Interference filter, optical device and method for manufacturing interference filter

Abstract

The interference filter comprises a substrate, a filter stack and at least one absorbing layer. The filter stack comprises alternating layers of optical coatings with different refractive indices arranged on the substrate. The at least one absorbing layer consists of a light absorbing material arranged on the substrate.

Description

[0001] The invention relates to an interference filter, an optical device and a method for manufacturing the interference filter.

[0002] Optical filters are generally considered to be devices that selectively transmit light of different wavelengths. Typically, optical filters are implemented using a substrate such as a glass or plastic plane that is either dyed as a whole, or has an interference coating. With regard to filter design, there are generally two categories of filters. Dichroic or interference filters are designed based on transmission and reflection. Layers of high and low refractive index materials are stacked to form a multilayer. Materials are intentionally selected to have low absorption in the wavelength region of interest. Absorption filters are typically made of dyed or colored glass or colored gelatin resins and operate by absorbing specific wavelengths while attenuating light. For dielectric dichroic filters, reflection and transmission are anti-coupled, which can cause problems in certain specific applications, such as image sensor applications.

[0003] Figure 4 An optical sensor device with an interference filter from the prior art is shown. The optical sensor device comprises an optical sensor OS, for example an image sensor, which is arranged in a housing HO behind an interference filter IF. The interference filter in this example is, for example, an infrared (IR) cut-off filter or a short-pass filter and is therefore, for example, designed to reflect or block mid-infrared wavelengths while passing visible light. The transmission spectrum of this filter is in the range Figure 4 The spectrum shows the cut-on wavelength at 635nm. The cut-off wavelength is the term used to denote the wavelength at which the transmission in a short-pass filter drops to 50% of the total. The cut-off wavelength is denoted by λ cut-off The operating wavelength is represented by λ cut-on represents, and corresponds to the wavelength at which the transmission in a longpass filter increases to 50% of the total. Bandpass filters have both an operating wavelength and a cut-off wavelength.

[0004] The figure shows several arrows of incident light transmitted or reflected at the optical interface of the optical sensor device. The percentages in the figure are based on the incident light intensity I in A relative intensity equal to 100% is given. In the figure, arrow A1 represents green or blue incident light. This light passes through the filter with high transmittance (for example 99%), as shown by arrow A11. At the interference filter, a smaller amount of light (for example 1%) is reflected, as shown by arrow A12. The light that passes through irradiates the optical sensor OS and most of it is absorbed by the sensor or the substrate of the sensor. A certain amount of light (for example 10%) is reflected back to the interference filter IF, as shown by arrow A13. Most of the incident light passes through the filter again, as shown by arrow A14, for example, about 9.9% of the incident light is reflected through the filter and the sensor.

[0005] If white light is incident on the optical sensor device, the situation is different. White light has a contribution from green or blue incident light similar to the above case and as shown by arrow A2 in the figure. Arrow A3 represents light at the operating wavelength (e.g. 635nm). This light is 50% transmitted and 50% reflected (see arrows A31 and A32 respectively). Likewise, as shown by arrow A33, a certain amount (e.g. 5%) of light is reflected from the sensor back to the interference filter IF. However, the filter passes and reflects light equally at the operating wavelength. For example, the filter passes another certain amount (e.g. about 2.5%) of the incident light, as shown by arrow A34. In addition, as shown by arrow A35, a certain amount (e.g. another 2.5%) of light is reflected back to the optical sensor. Such back reflections or internal reflections are a common problem and can result in undesired signals, thereby reducing the signal-to-noise ratio in the optical sensor system.

[0006] FIG. 5A to FIG. 5C An example of back reflection in a prior art interference filter is shown. Figure 5A A dichroic filter is described which comprises a substrate SB and a filter stack FS of alternating layers of optical coatings with different refractive indices. An interference filter is arranged at a distance from the optical sensor OS.

[0007] Light is represented by I in The incident light is partially reflected at the filter stack FS. The intensity of the reflected light is I r =R·I in , where R represents the reflectance or relative reflectance contribution. However, some light will eventually transmit through the filter stack, depending on its transmission spectrum. The transmitted intensity is given by I out =T·I in is given by , where T represents the transmission coefficient or the relative transmission contribution. The transmitted light can then be reflected at the optical sensor (e.g. at its substrate). The reflected intensity is given by T·R sub I in Given, where R sub represents the reflectance or relative reflectance contribution of the sensor. Some of this reflected light may be transmitted back to the filter stack FS and may experience additional reflections inside the filter stack (see the dashed arrows in the figure). In addition, there may be another reflection at the filter stack towards the optical sensor. The intensity of this "back-reflected" light is I br =BR·T·R sub I in , where BR represents the back reflection coefficient or relative back reflection contribution.

