinsic divergence of the beams. The communication area on Earth thus moves with the rotation of the Earth between the emission of the beam on Earth and its reception. When transmitting a beam to Earth, in GEO orbit, the direction of propagation of the downward flow is therefore oriented relative to the direction of propagation of the upward flow so as to form an angle between these two directions, called the "forward pointing angle".Thus, at a time t corresponding to the sending of the first beam and the reception of the second beam, the area where the station is positioned on Earth from which the second beam was emitted and the area towards which the first beam is directed on Earth are distinct due to the presence of this forward pointing angle, to take into account the rotation of the Earth.

[0068] By equating the distance between the GEO orbit and the Earth to infinity, the image of the Earth by the focusing optical function (of the focusing optical component) of the device can be observed on a plane (or a set of planes) close to or coincident with the image focal plane of the focusing optical function (of the focusing optical component). At this plane, due to the forward pointing angle, the distinct images of the first beam and the second beam at the Earth can be observed. Thus, at this plane, the device makes it possible to view the first beam distinctly from the second beam, in order to be able to separate them by the optical beam splitter module. The optical path of the first and second beams are therefore distinct at this plane, which allows their separation by the optical beam splitter module.

[0069] It is therefore understood that the device uses the forward pointing angle implemented in the GEO orbit to make a geometric separation of the first and second beams, and not a spectral separation as is the case for solutions implementing a dichroic filter. Consequently, the wavelengths of the first light beam and the second light beam are not taken into account in the process of separating the first beam from the second beam. The first beam and the second beam can thus spread over close spectral bands, for example contiguous, and preferably superimposed.

[0070] Furthermore, since the optical beam splitting module allows the interference of the other of the first light beam and the second beam to pass through without being in contact with one of the first beam and the second beam, light is limited, and preferably avoided. In addition, the beam transmitted without contact with the separation module does not suffer any power loss.

[0071] This solution is therefore particularly suitable for the transmission of data between the Earth and the GEO orbit. As this transmission is carried out by optical beams, the transmitted rate can be significant in comparison with those transmitted by means of communication satellites operating thanks to the emission of radio waves.

[0072] Also, the local pointing mirror and the global pointing mirror make it possible to manage the forward pointing angle of the beams. The use of two mirrors makes it possible to act independently on the transmission and the reception. In particular, the global pointing mirror makes it possible to receive and orient the second beam so that it heads in the desired direction and therefore reaches the separation module (directly or indirectly). The local pointing mirror makes it possible to receive and orient the first beam so that it also heads in the desired direction and therefore with the desired angle towards the Earth. The local pointing mirror also makes it possible to receive and orient the second beam so that it also heads towards the separation module (directly or indirectly) with the desired direction). According to one example, the local pointing mirror is configured to receive and orient the second light beam received from the Earth.

[0073] According to one example, the first optical component, the second optical component, preferably with the telescope, form the focusing optical component. According to another example, and as detailed later, the focusing optical component further comprises or is an additional optical component to the connecting module, for example a lens.

[0074] By configuring the connection module, the separation module can therefore be positioned on the second stage because the separation module allows the switching function and therefore the pointing function.

[0075] According to one example, the optical terminal device for a space satellite telescope further comprises a pupil having a diameter greater than or equal to 300 mm, preferably greater than or equal to 350 mm and preferably greater than 400 mm, the pupil is the exit pupil of a satellite telescope, preferably a geostationary space satellite. According to one example, the exit pupil is the exit pupil of the telescope of the assembly according to the second aspect of the invention.

[0076] In order for the first beam and the second beam to be separated, it is preferable for their divergence to be less than the front pointing angle. Given that their divergence is directly a function of the diameter of the pupil, and in particular of the exit pupil of the telescope and therefore of the internal pupil image of the exit pupil, a pupil diameter in these ranges allows the front pointing angle not to be negligible compared to the divergence of the beams.

[0077] According to one example, the beam splitting optical module is configured to reflect the other of the first light beam and the second light beam.

[0078] Thus, in this manner, the other of the first light beam and the second light beam can be, after having been in contact with the separation module, directed in a simple manner towards a direction different from the direction towards which one of the first light beam and the second light beam will be directed. The manufacture of the beam separation module is thus simplified, in particular compared to dichroic filter treatments.

[0079] According to one example, the beam splitting optical module comprises an opening positioned such that one of the first light beam and the second light beam passes through the opening into the beam splitting optical module, without being in contact with said module.

[0080] Thus, the positioning of this opening allows one of the first light beam and the second light beam to pass through the space where the separation module is located without being in contact with the separation module.

[0081] According to one example, the opening of the optical beam splitting module is a hole.

[0082] In the case where the opening describes a hole, that is to say an opening whose periphery is closed, and preferably a hole having a symmetry of revolution, for example a substantially circular or ellipsoidal hole, the separation module makes it possible to overcome the rotation of the satellite. Indeed, if the satellite rotates on itself, the hole can allow the light beam to pass regardless of the rotational position of the satellite, relative to other shapes of the separation module. The separation of the light beams is thus simplified.

[0083] According to one example, the beam splitting optical module comprises a mirror, the mirror comprising the aperture, preferably the hole.

[0084] Thus, the fact that the separation module is a mirror comprising the opening (and therefore the hole) makes it possible to form a reflective surface so that the other of the first light beam and the second light beam can be reflected on the separation module.

[0085] According to one example, the optical beam splitting module is based on a material chosen from the group consisting of: glass, crystal, metal and ceramic.

[0086] These materials allow a reflective surface to be formed on the surface of the separation module.

[0087] According to one example, in the method of transmitting and receiving optical beams by a space satellite telescope, the space satellite telescope being a space satellite telescope for transatmospheric link (and in particular, in the case of links between GEO orbit and Earth or between LEO orbit and Earth), preferably the space satellite telescope is a geostationary space satellite telescope.

[0088] According to an example, the method for transmitting and receiving optical beams by a space satellite telescope, implementing the optical terminal device for a space satellite telescope or the optical terminal assembly for a space satellite telescope comprising the optical terminal device for a space satellite telescope and a space satellite telescope, wherein the space satellite telescope is a geostationary space satellite telescope, comprises: • A formation in a plane of an image of the first light beam and an image of the second light beam by the focusing optical component, the image of the first light beam being distinct from the image of the second light beam, • Following the formation of said images, a separation at said plane, by the optical beam separation module, of the first light beam and the second light beam, the separation comprising a transmission of one of the first light beam and the second light beam without the optical separation module being in contact with said beam, and a deflection of the other of the first light beam and second light beam.

[0089] Thus, this method makes it possible to form on a plane an image of the first light beam distinct from that of the second light beam, in order to be able to geometrically separate the first light beam and the second light beam and to direct them. This method limits, and preferably avoids, interference of one of the beams on the other beam. Also, the wavelengths transported by the two beams can overlap at least in part, and preferably be identical. The transmitted data rates can be significant (in comparison to those transported by radio waves).

[0090] According to one example, in the method of transmitting and receiving optical beams by a space satellite telescope, the first light beam and the second light beam have a range of wavelength values ​​at least partially overlapping, preferably the first light beam and the second light beam have the same range of wavelength values.

[0091] Thus, the first light beam and the second light beam can have the same wavelengths. It is in particular possible for the entire C band to be used for the emission of beams and also for the reception of beams. This therefore allows a significant gain in throughput.

[0092] According to one example, in the method, the optical beam splitting module comprises a mirror, the mirror comprising an aperture, preferably a hole, when separating the first light beam and the second light beam, the beam splitting optical module transmits one of the first light beam and the second light beam through the aperture, and reflects the other of the first light beam and the second light beam through the mirror.

[0093] According to one example, in the method, when separating said beams, the first light beam is transmitted without contact with the beam splitting module, and the second light beam is deflected.

