Oscillator assembly and method
By using the laser components and mixer structure with a 2D grating structure in the THz oscillator, the problems of insufficient THz radiated output power and large equipment in the prior art are solved, and an oscillator design with high output power and miniaturization is realized.
Patent Information
- Application Number
- CN202380073458.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-10-21
- Filing Date
- 2023-10-19
- Publication Date
- 2025-05-27
AI Technical Summary
The prior art is difficult to achieve high output power when generating THz radiation, and the equipment is large, which limits the expansion of output power.
The laser assembly adopts a 2D grating structure, which emits a differential signal through an orthogonal surface outside the plane, combined with the mixer structure to achieve THz radiation with high output power.
High output power (milliwatt to watt level) with frequency stability in the THz range and significantly smaller device area than traditional solutions.
Smart Images
Figure CN120051902A_ABST
Abstract
Description
[0001] Related Applications
[0002] This application claims priority to German Application DE 10 2022 127 877.8 filed on October 21, 2022, the entire disclosure of which is hereby incorporated by reference in its entirety. Technical Field
[0003] The present invention relates to an oscillator circuit, in particular a THz oscillator, and a method for operating such an oscillator circuit. Background Art
[0004] Modern telecommunication systems require increasingly higher base frequencies due to the growing demand for bandwidth and data volume. For the sixth generation (6G) telecommunication standard, it is discussed to use transmission frequencies above the microwave range in the so-called THz (terahertz) range.
[0005] Microwave directional communication already exists, in which directional radiation in the range up to approximately 90 GHz is used in microwave directional communication. Higher base frequencies would allow significantly higher bandwidths and data volumes. Therefore, various institutions or enterprises have proposed frequency ranges above 300 GHz and corresponding to the THz range. This frequency range extends from 300 GHz to approximately 100 THz (in some definitions only up to approximately 30 THz), and thus has wavelengths from approximately 1 mm to approximately 3 μm, i.e., up to the mid-infrared range of the spectrum.
[0006] However, other applications can also be considered in addition to telecommunications. Thus, non-contact scanning can also be performed using THz radiation, since electromagnetic radiation in this range can also penetrate especially clothing and thus make the objects beneath visible. This type of application is known as body scanning and is also particularly used at airports, where only detectors sensitive to radiation in this range are used. Similar uses are in raw material inspection, since many raw materials react in a unique way to THz radiation, or in biological or medical research.
[0007] In addition, the challenge for these applications lies in generating preferably narrowband radiation in this range in particular. Systems with lower output power can even achieve using normal laser components for higher power, and the light of the laser components is processed in a suitable way. For example, it can be achieved that the light of two lasers is combined and amplified via a doped erbium fiber connection. However, this structure is relatively large and thus limits the output power.
[0008] Therefore, there is a need for other solutions with which a greater output power can be achieved. Summary of the Invention
[0009] The content of the independent claim takes this requirement into account. Improvements and design methods of the proposed principle are given in the dependent claims.
[0010] The present invention proposes to apply a special new laser device for generating THz radiation, and this laser device is combined with other measures. Here, the laser component to be used is characterized in that a 2D grating structure is applied, whereby light is scattered linearly in the plane and orthogonally outside the plane. However, the orthogonal surface emission, similar to that of a VCSEL, provides several performance advantages for the laser outside the plane, because the output power can be scaled with the emission surface of the device in the case of suitable heat dissipation.
[0011] Emission outside the plane can be achieved and stabilized by a 2D grating structure (such as a photonic crystal), which also affects the feedback. By appropriately selecting the structural elements of the grating structure and its form and arrangement, the laser device can be excited for multimode emission. Here, the threshold for multimode emission can be adjusted by the grating structure, so that it can be ensured that at least two modes to be used start to oscillate. The frequency or wavelength interval can be automatically adjusted by the material of the laser arrangement. Two laser modes can be input into a mixer structure, which in turn generates a differential signal and thus provides the desired radiation. By appropriately selecting the modes to be oscillated, the wavelength or frequency of the differential signal is set in the THz range by means of the design of the laser device and the grating structure.
