Spectrometer

Abstract

The present invention relates to a spectrometer comprising a housing (11) in which a planar optical grating (2) is arranged opposite an aperture (1) of the housing (11) and oriented at an angle of less than 45° to the normal to the aperture (1), an objective lens system (6), and a sensor element (7). The aperture (1) is dimensioned such that the surface of the optical grating (2) is fully illuminated when electromagnetic radiation is incident parallel to the normal to the aperture (1). To focus the electromagnetic radiation on the sensor element (7), the objective lens system (6) is arranged between the optical grating (2) and the sensor element (7) such that only the first or higher diffraction orders of the electromagnetic radiation diffracted by the optical grating (2) are directed towards the objective lens system (6) and the sensor element (7). [Selected Figure] Figure 1

Description

[Technical field]

[0001] The present invention relates to a spectrometer. [Background technology]

[0002] Various spectrometers are known from the prior art, in which miniaturization of the overall setup is achieved. For example, US Pat. No. 5,399,433 discloses a miniature spectrometer with only a few optical elements. However, this setup requires expensive curved optical gratings, small apertures, and electro-optical modulators. When using a large number of optical elements upstream of the optical grating, such as mirrors and lenses, scattered light becomes a major problem. Therefore, in US Pat. No. 5,399,433 a second aperture downstream of the entrance aperture is used to define the range of the incident beam. However, this likewise limits the sensitivity of the spectrometer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 6,870,619 [Patent Document 2] US Patent Application Publication No. 2012 / 0188542 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is therefore based on the object of proposing a spectrometer which avoids the aforementioned drawbacks, ie which makes it possible to achieve a miniaturized structure with high sensitivity with as few optical elements as possible. [Means for solving the problem]

[0005] The spectrometer comprises a planar optical grating arranged opposite an aperture of the housing, an objective arrangement and a housing in which a sensor element is arranged. The optical grating is arranged at an angle of less than 45° to the normal of the aperture. The aperture is dimensioned such that the surface of the optical grating is fully illuminated for electromagnetic radiation incident parallel to the normal of the aperture. To focus the incident electromagnetic radiation on the sensor element, the objective arrangement is arranged between the optical grating and the sensor element such that only first or higher diffraction orders of the electromagnetic radiation diffracted by the optical grating are directed towards the objective arrangement and the sensor element.

[0006] The use of a plane, i.e. planar, optical grating allows the structural components to be designed and installed easily. A relatively large aperture, the dimensions of which are precisely selected so that no point source is obtained, ensures that a lot of electromagnetic radiation is incident on the optical grating, which makes the overall spectrometer very sensitive. This is further supported at an acute angle, which also facilitates a compact construction of the overall spectrometer. Fully irradiating the optical grating here should be understood to mean in particular that the entire surface of the optical grating facing the aperture is illuminated by the incident electromagnetic radiation. In this case, the angle can be understood as being directed from the surface of the planar optical grating to the normal to the aperture and, as a second angle leg, from the normal to the aperture to the surface of the planar optical grating.

[0007] The incident electromagnetic radiation usually passes directly through the aperture to the optical grating. There is no need for additional optical elements such as mirrors or additional apertures, making the whole structure simple and compact, and almost no scattered light occurs.

[0008] The aperture may have a diameter or width of at least between 0.5 mm and 2.5 mm. A diameter or width of 1 mm is preferred. The aperture itself may be formed as a rectangular, in particular square, or circular opening in the housing. This allows a relatively large aperture to capture as much electromagnetic radiation as possible.

[0009] The angle at which the optical grating is aligned with respect to the normal may be between 5° and 15°, preferably between 7° and 10°, particularly preferably 7.5°, to allow a flat structure and reduce the space required.

[0010] The distance between the aperture and the optical grating is typically 1 mm to 40 mm, preferably 10 mm to 30 mm, particularly preferably 20 mm, so that the spectrometer has a correspondingly compact size.

[0011] In order to achieve a sufficiently high intensity in the sensor element, the optical grating may be provided with a coating which reflects at least 90%, preferably at least 95%, particularly preferably at least 99% of the incident electromagnetic radiation. The coating preferably contains or is made of aluminum.

[0012] The objective lens system may comprise at least two focusing lenses to ensure reliable focusing.