[0008] Figure 5BThe transmission and reflection contributions of a prior art interference filter are shown. All graphs assume normal incidence. Furthermore, the substrate reflection is assumed to be 100%. Graphs g1 and g2 show the transmission coefficient and reflection coefficient as a function of wavelength, respectively, as introduced above. Graph g3 shows the absorption of the filter stack FS as a function of wavelength. Finally, graph g4 shows the back reflection coefficient as a function of wavelength. Graphs g1 and g2 intersect at the operating wavelength and are essentially opposite for wavelengths greater than the operating wavelength. This is a characteristic of a long pass filter.

[0009] Figure 5C The transmission and back reflection contributions of a prior art interference filter are shown. The graph represents the product of the back reflection coefficient BR and the transmission coefficient T as a function of wavelength. The peak indicates that the back reflection intensity at the cut-off is approximately 25% of the incident light.

[0010] Fig. 6A and Figure 6B Shows Figure 5A Another example of back reflection in a prior art interference filter IF. In fact, these figures are similar to Figure 5B and Figure 5C The figure in Figure 2 corresponds to that in Figure 3, but is simulated for different angles of incidence AOI (i.e., 0°, 15°, 30°, and 40°). This situation is similar to normal incidence, as the maximum back-reflected intensity remains essentially constant at 25% for higher AOIs. In addition, the peak becomes spectrally broader for higher AOIs.

[0011] It is an object of the present invention to provide an interference filter, an optical device and a method for producing an interference filter which allow the influence of back reflections to be reduced.

[0012] These objects are achieved by the subject-matter of the independent claims. Further developments and embodiments are described in the dependent claims.

[0013] It should be understood that, unless described as an alternative, any feature described with respect to any embodiment may be used alone or in combination with other features described herein, and may also be used in combination with one or more features of any other embodiment, or in combination with any combination of any other embodiment. In addition, equivalents and modifications not described below may also be employed without departing from the scope of the interference filter, optical device, and method of manufacturing the interference filter as defined in the appended claims.

[0014] The following relates to improved concepts in the field of optical filters. The proposed concept provides a solution to undesired back reflections in optical filters (e.g. dichroic filters) based on a hybrid filter design. One aspect involves decoupling transmission and reflection from each other by introducing an absorption layer with a light absorbing material. The back reflection can be shifted to shorter wavelengths and lower levels. For example, the back reflection intensity can be reduced by about five times compared to an all-dielectric filter.

[0015] In at least one embodiment, an interference filter includes a substrate, a filter stack, and at least one absorbing layer. The filter stack includes alternating layers of optical coatings with different refractive indices arranged on the substrate. At least one absorbing layer is composed of a light absorbing material arranged on the substrate.

[0016] The substrate provides the base of the interference filter or dichroic filter. For example, the optical coating is arranged on the substrate by coating technology. A series of optical coatings can be applied to the substrate. These coatings may have different material properties (such as different refractive indices). The material properties can be selected so that the unwanted part of the light is reflected, while the rest is transmitted to a certain extent. In addition, the reflected light and the transmitted light may interfere with each other. For example, the alternating layers form a series of continuous reflection cavities that resonate with one or more desired wavelengths. When the peaks and troughs of the waves overlap, other wavelengths are destructively cancelled or reflected.

[0017] Interference filters comprise a filter stack and at least one absorbing layer. That is, as a whole, the filter stack and the at least one absorbing layer form an interference filter. The filter can be considered a hybrid interference filter. Individual absorption filters are usually made from a substrate such as glass to which various inorganic or organic compounds are added. These compounds or light absorbing materials absorb at certain wavelengths of light while transmitting at other wavelengths of light. These compounds can also be added to other substrates such as plastics (usually polycarbonate or acrylic) to produce gel filters, which are lighter and cheaper than glass-based filters.

[0018] It has been found that by introducing an absorption layer made of a light absorbing material, the back reflection effect can be significantly reduced. For example, the back reflection intensity can be reduced by a factor of 5 or more compared to an all-dielectric filter.