[0012] In this way, an oscillator is obtained that, on the one hand, stably provides a defined frequency in the THz range and, on the other hand, supplies a high output power in the milliwatt (m-Watt) range or even in the watt range. Here, the necessary area for such an implementation is significantly smaller than that for conventional solutions. The output signal can be amplitude-modulated by matching the current or changing the mixer structure.
[0013] In some aspects, the mixer structure can also be used as an antenna at the same time. In some other aspects, a separate antenna structure is provided, which is designed to emit radiation in a defined frequency range. In some aspects, the antenna structure is coupled to the mixer structure or the material of the mixer structure so that the radiation is guided to the antenna in the mixer structure. For this, a suitable waveguide structure can be provided in particular.
[0014] In some aspects, the oscillator component, especially in the form of a THz oscillator, includes an active laser layer structure based on a semiconductor material. The laser layer structure is implemented to emit laser of at least one wavelength, and the main radiation direction thereof is substantially perpendicular to the main radiation surface of the layer structure.
[0015] Connected effectively to the active laser layer structure is a grating structure, in particular a two-dimensional grating structure. In this case, a two-dimensional grating structure is understood as a structure whose elements are essentially located in a plane spanned by two mutually orthogonally extending spatial directions. Thereby this plane and the grating structure are arranged substantially parallel to the main surface. The grating structure interacts with the laser layer structure for exciting the active layer in the laser layer structure during operation to form two laser modes of different frequencies.
[0016] In other words, the laser layer structure generates two laser modes with slightly different frequencies under the interaction with the grating structure. The two signals generated in this way are relatively narrowband and are polarized in the same direction in some aspects. According to the proposed principle, a mixer structure arranged in the radiation direction is also provided, and this mixer structure is designed to form a differential signal from the two laser modes.
[0017] The differential signal forms the THz radiation according to the present invention and the output signal provided by the oscillator assembly according to the present invention.
[0018] Some aspects are devoted to the arrangement of different elements, namely the arrangement of the grating structure and the laser layer structure with respect to each other. In some aspects, the grating structure is made of a conductive material, so that the grating structure is also used for current conduction at the active layer of the laser layer structure. Here, it can be provided at least in some aspects that the material of the grating structure is different from the semiconductor material. This is suitable for using the differences in various refractive indices in addition to forms, calibrations and other parameters.
[0019] In some aspects, the grating structure interacting with the active laser layer structure is arranged on the side facing away from the main radiation surface. However, in particular, the grating structure in the form of a photon structure interacts with the active layer, so that only the laser is excited and scattered perpendicular to the plane and thus coupled out, and this laser follows the conditions of the band structure generated by the photon structure. In addition, the arrangement of the photon structure "under" the active layer has the advantage that the light energy output from the laser layer structure is separated by the mode by the photon structure, so that the two aspects can be optimized separately. Alternatively, the grating structure interacting with the active laser layer structure forms at least a part of the main radiation surface.
[0020] In both cases, in some embodiments, it can be provided that the grating structure interacting with the active laser layer structure is arranged between the active layer of the laser layer structure and the semiconductor layer for transporting carriers. In other words, the laser layer structure and the grating structure are integrated in a common body or implemented as a common body. In order to improve the interaction between the active layer of the laser layer structure and the grating structure, in some aspects the spacing can be made as small as possible and in the range below 1 μm. In order to ensure current transport, the grating structure is implemented as having a conductive material in these cases.
[0021] In some aspects, the active laser layer structure has a quantum well structure or a multiple quantum well structure. The quantum well structure or the multiple quantum well structure is spatially separated from a grating structure that interacts with the laser layer structure or the active layer (i.e., the quantum well or the multiple quantum well structure), and is even separated by a barrier layer that is conductive but prevents the diffusion of impurity atoms, especially doped atoms. The barrier layer is arranged adjacent to the quantum well structure or the multiple quantum well structure.
