Double waveguide structure for edge-emitting semiconductor laser and method of forming the same

Abstract

To provide a high-power edge-emitting semiconductor laser and a method of manufacturing the same.SOLUTION: There are disclosed: an edge-emitting semiconductor laser that includes a second passive waveguide and cladding layer disposed above the multi-layer arrangement of a first waveguiding layer and a first cladding layer; and a manufacturing method thereof. An active region of the laser is contained within or along a lower surface of the first waveguiding layer, as in standard devices. A regrowth interface is located along a top surface of the first cladding layer, as compared to the prior art where the interface is located within the first waveguiding layer. The resulting configuration exhibits an improved coupling efficiency by maintaining a propagating optical mode within an active waveguiding layer and away from the regrowth interface.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] This disclosure relates to edge-emitting semiconductor lasers, and more particularly to utilizing a dual waveguide structure to improve the high power performance of the laser in the presence of required levels of injection current. [Background technology]

[0002] High-power edge-emitting semiconductor lasers have become important components in a variety of applications, including high-power pump sources for doped fiber amplifiers, high-power cutting tools for machining, and high-power signal paths for free-space optical communication systems.

[0003] In many cases, features such as long life, reliable and stable output, high output power, high electro-optical efficiency and high beam quality are commonly desired. One key to the long-term reliability of such high-power lasers is directly related to the stability of the laser facets that are cleaved to form the opposing mirrors of the laser cavity. Degradation of the laser facets is a complex reaction caused by light, current and heat that results in a loss of output power and, in severe cases, catastrophic optical damage (COD) to the mirror surface itself.

[0004] One approach to improving the integrity of semiconductor laser structures is to remove (e.g., using an etching process) the active region material along the vertical depth from the front facet of the structure, followed by epitaxial regrowth of the passive layer arrangement, thereby improving the stability of the facet. As will be described in more detail below, this regrown epitaxial mirror is often referred to as a "non-absorbing mirror" type of laser facet. However, problems remain with non-absorbing mirrors, for example, in terms of coupling efficiency between the unetched part of the structure and the etched non-absorbing mirror part, or in that the regrowth interface may be too close to the active region, resulting in high absorption and possibly COD (which is what is intended to be avoided in the first place).

[0005] Another problem with the performance of high power edge-emitting lasers relates to the level of injection current required to obtain a desired power level. The presence of an injection current is known to increase the temperature of the localized region along the injection stripe, raising the relative refractive index of the current injection region by an amount sufficient to form a thermally induced waveguide capable of guiding multiple transverse modes, thereby degrading the beam quality of the high power output beam. Summary of the Invention

[0006] Disclosed herein are specific configurations of edge-emitting semiconductor lasers that provide the necessary protection for the facets of the edge-emitting semiconductor laser without affecting the optical coupling efficiency between the active and passive waveguide portions of the structure or creating the possibility of high absorption at the regrowth interface. The disclosed structures can be specifically tuned to compensate for thermally induced local changes in refractive index and to control the number of transverse modes that are excited.

[0007] According to the teachings of the present disclosure, an edge-emitting semiconductor laser is fabricated to include a second waveguide layer and a second cladding layer, which are arranged in sequence on top of the original cladding layers (typically, they are p-type layers). Once the first cladding layer is formed (grown), a portion of the structure is etched to define a non-absorbing mirror facet, as in the prior art. The second waveguide and cladding layers are then grown to form an "unetched region" (also defined as "epi I") that includes the complete stack of the first and second waveguide and cladding layers, and an "etched region" (also defined as "epi II") that includes only the second waveguide and cladding layers (no active region along the second waveguide layer). In one embodiment, the epi II region can be used to form a non-absorbing mirror arrangement at the front (emitting) facet or back facet of the edge-emitting semiconductor laser. In another embodiment of the dual-waveguide laser structure, a pair of epi II structures can be placed along the side endfaces of the centrally located injection stripe of the edge-emitting laser to minimize current spreading (without the need to create a ridge-type structure).

