Vertical-emitting semiconductor laser device for optical data transmission with an output coupling facet featuring a mode-selective macrostructure and a polarization-selective microstructure

Abstract

The present invention relates to a vertical-emitting semiconductor laser device (1), in particular a VCSEL, comprising an upper Bragg mirror (2) and a lower Bragg mirror (3), wherein an active zone (4) for generating laser radiation (5) is arranged between the upper Bragg mirror (2) and the lower Bragg mirror (3); wherein the vertical-emitting semiconductor laser device (1) has an upper output facet (20) for the laser radiation (5), the upper output facet (20) having both a mode-selective macrostructure (21) and a polarization-selective microstructure (22). The present invention further relates to the use of a surface relief on an output facet of a VCSEL, a communication system, and a method for fabricating a corresponding vertical-emitting semiconductor laser device.

Description

The present invention relates to the field of optical communication technology, in particular a vertical-cavity surface-emitting laser, in particular a VCSEL for short, for optical data transmission.VCSELs for optical data transmission are fundamentally known from the prior art. VCSELs for optical data transmission are also referred to as datacom VCSELs. An advantage of VCSELs is that they can offer the highest performance in data transmission with simultaneously low power consumption. In a VCSEL or a VCSEL (vertical-cavity surface-emitting laser) laser diode, the light is emitted perpendicularly to the plane of the semiconductor chip, in contrast to the edge-emitting laser diode, in which the light exits at one or two edges of the chip.U.S. Pat. No. 10,742,000 B2 relates to a VCSEL with an elliptical aperture with reduced RIN (stochastic or relative intensity noise). In summary, the VCSEL described therein is intended to include: an elliptical oxide aperture in an oxidized region located between an active region and an emission surface, the elliptical aperture having a short radius and a long radius with a radius ratio (short radius) / (long radius) of between 0.6 and 0.8, the VCSEL having a relative intensity noise (RIN) of less than -140 dB / Hz. The VCSEL may include an elliptical emission aperture having the same dimensions as the elliptical oxide aperture.In order to reduce the RIN, it is therefore proposed in the prior art to provide an elliptical oxide aperture or oxide diaphragm within the cavity of the laser.Against this background, it is an object of the present invention to provide a further improved or alternative vertical-emitting semiconductor laser component, in particular VCSEL, for optical data transmission. The inventors have recognized that it would be particularly desirable to provide a vertical-emitting semiconductor laser component that enables high speeds in optical data transmission over a wide range of ambient conditions, in particular over a wide temperature range. It would furthermore be desirable to provide a vertical-emitting semiconductor laser component which can be produced cost-effectively or with simplified process steps and / or with high yield (high yield). Further, it would be desirable to improve a lifetime of low RIN datacom VCSELs.The claimed subject matter is defined in the independent claims. Advantageous further developments are described in the dependent claims.According to a first aspect of the present invention, it is therefore proposed to provide a vertical-emitting semiconductor laser component, in particular a VCSEL, having an upper Bragg mirror and a lower Bragg mirror, wherein an active zone for generating laser radiation is arranged between the upper Bragg mirror and the lower Bragg mirror; wherein the vertical-emitting semiconductor laser component has an upper coupling-out facet for the laser radiation, wherein the upper coupling-out facet has both a mode-selective microstructure and a polarization-selective microstructure.According to a further aspect of the present invention, the use of a surface relief on an output coupling facet of a VCSEL, wherein the surface relief of the output coupling facet has a mode-selective microstructure and a polarization-selective microstructure, in a communication system for optical data transmission is proposed.According to a further aspect of the present invention, a vertical-emitting semiconductor laser component, in particular a VCSEL, is proposed, having an upper Bragg mirror and a lower Bragg mirror, wherein an active zone for generating laser radiation is arranged between the upper Bragg mirror and the lower Bragg mirror; wherein the vertical-emitting semiconductor laser component has an upper coupling-out facet for the laser radiation, wherein the upper coupling-out facet has a polarization-selective microstructure and the semiconductor laser component is configured to drop in its light intensity not more than 3 dB compared to an excitation at 1GHz when high-frequency excitation is up to a frequency of 25GHz, in particular when high-frequency excitation is at a frequency of 25GHz. Optionally, the upper coupling-out facet can have a mode-selective microstructure. It is understood that the further features and configurations described in connection with the first aspect within the scope of this disclosure can also be combined with this aspect.According to a further aspect of the present invention, a communication system is proposed having an input terminal for receiving data, a modulator and a vertically emitting semiconductor laser component, as mentioned above and / or described below.According to a further aspect of the present invention, a method for producing a vertically emitting semiconductor laser component is furthermore proposed, the method having the following steps: providing a semiconductor substrate; depositing a layer sequence for a lower Bragg mirror on the semiconductor substrate; depositing an active layer having an active zone for generating laser radiation on the lower Bragg mirror; depositing a layer sequence for an upper Bragg mirror on the active layer; providing an upper coupling-out facet for the laser radiation on the upper Bragg mirror, the upper coupling-out facet having both a mode-selective microstructure and a polarization-selective microstructure.According to a further aspect of the present invention, a method for producing a vertical-emitting semiconductor laser component is furthermore proposed, the method having the following steps: providing a semiconductor