Juan Ariel Levenson

Quantum non-demolition measurements in optics

Quantum non-demolition measurements are designed to circumvent the limitations imposed by Heisenbergs uncertainty principle when performing repeated measurements of quantum states. Recent progress in quantum optics has enabled the experimental realization of quantum non-demolition measurements of the photon flux of a light beam. This achievement bears on fundamental issues about the ultimate sensitivity of measurements, and may open the way for applications such as noise-free information tapping in optical telecommunications.

Enhancement of second-harmonic generation in a one-dimensional semiconductor photonic band gap

We demonstrate significant enhancement of second-order nonlinear interactions in a one-dimensional semiconductor Bragg mirror operating as a photonic band gap structure. The enhancement comes from a simultaneous availability of a high density of states, thanks to high field localization, and the improvement of effective coherent length near the photonic band edge.

Ultraslow light propagation in an inhomogeneously broadened rare-earth ion-doped crystal.

We show that coherent population oscillations effect allows us to burn a narrow spectral hole (26 Hz) within the homogeneous absorption line of the optical transition of an erbium ion-doped crystal. The large dispersion of the index of refraction associated with this hole permits us to achieve a group velocity as low as 2.7 m/s with a transmission of 40%. We especially benefit from the inhomogeneous absorption broadening of the ions to tune both the transmission coefficient, from 40% to 90%, and the light group velocity from 2.7 m/s to 100 m/s.

Phase-matched third-harmonic generation in highly germanium-doped fiber

Phase-matched third-harmonic generation is demonstrated in a germanium-doped optical fiber. Green light at 514.4 nm is generated in an LP(03) mode when a pump field at ~1543.3 nm is launched into the fiber in the fundamental LP(01) mode. The phase matching is achieved for a particular combination of the germanium doping concentration and the fiber core diameter.

Semiclassical model of triple photons generation in optical fibers.

In this Letter we study spontaneous generation of triple photon states in optical fibers by third order spontaneous downconversion. Using a semiclassical approach we derive an explicit expression for the triple photons generation efficiency as a function of fiber parameters. We show that optical fibers with well suited index profiles and standard outer diameters could be the key component of future triple photons sources.

Thermo-optical dynamics in an optically pumped Photonic Crystal nano-cavity

Linear and non-linear thermo-optical dynamical regimes were investigated in a photonic crystal cavity. First, we have measured the thermal relaxation time in an InP-based nano-cavity with quantum dots in the presence of optical pumping. The experimental method presented here allows one to obtain the dynamics of temperature in a nanocavity based on reflectivity measurements of a cw probe beam coupled through an adiabatically tapered fiber. Characteristic times of 1.0+/-0.2 micros and 0.9+/-0.2 micros for the heating and the cooling processes were obtained. Finally, thermal dynamics were also investigated in a thermo-optical bistable regime. Switch-on/off times of 2 micros and 4 micros respectively were measured, which could be explained in terms of a simple non-linear dynamical representation.

Small volume excitation and enhancement of dye fluorescence on a 2D photonic crystal surface

We demonstrate an easy-to-implement scheme for fluorescence enhancement and observation volume reduction using photonic crystals (PhCs) as substrates for microscopy. By normal incidence coupling to slow 2D-PhC guided modes, a 65 fold enhancement in the excitation is achieved in the near field region (100 nm deep and 1 microm wide) of the resonant mode. Such large enhancement together with the high spatial resolution makes this device an excellent substrate for fluorescence microscopies.

Radiation patterns from coupled photonic crystal nanocavities

We report on far field measurements on two coupled photonic crystal nanocavities. The distinct features of the antisymmetric modes (minima of intensity at zero-emission angles) allow us to demonstrate a π-phase difference between the cavity fields, a clear signature of evanescent coupling. Good agreement between experimental results and simulated radiation patterns has been found.

Discrete photonics in waveguide arrays

In homogeneous arrays of coupled waveguides, Floquet-Bloch waves are known to travel freely across the waveguides. We introduce a systematic discussion of the built-in patterning of the coupling constant between neighboring waveguides. Key patterns provide functions such as redirecting, guiding, and focusing these waves, up to nonlinear all-optical routing. This opens the way to light control in a functionalized discrete space, i.e., discrete photonics.

Confining light flow in weakly coupled waveguide arrays by structuring the coupling constant: towards discrete diffractive optics

Structuring the coupling constant in coupled waveguide arrays opens up a new route towards molding and controlling the flow of light in discrete structures. We show coupled mode theory is a reliable yet very simple and practical tool to design and explore new structures of patterned coupling constant. We validate our simulation and technological choices by successful fabrication of appropriate III-V semiconductor patterned waveguide arrays. We demonstrate confinement of light in designated areas of one-dimensional semi-conductor waveguide arrays.