Free-space optical telecommunication system

Abstract

The invention relates to a free-space optical telecommunication system (1) comprising a modulation device (DM) that produces a plurality of mutually incoherent elementary light beams (R1-RN), each elementary light beam (R1-RN) modulating the same digital data (M) to be transmitted, and a processing device (DT) configured to combine the elementary light beams (R1-RN) and thereby produce light radiation (Rc) referred to as "combined" light radiation. The system also comprises a beam expander optical device (T), optically coupled downstream of the processing device (DT), for receiving the combined light radiation (Rc) and for propagating free-space transmission radiation (I).

Description

Free space optical telecommunications system FIELD OF THE INVENTION

[0001] The invention relates to an optical telecommunications system aimed at overcoming transmission difficulties linked to the distortion of the wavefront of light radiation during its propagation. This distortion can originate from atmospheric disturbances during optical communication in free space. More generally, this distortion is caused by the propagation of light radiation in its medium. The invention finds particular application in the field of optical telecommunications in free space. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In free-space optical telecommunications, a transmitter modulates light radiation (usually produced by a laser) with the information to be transmitted, the light radiation taking the form of a narrow emission beam, typically from a few centimeters to 1 meter, which is emitted towards a receiver. After propagation in its medium (air will be taken as an example in the rest of this description, but the medium can be of any nature, such as water in the case of underwater telecommunications), the light radiation is collected at a receiver and demodulated to recover the transmitted information.

[0003] During its propagation, the radiation produced by the transmitter is subject to atmospheric disturbances, and in particular to temperature and pressure variations which induce a variation in the optical index and cause the radiation to deform. These erratic disturbances, whose variation dynamics typically extend between 100Hz and a few kHz, lead to its deformation, which affects its wavefront. More precisely, the disturbances tend to spatially redistribute the energy in the radiation, producing random fluctuations in amplitude and phase. This deformation materializes in the form of so-called "speckle" figures in the spot formed by the projection of the beam onto the radiation collection device and by a scintillation phenomenon. It leads to limiting the information rate of the link between the transmitter and the receiver, and therefore the quality of the link.This is particularly the case when the pupil of the radiation collection device is relatively small compared to the size of the beam when it reaches this device, and therefore little energy of the emission beam can be captured. Such a situation occurs particularly in so-called "uplink" communications to a receiver located in a satellite or during "point-to-point" terrestrial communication, during which the emission beam propagates entirely in the atmosphere. SUBJECT OF THE INVENTION

[0004] An aim of the invention is to propose an optical communication system which remedies, at least in part, the aforementioned problem. More specifically, an aim of the invention is to propose a free-space optical telecommunication system making it possible to make communication more reliable and / or having a preserved throughput despite the disturbances induced by the propagation medium. BRIEF DESCRIPTION OF THE INVENTION

[0005] In order to achieve this aim, the subject of the invention proposes a free space optical telecommunication system comprising: a modulation device producing a plurality of elementary light beams incoherent with each other, each elementary light beam modulating the same digital data to be transmitted; a processing device optically coupled downstream of the modulation device and configured to combine the elementary light beams and thus produce so-called "combined" light radiation; an optical beam expander device, optically coupled downstream of the processing device, to receive the combined light radiation and propagate emission radiation in free space.

[0006] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination: the processing device comprises at least one multi-plane conversion device; the multi-plane conversion device comprises a plurality of optical parts each having a reflective face for guiding the propagation of the elementary light beams, at least one of the reflective faces having a microstructuring configured to combine the elementary light beams and form, during a plurality of reflections, the combined light radiation; the microstructuring is also configured to shape the elementary light beams composing the combined light radiation; the system is configured to conform the combined light radiation to a flat-plate shape; the flat-plate shape has a circular section to form a ring or a disk;the modulation device comprises a plurality of light sources associated with a plurality of modulators to produce the plurality of elementary light beams;the light sources emit radiation having wavelengths distinct from one another;the modulation device comprises a broad spectrum source;the optical telecommunication system comprises a remote optical fiber, optically arranged between an output port of the processing device and the optical beam expander device, to guide the propagation of the recombined light beam;the elementary light beams are each shaped to a linear combination of modes having similar group delays.the remote optical fiber (F) is a degeneration-lifted fiber, such as a step-index fiber or an elliptical core fiber;The optical telecommunication system comprises an optical shaping block arranged between the optical fiber and the optical beam expander device; the optical beam expander device (T) is a telescope or a telescope. BRIEF DESCRIPTION OF THE FIGURES

