Optical phased array and method

Abstract

The present disclosure relates to an optical phased array including optical components for on-chip beamforming and steering, adapted to use at least one optical phase-shift control element configured to be electrically modulated to steer the direction of an output optical field of a radiation beam having a wavelength in the visible to short-wavelength infrared range. The optical components include simultaneously modulated optical phase shifters of monotonically varying dimensions independently positioned above, below, or otherwise integrated into each optical waveguide connected to a beam emitter. Such optical phased arrays are useful in LiDAR systems and transceivers.

Description

[Technical Field]

[0001] The present invention relates to beam steering of optical beams, e.g., light, and in particular to optical phased arrays for steering optical beams with control systems of significantly reduced complexity. [Background technology]

[0002] Non-guided signal transmission, i.e., signal propagation not physically guided within a solid medium, complements signal transmission through bounded media, especially when establishing a physical channel for guided signal transmission would be prohibitively expensive (e.g., in undeveloped regions) and when signal access or movement to the area to be reached is not otherwise convenient or possible. Such unbounded transmission can generally be divided into mechanical (e.g., acoustic / sound) and non-mechanical (i.e., electromagnetic) waves. The choice of the type of transmitted signal depends heavily on the environmental conditions and the application. For example, in the ocean, where there is a large amount of ionized water, sound waves (rather than radio waves) are used. This is due to their high volumetric mass density (which allows for relatively efficient transmission) and the fact that they are not significantly hindered by the presence of ionized charges within the medium.

[0003] However, signal transmission in air, where the volumetric mass density is quite low, requires a signal that does not easily fade out after a defined propagation distance in the medium, such as electromagnetic waves. Both radio waves and light waves are electromagnetic waves in the wavelength range of ~ meters (m) and ~ micrometers (μm), respectively, but when high data transmission rates (e.g., gigabytes per second (Gbps) in LiFi systems) or detailed maps of the surroundings (e.g., ~ millimeter (mm) resolution at ~ meters distances in LiDAR systems) are required, light waves with infrared (~1.55 μm) wavelengths are more suitable.

[0004] In applications involving non-guided optical signal transmission, it is important not only to be able to specifically direct an optical beam to an intended location, but also to be able to actively steer the beam in various directions. For example, a LiDAR system used to determine the extent of a structural area needs to be able to actively steer the beam to different points within the mapped area. Approaches to steering optical beams include mechanically altering structures with specific optical properties (e.g., optical microelectromechanical systems (MEMS)), altering the structural properties of materials (e.g., in liquid crystals), and modulating the optical properties of materials (e.g., using vertical-cavity surface-emitting lasers). One of the more common approaches to on-chip beam steering through optical property modulation is to control the optical amplitude and / or optical phase of light waves from an array of beam scatterers. Beam steering in such “optical phased arrays” (OPAs) is typically enabled by inducing a refractive index shift in the optical waveguides leading to the beam scatterers and / or in the vicinity of the beam scatterers.

[0005] Traditionally, OPAs require complex control systems, with each emitter (a form of scatterer) requiring its own independent control element. Given that the degree of beam directionality (i.e., field of view or angular reach) is directly governed by the number of emitters in an OPA, the number of control elements operating in an OPA can become undesirably large. Attempts have been made to mitigate the excessive reliance on numerous control elements for beam steering in OPAs. Examples of such attempts include simultaneously heating optical waveguides leading to beam emitters using a single voltage supply. For example, in the journal Opt. Lett. 34, 9, pp. 1477–1479 (2009), Acoleyan et al. reported beam steering controlled using a single voltage supply by simultaneously heating an array of optical waveguides using indium tin oxide / AlGaAs Schottky junction heating elements arranged in a serpentine, linearly increasing length pattern on the optical waveguides. However, heating the entire optical waveguide results in thermal crosstalk, i.e., undesirable degradation of steering performance (e.g., field of view) due to the temperature gradient experienced by the waveguide due to heat inflow from nearby heat sources, such as on adjacent waveguides. Furthermore, because electrical resistance, which leads to heat generation, increases with bending, higher heat generation efficiency at the ends of the waveguide array (mainly at the sites where bending is concentrated) is accompanied by a decrease in the uniformity of heat distribution along each waveguide (which is difficult to predict), reducing the precision of thermal control. Because OPAs primarily rely on regular optical phase shift differences, they are sensitive to discrepancies in the optical phase shift differences. Therefore, the lack of precise thermal control using a heating system is likely the cause of the low steering angle (less than ~10°), e.g., the 2.3° reported by Acoleyan KV et al. Summary of the Invention [Problem to be solved by the invention]

[0006] It would be desirable to provide improved optical components with elegant designs that reduce the complexity of optical phase shift control and improve the field of view. [Means for solving the problem]

[0007] According to a first aspect, an optical phased array is provided, including optical components for on-chip beam forming and steering, and adapted to use at least one phase-shift control element configured to be electrically modulated to steer the direction of an output optical field of a radiation beam having a wavelength in the visible to short-wavelength infrared region. The optical components include simultaneously modulated optical phase shifters of monotonically varying dimensions independently positioned above, below, or otherwise integrated into each optical waveguide connected to the beam emitter. Such optical phased arrays are useful in LiDAR systems and transceivers.