[0019] In at least one embodiment, at least one absorbing layer is arranged on a surface of the filter stack. Additionally, or alternatively, at least one absorbing layer is arranged between layers of the filter stack.

[0020] That is, the absorbing layer is associated with the filter stack in that the absorbing layer can be considered as an integral part of the filter stack, for example as one of the alternating layers or additional layers of the filter stack. This is in contrast to, for example, colored glass. Such glass is often used as an absorbing filter and light absorbing materials can be added to the glass. For example, there can be a certain distance between the absorbing layer and the filter stack relative to the substrate.

[0021] At least one absorbing layer has an absorption spectrum, for example characterized by an absorption spectrum or absorption coefficient of its light absorbing material. Back reflection of light originates from reflection from the substrate or photosensitive surface of the optical sensor. However, this reflected light needs to propagate through the absorbing layer. The intensity of the reflected light can be reduced by absorption, and thus the intensity of the back reflection can be reduced.

[0022] In the embodiments discussed herein, there may be more than one absorption layer. For example, a given light absorbing material may not be able to absorb reflected light sufficiently. Therefore, a combination of light absorbing materials arranged in the same absorption layer or in different absorption layers may increase the absorption to a desired level. Furthermore, the absorption layers may also be arranged at different levels of the filter stack, i.e. at different distances relative to the substrate. In this way, several absorption levels may be established, further reducing back reflections.

[0023] In at least one embodiment, at least one absorbing layer is disposed on the substrate-facing surface of the filter stack. Disposing the absorbing layer at least on the substrate-facing surface of the filter stack can minimize back reflections. Furthermore, this can be a fairly cost-effective approach, as the absorbing layer can be coated on the filter stack rather than incorporated into the filter stack.

[0024] In at least one embodiment, the surface of the substrate facing the filter stack has a limited distance from the at least one absorbing layer. In addition, there may be a certain distance between the at least one absorbing layer and the substrate, which is established, for example, by an intermediate layer (e.g., a dielectric layer) or by a spacer between the absorbing layer and / or the filter stack and the substrate. This distance can be used to reduce the effect of spectral broadening.

[0025] In at least one embodiment, a layer of the optical coating is characterized by a total transmission spectrum and a total reflection spectrum. The total transmission spectrum and the total reflection spectrum are coupled. For example, the two spectra are entangled so that the direction of the total transmission spectrum determines the direction of the total reflection spectrum and vice versa. At least one absorbing layer has an absorption spectrum that is arranged to decouple the total transmission spectrum from the total reflection spectrum.

[0026] For example, in common dichroic filters, the total transmission spectrum and the total reflection spectrum are coupled. This fact is one of the root causes of back reflections in prior art filter designs. In fact, the back reflection intensity at a given wavelength depends on the product of the transmission or reflection contribution and the absorption contribution. Usually, the back reflection intensity at the cut-off or operating wavelength is located at a peak. However, since the intensity also depends on the absorption due to the absorbing layer, the absorption contribution in the above product can be used to reduce the intensity peak.

[0027] In at least one embodiment, the total transmission spectrum and the total reflection spectrum are complementary, so that reflection and transmission are anti-entangled, that is, they are considered to be mathematically inverse functions. Absorbing layers can be used to decouple the spectra so that the anti-entanglement no longer holds. This allows the intensity of the back reflection to be reduced.

[0028] In at least one embodiment, the total transmission spectrum and the total reflection spectrum are arranged to give the interference filter a long-pass spectrum with at least one spectral working wavelength or a short-pass filter spectrum with at least one spectral cut-off wavelength. In addition, at least one absorption peak of the absorption spectrum of at least one absorption layer is matched to the cut-off or working wavelength.

[0029] Matching the cut-off or operating wavelength to the absorption peak provides an effective way to reduce the back reflection intensity. As described above, the coupling of the total transmission spectrum and the total reflection spectrum may result in a peak in the back reflection intensity. This peak may coincide with or be close to the cut-off or operating wavelength. Therefore, by matching the absorption peak, the intensity peak may be reduced. This can be seen from the product discussed above, i.e., the product of the transmission or reflection contribution and the absorption contribution. Absorption cancels out the transmission and reflection contributions and may result in a reduction in the overall intensity.

