High efficiency end-fire 3D optical phased array based on multi-layer platform

Abstract

Beam steering devices such as optical phased arrays (OPAs) are key components in applications of solid-state LIDAR and wireless communication. Conventional single-layer OPAs suffer from significant energy loss due to substrate leakage from the down-coupling of grating coupler structures. In this disclosure, we have investigated a structure based on a multi-layer Si3N4 / SiO2 platform that can form a 3D OPA to efficiently emit light from the edge of the device, end-fire the 2D converging out-coupled beam to air. Numerically demonstrated is the high efficiency and wide horizontal beam steering, also discussed are the effects of vertical crosstalk, delay length, number of waveguide layers, and manufacturing feasibility.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 62 / 984,004, filed March 2, 2020. The entire disclosure of the above application is incorporated herein by reference.

[0003] Government support

[0004] This invention was completed with government support under the National Science Foundation grant ECCS1644731. The government holds certain rights to this invention. Technical Field

[0005] This disclosure relates to a high-efficiency end-fire 3D optical phased array based on a multi-layer platform. Background Technology

[0006] This section provides background information relating to this disclosure, which is not necessarily prior art. This section provides a general overview of this disclosure, but not a complete disclosure of its entire scope or all features.

[0007] With the emergence of new applications such as solid-state LiDAR (optical detection and ranging), beam steering based on integrated optical phased arrays (OPAs) has attracted much research attention over the past decade. Significant progress has been made in areas including thermal tuning, electro-optic tuning, high-sensitivity wavelength tuning, integrated on-chip light sources, aperiodic sidelobe suppression, and apodized array placement.

[0008] Traditionally, on-chip integrated photonics research typically uses a single waveguide layer structure, which is also the case for most OPA research. For example, the device structure may be complex due to various requirements, but only contains a single waveguide layer; therefore, an OPA formed from a single layer can only have an upward-facing beam. This typically results in relatively low emission efficiency. When the OPA is placed in an environment where both the front and back sides are made of a homogeneous medium, the interference of light forms a beam on both the front and back sides of the environment. In the inventors' previous work, it was shown that more than 50% of the light can be emitted onto the substrate when the front side of the OPA is air and the back side is glass. However, as one of the main potential applications of integrated beam-directing devices, solid-state LiDARs typically require a detection range of at least 100 m. Despite all the development of light sources and detectors, the light emission efficiency of beam-directing devices is directly related to the detection range of LiDARs.

[0009] Some works have attempted to address the challenge of relatively low efficiency. In D. Kongeng et al.'s "1×12 Unequally Spaced Waveguide Array For Actively Tuned Optical Phased Array On A Silicon Nanomembrane," a structural configuration emitting light from the edge of the chip was utilized. Super-converging beams were also achieved in C. Qin et al.'s "1×256 Multi-Layer, Low-Loss, Si3N4 Waveguide Optical Phased Arrays With 0.050° Instantaneous-Field-Of-View." Further work aimed at confining the waveguide space to half a wavelength has been accomplished through various methods. However, these works also employed configurations with a single waveguide layer. This does facilitate the tuning of the phases of each waveguide, but the emitted beam from this configuration is indeed a fan-shaped beam because a single waveguide layer can only form a 1-DOPA at the edge of the chip. The possibility of emitting a 2D converging beam (end-fire) from the edge requires a 2D OPA on the edge side. Previously, the performance of 2D end-fired OPAs was numerically discussed, and a method for fabricating multilayer structures with blocking Si layers on SOI wafers using nanofilm transfer printing was proposed and experimentally verified. Furthermore, a direct-write method based on ultrafast laser inscription (ULI) was applied to realize structures for conversion between single-layer and 3D waveguides, thus enabling the formation of 2D OPAs on the edge side. Summary of the Invention

[0010] In this disclosure, a 3D structure configuration based on a multilayer Si3N4 / SiO2 platform is configured to achieve a 2D converged beam emitted from the edge. The performance of this structure has been demonstrated, and this disclosure presents major improvements in energy efficiency at both the optical input and emission ends. The effects of vertical crosstalk, delay length engineering, and the number of waveguide layers are also investigated.

[0011] Other application areas will become apparent from the description provided herein. The descriptions and specific examples in this invention are intended for illustrative purposes only and are not intended to limit the scope of this disclosure. Attached Figure Description

[0012] The accompanying drawings described herein are for illustrative purposes only, representing not all possible implementations, and are not intended to limit the scope of this disclosure.

[0013] Figure 1A A front view of the structure formed by the 3D OPA on the front edge of the device.

[0014] Figure 1B is a side view of the cross-sectional structure of the device, showing six Si3N4 layers with a thickness of 800 nm and five SiO2 layers with a thickness of 500 nm.

[0015] Figure 1C is a top view showing the structure of the pattern of each waveguide Si3N4 layer, which contains nine waveguides with a width of 800 nm and a spacing of 2 μm.

[0016] Figure 2 This is a diagram illustrating the apodization intensity distribution of the input coupling. The total thickness of the device is equivalent to the MFD of a standard single-mode fiber.

[0017] Figure 3 The image shows the far-field pattern of the device at 1550 nm, which emits a distinctly 2D converging beam.

[0018] Figure 4A for Figure 1A The simulation results of the structure in Figure 1C show a horizontal far-field contour map, with a clear main lobe shift of 24.78° / 100nm, and two side lobes can be observed.

[0019] Figure 4B for Figure 1A The simulation results of the structure in Figure 1C show a vertical far-field contour map, which shows only one main lobe and no vertical turning.

[0020] Figure 4C for Figure 1A The simulation results of the structure in Figure 1C show a comparison between the horizontal and vertical angles.

[0021] Figure 4D for Figure 1A The simulation results of the structure in Figure 1C show a comparison between the horizontal FWHM and the vertical FWHM.

[0022] Figure 4E for Figure 1A The simulation results of the structure in Figure 1C show the coupling efficiency of the total emitted energy.

[0023] Figure 5A The simulation results for a relatively thin SiO2 structure (eight Si3N4 layers with a thickness of 650 nm) are shown in the horizontal far-field contour plot.

[0024] Figure 5B The simulation results for a relatively thin SiO2 structure (eight Si3N4 layers with a thickness of 650 nm) are shown in the vertical far-field contour plot.

[0025] Figure 5C The simulation results for a thinner SiO2 structure (eight Si3N4 layers with a thickness of 650 nm) show a comparison of the vertical angles between the thinner SiO2 structure and the original structure.

[0026] Figure 5D Simulation results for a thinner SiO2 structure (eight Si3N4 layers with a thickness of 650 nm) are shown, with a comparison of vertical FWHM.

[0027] Figure 5E Simulation results for a thinner SiO2 structure (eight Si3N4 layers with a thickness of 650 nm) show a comparison of coupling efficiencies.

[0028] Figure 6A Simulation results for structures with different delay lengths (5400 nm and 7000 nm) are shown, with horizontal far-field contour plots of the structure with a delay length of 5400 nm displayed.

