Semiconductor laser component with a vertical emission direction for optically transmitting data, comprising a decoupling facet with a mode-selective macrostructure and a polarization-selective microstructure

Abstract

The invention relates to a semiconductor laser component (1) with a vertical emission direction, in particular a VCSEL, comprising an upper Bragg mirror (2) and a lower Bragg mirror (3). 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 semiconductor laser component (1) with a vertical emission direction has an upper decoupling facet (20) for the laser radiation (5), and the upper decoupling facet (20) has both a mode-selective macrostructure (21) as well as a polarization-selective microstructure (22). The invention additionally relates to the use of a surface relief on a decoupling facet of a VCSEL, to a communication system, and to a method for producing a corresponding semiconductor laser component with a vertical emission direction.

Description

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

[0001] The present invention relates to the field of optical communication technology, in particular a vertical-emitting semiconductor laser component, especially a “vertical-cavity surface-emitting laser”, abbreviated VCSEL, for optical data transmission.

[0002] VCSELs for optical data transmission are well-known technologies. They are also referred to as Datacom VCSELs. One advantage of VCSELs is their ability to offer high data transmission performance with low power consumption. In a VCSEL (vertical-cavity surface-emitting laser) laser diode, the light is emitted perpendicular to the plane of the semiconductor chip, unlike an edge-emitting laser diode, where the light exits at one or two edges of the chip.

[0003] US 10,742,000 B2 relates to a VCSEL with an elliptical aperture and reduced RIN (stochastic or relative intensity noise). According to the abstract, the VCSEL described therein shall comprise an elliptical oxide aperture in an oxidized region located between an active region and an emission surface, wherein the elliptical aperture has a short radius and a long radius with a radius ratio (short radius) / (long radius) between 0.6 and 0.8, and wherein the VCSEL has a relative intensity noise (RIN) of less than -140 dB / Hz. The VCSEL may include an elliptical emission aperture with the same dimensions as the elliptical oxide aperture.

[0004] To reduce the RIN, the prior art proposes providing an elliptical oxide aperture or oxide diaphragm within the laser cavity.

[0005] Against this background, an object of the present invention is to provide a further improved or alternative vertical-emitting semiconductor laser device, in particular a VCSEL, for optical data transmission. The inventors have recognized that it would be particularly desirable to provide a vertical-emitting semiconductor laser device that enables high speeds in optical data transmission over a wide range of environmental conditions, especially over a wide temperature range. Furthermore, it would be desirable to provide a vertical-emitting semiconductor laser device that can be manufactured cost-effectively or with simplified process steps and / or with high yield. It would also be desirable to improve the lifetime of datacom VCSELs with low RIN.

[0006] The claimed subject matter is defined in the independent claims. Advantageous further developments are described in the dependent claims.

[0007] According to a first aspect of the present invention, it is therefore proposed to provide a vertically emitting semiconductor laser device, in particular a VCSEL, comprising 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 vertically emitting semiconductor laser device has an upper output coupling facet for the laser radiation, wherein the upper output coupling facet has both a mode-selective macrostructure and a polarization-selective microstructure.

[0008] According to another aspect of the present invention, the use of a surface relief on an output facet of a VCSEL, wherein the surface relief of the output facet has a mode-selective macrostructure and a polarization-selective microstructure, is proposed in a communication system for optical data transmission.

[0009] According to a further aspect of the present invention, a vertically emitting semiconductor laser device, in particular a VCSEL, is proposed, comprising a The vertically emitting semiconductor laser device comprises an upper Bragg mirror and a lower Bragg mirror, wherein an active zone for generating laser radiation is arranged between the upper and lower Bragg mirrors; the device has an upper output coupling facet for the laser radiation, the upper output coupling facet having a polarization-selective microstructure, and the semiconductor laser device is configured to exhibit a light intensity drop of no more than 3 dB compared to excitation at 1 GHz when excited at high frequencies up to 25 GHz, particularly when excited at 25 GHz. Optionally, the upper output coupling facet can have a mode-selective macrostructure. It is understood that the further features and embodiments described in connection with the first aspect of this disclosure can also be combined with this aspect.

[0010] According to another aspect of the present invention, a communication system comprising an input terminal for receiving data, a modulator and a vertically emitting semiconductor laser component, as mentioned above and / or described below, is proposed.

[0011] According to a further aspect of the present invention, a method for fabricating a vertically emitting semiconductor laser device is further proposed, wherein the method comprises the following steps: providing a semiconductor substrate; depositing a layer sequence for a lower Bragg mirror on the semiconductor substrate; depositing an active layer with 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 output facet for the laser radiation on the upper Bragg mirror, wherein the upper output facet has both a mode-selective macrostructure and a polarization-selective microstructure.

