| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical isolator which exhibits a large isolation charac teristic even if a thin double refractive crytstlal is used, has high performance and is reduced in size and cost, by using an optical fiber having the specific refractive index difference of a core larger than a specific value and an optical fiber. SOLUTION: The highΔn optical fiber having the specific refractive index differenceΔn>1% of the core is used is used as the incident side optical fiber 1 and the photodetecting side optical fiber. The beam waist is narrowed (by changing the position of a lens) down to an arbitrary size by such fiber, thereby, the isolation at the same sepn. distance is made larger. of the highΔn optical fiber is used, the isolator is excellent in that the distance between the lenses is made wider and the threshold of the beam diameter at the beam waist is made smaller. The degree of freedom in design is improves and the higher isolation characteristics are obtd. While theΔn of the optical fiber is required to be larger than 1%, theΔn is preferably 1% or larger and 2% or smaller in terms of transmission loss, etc.
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