[0007] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures in which:

[0008]

[0009] The represents an optical telecommunications system in accordance with the invention;

[0010]

[0011] Illustrates an example of a multiplane conversion device;

[0012]

[0013] Illustrates a ring shape of recombinant radiation. DETAILED DESCRIPTION OF THE INVENTION

[0014] For the sake of clarity, in this description, light radiation or a light beam is defined as radiation formed from at least one mode of the electromagnetic field, each mode forming a spatio-frequency distribution of the amplitude, phase, and polarization of the field.

[0015] The "shape" of a radiation or beam will be the transverse distribution of the amplitude and phase of the mode or the combination of the transverse distributions of amplitude and phase of the modes composing this radiation.

[0016] With reference to the, an optical telecommunications system 1 according to the invention aims to produce an emission light radiation I carrying, by modulation, information to be transmitted. The emission light radiation is supplied to an optical receiver, capable of extracting the information from the received radiation. In the example shown in this, the optical receiver is arranged in a satellite SAT, but the telecommunications system of the invention is in no way limited to this particular application. Generally speaking, the transmitter and the receiver can be arranged indifferently on land, in the sea or in space, and propagate in any free space, the atmosphere in the case of terrestrial communication, water in the case of marine communication. The transmitter and the receiver can both be stationary, or move relative to each other.

[0017] The emission light radiation I takes the form of a narrow beam directed towards the receiver. During its propagation in free space, the emitted radiation is subject to atmospheric disturbances in the atmosphere, so that the incident light radiation I' arriving at the station hosting the receiver exhibits spatial and temporal fluctuations in amplitude and phase. This phenomenon affects the shape of this radiation, which takes a form that varies over time, in an erratic, irregular manner, and which tends to expand spatially and distort, so that the energy actually received by the radiation collection device at the receiver is limited or even intermittent.The optical telecommunication system of the present description 1 aims to overcome, at least in part, these difficulties by creating spatial diversity in the emission radiation I, this diversity making it possible to attenuate the effects of the fluctuations to allow the exploitation of the radiation by the optical receiver OR and the decoding of the transmitted message. This attenuation of the fluctuations is based on the fact that each spatial mode of the emission radiation I perceives a different atmospheric layer and therefore creates a different speckle pattern on the target. If the light beams carried by these spatial modes are incoherent with each other, their intensities are added and averaged into a more uniform pattern.

[0018] The optical telecommunications system 1 comprises for this purpose a modulation device DM producing a plurality of elementary light beams R1-R N incoherent with each other. Each elementary light beam R1-RN is modulated by the same digital data M to be transmitted. Generally speaking, an increasing number of elementary light beams makes it possible to increase the spatial diversity of the emission radiation I and the robustness of the link, at the cost, however, of a higher cost of the system. In practice, we can provide a number of elementary light beams R1-R N between 2 and 50, and preferably between 2 and 15.

[0019] By "mutually incoherent" we mean that the light beams are not likely to interfere with each other on time scales comparable to or longer than the duration of a symbol of the digital data M. Typically, the target rate is between 10 Gbauds / s to 50 Gbauds / s, or even up to 100 Gbauds / s.

[0020] Digital data can be encoded and modulated using any suitable protocol, for example amplitude modulation or coherent intradyne modulation.

[0021] The DM modulation device comprises at least one light source associated with at least one modulator to which the digital data are transmitted. Any modulation technique may be suitable, for example acousto-optic modulation (AOM for "Acousto-Optic Modulation" according to the English term), electro-optic modulation (EOM for "Electro-Optic Modulation"), by semiconductor optical amplification (SOA for "Semiconductor Optical Amplifiers") by direct modulation of the laser source.

[0022] The incoherent nature of the elementary light beams R1-R N products can be obtained in multiple ways accessible to those skilled in the art.

[0023] For illustration, the source can be chosen to present a wide spectrum. The source's spectrum width is determined by the target data rate and the number of elementary light beams. Thus, a 10 Gbaud transmission using 10 elementary light beams leads to choosing a source spectrum width greater than 100 GHz.

[0024] Each elementary light beam can be formed from a portion of this spectrum, this portion of the spectrum being obtained by filtering.

