INTERFEROMETER ELEMENT, SPECTROMETER AND METHOD FOR OPERATING AN INTERFEROMETER

Description

State of the art

[0001] The invention relates to an interferometer element, a spectrometer, and a method according to the preamble of the independent claims. The present invention also relates to a computer program.

[0002] Conventional micromechanical Fabry-Pérot interferometers (FPIs) consist of two mirror elements arranged on a substrate across an aperture. There are also interferometers constructed from two substrates with apertures. The light beam is guided through the sandwich design with two highly reflective mirrors, each transmitting narrowband regions around a resonance wavelength and its overtones depending on the distance between the two mirrors. By varying the distance, the desired resonance wavelength can be adjusted, measured in a subsequent detector, and a spectrum can be recorded serially. An additional bandpass filter upstream can filter out the desired order, minimizing errors caused by other orders. This limits the measurable wavelength range to a maximum of the range between the desired order and the next higher order.This wavelength range (free spectral range) is larger at lower orders, but at these frequencies, the resolution in the wavelength domain is degraded. Due to the static bandpass filter and the spectral spacing of the harmonics, the wavelength measurement range of the FPI is very limited, thus severely restricting the range of applications.

[0003] The document US 2014 / 098371 A1 discloses a Fourier transform microspectrometer based on spatially shifted interferrogram bursts.

[0004] Document US 2014 / 198388 A1 discloses a Fabry-Pérot device with a movable mirror.

[0005] Document US 7 844 145 B1 discloses a MEMS-based multi-channel Fabry-Pérot interferometer system with extended tuning range and resolution.

[0006] The document US 6 424 466 B1 discloses a two-cavity Fabry-Pérot filter which is movable by MEMS.

[0007] The document US 2010 / 097613 A1 discloses a spectrometer and a method for controlling the spectrometer. Disclosure of the invention

[0008] Against this background, the approach presented here presents an interferometer element, an interferometer, a method, and finally a corresponding computer program according to the main claims. The measures listed in the dependent claims enable advantageous refinements and improvements of the device specified in the independent claim.

[0009] The approach presented here provides an interferometer element according to claim 1 for use in an interferometer.

[0010] A mirror element can be understood as an optical element that partially reflects light. The three mirror elements can be arranged such that the distance between at least two of the mirror elements can be varied. A light path can be understood as a path or route that the light takes through the interferometer element. In particular, the light can pass through various optical components, such as the mirror elements, or be reflected by these elements.

[0011] The approach proposed here is based on the finding that by using at least three mirror elements, two Fabry-Pérot filters can be formed, which can be used specifically to increase the wavelength measurement range and the robustness of an evaluation of light from the light path against ambient light influences, especially in connection with the use of non-modulatable light sources.

[0012] It is further advantageous if, according to an embodiment of the approach presented here, the interferometer element has at least a fourth mirror element, which is arranged serially in the light path with respect to the first, second, and third mirror elements, and wherein a third distance between the third and fourth mirror elements is variable. Such an embodiment of the approach proposed here offers the advantage of creating two independent Fabry-Pérot filters by means of four mirror elements, in which a distance between two mirror elements of each of the Fabry-Pérot filters can be changed separately and independently of the distance between the two mirror elements of the other Fabry-Pérot filter. In this way, the transmission behavior of the interferometer element can be adjusted very flexibly.

[0013] An embodiment of the approach proposed here is advantageous in which a material of the first mirror element differs from a material of the second mirror element and / or the material of the second mirror element differs from a material of the third mirror element, in particular so that the resulting mirrors have different dispersions of the phase shift during reflection. Such an embodiment of the approach proposed here enables a very large (spectral) measurement range of a light passing through the interferometer, in which, for example, light frequencies of certain orders are suppressed.

[0014] According to a further embodiment of the approach proposed here, the material of the first, second, third, and / or fourth mirror element is a metallic or metal-containing material. Alternatively or additionally, the materials of the first, second, third, and / or fourth mirror element can differ in their refractive index. Such an embodiment of the approach proposed here offers the advantage of supporting a wavelength-dependent phase shift, so that a larger range of variation of the first and / or second distance can advantageously be achieved.

