All-solid-state light beam scanner based on acousto-optic effect

Abstract

A two-dimensional all-solid-state beam scanning device based on the acousto-optic effect is disclosed. By employing an interdigital transducer (IDT) array on-chip and combining it with electronic phased array technology, an acousto-optic grating with adjustable angle and period is formed on the beam propagation path on the chip, thereby realizing two-dimensional steering and scanning of the beam. The invention has a simple structure, no special requirements for the beam, and has broad application prospects.

Description

Technical Field

[0001] This invention relates to all-solid-state beam scanning, and in particular to an all-solid-state beam scanner based on the acousto-optic effect. Background Technology

[0002] Integrated beam scanning has wide-ranging applications in lidar, laser communication, and quantum manipulation. All-solid-state beam scanning techniques, such as optical phased arrays (OPA) and lens-assisted beam scanning (LABS), have been extensively studied, but they typically require wavelength scanning to achieve optimal performance. Acousto-optic effects offer another approach to achieving all-solid-state beam scanning. Traditional acousto-optic devices deflect beams by altering the beam's propagation direction within the acousto-optic material (e.g., Shao, Optics Express 28, 23728, 2020). Some reports have described forming gratings using acousto-optic effects, allowing the beam's propagation direction to detach from the acousto-optic material and propagate into free space (e.g., patent US20220206358A1). However, achieving two-dimensional beam steering requires introducing two acousto-optic gratings at a specific angle to the beam, controlling the wave vector of these gratings to achieve beam steering in a specific direction. Since the wave vector of the acousto-optic grating is related to the modulation frequency applied to the interdigital transducer (IDT), two mutually locked and independently adjustable signal sources are required, which makes control inconvenient. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, this invention provides a two-dimensional all-solid-state beam scanning device based on the acousto-optic effect. By employing an on-chip interdigital transducer (IDT) array combined with electronic phased array technology, an acousto-optic grating with adjustable angle and period is formed along the beam propagation path on the chip, thereby achieving two-dimensional beam steering and scanning. This solution has a simple structure, no special requirements for the beam, and broad application prospects.

[0004] The technical solution of the present invention is as follows:

[0005] An all-solid-state beam scanner based on the acousto-optic effect includes a chip, with an acousto-optic material thin film on the upper layer and a lower cladding layer on the lower layer; an input waveguide is fabricated on the acousto-optic material thin film, and a beam expander connected to the input waveguide is used to expand and collimate the light in the input waveguide to form a wide beam with small divergence in the propagation direction; and an interdigital transducer array consisting of N interdigital transducers (IDTs) arranged along the width direction of the output beam. The scanner is characterized by further including an electrical controller.

[0006] The interdigital transducer includes multiple interdigital electrodes, a reflector, and connecting traces. Each interdigital electrode is arranged along the beam propagation direction, and the direction of each interdigital electrode is perpendicular to the beam propagation direction. The period of the interdigital electrodes varies with chirping. A slot is formed on the interdigital electrode at the end of the beam propagation direction to reflect the sound wave generated by the IDT along the beam propagation direction into a sound wave that propagates in the opposite direction of the beam. The connecting traces connect each interdigital electrode in sequence and form a metal electrode at the tail end away from the beam propagation direction for connection to the electrical controller.

[0007] The electrical controller is electrically connected to each IDT via the connection traces, applying electrical signals of specific frequency, phase, and amplitude to each IDT. The frequency of the electrical signal matches the period of the interdigital electrodes. By applying electrical signals of the same frequency but different phases to all IDTs, an acousto-optic grating can be formed in the acousto-optic material film, between the beam expander and the interdigital transducer array. That is, the period of the acousto-optic grating is determined by the frequency of the electrical signals on the IDTs, and the direction of the acousto-optic grating is determined by the relative phase of the electrical signals on the IDTs. According to the direction of the acousto-optic grating, the power of the electrical signal applied to each IDT is adjusted to compensate for the difference in refractive index contrast of the acousto-optic grating caused by the anisotropy of the acousto-optic material film. The output beam is diffracted by the acousto-optic grating to form a free-space beam.

[0008] Furthermore, the periodic variation range of the interdigitated electrodes corresponds to the periodic variation range of the modulation signal applied to the IDT.

[0009] Furthermore, the acousto-optic material thin film is lithium niobate or aluminum nitride or other acousto-optic materials, and the thickness of the acousto-optic material thin film is less than 500 nm to enhance the moving boundry effect, so that the grating formed by the sound wave has a greater modulation depth (i.e., refractive index contrast).

[0010] Furthermore, the lower cladding layer is made of a low-refractive-index material, and is partially hollowed out in the region located between the output beam and the interdigital transducer array.

