Angle-variable and filter-based spectral sensor

Abstract

Filter-based spectral sensor for simultaneous spectral analysis of incident light, including: - a total filter (3) which is transparent to light of a specified spectral range, - a light entrance aperture (1) through which a light beam (2) to be analyzed, comprising a plurality of light rays (21), can fall onto the overall filter (3) with a diameter (D), - a composite reflector (4) arranged opposite the composite filter (3) and designed to reflect the light rays (21) of the light beam (2) in the direction of the composite filter (3), and - a total detector (5) designed to detect light rays (21) transmitted by the total filter (3), wherein - the path of the light beam (2) runs back and forth between the overall filter (3) and the overall reflector (4) and the light beam (2) is reflected at least partially at the overall reflector (4) and partially at the overall filter (3), - the overall reflector (4) and the overall filter (3) are planar and the overall reflector (4) is inclined relative to the overall filter (3) and the overall detector (5) by an angle of inclination (ε) such that the angle of incidence (β) i ) of the light rays (21) on the overall filter (3) change with each impact of the light rays (21), and - the overall filter (3) is angle-variable, so that a transmission range of the overall filter (3) depends on the angle of incidence (β) i ) the light rays (21) fall onto the overall filter (3), characterized in that - the light beam (2) spreads out divergently or convergently after the light entry aperture (1) in the spectral sensor.

Description

[0001] The invention relates to an angle-variable and filter-based spectral sensor for the simultaneous spectral analysis of incident light.

[0002] Spectral sensors, also known as spectrometers, are currently used in agriculture, the food industry, biomedicine, pharmaceuticals, and process control, among other fields. In these applications, compact, grating-based spectrometers are predominantly used. These spectrometers should ideally offer the widest possible spectral bandwidth, high spectral resolution, and a compact and robust design. Since grating-based spectrometers always require a compromise between spectral resolution, spectral bandwidth, and compact design, filter-based spectral sensors are used as an alternative.

[0003] Filter-based spectral sensors typically have multiple detectors, with each detector positioned in front of a filter in the beam path of the incident light. The filters differ in their absorption, reflection, and transmission properties, meaning each detector detects only a portion of the incident light corresponding to a specific wavelength or wavelength range. Often, a single filter-detector combination is used to detect one spectral reference point (wavelength or wavelength range). By using multiple filter-detector combinations, several spectral reference points can be measured. The total detectable spectral bandwidth of the filter-based spectral sensor therefore depends on the number and spectral width of the individual filter-detector combinations.In general, the complexity and installation space of the filter-based spectral sensor increase with the number of filter-detector combinations.

[0004] The properties of a filter-based spectral sensor depend heavily on the filters used. Various filter designs exist, such as absorption filters, interference filters, and graduated filters. Depending on the specific design, the absorption, reflection, and transmission properties can be either dependent on or independent of the angle and / or location of the light beam striking the filter. For example, due to their operating principle, interference filters typically exhibit a dependence of transmission and reflection behavior on the angle of incidence. If transmission and reflection properties are independent of the light beam's point of incidence, they are sometimes referred to as homogeneous or discrete filters.In contrast, graduated filters, also known as position-variable filters, exhibit transmission and reflection characteristics that change continuously depending on the point of impact of the light beam on the filter. For a specific filter area where the light beam strikes, the transmission and reflection properties of a position-variable filter are analogous to those of a discrete filter. Using a graduated filter can replace several discrete filters that would otherwise need to be arranged side-by-side in the spectral sensor, thus simplifying assembly. However, the production of graduated filters is typically more complex and expensive than the production of discrete filters.

[0005] Filter-based spectrometers can be very compact, but often suffer from the disadvantage that, due to the transmission properties of the filters used, only a small proportion of the incident light reaches the detectors. A conventional filter-based spectral sensor is described, for example, in the research article "Single-chip CMOS optical microspectrometer," by JH Correia et al., published in the journal Sensors and Actuators A: Physical, issue no. 82, 2000, pages 191-197.

[0006] To increase the detection efficiency of a filter-based spectral sensor, the spectrometer can be designed in a cascade configuration, so that an incident light beam initially strikes only one of the filters, and the portion of the incident light reflected by that filter is deflected onto a subsequent filter. Such a cascade configuration allows the spectrometer to achieve high spectral resolution in a compact design.