[0012] According to a further aspect of the present invention, a method for fabricating a vertically emitting semiconductor laser component is also proposed, the method comprising the following steps: providing a semiconductor substrate; depositing a layer sequence for a lower Bragg mirror on the Semiconductor substrate; deposition of an active layer with an active zone for generating laser radiation on the lower Bragg mirror; deposition of a layer sequence for an upper Bragg mirror on the active layer; provision of an upper output coupling facet for the laser radiation on the upper Bragg mirror, wherein the upper output coupling facet has a polarization-selective microstructure and the semiconductor laser device is configured to exhibit a light intensity that, when excited at high frequency up to a frequency of 25 GHz, in particular when excited at a frequency of 25 GHz, does not decrease by more than 3 dB compared to an excitation at 1 GHz.

[0013] It is understood that optionally further layers may be provided, which may 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.

[0014] The inventors recognized that VCSELs in datacom applications are often operated at relatively high currents with high-frequency signal modulation. The required output power is achieved in conventional VCSELs primarily through multimodal operation. This can lead to competition and degeneration of the many modes, resulting in significant relative intensity noise (RIN). The inventors recognized that even with a reduced number of modes, a similar noise contribution can occur through operation with unstable polarization. This regularly results in so-called "flips" of the polarization direction. Furthermore, conventional solutions often only improve the RIN for a narrow range of operating parameters, but not over a broad range, and especially not over a wide temperature range.Furthermore, solutions such as the VCSEL described in the aforementioned US 10,742,000 B2, with its elliptical current aperture located within the semiconductor's layer sequence at the active layer, can be susceptible to process variations in semiconductor manufacturing. Additionally, the current flow within the semiconductor can vary across the intended wide current and temperature range for the specific application of datacom VCSELs.

[0015] According to one aspect of the present invention, it is therefore proposed to provide an optical solution with a specially designed upper output facet of the vertical-emitting semiconductor laser device, wherein the upper output facet has both a mode-selective macrostructure and a polarization-selective microstructure. According to one aspect of the invention, the invention aims to reduce the number of competing modes while simultaneously stabilizing the polarization. This is achieved by using a surface structure, in particular a surface relief, of the output facet of the VCSEL, which has a spatial macrostructure and a polarization-selective structure. In the simplest case, a datacom VCSEL with an elliptically bounded relief structure with a polarization grating can be provided.

[0016] The coexistence of multiple modes in a VCSEL is a source of noise. A lateral macrostructure with dimensions typical of VCSEL modes can favor or hinder individual modes, thereby reducing the number of modes and the noise. For example, very small macrostructures (a few pm) can be used to force operation on a fundamental mode, which has a smaller diameter than higher-order modes. Similarly, elliptical cross-sections favor modes with greater extent along the long semi-axis.

[0017] The proposed special design of the upper output facet, which features both a mode-selective macrostructure and a polarization-selective microstructure, has the advantage that an improvement in noise reduction (RIN) can be achieved using purely optical means. The inventors have recognized that this solution can enable particularly favorable noise performance over a wide temperature range. It also prevents the VCSEL from operating in an unstable polarization region under certain operating conditions over a wide current range, while simultaneously ensuring operation in desired laser modes, especially at the high modulation frequencies required for datacom VCSELs.

[0018] Unlike the current aperture described in the aforementioned US 10,742,000 B2, a structure on the upper side of the output coupling mirror has a purely Optical function. The top surface of the upper Bragg mirror, or output coupler, can be referred to as the output coupler facet. The output-side DBR of the VCSEL typically terminates in an antinode of the standing wave field against air or a refracting medium. If, for example, the thickness of the DBR layer is increased by a quarter of the wavelength in the medium, this significantly reduces the reflectivity of the DBR, making laser operation more difficult. However, if the additional layer thickness is partially removed, the full reflectivity is restored in the etched area. This favors modes with high intensity in these regions. A structure on the top surface is easily accessible and therefore practically feasible. It is understood that one or more layers of the upper Bragg mirror can also be considered part of the upper output coupler facet.

[0019] The terms macrostructure and microstructure describe the relative relationship, with the mode-selective macrostructure having a larger structure size than the polarization-selective microstructure. Alternatively, one can speak of a first mode-selective structure of the output coupling facet and a second polarization-selective structure of the output coupling facet. The polarization-selective macrostructure of the output coupling facet is a structure designed to favor a limited number of laser modes, specifically, the mode-selective macrostructure is designed to favor a single laser mode. The polarization-selective microstructure is a structure designed to favor a specific polarization of the laser radiation. For example, the polarization-selective microstructure can be implemented as a lattice or as an optical metastructure.

