HK1239805B - Optical filter element for devices for converting spectral information into location information - Google Patents

Description

Optical filter element for a device for converting spectral information into positional information

Technical Field

The present invention relates to an optical filter element for a device for converting spectral information into position information, wherein the device has a detector connected for detecting a signal, and the optical filter element comprises at least two microresonators, wherein the microresonator has at least

- at least two face-superposed reflective layer structures consisting of at least layers of a material with a high refractive index and layers of a material with a low refractive index in an alternating sequence, and

At least one areally superimposed resonant layer, which is respectively arranged between two areally superimposed reflective layer structures.

Background Art

Spectral analysis of optical signals requires separating them into their individual wavelengths, which are then converted into an electrically usable data stream by a signal converter for evaluation. This is accomplished by converting the spectral information into positional information. To date, diffraction/refraction elements (gratings, prisms) have been used for this purpose, which must have sufficient geometric dimensions for high spectral resolution (i.e., sufficiently broad beam splitting of the incident light). Furthermore, the relative orientation of the optical elements must be sufficiently thermally and mechanically stable to avoid system failures during measurement. Consequently, existing spectrometers are either not suitable for all applications or are too costly for their intended purpose.

In the past, the direction of technical development of spectrometers was miniaturization and cost reduction. Current devices fit in the palm of your hand (e.g., USB spectrometers) and therefore achieve sufficient resolution (≈1 nm full width at half maximum (FWHM)) and an acceptable signal-to-noise ratio (1:1000). The basic principle of measurement has not changed significantly. The input signal is projected onto a dispersive element via optical components (e.g., lens systems, optical fibers) and an inlet slit. A prism or grid is usually used for this. The signal spectrally separated by the dispersive element is then directed to a detector, where its signal can then be further processed. In order for the separated signals to be resolvable by the individual elements of the detector, the signal path has a length that depends on the deflection angle of the dispersive element. This length cannot be shortened arbitrarily, so the spectrometer therefore has a minimum overall size.

An alternative implementation of a spectrometer involves the use of bandpass filters and detector units with locally variable filter characteristics. In document US Pat. No. 6,057,925 A, the filter element described under the term LVF “Linear variable filter” is based on interference effects and is usually composed of a layer system of metal thin layers and/or a layer system of dielectric thin layers, which are technically applied to the substrate in such a way that the layer thickness and therefore the transmission characteristics are variable with respect to direction. The individual components of the input signal are thus attenuated with different strengths depending on the position. By prior calibration, spectral information can be obtained from the positioning of the active detector element. Due to the flat structural shape of the filter and detector, the components can be implemented in a particularly compact and robust manner in the spectral resolution and spectral measurement parts.

However, exploiting interference effects to separate light results in filters that exhibit a directional dependence on the incident signal. The greater the angle of incidence from normal light incidence, the more strongly the spectral filter characteristics shift toward shorter wavelengths. Consequently, a clear correlation between active detector elements and filtered wavelengths no longer exists, and the actual spectral resolution deteriorates significantly compared to the theoretically possible spectral resolution (defined by the filter characteristics and the detector resolution). To avoid directional effects, the input signal must be optically adjusted accordingly before and during passage through the structural element so that it lies within a narrow angular range.

The document US 6 785 002 B2, "Variable filter-based optical spectrometer," or the document US 2004/032584 A, "Optical channel monitoring device," describes the basic structure and function of such integrated systems for use in the field of communications, using split-multiplexed signals. Here, light emerging from an optical fiber reaches a lens system and is then collimated onto a filter element. The individual spectral components are then detected by a downstream sensor. For high resolution, an etalon with a dielectric mirror is recommended for the variable filter element.

US 2003/058447 A1, "Colorimeter apparatus for color printer ink," describes a construction element in which the direction selection is performed by a matrix of glass fibers or by a flat collimator between the detector and the filter. To further increase the resolution, a second glass fiber matrix or a collimator can be used on the inlet side of the filter.

Self-focusing lens arrays, as described for example in US 2010/092083 A1 “In-line linear variable filter based spectrophotometer”, are also cited as further variants for directional limitation of the incident signal.

Another variant of a spectroscope using linear variable filters is described in US Pat. No. 5,144,498 A, "A variable wavelength light filter and sensor system." Here, incident light is deflected by reflection onto up to two variable filters, then onto an optional third filter element and subsequently onto a detector. In this configuration, the filters can also be located on the same side of the prism.

A disadvantage of the aforementioned solutions is that partially spatially extended optical systems or additional components that are complex to produce are required in order to obtain suitable spectral information from the combination of variable bandpass filter and detector.

Document US 2007/0148760 A1 describes a method for detecting chemicals and biomolecules, which comprises the following steps:

- light is generated by a light source,

- light is incident on/into the optical sensor, and when the optical sensor is illuminated with a broad optical wavelength band, the optical sensor emits a narrow optical wavelength band,

- transmitting the output light from the sensor to a detector having an entry face comprising at least one layer with transversely variable transmission properties, and

- Using the localization of the output light with the aid of a detector in order to detect the analyte present (chemical or biomolecule).

