WO2021176011A1

WO2021176011A1 - Arrangement and method for electromagnetic frequency modification

Info

Publication number: WO2021176011A1
Application number: PCT/EP2021/055508
Authority: WO
Inventors: Gerald Fuetterer
Original assignee: Technische Hochschule Deggendorf
Priority date: 2020-03-04
Filing date: 2021-03-04
Publication date: 2021-09-10
Also published as: EP4115542A1

Abstract

The invention relates to a modulator device for frequency modification of electromagnetic radiation by a reflecting current-carrying modulator layer. The invention also relates to an optical arrangement comprising such a modulator device and to a method for modulating a frequency and/or an amplitude of electromagnetic radiation using such a modulator device.

Description

Arrangement and method for electromagnetic frequency modification

FIELD OF THE INVENTION

The invention relates to an arrangement for the frequency modification of electromagnetic radiation, which is based on the interaction of electromagnetic wave fields with electrical charges under the action of an external field and is particularly compact and inexpensive. The invention further relates to an optical arrangement which comprises such a modulator device and a method for modulating a frequency and / or an amplitude of electromagnetic radiation using such a modulator device.

BACKGROUND OF THE INVENTION

The modulation of electromagnetic waves is one of the basis of the transmission of information. For example, amplitudes, frequencies, phases and polarization states can be modulated. In addition to the transmission of information, the modulation of electromagnetic waves is also playing an increasing role in optical measurement technology. Parameters such as the frequency bandwidth to be achieved for the modulation, the size, the number of components required, the technologies required for the components, the robustness of the system, the spectral properties of the system, the required manufacturing tolerances and the price of manufacture are decisive criteria for the respective Use.

Frequency modulation is playing an increasingly important role in three-dimensional measurement technology, in human-machine interaction and in sensor technology that is being developed for autonomous driving. A modulation of electromagnetic radiation can also take place in the form of a pulsed emission and a time-segmented sampling. Electromagnetic waves typically have wavelengths of 10 ¹³ m to about ^{10 4} m, see G. Joos, “Textbook of Theoretical Physics”, Akademische Verlagsgesellschaft Geest & Portig K.-G., Leipzig (1956).

There are a number of arrangements that are suitable for modulating electromagnetic radiation. These are each designed for a restricted wavelength range or can only be used for this. For the range of so-called radio waves (wavelengths from 1 m to 10 km) to microwaves (wavelengths from 1 mm to 1 m), which are playing an increasing role in mobile communication, there are tunable and for example frequency generators to be modulated in frequency. The resonance frequency of an oscillating circuit can be varied by means of a variable change or by modulating the inductance and capacitance of an oscillating circuit. An effective radiation of modulated wave fields can take place via antennas adapted to the wavelength range.

For the range of visible light, ie for wavelengths from 405 nm to 780 nm, for example, and for the near infrared spectral range used in telecommunications, ie for wavelengths from 780 nm to 3 pm, for example, so-called acousto-optical modulators are used to introduce a frequency shift . A Bragg grating moving through a crystal is used to diffract laser beams. In general, the modulation frequency with which a piezoelectric transducer is operated is modulated onto the electromagnetic radiation. Typical frequencies of the modulation are in the range from 1 MHz to 1 GHz. Frequency range extensions are possible by means of differential circuits or by means of one behind the other. This leads to a further increase in the installation space. The spectral transmission depends on the material, i.e. crystals. A necessary boundary condition and a limitation for acceptable wavelengths and angles is compliance with the so-called Bragg condition, with the exception of the so-called Raman-Nath regime, which has only low diffraction efficiencies.

Pockels cells can be used for phase modulation and / or for changing a polarization state. In combination with an analyzer, there is the possibility of amplitude modulation. For example, it is also possible to modulate in the MHz range. The high voltages (~ kV) to be generated and the price of the crystals and the electronics are disadvantageous. The spectral transmission depends on the material of the crystal, which generally has the highest possible electro-optical coefficient. A reduction in the design is limited.

In the low-frequency range, for example up to approx. 10 kHz, the amplitude of electromagnetic radiation can also be modulated with liquid crystal toes or with micromechanical components (MEMS). A sufficiently simple modulation of the phase or the polarization state is also possible by means of liquid crystal cells.

In the Sagnac interferometer, a light source moves in a ring resonator arrangement. Waves from this light source propagate along opposing optical paths. A frequency change in the interference signal can be detected as a function of the angular velocity present. The measuring principle is based on the Doppler shift. There are also a number of other options for modulating electromagnetic radiation, for example by means of variably rotated analyzers, ie by means of polarization filters, or by means of other arrangements. SUMMARY OF THE INVENTION

The present invention is based on the object of providing a device through which functions of various components, such as acousto-optical modulators, can be implemented as replacements, but in a more compact design, with a smaller number of components and / or in a smaller overall volume. This object is achieved by a modulator device for modulating a frequency and / or an amplitude of electromagnetic radiation according to claim 1.

“Modulator device” can in particular denote any device that is suitable for modulating a frequency and / or an amplitude of electromagnetic radiation or a light beam and / or each component of an optical arrangement that performs the function within the optical arrangement To modulate frequency and / or an amplitude of an electromagnetic radiation or a light beam. “Modulate frequency” here can mean in particular that a frequency of electromagnetic radiation or a light beam is specifically changed or shifted. “Modulate amplitude” can mean in particular that an amplitude of an electromagnetic radiation or a light beam is specifically changed or adjusted. An amplitude can also be modulated indirectly by frequency modulation. The modulator device according to the invention comprises a substrate which is coated at least in sections with a modulator layer. The substrate can have any material composition as long as it fulfills its tasks according to the invention, which mainly consist in supporting the modulator layer lying thereon. The substrate can in particular have a dielectric material.

The modulator layer is at least partially reflective for the electromagnetic radiation to be modulated. To this extent, the modulator layer can reflect at least part of the electromagnetic radiation to be modulated that is incident on the modulator layer. The modulator layer thus forms a reflective layer or a reflective surface of the modulator device. In some embodiments, the modulator layer can completely reflect electromagnetic radiation incident thereon. Furthermore, the modulator layer is electrically conductive. This means that the modulator layer comprises free charge carriers which, when an electrical field or an electrical voltage difference is applied to the modulator layer, create a corresponding electrical current. The charge carriers of the modulator layer can, for example, be or include negatively charged electrons, positively charged electron holes or charged ions.

The modulator device according to the invention further comprises an adjustable current source. The current source is set up in particular to generate an adjustable electrical field or an adjustable electrical voltage difference. The power source can be a direct current source or an alternating current source. The current source can preferably be a constant current source.

The modulator device according to the invention further comprises a first electrical contact and a second electrical contact. The first electrical contact and the second electrical contact are set up to apply an electrical field generated by the power source or an electrical voltage difference generated by the power source to the modulator layer. The first electrical contact and the second electrical contact can be electrically connected to the power source and the modulator layer, so that an electric field generated by the power source or an electrical voltage difference generated by the power source is applied to the modulator layer between the first electrical contact and the second electrical contact can be applied. The first electrical contact and the second electrical contact can be arranged on the modulator layer.

If an electrical field or an electrical voltage difference is applied to the modulator layer, this causes the free charge carriers of the modulator layer to set in motion and thus a corresponding electrical current through the modulator layer between the first electrical contact and the second Let electrical contact arise. The modulator layer thus forms a reflective layer or a reflective surface of the modulator device, on which electromagnetic radiation can be reflected and through which an electric current flows. To this extent, the modulator device of the invention can be used in an optical arrangement as a reflective component, for example to replace a mirror.

An electromagnetic radiation incident on the modulator layer represents an oscillating alternating field. The oscillation of the electromagnetic field drives the free Charge carriers of the modulator layer for oscillation, so that they emit the incident electromagnetic radiation. This creates a reflection. The sufficiently rapid movement of the charge carriers, which act as sources of electromagnetic radiation during reflection, creates a Doppler shift. In general, the magnitude of the spectral shift is maximal in the detection if this occurs in or against the direction of movement.

The modulator layer through which current flows thus not only functions as a reflective layer, but also as a secondary radiation source. The reflection of electromagnetic radiation, such as light, on charge carriers can be viewed as the implementation of a secondary radiation source. This opens up the possibility of targeted modification of the properties of the secondary radiation source, in particular through targeted adjustment of the applied electric field. The modification considered here relates in particular to frequency modulation. A frequency v _{0 of} electromagnetic radiation incident on the modulator layer is modified by a frequency shift Dn. The specifically set frequency shift can assume positive or negative values. That is, Dn can be positive or negative. The resulting at the output of a modulator frequency v _A usgan _g, ie the frequency of the light reflected from the modulator device electromagnetic radiation may thus be greater or less than the frequency v _0, which is present at the input of the modulator, ie, as the frequency of the on the modulator layer incident electromagnetic radiation.

Based on this, the modulator device according to the invention can functionally replace and / or improve an optical component. For example, the working range of a standard heterodyne interferometer can be enlarged by introducing an additional Doppler shift with the aid of a modulator device according to the invention. The modulator device according to the invention can add or subtract a frequency to the incident electromagnetic radiation. This corresponds to an adaptation of the frequency range. It is very advantageous if this can be implemented in a compact manner, with justifiable technological outlay and cost-effectively, as is possible with the modulator device according to the invention.

On the basis of the interaction of the incident electromagnetic radiation with charge carriers, in particular with the free charge carriers of the modulator layer, frequency shifts that can be controlled or set in a defined manner can be implemented. The free charge carriers of the modulator layer, just like charge carriers in metals or also in doped semiconductors, are converted into a directional movement by applying an electrical voltage generated by the power source. The resulting electrical current I is proportional to the applied voltage U and the resistance R with I = U / R. Considered for example in a defined volume, it corresponds to the change in charge carriers over time, ie I = dQ / dt.

The free charge carriers are accelerated in the applied electric field. This takes place until the point in time when the charge carriers have reached their drift speed V _d . This corresponds to an equilibrium of forces between the accelerating force and the force that arises from the resistance interaction with the modulator layer, which can have a metal grid, for example. With increasing voltage U, v increases, ie up to its maximum value v, i _max ., Which depends on temperature T, among other things.

A reduction in the temperature T generally leads to a reduction in the electrical resistance R. A reduction in the temperature can advantageously be used in the context of the invention to increase the drift speed V or to increase its maximum value V _{d max} . This results in an advantageous application of the embodiments disclosed herein at low and very low temperatures.

In some embodiments, the modulator layer can have a superconductor, preferably a high-temperature superconductor. The use of superconductors is advantageous. Electrons in superconductors, at the appropriate temperature, can reach higher speeds than electrons in standard metals, at room temperature. The so-called high-temperature superconductors, for example, are suitable as reflective conductors through which the current flows. High-temperature superconductors can be cooled with liquid nitrogen. Cooling with liquid nitrogen is much cheaper than cooling with liquid helium, as is required for the operation of standard superconductors. There are also ceramic superconductors that can be used.

In some embodiments, the modulator layer can have a normal conductor, in particular a metal. The use of moving charge carriers in the metal is, however, one of several possibilities. The methods and arrangements can generally be applied to moving charge carriers, ie for example also to moving charge carriers in solutions, to ions, anions and cations, and to holes in semiconductors. In some In embodiments, the modulator layer can thus comprise a semiconductor, for example.

The sum of the individual emissions from the charge carriers of the modulator layer results in an exponential drop in the radiation energy present perpendicular to the surface of the modulator layer. The penetration depth depends on the material of the modulator layer or on the charge carrier density of the modulator layer. In the case of metals, for example, it can be in the range of a fraction of a wavelength of the incident electromagnetic radiation. The reflection on a metallic modulator layer is therefore an effect that is very close to the surface.

The directional movement of the charge carriers of the modulator layer, which, as explained above, can function as a secondary radiation source and emit electromagnetic radiation, is the same as the introduction of a Doppler shift, which acts on an incident electromagnetic wave generated by the modulator -Layer is reflected. In this respect, a portion of the incident electromagnetic wave that is reflected on the modulator layer exhibits a frequency shift in relation to this. The modulator layer can preferably be relatively thin. The modulator layer can have a thickness in the visible wavelength range, for example a thickness of up to too pm, in particular from too nm to too pm, and the current source can preferably be a direct current source.

