Composite acousto-optic modulation device based on single radio frequency source driving and adjustment method thereof

Abstract

The invention relates to the technical field of acousto-optic modulation, in particular to a composite acousto-optic modulation device based on single radio frequency source driving and an adjusting method of the composite acousto-optic modulation device. The device comprises a radio frequency driving source, a power divider, a phase shifter, a first power amplifier, a second power amplifier, a first acousto-optic modulator, a second acousto-optic modulator, a first lens and a second lens. A radio frequency driving signal output by the radio frequency driving source is divided into two branches after passing through the power divider, the first branch drives the first acousto-optic modulator after passing through the first power amplifier, and the second branch drives the second acousto-optic modulator after passing through the second power amplifier; the first acousto-optic modulator, the first lens, the second lens and the second acousto-optic modulator are sequentially arranged on a light path; and the phase shifter is arranged in one branch of the radio frequency driving signal and is used for adjusting the phase of the radio frequency driving signal for driving the branch. The diffraction efficiency and the control flexibility of the composite acousto-optic modulation device are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of acousto-optic modulation, in particular to a composite acousto-optic modulation device driven by a single radio frequency source and an adjustment method thereof. Background Art

[0002] An acousto-optic modulator is a device that uses Bragg diffraction to quickly control the frequency, phase, intensity, and direction of light. It is widely used in optical communications, lidar, spectral analysis, fiber optic sensing, and optical applications and scientific research. The first-order diffraction efficiency of an acousto-optic modulator is affected by factors such as the wavelength of the light wave, the aspect ratio of the piezoelectric transducer, the ultrasonic power emitted by the piezoelectric transducer, and the quality factor of the acousto-optic medium itself. Affected by factors such as the properties of the acousto-optic crystal material, the impedance matching of the RF circuit, and the heat loss of ultrasonic energy, the diffraction efficiency of the acousto-optic modulator is difficult to exceed 85%, which limits the application of this technology in scenarios where light loss needs to be suppressed, such as high-power laser applications, long-distance optical quantum communications, micro-nano optical systems, and laser cumulative frequency shift based on acousto-optic modulators.

[0003] Moreover, traditional acousto-optic modulators also have the problem of narrow working bandwidth. Composite acousto-optic modulators can solve these problems. Through the cascade of two or more acousto-optic modulators, it uses the acousto-optic interaction to diffract the light beam, and achieves flexible switching of the optical path and efficient beam modulation by precisely controlling the phase and amplitude of the RF signal. It has high diffraction efficiency, low optical loss and wide working bandwidth, so it has attracted the attention of researchers: Mathevet et al. demonstrated the application of composite acousto-optic modulators at the single-photon level and realized the observation of single-photon beat frequency signals (American Journal of Physics, 88, 313, (2020)); Liu Ruijuan et al. used the composite acousto-optic modulation scheme to achieve wide-bandwidth and high-efficiency modulation of continuous lasers and pulsed lasers (Opt. Express, 30, 27780 (2022)); Li Wenqi et al. introduced a dual-frequency interferometer based on an acousto-optic modulator and demonstrated its application in quantum technology (Chin.Opt. Lett., 22, 022703 (2024)).

[0004] However, the existing composite acousto-optic modulation technology solutions often require the use of two or more RF sources to drive multiple acousto-optic modulators. Therefore, clock synchronization between the RF sources is required during operation, otherwise the phase difference of the optical signal cannot be kept constant, which leads to failure of the working conditions. Moreover, the solution of multiple RF sources not only increases the complexity of system design, but also the additional RF sources and synchronization equipment increase the system cost. Summary of the invention

[0005] In order to solve the above-mentioned technical problems existing in the prior art acousto-optic modulator, the present invention proposes a composite acousto-optic modulation device driven by a single radio frequency source and an adjustment method thereof, so as to simplify the structure of the device, reduce the cost, and improve the diffraction performance and phase stability of the device.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a composite acousto-optic modulation device based on single RF source drive, including a RF drive source, a power divider, a phase shifter, a first power amplifier, a second power amplifier, a first acousto-optic modulator, a second acousto-optic modulator, a first lens and a second lens; The RF driving signal output by the RF driving source is divided into two branches after passing through the power divider, wherein the first branch drives the first acousto-optic modulator after passing through the first power amplifier, and the second branch drives the second acousto-optic modulator after passing through the second power amplifier; the first acousto-optic modulator, the first lens, the second lens and the second acousto-optic modulator are arranged in sequence on the optical path; the first acousto-optic modulator is located at the focus of the first lens, and the second acousto-optic modulator is located at the focus of the second lens; the phase shifter is arranged in one of the branches of the RF driving signal, and is used to adjust the phase of the RF driving signal driving the branch.

