Methods, systems, and apparatus for suppressing higher-order modes

Abstract

A laser diode includes a lateral waveguide and a side waveguide, the lateral waveguide being orthogonal to the side waveguide. The side waveguide includes an active layer located between an n-type waveguide layer and a p-type waveguide layer. The lateral waveguide is defined by an n-type cladding on the n-side and a p-type cladding on the p-side. The side waveguide is defined at a first end by a high reflector (HR) coating and at a second end by a partial reflector (PR) coating along a longitudinal direction. The side waveguide further includes a buried high-order mode suppression layer (HOMSL) disposed below the p-type cladding and within the side waveguide, or on one or both sides of the side waveguide, or a combination thereof. The length of the HOMSL extending longitudinally from the HR surface is less than the distance between the HR surface and the PR surface.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 885,946, filed on August 13, 2019. Technical Field

[0003] The technology disclosed herein relates to diode lasers, and more specifically to methods, systems, and apparatus for high-order mode suppression in diode lasers. Background Technology

[0004] A laser is a light-emitting device. Light emission in a laser is the result of stimulated emission of electromagnetic radiation, amplified by light. Some lasers emit spatially and temporally coherent light, allowing them to emit narrow-bandwidth light that can be narrowly focused over long distances. There are many types of lasers, such as gas lasers, chemical lasers, dye lasers, metal vapor lasers, solid-state lasers, and semiconductor lasers. A laser diode is an electrically pumped semiconductor laser in which the active layer is formed by a pn junction of the semiconductor diode. Laser diodes typically consist of an active layer disposed between p-type and n-type semiconductor material layers. Many laser diodes are fabricated on semiconductor substrates such as gallium arsenide, which are doped with elements such as aluminum, silicon, zinc, carbon, or selenium to produce n-type and p-type semiconductor layers. The active layer is typically undoped gallium arsenide indium and may be only a few nanometers thick.

[0005] Laser diodes are formed by growing multiple layers of semiconductor material on a suitable substrate with a lattice constant that allows selection of materials to produce the desired emission wavelength. A typical laser diode consists of an n-type layer, a p-type layer, and an undoped active layer located between them, such that when the diode is forward biased, electrons and holes recombine in the active layer to generate light. The active layer (quantum well, quantum wire or quantum dot, type II quantum well) is located in the waveguide layer, which has a higher refractive index compared to the surrounding p-type and n-type doped cladding. The light generated by the active layer is confined within the waveguide plane.

[0006] Traditional edge-emitting Fabry-Perot wide-area laser diodes are arranged as rectangular gain- or refractive index-guided semiconductor structures. Opposite end faces of the waveguide define high reflectors and partial reflectors, providing feedback for optical oscillations within the resonator. Multilayer laser diode structures extend the length of the laser and have a wider width for electrical injection, extending to opposite side surfaces that also extend the laser length. The multilayer semiconductor material is typically arranged such that the laser operates in single-mode along the laser's growth direction, which is defined as the fast axis direction. Because semiconductor lasers operate in single-mode along the fast axis direction, the brightness of the laser diode along this direction cannot be further increased; hence, it is called the diffraction limit. Therefore, the distance between the top and bottom surfaces of the multilayer semiconductor laser structure provides a smaller end-face dimension, i.e., the fringe thickness, typically on the order of micrometers. On the other hand, the width of the multilayer laser structure provides a larger end-face dimension, i.e., the fringe width, typically from tens to hundreds of micrometers. This is called the "slow axis." Since the fringe width is much larger than the wavelength of light, the lateral characteristics of the optical field propagating along the optical axis of the waveguide are highly multimode along the wider fringe size, and the corresponding axis is described as the slow axis because the divergence angle is much smaller than that of the fast axis.

[0007] In high-power applications, "multimode laser diodes" or "wide-area lasers" (BALs) are used. BALs have multiple modes along the slow axis, resulting in a higher slow-axis beam parameter product (BPP) than single-mode laser diodes. Furthermore, as they are driven to higher currents, the thermal lensing effect becomes more pronounced, leading to a higher refractive index contrast distribution in the lateral direction, thus accommodating more and more lateral modes. Consequently, as the lateral divergence angle widens, this results in a decrease in lateral BPP and brightness (power ÷ BPP), along with a reduction in slow-axis brightness. This means that even though power typically increases with higher currents, slow-axis brightness degrades. The brightness of a BAL can be improved by reducing the emitter width; however, the current at which maximum brightness occurs also occurs at gradually decreasing current values. Therefore, the maximum output power at maximum brightness also decreases.

[0008] For power scaling applications and to reduce the cost per watt of producing diode lasers, higher brightness at higher output power per emitter is desired. Summary of the Invention

[0009] This document discloses methods, systems, and apparatus for reducing the magnitude of refractive index contrast of a lateral waveguide during operation of a laser diode. This may include a laser diode having a lateral waveguide orthogonal to a lateral waveguide, the lateral waveguide including an active layer located between an n-type waveguide layer and a p-type waveguide layer, wherein the lateral waveguide is defined by an n-type cladding on the n-side and a p-type cladding on the p-side, the lateral waveguide being defined longitudinally at a first end by a high reflector (HR) coated surface and at a second end by a partial reflector (PR) coated surface, the lateral waveguide further including a buried high-order mode suppression layer (HOMSL) disposed beneath the p-type cladding and within the lateral waveguide, or on one or both sides of the lateral waveguide, or a combination thereof, wherein the length of the HOMSL extending longitudinally from the HR surface is less than the distance between the HR surface and the PR surface.

[0010] In some examples, the refractive index of the HOMSL placed on one or both sides of the lateral waveguide can be higher than that of the p-type waveguide layer and the p-type cladding.

[0011] In some examples, the refractive index of the HOMSL disposed within the lateral waveguide can be lower than that of the n-type waveguide layer or the p-type waveguide layer or a combination thereof.

[0012] The thickness of the HOMSL can be selected based on the magnitude of the refractive index contrast in the lateral waveguide caused by thermal lensing within the lateral waveguide during laser diode operation. In the example, the thickness of the HOMSL is chosen to reduce the magnitude of the refractive index contrast in the lateral waveguide during operation. The magnitude of the refractive index contrast can be 10... -5 <Δn<10 -3 Within a certain range. In some examples, such lateral waveguides support fewer than ten lateral modes or may support a single lateral mode.

[0013] In some examples, the thickness of the HOMSL can be chosen to reduce the effective refractive index on the side of the lateral waveguide extending from the HR plane. In some examples, such a lateral waveguide is defined in the lateral direction by a ridge waveguide, wherein the ridge waveguide extends from the HR plane to the PR plane.

[0014] In some examples, the HOMSL overlaps laterally with the lateral waveguide, with an overlap of 0-10 μm on either side, or a total overlap of 0-20 μm.

[0015] In some examples, the HOMSL set in the lateral waveguide is 0-10µm narrower on either side than the lateral waveguide or 0-20µm narrower in total.

[0016] In some examples, the lateral waveguide is defined in the lateral direction by a ridge waveguide that extends from the PR surface in the longitudinal direction by a length less than the distance between the PR surface and the HR surface.

[0017] In some examples, the HOMSL includes a reduced lateral waveguide thickness located within the active stripe and can be formed by etching down or selectively depositing a thicker layer adjacent to the active stripe.

[0018] In some examples, HOMSL includes gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), and indium gallium phosphide (InGaAsP).

[0019] In an example where the HOMSL is a thinner, low-refractive-index layer, it can be formed from AlGaAs along the width of the lateral waveguide located in the region of the HOMSL. Attached Figure Description

[0020] The accompanying drawings (in which like reference numerals denote like elements) are incorporated in and form part of this specification and, together with the description, explain the advantages and principles of the currently disclosed technology. In the drawings,

[0021] Figure 1 The lateral effective refractive index profile of an example laser diode is depicted, wherein a higher-order mode suppression layer is configured to be adjacent to a lateral waveguide;

[0022] Figure 2 The lateral refractive index distribution and mode modeling of an example laser diode are depicted, wherein a higher-order mode suppression layer is set adjacent to the lateral waveguide;

[0023] Figure 3 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the example laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide;

[0024] Figure 4 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the example laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide;

[0025] Figure 5 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the example laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide;

[0026] Figure 6 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the example laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide;

[0027] Figure 7A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer disposed adjacent to the lateral waveguide along the longitudinal direction;

[0028] Figure 8 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the lateral waveguide in the longitudinal direction;

[0029] Figure 9 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer disposed along the longitudinal direction adjacent to the lateral waveguide, but only on a portion of its length on the side.

[0030] Figure 10 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the lateral waveguide in the longitudinal direction;

[0031] Figure 11 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer of a partial length disposed on only one side of the lateral waveguide along the longitudinal direction;

[0032] Figure 12 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the wide-area laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the lateral waveguide in the longitudinal direction;

[0033] Figure 13 A plan view depicting an example lateral waveguide for a wide-area laser diode is shown. This example lateral waveguide includes a portion of a high-order mode suppression layer that is disposed adjacent to and only on one side of a horn-shaped laser oscillator waveguide along the longitudinal direction.

[0034] Figure 14 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, the laser diode including a high-order mode suppression layer disposed adjacent to the horn-shaped laser oscillator waveguide in the longitudinal direction;

[0035] Figure 15 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, the laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the horn-shaped laser oscillator waveguide in the longitudinal direction;

[0036] Figure 16A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, which includes a high-order mode suppression layer of a partial length disposed on only one side of the horn-shaped laser oscillator waveguide along the longitudinal direction adjacent to it.