The described effect is close to the surface. The modulator device of the invention enables the use of the skin effect at sufficiently high frequencies of an alternating current for the charge carriers of the modulator layer for spatial restriction. Furthermore, the modulator device of the invention enables the use of the penetration depth of electromagnetic waves that fall on the modulator layer, even without a skin effect, to investigate the homogeneity of the drift speed in the vicinity of the surface. If the modulator layer is sufficiently thin, e.g. if the modulator layer is designed as a 10 nm thick chrome layer, measurements can be made in reflection and transmission, i.e. at least in the visible spectral range and also in the near infrared range, whereby a differential measurement up to a certain degree, ie according to the integration over the volume, enables a separation of surface and volume. In general, the depth of penetration can be increased by increasing the wavelength of the electromagnetic radiation. This means that, for example, non-destructive analysis down to the THz range of electromagnetic radiation can be used in this way. The reflective modulator layer of the modulator device according to the invention, which can be designed as a metallic surface, can be produced, for example, by a number of coating processes and also in compact form. A possibly necessary protection against corrosion or against degradation of the modulator layer can be implemented, for example, by an additionally applied transparent and thereby as compact as possible oxide layer, ie for example made of SiO ₂ .

The frequency shift as a result of a reflection at the modulator device according to the invention is maximized in the event of an oblique incidence of the incident electromagnetic radiation on the modulator layer. As an example, an xy plane is assumed for the plane of the modulator layer, in which the charge carriers move in the direction of the x-axis, ie in the direction of the unit vector of the x-axis, e _x . If the direction of incidence es _{0 of} the incident electromagnetic radiation is parallel to e _x , i.e. the angle a (e, s ₀ , v) between the incident electromagnetic wave and the direction of movement of the charge carriers is equal to zero, a fundamental frequency becomes at most positive Shifted value, which is determined by the speed of the charge carriers. The resulting frequency V of the part of the incident electromagnetic radiation that is reflected on the modulator layer results from Vi = v ₀ x (V (i-ß ² )) / (1 - ß x cos (a)) with ß = Vd / c. Here c is the speed of light and V _{d is} the speed of the charge carriers. A reflection at an incline or as inclined as possible is therefore preferred.

In order to keep the error of the introduced frequency shift Dn low, it is advantageous to operate the electrically conductive modulator layer, which contains the movable charge carriers, in a so-called measuring circuit. The generation of constant currents is state of the art.

A frequency shift Dn of a wave field can be converted into a time-modulated signal if two sufficiently coherent wave fields of different frequencies are superimposed. If the frequency difference between the two superimposed wave fields is constant, a sinusoidal modulation results in the amplitude, i.e. here, for example, with a fixed frequency, i.e. beat frequency, which corresponds to the frequency shift Dn.

In this respect, the modulator device according to the invention can be used to generate a time-modulated signal in that a portion of electromagnetic radiation incident on the modulator layer that is reflected on the modulator layer has a frequency shift compared to the incident electromagnetic radiation has, with the incident electromagnetic radiation or with a non-reflected part of the incident electromagnetic radiation is superimposed in an interfering manner. A non-reflected part of the incident electromagnetic radiation can be a part of the incident electromagnetic radiation transmitted through the modulator device. An interferometer arrangement which comprises a modulator device according to the invention, which, as explained above, is used as a frequency-shifting mirror, can be used for the superimposition required here. The interferometer arrangement can be, for example, a so-called Mach-Zehnder interferometer, a Twyman-Green interferometer or a Michelson interferometer. As a result of the integration of the modulator device according to the invention in an interferometer arrangement, the number of components required in total of the interferometer arrangement can be reduced. In comparison to the prior art, an interferometer arrangement can thus be implemented with a reduced installation space. A frequency modulation can be converted into an amplitude modulation with the aid of such an interferometer arrangement.

Another interferometer arrangement can be implemented by reflection on two reflection elements lying one behind the other, wherein at least one of the reflection elements can be a modulator device according to the invention, the modulator layer of which acts as a reflection surface.

The advantage of reducing the number of necessary components results, for example, from the fact that optical elements which are used in an optical system for beam deflection are designed as modulator devices according to the invention. Accordingly, a modulator device according to the invention can function both as a reflective element and as a frequency-shifting element at the same time.

A reflective surface, for example the hypotenuse of a prism used to deflect the beam, is preferably a sufficiently thin metallic, conductive surface over which a defined current flows. When it is reflected on the layer through which the current flows, the wave field experiences a Doppler shift. This can be set in a defined manner in terms of amount, direction and time sequence, ie in terms of time dependency. Even if a deflection of 90 ° is often used in optical systems, significantly higher deflection angles can also be achieved in the sense of a higher maximum frequency modification, ie with grazing incidence on metallic conductors through which a defined current flows. In some embodiments, the modulator layer can be partially transparent to the electromagnetic radiation to be modulated. The modulator layer can thus partially reflect and partially transmit the electromagnetic radiation to be modulated which is incident on the modulator layer. The modulator layer thus forms a partially reflective and partially transparent layer or a partially reflective and partially transparent surface of the modulator device. When “permeable” or “transparent” is used in the present application and in particular in the claims, this always means “permeable to electromagnetic radiation” or “transparent to electromagnetic radiation”, in particular for a wave range , in which a modulator device according to the invention is intended to interact with the electromagnetic radiation.

In addition, in some embodiments, the substrate can be at least partially permeable to the electromagnetic radiation to be modulated. This can in particular have the effect that part of the incident electromagnetic radiation transmitted by the modulator layer can also be transmitted through the substrate. Thus, considered together, the modulator layer and the substrate can be at least partially transparent to the electromagnetic radiation to be modulated. The substrate can be completely permeable or transparent to the electromagnetic radiation to be modulated.

In this respect, a modulator device according to the invention can be used as a beam splitter, in particular if both the modulator layer and the substrate are at least partially transparent to the electromagnetic radiation to be modulated. A modulator device according to the invention can accordingly be used in an optical arrangement at the same time as a beam splitter and as a frequency-shifting element, for example instead of a conventional beam splitter.

A reflective surface of the modulator layer, on which part of an incident electromagnetic radiation is deflected, can be designed as a sufficiently thin conductive - for example metallic - surface over which a defined current flows when the electrical field generated by the power source passes through the first and a second electrical contact is made. During the reflection on the modulator layer through which current flows, the reflected part of the incident electromagnetic radiation experiences a defined Doppler shift. This can be set in a defined manner in terms of magnitude, direction and time sequence, that is to say in terms of time dependency, in particular by setting the electric field generated by the power source. A non-reflected part of the incident electromagnetic radiation that is generated by the modulator device, in particular by the modulator layer and is transmitted through the substrate, however, experiences no Doppler shift. This means that the modulator layer can also be designed as a beam splitter. However, it does not have to, ie a standard beam splitter can also be used to separate an input wave field, for example in a 50/50 division. A frequency modification can then take place on one path, or on both paths.

A modulator device according to the invention, which is designed as a beam splitter, can, for example, as a beam splitter cube, as a beam splitter prism, as a beam splitter plate as a beam splitter membrane, or as one on a wire grid based beam splitter.

According to preferred embodiments of the invention, the substrate can be at least partially transparent to the electromagnetic radiation to be modulated and have a first, a second and a third outer surface, the second and the third outer surface being perpendicular to one another, and the first outer surface being oblique to the second and third outer surfaces to the third outer surface. The first outer surface can be coated with the modulator layer at least in sections. According to such embodiments, the modulator device according to the invention can be designed as a prism with a triangular cross section, which can be used as a beam splitter or as a reflective element. A reflective layer can be arranged over the first outer surface of the substrate and on the modulator layer, wherein the reflective layer can preferably be dielectric.

In some embodiments of the invention, the modulator device further comprises a further substrate having a first, a second and a third outer surface. The substrate and the further substrate can be at least partially transparent to the electromagnetic radiation to be modulated. The second and the third outer surface of the further substrate are perpendicular to one another. The first outer surface of the further substrate is oblique to the second and third outer surface of the further substrate and is arranged on the modulator layer. The modulator layer is thus arranged between the first outer surface of the substrate and the first outer surface of the further substrate. According to such embodiments, the modulator device according to the invention can be designed in the shape of a cube with a square cross section and can be used as a beam splitter.

In some embodiments, the modulator layer comprises a wire-grid polarizer. In particular, the modulator layer can be designed as a wire-grid polarizer be. The wire-grid polarizer can be used to selectively select or modify or modulate polarization states of the incident electromagnetic radiation. The electric current flowing through the modulator layer can be directed along the grid structures of the wire-grid polarizer. The grating structures can be metallic and / or have dimensions in the sub-wavelength range. In these embodiments, the vector of the beam propagation of the incident electromagnetic radiation must have a component in the direction of the grid lines of the wire-grid polarizer in order to experience a Doppler shift. Said vector can thus be directed in the direction of the electric current flowing along the lattice structures. As a result, a portion of the incident electromagnetic radiation reflected by the modulator layer or the wire-grid polarizer has a frequency shift in relation to the incident electromagnetic radiation, while a portion transmitted by the modulator layer or the wire-grid polarizer the incident electromagnetic radiation has no frequency shift in relation to the incident electromagnetic radiation. An oblique angle of incidence of the incident electromagnetic radiation, for example less than 45 °, is advantageous here, and the angle of incidence can also be greater. The grid lines of the wire-grid polarizer preferably lie in the plane of incidence, ie in the plane of the modulator layer.

In some embodiments, the modulator device can further comprise an additional reflective layer which is arranged on the modulator layer, the additional reflective layer being suitable for reflecting a portion of the electromagnetic radiation to be modulated. The additional reflective layer can be a dielectric layer or a conductive, in particular metallic, layer. The additional reflective layer is preferably not traversed by the electric current flowing through the modulator layer. The additional reflective layer can thus have the effect that part of the electromagnetic radiation incident on the device is reflected by the current-carrying modulator layer and consequently has a frequency shift, while part of the electromagnetic radiation incident on the device is reflected by the non-current-carrying additional reflective layer and has no frequency shift. In an arrangement of this type, a very compact design can be implemented through the immediate vicinity of the relevant layers (ie the modulator layer and the additional reflective layer), for example at an angle of incidence of 45 ^° . Such an embodiment of the modulator device according to the invention can be in an optical Arrangement can be used instead of a conventional mirror in an optical beam path.

The additional reflective layer can act selectively on polarization states of the electromagnetic radiation to be modulated. The additional reflective layer can reflect a polarization-defined portion of the incident electromagnetic radiation and transmit or let through another polarization-defined portion of the incident electromagnetic radiation, which can be reflected by the underlying modulator layer. The additional reflective layer can, for example, reflect a first portion of the incident electromagnetic radiation with a first polarization state and transmit or let through a second portion of the incident electromagnetic radiation with a second polarization state, which can for example be perpendicular to the first polarization state. The portion of the incident electromagnetic radiation that is transmitted by the polarization-selective additional reflective layer and reflected by the modulator layer experiences the frequency shift caused by the modulator layer, while the portion of the incident electromagnetic radiation that is reflected by the polarization-selective additional reflective layer, does not experience the frequency shift caused by the modulator layer.

A reverse arrangement of the additional reflective layer and the modulator view, in which the modulator layer acts selectively on polarization states of the electromagnetic radiation to be modulated and is arranged on the additional reflective layer, is also provided and allows the same effect to be achieved. The modulator layer can be designed as a wire-grid polarizer. In such embodiments, the modulator layer arranged over the additional reflective layer can reflect a polarization-defined portion of the incident electromagnetic radiation and transmit or let through another polarization-defined portion of the incident electromagnetic radiation, which can be reflected by the additional reflective layer underneath. The modulator layer can, for example, reflect a first portion of the incident electromagnetic radiation with a first polarization state and transmit or let through a second portion of the incident electromagnetic radiation with a second polarization state, which can for example be perpendicular to the first polarization state. The portion of the incident electromagnetic radiation that is reflected by the polarization-selective modulator layer experiences the frequency shift caused by the modulator layer, while the portion of the incident electromagnetic radiation, which is transmitted by the polarization-selective modulator layer and reflected by the additional reflective layer, which does not experience the frequency shift caused by the modulator layer. In some embodiments, the modulator device can comprise a diffraction grating that can be arranged over the modulator layer or formed within the modulator layer. The modulator layer can in particular be designed as a diffraction grating. In these embodiments, the diffraction grating can make it possible to selectively diffract the electromagnetic radiation incident on the modulator device before it is reflected at the modulator layer. The diffraction grating can, for example, make it possible to define a reflection angle with / at which a portion of the incident electromagnetic radiation reflected on the modulator layer is reflected, with different reflection angles in particular being able to correspond to different diffraction orders of the diffraction grating. The diffraction grating can be formed in the modulator layer or integrated into it. The modulator layer can be designed, for example, as a surface relief grating. A modulator layer designed as a surface relief grating can preferably be partially transparent to the incident electromagnetic radiation, in particular if the modulator layer is sufficiently thin. A modulator layer designed as a surface relief grating can thus partially reflect and partially transmit the incident electromagnetic radiation.

