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Silicon photonic crystals


Coupling to 2 x 106 ultra-high quality factor
silicon photonic crystal cavities

We have proposed an optimized design for the measurement in transmission of photonic crystal width-modulated line-defect cavities. By controlling the number of holes and rows that separate the cavity from the coupling waveguides, the measured quality factor of the cavity can be tuned to be close to the unloaded one. In the case of a weakly coupled cavity, we have measured an ultra-high quality factor that reaches a value of 2 x 106 .


Raman emission in silicon photonic crystals

We have shown that a deterministic value and measurement of the Purcell factor in a semiconductor microcavity can be obtained by using spontaneous Raman scattering as an internal source. In this case the emitter characteristics are entirely determined by the cavity design and do not depend on uncontrolled random factors, as it is usually the case when quantum dot emitters are used. We derive a theoretical expression for the Purcell factor of the cavity in the particular case of Raman scattering, in very good agreement with the experimental measurement.

We have studied the spontaneous Raman scattering in a W1 photonic crystal waveguide on silicon-on-insulator where the lower silica cladding remains. Despite the vertical asymmetry that exists in such a waveguide, we have numerically and experimentally shown that the propagation losses at the pump and the Stokes wavelengths remain low enough to allow a significant enhancement of the spontaneous Raman scattering. In particular, we have observed a reshaping of the Raman spectrum and a more than ten-fold enhancement of the Raman scattering efficiency in a W1 photonic crystal waveguide as compared to a single-mode ridge waveguide.


Quality factor of Si-based photonic crystal L3 nanocavities probed with an internal source

We have investigated the quality factors of silicon-based photonic crystal nanocavities using the photoluminescence of a single layer of Ge/Si self-assembled islands as an internal source. We have focused on membrane-type L3 elongated cavities with or without their lateral edge air holes shifted in position. The photoluminescence measurements were performed at room temperature. We have shown that the quality factor of the fundamental mode observed at a normalized frequency u = a/lambda = 0:25 is strongly dependent on the incident pump power. This dependence is associated with the free-carrier absorption of the photogenerated carriers. The slope of the quality factor vs. incident pump power gives access to the carrier recombination dynamics in these Si-based nanocavities. The measurements indicate that the carrier dynamics is controlled by nonradiative recombination associated with surface recombinations. A surface recombination velocity of 4.8 x 104 cm/s is deduced from the experiments. The spectral red-shift of the cavity modes as a function of incident pump power is correlated to the temperature rise due to thermo-optic effects. The measured temperature rise, which can reach 190 K, is correlated to the value estimated by a thermal analysis.