[0008] The combination of the original (first) waveguide and cladding layers with the second (passive) waveguide and cladding layers is also referred to below as a "dual waveguide" structure. The active region of the laser is contained within or along the lower surface of the first waveguide layer, as in standard devices. The regrowth interface in the disclosed structure is located between the first cladding layer and the second waveguide layer, thereby increasing (compared to the prior art) the vertical separation between the propagating mode and the regrowth interface.

[0009] The vertical mode profile of the disclosed semiconductor laser can be tailored by controlling the properties (e.g., thickness, composition, etc.) of the original (first) waveguide layer and associated cladding layers such that the propagating optical mode exhibits a minimum (substantially zero) along the regrowth interface within a defined internal region (also referred to as the "epi I" region). Selecting appropriate parameters (e.g., thickness, composition, etc.) for the second waveguide layer and cladding layers ensures efficient coupling of the propagating mode from the active epi I region along the facet to the adjacent non-absorbing mirror region (also referred to as the "epi II" region).

[0010] Furthermore, it is believed that control of the thickness and composition of a pair of dual waveguide structures contained along either side of the injection stripe region may be used to control the number of transverse modes excited as a result of the thermally induced change in refractive index along the injection stripe as described above. The composition and / or dimensions of the passive waveguide and cladding layers create a graded change in refractive index between the central active waveguide and the side passive waveguides. The choice of materials creates either a positive graded refractive index change (i.e., anti-guiding configuration) or a negative graded refractive index change (guiding configuration) across the lateral dimension of the device.

[0011] An embodiment of the present disclosure may take the form of an edge-emitting semiconductor laser comprising: a semiconductor substrate; a cladding layer of a first conductivity type formed on the semiconductor substrate; a waveguide layer of the first conductivity type formed on the cladding layer; an active region disposed over a defined region of the waveguide layer; a first waveguide layer of a second, opposite conductivity type formed on the active region; and a first cladding layer of a second conductivity type formed on the first waveguide layer, the first cladding layer having a defined region of the combination of the active region, the first waveguide layer and the first cladding layer removed to define a regrowth interface along a surface of the waveguide layer of the first conductivity type exposed by the removal. The laser structure further comprises a second waveguide layer of a second conductivity type formed on the regrown interface and a second cladding layer of a second conductivity type formed on the second waveguide layer of the second conductivity type, the compositions and thicknesses of the first waveguide layer of the second conductivity type and the cladding layer being selected to provide a defined separation between the propagating longitudinal optical mode and the regrowth interface.

[0012] Another embodiment may include a method of manufacturing such a semiconductor laser, comprising the steps of providing a semiconductor substrate of a first conductivity type; forming, in order, a cladding layer of the first conductivity type and a waveguide layer of the first conductivity type on the semiconductor substrate; forming an active region over an upper surface of the waveguide layer of the first conductivity type; forming, in order, a first waveguide layer of a second, opposite conductivity type and a first cladding layer of the second, opposite conductivity type on the active region, wherein the formed structure has a front facet and an opposing rear facet. the optical waveguide layer and the first cladding layer from a portion of the formed structure, the exposed surface formed by the removal being defined as a regrowth interface; and forming a second waveguide layer of a second conductivity type and a second cladding layer of a second conductivity type, in sequence, on the regrowth interface, selected to form a defined separation between a propagating longitudinal optical mode and the regrowth interface.

