On-chip interference of single photons from an embedded quantum dot and an external laser

In this work, we demonstrate the on-chip two-photon interference between single photons emitted by a single self-assembled InGaAs quantum dot and an external laser. The quantum dot is embedded within one arm of an air-clad directional coupler which acts as a beam-splitter for incoming light. Photons originating from an attenuated external laser are coupled to the second arm of the beam-splitter and then combined with the quantum dot photons, giving rise to two-photon quantum interference between dissimilar sources. We verify the occurrence of on-chip Hong-Ou-Mandel interference by cross-correlating the optical signal from the separate output ports of the directional coupler. This experimental approach allows us to use classical light source (laser) to assess in a single step the overall device performance in the quantum regime and probe quantum dot photon indistinguishability on application realistic time scales.Comment: 5 pages, 3 figure

A fully integrated high-Q Whispering-Gallery Wedge Resonator

Microresonator devices which posses ultra-high quality factors are essential for fundamental investigations and applications. Microsphere and microtoroid resonators support remarkably high Q's at optical frequencies, while planarity constrains preclude their integration into functional lightwave circuits. Conventional semiconductor processing can also be used to realize ultra-high-Q's with planar wedge-resonators. Still, their full integration with side-coupled dielectric waveguides remains an issue. Here we show the full monolithic integration of a wedge-resonator/waveguide vertically-coupled system on a silicon chip. In this approach the cavity and the waveguide lay in different planes. This permits to realize the shallow-angle wedge while the waveguide remains intact, allowing therefore to engineer a coupling of arbitrary strength between these two. The precise size-control and the robustness against post-processing operation due to its monolithic integration makes this system a prominent platform for industrial-scale integration of ultra-high-Q devices into planar lightwave chips.Comment: 6 pages, 4 figure

Erbium emission in MOS light emitting devices: from energy transfer to direct impact excitation

The electroluminescence (EL) at 1.54 µm of metal-oxide-semiconductor (MOS) devices with Er3+ ions embedded in the silicon-rich silicon oxide (SRSO) layer has been investigated under different polarization conditions and compared with that of erbium doped SiO2 layers. EL time-resolved measurements allowed us to distinguish between two different excitation mechanisms responsible for the Er3+ emission under an alternate pulsed voltage signal (APV). Energy transfer from silicon nanoclusters (Si-ncs) to Er3+ is clearly observed at low-field APV excitation. We demonstrate that sequential electron and hole injection at the edges of the pulses creates excited states in Si-ncs which upon recombination transfer their energy to Er3+ ions. On the contrary, direct impact excitation of Er3+ by hot injected carriers starts at the Fowler-Nordheim injection threshold (above 5 MV cm−1) and dominates for high-field APV excitation

Inter-mode reactive coupling induced by waveguide-resonator interaction

We report on a joint theoretical and experimental study of an integrated photonic device consisting of a single mode waveguide vertically coupled to a disk-shaped microresonator. Starting from the general theory of open systems, we show how the presence of a neighboring waveguide induces reactive inter-mode coupling in the resonator, analogous to an off-diagonal Lamb shift from atomic physics. Observable consequences of this coupling manifest as peculiar Fano lineshapes in the waveguide transmission spectra. The theoretical predictions are validated by full vectorial 3D finite element numerical simulations and are confirmed by the experiments

High Purcell factor generation of indistinguishable on-chip single photons

On-chip single-photon sources are key components for integrated photonic quantum technologies. Semiconductor quantum dots can exhibit near-ideal single-photon emission, but this can be significantly degraded in on-chip geometries owing to nearby etched surfaces. A long-proposed solution to improve the indistinguishablility is to use the Purcell effect to reduce the radiative lifetime. However, until now only modest Purcell enhancements have been observed. Here we use pulsed resonant excitation to eliminate slow relaxation paths, revealing a highly Purcell-shortened radiative lifetime (22.7 ps) in a waveguide-coupled quantum dot–photonic crystal cavity system. This leads to near-lifetime-limited single-photon emission that retains high indistinguishablility (93.9%) on a timescale in which 20 photons may be emitted. Nearly background-free pulsed resonance fluorescence is achieved under π-pulse excitation, enabling demonstration of an on-chip, on-demand single-photon source with very high potential repetition rates

