Apparatus and system for coherently recombining multi-wavelength light beams - Patents.com

Abstract

To provide an apparatus and system for coherently recombining multi-wavelength light beams.SOLUTION: A basic device 15 for coherently recombining a first fundamental beam F1 and a second fundamental beam F2, includes: a first input and a second input into which the first fundamental beam F1 and the second fundamental beam F2 are injected, respectively; an output for delivering an output beam corresponding to coherent recombination of the first and second fundamental beams; a delay line DL, arranged in one of paths of the basic beam, configured to induce a variable delay in the path; a variable coupler VC including a first 2×2 combiner Comb, a phase modulator PS, and a second 2×2 combiner Comb'; a control detector Det configured to generate an error signal ε from complementary beams; and a feedback loop BA for determining an applied delay and a phase difference from the error signal.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the field of optical communication through spatial multimode propagation channels, particularly in free space where the phase front of the information wave vector is more or less distorted when the wave strikes and passes through any disturbing medium, such as the atmospheric layer between the Earth and a satellite. According to another embodiment, the beam distortion occurs during the propagation through a multimode fiber due to coupling between spatial modes.

[0002] More precisely, the invention relates to devices and systems for receiving and optionally receiving / emitting light based on coherent recombination (and optionally splitting) of multi-wavelength light beams. [Background technology]

[0003] When the phase front of an information-carrying optical beam becomes distorted by travel through free space, the problem to be solved is to maintain an optimal link budget despite these distortions.

[0004] The first solution uses adaptive optics (e.g. a deformable mirror) to compensate for the distortions of the optical wavefront and optimize the light injection, typically into a single mode fiber connected to a detector. This approach has the advantages of addressing the entire pupil, handling both emission (before compensation) and reception cases, and being broadband (allowing WDM applications). In contrast, adaptive optics loops are limited in speed (in the order of ms in the best case) and prove insufficient for atmospheric distortions with bandwidths of around 1 kHz or larger.

[0005] The second solution is to use multiple aperture telescopes in an architecture that is said to have spatial diversity. It is assumed that each "sub-telescope" receives a part of the incident beam and the principle of the method is that spatial diversity allows to avoid spatial attenuation due to interference (speckle). Regardless of turbulence, at least one sub-telescope collects a non-zero signal. The signals delivered to detectors placed downstream of each telescope are summed electrically (non-coherently). The main disadvantage of this method is that the noise of each detector is summed, requiring as many detectors as there are sub-telescopes. Furthermore, it does not allow to improve the signal-to-noise ratio of the link.

[0006] A third solution, described in the document US 7974543, is proposed for use in a receiving system based on coherent recombination of modes / fundamental beams. The system comprises a matrix array of microlenses for sampling the incoming beam, said matrix array comprising two beams to be recombined as shown in FIG. M The beams are represented by two beams and are coupled to a coherent recombiner 10 which comprises a number of elementary 2×1 recombiners arranged in a cascade. Each elementary unit comprises two inputs, e.g. 1 and 2 or 3 and 4, corresponding to the two recombined beams of a phase shifter 16 arranged in the path of one of the beams and of a 2×2 coupler 11 having an output 12 which is detected by a detector 13. The signal detected by the detector 13 is minimized using electronics 15 (15a, 15b...), so that a phase shifter 16 (16a, 16b...) can apply a phase shift to the beam 2 to produce constructive interference at the second output 17 of the coupler 11.

[0007] The final output is 18, M All of the initial beams are combined into a single beam. A maximum signal of 18 is sought. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] U.S. Patent No. 7,974,543 Summary of the Invention [Problem to be solved by the invention]

[0009] One of the limitations of this type of system is the need to use a phase shifter (element 16) which limits the width of the spectral band of the incident beam that the system can process, as shown in Figure 2. Furthermore, the use of a single element does not allow for equalization of both the amplitude and phase of the two signals being recombined for optimal effect.

