DE112020003385T5 - Method, system and apparatus for higher-order mode suppression - Google Patents

Abstract

A laser diode includes a transverse waveguide orthogonal to a lateral waveguide containing an active layer sandwiched between an n-type waveguide layer and a p-type waveguide layer, the transverse waveguide being separated by an n-type cladding layer on an n- side and a p-type cladding layer on a p-side, and a lateral waveguide which is bounded in the longitudinal direction at a first end by a highly reflective (HR) coated facet and at a second end by a partially reflective (PR) coated facet, the lateral waveguide further including an embedded higher order mode suppression layer (HOMSL) disposed under the p-cladding within the lateral waveguide, or on one or both sides of the lateral waveguide, or a combination thereof is, where the HOMSL extends in a longitudinal direction from the HR facet üb it extends a length that is less than the distance between the HR facet and the PR facet.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims U.S. Provisional Patent Application No. 62/885,946, filed August 13, 2019.

TECHNICAL AREA

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

Lasers are light-emitting devices. Light emission in a laser is the result of optical amplification by stimulated emission of electromagnetic radiation. Some lasers emit spatially and temporally coherent light, which allows the lasers to emit light in a narrow bandwidth of light that can be tightly focused over long distances. There is a wide variety of lasers, e.g. B. Example gas lasers, chemical lasers, dye lasers, metal vapor lasers, solid state lasers and semiconductor lasers. Laser diodes are electrically pumped semiconductor lasers in which an active layer is formed from a p-n junction of a semiconductor diode. Laser diodes typically include an active layer sandwiched between a p-type layer of semiconductor material and an n-type layer of semiconductor material. Many laser diodes are fabricated on a semiconductor substrate, such as gallium arsenide, doped with elements such as aluminum, silicon, zinc, carbon, or selenium to create the n- and p-type semiconductor layers. The active layer is typically undoped gallium indium arsenide and can be only a few nanometers thick.

Laser diodes are fabricated by growing multiple layers of semiconductor materials on a suitable substrate with a lattice constant that allows the choice of materials to produce the desired emission wavelengths. A typical laser diode contains n-type layers, p-type layers and an undoped active layer in between such that when the diode is biased, electrons and holes in the active region layer recombine to produce light. The active layer (quantum wells, quantum wires or quantum dots, type II quantum wells) are in a waveguide layer that has a higher refractive index than the surrounding p- and n-doped cladding layers. Light generated by the active layer is confined in the plane of the waveguide.

A conventional broad area edge-emitting Fabry-Perot laser diode is implemented as a rectangular gain- or index-guided semiconductor structure. The opposing end facets of the waveguide define highly and partially reflective elements to provide feedback for light oscillation within the resonator. The multi-layer laser diode structure extends the length of the laser and has a large width for electrical injection that extends to opposite side surfaces that also extend the length of the laser. The multilayer semiconductor materials are typically designed so that the laser operates in a single mode along the growth direction of the laser, and this direction is defined as the fast axis direction. Since a semiconductor laser operates in a single mode along the fast axis direction, the brightness of a laser diode in this direction cannot be further improved; it is diffraction limited, so to speak. The spacing between the top and bottom surfaces of the multilayer semiconductor laser structure thus constitutes the minor dimension of the end facets, i. H. the thickness of the strip, which is typically of the order of microns. On the other hand, the width of the multilayer laser structure constitutes the major dimension of the end facets, i. H. the stripe width, which is typically on the order of tens of microns to hundreds of microns. This is referred to as the "slow axis". Because the stripe width is much larger than the light wavelength, the lateral property of an optical field propagating along the optical axis of the waveguide is highly multimodal along the wider stripe dimension, and the corresponding axis is described as the slow axis because the divergence angle is much smaller than that on the fast axis related divergence angle is.

"Multimode Laser Diodes" or "Broad Area Lasers" (BALs) are used in high power applications. BALs have multiple slow-axis modes, so their slow-axis beam parameter product (BPP) is higher than that of single-mode laser diodes. In addition, as they operate at higher currents, the thermal lensing effect becomes more pronounced, resulting in higher index contrast profile in the lateral direction, accommodating a larger number of lateral modes. The widening of the lateral divergence angle leads to a degradation of the lateral BPP and brightness (power: BPP) and at the same time a reduction of the brightness related to the slow axis. This means that the brightness related to the slow axis decreases, although the power typically increases with higher current. Brightness can be improved in BALs by reducing the emitter width; however, the current at which maximum brightness occurs is also at lower and lower current values. Thus, the maximum output power drops at maximum brightness.

Higher brightness at higher output power per emitter is desirable for power scaling applications and to reduce cost per watt in manufacturing diode lasers.

SUMMARY

Disclosed are methods, systems and apparatus for reducing the magnitude of the refractive index contrast of a lateral waveguide during operation of a laser diode. This may include a laser diode with a transverse waveguide orthogonal to the lateral waveguide containing an active layer between an n-type waveguide layer and a p-type waveguide layer, the transverse waveguide being covered by an n-type cladding layer an n-side and a p-type cladding layer on a p-side, and a lateral waveguide in a longitudinal direction bounded at a first end by a highly reflective (HR) coated facet and at a second end by a partially reflective (PR) coated facet facet, the lateral waveguide further including an embedded higher order mode suppression layer (HOMSL) disposed within the lateral waveguide under the p-cladding, or on one or both sides of the lateral waveguide, or a combination thereof , where the HOMSL extend in the longitudinal direction from the HR facet over ei ne length that is less than the distance between the HR facet and the PR facet.

A refractive index of the HOMSL located on one or both sides of the lateral waveguide may be higher than that of the p-type waveguide layer and the p-cladding layer in some examples.

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

A thickness of the HOMSL may be selected based on a magnitude of the refractive index contrast in the lateral waveguide induced by thermal lensing within the lateral waveguide during operation of the laser diode. The size of the refractive index contrast can be in a range of 10 ^-5 <Δn<10 ^-3 . In some examples, such a lateral waveguide supports fewer than 10 lateral modes or only a single lateral mode.

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

In some examples, the HOMSL overlaps the lateral waveguide by 0-10 µm on each side, or by 0-20 µm overall.

In some examples, the HOMSL located within the lateral waveguide is laterally narrower than the lateral waveguide by 0-10 µm on each side or by 0-20 µm overall.

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

In some examples, the HOMSL has a reduced transverse waveguide thickness in the active stripe and can be formed either by etching away or selectively depositing thicker layers adjacent to the active stripe.

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

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

character list

• 1 zeigt ein effektives laterales Indexprofil für eine beispielhafte Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, die angrenzend an einen lateralen Wellenleiter angeordnet ist;
• 2 zeigt ein laterales Indexprofil und eine modale Modellierung für eine beispielhafte Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, die angrenzend an den lateralen Wellenleiter angeordnet ist;
• 3 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter angeordnet ist;
• 4 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter angeordnet ist;
• 5 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter angeordnet ist;
• 6 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter angeordnet ist;
• 7 zeigt eine Draufsicht, die einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 8 zeigt eine Draufsicht, die einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 9 zeigt eine Draufsicht eines beispielhaften lateralen Wellenleiters einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung auf nur einer der Seiten angeordnet ist;
• 10 zeigt eine Draufsicht, die einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 11 zeigt eine Draufsicht, die einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung auf nur eine Seite angeordnet ist;
• 12 zeigt eine Draufsicht, die einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 13 zeigt eine Draufsicht auf einen beispielhaften lateralen Wellenleiter einer Breitstreifenlaserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung auf eine Seite angeordnet ist;
• 14 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung angeordnet ist;
• 15 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung angeordnet ist;
• 16 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung auf nur eine Seite angeordnet ist;
• 17 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung angeordnet ist;
• 18 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung auf nur eine Seite angeordnet ist;
• 19 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung angeordnet ist;
• 20 zeigt eine Draufsicht, die einen beispielhaften aufgeweiteten Laseroszillator-Wellenleiter (d. h. lateralen Wellenleiter) einer Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Teillängen-Schicht zeigt, die angrenzend an den aufgeweiteten Laseroszillator-Wellenleiter in Längsrichtung auf nur eine Seite angeordnet ist;
• 21A zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema und einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 21B zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema und einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 22 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema und einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 23 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema und einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 24 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema und einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 25 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 26 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht zeigt, die angrenzend an den lateralen Wellenleiter in Längsrichtung angeordnet ist;
• 27 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema zeigt;
• 28 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema zeigt;
• 29 zeigt eine perspektivische Querschnittsansicht, die eine vertikale Epitaxialschichtstruktur einer beispielhaften Laserdiode mit einem angepassten n-seitigen Strominjektionsschema zeigt;
• 30A ist ein Graph, der ein herkömmliches Stufenindexprofil in transversaler Richtung einer Einzelemitterlaserdiode bei Betrieb mit geringer Leistung ohne signifikante thermische Linsenwirkung zeigt;
• 30B ist ein Graph, der ein Stufenindexprofil mit einem hinzugefügten parabolischen Profil zeigt;
• 30C ist ein Graph, der ein beispielhaftes „negatives“ Stufenindexprofil mit einem hinzugefügten parabolischen Profil zeigt, welches das Indexprofil in dem Bereich mit negativer Kompensation modelliert;
• 31A ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die auf benachbarten Seiten eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 31B ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der teilreflektierenden (PR) Seite der in 31A dargestellten beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die auf benachbarten Seiten eines lateralen Wellenleiters angeordnet sind;
• 31C ist eine Draufsicht auf eine beispielhafte Laserdiode mit einer eingebetteten, zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, die auf benachbarten Seiten eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 31D ist eine perspektivische Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die auf benachbarten Seiten eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 32A ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 32B ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der teilreflektierenden (PR) Seite der in 32A gezeigten beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 32C ist eine Draufsicht auf eine beispielhafte Laserdiode mit einer eingebetteten, zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, die innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 32D ist eine perspektivische Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine eingebettete, zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 33A ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die einen Wellenleiterabschnitt mit verringerter Dicke aufweist, der innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 33B ist eine Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der teilreflektierenden (PR) Seite der in 33A dargestellten beispielhaften Laserdiode her gesehen, die eine zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht aufweist, die einen Wellenleiterabschnitt verringerter Dicke hat, der innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 33C ist eine Draufsicht einer beispielhaften Laserdiode mit einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, die einen Wellenleiterabschnitt verringerte Dicke aufweist, der innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt;
• 33D ist eine perspektivische Querschnittsansicht einer vertikalen Epitaxialschichtstruktur, von der hochreflektierenden (HR) Seite einer beispielhaften Laserdiode her gesehen, die eine zur Unterdrückung von Moden höherer Ordnung bestimmte Schicht enthält, die einen Wellenleiterabschnitt verringerter Dicke aufweist, der innerhalb eines lateralen Wellenleiters angeordnet ist und sich in Längsrichtung erstreckt.
• 34 ist ein beispielhaftes Diagramm 3400 zur Approximation einer optimierten Dicke einer zur Unterdrückung von Moden höherer Ordnung bestimmten Schicht, um ein spezifisches Delta in dem Index, das durch eine thermische Linsenwirkung verursacht wird, zu kompensieren; und
• 35 ist ein Graph 3500, der eine Simulation veranschaulicht, die beispielhafte Fernfelder von unterstützten Moden mit und ohne Unterdrückung von Moden höherer Ordnung durch Kompensation der thermischen Linsenwirkung vorhersagt.

