WO2022253946A1 - Laserbarren mit verringerter lateraler fernfelddivergenz - Google Patents
Laserbarren mit verringerter lateraler fernfelddivergenz Download PDFInfo
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- WO2022253946A1 WO2022253946A1 PCT/EP2022/065024 EP2022065024W WO2022253946A1 WO 2022253946 A1 WO2022253946 A1 WO 2022253946A1 EP 2022065024 W EP2022065024 W EP 2022065024W WO 2022253946 A1 WO2022253946 A1 WO 2022253946A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/024—Arrangements for thermal management
- H01S5/02461—Structure or details of the laser chip to manipulate the heat flow, e.g. passive layers in the chip with a low heat conductivity
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- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
- H01S5/0286—Coatings with a reflectivity that is not constant over the facets, e.g. apertures
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- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0425—Electrodes, e.g. characterised by the structure
- H01S5/04256—Electrodes, e.g. characterised by the structure characterised by the configuration
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
- H01S5/1203—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers over only a part of the length of the active region
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/16—Window-type lasers, i.e. with a region of non-absorbing material between the active region and the reflecting surface
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- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
- H01S5/4031—Edge-emitting structures
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- H01S2301/00—Functional characteristics
- H01S2301/18—Semiconductor lasers with special structural design for influencing the near- or far-field
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- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
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- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
- H01S5/0612—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by temperature
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- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/16—Window-type lasers, i.e. with a region of non-absorbing material between the active region and the reflecting surface
- H01S5/162—Window-type lasers, i.e. with a region of non-absorbing material between the active region and the reflecting surface with window regions made by diffusion or disordening of the active layer
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- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/2036—Broad area lasers
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- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
Definitions
- the present invention relates to a laser bar with reduced lateral far-field divergence, and more particularly to a laser bar with a uniform temperature profile in the lateral direction to reduce lateral far-field divergence.
- Laser bars typically consist of several broad-area diode lasers (BALs), which are arranged side by side in the lateral direction on a common substrate. This means that a total output power of 1500 W and more can be achieved.
- the number of broad area lasers arranged in a laser bar can vary, typical values for this are between 5 and 200.
- the lateral stripe width of the broad area laser is typically between 5 pm and 100 pm, but can also be significantly larger, such as 1200 pm.
- the individual laser elements are usually formed as separate emitter structures in a common layer structure, the charge carrier supply usually being structured to separate the emitter structures, in particular by structuring the p-contact layer opposite an n-substrate and the associated p-contacts.
- Charge carriers are injected via the p and n contacts into the active zone formed between the two contacts within the layer structure. Since the injected charge carriers mainly move directly in the direction of the active zone without lateral current widening, the generation of radiation within the active zone can also be correspondingly structured in the lateral direction by means of appropriate separating structures in the charge carrier feed.
- impurities or foreign atoms are usually implanted in the p-contact layer, trenches are formed or dielectric sections are locally introduced (e.g. produced by filling trenches with a dielectric material).
- a variation of the temperature profile in the lateral direction should result in an adaptation of the temperature of the outer emitter structures to a temperature of the inner emitter structures enclosed by the outer emitter structures.
- the lateral temperature distributions within the outer emitters can be adjusted so that they are as close as possible to those of the inner emitters by means of new bar constructions and arrangements. In this way, the formation of an asymmetrical temperature profile and the occurrence of a broadening of the lateral far-field divergence caused by this can be avoided.
- a laser bar according to the invention comprises a layer system made of a semiconductor material with an active layer, the layer system having an n-contact and p-contact for injecting charge carriers into the active layer, with structuring of the layer system forming a multiplicity of emitter structures arranged parallel to one another is, wherein the emitter structures extend in the longitudinal direction between a front facet and a rear facet and in the lateral direction from a first side to a second side and for structuring the emitter structures are each separated from one another by a separating structure extending in the longitudinal direction.
- the dissipated thermal power of the outer emitter structures facing the first side and the second side is adapted in relation to the inner emitter structures enclosed by the outer emitter structures.
- a largely homogeneous temperature profile with regard to the maximum temperature of the individual emitter structures during operation of the laser bar can be achieved by the adaptation in the lateral direction.