[0015] The invention also provides a control unit for electrically controlling a change in the first and second distances. In particular, the control unit can be designed and configured to cyclically repeat a change in the first and second distances. Such an embodiment of the approach proposed here offers the advantage that a transmission of light through the entire light path is enabled by a very simple adjustment of the positions of the mirror elements and thus of the first and second distances, allowing "shutter" operation, so that a light intensity at the wavelengths to be measured can be modulated, even when a non-modulatable light source is used. This enables signal correlation methods such as lock-in in the detection of the light, resulting in an improvement in the signal-to-noise ratio.

[0016] An embodiment of the approach proposed here is technically very simple and cost-effective to implement. The control unit is designed and configured to change the first and / or second distance piezoelectrically and / or magnetically. Such an embodiment offers the advantage of being able to cover a larger measurement range with the same frequency orders occurring in the light, thus avoiding switching to other orders. Such switching would result in additional errors in the transmission of light through the Fabry-Pérot interferometer (based on tolerances), and an additional settling time would have to be considered.

[0017] Furthermore, an embodiment of the approach proposed here is advantageous in which the control unit is designed and configured to change the first and / or second distance in response to a read-in distance signal, wherein the distance signal represents a current first and / or second distance. In particular, the control unit can be designed to set a maximum transmission of light through the interferometer element by changing it. In this way, it can advantageously be ensured that the first and / or second distance can be readjusted according to an optical detector signal, so that light can be detected by the interferometer element with high light intensity, from which a signal with sufficient or high signal quality can be obtained. This, in turn, makes it easy to evaluate this signal.

[0018] The inventive embodiment of the approach proposed here is technically very simple, in which the control unit is designed and configured to change the first distance by a different distance value than the second distance using a common control signal for changing the first and second distances. This avoids the numerical and / or circuitry complexity required to output different control signals for changing the first and / or second distances.

[0019] Another advantageous embodiment of the approach proposed here is one in which the spring tension and / or spring elasticity of the first, second, and / or third mirror element of the Fabry-Pérot filter element differs. Such an embodiment offers the advantage that such a spring tension and / or spring elasticity of the individual mirror elements can be implemented very easily in a manufacturing process, so that a control of the change in distance, which is also very easy to implement, can be implemented in a corresponding control unit.

[0020] Another advantageous embodiment of the approach proposed here is one in which the Fabry-Pérot filter element is designed such that an object to be examined using the interferometer element is positioned between the first and second mirror elements and / or between the second and third mirror elements. Such an embodiment offers the advantage of being able to divide the Fabry-Pérot filter element into several components, so that, for example, existing installation space can be used efficiently for arranging elements of an interferometer.

[0021] According to another embodiment of the approach proposed here, a spectral filter element can also be provided for attenuating and / or blocking the transmission of light of a predetermined wavelength range through the interferometer element. Such an embodiment offers the advantage of being able to efficiently filter out light with wavelength ranges that are relevant for analysis and desired.

[0022] The advantages of embodiments of the proposed approach presented here can also be realized in a spectrometer which further comprises a light source for providing the light beam through the interferometer element and a detector for detecting an evaluation light emerging from the spectrometer.

[0023] A particularly advantageous embodiment of the approach proposed here is one in which the detector has a plurality of detector elements configured for light of different wavelength ranges and / or in which the light source is designed for non-modulatable light output. Such an embodiment offers the advantage of increasing the light detectable by the detector with respect to a wavelength measurement range, as well as the use of a technically very simple and thus cost-effective light source for operating such an interferometer.

[0024] The approach presented here further provides a method for operating an embodiment of the interferometer presented here, the method having the features of claim 13.

[0025] Advantageously, in an optional step, light can also be emitted from the light source along the light path through the interferometer element.

[0026] The advantages described here can also be realized efficiently and technically simply by means of such an embodiment in the form of a method.

[0027] This method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

[0028] The approach presented here further provides a control unit configured to perform, control, or implement the steps of a variant of a method presented here in corresponding devices. This embodiment of the invention in the form of a control unit also allows the problem underlying the invention to be solved quickly and efficiently.