[0037] Figure 17 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, the laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the horn-shaped laser oscillator waveguide in the longitudinal direction;

[0038] Figure 18 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, which includes a high-order mode suppression layer of a partial length disposed on only one side of the horn-shaped laser oscillator waveguide along the longitudinal direction adjacent to it.

[0039] Figure 19 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, the laser diode including a high-order mode suppression layer of a portion length disposed adjacent to the horn-shaped laser oscillator waveguide in the longitudinal direction;

[0040] Figure 20 A plan view depicting an example horn-shaped laser oscillator waveguide (i.e., lateral waveguide) laser diode is shown, which includes a high-order mode suppression layer of a partial length disposed on only one side of the horn-shaped laser oscillator waveguide along the longitudinal direction adjacent to it.

[0041] Figure 21A A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0042] Figure 21B A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0043] Figure 22 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0044] Figure 23 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0045] Figure 24 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0046] Figure 25 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction; and

[0047] Figure 26 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, the laser diode including a high-order mode suppression layer disposed adjacent to a lateral waveguide along the longitudinal direction;

[0048] Figure 27 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown.

[0049] Figure 28 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown.

[0050] Figure 29 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown.

[0051] Figure 30A This is a graph showing the conventional step refractive index distribution of a single-emitter laser diode in the lateral direction under low-power operation without significant thermal lensing effects.

[0052] Figure 30B It is a graph showing the step refractive index distribution with parabolic distribution added;

[0053] Figure 30C This is a graph showing an example of a "negative" step refractive index distribution with added parabolic distribution, modeling the refractive index distribution in regions with negative compensation;

[0054] Figure 31A This is a cross-sectional view of a vertical epitaxial layer structure observed from the high reflection (HR) side of an example laser diode, which includes a buried high-order mode suppression layer disposed on an adjacent side of a lateral waveguide and extending in the longitudinal direction.

[0055] Figure 31B This is a cross-sectional view of a vertical epitaxial structure observed from the partial reflection (PR) side of an example laser diode depicted in Figure 31, which includes a buried high-order mode suppression layer disposed on an adjacent side of a lateral waveguide;

[0056] Figure 31C This is a plan view of an example laser diode, which includes a buried high-order mode suppression layer disposed on an adjacent side of a lateral waveguide and extending in the longitudinal direction.

[0057] Figure 31D This is a cross-sectional perspective view of a vertical epitaxial layer structure observed from the high reflection (HR) side of an example laser diode, which includes a buried high-order mode suppression layer disposed on an adjacent side of a lateral waveguide and extending in the longitudinal direction.

[0058] Figure 32A This is a cross-sectional view of a vertical epitaxial layer structure observed from the high reflection (HR) side of an example laser diode, which includes a buried high-order mode suppression layer disposed within a lateral waveguide and extending in the longitudinal direction.

[0059] Figure 32B This is a cross-sectional view of a vertical epitaxial layer structure observed from the partial reflection (PR) side of an example laser diode depicted in Figure 32, which includes a buried high-order mode suppression layer disposed within a lateral waveguide and extending in the longitudinal direction.

[0060] Figure 32C This is a plan view of an example laser diode, which includes a buried high-order mode suppression layer disposed within a lateral waveguide and extending longitudinally; and

[0061] Figure 32D This is a cross-sectional perspective view of a vertical epitaxial layer structure observed from the high reflectance (HR) of an example laser diode, which includes a buried high-order mode suppression layer disposed within a lateral waveguide and extending in the longitudinal direction.

[0062] Figure 33A This is a cross-sectional view of a vertical epitaxial layer structure observed from the high reflection (HR) side of an example laser diode, which includes a high-order mode suppression layer comprising a waveguide portion of decreasing thickness disposed within a lateral waveguide and extending in the longitudinal direction.

[0063] Figure 33B This is a cross-sectional view of a vertical epitaxial layer structure observed from the partial reflection (PR) side of an example laser diode depicted in Figure 33. The laser diode includes a high-order mode suppression layer comprising a waveguide portion of decreasing thickness disposed within a lateral waveguide and extending in the longitudinal direction.

[0064] Figure 33C This is a plan view of an example laser diode including a high-order mode suppression layer, which includes a waveguide portion of decreasing thickness disposed within a lateral waveguide and extending in the longitudinal direction; and

[0065] Figure 33D This is a cross-sectional perspective view of a vertical epitaxial layer structure observed from the high reflection (HR) side of an example laser diode, which includes a high-order mode suppression layer comprising a waveguide portion of decreasing thickness disposed within a lateral waveguide and extending in the longitudinal direction.

[0066] Figure 34 Example curve 3400 is used to approximate the optimized thickness of the higher-order mode suppression layer to compensate for a specific increment in refractive index caused by thermal lenses; and

[0067] Figure 35 Graph 3500 shows the simulation results of example far-field predictions of supported modes with and without higher-order mode suppression using thermal lens compensation. Detailed Implementation

[0068] The singular forms “a,” “an,” and “the” used in this application and claims include the plural forms unless the context clearly specifies otherwise. Additionally, the term “comprising…” means “including…”. Furthermore, the term “coupled (connected)…” does not exclude the existence of intermediate elements between coupled (connected) items.

[0069] The systems, apparatuses, and methods described herein should not be construed as limiting in any way. Rather, this disclosure relates to all novel and non-obvious features and aspects of the various disclosed embodiments (individually and in various combinations and sub-combinations of each other). The disclosed systems, methods, and apparatuses are not limited to any particular aspect or feature or combination thereof, nor are they required to have any one or more particular advantages or problems to be solved. Any operational theories are provided for ease of interpretation, but the disclosed systems, methods, and apparatuses are not limited to these operational theories.

[0070] Although the operations of some disclosed methods are described in a specific sequential order for ease of presentation, it should be understood that this descriptive method includes rearrangement unless the specific language described below requires a particular order. For example, the sequentially described operations may be rearranged or performed simultaneously in some cases. Furthermore, for simplicity, the accompanying drawings may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatuses. Additionally, the description sometimes uses terms such as “production” and “providation” to describe the disclosed techniques. These terms are high-level abstractions of the actual operations performed. The actual operations corresponding to these terms will vary depending on the specific implementation and will be readily recognized by those skilled in the art.

[0071] In some examples, values, processes, or devices may be referred to as “lowest,” “best,” “smallest,” etc. It should be understood that such descriptions are intended to indicate that a choice can be made among many functional alternatives used, and that such a choice is not necessarily better, smaller, or otherwise preferred than other choices. References are made to examples using directions such as “above,” “below,” “up,” “down,” etc. These terms are used for convenience of description and do not imply any particular spatial direction.

[0072] As discussed above, it is desirable to efficiently scale power and increase brightness in the BAL while minimizing output power loss. This paper describes methods, systems, and apparatuses aimed at achieving higher brightness at higher output power by reducing the slow-axis divergence angle without reducing the emitter width. The goal is to suppress higher-order modes in the slow axis while preserving lower-order laser modes.

[0073] High-order mode suppression layer (HOMSL)

[0074] Overcoming the shortcomings of conventional laser diodes discussed in the background section requires a laser diode configured to suppress higher-order modes in the lateral direction (i.e., orthogonal to the propagation direction) while retaining lower-order modes. This can be achieved by juxtaposing a higher-order mode suppression structure adjacent to the lateral waveguide of the laser diode. The higher-order mode suppression structure can include various materials and can be a refractive index guiding structure, an anti-waveguide structure, and / or a high-loss structure.

[0075] In one example, the High-Order Mode Suppression Layer (HOMSL) can be positioned adjacent to the lateral waveguide at or near the rear and extend longitudinally less than the full length of the waveguide. The HOMSL can include an index-guided structure, an anti-waveguide structure, and / or a high-loss structure. For example, the index-guided structure, anti-waveguide structure, and / or high-loss structure can extend up to 20% of the waveguide length measured from the rear, or in another example, between approximately 5% and 50%. Extending the HOMSL only a short distance longitudinally minimizes the loss of the unsuppressed modes of the laser diode and enables the diode to operate more efficiently than if the HOMSL structure were extended to its full length.

[0076] In another example, the HOMSL may be configured to be adjacent to the horn-shaped laser oscillator waveguide and extend the entire longitudinal length of the waveguide or a portion of the longitudinal length of the waveguide as measured from the rear. By assembling the diode in this manner, the benefits of reducing higher-order modes by using the HOMSL to suppress higher-order modes can be combined with the benefits of using the horn-shaped laser oscillator waveguide (FLOW) described in U.S. Patent No. 9,166,369, the disclosure of which is incorporated herein by reference in its entirety.

[0077] In yet another example, the laser diode may include buried, aperiodic high- and low-refractive-index structures with high losses in a high-refractive-index material disposed adjacent to the waveguide in the longitudinal direction. The aperiodic structure suppresses higher-order modes by disproportionately overlapping them, compared to lower-order modes and / or the fundamental mode. The aperiodic structure is chosen to introduce high losses into higher-order modes while minimizing losses in lower-order modes and / or the fundamental mode. The aperiodic structure may be disposed along the entire length of the waveguide in the longitudinal direction or along a shorter length extending from the rear. The aperiodic structure may also be disposed along the longitudinal direction of a wide-area laser (BAL) and / or a horn-shaped laser oscillation waveguide.

[0078] Figure 1 A refractive index distribution 100 is depicted, showing the relative refractive indices of an example lateral waveguide with adjacent HOMSLs. Segment 102 of the refractive index distribution 100 represents the relative refractive index of the lateral waveguide, while segment 104 represents the relative refractive index of adjacent HOMSLs.