[0094] Since the first light beam has a greater power compared to the second light beam, it is transmitted by the separation module while the second light beam is deflected by the separation module. In this way, the light beam having the higher power does not come into contact or only slightly with the separation module, which limits and preferably avoids the diffusion of the high-power beam on the separation module and increases the resistance of the reflective treatment of the separation module. The interference of the lower-power beam by the higher-power beam is therefore limited, and preferably avoided. Although this configuration is the most frequently implemented, another possible configuration is to allow the low-power beam to pass through the hole and to reflect the high-power beam.

[0095] According to one example, in the method of transmitting and receiving optical beams by a space satellite telescope, the power of the first light beam is between 1 W and 1000 W, preferably between 5 W and 1000 W.

[0096] Thus, the first light beam is configured to travel a significant distance and in particular to go from GEO orbit to Earth.

[0097] According to one example, the method comprises, before the step of providing a device, the following step: • reception by the device of the second light beam and sending by the device of the first light beam, the first light beam being transmitted towards the Earth and the second light beam being received from the Earth, the first light beam and the second light beam have between them a non-zero angular offset, and preferably greater than 15 prad.

[0098] The non-zero angular offset present between the first light beam and the second light beam corresponds to the forward pointing angle between the first and second light beams which is fixed so as to take into account the non-negligible distance traveled by the Earth (due to its rotation) during the propagation of the first light beam from the GEO orbit to the Earth.

[0099] In the context of the present invention, the term “distinct” in the expression “one image is distinct from another image” means that these two images are not in contact and that they are positioned at a distance from each other.

[0100] In the following detailed description, terms such as "horizontal", "vertical", "longitudinal", "transverse", "upper", "lower", "top", "bottom", "upstream", "downstream" may be used. These terms must be interpreted relatively in relation to the normal position of the optical terminal device for a space satellite telescope and the propagation of the light beams in this device. For example, an "upstream" element is an element of the module placed before another so-called "downstream" element following the direction of propagation of the light beams in the module. It is considered that the direction of propagation of the light beams in the module starts from the side of the optical terminal device for a space satellite telescope and goes towards the Earth (for the first light beam) and starts from the Earth and goes towards the optical terminal device for a space satellite telescope (for the second light beam)..

[0101] A reference will also be used whose longitudinal or rear / front direction corresponds to the x axis, the transverse or right / left direction corresponds to the y axis and the vertical or down / up direction corresponds to the z axis.

[0102] In the present invention, the term "geostationary space satellite" means a satellite positioned in the GEO orbit but also in orbits close to the GEO orbit, i.e. in orbits located at an altitude ranging from 30,000 km to 38,000 km above the surface of the Earth. The term transatmospheric (optical) link here more particularly reflects an optical link between two elements, for example between the Earth and a satellite or between two satellites, spaced apart by a distance at least greater than 350 km, and preferably greater than 800 km and preferably between 4000 km and 6000 km (in particular for a link between two LEO satellites communicating in a constellation).

[0103] The device, the optical terminal assembly and the method are now described according to several particular exemplary embodiments.

[0104] According to one embodiment, the optical terminal device for a space satellite telescope is associated with a space satellite telescope which can advantageously be located in a LEO, MEO or GEO orbit, and also be able to communicate with another satellite located in the same orbit (in the context of ISL links in English for "intersatellite links" in French). More precisely, for the implementation and use of the optical beam splitting module, the space satellite telescope can only be located in a GEO orbit and not in LEO or MEO orbits.

[0105] The satellite telescope may be configured in particular to transmit and receive beams in transatmospheric optical links. The optical terminal device for a space satellite telescope according to the invention, as illustrated in figures 3A and 3B, is configured to adapt the size, for example the diameter, of a first light beam 1 transmitted towards the Earth and of a second light beam 2 received from the Earth. The size of the beam may in particular correspond to the longest dimension located on a cross-section of the beam, and more particularly its diameter.

[0106] Thus, the device makes it possible to modulate the size of the beams according to the function to be performed at the different locations of the optical terminal. For this, the optical terminal device comprises a connection module 1 lab comprising a first optical component 1 la and a second optical component 11b. The first optical component 1 la and the second optical component 11b preferably each receive the first light beam 1 and the second light beam 2.

[0107] The link module 1 lab is configured to separate the path of the first 1 and second 2 beams into two sets or stages 1 labl, 1 lab2, the first 1 and second 2 beams having distinct sizes between these two stages llabl, llab2. In the following, it is considered, without limitation, that the diameters of the beams are modified by the link module. The two stages 1 labl, 1 lab2 allow the separation of the PAT (Pointing And Tracking) part on the upper stage llabl, traditionally handled by the satellite designer, and the beam routing and connection part with the fibers on the lower stage 1 lab2, traditionally handled by the terminal manufacturer. The link module 1 lab allows the size of the beams to be modified and thus to maintain a size for the PAT compatible with the transmission of a beam for transatmospheric links, and to reduce the diameter for the routing and connection part.Thus, according to this example and also in general, the fiber collimators can be located before the lens 10a according to the direction of propagation of the first light beam 1 and after the local pointing mirror 11d according to the direction of propagation of the second light beam 2 (see Figures 3A and 3B). The telescope interface can be located at the level of the global pointing mirror 11e (see Figures 3A and 3B) and the telescope can be located before the global mirror 11e according to the direction of propagation of the second light beam 2. Consequently, the emission beams can be extracted from optical fibers to then be guided towards the telescope. Conversely, the reception beams can be guided towards the reception optical fibers.

[0108] It is indeed important to adapt the size of the beams depending on whether they are a tracking and pointing function or a switching function. More precisely, as illustrated in [Fig.2A], which shows the reflection of an incident light beam 32a at 45° on an optical part, depending on whether an error in angle LA0 or in position Az is configured, it can be observed that an error in position and angle of the optical part generates an error on the reflected light beam 32b also in position and angle. Also, the graph presented in [Fig.2B] shows that the smaller the beam is, the greater the value of the uncertainty in the position (resulting from an error in the position of the part on which the light beam was reflected) and the smaller the value of the uncertainty in the angle (resulting from an error in the angle of the part on which the light beam was reflected). In addition, this graph indicates that an equilibrium zone between the value of the uncertainty in angle and that in position appears around 300 pm in diameter. The errors in angle LA0 and in position Az are configured in such a way that the modification of the position of the reflected beam (in angle and in translation) does not present a modification greater than 10% of the value of its diameter and its divergence compared to the case without error in angle or in position.

[0109] The first optical component 11a can be configured to receive and reduce the diameter (by converging it) of the second light beam 2 received from the Earth, up to the second optical component 11b which fixes the light beam to the desired diameter, and in particular by collimating it. The second optical component 11b can be configured to receive and increase the diameter of the first light beam 1 sent towards the Earth (by diverging it), up to the first optical component 11a which fixes the light beam to the desired diameter, and in particular by collimating it. Preferably, the first optical component 11a, the second optical component 11b and the telescope 7 form the focusing optical component 3 (as illustrated in [Fig.3A]), described in detail later.

[0110] According to one example, the first optical component 11a and the second optical component 11b are configured together so that the diameter of the first beam and that of the second beam is between 5 and 10 mm on the first stage and that they are less than 1 mm on the second stage.

