Vcsel for emitting laser light

Abstract

The invention relates to a VCSEL (10) for emitting laser light (17), having a resonator which comprises an out-coupling mirror (44) with an emission region (40) on the outer surface thereof, wherein a direction-selective optical element (46) is arranged on the emission region (40) such that most of the laser light (17) of a first direction (1) can exit the optical element (46), and most of the laser light (17) of a second direction (2) is reflected at the outer boundary surface (48) of the optical element (17). The invention also relates to an arrangement having the VCSEL (10), wherein the laser light (17) exiting the optical element (46) is in-coupled into a light guide element (12).

Description

[0001] VCSEL for emitting laser light

[0002] The invention relates to a VCSEL for emitting laser light according to the main claim.

[0003] State of the art

[0004] A VCSEL (vertical-cavity surface-emitting laser) is a semiconductor laser with an active region sandwiched between stacks of mirrors, which can be Bragg mirrors [NM Margalit et al., "Laterally Oxidized Long Wavelength CW Vertical Cavity Lasers", Appl. Phys. Lett., 69 (4), 22 July 1996, pp. 471-472] or a combination of semiconductor and dielectric DBRs [Y. [Oshio et al., "Vertical-Cavity Surface-Emitting Lasers with Wafer-Fused InGaAsP / lnP-GaAs / AIAs DBRs", Electronics Letters, Vol. 32, No. 16, 8. 1996] One of the mirror stacks is typically partially reflective to allow some of the coherent light to pass through, which builds up in a resonant cavity formed by the mirror stacks enclosing the active region. The VCSEL is driven by a current passed through the active region.Mirror stacks are typically formed from multiple pairs of layers made from a material system that generally consists of two materials with different refractive indices, slightly lattice-matched to the other parts of the VCSEL. For example, a GaAs-based VCSEL typically uses an AlAs / GaAs or AIGaAs / AIAs material system, with the different refractive index of each layer in a pair achieved by varying the aluminum content in the layers.

[0005] US Patent 11,392,248 B2 discloses structures for detecting touch and force inputs at multiple detection points on the surface of an electronic device using waveguide-based interferometry. A laser light source, such as a VCSEL, couples light into a waveguide positioned adjacent to the detection points. An input at a detection point influences the coupled light in the waveguide, enabling the determination of the touch or force input at that point. The light is coupled essentially perpendicularly into the waveguide's coupling points, resulting in back reflections. Due to these back reflections, not all of the VCSEL's light is coupled into the waveguide, thus reducing the efficiency of the arrangement or requiring a higher VCSEL power output to couple sufficient light into the waveguide.Furthermore, the reflected light can lead to undesirable influences, such as interference, in the VCSEL, which can disrupt the proper operation of the VCSEL or even lead to damage or destruction of the VCSEL.

[0006] Disclosure of the invention

[0007] The object of the invention is to provide a VCSEL (vertical-cavity surface-emitting laser) that can be used in an arrangement consisting of a VCSEL and a light guide, exhibiting lower reflection of the coupled light into the VCSEL compared to the prior art, thus reducing undesirable influences on the arrangement. A further object of the invention is to provide a VCSEL (vertical-cavity surface-emitting laser) that can be used in an arrangement consisting of a VCSEL and a light guide, requiring less power compared to conventional arrangements while maintaining the same efficiency.

[0008] It is proposed to provide a VCSEL for emitting laser light, wherein the VCSEL has a resonator having an output coupler having an emission region on its outer surface, wherein a direction-selective optical element is arranged on the emission region such that laser light of a first direction can mostly exit the optical element and laser light of a second direction is mostly reflected at the outer interface of the optical element.

[0009] The advantage of this VCSEL is that laser light of the first direction can be coupled into an optical fiber that is essentially parallel and perpendicular to the optical axis of the VCSEL, without strong feedback within the VCSEL caused by reflections of the laser light from the surface of the optical fiber. Such an arrangement exhibits improved coupling efficiency and reduced back reflection and feedback, since the laser light does not strike the optical fiber perpendicularly but along the first direction, thus reducing the amount of reflected light and consequently minimizing unwanted feedback.

