ES2989226B2 - Device for transmitting and detecting optical beams - Google Patents

Description

[0001] DESCRIPTION

[0003] Device for transmitting and detecting optical beams

[0005] OBJECT OF THE INVENTION

[0007] The present invention is related to the industry dedicated to the manufacture of optical integrated circuits or photonic integrated circuits (PIC: Photonic Integrated Circuit), especially for their application in lidar systems (acronym for LiDAR: “Light Detection and Ranging” or “Laser Imaging Detection and Ranging”).

[0009] The present invention relates to a device for the transmission and detection (or reception) of optical beams by means of a single integrated photonic chip.

[0011] BACKGROUND OF THE INVENTION

[0013] A lidar (or LiDAR) is a device that determines the distance from a laser emitter to an object or surface using a pulsed laser beam. LiDAR devices are used to capture the physical dimensions of a particular environment in three dimensions (3D), defined by an X, Y, and Z coordinate system, and/or in a six-dimensional (6D) environment with X, Y, and Z coordinates, along with those that define the velocity of objects in the 6D environment (V<X>, V<Y>, and V<Z> coordinates). LiDAR devices or systems are used in advanced driver assistance systems (ADAS), drones or automated guided vehicles (AGVs), surveying, archaeology, terrain reconnaissance, sensor systems, and more.

[0015] Many future applications, such as autonomous driving, industrial robots, image recognition, virtual/augmented reality, etc., will depend heavily on a device that can detect and measure the dimensions, coordinates, and distances of objects in a particular field of view with the highest degree of accuracy. Although considerable effort is being invested in using multiple cameras to extrapolate the X, Y, Z coordinates of the 3D environment from multiple photographs (photogrammetry) taken from different angles, such techniques will not be able to achieve the accuracy and resolution that a LiDAR system can potentially offer.

[0016] There are different types of LiDAR systems whose properties, advantages and disadvantages are summarized below:

[0018] - The simplest LiDAR system is called Time-of-Flight LiDAR (ToF): it works by transmitting a short pulse of light toward a specific object. The light then reflects off the object back to the detector, and the measured round-trip time is used to calculate the distance between the LiDAR device and the target object with high accuracy. By sending light pulses in different directions, a point cloud can be created containing the X, Y, Z coordinates of all objects in the field of view. ToF LiDAR systems are currently commercially available and are being used in many products, such as robotic vacuum cleaners, autonomous vehicles, and the iPhone.

[0020] - The system called FMCW (Frequency-Modulated Continuous Wave) LiDAR is a frequency-multiplexed continuous wave system. This type of system is still in the research and development phase due to the added complexity of interfering/mixing the received beam signal with the transmitted beam signal. Its main advantage is that it can be used to detect the velocity (V<X>, V<Y>, and V<Z>) of target objects in a single scan, in addition to the object's X, Y, and Z coordinates.

[0022] According to the manufacturing technology, the following LiDAR systems are distinguished:

[0024] - Mechanical Rotation LiDAR: Conventional LiDAR scanning uses mechanical rotation to spin the sensor for 360-degree detection. Its main advantages are that it uses mature hardware or electronics technology and provides wide field of view coverage, but it is large in size and cost, and reliability is low.

[0026] - Microelectromechanical mirror (MEMS) LiDARs are not completely solid-state like the previous ones. Among their advantages are low cost, versatile wavelength, and low optical losses, but they are sensitive to vibrations and shocks, have a limited field of view, and scanning is fast only at resonant frequencies.

[0028] - LiDAR based on OPA (Optical Phased Array) technology is a solid-state lidar that uses optical phased arrays (OPAs), which can produce low-divergence laser beams and be used to electronically control the emission angle without the need for moving mechanical parts. This allows for faster scanning and a more compact, smaller device because the OPAs can be integrated onto a chip.

[0030] Most state-of-the-art FMCW LiDAR chips are based on the concept of optical arrays (OPAs) to create a steerable beam from many individual emitters.