[0030] In at least one embodiment, the total transmission spectrum and the total reflection spectrum are arranged to give the interference filter a bandpass filter spectrum with one or more spectral cutoffs and / or one or more spectral operations. At least one absorption peak of the absorption spectrum of at least one absorption layer is matched to the one or more cutoffs and / or one or more operations.

[0031] In at least one embodiment, the light absorbing material comprises an indium tin oxide compound denoted as ITO. The ITO compound comprises a ternary composition of indium, tin and oxygen in given relative proportions. ITO is a high refractive index material and can be used in filter stacks. In ultraviolet (UV), ITO absorbs easily.

[0032] In at least one embodiment, the substrate comprises a glass, plastic or film substrate. The substrate can be arranged as an absorption filter, such as a colored glass, and also includes a light absorbing material. In this way, the substrate can contribute to the overall spectral characteristics of the interference filter hybrid. For example, the substrate can be configured as an IR cutoff filter, and the filter stack with the absorption layer cuts off in the UV. For this filter design, only one type of substrate, such as a colored glass, needs to be used, which reduces the overall cost of the filter. In at least one embodiment, the substrate is a monochromatic glass, which has a cutoff in the infrared region IR.

[0033] In at least one embodiment, the substrate has an absorption spectrum that is different from the light absorbing material of the at least one absorbing layer.Giving the substrate well-defined absorption characteristics allows for more freedom in designing the interference filter.

[0034] In at least one embodiment, the optical device comprises an optical sensor. According to the above aspects, the optical sensor is supplemented by at least one interference filter. For example, the resulting optical sensor is less susceptible to back reflections, which improves the signal-to-noise ratio. In addition, it has been found that the proposed concept also reduces the impact of spectral shifts due to different angles of incidence, which allows for improved spectral and color perception.

[0035] In at least one embodiment, the optical sensor includes an image sensor. Image sensors, which typically have a photodetector array, have the advantages of reducing back reflections, increasing the signal-to-noise ratio, and reducing spectral shifts. These allow applications, such as low-light, spectral, or wide-angle applications, even under optically unfavorable conditions.

[0036] In at least one embodiment, a method of manufacturing an interference filter includes the steps of providing a substrate and arranging a filter stack on the substrate. The filter stack includes alternating layers of optical coatings with different refractive indices. In addition, at least one absorption layer is arranged on the substrate and includes a light absorbing material.

[0037] In at least one embodiment, at least one absorbing layer is arranged on a surface of the filter stack.Alternatively or additionally, at least one absorbing layer is arranged between layers of the filter stack.

[0038] In the following, the above-proposed concepts will be described in more detail with reference to the accompanying drawings, in which examples of embodiments are presented. In the embodiments and drawings presented below, similar or identical elements may each have the same reference numerals. However, the elements shown in the drawings and their dimensional relationships to each other should not be regarded as true proportions, but individual elements such as layers, components and regions may be enlarged to achieve better illustration or better understanding.

[0039] Figures 1A to 1C shows the back reflection of an example hybrid interference filter,

[0040] FIG. 2A to FIG. 2B shows the back reflection of an example hybrid interference filter at different incident angles,

[0041] FIG. 3A to FIG. 3D Other example embodiments of interference filters are shown,

[0042] Figure 4 shows an optical sensor device with an interference filter from the prior art,

[0043] FIG. 5A to FIG. 5C shows an example of back reflection of a prior art interference filter at normal incidence, and

[0044] FIG. 6A to FIG. 6B Examples of back reflections from a prior art interference filter at various angles of incidence are shown.

[0045] Figure 1A to Figure 1C Back reflection in an example interference filter is shown. Figure 1A Depicted is a dichroic filter comprising a substrate SB and a filter stack FS of alternating layers of optical coatings with different refractive indices, arranged at a distance from an optical sensor OS, such as an image sensor. Furthermore, an absorption layer AL of a light absorbing material is arranged on the substrate.

[0046] The filter stack FS in this example is configured as a long pass filter with an operating wavelength λ at 412 nm. cut-on Such work is the result of specialized filter designs, for example based on simulations of alternating layers of optical coatings with different refractive indices and material properties.

[0047] The absorption layer AL is applied on the surface of the filter stack FS. This surface faces the substrate SB and thus the optical sensor OS. The light absorbing material comprises an indium tin oxide compound denoted ITO. The ITO compound comprises a ternary composition of indium, tin and oxygen in given relative proportions. ITO is a high refractive index material and has an absorption in the ultraviolet UV. In addition, as can be seen from Figure 1B As can be seen, the ITO compound has a wavelength close to the working wavelength λ at 412nm. cut-on Therefore, it can be considered that the working wavelength and the absorption peak match.

