FR2976131A1 - Electromagnetic signal emission control device for optoelectronic radar system used to locate people buried in location after e.g. earthquake, has mirrors separated by optical path whose length is greater than length of another optical path - Google Patents

Abstract

The device has an optical cavity (CO-1) including a mirror and a partially reflecting mirror, where the mirrors are separated by an optical path. An amplifier is adapted to amplify light pulses (s-1, s-2) received in the cavity to provide a train of light pulses that are successively refracted by the reflecting mirror. The path has length greater than that of another optical path to introduce a time delay between one light pulse in a row of the train of pulses on a processing channel (V-1) relative to another light pulse in the same row in the train on another processing channel (V-2). Independent claims are also included for the following: (1) an electromagnetic signal detection system (2) a method for controlling emission of electromagnetic signals.

Description

Electromagnetic emission control device, associated method and associated detection system The present invention relates to the field of electromagnetic signal transmission systems for emitting successively in different directions, so as to scan an area of interest. These systems comprise, for example, a number N of pulse sources each connected to a respective antenna of a fixed antenna array. The resulting electromagnetic signal is the coherent superposition of the fields radiated by each antenna taking into account the difference in operation. This sum of the radiated fields takes a maximum value at the points where the radiated signal fields are in phase, which determines the direction, or azimuth, of emission reached. When the pulses supplied to the different antennas are synchronous, the maximum signal is emitted in the axis of the network (azimuth 0 °). For example, with reference to FIG. 1, there is shown at the bottom a network 100 of antennas 101, 102, 103, 104, 105, each powered by a respective pulse transmitted synchronously at time to. The maximum signal is emitted in the direction of the network axis (azimuth 0 °) as represented by the dashed arrow between the lower part and the upper part of Figure 1. This upper part comprises a graph with the abscissa the azimuth, expressed in °, and as ordinate the time, expressed in nanoseconds (ns). The intensity of the resulting field is indicated by a gray intensity in accordance with the reference gradation on the right of the upper graph, on a scale of -100 to +100 (the darker the gray, the greater the amplitude of the field) . In order to transmit a maximum signal in a particular direction using the fixed antenna array, determined delays are introduced between the antenna supply signals. Referring to Figure 2, is shown in the lower part of the network 100 of antennas 101, 102, 103, 104, 105, each powered by a pulse. These pulses are transmitted asynchronously, respectively at times t0, t0 + at, t0 + 23t, t0 + 33t, t0 + 43t. The resulting maximum signal is emitted in a direction corresponding to an azimuth a = 20 ° with respect to the axis of the grating, as shown in connection with the upper part of the figure. The relationship between the delay is introduced between the supply signals of two neighboring antennas and the azimuth reached is as follows: at = c- '. d.sin a, where c is the speed of light, and d represents the distance between the center of two antennas close to the network.

