Fiber-coupled quantum sensor

Abstract

The invention relates to a fiber-coupled quantum sensor based on the color center principle, comprising: a sensor layer (1) in which color centers are formed, a first optical waveguide having a first numerical aperture for guiding an excitation light to the sensor layer (1), and at least one second optical waveguide having a second numerical aperture for guiding back a fluorescent light generated by the color centers, wherein the second numerical aperture is greater, in particular greater by at least a factor of 2, than the first numerical aperture.

Description

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[0003] Godfather Lawyers

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[0006] Fiber-coupled quantum sensor

[0007] DESCRIPTION

[0008] 5

[0009] The invention relates to a fiber-coupled quantum sensor based on the color center principle.

[0010] Quantum sensors based on the color center principle are primarily used as magnetic field sensors, especially in applications with high demands on magnetic field sensitivity, such as in biomedicine, materials science, and quantum computing. However, such sensors can also be used to determine other physical quantities, such as temperature and electric field.

[0011] The functional sensor layer of such quantum sensors contains so-called color centers. A typical example of these are nitrogen-vacancy centers (NV) in diamond. However, other color centers are also possible, e.g., silicon-vacancy centers (SiV), germanium-vacancy centers (GeV), nickel-vacancy centers (NiV), chromium-vacancy centers (CrV), silver-vacancy centers (AgV), tin-vacancy centers, or C60 color centers (fullerenes). The respective color centers are irradiated with excitation light of a defined wavelength and emit fluorescence, which depends, for example, on the present magnetic field. This fluorescence is detected and evaluated using various measurement techniques to obtain information about the quantity to be detected.

[0012] In fiber-coupled quantum sensors, the excitation light is guided to the sensor layer using an optical fiber. The fluorescence light can then also be transmitted through this optical fiber.

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[0016] -2- are reflected back and - typically after passing through a dichroic filter to separate the excitation light - are directed to a detector.

[0017] 5 To obtain the most powerful and sensitive fiber-coupled quantum sensor possible, it is necessary to excite the color centers as efficiently as possible and at the same time to collect the fluorescence light generated by the color centers as completely as possible. 0 The invention is based on the objective of providing a particularly sensitive fiber-coupled quantum sensor.

[0018] This problem is solved by a fiber-coupled quantum sensor with the features of claim 1. Advantageous embodiments are described in the dependent claims.

[0019] The fiber-coupled quantum sensor according to the invention, which is based on the color center principle, comprises: a sensor layer in which color centers are formed, a first optical waveguide with a first numerical aperture (NA) for guiding excitation light to the sensor layer, and at least one second optical waveguide with a second numerical aperture for guiding back fluorescence light generated by the color centers. The second numerical aperture is larger than the first numerical aperture.

[0020] In this way, the excitation light guided through the first optical waveguide with low NA creates a relatively small, concentrated excitation volume within the sensor layer. The fluorescence light returned through the second optical waveguide is collected at a relatively high percentage due to its large NA. Overall, this increases the sensitivity of the LÖSCH sensor.

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[0025] Quantum sensor compared to a quantum sensor in which the excitation light and the fluorescence light are guided through the same optical waveguide or through optical waveguides with the same NA.

[0026] 5 Preferably, the second numerical aperture is larger than the first numerical aperture by at least a factor of 2, in particular by a factor of 2 to 10, and most preferably by a factor of 2 to 5. This ensures that the sensitivity of the quantum sensor is significantly increased compared to a quantum sensor in which the excitation light and the fluorescence light are guided through the same optical waveguide or through optical waveguides with the same numerical aperture. Values ​​of 0.1 to 0.2 for the first numerical aperture and values ​​of 0.3 to 0.5 for the second numerical aperture have proven to be particularly advantageous. 5 The first optical waveguide and the second optical waveguide can be arranged coaxially with each other. In particular, the optical waveguides can be arranged coaxially with each other and surrounded by a common cladding. This simplifies the instrumental design of the quantum sensor and reduces its space requirements.

