  Deterministic light sources capable of generating quantum states on-demand at
wavelengths compatible with fiber optics and atmospheric transmission are
essential for practical applications in quantum communication, photonic quantum
computing, and quantum metrology. To this end, single-photon emission at 1500
nm is demonstrated from an InGaSb quantum dot (QD) grown by filling
droplet-etched nanoholes for the first time. The QD was embedded in a device
structure comprising an antimony-based high refractive index contrast
back-reflector designed for cryogenic operation and a solid immersion lens for
improved photon extraction. The longitudinal optical (LO) phonon assisted
excitation of the QD ground state and quasi-resonant excitation of the QD
excited state is realized with a novel compact wavelength-tunable
power-stabilized semiconductor laser. These direct approaches to exciting a
single QD unlock access to its excitonic fine structure. The neutral
exciton-biexciton structure exhibits a negative binding energy of 1.4 meV (2.6
nm) and a fine structure splitting of 24.1+/-0.4 ueV. Furthermore, spectrally
pure/isolated emission from a charged single exciton state with a single-photon
purity of 95 % is achieved with LO phonon assisted two-color excitation. These
results represent a major step forward for the use of the novel
antimonide-based QD emitters as deterministic quantum light sources in complex
quantum secure networks exploiting the wavelength compatibility with standard
telecom fibers.