The accompanying drawings, in which like reference numbers represent like elements, constitute a part of this specification and, together with the description, explain the advantages and principles of the technology disclosed herein. in the drawings,

• 1 Figure 12 shows an effective lateral index profile for an exemplary laser diode with a higher order mode suppression layer disposed adjacent a lateral waveguide;
• 2 Figure 12 shows a lateral index profile and modal modeling for an exemplary laser diode with a higher order mode suppression layer disposed adjacent to the lateral waveguide;
• 3 Figure 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher order mode suppression layer disposed adjacent the lateral waveguide;
• 4 Figure 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher order mode suppression layer disposed adjacent the lateral waveguide;
• 5 Figure 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher order mode suppression layer disposed adjacent the lateral waveguide;
• 6 Figure 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher order mode suppression layer disposed adjacent the lateral waveguide;
• 7 12 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a higher-order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 8th Fig. 12 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a part-length layer intended for higher-order mode suppression disposed longitudinally adjacent to the lateral waveguide;
• 9 Fig. 12 shows a plan view of an exemplary lateral waveguide of a broad area laser diode with a partial length layer intended for higher order mode suppression disposed longitudinally adjacent to the lateral waveguide on only one of the sides;
• 10 12 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a higher-order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 11 Fig. 14 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a partial length layer intended for higher order mode suppression disposed longitudinally adjacent to the lateral waveguide on only one side;
• 12 Fig. 12 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a part-length layer intended for higher-order mode suppression disposed longitudinally adjacent to the lateral waveguide;
• 13 Figure 12 shows a plan view of an exemplary lateral waveguide of a broad area laser diode with a part-length layer intended for higher order mode suppression disposed adjacent the flared laser oscillator waveguide longitudinally on one side;
• 14 12 is a plan view showing an exemplary laser oscillator expanded waveguide (ie, lateral waveguide) of a laser diode having a higher-order mode suppression layer disposed adjacent to the laser oscillator expanded waveguide in the longitudinal direction;
• 15 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed longitudinally adjacent to the laser oscillator flared waveguide;
• 16 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed adjacent to the laser oscillator flared waveguide in the longitudinal direction on only one side;
• 17 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed longitudinally adjacent to the laser oscillator flared waveguide;
• 18 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed adjacent to the laser oscillator flared waveguide in the longitudinal direction on only one side;
• 19 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed longitudinally adjacent to the laser oscillator flared waveguide;
• 20 Fig. 12 is a plan view showing an exemplary laser oscillator flared waveguide (ie, lateral waveguide) of a laser diode with a partial-length higher-order mode suppression layer disposed adjacent to the laser oscillator flared waveguide in the longitudinal direction on only one side;
• 21A Figure 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme and a higher order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 21B Figure 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme and a higher order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 22 Figure 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme and a higher order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 23 Figure 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme and a higher order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 24 Figure 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme and a higher order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 25 Fig. 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher-order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 26 Fig. 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher-order mode suppression layer longitudinally disposed adjacent the lateral waveguide;
• 27 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme;
• 28 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme;
• 29 12 is a perspective cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with an adapted n-side current injection scheme;
• 30A Figure 12 is a graph showing a conventional step index profile in the transverse direction of a single emitter laser diode operating at low power without significant thermal lensing;
• 30B Fig. 14 is a graph showing a step index profile with a parabolic profile added;
• 30C Figure 12 is a graph showing an example "negative" step index profile with an added parabolic profile that models the index profile in the negative compensation region;
• 31A Figure 12 is a cross-sectional view of a vertical epitaxial layer structure, viewed from the highly reflective (HR) side of an exemplary laser diode, including an embedded higher order mode suppression layer disposed on adjacent sides of a lateral waveguide and extending longitudinally;
• 31B Fig. 12 is a cross-sectional view of a vertical epitaxial layer structure taken from the partially reflective (PR) side of Figs 31A As seen from the exemplary laser diode illustrated, which includes an embedded higher-order mode suppression layer disposed on adjacent sides of a lateral waveguide;
• 31C Figure 12 is a plan view of an exemplary laser diode having an embedded higher order mode suppression layer disposed on adjacent sides of a lateral waveguide and extending longitudinally;
• 31D Figure 12 is a perspective cross-sectional view of a vertical epitaxial layer structure, viewed from the highly reflective (HR) side of an exemplary laser diode, including an embedded higher order mode suppression layer disposed on adjacent sides of a lateral waveguide and extending longitudinally;
• 32A Figure 13 is a cross-sectional view of a vertical epitaxial layer structure, viewed from the highly reflective (HR) side of an exemplary laser diode, including an embedded higher order mode suppression layer disposed within a lateral waveguide and extending longitudinally;
• 32B Fig. 12 is a cross-sectional view of a vertical epitaxial layer structure taken from the partially reflective (PR) side of Figs 32A Referring to the exemplary laser diode shown, which includes an embedded higher order mode suppression layer disposed within a lateral waveguide and extending longitudinally;
• 32C Figure 12 is a plan view of an exemplary laser diode having an embedded higher order mode suppression layer disposed within a lateral waveguide and extending longitudinally;
• 32D Figure 12 is a perspective cross-sectional view of a vertical epitaxial layer structure, viewed from the highly reflective (HR) side of an exemplary laser diode, including an embedded higher order mode suppression layer disposed within a lateral waveguide and extending longitudinally;
• 33A Figure 12 is a cross-sectional view of a vertical epitaxial layer structure, viewed from the highly reflective (HR) side of an exemplary laser diode, including a higher-order mode suppression layer having a reduced-thickness waveguide portion disposed within a lateral waveguide and extending into extends longitudinally;
• 33B Fig. 12 is a cross-sectional view of a vertical epitaxial layer structure taken from the partially reflective (PR) side of Figs 33A illustrated exemplary laser diode seen from here, which has a specific for suppression of higher-order modes layer that verrin a waveguide section gerter thickness disposed within a lateral waveguide and extending longitudinally;
• 33C Figure 12 is a plan view of an exemplary laser diode with a higher order mode suppression layer having a reduced thickness waveguide portion disposed within a lateral waveguide and extending longitudinally;
• 33D Fig. 12 is a perspective cross-sectional view of a vertical epitaxial layer structure seen from the highly reflective (HR) side of an exemplary laser diode including a higher order mode suppression layer having a reduced thickness waveguide portion disposed within a lateral waveguide and extending into extends longitudinally.
• 34 Figure 3400 is an example plot 3400 for approximating an optimized thickness of a higher order mode suppression layer to compensate for a specific delta in index caused by thermal lensing; and
• 35 FIG. 3500 is a graph illustrating a simulation that predicts exemplary far-fields of supported modes with and without suppression of higher-order modes through thermal lensing compensation.

DETAILED DESCRIPTION

As used in this application and the claims, the singular forms "a" and "the" include the plural forms unless the context clearly dictates otherwise. In addition, the term "contains" has the meaning "comprises". Furthermore, the term "coupled" does not exclude the presence of intermediate elements between the coupled elements.

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, whether alone or in various combinations and sub-combinations. The disclosed systems, methods, and devices are not limited to any particular aspect, feature, or combinations thereof, nor do the disclosed systems, methods, and devices require that one or more specific advantages be present or problems be solved. All principles of operation are intended to facilitate explanation, however, the disclosed systems, methods, and devices are not limited to such principles of operation.

Although the operations of some of the disclosed methods are described in a particular sequential order for convenience in presentation, it should be understood that this manner of description includes rearrangement unless specific language used hereinafter requires a particular order . For example, operations described sequentially may in some cases be reordered or performed concurrently. Furthermore, for the sake of simplicity, the accompanying figures show the various ways in which the disclosed systems, methods, and devices can be used in conjunction with other systems, methods, and devices. Additionally, terms such as "create" and "provide" are occasionally used in the description to describe the disclosed technology. These terms represent high-level abstractions of the actual operations performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily apparent to one skilled in the art.

