Vcsel

Abstract

The invention relates to a VCSEL (10), which has an electrically pumpable laser emission region (12) for generating laser radiation which is emitted in a laser emission direction (z). The electrically pumpable laser emission region (12) has a length (L) in a first dimension (x) in a plane perpendicular to the laser emission direction (z), and a width (B) in a second dimension (y) perpendicular to the first dimension (x), wherein the length (L) is greater than the width (B) at least by a factor of two. In order to improve the performance of the VCSEL (10), the width (B-x, B+x) in a longitudinal end region of the laser emission region (12), which longitudinal end region is located on one side of a central region of the laser emission region (12) in the direction of the first dimension (x), is greater than the width (B0) in the central region.

Description

VCSEL

[0001] The invention relates to a VCSEL with an electrically pumpable laser emission region for generating laser radiation emitted in a laser emission direction, wherein the electrically pumpable laser emission region has a length in a first dimension and a width in a second dimension perpendicular to the first dimension in a plane perpendicular to the laser emission direction, wherein the length is at least twice as large as the width.

[0002] Such a VCSEL (vertical cavity surface emitting laser) is known from EP 4 131 676 A1.

[0003] VCSELs exhibiting an elongated laser emission region, i.e., whose extent in a first dimension is greater, in particular many times greater, than its extent in a perpendicular second dimension, are suitable for emitting a single higher-order laser mode. The VCSEL can be configured with a laser mode stabilization structure to stabilize the desired single higher-order laser mode. It has been observed in VCSELs, for example, in the configuration described in the aforementioned document EP 4 131 676 A1, that the temperature profile along the long dimension of the laser emission region changes with different operating currents, thereby causing a change in the refractive index profile along the long dimension of the laser emission region. This effect is also known as thermal lensing.Changing the refractive index profile along the long axis of the laser emission domain alters the shape of the laser mode. If the VCSEL incorporates a laser mode stabilization structure, such as a grating, optimized for a specific operating current (also called the target current), the laser mode will increasingly deviate from the stabilization structure as the operating current differs from the target current. This, in turn, reduces the efficiency and output power of the VCSEL, or, in the worst case, causes the desired higher-order laser mode to shift unintentionally to another higher-order laser mode. Furthermore, if the laser mode is to be coupled into a waveguide, the shifted desired or the unwanted laser mode may not fit the waveguide.

[0004] The invention is therefore based on the objective of providing a VCSEL of the type mentioned at the outset which is capable of emitting a single higher-order laser mode stably with high efficiency and output power even when the operating current of the VCSEL deviates from the target current.

[0005] According to the invention, this problem is solved with regard to the aforementioned VCSEL by the fact that the width of the electrically pumpable laser emission region in a longitudinal end region of the laser emission region, which is located in the direction of the first dimension on one side of a middle region of the laser emission region, is greater than the width in the middle region.

[0006] While conventional VCSELs, which have an elongated laser emission region, have a uniform width along their length, the VCSEL according to the invention is designed such that the width along the long axis is greater in at least one, preferably both, longitudinal end regions than in the central region between the longitudinal end regions. This shape of the electrically pumpable laser emission region, which deviates from an elongated rectangular form, counteracts the large temperature gradient between the central region of the laser emission region and its outer end regions, viewed along the long axis.

[0007] It has been found that, due to the greater width of the electrically pumpable laser emission region in the longitudinal end region(s), the longitudinal shift of the intensity peaks of the individual higher-order laser modes is lower with increasing deviation of the operating current from the target current than in a VCSEL whose electrically pumpable laser emission region has a constant width along its entire length. If the VCSEL is equipped with a laser mode stabilization structure, a smaller shift of the intensity peaks means that the overlap of the intensity peaks of the individual higher-order laser modes is better preserved even at larger deviations of the operating current from the target current. This, in particular, prevents the desired higher-order laser mode from being stabilized instead of another. The higher-order laser mode in the laser emission range is amplified and emitted instead of the desired laser mode.

[0008] The VCSEL according to the invention is thus able to stably generate and emit a single higher-order laser mode with high efficiency and high output power in the desired power range, even when the operating current deviates from the target current.

[0009] Preferred embodiments of the VCSEL according to the invention are specified in the dependent claims and / or are described below.

[0010] Preferably, the width in two longitudinal end regions on both sides of the central region is greater than the width in the central region.

