Laser devices with curved mirror

Abstract

A VCSEL includes epitaxial layers on a main surface of a substrate layer. The epitaxial layers include an n-doped semiconductor layer, a p-doped semiconductor layer, and an active region arranged between the n-doped semiconductor layer and the p-doped semiconductor layer. The VCSEL includes a first distributed Bragg reflector (DBR) disposed on or over a second surface of the substrate layer opposite to the main surface, the first DBR including a concave portion with respect to a direction facing away from the substrate layer; a second DBR disposed on or over a side or surface of the plurality of layers facing away from the first DBR; and a metasurface structure arranged on or over a surface or side of the second DBR facing away from the first DBR. The concave portion of the first DBR is configured to cause the VCSEL to emit in a single transverse mode.

Description

[0001] LASER DEVICES WITH CURVED MIRROR

[0002] Field

[0003] This present disclosure relates to semiconductor-based lasers and methods for producing thereof.

[0004] Background

[0005] Vertical-cavity surface-emitting lasers (VCSELs) based on indium gallium nitride ( InGaN) have become an area of significant interest due to their potential in applications such as high-speed communication, displays (e. g, augmented-reality (AR) displays, virtual reality (VR) displays, and lighting. A key challenge in developing InGaN-based VCSELs lies in managing the optical modes within the cavity. In particular, VCSELs with long cavity lengths, typically ranging between 20 and 100 pm, present specific challenges related to mode control and stability.

[0006] For long cavity VCSELs, one of the primary concerns is the reduction in longitudinal mode spacing as the cavity length (L) increases. This narrowing of mode spacing, often reaching sub-nanometer values, results in reduced control over longitudinal modes and an increased likelihood of mode hopping during laser operation. Mode hopping can significantly degrade the performance of the laser, impacting the stability and coherence of the emitted light.

[0007] In long-cavity VCSELs, the use of a curved mirror combined with a metasurface can be used to address these challenges. The curved mirror can help achieve mode matching, ensuring that the fundamental transverse mode is preserved and diffraction losses are minimized. The relationship between the curvature of the mirror (R) and the beam waist of the laser (w0) must satisfy a specific condition to optimize performance:

[0008]

[0009] In this equation, L represents the length of the cavity, n is the refractive index of GaN, and is the resonance wavelength of the cavity. By satisfying this condition, the optical modes can be more effectively confined, reducing diffraction losses and improving the overall efficiency of the VCSEL.

[0010] Moreover, the length of the cavity (L) can plays an important role in determining the resonance wavelengths of the longitudinal modes, which are given by the expression:

[0011] A= (2nL) / (m)

[0012] where m is an arbitrary integer. The spacing between these longitudinal modes (A ) can be approximated by:

[0013] A (A2 ) / (2nL)

[0014] As the cavity length increases, the mode spacing decreases, leading to sub-nanometer mode separations. This reduction in mode spacing enhances the probability of longitudinal mode hopping, which can further complicate the stable operation of the VCSEL.

[0015] In general, VCSELs exhibit at least two modes:

[0016] a) Longitudinal modes: A long cavity can lead to mode hopping between the longitudinal modes of the cavity.

[0017] b) Transverse modes: Using a curved mirror geometry, one can achieve a single transverse mode.

[0018] The fundamental transverse mode of a VCSEL can exhibit a phase-profile (similar to a Gaussian mode), and it is known to design a metasurface to achieve a desired phase of the fundamental transverse mode of the VCSEL, as disclosed in J. -S. Park et al, "All-glass 100mm Diameter Visible Metalens for Imaging the Cosmos", https: / / arxiv. org / ftp / arxiv / papers / 2307 / 2307.08186. pdf.

[0019] However, controlling the longitudinal modes in long-cavity InGaN-based VCSELs remains a significant challenge. The incorporation of curved mirrors provides a practical solution to mode matching and diffraction loss minimization, but further optimization is required to fully suppress mode hopping and improve the stability of these devices during operation.

[0020] Summary

[0021] The invention is set out in the appended set of claims.

[0022] Brief Description of the Drawings

[0023] In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the disclosure. In the following description, various aspects of the disclosure are described with reference to the following drawings, in which:

[0024] FIG. 1 shows a cross-section of a semiconductor laser device / VCSEL;

[0025] FIG. 2A shows a graph of a plot of mode spacing versus cavity length for a VCSEL;

[0026] FIG. 2B shows a graph of a plot of transmission spectra of longitudinal modes for a VCSEL;

[0027] FIG. 3 shows a simplified cross-sectional view of a structure for a VCSEL 300 according to at least one aspect of the present disclosure; FIGS. 4A-4D show metasurface structures for VCSELs, according to at least one aspect of the present disclosure;

[0028] FIG. 5A includes a graph including a plot of reflectivity versus lasing wavelength for the VCSEL 300;

[0029] FIG. 5B includes a graph including a plot of bottom reflectivity versus lasing wavelength for VCSEL such as VCSEL 300;

[0030] FIG. 6 shows a simplified cross-sectional view of a structure for a VCSEL 600 according to at least one aspect of the present disclosure;

[0031] FIG. 7 shows a simplified cross-sectional view of a structure for a VCSEL 700 according to at least one aspect of the present disclosure;

[0032] FIG. 8 shows a simplified top view of a metalens according to at least one aspect of the present disclosure;

[0033] FIG. 9 shows a simplified cross-sectional view of a structure for a VCSEL 900 according to at least one aspect of the present disclosure; and

[0034] FIG. 10 shows a simplified cross-sectional view of a structure for a VCSEL 1000 according to at least one aspect of the present disclosure. Detailed Description

[0035] The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and aspects in which the disclosure may be practiced. One or more aspects are described in sufficient detail to enable those skilled in the art to practice the disclosure. Other aspects may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the disclosure. The various aspects described herein are not necessarily mutually exclusive, as some aspects can be combined with one or more other aspects to form new aspects. Various aspects are described in connection with methods and various aspects are described in connection with devices. However, it may be understood that aspects described in connection with methods may similarly apply to the devices, and vice versa. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. That is, it should be understood that, for clarity and consistency, the same or similar reference numerals are used throughout the figures to denote the same or similar elements, components, or features. Variations of the embodiments may include different combinations of these elements, but the reference numerals will maintain their correspondence to the particular elements where applicable. Throughout the drawings, it should be noted that proportions are not necessary to scale and that the size of features may be emphasized for ease of illustration.

[0036] FIG. 1 shows a cross-sectional view of a known structure for a semiconductor laser device 100, namely a Vertical Cavity Surface Emitting Laser (VCSEL) 100. The VCSEL or VCSEL structure 100 includes a first mirror element 110, in this case a first distributed Bragg reflector (DBR).

