Multispectral light emitting device and multispectral sensor including the same

Abstract

The invention relates to a multispectral light emitting device comprising at least one broadband light source 1, a filter array 4 with a plurality of spectral filters, and an optical switching device 2 for controlling the passage of light emitted by the light source 1 through the filter array 4. In one embodiment, the optical switching device 2 is formed by an array of micromirrors 16 or microapers, constructed and arranged to direct the light emitted by the light source 1 only through one or more arbitrarily configurable spectral filters of the filter array 4. The invention also relates to a multispectral sensor comprising such a multispectral light emitting device. This device allows the realization of a compact and inexpensive multispectral sensor with a large number of spectral channels.

Description

[Technical field]

[0001] The present invention relates to a multispectral light emitting device comprising at least one broadband light source emitting light in a (certain) spectral range, a filter array with a plurality of spectral filters having a (certain) spectral width within the (certain) spectral range of the light source, and an optical switching device for controlling the passage of light emitted from the light source through the filter array. The present invention also relates to a multispectral sensor comprising said device.

[0002] Numerous applications, for example for the selective analysis of liquid or gaseous media, require the use of optical radiation with variable wavelengths or wavelength ranges. Absorption spectroscopy or photoacoustic spectroscopy are examples. Each gas has a characteristic absorption spectrum (fingerprint) with one or more absorption peaks. In photoacoustic spectroscopy, the specific light absorption at the absorption peaks causes pressure changes or sound waves in the medium, which are detected and converted into an electrical signal. As detectors, for example, microphones can be used. The detected pressure changes are a measure for the concentration of the corresponding gas. Photoacoustic gas sensors (PGS) allow the measurement of a large number of substances in various aggregation states at very low concentrations. However, the measurement requires that the wavelength or wavelength range of the irradiated light is adapted to the gas to be measured. The excitation wavelength can be adjusted, for example, by means of spectral filters or by the use of tunable lasers. The number of gases that can be measured simultaneously by a photoacoustic gas sensor correlates with the number of optical spectral channels of this gas sensor. [Background technology]

[0003] For example, US Pat. No. 6,299,633 shows a photoacoustic gas sensor in which the light of a broadband IR (infrared) light source is directed through a bandpass filter into a measurement chamber with the gas to be measured. The optical bandpass filter passes only a specific part of the light spectrum. The central wavelength of the filter is adapted to the absorption maximum of the gas to be detected. By modulating the IR light source in time up to 100 Hz, the absorption of light in the gas generates an acoustic wave in the measurement chamber, which is measured via a highly sensitive pressure sensor in the measurement chamber. The measured amplitude is proportional to the concentration of the absorbing gas. For many applications, such a gas sensor needs to have a small volume, i.e. a miniaturized form, which is also realizable by the sensor described in US Pat. No. 6,299,633 due to its simple structure. However, since the gas sensor of US Pat. No. 6,299,633 only comprises a spectral filter, it can only detect gases that have an absorption maximum at the corresponding filter wavelength.

[0004] In principle, it is possible to use a filter wheel between the excitation light source and the measurement chamber to change the excitation wavelength. The number of gases that can be measured simultaneously correlates to the number of available optical spectral channels, i.e. the number of spectral filters. However, the number of different filters in a filter wheel is limited. Due to the mechanical construction size, miniaturization becomes very complicated and the measurement time increases with the number of filters installed. A further disadvantage of the filter wheel is that only one filter can be used at any one time.

[0005] When using a tunable laser, especially a quantum cascade laser (QCL), as the light source, no spectral filters are required. The wavelength can be freely adjusted within the tuning range of the laser. For example, a combination of multiple quantum cascade lasers can cover a wider spectral range and thus measure a larger number of gases. However, quantum cascade lasers are relatively expensive. The need for multiple quantum cascade lasers to cover a wide spectral range further increases the cost. Further miniaturization is not possible with such lasers.

[0006] Thus, currently only inexpensive photoacoustic sensors are known with a single bandpass filter, such as in the above-mentioned US Pat. No. 5,399,633, which are typically capable of measuring only one gas. For selective analysis of complex samples, even in the sub-ppb range, as is possible with photoacoustic sensors, there is no cost-effective solution available in a small form factor. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] European Patent No. 3508836 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to provide a multispectral light emitting device and a multispectral sensor based thereon that can be realized inexpensively with a compact structure, which device in particular allows a simple and rapid adaptation or change of the emission wavelengths. [Means for solving the problem]

[0009] The above problem is solved by an apparatus according to claims 1 and 2 and by a multispectral sensor according to claim 11. Advantageous configurations of the apparatus and the multispectral sensor are the subject matter of the dependent claims or can be found in the following description and exemplary embodiments.

