Fiber Optic Cables For Diode Laser Pumping

An optical fiber cable includes a fiber which consists of a core and a surroundingcladding. To facilitate handling, the cladding should be surrounded by a protectivecovering. The radiation is conducted in the core whose refractive index is higher thanthat of the cladding. The cladding should be substantially free from radiation. Thenumerical aperture of the fiber is determined by this difference in refractive index. Inthe transmission of high power laser light, radiation in the cladding may cause seriousproblems, since it is eventually absorbed in the covering, resulting in considerableheat generation and damage to the fiber cable. Radiation in the cladding may arise asa result of light scattering in the end surface of the fiber, for example caused byscratches or dust particles, or as a result of some of the incident radiation quite simplyfalling outside the numerical aperture of the fiber. These problems are most severe atthe inlet and outlet ends of the fiber cable, where the absorption of dust particles,gives rise to the harmful heat generation. At the outlet end, radiation can be reflectedfrom the workpiece directly into the cladding or fall completely outside the fiber. Inboth cases, the radiation is finally absorbed in the covering and the heat is generated.The object of this dissertation is to provide an optical fiber cable for transmittinghigh power laser light without causing any damage to the fiber or its covering andhaving a more efficient cooling capacity compared to the previous designs. The mainidea is summarized as follows:First, the surface protection and mechanical fiber fixation of the quartz blockwhich can endure high power laser are analysed in this paper. In this way, we couldgain three main advantages:1) Procecton of the entrance surface2) Mechanical mounting of the fiber is made via the transparent quartz block3) Anti-reflex coating at the inlet and outlet ends of the quartz block, reducingthe reflection losses through the fiberAccording to this technology, the structure of the quartz block is designed. Incontrast to conventional heat sourecs for splicing, a new splicing prosess that a carbondioxide laser heats optical fiber and quartz block by radiation is adopted.Second, a modestripper solution is made to clean the cladding from the radiationbefore the buffer and jacket enter the fiber. By applying a moderstripper whosematerial has the same or slightly larger refractive index compared to the claddingmaterial, radiation can leak out of the cladding, and can be dissipated somewhere else,where it is easier to cool the radiation away. The diameter and the length of themodestripper are calculated, and the producing process is introduced according to theexperiment. Third, the breakage feedback system of the optical fiber cable is presented. Thereare two copper wires travelling parallel and close to the optical fiber. This means thatif a fiber breakage should appear and power which is high enough to cut the wires willleak out, the interlock circuit will be broken to protect the optical fiber cable. At last,the connector and the structure of the optical fiber cable are designed.