substrate; depositing a layer sequence for a lower Bragg mirror on the semiconductor substrate; depositing an active layer having an active zone for generating laser radiation on the lower Bragg mirror; depositing a layer sequence for an upper Bragg mirror on the active layer; providing an upper coupling-out facet for the laser radiation on the upper Bragg mirror, wherein the upper coupling-out facet has a polarization-selective microstructure and the semiconductor laser component is configured to fall in its light intensity compared to an excitation at 1GHz in the case of high-frequency excitation up to a frequency of 25GHz, in particular in the case of high-frequency excitation at a frequency of 25GHz.It goes without saying that further layers can optionally be provided, which can also be arranged between the aforementioned layers. For example, one or more optional current aperture(s) between the active layer and the upper and / or lower Bragg mirror.The inventors have recognized that VCSELs in datacom applications are often operated at relatively high currents with high-frequency signal modulation. The required output power is provided in conventional VCSELs, especially in multimodal operation. This can lead to competition and degeneracy of the many modes, which can cause a high level of noise (RIN). The inventors have recognized that even with a reduced number of modes, however, the same amount of noise may likewise result from operation with unstable polarization. This usually results in so-called "flips" of the polarization direction. In conventional approaches, there is also the problem that they sometimes only make it possible to improve the RIN for a narrow range of operating parameters, but not over a wide range of operating parameters and in particular not over a wide temperature range. Furthermore, solutions, such as the VCSEL described in the initially mentioned U.S. Pat. No. 10,742,000 B2 with the elliptical current aperture arranged in the active layer within the layer sequence of the semiconductor, can be susceptible to process fluctuations in the semiconductor production. Furthermore, the current conduction within the semiconductor for the specific application of datacom VCSELs can vary over the desired broad current and temperature range.According to one aspect of the present invention, it is therefore proposed to provide an optical solution having a specially configured upper coupling-out facet of the vertically emitting semiconductor laser component, wherein the upper coupling-out facet has both a mode-selective microstructure and a polarization-selective microstructure. In one aspect, the invention aims to reduce the number of competing modes and simultaneously stabilize the polarization. This is achieved by using a surface structure, in particular a surface relief, of the coupling-out facet of the VCSEL, which has a spatial microstructure and a polarization-selective structure. In the simplest case, a datacom VCSEL with an elliptically bordered relief structure with a polarization grating can be provided.Coexistence of multiple modes in a VCSEL is a source of noise. A lateral microstructure with dimensions of typical VCSEL modes can promote or impede individual modes and thus reduce the number of modes and noise. For example, very small (a few microns) macro structures can be used to force operation on a fundamental mode that is smaller in diameter than higher order modes. Similarly, elliptical cross-sections promote modes of greater extension along the long half axis.The proposed special configuration of the upper coupling-out facet, wherein the upper coupling-out facet has both a mode-selective microstructure and a polarization-selective microstructure, has the advantage that an improvement in the RIN can be achieved using purely optical means. The inventors have recognized that this solution can enable in particular an advantageous noise behavior over a large temperature range. The VCSEL can also be prevented from operating in an unstable polarization range under certain operating conditions over a large current range and, at the same time, operation in desired laser modes can be ensured, in particular also at the high modulation frequencies required for datacom VCSELs.A structure on the upper side of the output coupling mirror has a purely optical function, unlike the current aperture described in the aforementioned U.S. Pat. No. 10,742,000 B2. The upper side of the upper Bragg mirror or decoupling mirror can be referred to as a decoupling facet. The coupling-out-side DBR of the VCSEL usually terminates in a bulge of the standing wave field towards air or a low-refractive-index medium. If, for example, the layer thickness of the DBR is increased by one quarter of the wavelength in the medium, this significantly reduces the reflectivity of the DBR and laser activity is made more difficult. However, if the additional layer thickness is partially removed again, the full reflectivity is again obtained in the region, for example, etched back. This promotes modes which have high intensity in these regions. A structure on the top side is easily accessible and therefore practical to implement. It is understood, however, that one or more layers of the upper Bragg mirror can also be considered part of the upper coupling-out facet.The terms microstructure and microstructure describe the relative relationship, wherein the mode-selective microstructure has a larger structure size than the polarization-selective microstructure. Alternatively, a first mode-selective structure of the coupling-out facet and a second polarization-selective structure of the coupling-out facet can also be referred to. The polarization-selective microstructure of the coupling-out facet is a structure which is configured to promote a limited number of laser modes, in particular wherein the mode-selective microstructure is configured to promote a single laser mode. The polarization-selective microstructure is a structure which is configured to promote polarization of the laser radiation. For example, the polarization-selective microstructure can be embodied as a grating or else as an optical meta-structure.According to one aspect of the present invention, wherein the upper coupling-out facet has a polarization-selective microstructure and the semiconductor laser component can be configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1GHz in the case of high-frequency excitation up to a frequency of 25GHz. One advantage can be that, thanks to the small drop in the