µ-Fibre-Coupled Microcavity Single Photon Sources

Efficient and fast on-demand single photon sources have been sought after as critical components of quantum information science. We explore an efficient and tunable single photon source based on an InAs quantum dot (QD) embedded in a photonic crystal cavity coupled with a highly curved μ-fibre. Exploiting evanescent coupling between the μ-fibre and the cavity, a high collection photon efficiency and Purcell-enhanced spontaneous emissions are observed. In our scheme, the spectral position of a resonance can be tuned by as much as 1.5 nm by adjusting the contact position of the μ-fibre, which increases the spectral coupling probability between the QD and the cavity mode. Taking advantage of the high photon count rate and the tunability, the collection efficiencies and the decay rates are systematically investigated as a function of the QD–cavity detuning.

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Sub-μW-Threshold Nanoisland Quantum Well Laser by Selective Wet-Etching

Ultralow threshold nanolasers have been sought after as power efficient light sources in photonic integrated circuits. We introduce nanoisland quantum well structure which enables the continuous operation of 1.5 μm laser at room temperature with ultralow lasing threshold of 210 nW in absorbed power. The size of the active medium is reduced to 0.7x0.25x0.02 μm3 by removing the absorptive quantum well region surrounding the central cavity through a selective wet-etching process. The nanoisland-based structures will provide a new platform to engineer fundamental light–matter interactions by controlling the size and the location of the nanoemitters, allowing the realization of highly efficient nanophotonic devices.

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Point-Like Metallic Cavity

Confining photon in the smallest possible volume has long been an objective of the nanophotonics community. We demonstrate a three-dimensional (3D) gap-plasmon antenna that enables extreme photon squeezing in a 3D fashion with a modal volume of 1.3x10-7 λ3 (~4x10x10 nm3) and an intensity enhancement of 400,000. A three-dimensionally tapered 4 nm air-gap is formed at the center of a complementary nanodiabolo structure by ion-milling 100 nm-thick gold film along all three dimensions using proximal milling techniques. From a 4 nm-gap antenna, a nonlinear second-harmonic signal more than 27,000-times stronger than that from a 100 nm-gap antenna is observed. In addition, scanning cathodoluminescence images confirm unambiguous photon confinement in a resolution-limited area 20×20 nm2 on top of the nano gap.

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High Purcell Enhancement in Metallic Nanocavity

By confining light in a small cavity, the spontaneous emission rate of an emitter can be controlled via the Purcell effect. However, while Purcell factors as large as ~10,000 have been predicted, actual reported values were in the range of about 10–30 only, leaving a huge gap between theory and experiment. We demonstrate an enhanced 1.54 μm emission from Er3+ ions placed in a very small metallic cavity. Using a cavity designed to enhance the overall Purcell effect instead of a particular component, and by systematically investigating its photonic properties, we demonstrate an unambiguous Purcell factor that is as high as 170 at room  temperature.  We  also  observe 490  times  increase  in  the  far-field  radiant  flux, indicating that as much as 55% of electromagnetic energy that was initially supplied to Er3+ ions in the cavity escape safely into the free space in just one to two optical cycles.

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