[0022] Some aspects are directed to the form and design of the grating structure. Thus, the grating structure can have a quantized symmetry, i.e., rotational symmetry or translational symmetry, which is not continuous but only has defined values. In the case of rotational symmetry, the rotational symmetry is achieved, for example, by means of a structural element whose rotational symmetry is restricted to discrete values, such as limited to values of 30°, 45°, 60°, 90°, 180°, and 360°. In translational symmetry, it can be that the periodicity does not repeat in the spatial direction after each structure, but perhaps only after every two or other values. In this case, the grating structure can also have a superlattice, so that the structure can form more symmetries.
[0023] In some other aspects, the grating structure includes a first periodically repeating structural element and a second periodically repeating structural element. The two structural elements can be independent of each other, and the periodicities can also be different. Thus, it can be achieved that the periodicity can not only be in the form of ABABAB... (where A and B correspond to the respective structural elements), but also other periodicities, such as ABBABBABBA... or ABABAABBAABABAABBAABA.... Similarly, other structural elements with additional periodicities can be considered, so that a superlattice can also be formed. For the structural elements, the form, size, and design can be different. For example, the structural element can be designed in the form of a half pyramid, and others in the form of a full pyramid or other forms. Similarly, an alternating structure can be achieved, which, for example, appears as a triangle, a quadrilateral, or a general polygon in a top view. Another structural element is cylindrical, which can be shaped as an ellipse or a circle in a top view.
[0024] In some aspects, it can be achieved that the structural element has a first periodicity in a first spatial direction and a second periodicity in a second spatial direction that is independent thereof. Here, the first periodicity and the second periodicity are different from each other. The different periodicities in various spatial directions can also be used for different structural elements.
[0025] Thus, on the one hand, the grating can have structural elements of different shapes or designs, and the structural elements can additionally have different periodicities in various spatial directions. Similarly, the grating can include structural elements, and the desired dual-mode can be made to work through the form of the structural elements but with a unified periodicity in two spatial directions. Similarly, with the desired design, combinations of the various parameters from materials, form, size, spatial direction, periodicity, and symmetry can also be achieved.
[0026] In other views, the oscillator assembly can also include an optical element, which is arranged between the main radiation surface and the mixer structure. The optical element is designed to deflect the light emitted from the active laser layer structure along the main radiation direction onto the mixer structure. The optical element can be part of the active laser layer structure, i.e., embedded in its material or arranged on the main radiation surface. In some aspects, the optical element is integrated such that the optical element forms the main radiation surface of the active laser layer structure.
[0027] In another design, the mixer structure has an absorption element arranged downstream in the main radiation direction, and the absorption element is opaque to two laser modes of different frequencies. The mixer structure can have surface active elements. In the low-frequency range, the mixer structure is formed by a nonlinear element, such as a diode. A nonlinear element made of or having such a semiconductor material is also required for generating radiation in the THz range. In addition, it can be based on Ga (gallium), such as GaAs (gallium arsenide).
[0028] In contrast, the absorption element includes a bandgap, which causes the absorption of light of the two laser modes. A suitable material for this is Si (silicon), which is opaque to light in the wavelength range of 900 nm to 1000 nm in the near-infrared and mid-infrared, but it allows the generated differential signal to pass through. The absorption element should have a semiconductor material different from that of the mixer structure.
[0029] In some aspects, the mixer structure is implemented to emit the differential signal directionally, especially along one spatial direction or two opposite spatial directions. In some embodiments, the wavelengths of the two laser modes are in the infrared part of the spectrum, especially exceeding 750 nm, especially exceeding 900 nm, and still especially exceeding 950 nm. As a result, the wavelength of the differential signal is in the range of 1 mm to 3 μm, especially in the range of 1 mm to 0.1 mm.
[0030] Another aspect relates to a method for operating an oscillator assembly according to the proposed principle. Here, the current for generating the laser for the two laser modes is modulated. In this way, the amplitude modulation of the generated THz radiation can be affected. However, at least what can be achieved in this way is to adjust the output power within a certain range and thus match the desired application.
[0031] The mixer structure can also change its mixing efficiency in the same way or in other ways, and thus can also change the amplitude of the differential signal here. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Additional aspects and embodiments in accordance with the proposed principles are disclosed by reference to various embodiments and examples described in conjunction with the accompanying drawings.