[0029] Figure 6B Simulation results for structures with different delay lengths (5400 nm and 7000 nm) are shown, with horizontal far-field contour plots of the structure with a delay length of 7000 nm displayed.

[0030] Figure 6C Simulation results for structures with different delay lengths (5400 nm and 7000 nm) are presented, showing a comparison of the horizontal angles between structures with different delay lengths (original 6200 nm, 5400 nm, 7000 nm).

[0031] Figure 6D Simulation results for structures with different delay lengths (5400 nm and 7000 nm) are shown, with a comparison of horizontal FWHM.

[0032] Figure 6E Simulation results for structures with different delay lengths (5400 nm and 7000 nm) show a comparison of coupling efficiency.

[0033] Figure 7A The simulation results for structures with different waveguide layers (4 layers and 8 layers) are shown, and the vertical far-field contour plots of the structure with 4 waveguide layers are displayed.

[0034] Figure 7BThe simulation results for structures with different waveguide layers (4 layers and 8 layers) are shown, and the vertical far-field contour plots of the structure with 8 waveguide layers are displayed.

[0035] Figure 7C The simulation results for structures with different waveguide layers (4 layers and 8 layers) show a comparison of the vertical angles between structures with different waveguide layers (original 6 layers, 4 layers, and 8 layers).

[0036] Figure 7D The simulation results for structures with different waveguide layers (4 layers and 8 layers) show a comparison of vertical FWHM.

[0037] Figure 7E Simulation results for structures with different waveguide layers (4 layers and 8 layers) are presented, showing a comparison of coupling efficiencies.

[0038] Figure 8 The structure of a single-period grating coupler is shown.

[0039] Figure 9 The structure of a composite periodic grating coupler is shown.

[0040] Figure 10 The results are from a far-field simulation of a composite periodic grating coupler at an applied wavelength of 15550 nm.

[0041] Figure 11A and Figure 11B These are the far-field contour plot and energy flow plot of the composite periodic grating coupler based on the applied wavelength, respectively.

[0042] Figure 12 A composite periodic grating structure with a DBR substrate is shown.

[0043] Figure 13A and Figure 13B The images show the far-field contour plot and energy flow plot of a composite periodic grating coupler with a DBR substrate, based on the applied wavelength.

[0044] Figure 14 The structure is shown in cases where certain gaps cannot be manufactured.

[0045] Figure 15A and 15B The far-field contour plot and energy flow plot are respectively for the performance of the composite periodic grating coupler considering the manufacturing tolerance of the high aspect ratio gap according to the applied wavelength.

[0046] Figure 16 The interference mechanism was demonstrated.

[0047] Figure 17 This demonstrates a multi-layered structure based on the principles of this teaching.

[0048] Figure 18 A far-field pattern with beam convergence in the y-direction at 1550 nm is shown.

[0049] Figure 19 The multi-layered structure and Fairfield pattern are shown based on the principles of this teaching.

[0050] Figure 20 The multi-layered structure and Fairfield pattern are shown according to the principles of this teaching.

[0051] Figure 21 It demonstrates the combined effect of beam convergence in the x and y directions.

[0052] Figure 22 It shows a comparison between ordinary periodic structures and quasi-periodic structures.

[0053] Figure 23 A table comparing ordinary periodic structures and quasi-periodic structures.

[0054] Throughout the various views of the accompanying drawings, corresponding reference numerals refer to the respective components. Detailed Implementation

[0055] Exemplary embodiments will now be described more fully with reference to the accompanying drawings.

[0056] The provision of exemplary embodiments will make this disclosure thorough and will fully convey the scope to those skilled in the art. Numerous specific details (such as examples of specific components, devices, and methods) are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the specific details are not required, that the exemplary embodiments may be implemented in many different forms, and that the specific details should not be construed as limiting the scope of this disclosure. In some exemplary embodiments, well-known processes, well-known device structures, and well-known techniques are not described in detail.

[0057] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be restrictive. As used herein, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” may be intended to include the plural forms. The terms “comprises,” “comprising,” “including,” and “having” are inclusive and therefore specifically refer to the presence of the stated feature, integer, step, operation, element, and / or component, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless expressly identified as an order of execution, the method steps, processes, and operations described herein should not be construed as necessarily having to be performed in the specific order discussed or shown. It should also be understood that additional or alternative steps may be employed.

[0058] When an element or layer is referred to as “on another element or layer,” “joined to,” “connected to,” or “coupled to” another element or layer, this element or layer may be directly on the other element or layer, directly joined to, connected to, or coupled to the other element or layer, or there may be intermediate elements or layers. Conversely, when an element is referred to as “directly on another element or layer,” “directly joined to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intermediate elements or layers. Other terms used to describe relationships between elements should be interpreted in a similar manner (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0059] Although the terms “first,” “second,” “third,” etc., may be used herein to describe different elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, and / or segment from another. When used herein, unless the context explicitly indicates otherwise, terms such as “first,” “second,” and other numerical terms do not imply order or sequence. Therefore, without departing from the teachings of the exemplary embodiments, the first element, first component, first region, first layer, or first segment discussed below may be referred to as a second element, second component, second region, second layer, or second segment.

[0060] For ease of description, spatial relative terms (such as "inside," "outside," "below," "below," "below," "above," and "above") may be used herein to describe the relationship of one element or feature shown in the accompanying drawings to another element (or other) element or feature. Spatial relative terms may be intended to cover different orientations of the device in use or operation other than those described in the accompanying drawings. For example, if the device in the figures is flipped, an element described as "below" or "below" other elements or features will subsequently be oriented "above" other elements or features. Thus, the example term "below" may cover both above and below orientations. The device may be oriented in other ways (rotated 90 degrees, or oriented in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0061] Based on this teaching, an OPA-based beam steering structure is provided to address the detection range problem in LiDAR. Furthermore, this disclosure numerically demonstrates a 3D optical phased array (OPA) based on a multilayer Si3N4 / SiO2 platform, featuring light emitted from the edge of the device. A CMOS-compatible fabrication strategy for this device is discussed. The multilayer structure enables high efficiency in input and emitt coupling, with end-fire emission efficiency reaching up to 82%. A 2D converged beam is clearly generated in the far-field pattern of the emitting OPA, and this 2D converged beam can be steered purely horizontally by wavelength tuning, suggesting the potential application of this device in building multi-line solid-state LiDARs. The interrelationships of the 3D OPA structure are investigated in detail: vertical crosstalk does not affect the output out-coupling angle; the length of the delay line can be designed to achieve high steering sensitivity or high steering resolution; and the number of waveguide layers can also be designed as a trade-off between fabrication complexity and device performance. The two key features—high efficiency and single-degree-of-freedom control—are explained in detail. This work promises to advance the research of solid-state beam steering devices and the application of solid-state LiDAR, as well as applications in other emerging fields such as wireless communication or optical microscopy.