[0111] The 1 lab link module may be selected so as to enable the beam size to be increased or decreased in order to obtain, after propagation of the beams in the 1 lab link module, the desired beam diameter. Typically, the 1 lab link module may be selected so as to enable an increase or decrease in the beam diameter of between a value of 5 and 10 (preferably to a value substantially equal to 6.5). This ratio of 5 to 10 may, for example, correspond to the ratio between the diameter of the beam in question before propagation of the beam in the 1 lab link module and the diameter of the beam in question after propagation of the beam in the 1 lab link module, for the received beam whose size is reduced.This ratio of 5 to 10 can for example correspond to the ratio between the diameter of the beam in question after the propagation of the beam in the 1 lab link module on the diameter of the beam in question before the propagation of the beam in the 1 lab link module, for the beam. transmitted whose size is increased. The link module 1 lab may in particular have a residual focal length. In [Fig.3C] the first assembly 13 and the second assembly 14 are represented. The first assembly 13 and the second assembly 14 are arranged respectively in the first 17 and second 18 zones. The first assembly 13 is configured to provide the interface between the link module 1 lab and the telescope 7. The first assembly is typically dedicated to metrology functions, such as beam tracking. The first assembly 13 may be called a “telescope interface assembly”. Typically, in the first assembly 13, the beams may have a diameter having a value between 10 mm and 20 mm.

[0112] The second assembly 14 is configured to steer the beams between the link module 1 lab and the optical fibers. The second assembly 14 may be referred to as a "steering assembly." Typically, in the second assembly 14, the beams may have a diameter having a value less than 1 mm.

[0113] The switching assembly 14 and the interface assembly 13 may be at least partly superimposed, to form a first stage and a second stage at least partly superimposed. The link module llab may then be considered as an elevator module. The advantage of this configuration is to allow a gain in compactness. Indeed, the available space is often limited in optical terminals.

[0114] Alternatively, the switching assembly and the interface assembly may be on the same floor, for example in continuity with one another.

[0115] In the context of the present application, these assemblies are designated in a non-limiting manner by the term stage, the first assembly 13 corresponding to the first stage, the second assembly 14 corresponding to the second stage.

[0116] The first set 13 may comprise the global pointing mirror lie.

[0117] The second assembly 14 may comprise the local pointing mirror 1 Id, the third mirror 1 le, the second lens 10b, the first lens 10a and the optical beam splitting module 5.

[0118] The second assembly may comprise the local pointing mirror 1 Id, the third mirror 1 le, the second lens 10b, the first lens 10a, the optical beam splitting module 5, the collimator 15 and the connection zone with the optical fibers 16.

[0119] Note that it is possible to use two converging mirrors for the link module 1 lab. However, this generates a focal point between the two mirrors which may not be desirable due to the optical power levels of the beams, and in particular of the first beam 1. However, given that the system is designed to operate in a vacuum and that there is no risk of plasma forming in the air by focusing, this risk is limited. Thus, a link module llab formed by two converging mirrors can be used to generate a focal point between the two mirrors, which can for example be used as a separation point for beams 1 and 2 by the beam splitter module.

[0120] According to a preferred example and in order to achieve the connecting function of the connecting module, at least one of, and preferably each of, the first optical component 11a and the second optical component 11b may be a mirror. The use of a mirror for the first optical component 11a and / or the second optical component 11b allows a certain compactness of the device and of the optical paths, which is advantageous for optimizing the volume occupied by the device in space applications. Provision may be made for the first 11b and / or second 11a optical components to be other optical components, for example lenses. In the following, it is considered, without limitation, that the second 11b and first 11a optical components are mirrors.

[0121] The first optical component 11a and the second optical component 11b may describe an off-axis parabola. The first optical component 11a and the second optical component 11b may consist of an afocal structure formed of two reflecting mirrors each having an off-axis parabolic surface. Equivalently, the first optical component 11a and the second optical component 11b may be off-axis parabolic mirrors.

[0122] Furthermore, the optical terminal device for a space satellite telescope further comprises a first steerable mirror 1 Id, a second steerable mirror 1 le and a pupil imaging optical module 10. The local pointing mirror » 1 Id, illustrated in [Fig.4], is configured to receive and give a desired direction to one of the beams, and preferably to the second light beam 2 coming from the Earth. The mirror 1 le, illustrated in [Fig.6], is configured to receive and give a desired direction to the first light beam 1 to be directed towards the Earth and to the second light beam 2 coming from the Earth. The local pointing mirror 1 Id is therefore arranged on the optical path of the second light beam 2, and the global pointing mirror 1 le on the optical path of the first 1 and second 2 light beams. The global pointing mirror 1 le is placed in the exit pupil of the telescope and acts on the transmission and reception at the same time.The local pointing mirror 1 Id is placed either on the transmission path or on the reception path. It therefore acts only on one of the two.

[0123] The pupil imaging module 10, illustrated in [Fig.4], may comprise at least one lens. The pupil imaging module 10 may comprise two lenses, a lens 10a and a lens 10b.

[0124] When the 1 lab link module is formed by two converging mirrors (instead of one converging mirror and one diverging mirror), the pupil imaging function can be performed by the 1 lab link module. The focal point is then located between the two mirrors, and in particular at the location where the separation module 5 can be located to separate the two beams 1 and 2. The third mirror 11 can therefore serve as pupil imaging optics.

[0125] In the case where the connection module 1 lab is formed of a converging mirror 1 la and a diverging mirror 11b, the assembly formed by the telescope and the connection module are in fact not capable of performing the pupil imaging function on their own. In this case, the focal point is outside the connection module and it is desirable to place a lens or a power optic after this focal point.

[0126] The configuration where the link module is formed by two converging mirrors is not the preferred configuration because it places a significant number of functions and therefore constraints on the mirrors of the link module.

[0127] The convergent and divergent optical components 11a and 11b coupled with the lenses 10a, 10b of the pupil imaging optical module, connect the local pointing mirror 11d and the global pointing mirror 11e so that they are the image of each other. A person skilled in the art is able to identify the possible architectures for obtaining this conjugation relationship. Pupil imaging ensures that the pupil is systematically imaged on the steerable mirrors. This means that at the level of the different images of the pupil, therefore of the mirrors, the beam remains stable. This is important because the original pupil is that of the entrance of the telescope and it is typically fixed. This therefore makes it possible to ensure that the steerable mirrors play a role in adjusting the pointing in the pupil without modifying the transverse position of the beams.

[0128] Without the pupil imaging module, a movement of the global pointing mirror 11e generates a lateral movement on the local pointing mirror 11d. Indeed, given that the local pointing mirror 11d cannot rectify a transverse position defect (while it can rectify an orientation defect), a movement of the global pointing mirror 11e causes a transverse displacement of beams which cannot be corrected by the positioning of the local pointing mirror 11d. This induces coupling losses.

[0129] The pupil imaging optical module makes it possible to remedy this problem. For this, the connection module 1 lab and the pupil imaging optical module connect the local pointing mirror 1 Id and the global pointing mirror 1 le so that they are the image of each other. Thus, a movement of the global pointing mirror 1 le no longer generates transverse displacement of the beam on the local pointing mirror 1 Id. At the level of the orientable mirrors, merged with the pupil planes of the device, an angular correction carried out by the local pointing mirror 1 Id puts the beam back in the right direction without it being displaced transversely. Coupling losses are therefore limited, and preferably avoided. On the other hand, when moving away from the pupil planes, the light beams necessarily move laterally.

[0130] According to one example, the link module 1 lab can play the role of the trans module formation. The first optical component 11a and the second optical component 11b may be mirrors configured such that after reaching the first optical component 11a and the second optical component 11b, the first light beam 1 has a uniform irradiance distribution and the second light beam 2 has a Gaussian irradiance distribution, and that before reaching the first optical component 11a and the second optical component 11b, the first light beam 1 has a Gaussian irradiance distribution and the second light beam 2 has a uniform irradiance distribution. More particularly, the shape of the mirrors may be adapted to modify the irradiance profile of the light beams.

[0131] When the optical transformation module and the linking module modify the irradiance distribution of one of the first light beam and the second light beam, they modify the irradiance distribution of the other of the first light beam and the second light beam.