[0037] Further a plurality of layers, e. g., epitaxially formed layers are formed on a substrate layer 150. The substrate layer 150, may be a semiconductor layer, e. g., a gallium nitride (GaN) substrate. On the substrate layer 150, can be formed a n-doped semiconductor layer 140 (e. g., n-doped GaN layer), an active region layer 130, and a p-doped semiconductor layer 120 (e. g., p-doped GaN layer). The active region 130 include a multiquantum well (MQW) region.

[0038] The VCSEL 100 further includes a second mirror element 160, in this case a second DBR. The substrate layers and the layers 120-140 are located between the first and second DBRs.

[0039] As shown in FIG. 1, the second mirror element 160 is curved, namely a curved mirror element / curved DBR. For example, the VCSEL 100 of FIG. 1 can realize suppressed diffraction loss by controlling the curvature of the curved mirror and achieving mode matching with the transverse mode of the cavity. Further, the VCSEL 100 can benefit from a long cavity (Lcavbetween 20 and 100 μm) and thick epitaxial stack (e. g. layers 120-150) and avoid crack issues and heat management issues. Further, only one pair of DBRs is shown in the FIG.

[0040] 1. Depending of the refractive indices of the DBR layers, more than 10 pairs of layers may be needed to achieve a large reflectivity.

[0041] However, the VCSEL 100 also experiences issues include mode hopping, e. g., a lack of longitudinal mode control, due to small mode spacing and lack of polarization control. That is, the VCSEL 100 can experience arbitrary polarization for its emissions. For example, reference numeral 170 can denote the (desired) fundamental optical mode in the VCSEL 100.

[0042] FIG. 2A shows a graph of a plot of mode spacing versus cavity length for VCSELs such as VCSEL 100. FIG. 2B shows a graph of a plot of transmission spectra of longitudinal modes for VCSEL such as 100 with a cavity length of L = 50 μm and with mode spacing of approximate 0.8 nm. Lasing, in VCSELs, such as VCSEL 100, can occur in any longitudinal resonance modes which lead to mode hoping due to small mode spacing. FIG. 3 shows a simplified cross-sectional view of a structure for a VCSEL 300 according to at least one aspect of the present disclosure.

[0043] The VCSEL or VCSEL structure 300 may in at least some respects have similar or some of the same components as the VCSEL 100. Accordingly, the components shown in FIG. 3 may be denoted by the same reference numerals, and repeated explanation is omitted as appropriate.

[0044] In the example of FIG. 3, the VCSEL 300 includes a metasurface structure 310. The metasurface structure 310 includes a plurality of metasurface elements 315. The metasurface structure 310 is configured to have a high-quality factor (Q-factor) with narrow resonances. In particular, the metasurface structure 310 is configured to improve or enhance the effective reflectivity of the DBR 110. The metasurface structure 310 combined with the DBR 110 can be considered a "hybrid mirror".

[0045] Further, to improve reflectivity, the VCSEL 300 includes a metal layer 380. The metal layer 380 is arranged over a side or surface of the of the DBR 160 facing away from the DBR 110. In the example of FIG. 3, the VCSEL 300 may include a dielectric spacer 370 arranged between the metal layer 380 and the DBR 160 to achieve large reflectivity.

[0046] For FIG. 3, the DBR 110 and 160 can include alternating layers 312 and 314. The layers can alternate between layers of high refractive index denoted by 312 and layers of low refractive index, denoted by 314.

[0047] FIGS. 4A-4D shows examples of a metasurface structures 310a-310d that may be implemented in VCSELs described herein including, for example, the VCSEL 300 of FIG. 3. For example, the metasurface structures 310a-310d include a plurality of metasurface elements 315 arranged in arrays, e. g., periodic arrays of metasurface elements 315. For example, FIG. 4A, shows one example of a metasurface structure 310a which includes a one-dimensional ( ID) array of metasurface elements 315. In this example, the metasurface elements 315 are elongated, from a top view. That is, the metasurface elements 315 of FIG. 4A extend in parallel in an elongated fashion in the XY-plane (e. g., a plane parallel to a back surface of the substrate layer of DBR 110). In this particular case, the major axis, from a top view, is elongated parallel to y-axis.

[0048] FIG. 4B shows is another exemplary metasurface structure 310b. In this case, the metasurface structure 310b has a plurality of metasurface elements 315 arranged in a two-dimensional (2D) array. The metasurface elements 315 can be pillar-like objects in a 2D array. In this case, the metasurface elements 315 can be circular-shaped pillars. In other words, the metasurface elements have a circular or circular-like shape from a top view facing a top side of the metasurface structure.

[0049] FIG. 4C is another exemplary metasurface structure 310c. As shown, the metasurface structure 310c is similar to the metasurface structure 310b in that the metasurface elements 315 are arranged in a 2D array. However, in this case, the metasurface elements 315 have an elliptical or oval-like shape from a top view perspective.

[0050] While in FIGS. 4A-4C the metasurface elements 315 arranged in arrays are uniform, this is not necessarily so. That is, one or more cases, the metasurface elements 315 may realize one or more different shapes, sizes, and orientations. For example, FIG. 4D shows another exemplary metasurface structure 310d which has metasurface elements 315 (315a and 315b) which are realized in two different sized elliptical or oval-shaped pillars. Both metasurface elements 315a and 315b have an oval or elliptical-like shape. However, the metasurface elements 315a have a larger area e. g., from a top perspective, than the metasurface elements 315b. Further, the metasurface elements 315a are oriented or rotated at an angle, 0. That is, the major axis of the metasurface elements 315a, with respect to a top view (e. g., in the XY-plane) is rotated at angle while the metasurface elements 315b are not rotated. Instead the major axis of the metasurface elements 315b is aligned or parallel to the Y-axis.

[0051] Other variations of metasurface structure or metasurface elements 315 arranged in arrays can be realized. For example, in other instances, metasurface elements can realize other shapes (e. g., from a top perspective), including other kinds or types of closed shapes, such as, for example different kinds of polygonal shapes.

[0052] The parameters of the metasurface structures, e. g., the width ( w), the pitch / periodicity (p, px, py), height (h), e. g. along z-axis, the rotation angle 0, can be defined or set. These parameters can control or influence the Q-factor for the metasurface structure and its resonance and reflectivity characteristics.

[0053] In one or more example, the metasurface structure (s) is subwavelength. That is, the periodicities (px and py) can be smaller or less than a wavelength in the medium (<180 nm). For example, the geometry of the metasurface are typically around 100 nm That is, the dimensions such as the pitches (p, px, py), the widths ( w), the heights (h), the diameters D can be at or around 100 nm. The rotation angle 0, can be around 0 to 45 degrees.

[0054] In one or more examples, the plurality of metasurface elements 315 are made of or include high refractive index materials. For example, the metasurface elements 315 can include or be made up of materials including Titanium dioxide (TiO₂), Niobium pentoxide (Nb₂O₅), and / or silicon nitride (SiN).

