Mass device for an optical acceleration sensor and optical acceleration sensor

Abstract

Embodiments provide a mass device for an optical acceleration sensor. The mass device comprises a seismic mass and a frame, wherein the seismic mass is suspended from the frame via spring elements, wherein a surface of the seismic mass has at least one optical diffraction grating.

Description

[0001] Embodiments of the present invention relate to a mass device with a seismic mass for an optical acceleration sensor. Further embodiments relate to an optical acceleration sensor. Some embodiments relate to an optically scanned acceleration sensor with diffraction gratings.

[0002] Various types of acceleration sensors are known. Capacitive and piezoresistive MEMS (Micro Electro Mechanical System) acceleration sensors are commonly used. Both consist of a multi-material composite and therefore exhibit drift.

[0003] In detail, MEMS acceleration sensors consist of a spring-suspended seismic mass and interdigital structures in silicon. The interdigital structures are equipped with metal electrodes, which are produced, for example, using physical vapor deposition (PVD), to capacitively detect the deflection of the seismic mass. The seismic mass and springs are created from bulk silicon using etching processes. Furthermore, additional materials are deposited to electrically contact the electrodes. Due to the multitude of different materials, each with its own thermal expansion coefficient, and the numerous processes involved in the manufacture of acceleration sensors, intrinsic mechanical stresses arise during production. These stresses are partially, but not completely, relieved after production through a burn-in process.The remaining mechanical stresses dissipate over the lifetime of the accelerometer, leading to a drift of the sensor signal, which is why regular calibration is required.

[0004] In the field of optical acceleration sensors, there are (fiber) Bragg acceleration sensors [1] [2], laser Doppler vibrometers [3], and cavity resonance-based MEMS [4], which can cover static and dynamic applications and offer very high performance in terms of measurement accuracy and temperature range. However, these are very complex in terms of excitation and readout (interferometers, spectrometers, etc.) and thus, as a complete solution, very expensive due to the complex measurement technology. There are also NEMS (Nano Electro Mechanical System) based on grating structures [5]. However, these are generally characterized by non-sinusoidal signal waveforms, which either results in ambiguous signals or means a limitation in resolution or measurement range, since these signals cannot be interpolated with high resolution over a wide range with reasonable effort.

[0005] In [7] a lattice diffraction type MOEMS accelerometer based on a lithium niobate crystal is described.

[0006] In [8], a micro-integrated three-axis acceleration sensor structure of the light interference type and a method for resolving it are described.

[0007] The present invention is therefore based on the object of creating a concept which enables the realization of an acceleration sensor with an improved resolution or an improved measuring range, and whose sensor signals exhibit no or only a minor shift over time.

[0008] This problem is solved by the independent patent claims.

[0009] Advantageous further developments can be found in the dependent patent claims.

[0010] Embodiments provide a mass device for an optical acceleration sensor. The mass device comprises a seismic mass and a frame, wherein the seismic mass is suspended from the frame via [e.g., at least two or at least four] spring elements, wherein a surface of the seismic mass has at least one optical diffraction grating.

[0011] Embodiments of the present invention enable the use of optical scanning in acceleration sensors, whereby shifts in signal parameters / signal properties of the sensor signals over time can be reduced.

[0012] In embodiments, the at least one optical diffraction grating is configured to diffract a monochromatic light [e.g., a laser] incident on the optical diffraction grating.

[0013] In embodiments, the surface of the seismic mass is structured to form the at least one optical diffraction grating.

[0014] In embodiments, the surface of the seismic mass has at least two optical diffraction gratings.

[0015] In embodiments, the at least two optical diffraction gratings have at least two different grating constants.

[0016] For example, the seismic mass may comprise two optical diffraction gratings, a first optical diffraction grating having a first grating constant, and a second optical diffraction grating having a second grating constant. Furthermore, the seismic mass may comprise four optical diffraction gratings, a first optical diffraction grating and a third optical diffraction grating having a first grating constant, and a second optical diffraction grating and a fourth optical diffraction grating having a second grating constant. Alternatively, the four optical diffraction gratings may also have more than two different grating constants, such as three or four different grating constants.

[0017] In embodiments, the grating structures of the at least two optical diffraction gratings are arranged along at least two different directions on the surface of the seismic mass.

