Polarization locked vector solitons and axis instability in optical fiber

We experimentally observe polarization-locked vector solitons in optical fi ber. Polarization locked-vector solitons use nonlinearity to preserve their polarization state despite the presence of birefringence. To achieve condi tions where the delicate balance between nonlinearity and birefringence can survive, we studied the polarization evolution of the pulses circulating i n a laser constructed entirely of optical fiber. We observe two distinct st ates with fixed polarization. This first state occurs for very small values birefringence and is elliptically polarized. We measure the relative phase between orthogonal components along the two principal axes to be +/-pi/2. The relative amplitude varies linearly with the magnitude of the birefringe nce. This state is a polarization locked vector soliton. The second, linear ly polarized, state occurs for larger values of birefringence. The second s tate is due to the fast axis instability. We provide complete characterizat ion of these states, and present a physical explanation of both of these st ates and the stability of the polarization locked vector solitons. (C) 2000 American Institute of Physics. [S1054-1500(00)00103-8].