[0029] For this purpose, the control unit can have at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, at least one interface to a sensor or an actuator for reading sensor signals from the sensor or for outputting control signals to the actuator, and / or at least one communication interface for reading or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a microcontroller, or the like, wherein the memory unit can be a flash memory, an EEPROM, or a magnetic storage unit.The communication interface can be designed to read in or output data wirelessly and / or wired, wherein a communication interface that can read in or output wired data can read this data, for example, electrically or optically from a corresponding data transmission line or output it to a corresponding data transmission line.

[0030] In this context, a control unit can be understood as an electrical device that processes sensor signals and outputs control and / or data signals depending on them. The control unit can have an interface that can be implemented in hardware and / or software. In a hardware implementation, the interfaces can, for example, be part of a so-called system ASIC, which contains a wide variety of functions of the control unit. However, it is also possible for the interfaces to be separate integrated circuits or to consist at least partially of discrete components. In a software implementation, the interfaces can be software modules that are present, for example, on a microcontroller alongside other software modules.

[0031] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer or a device.

[0032] Examples of the approach presented here are shown in the drawings and explained in more detail in the following description. It shows: Fig. 1 a schematic view of an interferometer according to an embodiment of the present invention with three mirror elements; Fig. 2 Diagrams showing a simulation result for an exemplary operation of the Fabry-Pérot filter element; Fig. 3 Diagrams according to the representation from the Fig. 2 , wherein an embodiment is now shown in which the surface finish of the third mirror element is provided with elevations / defects; Fig. 4 Diagrams according to the representation from the Fig. 2 or the Fig. 3 according to another embodiment of a simulation result of another embodiment of the present invention; Fig. 5 a schematic representation of an interferometer with a further embodiment of an interferometer element; Fig. 6 a schematic representation of an interferometer with a further embodiment of an interferometer element; Fig. 7 a schematic representation of an interferometer with a further embodiment of an interferometer element Fig. 8 Diagrams according to the representation from the Fig. 2 or the Fig. 3 for a simulation result of another embodiment of the present invention; Fig. 9 a flowchart of a method according to an embodiment;

[0033] In the following description of advantageous embodiments of the present invention, the same or similar reference numerals are used for the elements shown in the various figures and having a similar effect, whereby a repeated description of these elements is omitted.

[0034] Fig. 1 shows a schematic view of an interferometer 100 according to an embodiment of the present invention with three mirror elements. The spectrometer 100 comprises, for example, a light source 105, which is designed, for example, as a light bulb, light-emitting diode, or laser diode for emitting light 110 of a predetermined wavelength or a predetermined wavelength range in order to illuminate an object 115. The light 110 is reflected by the object 115 and guided along a light path 120 through an interferometer element 125. Along this light path 120, the light 110 first passes through a spectral filter element 130, which is formed, for example, by a bandpass filter for attenuating and / or suppressing predetermined wavelength ranges of the light 110.Subsequently, the light 110 passes through a first mirror element 135, a second mirror element 140, and a third mirror element 145, which are arranged serially with respect to the light path 120. The first mirror element 135, the second mirror element 140, and the third mirror element 145 are coupled to one another via a (first) micromechanical actuator 155 in order to change a first distance 160 between the first mirror element 135 and the second mirror element 140.

[0035] In addition, the first micromechanical actuator 155 and / or a micromechanical actuator 156 Fig. 1 For reasons of clarity, a second micromechanical actuator (not shown) also changes a second distance 165 between the second mirror element 140 and the third mirror element 145. If the light 110 now exits the interferometer element 125 along the light path 120, it can impinge on a detector unit 190 as output light 180 through a beam-shaping element 185, such as a lens. The detector unit 190 can be designed, for example, as a detector array with first sub-detectors 190a for measuring first wavelength ranges of the output light 180 and second sub-detectors 190b for measuring second wavelength ranges of the output light 180. For example, the first sub-detectors 190a can be implemented on a silicon basis, with the second sub-detectors 190b being manufactured on the basis of an InGaAs material.

