Two-dimensional light beam scanning device based on film lithium niobate

Abstract

The invention discloses a two-dimensional light beam scanning device based on thin-film lithium niobate, a light transmission area disclosed by the device comprises a plurality of electro-optical switches which are connected in sequence, and the electro-optical switches are expanded into a 1 * N switch array with a Log2 (N) order, so that one input end and N output ends are formed in the light transmission area. And when light beam scanning is realized, the cascaded electro-optical switches are regulated and controlled to control the light beam to be output from one of the N output ports and enter a specified radiator, so that scanning of the light beam on the waveguide layer is completed. In the process, only Log2 (N) electro-optical switches are turned on, so that the power consumption of the device is only Log2 (N) times of that of one electro-optical switch, the device has the advantages of high scanning speed, low power consumption loss and the like, the light output area array is provided with a plurality of light radiators, a planar two-dimensional array is formed, and by controlling the cascaded electro-optical switch array, the power consumption of the device is reduced. Therefore, the multiple radiators can be lightened at the same time, and the high-speed and low-loss two-dimensional display function can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of electro-optical switches and relates to a two-dimensional light beam scanning device based on thin-film lithium niobate. Background Art

[0002] LiDAR technology plays an indispensable role in autonomous driving, 3D mapping, environmental monitoring and other fields with its unique advantages. LiDAR accurately measures the distance and speed of objects by emitting and receiving laser pulses, and achieves high-resolution distance and speed detection of the surrounding environment through beam steering devices. Traditional beam steering devices, such as mechanical rotating mirrors and micro-electro-mechanical system (MEMS) mirrors, are susceptible to external vibrations due to the presence of mechanical moving parts, resulting in limited beam steering speed and poor reliability.

[0003] All-solid-state beam steering technology does not contain any moving parts, which significantly improves the beam steering speed and reliability of devices, such as optical phased arrays (OPA), lens-assisted focal plane arrays (FPA), liquid crystal spatial light modulators (SLM), etc. Due to the limitations of the liquid crystal material itself, its devices have a slower beam steering speed. In addition, when the OPA is working, all phase shifters operate simultaneously, which not only requires complex circuit control, but also introduces higher power consumption and optical losses, as well as limited sidelobe suppression ratio. In contrast, FPA only needs to operate log2(N) optical switches to control N optical transmitters, which greatly reduces the control complexity, power consumption and optical losses.

[0004] There are two main types of FPAs currently: FPAs based on MEMS optical switches and FPAs based on thermo-optical effects.

[0005] MEMS-based FPA, as described in the document "A large-scale microelectromechanical-systems-based silicon photonics LiDAR" (Nature, 2022, 603, 7900: 253-258). This scheme uses silicon waveguide to design MEMS switches to achieve beam selection and beam deflection. However, due to the two-photon absorption of silicon waveguides, the waveguide cannot withstand a power of more than 10mW, which limits the output power of the device. Secondly, the MEMS optical switch controls the up and down movement of the suspended silicon waveguide through electrostatic attraction to achieve the on and off of the optical path, and the operating speed is relatively slow, only 1.1μs.

[0006] Based on the thermo-optic effect, the waveguide materials of this scheme include silicon, silicon nitride and silicon oxide, and the thermo-optic coefficient of silicon photons is used to design optical switches. As described in the literature "Two-dimensional scanning of silicon-based focal plane array with field-of-view splicing technology (Optics Express, 2023, 31, 2, 1464-1474), a heating electrode is placed above the silicon waveguide to achieve phase modulation through heat conduction. A thermo-optic switch is designed based on the Mach-Zehnder interferometer (MZI) structure, and finally the beam deflection is achieved through an off-chip lens. However, the thermo-optic switch speed is only 43μs, and the power consumption is as high as 50mW / π.