In some examples, values, procedures, or facilities are labeled "lowest/least," "best," "minimum," or the like. It is understood that such descriptions are intended to indicate that a choice can be made among many functional alternatives used, and such choices need not be better, smaller, or otherwise preferable to other choices. Examples are described with reference to directions labeled "up," "down," "upper," "lower," and the like. These terms are used to facilitate description but do not imply a particular spatial orientation.

As discussed above, it is desirable to be able to efficiently scale power and improve brightness in BALs while minimizing output power-related penalties. Methods, systems and devices are described here which are aimed at higher brightness at higher output power direction by reducing the divergence angle related to the slow axis without reducing the emitter width. The goal is to suppress the higher order modes in the slow axis while preserving the lower order lasing modes.

Higher order mode suppression layer (HOMSL)

In order to overcome the disadvantages of conventional laser diodes discussed above in the Background section, what is needed is a laser diode that is configured to reject higher-order modes in the lateral direction (i.e. orthogonal to the direction of propagation) while preserving lower-order light modes. This can be achieved by placing higher order mode suppression structures adjacent to the lateral waveguide of the laser diode. Higher order mode suppression structures may include a variety of materials and may be index-guided, anti-wave-guided, and/or high-loss structures.

In one example, the higher order mode suppression layer (HOMSL) may be disposed adjacent the lateral waveguide at or near the back facet and may extend less than the full longitudinal length of the waveguide. The HOMSL may include: index-guided structures, anti-wave-guided structures, and/or high-loss structures. For example, the index-guided, anti-wave-guided, and/or lossy structures may extend up to 20%, or in another example between 5%-50% of the length of the waveguide measured from the back facet. If the HOMSL extends only a short longitudinal distance, the loss for the non-suppressed modes of the laser diode is minimized and the diode can operate more efficiently than if a HOMSL structure extended the full length.

In another example, the HOMSL may be placed adjacent to a flared laser oscillator waveguide and extend either a full longitudinal length of the waveguide or a partial longitudinal length of the waveguide as measured from the rear facet. By constructing the diode in this way, the advantage of reducing higher order modes by suppressing them using the HOMSL can be combined with the advantages of using a laser oscillator expanded waveguide (FLOW) as shown in FIG U.S. Patent No. 9,166,369 which is incorporated herein by reference.

In another example, a laser diode may include an embedded high- and low-index, high-loss aperiodic structure in the high-index material disposed adjacent the waveguide along the longitudinal direction. The aperiodic structure can suppress higher-order modes by disproportionately overlapping higher-order modes compared to lower-order modes and/or the fundamental mode. The aperiodic structures are chosen to introduce high losses for higher order modes but minimize losses for lower order modes and/or the fundamental mode. The aperiodic structure can be arranged over the entire length of the waveguide along the longitudinal direction or over a shorter length extending from the rear facet. The aperiodic structure can also be arranged along the longitudinal direction of a broad area laser (BAL) or a laser oscillator expanded waveguide.

1 FIG. 12 depicts the index profile 100 showing the relative refractive index for an exemplary lateral waveguide with adjacent HOMSL. A portion 102 of the index profile 100 represents the relative index of refraction of the lateral waveguide versus portions 104 representing the relative index of refraction of the adjacent HOMSL.

In one example, the HOMSL is an anti-wave guided structure that includes a variety of materials with a refractive index higher than the refractive index of the waveguide. The HOMSL can include a variety of doped and undoped materials. The HOMSL material can be judiciously chosen to optimize efficiency over the BPP under the laser operating conditions. Some examples of anti-wave guided HOMSL materials in the case where the original waveguide contains aluminum gallium arsenide (AlGaAs) include doped gallium arsenide (GaAs), indium gallium arsenide (InGaAs), or the like, or combinations thereof. Other combinations of materials forming the waveguide and anti-wave guided structures will occur to those skilled in the art and the claimed subject matter is not limited in such respects.

2 FIG. 20 depicts the index profile 200 that describes the relative index of refraction for an exemplary lateral waveguide with a HOSML placed adjacent to the lateral waveguide and a shows modal modeling for some of the first lateral waveguide modes. A portion 202 of the index profile 200 represents the relative index of refraction of the lateral waveguide versus portion 204 representing the relative indices of refraction of the HOMSL. In one example, the HOMSL is an index-guided aperiodic structure containing high and low index materials with high loss in the high index material that overlaps higher order modes disproportionately compared to the lower orders/fundamental modes. In one example, the low index material has an index of refraction that is lower than the effective index of refraction of the lateral waveguide and the high index material has an index of refraction that is higher than the effective index of refraction of the lateral waveguide. Sections 204 show the relative indices of the aperiodic structure with high and low index materials. The mean refractive index of the HOMSL may be lower than the modal index, such that the HOMSL is in the index-guided regime rather than the anti-guided regime, however, the locally high index regions pull in the electric field or intensity and interact locally with the material and lead high loss in the higher order modes. A modal modeling 206 illustrates the modal behavior of modes 0-4. The higher the mode number, the more overlap the mode has with the high-index region of the HOMSL, so the loss in the higher-order modes is higher compared to the lower-order (210-216)/fundamental (208) modes.

The examples in the 3-26 show examples of quantum well lasers for simplicity and illustrative purposes. However, various other types of lasers can be configured to have HOMSL features, such as: B. double heterostructure lasers, interband cascade lasers, Bragg mirror lasers, lasers with distributed feedback, quantum cascade lasers, lasers with a radiation vertical to the cavity surface (VCSEL) and / or lasers with a radiation vertical to external cavity surface (VECSEL), just to name a few. Therefore, the claimed subject matter is not limited to quantum well laser diodes.

3 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher-order mode suppression layer disposed adjacent to the lateral waveguide. In one example, a laser diode 300 is a quantum well laser.

In one 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. FIG. A quantum well 302 is located between the n-type semiconductor layer 306 and the p-type semiconductor layer 308. An n-cladding layer 310 is arranged outside the n-type semiconductor layer 306. FIG. A p-cladding layer 312 is arranged outside the p-type semiconductor layer 308. FIG. An n-metal contact 314 is arranged on the n-substrate 304. FIG. A p-metal contact 316 is disposed under the p-cladding layer 312. FIG. The quantum well 302, the n-type semiconductor layer 306 and the p-type semiconductor layer 308 form a transverse waveguide section 318 of the laser diode 300. The boundary of the lateral waveguide 340 is illustrated by dotted lines extending to the n-metal contact 314 along the extend in the longitudinal direction.

The lateral beam size of the 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 light wavelength, many modes are generated in the lateral direction. The HOMSL 320 is arranged adjacent to the lateral waveguide 340 along the longitudinal direction. In 3 Furthermore, the HOMSL 320 is located between air and the p-cladding layer 312 outside of the transverse waveguide 318 . However, it is not necessary for the HOMSL 320 to be there. The HOMSL 320 can be located in a variety of positions in the epitaxial structure, and the claimed subject matter is not limited in these respects.

In one example, the HOMSL 320 includes a high-index material, with the index of the HOMSL 320 being higher than the index of the lateral waveguide 340. The HOMSL 320 is configured to introduce differentially more loss for higher-order modes, reducing them in the lateral direction (ie orthogonal to propagation) can be suppressed. The inclusion of this high index embedded or surface material causes disproportionate antiguiding of higher order modes that overlap the high index material compared to lower order/fundamental modes.

A variety of known materials and methods may be used to fabricate the laser diode 300 . 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 310 and/or the p-cladding 318 can be grown on the GaAs substrate 304 and can contain one of the following materials: indium (In), gallium (Ga), aluminum (Al), arsenic (As), phosphorus (P), gallium arsenide (GaAs), indium phosphide (InP), or the like, or any combination thereof. N-type and p-type layers can be doped with dopants to produce the desired n-type or p-type materials. The claimed subject matter is not limited in this regard.

The material for the HOMSL 320 may be an absorbing material so that it absorbs higher order modes to optimize efficiency versus beam parameter product (BPP) under the operating conditions. The material of the HOMSL 320 can be absorbent or non-absorbent.

4 12 is a cross-sectional perspective view illustrating a vertical epitaxial layer structure of an exemplary laser diode with a higher-order mode suppression layer disposed adjacent the lateral waveguide. In one example, the laser diode 400 is a quantum well laser similar to that in FIG 3 shown laser diode. However, the laser diode 400 includes a HOMSL 402 that includes an absorbing material. The absorbing material chosen for the HOMSL 402 may include a semiconductor material such as those mentioned above, metal (e.g. titanium (Ti) or nickel (Ni)) or semi-metal (e.g. tin (Sn) or As). The HOMSL material 402 can be doped or undoped. The HOMSL 402 may be epitaxially grown or deposited on the surface of the substrate 304 instead of being buried. 5 12 is a cross-sectional perspective view illustrating a vertical epitaxial layer structure of an exemplary laser diode with a higher-order mode suppression layer disposed adjacent the lateral waveguide. In one example, the laser diode 500 is a quantum well laser similar to that in FIG 3 shown laser diode. However, the laser diode 500 includes an aperiodic HOMSL structure 502 comprising high and low index materials. A low-index material 506 has a lower index of refraction than a high-index material 504 and than the effective index of the lateral waveguide 340. The high-index material 504 and the low-index material 506 may contain the same materials doped differently to achieve different indices of refraction, or they may entirely contain different materials. For example, the high index material 504 may include a deposited dielectric or semiconductor, and the low index material may include air, dielectric, or semiconductor materials.