[0036] In order to be able to modulate the light 110 along the light path 120 as efficiently as possible, a control unit 195 can be provided, which varies the first distance 160 and the second distance 165 by appropriately electrically controlling one or both micromechanical actuators 155, which can be understood, for example, as part of the control unit 195, by means of a control signal 197. In this case, for example, a detector signal 198 can also be read in by the control unit 190 in order to be able to detect the actual current transmission behavior of the interferometer element 125 and to be able to adjust the first distance 160 and / or the second distance 165 accordingly via the first micromechanical actuator 155 or the second micromechanical actuator (not shown).It is also conceivable that the detector signal contains information about a currently applied first distance 160 and / or second distance 165, so that here too a feedback about the possibly required change can be given to the control unit 195 in order to realize the most optimal transmission behavior of the interferometer element 125.

[0037] In the Fig. 1 The basic structure of a Fabry-Pérot interferometer (FPI) system is shown as a spectrometer 100 with two FPIs connected in series. The resonator cavity (cavity) of a first Fabry-Pérot interferometer FPI1 (as the first Fabry-Pérot filter FPI1) ​​is formed between the first mirror element 135 and the second mirror element 140. The resonator cavity (cavity) of a second Fabry-Pérot interferometer (as the second Fabry-Pérot filter FPI2) is formed between the second mirror element 140 and the third mirror element 145. The distances 160 and 165 between the two resonators must be in a specific ratio to each other in order to achieve the best possible overall transmission of the Fabry-Pérot filter element 125. Depending on which wavelength order is operated in the respective cavity, the distances 160 and 165 should be set individually.

[0038] A downstream lens, as an example of a beam-shaping element 185, concentrates the light intensity of the output light 180 onto the active detector surfaces of the detector 190. The limited size of the detector 190 simultaneously limits the input angle interval of the Fabry-Pérot interferometer, since the light beams 110 and 180 no longer hit the active area of ​​the detector 190 at the boundary position. This increases the spectral resolution of the interferometer element 125 when non-collimated light is incident.

[0039] Integrating the Fabry-Pérot filter element 125 into a micromechanical, or more precisely, microelectromechanical system (MEMS) is advantageous, allowing the size advantages to be exploited and ensuring that the individual mirror elements operate under the same temperature conditions. An additional high-pass or bandpass filter as a spectral filter element 130 can limit the measurement range, ensuring that the non-measurable orders of the overall transmission behavior are suppressed.

[0040] Fig. 2 shows diagrams showing a simulation result for an exemplary operation of the Fabry-Pérot filter element 125 from the Fig. 1 as a transfer function (here as transmission behavior) between the normalized values ​​0 and 1 over the wavelength λ. In the left-hand diagram, each row shows an overview of the transmission behavior over a larger wavelength range λ, with the three right-hand diagrams in each row showing the transmission behavior in the range of one of the resonance frequencies. A first wavelength range 200 is blocked by the spectral filter element 130, whereas in a second wavelength range 205 the detector 190 is sensitive. In a first partial spectral range, a partial detector 190a, for example, based on a silicon element, is sensitive, whereas in a second partial spectral range the partial detector 190b, for example, based on InGaAs, is sensitive. Fig. 2 shows the functioning of the FPI composite as a Fabry-Pérot filter element 125 at a defined wavelength of, for example, 2100 nm, wherein the cavity lengths, ie the distances 160 and 165 between the mirror elements, are operated with different wavelength orders so that the unwanted resonator wavelengths of the first Fabry-Pérot filter FPI1 and the second Fabry-Pérot filter FPI2 can be suppressed.

[0041] In the top row of the diagrams from Fig. 2 is a transfer function of a first Fabry-Pérot filter (FPI1) ​​comprising the first mirror element 135 and the second mirror element 140, whereas in the middle row of the diagrams from the Fig. 2 a transfer function of a second Fabry-Pérot filter (FPI2) is shown, which comprises the second mirror element 140 and the third mirror element 145. In the lower row of the diagrams from the Fig. 2 A transfer function of the combination of the first and second Fabry-Pérot filters is shown. The first Fabry-Pérot filter FPI1 is operated at a first resonance wavelength of 2100 nm in an advantageous wavelength order 3 to achieve the smallest possible spectral full width at half maximum (FWHM). Orders 4 and 5, which could lead to a false signal, are integrated in the InGaAs detector measuring range of approximately 1050 to 2100 nm. Orders 7 and 8 are also integrated in the Si detector measuring range of approximately 700 to 1050 nm. With the help of the second Fabry-Pérot filter FPI2, the above-listed FPI1 orders 4, 5, 7, 8, etc. can be eliminated in the total transmission if the second Fabry-Pérot filter FPI2 is operated at 2100 nm, for example, in order 2.

