A composite cavity structure for generating multiple vortices

Abstract

A composite cavity structure for generating multiple vortices relates to the technical field of vortex lasers. To address the problem in the prior art that vortex lasers can only output a single vortex but not multiple vortices, the present application inserts a lens into the cavity and combines it with a plane reflector mirror engraved with a point defect. By adjusting the position of the plane mirror in the branch and the size of the point defect, high-order vortex beams can be effectively generated and the order can be adjusted. Vortex beams of different orders in multiple branches are output through the same output coupler, thereby generating multiple vortex beams.

Description

Technical Field

[0001] The present invention relates to the technical field of vortex lasers, in particular to a composite cavity structure for generating multiple vortices. Background Art

[0002] Vortex light carrying orbital angular momentum has a higher spatial dimension and can therefore carry more information. The orthogonality and infinite-dimensional nature of orbital angular momentum itself enable this type of light beam to greatly promote the development of high-speed optical communications. Therefore, the preparation of vortex light sources is very important. Using devices such as spiral phase plates and Q plates to directly load a spiral phase on a light beam is a common method. However, due to limitations in processing technology, these devices cannot have high resolution and accuracy, and devices suitable for high-power or broadband light sources are very expensive, thus limiting their wide-scale application. In contrast, it is more convenient to generate a vortex beam directly in a compact resonant cavity by controlling the gain distribution or loss distribution using the characteristics of laser oscillation, and this is more convenient, with high mode purity and low cost.

[0003] Currently, vortex beam generation has been achieved through methods such as point defect mirrors and ring pumping. However, despite their tunable order, most vortex lasers can only output a single vortex, thus failing to fully utilize orbital angular momentum to carry large amounts of information, limiting the further development of high-capacity optical communications. Summary of the Invention

[0004] The purpose of the present invention is to propose a composite cavity structure for generating multiple vortices in order to solve the problem that the vortex laser in the prior art can only output a single vortex but cannot output multiple vortices.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A composite cavity structure for generating multiple vortices, comprising: a main path, a first branch path, and at least one second branch path;

[0007] The main path includes an input mirror 2, a laser crystal 3 and a main focusing lens 4;

[0008] The first branch includes a first wave plate 7-1, a first focusing lens 7-2 and a first plane reflector 7-3;

[0009] The second branch includes a second wave plate 8-1, a second focusing lens 8-2, a second plane reflector 8-3 and a second polarization beam splitting prism 8-4;

[0010] The pump light source 1 is incident on the laser crystal 3 through the input mirror 2 to generate oscillating light. The oscillating light then enters the main focusing lens 4 to obtain the main oscillating light. The main oscillating light is then split into the first branch and the second branch after passing through the main wave plate 5 and the main polarization beam splitter prism 6 in sequence. The main wave plate 5 and the main polarization beam splitter prism 6 are used to control the splitting ratio of the light beam.

[0011] The oscillating light entering the first branch path passes through the first wave plate 7-1, the first focusing lens 7-2, and the first plane reflector 7-3 in sequence before returning. After the returning oscillating light passes through the main polarization beam splitter prism 6, part of the oscillating light is reflected and output, and the other part of the oscillating light is transmitted to the main path. The first wave plate 7-1 is used to control the reflection and transmission splitting ratio;

[0012] The oscillating light entering the second branch path passes through the second wave plate 8-1, the second polarization beam splitter prism 8-4, the second focusing lens 8-2 and the second plane reflector 8-3 in sequence before returning. After the returning oscillating light passes through the main polarization beam splitter prism 6, part of the oscillating light is transmitted and output, and the other part of the oscillating light is reflected to the main path. The second wave plate 8-1 is used to control the reflection and transmission splitting ratio;

[0013] The first plane reflector 7-3 and the second plane reflector 8-3 are machined with defects, and the defects are located at the center of the oscillating light beam;

[0014] The first branch oscillation light reflection output and the second branch oscillation light transmission output, i.e., a multi-vortex light beam;

[0015] The first branch and the main path form a resonant cavity, the second branch and the main path form a resonant cavity, and multiple resonant cavities form a composite cavity. Multiple resonant cavities share the main polarization beam splitter prism 6 for splitting light as an output coupler.