[0007] Both types of FPA mentioned above have certain problems. The MEMS-based FPA uses the electrostatic adsorption force of MEMS to control the up and down movement of the silicon waveguide, thereby realizing the on and off of the optical path. Due to the presence of mechanical moving parts, the device is easily affected by external vibrations and has poor stability; secondly, the beam scanning speed of the device depends on the operating speed of the MEMS optical switch, that is, the speed of the external circuit that provides the electrostatic force. At present, the maximum scanning speed of this solution is only in the microsecond level. The FPA based on the thermo-optical effect uses the thermo-optical coefficient of silicon photons to achieve phase modulation. It is a solid-state beam scanning device with high stability and service life. However, under the vertical layout of the electrode and the waveguide, the modulation method of its heat conduction causes the beam scanning speed to be limited to the microsecond level. At the same time, the heat absorption of the heating electrode also causes the loss of this solution to be as high as milliwatts. Summary of the invention

[0008] The purpose of the present invention is to solve the problems of slow speed and large power loss when completing light beam steering in the prior art, and to provide a two-dimensional light beam scanning device based on thin film lithium niobate.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A two-dimensional light beam scanning device based on thin-film lithium niobate comprises a substrate layer, a buried layer, a thin-film lithium niobate layer and a loading waveguide layer which are sequentially distributed from bottom to top;

[0011] The loading waveguide layer comprises a light coupling region, a light transmission region and a light output region connected in sequence;

[0012] The optical transmission area includes a plurality of electro-optical switches connected in sequence, and the plurality of electro-optical switches connected in sequence enable the optical transmission area to form an input end and a plurality of output ends, and the input end is connected to the output end of the optical coupling area;

[0013] The light output area array has a plurality of light radiators, and the input ends of the plurality of light radiators are correspondingly connected to the plurality of output ends of the light transmission area in sequence;

[0014] Electrodes are arranged at intervals on one side of the electro-optical switch.

[0015] A further improvement of the present invention is:

[0016] The plurality of sequentially connected electro-optical switches include a plurality of cascades connected end to end;

[0017] A plurality of end-to-end connected cascades include a first cascade, wherein the first cascade includes an electro-optical switch, the electro-optical switch of the first cascade includes a plurality of output terminals, and each output terminal of the first cascade is respectively connected to each input terminal of the second cascade;

[0018] Among the plurality of cascades connected end to end, the last cascade includes a plurality of output ends, and the plurality of output ends of the last cascade are all connected to the input end of the optical transmission area.

[0019] In the plurality of end-to-end connected cascades, the number of output terminals of each cascade is greater than the number of input terminals.

[0020] The plurality of sequentially connected electro-optical switches include a first cascade, a second cascade and a third cascade connected in sequence;

[0021] The second cascade comprises two electro-optical switches distributed in parallel, the two electro-optical switches are provided with four output terminals, and the input terminals of the two parallel arrays of electro-optical switches are respectively connected to the output terminals of the first cascade switches;

[0022] The third cascade comprises four parallel arrays of electro-optical switches, the four parallel arrays of electro-optical switches are provided with eight output terminals, and the input terminals of the four parallel arrays of electro-optical switches are respectively connected to the four output terminals in the second cascade.

[0023] The electro-optical switch comprises a first beam splitter, a dual-channel traveling wave modulator, and a second beam splitter connected in sequence;

[0024] The first beam splitter has one input end and two output ends;

[0025] The second beam splitter has two input ends and two output ends.

[0026] The number of the light radiators is N, where N≥4.

[0027] The N optical radiators are distributed in a manner of n×m, wherein n represents the number of rows in which the optical radiators are distributed, and m represents the number of columns in which the optical radiators are distributed, and both n and m are greater than or equal to 2.

[0028] The distance between any two adjacent light radiators is greater than or equal to 100 μm.

[0029] When the N optical radiators are distributed, a row spacing is 300 μm and a column spacing is 400 μm.