In one example, the low and high index materials extend outwardly from the sides of the lateral waveguide 314 in an alternating sequence. The low index material 506 is located adjacent to the lateral waveguide 340 . The low index material 506 is closer to the lateral waveguide 340 than the high index material 340. The high index material 504 is located outside of the low index material 506. FIG. The pattern of high index/low index material may be aperiodically repeated in the HOMSL structure 502 a number of times. As mentioned above, the aperiodic structure of the HOMSL 502 can have an average refractive index that is lower than the effective modal index in the lateral waveguide or higher than the modal index of the lateral waveguide. The materials selected for the aperiodic structure of the HOMSL 502 are chosen to introduce high loss for higher order modes but minimize loss for lower order/fundamental modes.

6 12 is a cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode with a higher order mode suppression layer disposed adjacent to the lateral waveguide. In one example, a laser diode 600 is a quantum well laser similar to that in FIG 5 shown laser diode. However, the laser diode 600 includes a HOMSL 502 located on one side of the lateral waveguide 340 only. In one example, HOMSL 502 is configured to suppress higher order modes when distributed asymmetrically (as in this configuration) about waveguide 340 and/or when HOMSL structures are symmetrically placed about waveguide 340.

7 12 is a plan view showing an exemplary lateral waveguide of a broad stripe laser diode with a higher-order mode suppression layer disposed adjacent to the lateral waveguide along the longitudinal direction. In one example, a broad area laser diode 700 includes a HOMSL 702 symmetrically placed about the lateral waveguide. The HOMSL 702 is an aperiodic layered structure designed to suppress higher order modes, comprising a region of low index material 706 alternating with a region of high index material 704 . The low index material 706 has an index of refraction that is lower than the effective index of refraction of the materials making up the lateral waveguide 340 . The HOMSL 702 extends the entire length of the lateral waveguide 340 from the rear facet 730 to the front facet 732.

8th 12 is a plan view showing an exemplary lateral waveguide of a broad area laser diode with a higher-order mode suppression layer disposed adjacent to the lateral waveguide along the longitudinal direction. In one example, a broad stripe laser 800 includes a truncated HOMSL 802 symmetrically placed about the lateral waveguide. The HOMSL 802 includes an aperiodic higher-order mode suppression layer comprising a low-index material 806 that is compatible with a high-index material 804 similar to that in FIG 5 shown alternates. However, the HOMSL 802 does not extend the full length of the lateral waveguide 340 from the rear facet 730 to the front facet 732. Rather, the HOMSL 802 extends only part of the length of the lateral waveguide 340, starting from the rear facet 730 The rear facet 730 is covered with a highly reflective (HR) coating and the front facet 732 is covered with a partially reflective (PR) coating. The fact that the HOMSL 802 only extends a short length from the rear facet 730 has the advantage that the loss for non-suppressed modes is minimized, allowing the laser diode to operate efficiently without the loss for lower order/ to significantly increase the fundamental mode, since the total intensity of the forward and backward propagating fields along the longitudinal direction is smaller towards the rear facet than towards the front facet. Thus the losses are proportionally smaller.

9 12 is a cross-sectional view showing an exemplary waveguide of a broad area laser diode with a higher-order mode suppression layer disposed adjacent the waveguide. In one example, a broad area laser 900 includes a truncated HOMSL 902 disposed asymmetrically about the lateral waveguide 340 along the longitudinal direction. HOMSL 902 includes an aperiodic, higher-order mode suppression layer structure comprising low-index materials 906 that interact with high-index materials 904 similar to FIG 8th alternate. A single HOMSL feature 902 extends only part of the length of the lateral waveguide 340 from the back facet 730. The back facet 730 is covered with an HR coating and the front facet 732 is covered with a PR coating. Again, the fact that the HOMSL extends only a short length from the rear facet 730 has the advantage of minimizing the loss for non-suppressed modes, allowing the laser diode to operate efficiently without the loss for lower order/ to increase the basic mode significantly.

10 12 is a cross-sectional plan view showing an exemplary broad area laser diode waveguide with a higher order mode suppression layer disposed adjacent the waveguide. In one example, a broad stripe laser 1000 includes a truncated HOMSL 1002 symmetrically disposed about lateral waveguide 340. FIG. The HOMSL 1002 includes a high index material that is configured such that its index of refraction is greater than the index of refraction of the lateral waveguide 340 . The high-index material of the HOMSL 1002 is able to suppress higher-order modes generated by antiguiding in the lateral waveguide 340 that overlap with the high-index material of the HOMSL 1000, while having little to no effect on lower-order/fundamental modes generated therein there is very little overlap between the lower order/fundamental modes and the high index material.

11 12 is a cross-sectional plan view showing an exemplary broad area laser diode waveguide with a higher order mode suppression layer disposed adjacent the waveguide. In one example, a broad area laser 1100 includes a truncated HOMSL 1102 placed asymmetrically about the lateral waveguide. The HOMSL 1102 contains a high index material similar to the im 10 shown. The HOMSL 1102 provides antiguiding for the higher order modes generated in the lateral waveguide 340 . The HOMSL 1102 is not required to be symmetrically distributed about the lateral waveguide 340 to provide anti-guiding with respect to at least some of the higher order modes. Furthermore, the single HOMSL feature 1102 extends only part of the length of the lateral waveguide 340 from the rear facet 730. The rear facet 730 is covered with an HR coating and the front facet 732 is covered with a PR coating . Again, the fact that the HOMSL 1102 only extends a small distance from the rear facet 1130 has the advantage that higher order modes are suppressed while the loss for non-unsuppressed modes is minimized so that the laser diode operates more efficiently , without significantly increasing the loss for lower-order and/or fundamental modes.

5 12 is a cross-sectional plan view showing an exemplary broad area laser waveguide with a higher-order mode suppression layer disposed adjacent a waveguide. In one example, a broad stripe laser 1200 includes a truncated HOMSL 1202 symmetrically disposed about lateral waveguide 340. FIG. The HOMSL 1202 includes an absorbing material composed of a semiconductor material in a variety of compositions, dopings, crystallinities and/or morphologies; from semimetals; or metals. The absorbing material has the function of suppressing higher order modes in the lateral direction in the lateral waveguide 340 by disproportionately increasing the round trip loss of the higher order modes. The HOMSL does not extend from the rear facet 730 over the full length of the lateral waveguide 340. The fact that the HOMSL 1202 extends from the rear facet 730 only over a short length has the advantage that the loss for the non-suppressed modes is minimized so that the laser diode operates more efficiently without significantly increasing the loss for the higher-order/fundamental modes.

13 12 is a cross-sectional plan view showing an exemplary laser oscillator flared waveguide with a higher-order mode suppression layer disposed adjacent a waveguide. In one example, a broad area laser 1300 includes a truncated HOMSL 1302 disposed asymmetrically about lateral waveguide 340. FIG. The HOMSL 1302 contains an absorbent material similar to that in 12 shown. The HOMSL 1302 disproportionately absorbs higher-order modes in the lateral waveguide 340, thereby suppressing higher-order modes that spatially overlap the HOMSL 1302 more. Therefore, the HOMSL 1302 suppresses higher order modes, while minimizing the impact on lower order modes and the fundamental mode. In addition, the single HOMSL feature 1302 extends from the rear facet 730 for only part of the length of the lateral waveguide 340. The rear facet 1330 is covered with an HR coating and the front facet 732 is covered with a PR coating . The fact that the HOMSL 1302 extends only a short length from the rear facet 730 has the advantage that higher order modes are suppressed while the loss for the non-suppressed modes is minimized, so that the laser diode operates more efficiently. without significantly increasing the loss for lower order/fundamental modes.

14 FIG. 14 is a plan view illustrating an exemplary laser oscillator flared waveguide with a higher order mode suppression layer disposed adjacent to a waveguide. In one example, a laser 1400 includes a laser oscillator flared waveguide (FLOW) 1418, which may be used in place of a broad area rectangular laser waveguide. The FLOW 1440 has a flared current injection region that extends and flares along the longitudinal direction between the rear facet 730, which has a highly reflective (HR) coating, and the front facet 732, which has a partially reflective (PR) coating. By reducing the width of the electrically pumped stripe towards the highly reflective facet, the higher order modes with larger divergence angles are prevented from being coupled back into the laser. The slow axis divergence of the laser is therefore smaller than for a device with rectangular geometry having the same width for the sub-reflector. Furthermore, light propagating in the expanded current injection region closer to the front PR facet 732 can form a thermal waveguide closer to the width of the narrower rear HR facet 730, resulting in a beam output at the front facet 732 with a much smaller beam width than the front facet 732 width. As a result, the beam parameter product BPP (width of the slow-axis near-field times the slow-axis divergence) is smaller for FLOW devices than for BAL devices. Because the near field is smaller than the physical width on the front facet 732 side, FLOW devices can be constructed with a larger total area than BAL without compromising the BPP. The increased total pumped area provided by the expansion of the expanded current injection area serves to reduce the thermal resistance and electrical series resistance in the device, resulting in higher electrical-to-optical power conversion efficiency. Compared to BAL devices, this results in higher output power for a given operating current. Higher power and smaller BPP result in increased beam brightness in the slow axis. In addition to being applied to broad area diode lasers, the FLOW concept can also be applied to other types of semiconductor-based Fabry-Perot lasers, such as: B. Quantum Cascade Laser (QCL), Interband Quantum Cascade Laser (IQL). Broad area diode lasers with expanded laser oscillator waveguides can also find special uses in particular in laser diode modules that can be configured for various applications such as fiber coupling and direct pumping.

In one example, HOSML 1402 may include an aperiodic structure of a first layer of low index material 1406, where the index of low index material 1406 is less than the effective index of refraction of the material making up FLOW 1440. The HOMSL 1402 further includes a second layer of high index material 1404, the index of the high index material 1404 being higher or lower ner than the effective index of refraction of the material forming the FLOW 1440. As above with reference to 5 described, the HOMSL 1402 may be in the index-guided or the anti-guided regime. Still referring to 14 For example, coupling the HOMSL 1402 to the FLOW 1440 combines the higher order mode suppression effects that could be achieved with either the HOMSL 1402 or the FLOW 1440 alone, thereby further reducing the BPP.

