Wide angle beam steering with reduced control complexity

Abstract

The present specification provides an optical phased array comprising photonic elements for on-chip beam formation and steering and adapted to use at least one electrically modulated optical phase shift control element to direct the direction of an output light field of an emitted beam having a wavelength range covering the visible to short wave infrared region. The photonic elements include simultaneously modulated, monotonically varying, optical phase shifters that are independently located above, below, or otherwise integrated into each optical waveguide connected to the beam emitter. The optical phased arrays function in lidar systems and transceivers.

Description

Field

[0001] The present invention relates to the steering of a light beam (e.g., light), and more particularly to an optical phased array that uses a control system with significantly reduced complexity to steer a light beam. Background

[0002] Non-guided signal transmission - i.e., signal propagation without being physically guided in a solid medium - is complementary to signal transmission through a bounded medium, especially in cases where establishing a physical channel for guided signal transmission would be prohibitively costly (e.g., in undeveloped areas), and where signal access or transmission to the area to be reached is inconvenient or impossible. Such unbounded transmission can generally be divided into mechanical waves (e.g., acoustic / sound waves) and non-mechanical waves (e.g., electromagnetic waves). The choice of the type of signal to be transmitted depends to a large extent on the environmental conditions and the application. For example, sound waves (instead of radio waves) are used in the ocean where there is a large amount of ionized water because they have a relatively high volumetric mass density (thus enabling relatively efficient transmission) and are not significantly impeded by the ionized charges in the medium.

[0003] However, signal transmission in air - where the volumetric mass density is significantly lower - requires the signal to have a low attenuation within the defined propagation distance in the medium, such as electromagnetic waves. Although radio waves and light waves are both electromagnetic waves in the wavelength ranges of ~ meters (m) and ~ micrometers (μm) respectively, light waves with an infrared (~1.55 μm) wavelength are preferred when high data transmission rates are required (e.g., ~ gigabytes per second (Gbps) in a LiFi (Light Fidelity) system) or a detailed map of the surrounding environment is needed (e.g., ~ millimeter (mm) resolution at a distance of ~ meters in a lidar system).

[0004] In applications of non-guided optical signal transmission, it is not only important to accurately direct a light beam to a predetermined position, but also to actively direct the light beam in different directions. For example, a lidar system for determining the extent of a structural area must be able to actively direct the light beam to different points in the area to be mapped. Methods for directing a light beam include mechanically changing a structure with specific optical properties (e.g., in an optical microelectromechanical systems (MEMS) system), changing the material structure properties (e.g., in a liquid crystal), and adjusting the optical properties of a material (e.g., using a vertical cavity surface emitting laser). A more common method for achieving on-chip light beam steering through optical property modulation is to control the light amplitude and / or light phase of the light waves from an array of light beam scatterers. Light beam steering in such an "optical phased array" (OPA) is typically achieved by inducing a refractive index shift in the optical waveguide leading to and / or near the light beam scatterer.

[0005] Traditionally, optical phased arrays have required complex control systems - each emitter (in the form of a scatterer) individually requires a control element. Considering that the degree of beam directivity (i.e., the field of view or angular range) is directly determined by the number of emitters in the optical phased array, the number of control elements in an operating optical phased array can be very large. There have been attempts to alleviate the unwieldy dependence on a large number of beam steering control elements in optical phased arrays. Examples of such attempts include simultaneously heating optical waveguides leading to beam emitters with a single voltage source. For example, Acoleyan K.V. et al. reported in the academic journal Optics Letters, Volume 34, Issue 9 (2009), pages 1477 - 1479, the use of a single voltage source to control beam steering by simultaneously heating an array of optical waveguides using a heating element in the form of an indium tin oxide / aluminum gallium arsenide Schottky junction, which is arranged in a serpentine shape on the optical waveguide array and has a linearly tapered length. However, due to thermal crosstalk, i.e., the waveguide experiences a temperature gradient due to the inflow of heat from nearby heat sources (e.g., heat sources above adjacent waveguides), heating on the optical waveguide introduces an unnecessary degradation in steering performance (e.g., field of view). In addition, as the resistance (which causes heat generation) increases with the addition of bent segments, the heat generation efficiency is higher at the edges of the waveguide array (where the bent structures are mainly concentrated), but at the cost of non-uniform heat distribution along each waveguide (resulting in reduced predictability), thereby reducing the accuracy of heating control. Given that optical phased arrays mainly rely on regular optical phase shift differences, they are very sensitive to optical phase shift difference mismatches. Therefore, the lack of precise heating control ability in the heating system may be the reason for the relatively small steering angle (less than 10°), for example, only a 2.3° deflection angle was achieved in the study by Acoleyan K.V. et al.

[0006] There is a desire to provide a cleverly designed improved photonic element that has both reduced optical phase shift control complexity and an enhanced field of view. Summary

[0007] According to a first aspect, there is provided an optical phased array comprising a photonic element for on-chip beam formation and steering and adapted to use at least one electrically modulated optical phase shift control element to direct the output optical field of an emitted beam, the wavelength range of the emitted beam covering the visible to short-wave infrared region. The photonic element includes simultaneously modulated optical phase shifters with monotonically varying sizes, which are independently located above, below, or otherwise integrated into each optical waveguide connected to a beam emitter. The optical phased array functions in lidar systems and transceivers.

[0008] Thus, an optical phased array (OPA) comprises: A photonic component for on-chip beam forming and steering, the photonic component comprising: A multi-row optical phase shifter, the size of the optical phase shifter varying monotonically row by row, and the multi-row optical phase shifter being operatively configured to simultaneously modulate the optical phases of optical fields in a plurality of optical waveguides, wherein each of the optical phase shifters passes through at most one of the plurality of optical waveguides.

[0009] In some embodiments of the first aspect, the optical phased array further comprises: at least one electrical control element operatively configured to control at least some of the rows of the multi-row optical phase shifter, wherein the number of the at least one electrical control element is less than the number of rows of the multi-row optical phase shifter.