2 The use of optoelectronics to generate the supply signals makes it possible to create the delays with a high accuracy (less than about 2 picoseconds). However, in order to emit electromagnetic waves in different successive directions and thus to scan an area of interest, it is necessary to modify the setting of the delays, successively, for each of the different directions to be aimed during the scanning. These delays settings between each transmission result in a low scanning speed and a lack of autonomy in the operation of the transmission system. Such systems are for example described in the following documents: "an ultra wideband impulse optoelectronic radar: RUGBI", M. Lalande et al., PIER B 11, pp 205-222, 2009; "Conception and realization of an agile (300 MHz-3Ghz) Ultra Wide Bandwidth Radar", A. Godard, doctoral thesis of the University of Limoges, 2009; "A transient UWB antenna array used with complex impedance surfaces," A. Godard et al, International Journal of antennas and propagation, vol. 2010, Article ID 243145, 2010. In order to overcome the disadvantages mentioned above, according to a first aspect, the present invention proposes an electromagnetic emission control device adapted to receive a light pulse on each of at least a first and a second processing path, and for introducing a time delay between said light pulses for feeding a first antenna, respectively a second antenna, according to said first, respectively second, light pulse; said control device being characterized in that it comprises at least one optical cavity on each channel comprising at least two mirrors including a semireflecting mirror, said mirrors being separated by an optical path and comprising an amplifier arranged on the optical path, and being adapted so that a light pulse received at the input of the optical cavity gives rise to a train of at least n successive light pulses refracted by the semi-reflecting mirror, with n fixed integer, greater than or equal to 2; the last n-1 luminous pulses of the train having been successively reflected by the two mirrors; in which the optical path of the optical cavity of the second path is of greater length than the optical path of the optical cavity of the first path, so as to introduce a time delay between at least one luminous pulse of a given rank in the train on the second lane with respect to the light pulse of the same rank given in the train on the first lane. Such a device, allowing the automatic creation of asynchronous pulse trains, allows a very fast, discrete and dynamic scanning of a large area to be scanned, without requiring adjustments between the transmissions to the different directions targeted during the scanning. According to the applications, in a detection system, for example of the radar type, it makes it possible to obtain an electromagnetic "image" of a place, confined or not. In embodiments, the device according to the invention furthermore comprises one or more of the following characteristics: each optical cavity is adapted so that a light pulse received at the input of the cavity is transmitted to the semi-reflecting mirror, said pulse light being partially partially refracted on the semi-reflecting mirror thus providing a first light pulse of the pulse train, and in a first iteration of an optical loop, said light pulse is, on the other hand, partially reflected on the semi-reflecting mirror for the other mirror, via the optical path, said partially reflected portion being reflected in turn on the other mirror, to the semi-reflecting mirror via the optical path, the light pulse being further amplified during the optical loop by the amplifier so that the light pulse received by the semi-r mirror reflecting at the end of the optical loop is substantially of the same power as the light pulse received by said semi-reflecting mirror and having given rise to the first light pulse of the pulse train, said light pulse received by the semi-reflective mirror reflecting at the end of the optical loop being in turn partially refracted on the semi-reflecting mirror, thereby providing a second light pulse of the pulse train; the device is adapted to receive a light pulse on each of the processing channels, with t integer greater than or equal to 2, to introduce a time delay between the row of rank i and the channel of rank i + 1, with i = 1 to t-1; the device comprising, on each processing channel, an optical cavity similar to the optical cavity of the first and second channels and adapted so that a light pulse received at the input of the optical cavity gives rise to a train of at least n light pulses successive, the length of the optical path varying according to the cavities; the time delay introduced between the first impulse of a train delivered on one channel and the first impulse of a train on another channel is increased by c - '* 2 * AChO, with respect to the time delay introduced between the jth pulse of said train delivered on said channel and the jth pulse of said train on said other path, where c is the speed of light and AChO is the difference in length of the optical path between the cavities of said path and said other path ; the device comprises, on each processing channel, an optoelectronic generator adapted to receive the stream of light pulses supplied by the optical cavity and to deliver a train of electrical pulses as a function of the stream of light pulses received; the device comprises, on each processing channel, an antenna adapted to receive the electrical pulse train delivered by the optoelectronic generator and to generate an electromagnetic radiation as a function of the electrical pulse train received; the optical cavity comprises an acousto-optical modulator adapted to modulate a light carrier in the cavity and being adapted to stop said modulation after n-1 iteration of an optical loop and being adapted to introduce the light pulse at the input of the optical cavity; the device comprises an input splitter adapted to receive at least one light pulse and distribute said received light pulse in at least one light pulse for each of the processing channels; the time delay introduced between a light pulse of a given rank in the train on the second channel with respect to the light pulse of the same rank given on the first channel determines an emission azimuth to be reached by the coherent superposition of the radiations provided by the first and second powered antennas according to said light pulses of the given rank of the first and second channels. According to a second aspect, the invention proposes an electromagnetic detection system comprising: a light source; a control device according to the first aspect of the invention, adapted to receive as input light pulses provided by the light source; and an analysis module adapted to receive and analyze reflections of electromagnetic radiation controlled by the control device. According to a third aspect, the invention proposes a method for controlling electromagnetic emissions by a first antenna and a second antenna, according to which: - a light pulse is received over at least two processing channels; the light pulse is delayed on the second path with respect to the light pulse on the first path, in order to supply the first antenna, respectively the second antenna, as a function of the first light pulse, respectively the second light pulse; , characterized in that a time delay is introduced using at least one optical cavity disposed on each channel, each optical cavity comprising at least two mirrors, including a semi-reflecting mirror, said mirrors being separated by a path optical amplifier comprising an amplifier disposed on the optical path, a light pulse received at the input of the optical cavity giving rise to a train of at least n successive light pulses refracted by the semireflective mirror, with n fixed integer, greater than or equal to 2; the last n-1 optical pulses of each train having been successively reflected by the two mirrors; said optical path of the optical cavity on the second path is of greater length than the optical path of the optical cavity on the first path, so as to introduce a time delay between at least one luminous pulse of a given rank in the train on the second way with respect to the light pulse of the same rank given in the train on the first track.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given by way of illustration, but in no way limitative, of the invention. These figures are as follows: FIG. 1 is a schematic view of signals supplying an antenna array and the resulting target azimuth, according to the prior art; FIG. 2 is a schematic view of signals supplying an antenna array and the resulting target azimuth, according to the prior art; FIG. 3 is a schematic view of an optoelectronic radar system in one embodiment of the invention; FIG. 4 is a schematic view of an optical cavity in one embodiment of the invention; FIG. 5 shows a part of the pulse trains obtained on different processing channels of the radar of FIG. 3 in one embodiment of the invention; FIG. 6 is a diagram illustrating the electromagnetic emissions as a function of the azimuth and the time obtained in one embodiment of the invention.