[0032] The objective technical problem presented is to provide a LiDAR device integrated into a photonic chip that allows easy combination of the signal from a transmitted beam with the signal reflected from a target object.

[0034] DESCRIPTION OF THE INVENTION

[0036] The present invention serves to solve the aforementioned problem by providing a device for transmitting and detecting optical beams by integrating all components into a single photonic integrated circuit (chip).

[0038] The invention relates to an optical beam transmitter and detector comprising the components described below integrated within a photonic chip, with a top and a bottom face, for receiving an input light signal from a lens system, with a transmission angle and wavelength, disposed above or below the top face of the chip. The components comprise:

[0039] a plurality of grid couplers aligned on the top face of the chip,

[0040] wherein each grid coupler is constructed with a length L<GC> in a waveguide and with a plurality of teeth,

[0041] wherein each tooth is tilted with an angle of inclination equal to the transmission angle of the lens system and the plurality of teeth of each grating coupler are arranged with a fixed tooth width equal for all teeth and tooth spacing, each grating coupler being apodized along its length L<GC> varying the tooth spacing gradually to emit a constant amount of light per unit length;

[0042] and where each waveguide is configured to guide the incoming light signal within the chip to each grid coupler that produces a beam, to transmit or receive through the lens system, the beam produced with

[0043] a first deviation angle determined by the tooth inclination angle and

[0044] a second angle of deviation determined by the wavelength of the incoming light;

[0045] where the light signal is processed exclusively in the optical domain within the chip, without needing to convert it to the analog and/or electronic domain for processing.

[0047] The advantages of the present invention compared to the prior art and in relation to currently existing integrated devices are fundamentally:

[0049] - Significant reduction in the size of the electronic device where the transmission and detection of a proposed optical beam is implemented, because both the beam, the transmitter and the receiver are integrated into a single compact chip.

[0051] - Possibility of processing on a single chip the transmitted and received beam signals that allow, for example, coherent beam processing, or beam data polarization-multiplexing.

[0053] - Applicable to multiple types of LiDAR systems, such as Time-of-Flight (ToF) LiDAR or Frequency-Multiplexed Continuous-Wave (FMCW) LiDAR. - Performs simultaneous targeting of multiple beams at the same time using only one control variable (i.e., the wavelength), and therefore does not require complex electronic control to target individual beams.

[0055] - Direct scalability towards the transmission and reception of an arbitrary (large) number of beams (corresponding to angular pixels).

[0057] - No electronic control is required to direct the beams.

[0059] - Reduced capture time of the coordinates of a 3D environment due to the fact that multiple beams are transmitted and received simultaneously (unlike common systems that use a single oriented beam; “pointed beam”, in English), allowing parallel processing of the received signals and rapid data acquisition.

[0061] - It is implementable in many different photonic chip material technologies and platforms: ranging from silicon-on-insulator (SOI) technology to polymer technology.

[0063] - Allows the integration of a complete LiDAR system when using an indium phosphide (InP) material platform (monolithic photonic circuit) with a cylindrical lens integrated into the chip's dielectric platform or substrate.

[0065] - Allows control of the power emitted by individual beams at a particular angle in the emitting network (splitting network).

[0067] - Rapid acquisition of the environment point cloud, since the proposed device contains no moving parts.

[0069] BRIEF DESCRIPTION OF THE FIGURES

[0071] Next, a series of drawings are briefly described which help to better understand the invention and which are expressly related to an embodiment of said invention which is presented as a non-limiting example thereof.

[0073] FIGURE 1.- Shows a schematic of the architecture of a transmitter and detector device for optical beams integrated into a photonic chip, according to a preferred embodiment of the invention.

[0075] FIGURE 2.- Shows an enlarged view of a grid-tooth coupler of the integrated device with the angles that characterize it according to a three-dimensional, 3D, coordinate system.