[0062] Structural configuration

[0063] According to this teaching, the structural configuration of the beam steering structure based on this OPA is as follows: Figure 1A As shown in Figure 1C. In some examples, as shown in Figure 1B, the device includes: six 800nm ​​thick Si3N4 layers and five 500nm thick SiO2 layers sandwiched between the Si3N4 layers. Each Si3N4 layer is patterned; Figure 1C is a top view of each Si3N4 layer, showing nine 800nm ​​wide waveguides with a center-to-center spacing of 2μm. In the red circle, the waveguide lengths gradually increase in 6200nm increments.

[0064] The manufacturing strategy for this device is discussed below. This structure can be fabricated on a Si substrate. First, a SiO2 layer can be fabricated. For example... Figure 1AAs shown in Figure 1C, six (6) patterned Si3N4 layers with identical patterns can be fabricated. There are two possible methods to fabricate this multilayer structure. First, the method proposed in “1×256 multi-layer, low-loss, Si3N4 waveguide optical phased arrays with 0.050° instantaneous-field-of-view” (C. Qin, K. Shang, S. Feng, G. Liu, S. Pathak and S. B. Yoo, CLEO 2017, pp. 1-2, IEEE, May 2017) can be used to fabricate this structure. The challenge of this method will be the control of the planarization step, which will affect the thickness of the SiO2 layer sandwiched in the middle, and the precise control of this thickness is crucial in this structure. Secondly, due to the identical pattern on each Si3N4 layer, it is possible to utilize "On the fabrication of three-dimensional silicon-on-insulator-based optical phased array for agile and large angle laser beam" The self-alignment method proposed in "Steering Systems [Fabrication of 3D Silicon-on-Insulator Based on Optical Phased Arrays for Agile and Large-Angle Laser Beam Steering Systems]" (A. Hosseini, D. Kwong, Y. Zhang, S.A. Chandorkar, F. Crnogorac, A. Carlson, B. Farah, S. Bank, E. Tutuc, J. Rogers, R.F.W. Pease, R.T. Chen, Vacuum Science and Technology Journal B, Nanotechnology and Microelectronics: Materials, Processing, Measurement and Phenomena, Vol. 28, No. 6, C6O1-C6O7, 2010). Si3N4 and SiO2 exhibit low etch selectivity towards each other, but the fact that both are highly selective relative to Si also contributes to this method: the selectivity difference allows for the possibility of etching multiple layers of Si3N4 and SiO2 in the same etch step using Si as a mask. However, the extremely high aspect ratio will be a hurdle here.Using a combination of these two methods to fabricate this structure is more practical: 2-3 Si3N4 layers are etched away in one step using a self-alignment method, and then the multi-step process described above is used to finally obtain 6 patterned Si3N4 layers. As long as the self-alignment method can process more than one Si3N4 layer in one step (in the case of two Si3N4 layers and a SiO2 layer sandwiched in between, the aspect ratio of the holes in the etching step will be 1.2μ / 2.1μm = 0.57), the total number of steps required will be significantly reduced.

[0065] After fabricating six patterned Si3N4 layers and five unpatterned SiO2 layers, a final passivation SiO2 layer is deposited. The wafer is then diced, and the edges of the die are polished to ensure input coupling from an external laser source and output coupling at the emitter. As a final step, a quarter-wavelength SiO2 layer (T = 1550 / 5 * 1.45 = 267 nm) is deposited on the edge sides, which performs anti-reflection functionality between the Si3N4 waveguide and air. The entire fabrication process follows standard microchip manufacturing processes, making this method CMOS compatible.

[0066] In this disclosure, we consider only 9 waveguides in each layer, and the total periodicity of the array at the transmitter is 2 μm. It is worth noting that even though only 9 waveguides are considered in this disclosure, more waveguides can be used in each layer by using a beam splitter tree. A phase difference can then be generated between the waveguides using an Ω-shaped delay length structure. The length difference between each waveguide is the same, and the periodicity of 2 μm can eliminate crosstalk between waveguides. Therefore, the phase difference between each array at the transmitter will be the same, which satisfies the phased array condition in equation (1) in each waveguide layer (horizontal direction). In the vertical direction, since the structure in each waveguide layer is exactly the same, the phase difference between each layer is 0, thus also satisfying the phased array condition between layers (vertical direction). Therefore, this structure is capable of transmitting a beam with 2D convergence from the edge of the device.

[0067] In this disclosure, we consider only 9 waveguides per layer and an array spacing of 2 μm at the transmitter. It is worth noting that although only 9 waveguides are considered in this disclosure, more waveguides can be included in each layer by using a beam splitter tree. Light convergence can be enhanced by a large number of array elements, so even though the convergence data presented in this disclosure is derived from 9 waveguides, it can actually be further improved in principle. Then, an Ω-shaped delay length structure is used to generate a uniform phase difference between the waveguides, and the 2 μm spacing eliminates crosstalk between waveguides. Therefore, the phase difference between the arrays at the transmitter will be the same, which satisfies the phased array condition for each waveguide layer (horizontal direction). In the vertical direction, since the structure in each waveguide layer is identical, the phase difference between layers is 0, thus also satisfying the phased array condition between layers (vertical direction). The overall result is that this structure can emit a beam with 2D convergence from the edge of the device. Equation 1 shows the phase condition:

[0068]

[0069] Where θ is the emission angle and λ0 is the vacuum wavelength. d represents the phase difference and spacing between each array element.

[0070] The significant improvement of this structure is its high energy efficiency. Firstly, most previous studies used external lasers from single-mode fibers as the light source. However, regardless of whether vertical or butt coupling was employed, the light suffered considerable loss at the input coupling point. This loss was particularly pronounced in butt coupling because the waveguide layer thickness was typically ten times smaller than the mode field diameter (MFD) of a standard 8.2 μm core-diameter single-mode fiber. In this multilayer structure, six Si3N4 layers and five interposed SiO2 layers vertically occupy 7.3 μm, resulting in a much higher coupling efficiency when light is coupled from the single-mode fiber to the on-chip waveguide compared to a single-waveguide layer structure. A similar coupling mechanism is used in the "On The Fabrication Of Three-Dimensional Silicon-On-Insulator Based Optical Phased Array For Agile And Large Angle Laser Beam Steering" project. Systems [Fabrication of 3D Silicon-on-Insulator Based on Optical Phased Arrays for Agile and Large-Angle Laser Beam Steering Systems] (A. Hosseini, D. Kwong, Y. Zhang, S.A. Chandorkar, F. Crnogorac, A. Carlson, B. Farah, S. Bank, E. Tutuc, J. A spot size converter (J. Rogers, R.F.W. Pease, R.T. Chen, Vacuum Science & Technology B, Nanotechnology & Microelectronics: Materials, Processing, Measurement & Phenomena, Vol. 28, No. 6, C6O1-C6O7, 2010) first couples light from a single-mode fiber to a tapered stack of Si3N4 / SiO2 layers of similar size, then converts the spot shape to a vertical line after tapering, and finally couples the light to a Si waveguide much smaller than the fiber. According to their results, the mode overlap between the single-mode fiber and the multilayer spot size converter can be as high as 94%–99%. In that work, the Si3N4 layer thickness was 225 nm, while in this disclosure, the Si3N4 waveguide layer thickness is 800 nm, so the coupling efficiency may not be as high as their results, but we believe that the ability of multiple Si3N4 layers to contribute to high input coupling efficiency is still evident.