FIG. 3 schematizes an optoelectronic radar system 1 incorporating an embodiment of the invention. The radar system 1 comprises a source of light pulses SI, a power distributor 2, a number of processing channels V ,, V2 ... V1, with t integer greater than or equal to 2, and a system 10 of antennas with antennas.

In the embodiment considered, the antennas of the network 10 are fixed.

The light source SI is adapted to produce short light pulses, for example of a duration less than 100 nanoseconds, which can be for example of the order of one picosecond or femtosecond. For example, the light source S1 comprises a pump laser, Nd: YAG type, with a pulse repetition frequency of 20 Hz, the duration of each pulse being 30 picoseconds. The power splitter 2 is adapted to receive a light pulse emitted by the source SI, and to distribute it in t light pulses s ,, s2 ..., st, each light pulse if, for i = 1 to t, being provided at the input ei of the respective processing channel V. Each processing channel V ;, i = 1 to t, comprises a delay line L1 i, an optical cavity CO; and a Gent optoelectronic generator. The delay lines L1 i are optional. They are for example of the optomechanical type.

In the embodiment considered, they are adjusted so as to delay the light pulses received at the input of a delay TL, + t ;. This delay TL, can take any value, which determines the direction of the first shot of the network. The variable t; has the value (ti) t, / 2 (where t1 is the time delay step between the channels considered successively during the second impulse of the pulse trains as detailed below), for i = 1 to t and makes it possible to so that each first pulse of the pulse trains provided by the optical cavities takes place (for example) at the same time. In FIG. 4, an optical cavity CO 1, i = 1 to t, is shown schematically. It constitutes an amplifying, oscillating multipass cavity. It comprises an input, a reflecting mirror R1; a delay line L2i for example of the opto-mechanical type, an optical amplifier 3i, an acousto-optical modulator 4i and a partially reflecting mirror R2; Such an optical cavity is adapted to receive a light pulse and from this light pulse, to provide a train of light pulses. In one embodiment, the mirror R1; is 100% reflective type `Rmax @ 1064nm) and mirror R2; is 50% reflective (R50% @ 1064nm). We are here at the wavelength of 1064 nm "but we can consider another wavelength depending on the type of semiconductor constituting the optoelectronic generators The optical amplifier 3i is adapted to amplify a pulse received at the input of in order to regenerate the energy of the pulse within the cavity to maintain it at a fixed value K.