[0010] Consider the following situation in Figure 2. A point source S emits a light field E 0 is emitted and travels along two different paths T1 and T2 to reach the detector D. The first path T1 has a length L 1 and the second path T2 has a length L 2 For simplicity, we assume that the medium separating the source S from the detector D is non-dispersive, i.e. the refractive index is wavelength independent. Again for simplicity we assume that the two paths have the same attenuation, so the optical field incident on the detector has the same intensity regardless of whether it has taken path T1 or path T2. The equation for the optical field at the detector is therefore: E DET =E trajet1 +E trajet2 E DET =E 0 (t-τ 1 )+E 0 (t-τ 2 ) Here, τ 1 and τ 2 is the time it takes for light to travel along each of paths T1 and T2, i.e.

number

[0011] E 0 is a particular spectral component (e.g., modulation sidebands, or indeed E 0The spectral content of the electrical signal output by the detector at frequency ω is then

number

[0012] Here, it is assumed that there is a means (such as phase shifter 16 in the above mentioned article) to control the optical phase difference between the optical fields emitted from paths 1 and 2. The optical field at the detector side can then be written as E DET =E 0 (t-τ 1 )×e -iφ +E 0 (t-τ 2 ) where φ can be adjusted to maximize the received signal. Here, a signal i at frequency ω DET is equal to

number

[0013] It can therefore be seen that the above condition depends on the frequency ω of interest, and that its application, particularly for single optical carriers (non-WDM), is limited to applications around this frequency. Typically, for phase modulators, millimeter-sized components and refractive index changes of 10 -3 There is a deviation of 1-2×λ with materials that are on the order of λ.

[0014] Also, the emitter / receiver architecture requires that the lasers of the emitter and receiver systems have close but not identical frequencies (typically a few nm difference), which may be a significant drawback in the case of systems mounted on satellites, for example, or to accommodate the aging of laser diodes.

[0015] One of the aims of the present invention is to overcome the above-mentioned shortcomings by providing a basic recombining device that makes it possible to realize coherent broad-spectrum band recombination, and thus makes it possible to realize broadband receiving systems (and receiving / emitting systems, as appropriate) that are compatible with WDM architectures. [Means for solving the problem]

[0016] One subject of the invention is an elementary device for coherently recombining a first and a second elementary beam obtained by sampling a distorted incident beam, the first and second elementary beams having a spectrum including M wavelengths each forming an information carrying channel, the distortion inducing a delay between the first and second elementary beams, the elementary device comprising: a first input and a second input into which the first and second elementary beams to be recombined are respectively injected, an output for delivering an output beam corresponding to a coherent recombination of the first and second fundamental beams; a delay line disposed in one of the paths of the fundamental beam and configured to induce a variable delay in said path; a variable coupler including a first 2×2 coupler, a phase modulator and a second 2×2 coupler, the second coupler having a main output forming the output of the basic device and delivering said output beam, and a complementary output delivering a beam complementary to the output beam; a control detector connected to the complementary output and configured to generate from the complementary beam an error signal that decreases to zero when the phase modulator is configured to apply a phase difference that equalizes the intensities of the first and second fundamental beams and when the delay line is configured to apply a delay that compensates for the delay between the first and second fundamental beams; a feedback loop configured to determine the delay and phase difference to apply from the error signal.

[0017] According to another aspect, the invention relates to a device for coherently recombining N elementary beams obtained by sampling said distorted beam, N being a strictly positive even integer, comprising a plurality of elementary devices according to the invention arranged in a cascade to obtain a single recombined beam.

[0018] According to yet another aspect, the present invention provides a method for producing a method for manufacturing a semiconductor device comprising the steps of: - a device for spatially demultiplexing an incident beam, the device being configured to sample said incident beam into N elementary beams; a device for coherently recombining N elementary beams according to the invention, - a device for demultiplexing the wavelengths to form M beams, each of the M wavelengths forming one channel for carrying information; - M detectors associated with said M beams.

[0019] According to an embodiment of the receiving system according to the invention, the diffraction of the fundamental beam is limited.

[0020] According to one embodiment, the spatial demultiplexing device includes a matrix array of microlenses configured to spatially sample the incident beam.

[0021] According to another embodiment, the spatial demultiplexing device includes a multi-aperture telescope.