light intensity in the case of a high-frequency excitation at 25 GHz compared to an excitation at 1 GHz, amplifier electronics mounted upstream can have a simpler design; in particular, a modulation-frequency-selective amplification adaptation can be omitted or at least simplified.All features of the subject matter described herein and of the claimed subject matter are both isolated and usable in combination with one another, compatible with one another and provided and usable for development with one another, provided that no logical contradiction arises, and are disclosed in this respect herewith. In the following, any reference to an article or feature (including the indefinite articles "a" and "an" and the certain articles "the", "the"), two articles or two features, or any other number of articles or features, unless expressly stated otherwise or a logical contradiction arises, is to be understood such that the presence of further such articles and features is not excluded from the invention but is also encompassed by the invention. The reference signs in the claims are not to be understood as limiting, but merely serve to better readability the claims.In one configuration, the coupling-out facet having the mode-selective microstructure and the polarization-selective microstructure can be a (purely) optical structure which is arranged on a top side of the upper Bragg mirror. An advantage of this embodiment can be that a structure on the upper side is easily accessible and can therefore be realized in practice. A further advantage can be that different mode profiles and / or presentations can be easily adapted to customer requirements, since only the output facet has to be adapted, but not the entire layer structure of the semiconductor. An existing layer structure of the semiconductor with an upper Bragg mirror, a lower Bragg mirror and the active region therebetween can thus be reused for different application cases. This allows simple and cost-effective production. The upper side of the upper Bragg mirror can be considered to be the side which is arranged in the beam direction of the laser beam in the direction in which the laser radiation is coupled out of the semiconductor laser component.The coupling-out facet can be designed as an (optical) relief structure. The mode-selective microstructure of the coupling-out facet can have a first region having a first layer thickness. The mode-selective microstructure of the coupling-out facet can have a second region having a second layer thickness, in particular wherein the second layer thickness is smaller than the first layer thickness. A difference in a layer thickness or an additional layer thickness and etching back can be effected in a semiconductor material of the VCSEL, i.e. for example in the uppermost layer of GaAs. Alternatively or additionally, a dielectric layer can be applied and subsequently structured. Alternatively or additionally, a dielectric layer stack can also be applied, in which a layer is selectively etched. The structuring can be effected lithographically, for example by e-beam lithography, UV lithography or else nanoimprint lithography.The mode selective microstructure may be configured to promote a limited number of laser modes. In particular, the mode-selective microstructure can be configured to promote a single laser mode. In particular, the microstructure can be configured to perform an adaptation of the lateral mode structure. An advantage of this configuration can be that the emission behavior of the semiconductor laser component can be adapted to a desired application. It is understood that a promoted mode need not necessarily be a fundamental mode used in single mode VCSELs, but may be any higher order mode.The mode-selective microstructure can have a first region with a first reflectivity and a second region with a second reflectivity which differs from the first reflectivity. The coupling-out facet can be provided accordingly with a tailored reflectivity in order to promote desired modes.The mode-selective microstructure of the coupling-out facet can have a relief with a non-rotationally symmetrical contour. The mode-selective microstructure of the coupling-out facet can have a relief with an oval contour, in particular with an elliptical contour. A corresponding relief structure makes it possible to reduce the number of competing modes and in particular to promote modes whose geometric dimensions match the non-rotationally symmetrical contour, in particular the oval or elliptical relief contour. For example, the relief with the oval contour can have an inner oval region with a smaller layer thickness and an outer region with a larger layer thickness surrounding the latter. This applies to other non-rotationally symmetrical or elliptical contours.In a development, the mode-selective microstructure of the coupling-out facet can have a non-rotationally symmetrical or oval relief with a constriction. In particular, the mode-selective microstructure can have an 8-shaped contour. This is a particularly advantageous example, wherein, thanks to the oval contour with constriction, in particular with an 8-shaped contour, further modes can also be promoted instead of or in addition to the basic mode, but not an uncontrolled high number of modes, but a limited number. The mode profile can thus advantageously be adapted to a desired application.The mode-selective microstructure cannot be formed rotationally symmetrically in a plane parallel to layers of the upper Bragg mirror. The mode selective microstructure may be configured to break a degeneracy of modes. An advantage of this embodiment with a non-rotationally symmetrical macro structure is that a degeneracy of modes can be counteracted. An advantage of this embodiment can be that the emission behavior of the laser can be further stabilized. Undesired jumping between different emission modes can be reduced. The noise behavior can thus be improved.The polarization-selective microstructure can have a grating structure for polarizing the laser light. In other words, a surface grating for polarising the light can thus be arranged on the output facet. However, not alone, but in conjunction with a mode selective microstructure. The inventors have recognized that the mode-selective microstructure and the polarization-sensitive microstructure advantageously interact or can bring about a synergy effect. In particular, this combination has proved to be particularly advantageous for stabilization over a wide temperature range.The