Multi-kW class blue laser system

Abstract

To provide Multi-kW-class blue fiber-delivered lasers and module configurations.SOLUTION: The lasers propagate laser beams having beam parameter products of less than 5 mm*mrad, which are used in materials processing, welding, and pumping a Raman laser. The laser system is an integration of fiber-coupled modules, which are in turn made up of submodules, the sub-modules having a plurality of lensed blue semiconductor gain chips with low reflectivity front facets. These are locked in wavelength with a wavelength spread of less than 1 nm by using volume Bragg gratings in an external cavity configuration. Modules including a plurality of submodules, are combined through wavelength multiplexing with a bandwidth of less than 10 nm, followed by polarization beam combining. The output of each module is fiber-coupled into a low NA fiber. A kW-level blue laser system is realized by fiber bundling and combining multiple modules into a single output fiber.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] This application claims the benefit under 35 U.S.C. §119(e)(1) of the filing date of U.S. Provisional Application No. 2 / 580,419, filed November 1, 2017, the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002] The present invention relates to high power laser systems that provide laser energy at shorter wavelengths, for example, from about 350 nm to about 700 nm, and uses of these systems and laser beams, including material processing and laser welding applications.

[0003] Infrared red (IR)-based (e.g., having wavelengths above 700 nm, especially above 1000 nm) additive manufacturing systems suffer from two major drawbacks: they limit both production volume and production speed.

[0004] As used herein, unless otherwise specified, "UV," "ultraviolet light," "UV spectrum," and "UV portion of the spectrum" and similar terms are to be given their broadest meaning and include wavelengths from about 10 nm to about 400 nm, and from 10 nm to 400 nm.

[0005] As used herein, unless otherwise specified, "high power," "multi-kilowatt," and "multi-kW" lasers, laser beams, and similar such terms refer to and include laser beams and systems providing or propagating them that are at least 1 kW of power (not low power, e.g., 1 kW or more), at least 2 kW (e.g., 2 kW or more), at least 3 kW (e.g., 3 kW or more), greater than 1 kW, greater than 2 kW, greater than 3 kW, from about 1 kW to about 3 kW, from about 1 kW to about 5 kW, from about 2 kW to about 10 kW, and within these ranges and greater power.

[0006] As used herein, unless otherwise specified, the terms "visible," "visible spectrum," and "visible portion of the spectrum" and similar terms are to be given their broadest meaning and include light from about 380 nm to about 750 nm, and from 400 nm to 700 nm.

[0007] As used herein, unless otherwise specified, the terms "blue laser beam," "blue laser," and "blue" should be given their broadest meaning and refer to a light source, such as a diode laser, that provides (e.g., propagates) light or laser having a wavelength from about 400 nm to about 495 nm, a laser beam, or a system that provides a laser.

[0008] As used herein, unless otherwise specified, the terms "green laser beam," "green laser," and "green" should be given their broadest meaning and generally refer to light sources, such as lasers and diode lasers, that provide (e.g., propagate) light having a wavelength of about 495 nm to about 570 nm, laser beams, and systems that provide lasers.

[0009] In general, the term "about" as used herein, unless otherwise specified, is meant to include a variation or range of ±10%, the experimental or instrumental error associated with obtaining the stated value, preferably the greater of these.

[0010] As used herein, unless otherwise specified, ranges of values, ranges from about "x" to about "y," and similar such terms and quantifications include each item, feature, value, amount, or quantity that falls within the range. As used herein, unless otherwise specified, all individual points within a range are incorporated herein and are part of this specification as if each point was individually set forth herein.

[0011] This "Background" section is intended to introduce various aspects of technology that may be related to embodiments of the present invention. As such, the preceding discussion in this section provides a framework for better understanding the present invention and should not be construed as admissions of prior art. Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention advances the technology and solves the long-felt need to provide and utilize high power blue, blue-green and green lasers, provides a solution to a long-standing problem with IR additive manufacturing systems and processes, and addresses these and other long-felt and future needs so that additive manufacturing processes and systems become more prevalent. The present invention solves these problems and needs by, among other things, advancing the technology and providing the products, devices, and processes disclosed and taught herein. [Means for solving the problem]

[0013] First, a blue (400nm-495nm) laser diode system is provided that delivers a laser beam of over 100 watts into a 50-200μm fiber.

[0014] Additionally, a high power blue (400nm-495nm) laser diode system is provided that delivers over 1000 watts of laser beam into a 150μm fiber.

[0015] Additionally, a high power blue laser diode system is provided having a beam parameter product of approximately 5 mm-mrad for pumping Raman fiber lasers or for processing materials, such as welding, cutting, cladding, and 3D printing.

[0016] Additionally, a high power blue laser diode system having a beam parameter product of about 10 mm-mrad is provided that can be used to pump a Raman fiber laser and process materials.

[0017] Also provided is a high power blue diode laser system that is spectrally beam combined to produce a sufficiently narrow (<10 nm) composite beam that can be used to pump a high power Raman laser system and process materials.

[0018] Furthermore, there is provided a high power blue diode laser system that is spectrally beam combined to produce a sufficiently narrow (<10 nm) composite beam that can be used to pump a high power Raman laser system or to process materials, where the high power blue diode laser system is adapted to spectrally combine the beams using a prism.

[0019] Also provided is a high power blue diode laser system that is spectrally beam combined using a diffractive element to produce a composite beam that is sufficiently narrow (<10 nm) that can be used to pump a high power Raman laser system or to process materials.

[0020] Additionally, a high power blue diode laser system is provided that is spectrally beam combined using a volume Bragg grating to produce a sufficiently narrow (<10 nm) composite beam that can be used to pump a high power Raman laser system or to process materials.

[0021] Furthermore, a high power blue diode laser system is provided that is spectrally combined using a dielectric coating as a filter to produce a composite beam that is sufficiently narrow (<10 nm) that can be used to pump a high power Raman laser system or to process materials.

[0022] Additionally, a blue laser diode system with a power output of 100-1,000 W and a beam parameter product of approximately 5 mm-mrad for pumping a Raman fiber laser or processing materials is provided.

[0023] Additionally, a blue laser diode system with 100-1,000 W output power and a beam parameter product of 10 mm-mrad is provided for pumping Raman fiber lasers or processing materials.

[0024] Also provided is a 100-1,000 W output power blue diode laser system that is spectrally beam combined to produce a composite beam that is sufficiently narrow (<10 nm) that can be used to pump a high power Raman laser system or to process materials.

[0025] Additionally, a 100-1,000 W blue diode laser system is provided that is spectrally beam combined using a prism to produce a sufficiently narrow (<10 nm) composite beam that can be used to pump a high power Raman laser system or to process materials.