[0020] According to one aspect of the present invention, the upper output coupling facet can have a polarization-selective microstructure, and the semiconductor laser component can be configured to exhibit a light intensity decrease of no more than 3 dB compared to excitation at 1 GHz when excited at high frequencies up to 25 GHz. An advantage can be that, thanks to the small decrease in light intensity when excited at 25 GHz compared to excitation at 1 GHz, the upstream amplifier electronics can have a simpler design; in particular, modulation frequency-selective gain matching can be eliminated or at least simplified.

[0021] All features of the objects described herein and also of the claimed objects are usable both individually and in combination with one another, are compatible with one another, and are intended and usable for further development in relation to one another, provided that no logical contradiction arises, and are hereby disclosed accordingly. In the following, any reference to an object or a feature (including the indefinite articles "a" and "an" and the definite articles "the"), two objects or two features, or any other number of objects or features, unless expressly stated otherwise or a logical contradiction arises, is to be understood as meaning that the existence of further such objects and features is not excluded by the invention, but rather is also encompassed by the invention.The reference numerals in the claims are not to be understood as restrictive, but merely serve to improve the readability of the claims.

[0022] In one embodiment, the output facet with its mode-selective macrostructure and polarization-selective microstructure can be a purely optical structure located on the top surface of the upper Bragg mirror. An advantage of this embodiment is that the top surface structure is easily accessible and therefore practical to implement. Another advantage is that different mode profiles and / or presentations can be easily adapted to customer requirements, as only the output facet needs to be modified, not the entire semiconductor layer structure. An existing semiconductor layer structure with an upper Bragg mirror, a lower Bragg mirror, and the active region in between can thus be reused for various applications. This allows for simple and cost-effective manufacturing.The top side of the upper Bragg mirror can be considered to be the side which is located in the direction of the laser beam in the direction in which the laser radiation is coupled out of the semiconductor laser component.

[0023] The output facet can be designed as an (optical) relief structure. The mode-selective macrostructure of the output facet can have a first region with a first layer thickness. The mode-selective microstructure of the output facet can have a second region with a second layer thickness, in particular where the second layer thickness is smaller than the first. A difference in layer thickness, or an additional layer thickness and back-etching, can occur in the semiconductor material of the VCSEL, for example, in the top layer made of GaAs. Alternatively or additionally, a dielectric layer can be deposited and subsequently patterned. Alternatively or additionally, a dielectric layer stack can be deposited, in which one layer is selectively etched. The patterning can be performed lithographically, for example, using e-beam lithography, UV lithography, or nanoimprint lithography.

[0024] The mode-selective macrostructure can be configured to favor a limited number of laser modes. In particular, the mode-selective macrostructure can be configured to favor a single laser mode. Specifically, the macrostructure can be configured to adapt the lateral mode structure. An advantage of this configuration is that the emission behavior of the semiconductor laser device can be tailored to a desired application. It is understood that a favored mode need not necessarily be a fundamental mode used in single-mode VCSELs, but can be any higher-order mode.

[0025] The mode-selective macrostructure can have a first region with a first reflectivity and a second region with a second reflectivity that differs from the first. The output coupling facet can thus be equipped with a tailored reflectivity to favor desired modes.

[0026] The mode-selective macrostructure of the output facet can have a relief with a non-rotationally symmetric contour. Specifically, the mode-selective macrostructure of the output facet can have a relief with an oval contour, particularly an elliptical one. Such a relief structure allows the number of competing modes to be reduced and, in particular, favors modes whose geometric dimensions match the non-rotationally symmetric contour, especially 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. as well as having a surrounding outer region with a greater layer thickness. This applies to other non-rotationally symmetric or elliptical contours.

[0027] In a further development, the mode-selective macrostructure of the output facet can have a non-rotationally symmetric or oval relief with a constriction. In particular, the mode-selective macrostructure can have a figure-eight contour. This is a particularly advantageous example, where, thanks to the oval contour with constriction, especially a figure-eight contour, additional modes can be favored instead of or alongside the basic mode, but not an uncontrollably high number of modes, rather a limited number. The mode profile can thus be advantageously adapted to a desired application.

[0028] The mode-selective macrostructure can be non-rotationally symmetric in a plane parallel to the layers of the upper Bragg mirror. The mode-selective macrostructure can be configured to break mode degeneracy. An advantage of this design with a non-rotationally symmetric macrostructure is that it counteracts mode degeneracy. Another advantage of this design is that the laser's emission behavior can be further stabilized. Unwanted hopping between different emission modes can be reduced, thus improving noise performance.