[0033] Figure 1 A first embodiment of a PCSEL-based THz oscillator in accordance with some aspects of the proposed principles is shown;
[0034] Figure 2 A second embodiment of a PCSEL-based THz oscillator in accordance with some aspects of the proposed principles is shown;
[0035] Figure 3 A third embodiment of a PCSEL-based THz oscillator in accordance with some aspects of the proposed principles is shown;
[0036] Figure 4 is a frequency plot showing the frequency of a differential signal from a dual mode in accordance with some aspects of the proposed principles;
[0037] Figure 5 is an embodiment of a laser layer structure for a PCSEL-based THz oscillator in accordance with some aspects of the proposed principles;
[0038] Figure 6 A through 6C are top views showing how various grating structures can be used in a PCSEL for a THz oscillator in accordance with some aspects of the proposed principles. DETAILED DESCRIPTION
[0039] The following embodiments and examples illustrate various aspects and combinations thereof in accordance with the proposed principles. The embodiments and examples are not always to scale. Similarly, different elements can be shown enlarged or reduced to highlight a single aspect. Of course, the features of the various aspects and the embodiments and examples shown can be readily combined with each other without departing from the principles of the present invention. The various aspects have regular structures or forms. It should be noted that in practice, minor deviations from the ideal form can occur, but do not violate the idea of the present invention.
[0040] In addition, the respective figures, features, and viewpoints are not necessarily shown in correct dimensions, and in principle, the ratios between the respective elements do not have to be correct either. Each aspect and feature is emphasized, in which it is shown enlarged. However, concepts such as "above", "on top of", "below", "beneath", "larger", "smaller", etc. are correctly shown with respect to the elements in the figures. Thus, it is possible to deduce the relationships between the elements based on the illustration.
[0041] Figure 1 The schematic diagram of the first embodiment of a THz oscillator according to the proposed principle is shown. The THz oscillator is mounted in the housing 3, enabling a space-saving design solution. Although the oscillator shown here consists of multiple independent components, it is possible to integrate the components into a common body, such as a semiconductor body. As will be further explained, this particularly includes the integration of the laser layer structure and the grating structure, as well as additional integration with optical elements or even with the mixer structure 30 that is also necessary.
[0042] According to Figure 1 The oscillator includes a laser layer structure 10 based on a semiconductor material in its housing 3. The laser layer structure 10 is configured as a so-called PCSEL, and the grating structure is integrated with the active laser material in a common semiconductor body. The term PCSEL stands for photonic crystal surface emitting laser, i.e., a laser for surface emission having a photonic crystal structure.
[0043] The PCSEL element uses a two-dimensional grating structure that causes the light generated in the active layer to scatter in a unique and adjustable manner. In particular, the scattering is achieved linearly and orthogonally in the plane, where orthogonal scattering is used because it can be easily integrated and further processed. Emission outside the plane can be achieved and stabilized by a 2G grating structure (photonic crystal), thereby generating feedback. Through a special design solution of the grating structure, according to the proposed principle, it is achieved that the active layer of the laser layer structure oscillates not only in one mode but in two different modes, but it shows energy-adjacent usage thresholds according to the underlying grating structure. In addition, the usage threshold is particularly given by the FSR (free spectral range), which, on the other hand, depends on the virtual band structure and the characteristic values of the underlying grating structure.
[0044] As shown, the grating structure only has a broken rotational symmetry (i.e., has a rotational symmetry with only a few values, such as 180° or 360°), which, for example, according to the form of the rotational symmetry, results in a band structure with a low usage threshold, and thus results in multiple lasing modes during laser operation. Due to the scalability of the grating structure, it can be realized on a large laser layer structure with sufficient heat dissipation, and thus high output power can be achieved.
[0045] The feedback of the grating structure in such a combined laser layer structure is two-dimensional in the plane, which enables the realization of a coherently coupled array. In this way, the light can be focused more simply, and thus a very high light density of the dual mode can be achieved.
