Device for processing at least two single-mode light beams

Abstract

The invention relates to a processing device (D) for at least two incident beams having phases and / or amplitudes that may vary. The processing device (D) comprises at least, successively connected by gaps or waveguides, a first phase actuator circuit (1) for adjusting the phases of the incident beams (I); a multiplane conversion device (2); and a second phase actuator circuit (1') disposed downstream of the multiplane conversion circuit (2). The invention also relates to an optical system (S) using such a processing device (D) to recombine the incident beams (I) into a recombined light beam (I''). Figure to be published with the abstract: Fig. 1

Description

Title of the invention: Device for processing at least two single-mode light beams FIELD OF THE INVENTION

[0001] The present invention relates to a device for processing at least two monomode and mutually coherent light beams, for example with a view to their recombination. This device can find numerous applications, and in particular for compensating for the distortion of the wavefront of light radiation. This distortion can originate from atmospheric disturbances during optical communication in free space. More generally, this distortion can be caused by the propagation of light radiation in its medium. The invention can find an application in the field of telecommunications or in the shaping of parts by laser. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] In the field of optics, it is sometimes sought to combine a plurality of single-mode and coherent light beams to form a single beam having, for example, an increased energy density, a chosen shape or point. This combination can be achieved by multiple means, for example using a diffractive grating as taught in document WO2007100752 or using a multiplane light conversion device (as proposed by the “TILBA” product from the company Cailabs or in document WO2020161126). In all cases, the optical quality of the combined beam is highly dependent on the phase matching and the equality of amplitude of the incident light beams.

[0003] However, these beams have properties that are not always perfectly controlled or directly controllable. For example, these beams may result from the modal decomposition of incident light radiation after propagation of this radiation in a medium (atmosphere, fiber, etc.). This propagation can cause significant distortion of the radiation and the beams that decompose it modally then have phase and amplitude variations between them, which also vary over time.

[0004] When the beams to be recombined are not perfectly controlled in phase or amplitude, the transformation carried out by the known coherent combining devices is not perfectly controlled, which can lead to deterioration of the quality or the power of the combined beam. Part of the energy present in the incident beams is in fact in this case absorbed, diffused or diffracted by the combining device and the combined beam is then not spatially concentrated. tially. It can thus present low amplitude radiation combined with a diffuse halo.

[0005] Generally speaking, it would be useful to have a device for regulating the relative phases and amplitudes of a plurality of light beams whose characteristics are not perfectly controlled, in order to make the subsequent manipulations that could be carried out on these beams robust. SUBJECT OF THE INVENTION

[0006] An aim of the invention is to propose such a device for processing at least two single-mode light beams. Another aim of the invention is to propose an optical system, taking advantage of this device, in particular to recombine the at least two single-mode light beams into a recombined single-mode beam. BRIEF DESCRIPTION OF THE INVENTION

[0007] In order to achieve this aim, the object of the invention proposes a device for processing of at least two monomode and mutually coherent light beams, called "incident beams", the incident beams having phases and amplitudes capable of varying, the processing device comprising at least, successively connected to each other by free spaces or by waveguides according to a main direction of propagation:

[0008] a first phase actuator circuit for adjusting the relative phases of the incident beams; a multi-plane conversion device for receiving, on a first optical port, the light beams from the first phase actuator circuit and configured to distribute the energy of these beams towards at least two single-mode light beams, called “converted beams”, produced at a second optical port; a second phase actuator circuit arranged downstream of the multiplane conversion device for adjusting the relative phases of the converted beams (D.

[0009] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically feasible combination:

[0010] the converted beams at the output of the second phase actuator have relative amplitudes and relative phases respectively conforming to setpoint relative amplitudes and setpoint relative phases; the multiplane conversion device comprises a plurality of micro-structured zones arranged on at least one optical element to intercept and spatially modify the respective phases of the incident beams during a plurality of reflections or transmissions separated by a propagation

[0011]

[0012]

[0013] free ; - the first phase actuator device and the second phase actuator device comprise a plurality of optical phase shifters associated with the incident beams and the processing device comprises at least one control device for generating control signals for the optical phase shifters; According to another aspect, the subject of the invention proposes an optical system comprising a processing device as presented previously and a spatial demultiplexer, arranged upstream of the first phase actuator device, the spatial demultiplexer receiving incident multimode light radiation and producing the incident beams. According to other advantageous and non-limiting characteristics of this aspect of the invention, taken alone or in any technically feasible combination: - the spatial demultiplexer is implemented by a multiplane conversion device; - the converted beams are arranged in a mosaic aperture configuration, the juxtaposition of the converted beams producing a single-mode recombined light beam; - The system comprises a spatial multiplexing device arranged downstream of the second phase actuator device, the spatial multiplexing device receiving the converted beams to recombine them into a single-mode recombined light beam; - The spatial multiplexing device is implemented by a multiplane conversion device; - The optical system comprises a reflective optical part arranged directly downstream of the second phase actuator circuit to back propagate the converted beams through the second phase actuator circuit and the multiplane conversion device and provide the single-mode recombined light beam at the first optical port of the multiplane conversion device; - The optical system comprises a device for extracting the single-mode recombined light beam, the extraction device being arranged between the first phase actuator circuit and the multi-plane conversion device; - the single-mode recombined light beam is formed only at a reserved mode of the first optical port of the multi-plane conversion device; - the processing device is coupled to a single-mode optical fiber into which the single-mode recombined light beam is injected; - The optical system comprises an optical receiver for receiving the single-mode recombined light beam; - the optical receiver comprises an optical amplifier of the single-mode recombined light beam, a spectral demultiplexer and / or a coherent or direct detection device; - the optical system comprises an optical transmitter for producing at least one single-mode emission light beam, called “emission beams”, the optical system emitting precompensated radiation in a direction opposite to that of the incident multimode radiation; - the optical system comprises a transmission subsystem, a reception subsystem, the transmission subsystem being configured from parameters determined in the reception subsystem; - the optical receiver and the optical transmitter are coupled to the processing device or to the spatial multiplexing device via an optical circulator; - the optical transmitter produces a plurality of emission beams and is arranged to counterpropagate at least part of each emission beam in a direction opposite to the main direction of propagation in the processing device; - The optical system includes a splitter device according to the wavelength or according to the polarization, such as a mirror or a dichroic filter; - The optical system comprises a light source, arranged upstream of the spatial demultiplexer, and producing the incident multimode light radiation; - The optical system comprises a shaping device arranged downstream of the second phase actuator device, the shaping device receiving the converted beams to produce a shaped light beam; - the relative phases and the relative amplitudes of the setpoint are chosen to give a predetermined shape to the shaped light beam. BRIEF DESCRIPTION OF THE FIGURES

