Fabrication and characterization of SiNx/Au cavities with colloidal nanocrystals.

We demonstrate the fabrication and characterization of on-chip vertically-emitting SiNx/Au nanopatch cavities containing a monolayer of colloidal quantum dots. The fabrication process is based on electron-beam lithography and deterministically positions both the cavity and the emitters within the cavity with an accuracy of 10 nm. The Purcell enhancement of the spontaneous emission of the quantum dots is studied theoretically and experimentally. The fabrication technique makes it possible to pattern the quantum dot monolayer such that the quantum dots only occupy the center of the nanopatch cavity where a Purcell factor up to 7 can be reached. The work paves the way towards scalable fabrication of bright and directive single-photon sources.

Nearly Blinking-Free, High-Purity Single-Photon Emission by Colloidal InP/ZnSe Quantum Dots.

Colloidal core/shell InP/ZnSe quantum dots (QDs), recently produced using an improved synthesis method, have a great potential in life-science applications as well as in integrated quantum photonics and quantum information processing as single-photon emitters. Single-particle spectroscopy of 10 nm QDs with 3.2 nm cores reveals strong photon antibunching attributed to fast (70 ps) Auger recombination of multiple excitons. The QDs exhibit very good photostability under strong optical excitation. We demonstrate that the antibunching is preserved when the QDs are excited above the saturation intensity of the fundamental-exciton transition. This result paves the way toward their usage as high-purity on-demand single-photon emitters at room temperature. Unconventionally, despite the strong Auger blockade mechanism, InP/ZnSe QDs also display very little luminescence intermittency ("blinking"), with a simple on/off blinking pattern. The analysis of single-particle luminescence statistics places these InP/ZnSe QDs in the class of nearly blinking-free QDs, with emission stability comparable to state-of-the-art thick-shell and alloyed-interface CdSe/CdS, but with improved single-photon purity.

On-Chip Integrated Quantum-Dot-Silicon-Nitride Microdisk Lasers.

Hybrid silicon nitride (SiN)-quantum-dot (QD) microlasers coupled to a passive SiN output waveguide with a 7 µm diameter and a record-low threshold density of 27 µJ cm-2 are demonstrated. A new design and processing scheme offers long-term stability and facilitates in-depth QD material and device characterization, thereby opening new paths for optical communication, sensing, and on-chip cavity quantum optics based on colloidal QDs.

Fabrication and characterization of on-chip silicon nitride microdisk integrated with colloidal quantum dots.

We designed and fabricated free-standing, waveguide-coupled silicon nitride microdisks hybridly integrated with embedded colloidal quantum dots. An efficient coupling of quantum dot emission to resonant disk modes and eventually to the access waveguides is demonstrated. The amount of light coupled out to the access waveguide can be tuned by controlling its dimensions and offset with the disk edge. These devices open up new opportunities for both on-chip silicon nitride integrated photonics and novel optoelectronic devices with quantum dots.

Atomic layer deposited second-order nonlinear optical metamaterial for back-end integration with CMOS-compatible nanophotonic circuitry.

We report the fabrication of artificial unidimensional crystals exhibiting an effective bulk second-order nonlinearity. The crystals are created by cycling atomic layer deposition of three dielectric materials such that the resulting metamaterial is noncentrosymmetric in the direction of the deposition. Characterization of the structures by second-harmonic generation Maker-fringe measurements shows that the main component of their nonlinear susceptibility tensor is about 5 pm/V, which is comparable to well-established materials and more than an order of magnitude greater than reported for a similar crystal [Appl. Phys. Lett.107, 121903 (2015)APPLAB0003-695110.1063/1.4931492]. Our demonstration opens new possibilities for second-order nonlinear effects on CMOS-compatible nanophotonic platforms.

Nanoscale and Single-Dot Patterning of Colloidal Quantum Dots.

Using an optimized lift-off process we develop a technique for both nanoscale and single-dot patterning of colloidal quantum dot films, demonstrating feature sizes down to ~30 nm for uniform films and a yield of 40% for single-dot positioning, which is in good agreement with a newly developed theoretical model. While first of all presenting a unique tool for studying physics of single quantum dots, the process also provides a pathway toward practical quantum dot-based optoelectronic devices.

Visible-to-near-infrared octave spanning supercontinuum generation in a silicon nitride waveguide.

The generation of an octave spanning supercontinuum covering 488-978 nm (at -30 dB) is demonstrated for the first time on-chip. This result is achieved by dispersion engineering a 1-cm-long Si3N4 waveguide and pumping it with an 100-fs Ti:Sapphire laser emitting at 795 nm. This work offers a bright broadband source for biophotonic applications and frequency metrology.

Broadband enhancement of single photon emission and polarization dependent coupling in silicon nitride waveguides.

Single-photon (SP) sources are important for a number of optical quantum information processing applications. We study the possibility to integrate triggered solid-state SP emitters directly on a photonic chip. A major challenge consists in efficiently extracting their emission into a single guided mode. Using 3D finite-difference time-domain simulations, we investigate the SP emission from dipole-like nanometer-sized inclusions embedded into different silicon nitride (SiNx) photonic nanowire waveguide designs. We elucidate the effect of the geometry on the emission lifetime and the polarization of the emitted SP. The results show that highly efficient and polarized SP sources can be realized using suspended SiNx slot-waveguides. Combining this with the well-established CMOS-compatible processing technology, fully integrated and complex optical circuits for quantum optics experiments can be developed.

Photon pair source based on parametric fluorescence in periodically poled twin-hole silica fiber.

We present observations of quasi-phase matched parametric fluorescence in a periodically poled twin-hole silica fiber. The phase matching condition in the fiber enables the generation of a degenerate signal field in the fiber-optic communication band centered on 1556 nm. We performed coincidence measurements and a Hong-Ou-Mandel experiment to validate that the signal arises from photon pairs. A coincidence peak with a signal to noise ratio (SNR) of 4 using 43 mW of pump power and a Hong-Ou-Mandel dip showing 40% net visibility were measured. Moreover, the experiments were performed with standard single mode fibers spliced at both ends of the poled section, which makes this source easy to integrate in fiber-optic quantum communication applications.

Enhanced cross phase modulation instability in birefringent photonic crystal fibers in the anomalous dispersion regime.

We study Cross Phase Modulational Instability (CPMI) -a particular form of vector modulational instability- in the anomalous dispersion regime in highly birefringent, strongly dispersive optical fibers. When the pump power is high, the detuning of the Scalar Modulational Instability (SMI) is comparable to the detuning of the CPMI. The gain of the CPMI -which is usually much smaller than the gain of the SMI-, is then strongly enhanced and becomes much larger than the gain of the SMI. This theoretical prediction is well verified experimentally using small core photonic crystal fibers.

Higher order harmonics of modulational instability.

We study the higher order harmonics of scalar modulational instability in the regime where it arises spontaneously through amplification of vacuum fluctuations. We obtain detailed predictions concerning the detunings, intensities, growth rates, and spectral widths of the harmonics. These predictions are well verified by experimental results obtained by propagating high intensity light pulses through optical fibers.