SPECTROMETER DEVICE AND METHOD FOR MANUFACTURING A SPECTROMETER DEVICE

Description

[0001] The present invention relates to a spectrometer device and a method for manufacturing a spectrometer device. In particular, the present invention relates to a spectrometer device configured as a Fabry-Pérot interferometer. State of the art

[0002] Optical spectrometers are used to analyze light beams by examining their spectrum. DE 196 81 285 T1 discloses an accessory for infrared microspectrometers. In particular, it discloses an internal reflection element that reduces the need to control the angle of the incident radiation through the optical design of the objective lens. DE 10 2005 055 860 B3 discloses a gas sensor arrangement with a concave mirror formed by a reflective inner wall of the housing, which ensures increased light sensitivity.

[0003] The spectral components of the light beam can be determined using an interferometer and a detection device. The optical interference filters used here exhibit transmission properties that are dependent on the angle of incidence. In particular, the transmitted central wavelength depends on the angle of incidence of the light beam. The larger the angle of incidence of the light beam relative to the perpendicular, the greater the shift in the transmitted central wavelength. Therefore, to achieve good resolution or full width at half maximum (FWHM) of the light transmitted by the spectral element, it is necessary to limit the angular range detectable by the detector. One possible way to limit the angular range is by means of an aperture, as known from WO 17057372 A1. Alternatively, lenses can be used that focus light beams with the same angle of incidence onto the same position in the focal plane.By appropriately selecting the size of the detector, only light from a desired angle of incidence interval is detected. Such an arrangement is known from US 2016 / 0112776 A1.

[0004] US 2010 / 0302535 discloses a spectrometer device with an optical interference filter and a focusing device having a reflective surface, wherein the focusing device is configured to focus the filtered light beam to a point by reflection off the surface.

[0005] The document Martin Ebenmann et al.: "Construction and Operation of an Infrared Microspectrometer Based on a MEMS FP Filter", tm-Technisches Messen / Platform for Methods, Systems and Applications of Measurement Technology, Vol. 77, No. 6, January 1, 2010, discloses a spectrometer device comprising a light source, a sample chamber, an optical interference filter, a detector assembly, and a focusing device. Light emitted from the light source passes through the sample chamber, strikes the focusing device, passes through the sample chamber again, then passes through the optical interference filter integrated into the detector assembly, and finally strikes the detector assembly. The light is thereby focused by the focusing device onto the detector assembly and thus onto the interference filter integrated therein.

[0006] US Patent 5,225,888 discloses a spectrometer device for detecting traces of plasma components. Light emissions from a processing chamber are collimated by a lens and directed to an interferometer that selectively transmits specific wavelengths of light characteristic of the excitation emissions of particular atoms. The light intensity of selected wavelengths is measured by a photomultiplier tube. The interferometer can be a Fabry-Perot type interferometer. Further prior art is disclosed in WO2018159533. Disclosure of the invention

[0007] The invention provides a spectrometer device with the features of claim 1 and a method for manufacturing this spectrometer device with the features of claim 8. Preferred embodiments are the subject of the respective dependent claims.

[0008] According to a first aspect, the invention relates to a spectrometer device comprising an optical interference filter, a detector assembly, and a focusing device. The optical interference filter comprises two mirrors spaced apart from each other and actuated relative to each other, and is configured to filter specific wavelength ranges of an incident light beam as it passes through the optical interference filter. The detector assembly is configured to detect the filtered light beam and is integrated into the optical interference filter on the light exit side of the optical interference filter, where the light beam emerges after passing through the interference filter. The detector assembly can also be arranged directly on the optical interference filter.Finally, the detector assembly can be arranged indirectly on the interference filter, with, for example, additional layers being formed between the detector assembly and the interference filter. The focusing device has a reflective surface and is configured to focus the filtered light beam onto the detector assembly by reflection off the surface. The spectrometer device further comprises a support structure. The optical interference filter, the detector assembly, and the focusing device are arranged directly or indirectly on the support structure. In particular, the optical interference filter and the focusing device can be arranged directly on the support structure. Furthermore, the electrical connections or wiring of the optical interference filter, the detector assembly, and the focusing device can be arranged on the support structure or at least partially integrated into it.