[0007] A spectrometer known from US Patent 7,623,243 B2 comprises a plurality of dichroic mirrors, each transmittable for different wavelength ranges, a reflecting element arranged parallel to and opposite the dichroic mirrors, and a photodetector. Due to its cascading design, the spectrometer is suitable for the spectroscopic separation of the detected light into light beams with different wavelength ranges, which can then be detected by a photodetector. German Patent DE 10 2017 129 096 A1 discloses a filter-based spectral sensor for the spectral splitting of incident light, in which a light beam is deflected multiple times at a mirrored surface and at a parallel dichroic interface opposite it, whereby different wavelength components are successively coupled out at the dichroic interface.A similar arrangement for a light beam is described in US 6 008 920 A using a wavelength-selective filter. While the two aforementioned documents use a light beam, US 2017 / 0139143 A1 describes a wavelength multiplexer or wavelength demultiplexer that uses a collimated beam throughout.

[0008] An infrared spectrometer is described in CN 106841105 A. The infrared spectrometer contains a broadband infrared light source with an objective lens to illuminate a sample, and an endoscope that collects the infrared radiation reflected from a surface of the sample. The collected light is collimated and spectrally split into several measurement branches. Infrared detectors are arranged in the measurement branches, which detect the portions of the infrared light transmitted into each branch.

[0009] From US Patent 7,466,419 B2, a spectrometer is known that includes a plurality of interference filters made of dielectric multilayer films, each with a different transmission waveband, arranged in sequence such that light reflected from a particular interference filter is incident on an interference filter at the next stage, and photodetection devices positioned at the points where the light transmitted through the respective interference filters is incident. The spectrometer also includes a collimating lens to collimate the incident light.

[0010] An alternative method for wavelength selection is the use of angle-variable filters, whose transmission and reflection properties depend on the angle at which the light strikes the filter. An angle-variable filter is disclosed, for example, in US 8,441,710 B2.

[0011] US Patent 8,059,327 B1 discloses a spectral sensor with an angle-variable filter. The angle-variable filter is rotatably mounted in holders, and rotating the filter around an axis continuously changes a transmission wavelength. A wavelength spectrum is thus recorded for each wavelength at a predetermined time, and simultaneous acquisition of multiple wavelengths is not possible.

[0012] WO 2010 / 002326 A1 discloses another filter-based spectral sensor with an angle-variable filter. An illumination arrangement described therein directs light beams onto the angle-variable filter at different angles of incidence. The arrangement is designed such that only a light beam with a specific angle of incidence or angle range strikes a particular location on the angle-variable filter, thus performing wavelength selection. Different wavelengths can therefore be detected by the detectors located downstream of the angle-variable filter. The arrangement allows for the simultaneous acquisition of the spectrum with a single angle-variable filter. However, here too, only a small wavelength range is transmitted through the filter for each angle of incidence, resulting in very low detection efficiency.

[0013] Due to the design of the described filter-based simultaneous spectrometers, the number of spectral support points always corresponds to the number of detectors and associated filters or filter sections, or the number of filter-detector combinations. Because of the cascading arrangement, the number of required filters or filter sections, as well as the size of the spectral sensor, increases with the number of spectral support points. This necessitates a compromise between the number of spectral support points and the compactness of the spectrometer. Furthermore, a large number of different filters or filter sections is required for a large number of spectral support points. This results in high effort for adjustment and assembly when using various individual filters. Conversely, the fabrication of the filter element is very complex and expensive when using graduated filters with different filter sections.

[0014] A cascading arrangement for increasing the efficiency of a filter-based spectrometer is described in the research article "Folded beam path architecture for highly efficient filter-based spectral sensors" by A. Kobylinskiy et al., published in the journal Applied Optics, Vol. 61, No. 33, pages 9996 to 10001, in 2022. In this arrangement, the light beam strikes the filters at a fixed angle, resulting in wavelength selection through the use of multiple individual filters or a position-variable filter. Using multiple individual filters significantly increases the adjustment and assembly effort during spectrometer manufacturing. While the position-variable filter allows for simpler assembly, its production is more complex and expensive than manufacturing multiple individual filters.

[0015] The object of the invention is to provide a compact, filter-based spectral sensor for the simultaneous spectral analysis of incident light with high detection efficiency and a large spectral bandwidth. Furthermore, the resolution and spectral bandwidth should be adjustable via the design of the spectral sensor.

[0016] The task is solved by a filter-based spectral sensor for the simultaneous spectral analysis of incident light, comprising a composite filter transparent to light of a specified spectral range, a light entrance aperture through which a light beam to be analyzed, comprising a multitude of light rays, can enter the composite filter with a diameter, a composite reflector arranged opposite the composite filter and designed to reflect the light rays of the beam towards the composite filter, and a composite detector designed to detect light rays transmitted by the composite filter, wherein the beam path of the light beam runs back and forth between the composite filter and the composite reflector, and the light beam is reflected at least partially at the composite reflector and partially at the composite filter.wherein the overall reflector and the overall filter are planar and the overall reflector is inclined relative to the overall filter and the overall detector by an angle of inclination, such that the angles of incidence of the light rays on the overall filter change with each impact of the light rays during propagation through the spectral sensor, and the overall filter is angle-variable, such that a transmission range of the overall filter depends on the angle of incidence of the light rays on the overall filter. According to the invention, the light beam propagates divergently or convergently after the light entrance aperture in the spectral sensor.