- the layer system of a laser bar according to the invention can, for example, have an n-contact (e.g. designed as a metallic contact surface); an n-substrate, the n-substrate being arranged on the n-contact; an n-cladding layer, the n-cladding layer being disposed on the n-substrate; an n-waveguide layer, the n-waveguide layer being disposed on the n-cladding layer; an active layer, the active layer being disposed on the n-waveguide layer; a p-waveguide layer, the p-waveguide layer being disposed on the active layer; a p-cladding layer, the p-cladding layer being disposed on the p-waveguide layer; a structured p-contact layer, the p-contact layer being arranged on the p-cladding layer and forming a multiplicity of emitter structures arranged parallel next to one another as a result of the structuring, the regions between the emitter structures being separated from one another
- the idea of the invention is therefore to provide a laser bar with reduced lateral far field divergence available, in which the temperature profile is varied in the lateral direction by adapting the dissipated thermal power (local heat) of the first side and the second Side facing outer emitter structures is made opposite the inner emitter structures enclosed by the outer emitter structures.
- the individual emitter elements are not designed identically to one another, but to reduce the lateral far field divergence, some of the emitter elements can be modified by suitable measures in such a way that their dissipated thermal power is adjusted.
- the temperature profile can be varied in the lateral direction in order to adapt the temperature of the outer emitter structures to a temperature of the inner emitter structures enclosed by the outer emitter structures.
- the dissipated thermal power of the outer emitter structures is preferably adapted gradually over a plurality of outer emitter structures lying next to one another.
- the inventors were able to show that just adjusting the dissipated thermal power of the respective outermost emitter elements of a laser bar can lead to a significant adjustment of the temperature profile in the lateral direction.
- an improved adaptation can be achieved in that, in addition to the outermost emitter structures in each case, the dissipated thermal power is also adapted accordingly in neighboring emitter structures.
- the strength of the adaptation particularly preferably decreases in the direction of the inner emitter structures.
- a gradual adaptation of the dissipated thermal power of the outer emitter structures across a plurality of outer emitter structures lying next to one another can specifically take place, for example, via three or four or more of the outer emitter elements in each case.
- the electrical and/or optical properties of the outer emitter structures are preferably adapted in relation to the inner emitter structures.
- the dissipated thermal power can be increased in particular by increasing the losses within the outer emitter structures.
- essentially optical (ie relating to the radiation guidance) essentially electrical (ie relating to the current guidance) or mixed (ie relating to the radiation guidance and the current guidance) adjustments can be made.
- An effective way of adjusting the electrical and/or optical properties of the emitters and thereby increasing the thermal power dissipated is to modify the outer emitter structures (ie the optical resonator formed within the emitter structures).
- the outer emitter structures for adaptation, higher optical power can be enclosed within the outer emitter structures for adaptation, the heat dissipation from the outer emitter structures can be deteriorated, additional internal optical losses (e.g. scattering losses) can be introduced in the outer emitter structures, the effectiveness of the active areas of the outer emitter structures can be deteriorated and/or high-impedance structures are introduced into the emitter structures (in particular into the inner emitter structures).
- additional internal optical losses e.g. scattering losses
- the facet reflectivity of the outer emitter structures is preferably increased compared to the facet reflectivity of the inner emitter structures. It could be shown that an effective way to adapt the thermal power output of the emitter elements is to change the facet reflectivity of the emitter structures (i.e. the optical resonator formed within the emitter structures). In this case, a higher facet reflectivity leads to an increase in the optical power stored in the emitter structures, which in turn leads to an increase in the internal resonator losses and thus also to an increase in the temperature of the respective emitter structures.
- the facet reflectivity of the emitter structures can be adjusted by reflectors by integrating distributed Bragg gratings (distributed Bragg reflector, DBR), in particular front-side DBR and/or rear-side DBR, or by applying dielectric mirror layers to the front facets and/or the rear facets is.
- DBR distributed Bragg reflector
- the facet reflectivity can be adjusted via the reflectivity of the reflector elements. Adjusting the optical properties of a resonator by adjusting the reflectivities at the ends is known per se to a person skilled in the art, but this dependency is used here for targeted adjustment of the temperature of individual emitter elements of a laser bar to reduce lateral far-field divergence.
- the intensity of the light enclosed in the emitter structures can be controlled.
- their mirror losses decrease, more optical energy is stored in the emitter structures and thus the heat input inside the emitter also increases emitter structures. Due to an increased heat input, the temperature of the outer emitter structures also increases.
