LASER DIODE WITH IMPROVED ELECTRICAL CONDUCTIVITY

Description

[0001] The invention relates to a laser diode with improved electrical conduction properties and a corresponding diode laser. Introduction

[0002] For high-performance applications, diode lasers are soldered onto a thermally conductive substrate. The epitaxial layers, usually the p-doped side, are soldered directly onto the substrate for optimal cooling. In this configuration, the entire p-side is electrically contacted and thus operated with a common voltage. In many areas, such as materials processing, larger systems with higher power levels are required. For this purpose, the diode lasers are arranged in larger areas (arrays) to form so-called laser bars. All laser bars are controlled jointly. State of the art

[0003] To achieve improved electro-optical properties, such as improved beam quality, individual sections of the laser diode are often controlled separately. A well-known example of such a component is a tapered laser diode.

[0004] Figure 1 shows a schematic representation of a conventional tapered laser diode 56. An n-type cladding layer 62, an n-type waveguide layer 64, a layer with an active zone 66, a p-type waveguide layer 68, and a p-type cladding layer 70 are applied to a substrate 58. Furthermore, the tapered laser diode 56 has a p-type contact region 72 and an n-type contact region 74, wherein the p-type contact region 72 consists of a ridge waveguide region 76 and a tapered region 78. The tapered laser diode 56 is bounded by a front facet 80 and a rear facet 82.

[0005] As known, for example, from C. Fiebig et al., IEEE JSTQE 15(3), pp. 978-983 (2009); K. Paschke et al., IEEE JSTQE 11(5), pp. 1223-1226 (2005) and B. Sumpf et al., Opt. Quant. Electron. 35, pp. 521-532 (2003), the beam quality and the achievable maximum power, or the conversion efficiency, depend on the ratio of the currents introduced into the ridge waveguide region 76 and the trapezoidal region 78 as well as on the geometries of these regions.

[0006] In individually constructed tapered lasers, the ratio of the currents introduced into the ridge waveguide region 76 and the trapezoidal region 78 is adjusted by separately controlling the ridge waveguide region and the trapezoidal region. However, this leads to disadvantages in terms of manufacturing costs as well as cooling and power scaling in larger systems. If the ridge waveguide 76 and the trapezoidal region 78 are short-circuited to enable joint control, this leads to deteriorated properties, such as reduced power, lower efficiency, and degraded beam quality. Known measures to counteract this include reducing the trapezoidal region while simultaneously lengthening the ridge waveguide region. However, these measures have not yet been able to compensate for these disadvantages.

[0007] A conventional broad area laser diode 84 is in Figure 2Due to the similar structure, the same reference numerals are used as for the tapered laser diode 56 from Figure 1 The broad-area laser diode 84 also has a front facet 80 and a rear facet 82. An n-type cladding layer 62, an n-type waveguide layer 64, a layer with an active zone 66, a p-type waveguide layer 68, and a p-type cladding layer 70 are applied to a substrate 58. Furthermore, the broad-area laser diode 84 has a p-type contact region 72 and an n-type contact region 74.

[0008] As is known, for example, from H. Wenzel et al., New J. Phys. 12, p. 085007 (2010), the occurrence of hole burning effects has proven to be detrimental in broad-area laser diodes. This refers to the formation of spatial zones within the laser diode that contribute less to the lasing process, for example, a local reduction in gain due to spatial hole burning or a reduced amplification of desired frequencies (spectral hole burning).

[0009] The problem of longitudinal hole burning is solved, for example, in J. Feng et al., Appl. Phys. Lett. 66, pp. 2028-2030 (1995) by separate contacting, which, however, is complex and therefore expensive. Another disadvantage is the formation of thermal lenses. In this case, an inhomogeneous temperature distribution in the optical medium, caused, for example, by the electric current flow and the resulting local self-heating, influences the additional waveguiding and creates a consequent undesirable increase in the divergence angle (P. Crump et al., Semicond. Sci. Technol. 27, 045001 (2012)).

[0010] The problem of the thermal lens was solved, for example, in E. O'Neill et al., IEE Proc. Optoelectron. 147, pp. 31-35 (2000) by using external heating elements (external laser radiation), which, however, is complex and therefore expensive.

[0011] US 6,148,013 A relates to an optoelectronic III-V semiconductor device for emitting high-power radiation at visible wavelengths with a laterally uniform, diffraction-limited, quasi-Gaussian beam profile. US 6,014,396 A discloses a similar expanded optoelectronic semiconductor device.

[0012] US 6,014,396 A shows differentially structured pumped semiconductor gain media. The amplifier is pumped at its input end with a current density lower than the current density at the output end to maintain beam coherence through differential pumping at high power levels.

[0013] An object of the present invention is therefore to provide a tapered laser diode with an improved design that, when the different regions are controlled jointly, does not have the disadvantages previously associated with it. A further object of the present invention is to provide a broad-area laser diode with an improved design that avoids the occurrence of hole burning effects and the formation of thermal lenses. Furthermore, an object is to provide a broad-area laser diode with an improved design that has a more stable emission spectrum. Disclosure of the invention

[0014] These objects are achieved by the features of independent patent claims 1 and 10. Further advantageous embodiments of the present invention emerge from the features mentioned in the subclaims.

