Photoelectron emitter with phased array antenna including flare laser source

Abstract

The invention relates to a phased array photoelectron emitter (1) comprising a laser chip (10) including a flare laser source (12) and an optical chip (20) including a phaser (24) and a basic transmitter (25) located in N arms (23). The optical chip (20) comprises a coupler (30) that ensures optical coupling between the flare laser source (12) and the arms (23). The coupler (30) has a collection input (31) located facing the emission surface (16) of the flare laser source (12) and is coupled to the N arms of the photoelectron emitter, whose longitudinal axes are aligned at the position z l and a transmit output (32) including N straight waveguides (34, 35) oriented to intersect at .

Description

[Technical Field]

[0001] The technical field of the present invention is the field of on-chip photonic circuits, and more precisely, the field of phased array photoelectron emitters manufactured on at least one optical chip (photonic chip). The present invention is particularly applicable to the field of LIDAR (LIDAR for light detection and ranging). [Background technology]

[0002] Optoelectronic emitters employing OPA technology (OPA being an acronym for Optical Phased Array) are optoelectronic devices capable of directionally emitting monochromatic light into free space. They are particularly applicable to laser-based optical detection and ranging (LIDAR) applications, but are also applicable to free-space optical communications, holographic screens, and medical imaging.

[0003] Figure 1A schematically illustrates the operating principle of such a photoelectron emitter 1. The laser source 3 emits an optical signal distributed by an output distributor 4 of the N arms 5 of the photoelectron emitter 1. Each arm 5 includes one phaser 6 and one basic transmitter 7, also called an optical antenna. Each basic transmitter 7 transmits the optical signal into free space, for example, by diffraction. The optical signals then combine via interference to form an optical beam. The latter has a far-field transmission pattern, which is particularly determined by the relative phase Δφ applied by the phaser to the optical signal propagating through the arms.

[0004] Such photoelectron emitters can be manufactured using integrated photonics, meaning that their various optical components (waveguides, output distributors, basic transmitters, etc.) are manufactured on and from the same optical chip.

[0005] In this regard, Figure 1B schematically and partially shows an example of such a photoelectron emitter 1, as described in the paper "Fully integrated hybrid silicon two-dimensional beam scanner" by Hume et al., Option, Express 23(5), 5861-5874 (2015). This photoelectron emitter 1 here comprises a III-V type laser source 3 and is fabricated on the same optical chip. Thus, it comprises a semiconductor laser source 3, an output distributor 4, a phase shifter 6, and a basic transmitter 7. In this example, the laser source 3 is fabricated by transferring III-V material to an (SOI type) optical chip and structuring the material to form a gain medium.

[0006] However, there is a need to provide photoelectron emitters equipped with high-power laser sources. Specifically, in distance estimation (LIDAR applications) in particular, the optical power of the signal backscattered by the scene is only a small portion of the optical power of the emitted optical signal. And to detect distant objects, it may be necessary to use a high-power laser source. However, generating a high-power optical beam in a waveguide with small dimensions in the optical cavity of a laser source can lead to gain saturation or even degradation of the gain medium. Furthermore, while it is possible to generate a high-power optical beam using a laser source with a very large optical cavity, the waveguide in the optical cavity is no longer single-mode, so the generated beam will be of mediocre quality.

[0007] Furthermore, U.S. Patent Publication No. 2018 / 0217472 and paper OThr3I.7 of Guo et al., "InP Photonic Integrated Circuit with on-chip Tunable Laser Source for 2D Optical Beam Steering," Optical Fiber Communication Conference / National Optical Fiber Engineers Conference, 2013, OSA Technical Digest (online) (Optical Society of America, 2013), describe an example of a photoelectron emitter comprising a laser chip coupled to an optical chip. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent Publication No. 2018 / 0217472 [Overview of the Initiative]

[0009] The object of the present invention is to improve upon at least some of the shortcomings of the prior art, and more specifically, to provide an on-chip phased array photoelectron emitter comprising a laser source capable of emitting a high-power optical signal of good quality, wherein the laser source is efficiently optically coupled to an array of basic transmitters.

[0010] To accomplish this, the subject of the present invention is a phased array photoelectron emitter comprising an optical chip. The optical chip comprises N (N>1) waveguide-forming arms of the photoelectron emitter, and a plurality of phasers and a plurality of fundamental transmitters located within the arms.