Accessory devices include

- a light source, which generates a broad band of optical wavelengths,

an optical sensor that outputs a narrow optical wavelength band when illuminated with a broad optical wavelength band from a light source,

- a detector comprising at least one layer with a transversely variable transmission property, which receives the output light that has passed through the optical sensor, wherein at least one layer allows a portion of the received light to pass through in a position of the at least one layer, and the detector uses this position to detect the current analyte.

Furthermore, document US 2007/0148760 A1 describes a method for obtaining information about an analyte, wherein the method comprises:

an excitation of the analyte at an analyte wavelength converter in that the converter generates output light, wherein the output light indicates analyte information,

Propagating the output light to an entry face of a transmission structure, wherein the transmission structure has an output face comprising two positioned groups or more positioned groups, wherein the transmission structure is a coated structure with a laterally variable energy transmission function, and

The output light is transmitted through the transmission structure to the output face so that a related quantity of photons generates localized groups, wherein the related quantity indicates analyte information.

Accessory devices include:

an analyte wavelength converter that responds to analyte excitation by generating output light that shows analyte information,

a transmission structure with an entry face and an exit face, wherein the exit face comprises at least two positioned groups, wherein the transmission structure is a coated structure with a laterally variable energy transmission function, and

A propagation component directs output light from the converter toward an entry face of a transmission structure, wherein the transmission structure generates photons at localized groups on the output face in such a manner that a related amount of photons generates localized groups showing analyte information.

The disadvantage of the two last-mentioned solutions is that the light signals to be analyzed must be aligned as parallel as possible before irradiation for good resolution. This requires additional optical components, such as lenses or lamellae (blades).

US Pat. No. 6,768,097 B1 describes an optoelectronic device in which two spaced-apart microresonators are coupled for wavelength filtering. The first microresonator has a relatively large extent (several hundred μm), thereby forming a large number of resonances known as frequency combs. Unlike the first microresonator, the second microresonator has an extent on the order of its resonance wavelength. Furthermore, the resonant layer of the second (thin) microresonator is electrically controllable to vary its optical properties (thickness, refractive index).

The resonances of the frequency comb can thus be filtered out.

One disadvantage is that the frequency comb of the first resonator does not allow for a continuous spectrum during measurement. Furthermore, electrical control is required to select the signals transmitted through the two microresonators. This also leads to the further disadvantage that only a continuous measurement of a broad spectrum is required, which limits the temporal resolution.

Summary of the Invention

The object of the present invention is to specify an optical filter element for a device for converting spectral information into positional information, which is suitably designed in such a way that its structure in a spectroscopic device or spectroscopic measuring device is space-saving and cost-effective with regard to the alignment of the light signal.

The object of the invention is achieved by means of an optical filter element of a device for converting spectral information into positional information.

The device has a detector connected for detecting signals, and the optical filter element includes at least two microresonators, wherein the microresonator has at least

at least two face-superposed reflective layer structures, said reflective layer structures consisting of at least layers of a material with a high refractive index and at least layers of a material with a low refractive index in an alternating sequence, and

at least one areally superposed resonant layer, which is respectively arranged between two areally superposed reflective layer structures,

It is characterized in that

The filter element comprises at least a transparent, plane-parallel substrate, which is used for optical decoupling of two microresonators.

The first microresonator is located on a first surface of two opposite surfaces of the substrate.

Wherein, on the substrate, the second microresonator is located on a second surface of the substrate opposite to the first surface, and

In this case, the resonant layer of at least one microresonator and/or the reflective layer structure respectively surrounding the resonant layer have a variable layer thickness along a horizontal axis of the filter element.

The device is preferably a spectroscopic device or a spectroscopic measuring device.

An optical filter element within the meaning of the present invention refers to a structure that, when introduced into a light path, interacts with photons in such a way that a measurable portion of the photons is lost after passing through the filter. According to the present invention, only a spectrally narrow band passes through the filter element, while the remaining spectrum is completely reflected or absorbed in the structure.

Within the meaning of the present invention, methods and devices are designated as spectroscopic applications/spectroscopic measurement applications in which a beam is split and spectroscopic measurement variables (wavelength, intensity) are assigned to readable detector elements.

The conversion of spectral information into spatial information within the meaning of the present invention means that the filter element operates in such a way that light strikes the filter over its entire surface and, after passing through, is separated into individual spectral components over the spatial extent of the filter element depending on its structure.

The following photoelectric sensors are designated as detectors within the meaning of the present invention, in which photons are converted into electrical signals by the photoelectric effect. These include, among others, photocells, photomultipliers or CMOS/CCD elements and photodiodes.

According to the invention, the detector comprises a series of individual sensor elements, which are, for example, arranged as a row or a matrix. The individual elements can be provided with different shapes/sizes and spectral sensitivities.

The following electromagnetic radiation is referred to as a signal within the meaning of the present invention, which reaches the filter monochromatically (one frequency/wavelength) or spectrally broadband. Here, the signal can have a temporal intensity modulation (single pulse, periodic and aperiodic variation) or appear with a constant intensity distribution.

A microresonator within the meaning of the present invention is a structural element that interacts with electromagnetic radiation in such a way that a standing wave (resonance layer) can be formed inside it. For this purpose, the walls of the structural element are (partially) reflectively formed as boundary surfaces.