[0007] The first lens and the second lens have the same focal length.

[0008] The distances between the first AOM, the first lens, the second lens and the second AOM are respectively: f, 2f, f, where f is the focal length of the first lens and the second lens.

[0009] The composite acousto-optic modulation device based on single RF source drive also includes an attenuator, which is arranged in one of the RF driving branches and is used to adjust the RF signal strength of the branch.

[0010] The attenuator is used to adjust the intensity of the radio frequency signal driving one of the AOMs so that the sum of the diffraction efficiencies of the first AOM and the second AOM is 1.

[0011] The first lens and the second lens are plano-convex lenses.

[0012] In addition, the present invention also provides a method for adjusting the composite acousto-optic modulation device driven by a single radio frequency source, comprising the following steps: Step 1: Set the operating frequency of the RF driving source to the central operating frequency of the AOM; make the laser incident on and focused to the crystal center of the first AOM, collimate the laser and keep the laser stable; Step 2: Adjust the angle of the first AOM to optimize its diffraction efficiency; Step 3: sequentially adjusting the distance between the first lens and the second lens and the angle of the second AOM, so that the two beams of light output by the second AOM are transmitted in a symmetrical distribution; Step 4: Adjust the angle of the second AOM to optimize its diffraction efficiency; Step 5: adjusting the driving voltage of one of the AOMs until its diffraction efficiency reaches a set value, and then adjusting the driving voltage of the other AOM until its diffraction efficiency reaches a set value, wherein the sum of the diffraction efficiency set values ​​of the two AOMs is 1; Step 5: Adjust the phase difference between the first AOM and the second AOM by using a phase shifter until the diffraction efficiency of the composite AOM device is maximized.

[0013] The specific method of step 5 is: adjusting the RF drive signal voltage output by the RF drive source until the diffraction efficiency of one of the AOMs reaches a set value; and adjusting the attenuation coefficient of the attenuator of the branch where the other AOM is located until the diffraction efficiency of the other AOM reaches the set value.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention proposes a composite acousto-optic modulation device driven by a single radio frequency source and an adjustment method thereof, wherein composite acousto-optic modulation is realized by a power divider and a phase shifter, and the diffraction efficiencies of two acousto-optic modulators are made complementary, and the phase difference between the two arms is adjusted by a phase shifter, so that the diffraction efficiency and control flexibility of the composite acousto-optic modulation device can be effectively and significantly improved; more efficient and more stable optical modulation output is achieved; and the structure is simple, reducing the system cost; the invention is suitable for the fields of quantum optics and quantum information technology, and can meet the high requirements for diffraction efficiency and amplitude stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of the structure of a composite acousto-optic modulation device driven by a single radio frequency source provided by an embodiment of the present invention; Figure 2 It is a schematic diagram of the principle of an embodiment of the present invention; Figure 3 A schematic diagram showing the variation of the diffraction efficiency of a composite acousto-optic modulation device driven by a single radio frequency source with respect to the relative phase provided in an embodiment of the present invention; Figure 4 A schematic diagram of the dependence of the maximum diffraction efficiency and the minimum diffraction efficiency of a composite acousto-optic modulation device driven by a single radio frequency source on the diffraction efficiency of a first acousto-optic modulator provided by an embodiment of the present invention; In the figure: 1 is the first power amplifier, 2 is the second power amplifier, 3 is the first lens, 4 is the second lens, 5 is the first acousto-optic modulator, 6 is the second acousto-optic modulator, and 7 is the optical fiber coupling head. DETAILED DESCRIPTION

[0016] 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. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0017] Embodiment 1 like Figure 1 As shown, embodiment 1 of the present invention provides a composite acousto-optic modulation device based on single RF source drive, including an RF drive source, a power divider, a phase shifter, a first power amplifier 1, a second power amplifier 2, a first acousto-optic modulator 5, a second acousto-optic modulator 6, a first lens 3 and a second lens 4.