[0018] For example, the seismic mass may have two optical diffraction gratings, wherein grating structures of a first optical diffraction grating are arranged in a first direction, wherein grating structures of a second optical diffraction grating are arranged in a second direction. Furthermore, the seismic mass may have four optical diffraction gratings, wherein grating structures of a first optical diffraction grating and a third optical diffraction grating are arranged in a first direction, wherein grating structures of a second optical diffraction grating and a fourth optical diffraction grating are arranged in a second direction. Alternatively, the grating structures of the four optical diffraction gratings may also be arranged in more than two different directions, such as in three or four different directions.

[0019] In embodiments, the at least two optical diffraction gratings have at least two different grating constants, wherein grating structures of the at least two optical diffraction gratings are arranged along at least two different directions on the surface of the seismic mass, so that a monochromatic light [e.g. of a laser] incident on the optical diffraction grating is diffracted in at least two different directions.

[0020] In embodiments, the seismic mass can be deflected parallel to the surface [e.g. by an acceleration acting on the seismic mass [e.g. parallel to the surface]].

[0021] In embodiments, the seismic mass is deflectable perpendicular to the surface [e.g. by an acceleration acting on the seismic mass [e.g. perpendicular to the surface]].

[0022] In embodiments, the seismic mass is suspended so as to be rotatable with respect to the frame [e.g., in a plane parallel to the surface of the seismic mass].

[0023] In embodiments, the seismic mass is suspended in a tiltable manner with respect to the frame.

[0024] In embodiments, the seismic mass and / or the frame and / or the spring elements comprise glass, metal, ceramic, silicon, crystal(s) [e.g., such as quartz(s)], an alloy, or [e.g., coated] plastic.

[0025] Further embodiments provide an optical acceleration sensor. The optical acceleration sensor comprises a mass device according to one of the embodiments described herein, a laser, and at least one optical detector. The laser is configured to generate monochromatic light [e.g., in the form of a laser beam] and to direct it onto the at least one optical diffraction grating on the surface of the seismic mass of the mass device. The at least one optical detector [e.g., a photodetector] is configured to detect light diffracted by the at least one optical diffraction grating and to provide a sensor signal dependent on the detected light.

[0026] In embodiments, the monochromatic light generated by the laser is focused via a lens.

[0027] In embodiments, the laser has a Gaussian beam profile.

[0028] In embodiments, the optical acceleration sensor has at least two optical detectors.

[0029] In embodiments, the at least two optical detectors are arranged at different positions along a beam path of the diffracted light.

[0030] In embodiments, the at least two optical detectors are arranged axially symmetrically with respect to the laser or laser beam [e.g., with respect to an axis intersecting the laser or laser beam].

[0031] In embodiments, the at least two optical detectors are arranged rotationally symmetrically with respect to the laser or laser beam.

[0032] In embodiments, the at least two optical detectors are arranged symmetrically with respect to a plane that is perpendicular to the surface of the seismic mass and that runs along a propagation direction of the monochromatic light [e.g., laser beam] generated by the laser.

[0033] In embodiments, the at least two optical detectors are arranged rotationally symmetrically with respect to an axis that is perpendicular to the surface of the seismic mass and hits a point at which the monochromatic light generated by the laser hits the at least one diffraction grating.

[0034] In embodiments, the optical acceleration sensor has at least four optical detectors.

[0035] In embodiments, the at least two optical detectors form a photodetector array.

[0036] In embodiments, the at least two optical detectors are implemented on a common substrate.

[0037] In embodiments, the optical acceleration sensor has evaluation electronics designed to evaluate the sensor signals provided by the at least two optical detectors in order to determine an acceleration of the seismic mass.

[0038] In embodiments, the sensor signals provided by the at least two optical detectors comprise photocurrents, wherein the evaluation electronics are designed to convert the photocurrents into voltage signals by means of transimpedance amplifiers.

[0039] In embodiments, the evaluation electronics are designed to convert the voltage signals into digital sensor signals by means of analog-to-digital converters and to perform an ATAN2 interpolation of the digital sensor signals.

[0040] In some embodiments, amplitude control and / or offset correction of the (digital) sensor signals can be performed prior to ATAN2 interpolation. For example, this can reduce interference effects such as tilting or twisting of the seismic mass with respect to the optical detectors and / or the laser.

[0041] In embodiments, the optical acceleration sensor comprises a drive circuit configured to generate a drive signal for operating the laser.

[0042] In embodiments, the control circuit is designed to provide the control signal based on a sum signal control, wherein the sum signal control uses the sum square of the digital sensor signals.