[0026] Furthermore, a 100-1,000 W output power blue diode laser system is provided that is spectrally beam combined using a diffractive element to produce a composite beam that is sufficiently narrow (<10 nm) that can be used to pump a high power Raman laser system or to process materials.

[0027] Additionally, a 100-1,000 W output power blue diode laser system is provided that is spectrally beam combined using a volume Bragg grating to produce a sufficiently narrow (<10 nm) composite beam that can be used to pump a high power Raman laser system or to process materials.

[0028] Also provided is a 100-1,000 W output power blue diode laser system that is spectrally beam combined using a series of dichroic filters based on dielectric coatings to produce a composite beam that is sufficiently narrow (<10 nm) that can be used to pump high power Raman laser systems or process materials.

[0029] Thus, a laser system for providing a multi-kW laser beam with a power output of 100-1,000 W, more preferably with a final output laser beam having a wavelength in the spectral range of about 400 nm to about 495 nm, is provided. The system includes one, two, five, tens, or hundreds of fiber-coupled modules, each having one, two, five, tens, or hundreds of sub-modules. The sub-modules are mounted on highly thermally conductive submounts with one, two, five, tens, or hundreds of lensed blue semiconductor gain chips from the GaN material system having an output facet reflectivity optimized for stable locking of the laser diode, with the low reflectivity facet facing outwards and a fast axis collimating lens mounted in front of the gain chips. The lensed blue semiconductor gain chips are mounted on stepped heat sinks in an external cavity for optimal alignment of the fast axis beamlets. The gain chips are configured such that the slow axis of each gain chip is collimated by a collimating lens. A volume Bragg grating can be placed before the slow axis collimator to provide direct feedback to the laser and lock it to a given wavelength. Alternatively, the volume Bragg grating can be integral with either the fast axis collimator or the slow axis collimator. Additionally, a volume Bragg grating can be placed after a turning mirror to form an external cavity. The polarization of each gain device is maintained in the external cavity.

[0030] Also provided is a laser system for providing a multi-kW laser beam with a final output laser beam having a wavelength in a spectral range of 100-1,000 W output, more preferably from about 400 nm to about 495 nm. The system includes one, two, five, tens, or hundreds of fiber-coupled modules, each module including one, two, five, tens, or hundreds of sub-modules. The sub-modules have one, two, five, tens, or hundreds of lensed blue semiconductor gain chips from the GaN material system with output facet reflectivity optimized for stable locking of the laser diode, mounted on a highly thermally conductive submount with the less reflective facet facing outward and a fast axis collimating lens mounted in front of the gain chip. The lensed blue semiconductor gain chips are mounted on a stepped heat sink in an external cavity for optimal alignment of the fast axis beamlets. The gain chips are configured such that the slow axis of each gain chip is collimated by a collimating lens. The output of each individual gain chip can be coupled into an optical fiber with a fiber Bragg grating to lock the element to a specific wavelength. The fiber output is then at a different wavelength for each submodule and can be spectrally combined by dichroic filters, volume Bragg gratings, transmission gratings, or prisms.

[0031] Also provided is a laser system for providing a multi-kW laser beam with a final output laser beam having a wavelength in the spectral range of 100-1,000 W, more preferably from about 400 nm to about 490 nm. The system includes one, two, five, tens, or hundreds of fiber-coupled modules, each having one, two, five, tens, or hundreds of sub-modules. The sub-modules include one, two, five, tens, or hundreds of lensed blue semiconductor gain chips from the GaN material system, incorporating Bragg gratings that set the wavelength of each device to a predetermined value. The chips are mounted on a thermally conductive submount with the reflectivity of the output facet optimized for the output power of the device facing outward, and a fast axis collimating lens mounted in front of the gain chip. The lensed blue semiconductor gain chips are mounted on a stepped heat sink in an external cavity for optimal alignment of the fast axis beamlets. The gain chips are configured to be collimated by the slow axis collimating lens of each gain chip. The outputs of the chips are at different wavelengths for each submodule and can be spectrally combined by dichroic filters, volume Bragg gratings, transmission gratings, or prisms. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a spectrum produced by an optical spectrum analyzer for a single blue gain element locked to a specific wavelength with a linewidth of 0.045 nm in accordance with the present invention.

[0033] [Figure 1A] FIG. 1A shows the spectrum of a single blue gain element of FIG. 1 locked to a particular wavelength with a linewidth of 0.045 nm.

[0034] [Diagram 2]FIG. 2 is a schematic diagram of an embodiment of a Lensed Chip-on-Submount (LCOS) submodule with an integrated VBG (Volume Bragg Grating) for establishing a specific wavelength in accordance with the present invention.

[0035] [Diagram 3] FIG. 3 is a schematic diagram of an embodiment of a six LCOS sub-module without integrated VBG according to the present invention.

[0036] [Figure 4] FIG. 4 is a schematic diagram of a laser module having two rows of six submodules of the type shown in FIG.

[0037] [Diagram 5] FIG. 5 is a schematic diagram of a complete kW-class laser system according to the invention having seven modules of the type shown in FIG.

[0038] [Figure 5A] FIG. 5A is a block diagram of the embodiment of FIG.

[0039] [Figure 6] FIG. 6 is a schematic diagram of a VBG-free dense wavelength beam combining system having two rows of submodules of the type shown in FIG.

[0040] [Figure 7] FIG. 7 is a spectrum (x-axis is wavelength in nanometers (nm) and y-axis is transmittance) of the bandpass function of each of the filters in FIG. [Figure 7A] FIG. 7A is a spectrum (x-axis is wavelength in nanometers (nm) and y-axis is transmittance) of the bandpass function of each of the filters in FIG.

[0041] [Figure 8] FIG. 8 is a perspective view of an embodiment of a spectral beam combining (SBC) assembly in accordance with the present invention.

[0042] [Figure 9] FIG. 9 is a spectrum (x-axis is wavelength in nanometers (nm) and y-axis is transmittance) of the bandpass function of the filter of FIG.

[0043] [Figure 10] FIG. 10 is a perspective view of a sub-module of the type shown in FIG. 2 on a staircase base plate.

[0044] [Figure 11] FIG. 11 is a perspective view of an LCOS according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] The present invention generally relates to high power lower wavelength laser systems, beam combining to produce high power laser beams, and applications and uses of these beams. In particular, embodiments of the present invention relate to multi-kW class blue fiber-coupled laser systems used for material processing and laser welding applications, particularly wavelengths in the wavelength range of about 400 nm to about 495 nm. These laser embodiments have multiple blue semiconductor gain chips and are output-coupled by step beam combining in an external cavity, wavelength multiplexing, polarized beam combining, and fiber beam combining.

