Chien-Chung Jeng

Nonlocal dark solitons under competing cubic–quintic nonlinearities

We investigate properties of dark solitons under competing nonlocal cubic-local quintic nonlinearities. Analytical results, based on a variational approach and confirmed by direct numerical simulations, reveal the existence of a unique dark soliton solutions with their width being independent of the degree of nonlocality, due to the competing cubic-quintic nonlinearities.

Induced spatiotemporal modulation instability in a noninstantaneous self-defocusing medium

We demonstrate theoretically and experimentally that induced spatiotemporal modulation instability can exist in a self-defocusing medium if the nonlinearity is noninstantaneous. We predict the growth rate as a function of the spatial and temporal frequencies of the modulation and the response time of the nonlinearity and confirm it by our experiments.

Vortex pairs in nonlocal nonlinear media

Dynamics of vortex pairs with the same and opposite circulations are studied theoretically in nonlocal nonlinear media with different intervortex separations. We demonstrate that the nonlocal nonlinear response not only leads to a dramatic suppression of the elliptical instabilities but also helps in the formation of quasi-stable rotating and breathing bound states for vortex–vortex and vortex–antivortex (vortex dipole) pairs, respectively.

Tunable pattern transitions in a liquid-crystal-monomer mixture using two-photon polymerization

Through two-photon lithographic processes, we report experimentally and numerically a series of photoinduced tunable polymerization patterns in shapes from straight channel, serpentine curve, to periodic grating when an ultrashort femtosecond laser pulse directly writes in a liquid-crystal-monomer mixture along a line for different scanning speeds. Laser beams with polarization perpendicular to the direction of writing and the alignment of liquid crystals, produce snake-shaped patterns at an intermediate scan rate.

Control modulation instability in photorefractive crystals by the intensity ratio of background to signal fields.

By experimental measurements and theoretical analyses, we demonstrate the control of modulation instability in photorefractive crystals though the intensity ratio of coherent background to signal fields. Appearance, suppression, and disappearance of modulated stripes are observed in a series of spontaneous optical pattern formations, as the intensity of input coherent beam increases. Theoretical curves based on the band transport model give good agreement to experimental data, both for different bias voltages and different intensity ratios.

Lasing on surface states in vertical-cavity surface-emission lasers

We report experimental observation of lasing on surface states, in the form of standing waves at the termination of a defect-free photonic crystal on top of vertical-cavity surface-emission lasers. Direct images of lasing modes at the truncated periodic potential, along one side of a square lattice, are demonstrated by collecting near-field radiation patterns, as well as in numerical simulations. Our results provide a step toward realizing surface and edge states in optical cavities.

Thermodynamical properties in spontaneous optical pattern formations

With a detailed series of spontaneous optical pattern formations, we reveal the existence of thermodynamical properties in nonlinear optical systems by defining the configurational entropy from the measured patterns. A phase diagram for pattern transitions in the form of stripes, reoriented stripes, hexagons, and spots is reported experimentally and theoretically for incoherent beams in non-instantaneous anisotropic photorefractive crystals, with demonstrations in the boundary of mixed-phase states. Emergence of optical pattern transitions is shown to occur at the local minimum values of effective optical temperature, and accompanied with the change of chemical potentials.

Pattern writing in a liquid-crystal-monomer mixture using two-photon polymerization

Through two-photon lithographic processes, we report experimentally and numerically a series of photoinduced tunable polymerization patterns in shapes from straight channel, serpentine curve, to periodic grating when an ultrashort femtosecond laser pulse directly writes in a liquid-crystal-monomer mixture along a line for different scanning speeds. Laser beams with polarization perpendicular to the direction of writing and the alignment of liquid crystals, produce snake-shaped patterns at an intermediate scan rate.

Optical pattern transitions in photorefractive crystals

We show by experimental measurements there exists an intensity dependent pattern transition from optical modulation instability to transverse instability in nonlinear media which is explained by our model of periodic strip-filamens on cnoidal waves.

Spatiotemporal modulation instability of coherent light in noninstantaneous nonlinear media

Summary form only given. Periodic pattern of optical modulation instability (MI) results from the interplay between the diffraction and self-focusing effects. This interplay amplifies the noise, carried by the light beam, of certain spatial frequency. If the noise is from a static source (e.g. material defects), the resulted MI patterns are no different in either instantaneous or noninstantaneous media. However, it is not the case if the noise is from a dynamic source (e.g. random light scattering). In instantaneous media, MI patterns form instantly depending on the noise distribution. If the material response is noninstantaneous, the always-changing noise cannot alter the index dramatically at any moment, but only to modify the index and consequent MI pattern a bit. Thus, the cumulative MI pattern movement will only be noticeable after a time longer than the material response time. Here, we report on the theoretical derivation and experimental observation of such spatiotemporal MI of coherent light beam in noninstantaneous media. We obtain the MI growth rate as a function of the noise frequency and the material response time. In the experiment, we observe that the varying speed of the MI patterns increases with the decreased material response time. We also observe that increasing the material response time can arrest the MI, agreeing with the theory.