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 at the focal plane of the exit lens , the first laser beam waist 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 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 at the focal plane of the exit lens , the first laser beam waist 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 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 . <EOS>