Photoelectron emitter with phased array antenna

Abstract

The present invention relates to a photoelectron emitter (1) comprising a plurality of optical antennas (7), each antenna comprising a lateral radiating waveguide structure (10) formed by an input waveguide (11) and a lateral diffraction grating (12) configured to extract an optical mode in a horizontal plane, and a vertical radiating waveguide structure (30), the vertical radiating waveguide structure being formed by a radiating waveguide (31) configured to receive the optical mode extracted by the diffraction grating (12) and a vertical diffraction grating (32) configured to extract the optical mode traveling through the radiating waveguide (31) to free space.

Description

[Technical field]

[0001] The technical field of the invention is that of phased array antenna type photoelectron emitters, preferably manufactured on a photonic chip of the photonic-on-silicon type, and is particularly applicable in the field of LIDAR (Light Detection and Ranging).

[0002] prior art Photoelectron emitters with phased array antennas (or Optical Phased Arrays (OPAs)) are optoelectronic devices that allow to radiate monochromatic optical radiation directionally into free space. They find applications in particular in the field of distance detection and estimation using lasers (LIDAR), but also in the field of free space optical communication, in holographic screens and in medical imaging.

[0003] Fig. 1A shows the operating principle of such an optoelectronic emitter 1 diagrammatically. A laser source 2 emits an optical signal, which is distributed by a power splitter 3 in arms 4 of the optoelectronic emitter 1. Each arm 4 comprises a phase shifter 6 and an elementary emitter 7, also called an optical antenna. Each optical antenna 7 emits an optical signal into free space, for example by diffraction, and these optical signals combine by interference to form an optical radiation. This optical radiation has a far-field radiation pattern, which depends in particular on the relative phase Δγ applied by the phase shifter 6 to the optical signals propagating in the arms 4.

[0004] Such photoelectron emitters can be manufactured using integrated photonics techniques, i.e. their various optical components (waveguides, power splitters, optical antennas, etc.) are manufactured on and from the same photonic chip. In this respect, FIG. 1B shows, in a schematic and partial manner, an example of such a photoelectron emitter 1, described in the article by Hulme et al. entitled “Fully integrated hybrid silicon two dimensional beam scanner”, Opt. Express 23 (5), 5861-5874 (2015). This photoelectron emitter 1 comprises a laser source 2, which, in the case of the III-V type, is manufactured on the same photonic chip. It therefore comprises, in addition to the semiconductor laser source 2, a power splitter 3, a waveguide called the input waveguide 5 (forming arm 4), a phase shifter 6 and an optical antenna 7 arranged in arm 4. In this example, the laser source 2 is made by transferring III-V material to the photonic chip (of the SOI type) and structuring the material to form the gain medium.

[0005] Inoue et al., entitled “Demonstration of a new optical scanner using silicon photonics integrated circuit”, Opt. Express 27(3), 2499-2508 (2019), describes an example of a photoelectron emitter with a two-dimensional periodic array of optical antennas, each having a large radiating surface area in free space. More specifically, each optical antenna is formed of an input waveguide, a vertical radiating waveguide structure formed of a waveguide wider than the input waveguide and a vertical grating, and a connecting structure formed of a flared waveguide (taper) and optically coupling the input waveguide and the vertical radiating waveguide structure. Such an optical antenna configuration is described in particular in Mekis et al., “A Grating-Coupler-Enabled CMOS Photonics Platform”, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 3, pp. 597-608, May-June 2011. Summary of the Invention [Problem to be solved by the invention]

[0006] However, there is a need to provide a photoelectron emitter having an optical antenna with a larger radiating surface area to reduce the far-field divergence of the emitted optical radiation.

[0007] The object of the present invention is to at least partially solve the problems of the prior art, and more particularly to propose a photoelectron emitter with a phased array antenna, which comprises an optical antenna having a large radiating surface area for optical radiation in free space, thereby reducing the divergence in the far field of the emitted optical radiation. [Means for solving the problem]

[0008] To this end, the subject of the invention is a photoelectron emitter with a phased array antenna, comprising a splitter configured to be connected to a laser light source, a plurality of waveguides, called input waveguides, connected to the splitter and extending along a longitudinal axis in a main plane and forming arms of the photoelectron emitter, and a plurality of phase shifters and optical antennas arranged in the arms.

[0009] Each optical antenna comprises an incident waveguide and a waveguide structure, called a vertical radiating waveguide structure, configured to receive the optical mode emitted by the incident waveguide, and is formed by a waveguide, called a radiating waveguide, that is wider than the incident waveguide, and a vertical diffraction grating connected to the radiating waveguide, the vertical diffraction grating configured to extract the optical mode flowing through the radiating waveguide into free space.

[0010] According to the invention, each optical antenna comprises a waveguiding structure formed by an incident waveguide, referred to as a horizontal radiating waveguide structure, and a transverse diffraction grating, the transverse diffraction grating being connected to the incident waveguide and configured to extract, in a principal plane, the optical modes flowing through the incident waveguide towards the radiating waveguide.

[0011] Some preferred, non-limiting aspects of this photoelectron emitter are as follows:

[0012] The photoelectron emitter may comprise a connecting structure formed by a graded index medium, which is disposed between the horizontal emitting waveguide structure and the vertical emitting waveguide structure and configured to optically couple the lateral diffraction grating and the emitting waveguide.

[0013] The connection structure may comprise an array of a plurality of elementary connections arranged laterally opposite the lateral diffraction grating, and may have a lateral dimension shorter than a dominant wavelength of the optical mode emitted by the laser light source, or may be formed by a medium having an aperture having a first refractive index, the aperture being filled with a medium having a lateral dimension shorter than a dominant wavelength of the optical mode emitted by the laser light source and a second refractive index smaller than the first refractive index.

[0014] Length of the connecting structure l sc is its overall width W tot,sc It can be the following:

[0015] The radiating waveguide and the vertical grating are each connected to a total width w tot,sc At least as wide as w ge and w tot,rv may have the following structure:

[0016] The optical antennas are arranged at a pitch Λ along an axis perpendicular to the longitudinal axis of the input waveguide. a,y The vertical gratings can be arranged periodically with a pitch Λ a,y The extraction length l is 50% or 80% or more of tot,rv The axial length of the axial portion of the axial tube is called the axial length.

[0017] The optical antennas are arranged with a pitch Λ along the longitudinal axis of the input waveguide. a,x The vertical gratings can be arranged periodically with a pitch Λ a,x Width w that is 50% or 80% or more of tot,rv has.

[0018] The transverse grating lies in a major plane and has a radiation angle φ with respect to an axis perpendicular to the longitudinal axis of the input waveguide. rl , and the vertical radiating waveguide structure can be configured to extract the optical mode at a radiation angle φ rl and disposed along a longitudinal axis parallel to the connecting structure.

[0019] Extraction length l tot,rlThe length of the transverse grating, referred to as the grating length, can be greater than the width of the input waveguide. ge is at least the extraction length l of the transverse grating tot,rl If necessary, the width of the connection structure w sc must be at least the extraction length l tot,rl can be made equal to

[0020] The width of the input waveguide may be 1 μm or less, and the widths of the output waveguide and vertical grating may each be 10 μm or more.

