Fiber Coupling of Laser Diode Arrays for High Brightness: Cladding Considerations

摘要

Diode laser arrays present challenges to delivering maximum brightness laser energy to remote sites. Coupling with optical fibers is key to achieving this goal. Fiber core diameters are chosen to capture all the energy from the slow axis, with fiber placement and/or lensing to assure capture output from the fast axis. Multiple fibers are then bundled as tightly as possible and their output focused into a single output fiber. The optimum brightness is achieved by using as small as possible bundle dimensions before reduction to the output fiber's dimensions. A major aim is thus to minimize jacketing and cladding thickness. Data and analysis of the effects of cladding thickness on the spectral transmission of optical fibers having core diameters between about 100 μm to about 300μm are presented. Particularly below a 200 μm core, cladding thickness can significantly alter the transmission of laser energy in the visible and near infrared spectral regions, especially between 600 nm and 1700 nm. Data primarily deals with low-OH, 'water-free' fibers having cladding thicknesses between 5 to 20μm. Especially for fibers having cladding/core ratios below 1.2, care must be taken to either use core sizes approaching 200 μm or work in the UV or lower visible wavelength region. Further guidelines are given below.