The acousto-optical modulator 4i is adapted to modulate the laser carrier and thus allow the propagation of the light pulse within the cavity. It is adapted to, as a function of a parameterizable setting value n, limit to (n-1) the number of loops formed within the optical cavity CO; as shown below.

In the embodiment considered, all the delay lines L2i, i = 1 to t, are set to introduce a common delay TL2 which makes it possible to adjust and set the basic 1 / T round-trip frequency of the system , as defined below. In the embodiment considered, it is considered that the mirror R2; has an adjustable position and that the mirror R2; +1 is shifted with respect to the mirror R2; a distance of common value AChO called, hereinafter, no difference in length, for all i = 1 to t-1, so that the optical path separating the two mirrors R1; +1 and R2; + 1 in the cavity CO; +1 is longer than the optical path separating the two mirrors R1; and R2; in the CO cavity; This difference step AChO causes a delay of value t, / 2, at the mirror R2; +1, for a light pulse part, at a given time, of the mirror R1; + ,, with respect to the arrival at the level the mirror R2 ;, a light pulse that would be part of the same time, the mirror R1 ;. The delay of value t, / 2 corresponds to the delay introduced by the cavity CO; +1 with respect to the cavity CO;, during a go along the optical path separating the two mirrors (a delay of 0-1 t1 / 2 by the cavity CO; relative to the CO cavity). And a round trip within the optical cavity CO; +1 during a loop therefore gives rise to a delay value t, of the cavity CO; +1 with respect to the cavity CO; (ie a delay of (i-1) t, by the cavity CO, with respect to the cavity CO,). It will be noted that the delay lines L1 i are optional. In the same way, L2i delay lines are optional. In the embodiment considered, the pitch AChO of difference in length between the optical cavities is introduced by means of the position adjustment of the mirrors R2; In other embodiments, it can be introduced using delay lines L2i, and / or mirrors R2; and / or mirrors R1 ;. Each optoelectronic generator Gent, also called optoelectronic switch, is adapted to convert a received light pulse into an electrical pulse, without temporal jitter with respect to the light pulse. It comprises, for example, doped silicon semiconductors. Optoelectronic generators are for example described in document WO 2009/133300 or WO 2007/074229. The output signal of the optoelectronic generator is supplied to the antenna Ai of the antenna array 10.

Each antenna Ai, i = 1 to t, of the network 10 is adapted to receive an electrical pulse and to radiate it. Consider now the processing of a light pulse P1 emitted by the source S1, and supplied at the input of the splitter 2. This pulse is distributed in power in t similar light pulses if, for i = 1 to t. Each light pulse if is supplied at the same time (or at different times) to the input e; of the processing channel V. Each pulse si is then provided at the input of the delay line L1 i and a time delay TL1 + t; it is applied to him. Each pulse, if delayed, of amplitude K, is supplied on channel V; at the entrance to the CO optical cavity ;. This pulse if enters the optical cavity thanks to the acousto-optic modulator 4 and oscillates between the mirrors R1; and R2; The amplitude of the oscillating pulse in the optical cavity is maintained at the value K via the regeneration performed by the optical amplifier 3i. At each reflection of the oscillating pulse on the mirror R2; it is reflected at 50% towards the inside of the optical cavity CO 2 and refracted at 50% towards the output of the optical cavity, giving rise to a first pulse B ,, of amplitude K / 2. All of these first t pulses B i, on the channels V i, for i = 1 to t, at the output of the optical cavity are transmitted synchronously, at the same time to as shown in FIG. 5, for the first three channels V ,, V2, V3.