[0029] The polarization-selective microstructure can incorporate a lattice structure for polarizing the laser light. In other words, a surface lattice for polarizing the light can be arranged on the output facet. However, this is not achieved in isolation, but rather in conjunction with a mode-selective macrostructure. The inventors recognized that the mode-selective macrostructure and the polarization-sensitive microstructure can interact advantageously, producing a synergistic effect. In particular, this combination has proven especially beneficial for stabilization over a wide temperature range.

[0030] The polarization-selective microstructure can have a structure size smaller than the laser wavelength. For example, a lattice structure with a lattice spacing or lattice period smaller than the laser wavelength can be implemented. Alternatively, an optical metastructure with structures smaller than the laser wavelength can be used. One advantage of this design is that, by avoiding diffraction, losses can be reduced when selecting structure sizes for the polarization-selective microstructure in this way.

[0031] The mode-selective macrostructure and the polarization-selective microstructure can be combined to form an elliptically shaped surface relief with a lattice structure enclosed by the surface relief. For example, the optical macrostructure could be an elliptical depression in the output coupling facet, and this depression could feature a polarization-selective lattice structure. It is understood that instead of a depression, a raised area or other modification of the reflection behavior could also be provided. Generally speaking, the upper output coupling facet can have a macrostructure which in turn contains a fine structure. Here, the macrostructure defines spatially lateral modes, while the fine structure determines the polarization. An example is an oval or circular structure with, for example, a diameter of 10 pm and a lattice with, for example, a pitch of 150 nm.

[0032] The mode-selective macrostructure and the polarization-selective microstructure can be formed by an optical metastructure of the output coupling facet, in particular where the output coupling facet exhibits an optical metastructure with spatially varying phase matching. The metastructure on the output coupling facet can essentially correspond to the mode image of a preferred mode. Such optical metastructures can be determined, for example, by means of numerical simulations.

[0033] The optical metastructure can be configured to provide a varying effective refractive index. Alternatively or additionally, the optical metastructure can exhibit a varying density of turrets of constant height and a size smaller than the wavelength. For example, elongated shapes of the individual turrets can be used to select the polarization. Providing an optical metastructure with varying density but constant height in the emission direction of the VCSEL laser radiation can be particularly advantageous, as this can be achieved by structuring a layer with a defined height. A layer to be structured can be created during semiconductor fabrication or wafer production. The structuring can be performed using established semiconductor fabrication methods. This enables efficient and cost-effective manufacturing with high quality. A further advantage of a metastructure compared to a relief with a hard step or relief edge is the avoidance of diffraction at the relief edge, which can cause losses. Another advantage is the ability to achieve a more precise match to a desired intensity profile of specific modes, thus improving selectivity and stability.

[0034] The vertical-emitting semiconductor laser device can have (at least) one current aperture, where the current aperture, measured in a plane orthogonal to the direction of the laser beam, has a larger diameter than the diameter of the mode-selective macrostructure of the output coupling facet with its 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 direction of the laser beam. By making the current aperture or current apparatus larger than the relief structure or mode-selective macrostructure, the current density within the VCSEL can be reduced. The current can then be electrically distributed over a larger area within the semiconductor. In this case, mode selection does not occur, or does not occur solely, through the current aperture.Rather, optical mode selection occurs through the macrostructure of the output coupling facet in conjunction with its polarization-selective microstructure. An advantage of this design is that the definition of the current aperture, for example by an oxide aperture, implantation, or buried tunnel diode, can be independent of the optical structure of the output coupling 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 charge carriers, for example in quantum trenches of an active zone, also contributes to amplification through current injection, which occurs approximately 1 pm or a few pm offset from the mode. This can be advantageously exploited by performing current injection across the entire surface and over a somewhat larger area than is typical for the (optical) Mode selection is used. This results in the current being guided over a larger diameter, despite a selected, spatially narrow mode. This reduces the current density and can lead to a significantly increased lifetime. This provides a substantial advantage over mode selection with an elliptical current aperture.

[0035] The vertical-emitting semiconductor laser device 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 recognized that the proposed solution with the specific output coupling facet, which exhibits both a mode-selective macrostructure and a polarization-selective microstructure, is particularly advantageous for VCSELs used for optical data transmission. Datacom VCSELs are often operated over a wide temperature range, which places special demands on them that do not arise in other applications or in purely research-oriented setups under laboratory conditions.