[0018] Among them, Figure 1 As shown, the output end of the RF driving source is connected to the power divider, and the two output ends of the power divider are connected to the phase shifter and the attenuator respectively. The output end of the phase shifter is connected to the first power amplifier 1, and the output end of the first power amplifier 1 is connected to the RF signal input end of the first acousto-optic modulator 5; the output end of the attenuator is connected to the second power amplifier 2, and the output end of the second power amplifier 2 is connected to the RF signal input end of the second acousto-optic modulator 6. Wherein, the RF driving signal output by the RF driving source is divided into two branches after passing through the power divider, wherein the first branch drives the first acousto-optic modulator 5 after passing through the first power amplifier 1, and the second branch drives the second acousto-optic modulator 6 after passing through the second power amplifier 2; the first acousto-optic modulator 5, the first lens 3, the second lens 4 and the second acousto-optic modulator 6 are arranged in sequence on the optical path; the first acousto-optic modulator 5 is located at the focus of the first lens 3, and the second acousto-optic modulator 6 is located at the focus of the second lens 4; the phase shifter is arranged in one of the branches of the RF driving signal, and is used to adjust the phase of the RF driving signal driving the branch.

[0019] Furthermore, in this embodiment, the focal lengths of the first lens and the second lens are the same. Furthermore, in the first AOM 5, the first lens 3, the second lens 4 and the second AOM 6, the distances between two adjacent ones are respectively: f, 2f, f, where f is the focal length of the first lens and the second lens.

[0020] Specifically, in this embodiment, the phase shifter is arranged in the RF driving branch where the first acousto-optic modulator 5 is located, that is, the phase shifter is located between the power divider and the first power amplifier 1. In addition, the phase shifter can also be arranged in the RF driving branch where the second acousto-optic modulator 6 is located, that is, the phase shifter can also be arranged between the power divider and the second power amplifier.

[0021] Furthermore, if Figure 1 As shown, a composite acousto-optic modulation device based on a single RF source drive in this embodiment further includes an attenuator, which is arranged in the RF driving branch where the second acousto-optic modulator 6 is located to adjust the RF signal strength driving the second acousto-optic modulator 6, and can be located between the power divider and the second power amplifier. In addition, in this embodiment, the attenuator can also be arranged in the RF driving branch where the first acousto-optic modulator 5 is located, which can be arranged between the power divider and the first power amplifier 1, and can be located before or after the phase shifter.

[0022] Specifically, in this embodiment, the first lens and the second lens are plano-convex lenses.

[0023] Specifically, in this embodiment, the attenuator is used to adjust the intensity of the radio frequency signal driving one of the AOMs so that the sum of the diffraction efficiencies of the first AOM 5 and the second AOM 6 is 1.

[0024] Combine the following Figure 2 The modulation principle of the present invention is introduced.

[0025] Treat the AOM as a beam splitter, each AOM has two input ports and two output ports, such as Figure 2 As shown. The beam transmission matrix U can express the relationship between input and output: ; (1) in, and are the diffraction coefficients between input port 1 and output port 3 and between input port 2 and output port 4, respectively. and are the transmission coefficients between input port 2 and output port 3 and between input port 1 and output port 4 respectively; d and t represent the diffraction coefficient and transmission coefficient respectively, and denote the complex conjugate of t and d respectively. Applying this transmission matrix to the first acousto-optic modulator 5 and considering the RF direction, the relationship between the output field and the input field can be obtained as follows: ; (2) in, , represent the two input fields of the first acousto-optic modulator 5, respectively, , They represent two output fields of the first AOM 5, U1 represents the transmission matrix of the first AOM 5, and denote the diffraction coefficient and transmission coefficient of the first acousto-optic modulator 5, respectively, and Respectively and The complex conjugate of , where, for the input field E1, E3 is level 1 and E4 is level 0; for the input field E2, E3 is level 0 and E4 is level -1.

[0026] Expanding formula (2), we have: ; (3) . (4) The transmission matrix is ​​used again for the second AOM 6. Note that the RF loading direction applied by the second AOM 6 is opposite to the RF loading direction of the first AOM 5. Figure 2 As shown, we get: ; (5) in, and They represent two output fields of the second AOM 6, U2 represents the transmission matrix of the second AOM 6, where: and denote the diffraction coefficient and transmission coefficient of the second AOM 6, respectively, and Respectively and The complex conjugate of. For the input field E3, E'3 is level 1 and E'4 is level 0; for the input field E4, E'3 is level 0 and E'4 is level 1. After passing through the AOM twice, the output field E'4 includes a level 1 signal. Expanding equation (5), we have: + + ; (6) ; (7) This theoretical model is applied to this embodiment. Since in this embodiment there is only one input field at the input end of the first AOM 5 ,therefore =0. The phase of light incident on the first AOM 5 is assumed to be the initial phase, and we can obtain: ; (8) ; (9) In the formula and are the laser circular frequency and the RF circular frequency respectively. Corresponding to the interference with the same frequency as the original laser, The corresponding frequency is larger than the original laser frequency The interference is usually the part that needs to be used (the frequency has changed). The phase caused by the light propagation process has been taken into account, where and denote the accumulated phase shifts along the upper and lower arms of the composite AOM device, respectively.