[0077] FIGURES 3A-3C.- Show in a cross-section of the grid couplers along the z-axis of the 3D coordinate system (FIG. 3A), the directions of the light beams transmitted (FIG.3B) to a first target and received (FIG.3C) from the first target, for different wavelengths.

[0079] FIGURES 4A-4C.- Show in a cross section of the grid couplers along the z-axis of the 3D coordinate system (FIG. 4A), the directions of the light beams transmitted (FIG.4B) to a second target and received (FIG.4C) from the second target, for different wavelengths.

[0081] FIGURES 5A-5C.- Show in a cross-section of the grid couplers along the x-axis of the 3D coordinate system (FIG. 5A), the directions of the light beams transmitted (FIG.5B) to a first target and received (FIG.5C) from the first target, for different wavelengths.

[0083] FIGURES 6A-6C.- Show in a cross-section of the grid couplers along the x-axis of the 3D coordinate system (FIG. 6A), the directions of the light beams transmitted (FIG.6B) to a second target and received (FIG.6C) from the second target, for different wavelengths.

[0085] FIGURE 7.- Shows a chip with an integrated LiDAR device, according to a possible embodiment of the invention.

[0087] FIGURE 8.- Shows a bird's-eye view of the LiDAR device integrated into the chip of the previous figure.

[0089] FIGURES 9A-9F.- Show the possible options for incorporating a lens system into the photonic chip for the transmission and detection of optical beams, and according to various possible embodiments of the invention with different types of lenses, placing the lens on the upper face of the chip (FIG.9A and FIG.9B) or on the lower face of the chip (FIG.9C and FIG.9D) or integrating the lens into the chip (FIG.9E and FIG.9F).

[0091] FIGURE 10.- Shows a graph of the divergence angle of the optical beam transmitter and detector device as a function of the length of its grid couplers.

[0093] FIGURES 11A-11B.- Show a structure with certain dimensions of the grid coupler respectively in the x-axis direction (FIG.11A) and in the z-axis direction (FIG.11B).

[0095] FIGURE 12.- Shows the beam deviation angle in a transverse plane on the x-axis as a function of the grating tooth inclination angle.

[0096] FIGURES 13A-13B.- Show, for two different values of the tilt angle (FIG.13A and FIG.13B) of the grating teeth, the beam deviation angle in a transverse plane on the z-axis as a function of the wavelength of the incoming light.

[0098] FIGURE 14.- Shows an example of implementation of the lens system which is a cylindrical lens integrated into the chip, according to a possible embodiment of the invention.

[0100] FIGURE 15A-15C.- Show, for three different values (FIG.15A, FIG.15B and FIG.15C) of the beam deviation angle in the transverse plane along the x-axis, the simulations of the focusing of the cylindrical lens according to the possible implementation shown in Figure 14.

[0102] PREFERRED EMBODIMENT OF THE INVENTION

[0104] Figure 1 shows a schematic to illustrate a possible embodiment of the invention consisting of a device integrated into a photonic chip100 containing an array of grid couplers110, with a lens system10 where an input light signal is incident and a lens under which the grid couplers110 are aligned on the top part or face of the chip100. The input light is guided within the chip100 to each of the grid couplers110, which all have a length LGC, by means of optical waveguides120. The array of grid couplers110 is at a separation distance fa along the lens system10.

[0106] The lens system10 comprises at least one lens which may be, to name a few of the applicable lens types, a cylindrical lens, refractive lens, Fresnel lens, metamaterial-based lens, or lens of diffractive optical elements (DOE lens; from the English, DOE: Diffractive-Optical Elements).