[0011] This measure further counteracts the large temperature gradient between the central region of the laser emission area and its outer end regions, viewed along the long axis.

[0012] The longitudinal end regions each have a longitudinal end of the laser emission region, wherein a maximum width of the laser emission region is achieved in a respective longitudinal end region, which has a distance in the range of 0 pm up to the maximum width, preferably in the range of 0 pm up to half the maximum width from the respective longitudinal end.

[0013] The foregoing design takes into account the fact that the longitudinal end(s) of the laser emission region may deviate from a strictly straight contour parallel to the y-dimension, for example, they may have a rounded contour. In this case, the foregoing measure defines that the maximum width of the laser emission region is achieved in a longitudinal end section that has a distance from the longitudinal end that is less than the maximum width, preferably less than half the maximum width of the laser emission region.

[0014] Preferably, the width of the laser emission area in the longitudinal end region(s) is at least 10% of the width in the middle region, more preferably at least 20% of the width in the middle region, further preferably at least 30% of the width in the middle region, further preferably at least 40% of the width in the middle region, larger than in the middle region between the longitudinal end regions.

[0015] As the width of the laser emission region outside its longitudinal center increases relative to the width in the central region of the laser emission region, the temperature gradient between the central region and the longitudinal end regions can be further improved, so that the shift of the intensity peaks of the laser mode is increasingly reduced when the operating current is varied.

[0016] The invention proves to be particularly advantageous when the electrically pumpable laser emission region has a laser mode stabilization structure designed to stabilize a predetermined single higher-order laser mode.

[0017] As described above, the inventive design of the electrically pumpable laser emission region results in a more stable position of the intensity peaks of the individual higher-order laser mode relative to the laser mode stabilization structure, which is optimized for the intensity peaks of the laser mode at the target current, even with deviations of the operating current from the target current, thereby optimally stabilizing the desired individual higher-order laser mode.

[0018] In a preferred embodiment, the width of the electrically pumpable laser emission area increases continuously, at least section by section, from the central region to the longitudinal end regions with increasing distance from the central region.

[0019] In this configuration, the width of the electrically pumpable laser emission range, extending from the central region to the longitudinal end regions, can be considered a monotonically increasing function of the first-dimensional coordinate. In this configuration, there are no regions extending from the central region to the Longitudinal end regions in which the width of the electrically pumpable laser emission region decreases locally, although this is not excluded within the scope of the invention.

[0020] In a further preferred embodiment, the width of the electrically pumpable laser emission area increases linearly, at least section by section, from the central region to the longitudinal end region(s) with increasing distance from the central region.

[0021] In this configuration, the laser emission region can have a 'bowtie' shape if its width increases linearly from the center of the emission region to its longitudinal ends. It has been shown that in this configuration, the temperature at the center of the emission region is lower than in a conventional laser emission region with a constant width along its entire length.

[0022] The central region of the laser emission region can have the longitudinal center of the electrically pumpable laser emission region, wherein the width of the electrically pumpable laser emission region can increase continuously from the longitudinal center to the longitudinal end region(s) with increasing distance from the longitudinal center.

[0023] In this configuration, the narrowest width of the laser emission region is located in the center of the laser emission region, relative to the long dimension of the laser emission region.

[0024] Instead of a linear increase in width, in another embodiment of the VCSEL according to the invention the width of the electrically pumpable laser emission area can increase disproportionately at least section by section from the central region to the longitudinal end regions with increasing distance from the central region, for example according to a quadratic function.

[0025] In a further embodiment, the width of the laser emission range can increase from the central region to the longitudinal end regions with increasing distance from the central region according to a continuously differentiable function.

[0026] In this design, the two longitudinal edges along the long dimension have a corner- and edge-free shape.

[0027] In contrast, the width of the laser emission range can increase from the central region to the longitudinal end region(s) with increasing distance from the central region according to a step function.

[0028] The width can increase abruptly at one or more steps.

[0029] In a further embodiment, the laser emission region can have at least one section which has a partial length of the laser emission region, wherein the width of the laser emission region is constant in the at least one section.

[0030] The at least one section can be the central region of the laser emission region and / or the longitudinal end region on at least one side of the central region.

[0031] In this configuration, the laser emission area in the long dimension can, for example, have the shape of a dumbbell or a bone.

