An optical apparatus configured to produce a multi-kW of laser radiation with emission in the blue wavelength of the spectrum in the range of 400- 495 nm, the optical apparatus comprising: a. M fiber-coupled modules, where each module is made up of N submodules, where M>1 and N>1; i. wherein submodules comprise P lensed blue semiconductor gain chips from a GaN material system, with coatings on front facets with lower reflectivity optimized for wavelength locking; ii. wherein each of the gain chips is mounted on a thermally conductive sub-mount, with the lower reflectivity facet facing outward and with a fast axis-collimating lens attached in front of the gain chip, thereby defining a Lensed Chip On Submount, LCOS; iii. wherein each of the LCOS is mounted on a staircase heatsink in an external cavity to optimally lock the wavelength of the gain chip to a predetermined wavelength; and, iv. a polarization of each gain chip is maintained in the external cavity; b. wherein the fiber-coupled module includes a plurality of submodules; i. two sets of submodules or more are combined through wavelength multiplexing with a bandwidth of < 10 nm; ii. whereas the two sets of wavelength multiplexed submodules are combined via polarization beam combining; and, iii. wherein the submodules are contained in sealed enclosures and are mounted on a heatsink; and, c. fibers of the plurality of fiber-coupled modules are bundled and combined into a single output fiber, producing a KW-level blue laser system. a. M fiber-coupled modules, where each module is made up of N submodules, where M>1 and N>1; i. wherein submodules comprise P lensed blue semiconductor gain chips from a GaN material system, with coatings on front facets with lower reflectivity optimized for wavelength locking; ii. wherein each of the gain chips is mounted on a thermally conductive sub-mount, with the lower reflectivity facet facing outward and with a fast axis-collimating lens attached in front of the gain chip, thereby defining a Lensed Chip On Submount, LCOS; iii. wherein each of the LCOS is mounted on a staircase heatsink in an external cavity to optimally lock the wavelength of the gain chip to a predetermined wavelength; and, iv. a polarization of each gain chip is maintained in the external cavity; i. wherein submodules comprise P lensed blue semiconductor gain chips from a GaN material system, with coatings on front facets with lower reflectivity optimized for wavelength locking; ii. wherein each of the gain chips is mounted on a thermally conductive sub-mount, with the lower reflectivity facet facing outward and with a fast axis-collimating lens attached in front of the gain chip, thereby defining a Lensed Chip On Submount, LCOS; iii. wherein each of the LCOS is mounted on a staircase heatsink in an external cavity to optimally lock the wavelength of the gain chip to a predetermined wavelength; and, iv. a polarization of each gain chip is maintained in the external cavity; b. wherein the fiber-coupled module includes a plurality of submodules; i. two sets of submodules or more are combined through wavelength multiplexing with a bandwidth of < 10 nm; ii. whereas the two sets of wavelength multiplexed submodules are combined via polarization beam combining; and, iii. wherein the submodules are contained in sealed enclosures and are mounted on a heatsink; and, i. two sets of submodules or more are combined through wavelength multiplexing with a bandwidth of < 10 nm; ii. whereas the two sets of wavelength multiplexed submodules are combined via polarization beam combining; and, iii. wherein the submodules are contained in sealed enclosures and are mounted on a heatsink; and, c. fibers of the plurality of fiber-coupled modules are bundled and combined into a single output fiber, producing a KW-level blue laser system.