- the reflectivity of a front reflector (Ri) of the outer emitter structures is preferably between 1% and 30%, particularly preferably between 1% and 12%. For typical laser bars, this value range results from the measured temperature drop in the outer emitter structures. With these values for the reflectivity, an increase in temperature in the range of up to 10 K can typically be achieved compared to emitter structures without additional reflectors.
- the length of the pumped area in the outer emitter structures is preferably shortened compared to the length of the pumped area of the inner emitter structures by forming non-pumped areas. It could be shown that another effective way of adapting the thermal power output of the emitter elements is to change the thermal resistance of the emitter structures.
- An increased thermal resistance reduces the heat dissipation from the emitter structures and can therefore also lead to an increase in the temperature of the respective emitter structures.
- the pumped region length of the outer emitter structures is between 90% and 20%, more preferably between 80% and 35%, compared to the pumped region length of the inner emitter structures.
- a typical length for the pumped region of an internal emitter structure is 4 mm and corresponds to the length of the resonator.
- the length of the pumped region of the outer emitter structures can then be shortened to 1.4 mm, for example, for a temperature increase that is typically required for these emitter structures.
- the heat dissipation ability of the outer emitter structures can be reduced.
- the electrical series resistance and the thermal resistance increase.
- the increased electrical series resistance reduces the maximum current through the outer emitter structures (at a constant voltage supplied) and thus the heat output of the emitter structures. Through the too strong However, increased thermal resistance increases the overall temperature within these emitter structures.
- non-pumped regions are formed adjacent to the front facet and the rear facet.
- a symmetrical arrangement of the non-pumped areas is preferred.
- the position of the pumped areas along the longitudinal axis of the emitter structures can be chosen freely and determined individually for different emitter structures.
- inert ions are preferably implanted in the non-pumped passive regions by means of deep ion implantation. It could be shown that the non-pumped areas can be formed more effectively by implanting inert ions. In this case, the depth of the implantation can be limited to an implantation down into the p-contact layer. However, the implantation can also extend beyond the p-contact layer into the p-waveguide layer. The conductivity of the highly p-doped contact, cladding and waveguide layers is eliminated by the ion implantation or the deep ion implantation. On the one hand, the flow of charge carriers to the pumped areas can be restricted by an ion implantation. On the other hand, this also prevents the charge carriers from diffusing into the non-pumped areas.
- Loss elements are preferably formed in the outer emitter structures in order to increase the internal optical losses (cr int ).
- the effect of an increase in internal resonator losses has already been explained above.
- These loss elements can be achieved by introducing 1-, 2- or 3-dimensional loss centers via local changes in the refractive index or by etching wavy structures along the longitudinal direction of the laser resonator or by locally increasing the charge carrier density, e.g. B. be generated by diffusing dopants into the crystal structure. Such structures cause additional scattering and absorption losses through interaction with the laser light.
- the resulting reduced transconductance efficiency ⁇ s ⁇ o P e) of the emitter increases the power loss and thus causes the temperature within the emitter structures to rise.
- the internal optical losses (cr int ) of the outer emitter structures are preferably between 0.6 cm 1 and 1.5 cm 1 , more preferably between 1 cm 1 and 1.5 cm 1 , and even more preferably between 1.2 cm 1 and 1 5 cm 1 .
- the internal optical losses in the epitaxial materials typically used for high-power laser diodes is between about 0.3 cm 1 and 0.4 cm 1 .
- inert ions are preferably implanted at least in sections in the direction of the active layer in the outer emitter structures to increase the radiationless recombination and thus to reduce the internal quantum efficiency ⁇ h ih i).
- the internal quantum efficiency in these emitter structures can be reduced, as a result of which the conversion efficiency (PCE) of the outer emitter structures is impaired.
- PCE conversion efficiency
- the emitter structure can be implemented as an arrangement of implanted and non-implanted regions.
- a symmetrical arrangement of the implanted and non-implanted areas is preferred; in particular, the individual areas can each have the same lengths.
- the position and length of the implanted and non-implanted areas along the longitudinal axis of the emitter structures can be chosen freely and determined individually for different emitter structures.
- the depth of the implant preferably extends from the p-contact layer through the p-cladding layer, p-waveguide layer and the active layer down to the n-waveguide layer.
- the outer emitter structures Preferably, sufficient defects are introduced into the outer emitter structures such that the internal quantum efficiencies ( ⁇ nt ) of the outer emitter structures are between 50% and 92%, more preferably between 84% and 92%.