[0030] A scanning method based on the device of the present invention comprises the following steps:

[0031] The off-chip light source is coupled into the on-chip waveguide through the optical coupling region and enters the optical transmission region along the output end of the optical coupling region;

[0032] In the light transmission area, the light beam is selectively inputted from one of the output ends into the corresponding light radiator;

[0033] The optical radiator transmits the light beam to the off-chip lens to complete the beam scanning.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The invention discloses a two-dimensional light beam scanning device based on thin-film lithium niobate. The light transmission area disclosed by the device includes a plurality of electro-optical switches connected in sequence. The electro-optical switches are expanded into a 1×N switch array with a Log2(N) order, so that the light transmission area forms an input end and a plurality of output ends. When light beam scanning is realized, the cascaded electro-optical switches are regulated to control the light beam to be output from one of the N output ports and enter a designated radiator to complete the scanning of the light beam in the waveguide layer. In this process, only Log2(N) electro-optical switches are turned on, so the power consumption of the device is only Log2(N) times that of one electro-optical switch, the scanning speed is fast, the power consumption loss is low, and the light output area array has a plurality of light radiators to form a planar two-dimensional array. By controlling the cascaded electro-optical switch array, multiple radiators are lit up at the same time to realize a high-speed, low-loss two-dimensional display function. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 It is a schematic diagram of a two-dimensional light beam scanning device based on thin-film lithium niobate proposed by the present invention.

[0038] Figure 2 It is a schematic diagram of a thin-film lithium niobate 1×2MZI electro-optical switch proposed by the present invention.

[0039] Figure 3 yes Figure 2 Cross-sectional view of the xoz plane at the A-A' position.

[0040] Figure 4 It is the relationship between the optical power and phase difference of the two output ports of the 1×2MZI electro-optical switch.

[0041] Figure 5 This is the far-field spot diagram of the single beam scanning in Example 1.

[0042] Figure 6 This is the two-dimensional display image in Example 2.

[0043] Wherein: 1-substrate layer; 2-buried layer; 3-thin-film lithium niobate layer; 4-electrode; 5-loaded waveguide layer; 6-off-chip lens;

[0044] 51-light coupling area; 52-light transmission area; 53-light output area;

[0045] 500 - electro-optic switch; 501 - first beam splitter; 502 - dual-channel traveling wave modulator; 503 - second beam splitter; 511 - optical coupler; 530 - optical radiator. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0049] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0050] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0051] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0052] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0053] See also Figure 1 The embodiment of the present invention discloses a two-dimensional light beam scanning device based on thin film lithium niobate, comprising a substrate layer 1, a buried layer 2, a thin film lithium niobate layer 3 and a loading waveguide layer 5 which are sequentially distributed from bottom to top; the loading waveguide layer 5 comprises an optical coupling area 51, an optical transmission area 52 and an optical output area 53 which are sequentially connected; the optical transmission area 52 comprises a plurality of electro-optical switches 500 which are sequentially connected, and the plurality of electro-optical switches 500 which are sequentially connected make the optical transmission area 52 form an input end and a plurality of output ends, and the input end is connected to the output end of the optical coupling area 51; the optical output area 53 has a plurality of optical radiators 530 in array, and the input ends of the plurality of optical radiators 530 are sequentially connected to the plurality of output ends of the optical transmission area 52; an electrode 4 is arranged at intervals on one side of the electro-optical switch 500.

[0054] Furthermore, the loading waveguide layer 5 is attached to the thin film lithium niobate layer (3) by a thin film deposition or bonding process, and together with the thin film lithium niobate layer 3, a heterogeneous ridge waveguide is constructed. The material of the loading waveguide layer 5 can be silicon nitride, silicon, sulfide, etc., but is not limited thereto. Specifically, the width of the loading waveguide layer 5 is 500nm~2μm, and the thickness is 100~500nm.

[0055] Furthermore, the material of the electrode 4 can be gold, aluminum, etc., but is not limited thereto. The thickness of the electrode 4 is 200nm-600nm, the width is 10μm-200μm, and the spacing between the electrode and the waveguide is not less than 1.5μm, which can effectively reduce the plasma absorption loss of the metal.