[0055] Referring back to FIG. 3, the metasurface structure 310 is arranged or formed over a back side of the VCSEL 300, e. g., over a back surface (e. g., a surface of DBR 110 facing away from the DBR 160) of the top DBR 110. In at least one instance, the metasurface structure 310 can be arranged directly at or directly on the back surface of the top DBR 110.

[0056] As previously mentioned, the metasurface structure 310 combined with the DBR 110 can realize improved (top) reflectivity for the VCSEL 300. Specifically, reflectivity of the combined DBR 110 and metasurface structure (Rtop) can be improved, e. g., to approximately 0.998 at the lasing f requency / wavelength of the VCSEL 300. (As previously mentioned, the metasurface structure 310 and the DBR 110 together can be considered as a "hybrid mirror").

[0057] FIG. 5A is a graph including a plot of reflectivity versus lasing wavelength for a hybrid mirror of a VCSEL such as VCSEL 300.

[0058] Further, for VCSELs such as the VCSEL 300, the bottom mirror, DBR 160, also can provide enhanced (bottom) reflectivity at the lasing wavelength due to its curved / concave shape. FIG.

[0059] 5B shows a graph including a plot of bottom reflectivity Rbot versus lasing wavelength for a VCSEL such as or similar to the VCSEL 300. In this case, the curved bottom mirror DBR can provide a reflectivity Rbot of approximately 0.998 at the laser frequency / wavelength.

[0060] In particular, the metasurface structures 310 described are configured to cause the VCSEL' s 300 emission (e. g., output light 350) to be realized in a single longitudinal mode. Further, the metasurface structure (s) 310 are configured to control the polarization of light 350 output by the VCSEL.

[0061] FIG. 6 shows a simplified cross-sectional view of a structure for a VCSEL 600 according to at least one aspect of the present disclosure. The VCSEL / VCSEL structure 600 may in at least some respects have similar or some of the same components as the VCSEL 100 and / or VCSEL 300. Accordingly, the components shown in FIG. 6 may be denoted by the same reference numerals, and repeated explanation is omitted as appropriate. For example, the metasurface structure 310 of the VCSEL 600 can have any of the metasurface structures described herein, e. g., the metasurface structures 310a-310d of FIGS. 4A-4D.

[0062] The VCSEL 600 is similar in many respects to the VCSEL 300. However, one difference is the VCSEL 600 a spacer or spacer layer 620. In at least this example, the spacer 620 is arranged or located vertically (e. g., along the z-direction) between the metasurface structure 310 and the DBR 110.

[0063] In at least one instance, the spacer 620 is a dielectric spacer. The dielectric spacer 620 may be made of or include one or more low refractive index materials, such as materials dielectric materials having a refractive index of less than 1.5. One example of such material is silicon dioxide (SiO2). The presence of such a spacer 620, e. g., dielectric spacer with low refractive index, improves, enhances, and maximizes the reflectivity of the hybrid mirror (DBR 110 and the metasurface 310 combined).

[0064] In addition, the DBR 160, as shown in FIG. 6, may be defined by a distance parameter d. In particular, the curved or concave portion of the DBR 160 can be defined the parameter d. For example, the DBR 160, includes a curve / concave portion, includes a plurality of layers. Each of the layers in the concave portion are realized according d, where d is a distance measured as a "vertical dip" or "vertical drop" of the concave portion.

[0065] For example, the distance d for one or more layers (e. g., layers 312, 314 ) of the DBR 110 can be defined as the vertical distance from a highest point (in the z-direction) of a top surface of a DBR layer to a lowest point of the top surface of the DBR layer. This lowest point can correspond to a vertex of the DBR layer. The DBR 110 can be tailored so that the distance or parameter d satisfies the following expression:

[0066]

[0067] wherein:

[0068] w0is beam waist of light output from VCSEL,

[0069] L cavity length of VCSEL, measured from p-doped semiconductor layer to substrate layer,

[0070] n is effective index of refraction for semiconductor layers, and

[0071] A is wavelength of light output by the VCSEL.

[0072] Moreover, by tailoring the curved DBR parameters (e. g., d, L, w0), the layers of the DBR 160 can satisfy the above equation. As a result, the VCSEL 600 can achieve a single transverse mode for its optical output 350.

[0073] Other VCSELs described herein, e. g., VCSEL 300, 700, 900, etc., for example, may also have its layers of its bottom, concave-shaped DBR, e. g., DBR 160, that satisfy the "vertical dip", according to the above equation so as to achieve a single transverse mode.

[0074] FIG. 7 shows a simplified cross-sectional view of a VCSEL / VCSEL structure 700 according to an aspect of the present disclosure. The VCSEL 700 may include or incorporate other VCSELs described herein. In particular, reference numeral 750 can designate a VCSEL, or VCSEL structure. For example, the VCSEL structure 750 may refer to the VCSELS described herein, e. g., VCSEL 300 or VCSEL 600. FOR instance, the VCSEL 700 can include the same type of curved mirror or DBR 160 as e. g., FIG. 6. Accordingly, the VCSEL 700 may refer in at least some respects have similar or some of the same components as the VCSEL 100, 300, or 600. Accordingly, the components in FIG. 7 also shown in FIGS. 1, 3 or 6 may be denoted by the same reference numerals, and repeated explanation is omitted as appropriate.

[0075] As shown in the example of FIG. 7, a metalens or meta lens structure 730 is arranged or formed over the first VCSEL structure 750. The metalens 730 is configured to collimate light 350 output by the VCSEL structure 750.

[0076] In at least the example of FIG. 7, the metalens 730 includes at least an array 710, e. g., a 2D array of nanopillars 715. In one or more instances, the 2D array of nanopillars 710 spans an area in a plane parallel to the main surface 150a of the substrate 150 (e. g., in the XY-plane) that is greater than twice a beam waist w0of light output by the VCSEL structure 750.

[0077] The metalens 730 can be arranged a vertical position (e. g., along z-axis) where the output beam 350 of the VCSEL structure 750 is twice the waist (2w0). This can correspond to a divergence angle Odiv) according to the following expression:

[0078] edlv~ (X / D) = X / (2w0)

[0079] In the case D or 2w0is 200 pm, and wavelength (X) is 450 nm, Qdiv is approximately 0.1 degrees.

[0080] FIG. 8 shows a top view perspective of the metalens or metalens structure 730. As The nanopillars 715 can have a circular cross-section shape from a top perspective e. g., facing the XY-plane. In at least the example of FIG. 8, the nanopillars 715 may varying radii. Further, the radii of the 2D array of nanopillars are designed to satisfy a position dependent phase of a fundamental mode of a cavity of the VCSEL 750.

[0081] That is, the fundamental transverse mode of the VCSEL 750 can exhibit a phase-profile (similar to a Gaussian mode). Each nanopillar of the metalens (radius, height, distance between pillars) can be designed to achieve the desire phase of the fundamental transverse mode of the VCSEL 750. (See also https: / / arxiv. org / ftp / arxiv / papers / 2307 / 2307.08186. pdf ).

