Optical phased array

Abstract

The optical phased array includes photonic components for on-chip beam forming and steering, and is configured to use an input optical field of a beam having a wavelength in the range from visible light to the short-wavelength infrared region. The photonic components include at least a waveguide and a plurality of scatterers. Here, each scatterer has a diagonal line that is at most about 1 / 10 of the wavelength of the input optical field.

Description

Technical Field

[0001] The present invention relates to photonic components for on-chip beam forming, and more particularly to photonic components formed as part of an apparatus for use in steering (guiding) an optical beam.

Background Art

[0002] Photonic components can be used to form and guide optical beams. Such platforms often operate in the visible, near-wavelength, and short-wavelength infrared regions, and applications have been found including, but not limited to, optical detection and ranging (LiDAR) systems and free-space transceivers. In a LiDAR system, beam steering can be used to detect objects, measure their range, and map their distance, and beam steering can be useful for, for example, autonomous vehicle systems and high-resolution mapping. In a free-space transceiver, beam steering can be used to selectively transmit and receive wireless data in a specific direction for use in data communication links such as local area networks (LANs) and optical fidelity (Li-Fi).

[0003] Known approaches to optical beam steering include the use of mechanical free-space optical components (e.g., mirrors, prisms, lenses), liquid crystals, phase change materials, and phased arrays. In particular, phased arrays are attractive because they enable beam steering without relying on mechanical moving parts or structural changes in materials, and such phased arrays are solid-state and semiconductor-based and can be fully realized on-chip using standard CMOS-compatible manufacturing processes. By modulating the optical phase of the optical field with respect to the phased array, the direction of the optical beam (emitted from the phased array) can be steered in a certain direction. In a typical phased array steering system, an input optical field (e.g., from a laser) is propagated through an optical waveguide before the optical field is radiated into free space through an emitter. The optical phase difference between the optical fields at adjacent emitters (e.g., in the x direction and / or y direction) can determine the overall beam directivity. Usually, in order to enhance the beam directivity, a feedback signal to a controller for fine-tuning the optical phase with respect to the emitter is required.

[0004] In recent years, efforts have been made to reduce the above-mentioned cumbersome dependence on feedback signals to enhance beam directivity. Examples of such efforts include leveraging the periodic nature of the optical phase of the optical field in a waveguide. For instance, U.S. Patent Application Publication No. 20201 / 0382371 issued by Ni et al. discloses a photonic component formed from a waveguide and an array of emitters in the form of meta-atoms. These meta-atoms are formed from a specially designed gold / dielectric / gold sandwich structure disposed on top of the waveguide. The special sandwich design is necessary to enable interactions between the electric dipoles within the structure to induce an additional optical phase shift inherent to this approach. The meta-atoms are structurally complex and increase the manufacturing complexity and assembly cost, especially when using conventional lithography techniques. Further, since Ni et al. require multiple meta-atoms for each repeating unit of the emitter, the optical loss in the waveguide after each repeating unit is substantially high, limiting the scalability of this approach and thus the device aperture size (usually on the <mm scale). A large effective aperture size is increasingly desired for several reasons, including to increase the lateral or angular resolution of the radiated beam (resolution ∝ wavelength ÷ effective aperture size), to reduce the impact the shield has on the system ("dead bug problem"), and to enable the emission of more optical power without exceeding the eye-safe power density. At a resolution of 0.1° at a communication wavelength (~1.55 μm), an aperture size of several hundred μm is often preferred. This is difficult due to the lack of scalability of Ni et al.'s devices. In a LiDAR system, such high resolution enables the addressing of fine targets / objects. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] It is desirable to provide an improved photonic component with an enlarged effective aperture size and a refined design that can improve the lateral and / or angular resolution. MEANS FOR SOLVING THE PROBLEMS

[0006] According to a first aspect, there is provided an optical phased array comprising photonic components for on-chip beam forming and steering and configured to use a beam input optical field having wavelengths in the range from visible light to the short wavelength infrared region. The photonic components comprise at least a waveguide and a plurality of scatterers each having a diagonal or diameter that is at most 1 / 10 of the wavelength of the input optical field. Such an optical phased array is useful in LiDAR systems and transceivers.

[0007] From the foregoing disclosure and the more detailed description of various embodiments below, it will be apparent to those skilled in the art that the present invention brings about a significant advancement in the technology of optical phased arrays. Particularly important in this regard is the possibility that the present invention can provide a relatively low-cost and simple structure. The additional features and advantages of the various embodiments will be better understood by considering the following detailed description.