[0043] In embodiments, the optical acceleration sensor has an optical element [e.g. a lens, such as a cylindrical lens] that is arranged in an optical path of the laser [e.g. between the laser and the grating structure], wherein the optical element is designed to cause an astigmatic aberration on the surface or the grating structure of the seismic mass, which leads to an elliptical distortion occurring in front of and behind the focal point [e.g. wherein the ellipse is rotated by 90° before and after the focus].

[0044] In embodiments, at least one optical detector of the at least one optical detector is a quadrant detector and is configured to detect a perpendicular movement [e.g., perpendicular to the surface] of the seismic mass.

[0045] In embodiments, the suspension of the seismic mass alternatively or additionally allows a rotation in the plane and / or a tilting relative to the frame.

[0046] In embodiments, the optical acceleration sensor has an optical element [e.g. beam splitter] that is arranged in an optical path of the laser and is designed to direct the monochromatic light generated by the laser in the form of at least two light beams or laser beams onto the surface or the optical diffraction gratings on the surface of the seismic mass. Alternatively, the optical acceleration sensor can also have two or more lasers to direct at least two light beams or laser beams onto the surface or the optical diffraction gratings on the surface of the seismic mass. In both cases, the optical acceleration sensor or the evaluation electronics can be designed to detect a rotation and / or tilt of the seismic mass with respect to the frame by comparing the sensor signals from at least two optical detectors.

[0047] For example, at least two light beams can strike the seismic mass and corresponding detectors are provided to detect a rotation in the plane and / or a tilt relative to the frame by comparing the signals of the two or more light beams.

[0048] Embodiments of the present invention are described in more detail with reference to the accompanying figures. They show: Fig. 1a is a schematic plan view of a mass device according to an embodiment of the present invention, Fig. 1b is a schematic sectional view through the mass device according to an embodiment of the present invention, Fig. 2a is a schematic plan view of an optical acceleration sensor according to an embodiment of the present invention, Fig. 2b is a schematic cross-sectional view through the optical acceleration sensor according to an embodiment of the present invention, Fig. 3 is a schematic plan view of an optical acceleration sensor according to a further embodiment of the present invention, Fig. 4 is a schematic plan view of an optical acceleration sensor according to a further embodiment of the present invention, Fig. 5 is a schematic view of an optical acceleration sensor according to another embodiment of the present invention.

[0049] In the following description of the embodiments of the present invention, identical or equivalent elements in the figures are provided with the same reference numerals so that their description is interchangeable.

[0050] The embodiments of the mass device and the optical acceleration sensor described below make it possible to solve the problem of sensor signal drift over time in existing acceleration sensor technologies by enabling or utilizing a different sensing principle. The use of optical sensing, for example, enables a reduction in the number of materials involved with different thermal expansion coefficients and a reduction in the number of process steps.

[0051] According to embodiments, at least one optical diffraction grating is introduced on a surface of a seismic mass into a substrate (e.g. silicon) of the seismic mass, which makes it possible to sense a deflection of the seismic mass with an optical module, whereby the seismic mass or the substrate of the seismic mass functions only as a passive element.

[0052] Fig. 1a shows a schematic plan view of a mass device 100 and Fig. 1b shows a schematic sectional view through the mass device 100, according to an embodiment of the present invention.

[0053] The mass device 100 comprises a seismic mass 102 and a frame 104, wherein the seismic mass 102 is suspended from the frame 104 via spring elements 106, wherein a surface 108 of the seismic mass 102 has at least one optical diffraction grating 110.

[0054] In embodiments, the at least one optical diffraction grating 110 can be configured to diffract a monochromatic light (e.g., a laser) incident on the at least one optical diffraction grating 110. The diffracted light can in turn be detected by an optical detector, whereby an optical acceleration sensor can be realized, as will be described further below with reference to the Fig. 2a to 5 are described in more detail.

[0055] In embodiments, the surface 108 of the seismic mass 102 may be structured to form the at least one optical diffraction grating 110.

[0056] In embodiments, the seismic mass 102 may also have more than one diffraction grating 110. In embodiments, the seismic mass 102 may generally have n diffraction gratings, where n is a natural number greater than or equal to one, n ≥ 1. If the seismic mass has two or more diffraction gratings, at least two of these diffraction gratings may have different grating constants, such as a first grating constant and a second grating constant, and / or extend along different directions on the surface 108 of the seismic mass 102, such as a first direction and a second direction (see also the Fig. 5 shown embodiment).