Indeed, the differences in delay resulting from the optical path length differences between the cavities (introduced by the position adjustment of the mirrors R2;) are compensated by the delay differences introduced at the delay lines L1 i. According to a first iteration, the part reflected at 50% towards the inside of the cavity CO;, named hereinafter if, of amplitude K / 2, passes through the optical path of the cavity, of the mirror R2; to the mirror R1 ;. This pulse if is reflected at 100% on the mirror R1; from which it travels again the optical path from the mirror R1; to the mirror R2; During this loop performed by the pulse if within the cavity using a modulation implemented by the acousto-optical modulator 4i, the amplitude of the pulse if is amplified to the value K via the regeneration performed by the optical amplifier 3i. When the light pulse reaches, at the end of this first loop, on the mirror R2, it is reflected in turn at 50% towards the inside of the optical cavity CO 2, and refracted at 50% towards the output of the optical cavity giving rise to a second pulse Bit, amplitude K / 2 as shown in Figure 5 for the first three channels V1, V2, V3. As can be seen in FIG. 5, these second pulses Bit are shifted between them.

Indeed, if one names T the period separating the first pulse B 'from the second pulse B12 provided in the pulse train on the processing channel V1, the period separating the first pulse B21 from the second pulse B22 provided on the channel V2 treatment is T + t1. Indeed, as indicated above, the difference in optical path length between the optical cavity CO1 and the optical cavity CO2 being AChO, the light pulse s2 having achieved a loop within the optical cavity CO2, has traveled, when it reaches the level of the mirror R22, an optical path longer than the optical path traveled during the loop made by the light pulse if within the optical cavity CO1, the difference being equal to 2 AChO, which results in a delay of t1 (equal to c-1 * 2 * AChO).

The period separating the first pulse B21 from the second pulse B22 of the pulse train supplied on the processing channel V2 is therefore equal to T + t1. And, more generally, the period separating the first pulse Bi1 from the second pulse Bit of the pulse train supplied on the processing path Vi is of a value equal to T + (i-1) t1i for i = 1 to t.

This amounts to saying that the second pulse on the i.e. i.e. B (i + 1) 2 channel is thus delayed by a time t1 with respect to the second pulse on the Vi, i.e. Bit channel, for i = 1 to t. The time delay step between the channels considered successively is therefore t1 for the 1st iteration, corresponding to the second pulses. T is named the base period of the radar. It corresponds to the time taken by a light pulse reflected on the mirror R21 to produce an optical loop within the optical cavity CO1. Its value is adaptable by adjusting the delay line L21 and / or the relative positioning of the mirrors R11i R21 delimiting the optical cavity CO1. F = 1 / T, corresponding to the base frequency, typically takes values between 1 and 100 MHz.

If n is greater than or equal to 2, n-2 iterations then take place in the same manner as described for the first iteration and give rise, at the output of the optical cavity COi, to each channel i, to n-2 other light pulses. s /, j = 2 to n-1, resulting from refractions on the mirror R2i. Thus at the end of a jth iteration, with j less than or equal to n-1, a j + lth pulse Bi; will be emitted at the output of the optical cavity on each channel Vi.

The period separating the (j-1) th pulse 6jOE1) from the jth pulse B; provided on treatment path V; is always T + (i-1) t ,, this magnitude being imposed by the optical path between the mirrors of the optical cavity V i, for i = 1 to t. At this point, these pulses B; are shifted between the V channels, the delays accumulating over the iterations. Indeed, the jth pulse on the path V; +1, i.e. B (; + 1); is delayed by a time (j-1) .t, with respect to the jth pulse on the path V; i.e. B ;; for i = 1 to t. The time delay step between the channels considered successively is therefore (j-1) .t, for the jth pulse, corresponding (j-1) th iteration.