[0042] Orders 3, 6, 9 of the first Fabry-Pérot filter FPI1, etc., would not be blocked, allowing measurement of the light intensities. For each measurable order, only one detector 190 should evaluate the measurement signal.

[0043] Fig. 3 shows diagrams according to the representation from the Fig. 2 , wherein an embodiment is now shown in which the surface finish of the third mirror element 145 is provided with elevations / defects, for example with a height of approximately 20 nm, so that the overall system is very fault-tolerant with regard to relative position errors between the first Fabry-Pérot filter FPI1 and the second Fabry-Pérot filter FPI2.

[0044] From the Figuren 2 and 3 It can also be seen that in the first Fabry-Pérot filter FPI1, order 3 is visible in the (external) InGaAs detector or in the InGaAs detector in a reduced measuring range (Zoom Z13 in Fig. 2 and 3). Furthermore, the Figuren 2 and 3 It can be seen that in the first Fabry-Pérot filter FPI1 the order 6 is visible in the Si detector (Zoom Z12 in Fig. 2 and 3 ). A high-pass filter at approximately 700 nm would block the higher wavelength orders (order 9, etc.).

[0045] By varying the mirror spacing, in this example, the wavelength range from approximately 1050 nm to 2100 nm can be measured with the FPI1 order 3, and the wavelength range from approximately 700 nm to 1050 nm can be measured simultaneously with the FPI1 order 6. The resolution is improved by using higher orders (3 and 6).

[0046] To achieve reproducible overall transmission, light intensity errors (which can arise from inaccurate positioning of the two resonator lengths relative to each other) should be minimized. Different technologies can be used for this purpose. Fig. 3 shows the effects of two of these technologies, which lead to a broadening of the FWHM (as can be seen, for example, in the third mirror element 145). A reduction in reflectivity also leads to a broadening of the FWHM and thus to a certain relative position insensitivity. A broadening of the FWHM can also occur due to a deviation in the surface shape or surface roughness, e.g., due to additional elevations on the third mirror element 145. The different resonator lengths in the second Fabry-Pérot filter FPI2 are advantageously implemented as a position-independent rectangular distribution in order to reduce the requirements regarding the positioning accuracy of FPI2.

[0047] Fig. 4 shows diagrams according to the representation from the Fig. 2 or the Fig. 3 . In the diagrams the Fig. 4 The effect of positioning the second Fabry-Pérot filter FPI2 by approximately 60 nm was simulated, whereby the resulting light intensity is significantly reduced. A modulation of the second distance 165, for example, of ± 60 nm, will also lead to an intensity modulation. This dependency could be used to establish a position control based on the optical signal, so that a maximum transmission is ensured depending on the position or the first distance 160 in the first Fabry-Pérot filter FPI1. This position control could be implemented in the control unit 195, for example, according to Fig 6 be accommodated.

[0048] Fig. 5 shows a schematic representation of an interferometer 100 with a further embodiment of an interferometer element 125. In this embodiment, a possibility for a simplified control of the two Fabry-Pérot filters FPI1 and FPI2 by the control unit 195 is shown. The actuators 155 of both Fabry-Pérot filters FPI1 and FPI2 are supplied with the same or similar actuator voltage and / or current. The corresponding stiffnesses or elasticities of the mirror elements and actuators, such as the first mirror element 135, the second mirror element 140, and / or the third mirror element 145, should be designed such that the required positions are set by the voltage / current jointly applied to the actuator 155 or the actuators 155 for changing the first 160 and second 165 distance. Fig. 5 thus shows an embodiment in which the spring constants of the respective mirror suspensions are coordinated with one another, so that the correct function or operation of the interferometer element 125 is ensured only by applying a single control voltage.