[0010] The proposed multispectral light emitting device comprises at least one broadband light source, a filter array and a switching device for controlling the passage of at least a part of the light emitted by the light source through the filter array. The broadband light source emits light in a specific spectral range. The spectral filters of the filter array have a corresponding small spectral width, at least a part of which is within the spectral range of the light source. The spectral width of the spectral filters is preferably less than 1 μm.

[0011] In a first alternative form of the proposed device, the switching device is configured as an optical switching device, the light source, the filter array and the optical switching device being arranged in such a way that light emitted from the light source is guided via the optical switching device, possibly also via further optical elements, such as for example deflection elements or lenses, and the filter array, to an outlet of the device, at which outlet correspondingly filtered light leaves the device. Here, the optical switching device comprises an array of micromirrors or microapertures and is constructed and arranged in such a way that the light emitted from the light source can be selectively guided to the outlet of the device only through one or more arbitrarily configurable spectral filters of the filter array. For this purpose, the optical switching device can be controlled accordingly.

[0012] In a second alternative, the light source comprises an array of light emitters, each of which can be controlled individually via a switching device, and is constructed and arranged such that the light emitted by the light source can be selectively directed only through one or more of the arbitrarily settable spectral filters of the filter array by controlling the light emitters via the switching device. In another version of this second alternative, the light source is formed by a single light emitter, and the switching device comprises a mechanical XY adjustment device for this single emitter or for the filter array, by means of which the single emitter can be positioned under different filters of the filter array, so that the light emitted by the light source can be selectively directed only through the arbitrarily settable spectral filters of the filter array. In this second alternative of the device, the light irradiation surface of the light emitter is preferably not larger than the lateral dimensions of the individual spectral filters of the filter array.

[0013] In a preferred embodiment, the individual spectral filters of the filter array have small lateral dimensions of 10 mm x 10 mm or less. The filter array is preferably constructed such that the spectral filters are arranged in a matrix format in the filter array. In principle, however, other arrangements of the individual filters in the filter array are also possible, for example a concentric arrangement, a purely linear arrangement or a completely arbitrary arrangement. The arrangement of the individual spectral filters of the filter array correlates with the arrangement of the micromirrors or microapers of the first alternative or the arrangement of the individual light emitters of the array by the light emitters of the second alternative, and therefore these are preferably arranged similarly, i.e., for example, correspondingly arranged in a matrix format. The number of units (micromirrors, microapers, light emitters) on the side of the optical switching device or the light source preferably corresponds to the number of spectral filters of the filter array, so that each unit is assigned a spectral filter through which only the light exiting the assigned unit is guided. The number of filters can also be selected to be greater than the number of units, in which case each unit is assigned a group of spectral filters arranged next to each other, for example two or four filters. Furthermore, the number of filters can be selected to be smaller than the number of units, in which case each filter is assigned a number of units arranged next to each other.

[0014] The proposed device allows for the adaptation or variation of the wavelength or spectral distribution of the emitted optical radiation, corresponding to the number and characteristics of different filters of the filter array, so that the spectral distribution of the emitted light can be adapted to the respective application. Due to the selected structure, the filter array and the light source can be constructed in a miniaturized manner, similar to the optical switching device. The device does not require expensive light sources.

[0015] Preferably, filters based on subwavelength structures or plasmonic filters are used in the filter array, which allows a large number of filters to be realized inexpensively in a minimum of space. This makes it possible, for example, to reproduce the absorption spectrum of almost any substance by a suitable combination of individual light channels or filters, i.e. by simultaneously directing light through several of the spectral filters. The filters can be configured as interference filters and can also be combined with polarizing filters. The configuration of this type of filter in a filter array is also possible in principle.

[0016] In the first alternative, the optical switching device can be realized together with the light source as a module or separately from the light source. In the second alternative, the array of light sources can also be configured together with the filter array as a module or separately from the filter array. In addition, in both alternatives, devices can also be arranged in the beam path between the light source and the filter array, which avoid optical crosstalk between the individual optical channels, for example in the form of a suitably configured aperture array and / or lens array.

[0017] The proposed device allows realizing a multispectral sensor comprising a measurement chamber into which the light exiting the device is coupled and one or more detectors, which allows detecting the result of the interaction of the light coupled into the measurement chamber with a medium introduced into the measurement chamber. Thus, the multispectral sensor can be configured, for example, as a photoacoustic gas sensor, in which case at least one of the detectors is a pressure sensor, for example a microphone. In this example, the light source of the proposed device is appropriately modulated in time during the measurement, so that the light coupled into the measurement chamber is absorbed in the gas to be measured, generating an acoustic wave. This gas sensor allows measuring a larger number of gases or gas components, corresponding to the number of filters in the filter array. Also other applications, such as, for example, absorption spectroscopy in combination with photoacoustic spectroscopy, can be realized by such a multispectral sensor.