[0010] In some embodiments of the first aspect, the optical phased array further comprises: a plurality of optical splitters having a plurality of optical splitter outputs operatively coupled to the multi-row optical phase shifter, the plurality of optical splitters being operatively configured to produce the plurality of optical splitter outputs with no optical amplitude difference or a negligible optical amplitude difference and no optical phase difference or a negligible optical phase difference.

[0011] According to a second aspect, there is provided a method for operating an optical phased array, the optical phased array comprising a photonic component for on-chip beam forming and steering, the method comprising: Controlling the beam in a steering direction of a propagation direction of an optical field in an azimuth-pointing optical waveguide by: Simultaneously modulating the optical phases of the optical fields in the plurality of optical waveguides by a multi-row optical phase shifter, the plurality of optical waveguides being operatively coupled to a plurality of beam emitters that generate a beam, wherein the size of the multi-row optical phase shifter varies monotonically row by row, and each of the optical phase shifters passes through at most one of the plurality of optical waveguides.

[0012] In some embodiments of the second aspect, simultaneously modulating the optical phases of the optical fields in the plurality of optical waveguides by a multi-row optical phase shifter comprises: controlling at least some of the rows of the multi-row optical phase shifter by at least one electrical control element, wherein the number of the at least one electrical control element is less than the number of rows of the multi-row optical phase shifter.

[0013] In some embodiments of the second aspect, the method further comprises: an optical splitter having a plurality of optical splitter outputs operatively coupled to the multi-row optical phase shifter, with no optical amplitude difference or a negligible optical amplitude difference and no optical phase difference or a negligible optical phase difference between the plurality of optical splitter outputs.

[0014] From the foregoing specification and the more detailed description of various embodiments below, it will be apparent to those skilled in the art that the present invention provides a significant advancement in the technology of optical phased arrays. Of particular importance in this regard is the potential provided by the present invention for wide field of view (large angular steering angle) control using simultaneously modulated optical phase shifters. Additional features and advantages of the various embodiments will be better understood from the detailed description provided below. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram showing the use of an optical phase shifter to direct a light beam according to certain embodiments of the present specification, by synchronously modulating the optical phase of the light field in a waveguide along a row of an optical phased array using fewer than M (≤M) electrical control elements connected to the phase shifter, where M is the total number of rows of the optical phase shifter rows.

[0016] Figure 2 A schematic diagram showing the use of an optical phase shifter to modulate the optical phase of the light field in a waveguide along a row of an optical phased array according to certain embodiments of the present specification.

[0017] Figure 3 A schematic diagram showing the use of an optical phase shifter to modulate the optical phase of the light field in a waveguide along a row of an optical phased array at the position of the last column according to certain embodiments of the present specification to determine the optical phase difference relative to an adjacent waveguide schematic diagram.

[0018] Figure 4 A schematic diagram showing the use of an optical phase shifter to modulate the optical phase of the light field scattered out of the plane by a light beam emitter located n columns after the optical phase shifter according to certain embodiments of the present specification and accordingly adjust the direction θ of the emitted light beam on the y-axis y schematic diagram.

[0019] Figure 5 A schematic diagram showing the use of a set of electrical control elements connected to the phase shifter in an example of a model in Figure 1 to direct a light beam by synchronously modulating the optical phase of the light field in a waveguide along a row of an optical phased array using a column of optical phase shifters.

[0020] Figure 6 A table showing a partial isometric schematic view of an optical splitter ( Figure 6 a multimode interferometer (MMI) optical splitter and a Y-branch splitter in two examples of a model in) according to multiple embodiments of the present specification.

[0021] Figure 7 A schematic diagram showing according to multiple embodiments of the present specification Figure 7Table of partial isometric schematic views of optical phase shifters (metal thermo-optic phase shifters, highly doped semiconductor thermo-optic phase shifters, and phase shifters based on the plasma dispersion effect of doped semiconductors) in the models of the four examples

[0022] Figure 8 Shows the phase shift of the metal thermo-optic phase shifter as shown in an embodiment of the present specification Example experimental measurement graph related to the length of the modulation element (metal heater)

[0023] Figure 9 Shows the phase shift of the pn-doped optical phase shifter according to an embodiment of the present specification Example numerical simulation graph related to the length of the modulation element (doped region)

[0024] Figure 10 Table showing schematic diagrams of optical phase shifters (thermo-optic type and pn-doped type) with monotonically varying lengths as shown in certain embodiments of the present specification. The length of the optical phase shifter varies monotonically such that the optical phase shifter can synchronously modulate the optical phase of the optical field in the waveguide along the rows of the optical phased array using a set of electrical control elements connected to the phase shifter.

[0025] Figure 11 Shows experimental characteristic graphs of the thermal crosstalk generated by the optical phase shifter at different physical distances between the thermo-optic heater and the adjacent waveguide in multiple embodiments of the thermo-optic phase shifter according to the present specification.

[0026] Figure 12 Is a table comparing the optical phase difference of the input optical field sent to the waveguide (i.e., the optical phase in the y direction ) When different, the polar plots of the far-field intensity generated with respect to the azimuth angle and the zenith viewing angle can be adjusted using a phase shifter located on or otherwise integrated into the waveguide of the beam emitter of the optical phased array.

[0027] Figure 13 Table showing schematic diagrams of different examples of the optical phase compensation element 190 according to multiple embodiments of the optical phase compensation element

[0028] Figure 14 Shows the flowchart 1400 describing a method of operating an optical phased array including photonic elements for on-chip beam forming and steering.

[0029] It should be understood that the drawings are not drawn to scale and present only simplified representations of the various features that illustrate the basic principles of the present invention. The specific design features of the optical phased array disclosed in this specification, including, for example, the specific dimensions of the optical phase shifters, will be determined in part by the particular intended application scenario and usage environment. To provide a clear understanding, some features of the illustrated embodiments are enlarged or distorted relative to other features. In particular, thin features may be thickened, for example, for clarity of illustration. Unless otherwise specified, all dimensions, directions, and positions mentioned are with reference to the directions shown in the drawings. Detailed Description of Embodiments

[0030] It should be understood that the articles "a," "an," and "the" used in reference to a feature or element include a reference to one or more of the features or elements. The term "and / or" includes any and all combinations of one or more of the associated features or elements. The terms "comprising," "including," "having," and any related terms used in the specification and claims are open-ended, meaning that other features or elements may exist in addition to the listed features or elements. Identifiers such as "first," "second," and "third" are used only as labels and are not intended to impose a numerical requirement on their objects nor to be understood as imposing any relative position or temporal order between them. The term "to" may include a reference to "configured to," "adapted to," and "constructed and arranged to," which may be used interchangeably.