[0049] Fig. 6 shows a schematic representation of an interferometer 100 with a further embodiment of an interferometer element 125. In Fig. 6 An advantageous embodiment is described which consists of a series connection of two separate Fabry-Pérot filters FPI1 and FPI2, which are positioned relative to one another, for example, using a bonding process, either directly or via a separate carrier. The first Fabry-Pérot filter FPI1 contains the first 135 and second 140 mirror elements, whereas the second Fabry-Pérot filter FPI2 contains the third 145 and a fourth mirror element 610, which are arranged at a variable third distance 160 from one another. This essentially makes it possible to decouple the second Fabry-Pérot filter FPI2 from the second mirror element 140. For example, the fourth mirror element 610 can be arranged serially in the light path between the second 140 and the third mirror element 145.The second distance 165 and / or the third distance 615 are changed by means of a second micromechanical, specifically microelectromechanical (MEMS) actuator 620, which is controlled, for example, by means of a corresponding (further) control signal 625. The use of identical Fabry-Pérot filters FPI1 and FPI2, which are operated with separate actuators 155 and 620, respectively, and with different orders and thus distances 160, 165, and 615, respectively, can lead to a simplification of the manufacturing effort for producing such an interferometer element 125. Fig. 6 thus shows an embodiment in which two actuators 155 and 620 designed as MEMS components are used, which can each change the distance 160 or 615 between two mirror elements.

[0050] Fig. 7 shows a schematic representation of an interferometer 100 with a further embodiment of an interferometer element 125. This interferometer element 125 has a modified distribution of the two Fabry-Pérot filters FPI1 and FPI2 in the light path 120. Here, the object 115 (as target) is arranged in the light path 120 between the second mirror element 140 and the third 145 or fourth 610 mirror element. Fig. 7 thus shows an embodiment in which a Fabry-Pérot filter FPI1 (whose mirror distance is changed by a first micromechanical actuator 155) is positioned in front of the light source 105 and a second Fabry-Pérot filter FPI2 (whose mirror distance is changed by a second micromechanical actuator 620) is positioned in front of the detector 190.

[0051] Fig. 8 shows diagrams according to the representation from the Fig. 2 or the Fig. 3 , in which the spectral behavior of two series-connected FPIs with a phase shift dispersion is shown. In the area of ​​the rectangle with order 6 (FPI1) ​​and order 4 (FPI2), a resonance wavelength was expected (according to the representation in the Fig. 2 Due to the phase shift dispersion, the used orders experience a different nonlinearity with regard to the behavior between gap distance and wavelength, so that these resonance wavelengths are also blocked and lead to a larger spectral measurement range / detector. In comparison to this advantage, in Fig. 2 a linear dependence between gap distance and wavelength is shown, so that orders 3 / 6 / .. (FPI1) ​​and order 2 / 4 / .. (FPI2) can pass the FPI combination. Fig. 8 The diagrams show an example in which phase-shift dispersion at different orders and thus gap distances can lead to an increase in the measurement range. In the region of the rectangle with order 6 (FPI1) ​​and order 4 (FPI2), a resonance wavelength was expected that can pass through the FPI combination (lower FWHM) comparable to order 3 (FPI1) ​​and order 2 (FPI2). Fig. 9 shows a flow diagram of a method 900 for operating a variant of an interferometer 100 presented here, wherein the method 900 has a step 910 of changing the first distance and the second distance in order to obtain an output light. Finally, the method 900 comprises a step 920 of detecting and / or analyzing output light emerging from the interferometer element. In summary, it should be noted that in embodiments of the approach presented here, an actuator 155 of the first Fabry-Pérot filter FPI1 is positioned directly in front of the light source 105 (e.g., as an emitter-lens combination) and can temporally modulate the spectral behavior of the light source 105 by temporally modifying the first distance 160. Alternatively or additionally, a second actuator 620 of the second Fabry-Pérot filter FPI2 can be used together, e.g., with a high-pass filter orA bandpass filter element 130 can be positioned in front of the detector 190 / detectors 190a, 190b. In this embodiment, the distance 160 of the respective FPI (different order compared to actuator 155 of the first Fabry-Pérot filter FPI1) ​​is kept static.