[0027] In this embodiment, the diffraction efficiency of the first AOM is required to be ) and the diffraction efficiency of the second AOM 6 ( ) is 1, that is: ; (10) Formula (10) is called the complementary condition.

[0028] In order to make the discussion consistent, let ,but , , , then: ; (11) signal light The corresponding light intensity is expressed as: ; (12) when ( is an integer), the maximum diffraction light intensity is obtained ;when When , the diffraction light intensity is minimum, and its value is .

[0029] Therefore, in this embodiment, under the premise of setting the diffraction efficiencies of the two AOMs to be complementary, the phase difference between the upper arm and the lower arm of the two composite AOM devices is adjusted by the phase shifter, so that the diffraction efficiency of the composite AOM device can be maximized.

[0030] Embodiment 2 Embodiment 2 of the present invention provides a method for adjusting a composite acousto-optic modulation device driven by a single radio frequency source, comprising the following steps: Step 1: Set the operating frequency of the RF driving source to the central operating frequency of the AOM; make the laser incident on and focused to the crystal center of the first AOM, collimate the laser and keep the laser stable.

[0031] In this embodiment, the operating frequency of the RF driving source is set to 250 MHz, and the RF amplitude is adjusted to be within the operating range of the two AOMs, with an initial value of 400 mV.

[0032] In this embodiment, the laser is introduced into the device through the fiber coupling head 7, the laser is collimated and the parameters are kept stable. In this embodiment, the laser wavelength λ = 689 nm, the power is 10 mW, and the waist spot is 0.2 mm. The output of the first acousto-optic modulator 5 is imaged to the second acousto-optic modulator 6 through a 4-f system. In the 4-f system, the focal lengths of the first lens and the second lens are equal, both f = 30 mm.

[0033] Step 2: Adjust the angle of the first AOM to optimize its diffraction efficiency.

[0034] In this embodiment, the Gaussian beam output by the fiber coupling head 7 passes through the first AOM 5, so that the beam waist position is at the crystal center of the first AOM 5, and the angle of the first AOM 5 is adjusted to optimize the diffraction efficiency.

[0035] Step 3: sequentially adjust the distance between the first lens 3 and the second lens 4 and the angle of the second AOM 6 so that the two light beams output by the second AOM 6 are transmitted in a symmetrical distribution.

[0036] Step 4: Adjust the angle of the second AOM 6 to optimize its diffraction efficiency.

[0037] Step 5: Adjust the driving voltage of one of the AOMs until its diffraction efficiency reaches a set value, and then adjust the driving voltage of the other AOM until its diffraction efficiency reaches a set value, wherein the sum of the diffraction efficiency set values ​​of the two AOMs is 1.

[0038] The specific method of step 5 is: adjusting the RF drive signal voltage output by the RF drive source until the diffraction efficiency of one of the AOMs reaches a set value; and adjusting the attenuation coefficient of the attenuator of the branch where the other AOM is located until the diffraction efficiency of the other AOM reaches the set value.

[0039] Specifically, in this embodiment, when measuring the diffraction efficiency of the first AOM 5, the second AOM 6 is turned off, and when measuring the diffraction efficiency of the second AOM 6, the first AOM 5 is turned off. During the measurement, the power meter is set behind the second AOM 6 for measurement.

[0040] Specifically, in this embodiment, four situations were selected for testing: the diffraction efficiencies of the first AOM 5 and the second AOM 6 were 0.5-0.5, 0.6-0.4, 0.7-0.3, and 0.8-0.2.

[0041] Step 6: The phase difference between the first AOM 5 and the second AOM 6 is adjusted by a phase shifter until the diffraction efficiency of the composite AOM device is maximized.

[0042] like Figure 3 The figure shows the dependence of the measured diffraction efficiency of the composite acousto-optic modulator on the relative phase of the phase shifter under different diffraction efficiency setting conditions. It can be seen from the figure that in the four cases (0.5--0.5, 0.6--0.4, 0.7--0.3, 0.8--0.2), the maximum diffraction efficiency is basically the same, and the relative phase corresponding to the maximum diffraction efficiency is consistent, which is consistent with the conclusion given in the principle part.

