WO2024083995A1

WO2024083995A1 - Oscillator arrangement and method

Info

Publication number: WO2024083995A1
Application number: PCT/EP2023/079166
Authority: WO
Inventors: Hubert Halbritter
Original assignee: Ams-Osram International Gmbh
Priority date: 2022-10-21
Filing date: 2023-10-19
Publication date: 2024-04-25
Also published as: DE102022127877A1

Abstract

The invention relates to an oscillator arrangement for generating THz radiation with an active laser layer structure (10) based on a semiconductor material for emitting laser light (107) of at least one wavelength, the main emission direction of which is substantially perpendicular to a main emission surface. A 2D grating structure (200), which is arranged substantially parallel to the main emission surface, interacts with the active laser layer structure, such that the active laser layer structure is excited to form two laser modes of different frequency (f1, f2). The oscillator arrangement further comprises a mixer structure (30) arranged in the emission direction, which is designed to form a difference signal from the two laser modes, and a downstream absorption element (301) which is non-transparent for the two laser modes.

Description

OSCILLATOR ARRANGEMENT AND METHOD

The present application claims the priority of the German application DE 10 2022 127 877 . 8 of October 21, 2022, the disclosure content of which is hereby incorporated in full by reference.

The present invention relates to an oscillator circuit, in particular a THz oscillator, and a method for operating such an oscillator.

BACKGROUND

Modern telecommunications systems require ever higher base frequencies due to the increasing demands on bandwidth and data volume. For the sixth generation telecommunications standard (6G), there is talk of using transmission frequencies that are above the microwave range in the so-called THz range.

Microwave radio already exists, using directed radiation in the range up to around 90 GHz. Even higher fundamental frequencies would allow a significantly higher bandwidth and thus data volume. Various institutes and companies have therefore proposed frequency ranges that are above 300 GHz and are assigned to the THz range. This range extends from 300 GHz to around 100 THz (in some definitions only up to around 30 THz) and thus has wavelengths from around 1 mm to around 3 pm, i.e. into the mid-infrared range of the spectrum.

However, other applications are also conceivable in addition to telecommunications. For example, THz radiation can also be used for contactless scanning, as electromagnetic radiation in this range can, among other things, penetrate clothing and thus make objects underneath visible. Applications of this type are known as body scanners and are used in airports, among other places, where only a detector is used that is sensitive to radiation in this range. A similar application is in material testing, as many materials react to THz radiation in a characteristic way, or in biological or medical research. One challenge for these applications is the

Generation of preferably narrow-band radiation in this range. Systems with lower output powers can be implemented, but for higher powers, laser arrangements are often used whose light is processed in a suitable manner. For example, it is possible to combine and amplify the light from two lasers via an erbium-doped fiber optic connection. However, this structure is relatively large and the output power is still limited.

There is therefore a need for other solutions that can achieve greater output power.

SUMMARY OF THE INVENTION

This need is taken into account by the subject matter of the independent patent claims. Further developments and embodiments of the proposed principle are specified in the subclaims.

The inventor proposes to use a special novel laser device to generate THz radiation and to combine this with other measures. The laser arrangement used is characterized by the fact that a 2D grating structure is used that scatters the light linearly in the plane and orthogonally out of the plane. However, the orthogonal surface emission, similar to an out-of-plane VCSEL, offers several performance advantages for lasers, since the output power can be scaled with the emission area of the device with suitable heat dissipation.

The out-of-plane emission is enabled and stabilized by the 2D grating structure (for example in the form of a photonic crystal), which also causes feedback, among other things. By selecting the structural elements of the grating structure and their shape and arrangement, the laser device can be excited to a multi-mode emission. The threshold for the multi-mode emission can be set by the grating structure, so that it can be guaranteed that both modes to be used also oscillate. A frequency or wavelength spacing is defined by the material of the laser arrangement itself is adjustable. The two laser modes can be fed into a mixed structure, which in turn generates a difference signal and thus provides the desired radiation. By appropriately selecting the modes to be oscillated by designing the laser device and the grating structure, the wavelength or the frequency of the difference signal is set in the THz range.

In this way, an oscillator is created that, on the one hand, provides a defined frequency in the THz range with a stable frequency and, on the other hand, delivers a high output power in the m-watt or even in the watt range. The area required for such an implementation is significantly smaller than for conventional solutions. The amplitude of the output signal can be modulated by adjusting the current or changing the mixer structure.