[0009] According to a second aspect, the invention relates to a method for manufacturing a spectrometer device. An optical interference filter is provided which is configured to filter out certain wavelength ranges of an incident light beam as it passes through the optical interference filter.

[0010] Furthermore, a detector device is provided, which is designed to detect the filtered light beam. Finally, a focusing device is provided, which has a reflective surface. The focusing device, the detector device, and the optical interference filter are arranged relative to each other such that the focusing device focuses the filtered light beam onto the detector device. Advantages of the invention

[0011] The spectrometer device according to the invention is characterized by its very compact design, i.e., its very low height. This is because additional lens elements can be omitted, and the focusing of the filtered light beam is achieved by the reflective surface of the focusing device, which can be designed with a low height or a low height with a large entrance aperture. Furthermore, an optical interference filter with a large entrance aperture and good angle of incidence limitation can be used. Overall, this allows for high light efficiency and a good signal-to-noise ratio of the spectrometer device. Due to the improved angle limitation, i.e., the limitation of the detected angle of incidence range, high resolution can also be achieved.

[0012] Another advantage of using a reflective surface over a lens is the practically negligible chromatic aberration of reflective surfaces, such as metal mirrors. This makes it possible to ensure high-quality restriction of the angle of incidence over a wide wavelength range. Furthermore, the absorption of reflective surfaces is significantly lower than that of lens elements, which can be significant in certain wavelength ranges depending on the lens material. Therefore, using reflective surfaces allows for the detection of as much light as possible.

[0013] Furthermore, the components used in the spectrometer device can be assembled with minimal adjustment effort, thus keeping manufacturing costs low.

[0014] Finally, it is possible to use a small and inexpensive detector system without reducing the light output. Despite the high light efficiency, costs can thus be reduced simultaneously.

[0015] In contrast to the use of lenses, the spectrometer device according to the invention requires fewer interfaces through which the light beam passes before it is detected by the detector. This reduces any potential reflection losses.

[0016] According to a preferred embodiment of the spectrometer device, the detector assembly overlaps at least partially with an axis passing through the center of the optical interference filter. The spectrometer device can, for example, have a circular or square cross-section, and the detector assembly is arranged at a position along the axis through the center of the circular or square cross-section. The detector assembly and the interference filter are symmetrically constructed, so the focusing assembly can also be symmetrically constructed. The focusing assembly can, for example, have the form of a parabolic mirror symmetrically shaped with respect to the axis, which focuses the light rays onto the detector assembly arranged along the axis.

[0017] According to the invention, the detector device is arranged directly on the optical interference filter on the light-exit side, i.e., indirectly on the support device or on the light-exit side of the optical interference filter adjacent to the interference filter on the support device. This prevents shadowing caused by the detector device.

[0018] According to a preferred embodiment of the spectrometer device, the support structure comprises at least one spacer element that connects the focusing device to the optical interference filter and separates the focusing device and the optical interference filter from each other. The at least one spacer element has, at least in some areas, a preferably broadband absorbing coating. This absorbing coating prevents possible cross- or back-emission and thereby improves the signal-to-noise ratio.

[0019] According to a preferred embodiment of the spectrometer device, a surface section of the optical interference filter and / or the support structure adjacent to the detector assembly has at least a portion of a preferably broadband absorbing coating. Alternatively or additionally, a surface section of the detector assembly can have an absorbing coating. In particular, the detector assembly can have a typically centrally located active area configured for detection, as well as an inactive edge region surrounding this area, which can have the absorbing coating completely or at least partially. The absorbing coating also serves to reduce cross- and back-emission. Furthermore, light rays that pass through the interference filter at a larger angle of incidence and are not focused onto the detector assembly by the focusing device are absorbed.h. outside the detection range of the spectrometer device, are absorbed by the absorbing coating. This allows a narrow and well-defined incidence angle range to be detected by the spectrometer device.

