Spatial response of cavity systems

We show that a plane-mirror Fabry-Perot cavity is capable of converting a spatially phase (amplitude) modulated input beam into an amplitude (phase) modulated output. For a cavity close to resonance the effect is most easily seen for negative detunings. When nonlinear elements are added to the mean-field cavity, the effect persists but acquires an intensity dependence, while the requirement of net negative dispersion remains. In addition, the output of a near-resonant nonlinear cavity can have the same type of modulation as the input, something which is impossible in the corresponding linear cavity. These results are demonstrated in cavities containing Kerr or two-level materials, as well as in optical parametric oscillators