- the typically achievable internal quantum efficiency in epitaxial materials commonly used for high-power laser diodes is approximately between 95% and 100%.
- inert ions are preferably implanted at least in sections in the direction of the active layer. By increasing the series resistance of the inner emitter structures, a higher current flow can be forced through the outer emitters, thereby causing additional heating of the outer emitter structures.
- parts of the semiconductor materials e.g. B.
- the contact area are implanted with inert ions.
- a symmetrical arrangement of the implanted and non-implanted areas is preferred here, in particular the individual areas can each have the same lengths.
- the emitter structure may be an array of implanted and non-implanted regions, or the implanted region may extend the entire length of an emitter structure.
- a symmetrical arrangement of the implanted and non-implanted areas is preferred; in particular, the individual areas can each have the same lengths.
- the position and length of the implanted and non-implanted areas along the longitudinal axis of the emitter structures can be chosen freely and determined individually for different emitter structures.
- the depth of the implant can range from an implant only into the p-contact layer to an implant extending from the p-contact layer into the p-waveguide layer.
- the specific series resistance of the inner emitter structures is preferably increased by a factor of 1.2 to 1.6 compared to the outer emitter structures.
- the tables on the left side show the thermal resistance R ih in K/W, the maximum temperatures of the inner and outer emitter structures 7j and T a for a conventional high-power laser diode and the resulting difference dT between the respective maximum temperatures of the emitter structures .
- the tables on the right side each show the corresponding variation parameter and its effects in an adaptation according to the invention.
- the temperature change dT achieved by the variation, a resulting change in the conversion efficiency ⁇ PCE and a factor P d iSS , by which the dissipated thermal power in the outer emitter structures is increased by the adjustments made, are given.
- Table 1 shows that a corresponding adaptation of the temperatures can be achieved with an increased degree of reflection R f of 12% or 29% of the front facet of the outer emitter structures.
- the optical properties of the outer emitter structures can be changed by an increased degree of reflection R f of the front facet and the optical power stored in the emitter structures can thus be increased. This also increases the losses that occur and thus also the temperature of the emitters.
- Table 2 shows that a corresponding adaptation of the temperatures can be achieved by shortening the length of the pumped region Lgain in the outer emitter structures compared to the length of the pumped region Lga in the inner emitter structures.
- the length of the pumped region L ga in the inner emitter structure corresponded to the resonator length of 4000 pm.
- Table 3 shows that the temperatures can be adjusted accordingly by increasing the internal optical losses cr int of the outer emitters.
- the internal optical losses can be increased in particular by introducing lossy elements into the emitter structures.
- the loss elements can be created by introducing 1-, 2- or 3-dimensional loss centers into the crystal structure.
- Table 4 shows that a corresponding adaptation of the temperatures can be achieved by reducing the internal quantum efficiency h ⁇ ih ⁇ of the outer emitter structures.
- the internal quantum efficiency h ⁇ ih i can in particular via an amplification the non-radiative recombination of injected charge carriers (ie electrons and holes).
- Table 5 shows that by increasing the specific series resistance p s of the inner emitter structures (e.g. through implanted inert ions) by a factor of 1.2 to 1.6 compared to the specific series resistance p s o of the outer emitter structures (ie those not with inert ions implanted emitter) a corresponding adjustment of the temperatures can be achieved.
- FIG. 1 shows a schematic representation of an exemplary conventional laser bar structure in a) oblique view, b) side view and c) top view;
- 3a shows a schematic representation of a first embodiment of a laser bar structure according to the invention in a combined plan view and oblique view;
- Fig. 4 is a schematic representation of a second embodiment of a laser bar structure according to the invention in combined up and down
- Fig. 5 is a schematic representation of a third embodiment of a laser bar structure according to the invention in combined up and down
- Fig. 6 is a schematic representation of a fourth embodiment of a laser bar structure according to the invention in combined up and down
- Fig. 7 is a schematic representation of a fifth embodiment of a laser bar structure according to the invention in combined up and down
- Fig. 8 is a schematic representation of a sixth embodiment of a laser bar structure according to the invention in combined up and down
- Fig. 9 is a schematic representation of a seventh embodiment of a laser bar structure according to the invention in combined up and down
- FIG. 1 shows a schematic representation of an exemplary conventional laser bar structure in a) an oblique view, b) a side view and c) a top view.