[0032] Likewise, a shape is possible in which the laser emission region has a first section and at least a second section on at least one side of the central region, wherein the first section is arranged closer to the central region than the at least one second section, wherein the first and the second section each have a partial length of the laser emission region, wherein the width of the laser emission region is constant in the first and at least one second section, and wherein the width of the at least one second section is greater than the width of the first section.

[0033] Preferably, the electrically pumpable laser emission region has mirror symmetry with respect to the first dimension and / or with respect to the second dimension.

[0034] The electrically pumpable laser emission region shapes described above can be achieved in various ways. For example, a mesa can be etched with a shape corresponding to the desired shape of the laser emission region, and then an oxide aperture is created by wet oxidation of an aluminum-rich layer of the semiconductor structure, which defines the electrically pumpable laser emission region.

[0035] Alternatively, several holes can be etched into the semiconductor layer structure along a corresponding outline contour, after which an aluminum-rich layer is oxidized to obtain an oxide aperture of the desired shape, which defines the active region or the electrically pumpable laser emission region.

[0036] The active region, or the electrically pumpable laser emission region, can alternatively be defined by ion implantation outside the laser emission region. Alternatively, the active region, or the electrically pumpable laser emission region, can also be defined by a laterally limited tunnel diode structure within the laser cavity.

[0037] Further advantages and features will become apparent from the following description and the attached drawing.

[0038] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0039] Exemplary embodiments of the invention are shown in the drawing and are described in more detail below with reference to them. The drawing shows: Fig. 1 schematically shows a VCSEL in a longitudinal section along line 11 in Fig. 2; Fig. 2 is a schematic top view of the VCSEL in Fig. 1 with a laser emission area according to the prior art; Fig. 3A is a diagram showing the dependence of the laser output power on the operating current; Fig. 3B shows a top view of a laser emission region of a prior art VCSEL, with an example of a laser mode with 16 intensity peaks when the operating current of the VCSEL is equal to the target current; Fig. 4A is a diagram illustrating the dependence of the laser output power on the operating current for three operating currents in a desired power range of the laser; Fig. 4B shows a top view of the laser emission area according to Fig. 3B at an operating current Imin that is smaller than the target current; Fig. 4C shows a top view of the laser emission area according to Fig. 3B at an operating current Lax that is greater than the target current; Fig. 5 schematically shows a top view of a VCSEL according to a first embodiment of the invention; Fig. 5A schematically shows a top view of a VCSEL according to an embodiment modified from Fig. 5; Fig. 6 shows a diagram that displays a temperature profile along the laser emission range for the VCSEL in Fig. 2 and the VCSEL in Fig. 5; Fig. 7A is the diagram of Fig. 4A; Fig. 7B is a top view as in Fig. 3B, but showing the laser emission area of ​​the VCSEL in Fig. 5 at an operating current that is smaller than the target current; Fig. 7C is a top view as in Fig. 4B, but showing the laser emission area of ​​the VCSEL in Fig. 5 when the operating current is equal to the target current; Fig. 7D is a top view as in Fig. 4C, but showing the laser emission area of ​​the VCSEL in Fig. 5 at an operating current Lax that is greater than the target current; Fig. 8 shows a diagram showing the shift of intensity peaks of a laser mode for a prior art VCSEL and for a VCSEL according to Fig. 5 at different operating currents; Fig. 9 schematically shows a top view of a VCSEL according to a further embodiment of the invention; Fig. 10 schematically shows a top view of a VCSEL according to a further embodiment; Fig. 11 schematically shows a top view of a VCSEL according to a further embodiment of the invention; Fig. 12 schematically shows a top view of a VCSEL according to a further embodiment of the invention; Fig. 13 schematically shows a top view of a VCSEL according to a further embodiment of the invention; Fig. 14 shows a diagram similar to the diagram in Fig. 6, which shows temperature profiles along the laser emission region for different configurations of the shape of the laser emission region.

[0040] With reference to Figures 1 to 4, a VCSEL 200 according to the state of the art and the technical problem existing with it are first described.

[0041] The VCSEL 200 has an electrically pumpable laser emission region 202. The laser emission region 202 is the active region of the VCSEL 200 in which laser light is generated. The laser light exits the VCSEL 200 perpendicular to the semiconductor layer structure of the VCSEL 200. The laser emission direction is along a z-axis (Fig. 1), either the positive z-axis or the negative z-axis, depending on whether the VCSEL 200 is a bottom-emitter or a top-emitter. The x-axis is subsequently referred to as the x-dimension or long dimension, and the y-axis as the y-dimension or short dimension.