Silicon nanocrystals: from bio-imager to erbium sensitizer

The work in this thesis has been centred on the light emitting properties of silicon nanocrystals and the possible applications of this particular material platform to various topics ranging from bio-imaging to erbium ion sensitization. Silicon nanocrystals as bio-imaging agent have been investigated by employing colloidal dispersion of individual silicon nanocrystals where surface properties could be controlled to a great extent. By using a suitable functionalization scheme, high quality hydrophilic luminescent nanoparticles were produced. Using the improvements in the physical coating, bio-imaging on living cells (in vitro) was demonstrated showing that silicon nanocrystals have a great potential in bio-imaging and offer a promising alternative to commonly used fluorescence dyes. A part from being good light emitters, silicon nanocrystals could also amplify the light. This is a reason why the part of the work in this thesis has been dedicated to the investigation of silicon nanocrystals as a gain material. While most of the studies on this topic are concentrated on the nanocrystal surface as a driving mechanism behind the optical amplification, the work presented in this thesis concerns the study of a zero phonon (direct) optical transition as a possible source of optical amplification in this material system. To this scope, investigation of the dynamics of the system on a nanosecond time-scale and under high excitation conditions has been employed. Additional insight on ultrafast dynamics has been obtained by using optical cavities in the form of optically active free-standing micro-disk resonators. Finally, in the last part of this thesis a study of Er3+-doped Silicon-Rich-Oxide (SRO) materials and Er3+-doped SRO based devices is presented. This part of the work differs from the rest of the work reported in this thesis as is not focused on the light emitting properties of silicon nanocrystals but mostly on their non-radiative process engineering (energy transfer to erbium ions). Er3+ doped SRO opens the route towards compact waveguide amplifiers and lasers and allows for the possibility of electrical injection schemes, which are not realizable in standard erbium amplifiers used in EDFA for telecom applications. To that end, novel opto-electronic structures were proposed, modeled and manufactured and preliminary results of their performance were presented. The sensitization mechanism between silicon nanoparticles and erbium ions was studied and its complex nature was illustrated. Although, the acquired knowledge of physics involved was not sufficient for formulation of a complete working theory of the energy transfer process, some important physical aspects of this process have been elucidated paving the way towards its complete understanding

Silicon nanocluster sensitization of erbium ions under low-energy optical excitation

The sensitizing action of amorphous silicon nanoclusters on erbium ions in thin silica films has been studied under low-energy (long wavelength) optical excitation. Profound differences in fast visible and infrared emission dynamics have been found with respect to the high-energy (short wavelength) case. These findings point out to a strong dependence of the energy transfer process on the optical excitation energy. Total inhibition of energy transfer to erbium states higher than the first excited state (4I13/2) has been demonstrated for excitation energy below 1.82 eV (excitation wavelength longer than 680 nm). Direct excitation of erbium ions to the first excited state (4I13/2) has been confirmed to be the dominant energy transfer mechanism over the whole spectral range of optical excitation used (540 nm¿680 nm)

Copropagating pump and probe experiments on Si-nc in SiO2 rib waveguides doped with Er: The optical role of non-emitting ions

We present a study that demonstrates the limits for achieving net optical gain in an optimized waveguide where Si nanoclusters in SiO2 codoped with Er3+ are the active material. By cross correlating absorption losses measurements with copropagant pump (λpump = 1.48 µm) and probe (λprobe = 1.54 µm) experiments we reveal that the role of more than 80% of the total Er3+ population present on the material (intended for optical amplification purposes) is to absorb the propagating light, since it is unfeasible to invert it