Design method of single transducer-dual-band AOTF device

Abstract

The invention relates to an acousto-optic tunable filter (Acoustical-optical tunable filter-AOTF), which is an electrically controlled tunable spectrum light splitting device, and is characterized in that the acousto-optic tunable filter (Acoustical-optical tunable filter-AOTF) is an electrically controlled tunable spectrum light splitting device. In a complex task, single-band information is often insufficient to support a decision, so that the invention provides a design method of a single transducer-dual-band acousto-optic tunable filter, a numerical calculation model is established through a dual-band wave vector geometry principle, and a dual-band tuning relationship under different cutting types is obtained. And furthermore, the design of the dual-band AOTF device with high diffraction efficiency and low power consumption is realized through the size optimization design of the transducer. Compared with an existing AOTF device design method, the single-transducer-dual-waveband AOTF device design method can utilize a single simple single-transducer AOTF device to obtain dual-waveband spectral data at the same time, the spectral range is expanded, the spectral detection efficiency is improved, and the detection capacity for a dynamic target is improved. Meanwhile, the dual-band detection can reduce the frequency of electrical power loading of the transducer, the thermal load of the device is reduced, and the working stability of the device is improved.

Description

Technical Field

[0001] This invention relates to the field of acousto-optic tunable filtering technology, specifically to a single transducer-dual-band design method for an acousto-optic tunable filter (AOTF). Background Technology

[0002] An acousto-optic transducer (AOTF) is a clever spectral element with advantages such as electrically tunable design, flexible band switching, small size, and all-solid-state construction with no moving parts. It is widely used in laser shaping, spectral analysis, hyperspectral imaging, and space exploration. An AOTF device mainly consists of a piezoelectric transducer, an acousto-optic crystal, and a sound absorber. The piezoelectric transducer receives radio frequency excitation and generates sound waves through the inverse piezoelectric effect. These waves are coupled into the acousto-optic crystal, altering its internal dielectric properties. Light waves of a specific wavelength that satisfy the Bragg condition undergo Bragg diffraction as they pass through the crystal, producing +1 (or -1) order diffracted light. Sub-millisecond-level rapid band tuning can be achieved by switching the radio frequency signal.

[0003] Multichannel technology is an important direction in the development of AOTF devices. Currently, polarization multiplexing design, multi-frequency control design, and AOTF dual-filter design have important applications in polarization analysis, laser shaping, device throughput optimization, spectral reconstruction, and stereo imaging. In complex environments, a single wavelength band, such as visible light or short-wave infrared, is often insufficient to acquire enough spectral features for accurate target detection and recognition. Existing solutions include dual AOTF system design and single AOTF dual-transducer design, which increases the difficulty of system design and device fabrication. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for a single transducer-dual-band AOTF device based on a vector matching model, which can be used to design dual-band AOTF devices with different characteristics and realize the synchronous and efficient acquisition of dual-band spectral information.

[0005] To address the aforementioned technical problems, the technical solution of this invention is as follows: a design method for a single transducer-dual-band AOTF device based on a vector matching model is proposed. This method first establishes a dual-band theoretical calculation model for the AOTF device based on the geometric matching relationship of wave vectors. Then, based on the required band range for the application, the available crystal cuts and the corresponding required frequency bandwidth are calculated and solved. Subsequently, within the available cut range, the transducer size is optimized for device performance indicators. Finally, the design is selected by comparing the performance parameters of different device designs.

[0006] The analytical method proposed in this invention mainly includes the following steps:

[0007] (1) By combining the device design parameters, acousto-optic crystal material parameters and external incident parameters, a dual-band theoretical calculation model of the single transducer-AOTF device is established;

[0008] (2) Determine the available crystal cuts that cover the required wavelength range and the required transducer frequency bandwidth;

[0009] (3) The transducer size can be optimized by using crystal cutting to improve device performance;

[0010] (4) Compare the design performance of several AOTF devices and make a selection.

[0011] Compared with existing methods for dual-band design of AOTF devices, the advantages of this invention are: (1) This method can achieve synchronous acquisition of dual-band data on a single-transducer AOTF device, improving device efficiency without increasing the difficulty of device fabrication; (2) This method can obtain dual-band data using a single power drive, reducing the number of device power loading times, which is beneficial to maintaining device stability; (3) The design method invented is not limited to a specific crystal material and is applicable to any crystal material. Attached Figure Description

[0012] The invention will be further described below with reference to the accompanying drawings:

[0013] Figure 1 Flowchart of design methodology for single transducer-dual-band AOTF devices;

[0014] Figure 2 This is a schematic diagram of the crystal cutting parameters for the AOTF device;

[0015] Figure 3 A schematic diagram of the acousto-optic wave vector layout of a dual-band AOTF device;

[0016] Figure 4 This is a schematic diagram of the tuning relationship of a dual-band AOTF device;

[0017] Figure 5 A transducer size design method for single-transducer-dual-band AOTF devices; Detailed Implementation

[0018] The design method of a single transducer-dual-band AOTF device proposed in this invention will be further described in detail below with reference to the accompanying drawings.