[0011] According to the present invention, the photoelectron emitter comprises a laser chip distinct from the optical chip. The laser chip is joined to the latter on the same plane and includes a flare laser source. The flare laser source consists of a linear single-mode section and a section that extends outward (towards the flare) in the principal plane, extends along the optical axis Δ, and ends in a plane that emits an optical signal. Furthermore, the flare laser source has a wavefront that is circular in the principal plane and is located at position z on the optical axis Δ in the flare section. l It is configured to emit an optical signal centered on [a specific point].

[0012] Furthermore, according to the present invention, the optical chip includes a coupler that ensures optical coupling with the flare's laser source for collecting and transmitting at least a portion of the emitted optical signal. The coupler is coupled to the collection input, which is located facing the radiating surface of the flare's laser source, and to N arms of the photoelectron emitter, whose vertical axes are positioned z l The system includes a transmit power output comprising N straight waveguides oriented to intersect at a given point.

[0013] The following are certain preferred but non-limiting embodiments of this optoelectronic emitter.

[0014] Each of the N straight waveguides may have an upstream end directed towards the collection input and an opposite downstream end. The downstream end may define the transmission output of the coupler and may be laterally disposed within an arc centered at a radius located at z l and located laterally within an arc centered at a radius located at z.

[0015] The coupler may be a star coupler comprising a free-propagation region made of a medium of uniform refractive index having an entrance face that forms the collection input and is coupled to the emission surface of the flare laser source, and an exit face that is arcuate and centered at a radius located at z l and located at z. The straight waveguides are each connected on one side to the exit face and on the other side to the N arms and are output waveguides that are straight and longitudinally oriented in the direction of z l and located at z. The downstream ends of these output waveguides are laterally disposed along a line that forms an arcuate transmission output centered at a radius located at z l and located at z.

[0016] The output waveguides may be tapered waveguides and may simply have a width that decreases from the exit face of the free-propagation region.

[0017] The straight waveguides are longitudinally oriented in the direction of z l and are straight tapered waveguides that are laterally disposed such that their upstream ends are located along a line that forms the collection input and their downstream ends are located along a line that forms the transmission output. The collection input and the transmission output are arcuate and centered at a radius located at z l and located at z.

[0018] The optical chip may be spaced from the laser chip by a value of 1 μm or less along the optical axis Δ. They may be joined to each other by an adhesive layer.

[0019] The arms are straight and parallel to each other and may be connected to the transmission output by connection segments of various lengths.

[0020] The optical chip can be made from an SOI substrate. [Brief explanation of the drawing]

[0021] Other aspects, purposes, advantages, and features of the present invention will become clearer by reading the following detailed description of preferred embodiments of the invention. This detailed description is made with reference to the accompanying drawings, which are non-limiting examples. [Figure 1A] This is a schematic sub-diagram of a photoelectron emitter, an example of prior art that has already been described. [Figure 1B] This is a schematic partial top view of a photoelectron emitter manufactured on the same optical chip, as described earlier as an example of prior art. [Figure 2A] This is a schematic partial top view of a photoelectron emitter according to one embodiment in which the coupler is a star coupler. [Figure 2B] This is a top view showing the laser tip and coupler of the photoelectron emitter in more detail, as shown in Figure 2A. [Figure 2C] This is a top view showing the optical chip of the photoelectron emitter in Figure 2A in more detail. [Figure 3] This is a schematic partial top view of a photoelectron emitter according to a modified example of one embodiment in which the coupler is formed from a tapered waveguide. [Figure 4] This is a schematic partial top view of a structure comprising multiple photoelectron emitters manufactured on the same laser and optical chip. [Modes for carrying out the invention]

[0022] In the remaining part of the drawings and the specification, the same reference numerals are used to designate the same or similar elements. Further, for the sake of clarity of the drawings, the scales of various elements are not shown. Further, various embodiments and modifications are not mutually exclusive and may be combined with each other. Unless otherwise specified, the terms "substantially", "about", and "on the order of" mean within 10%, preferably within 5%. Further, unless otherwise specified, the term "composed between ~ and ~" and its equivalents mean including the limit.

