Oscillator and method

Abstract

The present invention relates to an oscillator assembly for generating terahertz radiation, the oscillator assembly comprising an active laser layer structure (10) based on a semiconductor material for emitting laser light (107) of at least one wavelength, the main radiation direction of which is substantially perpendicular to the main radiation surface. A two-dimensional grating structure (200) arranged substantially parallel to the main radiation surface cooperates with the active laser layer structure, and the active laser layer structure is excited to form two laser modes of different frequencies (f1, f2). The oscillator assembly further comprises a mixer structure (30) arranged in the radiation direction and configured to generate a difference signal from the two laser modes, and an absorption element (301) arranged downstream and opaque to the two laser modes.

Description

[Technical Field]

[0001] This application claims priority from German application DE102022127877.8, filed October 21, 2022, the disclosure of which is incorporated herein by reference in its entirety. [Background technology]

[0002] The present invention relates to oscillator circuits, in particular terahertz oscillators, and to methods for operating such oscillators.

[0003] Modern telecommunications systems require increasingly higher fundamental frequencies due to increasing demands for bandwidth and data volume. For the sixth generation (6G) telecommunications standard, the use of transmission frequencies above the microwave band, in the so-called terahertz band, is being considered.

[0004] Microwave directional radio already exists, using directional radiation in the range up to about 90 GHz. A higher fundamental frequency would significantly increase the bandwidth and the data volume. Therefore, various research institutes and companies have proposed frequency bands above 300 GHz, allocated to the terahertz band. This frequency band extends from 300 GHz to about 100 THz (up to about 30 THz by definition), with wavelengths from about 1 mm to about 3 μm, i.e., in the mid-infrared region of the spectrum.

[0005] However, other applications are also conceivable, not just in telecommunications. For example, terahertz radiation can be used to perform contactless scanning, since electromagnetic radiation in this range can penetrate clothing in particular and make objects visible. This type of application is known as body scanners and is used especially in airports, where only detectors sensitive to radiation in this range are used. Since many materials exhibit a characteristic response to terahertz radiation, it is also used in material testing or biological or medical research.

[0006] The challenge for this application is to generate radiation in the relevant region, preferably with a narrow band. Although low-power systems are also feasible, for higher powers laser assemblies are often used, whose light is processed in an appropriate way. For example, it is possible to combine and amplify the light of two lasers via an erbium-doped fiber optic link. However, this configuration is relatively large and nevertheless has a limited power output. Summary of the Invention

[0007] Therefore, other solutions that provide higher power output are needed.

[0008] This need is met by the subject matter of the independent claims. Further developments and embodiments of the proposed principle are set out in the dependent claims.

[0009] The inventors propose to use a special modern laser device to generate terahertz radiation and to combine this laser device with additional means. The laser assembly used is characterized by the use of a two-dimensional grating structure that scatters light linearly in-plane and orthogonally out-of-plane. However, the orthogonal surface emission out-of-plane, similar to that of a VCSEL, offers the laser several performance advantages, since the output power can be expanded over the emitting area of ​​the device if heat dissipation is adequate.

[0010] Out-of-plane emission is enabled and stabilized by two-dimensional lattice structures (e.g., in the form of photonic crystals), which in particular provide feedback. By appropriately selecting the structural elements of the lattice structure and their shape and arrangement, the laser device can be excited to emit multimode light. In this case, the threshold for multimode emission can be set by the lattice structure, thereby ensuring that both modes utilized oscillate. The frequency or wavelength spacing can be set by the materials of the laser assembly itself. The two laser modes are fed into a mixer structure, which generates a difference signal and provides the desired radiation. The wavelength or frequency of the difference signal in the terahertz range is set by appropriately selecting the mode to oscillate through the design of the laser device and the lattice structure.

[0011] In this way, oscillators are created which, on the one hand, stably deliver a given frequency in the terahertz range and, on the other hand, deliver high power in the milliwatt or watt range, while requiring a significantly smaller area for such implementation than conventional solutions. By adjusting the current or modifying the mixer structure, the amplitude of the output signal can be modulated.