[0056] Furthermore, the thin film lithium niobate layer 3 is in the form of a planar waveguide. The tangent direction of the thin film lithium niobate is x-cut or y-cut, and the thickness is 300nm to 900nm.

[0057] Furthermore, the refractive index of the buried layer 2 is smaller than the refractive index of the loaded waveguide layer 5 and the thin film lithium niobate layer 3, which plays a role in binding the light beam and preventing the light beam from radiating to the outer layer.

[0058] Furthermore, the material of the substrate layer 1 includes one or more of silicon, glass, lithium niobate, sapphire, and quartz, and has a thickness of 450-550 μm, which plays a supporting role.

[0059] Furthermore, the optical coupling region 51 is an optical coupler 511 for coupling light in the off-chip optical fiber into the on-chip waveguide, including end face coupling and grating coupling, and the effective area of ​​the grating is 25 μm×20 μm.

[0060] Furthermore, the array structure of the electro-optical switches in the optical transmission area 52 is:

[0061] The electro-optical switch array is a 1×N electro-optical switch array, which includes a plurality of 1×2 MZI electro-optical switches connected end to end and cascaded, wherein 1×2 represents one input port and two output ports, and 1×N represents one input port and N output ports.

[0062] Specifically, the input end of the first cascaded 1×2MZI electro-optical switch is connected to the output end of the optical coupler, and the two output ports of the first cascaded 1×2MZI electro-optical switch are respectively connected to the input ports of the two 1×2MZI electro-optical switches of the second cascade, and the cascade is Log2(N) times to construct a 1×N electro-optical switch array, which has one input port and N output ports.

[0063] In this embodiment, due to the special array distribution mode, the number of output terminals of each cascade is greater than the number of input terminals.

[0064] Furthermore, in this embodiment, the structure of each electro-optical switch is:

[0065] It includes a first beam splitter 501, a dual-channel traveling wave modulator 502 and a second beam splitter 503 which are connected in sequence. The first beam splitter 501 has an input port and two output ports, and is used to split a single light beam into two light beams. The dual-channel traveling wave modulator 502 has two input ports and two output ports. The second beam splitter 503 has two input ports and two output ports. The two output ports of the first beam splitter 501 are connected to the two input ports of the dual-channel traveling wave modulator 502, and the output end of the dual-channel traveling wave modulator 502 is connected to the two input ends of the second beam splitter 503.

[0066] The input end of the first beam splitter 501 is the input end of the 1×2 MZI electro-optical switch, and the output end of the second beam splitter 503 is the output end of the 1×2 MZI electro-optical switch.

[0067] During operation, the light beam is split into two beams by the first beam splitter 501 and enters the dual-channel traveling wave modulator 502 respectively. A signal generator is used to apply a high-frequency microwave signal to the traveling wave electrode of the traveling wave modulator to achieve phase control of the light beam in the waveguide. The two beams with phase difference are output from the dual-channel traveling wave modulator 502 and enter the second beam splitter 503, and interfere with each other in the second beam splitter 503, and finally selectively output from the output port of the second beam splitter 503 according to the different phase differences.

[0068] Furthermore, in this embodiment, the type of the beam splitter may be one of a multimode interference beam splitter, a Y branch and a directional coupler.

[0069] Furthermore, in this embodiment, the dual-channel traveling wave modulator 502 is composed of coplanar electrodes and thin-film lithium niobate and silicon nitride heterogeneous integrated waveguides.

[0070] Furthermore, in this embodiment, the distribution of the electrodes 4 is as follows:

[0071] Electrode 4 includes a signal electrode and a ground electrode. The signal electrode is located in the middle of the dual-channel waveguide, and the two ground electrodes are located on both sides of the dual-channel waveguide. By applying a microwave signal to the signal electrode, a modulation electric field with opposite directions is generated in the waveguides on both sides, thereby achieving a push-pull modulation effect and effectively reducing the half-wave voltage. The size of the electrode is changed so that the group refractive index of the traveling wave electrode is the same as the group refractive index of the waveguide. At this time, the microwave signal in the traveling wave electrode and the optical transmission signal in the waveguide meet the speed matching, thereby achieving high-speed modulation efficiency. At the same time, the size of the electrode is changed so that the equivalent impedance of the traveling wave electrode is close to 50 ohms, thereby achieving impedance matching conditions, reducing the return loss of the microwave signal, and realizing a low-power traveling wave modulator.