[0048] The substrate SB is arranged as an absorption filter. In this embodiment, the substrate is a colored glass comprising a light absorbing material. The colored glass in this example is cut-off in the IR. For example, the absorption layer AL and the filter stack FS are applied to the glass using a multilayer coating. In this way, the colored glass contributes to the overall spectral properties of the interference filter IF, which can be regarded as a hybrid filter.

[0049] For this filter design, only one type of substrate, such as colored glass, needs to be used, which reduces the overall cost of the filter. The multilayer coating of the filter stack serves both as an anti-reflective coating ARC and as a UV cutoff.

[0050] Light is represented by I in The incident light is partially reflected at the filter stack FS. The intensity of the reflected light is I r =R·I in , where R represents the reflectance or relative reflectance contribution. However, some light eventually passes through the filter stack FS, depending on its transmission spectrum. The transmitted intensity is given by I out =T·I in where T denotes the transmission coefficient or the relative transmission contribution. The transmitted light can then be reflected at the optical sensor OS, for example at its substrate, with the reflection being expressed as T·R sub I in Given, where R sub represents the reflectance or relative reflectance contribution of the optical sensor. Some of this reflected light may be transmitted back to the filter stack and experience additional reflections (see the dashed arrows in the figure). In addition, there may be another reflection at the filter stack FS. The intensity of this back-reflected light is I br =BR·T·R sub I in , where BR represents the back reflection coefficient or the relative back reflection contribution. However, due to the absorption layer AL, the back reflection coefficient BR also depends on the absorption in the absorption layer AL. Therefore, the intensity of the back reflected light I is smaller than that in the absence of the absorption layer AL. br reduce.

[0051] Figure 1B Shows Figure 1A The transmission and reflection contributions of the interference filter are shown in Figure 1. All graphs assume normal incidence. Furthermore, the substrate reflection is assumed to be 100%. Graphs g1 and g2 show the transmission and reflection coefficients as functions of wavelength, respectively, as introduced above. Graph g3 shows the absorption of the filter stack as a function of wavelength. Finally, graph g4 shows the back reflection coefficient as a function of wavelength.

[0052] Graphs g1 and g2 intersect at the operating wavelength. However, it is clear that these graphs are decoupled, as they are no longer inverse for wavelengths greater than operation, as is the case in prior art filters without an absorption layer AL. Furthermore, graph g3 shows a peak that matches or is close to the operating wavelength. Thus, absorption cancels out the transmission and reflection contributions and results in a reduction in the overall intensity of the back reflection.

[0053] Figure 1C Shows Figure 1AThe transmission and back reflection contributions of the interference filter. The graph represents the product of the back reflection coefficient BR and the transmission coefficient T as a function of wavelength. The peak indicates that the back reflection intensity is about 5% of the incident light at the working wavelength. Therefore, by introducing an absorption layer and a light absorbing material arranged in the absorption layer, T and R can be decoupled from each other. By shifting BR to shorter wavelengths and lower levels, the back reflection intensity can be reduced by about 5 times compared to a full dielectric filter, for example FIG. 5A to FIG. 5C shown.

[0054] Figure 2A and Figure 2B The T, R and T*BR of the example hybrid interference filter at different incident angles are shown. In fact, these figures correspond to Figure 1B and Figure 1C These graphs are based on Figure 1A The same interference filter in Figure 1 is established. However, the same graphs g1 to g4 are modeled for different angles of incidence AOI (i.e. 0°, 15°, 30° and 40°) and indexed using these angles for easy reference. The situation is similar to normal incidence, i.e. the maximum back-reflected intensity remains essentially at a low level of about 5% for higher AOIs. There is only a low spectral broadening.

[0055] Figures 3A to 3D Other example embodiments of interference filters are shown. The proposed dichroic filter is based on the filters shown in the previous figures. The filter comprises a substrate SB and a filter stack FS of alternating layers of optical coatings with different refractive indices, to be arranged at a distance from an optical sensor OS (e.g. an image sensor).

