Monomode semiconductor laser with phase control

Description

[0001] The present invention relates to a method for producing a semiconductor laser according to the preamble of claim 1. Furthermore, the present invention relates to a semiconductor laser according to the preamble of claim 9.

[0002] According to the current state of the art, semiconductor lasers are a widely used technology for generating coherent electromagnetic radiation with properties optimized for each application. Application areas include, in particular, telecommunications, analytics, and sensor technology. Many of these applications require single-mode semiconductor lasers with a precisely adjustable, tuned, or predetermined wavelength of electromagnetic radiation. In addition, the radiation source typically has additional requirements regarding its electro-optical properties, such as output power, wavelength tuning range, or the level of side-mode suppression. The fundamental operating principle of semiconductor lasers is stimulated emission.In this case, the light of a mode or oscillation mode is amplified exponentially if it lies within the gain spectrum of the laser medium and losses are minimized. Without additional adjustments or further measures, a semiconductor laser initially contains a multitude of so-called Fabry-Perot modes, which can be excited to stimulated emission in the amplification range. This essentially results in a broad emission spectrum of a semiconductor laser.

[0003] An approach known from the prior art for achieving the required monomode operation of a semiconductor laser from the fundamentally broad emission spectrum is disclosed, for example, in EP 0 984 535 B1. This approach provides a semiconductor laser which, in addition to a waveguide ridge, has a periodic grating, in particular a metal grating, arranged parallel to the waveguide ridge. The grating period, i.e. the distance from the beginning of one grating ridge to the beginning of the next grating ridge, is set as half the wavelength, in particular half the effective wavelength, of the desired laser mode. The effective wavelength is the wavelength in the material. The grating material is selected such that a variation in the refractive index is generated in the vicinity of the grating bars, thus establishing a periodic modulation of the effective complex refractive index.

[0004] The periodic modulation of the refractive index results in a strong wavelength dependence of the losses or absorption. The periodic variation of the absorption coefficient also leads to losses with a strong wavelength dependence. This technology already allows for a significant restriction or reduction of the amplified or amplifiable modes. In other words, this means that the periodic structure or lateral structure, which does not necessarily have to be periodic, allows for a basic selection of the laser modes amplified or amplifiable by stimulated emission.

[0005] EP 1 283 571 A1 discloses another embodiment of a laser with a waveguide ridge and a lateral structure with periodic modulation of the effective complex refractive index. The lateral structure is weakly coupled to the waveguide ridge to induce interference effects in a large number of grating structure elements, thus increasing side-mode suppression while simultaneously achieving high output power.

[0006] Another embodiment of a laser with a grating structure made of materials with different refractive indices, which extends along the waveguide, is known from JP 2001 291929 A. The grating structure is preferably made of the metals titanium and gold.

[0007] US 2017 / 0299822 A1 discloses an optical transmission element for a laser with a grating structure arranged therein, consisting of materials with different refractive indices. The optical transmission element stabilizes the wavelength of the laser light, reduces the temperature dependence of the laser, and increases the controllability of the laser.

[0008] Furthermore, the document WO 2005 / 124951 A1 discloses a method for producing a semiconductor and a semiconductor according to the preamble of claims 1 and 9.

[0009] However, in the past, it was not possible to achieve true monomode operation of semiconductor lasers at the desired wavelengths with high reproducibility in accordance with theoretical expectations using the known approach. It was also previously unknown why true monomode operation of the semiconductor laser at the desired wavelength and operating parameters could not always be achieved using the technology described above.

[0010] However, this situation generally leads to the disadvantage that in the known production or in the known production processes for generic semiconductor lasers, a relatively large proportion of rejects was produced, namely precisely those semiconductor lasers which, despite corresponding lateral structures or periodic structures for modulating the refractive index, did not achieve truly monomode output spectra at the desired wavelength.

[0011] Against this background, the present invention has for its object to propose a semiconductor laser and a method for producing a semiconductor laser which overcome the disadvantages of the prior art and in particular allow a predictable and reliable production of genuine or actually monomode semiconductor lasers.

[0012] This object is achieved by a manufacturing method having the features of claim 1. Furthermore, this object is achieved by a semiconductor laser having the features of claim 9. Advantageous embodiments are the subject of the subclaims.

[0013] This object is achieved by a method for producing a semiconductor laser, which provides for the application of a multilayer structure on a semiconductor substrate, wherein the layers of the multilayer structure run parallel to a layer propagation plane defined by a surface of the semiconductor substrate, and wherein the application of the multilayer structure comprises at least the creation of an active region. Furthermore, within the scope of the method, it is provided in a manner known per se that a waveguide ridge is formed by removing material from the multilayer structure in at least two separate material removal regions, wherein the material removal occurs substantially perpendicular to the layer propagation plane.The method also comprises, in a generally known manner, the creation of an insulation layer on at least the material removal regions and the creation of a lateral structure, at least in the material removal regions, through which a basic selection of the laser modes amplified or amplified by stimulated emission is carried out. Furthermore, the method also provides, in a generally known manner, the creation of facet layer structures arranged perpendicular to the layer propagation plane in the longitudinal direction of the waveguide at one cavity end or at two opposite cavity ends for the reflection and / or coupling out of laser radiation.