[0082] For example, to achieve this condition (position dependent phase of fundamental mode of VCSEL cavity), the overall size (in XY-plane) of the metalens should be larger than 4w0.

[0083] In or more examples, the nanopillars 715 can include or made of material with a refractive index greater than 2, such as, for example, Titanium Dioxide (TiO2) and / or Nb₂O₅, to name a few.

[0084] The metalens 730 can further include a spacer layer 720. The nanopillars 715 can be formed over the spacer layer 720. For example, the spacer layer 720 can be arranged between the nanopillars 715 and the VCSEL structure 750. The spacer layer 720 can also be a dielectric layer, which can include or made up of dielectric materials, e. g., silicon dioxide (SiO2), in at least one example.

[0085] As previously mentioned, the metalens 730 is configured to collimate the laser light 350 output from the VCSEL structure 750. That is, due to the metalens 730, the VCSEL 700 outputs collimated laser light 740.

[0086] FIG. 9 shows a simplified cross-sectional view of a structure for a VCSEL 900 according to at least one aspect of the present disclosure.

[0087] The configuration of the VCSEL 900 can be similar to the other VCSELs described herein. That is, the VCSEL 900, may, in certain aspects, share similar or identical components with VCSELs 100, 300, 600, and / 700. Accordingly, these components may be identified using the same reference numerals, and redundant explanations are omitted where appropriate. For instance, the VCSEL 900 can include the same type of curved mirror or DBR 160 as e. g., FIG. 6. While, the other VCSELs or VCSEL structures described herein (e. g., VCSELs 300, 600, 700) are top emitters, the VCSEL 900 is a bottom emitter. That is, the output laser light 350 is emitted through the bottom curved mirror or DBR 160. For instance, the VCSEL 900 does not include a metal layer nor a dielectric spacer on or over a surface of the DBR 160 facing away from the top DBR 110.

[0088] In particular, the VCSEL 900 is similar to the VCSEL 600 as it includes a metasurface structure 300 which can be disposed over the top DBR 110. Like the VCSEL 600, a space layer 620 can be disposed or arranged between the metasurface structure 310 and the DBR 110. However, the VCSEL 900 further includes a metal layer 910 which is disposed vertically over the metasurface structure 310. That is, the metal layer 910 is formed over a side or surface of the metasurface structure 310 facing away from the second DBR 160.

[0089] A further spacer layer 920 may be arranged between the metasurface structure 310 and the metal layer 910. For example, the metal layer 910 may be arranged on (e. g., directly) or over a surface of the spacer layer 920 facing away from the metasurface structure 310. Further, at least some instances, the spacer layer 310 may further extend to embed the metasurface structure 310. The spacer layer may be a dielectric spacer layer as described herein.

[0090] FIG. 10 shows a simplified cross-sectional view of a structure for a VCSEL 1000 according to at least one aspect of the present disclosure. The VCSEL 1000 can be similar to the VCSEL 300 of FIG. 3. However, the VCSEL 1000 further includes an actuator device 1010 arranged near the metasurface structure 310. The actuator device 1010 can be a thermal and / or a mechanical actuator configured can change the resonance frequency of the metasurface structure 310 by manipulating its refractive index. In this case, a voltage source 1020 can apply a voltage to actuating device 1030 e. g., on or at a surface to top side of the VCSEL 1000, e. g., adjacent to the metasurface structure 310.

[0091] For instance, the actuating device 1030 could be a thermal element (e. g., metallization or others) configured or operable to change the temperature of the metasurface and thereby affecting or changing its refractive index to tune it, if needed. In at least one other example the actuating device 1030 could also be a type of piezoelectric element configured or operable to apply a force to the metasurface (e. g., cause a strain or stress thereto). This force can be used to manipulate its resonance frequency for tuning purposes.

[0092] The actuator device 1010 can play two roles. First, if for any reason, for example change of junction temperature of VCSEL 1000, its lasing frequency slightly changes, the actuator device 1010 can be configured or used to adjust the resonance frequency of nanostructure accordingly. Secondly, if the VCSEL 1000 is tunable, it may be necessary to change the resonance frequency of the nanostructure with lasing frequency of VCSEL 1000.

[0093] For at least the VCSELs 300, 600, 700, 900, and 1000 the DBR 110 includes layers that alternate between high-refractive index dielectric material (s) and low-refractive index material dielectric material (s). In at least one example the layers may alternate between, e. g., dielectric layers. For example, the low refractive index materials can have a refractive index less than 1.5 and the high refractive index materials having a refractive index greater than 2. In at least one example, for the DBR 110, the layers of low refractive index materials can include layers of silicon dioxide (SiO2) and niobium pentoxide (Nb2O5) while the layers of high refractive index materials comprise TiO2, Nb2O5, and / or SiN. Further, the layers of the DBR 110 can be planar or substantially planar. In one or more instances, the DBR 110 can have a maximum of 10 layers in total.

[0094] For at least the VCSELs, 300, 600, 700, 900, and 1000 the DBR 160 (e. g., bottom or curved DBR) also includes alternating layers of low refractive index materials and high refractive index materials, such as, for instance, alternating layers of silicon dioxide (SiO2) and niobium pentoxide (Nb2O5).

[0095] As previous mentioned, VCSELs exhibit longitudinal modes and transverse modes. The VCSELs described herein, e. g., VCSEL 300, 600, 700, 900, and 100 are configured to address the issues with longitudinal modes leading to mode hopping by use of metasurface to control polarization of light. Also, the VCSELs are configured to address the issues with transverse modes by use of curved mirror to minimize diffraction loss.

[0096] The following examples concern or relate to aspects of the present disclosure.

[0097] Example 1 is a vertical cavity surface emitting laser (VCSEL) including: a substrate layer; a plurality of epitaxial layers on a main surface of the substrate layer, the plurality of epitaxial layers including an n-doped semiconductor layer, a p-doped semiconductor layer, and an active region arranged between the n-doped semiconductor layer and the p-doped semiconductor layer; a first distributed Bragg reflector (DBR) disposed on or over a second surface of the substrate layer opposite to the main surface, the first DBR including a concave portion with respect to a direction facing away from the substrate layer; a second DBR disposed on or over a side or surface of the plurality of layers facing away from the first DBR, and a metasurface structure arranged on or over a surface or side of the second DBR facing away from the first DBR, wherein the concave portion of the first DBR is configured to cause the VCSEL to emit in a single transverse mode. In Example 2 the subj ect matter of Example 1 may further include a metal layer arranged over a side the first DBR facing away from the first DBR.

[0098] In Example 3 the subj ect matter of Example 2 may further include a first spacer layer arranged on or over the concave surface of the first DBR;

[0099] wherein the metal layer may be arranged over a side or surface of the first spacer layer facing away from the first DBR.