[0031] The terms "coupled" and the phrase "operably coupled" can be used to include a reference to an operational meaning and can also include, but are not limited to, direct or indirect physical, optical, and / or electrical connections or couplings. Thus, for example, two devices can be directly coupled or connected, or they can be indirectly coupled or connected through one or more intermediate devices. Based on this specification, those of ordinary skill in the art will understand the various ways of coupling as defined above. The terms "coupled" and "connected" can be used interchangeably. The term "operable" includes a reference to the term "operability."

[0032] The terms "dimension," "direction," and "axis" can be used interchangeably.

[0033] For those skilled in the art, that is, those with knowledge or experience in this technical field, it is obvious that the optical phased array (OPA) disclosed in this specification can have various uses and design variations. The following detailed discussion of various alternative features and embodiments will illustrate the general principles of the present invention with reference to an optical phased array that uses a control system with significantly reduced complexity to simultaneously modulate the beam steering angle and simultaneously provide a wide field of view. This is in sharp contrast to traditional optical phased arrays that use optical phase shifters scaled with the number of beam emitters and optical phased arrays that simultaneously control optical phase shifters with a limited beam steering angle (less than 10°). The optical phased array disclosed in this specification can be used as a beam steering system. For example, the system can be part of a lidar (LiDAR) system or a free-space transceiver; it can also be used as a transmitter and a receiver. Considering the beneficial effects of this specification, other embodiments applicable to other applications will be obvious to those skilled in the art.

[0034] Figure 1A schematic diagram of an optical phased array (OPA) 100 is shown, which shows a schematic diagram of using an optical phase shifter to direct a light beam according to certain embodiments of the present specification. By using fewer than M (≤M) electrical control elements connected to the phase shifter, the optical phase of the light field in the synchronous modulation waveguide along the row of the optical phased array is adjusted. The optical phased array includes an array of operably coupled photonic elements formed in rows, which has multiple rows (M≥1) of beam emitters 121 generally adjacent to or embedded in the sidewalls of the waveguide 110. The beam emitters 121 are operably coupled to at least one column (N≥1) of optical phase shifters 141 generally adjacent to (below, above, on one side or the other side of) the waveguide 130 or otherwise integrated into the waveguide 130 (or embedded in the waveguide 130), and the optical phase shifters 141 are configured to be electrically modulated by fewer than M (≤M) electrical control elements 151. In other words, the number of electrical control elements is less than or equal to the number of rows of the optical phase shifters 141. The electrical control elements can be incorporated into the optical phased array or located outside the optical phased array. The optical phased array is capable of directing the light beam to a dimension different from the x-dimension of the propagation direction (azimuth angle) of the light field along the waveguide. The above different dimension is generally referred to as the y-dimension (i.e., at a 90° azimuth angle to the x-dimension). At least one optical phase shifter 141 (forming the array 140) is adjacent to or otherwise integrated into at least one waveguide 130, the waveguide 130 is operably coupled to the waveguide 110, and a plurality of beam emitters 121 (in the form of optical scatterers) are positioned at the periodic points 111 of the waveguide 110 along the waveguide 110. Each optical phase shifter 141 forming part of the array 140 is configured to modulate the optical phase of the light field in the waveguide 130. The optical phased array can be scaled up to have any number of M optical waveguides. Each of the M optical waveguides 130 is configured to receive the light field propagating into m of the M optical waveguides 110. The subscripts m and n respectively represent the array rows and columns of the optical phase shifters 141. In one embodiment, each column can include the same type of optical phase shifter. Optionally, each optical phase shifter can be formed as a different layer. In addition, the optical phase shifters can include different materials.

[0035] Advantageously, such photonic components in an optical phased array can be implemented entirely on-chip using standard fabrication techniques (e.g., lithography and deposition) and standard photonic materials (e.g., including but not limited to silicon (Si), silicon nitride (Si3N4), germanium (Ge), lithium niobate (Li3NbO3), barium titanate (BaTiO3), and indium phosphide (InP)). Optionally, the wavelength of the input optical field can be in the short-wave infrared region of the electromagnetic spectrum, e.g., 1.4 μm to 1.7 μm. Depending on the application of the photonic component, visible light wavelengths (0.38 μm to 0.75 μm) and near-infrared wavelengths (0.75 μm to 1.4 μm) can also be used. One or more (≤M) electrical connections can be provided to the optical phase shifter. Additionally, in a lidar (LiDAR) system, the controller can be adapted to work with an array 140 of optical phase shifters 141 that are adjacent to or otherwise integrated into at least one waveguide 130, receive the emitted optical field reflected from an object, and, in combination with a processor, calculate information related to the surface characteristics of the object based on the scattered and reflected light received by the waveguide.

