WO2010115393A1

WO2010115393A1 - Assembly of a plurality of magnets for a faraday rotator

Info

Publication number: WO2010115393A1
Application number: PCT/DE2010/000285
Authority: WO
Inventors: Kolja Nicklaus
Original assignee: Jt Optical Engine Gmbh + Co. Kg
Priority date: 2009-04-09
Filing date: 2010-03-15
Publication date: 2010-10-14
Also published as: DE102009016949A1; DE102009016949B4

Abstract

The present invention relates to an optical Faraday rotator for high power optical radiation. The assembly of optical Faraday rotators comprises the following elements: one or more Faraday media (4) and a magnet assembly (1) that allows for the receiving of a plurality of Faraday media (4) in an aperture, and is characterized in that the magnet assembly (1) is formed by parallelepiped magnets (2).

Description

ARRANGEMENT OF SEVERAL MAGNETS FOR A FARADAY ROTATOR

The present invention relates to a Faraday rotator for high power optical radiation. Such a Faraday rotator consists of a polarization rotator based on the Faraday effect.

Faraday rotators are often used in conjunction with a polarizer assembly to form an optical isolator. Therefore, in the prior art, the Faraday rotators are typically described in the context of optical isolator arrangements.

Such optical isolators are known, for example, in the field of optical telecommunications for both polarized and unpolarized radiation. These insulators are used up to a power of about 1 W and use to rotate the polarization of the optical electromagnetic field ferromagnetic Faraday-active media (so-called Faraday media) with very large Verdetkonstante such as YIG or BIG crystals. Due to the large Verdetkonstante are comparatively small magnetic fields, which can be generated for example by a simple small permanent magnet.

For the high power range of a few watts and more of average optical power, the known ferromagnetic Faraday media are not suitable because of their low optical quality and high absorption. Typically, paramagnetic crystals and glasses are used, such as Tb: glass or TGG crystals, which have one to two orders of magnitude lower dilution constant. At a constant of TGG of 22.7 7 (Tcm) at a wavelength of 1064 nm, the required crystal length for a polarization rotation of 45 °, as required in Faraday isolators, at a magnetic field strength of 1 T is about 20 mm.

To produce such a magnetic field over a length of 20 mm at a typical aperture of a few millimeters, a single permanent magnet is not sufficient. Much more Certain arrangements are used by magnets that increase the magnetic field strength in the free aperture, while remaining as homogeneous as possible over the aperture cross-section.

EP 1660 931 B1 describes a rotationally symmetrical arrangement which enables a strong homogeneous magnetic field in the free aperture for a single cylindrical Faraday medium. In the case of two Faraday media or a medium with a high aspect ratio, however, a very large circular free aperture is needed, whereby the arrangement occupies a large space.

US Pat. No. 5,528,415 describes an arrangement of prism-shaped magnets with a trapezoid as the base surface with rectangular external dimensions, which has a square aperture and in which a homogeneous field is also achieved in the area of the enclosed inner circle. In the case of two Faraday media or a medium with a high aspect ratio, however, a very large square free aperture is needed, whereby the arrangement again occupies a large installation space. If the arrangement is only scaled in one direction, the magnetic field in the aperture becomes inhomogeneous, which impairs the rotation of the polarization or optical isolation.

Proceeding from this, it is an object of the invention to find an arrangement for a Faraday rotator for radiation of high optical power, which provides a homogeneous magnetic field within the aperture with a compact size.

According to the invention the object is achieved by an arrangement of a Faraday rotator consisting of one or more Faradaymedien and a magnet assembly which allows the recording of several Faradaymedien, characterized in that the arrangement of the magnetic field is formed from such shaped magnets that at least the outer Magnets are cuboid.

An advantage of such a magnet arrangement with at least the external magnets in cuboid shape is that a scaling of the free aperture of the arrangement along one direction while maintaining the homogeneity of the integrated over the length magnetic field of 5% (+2.5%) is possible. As a result, compared with the prior art, a very compact arrangement with simple, and therefore inexpensive, magnetic forms is made possible. The aspect ratio (length / width / depth) of the magnet assembly is to be optimized depending on the free aperture and required length of the Faraday medium so that a homogeneous, integrated over the length of the magnetic field in the free aperture, the deviation of the homogeneity no longer than 5%. The magnet arrangement preferably generates within the aperture a magnetic field of 0.7 T. The aperture of the magnet arrangement corresponds at least to the diameter of the Faraday medium and is preferably smaller than 2 times this diameter. The aperture can also be a multiple of the diameter of the Faraday medium or a multiple of the maximum 2 times the diameter of the Faraday medium, so that several Faradaymedien can be arranged side by side within the aperture.

The cuboid magnets of the magnet assembly may be chamfered in an exemplary embodiment at the outer corners of the assembly. The edge length of the magnet arrangement can be reduced by up to a quarter of this edge length, for example. This will be the

Space even more compact, so that the magnet assembly can be accommodated in cuboid or cylindrical housings, and the possibility exists

Attach fasteners such as screws or dowel pins to the recessed corners. The edge length reduction may be uniform at all four corners, but may vary.