It is important that at least one spatial direction has an extent in the order of magnitude of the spectral range to be investigated (eg for light of tens of nm to a few μm). For the filter element under consideration, this spatial direction is perpendicular to the extent of the film/surface of the substrate.

According to the present invention, a layer structure that appears to be superimposed on one another denotes a sequence of interconnected material layers (e.g., metal oxides, metals, polymers, organic molecules, etc.), each having a surface extent of several square millimeters to several hundred square centimeters and a thickness in the order of tens to several hundred nanometers. A boundary surface, whose extent differs somewhat from this, is formed between each of the two materials. In structures with more than two layers, the continuous boundary surfaces are parallel to one another within a certain range. Due to the relative size of their extents, layers are also referred to as films.

The membrane is manufactured by a method according to the prior art, such as vacuum sublimation, spraying, centrifugation, and immersion.

For the purposes of this invention, "reflective" refers to highly reflective photonic structures, also known as dielectric mirrors, in which a large portion of the radiation (approximately 100%) is completely reflected within a spectrally broad band (tens to hundreds of nanometers) due to interference effects. Unlike metallic mirrors, the efficiency is close to 100% because there is typically little or no radiation absorption. A simply designed dielectric mirror consists of an alternating sequence of layers made of materials transparent to the observed wavelength range, differing in their respective refractive indices. In the visible spectrum, these materials are, for example, silicon dioxide (n_SiO2 = 1.46) and titanium dioxide (n_TiO2 = 2.4 to 2.6), each configured to an optical thickness n x d of one-quarter of the maximum wavelength to be reflected. With a number of 7 to 9 alternating layer pairs, reflection values of >99% can be achieved. To adjust specific reflective properties within a broad spectral range of several hundred nanometers, additional layers or layer stacks can be added with precisely calculated layer thickness differences.

Variable layer thickness, within the meaning of the present invention, refers to a specifically defined thickness profile along the horizontal axis, in which the layer extends in a planar manner. This profile can have discrete steps or vary continuously. A possible manifestation is, for example, a wedge-shaped shape for the resonant layer, with a layer thickness increase of 10 to 20 nm per millimeter in the horizontal direction. The smaller the change per unit length, the greater the spectral resolving power or, when using larger detectors, the greater the sensitivity. This, on the other hand, results in a larger horizontal dimension while maintaining the same measuring range.

Production methods for variable layer thicknesses also include immersion methods with a temporally variable immersion depth, vapor-deposited or sprayed layers at a certain angle, and alternatively, a temporally variable shield that shields the source. The shield can cover the growth layer unevenly, periodically (e.g., rotatingly), or it can cover the growth layer increasingly from the start to the end of deposition.

At least one section of the reflective layer structure and/or at least one resonant layer can consist of a dielectric material.

The at least one reflective layer structure can be formed by a layer stack consisting of alternating layers of optically transparent materials having a high refractive index and optically transparent materials having a low refractive index.

At least one resonant mode of the microresonator has a transmittance higher than 10%, preferably higher than 50%, and particularly preferably higher than 90%.

The geometries and/or material compositions of the two microresonators can be symmetrical with respect to the substrate plane.

In the filter element, the course of the layer thickness of the reflective layer along the horizontal axis of the structural element or of the filter element can be dependent on the course of the resonant layer thickness.

The first resonant layer of the first microresonator can be composed of a different dielectric material than the second resonant layer of the second microresonator, and thus, one or more resonant modes can have dispersion parabolas with different curvatures from each other.

The extent of the surface of the substrate perpendicular to the direction of the layer gradient can be relatively small.

In the direction of incidence, elongated, absorbent wall elements can be arranged on the sides of the filter element.

A locally variable optical filter section can be arranged before one of the microresonators, in which a spectral preselection of the incoming signal occurs by means of an absorbing, transmitting or reflecting bandpass filter.

A spectral device or a spectral measuring device for converting spectral information into position information comprises at least

-light source,

-detector

an evaluation unit, which is connected to the detector via a connecting line,

- a display unit, and

- the previously mentioned filter element according to the invention,

In which the filter element is constructed in the following manner, that is, the filter element allows the short-wave portion of the light from the light source to pass through the filter element in the short-wave transparent area, and allows the long-wave portion of the light from the light source to pass through the filter element in the long-wave transparent area, and the filter element reflects the long-wave portion of the light from the light source after it is irradiated to the filter element in the short-wave transparent area, and reflects the short-wave portion of the light from the light source after it is irradiated to the filter element in the long-wave transparent area.

The spectroscopic device or spectroscopic measuring device can have a photoelectric line converter/matrix converter based on a CCD, a photodiode or a multiplier as a detector.

The bandpass filter of the filter element according to the invention is designed in such a way that the collimation takes place within the filter element and no additional optical elements are required. This allows for a particularly compact and inexpensive spectroscopic measuring element or device.

In summary, the following can be provided: an optical filter element according to the present invention is placed upstream of a detector (CCD matrix, diode array, diode row, diode array) as a spectral (linear) gradient filter. The gradient filter advantageously consists of at least one photonic crystal with at least one layer having a variable layer thickness depending on position. The gradient filter reflects all incident optical signals in a spectrally broad band, except for specific resonances that are structurally and position-dependent. Narrow spectral ranges (possibly less than 1 nm) that are not reflected pass through the filter virtually unimpeded and can subsequently be converted into electrical signals in a detector located directly downstream.