[0023] The present invention relates to a phased array optoelectronic emitter having a flare laser source. Such an optoelectronic emitter includes an optical chip (photonic chip) that manufactures all phase shifters and basic transmitters, and a laser chip different from the optical chip. The laser chip is joined to the optical chip on the same plane, and on it, a flare laser source is manufactured.

[0024] The optoelectronic emitter is designed to emit a light beam of intensity having a determined angular distribution around the main radiation axis in the far-field. This far-field angular distribution of the light beam emitted by the optoelectronic emitter is called the "far-field radiation pattern". Therefore, it is different from the near-field radiation pattern of the basic transmitter (optical antenna). The far field (or Fraunhofer zone) is the distance D greater than the ratio of the square of the large dimension of the basic transmitter (here, the length L e along the Z-axis) to the radiation wavelength λ ee ), in other words, D>2L ee 2 / λ e corresponds to.

[0025] Furthermore, the flare laser source may be of the type specifically described in the paper "High-brightness diode lasers" by Wenzel et al. (CR Physique 4 (2003), 649-661). It comprises an active waveguide (located within an optical cavity) formed from a linear single-mode section following a flare section ending at the radiating surface of the laser source. The linear single-mode section may be a ridge with small lateral dimensions to form a spatial filter and force the optical signal into a transverse single mode. The flare section may ensure amplification of the optical signal. The radiating surface of the flare laser source may have a width on the order of 1 to several hundred microns. Thus, such a flare laser source may emit a high-power optical signal, for example, on the order of several watts.

[0026] According to the present invention, the optical chip includes a coupler that performs the function of optical coupling between the flare laser source and N arms including a phase shifter and a basic transmitter, as well as the function of output division.

[0027] Figure 2A is a schematic partial top view of a photoelectron emitter 1 according to one embodiment. Here, the laser chip 10 is optically coupled to the optical chip 20 on the same plane.

[0028] Here, a direct Cartesian coordinate system XYZ is defined, which will be referenced in the remainder of the specification, in which the XZ planes are parallel to the principal planes of the laser chip 10 and the optical chip 20, and the longitudinal Z axis is oriented along the optical axis Δ of the laser source 12 of the flare. The X axis is called the horizontal axis and the Y axis is called the vertical axis. The terms “upstream” and “downstream” refer to the position where the distance in the direction of optical signal propagation, in this case the distance in the +Z direction, becomes longer.

[0029] Unlike the optical chip 20, the laser chip 10 includes a flare laser source 12. The latter has a wavelength λ equal to, for example, approximately 905 nm or 1550 nm. eIt is designed to emit pulsed or continuous-wave monochromatic optical signals. The active waveguide 13 located within the optical cavity is called a flare in the sense that it comprises a linear single-mode section 14 along the optical axis Δ, followed by a flare section 15 ending at the radiating surface 16. Thus, the spatial distribution of the intensity of the emitted optical signal in the XY plane is elliptical and "flattened," having small dimensions on the order of, for example, 1 micron along the vertical Y axis and large dimensions on the order of, for example, about 100 microns along the horizontal X axis, with an aspect ratio (large dimension vs. small dimension) on the order of 50 to 100 or more. The laser source 12 of the flare may be manufactured in the same or similar manner as described in the paper "How to Launch 1 W Into Single-Mode Fiber from a Single 1.48 μm Flared Resonator" by Delphine et al., IEEE Journal on Selected Topics in Quantum Electronics, Vol. 7, No. 2 (2001), pp. 111-123.

[0030] It includes a carrier substrate 11, on which an active layer (not shown) containing multiple quantum wells located in the XZ plane is placed. The active layer may be flanked by a confinement layer along the vertical Y axis. A structured upper layer covers the active layer, forming a waveguide called an active waveguide, which extends along the optical axis Δ.

[0031] This active waveguide 13 includes a linear single-mode ridge section 14 defined laterally in the XZ plane by localized etching. This linear single-mode section 14 has a single guide transverse optical mode, for example, a fundamental transverse mode with an emission wavelength λ e It has lateral dimensions such that it is supported by the linear single-mode section 14. Furthermore, the linear single-mode section 14 performs a modal filtering function unless higher-order transverse modes potentially excited in section 15 of the flare are guided by the linear single-mode section 14.

