| 摘要 |
A large mode area optical fiber includes a large diameter core (d 1 up to 60 mum), and a first cladding (diameter d 2 ) wherein the difference between refractive index (n 1 ) in the core and the first cladding (n 2 ) is very small (Deltan<0.002), thus providing a very low numerical aperture core (NA 1 between 0.02 and 0.06). The preferred ratio of d 2 /d 1 <2. The fiber further has a second cladding, preferably a layer of air holes, having a very low refractive index n 3 as compared to the core and first cladding such that the first cladding has a relatively high numerical aperture (NA 2 >0.4) (n 3 is preferably less than 1.3). The small change in refractive index between the core and inner cladding combined with a large change in refractive index between the first cladding and second cladding provides a significantly improved single mode holding waveguide.
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