[0013] Other and further embodiments and aspects of the present disclosure will become apparent during the course of the following description and by reference to the accompanying drawings. [Brief description of the drawings]

[0014] Reference is now made to the drawings. [Figure 1] FIG. 1 shows the structure of a prior art edge-emitting semiconductor laser after the initial epitaxial growth process. [Diagram 2] FIG. 2 illustrates a subsequent step in the manufacturing process for the prior art laser of FIG. 1, showing the formation of a recessed area along the front facet in which a non-absorbing mirror may later be formed. [Diagram 3] FIG. 3 shows the configuration of a prior art edge-emitting laser following an epitaxial regrowth process, including the formation of a non-absorbing mirror structure along the front facet region. [Figure 4] FIG. 4 is a side view of the prior art edge-emitting laser of FIGS. 1-3, illustrating the emergence of thermally induced waveguide upon application of an excitation current along the injection stripe of the device. [Diagram 5] FIG. 5 shows the initial configuration of an edge-emitting semiconductor laser formed in accordance with the present disclosure, including the formation of a complete p-type waveguide layer and a p-type cladding layer over the active region. [Figure 6] FIG. 6 illustrates the next step in the manufacturing process of the disclosed laser structure, showing the removal of a portion of the active region along with the waveguide and cladding layers thereover in preparation for the formation of a non-absorbing mirror structure at the front facet. [Figure 7] FIG. 7 illustrates the subsequent construction of the disclosed edge-emitting semiconductor laser, including epitaxial growth of a second waveguide layer and a second cladding layer, the distal portions of which form a non-absorbing mirror structure. [Figure 8] FIG. 8 shows the refractive index profile and associated mode intensities of the internal portion of the disclosed semiconductor laser, including the active region (ie, the "unetched" portion of the laser / also referred to as "epi I"). [Figure 9] FIG. 9 shows the refractive index profile and mode intensity of the end portion of the disclosed semiconductor laser relative to the region where the non-absorbing mirror structure is formed (i.e., the “etched” portion of the laser / also referred to as “epi II”). [Figure 10] FIG. 10 is a simulation of fundamental mode propagation in a prior art structure, illustrating the poor optical coupling between the interior portion and the associated non-absorbing mirror structure. [Figure 11] FIG. 11 is a simulation of the operation of a semiconductor laser having the dual waveguide structure described in the present disclosure, showing high coupling efficiency between a first (active) waveguide layer in the internal portion of the device and a second (passive) waveguide layer of a non-absorbing mirror structure along the front facet of the disclosed laser. [Figure 12] FIG. 12 is an isometric view of a semiconductor laser formed in accordance with the teachings of the present disclosure illustrating the use of a dual waveguide arrangement to modify the lateral confinement of a propagating optical mode. [Figure 13] FIG. 13 contains a set of plots relating to the device of FIG. 12 and shows the results of using a dual waveguide configuration which shows a positive change in effective refractive index for the central waveguiding region of the device. [Figure 14] FIG. 14 includes another set of plots related to the device of FIG. 12, where the properties of the dual waveguide have been controlled to exhibit a negative step change in effective refractive index for the central waveguide region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The principles of the present disclosure will be best understood by comparing its technical details with those of prior art semiconductor lasers formed to include non-absorbing mirrors along the front (light-emitting) and back facets. Figure 1 is an illustration of an intermediate step in the process of manufacturing a prior art edge-emitting semiconductor laser. For purposes of illustration, Figures 1-3 are longitudinal cross-sectional views of a laser device emitting output light in the direction of the arrows (i.e., exiting the front facet of the device structure).

[0016] As shown, a prior art semiconductor laser 1 includes a substrate 2 on which a first cladding layer 3 is grown (or deposited). Often, semiconductor lasers utilize an n-type substrate, with the first cladding layer 3 being an n-type material epitaxially grown on the exposed top surface of the substrate 2. An n-type waveguide layer 4 (having a higher refractive index value than the n-type cladding layer 3) is then formed, as shown, and an active region 5 is disposed over the exposed top surface of the n-type waveguide layer 4. The active region 5 may include any type of configuration known in the art for imparting gain to a propagating optical signal, such as one or more quantum wells (or similar quantum configurations). Following the formation of the active region 5, a p-type waveguide layer 6 of initial thickness t is formed over the active region 5 (also referred to as layer 6-1 below for reasons that will become apparent). The front facet 7F of the laser 1 is defined along the right end face of the arrangement shown in FIG. 1, with the emitted light waves propagating along the vertical direction as shown.