[0071] On the other hand, this multi-Si3N4 layer structure also contributes to the apodized field distribution. In "Two-Dimensional Apodized Silicon Photonic Phased Arrays" (J. Sun, E. Shah Hosseini, A. Yaacobi, D.B. Cole, G. Leake, D. Coolbaugh, and M.R. Watts, Optics Letters, Vol. 39, No. 2, pp. 367-370, 2014), Gaussian apodized phased arrays were used to suppress sidelobes. In this work, apodized field distribution across the array was specifically designed. In this disclosure, the apodized field distribution across each Si3N4 waveguide layer is automatically formed due to the coupling mechanism. This is... Figure 2 It is displayed in the middle.

[0072] The transmitting end also contributes to high efficiency. From Figure 1A As shown in Figure 1C, the OPA is formed on the edge of the device. The front of the OPA consists of an anti-reflective coating and air, a homogeneous medium that allows for output coupling beam generation through interference between the array elements. Furthermore, since the beam is directed into the air at the emitter end, backscattering is significantly suppressed. Simulation results show that the output coupling efficiency at the emitter end can reach as high as 82%.

[0073] In this disclosure, the FDTD (finite difference time domain) method is used to simulate the structure. In this simulation, the model is as follows: Figure 1A Configure the settings as shown in Figure 1C and apply TM-polarized Gaussian pulses as the light source, illuminating each waveguide. The wavelength range is set to 1400 nm to 1700 nm, covering a 100 nm wavelength tuning range. Figure 3The far-field plot of the device at 1550 nm is shown. It indicates that the device produces a distinct main lobe at horizontal –1.53° and vertical –6.99E –4°, with a horizontal FWHM (Full Width at Half Maximum) of 4.43° and a vertical FWHM of 10.96°; two side lobes are observed horizontally at –52.78° and –47.77°. The formation of the side lobes is due to the relatively large spacing between the waveguides in each layer, and because the periodicity (2 μm) is not much larger than the wavelength (1550 nm), the side lobes are far from the main lobe and are not strong. On the other hand, the vertical periodicity (i.e., the spacing between the centers of each waveguide layer) is 1.3 μm, thus producing only one distinct main lobe in the vertical direction. The vertical FWHM is larger than the horizontal FWHM because the OPA only covers 7.3 μm vertically, while it covers 18.8 μm horizontally.

[0074] The device's wavelength tuning performance is... Figures 4A to 4E As shown in the image. Figure 4A The horizontal far-field contour plot shows that the main lobe can be steered by wavelength tuning, shifting the beam from 10.99° at 1500 nm to –13.79° at 1600 nm, achieving a 24.78° steering range within the 100 nm wavelength range. This steering capability is achieved through a delay-length structure; the length difference between the waveguides is fixed, thus allowing for coherent alteration of the phase difference in the horizontal direction between the array elements through wavelength tuning. Figure 4B The vertical far-field contour map shows that there is no length difference between waveguides in different layers. Therefore, during wavelength tuning, the phase difference between array elements in the vertical direction is always 0. As a result, the overall range of the vertical far-field angle changes only slightly, by 3.13E–3°. Figure 4C This shows a comparison between the horizontal and vertical far-field angles. The beam steers linearly in the horizontal direction as the wavelength changes, and the steer in the vertical direction is negligible. Figure 4D The changes in horizontal and vertical FWHM are shown. The beam convergence is maintained throughout the entire wavelength tuning range, with horizontal FWHM variation of less than 7.67% and vertical FWHM variation of less than 7.12%. Figure 4E The coupling efficiency across the tuning range is shown. This efficiency is calculated by dividing the total transmitted energy by the energy in all waveguides just before the transmitted OPA. The efficiency is above 76.43% across the entire range, with a minimum observed at 1600 nm and a maximum of 82.22% observed at 1570 nm. Since the main lobe dominates across the entire range, the transmission efficiency of the main lobe is close to... Figure 4E The efficiency value is shown in Part 2. The high efficiency is a result of both the end-fire mechanism and the SiO2 anti-reflective coating.

[0075] The tuning capability with pure horizontal steering is achieved solely through wavelength tuning. In this device, precise phase control within each waveguide is unnecessary; therefore, the number of degrees of freedom required for operation is reduced from N (where N is the number of waveguides per layer) to 1, significantly simplifying the operating principle. In LiDAR applications, traditional mechanical LiDARs rotate the entire device to achieve the horizontal field of view (FOV), and the vertical field of view is achieved vertically using multiple beamlines, requiring each beam to maintain its vertical angle during rotation. This device can emit 2D converged beams that can be purely horizontally steered, thus enabling the construction of multi-line solid-state LiDARs using multiple devices together.

[0076] The effects of vertical crosstalk

[0077] The horizontal spacing between the waveguides was chosen to be 2 μm to eliminate crosstalk, taking into account the different phases of the light in each horizontal waveguide. On the other hand, the thickness of the SiO2 sandwiched in between was set to 500 nm. In practice, this thickness cannot completely eliminate crosstalk between waveguides in different layers. However, since the patterns in each waveguide layer are identical, this crosstalk does not contribute to the sidelobes. This is because the phase difference between the layers is zero, and the light intensity in each layer is comparable, so the vertical crosstalk in the entire system is in dynamic equilibrium: when the main pulse in one waveguide induces a delayed pulse in an adjacent waveguide, this waveguide will also receive the delayed pulse induced by the main pulse from this adjacent waveguide, and since the main pulses in each waveguide have zero phase difference, the induced delayed pulses in these waveguides also have zero phase difference. In this case, all induced pulses can also interfere with each other in the same direction with the output coupled beam, thus also contributing to the main lobe. Another simulation was performed to confirm this, and the results are shown in... Figures 5A to 5E As shown in the figure. In this simulation, we used eight 650nm Si3N4 layers and seven 300nm SiO2 layers, so the OPA still covers a range of 7.3μm vertically, which is consistent with... Figure 1A It is the same as the original structure in Figure 1C.

[0078] Figure 5A The horizontal angular turning range is 23.00° / 100nm, which is consistent with... Figures 4A to 4E The results are slightly different because the waveguide thickness is changed in this structure, which will change the effective refractive index of the waveguide; however, the pattern in this structure is the same as the previous one, so the change is not significant. Figures 5B to 5CThe vertical angle orientation of this structure is shown, revealing that even with a SiO2 layer thickness of only 300 nm, the beam's vertical angle is unaffected by crosstalk. However, the vertical FWHM and efficiency become significantly higher because the proportion of waveguide layers is higher even when the OPA covers the same vertical range. Therefore, this structure is comparable to that used for... Figures 4A to 4E The original structure is closer to a thick plate waveguide with a thickness of 7.3 μm than the original structure. And in either case, Figures 5A to 5E The results clearly show that vertical crosstalk between waveguides does not affect the angle of the transmitted beam.

