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    • 专利摘要:
    The invention relates to a device (200) for transmitting an electromagnetic wavefront, intended for use in connection with a light source (10) emitting a light beam (11), and comprising: - at least three emission waveguides (220), each having a rectilinear section (223) which receives one or more optical power extraction elements (230); - upstream of each of said rectilinear sections, a phase shift element (222) and an optical coupler (260) with an adjustable coupling ratio. At least two of the rectilinear sections (223) extend along lines that are not parallel to each other. An orientation of a transmission beam, defined in a far-field, is selected by adjusting the coupling ratio of each of the optical couplers, and the phase shift provided by the phase shift elements receiving optical power. The invention is particularly advantageous in the context of remote sensing.
    公开号:FR3070507A1
    申请号:FR1758017
    申请日:2017-08-31
    公开日:2019-03-01
    发明作者:Karim HASSAN；Salim BOUTAMI；Christophe Kopp
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    SIMPLIFIED ADDRESSING OPTICAL PHASE MATRIX
    DESCRIPTION
    TECHNICAL AREA
    The invention relates to an electromagnetic wavefront emission device, comprising a plurality of elementary light sources, and phase shift elements for controlling relative shifts of the optical phase of the light beams emitted by said elementary sources.
    The elementary sources together form, in the far field and by phenomena of constructive and destructive interference, a predetermined distribution of the electromagnetic field. They can in particular constitute a global source emitting a main beam of emission, defined in the far field, and whose orientation in space can be controlled using said phase shift elements.
    Such an emission device is commonly called an “optical phase matrix”.
    PRIOR STATE OF THE ART
    The document "High-resolution aliasing-free optical beam steering", David N. Hutchison & al., Optica, Vol. 3, No. 8, August 2016, pages 887-890, describes a device for transmitting an electromagnetic wavefront, comprising a tunable laser whose optical power is distributed over a plurality of emission waveguides .
    Each emission waveguide has an upstream portion, receiving a phase shift element, and a straight downstream portion, receiving an optical power extraction network. The extraction networks of the various emission waveguides therefore form elementary sources from which the relative optical phase shifts can be controlled.
    The rectilinear portions of the various emission waveguides are aligned side by side, mutually parallel.
    In the far field, the optical power emitted by this device is concentrated towards a preferred direction, the orientation of which is defined by two angles ψ and Θ.
    Throughout the text, the preferred direction of concentration of the optical power, in the far field, is called “main direction of emission”.
    The angle ψ is controlled by the phase shift elements.
    The angle θ is controlled by varying the wavelength of the signal supplied by the tunable laser. The wavelength range that can be scanned by the tunable laser is from 1260 nm to 1360 nm. This corresponds to a scanning amplitude of the angle θ of only 17 °.
    In the article “Large-scale nanophotonicphased array”, Nature, Vol. 493.10 January 2013, pages 195 to 199, the authors, Jie Sun & al., Describe a solution allowing to overcome this limitation on the angle Θ.
    They describe in particular a transmission device comprising a laser source whose optical power is distributed over a matrix of 64 x 64 silicon nano-antennas, distributed in rows and columns, according to a square mesh.
    Each nano-antenna forms an elementary source, and includes a heating portion forming a phase shift element.
    In the far field, the optical power emitted by this device can be concentrated towards a main direction of emission, the orientation of which is defined by two angles. The value taken by each of these two angles is controlled in the same way, using the phase shift elements.
    This eliminates the limitation described above, relating to a scanning amplitude.
    On the other hand, the measurements reported in the article show the existence of a beam replication phenomenon, resulting in the presence of secondary beams, of lesser intensity, around a main beam oriented in the main direction of program.
    In most cases, and in particular in remote sensing applications, these secondary beams are not desirable.
    An objective of the present invention is therefore to propose a device for transmitting an electromagnetic wavefront, of the optical phase matrix type, which can offer both:
    a wide scanning range in the space of a main emission direction; and emission without beam replication phenomenon.
    STATEMENT OF THE INVENTION
    This objective is achieved with a device for emitting an electromagnetic wavefront intended to, in use, be connected to a light source emitting a light beam, and comprising:
    at least three emission waveguides, each comprising a rectilinear section which receives one or more optical power extraction element (s), called extraction element (s); and upstream of each of said rectilinear sections, a respective phase shift element; and upstream of each of said phase shift elements, a respective optical coupler, each optical coupler having an adjustable coupling rate;
    at least two of said rectilinear sections extending along straight lines which are not parallel to each other.
    Said straight lines can be intersecting, when the corresponding emission waveguides extend on the same plane.
    Throughout the text, the term “upstream” refers to the direction of propagation, in the emission device according to the invention, of the light emitted by said light source.
    Each optical coupler and each phase shift element are therefore on the side of the input end of one of the straight sections.
    Each optical power extraction element forms an elementary source, adapted to emit a light beam, the phase of which is adjustable using the phase shift element located upstream of the corresponding rectilinear section. The phase adjustment here corresponds to the adjustment of a phase shift relative to an original optical phase. The original optical phase is that of the light beam emitted by the light source which, in use, is connected to the emission device according to the invention. The optical phase after phase shift is the optical phase of the beam emerging from the phase shift element, in the associated rectilinear section, and arriving on the first optical power extraction element along said section.
    Each elementary source emits a light beam only when a light signal enters the corresponding rectilinear section.
    The optical couplers, each having an adjustable coupling rate, make it possible to select at least two rectilinear sections which will receive a light signal as an input.
    The rectilinear sections thus selected together define the orientation of an extraction plane.
    The extraction plane is a plane receiving all of the main emission directions, accessible using the rectilinear sections selected.
    It is substantially orthogonal to the mean direction of these rectilinear sections.