[0072] Furthermore, in this embodiment, the specific distribution structure of the light output area 53 is:

[0073] The light output area 53 is composed of radiators 530 in n rows and m columns, where n×m=N. N is not less than 4, and n and m are not less than 2 (if the radiator layout is 1×N, only one-dimensional beam scanning can be achieved). The radiator can be a grating radiator or an end radiator. To avoid crosstalk between radiators, the spacing between radiators is not less than 100μm. The N radiators are connected to the output end of the 1×N optical switch array through S waveguides and correspond one to one.

[0074] Furthermore, in this embodiment, an off-chip lens 6 is also included. The off-chip lens 6 is a plano-convex lens located on the transmission path of the radiation beam, with a focal length of 35 mm, and its focal plane array coincides with the radiator plane. Before the radiation beam passes through the lens, the beams emitted by different radiators are parallel to each other. The beams are collimated and steered by the lens, and by lighting different radiators, the input light source is directed to different far-field beam directions.

[0075] Furthermore, the working principle of this embodiment is:

[0076] The off-chip light source is coupled into the on-chip waveguide through the optical coupler 511. When the light beam passes through the 1×2MZI electro-optical switch of the first cascade, the voltage of the traveling wave modulator is adjusted so that the light beam is selectively output from an output port of the electro-optical switch and enters an electro-optical switch of the second cascade. By analogy, only one of the N output ports of the 1×N optical switch array is selected. The light beam is guided to a radiator in the radiator array through the S waveguide. The off-chip lens 6 collimates the radiated light and converts the two-dimensional position relationship in the plane into a two-dimensional angular deflection in space. The scanning speed of the light beam and the power consumption of the chip in this embodiment depend on the performance of the optical switch. The present invention designs an electro-optical switch based on a traveling wave modulator of thin-film lithium niobate, and its modulation speed can reach the nanosecond level, and the power consumption per π phase shift is in the picojoule level.

[0077] The present invention applies an electro-optical switch based on thin-film lithium niobate to a focal plane array, improves the light beam scanning speed of the scanning scheme, reduces the power consumption of the device, has the advantages of convenient design, easy expansion, compact structure, etc., and has outstanding and significant technical effects.

[0078] See also Figure 1 In the device disclosed in this embodiment, the optical switch array is a 1×16 electro-optical switch array, which is formed by 15 1×2 MZI electro-optical switches 500 connected end to end in cascade.

[0079] The two output ports of the first cascaded 1×2 MZI electro-optical switch are respectively connected to the input ports of the two 1×2 MZI electro-optical switches of the second cascade, and the cascade is performed four times in sequence to construct a 1×16 electro-optical switch array having one input port and 16 output ports.

[0080] See also Figure 2 , is a schematic diagram of the structure of a 1×2MZI electro-optical switch. Each 1×2MZI electro-optical switch includes a first beam splitter 501, a dual-channel traveling wave modulator 502, and a second beam splitter 503. The first beam splitter 501 has an input port and two output ports, and is used to split a single light beam into two light beams; the second beam splitter 503 has two input ports and two output ports. The two output ports of the first beam splitter 501 are connected to the two input ports of the dual-channel traveling wave modulator, and the output end of the dual-channel traveling wave modulator 502 is connected to the two input ends of the second beam splitter 503. The input end of the first beam splitter 501 is the input end of the 1×2MZI electro-optical switch, and the output end of the second beam splitter 503 is the output end of the 1×2MZI electro-optical switch. The light beam is split into two light beams by the first beam splitter 501 and enters the dual-channel traveling wave modulator 502 respectively. A high-frequency microwave signal is applied to the traveling wave electrode of the traveling wave modulator by a signal generator to realize the phase control of the light beam in the waveguide. Two beams of light with a phase difference are output from the dual-channel traveling wave modulator 502 and enter the second beam splitter 503 , and interfere with each other in the second beam splitter 503 , and are finally selectively output from the output port of the second beam splitter 503 according to the different phase differences.