[0022] According to another embodiment, the spatial demultiplexer comprises N phase plates configured to perform a decomposition into N spatial modes.

[0023] According to another aspect, the present invention relates to a light receiving system according to the present invention, - M laser sources and M associated modulators configured to generate M beams at M wavelengths; a wavelength multiplexing device for forming a multi-wavelength beam; a device for coherently splitting the multi-wavelength beam into N elementary emission beams, i.e. a device substantially identical to the coherent recombination device according to the invention, but used in the opposite direction, in which the delay lines and the phase modulators apply respectively opposite delays and opposite phase differences to the delays and phase differences determined by the respective feedback loops of the coherent recombination device of the receiving system, thereby corresponding the N elementary emission beams to N beams which are conjugates of the N initial elementary beams, respectively; - a receiving / emitting system comprising an emitting system comprising a spatial multiplexing device which is substantially identical to the spatial demultiplexing device but is used in the opposite direction to convert the N elementary emitting beams into emitting beams which correspond to the conjugates of the incident beam, thereby pre-compensating for said distortion.

[0024] According to one embodiment of the receiving / emitting system, the coherent recombiner and the coherent splitter are identical, the spatial demultiplexer and the spatial multiplexer are identical, and the wavelength demultiplexer and M detectors on the one hand, and M laser sources, M associated modulators and the wavelength multiplexer on the other hand are coupled to the coherent recombiner / splitter by a circulator, and the system is further configured for alternating use for receiving and emitting.

[0025] In the following description several examples of embodiments of the device of the invention are presented, which do not limit the scope of the invention. These embodiment examples have both the essential features of the invention and additional features related to the embodiments in question. A better understanding of the invention, as well as other features, objects and advantages of the invention, will become apparent from the following detailed description, taken in conjunction with the attached drawings, given by way of non-limiting examples, in which: [Brief description of the drawings]

[0026] [Figure 1] As already mentioned, a receiving system based on coherent recombination of modes / fundamental beams according to the prior art is shown. [Diagram 2]As already described, we show the situation where a light field E0 is emitted from a point source S and reaches a detector D following two different paths T1 and T2. [Diagram 3] 1 shows a basic coherent recombination device according to the invention. [Figure 4] The optimal combining effect for each WDM channel is shown as a function of the residual delay value expressed in multiples of wavelengths. [Diagram 5] The intensity detected by the detector as a function of phase for a residual delay equal to 10×λ is shown for each channel being optimized. [Figure 6] The intensity detected by the detector as a function of phase for a residual delay equal to 35×λ is shown for each channel being optimized. [Figure 7] 1 shows a coherent recombination device according to the invention, comprising a number of elementary devices arranged in a cascade, such that a single recombined beam is obtained. [Figure 8] 1 shows a light receiving system according to the invention using a coherent recombination device. [Figure 9] 1 shows a first embodiment of a light receiving / emitting system according to the invention; [Figure 10] 2 shows a second embodiment of a light receiving / emitting system according to the invention.

[0027] For clarity, the same elements are designated by the same reference numerals throughout the drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] A basic coherent recombination device 15 according to the present invention is shown in FIG.

[0029] The device recombines a first fundamental beam F1 and a second fundamental beam F2 obtained by sampling an incident beam Fid that has been distorted, typically by free space propagation through atmospheric layers or by travelling through a multimode fiber with a small degree of depolarization. Due to the distortion, the beams F1 and F2 have different amplitudes and different phases.

[0030] I 0 is the intensity of the incident beam Fid, I1 is the intensity of F1 and I2 is the intensity of F2, where I1=ρ1.I 0 and I2 = ρ2.I 0 Let us assume that.

[0031] The spectrum of Fid is broad (a frequency comb or band) and has at least M wavelengths λ each forming a channel carrying information (e.g., WDM architecture). 1 , λ 2 , ...λ M (M is at least equal to 2).

[0032] The basic device 15 according to the invention has an architecture similar to that described in the document US 7974543, except for two equalization levels. The device comprises a first input Input1 and a second input Input2 into which the beams F1 and F2 to be recombined are injected, respectively, and an output Out delivering an output beam corresponding to the coherent recombination of the first and second basic beams that one wishes to maximize (constructive interference).

