CN114424417A

CN114424417A - Method, system and apparatus for high order mode suppression

Info

Publication number: CN114424417A
Application number: CN202080065748.3A
Authority: CN
Inventors: M·坎斯卡; 陈之纲; N·比克尔特
Original assignee: NLight Inc
Current assignee: NLight Inc
Priority date: 2019-08-13
Filing date: 2020-08-13
Publication date: 2022-04-29
Also published as: WO2021030639A1; DE112020003385T5

Abstract

A laser diode comprising a lateral waveguide and a lateral waveguide, the lateral waveguide being orthogonal to the lateral waveguide, the lateral waveguide comprising an active layer located between an n-type waveguide layer and a p-type waveguide layer, wherein the lateral waveguide is bounded by an n-type cladding layer on an n-side and a p-type cladding layer on a p-side, the lateral waveguide being bounded by a High Reflector (HR) coated facet at a first end and a Partial Reflector (PR) coated facet at a second end along a longitudinal direction, the lateral waveguide further comprising a buried Higher Order Mode Suppression Layer (HOMSL) disposed below the p-type cladding layer 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 from the HR facet along the longitudinal direction is less than the distance between the HR facet and the PR facet.

Description

Method, system and apparatus for high order mode suppression

Cross Reference to Related Applications

This application claims the benefit of U.S. provisional patent application No. 62/885,946 filed on 8/13/2019.

Technical Field

The technology disclosed herein relates to diode lasers, and more particularly to methods, systems, and apparatus for higher order mode suppression in diode lasers.

Background

The laser is a light emitting device. Light emission in lasers is the result of amplification of the light stimulated emission of electromagnetic radiation. Some lasers emit spatially and temporally coherent light, which allows the lasers to emit light of narrow optical bandwidths that can be narrowly focused over long distances. Lasers are of a wide variety, for example, gas lasers, chemical lasers, dye lasers, metal vapor lasers, solid state lasers, and semiconductor lasers. Laser diodes are electrically pumped semiconductor lasers, wherein the active layer is formed by the p-n junction of the semiconductor diode. Laser diodes typically include an active layer disposed between a layer of p-type semiconductor material and a layer of n-type semiconductor material. Many laser diodes are fabricated on a semiconductor substrate, such as gallium arsenide, that is 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 indium gallium arsenide, and may be only a few nanometers thick.

Laser diodes are formed by growing multiple layers of semiconductor material on a suitable substrate having a lattice constant that allows the materials to be selected to produce the desired emission wavelength. A typical laser diode includes an n-type layer, a p-type layer, and an undoped active layer therebetween 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 than the surrounding p-type and n-type doped cladding layers. The light generated by the active layer is confined in the waveguide plane.

Conventional edge-emitting Fabry Perot (Fabry Perot) wide area laser diodes are arranged in a rectangular gain or index guided semiconductor structure. The opposite end faces of the waveguide define a high reflector and a partial reflector to provide feedback for optical oscillations within the resonator. The multilayer laser diode structure extends the length of the laser and has a wider width for electrical injection that extends to the opposite side surface that also extends the length of the laser. The layers of semiconductor material are typically arranged such that the laser operates in a single mode in the growth direction of the laser, and this direction is defined as the fast axis direction. Since the semiconductor laser operates in a single mode in the fast axis direction, the brightness of the laser diode in that direction cannot be further improved; it is therefore called the diffraction limit. Thus, the distance between the top and bottom surfaces of the multilayer semiconductor laser structure provides a small dimension of the end facet, i.e., the thickness of the stripes, typically on the order of microns. On the other hand, the width of the multilayer laser structure provides a large dimension of the end facet, i.e. the stripe width, typically on the order of tens to hundreds of microns. This is called the "slow axis". Since the fringe width is much larger than the wavelength of the light, the lateral behavior of the optical field propagating along the optical axis of the waveguide is highly multimode along the wider fringe dimension, and the corresponding axis is described as the slow axis because the divergence angle is much smaller relative to the fast axis.

In high power applications "multimode laser diodes" or "wide area lasers" (BAL) are used. BAL has multiple modes in the slow axis, so their slow axis Beam Parameter Product (BPP) is higher than that of single mode laser diodes. Furthermore, thermal lensing becomes more pronounced as they are driven to higher currents, which results in a higher refractive index contrast distribution in the lateral direction, resulting in more and more lateral modes being accommodated. Thus, as the lateral divergence angle gets wider, this results in a decrease in lateral BPP and brightness (power BPP) while the slow axis brightness decreases. This means that slow axis brightness degrades even though power generally increases with higher current. The brightness of the BAL can be increased by reducing the emitter width; however, the current at which the maximum luminance occurs also occurs at a gradually decreasing current value. Therefore, the maximum output power at the maximum luminance also decreases.

For power scaling applications and to reduce the cost per watt of producing diode lasers, higher brightness at higher output power per emitter is desirable.

Disclosure of Invention

Methods, systems, and devices for reducing the magnitude of the refractive index contrast of a lateral waveguide during operation of a laser diode are disclosed herein. This may include a laser diode having a lateral waveguide orthogonal to a lateral waveguide comprising an active layer located between an n-type waveguide layer and a p-type waveguide layer, wherein the lateral waveguide is bounded by an n-type cladding layer on an n-side and a p-type cladding layer on a p-side, the lateral waveguide is bounded by a High Reflector (HR) coated facet at a first end and a Partial Reflector (PR) coated facet at a second end along a longitudinal direction, the lateral waveguide further comprising a buried Higher Order Mode Suppression Layer (HOMSL) disposed below the p-type cladding layer and within the lateral waveguide or on one or both sides of the lateral waveguide or a combination thereof, wherein a length of the HOMSL extending from the HR facet along the longitudinal direction is less than a distance between the HR facet and the PR facet.

In some examples, the refractive index of the HOMSL disposed on one or both sides of the lateral waveguide may be higher than the p-type waveguide layer and the p-type cladding layer.

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

The thickness of the HOMS may be selected based on the magnitude of the refractive index contrast in the lateral waveguide caused by a thermal lens within the lateral waveguide during operation of the laser diode. In an example, the thickness of the HOMSL is selected to reduce the magnitude of the refractive index contrast of the lateral waveguide during operation. The refractive index contrast may be of a magnitude of 10^-5<Δn<10^-3Within the range of (1). In some examples, such lateral waveguides support fewer than ten lateral modes or may support a single lateral mode.

In some examples, the thickness of the HOMSL may be selected to reduce the effective index on the side of the lateral waveguide extending from the HR facet. In some examples, such a lateral waveguide is bounded in a lateral direction by a ridge waveguide, wherein the ridge waveguide extends from the HR facet to the PR facet.

In some examples, the HOMSL overlaps the lateral waveguide laterally, and overlaps 0-10um on either side, or 0-20um in total.

In some examples, the HOMSL disposed within the lateral waveguide is laterally narrower than the lateral waveguide by 0-10um on either side or 0-20um in total laterally.

In some examples, the lateral waveguide is bounded in a lateral direction by a ridge waveguide that extends from the PR face in a longitudinal direction by a length that is less than a distance between the PR face and the HR face.

In some examples, the HOMSL includes a reduced lateral waveguide thickness in the active stripes, and may be formed by etching down or selectively depositing thicker layers adjacent to the active stripes.

In some examples, the HOMSL includes gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (inalgas), indium gallium phosphide (InGaAsP).

In examples where the HOMSL is a thin low index layer, it may be formed of AlGaAs along the width of the lateral waveguide located in the region of the HOMSL.