[0036] In one embodiment, the vertically emitting semiconductor laser component has a relative intensity noise (RIN) of less than -80 dμ / Hz, in particular less than -100 dμ / Hz, in particular less than -120 dμ / Hz, and in particular less than -140 dμ / Hz. This enables particularly high data transmission rates in optical communication systems. The specified values ​​can refer to relative intensity noise, RIN, in a frequency range up to 40 GHz, in particular in a range between 1 GHz and 40 GHz, in particular in a range between 2 GHz and 30 GHz, and in particular in a range between 5 GHz and 25 GHz.

[0037] The vertical-emitting semiconductor laser device can be configured to exhibit a light intensity drop of no more than 3 dB when excited at high frequencies up to 25 GHz, compared to excitation at 1 GHz. This makes the vertical-emitting semiconductor laser device particularly advantageous for optical data transmission. One benefit is that, thanks to the minimal drop in light intensity when excited at 25 GHz compared to 1 GHz, the upstream amplifier electronics can be designed more simply. This can result in, in particular, the elimination or at least simplification of modulation frequency-selective gain adjustment.

[0038] A particularly advantageous application of the proposed vertically emitting semiconductor laser device is its use in a communication system for optical data transmission. The communication system, or a transmitter for an optical communication system, can comprise an input terminal for receiving data, a modulator, and a vertically emitting semiconductor laser device. An input terminal can be understood as an interface for receiving data. The received data can be converted by the modulator and, for example, modulated onto the laser light emitted by the vertically emitting semiconductor laser device in the form of current or voltage modulation.The communication system may also include a receiver with a detector for detecting the modulated laser light and a demodulator which is designed to demodulate the detected laser light and convert it into data that can be output via an interface.

[0039] The advantages and optional further features described above in detail for the first aspect of the invention apply accordingly to the further aspects of the invention.

[0040] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0041] Exemplary embodiments of aspects of the invention are shown in the drawings and are explained in more detail in the following description. They show:

[0042] Fig. 1 shows a first schematic representation of a top view of an upper output coupling facet with a mode-selective macrostructure as well as a polarization-selective microstructure for a vertically emitting semiconductor laser device;

[0043] Fig. 2 shows a second schematic representation of a top view of an upper output coupling facet with a mode-selective macrostructure as well as a polarization-selective microstructure for a vertically emitting semiconductor laser device;

[0044] Fig. 3 shows a schematic sectional view of a vertically emitting semiconductor laser component;

[0045] Fig. 4 shows a schematic representation of a chip with a vertically emitting semiconductor laser component;

[0046] Fig. 5 shows a schematic representation of a communication system;

[0047] Fig. 6 shows a flowchart of a process for manufacturing a vertically emitting semiconductor laser component.

[0048] The same reference symbols used in the figures denote identical or at least equivalent elements. The terms "above," "below," "left," and "right," as well as direction-dependent indications derived from them, such as "top," refer to the writing / reading direction of the figure label "Fig." belonging to a drawing, which is printed on the drawing plane below the drawing. 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, right-to-right script, that is, primarily from left to right, as in Latin, English, and German.

[0049] Figures 1 and 2 each show schematic representations of a top view of an upper output facet with a mode-selective macrostructure as well as a polarization-selective microstructure for a vertically emitting Semiconductor laser component. Fig. 3 shows a schematic sectional view of a vertically emitting semiconductor laser component, illustrating an exemplary layer structure. Figs. 1 to 3 are described together below.

[0050] The vertical-emitting semiconductor laser device 1 shown in Fig. 3 is a VCSEL. The vertical-emitting semiconductor laser device 1 has 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 structure of a VCSEL is known to those skilled in the art. The Bragg mirrors can each have layer sequences with different refractive indices 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 transparent mirror through which the laser radiation 5 can be coupled out in a light emission direction 6. The light emission direction 6 is indicated by the arrow 6 in Figs. 1 to 3.

[0051] In the illustrated embodiment, the vertically emitting semiconductor laser component 1 is shown with a mesa 11 on a substrate 12. It is understood that the present disclosure is not limited to a mesa structure and that other embodiments of the semiconductor laser component 1 are also possible. For example, a planar embodiment with one or more semiconductor laser components 1 is possible, in particular an array of several semiconductor laser components 1. Several semiconductor laser components 1 can preferably be separated from each other by trenches, for example to avoid crosstalk.

[0052] For electrical contacting, as shown in the sectional view in Fig. 3, an upper terminal contact 13, also referred to as the top contact, and a lower terminal contact 14, also referred to as the bottom contact or substrate contact, can be provided. The upper terminal contact 13 can, for example, be designed as an electrode that is at least partially ring-shaped or C-shaped.