[0015] According to a first aspect of the present invention encompassed by the claims, a laser diode is disclosed, comprising: at least one active layer which is arranged within a resonator and is operatively connected to a coupling-out element and which has at least one contact layer for coupling charge carriers into the active layer, wherein the resonator has at least a first section and a second section, wherein the maximum width of the active layer in the first section differs from the maximum width of the active layer in the second section and a projection of the contact layer along a first axis extending perpendicular to the active layer overlaps both with the first section and with the second section.According to the invention, it is provided that the second section has a plurality of separate resistance elements introduced by implantation, the specific electrical resistance of which is greater than the specific electrical resistance of the regions between adjacent resistance elements and a width of the resistance elements along a longitudinal axis of the active layer is less than 20 µm and a projection of the resistance elements onto the active layer along the first axis overlaps with at least 10% of the active layer, wherein the first section and the second section have a common electrical contact and the ratio between the current component in the first section and the current component in the second section is set via the resistance elements.

[0016] The advantage of the present invention is that the total electrical resistance in the second section is increased to such an extent that a larger proportion of the current flows through the first section. By dimensioning the current in the first section based on the design, an optimal ratio can be achieved between the current share in the first section and the current share in the second section. This ensures optimal current distribution despite the shared contact between the first and second sections.

[0017] Preferably, the first section has no resistance elements.

[0018] Preferably, the second section is designed such that the current density within the second section (also referred to as amplifier section) is longitudinally uniform across each resistance element and across each region between two resistance elements. This means that a maximum current density and a minimum current density across each resistance element and across each region between two resistance elements deviate during operation preferably by less than 20%, more preferably by less than 10%, even more preferably by less than 5%, even more preferably by less than 2%, and even more preferably by less than 1%. Likewise, it is preferred that the second section is designed such that the specific electrical resistance within the second section is longitudinally uniform across each resistance element and across each region between two resistance elements.This preferably means that a maximum of the specific electrical resistance is followed by a minimum of the specific electrical resistance in the longitudinal direction (i.e. along the longitudinal axis (axis X1 in . Figure 3 )) across each resistance element and each region between two resistance elements by less than 20%, preferably by less than 10%, even more preferably by less than 5%, even more preferably by less than 2%, and even more preferably by less than 1%. This allows the current density to be advantageously increased only in the first section (also referred to as the single-mode section).

[0019] Preferably, the length of the second section is greater than 50%, more preferably greater than 60%, of the total length (=sum of the length of the first section and the length of the second section) to achieve sufficient amplification. Preferably, the device has only one trapezoidal amplifier section.

[0020] Preferably, the ratio (quotient) of the width of the trapezoidal second section in the region of the (exit) facet (region of maximum width) to the width of the first section in the region of the (opposite) facet (maximum width) is greater than 10, more preferably greater than 25, even more preferably greater than 30, even more preferably greater than 50, even more preferably greater than 75 and even more preferably greater than 100. This allows a particularly high reinforcement to be achieved.

[0021] Preferably, the device comprises semiconducting waveguide layers and semiconducting cladding layers. Preferably, the waveguide layers comprise aluminum gallium arsenide (Al x Ga (1-x) As with 0 ≤ x ≤ 1). Preferably, the cladding layers comprise aluminum gallium arsenide.

[0022] Preferably, the resistance elements extend (longitudinally) almost over the entire area of ​​the second section, ie preferably over at least 80%, more preferably over at least 90% and even more preferably over at least 95% of the second section.

[0023] The adjustment of the relevant design parameters is particularly important in a preferred embodiment of the present invention. Thus, the percentage of overlap of the projection of the resistance elements onto the active layer along the first axis with the active layer is preferably sufficiently large to advantageously influence the current distribution.The resistance elements must also be narrow enough to advantageously minimize optical losses or charge carrier losses. It can thus advantageously be provided that the projection of the resistance elements onto the active layer along the first axis extending perpendicular to the active layer covers at least 20%, preferably at least 30%, further preferably at least 40% and particularly preferably at least 50% of the entire area of ​​the active layer projected along the same axis, but preferably not more than 95% and particularly preferably not more than 99%.It is further preferred that the maximum extension of the respective resistance elements along the longitudinal axis of the active layer is not greater than 15 µm, further preferably not greater than 11 µm and particularly preferably not greater than 6 µm, but preferably not less than 1 µm, since it has been found that such an adjustment of the design parameters leads to improved performance and efficiency.

[0024] The resistance elements preferably have a specific electrical resistance that is significantly greater than the specific electrical resistance (hereinafter referred to as σ c , for example σ c = 1.0×10 -3< Ω·m) of the epitaxial layer structure used. Preferably, the specific electrical resistance of the resistance elements is more than 2σ c (for example 2.0×10 -3< Ω·m), further preferably more than 10σ c (for example 1.0×10 -2< Ω·m), further preferably more than 10 2< σ c (for example 1.0×10 -1< Ω·m), further preferably more than 10 3< σ c (for example 1.0x Ω·m), further preferably more than 10 4< σ c (for example 1.0×10 1< Ω·m), further preferably more than 10 5< σ c (for example 1.0×10 2< Ω·m), further preferably more than 10 6< σ c (for example 1.0×10 3< Ω·m), further preferably more than 10 7< σ c (for example 1.0x10 4< Ω·m), further preferably more than 10 8< σ c (for example 1.0×10 5< Ω·m), and particularly preferably more than 10 9< σ c (for example 1.0×10 6< Ω·m).

