Optical guide for magneto-optical current sensor

Abstract

The invention relates to a light guide (5) for a magneto-optical current sensor (1). The light guide (5) comprises a first end face (21) through which light can be coupled into the light guide (5) and a second end face (24) through which light can be coupled out of the light guide (5), wherein at least one of the two end faces (21, 24) has an anti-reflection coating (31, 32).

Description

Technical Field

[0001] The present invention relates to a light guide for a magneto-optical current sensor and a magneto-optical current sensor having such a light guide. Background Technology

[0002] Here, a magneto-optical current sensor with an optical guide is understood as an optical measuring device for measuring current in a conductor, wherein light is guided through the optical guide and its optical properties are altered by a magnetic field generated by the current within the optical guide. For example, magneto-optical current sensors are based on the magneto-optical Faraday effect. The Faraday effect is understood as the rotation of the polarization direction of a linearly polarized electromagnetic wave in a medium due to a magnetic field parallel to the wave's propagation direction. This rotation of the polarization direction is proportional to the magnetic flux density of the magnetic field.

[0003] In a magneto-optical current sensor based on the Faraday effect, linearly polarized light is guided through an optical guide positioned near a conductor, exhibiting the Faraday effect. The magnetic field generated by the current in the conductor causes a rotation of the light's polarization direction within the optical guide. Because the magnetic flux density in the optical guide is related to the current intensity in the conductor, the current intensity can be measured by detecting the rotation of the light's polarization direction within the optical guide. To detect this rotation, light output from the optical guide is guided, for example, through a polarizer on the output side, and the intensity of the light emitted from the polarizer is detected.

[0004] However, due to the optical characteristics of the light guide and / or the light source used, the light intensity of the light coupled into the magneto-optical current sensor is limited. Furthermore, due to light scattering, absorption, and reflection, the light intensity output from the light guide decreases compared to the light intensity coupled into it. The light intensity output from the light guide is determined, for example, by a photodiode. Photodiodes have background noise composed of various noise sources. The very low light intensity output from the light guide results in a low signal-to-noise ratio for the measurement signal and thus limits the accuracy of the light intensity measurement.

[0005] For various reasons, increasing the light intensity coupled into the optical guide by using a stronger light source is often impossible or not advantageous. For example, while it is possible to increase the light intensity by using a suitable semiconductor laser as the light source, the vibration sensitivity of the magneto-optical current sensor is significantly increased due to the increased coherence length of the light. Improving the signal-to-noise ratio of the measurement signal by applying appropriate filtering is also limited, as this filtering reduces the bandwidth of the resulting measurement signal, which in turn reduces the temporal resolution of the measurement signal. Summary of the Invention

[0006] The present invention is based on the objective of increasing the light intensity of the light output from the photoconductor of the magneto-optical current sensor.

[0007] According to the present invention, the objective is achieved by a light guide having the features of embodiments of the invention and a magneto-optical current sensor having the features of embodiments of the invention. Advantageous designs of the invention are the subject of subsequent embodiments.

[0008] The light guide according to the invention for use in a magneto-optical current sensor comprises: a first end face through which light can be coupled into the light guide, and a second end face through which light can be coupled out of the light guide, wherein at least one of the two end faces has an anti-reflection coating.

[0009] The anti-reflective coating reduces light reflection at the end face of the light guide according to the invention, thereby increasing light transmission through the end face. If the end face through which light is coupled into the light guide has an anti-reflective coating, the light intensity coupled into the light guide can be increased by approximately 10% to 20% compared to an embodiment of the light guide without such an anti-reflective coating. If the end face through which light is coupled out of the light guide has an anti-reflective coating, the light intensity coupled out of the light guide can be increased by approximately 10% to 20% compared to an embodiment of the light guide without such an anti-reflective coating. Furthermore, the anti-reflective coating at the end face through which light is coupled out of the light guide also advantageously reduces light reflection at that end face, which reflects the light back into the light guide.

[0010] One design of the light guide according to the invention has at least one anti-reflective coating disposed between two light guide segments having different refractive indices. At the boundary layer between the two light guide segments having different refractive indices, a portion of the light incident on the boundary layer is reflected. This reduces the transmission of light through the boundary layer and the intensity of the light output from the light guide. Furthermore, the light in the light guide is reflected back in a direction opposite to the direction of transmission. Compared to embodiments of the light guide without an anti-reflective coating, the anti-reflective coating between the two light guide segments advantageously reduces the reflection of light between the light guide segments and thereby increases the intensity of the light output from the light guide.