[0046] More particularly, embodiments of the present invention relate to the construction of multi-kW level blue laser systems operating in the spectral range of 400 nm to 495 nm and in the spectral range of about 400 nm to about 495 nm. The lasers here can achieve a beam parameter product (BPP) of <6 mm-mrad (mm*mrad, or mm mrad, i.e. mm×mrad). This type of laser is highly desirable for processing or welding materials with high optical absorption in the blue region of the spectrum, Cu being an example. This type of laser is also highly suitable for pumping Raman lasers or rare earth doped fiber lasers, among others.

[0047] The present laser system embodiments are multi-kW laser systems with emission in the blue wavelengths of the spectrum (about 400 to about 495 nm), more preferably in the range of 400 nm to 475 nm, which are highly effective in materials processing. The short emission wavelengths are preferentially absorbed by virtually all metals, especially Cu and Au, which are difficult to process using IR laser sources. In many embodiments, these systems use low numerical aperture (NA) fiber optic delivery systems for ease of delivery and high brightness. In a preferred embodiment of the invention, the laser system achieves a multi-kW laser beam with a beam parameter product of about 5 mm*mrad that allows for efficient fiber coupling.

[0048] One of the advances in the art according to the present invention, and on which embodiments of the present invention are based, is the ability to lock the wavelength of a blue laser diode gain chip to a specific wavelength with a linewidth of only 0.045 nm. Spectra of embodiments of such locked wavelength laser beams are shown in Figures 1 and 1A. The locked wavelength can be in the wavelength range of about 400 to 495 nm with a linewidth of about 0.050 nm or less, about 0.045 nm or less, about 0.040 nm or less, or a linewidth of 0.050 nm to 0.350 nm. The ability to lock blue laser diode gain chips, for example in GaN, allows modular dense wavelength beam combining designs based on this wavelength locking result.

[0049] This narrow linewidth can be achieved, for example, by using a volume Bragg grating as an external feedback filter and optimizing the reflectivity of the coating on the front facet. The optimized coating helps to achieve a narrow locked linewidth, among other things, by suppressing parasitic oscillations due to the subcavity. Suppressed subcavities include the laser diode element itself, or the subcavity between the laser diode and an external optical element such as collimating optics or the VBG itself.

[0050] An embodiment of the invention is a scalable laser system that contains individual sub-modules that are locked to specific wavelengths. These sub-modules are combined using dense wavelength beam combining techniques followed by one polarized beam combining with a second leg of the sub-module. The resulting beam can be directly fiber coupled with the lenses used and further combined with other modules to achieve high output power or coupled into a Raman gain fiber.

[0051] An embodiment of the sub-module consists of multiple lensed blue semiconductor gain chips with lower reflectivity front facets. The semiconductor gain chips are fabricated in the GaN material system, which is widely used in the fabrication of blue and green LEDs and blue laser diodes. The gain chips are mounted on a highly thermally conductive submount with the lower reflectivity facets facing outwards. A fast axis collimating (FAC) lens is mounted in front of the gain chips to collimate the emitted light in the fast axis. Lensed Chip On Sub-mount is abbreviated as LCOS.

[0052] In one embodiment, the LCOS elements are mounted in a staircase structure in the external cavity. Typically, there are two or more LCOS elements in a submodule, depending on the required beam parameter product. The slow axis of the LCOS elements is collimated by a separate slow axis collimating lens (SAC). The LCOS elements may be on conductive or electrically insulating substrates and can be electrically connected in series or in a series / parallel combination. Wire bonding is typically used to connect the LCOS elements to the submodule electrodes. A turning mirror is used to stack the collimated light in the fast axis and relay it to an external coupling element (e.g., a volume Bragg grating (VBG)). The turning mirror can also be advantageously combined with a SAC in a single optical element. Wavelength locking in the external cavity structure results in a spectral bandwidth of the submodule assembly of less than 1 nm, typically less than 0.1 nm.

[0053] In one embodiment, the LCOS elements are mounted in a staircase structure in the external cavity. Typically, there are two or more LCOS elements in a submodule, depending on the required beam parameter product. The slow axis of the LCOS elements is collimated by a separate slow axis collimating lens (SAC). The LCOS elements may be on conductive or electrically insulating substrates and can be electrically connected in series or in a series / parallel combination. Wire bonding is typically used to connect the LCOS elements to the submodule electrodes. In this embodiment, a VBG is integrated into the FAC to provide both collimation in the fast axis and locking of the GaN gain elements. Wavelength locking in the external cavity structure results in a spectral bandwidth of the submodule assembly of less than 1 nm, typically less than 0.1 nm.

[0054] In one embodiment, the LCOS elements are mounted in a staircase structure in the external cavity. Typically, there are two or more LCOS elements in a submodule, depending on the required beam parameter product. The slow axis of the LCOS elements is collimated by a separate slow axis collimating lens (SAC). The LCOS elements may be on conductive or electrically insulating substrates and can be electrically connected in series or in a series / parallel combination. Wire bonding is typically used to connect the LCOS elements to the submodule electrodes. In this embodiment, a VBG is integrated into the SAC, providing both collimation in the slow axis and locking of the GaN gain elements. Wavelength locking in the external cavity structure results in a spectral bandwidth of the submodule assembly of less than 1 nm, typically less than 0.1 nm.

[0055] In one embodiment, the LCOS elements are mounted in a staircase structure in the external cavity. The LCOS elements are collimated by a pair of FAC and SAC lenses. The collimated output of the LCOS elements is sent to a reflective or transmissive diffraction grating. Littrow reflections from each grating can be used to lock the LCOS elements and redirect the output of the LCOS / grating external cavity to a dichroic filter that is used to combine other locked elements in the module.

[0056] Individual sub-modules, locked to specific wavelengths, are then combined into higher power modules using bandpass, longpass, or shortpass dichroic filters, VBGs, or diffraction gratings and prisms. Sub-modules can be combined with these techniques to create modules with bandwidths less than 10 nm. For example, the output can be increased by combining a pair of wavelength-combined sub-modules using polarized beam combining methods. A typical module can use two sets of 13 or more sub-modules inside. Each set of 13 sub-modules typically has a chromatic dispersion less than 10 nm. The two sets are combined by polarized beam combining. In this case, a broadband waveplate is used to rotate the polarization of one sub-module group, or a pair of image-turning mirrors are used as achromatic polarization rotators to stack two separate groups of sub-modules. The module is then fiber-coupled to a low NA fiber using a focusing lens. The module is contained in a sealed enclosure and attached to a heat sink. The heat sink can be a conventional heat exchanger or a macro- or micro-channel type. Examples of various types of heat sinks are given in Design of Diode Laser Heat Sinks, Fraunhofer-Institut fur Lasertechnik ILT, (Jan 2007), http: / / ilt.fraunhofer.de / ilt / pdf / eng / products / Heatsinks.pdf, the entire disclosure of which is incorporated herein by reference.