[0057] To illustrate the position of the individual elements in relation to each other, the Fig. 1a and Fig. 1b an xyz coordinate system is drawn, with an x-axis, a y-axis and a z-axis, each perpendicular to each other.

[0058] As in the Fig. 1a and Fig. 1b, the surface 108 having the at least one optical diffraction grating 110 may be parallel to the xy plane.

[0059] In embodiments, the seismic mass 102 may be deflectable parallel to the surface (ie, in a direction parallel to the xy plane), as shown in Fig. 1b is indicated by the arrow 112, for example by an acceleration acting on the seismic mass 102 parallel to the surface 108 (ie an acceleration acting along a direction parallel to the xy plane).

[0060] In embodiments, the seismic mass 102 may be deflectable perpendicular to the surface (ie, in a direction perpendicular to the xy-plane or parallel to the z-axis), as shown in Fig. 1b is indicated by the arrow 114, for example by an acceleration acting on the seismic mass 102 perpendicular to the surface 108 (ie an acceleration acting along a direction perpendicular to the xy-plane or parallel to the z-axis).

[0061] In embodiments, the seismic mass 102 may be suspended tiltably with respect to the frame 104, for example, about an axis that is parallel to the xy-plane. Such tilting is Fig. 1b is indicated by the arrow 116.

[0062] In embodiments, the seismic mass 102 may be suspended rotatably with respect to the frame 104, for example, in a plane parallel to the xy plane. This is shown in Fig. 1a is indicated by the arrow 118.

[0063] In embodiments, the seismic mass 102 and / or the frame 104 and / or the spring elements 106 may comprise glass, metal, ceramic, silicon, crystals, alloys, or plastic.

[0064] For example, the seismic mass 102 (e.g., of the acceleration sensor) can be made of any material, such as glass, various metals and alloys, ceramics, crystals (e.g., quartz), and silicon. Monocrystalline silicon is particularly advantageous because, due to the absence of lattice defects, it enables fatigue-free bending springs; it does not creep and does not undergo plastic deformation—the elastic behavior of monocrystalline silicon extends to fracture. Furthermore, many processes for structuring monocrystalline silicon are known, not only for structuring the seismic mass 102 and its bending springs 106 themselves, but also for the dimensional scale on it, which is crucial for optical scanning.

[0065] Fig. 2a shows a schematic plan view of an optical acceleration sensor 120 and Fig. Figure 2b shows a schematic cross-sectional view through the optical acceleration sensor 120, according to an embodiment of the present invention.

[0066] The optical acceleration sensor 120 comprises a laser 122, at least one optical detector 124 and the Fig. 1a and Fig. 1b described mass device 100 with the seismic mass 102 suspended from the frame 104 with the at least one optical diffraction grating 110.

[0067] The laser 122 is configured to generate monochromatic light 130 and direct it onto the at least one optical diffraction grating 110 on the surface 108 of the seismic mass 102 of the mass device.

[0068] The at least one optical detector 124 (e.g., photodetector) is configured to detect a light 132 diffracted by the at least one optical diffraction grating 110 and to provide a sensor signal dependent on the detected light.

[0069] In embodiments, the optical acceleration sensor 120 may also include more than one optical detector 124. Thus, the optical acceleration sensor 120 may generally include m optical detectors 124, where m is a natural number greater than or equal to one, m ≥ 1. For example, the optical acceleration sensor 120 may include two, three, four, five, six, seven, or more optical detectors. If the optical acceleration sensor 120 includes two or more optical detectors, these may form a photodetector array and / or be implemented on a common substrate.

[0070] In embodiments, the monochromatic light generated by the laser 122 can be focused on the at least one diffraction grating 110, e.g., by means of a lens.

[0071] In embodiments, the laser 122 may have a Gaussian beam profile.

[0072] Fig. Figure 3 shows a schematic plan view of an optical acceleration sensor 120 according to another embodiment of the present invention. Compared to the Fig. 2a and Fig. 2b, the optical acceleration sensor 120 in the embodiment shown in Fig. 3, the embodiment shown has at least two optical detectors, as indicated by the two optical detectors 124_1 and 124_2 as well as the two optional optical detectors 124_3 and 124_4 shown in dashed lines.

[0073] As this is Fig. 3, the at least two optical detectors 124_1 and 124_2 can be arranged at different positions along the diffracted light.