[0021] Total extraction length l tot,rv The total length of the vertical grating, referred to as the grating length, can be 10 μm or more.

[0022] The transverse grating may be formed by periodic recesses in the input waveguide, or it may be formed by periodic pads spaced a distance from the input waveguide.

[0023] The input waveguide may have a longitudinal variation of at least one parameter representing its width according to a predetermined function p, and the transverse grating may have a pitch Λ of the array of periodic structures according to a predetermined function q. rl and the functions p and q correspond to a predetermined far-field target radiation profile S of the optical radiation extracted by the transverse grating. rl,c (x) and a given target radiation angle φ rl,c It is determined in advance according to.

[0024] The vertical grating may have a longitudinal variation of at least one dimensional parameter of the periodic structure according to a predetermined function, which defines a predetermined far-field target radiation profile Srv of the optical radiation extracted by the vertical grating. ,c (x) and a given target radiation angle φ rv,c It is determined in advance according to.

[0025] The photoelectron emitter may comprise an SOI type photonic chip, which includes a lateral emitting waveguide structure, a connecting structure, and, optionally, a vertical emitting waveguide structure. [Brief description of the drawings]

[0026] Other aspects, objects, advantages and features of the present invention will become more clearly apparent from a reading of the following detailed description of preferred embodiments of the invention, which is given by way of non-limiting example and which makes reference to the accompanying drawings, in which: [Figure 1A] FIG. 1A is a schematic and partial view of a photoelectron emitter with a phased array antenna according to one example of the prior art already described. [Figure 1B] FIG. 1B is a schematic and partial top view of a photoelectron emitter fabricated using integrated photonics techniques according to one example of the prior art already described. [Diagram 2] FIG. 2 is a schematic and partial top view of an optoelectronic emitter according to one embodiment, in which optical antennas are arranged in a two-dimensional periodic array, each with a large radiating surface area in free space. [Figure 3A] FIG. 3A is a schematic and partial diagram of a top view of an optical antenna of a photoelectron emitter according to an embodiment. [Figure 3B] FIG. 3B is a schematic and partial illustration in cross section of an optical antenna of a photoelectron emitter according to an embodiment. [Figure 3C] FIG. 3C is a schematic and partial top view of an optical antenna of an optoelectronic emitter according to another embodiment, in which the connecting structure and the vertical radiating waveguide structure are aligned along a longitudinal axis AL defined by the non-zero radiation angle φrl of the lateral diffraction grating. [Figure 4A] FIG. 4A is a schematic and partial cross-sectional view of an optical antenna of an optoelectronic emitter according to another embodiment, in which the lateral radiating waveguide structure, the connecting structure and the vertical radiating waveguide structure are fabricated from thin layers and share the same continuous sublayer (slab). [Figure 4B]FIG. 4B is a schematic and partial top view of various examples of input waveguides of a lateral radiating waveguide structure of an optical antenna. [Figure 4C] FIG. 4C is a schematic and partial top view of various examples of input waveguides of a lateral radiating waveguide structure of an optical antenna. [Figure 4D] FIG. 4D is a schematic and partial top view of various examples of input waveguides of a lateral radiating waveguide structure of an optical antenna. [Figure 5A] FIG. 5A is a schematic and partial top view of an optical antenna illustrating various examples of connection structures between lateral and vertical radiating waveguide structures. [Figure 5B] FIG. 5B is a schematic and partial top view of an optical antenna illustrating various examples of connection structures between the lateral radiating waveguide structure and the vertical radiating waveguide structure. [Figure 5C] FIG. 5C is a schematic and partial top view of an optical antenna illustrating various examples of connection structures between the lateral radiating waveguide structure and the vertical radiating waveguide structure. [Figure 6A] FIG. 6A is a flow chart illustrating method steps for dimensioning and fabricating an optical antenna of an optoelectronic emitter according to one embodiment, in which the lateral radiating waveguide structure is apodized. [Figure 6B] FIG. 6B is a schematic partial cross-sectional view of an optical antenna of a photoelectron emitter according to another embodiment, in which the vertical grating of the vertical radiating waveguide structure is apodized. [Figure 7A] FIG. 7A shows an example of a function p of the change in depth prl of a plurality of recesses in the longitudinal direction, prl=p(x). [Figure 7B] FIG. 7B shows an example of the gradual change in the radiation angle φrl. [Figure 7C] FIG. 7C shows an example of the gradual change between pitch Λrl and depth prl, Λrl=h(prl). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In the remainder of the drawings and description, the same reference numbers represent the same or similar elements. Moreover, for clarity of the figures, the various elements are not scaled. Moreover, the various embodiments and alternative embodiments are not mutually exclusive and may be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", and "on the order of" mean about 10%, preferably about 5%. Furthermore, the term "in the range of ... to ..." and equivalent terms mean that the upper and lower limits are included, unless otherwise indicated.

[0028] The present invention relates to a photoelectron emitter with a phased array antenna having an array of optical antennas, preferably fabricated on a photonic chip of the photonic-on-silicon type, configured to emit light with a predetermined far-field radiation profile, e.g. a constant profile or a Gaussian profile, oriented at a predetermined emission angle and with minimal divergence, at least in a vertical plane parallel to the optical antennas.

[0029] The far-field radiation profile is the angular distribution of the intensity of the far-field optical radiation emitted by a photoelectron emitter, centered on a principal axis oriented at the radiation angle. The far-field (Fraunhofer zone) extends beyond a distance D (e.g., the length L of a horizontal radiating waveguide structure) that is greater than the ratio of the square of the larger dimension of the optical antenna to the wavelength λ of the optical radiation. tot,rl , FIG. 3A), and more specifically, D>2L tot,rl 2 / λ.

[0030] 2 is a schematic and partial top view of a photoelectron emitter 1 according to one embodiment. The photoelectron emitter typically comprises a laser source 2, a power splitter 3, and multiple arms 4 with phase shifters 6 and optical antennas 7.

[0031] According to the invention, each optical antenna 7 comprises: A horizontal radiating waveguide structure 10 (i.e. in the XY plane) with a waveguide called the input waveguide 11 (reference number "5" in FIG. 1B) and a radiation angle φ rv a horizontal radiating waveguide structure 10 formed by a lateral grating 12 configured to extract an optical mode in the XY plane at A waveguide connected to the vertical radiating waveguide structure 10, called the radiating waveguide 31, and having a radiation angle θ with respect to the Z axis rv and a vertical radiating waveguide structure 30 formed by a vertical diffraction grating 32 configured to extract an optical mode at a radiating direction substantially parallel to the Z-axis (i.e., a direction substantially parallel to the Z-axis).

[0032] In the remainder of this specification and description, a direct XYZ Cartesian coordinate system is defined, with the XY plane parallel to the plane of the photonic chip, the X axis oriented along the longitudinal axis of the horizontal radiating waveguide structure 10 of the optical antenna 7, and the Z axis oriented towards free space where light is emitted by the photoelectron emitter 1. The terms "lower" and "upper" refer to the distance in the +Z direction from the supporting substrate.