[0033] The delay R between the two fundamental beams F1 and F2 induced by the distortion 12 The first stage acts on the fundamental beam F2, making it possible to realize an absolute phase compensation independent of wavelength, as will be described later. For this purpose, the fundamental device 15 includes a delay line DL arranged in one of the paths of the fundamental beam, in this example F2, and configured to introduce a variable delay in this path.

[0034] The second stage acts on the amplitude difference between the two beams. For this purpose, the basic device 15 includes a first 2x2 combiner Comb, a phase modulator PS and a variable coupler VC, which includes a second 2x2 combiner Comb of a Mach-Zehnder interferometer or MZI architecture with two inputs and two outputs. F1 and F2 are mixed after the first combiner, so PS can be located in either of the two arms of the MZI. As shown in Figure 3, the inputs of the first combiner Comb are the two fundamental beams, one of which is delayed by a delay line. The phase modulator is located at one of the two outputs of Comb.

[0035] The second combiner Comb' has a main output forming the output Out of the basic device 15 and from which the output beam is delivered, and a complementary output delivering a beam complementary to the output beam.

[0036] The control detector Det is connected to the complementary output Sc. The control detector signal is determined by the coupling coefficient of the variable coupler VC, which is proportional to the intensity ratio ρ 2 / ρ 1 and the delay line DL compensates for the delay between the two beams, i.e. the absolute phase shift between channels 1 and 2.

[0037] Thus, the detector Det detects from the complementary beams F1 and F2 a phase modulator PS configured to apply a phase difference that equalizes the intensity of each of F1 and F2, and a delay line DL configured to apply a delay R between F1 and F2. 12 . . . , which generates an error signal ε that decreases to zero when configured to apply a delay that compensates for .

[0038] Finally, a feedback loop BA is configured to determine from the error signal ε the delay to be applied through the delay line and the phase difference to be applied through the phase modulator. Together the detector / feedback loop acts on DL and PS to minimize the complementary signal and therefore maximize the output signal.

[0039] Due to the fact of acting on the delay between the two beams F1 and F2, it is possible to achieve a wavelength-independent coherent recombination. Returning to the situation in Fig. 2, in the case of compensation by a delay element of the optical fields emitted from paths T1 and T2, the equation of the optical field received by the detector is: E DET =E 0 (t-τ 1 -τ) × e -iφ +E 0 (t-τ 2 ) where τ is the adjustable delay.

[0040] where the signal i at frequency ω DET is equal to

number

[0041] To maximize the received signal, the following conditions must be met: cos[ω(τ 1 -τ 2 +τ)]=1 That is τ=τ 2 -τ 1

[0042] It can be seen that since the optimization conditions are now independent of the optical frequency, the received signal can be optimized regardless of the laser frequency and therefore for broadband and / or WDM signals or even for two emitter / receiver lasers of potentially widely different wavelengths.

[0043] Regarding the accuracy of the delay compensation, in order not to disturb the transmitted signal in telecommunications, the delay must be compensated with an accuracy called the residual delay δτ (residual delay after compensation) better than or equal to the symbol duration, where the symbol duration is defined as the duration of one bit of information, or the inverse of the modulation frequency (compatible with a single carrier wavelength).

[0044] For a single wavelength λ (single channel) signal modulated at 10 GHz, the symbol duration is equal to 100 ps. Thus, typically, a maximum residual delay of 10 ps (1 / 10 of the symbol time) is required, which corresponds to a phase shift of 2000×λ at λ=1550 nm (a wavelength typically used in telecommunications). This delay, expressed in multiples of wavelengths, is calculated by the fact that light travels at a speed of c=3×10 in a time of 10 ps. 8 ms -1 It is calculated by calculating the distance traveled by the light, expressed as a multiple of the wavelength. That is,

number

[0045] In practice, there are two types of delay: fixed or static delay, due for example to differences in fiber length between the various channels, and dynamic delay, due for example to atmospheric turbulence.

[0046] The delay difference due to atmospheric propagation (dynamic distortion) is much smaller than 2000×λ, and static compensation of the structural delay of the system (fiber length, etc.) is sufficient.

