Faraday rotator with high length-width ratio and rectangular aperture

Abstract

The invention relates to the technical field of high-power / high-energy optical passive devices, in particular to a high-length-width-ratio rectangular-aperture Faraday rotator which comprises a circular-hole rectangular light through hole, the middle of the circular-hole rectangular light through hole is rectangular, and the two ends of the circular-hole rectangular light through hole are semicircular. The space waste of a conventional circular light through hole Faraday rotator in the width direction of the rectangular light through surface is overcome, the adaptability of the light through hole of the device to a rectangular light spot application scene is improved, and the size, the weight and the cost of the device are remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of high-power / high-energy optical passive devices, and in particular to a high-aspect-ratio rectangular aperture Faraday rotator. Background Art

[0002] A Faraday rotator is an optical passive device that achieves a 45° non-reciprocal Faraday rotation based on the magneto-optical effect. It is typically placed between a polarizer and analyzer, whose transmission direction is 45°, to form a Faraday isolator. In laser systems, Faraday isolators enable unidirectional laser transmission and are commonly used at the back end of lasers and at both ends of optical amplifiers, playing an important role in protecting the laser front-end system and stabilizing laser output. As a key component in constructing Faraday isolators, Faraday rotators have been widely used in scientific research, military, and industrial applications, such as national large-scale laser scientific facilities, ultra-intense and ultra-short laser devices, and laser intelligent manufacturing equipment.

[0003] According to the Faraday effect, when plane linearly polarized light passes through a magneto-optically active medium magnetized along the direction of light propagation, its plane of polarization rotates. The Faraday rotation angle, or the angle of rotation of the polarization plane (θ), is proportional to the Verdet constant (V), length (L), and spatial magnetic flux density (B) of the magneto-optically active medium: θ = VBL. The direction of the Faraday rotation angle is independent of the incident direction of light and depends solely on the direction of the magnetic field, exhibiting a unique non-reciprocal property. For a given magneto-optically active medium, designing an appropriate magneto-optically active medium length and spatial magnetic flux density can achieve a 45° rotation of the polarization plane of incident linearly polarized laser light. The core functional components of a Faraday rotator include a rare earth permanent magnet circuit and a magneto-optical element. The rare earth permanent magnet circuit provides a steady static magnetic field and is typically composed of multiple neodymium iron boron or samarium cobalt permanent magnet rings with light-through apertures. The magneto-optical element is a low-loss magneto-optically active medium. To reduce surface reflections, an anti-reflection film is typically applied to both light-transmitting end faces of a magneto-optical element. For high-energy / high-power applications, the anti-reflection film must exhibit high resistance to laser damage and low residual reflectivity. Magneto-optical media primarily include magneto-optical glass and magneto-optical crystals. Magneto-optical crystals typically have higher Verdet constants and thermal conductivity, making them more suitable for high-power applications.

[0004] Currently, commercial Faraday rotators typically feature circular apertures, similar to the device disclosed in CN 101233160A. In recent years, high-energy / high-power rectangular light spots have shown promising applications in precision machining, medicine, and scientific research, driving demand for rectangular-aperture Faraday rotators. Circular-aperture Faraday rotators are inefficient for rectangular-spot lasers, especially in high-aspect-ratio applications. The increased volume, weight, and cost associated with wasted width-wise space make it difficult to achieve miniaturization, lightweighting, and low-cost applications with conventional circular-aperture Faraday rotators. Therefore, improving the magnetic field uniformity within the high-aspect-ratio aperture of Faraday rotators remains a core technical challenge. Summary of the Invention

[0005] The object of the present invention is to provide a high aspect ratio rectangular aperture Faraday rotator to solve the technical problem in the prior art that the magnetic field uniformity within the high aspect ratio light passage plane cannot be improved.

[0006] The invention discloses a high aspect ratio rectangular aperture Faraday rotator, comprising a circular hole and a rectangular light-through hole, wherein the circular hole and the rectangular light-through hole are rectangular in the middle and semicircular at both ends.

[0007] Furthermore, the rectangular length-to-width ratio of the circular-rectangular light-transmitting hole is greater than 1, and the width is greater than 5 mm.

[0008] Furthermore, a circular rectangular ring having a shape adapted to the circular rectangular light-through hole is provided outside the circular rectangular light-through hole.

[0009] Furthermore, the circular hole rectangular ring is made of soft magnetic material.

[0010] Furthermore, a light pipe is provided in the circular rectangular ring, and the shape of the light pipe is adapted to the circular rectangular light hole. No semicircular light holes are provided at both ends of the light pipe, and only a rectangular light hole is provided in the middle.

