Mirrorless optical parametric oscillator

Parametric interaction of counterpropagating photons has the unique property of automatically establishing distributed feedback and thus realizing novel sources of coherent and tunable radiation, such as mirrorless optical parametric oscillators. This device does not require alignment or any optical components other than the second-order nonlinear medium itself(1). Here we present the first experimental demonstration of such an oscillator, which was made feasible by quasi phase-matching in a nonlinear photonic structure with submicrometre periodicity. This type of oscillator has been extensively discussed as a theoretical possibility(1-5). It generates signal and idler waves in the near- and mid-infrared, respectively, and exhibits unique and useful spectral properties. The oscillator signal is essentially a wavelength-shifted replica of the pump spectrum, and the bandwidth of the idler is two orders of magnitude narrower than that of the pump. It also has very low output wavelength sensitivity to temperature variations.