Drawings

The accompanying drawings, in which like numerals represent like elements, are incorporated in and constitute a part of this specification, and together with the description, explain the advantages and principles of the presently disclosed technology. In the drawings, there is shown in the drawings,

FIG. 1 depicts a lateral effective index profile of an example laser diode in which a higher-order mode suppression layer is disposed adjacent to a lateral waveguide;

FIG. 2 depicts lateral refractive index profiles and modal modeling of an example laser diode with a higher-order mode suppression layer disposed adjacent to a lateral waveguide;

fig. 3 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide;

fig. 4 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide;

fig. 5 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide;

fig. 6 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide;

FIG. 7 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 8 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a partial length of a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 9 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a partial length of a high-order mode suppression layer on only a lateral side disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 10 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a partial length of a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 11 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a partial length of a high-order mode suppression layer on only one side disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 12 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a partial length of a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction;

FIG. 13 shows a plan view of an exemplary lateral waveguide depicting a wide area laser diode, the exemplary lateral waveguide including a partial length of a higher-order mode suppression layer disposed adjacent to and on only one side of a flared laser oscillator waveguide along a longitudinal direction;

FIG. 14 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a higher-order mode suppression layer disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 15 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a high-order mode suppression layer disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 16 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a high-order mode suppression layer on only one side disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 17 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a higher-order mode suppression layer disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 18 shows a plan view depicting an example flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a high-order mode suppression layer on only one side disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 19 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a high-order mode suppression layer disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

FIG. 20 shows a plan view depicting an exemplary flared laser oscillator waveguide (i.e., lateral waveguide) laser diode including a partial length of a high-order mode suppression layer on only one side disposed adjacent to the flared laser oscillator waveguide in the longitudinal direction;

fig. 21A shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 21B shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 22 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 23 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 24 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 25 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction; and

fig. 26 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a higher-order mode suppression layer disposed adjacent to a lateral waveguide in a longitudinal direction;

fig. 27 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme;

fig. 28 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme;

fig. 29 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme;

FIG. 30A is a graph showing a conventional step index profile in the lateral direction for a single emitter laser diode at low power operation without significant thermal lensing;

fig. 30B is a graph showing a step refractive index profile to which a parabolic profile is added;

FIG. 30C is a graph showing an example "negative" step index profile with the addition of a parabolic profile, modeling the index profile in the region with negative compensation;

fig. 31A is a cross-sectional view of a vertical epitaxial layer structure viewed from the High Reflection (HR) side of an example laser diode that includes a buried higher-order mode suppression layer disposed on an adjacent side of a lateral waveguide and extending in a longitudinal direction;

fig. 31B is a cross-sectional view of the vertical epitaxial layer structure viewed from the Partially Reflective (PR) side of the example laser diode depicted in fig. 31, including a buried higher-order mode suppression layer disposed on the adjacent side of the lateral waveguide;

fig. 31C is a plan view of an example laser diode including buried higher-order mode suppression layers disposed on adjacent sides of a lateral waveguide and extending in a longitudinal direction;

fig. 31D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from the High Reflection (HR) side of an example laser diode that includes a buried higher-order mode suppression layer disposed on an adjacent side of a lateral waveguide and extending in a longitudinal direction;

fig. 32A is a cross-sectional view of a vertical epitaxial layer structure viewed from the High Reflection (HR) side of an example laser diode that includes a buried higher-order mode suppression layer disposed within a lateral waveguide and extending in a longitudinal direction;

fig. 32B is a cross-sectional view of the vertical epitaxial layer structure viewed from the Partially Reflective (PR) side of the example laser diode depicted in fig. 32, including a buried higher-order mode suppression layer disposed within the lateral waveguide and extending in the longitudinal direction;

FIG. 32C is a plan view of an exemplary laser diode including a buried higher-order mode suppression layer disposed within a lateral waveguide and extending in a longitudinal direction; and

fig. 32D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from High Reflection (HR) of an example laser diode including a buried higher-order mode suppression layer disposed within a lateral waveguide and extending in a longitudinal direction.

Fig. 33A is a cross-sectional view of a vertical epitaxial layer structure viewed from the High Reflection (HR) side of an example laser diode that includes a higher-order mode suppression layer including a reduced thickness waveguide portion disposed within a lateral waveguide and extending in a longitudinal direction;

fig. 33B is a cross-sectional view of the vertical epitaxial layer structure viewed from the Partially Reflective (PR) side of the example laser diode depicted in fig. 33, the laser diode including a higher-order mode suppression layer including a reduced-thickness waveguide portion disposed within the lateral waveguide and extending in the longitudinal direction;

FIG. 33C is a plan view of an example laser diode including a higher-order mode suppression layer including a reduced thickness waveguide portion disposed within a lateral waveguide and extending in a longitudinal direction; and

fig. 33D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from the High Reflection (HR) side of an example laser diode that includes a higher-order mode suppression layer including a reduced thickness waveguide portion disposed within a lateral waveguide and extending in a longitudinal direction.

FIG. 34 is an exemplary curve 3400 for approximating an optimized thickness of a high-order mode-inhibiting layer to compensate for a particular increase in refractive index caused by a thermal lens; and

fig. 35 is a graph 3500 showing simulation results for predicting an example far field of supported modes with and without high order mode suppression by thermal lens compensation.

Detailed Description

As used in this application and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Additionally, the term "including …" means "including …". Furthermore, the term "coupled" … does not exclude the presence of intermediate elements between the coupled items.

The systems, devices, and methods described herein should not be construed as limiting in any way. Rather, the present disclosure is directed to all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combination thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theory of operation is for ease of explanation, but the disclosed systems, methods, and apparatus are not limited to these theories of operation.

Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular order is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. In addition, the description sometimes uses terms such as "producing" and "providing" to describe the disclosed technology. These terms are high-level abstractions of the actual operations that are performed. The actual operations corresponding to these terms will vary from implementation to implementation and will be readily recognized by those skilled in the art.

In some examples, a value, process, or device may be referred to as "lowest," "best," "smallest," or the like. It should be understood that such description is intended to indicate that a selection may be made among many used alternatives of functionality, and that such a selection need not be better, smaller, or otherwise more preferred than others. Examples are described with reference to directions indicated as "above," "below," "up," "down," and the like. These terms are used for convenience of description, but do not imply any particular spatial orientation.

As discussed above, it is desirable to efficiently scale power and improve brightness in the BAL while minimizing output power loss. Methods, systems, and devices are described herein that target higher brightness at higher output powers by reducing slow-axis divergence angles without reducing emitter widths. The objective is to suppress the high order modes in the slow axis while preserving the low order lasing modes.

Higher Order Mode Suppression Layer (HOMSL)

What is needed to overcome the disadvantages of conventional laser diodes discussed in the background above is a laser diode that is configured to suppress high order modes in the lateral direction (i.e., orthogonal to the direction of propagation) while retaining light in the low order modes. This may be achieved by juxtaposing the high-order mode suppression structure adjacent to the lateral waveguide of the laser diode. The higher-order mode-suppressing structure may include a variety of materials and may be a refractive index guiding structure, an inverse waveguide structure, and/or a high-loss structure.

In one example, a higher-order mode suppression layer (HOMSL) may be disposed adjacent to the lateral waveguide at or near the rear and extending along the longitudinal direction less than the full length of the waveguide. The HOMSL may include: index guiding structures, anti-waveguide structures, and/or high loss structures. For example, the index guiding structure, the counter waveguide structure and/or the high loss structure may extend up to 20% of the waveguide length measured from the rear, or in another example, between about 5-50%. Extending the HOMSL only a small distance in the longitudinal direction minimizes the loss of the unbounded mode of the laser diode and enables the diode to operate more efficiently than if the HOMSL structure extended the entire length.

In another example, the HOMSL may be disposed adjacent to a flared laser oscillator waveguide and extend the entire longitudinal length of the waveguide or a portion of the longitudinal length of the waveguide measured from behind. By assembling the diodes in this manner, the benefits of reducing higher order modes by suppressing them using HOMSL can be combined with the benefits of using a Flared Laser Oscillator Waveguide (FLOW) described in U.S. Pat. No. 9,166,369, the disclosure of which is incorporated by reference in its entirety.

In yet another example, the laser diode may include buried non-periodic high and low refractive index structures with high loss in a high refractive index material disposed adjacent to the waveguide in the longitudinal direction. The non-periodic structure may suppress the higher order modes by disproportionately overlapping the higher order modes as compared to the lower order modes and/or the fundamental modes. The non-periodic structure is selected to introduce high losses into the higher order modes, but to minimize losses in the lower order modes and/or fundamental modes. The non-periodic structure may be disposed along the entire length of the waveguide in the longitudinal direction or a shorter length extending from the rear face. The non-periodic structure may also be disposed along a longitudinal direction of a wide area laser (BAL) and/or a flared laser oscillation waveguide.

FIG. 1 depicts a refractive index profile 100 showing the relative refractive indices of example lateral waveguides with adjacent HOMSLs. Segment 102 of the refractive index profile 100 represents the relative refractive index of the lateral waveguide, while segment 104 represents the relative refractive index of the adjacent HOMSL.

