| 摘要 |
The present invention provides an optical fiber which has negative dispersion and negative dispersion slope in a wavelength band in use, and can carry out single-mode operation in which distortion due to the non-linear phenomenon can be suppressed so as to be suitable for wavelength multiplexed optical transmissions. When the relative index differences of center core (1), first side core (2), second side core (3), and inner cladding (4) from the silica level are DELTA1, DELTA2, DELTA3, and DELTA4, l.7%<=DELTA1, DELTA2<=-O.3%, 0.25%<=DELTA3, and DELTA4<0. Furthermore, the value A, determined by dividing the diameter a1 of the center core 1 by the diameter a2 of the first side core 2, is set to 0.15<=A<=0.2, and the value B, determined by dividing the diameter a3 of the second side core 2 by the diameter a2 of the first side core 3, is set to 1<B<=2. By such an arrangement, the absolute values of the negative dispersion and negative dispersion slope in a wavelength band of 1.55 mum can be made large, and in addition, light is confined within the core by the second side core (3), the effective core sectional area is made larger, and inner cladding (4) is provided, whereby the effective cut-off wavelength is shortened.
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