[0079] In the example, a HOMSL is an anti-waveguide structure comprising a variety of materials with a refractive index higher than that of the waveguide. HOMSLs can include a variety of doped or undoped materials. HOMSL materials can be judiciously chosen to optimize efficiency and BPP during laser operation. Some examples of anti-waveguide HOMSL materials when the native waveguide comprises aluminum gallium arsenide (AlGaAs) include doped gallium arsenide (GaAs), indium gallium arsenide (InGaAs), etc., or combinations thereof. Other combinations of materials forming the waveguide and anti-waveguide structures will be apparent to those skilled in the art, and the claimed subject matter is not limited thereto.

[0080] Figure 2A refractive index distribution 200 is depicted, illustrating the relative refractive index of an example lateral waveguide, where the HOMSL is set adjacent to the lateral waveguide, and the modal modeling of the first few lateral waveguide modes. Segment 202 of the refractive index distribution 200 represents the relative refractive index of the lateral waveguide, while segment 204 represents the relative refractive index of the HOMSL. In the example, the HOMSL is a refractive index-guided aperiodic structure comprising a high-refractive-index material and a low-refractive-index material, exhibiting high loss in the high-refractive-index material with disproportionately overlapping high-order modes compared to the lower-order / fundamental modes. In the example, the refractive index of the low-refractive-index material is lower than the effective refractive index of the lateral waveguide, while the refractive index of the high-refractive-index material is higher than the effective refractive index of the lateral waveguide. Segment 204 illustrates the relative refractive indices of the aperiodic structure with both high- and low-refractive-index materials. The average refractive index of the HOMSL may be lower than the modal refractive index. Therefore, the HOMSL is a refractive index-guided structure rather than an anti-guided structure. However, the locally high refractive index regions pull the electric field or intensity and interact locally with the material, introducing high losses to higher-order modes. Modal modeling 206 shows the modal behavior of modes 0-4. The higher the mode number, the more the mode overlaps with the high refractive index regions of the HOMSL, and therefore the higher the loss of the higher-order modes is compared to the lower-order modes (210-216) / fundamental mode (208).

[0081] For simplicity and illustrative purposes, Figures 3 to 26 The examples depicted illustrate quantum well lasers. However, various other laser types can be configured to include HOMSL features, such as dual heterostructure lasers, interband cascade lasers, distributed Bragg reflector lasers, distributed feedback lasers, quantum cascade lasers, vertical cavity surface-emitting lasers, and / or vertical external cavity surface-emitting lasers, to name just a few. Therefore, the claimed subject matter is not limited to quantum well laser diodes.

[0082] Figure 3 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a high-order mode suppression layer disposed adjacent to a lateral waveguide. In the example, laser diode 300 is a quantum well laser.

[0083] In this example, the laser diode 300 is fabricated to include a substrate 304, an n-type semiconductor layer 306, and a p-type semiconductor layer 308. A quantum well 302 is located between the n-type semiconductor layer 306 and the p-type semiconductor layer 308. An n-cladding layer 310 is disposed outside the n-type semiconductor layer 306. A p-cladding layer 312 is disposed outside the p-type semiconductor layer 308. An n-metal contact 314 is disposed on the n-substrate 304. A p-metal contact 316 is located below the p-cladding layer 312. The quantum well 302, the n-type semiconductor layer 306, and the p-type semiconductor layer 308 constitute the lateral waveguide 318 portion of the laser diode 300. The boundary of the lateral waveguide 340 is shown by a dashed line extending longitudinally along the n-metal contact 314.

[0084] The lateral beam size of a diode laser is determined by the width of the active region or the width of the lateral waveguide. Because the width of the waveguide in the lateral direction is significantly larger than the wavelength of light, many modes will be generated in the lateral direction. The HOMSL 320 is arranged adjacent to the lateral waveguide 340 along the longitudinal direction. Furthermore, in Figure 3 In this configuration, the HOMSL 320 is located between the air and the p-cladding 312 outside the transverse waveguide 318. However, the HOMSL 320 does not necessarily have to be positioned there. The HOMSL 320 can be located in multiple locations within the epitaxial structure, and the subject matter for which protection is claimed is not limited in this respect.

[0085] In the example, HOMSL 320 comprises a high-refractive-index material, wherein the refractive index of HOMSL 320 is higher than that of the lateral waveguide 340. HOMSL 320 is configured to introduce varying degrees of additional loss to higher-order modes, thereby suppressing higher-order modes in the lateral (i.e., orthogonal to propagation) direction. Compared to the lower-order / fundamental modes, the inclusion of this buried or surface high-refractive-index material disproportionately anti-guides higher-order modes that overlap with the high-refractive-index material.

[0086] The laser diode 300 can be fabricated using a variety of well-known materials and methods. For example, the substrate 304 may include gallium arsenide (GaAs). An n-type semiconductor layer 306, a p-type semiconductor layer 308, an n-coating layer 310, and / or a p-coating layer 312 may be grown on the GaAs substrate 304 and may include any of the following: indium (In), gallium (Ga), aluminum (Al), arsenic (As), phosphorus (P), gallium arsenide (GaAs), indium phosphide (InP), etc., or any combination thereof. The n-type and p-type layers may be doped with dopants to produce the desired n-type or p-type material. The claimed subject matter is not limited in this respect.

[0087] HOMSL 320 material can be an absorbing material, allowing it to absorb higher-order modes to optimize the efficiency-to-beam-parameter product (BPP) in operating conditions. HOMSL 320 material can be either absorbing or non-absorbing.

[0088] Figure 4 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a high-order mode suppression layer disposed adjacent to a lateral waveguide. In the example, laser diode 400 is similar to... Figure 3 The laser diode 400 depicts a quantum well laser. However, the laser diode 400 includes a HOMSL 402 with an absorber material. The absorber material selected for the HOMSL 402 can include those semiconductor materials, metals (e.g., titanium (Ti) or nickel (Ni)) or half-metals (e.g., tin (Sn) or As) mentioned above. The HOMSL material 402 can be doped or undoped. The HOMSL 402 can be epitaxially grown or deposited on the surface of the substrate 304 instead of being buried. Figure 5 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a high-order mode suppression layer disposed adjacent to a lateral waveguide. In the example, laser diode 500 is similar to... Figure 3 The laser diode 500 depicts a quantum well laser. However, the laser diode 500 includes a HOMSL aperiodic structure 502 comprising a high-refractive-index material and a low-refractive-index material. The low-refractive-index material 506 has a lower refractive index than the high-refractive-index material 504 and the lateral waveguide 340. The high-refractive-index material 504 and the low-refractive-index material 506 may comprise the same material doped in different ways to achieve different refractive indices, or they may comprise different materials together. For example, the high-refractive-index material 504 may comprise a deposited dielectric or semiconductor, while the low-refractive-index material may comprise air, a dielectric, or a semiconductor material.

[0089] In the example, low-refractive-index and high-refractive-index materials alternately extend outward from the side of the lateral waveguide 340. Low-refractive-index material 506 is positioned adjacent to the lateral waveguide 340. Low-refractive-index material 506 is closer to the lateral waveguide 340 than high-refractive-index material 340. High-refractive-index material 504 is positioned outside of low-refractive-index material 506. The pattern of high / low refractive-index materials can be repeated aperiodically multiple times in the HOMSL structure 502. As described above, the aperiodic structure of the HOMSL 502 can have an average refractive index lower than the modal effective refractive index in the lateral waveguide or higher than the modal refractive index of the lateral waveguide. The materials selected for the aperiodic structure of the HOMSL 502 are chosen to introduce high losses to higher-order modes but minimize losses to lower-order / fundamental modes.

[0090] Figure 6 A cross-sectional view depicting a vertical epitaxial layer structure of an example laser diode is shown, which includes a high-order mode suppression layer disposed adjacent to a lateral waveguide. In the example, the laser diode 600 is similar to... Figure 5 The laser diode 600 is a quantum well laser. However, the laser diode 600 includes a HOMSL 502 disposed only on one side of the lateral waveguide 340. In the example, the HOMSL 502 is configured to suppress higher-order modes when it is asymmetrically distributed with respect to the waveguide 340 (as in this configuration) and / or when the HOMSL structure is symmetrically disposed with respect to the waveguide 340.

[0091] Figure 7 A plan view depicting an example lateral waveguide of a wide-area laser diode is shown, the laser diode including a high-order mode suppression layer disposed adjacent to the lateral waveguide along the longitudinal direction. In the example, the wide-area laser diode 700 includes a HOMSL 702 symmetrically disposed about the lateral waveguide 340. The HOMSL 702 is a non-periodic high-order mode suppression layer structure comprising regions formed of a low-refractive-index material 706 alternating with regions formed of a high-refractive-index material 704. The low-refractive-index material 706 has a lower refractive index than the effective refractive index of the material constituting the lateral waveguide 340. The HOMSL 702 extends the entire length of the lateral waveguide 340 from the rear 730 to the front 732.

[0092] Figure 8 A plan view of an example lateral waveguide depicting a wide-area laser diode including a high-order mode suppression layer disposed adjacent to the lateral waveguide along the longitudinal direction is shown. In the example, the wide-area laser 800 includes a shortened HOMSL 802 symmetrically disposed about the lateral waveguide 340. The HOMSL 802 includes an aperiodic high-order mode suppression layer having alternating low-refractive-index material 806 with a high-refractive-index material 804, similar to... Figure 5 As depicted in [the document]. However, the HOMSL 802 does not extend the entire length of the lateral waveguide 340 from the rear 730 to the front 732. Instead, the HOMSL 802 extends only a portion of the length of the lateral waveguide 340, specifically from the rear 730. The rear 730 is coated with a high-reflectivity (HR) coating, and the front 732 is coated with a partial-reflectivity (PR) coating. Extending the HOMSL 802 only a shorter length from the rear 730 has the advantage of minimizing the loss of the unsuppressed mode, allowing the laser diode to operate more efficiently without significantly increasing the loss of the lower-order / fundamental modes, since the total intensity of the forward and backward propagation fields along the longitudinal direction is smaller towards the rear than towards the front. Therefore, the loss is correspondingly smaller.