[0011] Furthermore, two end surfaces of the light pipe are respectively provided with through liquid cooling channels along the light axis direction.

[0012] By setting up a liquid cooling channel, the internal heat dissipation capacity can be improved.

[0013] Furthermore, a magneto-optical element is provided in the light pipe.

[0014] Furthermore, a fixing hole for fixing the magneto-optical element is provided in the light pipe.

[0015] Furthermore, the magneto-optical element is a cuboid, with a light-transmitting surface aspect ratio (L:W) greater than 1, a width (W) greater than 5 mm, and a length along the light-transmitting direction, ie, a depth (D) of 10 to 50 mm.

[0016] Furthermore, the magneto-optical element is a magneto-optical glass material containing terbium, terbium gallium garnet (TGG) crystal, terbium oxide ceramic or TGG ceramic.

[0017] Furthermore, the aspect ratio of the light-transmitting surface of the magneto-optical element is 6, and the end surface is coated with a 1064nm high-threshold anti-reflection film.

[0018] Furthermore, the circular hole rectangular ring outer shell is provided with a plurality of magnetic rings.

[0019] Furthermore, the number of the plurality of magnetic rings is three, namely a first magnetic ring, a second magnetic ring and a third magnetic ring.

[0020] Furthermore, the first magnetic ring and the third magnetic ring are equal in length.

[0021] Furthermore, the first magnetic ring and the third magnetic ring are both composed of radially magnetized tile-type magnets and radially magnetized rectangular magnets, and the magnetization direction of each magnet is perpendicular to the light-passing direction. The magnets of the first magnetic ring are magnetized in such a way that the light-passing hole side becomes the N pole, and the magnets of the third magnetic ring are magnetized in such a way that the light-passing hole side becomes the S pole.

[0022] Furthermore, the second magnetic ring includes an axially magnetized semicircular ring magnet and an axially magnetized rectangular parallelepiped magnet, and the magnetization direction of each magnet is parallel to the light transmission direction, so that the side close to the first magnetic ring is magnetized in an N-pole manner.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention can achieve a high-precision Faraday rotation of 45°±2° within a rectangular area with a length:width ratio greater than 1:1;

[0025] 2. This invention overcomes the space waste in the width direction of the rectangular light-clearing surface of conventional circular aperture Faraday rotators, improves the adaptability of the device's aperture to rectangular light spot applications, and significantly reduces the device's size, weight, and cost.

[0026] 3. By providing a circular-aperture rectangular ring, the problem of magnetic field uniformity within the rectangular magneto-optical element in a large-aperture permanent magnet circuit is resolved, and the rotation angle accuracy of the rectangular-aperture Faraday rotator is improved to within ±2°.

[0027] 4. The light-transmitting surface of the magneto-optical element has a high aspect ratio feature, which can increase the heat dissipation area of ​​the magneto-optical element and improve the device's tolerable laser power level. It can be applied to various high-energy / high-power laser systems based on high-aspect-ratio rectangular spots and has strong practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only represent some embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Schematic diagram of the structure of the Faraday rotator of the present invention.

[0030] Figure 2 This is a schematic structural diagram of the first magnetic ring and the third magnetic ring of the present invention.

[0031] Figure 3 This is a schematic diagram of the second magnetic ring structure of the present invention.

[0032] Figure 4 Schematic diagram of the light pipe structure of the present invention.

[0033] Figure 5 It is a schematic diagram of the structure of the magneto-optical element of the present invention.

[0034] Figure 6 Schematic diagram of the structure of the Faraday rotator according to Example 2 of the present invention.

[0035] Figure 7 Schematic diagram of the structure of the Faraday rotator according to Example 3 of the present invention.

[0036] In the above drawings, the meanings of the various marks are: 1-first magnetic ring, 2-second magnetic ring, 3-third magnetic ring, 4-rectangular ring with circular hole, 5-light tube, 6-magneto-optical element, 7-fixing hole, 8-radially magnetized tile-type magnet, 9-radially magnetized rectangular parallelepiped magnet, 10-axially magnetized rectangular parallelepiped magnet, 11-axially magnetized semicircular ring magnet, 12-paramagnetic rectangular ring with circular hole, 13-liquid cooling channel. DETAILED DESCRIPTION

[0037] 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 are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0038] Example 1

[0039] This embodiment discloses a high aspect ratio rectangular aperture Faraday rotator, a large diameter rectangular aperture Faraday rotator, see Figure 1This embodiment provides a large-aperture rectangular aperture Faraday rotator with an aspect ratio greater than 1 and a width greater than 5 mm, which is composed of a first magnetic ring 1, a second magnetic ring 2, a third magnetic ring 3, a soft magnetic circular hole rectangular ring 4, a light pipe 5 and a magneto-optical element 6.