[0017] Preferably, the composite reflector is a further composite filter with another composite detector arranged on the side of the composite detector facing away from the composite detector. This allows the number of spectral support points to be increased even further, and the filter-based spectrometer can be designed to be even more compact for the same spectral range and / or its spectral resolution can be improved. Furthermore, potential reflection losses that can occur at the composite reflector are avoided. The second composite filter is then constructed analogously to the composite filter, and the second composite detector is constructed analogously to the composite detector.

[0018] The problem is further solved by a filter-based spectral sensor comprising a composite filter transparent to light of a predetermined spectral range, a light entrance aperture through which a light beam to be analyzed, comprising a plurality of light rays, can fall onto the composite filter with a diameter, a composite reflector arranged opposite the composite filter and designed to reflect the light rays of the light beam towards the composite filter, and a composite detector designed to detect light rays transmitted by the composite filter, wherein the beam path of the light beam runs back and forth between the composite filter and the composite reflector, and the light beam is reflected at least partially at the composite reflector and partially at the composite filter, characterized in that the composite reflector is curved at least section by section.such that the angles of incidence of the light rays on the overall filter change with each impact during propagation through the spectral sensor, and the overall filter is angle-variable, so that the transmission range of the overall filter depends on the angle at which the light rays strike the overall filter. According to the invention, the light beam propagates divergently or convergently after the light entrance aperture in the spectral sensor.

[0019] In principle, all angle-variable filters are suitable as overall filters. Interference filters, which can be designed as bandpass filters or edge filters (both longpass and shortpass filters), are particularly relevant as angle-variable filters. Angle-variable filters that exhibit high reflectance for the non-transmitted wavelengths are especially advantageous. This results in no or only very low losses due to absorption or scattering at the overall filter. The overall filter is preferably homogeneous or at least sectionally homogeneous. A homogeneous overall filter is generally less expensive to manufacture than variable filters or filter arrays. Alternatively, the overall filter can be a graduated filter.

[0020] Because the overall reflector is designed in such a way that the angle of incidence of the light rays on the overall filter changes with each impact of the light rays, because of the angular variability of the overall filter, and because the angles of incidence of the light rays are predetermined by the shape and arrangement of the overall reflector in relation to the overall filter, the resolution and spectral bandwidth of the filter-based spectral sensor can be adjusted very precisely.

[0021] The arrangement is designed such that each area of ​​the overall detector captures only the light of a specific spectral range transmitted through the overall filter. This is achieved by ensuring that the light rays of the beam strike a specific area of ​​the overall filter and the downstream detector at a desired angle or range of angles of incidence. In a further advantageous embodiment of the arrangement, an area of ​​the overall filter and overall detector is illuminated multiple times by the light rays of the beam at different angles or ranges of angles through back-and-forth reflection.This allows, on the one hand, a central wavelength with greater intensity but greater spectral bandwidth to be recorded, or on the other hand, several separate spectral ranges or adjacent spectral ranges to be recorded by a single detector or pixel of the overall detector, which reduces the resolution and allows a higher intensity to be detected.

[0022] Due to its cascading design, the filter-based spectral sensor offers high detection efficiency, while operating without moving parts and allowing for the simultaneous acquisition of a spectrum. Furthermore, the filter-based spectral sensor is very compact.

[0023] Due to the design of the filter-based spectral sensor, different spectral reference points can be measured using a variable-angle filter or at least homogeneous sections of the filter. The specific spectral range measured depends on the angle of incidence of the light rays from the light beam. This means that the same variable-angle filter can be used to capture many different spectral reference points.

[0024] A spectral sensor, also known as a spectral analyzer or spectrometer, is used to detect and analyze the spectrum of light or electromagnetic radiation, which usually originates from a sample under investigation.

[0025] The light to be analyzed can enter the spectral sensor as a divergent, convergent, or collimated beam. With divergent or convergent incidence, the diameter of the beam is not constant along its entire path, and the beam strikes the filter within a range of angles. In this context, the beam diameter refers to the diameter of the beam at the light entrance aperture.

[0026] Because the light beam is reflected back and forth between the overall filter and the overall reflector, the detection efficiency of the filter-based spectral sensor is increased compared to conventional filter-based spectrometers. The distance between the overall filter and the overall reflector is large enough that the light beam does not interfere with itself within the filter-based spectral sensor.

[0027] The filter-based spectrometer is preferably housed in a casing to minimize the amount of ambient light entering the device. The light entrance aperture can be integrated into the casing.

