Megahertz frequency magnitude laser amplitude modulation device

Abstract

The invention discloses a megahertz frequency magnitude laser amplitude modulation device which comprises a polarization laser, a first beam splitter prism, an acousto-optic modulator, a multi-axis displacement table, a second beam splitter prism, a first reflective mirror, a half-wave plate and a second reflective mirror. Wherein the acousto-optic modulator is arranged on the multi-axis displacement table; polarized laser emitted by the polarized laser passes through the first beam splitter prism and then is divided into transmitted light and reflected light, and the transmitted light enters the acousto-optic modulator. Diffracted light emitted from the acousto-optic modulator is transmitted by the second beam splitter prism to obtain second transmission light; the reflected light reaches the half-wave plate after being reflected by the second reflective mirror, then is transmitted by the half-wave plate, is reflected by the first reflective mirror, enters the second beam splitter prism and is reflected to obtain second reflected light; and adjusting the multi-axis displacement table to enable the second transmission light and the second reflection light to be collinear. The device has the advantages of being compact in structure, low in cost and stable in modulation waveform.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser amplitude modulation, and particularly relates to a laser amplitude modulation device in the megahertz frequency range. Background Art

[0002] Laser amplitude modulation is a key technology widely used in many fields such as optical communication, fiber optic sensing, and optoelectronic measurement. In particular, in the field of measuring the velocity of particles in a strong background environmental noise, modulating the incident laser in the megahertz frequency range, in order to reduce the influence of background noise on the measurement accuracy, it is necessary to perform band-pass filtering centered on the incident laser frequency on the laser scattered by the particles, and then perform cross-correlation calculation on the signals to determine the time delay between the two signals. A key point in this measurement technology is how to effectively modulate the incident laser in the megahertz frequency range.

[0003] Commonly used laser amplitude modulation technologies include optical shutters, optical choppers, built-in modulation optical paths, etc. Among them, the modulation frequency of optical shutters generally does not exceed one hundred hertz; optical choppers generally use the method of opening holes on a rotating disk and driving the rotating disk to rotate by a mechanical device, and usually the modulation frequency is not higher than one thousand hertz; the built-in modulation optical path is restricted by the circuit performance, and usually the modulation frequency is not higher than 30 kHz. In the patent "A Device for Measuring Particle Velocity under Strong Background Interference Using Modulated Laser" (CN 115166283 A), an amplitude modulation scheme is introduced. In this invention, a broadband optoelectronic amplitude modulator is used for amplitude modulation. The advantage of this amplitude modulation system is that the modulation frequency is adjustable, but it has strict requirements for RF input, especially for power amplifiers, resulting in a relatively large volume of this laser amplitude modulation system, being difficult to integrate, and having a high cost. Summary of the Invention

[0004] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a laser amplitude modulation device in the megahertz frequency range, which has the advantages of compact structure, low cost, and stable modulation waveform.

[0005] The object of the present invention is achieved by the following technical solutions: A laser amplitude modulation device in the megahertz frequency range, comprising: a polarized laser, a first beam splitting prism, an acousto-optic modulator, a multi-axis displacement stage, a second beam splitting prism, a first reflector, a half-wave plate and a second reflector; wherein, the acousto-optic modulator is arranged on the multi-axis displacement stage; the polarized laser emitted by the polarized laser is divided into a transmitted light and a reflected light after passing through the first beam splitting prism, and the transmitted light enters the acousto-optic modulator; the diffracted light emitted from the acousto-optic modulator passes through the second beam splitting prism to obtain a second transmitted light; the reflected light is reflected by the second reflector and reaches the half-wave plate, then passes through the half-wave plate and is reflected by the first reflector and then enters the second beam splitting prism and is reflected to obtain a second reflected light; the multi-axis displacement stage is adjusted so that the second transmitted light and the second reflected light are collinear.

[0006] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, it further comprises: a combined displacement stage; wherein, the first reflector is arranged on the combined displacement stage.

[0007] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the reflection and transmission ratio of the first beam splitting prism is 5:5.

[0008] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the reflection and transmission ratio of the second beam splitting prism is 5:5.

[0009] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the fast axis of the half-wave plate forms an angle of 45° with the polarization direction of the polarized light.

[0010] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the working principle of the acousto-optic modulator is the Bragg diffraction effect of acousto-optic interaction.