[0020] According to a preferred embodiment of the spectrometer device, the detector assembly comprises a ring detector, segmented detector elements, and / or array-arranged detector elements. This makes it possible to detect different angular intervals or different wavelength ranges. Array-arranged detector elements allow valuable additional information about a sample, such as its surface properties, to be obtained.

[0021] According to a preferred embodiment of the spectrometer device, the detector assembly comprises at least two stacked detector elements, each sensitive to different wavelength ranges. These detector elements can be understood to be, in particular, those sensitive to non-overlapping wavelength ranges. However, partial overlap of the wavelength ranges is also possible.

[0022] According to the invention, the optical interference filter is designed as a Fabry-Pérot interference filter.

[0023] According to a preferred embodiment of the spectrometer device, the detector assembly comprises at least one photodiode, in particular an InGaAs photodiode, a Si photodiode, a Ge photodiode, an ExInGaAs photodiode or a quantum dot detector. Short description of the drawings

[0024] They show: Figure 1 is a schematic cross-sectional view of a spectrometer device according to a first embodiment of the invention; Figure 2 is a schematic cross-sectional view of a spectrometer device according to a second embodiment of the invention; Figure 3 is a schematic cross-sectional view of a spectrometer device according to a third embodiment of the invention; Figure 4 is a schematic cross-sectional view of a spectrometer device according to a fourth embodiment of the invention; and Figure 5 is a flowchart illustrating a method for manufacturing a spectrometer device according to an embodiment of the invention.

[0025] In all figures, identical or functionally equivalent elements and devices are designated with the same reference numerals. The numbering of process steps serves for clarity and generally does not imply a specific chronological order. In particular, several process steps can be performed simultaneously. Description of the embodiments

[0026] Figure 1 Figure 1 shows a schematic cross-sectional view of a spectrometer device 1a, which has a support device 6a, which in turn comprises a substrate 61 in which an optical interference filter 2 or spectral element is integrated. The support device 6a further comprises holding elements 62, which hold a focusing device 4a.

[0027] The optical interference filter 2 is a Fabry-Pérot interference filter, preferably manufactured micromechanically. The optical interference filter comprises two mirrors spaced relative to each other and actuated relative to each other. Depending on the angle of incidence of the light rays L on the optical interference filter 2, light rays L with slightly different central wavelengths are transmitted. The central wavelength also depends on the distance between the two mirrors. Preferably, the optical interference filter 2 has a single-sided or, more preferably, a double-sided encapsulation. However, according to further embodiments, optical interference filters 2 of other designs and modes of operation are also possible.

[0028] A detector device 3 is arranged in a central position on one light-exit side of the optical interference filter 2. The detector device 3 is directly connected to the optical interference filter 2, for example by an adhesive bond or a bonded connection. The detector device 3 can, for instance, be mounted on a cap of the optical interference filter 2. The detector device 3 can have at least one photodiode as a detector element, which generates a photocurrent depending on the intensity of the incident light rays L. This photocurrent can be measured and further evaluated. The spectrometer device 1a can output a measurement signal depending on the photocurrent. According to further embodiments, the detector device 3 can have a plurality of detector elements, which are preferably sensitive at different wavelengths.Furthermore, a ring detector can be provided, which is arranged symmetrically around the center of the input aperture of the optical interference filter 2, i.e., around an axis through the center of the optical interference filter 2. The detector arrangement 3 can also include at least one segmented detector element. By using ring detectors or segmented detector elements, multiple angular intervals and / or different wavelength ranges can be detected. To detect different wavelength ranges, the detector arrangement 3 can also include stacked detectors, i.e., dual detectors. The material of the detector elements of the detector arrangement 3 can include, for example, silicon (Si), indium gallium arsenide (InGaAs), germanium (Ge), or lead selenide (PbSe). Quantum dot-based detector materials or dual detectors with InGaAs+Si material combinations are also possible.In addition to individual detectors, the detector assembly 3 can also include array detectors. Furthermore, the detector assembly 3 can include additional imaging optics.