The present invention therefore relates to an optical filter element for separating the electromagnetic spectrum in the ultraviolet to infrared range, which, in combination with a downstream signal converter, enables the separation of electromagnetic broadband signals into their individual components (spectroscopy, spectrophotometry). The proposed invention does not require upstream optical elements for signal shaping, thereby enabling a compact integrated component.

An arrangement of at least two variable microresonators serves to separate an electromagnetic signal into its individual components, the microresonators being situated opposite each other on respective surfaces of a transparent, planar-parallel substrate.

If a Fabry-Perot interferometer is used for a variable optical microresonator, a good or even very good signal-to-noise ratio can be achieved simultaneously with high spectral resolution. By adjusting the parameters of the filter element, it is possible to adjust the spectral width and measurement range, achieve high directional sensitivity, or achieve very high individual signal separation. At the same time, the compact design of the filter element enables integration into many processes that have hitherto been inaccessible to spectroscopy. Methods known from the prior art for producing thin-layer systems can be used to produce the filter element, including, among others, vacuum coating methods (PVD, CVD) and sol-gel methods.

The core element of an optical filter element, besides the transparent substrate, is a variable bandpass filter. The term optical filter element herein refers to a component that, when irradiated with electromagnetic signals of any spectral combination in the wavelength range of 100 nm to 10 μm (ultraviolet to infrared), reflects or transmits a portion of the spectrally combined electromagnetic signal at varying intensities, or optionally absorbs a portion of the spectrally combined electromagnetic signal. The signal content is determined by the specific design of the filter element and can encompass spectral bands ranging from a few nanometers to several hundred nanometers wide (bandpass/band rejection), but can also block various spectral ranges (e.g., transmitting short wavelengths when using a shortpass filter).

In the proposed invention, the substrate is designed to have a sufficient transparency of more than 25% for the desired wavelength range to be investigated. Suitable materials for this purpose include solids such as glass (in the UV/visible range) or silicon (in the infrared range), but plastics or comparable polymers can also be used. The substrate typically has a planar extent with side lengths of a few millimeters to a few centimeters. The thickness, as a third parameter, is crucial for the function of the filter element according to the invention and ranges from a few tenths of a millimeter to a few millimeters. It should therefore be ensured that the two microresonators are optically decoupled. This prevents any interaction between the two microresonators, which would lead to resonances and manifest as degradation, and thus result in line broadening and reduced resolution of the filter.

The two extended surfaces (hereinafter referred to as the first surface of the substrate and the opposite second surface of the substrate) have a mutually parallel planar orientation, that is, the thickness of the substrate is constant over the entire usable surface. In addition, it is advantageous that the surface quality is very high in order to avoid scattering effects.

Improvements and further embodiments of the invention are described in the further dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in detail with reference to several embodiments and several drawings, wherein:

FIG1 schematically shows a side view of an optical filter element in a common embodiment;

FIG2 shows the angle-dependent transmission spectrum of the microresonator, calculated for a wavelength of 550 nm, where

Figure 2a shows the case where the resonant layer is made of silicon dioxide and the layer thickness is 100%;

FIG2 b is a case where the resonant layer is made of silicon dioxide and the layer thickness is 100.5%; and

FIG. 2 c shows the case with a four-fold thicker resonant layer made of magnesium fluoride and a layer thickness of 100%;

FIG3 schematically illustrates the functional principle of direction selection of an incident electromagnetic signal passing through a varying optical geometry along a layer thickness gradient;

FIG4 a schematically shows an embodiment of a filter element with an additional, directionally limited wall element;

FIG4 b shows a side view of the embodiment shown in FIG4 a and a diagram of the functional principle;

5 shows a plurality of transmission spectra of the optical filter element according to FIG. 1 , which were calculated for three angles of incidence, wherein the first surface has a microresonator with titanium dioxide and the second surface has a resonator with magnesium fluoride as the central resonant layer;

FIG6 schematically illustrates positional limitations of an input signal passing through a variably absorbing or reflecting pre-filter; and

FIG7 schematically shows a spectroscopic device or a spectroscopic measuring device.

DETAILED DESCRIPTION

FIG1 schematically illustrates the structure of an optical filter element 50, such as a spectral device or spectral measurement device for converting spectral information into positional information. Optical filter element 50 includes at least two microresonators 10 and 11, wherein microresonators 10 and 11 have at least:

at least two flat superposed reflective layer structures 4, 6; 8, 9, which consist of at least layers 2 of a material with a high refractive index and layers 3 of a material with a low refractive index in an alternating sequence, and

At least one areally superimposed resonant layer 5 ; 7 , which is arranged between two areally superimposed reflective layer structures 4 , 6 ; 8 , 9 .

According to the present invention, a filter element 50 comprises at least one transparent, planar-parallel substrate 1 for optically decoupling two microresonators 10, 11, wherein a first microresonator 10; 11 is situated on a first of two opposite surfaces 51; 52 of substrate 1, wherein a second microresonator 11; 10 is situated on substrate 1 on a second surface 54 of substrate 1 opposite first surface 51, and wherein the resonant layer 5; 7 of at least one microresonator 10, 11 and/or the reflective layer structure 4, 6; 8, 9 respectively surrounding the resonant layer 5; 7 have a variable layer thickness along a horizontal axis 25 of the filter element 50.