[0011] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the refractive index of the material in the acousto-optic modulator satisfies the following relationship:

[0012] 2nΛsinθ = λm;

[0013] Wherein, n is the refractive index of the material in the acousto-optic modulator, Λ is the ultrasonic wavelength, θ is the angle between the light and the ultrasonic wave surface, m is the diffraction order, and λ is the light wavelength.

[0014] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, for Bragg diffraction, the ratio of the first-order diffracted light intensity I1 to the transmitted light intensity I0 satisfies the following formula:

[0015]

[0016] Among them, I1 is the first-order diffraction light intensity, I0 is the transmitted light intensity, L is the acousto-optic interaction intensity, P is the ultrasonic power, and M2 is the quality factor of the acousto-optic material.

[0017] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, the diffraction light frequency output by the acousto-optic modulator is:

[0018] f = f0 ± f s ;

[0019] Among them, f is the diffraction light frequency output by the acousto-optic modulator, f0 is the original frequency of the transmitted light, and f s is the diffraction light frequency shift.

[0020] In the above-mentioned laser amplitude modulation device in the megahertz frequency range, both the first reflector and the second reflector are coated with a film.

[0021] The present invention has the following beneficial effects compared with the prior art:

[0022] The present invention overcomes the deficiencies of the existing laser amplitude modulation technology in the megahertz frequency range, and has the advantages of compact structure, low cost, no need for a power voltage amplifier, and stable modulation waveform. Description of the Drawings

[0023] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0024] Figure 1 is a schematic diagram of a laser amplitude modulation device provided by an embodiment of the present invention;

[0025] Figure 2 is the laser amplitude modulation effect diagram provided by an embodiment of the present invention. Detailed Embodiments

[0026] Hereinafter, the exemplary embodiments of the present disclosure will be described in more detail with reference to the drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully communicated to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. Hereinafter, the present invention will be described in detail with reference to the drawings and in combination with the embodiments.

[0027] Figure 1It is a schematic diagram of a laser amplitude modulation device in the megahertz frequency range provided by an embodiment of the present invention. As Figure 1 shown, the laser amplitude modulation device in the megahertz frequency range includes: a polarization laser 1, a first beam splitting prism 2, an acousto-optic modulator 3, a multi-axis displacement stage 4, a second beam splitting prism 5, a first reflector 6, a half-wave plate 8, and a second reflector 9; wherein, the acousto-optic modulator 3 is disposed on the multi-axis displacement stage 4; the polarized laser emitted by the polarization laser 1 is divided into a transmitted light and a reflected light after passing through the first beam splitting prism 2, and the transmitted light enters the acousto-optic modulator 3; the diffracted light emitted from the acousto-optic modulator 3 passes through the second beam splitting prism 5 to obtain a second transmitted light; the reflected light is reflected by the second reflector 9 and then reaches the half-wave plate 8, and then passes through the half-wave plate 8 and is reflected by the first reflector 6 and then enters the second beam splitting prism 5 and is reflected to obtain a second reflected light; the multi-axis displacement stage 4 is adjusted so that the second transmitted light and the second reflected light are collinear, and the collinear light beam is the beam after intensity modulation.

[0028] As Figure 1 shown, the laser amplitude modulation device in the megahertz frequency range further includes: a combined displacement stage 7; wherein, the first reflector 6 is disposed on the combined displacement stage 7.

[0029] In this embodiment, an acousto-optic modulator is used to generate frequency-shifted polarized light, and then the frequency-shifted polarized light is collinear with the non-frequency-shifted polarized light having the same polarization direction to achieve amplitude modulation of the laser. In this embodiment, the polarized laser beam frequency-modulated by the acousto-optic modulator and the non-frequency-modulated laser beam with the same polarization direction are collinearly combined to obtain an amplitude-modulated laser beam, and the amplitude modulation frequency is the frequency of the acousto-optic modulator.

[0030] The laser amplitude modulation frequency is the frequency shift generated after the polarized light passes through the amplitude modulator.

[0031] The working principle of the acousto-optic modulator is the Bragg diffraction effect of acousto-optic interaction.

[0032] The refractive index of the material in the acousto-optic modulator satisfies the following relation:

[0033] 2nΛsinθ = λm;

[0034] wherein, n is the refractive index of the material in the acousto-optic modulator, Λ is the ultrasonic wavelength, θ is the angle between the light and the ultrasonic wave surface, m is the diffraction order, and λ is the light wavelength.