[0057] In one embodiment, a multi-kW level blue laser system is realized by fiber bundling to couple multiple modules to a single output fiber. Multiple modules are coupled using a fiber coupler designated as an N to 1 fiber coupler, where N is >1 and is the number of input fibers arranged in a geometric pattern optimized for the intended output fiber. Fiber and fiber coupler components are selected for low absorption in the blue region of the spectrum and high resistance to solarization, and the fabrication of the fiber coupler is optimized for blue light transmission.

[0058] In addition to such an optical train, embodiments of these multi-kW laser systems can include, among other things, cooling manifolds, electronics / power supplies, safety interlocks, optical power monitoring detectors, and temperature monitoring sensors.

[0059] The preferred diodes for use in the present laser system are blue GaN laser diodes, which generally have good output, efficiency, and reliability. These diodes are used as gain elements (with the reflectivity of the output end face coating optimized for alignment and locking) in the embodiments of the laser system of the present invention. In embodiments, the emission power of the individual lasers is superimposed by using them in a stepped external cavity structure at the submodule level. The stepped structure allows for more dense packing of the laser diode beams when combining multiple laser diode sources, with the fast axis lenses being made larger than the desired vertical pitch of the stacked laser sources. Furthermore, in embodiments, the coupling of the submodules at the fiber-coupled module level is performed by wavelength multiplexing of the submodules and by polarization beam combining.

[0060] In an embodiment, several modules (typically seven) are combined by fiber power combining. This embodiment has a unique beam combining sequence of blue gain chips using external cavity step beam combining, wavelength multiplexing, polarization and fiber power beam combining to add more power to the assembly at each stage, maximizing the emitted radiance (brightness) at the system level. The use of separate laser diodes allows the system to be designed with the highest possible brightness, so that this fiber power beam combining method can be used for incoherent power boost while still producing a laser source bright enough to weld, cut or pump other lasers.

[0061] Commercially available GaN multimode laser diodes in the blue region of the spectrum can achieve several watts of power from a single emitter (see for example the Nichia NDB7K75 multimode single emitter part rated at 3.5W output power in the 440-455nm wavelength range: product description at http: / / www.nichia.co.jp / en / product / laser.html). The output power of multiple GaN blue multimode semiconductor laser diodes or equivalent gain elements can be constructively added to maximize brightness and achieve kW power levels.

[0062] In one embodiment, the starting or basic building block of the laser system is a lensed chip-on-submount (LCOS) gain element. For example, the LCOS is comprised of a GaN-based semiconductor gain chip. GaN is a material system that is widely used in the manufacture of blue LEDs and laser diodes. In this embodiment, the blue laser diode gain element has a low reflectivity (LR) coating (<10%) on the forward emitting facet to facilitate wavelength locking in an external cavity configuration. Low reflectivity coatings are typical in semiconductor laser external cavity designs of the type described, for example, in U.S. Pat. Nos. 5,050,179, 6,208,679, 6,192,062, and WO 2016 / 042019, the disclosures of which are incorporated herein by reference in their entireties. The low reflectivity coating is selected to enable broadband locking as well as to be optimized for lasing the chip during lens alignment and mounting. Preferably, the gain chip is soldered onto a submount, which can be made from a number of materials, such as, for example, SiC, diamond, Cu, CuW, or Cu-AlN-Cu.

[0063] The blue gain chip is attached to the submount using solder, which can be Sn and Sn-based alloys (such as Au-Sn), or In and In-based alloys, or Nanofoil (a trademark of Indium Corporation for a reactive multilayer foil material that undergoes a self-heating reaction after a heat pulse). The fast axis of the gain element is collimated using a fast axis collimator (FAC). Chip-on-submount (COS) devices have found applications in IR diode systems (see, for example, WO 2016 / 160547, US 9,450,377 and US 6,044,096), but have not been considered to be a generally accepted commercial application for LCOS in the blue wavelength range. The blue FAC lens configuration of the present invention is tailored to the specific wavelength range and gain chip design, which can include manufacturing constraints and height considerations dictated by submount size.

[0064] In general, staircase beam combining of laser diodes is taught and disclosed in US 2004 / 0114648, US 7,738,178, US 7,7339,32, US 7,668,214, US 7,773,655, US 8,427,749, US 8,432,945, US 8,437,086, US 9,373,932 and US 9,318,876, the disclosures of each of which are incorporated herein by reference in their entirety.

[0065] In an embodiment of the present invention, the laser diode step beam combining is for blue GaN emitting laser diodes or blue GaN gain chips (low reflection (LR) coated chips), preferably for configurations where the gain chip is placed in an external cavity.

[0066] An embodiment of the present invention uses a blue LR coated gain chip in an external cavity configuration and a volume Bragg grating (VBG) as the external coupling element. In one embodiment, beam combining methods include, by way of example, step beam combining in an external cavity, patterned mirror combining in an external cavity, wavelength beam combining with multiplexing within a 10 nm bandwidth, polarization beam combining, fiber combining, and combinations or variations thereof to achieve an integrated system, preferably providing multi-kW blue wavelengths with beam parameter products less than 5 kW-mrad.

[0067] VBGs that may be used in embodiments of the present invention are described, for example, in U.S. Patent Nos. 7,394,842 and 7,031,573, the entire disclosures of which are incorporated herein by reference. Fiber couplers / splitters that may be used in embodiments of the present invention are described, for example, in U.S. Patent Nos. 7,218,828 and 7,532,792, the entire disclosures of each of which are incorporated herein by reference.

[0068] Embodiments of the present invention may be passively cooled (e.g., no forced movement of cooling medium, heat sink, ambient air, or both) or actively cooled. Examples of active cooling include flowing a gas, such as air, or a liquid cooling fluid, such as water, in thermal contact with the diode. A water cooling system for laser diodes is disclosed in U.S. Pat. No. 9,413,136, the entire disclosure of which is incorporated herein by reference.