[0017] As shown in FIG. 2, the next step in the prior art process to minimize facet degradation is to etch away the active region 5 and p-type cladding layer 6-1 adjacent facet 7F. As a result, the etched structure shown in FIG. 2 includes an internal step where the active region 5 terminates at a recessed location relative to the location of the front facet 7F. The top surface of the etched structure as shown in FIG. 2 is defined as the regrown interface 8 (upon which additional epitaxial layers will be formed). In this particular structure, the regrown interface 8 is shown as including a first regrown interface 8-1 section (the unetched top surface of the p-type cladding layer 6-1) and a second regrown interface section 8-2 on the exposed surface of the n-type waveguide layer 4.

[0018] 3 shows subsequent steps in the prior art manufacturing process, including the growth of epitaxial material (p-type) on the regrown interface sections 8-1, 8-2. The initial growth step is used to provide the remaining desired thickness of the p-type waveguide layer 6 (an additional waveguide sublayer, labeled 6-2 in FIG. 3), and the combination of the thicknesses of layers 6-1, 6-2 forms the desired thickness of the p-type waveguide structure. A p-type cladding layer 9 is then epitaxially grown on the p-type waveguide layer 6 (with an electrical contact layer 9C formed as the top layer of the structure). The combination of the waveguide sublayer 6-2 and the cladding layer 9 in the end portions of the structure forms a non-absorbing mirror configuration between the termination of the active region 5 and the front facet 7F, thereby supporting the continued propagation of the generated laser emission, but without adding any additional energy to the beam.

[0019] As mentioned above, the vertical separation between the active region 5 and the regrowth interface 8 is a critical factor in device performance: depending on the location of the regrowth interface 8, either the coupling efficiency between the unetched epi I and etched epi II portions of the laser structure is low, or defects that may occur at the regrowth interface during the overgrowth step may result in high levels of absorption of the propagating modes, potentially resulting in COD.

[0020] Furthermore, it is known that operation of edge-emitting semiconductor lasers under conditions necessary to produce high levels of output power requires a significant amount of injection current. Figure 4 shows a prior art cross-sectional view taken along line segment 4-4 of Figure 3. During operation of the laser device 1, current is injected at a defined location along the stripe position S, resulting in a local increase in temperature in the region under the injection stripe. The refractive index of this region also increases, creating a thermally induced waveguide structure Δn (as shown in Figure 4). T is formed. The thermally induced waveguide can support some unwanted transverse modes.

[0021] In accordance with the principles of the present disclosure, device performance is improved by including an additional p-type waveguide / cladding structure (i.e., a "dual waveguide") that serves to move the regrown interface away from the propagating optical mode, both in terms of efficient mode coupling and reduction of thermally induced waveguide. The dual waveguide configuration has been found to improve coupling efficiency between the active region and the non-absorbing mirror (i.e., epi I and epi II), and the inclusion of additional waveguide and cladding layers provides the ability to independently tailor the vertical profile within the laser body (epi I) and the profile of the facets (e.g., epi II regions).

[0022] 5-7 illustrate a series of fabrication steps that may be used to add a second (passive) p-type waveguide layer and associated cladding layers to an edge-emitting semiconductor laser structure to provide the desired non-absorbing mirror function along one or more facets without the reduced coupling efficiency (or increased COD) seen in prior art devices. FIG. 5 illustrates a portion of an edge-emitting semiconductor laser 10 at an intermediate step in the fabrication process. Similar to the description of the prior art laser 1, the edge-emitting semiconductor laser 10 is shown as including a substrate (n-type) 12 on which an n-type cladding layer 14 and an n-type waveguide layer 16 are formed. An active region 18 is then formed on the exposed upper major surface of the n-type waveguide layer 16, the active region 18 may include any one of several known types of configurations (quantum wells, dots, wires, etc.). FIG. 5 also illustrates how a first p-type waveguide layer 20 is formed on the active region 18, followed by a first p-type cladding layer 22 formed over the first p-type waveguide layer 20. The first p-type waveguide layer 20 is hereinafter also referred to as the "active" waveguide layer 20. The structure as shown in Figure 5 is defined as including a front (light-emitting) facet 24F.