[0008] Therefore, optical phased arrays (OPAs) Included are on-chip beamforming and steering optics, the optics comprising: Optical phase shifters having dimensions that vary monotonically across the row and operably configured to simultaneously modulate the optical phase of an optical field in optical waveguides operably coupled to the optical beam emitter, each optical phase shifter traversing at most one of the 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 a portion of the rows of the optical phase shifters, wherein the number of the at least one electrical control element is less than the number of the rows of the optical phase shifters.

[0010] In some embodiments of the first aspect, the optical phased array further comprises an optical splitter having an optical splitter output operably coupled to the rows of the optical phase shifters, the optical splitter operably configured to produce an optical splitter output having no or negligible optical amplitude difference and optical phase difference between the rows.

[0011] According to a second aspect, there is provided a method for operating an optical phased array including on-chip beamforming and steering optics, the method comprising: The optical beam is controlled in a steering direction that is azimuthal with respect to the propagation direction of the optical field within the optical waveguide. The optical phase shifters simultaneously modulate the optical phase of the optical fields in the optical waveguides operatively coupled to the optical beam emitters that generate the optical beams, the optical phase shifters having dimensions that vary monotonically across the row, and each optical phase shifter traversing at most one of the optical waveguides.

[0012] In some embodiments of the second aspect, simultaneously modulating the optical phase of the optical field in the optical waveguide by the optical phase shifter comprises controlling at least a portion of the rows of the 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 optical beam emitter.

[0013] In some embodiments of the second aspect, the method further includes generating, by an optical splitter operably coupled to the rows of the optical phase shifter, an optical splitter output having no or negligible optical amplitude difference and optical phase difference between the rows.

[0014] It will be apparent to those skilled in the art from the foregoing disclosure and the following detailed description of various embodiments that the present invention provides a significant advance in the art of OPAs. Of particular importance in this regard is the possibility that the present invention offers for providing a controlled wide field of view (large steering angle) using simultaneously modulated optical phase shifters. Additional features and advantages of various embodiments will be better understood in view of the detailed description provided below. [Brief explanation of the drawings]

[0015] [Figure 1] 1 shows a schematic diagram illustrating the use of an optical phase shifter to steer a light beam by simultaneously modulating the optical phase of an optical field in a waveguide along rows of the OPA using ≦M electrically controlled elements connected to the phase shifter, where M is the total number of rows of the OPA, according to some embodiments disclosed herein.

[0016] [Figure 2] FIG. 2 shows a schematic diagram illustrating the use of optical phase shifters to modulate the optical phase of an optical field in a waveguide along a row of an OPA, according to some embodiments disclosed herein.

[0017] [Figure 3] FIG. 3 shows a schematic diagram illustrating the use of optical phase shifters to modulate the optical phase of the optical field in the waveguides along a row of the OPA to define an optical phase difference Δφ relative to adjacent waveguides in the last column, according to some embodiments disclosed herein.

[0018] [Figure 4] FIG. 4 shows a schematic diagram illustrating the use of optical phase shifters to modulate the optical phase of an optical field φ scattered out-of-plane by a beam emitter positioned after a row n of optical phase shifters, thereby modulating the directionality of an output light beam θ in the y-axis, according to some embodiments disclosed herein.

[0019] [Figure 5] FIG. 5 shows a schematic diagram illustrating the use of a row of optical phase shifters to steer an optical beam by simultaneously modulating the optical phase of the optical field in the waveguides along a row of OPAs using a set of electrical control elements connected to the phase shifters in the model example of FIG. 1 , according to an embodiment disclosed herein.

[0020] [Figure 6] FIG. 6 is a table illustrating partial isometric schematic views of optical splitters (MMI optical splitter and Y-splitter in two examples of the model in FIG. 6) according to some embodiments disclosed herein.

[0021] [Figure 7] FIG. 7 is a table showing partial isometric schematic diagrams of optical phase shifters (metal thermo-optic phase shifter, highly doped semiconductor thermo-optic phase shifter, and doped semiconductor plasma dispersion effect phase shifter) in four examples of the model of FIG. 7 , according to some embodiments disclosed herein.

[0022] [Figure 8] FIG. 8 shows an example of an experimentally measured plot of phase shift Δφ with respect to the length of the modulating element (metal heater) of a metallic thermo-optic phase shifter according to one embodiment of the metallic thermo-optic phase shifter disclosed herein.

[0023] [Figure 9] FIG. 9 shows an example of a numerical simulation plot of the phase shift Δφ with respect to the length of the modulating element (doped region) of a pn-doped optical phase shifter, according to one embodiment disclosed herein.

[0024] [Figure 10] FIG. 10 is a table showing a schematic diagram illustrating monotonically varying length optical phase shifters (thermo-optic and pn-doped) that enable simultaneous modulation of the optical phase of the optical field in the waveguides along the rows of the OPA using a set of electrically controlled elements connected to the phase shifters, according to some embodiments disclosed herein.

[0025] [Figure 11] FIG. 11 is an experimental characterization plot of thermal crosstalk occurring in an optical phase shifter at different physical distances of the thermo-optic heater from adjacent waveguides according to some embodiments of the thermo-optic phase shifter disclosed herein.

[0026] [Figure 12] FIG. 12 is a table comparing polar plots of the resulting far-field intensity with respect to azimuthal and zenith angles for different optical phase differences Δφy (i.e., optical phase in the y direction Δφ) of the input optical field sent to the waveguide, which can be modulated using a phase shifter placed on or integrated into the waveguide to the OPA beam emitter.

[0027] [Figure 13] FIG. 13 is a table outlining different examples of optical phase compensation element 190, according to some embodiments of the optical phase compensation element.