[0053] As shown in Fig. 3, the vertically emitting semiconductor laser component 1 has an upper output facet 20 for the laser radiation 5, wherein the upper output facet 20 has both a mode-selective macrostructure 21 and a polarization-selective microstructure 22. Exemplary embodiments of the upper output facet 20 are shown in the top views in Fig. 1 and Fig. 2. The output facet 20 shown, with the mode-selective macrostructure 21 and the polarization-selective microstructure 22, is an optical structure arranged on a top surface of the upper Bragg mirror 2.

[0054] The mode-selective macrostructure 21 is configured to favor a limited number of laser modes, in particular a single laser mode. An exemplary geometry that can favor a single laser mode is shown in the top view in Fig. 1. However, it is also possible to choose a geometry that favors a limited number of multiple laser modes. An example is shown in the top view in Fig. 2.

[0055] In the embodiment shown in Fig. 1, the mode-selective macrostructure 21 of the output facet 20 is designed as a relief with an oval contour 23, in particular with an elliptical contour. This allows the lateral extent of the modes to be easily and precisely adapted to a desired mode profile using an optical layer.

[0056] In the embodiment shown in Fig. 2, the mode-selective macrostructure 21 of the output facet 20 has an oval relief 24 with a constriction 25. In particular, the mode-selective macrostructure 21 can have a figure-eight-shaped contour, as shown in Fig. 2 with the outline of a reclining figure eight.

[0057] In the embodiments shown in Fig. 1 and Fig. 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, for example, have different layer thicknesses and thus, adjacent to the upper Bragg mirror 2, different layer thicknesses and / or different reflectivities. exhibit and thus influence lateral mode propagation. As shown in the cross-sectional view in Fig. 3, for example, the layer thickness within contours 23, 24 can be reduced. The relief with the oval contour can therefore have an inner oval region with a smaller layer thickness and an outer region surrounding it with a larger layer thickness. The cross-sectional view in Fig. 3 can be considered, with respect to the upper output facet, as a section along line AA in Fig. 1.

[0058] The additional layer thickness and back-etching can be performed within the semiconductor material of the VCSEL, for example, in the top layer of GaAs. Alternatively, a dielectric layer can be deposited and subsequently patterned. Another option is to deposit a dielectric layer stack, selectively etching one layer at a time. Patterning is performed lithographically, for example, using e-beam lithography, UV lithography, or nano-imprint lithography.

[0059] As shown in the top views of Figures 1 and 2, the mode-selective macrostructure 21 is preferably non-rotationally symmetric in a plane parallel to the layers of the upper Bragg mirror 2 (and thus, in Figures 1 and 2, parallel to the plane of the drawing sheet) and is configured to break mode degeneracy. This allows the RIN of the emitted laser radiation of the semiconductor laser device to be further reduced.

[0060] In the embodiments shown in Figures 1 to 3, the contour 23, 24 of the mode-selective macrostructure surrounds the region with the polarization-selective microstructure 22. In the illustrated, non-limiting embodiments, the polarization-selective microstructure is designed as a lattice structure for polarizing the laser light. Here, the polarization-selective microstructure has a structure size smaller than the wavelength of the laser light. The lattice structure 26 can be provided, for example, by lithographically creating several parallel struts in the upper output facet 20 of the semiconductor laser component. A lattice period or a distance between adjacent struts is preferably smaller than the wavelength of the laser radiation. This allows scattering losses to be avoided or reduced. The mode-selective macrostructure 21 and the The polarization-selective microstructures 22 are formed together as an elliptically shaped surface relief with an enclosed lattice structure.

[0061] As shown in the sectional view in Fig. 3, the vertically emitting semiconductor laser component can optionally have a stroma 7. In the illustrated embodiment, the stroma is arranged between the active layer 4 and the upper Bragg mirror 2. However, other arrangements in the layer structure are also conceivable. A special feature is that the stroma 7 has a larger diameter in a plane orthogonal to a beam direction 6 of the laser beam 5 than the diameter of the mode-selective macrostructure 21 of the output coupling facet 20 with the polarization-selective microstructure 22. The size of the stroma 7 is shown in the top view in Figs. 1 and 2 and is larger than the mode-selective macrostructure 21, with a rectangular stroma 7 being provided as an example. Thus, lateral favoring of desired modes is more narrowly limited by the mode-selective macrostructure 21 of the output coupling facet, i.e.,By varying the optical properties instead of by constriction through a current aperture 7. By making the current aperture or current apparatus larger than the relief structure or mode-selective macrostructure, the current density within the VCSEL can be reduced. The current can be electrically distributed over a larger area within the semiconductor. In this case, mode selection does not occur, or at least not solely, through the current aperture. Rather, optical mode selection occurs through the macrostructure of the output coupling facet in conjunction with the polarization-selective microstructure of the output coupling facet. An advantage of this design can be that the definition of the current aperture, e.g., by an oxide aperture, implantation, or buried tunnel diode, can be independent of the optical structure of the output coupling facet described here. It is not necessary for the current aperture to precisely match the optical structure orThe inventors recognized that lateral transport of charge carriers, for example in quantum trenches of an active zone, also contributes to amplification through current injection, which occurs approximately 1 pm or a few pm offset from the mode. This can be advantageously exploited by performing current injection across the entire surface and over a slightly larger area than would correspond to (optical) mode selection. As a result, despite a selected, spatially narrow mode, the current is applied over a larger diameter. This reduces the current density and can result in a significantly increased lifespan.