[0056] Figure 3A Describes the Figure 1A A dichroic filter of the filter shown in . The filter comprises a substrate SB and a filter stack FS of alternating layers of optical coatings with different refractive indices, arranged at a distance from an optical sensor OS (e.g. an image sensor). In addition, an absorption layer AL of a light absorbing material is arranged on the substrate. The absorption layer AL is coated on the surface of the filter stack FS. This surface faces the substrate SB. As will be shown below, the absorption layer AL can be located anywhere in the filter stack, i.e. on the upper surface, the lower surface or between the upper and lower surfaces. In this embodiment, the filter stack FS is arranged on the lower surface of the substrate, i.e. on the surface facing the optical sensor OS. In order to emphasize the relative position of the absorption layers in the filter stack, these layers are not scaled.

[0057] As mentioned above, light can be represented as I in The incident light is partially reflected at the filter stack FS. The intensity of the reflected light is I r =R·Iin , where R represents the reflectance or relative reflectance contribution. However, some light eventually passes through the filter stack FS, depending on its transmission spectrum. The transmitted intensity is given by I out =T·I in where T denotes the transmission coefficient or the relative transmission contribution. The transmitted light can then be reflected at the optical sensor OS, for example at its substrate, with the reflection being expressed as T·R sub I in Given, where R sub represents the reflectance or relative reflectance contribution of the optical sensor. Some of this reflected light may be transmitted back to the filter stack and experience additional reflections (see the dashed arrows in the figure). In addition, there may be another reflection at the filter stack FS. The intensity of this back-reflected light is I br =BR·T·R sub I in , where BR represents the back reflection coefficient or the relative back reflection contribution. However, due to the absorption layer AL, the back reflection coefficient BR also depends on the absorption in the absorption layer AL. Therefore, the intensity of the back reflected light I is smaller than that in the absence of the absorption layer AL. br reduce.

[0058] In addition, Figure 3B In , an absorption layer AL of light absorbing material is arranged between the layers of the filter stack FS, ie alternating layers of optical coatings with different refractive indices. Figure 3C In , there are several absorbing layers AL arranged between the layers of the filter stack. Figure 3D In the embodiment shown, the absorption layer AL is located on the outer surface (top or bottom) of the filter stack FS. In fact, one or more absorption layers AL can be placed anywhere in the filter stack.

[0059] The absorbing layer(s) are associated with the filter stack in that the absorbing layer(s) can be considered as an integral part of the filter stack, for example as one of the alternating layers or additional layers of the filter stack. In other words, the alternating layers of the optical coating and the absorbing layer(s) constitute an interference filter. In terms of filter design, the total transmission spectrum and the total reflection spectrum are no longer coupled or entangled, as they are inverse functions. Instead, the contribution of one or more absorbing layers needs to be considered. Transmission, reflection and absorption need to satisfy the general requirement that the product of transmission, reflection and absorption is equal to 1.

[0060] Including absorbing layers as an integral part of the filter stack allows the need for these additional absorbing materials to be avoided by carefully selecting the optical constants of the materials in the interference filter itself. In other words, the interference filter multilayer structure no longer relies solely on the typical T and R, but instead incorporates materials with absorbing functions. Not only do these layers interfere constructively and destructively, they also absorb at specific wavelengths depending on the intended application. This is a completely different approach compared to the prior art, where optical filter designs for interference filters typically aim to use non-absorbing materials. However, the argument put forward here is that for applications such as image sensors, some absorption in interference filters may be advantageous, for example in reducing back reflections. The proposed concept simplifies the overall design by avoiding the need for additional absorbing materials such as colored glass, colored resins or dyes.

[0061] Reference numerals

[0062] A1 to A35 (light) arrow

[0063] FS Filter Stacks

[0064] G1 to G4 curve graph

[0065] HO Housing

[0066] IF Interference Filters

[0067] OS Optical Sensor

[0068] SB substrate

Claims

1. An interference filter, comprising: -Substrate (SB), - a filter stack (FS) comprising alternating layers of optical coatings with different refractive indices arranged on a substrate (SB), and - at least one absorbing layer (AL) of a light absorbing material arranged on the substrate (SB), - wherein the optical coating has an overall transmission spectrum having at least one spectral cut-off and / or at least one spectral working, and - at least one absorption peak of the absorption spectrum of the at least one absorption layer (AL) is matched to the at least one spectral cut-off and / or the at least one spectral working so that the intensity (I) of the back-reflected light transmitted through the interference filter (IF), subsequently partially reflected from the optical sensor (OS) back to the interference filter (IF) and further partially reflected at the filter stack (FS) back to the optical sensor (OS) is BR )reduce, The spectral cutoff is the wavelength at which the transmission in a short-pass filter is reduced to 50% of the total; the spectral working is the wavelength at which the transmission in a long-pass filter is increased to 50% of the total.