[0028] Because the overall reflector is curved, at least in sections, the angles of incidence of the light rays on the overall filter can change in more than one direction with each impact. The overall filter can be flat or also curved, at least in sections.

[0029] Preferably, the curved overall reflector has the shape of a circular sector or a conic section. Alternatively, the curved overall reflector can also preferably have a freeform shape, including curved shapes, asymmetrical shapes, or other freeform shapes.

[0030] The shape of the overall reflector serves two purposes: firstly, to adapt the filter-based spectral sensor to the spectral range being addressed, and secondly, to adjust the resolution for different wavelengths within the detectable spectral range. When the light beam strikes a large filter-detector area at various angles, the corresponding (spectral) range has a high resolution. Conversely, when the light beam strikes a small filter-detector area at various angles, the corresponding (spectral) range has a lower resolution, but offers high intensity and requires less installation space. If certain angles of incidence are not present due to the arrangement and shape of the overall reflector and filter, the spectral ranges corresponding to those angles are not measured.

[0031] It is advantageous if the overall detector is composed of several individual detectors, each designed to detect light within a specific spectral range, and the spectral ranges assigned to the individual detectors are pairwise distinct. Two elements or spectral ranges are pairwise distinct if no two of them are identical. Additionally, each individual detector can be a subset of the overall detector, or the individual detectors can be independent elements.

[0032] It is also advantageous if the overall reflector is formed from several individual reflectors, each designed to reflect the light beam towards the overall filter. Furthermore, each individual reflector can be formed by a section of the overall reflector, or the individual reflectors can be independent elements.

[0033] Advantageously, the overall filter is formed from several individual filters, each of which is transparent to light of a predetermined spectral range, and the spectral ranges specified for the individual filters are pairwise distinct. Furthermore, each individual filter can be formed by a sub-range of the overall filter, or the individual filters can be independent elements. Preferably, each individual filter is formed from at least two filter units, each of which is transparent to light of a predetermined wavelength, wherein each individual filter has an angle-dependent transmittance for light of a predetermined spectral range, and the angle-dependent spectral transmittances specified for the individual filters are pairwise distinct. In this case, preferably, at least one pixel of a single detector can be read out and is associated with each filter unit.

[0034] Designing individual detectors, filters, and / or reflectors as sub-components of the overall detector, filter, and / or reflector leads, with appropriate design of the filter-based spectral sensor, to higher detection efficiency. Designing individual detectors, filters, and / or reflectors as independent elements has the advantage that their production is generally more cost-effective.

[0035] Preferably, a beam-shaping optic is arranged in the beam path of the light beam in, before, or after the light entrance aperture and is designed to change or adjust the divergence angle of the light beam so that the light beam enters the spectral sensor divergently or convergently. The beam-shaping optic can comprise a converging lens or a parabolic mirror that deflects the light beam towards the light entrance aperture. The beam-shaping optic can also comprise other refractive, reflective, diffractive, and / or hybrid optics, for example, two crossed cylindrical lenses with different radii of curvature.

[0036] If the overall reflector and filter are flat, and the overall reflector is inclined relative to the overall filter and / or the overall detector at an angle, the beam-shaping optics are preferably designed to change the divergence angle of the light beam so that it equals the inclination angle. If the divergence angle is smaller than the inclination angle and the distance between the overall reflector and filter is sufficiently large, there are areas of the overall filter and reflector that are not illuminated by the light beam and therefore do not contribute to the spectral analysis of the light beam. If the divergence angle is larger than the inclination angle and the distance between the overall reflector and filter is sufficiently small, there are areas of the overall filter and reflector that the light beam strikes multiple times during a single pass through the filter-based spectrometer.This is particularly advantageous when the overall filter has a low transmittance. If the divergence angle equals the tilt angle and the distance between the mirror and the angle-variable filter is correctly chosen, all areas of the overall reflector and the overall filter are utilized without being illuminated by more than one light beam during a single pass of the light beam.

[0037] Preferably, at least one prism or at least one mirror is provided at the end of the overall filter and the overall reflector facing away from the light entrance aperture to reflect the light beam reflected by the overall filter or the overall reflector back onto the overall filter or the overall reflector, thereby increasing the light yield. Since, depending on the wavelength and the angle of incidence of the light rays, only a portion of the light beam is transmitted to the overall detector at the overall filter, not the entire intensity of the light beam is transmitted at the overall filter when passing through the filter-based spectral sensor, depending on the design of the filter-based spectral sensor. Therefore, to increase the light yield, it is advantageous for the light beam to pass through the filter-based spectral sensor multiple times.It is also advantageous if the light beam follows a different path through the filter-based spectral sensor with each pass. This allows different areas of the overall filter and / or the same areas of the overall filter to be illuminated at a different angle. Alternatively, the same areas of the overall filter can be illuminated again at the same angle by the light rays. For this purpose, the at least one prism or mirror can be arranged and designed such that the light beam path is inverted. The light beam path is inverted when edge rays of the light beam take the path of the other edge ray after being reflected by the mirror or prism.Inverting the light beam path can be advantageous because, due to the different transmission properties of the areas of the overall filter, not every light ray of the light beam has the same spectral composition after passing through the filter-based spectrometer.