[0093] Figure 9A cross-sectional plan view of an example waveguide depicting a wide-area laser diode including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the wide-area laser 900 includes a shortened HOMSL 902 disposed asymmetrically about the lateral waveguide 340 along the longitudinal direction. The HOMSL 902 includes an aperiodic high-order mode suppression layer structure having alternating low-refractive-index material 906 with high-refractive-index material 904, similar to... Figure 8 As depicted in the diagram, a single HOMSL 902 feature extends only a portion of the length of the lateral waveguide 340 extending from the rear 730. The rear 730 is coated with an HR coating and the front 732 is coated with a PR coating. Again, extending the HOMSL 902 only a short length from the rear 730 has the advantage of minimizing the loss of the unsuppressed mode, allowing the laser diode to operate more efficiently without significantly increasing the loss of the lower-order / fundamental mode.

[0094] Figure 10 A cross-sectional plan view of an example waveguide depicting a wide-area laser diode including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the wide-area laser 1000 includes a shortened HOMSL 1002 disposed symmetrically with respect to a lateral waveguide 340. The HOMSL 1002 includes a high-refractive-index material configured to have a refractive index greater than that of the lateral waveguide 340. The high-refractive-index material of the HOMSL 1002 is capable of suppressing high-order modes generated in the lateral waveguide 340 that spatially overlap with the high-refractive-index material of the HOMSL 1002 by anti-guiding, while having little effect on low-order / fundamental modes generated therein, since there is little overlap between the low-order / fundamental modes and the high-index material.

[0095] Figure 11 A cross-sectional plan view of an example waveguide depicting a wide-area laser diode including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the wide-area laser 1100 includes a shortened HOMSL 1102 asymmetrically disposed with respect to the lateral waveguide 340. The HOMSL 1102 includes a structure similar to... Figure 10 The high refractive index material is shown. HOMSL 1102 provides anti-guiding for higher-order modes generated in the lateral waveguide 340. To anti-guidance at least some of the higher-order modes, HOMSL 1102 does not need to be symmetrically distributed with respect to the lateral waveguide 340. Furthermore, a single HOMSL 1102 feature extends only a portion of the length of the lateral waveguide 340 extending from the rear 730. The rear 730 is coated with an HR coating, and the front 732 is coated with a PR coating. Similarly, extending the HOMSL 1102 only a shorter length from the rear 1130 has the advantage of suppressing higher-order modes while minimizing the loss of unsuppressed modes, allowing the laser diode to operate more efficiently without significantly increasing the loss of lower-order modes and / or the fundamental mode.

[0096] Figure 12 A cross-sectional plan view of an example waveguide depicting a wide-area laser including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the wide-area laser 1200 includes a shortened HOMSL 1202 disposed symmetrically about a lateral waveguide 340. The HOMSL 1202 includes an absorbing material, which may be a semiconductor material having various compositions, doping, crystallinity, and / or morphologies; a half-metal; or a metal. The role of the absorbing material is to suppress high-order modes in the lateral direction of the lateral waveguide 340 by disproportionately increasing the round-trip loss of high-order modes. The HOMSL 1202 does not extend the entire length of the lateral waveguide 340 from the rear 730. The HOMSL 1202 extends only a portion of the length of the lateral waveguide 340, specifically from the rear 730. Extending the HOMSL 1202 only a shorter length from the rear 730 has the advantage of minimizing the loss of unsuppressed modes, allowing the laser diode to operate more efficiently without significantly increasing the loss of low-order modes / base modes.

[0097] Figure 13 A cross-sectional plan view depicting an example horn-shaped laser oscillator waveguide including a high-order mode suppression layer disposed adjacent to the waveguide is shown. As an example, the wide-area laser 1300 includes a shortened HOMSL 1302 asymmetrically disposed with respect to the lateral waveguide 340. The HOMSL 1302 includes a structure similar to... Figure 12 The absorbing material shown is the HOMSL 1302. The HOMSL 1302 disproportionately absorbs higher-order modes in the lateral waveguide 340, thereby suppressing higher-order modes that spatially overlap with the HOMSL 1302. Therefore, the HOMSL 1302 suppresses higher-order modes, thus minimizing the impact on lower-order and fundamental modes. Furthermore, a single HOMSL 1302 feature extends only a portion of the length of the lateral waveguide 340 extending from the rear 730. The rear 1330 is coated with an HR coating, and the front 732 is coated with a PR coating. Extending the HOMSL 1302 only a short length from the rear 730 has the advantage of suppressing higher-order modes while minimizing the loss of unsuppressed modes, allowing the laser diode to operate more efficiently without significantly increasing the loss of lower-order / fundamental modes.

[0098] Figure 14A plan view depicting an example horn-shaped laser oscillator waveguide including a high-order mode suppression layer disposed adjacent to the waveguide is shown. As an example, laser 1400 includes a horn-shaped laser oscillator waveguide (FLOW) 1418, which can be used instead of a rectangular wide-area laser waveguide. FLOW 1440 includes a horn-shaped current injection region extending and widening longitudinally between a rear surface 730 including a high reflector (HR) coating and a front surface 732 including a partial reflector (PR) coating. By narrowing the width of the electric pump stripes toward the high reflector surface, high-order modes with higher divergence angles are prevented from coupling back to the laser. As a result, the slow-axis divergence of the laser is smaller compared to devices with a rectangular geometry having a partial reflector of the same width. Furthermore, light propagating in the horn-shaped current injection region closer to the PR front surface 732 can form a thermal waveguide with a width closer to the narrower HR rear surface 730 side, resulting in a beam output at the front surface 732 with a beam width significantly narrower than the width of the front surface 732. As a result, the beam parameter product (BPP, slow-axis near-field width multiplied by slow-axis divergence) of the FLOW device is smaller compared to the BAL device. Since the near field is smaller than the physical width on the 732 side, the FLOW device can be designed with a larger total area without sacrificing BPP compared to BAL. The extended total pump area provided by the horn-shaped current injection region is used to reduce thermal resistance and series resistance in the device, resulting in higher electro-optic power conversion efficiency. This results in higher output power at a given operating current compared to the BAL device. Higher power and smaller BPP lead to increased beam brightness on the slow axis. Besides its application in wide-area diode lasers, the FLOW concept can also be applied to other types of semiconductor-based Fabry-Perot lasers, such as quantum cascade lasers (QCLs) and interband quantum cascade lasers (IQLs). Wide-area diode lasers with horn-shaped laser oscillator waveguides can also find specific uses in laser diode modules, which can be configured for various applications such as fiber coupling or direct pumping.

[0099] In the example, HOMSL 1402 may include a first layer of a low-refractive-index material 1406 with a non-periodic structure, wherein the refractive index of the low-refractive-index material 1406 is less than the effective refractive index of the material constituting FLOW 1440. HOMSL 1402 also includes a second layer of a high-refractive-index material 1404, wherein the refractive index of the high-refractive-index material 1404 is greater than or less than the effective refractive index of the material constituting FLOW 1440. Therefore, as referenced above... Figure 5 As mentioned, HOMSL 1402 may be in a refractive index-guided or anti-guided state. (Still referencing...) Figure 14The coupling of HOMSL 1402 and FLOW 1440 combines any higher-order mode suppression effect, which can be achieved by using HOMSL 1402 or FLOW 1440 alone to further reduce BPP.

[0100] Figure 15 A cross-sectional plan view depicting an example horn-shaped laser oscillator waveguide including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the laser diode 1500 includes a FLOW 1440 and a shortened HOMSL 1502 disposed symmetrically about the FLOW 1440. The HOMSL 1502 includes an aperiodic structure comprising, for example... Figure 14 The assembly described above uses low-refractive-index material 1506 and high-refractive-index material 1504. In this example, HOMSL 1502 extends only a portion of the length of FLOW 1440 from the rear 730. HOMSL 1502 is not positioned near the front 732. This architecture combines high-order mode suppression achieved by a HOMSL structure in conjunction with a FLOW structure. Because the extension of HOMSL 1502 is less than the full length of FLOW 1440, the loss of unsuppressed modes is minimized, allowing the laser diode to operate more efficiently without significantly increasing the loss of low-order / fundamental modes, as described above. Figure 8 Explanation.

[0101] Figure 16 A cross-sectional plan view depicting an example of a horn-shaped laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the laser diode 1600 may include HOMSL 1602 asymmetrically distributed with respect to FLOW 1440. HOMSL 1602 may extend only a portion of the length of FLOW 1440 from the rear 730. In the example, a single shortened HOMSL 1602 combined with FLOW 1440 can operate to efficiently suppress higher-order modes. This architecture may be desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of the laser diode 1600.