[0032] Furthermore, it includes a flare section 15 defined in the upper XZ plane by local doping, and the optical modes are guided there via amplification gain. Section 15 is said to be flare insofar as it has a width in the XZ plane that increases proportionally to the distance from the linear single-mode section 14. It can have an inclination angle of the order of several degrees with respect to the optical axis Δ, for example, consisting of about 4° to 6°. The flare section 15 defines the radiating surface 16 of the flare laser source 12, which is perpendicular to the optical axis Δ. The radiating surface 16 has a width of the order of one to several hundred microns, here along the horizontal X axis. l It has.

[0033] It should be noted that the laser source 12 of the flare is essentially astigmatic in the sense that the plane of the horizontal waist (i.e., the waist of the XZ plane) is located at a different position from the plane of the vertical waist (i.e., the waist of the YZ plane). As is well known, the plane of the waist of the laser source is located at the position where the (horizontal or vertical) wavefront in question is a plane (infinite radius of curvature). As notably shown in the paper by Delepine et al. 2001, the plane of the horizontal waist is located within the active waveguide 13, more precisely within the section 15 of the flare, at a position zl a non-zero value δl along the optical axis Δ from the radiating surface 16, whereas the plane of the vertical waist is located on the radiating surface 16 (δl=0). The distance δl (and therefore the position zl) can be determined using a wavefront analyzer.

[0034] Thus, the emitted optical signal has its center at position z on the XZ plane, i.e., the main surface of the laser chip 10 and the main surface of the optical chip 20. l It has a circular wavefront located at position z. That is, in the XZ plane, the optical signal emitted by the flare's laser source 12 is at position z l It appears to be radiating from there.

[0035] The optical chip 20 comprises N arms 23 of a photoelectron emitter 1, with a phase shifter 24 and a basic transmitter 25 located within these arms. The optical chip 20 differs from the laser chip 10 in that each of these chips has its own carrier substrate 11, 21. This further includes an integrated coupler 30 (generated on the optical chip 20) which, on the one hand, ensures optical coupling to the laser chip 10, and on the other hand, divides the power of the received optical signal among the N arms 23.

[0036] The optical chip 20 or photonic integrated circuit (PIC) comprises a carrier substrate 21 from which optically coupled active photonic components (modulators, diodes, etc.) and passive photonic components (waveguides, multiplexers, or demultiplexers, etc.) can be generated. In on-silicon photonics, the carrier substrate 21 and photonic components are manufactured based on silicon. Therefore, the carrier substrate 21 may be a silicon-on-insulator (SOI) substrate. However, many other technological platforms may be used. Typically, the use of silicon waveguides for 905nm applications is not recommended because silicon absorbs at this frequency. Therefore, for example, guides made of silicon nitride (SiN), aluminum nitride (AlN), or doped silicon may be used.

[0037] The optical chip 20 has a first side facing the radiating surface 16 of the laser chip 10, so that the coupler 30 only needs to collect a significant portion of the optical signal emitted by the laser source 12 of the flare. The laser chip 10 and the optical chip 20 are assembled in the same plane, meaning that the optical signal propagates within the same XZ plane to pass from the laser chip 10 to the optical chip 20.

[0038] These are joined to each other by a layer 2 of adhesive material, such as an optical adhesive, whose refractive index is selected so as not to hinder the propagation of the optical signal. Therefore, the tips 10 and 20 are not optically coupled to each other by passive optical elements such as lenses. The refractive index of the optical adhesive 2 may be the same as that of the cladding material of the waveguide of the coupler 30. For example, the waveguides of the coupler 30 and arm 23 may be cladding of silicon nitride and silicon oxide. Furthermore, the distance between the laser tip 10 and the optical tip 20 along the longitudinal Z-axis is preferably less than 1 μm in order to capture the maximum value (range of signal divergence) of the optical signal emitted by the laser source 12 of the flare. However, the adhesive layer 2 may not be used, and the emitted optical signal may be transmitted through the air between the two tips. In any case, the photoelectron emitter 1 is very compact, and the coupling efficiency is not affected by the relative positioning errors of passive optical elements that would otherwise be required, particularly positioning errors along the X-axis.

[0039] The coupler 30 is configured to collect at least a portion of the optical signal emitted by the flare's laser source 12 and transmit it to N arms 23. Generally, the coupler 30 includes a collection input 31 for collecting the incident optical signal and a transmission output 32 for transmitting the collected optical signal, with the N arms 23 being coupled to the transmission output.