    The orientation, in the extraction plane, of the main direction of emission, is then a function of the relative phase shifts of the light beams emitted by the elementary sources associated with the selected rectilinear sections.
    According to the invention, the emission device comprises at least three emission waveguides each having a rectilinear section, and at least two of said rectilinear sections extend along straight lines which are not parallel to each other.
    We can therefore select at least two pairs of rectilinear sections, together defining two different orientations of the extraction plane.
    The invention therefore offers an original solution for controlling the main direction of emission of an optical phase matrix, based on one-dimensional addressing of a series of rectilinear sections of waveguides, and on an original arrangement of these straight sections.
    The parameters making it possible to define the orientation in space of the main direction of emission are optical phase shifts, and orientations of rectilinear sections of waveguides.
    One can thus access a multitude of different orientations of the main direction of emission, these orientations being distributed in a plurality of three-dimensional space planes. In particular, these orientations can be distributed over a plurality of planes inclined relative to one another, and distributed over an angular range of width much greater than 17 °, for example greater than 90 °, and possibly reaching for example 180 °.
    In addition, addressing in one dimension, with the phase shift elements upstream of the straight sections, makes it possible to bring the extraction elements closer to one another.
    This characteristic makes it possible to limit, and even to eliminate, beam replication phenomena.
    This effect is particularly advantageous in the context of the use of the device according to the invention, as transmitter of a laser remote sensing device (LIDAR, in English, for “light detection and ranging”), and more particularly still for detecting remotely the presence of an object, and measure its position. In such a use, the device according to the invention is used to carry out a three-dimensional scanning of a pulsed light beam, and a detection assembly receives a return signal originating from the reflection of this beam on a target object.
    Beam replication corresponds to the presence of secondary beams, around a main beam. These secondary beams can be returned by objects other than the target object, and thus distort or at least complicate the digital reconstruction of a three-dimensional scene. In addition, these secondary beams receive a portion of the total optical power emitted by the emission device, thereby reducing the optical power of the main beam, and therefore a maximum detection distance of an object.
    It is therefore particularly advantageous to limit the phenomena of beam replication, when the transmission device according to the invention is used in remote sensing.
    Addressing in one dimension, with the phase shift elements upstream of the straight sections, also makes it possible to use materials other than silicon to produce the emission waveguides with their phase shift elements, without this being translate by the appearance or the increase of beam replication phenomena. The particularly advantageous example of silicon nitride will be detailed below.
    According to the invention, an optical coupler having an adjustable coupling rate can simply denote a coupler that can couple or not couple light. Such an optical coupler then forms a simple optical switch.
    Advantageously, the emission device according to the invention further comprises an injection waveguide, along which the optical couplers are distributed, each optical coupler being located between the injection waveguide and the 'one of the phase shift elements.
    Preferably, each straight section comprises a plurality of extraction elements, distributed along said straight section at a regular pitch.
    Said regular pitch may be the same, on each of said rectilinear sections.
    Each straight section may include a plurality of extraction elements, having different extraction rates, and arranged along said section in ascending order of this extraction rate, from an entry end of said section, on the side of the 'corresponding phase shift element.
    Each rectilinear section advantageously comprises a plurality of extraction elements, and the extraction elements are distributed along a series of patterns, the different patterns being homothies of each other, and for each corresponding pattern an element d 'extraction of each of said sections.
    Preferably, each straight section comprises a plurality of extraction elements, each of said extraction elements is an extraction network, and the extraction networks of the same straight section are oriented in the same direction and have the same period.
    Advantageously, said rectilinear sections are all oriented towards the same zone, known as the core zone, situated, for each rectilinear section, on the side opposite to the corresponding phase-shifting element.
    In particular, said rectilinear sections can be oriented along radii of the same circle or the same cylinder.
    Said rectilinear sections can be arranged according to a regular angular distribution pitch.
    They can be distributed over a 360 ° angle or over an angle between 160 ° and 200 °. Preferably, the extraction elements of the different rectilinear sections are distributed along a series of concentric circles or concentric cylinders, to each circle, or cylinder, corresponding to an extraction element of each of said sections.
    The emission waveguides advantageously comprise silicon nitride. The invention also relates to a method of using a transmission device according to the invention, in which each optical coupler comprises a coupling ring and each phase-shifting element comprises a section of an emission waveguide , said phase shift section, the method comprising:
    a step of adjusting the respective coupling rate of each of the optical couplers, by adjusting the intensity of a voltage or an electric current, providing heating by Joule effect, to the corresponding coupling ring; and a step of adjusting a respective phase shift provided by each of the phase shift elements associated with the optical couplers whose coupling rate exceeds a predetermined threshold, by adjusting the intensity of a voltage or an electric current providing a heating, by Joule effect, to the corresponding phase shift section.
    BRIEF DESCRIPTION OF THE DRAWINGS
    The present invention will be better understood on reading the description of exemplary embodiments given purely by way of non-limiting indication, with reference to the appended drawings in which:
    FIGS. IA and IB respectively illustrate a distribution of the elementary sources in a transmission device according to the prior art, and a distribution of the optical power obtained in the far field using such a device;
    Figure 2 illustrates schematically, according to a top view, a first embodiment of a wavefront emission device according to the invention;
    FIGS. 3A and 3B schematically illustrate, respectively from a top view and from a perspective view, the emission device of FIG. 2 with an associated main emission direction;
    FIGS. 4A to 4D illustrate the scanning of the main direction of emission in a first extraction plane, using a transmission device according to the invention;
    FIGS. 5A to 5D illustrate the scanning of the main direction of emission in a second extraction plane, using a transmission device according to the invention;
    Figure 6 schematically illustrates, in a top view, a second embodiment of a transmission device according to the invention;
    FIG. 7 schematically illustrates, according to a top view, a third embodiment of a transmission device according to the invention; and FIG. 8 very schematically illustrates, in a perspective view, a fourth embodiment of a transmission device according to the invention.
    DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
    First of all, an analysis of the distribution of optical power in the far field is illustrated in a transmission device.
    In FIG. 1A, the distribution of the elementary sources 101 of a transmitting device as shown in the introduction is shown schematically, comprising a matrix of elementary sources 101 distributed in rows and columns.
    The elementary sources 101 are distributed along the axes (OX) and (OY), according to a distribution pitch P x , respectively P Y. The relative phase shift between two neighboring elementary sources, aligned along (OX), is equal to Δφ χ . The relative phase shift between two neighboring elementary sources, aligned along (OY), is equal to Δφ γ . The axes (OY) and (OX) belong to an orthonormal coordinate system (OXYZ).
    In Figure IB, there is shown schematically a distribution of the optical power in the far field, obtained using such a device. The power is distributed here over a main beam 110, and over a plurality of secondary beams 111. The orientation of these beams is defined by two angles Θ and ψ. The angles Θ and ψ correspond respectively to an angle of deviation in the plane (OXZ) and in the plane (OYZ).
    By looking at this distribution of optical power, the inventors have realized that the orientations that can receive optical power are defined by angles such as:
    + m * 2π sin (0 m ) = ------------ (1) k 0 * Ρχ
    Δφ ν + η * 2π sin Gu) = k * p— (2)
    A-0 * ΐγ, 2π with K o = -, λ the wavelength emitted by the elementary sources, and m and n A.
    relative integers.
    In addition, the possible orientations are those associated with the values of m and n such that:
    sin 2 (0m) + sin 2 (^ n) <1 (3)
    Consequently, the number of orientations that can receive optical power decreases when the values of P x and P Y decrease. In addition, these orientations move away from each other when the values of P x and P Y decrease.
    In other words, the distribution step of the elementary sources determines the existence, or not, of beam replication phenomena.
    The inventors have thus shown that a way to avoid or limit beam replication consists in bringing the elementary sources closer to one another.
    At a wavelength λ ρ = 1.55 μτη, the distribution step of the elementary sources must be less than or equal to 1.55 μιτι to avoid beam replication, which is not possible due to the size of the phase shift elements on each nano-antenna. Even a step of 3 μιτι, allowing a good reduction in the number of replications, is not achievable due to the size of the phase shift elements on each nanoantenne.
    The solution proposed by the inventors is illustrated below.
    FIG. 2 shows a first embodiment of a device 200 according to the invention.
    The device 200 here comprises:
    an injection waveguide 210, receiving at the input a light beam 11 supplied by a light source 10;
    a plurality of emission waveguides 220, arranged here in a star; and a plurality of optical couplers 260 distributed along the injection waveguide 210, each at the input of an emission waveguide 220.
    The light source 10 is a monochromatic source, in particular a laser source, emitting a light beam centered on a wavelength λ Ρ . It is arranged at the input of the injection waveguide 210, at a first end thereof. It emits the light beam 11 in the injection waveguide 210.
    The light source 10 is not an integral part of the device 200 according to the invention.
    The injection waveguide 210 is configured to receive and optically guide the light, at wavelengths around λ Ρ .
    The injection waveguide 210 here consists of silicon.
    It has an entry region 211, on the side of the light source 10, and an injection region 212, which here extends along almost all of a circle G, in the form of an open ring. .
    The emission waveguides 220 and the optical couplers 260 extend inside this circle G.
    Each optical coupler 260 is located along the injection waveguide 210, between a lateral surface of the injection waveguide 210 and the input end of an emission waveguide 220.
    Each optical coupler 260 has an adjustable coupling rate, at the wavelength λ Ρ .
    Each optical coupler 260 here consists of a heating coupling ring, that is to say a waveguide folded back on itself in the form of a ring, and electrically connected to a current or voltage source , not shown. Depending on the intensity of the current, respectively the voltage, the ring heats more or less, which changes its optical index, and therefore the condition of constructive phase in the ring. The coupling wavelength of the ring is thus modified, to distance it or bring it closer to the wavelength λ Ρ . Thus, the more or less intense heating of the ring modifies its capacity to optically couple, at the wavelength λ Ρ , the injection waveguide 210 and an emission waveguide 220. The coupling is of the evanescent type, generally without direct physical contact between the ring and the injection waveguide, respectively between the ring and the associated emission waveguide.
    Here, the optical couplers 260 are made of silicon.
    An optical coupler with adjustable coupling rate is known from the prior art, and will therefore not be described here in more detail.
    As a variant, each optical coupler 260 with adjustable coupling rate comprises a ring optical coupler and an additional heating element, disposed against the optical coupler and electrically connected to a current or voltage source.
    It is said that the optical coupler 260 is on when it is adapted to transfer, to the nearest emission waveguide, part of the light beam 11 at the wavelength λ Ρ passing through the guide injection wave 210.
    It is said that the optical coupler is blocking when it does not allow this transfer.
    A first threshold can be defined, an optical coupler whose coupling rate at the wavelength λ Ρ is greater than this first threshold being said to be on.
    A second threshold can be defined, an optical coupler whose coupling rate at the wavelength λ Ρ is less than this second threshold being said to be blocking. The first and second thresholds can be equal.
    Each optical coupler 260 is arranged at the input of a respective emission waveguide, which receives or does not receive light depending on whether the optical coupler is on or off. It can be considered that the injection waveguide 210 and the optical couplers 260 together form a multiplexer with channel selection.
    Each emission waveguide 220 is configured to receive and optically guide light, at wavelengths around λ Ρ .
