Modal group-velocity mismatch induced intermodal modulation instability in step-index fiber

Abstract

We present detailed experimental study on noise-seeded intermodal modulation instability (IM-MI) in normal dispersion region of a conventional step-index fiber. The sharp refractive index contrast between core and cladding leads to large group velocity mismatch between the spatial modes, coaxing to efficient IM-MI and generation of multiple spectral peaks along with Raman peaks. Evolution of the spectrum with pump powers and fiber lengths are observed. Experimental findings are well supported with the theoretical framework based on bimodal-MI model considering the distinct dispersion parameters of the participating modes.

Nonlinear chirped pulse amplification for a 100-W-class GHz femtosecond all-fiber laser system at 1.5 m

“…The LMA gain fiber used in the main fiber amplifier has a core diameter of 25 m and a numerical aperture (NA) of 0.1, which is larger than the minimum NA of 0.05 for single-mode guiding, such that it supports high-order modes (HOMs), that is, the LP 01 , LP 11 and LP 21 modes as shown in Figure 7(a). As a result, it can associate with IM-MI through cross-phase modulation (XPM) [ 50 , 51 ] . To study the potential IM-MI between the transverse modes, we utilize a coupled nonlinear Schrödinger equation in the formalism of the following: with where and are slowly varying field envelopes with respect to two distinct transverse modes, describes the transverse field distribution of transverse mode , ( ) represents the nonlinear coefficients responsible for nonlinear interaction between transverse modes and , is the speed of light and is the nonlinear refractive index.…”

“…Other key parameters are provided in Table 2. By applying linear stability analysis on the perturbations adding to the fields of A 1 and A 2 [52] , the gain spectrum of the IM-MI can be written as follows: Table 2. Key parameters used for calculating intermodal modulational instability.…”

Self-Phase Modulation-Induced Instability of High-Power Narrow-Linewidth Fiber Amplifiers

“…MI has been widely used in the generation of supercontinua [10], optical pulses with a high repetition rate and optical odd waves [11][12][13]. In recent years, MI in high-power fiber lasers has attracted the attention of researchers [14][15][16][17].…”