[0079] Engineering design of delay length

[0080] We have already pointed out that the horizontal convergence of the device can be further enhanced by using more waveguides in each layer. Therefore, in practice, the detection resolution of a wavelength-tuned LiDAR depends on the steering sensitivity of each wavelength and the wavelength tuning resolution of the light source. In this disclosure, we chose 6200 nm as the delay length of the structure; however, in practical applications, a larger delay length can be chosen to increase the steering sensitivity. Two simulations were performed with delay lengths of 5400 nm and 7000 nm, and the results are shown in... Figures 6A to 6E As shown in the image.

[0081] In this simulation, the differences between the structures lie in the patterns of each waveguide layer; therefore, information regarding the horizontal angle is plotted only in the... Figures 6A to 6E The most important comparison is in... Figure 6C In this graph, the red curve and Figure 4C The red curves in the diagram are identical, the yellow curve represents the structure with a 5400 nm delay length, and the pink curve represents the 7000 nm delay length. The steering sensitivity of the 5400 nm delay length structure is 21.58° / 100 nm wavelength, compared to 24.78° / 100 nm for the original device with a 6200 nm delay length, and 28.32° / 100 nm for the 7000 nm delay length. This indicates that the steering sensitivity can be altered by selecting different delay lengths: in most cases, a larger delay length is preferred for achieving higher steering sensitivity; however, in some cases, if the wavelength tuning resolution of the light source is limited, a lower steering sensitivity may be needed to improve detection resolution, which can be achieved by selecting a smaller delay length. Meanwhile, the horizontal FWHM and coupling efficiency do not change significantly because the spacing between the array elements remains constant in all three structures.

[0082] Selection of the number of waveguide layers

[0083] In this disclosure, we selected six Si3N4 layers to cover a 7.3 μm range in the vertical direction, ensuring that the total vertical dimension is similar to the mode field diameter (MFD) of a typical single-mode fiber. In this structure, the number of waveguides in each layer can be increased via a beam splitter tree, but the number of waveguide layers is limited by the MFD of the field. On the other hand, as discussed herein, fabricating multilayer structures becomes challenging when more layers are required. Therefore, choosing the number of layers to fabricate is a trade-off between fabrication complexity and device performance. In this disclosure, we also investigated this parameter. Two structures (these two structures are compared with those for…) were simulated. Figures 4A to 4E The same structure was used, but only the number of waveguide layers differed, and the results were... Figures 7A to 7E As shown in the image.

[0084] exist Figures 7A to 7E In the middle, only information about the vertical angle is drawn, and it is consistent with... Figures 6A to 6E similar, Figures 6C to 6E The blue curve in Figures 4A to 4E The blue and black curves in the diagram are identical. As mentioned earlier, the phase difference between the array elements in the vertical direction is always 0, so it is not surprising that both the 4-layer and 8-layer structures exhibit far-field steering curves similar to the original 6-layer structure. However, in Figure 7D In the analysis, it can be observed that the 6-layer structure actually exhibits the best FWHM results: the 4-layer structure exhibits a much larger FWHM due to a lack of sufficient array elements and vertical dimensions; and the 8-layer structure also shows a similar but slightly higher FWHM. The reason why the 8-layer structure does not show a better FWHM may be due to vertical crosstalk: vertical crosstalk is not a problem in fewer-layer structures, but it may become a problem in more-layer structures. Figure 7C In the figure, the vertical angle remains relatively constant across the entire wavelength range, but the entire light blue curve shifts slightly to the positive direction, which could also be due to vertical crosstalk. This suggests that six layers may be sufficient for this structural configuration. On the other hand, the four-layer structure also exhibits significant convergence, although the FWHM is wider than that of the six-layer structure. This could be helpful if vertical convergence is not critical in some applications, in which case the four-layer structure would significantly reduce manufacturing complexity.

[0085] As further teachings of this invention suggest, grating couplers are among the most fundamental integrated photonic structures. They have attracted considerable research interest due to their excellent performance in compact, non-mechanical beam steering. Based on these teachings, a novel composite periodic grating coupler is proposed, formed by combining two grating structures with different periods. This novel composite periodic grating coupler structure can couple waveguide modes to two radiation modes with different angles. Therefore, the beam steering range is doubled due to the additional beam. We numerically demonstrate this idea, observing a steering range of 26.20° within a wavelength tuning range of 1500 nm to 1600 nm. A composite periodic grating structure with a distributed Bragg reflector (DBR) substrate is also demonstrated, with highly suppressed energy leakage to the substrate. Furthermore, studies on manufacturing tolerances show that the new structure can be fabricated using current CMOS technology.

[0086] introduce

[0087] The emerging field of integrated photonics, which studies the generation, processing, and detection of light in chip-scale optical media, is one of the most important topics in modern optical research. A key issue in integrated photonics is the optical signal coupling between optical fibers and photonic chips. Grating couplers have become promising candidates due to their higher coupling efficiency compared to docking couplers and their simpler fabrication process compared to prism couplers and tapered docking couplers. Typical grating couplers can be fabricated on SOI (silicon-on-insulator) wafers using two-step UV (ultraviolet) lithography.

[0088] Over the past few decades, numerous studies have been conducted to modify traditional grating structures in various ways to improve fiber-to-chip coupling efficiency. For example, the entire grating can be designed in a parabolic shape to focus light directly onto the waveguide. In this case, a binary periodic grating structure is used to simulate a blazed grating. Polarization independence is achieved through the design of a 2D grating array. Furthermore, a metal layer can increase the reflectivity of the substrate interface, thereby enhancing the directionality of the coupling. The substrate thickness can also be optimized to mitigate leakage radiation. Recently, a study reported coupling efficiencies as high as 93%.

[0089] In recent years, research efforts have been made to couple light from photonic chips to free space using grating couplers, aiming to achieve spatial scanning with beams generated from photonic chips. By designing arrays of waveguide grating couplers, 2D scanning in free space has been achieved. Furthermore, by using photonic crystals to control the phase distribution of waveguide modes, the beam steering range can be further enhanced (in degrees / nm for wavelength tuning steering), and even the requirement for a physical grating can be eliminated.

[0090] This disclosure provides a novel structure for a composite-periodic grating coupler designed to simultaneously generate two output coupled beams. The novel composite-periodic grating coupler can simultaneously generate two different series of surface harmonics; therefore, energy in the waveguide mode can be coupled into two different radiation modes. Both radiation modes satisfy the grating diffraction equation, and thus both respond to wavelength tuning or refractive index tuning. Therefore, within a certain wavelength tuning range, each of the two beams exhibits a beam steering range comparable to that of a conventional single-periodic grating coupler, with the beam steering range of the new composite-periodic grating coupler approximately doubled compared to that of a single-periodic grating coupler.

[0091] 2. Coupling Mechanism

[0092] Traditional grating couplers are single-cycled. In most studies focusing on Si-based grating couplers, the device is located on an SOI (silicon-on-insulator) wafer. Figure 15 shows a typical side cross-section of an SOI-based grating coupler, which contains a 220 nm thick Si waveguide on top of a 2 μm thick oxide layer. This type of grating coupler is fabricated using two-step UV lithography. First, the 220 nm Si layer is etched to form the waveguide layout; second, the waveguide is etched 70 nm to form the grating structure on the waveguide.