[0014] 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:

[0015] [Fig.l]

[0016] [Fig.l] illustrates the principles implemented in a treatment device according to the invention;

[0017] [Fig.2]

[0018] [Fig.2] represents a phase actuator circuit;

[0019] [Fig.3]

[0020] [Fig.3] illustrates the design of a Walsh mode family;

[0021] [Fig.4a]

[0022] [Fig.4b]

[0023] [Fig.4c]

[0024] Figures 4a, 4b, 4c illustrate variants of a processing device;

[0025] [Fig.5a]

[0026] [Fig.5b]

[0027] [Fig.5a], 5b illustrate an optical beam recombination system;

[0028] [Fig.6a]

[0029] [Fig.6b]

[0030] Figures 6a and 6b show two clever configurations of a beam recombination optical system;

[0031] [Fig.7]

[0032] [Fig.7] illustrates an example of application of the optical system for wavefront compensation;

[0033] [Fig.8]

[0034] [Fig.8] represents an optical system for wavefront compensation;

[0035] [Fig.9a]

[0036] [Fig.9b]

[0037] [Fig.9c]

[0038] [Fig.9d]

[0039] [Fig.9a], 9b, 9c, 9d represent optical systems for emitting pre-compensated light radiation;

[0040] [Fig. 10]

[0041] [Fig. 10] represents an optical system used for beam shaping and beam shape changing. DETAILED DESCRIPTION OF THE INVENTION Definitions

[0042] For the sake of clarity, a light beam is defined in the present application 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.

[0043] The term "shape" of a beam will be used to designate 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.

[0044] The term "relative phases" of a plurality of single-mode beams will denote the phase differences existing between each beam of the plurality and a beam chosen as the reference beam. General principles

[0045] [Fig.l] illustrates the principles implemented in a processing device D conforming to several modes of implementation. The device D receives at its input at least two monomode and mutually coherent light beams I. These beams I are spatially separated, that is to say that their shapes do not intersect or only slightly at an input plane Pe of the device D. The device D produces at its output at least two output light beams I' (also called "converted beams"), also spatially separated, whose amplitudes and phases are regularized. The number of incident light beams I and the number of output light beams I' of the device are identical. The number of beams I, I' can be chosen very freely, according to the need. It is typically between 2 and 50, or between 2 and 100, or even more.

[0046] Several examples of application in which such incident beams, single-mode and coherent with each other, can be produced will be seen in a later section of this description. But generally speaking, it may be a multi-mode light radiation whose modes have been spatially separated or a plurality of single-mode beams from synchronized sources. In all cases, the incident light beams I are likely to fluctuate in time, in amplitude and in phase, independently of each other, even if it is not excluded that at a given instant, at least some of these incident beams I have the same phases and amplitudes.

[0047] The incident beams I can be distributed spatially freely in the input plane Pe of the device, for example along a line as in the schematic illustration of [Fig.l], or arranged in a matrix or in a hexagon. This arrangement can be ensured by a network of fibers forming an input stage of the device D (not shown in [Fig.l]) when the propagation of the incident light beams I, upstream and / or downstream of the input plane Pe, is guided. But the propagation of the incident light beams I can also take place in free space, and it is then possible to provide optical parts (mirrors, prisms, etc.) to ensure the arrangement of the beams between them according to the arrangement chosen in the input plane Pe. The same comments apply to the output light beams I' and their relative positioning in an output plane Ps.In this respect, it is possible to provide device D with an output stage, for example in the form of a fiber optic network.

[0048] In the schematic diagram of [Fig.l], a main direction of pro is shown propagation P of the incident beams I in the device D. This propagation is rectilinear here, but this does not constitute a limitation, and one could foresee that the beams propagate in the device D according to a more complex optical path, defined by waveguides connecting the different optical circuits of the device and / or by optical parts when this propagation takes place at least partly in free space.

[0049] Generally speaking, the processing device D seeks to regularize the amplitude and phase of the incident beams I. By "regularize", it is meant that the converted beams I' have relative phases and amplitudes which do not fluctuate in time with respect to each other, or in any case to a much lesser extent than the fluctuations affecting the relative phases and amplitudes of the incident light beams I. Generally speaking, the aim is to ensure that the relative phases of the converted beams I' conform to setpoint phases, and that the amplitudes of the beams conform to determined, setpoint relative amplitudes. For example, in certain cases, the device D may be configured so that the converted beams I' have zero relative phases, and amplitudes which are all equal to each other.But this choice is by no means imperative, and the device D can be configured and controlled for a wide variety of relative phase and relative amplitude setpoints of the output light beams I'. The relative phase and relative amplitude setpoints can also be modified over time, according to the needs of the application and / or a user. It is of course possible for the phases and amplitudes of the converted beams I' to fluctuate over time (particularly when the combined energy of the incident beams I varies), but these fluctuations in the parameters of the converted beams I' are not entirely independent of each other: for example, the respective amplitudes of the converted beams I' may fluctuate, but these fluctuations are substantially the same for each of the beams.Also, once the regulation implemented by the processing device D is well locked, the converted beams I' are much more stable over time than the incident beams I, i.e. the dispersion of their respective parameters (relative phases and relative amplitudes) is much more reduced.

