It is demonstrated that a collinear scheme of nonlinear-optical wave mixing
due to a second-order nonlinearity can be implemented in an isotropic gyro
tropic medium (the Koroteev problem of chiral nonlinear optics) through the
use of waveguide modes. The efficiency of wave mixing can be considerably
improved in such a scheme when material dispersion of a medium is partially
or completely offset by a controllable dispersion of waveguide modes.