[0035] For Bragg diffraction, the ratio of the intensity I1 of the first-order diffracted light to the intensity I0 of the transmitted light satisfies the following formula:

[0036]

[0037] Among them, I1 is the first-order diffraction light intensity, I0 is the transmitted light intensity, L is the acousto-optic interaction intensity, P is the ultrasonic power, and M2 is the quality factor of the acousto-optic material.

[0038] The diffraction light frequency output by the acousto-optic modulator is:

[0039] f = f0 ± f s ;

[0040] Among them, f is the diffraction light frequency output by the acousto-optic modulator, f0 is the original frequency of the transmitted light, and f s is the diffraction light frequency shift.

[0041] Both the first reflector and the second reflector are coated with a film.

[0042] Specifically, the polarized laser emitted by the polarized light laser is divided into transmitted light and reflected light after passing through the beam splitter prism. The transmitted light and the reflected light are two linearly polarized lights with perpendicular polarization directions, and the intensity ratio of the two lights is about 5:5.

[0043] The transmitted light enters the acousto-optic modulator, and the polarization direction of the transmitted light is parallel to the polarization crystal base of the acousto-optic modulator.

[0044] The acousto-optic modulator is placed on the multi-axis displacement stage. By adjusting the multi-axis displacement stage, the intensity of the first-order diffraction light passing through the acousto-optic modulator is maximized. The frequency of this first-order diffraction light is shifted compared with the transmitted light, and the frequency shift is related to the parameters of the acousto-optic modulator. The selected offset frequency in this embodiment is 40 MHz.

[0045] The polarization direction of the diffraction light emitted from the acousto-optic modulator rotates 90° compared with the incident light (it is still a linearly polarized light), and is transmitted after passing through the beam splitter prism. The reflection and transmission ratio of the beam splitter prism is about 5:5.

[0046] Another beam of light reflected by the beam splitter prism passes through the mirror and then passes through the half-wave plate. The fast axis of the half-wave plate forms a 45° angle with the polarization direction of the polarized light entering the half-wave plate. At this time, the polarization direction of the light passing through the half-wave plate rotates 90°, which is the same as the polarization direction of the light passing through the acousto-optic modulator.

[0047] The light passes through the half-wave plate and is then reflected by the mirror. The mirror is placed on the combined displacement stage. The reflected light enters the beam splitter prism and is reflected. By adjusting the multi-axis displacement stage, the reflected light and the transmitted light of the laser beam splitter prism are collinear.

[0048] Finally, the polarization directions of the two collinear lights are the same, but there is a frequency difference between the two lights. This frequency difference is 40 MHz. According to the interference principle, it can be known that the collinear light beam is the light after laser amplitude modulation, and the light intensity frequency is the frequency of the acousto-optic modulator.

[0049] In this embodiment, the main working principle of the acousto-optic modulator is the Bragg diffraction effect of acousto-optic interaction, and the following relationship holds among the parameters:

[0050] 2nΛsinθ=λm

[0051] Where n is the refractive index of the medium (the material in the acousto-optic modulator), Λ is the ultrasonic wavelength, θ is the angle between the light and the ultrasonic wavefront, m is the diffraction order, and λ is the light wavelength. The first-order diffraction has the maximum energy, so usually m = 1.

[0052] For Bragg diffraction, the ratio of the first-order diffracted light intensity I1 to the transmitted light intensity I0 satisfies:

[0053]

[0054] Where L is the acousto-optic interaction strength, P is the ultrasonic power, and M2 is the figure of merit of the acousto-optic material.

[0055] Due to the Doppler effect, the diffracted light will have a frequency shift relative to the incident light. The frequency shift amount of the diffracted light Δf = f s . Therefore, the frequency f of the diffracted light output by the acousto-optic modulator is:

[0056] f=f0±f s

[0057] Where f0 is the original frequency of the transmitted light, and the plus or minus sign is determined by the diffraction direction. f s Is determined by the characteristics of the acousto-optic modulator.

[0058] Light has the characteristics of waves. Assuming that the electric field form of the light source emitted from the laser is E0 = Asin(2πf0t + ψ), where A is the amplitude. The light passing through the acousto-optic modulator after passing through the beam splitter prism has a frequency shift as described above, and the frequency shift is f s . Then the electric field E1 of the outgoing light is:

[0059]

[0060] The other beam of light passing through the beam splitter prism only has its polarization direction deflected by 90° after passing through the half-wave plate, and the frequency remains unchanged. Therefore, the electric field E2 is

[0061]

[0062] The two beams of light are combined after passing through the second beam splitter prism. The combined electric field E out Is

[0063] E out =E1+E2

[0064]

[0065] The laser frequency f0 is much greater than fs , so the sine part can be regarded as a constant; since the light intensity is the square of the electric field strength, the combined laser is a laser modulated in amplitude with a frequency of f s .

