Gray and dark spatial solitons supported by two-photon isomerization

A theory is presented to show that gray and dark solitons can exist in bulk polymers with two-photon isomerization (TPI) nonlinearity. The soliton FWHM, intensity and phase profiles are discussed in detail. In addition, the stability properties of these TPI solitons are also investigated by employing the stability criterion based on the renormalized momentum.