An adjustable orthogonal polarization dual-wavelength laser based on an acousto-optic filter

Abstract

The application discloses a tunable orthogonal polarization dual-wavelength laser based on an acousto-optic filter, which comprises a broadband light source, a half-wave plate, an acousto-optic filter, a radio frequency drive, a light shield, a first optical wedge angle block, a second optical wedge angle block, a reflecting mirror and a polarization beam splitter prism. The polarization direction of the broadband light source is controlled through the half-wave plate, linearly polarized light with a certain angle is diffracted into two orthogonal polarization diffracted lights (o light and e light) matched with the linearly polarized light through the acousto-optic filter under the action of ultrasonic waves with a specific frequency, and finally the two diffracted lights with similar wavelengths are combined into one output beam through the polarization beam splitter prism. The application realizes the output of the orthogonal polarization dual-wavelength laser signal with tunable wavelength and power by controlling the driving radio frequency signal and the angle of the half-wave plate, and the first optical wedge angle block and the second optical wedge angle block are used for reducing the drift of the diffracted light caused by dispersion.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to an tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter, which can output an orthogonally polarized dual-wavelength laser with variable wavelength and adjustable polarization power. Background Technology

[0002] A dual-wavelength laser with similar wavelengths and orthogonal polarization states contains two linearly polarized laser beams that exhibit orthogonal polarization states, and the wavelengths of the two orthogonally polarized laser beams are similar.

[0003] This dual-wavelength laser, due to its unique polarization characteristics, is widely used in laser medicine, spectral analysis, laser ranging, lidar, terahertz waves, and other fields.

[0004] Laser crystals can be used to obtain dual-wavelength laser output. However, due to the influence of the crystal lattice structure, isotropic laser crystals are difficult to generate polarized lasers, and most require spectral line suppression or polarization modulation to obtain unbiased dual-wavelength laser output. In contrast, anisotropic laser crystals emit different polarized spectral lines from transitions between different energy levels and their sub-levels, exhibiting orthogonal polarization characteristics. By using different cutting directions, orthogonal polarized dual-wavelength output in a specific wavelength band can be obtained.

[0005] Especially Nd-doped 3+ Anisotropic laser crystals are often used as working media to obtain orthogonally polarized dual-wavelength lasers. For example, crystals such as Nd:YLF (Optics Letter, vol.40, p3979-3981, 2010; CN102468599B) and Nd:YAG (Photonics Research, vol.6(8), p815-820, 2018) can achieve orthogonally polarized dual-wavelength laser output in the same optical path under the action of pump light, through appropriate frequency selection, resonant cavity design and polarization control.

[0006] In recent years, scholars have conducted more in-depth research on the correlation characteristics of orthogonally polarized dual-wavelength light. For example, by utilizing the different Raman peak frequency shifts of KGW-type crystals in different polarization directions, and combining this with a half-wave plate, the power of the two wavelengths in the orthogonally polarized output light can be adjusted (CN111180987A). While this power adjustment method is simple, the output laser wavelength is fixed, making flexible tuning difficult. Alternatively, two pump sources can be used to pump two different working media, controlling the pump power to achieve the effect of adjusting the output dual-wavelength power. Two independent crystal temperature control systems cause the output laser wavelength to drift when the center temperature of the working media is changed. Based on this system, the wavelength can be adjusted while controlling the output power; however, its overall structure is complex and susceptible to temperature interference.

[0007] Therefore, how to realize an orthogonally polarized dual-wavelength laser in a simple and easy-to-operate manner, and how to adjust both the wavelength and power of the output laser, has become a technical problem that needs to be solved in the current technology. Summary of the Invention

[0008] The purpose of this invention is to propose a tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter. Utilizing the characteristic that the ±1 diffracted light from the acousto-optic filter is orthogonally polarized with different tuning relationships, dual-wavelength laser outputs with similar wavelengths and orthogonal polarization are obtained. Wavelength tuning and power adjustment of the output laser are achieved through radio frequency and polarization control.