2. The interference filter according to claim 1, wherein: - the at least one absorbing layer (AL) is arranged on a surface of the filter stack (FS), and / or - The at least one absorbing layer (AL) is arranged between the layers of the filter stack (FS).

3. The interference filter according to claim 1 or 2, wherein: - the layers of the optical coating are characterized by total transmission spectra and total reflection spectra, - the total transmission spectrum and the total reflection spectrum are coupled so that the trend of the total transmission spectrum depends on the trend of the total reflection spectrum and vice versa, and The at least one absorption layer has an absorption spectrum which is arranged to decouple the total transmission spectrum and the total reflection spectrum.

4. The interference filter according to claim 3, wherein: The total transmission spectrum and the total reflection spectrum are complementary, so that reflection and transmission are anti-entangled.

5. The interference filter according to claim 3, wherein: - the total transmission spectrum and the total reflection spectrum are arranged to impart a long pass spectrum to the interference filter, said long pass spectrum having at least one spectrally operating wavelength, or - the total transmission spectrum and the total reflection spectrum are arranged to impart a short-pass spectrum to the interference filter, the short-pass spectrum having at least one spectral cut-off wavelength, and - at least one absorption peak of the absorption spectrum of the at least one absorption layer matches the at least one spectral cut-off wavelength or the at least one spectral operating wavelength.

6. The interference filter according to claim 3, wherein: - the total transmission spectrum and the total reflection spectrum are arranged to give a bandpass filter spectrum as an interference filter, said bandpass filter spectrum having at least one spectral cut-off, and At least one absorption peak of the absorption spectrum of the at least one absorption layer is matched to the at least one spectral cutoff and / or to the at least one spectral operation.

7. The interference filter according to claim 1 or 2, in, The light absorbing material includes an indium tin oxide compound denoted as ITO, the indium tin oxide compound including a ternary composition of indium, tin and oxygen in given relative proportions.

8. The interference filter according to claim 1 or 2, wherein: The substrate (SB) includes a thin film substrate.

9. The interference filter according to claim 1 or 2, wherein: The substrate (SB) has an absorption spectrum that is different from the light absorbing material of the at least one absorbing layer (AL).

10. The interference filter according to claim 8, wherein: - The substrate (SB) is a monochromatic glass, and, - The monochromatic glass has a cut-off in the infrared region IR.

11. The interference filter according to claim 1 or 2, wherein: The surface of the substrate (SB) facing the filter stack (FS) is at a finite distance from the at least one absorbing layer (AL).

12. The interference filter according to claim 1 or 2, wherein: The substrate (SB) includes a glass substrate or a plastic substrate.

13. An optical device comprising: - Optical Sensor (OS), and - at least one interference filter (IF) according to one of claims 1 to 12.

14. The optical device according to claim 13, wherein: The optical sensor (OS) includes an image sensor.

15. A method for manufacturing an interference filter, comprising the following steps: - Provide a base plate (SB), - arranging a filter stack (FS) on a substrate (SB), said filter stack (FS) comprising alternating layers of optical coatings having different refractive indices, and - at least one absorbing layer (AL) of a light absorbing material is arranged on the substrate (SB), - wherein the optical coating has an overall transmission spectrum having at least one spectral cut-off and / or at least one spectral working, and - at least one absorption peak of the absorption spectrum of the at least one absorption layer (AL) is matched to the at least one spectral cut-off and / or the at least one spectral working so that the intensity (I) of the back-reflected light transmitted through the interference filter (IF), subsequently partially reflected from the optical sensor (OS) back to the interference filter (IF) and further partially reflected at the filter stack (FS) back to the optical sensor (OS) is BR )reduce, The spectral cutoff is the wavelength at which the transmission in a short-pass filter is reduced to 50% of the total; the spectral working is the wavelength at which the transmission in a long-pass filter is increased to 50% of the total.

16. The method according to claim 15, wherein: - the at least one absorbing layer (AL) is arranged on a surface of the filter stack (FS), and / or - The at least one absorbing layer (AL) is arranged between the layers of the filter stack (FS).

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