Broadband active mirror architecture for high-power optically pumped semiconductor disk lasers

Abstract

A vertical external cavity surface emitting laser (VECSEL) and a method of forming a VECSEL are disclosed. The VECSEL includes: a heat sink; a heat sink or a heat spreader formed on a top surface of the heat sink, wherein the heat spreader includes a first material having a first refractive index; and a high contrast grating formed on a top surface of the heat sink or an active region, wherein the high contrast grating includes an active region, and the high contrast grating includes a second material having a second refractive index, the second refractive index being greater than the first refractive index.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to U.S. Provisional Application No. 62 / 733,466, filed on September 19, 2018, the entire contents of which are hereby incorporated by reference herein.

[0003] Government funding

[0004] This invention was made with Government support provided by the Air Force Office of Scientific Research under Grant No. FA9550-16-1-0362. The Government has certain rights in this invention. Technical Field

[0005] The present teachings relate generally to semiconductor lasers and, more particularly, to high power continuous wave (CW) and multi-kilowatt output power operation of optically pumped semiconductor disk lasers. Background Art

[0006] Optically pumped semiconductor lasers (OPSLs), also known as vertical external cavity surface emitting lasers (VECSELs) or semiconductor disk lasers (SDLs), have rapidly become high power, good beam quality sources for a variety of applications. Unlike other solid-state disk lasers or fiber lasers, semiconductor lasers can be designed to operate over a larger wavelength range, which is difficult to achieve with other technologies. However, compared to several kW of fiber lasers and disk lasers, the output power of VECSELs is limited to about 100W. A limiting factor in output power is thermal management. VECSEL active mirrors are typically composed of a semiconductor active region (usually a quantum well (QW)) on top of a distributed Bragg reflector (DBR) in an external cavity. Figure 1The arrangement of a conventional high power VECSEL 100 is shown. The VECSEL 100 includes a laser diode 102 that produces a laser beam having a wavelength of, for example, 810 nm and a power of, for example, 70 W. A lens 104 directs the laser beam to pump an active / gain region located at the top of a DBR 106. The laser cavity of the VECSEL 100 is defined by the distance from the top surface of the DBR 106 and an external reflector 108. Heat from the active region is conducted out through the DBR 106 to a heat spreader typically made of diamond, and to a heat sink 110 coupled by a coupling layer 112. The DBR 106 is formed by alternating high refractive index semiconductor layers and low refractive index semiconductor layers (typically, more than 20 pairs and a total thickness of more than 5 microns) to achieve a desired reflectivity value. This thickness and a large number of material interfaces result in high thermal resistance in the DBR 106, which results in overheating of the active region, ultimately limiting the output power. Additional heat may also be generated in the DBR 106 by absorbing pump power that is not absorbed in the active region.

[0007] Figure 2 The setup of a conventional DBR-less SDL 200 is shown. The DBR-less SDL 200 includes a laser cavity defined by a reflector 202 and a reflector 204. A pump laser 206 provides optical energy that is absorbed in an active region 207, and a heat sink 208 conducts heat away from the DBR-less SDL 200. DBR-less SDLs eliminate the need for DBRs and thermal limitations. However, due to their transmission geometry, they must rely on lateral heat transfer in a heat sink 210, limiting their power scalability. Moreover, because the heat sink 210 is part of the laser cavity, it must be of extremely high purity to avoid excessive optical losses.

[0008] High contrast gratings (HCGs) have been proposed to act as high reflectors using only a relatively thin layer of high refractive index material that is laterally patterned (typically, in a stripe pattern). By controlling the grating and substrate materials (refractive index, thickness), grating design (etch depth, periodicity, duty cycle), the reflectivity of the HCG can be tailored to perform a variety of tasks (including use as a laser reflector). Such structures have been proposed and / or demonstrated for vertical cavity surface emitting lasers and VECSELs in which a silicon grating is deposited on top of a diamond heat sink. Figure 3 Three lasers using HCG are shown. However, it should be noted that in all cases the heat sink is located inside the laser cavity, leading to similar concerns as described above for DBR-free SDLs. The HCG used in such laser devices is of the so-called guided mode resonance (GMR) type with an extremely narrow bandwidth.