[0050] To carry out this regularization processing, the device D which is the subject of the present description comprises at least:

[0051] - a first optical phase 1 actuator circuit; - a multiplane optical conversion device 2 (designated “MPLC device”) in the rest of this description); - a second optical phase actuator circuit 1'.

[0052] These three elements are arranged successively in the main direction of propagation P, that is to say that the MPLC device 2 is arranged optically downstream of the first phase actuator circuit 1, and that the second optical phase actuator circuit 1' is optically arranged downstream of the MPLC device 2. These elements are connected to each other by free spaces or by waveguides allowing the propagation of the light beams. Advantageously, and to maintain its simplicity, the processing device D does not provide, directly downstream or directly upstream of the MPLC device 2, other circuits capable of significantly modifying the phase or the amplitude of the beams other than those listed above.

[0053] To simplify the expression, the term "incident beams" will refer to the beams incident on the processing device D and those propagating to a first optical port of the MPLC device 2. The term "converted beams" will refer to those produced by the MPLC device 2 at a second optical port and propagating downstream of this device 2 and at the output of the processing device D.

[0054] In certain embodiments, the MPLC device 2 has the function of regulating the amplitude of the incident beam I. To do this, it is important to properly control the relative phases of the light beams entering this circuit. For this purpose, the processing device 1 provides the first optical phase actuator circuit 1, arranged directly upstream of the MPLC device 2.

[0055] The transformations carried out by the MPLC device 2 on the amplitude of the incident beams I to regularize them, however, affect the relative phases of the converted beams I'. Also, the processing device D provides a second optical phase actuator circuit 1', directly downstream of the MPLC device 2, so that the converted beams I', once processed by this second circuit 1', have both well-controlled amplitudes and relative phases.

[0056] More generally, the optical phase actuator circuits 1,1' form adjustment variables for the beams propagating in the processing device D, which can therefore be modified at will depending on the intended application objective.

[0057] [Fig.2] represents by way of illustration a phase actuator circuit which can be used as first and / or second circuit 1, 1' of the processing device D of [Fig.l].

[0058] This circuit comprises a plurality of optical phase shifters A respectively associated with input light beams Ie of the circuit. Each optical phase shifter A provides a replica Is of the input light beam associated with it, phase-adjusted by a controllable value, but whose amplitude remains substantially unchanged. An optical phase shifter A can be implemented by a phase shifter or a delay line. It can thus be a continuously deformable mirror, or a segmented deformable mirror, a spatial light modulator, an electro-optical phase modulator, a fiber stretched by a piezoelectric module, a piezoelectric mirror on a wedge, or any other suitable means.

[0059] The circuit of [Fig.2] also comprises an electro-optical control circuit CDE. This control circuit receives as input quantities e; representative of the light beam(s) that are to be regulated, and produces control signals Sj for the optical phase shifters A aimed at controlling the phase adjustment value. The control circuit CDE can also receive a reference quantity c (or a vector of quantities) defining the quantities targeted for the parameters of the light beam(s) that are to be regulated. These representative quantities can correspond to phase or intensity information of the light beam(s) that are to be regulated.

[0060] In a very general manner, the control device CDE implements a regulation method, and produces the control signals Sj of the optical phase shifters A so that the light beam(s) that one seeks to regulate indeed have parameters equal to or approaching the setpoint quantity.

[0061] By way of illustration, and as reproduced in the example of [Fig.2], the inputs e; of the control device CDE can correspond to a sampling of the light beams Is produced directly by the circuit. The control circuit CDE can then determine the relative phases of these beams, for example by making them interfere with each other. In this case, the control device CDE can be configured so that it produces the control signals Sj aimed at adjusting the phase shift introduced by each optical phase shifter A so that the relative phases of the light beams produced at the output of the phase actuator circuit Is correspond to relative phases of the setpoint c, for example so that these relative phases are zero.

[0062] It is not necessary for the inputs e; of the device to correspond precisely to quantities representative of the light beams Is produced at the output of the actuator circuit. The inputs e; may correspond to quantities representative of one or a plurality of light beams produced further downstream.

[0063] By way of illustration, the regulation implemented by the CDE control device may seek to optimize a residual energy between a target beam (or a plurality of target beams), i.e. a beam having the desired phase and amplitude characteristics, and the beam actually produced (or beams actually produced). This optimization may be based on a gradient method, on a stochastic method, on an interpolator configured by learning, for example a neural network, on an interpolator configured by fuzzy logic, or more conventional regulation methods, for example Kalman, adaptive or robust.

[0064] When a processing device uses several phase actuator circuits, as is the case of a processing device D conforming to the implementation modes described in the present application, a single control device CDE can be shared to control the optical phase shifters A used in the constitution of each of these circuits.

[0065] The MPLC device 2 of the processing device has a first optical port for receiving the incident light beams I from the first phase actuator circuit 1. It also has a second optical port from which light beams I', called "converted", and produced by the MPLC device 2, propagate.

[0066] It is recalled that in such 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.

[0067] By "microstructured zone" is meant 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 there or which is transmitted there.

[0068] Thus, light radiation which propagates 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 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.

[0069] The theoretical foundations and examples of practical implementation 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 / November 2010; N. Fontaine et Al, (ECOC, 2017), “Design of High Order Mode-Multiplexers using Multiplane Light Conversion”; US9250454 and US2017010463.

[0070] The MPLC device 2 of the processing device D is configured to distribute the energy of the incident beams I received on the first optical port between the beams converted I' beams that propagate from the second optical port. This distribution aims to regularize the amplitude of the converted I' beams. As already stated, this distribution is not necessarily egalitarian, even if such an egalitarian distribution of energy between the converted I' beams is a possibility.

