Modulation instabilities in randomly birefringent two-mode optical fibers

Abstract

Modulation instabilities in the randomly birefringent two-mode optical fibers (RB-TMFs) are analyzed in detail by accounting the effects of the differential mode group delay (DMGD) and group velocity dispersion (GVD) ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers (RB-SMFs). New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD, no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by P cr , which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power (P cr ), which increases (decreases) distinctly with the increment of DMGD (GVD ratio of the two modes) but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than P cr , and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The MI analysis in this paper is verified by numerical simulation.

Soliton evolution and control in a two-mode fiber with two-photon absorption

“…The normalized GVD coefficient of the LP 11 mode β 2 is essentially the group velocity dispersion ratio of the LP 11 and LP 01 modes, and is calculated in the range of 0.9 < β 2 = β 2B /β 2A < 3.6. [13,14,17,18] Effects of the two-photon absorption on the soliton propagation can be investigated by using the split-step Fourier algorithm. The nonlinear coupling coefficients of f BB = 0.90, f AB = 0.60 and the normalized DMGD coefficient of D 1 = 2.0 are used in the following figures.…”

“…Namely, only the LP 01 and LP 11a modes are excited when the nonlinear pulses propagate in such a twomode fiber. [13,14] When nonlinear pulses propagate in a two-mode optical fiber with the two-photon absorption under the coupling between the LP 01 and LP 11 modes, the corresponding nonlinear coupling Schrödinger equations governing the pulse propagation are given by [13,14] j…”

“…β 2A and β 2B are the group velocity dispersion (GVD) coefficients of the LP 01 and LP 11 modes, respectively. γ, f AB , and f BB are the nonlinear coupling coefficients between the spatial modes, [13,14] and α is the two-photon absorption coefficient. To normalize Eqs.…”