[0033] In this embodiment, the photoelectron emitter 1 is integrated on a photonic chip, for example in the context of the "photonic on silicon" technology. The photonic chip, also called photonic integrated circuit (PIC), comprises a support substrate from which active (modulators, diodes, etc.) and passive (waveguides, multiplexers or demultiplexers, etc.) photonic components can be produced, which are optically coupled to each other. In the context of the photonic on silicon technology, the support substrate and the photonic components are made of silicon. The photonic chip can therefore be of the SOI (silicon on insulator) type. In this example, these structures 10, 20, 30 are therefore made of silicon. However, many other technological platforms can be used, depending on the intended application and the wavelength of the optical radiation. Thus, for example, waveguides can be manufactured from silicon nitride (SiN), aluminium nitride (AlN), doped silica, etc.

[0034] The photoelectron emitter 1 comprises a laser source 2 configured to emit a monochromatic light pulse signal or a continuous monochromatic light signal of wavelength λ. By way of example, the wavelength may be 1,550 nm. The laser source 2 is in particular aligned in the YZ plane or perpendicular to the Z axis and the longitudinal axis A. L Parallel to A L In the Z plane, the radiation angle θ formed by the optical radiation emitted by the optical antenna 7 with respect to the vertical Z axis rv The wavelength can be adjusted to change the angle φ (see FIG. 3C). rl . The laser source 2 can be a hybrid source formed by a gain medium made of III / V compounds and can be glued to the surface of the photonic chip. An optical reflector of the Bragg mirror type can then be provided in the integrated waveguide and connected to the gain medium. As an alternative embodiment, the photonic chip can not comprise a laser source 2, in which case the laser source is not assembled to the surface of the photonic chip, since it is located remotely. It can then be connected to the integrated waveguide of the photonic chip, in particular by means of a grating connection.

[0035] The power splitter 3 is connected to the output of the laser source 2. It therefore comprises an input and several outputs, each connected to a waveguide of the photoelectron emitter 1. The number of waveguides, called input waveguides 11, corresponds to the number of arms 4 of the photoelectron emitter 1. In this example, the power splitter 3 is formed by several MMI (Multimode Interferometer) type splitters arranged in a cascade, but other types of optical components may also be used (e.g. directional junctions, Y-junctions, star junctions, etc.).

[0036] The photoelectron emitter 1 comprises a number of input waveguides 11, which extend between a first end connected to one of the multiple outputs of the power splitter 3 and an opposite second end, forming a number of arms 4 of the photoelectron emitter 1. Each input waveguide 11 is thus configured to receive an optical signal emitted by the power splitter 3 and to propagate this optical signal to the optical antenna 7.

[0037] The photoelectron emitter 1 also comprises a number of phase shifters 6 arranged in the arms 4. More specifically, the input waveguides 11 are connected to at least one phase shifter 6 configured to modify the phase of the optical signal flowing in the input waveguide 11 of interest, thus generating a phase difference Δγ, i.e. the relative phase, of the optical modes flowing in adjacent input waveguides 11. The phase shifters 6 are arranged between the power splitter 3 and the optical antenna 7. Each input waveguide 11 can comprise a phase shifter, or only a part of the input waveguides 11, for example only one of the two input waveguides 11, can comprise a phase shifter. Furthermore, the reference input waveguide 11 may not comprise a phase shifter.

[0038] The phase shifter 6 can be an electrorefractive or thermo-optical phase shifter. In either case, the phase is proportional to the refractive index n gi This change in refractive index is obtained by changing the free carrier density in the case of electrorefractive phase shifters and by changing the applied temperature in the case of thermo-optical phase shifters.

[0039] The phase shifter 6 is configured to apply a predetermined phase value Δγ to the optical mode propagating in the input waveguide 11, thereby shifting the phase value Δγ in the YZ plane or the A LIn the Z-plane, a determined non-zero angle of the main emission axis with respect to the vertical Z-axis is obtained. However, the relative phase Δγ may not be the same for the multiple input waveguides 11 in order to obtain different far-field emission profiles or to take into account and compensate for possible phase errors. These phase errors may arise due to degradation of some components of the photoelectron emitter 1 over time, non-uniformities in the manufacturing method, non-zero tolerances of the manufacturing method, environmental influences on the photoelectron emitter 1 (for example possible influences of packaging components covering the basic emitter).

[0040] The phase shifter 6 is preferably connected to a control module (not shown). The phase shifter 6 is capable of generating a predetermined relative phase Δγ in the optical signals passing through the various input waveguides 11 in response to a control signal sent by the control module. An example of such a control module is described in the article by Hulme et al. entitled “Fully Integrated hybrid silicon two dimensional beam scanner”, Opt. Express 23 (5), 5861-5874 (2015), or in WO 2021 / 130149.

[0041] The photoelectron emitter 1 comprises several optical antennas 7 arranged downstream of the phase shifter 6, in this case one optical antenna 7 per arm 4. The relative phase Δγ between the optical signals emitted by the optical antennas 7 is in particular determined in the YZ or A plane of the photoelectron emitter 1. L Determine the value of the angle formed by the principal radiation axis of the far field ray with respect to the normal Z axis in the Z plane.

[0042] The optical antennas 7 are identical to each other. They are arranged laterally along the X-axis and the Y-axis (see FIG. 2). They are preferably arranged apart from each other at a distance ranging from λ / 2 to 2λ, where λ is the dominant wavelength of the optical mode emitted by the laser source 2. For reference, the number of optical antennas 7 can be in the range of about 10 to about 10,000, which can limit the divergence of the far-field optical radiation along the X-axis and the Y-axis.

[0043] In this case, the optical antennas 7 are arranged periodically along at least one principal axis, in this case the X-axis and the Y-axis, with a pitch Λ a,x and pitch Λ a,y are preferably of the same order of magnitude to make the far-field radiation profile of the emitted optical radiation symmetric about the radiation axis. As will be described later, the radiating surface area of ​​each optical antenna is spaced apart from each other by a pitch Λ to reduce the intensity of the secondary lobes of the far-field radiation profile of the photoelectron emitter 1. a,y and Λ a,x At least 50%, preferably 70%, and more preferably 80% of each dimension l rv , w tot、rv It is preferred that the compound has the formula:

[0044] 3A and 3B are schematic and partial illustrations of an optical antenna 7 of a photoelectron emitter according to one embodiment, in top view (FIG. 3A) and cross-sectional view (FIG. 3B).

[0045] For this purpose, each optical antenna 7 thus comprises a horizontal radiating waveguide structure 10 configured to extract the optical mode flowing in the input waveguide 11 and radiate it in the XY plane towards a vertical radiating waveguide structure 30 which receives the optical radiation radiated by the horizontal radiating waveguide structure 10 and radiates it in the YZ plane or the A plane. L It is configured to radiate into free space in the Z plane. Each waveguiding structure 10, 30 comprises a waveguide and a diffraction grating.

[0046] In this example, each optical antenna 7 further comprises a graded index connecting structure 20 that optimizes the optical coupling between the two waveguiding structures 10, 30. This connecting structure is optional but advantageous for improving the performance of the photoelectron emitter 1.