[0046] In the current embodiment, the laser layer structure 10 is embedded in the semiconductor body with its active region 103. There is also a grating structure 200 in the form of a photonic crystal on the surface of the laser layer structure, so that the emission region of the laser layer structure 10 is formed by the photonic structure. The emitted light in the two modes is realized to be substantially perpendicular to the emission surface. In addition, since the grating structure 200 provides high collimation. There is a lens 11 connected to the housing 3 in the optical path, and the lens deflects the output laser onto the mixer structure 30.
[0047] The mixer structure 30 is a non-linear element, and the mixer structure interacts alternately with the light of the two optical modes. A differential signal, i.e., radiation with a difference frequency, is generated from the frequencies of the two modes through the characteristics of the element. The mixer structure 30 can be an optical mixer, for example, in the form of a PLC, a photodiode, a photoconductor or the like. For this, there is an optical input line, such as an optical fiber, which accesses the light from the laser layer structure and forwards it to the mixer structure 30. On the other hand, the mixer structure is designed such that the output differential signal has a preferred direction, for example, along the radiation direction, because this simplifies further processing. The mixing frequency in the THz range is emitted via another antenna in an alternative embodiment, and the other antenna is coupled to the mixer structure 30.
[0048] In this case, Figure 4 A frequency diagram showing two modes adjacent to each other in the frequency domain with frequencies f1 and f2 is shown. The spacing can be adjusted by the grating structure, and it should be ensured that the usage thresholds for lasing are also adjacent to each other. Thus, it is achieved that the amplitudes of the two laser modes are approximately the same, which is advantageous for subsequent mixing.
[0049] The optical mixer 30 is a non-linear element. Thus, when light with multiple frequencies is delivered, mixed light, i.e., the difference or sum of the corresponding frequencies, is also obtained. Similarly, frequency doubling can occur at very high intensities. Generally, the frequency difference is obtained: f D = f 2 - f1 , where f 2 is the frequency of the high-energy light. Similarly, the frequencies f 2 + f 1 as well as additional frequencies (f 2 - f 1 ) / 2, 3 / 2*(f 2 - f 1 ) etc. However, these signals can be suppressed by appropriate design or measures of circuit technology.
[0050] In the wavelengths of two laser modes in the infrared part of the spectrum, especially wavelengths exceeding 900 nm and especially exceeding 950 nm, a differential signal is generated in this way, and the wavelength of the differential signal is between 1 mm and 3 μm, especially between 1 mm and 0.1 mm. Subsequently, the corresponding frequencies are from 300 GHz to approximately 30 THz.
[0051] Returning again to the embodiment according to Figure 1 , an absorption element 300 is arranged in the optical path after the mixer structure 30. The absorption element is transparent to the differential signal having a frequency in the THz range. In contrast, the absorption element 300 is opaque to the light generated by the laser layer structure 10. In particular, the element 300 is absorbable for light in the visible and near-infrared spectra in the range exceeding 800 nm. Such a material is, for example, silicon, which must be only a few μm thick. In addition, the absorption element 300 is designed to have sufficient thermal conductivity to ensure the heat transfer of the absorbed light. In addition, the absorption element can also have the characteristics of guiding the generated THz radiation. This allows the mixer structure to be connected to the antenna via the absorption material in order to radiate the generated radiation in a suitable manner.
[0052] The absorption element 300 in the optical path is suitable to prevent the possibly unconverted light of one of the two modes from reaching the observer's eyes or otherwise interacting with objects in the radiation direction. On the other hand, the absorption element 300 is also absorbable. Even a reflective element can be considered, but there is a risk here that the reflected light can return to the laser layer structure and / or the mixer structure and cause destructive interference or other adverse effects there. If these can be excluded, then the reflective element can even provide that the reflective element is arranged downstream of the mixer in the optical path, because the light reflected back in the mixer increases the conversion efficiency.
