Brian L. Lawrence

All‐optical switching by spatial walkoff compensation and solitary‐wave locking

We demonstrate a novel approach to phase insensitive, all‐optical steering and switching based on an intensity‐induced change in the propagation direction of multidimensional spatial solitary waves in bulk, birefringent, quadratic nonlinear media. Our demonstration is based on second‐harmonic generation in a KTP crystal. Compensation for the lateral displacements due to walkoff in SHG is observed.

Measurement of the complex nonlinear refractive index of single crystal p‐toluene sulfonate at 1064 nm

Z‐scan at 1064 nm was used with single, 35 ps pulses to measure the nonlinear refraction and absorption in single crystal PTS (p‐toluene sulfonate). Detailed analysis of the Z‐scan data based on Δn=n2I+n3I2 and Δα=α2I+α3I2 yielded n2=5(±1)×10−12 cm2/W, α2=100(±20) cm/GW, n3=−5(±1)×10−21 cm4/W2 and α3=−5(±1) cm3/GW.2 The resulting two photon figure of merit T for PTS is marginal for high throughput, all‐optical waveguide switching at 1064 nm.

Stable self-trapping and ring formation in polydiacetylene para -toluene sulfonate.

Summary form only given. We now report numerical simulations of beam propagation in polydiacetylene para-toluene sulfonate (PTS), using measured refractive index values, and demonstrate stable self-trapping and a new phenomenon in which a Gaussian input beam evolves into an expanding spatial ring and interpret these results in the context of the variational model of nonlinear Gaussian beam propagation. We also show preliminary experimental results suggesting the presence of ring formation.

Two-dimensional bright spatial solitons stable over limited intensities and ring formation in polydiacetylene para-toluene sulfonate.

Spatial soliton formation in the bulk single-crystal polydiacetylene para-toulene sulfonate has been studied experimentally. The unique nonlinearity of this material at 1600 nm leads to stable solitons below an intensity maximum, and for higher intensities the input beams form a ring and a soliton.

Beam reshaping by use of spatial solitons in the quadratic nonlinear medium KTP.

We have demonstrated the transformation of elliptical beams into cylindrically symmetric beams through the formation of quadratic spatial solitons. By use of type II phase-matched second-harmonic generation in a KTP crystal, input elliptical beams with aspect ratios as large as 8:1 were propagated through the KTP crystal, and they exited the crystal as a cylindrically symmetric beam. The threshold for soliton formation and the power throughput were measured versus ellipticity.

Two-photon saturation in the band gap of a molecular quantum wire

The saturation of the strongest two-photon band accessible with photon energies in the band gap of a onedimensional pi-electron conjugated molecular single crystal is observed with 200-fs pulses for optical intensities of the order of 2 GW/cm(2).

Assessment of single crystal p‐toluene sulfonate as an all‐optical switching material at 1.3 μm

We evaluate the potential of single crystal PTS (p‐toluene sulfonate) for all‐optical applications at the 1.32 μm communications wavelength by measuring the electronic and thermo‐optic nonlinearities, and the multiphoton absorption with picosecond pulses. With appropriate heat sinking, duty cycles greater than 25% should be possible without significant cumulative thermal effects for 1 W operating powers.

High-performance Er/Yb-doped waveguide optical amplifier

Single-mode optical amplification in novel rare-earth-doped multimode waveguides is demonstrated, at what we believe is the highest gain per unit length yet reported. Design and measurements of a single-pass and double-pass waveguide amplifier are presented.

Spatial switching of solitary waves in KTP

Here, the stable beams are a result of strongly coupled interacting waves. Indeed, the use of second-order effects has proven sucessful in stabilizing 2D beams in KTP both experimentally and in numerical simulations of beam propagation. We discuss experimental demonstrations of 2D spatial solitary waves, and the application of these beams to the practical problems of spatial beam clean-up and all-optical switching.

Nonlinear spectroscopy of polydiacetylenes

The third order susceptibility of a polydiacetylene polymer was investigated by three different nonlinear spectroscopic techniques in order to test two existing microscopic theories which predict the nonlinear response of such molecular systems. We previously found good agreement between a four essential state model and the THG spectra of (pi) -electron conjugated backbone polymers. However, when such a model was extended to two additional third order susceptibility spectra, poor agreement was found. In contrast the recently developed anharmonic oscillator model fitted well all four experimentally obtained spectra of the third order susceptibility.