[0023] It is at this point in fabrication that an etching process is performed to define the area where the non-absorbing mirror will be located on the front facet 24F. This is illustrated in Figure 6, which shows the removal of the active region 18, the first waveguide layer 20 and the first cladding layer 22 along a vertical extent recessed from the front facet 24F of the device (i.e., from an edge portion of the laser structure). This step terminates the active region 18 at a location internal to the laser 10, reducing the chance of damage to the laser facet 24F due to high temperatures associated with the active region 18.

[0024] Well-known patterning and etching processes can be used to create the structure as shown. The regrowth interface 26 is shown in this structure as including a first section 26-1 along the top surface 22S of the p-type cladding layer 22 that is not etched, and a second section 26-2 that extends onto the surface 16S of the n-type waveguide layer 16 that is exposed during the etching process. Hereinafter, the structure as shown in FIG. 6 will be defined as including an "unetched epitaxial region I" (or simply "epi I") and an "etched epitaxial region II" (or simply "epi II"). A non-absorbing mirror structure M is defined within epi II.

[0025] 7 illustrates the next step of forming a second p-type waveguide layer 30 followed by a p-type cladding layer 32 on the regrown interface 26. In particular, the second layers 30, 32 are grown on both sections of the regrown interfaces 26-1, 26-2. A contact layer 34 is then formed on the second p-type cladding layer 32. Although not shown in particular detail, a current is injected to initiate lasing at a defined location of a central stripe 35 formed along the contact layer 34. A structure such as that shown in FIG. 7 is considered as an example of a dual waveguide laser structure formed in accordance with the present disclosure.

[0026] As will be described in detail below, the complete stack of first and second waveguide and cladding layers in the epi I portion of the laser structure 10 allows for control of the location of the regrowth interface 26-1 relative to the propagating mode. In particular, the inclusion of the second (passive) waveguide and cladding layer allows for the regrowth interface to be shifted upward relative to the top surface of the first p-type cladding layer 22. The epi II portion of the laser structure includes a stack of the n-type cladding layer 14 and n-type waveguide layer 16 with the second waveguide and cladding layers 30, 32. Because the active region 18 is not present in the epi II portion of the structure (i.e., the second waveguide layer 30 is referred to as a "passive waveguide"), the formed non-absorbing mirror region M supports the propagation of the generated laser emission towards the front facet 24F but does not provide any additional gain to the signal.

[0027] In accordance with the principles of the present disclosure, the thickness and composition of the first p-type waveguide layer 20 and the associated p-type cladding layer 22 are preferably selected such that the minimum (i.e., “null”) of the propagating longitudinal optical mode is aligned with the location of the regrowth interface 26-1.

[0028] 8 includes an exemplary refractive index profile and associated optical mode intensity associated with a vertical design configuration of the interior portion of the semiconductor laser 10 (i.e., the epi I section defined above). The optical mode is shown as a dashed line in FIG. 8. In this particular example, the optical mode peak is shown to coincide with the active region 18. However, it should be noted that overlap of the optical mode peak with the active region 18 is not necessarily the case in state-of-the-art vertical high power laser cavities.

[0029] By controlling the composition and thickness of the first p-type waveguide layer 20 and the first p-type cladding layer 22 in the manner described above in connection with Figure 7, the refractive index profile shown in Figure 8 is such that the optical mode is essentially null at the regrown interface 26-1, as indicated by an "X" in Figure 8. This also supports the design objective of confining the propagation of the optical mode within the first p-type waveguide layer 20 (and away from the regrown interface 26), as described above. Thus, by creating a null in the optical mode at the regrown interface, the optical mode remains confined within the n-type waveguide layer 16 and the first p-type waveguide layer 20.

