Experimental evidence for detuning induced pattern selection in nonlinear optics

Spectral phase transitions in optical parametric oscillators

Driven nonlinear resonators provide a fertile ground for phenomena related to phase transitions far from equilibrium, which can open opportunities unattainable in their linear counterparts. Here, we show that optical parametric oscillators (OPOs) can undergo second-order phase transitions in the spectral domain between degenerate and non-degenerate regimes. This abrupt change in the spectral response follows a square-root dependence around the critical point, exhibiting high sensitivity to parameter variation akin to systems around an exceptional point. We experimentally demonstrate such a phase transition in a quadratic OPO. We show that the divergent susceptibility of the critical point is accompanied by spontaneous symmetry breaking and distinct phase noise properties in the two regimes, indicating the importance of a beyond nonlinear bifurcation interpretation. We also predict the occurrence of first-order spectral phase transitions in coupled OPOs. Our results on non-equilibrium spectral behaviors can be utilized for enhanced sensing, advanced computing, and quantum information processing.

Modulation Instability Induced Frequency Comb Generation in a Continuously Pumped Optical Parametric Oscillator

Continuously pumped passive nonlinear cavities can be harnessed for the creation of novel optical frequency combs. While most research has focused on third-order "Kerr" nonlinear interactions, recent studies have shown that frequency comb formation can also occur via second-order nonlinear effects. Here, we report on the formation of quadratic combs in optical parametric oscillator (OPO) configurations. Specifically, we demonstrate that optical frequency combs can be generated in the parametric region around half of the pump frequency in a continuously driven OPO. We also model the OPO dynamics through a single time-domain mean-field equation, identifying previously unknown dynamical regimes, induced by modulation instabilities, which lead to comb formation. Numerical simulation results are in good agreement with experimentally observed spectra. Moreover, the analysis of the coherence properties of the simulated spectra shows the existence of correlated and phase-locked combs. Our results reveal previously unnoticed dynamics of an apparently well assessed optical system, and can lead to a new class of frequency comb sources that may stimulate novel applications by enabling straightforward access to elusive spectral regions, such as the midinfrared.

A complex pattern with hexagonal lattice and white-eye stripe in dielectric barrier discharge

A novel type of white-eye pattern in a dielectric barrier discharge system has been investigated in this paper. It is a superposition of a hexagonal lattice and a white-eye stripe in appearance and evolves from a white-eye square grid state with the applied voltage increasing. Its spatio-temporal dynamics obtained by an intensified charge-coupled device shows that it consists of three transient rectangular sublattices. The spatiotemporally resolved evolutions of the molecular vibrational temperature and electron density of the pattern are measured by optical emission spectra. The evolution of surface charge distribution is given and its effect on the self-organized pattern formation is discussed.

Control and generation of drifting patterns by asymmetrical Fourier filtering

We report the theoretical and experimental demonstration of one-dimensional drifting patterns generated by asymmetrical Fourier filtering in the transverse plane of an optical feedback system with a Kerr type nonlinearity. We show, with good agreement between our theoretical (analytics and numerics) calculations and experimental observations that at the primary instability threshold the group velocity is always different from zero. Consequently, the system is convective at this threshold, then exhibits drifting patterns.

Spatiotemporal pulses in a liquid crystal optical oscillator

A nonlinear optical medium results by the collective orientation of liquid crystal molecules tightly coupled to a transparent photoconductive layer. We show that such a medium can give a large gain; thus, if inserted in a ring cavity, it results in an unidirectional optical oscillator. We report new dynamical regimes characterized by the generation of spatiotemporal pulses, localized in three dimensions and arising from the random superposition of many longitudinal and transverse modes with different frequencies.

Bistable phase locking of a nonlinear optical cavity via rocking: Transmuting vortices into phase patterns

We report the experimental observation of the conversion of a phase-invariant nonlinear system into a bistable phase-locked one via rocking [G. J. de Valcárcel and K. Staliunas, Phys. Rev. E 67, 026604 (2003)10.1103/PhysRevE.67.026604]. This conversion results in vortices of the phase-invariant system being replaced by phase patterns such as domain walls. A model for the experimental device, a photorefractive oscillator, is given that reproduces the observed behavior.

Tilted wave emission in optical parametric oscillators induced by a bichromatic pumping

Tilted wave emission is found in a mean-field model of a degenerate optical parametric oscillator pumped by a bichromatic field with a frequency offset much smaller than the cavity free-spectral range. Tilted wave emission arises due to a nonadiabatic mechanism induced by the slow pump modulation, and disappears when either one of the two pump waves is blocked.