15 12 is a cross-sectional plan view showing an exemplary laser oscillator flared waveguide with a higher-order mode suppression layer disposed adjacent the waveguide. In one example, a laser diode 1500 includes the FLOW 1440 and a truncated HOMSL 1502 symmetrically placed about the FLOW 1440. FIG. The HOMSL 1502 includes an aperiodic structure comprising a low index material 1506 and a high index material 1504, as shown in FIG 14 is composed as described. In one example, the HOMSL 1502 extends from the rear facet 730 only a portion of the length of the FLOW 1440. The HOMSL 1502 is not located close to the front facet 730. FIG. This architecture combines the higher order mode suppression achieved by a HOMSL structure in combination with a FLOW structure, since the HOMSL 1502 extends less than the full length of the FLOW 1440, thereby minimizing the loss for non-suppressed modes, so that the laser diode operates efficiently without significantly increasing the loss for the lower order/fundamental modes, as referred to in FIG 8th is explained.

16 Fig. 12 is a cross-sectional plan view showing an example of a flared laser oscillator waveguide having a higher order mode suppression layer disposed adjacent to the waveguide. In one example, a laser diode 1600 may include a HOMSL 1602 distributed asymmetrically around a FLOW 1440. FIG. The HOMSL 1602 may only extend a partial length of the FLOW 1440 from the rear facet 730 . In one example, a single truncated HOMSL 1602 can operate in combination with the FLOW 1440 to efficiently suppress higher order modes. Such an architecture is desirable, for example, to save material costs or to accommodate other structures in the epitaxial layer structure of the laser diode 1600.

17 12 is a plan view illustrating an exemplary laser diode waveguide with a higher-order mode suppression layer disposed adjacent the waveguide. In one example, a laser diode 1700 includes the FLOW 1440 and a HOMSL 1702 symmetrically placed about the FLOW 1440. FIG. The HOMSL 1702 is truncated, extending only part of the length of the FLOW 1440 from the rear facet 730. The HOMSL 1702 is a high index material compared to the material used in the FLOW 1440. Narrowing the width of the electrically pumped stripe of FLOW 1440 towards the highly reflective facet prevents the higher order modes with higher divergence angles from being coupled back into the laser. The shortened HOMSL 1702 provides further higher order mode suppression by disproportionately antiguiding higher order modes that overlap with the high index material towards the HR facet.

18 FIG. 14 is a plan view illustrating an exemplary laser waveguide with a higher-order mode suppression layer disposed adjacent a waveguide. In one example, a laser 1800 includes a truncated HOMSL 1802 distributed asymmetrically around the FLOW 1440. The HOMSL 1802 can be a high index material similar to that in 17 included. The HOMSL 1802 may only extend a partial length from the rear facet 730 of the FLOW 1440 . The only shortened HOMSL 1802 can work in combination with the FLOW 1440 in such a way that higher order modes are efficiently suppressed. This architecture is desirable, for example, to save on material costs or to accommodate other structures in the laser 1800 epitaxial layer structure.

19 FIG. 14 is a plan view illustrating an exemplary laser oscillator flared waveguide with a higher-order mode suppression layer disposed adjacent to the waveguide. In one example, a laser diode 1900 contains the FLOW 1440. A HOSML 1902 is symmetrically placed around the FLOW 1440. The HOMSL 1902 is truncated, extending only part of the length of the FLOW 1440 from the rear facet 730. The HOMSL 1902 contains absorbent material. As referring to 4 discussed, the absorbing material preferentially introduces higher loss for the higher order modes and thereby suppresses higher order modes that spatially overlap the HOMSL 1902.

20 12 is a cross-sectional plan view showing an exemplary laser oscillator flared waveguide with a higher-order mode suppression layer disposed adjacent the waveguide. In an example, a laser 2000 may include a truncated HOMSL 2002 symmetrically distributed around FLOW 1440 . The HOMSL 2002 may use an absorbent material similar to that referred to 19 included. The HOMSL 2002 may only extend a partial length from the rear facet 730 of the FLOW 1440 . A single truncated HOMSL 2002 can operate in combination with the FLOW 1440 to suppress higher order modes more efficiently than either the HOMSL 2002 or the FLOW 1440 alone. This architecture is desirable, for example, to save on material costs or to accommodate other structures in the laser 2000 epitaxial layer structure.

Gain Matching Approach

In one example, higher order modes in the lateral waveguide can be reduced by reducing the amount of current reaching the active layer in the lateral waveguide where higher order modes are more prevalent. This can be achieved by gain adjustment. Conventionally, gain matching involves current injection from the p-side of the heterostructure. However, gain adjustment from the p-side has inefficiencies. In contrast, gain matching from the n-side produces a diffuse carrier distribution that overlaps more primarily with the fundamental mode and then with the profiles of lower-order modes, giving the desired modes higher gain and the undesired higher-order modes lower gain .

27 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having an adapted n-side current injection scheme. In one example, gain adjustment is performed by current injection via an n-metal contact 2714 that is designed to be narrower than p-metal contact 316 . The n-metal contact 2714 is located at the center of the lateral waveguide 2714 in the longitudinal direction, and a cavity 2710 allows for a lateral carrier distribution pattern 2702.

28 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having an adapted n-side current injection scheme. A laser diode 2800 has an n-side 2820 and a p-side 2822 . The n-side 2820 contains an n-metal contact 2814, the n-cladding layer 310, the n-type semiconductor layer 306 and the n-substrate 304. The p-side contains the p-cladding layer 312, the p-type semiconductor layer 308 and p-metal contact 316. Transverse waveguide 318 includes quantum well 302, n-type semiconductor layer 306, and p-type semiconductor layer 308. A longitudinal waveguide 2814 can be defined in a variety of ways (e.g., by gain routing, ridge waveguide or index guide or the like or a combination thereof) as illustrated by dotted lines on the top side of the substrate 304 and the n-metal contact 2814. P-metal contact 316 is located under p-cladding layer 312 . The n-metal contact 2814 extends along the cavity 2810 of the longitudinal waveguide 2814.

Gain matching from the n-side can be achieved by introducing a lateral carrier distribution pattern 2802 by placing a narrow strip of n-metal contact 2814 on the n-side 2820 of the laser diode 2800 instead of the conventional full n-side metallization. The thin n-metal contact 2814 can be disposed in a variety of locations opposite the p-metal contact 316. FIG. In one example, n-metal contact 2814 is offset such that its edge is on emitter half-plane 2804 . A gain adjustment is made from the n-metal side 2820 which reduces higher order modes propagating in the waveguide 2840 by reducing the magnitude of the gain for the higher order modes.

In one example, the n-metal contact 2814 can have a variable width along the cavity to modulate the beam profile in the lateral and longitudinal directions. this is in 28 is shown wherein a width L1 of the n-metal contact 2814 is less than a second width L2. This provides a gain adjustment in the longitudinal direction that reduces the gain for the higher order modes toward the HR facet (highly reflective) so that the laser diode 2800 operates more efficiently without significantly increasing the lower order/fundamental mode loss.

29 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having an adapted n-side current injection scheme. In In one example, gain adjustment is made by current injection via a flared n-metal contact 2914 that is designed to be narrower than p-metal contact 316 . The n-metal contact 2914 is narrower on the HR side and wider on the PR side (but laterally centered). The n-metal contact 2914 is located in the middle of the lateral waveguide 2914 in the longitudinal direction, and a cavity 2910 allows for a lateral carrier distribution pattern 2902.

Hybrid Gain Matching/HOMSL Approach

Further reduction of higher order modes in a lateral waveguide can be done using a hybrid approach by 1) reducing the propagation of higher order modes in the waveguide by applying an adjusted current injection scheme to adjust the gain or the gain for higher order modes and thereby depriving them of gain and suppressing the higher order modes, and 2) inserting a HOMSL adjacent the lateral waveguide along the longitudinal direction to further suppress higher order modes generated despite the gain matching.

21A 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher order mode suppression layer disposed adjacent to the lateral waveguide. A laser diode 2100 has an n-side 2120 and a p-side 2122 . The n-side 2120 includes an n-metal contact 2114, the n-cladding layer 310, the n-type semiconductor layer 306, and the n-substrate 304. The p-side 2122 includes the p-cladding layer 312, the 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. Longitudinal waveguide 2114 can be defined in a number of ways (e.g .by gain guiding, ridge waveguide or index guiding or the like or a combination thereof). The longitudinal waveguide 2114 includes a cavity 2110 represented by dashed lines on the top of the substrate 304 and the n-metal contact 2140. FIG. P-metal contact 316 is located under p-cladding layer 312 . The n-metal contact 2114 extends along the cavity 2110 of the longitudinal waveguide 2140.

As discussed above, gain matching can be achieved from the n-side by introducing a lateral carrier distribution pattern 2102 by placing the n-metal contact 2114 on the n-side of the laser diode. In 21A the n-metal contact 2114 is offset so that its edge is on the emitter half-plane 2104. The carrier injection is carried out from the n-metal side. In addition, the HOMSL 320 includes a high-index material symmetrically disposed about the lateral waveguide 2110 along the longitudinal direction. This hybrid approach can reduce higher order modes propagating in the waveguide 2140 by reducing the amount of gain for the higher order modes and suppressing the higher order modes across the HOMSL 320 .

In another example, a HOMSL structure symmetrically placed about the waveguide 2140 may be used instead of a symmetrically placed HOMSL structure. In an example, an asymmetric HOMSL structure, as in the 9 , 11 , 16 , 18 and 20 shown, can be placed in series with the n-metal contact 2114 in the heterostructure, as in FIG 21B is shown. This configuration is more efficient than placing the HOMSL structure on the opposite side since gain is stripped from the higher order modes and it is below the threshold carrier density.