[0027] In an advantageous embodiment, the power cross-sectional area of ​​the second optical waveguide—or the total power cross-sectional area of ​​the second optical waveguides if more than one second optical waveguide is present—is larger than the power cross-sectional area of ​​the first optical waveguide. The relatively small cross-section of the first optical waveguide, in turn, creates a relatively small, concentrated excitation volume within the sensor layer. The relatively large cross-section of the second optical waveguide(s) further increases the percentage of fluorescent light that is collected. This significantly increases the sensitivity of the quantum sensor.

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[0031] -4- Preferably, the cross-sectional area of ​​the second optical waveguide is larger by a factor of 5, in particular by a factor of 5 to 500,000, most preferably by a factor of 5 to 10,000, than the

[0032] 5 Cross-sectional area of ​​the first optical waveguide.

[0033] In a preferred embodiment, the first optical waveguide is configured as the core of a double-clad fiber (DCF), and the second optical waveguide is configured as the cladding of the double-clad fiber. The core can, in particular, have a nominal area (NA) of 0.1 and a diameter of 25 micrometers, and the cladding can have an NA of 0.4 and a diameter of 500 micrometers.

[0034] In another preferred embodiment, the first optical waveguide is configured as a single fiber of an optical waveguide bundle, and the remaining fibers of the optical waveguide bundle are configured as second optical waveguides. In this way, too, the first optical waveguide has a relatively small cross-sectional area, while the second optical waveguides have a large total cross-sectional area. The sensitivity of the quantum sensor is correspondingly high.

[0035] Optical lenses can be arranged between the optical waveguides and the sensor layer to influence the propagation direction of the excitation light and / or the fluorescence light.

[0036] In a preferred embodiment, a GRIN (gradient index) lens is arranged between the first optical waveguide and the sensor layer and / or between the second optical waveguide and the sensor layer. This GRIN lens can be bonded to the axial end of the first and / or second optical waveguide. DELETE

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[0041] The GRIN lens is designed to collimate, or focus, the excitation light onto the sensor layer. Specifically, the GRIN lens can have a pitch of 0.2 to 0.3. With such a GRIN lens, the light emanating from the fiber is collimated so that all light rays travel straight in one direction and no longer radiate outwards in all directions. This collimated light creates a relatively small excitation volume within the sensor layer, where the intensity of the excitation light is uniform throughout. Alternatively, a GRIN lens with a pitch of approximately 0.5 can be used. Such a GRIN lens focuses the excitation light. This allows for an even smaller excitation volume, resulting in a very high intensity of the excitation light within that volume.

[0042] In a further preferred embodiment, two GRIN lenses and a microlens are arranged between the first optical waveguide and the sensor layer and / or between the second optical waveguide and the sensor layer, starting from the first or second optical waveguide respectively and extending towards the sensor layer. The GRIN lenses are specifically designed to collimate the excitation light, and the microlens is designed to focus the excitation light onto the sensor layer.

[0043] The first of the two GRIN lenses (directly on the optical fiber) has a pitch of 0.2 to 0.3. It collimates the light exiting the optical fiber. Conversely, this lens focuses the fluorescent light into the optical fiber. The microlens has the highest possible numerical aperture (NA), ideally 0.7 or higher. This enables high light collection efficiency. DELETE

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[0048] The invention is further explained with reference to exemplary embodiments in the drawings, where identical reference numerals denote identical or equivalently acting components. The drawings show:

[0049] 5 Fig. 1 a schematic sectional view of a sensor layer, a first optical waveguide and a second optical waveguide of a fiber-coupled quantum sensor;

[0050] Fig. 2 a sectional view along the section plane II - II in Fig. 1 ;

[0051] Fig. 3 shows a cross-sectional view of an optical waveguide bundle;

[0052] Fig. 4 shows an optical system consisting of optical waveguides and a GRIN lens for a fiber-coupled quantum sensor; and

[0053] Fig. 5 shows another optical system made of optical waveguides, GRIN-

[0054] Lenses and a microlens for a fiber-coupled quantum sensor.

