THE RAMAN EFFECT AND SOLITONS IN AN ELLIPTIC OPTICAL-FIBER

We derive a general system of coupled nonlinear Schrodinger equations, describing light in a bimodal optical fiber, taking into account the quasi-instantaneous Raman effect, group-velocity birefringence, phase- velocity birefringence, and optical activity, and for light with gener al ellipticity. The Raman coefficients prove to obey a relation which depends on the ellipticity. When group-velocity birefringence and opti cal activity are both non-zero, polarization couples to the changing f requency, so soliton polarization cannot be held constant in this case . Without optical activity, there are solitons with constant polarizat ion either entirely in one polarization (''simple'') or equally divide d between the two polarizations (''vector''). At ellipticity angle 0 d egrees to 35.3 degrees, the simple solitons are stable and the vector solitons are unstable, and vice versa for ellipticity angle 35.3 degre es to 90 degrees. With optical activity, the polarization can be const ant, but with a rather more complex form. Stability is also examined, and bistability is found in some circumstances.