[0102] Figure 17A plan view of an example waveguide depicting a laser diode including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the laser diode 1700 includes a FLOW 1440 and a HOMSL 1702 symmetrically disposed about the FLOW 1440. The HOMSL 1702 is shortened, extending only a portion of the length of the FLOW 1440 from the rear 730. The HOMSL 1702 comprises a high-refractive-index material compared to the material used in the FLOW 1440. By narrowing the width of the electric pump stripe of the FLOW 1440 towards the high-reflectivity surface, high-order modes with higher divergence angles are prevented from coupling back to the laser. The shortened HOMSL 1702 further suppresses high-order modes by disproportionately anti-guiding high-order modes overlapping with the high-refractive-index material towards the HR plane.

[0103] Figure 18 A plan view depicting an example waveguide of a laser including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, laser 1800 may include a shortened HOMSL 1802 asymmetrically distributed with respect to FLOW 1440. HOMSL 1802 may include a structure similar to Figure 17 The high refractive index material described herein. HOMSL 1802 can be extended only a portion of the length from the rear 730 of FLOW 1440. A single shortened HOMSL 1802 combined with FLOW 1440 can be operated to efficiently suppress higher-order modes. For example, this architecture may be desirable to save material costs or to accommodate other structures in the epitaxial layer structure of laser 1800.

[0104] Figure 19 A plan view depicting an example horn-shaped laser oscillator waveguide including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, the laser diode 1900 includes a FLOW 1440. A HOMSL 1902 is arranged symmetrically about the FLOW 1440. The HOMSL 1902 is shortened, extending only a portion of the length of the FLOW 1440 from the rear 730. The HOMSL 1902 includes an absorbing material. (See reference...) Figure 4 The absorbing material discussed here preferably introduces higher losses to higher-order modes, thereby suppressing higher-order modes that spatially overlap with HOMSL 1902.

[0105] Figure 20 A cross-sectional plan view depicting an example horn-shaped laser oscillator waveguide including a high-order mode suppression layer disposed adjacent to the waveguide is shown. In the example, laser 2000 may include a shortened HOMSL 2002 asymmetrically distributed about FLOW 1440. HOMSL 2002 may include similar... Figure 19The aforementioned absorbing material, HOMSL 2002, can extend only 730 mm from the rear of FLOW 1440. A single, shortened HOMSL 2002 in combination with FLOW 1440 can more efficiently suppress higher-order modes compared to either HOMSL 2002 alone or FLOW 1440 alone. This architecture may be desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of laser 2000.

[0106] Gain Customization Method

[0107] In the example, higher-order modes in the side waveguide can be reduced by decreasing the amount of current reaching the active layer (where higher-order modes diffuse) in the side waveguide. This can be achieved through gain customization. Typically, gain customization involves injecting current from the p-side of the heterostructure. However, gain customization from the p-side is fraught with inefficiencies. On the other hand, gain customization from the n-side produces a diffused carrier distribution that more closely overlaps with the fundamental mode, followed by the lower-order mode distribution, thus providing higher gain for the desired modes and lower gain for the undesired higher-order modes.

[0108] Figure 27 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown. In this example, gain customization is performed via current injection through an n-metal contact 2714, which is patterned to be narrower than the p-metal contact 316. The n-metal contact 2714 is positioned longitudinally at the center of a lateral waveguide 2740 and within a cavity 2740, thereby enabling a lateral carrier distribution pattern 2702.

[0109] Figure 28 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown. The laser diode 2800 includes an n-side 2820 and a p-side 2822. The n-side 2820 includes an n-metal contact 2814, an n-cladding layer 310, an n-type semiconductor layer 306, and an n-substrate 304. The p-side 2822 includes a p-cladding layer 312, a p-type semiconductor layer 308, and a p-metal contact 316. A lateral waveguide 318 includes a quantum well 302, an n-type semiconductor layer 306, and a p-type semiconductor layer 308. A longitudinal waveguide 2840 can be defined in various ways (e.g., by gain guidance, a ridge waveguide, or refractive index guidance, or combinations thereof), as shown by the dashed lines on top of the substrate 304 and the n-metal contact 2814. The p-metal contact 316 is located below the p-cladding layer 312. n-metal contact 2814 extends along cavity 2810 of longitudinal waveguide 2840.

[0110] Gain customization from the n-side can be achieved by introducing a lateral carrier distribution pattern 2802 through a narrow strip of n-metallic contact 2814 on the n-side 2820 of the laser diode 2800, instead of conventionally metallizing the entire n-side. The thin n-metallic contact 2814 can be positioned at multiple locations opposite the p-metallic contact 316. In one example, the n-metallic contact 2814 is offset such that its edge is located at the emitter half-plane 2804. Gain customization is performed from the n-metallic side 2820, reducing the amount of gain for higher-order modes propagating in the waveguide 2840.

[0111] In the example, the n-metallic contact 2814 can have a variable width along the cavity to modulate carrier distribution in both lateral and longitudinal directions. This is in Figure 28 As shown, the first width L1 of the n-metal contact 2814 is smaller than the second width L2. This provides gain customization in the longitudinal direction, reducing the gain of higher-order modes toward the HR (high reflectivity) surface, allowing the laser diode 2800 to operate more efficiently without significantly increasing the loss of lower-order / fundamental modes.

[0112] Figure 29 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a customized n-side current injection scheme is shown. In this example, gain customization is performed via current injection through a horn-shaped n-metal contact 2914, which is patterned to be narrower than the p-metal contact 316. The n-metal contact 2914 is narrower on the HR side and wider on the PR side (but laterally centered). The n-metal contact 2914 is positioned longitudinally at the center of the lateral waveguide 2940 and within the cavity 2910, thereby enabling a lateral carrier distribution pattern 2902.

[0113] Hybrid Gain Customization / HOMSL Method

[0114] Further reduction of higher-order modes in the lateral waveguide can be achieved using a hybrid approach by: 1) tailoring the gain or differential gain of higher-order modes by using a custom current injection scheme to reduce the diffusion of higher-order modes in the waveguide, thereby depriving them of gain and suppressing higher-order modes; 2) including a HOMSL structure adjacent to the lateral waveguide in the longitudinal direction to further suppress higher-order modes, although the gain is customized.

[0115] Figure 21AA cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, comprising a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a lateral waveguide. The laser diode 2100 includes an n-side 2120 and a p-side 2122. The n-side 2120 includes an n-metal contact 2114, an n-cladding layer 310, an n-type semiconductor layer 306, and an n-substrate 304. The p-side 2122 includes a p-cladding layer 312, a p-type semiconductor layer 308, a p-metal contact 316, and a HOMSL 320. The waveguide 318 includes a quantum well 302, an n-type semiconductor layer 306, and a p-type semiconductor layer 308. A longitudinal waveguide 2140 is defined in various ways (e.g., by gain guidance, a ridge waveguide, or refractive index guidance, or combinations thereof). The longitudinal waveguide 2140 includes a cavity 2110, indicated by a dashed line on top of the substrate 304 and the n-metal contact 2114. p-metal contact 316 is located below p-cladding 312. n-metal contact 2114 extends along cavity 2110 of longitudinal waveguide 2140.

[0116] As discussed above, a lateral carrier distribution pattern 2102 can be introduced by setting an n-metal contact 2114 on the n-side of the laser diode, thereby enabling gain customization from the n-side. Figure 21A In this configuration, the n-metal contact 2114 is offset such that its edge is located at the emitter half-plane 2104. Carrier injection is performed from the n-metal side. Additionally, a HOMSL 320, comprising a high-refractive-index material, is symmetrically arranged about the lateral waveguide 2110 along the longitudinal direction. This hybrid approach reduces higher-order modes propagating in waveguide 2140 by decreasing the gain on higher-order modes and suppressing them via the HOMSL 320.

[0117] In another example, a HOMSL structure asymmetrically configured with respect to waveguide 2140 can be used instead of a symmetrically configured HOMSL structure. In one example, such as... Figure 9 , Figure 11 , Figure 16 , Figure 18 and Figure 20 The asymmetric HOMSL structure shown should be similar to... Figure 21B The n-metal contacts 2114 shown are arranged in series as a heterogeneous structure. This configuration is more efficient than having a HOMSL structure on opposite sides because the higher-order mode gain is insufficient and will fall below the threshold carrier density.

[0118] Furthermore, other HOMSL structures can be used to implement the hybrid gain custom / HOMSL higher-order mode suppression method described in this paper. For example, instead of using the high-refractive-index material HOMSL 320, the structures described above can be used. Figure 4 HOMSL 402 and Figure 5The absorbing and / or aperiodic materials described in HOMSL 502. Furthermore, the hybrid gain customization / HOMSL approach using p-side gain customization will provide improved higher-order mode suppression compared to conventional p-side gain customization or simply using a HOMSL structure. Figure 22 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, comprising a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a waveguide. In the example, the n-metal contact 2214 is patterned to be narrower than the p-metal contact 316. The n-metal contact 2214 is centered on half-plane 2204 of waveguide 2240. This produces a diffused carrier distribution in the lateral direction along the path indicated by 2202, thus creating a carrier density distribution that more closely overlaps with the fundamental mode, followed by the low-order mode distribution, compared to the suppressed high-order modes. This current injection distribution is configured to optimize the overlap with the lateral low-order modes and the fundamental mode by providing higher gain to the desired modes and lower gain to the undesired high-order modes. Additionally, the width of the n-metal contact 2214 can be varied along cavity 2210 to adjust the amount of carriers injected along the longitudinal direction of cavity 2210.

[0119] Figure 23 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, comprising a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a waveguide. In this example, gain customization is performed via current injection through an n-metal contact 2314 offset with respect to a p-metal contact 316. HOMSL 402 (see HOMSL 402) Figure 4 The HOMSL 402 is symmetrically positioned about the lateral waveguide 2340 along the longitudinal direction and includes an absorbing material. In the example, the HOMSL 402 can be an n- or p-doped GaAs or an ordered or disordered InGaAs with a band gap lower than the laser wavelength.