In some aspects, the mixer structure can also serve as an antenna. In some other aspects, a separate antenna structure is provided, which is designed to emit radiation in the defined frequency range. In some aspects, the antenna structure is coupled to the mixer structure or the material of the mixer structure in such a way that the radiation in the mixer structure is guided to the antenna. Suitable waveguide structures can be provided for this purpose, among other things.

In one aspect, the oscillator arrangement, in particular in the form of a THz oscillator, comprises an active laser layer structure based on a semiconductor material. The laser layer structure is designed to emit laser light of at least one wavelength whose main emission direction is substantially perpendicular to a main emission surface of the layer structure.

A lattice structure, in particular a two-dimensional lattice structure, is operatively connected to the active laser layer structure. In this context, a two-dimensional lattice structure is understood to mean a structure whose elements are essentially arranged in a spatial direction that runs orthogonally to one another. spanned plane. This plane and thus the grating structure is arranged essentially parallel to the main surface. It interacts with the laser layer structure in such a way that the active layer in the laser layer structure is excited during operation to form two laser modes of different frequencies.

In other words, the laser layer structure, in cooperation with the grating structure, generates two laser modes whose frequencies differ slightly. The two signals generated in this way are relatively narrow-band and in some aspects polarized in the same direction. According to the proposed principle, a mixer structure arranged in the radiation direction is also provided, which is designed to form a difference signal from the two laser modes.

The difference signal forms the THz radiation according to the invention and thus the output signal provided by the oscillator arrangement according to the invention.

Some aspects deal with the arrangement of the various elements, i.e. the grating structure and the laser layer structure among each other. In some aspects, the grating structure is made of a conductive material so that it also serves to conduct current to an active layer of the laser layer structure. In this case, at least in some aspects, it can be provided that the material of the grating structure is different from the semiconductor material. This is useful in order to be able to use differences in the various refractive indices in addition to shape, alignment and other parameters.

In some aspects, the grating structure interacting with the active laser layer structure is arranged on a side facing away from the main emission surface. However, the grating structure, in particular in the form of a photonic structure, interacts with the active layer so that only laser light is excited and scattered perpendicular to the plane and thus coupled out, which follows the conditions of the band structure generated by the photonic structure. The arrangement of the photonic structure "below" the active layer may also have the advantage that the coupling out of the light from the laser layer structure can be separated from the mode shaping by the photonic structure so that both aspects can be optimized separately. Alternatively, the grating structure interacting with the active laser layer structure can form at least part of the main emission surface.

In both cases, in some embodiments, it may be provided to arrange the grating structure interacting with the active laser layer structure between an active layer of the laser layer structure and a semiconductor layer for supplying the charge carriers. In other words, the laser layer structure and the grating structure are integrated in a common body or are also designed as a common body. In order to increase the interaction between the active layer of the laser layer structure and the grating structure, in some aspects the distance can be as small as possible and lie in the range of less than 1 pm. In order to ensure current transport, in these cases the grating structure is designed with conductive materials.

In some aspects, the active laser layer structure comprises a quantum well structure or a multiple quantum well structure. This is spatially separated from the lattice structure interacting with the laser layer structure or the active layer (i.e. the quantum well or multiple quantum well structure), namely by a blocking layer which is electrically conductive but prevents diffusion of foreign atoms, in particular doping atoms. The blocking layer is arranged adjacent to the quantum well structure or a multiple quantum well structure.

Some aspects deal with the form and design of the lattice structure. For example, the lattice structure can have a quantized symmetry, i.e. a rotational or translational symmetry that is not continuous but only has defined values. In the case of rotational symmetry, this would be fulfilled, for example, by means of a structural element whose rotational symmetry is limited to discrete values, for example to one of the values 30 °, 45 °, 60 °, 90 °, 180 ° and 360 °. In the case of translational symmetry, it may be that the periodicity does not change after each structure in a spatial direction is repeated, but perhaps only after every second or another value. In this context, the lattice structure can also have a superlattice, so that the structure can form several symmetries.

In another aspect, the lattice structure comprises a first periodically repeating structural element and a second periodically repeating structural element. Both structural elements can be independent of one another and the periodicity can also differ. It is therefore possible for not only a periodicity of the form ABABAB... to occur (with A and B corresponding to the respective structural elements), but also other periodicities, for example ABBABBABBA... or AB AB AABBAAB ABAABBAABA.... Other structural elements with other periodicities are also conceivable, so that superlattices can also be formed. The shape and also size and configuration can be different for the structural elements. For example, one structural element can be in the form of a half pyramid, the other in the form of a full pyramid or in another shape. Alternating structures are also possible, which, for example, show a triangle in plan view, or also a square or generally polygons. Other structural elements are cylinders, which can be elliptical or round in plan view.