[0018] The proposed device and the multispectral sensor comprising it can be used in many fields of application, for example in medicine, the environmental sector, process engineering and civil security. This includes, for example, the analysis of industrial processes and parameters (process monitoring), quality assurance, early detection of fires, aroma analysis, detection of abnormal odors, respiratory gas analysis, security applications, environmental analysis, non-destructive surface inspection by reflectance measurements, use as an electronic nose or tongue. Naturally, this is not an exhaustive list.

[0019] In the following, the proposed device and a multispectral sensor comprising this device are explained in more detail on the basis of exemplary embodiments in conjunction with the drawings. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of a multispectral sensor according to the present invention comprising an optical switching device; [Diagram 2] FIG. 1 shows an example of flexible adaptation of the light spectrum to the absorption spectrum of the gas to be measured using the proposed device. [Diagram 3] 1 is a schematic diagram of a multispectral sensor according to the present invention having an array of light sources. [Figure 4] FIG. 1 shows an example of a proposed device configuration based on an array of light sources. [Diagram 5] 13A-13D show further examples of the proposed device configurations based on an array of light sources. [Figure 6] FIG. 1 shows an example of the proposed configuration of the apparatus, comprising a micro-aperture array as an optical switching device. [Figure 7] FIG. 1 shows an example of the proposed configuration of the device based on a single emitter with a mechanical XY adjustment device. [Figure 8] FIG. 1 shows a first example of the structure of the proposed multispectral sensor. [Figure 9] FIG. 1 shows an example of a proposed configuration of the apparatus, comprising a micromirror array as an optical switching device. [Figure 10] FIG. 2 shows an example of a micromirror array in which the spectral filters of the filter array are applied to the micromirrors. [Figure 11] FIG. 2 shows a second example of the structure of the proposed multispectral sensor. [Figure 12] FIG. 1 shows an example of the proposed multispectral sensor configuration comprising multiple measurement chambers. [Figure 13] FIG. 1 shows an example of a filter array that can be used in the proposed device. [Figure 14] FIG. 1 shows an example of a spectral filter configuration of a filter array with polarizing filters that can be used in the proposed device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In Fig. 1 the structure of a multispectral sensor according to the invention is shown very diagrammatically, in which the proposed multispectral light emitting device 14 is combined with a measuring device 15. The light of the desired spectral distribution emerging from the device 14 leaves the outlet of the device as shown in the figure and enters the measuring device 15. The multispectral light emitting device 14 comprises a broadband light source 1, a device, hereafter called optical switch array 2, and a filter array 4. The measuring device 15 comprises a measuring chamber 5, one or more receivers 6 and an electronic device 7 for signal processing and evaluation. The light of the light source 1 is directed to the filter array 4 via the optical switch array 2 (optical switching device). The optical switch array 2 is configured to direct the light to one or more selected filters 4(A), 4(B), 4(C).

[0022] In the case of transmission, the optical switch array 2 is realized by a micro-aperture array, where each element 3(A), 3(B), 3(C), also called optical switch in the following, represents a micro-aperture that can be controlled to open or close independently of the other. Preferably, a control is also possible to change the aperture diameter (when the aperture opening is open). Through each selected micro-aperture, the light is directed to one or more of the filters of the filter array 4. The remaining apertures are closed.

[0023] In the reflective case, the optical switch array 2 is configured as a micromirror array. Each element of the switch array is a micromirror. The mirrors can also be individually controlled to direct incident light towards one or more filters 4(A), 4(B), 4(C) of the filter array 4. Other mirrors are adjusted so that incident light is not directed towards the filter array 4. The areas between the micromirrors (or microapers in the above example) are configured to not transmit light.

[0024] The filter array 4 consists of a number of spectral filters. In the example shown in FIG. 1, only the filters or filter elements 4(A), 4(B), 4(C) are exposed, so that only certain wavelengths corresponding to the filter characteristics of these filters can pass and enter the measurement chamber 5. Using the optical switch array 2, light can be transmitted sequentially or simultaneously through any filters of the filter array 4 in order to generate an optimal spectrum for the respective measurement task. As an example, the required filters can be controlled or exposed in sequence, as in the case of measurements with a monochromator. As an example, light of a single wavelength can be generated by solely controlling element 3(A) for the exposure of filter 4(A), if filter 4(A) is configured with a correspondingly narrow band.