[0010] The technical effect is that the arrangement of the VCSEL and the optical fiber reduces back reflection by preventing the laser light from being coupled perpendicularly into the optical fiber. This further leads to improved signal transmission quality and efficiency. Such an arrangement is particularly advantageous for data communication applications.

[0011] Data communication applications using light refer to the transmission of information through light waves, also known as optical transmission. The transmission of information through light has gained importance in recent years and is used in many applications, particularly in telecommunications, data communication, and computer data transmission.

[0012] In telecommunications, waveguides are used to transmit large amounts of data over long distances. Light pulses are used to transmit digital information from a transmitter to a receiver. In computer data transmission, optical transmission systems are used to transfer data between devices in high-speed networks.

[0013] The advantages of optical transmission over conventional electronic transmission lie primarily in its higher transmission capacity, lower latency, higher signal quality, and reduced susceptibility to interference. This makes optical transmission particularly attractive for applications requiring the fast and reliable transmission of large amounts of data, such as HD or UHD television broadcasting, medical applications, and data transmission in data centers.

[0014] Further advantageous aspects of the invention are contained in the dependent claims.

[0015] Advantageously, the first and second directions are oriented differently relative to an optical axis of the VCSEL that is perpendicular to its surface. The optical axis of a VCSEL is an axis that runs essentially through the center of the VCSEL structure and is perpendicular to its surface. This axis forms the reference line for the symmetrical arrangement of components such as the emission regions of the VCSEL. For example, in the case of divergently emitted light, the optical axis can be the axis of symmetry of the light cone. It is particularly preferred that the optical element is applied to the outer surface without an air gap between the optical element and the outer surface, with the laser light entering the optical element from the emission region and propagating within the material of the optical element to the interface. It can be bonded or etched from the material of the VCSEL.

[0016] The VCSEL can be designed to have multiple emission regions on its surface that favor a higher-order laser mode. This can promote a laser mode that, for example, exhibits two intensity maxima in the far field.

[0017] Furthermore, the laser light can be in a laser mode which has a first and a second wavefront of maximum intensity in the far field of the laser light, which move along a first and second propagation axis respectively, diverging from each other by a travel angle.

[0018] In a particular embodiment of the invention, the first propagation axis is aligned along the first direction and the second propagation axis is aligned along the second direction, so that the first wavefront can largely exit the optical element and the second wavefront is largely reflected at the outer interface of the optical element.

[0019] Preferably, the optical element has a plane on the interface where laser light of the first direction exits and laser light of the second direction is reflected.

[0020] Preferably, a plurality of planes are provided at the interface, wherein the planes are aligned parallel to each other and not perpendicular to the optical axis. The planes are connected to each other by intermediate surfaces that form a different angle with the optical axis than the planes themselves. For example, these surfaces can be aligned parallel to the optical axis, so that the optical element has a sawtooth cross-section.

[0021] The planes can have a reflective coating on their outer surface. This allows the reflection at or transmission through the interface to be adjusted. In the simpler case, the refractive index difference between typical semiconductors and air is sufficient for a noticeable phase shift of the wavefront.

[0022] Advantageously, the planes are separated from each other by a distance in the direction of the optical axis, so that the exit light and the reflected light from different planes of the interface are phase-shifted. In particular, the optical element can be a Littrow grating.

[0023] Furthermore, a reduction of the total reflection in the first direction can be adjusted if the laser light hits the interface perpendicularly and, after the perpendicular reflection, is not in phase with the laser light coupled out of the output mirror, so that the laser light exits the optical element.