In some aspects, it is possible for the structural element to have a first periodicity in a first spatial direction and a second periodicity in a second, independent spatial direction. The first periodicity and the second periodicity are different from one another. Different periodicities in the different spatial directions are also possible for different structural elements.

This means that the grid can have structural elements of different shapes or designs, which can also have different periodicities in the different spatial directions. The grid can also include a structural element that, due to its shape but uniform periodicity in both spatial directions, causes the desired dual modes. Likewise, depending on the desired design, Combinations of the various parameters mentioned above, namely material, shape, size, spatial direction, periodicity and symmetry, are also possible.

In some further aspects, the oscillator arrangement further comprises an optical element that is arranged between the main emission surface and the mixer structure. The optical element is designed to direct the light emitted by the active laser layer structure along the main emission direction onto the mixer structure. It can be part of the active laser layer structure, i.e. embedded in its material or arranged on the main emission surface; in some aspects, the optical element is integrated in such a way that it forms the main emission surface of the active laser layer structure.

In a further embodiment, the mixer structure comprises an absorption element arranged downstream in the main radiation direction, which is essentially opaque to the two laser modes of different frequencies. The mixer structure can have a surface-active element. In lower frequency ranges, the mixer structure is formed by a non-linear element, for example a diode. A non-linear element made of a semiconductor material or comprising such a material is also required for generating radiation in the THz range. This can be based on Ga, for example GaAs.

The absorption element, on the other hand, has a band gap that leads to the absorption of light from both laser modes. A suitable material for this would be Si, which is opaque to light in the near and mid-infrared at wavelengths in the range of 900 nm to 1000 nm, but allows the generated difference signal to pass through. The absorption element should have a different semiconductor material to the mixer structure.

In some aspects, the mixer structure is designed for a directed output of the difference signal, in particular along one spatial direction or two opposite spatial directions. In some embodiments, a wavelength of the two laser modes lies in an inf- red part of a spectrum, in particular above 900nm and in particular above 950 nm. This results in a wavelength of the difference signal in the range of 1 mm to 3pm, in particular in the range of 1 mm to 0.1 mm.

A further aspect relates to a method for operating an oscillator arrangement according to the proposed principle. In this case, a current is modulated to generate laser light of the two laser modes. In this way, an amplitude modulation of the generated THz radiation can be achieved. At least in this way it is possible to regulate the output power within a certain range and thus adapt it to the desired application.

In the same way, the mixer structure can be changed in its mixing efficiency or in other ways, so that the amplitude of the difference signal can also be changed.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and embodiments according to the proposed principle will become apparent with reference to the various embodiments and examples which will be described in detail in connection with the accompanying drawings.

Figure 1 shows a first embodiment of a THz oscillator based on a PCSEL according to some aspects of the proposed principle;

Figure 2 illustrates a second embodiment of a THz oscillator based on a PCSEL according to some aspects of the proposed principle;

Figure 3 shows a third embodiment of a THz oscillator based on a PCSEL according to some aspects of the proposed principle;

Figure 4 is a frequency diagram illustrating a frequency of the difference signal from the frequencies of the dual modes according to some aspects of the proposed principle; Figure 5 is an embodiment of a laser layer structure for a THz oscillator based on a PCSEL according to some aspects of the proposed principle;

Figures 6A to 6C are plan views of various grating structures that can be used in a PCSEL for a THz oscillator according to some aspects of the proposed principle.

DETAILED DESCRIPTION

The following embodiments and examples show various aspects and their combinations according to the proposed principle. The embodiments and examples are not always to scale. Likewise, various elements can be shown enlarged or reduced in size in order to emphasize individual aspects. It goes without saying that the individual aspects and features of the embodiments and examples shown in the figures can easily be combined with one another without affecting the inventive principle. Some aspects have a regular structure or shape. It should be noted that in practice, slight deviations from the ideal shape can occur without, however, contradicting the inventive idea.

