The
optical fiber consists of four pure silica circular cores, a trench region, and a cladding. The
radius of each of the four cores is ax = 2.5 μm. The center coordinates of the four cores are [coordinates missing in original text]. The inner
radius of the trench region is bx = 14.4 μm, and the outer
radius is cx = 23.4 μm. The remaining portion is the cladding, with the outermost cladding having a radius R = 62.5 μm. The two cores in the X direction have the same
refractive index, and the two cores in the Y direction have the same
refractive index, while the cores in the X and Y directions have different refractive indices. The
refractive index of the two cores in the X direction is n1 = 1.44402. The refractive indices of the two cores in the Y direction are n2 = 1.44102, the refractive index of the cladding is n3 = 1.43232, and the refractive index of the trench region is n4 = 1.42881. The mode field characteristics of the spatial
modes in this
fiber can be changed by altering the size, position, and refractive index distribution of the core, cladding, and trench. By employing
optical field modulation, the mode degeneracy of the circular core
fiber is broken, achieving low intrinsic loss and low
crosstalk operation. This eliminates the need for complex
MIMO-DSP
processing and enables good transmission for
MIMO-FREE applications.