[0009] There is a need for an improved laser design that addresses the above-mentioned problems. Summary of the invention

[0010] According to an example of the present disclosure, a vertical external cavity surface emitting laser (VECSEL) is provided, comprising: a heat sink; a heat sink attached or bonded to the heat sink, wherein the heat sink comprises a first material having a first refractive index; an active region attached or bonded to the heat sink, wherein the active region comprises a second material (or combination of materials) having a second refractive index; and a high contrast grating formed in or attached or bonded to a top surface of the active region, wherein the high contrast grating comprises a third material having a third refractive index, wherein the second refractive index is greater than the first refractive index. The high contrast grating can be formed of any material that is transparent to the laser (and in some examples, the pump wavelength).

[0011] According to an example of the present disclosure, a method of forming a vertical external cavity surface emitting laser (VECSEL) is provided. The method includes: bonding a heat sink to a top surface of a heat sink, wherein the heat sink includes a first material having a first refractive index; bonding an active region to the top surface of the heat sink, wherein the active region includes a second material having a second refractive index; and bonding a high contrast grating to the top surface of the active region, wherein the high contrast grating includes a third material having a third refractive index, wherein the second refractive index is greater than the first refractive index. The high contrast grating can be formed of any material that is transparent to the laser (and in some examples, the pump wavelength).

[0012] In some examples, the heat spreader is bonded to the heat sink using a thermally conductive adhesive.

[0013] In some examples, the high contrast grating and active region are bonded to the heat sink using Van der Waals bonds.

[0014] In some examples, the active region includes a semiconductor active region. The active region may be surrounded by a carrier confinement / window layer. The HCG may be divided into four.

[0015] In some examples, the active region includes a bulk semiconductor, a heterostructure, one or more quantum wells, or one or more quantum dot layers.

[0016] In some examples, the active region includes GaAs, AlGaAs, InGaAs, InP / AlInGaAs / InGaAs, GaSb / AlGaAsSb / InGaAsSb, or GaAs / AlAs / AlGaAs / GaInP / AlGaInP.

[0017] In some examples, the period, fill factor, etch depth, refractive index of the high contrast grating are optimized so that the zeroth order diffraction from the high contrast grating is minimized and higher diffraction orders are transmitted to achieve total internal reflection at the interface of the heat sink.

[0018] In some examples, the heat sink is diamond, silicon carbide, sapphire, or another transparent material with high thermal conductivity.

[0019] In some examples, the heat sink is cooled via direct contact with a cooling medium or by attachment to a heat sink.

[0020] In some examples, the heat spreader is bonded to the heat sink using a thermally conductive paste or solder (eg, indium). BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and, together with the description, serve to explain the principles of the present disclosure. In the drawings:

[0022] Figure 1 A conventional high power VECSEL setup is shown.

[0023] Figure 2 A conventional DBR-free SDL setup is shown.

[0024] Figure 3 A conventional grating-based laser design is shown.

[0025] Figure 4 An active mirror design with HCG integrated into a semiconductor active region is shown according to an example of the present disclosure, where the HCG is formed separately and bonded to a gain chip.

[0026] Figure 5 A graph showing the HCG zero order transmission as a function of grating depth and period for a semi-infinite AlGaAs grating designed for 890nm is shown, with the region outlined by the dashed curve having <1% transmission in the zero diffraction order. The vertical dashed line indicates the upper limit of nΛ / λ0 for obtaining high reflectivity HCG on a diamond substrate.

[0027] Figure 6 The reflectance spectrum of the HCG designed for 890 nm operation is shown at 212 cm with constant material gain. -1 6. The graph 600 is shown with a gain (represented by line 602) and without a gain (represented by line 604).

[0028] Figure 7The thermal modeling curve of the active region temperature rise as a function of the incident pump power is shown. Thermal modeling shows that, assuming a maximum allowable temperature rise of 100 degrees, the dissipated power of the TAG-VECSEL structure is nearly five times that of a standard VECSEL. This means that a kW (or several kW) semiconductor disk laser can eventually be realized.

[0029] Figure 8 A method of forming a vertical external cavity surface emitting laser (VECSEL) according to an example of the present disclosure is shown.

[0030] Fig. 9 An active mirror design with HCG integrated into a semiconductor active region according to an example of the present disclosure is shown.