[0028] [Figure 14] FIG. 14 shows a flowchart 1400 illustrating a method of operating an OPA including optical components for on-chip beamforming and steering.

[0029] It should be understood that the accompanying drawings are not necessarily to scale and depict somewhat simplified representations of various features illustrating the underlying principles of the present invention. The specific design features of the OPAs disclosed herein, including, for example, the specific dimensions of the optical phase shifters, are determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate clear understanding. In particular, for example, thin features may be thickened for clarity of illustration. All references to dimensions, directions, and positions refer to the directions shown in the drawings unless otherwise indicated. DETAILED DESCRIPTION OF THE INVENTION

[0030] The articles "a," "an," and "the" when used in reference to features or elements should be understood to include a reference to one or more features or elements. The term "and / or" includes any combination of one or more of the associated features or elements. As used in this specification and claims, the terms "comprising," "including," "having," and any of their related terms are intended to be open-ended, meaning that there may be additional features or elements other than those listed. Identifiers such as "first," "second," and "third" are used merely as labels and are not intended to impose numerical requirements on their objects, nor should they be construed to impose limitations on relative location or chronological order. The term "to" can include the terms "configured to," "adapted to," and "constructed and arranged to," which may be used interchangeably.

[0031] The terms "coupled" and "operatively coupled" may be used to include an operational connotation and may include, but are not necessarily limited to, a physical, optical, and / or electrical connection or direct or indirect coupling. For example, two devices may be coupled or connected directly or indirectly through one or more intermediary devices. Based on this disclosure, one of ordinary skill in the art will recognize various ways in which a coupling exists according to the foregoing definition. The terms "coupled" and "connected" may be used interchangeably. The term "operatively" includes a reference to the term "operatively."

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

[0033] It will be apparent to those skilled in the art, i.e., those with knowledge or experience in this technical field, that many uses and design variations of the optical phased array (OPA) disclosed herein are possible. The following detailed description of various alternative features and embodiments explains the general principles of the present invention in terms of an OPA that uses a control system of significantly reduced complexity to simultaneously modulate the beam steering angle while providing a wide field of view. This contrasts with conventional OPAs that use optical phase shifters that scale with the number of beam emitters and OPAs that use simultaneously controlled optical phase shifters with limited beam steering angles (less than 10°). The OPAs disclosed herein can be used, for example, as beam steering systems that are part of LiDAR systems or free-space transceivers, and can be used as both transmitters and receivers. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure.

[0034] 1 shows a schematic diagram of an optical phased array (OPA) 100 illustrating the use of optical phase shifters to steer an optical beam by simultaneously modulating the optical phase of an optical field in a waveguide along rows (M) of the OPA using ≦M electrically controlled elements connected to the phase shifters, according to some embodiments disclosed herein. The OPA comprises an array of operably coupled optical components formed in rows, with multiple rows (M≧1) of beam emitters 121 positioned approximately adjacent to a sidewall of or embedded in a waveguide 110. The beam emitters 121 are operably coupled to at least one column (N≧1) of optical phase shifters 141 positioned approximately adjacent (below, above, on one side, or both sides) to or integrated into (or embedded in) the waveguide 130, and the optical phase shifters 141 are configured to be electrically modulated via ≦M electrically controlled elements 151. In other words, the number of electrical control elements is equal to or less than the number of rows of phase shifters 141. The electrical control elements may be integrated into the OPA or may be external to the OPA. The OPA allows steering of an optical beam in a dimension different from the x-dimension, which is along the propagation direction (azimuthal direction) of the optical field in the waveguide. The different dimension is typically referred to as the y-dimension (i.e., 90° azimuthal from the x-dimension). At least one optical phase shifter 141 (forming an array 140) is positioned adjacent to or integral with at least one waveguide 130 operatively coupled to at least one waveguide 110, and multiple beam emitters 121 (in the form of optical scatterers) are positioned along the waveguide 110 at periodic points 111 of the waveguide 110. Each phase shifter 141 forming part of the array 140 is configured to modulate the optical phase of the optical field in the optical waveguide 130. The OPA may be scaled to have any number M of optical waveguides. Each m of the M optical waveguides 130 is configured to receive an optical field propagating to m of the M optical waveguides 110. The subscripts m and n refer to the row and column, respectively, of the array of optical phase shifters 141. In one embodiment, each column may include the same type of optical phase shifter. Optionally, each of the optical phase shifters may be formed as a different layer. Also, the optical phase shifters may include different materials.

[0035] Advantageously, such optical components in the OPA can be implemented entirely on-chip using standard fabrication techniques, such as lithography and deposition, and standard optical materials, 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 may be in the short-wave infrared region of the electromagnetic spectrum, for example, from 1.4 μm to 1.7 μm. Visible wavelengths (0.38 μm to 0.75 μm) and near-infrared wavelengths (0.75 μm to 1.4 μm) can also be used, depending on the application of the optical components. One or more (≦M) electrical connections may be provided to the optical phase shifter. Further, in a LiDAR system, the controller may be adapted to incorporate a processor that operates in conjunction with an array 140 of optical phase shifters 141 positioned adjacent to or integrated with at least one waveguide 130, receives the outgoing optical field reflected from the object, and calculates information regarding the surface characteristics of the object based on the scatterers and the reflected light received by the waveguide.