[0132] To achieve this function of adapting the irradiance distribution according to the desired location, the first optical component 11a and the second optical component 11b may for example be mirrors having a free form (for "freeform mirror" in English) (or having an arbitrary shape or having a non-symmetrical optical surface). These mirrors having a free form may be produced using SPDT technology (for "Single-Point Diamond Tuning" in English meaning "Single-Point Diamond Machining" in French). [Fig.7] shows the significant slope of the optical zone of the first optical component 11a and the second optical component 11b (being mirrors having a free form) seen by the beams making it possible to carry out the desired modification of the energy distribution at the output of the connection module.

[0133] More precisely, in order to carry out the function of transforming a uniform irradiance distribution profile into a Gaussian irradiance distribution profile, the linking module may comprise two mirrors 11a and 11b which may have surfaces whose equations make it possible to describe complex solutions known as free forms. As an example, we are interested here in the case of a transformation carried out by two mirrors 11a and 11b forming a linking module between the telescope interface zone (i.e. the first zone 17) and the switching zone (i.e. the second zone 18). It is also assumed that the optical axes in the two zones (telescope interface zone and switching zone) share the same direction of propagation. In this example, it is relevant to have a uniform distribution on the side of the mirror 11a, in the interface zone with the telescope, because the latter has a uniform pupil.Let 2co be the radius of the uniform beam at the mirror 11a, in the telescope interface zone, the equation of the surface of the mirror 11a can be written: .

[0134] 0

[0135] In this equation, r and 0 represent the radial coordinates relative to the center of the beam on the mirror 11a.

[0136] In the same way, it is relevant to have a Gaussian distribution on the side of the mirror 11b, in the switching zone because this zone is connected with the optical fibers naturally having Gaussian beams. Let co be the radius of the Gaussian beam at 1 / e2 in intensity, the equation of the surface of the mirror 11b can be written:

[0137] -------______ SUh(fi i(£ ) -2.011 J ^1-^(4) dr'+^sin(8)

[0138] In this equation, r and 0 represent the radial coordinates relative to the center of the beam on the mirror 11b.

[0139] For the two equations above, Lo, 1 and h respectively represent the absolute distance between the two mirrors 11a and 11b, this same distance projected along the direction of the optical axis shared between the two zones (first zone 17 and second zone 18) and the same distance projected along the direction perpendicular to the optical axis shared between the two zones (first zone 17 and second zone 18). These equations presented as an example do not integrate the variation in the dimension of the beam between the uniform and Gaussian part. These equations can however be accommodated if an additional beam magnification function is desired. In this case, these equations define the modification of the shape of the surface to be introduced to add the desired profile transformation effect (between a uniform shape and a Gaussian shape).

[0140] [Fig.8A] shows the principle of the link module according to the example in which the beams are only moved and their size is modified. In [Fig.8A], the two transmission and reception paths retain their own profiles. [Fig.8B] shows an example in which the link module 1 lab allows a modification of the irradiance distribution of the beams in addition to allowing a displacement and a modification of the size of the beams. The type of profile then no longer depends on the nature of the beam, in transmission or in reception, but on its position in the structure, on the first or second floor. On the upper floor, or equivalently the first floor, all the beams are uniform, in line with the telescope interface. On the lower floor, or equivalently the second floor, these same beams are now Gaussian, in line with the behavior of the optical fibers located on the same floor.

[0141] In order to obtain a transformation module allowing a modification to be carried out of the irradiance distribution of the beams, elements (based on stacks of free-form lenses or axicons) can supplement or replace the connection module.

[0142] In order to obtain a transformation module, it is also possible to position a series of highly aspherical lenses. In the case of positioning a series of highly aspherical lenses, the transformation function performed by this series is performed solely by this series independently of the other components of the device. This series can be placed before or after the optical beam splitting module in the direction of propagation of beam 1. If it is placed before, only one series (and therefore only one transformer) can be placed. If it is placed after, two series (and therefore two transformers) can be placed so that there is one series per light beam.

[0143] In order to obtain a transformation module, it is also possible to use a series of successive phase masks placed one behind the other. These masks can be 2, 3, 4, 5, 6, 8 or 10 in number. This series of masks can be placed before or after the optical beam splitting module.

[0144] The choice of elements to obtain a transformation of the distribution into irradiance is a compromise between the number of elements crossed and the complexity of the requested shape. It is important to take into account that the requested shape may in particular be a source of significant diffusion which could alter the correct functioning of the connection module.

[0145] The first optical component 11a and the second optical component 11b may also be lenses or a stack of free-form lenses. The first optical component 11a and the second optical component 11b may also be axicons. In general, a person skilled in the art is able to identify the optical component capable of performing the function of adapting the desired irradiance distribution.

[0146] Generally, the optical components involved in a telescope are mirrors. However, it is also possible to find telescopes made from lenses. In the context of the present invention, the telescope may preferably be formed from concave and convex mirrors which may be accompanied or replaced by lenses.

[0147] Generally speaking, a telescope's role is to generate significant magnification. More precisely, its role is to reproduce the exit pupil of the telescope (the one with a diameter of typically around 500 mm and which is positioned on the "space" side (as opposed to the "terminal" side), into a smaller one on the "terminal" side. This second pupil, also called the "internal" pupil, the image of the exit pupil, can typically have a diameter of 5 mm to 10 mm.

[0148] In order to express the gain that the "transformer" version of the link module allows compared to the classic version, on the quality of the downlink (i.e. the emitted beam), three quantities (grouped in the antenna gain) can be cited, the power Pr, the PRIB (for "Power Ratio In the Bucket" in English translated into French by "power ratio in the bucket") and the irradiance Imax. The power Pr corresponds to the power that it is possible to extract from the pupil in the direction of emission. If the irradiance profile of the beam is Gaussian, it will necessarily be desirable to diaphragm a part of the signal corresponding to the legs of the irradiance distribution. The PRIB corresponds to the quantity of energy actually coupled into the reception pupil. More precisely, the PRIB is only interested in the energy distribution on the target, therefore on the ground.To perform this measurement, a ground target corresponding to a 100 m diameter disc is used. If all the energy is included in the 100 m circle, the PRIB is then equal to 1. The PRIB therefore does not include diaphragm losses. Thus, to calculate the energy received inside the 100 m disc by considering the energy emitted before the diaphragm, it is necessary to multiply the power Pr by the PRIB. The power Pr and the PRIB are therefore two quantities defining independent phenomena. The irradiance Imax corresponds to the most intense point of the beam on the ground. It is important to note that it would have been possible to look at the uplink as well (i.e. the received beam).

[0149] Thus, the ideal case of an emission from a full and uniform pupil of diameter 500 mm, without central obscuration is represented in [Fig.9A]. The diagram of [Fig.9A] shows that in this case, there is no loss by diaphragmation and the emitted power is therefore Pr equal to 1. In addition, the maximum irradiance at the ground is optimal and its value is used as normalization for Imax equal to 1. Finally, the PRIB is calculated at 36.3%.

[0150] The classic case of a Gaussian emission with a central obscuration on the telescope is shown in [Fig.9B]. This is the solution using the simple link module, without modification of the irradiance profile of the beams. The curves in the diagram of [Fig.9B] show the values ​​of the power Pr, the PRIB and the irradiance Imax (normalized with respect to the values ​​of the ideal case) as a function of the beam diameter. On these curves, we can observe an optimum for a diameter of approximately 420 mm, although the three parameters (power Pr, PRIB and irradiance Imax) remain much lower than the ideal case of an emission from a full and uniform pupil with a diameter of 500 mm, without central obscuration.