[0029] The focusing device 4a is designed as a parabolic mirror with a focal length f. The detector device is arranged in the center of the entrance aperture of the optical interference filter 2, i.e., at the focal point of the symmetrically designed focusing device 4a. The focusing device 4a focuses light rays L, which pass through the optical interference filter 2 and whose angle of incidence does not exceed a predetermined threshold, onto the detector device 3. Light rays L with a higher angle of incidence are deflected into an area adjacent to the detector device 3. Preferably, a coating of an absorbing material, which absorbs the light rays L, is applied in this area adjacent to the detector device 3 on the back or light-exit side of the optical interference filter 2. The focusing device 4a can have a coating of a reflective material, in particular silver, gold, or aluminum.Additionally, at least one protective layer may be provided. In particular, the focusing device 4a may be designed as a coated or vapor-deposited injection-molded part. According to further embodiments, the focusing device 4a may comprise turned or milled parts, especially made of aluminum. The focusing device 4a may, instead of or in addition to reflective focusing mirrors, also include other reflective optical components such as reflective metasurfaces.

[0030] Depending on the usable aperture a of the optical interference filter 2 or the usable diameter of the focusing device 4a, the focal length of the focusing device f and the size of the sensitive area of ​​the detector device 3, the detectable angle of incidence interval is restricted and thus the resolution of the spectrometer device 1a is set or optimized.

[0031] Figure 2Figure 1b shows a spectrometer device, which is a modification of the spectrometer device 1a described above and differs in the design of the support structure 6b. Accordingly, the support structure 6b comprises spacer elements 7 that connect the focusing element 4a to the optical interference filter 2 and space these elements apart from each other. The support structure 6b can, in particular, be cylindrical. The spacer elements 7 preferably have an absorbing coating on their inner surface, which absorbs any stray light. The spacer elements 7 can be an additional layer or a stack of layers, or an element connected via an adhesive bond or a bonding connection, such as a wafer. According to further embodiments, the focusing element 4a can be directly connected to the optical interference filter 2, for example, via an adhesive bond or a bonding connection.

[0032] Figure 3Figure 1 shows another spectrometer device 1c, which is a modification of the spectrometer devices 1a and 1b described above. The support structure 6c can correspond to one of the support structures 6a and 6b described above. In contrast to the spectrometer devices 1a and 1b shown above, the focusing device 4c is asymmetrically designed, for example as a so-called off-axis reflector, i.e., the focal point of the focusing device 4c is not located in the center of the optical interference filter 2 but in a region outside the optical interference filter 2. Accordingly, the detector device 3 is arranged on the support structure 6c outside the optical interference filter 2 on a side facing the focusing device 4c, wherein the focusing device 4c focuses the light beam L onto the detector device 3 after it has passed through the optical interference filter 2.By arranging the detector device 3 next to the optical interference filter 2, shadowing caused by the detector device 3 and by the leads of the detector device 3 can be avoided, which can be particularly advantageous for smaller input apertures despite the worse ratio of input aperture a to focal length f due to the lower light efficiency or the greater height, as well as the increased reflection losses during light coupling into the detector device 3.

[0033] Figure 4 shows a cross-sectional view of another spectrometer device 1d, which is a modification of the one described in Figure 3 The spectrometer device 1c shown is shown. According to this embodiment, the support element 6d has a housing 63 of the optical interference filter 2 and a support plate 64, wherein the detector device 3 is arranged on one side of the support plate 64 facing the symmetrical focusing device 4c.

[0034] In Figure 5 is a flowchart of a process for manufacturing a spectrometer device, in particular one of the spectrometer devices 1a, 1b, 1c, 1d described above.

[0035] In a first step S1, an optical interference filter 2 is provided, wherein the optical interference filter 2 is an interference filter for a Fabry-Pérot interferometer. The optical interference filter 2 is designed such that certain wavelength ranges of an incident light beam L are filtered as it passes through the optical interference filter 2.