In addition, the individual figures, features and aspects are not necessarily shown in the correct size, nor do the proportions between the individual elements have to be fundamentally correct. Some aspects and features are emphasized by showing them in an enlarged manner. However, terms such as "above", "below", "below", "larger", "smaller" and the like are correctly shown in relation to the elements in the figures. Thus, it is possible to deduce such relationships between the elements from the illustrations.

Figure 1 shows a schematic representation of a first embodiment of a THz oscillator according to the proposed principle. The THz oscillator is installed in a housing 3, so that a space-saving design is possible. Although the oscillator shown here is made up of several separate components, it is possible to integrate them into a common body, for example into a semiconductor body. As will be explained, this includes, among other things, an integration of the laser layer structure with the grating structure, but also a further integration with optical elements or even with the mixer structure 30, which is also necessary.

The oscillator according to Figure 1 comprises a laser layer structure 10 based on a semiconductor material in its housing 3. The laser layer structure 10 is designed as a so-called PCSEL and integrates a grating structure with an active laser material in a common semiconductor body. The term PCSEL stands for photonic crystal surface emitting laser, i.e. for a surface emitting laser with a photonic crystal structure.

PCSEL elements use a two-dimensional grating structure which scatters the light generated in the active layer in a characteristic and adjustable manner. In particular, the scattering occurs both linearly in the plane and orthogonally to it, with orthogonal scattering being used as this is easy to integrate and process further. Out-of-plane emission is enabled and stabilized by the 2D grating structure (photonic crystal), which creates the feedback. A special design of the grating structure according to the proposed principle ensures that the active layer of the laser layer structure does not just oscillate in one mode, but in two different ones, which, however, have an energetically close threshold due to the underlying grating structure. This threshold is given, among other things, by the FSR (free spectral range), which in turn depends on the virtual band structure and the eigenvalues of the underlying grating structure.

It has been shown that grating structures that only have a broken rotational symmetry (i.e. a rotational symmetry with only a few values, e.g. 180 ° or 360 °) lead to a band structure with low thresholds due to their shape and thus lead to the generation of several oscillating modes in laser operation. Due to the scalability of the grating structure, With sufficient heat dissipation, large laser layer structures can be used and high output powers can be achieved.

The in-plane feedback of the grating structure in such composite laser layer structures is two-dimensional, which enables coherently coupled arrays. In this way, the light can be focused more easily and very high luminances of dual modes can be achieved.

In the present embodiment, the laser layer structure 10 with its active zone 103 is embedded in a semiconductor body. The grating structure 200 in the form of a photonic crystal is also located on the surface of the semiconductor body, so that the emission region of the laser layer structure 10 is formed by the photonic structure. The emission of light with the two modes takes place essentially perpendicular to the emission surface. In addition, a high level of collimation is provided due to the grating structure 200. In the beam path, an optic 11 is connected to the housing 3 and directs the emitted laser light onto a mixer structure 30.

The mixer structure 30 is a non-linear element which interacts with the light of the two optical modes. The properties of the element generate a difference signal, i.e. radiation with a difference frequency from the frequencies of the two modes. The mixer structure 30 can be an optical mixer, for example in the form of a PLC, a photodiode, a photoconductor or similar. For this purpose, optical feed lines, for example glass fibers, are provided which couple the light from the laser layer structure and transmit it to the mixer structure 30. The mixer structure is in turn designed such that the emitted difference signal has a preferred direction, e.g. along the beam direction, since this simplifies further processing. In an alternative embodiment, the mixing frequency in the THz range is emitted via a further antenna which is coupled to the mixer structure 30.

In this context, Figure 4 shows a frequency diagram with the two modes lying quite close to each other in the frequency space with the Frequencies fl and f2. The distance can be adjusted using the grating structure, whereby it should be ensured that the thresholds for starting oscillation are also very close to each other. This ensures that the amplitudes of the two laser modes are almost equal, which is an advantage during later mixing.

The optical mixer 30 is a non-linear element. This means that when light with multiple frequencies is supplied, a mixed light is also produced, i.e. a difference or sum of the respective frequencies. Frequency multiplication can also occur at very high intensities. In general, a difference frequency results: f _D = f2 - fi, where fi is the frequency of the light with the higher energy. The sum frequency f ₂ + fi also occurs, as well as other frequencies (f ₂ - fi) /2, 3 /2 * (f ₂ - fi), etc. However, these signals can be suppressed by suitable designs or circuitry measures.