[0151] The case of a link module capable of transforming the Gaussian profile into a uniform profile is shown in [Fig.9C]. Compared to the ideal case (of an emission from a full and uniform pupil with a diameter of 500 mm, without central obscuration), obscuration is present and is imposed by the telescope. The curves shown in [Fig.9C] show the power Pr, PRIB and irradiance Imax (normalized to the ideal case values) as a function of the beam diameter. It can be seen from these curves that the optimum is reached for a beam diameter of 500 mm, corresponding to the diameter of the telescope pupil. Although for this case, the values ​​of Pr, PRIB and irradiance Imax do not reach the values ​​of power Pr, PRIB and irradiance Imax of the ideal case (of an emission from a full and uniform pupil of diameter 500 mm, without central obscuration), they are very close to it.

[0152] Preferably, the optical terminal device is further configured to separate and direct the first and second light beams. Advantageously, the optical terminal device for a space satellite telescope comprises an optical beam-splitting module 5 and a focusing optical component 3 configured to form, at a plane 4, an image of the Earth along the optical paths of the first 1 and second 2 beams. This makes it possible to form an image of the first light beam 1 and an image of the second light beam 2 (the object being the Earth). By "image", it is meant here that the beams can be observed at this plane 4, and the sections of these beams in this plane 4 being distinct from each other. Equivalently, at said plane 4, the paths of the first 1 and second 2 light beams are distinct and do not intersect with each other.

[0153] Due to the forward pointing angle a, illustrated in [Fig. 5], the image of the first light beam 1 is distinct from the image of the second light beam 2 ( [Fig. 10]). The optical beam splitter module 5 is positioned at said plane 4 in order to be able to separate and direct the two beams 1, 2 which can be observed as being distinct at the plane 4. The optical beam splitter module 5 occupies a position configured in such a way that 1) one of the first light beam 1 and the second light beam 2 passes through the space where the splitter module 5 is positioned without coming into contact, i.e. without touching the splitter module 5, and 2) the other of the first light beam 1 and second light beam 2 has its direction changed (or is reflected) after its contact with the splitter module 5 (Figures 10, 11 and 12). In [Fig.12], the top spot represents the beam (or the irradiance distribution of the beam) having been transmitted and the bottom spot represents the beam (or the irradiance distribution of the beam) having been reflected.

[0154] In [Fig. 10], it can be observed, at the image focal plane 3a of the lens 3, the Airy diffraction task t of the light points formed by the emission beams 1 and reception beams 2. The distance between the light points formed by the emission beams 1 and reception beams 2 is directly related to the front pointing angle a. The dimension of these light points (necessary for their separation) is itself a direct function of the divergence of the beams in the telescope 7. Given that the divergence of the beams is a direct function of the diameter of the exit pupil of the telescope 7, a pupil diameter 7a in precisely selected ranges allows the forward pointing angle a not to be negligible compared to the divergence of the beams.

[0155] More precisely, in GEO orbit, the value of the forward pointing angle a can typically be 18.5 prad, which represents a ground displacement of 660 m. A formula (based on the dimension of the Airy spot, corresponding to a uniform pupil in irradiance) linking the diameter D of the exit pupil of the telescope 7 with the divergence half-angle 0 of the beams of wavelength X considered can be:

[0156] 8 =1.22.2 / 0

[0157] In order to take into consideration different configurations (i.e. a central obscuration of the pupil 7a or an irradiance as a function of the position considered defined by a Gaussian distribution) and not only a configuration having a pupil 7a uniform in irradiance, preferably the half-angle of divergence 0 of the beams is strictly less than 4.6 prad (or 20<18.5 / 2 prad), (and preferably strictly less than 6 prad), which corresponds to a value of diameter of the exit pupil, preferably strictly greater than 410 nm (and preferably strictly greater than 300 nm) (taking into consideration a wavelength of 1550 nm) ([Fig. 10]). The wavelength X was taken equal to 1550 nm.

[0158] Thus, advantageously, the optical terminal device for a space satellite telescope further comprises a pupil 7a having a diameter greater than or equal to 300 mm. Preferably, the pupil 7a has a diameter greater than or equal to 350 mm. Preferably, the pupil 7a has a diameter greater than 400 mm. The pupil 7a is the exit pupil of a satellite telescope 7, preferably a geostationary space satellite.

[0159] The optical component 3 may be called a “focusing optical component”. In general, a person skilled in the art is able to identify the optical component capable of performing the desired focusing function. The focusing optical component 3 may, for example, be a lens. The focusing optical component 3 may, as an alternative or in addition, be a concave mirror. The focusing optical component 3 may also be an assembly of several optical parts, such as concave mirrors and / or lenses. More specifically, the focusing optical component 3 may be an assembly comprising two concave mirrors and a lens.

[0160] In the case of [Fig.3A], the focusing optical component 3 comprises the telescope 7 and the mirrors 11a and 11b of the “linking” module. In this case, the optics of the linking module allow the generation of the focal plane on which it is possible to position the beam splitting optical module 5. The focal length of the component focusing optics 3 (considering the satellite telescope) can be from 10 to 40 m. The diameter of the pupil 7a can be 500 mm. The focal length of the focusing optical component 3 considering only the terminal is between 50 mm and 1000 mm. According to an example, it is also possible that the so-called focusing optical component 3 only comprises the optics 11a and 11b of the "link" module. In this case, a smaller image of the entrance pupil of the telescope (which is the entrance pupil of the terminal) is generated on the side where the second beam arrives at the telescope. The size of this image can be a function of the magnification of the telescope. Generally, the size of this image can be between 5 mm and 10 mm. In this case, the dimensions of the entrance pupil of the terminal can no longer be between 350 mm and 450 mm, in order to satisfy the function of the switching device.

[0161] In the case of [Fig.3B], the focusing optical component 3 may be a lens or a mirror, such as the mirror 11e, having an optical power. The connecting module may in this case be a mirror system without focusing power.

[0162] The deflection of a beam on the separation module 5 can cause light scattering. This is the case in particular when the deflected beam is a high-power beam. In order to limit, and preferably to avoid, interference in brightness on the transmitted beam, the deflected beam can be the beam having the lowest power, i.e. the second beam 2. This is particularly advantageous due to the significant difference in power between the beam transmitted to Earth 1 and the beam 2 received from Earth. Even a low interference of the second beam 2 by the first beam 1 can disrupt the telecommunication. Note, however, that it is possible to provide that the deflected beam is alternatively the first beam 1. In the following, it is considered, without limitation, that the undeflected beam is the first beam 1 and that the beam deflected by the module 5 is the second beam 2.

[0163] The invention provides for the possibility that there are several first light beams 1 and several second light beams 2. Thus, there may be 2, 3, 4, 5 or 8 first light beams 1 and 2, 3, 4, 5 or 8 second light beams 2.

[0164] The first light beam 1 may have a diameter between 5 mm and 10 mm on the lower stage. The second light beam 2 may have a diameter between 5 mm and 10 mm on the lower stage.

[0165] Given that the first light beam 1 is emitted towards the Earth from the separation module 5 and that the second light beam 2 is emitted from the Earth towards the separation module 5, at the level of the separation module 5 (and more particularly after the first beam 1 has passed close to the separation module 5 and before the second beam 2 has been deflected by the separation module 5), it can be considered that the first light beam 1 and the second light beam 2 have quasi-parallel propagation directions, being offset due to the consideration of the forward pointing angle a. After the first beam 1 has passed close to the separation module 5 and before the second beam 2 has been deflected by the separation module 5, the first light beam 1 and the second light beam 2 can thus be adjacent. Downstream of the lens 3 considering the direction of propagation of the first beam 1 emitted towards the Earth, and upstream of the lens 3 considering the direction of propagation of the second beam coming from the Earth, the first light beam 1 and the second light beam 2 can be in contact in part or in whole.Given the difference in pointing, it is understood that the separation module 5 can be arranged in an angular interval relative to a plane perpendicular to the direction of propagation of each beam 1, 2, in order to be able to separate the beams 1 and 2 after passing through the plane 4 at which these two beams are separated over a relatively short distance. Upstream of the separation module for beam 1 and downstream for beam 2, the angle that these two beams make with the reflection plane 12a of the separation module 5 is substantially the same (except for the effect of the forward pointing). It is then possible to arrange the separation module 5 so that it is inclined by a minimum of 5° relative to a position perpendicular to the direction of propagation of each beam 1, 2. This inclination can be between 5° and 85°, preferably between 20° and 70° and preferably between 30° and 60°.