[0025] In a further preferred embodiment, the first section is designed as a ridge waveguide region and the second section as a trapezoidal region. This offers the advantage that the properties of known tapered lasers with regard to higher power and improved beam quality can be utilized, eliminating the previously required decentralized control of such tapered lasers. In other words, both the ridge waveguide region (first section) and the trapezoidal region (second section) have one (preferably two) common contact layer(s) for coupling and decoupling charge carriers. The trapezoidal region is preferably triangular and axially symmetrical to a longitudinal axis of the active layer.

[0026] In a further advantageous embodiment of the present invention, the resistance elements have at least two plane-parallel surfaces whose normal vectors are oriented parallel to the longitudinal axis of the active layer. This offers the advantage of reducing lateral local filamentation. Particularly preferred are the (preferably strip-shaped) resistance elements with a uniform layer thickness (across their longitudinal extent).

[0027] In a particularly preferred embodiment, filamentation is advantageously avoided by providing the resistance elements with at least two plane-parallel surfaces that extend over the entire length of the respective resistance element and whose normal vectors are oriented parallel to the longitudinal axis of the active layer. In other words, in this preferred embodiment, the resistance elements have a constant width at every point, and furthermore, all resistance elements are oriented parallel to one another. This also offers the advantage of minimizing optical and charge carrier losses.

[0028] In a further preferred embodiment, the resistance elements are arranged equidistant from one another, i.e., the resistance elements are arranged periodically along the longitudinal axis of the active layer. This advantageously contributes to the electrical and thermal properties of the second section remaining constant on average along the longitudinal axis of the active layer (i.e., longitudinally) across each resistance element and each region between two resistance elements, thus improving performance and beam quality.

[0029] In a further preferred embodiment, a ratio of the specific resistances of the resistance elements relative to the specific resistance of the regions between adjacent resistance elements is greater than 2, further preferably greater than 10, further preferably greater than 10 2< , further preferably greater than 10 3< , further preferably greater than 10 4< , further preferably greater than 10 5< , further preferably greater than 10 6< , further preferably greater than 10 7< , further preferably greater than 10 8< , and particularly preferably greater than 10 9< .

[0030] Furthermore, the present invention relates to a laser which contains at least one laser diode according to the invention as described above. By integrating several laser diodes, the overall power of the system can be advantageously increased, for example for material processing. In a preferred embodiment, several laser diodes according to the invention can be combined with one another in order to advantageously increase the power of the overall system. A parallel connection of several laser diodes to form so-called arrays is particularly preferred. This offers the advantage that the contact layers of the individual laser diodes or the laser diodes in a bar assembly (so-called laser bars) can be arranged on a common circuit board or can be controlled jointly. A series connection of several laser diodes or laser bars to form so-called stacks is also particularly preferred.On the one hand, this offers the advantage that the installation space is reduced in terms of the horizontal area required and, on the other hand, the laser diodes can be controlled jointly by contacting one contact layer each of the lowest and the highest laser diode of the bar assembly, advantageously achieving maximum power density and minimum manufacturing costs.

[0031] According to a second aspect of the invention not covered by the claims, a laser diode is disclosed, comprising at least one active layer which is arranged within a resonator and is operatively connected to a first facet and a second facet, wherein the second facet is designed as a coupling-out element, at least one contact layer for coupling charge carriers into the active layer and a plurality of separate resistance elements which are arranged between the first facet and the second facet, wherein the specific electrical resistance of the resistance elements is greater than the specific electrical resistance of regions between adjacent resistance elements.According to the invention, it is provided that a maximum extension of the respective resistance elements along a longitudinal axis of the active layer is less than 20 µm and a total area of ​​the resistance elements in a half of the resonator facing the first facet is greater than or equal to the total area of ​​the resistance elements in a half of the resonator facing the second facet.

[0032] This offers the advantage that with simple electrical contacting of the contact layer to supply the entire laser diode with electrical energy, the current distribution within the laser diode can be specifically adjusted.

[0033] In a preferred embodiment, the laser diode has two contact layers for coupling charge carriers into or out of the active layer(s).