[0069] In one embodiment, the optical device is configured to generate multi-kW laser radiation with emission in the blue wavelengths of the spectrum (400-495 nm), the optical device comprising:

[0070] a) comprising M fiber-coupled modules, each module comprised of N sub-modules, where M>1 and N>1: (i) the sub-modules are comprised of P lensed blue semiconductor gain chips in the GaN material system, the front facets of the gain chips having a lower reflectivity coating optimized for locking; (ii) the sub-modules are mounted on a thermally conductive submount with the lower reflectivity facets facing outwards and a fast axis collimating lens mounted in front of the gain chips; (iii) the lensed blue semiconductor gain chips are mounted on a stepped heat sink within an external cavity to optimally lock the wavelength of the gain element to a predetermined wavelength; (iv) the polarization of each gain device is maintained within the external cavity design;

[0071] b) a fiber-coupled module comprising a plurality of sub-modules; where (i) two or more sets of sub-modules are coupled by wavelength multiplexing with a bandwidth of less than 10 nm; (ii) while two sets of wavelength multiplexed sub-modules are coupled by polarized beam coupling; (iii) said plurality of modules are mounted on a heat sink within a sealed housing; and

[0072] c) The fibers of multiple modules are bundled and combined into a single output fiber to generate a KW level blue laser system.

[0073] These laser system, module, sub-module and method embodiments may have one or more of the following features: the output of the gain element of the optical device is collimated and redirected with a turning mirror to the next beam combining element; the output of the gain element of the optical device is collimated and aligned with the next beam combining element; having a GaN gain element with a lower reflectivity end face facing outward and a volume Bragg grating integrated with a fast axis collimating lens; having a GaN gain element with a lower reflectivity end face facing outward and a volume Bragg grating after the fast axis collimating lens; having a GaN gain element with a lower reflectivity end face facing outward and a volume Bragg grating after the slow axis collimating lens; using a reflective grating operated in a retro configuration after the GaN gain element with a lower reflectivity end face facing outward and the slow axis collimating lens to redirect the output to a dichroic filter. The apparatus includes a GaN gain element with a less reflective end face facing outward and a transmissive grating working in combination with a mirror to provide feedback to the gain element and redirect the output to a dichroic filter. The apparatus includes a GaN gain element with a less reflective end face facing outward and a collimating optical system with an output coupled to an optical fiber having a fiber Bragg grating embedded therein to determine the feedback and wavelength of the GaN gain. The apparatus is configured to provide a laser beam having a beam parameter product on the fast axis of <3.5 mm*mrad. The apparatus is configured to provide a laser beam having a beam parameter product on the slow axis of less than 5 mm*mrad. The apparatus is configured to provide a laser beam having a beam parameter product greater than 3.5 mm-mrad overall but less than 5 mm-mrad. The apparatus is configured to provide laser parameters having a beam parameter product greater than 5 mm-mrad overall but less than 10 mm-mrad. The apparatus is configured to provide a spectral emission of less than 10 nm in the 400-495 nm spectral region.The device is configured to provide spectral emissions greater than 1 nm but less than 5 nm, greater than 1 nm but less than 10 nm, greater than 1 nm but less than 15 nm, and greater than 1 nm but less than 20 nm. The reflectivity of the front facet of the gain chip is less than 10%. The reflectivity of the front facet of the gain chip is selected from the group of greater than 10% but less than 15%, greater than 15% but less than 20%, and greater than 20% but less than 30%. Each submodule has P lensed blue semiconductor gain chips on a submount, where P is greater than 1. The lensed blue GaN-based semiconductor gain chips are electrically connected in series or in a series / parallel electrical combination and wire bonded to the submodule electrodes. The fiber should be selected to have low absorption in the blue region of the spectrum, and the fabrication of the fiber coupler should be optimized for blue light transmission. Each submodule has a spectral distribution less than 1 nm following wavelength locking in the external cavity structure. There are two sets of 12 submodules in the module. M modules (M>1) are coupled to K input fibers (K>M) using a fiber coupler in any geometric packaging arrangement optimized for a selected output fiber or output beam. The kW laser system is characterized by having a cooled manifold. The kW laser system is characterized by including electronics / power supplies. The kW laser system is characterized by including a safety interlock. The kW laser system is characterized by having an optical power monitoring detector. And, the kW laser system is characterized by including a temperature monitoring sensor.

[0074] In one embodiment, the optical device is configured to generate multi-kW laser radiation with emission in the blue wavelengths of the spectrum (400-495 nm), the optical device comprising:

[0075] a) M fiber-coupled modules, each module composed of N sub-modules, where M>1, N>1, (i) the sub-modules are composed of P lensed blue semiconductor gain chips in a GaN material system with a coating on their front facets that are low reflectivity and optimized for locking; (ii) the sub-modules are mounted on a thermally conductive submount with the lower reflectivity facets facing outwards and a fast axis collimating lens mounted in front of the gain chips; (iii) the lensed blue semiconductor gain chips are mounted on a stepped heat sink within an external cavity for optimal alignment of the fast axis beamlets; (iv) each gain chip has a slow axis that is collimated by a slow axis collimating lens such that a turning mirror directs the emission to an output coupler; and (v) each LCOS is matched by a dichroic filter, the output coupler providing feedback to each of the gain elements, and a dichroic filter element determining the operating wavelength of each LCOS assembly;

[0076] b) a fiber-coupled module comprising a plurality of sub-modules: (i) two sets of sub-modules coupled by wavelength multiplexing with a bandwidth of less than 10 nm; (ii) two sets of wavelength-multiplexed sub-modules coupled by polarized beam coupling; (iii) the aforementioned modules are contained in a sealed housing and mounted on an actively cooled heat sink; and

[0077] c) The fibers of multiple modules are bundled and combined into a single output fiber to generate a KW level blue laser system.

[0078] These laser system, module, sub-module and method embodiments may have one or more of the following features: a beam parameter product on the fast axis of greater than 3.5 mm*mrad; a beam parameter product on the slow axis of less than 5 mm*mrad; a beam parameter product of greater than 3.5 mm-mrad but less than 5 mm-mrad overall; a beam parameter product of greater than 5 mm-mrad but less than 10 mm-mrad overall; a spectrum of less than 10 nm in the 400-495 nm region of the spectrum; a spectrum of greater than 1 m but less than 5 nm, greater than 1 nm but less than 10 nm, greater than 1 nm but less than 15 nm, greater than 1 nm but less than 20 nm; a reflectivity of the front facet of the gain chip less than 10%; a reflectivity of the front facet of the gain chip greater than 10% but less than 15%, greater than 15% but less than 20%, greater than 20% but less than 30%; and a number P of lensed blue semiconductor gain chips on the submount of each sub-module, where P is greater than 1. The lensed blue GaN-based semiconductor gain chips are electrically connected in series or in a series / parallel electrical combination and wire bonded to the submodule electrodes. The fibers should be selected for low absorption in the blue region of the spectrum and the fabrication of the fiber coupler should be optimized for blue light transmission. Each submodule has a spectral distribution of less than 1 nm following wavelength locking within the external cavity structure. The module has two sets of 12 submodules. M modules (M>1) are coupled with K fibers (K>M) using fiber couplers in any geometric packaging arrangement optimized for the selected output fiber or output beam. The kW laser system includes: the kW laser system has a cooled manifold; the kW laser system includes electronics / power supply; the kW laser system includes a safety interlock; the kW laser system has an optical power monitoring detector; and the kW laser system includes a temperature monitoring sensor.