[0071] As presented in detail in the aforementioned documents, the micro-structured zones carried by the optical part(s) forming the MPLC device 2 are designed and configured to carry out a modal conversion aimed at decomposing the light radiation received on the first optical port (this radiation being constituted, in combination, by the incident beams I) into a family of modes called “input”. The energies present in the modes of the input family are transported and respectively conformed to the modes of a family of “output” modes at the second optical port. The MPLC device is configured to respectively match the modes of the input base and the modes of the output base. It is a passive device and the transfer function of which is particularly stable and robust.

[0072] In the case of the processing device D of [Fig.l], each mode of the input family is associated with a single light beam received on the first optical port. Simultaneously, each mode of the output family is associated with the plurality of converted beams I', at the second optical port. The energy of a beam, and more precisely the portion of energy of the beam which is projected into the mode of the input base with which it is associated, is therefore distributed in one of the modes of the output base, and therefore in the plurality of output beams.

[0073] As an example of a configuration of the MPLC device 2, the family of input modes may comprise a base of N separate Gaussian modes, each mode of the base being spatially matched to one of the N light beams received on the first optical port. The family of output modes may be formed of N Walsh modes. It is recalled that Walsh modes are modes comprising several distinct lobes, for example Gaussian lobes. A family of N Walsh modes may be constructed from a base distribution respectively multiplied by the Walsh function Wk(x), for k = 1, 2.. .N, as illustrated in [Fig. 3] in the case of a family composed of 4 modes Wl, W2, W3, W4 (in one dimension in this figure, it being understood that in the context of the application these modes extend spatially). In the representation of [Fig.3], the N lobes of the basic distribution are Gaussian and of identical amplitudes, but this is not necessarily the case.

[0074] The MPLC device 2 is configured to associate a Gaussian mode of the input base with a Walsh mode of the output base. The energy of a beam received on the first optical port (in correspondence with one of the modes of the input base) is transported in the MPLC device to conform to the Walsh mode with which this mode of the input base is associated. This energy is therefore distributed in each of the lobes of this mode. When we take into account all the incident beams I received on the first input port, we understand that the light radiation at the second optical port has N lobes in which all the energy of the incident beams is concentrated and distributed. The converted light beams correspond to the lobes of this radiation.

[0075] Of course, the Gaussian and Walsh modes taken as examples are given only for illustration purposes. One could choose modes other than those of Gauss to constitute the family of input modes and modes other than those of Walsh to constitute the family of output modes. It can thus be a collection of output modes corresponding to the discrete Fourier transform of the input modes. Thus, for the j-th input mode (among N input modes), the associated output mode, corresponding to a converted beam I', can be made up of N lobes, for example Gaussian lobes, for which the phase of the k-th lobe is equal to:

[0076] 2njk

[0077] According to a particularly advantageous embodiment, each mode of the family of output modes comprises a plurality of lobes (as is the case in the example shown in [Fig. 3]), but these lobes are not of purely Gaussian shapes: they are made up of a main lobe (which may be Gaussian) and a secondary lobe, of smaller dimension and lower amplitude. These secondary lobes are not intended to collect a lot of energy, but can be used to produce the inputs ei of the control devices CDE, for example that of the first and / or second phase actuator circuit 1. By producing secondary beams by the MPLC 2 (in correspondence with the secondary lobes of the modes of the family of output modes), it is possible to avoid taking from the converted beams the portion of energy necessary for implementing the phase regulation and the insertion of an optical part to carry out this taking.

[0078] It is possible to supplement the processing device D of [Fig.l], downstream of the second optical phase actuator circuit 1', with at least one block B consisting of another MPLC device 2 optically coupled to another optical phase actuator circuit 1'. The processing device D, in general, can therefore be constituted by a concatenation of a number M of such blocks B, downstream of the first phase activator circuit 1, and can therefore comprise, in an interlaced manner, M+1 phase activator circuits 1' and M MPLC device 2. It is thus possible, in composing the optical processing applied to the incident beams I in several stages - each implemented by a block B - better control the optical transformations carried out by simplifying the operations carried out in each stage. Such a configuration in several stages is represented in [Fig.4a].

[0079] Alternatively or in addition to this variant, it may be provided that the processing device D comprises a second MPLC device 2', in parallel with the first MPLC device 2, as shown in [Fig.4b]. Only a portion of the incident beams I are applied to the input of the first MPLC device 2, the complementary incident beams being applied to the second MPLC device 2'. This configuration may be particularly useful when the number of incident beams is large, for example of the order of 100 or more, in order to simplify the design of the MPLC devices 2, 2'.

[0080] Finally, it can be provided that the processing device D comprises two processing devices D1, D2, each of these devices being in accordance with the general description which has just been given of such a processing device. Such a configuration is shown in [Fig.4c]. Optical beam recombination system

[0081] A possible application of the processing device D which has just been presented is that of the recombination of the incident beams I into at least one single-mode recombined light beam I”, called “recombined beam”.

[0082] In this application, illustrated in Figures 5a and 5b, an optical system S is formed by arranging downstream of the processing device D, directly behind the last phase actuator circuit 1, a spatial multiplexing device MX. This spatial multiplexing device MX (which could also be referred to as an “optical mixer” or “combining device”) receives as input the converted beams I' to recombine them together into at least one recombined beam I”. It is noted that it is possible for the spatial multiplexing device MX to have several outputs, and therefore for it to recombine the converted beams F into several recombined beams I”. The beam(s) I” recombined by the spatial multiplexing device MX then concentrate all the energy of the incident beams I.

[0083] The MX spatial multiplexing device can be produced in any suitable form, for example by means of an MPLC device, configured like that described in document WO2020161126, by a photonic lantern, freeform optics, a spatial light modulator, diffractive optical elements, an interferometric system, a Dammann grating, etc. The MX spatial multiplexing device, whatever its mode of implementation, can take a photonic integrated form or a discrete optical component form.