A substrate 1, transparent for the spectral range to be analyzed, is located in the center and has parallel, visually smooth surfaces 51 and 52. The thickness h of the substrate 1, in conjunction with the relative thickness gradients of the dielectric layers 2 and 3, is a crucial parameter for the directional selectivity or resolution of the filter element 50. A first layer stack 4, which acts as a broadband reflector (a one-dimensional photonic crystal), is now produced on the first surface 51 of the substrate 1 by alternately depositing layers 2 of a dielectric material with a high refractive index and layers 3 of a dielectric material with a low refractive index. The first dielectric layer stack 4 in FIG. 1 does not have a constant thickness, but rather a continuous layer thickness gradient. The relative thickness difference between the two sides 53 and 54 of the filter element 50 is dictated by the requirements for the width of the measurement range. The number of alternating layers 2 and 3 determines the resolution of the optical filter element 50. Using many layers 2 and 3 allows for better separation of signals that are close together, but can negatively impact sensitivity and increase manufacturing requirements.

A resonant layer 5 is now applied to the first reflector 4, which corresponds visually to a photonic crystal interference. Typically, the thickness of the resonant layer corresponds to a multiple of the thickness of the material layers 2 and 3. This is true even if a gradient exists in the material layers 2 and 3 that follows the relative layer thickness of the reflector 4.

The first part of the filter element 50 is closed by the second dielectric reflector 6, whereby a so-called microresonator 10 with locally variable layer thickness and thus continuously varying transmission properties is now formed. As in every resonator, in the microresonator 10, at least one frequency corresponding to the geometry is enhanced by multiple reflections, and all other components of the spectrum are suppressed.

The electromagnetic radiation incident on the first portion within the measurement range is locally spectrally separated and can pass through substrate 1. To circumvent the inherent dispersion problem of microresonator 10, which makes calibration impossible, it is necessary to limit the direction of the signal to be measured. According to the present invention, a second microresonator 11 with a similar geometry is used for this purpose. Second microresonator 11 also consists of a first dielectric mirror 8 and a second dielectric mirror 9, as well as a resonant layer 7 between the two mirrors/reflectors 8 and 9.

In the simplest case, the second microresonator 11 is a completely symmetrical copy of the first microresonator 10. However, the number or material composition of layers 2 and 3 can also be varied, or the thickness of resonant layers 5 and 7 can also be varied. What is crucial is that, for a given angle, one or more resonant wavelengths are consistent across the entire extent of the filter element 50. Accordingly, the layer thickness gradients are matched to one another.

FIG2 shows the angle-dependent transmission spectrum of the microresonator 10 , which was calculated for a wavelength of 550 nm, FIG2a showing the case of a resonant layer composed of silicon dioxide and a layer thickness of 100%, FIG2b showing the case of a resonant layer composed of silicon dioxide and a layer thickness of 100.5%, and FIG2c showing the case of a resonant layer composed of magnesium fluoride with a fourfold thickness and a layer thickness of 100%.

Here, typical energy curves (dispersion) of the resonance modes for three different, exemplarily calculated microresonators 10 are shown. With normal material dispersion, the spectrally narrow (<1 nm full width at half maximum), transparent region shifts toward shorter wavelengths (higher energy) as the angle of incidence increases according to the relationship 1/(ndcos(α)). Here, n is the refractive index of the material, d is the thickness of the resonator layer 5, and α is the propagation angle.

Real material values are used for the calculations. A dielectric mirror 4 is assumed as an exemplary filter element 50, consisting of alternating titanium dioxide layers 2 and silicon dioxide layers 3 with a thickness of 550 nm/(4n _material ). 7.5 pairs of titanium dioxide and silicon dioxide layers are arranged on a glass substrate 1, followed by a resonant layer 5, and a second dielectric mirror 6 is arranged on the resonant layer. The thicknesses of the individual layers 2, 3 are:

In FIG. 2 a , this corresponds to 100% of a thickness of 550 nm/(4n _material ), wherein a silicon dioxide layer with a thickness of 550 nm/(2n _{silicon dioxide} ) is used as the resonator layer 5 .

2b corresponds to 100.5% of the thickness of 550 nm/(4n _material ), wherein a silicon dioxide layer is used as the resonator layer 5 with an increased thickness of 100.5% of the value 550 nm/(2n _{silicon dioxide} ), and

In FIG. 2 c , this corresponds to 100% of a thickness of 550 nm/(4n _material ), wherein a magnesium fluoride layer with a thickness of (2·550 nm)/n _{magnesium fluoride} is used as the resonator layer 5 .

Despite the very similar curves, differences can be seen. Comparing the spectra in FIG. 2a with those in FIG. 2b reveals the influence of the layer thickness d of the resonant layer 5 on the positioning of the resonant modes. A 0.5% increase (corresponding to a physical thickness of 1 nm) shifts the overall dispersion parabola by approximately 3 nm toward longer wavelengths. Given sufficiently narrow resonant widths (<1 nm) for both modes, the resonances in FIG. 2a and FIG. 2b do not intersect at any angle.