Thus an optical cavity CO; is adapted to provide, from a light pulse received at the input, a stream of n light pulses, of frequency equal to (T + (i-1) t,) - 'for i = 1 to t. The time lag between the channels considered successively, for the pulses of the same rank in the respective trains, increases according to the rank and is equal to (j-1) t for the pulses of rank j. The number of iterations corresponding to the number of loops performed within the optical cavities is equal to n-1, where the value of n can be parameterized according to the number of pulses desired in a pulse train at the output of the optical cavities. The value of n is an integer greater than or equal to 2. When the number of loops realized is equal to the number n-1, the acousto-optical modulator 4i stops the modulation in each channel V. These pulse trains thus generated by the optical cavities on each channel Vi are then supplied to the optoelectronic generators, which convert these trains of light pulses into trains of electrical pulses while keeping the frequency, the time offsets between pulses of the same rank in the trains being maintained at the same values than those presented by light pulse trains. The resulting electrical pulse train on each V-channel; is then provided at the input of the antenna Ai, as a control signal, each pulse controlling a pulse radiation from the antenna Ai.

The combination of the radiations coming from the t antennas thus controlled by the first electrical pulse on each channel will give rise to a signal resulting from maximum energy (corresponding to a direction in which the signals arrive in phase) in the direction of the axis of the network, therefore corresponding to an azimuth 0 ° with respect to this axis (these first pulses being synchronous with each other).

The combination of the rays of the t antennas controlled by the second electrical pulse on each channel will give rise to a resulting signal of energy.

11 maximum in a direction corresponding to an azimuth e2 = arcin (tl ~ c) with respect to the axis of the network, since the second pulse on the channel V; +1 is delayed by a time t1 with respect to the second pulse on the V path, for = 1 to t-1. And more generally, the combination of the rays of the t antennas controlled by the jth electrical impulse of the pulse trains, for j = 1 to n, on each channel, will give rise to a signal resulting from higher energy in a direction corresponding to an azimuth 8j = arcin ((i -1) dx tl xc) with respect to the axis of the lattice, since the jth impulse on the channel V; +1 is delayed by a time (j -1) x tl relative to at the jth pulse on the V path ;, for i = 1 to t-1.

The number n also determines the number n of points automatically and successively scanned by the optical radar following the emission of a light pulse by the source SI. In FIG. 6, in the left-hand part are represented the electric pulse trains obtained at the output of the optoelectronic generators in one embodiment of the invention, with a network comprising 5 antennas A1, A2, A3, A4, A5. On the abscissa is the time in nanoseconds and the ordinate is the amplitude in V. Each pulse train has 4 pulses, which corresponds to 3 loops in each optical cavity.

On the right-hand part of FIG. 6 is a diagram illustrating the directions successively swept in time, expressed in nanoseconds, by the radiation resulting from the 5 antennas. Thus all the first pulses give rise to a maximum resultant radiation in the 0 ° azimuth direction, the set of second pulses give rise to a maximum resultant radiation in the 5 ° azimuth direction, the set of thirds pulses give rise to a maximum resultant radiation in the 10 ° azimuth direction and all of the fourth pulses give rise to a maximum resultant radiation in the azimuth direction 15 °. A scan is thus obtained from 0 ° to 15 ° in steps of 5 °, with a network of 5 antennas, the delay between each point of the scan being of the order of 2 nanoseconds. The invention therefore makes it possible to perform a very rapid scan of a zone by radiation resulting from an antenna array, without the need to successively adjust the delays to target the different directions targeted during this scan.

Such a system is also very easily configurable so as to adapt the scan. For example, adjusting the position of mirrors R2; makes it easy to change the period of a pulse train. A displacement of a mirror R2; 1 mm causes a time shift for example of 6 picoseconds (round trip). Furthermore, if it is desired to "zoom" on the area scanned by a first scan using a system according to the invention, it is sufficient to set a smaller scanning step, by choosing a value of the parameter t, lower and therefore decreasing the value of the AChO parameter by setting the mirrors R2 ;. If a wider scanned area is desired, simply choose a larger value for the parameter n setting the number of pulses in each pulse train. The starting azimuth of the scan can also be changed by adjusting the delays of the system delay lines and / or the positioning of the mirrors.