[0042] As shown in Fig. 1, the VCSEL has a semiconductor layer structure. Generally, the VCSEL 200 comprises a first mirror 204, a second mirror 206, and an active region 208 between the first mirror 204 and the second mirror 206. Laser light is generated in the active region 208 by electrically pumping the VCSEL 200. One of the two mirrors 204 and 206 is an output coupler for coupling the laser light out of the VCSEL 200. The first mirror 204 and the second mirror 206 can be configured as Bragg mirrors, as is known in the field of VCSELs. The active region 208 can include one or more quantum wells.

[0043] The electrically pumpable laser emission region 202 has a length L in the x-dimension from a first longitudinal end 210 to a second longitudinal end 212 of the laser emission region 202, which is greater than a width B of the laser emission region 202 in the y-dimension. The ratio of the length L to the width B can be very large, is at least 2, and can, for example, also be greater than 5, or even greater than 10.

[0044] In the fabrication of the VCSEL 200, after the semiconductor layer structure has been built up, a trench 214 is etched into the semiconductor layer structure. An outer edge 216 of the trench 214 is indicated by a dashed line in Fig. 2. Within the trench, the VCSEL 200 has the shape of a mesa in the xy-plane.

[0045] The VCSEL 200 features an oxide aperture 218, which has a non-oxidized inner region 220 and an oxidized outer region 222. The oxide aperture 218 is typically created by oxidizing one or more layers with a high aluminum content, located, for example, near the active region 208. The oxidized outer region 222 acts as an electrical insulator, so that during electrical pumping of the VCSEL 200, the current flows only through the non-oxidized inner region 220 of the oxide aperture 218. The shape and size of the non-oxidized region 220 correspond to the shape and size of the laser emission region 202.

[0046] The preceding description also applies to a VCSEL according to the invention. In contrast to a VCSEL according to the invention, the electrically pumpable laser emission region 202 of the VCSEL 200 according to Fig. 2 has a homogeneous or constant width B over its entire length L. It has been shown that with different operating currents, at which the VCSEL 200 is operated in a desired power range, the temperature profile along the long dimension, i.e., the x-dimension, changes, which in turn leads to a change in the refractive index. This is also referred to as thermal lensing. The change in the refractive index profile alters the shape of the single higher-order laser mode emitted by the VCSEL 200.If the VCSEL 200 has a laser mode stabilization structure optimized for a specific target current within the desired power range, the generated laser mode will increasingly mismatch the laser mode stabilization structure as the operating current deviates from the target current. This reduces the efficiency and output power of the VCSEL 200, or in the worst case, results in the emission of a different, higher-order laser mode instead of the desired one. This is explained in more detail below.

[0047] Fig. 3B shows a laser mode that exemplarily exhibits 16 intensity peaks 240; (i = 1 , ... ., 16). In Fig. 3B, a laser mode is indicated by white outline lines 242;, i = 1 , ...., n A stabilization structure is shown, which has a corresponding number of facets or localized gratings corresponding to the number of intensity peaks, with each of the facets 242 being centered with respect to one of the intensity peaks 240, and with the facets 242j providing higher reflectivity than the areas outside the facets. For high efficiency and output power, it is important that the individual intensity peaks 240 of the laser mode have as large an overlap as possible with the facets 242. In Fig. 3B, the calculated overlap in this example is 93%. This comparatively high overlap results for an operating current I that exactly matches the target current l. t according to Fig. 3A, to which the laser mode stabilization structure, i.e. the position of the facets 242, is optimally adapted.

[0048] However, if the operating current in a power range 246 according to Fig. 4A differs from the target current l tdeviates, i.e., is lower or higher than the target flow l t Depending on the specific circumstances, the forming thermal lens exhibits a lower or higher refractive power, so that the intensity peaks of the desired laser mode are shifted outwards in the x-dimension when the current in is smaller than the target current, as shown in Fig. 4B, or when the current Lax is larger than the target current l t is shifted towards the center of the laser emission region 202 in the x-dimension, as shown in Fig. 40. This means that the intensity peaks of the desired laser mode are shifted at a current Lin that is smaller than the target current l. t , and in the case of a current Lax that is greater than the target current l t, relative to the facets 242; of the laser mode stabilization structure are shifted, so that the overlap of the intensity peaks 240; with the facets 242; is reduced, in the example shown in Fig. 4B to about 71% and to 79% in Fig. 40. It can even happen that if a different higher-order laser mode with a number of intensity peaks greater or less than 16 better matches the laser mode stabilization structure and thus begins to form lasers, the VCSEL emits this undesired mode either in addition to or instead of the desired laser mode.