[0053] Figure 2Shows a second embodiment of a THz oscillator according to the proposed principle. This THz oscillator is also integrated in the housing 3 and has a radiation window on one side, in which a collimating lens 40 for the shown THz radiation is arranged. The collimating lens and the focusing lens 11 are placed on the emitting surface of the laser layer structure 10. The collimating lens and the focusing lens are spaced apart from the mixer structure 30 by a distance d, wherein the collimating lens and the focusing lens are also fixed to the housing 3. This distance is suitable to ensure sufficient thermal decoupling between these two main components.
[0054] The grating structure, i.e., the photonic structure designed to generate dual modes, is arranged on one side of the back-emitting side in the laser layer structure in this embodiment. In other words, the grating structure 200 is no longer in the optical path, but is behind or below the active layer 102 for generating light when viewed from the emitting surface outwards. It is possible to implement that the photonic structure is implemented near the active layer in the laser layer structure 20, i.e., only a few 10 nm or 100 nm away from the active layer. In this way, the grating structure 200 interacts with the active layer 103 and causes the above-mentioned coupling. Similarly, the emitting surface can also be optimized in this way, so that the coupled output of the generated laser can be optimized regardless of the form or structure of the photonic layer 103.
[0055] An absorption element 301 and the already mentioned collimating lens are arranged downstream in the optical path of the mixer structure 30 in the optical path. In this embodiment, the mixer structure 30 is integrated into the semiconductor body, wherein the semiconductor body also forms part of the absorption element 301. For example, the absorption element and the mixer structure 30 are jointly formed of III / V semiconductor materials. Suitable materials are especially InP, (LT)GaAs (at 780 nm), GaN, SiGe, LTG InAlAs / InGaAs (at 1500 nm) or Sb. Additionally, Si is also exactly suitable for the absorption element, because the absorption element has a strong absorption effect on light in the infrared part of the spectrum, yet is transparent to THz radiation. Thus, it is avoided that the light not converted by the mixing element 30 is collimated by the downstream lens 40 or exits the oscillator housing 3.
[0056] In Figure 3 Another miniaturization is carried out in the shown embodiment. In this embodiment, the laser layer structure 10 and the lens arranged on the emitting surface are directly arranged on the 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 avoids feedback into the laser layer structure 10. The grating structure is arranged above the active layer 103 but below the emitting surface with the material of the laser layer structure.
[0057] The mixer structure generates a differential signal from light using two mode inputs, and the differential signal is collimated and emitted by the lens 40. In this embodiment, the elements 301', 30, and 40 are directly disposed on the material of the laser layer structure 10. However, this material dissipates heat well to the heat sink 3' connected to the laser layer structure.
[0058] Figure 5 is an embodiment of a surface-emitting laser in a semiconductor material, in which a grating structure is also integrated in the material. Here, the grating structure must be designed to be conductive to ensure current transport in the active layer. The laser layer structure 10 in the current embodiment includes a bottom p-contact 100 made of a conductive material, such as metal. The contact 100 can be connected to the housing or itself forms part of the housing (not shown here).
[0059] Subsequently, the layer structure 10 includes a similarly p-doped contact layer 101, made of doped GaAs material here. The doped GaAs disperses the current applied via the contact 100 over the surface. Then there is a separation layer (coating) 102, on which the grating structure 200 is provided. The grating structure is constructed from the same material system as the layers already described, i.e., GaAs or AlGaAs in this case, and this material system can already be doped to have as small a surface resistance as possible. The grating structure is now separated from the active layer 103 by an undoped barrier layer 102'. The undoped barrier layer is even conductive, but it prevents dopant atoms from diffusing into or out of the active layer. Thus, degradation of the active layer 103 over time is avoided or reduced.
[0060] The active layer 103 includes a quantum well or a multiple quantum well structure. For example, GaAs / AlGaAs layers can be applied for this, where the GaAs / AlGaAs layers are also doped and thus continue to form barrier layers and well layers. Alternatively, other ternary material systems can also be applied to form such a multiple quantum well structure. For example, Al in the material AlGaAs can be partially or completely replaced by In. Subsequently, it is appropriate because the wavelength of the emitted light depends essentially on the ratio on the multiple quantum well structure. By applying different concentrations of In and Al, the regulation (not only the wavelength but also the width) can be used to generate the wavelength of the light, so that two modes shifted by a certain frequency value are excited interactively with the photon structure 200, and the difference gives the desired THz radiation.