[0014] According to the present invention, the method further provides a method step for producing an optical element for defining the phase position of the amplified or amplified laser modes, wherein the production of the optical element comprises the formation of meta-optical metal structures on one of the facet layer structures, and wherein the optical element is produced such that the distance in the longitudinal direction of the waveguide ridge is adjusted such that the phase position between the lateral structure and the optical element can be controlled better than π / 4. It follows that the following applies to the distance d: min d − m ⋅ λ eff / 2 ≤ λ eff / 4 .

[0015] Here m is a natural number ( m ∈ ℕ ) and λ eff is the effective wavelength in the material.

[0016] According to the invention, it is therefore provided that the optical element is arranged with a precise arrangement or with a precise distance from the end of the lateral structure layer and is also suitable for adjusting the phase position of the amplified or amplified laser modes, so that ultimately only exactly one laser mode is or can be amplified and, accordingly, true monomode operation of the semiconductor laser can be reliably generated or achieved. As can be seen from the above condition, there are a multitude of possible distances that can fulfill the criterion and can thus serve to define the phase position according to the invention. This particularly facilitates the implementation of the invention because, depending on the manner in which the optical element is produced, a corresponding distance can be selected in accordance with the condition and the optical element can be produced.

[0017] As will be explained in more detail below, there are fundamentally different ways or different modes of action by which the optical element can influence the phase position of the amplified laser modes. However, influencing the phase position is fundamentally linked to influencing the effective refractive index of the laser cavity. This means, conversely, that the optical element is, or must be, suitable for influencing the effective refractive index of the laser cavity as a whole.

[0018] This influence on the effective refractive index can be achieved through periodic structures. However, as will be explained in more detail below, other measures and associated or optically effective structures can also exert the desired influence.

[0019] The effective refractive index of the laser cavity is a global property of the laser cavity that results from the solution of the wave equation or wave equations of the laser cavity. In other words, this means that by precisely positioning the optical element at a distance d from the lateral structure, in particular one end of the lateral structure, for which min|d - m λ eff / 2| ≤ λ eff / 4 applies, taking into account the effect of the optical element on the effective refractive index of the entire laser cavity, mode selection to exactly one laser mode can be achieved. This also means that, for the realization of the optical elements according to the invention, the wave equation for the laser cavity co-determines or specifies the properties of the optical element.

[0020] By solving the aforementioned wave equation of the laser, the desired effect of the optical element on the effective refractive index can be determined, and an explanation for the hitherto unreliable production of single-mode semiconductor lasers can be found.

[0021] In the previous state of the art, the edges of semiconductor lasers were inaccurately refracted or cleaved to a certain extent, resulting in a relatively inaccurate total length of the laser cavity. This inaccuracy regarding the length of the laser cavity of approximately + / - 15 micrometers led to an undefined distance between the lateral structure or the periodic grating for the basic selection of the amplified laser modes, on the one hand, and the facet defining the cavity length, on the other. Due to the aforementioned inaccuracy, this undefined distance was not always within the range min|d - m λ eff / 2| ≤ λ eff / 4. Consequently, the phase position of the amplifiable laser modes remained uncontrolled according to the aforementioned state of the art, and modes other than the desired laser mode could be amplified based on beat effects that did not exactly correspond to the mode intended by the lateral structure layer or the wavelength-selective element.This led to the inaccurate or unreliable mode selection prevailing in the state of the art.

[0022] The beat effects, which are prevented or suppressed by the precise phase position due to the optical element according to the invention and / or by the precise positioning of the optical element, are most likely due to Floquet theory, which, as the mathematical basis of the Bloch theorem, states that the solutions to the wave equation or mode equation can be represented as a superposition of a right- and a left-propagating wave, which, depending on the cavity properties and boundary conditions, particularly in the shape of the facets, can lead not only to the desired stationary standing waves, but also to standing waves with a beat. It is suspected that such beats or beat frequencies are the reason, or at least a significant reason, for the previously unsatisfactory or at least unreliably reproducible production of single-mode semiconductor lasers.

[0023] However, by the method according to the invention and in particular by the generation and positioning of the optical element for defining the phase position and the effective refractive index of the amplified or amplified laser modes, said beating is prevented or suppressed, so that reliable single-mode semiconductor lasers can be manufactured.

[0024] In other words, this means that by producing the optical element according to the invention, a preselection or basic selection of amplified or amplified modes made by the lateral structure layer, in particular by the periodic grating, is further specified or determined by the precise definition of the phase position of the modes in the resonator or in the laser cavity, with the result that in the end only exactly one laser mode with a desired wavelength is amplified and coupled out.