It will be noted that the power of the initial pulse supplied by the source S1 must be adapted to enable switching of the optoelectronic generator. In other embodiments, the optoelectronic switches are integrated in the antennas. In one embodiment, the radar further comprises a detector coupled to a receiving antenna, the receiving antenna being adapted to receive radiation from the emission scan performed by the antenna array. The detector is adapted to analyze the received radiation, and deduce an "image" of the scan, identifying possible "targets". In one embodiment, the antenna used in reception is synchronized with the central antenna of the transmission antenna array. ("central antenna" means that which is geographically in the middle of the distance separating the two furthest antennas). The invention relates to the control of electromagnetic pulses by the synthesis of asynchronous trains of light pulses, the time shifts introduced being perfectly controlled, has been described above in an electromagnetic detection application, for example in a radar system. optoelectronics. Such a detection system can be used for example to locate buried people following earthquakes, avalanches and so on. In another embodiment, the invention may be used in an electromagnetic interference system, disrupting / paralyzing electronic systems by coherently summing the signals in a desired direction. The invention is particularly suitable for very fast target blindness operations, to avoid possible detection by the target and countermeasures. The invention can be implemented in several frequency ranges from megahertz to terahertz, making it possible to scan through multiple walls using low level pulse signals. The invention can also be implemented in a system combining fixed and mobile antennas. The invention has been described above in an embodiment where the delay introduced by the optical cavity CO; +1 with respect to the CO; is the same for i = 1 to t.

In another embodiment, the introduced delay may assume distinct values as a function of i. In this case, the radiation from the impulses of each rank i in the train with i = 1 to n, will give rise to as many target directions as there are distinct delay values, instead of a single target direction. .

Claims (5)