polarization-selective microstructure may have a structure size smaller than a laser wavelength of the laser light. For example, a grating structure with a grating spacing or grating period smaller than the laser wavelength can be provided. However, an optical meta-structure with structures smaller than the laser wavelength can also be provided. An advantage of this embodiment can be that, in the case of this selection of structure sizes of the polarization-selective microstructure, losses can be reduced by avoiding diffraction.The mode-selective microstructure and the polarization-selective microstructure can together be formed as an elliptically shaped surface relief having a grating structure enclosed by the surface relief. For example, an elliptical depression of the coupling-out facet can be provided as the optical microstructure, and this depressed region can have a polarization-selective grating structure. It is understood that instead of a depression, an increase or other influencing of the reflection behavior can also be provided. Generally speaking, the upper coupling-out facet can have a microstructure which in turn contains a fine structure. Here, the microstructure defines spatially lateral modes, the fine structure specifies the polarization. An example is an oval or circular structure of e.g. 10 μm diameter with a grating of e.g. 150 nm pitch.The mode-selective microstructure and the polarization-selective microstructure can be formed by an optical meta-structure of the coupling-out facet, in particular wherein the coupling-out facet has an optical meta-structure having a structure with spatially varying phase matching. The meta-structure on the coupling-out facet can substantially correspond to the mode image of a preferred mode. Corresponding optical meta structures can be determined, for example, by numerical simulations.The optical meta-structure may be configured to provide a varying effective refractive index. Alternatively or additionally, the optical meta-structure can have a varying density of constant height turrets and an extension smaller than the wavelength. For example, by means of an elongate shaping of the individual turrets, the polarization can be selected. The provision of an optical meta-structure with varying density but the same height in the emission direction of the laser radiation of the VCSEL can be particularly advantageous, since this can be provided by structuring a layer with a defined height. A layer to be patterned may be provided in the semiconductor manufacturing of a wafer. The structuring can be effected using known methods of semiconductor production. This allows efficient and cost-effective production with high quality. A further advantage of a meta-structure compared to a relief having a hard step or relief edge can be the avoidance of diffraction at the edge of the relief, which can cause losses. A further advantage can be that a more precise adaptation to a desired intensity profile of certain modes and thus an improved selectivity or stability can be achieved.The vertical-emitting semiconductor laser component can have (at least) one current aperture, wherein the current aperture has a larger diameter in a plane orthogonal to a beam direction of the laser beam than a diameter of the mode-selective microstructure of the coupling-out facet having the polarization-selective microstructure. In other words, the diameter, measured in a plane parallel to layers of the upper Bragg mirror, can be orthogonal to the beam direction of the laser beam. By making the current shutter or current apparatus larger than the relief structure or mode-selective microstructure, a current density within the VCSEL can be reduced. The current may be distributed electrically over a larger area within the semiconductor. In this case, the mode selection therefore does not take place or does not take place solely by the current diaphragm. Rather, an optical mode selection takes place through the microstructure of the coupling-out facet in conjunction with the polarization-selective microstructure of the coupling-out facet. An advantage of this configuration can be that the definition of the current aperture, by e.g. an oxide aperture, implantation or buried tunnel diode, can be effected independently of the optical structure of the coupling-out facet described here. It is not necessary for the current aperture to correspond exactly to the optical structure or the mode. The inventors have recognized that lateral transport of the charge carriers, for example in quantum trenches of an active zone, also contributes to amplification by current injection, which takes place offset from the mode by approximately 1 μm or a few μm. This can be used advantageously in that current injection takes place over the full area and over a somewhat larger range than corresponds to the (optical) mode selection. As a result, despite a selected spatially narrow mode, the current is guided in a larger diameter. This lowers the current density and this can result in a significantly increased service life. This can provide a substantial advantage over mode selection with an elliptical current aperture.The vertical-emitting semiconductor laser component can be a VCSEL for optical data transmission. A VCSEL for optical data transmission can also be referred to as a datacom VCSEL. The inventors have recognized that the proposed solution with the specific coupling-out facet, which has both a mode-selective microstructure and a polarization-selective microstructure, is advantageous in particular in the case of VCSELs for optical data transmission. Datacom VCSELs are often operated over a broad temperature range, so that particular requirements are placed here, which do not arise in other applications or in pure research arrangements under laboratory conditions.In one configuration, the vertical-emitting semiconductor laser component has a relative intensity noise (RIN) of less than -80 dB / Hz, in particular of less than -100 dB / Hz, in particular of less than -120 dB / Hz, in particular of less than -140 dB / Hz. This allows particularly high data transmission rates to be made possible in optical communication systems. The values indicated can be a relative intensity noise, RIN; in a frequency range of up to 40 GHz, in particular in a range of between 1 GHz and 40 GHz, in particular in a range of between 2 GHz and 30 GHz, in particular in a range of between 5 GHz and 25 GHz.The vertical-emitting semiconductor laser component can be configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1 