[0016] Furthermore, the first wave plate 7 - 1 , the second wave plate 8 - 1 and the main wave plate 5 are half wave plates or quarter wave plates.

[0017] Furthermore, the first wave plate 7 - 1 , the second wave plate 8 - 1 and the main wave plate 5 are half wave plates.

[0018] Furthermore, the defects on the first plane reflector 7 - 3 and the second plane reflector 8 - 3 are circular point defects.

[0019] Furthermore, the oscillation order in the resonant cavity formed by the second branch and the main path is l n The normalized threshold power of the vortex beam Expressed as:

[0020]

[0021]

[0022]

[0023] Where w0 is the radius of the fundamental mode Gaussian beam in the laser crystal, δ = w p / w0 is the radius ratio of the pump source to the fundamental mode Gaussian beam, L n is the transmission loss of the nth branch, [·] is the additional loss introduced by the circular point defect of the branch, is the threshold power Proportional to the cavity loss is the threshold power Inversely proportional to the spatial mode overlap integral of the pump source and the oscillating beam in the crystal, d n is the diameter of the circular point defect of the nth second branch, w n is the size of the fundamental mode beam on the plane reflector in the first branch and the second branch, w p It is the beam size of the oscillating light generated by the pump light source incident on the laser crystal through the input mirror.

[0024] Furthermore, the flat surface and concave surface of the input mirror 2 are coated with an anti-reflection film.

[0025] Furthermore, the concave surface of the input mirror 2 is coated with a high-reflection film.

[0026] Furthermore, the pump light source 1 has a wavelength of 808 nm, a beam diameter of 400 μm, and a maximum output power of 50 W.

[0027] Furthermore, the input mirror 2 is a plano-concave mirror with a curvature radius of 50 mm.

[0028] Furthermore, the laser crystal 3 is selected to have a size of 3×3×10 mm. 3 Nd:YAG crystal.

[0029] The beneficial effects of the present invention are:

[0030] 1. This application inserts a lens into the cavity and combines it with a plane reflector with a point defect. By adjusting the position of the plane mirror in the branch and the size of the point defect, high-order vortex beams can be effectively generated and the order can be adjusted. Vortex beams of different orders in multiple branches are output through the same output coupler, thus generating multiple vortex beams.

[0031] 2. This application combines a wave plate and a polarization beam splitter prism to perform optical path splitting and beam output. By adjusting the angle of the wave plate, the polarization state of the beam is adjusted to achieve output power tuning.

[0032] 3. The composite cavity provided in this application has a simple structure and excellent stability. It can be combined with short pulse technology, nonlinear conversion technology, etc. to achieve continuous operation with wavelength expansion or pulsed multi-vortex beam output, and is suitable for fields such as high-speed optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the composite cavity structure of this application;

[0034] Figure 2 Schematic diagram of a plane mirror with a point defect;

[0035] Figure 3 Schematic diagram of the structure of the first branch;

[0036] Figure 4 Schematic diagram of the structure of the second branch;

[0037] Figure 5 Schematic diagram of the structure of the composite multi-vortex dual-cavity laser. DETAILED DESCRIPTION

[0038] It should be noted that, unless there is any conflict, the various embodiments disclosed in this application can be combined with each other.