[0030] By appropriately selecting the composition and thickness of the second passive p-type waveguide layer 30 and the cladding layer 32, the propagating mode is efficiently coupled into the second passive p-type waveguide layer 30 (i.e., epi II). In particular, FIG. 9 includes the refractive index profile and associated optical mode field (dashed line) of the epi II region of the edge-emitting dual-waveguide semiconductor laser 10. The properties of the passive p-type waveguide layer 30 and the second p-type cladding layer 32 are selected to ensure good coupling efficiency between the two sections of the laser structure (i.e., between epi I and epi II). As a result, a relatively high optical output power can be emitted from the non-absorbing mirror M, as opposed to the rather weak output found in some prior art non-absorbing mirror configurations.

[0031] The improvement in laser operation associated with the disclosed dual waveguide structure can be confirmed by comparing the simulation diagrams of Figures 10 and 11. Figure 10 is associated with a prior art device (as shown in Figures 1-4) and shows a relatively low coupling efficiency between the unetched epi I and etched epi II portions of the laser structure. In contrast, the simulation of Figure 11 (associated with the disclosed dual waveguide arrangement) shows good coupling efficiency; in fact, nearly 100% of the propagating optical mode is coupled to the passive waveguide in the non-absorbing mirror structure.

[0032] The disclosed dual waveguide edge-emitting lasers can also be configured with a pair of (epi II) side region configurations disposed on either side of a central injection stripe (epi I) of the edge-emitting laser structure, as described above. Figure 12 shows an example of a dual waveguide laser structure 40 formed to include a central injection stripe (i.e., central waveguide region) 60 in accordance with this embodiment, with a pair of dual waveguide structures 62, 64 disposed along either side of the central waveguide region 60.

[0033] Similar to the dual waveguide laser structure 10 described above, the dual waveguide laser structure 40 is an edge-emitting device and includes n-type and p-type waveguide and cladding layers formed (grown) on a semiconductor substrate of a suitable material. In this particular example, the dual waveguide laser 40 includes a substrate 42 on which an n-type cladding layer 44 and an n-type waveguide layer 46 are formed. An active region 48 is formed on the n-type waveguide layer 46. Also similar to the dual waveguide laser structure 10 described above, a first p-type waveguide layer 50 and a first p-type cladding layer 52 are formed on the active region 48.

[0034] In this particular arrangement, both sides of the resulting structure are etched in a known manner to remove the active region 48, the first waveguide layer 50 and the first cladding layer 52. A regrowth interface 54 defines this etched surface, and a subsequent second p-type waveguide layer 56 and second p-type cladding layer 58 are grown on the interface 54. The resulting dual waveguide structure includes a pair of side passive structures (epi II) of the second p-type waveguide and cladding layers 56, 58, and a central complete "stack" of both the first p-type waveguide and cladding layers 50, 52 and the second p-type waveguide and cladding layers 56, 58, as shown in FIG.

[0035] It has also been found that by including a dual waveguide structure extending longitudinally along the side of the laser structure and along its optical axis, it is possible to control the properties of thermally induced waveguides that may support the propagation of unwanted higher order modes. As noted in the description of prior art FIG. 4, the presence of high current levels in the injection stripe is known to increase the temperature and refractive index profile of the semiconductor layers in close proximity to the current flow. The thermally induced waveguides created by this temperature difference are known to support transverse modes that adversely affect the performance of the laser device (even more so as current levels increase and the temperature / refractive index difference increases).