In the spectrum in Figure 2c, the steeper rise of the associated dispersion parabola, resulting from the lower refractive index of magnesium fluoride and the fourfold layer thickness, can be seen. If the spectra in Figure 2a and Figure 2c are now compared, it can be seen that at small angles, the resonance modes intersect and separate from each other as the angle increases (the resonances are each determined, for example, at 10°).

FIG3 illustrates the directionally selective functional principle of the filter element 50 introduced in FIG1 , which is based on the effects mentioned in the description of FIG2 . Two microresonators 10 and 11 have the same gradient and are located opposite each other on the surface of a substrate 1 having a thickness h. A vertically incident signal 12 strikes the first microresonator 10 , and a signal component of the intermediate signal 14 corresponding to the 0° angle illustrated in FIG2 a is transmitted and, after passing through substrate 1 , reaches the second microresonator 11 . Because the two resonators 5 and 7 are symmetrical, the second microresonator 11 has the same transmission properties with respect to the entry position of the signal component 14 , so that the (possibly attenuated) signal component 14 can pass through the second microresonator 11 and be detected as an output signal 14 a.

If the obliquely incident signal 13 reaches the first microresonator 10 at a greater angle, then, according to FIG. 2 a , a signal component 15 corresponding to this angle is transmitted as a resonant mode, the wavelength of which is smaller than that of the perpendicularly incident signal 12. In substrate 1, which is very thick compared to microresonators 10, 11, this mode travels along the layer thickness gradient of microresonators 10, 11 over a distance component L resulting from the substrate thickness h and the angle of incidence of the obliquely incident signal 13.

At the entry position relative to the second microresonator 11, the obliquely incident signal 13 now strikes a different layer thickness (thinner or thicker) due to the gradient. Consequently, as explained in the description of FIG. 2 , the dispersion parabolas do not intersect at any point while maintaining the oblique angle, and signal 15 is not transmitted but reflected as signal 15 a. Important for the approach angle (where the resonant mode passes through both microresonators 10, 11) are the spectral resolution (finess) of the individual microresonators 10, 11, the thickness h of the substrate 1, and the relative layer thickness gradient.

FIG4 a shows an embodiment of a structural element 60 with a filter element 50, in which highly absorptive wall elements 18, 19 ensure that directional selection also occurs perpendicular to the thickness gradient of microresonators 10, 11. In this direction, the same geometry ensures that the transmission parabolas according to FIG2 overlap, making wavelength calibration impossible for obliquely incident light of input signal 13. The angular range of input signal 13 is now selected using wall elements 18, 19. For this purpose, the extent of filter element 50 perpendicular to the gradient is significantly smaller, and for example, linear elements are used as possible sensors.

FIG4 b shows a side view of a specific embodiment of structural element 60 according to FIG4 a to illustrate the selection of the tilt angle for incident signal 22. If input signal 20 strikes structural element 60 with filter element 50 perpendicularly in the plane shown, it is unaffected by wall elements 18 , 19 and can subsequently be detected as signal 25 a on the rear side after passing through microresonators 10 , 11 , as shown in FIG3 . An inclined beam 22 at a sufficiently large angle passes through structural element 60 on its way to one of wall elements 18 , 19 and is absorbed there as signal 22 a. The approach angle, and therefore the spectral resolution of filter element 50 in the plane shown, is determined by the relationship between the wall height and the wall spacing of wall elements 18 , 19. Thus, minimizing the overall structural element is possible if the width of filter element 50 perpendicular to the layer gradient is very narrow. However, the extension should be a multiple of the average wavelength to be analyzed to suppress the influence of diffraction effects and, at the same time, achieve a sufficiently strong input signal for a high signal-to-noise ratio.

FIG5 illustrates an alternative approach for selecting the direction of input signal 20 perpendicular to the thickness gradient of microresonator 10 using three calculated transmission spectra for different angles of incidence. Transmission modes within a wavelength range that is otherwise spectrally impermeable (the rejection band) are shown. Filter element 50 has a resonator layer 5 of a high-refractive titanium oxide material (n=2.1) with a thickness of 550 nm/(2n _{titanium oxide} ) on its first side and a low-refractive microresonator 11 of magnesium fluoride (n=1.35) with a thickness of (3.550 nm)/2n _{magnesium fluoride} on its second side. The gradient is symmetrical relative to substrate 1, so that, according to FIG2a and FIG2c , the modes of the two microresonators 10 and 11 coincide with each other under normal light incidence. As the angle of incidence increases (in the cases of 5° and 10°), the resonance shifts toward shorter wavelengths, as expected, but at the same time, the signal intensity decreases significantly, since the two parabolas gradually separate due to the different dispersions.

Due to this effect, the spectral resolution is broadened in the direction of shorter wavelengths compared to the transmission at normal light incidence, but the spectral resolution can still be very low (<1 nm) depending on the specific design of the filter element 50 .

In the simulations assuming a microresonator 10 consisting of 7.5 pairs of alternating silicon dioxide and titanium dioxide layers (thickness 550 nm/(4n _material )), the reduction increases the possible signal intensity but weakens the angular selectivity and thus reduces the spectral resolution.

Unlike the implementation of the structural element 60 shown in Figures 4a and 4b, no additional elements are required here to limit the signal perpendicular to the slice gradient. As a result, the structural element 60 can also extend in a two-dimensional manner and is therefore suitable for performing spectral detection along positional coordinates or mapped angular coordinates using a matrix detector.