    Each emission waveguide 220 here consists of silicon.
    Preferably, the injection waveguide 220, the optical couplers 260, and the emission waveguides 220 all have the same chemical composition, except where appropriate in terms of a concentration of doping ions. .
    The emission waveguides 220 extend here, with the optical couplers 260 and the injection waveguide 220, on the same plane (OXY) of an orthonormal reference (OXYZ).
    The emission waveguides 220 in particular have respective coplanar lower faces, parallel to the plane (OXY).
    Each emission waveguide 220 here has three sections:
    a coupling section 221, located upstream of the emission waveguide 220 (relative to the direction of propagation, in said waveguide, of the light emitted by the light source 10);
    a phase shift section 222, downstream of the section 221; and a straight section 223, downstream of the phase shift section 222.
    At least part of the coupling section 221 extends parallel to a tangent to the corresponding coupling ring 260. The coupling section 221 forms an intake region of the emission waveguide 220, adapted to receive a signal at the wavelength λ Ρ coming from the injection waveguide 210, when the optical coupler 260 correspondent is passing.
    The phase shift section 222 here has a serpentine shape.
    It is electrically connected to a current or voltage source, not shown. Depending on the intensity of the current, respectively the voltage, the section 222 heats more or less, which changes its optical index. The more or less significant modification of this optical index leads to a more or less significant shift of the optical phase of a light signal propagating in said section 222, by thermooptic effect.
    According to a variant not shown, the phase shift section is heated by means of an additional heating element. The auxiliary heating element is disposed against said phase shift section. The auxiliary heating element is for example a metal strip, electrically connected to a current or voltage source.
    As a variant, the phase-shifting section 222 is made of doped material, and the adjustment of the phase-shift which it provides is carried out by injection or desertion of carriers.
    The section 222 thus forms a phase shift element, disposed downstream of an optical coupler 260 and upstream of a straight section 223 according to the invention, making it possible to provide a desired phase shift to a light signal coming from the waveguide injection, before it reaches said straight section 223.
    Such a phase shift element is known from the prior art, and will therefore not be described here in more detail.
    The rectilinear sections 223 here extend each along a radius of the circle C mentioned above.
    They are distributed regularly, at an angular step β. For reasons of readability, an example has been shown in which this step β is equal to 30 °. In practice, this pitch β is preferably less than or equal to 10 °, or even less than or equal to 5 °.
    The rectilinear sections 223 are distributed here over an angular range of 360 °.
    The rectilinear sections 223 each have an inlet end 2231, and an outlet end 2232, on the side opposite to the inlet end 2231.
    The input ends 2231 of the various emission waveguides are all located on the side of the injection waveguide 210.
    The output ends 2232 of the various emission waveguides are all positioned in an area 240, called the core area.
    It is at the output ends 2232 that the distance between two emission waveguides is minimum. The center-to-center distance between two neighboring emission waveguides is however greater than  P / 2, in order to avoid optical coupling between them.
    Each rectilinear section 223 receives a plurality of optical power extraction elements, called extraction elements 230, illustrated by respective black squares.
    The extraction elements 230 each make it possible to extract at least part of an incident light signal circulating in said section, towards the same half-space delimited by the rectilinear sections, here an upper half-space situated above the sections rectilinear.
    On the same rectilinear section, the different extraction elements are distributed along the longitudinal axis of said section. Their extraction rates are adapted so that everyone can emit part of a light signal arriving at the input of said section.
    Each extraction element 230 consists of a diffracting or diffusing structure. Each structure can be surface, extending here only in an upper region of one of the rectilinear sections 223. As a variant, said structure can be through. In any event, reflection means such as a mirror or a diopter can extend with regard to said structure, here on the side of a lower face of the rectilinear section, to extract the light towards the upper half-space. above the plane of the straight sections.
    Each extraction element 230 is for example a surface extraction network, or even a simple hole, traversing or not.
    When the extraction elements 230 are extraction networks, the different networks of the same rectilinear section 223 have the same orientation and the same period.
    The angular offset between the orientation of the extraction networks and the orientation of the corresponding rectilinear section 223 can be constant. In this case, in the embodiment illustrated in FIG. 2, the networks of two different straight sections 223 have different orientations.
    In any event, whether or not they are extraction networks, the extraction elements 230 of the same straight section 223 are advantageously phase-shifted by 2kn, k whole. This phase shift of 2kn is allowed by spacing the extraction elements 230 along the rectilinear section 223 by a distance d multiple of k * ——, with and N e pp the effective index of the guided mode in the rectilinear section 223. In other words, the extraction elements of the same rectilinear section 223 are preferably spaced two by two by a distance d such that:
    (4) with j a positive integer and N e pp the effective index of the guided mode in the rectilinear section 223.
    The distance d is a center to center distance.
    Preferably, this distance d is constant along the same straight section 223. In other words, on each straight section 223, the extraction elements 230 are distributed in a regular pitch p.
    The pitch p is advantageously the same on all the straight sections 223.
    The extraction elements 230 of the various rectilinear sections 223 are distributed here along a series of concentric circles. Each of these circles receives a single extraction element from each of the rectilinear sections 223.
    Preferably, the center-to-center distance between two extraction elements 230 belonging to two neighboring emission waveguides remains less than a few λ Ρ , for example less than 5 * λ Ρ .
    In practice, the injection waveguide 210, the optical couplers 260 and the emission waveguides 220 are advantageously embedded in silicon oxide (silica), the latter acting as a sheath for the guides. emission wave 220.
    An orientation of a main emission beam, defined in the far field, is selected by adjusting the coupling rate of each of the optical couplers, and the phase shift provided by the phase shift elements receiving optical power.
    Illustrated in detail, with the aid of FIGS. 3A and 3B, the operation of the emission device 200.