[0025] In a further embodiment, as will be explained in more detail below in conjunction with Fig. 3, the light source 1 can be configured as an array of light emitters. Individual light emitters can be optionally controlled to direct light in a targeted manner to one or more filters of the filter array 4. Here, the light source and the filter array preferably form one unit. In this embodiment, the optical switch array 2 is not required.

[0026] The sample to be measured is placed in the measurement chamber 5. The sample can be in various states of concentration, for example as a liquid or gas. The measurement can be performed in reflection or transmission. As receiver 6, different sensors or detectors can be used, which use different physical measurement principles. Examples are an IR detector for absorption spectroscopy or a pressure sensor, for example in the form of one or more MEMS microphones in photoacoustic spectroscopy. It is also possible to use a combination of several detectors or sensors, for example a pressure sensor in a light transmission measurement chamber together with an absorption detector outside the measurement chamber.

[0027] During the measurement, by suitable control of the switch array 2 or, in the case of an array with light emitters, the light emitters, one or more filters of the filter array 4 can be optionally used to generate a desired spectral distribution, for example only a single wavelength or a superposition of specific wavelengths, which can be used depending on the application. A change of this spectral distribution is possible at any time by a further control. The control, the output of the detection data, the signal processing and the evaluation are realized via electronics and software.

[0028] The light spectrum generated by the proposed device can be flexibly adapted to the absorption spectrum of the sample in the measurement chamber. In FIG. 2, an example of such a flexible adaptation is shown. In this regard, FIG. 2a shows an abstract absorption spectrum of the substance to be measured. This substance has three characteristic absorption peaks (A1, A2, A3). This absorption spectrum can be reproduced by a combination of suitable elements of the optical switch array 2 and the filter array 4. In this example, the optical switches 3(A), 3(B), 3(C) are open, which exposes the filters 4(A), 4(B) and 4(C) by the filter array 4. In certain configurations, not only the positions of the individual absorption peaks can be reproduced, but also the amplitude ratio between the peaks can be adjusted. FIG. 2b shows the three individual spectra of the filters 4(A), 4(B), 4(C). The simultaneously exposed filters of the filter array 4 are shown in white in FIG. 2d, while the non-exposed filters are shown in black. Figure 2c shows the complete spectrum 4(A)+4(B)+4(C) of light after the filter array 4. This light spectrum is optimally adapted to the absorption spectrum of the substance to be measured shown in figure 2a. The intensity adaptation can be adjusted, for example, by adapting parameters such as the current of the individual emitters in case of using an emitter array without an optical switch array, or via the transmittance of the optical switch array. The latter in particular relates to the use of micro-aperture arrays with an adaptable aperture opening or to the use of liquid crystal-based micro-aperture arrays with configurable transmittance.

[0029] FIG. 3 shows an example of the configuration of the proposed multispectral sensor and the multispectral light emitting device used therein, in which the light source 1 is formed by an array of a number of individual light emitters 1(N). Here, in the partial view on the left, the structure of the multispectral sensor is shown diagrammatically, and in the partial view on the right, the structure of the associated device is shown. In this configuration, no optical switching device as in FIG. 1 is required. The individual light emitters of the arrayed light source 1 can be individually controlled or switched on and off as required. This allows a flexible adaptation of the light spectrum emitted by the device to the absorption spectrum of the sample to be measured, similar to what has already been explained in conjunction with FIGS. 1 and 2. In the example of FIG. 3, two light emitters 1(A), 1(B) are on, while the remaining light emitters of the light source 1 are off. Thereby, only the filters 4(A) and 4(B) are exposed on the filter array 4 arranged above, as shown diagrammatically in the figure. In this example, as shown in the partial view on the right of FIG. 3, the light emitting surface of the light emitter 1 has an area smaller than the dimensions of the filters 4(N) of the filter array 4. The distance between the filter array 4 and the light source 1 is small enough that by appropriately controlling the individual light emitters 1(N), only the filters in the filter array 4 that are directly above each light emitter can be exposed.

[0030] Here, as light source 7, an array of IR light sources emitting light in the spectral range of 1 μm to 15 μm is preferably used. This allows, for example, the measurement of a gas sample in the measurement chamber 5 by photoacoustic spectroscopy. As receiver 6, one or more pressure sensors, for example in the form of one or more microphones, are used. Thus, in the embodiment according to FIG. 3, for example, the method described in LD Williams et al. "Design and characterization of a microheater array device fabricated with SwIFT-Lite" is used. TMIt is possible to use arrays of light sources, for example arrays of so-called microheaters, as described in J. Micro / Nanolith. MEMS MOEMS 7(4), 043035 (2008). Such arrays can be manufactured using MEMS technology.