[0012] In some aspects, the mixer structure may also be used as an antenna. In other aspects, a separate antenna structure is provided that is configured to radiate in a predetermined frequency band. In some aspects, the antenna structure is coupled to the mixer structure or to a material of the mixer structure, and the antenna structure is guided within the mixer structure. A particularly suitable waveguide structure may be provided for this purpose.

[0013] In one embodiment, an oscillator assembly, particularly in the form of a terahertz oscillator, comprises an active laser layer structure based on semiconductor material, the laser layer structure being configured to emit laser light of at least one wavelength, the main emission direction of which is substantially perpendicular to the main emission surface of the layer structure.

[0014] The grating structure, particularly a two-dimensional grating structure, is operatively connected to the active laser layer structure. In this context, a two-dimensional grating structure is understood to be a structure whose elements lie generally in a plane formed by two mutually perpendicular spatial directions. This plane, and therefore the grating structure, is arranged approximately parallel to the main surface. The grating structure cooperates with the laser layer structure so that the active layer in the laser layer structure is excited during operation, generating two laser modes with different frequencies.

[0015] In other words, the laser layer structure cooperates with the grating structure to generate two laser modes with slightly different frequencies. The two signals thus generated are relatively narrowband and, in some embodiments, polarized in the same direction. According to the proposed principle, a mixer structure arranged in the radial direction is further provided, and the mixer structure is configured to generate a difference signal from the two laser modes.

[0016] The difference signal generates the terahertz radiation according to the present invention and thus the output signal provided by the oscillator assembly according to the present invention.

[0017] Some embodiments relate to the mutual arrangement of various elements, namely, the grating structure and the laser layer structure. In some embodiments, the grating structure is made of a conductive material and is also used to pass current through the active layer of the laser layer structure. In this regard, it may be provided that, at least in some embodiments, the material of the grating structure is different from the semiconductor material. This is suitable to enable the utilization of various refractive index differences in addition to shape, alignment, and other parameters.

[0018] In some embodiments, the lattice structure cooperating with the active laser layer structure is located on the side opposite to the primary emission surface. However, the lattice structure, particularly in the form of a photonic structure, interacts with the active layer so that only laser light that complies with the band structure conditioned by the photonic structure is excited, scattered perpendicular to the plane, and decoupled. Locating the photonic structure "below" the active layer has the additional advantage that the decoupling of light from the laser layer structure can be separated from the mode formation by the photonic structure, thus allowing both aspects to be optimized separately. Alternatively, the lattice structure cooperating with the active laser layer structure can form at least a portion of the primary emission surface.

[0019] In either case, in some embodiments, a lattice structure cooperating with the active laser layer structure can be disposed between the active layer of the laser layer structure and the semiconductor layer for supplying charge carriers. In other words, the laser layer structure and the lattice structure are integrated into or formed as a common body. To enhance the interaction between the active layer of the laser layer structure and the lattice structure, in some embodiments, the spacing can be as small as possible, in the range of less than 1 μm. In such cases, the lattice structure is formed of a conductive material to ensure current transport.

[0020] In some embodiments, the active laser layer structure includes a quantum well structure or a multiple quantum well structure. The active laser layer structure is spatially separated from the lattice structure cooperating with the laser layer structure or active layer (i.e., the quantum well structure or multiple quantum well structure) by a conductive blocking layer that prevents the diffusion of foreign atoms, particularly dopant atoms. The blocking layer is disposed adjacent to the quantum well structure or multiple quantum well structure.

[0021] Some aspects relate to the shape and configuration of the lattice structure. For example, the lattice structure may have quantized symmetry, i.e., rotational symmetry or translational symmetry that is not continuous but has only defined values. In the case of rotational symmetry, this is, for example, fulfilled by structural elements whose rotational symmetry is limited to discrete values, such as 30°, 45°, 60°, 90°, 180°, and 360°. In the case of translational symmetry, the periodicity may not be repeated after every structure in one spatial direction, but may be repeated after a second or other value. In this regard, the lattice structure may also have a superlattice, so that the structure can thus form multiple symmetries.