The diffraction grating can have a first grating segment and a second grating segment and can be configured to reflect an incidence of the electromagnetic radiation incident on the modulator device at a certain angle of incidence, for example at a perpendicular angle of incidence, with a reflection of a reflected part of the incident electromagnetic radiation to combine a certain angle of reflection, for example a perpendicular (back) angle of reflection. The angle of incidence and the angle of reflection can be selected almost at will. Grating segmentation generally reduces the technical effort involved in implementing the diffraction grating and the beam path. An example of a first grating segment of a diffraction grating that can be used for this purpose, which can be designed, for example, as a surface relief grating, is a so-called sawtooth profile. The first grating segment can be configured, for example, to generate a certain diffraction order, for example an i-th diffraction order, with maximum diffraction efficiency when the incident electromagnetic radiation is perpendicular to the modulator device or the first grating segment of the diffraction grating. The incident electromagnetic radiation can be diffracted by the first grating segment in such a way that this diffraction order - despite the perpendicular Incidence on the diffraction grating - incident obliquely on the modulator layer located below the diffraction grating. The portion of the incident electromagnetic radiation reflected on the modulator layer strikes a further grating segment of the diffraction grating, which, for example, can also be implemented as a sawtooth profile surface relief grating, mirror-symmetrical to the first grating segment. The second grating segment can be set up to diffract the part of the electromagnetic radiation reflected by the modulator layer in such a way that it is reflected by the modulator device at a certain angle of reflection, for example back onto the original axis of incidence, which is perpendicular to the diffraction grating or the diffraction grating. can be to the optical axis of the system.

The diffraction grating can, however, also be unsegmented and can also be used to combine a perpendicular light incidence on the modulator device or on the diffraction grating with a perpendicular back reflection. An example in this sense is the use of a diffraction grating which realizes a symmetrical beam splitting.

In some embodiments, the diffraction grating can be designed as a surface relief grating or as a volume grating based on Bragg diffraction at grating planes. In the case of a symmetrical design, the incident electromagnetic radiation can be incident at an angle of incidence below 0 °, wherein the diffraction grating can be set up, for example, to generate the -i th and the + i th diffraction order. Two symmetrically designed diffraction orders can thus fall obliquely on the modulator layer in different directions and can thus experience opposing frequency shifts. After reflection, they can be reflected back by the diffraction grating, i.e. in the opposite direction to the direction of incidence of the incident electromagnetic radiation, for example.

If the diffraction grating is designed so that there is a significant intensity in the o-th diffraction order, three frequency components can be generated, for example, in the back-reflected and in the partially diffracted part of the electromagnetic radiation, v ₀ , v _o + Dn, v _o - Ie. This means that if there is a coherent superposition, several interference terms can be present.

For example, the modulator device according to the invention can be operated with perpendicular incidence of the incident electromagnetic radiation on the modulator layer, while the modulator layer has a current that can be set in a defined manner. The modulator layer may be implemented as surface relief grating, which is adapted to generate the ± i-th diffraction orders, which can for example be ± 84.26 °, or ± 72 ^0, and an opposite frequency modulation can experience. The modulator layer can, for example, be a 20 nm thick gold layer that forms a sinusoidal grating.

In other embodiments, the substrate can be transparent and the diffraction grating can be formed on a surface of the substrate that is opposite to the modulator layer.

If the diffraction grating and the modulator layer are not plane-parallel to one another, but rather have a wedge angle k, then the wedge angle K can be determined by determining the frequency shifts that the individual interference terms experience. Accordingly, a modulator device according to the invention can be used for angle measurement or as a component of an angle measurement system.

It should be noted that a measurable asymmetry can be introduced both by the angle of incidence of the incident electromagnetic radiation and by the wedge angle between the diffraction grating and the modulator layer. In terms of parameter variation, several wavelengths and several angles of incidence of the incident electromagnetic radiation and combinations thereof can be used to separate the two influences, the influence of the angle of incidence of the incident electromagnetic radiation and the influence of the wedge angle. This results in the possibility of angle measurement using the measured variable frequency.

A wave field that falls on a surface can generally have a reflected portion, a transmitted portion and a diffracted portion or portions. The individual diffraction orders have a fixed angular relation to one another or an angular relation which can be determined in a defined manner in the case of a relative rotation or in the case of a change in the wavelength. In the modulator device according to the invention, this can be used, inter alia, to correct the uncertainty of the angle of incidence or to measure it. For this purpose, several beat frequencies or several frequency shifts caused by the modulator layer can be measured, which are assigned to several diffraction orders, for example. Since the angle of incidence is part of the lattice equation, ie a term thereof, the angle of incidence can be determined uniquely via a system of equations. The angle measurement via frequencies can be realized by means of a diffraction grating and / or without it. The use of an internal reference arrangement within a measurement arrangement that is for example an angle measuring arrangement and which also detects, for example, a drift in the wavelength used when an angle measurement is carried out, reduces the measurement uncertainty.

In this respect, a modulator device according to the invention can be set up to determine an angle of incidence of the electromagnetic radiation incident on the modulator device. This can be used to correct a value that is not sufficiently exact, or it can also be used directly in the sense of a measuring arrangement. Angle measuring systems can be built on the principle disclosed here.

Modulator devices according to some embodiments of the invention can be designed to implement multiple reflections.

In some embodiments, a surface of the substrate which is opposite the modulator layer and which is preferably parallel to it can be coated with a further modulator layer. The further modulator layer is at least partially reflective and electrically conductive for the electromagnetic radiation to be modulated. The further modulator layer can have the same structural properties as the first-mentioned modulator layer. The modulator device can further comprise a third electrical contact and a fourth electrical contact, which are set up to apply the electrical field generated by the power source or a further electric field generated by a further power source to the further modulator layer. In such embodiments it is possible to mediate a series of reflections between the two opposite modulator layers, which can preferably be parallel to one another, through which a respective electric current flows. The use of multiple reflections is important in connection with the modulation principle disclosed herein because, for example, a metallic conductor can generate relatively low modulation frequencies or frequency shifts at room temperature. The achievable frequency shift can be increased by a factor N by multiple reflection, where N can be 20 or 100, for example. If the number of multiple reflections is, for example, N = 100, the maximum frequency shift is proportional to 2 x 100 xv, i _ma x. The factor 2 results from the possibility of reversing the direction of the current flow. The speed of the free charge carriers can be tuned from o to v, i _max . This results in a significant increase in the frequency range to be set for the modulation. The two opposite modulator layers can have an angle not equal to 0 ° to one another, in other words they can also not be aligned parallel to one another. One application of multiple reflection with a modulator device according to the invention is to determine the frequency shift achieved with the modulator device. Another application of multiple reflection with a modulator device according to the invention is the expansion of the frequency shift range that can be achieved with the modulator device. A further input wavelength or further modulated and / or also non-modulated input wavelengths can be used for checking, but generally also for expanding the frequency range to be modulated. One possibility is, for example, to allow electromagnetic radiation with a first wavelength and electromagnetic radiation with a second wavelength to enter the modulator device as input control radiation coaxially to electromagnetic radiation with the first wavelength. As explained above, the modulator device can be set up to realize multiple reflections. The second wavelength can be different from the first wavelength, the difference being, for example, 1 nm or 10 nm. A check of the Doppler shift or frequency shift brought about by the modulator device can be determined from the known ratio of the wavelengths. Different wavelengths can be separated using dichroic filters for separate detection.

Another application of multiple reflections with a modulator device according to the invention is the use of multiple reflections for the purpose of reducing the frequency. If, for example, a relatively high charge carrier speed is available in a very stable manner, then this can also be used to generate sufficiently low frequencies.

A series of reflections can be implemented between two opposing current-carrying modulator layers which are at an angle to one another. The two modulator layers can belong to different modulator devices according to the invention. For example, there can be an angle k = 10 ° between the two modulator layers. If there is a relative angle between the - here two - modulator layers, an angle increase occurs with each reflection. In general, the frequency change is dependent on the relative position of the reflective modulator layers used and on the charge carrier velocities present in them. The multiple reflection at two modulator layers that can be adjusted or adjusted in angle to one another enables the angle that is present between these modulator layers to be determined. A small change in angle makes a significant one Frequency change. If measurements are carried out at several points on a structure that can be rotated in space, an angle measurement can also be carried out. More than two modulator layers or modulator devices can be used, for example three or more, each at an angle to one another. The relative frequency shifts resulting from an optical query can be assigned to the changes in the angles in space. There are several ways to do this. A measuring structure can, for example, comprise a plurality of modulator devices according to the invention which have fixed angles to one another, a rotation of the structure in space being measurable. However, it is also possible for the individual modulator devices to be individually rotatably mounted and for the angle changes to be detected via frequency shifts.

According to some embodiments, the substrate and the modulator layer can each be rotationally symmetrical and the modulator layer can be arranged in a surrounding manner on the surface of the substrate. The substrate can preferably form a waveguide which is coated with the modulator layer.

According to some embodiments of the invention, the substrate can have a polygonal surface, wherein at least a first surface section of the substrate, which corresponds in particular to a first polygon side, is coated with the modulator layer, and wherein at least a second surface section of the substrate, which is in particular a second polygon side corresponds, has a first lattice structure. The lattice structure is designed to couple light into the substrate that is incident on the outside of the lattice structure and / or to extract light from the substrate that is reflected inside the substrate and is incident on the inside of the lattice structure. The different surface sections in particular have relative angles to one another. In addition to the first surface section of the substrate, further surface sections can be coated with the modulator layer or each with a further modulator layer, wherein the further surface sections can in particular correspond to further polygon sides. An electric current can also flow through the further modulator layers. For this purpose, the further modulator layers can be electrically connected to the modulator layer or be electrically coupled to further current sources.

According to these embodiments, electromagnetic radiation coupled into the substrate can be reflected on a plurality of surface sections of the substrate which have different spatial angles or which each have an angle to one another. The reflective surface sections of the substrate can, for example, be surfaces on the outer, or, depending on the embodiment, also inner, Sides / faces of a polygon correspond. Multiple reflections on / along an approximate circular path are thus possible. The aim is to be able to capture the highest possible frequency bandwidth in the modulation. In general, line broadening is negligible.

In some embodiments, the substrate has a polygonal surface. At least a first surface section of the substrate, which can in particular correspond to a first polygon side, is coated with the modulator layer. A second surface section of the substrate, which can in particular correspond to a second polygon side, is at least partially permeable and is designed to couple light into the substrate that is incident on the outside of the second surface section. The substrate has an inner intermediate surface which is configured to partially reflect and partially transmit a light beam that is coupled into the substrate through the second surface section. The light beam that has entered the substrate through the second surface section is thus divided within the substrate by the inner intermediate surface, in particular into a reflected light beam portion and a transmitted light beam portion. A third surface section of the substrate, which can in particular correspond to a third polygon side, is at least partially permeable and is designed to couple out from the substrate a portion of the light beam that is reflected or transmitted by the inner intermediate surface and is reflected on the modulator layer. A fourth surface section of the substrate, which can in particular correspond to a fourth polygon side, is at least partially permeable and is designed to couple a light beam portion transmitted or reflected by the inner intermediate surface out of the substrate.

