Fig. 1. Epitaxial growth of telecom band QDs. (a) Layer sequence of the investigated sample. (b) Representative AFM image of the QDs.

Fig. 2. h-CBR device for telecom band single-photon sources. (a) Schematic illustration of an h-CBR device. (b) Scanning electron micrograph of the fabricated h-CBR. (c) Simulated Purcell factor (blue) and collection efficiency (red) of the h-CBR as a function of wavelength. The collection efficiency is based on a 40° azimuth angle, corresponding to a lens with a numerical aperture (NA) of 0.65. The inset is the far-field intensity distribution of the cavity mode.

Fig. 3. Deterministically coupled QD-CBR device. Fluorescence images (34  μm×34  μm) of the QDs (a) before and (b) after fabrication of the h-CBRs. (a) and (b) share the same scale bar. (c) Normalized micro-photoluminescence spectrum (red trace) and cavity mode (shaded area) under quasi-resonant (p-shell) excitation. The small black arrow denotes the investigated emission line at 1322.99 nm. (d) Lifetimes of the selected QD emission line (1322.99 nm) coupled with h-CBR (red point) and an exemplary reference QD outside the device (black point), indicating pronounced Purcell enhancement. Solid red and black lines are the exponential function fits.

Fig. 4. Characterizations of the telecom band single-photon emissions. Autocorrelation measurements of single-photon emissions for (a) low-power (0.2 μW) and (b) high-power (4.8 μW) CW excitation. (c) Power dependences of the emission count rate and g(2)(0) value for CW excitation. Autocorrelation measurements of single-photon emissions for (d) low-power (1.1 μW) and (e) high-power (5.4 μW) pulsed excitation. (f) Power dependences of the emission count rate and g(2)(0) value for pulsed excitation.

Fig. 5. Estimation of the extraction efficiency at the first lens. Left: schematic of the experimental setup (λ/2, half-wave plate; λ/4, quarter-wave plate). Right table: transmissions of the optical elements used in efficiency measurement.