[0011] Furthermore, the beam expander employs perforations of varying density and size on an acousto-optic material film to adjust the refractive index distribution, thereby realizing an on-chip planar lens.

[0012] The chip edge is provided with a structure for directional reflection or elimination of sound wave reflection.

[0013] Preferably, the beam propagation region and the lower cladding below the IDT array are hollowed out, so that the sound waves can be completely confined in the acousto-optic material film, enhancing the interaction between the beam and the acousto-optic grating.

[0014] Preferably, the beam width should be greater than 100 μm;

[0015] Preferably, the modulation frequency range corresponding to the period of the interdigitated electrodes of the IDT is in the GHz range;

[0016] Preferably, the distance between the IDT array and the beam expander is on the order of millimeters to centimeters;

[0017] Preferably, the width of the IDT array in the y-direction should be more than 5 times the width of the beam to ensure that even when the generated sound wave has an angle with the beam, a long grating working area can still be guaranteed to achieve efficient deflection of the beam.

[0018] Preferably, the electrical controller 4 is connected to the IDT array 3 by wire bonding.

[0019] Preferably, in order to prevent acoustic waves propagating to the edge of the chip from being reflected back into the chip and affecting the deflection of the beam by the grating, a structure that can directionally reflect or eliminate acoustic wave reflection should be added to the edge of the chip.

[0020] The core of this invention is to achieve control over the period and direction of an acousto-optic grating. According to the IDT principle, when the period of the modulation frequency f applied to the IDT is the same as the period of the interdigital electrodes, sound waves (mechanical waves) can be generated in the acousto-optic material through its piezoelectric effect. Subsequently, through the photoelastic effect and moving boundry effect of the acousto-optic material, the refractive index of the thin film 1 is periodically changed, forming a grating. Therefore, changing the modulation frequency f on the IDT changes the grating period, with the relationship Λ = v / f, where v is the propagation speed of the sound wave in the acousto-optic material thin film 1. Therefore, the period of the interdigital electrodes of the IDT must be chirped to support the broadband modulation frequency f. On the other hand, by controlling the phase of the modulation frequency f applied to each IDT through the electrical controller 4, and combining this with the phased array principle, the propagation direction of the generated sound waves can be controlled, thus achieving adjustment of the grating direction.

[0021] The specific method for controlling the emission angle of beam 104 is as follows: The desired emission angle (corresponding to a wave vector in a vacuum) is... ), calculate its projection on the xy plane. The wave vector of the required grating Based on the calculated wave vector The value of is used, combined with the sound velocity v in the material, to calculate the required IDT modulation frequency f. Then, based on the wave vector... The direction of the acoustic wave and the direction of the grating can be controlled by adjusting the phase of the modulation frequencies on different IDTs. Furthermore, since acousto-optic materials are typically anisotropic, when controlling the acoustic wave direction using a phased array, compensation can be achieved by controlling the modulation power applied to the IDT to ensure that the resulting grating has a strong modulation depth (i.e., refractive index contrast).

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1) This invention uses electro-phase array technology to control the direction of the acousto-optic grating generated by the IDT array, and controls the period of the acousto-optic grating by the frequency of the electrical signal. A grating with both direction and period that can be continuously adjusted is generated on the beam propagation path, thereby realizing a continuous two-dimensional beam deflection and scanning without the need for optical signal wavelength-assisted adjustment.

[0024] 2) Compared with similar solutions based on acousto-optic effects (such as patent US20220206358A1), the electronic controller of the present invention only requires one adjustable signal source. By splitting and controlling the phase of the signal source, two-dimensional scanning of the beam can be achieved without multiple signal sources. Side lobes and stray signals distributed in the space of the beam can be effectively suppressed, and there are no blind spots in the scanning field of view. Attached Figure Description

[0025] Figure 1 (a) is a schematic diagram of the all-solid-state beam scanning device based on the acousto-optic effect of the present invention. Figure 1 (b) is an enlarged view of IDT.

[0026] In the figure: 1-Acousto-optic material thin film, 101-Input waveguide, 102-Beam expander, 103-Beam expanded after beam expansion, 104-Beam deflected and emitted into free space, 2-Lower cladding, 3-IDT array, 301-Single IDT, 3011-Interdigital electrode, 3012-Reflector, 3013-Connection trace, 302-Acoustic wave generated by the IDT array, 4-Electrical controller.

[0027] Figure 2 This is a schematic diagram of the synthesis of a beam and a grating wave vector.