Since the portion of the light beam extracted by the third surface portion of the substrate was reflected within the substrate at the modulator layer, it has, with respect to the portion of light beam extracted by the fourth surface portion of the substrate, one caused by the modulator layer Frequency shift on. Both light beam components can thus be overlapped with one another in order to obtain an interference pattern. For this purpose, the modulator device can further comprise a first focusing lens and a second focusing lens, the first focusing lens being configured to partially focus the light beam coupled out through the third surface section onto an interference plane, and the second focusing lens being configured to do so Part to focus the light beam coupled out through the fourth surface section onto said interference plane. Thus, in the interference plane, both light beam components overlap with one another in an interfering manner. One application of these embodiments of the invention is to use the frequency difference between the light beam portion coupled out through the third surface section and the light beam portion coupled out through the fourth surface section for measurements in which directions of movement are determined and velocity distributions are precisely determined. This can be used, for example, when determining particle movements, that is to say in laser Doppler anemometry. For example, an interference pattern can quickly be shifted in space, ie in its phase. This modification makes it possible not only to determine the amount of movement from the light that is scattered by the particles, but to differentiate between directions of movement. This is the part of the movement that the particles have in the plane of the interference pattern. The advantage of the modulation disclosed herein lies in the possibility of simple and compact implementation thereof. In other words, the components required for changing the interference pattern can be made more compact and less expensive compared to the prior art. The interference pattern can run with a defined amount of speed and in a defined direction. For the complete vectorial acquisition of velocity vector fields, it may be necessary to use at least three interference patterns that are as orthogonal to one another as possible. It is advantageous to work in three channels that are spectrally separated from one another. To generate three, for example, interference patterns arranged orthogonally to one another, three wavelengths can be used which differ from one another, for example, by 10 nm or by 20 nm. Three detectors can be used, each of which has a spectral filter that is assigned to its wavelength to be detected and each has a spectral window of 5 nm. The interference patterns are preferably modulated in all spectral channels used.

Another aspect of the invention relates to optical arrangements in which at least one modulator device according to the invention is integrated, in particular an optical arrangement according to claim 19 and an optical arrangement according to claim 20.

According to one embodiment, an optical arrangement can comprise a modulator device according to the invention, the substrate and the modulator layer of which can in particular be at least partially transparent. The modulator device is set up to split a light beam, part of the light beam to be split being transmitted by the modulator device, and part of the light beam to be split being reflected by the modulator layer of the modulator device. Accordingly, the The modulator device according to the invention can be used in an optical arrangement as a beam splitter and as a frequency-modulating element.

An example of such an optical arrangement is an angle measuring system, which can in particular be an autocollimation telescope or an autocollimator. A change in an angle of a light beam reflected back from a measurement object can be viewed as a change in the angle of incidence of the electromagnetic radiation incident on the modulator device, which results in a frequency change in a frequency measurement. An angle measurement can thus be carried out using a frequency measurement

In an autocollimator, for example, a modulator device according to the invention can be used which has a single, for example also planar, metallic, electrically conductive modulator layer through which a current I flows. The modulator layer can also be designed as a surface relief grating which has a metallic or generally electrically conductive coating through which a current I flows. The evaluation of the frequency modification present in several diffraction orders reduces the budget of the measurement uncertainty. Parameters such as position deviations and frequency deviations can also be used in combination in an angle measuring system. For example, measurements can be made at two wavelengths, which preferably run coaxially. A fixed relationship results from the two frequencies resulting for the respective wavelength, ie a differential measurement can be carried out. By separating wavelengths and / or polarization states, it is also possible to combine an angle measurement based on position deviation and an angle measurement based on frequency deviation in one device. It is also possible to combine an angle measurement based on a position deviation and an angle measurement based on a frequency deviation without the separation of partial beam paths in one device. A sufficiently fast detector which is used to determine the position of a pattern can be used to determine a beat frequency of the pattern. If this detector or this detector field works with a maximum frequency v _Dmax , then frequencies up to v _Dmax / 2 or practically up to v _Dmax / 3 can theoretically be detected. An example of this procedure is the use of a laser beam with a Gaussian intensity profile in connection with a four-quadrant photodiode (also four-quadrant detector). An example of a detector field that can be used is a CMOS camera which, for example, operates at a refresh rate of 1 kHz.

According to one embodiment, an optical arrangement can comprise a modulator device according to the invention which follows in a beam path of the optical arrangement a beam splitter is arranged which divides an input light beam into at least two beam portions. The modulator device is set up to modulate a frequency and / or an amplitude of one of the at least two beam components by at least partially reflecting one of the at least two beam components on the modulator layer of the modulator device. Such an optical arrangement can for example comprise a further modulator device according to the invention which is arranged in the beam path of the optical arrangement after the beam splitter and which is set up to modulate a frequency and / or an amplitude of the other of the at least two beam components by the other of the at least two beam components is at least partially reflected on the modulator layer of the further modulator device. The further modulator device can in particular be used to introduce a frequency shift into the beam portion reflected thereon, which differs from a frequency shift which is introduced by the modulator device into the beam portion reflected thereon. The optical arrangement can furthermore comprise a first retardation plate, which is arranged in the beam path in front of the modulator device or in front of the further modulator device, and / or a second retardation plate, which is arranged in the beam path after the modulator device or after the further modulator device is arranged. The first retardation plate and / or the second retardation plate can preferably each be a 1/2 plate.

An example of such an optical arrangement, in which one or more modulator devices according to the invention are used in particular as frequency-shifting reflective elements, is an interferometer arrangement, in particular a Mach-Zehnder interferometer, a Twyman-Green interferometer or a Michelson - Can be an interferometer.

Another aspect of the invention generally relates to a method for modulating a frequency and / or an amplitude of electromagnetic radiation or a light beam using a modulator device according to the invention, in particular a method according to claim 23. The method comprises reflecting at least one part the electromagnetic radiation or the light beam at the modulator layer of the modulator device, while the electric field generated by the power source or the electric voltage difference generated by the power source is applied to the modulator layer. The method can further include transmitting at least another part of the electromagnetic radiation or the light beam through the modulator device. Preferred embodiments of the invention are given in the accompanying dependent claims.

A modulator device according to the invention can be used to use diffractions on the electrically conductive grating through which the current flows, in order to convert the angular distributions, including the discrete angles of the discrete diffraction orders, into frequency distributions. For example, ID, 2D or 3D grids can be traversed by a current or by a spatial current distribution. Discrete diffraction orders correspond to discrete directions of propagation and receive discrete values for the modulation of the output frequency v ₀ = v ₀ / c, or v ₀ = v ₀ / (nxc), if the propagation of the electromagnetic waves or wave fields in the medium with the refractive index to be considered n is present.

A modulator device according to the invention can be used to make a light source so that its emission frequency or also several emission frequencies can be tuned and stabilized. For example, a grid through which the current flows can be used in a so-called Littrow AO, which enables a very fine frequency setting to be obtained through the flow of current. This is advantageous if the angle adjustment of a standard grating used for this purpose cannot be carried out finely enough or not quickly enough. In general, high accelerations lead to geometric deformations of components, e.g. grids used here for frequency setting. This design results in very fast modulations for lasers. The implementation of a very finely adjustable emission frequency opens up the possibility of setting multiple lasers to exactly one frequency by generating beat frequencies, measuring them and using closed control loops. However, this requires a very high level of parameter stabilization.

A modulator device according to the invention can be used to generate a scatter distribution which corresponds to a distribution of modulation frequencies. The modulator layer can in particular have a rough surface. A surface relief profile can be designed statistically in such a way that a defined target intensity distribution is present in the diffracted field. The definedly designed spreader can be moved or rotated in order, for example, to achieve a far field that is sufficiently speckle-free in the time average considered. The power supply can be adapted to this. It is also possible to hold the spreader through which the current flows and to display an illuminated and moving, for example, standard spreader on it. This corresponds to the realization of a statistically randomized and at the same time in its distribution defined temporal, spatial phase variation in the illumination of the metallized surface relief scatterer through which a defined current flows. When superimposed with a reference wave field, a defined distribution of beat frequencies results. In the case of mapping a spreader onto a surface through which the current flows, this can also be smooth, that is to say, for example, can be made flat. The angular distribution gives a distribution of the Doppler shift. Depending on the spectral position or the associated frequency of the reference wave field, for example, the beat frequency that occurs locally in the event of a superposition increases or decreases towards the outside. That is to say, the frequency of a reference wave field can also _{deviate from an output frequency v 0} in one or the other direction as required. It is also possible to superimpose two wave fields with different frequency distribution modifications. This increases the variety of realizable distributions of beat frequencies. This procedure can also be used several times in a row in a system. An image on or from the modulator layer through which the current flows can also take place at an angle. The distortion can be corrected by adhering to the so-called Scheimpflug condition, ie by using a so-called Scheimpflug system. This generally applies to arrangements that work with oblique lighting and oblique imaging. A modulator device according to the invention can be used to generate an electrical current. Electromagnetic radiation which is preferably incident on the modulator layer at a very oblique angle, ie for example below 72 ^° to the surface normal, can generate a current. A pulse carryover takes place. This makes it possible to read out an optical frequency modulation directly electrically. By superimposing a second optical, frequency-modulated signal, higher and lower frequency terms can be generated. The generation of low-frequency signals is advisable when the optical signal to be recorded has a modulation frequency that is above the maximum frequency that can be detected by sensors or detectors. In the case of semiconductor diodes, frequency detection and frequency generation are generally limited to <10 THz. In general, the efficiency is also low.

Electrical signals that have been generated on the basis of a pulse transmission of electromagnetic radiation can be used as input signals for circuits. For example, the optically generated electrical signals can also be input signals for frequency mixers, such as up and down mixers, frequency multipliers and phase shifters. This results in a number of applications in high-frequency technology in modulation and detection. The direction of oscillation of the electric field, which is advantageous for the momentum transfer from charge carriers to light or from light to charge carriers during reflection, is perpendicular to the plane of incidence. An electric field oscillating in the plane of incidence experiences less reflection when inclined at an angle. If, for example, circularly polarized light is present, the reflection at an oblique incidence corresponds to a change in the polarization state, here in combination with a pulse transfer to be modulated.

If, for example, an electromagnetic wave with a modulated amplitude falls obliquely on a detector surface that contains free charge carriers, the pulse transfer to this can be measured. There is a change in the current flow. For example, if a current flows that is constant without the incidence of the modulated electromagnetic wave, there is an additional change, i.e. d / dt of I. For example, if an electromagnetic wave with modulated amplitude falls obliquely on a surface or detector surface, the free Contains charge carriers, a pulse transfer to these charge carriers can take place, which is modulated. This modulated pulse can in turn be transferred by the charge carriers to another electromagnetic wave that falls obliquely on this surface. This corresponds to the mediation of an interaction, i.e. here the transmission of an amplitude modulation, between two electromagnetic wave fields via the free charge carriers. For example, it is also possible to have two wave fields, between which a pulse transfer is to take place, propagate together in a ring resonator. Depending on the wiring of the reflective surfaces that contain the free charge carriers, different operating modes can be implemented, for example those described here.

As part of this interaction, frequency changes can be achieved by using different wavelengths and / or by setting different angles of incidence. In this way, modulation frequencies that exist on electromagnetic wave fields can be converted into one another. For example, more than two light beams can also be used. If there is an amplitude modulation on at least two light beams, this is transferred to the other beams. It is thus also possible to use this in the sense of data processing circuits. Logical operations can thus be carried out optically. In addition, this can be controlled electrically and read out electrically. IA have very small currents, which are converted into currents by means of an amplifier circuit which are sufficiently large to introduce a Doppler shift of electromagnetic waves by means of a modulator device according to the invention.

It is possible to use a diffraction grating on the uniting element, ie just before the exit of an interferometer arrangement, which can be, for example, a Mach-Zehnder interferometer. It is also possible to use a diffraction grating at the initial beam splitter, ie at the entrance of an interferometer arrangement, for example to achieve a ^{reflection angle that clearly differs from 45 0} , ie for example 65 ⁰ or 72 ⁰ to the surface normal of the surface, on which the light falls. This allows a compact construction, in which the conductive surface can also be arranged inclined than 45 ^0th A monolithic arrangement using the outer surfaces of an individual transparent component, ie for example the sides of a prism, is advantageous here.

A modulator device according to the invention can be used for position measurement. The modulator layer of the modulator device can be curved or flat and have a locally changing sheet resistance or a locally changing charge carrier speed. The electromagnetic radiation incident on the modulator device can be incident at an angle to the surface normal for position measurement. The locally present charge carrier velocities can also be segmented, that is to say in such a way that the Doppler shift changes, for example, in steps along a length Az. In the simplest case, the sheet resistance can vary periodically. By mapping the locally illuminated area onto a detector field, advantageously in compliance with the Scheimpflug condition, the implementation of a material measure, ie here, for example, a linear scale or an angular scale, ie a circular grid, which is used as an angle - Scale is used, for example also for the full circle. Parameter variations present locally on the surface, for example electrical and / or mechanical, can, for example in the sense of calibration, also tactile or contactless, ie for example optically, or via the local interaction of the electric field, ie for example also via a local resistance measurement to be read out. If the local surface resistances are applied in the sense of an absolute coding, ie locally, or at least coded absolutely in a sufficiently small segment, for example with the help of a local reference mark, the absolute position is not lost even after the measuring system has been completely switched off. For example, with several tracks of different spatial period of the drift speed and / or with a spatially high-frequency track of the varying drift speed and in a, for example, fixed distance following reference marks, here based on a spatial distribution of the drift speed to be worked or this is implemented in the spatial coding.