[0009] To achieve this objective, the present invention adopts the following technical solution: A tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter, comprising: Broadband light source, half-wave plate, acousto-optic filter, radio frequency driver, first optical wedge block, second optical wedge block, reflector and polarizing beam splitter; The broadband light source is used to emit first linearly polarized light. The half-wave plate is used to control the polarization direction of the first linearly polarized light to obtain the second linearly polarized light, which is then incident on the acousto-optic filter. The acousto-optic filter is used to cause the second linearly polarized light to diffract under the control of the radio frequency drive, diffracting into +1st order o-light and -1st order e-light, wherein the o-light and e-light are orthogonally polarized. The radio frequency driver is connected to the acousto-optic filter and is used to control the generation and frequency of ultrasonic waves. The first optical wedge block is used to direct the +1 order o-light onto the polarizing beam splitter; The second optical wedge block is used to direct the -1st order e-beam onto the polarizing beam splitter; Specifically, the reflector is used to guide one of the +1st order o-beams passing through the first optical wedge block and the -1st order e-beams passing through the second optical wedge block to be incident on the polarizing beam splitter. Another beam, one of the +1st order o-beam passing through the first optical wedge block and the other of the -1st order e-beam passing through the second optical wedge block, is directly incident on the polarizing beam splitter. The polarizing beam splitter is used to combine the incident +1st order o-beam and -1st order e-beam into a single beam for output.

[0010] Optionally, on the other side of the acousto-optic filter relative to the half-wave plate, there is also a light-shielding plate, which is located on the same optical axis as the broadband light source, the half-wave plate and the acousto-optic filter.

[0011] Optionally, the wavelength of the broadband light source can be selected as needed.

[0012] Optionally, the broadband light source is an SLED light source with a bandwidth >40nm.

[0013] Optionally, the half-wave plate, the acousto-optic filter, the first optical wedge block, and the second optical wedge block are coated with anti-reflection films corresponding to the wavelength of the light beam; the reflector is coated with a high-reflection film corresponding to the wavelength of the light beam; the reflecting slope of the polarizing beam splitter is coated with a polarizing film corresponding to the wavelength of the light source, and the transmission end face is coated with an anti-reflection film corresponding to the wavelength of the light source.

[0014] Optionally, the acousto-optic filter operates based on the anomalous acousto-optic effect. The selected acousto-optic medium is off-axis slow-cut wave tellurium dioxide. When acousto-optic diffraction occurs, the polarization state of the diffracted light changes. Its +1st and -1st order diffracted lights have different but similar tuning relationships, and at the same time, it outputs orthogonally polarized dual-wavelength lasers with similar wavelengths.

[0015] Optionally, the half-wave plate is rotatable. By rotating the half-wave plate, the polarization direction of the incident linearly polarized light is changed, thereby controlling the component ratio of the e-ray and o-ray in the second linearly polarized light and realizing the power adjustment of the output orthogonally polarized dual wavelengths.

[0016] Optionally, the light-shielding plate is a metal panel with a black oxidized and sandblasted surface.

[0017] The present invention has the following advantages: 1. By using a half-wave plate to adjust the polarization state of the incident light, the ratio of o-light and e-light after passing through the acousto-optic filter can be controlled, thereby achieving power adjustment of the output orthogonally polarized dual wavelengths.

[0018] 2. By changing the frequency signal output of the RF driver f By adjusting the wavelength of the ±1 diffracted light, the final output diffracted wavelength λ can be controlled.

[0019] 3. The first and second optical wedge blocks are used to reduce diffraction drift caused by dispersion. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter according to a specific embodiment of the present invention.

[0021] Figure 2 This is the first set of tuning relationships for orthogonally polarized light in the wavelength range of 1060±30nm according to a specific embodiment of the present invention.

[0022] Figure 3 This is a second set of tuning relationships for orthogonally polarized light in the wavelength range of 1060±30nm, according to a specific embodiment of the present invention.

[0023] Figure 4 This refers to a set of tuning relationships for orthogonally polarized light in the wavelength range of 600-1400nm according to a specific embodiment of the present invention.

[0024] The technical features referred to by the reference numerals in the figure are as follows: 10. Broadband light source; 11. Half-wave plate; 12. First linearly polarized light; 13. Second linearly polarized light; 20. Radio frequency drive; 21. Acousto-optic filter; 22. Partial light; 23. O-light; 24. E-light; 4. Light shield; 5. First optical wedge block; 6. First optical wedge block; 7. Reflector; 8. Polarizing beam splitter. Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0026] The main features of this invention are: using a polarized broadband light source as the light source, using a half-wave plate to adjust the polarization state of the incident light, thereby controlling the ratio of o-light and e-light after passing through an acousto-optic filter, and then adjusting the power of the beam. The wavelength of the ±1 diffracted light is adjusted by the acousto-optic filter, and finally the two beams are combined to obtain a dual-wavelength laser with similar wavelengths and orthogonal polarization.