- the laser bar 1 comprises an n-contact 4 (embodied, for example, as a metallic contact surface); an n-substrate 3, the n-substrate 3 being disposed on the n-contact 4; an n-cladding layer 6, the n-cladding layer 6 being disposed on the n-substrate 3; an n-waveguide layer 8, the n-waveguide layer 8 being disposed on the n-cladding layer 6; an active layer 2, the active layer 2 being arranged on the n-waveguide layer 8; a p-waveguide layer 9, the p-waveguide layer 9 being disposed on the active layer 2; a p-cladding layer 7, the p-cladding layer 7 being disposed on the p-waveguide layer 9; a structured p-contact layer 10, the p-contact layer 10 being arranged
- a second side e.g. right
- a plurality of p-contacts 5 e.g. in the form of metallic contact elements, the p-contacts 5 resting on the structures of the p-contact layer 10 and enabling charge carriers to be injected into the respective emitter structures.
- the end of the two outer sides of the laser bar 1 typically forms a non-active dummy emitter 12, which can be designed in particular as a simple dielectric region, as a trench or as a non-radiative emitter.
- the dummy emitters 12 serve in particular to protect the laser bar 1 on the side surfaces.
- the area in the middle of the laser bar 1 was only indicated for the sake of a better overview, but it is a simple continuation of the structures shown adjacent.
- the layer structure can deviate from that shown, in particular the n and p sides can be interchanged with regard to the substrate (p substrate).
- the individual laser elements are formed in a common layer structure, the p-contact layer 10 being structured for the purpose of separation.
- the introduced separating structures 11 can in particular be areas implanted with ions (first ion implantation zones), trenches or dielectric areas.
- the individual laser Elements can also be separated by appropriate structuring of an n-contact layer, by individual n-contacts or by a p-contact layer and an n-contact layer.
- a laser bar 1 can typically include a number N of 5 to 200 laser elements, with the laser elements being able to be designed as broad area lasers with a lateral width w between 5 ⁇ m and 1200 ⁇ m, the length of the laser elements in the longitudinal direction being between approximately 2 mm and 6 mm, for example and the distance d between the individual laser elements is typically about 30 pm to 100 pm.
- these are temperature profiles of a laser bar of the kW class with a dissipated thermal power loss P d iSS (“dissipated power”) of 603 W, with the conversion efficiency (“PCE”) being 60%.
- the individual laser elements were spaced 64 pm apart.
- the three outer laser elements in particular have a lower temperature during operation (equilibrium temperature between heat input through the laser process and heat output through appropriate cooling, each measured in the middle of the active zone of the individual laser elements). than the inner laser elements.
- the respective outer laser element in particular can have a maximum temperature that is up to 20% lower in comparison to the other laser elements of the laser bar.
- the middle laser elements show uniform temperatures between about 45 °C and 75 °C, depending on the operating power P op .
- the temperature can drop by up to 45% compared to the respective maximum value, as shown in FIG. 2b by way of example.
- the lateral temperature profile of the laser bar can be modified by a targeted increase in the power loss (ie the dissipated heat) at the edge emitters and thus a uniform temperature distribution among the emitter structures in the bar can be achieved.
- a relative A measure for estimating the extent of the required adjustment is a so-called boundary heat factor BH (“boundary heat factor”) of the outermost emitter structures, which specifies the factor by which the power loss P d iSS of the outer emitter structures must be increased in order to achieve a largely homogeneous temperature profile to obtain.
- boundary heat factor BH boundary heat factor
- a boundary heat factor BH of 1.16 leads to an approximately homogeneous temperature distribution between the emitter structures.
- the edge heat factor BH also acts on the inner emitter structures directly adjacent to the outermost emitter structures and can therefore also influence their temperatures.
- An increase in the edge heat factor BH can therefore be used to compensate for the temperature drop in the emitter structures at the outer edges of a laser bar.
- a reduction in the lateral divergence angle of the total emission of the laser bar can be achieved in that a lens effect occurring as a result of an asymmetrical temperature profile is reduced.
- FIG. 3a shows a schematic representation of a first embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 1, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- a distributed Bragg grating 15 (distributed Bragg reflector, DBR) was integrated into the structure in the area of the front facets 13 of these laser elements.
- DBR structures are known to those skilled in the art as feedback elements for spectral filtering of the emitted laser radiation, so that they can be implemented without further ado using known technologies.