[0100] In Example 4 the subj ect matter of Example 2 or 3 may further include that the metasurface structure may be arranged directly at or on a surface of the second DBR facing away from the first DBR.

[0101] In Example 5 the subj ect matter of Example 2 or 3 may further include a second spacer layer arranged on or over a surface of the second DBR facing away from the first DBR so that the second spacer layer is arranged between the metal layer and the second DBR.

[0102] In Example 6 the subj ect matter of Example 5 may further include that the second spacer layer may be configured to achieve a phase matching.

[0103] In Example 7 the subj ect matter of Example 1 may further include a metal layer arranged over a side of the metasurface structure facing away from the substrate layer.

[0104] In Example 8 the subj ect matter of Example 7 may further include: a first spacer layer arranged between the metasurface structure and the second DBR; and a second spacer structure arranged between the metasurface structure and the metal layer.

[0105] In Example 9 the subj ect matter of any one of Examples 3 to 8 may further include that the first spacer layer and the second spacer layer may each include a dielectric layer. In Example 10 the subj ect matter of Example 9 may include that the dielectric layer may optionally be a low refractive index material having a refractive index of less than 1.5.

[0106] In Example 11 the subj ect matter of Example 10 may include that the low refractive index material may optionally be or include silicon dioxide (SiO2).

[0107] In Example 12 the subj ect matter of any one of Examples 1 to 11 includes that the metasurface structure may optionally be an array of metasurface elements.

[0108] In Example 13 the subj ect matter of Example 12 may include that metasurface elements include metaatoms.

[0109] In Example 14 the subj ect matter of Example 12 or 13 may include that the array of metasurface elements may optionally be a periodic array of metasurface elements, and

[0110] wherein the periodic array of metasurface elements may be a series of elongated metasurface elements extending in parallel orthogonal a plane parallel to the main surface of the substrate layer.

[0111] In Example 15 the subj ect matter of Example 14 may include that the periodic array of metasurface elements may optionally be a two-dimensional (2D) array of metasurface elements.

[0112] In Example 16 the subj ect matter of any one of Examples 12 to 15 may include that the metasurface element may optionally be or include high refractive index materials, the high refractive index materials having a refractive index greater than 2.

[0113] In Example 17 the subj ect matter of Example 16 may include that the high refractive index materials may optionally be or include TiO2, Nb2O5, and / or SiN. In Example 18 the subj ect matter of any of Examples 1 to 5 may further include: a metalens arranged on or over the surface of the metasurface structure, wherein the metalens is configured to collimate light output by the VCSEL.

[0114] In Example 19 the subj ect matter of Example 18 may include that the metalens includes or be a 2D array of nanopillars.

[0115] In Example 20 the subj ect matter of Example 19 may include that the 2D array of nanopillars may optionally span an area in a plane parallel to the main surface substrate that is greater than twice a beam waist w0of light output by the VCSEL.

[0116] In Example 21 the subj ect matter of Example 19 or 20 may include that each nanopillar includes or be a material with a refractive index greater than 2.

[0117] In Example 22 the subj ect matter of Example 21 may include that each nanopillar includes Titanium Dioxide (TiO2) or Nb₂O₅.

[0118] In Example 23 the subj ect matter of any of Examples 19 to 22 may include that the radii of the 2D array of nanopillars are optionally designed to satisfy a position dependent phase of a fundamental mode of a cavity of the VCSEL.

[0119] In Example 24 the subj ect matter of any of Examples 1 to 23 may include that the first DBR includes a plurality of layers including alternating layers of silicon dioxide (SiO2) and niobium pentoxide (Nb2O5).

[0120] In Example 25 the subj ect matter of any of Examples 1 to 24 may include that the concave portion of the first DBR includes a plurality of layers which are each defined by a parameter d, where d is a distance measured in a vertical direction perpendicular to main surface of substrate, from a vertex of the respective layer in concave portion to an end point of that layer within the concave portion, wherein the parameter d satisfies the following expression:

[0121] πwn / λ√d / L< 2

[0122] wherein:

[0123] w0is beam waist of light output from VCSEL, L cavity length of VCSEL, measured from p-doped semiconductor layer to substrate layer,

[0124] n is effective index of refraction for semiconductor layers, and

[0125] A is wavelength of light output by the VCSEL.

[0126] In Example 26 the subj ect matter of any of Examples 1 to 25 may include that the second DBR includes a plurality of planar layers.

[0127] In Example 27 the subj ect matter of any of Examples 1 to 26 may include that the second DBR may include a plurality of layers including alternating layers of low refractive index materials and high refractive index materials, the law refractive index materials having a refractive index less than 1.5 and the high refractive index materials having a refractive index greater than 2.

[0128] In Example 28 is the subj ect matter of Example 27 may include that layers of low refractive index materials includes silicon dioxide (SiO2) and the layers of high refractive index materials include Ti02, Nb2O5, and / or SiN.

[0129] In Example 29 the subj ect matter of any one of Examples 26 to 28 may include that the second DBR may have a maximum of 10 layers.

[0130] In Example 30 the subj ect matter of any of Examples 1 to 29 may further include an actuator device arranged in proximity or adjacent to the metasurface structure, wherein the actuator device is configured to modify a refractive index of the metasurface structure.

[0131] In Example 31 the subj ect matter of Example 29 may include that the actuator device is a mechanical actuator or a thermal actuator device coupled to the metasurface structure.

[0132] In Example 32 is the subj ect matter of any of Examples 1 to 30 may include that the substrate layer includes or is a layer of gallium nitride (GaN), wherein the n-doped semiconductor layer may optionally be or include an n-doped GaN layer, and wherein the p-doped semiconductor layer may optionally be or include an p-doped GaN layer.

[0133] In Example 33 the subj ect matter of any one of Examples 1 to 31 may include that the active region may optionally be or include a single multiple-quantum-well (MQW) active region.

[0134] In Example 34 the subj ect matter of any of Examples 1 to 31 may include that the active region includes or be a plurality of multiple-quantum-well (MQW) active regions.

[0135] In Example 35 the subj ect matter of any of Examples 1 to 33 may include that a cavity length of the VCSEL, may optionally be a distance measured vertically between first DBR and the second DBR along a direction perpendicular to the main surface, in a range of about 20 microns to about 100 microns.

[0136] In Example 36 the subj ect matter of any of Examples 1 to 34 may include that the metasurface structure can be configured to cause the VCSEL emit a single longitudinal mode.

[0137] In Example 37 the subj ect matter of any of Examples 1 to 35 may include that the metasurface structure can be configured to control a polarization of light output by the VCSEL.