[0025] The inventive spacing of the optical element from the end of a lateral structure layer or a periodic grating determining the basic selection of modes also ensures a sufficiently precise determination or specification of the cavity length of the laser cavity.

[0026] According to a first, advantageous embodiment of the method, it can be provided that the optical element is produced together with the formation of the facet layer structure or is produced on it following the formation of the facet layer structure. The optical element itself can also be formed as a facet layer structure. This means that it can generally be provided that the optical element has no or only a partial overlap with the said lateral structure layer perpendicular to the layer propagation plane. This is because when the optical element is applied or formed as part of the formation of the facet layer structure or following the formation of the facet layer structure, it can be provided, for example, that the optical element is formed in regions of the multilayer structure on the facet that is arranged below the lateral structure perpendicular to the layer propagation plane.Despite all this, the distance according to the invention of the optical element to the end of the lateral structure layer in the longitudinal direction of a waveguide ridge should be defined by corresponding distances which relate to planes which, on the one hand, run parallel to the respective facet and thus perpendicular to the layer propagation plane and equally perpendicular to the longitudinal direction or at least substantially perpendicular to the longitudinal direction of the waveguide ridge.

[0027] When forming the optical element together with or subsequent to the formation of the facet layer structure, or as a facet layer structure, there are fundamentally different possibilities or options, as will be explained in more detail below. As already explained above, it is important that not only the distance d is controlled precisely enough, but also that the optical element achieves the desired phase position by appropriately adjusting the effective refractive index of the laser cavity.

[0028] When forming the optical elements together with the facet layer structure or on the facet layer structure, it can be advantageously exploited that the lateral structure layer of the semiconductor laser which accomplishes the coarse selection can generally be formed without problems up to a fracture or cleavage edge of a semiconductor laser or a corresponding laser layer structure, so that the positioning of the optical element according to the invention at a distance d with the precision of min|d - m λ eff / 2| ≤ λ eff / 4 - or, for example, for m=1 of at most half the wavelength, in particular of less than half the effective wavelength, is readily possible, even if, for example, a facet layer structure is first formed or deposited on a correspondingly cleaved or broken facet.Such faceted layer structures can usually be formed with a total thickness or a total layer thickness of less than half the effective wavelength of the semiconductor laser. The faceted layer structures are typically a few tens to a few hundred nanometers thick.

[0029] In a particularly preferred embodiment of the method, it can be provided that the optical element is produced by varying layers and / or layer properties of layers of the facet layer structure, which are otherwise intended for optimizing and / or adjusting a laser threshold or an output power. This method can particularly advantageously ensure that the facet layer structure not only ensures the function of adjusting or optimizing the laser threshold and / or adjusting or optimizing the output power, but also simultaneously functions as an optical element as a whole or at least in part within the meaning of the present invention.For this purpose, it may or must be necessary to optimize the facet layer structure both with regard to the other laser properties and with regard to the effect as an optical element or to find an appropriate compromise which, however, at least also ensures an effect as an optical element according to the invention.

[0030] The embodiment described above is particularly advantageous because it enables effective process control for producing the semiconductor lasers according to the invention. Because many semiconductor lasers typically have a facet coating with a facet layer structure, potentially additional process steps can be dispensed with when a facet layer structure is combined with an optical element according to the invention. Instead, it may be sufficient to modify the layer properties and / or the layer sequences that are provided anyway for producing the facet layer structure in such a way that, in addition to a corresponding influence on the laser threshold and / or the output power, an inventive definition of the phase position of the amplified laser modes is also enabled, while maintaining an equally inventive distance between the optical element and the lateral structure layer.

[0031] In a further, particularly advantageous variant of the method according to the invention, it can be provided that the production of the optical element includes the formation of meta-optical metal structures. Such meta-optical metal structures with suitable resonance properties are well suited for influencing the effective refractive index of the entire laser cavity. At the same time, such meta-optical metal structures can be produced with sufficient precision using the basically known method. This advantageously allows a corresponding influence on the phase position of the amplifiable laser modes. As an example of possible structures, reference is made to N. Yu et al., Optics Express volume 16, issue 24, page 19447 (2008).