[0024] According to another embodiment, an increase in the total reflection in the first direction can be achieved if the laser light incident perpendicularly on the interface and reflected from the interface is in phase with the laser light coupled out from the output mirror, so that the laser light largely does not exit the optical element. The optical element can be made of GaAs as a refractive optical element or of Si as a meta-optic element. Meta-optic elements can be fabricated in various shapes and sizes, from tiny nanostructures to macroscopic materials. They can also be made of various materials, including metals, semiconductors, and polymers, depending on the application and desired functionality.

[0025] Furthermore, an arrangement with a VCSEL is provided which couples laser light exiting the optical element into a light guide element, wherein the propagation axis of the laser light encloses an angle with a coupling surface of the coupling area which is different from 90°.

[0026] The optical waveguide element is a waveguide for electromagnetic waves, and the coupling surface is part of a coupling grating. The coupling grating can have multiple coupling surfaces, which are preferably at least partially parallel and / or coplanar to each other. The wavefronts of the light propagate with high intensity along the propagation axis. The propagation axis of the laser light refers to the direction in which the light wave propagates. With respect to the wavefronts of the laser light, the propagation axis corresponds to the normal to the wavefront. These normals are lines perpendicular to the wavefront and indicate the direction of light propagation. The propagation axis is thus the axis that defines the direction of propagation of the laser light and along which the wavefronts move.

[0027] The advantage of this arrangement is that it offers improved coupling efficiency and reduced back reflection. Since the laser light is coupled into the optical fiber at a different angle, the amount of reflected light can be reduced, resulting in improved signal transmission quality. Further features and advantages of the invention will become apparent from the following description with reference to exemplary embodiments and the drawings. Although the invention is shown and disclosed in detail in the figures and the preceding description, these illustrations and descriptions are to be considered purely illustrative or exemplary and not as limiting. 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 individually.Directions given in the text correspond to the reading direction of the drawings.

[0028] Brief description of the drawings

[0029] They show:

[0030] Fig. 1 shows a top view of a VCSEL with a plurality of

[0031] Emission ranges for generating a higher-order laser mode,

[0032] Figs. 2A to 2B show several images of intensity distributions in the afterfield and farfield of laser light emitted by the VCSEL.

[0033] Figs. 3A and 3B show an arrangement consisting of a VCSEL and a chip with a light guide.

[0034] Fig. 4 shows a coupling grid for coupling laser light into the

[0035] Optical fibers

[0036] Fig. 5 shows a VCSEL with an optical element for conveying a

[0037] Propagation direction of the light, and Fig. 6 a section through the optical element.

[0038] Figure 1 shows an exemplary VCSEL 10, which has a plurality of emission regions 40 on its surface 42 that favor a higher-order laser mode. The emission regions 40 are arranged linearly along an axis 13. Because the reflectivity at the locations of the emission regions 40 is increased compared to the rest of the surface 42, a specific laser mode is favored. In particular, a laser mode is favored whose laser light in the near field of the VCSEL 10 has a number of intensity maxima 11 that corresponds to the number of emission regions 40. The advantage of such a VCSEL 10 is that an intensity distribution with a desired shape can be generated in the far field of the VCSEL 10.

[0039] Figure 2A shows a representation of the near field of a VCSEL 10 formed according to the principles of Figure 1. The near field refers to the region in the immediate vicinity of the VCSEL 10 where the wavefronts of the laser light are not yet fully formed and the light field behaves irregularly. A plurality of intensity maxima 11 of the laser light are shown there, arranged along an imaginary line and generated by the VCSEL 10. The intensity maxima 11 are approximately equidistant from their neighbors along the entire axis 13, and the intensity of the individual maxima is approximately the same. Figure 2B shows the spatial distribution along the axis 13 in micrometers. The intensity maxima 11 along the axis 13 are equidistant and have approximately the same intensity.

[0040] Figure 2B shows the local distribution along axis 13 in micrometers, with the numerical values ​​being exemplary. It shows that the zero point of axis 13 is located in the center, with the intensity maxima 11 along axis 13 being equidistant and exhibiting approximately the same intensity as read from the y-axis 15.