[0039] Specific implementation method 1: refer to Figure 1 Specifically describing this embodiment, a composite cavity structure for generating multiple vortices described in this embodiment includes: a main path, a first branch path, and at least one second branch path;

[0040] The main path includes an input mirror 2, a laser crystal 3 and a main focusing lens 4;

[0041] The first branch includes a first wave plate 7-1, a first focusing lens 7-2 and a first plane reflector 7-3;

[0042] The second branch includes a second wave plate 8-1, a second focusing lens 8-2, a second plane reflector 8-3 and a second polarization beam splitting prism 8-4;

[0043] The pump light source 1 is incident on the laser crystal 3 through the input mirror 2 to generate oscillating light. The oscillating light then enters the main focusing lens 4 to obtain the main oscillating light. The main oscillating light is then split into the first branch and the second branch after passing through the main wave plate 5 and the main polarization beam splitter prism 6 in sequence. The main wave plate 5 and the main polarization beam splitter prism 6 are used to control the splitting ratio of the light beam.

[0044] The oscillating light entering the first branch path passes through the first wave plate 7-1, the first focusing lens 7-2, and the first plane reflector 7-3 in sequence before returning. After the returning oscillating light passes through the main polarization beam splitter prism 6, part of the oscillating light is reflected and output, and the other part of the oscillating light is transmitted to the main path. The first wave plate 7-1 is used to control the reflection and transmission splitting ratio;

[0045] The oscillating light entering the second branch path passes through the second wave plate 8-1, the second focusing lens 8-2, the second plane reflector 8-3 and the second polarization beam splitter prism 8-4 in sequence before returning. After the returning oscillating light passes through the main polarization beam splitter prism 6, part of the oscillating light is transmitted and output, and the other part of the oscillating light is reflected to the main path. The second wave plate 8-1 is used to control the reflection and transmission splitting ratio;

[0046] The first plane reflector 7-3 and the second plane reflector 8-3 are machined with defects, and the defects are located at the center of the oscillating light beam;

[0047] The first branch oscillation light reflection output and the second branch oscillation light transmission output, that is, a multi-vortex light beam.

[0048] Intracavity mode selection methods that can directly generate vortex beams include gain control and loss control methods. The former generally requires the combination of an astigmatism mode converter and is therefore not suitable for directly generating vortex beams in the cavity. In contrast, it is simpler and more effective to use a point defect mirror to generate a pure high-order vortex beam. By inserting a focusing lens to control the mode size and adjusting its ratio to the point defect size, the order of the vortex beam can be controlled. By using a polarization beam splitter prism to split the optical path, that is, to form multiple resonant cavities, vortex beams of different orders can be excited in each path and independently manipulated. At the same time, multiple vortex beams can extract energy provided by the pump source in different distribution areas, thus having higher efficiency. Multiple resonant cavities are compounded through the same polarization beam splitter prism, that is, multiple vortex beams are coupled and output at the same time, thereby obtaining a multi-vortex beam output with adjustable order.

[0049] Using a composite cavity to generate multi-vortex beams can further expand the dimension of the beam, giving it a higher information carrying capacity, and is therefore of great significance for promoting the development of high-capacity optical communications.

[0050] Example 1

[0051] Combine Figure 1 、 Figure 2 、 Figure 3 and Figure 4 This embodiment provides a composite cavity structure for generating multiple vortices, including a pump light source 1, an input mirror 2, a laser crystal 3, a primary focusing lens 4, a primary wave plate 5, a primary polarization beam splitter prism 6, a first branch 7, and n-1 branches such as a second branch 8 and a third branch 8.

[0052] A composite cavity structure for generating multiple vortices, wherein the main path has a curvature radius of R IC The oscillating light beam is divided into a first branch 7 and a second branch 8 by a main wave plate 5 and a main polarization beam splitting prism 6; the first branch 7 comprises a first wave plate 7-1, a first focusing lens 7-2 with a focal length of f1, and a first plane reflector 7-3 etched with a circular point defect of diameter d1; the second branch 8 or the nth branch 8 comprises a second wave plate 8-1, a second focusing lens 8-2 with a focal length of f2, a second plane reflector 8-3 etched with a circular point defect 9 of diameter d2, and a second polarization beam splitting prism 8-4; the wave plates 7-1 and 8-1 in each branch are combined with the main polarization beam splitting prism 6 to respectively perform polarization control of the branch light beams; the point defects etched on the plane reflectors 7-3 and 8-3 are used to generate vortex light beams carrying orbital angular momentum; the wavelength is λ p The pump source 1 is incident on the laser crystal 3 through the input mirror 2. The wave plate can be a half-wave plate or a quarter-wave plate, with the half-wave plate being more effective. The point defect can be of any shape (circular point defects are most effective), as long as the defect is located at the center of the oscillating beam.