[0066] Adopting this amplitude modulation method, compared with mechanical amplitude modulation, the amplitude modulation frequency is at least two orders of magnitude higher (the frequency is at least 100 times higher); compared with acousto-optic amplitude modulation, it does not require an expensive and bulky power amplifier, and is easy to integrate and miniaturize.

[0067] Figure 2 It is the laser amplitude modulation effect diagram provided by the embodiment of the present invention.

[0068] This embodiment solves the problems of the existing laser amplitude modulation system's demanding requirements for power amplifiers, large volume of the modulation system, difficulty in integration, and unstable modulation waveforms. This embodiment has a compact structure, low cost, does not require a power voltage amplifier, and has a stable modulation waveform.

[0069] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solutions of the present invention all fall within the protection scope of the technical solutions of the present invention.

Claims

1. A laser amplitude modulation device in the order of magnitude of megahertz frequency, characterized in that Including: A polarization laser (1), a first beam splitter prism (2), an acousto-optic modulator (3), a multi-axis displacement stage (4), a second beam splitter prism (5), a first reflector (6), a half-wave plate (8), and a second reflector (9); wherein, The acousto-optic modulator (3) is disposed on the multi-axis displacement stage (4); The polarized laser emitted by the polarization laser (1) is divided into a transmitted light and a reflected light after passing through the first beam splitter prism (2), and the transmitted light enters the acousto-optic modulator (3); the diffracted light emitted from the acousto-optic modulator (3) passes through the second beam splitter prism (5) to obtain a second transmitted light; the reflected light is reflected by the second reflector (9) and then reaches the half-wave plate (8), then passes through the half-wave plate (8) and is transmitted and then reflected by the first reflector (6) and enters the second beam splitter prism (5) and is reflected to obtain a second reflected light; the multi-axis displacement stage (4) is adjusted so that the second transmitted light and the second reflected light are collinear.

2. The MHz-frequency-range laser amplitude modulation device according to claim 1, characterized in that Further including: a combined displacement stage (7); wherein, the first reflector (6) is disposed on the combined displacement stage (7).

3. The MHz-frequency-range laser amplitude modulation device according to claim 1, characterized in that: The reflection and transmission ratio of the first beam splitter prism (2) is 5:

5.

4. The MHz-frequency-range laser amplitude modulation device according to claim 1, wherein: The reflection and transmission ratio of the second beam splitter prism (5) is 5:

5.

5. The MHz frequency range laser amplitude modulation device according to claim 1, characterized in that: The fast axis of the half-wave plate (8) forms an angle of 45° with the polarization direction of the polarized light.

6. The MHz-frequency-range laser amplitude modulation device according to claim 1, characterized in that: The working principle of the acousto-optic modulator (3) is the Bragg diffraction effect of acousto-optic interaction.

7. The MHz-frequency-range laser amplitude modulation device according to claim 1 or 6, characterized in that: The material refractive index in the acousto-optic modulator (3) satisfies the following relationship: 2nΛsinθ = λm; Wherein, n is the material refractive index in the acousto-optic modulator, Λ is the ultrasonic wavelength, θ is the angle between the light and the ultrasonic wave surface, m is the diffraction order, and λ is the light wavelength.

8. The MHz frequency range laser amplitude modulation device according to claim 6, characterized in that: For Bragg diffraction, the ratio of the first-order diffracted light intensity I1 to the transmitted light intensity I0 satisfies the following formula: Wherein, I1 is the first-order diffracted light intensity, I0 is the transmitted light intensity, L is the acousto-optic interaction intensity, P is the ultrasonic power, and M2 is the acousto-optic material quality factor.

9. The laser amplitude modulation device in the megahertz frequency range according to claim 1 or 6, characterized in that: The frequency of the diffracted light output by the acousto-optic modulator is: f = f0 ± f s ; Among them, f is the diffraction light frequency output by the acousto-optic modulator, f0 is the original frequency of the transmitted light, and f s is the diffraction light frequency shift amount.

10. The MHz-frequency-range laser amplitude modulation device according to claim 1, characterized in that: Both the first reflector (6) and the second reflector (9) are coated with a film.

Images