[0041] Figure 2C shows the intensity distribution in the far field of the laser. In the far field, the light field has stabilized and exhibits a higher intensity pattern. The laser light from Figures 2A and 2B shows, as illustrated in Figure 2C, two intensity maxima 11 in the far field, whose intensity (relative to the secondary maxima in Figures 2C and 2D, respectively) is higher than the relative intensity of the intensity maxima 11 from Figure 2A.

[0042] Figure 2D shows the intensity distribution of the intensity maxima from Figure 2C, where in the far field the x-axis indicates the propagation angle b, which is enclosed by the propagation axes of the wavefronts that produce the highest intensity. For example, the propagation angle b in Figure 2D is approximately 12° to 14°.

[0043] Figure 3A shows an arrangement consisting of a VCSEL 10 and an optical fiber 12, wherein the laser light from the VCSEL 10 is coupled into the optical fiber 12 via a coupling area 141, 142 located on the optical fiber 12. The coupling area 141, 142 is located on the surface 26 of the chip 24. After the laser light 17 has been coupled in, it is guided along the optical fiber 12 along the arrow shown in Figure 3A. The optical fiber 12 is preferably formed along the surface 26 of the chip body within the chip 24. The optical fiber 12 is particularly strip-shaped.

[0044] An optical fiber is a flexible or rigid, transparent strand that can transport light over long distances by reflecting it back through total internal reflection. This total internal reflection makes optical fibers very efficient, as very little light is lost. Optical fibers typically consist of a core made of transparent material with a higher refractive index than the surrounding material, and a cladding that encloses and reflects the light within the core. The surface of the core can be either smooth or textured to influence the propagation of the light.

[0045] Optical fibers are used in various applications, for example in data communication, where they serve as optical cables to transmit data in the form of light signals over long distances. In medical technology, optical fibers are used in endoscopes to transmit images from inside the body. In lighting technology, optical fibers can be used to direct or distribute light.

[0046] Figure 3B shows a top view of the arrangement from Figure 3A. The optical fiber is configured as a waveguide within the chip 24. Furthermore, the optical fiber element 12 is a waveguide within the chip 24, arranged on or in the surface 26 of the chip 24 and having the coupling area 141, 142, which points away from the surface so that the laser light 17 can be coupled in. The waveguide can contain silicon, silicon nitride, silicon oxide, and / or lithium niobate. The material is determined in particular by the wavelength of the introduced light and / or the intended application of the arrangement.

[0047] Figure 4 shows a coupling area 141, 142, which has at least one coupling surface 16. The coupling area 141, 142 is arranged on the surface of the light guide element 12. In particular, the coupling surfaces 16 are arranged on a structure having a crenellated cross-section.

[0048] A coupling grating is an optical component used to couple light from a light source into an optical fiber. The principle is based on a periodic grating of narrow lines or grooves created on a transparent substrate surface. This periodic grating acts like an optical grating filter, reflecting a specific wavelength of light and coupling the rest into the optical fiber.

[0049] The properties of the coupling grating depend on its geometry and materials. Typically, the grating consists of silicon-containing or another semiconducting material and is manufactured using lithography and etching processes. The width and depth of the grooves, as well as the spacing between them, determine the coupling efficiency.

[0050] The coupling grid is typically attached to one end of the optical fiber and allows light to be coupled into or out of the fiber. It is used in various applications, such as optical sensors, optical switches, optical interferometers, optical data transmission systems, and optical signal processing devices.