[0053] The main wave plate 5 and the main polarization beam splitter prism 6 are used to control the splitting ratio of the light beam to the first and second branches;

[0054] The return beam of the first branched path passes through the first wave plate 7-1 and the main polarization beam splitter prism 6. Part of the beam is reflected and output by the main polarization beam splitter prism 6, and the other part of the beam is transmitted to the main path and oscillates again. The reflection and transmission splitting ratio is adjusted by rotating the wave plate 7-1.

[0055] The return beam of the nth branch passes through the second polarization beam splitter prism 8-4, the second wave plate 8-1 and the main polarization beam splitter prism 6 in sequence. Part of the beam is transmitted and output through the main polarization beam splitter prism 6, and the other part of the beam is reflected back to the main path and oscillates again. The reflection and transmission splitting ratio is controlled by rotating the wave plate 8-1.

[0056] The radius of curvature is R IC The input mirror 2 is plated with a wavelength of λ p The anti-reflection coating of the pump light source and the concave surface are coated with a wavelength of λ s The high-reflection film for oscillating light, all branching plane mirrors are highly reflective to the oscillating light, and other components are all anti-reflective to the oscillating light.

[0057] The main focusing lens 4 with a focal length of f0, the first focusing lens 7-2 with a focal length of f1 in the first branch, and the second focusing lens 8-2 with a focal length of f2 in the second branch each constitute an imaging system. A collimated light beam can be formed between the two lenses constituting the imaging system to facilitate transmission in the cavity and protect the components from damage by high-power light beams. At the same time, the oscillating light beam can be imaged on the plane mirrors of each branch, that is, the beam size radius on the first plane mirror 7-3 is w1, and the beam size radius on the second plane mirror 8-3 is w2.

[0058] Example 2

[0059] Combine Figure 1 、 Figure 2 The point defects located in the first branch and the second branch have different sizes d1 and d2, so as to generate vortex beams with different orbital angular momentum. The vortex beams of different orders have different beam sizes and can extract pump energy from different areas at the same time. The oscillation order in the resonant cavity formed by each of the first branch 7 and the second branch 8 is l n n is 1 or 2, corresponding to the vortex beams of the first and second branches. For a certain laser crystal, since the beam size changes slightly in the short crystal, the beam size can be assumed to be constant. The threshold power Equation 1 is proportional to the cavity loss Formula 2 is inversely proportional to the spatial mode overlap integral of the pump source and the oscillating beam in the crystal. Formula 3, that is

[0060]

[0061]

[0062]

[0063] Among them, w n is the size of the fundamental mode beam on the plane reflector in the first branch and the second branch, d n is the diameter of the circular point defect on the plane reflector in the first branch and the second branch, w0 is the radius of the fundamental mode Gaussian beam in the laser crystal, δ = w p / w0 is the radius ratio of the pump source to the fundamental mode Gaussian beam, L n is the transmission loss of the nth branch, ignoring other losses, [·] is the additional loss introduced by the defect at the branch point;

[0064] A plurality of circular point defects of different sizes are etched on the plane mirrors 7-3 and 8-3 located in the first branch 7 and the second branch 8. The plane mirrors 7-3 and 8-3 are both placed on a platform that can be displaced along the optical axis. The size of the oscillating light on the plane mirror and the ratio δ of the point defect size thereto are controlled by adjusting the distance D1 between the first focusing lens and the first plane mirror, as well as the distance D2 between the second focusing lens and the second plane mirror. The larger light beams in the two branches will have more significant spherical aberration when passing through the first focusing lens 7-2 with a focal length f1 and the first focusing lens 8-2 with a focal length f2 of the branch, respectively. Therefore, the positions of the plane mirrors 7-3 and 8-3 can affect the order of the return vortex light beam. The order of the vortex light can be tuned by combining point defects of different sizes.