In an example, the HOMSL is an inverted waveguide structure that includes multiple materials with refractive indices higher than that of the waveguide. The HOMSL may comprise various doped or undoped materials. The HOMSL material can be judiciously chosen to optimize efficiency and BPP under laser operating conditions. When the local waveguide comprises aluminum gallium arsenide (AlGaAs), some examples of inverted waveguide HOMSL materials include doped gallium arsenide (GaAs), indium gallium arsenide (InGaAs), the like, or combinations thereof. Other combinations of materials forming waveguide and anti-waveguide structures will occur to those of skill in the art and claimed subject matter is not limited in this respect.

FIG. 2 depicts a refractive index profile 200 showing the relative refractive indices of an example lateral waveguide, where the HOMSL is disposed adjacent to the lateral waveguide, and modal modeling of the first few lateral waveguide modes. Segment 202 of the refractive index profile 200 represents the relative refractive index of the lateral waveguide, while segment 204 represents the relative refractive index of the HOMSL. In an example, a HOMSL is a refractive index guided aperiodic structure that includes a high index material and a low index material and has high loss in the high index material that disproportionately overlaps high order modes compared to low order/fundamental modes. In an example, the low index material has a refractive index lower than the effective refractive index of the lateral waveguide, and the high index material has a refractive index higher than the effective refractive index of the lateral waveguide. Section 204 shows the relative refractive index of the non-periodic structure with high and low index materials. The average refractive index of the HOMSL may be lower than the modal index, so the HOMSL is in a refractive index guided structure rather than an anti-guided structure, but the local high index region pulls the electric field or intensity and locally interacts with the material and introduces high losses to higher order modes. The modal modeling 206 shows modal behavior of the modes 0-4. The higher the mode number, the more this mode overlaps with the high index region of the HOMSL, so the higher order mode is more lossy than the lower order (210-216)/fundamental (208) mode.

For simplicity and illustrative purposes, the examples in fig. 3-26 depict examples of quantum well lasers. However, various other laser types may be configured to include HOMSL features, such as a double heterostructure laser, an interband cascade laser, a distributed bragg reflector laser, a distributed feedback laser, a quantum cascade laser, a vertical cavity surface emitting laser, and/or a vertical external cavity surface emitting laser, to name a few. Accordingly, the claimed subject matter is not limited to quantum well laser diodes.

Fig. 3 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a higher-order mode suppression layer disposed adjacent to a lateral waveguide. In an example, the laser diode 300 is a quantum well laser.

In an 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. The quantum well 302 is located between an n-type semiconductor layer 306 and a p-type semiconductor layer 308. An n-cladding layer 310 is disposed outside the n-type semiconductor layer 306. The 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 under the p-cladding layer 312. The quantum well 302, the n-type semiconductor layer 306, and the p-type semiconductor layer 308 form a lateral waveguide 318 portion of the laser diode 300. The boundaries of lateral waveguide 340 are shown by dashed lines extending in the longitudinal direction on n-metal contact 314.

The lateral beam size of a diode laser is determined by the width of the active region or the width of the lateral waveguide. Since the width of the waveguide in the lateral direction is significantly larger than the wavelength of the light, a large number of modes will be generated in the lateral direction. The HOMSL320 is disposed adjacent to the lateral waveguide 340 along the longitudinal direction. Further, in FIG. 3, HOMSL320 is located between the air and the p-cladding 312 outside of the lateral waveguide 318. However, the HOMSL320 need not be located there. HOMSL320 may be located in multiple locations in an epitaxial structure, and claimed subject matter is not limited in this respect.

In an example, the HOMSL320 comprises a high index material, wherein the index of refraction of the HOMSL320 is higher than the index of refraction of the lateral waveguide 340. The HOMSL320 is configured to introduce more loss to higher order modes to varying degrees, thereby suppressing higher order modes in the lateral (i.e., orthogonal to propagation) direction. The inclusion of such buried or surface high index material disproportionately counter-guides the higher order modes that overlap with the high index material as compared to the lower order/fundamental modes.

The laser diode 300 may be fabricated using a variety of well-known materials and methods. For example, the substrate 304 may include gallium arsenide (GaAs). The n-type semiconductor layer 306, the p-type semiconductor layer 308, the n-cladding layer 310, and/or the p-cladding layer 312 may be grown on the GaAs substrate 304 and include any one of: indium (In), gallium (Ga), aluminum (Al), arsenic (As), phosphorus (P), gallium arsenide (GaAs), indium phosphide (InP), the like, 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. Claimed subject matter is not limited in this respect.

The HOMSL320 material may be an absorbing material such that it absorbs higher order modes to optimize the efficiency versus Beam Parameter Product (BPP) under operating conditions. The HOMSL320 material may be absorptive or non-absorptive.

Fig. 4 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a higher-order mode suppression layer disposed adjacent to a lateral waveguide. In an example, the laser diode 400 is a quantum well laser similar to the laser diode depicted in fig. 3. However, laser diode 400 includes a HOMSL 402 having an absorbing material. The absorbing material selected for the HOMSL 402 may include semiconductor materials such As those mentioned above, metals (e.g., titanium (Ti) or nickel (Ni)) or semi-metals (e.g., tin (Sn) or As). The HOMSL material 402 may be doped or undoped. The HOMSL 402 may be epitaxially grown or deposited on the surface of the substrate 304 rather than buried. Fig. 5 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a higher-order mode suppression layer disposed adjacent to a lateral waveguide. In an example, the laser diode 500 is a quantum well laser similar to the laser diode depicted in fig. 3. However, laser diode 500 includes a HOMSL non-periodic structure 502 that includes a high index material and a low index material. The low index material 506 has a lower index of refraction than the effective indices of refraction of the high index material 504 and the lateral waveguides 340. The high-index material 504 and the low-index material 506 may comprise the same material doped differently to achieve different indices of refraction, or may together comprise different materials. For example, the high index material 504 may include a deposited dielectric or semiconductor, while the low index material may include air, a dielectric, or a semiconductor material.

In an example, the low index material and the high index material alternately extend outward from the sides of the lateral waveguide 340. A low index material 506 is disposed adjacent to lateral waveguide 340. Low index material 506 is closer to lateral waveguide 340 than high index material 340. The high index material 504 is disposed outside of the low index material 506. The pattern of high/low index material may be repeated a plurality of times aperiodically in the HOMSL structure 502. As described above, the non-periodic structure of the HOMSL502 can have an average refractive index that is lower than the modal effective index in the lateral waveguide or higher than the modal index of the lateral waveguide. The material selected for the non-periodic structure of the HOMSL502 is selected to introduce high loss to the higher order modes, but minimize the loss of the lower order/fundamental modes.

Fig. 6 shows a cross-sectional view depicting a vertical epitaxial layer structure of an example laser diode that includes a higher-order mode suppression layer disposed adjacent to a lateral waveguide. In an example, the laser diode 600 is a quantum well laser similar to the laser diode depicted in fig. 5. However, laser diode 600 includes HOMSL502 disposed on only one side of lateral waveguide 340. In an example, the HOMSL502 is configured to suppress higher order modes when asymmetrically distributed about the waveguide 340 (as in this configuration) and/or in cases where the HOMSL structure is symmetrically disposed about the waveguide 340.

Fig. 7 shows a plan view depicting an example lateral waveguide of a wide area laser diode including a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction. In an example, a wide-area laser diode 700 includes a HOMSL 702 disposed symmetrically about a lateral waveguide 340. The HOMSL 702 is a non-periodic, higher-order mode-suppressing layer structure that includes regions of low-index material 706 alternating with regions of high-index material 704. Low index material 706 has a refractive index that is lower than the effective refractive index of the material comprising lateral waveguide 340. The HOMSL 702 extends the entire length of lateral waveguide 340 from rear face 730 to front face 732.

Fig. 8 shows a plan view depicting an example lateral waveguide of a wide-area laser diode including a higher-order mode suppression layer disposed adjacent to the lateral waveguide in a longitudinal direction. In an example, wide-area laser 800 includes a shortened HOMSL 802 disposed symmetrically about lateral waveguide 340. The HOMSL 802 includes an aperiodic higher-order mode suppression layer with low-index material 806 alternating with high-index material 804, similar to that depicted in FIG. 5. However, HOMSL 802 does not extend the entire length of lateral waveguide 340 from rear face 730 to front face 732. In contrast, HOMSL 802 extends only a portion of the length of lateral waveguide 340, and in particular from rear face 730. The rear face 730 is coated with a Highly Reflective (HR) coating and the front face 732 is coated with a Partially Reflective (PR) coating. Extending the HOMSL 802 only a short length from the back facet 730 has the advantage of minimizing the loss of the uninhibited mode, so that the laser diode operates more efficiently without significantly increasing the loss of the lower order/fundamental modes, since the total intensity of the forward and backward propagating fields in the longitudinal direction is smaller towards the back facet than towards the front facet. Thus, the losses are commensurately smaller.