[0084] According to a particularly interesting variant, the converted beams I' do not require a spatial multiplexing device MX to be recombined and form the recombined beam I”. According to this variant, at the output of the processing device D, the converted beams I' are arranged close to each other, in a mosaic aperture configuration (or "tiled aperture" according to the established English expression). Such an arrangement can be produced by the MPLC 2, if the latter has been designed to produce such a result. In this configuration, the recombined beam I” can be very simply formed by the simple juxtaposition of the converted beams I', and the spatial multiplexing device MX can be substituted, optionally, by simple collimating lenses arranged opposite each converted beam I' in order to constitute the recombined beam I”.

[0085] In the illustration of [Fig.5a], the inputs ei of the control devices of the first and second phase actuator circuits 1,1' correspond, respectively, to the converted beams supplied by the MPLC device, and to the recombined beam I”. In the illustration of [Fig.5b], the inputs e; of the control devices of the first and second phase actuator circuits 1,1' are formed solely from the recombined beam I”. As already mentioned, it could be envisaged to share a single control circuit CDE 'for the two phase actuator circuits 1,1'.

[0086] [Fig.6a] represents a clever configuration of an optical system S implementing a processing device D for this recombination application. This configuration results from the fact that the MPLC device 2 of the processing device (or the most downstream of these devices if several are present) itself carries out a demultiplexing operation: the energy supplied by an incident beam I on the first optical port of the MPLC device 2 is distributed over all the converted beams I' of the second port of this device. Such an MPLC device being reversible, it carries out a multiplexing operation identical to that implemented by the spatial multiplexing device MX when the light beams propagate in the opposite direction to the main direction P, therefore from the second optical port to the first optical port.

[0087] This observation is taken advantage of in the arrangement of the system S shown in [Fig.6a]. In this arrangement, a reflecting optical part M, for example a mirror, is placed downstream of the processing device D. The converted beams I' are reflected on this reflecting optical part M, and the reflected beams Ir, in dotted lines in [Fig.6a], propagate in the processing device D in the opposite direction to the main propagation direction P. In doing so, the reflected beams Ir propagate successively in the second phase actuator circuit 1' and then in the MPLC device 2, via the second optical port. The latter recombines these light beams Ir to form a recombined beam I”, made available on the first optical port of the MPLC device 2. To simplify [Fig.6a], [Fig.6a] has not been shown in This figure shows the inputs e; of the phase actuator circuits 1,1', but they are naturally present.

[0088] An extraction device 4, for example an optical circulator, of the recombined light beam I”, may be provided, the extraction device 4 being arranged between the first phase actuator circuit 1 and the multiplane conversion device 2, so as to redirect the recombined light beam and extract it from the processing device D, before it propagates in the first phase actuator circuit 1. In the configuration of [Fig.6a], the setpoint values ​​of the processing device D, in phases and amplitudes, are chosen so that the reflected beams Ir, propagating through the MPLC device 2, recombine into a recombined beam I” (or a plurality of recombined beams I”) in correspondence with at least one mode of the input base of this device 2.

[0089] In a variant of this configuration shown in [Fig.6b], it is possible to design the MPLC with a family of input and output modes each having N+1 modes, N corresponding to the number of incident radiations received on the first optical port of the MPLC device 2. A mode of the input family is reserved, that is to say that none of the incident beams I is matched, in the input plane Pe of the MPLC device 2, with this reserved mode.

[0090] At the same time, the MPLC device 2 can be configured so that the illumination of this reserved mode produces converted beams F having determined relative phase and amplitude characteristics. These characteristics form the relative phase and amplitude setpoints of the processing device D which apply to the reflected radiation Ir at the output of the second phase actuator circuit 1'. When the regulation implemented by the control device(s) CDE is properly locked to these relative phase and amplitude setpoints, the reflected radiation Ir is recombined by the MPLC device into a combined radiation I” generated on the first optical port only at the level of the reserved mode of the input mode family. In this way, it is possible to avoid placing a complex extraction device in the processing device, as is the case in the configuration of [Fig.6a].

[0091] It is noted that in the optical system of figures 6a, 6b, the second phase actuator circuit 1' is crossed a first time by the converted beam F then by the reflection of this beam, and that therefore the phase shifts imparted to the beams are double that imposed by the optical phase shifters A. This can naturally be taken into account in the regulation implemented by the control device CDE of these circuits. In the configurations of figures 6a, 6b the MPLC device 2 constitutes the spatial multiplexing device MX making it possible to recombine the converted light beams F.

[0092] Application of the optical recombination system for compensating for the distortion of light radiation

[0093] With reference to [Fig.7], an example of use in the field of telecommunications of the optical recombination system S for compensating for the distortion of a wavefront is presented.

[0094] In this purely illustrative example, a transmitter SAT - here a communication satellite - emits light radiation for transmitting a message towards a base station BASE in a perfectly conventional manner. The light radiation can have several wavelengths, as is usually the case for WDM type transmissions. The light radiation directly emitted by the satellite SAT has a regular shape. During its propagation in free space, the emitted radiation is subject to atmospheric disturbances in the atmosphere PA, so that the light radiation arriving at the base station BASE has amplitude and phase aberrations. This phenomenon affects the shape of this radiation, which takes on a shape that varies over time, in an erratic and irregular manner.As a result, this radiation is injected with little efficiency, and in a time-varying manner, into a single-mode optical fiber necessary for the optical amplification of the signal and its coherent detection.