[0013] The focal length of the objective lens system is usually 1 mm to 4 mm, preferably 2 mm.

[0014] The sensor element may be a photodiode line array or a CCD line array (charge-coupled device) or an image sensor, for example a CMOS sensor (complementary metal oxide semiconductor) or a CCD sensor.

[0015] The sensor element is typically sensitive to electromagnetic radiation in the visible wavelength range of 380 nm to 780 nm. Alternatively or additionally, the sensor element may also be sensitive to electromagnetic radiation in the infrared wavelength range, in particular with wavelengths of 780 nm to 1700 nm, or in the ultraviolet wavelength range, in particular with wavelengths of 200 nm to 380 nm. However, at least one of the grating period and the tilt angle of the optical grating is typically adjusted depending on the wavelength to be detected.

[0016] Preferably, the mobile phone is equipped with the spectrometer described above, which may be either integrated into the housing of the mobile phone or attached to the mobile phone. Effect of the Invention

[0017] According to the invention, this object is achieved by a spectrometer as claimed in claim 1. Advantageous refinements and developments are set forth in the dependent claims. [Brief description of the drawings]

[0018] An exemplary embodiment of a spectrometer is shown in the drawings and will be described below with reference to FIGS. [Figure 1] 1 shows a schematic side view of a spectrometer. [Diagram 2] FIG. 1 is a side view of a mobile phone equipped with a spectrometer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A schematic side view of a spectrometer is shown in figure 1. A beam 5 of electromagnetic radiation in the visible wavelength range enters through an aperture 1 into the housing 11 of the spectrometer, the interior space 3 of this housing 11 being made of plastic or metal.

[0020] The aperture 1 in the illustrated exemplary embodiment is circular and has a diameter of 1 mm, so that no point source is generated by the aperture 1 at the entrance of the spectrometer. The size of the aperture 1 makes the spectrometer very sensitive since there is a quadratic relationship between the size of the area of ​​the aperture 1 and the incoming radiation or light intensity.

[0021] Electromagnetic radiation is incident through an aperture 1 on an optical grating 2 with a grating constant between 200 nm and 1200 nm, preferably between 400 nm and 700 nm, which is mounted in a housing 11 with a holder. Since no other optical elements are arranged in the beam path of the electromagnetic radiation, the formation of scattered light is minimized and no further aperture is required. In the illustrated embodiment, the optical grating 2 is inclined at a shallow angle 4 of 7.5° with respect to the propagation direction of the electromagnetic radiation, which is directed parallel to the normal of the aperture 1. The distance between the aperture 1 and the optical grating 2 is 20 mm.

[0022] For electromagnetic radiation incident parallel to the normal to the aperture 1, the aperture 1 is dimensioned such that the surface of the optical grating 2 facing the aperture 1 is fully illuminated. Thus, the optical grating 2 may have at least the size of the diameter of the incident beam 5 passing through the aperture 1, but the area of ​​the optical grating 2 may be smaller than the radiation beam 5.

[0023] The optical grating 2, as a reflective diffraction grating, is equipped with a highly reflective aluminum coating that reflects at least 90% of the incident intensity. The tilt angle 4 of the optical grating 2 is determined by the Bragg condition and depends on the grating period of the optical grating 2 and the wavelength range of the incident electromagnetic radiation. This incident electromagnetic radiation is reflected at a different angular range from the optical grating 2, so that the first diffraction order 9 is incident on the objective lens system 6, which consists of two plano-convex lenses.

[0024] This objective lens system 6 is arranged at an angle of 90° to the propagation direction of the electromagnetic radiation. The zeroth diffraction order 8 is not irradiated onto the objective lens system 6 but onto the inner wall of the housing 11 of the inner space 3. The focal point 10 of the objective lens system 6 is on one side of the objective lens system 6 on the surface of the optical grating 2 and on the opposite side of the image sensor 7. The objective lens system 6 is provided with a second aperture 12 to prevent scattered light from reaching the image sensor 7. The second aperture has a diameter or width between 1 mm and 10 mm. The focal length of the objective lens system 6 is 2 mm in the illustrated embodiment. This can lead to image distortions, which can be corrected by an evaluation unit to which the image sensor 7 is electrically connected. However, the focal length must be selected such that the zeroth diffraction order 8 does not fall on the objective lens system 6.