Fig. 9 shows a cross-sectional plan view depicting an example waveguide of a wide-area laser diode including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, wide-area laser 900 includes a shortened HOMSL902 disposed asymmetrically with respect to lateral waveguide 340 along the longitudinal direction. The HOMSL902 includes an aperiodic higher-order mode-suppressing layer structure with low-index material 906 alternating with high-index material 904, similar to that depicted in FIG. 8. A single HOMSL902 feature extends only a portion of the length of lateral waveguide 340 extending from rear face 730. The rear face 730 is coated with an HR coating and the front face 732 is coated with a PR coating. Again, extending the HOMSL902 only a short length from the rear face 73 has the advantage of minimizing the loss of the uninhibited modes, so that the laser diode operates more efficiently without significantly increasing the loss of the lower order/fundamental modes.

Fig. 10 shows a cross-sectional plan view depicting an example waveguide of a wide-area laser diode including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, wide-area laser 1000 includes a shortened HOMSL1002 disposed symmetrically about lateral waveguide 340. The HOMSL1002 comprises a high index material configured to have an index of refraction greater than that of the lateral waveguide 340. The high index material of the HOMSL1002 is capable of suppressing high order modes generated in the lateral waveguide 340 that spatially overlap with the high index material of the HOMSL1002 by reverse guiding, while having little effect on the low order/fundamental modes generated therein, since there is little overlap between the low order/fundamental modes and the high index material.

Fig. 11 shows a cross-sectional plan view depicting an example waveguide of a wide-area laser diode including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, wide-area laser 1100 includes a shortened HOMSL 1102 disposed asymmetrically with respect to lateral waveguide 340. The HOMSL 1102 includes a high index material similar to that shown in FIG. 10. HOMSL 1102 provides counter-guiding for higher-order modes generated in lateral waveguide 340. To counter-guide at least some of the higher-order modes, the HOMSL 1102 does not have to be symmetrically distributed about the lateral waveguide 340. Furthermore, a single HOMSL 1102 feature extends only a portion of the length of lateral waveguide 340 extending from rear face 730. The rear face 730 is coated with an HR coating and the front face 732 is coated with a PR coating. Also, extending the HOMSL 1102 only a short length from the back face 1130 has the advantage of suppressing higher order modes while minimizing the loss of the unsuppressed modes, so that the laser diode operates more efficiently without significantly increasing the loss of the lower order and/or fundamental modes.

Fig. 12 shows a cross-sectional plan view depicting an example waveguide of a wide-area laser including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, wide-area laser 1200 includes a shortened HOMSL 1202 disposed symmetrically about lateral waveguide 340. The HOMSL 1202 comprises an absorbing material, which may be a semiconductor material with multiple compositions, dopings, crystallinities, and/or morphologies; a semimetal; or a metal. The effect of the absorbing material is to suppress the higher order modes in the lateral direction in the lateral waveguide 340 by disproportionately increasing the round-trip loss of the higher order modes. HOMSL 1202 does not extend the entire length of lateral waveguide 340 from rear face 730. HOMSL 1202 extends only a portion of the length of lateral waveguide 340, specifically from rear face 730. Extending the HOMSL 1202 only a short length from the rear facet 730 has the advantage of minimizing the loss of the uninhibited mode, so that the laser diode operates more efficiently without significantly increasing the loss of the lower order/fundamental mode.

Fig. 13 shows a cross-sectional plan view depicting an example flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. For one example, wide-area laser 1300 includes a shortened HOMSL 1302 disposed asymmetrically with respect to lateral waveguide 340. The HOMSL 1302 includes an absorbing material similar to that shown in FIG. 12. The HOMSL 1302 absorbs higher order modes in the lateral waveguide 340 disproportionately, thereby suppressing higher order modes that overlap more spatially with the HOMSL 1302. Thus, the HOMSL 1302 suppresses higher order modes, thereby minimizing the impact on lower order and fundamental modes. In addition, a single HOMSL 1302 feature extends only a portion of the length of lateral waveguide 340 extending from rear face 730. Rear face 1330 is coated with an HR coating and front face 732 is coated with a PR coating. Extending the HOMSL 1302 only a short length from the rear face 730 has the advantage of suppressing higher order modes while minimizing the loss of the unsuppressed modes, so that the laser diode operates more efficiently and without significantly increasing the loss of the lower order/fundamental modes.

Fig. 14 shows a plan view depicting an example flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. As one example, laser 1400 includes a Flared Laser Oscillator Waveguide (FLOW)1418, which can be used in place of a rectangular wide area laser waveguide. FLOW1440 includes a flared current injection region extending and widening in a longitudinal direction between a rear face 730 comprising a High Reflector (HR) coating and a front face 732 comprising a Partial Reflector (PR) coating. By narrowing the width of the electrically pumped stripe towards the highly reflective surface, higher order modes with higher divergence angles are prevented from coupling back into the laser. As a result, the slow axis divergence of the laser is smaller compared to a rectangular geometry device with partial reflectors of the same width. Furthermore, light propagating in the flared current injection region closer to the PR front face 732 may form a thermal waveguide closer to the narrower width on the HR rear face 730 side, thereby causing the beam output at the front face 732 to have a significantly narrower beam width than the width of the front face 732. As a result, the FLOW device has a smaller beam parameter product BPP (slow axis near field width multiplied by slow axis divergence) compared to the BAL device. Since the near field is smaller than the physical width of the front face 732 side, the FLOW device can be designed to have a larger total area than the BAL without sacrificing BPP. The enlarged total pumping area provided by the extension of the flared current injection region serves to reduce thermal and series resistance in the device, resulting in higher electrical-to-optical power conversion efficiency. This results in higher output power at a given operating current compared to BAL devices. Higher power and smaller BPP cause the beam brightness on the slow axis to increase. In addition to being applied to wide area diode lasers, the FLOW concept may also be applied to other types of semiconductor-based fabry-perot lasers, such as Quantum Cascade Lasers (QCLs), interband quantum cascade lasers (IQLs), as examples. Wide area diode lasers with flared laser oscillator waveguides may also find particular use in laser diode modules that may be configured for various applications, such as fiber coupling or direct pumping.

In an example, the HOMSL 1402 can include a non-periodic structure of a first layer of low index material 1406, wherein the index of refraction of the low index material 1406 is less than the effective index of refraction of the material comprising the FLOW 1440. The HOMSL 1402 also includes a second layer of high index material 1404, wherein the high index material 1404 has a refractive index that is greater than or lower than the effective refractive index of the material from which the FLOW1440 is composed. Thus, as described above with reference to FIG. 5, the HOMSL 1402 may be in an index-guided or anti-guided state. Still referring to fig. 14, the HOMSL 1402 is coupled with the FLOW1440, compounding any higher order mode suppression effects that can be achieved using either the HOMSL 1402 or the FLOW1440 alone to further reduce BPP.

Fig. 15 shows a cross-sectional plan view depicting an example flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, laser diode 1500 includes FLOW1440 and a shortened HOMSL1502 disposed symmetrically about FLOW 1440. HOMSL1502 includes a non-periodic structure that includes a low index material 1506 and a high index material 1504 assembled as described in FIG. 14. In an example, HOMSL1502 extends only a portion of the length of FLOW1440 from rear face 730. HOMSL1502 is not disposed near front 732. This architecture compounds the higher-order mode suppression achieved by the HOMSL structure in combination with the FLOW structure, because extension of the HOMSL1502 less than the full length of the FLOW1440 minimizes the loss of the uninhibited mode, making the laser diode more efficient to operate, and does not significantly increase the loss of the lower-order/fundamental modes, as explained above with respect to fig. 8.

Fig. 16 shows a cross-sectional plan view depicting an example of a flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, the laser diode 1600 can include a HOMSL 1602 that is asymmetrically distributed about the FLOW 1440. The HOMSL 1602 may extend only a portion of the length of the FLOW1440 from the rear face 730. In an example, a single shortened HOMSL 1602 combined with FLOW1440 may operate to efficiently suppress higher order modes. Such a configuration may be desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of the laser diode 1600.