[0019] like Figure 1As shown, the design method proposed in this invention mainly includes three key steps: establishing a theoretical parameter calculation model for a dual-band AOTF device, using cut-type solutions to achieve the required dual-band design, and optimizing transducer size design. The main objective is to obtain design parameters (ultrasonic cut-type) for a dual-band AOTF device that meet application requirements. Angle of incident plane ) and transducer design parameters (length L, width H), such as Figure 2 As shown.

[0020] Firstly, regarding the establishment of the dual-band theoretical model, the main basis is... Figure 3 The diagram illustrates the geometric relationship between the momentum-matched wave vectors in the dual-band system. Both bands simultaneously satisfy the momentum-matching relationship, i.e.:

[0021] (1)

[0022] in, These are the incident light, diffracted light, and sound wave vectors, respectively. , , . The wavelength of light For ultrasonic frequency, For the speed of sound, , , , are the refractive indices of the incident and diffracted light, respectively. In anisotropic birefringent acousto-optic crystals, the ordinary (-o) and extraordinary (-e) rays have different refractive indices, and the refractive index of the e ray depends on the direction of light propagation:

[0023] (2)

[0024] The superscripts o and e are used for o-light and e-light, respectively. and is the intrinsic refractive index of the acousto-optic crystal. The angle between the light wave vector within the crystal and the crystal axis

[001] . Anisotropic crystals are also acoustically anisotropic; the direction of the sound energy velocity deviates from the direction of the sound wave vector, and the magnitude of the sound phase velocity depends on the propagation direction.

[0025] (3)

[0026] in The ultrasonic cutting angle is defined as the angle between the crystal ultrasonic transducer surface and the crystal axis

[001] . , The sound velocities along the

[110] and

[001] axes, respectively, are determined by the elastic stiffness coefficient and density of the crystal.

[0027] The geometric basis of the design of a single transducer-dual-band AOTF device is that the crystal wave vector circle (ellipse) and the straight line of the acoustic wave vector direction may have two intersection points, which can form two vector matching triangles with different acoustic wave frequencies. That is, under the same crystal cut, the same incident conditions and the same wavelength, there are two acoustic waves with different frequencies that can satisfy the momentum matching condition. Figure 3 A schematic diagram of the wave vector geometry designed for dual-band operation. In e→o mode, and Both interact with sound waves to produce +1st order Bragg diffraction; the difference lies in their interaction with sound waves. The interacting acoustic vectors intersect the o-light wave vector circle twice, ultimately forming a vector matching triangle, utilizing high-frequency acoustic waves. And with... The interacting acoustic vector intersects the o-wave vector circle only once, utilizing low-frequency acoustic waves. For the o→e mode, and and The interacting acoustic vectors originate from the o-wave vector circle and intersect the e-wave vector circle to the right and left, respectively, producing +1st and -1st order diffraction. (Synthesis) Figure 3 Given the geometric relationship of the wave vector, substituting equations (2) and (3) into equation (1), we can obtain the following system of equations:

[0028] (4)

[0029] (5)

[0030] Equations (4) and (5) are the theoretical calculation formulas for the tuning relationship of the dual bands in e→o and o→e modes, respectively. , The center wavelength of the dual channels The incident plane tangent in the working mode of the e-light incident and o-light emitting device is defined as the angle between the crystal incident plane and the crystal axis

[110] . and These represent the center wavelengths of the dual channels in the operating mode of the o-light incident and e-light emitting devices. and The diffraction angle is defined as the angle between the diffracted light within the crystal and the crystal axis

[001] . The center wavelength of the dual channels can be obtained by numerically solving the equations: such as Figure 4 for The dual-band tuning relationship of the e→o mode under the cut-out design will Figure 4 In Substituting into formula (4) The solution can then be obtained from the formula. For another channel wavelength At the same time, the corresponding frequency can be obtained. Similarly, substitute... The wavelength of the other channel was obtained by solving the problem. and the corresponding frequency It was achieved in Within the frequency range, and Dual-band tuning.

[0031] Then, based on the theoretical formula for diffraction efficiency, parameters such as peak power and diffraction efficiency can be obtained:

[0032] (6)

[0033] (7)

[0034] (8)

[0035] Let momentum mismatch be defined in the direction perpendicular to the velocity of sound wave energy. The length of the acoustic-optical interaction; The coupling parameters for the acousto-optic interaction, and the acousto-optic figure of merit. and sound power density related. For the effective acousto-optic coefficient, and the acousto-optic crystal density Acousto-optic coefficient And crystal cut parameters, momentum matching e-wave vector angle related.

[0036] Further, based on the required band range, calculate the available cut types and their covered band range and frequency bandwidth. In practical designs, the number of dual-band cut types that perfectly match a specific band range is limited. Therefore, based on a trade-off of various design parameters, the band range is allowed to be expanded. The specific operation is as follows: traverse the cut types, calculate the other band range under that cut type based on the band range of a certain channel, and check if it meets the requirements. If not, select the band range of another channel, perform the same calculation, and verify. The cut type that meets the requirements is the usable cut type, and record the corresponding frequency bandwidth of the dual bands. The longer wavelength band is designated as CH1, and the shorter wavelength band as CH2.

