Ron Daisy

Linewidth-narrowing mechanism in lasers by nonlinear wave mixing

We propose a linewidth-narrowing mechanism in lasers by nonlinear absorptive wave mixing of the counterpropagating beams in the cavity. We give a theoretical analysis and report on a demonstration of the effect with an erbium-doped fiber laser. The system also exhibits bistability in the dependence of the oscillation intensity versus pump power.

Large thermal nonlinearities and spatial self-phase modulation in SrxBa 1− xNb 2 O 6 and BaTiO 3 crystals

We find strong optical nonlinearities in Sr(x)Ba(1-x)Nb(2)O(6) (x = 0.61 and x = 0.75) and in BaTiO(3) crystals caused by thermally induced changes of the refractive indices. This gives strong spatial self-phase modulation and self-focusing of Gaussian light beams and light-induced birefringence. The light intensities are of the order of 10(2)-10(3)m W/mm(2), and the time response of the effect is of the order of milliseconds.

Synchronization of chaotic nonlinear optical ring oscillators

Abstract We find, by a numerical study, that coupled chaotic nonlinear optical ring cavities, described by delay-differential equations, can show synchronization. This can be useful for encryption in optical communication.

Light waves at the interface of linear and photorefractive media

We study the behavior of light waves at an interface between linear and photorefractive media, where the incident wave propagates from the linear side. We find bistable behavior of the reflection coefficient as a function of the incident angle at incident wave directions in the vicinity of the critical angle for total internal reflection. The analysis is based on approximations in the photorefractive-process equations, for which an analytical plane-wave solution for the boundary problem is found. In this regime an exponentially decaying evanescent field induces a uniform change of the refractive index. The limitation of this solution is also studied by a numerical analysis.

Signal-to-pump ratio dependence of buildup and decay rates in photorefractive nonlinear two-beam coupling

The buildup and the decay of photorefractive two-beam coupling are experimentally demonstrated to be strongly dependent on the intensity ratio of the two beams (signal-to-pump ratio). The experiment, done with a BaTiO3 crystal, shows good agreement with the theory of two-beam coupling in the depleted-pump regime. The deviation of the response behavior from the small-signal regime is seen for ratios as small as ∼10−5. These results are significant for applications of two-beam coupling as gain media, especially for the elimination of amplified noise (fanning).

Filtering behavior of a self-induced three-mirror cavity formed by intracavity wave mixing in a saturable absorber.

Wave mixing with a self-induced grating in a saturable absorber, which is inserted into a resonator, gives special filtering behavior. In a linear Fabry-Perot cavity with gain, the grating forms a self-matched, threemirror laser cavity that can discriminate between modes whose frequency difference is much lower than the grating bandwidth. The effect was used to obtain single-mode lasers with narrow linewidths. The selfinduced grating can dynamically adjust itself to small disturbances and changes in the cavity parameters.

Optical bistability in a nonlinear - linear interface with two-wave mixing.

We introduce a new mechanism for optical bistability at an interface between nonlinear (Kerr or photorefractive) and linear media for a light wave that propagates from the nonlinear side near the critical angle. The origin for this effect is the nonlinear coupling between the incident and reflected (from the interface) waves. We derive the laws of reflectivity and transmissivity and find a bistable behavior as a function of the incident power or the angle.

Forward phase conjugation by three-wave mixing with bacteriorhodopsin

Abstract Forward phase conjugate images are obtained by three-wave mixing in bacteriorhodospin. A possible use of the process for spatial filtering is discussed.

Self-pumped forward phase conjugator.

A self-pumped forward phase-conjugate mirror based on nonlinear wave mixing in photorefractive media is demonstrated. A single input beam to a BaTiO3 crystal excites an oscillation of pump beams between surfaces of the crystal and a forward phase-conjugate beam. The phase conjugation is carried on the first-order diffraction from the grating induced by the input and the self-generated pump beams.