[0108] Figure 2 depicts any one of the multiple grid couplers 110, each with a width wGC, which may or may not be the same for all grid couplers 110 (i.e., the different couplers in the plurality of couplers do not have to have the same width, but a single coupler has only one width; for example, Figure 15 shows how the width is determined, which may be different for different beam deflection angles κ). Each grid coupler 110 comprises a plurality of teeth 210 with a fixed tooth spacing or tooth width Ʌ that is the same for each of the teeth 210 of each grid coupler 110 and a tooth spacing ε that is not fixed, but rather varies along the grid coupler 110 so that a constant amount of light is emitted per unit length. The grid teeth 210 along the array (aligned plurality) of grid couplers 110 are gradually tilted at a specific tilt angle θ, as shown in Figure 2, within a 3D environment defined by a coordinate system: a first x-axis, a second y-axis, and a third z-axis. The tilt angle θ of the grid teeth 210 determines the direction in which the incoming light is directed (or received), given by a (first) beam deflection angle κ in a transverse plane along the direction of the first x-axis. If a transverse plane is considered along the direction of the third z-axis, a (second) beam deflection angle φ is obtained.

[0110] The tilt angle θ determines the lateral direction in which the light exits the transmitting grating coupler (or, respectively, the direction from which the receiving grating coupler will accept the light) given by the above referred to as the first beam deflection angle κ. The wavelength of the light, wavelength designated as λ1 or λ2 in Figures 3-6, determines in what transverse direction the light exits/enters the grating coupler defined by the above referred to as the second beam deflection angle φ.

[0112] The method of transmitting and detecting (or receiving) an optical beam using the device proposed here is based on one principle: matching the tilt angle θ of the grating teeth 210 formed in the grating couplers 110 with the transmission angle of the lens or lens system 10. Light entering a specific grating coupler 110 is thus transmitted in a specific direction. Light reflected by the target object is directed back to the same grating coupler at the same angle and, therefore, due to the principle of reciprocity, the light will exit through the same grating coupler.

[0114] Figures 3A-C, 4A-4C, 5A-5C, and 6A-6C show that this combination of grating couplers110 with inclined grating teeth210 as described, together with the cylindrical lens or lens system10, can be used to produce light beams in two directions: in the direction of the first axis x with the first beam deflection angle κ and in the direction of the third axis z with the second beam deflection angle φ. Thus, in Figures 3A, 4A, 5A, and 6A, a cross-section of the grating coupler assembly110 along the direction of the axis x is considered, such a cross-section on the axis x is represented as section STx, and a cross-section of the grating coupler assembly110 along the direction of the axis z is represented as section STz.

[0115] Figures 3A-3C and 4A-4C illustrate the principle for transmission and detection described above, where, for a first beam deflection angle κ1 in section STx along the x-axis, a variation of the values φ1 and φ2 of the second beam deflection angle φ from section STza along the z-axis is observed respectively in Figures 3A and 4A. Figures 3B and 3C illustrate the directions of the light beams transmitted to a first target 30 and received from the first target 30. Figures 4B and 4C illustrate the directions of the light beams transmitted to a second target 40 and received from that second target 40. The transmitted light beams (towards the target30, 40) are represented as black arrows and the received light beams (coming from the target30, 40) are represented by striped arrows in Figures 3A-3C and 4A-4C, which illustrate how the wavelength, λ1, λ2, of the input light signal determines the transverse direction of the light leaving/entering (transmitted/received beam) in the grid coupler110, given in each case, as shown in Figures 3 and 4, respectively by the values φ1 and φ2 of the beam deviation angle in the transverse plane along the z-axis, the direction of the transmitted/received beam in the transverse plane along the x-axis being given by the value κ1 of the beam deviation angle. It is observed that the transmitted beam is slightly divergent, with an angle φ1 in Figure 3B towards the objective 30 and φ2 in Figure 4B towards the objective 40. In Figures 3C and 4C, the received beams are seen passing through the transverse STz section in the z direction of the lens system 10 and the grid coupler array 110 arranged on the light-absorbing substrate 1000.

