| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical attenuator which has high long-period reliability, requires no electric power, and has small insertion loss, a wide in-use wavelength area, and a simple structure and is easy to manufacture. SOLUTION: A clad mode propagation part 3 is formed as a lengthwise part of an optical fiber 2 by increasing the mold field diameter, the outer periphery of the clad mode propagation part 3 is covered with resin to form a light leak part 5, and the clad mode propagation part 3 is tapered so that its external diameter is gradually reduced from both start end parts of the clad mode propagation part 3 toward the center part.
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