[0040] The acquisition input 31 preferably has lateral dimensions in the XY plane having an aspect ratio of at least the same magnitude as the spatial distribution of the intensity of the emitted optical signal. More precisely, the acquisition input 31 has a height along the vertical Y axis corresponding to the thickness of the waveguide layer of the photonic layer that generates the waveguides of the coupler 30 and the arm 23, for example on the order of 1 micron (tens of nanometers to several microns), and a width along the horizontal X axis on the order of 1 micron to several hundred microns. This allows the coupler 30 to receive a significant portion of the emitted optical signal.

[0041] Furthermore, the transmission output 32 is coupled to the N arms 23 of the photoelectron emitter 1, and their vertical axes are z lIt includes N straight waveguides oriented to separate at a certain position (within manufacturing tolerances). The straight waveguides may be the output waveguide 34 shown in Figures 2A to 2C, or the tapered waveguide 35 shown in Figure 3. This longitudinal orientation of the N straight waveguides allows for optimization of the collection efficiency of the radiated optical signal.

[0042] Each of the N straight waveguides has an upstream end directed toward the acquisition input 31 and a downstream end opposite it. Preferably, the downstream end of the straight waveguide defines the transmission output 32 and is positioned laterally (i.e., along the X-axis) in an arc shape with the center of the arc radius located at position zl, thereby optimizing the transmission efficiency of the acquired optical signal in the direction of the arm 23 of the photoelectron emitter 1.

[0043] In the example shown in Figures 2A and 2C, the transmission power 32 is when the center of the radius of the arc is at position z l It is arranged in an arc shape at the position. Therefore, the output of the coupler 30 has a curvature that matches the curvature of the wavefront of the optical signal radiated by the flare's laser source 12 and received by the coupler 30. This optimizes the transmission efficiency of the collected optical signal (in addition to optimizing the collection efficiency of the radiated optical signal) as described above, and also avoids the introduction of phase errors into the transmitted optical signal (although the phase error is corrected by the phase shifter 24). Here, a slight difference between the wavefront of the optical signal radiated from the light source and the wavefront of the optical signal received by the coupler 30 may be considered due to the difference in refractive index between the material of the active layer of the flare's laser source 12 and the material of the coupler 30.

[0044] In this embodiment, the coupler 30 is a star coupler. It includes a free propagation region 33 (FPR) and an output waveguide 34. The acquisition input 31 is here the inlet surface of the FPR 33, which is perpendicular to the optical axis Δ and positioned facing the laser source 12 of the flare. The longitudinal dimension along the X axis may be larger than the dimension of the radiating surface 16. The transmission output 32 is here formed by the downstream end of the output waveguide 34 and is arc-shaped, with the center of the radius of the arc at the position z of the laser source 12 of the flare. lIt is located at z. The FPR33 is formed of a medium with a uniform refractive index and is surrounded by an exit surface 33.1 along the optical axis Δ, to which the collection input 31 and output waveguide 34 are coupled. The exit surface 33.1 is also arc-shaped, and the center of the radius of its arc is also the position z of the laser source 12 of the flare. l It is located at [location]. Therefore, the coupler 30 includes N output waveguides 34, which are sized to optimize the collection of the radiated optical signal and then the transmission of the collected optical signal, and are preferably geometrically identical to one another. In Figure 2A, they extend from the exit surface 33.1 of the FPR 33 to the dashed arc line indicating the transmit power 32.

[0045] N output waveguides 34 transmit the collected optical signals to N waveguides of arm 23. These are connected to arm 23 by connecting segments 22, as shown in more detail in Figure 2C. Here, these are tapered waveguides having a width in the XY plane that decreases adiabatically in the direction of optical signal propagation to optimize the transmission efficiency of the coupler 30. Thus, the width can decrease monotonically or linearly. As shown in Figure 2B, they are all of length L t and the horizontal dimension w t They have the same dimensions with respect to (z). These are linear, and each is at the position z of the laser source 12 of the flare. l It is oriented vertically in the direction of z. The upstream and downstream ends of the output waveguide 34 have the center of the arc radius at position z l It is positioned laterally (along the XZ plane and the X axis) along the arc located at z. The upstream end of the output waveguide 34 is connected to the arc-shaped exit surface 33.1 of the FPR 33, and the downstream end of the output waveguide 34 is located at z l It is positioned on the transmission power 32, which is indicated by an arc-shaped line centered on [the specified point].