[0025] Alternatively, light radiation produced by the broad spectrum source and modulated by the modulator may be split to produce the plurality of elementary light beams R1-R N The modulation device DM may comprise a plurality of optionally adjustable delays respectively arranged in the optical paths of the elementary light beams R1-R Nin order to make them incoherent with each other, by choosing the delays so that they are large compared to the coherence time of the source, but small compared to the duration of a modulation symbol. The delays can be achieved by optical fibers of different lengths, patch cords of different lengths, free space lines with fixed or adjustable delays.

[0026] For illustration, the broad spectrum source can be an amplified spontaneous emission source (or "Amplified spontaneous emission"), a superluminescent diode, an EDFA (erbium ion doped fiber optic amplifier) ​​source. It can also be a spectrum sliced ​​incoherent light source (or "spectrum sliced ​​incoherent light source") described in the paper by D. Lee, VV Mai and H. Kim, "Mitigation of Scintillation in FSOC Using RSOA-Based Spectrum-Sliced ​​Incoherent Light," in IEEE Photonics Technology Letters, vol. 33, no. 5, pp. 227-230, 1 March, 2021.

[0027] But, advantageously, the modulation device DM comprises a plurality of light sources associated with a plurality of modulators to independently produce the plurality of elementary light beams R1-R N. The light sources can be chosen to emit radiation with wavelengths distinct from each other and sufficiently spaced to ensure their incoherence (for example, distinct by 10 GHz or 100 GHz or by a few hundred GHz). This approach is advantageous in that it makes it possible to produce high-power light emission radiation I, by combining a plurality of independent sources.

[0028] Continuing the description of the, the optical telecommunication system 1 also comprises a DT processing device optically coupled to the DM modulation device, downstream thereof. A plurality of optical connecting fibers, for example a plurality of single-mode fibers, may be provided optically arranged between the DM modulation device and the DT processing device to guide the elementary light beams R1-R N on input ports of the DM processing device.

[0029] The DT treatment device is configured to combine the elementary light beams R1-R N and thus produce a so-called “combined” light radiation R c . By "combined light radiation" we mean radiation formed from elementary light beams R1-R N copropagating (i.e. propagating in a single direction).

[0030] In addition to this combination function, the processing device can also have the function of shaping the elementary light beams R1-R N composing the combined light radiation R c .

[0031] The DT treatment device can be realized by assembling the ends of the connecting optical fibers into a bundle, parallel to each other. This bundle of optical fibers can, optionally, be collimated with microlenses. In any case, the light radiation emerging from the fiber bundle forms the combined radiation R c The fiber bundle may be arranged in a matrix, or more generally the ends of the fibers in the bundle may be arranged in a line or in a plane, for example in the form of a disc or inscribed in a disc, to best form the combined light radiation R c The fiber optic bundle may be arranged so that the ends of the fibers are arranged in a ring, the central portion of the ring being unfibered and corresponding to a central obstructed area of ​​a telescope as will be described in a later section of this description.

[0032] The DT processing device may also include various optical parts to help shape the elementary light beams R1-R N composing the combined light radiation R c . It may for example be at least one diffractive optical element (DOE for Diffractive Optical Element according to the English expression), a spatial phase modulator (SLM for “Spatial Light Modulator” according to the English expression), an optical system imaging or comprising at least one lens, an axicon, at least one optical element, transmissive or reflective, non-spherical and non-planar, such as an aspherical or freeform optical element (from the translation of the English expression “freeform optics”).

[0033] But preferably, the processing device comprises, instead of or in addition to the elements which have just been described, at least one multiplane conversion device designated “MPLC device” in the remainder of this description. Such a device makes it possible to properly control the spatial parameters of the elementary light beams R1-R N treated by the treatment device and constituting the combined light radiation R c such as the direction of propagation of elementary light beams R1-R N (this direction can be defined by means of the average linear phase of the associated electromagnetic field), the position of the elementary light beams R1-R N in the combined beam R c(defined as the position of the center of gravity of the beam intensity distribution in a plane perpendicular to the direction of propagation of these beams), the horizontal or vertical size of the elementary light beams R1-R N (defined as the standard deviation of the horizontal or vertical marginal intensity distribution), the ellipticity and divergence of the elementary light beams R1-R N in the combined radiation R c .