[0061] An n-type doped injection layer 104 is provided on the multiple quantum well structure 103, for example made of n-type doped AlGaAs, and another layer 105 is provided on the injection layer, and this other layer is also composed of a semiconductor material. It is feasible to reverse the manufacturing sequence, so that the layer 105 forms a doped growth substrate, and the subsequent layers and especially the grating structure 200 are epitaxially deposited on the growth substrate.
[0062] The surface of the layer 105 also simultaneously forms the main emission surface of the laser layer structure 10 for the laser 107. In addition, for current delivery, metal contacts 106 in the form of windows are arranged on the surface of the layer 105. The contact 106 surrounds the emission region.
[0063] Therefore, in this embodiment, the photon structure is arranged under the active layer, that is, the emission region is arranged on the side facing away from the surface. However, the photon structure can also be arranged between the emission region and the active layer. It is also possible to arrange the photon structure on the surface of the layer 105. For this, after manufacturing the respective layers, the surface of the layer 105 is exposed, and the photon layer 200 is generated as a grating structure on this layer according to the proposed principle. The grating structure can not only increase, that is, by generating a structure by means of a structured deposition process, but also remove material, that is, by etching the structure. In practice, a combination of etching and deposition processes can also be realized.
[0064] Figure 6 A to 6C show top views of various embodiments of the photon structure 200, for example how the photon structure can be used in a surface-emitting laser to form a dual mode. The structures each have one or more structural elements 210 to 214, and these structures can also be arranged periodically. The dimensions of these structures are in the range of several μm, for example between 10 μm and 35 μm. It is possible here that the individual structural elements in the grating structure have different periodicities, as shown for example in Figure 6 the structural elements 213 and 214 in C. The adjacent elements 213 have a greater spacing from each other than the adjacent elements 214.
[0065] In addition, the symmetry in the corresponding spatial directions can also be different, that is, for example, there is translational symmetry in the x direction, which is different from the translational symmetry in the y direction. Here, the corresponding periodicity can be complex and matched to the corresponding application.
[0066] In addition, for example, in Figure 6 the structural elements in A and 6C are implemented differently. Here, the structure of each element is implemented such that there is no continuous rotational symmetry, but the rotational symmetry that currently exists can only take some discrete values. Therefore, for example Figure 6A shows a photonic structure 200 having two structural elements 210 and 211. While the element 211 is rotationally symmetric as a ring-shaped or cylindrical structure, this is violated for the element 211, i.e., it only rotates 180° and 360° around the central axis to reach the same element again. The element 211 shows an oval shape in a top view.
[0067] If now the two elements 210 and 211 are understood together as a unit, then the rotational symmetry is further reduced. The original elements are obtained again only when rotated 360°. The same applies to Figure 6 the embodiment of B. Here, the structural element 212 is constructed as a semi-pyramid, so that it forms an isosceles triangle in a top view. Rotational symmetry is also violated in this case, i.e., the structural element only images itself when rotated 360°.
[0068] The embodiments shown here can be combined in various ways. The basic principle of forming THz radiation by mixing the light generated by a PCSEL as a dual-mode laser is not affected. In addition, the THz oscillator according to the proposed principle can be further developed into amplitude modulation. For this, the laser current can be made to vary. Thereby, the amplitude of the generated light is changed, and thus amplitude modulation of the generated THz radiation is achieved.
[0069] Alternatively, it can also be achieved that the mixer structure changes in its conversion rate, i.e., its efficiency regarding the conversion of the differential signal and the formation of the differential signal, so that the intensity of the differential signal can be changed and thus the amplitude of the THz radiation can be changed. However, the first solution is preferred due to a higher conversion rate, because, unlike the second solution, it does not modulate the efficiency of the conversion into THz radiation itself, but only the output power of the laser.
[0070] The proposed solution forms a THz oscillator that can be scaled particularly simply in terms of its size and output power. The proposed solution can be implemented in a space-saving manner. With good heat dissipation, a large output power in the range from mW to several W can be achieved.
