The size of the spot and its Rayleigh range is determinded by the fiber properties and by the focal lengths of the fiber collimator and of the micro focus optics. For single-mode fibers the Gaussian intensity distribution and beam shape are maintained. Naturally, devices for larger collimated beams need to be both longer and larger in diameter. The largest fiber collimators are those for high-power multimode fibers. and many more brands available!Fiber-optic collimators are used to launch the light from an optical fiber into a free space collimated beam with specified beam diameter or spot size. They can also be used in reverse to focus light into a fiber.
