Hole assisted fiber and design method

A method for designing a hole-assisted optical fiber,

• wherein the hole-assisted optical fiber has a structure including a core region having a diameter 2a and a uniform refractive index distribution, a uniform cladding region that surrounds the core region and has a relative refractive index difference Δ from the core region, and holes arranged in a single layer or a plurality of layers in a circumferential direction within the cladding region excluding the core region to be a hexagonal close-packed manner, and
• wherein the method comprises:
• calculating a desired bending loss condition, a desired confinement loss condition, and a desired cutoff condition when a core radius a and a radius Rin of an inscribed circle inscribed in an innermost layer of the layers of the holes are changed in any relative refractive index difference Δ and any hole occupancy rate S;
• plotting the bending loss condition, the confinement loss condition, and the cutoff condition on a graph having the core radius a and the radius Rin as axes;
• calculating a Rayleigh scattering loss of the hole-assisted optical fiber when the core radius a and the radius Rin are changed;
• calculating a Rayleigh scattering loss when the core radius a is changed for a normal optical fiber whose structure is the same as the hole-assisted optical fiber except for the absence of holes;
• plotting a ratio ΔαR on the graph, which is a ratio of the Rayleigh scattering loss of the hole-assisted optical fiber to the Rayleigh scattering loss of the normal optical fiber;
• detecting, on the graph, an overlapping region where a right-hand region of the bending loss condition or the confinement loss condition, a left-hand region of the cutoff condition, and a left-hand region of any ratio ΔαR overlap each other;
• and
• defining the core radius a and the radius Rin included in the overlapping region as design values of the hole-assisted optical fiber.