[0095] Despite this phenomenon, an attempt is made to exploit in the base station BASE the radiation received via an optical receiver OR in order to decode the transmitted message, by direct or coherent detection. For this purpose, a telescope T is provided to collect a portion of the light radiation received with the possible assistance of other optical elements such as an orientable mirror M. The radiation received (and more precisely the portion collected by the telescope T of this radiation) is directed towards the optical system S used here for the compensation of the distortion of a light radiation / Io. This system seeks to compensate at least in part for this distortion in order to provide a recombined single-mode light beam I” whose distortion is less than that of the received radiation Io. The recombined single-mode light beam I” is then coupled with greater efficiency and stability into a single-mode fiber SMF which makes it possible to guide this beam towards the optical receiver OR..

[0096] In this application example, the radiation energy received at the telescope T is generally very low, in particular because the power of the transmitter on board the satellite SAT is limited, and because of the pointing errors, deformation, expansion of the light beam emitted during its propagation in free space. It is therefore important, for reasons of transmission bandwidth, that the optical system S transmits a maximum of the collected energy to the receiver OR.

[0097] [Fig.8] illustrates the optical system S used for distortion compensation of a wavefront shown in [Fig.7]. In this system S, we recognize the processing device D and the spatial multiplexing device MX. It is noted that any of the optical systems S presented in connection with the description of Figures 5a, 5b 6a, and 6b could be suitable in this particular application. The optical system of [Fig.8] further comprises a spatial demultiplexer DX, arranged upstream of the first phase actuator device 1, the spatial demultiplexer DX receiving incident multimode light radiation Io and producing the incident beams I. Again, this demultiplexer DX can take any suitable form, an MPLC device, a photonic lantern, etc.

[0098] The optical system S therefore receives the incident multimode light radiation Io which it decomposes into the plurality of incident beams I. These single-mode beams I, whose characteristics (amplitudes and phases) are very variable due to the amplitude and phase aberrations of the incident radiation 10 received, are projected into the processing device D. The latter regularizes these incident beams I, as was presented in an initial section of this description, by adjusting the optical phase shifters A of the phase actuator circuits 1,1'. The converted beams F, and therefore regularized, are recombined by the spatial multiplexing device MX to form the recombined single-mode light beam I”,. This can be injected into the single-mode fiber SMF allowing it to be guided to the receiver OR for the purpose of analyzing and / or decoding the transmitted message.It is possible to envisage that the OR receiver integrates functions of amplification of the recombined light beam I”, of spectral demultiplexing, in particular in the context of WDM transmission, and coherent or direct detection.

[0099] It is noted that the proposed solution is particularly original, insofar as it does not require processing the incident multimode light radiation Io by an adaptive optics device as is often the case in state-of-the-art solutions aimed at compensating for the distortion of a wavefront of light radiation.

[0100] The phase shifts imparted by the optical phase shifters A of the phase actuator circuits 1, 1', when the regulation implemented by the control device(s) CDE is properly locked, form in a way a signature of the disturbances undergone by the incident multimode radiation 10 during its propagation.

[0101] In an improved version of the optical system S which has just been presented, we take advantage of the locking of this regulation to exploit this optical system S, or a Siamese optical system, in emission. In this emission mode, we emit and propagate a “pre-compensated” emission radiation, that is to say deformed in such a way that, when this radiation reaches its target (here the emitter S AT which emits the original transmission light radiation), this radiation presents a deformation of its reduced wavefront. This pre-compensation is precisely that defined by the phase shifts imparted by the optical phase shifters A of the phase actuator circuits 1, 1'.

[0102] Figures 9a, 9b and 9c show optical systems S configured to implement such emission of precompensated radiation.

[0103] The optical system S of [Fig.9a], is composed of two perfectly identical, conjoined subsystems SI, S2. The first subsystem SI is a reception subsystem, such as that described previously in the various configurations described. It is composed of a demultiplexer DX, a processing system D and a spatial multiplexing device MX. It therefore receives incident multimode light radiation 10 and provides a recombined light beam I”. This transformation leads the control device(s) CDE to establish, for determined durations, the values ​​of the phase shifts applied to the optical phase shifters A of the phase actuator circuits 1, 1'. As has just been stated, these phase shift values ​​"sign" the nature of the disturbances undergone by the incident multimode radiation 10 during its propagation.

[0104] The second subsystem S2 is a transmission subsystem. In this subsystem S2, we find the same demultiplexer DX, processing system D, spatial multiplexing device MX as in the subsystem SL. In addition, the subsystem S2 is associated with an optical transmitter OE, for example a telecom transmitter producing radiation modulated in amplitude or in phase by direct or coherent modulation. This transmitter OE emits a single-mode beam E which propagates successively in the spatial multiplexing device MX, the processing system D and the demultiplexer DX, in order to emit emission radiation E0 in a direction opposite to that of the incident radiation 10.In order to compensate for the phase and amplitude distortions that this radiation E0 will undergo during its propagation, provision is made to configure the transmission subsystem S2 by applying to the optical phase shifters A of its phase actuator circuits the same values ​​as those determined by the control device CDE of the first reception subsystem SI, or values ​​derived therefrom. In other words, the transmission subsystem S2 is configured from parameters determined in the reception subsystem SL. These parameters may correspond to the values ​​of the phase shifts applied to the optical phase shifters A of the phase actuator circuits 1, 1' of the reception subsystem SI, or to parameters linked to these values. In this way, the two subsystems SI, S2 are perfectly conjoined, and the transmission radiation E0 is pre-compensated from the distortion information collected in the reception subsystem SL.

[0105] In the optical system S of [Fig.9b], a single device is used processing to simultaneously receive the multimode incident radiation 10 and emit the pre-compensated emission beam E. The optical receiver OR and the optical transmitter EO are both arranged downstream of the spatial multiplexing device (in the direction of propagation of the recombined radiation I”), and these radiations propagate, in the demultiplexer DX, the processing system D and the spatial multiplexing device MX along the same optical paths, but in opposite directions. An optical circulator C is provided in the assembly shown in [Fig.9b] to direct the recombined beam I' ' towards the optical receiver, and to direct the emission radiation towards the spatial multiplexing device MX. These propagations can be fibered.

