An optical device for varying a beam parameter product of a laser beam, the optical device comprising: an input port for inputting the laser beam into the optical device; a beam launcher optically coupled to the input port; and an optical waveguide subassembly optically coupled to the beam launcher, the optical waveguide subassembly comprising an optical waveguide having first and second ends, a core, and a cladding surrounding the core, the core and the cladding extending between the first and second ends of the optical waveguide, and an exit lens coupled to the second end and having a focal length no greater than 10 mm; wherein the beam launcher is configured for launching the laser beam at a convergence angle (α) and a launch angle (γ 1) into the core of the optical waveguide at the first end of the optical waveguide, wherein the beam launcher is configured for varying the convergence angle (α) and/or the launch angle (γ 1); wherein, in operation, the launched laser beam propagates from the first to the second end of the optical waveguide and through the exit lens, wherein the laser beam gets collimated by the exit lens thereby forming a first laser beam waist (217, 231) at the focal plane of the exit lens, the first laser beam waist (217, 231) having a diameter, wherein a distribution of local ray angles at the second end of the optical waveguide is substantially rotationally symmetric about a waveguide axis proximate the second end, and wherein the convergence angle (α) and/or the launch angle (γ 1) influences the size and/or shape of the first laser beam waist (217,231) formed at the focal plane of the exit lens, such that the diameter of the first laser beam is varied, thereby varying the beam parameter product of the laser beam exiting the exit lens. an input port for inputting the laser beam into the optical device; a beam launcher optically coupled to the input port; and an optical waveguide subassembly optically coupled to the beam launcher, the optical waveguide subassembly comprising an optical waveguide having first and second ends, a core, and a cladding surrounding the core, the core and the cladding extending between the first and second ends of the optical waveguide, and an exit lens coupled to the second end and having a focal length no greater than 10 mm; wherein the beam launcher is configured for launching the laser beam at a convergence angle (α) and a launch angle (γ 1) into the core of the optical waveguide at the first end of the optical waveguide, wherein the beam launcher is configured for varying the convergence angle (α) and/or the launch angle (γ 1); wherein, in operation, the launched laser beam propagates from the first to the second end of the optical waveguide and through the exit lens, wherein the laser beam gets collimated by the exit lens thereby forming a first laser beam waist (217, 231) at the focal plane of the exit lens, the first laser beam waist (217, 231) having a diameter, wherein a distribution of local ray angles at the second end of the optical waveguide is substantially rotationally symmetric about a waveguide axis proximate the second end, and wherein the convergence angle (α) and/or the launch angle (γ 1) influences the size and/or shape of the first laser beam waist (217,231) formed at the focal plane of the exit lens, such that the diameter of the first laser beam is varied, thereby varying the beam parameter product of the laser beam exiting the exit lens.