[0031] It should be noted that some details in the drawings are simplified and are drawn to facilitate understanding of the present teachings rather than to maintain strict structural accuracy, detail, and scale. DETAILED DESCRIPTION

[0032] Examples of the present disclosure describe high contrast grating based active mirror architectures that can provide kilowatt-class continuous wave (CW) operation of optically pumped semiconductor disk lasers. The optically pumped gain medium is sandwiched between a high fill factor, high contrast grating and a heat sink (e.g., diamond, silicon carbide, or sapphire). The proximity of the gain medium to the heat sink heat sink and the absence of distributed Bragg reflectors (with high thermal resistance and parasitic absorption) enable improved heat sinking and higher power operation in the multi-kW regime.

[0033] Broadband HCG reflectors are used in active geometries (with optical pump gain). We have discovered active HCG geometries that can be integrated with (or bonded to) high-index / high-thermal-conductivity heat sinks (diamond or SiC), making the long-term goal of pushing VECSELs into the kW regime finally a reality. For brevity, we refer to these structures hereinafter as "thermally managed active grating" VECSELs or TAG-VECSELs.

[0034] Fig. 9 An active mirror design of a broadband high contrast grating 900 according to an example of the present disclosure is shown, where the HCG is a monolithic part of the gain chip or semiconductor active region. In this example, the active mirror with the HCG is etched into the top surface of the gain chip with the semiconductor active region. Fig. 9As shown, the broadband high contrast grating 900 includes a heat sink 902, which is composed of a suitable thermally conductive material (e.g., copper or other similar thermally conductive materials). The broadband high contrast grating 900 also includes a heat sink 908, which is disposed on and bonded to the top surface of the heat sink 902 through a thermally conductive adhesive 904 and a metallization layer 906. The thermally conductive adhesive 904 can be composed of a thermally conductive epoxy resin. In some examples, the heat sink 902 and the heat sink 908 are bonded using mechanical attachments (e.g., screws or bolts) and optionally using a heat sink compound or indium foil at the interface of the heat sink 902 and the heat sink 908.

[0035] The heat sink 908 is made of a material that may include, for example, diamond, silicon carbide, sapphire, and the refractive index of the material is represented by n3. The broadband high contrast grating 900 also includes a gain chip 912, which includes a semiconductor active region, which is disposed on the top surface of the heat sink 908 and bonded to the top surface. In some examples, the gain chip 912 or the semiconductor active region is bonded to the heat sink 908 using van der Waals bonding 910. In some examples, the semiconductor active region may include a bulk semiconductor, a heterostructure, one or more quantum wells, or one or more quantum dot layers. In some examples, the semiconductor active region may include GaAs, AlGaAs, InGaAs, InP, AlInGaAs, InGaAs, GaSb, AlGaAsSb, InGaAsSb, or GaAs, AlAs, AlGaAs, GaInP, AlGaInP. The semiconductor active region is made of a semiconductor active region with a refractive index represented by n3. a Indicates the material composition.

[0036] The broadband high contrast grating 900 also includes a HGC 916 integrally formed by etching the gain chip 912. The HCG 916 can be formed of any material that is transparent to the laser (and in some examples, the pump wavelength). The HCG 916 is composed of a material with a refractive index represented by n2. Fig. 9 As shown, incident radiation 918, as indicated by a downward pointing arrow, is provided to the broadband high contrast grating 900 from an environment having a refractive index represented by n1 (which is 1 for air), and output radiation 920 is shown by an upward pointing arrow. Fig. 9 In the arrangement of a )>n3>n1.

[0037] Figure 4 An active mirror design of a broadband high contrast grating 400 according to an example of the present disclosure is shown, wherein the HCG is formed separately and bonded to a gain chip. Figure 4As shown, the broadband high contrast grating 400 includes a heat sink 402, which is composed of a suitable thermally conductive material (e.g., copper or other similar thermally conductive materials). The broadband high contrast grating 400 also includes a heat sink 404, which is disposed on and bonded to the top surface of the heat sink 402 through a thermally conductive adhesive 408 and a metallization layer. The thermally conductive adhesive 408 can be composed of a thermally conductive epoxy resin. In some examples, the heat sink 402 and the heat sink 404 are bonded using mechanical attachments (e.g., screws or bolts) and optionally using a heat sink compound or indium foil at the interface of the heat sink 402 and the heat sink 404.

