Figure 4

Optical characterization of tapered fiber-coupled diamond micro-waveguides. (a) Spectra in blue (red) show NV fluorescence collected through left (right) ends. The zero-phonon line and sideband are clearly detected. We observe stronger signal from the right side, as both spectra are taken under the same integration time. (b) Saturation curves showing photon count rates from NV center versus pump power collected through the fiber. The blue (red) shows collection from the left (right) without background correction. The collection from the right fiber end exhibits more background due to increased scattering into this direction of the fiber (see Figure 3d). The green curve is the sum of the left and right collection curves, with the linear background subtracted. (c) Saturation curve using objective collection with an NA = 0.75 objective. (d) Second order autocorrelation function taken using both fiber ends in a Hanbury Brown–Twiss setup. Strong photon anti-bunching with g⁽²⁾ (0) < 0.2 is observed with an incident pump power on the objective of 114 μW. (e) Strong photon anti-bunching is detected with g⁽²⁾ (0) < 0.5 over a range of powers below about 2.3 mW. The blue line is a guide to the eye, while the red dotted line denotes 0.5. (f) Measurements of the g⁽²⁾ (τ) time constant (describing the central dip at low pump power) fitted to a linear model yield a lifetime of 15.7 ns. Error bars denote a one standard deviation error on fit parameters. (Inset) Electron-spin-resonance fluorescence dip in zero external DC magnetic field.