Peter W. E. Smith

Observation of spatial optical solitons in a nonlinear glass waveguide

We report the observation of spatial optical solitons due to the Kerr nonlinearity in a planar glass waveguide and present measurements of the nonlinear response obtained by placing a pinhole at the output of the waveguide. For input intensities greater than that required for the fundamental soliton, we observe breakup of the output owing to the effect of two-photon absorption.

All-fiber multimode interference bandpass filter

A novel design for an all-fiber bandpass filter based on a multimode interference reimaging phenomenon is presented. The filter has achieved low insertion loss with adequate bandwidth and isolation for coarse wavelength-division multiplexing. The filter can easily be made with any central wavelength that is compatible with the single-mode fiber used for its construction. The measured filter performance matches the theoretical predictions well. The filter can have broad applications in fiber-optic telecommunications, spectroscopy, and sensing.

Experimental observation of spatial soliton interactions

We report the experimental observation of interaction forces between two fundamental spatial optical solitons in a nonlinear glass waveguide. Both attraction and repulsion were observed, depending on the relative phase between the solitons.

Use of femtosecond square pulses to avoid pulse breakup in all-optical switching

The authors report measurements of ultrafast all-optical switching in dual-core fiber nonlinear couplers. By performing the measurements with square optical pulses, the pulse breakup which occurs in experiments performed by using conventional bell-shaped pulses is minimized. Compared to measurements performed by using conventional bell-shaped pulses, the measurements yield decreased switching power, a sharper switching transition, and improved power transfer. It is concluded that square pulse switching can be utilized to enhance the switching performance of any ultrafast all-optical switching device triggered by instantaneous intensity. >

Ultrashort pulse reflection from fiber gratings: a numerical investigation

We consider the linear reflection of ultrashort broadband pulses by uniform and nonuniform narrowband fiber gratings. We examine the effects of grating characteristics, including peak reflectivity, bandwidth, phase response (dispersion and chirp), and apodization on the reflection of such pulses from various gratings. A symmetric transform-limited 1-ps Gaussian pulse is assumed as the ultrashort broadband input to the gratings; the reflected pulses take on significantly different shapes and vary in duration. The prominent features observed are qualitatively explained in order to gain physical insight into the nature of the ultrashort pulse response and corresponding interaction. The results of this study indicate that there is the potential for a new class of applications, including temporal pulse shaping and novel devices for optical communications systems, by combining ultrashort broadband pulses with narrowband fiber gratings.

Ultrafast dynamics of nonlinear absorption in low‐temperature‐grown GaAs

We present the results of a study of the subpicosecond dynamic behavior of optically induced absorption changes in low‐temperature‐grown GaAs. We show that the observed behavior is dominated by mid‐gap trap states, and can be accurately modeled by the rate equations previously developed to describe quasi‐cw results. Our data give the first approximate values for trap emptying times in this material.

Time-division multiplexing of large serial fiber-optic Bragg grating sensor arrays

Time-division multiplexing is a promising method for the interrogation of fiber-optic Bragg grating sensors arrays for measurement of strain and temperature. We examine the performance of these systems to determine the parameters for high-sensitivity, low-cross-talk operation. It is shown that the performance can be greatly improved by use of a short time resolution in the demultiplexing process. We propose a new method of demultiplexing with an electro-optic modulator to read out the sensor pulses by gating the signal with 400-ps resolution. The system is demonstrated experimentally to provide 0.15-microepsilon/square root(Hz) strain resolution in a 50-Hz bandwidth within a full-scale range of 8000 microepsilon. The system parameters are capable of handling at least 50 time-addressed sensors on a single fiber.

Dispersion of the nonlinear refractive index in sapphire

The nonlinear refractive index, n2, of sapphire was experimentally measured in the 550-1550-nm wavelength range by use of a picosecond Z-scan technique. It was found that in this spectral region the value of n2 decreases monotonically from approximately 3.3 x 10(-16) to approximately 2.8 x 10(-16) cm2/W. An empirical expression for the wavelength dependence of the nonlinear refractive index in the 270-1550-nm range was obtained.

Optical characterization of low-temperature-grown GaAs for ultrafast all-optical switching devices

Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching.

Role of two‐photon absorption in ultrafast semiconductor optical switching devices

We report measurements of the two‐photon absorption coefficient of GaAs optical waveguide structures at 1.06 μm. We show that for pulse lengths longer than ∼1 ps, light‐induced index changes sufficient to induce all‐optical switching will be predominantly due to carriers generated by two‐photon absorption. These results allow us to predict limitations for ultrafast all‐optical GaAs devices.