[0034] The resistance elements preferably have a specific electrical resistance that is significantly greater than the specific electrical resistance (hereinafter referred to as σ c , for example σ< c = 1.0×10 -3< Ω·m) of the epitaxial layer structure used. The specific electrical resistance of the resistance elements is preferably more than 2 σ c (for example 2.0×10 -3 < Ω·m), further preferably more than 10 σ c (for example 1.0×10 -2 < Ω·m), further preferably more than 10 2 < σ c (for example 1.0×10 -1 < Ω·m), further preferably more than 10 3 < σ c (for example 1.0 Ω·m), further preferably more than 10 4 < σ c (for example 1.0×10 1 < Ω·m), further preferably more than 10 5 < σ c (for example 1.0×10 2 < Ω·m), further preferably more than 10 6 < σ c (for example 1.0×10 3 < Ω·m), further preferably more than 10 7 < σ c (for example 1.0x10 4< Ω·m), further preferably more than 10 8< σ c (for example 1.0×10 5< Ω·m), and particularly preferably more than 10 9< σ c (for example 1.0×10 6< Ω·m).

[0035] The facets, as elements defining the resonator, preferably have planar surfaces. The halves of the resonator are defined by a separation plane oriented parallel to the preferably planar facets, or in other words, cut perpendicularly by the longitudinal axis of the active layer, and located halfway between the plane of the first facet and the plane of the second facet of the resonator along the longitudinal axis of the active layer.

[0036] Further advantageous embodiments of the present invention result from the features mentioned in the subclaims.

[0037] In a preferred embodiment, the total area of ​​the resistance elements in the half of the resonator facing the second facet is 90%, or 0.9 times, the total area of ​​the resistance elements in the half of the resonator facing the first facet. In a further preferred embodiment, the total area of ​​the resistance elements in the half of the resonator facing the second facet is 80% (or 0.8 times), further preferably 70%, particularly preferably 66%, further preferably 60%, further preferably 50%, further preferably 40%, further preferably 30%, further preferably 20%, and further preferably 10% of the total area of ​​the resistance elements in the half of the resonator facing the first facet.Finally, a variant represents a preferred embodiment in which the resistance elements are located only in the half of the resonator facing the first facet, and thus the total area of ​​the resistance elements in the half of the resonator facing the second facet is 0% of the total area of ​​the resistance elements in the half of the resonator facing the first facet. These embodiments offer the advantage that adjustable additional current can be supplied to the region of the second facet, which is designed as an output facet, thereby counteracting a hole-burning effect.

[0038] In a further preferred embodiment, the resistance elements extend along a transverse axis of the active layer only over a portion of the active layer. The active layer thus extends along the same axis over a longer distance than the resistance elements. The resistance elements preferably extend axially symmetrically or point-symmetrically to this transverse axis. This results in regions without resistance elements on the flanks of the active layer. This offers the advantage that additional current can be supplied to the flanks of the laser diode, thus counteracting the formation of a current-induced thermal lens.

[0039] Preferably, a ratio of the extension of the resistance elements to the total width of the active layer transverse to the longitudinal axis of the active layer is between 1 and 0.1, more preferably between 0.9 and 0.5 and particularly preferably between 0.8 and 0.6.

[0040] In a further advantageous embodiment of the present invention, the resistance elements have at least two plane-parallel surfaces whose normal vectors are oriented parallel to the longitudinal axis of the active layer. This offers the advantage of reducing filamentation. Particularly preferably, the resistance elements are strip-shaped with a uniform layer thickness (across their longitudinal extent).

[0041] In a particularly preferred embodiment, filamentation is advantageously avoided by providing the resistance elements with at least two plane-parallel surfaces that extend over the entire length of the respective resistance element and whose normal vectors are oriented parallel to the longitudinal axis of the active layer. In other words, in this preferred embodiment, the resistance elements have a constant width at every point, and furthermore, all resistance elements are oriented parallel to one another. This also offers the advantage of minimizing optical and charge carrier losses.

[0042] In a further preferred embodiment, the resistance elements are arranged equidistant from one another, i.e., the resistance elements are arranged periodically along the longitudinal axis of the active layer in the regions provided with resistance elements. This advantageously contributes to ensuring that the electrical and thermal properties along the longitudinal axis of the active layer remain constant on average across each resistance element and each region between two resistance elements, thus improving performance and beam quality.

[0043] The resistance elements preferably have a specific electrical resistance that is significantly greater than the specific electrical resistance (hereinafter referred to as σ< c, for example σ c = 1.0×10 -3< Ω·m) of the epitaxial layer structure used. The specific electrical resistance of the resistance elements is preferably more than 2 σ c (for example 2.0×10 -3 < Ω·m), further preferably more than 10 σ c (for example 1.0×10 -2 < Ω·m), further preferably more than 10 2 < σ c (for example 1.0×10 -1 < Ω·m), further preferably more than 10 3 < σ c (for example 1.0 Ω·m), further preferably more than 10 4 < σ c (for example 1.0×10 1 < Ω·m), further preferably more than 10 5 < σ c (for example 1.0×10 2 < Ω·m), further preferably more than 10 6 < σ c (for example 1.0×10 3 < Ω·m), further preferably more than 10 7 < σ c (for example 1.0×10 4< Ω·m), further preferably more than 10 8< σ c (for example 1.0×10 5< Ω·m), and particularly preferably more than 10 9< σ c (for example 1.0×10 6< Ω·m).

[0044] In a further advantageous embodiment, the laser diode is a single-band laser diode. This offers the advantage that the design is based on a well-known, flexible, and thus cost-effective type of laser diode, while simultaneously increasing or improving power and beam quality.