GHz in the case of high-frequency excitation up to a frequency of 25 GHz. As a result, the vertical-emitting semiconductor laser component can be used particularly advantageously for optical data transmission. One advantage can be that, thanks to the small drop in the light intensity in the case of a high-frequency excitation at 25 GHz compared to an excitation at 1 GHz, amplifier electronics mounted upstream can have a simpler design; in particular, a modulation-frequency-selective amplification adaptation can be omitted or at least simplified.A particularly advantageous application of the proposed vertical-emitting semiconductor laser component is the use in a communication system for optical data transmission. The communication system or transmitter for an optical communication system may comprise an input terminal for receiving data, a modulator and a vertical emission semiconductor laser device. An input terminal can be understood to mean an interface for receiving data. The received data can be converted by the modulator and modulated, for example, in the form of current modulation or voltage modulation onto the laser light emitted by the vertically emitting semiconductor laser component. The communication system may further comprise a receiver having a detector for detecting the modulated laser light and a demodulator configured to demodulate and convert the detected laser light into data which may be output via an interface for outputting data.The advantages and optional further features described in detail above for the first aspect of the invention apply correspondingly to the further aspects of the invention.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Exemplary embodiments for aspects of the invention are illustrated in the drawings and are explained in more detail in the description which follows. The following are shown: FIG. 1 shows a first schematic illustration of a plan view of an upper coupling-out facet having a mode-selective microstructure and also a polarization-selective microstructure for a vertical-emitting semiconductor laser component; FIG. 2 shows a second schematic illustration of a plan view of an upper coupling-out facet having a mode-selective microstructure and also a polarization-selective microstructure for a vertical-emitting semiconductor laser component; FIG. 3 is a schematic sectional view of a vertical-emission semiconductor laser device; FIG. 4 shows a schematic illustration of a chip having a vertical-emitting semiconductor laser component; FIG. 5 shows a schematic illustration of a communication system; FIG. 6 is a flow chart of a method for manufacturing a vertical-emitting semiconductor laser device.Identical reference numerals used in the figures denote identical or at least identically acting elements. The terms "upper", "lower", "left" and "right" and directional information derived therefrom, such as "upper side", refer to the writing direction / reading direction of the figure designation "FIG." which is associated with a drawing and is printed onto the plane of the drawing under the drawing. Here, the horizontal direction is parallel to the writing direction of "Fig." and the vertical direction is perpendicular to the writing direction of "Fig.". The writing direction is based on a horizontal clockwise writing, that is to say primarily from left to right, as in Latin, English and Deutsche, for example.FIGS. 1 and 2 each show schematic representations of a plan view of an upper coupling-out facet with a mode-selective microstructure and also a polarization-selective microstructure for a vertical-emitting semiconductor laser component. FIG. 3 shows a schematic sectional illustration of a vertical-emitting semiconductor laser component, from which an exemplary layer structure can be seen. Figures 1 to 3 will be described together below.The vertically emitting semiconductor laser component 1 illustrated in FIG. 3 is a VCSEL. The vertical emitting semiconductor laser device 1 includes an upper Bragg mirror 2 and a lower Bragg mirror 3. An active zone 4 for generating laser radiation 6 is arranged between the upper Bragg mirror 2 and the lower Bragg mirror 3. The basic construction of a VCSEL is known to the person skilled in the art. The Bragg mirrors can each have layer sequences with different indices of refraction and provide a resonator or a laser cavity for the laser radiation generated in the active zone 4. The upper Bragg mirror is designed as a partially transmissive mirror, by means of which the laser radiation 5 can be coupled out in a light emission direction 6. The light emission direction 6 is represented in FIGS. 1 to 3 by the arrow 6, respectively.In the exemplary embodiment shown, the vertical-emitting semiconductor laser component 1 is illustrated as having a mesa 11 on a substrate 12. It is understood that the present disclosure is not limited to a mesa structure, and other configurations of the semiconductor laser device 1 may be provided as well. For example, a planar configuration with one or more semiconductor laser components 1 can be provided, in particular an array of a plurality of semiconductor laser components 1. A plurality of semiconductor laser components 1 can preferably be separated from one another by trenches or trenches, for example in order to avoid crosstalk.For electrical contacting, as shown in the sectional representation in FIG. 3, an upper connection contact 13, also referred to as top contact, and a lower connection contact 14, also referred to as bottom contact or substrate contact, can be provided. The upper connection contact 13 can be designed, for example, as an at least sectionally annular or C-shaped electrode.As illustrated in FIG. 3, the vertical-emitting semiconductor laser component 1 has an upper coupling-out facet 20 for the laser radiation 5, wherein the upper coupling-out facet 20 has both a mode-selective microstructure 21 and a polarization-selective microstructure 22. Exemplary embodiments of the upper coupling-out facet 20 are illustrated in the plan views in FIGS. 1 and 2. The coupling-out facet 20 shown with the mode-selective microstructure 21 and the polarization-selective microstructure 22 is an optical structure which is arranged on an upper side of the upper Bragg mirror 2.The mode selective microstructure 21 is configured to promote a limited number of laser modes, in particular a single laser mode. An exemplary geometry with which a single laser mode can be promoted is illustrated in the plan view in FIG. 