Brief Description of the Drawings

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[0020] It should be understood that the accompanying drawings are not necessarily to scale and represent, with some simplification, various features showing the basic principles of the present invention. For example, certain design features of the optical phased array disclosed herein, including certain dimensions of the scatterers, are determined in part by the particular intended use and the environment of use. The particular features of the illustrated embodiments are enlarged or distorted relative to other features to assist in a clear understanding. In particular, thin features may be thickened, for example, to clarify the illustration. All references to direction and position refer to the directions shown in the drawings unless otherwise indicated.

Best Mode for Carrying Out the Invention

[0021] It will be apparent to those skilled in the art, i.e., those having knowledge or experience in this technical field, that many applications and design variations are possible for the optical phased array disclosed herein. The following detailed description of various alternative features and embodiments explains the general principles of the present invention with reference to photonic components suitable for use as part of an optical phased array. Such optical phased arrays can be, for example, beam steering systems that can be part of a LiDAR system or can be used as free space transceivers. Other embodiments suitable for other applications will be apparent to those skilled in the art in view of the advantages of the present disclosure.

[0022] Next, referring to the drawings, FIG. 1 is a schematic diagram of an optical phased array having a photonic component 90 according to an embodiment suitable for on-chip beam forming and steering. Such an optical phased array can be used in many applications such as LiDAR. The optical field input source can be, for example, from a laser having a certain wavelength. The optical phased array can act as a transceiver that emits / receives an optical beam to / from an object in a controlled manner. A part of the emitted optical beam is reflected to the phased array for processing. Optionally, the wavelength of the input optical field may be, for example, in the short-wavelength infrared region of the electromagnetic spectrum from 1.4 μm to 1.7 μm. Also, depending on the application of the photonic component, visible wavelengths (from 0.38 μm to 0.75 μm) and near-infrared wavelengths (from 0.75 μm to 1.4 μm) may be used. The photonic component 90 is shown together with a waveguide 110 and a plurality of scatterers 121 arranged along the waveguide. The waveguide 110 may be circular or a rectangular (rib or ridge) waveguide. The refractive index of the core layer 110 can be made larger than the refractive index of the surrounding waveguide cladding. The waveguide cladding can include an underclad 114 and an overclad 113.

[0023] The optical phased array can be implemented entirely on-chip using photonic circuit components 90. Advantageously, such photonic components can be manufactured using standard manufacturing techniques such as lithography and deposition, and standard photonic materials including, but not limited to, silicon (Si), silicon nitride (Si3N4), germanium (Ge), lithium niobate (Li3NbO3), and indium phosphide (InP). The phased array comprises at least one (M≥1) optical waveguide 110, and each optical waveguide has a plurality (N) of optical nanostructure arrays (also called scatterers or emitters) representing M columns and N rows of the phased array 100. FIG. 1 shows only one optical waveguide 110 and three scatterers 121 for clarity. However, the optical phased array can be scaled up to have any number M×N of optical waveguides and scatterers. Each m of the M optical waveguides 110 is configured to receive an optical field of wavelength λ iφ in,m which can be represented using the plane wave approximation αe o . Here, α and φ in,m represent the amplitude and phase of the optical field sent to each of the waveguides, respectively.

[0024] According to a highly advantageous element, the rectangular waveguide shown in the embodiment of FIG. 1 has an elongated upper surface 111 and sidewalls 116 extending downward from the upper surface 111. A plurality of scatterers 121 are arranged along at least one of the sidewalls of the waveguide and may be arranged along both sidewalls. The scatterers need to be arranged substantially adjacent to at least the sidewall 116 of the waveguide tube 110. Optionally, as shown in FIG. 1, the plurality of scatterers 121 contact the corresponding side of the waveguide 110. Also, the plurality of scatterers may be embedded in the waveguide, and the scatterers may be formed, for example, as either a single part or an integral part of the waveguide. Also, the scatterers 121 can be equidistantly spaced from each other by a pitch distance 124 and preferably are formed such that each has the same height 122. Each scatterer may include, for example, a dielectric material such as Si, Si3N4, Ge, Li3NbO3, InP, and polymers. The waveguide sidewall 116 has a thickness 115, and each of the plurality of scatterers 121 has a height 122. Preferably, the thickness 115 of the sidewall 116 of the waveguide 110 is equal to the height 122 of the plurality of scatterers 121. Advantageously, the scatterers can be arranged away from the upper surface 111 of the waveguide as shown in FIGS. 1 and 2. The waveguide core 110 has a higher refractive index than the surrounding waveguide cladding 113.