[0065] The pump source 1 incident on the laser crystal 3 by the input mirror 2 should have a sufficiently large beam size w p , and a sufficiently high power, so as to provide gain for multiple vortex beams to make them oscillate, while ensuring the high order of the oscillated vortex beams.

[0066] Example 3

[0067] Combine Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 This embodiment provides a composite multi-vortex dual-cavity laser, which uses a pump light source with a wavelength of 808 nm, a beam diameter of 400 μm, and a maximum output power of 50 W. The input mirror uses a plano-concave mirror with a curvature radius of 50 mm, and the laser crystal has a size of 3×3×10 mm. 3 The Nd:YAG crystal has a main lens focal length of 100mm, the main polarization beam splitter prism and the second polarization beam splitter prism have an aperture of 10mm, the wave plates are both 20mm in diameter, and the focal lengths of the first and second lenses are both 100mm; the input mirror is coated with an 808nm anti-reflection film on both sides, and the concave surface is coated with a 1064nm high-reflection film; the front face of the Nd:YAG crystal for pump light incident light is coated with an 808nm anti-reflection film and a unique 1064nm anti-reflection film on both sides; the plane mirrors in the two branches are highly reflective to 1064nm, and the other devices are all coated with an anti-reflection film for 1064nm; the first and second polarization beam splitter prisms are adjusted respectively so that the transmission losses L1 and L2 are both 5%, where for the first branch, 5% is the output rate, and the light beam of the second branch is transmitted once through the main polarization beam splitter prism and the second polarization beam splitter prism within one oscillation cycle, that is, the output is 2.5%.

[0068] The specific geometric parameters of the composite cavity are: the distance between the input mirror and the Nd:YAG crystal is 4mm, the distance between the Nd:YAG crystal and the main focusing lens is 100mm, the distance between the first and second focusing lenses is 200mm, and the plane mirror is placed 100mm behind each branch focusing lens. When circular point defects with diameters of 10μm, 30μm, 110μm, and 200μm are etched on the plane mirror, vortex beams of orders 1, 2, 5, and 10 are generated, respectively. In other words, order tuning can be achieved by adjusting the diameter of the point defects. For the two branches, adjusting the distance between the plane mirror and the branch focusing lens from 91mm to 100mm, when the point defect diameter is 40μm, the vortex beam order changes from 4th to 2nd order; when the point defect diameter is 60μm, the vortex beam order changes from 5th to 3rd order; when the point defect diameter is 120μm, the vortex beam order changes from 9th to 6th order. In other words, adjusting the beam size on the plane mirror can also achieve order tuning. When the plane mirrors of the first and second branches are etched with circular point defects with diameters of 40μm and 120μm, respectively, if the distance D1 between the first focusing lens and the first plane mirror and the distance D2 between the second focusing lens and the second plane mirror are adjusted from 91mm to 100mm respectively, the first branch of the composite cavity can output 2nd to 4th order vortex light, and the second branch can output 6th to 9th order vortex light, which can be combined in sequence to obtain different types of multi-vortex beam outputs.