[0047] 3C is a schematic and partial top view of an optical antenna 7 according to another embodiment. In this example, the connecting structure 20 and the vertical radiating waveguide structure 30 are aligned in such a way that the radiating angle φ of the lateral radiating waveguide structure 10 is smaller than the radiating angle φ of the lateral radiating waveguide structure 10.rl Thus, the connecting structure 20 and the vertical radiating waveguide structure 30 are oriented in the XY plane according to φ rl The longitudinal axis A forms the same angle as L In this case, the radiation angle θ of the waveguiding structure 30 rv is defined relative to the vertical Z axis, which is also perpendicular to the longitudinal axis A L and A passing through the vertical Z axis L It should be noted that the far-field radiation profile S of the vertical radiating waveguide structure 30 is included in the Z plane. However, for clarity, rv (y) and radiation angle θ rv (y) depends on the abscissa y and, more precisely, on the longitudinal axis A L It should be noted that the abscissa is determined along the

[0048] In this case, the angle φ rl The value of is the pitch Λ of the transverse diffraction grating 11. rl The radiation angle θ of each optical antenna 7 is set by rv The value of is the pitch Λ of the vertical diffraction grating 31 (rather than the phase shift Δγ between the optical antennas 7). rv It should be noted that the radiation angle of the photoelectron emitter 1 is set by these two parameters. These two parameters control the radiation direction of the envelope formed by the radiation emitted by the optical antenna 7. The phase shift Δγ between the optical antennas 7 for its part can redirect the light beam emitted by the photoelectron emitter 1 (caused by the interference of the light beams emitted by the optical antennas 7), which is necessarily located within the envelope of the optical antenna 7. In this example, the radiation angle of the photoelectron emitter 1 is actually smaller than the radiation angle θ of the optical antenna 7 (due to the large radiation surface area of ​​the optical antenna 7) as long as the antenna envelope is very narrow (due to the large radiation surface area of ​​the optical antenna 7). rv Close to.

[0049] In this case, the optical antenna 7 is formed in a photonic chip, in this case using photonic-on-silicon technology. The chip is formed by a support substrate, in this case made of silicon (not shown), a lower layer 40 of buried oxide (BOX) which helps to form the metallization (cladding) of the waveguide, a number of diffraction gratings provided in the silicon layer, and an upper layer 42 made of silicon oxide which helps to form the metallization. In the example of Figure 3B, the lateral radiating waveguide structure 10 and the connection structure 20 are physically separate and therefore separated in the XY plane by silicon oxide which in this case helps to define the metallization of the waveguide.

[0050] 4A is a schematic and partial cross-sectional view of an optical antenna 7 according to another embodiment, in which the wave-guiding structures 10, 30 and the connecting structure 20 are configured to define these structures with a continuous lower sub-layer 41, called base or slab, common to the three structures 10, 20, 30, covered by an upper sub-layer, called rib. The base 41 can thus improve the optical coupling, in particular between the laterally radiating wave-guiding structures 10 and the connecting structure 20.

[0051] The lateral radiating waveguide structure 10 is therefore configured to receive the optical mode emitted by the laser source 2 and extract it in the XY plane towards the connection structure 20. For this purpose, the lateral radiating waveguide structure 10 comprises an input waveguide 11 and a lateral diffraction grating 12. It is essentially one-dimensional, i.e. linear, in the XY plane, in the sense that its width is very small compared to its extraction length, for example at least 10 times smaller or at least 100 times smaller.

[0052] As an example, the width (width w of the input waveguide 11) gi ) is the extraction length l tot,rl (length of the lateral diffraction grating 12), for example, it can be 1 μm or less, for example, about 0.5 μm, and this extraction length is at least equal to 10 μm, for example, about 60 μm or more (100 μm or more). Furthermore, the extraction length is the length l of the lateral diffraction grating tot,rlIn this case, the width w of the entrance face of the radiating waveguide 31 of the vertical radiating waveguide structure 30 is defined as ge It is about the following size.

[0053] The input waveguide 11 is intended to transmit the optical mode from the power splitter 3. It is determined by physical parameters, such as the refractive index of the waveguide (i.e. of the core of the waveguide), n gi , the refractive index of the metal coating n gg , thickness along the Z axis e gi The horizontal dimension of the gi The thickness e is determined by the lateral dimensions of the gi is preferably constant along the longitudinal axis X, and the width w gi can be kept constant. In an alternative embodiment, the width w gi can vary along the longitudinal axis X, for example between an upstream maximum and a downstream minimum, so that, in particular, the far-field radiation profile S of the extracted optical radiation rl (x) is a given target profile S rl,c (x).

[0054] The transverse grating 12 is configured to extract an optical mode that flows through the input waveguide 11 towards the connecting structure 20 in the XY plane. The optical mode has a far-field radiation profile S rl According to (x), the radiation angle φ rl (x) is extracted in the XY plane. The radiation profile S rl (x) is the target profile S rl,c (x) and the radiation angle φ rl (x) is constant and the target value φ rl,c This target value is predefined with respect to the Y axis, which is orthogonal to the longitudinal axis X. The transverse grating 12 preferably extends a length sufficient to extract nearly all or all of the optical mode. This extraction length is determined by the dimension l of the transverse grating 12. tot,rl which is the total width w tot,sc Smaller is preferable.

[0055] The transverse grating 12 can be provided in the input waveguide 11, for example as a number of recesses, or it can be provided remotely from the input waveguide, for example in the form of a number of pads of high refractive index surrounded by a metal cladding of low refractive index. It therefore comprises a periodic structure 13 (a number of recesses or pads) arranged along the input waveguide 11 along the longitudinal axis X.

[0056] It depends on the physical parameters describing the diffraction (and therefore extraction) of the optical mode passing through the input waveguide 11. It is especially the arrangement pitch Λ rl and the length along the X-axis, l rl and the depth or width along the Y axis p rl The dimensions of the and the filling factor ff of the refractive index of the material used rl =l rl / Λ rl and, optionally, their spacing d with respect to the input waveguide 11 rl (See Figure 4C).

[0057] If the lateral radiating waveguide structure 10 does not comprise a base 41, the periodic structures 13 can be provided as recesses in the entire thickness of the input waveguide 11. Moreover, if the lateral radiating waveguide structure 10 comprises a base 41, they can be provided only in the thickness of the ribs. Moreover, they can be located on one and / or the other side of the input waveguide 11 along the Y axis. In this case, they are not located opposite the input waveguide 11 along the perpendicular Z axis. In this regard, Figures 3A and 3C show an example of a lateral diffraction grating 12, in which the periodic structures 13 are recesses in the form of slots (rectangular recesses) formed in the input waveguide 11, in this case located on the opposite side of the connecting structure 20.

[0058] FIG. 4B is a schematic and partial top view of another example of a transverse diffraction grating 12, in which the periodic structures 13 are formed by recesses in the form of rectangular slots formed in the input waveguide 11, located on either side of the input waveguide 11, in this case arranged asymmetrically along the X-axis.