[0062] It is understood 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 stromal aperture. Simple examples are: (a) a circular stromal aperture with an elliptical or annular facet; (b) an essentially oval facet, possibly with an additional constriction; (c) a rectangular stromal aperture with an elliptical facet or a facet with multiple maxima, as exemplified in Figs. 1 and 2; (d) a circular or rectangular stromal aperture with a metastructure on the output coupling facet, which essentially corresponds to the mode pattern of a preferred mode.

[0063] In a further variation of the vertical-emitting semiconductor laser device 1 shown in Fig. 3, the mode-selective macrostructure is an optional feature. The vertical-emitting semiconductor laser device 1 can be a VCSEL with 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 device 1 has an upper output facet 20 for the laser radiation 5. The upper output facet 20 has a polarization-selective microstructure 22. The semiconductor laser device 1 is configured to exhibit a light intensity decrease of no more than 3 dB compared to excitation at 1 GHz when excited at high frequencies up to 25 GHz, and particularly when excited at 25 GHz.

[0064] Fig. 4 shows a schematic representation of a chip 40 with a vertically emitting semiconductor laser component 1. The chip 40 has a carrier 41 on which the semiconductor laser component 1 is arranged. 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 bond wires 44, 45. The provision of such a chip facilitates the handling of the vertically emitting semiconductor laser component 1. Optionally, the chip 40 can include further functional elements, such as... include an amplifier, a modulator, or protective circuits such as ESD protection elements.

[0065] Fig. 5 shows a schematic representation of a communication system or transmitter for an optical communication system 50. The communication system or transmitter for an optical communication system comprises an input terminal 51 for receiving data, a modulator 52, and a vertically emitting semiconductor laser component 1 or a chip 40 containing such a laser. As described above, an input terminal 51 can be understood as an interface for receiving data. The received data can be converted by the modulator 52 and, for example, modulated onto the laser light 5 emitted by the vertically emitting semiconductor laser component 1 in the form of current modulation or voltage modulation.The communication system may also include a receiver (not shown) with a detector for detecting the modulated laser light and a demodulator which is designed to demodulate the detected laser light and convert it into data which can be output via an interface for data output.

[0066] Fig. 6 shows a flowchart of a process 100 for fabricating a vertically emitting semiconductor laser device. In a first step S101, a semiconductor substrate 12 is provided. In a second step S102, a layer sequence for a lower Bragg mirror is deposited on the semiconductor substrate. In a third step S103, an active layer with an active zone for generating laser radiation is deposited on the lower Bragg mirror. In a fourth step S104, a layer sequence for an upper Bragg mirror is deposited on the active layer.In a first variant of a method for fabricating a vertically emitting semiconductor laser device, a fifth step (S105) provides an upper output facet for the laser radiation on the upper Bragg mirror, wherein the upper output facet has both a mode-selective macrostructure and a polarization-selective microstructure. Such an output facet can be provided by depositing further layers and structuring them, or by structuring one or more existing layers, such as the upper layers of the upper Bragg mirror. In a second variant... In a method for manufacturing a vertically emitting semiconductor laser device, in a fifth step S105 an upper output coupling facet for the laser radiation is provided on the upper Bragg mirror, wherein the upper output coupling facet has both a polarization-selective microstructure and wherein the semiconductor laser device is configured to have a light intensity decrease by no more than 3dB compared to an excitation at 1GHz when excited at high frequency up to a frequency of 25GHz.

[0067] According to one embodiment, an elliptically shaped surface relief with a grid structure can be applied to reduce noise (RIN) in datacom VCSELs. The number of modes can be reduced, and areas of unstable polarization can be avoided over a wide temperature and current range. By dimensioning the grid structure smaller than the wavelength, scattering losses can be avoided. Grids can also be implemented as an optical metastructure.