[0069] It should be noted that the specific embodiments are merely explanations and illustrations of the technical solutions of the present invention and cannot be used to limit the scope of protection. Any minor changes made based on the claims and description of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. A composite cavity structure for generating multiple vortices, characterized in that include: Main road, first branch road and at least one second branch road; The main path includes an input mirror (2), a laser crystal (3) and a main focusing lens (4); The first branch includes a first wave plate (7-1), a first focusing lens (7-2) and a first plane reflecting mirror (7-3); The second branch path includes a second wave plate (8-1), a second focusing lens (8-2), a second plane reflector (8-3) and a second polarization beam splitting prism (8-4); The pump light source (1) is incident on the laser crystal (3) through the input mirror (2) to generate oscillating light, and then the oscillating light enters the main focusing lens (4) to obtain the main path oscillating light, and the main path oscillating light passes through the main wave plate (5) and the main polarization beam splitting prism (6) in sequence and is then split into a first branch and a second branch, and the main wave plate (5) and the main polarization beam splitting prism (6) are used to control the splitting ratio of the light beam; The oscillating light entering the first branch path passes through the first wave plate (7-1), the first focusing lens (7-2) and the first plane reflector (7-3) in sequence and then returns. After the returning oscillating light passes through the main polarization beam splitting prism (6), a portion of the oscillating light is reflected and output, and the other portion of the oscillating light is transmitted to the main path. The first wave plate (7-1) is used to control the reflection and transmission splitting ratio. The oscillating light entering the second branch path passes through the second wave plate (8-1), the second polarization beam splitting prism (8-4), the second focusing lens (8-2) and the second plane reflector (8-3) in sequence before returning. After the returning oscillating light passes through the main polarization beam splitting prism (6), a portion of the oscillating light is transmitted and output, and the other portion of the oscillating light is reflected to the main path. The second wave plate (8-1) is used to control the reflection and transmission splitting ratio. The first plane reflecting mirror (7-3) and the second plane reflecting mirror (8-3) are processed with defects, and the defects are located at the center of the oscillating light beam; The first branch oscillation light reflection output and the second branch oscillation light transmission output, i.e., a multi-vortex light beam; The first branch and the main path form a resonant cavity, the second branch and the main path form a resonant cavity, a plurality of resonant cavities form a composite cavity, and the plurality of resonant cavities share a main polarization beam splitting prism (6) for light splitting as an output coupler.

2. A composite cavity structure for generating multiple vortices according to claim 1, characterized in that The first wave plate (7-1), the second wave plate (8-1) and the main wave plate (5) are half wave plates or quarter wave plates.

3. A composite cavity structure for generating multiple vortices according to claim 2, characterized in that The first wave plate (7-1), the second wave plate (8-1) and the main wave plate (5) are half wave plates.

4. A composite cavity structure for generating multiple vortices according to claim 3, characterized in that The defects on the first plane reflecting mirror (7-3) and the second plane reflecting mirror (8-3) are circular point defects.

5. A composite cavity structure for generating multiple vortices according to claim 4, characterized in that The oscillation order in the resonant cavity formed by the second branch and the main path is l n The normalized threshold power of the vortex beam Expressed as: Where w0 is the radius of the fundamental mode Gaussian beam in the laser crystal, δ = w p / w0 is the radius ratio of the pump source to the fundamental mode Gaussian beam, L n is the transmission loss of the nth branch, is the threshold power Proportional to the loss of the resonant cavity is the threshold power Inversely proportional to the spatial mode overlap integral of the pump source and the oscillating beam in the crystal, d n is the diameter of the circular point defect of the nth second branch, w n is the size of the fundamental mode beam on the plane reflector in the first branch and the second branch, w p It is the beam size of the oscillating light generated by the pump light source incident on the laser crystal through the input mirror.

6. A composite cavity structure for generating multiple vortices according to claim 1, characterized in that The flat surface and concave surface of the input mirror (2) are coated with anti-reflection films.

7. A composite cavity structure for generating multiple vortices according to claim 1, characterized in that The concave surface of the input mirror (2) is plated with a high-reflection film.

8. The composite cavity structure for generating multiple vortices according to claim 1, characterized in that The pump light source (1) has a wavelength of 808 nm, a beam diameter of 400 μm, and a maximum output power of 50 W.

9. A composite cavity structure for generating multiple vortices according to claim 1, characterized in that The input mirror (2) is a plano-concave mirror with a curvature radius of 50 mm.

10. The composite cavity structure for generating multiple vortices according to claim 1, characterized in that The laser crystal (3) is selected to have a size of 3×3×10 mm. 3 Nd:YAG crystal.

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