[0032] Furthermore, it can be provided that the production of the optical element comprises the formation of metallic and / or organic three-dimensional structures, which are preferably selectively solidified from a liquid or viscous precursor in a two-photon polymerization process. Both the formation of meta-optical metal structures and the formation of metallic and / or organic three-dimensional structures particularly preferably take place on a corresponding facet layer structure while maintaining the distance according to the invention from the lateral structure layer, in particular from the end of the lateral structure layer.The methods for producing such three-dimensional structures, preferably within the framework of a two-photon polymerization process, can provide correspondingly fine structures with sufficient precision, which in turn can be used to influence the phase position or to influence the effective refractive index of the entire laser cavity. It can also advantageously be provided that the production of the optical element includes the formation of dielectric and / or mirror layer structures, taking into account the influence on the phase position of the amplified or amplifiable laser modes. The said optical layer structures, namely the electrical layer structures or mirror layer structures, are known and widely used and can therefore be produced with appropriate accuracy and reliability or with high reproducibility.A special prerequisite, however, is that according to the present invention, the corresponding layer structures are not only used for mirroring or anti-reflection as such, but are selected or formed together with the lateral structure layer with regard to their property with regard to defining the phase position. This means that the inventive condition of the distance d to the end of the lateral structure layer ensures that the optical element is in phase with the lateral structure layer and thus guarantees mode selection to a single mode. This applies quite generally to the optical element and to other or similar types of mirrors or reflection elements. Likewise, the other effects, for example the effects as a mirror or reflection element, must be taken into account in the design or dimensioning of the entire semiconductor laser arrangement or semiconductor laser diode.For example, a distributed Bragg reflector (DBR) element can be provided. This can also be arranged in the area of ​​the material removal regions and / or the waveguide ridge. Alternatively, a precisely phase-matched dielectric mirror can be formed on a facet layer structure.

[0033] It is also possible to influence the facet itself to form the optical element. For example, the properties according to the invention, and thus the optical element, can also be achieved by an etching process for processing the facets.

[0034] As an alternative to forming the optical element perpendicular to the layer propagation plane, in particular parallel to a facet layer structure, it may also be expedient to provide or form the optical element with an extension or propagation substantially or at least also parallel to the layer propagation plane.

[0035] Accordingly, an advantageous embodiment, as already indicated above, provides that the optical element is formed in the region of the multilayer structure, preferably in the region of the waveguide ridge or in the region between a waveguide ridge and a cavity end.

[0036] This can, for example, provide the advantage that the optical element can already be formed before the semiconductor lasers are separated from a composite comprising a plurality of semiconductor lasers, in particular a corresponding wafer. Likewise, it is then advantageously possible to form a corresponding plurality of optical elements simultaneously or simultaneously for a plurality of semiconductor lasers present in a composite using appropriate process steps.

[0037] In this case, it may be advantageous if the lateral structure layer or the element providing the basic mode selection, in particular the grating or lateral structure layer, is not formed all the way to one end of a laser cavity or a later partially separated or separated laser cavity. This allows the optical element to function as a length-defining element of the laser or laser cavity in addition to its phase-defining effect, whereby the distance d between the optical element on the one hand and the end of the lateral structure must also be ensured, as per the invention.

[0038] Forming the optical element in the region of the multilayer structure, preferably in the region of the waveguide ridge or in the region between a waveguide ridge and a cavity end, also has the advantage of deliberately creating a distance between the end of the lateral structure and the original or actual cavity end. This can also have a beneficial effect on the far field of the semiconductor laser, independent of the inventive action of the optical element.

[0039] According to a particularly preferred embodiment, it can be provided, for example, that the production of the optical element comprises the formation of an active or passive phase segment, which is preferably formed on or at the waveguide ridge. Active or passive heating elements, among others, can be provided as phase segments, which, via an electrical or ohmic heating effect or the corresponding heat development due to a current flow, cause the environment in the semiconductor laser to heat up, which in turn then leads to an influence on the effective refractive index and thus to a definition of the phase position of the amplified laser modes. An active phase segment can, for example, have a separately controllable electrical supply and / or have a corresponding separate contact.With a passive phase segment, for example, current flow and a heating effect or heat generation due to the laser pump current can be exploited to at least deliberately cause heat generation or heating. By appropriately arranging the phase segment, in addition to specifically influencing the effective refractive index, the distance to the end of the lateral structure layer required according to the invention can also be maintained.

[0040] Alternatively, a phase segment can be realized using the Kerr effect.

[0041] Forming the optical element in the region of the multilayer structure, preferably in the region of the waveguide ridge or in the region between a waveguide ridge and a cavity end, for example, in a kind of interrupted or direct continuation of the waveguide ridge while maintaining the distance d from the end of the lateral structure layer, also has the advantage of deliberately creating a distance between the end of the lateral structure and the original or actual cavity end. This can also exert a beneficial effect on the far field of the semiconductor laser, independent of the inventive action of the optical element.

[0042] A further advantageous embodiment of the method can provide for the optical element to be formed by ion implantation into the multilayer structure. Ion implantation is preferably also performed in the active region. Further preferably, the ion implantation can take place in a region located in the layer propagation plane between one end of a waveguide ridge and an original or physical end of the laser cavity or semiconductor laser.

[0043] Furthermore, it can advantageously be provided that the optical element is formed by generating photonic crystals in the multilayer structure. It can preferably be provided that the structures, in particular the holes that form the photonic crystal, are structured throughout the entire epitaxial structure of the semiconductor up to a buffer layer, although variations for adjusting the coupling strength are possible.

