Abstract
Distributed grating coupling of light pulses into planar waveguides, exhibiting third-order nonlinear-optical effects, is studied theoretically. The nonlinear interaction taking place between a beam that is Gaussian in time and space and one or more waveguide media with intensity-dependent refractive indexes or absorptions is analyzed, with emphasis on the different effects that result from the relative importance of two-photon absorption, dispersive index changes, and their saturation. Criteria for the evaluation of real and imaginary parts of chi-(3) by means of grating coupling are outlined.

Abstract
We report the experimental evaluation of the intensity-dependent index of refraction of a new class of third order nonlinear materials, side chain polymers containing 4-dialkylamino-4'-nitro-stilbene and 4-dialkylamino-4'-nitro-diphenylbutadiene as side groups. The measurements, based on nonlinear grating coupling into planar waveguides with 30 ps pulses at 1.064-mu-m, showed large electronic nonresonant n2 Kerr coefficients.

Abstract
Optical fibers are used to provide object and reference illumination in the context of the electronic speckle-pattern interferometry technique. An all-fiber Michelson interferometer is used, with an electronic servo and a piezoelectric phase modulator, to obtain compensation for environmentally induced phase coupling into the fiber arms. © 1990 Optical Society of America.

Abstract
A system employing optical fibres for electronic speckle pattern interferometry is demonstrated. Single mode optical fibres are used to provide a reference beam and illumination of the object. The Michelson interferometer formed by the reference fibre and the fibre illuminating the target is used to compensate for environmentally induced phase noise. This compensation is achieved by using an electronic servo and a piezoelectric phase modulator to lock the Michelson at its quadrature point.

Abstract
A time division multiplexing technique is described in which the frequency of a laser source is modulated with a sampled ramp. The concept is demonstrated with two Mach-Zehnder interferometers in a parallel configuration, separated by a fibre delay line whose length is determined by the characteristics of the sampling waveform. Pseudo-heterodyne processing was used to recover the phase information from each interferometer. The expansion of the technique to a combined frequency and time division multiplexed fibre-optic sensing system is considered.

Abstract
A time division multiplexing technique is described in which the frequency of a laser source is modulated with a sampled ramp. The concept is demonstrated with two Mach-Zehnder interferometers in a parallel configuration, separated by a fibre delay line whose length is determined by the characteristics of the sampling waveform. Pseudo-heterodyne processing was used to recover the phase information from each interferometer. The expansion of the technique to a combined frequency and time division multiplexed fibre-optic sensing system is considered. © 1990.