[0027] For details, see Figure 1 The present invention illustrates an tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter, comprising: a broadband light source 10, a half-wave plate 11, an acousto-optic filter 21, an RF driver 20, a first optical wedge block 5, a second optical wedge block 6, a reflector 7, and a polarizing beam splitter 8. The broadband light source 10 is used to emit first linearly polarized light 12 with a high degree of polarization. In an optional embodiment, the broadband light source is an SLED light source with a bandwidth > 40 nm.

[0028] The wavelength of the broadband light source 10 can be selected as needed, for example, it can be in the wavelength range of 1060±30nm or 600-1400nm.

[0029] The half-wave plate 11 is used to control the polarization direction of the first linearly polarized light 12 to obtain the second linearly polarized light 13, and the second linearly polarized light 13 is incident on the acousto-optic filter 21. The acousto-optic filter 21 is used to cause the second linearly polarized light 13 to diffract under the control of the radio frequency drive 20, diffracting a +1st order o-light 23 and a -1st order e-light 24, wherein the o-light 23 and the e-light 24 are orthogonally polarized to each other. The radio frequency driver 20 is connected to the acousto-optic filter 21 and is used to control the generation and frequency of ultrasonic waves. The first optical wedge block 5 is used to direct the +1 level o-light 23 onto the reflector 7; The second optical wedge block 6 is used to directly incident the -1st order e-beam 24 onto the polarizing beam splitter 8; In this invention, the first optical wedge block and the second optical wedge block are used to reduce diffraction drift caused by dispersion.

[0030] The reflector 7 directs the +1 order o-light onto the polarizing beam splitter 8; The polarizing beam splitter 8 is used to combine the incident +1st order o-beam and -1st order e-beam into a single beam for output.

[0031] In an optional embodiment, the +1st order o-beam 23 passes through the first optical wedge block 5, is reflected by the reflector 7, enters the polarizing beam splitter 8, and is then reflected out as o-beam. Meanwhile, the -1st order e-beam 24 passes through the second optical wedge block 6, is directly incident on the polarizing beam splitter 8, and is then transmitted out as e-beam. By adjusting the angles of the reflector 7 and the polarizing beam splitter 8, both beams (23 and 24) are perpendicularly incident on the surface of the polarizing beam splitter 8, and finally, two orthogonally polarized beams are output along the same optical path.

[0032] The present invention is not limited thereto; it may also allow the -1st order e-beam 24 to be incident on the polarizing beam splitter via a reflector, and the +1st order o-beam 23 to be incident directly on the polarizing beam splitter 8, with the polarizing beam splitter 8 combining the two beams.

[0033] Furthermore, on the other side of the acousto-optic filter 21 opposite to the half-wave plate 11, there is a light-shielding plate 4. The light-shielding plate 4 is located on the same optical axis as the broadband light source 10, the half-wave plate 11, and the acousto-optic filter 21, and can block the portion of light 22 that has not been diffracted. For example, the light-shielding plate 4 can be a metal panel with a black anodized and sandblasted surface.

[0034] The acousto-optic filter operates based on the anomalous acousto-optic effect. The selected acousto-optic medium is off-axis slow-cut wave tellurium dioxide. During acousto-optic diffraction, the polarization state of the diffracted light changes. Its +1st and -1st order diffracted lights have different but similar tuning relationships, allowing for the simultaneous output of orthogonally polarized dual-wavelength lasers with similar wavelengths.

[0035] Specifically, the acousto-optic filter 21 adopts an ultrasonic mode with a certain off-axis angle to the

[110] direction (also known as the t direction). In this acoustic mode, acousto-optic diffraction exists in e →o and o → e diffraction modes. The two diffraction modes are similar; the acousto-optic interaction in the e →o diffraction mode will be analyzed below. In the acousto-optic interaction plane, the incident light wave vector...K i Diffraction wave vector K d and ultrasonic vector K a Satisfy the momentum matching condition ( K d =K i +K a In the e → o diffraction mode, the incident light is the e-ray, and after the acousto-optic effect, the resulting diffracted light is the o-ray. The refractive index of the incident light is... n ie and the refractive index of diffracted light n do Decibels are expressed as:

[0036] In the formula, θ i and θ do For the incident polar angle and the diffraction polar angle; n e and n o Let be the refractive index of the e-ray and o-ray of tellurium dioxide crystal, which has a functional relationship with wavelength.