At a wavelength of the two laser modes in an infrared part of the spectrum, in particular above 900 nm and in particular above 950 nm, a difference signal is generated in this way, the wavelength of which is in the range from 1 mm to 3 pm, in particular in the range from 1 mm to 0.1 mm. The corresponding frequency would then be 300 GHz to approx. 30 THz.

Referring back to the embodiment according to Figure 1, an absorption element 300 is arranged in the beam path behind the mixer structure 30. This is transparent for the difference signal with the frequency in the THz range. In contrast, the absorption element 300 is opaque for the light generated by the laser layer structure 10. In particular, the element 300 is absorbent for light in the visible and near infrared spectrum in the range above 800 nm. Such a material would be silicon, for example, which only needs to be a few pm thick. The absorption element 300 is also designed with sufficient thermal conductivity to ensure heat transport of the absorbed light. Furthermore, this absorption element can also have wave-guiding properties for the generated THz radiation. This allows the mixer structure to be equipped with a Antenna must be connected via the absorption material so that the antenna radiates the generated radiation in an appropriate manner.

An absorption element 300 in the beam path is useful to prevent any unconverted light from one of the two modes from reaching the eye of a viewer or otherwise interacting with objects in the direction of radiation. On the other hand, the absorption element 300 should also be absorbent. Although a reflective element is also conceivable, there is a risk that reflected light can get back into the laser layer structure and/or the mixer structure and lead to destructive interference or other disadvantageous effects. If this can be ruled out, a reflective element may even be suitable for arranging it downstream of the mixer in the beam path, since light reflected back into the mixer increases the conversion efficiency.

Figure 2 shows a second embodiment of a THz oscillator according to the proposed principle. This is also integrated in a housing 3 and has an exit window on one side in which a collimation optic 40 for the THz radiation shown is arranged. A collimation or focusing optic 11 is placed on the emission surface of the laser layer structure 10. This is slightly spaced from the mixer structure 30 by the distance d, which is also attached to the housing 3. The distance is appropriate to ensure sufficient thermal decoupling between these two main elements.

The grating structure, i.e. the photonic structure which is designed to generate the dual modes, is arranged in this embodiment on the side facing away from the emission side in the laser layer structure. In other words, the grating structure 200 is no longer in the beam path, but rather, viewed from the emission surface, behind or below the active layer 102 for generating light. It is possible to place the photonic structure in the laser layer structure 20 close to the active layer, i.e. only a few 10 nm or 100 nm away from it. In this way, the grating structure 200 interacts with the active layer 103 and leads to the above-mentioned coupling. The emission surface can also be optimized in this way, so that the coupling out of the generated laser light can be optimized independently of the shape or structure of the photonic layer 103.

An absorption element 301 and the collimation optics already mentioned are arranged downstream in the beam path of the mixer structure 30. In this exemplary embodiment, the mixer structure 30 is integrated into a semiconductor body, which also forms part of the absorption element 301. For example, this is formed together with the mixer structure 30 in a I II /V semiconductor material. Suitable materials would include InP, (LT) GaAs (at 780 nm), GaN, SiGe, LTG InAlAs/InGaAs (at 1500 nm) or Sb. Si is also particularly suitable for the absorption element, as it has a strong absorbent effect on light in the infrared part of the spectrum, but is transparent to THz radiation. This prevents light that is not converted by the mixer element 30 from being collimated by the downstream optics 40 or from leaving the oscillator housing 3.

In the embodiment shown in Figure 3, further miniaturization is carried out. In this embodiment, the laser layer structure 10 and an optic arranged on the emission surface are arranged directly on a light guide element 301', which on the one hand guides the light emitted by the laser layer structure 10 to the mixer structure and on the other hand prevents feedback into the laser layer structure 10. The grating structure is arranged in the material of the laser layer structure above the active layer 103 but below the emission surface.

The mixer structure generates a differential signal from the coupled light with the two modes, which is collimated and emitted by the optics 40. In this embodiment, the elements 301' and 30 and 40 are arranged directly on the material of the laser layer structure 10. However, this conducts the heat effectively to a heat sink 3' connected to the laser layer structure. Figure 5 is an embodiment of a surface-emitting laser in a semiconductor material, in which the grating structure is also integrated. The grating structure must be conductive in order to ensure the transport of current into the active layer. In the present embodiment, the laser layer structure 10 comprises a bottom-side p-contact 100 made of a conductive material, for example a metal. The contact 100 can be connected to the housing, or can itself form part of the housing (not shown here).