[0047] In contrast, length differences between fibers can amount to thousands or tens of thousands of λ and therefore need to be corrected for, but since they do not move, a one-time static compensation is sufficient.

[0048] Therefore, in the mono-lambda case, there is no need to use servo control or feedback loops for phase adjustment; calibration is sufficient.

[0049] When multiple wavelengths are used, the tolerance to residual delay between channels is greatly reduced, since recombination is an interferometric process that requires perfect equalization of the delays if it is to function independently of wavelength (a condition for white light interference).

[0050] In practice, the above mentioned tolerances depend on the intensity of the WDM spectrum. Thus, for a typical case of 10 WDM channels (1 to 10) spaced 200 GHz apart, Fig. 4 shows the optimal combining efficiency CEff per WDM channel (obtained by minimizing the error signal) as a function of the value of the residual delay δτ expressed as a multiple of λ (λ = 1.55 μm). It can be seen that a residual delay δτ of 10 × λ leads to an average recombination efficiency (averaged over all WDM channels) higher than 99%.

[0051] In contrast, if the residual delay is 35×λ, the average recombination efficiency drops to 90% (80% for channels at both ends of the spectrum). To obtain 90% across the entire spectrum, the delay must be equalized to better than 20×λ. Therefore, it is necessary to dynamically correct the delay variation between the recombined channels, since delay variations due to propagation through the atmosphere, thermal effects, mechanical defects, or other influences are typically greater than 20λ. Therefore, a dynamic recombination device with delay correction as described in this invention is needed.

[0052] The residual delay of approximately 20λ is compatible with variable delay lines made with conventional elements such as fiber (fiber stretched by a piezoelectric module) or mirrors (mirrors on a piezoelectric chip).

[0053] Typically, dynamic delay correction with fiber wrapped around a piezoelectric tip can provide bandwidths of 10 kHz, precision better than 1 / 20 micron, and deviations of over 100 λ.

[0054] The signal received by the control detector decreases to zero only if the condition is met (white light interference) such that the delay is accurately compensated for, thus delivering an error signal suitable for dynamic servo control.

[0055] In figure 5 the intensity I detected by the detector Det is shown as a function of the phase applied by PS for each channel being optimized, for a residual delay δτ of 10×λ (i.e. the delay line DL compensates for the delay difference between the two channels with a residual error δτ of 10λ). It is the minimum value 51 of the intensity that allows the adjustment of the servo control (error signal ε) while a maximum value 50 is delivered to the output of the device. Curve 52 shows the intensity averaged over the 10 channels.

[0056] A residual delay of 10λ is found to be acceptable for the device.

[0057] In figure 6 the intensity I detected by the detector Det for each channel is shown for a residual delay δτ of 35×λ. The minimum intensity value 61 allows for the adjustment of the servo control, whereas the maximum value 60 is delivered to the output of the device. Curve 62 shows the intensity averaged over the 10 channels. The recombination effect is reduced, clearly showing that a residual delay of 35λ leads to an attenuated device error signal.

[0058] The elementary devices 15 are intended to be cascaded to form a coherent recombiner 20 so as to obtain a single recombined beam Frecomb, as shown in FIG.

[0059] The distorted input beam Fid is considered to be sampled into N elementary beams F1, F2, FN, where N is a strictly positive even integer.

[0060] 7 shows a device 20 for N=4 (easily generalizable to larger numbers) consisting of three elementary devices 15. The incoming beams are recombined into 2x2.

[0061] The variable delay lines DL1, DL2 firstly make it possible to adjust the optical delay (absolute phase) between the beams F1 and F2 on the one hand, and F3 and F4 on the other hand.

[0062] Second, two tunable couplers, in this example consisting of Mach-Zehnder interferometers (MZIs) each with an adjustable phase shift (PS1 or PS2), compensate for intensity ratios in the ranges 1 to 2 (PS1) and 3 to 4 (PS2).

[0063] Intensity detectors (Det1, Det2) are placed at the complementary outputs of the MZI to generate error signals that adjust DL1 / PS1 and DL2 / PS2.