[0046] As an example, as shown in Figure 2B, a schematic and partial top view detailing the flare laser source 12 and coupler 30, the flare laser source 12 emits a wavelength λ equal to 905 nm. e The optical signal may be emitted. Section 15 of the flare has a length L on the radiating surface 16. lThe thickness is 2000 μm, and the maximum width is w l The distance is 150 μm. Here, the laser source 12 of the flare is at a distance δ l The astigmatism is equal to approximately 600 μm. Here, the coupler 30 consists of 100 output waveguides 34 formed in a silicon nitride waveguide layer with a thickness of 0.3 μm, and is arranged on the radiating surface of the FPR 33 such that the pitch P in the X-axis direction is approximately 1.3 μm. Each output waveguide 34 has a length L at its upstream end. t The thickness is 100 μm, and the maximum width is w t The width is 1.2 μm. The upstream ends are spaced apart by a distance g equal to approximately 0.1 μm. Under these conditions, at least 90% of the emitted optical signal is collected and transmitted to the output waveguide 34.

[0047] Thus, the coupler 30 has an output waveguide 34 that is in a straight line and is located z l As long as it is oriented longitudinally toward, and the transmission output 32 is circular and its center is at position z l Insofar as it is located, that is, insofar as it has substantially the same curvature as the wavefront curvature of the emitted optical signal, it has high collection and transmission efficiency. The introduction of phase errors into the optical signal transmitted by various output waveguides 34 is also avoided (nevertheless, phase errors can be corrected by the phase shifter 24), and the transmission efficiency is optimized. Furthermore, the collection input 31 of the coupler 30 advantageously has lateral dimensions (horizontal along the X axis, vertical along the Y axis) of at least the same magnitude as those of the spatial distribution of the intensity of the emitted optical signal in the XY plane, and thus improves collection efficiency. Also, such a coupler 30 (that of Figure 2A or that of Figure 3) ensures that the intensity distribution in arm 23 is in Gaussian form and not a uniform distribution from one arm to the next. This Gaussian distribution makes it possible to remove the side lobes of the far-field intensity distribution of the optical beam emitted by the photoelectron emitter 1. Specifically, the uniform distribution becomes a far-field intensity distribution in the form of a sinc function.

[0048] Therefore, the coupler 30 serves to divide the power of the collected optical signal among the N arms 23. The output waveguide 34 is connected to the N arms 23 by connecting segments 22. Here, the connecting segments 22 are curved (except for those on the extension of the optical axis Δ) and each connecting segment has a different length, as long as the N arms 23 are preferably straight and parallel to each other. The connecting segments 22 and the arms 23 may have the same width as the output waveguide 34 at the downstream end. As shown below, the phase shift introduced by the connecting segments 22 is corrected by the phase shifter 24.

[0049] Furthermore, the photoelectron emitter 1 also includes a pair of phasers 24 and a basic transmitter 25. More precisely, at least a portion of the arms 23 are equipped with at least one phaser 24 designed to change the phase of the optical signal propagating through that arm 23, and thus generate a phase difference Δφ, i.e., relative phase, between optical signals propagating through adjacent arms 23. The phasers 24 are positioned between the coupler 30 and the basic transmitter 25. Each arm 23 may be equipped with a phaser, or only a portion of the arms 23 may be equipped with one phaser, for example, in a pair of arms 23. Moreover, the reference arm 23 does not need to be equipped with any phasers 24.

[0050] The phase shifter 24 may be a phase shifter that uses the electric refraction effect or the thermo-optic effect. In either case, phase correction is obtained by correcting the refractive index of the material forming the core of the waveguide. This correction of the refractive index is obtained by correcting the free carrier density in the case of the electric refraction phase shifter 24, and by correcting the applied temperature in the case of the thermo-optic phase shifter 24.

