We employ mirror enhanced grating couplers as convenient output ports for ridge Si3N4 waveguide to detect single photons emitted from Dibenzoterrylene (DBT) molecules coupled into propagating modes at room temperature. The coupling ports are designed for waveguide structures on transparent silica substrates for light extraction from the chip backside. Thus the coupling ports enable contact free readout of the waveguide devices by imaging through the silica substrate.
Optimized grating structures provide maximum out-coupling efficiency at 785nm (the central emission wavelength of DBT) with a bandwidth of 50 nm and fulfill mode-matching to a Gaussian mode in free space (FWHM ≈ 4μm). Covering fully etched grating devices with a Hydrogen silsesquioxane buffer layer and a gold mirror increase the coupling efficiency compared to bare grating structures. The maximum single coupler efficiency predicted by finite element simulations is 90% which reduces to 60% when adapted to fabrication constrains, whereas the average measured coupling efficiency is 35±5%.
We employ such grating ports to read out optical waveguides designed for single-mode operation at λ=785 nm. DBT molecules are coupled evanescently to the waveguides and transport emitted single photon signals to the coupling region upon optical pumping. Using a Hanbury Brown and Twiss setup we observe pronounced antibunching with g(2)(0)=0.50±0.05 from the grating couplers by excitation (λ=767nm) of a single DBT molecule which confirms the quantum nature of the outcoupled fluorescent light.
Efficient quantum light sources and non-linear optical elements at the few photon level are the basic
ingredients for most applications in nano and quantum technologies. On the other hand, a scalable platform for quantum ICT typically requires reliable light matter interfaces and on-chip integration. In this work we demonstrate the potential of a novel hybrid technology which combines single organic molecules as quantum emitters and dielectric chips .
Dibenzoterrylene molecules in anthracene crystals (DBT:Ac) are particularly suitable quantum systems for this task, since they exhibit long-term photostability in thin samples , easy fabrication methods and life-time limited emission at cryogenic temperatures .
We demonstrate at room temperature the emission of single photons from DBT molecules into ridge waveguides with a branching ratio up to 40%. The overall single-photon source efficiency, including emission into the guided mode, propagation losses, and emission into a quasi-gaussian mode in free space, is estimated around 16%. These results are competitive with state-of-the-art single photon emission into propagating guided modes from solid state systems , while offering a novel platform with unprecedented versatility.
 P. Lombardi et al., Arxiv: 1701.00459v1 (2017).
 C. Toninelli et al., Opt. Express 18, 6577 (2010).
 A. A. L. Nicolet et al., ChemPhysChem 8, 1929 (2007).
 I. Zadeh et al., Nano Lett. 16, 2289 (2016); R. S. Daveau et al., Arxiv: 1610.08670v1 (2016).
 J. Hwang et. al., New J. Phys. 13, 085009 (2011); H.-W. Lee et al., Phys. Rev. A 63, 012305 (2000).