[0071] List of reference numerals
[0072] 3, 3’ housing
[0073] 10 laser layer structure
[0074] 11 lens
[0075] 30 mixer structure
[0076] 40 lens
[0077] 100 contact
[0078] 101 Contact layer
[0079] 102 Separation layer
[0080] 102’ Barrier layer
[0081] 103 Active layer
[0082] 104 Injection layer
[0083] 105 Layer
[0084] 106 Contact
[0085] 107 Laser
[0086] 200 Grating structure
[0087] 210 Structural element
[0088] 211 Structural element
[0089] 212 Structural element
[0090] 213 Structural element
[0091] 301 Absorbing element.
Claims
1. An oscillator assembly, in particular a THz oscillator, the oscillator assembly comprises: - An active laser layer structure (10) based on a semiconductor material, the semiconductor material being used to emit laser light of at least one wavelength, the main radiation direction of the active laser layer structure being substantially perpendicular to the main radiation surface; - A grating structure (200) interacting with the active laser layer structure (10), the grating structure being in particular a 2D grating structure, the grating structure being arranged substantially parallel to the main surface, the grating structure being designed to excite the active laser layer structure (10) to form two laser modes of different frequencies (f1, f2); - A mixer structure (30) arranged in the radiation direction, the mixer structure being designed to form a differential signal from the two laser modes, the differential signal having a frequency resulting from the difference between the two laser modes; - An absorption element (301) arranged downstream of the mixer structure (30) when observed in the main radiation direction, the absorption element especially comprising silicon, the absorption element being substantially opaque to the two laser modes of different frequencies.
2. The oscillator assembly according to claim 1, wherein, the grating structure (200) interacting with the active laser layer structure (10) is arranged on a side facing away from the main radiation surface; or wherein the grating structure (200) interacting with the active laser layer structure (10) forms at least a part of the main radiation surface.
3. The oscillator assembly according to any one of claims 1 or 2, wherein, the grating structure (200) interacting with the active laser layer structure (10) is arranged between the active layer (103) of the laser layer structure and the semiconductor layer for transporting charge carriers.
4. The oscillator assembly according to any one of the preceding claims, wherein, 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 the multiple quantum well structure and separated by a conductive but diffusion-blocking barrier layer that prevents impurity atoms, especially doping atoms, from diffusing.
5. The oscillator assembly according to any one of the preceding claims, wherein, the grating structure (200) comprises periodically repeating structural elements, the rotational symmetry of the structural elements being particularly limited to one of the values 30°, 45°, 60°, 90°, 180° and 360°.
6. The oscillator assembly according to any 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), the second periodically repeating structural element being different from the first structural element in terms of size and / or shape.
7. The oscillator assembly according to any one of claims 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. The oscillator assembly according to any one of the preceding claims, further comprises: - an optical element (11) arranged between the main radiation surface and the mixer structure (30) and designed to deflect the light emitted from the active laser layer structure along the main radiation direction onto the mixer structure.
9. The oscillator assembly according to any one of the preceding claims, wherein, the absorption element (301) has a semiconductor material different from that of the mixer structure (30), in particular silicon.
10. The oscillator assembly according to any one of the preceding claims, wherein, the mixer structure (30) is configured to emit the differential signal directionally, in particular along one spatial direction or two opposite spatial directions.
11. The oscillator assembly according to any one of the preceding claims, wherein, the wavelengths of the two laser modes are in the infrared part of the spectrum, in particular above 750 nm, in particular above 900 nm, and still in particular above 950 nm; and / or wherein, the wavelength of the differential signal is in the range of 1 mm to 3 μm, in particular in the range of 1 mm to 0.1 mm.
12. The oscillator assembly according to any one of the preceding claims, further comprising an antenna structure coupled to the mixer structure for forwarding and emitting the generated radiation.
13. A method for operating an oscillator assembly according to any one of the preceding claims, wherein, modulating a current for generating the laser of the two laser modes; or wherein, changing the mixer structure in terms of the mixing efficiency of the mixer structure for generating an amplitude-modulated differential signal.