[0049] This undesirable effect occurs both with operating currents that are smaller than the target current l t , as well as in the case of operating currents that are greater than the target current l t , in the latter case the overlap of the intensity peaks 240; with the facets 242; in the example shown is reduced to 79% compared to the state in Fig. 3B.

[0050] With reference to Figures 5 ff., exemplary embodiments of VCSELs are described below in which the aforementioned problem is solved or at least reduced.

[0051] The semiconductor layer structure of the VCSEL 10 described below can be the same as that shown in Fig. 1, i.e., with the mirrors 204, 206, the active region 208, and the oxide aperture 218. Therefore, the VCSELs 10 in Figures 5 ff. are shown only in a view corresponding to the view in Fig. 2, i.e., a top view of a laser emission region 12 of the respective VCSEL 10. The active region, or the electrically pumpable laser emission region, can alternatively be defined by ion implantation instead of the oxide aperture 218, or by a laterally limited tunnel diode structure within the laser cavity.

[0052] Fig. 5 shows a first embodiment of a VCSEL 10 with a laser emission region 12 having a length L in the x-dimension from a first longitudinal end 14 to a second longitudinal end 16. Fig. 5 further shows an oxidized region 18 of an oxide aperture, the inner edge of which forms a circumferential border 15 of the electrically pumpable laser emission region 12. Fig. 5 also shows a trench 20 surrounding the VCSEL 10, as already described above with reference to Fig. 2.

[0053] While in Fig. 5 and the following figures the end faces of the laser emission region 12 forming the longitudinal ends 14, 16 are shown as straight lines, it is understood that the end faces can also be rounded, at least at their transition to the longitudinal sides 15 of the laser emission region, as shown in Fig. 5A for the embodiment in Fig. 5. Fig. 5A shows, by way of example, semicircular longitudinal ends 14, 16 of the laser emission region 12.

[0054] In contrast to the VCSEL 200 according to Fig. 2, the laser emission region 12 of the VCSEL 10 does not have a consistently constant width B in the x-dimension, but rather a variable width B. The laser emission region 12 has a width B_ in one, preferably both, longitudinal end regions LE and L+E. x or B +x on, which is or are larger than a width Bo in a central region between the longitudinal end regions. The central region can be limited to the center or longitudinal midpoint (x = 0) of the laser emission region 12 in the x-dimension, or it can include a region on both sides of the longitudinal midpoint.

[0055] In the embodiment shown in Fig. 5, the width increases continuously in the x-dimension with increasing distance from the longitudinal center, starting from the width Bo at the center of the laser emission region 12, and in the embodiment according to Fig. 5, particularly linearly. The laser emission region 12 of the VCSEL 10 in Fig. 5 thus has the contour of a 'bowtie'.

[0056] In the embodiment shown in Fig. 5, the maximum width is B. x of the laser emission area 12 at the longitudinal end 14 or the maximum width B +xat the longitudinal end 16 of the laser emission area 12, i.e. at a respective distance of 0 pm from the respective longitudinal end 14 or 16. In the embodiment shown in Fig. 5A, the maximum width is B. x at a distance of B. x / 2 from the longitudinal end 14 is reached. In general, the maximum width is B. x or B +x in a longitudinal end section LE or L+E, the distance of which to the longitudinal end 14 or 16 is less than or equal to B. x or B +x In other words, the maximum width of the laser emission region 12 at a position of one or both longitudinal end regions can be between L / 2 and L / 2 - B. +x , preferably between L / 2 and L / 2 - B. +x / 2, are located

[0057] For this and all subsequent embodiments to be described, the (maximum) width B_ x or B +xof the electrically pumpable laser emission region 12 in the longitudinal end regions LE and L+E is at least 10% larger than the width Bo, where the width B_ x or B +x Bo can even be up to 50% or more larger in width than Bo.