[0036] The waveguide (which is operatively coupled to 110, 130, and the optical splitter tree 160) can be circular or rectangular (rib or ridge type) with an elongated top surface and sidewalls extending from the top surface. The refractive index of the waveguide core can be greater than that of the surrounding waveguide cladding. The waveguide cladding can include a lower cladding and an upper cladding. The waveguide can be any of several different types of waveguides. For example, the waveguide can be a waveguide based on total internal reflection (which constitutes the vast majority of optical waveguides conventionally used in integrated photonics), a slot waveguide, or a surface plasmon polariton waveguide. Alternatively, in-plane scattering waveguides can be used, such as waveguides formed by photonic crystals (which also use total internal reflection) and metamaterials. The composition of each of the plurality of waveguides can be, for example, at least one of the following: silicon (Si), silicon dioxide (SiO2), barium titanate (BaTiO3), lithium niobate (Li3NbO3), indium phosphide (InP), III-V compounds, II-VI compounds, and polymers. Each of the plurality of waveguides can be doped with p-type or n-type materials. The waveguide can support any optical waveguide mode, such as the transverse electric mode and the transverse magnetic mode. The scatterer / emitter 121 can be a Mie scatterer or a Rayleigh scatterer. More specifically, Mie scattering mainly refers to the scattering of the light field by a scatterer whose diameter, width, or diagonal is typically close to the wavelength of the incident light field, while in Rayleigh scattering, the diameter, width, or diagonal of the scatterer is at most one-tenth of the wavelength of the incident light field. For example, the composition of each of the plurality of scatterers can include, for example, at least one of the following: silicon (Si), silicon dioxide (SiO2), barium titanate (BaTiO3), lithium niobate (Li3NbO3), indium phosphide (InP), III-V compounds, II-VI compounds, and polymers. Each of the plurality of scatterers can also be doped with a positively charged dopant (p-type material) or a negatively charged dopant (n-type material). Types of positively charged dopants include, for example, boron, gallium, and aluminum; while types of negatively charged dopants include, for example, arsenic, phosphorus, and antimony. Each of the plurality of scatterers can be embedded in the corresponding waveguide, and / or each of the plurality of scatterers can be in contact with the top wall or sidewall of the corresponding waveguide.

[0037] Figure 2 A schematic diagram shows multiple columns (N) of optical phase shifters on m rows according to an embodiment of the present invention. Each row includes at least one optical phase shifter 141 configured to shift the optical phase of the light field in the waveguide 130. The optical phase shifter is placed at point 131 on the waveguide 130. Each optical phase shifter 131 is configured to shift the optical phase of the light field in the waveguide (by an offset of ) and cause a loss of a portion of the light field in the waveguide (with a loss coefficient of γ m,n) where a represents the amplitude of the optical field before passing through the optical phase shifter. Each m out of the M waveguides 130 are configured to receive an optical field with a wavelength of λ0, which can be represented using the plane-wave approximation as where a and represent the amplitude and phase of the optical field sent to each waveguide, respectively. The subscripts m and n again represent the rows and columns of the array of phase shifters in 140, respectively.

[0038] Figure 3 shows a schematic diagram similar to Figure 2 but shows multiple rows of the optical phased array on the last column (n = N) according to an embodiment of the present invention. Each column includes an array 140 of a plurality of optical phase shifters 141 configured to shift the optical phase of the optical field in the waveguide 130 to define an optical phase difference between adjacent optical waveguides The waveguide 130 is connected to the waveguide 110 perturbed by a plurality (120) of scatterers 121 (see Figure 4 ). Each scatterer 121 causes an evanescent coupling 170 of a part of the optical field in the waveguide 130 (see Figure 4 ), and is scattered out of the plane 180 in the y dimension. The subscripts m and n represent the rows and columns of the phase shifters in the array 140, respectively.

[0039] Figure 4 summarizes the beam steering function of the optical phased array and shows a schematic diagram showing the optical phase of the optical field in the waveguide 130 operably coupled to the waveguide 110 being shifted by the optical phase shifter 141 according to an embodiment, causing the optical field to undergo evanescent coupling 170 and be scattered out of the plane 180 by the scatterer 121, thereby regulating the direction of the scattered beam in the θ direction on the y-axis for m rows y The subscripts m and n represent the rows and columns of the phase shifters in the array 140, respectively. λ eff,fs , and d y are the effective wavelength of the optical field in free space, the optical phase difference of the optical field at the scatterer (in the y direction), and the scatterer spacing (in the y direction), respectively. a' is the approximate amplitude of the optical field scattered out of the plane from each scatterer.

[0040] The beam directivity (or beam steering angle) θ of the optical phased array, which is a function of the emitter spacing d (i.e., the distance between the centers of adjacent scatterers acting as emitters), can be designed according to the following equation: where, λ eff,fs = λ0 / n eff,fs is the effective wavelength of the optical field in free space, λ0 is the wavelength of the optical field, neff,fs is the effective refractive index of the medium in free space, and is the optical phase difference of the optical field at the emitter / scatterer 121.

[0041] The optical phase of the optical field in the waveguide 130 determines the directivity of the light beam in the y-direction / dimension, which can be changed by changing the refractive index of the waveguides in the array. The optical phase shifter can include any of the phase shifters based on the thermo-optic effect, plasma dispersion effect, electro-optic effect (e.g., Pockel’s effect), microelectromechanical (MEMS)-regulated evanescent field perturbation (changing the effective refractive index of the optical phased array waveguide), or material structure change (e.g., liquid crystal, ferroelectric, and phase change materials). The thermo-optic phase shifter can include a metal heater, alloy heater, ceramic heater, or highly doped semiconductor heater; the doped phase shifter based on the plasma dispersion effect can include pn-doped or pin-doped semiconductors; the phase shifter based on the electro-optic effect can include a modulator based on the Pockel’s effect, e.g., lithium niobate (Li3NbO3) and barium titanate (BaTiO3), or a modulator based on the Kerr’s effect; the photonic MEMS switch phase shifter can include an MEMS switch that introduces a change in the evanescent field perturbation to change the effective refractive index of the optical phased array waveguide; the phase shifter based on the material structure change can include liquid crystal, ferroelectric, or phase change materials. Depending on the needs of a specific intended function, the phase shifters that change the refractive index of the waveguides in the optical phased array can be the same or different from each other. The change in the refractive index can be advantageously induced, for example, by electrically heating the waveguide (through the thermo-optic effect), electrically changing the spatial carrier concentration in a doped semiconductor waveguide (changing the refractive index and absorption of the phase shifter through the plasma dispersion effect), and electrically changing the birefringence of the waveguide (through the electro-optic effect). The heating of the waveguide, the change in the spatial carrier concentration, and the change in the optical birefringence can be introduced by applying a voltage to the thermo-optic phase shifter (which can be a metal, ceramic / alloy, e.g., indium tin oxide, or a highly doped semiconductor heater near the waveguide), by using a doped / ion-implanted semiconductor region extending along the waveguide (hereinafter referred to as the doped semiconductor phase shifter), or by applying a voltage to the electro-optic phase shifter (formed using a material with a high electro-optic coefficient, e.g., a material exhibiting the Pockel’s effect). The metal heater can be constructed using a material with a high thermo-optic coefficient, including but not limited to titanium nitride (TiN), nickel-chromium alloy (NiCr), and the doped semiconductor heater can include a semiconductor material heavily doped with a positively charged (p++) or negatively charged (n++) dopant. For the n++ heater, the doping concentration of the heavily doped heater region can be N a ~10 20 cm -3 and, for the p++ heater, the doping concentration can be N d ~1020 cm -3 Alternatively, a phase shifter based on the plasma dispersion effect may include a pn-doped or pin-doped semiconductor. The doping concentration of the doped semiconductor region based on the plasma dispersion effect may be N for the n-type doped region a ~10 17 to 10 18 cm -3 and may be N for the p-type doped region d ~10 17 to 10 18 cm -3 。The doping on the waveguide that realizes the change in the spatial carrier concentration in the waveguide can be formed using a pn junction or a pin junction. A pn junction refers to a junction where a region implanted with a positively charged dopant (p-type doped region) in the waveguide is adjacent to a region implanted with a negatively charged dopant (n-type doped region), while a pin-junction is a junction having a p-type doped region adjacent to an undoped region (or "intrinsic" region) adjacent to the n-type doped region. A phase shifter based on the electro-optic effect can be constructed using materials with a high electro-optic coefficient, such as lithium niobate (Li3NbO3) and barium titanate (BaTiO3). In some embodiments, each thermo-optic heater includes a doped region with a doping concentration of at least 10 19 cm -3 order of magnitude.