[0028] In the picture: -The wave vector of a beam of light emitted into free space. - The wave vector of a light beam propagating in an acousto-optic thin film. - Wave vector of the grating - The projection of the wave vector of a beam in free space onto the xy plane. -Haiya and The angle between the sound wave 302 and the light beam 103 in the acousto-optic material film, θ - wave vector. The angle between the xy plane and the xy plane. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention. Embodiments of the present invention include, but are not limited to, the following embodiments.

[0030] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the all-solid-state beam scanning device based on the acousto-optic effect of the present invention. As shown in the figure, a two-dimensional all-solid-state beam scanning system based on the acousto-optic effect includes: a chip, an acousto-optic material thin film 1 on the upper layer of the chip, a lower cladding layer 2 on the lower layer, an input waveguide 101 and a beam expander 102 are fabricated on the acousto-optic material thin film 1, and an IDT array 3 is arranged laterally on the propagation path of the beam after passing through the beam expander 102. The IDT array 3 is controlled by an electronic controller 4.

[0031] The acousto-optic material thin film 1 has a film plane that is an xy plane and a film thickness direction (i.e., the normal direction of the chip) that is a z direction.

[0032] The input waveguide 101 is fabricated on the acousto-optic material thin film 1, and the waveguide propagation direction is along the +x direction; the input end of the input waveguide 101 is connected to the edge of the acousto-optic material thin film 1 for coupling of input light; the output end of the input waveguide 101 is connected to the beam expander 102; the input waveguide 101 supports the operation of the fundamental mode transverse electric (TE) mode or transverse magnetic (TM) mode.

[0033] The beam expander 102 expands and collimates the light input from the input waveguide 101, so that the output beam 103 of the beam expander 102 has a wider beam width in the y direction, while maintaining a small divergence in the propagation direction +x direction.

[0034] The IDT array 3 is located on the propagation path of the beam 103 after it has been expanded and collimated by the beam expander 102. The IDT array 3 consists of N IDTs 301 arranged along the y-direction. Each IDT 301 has the same design, including interdigitated electrodes 3011, reflectors 3012 and connecting lines 3013.

[0035] The interdigitated electrodes 3011 of the IDT 301 are arranged along the x-direction, and the period of the interdigitated electrodes varies with chirp, that is, the period gradually increases or decreases along the x-direction. The range of electrode period variation corresponds to the range of modulation signal period variation applied to the IDT. The reflector 3012 is a slot used to reflect the sound wave propagating along the +x direction generated by a single IDT into a sound wave propagating in the -x direction, thereby improving the conversion efficiency of the IDT. The connecting trace 3013 is used to connect the interdigitated electrodes 3011 and forms a metal electrode at the end of the IDT away from the propagation direction of the beam 103, which can be connected to the electronic controller 4.

[0036] The electrical controller 4 is electrically connected to each IDT through the connection trace 3013 of IDT3. The connection method can be wire bonding, flip-chip bonding, etc.

[0037] The acoustic wave 302 generated by the IDT array 3 forms a grating in the acousto-optic material film 1. The area where the grating and the beam 103 overlap is the grating action area. Through the interaction between the beam 103 and the grating, the beam is deflected in the direction of free space to form a free space beam 104.

[0038] The IDT array 3 and the beam expander 102 need to maintain a suitable distance. It is necessary to avoid the distance being too close, which would result in the grating's active area being too short and unable to effectively deflect the beam. It is also necessary to avoid the distance being too far, which would result in the beam 103 having already experienced a large propagation loss when it reaches the grating's active area, thus reducing the beam deflection efficiency.

[0039] The system's working principle and operation mode are as follows:

[0040] like Figure 2 As shown, a grating is formed in the acousto-optic material thin film 1 using an IDT array 3. The grating diffracts the beam 103, changing its propagation direction and directing it towards a specific angle in free space. Based on grating theory, assuming the grating period is Λ, its corresponding wave vector... The direction points towards the grating and lies in the xy plane, with a value K = 2π / Λ. The wave vector of beam 103 in thin film 1 is... The direction points in the direction of beam propagation, i.e., the +x direction, and its value is k1 = n. eff k0, where n eff Let k0 = 2π / λ = ω0 / c be the effective refractive index, k0 = 2π / λ = ω0 / c be the wave vector of the beam in vacuum, λ be the wavelength in vacuum, and ω0 be the angular frequency of the light. The synthesized wave vector is... Where m is an integer representing the diffraction order, we take first-order diffraction, i.e., m = 1. Clearly, by controlling the grating direction (i.e., the wave vector)... (direction) and grating period (i.e., wave vector) (size), then it can achieve the control of Control of any angle and magnitude within a plane. As long as the value satisfies k2 < k0, the light beam 103 can be emitted into free space, and the wave vector direction of the emitted light beam 104 satisfies k0 cosθ = k2, where θ is the angle between the emitted light beam and the xy plane.