[0058] Fig. 6 shows a diagram in which the temperature of the laser emission region 12 is plotted along the x-dimension, once for the laser emission region 12 of the VCSEL 10 in Fig. 5 and once for the laser emission region 202 of the VCSEL 200. Curve 22 shows the temperature profile for the VCSEL 10 in Fig. 5, and curve 24 shows the temperature profile for the VCSEL 200 in Fig. 2.

[0059] Figure 6 shows that the temperature Toi at the center of the laser emission region 12, relative to the x-dimension, of the VCSEL 10 is lower than the temperature T02 at the center of the laser emission region 202, relative to the x-dimension, of the VCSEL 200 in Figure 2. Accordingly, the temperature difference between T01 and the temperature TL-E or TL+E at the outer edge regions relative to the x-dimension, here in the example shown at a distance of approximately -30 pm and +30 pm from the center, is smaller than the difference between the temperature T02 at the center of the laser emission region 202 and the temperature TL-E or TL+E at the outer edge regions relative to the x-dimension at -30 pm and 30 pm, respectively, of the VCSEL 200 in Figure 2.The lower temperature gradient between the center of the laser emission region 12 and the longitudinal outer regions of the laser emission region 12 results in a smaller shift of the intensity peaks 240j relative to the facets 242; when the operating current in the desired power range 246 differs from the target current l. t deviates downwards or upwards. This is illustrated in Figs. 7A to 7D. Fig. 7A shows the desired power range of the VCSEL 10 in Fig. 5, and Fig. 7B shows the intensity peaks 240; the laser mode relative to the facets 242j of the laser mode stabilization structure at the current < It, Fig. 7C at the current l t (Target stream), and Fig. 7D at stream l max > lt . Figures 7B and 7D show a significantly improved overlap of the intensity peaks 240; with the facets 242j for the current hin and for the current hax compared to the overlap in the corresponding cases of the laser emission region 202 of the VCSEL 200. The overlap of the intensity peaks 240; with the facets 242; for the current hin is 85% in this example, and for hax it is 91%, compared to the values ​​of 71% and 79% for the conventional VCSEL 200.

[0060] Due to the shape of the laser emission area 12 and the resulting different thermal lensing at the target current l t The shape of the laser mode may differ slightly from that of the VCSEL 200. However, by adjusting the positions of the facets 242 and the laser mode stabilization structure, the same overlap in the target current l can be achieved. t as achieved with the VCSEL 200.

[0061] Fig. 8 shows the shift of the positions of the intensity peaks 240 for the laser emission range 12 according to Fig. 5; for the 9th to 16th intensity peak, at a current I that is 50% of the target current l t is (curve 40 in Fig. 8), at a current I that is 150% of the target current l t is (curve 42 in Fig. 8). Furthermore, Fig. 8 shows, for a laser emission range such as the laser emission range 202 of the conventional VCSEL 200, the shift in the positions of the intensity peaks 240; for the 9th to 16th intensity peak at a current I that is 50% of the target current l t is (curve 44 in Fig. 8), at a current I that is 150% of the target current l t is (curve 46 in Fig. 8), at a current I that is 66% of the target current l t is (curve 48 in Fig. 8), as well as at a current I that is 133% of the target current l tThe curve is shown in Fig. 8 (curve 50). It can be seen from Fig. 8 that all intensity peaks shift significantly more in the VCSEL 200 than in the VCSEL 10 in Fig. 5, and that the shift of the intensity peaks in the VCSEL 10 in Fig. 5 is even smaller at larger deviations of the operating current from the target current (50% and 150%) than the shift of the intensity peaks in the VCSEL 200 at only smaller deviations of the operating current from the target current (66% and 133%). This shows that the stability of the desired laser mode with respect to varying operating currents or ambient temperatures is significantly increased in the VCSEL 10 according to the invention compared to the VCSEL 200.

[0062] Figures 9 to 13 show further embodiments of VCSELn 10, the representation in Figures 9 to 13 corresponding to the representation in Figure 5. However, for the sake of simplicity, the oxide blend 18 and the trench 20 have been omitted compared to Figure 5. Furthermore, for elements of the VCSELn 10 in Figures 9 to 13 that are comparable, similar, or identical to elements of the VCSEL 10 in Figure 5, the same reference numerals are used as in Figure 5 for the sake of simplicity.