[0064] The way in which the outputs of the two MZIs are combined is the same, with a delay line DL3 to adjust the delay, and then another MZI to combine and adjust the intensity ratio.

[0065] I k =ρ k I 0 The incident intensity I is equal to k If the signal delivered to the control detector is zero, then I recomb =I 0 Σρ k A beam F with a coupling strength equal to recomb is output from the device.

[0066] According to another aspect, the invention also relates to a light receiving system 100 using a device 20 according to the invention as shown in FIG.

[0067] The multi-lambda system described above is based on decomposing the extraordinary incident wavefront into multiple sub-beams with flat wavefronts (spatial demultiplexing) and then implementing a coherent combining technique using device 20 with the aim of bringing the sub-beams back in phase and maximizing the collected optical power and therefore the link budget, independent of wavelength.

[0068] The optical receiving system 100 of FIG. 8 receives M multiplexed wavelengths λ each carrying a modulated signal. 1 , λ 2 , ...λ M) (modulators mod1, mod2 ... and a multiplexer λMUX) into free space. After propagation through the atmosphere FS, the beam has a highly distorted amplitude and phase, forming the input beam Fid upon reception.

[0069] The system 100 first includes a device 14 for spatially demultiplexing an input beam Fid, the device 14 being configured to sample Fid into N fundamental beams, the fundamental beams having different amplitudes and different phases, and preferably being diffraction limited so that they can be easily coupled into a single mode fiber or an integrated optical circuit.

[0070] Multiple devices may perform the function of spatially demultiplexing the extraordinary beam.

[0071] The first spatial demultiplexer 14 contains a matrix array of microlenses which pixellates the incident beam by spatially sampling the extraordinary beam. The spatial sampling pitch (size of the pixel) is chosen so that the diffraction of each elementary beam is limited. It may turn out that a very small pixel size and therefore a large number of elementary beams is required.

[0072] The second device includes a multi-aperture telescope in which the tip / tilt scheme of each fundamental beam is modified.

[0073] Finally, the third device is configured to perform the decomposition into N spatial modes using N phase plates. Assuming that the extraordinary beam is decomposed into a basis of higher spatial modes, the phase plates are then designed to convert these higher modes into Gaussian modes via free propagation and movement through the phase plates.

[0074] The receiving system 100 also includes a device 20 for coherently recombining the N elementary beams, as described above. The problem is now to compensate for the optical delay and amplitude variations between the elementary beams before they are optically added (coherent sum) and to form the beam Frecomb. The device 20 thus allows to improve the signal-to-noise ratio compared to non-coherent approaches by concentrating all the optical energy on a single detector.

[0075] The beam sum Frecomb is then demultiplexed by a wavelength demultiplexer λDEMUX to form M beams at M wavelengths, each of which forms an information-carrying channel. Each of the M beams is then coupled to M detectors PD 1 , P.D. 2 , ... P.D. M (for M WDM channels). A receiving system (WDM architecture) is thus obtained which employs coherent recombination and has a very good recombination effect over a wide spectral band or frequency comb.

[0076] Furthermore, the above-described system is compatible with optical integration technology, making it possible to integrate the functions of a 2×2 switch (including a control information receiver (detector) and, optionally, a WDM receiver) and a demultiplexer (e.g., a cascaded asymmetric MZI or a planar phased array) on an optical chip.

[0077] The optical integration approach makes the system simpler and less expensive than the adaptive optics approach.

[0078] According to another aspect, the present invention also relates to a light receiving / emitting system 300 including the light receiving system 100 and the light emitting system 200 as described above, two embodiments of which are shown in FIGS.

[0079] The light emission system is made up of M laser sources L 1 , L 2 , ...L M, and M associated modulators mod configured to generate M beams at M wavelengths, each beam forming an information-carrying channel. 1 , mod 2 , ...mod M , and a wavelength multiplexer λMUX to form a multi-wavelength beam.

