David C. Hutchings

The nonlinear optical properties of AlGaAs at the half band gap

We report experimental values for the nonlinear optical coefficients of AlGaAs, in the half-band-gap spectral region. The dispersion of the nonlinear refractive-index coefficient, n/sub 2/, is measured for both TE- and TM-polarized light. We observe n/sub 2/(TE)>n/sub 2/(TM) and a ratio of cross-phase modulation to self-phase modulation (TE) of /spl sim/0.95, as predicted from band structure calculations. The spectral dependence of the two- and three-photon absorption coefficients are also measured. Finally, the implications for all-optical switching and spatial soliton propagation are discussed.

Quasi phase matching in GaAs--AlAs superlattice waveguides through bandgap tuning by use of quantum-well intermixing.

We report the observation of second-harmonic generation by type I quasi phase matching in a GaAs-AlAs superlattice waveguide. Quasi phase matching was achieved through modulation of the nonlinear coefficient chi((2))(zxy), which we realized by periodically tuning the superlattice bandgap. Second-harmonic generation was demonstrated for fundamental wavelengths from 1480 to 1520 nm, from the third-order gratings with periods from 10.5 to 12.4microm . The second-harmonic signal spectra demonstrated narrowing owing to the finite bandwidth of the quasi-phase-matching grating. An average power of ~110 nW was obtained for the second harmonic by use of an average launched pump power of ?2.3mW .

All-optical switching based on nondegenerate phase shifts from a cascaded second-order nonlinearity

All-optical switching by using a nondegenerate cascaded second-order nonlinearity is described wherein a phase shift is induced at one frequency owing to the presence of intense light at a different frequency. A Mach-Zehnder waveguide device is proposed to take advantage of this process and has applications for all-optical switching and demultiplexing, potentially at power levels near 10 W by using quasi-phase matching in semiconductor waveguides.

Realization of novel low-loss monolithically integrated passive waveguide mode converters

The novel design and fabrication of monolithically integrated passive waveguide mode converters (WMCs), realized through the utilization of the reactive ion-etch lag (RIE Lag) phenomenon, is reported. The low-loss GaAs-AlGaAs WMCs have been characterized over a wavelength range of 900-940 nm, resulting in TE-TM (TM-TE) mode conversion with efficiencies of greater than 96% and low-loss devices with conversion lengths as short as 150 /spl mu/m. The properties and characteristics of the fully integrated WMCs, fabricated with a single masking and etch process, are in agreement with theoretical predictions.

Prospects for the implementation of magneto-optic elements in optoelectronic integrated circuits: a personal perspective

A review is performed of the major challenges to the implementation of the non-reciprocal functionality provided by magneto-optics in standard optoelectric or photonic integrated circuits. The polarization dynamics in the presence of an unavoidable, structurally-induced birefringence are discussed by making use of a Hamiltonian approach. Normally, the additional birefringence would place a limitation on the degree of polarization rotation achievable, but solutions based on quasi-phase-matching or the transverse Kerr effect are discussed. It is shown that the magneto-optic response of III?V semiconductors and other common substrate materials is small and some of the approaches to incorporating materials with a larger response are reviewed. Approaches to combining a polarization rotation element with the required polarization selectivity in a planar waveguide is also discussed.

Quasi-phase-matched second-harmonic generation in a GaAs/AlAs superlattice waveguide by ion-implantation-induced intermixing

We report type I second-harmonic generation by use of first-order quasi-phase matching in a GaAs/AlAs symmetric superlattice structure with femtosecond fundamental pulses at 1.55 microm. Periodic spatial modulation of the bulklike second-order susceptibility chi(zxy)(2) was achieved with quantum-well intermixing for which the group III vacancies were created by As+-ion implantation. A narrow second-harmonic bandwidth of approximately 0.9 nm (FWHM) with an average power of approximately 1.5 microW was detected, corresponding to an internal conversion efficiency of approximately 0.06%, which was considerably limited by the spectral bandwidth of the fundamental.

Modulation of the second-order nonlinear tensor components in multiple-quantum-well structures

In this paper, we present experimental results which demonstrate that quantum-well intermixing techniques can be used to modulate the magnitude of the second-order nonlinear coefficient /spl chi//sup (2)/. Impurity-free vacancy disordering with SiO/sub 2/ and Ga/sub 2/O/sub 3/ caps was used to modulate the position of the band edge and hence, the magnitude of /spl chi//sub eff//sup (2)/. Using a coupled quantum-well structure we were able to demonstrate modulation of the d/sub 33/ tensor components associated with the asymmetric structure and of the d/sub 14/ component associated with the bulk crystal structure.

A Waveguide Polarization Toolset Design Based on Mode Beating

A toolset of waveguide elements is examined, which can be combined to produce polarization functional devices in a single contiguous waveguide. In particular, waveguide implementations of an optical isolator and a polarization modulator are discussed. The waveguide elements, i.e., quasi-phase-matched nonreciprocal polarization mode converter, reciprocal polarization mode converter (R-PMC), and a differential phase shifter, are all based on mode beating. A universal 3-dB R-PMC specification is identified, which suffices for all the polarization functional devices considered here. A full-vectorial modesolver is used to determine the modes in a number of example III-V waveguide structures, and the polarization state evolution is considered by using an averaged Stokes vector illustrated on the Poincaré sphere construct.

Theory of ultrafast nonlinear refraction in semiconductor superlattices

A theoretical study is undertaken into the Kerr nonlinear refraction observable in the transparency window in semiconductor heterostructures. Symmetry considerations indicate that the number of nonzero, independent tensor components increases from three to eight for single wavelength third-order nonlinear processes with the usual growth orientation. These are related to the observable phenomena of self-phase-modulation, cross-phase-modulation, and four-wave-mixing of the orthogonal polarization components in the usual waveguide geometry. For a 14:14 GaAs-AlAs superlattice, all eight independent elements are calculated. It is shown that the nonlinear response is highly anisotropic. The modification of the nonlinear coefficients with quantum well intermixing is investigated, with a several-fold reduction in value predicted. This modification could be exploited in some long-standing and novel nonlinear optical experiments.

Demonstration of quasi-phase-matched nonreciprocal polarization rotation in III-V semiconductor waveguides incorporating magneto-optic upper claddings

The demonstration of quasi-phase-matched nonreciprocal polarization rotation in a waveguide comprising a conventional III-V semiconductor core and lower cladding is reported. The approach, which is achieved through the incorporation of a periodic upper cladding that alternates between magneto-optic and nonmagneto-optic media, overcomes many of the problems traditionally encountered when transferring the principles of free-space Faraday-effect optical isolators into waveguide geometries. An enhancement of polarization rotation many times greater than that achievable in the absence of phase matching is observed. Additionally, the technique facilitates an ability to select and/or manipulate individual modes from multimode waveguides.