1. However, it is also possible for a geometry to be selected in which a limited number of multiple laser modes are favored. An example is shown in plan view in Fig. 2.In the exemplary embodiment shown in FIG. 1, the mode-selective microstructure 21 of the coupling-out facet 20 is formed as a relief having an oval contour 23, in particular having an elliptical contour. As a result, the lateral extent of the modes can be adapted in a simple manner in a targeted manner to a desired mode profile with an optical layer.In the exemplary embodiment shown in FIG. 2, the mode-selective microstructure 21 of the coupling-out facet 20 has an oval relief 24 with a constriction 25. In particular, the mode-selective microstructure 21 can have an 8-shaped contour, as illustrated in FIG. 2 with the contour of a lying figure of eight.In the exemplary embodiments illustrated in FIGS. 1 and 2, an inner region, i.e. a region lying within the contours 23 or 24, and an outer region, i.e. a region lying outside the contours 23 or 24, can have, for example, different layer thicknesses and therefore, adjacent to the upper Bragg mirror 2, have different layer thicknesses and / or different reflectivities and thus influence lateral mode propagation. As shown in the sectional illustration in FIG. 3, a layer thickness within the contours 23, 24 can be reduced, for example. The relief with the oval contour can therefore have an inner oval region with a smaller layer thickness and an outer region with a larger layer thickness surrounding the latter. The sectional illustration in FIG. 3 can be regarded as a section along the line A-A in FIG. 1 with respect to the upper decoupling facet.The additional layer thickness and etching back can be effected in the semiconductor material of the VCSEL, i.e. for example in the uppermost layer of GaAs. Alternatively, a dielectric layer can be applied and subsequently structured. Alternatively, a dielectric layer stack can also be applied, in which a layer is selectively etched. The structuring is effected lithographically, for example by e-beam lithography, UV lithography or else nano-imprint lithography.As shown in the plan views FIGS. 1 and 2, the mode-selective microstructure 21 is preferably formed in a plane parallel to the layers of the upper Bragg mirror 2 (and therefore in FIGS. 1 and 2 parallel to the plane of the drawing sheet) in a rotationally non-symmetrical manner and is configured to break a degeneracy of modes. As a result, an RINof the emitted laser radiation of the semiconductor laser component can be further reduced.In the embodiments shown in FIGS. 1 to 3, the contour 23, 24 of the mode selective microstructure surrounds the region with the polarization selective microstructure 22. In this case, the polarization-selective microstructure has a structure size smaller than a laser wavelength of the laser light. The grating structure 26 can be provided, for example, by using lithographic methods to provide a plurality of parallel webs in the upper coupling-out facet 20 of the semiconductor laser component. A grating period or a distance between adjacent ridges is preferably smaller than the wavelength of the laser radiation. As a result, scattering losses can be avoided or reduced. The mode-selective microstructure 21 and the polarization-selective microstructure 22 are formed together as an elliptically shaped surface relief having a framed lattice structure.As shown in the sectional illustration in FIG. 3, the vertical-emitting semiconductor laser component can optionally have a current aperture 7. In the exemplary embodiment shown, the current aperture is arranged between the active layer 4 and the upper Bragg mirror 2. However, other arrangements in the layer structure are also conceivable. One particular feature is that the current aperture 7 has a larger diameter in a plane orthogonal to a beam direction 6 of the laser beam 5 than a diameter of the mode-selective microstructure 21 of the coupling-out facet 20 having the polarization-selective microstructure 22. Thus, a lateral promotion of desired modes is effected more closely limited by the mode selective microstructure 21 of the coupling-out facet, i.e. by variation of the optical properties instead of by a constriction by a current aperture 7. The current may be distributed electrically over a larger area within the semiconductor. In this case, the mode selection therefore does not take place or does not take place solely by the current diaphragm. Rather, an optical mode selection takes place through the microstructure of the coupling-out facet in conjunction with the polarization-selective microstructure of the coupling-out facet. An advantage of this configuration can be that the definition of the current aperture, by e.g. an oxide aperture, implantation or buried tunnel diode, can be effected independently of the optical structure of the coupling-out facet described here. It is not necessary for the current aperture to correspond exactly to the optical structure or the mode. The inventors have recognized that lateral transport of the charge carriers, for example in quantum trenches of an active zone, also contributes to amplification by current injection, which takes place offset from the mode by approximately 1 μm or a few μm. This can be used advantageously in that current injection takes place over the full area and over a somewhat larger range than corresponds to the (optical) mode selection. As a result, despite a selected spatially narrow mode, the current is guided in a larger diameter. This lowers the current density and this can result in a significantly increased service life.It will be appreciated that the choice of the exact structure is relatively free and should follow typical lateral mode structures. These can be combined with a (slightly) differently shaped current aperture. Simple examples are: (a) a circular current diaphragm with an elliptical or circular facet; (b) a substantially oval facet, optionally with an additional constriction; (c) a rectangular current aperture with an elliptical facet or facet with a plurality of maxima, as illustrated by way of example in FIGS. 1 and 2; (d) a circular or rectangular current aperture with a meta structure on the decoupling facet, which substantially corresponds to the mode image of a preferred mode.In a further variation of the vertical-emitting semiconductor laser component 1 illustrated in FIG. 3, the mode-selective microstructure is an optional feature. The vertically emitting semiconductor laser component 1 