[0031] FIG. 4 shows a further example of a multispectral light emitting device with an array of light sources. Such a device can also be used in the multispectral sensor according to FIG. 3. In this example, the filter array and the array of light sources form one unit. In this respect, FIG. 4 shows an array with monolithically constructed spectral channels. The spectral channels are a combination of light sources or light emitters 9(1), 9(2), ..., 9(n) and filters 4(1), 4(2), ..., 4(n) of the filter array. The array shown in FIG. 4 can be manufactured by semiconductor techniques or post-processing. In this way, the desired number of spectral channels can be arranged as an array on the substrate 20. Both the individual filters, which can be formed for example as plasmonic filters or filters based on subwavelength structures, and the light sources, for example in the form of MEMS microheaters, can be realized in semiconductor techniques. Here, the filters can consist of one or more structured metal or dielectric layers. FIG. 4 shows a cross section of such a unit. From the figure one can clearly see a layered structure on a substrate 20 with several layers 21-25 with through contacts or vias 26, as is often used in semiconductor processing. In this example, layer 22 represents an IR light source array with light emitters 9(1), 9(2), ..., 9(n). The IR light sources can be realized, for example, by microspirals or microheaters. A filter array with filters 4(1), 4(2), ..., 4(n) is realized in the top layer 25. Each filter can consist of one or more single layers. The filter layers can consist of at least one array of subwavelength-sized structured metal or dielectric layers. The filter properties can be freely defined for each spectral channel. The optical properties of the filters depend on the structure size, the structure form (for example holes or islands) and the periodicity and can be defined by the filter design. Filter arrays in the form of optical switching devices can also be realized in this way.Layer 21 represents one of the layers of a typical layer structure in a semiconductor process and can also act as a reflector for the light source in layer 22, for example. In layers 23, 24, openings suitable for the passage of light are formed. These layers are usually made of metallic materials and are separated from each other by dielectric layers. Vias 26 prevent the passage of light between the individual spectral channels in the array.

[0032] Examples of suitable infrared optical filters can be found in IJH McCrindle et al., "Infrared plasmonic filters integrated with an optical and terahertz multi-spectral material," Phys. Status Solidi A 212, No. 8, 1625-1633 (2015) and A. Wang et al., "Mid-infrared plasmonic multispectral filters," Scientific Reports (2018) 8: 11257. The filters shown in these publications are based on structured metal layers and can be modeled by the finite difference time domain (FDTD) method. By simulation, the design of the filter for the desired spectral transmission, bandwidth, and position of the central wavelength can be determined.

[0033] FIG. 5 shows a modification of the multispectral light emitting device of FIG. 3. In this device, the light source 1 and the filter array 4 are manufactured separately and placed one above the other, so that a free space is created between the light source 1 and the filter array 4. In order to prevent optical crosstalk between the individual optical channels, in the example of FIG. 5, an aperture array or lens array 8, which is appropriately designed for preventing optical crosstalk between the individual channels, is placed in this free space. Without this aperture array or lens array 8, the light of the light emitter may possibly hit not only the filter directly above it, but also the adjacent filters. So, for example, the light from the light emitter 1 (B) hits only the filter 4 (B) above by using this aperture array or lens array 8. Without the aperture array or lens array 8, due to the large illumination angle of the light emitter 1 (B), its light may also hit the adjacent filters, for example filter 4 (C).

[0034] In Fig. 6 an example of a multispectral light emitting device is shown, in which a micro aperture array is used as an optical switch array 2 above the light source 1. Such a micro aperture array can be manufactured, for example, in MEMS technology, as known, for example, from MJ Li et al. "Fabrication of Microshutter Arrays for Space Application", Proceedings of SPIE vol. 4407 (2001), 295-303. In the example of Fig. 6, the shutters or micro apertures 2(A) and 2(B) are open, and filters 4(A) and 4(B) are exposed. The remaining micro apertures are closed, and their associated filters are not exposed. The elements of the aperture array can be controlled to open or close individually or in groups. This allows, as in the previous example, to flexibly adapt the light spectrum emitted by the device to the absorption spectrum of the sample. The micro aperture array or optical switch array 2 and the light source 1 below it can be realized as one unit. In order to avoid crosstalk between the individual channels, again, as shown in the left partial view of Figure 6, a further aperture array or lens array 8 can be arranged not only between the light source 1 and the optical switch array 2, but also between the optical switch array 2 and the filter array 4.