[0093] The output coupling angle of this grating coupler structure is controlled by the grating equation, as shown in [2]:

[0094]

[0095] Where Λ is the periodicity of the grating; θ is the output coupling angle; k0 is the free space wavenumber; β0 is the propagation constant of the guided mode in the grating region; and m is the diffraction order, which is -1 in most cases. This equation describes the phase matching condition between the waveguide mode and the radiation mode. The term k0sinθ is the projection of the wavenumber of the radiation mode onto the waveguide direction. When the propagation constant of the waveguide mode satisfies k0sinθ, energy can be coupled from the waveguide mode to the radiation mode. The grating structure makes this possible because the grating structure generates a series of surface harmonics due to the periodic spatial fluctuations of the refractive index in the grating region, and the electric field distribution of the waveguide mode can be expressed as the sum of all harmonics [3], that is:

[0096]

[0097] Among them, S mLet βm be the amplitude of the m-th harmonic, β0 be the propagation constant of the fundamental waveguide mode, and Λ be the periodicity. Here, we call the term m(2π / Λ) the harmonic alteration factor. The propagation constant of the waveguide mode is altered by this factor. In a typical grating coupler, one of these altered propagation constants perfectly matches the wavenumber of a particular radiation mode, while the other propagation constants do not satisfy this phase match. Therefore, energy in the waveguide mode can be coupled to this radiation mode, and the coupling efficiency tends to approach 1 (unity) as the number of gratings increases. The reason why only one propagation constant satisfies the phase match condition is that the term sinθ in Equation 1 must be in the range (-1, 1).

[0098] In principle, if a structure can generate different series of surface harmonics with different periodicities, then the electric field in the structure can be expressed as:

[0099] In this case, it is possible that more than one harmonic can satisfy the phase matching condition. Therefore, multiple output coupled beams will be emitted from this structure.

[0100] In this disclosure, a grating structure is provided, wherein the grating is configured as a combination of two gratings with different periods. Figure 9 The structure is shown. We combined 25 gratings with a periodicity of 720 nm and 36 gratings with a periodicity of 500 nm to form a new grating structure with an envelope periodicity of 18000 nm; here, we named the two gratings with single periodicity as component gratings and the new structure as a composite periodic grating. To ensure consistency with previous studies, the grating thickness was 70 nm; the waveguide layer thickness was 220 nm; a 2 μm SiO2 substrate layer was placed below the waveguide layer; and only one envelope period of the composite periodic grating was considered in this work. The fill factor of the two component gratings was 0.5, and the fill factor of the new composite periodic grating was 0.64. The refractive indices of Si and SiO2 were set to 3.477 and 1.450, respectively, at a wavelength of 1550 nm. In this work, FDTD (finite-difference time domain) was utilized. A sinusoidal pulse with TE polarization was applied to the Si waveguide for simulation.

[0101] Due to the combination of the two periodicities, the electric field distribution of the waveguide mode becomes the sum of two series of harmonics:

[0102] Wherein, Λ1 = 720nm and Λ2 = 500nm.

[0103] Therefore, the waveguide mode and both radiation modes simultaneously satisfy the phase-matching condition. The first radiation mode forms a beam with an output coupling angle θ1, which satisfies:

[0104]

[0105] And the second radiation mode satisfies:

[0106]

[0107] Figure 10 The image shows the far-field angular distribution of the composite periodic grating coupler at a wavelength of 1550 nm, calculated using a far-field calculator. The intensities in the far-field pattern are automatically normalized, and knowing how much energy is distributed in this far-field pattern, we can estimate the intensity of each beam. For this wavelength, the ratio of energy coupled to air to the input energy is 31.60%; this ratio of input energy is distributed across both beams. Positive values ​​in the far-field angle are... Figure 9 The value is θ1, and the negative value is the opposite θ2.

[0108] like Figure 10 As shown, when the input wavelength is 1550 nm, two beams are generated through a composite periodic grating structure. The first beam has a far-field angle of 35.67°, a normalized intensity of 0.0324, and an FWHM (full width at half maximum) of 5.48°, while the second beam has a far-field angle of -21.38°, a normalized intensity of 0.0375, and an FWHM of 4.86°. The first beam is generated by a harmonic with a period of 720 nm, and the second beam is generated by a harmonic with a period of 500 nm, labeled beam 1 and beam 2, respectively. Beam 2 has a slightly higher intensity and a narrower FWHM, showing better performance than beam 1. This is because the 500 nm periodic grating has 11 more gratings than the 720 nm periodic grating. The SiO2 substrate has a higher refractive index than air, therefore 56.86% of the input energy is coupled to the substrate, which is more than the energy coupled to air (31.60%). Aside from the energy coupled to the radiation mode, 4.86% of the light is transmitted; it remains propagating inside the waveguide because the number of gratings in this structure is insufficient to couple all the energy out of the waveguide mode. 7.15% of the input energy is reflected in the opposite direction of the waveguide; this is because the spatial fluctuations generated by the grating structure also create a weak DBR (Distributed Bragg Reflector) structure, resulting in reflection.

[0109] To achieve solid-state beam steering, we utilized wavelength tuning in this work. Figure 11A The relationship between the far-field angle contour plot of the composite periodic grating structure and wavelength is shown; we tested wavelengths from 1300 nm to 1800 nm at 10 nm intervals.

[0110] To maintain consistency with previous studies, the beam steering range within the 1500 nm to 1600 nm wavelength range was analyzed. For example... Figure 11AAs shown, the red line represents the beam steering range of the two beams within this wavelength range. Beam 1 varies from 42.59° at 1500 nm to 30.53° at 1600 nm, achieving a beam steering range of 12.06° only through small variations in FWHM (e.g., 5.73° at 1500 nm and 5.79° at 1600 nm). Beam 2 varies from -13.94° at 1500 nm to -28.08° at 1600 nm, with a beam steering range of 14.14°. The FWHM of beam 2 also varies negligibly: 4.50° at 1500 nm and 5.85° at 1600 nm. The total beam steering range is calculated to be 26.20° by adding the two beam steering ranges together. For comparison, previous studies on single-period grating structures achieved a beam steering range of 14.10° within the same wavelength tuning range. On the other hand, the composite periodic grating structure produces two beams with steering ranges of 12.06° and 14.14°, both comparable to the single beam in previous work. Therefore, by using composite periodicity instead of single periodicity, the total beam steering range of the device is approximately doubled.