[0051] Preferably, the phase shifter 24 is configured to apply the same relative phase value Δφ to the optical signal propagating through the arm 23 so as to obtain a non-zero angle θ determined by the inclination of the main radiation axis toward the Y axis in the XY plane (perpendicular to the axis of the base transmitter 25). However, the relative phase Δφ does not have to be identical between the arms 23 in order to obtain different far-field patterns or to account for and compensate for any phase errors. These phase errors may be caused by the aging degradation of certain components of the photoelectron emitter 1, non-uniformity in the manufacturing process, non-zero tolerances in the manufacturing process, and / or environmental influences of the photoelectron emitter 1 (e.g., potential influences of the packaging including the base transmitter 25).

[0052] Therefore, it should be noted that the phase shifter 24 can compensate for undesirable phase shifts caused by the connecting segment 22 (as a result of different lengths between segments). This compensation may be performed prior to the calibration of the photoelectron emitter.

[0053] The photoelectron emitter 1 comprises N basic transmitters 25 or optical antennas coupled to the arm 23 and therefore located downstream of the phaser 24. The relative phase Δφ between the optical signals emitted by the basic transmitters 25 particularly determines the value of the angle θ made by the main radiation axis of the optical beam in the far field with respect to the Y axis in the XY plane of the photoelectron emitter 1.

[0054] Here, the basic transmitter 25 is a diffraction grating formed in the waveguide of arm 23. They extend parallel to each other along the Z-axis and are aligned along the X-axis. In other words, the first end is in the same position along the Z-axis as the second end. These ends are λ e / 2 and 2λ e They are spaced apart by a preferred distance between them. For informational purposes, the number N of the basic transmitters 25 may range from about 10 to about 10,000.

[0055] Thus, the optical signal propagating through arm 23 is partially transmitted into free space via diffraction by the basic transmitter 25. The extracted optical signal propagates in free space, recombines through interference, and forms a far-field optical beam emitted by photoelectron emitter 1, the angular distribution around its main emission axis is determined, and the far-field emission pattern of photoelectron emitter 1 is defined.

[0056] The angle θ that the main radiation axis makes with the Y-axis of the YZ plane is, as is well known, the radiation wavelength λ of the laser source 12 of the flare. e This also depends on the period Λ of the diffraction grating formed by the basic transmitter 25. As described above, the angle θ of the main radiation axis with respect to the Y axis in the XY plane depends on the value of the relative phase Δφ that the phase shifter 24 applies to the optical signal propagating through the arm 23. Generally, if the relative phase Δφ is 0, the angle θ is 0, that is, it is desirable that the main radiation axis of the far-field light beam is parallel to the Y axis. This is generally determined in the preliminary stages of the photoelectron emitter calibration.

[0057] It should be noted that it is desirable to connect the phase shifter 24 to a control device (not shown) suitable for calibrating and controlling the phase shifter according to the actual far-field emission pattern of the photoelectron emitter. In response to control signals sent from the control device, the phase shifter 24 can generate a predetermined relative phase Δφ in the optical signals propagating through various arms 23 in order to obtain a desired far-field emission pattern. The control device may consist of an interference focusing lens, a plurality of photodetectors, and a control module, as described in international application PCT / EP2020 / 087385 filed on December 21, 2020.

[0058] Figure 3 is a schematic and partial top view of a photoelectron emitter 1 including a coupler 30 according to one modified embodiment. In this example, the coupler 30 is formed from an array of tapered waveguides 35 having an adiabatic change in their width. Unlike the output waveguide 34 connected to the FPR 33 (Figure 2A), the width of the tapered waveguide 35 here increases in the direction of the optical signal. Furthermore, the coupler 30 does not have an FPR, and therefore the upstream and downstream ends of the tapered waveguide 35 form the collection input 31 and transmission output 32 of the coupler 30, respectively. The tapered waveguide 35 is linear and oriented longitudinally toward position zl. The upstream end is positioned laterally on a first line that forms a circular arc in the XZ plane, with the circular arc centered at position zl, and the downstream end is similarly positioned laterally on a second line that forms a circular arc in the XZ plane, with the circular arc centered at position zl. Thus, the tapered waveguide 35 has the same length. As shown in the example in Figure 2A, the number, width, and length of the tapered waveguides 35, as well as their lateral arrangement, can be determined to optimize coupling efficiency and transmission efficiency.