[0022] In another embodiment, the lattice structure includes a first structural element that repeats periodically and a second structural element that repeats periodically. Both structural elements may be independent of each other and may have different periodicities. Therefore, not only a periodicity of the form ABABAB... (where A and B correspond to each structural element) but also other periodicities, such as ABBABBABBA... or ABABAABBAABABAABBAABA..., are possible. Similarly, other structural elements with other periodicities are conceivable, thus forming superlattices. The structural elements may have different shapes, dimensions, and configurations. For example, one structural element may be formed as a half-pyramid, while the other structural element may be formed as a full pyramid or another shape. Similarly, alternating structures are possible, e.g., triangular, rectangular, or generally polygonal in top view. Other structural elements include cylinders, which may be elliptical or circular in top view.

[0023] In some embodiments, a structural element can have a first periodicity in a first spatial direction and a second periodicity in a second spatial direction independent of the first spatial direction, where the first periodicity and the second periodicity are different from each other. Different periodicities in different spatial directions are also possible for different structural elements.

[0024] That is, a grating can have structural elements of different shapes or configurations that may have different periodicities in different spatial directions. Similarly, a grating can include structural elements that provide the desired dual mode by shape but with uniform periodicity in both spatial directions. Similarly, combinations of the various parameters mentioned above - material, shape, size, spatial direction, periodicity, and symmetry - are also possible depending on the desired configuration.

[0025] In some further aspects, the oscillator assembly further includes an optical element disposed between the primary emission surface and the mixer structure. The optical element is configured to direct light emitted from the active laser layer structure along the primary emission direction to the mixer structure. The optical element may be part of the active laser layer structure, i.e., embedded in its material, or disposed on the primary emission surface. In some aspects, the optical element is integrated to form the primary emission surface of the active laser layer structure.

[0026] In a further embodiment, the mixer structure comprises an absorbing element arranged downstream in the main radiation direction, which is substantially opaque to two laser modes of different frequencies. The mixer structure can have surface-active elements. In the lower frequency range, the mixer structure is formed by a nonlinear element, for example, a diode. To generate radiation in the terahertz range, a nonlinear element made of a semiconductor material or comprising such a material is also required. This can in particular be based on Ga, for example GaAs.

[0027] In contrast, the absorbing element contains a band gap that allows absorption of light in both laser modes. A suitable material for this is silicon, which is opaque to near- and mid-infrared light in the wavelength range of 900 nm to 1000 nm, but allows the generated difference signal to pass. The absorbing element should preferably be made of a different semiconductor material than the mixer structure.

[0028] In some aspects, the mixer structure is configured for directional output of the difference signal, particularly along one spatial direction or two opposing spatial directions. In some embodiments, the wavelengths of the two laser modes are in the infrared part of the spectrum, particularly above 900 nm, particularly above 950 nm. This results in a wavelength of the difference signal in the range of 1 mm to 3 μm, particularly in the range of 1 mm to 0.1 mm.

[0029] A further aspect relates to a method for operating an oscillator assembly based on the proposed principle, in which the current is modulated to generate laser light in two laser modes. In this way, amplitude modulation of the generated terahertz radiation can be achieved. However, this method at least allows the output power to be adjusted within a certain range, so that it can be adapted to the desired application.

[0030] In the same way or in another way, the mixing efficiency of the mixer structure can also be changed, and so the amplitude of the difference signal can also be changed.