[0045] In a further advantageous embodiment, the resistance elements are periodically assigned, with a period A that corresponds to Bragg conditions. This offers the advantage of wavelength stabilization. The period required to stabilize diode lasers at a wavelength around λ 0 can be calculated using an equation: λ 0 = 2 n eff Λ N .

[0046] N denotes a grating order and n eff denotes the effective refractive index of a considered optical mode.

[0047] Furthermore, a laser not covered by the claims is disclosed which contains at least one laser diode according to the invention as described above. By integrating several laser diodes, the overall power of the system can be advantageously increased, for example for material processing. In a preferred embodiment, several laser diodes according to the invention can be combined with one another in order to advantageously increase the power of the overall system. Particularly preferred is a parallel connection of several laser diodes to form so-called arrays, or in other words to form laser bars. This offers the advantage that the contact layers of the individual laser diodes can be arranged on a common circuit board or controlled jointly. Furthermore, particularly preferred is a series connection of several laser diodes to form so-called stacks, or in other words to form a bar assembly.On the one hand, this offers the advantage that the installation space is reduced in terms of the horizontal area required and, on the other hand, the laser diodes can be controlled jointly by contacting one contact layer each of the lowest and the highest laser diode of the bar assembly. Short description of the characters

[0048] The invention is explained in more detail below using two exemplary embodiments and the accompanying drawings. The figures show: Figure 1 shows a conventional tapered laser diode in a schematic perspective view; Figure 2 shows a conventional broad-area laser in a schematic perspective view; Figure 3 shows a laser diode according to the invention in a schematic perspective view according to a preferred embodiment; Figure 4 shows a preferred embodiment of a laser diode not covered by the claims in a schematic perspective view; Figure 5 shows an exemplary graphic representation of a dependence of the maximum laser power P on the width W3 of the resistance elements for a laser diode according to the invention; Figure 6 shows an exemplary graphic representation of the dependence of the maximum laser power P on the total current I for a laser diode according to the invention with an overlap U of 50% and for a laser diode with an overlap U of 0% (this corresponds to the prior art);Figure 7 shows a schematic representation of further preferred embodiments of the resistance elements; Figure 8 shows an exemplary profile of an optical gain G across a longitudinal cross-section of a conventional broad-area laser diode; and Figure 9 shows an exemplary profile of a temperature T across a lateral cross-section of a conventional broad-area laser diode. Detailed description of the characters

[0049] Figure 3 shows a laser diode 10 according to the invention according to a preferred embodiment. The reference numerals, insofar as they refer to identical features, are identical to those of the Figure 1described prior art. The laser diode 10 has an active layer 12 arranged within a resonator 14 and operatively connected to a coupling-out element 16. Furthermore, the laser diode 10 has a first contact layer 18 for coupling charge carriers into the active layer 12 and a second contact layer 32 for coupling charge carriers out of the active layer 12. Furthermore, the laser diode 10 has a substrate 58, an n-cladding layer 62, an n-waveguide layer 64, a p-waveguide layer 68, and a p-cladding layer 70. The respective layer thicknesses and layer materials are shown in Table 1. Table 1: Exemplary layer thicknesses and layer materials layer Thickness of the layer in µm Material of the layer second contact layer 32 No information, because substrate GaAs (substrate) Substrate 58 ~ 120 GaAs n-cladding layer 62 ~ 1 Al 0.85 Ga 0.15 As active layer 12 Total: 0.052 In 0.15 Ga 0.85 As 3 x quantum wells (0.009) GaAs x P 1-x (x: 0...0.55) 2x spacers (0.005) GaAs x P 1-x (x: 0...0.55) 2x Barriers (0.0075) n-waveguide layer 64 3.1 Al 0.20 Ga 0.80 As p-waveguide layer 68 1.7 Al 0.20 Ga 0.80 As p-cladding layer 70 ~ 1 Al 0.85 Ga 0.15 As first contact layer 18 ~ 0.1 GaAs

[0050] The resonator 14 comprises a first section 20 and a second section 22. The first section 20 comprises a ridge waveguide region 28, and the second section 22 comprises a trapezoidal region 30. The maximum width W1 of the active layer 12 in the first section 20 is 4 µm (microns), smaller than the maximum width W2 of the active layer 12 in the second section 22, which is 426 µm. The width of the active layer 12 in the first section 20 is constant and expands uniformly across the second section 22 to the maximum width W2. The length of the first section 20 is 2 mm, and the length of the second section 22 is 4 mm. The projection of the contact layer 18 along a first axis Z1 extending perpendicular to the active layer 12 overlaps both the first section 20 and the second section 22.The second section 22 also has a plurality of separate resistance elements 24, introduced by implantation, which have a specific resistance of 1×10 -1< Ω·m and whose specific electrical resistance is greater by a factor of -100 than the specific electrical resistance of the regions 26 between adjacent resistance elements 24. If an exemplary diode laser layer structure based on Al x Ga 1-x As is used, the total electrical resistance for an exemplary broad-area laser diode 84 with a 3 mm resonator length, 90 µm stripe width and an epitaxial layer thickness of 5 µm is 20 mΩ. The specific electrical resistance σ c is approximately 1.0×10 -3< Ω·m (and thus, for example, slightly larger than the specific resistance of a highly doped Al 0.85 Ga 0.15 As layer of approximately 4.2×10 -4< Ω·m).