[0166] Furthermore, the first light beam 1 and the second light beam 2 may form an angle of 90° plus or minus 20° with the plane 4. The first light beam 1 and the second light beam 2 may also form an angle of 90° plus or minus 10° with the plane 4. The first light beam 1 and the second light beam 2 may also form an angle of 90° plus or minus 5° with the plane 4. The plane 4 may be substantially perpendicular to the direction of propagation of the first light beam 1, taking into account the forward pointing angle a. Alternatively, the plane 4 may be substantially perpendicular to the direction of propagation of the second light beam 2, taking into account the forward pointing angle a.

[0167] When separating the first light beam 1 and the second light beam 2, the deflected beam is deflected by a first face 12a of the separation module 5 and the beam which passes through the space without being in contact with the separation module 5 propagates from a second face 12b towards the first face 12a. The first face 12a of the separation module 5 is preferably opposite the second face 12b of the separation module 5. Due to the deflection of the second light beam 2 by the separation module 5, the direction of propagation of the second light beam 2 before its deflection by the separation module 5 is different from its direction of propagation after its deflection by the separation module 5.

[0168] According to a possible example, the separation module 5 has at least one surface forming a diopter 5a. The separation module 5 is then configured to allow one of the first light beam 1 and the second light beam 2 to pass without the beam in question being in contact with the diopter 5a, i.e. without the beam in question passing through the diopter 5a.

[0169] Plane 4 may be confused with image plane 3a of focusing optical component 3. Plane 4 may therefore be positioned at a distance DistF from focusing optical component 3, as illustrated in [Fig. 10]. Distance DistF is the focal length of focusing optical component 3. Plane 4 may be at a distance from image plane 3a of focusing optical component 3, and preferably parallel to this image plane 3a. Plane 4 may be positioned on one side or the other of the image plane of focusing optical component 3 at a distance of up to 5 mm. Preferably, the distance between plane 4 and the image plane of focusing optical component 3 may be between 0 mm and 1 mm. Preferably, the plane 4 coincides with the image plane 3a of the focusing optical component 3. Indeed, when the plane 4 moves away from the image plane of the focusing optical component 3, the first light beam 1 and the second light beam 2 begin to move closer together.However, for an offset of a few millimeters (up to 5 mm) between the plane 4 and the image plane of the focusing optical component 3, the first light beam 1 and the second light beam 2 are sufficiently separated.

[0170] Preferably, the optical beam splitting module 5 is configured so that the second beam 2 is deflected by the module 5 by reflection.

[0171] For this, the optical beam separation module 5 may comprise an opening 8 allowing the first beam 1 to pass through this opening 8. The opening 8 then delimits a passage through which the first light beam 1 propagates. In this way, the first beam 1 passes through the space where the separation module 5 is positioned without coming into contact with said module 5.

[0172] The separation module 5 may further comprise a body 5b configured to deflect the second beam 2. The body 5b may for example be configured to transmit the second beam 2 and deflect it. This deflection of the beam may for example be done according to the optical properties of the beam to be deflected. For example, the second beam 2 may be deflected according to its wavelength. The body 5b of the separation module 5 may for example comprise or be a dichroic filter. Preferably, the deflection of the second beam 2 is done by reflection. The body 5b may for example comprise or be a mirror. The deflection and therefore the separation of the beams is thus simplified. The opening 8 may be at least partly surrounded, and preferably delimited, by the body 5b of the separation module 5.

[0173] The opening 8 can be configured so that the first beam 1 passes into the space defined by the opening 8. It is therefore understood that the first beam 1 passes through the separation module 5 without being in contact with this separation module 5. According to one example, the separation module 5 is positioned so that the opening 8 forms a passage aligned with the direction of propagation of the light beam that the opening lets pass. Equivalently, the passage formed by the opening 8 is arranged on the optical path of the light beam that the opening 8 lets pass.

[0174] According to an advantageous example, the opening 8 of the optical beam splitting module 5 is a hole, that is to say an opening 8 whose periphery is closed. As illustrated in [Fig. 11], the hole 8 can advantageously be centered on the direction of propagation of the light beam passing through the hole 8, and in particular the first beam 1. The hole 8 can be entirely surrounded, and preferably delimited, by the body 5b of the splitting module 5. Thus, it is understood that if the satellite rotates, the optical beam splitting device can rotate around the direction of propagation of the beam passing through the opening 8. When the opening 8 is a hole surrounded by the body 5b of the splitting module 5, it is possible to avoid this rotation.The separation module 5 rotating around an axis substantially coincident with the direction of propagation of the first beam 1 passing through the hole 8, a deviation of the second beam 2 can be made whatever the rotational position of the separation module 5.

[0175] Preferably, the hole has a symmetry of revolution around an axis 8a, this axis 8a being substantially coincident with the direction of propagation of the light beam passing through the hole 8, and in particular the first beam 1. The hole 8 can form a passage of circular, square, rectangular or oval section configured so that the beams are not in contact with the separation module 5 when it passes through the space where the separation module 5 is positioned.

[0176] The opening 8 can be produced by mechanical machining, chemical machining or laser machining. The beam splitting module 5 is thus simple to manufacture, which reduces the cost of the device and the associated method.

[0177] Advantageously, the body 5b of the optical beam splitting module 5 is a mirror. The mirror in question comprises the opening 8. Preferably, the opening 8 is a hole.

[0178] According to an example illustrated by [Fig. 13], the opening 8 may not have a closed perimeter. The opening 8 may be a recess in the body 5b of the separation module 5, the recess opening onto at least one of the edges of the body 5b of the separation module 5. The beam separation module 5 may for example be U-shaped. In this way, when the beam separation module 5 lets the first light beam 1 pass, the first light beam 1 passes through the area partially surrounded by the U. The separation module 5 can then be oriented so that the second beam 2 is deflected by the body 5b of the separation module 5.

[0179] Due to the dimensions of the light beams in GEO orbit, which are typically between 5 mm and 10 mm (on the lower stage), the optical components of the separation and switching module are configured, and in particular dimensioned, to act on beams with a diameter of the order of a millimeter, and more particularly beams with a diameter of between 5 mm and 10 mm (on the lower stage). For example, the opening 8 may be dimensioned so as to have a section substantially perpendicular to the direction of propagation of the beam, with an area greater than at least one, preferably at least two, and preferably at least three times the size of the beam passing through the opening 8. In this section, the opening 8 may have a smaller dimension, for example a diameter, of between 0.1 mm and 0.5 mm.The opening 8 may also be configured so that it has the minimum size allowing it to pass without being in contact with the first light beam 1. For example, the opening 8 may for this purpose have a substantially circular perimeter. Furthermore, the opening 8 may have a size defined so as to take into account the problems of manufacturing tolerance, alignment and variation during use. Thus, the size of the opening 8 may correspond to the minimum size allowing it to pass the beams without being in contact with to which is added 30% to 40% of this minimum size.

[0180] According to another example illustrated by [Fig. 14], the body 5b of the separation module 5 may have a shape without an opening, for example a half-spherical or rectangular shape. The separation module 5 may then be arranged on the optical path of the first 1 and second 2 beams so that the first beam 1 passes next to the body 5b without being in contact with this body 5b. The second beam 2 may be incident on the body 5b and therefore be deflected.