[0034] It is recalled that in an MPLC device, incident light radiation undergoes a succession of reflections and / or transmissions, each reflection and / or transmission being followed by propagation of the radiation in free space. At least some of the optical parts on which the reflections and / or transmissions take place, and which guide the propagation of the incident radiation, have microstructured zones which modify the incident light radiation.

[0035] By "microstructured zone" we mean that the surface of the optical part has a relief on this zone, which can for example be broken down into the form of "pixels" whose dimensions can be between a few microns and a few hundred microns. These can be metasurfaces. The relief or each pixel of this relief has a variable elevation relative to a mean plane defining the surface in question, of at most a few microns or at most a few hundred microns. Whatever the nature of the microstructuring of the zones, an optical part having such zones forms a phase mask introducing a local phase shift within the transverse section of the radiation which is reflected or transmitted there.

[0036] Thus, light radiation propagating within an MPLC device undergoes a succession of local phase shifts separated by propagations. The succession of these elementary transformations (for example at least four successive transformations such as for example 8, 10, 12, 14, or even at least 20 transformations) establishes a global transformation of the spatial profile of the incident radiation. It is thus possible to configure the microstructuring of the microstructured reflection or transmission zones to transform a first light radiation, which in particular has a specific shape, into a second radiation whose shape is different.

[0037] Theoretical foundations and practical implementation examples of an MPLC device can be found in the documents “Programmable unitary spatial mode manipulation”, Morizur et al, J.Opt. Soc. Am. A / Vol. 27, No. 11 / November2010; N. Fontaine et al, (ECOC, 2017), “Design of High Order Mode-Multiplexers using Multiplane Light Conversion”; US9250454 and US2017010463.

[0038] As presented in detail in the aforementioned documents, and with reference to the illustration of the optical part(s) 2a, 2b forming the MPLC device as well as the microstructured zones 3 carried by this or these optical parts are designed and configured to combine the elementary light beams R1-R N and form, during a plurality of reflections, the combined light radiation R c . Microstructuring can also be configured to shape the elementary light beams R1-R N composing the combined light radiation Rc .

[0039]

[0040] The elementary light beams R1-R N received on the input ports are respectively decomposed according to a family of modes called "input". The energies of the elementary light beams R1-R N respectively present in the modes of the input family are transported and respectively conformed to the modes of a family of "output" modes at the output port of the MPLC device. The MPLC device is configured, in particular through the microstructuring of the microstructured zones, to respectively match the modes of the input family and the modes of the output family. It is a passive device and whose transfer function is particularly stable and robust.

[0041] In the context of the present description, and by way of example, the family of input modes may comprise Gaussian modes arranged spatially opposite the elementary light beams R1-R N . The output mode family can be formed by N Hermite-Gauss modes or N Laguerre-Gauss modes. The MPLC device is configured to associate a Gaussian mode from the input mode family to a mode from the output mode family. The energy of a light beam R1-R N received on an input port is transported into the MPLC device to be distributed and conform to the output mode with which it is associated.

[0042] Of course, the Gaussian, Hermite-Gauss or Laguerre-Gauss modes taken as examples are given only for illustration purposes and other modes could be chosen to carry out this transformation.

[0043] It is not necessary for the output modes to be spatially superimposed. This is particularly the case when it is desired that the combined light radiation R c has a ring shape. This is illustrated in the, which shows the shape of the combined light radiation R c "ring-shaped" formed from the combination of three elementary light beams R1-R3. These beams have shapes, in annular sectors, which are distributed homogeneously in the ring, without overlapping.

[0044] It is not necessary for the beams to be perfectly joined to completely cover the annular surface, as illustrated in the. In other embodiments, one can for example envisage that the elementary beams are of Gaussian shapes, spatially arranged in a ring. Alternatively, the elementary beams can be respectively formed of groups of Hermite Gauss modes, each group being spatially arranged within the ring.

[0045] By spatially spreading the elementary light beams R1-R N(more precisely, the output modes of the MPLC device) without them overlapping, for example in disjoint annular sectors, we limit the spatial energy density in the combined radiation and, further downstream, in the emission radiation I. We can therefore control this energy density present in the emission radiation I so that it is safe for the eyes, which is an essential safety criterion to be respected in an optical telecommunications system implementing propagation in free space.