[0052] The temporal modulation of the light intensity of the light source 105 of a wavelength can lead to an improved suppression of the ambient light and the subsequent electronics or an evaluation unit (which is formed, for example, as part of the control unit 195) if the detector signals are filtered and evaluated according to the modulation frequency. Fig. 3 (Maximum) and Fig. 4 (Minimum) show examples of the spectral intensity values ​​obtained in this way.

[0053] Due to the increase in the measuring range, an embodiment that can adjust a larger gap distance variation is advantageous. This is advantageously possible, for example, with an electrostatic and / or magnetic and / or piezoelectric drive as actuator 155 or 620 and with, for example, a detection of the gap distance (capacitive, piezoresistive).

[0054] One specific goal of the approach presented here is to increase the wavelength measurement range and robustness against ambient light influences for non-modulatable light sources. The wavelength measurement range can also be increased by suppressing unwanted wavelength orders of an FPI cavity in the entire light path while simultaneously maintaining a narrow spectral half-width and high resolution. Additionally or alternatively, parallel or serially mounted detectors can be used, whose spectral sensitivity and transmittance allow for an increase in the wavelength measurement range. Furthermore, the robustness of embodiments of an interferometer element presented here against ambient light influences is increased by modulating the transmission of the FPI light path, for example, in "shutter" mode.

[0055] To achieve such advantages, embodiments of the approach presented here can comprise an interferometer element as a component, which can be used in a miniature spectrometer and comprises a light source, a spectral element, and a photodetector. Another advantageous embodiment is one in which the spectral element is constructed from micromechanical Fabry-Pérot interferometer components with greater than or equal to three mirror elements arranged one above the other, which are positioned by adjustable spacings of at least two. Furthermore, the photodetector can also consist of individual detectors with different spectral sensitivities (optionally with upstream filter(s)), which, when suitably positioned, allow an overall increase in the wavelength measurement range.In another embodiment, the transmission of the entire light path can be influenced by adjusting the two mirror positions in a "shutter" mode, allowing the light intensity to be modulated at the wavelengths to be measured. Another advantageous embodiment of the approach presented here is one with an upstream filter element to restrict the entire measurement range and exclude unwanted wavelength ranges. In one embodiment, the necessary mirror spacings can also be measured, and the control unit can control or regulate the required mirror spacings, enabling evaluation of the detector signals. According to another embodiment, only the first mirror spacing, for example, can be measured according to the desired wavelength, and the other mirror spacings can be adjusted according to the optical detector signal, ensuring maximum transmission at every time range.Another advantageous embodiment is one in which the mirror elements are driven piezoelectrically or magnetically, so that a larger gap adjustment range, i.e. a range of changes in the first and second distance, can be used, in contrast to an electrostatic drive. This makes it possible to cover a larger measuring range with the same orders, and switching to other orders (e.g. from order 2 / 3 to orders 2 / 5 or 5 / 3) is avoided. Switching would result in additional errors in the transmission of the FPI (based on tolerances), and an additional settling time must be taken into account. In a further embodiment, the material of the mirror elements can be selected such that a wavelength-dependent phase shift (dispersion) creates a very large measuring range, whereby, for example, further orders are suppressed. By selecting a broadband mirror material (metal orBRAGG structure), the wavelength-dependent phase shift is supported, so that a larger gap adjustment range is advantageous. One embodiment of the approach presented here is particularly easy to implement, with an FPI design, so that the required position of both mirror spacings is achieved with just one control voltage (e.g., by different design of the spring geometries of the respective FPI mirror elements when the FPI cavities or spacings are operated with different orders). Overall, one advantage of one or more embodiments is that an increase in the spectral measurement range is possible compared to a standard FPI. The spectral measurement range can also be increased by wavelength-dependent phase shift.Alternatively or additionally, a better spectral half-width can be achieved by using higher orders, where the measurable wavelength range would be very small with a conventional setup. Parallel measurement of different spectral ranges (using different detectors) also leads to a reduction in measurement time. Finally, modulating the light intensity allows the use of non-modulatable light sources while simultaneously improving noise suppression of the ambient light and the downstream electronics.

[0056] If an embodiment includes an "and / or" link between a first feature and a second feature, this should be read as meaning that the embodiment according to one embodiment has both the first feature and the second feature and according to another embodiment has either only the first feature or only the second feature.