[0117] Light enters a grating coupler110 at z=0 and, along its length LGC, light is gradually emitted from the grating coupler110 to the lens or lens system10. It is important that the amount of light emitted per unit length be constant along the grating coupler because the light received from the objective30, 40 definitely has a uniform intensity distribution along the grating coupler110. When there is a fixed spacing ε between the teeth, the intensity of the light exiting along the entire grating coupler follows an exponential curve, as shown in Figure 3B. Therefore, grating couplers110 are apodized, which is achieved when the spacing ε1, ε2 between the teeth are gradually adjusted while maintaining a constant periodic tooth spacing 210 with a fixed tooth width Λ.

[0119] Figures 5A-5C and 6A-6C show the beams passing through the cross-section STx of the lens system10 in the x-direction when light enters/exits two grating couplers arranged at different locations x1, x2 along the array110: one coupler arranged at x = x1 as shown in Figures 5B-5C and another coupler arranged at x = x2 as shown in Figures 6B-6C. The tilt angle θ of the teeth of the grating couplers is designed such that the angle of the light emitted by the grating coupler is in the same direction as when the light is focused on that grating coupler. Therefore, the tilt angle θ of the teeth210 of the grating coupler at location x1 is positive, and negative for the grating coupler at location x2. The lens10 then collimates the light from these grating couplers towards a direction κ1 and κ2. Therefore, Figures 5 and 6 illustrate that the value of the first beam deviation angle κ which determines the transverse beam direction κ1 in Figures 5A-5C and κ2 in Figures 6A-6C is determined by the location, x1, x2 in the respective illustrated cases, of the grating coupler in the “array”110 on the first axis x.

[0121] The schematic in Figure 7 shows a possible design of a chip100 with integrated photodetectors that is a frequency-multiplexed continuous-wave lidar (FMCW LiDAR) device and, in particular, is based on Silicon-on-Insulator (SSI) technology, which allows the integration of balanced photodetectors. The chip100 receives a laser light input signal500 through lens or fiber coupling, tunable to a desired wavelength. The laser light input signal500 passes through a polarization divider510 connected to an absorbing element520 (“absorber”) for light absorption and to a star coupler or divider network530 to which a plurality of optical waveguides are connected that guide the light120 to the plurality of grating couplers110, connected in turn to a series of photodetectors1100 of the on-chip balanced detector type (“on-chip balanced detector”) which at their output are connected to electrical contact pads1200, forming the FMCW LiDAR chip, whose bird's-eye view is shown in Figure 8, where the beams with different wavelengths, λ1 and λ2, transmitted to different target objects61, 62, 63 and reflected by the targets61, 62, 63 are represented.

[0123] The lidar device described above can be made with different types of lenses: cylindrical lens, Fresnel lens, metamaterial lens, or a diffractive optical element (DOE) system.

[0125] Regarding the position of the lens system10 with respect to the chip100, there are three distinct situations: i) lens system10 incorporated on top of the chip100, ii) lens system10 incorporated below the chip100 of the device, and iii) lens system10 integrated into the chip100 of the device (i.e., the lens is part of the chip itself). Examples of these positions can be seen in Figures 9A-9F. The lens or lens system10 can be incorporated into the chip100, placing the lens system10 either on the upper/front face of the chip100 as shown in Figures 9A and 9B, or on the lower/rear face of the chip100 as shown in Figures 9C and 9D, and different types of lenses can be applied to both the upper and lower parts of the chip100: for example, a cylindrical or refractive lens system or lens811, 812 represented in Figures 9A and 9B, or a Fresnel lens system, metamaterial lens, or diffractive optical element system821, 822 represented in Figures 9C and 9D. And the lens system10 can also be integrated into the back of the chip100, as shown in Figures 9E and 9F, respectively for cylindrical lens813 and for Fresnel lens, metamaterial lens or DOE823.

[0127] Figure 10 is a graph that represents the divergence angleξ as a function of the LGC length of the grid coupler110 measured in micrometers, µm.

[0129] Figures 11A and 11B describe the structure of the waveguide120 respectively in the direction of the first axis and in the direction of the third axis. The waveguide120 comprises two layers, 702 and 704, of Silicon, Si, between which there is an intermediate layer703 of silicon oxide, SiO2. Figure 11B further shows how the light beam700 is incident, through the air701, on the upper layer702 of the waveguide120.