[0025] The wavelength range of the input optical field is in the range from visible light to short-wavelength infrared light. Preferably, each scatterer 121 of the plurality of scatterers is generally in the shape of a rectangular parallelepiped or a cylinder, and has a cross section such as a diagonal line or (in the case where the scatterer is cylindrical) a diameter D, which is at most about 1 / 10 of the maximum (at most) of the wavelength of the incident optical field (i.e., from the input optical field in the range from visible light to short-wavelength infrared light). Such optical field scattering is called Rayleigh scattering. Each Rayleigh scatterer is an example of an emitter, and the emitter emits an optical field having a radiation light intensity of less than 5% of the light intensity of the optical field of the beam incident on the emitter. Rayleigh scattering can be contrasted mainly with Mie scattering, which refers to the scattering of an optical field from a scatterer having a diameter much larger than 1 / 10 of the wavelength of the incident optical field. For example, see the known grating coupler that employs a grating-shaped Mie scatterer described in Taillaert et al., Appl. Phys. 45, 2006. Hereinafter, the Rayleigh scattering formed by the photonic components disclosed in this specification will be discussed in more detail.

[0026] The waveguide can include any of several different types of waveguides. For example, the waveguide can be a total internal reflection type waveguide (which accounts for the overwhelming majority of the optical waveguides conventionally used in integrated photonics), a slot waveguide, a surface plasmon polariton waveguide. Alternatively, an in-plane scattering waveguide such as a waveguide formed from a photonic crystal (which also uses total internal reflection) and a metamaterial may be used. The composition of the waveguide can be, for example, at least one of Si, Si3N4, Ge, Li3NbO3, InP, and polymers. The waveguide can support any optical waveguide mode. For example, the transverse electric mode and the transverse magnetic mode. In the LiDAR system, the controller can be configured to incorporate a processor that cooperates with the waveguide 110 and the scatterer 121, receives the radiation optical field reflected from the object, and calculates information regarding the surface characteristics of the object based on the reflected light received by the scatterer and the waveguide.

[0027] In addition to the wavelength of the optical input field, another important variable that determines the directionality of the beam is the scatterer pitch distance, which is the distance between adjacent scatterers when multiple scatterers are used. For example, as shown in FIG. 1, the rows of scatterers may be formed in a line such that each scatterer is spaced from adjacent scatterers by a scatterer pitch distance d. The scatterers may be apodized. That is, the diagonal or diameter of the scatterers may vary stepwise or continuously along the length of the row of scatterers. The optical phase of the optical field in the perturbation scatterer (as an emitter) can be accurately determined from the periodic nature of the optical field in the waveguide. Advantageously, by using photonic components as disclosed herein, the beam can be formed over a field of view exceeding 100 degrees, more preferably exceeding 150 degrees. The use of wavelength division multiplexing enables the formation of a beam having a wide directivity. The directivity of the emitted beam is discussed in more detail below.

[0028] The beam directivity (or beam steering angle) is a function of the emitter pitch d, which is the distance 124 between the centers of adjacent scatterers acting as emitters. The equation relating d and the beam directivity e is as follows:

Equation

Equation

[0029] Figure 3 shows the z-component of the electric field (E z ) profile of an embodiment of a photonic component at d = 0.78 μm along the xz cross-section disclosed at different wavelengths (1.4 μm, 1.55 μm, and 1.7 μm in three examples of the model in Figure 3) simulated by finite-difference time-domain (FDTD) numerical simulation, and a polar plot of the results of the far-field intensity versus the azimuth and zenith angles of the field of view. From Equation 1, in particular for e in the x-direction (or θ x : the direction specified by the subscript), when Δφ = 0, i.e., when d = λ eff,wg (where λ eff,wg = λ o / n eff,wg is the effective wavelength of the optical field in the waveguide (in this case, λ eff,wg = 0.78n) and n eff,wg is the effective refractive index of the waveguide medium), it can be seen that the scattered (or radiated) optical field propagates in free space in a direction exactly perpendicular to the waveguide structure. Changing λ eff,wg / d and / or Δφ shifts the beam directivity from the vertical direction (z-axis). For example, according to one embodiment using a wavelength of 1.55 μm for the optical field, the scatterer can be formed of Si having a diameter of about 160 nm, and the waveguide supports a transverse magnetic optical waveguide mode with a width of 0.3 μm and a sidewall thickness or height of 0.3 μm together with an air overclad and a SiO2 underclad.