[0111] Figure 11A The yellow line in the diagram represents the total variation range of the composite periodic grating structure. This range was chosen because the intensities of both beams are sufficiently high. The total wavelength range is 1400 nm to 1750 nm. Within this range, the far-field angle of beam 1 varies from 60.94° to 12.48°. When the wavelength is less than 1400 nm, beam 1 gradually disappears because it no longer satisfies Equation 4. The FWHM of beam 1 has a maximum value of 7.90° at 1400 nm within the dual-beam range; this large FWHM is formed because it becomes more difficult for the grating structure to converge energy when the output coupled beams have large angles. The minimum FWHM of beam 1 is 4.53° at 1630 nm, thus beam 1 can be observed to converge within the total two-beam range. The far-field angle of beam 2 varies from 1.18° at 1400 nm to -58.02° at 1750 nm, with a total azimuth angle of 59.20°, which is 10.74° higher than that of beam 1. This is because beam 2 is generated by surface harmonics with a periodicity of 500 nm, while the surface harmonics of beam 1 have a periodicity of 720 nm. Therefore, according to equations 4 and 5, the far-field angle is more sensitive to the wavelength of beam 2 than that of beam 1. The FWHM of beam 2 has a maximum value of 8.67° at 1750 nm and a minimum value of 4.07° at 1410 nm.

[0112] In summary, beam 1 covers an angle from 60.94° to 12.48° from 1400nm to 1750nm, while beam 2 covers an angle from 1.18° to -58.02°; a total steering range of 107.66° is achieved through a wavelength tuning range of 350nm (1400nm to 1750nm). Furthermore, the center angle range of 1.18° to 12.48° can also be covered in two ways: one is by using beam 1 with a wavelength higher than 1750nm, and the other is by using beam 2 with a wavelength lower than 1400nm.

[0113] The normalized intensities of the two beams are shown in the color plot in Figure 11(A), calculated by a far-field calculator. Figure 11(B) shows the energy flow of the entire system, where the red line represents the energy coupled to the air and shows how much energy is distributed in the two beams according to wavelength; the blue line represents the energy coupled to the SiO2 substrate, which is higher than the energy of the air over the entire range; the pink line represents transmission; and the black line represents reflection.

[0114] exist Figure 11A In the middle, both beams are weak at wavelengths near 1610nm, and Figure 11B Significant reflection peaks were observed at this wavelength, with 59.29% and 58.61% of the energy reflected at 1610 nm and 1620 nm, respectively. This is likely because the two surface harmonics with periodicity of 720 nm and 500 nm both form weak DBR structures and exhibit high reflectivity at this wavelength, resulting in particularly high reflection peaks at 1610 nm and 1620 nm. On the other hand, the lowest energy coupled to air at 1620 nm is 9.00%, while the highest energy in air within the dual-beam range is 34.30% at 1470 nm; therefore, the lowest energy coupled to air (9.00%) is 26.24% of the highest energy (34.30%). Considering that the two beams share energy approximately uniformly at 1620 nm, we estimate that the intensity of the two beams at this wavelength is still sufficient to be detected. Figure 11 also shows that when the wavelength approaches 1300 nm or 1800 nm, one of the two beams gradually disappears, resulting in a reduction in the energy coupled to the air. As the air energy decreases, the reduced portion either couples to the substrate or remains in waveguide mode. In summary, it can be concluded that the composite periodic grating structure exhibits good performance across the entire dual-beam range.

[0115] 3. Composite periodic grating structure with DBR substrate

[0116] A significant problem with grating couplers on SiO2 substrates is that energy leakage to the substrate can exceed 50% when energy is coupled from the waveguide mode to the air. This is because the refractive index of the SiO2 substrate is higher than 1, making it easier for energy to couple to the substrate rather than the air. A considerable amount of energy coupling to the substrate can be observed in Figure 11(B). This problem also occurs when grating couplers are used for fiber-to-chip coupling. One possible solution is to use a metal layer at the substrate to suppress energy leakage. In this work, we utilize a DBR (Distributed Bragg Reflector) structure as the substrate to achieve energy leakage suppression while keeping the device purely Si-based. Figure 12 A composite periodic grating structure with a DBR substrate is shown.

[0117] In this work, Si and SiO2 were chosen to create a DBR structure with a center wavelength of 1550 nm. The thicknesses of the Si and SiO2 layers were set to 111.45 nm and 267.24 nm, respectively. Ten pairs of Si / SiO2 stacks were used in this work. A more complex process is required to fabricate this device. First, a DBR with ten pairs of stacks will be fabricated. Then, the top surface of the SOI wafer is bonded to the DBR layer, and the buried oxide layer and substrate Si layer are removed by dry etching. Finally, the grating coupler structure is fabricated on the left Si layer. This complex process ensures that the grating coupler is made from a single-crystal Si layer.

[0118] Figure 13 shows the far-field angle contour plot and energy flow plot of this structure. From Figure 13A It can be observed that the total range of the two beams decreases, and the total beam turning range of the two beams is 73.70°. The red arrow indicates a beam turning range of 26.67° in the wavelength range of 1500nm to 1600nm, which is similar to that of the SiO2 substrate structure.

[0119] from Figure 13B This demonstrates the most significant advantage of the DBR substrate structure: suppression of energy leakage to the substrate across the entire dual-beam range. The DBR structure is a typical 1-D photonic crystal, making it virtually impossible for energy in the waveguide mode to couple to the substrate's radiation mode. In this case, the intensity of the two beams coupled to air is enhanced. Figure 13B It can be noted that as the wavelength increases, the grating coupler exhibits a reduced ability to couple energy from the waveguide mode to the radiation mode; this problem can be addressed by increasing the number of periods in the grating coupler. In this work, a composite periodic grating comprises 25 720 nm periodic gratings and 36 500 nm periodic gratings, resulting in a transmission energy exceeding 50% when the wavelength is greater than 1590 nm.

[0120] In summary, the composite periodic grating structure with a DBR substrate exhibits extremely low energy leakage, while the overall beam steering range is also suppressed due to the enhanced waveguide modes at longer wavelengths. This makes it possible to balance beam intensity and beam steering range depending on the specific application of the device.

[0121] 4. Manufacturing tolerances

[0122] In this work, two component gratings are combined to form a composite periodic grating structure. However, the composite periodic grating structure contains several gaps with extremely small widths. The smallest gap has a width of 10 nm, and considering the grating depth of 70 nm, the aspect ratio of this gap is 7; this high aspect ratio and small feature size structure is difficult to fabricate using CMOS processing techniques. On the other hand, the coupling between waveguide modes and radiation modes is achieved through surface harmonics; therefore, the disappearance of a portion of the grating in a large number of gratings will weaken the surface harmonics, but will not eliminate them.

[0123] Therefore, we can predict that if certain narrow gaps cannot be manufactured, the overall performance of the equipment will not change significantly. Figure 14 It shows what a structure would look like if certain gaps could not be manufactured.

[0124] Figure 15 shows the far-field contour plot and energy flow plot when certain gaps cannot be fabricated. Conventional SiO2 substrate structures are considered in these results. Here, we tested all gaps with widths less than 100 nm, because in principle, gaps with a width of 100 nm and a depth of 70 nm can be fabricated using current CMOS processing techniques.

