| 摘要 |
<p>PROBLEM TO BE SOLVED: To propagate a high power laser beam and radiate a laser beam having a small diffusion angle. SOLUTION: An optical fiber comprises a core element 5 having a large diffraction index and a clad part 6 which is formed in the circumference of the core part 5 and has a smaller diffraction index than that of the core part 5. In addition, the amount of impurities contained in the clad part 6, which lower the diffraction index, becomes smaller gradually from the incidence side to the radiation side.</p> |