[0055] Fig. 1 shows a schematic and partial view of a fiber-coupled quantum sensor. The quantum sensor of the described embodiment is designed as a magnetic field sensor. Fig. 1 shows in particular a sensor layer 1 and a double-clad fiber 2. The sensor layer 1 consists of a diamond with nitrogen-vacancy (NV) centers. The NV center density is approximately 0.1 ppm to 100 ppm.

[0056] The double-clad fiber 2 is a so-called DCF, i.e., an optical fiber with two separate optical waveguides. As can also be seen in Fig. 2, the double-clad fiber 2 has a core 3, an inner cladding 4 surrounding the core 3, an outer cladding 5 surrounding the inner cladding 4, and a quenching layer surrounding the outer cladding.

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[0061] Shell 6. Through appropriate doping or material selection, the core 3, the inner shell 4, and the outer shell 5 possess refractive indices that differ from one another. In this way, initial light waves can be guided through the core 3 and from there

[0062] 5 independent second light waves through the inner sheath 4. The core 3 - also called core conductor of the double sheath fiber 2 - represents a first optical waveguide in the sense of the present invention and the inner sheath 4 - also called sheath conductor of the double sheath fiber 2 - represents a second optical waveguide in the sense of the present invention.

[0063] The excitation light (shown as a dotted line in Fig. 1), typically generated by a laser diode, is guided through the core conductor to the sensor layer 1. The fluorescence light generated by the NV centers of the sensor layer 1 (shown as a dashed line in Fig. 1) enters the sheath conductor and is guided through it to a detector (not shown in the figures).

[0064] The core, for example, has a diameter of approximately 25 micrometers and a numerical aperture (NA) of 0.1. The sheath has a diameter of approximately 500 micrometers and an NA of 0.4. Therefore, the numerical aperture and the cross-sectional area of ​​the second optical waveguide are larger than those of the first. The first and second optical waveguides are arranged coaxially and surrounded by a common sheath 6.

[0065] Fig. 3 shows a further embodiment for a first optical waveguide and a second optical waveguide according to the present invention. Fig. 3 shows an optical waveguide bundle 7, which – purely by way of example – consists of seven individual fibers 8, 9, 10, 11, 12, 13, 14 and a sheath 15. The central individual fiber 8, which has a longer diameter compared to the remaining fibers 9, is connected to the central single fiber 9.

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[0069] Since fibers 8 to 14 have a lower NA, the excitation light is coupled in. The single fiber 8 thus represents a first optical waveguide in the sense of the present invention. The remaining fibers 9 to 14 are each a second optical waveguide in the sense of the present invention.

[0070] Five individual fibers 8 to 14 each possess a core 16 (shown in Fig. 3 only in relation to individual fiber 8) and a cladding 17 (shown in Fig. 3 only in relation to individual fiber 8) and therefore represent conventional optical fibers. In particular, they do not need to be double-clad fibers. The fiber cross-section (outer diameter of the cladding) of the individual fibers 8 to 14 is generally the same and can be in the range of approximately 100 to 200 micrometers. Since only the central individual fiber 8 serves as the first optical waveguide and the remaining fibers 9 to 14 function as the second optical waveguide, the total cross-sectional area of ​​the second optical waveguide is larger than the cross-sectional area of ​​the first optical waveguide.

[0071] Fig. 4 shows a first optical system 18 for a fiber-coupled quantum sensor. An optical waveguide structure 19 consists of the first and second optical waveguides described above, arranged coaxially to each other, in accordance with the present invention. In particular, the optical waveguide structure 19 can be configured as a double-clad fiber 2 or as an optical waveguide bundle 7. A GRIN lens is arranged between an axial end of the optical waveguide structure 19 and the sensor layer 1; more precisely, the GRIN lens is bonded to the axial end of the optical waveguide structure 19 by means of a UV-curing, optically transparent adhesive. The GRIN lens has a pitch of approximately 0.2 to 0.3 or 0.5. In this way, the excitation light is collimated or focused. Fig. 5 shows a further optical system 21 for a fiber-coupled quantum sensor. Between the axial end of the optical waveguide structure 19

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[0075] -9- and sensor layer 1 are arranged with two GRIN lenses 20 and one microlens 22. These components are bonded to each other using a UV-curing, optically transparent adhesive. The GRIN lenses have a pitch of approximately 0.2 to 0.3. The optical microlens 22 has

[0076] 5 a “pitch” of approximately 0.7.