[0120] Figure 24 A cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode is shown, comprising a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a waveguide. In this example, gain customization is performed via current injection through an n-metal contact 2414, which is patterned to be narrower than a p-metal contact 316. The n-metal contact 2414 is positioned at the center of the lateral waveguide 2440 and the cavity 2410. HOMSL 402 (see HOMSL 402) Figure 4 It is symmetrically positioned about the lateral waveguide 2440 and includes absorbing material.

[0121] Figure 25A cross-sectional view depicting the vertical epitaxial layer structure of an example laser diode is shown, which includes a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to the waveguide. In the example, gain customization is performed via an n-metal contact 2514 offset relative to the p-metal contact 316. A HOMSL 502 (see [reference]) includes an aperiodic high-refractive-index layer 504 and a low-refractive-index layer 506. Figure 5 The lateral waveguide 2540 is symmetrically positioned.

[0122] Figure 26 A cross-sectional view depicting a vertical epitaxial layer structure of an example laser diode is shown, comprising a customized n-side current injection scheme and a high-order mode suppression layer disposed adjacent to a waveguide. In the example, gain customization is performed via current injection through an n-metal contact 2614 patterned to be narrower than the p-metal contact 316. The n-metal contact 2614 is disposed at the center of the waveguide 2640 and the cavity 2610. HOMSL 502 (see HOMSL 502) Figure 5 It is symmetrically positioned about the longitudinal waveguide 2640 and includes absorbing material.

[0123] HOMSL features for thermal lensing compensation

[0124] Refractive index guidance and gain guidance are the primary confinement mechanisms by which lateral optical modes (i.e., those spanning the slow axis) are confined within the cavity of a wide-area laser. Vertical mode confinement (i.e., those spanning the fast axis) is typically achieved through refractive index guidance using n-type and p-type claddings with predetermined refractive indices. Generally, lateral optical modes supported by a semiconductor laser cavity with zero lateral refractive index change in the unpowered, cold state become gain-guided during the powered state because the injected current induces a lateral refractive index change between the electrically pumped and unpumped regions.

[0125] Under high-power operation, the lateral thermal gradient induces a positive lateral refractive index difference between the lateral waveguide and the cladding associated with the thermal lens. The magnitude of the positive lateral refractive index contrast caused by the thermal lens can depend on various characteristics and parameters of the cavity, including length, semiconductor layer thickness, carrier density, active layer type and thickness, emitter / reflector width, gain, operating wavelength, the amount of waste heat generated by the diode laser, and heat transfer between the diode junction and the heat sink, which should be readily understood by those skilled in the art.

[0126] The slow-axis divergence angle of an output beam emitted by a semiconductor device can be strongly influenced by the lateral waveguides near the highly reflective surface. Refractive index guidance in the lateral waveguides near the highly reflective surface (caused by thermal lensing) can support unwanted higher-order lateral modes, resulting in slow-axis divergence and reduced beam quality.

[0127] Examples in this paper describe methods, systems, and apparatus for suppressing the onset of higher-order lateral modes caused by high refractive index contrast due to thermal lensing during device operation. The increased waveguide refractive index contrast from thermal lensing is offset or compensated by forming a refractive index compensation region on the HR side of the Fabry-Perot cavity. This reduces the magnitude of the refractive index contrast caused by thermal lensing.

[0128] Figure 30A Figure 3002 shows the conventional step refractive index distribution of a single-emitter laser diode in the lateral direction under low-power operation without significant thermal lensing effects. Figure 30B Figure 3004 shows the step refractive index distribution in the lateral direction of a single-emitter laser diode with an added parabolic distribution. This is a model of the refractive index distribution of a conventional waveguide with thermal lensing effect under higher power operation. This illustrates how the distribution evolves under thermal lensing effect at high operating currents. Figure 30C Figure 3006 shows the potential refractive index distribution in the lateral direction of a single-emitter laser diode that compensates for the thermal lensing effect under high-power operation. A "negative" step exponential distribution with a parabolic distribution is added to model the refractive index distribution in the region with negative compensation. The thermal lensing refractive index distribution produces a weak refractive index guiding region under operating conditions.

[0129] As will be described in more detail below, methods for achieving this distribution include introducing lateral features with a high refractive index that are adjacent to and / or overlap with the lateral waveguide, reducing the lateral waveguide thickness in the active stripe, and / or inserting a thin layer with a low refractive index within the lateral waveguide.

[0130] Figures 31A to 31D Various views of the laser diode 3100 are shown.

[0131] Figure 31A This is a cross-sectional view of the vertical epitaxial layer structure of an example laser diode 3100, which includes a buried high-mode suppression layer (HOMSL) 3104 disposed on an adjacent side of a lateral waveguide 3106. The laser diode 3100 can include various geometries and configurations, and includes various arrangements of p-type, n-type, active layers, caps, and dielectric layers. The term "buried" as used herein is intended to refer to the high-mode suppression layer and / or feature disposed between layers within the epitaxial layer structure of the laser diode 3100 (or other laser diodes described herein). However, in some examples, the high-mode suppression layer or feature may not be buried and may operate in the same or similar manner as a buried high-mode suppression layer or feature.

[0132] In the example, the laser diode 3100 is represented by a simplified epitaxial structure and includes an n-type cladding layer 3108 and a p-type cladding layer 3110, with a lateral waveguide or cavity 3112 formed between them. The lateral waveguide 3112 is orthogonal to the lateral waveguide 3106 and includes an n-type waveguide layer 3114, a p-type waveguide layer 3116, and an active layer 3118. The active layer 3118 typically includes one or more quantum wells, but other configurations are possible, including pn junction homogeneous structures, heterogeneous structures, double heterogeneous structures, quantum wires, quantum dots, etc. The p-type cladding layer 3110 can be etched into various shapes to form a ridge structure 3120 or a mesa, either extending the entire longitudinal length of the diode 3100 or extending only a portion of the length of the diode 3100 from the partial reflector (PR) side 3122. Additionally, one or more dielectric layers and / or capping layers (not shown) can be formed on the laser diode 3100 to guide current through the active layer 3118.

[0133] Figure 31B From Figure 30A A cross-sectional view of the vertical epitaxial layer structure observed on the partially reflective (PR) side 3122 of the example laser diode 3100 depicted in the figure.

[0134] The lateral waveguide 3106 is defined longitudinally at a first end by an HR-coated surface 3124 and at a second end by a PR-coated surface 3126. In the example, a HOMSL 3104 is formed beneath the p-type cladding 3110 and is located on one or both sides of the lateral waveguide. The length of the HOMSL 3104 extending longitudinally from the HR-coated surface 3124 is less than the distance between the HR and PR surfaces. The buried HOMSL 3104 does not extend to the PR side 3122, and therefore is not visible in the epitaxial layer when viewed from the PR side 3122.

[0135] Figure 31C This is a planar top side view of an example laser diode 3100, which includes a buried HOMSL 3104 feature disposed on an adjacent side of a lateral waveguide 3106 and extending longitudinally from the HR plane 3124.

[0136] During high-power operation of the laser diode 3100, the temperature distribution resulting from lateral thermal diffusion causes a thermal lensing effect in the lateral waveguide 3106, which induces refractive index contrast in the lateral waveguide 3106. In the example, partial or complete compensation for the increased refractive index contrast in the lateral waveguide 3106 can be achieved by strategically placing a HOMSL 3104 feature adjacent to the lateral waveguide 3106 on one or both of the lateral sides. The HOMSL 3104 is formed between the p-type waveguide layer 3116 and the p-type cladding layer 3110. Alternatively, the HOMSL 3104 can be formed between the n-type waveguide layer 3114 and the n-type cladding layer 3108. The HOMSL 3104 can be further formed to slightly overlap with the lateral waveguide 3106 to compensate for mode size mismatch between the two regions or for other reasons.

[0137] Adding a HOMSL 3104 structure (e.g., including GaAs) to a BAL can be performed using a variety of methods known to those skilled in the art, and the claimed subject matter is not limited in this respect. For example, modified masking and etching can be used to form the HOMSL 3104 at a selected bias offset from the ridge waveguide 3120. The high refractive index characteristics of the HOMSL 3104 placed on the edge of the ridge waveguide 3120 may disproportionately overlap higher-order modes, but the mode size mismatch of modes of the same order between the HR side and the PR side means that a lateral bias between the oxide ridge 3120 and the HOMSL 3104 can be selected to avoid excessive loss due to external coupling of the supported laser modes.

[0138] Various simulations show that the trend in modulus size is predictable for different orders of refractive index contrast, regardless of the modulus order. The order of refractive index contrast is in the 10^6 ... -5 <Δn<10 -3 Within the range. The predicted mismatch of the lateral waveguide 3106 size (or the overlap of HOMSL 3104 on the lateral waveguide) can be in the range of 2-6 μm on either side or in the range of 4-12 μm in total.

[0139] In another example, the HOMSL 3104 is formed to laterally overlap with the lateral waveguide 3106 to compensate for the mismatch in the lateral mode regions between the HOMSL 3104 region and the refractive index guiding region, which is between 0 and 10 μm on either side or between 0 and 20 μm in total.

[0140] Figure 31D This is a cross-sectional perspective view of a vertical epitaxial layer structure observed from the HR side 3102 of an example laser diode 3100, which includes a buried HOMSL 3104 disposed on an adjacent side of a lateral waveguide 3106 and extending longitudinally from the HR coating surface 3124.