[0042] The optical phase shifter 141 may not extend along the entire length of the waveguide 130. Changing a portion of the segment to which the phase shifter extends can modify the desired optical phase shift, thereby generating an optical phase shift region in each segment.

[0043] Figure 5 Shows an example of the use of a set of electrical control elements of a phase shifter in a model connected to Figure 1 in, thereby using a column of optical phase shifters to synchronously modulate the optical phase of the optical field in the waveguide along the rows of the optical phased array to direct the schematic diagram of the light beam.

[0044] Figure 6 Shows an optical splitter 161 according to multiple embodiments of the present specification ( Figure 6Table of partial isometric schematic views of multimode interferometer (MMI) optical splitters 165 and Y-junction splitters 166 in the models in two examples. The optical splitter divides the optical field into two optical splitter outputs on average, and there is no optical amplitude difference or a negligible optical amplitude difference between these two outputs, and there is no optical phase difference or a negligible optical phase difference. Although the multimode interferometer splitter 165 has better process tolerance and generally has a shorter length compared to the Y-junction splitter 166, the multimode interferometer splitter 165 is generally sensitive to wavelength. The optical splitter can be adapted to be used in the optical phased array 100 to form an optical splitter tree 160, which is formed by cascading the optical splitter 161 multiple stages to provide M optical fields with equal amplitudes and advantageously with equal optical phase differences. For example, three-stage, four-stage, and five-stage optical splitter trees will respectively generate M = 2 3 、M = 2 4 and M = 2 5 equi-amplitude optical fields. The optical phased array 100 can include an optical splitter tree to generate M optical fields (instead of directly guiding M optical waveguides to the optical phased array 100). Since the optical field is usually prone to optical phase fluctuations before being optically coupled to on-chip devices (such as the optical phased array 100), this is not ideal because the beam steering angle of the optical phased array 100 is a direct function of the optical phase difference of the optical field relative to the beam emitter 121. By using the optical splitter tree, the optical phase of each corresponding optical field output by the splitter tree can be advantageously locked to ensure a reliable beam steering optical phased array device 100.

[0045] Figure 7 Shows different optical phase shifters according to multiple embodiments of this specification ( Figure 7 In four examples, the metal thermo-optic phase shifters 135 and 136 located above and below the optical waveguide 211 respectively (which can seamlessly extend to the outer plate region 212 in the rib waveguide), the highly doped semiconductor thermo-optic phase shifter 137, and the pn-doped semiconductor phase shifter 138, which are related to Figure 1Table of partial isometric schematic views corresponding to the optical phase shifters shown therein. For example, according to one embodiment of the optical phased array, the optical phased array 100 may include multiple rows (M rows) of metal thermo-optic phase shifters (135 and / or 136) adjacent to or otherwise integrated into the total internal reflection-based waveguide 130 formed of Si3N4. The thermo-optic phase shifter 135 (an example of the optical phase shifter 141) including the titanium nitride (TiN) thermo-optic heater 215 (above or inside the upper cladding 213) is configured to modulate the optical phase of the optical field in the waveguide 130, while the thermo-optic phase shifter 136 (also an example of the optical phase shifter 141) including the titanium nitride (TiN) thermo-optic heater 215 (below or inside the lower cladding 214) is configured to modulate the optical phase of the optical field in the waveguide 130. The waveguide cladding may include the lower cladding 214 and the upper cladding 213. The heater is configured to heat the waveguide, thereby modulating the refractive index of the waveguide such that the optical phase difference of the optical field is shifted between the waveguide 130 and the waveguide 110, wherein the beam emitter 121 is typically located near or embedded in the waveguide sidewall. The shift of the optical phase difference in turn steers the beam in the y direction. Each thermo-optic heater 215 may be coupled to a metal structure (on an adjacent layer) and electrically connected to another metal structure (on the top layer) through an electrical via. Advantageously, the heating of the thermo-optic heater can be introduced by applying a voltage to the pad electrically connected to the metal structure.