[0077] Both optical systems 18 and 21 enable a particularly well-defined and locally confined excitation volume and ensure that a high percentage of the fluorescence light is collected. This improves the 0 sensitivity of the quantum sensor.

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[0083] REFERENCE MARK LIST

[0084] 1 sensor layer

[0085] 2 Double-layer fiber

[0086] 3 core

[0087] 4 Inner coat

[0088] 5 Outer coat

[0089] 6. Sheathing

[0090] 7 optical fiber bundles

[0091] 8 (central) single fibers

[0092] 9 - 14 single fibers

[0093] 15 Sheathing

[0094] 16 core

[0095] 17 coat

[0096] 18 Optical System

[0097] 19 Optical fiber structure

[0098] 20 GRIN lenses

[0099] 21 Optical System

[0100] 22 microlens

Claims

DELETE FAU Godfather Lawyers 251027-WO -11- PATENT CLAIMS 1. Fiber-coupled quantum sensor based on the color center principle 5 is based on: a sensor layer (1) in which color centers are formed, a first optical waveguide with a first numerical aperture for guiding excitation light to the sensor layer (1), and at least a second optical waveguide with a second numerical aperture for guiding back fluorescence light generated by the color centers, wherein the second numerical aperture is larger, in particular by at least a factor of 2, than the first numerical aperture.

2. Quantum sensor according to claim 1, wherein the first numerical aperture is 0.1 to 0.2 and / or the second numerical aperture is 0.3 to 0.

5.

3. Quantum sensor according to one of the preceding claims, wherein the first optical waveguide and the second optical waveguide are arranged coaxially to each other.

4. Quantum sensor according to any one of the preceding claims, wherein the cross-sectional area of ​​the second optical waveguide, or the total cross-sectional area of ​​the second optical waveguide, is larger, in particular by at least a factor of 5, than the cross-sectional area of ​​the first optical waveguide.

5. Quantum sensor according to any one of the preceding claims, wherein the first optical waveguide is the core conductor of a double-clad fiber (2) and DELETE FAU Godfather Lawyers 251027-WO -12- the second optical waveguide is designed as the sheath of the double sheath fiber (2).

6. Quantum sensor according to one of claims 1 to 4, wherein the first 5. One optical waveguide is configured as a single fiber (8) of an optical waveguide bundle (7), and the remaining fibers (9-14) of the optical waveguide bundle (7) are configured as a second optical waveguide.

7. Quantum sensor according to one of the preceding claims, wherein a GRIN (gradient index) lens (20) is arranged between the first optical waveguide and the sensor layer (1) and / or between the second optical waveguide and the sensor layer (1).

8. Quantum sensor according to claim 7, wherein the GRIN lens (20) is configured to collimate the excitation light or to focus it onto the sensor layer (1).

9. Quantum sensor according to one of the preceding claims, wherein two GRIN lenses (20) and a microlens (22) are arranged between the first optical waveguide and the sensor layer (1) and / or between the second optical waveguide and the sensor layer (1), starting from the first or second optical waveguide in the direction of the sensor layer (1).

10. Quantum sensor according to claim 9, wherein the GRIN lenses (20) are configured to collimate the excitation light, and the microlens (22) is configured to focus the excitation light onto the sensor layer (1). DELETE FAU Godfather Lawyers 251027-WO -13- 11. Quantum sensor according to one of claims 7 to 10, wherein the GRIN lens (20) is bonded to an axial end of the first and / or second optical waveguide. 5 12. Quantum sensor according to one of the preceding claims, wherein the Sensor layer (1) consisting of a diamond with NV (nitrogen vacancy) centers, preferably with an NV center density of 0.1 ppm to 100 ppm. 0 13. Quantum sensor according to one of the preceding claims, which as It is designed as a magnetic field sensor.

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