[0036] The waveguides (operably coupled to 110, 130, and the optical splitter tree 160) may be circular or rectangular (rib or ridge) waveguides with an elongated top surface and sidewalls extending from the top surface. The refractive index of the waveguide core may be greater than the refractive index of the surrounding waveguide cladding. The waveguide cladding may include an undercladding and an overcladding. The waveguides may comprise any of several different types of waveguides. For example, the waveguides may be total internal reflection-based waveguides (which constitute the vast majority of optical waveguides traditionally used in integrated photonics), slot waveguides, or surface plasmon polariton waveguides. Alternatively, in-plane scattering waveguides, such as waveguides formed from optical crystals and metamaterials (which use total internal reflection), may be used. The composition of each of the multiple waveguides may be, for example, Si, SiO2, BaTiO3, Li3NbO 3、The material may be at least one of InP, III-V compounds, II-VI compounds, and polymers. Each of the plurality of waveguides may be doped with p-type or n-type material. The waveguide may support an optical waveguide mode, for example, either a transverse electric mode or a transverse magnetic mode. The scatterer / emitter 121 may be either a Mie scatterer or a Rayleigh scatterer. More specifically, Mie scattering primarily refers to scattering of an optical field from a scatterer whose diameter, width, or diagonal is typically close to the wavelength of the incident optical field, while in Rayleigh scattering, the diameter, width, or diagonal is at most 1 / 10 of the wavelength of the incident optical field. The composition of each of the plurality of scatterers may include, for example, at least one of the following: e.g., Si, SiO 2、 BaTiO 3、 LiNbO 3、 The scatterers may be InP, III-V compounds, II-VI compounds, or polymers. Each of the plurality of scatterers may 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. Types of negatively charged dopants include, for example, arsenic, phosphorus, and antimony. Each of the plurality of scatterers may be embedded in a corresponding waveguide and / or each of the plurality of scatterers may contact a top wall or a side wall of a corresponding waveguide.

[0037] 2 shows a schematic diagram of a column (N) of optical phase shifters on row m, according to one embodiment of the present invention. Each row includes at least one optical phase shifter 141 configured to shift the optical phase of an optical field in a waveguide 130. The optical phase shifters are located at points 131 on the waveguide 130. Each optical phase shifter 131 shifts the optical phase of the optical field in the waveguide (optical phase shift φ m,n ) and shift the part of the optical field from the waveguide (by a factor γ m,n The optical waveguides 130 are configured to dissipate the optical field by a (a) and a (b) and the optical field amplitude before passing through the optical phase shifter. Each of the M optical waveguides 130 is configured to dissipate the optical field by a (a) and the optical field amplitude before passing through the optical phase shifter. iφ m,n The wavelength λ can be expressed usingo configured to receive an optical field of a and φ m,n denote the amplitude and phase, respectively, of the optical field sent to each waveguide. The subscripts m and n again denote the array row and column of phase shifters in 140, respectively.

[0038] 3 shows a similar schematic diagram to FIG. 2, but showing the last (n=N) rows of OPAs, according to one embodiment of the present invention. Each column shifts the optical phase of the optical field in waveguide 130 to reduce the optical phase difference Δφ between adjacent optical waveguides. m The optical phase shifter 140 includes an array 140 of optical phase shifters 141 configured to define a phase shifter 140. The waveguide 130 is connected to a waveguide 110 that is perturbed by a plurality of scatterers 121 (see FIG. 4) 120. Each scatterer 121 evanescently couples 170 (see FIG. 4) a portion of the optical field in the waveguide 130 and scatters it out-of-plane 180, i.e., into the y-dimension. The subscripts m and n denote the rows and columns of the array of phase shifters in 140, respectively.

[0039] FIG. 4 summarizes the beam steering function of the OPA, which shifts the optical phase of the optical field in waveguide 130 operatively coupled to waveguide 110 via optical phase shifter 141, and is evanescently coupled 170 and scattered out-of-plane 180 by scatterer 121, thereby steering the optical field along a y-axis θ on line m, according to one embodiment. y 1 shows a schematic diagram illustrating the use of optical phase shifters to modulate the directionality of scattered light beams within a λ λ array. The subscripts m and n refer to the rows and columns, respectively, of the array of phase shifters in 140. eff,fs , Δφ y , and d y are the effective wavelength of the optical field in free space, the optical phase difference of the optical field in the scatterers (y-direction), and the scatterer pitch (y-direction), respectively. a' is the approximate amplitude of the optical field scattered out-of-plane from each scatterer.

[0040] The beam directivity (or beam steering angle) θ of an OPA is a function of the emitter pitch d, which is the distance between the centers of adjacent scatterers that function as emitters, and can be designed based on the following equation:

number

[0041] The optical phase of the optical field in the waveguide 130, which determines the beam directivity in the y-direction / dimension, can be varied by changing the refractive index of the waveguides in the array. Optical phase shifters can include phase shifters based on the thermo-optic effect, plasma dispersion effect, electro-optic effect (e.g., Pockels effect), microelectromechanically tuned evanescent field perturbation (which changes the effective refractive index of the OPA waveguide), or material structure changes (e.g., liquid crystal, ferroelectric, phase change material). Thermo-optic phase shifters can include metal heaters, alloy heaters, ceramic heaters, or highly doped semiconductor heaters. Doped phase shifters based on the plasma dispersion effect can include pn-doped or pn-doped semiconductors. Phase shifters based on the electro-optic effect can include modulators based on the Pockels effect, such as Li3NbO3 or BaTiO3, or modulators based on the Kerr effect. Optical microelectromechanical system switching phase shifters can include microelectromechanical system switches that introduce variations in the evanescent field perturbation to change the effective refractive index of the optical phased array waveguide. Phase shifters based on material structure changes can include liquid crystals, ferroelectrics, or phase-change materials. The phase shifters that change the refractive index of the waveguides in the OPA can be the same or different from one another as needed for the particular intended function. Refractive index changes can be advantageously induced, for example, by electrically heating the waveguide (via the thermo-optic effect), electrically changing the spatial carrier concentration in a doped semiconductor waveguide (via the plasma dispersion effect, which changes the refractive index and absorption of the phase shifter), and electrically changing the birefringence of the waveguide (via the electro-optic effect). Heat, spatial carrier concentration changes, and optical birefringence changes within the waveguide can be induced, respectively, by applying a voltage to a thermo-optic phase shifter (a metal, ceramic / alloy such as indium tin oxide, or highly doped semiconductor heater near the waveguide), or by using a doped / ion-implanted semiconductor region (hereafter, doped semiconductor phase shifter) extending along the waveguide, or by applying a voltage to an electro-optic phase shifter (formed using a material with a high electro-optic coefficient, such as one exhibiting the Pockels effect).Metallic heaters can be constructed using materials with high thermo-optic coefficients, including but not limited to titanium nitride (TiN) and nickel chromium (NiCr), and doped semiconductor heaters can include semiconductor materials highly doped with positively charged (p++) or negatively charged (n++) dopants. The doping concentration of the highly doped heater region is N for n++ heaters. a ~10 20 cm -3 and for p++ heaters, N d ~10 20 cm -3 Alternatively, the phase shifter based on the plasma dispersion effect may include either a pn-doped semiconductor or a pin-doped semiconductor. The doping concentration of the doped semiconductor region based on the plasma dispersion effect may be N for the n-doped region. a ~10 17 From 10 18 cm -3 and in the p-doped region, N d ~10 17 From 10 18 cm -3 Doping on the waveguide to enable spatial carrier concentration variation in the waveguide may be formed using a pn junction or a pin junction. A pn ​​junction is a junction having a region where a positively charged dopant has been implanted in the waveguide (a p-doped region) adjacent to a region where a negatively charged dopant has been implanted in the waveguide (an n-doped region), and a pin junction is a junction having a p-doped region adjacent to an undoped region (or "intrinsic" region) adjacent to an n-doped region. Phase shifters based on the electro-optic effect may be constructed using materials with high electro-optic coefficients, such as Li3NbO3 and BaTiO3. In some embodiments, each thermo-optic heater has at least 10 19 cm -3 The doped region has a doping concentration on the order of .mu.m.

[0042] The phase shifter 141 does not have to extend along the entire length of the waveguide 130. The desired optical phase shift may be modified by varying the portion of the segment over which the phase shifter extends, creating an optical phase shift region in each segment.

[0043] FIG. 5 shows a schematic diagram illustrating the use of a row of optical phase shifters to steer an optical beam by simultaneously modulating the optical phase of the optical field in the waveguides along a row of OPAs using a set of electrical control elements connected to the phase shifters in the model example of FIG. 1 , according to an embodiment disclosed herein.

[0044] FIG. 6 is a table illustrating an isometric schematic diagram of an optical splitter 161 (a multimode interferometer (MMI) optical splitter 165 and a Y-splitter 166 in two examples of the model in FIG. 6 ) according to some embodiments disclosed herein. The optical splitter equally divides the optical field into two splitter outputs with no or negligible optical amplitude difference and negligible or no optical phase difference. While the MMI splitter 165 has good manufacturing tolerances and is typically short compared to the Y-splitter 166, the MMI splitter 165 is generally wavelength sensitive. Optical splitters can be adapted for use in the OPA 100 to form an optical splitter tree 160 formed by cascading optical splitters 161 in multiple stages to provide M optical fields of equal amplitude and advantageously equal optical phase difference. For example, three-stage, four-stage, and five-stage optical splitter trees can be formed with M=2 optical fields, respectively. 3 , M=2 4 , and M=2 5The OPA 100 generates M equal-amplitude optical fields. The OPA 100 can include an optical splitter tree that generates the M optical fields (rather than directly directing the M optical waveguides into the OPA 100). This is because the beam steering angle of the OPA 100 is a direct function of the optical phase difference of the optical fields relative to the beam emitter 121, and therefore the optical fields are typically prone to undesirable optical phase variations before being optically coupled to an on-chip device (e.g., the OPA 100). Advantageously, the use of an optical splitter tree can lock the optical phase for each optical field at the splitter tree output, ensuring a reliable beam steering OPA device 100.