Following this, the layer structure 10 comprises a contact layer 101 which is also p-doped and here made of doped GaAs. The doped GaAs distributes the current impressed via the contact 100 over the surface. This is followed by a separating layer (cladding) 102 onto which the grid structure 200 is applied. The grid structure is made of the same material system as the layers already mentioned, i.e. in this case GaAs or AlGaAs, which can also be doped in order to have the lowest possible surface resistance. The grid structure is now separated from the active layer 103 by an undoped blocking layer 102'. Although this is conductive, it prevents the diffusion of doping atoms into or out of the active layer. This prevents or reduces degradation of the active layer 103 over time.

The active layer 103 comprises a quantum well or a multiple quantum well structure. For example, GaAs/AlGaAs layers can be used for this, whereby these are also doped and thus form a sequence of barrier and well layers. Alternatively, other ternary material systems can also be used to form such a multiple quantum well structure. For example, the Al in the material AlGaAs can be partially or completely replaced by In. This is useful because the wavelength of the emitted light depends essentially on the conditions in the multiple quantum well structure. By using In and Al in different concentrations, the wavelength for generating light can be set (both wavelength and width) so that in cooperation with the photonic structure 200, two wavelengths around a frequency quency shifted modes oscillate, the difference of which produces the desired THz radiation.

An n-doped injection layer 104 is applied to the multiple quantum well structure 103, e.g. made of n-doped AlGaAs, and on this a further layer 105, which also consists of a semiconductor material. It is possible to reverse the production sequence so that the layer 105 forms a doped growth substrate onto which the following layers and in particular also the lattice structure 200 are deposited epitaxially.

The surface of the layer 105 also simultaneously forms the main emission surface of the laser layer structure 10 for the laser light 107. In addition, a metallic contact 106 in the form of a window is arranged on the surface of the layer 105 for supplying current. The contact 106 surrounds the emission region.

In this exemplary embodiment, the photonic structure is therefore arranged below the active layer, i.e. on the side facing away from the surface of the emission region. However, this can also be provided between the emission region and the active layer. It is also possible to provide this on the surface of the layer 105. For this purpose, after the individual layers have been produced, the surface of the layer 105 is exposed and the photonic layer 200 is produced on it as a lattice structure according to the proposed principle. This can be done both additively, i.e. by producing the structure using a structured deposition process, and subtractively, i.e. by etching the structures. In practice, combinations of etching and deposition processes are also possible.

Figures 6A to 6C show various designs of a photonic structure 200 in their top view, as they can be used, for example, to form dual modes in a surface-emitting laser. The structures each have one or more structural elements 210 to 214, which in turn can be arranged periodically. The size of these structures is in the range of a few pm, for example between 10 pm and 35 pm. It is possible It is possible that the individual structural elements in a lattice structure have a different periodicity, as is shown, for example, in the structural elements 213 and 214 in Figure 6C. Neighboring elements 213 are spaced further apart than neighboring elements 214.

In addition, the symmetry can also differ in the respective spatial directions, i.e., there may be, for example, a translational symmetry in the x-direction that differs from a translational symmetry in the y-direction. The respective periodicities can be complex and adapted to the respective application.

In addition, the structural elements themselves are designed differently, for example in Figures 6A and 6C. The structure of the individual elements is designed such that no continuous rotational symmetry exists, but rather this can only assume a few discrete values, if present. For example, Figure 6A shows a photonic structure 200 with two structural elements 210 and 211. While element 211 is rotationally symmetrical as a circular or cylindrical structure, this is broken for element 211 in that a rotation merely around the central axis by 180 ° and 360 ° leads back to the same element. Element 211 has the shape of an ellipse in plan view.

If both elements 210 and 211 are now considered together as a cell, the rotational symmetry is reduced even further. Only with a rotation of 360° does one return to the original element. The same applies to the design in Figure 6B. Here, the structural elements 212 are designed as half pyramids, so that they form an isosceles triangle when viewed from above. The rotational symmetry is also broken in these, i.e. the structural elements only map onto themselves with a rotation of 360°.

The designs shown here can be combined in various ways. The underlying principle of creating THz radiation by mixing light that is emitted by a PCSEL as a dual mode laser generated remains unaffected. The THz oscillator according to the proposed principle can also be further developed to provide amplitude modulation. To do this, the laser current can be varied. This changes the amplitudes of the generated light and thus achieves amplitude modulation of the generated THz radiation.