[0138] The term "metasurface" refers specifically to a two-dimensional arrangement of subwavelength-scale nanostructures designed to impose spatially varying phase, amplitude, or polarization modifications to incident electromagnetic waves. It should not be interpreted merely as a general structured surface, but as a functionally engineered layer for manipulating optical wavefronts. Thus, a metasurface refers to a two-dimensional array of subwavelength-structured elements (nanoelements, nanopillars, nanoresonators or scatterers), typically formed on a substrate, engineered to manipulate electromagnetic waves in a spatially varying manner. In the context of VCSEL (Vertical-Cavity Surface-Emitting Laser) technology, a metasurface may be integrated at the cavity termination to tailor the optical response, such as reflectivity or phase profile, across different spatial locations of the beam. The optical behavior of a metasurface, including amplitude, phase, polarization conversion, and spectral selectivity, is defined by the geometry, arrangement, and material composition of its constituent elements. Key design parameters influencing the metasurface response include periodicity, orientation, aspect ratio, and refractive index contrast. Metasurfaces may serve as metamirrors, enabling high reflectivity at targeted wavelengths or angular ranges, while allowing phase control at subwavelength resolution. Such functionalities are leveraged for beam shaping, polarization control, and modal selection in laser applications.

[0139] A metalens is a type of flat optical component formed from a metasurface, designed to focus or otherwise manipulate electromagnetic radiation by introducing spatially varying phase shifts across its aperture using subwavelength-scale nanostructures. Unlike conventional refractive lenses that rely on gradual phase accumulation through material thickness, a metalens achieves the desired wavefront shaping through engineered phase discontinuities at the surface level. The expression "phase discontinuity" is to be understood as a spatially localized and abrupt change in the optical phase of a wavefront, introduced intentionally by modifying the geometry or orientation of the underlying nanoelements. This is distinct from physical discontinuities and should be interpreted in the electromagnetic phase domain. The constituent elements of a metalens— often referred to as nanoantennas or metaatoms— are arranged in a two-dimensional pattern, with each element imparting a specific phase delay to the incident light. These phase delays are tailored through precise control of the geometry, orientation, and material composition of the nanoelements. Depending on the design strategy, the phase control may be realized via geometric phase (Pancharatnam-Berry phase), propagation phase due to optical path length, or resonant phase arising from Mie or Fabry-Perot-type resonances. Metalenses are inherently compact and lightweight, offering a high degree of optical control within a minimal footprint. They are capable of achieving diffraction-limited focusing, chromatic dispersion engineering, and polarization-dependent manipulation. In VCSEL-related applications, metalenses may be monolithically integrated at the wafer level to collimate, focus, or direct emitted laser beams, providing an efficient and scalable alternative to traditional refractive or diffractive optics. The performance characteristics of a metalens— such as focal length, numerical aperture, chromatic bandwidth, and polarization behavior— are functions of the phase profile distribution and the nanostructure configuration. Their planar form factor and fabrication compatibility with semiconductor processes render them especially suitable for on-chip photonics, optoelectronics, and miniaturized imaging systems.

[0140] "Nanoelement" (also referred to as nanopillar, nanoresonator, or nanostructure) describes the physical subwavelength feature constituting the metasurface. These are typically fabricated from dielectric or semiconductor materials and function as localized scatterers whose geometry and material composition determine their optical response. The distinction between nanoelement and metaatom is made to emphasize the difference between physical structure and functional design abstraction. Each nanoelement functions as a localized scattering center, with its optical characteristics— such as scattering phase and amplitude— governed by its physical dimensions (e. g., height, diameter, shape), its material properties (e. g., refractive index, absorption), and its relative orientation. In a VCSEL-integrated metasurface, nanoelements are typically fabricated using dielectric or semiconductor materials and arranged in a deterministically patterned lattice. They may possess cylindrical, elliptical, rectangular, or more complex cross-sectional geometries, each selected to support desired resonances or phase delays. Nanoelements may operate individually or collectively, depending on the design regime (localized or collective resonance). Their spatial configuration across the metasurface plane determines the overall optical function, such as focusing, beam steering, or wavelength filtering.

[0141] A "metaatom" denotes a discrete functional unit of the metasurface. While it may physically comprise a single nanoelement (e. g., a nanopillar), the term emphasizes its role in imparting a defined optical response— typically a phase delay— to the incident light. The use of the word "atom" here is conceptual and does not imply chemical indivisibility. In some embodiments, a metaatom may consist of a combination of nanostructures that collectively define a single unit of optical functionality. While in many cases the terms metaatom and nanoelement are used interchangeably, particularly in single-pillar metasurfaces, a metaatom more broadly denotes any composite unit responsible for imparting a defined optical response within a metasurface. In VCSEL-integrated metasurfaces, metaatoms are typically designed to engineer the local reflection coefficient (both amplitude and phase) at a specific design wavelength and for a specific polarization state. A metaatom may consist of a single dielectric post or a combination of structures, and may exploit geometric phase (Pancharatnam-Berry phase), propagation phase, or resonance-based phase mechanisms. Design variations among metaatoms across the metasurface enable functionalities such as broadband reflectivity modulation, polarization-dependent reflectivity, angular selectivity, or phase gradient implementations for beam redirection.

[0142] The optical performance of metasurfaces is governed by a variety of interdependent parameters, each of which may be deliberately varied across the structure to achieve a desired optical functionality. The dimensions of the nanoelements, along with the dispersion properties of the materials from which they are fabricated, may directly determine the spectral response of the metasurface— e. g. its bandwidth and the position of any resonance peaks. When the nanoelements possess an asymmetric geometry, such as elliptical or rectangular cross-sections, they may induce birefringent effects or enable polarization conversion. This permits polarization-dependent control over reflectivity or transmission. Metasurfaces can be engineered for optimal performance under normal or oblique light incidence, with reflectivity characteristics adapted to the angular distribution of incoming light. The periodicity and lattice symmetry of the nanoelement arrangement— whether square, hexagonal, or chirped— affect the metasurface' s diffraction behavior and its capacity to couple or suppress specific optical modes. Furthermore, the substrate and surrounding media contribute significantly to optical behavior. The refractive index contrast between the nanoelements and their immediate environment, such as the substrate or cladding layers, influences the effective impedance profile of the surface and thereby impacts overall reflectivity. The mechanism of phase control— be it geometric phase, propagation phase, or Mie resonance— defines not only how phase modulation is achieved at the nanoscale but also the range and precision with which it can be implemented across the metasurface.

[0143] The "fundamental mode" of a VCSEL denotes the lowest-order transverse optical mode supported by the cavity structure. Typically characterized by radial symmetry and a Gaussian-like intensity profile (e. g., LP01or TEM00), it represents the mode with the smallest divergence and highest modal gain. In a VCSEL, the fundamental mode may be selected through a combination of cavity design parameters— such as aperture size, index-guiding profile, and reflective mirror configuration— to suppress higher-order modes. Achieving single-mode operation may be important in applications requiring coherent, diffraction-limited beams, such as optical interconnects or sensing systems.