[0141] In the example, the HR side 3102 extends from the HR coating surface 3124 to approximately the midpoint 3130 (dashed line). The PR side 3122 extends from the PR coating surface 3126 to approximately the midpoint 3130.

[0142] In operation, the HR side 3102 experiences a thermal lensing effect; however, with the suppression or compensation of the HOMSL 3104, this region is guided by a weak refractive index; thus, it has approximately the same refractive index as... Figure 30C The refractive index distribution is shown. Similarly, the PR side 3122 includes a refractive index guiding region that also experiences a thermal lensing effect during operation, without the suppression or compensation of the HOMSL3104, and thus approximately corresponds to... Figure 30B The refractive index distribution shown is illustrated.

[0143] To reduce the magnitude of the refractive index contrast caused by the thermal lensing on the HR side 3102 of the laser diode 3100, the HOMSL 3104 may include a material with a higher refractive index than the surrounding material. The relative refractive index (n) of the HOMSL 3104 with respect to the transverse waveguide layer is n HOMSL 3104 >n p型覆层3110 / n n型覆层3108 >n p型波导层3116 / n n型波导层 .

[0144] Furthermore, to reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3102, the refractive index and thickness 3128 of the HOMSL 3104 are wisely chosen. The choice of thickness 3128 should be based on its impact on the magnitude of refractive index contrast (i.e., the potential effective refractive index contrast on the HR side 3102 of the lateral waveguide 3106). Specific thicknesses 3128, threshold thicknesses, or thickness ranges (collectively referred to herein as "thicknesses") of the HOMSL 3104 that will sufficiently reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3102 can be identified through various methods, including simulation, experiments, reference tables, and predictive analysis.

[0145] Thickness 3128 determines the Δn relative to the thermal lens on the HR side 3102 and reduces the guiding capability of the lateral waveguide 3106 in the region near the HOMSL 3104. In various examples, the thickness can be chosen such that most of the thermal lens is compensated to create a weakly refractive index guiding region. This makes weakly refractive index guiding of a few lateral modes possible at high operating currents on the HR side 3102, or, in extreme cases, weakly refractive index guiding of only a single lateral mode. This weakly guiding region can support 10 or fewer lateral modes, or even just one mode. Therefore, compared to a conventional BAL, the lateral waveguide 3106 on the HR side supports fewer lateral modes and enables reduced slow-axis divergence and higher brightness.

[0146] Since the HOMSL is designed primarily to compensate for thermal lenses under high-power operation, an anti-guiding region for low-power operation can be effectively present on the HR side 3102, which transforms into a weakly refractive index guided region for higher-power operation as the thermal lens is activated.

[0147] Figures 32A to 32D Various views of the laser diode 3200 are depicted.

[0148] Figure 32A This is a cross-sectional view of the vertical epitaxial layer structure of an example laser diode 3200, including the buried HOMSL 3204.

[0149] The laser diode 3200 is represented by a simplified epitaxial structure and includes an n-type cladding layer 3208 and a p-type cladding layer 3210, with a lateral waveguide or cavity 3212 formed between them. The lateral waveguide 3212 is orthogonal to the lateral waveguide 3206 and includes an n-type waveguide layer 3214, a p-type waveguide layer 3216, and an active layer 3218. A ridge structure 3220 may extend part or the entire longitudinal length of the diode 3200 between the HR side 3202 and the PR side 3222.

[0150] HOMSL 3204 is disposed within a transverse waveguide 3212 within a p-type waveguide layer 3216. Alternatively, HOMSL 3204 may be disposed within an n-type waveguide layer 3214.

[0151] In this example, HOMSL 3204 may comprise a thin layer of a low-refractive-index material. Although HOMSL 3204 is disposed in the transverse waveguide 3212, it is also present in the lateral waveguide 3206; thus, the effective refractive index of the lateral waveguide 3206 is reduced due to the presence of the lower-refractive-index HOMSL 3204. The refractive index of the lateral cladding 3210 remains unchanged.

[0152] Figure 32BFigure 32 shows a cross-sectional view of the vertical epitaxial layer structure of an example laser diode 3200, depicted on the PR side 3222, which includes a HOMSL 3204 disposed within a lateral waveguide 3206. The lateral waveguide 3206 is defined in the longitudinal direction by an HR coating surface 3224 at a first end and a PR coating surface 3226 at a second end. In this example, the HOMSL 3204 is buried within a p-type waveguide layer 3216 (or an n-type waveguide layer 3214). However, because the length of the HOMSL 3204 extending longitudinally from the HR coating surface 3224 is less than the distance between the HR surface and the PR surface, it is not visible in the epitaxial layer when viewed from the PR side 3222.

[0153] Figure 32C This is a plan view of an example laser diode 3200, which includes a buried HOMSL 3204 disposed within a lateral waveguide and extending in the longitudinal direction.

[0154] During high-power operation of the laser diode 3200, the temperature distribution caused by lateral thermal diffusion induces a thermal lensing effect in the lateral waveguide 3206, which in turn causes refractive index contrast in the lateral waveguide 3206. In this example, partial or complete compensation for the increased refractive index contrast in the lateral waveguide 3206 can be achieved by strategically placing a low-refractive-index HOMSL 3204 within the lateral waveguide 3206. The HOMSL 3204 can be 0-10 μm narrower laterally on either side or 0-20 μm narrower in total than the lateral waveguide 3206.

[0155] Adding a HOMSL 3204 structure (e.g., including AlGaAs) to BAL can be done by various methods known to those skilled in the art, and the claimed subject matter is not limited in this respect.

[0156] Figure 32D This is a cross-sectional perspective view of a vertical epitaxial layer structure observed from the HR side 3202 of an example laser diode 3200, which includes a buried HOMSL 3204 disposed within a lateral waveguide 3206 and extending longitudinally from the HR coating surface 3224. For example, the HR side 3202 extends from the HR coating surface 3224 to approximately the midpoint 3230 (dashed line). The PR side 3222 extends from the PR coating surface 3226 to approximately the midpoint 3230.

[0157] In operation, the HR side 3202 experiences a thermal lensing effect. However, thanks to the suppression or compensation of the HOMSL 3204 by introducing a lower refractive index material into the lateral waveguide 3206 to reduce the refractive index contrast, the HR side 3202 region becomes guided by a weaker refractive index. To reduce the magnitude of the refractive index contrast caused by thermal lensing on the HR side 3202, the HOMSL 3204 can include a low refractive index material lower than the surrounding material. The relative refractive index (n) of the HOMSL 3204 with respect to the lateral waveguide layer is: n 低折射率层 <n p-波导 / n n-波导 <n p-覆层 / n n-覆层 .

[0158] Similar to HOMSL 3104, the thickness 3228 and refractive index of HOMSL 3204 are carefully chosen to reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3202. The choice of thickness 3228 is based on its impact on the magnitude of refractive index contrast (i.e., the potential effective refractive index contrast on the HR side 3202 of the lateral waveguide 3206). Various methods can be used to identify the specific thickness 3228 of HOMSL 3204 that will sufficiently reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3202, including simulation, experiment, reference tables, and predictive analysis.

[0159] Thickness 3228 determines the Δn relative to the thermal lens on the HR side 3202 and reduces the guiding capability of the lateral waveguide 3206 in the region near the HOMSL 3204. In various examples, the thickness can be chosen such that the thermal lens is largely compensated to create a weakly refractive index guiding region. This enables weakly refractive index guiding of a few lateral modes at high operating currents on the HR side 3202, or, in extreme cases, weakly refractive index guiding of only a single lateral mode. This weakly guided region can support 10 or fewer lateral modes, or even just one mode. Therefore, compared to a conventional BAL, the lateral waveguide 3206 at the HR side 3202 supports fewer lateral modes and enables reduced slow-axis divergence and higher brightness.

[0160] In various examples, HOMSL 3104 and HOMSL 3204 can be formed from any of a variety of materials known to those skilled in the art, which satisfy the disclosed limitations on size and relative refractive index sufficient to reduce the refractive index contrast caused by thermal lensing in the lateral waveguide, and the claimed subject matter is not limited in this respect. For example, HOMSL 3104 and / or HOMSL 3204 can be formed from a variety of materials, including gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), and / or indium gallium phosphide (InGaAsP).

[0161] Figures 33A to 33D Various views of the laser diode 3300 are depicted.

[0162] Figure 33A This is a cross-sectional view of the vertical epitaxial layer structure of an example laser diode 3300, which includes a reduced-thickness lateral waveguide portion referred to herein as HOMSL 3304. The laser diode 3300 is represented in a simplified epitaxial structure and includes an n-type cladding layer 3308 and a p-type cladding layer 3310, with a lateral waveguide or cavity 3312 formed between them. The lateral waveguide 3312 is orthogonal to the lateral waveguide 3306 and includes an n-type waveguide layer 3314, a p-type waveguide layer 3316, and an active layer 3318. A ridge structure 3320 may extend a portion or the entire longitudinal length of the diode 3300 between the HR side 3202 and the PR side 3222. HOMSL 3304 may be formed within the lateral waveguide 3312 in the p-type waveguide layer 3316. Alternatively, the reduced-thickness lateral waveguide portion HOMSL 3304 may be formed in the n-type waveguide layer 3314. HOMSL 3304 features can be formed as grooves, fragments, channels, or combinations thereof.

[0163] Although HOMSL 3304 is disposed in the transverse waveguide 3212 in the p-type waveguide layer 3316, it is also in the lateral waveguide 3306; therefore, the effective refractive index of the lateral waveguide 3306 is reduced due to the presence of HOMSL 3304.