[0037] Based on the condition that the tangents are parallel, we know that:

[0038] Therefore, the tuning relationship of the non-collinear acousto-optic filter in the e →o diffraction mode can be obtained as follows:

[0039] Similarly, in the o → e diffraction mode, the tuning relationship of the non-collinear acousto-optic filter is:

[0040] In the formula, V t For along t Slow shear wave velocity in the direction, V z For along z The speed of the fast shear wave in the direction, θ a For crystals in tz In-plane sound wave vector and t The angle between the axes is also called the off-axis angle.

[0041] Based on the tuning relationship corresponding to the two diffraction modes, it can be seen that under the same radio frequency signal, the two diffracted beams of the non-collinear acousto-optic filter are orthogonally polarized and have similar wavelengths. This can be achieved by changing the frequency signal output by the radio frequency drive. f It can control the diffraction wavelength of the final output. λ .

[0042] The power ratio of the orthogonally polarized o-ray and e-ray diffracted light depends on the e-ray and o-ray components incident on the acousto-optic filter. By rotating the half-wave plate 11 to change the polarization direction of the highly polarized broadband light source 10, the component ratio of the e-ray and o-ray in the second linearly polarized light 13 in the two polarization directions is controlled, thereby realizing the power adjustment of the output orthogonally polarized dual wavelengths.

[0043] Furthermore, the half-wave plate 11, the acousto-optic filter 21, the first optical wedge block 5, and the second optical wedge block 6 are coated with anti-reflection films corresponding to the wavelength of the light source; the reflector 7 is coated with a high-reflection film corresponding to the wavelength of the broadband light source 10; the reflecting slope of the polarizing beam splitter 8 is coated with a polarizing film corresponding to the wavelength of the light source, and the transmission end face is coated with an anti-reflection film corresponding to the wavelength of the light source.

[0044] The following are three embodiments of the present invention: Example

[0045] Figure 2 The diagram shows a set of tuning relationships for orthogonally polarized light within a wavelength range of 1060±30nm. The off-axis angle of the non-collinear acousto-optic filter used is 15°, and the incident polar angle is 36.8°. It can be seen that the tuning relationships of the output o-light and e-light are different but similar. Adjusting the frequency of the RF drive can output o-light and e-light of different wavelengths. For example, at a frequency of 113.2MHz, the output o-light is 1064nm and e-light is 1083nm; at a frequency of 115MHz, the output o-light is 1049nm and e-light is 1067nm.

[0046] Example 2 Figure 3 The diagram shows the second set of tuning relationships for orthogonally polarized light within a wavelength range of 1060±30nm. The non-collinear acousto-optic filter used has an off-axis angle of 13° and an incident polar angle of 31°. The output tuning relationship can be controlled by changing the parameters of the acousto-optic filter crystal. Under this tuning relationship, at a frequency of 96.9MHz, the output is 1049nm o-light and 1081nm e-light.

[0047] Example 3 Figure 4 The diagram shows a set of tuning relationships for orthogonally polarized light in the wavelength range of 600-1400 nm. The non-collinear acousto-optic filter used has an off-axis angle of 15° and an incident polar angle of 36.8°. After bandwidth optimization, the acousto-optic filter can be applied to a wider wavelength range, such as... Figure 4 The tuning relationship in the diagram shows that at a frequency of 158.6MHz, the output is 780nm o-light and 793nm e-light; at a frequency of 88.8MHz, the output is 1342nm o-light and 1366nm e-light.

[0048] Off-axis angle and incident polar angle are characteristic parameters of slow-shear wave tellurium dioxide crystals, achieved through crystal design and fabrication. Different crystal designs produce different tuning curves, selectable according to application requirements. For example, in Example 1, the RF drive frequency is 115 MHz, outputting 1049 nm o-ray and 1067 nm e-ray with a wavelength interval of 18 nm; in Example 2, the RF drive frequency is 96.9 MHz, outputting 1049 nm o-ray and 1081 nm e-ray with a wavelength interval of 32 nm. Although both produce an o-ray wavelength of 1049 nm, the different frequencies result in different e-ray wavelengths and wavelength intervals.