[0063] In Figures 9 to 13, B_ x and B +x The width of the laser emission region 12 in the longitudinal end regions LE and L+E (see Fig. 5) of the laser emission region 12 is given by , and Bo is the width of the laser emission region in the middle region, relative to the x-dimension of the laser emission region 12. The y- and x-axes are not shown in Figures 9 and 13, with reference to Fig. 5 for orientation.

[0064] Fig. 9 shows an embodiment of the laser emission region 12, in which the electrically pumpable laser emission region 12 has a section in the x-dimension with a partial length Lo of the entire electrically pumpable laser emission region 12, wherein the width Bo of the electrically pumpable laser emission region 12 is constant along the partial length Lo. The section with partial length Lo is the central region of the laser emission region 12. From the section with partial length Lo, the width B of the laser emission region 12 increases continuously towards the longitudinal end sections, here up to the longitudinal ends of the laser emission region. The increase in width B can be linear, as shown.

[0065] Fig. 10 shows an embodiment of the laser emission region 12, in which the width B increases from the width Bo in the center of the laser emission region 12 with increasing distance from the center according to a non-linear function towards the longitudinal end regions. The width B can increase disproportionately, at least section by section, with increasing distance from the center of the laser emission region 12, e.g. according to a function ~x n , where n is a natural or real number > 1.

[0066] Fig. 11 shows an embodiment of the laser emission region 12 in which the longitudinal end regions extend over a partial length L x or L +x of the entire laser emission range 12, where the width B_ x or B +x over the partial length L_ x or L +xis constant. From the center of the laser emission region 12, the width Bo remains constant up to the longitudinal end regions, with the width Bo decreasing stepwise into the width B_. x or B +x transitions. Here too, the width B_ applies. x or B +x is greater than the width Bo. The shape of the laser emission area in Fig. 11 can be described as a dumbbell or bone with rectangular end sections. In Fig. 11, a modified embodiment of the laser emission area 12 is shown with dashed lines 70, in which the longitudinal end sections widen towards the longitudinal ends, i.e., the width B_ x or B +x in the longitudinal end sections is not constant, but viewed from the center of the laser emission region 12, from width Bo continuously, in particular linearly, to width B_ x or B +x increases.

[0067] Fig. 12 shows a modified embodiment of a VCSEL 10 compared to Fig. 11, with a laser emission area 12 whose width B is determined from a width Bo in the The middle region of the laser emission range 12 in the x-dimension increases stepwise in two successive sections 72, 74, namely in a first section 72 initially to a width B2, and then in a second section 74, which includes the longitudinal end sections, via a further step to the width B_ x or B +x The width B2 in section 72 facing the central area is greater than Bo and less than the width B_ x or B +x .

[0068] Fig. 13 shows an embodiment of a VCSEL 10 with a laser emission area 12 in a modification of the embodiment in Fig. 12, in which the transition from width B to width B2 and from there to width B_ x or B +xsteadily and differently increasing, so that there are no sharp edges in the longitudinal edges of the laser emission area 12.

[0069] Fig. 14 shows the diagram from Fig. 6 again, with the addition of the temperature profiles for the embodiment in Fig. 5 (curve 22) and for the VCSEL 200 according to Fig. 2 (curve 24) to the temperature profiles for the embodiment in Fig. 11 with longitudinal end sections of constant width (curve 60) and with widening longitudinal end sections (curve 62). Fig. 14 shows that in the embodiment according to Fig. 11, in both variants (constant width longitudinal end sections or widening longitudinal end sections), a further reduction of the temperature gradient between the center of the laser emission region 12 (relative to the x-dimension) and the longitudinal outer regions can be achieved, thereby enabling even better stabilization of the desired single higher-order laser mode.

[0070] In all embodiments, the laser emission regions 12 exhibit mirror symmetry with respect to both the x-dimension and the y-dimension. If mirror symmetry is lacking in one or both dimensions, the two longitudinal end sections on either side of the center of the laser emission region can have different widths.