REVENDICATIONS1. An electromagnetic emission control device (1) adapted to receive a light pulse (s1, s2) on each of at least a first and a second processing channel (V1, V2), and to introduce a time delay between said pulses lights for supplying a first antenna (A1), respectively a second antenna (A2), according to said first, respectively second, light pulse; said control device (1) being characterized in that it comprises at least one optical cavity (CO) on each channel (V;) comprising at least two mirrors (R1; R2;) including a semi-reflecting mirror ( R2;), said mirrors being separated by an optical path and comprising an amplifier (3;) arranged on the optical path, and being adapted so that a light pulse received at the input of the optical cavity gives rise to a train of less than n successive light pulses (B11, B12) refracted by the semi-reflecting mirror, with n fixed integer, greater than or equal to 2; the last n-1 luminous pulses of the train having been successively reflected by the two mirrors; in which the optical path of the optical cavity of the second path is of greater length than the optical path of the optical cavity of the first path, so as to introduce a time delay between at least one luminous pulse of a given rank in the train on the second lane with respect to the light pulse of the same rank given in the train on the first lane. 2. Device (1) for controlling electromagnetic emissions according to claim 1, wherein each optical cavity (CO) is adapted so that a light pulse received at the entrance of the cavity is transmitted to the semi-reflecting mirror (R2; ), said light pulse being partly partially refracted on the semi-reflecting mirror thereby providing a first light pulse (B1i) of the pulse train, and in a first iteration of an optical loop, said light pulse is, d on the other hand, partially reflected on the semi-reflecting mirror (R2;) to the other mirror (R1;), via the optical path, said partially reflected part being reflected in turn on the other mirror, to of the semireflecting mirror via the optical path, the light pulse being further amplified. 3. 15 20 4. 25 5.30 356.when the optical loop by the amplifier (3i) so that the light pulse received by the semi-reflecting mirror at the end of the optical loop is substantially of the same power as the received light pulse by said semi-reflecting mirror and having given rise to the first light pulse of the pulse train, said light pulse received by the semi-reflecting mirror at the end of the optical loop being in turn partially refracted on the semi-reflective mirror. reflective, thereby providing a second light pulse (Bi2) of the pulse train. An electromagnetic emission control device (1) according to claim 1 or 2, adapted to receive a light pulse (s) on each of the processing channels, with t integer greater than or equal to 2, to introduce a time delay. between the row of rank i and the row of rank i + 1, with i = 1 to t-1; the device comprising, on each treatment channel (V;), an optical cavity similar to the optical cavity of the first and second channels and adapted so that a light pulse received at the input of the optical cavity gives rise to a train of less n successive light pulses, the length of the optical path varies with the cavities. Device (1) for controlling electromagnetic emissions according to one of the preceding claims, wherein the time delay introduced between the j + 1 th pulse of a train delivered on a track and the j + 1 th pulse of a train on another channel is increased by c-1 * 2 * AChO, in relation to the time delay introduced between the jth pulse of said train delivered on said channel and the jth pulse of said train on said other path, where c is the speed of light and AChO is the difference in length of the optical path between the cavities of said path and said other path. An electromagnetic emission control device (1) according to any one of the preceding claims, comprising on each processing channel (V;) an optoelectronic generator (gen i) adapted to receive the light pulse train provided by the optical cavity (CO;) and to deliver a train of electrical pulses according to the received light pulse train. An electromagnetic emission control device according to claim 5, comprising on each processing channel (V;) an antenna (A;) adapted to receive the electrical pulse train. delivered by the optoelectronic generator (gen i) and generate electromagnetic radiation as a function of the received electrical pulse train. An electromagnetic emission control device (1) according to any one of the preceding claims, wherein the optical cavity comprises an acousto-optical modulator adapted to modulate a light carrier in the cavity and being adapted to stop said modulation after n-1. iteration of optical loop and being adapted to introduce the light pulse at the entrance of the optical cavity. An electromagnetic emission control device (1) according to any one of the preceding claims, comprising an input splitter adapted to receive at least one light pulse and to distribute said received light pulse in at least one light pulse for each of the light pathways. treatment. An electromagnetic emission control device (1) according to any one of the preceding claims, wherein the time delay introduced between a light pulse of a given rank in the train on the second path with respect to the light pulse of the same given rank on the first channel determines a transmission azimuth to be achieved by the coherent superposition of the radiation provided by the first and second fed antennas according to said light pulses of the given rank of the first and second channels. An electromagnetic detection system (1) comprising: a light source (SI); a control device (1) according to one of the preceding claims adapted to receive as input light pulses provided by the light source; and an analysis module adapted to receive and analyze electromagnetic radiation reflections controlled by the control device. A method of controlling electromagnetic emissions by a first antenna (A,) and a second antenna (A2), wherein: - a light pulse (si, s2) is received on at least two processing channels; the light pulse is delayed on the second path with respect to the light pulse on the first path, in order to supply the first antenna, respectively the second antenna, as a function of the first light pulse, respectively the second light pulse; , characterized in that a time delay is introduced by means of at least one optical cavity (CO ,, CO2) disposed on each channel, each optical cavity comprising at least two mirrors (R1; R2;), of which a semi-reflecting mirror (R2;), said mirrors being separated by an optical path and comprising an amplifier (3;) disposed on the optical path, a light pulse received at the input of the optical cavity giving rise to a train of minus n successive luminous pulses refracted by the semi-reflecting mirror, with n fixed integer, greater than or equal to 2; the last n-1 optical pulses of each train having been successively reflected by the two mirrors; said optical path of the optical cavity on the second path is of greater length than the optical path of the optical cavity on the first path, so as to introduce a time delay between at least one luminous pulse of a given rank in the train on the second way with respect to the light pulse of the same rank given in the train on the first track.