Fig. 17 shows a plan view depicting an example waveguide of a laser diode including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, the laser diode 1700 includes a FLOW1440 and an HOMSL 1702 disposed symmetrically about the FLOW 1440. The HOMSL 1702 is shortened, extending only a portion of the length of FLOW1440 from the rear face 730. HOMSL 1702 comprises a high index material, as compared to the materials used in FLOW 1440. By narrowing the width of the electrically pumped stripes of FLOW1440 beyond the highly reflective surface, higher order modes with higher divergence angles can be prevented from coupling back into the laser. The shortened HOMSL 1702 further suppresses higher modes by disproportionately directing the higher modes overlapping with the high index material back toward the HR face.

Fig. 18 shows a plan view depicting an example waveguide of a laser including a higher-order mode-suppression layer disposed adjacent to the waveguide. In an example, laser 1800 may include shortened HOMSL 1802 asymmetrically distributed with respect to FL0W 1440. The HOMSL 1802 can include a high index of refraction material similar to that described in FIG. 17. The HOMSL 1802 may extend only a partial length from the rear face 730 of the FLOW1440 from the rear face 730. A single shortened HOMSL 1802 combined with FLOW1440 may operate to efficiently suppress higher order modes. Such a configuration may be desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of the laser 1800.

Fig. 19 shows a plan view depicting an example flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, the laser diode 1900 includes a FLOW 1440. The HOMSL 1902 is symmetrically arranged about the FLOW 1440. The HOMSL 1902 is shortened, extending only a portion of the length of FLOW1440 from the rear face 730. The HOMSL 1902 includes an absorbing material. As discussed with reference to fig. 4, the absorbing material preferably introduces higher losses to higher order modes, thereby suppressing higher order modes that spatially overlap the HOMSL 1902.

Fig. 20 shows a cross-sectional plan view depicting an example flared laser oscillator waveguide including a higher-order mode suppression layer disposed adjacent to the waveguide. In an example, the laser 2000 may include a shortened HOMSL 2002 that is asymmetrically distributed about the FLOW 1440. The HOMSL 2002 may include an absorbing material similar to that described with respect to FIG. 19. The HOMSL 2002 may extend only a partial length from the back side 730 of the FLOW 1440. A single shortened HOMSL 2002 combined with FLOW1440 may suppress higher order modes more efficiently than either the HOMSL 2002 or FLOW1440 alone. Such a configuration may be desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of laser 2000.

Gain customization method

In an example, higher order modes in the lateral waveguide may be reduced by reducing the amount of current reaching an active layer (in which the higher order modes diffuse) in the lateral waveguide. This can be achieved by gain customization. Typically, gain tailoring involves injecting current from the p-side of the heterostructure. However, making gain customization from the p-side is fraught with inefficiencies. Gain tailoring from the n-side, on the other hand, produces a diffused carrier profile that more closely overlaps primarily with the fundamental mode, followed by a lower order mode profile, providing higher gain for the desired mode and lower gain for the undesired higher order modes.

Fig. 27 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme. In an example, gain customization is performed by current injection through n-metal contact 2714, which n-metal contact 2714 is patterned to be narrower than p-metal contact 316. The n-metal contacts 2714 are disposed in the center of the lateral waveguide 2740 and in the cavity 2740 in the longitudinal direction, enabling the lateral carrier distribution pattern 2702.

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

Gain tailoring from the n-side may be achieved by introducing a lateral carrier distribution pattern 2802 by providing a narrow n-metal contact 2814 on the n-side 2820 of the laser diode 2800, rather than conventional metallization of the entire n-side. Thin n-metal contacts 2814 may be disposed at multiple locations opposite p-metal contacts 316. In one example, the n-metal contact 2814 is offset such that its edge is located at the transmitter half-plane 2804. Gain tailoring is performed from the n-metal side 2820 to reduce the higher order modes propagating in the waveguide 2840 by reducing the amount of gain to the higher order modes.

In an example, the n-metal contact 2814 may have a variable width along the cavity in order to modulate the carrier distribution in the lateral and longitudinal directions. This is shown in fig. 28, where the first width L1 of the n-metal contact 2814 is less than the second width L2. This provides gain tailoring in the longitudinal direction, reducing the gain of the higher order modes towards the HR (highly reflective) plane, allowing the laser diode 2800 to operate more efficiently without significantly increasing the loss of the lower order/fundamental modes.

Fig. 29 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme. In an example, gain customization is performed by current injection through the flared n-metal contact 2914, which n-metal contact 2914 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). An n-metal contact 2914 is disposed in the longitudinal direction in the center of the lateral waveguide 2940 and the cavity 2910, enabling a lateral carrier distribution pattern 2902.

Hybrid gain tailoring/HOMSL method

Further reduction of higher order modes in the lateral waveguide can be performed using a hybrid approach by: 1) tailoring the gain or discriminating the gain for the higher order modes by using a tailored current injection scheme to reduce higher order mode dispersion in the waveguide, thereby starving them of gain and suppressing the higher order modes; 2) a HOMSL structure is included adjacent to the lateral waveguide in the longitudinal direction to further suppress the higher order modes despite gain tailoring.

Fig. 21A shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode including a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a lateral waveguide. Laser diode 2100 includes an n-side 2120 and a p-side 2122. n-side 2120 includes n-metal contact 2114, n-cladding layer 310, n-type semiconductor layer 306, and n-substrate 304. p-side 2122 includes p-cladding layer 312, p-type semiconductor layer 308, p-metal contact 316, and HOMSL 320. Waveguide 318 includes quantum well 302, n-type semiconductor layer 306, and p-type semiconductor layer 308. The longitudinal waveguide 2140 is defined in a variety of ways (e.g., by gain guiding, ridge waveguide, or index guiding, etc., or combinations thereof). The longitudinal waveguide 2140 includes a cavity 2110 shown in dashed lines on top of the substrate 304 and the n-metal contact 2114. A p-metal contact 316 is located under the p-cladding layer 312. The n-metal contact 2114 extends along the cavity 2110 of the longitudinal waveguide 2140.

As discussed above, gain tailoring from the n-side can be achieved by introducing lateral carrier distribution pattern 2102 by providing n-metal contact 2114 on the n-side of the laser diode. In fig. 21A, the n-metal contact 2114 is offset so that its edge is at the transmitter half-plane 2104. Carrier injection is performed from the n-metal side. In addition, the HOMSL320 comprising a high index material is disposed symmetrically about the lateral waveguide 2110 along the longitudinal direction. This mixing approach may reduce the higher-order modes propagating in the waveguide 2140 by reducing the amount of gain to the higher-order modes and suppressing the higher-order modes via the HOMSL 320.

In another example, a HOMSL structure disposed asymmetrically with respect to the waveguide 2140 may be used instead of a symmetrically disposed HOMSL structure. In one example, an asymmetric HOMSL structure as shown in FIGS. 9, 11, 16, 18, and 20 should be placed in series with an n-metal contact 2114 as shown in FIG. 21B as a heterostructure. This configuration is more efficient than having a HOMSL structure on the opposite side because the higher-order mode gain is insufficient and will be below the threshold carrier density.

In addition, other HOMSL structures may be used to perform the hybrid gain tailoring/HOMSL higher-order mode suppression methods described herein. For example, rather than using the high index material of the HOMSL320, an absorbing and/or non-periodic material as described above with respect to HOMSL 402 of FIG. 4 and HOMSL502 of FIG. 5 may be used. Furthermore, a hybrid gain tailored/HOMSL approach using p-side gain tailoring will provide improved higher-order mode suppression over conventional p-side gain tailoring or higher-order mode suppression using only the HOMSL structure. Fig. 22 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a waveguide. In an example, n-metal contact 2214 is patterned to be narrower than the width of p-metal contact 316. n-metal contact 2214 is centered on a half-plane 2204 of waveguide 2240. Doing so produces a diffuse carrier distribution along the path indicated at 2202 in the lateral direction, thus producing a carrier density distribution that overlaps primarily with the fundamental mode more closely than with the suppressed high order modes, followed by a low order mode distribution. The current injection profile is configured to optimize overlap with lateral low-order and fundamental modes by providing higher gain for desired modes and lower gain for undesired higher-order modes. In addition, the width of n-metal contact 2214 may be varied along cavity 2210 to adjust the magnitude of carriers injected along the longitudinal direction of cavity 2210.

Fig. 23 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a waveguide. In an example, gain customization is performed by current injection through n-metal contact 2314 offset with respect to p-metal contact 316. The HOMSL 402 (see fig. 4) is positioned symmetrically about the lateral waveguide 2340 in the longitudinal direction and includes an absorbing material. In an example, the HOMSL 402 can be n-or p-doped GaAs or ordered or disordered InGaAs with a lower bandgap than the laser wavelength.

