V. Berger

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 phase matching in THz semiconductor waveguides

Waveguide phase matching of a frequency conversion process within an isotropic semiconductor is studied. The three-wave interaction involves pump and signal beams in the near infrared, and the idler at THz frequencies, i.e. with a wavelength greater than 50 µm in GaAs. Phase matching is obtained by exploiting modal dispersion and, for energies below the reststrahlen region, the semiconductor anomalous dispersion. This original phase matching scheme provides simultaneously a long interaction length, due to waveguide confinement, and efficient wave mixing because only the fundamental modes are involved in a modal phase matching process. Two different types of waveguides are studied: bulk semiconductor rods and plasmon waveguides.

Interface band gap engineering in InAsSb photodiodes

The optimization of an InAs0.91Sb0.09 based infrared detector has been performed. The importance of the interfaces between the active region and the contacts in generation recombination phenomena is demonstrated. The two sides of the active region are optimized independently through heterostructure band gap engineering. The use of an Al0.15In0.85As0.91Sb0.09 quaternary makes it possible reach a detectivity of 4.4×109cm√Hz∕W at 290 K and 1.4×1010cm√Hz∕W at 250 K at 3.39μm, offering the perspective of a noncryogenic infrared imaging in the 3–5μm band with quantum detectors.

Integrated terahertz source based on three-wave mixing of whispering-gallery modes

We propose an integrated terahertz emitter operating at room temperature between 2.4 and 6 THz. Based on difference-frequency generation in a triply resonant Au/AlAs/GaAs/AlAs/Au microcylinder, this nonlinear source is pumped by two near-IR whispering-gallery modes that are excited by InAs quantum dots embedded in the resonator. In the vertical direction, these pump modes are due to total internal reflection at GaAs/AlAs interfaces, while the terahertz mode is confined between the metallic layers. This parametric source offers potential advantages with respect to existing terahertz sources for spectroscopic applications, such as room-temperature operation and electrical pumping.

Quantum cascade detectors for very long wave infrared detection

A high responsivity GaAs/AlGaAs quantum cascade detector is demonstrated at a wavelength of 15u2002μm. The quantum design is optimized for negative bias operation, so that the capture of photoexcited electrons back to the fundamental level is minimized. The detectivity of the detector presented here reaches 1.1×1012 Jones at 25 K for an applied bias of −0.6 V.

Strategy for the design of a non-cryogenic quantum infrared detector

A study of the optimization of the detectivity of a mid-infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and give physical insight into the mechanisms dominating the dark current. The analysis is performed step by step in different structures, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure and doping density in the active region, on diffusion and generation–recombination mechanisms is analysed. It is finally shown how the performances of a double heterostructure photovoltaic detector can be improved by a controlled doping of the active region, especially at low temperature.

A semiconductor source of counterpropagating twin photons : a versatile device allowing the control of the two-photon state

We report on an integrated source of twin photons at telecom wavelength operating at room temperature, in which a pump beam impinging on top of an AlGaAs waveguide generates two counterpropagating, orthogonally polarized guided modes by parametric fluorescence. This scheme allows an unprecedented flexibility in controlling the quantum properties of the emitted photons, by a simple shaping of the spatial and spectral profiles of the pump. The source versatility permits us to tailor the degree of frequency correlation and the spectrum of the emitted photons.

High contrast polarization sensitive quantum well infrared photodetectors

The responsivity of polarization sensitive quantum well infrared photodetectors with small pixel size (down to 20μm) is investigated. It is shown that pixels suitable for integration into very large focal plane arrays (1000×1000) can discriminate the polarization of the incoming signal. A responsivity contrast higher than 60% is obtained although the grating size is reduced to only six periods. The quantum efficiency and polarimetric capabilities can be both optimized with the same grating parameters.

Estimation of parametric gain in GaAs∕AlOx waveguides by fluorescence and second harmonic generation measurements

Efficient parametric fluorescence is obtained from a pump wavelength λ=1.06μm in low-loss, form-birefringent GaAs∕AlOx waveguides. Besides showing a 1μm wide tuning range and the onset of amplification regime for continuous-wave pump levels around 50mW, an 8% parametric gain is determined. This is the highest figure reported to date in semiconductor waveguides, and confirms GaAs∕AlOx waveguides as a candidate for an integrated parametric optical source.

Third order mode optically pumped semiconductor laser

Lasing action on a third order waveguide mode is demonstrated at room temperature under optical pumping, in a specifically designed quantum well laser structure. The AlGaAs heterostructure involves barriers which ensure that the third order waveguide mode has a higher overlap with the single quantum well emitter than the fundamental mode. Third order mode operation of a laser structure opens the way to modal phase matched parametric down conversion inside the semiconductor laser itself. It is a first step towards the realization of semiconductor twin photon laser sources, needed for quantum information experiments.