Analysis of «O»-band optical signal launching to graded multimode optical fiber with great central defect of refractive index profile via standard singlemode optical fiber

We present mathematical description for excitation of weakly guiding silica graded multimode optical fibers with arbitrary axial symmetric refractive index profile providing to take into account launching conditions, including transversal mode staff of emission generating by laser, radial or angular misalignments. Proposed solution is based on mode coupling coefficients estimation by combination of earlier on developed modified Gaussian approximation and well known overlap integral method. We developed method for mode coupling computing and performed calculation of mode coupling coefficients at the splice of standard singlemode and mentioned multimode optical fibers. Mode power redistribution was researched during optical signal launching to excited multimode optical fiber via standard singlemode fiber pigtail jointed to laser source operating over central region of «O»-band that corresponds to 1310 nm. Some research results in the form of diagrams of excited mode normalized amplitudes depending on precision misalignment at 1310 nm as well as mode coupling coefficients spectral curves are presented.