An optical fiber treatment system is provided for high power laser transmission to an area of medical treatment. A side fire optical fiber tip for use in high power laser applications having outputs of greater than or equal to 50 Watts is a key to the system. Embodiments are particularly appropriate for the medical treatment of benign prostate hyperplasia (BPH) with a side fire optical fiber tip using a Holmium:YAG laser or a high power diode laser. Such procedures can be done with only local anesthesia A predetermined length of an output tip on the distal end of the optical fiber of the present invention is formed with an optical fiber core and cladding layer of preselected thickness wherein the cladding to core diameter ratio is at least as great as 1.2. A side fire surface is formed on the distal end of the core/clad output end. Over this optical fiber output end, a pure silica capillary tube is fused to the predetermined length of exposed cladding where the outermost cladding is also pure silica to reduce thermal mismatch during the fusion process. By having the refractive index at the fusing interface of the tube to the cladding matched, and bubbles or gaps eliminated or prevented, it is possible to substantially eliminate Fresnel reflection losses at this interface. Further, the outer surface area where the laser energy is exiting from the tube may be heat treated with a laser to increase durability for high power laser energy transmission in fluid environments. Germanium-doped silica as well as pure silica can be used as fiber core material.