can be a VCSEL having an upper Bragg mirror 2 and a lower Bragg mirror 3, wherein an active zone 4 for generating laser radiation 5 is arranged between the upper Bragg mirror 2 and the lower Bragg mirror 3. The vertical-emitting semiconductor laser component 1 has an upper coupling-out facet 20 for the laser radiation 5. The upper coupling-out facet 20 has a polarization-selective microstructure 22. The semiconductor laser component 1 is configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1 GHz in the case of high-frequency excitation up to a frequency of 25 GHz, in particular in the case of high-frequency excitation at a frequency of 25 GHz.FIG. 4 shows a schematic illustration of a chip 40 having a vertical-emitting semiconductor laser component 1. the chip 40 has a carrier 41 on which the semiconductor laser component 1 is arranged. In this case, connection contacts 42, 43 can be provided, which are connected to the respective electrical connection contacts 13, 14 of the semiconductor laser component 1 by means of bonding wires 44, 45. The provision of such a chip facilitates the handling of the vertical-emitting semiconductor laser component 1. optionally, the chip 40 can have further functional elements, such as, for example, an amplifier, a modulator or protective circuits, such as, for example, ESD protective elements.FIG. 5 shows a schematic illustration of a communication system or a transmitter for an optical communication system 50, the communication system or a transmitter for an optical communication system having an input terminal 51 for receiving data, a modulator 52 and a vertical-emitting semiconductor laser component 1 or a chip 40 with such a component. As described in the introduction, an input terminal 51 can be understood to mean an interface for receiving data. The received data can be converted by the modulator 52 and modulated, for example, in the form of current modulation or voltage modulation onto the laser light 5 emitted by the vertically emitting semiconductor laser component 1. The communication system may further include a receiver (not shown) having a detector for detecting the modulated laser light and a demodulator configured to demodulate and convert the detected laser light into data that may be output via an interface for outputting data.FIG. 6 is a flow diagram of a method 100 for producing a vertical-emitting semiconductor laser component. In a first step S 101, a semiconductor substrate 12 is provided. In a second step S 102, a layer sequence for a lower Bragg mirror is deposited on the semiconductor substrate. In a third step S 103, an active layer having an active zone for generating laser radiation is deposited on the lower Bragg mirror. In a fourth step S 104, a layer sequence for an upper Bragg mirror is deposited on the active layer. In a first variant of a method for producing a method for producing a vertically emitting semiconductor laser component, in a fifth step S 105, an upper coupling-out facet for the laser radiation is provided on the upper Bragg mirror, wherein the upper coupling-out facet has both a mode-selective microstructure and a polarization-selective microstructure. Such an output coupling facet can be provided by applying further layers and structuring them or by structuring one or more existing layers, such as, for example, upper layers of the upper Bragg mirror. In a second variant of a method for producing a method for producing a vertically emitting semiconductor laser component, in a fifth step S 105, an upper coupling-out facet for the laser radiation is provided on the upper Bragg mirror, wherein the upper coupling-out facet has both a polarization-selective microstructure and wherein the semiconductor laser component is configured to decrease in its light intensity compared to an excitation at 1GHz by not more than 3 dB in the case of high-frequency excitation up to a frequency of 25GHz.According to one configuration, in order to reduce the noise (RIN), an elliptically shaped surface relief having a grating structure can be applied in the case of datacom VCSELs. The number of modes can be reduced, regions of unstable polarization can be avoided over a wide temperature and current range. By dimensioning the grating structure smaller than the wavelength, scattering losses can be avoided. Gratings can also be designed as an optical meta-structure.In summary, advantages of one or more aspects of the present invention can consist in particular in that a further improved or alternative vertical-emitting semiconductor laser component, in particular VCSEL, can be provided for optical data transmission. One advantage may be that a vertical-emitting semiconductor laser component can be provided which enables high speeds in the optical data transmission over a wide range of ambient conditions, in particular over a wide temperature range. Alternatively or additionally, there may be an advantage in that a vertical-emitting semiconductor laser component can be provided, which can be produced cost-effectively or with simplified process steps and / or with high yield (high yield). Alternatively or additionally, there may be an advantage in that a vertical emitting semiconductor laser device can be provided which improves a lifetime of datacom VCSELs with low RIN.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 10,742,000 B2 [0003, 0014, 0018]

Claims

Vertical-emitting semiconductor laser component (1), in particular VCSEL, having an upper Bragg mirror (2) and a lower Bragg mirror (3), wherein an active zone (4) for generating laser radiation (5) is arranged between the upper Bragg mirror (2) and the lower Bragg mirror (3); characterized in that the vertical-emitting semiconductor laser component (1) has an upper coupling-out facet (20) for the laser radiation (5), wherein the upper coupling-out facet (20) has both a mode-selective microstructure (21) and a polarization-selective microstructure (22).The vertical emitting semiconductor laser component (1) according to claim 1, wherein the coupling-out facet (20) having the mode selective microstructure (21) and the polarization selective microstructure (22) is an optical structure arranged on a top side of the upper Bragg mirror (2).Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the coupling-out facet (20) is formed as a relief structure, wherein the mode-selective microstructure (21) of the coupling-out facet has a first region having a first layer thickness, and wherein the mode-selective microstructure (22) of the coupling-out facet has a second region having a second layer thickness, in particular wherein the second layer thickness is smaller than the first layer thickness.The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the mode selective microstructure (21) is configured to promote a limited number of laser modes, in particular wherein the mode selective microstructure (21) is configured to promote a single laser mode.The vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective microstructure (21) has a first region having a first reflectivity and a second region having a second reflectivity which differs from the first reflectivity.The vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective microstructure (21) of the coupling-out facet (20) has a relief with a non-rotationally symmetrical contour (23), in particular with an oval contour (23), in particular with an elliptical contour.The vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective microstructure (21) of the coupling-out facet (20) has an oval relief (24) with a constriction (25), in particular wherein the mode-selective microstructure has an 8-shaped contour.Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective microstructure (21) is formed in a plane parallel to layers of the upper Bragg mirror in a rotationally non-symmetrical manner and is configured to break a degeneracy of modes.Vertical emitting semiconductor laser component (1) according to one of the preceding claims, wherein the polarization-selective microstructure (22) has a grating structure (26) for polarising the laser light (5).The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the polarization selective microstructure (22) has a structure size smaller than a laser wavelength of the laser light (5).Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective microstructure (21) and the polarization-selective microstructure (22) are formed together as an elliptically shaped surface relief (23) having a framed grating structure (26).The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the mode selective microstructure (21) and the polarization selective microstructure (22) are formed by an optical meta-structure of the decoupling facet (20), in particular wherein the decoupling facet has an optical meta-structure having a structure with spatially varying phase matching.The vertical emitting semiconductor laser device (1) according to claim 12, wherein the optical meta-structure is configured to provide a varying effective refractive index, wherein the optical meta-structure has a varying density of constant height turrets and an extension smaller than the wavelength.The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the vertical emitting semiconductor laser component (1) has a current aperture (7), wherein the current aperture (7) has a larger diameter in a plane orthogonal to a beam direction (6) of the laser beam (5) than a diameter of the mode selective microstructure (21, 23) of the decoupling facet (20) having the polarization selective microstructure (22).The vertical emitting semiconductor laser device (1) according to any one of the preceding claims, wherein the vertical emitting semiconductor laser device (1) is a VCSEL for optical data transmission.The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the vertical emitting semiconductor laser component (1) has a relative intensity noise (RIN) of less than -80 dB / Hz, in particular of less than -100 dB / Hz, in particular of less than -120 dB / Hz, in particular of less than -140 dB / Hz.The vertical emitting semiconductor laser component (1) according to any one of the preceding claims, wherein the vertical emitting semiconductor laser component (1) is configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1GHz when excited at high frequency up to a frequency of 25GHz.Use of a surface relief on an output coupling facet (20) of a VCSEL, wherein the surface relief of the output coupling facet (20) has a mode-selective microstructure (21) and a polarization-selective microstructure (22), in a communication system (50) for optical data transmission.A vertical-emitting semiconductor laser component (1), in particular a VCSEL, having an upper Bragg mirror (2) and a lower Bragg mirror (3), wherein an active zone (4) for generating laser radiation (5) is arranged between the upper Bragg mirror (2) and the lower Bragg mirror (3); characterized in that the vertical-emitting semiconductor laser component (1) has an upper coupling-out facet (20) for the laser radiation (5), wherein the upper coupling-out facet (20) has a polarization-selective microstructure (22) and the semiconductor laser component is configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1GHz when excited at high frequency up to a frequency of 25GHz.A communication system (50) comprising an input terminal (51) for receiving data, a modulator (52) and a vertical emission semiconductor laser device (1) according to any preceding claim.Method (100) for producing a vertical-emitting semiconductor laser component, the method comprising the following steps: - providing (S101) a semiconductor substrate; - depositing a layer sequence for a lower Bragg mirror on the semiconductor substrate (S102); - depositing an active layer having an active zone for generating laser radiation on the lower Bragg mirror (S103); - depositing a layer sequence for an upper Bragg mirror on the active layer (S104); - providing an upper coupling-out facet for the laser radiation on the upper Bragg mirror, wherein the upper coupling-out facet has both a mode-selective microstructure and a polarization-selective microstructure (S105).Method (100) for producing a vertical-emitting semiconductor laser component, the method comprising the following steps: - providing (S101) a semiconductor substrate; - depositing a layer sequence for a lower Bragg mirror on the semiconductor substrate (S102); - depositing an active layer having an active zone for generating laser radiation on the lower Bragg mirror (S103); - depositing a layer sequence for an upper Bragg mirror on the active layer (S104); providing an upper coupling-out facet for the laser radiation on the upper Bragg mirror, wherein the upper coupling-out facet has a polarization-selective microstructure and the semiconductor laser component is configured to decrease in its light intensity by not more than 3 dB compared to an excitation at 1GHz in the case of high-frequency excitation up to a frequency of 25GHz (S 105).

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