    In Figure 3A, the transmitting device is shown in a top view.
    In Figure 3B, it is shown schematically, in a perspective view.
    In FIG. 3B, the orthonormal coordinate system (OXYZ) is centered on the center of the circle G mentioned above. FIG. 3B also shows a reference frame (OX'Y '), projection along (OZ), in the far field, of the reference frame (OXY).
    According to the invention, all the optical couplers do not have the same coupling rate, at all times.
    At all times, the pass-through optical couplers are optical couplers directly adjacent to each other (or two groups of opposite neighboring optical couplers, associated with the same mean direction due to the symmetry of the transmission device, see below).
    In FIG. 3A, the optical couplers 260i in the conducting state are represented by a black disc, and the optical couplers 26Oo in the blocking state are represented by a simple circle.
    Here, only three optical couplers are passable, the others being blocking.
    The three pass-through optical couplers 260i are associated respectively with three emission waveguides 220i, called activated, each represented by a thick solid line. The light passing through the injection waveguide 210 is coupled to these three activated waveguides 220i. The other emission waveguides 220ο do not receive light.
    The adjustment of the coupling rates of the optical couplers can be binary. The coupling rate can then only take two values, either a low value, corresponding to a blocking coupler, or a high value corresponding to a passing coupler.
    As a variant, the adjustment of the coupling rates can offer fine adjustment, for example to refine the width of the main emission beam emitted, in the far field, by the emission device according to the invention.
    One can also provide a precise adjustment of the coupling rates, so as to couple the same amount of light in each of the activated waveguides 220i. For this, the coupling rate associated with each of the pass-through optical couplers 260i increases as one moves away from the input region 211 of the injection waveguide.
    In operation, the light propagates in the injection waveguide, then it is injected into the activated waveguides 220i, via the pass-through optical couplers 260i.
    In each activity waveguide, light passes through the phase shift section, where its optical phase is offset by a predetermined value (this value can be zero).
    Then, the light successively reaches each of the extraction elements of the straight section. Each extraction element extracts part of the optical power from the emission waveguide, and thus forms an elementary source of light.
    According to an advantageous variant, the extraction elements of the same rectilinear section have different values of the rate of extraction of the optical power, and this value increases as one moves away from the entry. of said section. Thus, the loss of optical power at the input of an extraction element, due to the extraction in the extraction element (s) upstream, is compensated by a higher extraction rate. It is thus possible to equalize the optical powers extracted by each of the extraction elements from the same rectilinear section.
    To obtain these increasing extraction rates, the extraction elements may have an increasing width as one moves away from the entrance to the straight section (increasingly wide holes, or networks of longer and longer extraction). In addition or as a variant, the extraction elements may have an etching depth which increases as one moves away from the entrance to the section.
    The mean direction, 31, associated with the rectilinear sections of the activated waveguides 220i is defined by an angle a. This angle is defined relative to the axis (OX) of the orthonormal coordinate system (OXYZ).
    This mean direction defines an extraction plane 310, orthogonal to said mean direction 31, at the wavelength λ Ρ .
    The extraction plane 310 is a vertical plane, parallel to the axis (OZ), inclined by the angle a relative to the plane (OYZ).
    The extraction plane 310 is the plane receiving all of the main emission directions, accessible using the three activated waveguides 220i.
    The main emission directions are defined in the far field, that is to say at a distance from the emission device greater than the characteristic size of said device, and even in practice, at a distance from the emission device greater a few centimeters, for example greater than 5 cm.
    The main direction of emission is represented in FIG. 3B by an arrow 32. It is defined only in the far field, and extends in the extraction plane 310. Its orientation depends on the phase shifts between the light signals emitted by the elements d extraction of the activated waveguides 220i. This orientation is defined, in three-dimensional space, by two angles Θ and ψ. The angles 0 and correspond respectively to an angle of deviation in the plane (OXZ) and in the plane (OYZ).
    By controlling the on or off state of optical couplers 260, it is therefore possible to select an average orientation of the activated rectilinear sections, and therefore a desired orientation of the extraction plane.
    FIG. 3A, in particular, shows that the offset of the three activated waveguides 220i results in a rotation of the extraction plane around the axis (OZ).
    Controlling the coupling rate of an optical coupler is advantageously achieved by controlling a current or voltage intensity value, an electrical signal providing heating, by Joule effect, to this optical coupler.
    Then, by controlling the phase shift provided by each of the phase shift elements 250 associated with the activated waveguides 220i, it is possible to select a desired orientation of the main direction of emission, in the extraction plane.
    The control of the phase shift is advantageously achieved by the control of a current or voltage intensity value, of an electrical signal providing heating, by Joule effect, to a phase shift element according to the invention.
    The elements making it possible to define a predetermined orientation of the main direction of emission are therefore deported from a region receiving the elementary sources (here, the extraction elements).
    These elements are also located in a region where they are distant from each other, due to the radial arrangement of the rectilinear sections receiving the elementary sources.
    It is thus possible to reconcile both a large bulk of the phase shift elements, and a very small distance between two neighboring elementary sources.
    The silicon nitride (S13N4) waveguides support optical powers much higher than those that can be supported by silicon waveguides. They can in particular transport beams of high optical power without this inducing the appearance of non-linear effects capable of deforming these beams.
    On the other hand, since the silicon nitride is not very sensitive to temperature variations, phase-shift sections of silicon nitride must be longer than when they are made of silicon.
    By deporting these phase-shifting sections outside an emissive zone receiving the elementary sources, the invention makes it possible to produce the emission waveguides in silicon nitride (S13N4), rather than in silicon, without this being reflected. by an increase in the distance between two neighboring elementary sources.