[0040] The structural diagram of the first magnetic ring 1 and the third magnetic ring 3 is as follows Figure 2 As shown, its outer shape and internal light-passing aperture exhibit distinct circular-rectangular characteristics, and the two magnetic rings are of equal length. Under optimal conditions, the magnetic rings are composed of eight radially magnetized tile-shaped magnets 8 and four radially magnetized rectangular-shaped magnets 9. Each magnet is magnetized perpendicular to the direction of light transmission (radial magnetization). The magnets of the first magnetic ring 1 are magnetized with the light-passing aperture side facing the north pole, while the magnets of the third magnetic ring are magnetized with the light-passing aperture side facing the south pole. The greater the length and width of the rectangular aperture, the greater the number of radially magnetized tile-shaped magnets 8 and radially magnetized rectangular-shaped magnets 9 required to form the first magnetic ring 1 and the third magnetic ring 3. The magnets constituting the first magnetic ring 1 and the third magnetic ring 3 are made of the same material, which can be NdFeB or SmCo permanent magnets. By integrating soft magnetic circular-shaped rectangular rings 4 into the first and third magnetic rings, the problem of magnetic field uniformity within the region where the rectangular magneto-optical elements are located in large-diameter permanent magnet circuits is solved.

[0041] The structural diagram of the second magnetic ring 2 is as follows Figure 3 As shown, its outer shape and internal light-transmitting aperture also have distinct circular-shaped rectangular features. Under preferred conditions, the magnetic ring is composed of two axially magnetized semicircular ring magnets 11 and four axially magnetized rectangular parallelepiped magnets 10. The magnetization direction of each magnet is parallel to the light transmission direction (axial magnetization), so that the side close to the first magnetic ring 1 is magnetized in a north-pole manner. The larger the length and width of the rectangular aperture, the greater the number of axially magnetized rectangular parallelepiped magnets 10 required to form the second magnetic ring 2. The axially magnetized semicircular ring magnets 11 can be composed of two or more tile-shaped magnets. The magnet materials that constitute the second magnetic ring 2 are the same as those of the first magnetic ring 1 and the third magnetic ring 3, and can be NdFeB and SmCo permanent magnet materials.

[0042] The structural diagram of the light pipe 5 is as follows Figure 4 As shown, its external structure has a circular hole rectangular feature that matches the first to third magnetic ring light holes. The internal light hole is rectangular, and the side wall has a fixing hole 7 for fixing the magneto-optical element, which can be fixed by tightening screws or adhesives.

[0043] The structural diagram of the magneto-optical element 6 is shown in FIG. Figure 5As shown, it has a typical rectangular parallelepiped shape, with a light-transmitting surface aspect ratio (L:W) greater than 1, a width (W) greater than 5mm, and a length along the light-transmitting direction, i.e., a depth (D), within 10 to 50mm. Under preferred conditions, the magneto-optical element is made of terbium-containing magneto-optical glass, with a light-transmitting surface aspect ratio of 6, and a 1064nm high-threshold anti-reflection film coated on the end faces. The magneto-optical element is not limited to this type of magneto-optical material. Terbium gallium garnet (TGG) crystals with higher Verdet constants and magneto-optical ceramic materials that are easy to manufacture in large sizes, such as terbium oxide ceramics and TGG ceramics, can be used to further reduce the size and weight of the device. The light-transmitting surface length L and width W of the magneto-optical element are matched to the specific application laser spot size. The light-transmitting direction length D is affected by the material's Verdet constant and the magnetic induction intensity provided by the magnetic circuit formed by the first, second, and third magnetic rings, ultimately oriented to achieve a 45° Faraday rotation. Furthermore, the operating wavelength of the magneto-optical element's end-face anti-reflection film is determined by the specific application laser wavelength.

[0044] Example 2:

[0045] Small rectangular aperture Faraday rotator

[0046] See also Figure 6 This embodiment provides a small-aperture rectangular Faraday rotator with an aspect ratio greater than 1 and a width ≤ 5 mm. The device comprises a first magnetic ring 1, a third magnetic ring 3, a soft magnetic rectangular ring 4 with a circular aperture, a light pipe 5, a magneto-optical element 6, and a paramagnetic rectangular ring 12 with a circular aperture. The device differs from Example 1 in that the second magnetic ring 2 is removed. The first and third magnetic rings 1 and 3 have equal lengths along the light transmission direction. The internal soft magnetic rectangular ring 4 is 0.5-0.8 times the length of the first magnetic ring 1. Between the soft magnetic rectangular rings 4 of the first and third magnetic rings 1 and 3 is a paramagnetic rectangular ring 12 with a length 0.4-0.8 times the length of the magneto-optical element 6. The magneto-optical element 6 can be made of terbium-containing magneto-optical glass, but is preferably made of a magneto-optical material with a large Verdet constant, such as TGG crystal, TGG ceramic, or terbium oxide ceramic. Its length in the light transmission direction is shorter than that of the first magnetic ring 1.