[0144] In this context, "phase matching" refers to the optical condition where the phase velocity and accumulated phase of light within the laser cavity align with the resonant condition required for constructive interference. This is important to supporting stable lasing modes and should not be confused with signal synchronization or electrical phase alignment. Thus, phase matching in the context of VCSELs refers to the condition in which the propagation constant (or phase velocity) of the electromagnetic wave within the active cavity of the VCSEL is matched with that of the resonant structure, such as distributed Bragg reflectors (DBRs) or metasurfaces, across the emission spectrum. This ensures constructive interference upon each round-trip within the cavity, maximizing the optical field enhancement and enabling lasing action at specific wavelengths. Effective phase matching allows to minimize cavity losses and ensures high modal gain. In VCSEL designs including metastructures or dielectric patterning, phase matching accounts for spatially varying phase profiles and the dispersion characteristics of the structuring nanoelements.

[0145] In VCSEL structures, the refractive index of constituent materials may play a central role in guiding, confining, and reflecting optical modes within the vertical cavity. Materials used in the active and mirror regions typically fall into two refractive index regimes: high-index and low-index, depending on their optical contrast and function within multilayer stacks. High-refractive-index materials generally exhibit a refractive index n larger than 2, e. g. in the range of approximately 2.8 to 3. 6, depending on the wavelength and composition. Examples include Gallium Arsenide (GaAs, n»3.5 at 850 nm) or Indium Phosphide ( InP). In contrast, low-refractive-index materials typically have n values lower than 2, e. g. between 1.4 and 2, with common examples including Aluminum Oxide (Al2O3, n»1. 6) or Silicon Dioxide (SiO2, n»1.45). In VCSELs, these materials are used to create index contrast in the mirror stacks or for dielectric apertures to enhance mode confinement. The index contrast between adjacent layers, particularly in DBRs or engineered metasurfaces, defines the reflectivity, bandwidth, and modal confinement characteristics of the laser. A higher refractive index contrast enables stronger reflection with fewer periods, thereby reducing overall device thickness and enhancing thermal performance.

[0146] Any of the aspects, examples, and / or embodiments described herein may be suitable or appropriately combined including combined with the embodiments or examples described herein.

[0147] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any example or design described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other examples or designs.

[0148] For the purposes of the present disclosure, the phrase "A and / or B" means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0149] Reference to "one embodiment" or "an embodiment" in the present disclosure means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" or "in an embodiment" are not necessarily all referring to the same embodiment. The appearances of the phrase "for example, " "in an example, " or " in some examples" are not necessarily all referring to the same example.

[0150] The words "plurality" and "multiple" in the description or the claims expressly refer to a quantity greater than one. The terms "group ( of ) ", " set [ of ] ", "collection ( of ) ", " series (of ) ", " sequence ( of ) ", "grouping ( of ) ", etc., and the like in the description or in the claims refer to a quantity equal to or greater than one, i. e. one or more. Any term expressed in plural form that does not expressly state "plurality" or "multiple" likewise refers to a quantity equal to or greater than one.

[0151] The term "connected" or "on" can be understood in the sense of a ( e. g. mechanical, optical and / or electrical ), e. g. direct or indirect, connection and / or interaction. For example, several elements can be connected together mechanically such that they are physically retained ( e. g., a plug connected to a socket ) and electrically such that they have an electrically conductive path ( e. g., signal paths exist along a communicative chain).

[0152] As used herein, unless otherwise specified the use of the ordinal adjectives " first", " second", "third" etc., to describe a common obj ect, merely indicate that di f ferent instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[0153] As utilized herein, terms "module", " component, " " system, " "circuit, " " element, " " slice, " " circuitry, " and the like are intended to refer to a set of one or more electronic components, a computer-related entity, hardware, software ( e. g., in execution), and / or firmware. For example, circuitry or a similar term can be a processor, a process running on a processor, a controller, an object, an executable program, a storage device, and / or a computer with a processing device. By way of illustration, an application running on a server and the server can also be circuitry. One or more circuits can reside within the same circuitry, and circuitry can be localized on one computer and / or distributed between two or more computers. A set of elements or a set of other circuits can be described herein, in which the term "set" can be interpreted as "one or more. "

[0154] Such electric or electronic circuitry can be operated by a software application or a firmware application executed by one or more processors. The one or more processors can be internal or external to the apparatus and can execute at least a part of the software or firmware application. As yet another example, circuitry can be an apparatus that provides specific functionality through electronic components without mechanical parts; the electronic components can include one or more processors therein to execute executable instructions stored in computer readable storage medium and / or firmware that confer (s), at least in part, the functionality of the electronic components. As another example, circuitry or similar term can be implemented in hardware such as application specific integrated circuit (ASIC), programmable gate array (PGA), discrete digital circuits, etc. ) or in a combination of hardware and software (e. g., a software model executed by a corresponding processor).

[0155] The term "semiconductor substrate" can mean any construction comprising semiconductor material, for example, a silicon substrate with or without an epitaxial layer, a silicon-on-insulator substrate containing a buried insulator layer, or a substrate with a silicon germanium layer.

[0156] A lateral direction is understood to mean a direction that runs, in particular, parallel to a main extension surface of the component, in particular of a layer. A vertical direction is understood to mean a direction that is oriented, in particular, perpendicular to the main extension surface of the component and / or layer. The vertical direction and the lateral direction are approximately orthogonal to each other.

[0157] Further, spatially relative terms, such as "beneath, " "below, " "lower, " "above, " "upper" and the like, may be used herein for ease of description to describe one element or feature ' s relationship to another element (s) or feature (s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0158] The term "data" as used herein may be understood to include information in any suitable analog or digital form, e. g., provided as a file, a portion of a file, a set of files, a signal or stream, a portion of a signal or stream, a set of signals or streams, and the like. Further, the term "data" may also be used to mean a reference to information, e. g., in form of a pointer. The term data, however, is not limited to the aforementioned examples and may take various forms and represent any information as understood in the art.

[0159] As used herein, a signal that is "indicative of" a value or other information may be a digital or analog signal that encodes or otherwise communicates the value or other information in a manner that can be decoded by and / or cause a responsive action in a component receiving the signal. The signal may be stored or buffered in computer readable storage medium prior to its receipt by the receiving component and the receiving component may retrieve the signal from the storage medium. Further, a "value" that is "indicative of" some quantity, state, or parameter may be physically embodied as a digital signal, an analog signal, or stored bits that encode or otherwise communicate the value. Unless otherwise stated, the words "about" and "substantially" as used herein are to be construed as meaning the normal measuring and / or fabrication limitations related to the value or condition which the word "about" or "substantially" modifies. Unless expressly stated otherwise, the term "embodiment" is used herein to mean an embodiment of the present disclosure.