[0035] FIG. 7 shows a further example of a possible form of the proposed multispectral light emitting device. In the example of FIG. 7, a single light emitter is used as light source 1, which can be moved via a mechanical XY adjuster 12 below the filter array 4. Here too, an aperture array or lens array 8 as in some of the above exemplary embodiments can be further integrated to avoid optical crosstalk. This limits the illumination angle so that the respective adjacent filters are not undesirably exposed. In this example, the filter array 4 is arranged on a substrate that is transparent to the light of the light source, for example made of Si in the case of an IR light source. The light source 1 is arranged on the XY adjuster 12. The filter array 4 is scanned by the light source 1 according to the desired filters or the spectral characteristics that result therefrom. Thereby, different spectral characteristics can be sequentially brought about, as is shown diagrammatically in the left partial view of FIG. 7, which is a top view of the filter array 4. Small movements of the XY adjuster in the corresponding small lateral dimensions of the individual filters of the filter array 4 can be realized, for example, by a piezo drive. Alternatively, the light source 1 can be arranged stationary and the filter array 4 above the light source can be moved. In the example of FIG. 7, the filters F1 to Fx of the filter array 4 are scanned sequentially.

[0036] FIG. 8 shows an example of a photoacoustic gas sensor (PGS) that can be realized according to the invention. The multispectral light emitting device realized by the module 13 in FIG. 8 can in principle be realized similarly to one of the exemplary embodiments described above, in this example comprising a micro-aperture array 11 as an optical switching device. In this example, between the light source 1 and the micro-aperture array 11 a lens array 8 is arranged, which prevents crosstalk between the individual spectral channels. The lenses of this lens array 8 collimate or focus the light emitted by the light source 1 in the direction of the respective micro-aperture. In this example, the electronics (instruments) of the gas sensor are separated by a measurement chamber 5. The measurement chamber has an optical window 10 for coupling out the excitation radiation. In this example, the filter substrate of the optical filter array 4 is used as the optical window 10. In this case, the filters of the filter array can be arranged above or below this optical window. In this example, the filters are arranged above the optical window 10, i.e. in the measurement chamber 5. In the measurement chamber 5, a pressure sensor, for example in the form of a MEMS microphone, is present as a receiver 6. The output signal of this microphone is evaluated in a signal processing and evaluation device 7 (electronics, software). In the left partial view of FIG. 8, a top view of the filter array 4 is shown. On the filter array, for example, filter 4 (A) is exposed (spot 42). The other filters of the filter array 4 are not exposed. Of course, several filters can also be exposed simultaneously, as explained in the above exemplary embodiment. In the case of PGS sensors, as light source 1, most often an IR light source is used, which emits light in the wavelength range from 1 μm to 15 μm. The measurement chamber 5 has at least one inlet for supplying the sample. In the measurement chamber 5, further sensors, for example for temperature and humidity, can also be placed.

[0037] FIG. 9 shows a further example of a multispectral light-emitting device according to the invention. In this example, a micromirror array 16 is used as an optical switch array. This mirror array 16 can be, for example, a DLP module (MEMS). In this module, individual mirrors or mirror areas, i.e. areas comprising a number of mirrors, can be switched on and off or tilted accordingly. The individual mirrors of the module can be constructed with very small dimensions, for example 10 μm×10 μm. In the example of FIG. 9, the individual mirrors of the mirror array 16 direct light either in direction 1 or in direction 2. Here, light from a light source 1 is irradiated onto the mirror array 16. When deflected in direction 2, the respective light beam is directed via an optical system 18, for example a concave mirror, to an optical filter array 4, exposing, for example, a filter 4 (A), as shown diagrammatically in FIG. 9. The optical system 18 is based either on lens optics or on mirror optics. Mirror optics is preferred, since the mirror coating allows very low absorption over a very wide spectral range. Selection of individual filters in filter array 4 is done by switching on regions of the optical mirror array. In this example, mirror or mirror region 16(A) is switched on, thus deflecting the incident light in direction 2. Mirror or mirror region 16(B) is switched off, thus causing the associated mirror or mirrors to deflect the light in direction 1 towards absorber 17, where the deflected light is absorbed. By appropriately controlling the individual mirrors of the mirror array, each desired filter in filter array 4 can be exposed.

[0038] Alternatively, as shown diagrammatically in Figure 10, a filter array 4 with individual filters, preferably plasmonic filters, may be applied directly to the mirrors of the mirror array 16. A separate filter array 4 as in the left part of Figure 9 is not required.