[0046] The thermo-optic phase shifter 137 may include an n++ (heavily doped, e.g., acceptor concentration N a = 1x 10 20 cm 3 ) doped (ion implanted) thermo-optic heater 216 to modulate the optical phase of the optical field in the waveguide 130. The waveguide cladding may include the lower cladding 214 and the upper cladding 213. The heater is configured to heat the waveguide, thereby modulating the refractive index of the waveguide such that the optical phase difference of the optical field is shifted between the waveguide 130 and the waveguide 110, wherein the beam emitter 121 is typically located near or embedded in the waveguide sidewall. The shift of the optical phase difference in turn steers the beam in the y direction. Each thermo-optic heater 216 may be electrically connected to a metal structure (on the bottom layer) and electrically connected to another metal structure (on the top layer) through an electrical via. Advantageously, the heating of the thermo-optic heater can be introduced by applying a voltage to the pad electrically connected to the metal structure.

[0047] The optical phase shifter 138 may include a pn junction (p-type doped regions labeled 217 and 219, n-type doped regions labeled 218 and 220; an inner rib region and an outer plate region of the waveguide for forming the phase shifter respectively) configured to modulate the optical phase of the optical field in the waveguide 130. The voltage applied across the pn junction forming the optical phase shifter 141 introduces a plasma dispersion effect in the waveguide 130 at 131, thereby modulating the refractive index of the waveguide, such that the optical phase difference of the optical field is shifted between the waveguide 130 and the waveguide 110, where the beam emitter 121 is typically located near or embedded in the waveguide sidewall. The shift of the optical phase difference in turn steers the beam in the y direction. The doped semiconductor waveguide outer plate regions 219 and 220 may be connected to a metal structure (on the bottom layer) and electrically connected to another metal structure (on the top layer) through electrical vias. Advantageously, by applying a voltage to the pads electrically connected to the metal structure, a plasma dispersion effect can be introduced from the doped semiconductor waveguide outer plate regions 219 and 220.

[0048] The optical phase shift caused by the optical phase shifter for beam steering varies depending on the design parameters. For a thermo-optic phase shifter, the optical phase shift depends on the temperature coefficient dn / dT of the waveguide material and the length L of the heated waveguide region. The induced optical phase shift can be conveniently described as a function of the waveguide temperature increase ΔT and the effective wavelength λ of the optical field in the waveguide eff,wg of: For example, to use ΔT = 50K (or 50 °C) to cause a 2π phase shift in the case of parameters dn / dT = 3.3×10 -4 K -1 and λ eff,wg ≈ 1μm, the estimated length L of the thermo-optic phase shifter is approximately 60μm. Figure 8 An embodiment of a metal thermo-optic phase shifter according to this specification is shown. When modulated at a constant voltage, the phase shift of the metal thermo-optic phase shifter (150μm to 300μm in the model example of the thermo-optic phase shifter 135 in Figure 7 ) is an exemplary experimental measurement graph with respect to the length of the modulation element (a TiN metal heater with a width of 2μm and a thickness of 120nm), where there is a 2μm silica (SiO2) upper cladding gap between the metal heater and the optical waveguide. For a doped semiconductor optical phase shifter based on the plasma dispersion effect, the optical phase shift depends on the doping concentration on the waveguide forming the phase shifter. For a doped semiconductor optical phase shifter based on the plasma dispersion effect, the optical phase shift depends on the doping concentration on the waveguide forming the phase shifter.

[0049] Figure 9shows, according to an embodiment of the present specification, the phase shift of voltage and length of the modulation element (doped region) of a pn-doped optical phase shifter (from 0 to 6 mm in the model example of the pn-doped optical phase shifter 138 at Figure 7 obtained using the Silvaco simulation software tool in the range of 0 to 5V). This is an example diagram of numerical simulation. In the simulation embodiment, on an optical waveguide with a height of 0.22μm, the doping concentrations of acceptor N a and donor N d are N a =N d =3x10 18 cm -3 . The optical waveguide is partially etched to a plate height of 90nm. The simulation results show that the optical phase shift has a linear relationship with the physical length of the modulation element, and the optical phase modulation efficiency is 1.494 V·cm.

[0050] Advantageously, the optical phase modulation elements of the optical phase shifters 141 in the optical phased array 100 (e.g., the heaters in thermo-optic phase shifters and the doped regions of pn phase shifters) can be implemented with a constant physical thickness and physical width (thus having a constant physical area A). In order to maintain a constant optical phase shift on the rows of the optical phased array through the phase modulation elements independently formed but simultaneously modulated on the m rows of the optical phased array According to an embodiment of the present invention, the length L of the modulation element can vary monotonically. For example, according to an embodiment of the present invention, the monotonic variation can be a non-linear variation. The non-linear variation can refer to reciprocal or other variations. For example, according to an embodiment of the present invention, in a thermo-optic phase shifter, L can vary reciprocally or substantially reciprocally between the m rows of the optical phased array. Given that thermal energy is proportional to the temperature change (i.e., E thermal = mass × specific heat capacity × ΔT), it can be derived from formula (2) that: In a thermo-optic phase shifter, electrical energy E electric is used to heat the phase shifter and cause an optical phase shift Since E electric is directly converted into E thermal in the heater forming the thermo-optic phase shifter, the relationship provides an overall reciprocal relationship between the induced optical phase shift and the physical length L of the heater in the thermo-optic phase shifter: where E thermalwhere \(P\) is the thermal power, \(\Delta t\) is the time period of power supply, \(V\) is the voltage, \(R\) is the resistance, and \(\rho\) is the resistivity of the material constituting the heater. In another embodiment, according to an embodiment of the present invention, in a pn-doped phase shifter, \(L\) can vary linearly or substantially linearly between \(m\) rows of an optical phased array. The resulting optical phase shift and the overall linear relationship between the physical length \(L\) of the doped region in the pn-phase shifter is:

[0051] Figure 10 is a table showing a schematic top view of the length variation of the waveguide region 132 phase-modulated by the phase shifter 131 between \(m\) rows of an optical phased array for thermo-optic phase shifters 135, 136, and / or 137 and / or pn-doped optical phase shifter 138 according to various embodiments of the optical phase shifter. In contrast, the waveguide region 133 is not phase-modulated by the phase shifter 131. For thermo-optic phase shifters and pn-doped optical phase shifters, the modulation element lengths can vary non-linearly (e.g., inverse relationship \(1 / L\) m \(= 1 / L_1 + m / \Delta L\)) and linearly (\(L\) m \(= L_1 + m\Delta L\)), respectively.