[0059] FIG. 4C is a schematic and partial top view of another example of a transverse diffraction grating 12, in which the periodic structure 13 is spaced a distance d from the input waveguide 11. rl The pads are made of a material with a high refractive index, for example silicon or silicon nitride in this case, and are surrounded by a material with a low refractive index, in this case silicon oxide. They are arranged opposite each other on both sides of the input waveguide 11. As an alternative, the pads can be arranged only opposite one or the other side of the input waveguide 11. In this case, they are arranged asymmetrically along the longitudinal axis X. In this case, they are arranged at a non-zero distance d from the input waveguide. rl and are therefore spaced from the input waveguide by the silicon oxide. rl and therefore may be connected to the input waveguide 11. rl is defined as the distance between the face of the periodic pad and the waveguide. In these examples, the transverse grating 12 only affects the evanescent part of the optical mode, which allows the extraction ratio to be small, so the extraction length ltot,rl It should be noted that the

[0060] FIG. 4D is a schematic and partial top view of another example of a transverse diffraction grating 12, in which the periodic structures 13 are recesses formed in the input waveguide 11 and are triangular. They are located opposite the connection structure 20. Also in this case they are defined by an angle β with respect to the longitudinal axis X, formed by the hypotenuse of a triangle (in this case a right-angled triangle). Of course, the shape of the triangle in this case is shown diagrammatically and in reality may differ slightly (especially in the corners) due to technical manufacturing constraints. In this case, the diffraction grating is a blazed grating (echelette grating), the angle β being the blaze angle. This angle is chosen so that the diffraction grating operates in reflection (total internal reflection regime) and may be, for example, 30°.

[0061] In this case, the grating generally has an extraction ratio α for the optical mode flowing through the waveguide, which can be referred to as the radiative or scattered intensity. As shown in the paper by Zhao et al., entitled “Design principles of apodized grating couplers”, Journal of Lightware Technology, Vol. 38, No. 16, pp. 4435-4446, 2020, the extracted local optical power defines the radiative profile S(x) and depends on the local optical power of the optical mode P(x) (or the local optical power of the evanescent part, if applicable) and the local optical power of the extracted intensity α(x) according to the relationship S(x) ≈ α(x) × P(x).

[0062] As will be explained below, the input waveguide 11 and the transverse grating 12 preferably have dimensional parameters that vary longitudinally according to a predetermined function, resulting in a far-field radiation profile S rl (x) is a given target profile S rl,c (x) and has a constant target value φ along the longitudinal axis X. rl,c The same radiation angle φ rl These dimensional parameters correspond to the depth p of the transverse grating 12. rl and / or width w gi , and pitch Λ rl It is possible.

[0063] The optical antenna 7 also comprises a connecting structure 20 configured to optically couple the lateral radiating waveguide structure 10 and the vertical radiating waveguide structure 30. It is therefore disposed between the two waveguide structures 10, 30. The extraction length l of the lateral grating tot,rl is the width w ge As long as the size of the connection structure 20 is about the same as that of the metal coating, the connection structure 20 does not need to adjust the spatial distribution of the optical mode in the XY plane, but basically needs to adjust the average refractive index (and therefore the effective refractive index of the optical mode) between a minimum value close to the refractive index of the metal coating and a maximum value equal to the refractive index of the radiation waveguide 31.

[0064] In this case, in general, the effective refractive index n associated with the optical mode supported by the waveguide eff It should be noted that is defined as the product of the propagation constant β and λ / 2π. The propagation constant β depends on the wavelength λ of the optical mode, as well as on the properties of the waveguide, in this case the connecting structure (refractive index and lateral dimensions of the core and metal cladding). The effective refractive index of the optical mode, n eff corresponds to some extent to the refractive index of the waveguide as "seen" by the optical mode, which is usually between the refractive index of the waveguide and the refractive index of the metal cladding.

[0065] The connecting structure 20 is therefore a gradient index optical structure, which can adjust the effective refractive index of the optical mode so that the optical mode is transmitted between the input waveguide 11 and the output waveguide 31. It has a pattern smaller than the wavelength of the optical mode to be transmitted, and is therefore a sub-wavelength grating graded index structure (SWG GRIN). It is formed, for example, by at least two materials with different refractive indices, with the average refractive index being oriented along the longitudinal axis A. L , from its upstream face (facing the transverse grating 12) to its downstream face (facing the radiation waveguide 31). The average refractive index varies monotonically along its width, i.e., along a longitudinal axis A L It can vary along an axis perpendicular to the axis of interest, i.e., the overall width w tot,sc As a first-order average of the refractive index of the material of the connecting structure in the longitudinal axis A L can be defined on any horizontal axis.

[0066] The connecting structure 20 is aligned along the axis A L Overall width along an axis perpendicular to tot,sc In this case, axis A L along the length l tot,sc and in this example, length l tot,sc The overall width w tot,scThe lateral diffraction grating 12 can be effectively connected to the radiation waveguide 31 with a limited connection length smaller than 1000 nm. This eliminates the need to use a taper to connect the input waveguide 11 and the radiation waveguide 31 as in the above-mentioned prior art example, and thus the connection length between the waveguide structure 10 and the waveguide structure 30 can be significantly shortened, thereby increasing the free space radiation surface area of ​​the optical antenna 7.

[0067] 5A is a schematic and partial view of an optical antenna 7 with a connection structure 20 according to a first example. In this case, the connection structure 20 is formed by an array of elementary connections 21, such as tapered trapezoids or tips with subwavelength dimensions. These are made integrally with a radiating waveguide 31. The elementary connections 21 are arranged with a pitch Λ of about 250 nm in this case. sc , the width of the upstream side is about 50 nm, the width of the downstream side is about 200 nm, and the length l sc In this case, they are located at a distance d of about 500 nm from the input waveguide 11. sc It is just a few meters away.

[0068] 5B is a schematic and partial view of an optical antenna 7 with a connecting structure 20 according to another example. In this case, the connecting structure 20 differs fundamentally from the connecting structure of FIG. 5A in that the basic connection 21 is directly connected to the input waveguide 11 by a narrow waveguide 22 with a width of about 50 nm. Moreover, the connecting structure 20 is located at zero distance d from the input waveguide 11. sc Located in.

[0069] 5C is a schematic and partial view of an optical antenna 7 with a connecting structure 20 according to another example. In this case, the connecting structure 20 is formed by a portion of a layer of a high refractive index material, in this case silicon, directly connecting the input waveguide 11 to the output waveguide 31 and has a two-dimensional array of subwavelength dimension apertures 23 filled with a medium of low refractive index (silicon oxide), which are formed in a continuous medium 24 of high refractive index (silicon).

[0070] The vertical radiating waveguide structure 30 comprises a waveguide, referred to as the radiating waveguide 31, which is wider than the incident waveguide 11, and a vertical diffraction grating 32. The radiating waveguide 31 is configured to receive the optical mode transmitted by the connecting structure 20 and extracted from the incident waveguide 11 by the transverse diffraction grating 12. The vertical diffraction grating 32 extracts the optical mode flowing in the radiating waveguide 31 and propagates it in a radiation direction θ rv The antenna is configured to radiate into free space at

[0071] It is preferable that the width of the radiating waveguide 31 is essentially two-dimensional in the XY plane, in the sense that the width is approximately the same as the extraction length, and is 10 μm or more, for example, about 60 μm. ge is the width w of the input waveguide 11 gi In this case, the emitting surface area is much larger than the total width w tot,rv and total length l tot,rv In this example, it is about 60 μm×60 μm.