[0074] For example, the at least two optical detectors 124_1 and 124_2 can be arranged axially symmetrically with respect to the laser 122 or laser beam, for example with respect to an axis 140 that intersects the laser 122 or laser beam and, for example, runs parallel to the surface of the seismic mass 102. In other words, the at least two optical detectors 124_1 and 124_2 can be arranged symmetrically with respect to a plane that is perpendicular to the surface of the seismic mass 102 and that runs along a propagation direction of the monochromatic light generated by the laser [e.g., laser beam].

[0075] Fig. Figure 4 shows a schematic plan view of an optical acceleration sensor 120 according to another embodiment of the present invention. Compared to the Fig. 2a and Fig. 2b, the optical acceleration sensor 120 in the embodiment shown in Fig. 4, the embodiment shown has at least two optical detectors, as indicated by the two optical detectors 124_1 and 124_2 as well as the two optional optical detectors 124_3 and 124_4 shown in dashed lines.

[0076] As this is Fig. 4, the at least two optical detectors 124_1 and 124_2 can be arranged at different positions along the diffracted light.

[0077] For example, the at least two optical detectors 124_1 and 124_2 can be arranged rotationally symmetrically with respect to the laser 122 or laser beam. For example, the at least two optical detectors 124_1 and 124_2 can be arranged rotationally symmetrically with respect to an axis 142 that is perpendicular to the surface of the seismic mass 120 and, for example, strikes a point at which the monochromatic light generated by the laser strikes the at least one diffraction grating 110.

[0078] Fig. 5 shows a schematic view of an optical acceleration sensor 120 according to an embodiment of the present invention.

[0079] The optical acceleration sensor 120 comprises a mass device with a seismic mass 102, which is suspended from a frame 104 via spring elements 106, as already described above, wherein the seismic mass 102 in the Fig. 5, for illustrative purposes, comprises a plurality of diffraction gratings 110_1-110_4, as shown in the section 150 on the surface 108 of the seismic mass 102.

[0080] Furthermore, the optical acceleration sensor 120 comprises a laser 122 configured to generate monochromatic light 130 and to direct it onto the optical diffraction gratings 110_1-110_4 on the surface 108 of the seismic mass 102. As shown in Fig. 5, the optical acceleration sensor 120 may include an optical element 123, such as a lens, disposed in the optical path of the laser 122.

[0081] Furthermore, the optical acceleration sensor 120 comprises at least one optical detector, as already described above, wherein in the Fig. In the exemplary embodiment shown in Figure 5, it is assumed, by way of example, that the optical acceleration sensor 120 has five optical detectors 124_1-124_5. The optical detectors 124_1-124_5 can be arranged at different positions along a beam path of the diffracted light 132.

[0082] As this is Fig. 5, the diffraction gratings 110_1-110_4 may have different grating constants and extend in different directions on the surface 108 of the seismic mass.

[0083] For example, a first diffraction grating 110_1 may have a first grating constant and extend in a first direction, while a second diffraction grating 110_2 may have a second grating constant and extend in a second direction. A third diffraction grating 110_3 may have a third grating constant and extend in a third direction, while a fourth diffraction grating 110_4 may have a fourth grating constant and extend in a fourth direction.

[0084] In embodiments, the seismic mass 102 of the acceleration sensor can be structured on its surface 108 such that this surface 108 represents a diffraction grating for a specific optical wavelength. In embodiments, this diffraction grating can be divided into strips whose grating structures are tilted at different angles and contain different grating constants. Therefore, they diffract the monochromatic and coherent laser light in different directions. In embodiments, these segments can be placed equidistantly, and the sequence of grating tilt angles can repeat regularly. In the simplest differential case, such a repeating unit is composed of four large segments and four separating bars between them. The beam diameter of the incident Gaussian beam should be as identical as possible to the length of such a repeating unit.The convolution of the rectangular grid segments and the Gaussian profile of the laser beam produces sinusoidally intensity-modulated signals as the seismic mass moves. These signals are deflected by the diffraction angle relative to the laser's impact point on the seismic mass. This allows the generation of sinusoidal and cosinusoidal signals, as well as signals for an index mark.

[0085] The optics module (see Fig. 7) can comprise a light source with a Gaussian beam profile and photodetectors. When the beam from the light source of the optics module hits the optical diffraction grating on the seismic mass, it is deflected in the corresponding spatial directions and impinges on the photodetectors. If the seismic mass is then deflected, the intensity of the diffracted light from the light source striking the photodetectors is sinusoidally modulated, resulting in modulated photocurrents. The period length of the diffraction grating corresponds to the beam diameter of the laser.