[0068] In summary, advantages of one or more aspects of the present invention may consist, in particular, of providing a further improved or alternative vertical-emitting semiconductor laser device, especially a VCSEL, for optical data transmission. One advantage may be that a vertical-emitting semiconductor laser device can be provided which enables high speeds in optical data transmission over a wide range of environmental conditions, especially over a wide temperature range. Alternatively or additionally, an advantage may be that a vertical-emitting semiconductor laser device can be provided which can be manufactured cost-effectively or with simplified process steps and / or with high yield.Alternatively or additionally, an advantage may be that a vertically emitting semiconductor laser can be provided, which improves the lifetime of Datacom VCSELs with low RIN.

Claims

Patent claims 1. A vertically emitting semiconductor laser component (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); characterized in that the vertically 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 macrostructure (21) and a polarization-selective microstructure (22).

2. Vertical-emitting semiconductor laser component (1) according to claim 1, wherein the coupling-out facet (20) with the mode-selective macrostructure (21) and the polarization-selective microstructure (22) is an optical structure which is arranged on an upper side of the upper Bragg mirror (2).

3. Vertically 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 macrostructure (21) of the coupling-out facet has a first region with a first layer thickness and wherein the mode-selective microstructure (22) of the coupling-out facet has a second region with a second layer thickness, in particular wherein the second layer thickness is smaller than the first layer thickness.

4. Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) is configured to favor a limited number of laser modes, in particular wherein the mode-selective macrostructure (21) is configured to favor a single laser mode.

5. Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) has a first region with a first reflectivity and a second region with a second reflectivity which differs from the first reflectivity.

6. Vertically emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (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.

7. Vertically emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) of the coupling-out facet (20) has an oval relief (24) with a constriction (25), in particular wherein the mode-selective macrostructure has an 8-shaped contour.

8. Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) is not rotationally symmetrical in a plane parallel to layers of the upper Bragg mirror and is designed to break a degeneracy of modes.

9. 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 polarizing the laser light (5).

10. Vertical-emitting semiconductor laser component (1) according to 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).

11. Vertically emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) and the polarization-selective microstructure (22) are formed together as an elliptically shaped surface relief (23) with an enclosed grating structure (26).

12. Vertically emitting semiconductor laser component (1) according to one of the preceding claims, wherein the mode-selective macrostructure (21) and the polarization-selective microstructure (22) are formed by an optical metastructure of the coupling-out facet (20), in particular wherein the coupling-out facet has an optical metastructure, a structure with spatially varying phase adaptation.

13. Vertical emitting semiconductor laser component (1) according to claim 12, wherein the optical metastructure is configured to provide a varying effective refractive index, wherein the optical metastructure has a varying density of turrets of constant height and an extension smaller than the wavelength.

14. Vertically emitting semiconductor laser component (1) according to one of the preceding claims, wherein the vertically 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 macrostructure (21, 23) of the coupling-out facet (20) with the polarization-selective microstructure (22).

15. Vertical emitting semiconductor laser component (1) according to one of the preceding claims, wherein the vertical emitting semiconductor laser component (1) is a VCSEL for optical data transmission.

16. Vertical-emitting semiconductor laser component (1) according to 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 less than -100 dB / Hz, in particular less than -120 dB / Hz, in particular less than -140 dB / Hz.

17. Vertical-emitting semiconductor laser component (1) according to one of the preceding claims, wherein the vertical-emitting semiconductor laser component (1) is designed to be able to change the wavelength range by not more than to drop in its light intensity by more than 3dB compared to an excitation at 1GHz.

18. Use of a surface relief on an output facet (20) of a VCSEL, wherein the surface relief of the output facet (20) has a mode-selective macrostructure (21) and a polarization-selective microstructure (22), in a communication system (50) for optical data transmission.

19. A vertically emitting semiconductor laser component (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); characterized in that the vertically 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 have a light intensity drop of no more than 3 dB upon high-frequency excitation up to a frequency of 25 GHz compared to excitation at 1 GHz.

20. A communication system (50) comprising an input terminal (51) for receiving data, a modulator (52) and a vertical emitting semiconductor laser component (1) according to one of the preceding claims.

21. A method (100) for manufacturing a vertical emitting semiconductor laser device, 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 with 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 facet for the laser radiation on the upper Bragg mirror, wherein the upper coupling facet has both a mode-selective macrostructure and a polarization-selective microstructure (S105).

22. A method (100) for manufacturing a vertical emitting semiconductor laser device, 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 with 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 no more than 3 dB when excited at high frequency up to a frequency of 25 GHz compared to an excitation at 1 GHz (S105).

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