In the free aperture spacers can be introduced, which prevent individual magnets can reduce the free aperture. Such spacers are advantageous because the individual magnets of the arrangement can exert large forces on each other by their magnetization. The spacers may be part of the outer housing, part of the holder of the Faraday medium or the Faraday media, separate components or fused with the magnets.

The Faraday rotator can also be passed several times by folding with the aid of folding elements.

For example, Tb: glass or TGG crystals can be used as Faraday media. The shape of the Faraday media is typically rod-shaped, but may also have a high aspect ratio (so-called "slab") or be formed as a prism body.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. Show it: Fig. 1a is a schematic view of an annular magnet arrangement (prior art);

Fig. 1 b scaling of an annular magnet arrangement (prior art);

Fig. 2a is a schematic view of a cuboid magnet arrangement according to the invention;

FIG. 2b shows the scaling of a cuboid magnet arrangement according to the invention; FIG.

3 shows a schematic view of an optical Faraday rotator according to the invention with optical beam path;

4 shows a schematic view of a folded optical Faraday rotator according to the invention with optical beam path;

5 shows a schematic view of another folded optical Faraday rotator according to the invention with optical beam path;

6 shows a schematic view of another folded optical Faraday rotator according to the invention with optical beam path;

7 shows an embodiment according to the invention of a compact cuboidal

Magnet arrangement for 2-rod Faraday media;

Fig. 8 is a sectional view of magnets of an embodiment of the invention;

FIG. 9 Simulation of the integrated magnetic field along the optical axis according to FIG

Magnet assembly of Figure 7 using the magnets in Fig. 8;

FIG. 10 a calculation of the strength of the magnetic field integrated along the optical axis as a function of the crystal length of the Faraday medium according to the embodiment according to the invention from FIG. 7; FIG.

Fig. 10b Calculation of the homogeneity of the integrated along the optical axis

Magnetic field as a function of the crystal length of the Faraday medium according to the embodiment of the invention of FIG. 7; 11a is a schematic view of an embodiment according to the invention of magnets with chamfered outer corners of the magnet assembly;

Fig. 11b is a schematic view of another embodiment of the magnets with chamfered outer corners of the magnet assembly according to the invention;

Fig. 12 is a sectional view of magnets of another embodiment of the invention;

Fig. 13 Simulation of the integrated magnetic field along the optical axis according to the magnet arrangement of Fig. 11a using the magnets in Fig. 12;

FIG. 14: calculation of the strength of the magnetic field integrated along the optical axis as a function of the crystal length of the Faraday medium according to the embodiment according to the invention from FIG. 11a; FIG.

Fig. 15 Calculation of the homogeneity of the integrated along the optical axis

Magnetic field as a function of the crystal length of the Faraday medium according to the embodiment of the invention of Figure 11a.

16 shows a schematic view of a further magnet arrangement according to the invention, consisting of 12 cuboid magnets;

17 shows an inventive embodiment of a compact cuboidal magnet arrangement for 2 rod-shaped Faraday media with spacers in the free one

aperture;

The embodiments shown in FIGS. 1a and 1b are arrangements of the prior art, the magnet arrangement (1) consisting of cylindrical magnets (2) having an aperture (3) and a Faraday medium (4) in the aperture (3). consists.

The embodiments shown in FIGS. 2-22 are embodiments according to the invention of the optical Faraday rotator and its components.

In the embodiment shown in Figure 2a is a schematic representation of the magnet assembly (1) consisting of parallelepiped magnet (2), which generates an aperture (3) corresponding to the diameter of the Faradaymediums (4). FIG. 2b shows an embodiment of the magnet arrangement (1) consisting of parallelepiped magnets (2) which produce an aperture (3) which corresponds in one direction to twice the diameter of a Faraday medium (4), so that two Faraday media (4) are arranged side by side within the Aperture (3) can be arranged.

Figures 3 - 6 show schematic views of various embodiments of the optical Faraday rotator (5) according to the invention, consisting of a magnet assembly (1) and a Faradaymedium (4) with the optical beam path (6).

The Faraday rotator (5) can also be passed through folding by means of folding elements (7) two or more times, as for example in the embodiments shown in Figures 4, 5 and 6. In the embodiment in FIGS. 4 and 5, it is advantageous that the length in which a strong magnetic field must be generated in the free aperture (3) can be halved compared with the linear arrangement, which reduces the size of the necessary magnet arrangement (1) , In the embodiment shown in FIG. 6, the length in which a strong magnetic field has to be generated in the free aperture (3) can be divided by three than the linear arrangement, which further reduces the size of the necessary magnet arrangement (1).

In the embodiment shown in Figure 7 is a schematic representation of a magnet assembly (1) according to the invention, which consists of 8 cuboid magnets (2), and a cuboid magnet (2) with a bore. As a result, three magnetic planes (8, 8 ', 8 ") are formed, wherein the first and third plane (8, 8") is composed of 4 parallelepiped magnets (2) and the second (middle) plane (8') through the Magnet (2) is formed with the bore. The size of the hole corresponds to the free aperture (3) of the enclosing magnetic planes (8, 8 "), which in turn corresponds in one direction to twice the diameter of the Faraday medium (4), so that two Faraday media (4) can be arranged side by side.