It is possible to contact conductive surfaces locally and to measure the local charge carrier mobility between the contact electrodes, i.e. between at least two, or between several, differentially. Larger areas can be measured by scanning or sliding, i.e. by combining individual measuring areas. This can be used to calibrate local resistances or to calibrate resistance distributions. A contactless query is possible by determining frequency distributions.

The basic principles and arrangements disclosed here result in a number of applications and further, adapted arrangements. This also includes, inter alia, embodiments and applications that result from a combination with other modulators of the prior art or correspond to a combination.

It can also be measured bilaterally, i.e. the reflection R (x, y) and the transmission T (x, y), i.e. the local reflection coefficient and the local transmission coefficient. The prior art can be expanded by determining the local drift speed. This can be used for defect detection, for example on sufficiently thin, electrically conductive surfaces or coatings.

In metallography, for example, the local drift speed V _d can be measured on ground, polished and / or etched surfaces. This complements polarization microscopy methods. Crystallites can have different drift speeds depending on their composition and orientation. This can be used as a method of analysis.

A parameter that influences the drift speed can be measured using this. For example, a temperature measurement can be converted into a frequency measurement via the relationship with v, ie via V _{d (T).} Further measurement methods can be implemented, for example, by contaminating conductive surfaces, ie in the sense of a sensor system and also in terms of surfaces prepared for them. The drift speed can also be influenced by external electrical and / or magnetic fields. IA results in a sensor system for the parameter X with V _d (X). The measured variable can be converted into a frequency modification which, for example, can also be converted into an amplitude modification by means of interference. A modulator device according to the invention in which the speed of the charge carriers in front of the modulator layer or the drift speed V _{d shows} a sufficiently strong temperature dependency V _LT (T) can be used to measure the temperature T by adding the current I applied to the modulator layer and the frequency shift caused by the modulator layer can be measured. _{If the function V LT} (T), or V _LT (R, T), or V _LT (I, T), or V _LT (I, R (T)) is known and as calibrated as possible, this can be used to determine the temperature. For this purpose, hot or cold conductor materials can be used. For example, platinum (Pt) can be used as a measuring resistor in the sense of the procedure disclosed here, which shows a sufficient temperature dependency V _LT (T). Above (o - 100) ⁰ C, the mean temperature coefficient is Pt a ₀ = (R ₁₀₀ - Ro) / (Ro * 100 ⁰ C) = 3.85 x 10 ³ KA For higher temperatures, an arrangement is advantageous that Tungsten was used as the material of an electrically conductive surface (ao = 4.11 x io ^-3 K ^_1 ). Sapphire or diamond, for example, are suitable as the transparent substrate material at high temperatures. For arrangements that do not require a transparent substrate, ceramics or, for example, tungsten, are suitable at high temperatures, it being possible to use an electrically insulating coating between the substrate and the modulator layer. The result is a sensor for high temperatures that generates a temperature-dependent frequency shift. This can be used advantageously when the direct measurement of the electrical resistance at the measuring location is not possible, but a known current I can still be generated at the measuring location.

Another application of a modulator device according to the invention is based on the utilization of the thermoelectric effect (Seebeck effect). A voltage is generated between two different conductor materials (thermal pairs) via a temperature difference DT. This voltage U can usually be measured directly, which corresponds to the state of the art. However, by closing a circuit it is possible to generate a current I which can be used in the manner disclosed herein to generate a frequency change. The frequency measurement can also be carried out over large distances. A compact arrangement can be built up monolithically. One side of the arrangement is connected to a temperature reservoir in order to obtain the necessary temperature difference. A change in the temperature difference results in a frequency change. This can be used advantageously when the direct measurement of the electrical resistance at the measuring location is not possible.

Another application of a modulator device according to the invention consists in the modulator layer through which the current I flows, which is advantageously more flat electrical conductor can be designed to illuminate obliquely with at least one incident electromagnetic wave and optically via the frequency shifts present in different directions the distribution of the magnetic flux density B, ie the vector components Bi (x, y) (i = 1, 2, 3 ) read the magnetic flux density optically. Thus, for example, a current can also be measured that runs transversely to the current that is generated by the application of a voltage. These frequency shifts result from the speed distribution v _LT (x, y), which is dependent on the magnetic flux density that is present in the area of the current flow. This is an alternative to the direct measurement of a transverse voltage generated by the magnetic field, which can be used advantageously.

A modulator device according to the invention can also be used in control loops. For example, a light source moves in the Sagnac interferometer. Waves from this light source propagate along opposing optical paths. In addition to a Doppler shift that results from the real rotation of the circumferential ring, a modulator device according to the invention can be used to generate an additional Doppler shift that is variably adjustable. The resulting modulation frequency can therefore also be set to a fixed value, i.e. it can also be fixed in the sense of a regulation. This is also possible when the angular speed changes. The measured variable can be the additional frequency to be compensated.

In order to keep the error in the temporal synchronization of a modulator unit with a detector, ie for example also with a detector field, which can be a detector line, a camera line, or a camera, it is advantageous in the Modulator device according to the invention, which is used to modify the frequency to measure the beat frequency generated between - at least - two electromagnetic wave fields directly. If, for example, a photodiode is used, the sinusoidal measurement signal obtained can be used for the time synchronization of the components used. For example, this signal from the photodiode can be used to generate a trigger signal for a camera. The principle of modulation makes it possible to implement closed control loops in inexpensive electronics.

The signal of a photodiode used, for example, can be evaluated via a frequency determination and, within a closed control loop, can be used to set a fixed frequency exactly. When generating a defined frequency shift, this reduces the effects of errors. Thus, in a measurement technology Application reduces the error budget. A possible error influence is, for example, a temperature change that is present at least locally on the frequency-shifting component.

A further application of a modulator device according to the invention consists in introducing a frequency shift between two, ie at least two, wave fields to be superimposed in arrangements based on coherent superposition of electromagnetic waves. Thus, resulting interference patterns are dynamic. By means of time synchronization of the detector or the detector field, a set of measurements shifted in the phase can be obtained in the sense of phase-shifting interferometry. Mathematically, exactly two slightly different wavelengths are superimposed. Nevertheless, taking into account the time-synchronized detection, the description with the aid of the phase shift in a homodyne interferometer is sufficiently exact, ie for example with a maximum absolute error of a certain phase of Df «2p x 10 ^-4 . For example, as an alternative to using l ₂ = (l ₀ + l 0/2 and Acpi of the phase-shifting interferometry in the interference term, l _o and l _i can also be used, which in this sense leads to an equivalent measurement result.

An arrangement assigned to this procedure contains at least one modulator device according to the invention, which is located in the beam path behind a beam splitter, so that the frequency modification is only present in one of the previously separated portions of the electromagnetic radiation. A further embodiment consists in undertaking a frequency modification in both separated parts with a respective modulator device according to the invention, which, however, is different, or at least can be. When using this procedure for interferometry by means of a carrier frequency or when setting a carrier frequency, for example by setting an interference wedge, the interference pattern runs over the image. Images are to be recorded or evaluated synchronously with the set time period. If the wedge angle is set to close to zero, i.e. if the number of stripes in the image is set as low as possible, images must also be recorded synchronously with the set time period, for example five images within one period of the modulation frequency, so that, for example, 5 images are made in the course of one modulation period.

An advantageous embodiment results from the use of a polarization beam splitter. The electromagnetic field from a source can be divided into orthogonal polarizations. A frequency modification can be introduced between these. The components of orthogonal polarization can be assigned to the object and the reference beam path. The object and reference beam path can, for example, be coaxial be arranged, or also have a greater spatial separation, as is the case, for example, with the Twyman-Green interferometer or the Mach-Zehnder interferometer.

Another application of a modulator device according to the invention is to provide frequency modifications for pulse or signal modulation, which are used for distance measurement and for three-dimensional object detection. The transit time of modulated signals of electromagnetic radiation can be determined. The implementation of the signal modulation is compact and inexpensive with a modulator device according to the invention. Amplitude and / or frequency modulation can be used here.

A modulator device according to the invention can also be used in the field of optical communication. For data transmission, for example in optical glass fibers or in free-jet arrangements, it is advisable to use a modulator device according to the invention. There is the possibility of generating frequency modifications and their detection, for example also via pulse transfer to charge carriers. Amplitude and / or frequency modulation can be used here.

Another application of a modulator device according to the invention consists in high-resolution spectroscopy. A primary frequency can be shifted in a targeted manner by means of a modulator device according to the invention. For example, in the manner disclosed, a frequency can be set exactly to an absorption line of narrow spectral width or narrow frequency bandwidth. This also enables spectral adjustment in ion traps. One embodiment is the use of the frequency modification described in computers that use quantum states. In doing so, energy states can be excited and queried in an optically spectrally precisely adjustable manner. Integration in a vacuum and / or in a low-temperature environment is simple and possible with little installation space. This enables compact designs of the devices under consideration. Suitable materials for the modulator layer are superconductors, which enable tuning over a large frequency range Dn.

Some embodiments of the modulator device according to the invention can be based on multiple reflections. In an arrangement that corresponds, for example, to a hollow, metallically coated cavity, at the ends of which a voltage to be modulated is applied, a very high mean frequency shift can occur due to the occurrence of very many multiple reflections, even with a relatively large angle spectrum can be achieved, which here is accompanied by a significant line broadening. A capillary that is metallically coated on the inside and electrically contacted on both sides can be used to implement this frequency modification. It is also possible to use a superconducting coating at sufficiently low temperatures. It is also possible to coat an optical, light-conducting fiber in an electrically conductive manner on the outside and to allow a current to flow through the coating. The fiber must be designed so thin that there is an interaction between the free electrons of the conduction band and the electromagnetic radiation. With the increase in the angular spectrum present during propagation, there is an increased line broadening. Reducing the number of modes reduces the line broadening. In general, multiple reflections on metals lead to significant absorption, which results in a limited propagation length. A fiber encased in an electrically conductive manner at a sufficiently small radial distance p from the optical axis or from the fiber core can have a large number of refractive index profiles, for example a step index profile with a high refractive index on the axis, a gradient index Profile with a radially decreasing refractive index or here also a homogeneous distribution of the refractive index. The mentioned “sufficiently small radial distance” can in particular be selected in such a way that relatively little energy is absorbed.

It is also possible to use an electrically conductive core with a high refractive index as the fiber core, also in order to implement mono-mode propagation over a short distance. Such a core has a diameter of 10 nm or less, for example. Waveguiding can also be achieved using a very thin electrically conductive, cylindrical-coaxial coating such that a significant portion of the propagating electromagnetic wave is radially outside of the thin electrically conductive cylinder. The thickness of the electrically conductive, coaxial layer is, for example, 5 nm. Electrical contacting is possible, but sometimes complex. A current can also be generated, for example, via induction and external electrical fields. Due to the absorption, the realizable propagation lengths are small. The resulting effective refractive index, which determines the propagation speed as a function of the discrete propagation mode, depends, among other things, on the wavelength, the geometric structure of the waveguide and material parameters such as the refractive index. There are also transparent, electrically conductive materials that can be used, such as indium tin oxide or carbon nanotubes. Due to the relatively high refractive index, indium tin oxide can be used as the fiber core, but also only at a short distance due to the relatively high absorption. One possible embodiment of a wave-guiding structure, which can also be a hollow conductor, for example can, or an electrically conductive lined conductor filled with a homogeneous refractive index, results in the design for propagation, ie propagation of the electromagnetic field in the basic mode and in the first, in this subsequent mode. In this case there are only two modes capable of propagation. These can, for example, be separated from one another in the far field behind the waveguide.