[0044] It can also advantageously be provided that the optical element is formed by generating photonic integrated circuits. The elements that form the photonic integrated circuit can be structured, in particular etched, into part or all of the multilayer structure, for example, adjacent to a waveguide, i.e., in the longitudinal direction, and thus between the end of a waveguide and the physical or material end of the laser or the laser cavity. It is possible, for example, for a part of a lower cladding or a lower cladding layer to be deliberately left untouched or unstructured. The optical element can, for example, have the shape of a circle or a closed curve.

[0045] Furthermore, it can advantageously be provided that a plurality of semiconductor lasers are formed adjacent to one another or adjacent to one another on a common semiconductor substrate, in particular a wafer, and that subsequent singulation of the semiconductor laser takes place, preferably by forming an array or matrix arrangement with a plurality of semiconductor lasers arranged next to one another and connected to one another, in particular by a suitable singulation method.

[0046] As already indicated above, it can advantageously be provided that the optical element is formed for a plurality of semiconductor lasers arranged next to one another, preferably for all semiconductor lasers of a common array or matrix arrangement together, in particular simultaneously. This applies both to the formation of the optical element in the region of the facet or in the region of the facet layer structure, and to the formation of the optical element in the region of the waveguide ridge or in the region of the material removal regions, in particular with propagation parallel to the layer propagation plane. Particularly preferably, it can be provided that the optical element is formed before groups of semiconductor lasers or groups of semiconductor laser cavities are separated.The groups can then each be intended for the operation of individual semiconductor lasers or the combined operation of several semiconductor lasers or can be suitable for such operating modes.

[0047] With regard to the semiconductor laser, the above-mentioned object is achieved by a semiconductor laser having a multilayer structure comprising at least one waveguide ridge and a material removal region laterally adjacent to the waveguide ridge, wherein the multilayer structure is arranged on a semiconductor substrate and wherein a layer propagation plane is defined by a surface of the semiconductor substrate, wherein the multilayer structure has at least one active region, and wherein the active region has a layer or material structure for forming a laser layer based on the principle of stimulated emission, and wherein furthermore, at least in the material removal regions, preferably on an insulation layer, a lateral structure layer is provided, by means of which a basic selection of the laser modes amplified or amplified by stimulated emission takes place,and wherein, perpendicular to the layer propagation plane in the longitudinal direction of the waveguide ridge, facet layer structures for reflecting and / or coupling out laser radiation are formed at one cavity end or at two opposite cavity ends, achieved in that the semiconductor laser has an optical element for defining the phase position of the amplified or amplified laser modes, wherein the optical element in the longitudinal direction of the waveguide ridge has a distance d from the lateral structure layer that satisfies the condition min|d - m λ eff / 2| ≤ λ eff / 4, and in that the optical element has meta-optical metal structures arranged on one of the facet structure layers.

[0048] The optical element according to the invention thus achieves, on the one hand, a defined cavity length of the semiconductor laser or, in other words, prevents the formation or presence of a region in the longitudinal direction of the waveguide ridge in which a lack of phase definition promotes or causes the formation or amplification of beat modes. Furthermore, in addition to or alongside the definition of the cavity length, the phase position of the amplified or amplifiable laser modes is also defined, so that the optical element as a whole reduces a number of amplifiable or amplified modes already restricted or predefined by the lateral structure layer to precisely one amplified laser mode, thus enabling safe and reliable operation of the semiconductor laser in a monomode operating mode.

[0049] To avoid unnecessary repetition, with regard to the advantages and advantageous effects, as well as with regard to the features of the semiconductor laser device, reference should be made to the above-described embodiment of the method according to the invention and its advantageous embodiments. In other words, features disclosed in the method should also be considered disclosed as material features or device features, and vice versa.

[0050] According to a first advantageous embodiment of the semiconductor laser, the optical element can be embedded in the facet layer structure, arranged on the facet layer structure, or formed as a facet layer structure. This advantageously achieves both the required maximum distance from the end of the lateral structure layer and the desired influence on the effective refractive index of the entire laser cavity and thus on the phase position of the amplifiable laser modes.

[0051] The optical element is intended to have meta-optical metal structures. The meta-optical metal structures are formed on a facet layer structure in such a way that the phase-defining effect of the optical element is particularly effective.

[0052] It can also advantageously be provided that the optical element has metallic and / or organic three-dimensional structures, which are preferably selectively solidified from a liquid or viscous precursor in a two-photon polymerization process. Such structures, in particular three-dimensional structures, are also well suited for adjusting the phase position of the laser radiation or the amplified laser modes and can be formed reliably and precisely, for example on a facet layer structure. Such structures can also be referred to as printed structures, even if the process is an additive manufacturing process rather than a conventional printing process. It can also advantageously be provided that the optical element has dielectric and / or mirror layer structures.The said structures are sufficiently known in the field of semiconductor optics and, in addition to their function as mirrors, filters or the like, can also be used advantageously as optical elements within the meaning of the present invention, which then serve primarily or overall for the precise adjustment of the phase position of the amplifiable laser modes at a specific distance from the end of the lateral structure layer.