Fig. 24 shows a cross-sectional perspective view depicting a vertical epitaxial layer structure of an example laser diode that includes a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a waveguide. In an example, gain customization is performed by current injection through n-metal contact 2414, which n-metal contact 2414 is patterned to be narrower than p-metal contact 316. An n-metal contact 2414 is disposed in the center of the lateral waveguide 2440 and cavity 2410. The HOMSL 402 (see fig. 4) is symmetrically positioned about the lateral waveguide 2440 and includes an absorbing material.

Fig. 25 shows a cross-sectional view depicting a vertical epitaxial layer structure of an example laser diode that includes a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a waveguide. In an example, gain customization is performed with n-metal contact 2514 offset with respect to p-metal contact 316. The HOMSL502 (see fig. 5), which includes a non-periodic high index layer 504 and a low index layer 506, is positioned symmetrically about the lateral waveguide 2540.

Fig. 26 shows a cross-sectional view depicting a vertical epitaxial layer structure of an example laser diode that includes a tailored n-side current injection scheme and a higher-order mode suppression layer disposed adjacent to a waveguide. In an example, gain tailoring is performed by current injection through n-metal contact 2614, which is patterned to be narrower than p-metal contact 316. An n-metal contact 2614 is disposed in the center of the waveguide 2640 and the cavity 2610. The HOMSL502 (see FIG. 5) is positioned symmetrically about the longitudinal waveguide 2640 and includes an absorbing material.

Buried HOMSL features for thermal lens compensation

Index guiding and gain guiding are the primary confinement mechanisms by which the lateral optical modes (i.e., transverse to the slow axis) are confined in the cavity of a wide-area laser. Vertical mode confinement (i.e., across the fast axis) typically uses n-type and p-type cladding layers with a predetermined index of refraction for index guiding. Typically, the lateral optical mode supported by a semiconductor laser cavity with zero lateral refractive index change in the unpowered, cold state becomes gain guided during the powered state because the injected current causes a lateral refractive index change between the electrically pumped and unpumped regions.

At high power operation, the lateral thermal gradient causes 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 induced by the thermal lens may 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, amount of waste heat generated by the diode laser, and heat transfer between the diode junction and heat sink, among others, as will be readily understood by those skilled in the art.

The slow-axis divergence of the output beam emitted by the semiconductor device may be strongly affected by the lateral waveguide confinement near the high reflector facet. Index guiding (caused by thermal lenses) in the lateral waveguide near the highly reflective surface can support unwanted high order lateral modes, leading to slow axis divergence and reduced beam quality.

Examples herein describe methods, systems, and apparatus for suppressing the onset of high order lateral modes in device operation caused by high index contrast due to thermal lenses. The increased waveguide index contrast from the thermal lens is biased or compensated for by forming an index compensation region on the HR side of the fabry-perot cavity. This reduces the magnitude of the refractive index contrast induced by the thermal lens.

Fig. 30A is a graph 3002 showing a conventional step index profile in the lateral direction for a single emitter laser diode under low power operation without significant thermal lensing. Fig. 30B is a graph 3004 showing a step index profile in the lateral direction for a single emitter laser diode with the addition of a parabolic profile. This is a refractive index model of the conventional waveguide profile with thermal lensing at higher power operation. This shows how the profile evolves under thermal lensing at high operating currents. Fig. 30C is a graph 3006 illustrating a potential refractive index profile in the lateral direction of a single emitter laser diode that compensates for thermal lensing at higher power operation. The "negative" step index profile with the addition of the parabolic profile models the refractive index profile in the region with negative compensation. The thermal lens refractive index profile creates a weak index guiding region in the operating state.

As will be described in more detail below, methods for achieving this profile include introducing lateral features adjacent and/or overlapping the lateral waveguides with higher refractive indices, reducing the lateral waveguide thickness in the active stripes, and/or inserting a thin low index layer within the lateral waveguides.

Fig. 31A to 31D show various views of the laser diode 3100.

Fig. 31A is a cross-sectional view of a vertical epitaxial layer structure of an example laser diode 3100 that includes a buried higher-order mode suppression layer (HOMSL)3104 disposed on an adjacent side of a lateral waveguide 3106. The laser diode 3100 may include various geometries and configurations, and include various arrangements of p-type, n-type, active layers, caps, and dielectric layers. The term "buried" herein is intended to refer to a higher-order 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 higher-order mode suppression layer or feature may not be buried and may operate in the same or similar manner as the buried higher-order mode suppression layer or feature.

In the example, the laser diode 3100 is represented in a simplified epitaxial structure and includes an n-type cladding layer 3108 and a p-type cladding layer 3110 forming a lateral waveguide or cavity 3112 therebetween. Lateral waveguide 3112 is orthogonal to 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 p-n junction homostructures, heterostructures, double heterostructures, quantum wires, quantum dots, and the like. The P-type cladding layer 3110 may be etched into various shapes to form a ridge structure 3120 or mesa, either of which may extend the entire longitudinal length of the diode 3100 or may extend 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) may be formed on the laser diode 3100 to direct current through the active layer 3118.

Fig. 31B is a cross-sectional view of the vertical epitaxial layer structure viewed from the Partially Reflective (PR) side 3122 of the example laser diode 3100 depicted in fig. 30A.

The lateral waveguide 3106 is bounded at a first end by an HR coated face 3124 and at a second end by a PR coated face 3126 in the longitudinal direction. In an example, the HOMSL 3104 is formed below the p-type cladding layer 3110 and on one or both sides of the lateral waveguide. The length of the HOMSL 3104 extending longitudinally from the HR coated face 3124 is less than the distance between the HR and PR faces. The buried HOMSL 3104 does not extend to the PR side 3122 and is therefore not visible in the epitaxial layer as seen from the PR side 3122.

Fig. 31C is a top plan view of an example laser diode 3100 that includes buried HOMSL 3104 features disposed on adjacent sides of a lateral waveguide 3106 and extending in a longitudinal direction from an HR facet 3124.

During high power operation of the laser diode 3100, the temperature distribution generated by lateral thermal diffusion causes a thermal lens effect in the lateral waveguide 3106, which causes a refractive index contrast in the lateral waveguide 3106. In an example, partially or fully compensating for increased index contrast in the lateral waveguides 3106 can be achieved by strategically placing the HOMSL 3104 features on one or both of the lateral sides adjacent to the lateral waveguides 3106. The HOMSL 3104 is formed between the p-type waveguide layer 3116 and the p-type cladding layer 3110. Alternatively, the HOMSL 3104 may be formed between the n-type waveguide layer 3114 and the n-type cladding layer 3108. The HOMSL 3104 may be further formed to slightly overlap the lateral waveguides 3106 to compensate for mode size mismatch between the two regions or for other reasons.

The addition of the HOMSL 3104 structure (e.g., comprising GaAs) to the BAL may be performed by a variety of methods known to those skilled in the art, and claimed subject matter is not limited in this respect. For example, a modified mask and etch may be used to form the HOMSL 3104 at a selected bias from the ridge waveguide 3120. The high index features 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 the same order modes between the HR and PR sides means that the offset between the oxide ridge 3120 and the HOMSL 3104 in the lateral direction can be chosen to avoid excessive loss due to out-coupling of the supported lasing mode.

Various simulations indicate that the mode size trend is predictable for different magnitudes of refractive index contrast, regardless of which order mode. The refractive index contrast is of the order of 10^-5<Δn<10^-3Within the range of (1). The predicted mismatch in the size of the lateral waveguide 3106 (or the overlap of the HOMSL 3104 on the lateral waveguide) may be in the range of 2-6um on either side or in the range of 4-12um in total.

In another example, the HOMSL 3104 is formed to laterally overlap the lateral waveguides 3106 to compensate for the mismatch of the lateral mode regions between the HOMSL 3104 region and the index guiding region, which is between 0-10um on either side or between 0-20um in total.

Fig. 31D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed 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 an HR coated facet 3124.

In an example, the HR side 3102 extends from the HR coated face 3124 to about a mid point 3130 (dashed line). The PR side 3122 extends from the PR coated surface 3126 to approximately a mid point 3130.

In the operating state, the HR side 3102 experiences a thermal lens effect, however, under suppression or compensation of the HOMSL 3104, this region is guided by the weak index of refraction; thus, it has a refractive index profile approximately corresponding to that shown in fig. 30C. Likewise, the PR side 3122 includes an index guiding region that also experiences thermal lensing during operation, and is free of suppression or compensation by the HOMSL 3104, thus corresponding approximately to the index profile shown in fig. 30B.