Also, other HOMSL structures can be used to implement the hybrid gain matching/HOMSL higher order mode suppression method described herein. For example, instead of employing the high index materials of HOMSL 320, absorptive and/or aperiodic materials may be used, as discussed above with respect to HOMSL 402 of US Pat 4 and the HOMSL 502 of the 5 is described. Furthermore, the hybrid gain matching/HOMSL approach using p-side gain matching provides higher order mode rejection that is improved over conventional p-side gain matching or higher order mode rejection using a HOMSL structure alone . 22 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher-order mode suppression layer disposed adjacent the waveguide. In one example, n-metal contact 2214 is designed to be narrower than the width of p-metal contact 316 . N-metal contact 2214 is at half-plane 2204 of the waveguide 2240 centered. This creates a diffuse carrier distribution along the path labeled 2202 in the lateral direction, creating a carrier density profile that overlaps primarily with the fundamental mode and then with the profiles of the lower order modes than the suppressed higher order modes. This current injection profile is configured to optimize the overlap with the lower order lateral modes and the fundamental modes by providing higher gain to the desired modes and lower gain to the higher order undesired modes. Furthermore, the width of the n-metal contact 2214 along the cavity 2210 may be variable to model the amount of carriers injected along the longitudinal direction of the cavity 2210. FIG.

23 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher order mode suppression layer disposed adjacent the waveguide. In one example, gain adjustment is made by current injection via n-metal contact 2314 that is offset from p-metal contact 316 . The HOMSL 402 (cf. 4 ) is arranged symmetrically about the lateral waveguide 2314 along the longitudinal direction and contains an absorbing material. In an example, the HOMSL can be n- or p-doped GaAs, or ordered or disordered InGaAs with a bandgap lower than the lasing wavelength.

24 12 is a cross-sectional perspective view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher order mode suppression layer adjacent to the waveguide. In one example, gain adjustment is made by current injection via an n-metal contact 2414 that is designed to be narrower than p-metal contact 316 . The n-metal contact 2414 is placed in the center of the lateral waveguide 2414 and the cavity 2410 . The HOMS1 402 (cf. 4 ) is arranged symmetrically around the lateral waveguide 2414 and contains an absorbing material.

25 12 is a cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher order mode suppression layer disposed adjacent to the waveguide. In one example, a gain adjustment is made via an n-metal contact 2514 that is offset from p-metal contact 316 . The HOMSL 502 (cf. 5 ) comprising an aperiodic high-index layer 504 and a low-index layer 506 is arranged symmetrically about the lateral waveguide 2514.

26 12 is a cross-sectional view showing a vertical epitaxial layer structure of an exemplary laser diode having a matched n-side current injection scheme and a higher order mode suppression layer disposed adjacent to the waveguide. In one example, gain adjustment is made by current injection via an n-metal contact 2614 that is designed to be narrower than p-metal contact 316 . The n-metal contact 2614 is placed in the center of the waveguide 2640 and a cavity 2610 . The HOMSL 502 (cf. 5 ) is arranged symmetrically about the longitudinal waveguide 2640 and contains an absorbing material.

Features of the embedded HOMSL to compensate for thermal lensing

Index guidance and gain guidance are the dominant confinement mechanisms used to confine lateral (i.e., transverse to the slow axis) optical modes in broad area laser cavities. Vertical mode confinement (i.e., transverse to the fast axis) is typically performed with index guidance using n-type and p-type cladding layers of predetermined refractive indices. In general, lateral optical modes supported by a semiconductor laser cavity that has zero lateral refractive index variation in an unpowered, cold state are gain-guided during a driven state because the injected current introduces a lateral index variation between electrically pumped and unpumped regions induced.

During high power operation, a lateral thermal gradient causes a lateral index difference between the lateral waveguide and the cladding, which is associated with thermal lensing. The magnitude of positive lateral index contrast caused by thermal lensing can depend on various cavity properties and parameters, including length, semiconductor layer thicknesses, carrier densities, active layer type and thickness, emitter/reflector widths, gain, operating wavelength length, amount of waste heat generated by the diode laser, and heat transfer between the diode junction and the heat sink, etc., as will be readily appreciated by one skilled in the art.

The slow-axis divergence angle of an output beam emitted from the semiconductor device can be strongly affected by the lateral waveguide confinement near the highly reflective facet. Index guiding (caused by thermal lensing) in the lateral waveguide near the highly reflective facet can support unwanted higher-order lateral modes, resulting in slow-axis divergence and reduced beam quality.

These examples describe methods, systems and devices for reducing the occurrence of higher order lateral modes in device operation caused by high index contrast induced thermal lensing. The increased waveguide index contrast due to thermal lensing is offset or compensated for by forming an index compensation region on the HR side of the Fabry-Perot cavity. This reduces the magnitude of index contrast induced thermal lensing.

30A FIG. 3002 is a graph showing a conventional step index profile in the lateral direction of a single emitter laser diode operating at low power without significant thermal lensing. 30B FIG. 3004 is a graph showing a step index profile in the lateral direction of a single emitter laser diode with a parabolic profile added. This is an index model for a conventional thermal lensing waveguide profile operating at higher power. This shows how the profile evolves under thermal lensing at high operating current. 30C FIG. 3006 is a graph showing a potential index profile in the lateral direction of a single emitter laser diode that provides compensation for thermal lensing during higher power operation. The "negative" step index profile, with a parabolic profile added, models the index profile in the negative compensation region. The thermal lensing related index profile produces a weak index guided area under operating conditions.

As described in more detail below, methods for achieving such a profile include introducing higher index of refraction lateral features adjacent and/or overlapping the lateral waveguide, reducing the transverse waveguide thickness in the active stripe, and/or introducing a thin one Low-index layer within the transverse waveguide.

the 31A - 31D show different views of a laser diode 3100.

31A 12 is a cross-sectional view of a vertical epitaxial layer structure of an exemplary laser diode 3100 with an embedded higher order mode suppression layer (HOMSL) 3104 disposed on adjacent sides of a lateral waveguide 3106. FIG. The laser diode 3100 can have various geometries and configurations and can include various arrangements of p-type, n-type, active, capped, and dielectric layers. As used herein, the term “embedded” is intended to refer to a higher order mode suppression layer and/or a feature interposed 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 embedded and may operate in the same or similar manner as the higher order mode suppression layer or feature embedded.

In one example, the laser diode 3100 is shown in a simplified epitaxial structure and includes an n-type cladding layer 3108 and a p-type cladding layer 3110 between which a transverse waveguide or cavity 3112 is formed. Transverse waveguide 3112 is orthogonal to lateral waveguide 3106 and includes an n-type waveguide layer 3114, a p-type waveguide layer 3116, or an active layer 3118. Active layer 3118 typically includes one or more quantum wells, but other configurations are also possible possible, including pn-junction, homostructure, heterostructure, double-heterostructure, quantum wires, quantum dots, etc. The p-type cladding layer 3110 can be etched into various shapes to form ridge structures 3120 or mesas extending either along the entire longitudinal length of the diode 3100 or extending from the side of the partial reflector (PR) 3122 over only a partial length of the diode 3100. Additionally, one or more dielectric and/or cap layers (not shown) may be formed on laser diode 3100 to conduct current through active layer 3118 .

31B is one of the partially reflective (PR) side 3122 of in 30A The exemplary laser diode 3100 shown in FIG.

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

31C 12 is a top view of an exemplary laser diode 3100 that includes embedded HOMSL features 3104 disposed on adjacent sides of a lateral waveguide 3106 and extending from the HR facet 3124 in the longitudinal direction.

During high power operation of the laser diode 3100, the temperature profile resulting from lateral heat propagation results in a thermal lensing effect in the lateral waveguide 3106 that causes a refractive index contrast in the lateral waveguide 3106. In one example, partial or full compensation for the increased refractive index contrast in the lateral waveguide 3106 can be achieved by strategically placing the HOMSL features 3104 adjacent to the lateral waveguide 3106 on one or both lateral sides. The HOMSL 3104 is formed between the p-type waveguide layer 3116 and the p-type cladding layer 3110 . Alternatively, the HOMSL 3104 can also be formed between the n-type waveguide layer 3114 and the n-type cladding layer 3108 . The HOMSL 3104 may also be formed to slightly overlap the lateral waveguide 3106 to compensate for a mode size mismatch between the two regions or for other reasons.

Adding HOMSL structures 3104 (e.g., with GaAs) to a BAL can be done using a variety of methods well known to those skilled in the art, and the claimed subject matter is not limited in this regard. For example, a modified mask and etch may be employed to form a HOMSL 3104 with selected offsets from the ridge waveguide 3120. FIG. The HOMSL high-index features 3104 located at the edges of the ridge waveguide 3120 may disproportionately overlap higher order modes, however, the mismatch in mode size of identical order modes between the HR side and the PR side means that the offset between the Oxide ridge 3120 and the HOMSL 3104 in the lateral direction is chosen so that the occurrence of excessive losses is avoided by the supported laser modes are coupled out.

Various simulations indicate that for different orders of index contrasts, the trend in mode size is predictable regardless of which order it is. The order of magnitude of the index contrasts is in a range of 10-5<Δn<10-3. The predicted mismatch in size of the lateral waveguide 3106 (or the overlap in the HOMSL 3104 over the lateral waveguide) can be in a range of 2-6 µm on each side or 4-12 µm overall.

In another example, the HOMSL 3104 is formed to laterally overlap the lateral waveguide 3106 to reduce a mismatch in the lateral mode region between a HOMSL region 3104 and an index-guided region by a value between 0-10um on each side or 0- 20to compensate in total.