[0160] As used herein, a signal may be transmitted or conducted through a signal chain in which the signal is processed to change characteristics such as phase, amplitude, frequency, and so on. The signal may be referred to as the same signal even as such characteristics are adapted. In general, so long as a signal continues to encode the same information, the signal may be considered as the same signal. For example, a transmit signal may be considered as referring to the transmit signal in baseband, intermediate, and radio frequencies.

[0161] While the above descriptions and connected figures may depict device components as separate elements, skilled persons will appreciate the various possibilities to combine or integrate discrete features, functions into a single element. Such may include combining two or more components into a single component. Conversely, skilled persons will recognize the possibility to separate a single element into two or more discrete elements, such as splitting a single component into two or more separate components.

[0162] It is appreciated that implementations of methods detailed herein are exemplary in nature, and are thus understood as capable of being implemented in a corresponding device. Likewise, it is appreciated that implementations of devices detailed herein are understood as capable of being implemented as a corresponding method. It is thus understood that a device corresponding to a method detailed herein may include one or more components configured to perform each aspect of the related method. All acronyms defined in the above description additionally hold in all claims included herein.

[0163] While embodiments of the present disclosure have been described above, it is obvious that further embodiments may be implemented. For example, further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above. Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

[0164] While the disclosure has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims. The scope of the disclosure is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced. Reference Numeral List

[0165] 100 semiconductor laser device / VCSEL 110 mirror element / DBR

[0166] 120 p-doped semiconductor layer

[0167] 130 active region

[0168] 140 n-doped semiconductor layer

[0169] 150 (semiconductor) substrate layer

[0170] 160 mirror element / DBR

[0171] 170 optical mode

[0172] 300 semiconductor laser device / VCSEL 310, 310a-310d metasurface structure (s) 315, 315a, 315b metasurface elements 312 (high refractive index) DBR layer 314 (low refractive index) DBR layer

[0173] 350 output light / output beam

[0174] 370 dielectric spacer

[0175] 380 metal layer

[0176] 600 semiconductor laser device / VCSEL 620 spacer / spacer layer

[0177] 700 semiconductor laser device / VCSEL 710 array of nanopillars

[0178] 715 nanopillar

[0179] 720 spacer layer

[0180] 730 metalens

[0181] 740 collimated laser light

[0182] 750 VCSEL structure

[0183] 900 semiconductor laser device / VCSEL 910 metal layer

[0184] 920 spacer layer

[0185] 1000 semiconductor laser device / VCSEL 1010 actuator device

[0186] 1020 voltage source

[0187] 1030 actuating device

Claims

CLAIMS1. A vertical cavity surface emitting laser, VCSEL, comprising:a substrate layer;a plurality of epitaxial layers on a main surface of the substrate layer, the plurality of epitaxial layers comprising an n-doped semiconductor layer, a p-doped semiconductor layer, and an active region arranged between the n-doped semiconductor layer and the p-doped semiconductor layer;a first distributed Bragg reflector, DBR, disposed on or over a second surface of the substrate layer opposite to the main surface, the first DBR including a concave portion with respect to a direction facing away from the substrate layer;a second DBR disposed on or over a side or surface of the plurality of layers facing away from the first DBR; and a metasurface structure arranged on or over a surface or side of the second DBR facing away from the first DBR; wherein the concave portion of the first DBR is configured to cause the VCSEL to emit in a single transverse mode.

2. The VCSEL of claim 1, further comprisinga metal layer arranged over a side the first DBR facing away from the first DBR.

3. The VCSEL of claim 2, further comprisinga first spacer layer arranged on or over the concave surface of the first DBR; andwherein the metal layer is arranged over a side or surface of the first spacer layer facing away from the first DBR.

4. The VCSEL of claim 2 or 3,wherein the metasurface structure is arranged directly at or on a surface of the second DBR facing away from the first DBR.

5. The VCSEL of claim 2 or 3, further comprising:a second spacer layer arranged on or over a surface of the second DBR facing away from the first DBR so that the second spacer layer is arranged between the metal layer and the second DBR.

6. The VCSEL of claim 5,wherein the second spacer layer is configured to achieve a phase matching.

7. The VCSEL of claim 1, further comprising:a metal layer arranged over a side of the metasurface structure facing away from the substrate layer.

8. The VCSEL of claim 7, further comprising:a first spacer layer arranged between the metasurface structure and the second DBR; anda second spacer structure arranged between the metasurface structure and the metal layer,wherein the first spacer layer and the second spacer layer each comprise a dielectric layer.

9. The VCSEL of any of claims 1 to 8,wherein the metasurface structure is an array of metasurface elements.

10. The VCSEL of claim 9, wherein metasurface elements comprise metaatoms.

11. The VCSEL of claim 9 or 10,wherein the array of metasurface elements is a periodic array of metasurface elements,wherein the periodic array of metasurface elements comprises a series of elongated metasurface elements extending in parallel orthogonal a plane parallel to the main surface of the substrate layer.

12. The VCSEL of claim 11,wherein the periodic array of metasurface elements comprises a two-dimensional (2D) array of metasurface elements,wherein the metasurface element comprise high refractive index materials, the high refractive index materials having a refractive index greater than 2.

13. The VCSEL of any of claims 1 to 5, further comprising: a metalens arranged on or over the surface of the metasurface structure,wherein the metalens is configured to collimate light output by the VCSEL.

14. The VCSEL of claim 13,wherein the metalens comprises a 2D array of nanopillars.

15. The VCSEL of claim 14,wherein the 2D array of nanopillars spans an area in a plane parallel to the main surface substrate that is greater than twice a beam waist w0of light output by the VCSEL.

16. The VCSEL of claim 14 or 15,wherein each nanopillar comprises a material with a refractive index greater than 2.

17. The VCSEL of claim of any of claims 14 to 16,wherein the radii of the 2D array of nanopillars are designed to satisfy a position dependent phase of a fundamental mode of a cavity of the VCSEL.

18. The VCSEL of claims 1 to 17,wherein the concave portion of the first DBR comprises a plurality of layers which are each defined by a parameter d,where d is a distance measured in a vertical direction perpendicular to main surface of substrate, from a vertexof the respective layer in concave portion to an end point of that layer within the concave portion,wherein the parameter d satisfies the following expression:πwn / λ√d / L< 2wherein:w0is beam waist of light output from VCSEL, L cavity length of VCSEL, measured from p-doped semiconductor layer to substrate layer,n is effective index of refraction for semiconductor layers, andA is wavelength of light output by the VCSEL.

19. The VCSEL of any of claims 1 to 18,wherein the second DBR comprises a plurality of layers comprising alternating layers of low refractive index materials and high refractive index materials, the law refractive index materials having a refractive index less than 1.5 and the high refractive index materials having a refractive index greater than 2.

20. The VCSEL of any of claims 1 to 19, further comprising:an actuator device arranged in proximity or adjacent to the metasurface structure,wherein the actuator device is configured to modify a refractive index of the metasurface structure.

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