[0051] Figure 5 shows the VCSEL 10, which is designed to emit laser light 17. The VCSEL 10 has a resonator with an output coupling mirror 44, which has the emission region 40 on its outer surface. A direction-selective optical element 46 is arranged on the emission region 40, such that the laser light 17 in a first direction 1 can largely exit the optical element 46, while laser light 17 in a second direction 2 is largely reflected at the outer interface 48 of the optical element 40. Along the first direction 1, 0.1 to 1% of the laser light can be coupled out, and along the second direction 2, the effective total reflectivity of the interface 48 of the optical element 40 is higher, and thus the output coupling efficiency is lower. Three emission regions 40, each with an optical element 46, are shown in a side view in Figure 5 as examples.Accordingly, an optical element 46 can be arranged on each of the emission areas 40 in Figure 1.

[0052] The advantage of this VCSEL is that laser light 17 of the first direction 1 can be coupled into the optical fiber 12, which is oriented essentially perpendicular to the optical axis 18 of the VCSEL 10, without strong reflections of the laser light 17 at the surface of the optical fiber 12. For example, the first propagation axis 201 can be aligned with the first direction 1, so that the first wavefronts 181 along the first direction 1 can exit the optical element 46 and enter the optical fiber 12 without significant reflection losses, while the second wavefronts 182 of the second direction 2 are suppressed.

[0053] Preferably, the angle y is the same size as the angle x and is arranged on opposite sides of the optical axis 18.

[0054] The optical element 46 is applied to the outer surface 42 of the VCSEL 10 without an air gap. The laser light 17 enters the optical element 46 from the emission region 40 and propagates within the material of the optical element 46 to the interface 48. The optical element 46 can be bonded or etched from the material of the VCSEL 10.

[0055] The optical element 46 can be made of GaAs or Si and can be configured as a refractive optical element or as a meta-optic element. Meta-optic elements can be manufactured in various shapes and sizes, with nanostructures on the surface being optically active.

[0056] The first and second directions 1, 2 are oriented differently with respect to the optical axis 18 of the VCSEL 10, which is oriented perpendicular to the surface 42 of the VCSEL. According to Figure 6, the first direction 1 forms an angle x and the second direction 2 an angle y with the optical axis 18. Figure 6 shows a sectional view of a possible embodiment of the optical element 46. The interface 48 has a plurality of planes 50 at which laser light 17 of the first direction 1 and laser light 17 of the second direction 2 is partially reflected and partially transmitted. The planes 50 are planar and aligned parallel to each other. The planes 50 are not oriented perpendicular or parallel to the optical axis 18. The planes 50 are connected to each other by intermediate surfaces 52, which are aligned parallel to the optical axis 18, so that the optical element 46 has a sawtooth cross-section.Furthermore, the outer layers 50 may have a reflective coating.

[0057] The planes 50 are separated from each other by a distance s in the direction of the optical axis 18, such that the emitted and reflected light from different planes 50 of the interface 46 are phase-shifted. In particular, the optical element 46 can be a Littrow grating. The shortest distance f between two adjacent planes 50, which is oriented perpendicular to the planes 50, is obtained from the cosine of the angle x together with the distance s. The distance f ultimately determines the optical length that leads to the phase shift of the light 17 between the planes 50.

[0058] The laser light 17 from the emission region 40, which, for example, strikes the interface 48 at an angle x along the first direction 1 within the material of the optical element 46 perpendicularly, is reflected perpendicularly again. The laser light 17, which strikes the plane 50 at an angle y, is not perpendicular to the plane 50 and is not reflected directly back to the emission region along the second direction 2.

[0059] Furthermore, a reduction of the total reflection from the optical element 46 and the output coupler of the VCSEL in the first direction 1 is adjustable if the laser light 17 strikes the plane 50 perpendicularly and, after perpendicular reflection, is not in phase, preferably exactly out of phase, with the laser light 17 coupled out of the emission region 40, so that the laser light 17 exits the optical element 46. The laser light 17, which strikes the plane 50 along the second direction 2, ideally undergoes total internal reflection.

[0060] According to a further embodiment, an increase in the total reflection in the first direction 1 can be achieved if the laser light 17 incident perpendicularly on and reflected from the plane 50 is in phase with the laser light 17 coupled out of the output coupler mirror 44, so that the laser light 17 largely does not exit the optical element 46. At the same time, however, the laser light 17 in the second direction 2 can be coupled out.