31D 12 is a perspective cross-sectional view of a vertical epitaxial layer structure seen from the HR side 3102 of an exemplary laser diode 3100 having an embedded HOMSL 3104 disposed on adjacent sides of a lateral waveguide 3106 and extending longitudinally from the HR coated facet 3124 extends.

In one example, the HR side 3102 extends from the HR coated facet 3124 to about a midpoint 3130 (dashed line). PR side 3122 extends from PR coated facet 3126 to about midpoint 3130.

Under operating conditions, the HR side 3102 experiences thermal lensing, but when suppressed or compensated by the HOMSL 3104, this area is weakly index-guided; therefore, it has an index profile that approximates that in 30C shown. Likewise contains the PR side 3122 an index-guided area, which also experiences a lens effect during operation without suppression or compensation by the HOMSL 3104 and therefore approximates that in 30B index profile shown.

In order to reduce the magnitude of thermal lensing induced by the index contrast on the HR side 3102 of the laser diode 3100, the HOMSL 3104 may contain a material with a higher index of refraction than the surrounding materials. The relative index of refraction (n) for the HOMSL 3104 with respect to the transverse waveguide layers 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} .

In addition, to reduce the magnitude of the thermal lensing-induced index contrast on the HR side 3102, the refractive index and thickness 3128 of the HOMSL 3104 are carefully chosen. The choice of thickness 3128 should be based on its effect on the magnitude of the refractive index contrast (i.e. the potential effective index contrast on the HR side 3102 of the lateral waveguide 3106). A particular HOMSL 3104 thickness 3128, threshold thickness, or range of thicknesses (collectively referred to herein as "thickness") that sufficiently reduces the magnitude of index contrast-induced thermal lensing on the HR side 3102 may be identified by a variety of methods , including simulation, experiments, reference tables and predictive analysis, etc.

The thickness 3128 determines the Δn on the HR side 3102 relative to thermal lensing and reduces the guiding ability of the lateral waveguide 3106 in the region near the HOMSL 3104. In various examples, the thicknesses can be chosen such that the lensing effect is largely compensated for to create such a weak index-guided area. This allows weak index guidance of a few lateral modes or, in the extreme case, just a single lateral mode at high operating current on the HR side 3102. Such a weakly guided region can support 10 or fewer lateral modes, or just one mode. As a result, the lateral waveguide 3106 on the HR side supports fewer lateral modes and allows for a reduction in slow-axis divergence and higher brightness compared to conventional BALs.

Because the HOMSL is designed to largely compensate for thermal lensing in high power operation, there can effectively be an anti-guided region on the HR side 3102 for low power operation, which at higher power operation coincides with the onset of thermal lensing in merges into a weakly indexed area.

32A - 32D show different views of a laser diode 3200.

32A FIG. 3 is a cross-sectional view of a vertical epitaxial layer structure of an exemplary laser diode 3200 that includes an embedded HOMSL 3204. FIG.

Laser diode 3200 is shown in a simplified epitaxial structure and includes an n-type cladding layer 3208 and a p-type cladding layer 3210 between which a transverse waveguide or cavity 3212 is formed. The transverse waveguide 3212 is orthogonal to the lateral waveguide 3206 and includes an n-type waveguide layer 3214, a p-type waveguide layer 3216 and an active layer 3218. Fin structures 3220 may span part or all of the longitudinal length of the diode 3200 between the HR side 3202 and the PR side 3222 extend.

HOMSL 3204 is disposed within transverse waveguide 3212 within p-type waveguide layer 3216 . Alternatively, the HOMSL 3204 can be arranged in the n-type waveguide layer 3214 .

In one example, the HOMSL 3204 may include a thin layer of lower index material. Although HOMSL 3204 is located within transverse waveguide 3212, it is also located within lateral waveguide 3206; therefore the effective index of the lateral waveguide 3206 is reduced by the presence of the lower index HOMSL 3204 . The index of the lateral cladding 3210 remains unchanged.

32B 12 is a cross-sectional view of a vertical epitaxial layer structure taken from the PR side 3222 of FIG 32A See the exemplary laser diode 3200 shown that includes the HOMSL 3204 disposed within the lateral waveguide 3206 . The lateral waveguide 3206 is in the longitudinal Direction limited at a first end by HR coated facet 3224 and at a second end by PR coated facet 3226 . In one example, the HOMSL 3204 is embedded in a p-type waveguide layer 3216 (or n-type waveguide layer 3214). However, since the HOMSL 3204 extends longitudinally from the HR coated facet 3224 for a length less than the distance between the HR facet and the PR facet, it is viewed from the PR side 3222 in not visible in the epitaxial layers.

32C 12 is a top view of an exemplary laser diode 3200 that includes an embedded HOMSL 3204 disposed within a lateral waveguide and extending in the longitudinal direction.

During high power operation of the laser diode 3200, the temperature profile resulting from lateral heat propagation results in a thermal lensing effect in the lateral waveguide 3206 that induces a refractive index contrast in the lateral waveguide 3206. In one example, partial or full compensation for the increased refractive index contrast in the lateral waveguide 3206 can be achieved by strategically placing a HOMSL 3204 within the lateral waveguide 3206 . HOMSL 3204 may be laterally narrower than lateral waveguide 3206 by 0-10 µm on each side or 0-20 µm overall.

Adding the HOMSL structures 3204 (e.g., with AlGaAs) to a BAL can be done using a variety of methods known to those skilled in the art, and the claimed subject matter is not limited in these respects.

32D Figure 12 is a perspective cross-sectional view of a vertical epitaxial layer structure seen from the HR side 3202 of an exemplary laser diode 3200 that includes an embedded HOMSL 3204 disposed within the lateral waveguide 3206 and extending from the HR coated facet 3224 in the longitudinal direction extends. In one example, HR side 3202 extends from HR coated facet 3224 to about midpoint 3230 (dashed line). The PR side 3222 extends from the PR coated facet 3226 to about the midpoint 3230.

Under operating conditions, the HR side 3202 experiences a thermal lensing effect, however, with suppression or compensation by the HOMSL 3204, in which the index contrast is reduced by introducing a lower index material into the lateral waveguide 3206, the area of the HR side 3202 weakly indexed. To reduce the magnitude of index contrast induced thermal lensing on the HR side 3202, the HOMSL 3204 may contain a lower index material than the surrounding materials. The relative index of refraction (n) for the HOMSL 3204 with respect to the transverse waveguide layers is: n low- _{index layer} <n _p-waveguide /n _n-waveguide <n _n-clad /n _n-clad .

To reduce the magnitude of the index contrast induced thermal lensing effect on the HR side 3202, similar to the HOMSL 3104, the thickness 3228 and refractive index of the HOMSL 3204 are carefully chosen. The choice of thickness 3228 is based on its effect on the magnitude of the refractive index contrast (i.e. the potential effective index contrast on the HR side 3202 of the lateral waveguide 3206). A particular thickness 3228 of HOMSL 3204 that sufficiently reduces the magnitude of index contrast induced thermal lensing on the HR side 3202 can be identified by a variety of methods including simulation, experimentation, look-up table and predictive analysis, etc.

The thickness 3228 determines the Δn on the HR side 3202 in relation to thermal lensing and reduces the guiding ability of the lateral waveguide 3206 in the region near the HOMSL 3204. In various examples, the thicknesses can be chosen such that the thermal lensing is largely compensated to create a weak index-guided area. This allows weak index guidance of a few lateral modes or, in the extreme case, just a single lateral mode at high operating current on the HR side 3202. Such a weakly guided region can support 10 or fewer lateral modes, or just a single mode. As a result, the lateral waveguide 3206 on the HR side 3202 supports fewer lateral modes and allows for a reduction in slow-axis divergence and higher brightness compared to conventional BALs.

In various examples, HOMSL 3104 and HOMSL 3204 may be formed from a variety of materials known to those skilled in the art that sufficiently meet the dimensional and relative refractive index constraints disclosed herein to limit the magnitude of the index contrast induced thermal lensing in the lateral waveguide and the claimed subject matter is not limited in this regard. For example, HOMSL 3104 and/or HOMSL 3204 may be formed from a variety of materials including gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), and/or indium gallium phosphide (InGaAsP).

the 33A - 33D show different views of a laser diode 3300.

33A FIG. 3300 is a cross-sectional view of a vertical epitaxial layer structure of an exemplary laser diode 3300 that includes a reduced thickness transverse wavelength section, referred to herein as HOMSL 3304. FIG. The laser diode 3300 is shown in a simplified epitaxial structure and includes an n-type cladding layer 3308 and a p-type cladding layer 3310 between which a transverse waveguide or cavity 3312 is formed. The transverse 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 HR side 3202 and the PR side 3222 extend. HOMSL 3304 may be formed within transverse waveguide 3312 in p-type waveguide layer 16 . Alternatively, a reduced thickness transverse waveguide section HOMSL 3304 may be formed in the n-type waveguide layer 3314 . The HOMSL feature 3304 may be formed as a groove, indentation, channel, or the like, or a combination thereof.

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

33B Fig. 13 is a cross-sectional view of a vertical epitaxial layer structure taken from the PR side 3322 of Fig 33A See the exemplary laser diode 3300 shown, which includes the HOMSL 3304 disposed within the lateral waveguide 3306. FIG. Lateral waveguide 3306 is bounded in a longitudinal direction by HR coated facet 3324 at a first end and by PR coated facet 3326 at a second end. In one example, HOMSL 3304 is formed in p-type waveguide layer 3316 (or n-type waveguide layer 3314). However, because the HOMSL 3304 extends longitudinally from the HR coated facet 3324 for a length less than the distance between the HR facet 3324 and the PR facet 3326, it is from the PR side 3322 seen in the epitaxial layers.

