Design of Depressed-core Four-ring Few-mode Fiber for Next-Generation Communication

The authors show how to keep a flattened and low dispersion in a graded-index depressed core fiber for a few-mode operation in this paper. The proposed design supports seven linearly polarized modes over the C band. However, this design yields a dispersion flattened characteristic over the C-band of the optical communication spectrum. Moreover, this proposed few-mode structure exhibits zero-dispersion for the fundamental LP
01
mode at 1550 nm first time according to our knowledge. The results show the dispersion slope of 0.007ps/nm
²
km and the flatness of dispersion is about 1ps/nm km over the C-band. The proposed few-mode fiber is designed with an inner-core of 13.5% GeO
2
doped silica, a trench with 2% F doped silica, and an outer-core with 3.5% GeO
2
doped silica. The cladding is assumed to be fused Silica to maintain low optical losses and dispersion. Simulation is used to select the design parameters and the molar percentage of the dopants. The proposed fiber is suitably designed to guide 7 linearly polarized modes namely, LP
01
, LP
11
, LP
21
, LP
02
, LP
31
, LP
12
, and LP
22
. The proposed few-mode fiber exhibits large mode separation, flattened dispersion, low bending loss, low and flat differential mode delay, and large effective mode-area over the C-band. In summary, the proposed depressed core few-mode fiber is a prospective aspirant for new-generation mode-division multiplexing transmission.