[0049] In summary, the present invention has the following advantages: 1. By using a half-wave plate to adjust the polarization state of the incident light, the ratio of o-light and e-light after passing through the acousto-optic filter can be controlled, thereby achieving power adjustment of the output orthogonally polarized dual wavelengths.

[0050] 2. By changing the frequency signal output of the RF driver f By adjusting the wavelength of the ±1 diffracted light, the final output diffracted wavelength λ can be controlled.

[0051] 3. The first and second optical wedge blocks are used to reduce diffraction drift caused by dispersion.

[0052] The above description is a further detailed explanation of the present invention in conjunction with specific preferred embodiments. It should not be considered that the specific embodiments of the present invention are limited to this. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection of the present invention as defined by the submitted claims.

Claims

1. A tunable orthogonally polarized dual-wavelength laser based on an acousto-optic filter, characterized in that, include: Broadband light source, half-wave plate, acousto-optic filter, radio frequency driver, first optical wedge block, second optical wedge block, reflector and polarizing beam splitter; The broadband light source is used to emit first linearly polarized light. The half-wave plate is used to control the polarization direction of the first linearly polarized light to obtain the second linearly polarized light, which is then incident on the acousto-optic filter. The acousto-optic filter is used to cause the second linearly polarized light to diffract under the control of the radio frequency drive, diffracting into +1st order o-light and -1st order e-light, wherein the o-light and e-light are orthogonally polarized. The radio frequency driver is connected to the acousto-optic filter and is used to control the generation and frequency of ultrasonic waves. The first optical wedge block is used to direct the +1 order o-light onto the polarizing beam splitter; The second optical wedge block is used to direct the -1st order e-beam onto the polarizing beam splitter; Specifically, the reflector is used to guide one of the +1st order o-beams passing through the first optical wedge block and the -1st order e-beams passing through the second optical wedge block to be incident on the polarizing beam splitter. Another beam, one of the +1st order o-beam passing through the first optical wedge block and the other of the -1st order e-beam passing through the second optical wedge block, is directly incident on the polarizing beam splitter. The polarizing beam splitter is used to combine the incident +1st order o-beam and -1st order e-beam into a single beam for output.

2. The tunable orthogonally polarized dual-wavelength laser according to claim 1, characterized in that, include: On the other side of the acousto-optic filter relative to the half-wave plate, there is also a light-shielding plate, which is located on the same optical axis as the broadband light source, the half-wave plate and the acousto-optic filter.

3. The tunable orthogonally polarized dual-wavelength laser according to claim 1 or 2, characterized in that, include: The wavelength of the broadband light source is selected as needed.

4. The tunable orthogonally polarized dual-wavelength laser according to claim 3, characterized in that, include: The broadband light source is an SLED light source with a bandwidth >40nm.

5. The tunable orthogonally polarized dual-wavelength laser according to claim 3, characterized in that, include: The half-wave plate, acousto-optic filter, first optical wedge block, and second optical wedge block are coated with anti-reflection films corresponding to the wavelength of the light beam; the reflector is coated with a high-reflection film corresponding to the wavelength of the light beam; the reflecting slope of the polarizing beam splitter is coated with a polarizing film corresponding to the wavelength of the light source, and the transmission end face is coated with an anti-reflection film corresponding to the wavelength of the light source.

6. The tunable orthogonally polarized dual-wavelength laser according to claim 3, characterized in that, include: The acousto-optic filter operates based on the anomalous acousto-optic effect. The selected acousto-optic medium is off-axis slow-cut wave tellurium dioxide. When acousto-optic diffraction occurs, the polarization state of the diffracted light changes. Its +1st and -1st order diffracted lights have different but similar tuning relationships, and at the same time, it outputs orthogonally polarized dual-wavelength lasers with similar wavelengths.

7. The tunable orthogonally polarized dual-wavelength laser according to claim 3, characterized in that, include: The half-wave plate is rotatable. By rotating the half-wave plate, the polarization direction of the incident linearly polarized light is changed, thereby controlling the component ratio of the e-ray and o-ray in the second linearly polarized light and realizing the power adjustment of the output orthogonally polarized dual wavelengths.

8. The tunable orthogonally polarized dual-wavelength laser according to claim 2, characterized in that, include: The light-shielding plate is a metal panel with a black oxidized and sandblasted surface.

Images