[0036] It is proposed that the inclusion of dual waveguide passive sections 62, 64 along either side of the central waveguiding region 60 of the edge-emitting semiconductor laser 40 provides a mechanism by which optical properties affected by the temperature rise associated with injection current can be controlled. In particular, the passive waveguide / cladding layers 56, 58 act to shift the position of the propagating transverse modes (similar to the shift provided to the longitudinal modes between epi I and epi II) and minimize the influence / appearance of those transverse modes.

[0037] It has been found that by forming the semiconductor laser 40 to include dual waveguide passive sections 62, 64 as shown in Figure 12, the excitation of undesired transverse modes is suppressed. The thickness and composition of the passive waveguide and cladding layers 62, 64 can be tailored to provide the desired amount of mode suppression required. In fact, the composition of the layers can be such as to produce either a "positive" refractive index step change relative to the central waveguiding region 60, or a "negative" refractive index step change relative to the waveguiding region 60.

[0038] 13 includes plots illustrating the effect of a positive step change in refractive index between the epi II and epi I regions of the dual waveguide laser structure 40. Plot (a) illustrates the positive step change itself, configured such that the effective refractive index of epi II (i.e., regions 62, 64) is greater than the effective refractive index of epi I (i.e., central waveguide region 60). As shown, this positive step relationship is referred to as an "anti-guiding" structure, and the difference in effective refractive index is Δn antiguide When a laser with this positive step relationship is energized, the resulting increase in temperature in the central guiding region 60 increases its effective index, as in the prior art laser (compare FIG. 4), but the additional effective index change in the antiguiding results in an increase in the effective index in regions 62, 64, as shown in plot (b) of FIG. 13. Higher order transverse modes have a lower modal index n m , which is suppressed. Plot (c) shows the intensity of the non-guided transverse modes that result in high radiation losses.

[0039] Figure 14 contains plots similar to those in Figure 13, except for the negative step change in effective index between epi II and epi I. The change in effective index across this boundary is Δn guide In this case, the modal refractive index n m An exemplary transverse mode having a mode refractive index n m As shown by the position of Δn, the waveguide remains guided within the central active region 60, and the specific characteristics of the passive sections 62, 64 can be tailored to control the number of excited transverse modes that contribute to the propagating field. guide The value of Δn can be used to stabilize the near-field width of the longitudinal mode. guide 4 shows the intensities of the transverse modes related to the relation

[0040] The disclosed laser structure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the disclosure is therefore indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. An edge-emitting semiconductor laser, A semiconductor substrate; a cladding layer of a first conductivity type formed on the semiconductor substrate; a waveguide layer of a first conductivity type formed on the cladding layer; an active region disposed on a defined area of ​​the waveguide layer; a first waveguide layer of a second opposite conductivity type formed on the active region; a first cladding layer of a second conductivity type formed on the first waveguide layer, the first cladding layer having a defined area of ​​the combination of the active region, the first waveguide layer and the first cladding layer removed to define a regrowth interface along a surface of the waveguide layer of the first conductivity type exposed by the removal; a second waveguide layer of a second conductivity type formed on the regrowth interface; and a second cladding layer of a second conductivity type formed on said second waveguide layer of a second conductivity type, wherein compositions and thicknesses of said first waveguide layer of a second conductivity type and said cladding layer are selected to form a defined separation between a propagating longitudinal optical mode and said regrowth interface.

2. 2. The edge emitting laser according to claim 1, 1. An edge-emitting laser, wherein the defined area of ​​removal of the active region, the first waveguide layer and the first cladding layer includes a recessed area along a front facet of the edge-emitting laser, and a second waveguide layer and a cladding layer formed in the recessed area form a non-absorbing mirror of the edge-emitting laser.

3. 3. The edge emitting laser according to claim 2, the compositions and thicknesses of the first waveguide layer of second conductivity type and the first cladding layer of second conductivity type are selected such that a propagating longitudinal mode coincident with a location of the regrowth interface has an intensity value close to zero.