[0047] Example 3:

[0048] Liquid-cooled rectangular aperture Faraday rotator

[0049] See also Figure 7This embodiment provides a liquid-cooled rectangular-aperture Faraday rotator with an aspect ratio greater than 1. The device comprises a first magnetic ring 1, a second magnetic ring 2, a third magnetic ring 3, a soft magnetic rectangular ring with a circular aperture 4, a light pipe 5, and a magneto-optical element 6. Differences from Example 1 are that this embodiment utilizes the unique rectangular shape of the light pipe to add two through-hole liquid cooling channels 13 along the light axis at the end of the light pipe to enhance efficient heat dissipation of the internal magneto-optical element 6. This embodiment preferably utilizes magneto-optical crystal materials such as TGG crystals with higher thermal conductivity.

[0050] In Examples 1 to 3, the rotation angle deviation of the rectangular aperture Faraday rotator within the rectangular light-transmitting surface is within ±2°.

[0051] The above are the implementation methods listed in this embodiment, but this embodiment is not limited to the above optional implementation methods. Those skilled in the art can arbitrarily combine the above methods to obtain other various implementation methods. Anyone can derive other various forms of implementation methods based on the inspiration of this embodiment. The above specific implementation methods should not be understood as limiting the scope of protection of this embodiment. The scope of protection of this embodiment shall be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A high aspect ratio rectangular aperture Faraday rotator, characterized by: It includes a circular hole and a rectangular light-through hole, wherein the circular hole and the rectangular light-through hole are rectangular in the middle and semicircular at both ends.

2. The high aspect ratio rectangular aperture Faraday rotator according to claim 1, characterized in that: The rectangular length-to-width ratio of the circular hole and the rectangular light-through hole is greater than 1, and the width is greater than 5 mm.

3. The high aspect ratio rectangular aperture Faraday rotator according to claim 1, characterized in that: A circular rectangular ring (4) having a shape adapted to the circular rectangular light-through hole is arranged outside the circular rectangular light-through hole.

4. The high aspect ratio rectangular aperture Faraday rotator according to claim 3, characterized in that: A light pipe (5) is provided in the circular rectangular ring (4); the shape of the light pipe (5) is adapted to the circular rectangular light hole; no semicircular light holes are provided at either end of the light pipe (5); only a rectangular light hole is provided in the middle.

5. The high aspect ratio rectangular aperture Faraday rotator according to claim 4, characterized in that: A magneto-optical element (6) is arranged in the light pipe (5).

6. The high aspect ratio rectangular aperture Faraday rotator according to claim 5, characterized in that: The magneto-optical element (6) is a rectangular parallelepiped, with a light-transmitting surface aspect ratio (L:W) greater than 1, a width (W) greater than 5 mm, and a length along the light-transmitting direction, i.e., a depth (D) of 10 to 50 mm.

7. The high aspect ratio rectangular aperture Faraday rotator according to claim 3, characterized in that: The circular hole rectangular ring (4) is provided with a plurality of magnetic rings on its outer shell.

8. The high aspect ratio rectangular aperture Faraday rotator according to claim 7, characterized in that: The number of the plurality of magnetic rings is three, namely a first magnetic ring (1), a second magnetic ring (2) and a third magnetic ring (3).

9. The high aspect ratio rectangular aperture Faraday rotator according to claim 8, characterized in that: The first magnetic ring (1) and the third magnetic ring (3) both comprise a radially magnetized tile-shaped magnet (8) and a radially magnetized rectangular parallelepiped magnet (9), the magnetization direction of each magnet being perpendicular to the light-through direction; the magnet of the first magnetic ring (1) is magnetized in such a way that the light-through hole side becomes an N pole, and the magnet of the third magnetic ring (3) is magnetized in such a way that the light-through hole side becomes an S pole.

10. The high aspect ratio rectangular aperture Faraday rotator according to claim 8, characterized in that: The second magnetic ring (2) comprises an axially magnetized semicircular ring magnet (11) and an axially magnetized rectangular parallelepiped magnet (10), the magnetization direction of each magnet being parallel to the light transmission direction, so that the side close to the first magnetic ring (1) is magnetized in an N-pole manner.

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