[0181] According to a preferred example, the separation module 5 may comprise a pierced mirror. Thus, the first beam 1 passes through the hole, and the second beam 2 is deflected by reflection on the mirror. The separation and the switching of the first 1 and second 2 beams is thus made reliable and simplified.

[0182] According to a possible example, the body 5b of the separation module 5 is based on, and preferably made of, one of the following materials: glass, crystal, metal and ceramic. The body 5b of the separation module 5 may be at least partly covered by a coating configured to deflect the second beam 2 by reflection.

[0183] The separation module 5 may comprise a drilled dichroic filter. Thus, the hole 8 in the dichroic filter allows the passage of the first beam 1, and the second beam 2 is deflected by the dichroic filter according to its wavelength.

[0184] In order to separate the first 1 and second 2 beams between the local 1 Id and global 1 le mirrors, the optical beam splitting module 5 can be positioned between the local pointing mirror 1 Id and the global pointing mirror lie (as seen in FIGS. 3A, 3B and 4 for example). Thus, the global pointing mirror 1 le manages the two beams 1, 2, while the local pointing mirror 1 Id only directs the second beam 2.

[0185] The pupil imaging optical module 10 may comprise two lenses, a first lens 10a and a second lens 10b (Figures 3A and 3B). The lens 10a is positioned on the path of the first light beam 1. The lens 10b is positioned on the path of the second light beam 2. The lens 10b makes it possible in particular to fix the desired transverse position of the second light beam 2. The lens 10a makes it possible in particular to fix the desired transverse position of the first light beam 1.

[0186] Advantageously, the device may comprise a third mirror 11e. The third mirror 11e has the function of receiving the second light beam 2 (after it has been reflected by the second optical component 11b) to reflect it by directing it towards the separation module 5. The third mirror 11e also has the function of receiving the first light beam 1 (after it has passed close to the optical beam separation module 5) to reflect it by directing it towards the second optical component 11b. The third mirror 11e can therefore be used for alignment and adjustment issues.

[0187] According to an example illustrated by [Fig.4], the first optical component 11a and the global pointing mirror 11e are on the upper stage 1lab1. The diverging mirror 11b, the global pointing mirror 11e, the third mirror 11e, the pupil imaging module 10 and the separation module 5 are on the lower stage 1lab2.

[0188] Regarding the pupil imaging module 10, the first lens 10a can be positioned so that the first light beam 1 passes through the first lens 10a before reaching the separation module 5, according to the direction of propagation of the first beam 1 in the device. The second lens 10b can be positioned so that the second light beam 2 passes through the second lens 10b after reaching the optical beam separation module 5, according to the direction of propagation of the second beam 2 in the device.

[0189] The second optical component of the connection module 11b (located on the lower stage 1 lab2) can be positioned so that it reflects the first light beam 1 towards the first optical component of the connection module 11a (located on the upper stage 1 labl) after it has been reflected by a third mirror 1le and so that it reflects the second light beam 2 after it has been reflected by the first optical component of the connection module 1la (located on the upper stage llabl).

[0190] The third mirror 11e can be positioned so that it reflects the first light beam 1 before it has been reflected by the second optical component of the connection module 11b (located on the lower stage 1 lab2) and so that it reflects the second light beam 2 after it has been reflected by the second optical component of the connection module 11b (located on the lower stage 1 lab2) (see FIGS. 3A and 3B).

[0191] The optical beam splitting module 5 can be positioned so that the second light beam 2 reaches the optical beam splitting module 5 after having reached the third mirror 11e and so that the first light beam 1 reaches the optical beam splitting module 5 before having reached the third mirror 11e (see FIGS. 3A and 3B).

[0192] The local pointing mirror 1 Id can be positioned so that it reflects the second light beam 2 after it has reached the second lens 10b pupil imaging module 10 (see Figures 3A and 3B).

[0193] In the case where the focusing optical component 3 is a lens, this lens can be positioned between the optical beam splitting module 5 and the third mirror 11c (see [Fig.3B]).

[0194] Preferably, the invention provides an optical terminal assembly for a geostationary space satellite telescope comprising an optical terminal device for a space satellite telescope as described above and a satellite telescope, preferably a geostationary space satellite.

[0195] According to one example, the assembly comprises a device according to the invention and a space satellite telescope 7 comprising a pupil 7a having a diameter greater than or equal to 300 mm. Advantageously, the assembly comprises a device according to the invention and a space satellite telescope 7 comprising a pupil 7a having a diameter greater than or equal to 350 mm. Advantageously, the assembly comprises a device according to the invention and a space satellite telescope 7 comprising a pupil 7a having a diameter greater than 400 mm. Preferably, the telescope 7 is a space satellite telescope for transatmospheric link. Preferably, the telescope 7 is a geostationary space satellite telescope. The pupil 7a may be the exit pupil of the telescope 7. The magnification of the telescope may typically be 50.

[0196] On reading the above, it is understood that the invention describes a method for transmitting, receiving, pointing, tracking and directing optical beams by a space satellite telescope for transatmospheric link, of a first light beam 1 transmitted towards the Earth and of a second light beam 2 received from the Earth. The method for transmitting and receiving optical beams by a space satellite telescope comprises in particular: • An implementation of the previously described satellite telescope optical terminal device or space satellite telescope optical terminal assembly, • A reception and an increase in the diameter of the first light beam 1 by the connection module 1 lab, comprising a passage of the first light beam 1 from the second optical component 11b to the first optical component 11a, • A reception and a reduction of the size of the second light beam 2 by the connection module 1 lab, comprising a passage of the second light beam 2 from the first optical component 11a to the second optical component 11b, • After the reception and the increase of the diameter of the first light beam 1 by the linking module 1 lab, and before the reception and the reduction of the diameter of the second light beam 2 by the linking module 1 lab, a direction of the first 1 and second 2 light beams by the second orientable mirror lie, • After the reception and the reduction of the diameter of the second light beam 2 by the connection module 1 lab, a direction of the second light beam 2 by the local pointing mirror 1 Id, or before the reception and the increase of the diameter of the first light beam 1 by the connection module 1 lab, a direction of the first light beam 1 by the local pointing mirror 1 Id.

[0197] The method may comprise any step enabling the implementation or resulting from the characteristics of the optical terminal device for satellite telescope, and conversely the device may have any characteristic resulting from the implementation of the method.

[0198] Preferably, in the method of transmitting and receiving optical beams by a space satellite telescope, the space satellite telescope being a space satellite telescope for transatmospheric link. Preferably, the space satellite telescope is a geostationary space satellite telescope.

[0199] Preferably, the method further comprises: • A positioning of the separation module 5, in a plane 4 close to or merged with the image plane 3a of the focusing optical component 3, so that the image of the first light beam 1 and the image of the second light beam 2 by the focusing optical component 3 (the object being the Earth which is positioned at infinity), are distinct in this plane 4. Due to the forward pointing angle a, the image of the first light beam 1 is distinct from the image of the second light beam 2, • Following the formation of said images, a separation at the level of said plane 4, by the separation module 5, of the first light beam 1 and the second light beam 2 is carried out.

[0200] According to a preferred example, in the method, the first light beam 1 and the second light beam 2 each have a range of wavelength values ​​which can overlap at least partially. Thus, the entire C band can be used for the emission of beams and also for the reception of beams. This therefore allows a significant gain in throughput.

[0201] The method may comprise a step making it possible to adjust the orientation of the global pointing mirror 1 le and of the local pointing mirror 1 Id, in the case where the light beams 1, 2 have been offset relative to the direction that they should have to go towards the separation module 5. The global pointing mirror and the local pointing mirror therefore have the role of finely adjusting the direction of the beams according to the conditions of alignment of the satellite with the ground station.

