US 12,248,171 B2
Multi-core optical amplifying fiber, multi-core optical fiber amplifier, and optical communication system
Shigehiro Takasaka, Tokyo (JP); Koichi Maeda, Tokyo (JP); and Ryuichi Sugizaki, Tokyo (JP)
Assigned to FURUKAWA ELECTRIC CO., LTD., Tokyo (JP)
Filed by FURUKAWA ELECTRIC CO., LTD., Tokyo (JP)
Filed on Sep. 13, 2022, as Appl. No. 17/931,732.
Application 17/931,732 is a continuation of application No. PCT/JP2021/009354, filed on Mar. 9, 2021.
Claims priority of application No. 2020-060718 (JP), filed on Mar. 30, 2020.
Prior Publication US 2023/0003934 A1, Jan. 5, 2023
Int. Cl. G02B 6/02 (2006.01); G02B 6/036 (2006.01); G02B 6/04 (2006.01); H01S 3/094 (2006.01)
CPC G02B 6/02042 (2013.01) [G02B 6/03616 (2013.01); G02B 6/04 (2013.01); H01S 3/094007 (2013.01)] 13 Claims
OG exemplary drawing
 
1. A multi-core optical amplifying fiber comprising:
a plurality of core portions doped with a rare-earth element;
an inner cladding portion surrounding the core portions and having a refractive index lower than a maximum refractive index of the core portions; and
an outer cladding portion surrounding the inner cladding portion and having a refractive index lower than the refractive index of the inner cladding portion, wherein
a mode field diameter of each of the core portions at a wavelength at which the rare-earth element performs optical amplification is 5 μm to 11 μm,
a relative refractive-index difference of the maximum refractive index of each of the core portions with respect to the inner cladding portion is 0.35% to 2%,
a core-to-core distance that is a separation distance between centers of the respective core portions on a section perpendicular to a longitudinal direction is set such that total inter-core crosstalk is −40 dB/100 m or lower in an optical amplification wavelength band subjected to the optical amplification,
a cladding thickness that is a distance from a center of a core portion closest to an outer end of the inner cladding portion out of the core portions to the outer end is smaller than a value obtained by adding the mode field diameter to a minimum value of the core-to-core distance, and
a ratio of a total sectional area of the plurality of core portions to a sectional area of the inner cladding portion is 1.9% or more.