[0030] Figure 4 is another table similar to Figure 3, but shows additional embodiments of the photonic component along the xz cross-section disclosed herein at different pitch distances 124 (in three examples of the model of Figure 4, 0.65 μm, 0.78 μm, and 1.0 μm). z Shows the change in the estimated results of the z-component of the electric field profile and the polar plot of the far-field intensity results with respect to the azimuth and zenith angles of the viewing angle.

[0031] Figure 5 is for waveguide Δφ y Another evaluation comparing the polar plots of the far-field intensity results with respect to the azimuth and zenith angles of the viewing angle at different optical phase differences of the input optical field sent to (i.e., the optical phase Δφ in the y direction).

[0032] Figures 6 and 7 compare and contrast known Mie scattering with a photonic component incorporating Rayleigh scattering disclosed herein. FIG. 6 shows a plot simulated by FDTD numerical simulation of the modeled electric field strength along the xz cross-section for a waveguide using a conventional grating including a plurality of Mie scatterers. The scatterers are formed of Si having a length of 0.4 μm and a width of 0.4 μm, and the waveguide supports a transverse magnetic optical waveguide mode having a width of 0.3 μm and a sidewall thickness or height of 0.3 μm together with an air overclad and a SiO2 underclad. The light intensity of the scattered radiation from each Mie scatterer can be orders of magnitude greater than that from a Rayleigh scatterer. As a result, the remaining optical field in the waveguide after encountering each Mie scatterer becomes weak, and as a result, the scattered (or radiated) field mainly from the first few scatterers as a whole becomes spatially concentrated. This is undesirable because the directivity of the scattered beam from the phased array results from many scatterers rather than one or a few scatterers. In contrast, FIG. 7 shows a plot simulated by FDTD numerical simulation of the modeled electric field strength along the xz cross-section for a waveguide using a plurality of Rayleigh scatterers (30 scatterers in this model) according to an embodiment of the present invention. The light intensity of the scattered radiation from each Rayleigh scatterer is relatively weak compared to that from each Mie scatterer. For example, in the optical phased array disclosed herein, out-of-plane scattering, i.e., scattering from the xy plane (or inner surface) defined by the photonic component, is as small as less than 5% of the beam intensity. As a result, the remaining optical field in the waveguide after encountering each scatterer remains significant, and as a result, a more dispersed and uniform scattered (or radiated) field is obtained as a whole. This is desirable because the directivity of the scattered beam from the optical phased array results from many scatterers rather than just a few.

[0033] Figure 8 shows a schematic diagram of a column (N) of an optical phased array on row m according to an embodiment of the present invention. The optical phased array can include an array of operably connected photonic components formed in rows and columns. Each row 100 includes a plurality 120 of Rayleigh scatterers 121 that perturb the optical waveguide 110. The Rayleigh scatterers are disposed at periodic points 112 generally adjacent to the waveguide 110. Each Rayleigh scatterer 121 evanescently couples (by coefficient α) a portion of the optical field from the waveguide (α and φ in,m which respectively represent the amplitude and phase of the optical field), and scatters it out-of-plane (by coefficient γ). The subscripts m and n respectively indicate the row and column of the array.

[0034] Figure 9 is similar to Figure 8, but shows a schematic diagram of the rows of an optical phased array on the first (n = 1) column according to an embodiment of the present invention. Each column includes a plurality of optical waveguides 110 perturbed by a row 120 of Rayleigh scatterers 121 disposed at periodic points 112 along the waveguide 110. Each Rayleigh scatterer 121 evanescently couples (by coefficient α) a portion of the optical field from the waveguide (α and φ in,m which respectively represent the amplitude and phase of the optical field), and scatters it out-of-plane (by coefficient γ). The subscripts m and n respectively indicate the row and column of the array.

[0035] Figure 10 shows, according to an embodiment, the rows of an optical phased array on the last (n = N) column, and a schematic diagram of the result of evanescently coupling (by coefficient α) a portion of the optical field from the waveguide 110 (α and φ in,m which respectively represent the amplitude and phase of the optical field), and scattering it out-of-plane (by coefficient γ) by the Rayleigh scatterer 121. The subscripts m and n respectively indicate the row and column of the array.