[0059] Figure 4 is a schematic and partial top view of a structure including multiple photoelectron emitters 1 arranged side by side. Thus, the laser chip 10 comprises multiple flares laser sources 12 oriented along optical axes parallel to each other and generated on the same carrier substrate 11. Preferably, the flares' laser sources 12 are identical to each other. The optical chip 20 comprises multiple sets of couplers 30, phase shifters 24, and basic transmitters 25, each set optically coupled to one flare's laser source 12. These sets are manufactured on the same carrier substrate 21.

[0060] This structure is made possible by the compactness of the photoelectron emitter 1. Furthermore, because the optical signal emitted from the flare's laser source 12 is elliptical in shape, constraints on the alignment of the two chips can be reduced while maintaining particularly high-efficiency coupling between the flare's laser source 12 and the coupler 30. Therefore, this structure enables two-dimensional scanning of a scene without the use of particularly expensive tunable laser sources. Specifically, each photoelectron emitter 1 can be configured to scan the scene in different angular planes.

[0061] Specific embodiments have been described. Various modifications and variations will be obvious to those skilled in the art.

Claims

1. An optical chip (20) including N (N>1) waveguide forming arms (23) of a photoelectron emitter (1), a plurality of phase shifters (24) and a basic transmitter (25) arranged within the arms (23), The system includes a laser source (12) and a laser chip (10) which is different from the optical chip (20), The laser chip (10) is bonded to the optical chip (20) on the same plane. The laser source (12) is a laser source for the flare, and the laser source for the flare is It consists of a linear single-mode section (14) and a section (15) that extends outward within the main plane, extends along the optical axis Δ, and ends with a surface (16) that emits an optical signal. The position z is circular within the main plane and located in the section (15) of the flare along the optical axis Δ. ｌ The optical signal having a wavefront centered on is configured to emit such a signal. The optical chip (20) includes a coupler (30) that ensures optical coupling with the laser source (12) of the flare for collecting and transmitting at least a portion of the emitted optical signal. The aforementioned coupler (30) is The collection input (31) is located facing the radiating surface (16) of the laser source (12) of the flare, The N arms (23) of the photoelectron emitter (1) are coupled, and their propagation axes are at position z ｌ A transmission power (32) including N straight waveguides (34, 35) oriented to intersect, A phased array photoelectron emitter (1) including the above.

2. Each of the N straight waveguides (34, 35) has an upstream end directed toward the acquisition input (31) and an opposite downstream end, the downstream end defining the transmit output (32) of the coupler (30), and the center of the radius of the arc is at position z ｌ Located in an arc shape, arranged horizontally, The photoelectron emitter (1) according to claim 1.

3. The coupler (30) is a star coupler, The aforementioned star coupler is The collection input (31) is formed by an inlet surface that is coupled to the radiating surface (16) of the laser source (12) of the flare, and the center of the radius of the arc is at position z ｌ The free propagation region (33) comprises a medium with a uniform refractive index and an arc-shaped exit surface (33, 1) located at the position, Each of the straight waveguides is an output waveguide (34) connected on one side to the exit surface (33, 1) and on the other side to the N arms (23), and its downstream end is such that the center of the radius of the arc is at position z ｌ Arranged laterally along the line forming the arc-shaped transmission output (32) located at, The photoelectron emitter (1) according to claim 2.

4. The output waveguide (34) is a tapered waveguide and has a width that decreases from the exit surface (33, 1) of the free propagation region (33). The photoelectron emitter (1) according to claim 3.

5. The straight waveguide is a tapered waveguide (35) positioned laterally such that its upstream end is located along the line forming the collection input (31) and its downstream end is located along the line forming the transmission output (32), and the collection input (31) and the transmission output (32) are located such that the center of the radius of the arc is at position z ｌ It is arc-shaped and located in a circular position. The photoelectron emitter (1) according to claim 2.

6. The optical chip (20) is spaced less than 1 μm away from the laser chip (10) along the optical axis Δ. The photoelectron emitter (1) according to any one of claims 1 to 5.

7. The laser chip (10) and the optical chip (20) are joined to each other by an adhesive layer (2). The photoelectron emitter (1) according to any one of claims 1 to 6.

8. The arms (23) are linear and parallel to each other, and are connected to the transmit output (32) by connecting segments (22) of various lengths. The photoelectron emitter (1) according to any one of claims 1 to 7.

9. The optical chip (20) is made of an SOI substrate. The photoelectron emitter (1) according to any one of claims 1 to 8.

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