[0125] exist Figure 15A In the results, the far-field angle of beam 1 is observed to be 35.67° when all gaps can be fabricated, and changes to 36.57° when all gaps below 100 nm cannot be fabricated. This slight increase in far-field angle is due to the increase in total effective refractive index when the air gaps are replaced by Si. The FWHM of beam 1 remains almost unchanged. Beam 2 exhibits the same trend as beam 1. Figure 15A The far-field angle changes from -21.38° to -20.42°.

[0126] Figure 15B The energy flow plot of the results is shown. It can be observed that all lines are approximately flat; the energy of air varies negligibly from 31.60% to 28.97%. Therefore, it can be concluded that the composite periodic grating structure has non-stringent manufacturing tolerances.

[0127] 5. Conclusion

[0128] Based on this teaching, a composite periodic grating structure has been shown and numerically demonstrated. Using this design, conventional grating couplers can be modified to simultaneously generate two output coupled beams, and the beam steering range of the device is doubled due to the additional beam. A total beam steering range of 26.20° was achieved within a 100 nm wavelength tuning range (1500 nm to 1600 nm). Furthermore, this result can potentially be improved through optimization and integration with other studies, such as using photonic crystals as waveguides. Additionally, studies on DBR substrate structures show enhanced beam intensity while slightly suppressing the steering range, demonstrating a trade-off between beam intensity and beam steering range. Considering cost efficiency, the fabrication tolerances of the composite periodic grating structure were investigated, showing that this structure maintains good performance even when all gaps below 100 nm cannot be fabricated. Therefore, the composite periodic grating structure holds great potential for many applications, such as telecommunications and sensing, particularly for solid-state LiDAR technology.

[0129] According to further teachings of the present invention, OPA is based on an interference mechanism. If the phase is uniformly distributed in all array elements, a beam can be formed upwards through constructive interference, such as... Figure 16 The radiation beam is shown in the diagram. However, in a single-layer device, the substrate is also a homogeneous material, so the OPA will form another downward beam, as shown in the diagram. Figure 16 The leakage beam is shown in the diagram. Unfortunately, this portion of the light will ultimately be wasted. According to simulation results, in the case of Si waveguides on SiO2 substrates, the efficiency loss caused by the leakage beam can be as high as 60%, resulting in an efficiency of less than 40%.

[0130] To overcome this problem, the OPA can be arranged to face only one direction of the homogeneous material. According to this teaching, an end-firing OPA structure is provided to achieve this. In this structure, the OPA is formed on the side of the device. In this case, the OPA faces the air, allowing for the formation of an emitted beam as usual; while the backward direction of the OPA consists of a series of waveguides in a non-homogeneous medium, thus suppressing leakage beams.

[0131] This configuration is achieved by applying a multilayer structure. High-refractive-index material is uniformly distributed to form periodic phase elements (see [link]). Figure 17 The simulation window for the structure is shown in the figure. A multilayer structure is formed by periodic Si3N4 / SiO2 stacks. Light propagates through the Si3N4 layers (we use 6 layers in the simulation as an example), forming a 1-D periodic phase array at the ends, thus creating a fan-shaped beam that converges in the vertical direction (see Figure 1). Figure 18 ).

[0132] To converge the beam in the horizontal direction, a delay line configuration was used (see...). Figure 19Initially, this configuration is simulated using only one waveguide layer. The emitted beam will converge horizontally. By adding an etching layer that etches all the Si3N4 layers into the same delay line structure, a 2-D OPA can be formed on the side (see [link]). Figure 20 and Figure 21 ).

[0133] Therefore, recall that in this structure, a 2-D OPA is formed on the sidewall of the device. The OPA faces the air and will generate a 2-D converging beam, and the backward direction of the OPA consists of a series of waveguides with a non-uniform dielectric, thus highly suppressing backward emission. According to simulation results, the emission efficiency of the entire device can reach approximately 70% across the entire wavelength range of 1500nm to 1600nm. Compared to a single-layer OPA that emits an upward beam, the efficiency can be improved by 75% (assuming the efficiency of a single-layer OPA is 40%).

[0134] Beam steering of this device can be achieved through a combination of wavelength tuning and thermal tuning.

[0135] 1. The delay line structure is applied across all Si3N4 layers and is highly sensitive to wavelength tuning. Therefore, wavelength tuning will redirect the beam in the horizontal direction. Furthermore, unlike waveguide grating couplers, the delay length of this structure can be freely chosen; we can actually select the degree / wavelength sensitivity. As an example, we chose a delay length of 2.7 μm in this simulation and obtained a redirection sensitivity of 0.3 degrees / 1 nm. The table shows the data for this simulation in the horizontal (x) direction.

[0136] 2. Vertical beam focusing is achieved through a periodically distributed multilayer structure that is insensitive to wavelength tuning. In fact, the angle in the y-axis varies by only 0.034 degrees across the entire 100nm wavelength range. Therefore, we can use thermal tuning to vertically steer the beam. By fabricating metal heaters on the surface, we can heat the device from the top. In this case, a temperature gradient will be generated in the vertical direction, thus vertically steer the beam.

[0137] The number of layers in this structure is limited by the size that the light source can cover. Therefore, it may be difficult to achieve a truly low FWHM in the vertical (y) direction. One possible solution is to use a quasi-periodic layer structure in the vertical direction. For example... Figure 22 As shown, A = Si3N4, B = SiO2. Even using the same number of Si3N4 layers (6 layers in this simulation), the quasi-periodic structure can produce a lower FWHM than the ordinary periodic structure (see [reference]). Figure 23 Meanwhile, the wavelength sensitivity remains the same.

[0138] The foregoing description of the embodiments has been provided for illustrative and descriptive purposes. It is not intended to be exhaustive or limiting of this disclosure. Elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable where applicable and may be used in the chosen embodiment even if not specifically shown or described. Variations are also possible in many ways. Such variations should not be considered as departing from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

Claims

1. A beam steering device, the beam steering device comprising: The structure has multiple layers, each having alternating first and second material layers, which are configured to form a 3D optical phased array to emit light from the edges of the structure and output a 2D converged coupled beam from the elongated ends of the structure. The structure has an Ω-shaped delay line. The plurality of layers in the structure include a quasi-periodic configuration.

2. The beam steering device according to claim 1, wherein, Each of the first material layers in the first material layer has a thickness of 800 nm, and each of the second material layers in the second material layer has a thickness of 500 nm and is sandwiched between the first material layers.

3. The beam steering device according to claim 2, wherein, The spacing between adjacent layers in the plurality of layers is 2µm.

4. The beam steering device according to claim 1, wherein, Each of the first material layers has a thickness of 800 nm or less.

5. The beam steering device according to claim 1, wherein, Each of the second material layers has a thickness of 500 nm or less and is disposed between the first material layers.

6. The beam steering device according to claim 1, wherein, The structure includes docking coupling at the input end.

7. The beam steering device according to claim 1, wherein, The first material is Si3N4, and the second material is SiO2.

8. The beam steering device according to claim 1, wherein, The first material is Si, and the second material is SiO2.

9. The beam steering device according to claim 1, wherein, The first material is Si, and the second material is Si3N4.

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