As an alternative, it is also possible to vary the mixer structure in its conversion efficiency, i.e. its efficiency with regard to the conversion and formation of the difference signal, so that the intensity of the difference signal and thus the amplitude of the THz radiation can be varied. However, the first solution is preferred due to a higher conversion efficiency, since in contrast to the second solution, it is not the efficiency of the conversion into THz radiation as such that is modulated, but only the output power of the laser light.

The proposed solution forms a THz oscillator that can be scaled particularly easily in terms of size and thus output power. The proposed solution can be implemented in a space-saving manner. With good heat dissipation, a high output power in the range of mW to several W can be achieved.

LIST OF REFERENCE SYMBOLS , 3 Housing 0 Laser light structure 1 Optics 0 Mixing structure 0 Optics 00 Contact 01 Contact layer 02 Separating layer 02 ' Blocking layer 03 Active layer 04 Injection layer 05 Layer 06 Contact 07 Laser light 00 Grating structure 10 Structural element 11 Structural element 12 Structural element 13 Structural element 01 Absorption element

Claims

PATENT CLAIMS Oscillator arrangement, in particular THz oscillator, comprising: an active laser layer structure (10) based on a semiconductor material for emitting laser light of at least one wavelength, the main emission direction of which is substantially perpendicular to a main emission surface; a grating structure (200) which interacts with the active laser layer structure (10), in particular a 2D grating structure, which is arranged substantially parallel to the main surface and is designed such that the active laser layer structure (10) is excited to form two laser modes of different frequencies (fl, f2); a mixer structure (30) arranged in the emission direction, which is designed to form a difference signal from the two laser modes with a frequency from the difference between the two laser modes; an absorption element (301) arranged downstream of the mixer structure (30) in the main emission direction, in particular comprising silicon, which is substantially opaque to the two laser modes of different frequencies. Oscillator arrangement according to claim 1, in which the grating structure (200) interacting with the active laser layer structure (10) is arranged on a side facing away from the main emission surface; or in which the grating structure (200) interacting with the active laser layer structure (10) forms at least part of the main emission surface. Oscillator arrangement according to one of claims 1 or 2, in which the grating structure (200) interacting with the active laser layer structure (10) is arranged between an active layer (103) of the laser layer structure and a semiconductor layer for supplying the charge carriers.

4. Oscillator arrangement according to one of the preceding claims, in which the active laser layer structure (10) has a quantum well structure or a multiple quantum well structure, and the grating structure (200) interacting with the active laser layer structure is arranged adjacent to the quantum well structure or a multiple quantum well structure separated by an electrically conductive blocking layer which prevents diffusion of foreign atoms, in particular doping atoms.

5. Oscillator arrangement according to one of the preceding claims, in which the grating structure (200) comprises a periodically repeating structural element whose rotational symmetry is limited in particular to one of the values 30°, 45°, 60°, 90°, 180° and 360°.

6. Oscillator arrangement according to one of the preceding claims, wherein the grating structure comprises a first periodically repeating structural element (210) and a second periodically repeating structural element (211) whose size and/or shape differs from the first structural element.

7. Oscillator arrangement according to one of claims 5 or 6, wherein a periodicity of the structural element in a first spatial direction is different from a periodicity in a second spatial direction.

8. Oscillator arrangement according to one of the preceding claims, further comprising: an optical element (11) which is arranged between the main emission surface and the mixer structure (30) and is designed to direct the light emitted by the active laser layer structure along the main emission direction onto the mixer structure.

9. Oscillator arrangement according to one of the preceding claims, in which the absorption element (301) has a different semiconductor material to the mixer structure (30), in particular silicon. Oscillator arrangement according to one of the preceding claims, in which the mixer structure (30) is designed for a directed output of the difference signal, in particular along one spatial direction or two opposite spatial directions. Oscillator arrangement according to one of the preceding claims, in which a wavelength of the two laser modes lies in an infrared part of a spectrum, in particular above 750 nm, in particular above 900 nm and in particular above 950 nm; and/or in which a wavelength of the difference signal lies in the range from 1 mm to 3 pm, in particular in the range from 1 mm to 0.1 mm. Oscillator arrangement according to one of the preceding claims, further comprising an antenna structure which is coupled to the mixer structure for forwarding and transmitting the radiation generated. Method for operating an oscillator arrangement according to one of the preceding claims, in which a current is modulated to generate laser light of the two laser modes; or in which the mixer structure is modified in its mixing efficiency to produce an amplitude modulated difference signal.