A modulator device according to the invention, which introduces amplitude modulation dependent on the speed of moving charge carriers, in such a way that this is dependent on the wavelength, can be used to analyze the spectral distribution of the incident electromagnetic radiation. A frequency analysis of the signal reveals the present wavelengths via the relationship with the speed of the moving charge carriers. An array of modulator cells that introduce amplitude modulation can thus be used together with an assigned detector array for spectral imaging. A boundary condition is a known angle of incidence. Conversely, if the spectral distribution is known, conclusions can be drawn about the angular distribution. This can be done with a single detector, or with a detector field that can serve as a wavefront sensor. Even if the spectrum of the lighting is not known, at least deviations from a plan wave can be determined. This means that the angle of incidence of a plane wave, ie also a wedge angle, is not determined, which is usually not exactly necessary for wavefront measurements. This corresponds to a wavefront measurement after the wedge has been withdrawn. For a single element of the combination of amplitude modulator field and detector field there is the possibility of angle measurement. In total, there is the possibility of a wavefront measurement. In terms of measuring a wavelength or a wavelength distribution, measurements can be carried out at several angles or even over a larger angle range that is tuned through. The measurement uncertainty can be minimized by means of a fit, for example using the method of minimizing the squares of the deviations. Starting from a known wavelength or starting from a known spectral distribution, an angle measurement can be used to measure a set of angles, and also to measure the tuning of an angle range. For example, a measurement can be made using a set of two, three or more angles or wavelengths. For example, to determine the angle of impingement on a layer through which the current flows, a set of three beams can be used which have a slight difference in their direction of propagation. It is also possible to use three coaxial wave fields with different wavelengths, for example or preferably also with the inclusion of a reference wavelength that is known with sufficient accuracy, to determine the angle of impact on a layer through which the current flows. This enables the realization of very compact spectrometers.

A further application of a modulator device according to the invention is that the implementation of a phase shift can be achieved via the time-shifted recording of a detector field using a control signal. For example, the image recording of a camera that is used in an interferometer can be triggered via a control signal which, at the specifically introduced modulation frequency, shifts in its temporal phase position relative to this. Thus, interference patterns shifted in phase are recorded. There is also the possibility of combining a periodic control signal with a specifically varying tuning time span. This possibility of targeted setting of a time delay is often implemented in cameras that can be addressed via control signals. Another possibility is the specific choice of the ratio of modulation frequency and fixed frequency of the image recording. In this way, a set of images can be obtained which have a specific phase relationship to one another.

Another application of a modulator device according to the invention is to implement a phase shift in interferometer arrangements by means of a time-shifted recording, with modulation frequencies that are significantly higher than the image repetition frequency of cameras used. Boundary conditions are sufficiently short exposure times, i.e. at least <half the period of the modulation frequency introduced. The time shift of this sufficiently narrow detection window within the image repetition frequency of the camera enables the recording of images which are shifted in phase with respect to the modulation frequency.

A further application of a modulator device according to the invention consists in varying the introduced modulation frequency over time, i.e. over the period of the recording of several interferograms. Thus, even with a fixed image repetition frequency and a fixed position of the recording window within this phase-shifted interferograms can be recorded. The methods shown can be combined with one another.

The modulator layer of the modulator device according to the invention can be a thin metallic surface through which the current flows. A modulator device can thus be implemented, inter alia, with the beam guidance of a retro reflector. In individual cases it can also be advantageous to use curved modulator layers. Another application of a modulator device according to the invention is that a relative change in angle between the modulator layer, which can also be implemented, for example, in the form of a segment which is part of a detector field, and locally incident, ie locally illuminating, waves Field, which is converted into a frequency change, can be used in a wavefront sensor to measure wavefronts.

Another application of a modulator device according to the invention is that a relative change in angle between the modulator layer, which can also be implemented, for example, in the form of a segment which is part of a detector field, and locally incident, ie locally illuminating, waves Field, which is converted into a frequency change, can be used in an imaging sensor for spectrally sensitive imaging. For example, a double image can be generated in this way, which can be recorded by a detector field which has a sufficiently high image repetition rate. Spectral components can be determined on the basis of a frequency analysis that is carried out. This can be used in telescopes, for example. An advantage here is explicitly the large spectral range in which the disclosed principle of modulation can be applied. For example, it is possible to work in the UV or also in the IR range.

The very compact design of possible modulator devices according to the present invention is advantageous for mobile systems such as those used in cars, for example, in order to detect 3D objects via frequency modulation and 2D scanning. In addition, low power consumption is also advantageous, especially for mobile systems.

BRIEF DESCRIPTION OF THE FIGURES

1 to 11, 14 and 15 and 19 to 21 show modulator devices according to various embodiments of the invention.

12 and 13 each show an angle measuring system according to embodiments of the invention which use a modulator device according to the invention.

16 to 18 each show an interferometer according to embodiments of the invention which use one or more modulator devices according to the invention. DESCRIPTION OF THE FIGURES

FIG. 1 shows a modulator device 1319 according to an embodiment of the invention which introduces a frequency modification of the reflected light. The modulator device 1319 comprises a substrate which is coated with a modulator layer which forms an electrically conductive, reflective surface to which a voltage can be applied. This leads to a current flow. In the event of an oblique incidence on the electrically conductive surface, caused by moving charge carriers, a Doppler shift can be introduced, ie in that part of the incident electromagnetic wave which is reflected on directionally moving charge carriers. A voltage is applied to each of the contacts 2i and 2i _{2 in} such a way that there is a voltage difference between the contacts, which leads to the flow of current. Since, depending on the parameters of the materials used, the part of the incident electromagnetic wave that is reflected on directionally moving charge carriers can also make up a portion of <100% of the reflected light, the reflected portion of an electromagnetic wave incident on the modulator 1319 can both there is a component that is shifted in frequency, as well as a component that is not. The superposition of both components in the reflected beam results in an amplitude modulation with the existing beat frequency, ie with the difference frequency, which here corresponds to the frequency shift introduced. The modulator device 1319 from FIG. 1 can thus be viewed both as a purely frequency-shifting component and as an amplitude modulator or as a representative thereof.

The modulator device 1319 can be functionally combined with other components, for example also used in a beam path. The modulator device 1319 from FIG. 1 can be integrated on the hypotenuse of a transparent prism. The result is a modulator device 1316 which is based on a prism. This is shown in FIG. The current flowing over the conductive surface can be set in a defined manner. The substrate of the modulator device 1316 is at least partially transparent to the incident electromagnetic radiation and has a first (hypotenuse), a second and a third outer surface. The second and third outer surfaces are perpendicular to each other. The first outer surface (hypotenuse), which is inclined to the second and third outer surface, is coated with the modulator layer.

The modulator layer of the modulator device can be partially transparent. A beam splitter can be implemented in this way. The modulator device can be constructed in the form of a beam splitter cube 1920-1323. This is shown in FIG. Of the The transmitted portion has no frequency modification here. The current flowing through the conductive, partially permeable modulator layer can be set in a defined manner.

The modulator device, which consists for example of a substrate coated with an electrically conductive surface or modulator layer (1319), including the electrical contact (2I ₁ , 2i ₂ ) necessary for the flow of current, can be provided with a number of additional layers will. Thus, an additional reflective layer 1819 in FIG. 4 can be used to reflect a portion of the incident electromagnetic radiation in front of the electrically conductive layer or the modulator layer, ie without introducing a frequency modification in this portion. The reflective layer can act selectively on different polarization states of an incident wave field. The reflective layer 1819 in FIG. 4 can, for example, be designed in such a way that a polarization is sufficiently fully reflected on it and the polarization orthogonal thereto is not, ie, that it is only reflected on the electrically conductive modulator layer.

A number of embodiments of a modulator device result from the use of wire-grid polarizers, as shown by layer 4716 in FIG. This design of the electrically conductive modulator layer, through which a defined, adjustable current flows, as a wire-grid polarizer enables the introduction of a frequency shift which only affects one polarization state of the incident light. As shown in FIG. 5, a polarization state is reflected and the polarization state orthogonal thereto passes the wire-grid polarizer and is reflected here, for example, by a mirror layer 19. This second part of the incident electromagnetic wave field does not experience any frequency shift. The portion of the incident electromagnetic wave field reflected by the modulator device can contain a portion that is shifted in frequency and a portion that is not shifted in frequency.

In the modulator device shown in FIG. 6, a Doppler shift is introduced into part of the reflected electromagnetic radiation at the hypotenuse of a prism that is sufficiently transparent for the radiation. The modulator layer 4716 represents a wire-grid polarizer which is electrically conductive and at which a voltage difference _{can be generated between the contacts 2i and 2i 2} , which leads to the flow of current. The wire-grid polarizer shows a reflection which is different for orthogonal polarization states, ie a reflection which is selective in terms of polarization. The portion of the electromagnetic field passing the wire-grid polarizer is on the back of the Prism hypotenuse reflected by a reflection layer 419-1819, which can also be a dielectric layer structure, for example. A metal coating can also be used or the fact of total reflection can be used, which does not require a coating.

A reflective structure, such as a wire-grid polarizer, can be arranged in an electrically contacted form between two prisms. This results in a polarization beam splitter which allows a Doppler shift to be introduced only in one of the two paths / outputs. This wire-grid polarizer based beam splitter cube 47-1323 is shown in FIG.

The disclosed modulator principle can be combined with the use of diffraction gratings. FIG. 8 shows a modulator device, the modulator layer of which is designed as a diffraction grating which has an electrically conductive layer with which electrical contact is made. A voltage difference can be generated between the contacts 2i and 2i ₂ , which leads to the flow of current. One embodiment consists of a surface relief grid which has an electrically conductive coating. This grating modulator arrangement 71319 can generate several diffraction orders or be designed accordingly. It is also possible that only one or only two diffraction orders are present. In FIG. 8, the +2th order of diffraction is evanescent and the -4th order of diffraction is arranged in the opposite direction to the incident beam. There are different Doppler shifts in the different diffraction orders. When superimposed with components that are not shifted in frequency or with components shifted differently in frequency, different beat frequencies result, ie different frequencies of the amplitude modulation. Grating modulators can produce a set of Doppler shifts or a set of frequencies of amplitude modulation. To implement an angle measurement, the grating can be rotated and a change in at least one beat frequency can be measured. For an angle measurement, for example, the diffraction order can also be used, which results in the so-called Littrow configuration. If the grating period L is correspondingly small, it can also be the - i-th diffraction order. If the grating period L is smaller than the wavelength of the electromagnetic radiation incident on the grating, only a single diffraction order (and the o-th diffraction order) may propagate. The measurement of several beat frequencies enables a significant reduction in the measurement uncertainty. That is to say, it is possible to work in an advantageous manner with a set of diffraction angles which are assigned to the individual diffraction orders and / or with a set of several wavelengths. There are very diverse design possibilities, which on this Build principle. It is also possible, for example, to illuminate the surface relief grating with perpendicular incidence, that is to say, for example, to use this position as the zero position of an angle measurement. The implementation of a perpendicular incidence on a modulator device 1319 can take place, for example, by means of grids, which can be segmented. This is shown in FIG. The input wavefront hits a coupling-in grating segment 5722, which is designed, for example, as a volume grating based on Bragg diffraction. It can be designed for a single diffraction order. The light reflected by the modulator layer strikes a coupling-out grating segment 1722, which here bends the light in the direction of retro-reflection. A multiplex of volume grating geometries can also be used, for example to enable operation at several primary wavelengths or, for example, also in combination with a set of several angles. Surface relief grids can also be used. Depending on the surface relief, defined intensities can be realized in defined diffraction orders, that is to say, for example, only in a diffracted order.

In the sense of an angle measurement, a variable angle k to be determined here can be introduced between the plane which carries the grating segments and the modulator device 1319. The Doppler shift acting on the beam emerging from the modulator layer changes with a change in angle. In order to reduce the measurement uncertainty, it is also possible to work with a set of diffraction angles and / or with a set of wavelengths, so that several frequencies are shifted. An arrangement for angle measurement can generally be run through in two directions, in such a way that two Doppler shifts can be detected, which can also cancel each other out if the angle is symmetrical and if the same wavelength is used.

A set of diffraction angles can be generated, for example, with a surface relief grating. FIG. 10 shows the use of a surface relief grating which is operated in transmission, here directly in front of the modulator layer. A modulator device 1319 is illuminated with different, here symmetrical diffraction orders, for example the + i-th and the -i-th. The grating period L can be selected in such a way that higher diffraction orders are evanescent. The phase deviation of the grating can be selected in such a way that only the ± i-th diffraction orders are present. The design of the phase deviation or the design of the profile depth can also take place in such a way that a portion of the o-th diffraction order is present, ie for example 1/10 to 1/3 of the total energy, which is used directly to generate a beat frequency can. The symmetrical grating coupler 19711 can be designed as a sinusoidal grating, for example. For the sake of clarity, FIG. 10 does not show the diffraction orders which arise on the return path of the wave field reflected by the modulator layer and do not propagate back in the direction of the incident wave field.