- the front-side DBR 15 shown is produced by a comb structure which is arranged in the p-contact layer 10 and preferably extends into the p-cladding layer 7 and has trenches or a refractive index modulation corresponding to the trenches.
- the front facets 13 can also be dielectrically mirrored to form a reflector.
- the degree of reflection R f on the front facet 13 can be adjusted by the structure of the DBR 15 or another reflector. As a result, the optical properties of the resonator can be changed, which reduces its decoupling losses. In the case of the DBR 15, the degree of reflection R f can be adjusted in particular via the number of pairs of layers in the mirror. A higher reflectance R f leads to a lower one
- the temperature of the outer laser elements can thus be adapted to the temperature level of the inner laser elements via a corresponding design of the degree of reflection R f on the front facet 13 in the case of the outer laser elements.
- the second and third outer laser elements are also provided with a DBR 15 in the area of the front facets 13 .
- the different lengths of the DBR structures shown are intended to indicate that the set degree of reflection R f should decrease in the direction of the inner laser elements.
- the exact type of the removal function and how many laser elements are detected on the outside thereof depends on the specific design of the laser bars 1 and the thermal coupling between the individual laser elements. The representation of this embodiment is therefore purely exemplary and represents a large number of possible embodiments.
- the DBR used to increase the degree of reflection R and thus the thermal power loss that occurs can also be a rear reflector, or the arrangement of the individual reflectors can be determined individually for each correspondingly modified laser element.
- a highly reflective rear-side reflector e.g. a DBR or a dielectric mirror layer
- FIG. 3b shows a dependency of the reflector losses (“mirror loss”), the slope efficiency q s ⁇ 0P e (“slope efficiency”) and the threshold current Ah (“threshold current”) as a function of the degree of reflection R f at the front facet.
- the radiant power coupled out of the laser element through the reflector is considered to be the reflector loss (ar m in cm 1 ).
- the threshold current Ah shows a very similar behavior.
- the gradient efficiency q s ⁇ 0P e decreases approximately linearly with the degree of reflection R f at the front facet.
- FIG. 3c shows a dependence of the output power P out (“output power”) and the conversion efficiency PCE as a function of the operating current / for different
- Reflectivities R f at the front facet Corresponding to those shown in Fig. 3b As the degree of reflection Rf increases, dependencies decrease, as do the achievable output powers Pout and the conversion efficiencies PCE. On the other hand, however, this means that a larger proportion of the energy introduced into the laser elements is converted into heat loss and this can be used to adjust the temperature of the outer laser elements.
- FIG. 3d shows a dependency of the power loss P d iSS (“dissipated power”), the conversion efficiency PCE and the temperature rise dT in the active zone as a function of the degree of reflection R f on the front facet at maximum operating voltage ( ⁇ 1.55 V).
- the power loss P diss and the conversion efficiency PCE show an opposing linear increase behavior, with the power loss P diss being able to vary by a factor of 1.6 with degrees of reflection R f between 1% and 50% at the front facet.
- the dependency in the curve of the power loss P diss can be assigned directly to a corresponding temperature rise dT within the active zone.
- FIG. 4 shows a schematic representation of a second embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 3a, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- rear DBRs 16 are also arranged in the region of the rear facet 14.
- optical feedback from spectrally narrow-band DBR gratings is also possible here, which can produce a more stable and narrow-band emission spectrum.
- the arrangement of the individual DBRs can also be reversed. It is also possible for the arrangement of the two DBRs to be determined individually for each correspondingly modified laser element.
- FIG. 5 shows a schematic representation of a third embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 1, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- the length of the pumped area L ga in shortened. This can be achieved, for example, by not forming the metallic p-contact 5 resting on the p-contact layer 10 over the entire length L resonator of the laser elements, but instead injecting charge carriers only over a specific partial area.
- the three outer laser elements are respectively adapted accordingly, with the length of the pumped regions L ga in decreasing towards the outside. The shortening preferably takes place symmetrically to both ends of the laser elements.
- the shortening of the length of the pumped regions L gain leads to an increase in the electrical series resistance and the thermal resistance.
- the maximum current flowing through the emitter structure is reduced by the increased series resistance.
- the temperature within the emitter structures is also increased due to the significantly increased thermal resistance.
- the position of the pumped areas along the longitudinal axis of the emitter structures can be freely selected and determined individually for different laser elements.
