| 摘要 |
PURPOSE:To obtain the broad-band optical fiber coupler which is mechanically stable and has the small dependency of a branching ratio on wavelengths by varying a refractive index distribution by a thermal diffusion treatment and prestretching respective optical fibers by the same length before fusing and stretching CONSTITUTION:The optical fiber 100 is stretched at a high speed at the temp. higher than the softening point of the fiber. Then, the optical fiber is reduced in diameter without thermally diffusing the dopant of a core 102 having a high refractive index from a clad 101. The optical fiber 200 is heated and stretched at a low speed at the temp. of the extent that the dopant of the core 202 is thermally diffused at the time of stretching. Then, the core 202 having the higher refractive index than the refractive index of the clad 201 is reduced in diameter and the dopant of the core 202 is diffused. The stretched parts of the optical fibers 100, 200 prestretched to the same length are fused to each other and the fused part is heated and stretched under such different thermal diffusing conditions, by which the coupling part is formed. As a result, the imperfect mode coupling is attained and the symmetrical shape of the coupling part is formed. |