[0052] Although the above embodiments provide an optical phase shifter with a monotonically varying length, it should be understood that in some other embodiments, the optical phase shifter can have a monotonically varying length, width, and / or height.

[0053] Figure 11 shows the experimental measurement results of the thermal crosstalk generated by the optical phase shifter according to various embodiments of the thermo-optic phase shifter of the present specification at different physical gaps (4 μm, 6 μm, 8 μm, 10 μm, 12 μm, and 14 μm in six distance examples of the thermo-optic phase shifter 135) between adjacent phase shifters. Advantageously, the phase shifter can achieve a sufficiently wide physical gap (e.g., 25 μm) between adjacent independently positioned phase shifters to prevent thermal crosstalk between the optical phase shifters, which enables the optical phase shift to be precisely defined to ensure wide-angle beam steering from the simultaneously modulated optical phased array 100. Advantageously, other forms of optical phase shifters (e.g., pn-doped optical phase shifters) can also be implemented using simultaneously modulated optical phase shifters 141 with monotonically varying dimensions, which are independently located above, below, or otherwise integrated into the waveguide 130 to ensure precise definition of the optical phase shift (and the resulting optical phase difference) between \(m\) rows of the optical phased array.

[0054] Figure 12is a table that compares the far - field intensity polar plots generated when the optical phase difference of the input optical field sent to the waveguide (i.e., the optical phase in the y - direction) is different. It can be adjusted using a phase shifter located on or otherwise integrated into the waveguide of the optical phased array. This specification presents different ( Figure 12 in two examples of the model of which are - 145° and 145°). According to one embodiment, a wavelength of 1.55 μm is used as the optical field, the waveguide spacing between each row is 1.5 μm, the scatterer is formed of silicon with a diameter of about 160 nm, the waveguide supports a transverse magnetic optical waveguide mode, has a width of 0.7 μm, a side - wall thickness or height of 0.22 μm, and is partially etched with a plate height of 90 nm and has an air upper cladding and a silica lower cladding. In one embodiment, an optical phase shifter 123 can be located on or otherwise integrated into each waveguide connected to the waveguide 110 for beam steering in the y - direction. Advantageously, when this configuration is obtained by simultaneously modulating (via the control element 150) the optical phase shifters 141 that are independently located above, below, or otherwise integrated into the waveguide 130 with a monotonically varying length, the control complexity of the optical phased array can be significantly reduced.

[0055] Figure 13 is a table showing schematic diagrams of different examples of an optical phase compensation element 190 (e.g., a waveguide) according to multiple embodiments of the optical phase compensation element. Advantageously, the compensation element 190 can be used to increase the gap d between the optical phase shifters on m rows A (e.g., to prevent thermal crosstalk in the thermo - optical phase shifters), while reducing the gap d between the waveguides 110 on m rows B (as well as the scatterer / beam emitter distance d y ) to expand the field of view of the optical phased array. To ensure that the optical phase difference at the waveguide 110 (and thus also the beam emitter 120) is zero before applying a voltage to the optical phase shifter, the physical length of the waveguide between two points is extended by the optical phase compensation element 190 to ensure that the optical path lengths (physical length × effective refractive index of the optical waveguide) from the optical splitter tree 160 to the front point of the waveguide 110 in row m are equal. In one embodiment, the optical path lengths from the optical splitter tree 160 to the front points of the waveguide 130 (where the array of optical phase shifters 141 is located above, below, or otherwise integrated with it) are made equal to facilitate the simultaneous modulation of the optical phase shifters 141.

[0056] According to another embodiment of the optical phased array, the optical phased array 100 may include multiple rows (M rows) of any one of several different types of optical phase shifters (metal thermo-optic phase shifter, pn-doped optical phase shifter, pin-doped optical phase shifter, doped semiconductor thermo-optic phase shifter, thermo-optic effect-based optical phase shifter). Optionally, for example, the number of rows (M) of the optical phased array 100 and the number of columns (N) of the phase shifters 140 may range from 2 to 10,000. The optical phased array 100 may be applicable to, for example, a lidar (LiDAR) system or a free-space transceiver.

[0057] Figure 14 A flowchart 1400 is shown that describes a method of operating an optical phased array including photonic elements for on-chip beam forming and steering.

[0058] In step 1402, the method includes: generating, by a plurality of optical splitters operably coupled to the multiple rows of optical phase shifters, a plurality of optical splitter outputs that have no optical amplitude difference or a negligible optical amplitude difference between different rows and no optical phase difference or a negligible optical phase difference.

[0059] In step 1404, the method includes: controlling the beam in a steering direction that is in an azimuthal relationship with the propagation direction of the optical field in the optical waveguide by: simultaneously modulating the optical phase of the optical field in the optical waveguide by the optical phase shifters, where the optical waveguide is operably coupled to a beam emitter that generates the beam, and where the size of the optical phase shifters monotonically changes row by row, with each optical phase shifter passing through at most one of the optical waveguides. The simultaneous modulation may be achieved by controlling at least a portion of the rows of the optical phase shifters by at least one electrical control element, where the number of at least one electrical control element is less than the number of rows of the beam emitter. The control by at least one electrical control element may be achieved by applying a voltage to at least a portion of the rows of the multiple rows of optical phase shifters by the electrical control element.

[0060] In step 1406, the method may optionally include equalizing the optical path lengths between the optical splitters and the beam emitters of different rows. This may be achieved by a first optical phase compensation element operably coupled between the plurality of optical splitters and the multiple rows of optical phase shifters; or a second optical phase compensation element working in cooperation with the first optical phase compensation element and operably coupled between the multiple rows of optical phase shifters and the plurality of beam emitters.

[0061] It should be understood that the above order of method 1400 may be modified or interchanged.

[0062] It will be apparent from the foregoing specification and the detailed description of certain embodiments that various modifications, additions, and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were chosen and described in order to provide the best illustration of the principles of the invention and its practical application, so that one of ordinary skill in the art could use the invention in various embodiments and various modifications suitable for the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with their fair, legal, and equitable breadth.

