Herbert G. Winful

Theory of bistability in nonlinear distributed feedback structures

We show that optical bistability can occur in a distributed feedback structure with an intensity‐dependent refractive index. Analytical expressions for the transmissivity are obtained and a comparison with Fabry‐Perot‐type devices is presented.

Generation of narrow-band terahertz radiation via optical rectification of femtosecond pulses in periodically poled lithium niobate

We demonstrate a promising technique for generating narrow-band terahertz electromagnetic radiation. Femtosecond optical pulses are propagated through a periodically poled lithium-niobate crystal, where the domain length is matched to the walk-off length between the optical and THz pulses. The bandwidth of the THz wave forms is 0.11 at 1.7 THz. Optical rectification gives rise to a THz wave form which corresponds to the domain structure of the periodically poled lithium niobate.

Physical origin of the Gouy phase shift

We show explicitly that the well-known Gouy phase shift of any focused beam originates from transverse spatial confinement, which, through the uncertainty principle, introduces a spread in the transverse momenta and hence a shift in the expectation value of the axial propagation constant. A general expression is given for the Gouy phase shift in terms of expectation values of the squares of the transverse momenta. Our result also explains the phase shift in front of the Kirchhoff diffraction integral.

Pulse compression in optical fiber filters

A method is described for compressing optical pulses at any wavelength in an optical fiber. It uses the negative dispersion property of permanent phase gratings created within the fiber. No external grating pair is required.

Polarization instabilities in birefringent nonlinear media: application to fiber-optic devices

The intensity-dependent refractive index leads to an instability in the polarization state of an intense light beam oriented along the fast axis of a birefringent nonlinear medium. Depending on initial conditions, the spatial evolution of the polarization state can be oscillatory or rotatory, in a manner analogous to the motion of a nonlinear pendulum.

Self‐pulsing and chaos in distributed feedback bistable optical devices

We show that the light transmitted by a nonlinear distributed feedback structure can be steady (time independent), periodic, or chaotic depending on the intensity of the input cw beam. The feasibility of an experimental demonstration of such behavior is discussed.

Self‐induced polarization changes in birefringent optical fibers

Exact solutions are presented for the intensity‐dependent polarization state of a light wave in a birefringent optical fiber. The theory takes into account both the linear polarization evolution and the nonlinear ellipse rotation. It is shown that, contrary to current belief, self‐induced polarization changes are possible even with equal excitation of the fiber’s principal axes. The theory is applicable to the operation of recently demonstrated fiber‐optic logic gates, pulse shapers, and intensity discriminators.

Stability of phase locking in coupled semiconductor laser arrays

It is shown that amplitude phase coupling (as described by the linewidth enhancement factor α) leads to unstable phase locking in semiconductor laser arrays with evanescent coupling.

Nonlinear Guided Wave Applications

Potential device applications of third-order nonlinear phenomena in guided wave structures are discussed. One of the waveguiding media is assumed to exhibit an intensity-dependent refractive index that results in both an intensity-dependent propagation wavevector and field distribution for the guided waves. These two characteristics lead to many interesting all-optical devices whose operating principles and power levels are outlined here. For example, the intensity-dependent field patterns can be used for thresholding and switching operations in a waveguide context. The intensity-dependent wavevector, used in conjuction with a distributed input or output coupler, can lead to devices such as optical limiters and light-controlled spatial scanners. When gratings are used as distributed feedback elements within a nonlinear waveguide, a whole class of novel devices such as bistable switches and optically tunable optical filters should be feasible.

Nonlinear Schrödinger solitons in a periodic structure

It is demonstrated theoretically that a nonlinear medium with a spatially periodic refractive index can support solitons of the nonlinear Schrodinger equation.