[0079] In one embodiment, the optical device is configured to generate multi-kW laser radiation with emission in the blue wavelengths of the spectrum (400-495 nm), the optical device including the following features:

[0080] a) M fiber-coupled modules, each module composed of N sub-modules, where M>1 and N>1; (i) the sub-modules are composed of P lensed blue semiconductor laser chips from the GaN material system, with distributed Bragg or feedback gratings integrated into the GaN chips to select their operating wavelengths; (ii) the sub-modules are mounted on highly thermally conductive submounts with their lower reflectivity end faces facing outwards and with a fast axis collimating lens mounted in front of the lasers; (iii) mounted on a thermally conductive heat sink, with the fast axis collimating lens followed by a slow axis collimating lens; (iv) the lensed blue semiconductor lasers are mounted on a stepped heat sink; (v) the polarization of each laser device is established by the waveguide configuration of the laser device;

[0081] b) a fiber-coupled module comprising a plurality of sub-modules: where (i) two or more sets of sub-modules are coupled by wavelength multiplexing having a bandwidth of less than 10 nm; (ii) the two sets of wavelength multiplexed sub-modules are coupled by polarized beam coupling; and (iii) the aforementioned modules are contained in a sealed housing and attached to a heat sink; and

[0082] c) The fibers of multiple modules are bundled and combined into a single output fiber to generate a KW level blue laser system.

[0083] These laser system, module, sub-module and method embodiments may have one or more of the following features: the output of the gain element of the optical device is collimated and redirected with a turning mirror to the next beam combining element; the output of the gain element of the optical device is collimated and aligned with the next beam combining element; a reactive multilayer foil, which undergoes a self-sustaining exothermic reaction after a heat pulse; bonding the individual LCOS assemblies to the sub-module and bonding the sub-module to the module; the foil is a NANOFOIL (provided by Indium Corporation); and configured to provide a linewidth narrow enough to pump a fiber-based Raman laser (less than 10 nm for fused silica and less than 3 nm for phosphate-doped glass); and features: all optical components must be selected for low absorption in the blue region of the spectrum, and the fabrication of the fiber coupler must be optimized for blue light transmission; one or more of the optical components must be selected for low absorption in the blue region of the spectrum, and the fabrication of the fiber coupler must be optimized for blue light transmission.

[0084] These laser system, module, and sub-module embodiments preform a laser operation. In these laser system, module, and sub-module preform laser operation embodiments, the laser operation is selected from a group of operations including 3D printing, additive manufacturing, subtractive / additive manufacturing, welding, surface treatment, and cutting.

[0085] The following examples are provided to illustrate various embodiments of the laser system and components of the present invention. These examples are for illustrative purposes and may be prophetic, and should not be considered limiting and do not restrict the scope of the invention.

[0086] Example 1

[0087] An embodiment of an assembly (e.g., sub-module) 100 is a configuration of six lensed chips on submounts (LCOS), and is shown diagrammatically in FIG. 2. In the sub-module 100, each LCOS has a gain element 101a, 101b, 101c, 101d, 101e, 101f, each of which generates a laser beam, e.g., 180a, traveling along a laser beam path, e.g., 181a (shown as a single arrow because the laser beam is on, i.e., coincident with, the laser beam path). The ability to lock the gain elements 101a-101f to a single element is enhanced by a lower reflectivity (LR) end face coating, e.g., 102a, preferably on each GaN gain element 101a-101f. Each of the gain elements 101a-101f has a fast axis collimating lens, e.g., 103a, and a slow axis collimating lens, e.g., 104a. Each gain element 101a-101f has a turning mirror, e.g. 105a. In this way, the laser beam and laser beam path, respectively, travels from a gain element, e.g. 101a, through a fast axis collimator (FAC), e.g. 103a, then through a slow axis collimator (SAC), e.g. 104a, and then to a turning mirror, e.g. 105a. The first turning mirror 105a redirects the laser beam path and laser beam to the second turning mirror 105b and subsequent turning mirrors. The redirected laser beam 180a' and laser beam path 181a' are combined with the laser beams and laser beam paths from the other gain elements 101b, 101c, 101d, 101e, 101f by subsequent turning mirrors, e.g. 105b. The redirected and combined laser beam and laser beam path then exits through the VBG 106.

[0088] The VBG 106 is at the exit of the submodule 100 and is intended to lock all gain elements on the submodule 100 to a single wavelength. The VBG can be integrated into the FAC or SAC. Similarly, the locking element, the grating, can be a turning mirror as shown in this figure, eliminating the need for a VBG.

[0089] The LOCS can be assembled on a base, such as a submount (not shown in FIG. 1), which can also function as a heat sink.

[0090] It will be understood that 2, 3, 4, 5, 7, 8, 9, 10, tens, and hundreds of gain elements may be used in a single sub-module or assembly. Additionally, while the optical components along the beam path as shown in the embodiment of FIG. 2 are preferred, in other embodiments, several laser beam paths from one gain element may not have all of the optical components along the beam path as shown in the embodiment of FIG.

[0091] The embodiment of Figure 2 can provide, for example, a laser beam achieved by locking a single GaN gain element to a specific wavelength as shown in Figures 1 and 1A, with the external cavity laser operating with a linewidth of 0.045 nm, which is well below the requirements of the embodiments of the dense wavelength beam combining methods described herein.

[0092] Example 1A

[0093] The sub-module embodiment of FIG. 2 includes Zener diodes for back bias protection located along one or more and all beam paths.

[0094] Example 1B

[0095] 2, the slow-axis collimating (SAC) lens 104 is separate from the turning mirror 105. In one embodiment, depending on the design goals of the sub-module, the two can be combined using an off-axis parabola approach or the SAC lens can be mounted after the turning mirror.

[0096] Example 2

[0097] Referring to Fig. 3, a schematic diagram of an embodiment of an assembly that allows the gain elements to be locked by a combination of individual dichroic mirrors and a common output coupler is shown. In this embodiment, an assembly such as a sub-module includes six LCOS, 3000a, 3000b, 3000c, 3000d, 3000e, 3000f, integrated into the sub-module, and is attached to a base 3300 (e.g., base plate, heat sink, mounting block). Each of the six LCOS has a gain element 3101 with a lower reflectivity (LR) end coating 3102, a FAC 3103, a SAC 3104, and a turning beam combining element 3105.