[0011] In another design of the light guide according to the invention, the light guide is at least partially made of glass, for example, optical flint glass. If the light guide has light guide sections made of different glasses having different refractive indices, then, corresponding to the above-described design of the light guide according to the invention, it is preferable to provide an anti-reflection layer between two adjacent such light guide sections. Alternatively or additionally, an adhesive layer can be provided between two such light guide sections, through which the two light guide sections are bonded together, wherein the adhesive layer has a refractive index between the refractive indices of the two light guide sections. For example, compared to using optical fiber light guides, producing light guides from glass has the advantage that expensive optical waveguides are not required, which maintain the linear polarization of light. If the adhesive layer between two light guide sections made of glasses having different refractive indices has a refractive index between the refractive indices of the two light guide sections, then the adhesive layer also advantageously reduces reflection at the boundary layer between the light guide sections.

[0012] In another design of the optical guide according to the invention, the optical guide is at least partially configured as an optical fiber waveguide. If the optical guide has optical guide segments configured as optical fiber waveguides with different refractive indices, then, corresponding to the design of the optical guide according to the invention already mentioned above, it is preferable to provide an anti-reflection layer between two adjacent such optical guide segments. In the case of an optical guide formed by one or more optical fiber waveguides, the end face with the anti-reflection coating is, for example, the end face of the optical fiber waveguide or the end face of the clamp of the optical fiber waveguide.

[0013] The magneto-optical current sensor according to the invention for detecting the current intensity in a conductor includes at least one optical guide according to the invention disposed in a region of the conductor.

[0014] The advantages of the magneto-optical current sensor according to the invention correspond to the advantages of the photoconductor according to the invention mentioned above.

[0015] In one design of the magneto-optical current sensor according to the invention, at least one optical guide extends in a ring around a conductor. Therefore, the measurement of the current intensity in the conductor is largely independent of the position of the conductor relative to the optical guide and the influence of external fields on the measurement is reduced. Attached Figure Description

[0016] The features, characteristics, and advantages of the present invention described above, and the ways and methods of achieving these features, characteristics, and advantages, become clearer and easier to understand in conjunction with the following description of embodiments, which will be explained in detail with reference to the accompanying drawings. Hereinafter shown:

[0017] Figure 1A first embodiment of a magneto-optical current sensor is shown.

[0018] Figure 2 This shows a portion of a light guide with two light guide segments and an adhesive layer.

[0019] Figure 3 A second embodiment of the magneto-optical current sensor is shown.

[0020] Figure 4 A portion of a light guide with two light guide segments and an anti-reflective layer is shown.

[0021] Corresponding parts are given the same reference numerals in the accompanying drawings. Detailed Implementation

[0022] Figure 1 (FIG 1) illustrates a first embodiment of a magneto-optical current sensor 1 for detecting the current intensity in a conductor 2. The current converter 1 includes an optically coupled input unit 3, a photoconductor 5 according to the first embodiment, and an optically coupled output unit 7.

[0023] The optical coupling input unit 3 has an input collimator 9 and a linear input polarizer 11. The input collimator 9 is configured to beam light from a light source (not shown), such as a light-emitting diode. The input polarizer 11 polarizes the light so that linearly polarized light is delivered to the optical guide 5.

[0024] The light guide 5 is configured to transmit light from the optically coupled input unit 3 to the optically coupled output unit 7. The light guide 5 exhibits the Faraday effect. When current flows in the conductor 2, the polarization direction of the light rotates as it passes through the light guide 5 due to the Faraday effect.

[0025] The optical coupling output unit 7 has an output polarizer 13 and a linear output collimator 15. A portion of the light output from the light guide 5, parallel to the polarization axis of the output polarizer 13, is emitted from the output polarizer 13. The output collimator 15 beams the light transmitted from the output polarizer 13 and guides it to a photodetector (not shown). The photodetector is configured to detect the light intensity delivered to it. For example, the photodetector is configured as a photodiode. The current intensity passing through the conductor 2 is determined based on the light intensity detected by the photodetector.

[0026] In this embodiment, the optical guide 5 is configured as a glass ring, which extends circumferentially around the conductor 2. The conductor 2 and... Figure 1The drawing plane extends orthogonally. The light guide 5 is formed by four light guide segments 17 to 20, each configured as a prism made of glass. The first light guide segment 17 extends from the optical coupling input unit 3 to the second light guide segment 18. The second light guide segment 18 extends between the first light guide segment 17 and the third light guide segment 19. The third light guide segment 19 extends between the second light guide segment 18 and the fourth light guide segment 20. The fourth light guide segment 20 extends from the third light guide segment 19 to the optical coupling output unit 7. The longitudinal axis of the first light guide segment 17 is orthogonal to the longitudinal axes of the second light guide segment 18 and the fourth light guide segment 20 and parallel to the longitudinal axis of the third light guide segment 19.