[0039] Here, the filter array and the MEMS mirror array can be realized together in semiconductor technology. Each filter can consist of one or more structured metal or dielectric layers. Figure 10 shows an example of such a micromirror array 16 in a top view, to which a filter is applied. In this example, four mirrors each are grouped in one group or mirror area 16(A), 16(B), ..., 16(n), each coated with the same filter. This is shown in Figure 10 by the respective patterns. Here, as filters, filters based on subwavelength structures or plasmonic filters are preferably used. Thereby, by a combination of the different mirror areas 16(A), 16(B), ..., 16(n), the reflection spectrum of almost any substance to be measured can be reproduced. In this regard, the radiation incident on the measurement chamber is reflected by simply switching on the corresponding mirror. Here, each mirror area can be applied with a specific filter optimized for a specific wavelength. The mirror area can consist of one or more mirrors, in the example of Figure 10, four mirrors.

[0040] FIG. 11 shows an example of the configuration of a photoacoustic gas sensor comprising a multispectral light-emitting device as shown in FIG. 9 or FIG. 10. In this example, the electronics (instruments) and the optical system are separated from the measurement chamber 5. The measurement chamber comprises an optical window 10, which in this example is formed by a filter substrate of an optical filter array 4. The filters of the filter array can again be arranged above or below the optical window 10. In this example, the filters are arranged below the optical window 10, i.e. outside the measurement chamber. In the measurement chamber 5, at least one pressure sensor is arranged as receiver 6, which can be configured as a MEMS microphone. The output signal of this pressure sensor is evaluated in a signal processing and evaluation device 7 (electronics, software). In the left partial view of FIG. 11, a top view of the filter array 4 is shown. On the filter array, for example, filter 4 (A) is exposed (spot 42). The other filters of the array are not exposed. Of course, it is also possible to expose several filters simultaneously, as shown in the above exemplary embodiment. In the case of a PGS sensor, typically an IR light source emitting in the wide range from 1 μm to 15 μm is used as light source 1. The measurement chamber 5 again has at least one inlet 19 for feeding the sample. Further sensors, for example for measuring temperature and humidity, can also be placed in the measurement chamber.

[0041] FIG. 12 shows an example of the structure of a multispectral sensor according to the invention, in which more than one measurement chamber is used. In this example, three measurement chambers 5(A), 5(B), 5(C) are installed in series. This is possible because, when measuring gases, the excitation light irradiated to the measurement chambers is only slightly attenuated when passing through the measurement chambers due to the weak absorption of the gases. The measurement chambers have optical windows 35(A), 35(B), 35(C), 35(D), respectively. The beam bundle 37 emitted by the multispectral light emitting device propagates through the individual chambers 5(A), 5(B), 5(C). After the last chamber, a radiation receiver 27 can be installed. This allows the variation of the light output to be measured. The measurement chambers can be supplied with various samples. These can be unknown gases or calibration gases. The calibration gas has a defined concentration and a known spectrum. By using several measurement chambers, a multiport sampler can be realized. As radiation receiver 27, for example, an IR detector or a photodiode can be used.

[0042] Fig. 13 shows an example of a filter array that can be used in the proposed device and in the proposed multispectral sensor as well. Such a filter array, in this example in the form of an "Infrared Linear Variable Filter" as marketed by the company Vortex Optical Coatings Ltd., can be manufactured in thin-film technology. This kind of filter has multiple spectral channels (band-pass filters) and can be optimized for a specific spectral range. The filter array 4 according to the above exemplary embodiment can be replaced by such a filter. The filters F1, F2, Fn can be exposed individually or in groups via an optical switch.

[0043] In the proposed multispectral light emitting device and the related multispectral sensor, the spectral filter can also be combined with a polarizing filter. Thus, FIG. 14 shows a combination of a spectral filter with multiple polarizing filters. The absorption and scattering spectra of a substance can depend on the polarization state of the light. Through polarized spectral illumination, additional information about the substance can therefore be obtained. In the above exemplary embodiments, unpolarized light was used in each case. In this example, a spectral channel or filter 4(A) is combined with multiple polarizing filters 40(A), 40(B), 40(C). There is no polarizing filter at position 41. This position represents the reference channel with unpolarized light. Via an optical switch array, the filters 40(A), 40(B), 40(C) can be exposed sequentially. In this example, the spot 42 is on the polarizing filter 40(A). The light after the spectral filter 4(A) always has the same spectrum, but can have different polarizations depending on the local exposure. In the right-hand partial view, an example of the structure of such a filter in semiconductor technology is shown. The basic structure has already been explained in conjunction with FIG. 4. In this example, a lattice-like structure is realized in the metal layer 23. These lattice-like metal webs polarize the light depending on the angle. In this example, angles of +90 degrees, +45 degrees and -45 degrees are used. A spectral filter 4(A) is constructed in the top layer 25. This filter can be based, for example, on a subwavelength structure. [Explanation of symbols]