    A short distance between two neighboring elementary sources makes it possible to avoid beam replication phenomena.
    It is thus possible to increase an optical power circulating in the transmission device according to the invention, and therefore an optical power re-emitted by the latter, without this resulting in the appearance of beam replication phenomena. In other words, an optical phase matrix is proposed which can deliver more useful power than in the prior art, without deterioration of the beam quality.
    These high optical powers are particularly advantageous in the context of the use of the device according to the invention, as a transmitter of a laser remote sensing device. Indeed, the increase in the optical power emitted by the device according to the invention then results in an increase in the maximum detection distance. Thanks to the invention, this increase in the detection distance is not accompanied by the appearance of beam replication phenomena, which may disturb the detection. Possible beam replications are angularly distant enough from the main beam so that they do not interfere with detection.
    The use of silicon nitride emission waveguides makes it possible in particular to detect objects located more than 100 meters, or even 200 meters from the emission device according to the invention. For comparison, this distance is less than a meter, in silicon technology.
    Such detection distances can be of particular interest, in particular in the automotive field.
    It will be shown below that the reduced distance between two neighboring extraction elements makes it possible to limit beam replication phenomena, even in the particular configuration of the invention.
    In a transmission device according to the invention, all the extraction elements of the same rectilinear section transmit with the same optical phase.
    We note 6 m and ip m the angles defining the orientation in space of the main direction of emission (m = 1) and of possible beam replications (m> 1).
    The orientation of the main direction of emission, respectively of possible beam replications, is defined by:
    (5) with Δφ the phase shift between two neighboring straight sections, P the characteristic distance between two extraction elements from two neighboring straight sections, and m an integer such that:
    sin 2 (em ~) + sin 2 (V> n) <1 (6)
    The two angles 6 m and are therefore not independent of each other (same variable m). However, they are linked by:
    (7)
    By varying the values of a (via the choice of the on or off state of the optical couplers 260), and Δφ (via the phase shift elements 250), it is therefore possible to access all the possible values of 6 m and ip m .
    According to equations (5) and (6), non-beam replication is achieved for low values of P, which is possible since the phase shift elements 250 are offset from the rectilinear sections receiving the extraction elements.
    We then illustrate the results obtained by numerical simulations, using an analytical model based on Green's functions.
    This model is based on the assumption that the elementary sources that are the extraction elements are dipole sources, the orientation of the dipole being that of the electric field in the corresponding emission waveguide.
    The electric field radiated by an elementary source is defined as a combination of the electric field radiated by a dipole oriented along (OX), and the electric field radiated by a dipole oriented along (OY).
    By summing the electric fields from the different elementary sources, we obtain the electric intensity (modulus of the total electric field squared) in a distant observation plane (here 1000 * λ ρ ), which describes the set of angles Θ etip and thus allows you to view the extraction diagram.
    FIGS. 4A to 4D illustrate a simulation of the selection of a first extraction plane, using a transmission device according to the invention, and a scanning of the main direction of emission in said plane d 'extraction.
    FIG. 4A schematically illustrates, according to a top view, the extraction elements of an emission device of the type of that represented in FIG. 2, comprising 25 polarized emission waveguides TE (perpendicular electric field guides).
    The emission wavelength is λ ρ = 1.55 μητ.
    The emission waveguides are made of silicon.
    The distribution step of the extraction elements on an emission waveguide is worth 3 μιτι.
    The center-to-center distance between the extraction elements of two neighboring straight sections is also around 3 μητ
    The extraction elements surrounded correspond to the activated emission waveguides, here three in number.
    The mean direction of the rectilinear sections of the activated waveguides is a = 90 °.
    FIGS. 4B to 4D illustrate the distribution of the optical power in the far field for different values of the phase shift provided by the phase shift elements of the activated waveguides.
    These different values of the phase shift here correspond to a phase shift Δφ between the beams circulating on the rectilinear sections of two directly adjacent activated waveguides.
    The abscissa axis and the ordinate axis correspond respectively to the angles Θ and ψ defined above.
    In each of these figures, there is a light point corresponding to the main direction of emission.
    In FIG. 4B, the phase shift Δφ is zero (the optical phases associated with the three activated waveguides are respectively φ = 0 °; φ = 0 °; φ = 0 °). The light point is positioned at (Θ = 0 °; ψ = 0 °).
    In FIG. 4C, the phase shift Δφ is 60 ° (the optical phases associated with the three activated waveguides are respectively φ = —60 °; φ = 0 °; φ = + 60 °). The light point is positioned at (θ = 3 °; ψ = 0 °).
    In FIG. 4D, the phase shift Δφ is 120 ° (the optical phases associated with the three activated waveguides are respectively φ = —120 °; φ = 0 °; φ = + 120 °). The light point is positioned at (θ = 8 °; ψ = 0 °).
    We can clearly observe an extraction plan defined pan /; = 0 °, parallel to the plane (OXZ).
    Adjusting the phase shifts allows scanning in this plane.
    FIGS. 5A to 5D illustrate a simulation of the selection of a second extraction plane, using a transmission device according to the invention, and a scanning of the main direction of emission in this plane d 'extraction.
    FIG. 5A differs from FIG. 4A only in that the angle a is this time 45 °.
    FIGS. 5B to 5D correspond respectively to the same three phases of the activated waveguides as in FIGS. 4B to 4D.
    We can observe an extraction plan defined by θ = - ψ. Adjusting the phase shifts allows scanning in this plane.
    It can be noted that the transmission device illustrated in FIG. 2 has a certain redundancy, due to its central symmetry. Each orientation of the extraction plane can be obtained in two different ways, using a first or a second series of activated waveguides, symmetrical to one another.
    In Figure 6, there is illustrated, in a top view, a second embodiment of a device 600 according to the invention.