[0080] The system 200 also divides the multi-wavelength beam into N elementary emission beams F 1 ',F 2 ',...F N The coherent recombination system 100 includes a coherently splitting device 20' for splitting the N fundamental emission beams into N beams F', which are substantially identical to the coherent recombination device 20, but used in the opposite direction, with each delay line and each phase modulator applying an opposite delay and an opposite phase difference, respectively, determined by each feedback loop of the coherent recombination device 20 of the receiving system 100, thereby splitting the N fundamental emission beams into N beams F', each of which is conjugate to the N initial fundamental beams. 1 ',...F N ' to correspond to

[0081] Finally, the system 200 includes a spatial multiplexing device 14' that is substantially identical to the spatial demultiplexing device 14, but is used in the opposite direction to convert the N elementary emission beams F1', ...FN' into an emission beam Fe that corresponds to the conjugate of the incident beam Fid, thereby pre-compensating for distortions.

[0082] In other words, the amplitude and delay weights determined for the receiver coherent combining are now used to apply a weighting law to the N elementary emission beams, which makes it possible to inversely pre-compensate for atmospheric turbulence.

[0083] In the embodiment of FIG. 9, systems 100, 200 each include different devices 20 / 20' and 14 / 14'.

[0084] In the embodiment of FIG. 10, the coherent recombiner 20 and the coherent splitter 20' are identical, and the spatial demultiplexer 14 and the spatial multiplexer 14' are identical.

[0085] On the other hand, the wavelength demultiplexer λDEMUX and M detectors PD 1 , P.D. 2 , P.D. M On the other hand, M laser sources L 1 , L 2 , ...L M , M associated modulators mod 1 , mod 2 , mod M and the wavelength multiplexer λMUX is then coupled by a circulator OC to a coherent recombiner / splitting device.

[0086] In principle, the system 200 can function in two directions, i.e. emitting and receiving light simultaneously. However, at the component level, the emitting signal is much stronger than the receiving signal, whereas the device is designed to optimize the receiving signal. Parasitic reflections of the emitted light can therefore interfere with the optimization of the receiving light and thus the tuning of the components. In that case, the system works alternately in emitting / receiving mode. [Explanation of symbols]

[0087] 10 Coherent Recombination Device 11 Coupler 12,17 Output 13 Detectors 14 Spatial demultiplexer 14' spatial multiplexer 15,15a,15b Basic equipment 16,16a,16b Phase shifter 18 Final Output 20 Coherent Recombination Device 20' Coherent splitter 50,60 maximum strength 51,61 Minimum Strength 52,62 average intensity 100 Light receiving system 200 Lighting System 300 Light receiving / emitting system BA Feedback Loop CEff Optimal Combination Effect Comb,Comb' combiner D, Det Detector DL Delay Line DL1, DL2 variable delay lines E 0 light field F1, F2 Basic beam F3, F4 Beam F 1 ', F 2 ',...F N ' Basic light beam Fe emission beam Fid incident beam FS Atmosphere I 0 , I 1 ,I 2 strength I k Incident intensity I recomb bond strength Input1, Input2 L 1 ,L 2 ,...L M Laser source mod 1 ,mod 2 ,...mod M Modulator MZI Mach-Zehnder Interferometer OC Cardiology Out Output PD 1 ,PD 2 ,PD M Detector PS Phase Modulator PS1,PS2 phase shift R 12 delay S point light source Sc complementary output T1,T2 route VC Variable Coupler δτ residual delay ε error signal λ 1 ,λ 2 ,...λ M wavelength λMUX Wavelength multiplexing device λDEMUX wavelength non-multiplexing device