[0081] In this embodiment, the beam splitter adopts a multimode interference beam splitter. Compared with the Y branch or directional coupler, the multimode interference beam splitter has more friendly processing tolerance and lower insertion loss.

[0082] like Figure 3 The figure shows a cross-sectional view of a dual-channel traveling wave modulator, which is composed of a coplanar electrode and a thin-film lithium niobate and silicon nitride heterogeneous integrated waveguide. The signal electrode is located in the middle of the dual-channel waveguide, and the two ground electrodes are located on both sides of the dual-channel waveguide. By applying a microwave signal to the signal electrode, a modulation electric field in opposite directions is generated in the waveguides on both sides, thereby achieving the effect of push-pull modulation and effectively reducing the half-wave voltage. The size of the electrode is changed so that the group refractive index of the traveling wave electrode is approximately the same as the group refractive index of the waveguide. At this time, the microwave signal in the traveling wave electrode and the optical transmission signal in the waveguide meet the speed matching, achieving high-speed modulation efficiency. At the same time, the size of the electrode is changed so that the equivalent impedance of the traveling wave electrode is close to 50 ohms, achieving impedance matching conditions, reducing the return loss of the microwave signal, and realizing a low-power traveling wave modulator.

[0083] The radiator array is 16 focusing gratings, which radiate the light in the waveguide into free space through the diffraction radiation mode. The layout of the radiator array is 4 rows and 4 columns, the row spacing is 300μm, the column spacing is 400μm, and the effective radiation area of ​​the grating is 25μm×20μm. The 16 radiators 530 are connected to the output end of the 1×16 optical switch array through an S waveguide with a radius of 300μm and correspond one to one.

[0084] The off-chip lens 6 is a plano-convex lens located above the radiator array, with a focal length of 35 mm, and its focal plane array coincides with the radiator plane. Before the radiation beam passes through the lens, the beams emitted by different radiators are parallel to each other. The beams are collimated and turned by the lens, and by lighting different radiators, the input light source is pointed to different far-field beam directions.

[0085] The waveguide structure of this embodiment is a heterogeneous integrated waveguide of thin-film lithium niobate and silicon nitride. The thin-film lithium niobate is a planar waveguide, silicon nitride is recorded on the surface of the thin-film lithium niobate, and the light mode is transmitted together in the two media. The thickness of the X-cut thin-film lithium niobate is 300nm, the thickness of the silicon nitride waveguide is 300nm, the thickness of the buried layer silicon dioxide is 4.7μm, and the thickness of the silicon substrate is 525μm. The working band is 1550nm. In order to better limit the base film TE0 and TM0 of the transverse electric mode, the width of the silicon nitride waveguide is 1μm. The traveling wave electrode is in the same layer as the silicon nitride waveguide and is located on both sides of the silicon nitride waveguide, 3μm away from the silicon nitride waveguide, with a thickness of 500nm, a signal width of 120μm, a width of 50μm, and a length of 8mm. The material is gold.

[0086] like Figure 4 As shown in the figure, it is the relationship between the phase difference of the two arms after modulation by the traveling wave modulator and the optical power of the two output ports of the 1×2MZI electro-optical switch. It can be seen from the figure that the optical power of the two output ports shows an inverse relationship with the phase difference. Generally, when the phase difference changes from 0 to 2π, the electro-optical switch can realize an actively controlled beam splitter with an arbitrary beam splitting ratio. In particular, when the phase difference is an integer multiple of π, the optical power of the two output ports is the same, and the electro-optical switch realizes a 3dB beam splitter function. When the phase difference is an odd multiple of π / 2, the light beam is selectively output from output port 1 or port 2 to realize the optical switch function. In particular, when the phase difference is π / 2, the normalized output optical power of output port 1 is 1, the normalized output optical power of output port 2 is 0, and the light beam is almost output from output port 1. At this time, output port 1 is opened and output port 2 is closed. In particular, when the phase difference is 3π / 2, the normalized output optical power of output port 1 is 0, the normalized output optical power of output port 2 is 1, and the light beam is almost output from output port 2. At this time, output port 1 is closed and output port 2 is opened. Based on this, two specific embodiments are also disclosed.