Claims

Claims 1. VCSEL (10) for emitting laser light (17) with a resonator having an output coupler (44) having an emission region (40) on its outer surface, wherein a direction-selective optical element (46) is arranged on the emission region (40) such that laser light (17) of a first direction (1) can mostly exit the optical element (46) and laser light (17) of a second direction (2) is mostly reflected at the outer interface (48) of the optical element (46).

2. VCSEL (10) according to claim 1 , characterized in that the first and the second direction (1 , 2) are oriented differently to an optical axis (18) of the VCSEL (10) oriented perpendicular to the surface of the VCSEL (10).

3. VCSEL (10) according to claim 1 or 2, characterized in that the optical element (46) is applied to the outer surface without an air gap between the optical element (46) and the outer surface, wherein the laser light (17) enters the optical element (46) from the emission area (40) and propagates within the material of the optical element (46) to the interface (48).

4. VCSEL (10) according to one of the preceding claims, characterized in that the VCSEL (10) has a plurality of emission regions (40) on its surface (42) which favor a higher order laser mode.

5. VCSEL (10) according to one of the preceding claims, characterized in that the laser light (17) is in a laser mode which in the far field of the laser light (17) has a first and a second wavefront (181 , 182) of maximum intensity, which respectively move along a first and second propagation axis (201 , 202) which diverge from each other by a travel angle (b).

6. VCSEL (10) according to claim 5, characterized in that the first propagation axis (201) is aligned along the first direction (1) and the second propagation axis (202) is aligned along the second direction (2), so that the first wavefront (181) can largely exit the optical element (46) and the second wavefront (182) is largely reflected at the outer interface (20) of the optical element (46).

7. VCSEL (10) according to a preceding claim, characterized in that the optical element (46) has a plane (50) on the interface (48) at which laser light (17) of the first direction (1) can exit and laser light (17) of the second direction (2) is reflected.

8. VCSEL (10) according to claim 7, characterized in that a plurality of planes (50) are provided at the interface (48), wherein the planes (50) are aligned parallel to each other and are not aligned perpendicular to the optical axis (18).

9. VCSEL (10) according to claim 7 or 8, characterized in that the plane (50) has a reflective coating on the outside.

10. VCSEL (10) according to claim 9, characterized in that the planes (50) are offset from each other by a distance (s) in the direction of the optical axis (18) such that the partial rays reflected at the different planes are in phase with each other.

11. VCSEL (10) according to claim 10, characterized by a reduction of the total reflection in the first direction (1) compared to the total reflection in the second direction (2) when the laser light (17) in the first direction (1) strikes the interface (20) perpendicularly and after the perpendicular reflection is not in phase with the laser light (17) coupled out of the output coupler (44), such that more laser light (17) exits the optical element (46) in the first direction (1) than in the second direction (2).

12. VCSEL (10) according to claim 10, characterized by an increase in the total reflection in the first direction (1) compared to the total reflection in the second direction (2), when the laser light (17) incident perpendicularly on the interface (48) and reflected from the interface (48) is in phase with the laser light (17) coupled out of the output coupler (44), so that the laser light (17) does not exit the optical element (46) mostly in the first direction (1) but significantly more in the second direction (2).

13. VCSEL (10) according to any one of the preceding claims, countersigned in that the optical element (46) consists of GaAs or Si or SiOxide and is configured either as a refractive optical element (46) or as a meta-optic element.

14. VCSEL (10) according to any one of the preceding claims, countersigned in that the optical element (46) is a Littrow grating or a meta-optic element with reflection and transmission characteristics similar to a Littrow grating.

15. Arrangement with a VCSEL (10) according to one of the preceding claims, characterized in that the laser light (17) exiting the optical element (46) is coupled into a light guide element (12).

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