- FIG. 6 shows a schematic representation of a fourth embodiment of a laser bar structure according to the invention in a combined elevation and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 5, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- an additional implantation of inert ions into the non-pumped regions of the outer laser elements took place. As a result, a diffusion of charge carriers into the non-pumped regions can be suppressed.
- the depth 18 of these second implantation zones 17 preferably extends from the p-contact layer 10 down into the p-waveguide layer 9.
- FIG. 7 shows a schematic representation of a fifth embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 1, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- additional loss elements 19 are added as loss-inducing structures.
- the loss elements 19 can be, for example, 1-, 2- or 3-dimensional loss centers via a locally changed refractive index, etched wave-like structures along the longitudinal direction of the laser resonator, or crystal areas with locally increased charge carrier density, for example due to indiffusing dopants.
- etched wave-shaped structures are shown as the example for loss elements 19 .
- the resulting reduced transconductance efficiency of the emitter would increase power dissipation and increase the temperature inside the outer emitters.
- the shape and size of the loss centers are not limited to those shown in the figure. However, the loss elements 19 can also be arranged elsewhere in the layer system. A reduction in the width of the p-contacts 5 is not necessary.
- FIG. 8 shows a schematic representation of a sixth embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 1, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- inert ions are implanted at least in sections right into the active layer 2 in the outer emitter structures.
- the depth 21 of these third implantation zones 20 can preferably extend from the p-contact layer 10 through the active layer 2 down into the n-waveguide layer 8, more preferably down into the n-cladding layer 6.
- the losses of injected charge carriers are significantly increased by non-radiative recombination and the internal quantum efficiency h ⁇ ih i is thus reduced.
- the injected charge carriers which as a result preferably recombine without radiation, thus increase the temperature of the respective emitter structure.
- the implantation extends beyond (or at least into) the active region.
- FIG. 9 shows a schematic illustration of a seventh embodiment of a laser bar structure according to the invention in a combined plan view and oblique view.
- the basic structure of the layer system shown corresponds to that described for FIG. 1, the respective reference symbols and their assignment to individual features therefore apply accordingly.
- inert ions are implanted at least in sections up into the p-waveguide layer 9 in the inner emitter structures.
- the depth 23 of these fourth implantation zones 22 can preferably extend from the p-contact layer 10 down into the p-waveguide layer 9.
- inert ionized portions 22 are introduced to increase the series resistivity of the semiconductor layers.
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US6038242A (en) * | 1998-02-12 | 2000-03-14 | Fujitsu Limited | Multiwavelength light source |
US20070223552A1 (en) * | 2005-11-18 | 2007-09-27 | Jds Uniphase Corporation | High Efficiency, Wavelength Stabilized Laser Diode Using AWG's And Architecture For Combining Same With Brightness Conservation |
US20170310081A1 (en) * | 2011-11-30 | 2017-10-26 | Osram Opto Semiconductors Gmbh | Semiconductor Laser Diode |
US20170330757A1 (en) * | 2016-05-13 | 2017-11-16 | Osram Opto Semiconductors Gmbh | Method for producing a semiconductor chip and semiconductor chip |
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CA2011155C (en) | 1989-03-06 | 1994-04-19 | Misuzu Sagawa | Semiconductor laser device |
DE102006044782A1 (de) | 2005-09-29 | 2007-04-05 | Osram Opto Semiconductors Gmbh | Laserdiodenvorrichtung, Laseranordnung mit mindestens einer Laserdiodenvorrichtung und optisch gepumpter Laser |
CN106058643A (zh) | 2016-06-23 | 2016-10-26 | 中国科学院西安光学精密机械研究所 | 一种半导体激光器bar条 |
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US6038242A (en) * | 1998-02-12 | 2000-03-14 | Fujitsu Limited | Multiwavelength light source |
US20070223552A1 (en) * | 2005-11-18 | 2007-09-27 | Jds Uniphase Corporation | High Efficiency, Wavelength Stabilized Laser Diode Using AWG's And Architecture For Combining Same With Brightness Conservation |
US20170310081A1 (en) * | 2011-11-30 | 2017-10-26 | Osram Opto Semiconductors Gmbh | Semiconductor Laser Diode |
US20170330757A1 (en) * | 2016-05-13 | 2017-11-16 | Osram Opto Semiconductors Gmbh | Method for producing a semiconductor chip and semiconductor chip |
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