Claims

1. Interferometer element (125) for use in a spectrometer (100), with the interferometer element (125) having the following feature: - a micromechanical Fabry-Pérot filter element (FPI1, FPI2), which has at least a first mirror element (135), a second mirror element (140), and a third mirror element (145), which are arranged in series in an optical path (120) of the interferometer element (125), and with a first distance (160) between the first (135) and second (140) mirror elements and a second distance (165) between the second (140) and third (145) mirror elements being modifiable, a resonator cavity of a first Fabry-Pérot interferometer (FPI1) being formed between the first mirror element (135) and the second mirror element (140), and a resonator cavity of a second Fabry-Pérot interferometer (FPI2) being formed between the second mirror element (140) and the third mirror element (145), - a control unit (195) for electrically controlling a modification of the first (160) and second (165) distances, characterized in that the control unit (195) is embodied and configured to modify, with a jointly applied voltage and / or a jointly applied current for changing the first and second distances (160, 165), the first distance (160) by a distance value other than the second distance (165).

2. Interferometer element (125) according to Claim 1, wherein a material of the first mirror element (135) differs from a material of the second mirror element (140), and / or the material of the second mirror element (140) differs from a material of the third mirror element (145), in particular in a manner such that the mirrors formed have different dispersions of the phase jump during the reflection.

3. Interferometer element (125) according to Claim 2, wherein the material of the first (135), second (140), and / or third (145) mirror elements is a metallic or metal-containing material and / or differs with respect to the refractive index.

4. Interferometer element (125) according to any of the preceding claims, wherein the control unit (195) is embodied and configured to cyclically repeat a modification of the first (160) and second (165) distances.

5. Interferometer element (125) according to Claim 4, wherein the control unit (195) is embodied and configured to modify the first (160) and / or second (165) distance electrostatically, piezoelectrically and / or magnetically.

6. Interferometer element (125) according to Claim 4 or 5, wherein the control unit (195) is embodied and configured to modify the first (160) and / or second (165) distance in response to a read distance signal (198), wherein the distance signal (198) represents a current first (160) and / or a second (165) distance and / or wherein the control unit (195) is embodied to set a maximum transmission of light through the Fabry-Pérot filter element (FPI1, FPI2) by way of the modification.

7. Interferometer element (125) according to any of the preceding claims, wherein spring tensions and / or spring elasticities of the first (135), second (140), and / or third (145) mirror element of the Fabry-Pérot filter element (FPI1, FPI2) differ.

8. Interferometer element (125) according to any of the preceding claims, wherein the Fabry-Pérot filter element (FPI1, FPI2) is designed such that an object (115) that is to be examined using the interferometer element (125) should be positioned between the first (135) and second (140) mirror elements and / or between the second (140) and third (145) mirror elements.

9. Interferometer element (125) according to any of the preceding claims, having a spectral filter element (130) for attenuating and / or blocking a transmission of light (110) of a predetermined wavelength range through the interferometer element (125).

10. Interferometer element (125) according to any of the preceding claims, having at least a fourth mirror element (610), which is arranged in the optical path (120) in series with respect to the first (135), second (140), and third (145) mirror elements, and wherein a third distance (615) between the third (145) and fourth (610) mirror elements is modifiable.

11. Spectrometer (100) with an interferometer element (125) according to any of the preceding claims, a light source (105) for providing the light beam (110) through the interferometer element (125), and a detector (190) for capturing output light (180) emerging from the spectrometer (100).

12. Spectrometer (100) according to Claim 11, wherein the detector (190) has a plurality of detector elements (190a, 190b) that are embodied for light (110) of different wavelength ranges and / or wherein the light source (105) is designed for the non-modulatable output of light (110).

13. Method (900) for operating an interferometer (100) according to Claim 11 or 12, wherein the method (900) has the following features: - modifying (910) the first distance (160) and the second distance (165) to obtain output light (180); and - detecting (920) and / or analysing output light (180) emerging from the interferometer element (125).

14. Computer program configured for performing and / or controlling the method (900) according to Claim 13.

15. Machine-readable storage medium on which the computer program according to Claim 14 is stored.