We discuss the nonlinear process of backward-wave parametric amplification and oscillation, phase matched using a nonlinear grating inside a chiral medium. Our theory shows a remarkable feature manifesting as photoinduced flipping of optical chirality between the signal and the idler waves, without any change in the structural chirality of the medium. We show that circular birefringence, induced by chirality, leads to two different nonlinear processes with different phase-matching conditions that are associated with opposite states of circular polarizations. When the incident pump and signal beams are linearly polarized initially, their state of polarization evolves in an elliptical fashion because of the two competing nonlinear processes taking place in parallel. We also discuss the properties of such cavityless optical parametric oscillators based on distributed feedback provided by the nonlinear grating used for quasi phase matching.

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• Chirality
• Nonlinear optics
• Second order nonlinear optical processes