[0072] The emission waveguide 31 receives the light emitted from the input waveguide 11, extracted by the transverse grating 12 and transmitted by the connecting structure 20. It is determined by a physical parameter, e.g. the refractive index of the waveguide (i.e. of the core of the waveguide) n ge , the refractive index of the metal coating n gg , thickness along the Z axis e ge Transverse dimension and axis A L Width along the axis perpendicular to ge It is determined by the lateral dimensions, etc.

[0073] Thus, the radiating waveguide 31 has a width w ge is different from the input waveguide 11 and has a width w ge is the width w gi , for example, 100 times larger. Furthermore, its longitudinal axis A L is not coplanar with the longitudinal axis X of the input waveguide 11 but is adjacent to the radiation angle φ rl is nearly perpendicular to

[0074] The vertical grating 32 is configured to extract, in free space, the optical mode that flows through the radiation waveguide 31. The optical mode has a far-field radiation profile S rv According to (y), A L Radiation angle θ in the Z plane rv (y) is extracted. The radiation profile S rv (y) is the target profile S rv,c (y) and the radiation angle θ rv Preferably, (y) is constant. Furthermore, the vertical grating 32 preferably extends a length sufficient to extract most or all of the optical mode. This extraction length is determined by the dimension l of the vertical grating 32. tot,rv It is.

[0075] The vertical diffraction grating 32 is disposed above the radiating waveguide 31 and is disposed at a distance d rv (zero or non-zero). Also, the thickness e ge is defined as the maximum value along the Z axis. ge can be constant or along the longitudinal axis A L , whereby the radiation profile S of the extracted optical radiation may vary along yz (y) has a predetermined target profile.

[0076] For this purpose, the vertical diffraction grating 32 comprises a periodic structure 33 arranged along the radiation waveguide 31. It is therefore determined by physical parameters describing the diffraction (and therefore the extraction) of the optical mode flowing through the radiation waveguide 32. It is in particular the arrangement pitch Λ rv , longitudinal axis A L Length along l rv Dimensions, height or depth p rv , the filling factor ff rv =l rv / Λ rv , and the refractive indices of the materials used and, optionally, their spacing d relative to the radiation waveguide 31. rvTo obtain a desired target radiation profile, at least one dimensional parameter has a predetermined longitudinal variation, e.g., a filling factor ff rv with pitch Λ rv Also, (filling factor ff rv (to compensate for the change in effective refractive index associated with the change in radiation angle θ rv In order to keep the thickness constant, the thickness of the slit may have a predetermined longitudinal variation.

[0077] 3B is a schematic and partial cross-sectional view of an example of a vertical diffraction grating 32, in which the periodic structure 33 is a recess in the form of a rectangular slot formed in the radiation waveguide 31 from its top side. Of course, the recess may have shapes other than rectangular.

[0078] 4A is a schematic and partial cross-sectional view of another example of a vertical diffraction grating 32, where the periodic structure 33 is a number of pads of high refractive index (e.g. silicon or silicon nitride) surrounded by a metallization made of silicon oxide. The pads are located at a distance d from the radiating waveguide 31. rv , this distance can be non-zero as in this case, or it can be zero (so the pad is connected to the radiating waveguide 31). It should be noted that in this example the vertical grating 32 only affects the evanescent part of the optical mode, which allows for small values ​​of the extraction ratio and therefore a long extraction length.

[0079] Thus, the optical signal flowing in the input waveguide 11 is extracted by the transverse grating 12, transmitted by the connecting structure 20 to the output waveguide 31, and then extracted by the vertical grating 32 and emitted into free space. In this way, the emitted optical radiation propagates in free space and recombines by interference, thereby forming in the far field the optical radiation emitted by the photoelectron emitter 1, the angular distribution of which around the main emission axis defines the far-field radiation profile of the photoelectron emitter 1.

[0080] Therefore, the photoelectron emitter 1 is at least YZ or A LFar-field radiation can be emitted with minimal divergence in the Z-plane, and in this case also in the XZ-plane, due to the large radiating surface area of ​​each optical antenna 7 and the fact that the optical coupling between the input waveguide 11 and the vertical radiating waveguide structure 30 is performed laterally by the lateral diffraction grating 12 and the graded index connecting structure 20, rather than horizontally by a taper as in the prior art example described above.

[0081] The unchanged pitch value Λ of the optical antenna 7 a,x and Λ a,y With respect to the radiation angle θ, the fact that the radiation surface area can be increased can in particular reduce the radiation intensity of the secondary lobe of the far-field radiation profile of the optical radiation emitted by the photoelectron emitter 1. rv When is small, i.e., on the order of a few degrees, for example, 15° or less, the width w of the vertical diffraction grating 32 tot,rv (which corresponds to the width of the radiating surface area) is the pitch Λ a,x , the total length l of the vertical grating 32 can be reduced or even eliminated, if the total length l of the vertical grating 32 is at least 50%, preferably at least 80%, of the total length l of the vertical grating 32. tot,rv (which corresponds to the length of the radiating surface area) is the pitch Λ a,y , it is possible to reduce or even eliminate the secondary lobes of the far-field radiation profile of the radiated optical radiation in the YZ plane, provided that the number of optical antennas 7 is at least 50%, preferably at least 80% of the total number of optical antennas 7. Finally, it should be noted that in this case, by increasing the number of optical antennas 7, the directivity of the radiated optical radiation can be increased, in other words the width of the mid-height of the far-field radiation profile can be reduced.

[0082] Furthermore, the far-field radiation profile of each optical antenna 7 can be made the same as a predetermined target profile, and the radiation angle θ can be made the same as the predetermined target value. rvThis is obtained by the fact that the lateral radiating waveguide structure 10 and / or the vertical radiating waveguide structure 30 can be apodized, in other words, can have dimensional parameters that vary in the longitudinal direction according to a predetermined function. Thus, unlike the apodization that can be performed in the prior art, where the creator only changes the dimensions of the periodic structure, the width w of the input waveguide 11 can be apodized, as shown, for example, in the article by Mekis et al., entitled “A Grating-Coupler-Enabled CMOS Photonics Platform”, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 17, No. 3, pp. 597-608, May-June 2011, the width w gi Using the above, the extraction rate α rl Finally, the width w of the input waveguide 11 can be easily adjusted. gi and at least the pitch Λ of the transverse grating 12 rl Varying the length of the periodic structure limits the constraints on determining the dimensions of the periodic structure, which may be so small that they are largely or even incompatible with conventional techniques commonly used in fabrication methods, such as photonic-on-silicon techniques.