FIG6 schematically illustrates how input signals 20 in locations 23 and 24 that spectrally exceed the impermeable wavelength range (blocking range) can still be unambiguously detected using the described structural element 60. At the first location 23 of the input signal 20, the spectrally broad input signal 20 lies within the boundaries of the blocking range. Detection can be performed using the intermediate signal 25 and the output signal 25a, after prior passage through the microresonators 10 and 11, according to the principles described in the previous embodiments. At the second location 24 of the input signal 20, the spectrally broad input signal 20 exceeds the boundaries of the blocking range, whereby a clear assignment of the detectable signal 25a is no longer possible (either the resonant mode or the transmitted light lies outside the blocking range). For this reason, spectral portions outside the respective blocking range are suppressed by upstream, locally variable filter sections 26. Filter sections 26 can have either an absorptive effect (e.g., a functional pigment) or a reflective effect (a bandpass filter). Both discrete steps and layer gradients are possible for the local arrangement of filter sections 26.

FIG7 illustrates a spectral device or spectral measurement device 70 for converting spectral information into position information, which comprises at least:

- a light source 16,

- detector 30,

an evaluation unit 40 , which is connected to the detector 30 via a connecting line 35 ,

- a display unit 17, and

- the previously mentioned filter element 50 according to the invention,

In which, the filter element 50 is constructed as follows, that is, the filter element allows the short-wave portion 32b of the light from the light source 16 to pass through the filter element 50 in the short-wave transparent area, and allows the long-wave portion 33b of the light from the light source 16 to pass through the filter element 50 in the long-wave transparent area, and the filter element reflects the long-wave portion 31b of the light from the light source 16 that is irradiated to the filter element 50 in the short-wave transparent area, and reflects the short-wave portion 34b of the light from the light source 16 that is irradiated to the filter element 50 in the long-wave transparent area.

The following light components are illustrated in FIG7 :

The long-wavelength portion 31a of the light from the light source 16 before it strikes the filter element 50 in the short-wavelength transparent region,

The long-wavelength portion 31b of the light from the light source 16 that is irradiated to the filter element 50 in the short-wavelength transparent region is

The short-wave portion 32a of the light from the light source 16 before passing through the filter element 50 in the short-wave transparent region,

The short-wave portion 32b of the light from the light source 16 after passing through the filter element 50 in the short-wave transparent region,

The long-wave portion 33a of the light from the light source 16 before passing through the filter element 50 in the long-wave transparent region,

The long-wave portion 33b of the light from the light source 16 after passing through the filter element 50 in the long-wave transparent region,

The short-wavelength portion 34a of the light from the light source 16 before it strikes the filter element 50 in the long-wavelength transparent region,

The short-wavelength portion 34 b of the light from the light source 16 in the long-wavelength transparent region strikes the filter element 50 .

The advantages of the filter element 50 for the spectrometer 70 according to the present invention are as follows:

The structure according to the invention enables a particularly space-saving spectrometer 70 in the propagation direction of the light signal, since, with a minimum distance between the filter element 50 and the detector 30 according to FIG. 7 , only their vertical extent and the size of the spectrometer 70 are limited.

If two-dimensional elements (matrix) are used for the detector 30 , then, depending on the optical configuration on the input side, the signal quality (integration) can be increased or position/angle-dependent spectral measurements can be performed.

By using dielectric materials, high sensitivity (resonant transmission close to 100%) can be achieved with simultaneously high selectivity (narrow half-value width of the signal) and a favorable signal-to-noise ratio (spectral environment with resonances with transmission <0.1%). The selection of the lateral extent of the filter element-detector combination and the thickness of the detector element also provides the possibility of influencing the resolution of the spectrometer.

The use of non-uniform layer thickness profiles allows the production of specialized spectrometers with different measurement ranges (e.g., coarse spectral overview and high-resolution segments) in one facility. Furthermore, the basic design can be easily packaged and, due to the small number of required components, can be used in demanding environments.

Furthermore, the components, such as the high-resolution detector 30 , are mass-produced products and the filter elements 50 can be produced in parallel in larger quantities, so that the overall costs of the spectrometer 70 with the optical filter element 50 according to the invention can be kept low.

Reference Signs List

1 base

2 High refractive index material layer

3 Low refractive index material layer

4 First layer stack/first reflector

5. First resonant layer

6 Second layer stack/second reflector

7 Second resonant layer

8-layer stack/reflector

9-layer stack/reflector

10. The First Microresonator

11 Second microresonator

12 Incident signal

13 Input Signal

14 Intermediate Signal

14a Output signal

15 Reflected signal part

15a Transmitted signal part

16 Light Source

17 Display unit

18 First wall element

19 Second wall element

20 Input Signal

21 Horizontal axis of filter element

22 Signal with oblique incidence

22a Absorbed signal

23 Positioning

24 Positioning

25 Intermediate signal

25a output signal

26 Filter Section

30 detectors

31a The long-wavelength portion of light before it strikes the filter element in the short-wavelength transparent region

31b The long-wavelength portion of light that strikes the filter element in the short-wavelength transparent region