Claims

1. An optical phased array, characterized in that, Comprising: A photonic element for on-chip beam forming and steering, the photonic element comprising: A multi-row optical phase shifter, the size of the multi-row optical phase shifter monotonically varying row by row, the multi-row optical phase shifter being operatively configured to simultaneously modulate the optical phases of optical fields in a plurality of optical waveguides, the plurality of optical waveguides being operatively coupled to a plurality of beam emitters, wherein each of the optical phase shifters passes through at most one of the plurality of optical waveguides.

2. The optical phased array according to claim 1, wherein Further comprising: At least one electrical control element, operatively configured to control at least some of the rows of the multi-row optical phase shifter, wherein the number of the at least one electrical control element is less than the number of rows of the optical phase shifter.

3. The optical phased array according to any one of claims 1 to 2, characterized in that Further comprising: A plurality of optical splitters, having a plurality of optical splitter outputs operatively coupled to the multi-row optical phase shifter, the plurality of optical splitters being operatively configured to generate the plurality of optical splitter outputs, wherein there is no optical amplitude difference or a negligible optical amplitude difference between different rows, and there is no optical phase difference or a negligible optical phase difference.

4. The optical phased array according to claim 3, wherein Further comprising: A plurality of first optical phase compensation elements, operatively coupled between the plurality of optical splitters and the multi-row optical phase shifter, and operatively configured to equalize the optical path lengths between the optical splitters and the beam emitters of different rows.

5. The optical phased array according to claim 4, wherein Further comprising: A plurality of second optical phase compensation elements, operatively coupled between the multi-row optical phase shifter and the plurality of beam emitters, and operatively configured to cooperate with the plurality of first optical phase compensation elements to equalize the optical path lengths between the optical splitters and the beam emitters of different rows.

6. The optical phased array according to claim 2, wherein, The number of the at least one electrical control element is one, and at least some of the rows of the multi-row optical phase shifter include all of the rows of the multi-row optical phase shifter.

7. The optical phased array according to any one of claims 1 to 6, characterized in that, The multi-row optical phase shifter comprises a thermo-optic phase shifter with a non-linear size change.

8. The optical phased array according to any one of claims 1 to 6, characterized in that, The multi-row optical phase shifter comprises a pn-doped phase shifter with a linear or approximately linear size change.

9. The optical phased array according to any one of claims 1 to 6, characterized in that, The multi-row optical phase shifter comprises at least two of a thermo-optic phase shifter, a doping phase shifter based on the plasma dispersion effect, a phase shifter based on the electro-optic effect, a photonic microelectromechanical system switch phase shifter, and a phase shifter based on a change in material structure.

10. The optical phased array according to any one of claims 1 to 9, characterized in that, The multi-row optical phase shifter traverses at most partially along the length direction of the optical waveguide.

11. The optical phased array according to any one of claims 1 to 6, wherein The multi-row optical phase shifter comprises a metal thermo-optic phase shifter arranged above the plurality of optical waveguides, the metal thermo-optic phase shifter comprising a thermo-optic heater arranged above or inside the plurality of optical waveguides, Or The multi-row optical phase shifter comprises a metal thermo-optic phase shifter arranged below the plurality of optical waveguides, the metal thermo-optic phase shifter comprising a thermo-optic heater arranged below or inside the plurality of optical waveguides.

12. The optical phased array according to any one of claims 1 to 6, characterized in that, The multi-line optical phase shifter includes a plurality of thermo-optic heaters thermally and cooperatively arranged with the plurality of optical waves, wherein each of the thermo-optic heaters includes a doped region having a doping concentration of at least 10 19 cm -3 order of magnitude.

13. The optical phased array according to any one of claims 1 to 6, characterized in that, The multi-row optical phase shifter comprises a plasma-dispersion-effect-based optical phase shifter integrated with the plurality of optical waveguides.

14. A method for operating an optical phased array, the optical phased array comprising photon elements for on-chip beam forming and steering, characterized in that, The method comprises: Controlling the beam in a steering direction of the propagation direction of the optical fields in a plurality of optical waveguides in an azimuth by the following method: The optical phases of the multiple optical fields in the multiple optical waveguides are simultaneously modulated by a multi-line optical phase shifter, and the multiple optical waveguides are operably coupled to multiple beam emitters that generate light beams, wherein the size of the multi-line optical phase shifter monotonically changes row by row, and each of the optical phase shifters passes through at most one of the multiple optical waveguides.

15. The method according to claim 14, wherein The simultaneous modulation of the optical phases of the multiple optical fields in the multiple optical waveguides by the multi-line optical phase shifter is achieved by the following method: At least some rows of the multi-line optical phase shifter are controlled by at least one electrical control element, wherein the number of the at least one electrical control element is less than the number of rows of the optical phase shifter.

16. The method according to any one of claims 14 to 15, characterized in that Further included is: Multiple optical splitter outputs are generated by multiple optical splitters operably coupled to the multi-line optical phase shifter, and there is no optical amplitude difference or a negligible optical amplitude difference between the multiple optical splitter outputs, and there is no optical phase difference or a negligible optical phase difference.

17. The method according to any one of claims 15 to 16, characterized in that The control of at least some rows of the multi-line optical phase shifter by at least one electrical control element is achieved by the following method: A voltage is applied to at least some rows of the multi-line optical phase shifter by the at least one electrical control element.

18. The method according to claim 17, wherein Further included is: The optical path lengths between the optical splitters and the beam emitters of different rows are equalized by the following method: A plurality of first optical phase compensation elements are provided, and the plurality of first optical phase compensation elements are operably coupled between the plurality of optical splitters and the multi-line optical phase shifter.

19. The method according to claim 18, wherein, Further included is: The optical path lengths between the optical splitters and the beam emitters of different rows are equalized by the following method: A plurality of second optical phase compensation elements are provided, which are operably coupled between the multi-line optical phase shifter and the plurality of beam emitters and cooperate with the plurality of first optical phase compensation elements.

Images