[0031] Further aspects and embodiments based on the proposed principles will become apparent by reference to the various embodiments and examples described in detail in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0032] [Figure 1] FIG. 1 illustrates a first embodiment of a PCSEL-based terahertz oscillator according to some aspects of the proposed principles. [Figure 2] FIG. 1 illustrates a second embodiment of a PCSEL-based terahertz oscillator according to some aspects of the proposed principles. [Figure 3] FIG. 10 illustrates a third embodiment of a PCSEL-based terahertz oscillator according to some aspects of the proposed principles. [Figure 4] FIG. 10 is a frequency diagram illustrating the frequency of the difference signal from the frequency of the dual mode according to some aspects of the proposed principles. [Figure 5]1A-1C illustrate embodiments of the laser layer structure of a PCSEL-based terahertz oscillator according to some aspects of the proposed principles. [Figure 6A] 1A-1C are top views illustrating various grating structures that can be used in a PCSEL of a terahertz oscillator according to some aspects of the proposed principles. [Figure 6B] 1A-1C are top views illustrating various grating structures that can be used in a PCSEL of a terahertz oscillator according to some aspects of the proposed principles. [Figure 6C] 1A-1C are top views illustrating various grating structures that can be used in a PCSEL of a terahertz oscillator according to some aspects of the proposed principles. DETAILED DESCRIPTION OF THE INVENTION

[0033] The following embodiments and examples illustrate various aspects and combinations thereof based on the proposed principles. The embodiments and examples are not necessarily drawn to scale. Similarly, various elements may be enlarged or reduced in size to emphasize individual aspects. It is clear that the individual aspects and features of the illustrated embodiments and examples can be easily combined with one another without affecting the principles of the present invention. Some aspects have regular structures or shapes. However, it should be noted that slight deviations from the ideal shapes may occur in practice without departing from the spirit of the present invention.

[0034] Furthermore, the individual figures, features, and aspects are not necessarily drawn to scale, and the proportions between the individual elements are not necessarily correct in principle. Some aspects and features are emphasized by being shown enlarged. However, concepts such as "top," "upper," "lower," "below," "larger," and "smaller" are properly shown in relation to the elements in the figures. Therefore, it is possible to derive such relationships between elements based on the figures.

[0035] Figure 1 shows a schematic diagram of a first embodiment of a terahertz oscillator based on the proposed principle. The terahertz oscillator is mounted in a housing 3 to allow for a space-saving design. The oscillator shown in this figure is formed from several separate assemblies, but it is also possible to integrate these assemblies into a common body, for example a semiconductor body. As will be explained below, this includes in particular the integration of laser layer structures with grating structures, but also with optical elements or a mixer structure 30, which may also be required.

[0036] The oscillator according to Fig. 1 contains in its housing 3 a laser layer structure 10 based on semiconductor material. The laser layer structure 10 is formed as a so-called PCSEL, which combines a lattice structure with an active laser material in a common semiconductor body. The term PCSEL stands for photonic crystal surface-emitting laser, i.e. a surface-emitting laser with a photonic crystal structure.

[0037] PCSEL devices utilize a two-dimensional lattice structure that scatters light generated in the active layer in a distinctive and tunable manner. In particular, scattering occurs both linearly within the plane and perpendicular to the plane, and orthogonal scattering is utilized because it is easily collected and processed. Out-of-plane emission is enabled and stabilized by the two-dimensional lattice structure (photonic crystal), which generates feedback. The special configuration of the lattice structure according to the proposed principle allows the active layer of the laser layer structure to oscillate in not just one mode, but two distinct modes, which, due to the underlying lattice structure, exhibit energetically close thresholds. This threshold is given, inter alia, by the free spectral range (FSR), which depends on the virtual band structure and the eigenvalues ​​of the underlying lattice structure.

[0038] It has been shown that lattice structures with only broken rotational symmetry (i.e., rotational symmetry with only a small value, e.g., 180° or 360°), e.g., due to their geometry, result in band structures with low thresholds, leading to the occurrence of multiple oscillation modes in laser operation. The scalability of lattice structures allows for large laser layer structures, and therefore high power output, if heat dissipation is sufficient.

[0039] In such a composite laser layer structure, the feedback of the grating structure in the plane is two-dimensional, which allows for coherent combining arrays. In this way, the light can be more easily focused, and therefore very high dual-mode brightness can be achieved.

