A bright single-photon source based on a photonic trumpet

Publication: Research - peer-reviewConference abstract for conference – Annual report year: 2012

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Fiber-like photonic nanowires, which are optical waveguides made of a high refractive index material n, have recently emerged as non-resonant systems providing an efficient spontaneous emission (SE) control. When they embed a quantum emitter like a quantum dot (QD), they find application to the realization of bright sources of quantum light and, reversibly, provide an efficient interface between propagating photons and the QD. For a wire diameter ∼ λ/n (λ is the operation wavelength), the fraction of QD SE coupled to the fundamental guided mode exceeds 90%. The collection of the photons can be brought close to unity with a proper engineering of the wire ends. In particular, a tapering of the top wire end is necessary to achieve a directive far-field emission pattern [1].
Recently, we have realized a single-photon source featuring a needle-like taper. The source efficiency, though record-high, was found to be limited by the geometry of the taper [2]. Here, we propose an alternative, high performance, trumpet-like tapering of the wire and demonstrate its implementation in a bright single-photon source. Specifically, we consider a GaAs structure, for which the wire diameter is progressively increased from 220 nm to 1.5 µm, for a total height of 12 µm. Such trumpet-like tapers present a number of key assets: i) a nearly perfect adiabatic expansion (less than 5% losses) of the fundamental mode is achieved for tapering angle as large as 7o. ii) the emitted mode features a Gaussian profile with a divergence controlled by the top-facet diameter: for a top diameter of 1.5 µm, less than 5% of the light is scattered outside the collection cone of a lens with a 0.75 NA. iii) the large top facet also simplifies the implementation of a top electrode, to achieve an electrical driving of the device [3].
Using top-down fabrication techniques, we have fabricated a single photon source based on this geometry. The trumpet lies on an integrated mirror and embeds a single layer of InAs QDs, located 110 nm above the mirror. We obtain collection efficiencies higher than 40% for a bunch of QDs spread over 35 nm in a single wire, with a maximum of 65%. This result, which approaches the state of the art (70%), is also close to the predicted value of 80%, obtained for a perfect emitter [4]. Eventually, we map the field profile at the top facet and evidence its Gaussian profile. This is desirable to achieve a good coupling to a monomode fiber, in view of the long range distribution of single photons. This is also crucial to increase the mode matching when addressing a single QD with an optical Gaussian beam.
Original languageEnglish
Publication date2012
StatePublished

Conference

Conference31st International Conference on the Physics of Semiconductors
CountrySwitzerland
CityZurich
Period29/07/1203/08/12
Internet addresshttp://www.icps2012.ethz.ch/

Bibliographical note

Oral presentation, Tuesday, July 31, 2012, 11:00–11:15.

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