[0045] FIG. 7 is a table showing partial isometric schematic diagrams of different optical phase shifters (metal thermo-optic phase shifters 135 and 136, a highly doped semiconductor thermo-optic phase shifter 137, and a pn-doped semiconductor phase shifter 138) above and below the optical waveguide 211 (which may extend seamlessly to the outer slab region 212 of the rib waveguide) in four examples of the model in FIG. 7 , corresponding to the optical phase shifters shown in FIG. 1 ) according to some embodiments of the optical phase shifter. For example, according to one embodiment of the OPA, the OPA 100 can include a row (M) of metal thermo-optic phase shifters (135 and / or 136) disposed adjacent to or integrated with the total internal reflection-based waveguide 130 formed from Si3N4. The thermo-optic phase shifter 135 (an example of an optical phase shifter 141) comprising a titanium nitride (TiN) thermo-optic heater 215 (above or within the overclad 213) is configured to modulate the optical phase of the optical field in the waveguide 130. A thermo-optical phase shifter 136 (also an example of an optical phase shifter 141) comprising a titanium nitride (TiN) thermo-optical heater 215 (below or within the underclad 214) is configured to modulate the optical phase of the optical field in the waveguide 130. The waveguide clad comprises an underclad 214 and an overclad 213. The heater is configured to heat the waveguide, thereby modulating the refractive index of the waveguide and shifting the optical phase difference of the optical field between the waveguide 130 and the waveguide 110 in which the beam emitter 121 is disposed generally adjacent to a sidewall or embedded. The shift in the optical phase difference steers the optical beam along the y-direction. Each thermo-optical heater 215 may be coupled to a metal structure (on an adjacent layer) and electrically connected to other metal structures (on the top layer) through electrical vias. Advantageously, heating of the thermo-optical heater may be induced by applying a voltage to an electrical pad electrically connected to the metal structure.

[0046] The thermo-optic phase shifter 137 is n++ doped (e.g., acceptor concentration N a =1×10 20 cm 3The waveguide 130 includes a thermo-optical heater 216 (heavily doped, e.g., ion-implanted) that can modulate the optical phase of the optical field within the waveguide 130. The waveguide cladding may include an underclad 214 and an overclad 213. The heater is configured to heat the waveguide, thereby modulating the refractive index of the waveguide and shifting the optical phase difference of the optical field between the waveguide 130 and the waveguide 110 in which the beam emitter 121 is located generally adjacent to a sidewall or embedded. The shift in the optical phase difference steers the optical beam along the y-direction. Each thermo-optical heater 216 may be electrically connected to a metal structure (on a bottom layer) and to other metal structures (on a top layer) through electrical vias. Advantageously, heating of the thermo-optical heater may be induced by applying a voltage to an electrical pad electrically connected to the metal structure.

[0047] The optical phase shifter 138 may include a p-n junction (p-doped regions labeled 217 and 219, and n-doped regions labeled 218 and 220, the inner rib region and outer slab region of the waveguide forming the phase shifter) configured to modulate the optical phase of the optical field within the waveguide 130. A voltage applied across the p-n 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 and shifting the optical phase difference of the optical field between the waveguide 130 and the waveguide 110 in which the beam emitter 121 is disposed generally adjacent to or embedded in the sidewall. The shift in the optical phase difference steers the optical beam along the y-direction. The doped semiconductor waveguide outer slab regions 219 and 220 may be connected to a metal structure (on a bottom layer) or electrically connected to another metal structure (on a top layer) through electrical vias. Advantageously, plasma dispersion effects may be introduced from the doped semiconductor waveguide outer slab regions 219 and 220 by applying voltages to electrical pads electrically connected to the metal structures.

[0048] The optical phase shift induced by an optical phase shifter for beam steering depends on the design parameters. In the case of a thermo-optic phase shifter, the optical phase shift depends on the temperature coefficient dn / dT of the waveguide material and the length of the heated waveguide region L. The induced optical phase shift is a function of the waveguide temperature rise ΔT and the effective wavelength λ of the optical field in the waveguide. eff,wg can be conveniently written as a function of

number

[0049] 9 shows an example numerical simulation plot of the phase shift Δφ with respect to voltage and length of the modulating element (doped region) of a pn-doped optical phase shifter (0 to 6 mm for the example model of pn-doped optical phase shifter 138 of FIG. 7) according to one embodiment disclosed herein, obtained using Silvaco simulation software tools. In the example simulation, the acceptor N a and donor N d The doping concentration is N on a 0.22 μm high optical waveguide that is partially etched with a 90 nm slab height. a =N d =3×10 18 cm -3The simulation results show a linear optical phase shift relationship with the physical length of the modulator, with an optical phase modulation efficiency of 1.494 V cm.

[0050] Advantageously, the optical phase modulation elements (e.g., heaters in a thermo-optic phase shifter and doped regions in a pn phase shifter) of such optical phase shifter 141 in OPA 100 can be implemented with a constant physical thickness and physical width (and therefore a constant physical area A). To maintain a constant optical phase shift Δφ′ across the OPA row via independently formed but simultaneously modulated phase modulation elements across OPA row m, according to embodiments of the present invention, the length L of the modulation element can be monotonically varied. For example, according to embodiments of the present invention, the monotonic variation can be a nonlinear variation. A nonlinear variation can refer to a reciprocal or other variation. For example, according to embodiments of the present invention, in a thermo-optic phase shifter, L can be varied reciprocally or substantially reciprocally across OPA row m. When thermal energy is applied to the OPA row m, the temperature (i.e., E thermal = mass × specific heat capacity × ΔT), then from equation (2) we obtain Δφ' ∝ E thermal In the thermo-optic phase shifter, the electric energy E electric is supplied to heat the phase shifter and induce an optical phase shift Δφ′. E electric is the E in the heater that forms the thermo-optic phase shifter. thermal , which directly translates to Δφ' ∝ E electric provides a general reciprocal relationship between the induced optical phase shift Δφ′ and the physical length L of the heater in the thermo-optic phase shifter.