[0046] We generally seek to produce an emission beam that has maximum irradiance in the far field in its propagation axis, in order to best illuminate the target and promote optical communication. This configuration can be obtained by forming in the near field, at the beam expander device T, a flat-plate emission beam (called a "top hat" in the field). This beam can have a substantially circular section, to form a disk or a ring. We can therefore advantageously choose the output modes of the MPLC device so that the combination carried out by this device of the elementary light beams R1-R N best conforms to such a flat-top beam.

[0047] Returning to the description of the, the optical telecommunication system 1 also comprises an optical beam expander device T, optically coupled to the processing device DT, downstream thereof. The optical beam expander device T receives the combined light radiation R c and propagates the emission radiation I in free space.

[0048] The beam expander optical device T can take any suitable form, for example a telescope or a refractor.

[0049] As is well known, a telescope can be formed from an objective lens that includes a concave mirror for propagating light radiation in free space. Here, the combined radiation R creceived on an optical port P of the telescope can be projected onto the concave mirror using a second plane or convex mirror of the objective O. The second mirror, when present, leads to the formation of an obstructed central zone, of very low intensity, in the emission light radiation I. This is why it may be interesting to form a combined radiation R c in a ring (as mentioned in two previous passages of this description), so as not to place light energy unnecessarily in a central portion of the combined radiation R c , this energy cannot be propagated in free space.

[0050] When the beam expander optical device T is a telescope, the combined radiation R c can take the form of a disc.

[0051] The optical beam expander device T can be steerable in order to point and / or track a receiver, here arranged in the satellite SAT. The optical telecommunications system 1 can also comprise a device for guiding the emission radiation I (such as a tilt mirror or "tip tilt mirror" according to the English expression usually used in the field) in order to best guide the emission radiation and, more generally, correct any deviations in the pointing of the telescope T.

[0052] The DM modulation and DT processing device are composed of a plurality of precisely assembled optical or photonic elements which can be particularly sensitive to their operating environment. They are thus generally arranged in a cabinet, a room, in a vehicle or any other shelter of an operations center. It can therefore be advantageous to mechanically decouple and remote the optical beam expander device T from the other elements of the system. It can thus be positioned in a location favorable to the emission of the emission radiation I without inducing vibration on the upstream optical chain when, for example, the optical beam expander device T is mobile.

[0053] To enable this distancing, at least one offset optical fiber F can be provided, optically arranged between an output port of the processing device DT and the port P1 of the optical beam expander device T, to guide the propagation of the recombined light beam R c . This fiber is advantageously multimode. This fiber F can have a length typically between 1 m and 10 m or between 1 m and 50 m. A very short fiber can also be provided, for example from 10 cm to 1 m, if it is simply a matter of mechanically decoupling the optical beam expander device T from the rest of the system.

[0054] When the output port of the MPLC device is coupled to such a multimode offset fiber, the modes of the output mode family will preferably be chosen so that they correspond to the natural modes of this offset fiber. This configuration makes it possible to control the modal content of the radiation emitted at the output of the fiber and therefore its divergence, and more generally the properties of the emission beam I, in particular its stability. To this end, it may be preferable to exploit the guided modes of the offset fiber with the lowest indices, which favors low divergence. It will also be possible to control the shape of the radiation at the output of the offset fiber F so that it conforms to or maximizes the energy density supplied to the pupil of the optical beam expander device T.

[0055] Advantageously, the offset fiber is a degeneration-lifted fiber, which therefore offers a single so-called "clean" mode for at least some of the mode groups. This could be, for example, a step-index fiber or an elliptical core fiber.

[0056] More generally, the modes of the output mode family can be chosen so that each of these modes is formed by a linear combination of the modes having similar group delays in the offset fiber. By similar, we mean that these delays are not different from each other by more than 10% of the symbol delay (defined as the inverse of the transmission rate in GBauds), advantageously to within 5%.

[0057] For example, each mode of the input mode family can be chosen as a linear combination of the modes of the same mode group of the fiber. It is recalled that the modes of the same mode group of a fiber propagate with identical speeds. Also, by configuring the MPLC device as proposed above, the time spread of the transmitted symbols is limited, which allows high-speed transmission, for example greater than 10 GBd, 25 GBd, or even 33 GBd. By avoiding propagating an elementary light beam over several mode groups of the fiber, it is also ensured that the differences in propagation times of the elementary light beams, beam by beam, can be pre-compensated, for example using a static delay element. This characteristic is particularly interesting when the offset fiber is relatively long, for example when it has a length of 10 m or more.