[0083] 6A is a flow chart of a method for determining dimensions of a lateral radiating waveguide structure 10 and fabricating a corresponding optical antenna 7 of a photoelectron emitter 1, according to one embodiment. The input waveguide 11 and the lateral grating 12 of the waveguide structure 10 have dimensional parameters that vary along the longitudinal axis X, such that the radiation profile S rl (x) is a given target profile S rl,c (x) and the radiation angle φ rl (x) is constant and the target angle φ rl,c (x). Thus, reference is made to the apodization of the input waveguide 11 and transverse grating 12, which may include the entire length of the input waveguide 11 and transverse grating 12 (in the corresponding antenna) or only a portion of their length.

[0084] In this example, the transverse grating 12 is formed by a number of triangular recesses in the input waveguide 11, as shown in Fig. 4D. These recesses have a depth p according to a given function p (in this case an increasing function). rl Change in the longitudinal direction of p rl = p(x), so the far-field radiation profile S rl (x) is the target profile S rl,c (x) except that the depth of the recess p rl The change in the length of the saw is the width w gi and the value p rl The minimum width w is defined as the difference between gi,min The minimum width w of the input waveguide 11 is gi,min This longitudinal change in (x) results in a change in the effective refractive index of the optical mode. However, the radiation angle θ rl (x) depends on the local value of the effective refractive index according to the following equation:

number

[0085] Therefore, the radiation angle φ rl (x) is the target value φ rl,c and to remain constant along the longitudinal axis X, the longitudinal variation of a dimensional parameter of the transverse grating 12, for example the pitch Λ, according to a predetermined function q. rl The longitudinal change in Λ rl It is also important to determine the dimensional parameters of each period, Λ = q(x). The dimensional parameters of each period can be expressed with a subscript i that varies from 1 to M, where M is the number of periods of the transverse grating in the apodized section. This gives the pitch Λ for the period with subscript i. rl (i) and depth p rl (i) is obtained.

[0086] In this example, the lateral radiating waveguide structure 10 has a minimum width w gi,min The depth p of the recesses represents the change in the longitudinal direction of rlChange in the longitudinal direction of p rl =p(x), while the longitudinal variation Λ of the pitch of the transverse grating 12 rl =q(x). These functions p and q depend on the radiation angle φ rl The far-field radiation profile S oriented at rl (x) is the angle φ rl,c Target profile oriented at Srl,c is determined to be the same as

[0087] In step 10, a far-field target radiation profile S of the optical radiation radiated by the waveguiding structure 10 of each optical antenna 7 is calculated. rl,c (x) is the target radiation angle φ rl,c As an example, the radiation profile S rl,c (x) is a Gaussian distribution. Furthermore, the target radiation angle φ rl,c is constant for any value x of the longitudinal axis X, which in this case is 5°. In this case, the wavelength λ of the optical mode is considered to be, for example, 1,550 nm.

[0088] Also, for the waveguide structure 10, the same reference structure arrangement Cs ref is determined. This structural arrangement Cs ref is a physical parameter Pp of the input waveguide 11 that defines the optical transmission characteristics of the optical mode by the input waveguide 11. gi In other words, the refractive index n gi and n gg and the thickness of the waveguide e gi and therefore, Pp gi ={n gi ,n gg ,e gi As an example, the input waveguide 11 can be made of silicon, with a refractive index n gi is 3.48, and the metal coating can be made of SiO2, with a refractive index of n gg Moreover, in this case, the input waveguide 11 has a constant thickness e c These physical parameters Pp giThe list is based on the minimum width w of the input waveguide 11, which will be determined later. gi,min The depth p of the periodic recesses in the transverse grating affects rl Change in the longitudinal direction of p rl Complemented by (x).

[0089] Structural arrangement Cs ref is also a physical parameter Pp of the transverse diffraction grating 12 that defines the diffraction characteristics of light of the optical mode by the transverse diffraction grating 12. rl Therefore, the physical parameter Pp rl is the refractive index n of the input waveguide 11 gi , the refractive index of the metal coating n gg , in this case 1.45 for SiO2, and the inclination angle β of the hypotenuse, in this case 30°. These physical parameters Pp rl The list of values ​​is determined later on by the pitch Λ of the transverse grating 12. r The longitudinal change in Λ r Complemented by (x).

[0090] In step 20, the reference structure configuration Cs ref , in this case the pitch Λ defined by the triangle of the recess. rl For extraction rate α rl The longitudinal variation of (x) is the target radiation profile S rl、c The same far-field radiation profile S as (x) rl The depth p of the recesses of the transverse grating 12 is rl Change in the longitudinal direction of p rl =p(x) is determined. More specifically, the recesses are successively spaced apart along the longitudinal axis X between the end of the hypotenuse of a triangle and the end of the base oriented along the Y axis of an adjacent triangle. It should be noted that the inclination angle β is constant from one recess to the next and is 30°.

[0091] FIG. 7A shows a depth p rl Change in the longitudinal direction of p rl Here is an example of a function p of =p(x). In this example, the function p is of the following type: rl(x)=p rl,max ×exp(-x 2 / 2σ 2 ), where p rl,max is the predetermined maximum recess depth, in this case 300 nm, and σ is the target emission profile S rl,c This is the Gaussian variance of (x).

[0092] In step 30, the reference structure configuration Cs ref In the case of , the radiation angle φ rl The gradual change in rl Pitch Λ for various values ​​of rl FIG. 7B shows an example of such a gradual change. In this case, the pitch is varied from 650 to 750 nm, and several FDTD simulations have been performed to obtain a maximum value of p rl、max Depth of p up to 300 nm rl This is done for depth p rl For each value of , a number of curves are defined that pass through the associated points.

[0093] Next, the pitch Λ rl and depth p rl The gradual change between Λ rl =h(p rl ) is derived, where the radiation angle φ rl is the target angle φ of 5° rl、c FIG. 7C shows an example of such a gradual change, where the function h is a power function. The curve passes through the points resulting from FIG. 7B. Finally, the longitudinal change p rl =p(x) and the relation Λ rl =h(p rl ), the pitch Λ of the transverse diffraction grating 12 is obtained. rl The longitudinal change in Λ rl = q(x) can be determined.

[0094] Finally, in step 40, all the structures are arranged in the same way, Cs ref Thus, this structural arrangement can be realized with the just determined input waveguide depth p rlChange in the longitudinal direction of p rl =p(x) and the longitudinal change in the pitch of the transverse grating, Λ rl =q(x), where x is the optical axis of the light, and q is the optical axis of the light.

[0095] This example also applies to transverse diffraction gratings 12 of the type shown in FIG. 4C, which are It should be noted that the method is formed by pads arranged at a distance on one and / or the other side of the input waveguide 11. In this case, by way of example, the method is performed by adjusting the width w of the input waveguide 11. gi The longitudinal change of w gi =p(x) and the longitudinal change Λ of the pitch of the transverse diffraction grating 12 rl = q(x) can be determined. Other physical parameters can be varied, e.g., fill factor, pad dimensions, etc.