Claims

1. The input beam (Fid) is spatially demultiplexed and N fundamental beams (F １ , F ２ , . . F Ｎ ), the spectrum of the incident beam being divided into M wavelengths (λ 2 ), each of which forms an information-carrying channel. １ , λ ２ ,... . . . λ Ｍ ) , said apparatus comprising: - dividing the incident beam into N elementary beams (F １ , F ２ , . . F Ｎ a device (14) for spatially demultiplexing an incident beam (Fid) configured to sample the incident beam (Fid) into - the N elementary beams (F １ , F ２ , . . F Ｎ ), where N is a strictly positive even integer, and the device (20) comprises a number of elementary devices (15) arranged in a cascade to obtain a single recombined beam (Frecomb); a fundamental device (15) for coherently recombining a first fundamental beam (F1) and a second fundamental beam (F2), said distortion resulting in a delay (R １２ ) and the basic device is a first input (Input1) and a second input (Input2) into which the first and second fundamental beams (F1) and (F2) to be recombined are respectively injected, an output (Out) delivering an output beam corresponding to a coherent recombination of said first and second fundamental beams; a delay line (DL) arranged in one of the paths of said fundamental beams and configured to induce a variable delay in said path; a variable coupler (VC) including a first 2×2 combiner (Comb), a phase modulator (PS) arranged at one of the two outputs of said first combiner, and a second 2×2 combiner (Comb′), said second combiner having a main output forming said output (Out) of said basic device (15) and delivering said output beam, and a complementary output (Sc) delivering a complementary beam complementary to said output beam; - connected to the complementary output (Sc), the phase modulator (PS) is configured to apply a phase difference that equalizes the intensities of the first and second fundamental beams, and the delay line (DL) adjusts the delay (R １２ a control detector (Det) configured to generate from said complementary beams an error signal (ε) which decreases to zero when the control detector is configured to apply a delay compensating for the delay; a feedback loop (BA) configured to determine said applied delay and phase difference from said error signal; An apparatus comprising:

2. - a spatial demultiplexing device (14) for spatially demultiplexing the incident beam according to claim 1, - a device (20) for coherently recombining N elementary beams according to claim 1, a wavelength demultiplexer (λDEMUX) for demultiplexing the wavelengths to form M beams, each of the M wavelengths forming one channel for carrying information; M detectors (PDs) associated with the M beams １ , P.D. ２ , P.D. Ｍ . . . a receiving system (100).

3. The receiving system of claim 2 , wherein the fundamental beam is diffraction limited.

4. 3. The receiving system of claim 2, wherein the spatial demultiplexing device (14) comprises a matrix array of microlenses configured to spatially sample the incident beam.

5. The receiving system of claim 2 , wherein the spatial demultiplexing device (14) comprises a multi-aperture telescope.

6. 3. The receiving system of claim 2, wherein the spatial demultiplexing device (14) comprises N phase plates configured to perform a decomposition into N spatial modes.

7. A light receiving system (100) according to any one of claims 2 to 6, - M laser sources (L) configured to generate M beams at M wavelengths １ , L ２ , . . . L Ｍ ) and M associated modulators (mod １ , mod ２ , mod Ｍ )and, - a wavelength multiplexer (λMUX) for forming a multi-wavelength beam; - dividing the multi-wavelength beam into N elementary emission beams (F' １ , F' ２ , . . F' Ｎ ), i.e. a coherent splitting device (20') identical to the coherent recombining device (20) but used in the opposite direction, with each delay line and each phase modulator applying an opposite delay and an opposite phase difference, respectively, to the delay and phase difference determined by each feedback loop of the coherent recombining device (20) of the receiving system (100), thereby １ ',....F Ｎ a coherent splitting device (20') for splitting the N beams into N beams each conjugate to the N initial fundamental beams; - a spatial demultiplexing device (14) identical to the one described above, but used in the opposite direction to generate the N elementary emission beams (F １ ',....F Ｎ and a spatial multiplexing device (14') for converting the incident beam (Fid) from the reflected light (Fd) to an emitted light beam (Fe) corresponding to a conjugate of the incident beam (Fid) to pre-compensate for the distortion.

8. - the coherent recombination device (20) and the coherent splitting device (20') are identical, the spatial demultiplexing device (14) and the spatial multiplexing device (14') are identical, On the other hand, the wavelength demultiplexer (λDEMUX) and the M detectors (PD １ , P.D. ２ , P.D. Ｍ ), on the other hand, the M laser sources (L １ , L ２ , . . . L Ｍ ), the M associated modulators (mod １ , mod ２ , mod Ｍ ) and the wavelength multiplexing device (λMUX) are coupled to a coherent recombining / splitting device by a circulator (OC); The light receiving / emitting system of claim 7 , further configured for alternating use for receiving and emitting light.

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