[0036] In a further process step S2, a detector device 3 is provided, which is configured to detect the filtered light beam L. In particular, the optical interference filter 2 and the detector device 3 can be arranged on a common support device 6. The detector device 3 can also be arranged directly on the optical interference filter 2, optionally by means of additional intermediate layers.

[0037] In process step S3, a focusing device 4a, 4c is provided, which has a reflective surface 5. The focusing device 4a, 4c can be designed symmetrically or asymmetrically, wherein the arrangement of the focusing device 4a, 4c, detector device 3 and optical interference filter 2 is such that a light beam L filtered by the optical interference filter 2 is focused onto the detector device 3 by means of the focusing device 4a, 4c.

[0038] The process steps S1, S2, S3 can be carried out in any order and, in particular, simultaneously.

Claims

1. Spectrometer apparatus (1a; 1b; 1c; 1d), having: an optical interference filter (2), which comprises two mirrors spaced apart relative to one another and actuable relative to one another and which is configured to filter particular wavelength ranges of an incident light beam (L) as it passes through the optical interference filter (2), wherein the optical interference filter (2) is configured as a Fabry-Pérot interference filter; a detector device (3), which is configured to detect the filtered light beam (L) and which is integrated into the interference filter (2), or arranged directly or by way of additional layers on the interference filter (2), on a light exit side of the interference filter (2); and a focusing device (4a; 4c) having a reflective surface (5), wherein the focusing device (4a; 4c) is configured to focus the filtered light beam (L) onto the detector device (3) by reflection at the surface (5); and a carrier device (6a; 6b; 6c; 6d), wherein the optical interference filter (2), the detector device (3) and the focusing device (4a; 4c) are arranged directly or indirectly on the carrier device (6a; 6b; 6c; 6d).

2. Spectrometer apparatus (1a; 1b) according to Claim 1, wherein the detector device (3) at least partially overlaps an axis (A) extending through a centre of the optical interference filter (2).

3. Spectrometer apparatus (1c; 1d) according to Claim 1 or 2, wherein the detector device (3) is arranged adjacent to the interference filter (2) on the carrier device (6c; 6d) on a light exit side of the optical interference filter (2).

4. Spectrometer apparatus (1b) according to Claims 1 to 3, wherein the carrier device (6b) comprises at least one spacer element (7), which connects the focusing device (4a) to the optical interference filter (2) and spaces them apart from one another, wherein the at least one spacer element (7) at least regionally has an absorbent coating for reducing transverse and back radiation.

5. Spectrometer apparatus (1a; 1b; 1c; 1d) according to any of Claims 1 to 4, wherein a surface section of the detector device (3) and / or a surface section, adjacent to the detector device (3), of the interference filter (2) and / or of the carrier device (6a; 6b; 6c; 6d) at least regionally has an absorbent coating for reducing transverse and back radiation.

6. Spectrometer apparatus (1a; 1b; 1c; 1d) according to any of the preceding claims, wherein the detector device (3) comprises a ring detector, segmented detector elements and / or detector elements arranged so as to form an array.

7. Spectrometer apparatus (1a; 1b; 1c; 1d) according to any of the preceding claims, wherein the detector device (3) comprises at least two stacked detector elements, which are sensitive to different wavelength ranges.

8. Method for producing a spectrometer apparatus (1a; 1b; 1c; 1d) according to any of the preceding claims, having the following steps: providing (S1) an optical interference filter (2), which is configured to filter particular wavelength ranges of an incident light beam (L) as it passes through the optical interference filter (2); providing (S2) a detector device (3), which is configured to detect the filtered light beam (L); and providing (S3) a focusing device (4a; 4c) having a reflective surface (5), wherein the focusing device (4a; 4c), the detector device (3) and the optical interference filter (2) are arranged with respect to one another in such a way that the focusing device (4a; 4c) can focus the filtered light beam (L) onto the detector device (3).