4. 2. The edge emitting laser according to claim 1, 1. An edge-emitting laser, comprising: a first cladding layer and a second cladding layer formed along said first and second side regions; a first cladding layer and a second waveguide layer formed along said first and second side regions; a first cladding layer and a second waveguide layer formed along said first and second side regions; a first cladding layer and a second waveguide layer formed along said first and second side regions;

5. 5. The edge emitting laser according to claim 4, the composition and thickness of the second waveguide layer and cladding layer are selected, relative to the composition and thickness of the first waveguide layer and cladding layer, such that the refractive index of the second waveguide layer is greater than the refractive index of the first waveguide layer, thereby forming an anti-waveguiding laser structure in the presence of thermally induced waveguide.

6. 5. The edge emitting laser according to claim 4, the composition and thickness of the second waveguide layer and cladding layer are selected, relative to the composition and thickness of the first waveguide layer and cladding layer, such that the refractive index of the second waveguide layer is less than the refractive index of the first waveguide layer, thereby forming controlled guiding of a transverse mode in the presence of thermally induced waveguide.

7. 1. A method of manufacturing a laser structure, comprising the steps of: Providing a semiconductor substrate of a first conductivity type; forming a cladding layer of the first conductivity type and a waveguide layer of the first conductivity type in sequence on the semiconductor substrate; forming an active region over an upper surface of the waveguide layer of first conductivity type; forming, in order, a first waveguide layer of a second opposite conductivity type and a first cladding layer of a second opposite conductivity type over the active region, the formed structure being defined as having a front facet and an opposing rear facet, and in operation, a light beam is emitted through at least the front facet; removing the combination of the active region, the first waveguide layer, and the first cladding layer from a portion of the formed structure, an exposed surface formed by the removal being defined as a regrowth interface; forming, in order, a second waveguide layer of a second conductivity type and a second cladding layer of a second conductivity type on the regrowth interface, selected to form a defined separation between a propagating longitudinal optical mode and the regrowth interface.

8. 8. The method of claim 7, wherein in performing the removing step, ends of the combination of the active region, the first waveguide layer and the first cladding layer proximate a front facet of the laser structure are removed, thereby forming a non-absorbing mirror during the steps of sequentially forming a second waveguide layer and a second cladding layer of a second conductivity type.

9. 8. The method of claim 7, wherein, in performing the removing step, a side of the combination of the active region, the first waveguide layer and the first cladding layer adjacent a current injection region of the laser structure is removed, thereby forming a current confinement and lateral mode suppression structure.

10. An edge-emitting semiconductor laser, A semiconductor substrate; a cladding layer of a first conductivity type formed on the semiconductor substrate; a waveguide layer of a first conductivity type formed on the cladding layer; an active region disposed on a defined area of ​​the waveguide layer; a first waveguide layer of a second opposite conductivity type formed on the active region; a first cladding layer of a second conductivity type formed on the first waveguide layer, the first cladding layer having a defined area of ​​the combination of the active region, the first waveguide layer and the first cladding layer removed to define a regrowth interface along a surface of the waveguide layer of the first conductivity type exposed by the removal; a second waveguide layer of a second conductivity type formed on the regrowth interface; a second cladding layer of a second conductivity type formed on said second waveguide layer of a second conductivity type, the composition and thickness of said first waveguide layer of a second conductivity type and the cladding layer being selected to form a defined separation between a propagating longitudinal optical mode and said regrowth interface; a first defined area of ​​removal of the active region, the first waveguide layer and the first cladding layer includes a recessed area along a front facet of the edge-emitting laser, a second waveguide layer and a cladding layer formed in the recessed area forming a non-absorbing mirror of the edge-emitting laser; and a second defined area of ​​removal of the active region, the first waveguide layer and the first cladding layer includes opposing side regions of the edge-emitting laser adjacent a central injection stripe and a current injection region forming a waveguiding region, and wherein passive current confinement and lateral mode suppression are provided by a combination of a second waveguide layer and a cladding layer of the second conductivity type formed along the opposing side regions.

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