[0106] More generally, and depending on whether or not a spatial multiplexing device MX is included in the optical system S, the optical receiver OR and the optical transmitter OE can be coupled to the processing device D or to the spatial multiplexing device MX via an optical circulator C.

[0107] In a variant not shown of the system of [Fig.9b], the optical circulator C can be omitted. However, the optical system S can be used in both transmission and reception, for example by alternating its operation between one and the other of these two modes. Alternatively, the transmission beam E can be chosen so that it has a polarization or a wavelength different from a polarization or a wavelength of the incident beams I, and a splitter device can be inserted according to the wavelength or according to the polarization, such as a mirror or a dichroic filter.

[0108] In the optical systems S of figures 9c, 9d, the optical transmitter OE produces a plurality of single-mode emission beams E. These beams have well-controlled relative amplitudes and relative phases, which are therefore stable over time. The transmitter OE comprises a master source producing master light radiation. This may for example be a laser source. The master source is connected to an optical splitter to establish a plurality of beams from the master light radiation. To allow phase control of the light beams produced, the beams are coupled to a phase actuator circuit conforming to the circuit shown in [Fig.2]. The optical transmitter OE LS may also provide an optical amplification stage associated with each beam to provide usable emission light beams E.And as already noted, the optical transmitter OE may include an amplitude and / or phase modulator for each beam.

[0109] In the optical systems S configured in transmission-reception of figures 9c and 9d, the optical transmitter OE is arranged to counter-propagate at least part of each transmission beam E in a direction opposite to the main direction of pro pagation P in the treatment device D. The emission beams E advantageously have a polarization or a wavelength different from a polarization or a wavelength of the incident beams I.

[0110] The emission beams E therefore propagate in this processing device D and therefore undergo the inverse transformations to those applied to the incident light beam I. Just as in the two previous examples, the processing device D therefore establishes a plurality of converted emission beams E' which are recombined by the demultiplexer DX to provide the pre-compensated emission radiation E0.

[0111] In the optical system S of [Fig.9c], the inputs p; of the control device CDE of the phase actuator circuit of the optical transmitter OE correspond to a sampling of the light beams E produced directly by this transmitter OE. In the system of [Fig.9d], the emission beams are separated by an optical splitter (not shown) and a part of the emission beams E are also directed towards the spatial multiplexing device MX, for example by beam splitter mirror or an optical circulator. This part of the emission beams are therefore recombined into a single-mode beam E” whose characteristics form the inputs p; of the control device of the phase actuator circuit of the transmitter OE. In this figure, the output of the spatial multiplexing device MX is therefore used to control the optical transmitter OE.

[0112] Application of the processing device D to changing the shape of a beam

[0113] [Fig. 10] represents an optical system S' used for shaping a beam and / or changing the shape of a beam. This system can be particularly useful in applications for dynamic shaping of laser light, for example for laser processing of parts, shaping, cutting, welding, drilling, surface functionalization, ablation of thin layers, or additive manufacturing. It is known that in these applications it can be useful to modify the shape of the beam which is projected onto the part, depending on the nature of this part or the treatment to be carried out. It is also known that in these applications the beam which is projected onto the part has a particularly high power, for example of the order of 100W up to 20kW in continuous mode and, in pulsed mode, from 10 micro-Joules to a few milli-Joules, or more.

[0114] In the system S' shown in this figure, there is a light source LS producing incident light radiation 10, separated by the demultiplexer DX into a plurality of single-mode incident beams I. These beams I have relative amplitudes and relative phases which are not perfectly controlled. One of the reasons may come from the fact that, in an industrial environment in which the laser source LS operates, it may be subject to uncontrolled movements, such as vibrations. These uncontrolled movements affect the regularity of the incident beams and in particular their respective phases.

[0115] We also find on this optical system S' of [Fig. 10], downstream of the treatment device D, directly behind the last phase actuator circuit 1, a shaping device BS which here has an output making it possible to supply the single-mode beam shaped J, this beam forming the laser treatment beam of the parts.

[0116] When the converted beams I' at the input of the shaping device BS are prepared by the processing device D according to a first configuration defined by the relative amplitudes and the relative setpoint phases, the shaping device BS combines these converted beams I' and transports their energy to form a shaped beam J of substantially round shape. In the same way, when the converted beams I' at the input of the shaping device BS are prepared by the processing device D according to a second configuration defined by second relative amplitudes and relative setpoint phases, the shaping device BS processes these converted beams I' and transports their energy to form a shaped beam J of substantially oval shape.

[0117] The shaping device BS can advantageously be implemented by an MPLC shaping device, specifically configured to carry out this transformation, i.e. transform the converted beams, when these conform to the relative setpoint amplitudes and phases of the first configuration, to produce combined radiation of round shape, and transform the converted beams, when these conform to the relative setpoint amplitudes and phases of the second configuration, to produce combined radiation of oval shape. The shaping device BS can alternatively or additionally comprise free-form optics, diffractive optical elements, etc. The relative setpoint amplitudes and phases constitute, as it were, a shape setpoint, making it possible to give a predetermined shape to the recombined beam I”, choosing here between a round shape and an oval shape.

[0118] Of course, the round and oval shapes of the J-shaped beam are given for illustration purposes only, and more generally, the shaping circuit BS can be configured to form a J-shaped beam that can have various shapes. For example, the family of output modes used to design the shaping circuit BS can include Hermite-Gauss modes, and specific combinations of these modes can be chosen via the “shape” instruction C applied to the optical system S'. In this way, the shape of the J-shaped beam, for example its size, and its defocus, can be changed.