FIG. 8 shows the dimensions of magnets (2) for the magnet arrangement (1) shown schematically in FIG. 7 with magnets (2) of the class N40UH with a remanence magnetization of Br = 1.28T. The edge lengths A and B or B "and C and D in the present example A = 65 mm, B = 18.5 mm, B" = 63 mm, C = 27.8 mm and D = 25.8 mm. The height h of the magnets (2), which can not be represented in the sectional drawing, is h = 20 mm for all three magnets (2) in this particular case. The free aperture (3) is E x F, where E = 9.3 mm and F = 26 mm, and the crystal length of the Faraday medium (4) is designed for about 15 mm and for a wavelength of 1064 mm. By this arrangement, a very homogeneous, integrated along the optical axis, magnetic field with a deviation of less than 4% over the height and width of 8 mm, or less than 1% over a height and width of 4 mm is achieved, as the simulation in Fig. 9 and the calculations in Figs. 10a and 10b show.

FIGS. 11a and 11b show further embodiments of the magnet arrangement (1) according to the invention. The magnets (2) shown are magnets (2) of the class N40UH with a remanence magnetization of Br = 1, 28 T. The free aperture (3) of the magnet arrangement is E x F, where E = 5 mm and F = 8 mm, and is designed for a crystal length of the Faraday medium of about 15 mm and at a wavelength of 1064 mm. The cuboid magnets (2) of the magnet assembly (1) are chamfered at the outer corners of the assembly (1), whereby the edge lengths A and B are shortened by one part and thus have an edge length of A 'and B'.

In the present example, the edge lengths A = 34 mm, A '= 24 mm, B = 13 mm, B' = 8 mm, C = 14.5 mm and D = 7.6 mm: the height h of the magnets (2) is h = 15 mm, and for the magnet (2) with hole h '= 14 mm. With the dimensions of the magnets (2) shown in Figure 12 is a very homogeneous, integrated along the optical axis, magnetic field with a deviation of less than 3.5% over the height and width of 3 mm, and less than 1% over a height and width of 1, 5 mm reached. Figures 13-15 show the associated simulations and calculations analogous to the previous embodiment.

The inventive embodiment of the magnet assembly (1) shown in Figure 16 consists of 12 cuboid magnets (2), in turn, three magnetic planes (8, 8 ', 8 ") are formed, which in the present embodiment of four parallelepiped magnets (2) composed This offers the advantage of a simple and thus inexpensive manufacturability of the magnets (2).

The inventive embodiment of the magnet arrangement (1) shown in FIG. 17 consists of parallelepiped magnets (2) with spacers (9) in the free aperture (3), in which two Faraday media (4) are arranged by way of example here.

Claims

claims

An arrangement for a Faraday optical rotator (5) comprising: one or more Faraday media (4) and a magnet assembly (1) enabling the inclusion of a plurality of Faraday media (4); characterized in that the magnet arrangement (1) is formed from magnets (2) shaped in such a way that at least the external magnets (2) are cuboidal.

2. Arrangement for an optical Faraday rotator (5) according to claim 1, characterized in that the outer corners of the magnet assembly (1) are chamfered.

3. Arrangement for an optical Faraday rotator (5) according to claim 2, characterized in that the edge length of the magnet assembly (1) is reduced by up to a quarter.

4. Arrangement for an optical Faraday rotator (5) according to one of the above claims, characterized in that the magnet arrangement (1) within the aperture (3) a

Magnetic field of = 0.7 T generated.

5. Arrangement for an optical Faraday rotator (5) according to one of the above claims, characterized in that the edge length of the free aperture (3) of the magnet arrangement (1) corresponds at least to the diameter of the Faraday medium (4).

6. Arrangement for an optical Faraday rotator (5) according to one of the above claims, characterized in that the aperture (3) of the magnet arrangement (1) at least the Diameter of the Faraday medium (4) and is preferably smaller than 2 times this diameter.

7. Arrangement for an optical Faraday rotator (5) according to one of the above claims, characterized in that the aperture (3) of the magnet arrangement (1) corresponds at least to the summed diameters of the Faraday media (4) in the respective direction, and preferably smaller than which is 2 times that diameter.

8. Arrangement for an optical Faraday rotator (5) according to one of the above claims, characterized in that two or more optical Faraday rotors according to the invention

Rotators (5) are arranged one behind the other, whereby a 1- or multi-stage Faraday rotator (5) is provided.

9. Arrangement for an optical Faraday rotator (5) according to claim 8, characterized in that the magnets (2) of the contacting magnetic planes (8 ", 8 '") are fused.

10. Arrangement for an optical Faraday rotator (5) according to any one of the above claims, characterized in that in the free aperture (3) of the magnet assembly (1) spacers (9) for magnets (2) are arranged.