[0038] It is also possible to design the shape of the overall reflector so that the light beam passes through the filter-based spectral sensor multiple times without the need for a mirror or prism. This allows different areas of the overall filter, and / or the same areas of the overall filter, to be illuminated at a different angle. Alternatively, the same areas of the overall filter can be illuminated again at the same angle by the light rays.

[0039] The task is also solved by a sensor arrangement comprising at least two filter-based spectral sensors, wherein the at least two filter-based spectral sensors are coupled together in such a way that a beam of light entering a light entrance aperture passes through all filter-based spectral sensors at least once.

[0040] The invention is explained in more detail below with reference to exemplary embodiments and the accompanying drawings, which also disclose essential features of the invention. These exemplary embodiments serve only for illustration and are not to be interpreted as limiting. For example, a description of an exemplary embodiment with a plurality of elements or components is not to be interpreted as meaning that all of these elements or components are necessary for implementation. Rather, other exemplary embodiments may also contain alternative elements and components, fewer elements or components, or additional elements or components. Elements or components from different exemplary embodiments may be combined with one another unless otherwise specified.Modifications and variations described for one embodiment may also be applicable to other embodiments. To avoid repetition, identical or corresponding elements in different figures are designated with the same reference numerals and are not explained multiple times. The figures show: Fig. 1 A side view of a first embodiment of a filter-based spectral sensor and the beam path of a light beam in the filter-based spectral sensor, Fig. 2 a side view of a second embodiment of the filter-based spectral sensor, wherein the overall reflector is another overall filter, on the side of which facing away from the overall detector another overall detector is arranged, and wherein a beam shaping optic is present in the beam path of the light beam in front of the light entrance aperture, Fig. 3 a side view of a third embodiment of the filter-based spectral sensor, wherein the light beam diverges into the filter-based spectral sensor, Fig. 4 a side view of a fourth embodiment of the filter-based spectral sensor, wherein a mirror is provided at the end of the overall filter and overall reflector facing away from the light entrance aperture, and the overall filter is formed from several individual filters, the overall reflector is formed from several individual reflectors, and the overall detector is formed from several individual detectors. Fig. 5A a side view of a first embodiment of a sensor arrangement comprising two filter-based spectral sensors, wherein the filter-based spectral sensors are coupled such that a beam of light incident into a light entrance aperture of the first spectral sensor passes through both spectral sensors once, Fig. 5B a side view of a second embodiment of the sensor arrangement comprising two filter-based spectral sensors, wherein the filter-based spectral sensors are coupled such that a beam of light incident on a light entrance aperture of the first spectral sensor passes through both spectral sensors once, and Fig. 6 a side view of a fifth embodiment of the filter-based spectral sensor, wherein the overall reflector is curved and has a freeform shape.

[0041] In Fig. Figure 1 shows a first embodiment, not included in the invention, of a filter-based spectral sensor for the simultaneous spectral analysis of incident light, as well as a beam path of a light beam 2 originating from a sample and entering through a light entrance aperture 1. The spectral sensor has a total filter 3, which is transparent to light of a predetermined spectral range and is angle-variable. Due to the angular variability of the total filter 3, its transmission range depends on the angle of incidence β. iThe light rays 21 are incident on the composite filter 3. The light beam 2 has a diameter D and comprises a plurality of light rays 21 incident on the composite filter 3. The spectral sensor further comprises a composite reflector 4, which is arranged opposite the composite filter 3 and is designed to reflect the light rays 21 of the light beam 2 towards the composite filter 3. The spectral sensor also has a composite detector 5, which is designed to detect light rays 21 transmitted by the composite filter 3 and is arranged behind the composite filter 3 from the direction of the composite reflector 4. The composite reflector 4 and the composite filter 3 are planar, and the composite reflector 4 is inclined relative to the composite filter 3 and the composite detector 5 by an angle of inclination ε such that the angles of incidence β i The light rays 21 on the overall filter 3 change with each impact of the light rays 21. In Fig. 1 is this change in the angle of impact β i The angles of incidence β1 to β3 are indicated for the central ray of the light beam 2. Due to the inclination of the overall reflector 4 relative to the overall filter 3 by the angle of inclination ε, the difference between two adjacent angles of incidence β is i always 2ε. Therefore, for adjacent angles of incidence: β2 - β1 = 2ε.