[0051] The resistance elements 24 are strip-shaped, in other words, they each have two plane-parallel surfaces that extend over the entire length of the respective resistance element 24 and whose normal vectors are oriented parallel to a longitudinal axis X1 of the resonator 14. This means that the resistance elements 24 are oriented parallel to one another and to the resonator 14. The width W3 of the resistance elements 24 along the longitudinal axis X1 of the active layer 12 is 5 µm at every point on the respective resistance element 24. The width of the resistance elements 24 over their length, or along a transverse axis Y1, is therefore constant. The resistance elements 24 are arranged periodically, or equidistantly. The period length is 10 µm. The projection of the resistance elements 24 onto the active layer 12 along the first axis Z1 overlaps with the active layer by 50%.Furthermore, the laser diode 10 is designed to be operated with a DC voltage in the range of 1.2 to 1.6 volts, preferably in the range of 1.4 to 1.6 volts.

[0052] Figure 4 shows a preferred embodiment of a laser diode 34 not covered by the claims. This is a single broad-area laser diode. The reference numerals, insofar as they refer to identical features, are identical to those of the Figure 2 described state of the art, or with those of the Figure 3described laser diode 10 according to the invention. Various layers 60 are applied to a substrate 58. These consist of an n-cladding layer 62, an n-waveguide layer 64, a p-waveguide layer 68, and a p-cladding layer 70. In this exemplary embodiment, the laser diode 34 further comprises at least one active layer 36, which is arranged within a resonator 38 and is operatively connected to a first facet 40 and a second facet 42. The second facet 42 is designed as an output coupling element. The laser diode 34 further comprises a contact layer 44, which functions as a p-contact region 72 and is designed to supply current to the active layer 36, and a contact layer 32, which functions as an n-contact region 74, which is designed to derive current from the active layer 36. The respective layer thicknesses and layer materials can be seen from Table 2. Table 2: Layer thicknesses and layer materials layer Thickness of the layer in µm Material of the layer second contact layer 32 No information, because substrate GaAs (substrate) Substrate 58 ~ 120 GaAs n-cladding layer 62 ~ 1 Al 0.85 Ga 0.15 As active layer 12 Total: 0.052 In 0.15 Ga 0.85 As 3 x quantum wells (0.009) GaAs x P 1-x (x: 0...0.55) 2x spacers (0.005) GaAs x P 1-x (x: 0...0.55) 2x Barriers (0.0075) n-waveguide layer 64 3.1 Al 0.20 Ga 0.80 As p-waveguide layer 68 1.7 Al 0.20 Ga 0.80 As p-cladding layer 70 ~ 1 Al 0.85 Ga 0.15 As first contact layer 18 ~ 0.1 GaAs

[0053] Between the first facet 40 and the second facet 42, a plurality of separate resistance elements 46 are arranged periodically (period length 10 µm) or equidistantly, wherein the specific electrical resistance of the resistance elements 46 is 100 times greater than the specific electrical resistance of regions 48 between adjacent resistance elements 46. The specific electrical resistance of the resistance elements 46 is ~1×10 -1< Ω m. The resistance elements 46 also each have two plane-parallel surfaces that extend over the entire length L of the respective resistance element 46 and whose normal vectors are oriented parallel to a longitudinal axis X2 of the active layer 36 or of the resonator 38. This means that the resistance elements 46 are oriented parallel to one another and to the resonator 38.The dimension W3 of the respective resistance elements 46 along the longitudinal axis X2 of the active layer 36 is 5 µm at any point, thus their width is constant. The length L of the resistance elements 46 is 60 µm.

[0054] In this case, a total area of ​​the resistance elements 46 in a half 52 of the resonator 38 facing the second facet 42 amounts to approximately 66% of the total area of ​​the resistance elements 46 in a half 50 of the resonator 38 facing the first facet 40.

[0055] Both halves 50, 52 of the resonator 38 extend along the longitudinal axis X2. The width W of the active layer 36 over the entire length of the resonator 38 is constant and amounts to 90 µm. In the regions provided with the resistance elements 46, the resistance elements 46 are uniformly spaced from one another. Starting from the longitudinal axis X2, the resistance elements 46 extend, axially symmetrical to the longitudinal axis X2, along a transverse axis Y2. The length L of the respective resistance elements 46 is 65% of the width W of the active layer 36 along the transverse axis Y2. At the flanks 85, there are thus regions without resistance elements 46, each of which has an extension along the transverse axis Y2 of 35% of the width W of the active layer 36. The ratio of the width W of the active layer 36 to the length L of the resistance elements 46 transverse to the longitudinal axis of the active layer is 0.7.Furthermore, the laser diode 34 is designed to be operated with a DC voltage in the range of 1.2 to 1.6 volts, preferably in the range of 1.4 to 1.6 volts.