    This second embodiment differs from the first embodiment only in that the rectilinear sections 623 are distributed over 180 °, and not over 360 °.
    The number of straight sections 623 is halved. It is therefore the same for the number of optical couplers 660 and the number of phase shift elements.
    For the reasons mentioned above, this does not reduce the number of possible orientations for the extraction plane.
    The injection waveguide 610 has an inlet region 611 and an injection region 612, which then extends along a semicircle, in the form of a half-ring.
    This second embodiment has the advantage of offering great compactness on the surface (footprint).
    FIG. 7 schematically illustrates, according to a top view, a third embodiment of a device 700 according to the invention.
    This embodiment will only be described for its differences relative to the embodiment of FIG. 6.
    Here, the rectilinear sections of the emission waveguides 720 are not oriented along radii of the same circle.
    Some neighboring rectilinear sections are arranged parallel to each other, while other neighboring rectilinear sections are arranged inclined to each other by an angle β.
    The different rectilinear sections are all oriented towards the same core area 740, located, for each rectilinear section, on the side opposite to the associated optical coupler.
    This embodiment makes it possible to favor certain extraction plans.
    FIG. 8 schematically illustrates, in a perspective view, a fourth embodiment of a device 800 according to the invention.
    FIG. 8 simply shows the axes 824 for orienting the rectilinear sections of the various emission waveguides.
    According to this embodiment, the emission waveguides are not all located on the same plane parallel to (OXY). In particular, the lower faces of the different emission waveguides are not all located in the same plane parallel to (OXY).
    At least two emission waveguides have lower faces located in two different planes, both parallel to (OXY). The transmission device is said to be multi-level.
    The different rectilinear sections here are oriented not along radii of the same circle, but along radii of the same cylinder of revolution. In other words, they are oriented along radii of different circles, corresponding to orthogonal sections, at different heights, of the same cylinder of revolution.
    The extraction elements can then be distributed along the lateral faces of concentric cylinders of revolution.
    This embodiment makes it possible to have neighboring phase-shifting elements in separate planes parallel to (OXY), which makes it possible to further densify the arrangement of the phase-shifting elements, and therefore to further densify the straight sections and the extraction elements. optical power. We can thus further limit the replication of beams.
    According to an advantageous variant, the emission waveguides, and more particularly their lower faces, are distributed alternately in a first and in a second plane parallel to (OXY). The phase shift elements are distributed, in the same way, alternately in this first and this second plane. In this case, the injection waveguide can extend at the level of one of this first and this second plane. It then performs an evanescent coupling from the side in one of this first and this second plane, and from below in the other among this first and this second plane.
    The invention is not limited to the examples detailed above, and numerous variants can be implemented without departing from the scope of the invention.
    For example, a distribution pitch of the extraction elements is not necessarily identical over all the straight sections.
    In addition, the rectilinear sections do not necessarily all have the same number of extraction elements.
    Each straight section may even have only one extraction element. The different extraction elements are then arranged, preferably, along the same circle. The far field emission diagram then has a light line, not a light point.
    The extraction elements of the different rectilinear sections can be arranged along different patterns, where each pattern receives a single extraction element from each of the rectilinear sections, and where the patterns are all homotheties of the same basic shape whatever , with different magnification ratios.
    As an example of an optical coupler with an adjustable coupling rate, a heating coupling ring has been cited. The invention is not however limited to this example. For example, the optical coupler can consist of a coupling ring of doped material, in which the adjustment of the coupling rate is carried out by injection or desertion of carriers. As a variant, each optical coupler with adjustable coupling rate may comprise a segment of guide resonant with Bragg mirrors, a resonator with photonic crystals, micro-discs. As stated previously, each optical coupler according to the invention can consist of a simple optical switch. Any switch with one input channel and two output channels can then be used, for example a multimode interferometer, a Mach-Zehnder inter being, etc.
    The invention may also relate to a complete system for transmitting an electromagnetic wavefront, comprising the transmission device according to the invention, each optical coupler comprising a coupling ring and each phase-shifting element comprising a section of the guide. corresponding emission wave, said 5 phase shift section, the system further comprising:
    a device for controlling the intensities of a series of voltages or electric currents providing heating by Joule effect, to each of the coupling rings; and a device for controlling the intensities of a series of voltages or electric currents providing heating by the Joule effect, to each of the phase-shifting sections associated with an optical coupler whose coupling rate is greater than a predetermined threshold.
    权利要求:
    Claims (15)
    [1" id="c-fr-0001]
    1. Device (200; 600; 700) for emitting an electromagnetic wavefront, intended to, in use, be connected to a light source (10) emitting a light beam (11), and comprising:
    at least three emission waveguides (220; 720), each comprising a rectilinear section (223; 623) which receives one or more optical power extraction element (s), called element (s) extraction (230); and upstream of each of said rectilinear sections, a respective phase shift element (222);
    characterized in that:
    the device further comprises, upstream of each of said phase shift elements, a respective optical coupler (260; 660), each optical coupler having an adjustable coupling rate; and at least two of said rectilinear sections (223; 623) extend along straight lines which are not parallel to each other.
    [2" id="c-fr-0002]
    2. Device (200; 600; 700) according to claim 1, characterized in that it further comprises, an injection waveguide (210; 610), along which the optical couplers (260; 660), each optical coupler (260; 660) being located between the injection waveguide (210; 610) and one of the phase shift elements (222).
    [3" id="c-fr-0003]
    3. Device (200; 600; 700) according to claim 1 or 2, characterized in that each rectilinear section (223; 623) comprises a plurality of extraction elements (230), distributed along said rectilinear section according to a not regular.