[0131] For this particular waveguide structure120prepresented in Figure 11 as described above, as can be seen in the following graphs in Figures 12 and 13, a maximum tilt angleθ of ±14º results in a beam deflection angleκ in the x-direction of ±50º, and a change in the input light wavelengthλ of 300 nm results in a beam deflection angleφ in the third axis z-direction, which has a value of 40º.

[0133] Figure 12 is a graph representing the beam deviation angle κ in the transverse plane in the direction of the first axis x as a function of the grating tooth inclination angle θ. Figure 12 shows the simulation results of this transverse angle of the light emitted by the grating coupler κ, where it can be seen that by inclining the grating coupler teeth by up to 14 degrees, the emitted beam can be directed to an angle of 50 degrees.

[0134] Figures 13A and 13B show the beam deflection angle φ in the z direction when the wavelength of the input light is changed for two values of the tilt angle θ that is held fixed, θ = 0º in Figure 13A and θ = 10º in Figure 13B of the grating teeth210.

[0136] Figure 14 shows the parameter details of an example implementation of the lens system10 which in this case is a commercial cylindrical lens used in the integrated chip design100.

[0138] Figures 15A, 15B, and 15C show, for three different beam tilt angles κ (κ = 0°, κ = -10°, and κ = -20°), the simulation results of the focusing properties (amplitude and phase distribution) of light from the cylindrical lens comprising the on-chip lens system 10 along its cross-section STx when a plane wave enters said cylindrical lens. From this type of simulation, the locations x and widths wGC of all the grid couplers in the array 110 can be recovered. The phase slope is used to determine the tilt angles θ of the grid coupler teeth 210.

Claims (7)

1. CLAIMS 1. An optical beam transmitter and detector device, characterized in that it comprises the following components integrated within a photonic chip (100), having an upper face and a lower face, for receiving an input light signal from a lens system (10) with a transmission angle and wavelength (λ, λ<1>, λ<2>) arranged above the upper face of the chip (100) or below the lower face of the chip (100): - a plurality of grid couplers (110) aligned on the top face of the chip (100), each grid coupler (110) constructed with a length (L<GC>) in a waveguide (120) and with a plurality of teeth (210), and each tooth (210) inclined with an inclination angle (θ) equal to the transmission angle of the lens system (10), and the plurality of teeth (210) of each grid coupler (110) arranged with a fixed tooth width (Ʌ) equal for all teeth (210) and a space (ε) between teeth (210), each grid coupler (110) being apodized along its length (L<GC>) varying the spacing (ε) between teeth (210) gradually to emit a constant amount of light per unit length; where each waveguide (120) is configured to guide the incoming light signal within the chip (100) to each grating coupler (110) which produces a beam with a first deflection angle (κ) determined by the tilt angle (θ) and a second deflection angle (φ) determined by the wavelength (λ) of the incoming light, the beam produced to transmit or receive through the lens system (10), and where the light signal is processed exclusively in the optical domain within the chip (100), where the light signal is not converted to the analog and/or electronic domain for processing. 2. The device according to claim 1, characterized in that the chip (100) receives the input light signal from the lens system (10) comprising at least one lens which may be a cylindrical lens (811, 812, 813), a Fresnel lens, a metamaterial lens, or a system of diffractive optical elements (821, 822, 823). 3. The device according to claim 2, characterized in that the system of lenses (10) is integrated into the chip (100). 4. The device according to claim 3, characterized in that it is a lidar device. 5. The device according to claim 4, characterized in that the lidar device is time-of-flight or frequency-multiplexed continuous wave. 6. The device according to any of the preceding claims, characterized in that the chip (100) is manufactured using silicon-on-insulator technology. 7. The device according to any of the preceding claims, characterized in that the chip (100) is made of indium phosphide.