[0056] The Figures 5 and 6 show exemplary evaluations of measurement series that were carried out to determine optimal design parameters for a laser diode according to the invention. The same reference numerals apply as in Figure 3 In the experiments, tapered lasers were fabricated with resistance elements 24 in a trapezoidal region 30. The resistance elements 24 were fabricated with varying widths from 5 µm to 15 µm. The projection of the resistance elements 24 onto the active layer 12 along the first axis Z1 was fabricated with 0%, 30%, and 50% overlap with the active layer 12.

[0057] An exemplary graphical representation of a dependence of the maximum laser power P on the width W3 of the resistance elements 24 for a laser diode 10 according to the invention is shown in Figure 5for a constant overlap U (the projection of the resistance elements 24 onto the active layer 12 along an axis Z1 extending perpendicular to the active layer 12, 36 with the entire area of ​​the active layer 12 projected along the same axis Z1). The diagram is based on a laser diode 10 according to the invention, which was operated with a constant current I. The ridge waveguide region 28 and the trapezoidal region 30 were electrically contacted together. Tests were carried out with three laser diodes 10 according to the invention, wherein the overlap U was constant at 50% and the width W3 of the resistance elements 24 was varied from 5 µm to 15 µm. An overlap of 0% corresponds to a tapered laser diode according to the prior art as a reference.The experiments reveal a preferred design window 86 for the width W3 of the resistance elements 24, where the maximum laser power P is above a prior art reference value. A preferred range for the width W3 of the resistance elements 24 is 1 µm to 9 µm, more preferably 3 µm to 7 µm, and particularly preferably 4 µm to 6 µm.

[0058] An exemplary graphical representation of a dependence of the maximum laser power P on the overlap U (projection of the resistance elements 24 onto the active layer 12 along an axis Z1 extending perpendicularly to the active layer 12 with the entire area of ​​the active layer 12 projected along the same axis Z1) with a constant width W3 of the resistance elements 24 for a laser diode according to the invention is shown in Figure 6summarized. The tests were carried out with two laser diodes 10. The width W3 of the resistance elements 24 was constant at 5 µm and the total current I for supplying the trapezoidal (30) and ridge waveguide regions (28) was varied in order to record characteristics of the two laser diodes 10. Characteristic curves of one laser diode 10 each with an overlap U of 0% (this corresponds to the prior art) and 50% are shown. It can be seen that the maximum power P also increases with increased overlap U. An overlap U of more than 10%, preferably more than 30% and particularly preferably more than 50% has proven advantageous. Advantageous results are obtained up to an overlap U of preferably not more than 95%, particularly preferably not more than 99%.

[0059] Figure 7 shows a schematic representation of further preferred embodiments of the resistance elements 24, 46. The representation and the reference numerals are adapted to the Figure 4 However, the different shapes of the resistance elements 24, 46 are transferable to laser diodes according to all aspects of the invention.

[0060] Figure 8 shows an exemplary curve of an optical amplification or gain G over a longitudinal cross section of a conventional broad area laser diode 84 along the X-axis (X-axis as in Figure 2shown). A cutting plane lies in the XZ plane and intersects the broad-area laser diode 84 centrally. From the gain profile across the X position (the X zero point lies in the plane of the output facet 80), a design rule for further preferred embodiments of laser diodes 34 according to the invention can be derived. The diagram shows that the optical amplification or gain G is significantly smaller in a region B, the majority of which faces the front facet 80, than in a region A, the majority of which faces the rear facet 82. In this exemplary case, the region B with the smaller gain G extends over approximately 63% of the entire length of the resonator, i.e., over approximately 63% of the length from the front facet 80 to the rear facet 82.

[0061] The goal is therefore to achieve an increased current flow in region B and a reduced current flow through region A, which in this exemplary case extends over approximately 37% of the length from the back facet 82 to the front facet 80, in order to compensate for the difference in gain G. The resistance elements 46 are therefore to be implanted in region A. This design rule is transferable or applicable to any optical amplification profiles, for example by implanting the resistance elements 46 in the regions in which the current flow is to be reduced. The corresponding design measure advantageously increases the current flow through the regions in which no resistance elements are implanted and thus has an advantageous effect against longitudinal hole burning.It has been found that preferred dimensions for the region A in which the resistance elements 46 are introduced are more than 10%, further preferably more than 30%, further preferably more than 50%, and particularly preferably more than 60% of the length from the rear facet 82 to the front facet 80. This corresponds to typical gain distributions of known broad-area laser diodes 84.