[0043] In order to quantify the maximum diffraction efficiency and minimum diffraction efficiency of the composite acousto-optic modulation device driven by a single RF source of the present invention under the "complementary condition" of the diffraction efficiency of the two acousto-optic modulators, the dependence of the maximum diffraction efficiency and the minimum diffraction efficiency on the diffraction efficiency of the first acousto-optic modulator 5 is recorded, as shown in FIG. Figure 4 As shown. Figure 4 It can be seen that under various complementary conditions, the maximum diffraction efficiency of the device is basically the same, with an average value of 0.95 and a measurement variance of 0.01. The minimum diffraction efficiency of the device decreases with the increase of the diffraction efficiency of the first acousto-optic modulator 5, which is consistent with the theoretical expected value (1-2x) 2 (The curve in the figure) is consistent.

[0044] In summary, the present invention proposes a composite acousto-optic modulation device driven by a single radio frequency source and an adjustment method thereof, wherein composite acousto-optic modulation is realized by a power divider and a phase shifter, and the diffraction efficiencies of the two acousto-optic modulators are made complementary, and the phase difference between the two arms is adjusted by a phase shifter, so that the diffraction efficiency and control flexibility of the composite acousto-optic modulation device can be effectively and significantly improved; more efficient and more stable optical modulation output is achieved; and the structure is simple, which reduces the system cost; the present invention is suitable for the fields of quantum optics and quantum information technology, and can meet the high requirements for diffraction efficiency and amplitude stability.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite acousto-optic modulation device driven by a single radio frequency source, characterized in that: It includes a radio frequency driving source, a power divider, a phase shifter, a first power amplifier, a second power amplifier, a first acousto-optic modulator, a second acousto-optic modulator, a first lens, and a second lens; The RF driving signal output by the RF driving source is divided into two branches after passing through the power divider, wherein the first branch drives the first acousto-optic modulator after passing through the first power amplifier, and the second branch drives the second acousto-optic modulator after passing through the second power amplifier; the first acousto-optic modulator, the first lens, the second lens and the second acousto-optic modulator are arranged in sequence on the optical path; the first acousto-optic modulator is located at the focus of the first lens, and the second acousto-optic modulator is located at the focus of the second lens; the phase shifter is arranged in one of the branches of the RF driving signal, and is used to adjust the phase of the RF driving signal driving the branch.

2. A composite acousto-optic modulation device driven by a single radio frequency source according to claim 1, characterized in that: The first lens and the second lens have the same focal length.

3. A composite acousto-optic modulation device based on single RF source drive according to claim 2, characterized in that: The distances between the first AOM, the first lens, the second lens and the second AOM are respectively: f, 2f, f, where f is the focal length of the first lens and the second lens.

4. The composite acousto-optic modulation device driven by a single radio frequency source according to claim 1, characterized in that: It also includes an attenuator, which is arranged in one of the radio frequency driving branches and is used to adjust the radio frequency signal strength of the branch.

5. The composite acousto-optic modulation device based on single RF source drive according to claim 4, characterized in that: The attenuator is used to adjust the intensity of the radio frequency signal driving one of the AOMs so that the sum of the diffraction efficiencies of the first AOM and the second AOM is 1.

6. The composite acousto-optic modulation device driven by a single radio frequency source according to claim 1, characterized in that: The first lens and the second lens are plano-convex lenses.

7. The method for adjusting a composite acousto-optic modulation device driven by a single radio frequency source according to claim 1, characterized in that: The following steps are involved: Step 1: Set the operating frequency of the RF driving source to the central operating frequency of the AOM; make the laser incident on and focused to the crystal center of the first AOM, collimate the laser and keep the laser stable; Step 2: Adjust the angle of the first AOM to optimize its diffraction efficiency; Step 3: sequentially adjusting the distance between the first lens and the second lens and the angle of the second AOM, so that the two beams of light output by the second AOM are transmitted in a symmetrical distribution; Step 4: Adjust the angle of the second AOM to optimize its diffraction efficiency; Step 5: adjusting the driving voltage of one of the AOMs until its diffraction efficiency reaches a set value, and then adjusting the driving voltage of the other AOM until its diffraction efficiency reaches a set value, wherein the sum of the diffraction efficiency set values ​​of the two AOMs is 1; Step 5: Adjust the phase difference between the first AOM and the second AOM by using a phase shifter until the diffraction efficiency of the composite AOM device is maximized.

8. The method for adjusting a composite acousto-optic modulation device driven by a single radio frequency source according to claim 7, characterized in that: The specific method of step 5 is: adjusting the RF drive signal voltage output by the RF drive source until the diffraction efficiency of one of the AOMs reaches a set value; and adjusting the attenuation coefficient of the attenuator of the branch where the other AOM is located until the diffraction efficiency of the other AOM reaches the set value.

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