[0098] Example 3

[0099] Referring to Figure 4, a schematic diagram of a laser module 290 on a base 200 is shown. The laser module 290 has two columns 291, 292 of LCOS submodules. In this embodiment, each column 291, 292 has six LCOS submodules. In this embodiment, all twelve LCOS submodules are submodules 100 of the embodiment of Figure 1. It is understood that more or fewer columns, more or fewer submodules, and the same or different types of submodules can be used.

[0100] The sub-modules are optically coupled with a series of combining optical elements, e.g., dichroic filters, VBGs, or diffraction gratings. That is, in this embodiment, each sub-module (e.g., 100) in row 292 directs its laser beam path and laser to a dichroic filter 201a, 202a, 203a, 204a, 205a, 206a, which form combined laser beam 185a along laser beam path 186a. Each sub-module in row 291 directs its laser beam path and laser to a dichroic filter 201, 202, 203, 204, 205, 206, which form combined laser beam 185 along laser beam path 186. (In the drawings, only one line is shown for both the laser beam and its path, as the laser beam travels along the laser beam path.)

[0101] The passband functions of each dichroic filter are shown in Figures 7 and 7A (like numbers indicate corresponding filters). Filters 202, 202a are for a nominal 446 nm wavelength beam with a lower cutoff at 440.5 nm and an upper cutoff at 447.25 nm. Filters 203, 203a are for a nominal 447 nm wavelength beam with a lower cutoff at 441.5 nm and an upper cutoff at 448.25 nm. Filters 204, 204a are for a nominal 448 nm wavelength beam with a lower cutoff at 442.5 nm and an upper cutoff at 449.25 nm. Filters 205, 205a are for a nominal 449 nm wavelength beam with a lower cutoff at 443.5 nm and an upper cutoff at 450.25 nm. Filters 206, 206a are for a nominal 450 nm wavelength beam with a lower cutoff at 444.5 nm and an upper cutoff at 451.25 nm. (The lower and upper cutoffs refer to the points in the spectrum where the transmission changes from or to zero.)

[0102] Thus, each passband is overlapped to create a transmission window at the red edge of each bandpass filter. By reversing the order of the dichroic filters (206, 206a to 201, 201a), the passband can be shifted to the blue edge of each bandpass filter. The bandpass filter functions are calculated using a thin film coating model and optimized for edge steepness and transmission. The transmission windows can be shifted by about 0.75 nm, and more offset positions can also be used, for example, 0.8 nm to 3 nm, 0.8 nm to 1.8 nm, about 0.8 nm, about 1.0 nm, about 1.5 nm, etc. In the embodiment shown in FIG. 7, the transmission windows are shifted by 1 nm. The filters used in this embodiment can be bandpass, lowpass, or highpass, and some bandpass filters can provide steeper edge transitions and therefore a tighter wavelength combination than any other laser currently on the market. After the sub-modules are all collinearly aligned, the outputs from columns 292 and 291 overlap each other in polarization state. Thus, output laser beam 185a from column 292 and output laser beam 185 from column 291 are combined in an overlapping polarization relationship. This relationship is achieved by turning mirror 207, which receives beam 185 and beam path 186 and directs beam 185 and beam path 186 to polarization rotation element 209. Polarizing beam splitter 208 receives laser beam 185a and beam path 186a and combines them with beam 185 and path 186 to provide further combined laser beam 187 along beam path 188. The combined laser beam 187 is launched into optical fiber 211 by optical element 210, e.g., a lens. This lens is designed to focus all the sub-modules to a single point within the bandwidth (~10 nm) of the combined beam. This type of lens can be, for example, an aspheric lens, a simple doublet lens, or a Cook triplet lens, depending on the speed of the optics.Due to the high laser power delivered by these elements, e.g., 209, 208, 210, 211, they may be configured to be optically contacted, spatially spaced, or both, to minimize heating and distortion of the output beam.

[0103] Example 4

[0104] In FIG. 10 (where the same numerals as in FIG. 2 refer to the same things), an LCOS submodule 100 of the type shown in FIG. 2 is assembled on a stepped submount 107 that also functions as a heat sink. (Beam paths and laser beams are shown in FIG. 10, but for simplicity they are not labeled with reference numbers, but are of the same beam paths as in FIG. 2). The submodule 100 has six LCOS assemblies or elements. Each LCOS has a gain element, e.g., 101a, a FAC, e.g., 103a, a SAC, e.g., 104a, and a turning mirror, e.g., 105a. The first turning mirror 105a redirects the laser beam path and the laser beam to the second turning mirror 105b and subsequent turning mirrors. The redirected laser beam and the laser beam path are combined with the laser beam and the laser beam path from the other gain elements by subsequent turning mirrors, e.g., 105b. The redirected and combined laser beam and laser beam path exits through the VBG 106 .

[0105] The six LCOS elements are mounted on a base 107, which can be a heat sink, for example a plated Cu heat sink. The light beams are collimated in the slow axis using a slow axis collimating (SAC) lens. The beams are reflected by a turning mirror, which directs them to a volume Bragg grating (VBG) 106, which is an outcoupling mirror of an external cavity formed between the semiconductor gain element and the VBG. The number of diodes determines the numerical aperture and spot size of the module, or the brightness of the module. In this example, they are optimized to provide a beam parameter product of about 5 mm-mrad.

[0106] Example 5

[0107] In one embodiment, the SBC module of Figure 4 includes N sub-modules or equivalent elements mounted on either side of a base 200. The base of the package is made from Cu or equivalent thermally conductive material and is attached to a macro- or micro-channel type fluid-cooled heat sink.

[0108] Example 6

[0109] Referring to FIG. 8, a perspective view of an embodiment of a Spectral Beam Combining (SBC) module 600 is shown, which includes 26 submodules of the type shown in FIG. 10. That is, two rows 602, 603 of 13 submodules are mounted on a base 601. Each module in each row has a series of dichroic mirrors, e.g., 604, 605, 606. These mirrors are arranged in front of each submodule with a wavelength distribution, e.g., generally along the lines of FIG. 7 and 7A. Thus, there are 26 dichroic mirrors, each associated with a corresponding submodule. The dichroic mirrors reflect the narrow spectral emission (typically 0.75 nm wide) from the submodules and allow the transmission of other wavelengths. The wavelengths are multiplexed, the sum of all emitted wavelengths being around 10 nm wide. A turning mirror 607 reflects the multiplexed beams from the 13 submodules of row 602 towards a polarizing beam combining optical element 609.

[0110] The laser beams from the two rows are combined using polarization combining optics 609, which consists of a polarization rotating half-wave plate and a polarizing beam combining beam splitter. The broadband half-wave plate and the polarizing beam combining cube are in optical contact to form a compact beam combiner assembly. The combined beam is shaped by fiber coupling optics 620 and finally coupled into an optical fiber 621.