[0096] Radiation profile S rv (y) is the target profile S rv,c (y) and the longitudinal axis A L A constant target radiation angle θ rv,c It should be noted that the waveguiding structure 30 can also be apodized so that it is oriented at . Methods similar to those described above can be used. Thus, the parameters, e.g., the pitch Λ of the vertical grating 32, rv , any one of the multiple dimensions of the multiple periodic structures 33, or the filling rate, etc., is L In this regard, Figure 6B is a schematic, partial cross-sectional view of a waveguiding structure 30 in which a vertical grating 32 has a pitch Λ that varies longitudinally according to a predetermined function. rv In this case, the length of the recess I rv varies in the longitudinal direction according to a given function. Therefore, the length I rv By varying the length (and therefore the filling factor) in the longitudinal direction, a desired radiation profile can be obtained, and the pitch Λ according to another predetermined function. rv By changing in the longitudinal direction, the radiation angle θrv can be kept constant and equal to the target value (hence the length l rv (compensating for the change in effective refractive index caused by the change in

[0097] This dimensioning method and manufacturing method therefore allows the manufacture of an apodized waveguide structure 10, in other words, which has a width w of the input waveguide 11 at least over a portion of the length of the waveguide structure 10 of the optical antenna 7. gi and the pitch Λ of the transverse grating 12. rl , whereby the extracted optical radiation has a desired far-field radiation profile oriented at a desired emission angle. This method can also be applied to the waveguiding structure 30.

[0098] While specific embodiments have been described above, various alternative embodiments and modifications will be apparent to those skilled in the art.

Claims

1. A photoelectron emitter (1) with a phased array antenna, a splitter (3) adapted to be connected to the laser light source (2); a plurality of waveguides, called input waveguides (11), connected to the splitter (3) and extending along a longitudinal axis in a major plane, forming the arms (4) of the photoelectron emitter; - a plurality of phase shifters (6) and a plurality of optical antennas (7) arranged in said arms (4), each optical antenna (7) comprising: said input waveguide (11); a waveguiding structure called vertical radiating waveguiding structure (30), adapted to receive the optical mode emitted by said input waveguide (11); a waveguide called the radiation waveguide (31) that is wider than said entrance waveguide (11); a vertical diffraction grating (32) connected to said radiation waveguide (31) and adapted to extract the optical mode flowing in said radiation waveguide (31) into free space; a waveguide structure formed by Each optical antenna (7) a waveguide structure called horizontal radiating waveguide structure (10), said input waveguide (11); a transverse diffraction grating (12) connected to the input waveguide (11) for extracting the optical mode flowing in the input waveguide (11) towards the radiation waveguide (31) at a major surface thereof, Photoelectron emitter (1).

2. 2. The photoelectron emitter (1) according to claim 1, further comprising a connecting structure (20) formed of a refractive index gradient medium, arranged between the horizontal radiation waveguide structure (10) and the vertical radiation waveguide structure (30), and configured to optically couple the lateral diffraction grating (12) and the radiation waveguide (31).

3. The connection structure (20) is an array of elementary connections (21) arranged laterally opposite the transverse diffraction grating (12); has a lateral dimension shorter than the dominant wavelength of the optical mode emitted by the laser light source (2), or formed of a medium having a first refractive index with an aperture; the aperture has a lateral dimension shorter than a dominant wavelength of an optical mode emitted by the laser light source (2) and is filled with a medium having a second refractive index smaller than the first refractive index; A photoelectron emitter (1) according to claim 2.

4. A photoelectron emitter (1) according to claim 2 or 3, wherein the length of the connecting structure (20) is less than or equal to its overall width.

5. 4. A photoelectron emitter (1) according to claim 2 or 3, wherein the radiation waveguide (31) and the vertical grating (32) each have a width at least as wide as the overall width of the connecting structure (20).

6. The optical antenna (7) has a pitch Λ along an axis perpendicular to the longitudinal axis of the input waveguide (11). ａ，ｙ are arranged periodically in The vertical diffraction grating (32) has an extraction length l ｔｏｔ，ｒｖ The pitch Λ, referred to as ａ，ｙ The photoelectron emitter (1) according to any one of claims 1 to 3, having a total length of at least 50% or 80% of the total length of the photoelectron emitter (1).

7. The optical antennas (7) are spaced apart at a pitch Λ along the longitudinal axis of the input waveguide (11). ａ，ｘ are arranged periodically in The vertical diffraction grating (32) has the pitch Λ ａ，ｘ Width w of 50% or 80% or more of ｔｏｔ，ｒｖ A photoelectron emitter (1) according to any one of claims 1 to 3, comprising:

8. The transverse grating (12) has a radiation angle φ with respect to an axis in a major plane perpendicular to the longitudinal axis of the input waveguide (11). ｒｌ configured to extract the optical mode with The vertical radiation waveguide structure (30) has a radiation angle φ ｒｌ A photoelectron emitter (1) according to any one of claims 1 to 3, arranged along a longitudinal axis parallel to the

9. Extraction length l ｔｏｔ，ｒｌ the length of the transverse grating (12), referred to as The width of the radiation waveguide (31) is equal to the extraction length l of the transverse diffraction grating (12). ｔｏｔ，ｒｌ The photoelectron emitter (1) according to any one of claims 1 to 3, wherein the photoelectron emitter (1) is at least equal to

10. The width of the incident waveguide (11) is 1 μm or less, The photoelectron emitter (1) according to any one of claims 1 to 3, wherein the width of the radiation waveguide (31) and the vertical diffraction grating (32) is each 10 μm or more.

11. Total extraction length l ｔｏｔ，ｒｖ The photoelectron emitter (1) according to any one of claims 1 to 3, wherein the length of the vertical diffraction grating (32), referred to as .gtoreq.10 μm, is 10 μm or greater.

12. The transverse diffraction grating (12) formed by a plurality of periodic recesses in the input waveguide (11), or A photoelectron emitter (1) according to any one of claims 1 to 3, formed by a periodic plurality of pads arranged at a distance from the input waveguide (11).

13. said input waveguide (11) having a longitudinal variation of at least one parameter representing its width according to a predetermined function p; The transverse diffraction grating (12) has a pitch Λ of the arrangement of the periodic structures (13) according to a predetermined function q. ｒｌ and having a longitudinal change of The function p and the function q correspond to a predetermined far-field target radiation profile S of the optical radiation extracted by the transverse diffraction grating (12). ｒｌ，ｃ (x), and a predetermined target radiation angle φ ｒｌ，ｃ The photoelectron emitter (1) according to any one of claims 1 to 3, wherein the photoelectron emitter (1) is predefined as a function of

14. the vertical grating (32) has a longitudinal variation of at least one dimensional parameter of the periodic structure (33) according to a predetermined function, The predetermined function defines a predetermined far-field target radiation profile Srv of the optical radiation extracted by the vertical grating (32). ，ｃ (x), and a predetermined target radiation angle φ ｒｖ，ｃ The photoelectron emitter (1) according to any one of claims 1 to 3, wherein the photoelectron emitter (1) is predefined as a function of

15. A photoelectron emitter (1) according to any one of claims 1 to 3, comprising a silicon-on-insulator (SOI) photonic chip comprising the horizontal radiating waveguide structure (10) and the vertical radiating waveguide structure (30).

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