[0040] In this embodiment, the laser layer structure 10 is attached to the semiconductor body in its active zone 103. A lattice structure 200 in the form of a photonic crystal is also present on its surface, and the light-emitting area of ​​the laser layer structure 10 is formed by the photonic structure. The light emission in two modes is essentially perpendicular to the light-emitting surface. Furthermore, a high degree of collimation is provided by the lattice structure 200. In the light path, an optical system 11 is present, which is connected to the housing 3 and which guides the emitted laser light to the mixer structure 30.

[0041] The mixer structure 30 is a nonlinear element that interacts with light of two optical modes. Due to the characteristics of this element, a difference signal, i.e., radiation with the difference frequency between the frequencies of the two modes, is generated. The mixer structure 30 can be an optical mixer, for example in the form of a PLC, a photodiode, a photoconductor, etc. For this purpose, an optical feed line, for example a glass fiber, is provided that couples the light from the laser layer structure and transmits it to the mixer structure 30. The mixer structure is configured so that the emitted difference signal has a preferential direction, for example along the radiation direction, as this facilitates further processing. In an alternative embodiment, the mixed frequency in the terahertz range is emitted via an additional antenna coupled to the mixer structure 30.

[0042] Figure 4 shows in this context a frequency diagram showing that two modes with frequencies f1 and f2 are located fairly close to each other in frequency space. This spacing can be adjusted by the grating structure, which must ensure that the thresholds for oscillation are also fairly close to each other. This ensures that the amplitudes of the two laser modes are approximately the same, which is advantageous for subsequent mixing.

[0043] The optical mixer 30 is a nonlinear element that, when fed with light of multiple frequencies, produces mixed light, i.e., the difference or sum of the respective frequencies. Similarly, if the intensity is very high, frequency multiplication can occur. In general, the difference frequency is f D = f2 - f1, where f2 is the frequency of high-energy light. Similarly, the sum frequency f2 + f1 and other frequencies (f2 - f1) / 2, 3 / 2 * However, these signals can be suppressed by appropriate design or circuit engineering measures.

[0044] If the wavelengths of the two laser modes are in the infrared part of the spectrum, especially above 900 nm, and especially above 950 nm, a difference signal is thus generated, the wavelength of which is also in the range of 1 mm to 3 μm, especially in the range of 1 mm to 0.1 mm, and the corresponding frequency is from 300 GHz to about 30 THz.

[0045] Returning to the embodiment of FIG. 1 , an absorbing element 300 is arranged in the optical path after the mixer structure 30. The absorbing element 300 transmits the difference signal having a frequency in the terahertz range. In contrast, the absorbing element 300 does not transmit the light generated by the laser layer structure 10. In particular, the element 300 is absorbing for light in the visible spectrum and the near-infrared spectrum in the range above 800 nm. Such a material can be, for example, silicon, which only needs to be a few micrometers thick. Furthermore, the absorbing element 300 is configured to have sufficient thermal conductivity to ensure thermal transport of the absorbed light. Furthermore, the absorbing element can have waveguiding properties for the generated terahertz radiation. This allows the mixer structure to be connected to an antenna through the absorbing material, which then radiates the generated radiation in an appropriate manner.

[0046] The absorbing element 300 in the optical path is suitable to prevent unconverted light of one of the two modes from entering the observer's eye or otherwise interacting with objects in the direction of radiation. On the other hand, the absorbing element 300 should be absorbing as well. A reflective element is also conceivable, but here there is a risk that the reflected light will return to the laser layer structure and / or the mixer structure and cause destructive interference or other harmful effects. If this can be eliminated, it may even be suitable to place a reflective element downstream of the mixer in the optical path, since the light reflected by the mixer will increase the conversion efficiency.

