Oscillation dependence of two-wave mixing gain for unidirectional ring resonator in photorefractive materials

Effect of photoconductivity and dielectric constant of the photorefractive materials on two-beam coupling gain and phase-shifts for a single unidirectional photorefractive ring resonator

“…(43) indicates that the frequency difference between the oscillating and pumping beams in a single unidirectional ring resonator depends on the optical cavity-length detuning (DG). This dependence supports for the photorefractive phase-shift associated with slightly non-degenerate two-wave mixing to satisfy the round-trip phase-oscillation condition for the oscillating beam [26]. From Eq.…”

“…The unidirectional photorefractive ring resonators rely on twobeam coupling interaction and/or phase conjugation to provide the basis for oscillations inside the cavity [26,27]. The basic principle of a photorefractive ring resonator operation can be described as follows.…”

“…The oscillation beam builds up provided the coupling efficiency exceeds the combined absorption and resonator losses. Such a ring resonator has the capability of providing large amplification of weak signals and is very sensitive to minute changes in its length [26,28,31]. Any scattered light propagating in the opposite direction should experience loss and therefore will not get amplified as observed in the experiments on photorefractive resonators.…”

“…In the presence of material absorption (i.e., a40), the signal beam can still be amplified provided the gain due to the beam coupling is large enough to overcome the cavity losses. Such amplification is responsible for the oscillation [26].…”

“…Thus, oscillation can be sustained only when the cavity detuning is compensated by the photorefractive phase-shift Dc c p which helps to fulfill the round-trip resonator condition [25,26,29]. Furthermore, the oscillating condition requires not only the loss of the beam intensity to be compensated for by the amplification; it also means that the degree of the mutual coherence between interacting beams has to be preserved after each round-trip in the cavity.…”