One of the bottlenecks for the widespread application of Silicon Photonics, and for the merging of electronic and optical functions on the same chip, is the lack of efficient light sources in Silicon. The material itself is known to be a poor light emitter because of its indirect fundamental band gap. By doping silicon with erbium ions, it is possible to obtain a radiative transition in the 4f shell of the rare earth at ~1.54 µm. This system is very promising for obtaining controlled (and, possibly, electrically driven) light emission at telecom wavelengths and is especially interesting at low temperature, where several narrow emission lines are observed due to the crystal-field splitting. Moreover, the excitation cross section for Er in crystalline Si is particularly high being achieved through carrier recombination processes, thus yielding a good emission efficiency.

Much progress has been made in recent years in the control of radiation-matter interaction in III-V semiconductors through the use of micro- and nanocavities. A particularly interesting phenomenon is the Purcell effect, namely the reduction of radiative lifetime due to the interaction of the excited "atom" (usually a quantum dot) with a high Q cavity mode. The radiative decay rate then scales as Q/V, where Q is the quality factor and V is the mode volume. Ultra-high Q factors with low mode volumes were demonstrated for photonic crystal nanocavities in Si membranes, however those results were obtained in passive Si systems and only few studies of radiation-matter interaction in active Si-based photonic nanostructures have been reported up to now.

The project focuses on the control of radiative emission of Erbium ions in photonic crystal nanostructures made of crystalline Silicon, with the final goal of achieving laser emission around 1.54 micron wavelength. To this purpose, photonic crystal waveguides and nanocavities will be fabricated in Si membranes doped with Er3+ ions. Nanocavity structures that are resonant with the narrow emission lines of Er3+ at low temperature will tailor the radiative dynamics and enhance optical gain. Micro-photoluminescence experiments under suitable pumping conditions will allow studying the radiative emission of Er3+ ions, towards achieving net gain and lasing threshold. Theoretical studies of Er3+ emission coupled to nanocavity modes will allow exploring cavity quantum electrodynamic effects.

The LECSIN (Lasing of Erbium in Crystalline Silicon Photonic Nanostructures) project builds on a new European partnership by four groups at Catania, St Andrews, Pavia, and Grenoble, with complementary expertise in Silicon photonics, nano-technonology and nano-photonics, theoretical simulation and design, quantum optics. It is organized in two workpackages and eight tasks as follows:

• WP1: ERBIUM-OXYGEN CLUSTERS IN PHOTONIC NANOSTRUCTURES

• Task 1.1: Erbium-Oxygen Nanoclusters
• Task 1.2: Photonic Nanostructures
• Task 1.3: Active Properties of Er-Doped Silicon Nanostructures
• Task 1.4: QED of Er in Si Photonic Nanostructures

• WP2: AMPLIFICATION, LASING AND COLLECTIVE EFFECTS

• Task 2.1: Amplification in Silicon-on-Insulator Waveguides
• Task 2.2: Optical Pumped Lasing and Superradiance
• Task 2.3: Electrically Driven Lasing
• Task 2.4: Theory of Low-Threshold Lasing and Superradiance