[0071] The VCSEL 10 can be fabricated according to the embodiments described above by etching a mesa of a corresponding shape and subsequently oxidizing an aluminum-rich layer to achieve the desired shape of the oxide aperture that defines the electrically pumpable laser emission region. Alternatively, several holes can be etched along a corresponding contour into the semiconductor layer structure, followed by oxidation of an aluminum-rich layer to achieve the desired shape of the oxide aperture that defines the electrically pumpable laser emission region. As a further alternative, the electrically pumpable laser emission region can be defined by ion implantation on the outside of the desired shape of the laser emission region. As a further alternative, the active region or the electrically pumpable laser emission region can also be defined by a laterally confined tunnel diode structure within the laser cavity.

Claims

Claims 1. VCSEL, comprising an electrically pumpable laser emission region (12) for generating laser radiation emitted in a laser emission direction (z), wherein the electrically pumpable laser emission region (12) has a length (L) in a first dimension (x) and a width (B) in a second dimension (y) perpendicular to the first dimension (x), wherein the length (L) is at least two times greater than the width (B), characterized in that the width (B) x , B +x ) in a longitudinal end region of the laser emission region (12), which is located in the direction of the first dimension (x) on one side of a middle region of the laser emission region (12), is greater than the width (Bo) in the middle region.

2. VCSEL according to claim 1, wherein the width (B. x , B +x) in two longitudinal end regions on both sides of the middle region is greater than the width (Bo) in the middle region.

3. VCSEL according to claim 1 or 2, wherein the longitudinal end regions each comprise a longitudinal end (14, 16) of the laser emission region (12), and wherein a maximum width (B. x , B +x ) of the laser emission range (12) is reached in a respective longitudinal end region which has a distance in the range from 0 pm to the maximum width (B. x , B+ x ), preferably in the range from 0 pm to half the maximum width (B. x , B +x ) from the respective longitudinal end (14, 16).

4. VCSEL according to any one of claims 1 to 3, wherein the width (B. x , B +x) of the laser emission region (12) in the longitudinal end regions by at least 10% of the width (Bo) in the middle region, preferably at least 20% of the width (Bo) in the middle region, further preferably at least 30% of the width (Bo) in the middle region, further preferably at least 40% of the width (Bo) in the middle region is greater than the width (Bo) of the laser emission region (12) in the middle region.

5. VCSEL according to any one of claims 1 to 4, wherein the laser emission region (12) has a laser mode stabilization structure (242) designed to stabilize a predetermined single higher-order laser mode.

6. VCSEL according to any one of claims 1 to 5, wherein the width (B) of the laser emission area (12) increases continuously, at least section by section, from the central region to the longitudinal end regions with increasing distance from the central region.

7. VCSEL according to any one of claims 1 to 6, wherein the width (B) of the laser emission area (12) increases linearly at least section by section from the central area to the longitudinal end area(s).

8. VCSEL according to any one of claims 1 to 6, wherein the width (B) of the laser emission area (12) increases disproportionately from the central area to the longitudinal end areas with increasing distance from the central area.

9. VCSEL according to any one of claims 1 to 8, wherein the width (B) of the laser emission area increases from the central region to the longitudinal end regions with increasing distance from the central region according to a continuously differentiable function.

10. VCSEL according to any one of claims 1 to 8, wherein the width of the laser emission area increases from the central region to the longitudinal end regions with increasing distance from the central region according to a step function.

11. VCSEL according to any one of claims 1 to 10, wherein the laser emission region (12) has at least one section comprising a partial length (Lo, L. x , L +x ) of the laser emission range (12) wherein in at least one section the width (Bo, B. x , B +x , B2) of the laser emission range (12) is constant.

12. VCSEL according to claim 11, wherein the at least one section is the central region of the laser emission region (12).

13. VCSEL according to claim 11 or 12, wherein the at least one section is the longitudinal end region on at least one side of the central region.

14. VCSEL according to any one of claims 1 to 13, wherein the laser emission region (12) has a first section (72) and at least a second section (74) on at least one side of the central region, wherein the first section (72) is arranged closer to the central region than the at least one second section (74), wherein the first and the second section (72, 74) each have a partial length of the laser emission region (12), wherein in the first and at least one second section (72, 74) the width (B. x , B +x , B2) of the laser emission range (12) is constant, and where the width (B. x , B +X )of at least one second section (74) is larger than the width (B2) of the first section (72).

15. VCSEL according to any one of claims 1 to 14, wherein the laser emission area (12) is mirror-symmetric with respect to the first dimension (x).

16. VCSEL according to any one of claims 1 to 15, wherein the laser emission area (12) is mirror-symmetric with respect to the second dimension (y).

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