To reduce the magnitude of the refractive index contrast caused by the thermal lens on the HR side 3102 of the laser diode 3100, the HOMSL 3104 may comprise a higher index material than the surrounding material. The relative refractive index (n) of HOMSL 3104 with respect to the lateral waveguide layer is n_{HOMSL 3104}>n_{P-type cladding layer 3110}/n_{n-type cladding layer 3108}>n_{p-type waveguide layer 3116}/n_{N-type waveguide layer}。

Additionally, to reduce the magnitude of the refractive index contrast induced by the thermal lens on the HR side 3102, the refractive index and thickness 3128 of the HOMSL 3104 are judiciously selected. The thickness 3128 should be selected based on its effect on the magnitude of the refractive index contrast (i.e., the potential effective refractive index contrast on the HR side 3102 of the lateral waveguide 3106). The thickness 3128, threshold thickness, or range of thicknesses (collectively referred to herein as "thicknesses") of a particular HOMSL 3104 that will substantially reduce the magnitude of the thermal lens induced index contrast on the HR side 3102 can be identified by a variety of methods, including simulations, experiments, reference tables, and predictive analysis, among others.

The thickness 3128 determines Δ n on the HR side 3102 relative to the thermal lens and reduces the guiding ability of the lateral waveguide 3106 in the region near the HOMSL 3104. In various examples, the thickness may be selected such that the thermal lens is largely compensated to produce a weak index guiding region. This enables weak index guiding of few lateral modes, or in the extreme case only a single lateral mode, at high operating currents on the HR side 3102. Such a weak guiding region may support 10 or fewer lateral modes, or may support only one mode. Therefore, the HR-side lateral waveguide 3106 supports fewer lateral modes and can achieve a reduction in slow-axis divergence and higher brightness compared to the conventional BAL.

Since the HOMSL is designed to compensate primarily for the thermal lens under high power operation, there can be effectively a counter-guiding region for low power operation on HR side 3102 that transitions to weakly index-guiding for higher power operation as the thermal lens begins.

Fig. 32A-32D depict various views of a laser diode 3200.

Fig. 32A is a cross-sectional view of a vertical epitaxial layer structure of an example laser diode 3200 that includes a buried HOMSL 3204.

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 forming a lateral waveguide or cavity 3212 therebetween. Lateral waveguide 3212 is orthogonal to lateral waveguide 3206 and includes an n-type waveguide layer 3214, a p-type waveguide layer 3216, and an active layer 3218. The ridge structure 3220 may extend a portion or the entire longitudinal length of the diode 3200 between the HR side 3202 and the PR side 3222.

HOMSL3204 is disposed within lateral waveguide 3212 within p-type waveguide layer 3216. Alternatively, HOMSL3204 may be disposed in n-type waveguide layer 3214.

In an example, HOMSL3204 may include a thin layer of low refractive index material. Although HOMSL3204 is disposed in lateral waveguide 3212, it is also within lateral waveguide 3206; thus, the effective index of lateral waveguide 3206 is reduced by the presence of lower index HOMSL 3204. The refractive index of the lateral cladding 3210 is unchanged.

Fig. 32B is a cross-sectional view of the vertical epitaxial layer structure viewed from the PR side 3222 of the example laser diode 3200 depicted in fig. 32, including the HOMSL3204 disposed within the lateral waveguide 3206. The lateral waveguide 3206 is bounded at a first end by the HR coated face 3224 and at a second end by the PR coated face 3226 in the longitudinal direction. In an example, HOMSL3204 is buried in p-type waveguide layer 3216 (or n-type waveguide layer 3214). However, because the length of the HOMSL3204 extending longitudinally from the HR coated facet 3224 is less than the distance between the HR facet and the PR facet, it is not visible in the epitaxial layer when viewed from the PR side 3222.

Fig. 32C is a plan view of an example laser diode 3200 that includes a buried HOMSL3204 disposed within a lateral waveguide and extending in a longitudinal direction.

During high power operation of the laser diode 3200, the temperature distribution generated by lateral thermal diffusion causes thermal lens effects in the lateral waveguide 3206, which causes refractive index contrast in the lateral waveguide 3206. In an example, partially or fully compensating for increased index contrast in lateral waveguides 3206 may be achieved by strategically placing lower index HOMSL3204 within lateral waveguides 3206. HOMSL3204 may be laterally narrower than lateral waveguides 3206 by 0-10um on either side or 0-20um in total.

Adding a HOMSL3204 structure (e.g., comprising AlGaAs) to BAL may be performed by various methods known to those skilled in the art, and claimed subject matter is not limited in this respect.

Fig. 32D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from the HR side 3202 of an example laser diode 3200 that includes a buried HOMSL3204 disposed within a lateral waveguide 3206 and extending in a longitudinal direction from an HR coated facet 3224. For example, the HR side 3202 extends from the HR-coated face 3224 to approximately the mid-point 3230 (dashed line). The PR side 3222 extends from the PR coated face 3226 to approximately a midpoint 3230.

In the operating state, the HR side 3202 experiences a thermal lens effect, however, the HR side 3202 region becomes weakly index guided with suppression or compensation of the HOMSL3204 achieved by reducing index contrast by introducing lower index material in the lateral waveguides 3206. To reduce the magnitude of the index contrast caused by the thermal lens on the HR side 3202, the HOMSL3204 may include a lower index material than the surrounding material. The relative refractive index (n) of HOMSL3204 with respect to the lateral waveguide layers is: n is_{Low refractive index layer}<n_{P-wave guide}/n_{n-wave guide}<n_{P-cladding layer}/n_{n-cladding layer}。

Similar to the HOMSL 3104, the thickness 3228 and refractive index of the HOMSL3204 are judiciously chosen in order to reduce the magnitude of the thermal lens induced refractive index contrast on the HR side 3202. The selection of the thickness 3228 is based on its effect on the magnitude of the refractive index contrast (i.e., the potential effective refractive index contrast on the HR side 3202 of the lateral waveguide 3206). The thickness 3228 of a particular HOMSL3204 that will substantially reduce the magnitude of the index contrast caused by the thermal lens on the HR side 3202 can be identified by various methods, including simulations, experiments, reference tables, and predictive analysis, among others.

Thickness 3228 determines an Δ n on HR side 3202 relative to the thermal lens and reduces the guiding ability of lateral waveguide 3206 in the region near HOMSL 3204. In various examples, the thickness may be selected such that the thermal lens is largely compensated to produce a weak index guiding region. This enables weak index guiding of a few lateral modes, or in the extreme case, of only a single lateral mode, at high operating currents on the HR side 3202. Such weakly guided regions may support 10 or fewer lateral modes, or may support only one mode. Thus, the lateral waveguide 3206 at the HR side 3202 supports fewer lateral modes and enables a reduction in slow axis divergence and higher brightness than conventional BALs.

In various examples, HOMSL 3104 and HOMSL3204 may be formed from any of a variety of materials known to those skilled in the art that satisfy the disclosed limitations on the size and relative refractive index sufficient to reduce the magnitude of the index contrast caused by the thermal lens in the lateral waveguide, and claimed subject matter is not limited in this respect. For example, HOMSL 3104 and/or HOMSL3204 may be formed from a variety of materials, including gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (inalgas), and/or indium gallium phosphide (InGaAsP).

Fig. 33A-33D depict various views of the laser diode 3300.

Fig. 33A is a cross-sectional view of a vertical epitaxial layer structure of an example laser diode 3300 that includes a reduced thickness lateral waveguide portion, referred to herein as a HOMSL 3304. Laser diode 3300 is represented by 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 therebetween. 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. The ridge structure 3320 may extend part or the entire longitudinal length of the diode 3300 between the HR side 3202 and the PR side 3222. The HOMSL 3304 may be formed within a lateral waveguide 3312 in a p-type waveguide layer 3316. Alternatively, a reduced thickness transverse waveguide portion HOMSL 3304 may be formed in the n-type waveguide layer 3314. The HOMSL 3304 features may be formed as trenches, segments, channels, etc., or combinations thereof.

Although the HOMSL 3304 is disposed in the lateral waveguide 3212 in the p-type waveguide layer 3316, it is also within the lateral waveguide 3306; thus, the effective index of lateral waveguide 3306 is reduced by the presence of HOMSL 3304.