[0037] Next, the device performance parameters under different available cut types are calculated, and the transducer size is optimized to achieve high diffraction efficiency under low power consumption. According to equations (6) to (8), under the condition of momentum matching, the diffraction efficiency fluctuates periodically with the increase of power. Under the same conditions, there are multiple powers that can make the diffraction efficiency reach 100%, which are defined as peak powers, and the minimum value is the minimum peak power. If the wavelength difference between the two channels is large, the minimum peak power required will be large. Therefore, it is necessary to use the periodic relationship between diffraction efficiency and power to design the transducer size so that the corresponding wavelengths of the two channels can obtain high diffraction efficiency at the same power. Under the same conditions, the power consumption characteristics of the device depend on the aspect ratio of the transducer. Therefore, the specific design optimization operation is to traverse the aspect ratio of the transducer, expand the calculation on the center wavelength of the CH1 channel and the corresponding wavelength of the CH2 channel, select the value of the multiple peak power of CH2 that is closest to the minimum peak power of CH1, so that the difference between the two is minimized, so that the peak power of the two channels is close throughout the entire band, and each can obtain high diffraction efficiency with the same power. Figure 5 In e→o mode, Under the given conditions, the calculation results show that as the aspect ratio of the transducer increases, the peak power difference between the two channels decreases monotonically. At the intersection of the power-diffraction efficiency curves of the two bands, higher diffraction efficiency can be obtained simultaneously, while the overall power consumption of the device also decreases.

[0038] Finally, the performance parameters of different cut types after certain optimization, including band range, frequency bandwidth, device power consumption, and diffraction efficiency, are summarized and compared to select the dual-band AOTF device design that meets the requirements.

[0039] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A design method for a single transducer-dual-band AOTF device, characterized in that, The dual-band AOTF device, under the same polarization mode, frequency, and incident angle, simultaneously satisfies the momentum matching relationship, forming two closed vector triangles on the wave vector schematic. The two bands have different separation angles. This design method includes the following steps: (1) By combining the device design parameters, acousto-optic crystal material parameters and external incident parameters, a dual-band theoretical calculation model of the single transducer-AOTF device is established; (2) Determine the available crystal cuts that cover the required wavelength range and the required transducer frequency bandwidth; (3) The transducer size can be optimized by using crystal cutting to improve device performance; (4) Compare the design performance of several AOTF devices and make a selection.

2. The design method of a single transducer-dual-band AOTF device as described in claim 1, characterized in that, In step (1), the device design parameters include: the angle between the crystal incident plane and the crystal axis [110]. Hereinafter referred to as the incident plane tangent; the angle between the crystal ultrasonic transducer surface and the crystal axis [001]. Hereinafter referred to as ultrasonic shear angle; the theoretical calculation of the dual-band tuning relationship is based on solving the following system of equations: ； in, For driving frequency, The velocity of ultrasound in an acousto-optic crystal. The center wavelength of the dual channels For ultrasonic cutting angle, The incident plane chamfer angle in the operating mode of the e-light incident and o-light emitting device. The refractive index of the incident light, Let be the intrinsic refractive index of the acousto-optic crystal under ordinary light conditions; the calculation for the o-light incident and e-light emitting device operating mode is based on the following formula: ； in Refractive index of diffracted light and The center wavelengths of the two channels are respectively and The diffraction angle is defined as the angle between the diffracted light in the crystal and the crystal axis [001].

3. The design method of a single transducer-dual-band AOTF device as described in claim 1, characterized in that, In step (2), the selection method for the dual-band AOTF device to be cut is as follows: within one band range of the dual-band requirement, the other channel of its corresponding dual-channel design includes the other band range of the dual-band requirement, so that the dual channels can cover the complete band requirement range; the frequency bandwidth is defined as the minimum frequency bandwidth required to cover the complete band.

4. The design method of a single transducer-dual-band AOTF device as described in claim 1, characterized in that, In step (3), a transducer size optimization design method for synchronous acquisition of high diffraction efficiency of dual channels in single transducer-dual-band AOTF device is proposed: by designing the aspect ratio of the transducer, the difference between the minimum peak power of the long wavelength channel and the peak power of the short wavelength channel closest to it at the center wavelength of the dual channels (the center wavelength of the long wavelength channel and the wavelength of the corresponding short wavelength channel) is minimized, so that the center wavelength of the dual channels can simultaneously obtain high diffraction efficiency at the same and smaller power.

5. The design method of a single transducer-dual-band AOTF device as described in claim 1, characterized in that, The design method for the drive power of the device at the same frequency is as follows: between the minimum peak power of the long wavelength channel and the peak power of the short wavelength channel that is closest to it, select the power corresponding to the intersection of the power-efficiency curves of the dual-channel wavelengths as the drive power at that frequency.

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