[0111] Example 7

[0112] Referring to FIG. 5, there is shown a schematic diagram of an embodiment of a complete KW class laser system 500 having seven SBC modules of the type shown in FIG. 4. Each SBC module, e.g. 501, is of the type shown in FIG. 4 and is fiber coupled. A fiber combiner 301 is used to combine the seven fibers, e.g. 302, into a single delivery fiber 303, where the SBC module fiber 302 has a diameter of 50 μm, while the delivery fiber 303 has a diameter of, e.g., about 150 μm. Depending on factors such as the number and size of the module fibers and the number of gain elements in each sub-module, the diameter of the delivery fiber is envisioned to be, e.g., about 75 μm to about 400 μm or more.

[0113] In an embodiment of the laser system optically coupled by a fiber combiner, the combiner may be based, for example, on the principle of dense hexagonal packing of optical fibers.

[0114] FIG. 5A is a schematic block diagram of the arrangement of FIG. 5 (where like numbers correspond to like components), showing a detailed schematic diagram of fiber combiner 301a.

[0115] Example 8

[0116] Referring to FIG. 6, a schematic diagram of an embodiment of a method for constructing a dense wavelength beam combining system without using a VBG is shown. In FIG. 6, a schematic diagram of a laser module 500 on a base 590 is shown. The laser module 500 has two rows of LCOS submodules. In this embodiment, each row has six LCOS submodules. In this embodiment, all twelve LCOS submodules are submodules of the embodiment shown in FIG. 3. More or fewer rows, more or fewer submodules, and the same or different types of submodules can be used.

[0117] Here, all the individual submodules are collinearly aligned and a common output coupler 501 provides feedback signals to each of the submodules by means of a pair of dichroic filters 501-506. These beams are combined with a turning mirror 507 that receives the laser beams and beam paths and directs them to a polarization rotation element 509. A polarizing beam splitter 508 then receives the laser beams and beam paths and combines them with the other beams and paths from 507. The combined beam is launched into an optical fiber 511 by an optical element 510, e.g. a lens. This lens is designed to focus all the submodules of the combined beam bandwidth (~10 nm) to a single point. This type of lens can be, for example, an aspheric lens, a simple doublet lens, or a Cook triplet lens, depending on the speed of the optical components. The high laser power delivered by these elements may result in optical contact, air space, or both.

[0118] Figure 9 shows how the round trip transfer functions for each of the individual sources, and hence the oscillation bandwidth of each source, can be established for the configuration of Figure 6, with the laser cavity defined so that all of their beams are collinear and form a full-power composite beam. These beams can be combined in the same way as in the previous example, using a polarizing beam rotator followed by a polarizing beam combining cube or pellicle.

[0119] Example 9

[0120] The LCOS shown in FIG. 11 includes a gain element 1101 with a lower reflectivity coating 1102 , a Zener diode 1110 for back bias protection, a fast axis collimating lens 1103 , and a submount 1111 .

[0121] It should be noted that it is not necessary to provide or address the theory underlying any novel and groundbreaking process, material, performance, or other beneficial features and characteristics that are the subject of or related to embodiments of the present invention. Nevertheless, various theories are provided herein to further advance the art in this field. The theories described herein in no way limit, restrict, or narrow the scope of protection afforded to the claimed inventions, unless specifically stated otherwise. These theories are not likely to be required or practiced utilizing the present invention. Furthermore, it should be understood that the present invention may lead to new, previously unknown theories for explaining the functional features of embodiments of the methods, articles, materials, devices, and systems of the present invention. And such subsequently developed theories shall not limit the scope of protection afforded to the present invention.

[0122] The various embodiments of the systems, devices, techniques, methods, activities and operations described herein may be used in various other activities and other fields in addition to those described herein. Moreover, these embodiments may be used, for example, in: other devices or activities that may be developed in the future; and existing devices or activities that may be modified based on the teachings of this specification. Moreover, the various embodiments described herein may be used with each other in different combinations. Thus, for example, configurations provided in various embodiments herein may be used with each other. Also, the scope of protection offered by the present invention should not be limited to the specific embodiments, configurations or arrangements described in the specific embodiments, examples, or in the specific figures.

[0123] The present invention may be embodied in forms other than those specifically disclosed herein without departing from its spirit or essential characteristics, and the described embodiments are to be considered in all respects as illustrative and not restrictive.

Claims

1. An optical device configured to generate kW or more of laser radiation at blue wavelengths in the 400-495 nm range of the spectrum, comprising: a. M fiber-coupled modules, each fiber-coupled module being composed of N sub-modules, where M≧1 and N>1; i. the sub-module comprises P lensed blue semiconductor gain chips, each lensed blue semiconductor gain chip having a low reflectivity coating on its front facet optimized for locking; ii. each submodule is mounted on a thermally conductive submount with the low reflectivity front facet facing outward and a fast axis collimating lens mounted in front of the gain chip to define a lensed chip on submount (LCOS); iii. each LCOS is mounted to a heat sink within an external cavity to optimally lock the wavelength of the gain chip to a predetermined wavelength; iv. the polarization of each gain chip is maintained within the external cavity; b. the fiber-coupled module comprises a plurality of sub-modules; i. two or more sets of said sub-modules are coupled by wavelength multiplexing having a bandwidth of less than 10 nm; ii. the two sets of wavelength multiplexed sub-modules are combined by polarized beam combining; iii. the sub-module is contained within a sealed enclosure and attached to a heat sink; c) an optical device, wherein the fibers of the multiple fiber-coupled modules are bundled and coupled into a single fiber to generate a kW level blue laser system.

2. An optical device as described in claim 1, wherein the output of the gain chip of the optical device is collimated and redirected with a turning mirror towards the output of another gain chip, or the output of the gain chip of the optical device is collimated and aligned with the output of another gain chip.

3. The optical device of claim 1, comprising: a GaN gain chip with a low reflectivity front facet facing outward; and a volume Bragg grating integrated into the fast axis collimating lens, or a volume Bragg grating after the fast axis collimating lens, or a volume Bragg grating after the slow axis collimating lens, or a reflective diffraction grating operating in a retro-configuration to redirect the output after the slow axis collimating lens to a dichroic filter, or a transmissive diffraction grating operating in combination with a mirror to provide feedback to the gain chip to redirect the output to the dichroic filter.

4. The optical device of claim 1, comprising a GaN gain chip with a low reflectivity front end face facing outward, and a collimating optical system having an output coupled to an optical fiber having a fiber Bragg grating embedded therein to determine the feedback and wavelength of the GaN gain chip.

Images