Fig. 33B is a cross-sectional view of the vertical epitaxial layer structure viewed from the PR side 3322 of the example laser diode 3300 depicted in fig. 33, which includes a HOMSL 3304 disposed within a lateral waveguide 3306. The lateral waveguide 3306 is bounded at a first end by an HR coating face 3324 and at a second end by a PR coating face 3326 in the longitudinal direction. In an example, the HOMSL 3304 is formed in a p-type waveguide layer 3316 (or an n-type waveguide layer 3314). However, because the HOMSL 3304 extends longitudinally from the HR coated face 3324 a length that is less than the distance between the HR face 3324 and the PR face 3326, it is not visible in the epitaxial layers when viewed from the PR side 3322.

Fig. 33C is a plan view of an example laser diode 3200 that includes a HOMSL 3304 disposed within a lateral waveguide and extending from an HR coated face 3324 in a longitudinal direction a length that is less than the distance between the HR face 3324 and a PR face 3326.

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

The addition of the HOMSL 3304 trenches, segments, channels, etc. to the BAL may be performed by a variety of methods known to those skilled in the art, and claimed subject matter is not limited in this respect. For example, the HOMSL 3304 may be formed using a down etch or selective deposition of a thicker layer adjacent to the active stripes.

Fig. 33D is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from the HR side 3302 of an example laser diode 3300 that includes a buried HOMSL 3304 disposed within a lateral waveguide 3306 and extending in a longitudinal direction from the HR coated face 3324. For example, the HR side 3302 extends from the HR coated face 3324 to about a mid-point 3330 (dashed line). The PR side 3322 extends from the PR coated face 3326 to about a mid point 3330.

In the operating state, the HR side 3302 experiences thermal lensing, however, with suppression or compensation of the HOMSL 3304 by providing a thinner portion of the lateral waveguide thickness, the HR side 3302 region becomes weakly index guided, thereby reducing the magnitude of the index contrast on the HR side 3302 caused by thermal lensing. In an example, the thinner the thickness of lateral waveguide 3312, the higher the effective index, which may cause the index of refraction of lateral waveguide 3306 to be lower than the index of refraction of the lateral cladding.

Similar to the HOMSL 3104, thickness 3328 is judiciously chosen in order to reduce the magnitude of the thermal lens induced refractive index contrast on the HR side 3302. The thickness 3328 is selected based on its effect on the magnitude of the refractive index contrast (i.e., the potential effective index contrast on the HR side 3302 of the lateral waveguide 3306). The thickness 3328 of a particular HOMSL 3304 that will substantially reduce the magnitude of the thermal lens induced index contrast on the HR side 3302 can be identified by various methods, including simulations, experiments, reference tables, and predictive analysis, among others.

Thickness 3328 determines Δ n on HR side 3302 relative to the thermal lens and reduces the guiding ability of lateral waveguide 3306 in the region near HOMSL 3304. In various examples, the thickness may be selected such that the thermal lens is largely compensated to produce the weak index guiding region. This enables weak index guiding of few lateral modes, or in the extreme case, only a single lateral mode, at high operating currents on the HR side 3302. Such a weak guiding region may support 10 or fewer lateral modes, or may support only one mode. Thus, lateral waveguide 3306 at HR side 3302 supports fewer lateral modes and enables a reduction in slow-axis divergence and higher brightness than conventional BALs.

Simulation and examples

HOMSL 3104 and HOMSL3204, respectively, may be fabricated by various methods known to those skilled in the art, and claimed subject matter is not limited in this respect. For manufacturing, it may be necessary to determine a suitable thickness of the HOMSL 3104 sufficient to reduce the refractive index contrast on the HR side. This relative difference in Δ n may be considered in the simulation calculation of the relationship between the thickness of HOMSL 3104 and Δ n.

FIG. 34 is a graph 3400 showing simulation results of the effect of thickness on Δ n to approximate the optimized thickness of a buried HOMSL 3104 to compensate for a particular increase in refractive index caused by a thermal lens. A particular HOMSL 3104 may be made of GaAs and formed between the p-type waveguide layer 3116 and the p-type cladding layer 3110, which has a lower refractive index than GaAs. Negative Δ n means a negative lateral refractive index difference between the lateral waveguide and the cladding. Using graph 3400, the thickness of HOMSL 3104 is optimized to compensate for a particular increase in refractive index caused by the thermal lens, and may be approximated. While the simulation is specific to the geometric approach shown in fig. 34, there are other approaches to achieve the weakly index guided HR side 3102 of the emitter. These methods include reducing the lateral waveguide thickness in the active stripes. Both methods will reduce the refractive index contrast between the lateral waveguide and the cladding.

The approximate refractive index compensation required for the thermal lens is determined by using the simulated beam propagation of the waveguide and simultaneously the simulated far field.

Fig. 35 is a graph 3500 showing simulation results predicting far fields of supported modes with and without high-order mode suppression by thermal lens compensation. A specific example is a BAL with a lateral waveguide width of 200um and a typical step index and thermal lens. The reduction in supported modes means that the far field is reduced from about 10.9 degrees to about 4.3 degrees. The slow-axis far-field divergence of various homo-banded BALs at different step indices and thermal lenses was modeled and summarized in the following table:

as described above, the flat index step is used to determine the index contrast necessary to match the far field at low operating powers. The HOM column is the order of the highest order mode predicted.

The foregoing descriptions of various features/structures within laser diodes, epitaxial layer structures, epitaxial layers, and waveguides are merely examples and are included for illustrative purposes; 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.

Having described and illustrated the general and specific principles of examples of the presently disclosed technology, it will be apparent that the examples can be modified in arrangement and detail without departing from such principles. We claim all modifications and variations coming within the spirit and scope of the following claims.

Claims

1. A laser diode, comprising:

a lateral waveguide orthogonal to the lateral waveguide, the lateral waveguide comprising 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 layer on an n-side and a p-type cladding layer on a p-side; and

a lateral waveguide defined at a first end by a High Reflector (HR) coated face and at a second end by a Partial Reflector (PR) coated face along a longitudinal direction, the lateral waveguide further comprising a buried Higher Order Mode Suppression Layer (HOMSL) disposed below the p-type cladding layer and within the lateral waveguide or on one or both sides of the lateral waveguide or a combination thereof, wherein a length of the HOMSL extending from the HR face along the longitudinal direction is less than a distance between the HR face and the PR face.

2. The laser diode of claim 1, wherein the HOMSL disposed on one or both sides of the lateral waveguide has a higher index of refraction than the p-type waveguide layer and the p-cladding layer.

3. The laser diode of claim 1, wherein the HOMSL disposed within the lateral waveguide has a lower index of refraction than the n-type waveguide layer or the p-type waveguide layer, or a combination thereof.

4. The laser diode of claim 1, wherein the thickness of the HOMS is selected based on a magnitude of refractive index contrast within the lateral waveguide caused by a thermal lens effect within the lateral waveguide during operation of the laser diode.

5. The laser diode of claim 4, wherein a thickness of the HOMSL is further selected to reduce a magnitude of the index contrast of the lateral waveguide during operation.

6. The laser diode of claim 5, wherein the refractive index contrast is of a magnitude of 10^-5<Δn<10^-3Within the range of (1).

7. The laser diode of claim 5, wherein the lateral waveguide supports fewer than ten lateral modes.

8. The laser diode of claim 5, wherein the lateral waveguide supports a single lateral mode.

9. The laser diode of claim 1, wherein a thickness of the HOMSL is selected to reduce an effective index on a side of the lateral waveguide extending from the HR facet.

10. The laser diode of claim 1, wherein the HOMSL comprises gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), indium gallium phosphide (InGaAsP).

11. The laser diode of claim 1, wherein the lateral waveguide is bounded in the lateral direction by a ridge waveguide, wherein the ridge waveguide extends from the HR facet to the PR facet.

12. The laser diode of claim 2, wherein the HOMSL laterally overlaps the lateral waveguide with 0-10um overlap on either side, or 0-20um total overlap.

13. The laser diode of claim 3, wherein the HOMSL disposed within the lateral waveguide is laterally narrower than the lateral waveguide by 0-10um on either side or 0-20um total.

14. The laser diode of claim 1, wherein the lateral waveguide is bounded in the lateral direction by a ridge waveguide that extends from the PR facet in a longitudinal direction by a length that is less than a distance between the PR facet and the HR facet.

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

16. The laser diode of claim 1, wherein a thinner low index layer is provided along the width of the lateral waveguide in the region of the HOMSL.