[0047] 2 shows a second embodiment of a terahertz oscillator based on the proposed principle. The oscillator is also integrated into a housing 3 and has an exit port on one side, in which the collimation optics 40 for the terahertz radiation shown are arranged. A collimation or focusing optics 11 is mounted on the light-emitting surface of the laser layer structure 10. The collimation or focusing optics 11 is somewhat separated from the mixer structure 30, at a distance d, and is also attached to the housing 3. This distance is appropriate to ensure sufficient thermal isolation between these two main elements.

[0048] In this embodiment, the lattice structure, i.e., the photonic structure configured to form the dual mode, is located in the laser layer structure on the side opposite to the light-emitting surface. In other words, the lattice structure 200 is no longer in the optical path, but is located behind or below the active layer 102 for generating light, as viewed from the light-emitting surface. It is also possible to form the photonic structure in the laser layer structure 20 close to the active layer, i.e., a few tens or hundreds of nanometers away from the active layer. In this way, the lattice structure 200 interacts with the active layer 103, resulting in the aforementioned coupling. Similarly, the light-emitting surface can be optimized in this way, optimizing the decoupling of the generated laser light, regardless of the shape or structure of the photonic layer 103.

[0049] Downstream of the mixer structure 30 in the optical path are an absorbing element 301 and the above-mentioned collimation optics. In this embodiment, the mixer structure 30 is integrated into a semiconductor body, which also forms part of the absorbing element 301. For example, the absorbing element 301, together with the mixer structure 30, is formed of a III / V semiconductor material. Suitable materials include, inter alia, InP, (LT)GaAs (at 780 nm), GaN, SiGe, LTG InAlAs / InGaAs (at 1500 nm), or Sb. In addition, Si is also suitable for the absorbing element, since it has a strong absorption effect for light in the infrared part of the spectrum but is transparent to terahertz radiation. This prevents light not converted by the mixer element 30 from being collimated by the downstream optics 40 or from being emitted from the oscillator housing 3.

[0050] Further miniaturization is achieved in the embodiment shown in Fig. 3, in which the laser layer structure 10 and the optics arranged at the light-emitting surface are arranged directly on a light-guiding 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. A grating structure is arranged in the material of the laser layer structure above the active layer 103 and below the light-emitting surface.

[0051] The mixer structure generates a difference signal from the combined light of the two modes, which is collimated and emitted by an optical system 40. In this embodiment, the elements 301′, 30 and 40 are located directly on the material of the laser layer structure 10. However, this material conducts heat well to a heat sink 3′ connected to the laser layer structure.

[0052] FIG. 5 shows an example of a surface-emitting laser in semiconductor material, in which a lattice structure is also integrated. The lattice structure must be electrically conductive to ensure current transport to the active layer. In this example, the laser layer structure 10 includes a bottom-side p-contact 100 made of an electrically conductive material, such as a metal. The contact 100 can be connected to a housing or can itself form part of the housing (not shown here).

[0053] Adjacent to this, the layer structure 10 also includes a p-doped contact layer 101, in this case made of doped GaAs. The doped GaAs distributes the current applied via the contact 100 over the surface. Subsequently, an isolation layer (cladding) 102 is formed on the lattice structure 200. The lattice structure is made of the same material system as the previously mentioned layers, in this case GaAs or AlGaAs, which can also be doped to have the lowest possible sheet resistance. The lattice structure is now separated from the active layer 103 by an undoped blocking layer 102'. The blocking layer 102' is electrically conductive but prevents the diffusion of dopant atoms into or out of the active layer. This prevents or reduces degradation of the active layer 103 over time.

[0054] The active layer 103 includes a quantum well or multiple quantum well structure. For example, GaAs / AlGaAs layers can be used for this purpose, and the GaAs / AlGaAs layers are further doped to form a series of barrier and well layers. Alternatively, other ternary material systems can be used to form such multiple quantum well structures. For example, some or all of the Al in the AlGaAs material can be replaced with In. This is useful because the wavelength of the emitted light largely depends on the ratio of the multiple quantum well structure. By using different concentrations of In and Al, the wavelength can be tuned (both in wavelength and width) to generate light; upon interaction with the photonic structure 200, two modes oscillate with a frequency shift, the difference of which produces the desired terahertz radiation.