[0086] In embodiments, at least two or at least four photodetectors can be arranged at a suitable location along the path of the diffracted beams, which then supply, for example, at least two or at least four sinusoidal signals that are phase-shifted by 90° relative to one another, i.e., a differential sine and a differential cosine. This makes it possible to eliminate interference effects such as offset, extraneous light, etc. The separating webs between the large grating segments can also contain diffraction gratings and thus generate an index signal. This is then not repeated, for example, across all four grating segments, but has the same shape across the entire measuring scale, differing only at the location of the index signal. Here, a simple index signal can be generated with one photodetector, or a differential index signal with two photodetectors. In addition, the negative first diffraction order can also be used, in which case the number of photodetectors is doubled accordingly, for example12 with a point-symmetric arrangement around the laser. This leads to an improved signal-to-noise ratio (SNR) and increased error tolerance. Point or axial symmetry of the arrangement is advantageous for compensating for geometric interference and temperature effects. The system is scalable from low-cost to high-resolution.

[0087] In exemplary embodiments, the photodetectors can be positioned almost arbitrarily in conjunction with the grating constant and the grating inclination. They do not have to be present as discrete components, but can also be part of a photodetector array or opto-ASIC. The latter could theoretically also contain the light source. In the simplest case, a VCSEL (Vertical Cavity Surface Emitting Laser, a laser diode that emits light in a conical beam vertically from the surface of a manufactured wafer) can be used, ideally with a Gaussian profile. However, other light sources, possibly with optics, should also be considered.

[0088] In some embodiments, voltage signals can be generated from the photocurrents using transient impedance amplifiers, which are then sampled and digitized by an analog-to-digital converter. Subsequent ATAN2 interpolation of the digitized signals can further increase the resolution of the signals, resulting in a higher spatial resolution of the deflected seismic mass. This is not feasible with other grid arrangements. Grid arrangements that generate linear or other curves can only be interpolated to a very limited extent.

[0089] Furthermore, it is possible to operate the light source via a sum signal control in order to compensate for temperature and aging effects of the optoelectric components.

[0090] In some embodiments, smaller feature sizes (shorter period lengths) can lead to higher resolution. For example, excitation can be achieved with shorter-wavelength light (e.g., infrared light, red light, green light, blue light, or ultraviolet light), e.g., using a corresponding VCSEL (VCSEL = Vertical Cavity Surface Emitting Laser, a laser diode that emits light in a conical beam vertically from the surface of a fabricated wafer), or with frequency-doubling crystals, or with edge-emitting laser diodes, and seismic masses can be fabricated in SiO2 / glass, glassomers, or electroplated.

[0091] In some embodiments, the optical readout technology can also be extended to detect vertical deflection in addition to in-plane deflection using a laser spot (see focus control in CD / DVD readers). This also enables sensor setups that can detect acceleration in all three spatial directions. A further extension is the use of two or three laser spots to detect tilting of the seismic mass.

[0092] In some embodiments, the MEMS element can be used in high-temperature applications, as the MEMS element can be used as a passive element. Illumination and sensing could then be performed via fiber optics, with coupling into the fiber optics occurring via the optics module, which is located in a moderate-temperature environment. The optics module could also be implemented as an OptoASIC.

[0093] In some embodiments, the optical scanning of the acceleration sensor can be based on the rotary encoder technology described in [6], which results in low drift. In some embodiments, the optical readout technology known from [6] can be applied to acceleration sensors, thereby creating an acceleration sensor with particularly advantageous properties.

[0094] Embodiments enable a reduction (or even minimization) of layers on the sensor element (seismic mass) and thus the avoidance of stress relaxation / drift (seismic mass can thus be regarded as a nearly ideally elastic element). This is made possible in embodiments by a contactless optical readout principle. For example, the readout principle described in [6] can be used for this purpose, for which only optical grating structures are introduced into a seismic mass (e.g., silicon of a MEMS), and an optics module can be used. This enables a significant reduction in the technical complexity of the sensor compared to other optical acceleration sensors with their complex excitation and readout processes.

[0095] The readout principle has so far only been used in rotary encoders and linear scales, and most acceleration sensor manufacturers are not familiar with the optical readout principle and do not produce rotary encoders or linear scales at the same time.