[0042] The path of the light beam 2 runs back and forth between the composite filter 3 and the composite reflector 4, and the light beam 2 is completely reflected at the composite reflector 4 and partially reflected at the composite filter 3. Thus, at each point where the light beam 2 strikes the composite filter 3, a spectral component of the light beam 2 is reflected, depending on the angle of incidence β. i , transmitted and thus reaches the overall detector 5. This transmission is in Fig. 1 indicated by dashed lines.

[0043] The overall reflector 4 can be a further overall filter 6, on the side of which facing away from the overall detector 5 another overall detector 7 is arranged. A second embodiment of the filter-based spectral sensor, not included in the invention, with a further overall filter 6 and a further overall detector 7, is described in Fig. 2 shown. Also in Fig. 2 is the angle of impact β i The following are shown for the central ray of the light beam 2 for the first three angles of incidence β1 to β3.

[0044] The second embodiment also includes a beam shaping optic 8 in the beam path of the light beam 2, which is arranged in front of the light entrance aperture 1 and is designed to change a divergence angle γ of the light beam 2 so that the light beam 2 enters the spectral sensor collimated, divergent or convergent.

[0045] The beam-shaping optics 8 can be designed, in particular, to change the divergence angle γ of the light beam 2 so that it is equal to the inclination angle ε (not shown). In this case, the area of ​​the overall reflector 4 and the overall filter 3 is optimally utilized, provided the overall filter 3 is correctly spaced from the overall reflector 4.

[0046] Fig. Figure 3 shows a third embodiment of the filter-based spectral sensor. Here, too, the overall reflector 4 and the overall filter 3 are planar, and the overall reflector 4 is inclined relative to the overall filter 3 and the overall detector 5 by an angle of inclination ε. In this third embodiment, the light beam 2 enters the spectral sensor divergently through the light entrance aperture 1 and thus exhibits a divergence angle γ between the two marginal rays of the light beam 2. The angles of incidence β iThe light rays 21 of the light beam 2 are no longer the same for every light ray 21 in the case of a divergent light beam 2. Thus, the initial angle of incidence of the first light ray β differs. 11 due to the divergence of light beam 2 from the first angle of incidence of the second light beam β 21 and due to the inclination of the overall reflector 4 from the second angle of incidence of the first light ray β 12 .

[0047] A fourth embodiment of the filter-based spectrometer, not covered by the invention, is described in Fig. Figure 4 illustrates this. In the fourth embodiment, the overall detector 5 is formed from several individual detectors 51, each designed to detect light within a predetermined spectral range. The spectral ranges defined for the individual detectors 51 are pairwise distinct. The individual detectors 51 are independent elements. The overall reflector 4 is formed from several individual reflectors 41, each designed to reflect the light beam 2 towards the overall filter 3. The individual reflectors 41 are independent elements. Furthermore, the overall filter 3 is formed from several individual filters 31, each of which is transparent to light within a predetermined spectral range, and the spectral ranges defined for the individual filters 31 are pairwise distinct. The individual filters 31 are independent elements.The dimensioning of individual filters 31, individual reflectors 41 and individual detectors 51 depends on the diameter D of the light beam 2, the distance between the total filter 3 and the total reflector 4, the divergence of the light beam 2 and the shape of the total reflector 4.

[0048] Each individual filter 31 is formed from two filter units 32, each of which is transparent to light of a given wavelength, the wavelengths being different from each other.

[0049] At the end of the combined filter 3 and the combined reflector 4 facing away from the light entrance aperture 1, a mirror 9 is provided to reflect the light beam 2 reflected by the combined filter 3 or the combined reflector 4 back onto the combined filter 3 or the combined reflector 4, thereby increasing the light output. The path of the light beam 2 is inverted in this process, as the marginal light rays of the light beam 2 follow the path of the other marginal light ray after being reflected by the mirror 9.

[0050] In Fig. Figure 4 does not show all light rays 21 of the light beam 2; the middle light rays have not been drawn for the sake of clarity.

[0051] Fig. Figure 5A shows a first embodiment of a sensor arrangement with two filter-based spectral sensors. The two filter-based spectral sensors are coupled such that the light beam 2 incident into the light entrance aperture 1 passes through each of the filter-based spectral sensors once. The first overall reflector 4A of the first spectral sensor is tilted by a first angle ε. A inclined relative to the first overall filter 3A of the first spectral sensor and the second overall reflector 4B of the second spectral sensor is inclined by an angle ε B = - ε A inclined relative to the second overall filter 3B of the second spectral sensor. This results in the angles of incidence β i The angle of incidence is small shortly behind the light entrance aperture 1 of the first spectral sensor and large at the transition between the first and second spectral sensors. At the light exit aperture of the second spectral sensor, the angles of incidence β are... iagain small. The first filter-based spectral sensor also includes a first total detector 5A and the second filter-based spectral sensor includes a second total detector 5B.