32a The short-wave portion of the light before it passes through the filter element in the short-wave transparent region

32b The short-wave portion of light after passing through the filter element in the short-wave transparent region

33a The long-wave portion of light before it passes through the filter element in the long-wave transparent region

33b The long-wave portion of light after passing through the filter element in the long-wave transparent region

34a The short-wavelength portion of light that strikes the filter element in the long-wavelength transparent region

34b The short-wave portion of light that strikes the filter element in the long-wave transparent region

35 connection lines

40 evaluation units

50 filter elements for converting spectral information into positional information

51 First Surface

52 Second Surface

53 First filter element side

54 Second filter element side

60 structural elements

70 Spectral Device

h thickness of the substrate

d thickness of the resonator layer

α propagation angle

n Refractive index

Claims (14)

1. An optical filter element (50) for a device (70) for converting spectral information into positional information, the device having an access detector (30) for detecting a signal, the optical filter element comprising at least two microresonators (10, 11), wherein the microresonators (10; 11) have at least - A reflective layer structure (4, 6; 8, 9) with at least two surfaces stacked, the reflective layer structure being composed of at least a high-refractive-index material layer (2) and at least a low-refractive-index material layer (3) in an alternating sequence, and - At least one surface-stacked resonant layer (5; 7), said resonant layer being arranged between two surface-stacked reflective layer structures (4, 6; 8, 9), Its features are, The filter element (50) includes at least a transparent, parallel-planar substrate (1) for optical decoupling of the two microresonators (10, 11). The first microresonator (10; 11) is located on the first surface of the two opposing surfaces (51; 52) of the substrate (1). In this embodiment, on the substrate (1), the second micro-resonator (11; 10) is located on the second surface (54) of the substrate (1) opposite to the first surface (51), and The resonant layer (5; 7) of at least one microresonator (10; 11) and/or the reflective layer structures (4, 6; 8, 9) surrounding the resonant layer (5; 7) respectively have variable layer thicknesses along the horizontal axis (25) of the filter element (50). 2. The optical filter element according to claim 1, Its features are, At least one segment of the reflective layer structure (4, 6; 8, 9) and/or at least one resonant layer (5; 7) is made of dielectric material. 3. The optical filter element according to claim 1, Its features are, At least one of the reflective layer structures (4, 6; 8, 9) is formed by a stack of alternating layers of highly refractive optically transparent material and low refractive optically transparent material. 4. The optical filter element according to any one of claims 1 to 3, Its features are, At least one resonant mode of the microresonators (10, 11) has a transmittance of more than 10%. 5. The optical filter element according to any one of claims 1 to 3, Its features are, The geometry and/or material composition of the two microresonators (10, 11) are symmetrical with respect to the substrate plane. 6. The optical filter element according to claim 1, Its features are, In the filter element (50), the thickness of the reflective layer (2, 3) along the horizontal axis (21) of the structural element (60) or the filter element (50) is related to the thickness of the resonant layer. 7. The optical filter element according to claim 1, Its features are, The first resonant layer (5) of the first microresonator (10) is made of a different dielectric material than the second resonant layer (7) of the second microresonator (11), and therefore, the resonant modes have dispersed parabolas with different curvatures. 8. The optical filter element according to claim 1, Its features are, The extension dimension of the surface (51, 52) of the substrate (1) perpendicular to the layer gradient direction is relatively small. 9. The optical filter element according to claim 1, Its features are, The wall elements (18, 19) that extend in the injection direction and serve an absorptive function are disposed on the sides (53, 54) of the filter element (50). 10. The optical filter element according to claim 1, Its features are, A locally variable optical filter section (26) is placed before one of the microresonators (10, 11), wherein the spectrum of the incoming signal (20) is preselected by a bandpass that acts as an absorber, transmitter or reflector. 11. The optical filter element according to any one of claims 1 to 3, Its features are, At least one resonant mode of the microresonators (10, 11) has a transmittance of more than 50%. 12. The optical filter element according to any one of claims 1 to 3, Its features are, At least one resonant mode of the microresonators (10, 11) has a transmittance of more than 90%. 13. A spectroscopic device or spectroscopic measuring device (70) for converting spectral information into positional information, wherein the spectroscopic device or spectroscopic measuring device includes at least... -Light source (16), - Detector (30), - Evaluation unit (40), which is connected to the detector (30) via a connection line (35). - Display unit (17), and - The filter element (50) according to any one of claims 1 to 12, Its features are, The filter element (50) is constructed in such a way that, The filter element allows light from the light source (16) to pass through the short-wavelength portion (32b) after passing through the filter element (50) in the short-wavelength transparent region, and allows light from the light source (16) to pass through the long-wavelength portion (33b) after passing through the filter element (50) in the long-wavelength transparent region, and The filter element causes the long-wave portion (31b) of the light from the light source (16) after it has been irradiated by the filter element (50) in the short-wave transparent region to be reflected, and causes the short-wave portion (34b) of the light from the light source (16) after it has been irradiated by the filter element (50) in the long-wave transparent region to be reflected. 14. The spectroscopic device or spectroscopic measuring device (70) according to claim 13, Its features are, The spectroscopic device or spectroscopic measurement device has a photoelectric row converter/matrix converter based on a CCD, photodiode, or multiplier as a detector (30).