[0038] The heat sink 404 is made of a material that may include, for example, diamond, silicon carbide, sapphire, and the refractive index of the material is represented by n3. The broadband high contrast grating 400 also includes a gain chip, which includes a semiconductor active region 410, which is disposed on the top surface of the heat sink 404 and bonded to the top surface. In some examples, the gain chip is bonded to the heat sink 404 using van der Waals bonding 412. In some examples, the semiconductor active region 410 of the gain chip includes a bulk semiconductor, a heterostructure, one or more quantum wells, or one or more quantum dot layers. In some examples, the semiconductor active region 410 may include GaAs, AlGaAs, InGaAs, InP, AlInGaAs, InGaAs, GaSb, AlGaAsSb, InGaAsSb, or GaAs, AlAs, AlGaAs, GaInP, AlGaInP. The semiconductor active region 410 is made of a material with a refractive index represented by n3. a Indicates the material composition.

[0039] The broadband high contrast grating 400 also includes a HGC 414 disposed on and bonded to the top surface of the gain chip using wafer bonding 416. The HCG 414 can be formed of any material that is transparent to the laser (and in some examples, the pump wavelength). The HCG 414 is composed of a material with a refractive index represented by n2. Figure 4 As shown, incident radiation, as indicated by the downward pointing arrow, is provided to the broadband high contrast grating 400 from an environment having a refractive index represented by n1 (which is 1 for air), and output radiation is shown by the upward pointing arrow. Figure 4 In the arrangement of a )>n3>n1.

[0040] and Figures 1 to 3 The design of the active mirrors (e.g. Fig. 9Instead of using a separate material for the grating (e.g., silicon as proposed in [Iakovlev 2013]), the HCG 916 can be formed directly on the semiconductor active region 410 or the gain chip 912. In order to achieve high reflectivity of the HCG, the grating parameters (period Λ, fill factor f, etch depth h, refractive index n2) are selected in such a way that the zeroth order diffraction from the grating (i.e., light is directly transmitted through the grating, see Figure 5 ) minimized. Figure 5 A graph 500 of HCG zero order transmittance as a function of grating depth and period for a semi-infinite AlGaAs grating designed for 890 nm is shown, with the region outlined by dashed curve 502 having <1% transmittance in the zero diffraction order. The vertical dashed line 504 represents the upper limit of n2Λ / λ0 for obtaining high reflectivity HCG on a diamond substrate. In addition, the higher diffraction orders (typically + / -1) are at sufficiently large angles to achieve total internal reflection at the interface of the heat sink (refractive index n3). This angle is much larger than the critical angle for total internal reflection. For a heat sink with refractive index n3 and a refractive index n a The critical angle is given by arcsin(n3 / n a )(~arcsin(n3 / n2). Assuming a diamond heat sink and GaAs active region and a wavelength of 1000nm, the critical angle is about 43°. In some examples, if the zero-order transmission cannot be sufficiently minimized, the rear surface of the heat sink attached to the heat sink can be metallized using, for example, gold, silver, or other suitable metal to reflect any zero-order transmission back into the cavity with only minor losses.

[0041] Although passive HCGs with similar designs (acting only as reflectors) have been demonstrated before, Figure 4 and Fig. 9 The design is optimized to exhibit high reflectivity over a wide wavelength range ( Figure 6 ) to allow a good overlap with the emission wavelength of the gain medium used. Figure 6 The reflectance spectrum of the HCG designed for 890 nm operation is shown at 212 cm with constant material gain. -1 600 with gain (represented by line 602) and without gain (represented by line 604). This also makes the design more robust to small errors in the manufacturing process. Most importantly, we have found that by fine-tuning the grating fill factor, high reflectivity can still be achieved when combined with a high refractive index heat sink material, because most high thermal conductivity materials (e.g., diamond, silicon carbide, sapphire) have a relatively high refractive index.

[0042] Cavity Design and Thermal Modeling: In cases where the active region (e.g., heterostructures, quantum wells, quantum dots) is embedded beneath the HCG, the semiconductor can be attached to a heat sink. Because good thermal contact is required, van der Waals bonding or adhesiveless bonding [Cole 2017] are the preferred methods for forming this interface, but other techniques (including adhesives) are also possible. Because the heat sink is not part of the laser cavity and only a small amount of the electric field penetrates it, the optical properties of the heat sink are far less important than in other designs, and lower quality (and cheaper) materials can also be incorporated. The heat sink must in turn be cooled, which can be achieved by direct contact with the cooling medium (e.g., via water jet impingement cooling [Albrecht 2011]) or by attaching it to a separate heat sink. Adhesiveless bonding is typically not an option because most heat sink materials are not single crystalline (e.g., polycrystalline diamond, copper), so an intermediate material (e.g., thermally conductive glue, indium) is required to make good mechanical and thermal contact.