[0036] Figure 11 shows, according to an embodiment, the x-axis θ on row m xThe directivity of the scattered light beam in, evanescent coupling (by coefficient α), out-of-plane scattering (by coefficient γ) by the Rayleigh scatterer 121 arranged in the n-th row of the optical phased array, waveguide (α and φ in,m shows a schematic diagram showing the relationship between the optical phase of the optical field from (which shows the amplitude and phase of the optical field respectively). Subscripts m and n indicate the row and column of the array respectively. λ eff,fs , Δφ x , and d x are, respectively, the effective wavelength of the optical field in free space, the optical phase difference (x direction) of the optical field in the Rayleigh scatterer, and the Rayleigh scatterer pitch (x direction). α' is the approximate amplitude of the optical field scattered out-of-plane from each Rayleigh scatterer (considering the waveguide-scatterer evanescent coupling coefficient α≪1 and out-of-plane scattering coefficient γ≪1 due to Rayleigh scattering).

[0037] FIG. 12 shows, according to one embodiment, the directivity of the light beam scattered out-of-plane at the y-axis θ on the n = 1 row y in, evanescent coupling, out-of-plane scattering by the Rayleigh scatterer 121 arranged in the m-th row of the optical phased array, waveguide (α and φ in,m shows a schematic diagram showing the relationship with the optical field from (which shows the amplitude and phase of the optical field respectively). The relationship applies to the Rayleigh scatterers in other columns n. Subscripts m and n indicate the row and column of the array respectively. λ eff,fs , Δφ y , and d y are, respectively, the effective wavelength of the optical field in free space, the optical phase difference (y direction) of the optical field in the Rayleigh scatterer, and the Rayleigh scatterer pitch (y direction). α' is the approximate amplitude of the optical field scattered out-of-plane from each Rayleigh scatterer (considering the waveguide-scatterer evanescent coupling coefficient α≪1 and out-of-plane scattering coefficient γ≪1 due to Rayleigh scattering).

[0038] From the foregoing disclosure and detailed description of specific embodiments, it will be apparent that various changes, additions, and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were selected and described in order to best explain the principles of the invention and its practical application, thereby enabling one of ordinary skill in the art to use the invention with various modifications suitable for the particular purposes contemplated in various embodiments. All such changes and modifications are within the scope of the invention as determined by the appended claims when interpreted in accordance with the scope permitted by law, legally, and equitably.

Claims

1. An optical phased array comprising at least one photonic component for on-chip beam formation and steering, configured to use a beam input optical field having a wavelength in the range from visible light to the short-wavelength infrared region, wherein the photonic component comprises a waveguide and a plurality of scatterers each having a diagonal line that is at most 1 / 10 of the wavelength of the beam input optical field, the optical phased array.

2. The beam formed by the photonic component has a certain optical intensity, the photonic component defines an xy plane, and the scattering of the beam from the xy plane includes an optical field radiated from each scatterer having a radiated optical intensity of less than 5% of the optical intensity incident on the scatterer, The optical phased array according to claim 1.

3. The waveguide is a rectangular waveguide having an elongated upper surface and side walls extending from the upper surface, The optical phased array according to claim 1.

4. Some of the plurality of scatterers are spaced equidistantly from each other by a pitch distance, The optical phased array according to claim 1.

5. Each of the plurality of scatterers includes a dielectric material, The optical phased array according to claim 1.

6. Formed as an array of photonic components including columns and rows, The optical phased array according to claim 1.

7. The waveguide is either a total internal reflection waveguide or an in-plane scattering waveguide, The optical phased array according to claim 1.

8. The scatterer is cylindrical and the diagonal line is the diameter, The optical phased array according to claim 1.

9. The scatterer is embedded in the waveguide, The optical phased array according to claim 1.

10. The plurality of scatterers are in contact with the corresponding side walls of the waveguide, The optical phased array according to claim 1.

11. Further comprising scatterers located on opposite side wall-like portions of the waveguide, The optical phased array according to claim 1.

12. The plurality of scatterers are apodized, The optical phased array according to claim 1.

13. The formed beam has a field of view exceeding 100 degrees, The optical phased array according to claim 2.

14. The side walls of the waveguide have a certain thickness, each of the plurality of scatterers has a certain height, and the thickness of the side walls is equal to the height of the plurality of scatterers, The optical phased array according to claim 3.

15. The waveguide is made of at least one of Si, Si ３ N ４ , Ge, Li ３ NbO ３ , InP, and polymers The optical phased array according to claim 3.

16. The dielectric material is at least one of Si, Si ３ N ４ , Ge, Li ３ NbO ３ , InP, and a polymer The optical phased array according to claim 5.

17. Further comprising a controller operably connected to the optical phased array, receiving a radiation beam reflected from an object, and configured to calculate information about the object. The optical phased array according to claim 6.

18. The formed beam has a field of view exceeding 150 degrees. The optical phased array according to claim 13.

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