[0096] Some embodiments use the optical readout principle described in [6].

[0097] In some embodiments, a cost-effective micro / nano-structuring process (nanoimprint) can be used to cost-efficiently and precisely manufacture the optical grating structures on silicon.

[0098] In some embodiments, a standard micromachining process can be used to manufacture the spring-mass system.

[0099] In some embodiments, a micro-assembly technique can be used for the entire system comprising the optics module and MEMS (bare chip assembly and active alignment of the lens).

[0100] Although embodiments of an optical acceleration sensor have been described herein, it should be noted that the concept described herein of optical scanning of at least one diffraction grating is also applicable to other fields, such as optical tilt angle sensors (e.g., structural monitoring, deep drilling, leveling) or optical microphones. In the case of a tilt angle sensor, for example, a seismic mass comprising at least one optical diffraction grating could be tiltably / rotatably suspended from a frame. In the case of an optical microphone, for example, a membrane could be suspended in a frame, the membrane comprising at least one optical diffraction grating.

[0101] Although some aspects have been described in the context of a device, it should be understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Analogously, aspects described in the context of or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the method steps may be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or more of the key method steps may be performed by such an apparatus.

[0102] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. Bibliography [1] Hottinger Baldwin Messtechnik GmbH, “Optical Accelerometer FS65:,” [Online]. Available: https: / / www.hbm.com / de / 4607 / fs65-optischerbeschleunigungsmesser-fibersensing / . [Accessed 13 03 2019]. [2] K. Zandi, J. Zou, B. Wong, RV Kruzelecky and Y.-A. Peter, “VOA-based optical MEMS accelerometer,” Istanbul, Turkey, 2011. [3] Polytec GmbH, „Laser-Doppler Vibrometer,“ [Online]. Available: https: / / www.polytec.com / de / vibrometrie / produkte / . [Accessed 13 03 2019]. [4] Y. Bao, F. Zhou, T. W. LeBrun and J. J. Gorman, „A photonic MEMS accelerometer with a low-finesse hemispherical microcavity readout,“ Santa Fe, NM, USA, 2017. [5] J. B. W. L. S. L. Qianbo Lu, „A Novel Scheme Design of a High-g Optical NEMS Accelerometer based on a Single Chip Grating with proper Sensitivity and Large Bandwidth,“ in Proceedings of the 10th IEEE International Conference onNano / Micro Engineered and Molecular Systems, Xi'an, China, 2015. [6] DE 10 2006 062691 A1 [7] CN 1 16 338 243 A [8] CN 1 17 929 786 A