In FIG. 10, as well as in other figures, rays and propagating wave fields are shown by way of example in the form of arrows for reasons of clarity. A beam or a wave field can have an extension or a beam diameter which takes up a large part of the free aperture of the component or also the entire aperture. The wave field incident on the modulator device shown in FIG. 10 can also be an extended wave front or an extended wave field which, for example, occupies 70% of the free aperture of the symmetrical grating coupler 19711. With a suitable profile height, i.e. with the existence of the o-th diffraction order of the incident wave field, there are three wave fields that propagate against the exit direction. These wave fields partially overlap. There are different beat frequencies in the overlapping areas. In this arrangement, in the sense of an angle measurement between the grating plane and the modulator unit 1319, a variable angle k to be determined here can be introduced. The Doppler shifts acting on the rays or wave fields emerging from the modulator device change with a change in angle.

The arrangement shown in FIG. 10 can be modified in such a way that a monolithic modulator device 13713 results, which has a symmetrical grating coupler 19711 on the input side of a transparent substrate and a reflective modulator layer on the back which represents the actual modulator device 1319. A monolithic embodiment is shown in FIG. This arrangement can also be used to measure the angle between the incident wave or incident beam and the modulator unit. A deviation of the angle of incidence q is _0, which is in its zero position, for example 90 ^0, can be detected as frequency deviation. A tilt of the input wave field changes the introduced Doppler shift. The influence of the change in the angle of the propagation in the direction of the detector on the detected intensity can be minimized, for example, with the aid of a lens which is arranged at a distance from its focal length in front of the modulator device.

The relative change in angle between the modulator layer, which can also be designed, for example, in the form of a surface relief grating, and the incident, ie illuminating wave field, which is converted into a frequency change, can be used in an autocollimator to measure angles of surfaces to be scanned. FIG. 12 shows an exemplary embodiment of an autocollimator which has a modulator device 1920-135 according to the invention, which is part of a beam splitter. The light emanating from the plane of a measuring mark 185 is collimated by a lens, in the front focal plane of which the plane of the measuring mark is located. For example, if the measuring mark is only a point, there is a plane wave behind the collimator. Optionally, the portion that is reflected on the rear side of the modulator device can be used in a reference beam path 13-197 for measuring the basic modulation. A detector unit 54-45 which can be used at least on a small area and which can also be a photodiode, for example, can be used to generate a reference frequency in such a way that a misalignment and / or a spectral drift and / or a change in the spectral distribution of the light source used can be determined and compensated for in relation to the measurement result. An expansion optic 12315 is used to adapt the measuring beam diameter to the measuring object 192120 to be optically touched.

There are a number of different arrangements for implementing optics for collimation or beam expansion. Refractive, reflective and diffractive components can be used. FIG. 13 shows the expansion optics 123157 of an autocollimator in the form of a Galilean telescope. This enables a compact design. The combination of beam splitter and modulator element 1920-135-47 is based on prisms that are put together to form a cube.

As in FIG. 12, only the introduction of a frequency modification along one direction is shown in FIG. This is for the sake of clarity. The integration of two modulator devices according to the invention, which can introduce a Doppler shift along two orthogonal directions, enables two orthogonal angles to be determined via the frequency change. Advantageously, both frequency ranges that can be introduced are designed without overlap. In addition, for example, a different modulation of the signal for each area enables separation, even with the same fundamental frequency. FIG. 14 shows two suitably arranged modulator layers in a compact design 1920-135-47-264.

The light that comes from the plane of the measurement mark - in the example used within an autocollimator - hits the modulator beam splitter at the bottom left. It propagates to the right, where an expansion optic can connect. Optionally, a downward reflected portion can be used to determine a reference frequency (See also Fig. 12, 13-197 in this regard, for example). The light reflected from the optically scanned surface hits the lower modulator layer from the right. This modulator layer can, for example, have a wire-grid polarizer through which the current flows. The double arrow represents the orientation of the grid lines and the advantageously present oscillating electric field of the incident light. Optionally, a so-called half-wave plate 82316 or a corresponding one is located in front of the second modulator layer of the 2D modulator 1920-135-47-264 birefringent layer. This changes the polarization state. This option is advantageous if a wire-grid polarizer through which the current flows is also used in the second, ie upper, modulator layer. The second, ie upper, modulator layer can also be designed as a non-structured, metallic, electrically conductive surface. This generally does not require a half-wave plate arranged directly in front of it.

Another embodiment is the use of a non-structured, metallic, electrically conductive surface as the lower modulator layer (see FIG. 14). It is advantageous that the light coming from the right, i.e. the light reflected back from the surface to be optically touched, has a horizontally oscillating electrical field, i.e. that the E-field of the light oscillates perpendicular to the plane of incidence of the light modulator. In this embodiment it is advantageous to use the half-wave plate 82316 optionally shown in FIG. 14, i.e. if the following modulator layer is designed, for example, as a non-structured, metallic, electrically conductive surface. Alternatively, it is also possible to separate the 2D modulation, i.e. for example using beam splitter arrangements in such a way that two separate detector units are used or two separate parts of a detector unit. Neutral beam splitters and polarization beam splitters are generally suitable for this. Diffractive beam splitters can also be used, i.e. if, for example, a fixed design wavelength is used or several fixed design wavelengths. If different wavelengths are used, dichroic beam splitters can also be used for this.

An embodiment which serves to increase the frequency range which can be modulated is shown in FIG. An electromagnetic wave incident from the left is reflected several times on - here parallel - modulator layers. Thus, for example, significantly more than 10 reflections can be realized on a metallic, electrically conductive modulator layer through which the current flows. With an adapted design of the end face, this arrangement can also be expanded to a reflector or also to a retro reflector. Here and in general, a direct current or an alternating current can be applied to the contacts, ie here to the contacts 2i and 2I _{2 of} the lower modulator layer and at the contacts 22 and 22 _{2 of} the upper modulator layer. It is also possible to convert this modulator device into a rotationally symmetrical arrangement. There is a first contact on the entry side and a second contact on the exit side. In FIG. 15, the contacts 2i with 22 and 2i ₂ with 22 _{2 would} coincide. For example, a capillary can be designed to be electrically conductive on its inside, that is to say, for example, have a thin metal layer there. Contacts are attached to both ends. A direct current or an alternating current can be applied to the contacts of a capillary. The directed current flow is set by the voltage difference AU ₁₂ .

Polarization beam splitter, or non-polarization-selective diffraction geometries, for example volume grating multiplex geometries, which are designed for perpendicular incidence and, however, a - component internal - reflection at a sufficiently large angle of incidence on a reflective surface, ie for example, have an angle of incidence> 10 ⁰ , can be arranged over a modulator layer on which the - component internally - non-perpendicular reflection takes place. For example, some polarization beam splitters are listed in patent application DE102006016053B4 [2].

The use of a polarization change or polarization switch in connection with polarization beam splitters, for example also with diffractive polarization beam splitters, enables a sufficiently rapid switchover between different optical paths. These can be different modulation paths. For example, the angle can be changed in that the electromagnetic radiation hits the moving charge carriers of the modulator layer.

The use of polarization switching can also be used in connection with switching between different optical paths to implement a sequential 2D frequency modification. For example, multiplex volume grids can be used for this purpose, which enable orthogonal polarizations to be separated. In volume holographic gratings, which is based on the Bragg diffraction this among others at diffraction angles of 90 ⁰ to 60 ⁰ the case. A polarization switch based on liquid crystal, for example, can be synchronized in time with a changing current direction. Two orthogonal directions of incidence can thus be combined with two orthogonal current directions and synchronized in time.

A 2D frequency modification that takes place simultaneously, for example, can be implemented by, for example, orthogonally polarized components of a wavefront simultaneously fall on the modulator layer of a modulator device according to the invention. These can have different values of the direction cosine in relation to the direction of the current flow. For example, a wavefront measurement can take place at a fixed, spectrally sufficiently narrow-band wavelength. Due to the relatively different values of the direction cosine, the frequency shift for orthogonal directions takes place along the wavefront to be measured in sufficiently different frequency ranges. In the case of strongly curved wavefronts, in comparison to less strongly curved wavefronts, an increased difference in the values of the direction cosine must generally be implemented in the geometric design. A stronger curvature, in one direction or the other, requires a wider frequency range, ie in one direction or the other. For example, a multiplex twice along two directions separated by 90 ⁰ may be for a wavelength or a wavelength range. This can be combined with polarization switching in order to implement a 2D Doppler frequency modification. In the case of an oblique imaging, here for example on a modulator substrate, compliance with the Scheimpflug condition avoids perspective image distortion.

A 2D Doppler frequency modification is also possible without polarization switching, i.e. passively and in parallel. A time-sequential switchover can also take place, which is explicitly not polarization-selective. An arrangement of reduced complexity results from the reflection on a modulator layer in such a way that a wavefront to be measured experiences different Doppler shifts, for example along sufficiently orthogonal directions. The reflected wavefront, which is modulated in frequency in two directions, can be superimposed with a reference wavefront of a sufficiently small difference between the local angles of the wavefront normals.

The spatially resolved frequency analysis gives the value of orthogonal components of the locally present surface normal vector of the wavefront to be measured. It is also possible to work with a plane wave spectrum or with spectrally broad light sources, also in combination. The boundary condition is compliance with the clear assignment of the frequency analysis to the wave field to be measured or the enabling of this by means of an adapted parameter variation, as is the case, for example, on the error separation method.

The procedure disclosed can advantageously be used in various interferometer arrangements. An interferometer arrangement is shown in FIG. The basic type corresponds to a so-called Mach-Zehnder arrangement. A The first, here selective beam part with regard to the input polarization, cube 161920-I, separates an incoming wave field. A part (rq / in plane of incidence) passes the beam splitter without deflection and hits a mirror substrate 19. In the further course, this part passes a second beam splitter cube 161920- II, which is selective with regard to the input polarization. The one deflected at the first beam splitter Part (njT 1 to the plane of incidence) hits a modulator device 1319 according to the invention. A voltage is applied to _{the contacts 2i and 2i 2.} In the further course, this part passes the second beam splitter cube 161920-II, which is selective here with regard to the input polarization, with a deflection. The path difference based on the separation of the optical paths lies within the coherence length z _c . The interferometer arrangement can serve as an amplitude modulator, for example. Furthermore, a measurement object can be arranged at least in one arm of the interferometer arrangement. This can be spatially extended and mapped onto a detector unit, for example a camera with a sufficiently high image repetition rate.

In addition to the interferometer arrangement, which is shown in FIG. 16, a Doppler shift can be introduced in several arms with a modulator device according to the invention. This is shown in FIG. For this purpose, the mirror substrate 19 from FIG. 16 has been replaced by a second modulator device 1319-II according to the invention, at the contacts 2i _2i and 2i _{22 of which} a voltage Un is applied, which causes a current I. A voltage Ui is applied to the contacts 2i _u and 2i _{2 of} the first modulator substrate 1319-I, which causes a current h. The two Doppler shifts introduced can have different amounts and different signs. The arrangement can serve as an amplitude modulator, for example. A frequency shift can also be introduced on both optical paths in such a way that no amplitude modulation takes place. A measurement object can be introduced into at least one of the two optical paths.

In addition to the interferometer arrangement from FIG. 17, the arrangement in FIG. 18 shows how the polarization can be changed in such a way that the highest possible reflection coefficient is present at the modulator device. Here, for example, a first 1/2 plate 823-I is arranged in front of the modulator device 1319-II and a second 1/2 plate 823- II behind the modulator device 1319-II. In an arrangement that is not based on a separation of the partial beam paths via orthogonal polarization states, this additional adaptation can be dispensed with by an adapted selection of the input polarization. A Mach-Zehnder interferometer arrangement can be made monolithic. This is shown in FIG. 19, which shows a modulator device according to an embodiment of the invention, in which the substrate has a polygonal surface, a first surface section of the substrate, which corresponds to a first (lower in FIG. 19) side of the polygon, with the Modulator layer 135 is coated. A second surface section of the substrate, which corresponds to a second (left in FIG. 19) side of the polygon, has a first grating structure 511-227, which is set up to couple light into the substrate, which is directed from the left onto the first grating structure 511-227 on the outside occurs. A third surface section of the substrate, which corresponds to a third (on the right in FIG second lattice structure 111-227 is incident. The monolithic modulator device 131326 has the coupling-in grating 511-227 on the input side, which can be a volume grating, for example. Part of the electromagnetic radiation is reflected by the modulator layer 135, at the contacts 2i and 2i _{2 of which} a voltage U is applied and through which a current I can flow. The coupling-out grating 111-227, which can be, for example, a volume grating or a surface relief grating, is located on the exit side.