[0043] The above active mirror assembly can be used in a standard VECSEL cavity ( Figure 1 ) without any changes. Various other linear, folded or annular cavity geometries are also possible.

[0044] One advantage of this design over existing VECSELs is the reduced thermal resistance of the device. To investigate this, detailed thermal modeling was performed based on actual device performance from the literature [Kemp 2005]. Keeping the pump intensity (pump power / pump spot area) constant, we increased the incident pump power and modeled the maximum temperature rise at the center of the active region. When the temperature rise in the active region approaches 100 degrees, the laser output power is typically limited by thermal inversion. Figure 7 A thermal modeling curve 700 showing the temperature rise of the active region as a function of the incident pump power is shown. Thermal modeling shows that, assuming a maximum allowable temperature rise of 100 degrees, the power dissipation of the TAG-VECSEL structure is nearly five times that of a standard VECSEL. This means that a kW (or several kW) semiconductor disk laser can eventually be realized. Figure 7 As can be seen in Figure 7, in a typical VECSEL this occurs at nearly 900W of incident pump power, as represented by curve 702, while in the present grating-based active mirror design, 4kW of pump power can be tolerated, as represented by curve 704. Assuming efficiencies consistent with current VECSEL performance, this guarantees kW-level output power for our device.

[0045] Figure 8A method 800 of forming a vertical external cavity surface emitting laser (VECSEL) according to an example of the present disclosure is shown. The method 800 includes bonding a heat sink to a top surface of a heat sink at 802, wherein the heat sink includes a first material having a first refractive index. The method 800 continues with bonding a semiconductor active region or a gain chip to a top surface of the heat sink at 804, wherein the semiconductor active region includes a second material having a second refractive index. The method 800 continues with bonding and / or etching a high contrast grating to a top surface of the semiconductor active region or the gain chip at 806, wherein the high contrast grating includes a third material having a third refractive index, wherein the second refractive index is greater than the first refractive index.

[0046] Although the numerical ranges and parameters of the wide range of the present teachings are approximate values, the numerical values ​​described in the specific examples are reported as accurately as possible. However, any numerical value inherently contains certain errors that must be caused by the standard deviation in their respective test measurement results. In addition, all ranges disclosed herein should be understood to cover any and all sub-ranges contained therein. For example, the scope of "less than 10" may include any and all sub-ranges (including endpoints) between a minimum value of 0 and a maximum value of 10, that is, any and all sub-ranges, such as 1 to 5, where the minimum value is equal to or greater than zero and the maximum value is equal to or less than 10. In some cases, the numerical value of the parameter can take a negative value. In this case, the example value of the scope stated as "less than 10" can take a negative value, such as -1, -2, -3, -10, -20, -30, etc.

[0047] Although the present teaching has been described with respect to one or more embodiments, the examples shown may be changed and / or modified without departing from the spirit and scope of the appended claims. For example, it will be appreciated that although the process is described as a series of actions or events, the present teaching is not limited by the order of these actions or events. Certain actions may occur in different orders and / or occur simultaneously with other actions or events other than those described herein. Moreover, all process stages may not be required to implement the method according to one or more aspects or embodiments of the present teaching. It will be understood that structural components and / or processing stages may be added, or existing structural components and / or processing stages may be removed or modified. In addition, one or more actions described herein may be performed in one or more separate actions and / or stages. In addition, to the extent that the terms "including", "includes", "having", "has", "with" or their variants are used in the specific embodiments and claims, these terms are intended to be inclusive in a manner similar to the term "comprising". The term "at least one of..." is used to indicate that one or more items listed may be selected. As used herein, the term "one or more of" in relation to a list of items such as A and B means A alone, B alone, or A and B. Further, in the discussion and claims herein, the term "on" used with respect to two materials, one material "on another material" means that there is at least some contact between the materials, while "over" means that the materials are close, but may have one or more other intermediate materials, so that there can be contact, but not required. As used herein, "on" or "over" do not imply any directionality. The term "about" means that the listed values ​​can be changed, as long as the change does not cause the process or structure to be inconsistent with the illustrated embodiment. Finally, "exemplary" means that the description is used as an example, rather than implying that it is ideal. Other embodiments of the present teaching will be apparent to those skilled in the art by considering the description and practice of the contents disclosed herein. The description and examples are intended to be considered as exemplary only, and the true scope and spirit of the present teaching are indicated by the appended claims.