[0025] The objective lens system 6 is adjusted to the size of the image sensor 7 so that the entire spectrum to be analysed can be imaged over the entire range of the image sensor 7. The smaller the image sensor 7, the larger the so-called crop factor or format factor, which indicates the aspect ratio between the diagonals of the two recording formats, and the smaller the objective lens system 6 can be. The pixel size of the image sensor 7 is typically 1.5 μm (but in other embodiments it may be up to 6 μm), but if a photodiode line array is used instead of the image sensor 7, the pixel size may be 5.5 μm. In order to fulfill the Nyquist criterion, a correspondingly large number of pixels must be present.

[0026] The configuration described above and shown in FIG. 1 allows a spectral resolution of 1 nm despite an aperture diameter of 1 mm.

[0027] FIG. 2 shows a schematic side view of a mobile phone 13, more specifically a smartphone, with the above-mentioned spectrometer. Features repeated in this figure are given the same reference numbers as in the previous figures. The objective lens system 6 and the image sensor 7 can here be implemented by a camera already installed in the mobile phone 13. The evaluation unit is typically arranged in the mobile phone 13, whose display serves as an output unit of the spectrometer, on which the data determined by the evaluation unit are reproduced. In the exemplary embodiment shown in FIG. 2, the spectrometer with the housing 12 is arranged on the mobile phone 13, but the spectrometer may also be integrated in the mobile phone 13, such that the housing of the mobile phone 13 also surrounds the spectrometer.

Claims

1. a planar optical grating (2) disposed opposite an aperture (1) formed in a side wall of the housing (11), the plane of the optical grating (2) being oriented at an angle of less than 45° with respect to a normal to the aperture (1); a second aperture (12) arranged below the optical grating (2) and parallel to the normal of the aperture (1); an objective lens system (6) arranged below the second aperture (12) and parallel to a normal to the aperture (1), the objective lens system (6) having at least two focusing lenses; A spectrometer having a housing (11) in which a sensor element (7) is arranged on a bottom surface of the housing (11) below the objective lens system (6), the aperture (1) and the optical grating (2) are dimensioned such that the entire surface of the optical grating (2) is illuminated by the electromagnetic radiation incident from the aperture (1) such that the cross-sectional shape of the electromagnetic radiation passing through the aperture (1), which is a light beam parallel to a normal to the aperture (1), is large enough to cover the surface shape of the optical grating; the objective lens system (6) is disposed between the optical grating (2) and the sensor element (7) for focusing the diffracted electromagnetic radiation onto the sensor element (7) such that only one or more diffraction orders of the electromagnetic radiation diffracted by the optical grating (2) are directed towards the objective lens system (6) and the sensor element (7) via the second aperture (12); a focal point (10) of the objective lens system (6) is on one side of the objective lens system (6) on the surface of the optical grating (2) and opposite the sensor element (7); Spectrometer.

2. 2. The spectrometer of claim 1, wherein the electromagnetic radiation incident through the aperture (1) passes directly to the optical grating (2).

3. 3. A spectrometer according to claim 1 or 2, characterised in that the aperture (1) has a diameter or width of at least between 0.5 mm and 2.5 mm, preferably 1 mm.

4. 4. The spectrometer according to claim 1, wherein the angle at which the optical grating (2) is aligned relative to the normal is between 5° and 15°, preferably between 7° and 10°, particularly preferably 7.5°.

5. 5. The spectrometer according to claim 1, wherein the distance between the aperture (1) and the optical grating (2) is maintained at 1 mm to 40 mm, preferably at 10 mm to 30 mm, particularly preferably at 20 mm.

6. 6. Spectrometer according to any one of the preceding claims, characterized in that the optical grating (2) is provided with a coating which reflects at least 90% of the electromagnetic radiation incident thereon.

7. Spectrometer according to any one of the preceding claims, characterized in that the objective lens system (6) has a focal length of 1 to 4 mm, preferably 2 mm.

8. Spectrometer according to any one of the preceding claims, characterized in that the sensor element (7) is a photodiode line array or an image sensor.

9. A mobile phone (13) comprising a spectrometer according to any one of claims 1 to 8.

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