[0164] Figure 33BFigure 33 shows a cross-sectional view of the vertical epitaxial layer structure of an example laser diode 3300, depicted on the PR side 3322, which includes a HOMSL 3304 disposed within a lateral waveguide 3306. The lateral waveguide 3306 is defined in the longitudinal direction by an HR coating surface 3324 at a first end and a PR coating surface 3326 at a second end. In this example, the HOMSL 3304 is formed within a p-type waveguide layer 3316 (or an n-type waveguide layer 3314). However, because the length of the HOMSL 3304 extending longitudinally from the HR coating surface 3324 is less than the distance between the HR surface 3324 and the PR surface 3326, it is not visible in the epitaxial layer when viewed from the PR side 3322.

[0165] Figure 33C This is a plan view of an example laser diode 3200 including a HOMSL 3304, which is disposed within a lateral waveguide and extends longitudinally from the HR-coated surface 3324 by a length less than the distance between the HR surface 3324 and the PR surface 3326.

[0166] During high-power operation of the laser diode 3300, the temperature distribution caused by lateral thermal diffusion results in a thermal lensing effect in the lateral waveguide 3306, which induces refractive index contrast within the lateral waveguide 3306. In this example, partial or complete compensation for the increased refractive index contrast within the lateral waveguide 3306 can be achieved by strategically placing a HOMSL 3304 within the lateral waveguide 3306. The HOMSL 3304 trench can be formed to be laterally narrower than the lateral waveguide 3306, for example, by 0-10 μm on either side or by 0-20 μm in total.

[0167] Adding HOMSL 3304 trenches, fragments, channels, etc. to BAL can be performed using a variety of methods known to those skilled in the art, and the claimed subject matter is not limited in this respect. For example, HOMSL 3304 can be formed using down etching or selective deposition of a thicker layer adjacent to the active stripe.

[0168] Figure 33D This is a cross-sectional perspective view of the vertical epitaxial layer structure observed from the HR side 3302 of an example laser diode 3300, which includes a buried HOMSL 3304 disposed within a lateral waveguide 3306 and extending longitudinally from the HR coating surface 3324. For example, the HR side 3302 extends from the HR coating surface 3324 to approximately the midpoint 3330 (dashed line). The PR side 3322 extends from the PR coating surface 3326 to approximately the midpoint 3330.

[0169] In operation, the HR side 3302 experiences a thermal lensing effect. However, by suppressing or compensating for this effect through the HOMSL 3304, which provides a thinner portion of the lateral waveguide thickness, the HR side 3302 region becomes weakly refractive-index guided, thereby reducing the magnitude of the refractive index contrast on the HR side 3302 caused by the thermal lensing effect. In the example, the thinner the lateral waveguide 3312, the higher the effective refractive index, which allows the refractive index of the lateral waveguide 3306 to be lower than that of the lateral cladding.

[0170] Similar to HOMSL 3104, thickness 3328 is wisely chosen to reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3302. The choice of thickness 3328 is based on its impact on the magnitude of refractive index contrast (i.e., the potential effective refractive index contrast on the HR side 3302 of the lateral waveguide 3306). The thickness 3328 of a specific HOMSL 3304 that will sufficiently reduce the magnitude of refractive index contrast caused by thermal lensing on the HR side 3302 can be identified through various methods, including simulation, experiments, reference tables, and predictive analysis.

[0171] Thickness 3328 determines the Δn relative to the thermal lens on the HR side 3302 and reduces the guiding capability of the lateral waveguide 3306 in the region near the HOMSL 3304. In various examples, the thickness can be chosen such that the thermal lens is largely compensated to create a weakly refractive index guiding region. This enables weakly refractive index guiding of a few lateral modes at high operating currents on the HR side 3302, or, in extreme cases, weakly refractive index guiding of only a single lateral mode. This weakly guiding region can support 10 or fewer lateral modes, or even just one mode. Therefore, compared to a conventional BAL, the lateral waveguide 3306 at the HR side 3302 supports fewer lateral modes and enables reduced slow-axis divergence and higher brightness.

[0172] Simulations and Examples

[0173] HOMSL 3104 and HOMSL 3204 can be manufactured by various methods known to those skilled in the art, and the claimed subject matter is not limited in this respect. For manufacturing purposes, it may be necessary to determine a suitable thickness of HOMSL 3104 sufficient to reduce the refractive index contrast on the HR side. This relative difference in Δn can be taken into account when simulating the relationship between the thickness of HOMSL 3104 and Δn.

[0174] Figure 34Figure 3400 shows the simulation results of the effect of thickness on Δn in order to approximate the optimized thickness of the buried HOMSL 3104 to compensate for a specific increment in refractive index caused by thermal lensing. The specific HOMSL 3104 can be made of GaAs and formed between a p-type waveguide layer 3116 and a p-type cladding 3110 with a lower refractive index than GaAs. A negative Δn means a negative lateral refractive index difference between the lateral waveguide and the cladding. Using Figure 3400, the thickness of the HOMSL 3104 is optimized to compensate for a specific increment in refractive index caused by thermal lensing and can be approximated. Although the simulation is specific to… Figure 34 The geometric approach shown is not limited to the emitter's weakly refractive index-guided HR side 3102; other methods exist. These methods include reducing the lateral waveguide thickness in the active stripe. Both methods will reduce the refractive index contrast between the lateral waveguide and the cladding.

[0175] The approximate refractive index compensation required for the thermal lens is determined by using simulated beam propagation in the waveguide and simultaneously simulating the far field.

[0176] Figure 35 Graph 3500 shows the simulation results for the predicted far field of supported modes with and without high-order mode suppression achieved through thermal lensing compensation. A specific example is a BAL with a 200 μm lateral waveguide width and typical step refractive index and thermal lensing. The reduction in supported modes means a decrease in far field from approximately 10.9 degrees to approximately 4.3 degrees. The slow-axis far-field divergence of various BALs with HOMSL under different step refractive indices and thermal lenses is simulated and summarized in the table below:

[0177]

[0178] As mentioned above, a flat refractive index step is used to determine the refractive index contrast necessary for matching the far field at low operating power. The HOM column represents the order of the predicted highest-order mode.

[0179] The foregoing description of laser diodes, epitaxial layer structures, and various features / structures within epitaxial layers and waveguides is merely illustrative and included for purposes of explanation; other structures and features, or combinations of structures and / or features, are contemplated and are within the scope of the disclosed subject matter, and the claimed subject matter is not limited in this respect.

[0180] The general and specific principles of the examples of the currently disclosed art have been described and illustrated, and it will be apparent that modifications can be made to the examples in terms of arrangement and detail without departing from these principles. We claim all modifications and variations within the spirit and scope of the appended claims.

Claims

1. A laser diode, comprising: A transverse waveguide, the transverse waveguide including an active layer located between an n-type waveguide layer and a p-type waveguide layer, wherein the transverse waveguide is defined by an n-type cladding layer on the n side and a p-type cladding layer on the p side; A lateral waveguide, orthogonal to the transverse waveguide and defined at a first end by a high reflector (HR) coated surface and at a second end by a partial reflector (PR) coated surface along the longitudinal direction; as well as A buried high-order mode suppression layer (HOMSL) is disposed between the p-type cladding layer and the p-type waveguide layer, within the p-type waveguide layer, within the n-type waveguide layer, or between the n-type cladding layer and the n-type waveguide layer, and is disposed within the lateral waveguide, wherein the length of the HOMSL extending from the HR coating surface in the longitudinal direction is less than the distance between the HR coating surface and the PR coating surface; The thickness of the HOMS is selected based on the magnitude of the refractive index contrast within the lateral waveguide caused by the thermal lensing effect within the lateral waveguide during operation of the laser diode.

2. The laser diode according to claim 1, wherein, The refractive index of the HOMSL disposed within the lateral waveguide is lower than that of the n-type waveguide layer or the p-type waveguide layer or a combination thereof.

3. The laser diode according to claim 2, wherein, The thickness of the HOMSL is further selected to reduce the amount of refractive index contrast of the lateral waveguide during operation.

4. The laser diode according to claim 3, wherein, The value of the refractive index contrast is in the range of 10. -5 <Δn<10 -3 Within the range.

5. The laser diode according to claim 3, wherein, The lateral waveguide supports fewer than ten lateral modes.

6. The laser diode according to claim 3, wherein, The lateral waveguide supports a single lateral mode.

7. The laser diode according to claim 1, wherein, The thickness of the HOMSL is selected to reduce the effective refractive index of the lateral waveguide on the side extending from the HR coating surface.

8. The laser diode according to claim 1, wherein, The HOMSL includes gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), and indium gallium phosphide (InGaAsP).

9. The laser diode according to claim 1, wherein, The lateral waveguide is defined in the lateral direction by a ridge waveguide, wherein the ridge waveguide extends from the HR coating surface to the PR coating surface.

10. The laser diode according to claim 2, wherein, The HOMSL disposed within the lateral waveguide is 0-10 µm narrower than the lateral waveguide on either side, or 0-20 µm narrower in total.

11. The laser diode according to claim 1, wherein, The lateral waveguide is defined by a ridge waveguide in the lateral direction, and the length of the ridge waveguide extending from the PR coating surface in the longitudinal direction is less than the distance between the PR coating surface and the HR coating surface.

12. The laser diode according to claim 1, wherein, The thickness of the lateral waveguide in the active stripe is reduced by etching down or selectively depositing a thicker layer adjacent to the active stripe.

13. The laser diode according to claim 1, wherein, A low-refractive-index thin layer is disposed along the width of the lateral waveguide located in the region of the HOMSL.

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