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[0051] 10 is a table showing a schematic top view of the length change of the waveguide region 132 phase-shift modulated by the phase shifter 131 across the OPA row m for thermo-optic phase shifters 135, 136, and / or 137 and pn-doped optical phase shifter 138 according to some embodiments of the optical phase shifter. Meanwhile, the waveguide region 133 is not phase-shift modulated by the phase shifter 131. In the case of the thermo-optic phase shifter and the pn-doped optical phase shifter, the modulation element lengths are nonlinearly related to each other (e.g., 1 / L m =1 / L1+m / ΔL) and linear (L m =L1+mΔL).

[0052] While the above examples provide optical phase shifters with monotonically varying lengths, it should be understood that in some other examples the optical phase shifters may provide monotonically varying lengths, widths and / or heights.

[0053] 11 shows experimental measurements of thermal crosstalk in optical phase shifters according to some embodiments of the thermo-optic phase shifters disclosed herein at different physical gaps between adjacent phase shifters (4 μm, 6 μm, 8 μm, 10 μm, 12 μm, and 14 μm) for six example distances of the thermo-optic phase shifters 135. Advantageously, the phase shifters can be implemented with a sufficiently wide physical gap (e.g., 25 μm) between adjacent independently positioned phase shifters to prevent thermal crosstalk between the optical phase shifters, thereby enabling precisely defined optical phase shifts to ensure wide-angle optical beam steering from simultaneously modulated OPAs 100. Advantageously, other forms of optical phase shifters (e.g., pn-doped optical phase shifters) can similarly be implemented using simultaneously modulating optical phase shifters 141 of monotonically varying dimensions independently positioned above, below, or otherwise integrated into the optical waveguide 130, ensuring precise definition of the optical phase shift (and therefore the optical phase difference) across the OPA array m.

[0054] Figure 12 shows the different Δφ y (-145° and 145° in the two examples of the model in FIG. 12 ) and the different optical phase differences Δφ of the input optical field sent to the waveguide (i.e., the optical phase Δφ in the y-direction) can be modulated using a phase shifter disposed on or integrated into the waveguide to the OPA, as disclosed herein. y1 is a table comparing polar plots of the resulting far-field intensity with respect to azimuth and zenith angles at 1.55 μm. According to one embodiment using a wavelength of 1.55 μm as the optical field, each row of waveguides is separated by 1.5 μm with scatterers formed from Si with a diameter of approximately 160 nm, and the waveguides support a transverse magneto-optical waveguide mode with a width of 0.7 μm and a sidewall thickness or height of 0.22 μm, partially etched with an air overclad and a SiO underclad at a slab height of 90 nm. In one embodiment, one optical phase shifter 123 is disposed on or integrated into each waveguide connected to the waveguide 110 for beam steering in the y-direction. Advantageously, if this configuration is obtained by simultaneously modulating (via control element 150) optical phase shifters 141 of monotonically varying length that are independently positioned above, below, or integrated into the optical waveguide 130, the complexity of controlling the OPA can be significantly reduced.

[0055] 13 is a table outlining different examples of optical phase compensation elements 190, e.g., waveguides, according to some embodiments of the optical phase compensation element. Advantageously, compensation elements 190 can be used to reduce gaps d between optical phase shifters across rows m (e.g., to prevent thermal crosstalk in thermo-optic phase shifters). A , allowing the gap d between the optical waveguides 110 across the row m to be increased. B (Therefore, the scatterer / beam emitter distance d y) can be reduced to increase the field of view of the OPA. To ensure that the optical phase difference at the point before the optical waveguide 110 (and thus the beam emitter 120) is zero before applying a voltage supply to the optical phase shifter, the optical path lengths (physical length times the effective refractive index of the optical waveguide) from the optical splitter tree 160 to the point before the optical waveguide 110 across row m are guaranteed to be equal by extending the physical length of the waveguide between the two points via an optical phase compensation element 190. In one embodiment, to facilitate simultaneous modulation of the optical phase shifters 141, the optical path lengths from the optical splitter tree 160 to the point before the waveguide 130 (on which the array of optical phase shifters 141 is located, below, or otherwise integrated) are guaranteed to be equal.

[0056] According to another embodiment of the OPA, the OPA 100 can include rows (M) of any of several different types of optical phase shifters: metallic thermo-optic phase shifters, pn-doped optical phase shifters, pn-doped optical phase shifters, doped semiconductor thermo-optic phase shifters, and optical phase shifters based on the thermo-optic effect. Optionally, the number of rows (M) of the OPA 100 and columns (N) of phase shifters 140 can range, for example, from 2 to 10,000. The OPA 100 can be adapted for use in, for example, a LiDAR system or a free-space transceiver.

[0057] FIG. 14 shows a flowchart 1400 illustrating a method for operating an optical phased array including optical components for on-chip beamforming and steering.

[0058] At block 1402, the method includes generating, with an optical splitter operably coupled to rows of optical phase shifters, an optical splitter output having no or negligible optical amplitude difference and optical phase difference between the rows.

[0059] At block 1404, the method includes controlling the optical beam in a steering direction, which is an azimuthal angle relative to the propagation direction of the optical field in the optical waveguide, by simultaneously modulating, with optical phase shifters, the optical phase of the optical field in optical waveguides operably coupled to the optical beam emitters that generate the optical beam. The optical phase shifters have dimensions that vary monotonically between rows, and each optical phase shifter traverses at most one of the optical waveguides. This simultaneous modulation can be performed by controlling at least a portion of the rows of the optical phase shifters with at least one electrically controlled element, where the number of the at least one electrically controlled element is less than the number of rows of the optical beam emitters. The control with the at least one electrically controlled element can be performed by applying a voltage to at least a portion of the optical phase shifters with the at least one electrically controlled element.