Claims

[1] Mass device (100) for an optical acceleration sensor, with a seismic mass (102), and a frame (104), wherein the seismic mass (102) is suspended from the frame (104) via spring elements (106), wherein a surface (108) of the seismic mass (102) has at least one optical diffraction grating (110), wherein the at least one optical diffraction grating (110) is at least two optical diffraction gratings (110_1-110_4). [2] The mass device (100) according to claim 1, wherein the at least one optical diffraction grating (110) is configured to diffract a monochromatic light (130) incident on the optical diffraction grating (110). [3] Mass device (100) according to one of claims 1 and 2, wherein the surface (108) of the seismic mass (102) is structured to form the at least one optical diffraction grating (110). [4] Mass device (100) according to one of claims 1 to 3, wherein the at least two optical diffraction gratings (110_1-110_4) have at least two different grating constants. [5] Mass device (100) according to one of claims 1 to 4, wherein grating structures of the at least two optical diffraction gratings (110_1-110_4) are arranged along at least two different directions on the surface (108) of the seismic mass (102). [6] Mass device (100) according to claim 4 and 5, wherein the at least two optical diffraction gratings (110_1-110_4) have at least two different grating constants and grating structures of the at least two optical diffraction gratings (110_1-110_4) are arranged along at least two different directions on the surface (108) of the seismic mass (102), so that a monochromatic light (130) incident on the optical diffraction grating (110_1-110_4) is diffracted in at least two different directions. [7] Mass device (100) according to one of claims 1 to 6, wherein the seismic mass (102) is deflectable parallel to the surface (108) and / or wherein the seismic mass (102) is deflectable perpendicular to the surface (108). [8] Mass device (100) according to one of claims 1 to 7, wherein the seismic mass (102) comprises glass, metal, ceramic, silicon, crystal, alloys or plastic. [9] Optical acceleration sensor (120), having the following features: a mass device (100) according to one of claims 1 to 8, a laser (122) configured to generate monochromatic light (130) and to direct it onto the at least one optical diffraction grating (110) on the surface (108) of the seismic mass (102) of the mass device (100), at least one optical detector (124) configured to detect light diffracted by the at least one optical diffraction grating (110) and to provide a sensor signal dependent on the detected light. [10] Optical acceleration sensor (120) according to claim 9, wherein the monochromatic light generated by the laser (122) is focused via a lens. [11] Optical acceleration sensor (120) according to claim 9 or 10, wherein the laser (122) has a Gaussian beam profile. [12] Optical acceleration sensor (120) according to one of claims 9 to 11, wherein the at least one optical detector (124) is at least two optical detectors (124_1-124_2). [13] Optical acceleration sensor (120) according to claim 12, wherein the at least two optical detectors (124_1-124_2) are arranged at different positions along a beam path of the diffracted light. [14] Optical acceleration sensor (120) according to claim 12 or 13, wherein the at least two optical detectors (124_1-124_2) are arranged axially symmetrically with respect to the laser (122) or laser beam, or wherein the at least two optical detectors (124_1-124_2) are arranged rotationally symmetrically with respect to the laser (122) or laser beam. [15] Optical acceleration sensor (120) according to one of claims 12 to 13, wherein the at least two optical detectors (124_1-124_2) are arranged symmetrically with respect to a plane which is perpendicular to the surface (108) of the seismic mass (102) and which runs along a propagation direction of the monochromatic light generated by the laser (122). [16] Optical acceleration sensor (120) according to one of claims 12 to 13, wherein the at least two optical detectors (124_1-124_2) are arranged rotationally symmetrically with respect to an axis which is perpendicular to the surface (108) of the seismic mass (102) and strikes a point at which the monochromatic light generated by the laser (122) strikes the at least one diffraction grating (110). [17] Optical acceleration sensor (120) according to one of claims 12 to 16, wherein the at least two optical detectors (124_1-124_2) are at least four optical detectors. [18] Optical acceleration sensor (120) according to one of claims 12 to 16, wherein the at least two optical detectors (124_1-124_2) form a photodetector array, and / or wherein the at least two optical detectors (124_1-124_2) are implemented on a common substrate. [19] Optical acceleration sensor (120) according to one of claims 12 to 16, wherein the optical acceleration sensor (120) has evaluation electronics which are designed to evaluate the sensor signals provided by the at least two optical detectors (124_1-124_2) in order to determine an acceleration of the seismic mass (102). [20] Optical acceleration sensor (120) according to claim 19, wherein the sensor signals provided by the at least two optical detectors (124_1-124_2) comprise photocurrents, wherein the evaluation electronics are designed to convert the photocurrents into voltage signals by means of transimpedance amplifiers. [21] Optical acceleration sensor (120) according to claim 20, wherein the evaluation electronics are designed to convert the voltage signals into digital sensor signals by means of analog-to-digital converters and to carry out an ATAN2 interpolation of the digital sensor signals. [22] Optical acceleration sensor (120) according to claim 21, wherein the optical acceleration sensor (120) has a drive circuit configured to generate a drive signal for operating the laser (122), or wherein the control circuit is configured to provide the control signal based on a sum signal control, wherein the sum signal control uses the sum square of the digital sensor signals. [23] Optical acceleration sensor (120) according to one of claims 9 to 22, wherein the optical acceleration sensor (120) comprises an optical element (123) arranged in an optical path of the laser (122), wherein the optical element (123) is designed to cause an astigmatic imaging error on the surface (108) or the lattice structure of the seismic mass (102), which leads to an elliptical distortion occurring in front of and behind the focal point. [24] Optical acceleration sensor (120) according to claim 23, wherein at least one of the detectors (124_1-124_2) is designed as a quadrant detector to detect a vertical movement of the seismic mass (102). [25] Mass device (100) for an acceleration sensor according to claim 7, wherein the suspension of the seismic mass (102) alternatively or additionally allows a rotation in the plane and / or a tilting relative to the frame (104). [26] Optical acceleration sensor (120) according to one of claims 12 to 22, wherein at least two light beams impinge on the seismic mass (102) and corresponding detectors (124_1-124_2) are provided to detect a rotation in the plane and / or a tilt relative to the frame (104) by comparing the signals of the two or more light beams.

Images