[0058] Naturally, this optical fiber offset is not obligatory and one can also choose to optically couple these two elements by simple propagation in free space of the combined radiation R c This is particularly the case when the treatment device DT shapes the combined light radiation R c , for example in a ring shape, as proposed in a previous section.

[0059] The optical telecommunication system which has just been presented makes it possible to form an emission radiation I presenting a significant modal diversity thus making it possible to attenuate the effects of the fluctuations generated in the radiation by atmospheric disturbances.

[0060] Of course, the invention is not limited to the embodiments described and variant embodiments can be made without departing from the scope of the invention as defined by the claims.

[0061] A communication system according to the present invention may include other elements or devices than those presented in detail in this description.

[0062] For example, when a deport fiber F is provided between the processing device DT and the optical beam expander device T, an optical block for shaping the radiation produced by this fiber F can be added before injecting it into the optical beam expander device T. This optical shaping block can thus make it possible to adjust the shape of the recombined radiation to the nature of the optical beam expander device T: for example, in a disk for a telescope and in a ring for a telescope. This optical shaping block can be implemented using any suitable optical element: diffractive optical parts, spatial phase modulators, optical systems imaging or comprising at least one lens, axicons, an aspherical or free-form optical element, an MPLC device.

[0063] It is also possible to provide that some of the elements that make up the system can be used for both transmission and reception. This is particularly the case for the optical beam expander device T, telescope or telescope for example, the offset fiber F when it is present, or even the processing device DT.

Claims

Optical telecommunication system (1) in free space comprising: a modulation device (DM) producing a plurality of elementary light beams (R1-R N ) incoherent between them, each elementary light beam (R1-R N ) modulating the same digital data (M) to be transmitted; a processing device (DT) optically coupled downstream of the modulation device (DM) and configured to combine the elementary light beams (R1-R N ) and thus produce a so-called “combined” light radiation (R c ); an optical beam expander device (T), optically coupled downstream of the processing device (DT), for receiving the combined light radiation (R c ) and propagate emission radiation (I) in free space. Optical telecommunication system (1) according to claim 1 wherein the processing device (DT) comprises at least one multi-plane conversion device. Optical telecommunication system (1) according to the preceding claim in which the multiplane conversion device comprises a plurality of optical parts each having a reflective face for guiding the propagation of the elementary light beams (R1-R N ), at least one of the reflective faces having a microstructuring configured to combine the elementary light beams (R1-R N ) and form, during a plurality of reflections, the combined light radiation (R c ). Optical telecommunication system (1) according to the preceding claim in which the microstructuring is also configured to shape the elementary light beams (R1-R N ) composing the combined light radiation (R c ). Optical telecommunication system (1) according to one of the preceding claims configured to conform the combined light radiation (R c) to a flat-top shape. Optical telecommunication system (1) according to the preceding claim wherein the flat plate shape has a circular section to form a ring or a disc. Optical telecommunication system (1) according to one of the preceding claims in which the modulation device (DM) comprises a plurality of light sources associated with a plurality of modulators to produce the plurality of elementary light beams (R1-R N ). Optical telecommunication system (1) according to the preceding claim in which the light sources emit radiation having wavelengths distinct from each other. Optical telecommunication system (1) according to one of claims 1 to 6 in which the modulation device (DM) comprises a wide spectrum source. Optical telecommunication system (1) according to one of the preceding claims comprising a remote optical fiber (F), optically arranged between an output port of the processing device and the optical beam expander device (T), to guide the propagation of the recombined light beam. Optical telecommunication system (1) according to the preceding claim when combined with claim 4 in which the elementary light beams (R1-R N ) are each conformed to a linear combination of modes exhibiting similar group delays. Optical telecommunication system (1) according to one of the two preceding claims in which the offset optical fiber (F) is a degeneration-raised fiber, such as a step-index fiber or an elliptical core fiber. Optical telecommunication system (1) according to one of claims 10 to 12 comprising an optical shaping block arranged between the optical offset fiber (F) and the optical beam expander device (T). Optical telecommunication system (1) according to one of the preceding claims in which the optical beam expander device (T) is a telescope or a telescope.

Images