[0055] An n-doped injection layer 104, for example made of n-doped AlGaAs, is applied to the multiple quantum well structure 103, followed by a further layer 105, also made of a semiconductor material, although the manufacturing sequence can be reversed so that layer 105 forms the doped growth substrate onto which subsequent layers, in particular lattice structure 200, are epitaxially deposited.

[0056] The surface of layer 105 also simultaneously forms the main emission surface of the laser layer structure 10 for laser light 107. For the current supply, a metal contact 106 in the form of a window is also arranged on the surface of layer 105. Contact 106 surrounds the emission area.

[0057] In this embodiment, the photonic structure is arranged below the active layer, i.e., on the surface opposite to the light-emitting region. However, it is also possible to arrange the photonic structure between the light-emitting region and the active layer. Similarly, it is also possible to arrange the photonic structure on the surface of layer 105. For this purpose, after the individual layers have been manufactured, the surface of layer 105 is exposed and the photonic layer 200 is formed on this surface as a lattice structure according to the proposed principle. This can be done either additively, i.e., by forming the structure by a patterned deposition process, or subtractively, i.e., by etching the structure. In fact, a combination of etching and deposition processes is also possible.

[0058] 6A-6C show various embodiments of photonic structures 200 in top view, which can be used, for example, to form dual modes in a surface-emitting laser. Each of the structures includes one or more structural elements 210-214, which may be periodically arranged. The dimensions of the structures are in the range of a few microns, e.g., between 10 and 35 microns. Individual structural elements within the lattice structure can have different periodicities, as shown, for example, by structural elements 213 and 214 in FIG. 6C. Adjacent elements 213 are spaced apart more widely than adjacent elements 214.

[0059] Furthermore, the symmetry can be different in different spatial directions, i.e., the x-direction can have a translational symmetry that is different from the translational symmetry in the y-direction, and the respective periodicity can be complex and adapted to the respective application.

[0060] Furthermore, the structural elements themselves differ in configuration, for example, between Figures 6A and 6C. Here, the structure of the individual elements does not have continuous rotational symmetry, but rather is configured to take on only a few discrete values, if any. For example, Figure 6A shows a photonic structure 200 having two structural elements 210 and 211. Element 211 is rotationally symmetric as a circular or cylindrical structure, but this structure is broken down with respect to element 211 in that a simple 180° and 360° rotation around the central axis results in the same element again. Element 211 exhibits an elliptical shape in top view.

[0061] If we now consider the two elements 210 and 211 together as a cell, the rotational symmetry is further reduced. Only when rotated 360° does it return to the original element. The same applies to the embodiment of Figure 6B, where the structural element 212 is shaped as a half-pyramid, forming an isosceles triangle in top view. Here too, the rotational symmetry is broken, i.e., the structural element is only visualized on itself when rotated 360°.

[0062] The embodiments shown here can be combined in various ways. The basic principle of generating terahertz radiation by mixing the light generated by a PCSEL as a dual-mode laser remains unchanged. Terahertz oscillators based on the proposed principle can also be further developed for amplitude modulation. For this purpose, the laser current can be varied, which changes the amplitude of the generated light and results in an amplitude modulation of the formed terahertz radiation.

[0063] Alternatively, it is possible to vary the conversion efficiency of the mixer structure, i.e. the efficiency with respect to converting and generating the difference signal, thereby varying the intensity of the difference signal and thus the amplitude of the terahertz radiation. However, in contrast to the second solution, the first solution is preferred due to its higher conversion efficiency, since the conversion efficiency to terahertz radiation is not modulated, but only the power of the laser light is modulated.