[0053] Furthermore, it can advantageously be provided that the optical element is formed in the region of the multilayer structure, preferably in the region of the waveguide ridge or in the region between a waveguide ridge and a cavity end. In contrast to a formation in the region of the facet layer structures, a formation in the region of the multilayer structure provides for an extension at least also parallel to the layer propagation plane. However, this does not mean, conversely, that no propagation in a direction perpendicular to the layer propagation plane can be provided. Rather, the optical elements in the region of the multilayer structure can also be present as three-dimensional structures, which then preferably extend in the region of the waveguide ridge or between the waveguide ridge and the physical cavity end both over a region in the layer propagation plane and over a region perpendicular to the layer propagation plane.

[0054] The optical element can preferably be designed as an active or passive phase segment, which is arranged in particular on or at the waveguide ridge. The phase segment can influence the phase position by influencing the effective refractive index through heat generation due to an electric current. The effect of the phase segment can be easily dimensioned so precisely that the distance between the optical element and the lateral structure layer is specified with the precision of min|d - m λ eff / 2| ≤ λ eff / 4.

[0055] It can also be advantageous for the optical element to be formed as an ion implantation region of the multilayer structure.

[0056] For example, a corresponding ion implantation region can locally modulate the refractive index, which then also affects the effective refractive index of the entire laser cavity and thus contributes to the phase definition of the amplified or amplified laser modes. An ion implantation region can also be formed according to the invention, maintaining the distance d with the precision min|d - m λ eff / 2| ≤ λ eff / 4 to one end of the lateral structure layer.

[0057] Equally advantageously, the optical element can also be formed as a region in the multilayer structure with photonic crystals. It can also advantageously be provided that the optical element is formed as a component of a photonic integrated circuit. This can be formed, for example, by known masking, exposure, and etching processes in the multilayer structure, for example between one end of or directly adjacent to a waveguide ridge and a physical cavity end. Furthermore, heating or active temperature control of a corresponding component of the photonic integrated circuit can be provided, for example, in order to achieve even better definition of the phase position of the amplifiable laser modes.

[0058] Examples and advantageous developments of the present invention emerge from the attached, purely schematic drawings.

[0059] They show: Fig. 1 a schematic representation of the operation of the semiconductor laser according to the invention; Fig. 2 an exemplary schematic representation of a semiconductor according to the invention in a perspective view; Fig. 3 a schematic representation of the electric field of the light mode of a semiconductor laser according to the invention.

[0060] Fig. 1 shows in a plan view of a layer propagation plane the basic functionality or the basic arrangement of the optical element 2 according to the invention relative to a lateral structure layer 1. The only indicated lateral structure layer 1 can be formed from parallel webs, for example of a metallic material, as a so-called DFB structure or distributed feedback structure, wherein in the illustration of the Fig. 1 Only corresponding lines are drawn to symbolize the ridges. According to recent findings, a lateral structure layer that does not consist of parallel ridges but is optimized in two spatial directions can also lead to an improvement in the properties of a semiconductor laser.

[0061] Accordingly, the lateral structure layer should not be understood exclusively as an arrangement of parallel, preferably metallic webs with a uniform spacing to produce a periodic grating, but generally as structural layers that at least also effect a basic selection of a very large number of laser modes that can be amplified in a laser cavity.

[0062] In the Fig. 1 Two rows of ridges of the lateral structure layer 1 are indicated. Between these, a Fig. 1 a waveguide ridge (not shown) may be arranged. The optical element 2 according to the invention is located at a distance d from the end of the lateral structure layer 1, wherein the distance d amounts to at most half the effective wavelength of the desired laser radiation. As a result, the optical element has a length-defining effect on the laser cavity. Furthermore, the precisely adjusted distance d effectively suppresses the generation and amplification of beat modes. In addition, a precise phase position of the amplified laser modes is defined by the appropriate design of the optical element at the distance d, namely by adjusting the effective refractive index of the entire laser cavity while taking the optical element 2 into account, so that ultimately only a single laser mode is amplified and coupled out, thus enabling monomode operation of the laser.

[0063] In the example of Fig. 1 An optical element 2 is arranged at each end of the lateral structure layer 1. Such an arrangement may be advantageous, but does not have to be implemented. For example, a single optical element 2 may be sufficient to determine the phase position of the amplified laser modes and to suppress or prevent beat modes.

[0064] Fig. 2 shows, by way of example and schematically, a perspective view of an embodiment of a semiconductor according to the invention. The semiconductor laser comprises a substrate 3 on which a layer structure or multilayer structure 4-8 suitable for generating and coupling out laser beams is epitaxially applied.

[0065] For example, the multilayer structure 4-8 can be used to form a semiconductor laser, such as an interband or quantum cascade laser. The multilayer structure 4-8 comprises an active zone 6 surrounded by an upper and a lower waveguide layer 5, 7, which in turn are embedded in an upper and lower cladding layer 4, 8. A waveguide ridge 9 is formed from the upper cladding layer 8 in the region of material removal areas 10 by a material removal process. The contact layers 11, 12 serve for current injection.