[0202] According to a preferred example, in the method, the power of the first light beam 1 is between 1 W and 1000 W. Preferably, the power of the first light beam 1 is between 5 W and 1000 W.

[0203] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

[0204] List of references: 1. first light beam 2. second light beam 3. optical component called focusing 3 a. image plan 4. plan 5. optical beam splitting module 5 a. diopter 5b.body 7. telescope 7a. pupil 8. opening 8 a. axis 10. pupil imaging optical module 10a. first lens 10b. second lens 1 Id. local pointing mirror lie. global pointing mirror 1 lab. optical link module lia. first optical component 11b. second optical component llabl. upper stage 1 lab2. lower stage lie. third mirror 12a. first face 12b. second face 13. first set 14. second set 15. collimator 16. connection area with optical fibers 17. first zone 18. second zone 30. Earth 31. Satellite 32a. incident beam 32b. reflected beam 20. divergence angle a. forward pointing angle DistF. focal length D. diameter of the telescope exit pupil t. diffraction spot Fl. arrow of descending signals F2. arrow of ascending signals

Claims

Claims

1. Optical terminal device for a space satellite telescope, of a first light beam (1) transmitted towards the Earth and of a second light beam (2) received from the Earth characterized in that it comprises: • a first steerable mirror, called “local pointing mirror” (1 Id), configured to receive and steer one of the first light beam (1) and the second light beam (2), • a second steerable mirror, called “global pointing mirror” (lie), configured to receive and steer the first light beam (1) and the second light beam (2), • an optical module called “linking module” (1 lab) comprising a first optical component (1 la) and a second optical component (11b),the linking module (1 lab) being configured to make a link between the global pointing mirror (1 le) and the local pointing mirror (1 Id) by being arranged between the global pointing mirror (lie) and the local pointing mirror (1 Id), the first optical component (lia) and the second optical component (11b) being configured together to increase a size of the first light beam (1) transmitted and decrease a size of the second light beam (2) received, during their propagation in the linking module (llab), • a so-called “pupil imaging” optical module (10), • the pupil imaging optical module (10) and the linking module (llab) being configured, with the local pointing mirror (1 Id) and the global pointing mirror (1 le) so that the local pointing mirror (1 Id) and the global pointing mirror (lie) are the image of each other.,

2. Device according to the preceding claim, in which: • the first optical component (11a) is convergent and the second optical component (11b) is divergent, the pupil imaging optical module (10) preferably comprising at least one lens, or • in which the first optical component (11a) is convergent and the second optical component (11b) is convergent.

3. Device according to any one of the preceding claims, wherein the linking module (1 lab) is configured so that the ratio between the size of the first light beam (1) after its propagation in the linking module (1 lab) and the size of the first light beam (1) before its propagation in the linking module (1 lab), and the ratio between the size of the second light beam (2) before its propagation in the linking module (1 lab) and the size of the second light beam (2) after its propagation in the linking module (1 lab) are between 5 and 10, preferably are equal to 6.

5.

4. A device according to any preceding claim wherein at least one of the first optical component (11a) and the second optical component (11b) is a mirror.

5. Device according to any one of the preceding claims, in which the connection module (1 lab) is configured so that: • upstream of the first optical component (11a), the first (1) and second (2) light beams propagate in a first zone (17), • downstream of the second optical component (11b), the first (1) and second (2) light beams propagate in a second zone (18), • the first zone (17) and the second zone (18) being distinct and at least partly superimposed on each other.

6. Device according to any one of the preceding claims, comprising a so-called “transformation” optical module configured so that: • after the linking module (1 lab), the first light beam (1) has a uniform irradiance distribution, and, before the linking module (1 lab), the first light beam (1) has a Gaussian irradiance distribution, and • after the linking module (1 lab), the second light beam (2) has a Gaussian irradiance distribution, and, before the linking module (1 lab), the second light beam (2) has a uniform irradiance distribution.

7. Device according to the preceding claim, in which, the first optical component (11a) and the second optical component (11b) being mirrors, the transformation module comprises the connection module (llab).

8. Device according to any one of the preceding claims comprising: • a so-called focusing optical component (3) configured to form, at a plane (4), an image of the first light beam (1) and an image of the second light beam (2), the image of the first light beam (1) being distinct from the image of the second light beam (2), • an optical beam splitting module (5) configured to allow one of the first light beam (1) and the second light beam (2) to pass, and to deflect the other of the first light beam (1) and the second light beam (2).

9. Device according to the preceding claim further comprising a pupil (7a) having a diameter greater than or equal to 300 mm, preferably greater than or equal to 350 mm and preferably greater than 400 mm, the pupil (7a) is the exit pupil of a satellite telescope (7), preferably of a geostationary space satellite.

10. A device according to any one of the two preceding claims wherein the optical beam splitting module (5) is configured to reflect the other of the first light beam (1) and the second light beam (2).

11. Device according to any one of the three preceding claims wherein the optical beam splitting module (5) comprises an opening (8) positioned so that one of the first light beam (1) and the second light beam (2) passes through the opening (8) the optical beam splitting module (5), without being in contact with said module (5).

12. Optical terminal assembly for space satellite telescope comprising the device according to any one of the preceding claims and a satellite telescope, preferably a geostationary space satellite.

13. A method of transmitting and receiving optical beams by a space satellite telescope, a first light beam (1) transmitted towards the Earth and a second light beam (2) received from the Earth, implementing the device according to any one of claims 1 to 11 or the optical terminal assembly according to claim 12, comprising: • A support and an increase in the size of the first light beam (1) by the link module (1 lab), comprising a propagation of the first light beam (1) from the second optical component (11b) towards the first optical component (11a), • A support and a reduction of the size of the second light beam (2) by the connection module (1 lab), comprising a propagation of the second light beam (2) from the first optical component (11a) to the second optical component (11b), • After the first light beam (1) has been taken over and increased in size by the linking module (1 lab), and before the second light beam (2) has been taken over and decreased in size by the linking module (1 lab), an orientation of the first (1) and second (2) light beams by the global pointing mirror (lie), • After the second light beam (1) has been taken over and reduced in size by the link module (1 lab), the second light beam (2) is oriented by the local pointing mirror (1 Id), or before the first light beam (1) has been taken over and increased in size by the link module (1 lab), the first light beam (1) is oriented by the local pointing mirror (1 Id).

14. Method according to the preceding claim, the space satellite telescope being a space satellite telescope for transatmospheric link, preferably, the telescope is a geostationary space satellite telescope.

15. A method according to any one of the two preceding claims, implementing the optical terminal device for a space satellite telescope according to any one of claims 8 to 11 or the optical terminal assembly for a space satellite telescope according to claim 12, the assembly comprising the optical terminal device for a space satellite telescope according to any one of claims 8 to 11 and a space satellite telescope (7), wherein the space satellite telescope is a geostationary space satellite telescope, comprising: • A formation in a plane (4) of an image of the first light beam (1) and an image of the second light beam (2) by the focusing optical component (3), the image of the first light beam (1) being distinct from the image of the second light beam (2), • Following the formation of said images, a separation at said plane,by the optical beam splitting module (5), of the first light beam (1) and the second light beam (2), the splitting comprising a transmission of one of the first light beam (1) and the second light beam (2) without the optical beam splitting module (5) being in contact with said beam, and a deflection of the other of the first light beam (1) and second light beam (2).,

16. Method according to the preceding claim in which the first light beam (1) and the second light beam (2) have a range of wavelength values which at least partially overlap.

17. Method according to any one of the four preceding claims in which the power of the first light beam (1) is between 1 W and 1000 W, preferably between 5 W and 1000 W.