[0064] The proposed solution forms a terahertz oscillator that is particularly easy to scale in size and power. The proposed solution can be realized in a small space. With good heat dissipation, high power outputs can be obtained, ranging from milliwatts to several watts. [Explanation of symbols]

[0065] 3, 3' housing 10 Laser layer structure 11 Optical system 30 Mixer Structure 40 Optical system 100 contacts 101 Contact layer 102 Separation layer 102' Blocking Layer 103 Active layer 104 Injection layer 105 layers 106 Contacts 107 Laser Light 200 lattice structure 210 Structural Elements 211 Structural Elements 212 Structural Elements 213 Structural Elements 301 Absorbing element

Claims

1. 1. An oscillator assembly, in particular a terahertz oscillator, comprising: an active laser layer structure (10) based on semiconductor material for emitting laser light of at least one wavelength, the main emission direction of which is substantially perpendicular to the main emission surface; a grating structure (200) arranged substantially parallel to the main faces and cooperating with the active laser layer structure (10), in particular a two-dimensional grating structure (200), in which the active laser layer structure (10) is configured to be excited to form two laser modes of different frequencies (f1, f2); a radially arranged mixer structure (30) configured to generate a difference signal of the two laser modes at the difference in frequency of the two laser modes; an absorbing element (301), in particular comprising silicon, arranged downstream of the mixer structure (30) in the main radiation direction, which is substantially opaque to the two laser modes of different frequencies; an oscillator assembly including:

2. the grating structure (200) cooperating with the active laser layer structure (10) is arranged on the side opposite to the primary emission surface; or 2. The oscillator assembly of claim 1, wherein the grating structure (200) cooperating with the active laser layer structure (10) forms at least a part of the primary emission surface.

3. 3. An oscillator assembly according to claim 1 or 2, wherein the grating structure (200) cooperating 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 charge carriers.

4. 4. An oscillator assembly according to claim 1, wherein the active laser layer structure (10) has a quantum well or multiple quantum well structure, and a lattice structure (200) cooperating with the active laser layer structure is arranged adjacent to the quantum well or multiple quantum well structure, separated by a blocking layer which is electrically conductive but prevents the diffusion of foreign atoms, in particular dopant atoms.

5. 5. The oscillator assembly according to claim 1, wherein the grating structure (200) comprises periodically repeating structural elements, the rotational symmetry of which is limited to values ​​in particular of 30°, 45°, 60°, 90°, 180° and 360°.

6. 6. The oscillator assembly of claim 1, wherein the grating structure comprises periodically repeating first structural elements (210) and periodically repeating second structural elements (211), the second structural elements having different dimensions and / or shapes than the first structural elements.

7. 7. An oscillator assembly according to claim 5 or 6, wherein the periodicity of the structural elements in a first spatial direction is different from the periodicity in a second spatial direction.

8. 8. The oscillator assembly according to claim 1, further comprising an optical element (11) arranged between the primary emission surface and the mixer structure (30), configured to guide light emitted from the active laser layer structure along a primary emission direction to the mixer structure.

9. 9. The oscillator assembly according to any one of the preceding claims, wherein the absorbing element (301) comprises a different semiconductor material than the mixer structure (30), in particular silicon.

10. 10. The oscillator assembly according to any one of claims 1 to 9, wherein the mixer structure (30) is configured for directional output of the difference signal, in particular along one spatial direction or two opposite spatial directions.

11. 11. An oscillator assembly according to any one of claims 1 to 10, wherein the wavelengths of the two laser modes are in the infrared part of the spectrum, in particular 750 nm or more, in particular 900 nm or more, in particular 950 nm or more, and / or the wavelength of the difference signal is in the range of 1 mm to 3 μm, in particular in the range of 1 mm to 0.1 mm.

12. 12. The oscillator assembly of claim 1, further comprising an antenna structure coupled to the mixer structure for transferring and transmitting the generated radiation.

13. A method for operating an oscillator assembly according to any one of claims 1 to 12, comprising the steps of: The current is modulated to generate laser light in two laser modes, or A method in which the mixing efficiency of a mixer structure is modified for the generation of an amplitude modulated difference signal.

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