[0066] In addition to the waveguide ridge 9, the optical element 2 according to the invention is also formed by the material removal process. In the example of the Fig. 2 in the form of a mirror layer structure, namely in the form of a Distributed Bragg Reflector, which on the one hand reflects the Fig. 1 already schematically shown arrangement, in particular the one shown in the Fig. 1 The optical element 2 has a distance d from the end of the lateral structure layer 1, as shown in the figure, and further defines the phase position of the amplified or amplified laser modes and thus contributes to further mode selection, down to exactly one laser mode. The optical element 2 is in the example of the

[0067] Fig. 2 arranged in the region of the multilayer structure 4 to 8, namely in the longitudinal direction of the waveguide ridge 9 between one end of the waveguide ridge 9 and one end of the laser cavity.

[0068] Alternatively or additionally, it can also be provided that the optical element 2 is arranged in the region of a facet 13. In this case, it can be provided that the optical element 2 is either integrated into a facet layer structure which is Fig. 2 itself is not shown, or is applied to the outside of the facet layer structure in the longitudinal direction of the waveguide ridge 9. As at the right end of the laser cavity according to Fig. 2 As can be seen, the lateral structure layer 1 can be brought or formed up to the cavity end without any problems, so that even when the optical element 2 is formed in the region of the facet of the semiconductor laser, in particular on a facet layer structure or within a facet layer structure, the inventive distance d of the desired laser mode can be easily maintained. This is because the facet layer structure, which is otherwise provided for optimizing or adjusting the laser threshold and / or the output power, generally has a total thickness of only a few tens to a few hundred nanometers.Particularly preferably, it can even be provided that the optical element 2 is introduced, in particular integrated, into the facet layer structure in such a way that the otherwise provided layers of the facet layer structure are only adapted in their properties and / or in their sequence, so that the optical element 2 according to the invention can also be formed simultaneously with the method steps for forming the facet layer structure.

[0069] Fig. 3shows a schematic representation of the electric field E of the light mode of a semiconductor laser according to the invention. The arrows represent the field strength E and direction of the electric field of the light mode at a fixed point in time. The distance d between the end 14 of the wavelength-selective element or the lateral structure layer 1 and the beginning 15 of an optical element 2 according to the invention in the form of a DBR mirror, which is determined by the first transition from the left from a higher to a lower refractive medium, is, in the optimal case according to the invention, an integer multiple of half the wavelength in the medium. The example shows four half wavelengths in the medium. According to the invention, the phase position between the wavelength-selective element or the lateral structure layer 1 and the DBR segment or optical element 2 is therefore adjusted such that both elements are in phase at the desired wavelength.This is sufficiently ensured by the required accuracy of the inventive condition min|d - m·λ eff / 2| ≤ λ eff / 4.

Claims

1. A method for producing a semiconductor laser comprising the method steps: - applying a multilayer structure (4 - 9) on a semiconductor substrate (3), the layers of the multilayer structure (4 - 9) extending parallel to a layer extension plane defined by a surface of the semiconductor substrate (3) and the application of the multilayer structure (4 - 9) including at least the generation of an active region; - abrading material of the multilayer structure (4 - 9) in at least two material abrasion areas (10) separated from one another, the material being abraded substantially perpendicular to the layer extension plane, whereby a waveguide ridge (9) is formed; - generating an insulation layer on at least the material abrasion areas (10); - generating a lateral structure layer (1), at least in the material abrasion areas (10), a basic selection of the laser modes amplified or amplifiable through stimulated emission taking place via the lateral structure layer; - generating facet layer structures which serve for reflecting and / or decoupling laser radiation and are disposed on a cavity end or on two opposite cavity ends perpendicular to the layer extension plane in the longitudinal direction of the waveguide ridge (9), characterized by - generating an optical element (2) for defining the phasing of the amplified or amplifiable laser modes, the generation of the optical element (2) including the formation of meta-optical metal structures on one of the facet layer structures and the optical element (2) being generated in such a manner that it has a distance d to an end (14) of the lateral structure layer (1) in the longitudinal direction of the waveguide ridge (9), distance d fulfilling the condition min|d - m·λeff / 2| ≤ λeff / 4, m being a natural number ( m ∈ ℕ) and λeff being the effective wavelength in the material.

2. The method according to claim 1, characterized in that the optical element (2) is generated simultaneously with the formation of the facet layer structures or on the facet layer structure in subsequence to the formation of said facet layer structure, in particular the optical element (2) being generated by a variation of layers and / or layer properties of layers of the facet layer structure, the layers and / or layer properties otherwise being intended for optimizing and / or setting a laser threshold or an output power.

3. The method according to claim 1 or 2, characterized in that the generation of the optical element (2) includes the formation of metallic and / or organic three-dimensional structures, which are hardened selectively from a liquid or viscous precursor preferably in a two-photon polymerization method.