[0027] The first optical guide section 17 is oriented towards the optical coupling input unit 3 and... Figure 1 The end face 21, orthogonal to the drawing plane, has a first anti-reflective coating 31. The end face 22 of the first light-guiding section 17, opposite to this end face 21, is relative to... Figure 1 The drawing plane is tilted at 45 degrees (see also...) Figure 2 At end face 22, light passing through the first light guide section 17 along its longitudinal axis undergoes total internal reflection towards the second light guide section 18. In the second light guide section 18, light strikes its end face 23 (see end face 23). Figure 2 On the end face, relative to Figure 1 The drawing plane is also tilted at 45 degrees, and total internal reflection redirects the light to be parallel to the longitudinal axis of the second light guide section 18. Therefore, light is guided from the second light guide section 18 to the third light guide section 19 and from the third light guide section 19 to the fourth light guide section 20. The fourth light guide section 20 is oriented towards the optical coupling output unit 7. Figure 1 The end face 24, which is orthogonal to the drawing plane, has a second anti-reflective coating 32.

[0028] Compared to an embodiment of the light guide 5 without the first anti-reflective coating 31, the first anti-reflective coating 31 increases the light intensity coupled into the light guide 5 by approximately 10% to 20%. Compared to an embodiment of the light guide 5 without the second anti-reflective coating 32, the second anti-reflective coating 32 increases the light intensity coupled out of the light guide by approximately 10% to 20%. Furthermore, the second anti-reflective coating 32 reduces light reflection at the end face 24, which reflects the light back into the light guide 5.

[0029] Figure 2 (FIG 2) shows the relationship between the following areas and Figure 1Similarly configured light guide 5, in which a first light guide segment 17 and a second light guide segment 18 are adjacent in the region. In this example, the first light guide segment 17 and the second light guide segment 18 are made of different glasses with different refractive indices. The first light guide segment 17 and the second light guide segment 18 are bonded together by an adhesive layer 33 having a refractive index between the refractive indices of the two light guide segments 17 and 18. This advantageously reduces the reflection of light as it transfers from the first light guide segment 17 to the second light guide segment 18 compared to embodiments of light guide 5 without the adhesive layer 33.

[0030] Figure 3 (FIG 3) illustrates a second embodiment of a magneto-optical current sensor 1 for detecting the current intensity in a conductor 2. This embodiment has a light guide 5 configured as an optical fiber waveguide and extending annularly around the conductor 2 in multiple loops. The ends of the light guide 5 have clamps 41 and 42, respectively. Each clamp 41 and 42 has end faces 21 and 24, which have anti-reflective coatings 31 and 32.

[0031] Figure 4 FIG 4 shows a portion of a light guide 5 for a magneto-optical current sensor 1, the light guide having light guide segments 43 and 44 with different refractive indices. For example, light guide segments 43 and 44 may be made of different types of glass or formed from different optical fiber waveguides. An anti-reflection layer 45 is provided between two adjacent light guide segments 43 and 44, which reduces light reflection as light passes between the light guide segments 43 and 44 compared to an embodiment of the light guide 5 without an anti-reflection layer 45.

[0032] Although the present invention has been described and illustrated in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the invention.

Claims

1. A magneto-optical current sensor (1) for detecting the current intensity in a conductor (2), the magneto-optical current sensor (1) comprising: At least one light guide (5) disposed in a region of the conductor (2), the light guide (5) comprising: - First end face (21), through which light can be coupled into the light guide (5); and - Second end face (24), through which light can be coupled out from the light guide (5), The optical guide is at least partially configured as an optical fiber waveguide. At least one of the first end face (21) and the second end face (24) has an anti-reflection coating (31, 32), and the at least one end face is the end face of the clamp (41, 42) of the optical fiber waveguide.

2. The magneto-optical current sensor (1) according to claim 1, wherein the light guide (5) further comprises at least one anti-reflection layer (45) disposed between two light guide segments having different refractive indices.

3. The magneto-optical current sensor (1) according to claim 1 or 2, wherein the light guide (5) is at least partially made of glass.

4. The magneto-optical current sensor (1) according to claim 3, wherein at least one anti-reflective layer (45) is disposed between two light-conducting segments, the light-conducting segments being made of different glasses having different refractive indices.

5. The magneto-optical current sensor (1) according to claim 3, wherein the light guide (5) has at least one adhesive layer (33) through which two light guide segments made of different glass having different refractive indices are bonded together, wherein the adhesive layer (33) has a refractive index between the refractive indices of the two light guide segments.

6. The magneto-optical current sensor (1) according to claim 1, wherein at least one anti-reflection layer (45) is disposed between two optical guide segments (43, 44), the optical guide segments being configured as different optical fiber waveguides.

7. The magneto-optical current sensor (1) according to claim 1, wherein at least one of the light guides (5) extends circumferentially around the conductor (2).

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