Claims

1. A vertical external cavity surface emitting laser (VECSEL), comprising: Heat sink; a heat sink formed on a top surface of the heat sink, wherein the heat sink comprises a first material having a first refractive index; a semiconductor active region formed on a top surface of the heat sink, wherein the semiconductor active region comprises a second material having a second refractive index; as well as a high contrast grating formed on a top surface of the semiconductor active region, wherein the high contrast grating comprises a third material having a third refractive index, wherein the second refractive index is greater than the first refractive index and a third refractive index, the third refractive index representing a medium of pump laser light incident on the high contrast grating; The period, fill factor, etching depth and refractive index of the high contrast grating are optimized so that the zeroth order diffraction from the high contrast grating is minimized and higher diffraction orders are transmitted to achieve total internal reflection at the interface of the heat sink.

2. The VECSEL according to claim 1, wherein: The heat spreader is bonded to the heat sink using a thermally conductive adhesive.

3. The VECSEL according to claim 1, wherein: The semiconductor active region is bonded to the heat sink using van der Waals bonding.

4. The VECSEL according to claim 1, wherein: The semiconductor active region includes a gain chip.

5. The VECSEL according to claim 1, wherein: The semiconductor active region includes GaAs, AlGaAs or InGaAs.

6. The VECSEL according to claim 1, wherein: The semiconductor active region includes InP / AlInGaAs / InGaA.

7. The VECSEL according to claim 1, wherein: The semiconductor active region includes GaSb / AlGaAsSb / InGaAsSb.

8. The VECSEL according to claim 1, wherein: The semiconductor active region includes GaAs / AlAs / AlGaAs / GaInP / AlGaInP.

9. The VECSEL according to claim 1, wherein: The heat sink is diamond, silicon carbide, sapphire or another transparent heat sink with high thermal conductivity.

10. The VECSEL according to claim 1, wherein: The semiconductor active region includes a bulk semiconductor, a heterostructure, one or more quantum wells, or one or more quantum dot layers.

11. The VECSEL according to claim 1, wherein: The heat sink is cooled via direct contact with a cooling medium or by attachment to the heat sink.

12. The VECSEL according to claim 11, wherein: The heat spreader is bonded to the heat sink using thermally conductive adhesive, solder, or mechanical attachments.

13. A method of forming a vertical external cavity surface emitting laser (VECSEL), the method comprising: bonding a heat spreader to a top surface of the heat sink, wherein the heat spreader comprises a first material having a first refractive index; bonding an active region to the top surface of the heat sink, wherein the active region comprises a second material having a second refractive index; as well as bonding a high contrast grating to a top surface of the active region, wherein the high contrast grating comprises a third material having a third refractive index, wherein the second refractive index is greater than the first refractive index and the third refractive index, the third refractive index representing a medium of pump laser light incident on the high contrast grating; The period, fill factor, etching depth and refractive index of the high contrast grating are optimized so that the zeroth order diffraction from the high contrast grating is minimized and higher diffraction orders are transmitted to achieve total internal reflection at the interface of the heat sink.

14. The method of claim 13, wherein: The heat spreader is bonded to the heat sink using a thermally conductive adhesive.

15. The method of claim 13, wherein: The active region is bonded to the heat sink using van der Waals bonding.

16. The method of claim 13, wherein: The active region includes a semiconductor active region.

17. The method of claim 13, wherein: The active region includes GaAs, AlGaAs or InGaAs.

18. The method of claim 13, wherein: The active region includes InP / AlInGaAs / InGaAs.

19. The method of claim 13, wherein: The active region includes GaSb / AlGaAsSb / InGaAsSb.

20. The method of claim 13, wherein: The active region includes GaAs / AlAs / AlGaAs / GaInP / AlGaInP.

21. The method of claim 13, wherein: The heat sink is diamond, silicon carbide, sapphire or another transparent heat sink with high thermal conductivity.

22. The method of claim 13, wherein: The active region includes a bulk semiconductor, a heterostructure, one or more quantum wells, or one or more quantum dot layers.

23. The method of claim 13, wherein: The heat sink is cooled via direct contact with a cooling medium or by attachment to the heat sink.

24. The method of claim 23, wherein: The heat spreader is bonded to the heat sink using thermally conductive adhesive, solder, or mechanical attachments.

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