[0119] We thus find in the illustration of [Fig. 10] the treatment device D in accordance with the general description given in a previous section of this description. This device therefore receives here a shape instruction C supplied as input to a control device CDE of the phase actuator circuits 1,1'. This shape instruction is interpreted by the control device CDE to selectively conform the converted beams I' to the first configuration of relative amplitudes and relative phases or to the second configuration of relative amplitudes and relative phases. In other words, when a first shape instruction C is applied to the processing device D, it produces converted beams I' conforming to the first configuration, and when a second shape instruction C is applied, different from the first, the processing device D produces converted beams I' conforming to the second.

[0120] Thus, with the system S' shown in [Fig. 10], it is possible to choose the shape of the power beam J which will be applied to the part to be treated, and to modify it continuously, by choosing and changing over time the shape instruction C applied to the treatment device D.

[0121] 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.

Claims

Claims

1. Device (D) for processing at least two monomode and mutually coherent light beams, called "incident beams", the incident beams (I) having phases and / or amplitudes capable of varying, the processing device (D) comprising at least, successively connected to each other by free spaces or by waveguides according to a main direction of propagation (P): - a first phase actuator circuit (1) for adjusting the relative phases of the incident beams (I); - a multiplane conversion device (2) for receiving, on a first optical port, the light beams coming from the first phase actuator circuit (1) and configured to distribute the energy of these beams towards at least two monomode light beams, called "converted beams", produced at a second optical port;- a second phase actuator circuit (1') arranged downstream of the multiplane conversion device (2) to adjust the relative phases of the converted beams (!').;

2. Processing device (D) according to the preceding claim in which the converted beams (!') at the output of the second phase actuator (1') have relative amplitudes and relative phases respectively in accordance with relative setpoint amplitudes and relative setpoint phases.

3. Processing device (D) according to one of the two preceding claims in which the multiplane conversion device (2) comprises a plurality of micro-structured zones arranged on at least one optical element to intercept and spatially modify the respective phases of the incident beams (I) during a plurality of reflections or transmissions separated by free propagation.

4. Processing device (D) according to one of the preceding claims in which the first phase actuator device (1) and the second phase actuator device (1') comprise a plurality of optical phase shifters (A) associated with the incident beams (I) and the processing device (D) comprises at least one control device (CDE) for developing control signals (Sj) of the de- optical phasers (A).

5. Optical system (S, S') comprising a processing device (D) according to one of the preceding claims and comprising a spatial demultiplexer (DX), arranged upstream of the first phase actuator device (1), the spatial demultiplexer (DX) receiving incident multimode light radiation (Io) and producing the incident beams

6. U)- Optical system (S, S') according to the preceding claim in which the spatial demultiplexer (DX) is implemented by a multiplane conversion device.

7. Optical system (S, S') according to one of the two preceding claims, the converted beams (!') being arranged in a mosaic aperture configuration, the juxtaposition of the converted beams (!') producing a single-mode recombined light beam rr”'»

8. Optical system (S, S') according to one of claims 5 to 6 comprising a spatial multiplexing device (MX; 2) arranged downstream of the second phase actuator device (1'), the spatial multiplexing device (MX; 2) receiving the converted beams (!') to recombine them into a single-mode recombined light beam (I”).

9. Optical system (S, S') according to the preceding claim in which the spatial multiplexing device (MX) is implemented by a multiplane conversion device.

10. Optical system (S, S') according to one of the two preceding claims, comprising a reflective optical part (M) arranged directly downstream of the second phase actuator circuit (1') to back propagate the converted beams (!') through the second phase actuator circuit (1') and the multiplane conversion device (2) and provide the single-mode recombined light beam (I”) at the first optical port of the multiplane conversion device (2).

11. Optical system (S, S') according to the preceding claim comprising a device (4) for extracting the single-mode recombined light beam (I”), the extraction device being arranged between the first phase actuator circuit (1) and the multiplane conversion device (2).

12. Optical system (S, S') according to claim 10 wherein the single-mode recombined light beam (I”) is formed only at a reserved mode of the first optical port of the multi-plane conversion device (2).

13. Optical system (S) according to one of claims 7 to 12 in which the processing device is coupled to a single-mode optical fiber (SMF) into which the single-mode recombined light beam (I”) is injected.

14. Optical system (S) according to the preceding claim comprising an optical receiver (OR) for receiving the single-mode recombined light beam (I”).

15. Optical system (S) according to the preceding claim, in which the optical receiver (OR) comprises an optical amplifier of the single-mode recombined light beam (I”), a spectral demultiplexer and / or a coherent or direct detection device.

16. Optical system (S) according to one of claims 13 to 15 comprising an optical transmitter (OE) for producing at least one single-mode emission light beam (E), called “emission beams”, the optical system (S) emitting precompensated radiation (E0) in a direction opposite to that of the incident multimode radiation (10).

17. Optical system (S) according to the preceding claim comprising a transmission subsystem (SI), a reception subsystem (S2), the transmission subsystem (S2) being configured from parameters determined in the reception subsystem (SI).

18. Optical system (S) according to claim 16 wherein the optical receiver (OR) and the optical transmitter (OE) are coupled to the processing device (D) or to the spatial multiplexing device (MX) via an optical circulator (C).

19. Optical system (S) according to claim 16 in which the optical transmitter (OE) produces a plurality of emission beams (E) and is arranged to counterpropagate at least part of each emission beam (E) in a direction opposite to the main direction of propagation (P) in the processing device (D).

20. Optical system (S) according to one of claims 11 to 16 comprising a splitter device according to the wavelength or according to the polarization, such as a mirror or a dichroic filter.

21. Optical system (S') according to claim 5 comprising a light source (LS), arranged upstream of the spatial demultiplexer (DX), and producing the incident multimode light radiation (Io).

22. Optical system (S') according to the preceding claim comprising a shaping device (BS) arranged downstream of the second phase actuator device (1'), the shaping device (BS) receiving the converted beams (!') to produce a shaped light beam (J).

23. Optical system (S') according to one of the two preceding claims in which the relative phases and the relative setpoint amplitudes (C) can be chosen to give a predetermined shape to the shaped light beam (J).

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