[0060] At block 1406, the method may optionally include equalizing optical path lengths between the optical splitter and the optical beam emitter across the rows. This may be done by having a first optical phase compensation element operably coupled between the optical splitter and the row of optical phase shifters, or by having a second optical phase compensation element operably coupled in cooperation with the first optical phase compensation element between the row of optical phase shifters and the optical beam emitter.

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

[0062] It will be apparent from the foregoing disclosure and detailed description of specific 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 have been chosen and described to provide the best explanation of the principles of the invention and its practical application, thereby enabling those skilled in the art to use the invention in various embodiments with various modifications suited to the particular uses intended. All such modifications and variations are within the scope of the invention, as determined by the appended claims when interpreted in accordance with the breadth and breadth permitted in fairness, law, and equity.

Claims

1. with on-chip beam forming and control optics; The optical component is optical phase shifters having dimensions that vary monotonically across the rows and operably configured to simultaneously modulate the optical phase of an optical field in optical waveguides operably coupled to the optical beam emitters, each optical phase shifter traversing at most one of the optical waveguides; Optical phased array.

2. at least one electrical control element operatively configured to control at least some of the rows of the optical phase shifter; the number of the at least one electrically controlled element is less than the number of rows of the optical phase shifter; The optical phased array of claim 1 .

3. an optical splitter having an optical splitter output operatively coupled to the row of optical phase shifters; the optical splitter is operatively configured to produce an optical splitter output having no or negligible optical amplitude and optical phase differences between rows. The optical phased array according to claim 1 or 2.

4. a first optical phase compensation element operably coupled between the optical splitter and the row of optical phase shifters and operably configured to equalize an optical path length between the optical splitter and the optical beam emitter across the row; The optical phased array of claim 3 .

5. a second optical phase compensation element operatively coupled between the row of optical phase shifters and the optical beam emitter, the second optical phase compensation element operatively configured to cooperate with the first optical phase compensation element to equalize an optical path length between the optical splitter and the optical beam emitter across the row; The optical phased array of claim 4.

6. the number of the at least one electrically controlled element is one, and the at least some of the rows of the optical phase shifter include all of the rows of the optical phase shifter; The optical phased array of claim 2 .

7. the optical phase shifter comprises a thermo-optic phase shifter having a nonlinearly varying dimension; The optical phased array of claim 1 .

8. the optical phase shifter comprises a pn-doped phase shifter having a linearly or substantially linearly varying dimension; The optical phased array of claim 1 .

9. The optical phase shifter includes at least two types of optical phase shifters selected from the group consisting of a thermo-optical phase shifter, a doped phase shifter based on plasma dispersion effect, a phase shifter based on electro-optic effect, an optical micro-electro-mechanical system switching phase shifter, and a phase shifter based on material structure change; The optical phased array according to claim 1 .

10. the optical phase shifter extends at most partially across the length of the optical waveguide; The optical phased array according to any one of claims 1 to 9.

11. the optical phase shifter includes a metal thermo-optic phase shifter disposed above the optical waveguide; the metallic thermo-optic phase shifter includes a thermo-optic heater disposed above or within an overclad of the optical waveguide; Or, the optical phase shifter includes a metal thermo-optic phase shifter disposed below the optical waveguide; the metallic thermo-optic phase shifter includes a thermo-optic heater disposed below or within an underclad of the optical waveguide; The optical phased array according to claim 1 .

12. the optical phase shifter includes a thermo-optical heater disposed in thermal cooperation with the optical waveguide; each of the thermo-optical heaters includes a doped region having a doping concentration on the order of at least 10 cm; The optical phased array according to claim 1 .

13. the optical phase shifter comprises an optical phase shifter based on a plasma dispersion effect integrated with the optical waveguide; The optical phased array according to claim 1 .

14. 1. A method for operating an optical phased array including on-chip beamforming and steering optics, comprising: The method comprises: controlling the optical beam in a steering direction, which is an azimuthal angle relative to a propagation direction of the optical field in the optical waveguide, by simultaneously modulating, with an optical phase shifter, an optical phase of the optical field in an optical waveguide operatively coupled to an optical beam emitter that generates the optical beam; the optical phase shifters have dimensions that vary monotonically across the rows; Each optical phase shifter crosses at most one optical waveguide. method.

15. simultaneously modulating the optical phase of the optical field in the optical waveguide by the optical phase shifters by controlling at least a portion of the rows of the optical phase shifters by at least one electrically controlled element; the number of said at least one electrically controlled element is less than the number of rows of said light beam emitters; 15. The method of claim 14.

16. an optical splitter operably coupled to the rows of the optical phase shifter to generate an optical splitter output having no or negligible optical amplitude difference and optical phase difference between the rows; 16. The method of claim 14 or 15.

17. controlling at least a portion of the optical phase shifter by at least one electrically controlled element comprises applying a voltage to at least a portion of the optical phase shifter by at least one electrically controlled element; 17. The method of claim 15 or 16.

18. Equalizing the optical path length between the optical splitter and the optical beam emitter across the rows; further comprising a first optical phase compensation element operably coupled between the optical splitter and the row of optical phase shifters.

18. The method of claim 17.

19. and equalizing the optical path length between the optical splitter and the optical beam emitter across the row further comprises having a second optical phase compensation element operatively coupled between the row of optical phase shifters and the optical beam emitter in cooperation with a first optical phase compensation element.

20. The method of claim 18.

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