[0062] Figure 9 shows an exemplary course of a temperature T over a lateral cross section along the Y-axis (Y-axis as in Figure 2shown) of a conventional broad-area laser diode 84. A cutting plane lies in the YZ plane and intersects the broad-area laser diode centrally. From the gain profile over the Y position (the Y zero point lies centrally in the broad-area laser diode 84), a design rule for further preferred embodiments of laser diodes 34 according to the invention can be derived. A Y position of 0 mm, which is derived from the Figure 9 corresponds to the center of the laser diode in the Y direction. The diagram shows that the temperature T there and in a central area C is higher than in other areas. Figure 9that the temperature T in flanks A1, A2 of the contact region 72 is lower than in the central region C. In this exemplary case, the region C extends in the Y direction over approximately 66% of the width W of the contact region 72. In this exemplary case, the flanks A1, A2 each extend in the Y direction over approximately 17% of the width W of the contact region 72. The aim is therefore to realize an increased current flow in the flanks A1, A2 and a reduced current flow in the region C. The resistance elements 46 are therefore to be implanted in the region C. This design rule can be transferred or applied to any temperature profiles by implanting the resistance elements 46 in the regions in which the current flow is to be reduced.The corresponding design measure advantageously increases the current flow through the areas in which no resistance elements are implanted and thus advantageously counteracts the formation of a thermal lens. List of reference symbols

[0063] 10Laser diode 12Active layer 14Resonator 16Output coupling element 18Contact layer 20First section 22Second section 24Resistance elements 26Regions 28Ridge waveguide region 30Trapezoid region 32Contact layer 34Laser diode 36Active layer 38Resonator 40First facet 42Second facet 44Contact layer 46Resistance elements 48Regions 50Half 52Half 54Laser 56Tapered laser diode 58Substrate 60Layers 62n-cladding layer 64n-waveguide layer 66Active zone 68p-waveguide layer 70p-cladding layer 72p-contact region 74n-contact region 76Ridge waveguide region 78Trapezoid region 80Front facet 82Rear facet 84Broad area laser diode 85Flank 86Design window 87Ideal uniform longitudinal distribution of the local gain constant.ARear facing the back facet A1left flank of the contact area A2right flank of the contact area Barea facing the front facet Cmiddle area of ​​the contact area GOptic amplification (gain) ICElectric LLength Pmaximum laser power TTemperature UOpply WLidth W1maximum width W2maximum width W3Width XLongitudinal axis (longitudinal direction) X1Longitudinal axis (longitudinal direction) X2Longitudinal axis (longitudinal direction) YTransverse axis (lateral direction) Y1Transverse axis (lateral direction) Y2Transverse axis (lateral direction) Z1first axis (vertical direction) Z2first axis (vertical direction) Z3first axis (vertical direction) ηConversion efficiency.

Claims

1. A laser diode (10) including: at least one active layer (12), which is arranged within a resonator (14) and is operatively connected to an out-coupling element (16), at least one contact layer (18) for coupling charge carriers into the active layer (12), wherein the resonator (14) includes at least one first section (20) and at least one second section (22), wherein the maximum width (W1) of the active layer (12) in the first section (20) differs from the maximum width (W2) of the active layer (12) in the second section (22), and a projection of the contact layer (18) along a first axis (Z1) extending perpendicularly to the active layer (12) overlaps both with the first section (20) and with the second section (22), wherein the second section (22) includes a plurality of separate resistance elements (24) introduced by means of implantation, the specific electrical resistance of which is greater than the specific electrical resistance of the regions (26) between adjacent resistance elements (24), wherein a width (W3) of the resistance elements (24) along a longitudinal axis (X1) of the active layer (12) is less than 20 µm and a projection of the resistance elements (24) onto the active layer (12) along the first axis (Z1) overlaps with at least 10% of the active layer (12), wherein the first section (20) and the second section (22) have joint electrical contacting and the ratio between the proportion of current in the first section (20) and the proportion of current in the second section (22) is set by means of the resistance elements (24).

2. The laser diode (10) according to claim 1, wherein a specific electrical resistance within the second section (22) is uniform across each resistance element (24) and each region (26) between two resistance elements (24) along the longitudinal axis (X1) of the active layer (12).

3. The laser diode (10) according to claim 1, wherein all the resistance elements (26) within the second section (22) are arranged to be equidistant from one another.

4. The laser diode (10) according to any one of the preceding claims, wherein the ratio of the specific electrical resistance of the resistance elements (24) to the specific electrical resistance of the regions (26) between adjacent resistance elements (24) is greater than 1000.

5. The laser diode (10) according to any one of the preceding claims, wherein the first section (20) and the second section (22) are arranged between two facets within the resonator (14), wherein the ratio of the maximum width of the second section (22) to the maximum width of the first section (20) is greater than 30.

6. The laser diode (10) according to any one of the preceding claims, wherein the projection of the resistance elements (24) onto the active layer (12) along the first axis (Z1) covers at least 50% of the entire surface area of the active layer (12) projected along the same first axis (Z1).

7. The laser diode (10) according to any one of the preceding claims, wherein the maximum extent (W3) of the respective resistance elements (24) along the longitudinal axis (X1) of the active layer (12) is no greater than 11 µm.

8. The laser diode (10) according to any one of the preceding claims, wherein the resistance elements (24) include at least two plane-parallel surfaces, the normal vectors of which are oriented in parallel with the longitudinal axis (X1) of the active layer (12).

9. The laser diode (10) according to any one of the preceding claims, wherein the first section (20) comprises a ridge waveguide region (28) and the second section (22) comprises a trapezoidal region (30).

10. A laser (54) including: at least one laser diode (10) according to any one of the preceding claims.