33C 12 is a plan view of an exemplary laser diode 3200 that includes a HOMSL 3304 disposed within a lateral waveguide and extending in the longitudinal direction from the HR coated facet 3324 a length less than the spacing between the HR facet 3324 and the PR facet 3326.

During high power operation of the laser diode 3300, the temperature profile resulting from lateral heat propagation results in a thermal lensing effect in the lateral waveguide 3306 that induces a refractive index contrast in the lateral waveguide 3306. In one example, partial or full compensation for the increased refractive index contrast in the lateral waveguide 3306 can be achieved by strategically placing the HOMSL 3304 within the lateral waveguide 3306 . A trough for the HOMSL 3304 can be formed to be laterally narrower than the lateral waveguide 3306 by 0-10 µm on each side or 0-20 µm overall.

The addition of a HOMSL 3304 related gully, incision, channel, etc. to a BAL can be done by a variety of methods known to those skilled in the art, and the claimed subject matter is not limited in this regard. For example, the HOMSL 3304 can be formed by etching away or selectively depositing thicker layers adjacent to the active stripe.

33D FIG. 3 is a cross-sectional perspective view of a vertical epitaxial layer structure viewed from the HR side 3302 of an exemplary laser diode 3300 that includes an embedded HOMSL 3304 disposed within the lateral waveguide 3306 and extending from the HR layer th facet 3324 extends in the longitudinal direction. In one example, the HR side 3302 extends from the HR coated facet 3324 to about the middle 3330 (dashed line). The PR side 3322 extends from the PR coated facet 3326 to about the middle 3330.

Under operating conditions, the HR side 3302 experiences a thermal lensing effect, however, with the suppression or compensation by the HOMSL 3304, by providing the section with thinner transverse wavelength thickness, the area of the HR side 3302 is weakly index guided, reducing the magnitude of an index contrast induced thermal lensing on the HR side 3302 is reduced. In one example, the smaller the thickness of the transverse waveguide 3312, the higher the effective index of refraction, allowing the lateral waveguide 3306 to have a lower index of refraction than the lateral cladding.

To reduce the magnitude of the index contrast induced thermal lensing effect on the HR side 3302, the thickness 3328 is chosen judiciously, similar to the HOMSL 3104. The choice of thickness 3328 is 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). A particular thickness 3328 of HOMSL 3304 that sufficiently reduces the magnitude of the index contrast induced thermal lensing effect on the HR side 3302 can be identified by a variety of methods including simulation, experimentation, look-up table and predictive analysis, etc.

The thickness 3328 determines the Δn on the HR side 3302 in relation to thermal lensing and reduces the guiding ability of the lateral waveguide 3306 in the region near the HOMSL 3304. In various examples, the thicknesses can be chosen such that the thermal lensing is largely compensated to run a weakly indexed region. This allows weak index guidance of a few lateral modes or, in the extreme case, just a single lateral mode at high operating current on the HR side 33002. Such a weakly guided region can support 10 or fewer lateral modes, or even just one mode. As a result, the lateral waveguide 3306 on the HR side 3302 supports fewer lateral modes and allows for a reduction in slow-axis divergence and higher brightness compared to conventional BALs.

SIMULATIONS AND EXAMPLES

HOMSL 3104 and HOMSL 3204 can each be fabricated by a variety of methods known to those skilled in the art, and the claimed subject matter is not limited in these respects. Manufacturing may require determining a suitable thickness of HOMSL 3104 sufficient to reduce the index contrast on the HR side. This relative difference in Δn can be considered for a simulation calculation of the relationship between the thickness of the HOMSL 3104 and Δn.

34 FIG. 3400 is a graph 3400 showing a simulation of the effect of thickness on Δn to approximate an optimized thickness of an embedded HOMSL 3104 to compensate for a certain delta in index caused by thermal lensing. The specific HOMSL 3104 can be made of GaAs and is formed between the p-type waveguide layer 3116 and the p-type cladding layer 3110 with a refractive index lower than that of GaAs. A negative Δn means a negative lateral index difference between the lateral waveguide and the cladding. Using the graph 3400, by approximation, the thickness of the HOMSL 3104 can be optimized to compensate for a specific delta in the index caused by thermal lensing. Although the simulation is specific to the in 34 geometric approach shown, there are other methods to reach the weakly index-guided HR side 3102 of the emitter. These include reducing the thickness of the transverse waveguide in the active stripes. Both approaches would achieve reduced index contrast between the lateral waveguide and the cladding.

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

35 Figure 3500 is a graph showing a simulation for predicting the far fields of assisted modes with or without suppression of higher order modes by thermal lensing compensation. The specific example is a BAL with 200 µm lateral waveguide width and typical step index and thermal lensing. The reduction of the supported modes implies a Ver reduction in the far field from -10.9 degrees to ~4.3 degrees. The slow-axis referenced far-field divergence of a variety of BALs with HOMSLs under different step indices and thermal lens powers are simulated and summarized in the table below: begin waveguide width Δn "Therma" parable in total HOM Widefield 1/e^2 around index index index M Degree multimode 100 0.0004 0 0.0004 - 6.7 Fashion of the highest order 100 0.0004 0.0004 0.0008 12 8.9 Fashion of the highest order 100 0.0004 0.0004 0.0008 13 9.3 Fashion of the highest order 100 0.0004 0.0008 0.0012 15 11.2 Fashion of the highest order 100 0.0004 0.001 0.0014 16 12.3 Fashion of the highest order 100 -0.001 0.0012 0.0002 1 5.2 Fashion of the highest order 100 -0.0008 0.001 0.0002 1 4.85 multimode 200 0.0004 0 0.0004 - 6.35 Fashion of the highest order 200 0.0004 0.0004 0.0008 26 9.1 Fashion of the highest order 200 0.0004 0.0008 0.0012 31 10.9 Fashion of the highest order 200 0.0004 0.0012 0.0016 35 12.55 Fashion of the highest order 200 -0.0004 0.0012 0.0008 17 9.1 Fashion of the highest order 200 -0.0008 0.0012 0.0004 7 6.3 Fashion of the highest order 200 -0.0006 0.0008 0.0002 3 4.3 Fashion of the highest order 200 -0.0007 0.0008 0.0001 1 3.3

As described above, a flat index step is used to determine the index contrast required to match the far field at low operating power. The HOM column denotes the order of the predicted mode with the highest order.

The foregoing description of laser diodes, epitaxial layer structures, various features/structures within the epitaxial layers, and waveguides are merely examples and are for purposes of illustration; other structures and features or combinations of structures and/or features are contemplated and are within the scope of the disclosed subject matter; the claimed subject matter is not limited in this regard.

Having described and illustrated the general and specific principles of examples of the technology disclosed herein, it should be apparent that the examples may 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.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US9166369 [0027]

Claims (16)

Laser diodes, comprising: a transverse waveguide orthogonal to the lateral waveguide comprising an active layer between an n-type waveguide layer and a p-type waveguide layer, the transverse waveguide being penetrated by an n-type cladding layer on an n-side and through a p-type cladding layer is defined on a p-side; a lateral waveguide bounded in a longitudinal direction at a first end by a highly reflective (HR) coated facet and at a second end by a partially reflective (PR) coated facet, the lateral waveguide further having an embedded, for suppression of higher modes Order specific layer (HOMSL) which is arranged under the p-cladding within the lateral waveguide or on one or both sides of the lateral waveguide or a combination thereof, the HOMSL extending in a longitudinal direction starting from the HR facet over a length that is less than the distance between the HR facet and the PR facet. laser diode after claim 1 , wherein the refractive index of the HOMSL arranged on one or both sides of the lateral waveguide is higher than that of the p-type waveguide layer and the p-cladding layer. laser diode after claim 1 , wherein the refractive index of the HOMSL arranged inside the lateral waveguide is lower than that of the n-type waveguide layer or the p-type waveguide layer or a combination thereof. laser diode after claim 1 wherein a thickness of the HOMSL is selected based on a magnitude of the refractive index contrast in the lateral waveguide induced by thermal lensing within the lateral waveguide during operation of the laser diode. laser diode after claim 4 , wherein the thickness of the HOMSL is further chosen to reduce the magnitude of the refractive index contrast of the lateral waveguide during operation. laser diode after claim 5 , where the magnitude of the refractive index contrast is in the range of 10 ^-5 < Δn < 10 ^-3 . laser diode after claim 5 , where the lateral waveguide supports fewer than ten lateral modes. laser diode after claim 5 , where the lateral waveguide supports a single lateral mode. laser diode after claim 1 , wherein a thickness of the HOMSL is chosen to reduce an effective index on a side of the lateral waveguide extending from the HR facet. laser diode after claim 1 , where the HOMSL contains gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), indium gallium arsenide (InGaAs), indium aluminum gallium arsenide (InAlGaAs), indium gallium phosphide (InGaAsP). laser diode after claim 1 wherein the lateral waveguide is bounded in the lateral direction by a ridge waveguide, the ridge waveguide extending from the HR facet to the PR facet. laser diode after claim 2 , where the HOMSL laterally overlaps the lateral waveguide by 0-10 µm on each side or by 0-20 µm overall. laser diode after claim 1 , where the HOMSL located within the lateral waveguide is laterally narrower than the lateral waveguide by 0-10 µm on each side or by 0-20 µm overall. laser diode after claim 1 wherein the lateral waveguide is bounded in the lateral direction by a ridge waveguide extending in the longitudinal direction from the PR facet over a length less than the distance between the PR facet and the HR facet. laser diode after claim 1 , wherein the transverse waveguide thickness in the active stripe is reduced either by etching away or selectively depositing thicker layers adjacent to an active stripe. laser diode after claim 1 , where a thinner low-index layer is placed along the width of the lateral waveguide in a region of the HOMSL.

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