[0044] 1 light source 1(N) Light emitter 2. Optical switch array 2(N) Micro aperture 3(N) Switch array elements 4. Filter Array 4(N) Selected Filters 5. Measurement chamber 6 Receiver 7 Signal Processing and Evaluation Devices 8 Lens array or aperture array 9(N) Light emitter 10 Optical window 11 Micro Aperture Array 12 XY adjuster 13 Modules 14 Multispectral light emitting device 15 Measuring Devices 16 Micromirror Array 16(N) Micromirror, Micromirror Area 17 Absorber 18 Optical system 19 Inlet 20 Substrate 21~25 layers 26 Through Contact (Via) 27 Radiation Receiver 35 Optical window 37 Beam flux 40 Polarizing Filter 41 Position on Spectral Filter 42 Exposure Spot

Claims

1. A multispectral light emitting device comprising at least A broadband light source (1) emitting light in a spectral range; a filter array (4) with a plurality of spectral filters having a spectral width at least partially within the spectral range of the light source (1); an optical switching device (2) for controlling the passage of the light emitted from the light source through the filter array (4), the optical switching device (2) being arranged to direct the light emitted from the light source (1) through the optical switching device (2) and the filter array (4) to an outlet of the apparatus; Equipped with The optical switching device (2) comprises an array of micromirrors (16) or microapers and is constructed and arranged to selectively direct the light emitted from the light source (1) to an outlet of the device only through one or more arbitrarily configurable spectral filters of the filter array (4).

2. A multispectral light emitting device comprising at least A broadband light source (1) emitting light in a spectral range; a filter array (4) of a plurality of spectral filters having a spectral width at least a portion of which is within the spectral range of the light source (1); a switching device for controlling the passage of the light emitted from the light source (1) through the filter array (4); Equipped with The light source (1) is or 1. A multispectral light emitting device formed by at least one single emitter, the switching device comprising an XY adjustment device (21) for the single emitter or for the filter array (4), by means of which the single emitter can be positioned through different filters of the filter array (4) such that the light emitted by the light source (1) can be directed only through the arbitrarily settable spectral filters of the filter array (4).

3. 3. Apparatus according to claim 2, characterized in that the filter array (4) is arranged directly above the array of light emitters which are individually controllable via the switching devices.

4. 4. The apparatus according to claim 3, characterized in that each combination of one or more light emitters and a spectral filter of the filter array (4) arranged directly above it forms an optical channel, and a device for avoiding optical crosstalk between the optical channels is arranged between the array of light emitters that can be individually controlled via the switching device and the filter array (4).

5. 2. The apparatus of claim 1, characterized in that each combination of one or more elements (3) of the optical switching device (2) and an associated spectral filter of the filter array (4) forms an optical channel, and a device (8) for avoiding optical crosstalk between the optical channels is arranged between the light source (1) and the filter array (4).

6. 6. Apparatus according to any one of the preceding claims, characterized in that the individual spectral filters of the filter array (4) have small lateral dimensions of less than or equal to 10 mm x 10 mm.

7. 7. The device according to any one of the preceding claims, characterized in that the filter array (4) is a filter array based on subwavelength structures or a plasmonic filter array.

8. 8. The device according to claim 1, wherein the spectral filters are arranged in a matrix in the filter array (4).

9. 9. An apparatus according to claim 1, 5 to 8, characterized in that, when the optical switching device (2) is formed as an array with micromirrors (16), the filters of the filter array (4) are applied directly above the micromirrors.

10. Device according to any one of the preceding claims, characterized in that the spectral filters in the filter array (4) are combined with polarizing filters (40).

11. A device according to one or more of claims 1 to 10, a measurement chamber (5) into which the light exiting the device is coupled; one or more detectors (6) capable of detecting the result of an interaction between the light coupled into the measurement chamber (5) and a medium introduced into the measurement chamber (5); A multispectral sensor comprising:

12. 12. A multispectral sensor according to claim 11, characterized in that the entrance window (10) of the measurement chamber (5) is formed by a carrier substrate of the filter array (4) of the device.

13. 13. The multispectral sensor of claim 11 or 12 configured as a photoacoustic sensor.

14. 13. A multispectral sensor according to claim 11 or 12 configured as an absorption sensor or as a combination absorption sensor and photoacoustic sensor.

Images