[0052] Fig. Figure 5B shows a second embodiment of the sensor arrangement with two filter-based spectral sensors. The first overall reflector 4A of the first spectral sensor is tilted by an angle ε. A inclined relative to the first overall filter 3A of the first spectral sensor and the second overall reflector 4B of the second spectral sensor is inclined by an angle ε B = - ε A inclined relative to the second overall filter 3B of the second spectral sensor. This results in the angles of incidence β i The angle of incidence is large shortly behind the light entrance aperture 1 of the first spectral sensor and small at the transition between the first and second spectral sensors. At the light exit aperture of the second spectral sensor, the angles of incidence β are... iagain large. The first filter-based spectral sensor also includes a first total detector 5A and the second filter-based spectral sensor includes a second total detector 5B.

[0053] Due to different tilt angles ε of the overall reflectors 4A and 4B relative to the overall filters 3A and 3B, the impact angles β can be varied in a sensor arrangement. i and thus tailor the spectral properties of the spectral sensor.

[0054] The combination of two filter-based spectral sensors in the sensor arrangement is particularly advantageous when the first angle-variable overall filter 3A of the first spectral sensor and the second angle-variable overall filter 3B of the second spectral sensor differ. In the illustrated arrangement, both overall filters exhibit the same angles of incidence β. i of the light rays 21. For a specific angle of incidence β iHowever, the two composite filters are transmissive in different spectral ranges. For example, the first composite filter 3A might transmit a spectral range of 400–600 nm for the same angular range, while the second composite filter 3B transmits a spectral range of 600–800 nm for the same angular range. Thus, a larger spectral range can be analyzed with the same resolution, or the same spectral range with a higher resolution, using a compact and simple setup.

[0055] In Fig. Figure 6 shows a fifth embodiment of the filter-based spectrometer, which is also not covered by the invention. In the fifth embodiment, the overall reflector 4 is curved, such that the angle of incidence β iThe angles of incidence of the light rays 21 on the overall filter 3 change with each impact of the light rays 21. The light beam 2 enters the light entrance aperture 1 at a divergent angle. The overall reflector 4 has a curved freeform shape. Due to the curved shape, both the angles of incidence β i The light rays 21 as well as the area illuminated by the light rays 21 or the illuminated surface on the overall filter 3 are specified. If the light beam 2 is directed onto a large area of ​​the overall filter 3 with different angles of incidence β i When the light beam 2 strikes a small area with different angles of incidence β, a high resolution is achieved for the corresponding (spectral) range. i When the light hits the sensor, the corresponding (spectral) range has a lower resolution, but high intensity and requires less installation space. This is especially true when certain angles of incidence β are used. iBecause of the arrangement and shape of the overall reflector 4 and overall filter 3, the following do not occur at these angles of incidence β i Corresponding spectral ranges were not measured. Reference symbol list 1 light entry opening 2 light beams 21 Light beam 3 Total filters 3A first overall filter 3B second overall filter 31 individual filters 32 filter units 4 Total reflector 4A first overall reflector 4B second overall reflector 41 single reflector 5 Total detector 5A first total detector 5B second total detector 51 single detector 6 additional total filters 7 additional total detectors 8 Beam shaping optics 9 mirrors β i angle of impact γ Divergence angle ε Angle of inclination ε Afirst angle of inclination ε B second angle of inclination Diameter