    [4" id="c-fr-0004]
    4. Device (200; 600; 700) according to claim 3, characterized in that said regular pitch is the same, on each of said rectilinear sections (223; 623).
    [5" id="c-fr-0005]
    5. Device (200; 600; 700) according to any one of claims 1 to 4, characterized in that each rectilinear section (223; 623) comprises a plurality of extraction elements (230), having different rates d extraction, and arranged along said section in ascending order of this rate of extraction, from an inlet end (2231) of said section, on the side of the corresponding phase shift element (222).
    [6" id="c-fr-0006]
    6. Device (200; 600; 700) according to any one of claims 1 to 5, characterized in that each rectilinear section (223; 623) comprises a plurality of extraction elements (230), and in that the extraction elements are distributed along a series of patterns, the different patterns being homothies of each other, and for each corresponding pattern an extraction element (230) from each of said sections.
    [7" id="c-fr-0007]
    7. Device (200; 600; 700) according to any one of claims 1 to 6, characterized in that each rectilinear section (223; 623) comprises a plurality of extraction elements (230), in that each of said extraction elements is an extraction network, and in that the extraction networks of the same rectilinear section are oriented in the same direction and have the same period.
    [8" id="c-fr-0008]
    8. Device (200; 600; 700) according to any one of claims 1 to 7, characterized in that said rectilinear sections (223; 623) are all oriented towards the same area, called the core area (240; 740) , located, for each rectilinear section (223; 623), on the side opposite to the corresponding phase shift element (222).
    [9" id="c-fr-0009]
    9. Device (200; 600) according to claim 8, characterized in that said rectilinear sections (223; 623) are oriented along radii of the same circle (C) or of the same cylinder.
    [10" id="c-fr-0010]
    10. Device (200; 600) according to claim 9, characterized in that said rectilinear sections (223; 623) are arranged according to a regular angular distribution pitch (β).
    [11" id="c-fr-0011]
    11. Device (200) according to claim 10, characterized in that said rectilinear sections (223) are distributed over 360 ° of angle.
    [12" id="c-fr-0012]
    12. Device (600) according to claim 10, characterized in that said rectilinear sections (623) are distributed over an angle between 160 ° and 200 °.
    [13" id="c-fr-0013]
    13. Device (200; 600) according to any one of claims 9 to 12, characterized in that the extraction elements (230) of the different rectilinear sections (223; 623) are distributed along a series of circles concentric or concentric cylinders, to each circle, or cylinder, corresponding to an extraction element (230) of each of said sections.
    [14" id="c-fr-0014]
    14. Device (200; 600; 700) according to any one of claims 1 to 13, characterized in that the emission waveguides (220; 720) comprise silicon nitride.
    [15" id="c-fr-0015]
    15. A method of using a transmission device (200; 600; 700) according to any one of claims 1 to 14, in which each optical coupler (260; 660) comprises a coupling ring and each element of phase shift (222) comprises a section of an emission waveguide, known as a phase shift section, the method comprising:
    - a step of adjusting the respective coupling rate of each of the optical couplers (260; 660), by adjusting the intensity of a voltage or an electric current, providing heating by Joule effect, to the ring corresponding coupling; and
    - A step of adjusting a respective phase shift provided by each of the phase shift elements (222) associated with the optical couplers whose coupling rate exceeds a predetermined threshold, by adjusting the intensity of a voltage or a current electric providing heating, by Joule effect, to the corresponding phase shift section.
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    US20190064632A1|2019-02-28|
    FR3070507B1|2019-09-13|
    引用文献:
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    US9476981B2|2013-01-08|2016-10-25|Massachusetts Institute Of Technology|Optical phased arrays|
    FR3028050B1|2014-10-29|2016-12-30|Commissariat Energie Atomique|PRE-STRUCTURED SUBSTRATE FOR THE PRODUCTION OF PHOTONIC COMPONENTS, PHOTONIC CIRCUIT, AND METHOD OF MANUFACTURING THE SAME|
    FR3042038B1|2015-10-01|2017-12-08|Commissariat Energie Atomique|METHOD FOR OPTIMIZING DETECTION WAVE LENGTHS FOR A MULTI-GAS DETECTION|
    FR3054664B1|2016-07-27|2018-09-07|Commissariat A L'energie Atomique Et Aux Energies Alternatives|SEGMENTED RING MICRO RESONATOR OPTICAL DEVICE FOR BIOLOGICAL OR CHEMICAL SENSOR|
    FR3061991A1|2017-01-13|2018-07-20|Commissariat A L'energie Atomique Et Aux Energies Alternatives|COLLIMATED LIGHT SOURCE, METHOD FOR MANUFACTURING SAME AND USE THEREOF FOR SINGLE PHOTON TRANSMISSION|FR3056306B1|2016-09-20|2019-11-22|Commissariat A L'energie Atomique Et Aux Energies Alternatives|OPTICAL GUIDE HAVING A PSEUDO-GRADIENT INDEX RISE|
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    法律状态:
    2019-03-01| PLSC| Search report ready|Effective date: 20190301 |
    2019-08-30| PLFP| Fee payment|Year of fee payment: 3 |
    2020-08-31| PLFP| Fee payment|Year of fee payment: 4 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1758017|2017-08-31|
    FR1758017A|FR3070507B1|2017-08-31|2017-08-31|OPTICAL PHASE MATRIX WITH SIMPLIFIED ADDRESSING|FR1758017A| FR3070507B1|2017-08-31|2017-08-31|OPTICAL PHASE MATRIX WITH SIMPLIFIED ADDRESSING|
    US16/110,757| US10466570B2|2017-08-31|2018-08-23|Optical phased array with simplified addressing|
    EP18191592.7A| EP3451054B1|2017-08-31|2018-08-30|Optical phase matrix with simplified addressing|
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