4. The method according to any one of the claims 1 to 3, characterized in that the generation of the optical element (2) includes the formation of dielectric layer structures and / or mirror layer structures while taking into consideration the influencing of the phasing of the amplified or amplifiable laser modes.

5. The method according to any one of the claims 1 to 4, wherein a further optical element (2) for defining the phasing of the amplified or amplifiable laser modes is generated, the further optical element (2) being generated in such a manner that it has a distance d to an end (14) of the lateral structure layer (1) in the longitudinal direction of the waveguide ridge (9), distance d fulfilling the condition min|d - m·λeff / 2| ≤ λeff / 4, m being a natural number ( m ∈ ℕ) and λeff being the effective wavelength in the material and wherein the further optical element (2) is formed in the area of the multilayer structure (4 - 9), preferably in the area of the waveguide ridge (9) or in the area between a waveguide ridge (9) and a cavity end.

6. The method according to claim 5, characterized in that the further optical element (2) is formed by ion implantation in the multilayer structure (4 - 9) or by generating photonic crystals in the multilayer structure (4 - 9) or by generating photonically integrated circuits.

7. The method according to any one of the claims 1 to 6, characterized in that a plurality of semiconductor lasers are realized to be adjacent to one another or to abut against one another on a shared semiconductor substrate (3) and in that the semiconductor lasers are separated in subsequence to the formation, preferably by forming an array or matrix arrangement having several adjacent and interconnected semiconductor lasers, in particular by mechanical splitting and / or sawing, the optical element (2) in particular being formed together, in particular simultaneously, for several adjacent semiconductor lasers, preferably for the semiconductor lasers of a shared array or matrix arrangement.

8. The method according to any one of the claims 1 to 7, characterized in that distance d is set in the longitudinal direction of the waveguide ridge such that the phasing between the lateral structure and the optical element (2) and / or between the lateral structure and the further optical element (2) is controlled better than π / 4.

9. A semiconductor laser, comprising a multilayer structure (4 - 9) comprising at least one waveguide ridge (9) and material abrasion areas (10) laterally abutting against the waveguide ridge (9), the multilayer structure (4 - 9) being disposed on a semiconductor substrate (3) and a layer extension plane being defined by a surface of the semiconductor substrate (3), the multilayer structure (4 - 9) having at least one active region, the active region having a layer structure and / or material structure for forming a laser layer based on the principle of stimulated emission, a lateral structure layer (1) being provided at least in the material abrasion areas (10), preferably on an insulation layer, a basic selection of the laser modes amplified or amplifiable via stimulated emission taking place via the lateral structure layer, and facet layer structures, which serve for reflecting and / or decoupling laser radiation, being formed on a cavity end or on two opposite cavity ends perpendicular to the layer extension plane in the longitudinal direction of the waveguide ridge (9), characterized in that the semiconductor laser has an optical element (2) for defining the phasing of the amplified or amplifiable laser modes, the optical element (2) having a distance d to an end (14) of the lateral structure layer (1) in the longitudinal direction of the waveguide ridge (9), distance d fulfilling the condition min|d - m λeff / 2| ≤ λeff / 4, m being a natural number ( m ∈ ℕ) and λeff being the effective wavelength in the material and in that the optical element (2) has meta-optical metal structures disposed on one of the facet layer structures.

10. The semiconductor laser according to claim 9, characterized in that the optical element (2) is embedded in the facet layer structure or is disposed on the facet layer structure.

11. The semiconductor laser according to claim 9 or 10, characterized in that the optical element (2) has metallic and / or organic three-dimensional structures, which are hardened selectively from a liquid or viscous precursor preferably in a two-photon polymerization method.

12. The semiconductor laser according to any one of the claims 9 to 11, characterized in that the optical element (2) has dielectric layer structures and / or mirror layer structures.

13. The semiconductor laser according to any one of the claims 9 to 12, characterized in that the semiconductor laser comprises a further optical element (2) for defining the phasing of the amplified or amplifiable laser modes, the optical element (2) having a distance d to an end (14) of the lateral structure layer (1) in the longitudinal direction of the waveguide ridge (9), distance d fulfilling the condition min|d - m·λeff / 2| ≤ λeff / 4, m being a natural number ( m ∈ ℕ) and λeff being the effective wavelength in the material and the further optical element (2) being formed in the area of the multilayer structure (4 - 9), preferably in the area of the waveguide ridge (9) or in the area between a waveguide ridge (9) and a cavity end.

14. The semiconductor laser according to claim 13, characterized in that the further optical element (2) is realized as an ion implantation area of the multilayer structure (4 - 9) or as an area of the multilayer structure (4 - 9) having photonic crystals or as a component of a photonically integrated circuit.

15. The semiconductor laser according to any one of claims 9 to 14, characterized in that distance d is set in the longitudinal direction of the waveguide ridge such that the phasing between the lateral structure and the optical element (2) and / or between the lateral structure and the further optical element (2) can be controlled better than π / 4.