[0087] Example 1

[0088] When the incident light beam enters the optical switch array, the phase difference of the first 1×2MZI electro-optical switch through which the light beam passes is regulated to be an odd multiple of π / 2, so that the light beam is output from only one output port of the first 1×2MZI electro-optical switch and enters the second cascaded 1×2MZI electro-optical switch. Similarly, in the present embodiment, only four electro-optical switches need to be controlled to guide the incident light beam to one of the 16 radiators. The radiation light beam is collimated and deflected by an off-chip lens to achieve two-dimensional scanning of a single light beam. Figure 5 Shown is the far-field spot diagram when one radiator is illuminated.

[0089] Example 2

[0090] When the incident light beam enters the optical switch array, the phase difference of the 1×2MZI electro-optical switch at a specific position is adjusted to an integer multiple of π, so that the light beam is output from both output ports of the electro-optical switch, achieving an output state of 3dB. The two output beams will simultaneously enter the next cascaded 1×2MZI electro-optical switch. Similarly, more light beams are output from the electro-optical switch array to the radiator array, and eventually multiple light spots appear in the far field, based on which two-dimensional imaging of multiple light beams can be achieved. Figure 6 As shown, by adjusting the phase difference of the electro-optical switch at a specific position to an integer multiple of π, multiple radiators at a specific position are lit up, and letter images of "N", "P" and "U" are constructed in the far field through discrete light spots to achieve a two-dimensional display function.

[0091] The scanning speed of the light beam and the power consumption of the chip depend on the performance of the optical switch. The present invention designs an electro-optical switch based on a traveling wave modulator of thin-film lithium niobate. The insertion loss of the modulation process is below 0.32dB, the modulation speed can reach the nanosecond level, and the power consumption per π phase shift is in the picojoule level. In summary, the present invention can simultaneously achieve extremely low insertion loss, extremely low power consumption and high-speed light beam scanning, while various solutions of the comparative technology cannot simultaneously achieve these performances.

[0092] The present invention expands the thin-film lithium niobate 1×2MZI electro-optical switch into a 1×N switch array with Log2(N) order by cascading end to end, wherein the number of optical switches of the i-th order is 2i–1, i=1,2,3…Log2(N). When beam scanning is realized, the cascaded electro-optical switches are regulated to control the light beam to be output from one of the N output ports and enter the designated radiator through the S waveguide. The radiated light is then collimated by an off-chip lens, and the two-dimensional position relationship of the radiator in the plane is converted into a two-dimensional angle deflection in space. In this process, only Log2(N) electro-optical switches are turned on, so the power consumption of the device is only Log2(N) times that of one electro-optical switch, and the beam scanning speed of the device is determined by the speed of the thin-film lithium niobate 1×2MZI electro-optical switch. The designed thin-film lithium niobate 1×2MZI electro-optical switch has a switching speed of the order of nanoseconds and a power consumption of the order of picojoules per π phase shift. Therefore, the two-dimensional light beam scanning device based on thin-film lithium niobate proposed in the present invention has a switching speed of nanoseconds and a power consumption of picojoules per π phase shift, which solves the problems of slow speed and high loss of traditional light beam scanning technology.

[0093] Furthermore, the radiator array is a planar two-dimensional array. By controlling the cascaded electro-optical switch array, multiple radiators can be lit up at the same time to achieve a high-speed, low-loss two-dimensional display function.