Claims

[1] Filter-based spectral sensor for simultaneous spectral analysis of incident light, comprising: - a total filter (3) which is transparent to light of a specified spectral range, - a light entrance aperture (1) through which a light beam (2) to be analyzed, comprising a plurality of light rays (21), can fall onto the overall filter (3) with a diameter (D), - a composite reflector (4) arranged opposite the composite filter (3) and designed to reflect the light rays (21) of the light beam (2) in the direction of the composite filter (3), and - a total detector (5) designed to detect light rays (21) transmitted by the total filter (3), wherein - the path of the light beam (2) runs back and forth between the overall filter (3) and the overall reflector (4) and the light beam (2) is reflected at least partially at the overall reflector (4) and partially at the overall filter (3), - the overall reflector (4) and the overall filter (3) are planar and the overall reflector (4) is inclined relative to the overall filter (3) and the overall detector (5) by an angle of inclination (ε) such that the angle of incidence (β) i ) of the light rays (21) on the overall filter (3) change with each impact of the light rays (21), and - the overall filter (3) is angle-variable, so that a transmission range of the overall filter (3) depends on the angle of incidence (β) i ) the light rays (21) fall on the overall filter (3), characterized by , that - the light beam (2) spreads out divergently or convergently after the light entry aperture (1) in the spectral sensor. [2] Filter-based spectral sensor according to claim 1, wherein the total reflector (4) is a further total filter (6) on the side of which facing away from the total detector (5) a further total detector (7) is arranged. [3] Filter-based spectral sensor, comprising: - a total filter (3) which is transparent to light of a specified spectral range, - a light entrance aperture (1) through which a light beam (2) to be analyzed, comprising a plurality of light rays (21), can fall onto the overall filter (3) with a diameter (D), - a composite reflector (4) arranged opposite the composite filter (3) and designed to reflect the light rays (21) of the light beam (2) in the direction of the composite filter (3), and - a total detector (5) designed to detect light rays (21) transmitted by the total filter (3), wherein - the path of the light beam (2) runs back and forth between the overall filter (3) and the overall reflector (4) and the light beam (2) is reflected at least partially at the overall reflector (4) and partially at the overall filter (3), - the overall reflector (4) is curved at least section by section, such that the angle of incidence (β i ) of the light rays (21) on the overall filter (3) change with each impact of the light rays (21), and - the overall filter (3) is angle-variable, so that a transmission range of the overall filter (3) depends on the angle of incidence (β) i ) the light rays (21) fall on the overall filter (3), characterized by , that - the light beam (2) spreads out divergently or convergently after the light entry aperture (1) in the spectral sensor. [4] Filter-based spectral sensor according to claim 3, wherein the overall reflector (4) has the shape of a circular segment or a conic section. [5] Filter-based spectral sensor according to claim 3, wherein the overall reflector (4) has a freeform shape comprising curved shapes, asymmetric shapes or other freeform shapes. [6] Filter-based spectral sensor according to one of claims 1 to 5, wherein the overall detector (5) is formed from several individual detectors (51) and each individual detector (51) is designed to detect light of a predetermined spectral range and the spectral ranges predetermined for the individual detectors (51) are pairwise different. [7] Filter-based spectral sensor according to claim 6, wherein each individual detector (51) is formed by a sub-area of ​​the total detector (5) or the individual detectors (51) are independent elements of each other. [8] Filter-based spectral sensor according to any one of claims 1 to 7, wherein the overall reflector (4) is formed from several individual reflectors (41), each individual reflector (41) being designed to reflect the light beam (2) in the direction of the overall filter (3). [9] Filter-based spectral sensor according to claim 8, wherein each individual reflector (41) is formed by a part of the total reflector (4) or the individual reflectors (41) are independent elements of each other. [10] Filter-based spectral sensor according to one of claims 1 to 9, wherein the overall filter (3) is formed from several individual filters (31), wherein each individual filter (31) is transparent to light of a predetermined spectral range and the spectral ranges predetermined for the individual filters (31) are pairwise different. [11] Filter-based spectral sensor according to claim 10, wherein each individual filter (31) is formed by a sub-area of ​​the total filter (3) or the individual filters (31) are independent elements of each other. [12] Filter-based spectral sensor according to one of claims 10 or 11, wherein each individual filter (31) is formed from at least two filter units (32) which are each transparent to light of a predetermined wavelength, wherein each individual filter (31) has an angle-dependent transmittance to light of a predetermined spectral range and the angle-dependent spectral transmittances predetermined for the individual filters (31) are pairwise different. [13] Filter-based spectral sensor according to claim 12, wherein at least one pixel of a single detector (51) is assigned to each filter unit (32) and can be read out. [14] Filter-based spectral sensor according to one of claims 1 to 13, wherein a beam shaping optic (8) is arranged in the beam path of the light beam (2) in, before or after the light entrance aperture (1) and is designed to change a divergence angle (γ) of the light beam (2) such that the light beam (2) propagates divergently or convergently in the spectral sensor. [15] Filter-based spectral sensor according to claim 14, if referring back to claim 1 or 2, wherein the beam shaping optics (8) is designed to change the divergence angle (γ) of the light beam (2) so that it is equal to the tilt angle (ε). [16] Filter-based spectral sensor according to any one of claims 1 to 15, wherein at least one prism or at least one mirror (9) is provided at the end of the overall filter (3) and the overall reflector (4) opposite the light entrance aperture (1) to reflect the light beam (2) reflected from the overall filter (3) or the overall reflector (4) back onto the overall filter (3) or the overall reflector (4), thereby increasing the light yield. [17] Sensor arrangement comprising at least two filter-based spectral sensors according to any one of claims 1 to 16, wherein the at least two filter-based spectral sensors are coupled together such that a beam of light (2) incident into a light entry aperture (1) passes through all filter-based spectral sensors at least once.

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