[0041] The core of this invention is to achieve control over the period and direction of the acousto-optic grating. According to the IDT principle, when the period of the modulation frequency f applied on the IDT is the same as the period of the interdigital electrodes, acoustic waves (mechanical waves) can be generated in the acousto-optic material through its piezoelectric effect. Subsequently, through the photoelastic effect and moving boundary effect of the acousto-optic material, the refractive index of the thin film 1 is periodically changed to form a grating. Therefore, by changing the modulation frequency f on the IDT, the grating period can be changed, and the relationship is Λ = v / f, where v is the propagation speed of the acoustic wave in the acousto-optic material thin film 1. So the period of the interdigital electrodes of the IDT must be chirped to support the broadband modulation frequency f. On the other hand, by controlling the phase of the modulation frequency f applied on each IDT through the electrical controller 4 and combining with the phased array principle, the propagation direction of the formed acoustic wave can be controlled to achieve adjustment of the grating direction.

[0042] The specific method for controlling the emission angle of the light beam 104 is as follows: For the required emission angle (corresponding to a wave vector in vacuum ), calculate its projection on the xy plane Then the required wave vector of the grating -According to the calculated wave vector -value, combined with the sound speed v in the material, calculate the required IDT modulation frequency f. Then, according to the direction of the wave vector -, by controlling the phase of the modulation frequency on different IDTs, the control of the acoustic wave direction and grating direction can be achieved. In addition, since acousto-optic materials usually have anisotropy, when controlling the acoustic wave direction through a phased array, in order to ensure that the generated grating has a strong modulation depth (i.e., refractive index contrast), the modulation power applied on the IDT can be controlled for compensation.

Claims

1. An all-solid-state beam scanner based on acousto-optic effect, comprising a chip, an acousto-optic material thin film on the upper layer of the chip, and a lower cladding layer on the lower layer of the chip; an input waveguide is fabricated on the acousto-optic material thin film, and a beam expander connected to the input waveguide is used to expand and collimate the light in the input waveguide to form a wide beam with small divergence in the propagation direction; and an interdigital transducer array composed of N interdigital transducers (IDTs) arranged along the width direction of the output beam, characterized in that, It also includes the electrical controller; The interdigital transducer includes multiple interdigital electrodes, a reflector, and connecting traces. Each interdigital electrode is arranged along the beam propagation direction, and the direction of each interdigital electrode is perpendicular to the beam propagation direction. The period of the interdigital electrodes varies with chirping. A slot is formed on the interdigital electrode at the end of the beam propagation direction to reflect the sound wave generated by the IDT along the beam propagation direction into a sound wave that propagates in the opposite direction of the beam. The connecting traces connect each interdigital electrode in sequence and form a metal electrode at the tail end away from the beam propagation direction for connection to the electrical controller. The electrical controller is electrically connected to each IDT via the connection traces, applying electrical signals of specific frequency, phase, and amplitude to each IDT. The frequency of the electrical signal matches the period of the interdigital electrodes. By applying electrical signals of the same frequency but different phases to all IDTs, an acousto-optic grating can be formed in the acousto-optic material film, between the beam expander and the interdigital transducer array. That is, the period of the acousto-optic grating is determined by the frequency of the electrical signals on the IDTs, and the direction of the acousto-optic grating is determined by the relative phase of the electrical signals on the IDTs. According to the direction of the acousto-optic grating, the power of the electrical signal applied to each IDT is adjusted to compensate for the difference in refractive index contrast of the acousto-optic grating caused by the anisotropy of the acousto-optic material film. The output beam is diffracted by the acousto-optic grating to form a free-space beam.

2. The all-solid-state beam scanner based on acousto-optic effect according to claim 1, characterized in that, The periodic variation range of the interdigitated electrodes corresponds to the periodic variation range of the modulation signal applied to the IDT.

3. The all-solid-state beam scanner based on acousto-optic effect according to claim 1, characterized in that, The acousto-optic material film is lithium niobate, aluminum nitride, or other acousto-optic materials, and the thickness of the acousto-optic material film is less than 500 nm.

4. The all-solid-state beam scanner based on acousto-optic effect according to claim 1, characterized in that, The lower cladding is made of a low-refractive-index material and is partially hollowed out in the region located between the output beam and the interdigital transducer array.

5. The all-solid-state beam scanner based on acousto-optic effect according to claim 1, characterized in that, The beam expander uses perforations of varying density and size on an acousto-optic material film to adjust the refractive index distribution, thereby achieving an on-chip planar lens.

6. The all-solid-state beam scanner based on acousto-optic effect according to claim 1, characterized in that, The chip edge is provided with a structure for directional reflection or elimination of sound wave reflection.

Images