[0094] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A two-dimensional beam scanning device based on thin film lithium niobate, characterized in that: It comprises a substrate layer (1), a buried layer (2), a thin-film lithium niobate layer (3) and a loaded waveguide layer (5) which are sequentially distributed from bottom to top; The loading waveguide layer (5) comprises a light coupling region (51), a light transmission region (52) and a light output region (53) which are connected in sequence; The optical transmission area (52) comprises a plurality of electro-optical switches (500) connected in sequence, wherein the plurality of electro-optical switches (500) connected in sequence enable the optical transmission area (52) to form an input end and a plurality of output ends, wherein the input end is connected to the output end of the optical coupling area (51); The light output area (53) array has a plurality of light radiators (530), and the input ends of the plurality of light radiators (530) are sequentially connected to the plurality of output ends of the light transmission area (52); Electrodes (4) are arranged at intervals on one side of the electro-optical switch (500).

2. A two-dimensional light beam scanning device based on thin film lithium niobate according to claim 1, characterized in that: The plurality of sequentially connected electro-optical switches (500) include a plurality of cascades connected end to end; A plurality of end-to-end connected cascades include a first cascade, wherein the first cascade includes an electro-optical switch, the electro-optical switch of the first cascade includes a plurality of output terminals, and each output terminal of the first cascade is respectively connected to each input terminal of the second cascade; Among the plurality of cascades connected end to end, the last cascade comprises a plurality of output ends, and the plurality of output ends of the last cascade are all connected to the input end of the optical transmission area (52).

3. A two-dimensional light beam scanning device based on thin film lithium niobate according to claim 2, characterized in that: In the plurality of end-to-end connected cascades, the number of output terminals of each cascade is greater than the number of input terminals.

4. A two-dimensional light beam scanning device based on thin film lithium niobate according to claim 2, characterized in that: The plurality of sequentially connected electro-optical switches (500) include a first cascade, a second cascade and a third cascade connected in sequence; The second cascade comprises two electro-optical switches distributed in parallel, the two electro-optical switches are provided with four output terminals, and the input terminals of the two parallel arrays of electro-optical switches are respectively connected to the output terminals of the first cascade switches; The third cascade comprises four parallel arrays of electro-optical switches, the four parallel arrays of electro-optical switches are provided with eight output terminals, and the input terminals of the four parallel arrays of electro-optical switches are respectively connected to the four output terminals in the second cascade.

5. The two-dimensional light beam scanning device based on thin film lithium niobate according to claim 1, characterized in that: The electro-optical switch comprises a first beam splitter (501), a dual-channel traveling wave modulator (502) and a second beam splitter (503) connected in sequence; The first beam splitter (501) has one input end and two output ends; The second beam splitter (503) includes two input ends and two output ends.

6. The two-dimensional light beam scanning device based on thin film lithium niobate according to claim 1, characterized in that: The number of the light radiators (530) is N, where N≥4.

7. A two-dimensional light beam scanning device based on thin film lithium niobate according to claim 6, characterized in that: The N optical radiators (530) are distributed in an n×m manner, wherein n represents the number of rows in which the optical radiators are distributed, and m represents the number of columns in which the optical radiators are distributed, and both n and m are greater than or equal to 2.

8. The two-dimensional light beam scanning device based on thin film lithium niobate according to claim 7, characterized in that: The distance between every two adjacent light radiators (530) is greater than or equal to 100 μm.

9. A two-dimensional light beam scanning device based on thin film lithium niobate according to claim 8, characterized in that: When the N optical radiators (530) are distributed, a row spacing is 300 μm and a column spacing is 400 μm.

10. A scanning method based on the device of claim 1, characterized in that: The following steps are involved: The off-chip light source is coupled into the on-chip waveguide through the light coupling region (51), and enters the light transmission region (52) along the output end of the light coupling region (51); In the light transmission area (52), the light beam is selectively input from one of the output ends to the corresponding light radiator (530); The optical radiator (530) transmits the light beam to an off-chip lens to complete the light beam scanning.

Images