The modulator device from FIG. 19 can be modified in such a way that a retroreflector results. Modulator devices which correspond to a retroreflector are shown in FIG. A cube-shaped modulator device 131323 which is monolithic is shown in FIG. 20 a). The grating structure 5111-7 represents the coupling-in grating and the coupling-out grating. For the sake of simplicity, only one modulator layer 135 with the contacts 2i and 2i _{2 is} shown. A centrally arranged absorber structure 151-1 is shown as an option. A modulator device 131316, which has the shape of a polygon, is shown in FIG. 20 b). The modulator layer 135 is composed here of seven subregions, ie, apart from the entry and exit areas, it is present on the entire circumference or on all polygon sides / surface sections. In the middle of the modulator, an optional absorber 151-2 is shown, which can serve to suppress stray light. A modulator device 141316, which has the shape of an inner or negative polygon, is shown in FIG. 20 c). The modulator layer 135 is on the inside of a negative polygon. The contacts 2i and 2i ₂ are passed through the wall of the polygon. Optionally, for example, the o-th diffraction order of the coupling-in and coupling-out grating 5111-7, shown here with 15-1215, can be used as a non-Doppler-shifted reference component. The modulator units which are shown in FIGS. 20 a), b) and c) represent retro-reflectors or can be designed in such a way, or also in such a way that the waves of incidence and incidence do not run antiparallel. The interpretation can take place in such a way that there is one direction of rotation, or also in such a way that there are two opposite directions of rotation.

With an adapted design of the coupling-in and coupling-out grating, the internal circulation can, for example, also take place in two mutually orthogonal circulation planes. To separate the beam paths, for example, the polarization selectivity and / or the wavelength selectivity of diffraction gratings can be designed in an adapted form. Bragg diffraction-based volume gratings are advantageously suitable. The arrangement in FIG. 21 shows an exemplary implementation of a Doppler frequency modification for applications in laser Doppler anemometry. A modulator device according to the invention, which is designed as a monolithic beam splitter 192016-23, has a modulator layer 135. The substrate has a polygonal surface, a first surface section of the substrate, which corresponds to a first polygon side, being coated with the modulator layer 135. The existing prism angles of the exit

Areas are shown so large that the function is clearly visible. A second surface section of the substrate, which corresponds to a second polygon side, is permeable and is designed to couple a light beam into the substrate which is incident on the outside from the left on the second surface section. The substrate has an inner inclined intermediate surface which is designed to partially reflect and partially transmit the light beam that is coupled into the substrate through the second surface section. The light beam portion reflected on the inner intermediate surface is reflected inside the substrate, also on the modulator layer 135 and, after multiple internal reflection, is decoupled from the substrate by a third surface section of the substrate which corresponds to a third polygon side. The portion of the light beam transmitted through the inner intermediate surface is reflected within the substrate and, after multiple internal reflection, is decoupled from the substrate by a fourth surface section of the substrate which corresponds to a fourth polygon side. Two focusing lenses 12141-12 with relatively long focal lengths bundle the light beam components, which are respectively extracted through the third and fourth surface sections, in one

Interference plane or a measurement volume 1322-22. There is an interference pattern in this. The integration of the modulator principle disclosed herein into the components of the laser Doppler anemometry can also take place using a diffractive beam splitting. The running speed of the interference pattern and the running direction can be modulated. For example, the mutually orthogonal arrangement of three such arrangements can be used to detect flows three-dimensionally. EXAMPLES

The present disclosure relates to the following examples: Example 1:

Structure such that electromagnetic radiation incident on a modulator unit experiences a frequency shift which is based on the movement of charge carriers and / or this sets the charge carriers in motion. Example 2:

Structure according to Example 1, such that the interaction of the incident electromagnetic radiation with charge carriers takes place in an electrically conductive layer.

Example 3: Structure according to Example 2, such that the electrically conductive layer is a thin layer that is metallic.

Example 4:

Structure according to Example 1, such that the charge carriers move in a superconductor.

Example 5:

Structure according to example 1, in such a way that part of the incident electromagnetic radiation experiences a frequency shift and part experiences no frequency shift.

Example 6:

Structure according to example 5, in such a way that the part of the electromagnetic radiation that experiences a frequency shift is brought to interference with the part that experiences no frequency shift.

Example 7:

Structure according to example 6, such that an analysis of the interference yields a statement about the spectral power density of incident electromagnetic radiation. Example 8:

Device according to example 6, such that it is an autocollimator in which the resulting modulation is implemented as a principle for angle measurement. Example 9:

Structure according to Example 1, such that the charge carriers move in a near-surface, electrically conductive layer of a surface relief grid.

Example 10:

Method of using a Doppler frequency modification based on the movement of charge carriers in interferometers, spectrometers, laser Doppler anemometry based devices, 3D object measuring devices, distance measuring devices or in control loops.

Example 11:

Structure according to Example 1, such that the charge carriers move in a capillary or in a light guide. Example 12:

Structure according to example 1, such that the interaction between electromagnetic radiation and charge carriers is implemented in the form of multiple reflections.

Example 13: Method according to Example 10, such that a set of angles and / or a set of wavelengths can be used in measuring devices.

Example 14:

Structure according to example 5, in such a way that a wavefront measurement is carried out.

Claims

EXPECTATIONS

1. A modulator device for modulating a frequency and / or an amplitude of electromagnetic radiation, the modulator device comprising: a substrate which is coated at least in sections with a modulator layer, the modulator layer for the electromagnetic radiation to be modulated Radiation is at least partially reflective and is electrically conductive; an adjustable power source; and a first electrical contact (21O and a second electrical contact (21 ₂ ), which are set up to apply an electrical field generated by the power source to the modulator layer.

2. Modulator device according to claim 1, wherein the modulator layer comprises a metal, a semiconductor or a superconductor, preferably a high-temperature superconductor.

3. Modulator device according to claim 1 or 2, wherein the modulator layer is partially transparent to the electromagnetic radiation to be modulated.

4. Modulator device according to one of the preceding claims, wherein the substrate is at least partially permeable to the electromagnetic radiation to be modulated.

5. Modulator device according to one of the preceding claims, wherein the substrate is at least partially transparent to the electromagnetic radiation to be modulated, wherein the substrate has a first, a second and a third outer surface, wherein the second and the third outer surface are perpendicular to one another, and wherein the first outer surface is oblique to the second and third outer surface and is coated at least in sections with the modulator layer.

6. The modulator device of claim 5, wherein a reflective layer (419-1819) is disposed over the first outer surface of the substrate and on the modulator layer, the reflective layer (419-1819) preferably being dielectric.

7. The modulator device according to claim 5, further comprising a further substrate having a first, a second and a third outer surface, the substrate and the further substrate for the electromagnetic to be modulated Radiation are at least partially transparent, wherein the second and the third outer surface of the further substrate are perpendicular to each other, and wherein the first outer surface of the further substrate is oblique to the second and third outer surface of the further substrate and is arranged on the modulator layer, so that the modulator layer is arranged between the first outer surface of the substrate and the first outer surface of the further substrate.

8. Modulator device according to one of the preceding claims, wherein the modulator layer comprises a wire-grid polarizer.

9. Modulator device according to one of the preceding claims, wherein the current source is a direct current source and / or is a constant current source.

10. Modulator device according to one of the preceding claims, which further comprises an additional reflective layer (1819), which is arranged on the modulator layer, which is suitable for reflecting a portion of the electromagnetic radiation to be modulated, wherein the additional reflective layer (1819) or the modulator layer preferably acts selectively on polarization states of the electromagnetic radiation to be modulated.

11. The modulator device according to any one of the preceding claims, further comprising a diffraction grating disposed over the modulator layer or formed within the modulator layer.

12. Modulator device according to claim 11, wherein the diffraction grating is a surface relief grating or a volume grating.

13. The modulator device according to claim 11, wherein the substrate is transparent and wherein the diffraction grating (19711) is formed on a surface of the substrate which is opposite to the modulator layer.

14. Modulator device according to one of the preceding claims, wherein a surface of the substrate which lies opposite the modulator layer is coated with a further modulator layer, the further modulator layer being at least partially reflective for the electromagnetic radiation to be modulated and is electrically conductive; and wherein the modulator device further comprises a third electrical contact (22O and a fourth electrical contact (22 ₂ ), which is used for applying the from the Electric field generated by a power source or a further electric field generated by a further power source are set up on the further modulator layer.

15. modulator device according to one of claims 1 to 14, wherein the substrate and the modulator layer are each rotationally symmetrical and wherein the modulator layer is arranged on the surface of the substrate surrounding, the substrate preferably forms a waveguide that with the Modulator layer is coated.

16. Modulator device according to one of claims 1 to 4, wherein the substrate has a polygonal surface, wherein at least a first surface section of the substrate, which corresponds in particular to a first polygon side, is coated with the modulator layer and wherein at least a second surface section of the substrate , which corresponds in particular to a second polygon side, has a first lattice structure, wherein the first lattice structure is set up to couple light into the substrate that is incident on the outside of the first lattice structure and / or to extract light from the substrate that is reflected inside the substrate and is incident on the inside of the first lattice structure.

17. Modulator device according to one of claims 1 to 4, wherein the substrate has a polygonal surface, wherein at least a first surface section of the substrate, which corresponds in particular to a first polygon side, is coated with the modulator layer, wherein a second surface section of the substrate which corresponds in particular to a second polygon side, is at least partially permeable and is set up to couple light into the substrate which is incident on the outside of the second surface section; wherein the substrate has an inner intermediate surface which is configured to partially reflect and partially transmit a light beam that is coupled into the substrate through the second surface section; wherein a third surface section of the substrate, which corresponds in particular to a third polygon side, is at least partially permeable and is set up to decouple from the substrate a light beam portion that is reflected or transmitted by the inner intermediate surface and is reflected on the modulator layer; wherein a fourth surface section of the substrate, which corresponds in particular to a fourth polygon side, is at least partially permeable and is designed to a portion of the light beam transmitted or reflected by the inner intermediate surface is coupled out of the substrate.

18. The modulator device according to claim 17, further comprising: a first focusing lens which is configured to focus the portion of the light beam coupled out by the third surface section onto an interference plane; and a second focusing lens which is configured to focus the portion of the light beam coupled out by the fourth surface section onto said interference plane.

19. An optical arrangement comprising a modulator device according to one of claims 1 to 13, wherein the modulator device is set up for splitting a light beam, wherein a part of the light beam to be split is transmitted by the modulator device, and wherein a part of the light beam to be split is reflected by the modulator layer of the modulator device.

20. Optical arrangement comprising a modulator device according to one of claims 1 to 13, wherein the modulator device is arranged in a beam path of the optical arrangement after a beam splitter which splits an input light beam into at least two beam components, the modulator device is set up to modulate a frequency and / or an amplitude of one of the at least two beam components, wherein the one of the at least two beam components is at least partially reflected on the modulator layer of the modulator device.

21. Optical arrangement according to claim 20, which comprises a further modulator device according to one of claims 1 to 13, wherein the further modulator device is arranged in the beam path of the optical arrangement after the beam splitter, wherein the further modulator device is set up to to modulate a frequency and / or an amplitude of the other of the at least two beam components, the other of the at least two beam components being at least partially reflected on the modulator layer of the further modulator device.

22. Optical arrangement according to claim 20 or 21, further comprising: a first retardation plate (823-I) which is arranged in the beam path in front of the modulator device or in front of the further modulator device, wherein the first retardation plate (823-I ) is preferably a 1/2 plate, and / or a second retardation plate (823-II) which is arranged in the beam path after the modulator device or after the further modulator device, the second retardation plate (823-II) preferably being a 1/2 plate.

23. A method for modulating a frequency and / or an amplitude of electromagnetic radiation using a modulator device according to one of claims 1 to 18, wherein the method comprises reflecting at least part of the electromagnetic radiation on the modulator layer of the modulator device while the electric field generated by the power source is applied to the modulator layer.