C. Cacciatore

Loss analysis and interference effect in semiconductor integrated waveguide turning mirrors

Semiconductor integrated waveguide turning mirrors (IWTM) are investigated using the beam propagation method. A mirror is fabricated and modeled along with realistic geometries in the presence of offset and roughness of the mirror surface. An interference effect between waves reflected at different surfaces in the device is evidenced, that has strong impact on the device performance in the case of weakly-confining structures. A widely-accepted fabrication approach is criticized in view of this effect. A solution is outlined that minimizes the losses due to either technological limitations or interference.

Measurement of the refractive index of GaInAs/InP quantum wells by a grating coupling technique

Effective indices of modes propagating in multiple GaInAs wells on InP barriers (MQW) waveguides are accurately measured in the 1.4–1.75 μm wavelength range using the grating coupling technique. Quantum size effects cause a selective polarization absorption and high birefringence, strongly depending on wavelength. The temperature dependence of refractive index and absorption originating from the temperature‐dependent band gap is also observed. In the transparency region the refractive indices of GaInAs wells in InP barriers are deduced for two well widths using a multilayer slab waveguide model and an exciton model based on Lorentzian oscillator.

BUTTERFLY BISTABILITY IN AN INGAAS/INP MULTIPLE-QUANTUM WELL WAVEGUIDE WITH DISTRIBUTED FEEDBACK

We report the experimental observation of butterfly bistability in an InGaAs/InP multiple‐quantum well waveguide with a distributed feedback grating, under cw operation and at sub‐milliwatt input power. Plasma effects on the excitonic optical properties in multiple‐quantum well structures are the basis of the observed bistability. Insight provided by a simple coupled‐mode description of the device and by many‐body theory of the field‐matter interaction is used both for device design and for interpretation of the results. In particular, the unconventional shape of the hysteresis is due to increased optical absorption at high injected optical power.

Nonlinear contradirectional coupler

Results of room-temperature experiments with a multiple-quantum-well, nonlinear, contradirectional coupler are reported. A power-dependent, contradirectional coupling condition is demonstrated, inducing an optically controlled switching of optical signals, with a switching energy of 1 pJ.

Observation of Superlattice Franz-Keldysh Oscillations

Using electroreflectance we report the first observation of the Franz-Keldysh oscillations originating from the band gap of a GaAs/Ga0.67Al0.33As short-period superlattice. The observed effect enables to measure the reduced effective mass in the direction of the growth axis.

InGaAs-InP superlattice electroabsorption waveguide modulator

An electroabsorption waveguide modulator with an extinction ratio for TE-polarized light at 1550 nm of more than 20 dB for a voltage swing of less than 3 V, and low insertion losses has been realized, which exploits the Wannier-Stark effect in an InGaAs-InP short period superlattice, grown by chemical beam epitaxy. Even for a fixed voltage swing of 2.6 V, a good transmission contrast has been obtained in a wide wavelength range.<<ETX>>

Enhanced confinement of electrons at room temperature using a superlattice reflector

We report the experimental study of the thermionic emission of electrons into overbarrier states of a superlattice, tailored to enhance electron confinement within a closely spaced quantum well. Partial suppression of the thermionic current is observed at room temperature. A critical evaluation of the practical applications of the effect is offered. Furthermore, the tunnel injection into partially delocalized Stark states of the superlattice is observed at low temperature.

Optically multistable operation of a waveguide device based on the Wannier–Stark effect in an InGaAs/InP superlattice

An optically multistable device in waveguide configuration has been fabricated, which is based on the Wannier–Stark effect in an InGaAs/InP superlattice. It implements a waveguided version of the self‐electro‐optic effect device and it operates at room temperature at a wavelength of 1.55 μm.

Demonstration of low-power nonlinearity in InGaAs/InP multiple-quantum-well waveguides

We report both linear and nonlinear grating coupling to a planar multiple quantum well (MQW) waveguide grown by chemical beam epitaxy. We demonstrate a strong dependence of the coupling angle on the incident power in the wavelength range (lambda) equals 1.57 - 1.60 micrometers . The obtained nonlinear variation of neff were found to be negative, and on the order of 10-3, in agreement with many-body calculations performed by the authors. We show that thermal effects can be ruled out. At coupled light intensity as low as 40 mW, nonlinear switching condition was achieved; the power density to obtain the switching process is substantially lower than in previous works. As part of this work, we report the systematic investigation of the linear and nonlinear absorption properties of several InGaAs/InP MQW structures, measuring a series of transmission spectra in the region of the band edge for various pump intensities and observing large changes in the absorption coefficient. Through comparison with these results, we speculate that the mechanism responsible for the refractive nonlinearity observed in the waveguide is consistent with purely excitonic effects.

Electric field dependence of optical properties of a double quantum well: experiment and applications

In the present work, we report the systematic observation of the optical blue shift induced by electric field in a GaAs/GaAIAs double-well system as far as 18 meV at room temperature. To this end, a detailed electroreflectance study of a GaAs-Alo.3 Gao.7 As double quantum well structure was carried out at room temperature. This effect occurs at moderate values ofthe applied field. In addition, a computer modeling of the electric field dependent optical properties is presented, which is based upon a variational calculation, in the frame of the effective mass approximation. The calculated spectra agree with the expefimental results. The model was used to engineer a coupled QW structure, which optimises the achievable modulation depth, due to application of an electric field.