K. Moutzouris

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 .

Second-harmonic generation through optimized modal phase matching in semiconductor waveguides

We report optical second-harmonic generation (SHG) through modal phase matching in GaAs/AlGaAs semiconductor waveguides. Using femtosecond pulses, both type-I and type-II SHG is demonstrated for fundamental wavelengths near 1.55 μm.

Nonlinear frequency conversion in semiconductor optical waveguides using birefringent, modal and quasi-phase-matching techniques

We describe the use of GaAs-based semiconductor optical waveguides for nonlinear frequency conversion of femtosecond pulses in the infrared. Different techniques for the realization of phase matching, including artificial birefringence, quasi-phase-matching and modal dispersion, are reported and analysed and key issues relating to efficiency, practicality and applicability are discussed. Using the data obtained from these experiments, an overall comparison is made with other prominent techniques in order to identify the most promising and viable route to the development of efficient semiconductor waveguide frequency conversion devices for incorporation in the future generation of integrated photonic networks.

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.

Efficient second-harmonic generation in birefringently phase-matched GaAs/Al(2)O(3) waveguides.

We report efficient second-harmonic generation of femtosecond pulses in birefringently phase-matched GaAs/Al(2)O(3) waveguides pumped at 2.01mum. By use of pump pulses of ~200-fs duration and type I interaction, practical second-harmonic average powers of up to ~650muW were obtained, with an average input power of ~50muW. Waveguides of four different widths and two different lengths were investigated, and a normalized conversion efficiency of greater than 1000%W(-1)cm(-2) was obtained for a 1-mm waveguide. Measurements of pump and second-harmonic spectra provided clear evidence of phase matching and depletion of the pump spectrum. The measured bandwidth of the second harmonic was ~1.3nm. From the measurements of transmitted pump power at the phase-matching wavelength, pump depletions of more than 80% were recorded.

Measurements of optical loss in GaAs/Al2O3 nonlinear waveguides in the infrared using femtosecond scattering technique

Abstract We report measurements of optical loss in GaAs/Al 2 O 3 nonlinear waveguides over the spectral range 1.3– 2.1 μ m in the infrared using a scattering technique. The optical source was a tunable femtosecond optical parametric oscillator (OPO) generating output pulses with durations of 200–250 fs at a repetition rate of ∼90 MHz and an average power of ∼50 mW. Loss coefficients of ∼1.15–2.55 cm −1 , corresponding to losses of ∼5–11 dB/cm were obtained from the measured data. The loss decreases with increasing wavelength due to the Rayleigh scattering contribution.

Influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ nonlinear waveguides measured using femtosecond pulses

The influence of scattering and two-photon absorption on the optical loss in GaAs-Al/sub 2/O/sub 3/ semiconductor nonlinear waveguides has been studied using femtosecond pulses. By deploying a scattering technique, loss coefficients were evaluated over an extended wavelength range of 1.3-2.1 /spl mu/m in the near-infrared. A systematic study involving intensity and wavelength dependence of the loss revealed the presence of two-photon absorption for wavelengths below 1.6 /spl mu/m. A simple nonlinear transmission study enabled the separation of the two-photon absorption coefficient from scattering and linear absorption. The calculated two-photon absorption coefficients were /spl sim/9-20 cm/GW.

Measurements of optical loss in GaAs/Al/sub 2/O/sub 3/ nonlinear waveguides in the infrared using femtosecond scattering technique

Summary from only given. We measured the loss coefficient for GaAs/Al/sub 2/O/sub 3/ waveguides in the telecommunication window (near 1.5 /spl mu/m) and near 2.0 /spl mu/m, where these waveguides are proven to be strong candidates for nonlinear frequency conversion. Using the scattering technique and femtosecond pulses for the first time the losses were evaluated for semiconductor waveguides over an extended wavelength range from 1.3 to 2.1 /spl mu/m.

Generation of ultrashort electrical pulses in semiconductor waveguides

Summary form only given. Describes the results obtained from a device designed to generate an electrical signal using optical rectification at an input wavelength in the 1.55 /spl mu/m telecommunications window. The optical rectification effect (ORE) device consists of a ridge optical waveguide with a coplanar transmission line (CPW) deposited on top. The central conductor of the CPW line is carefully aligned on top of the ridge with the ground electrodes in close proximity in order to maximize the overlap between the optical and the microwave mode. The ground electrodes of the CPW line are periodically loaded to create a travelling wave device where the phase velocity of the electrical signal is matched to the group velocity of the optical signal.

First-order quasiphase matched second harmonic generation in GaAs/AlAs superlattice waveguides by use of ion-implantation induced intermixing

In this paper we report type-I second harmonic generation by use of first order quasiphase-matching in a GaAs/AlAs symmetric superlattice structure with femtosecond fundamental pulses at 1.55 /spl mu/m.