Fig. 1. Experimental scheme consisting of the heralded single-photon source, OAM emitter, spatial optical system, and detector. FPC, fiber polarization controller; OL, objective lens; M, mirror; QWP, quarter-wave plate; P, polarizer.

Fig. 2. (a) Microscopic photograph of the OAM emitter; (b) scanning electron microscopy (SEM) image of the concentric scattering grating in the center of the OAM emitter; SEM images of (c) the shallow ridge waveguide and (d) the grating for vertical coupling.

Fig. 3. Experimental setup for measuring the topological charge and mode purity. BS, beam splitter; FBS, fiber beam splitter.

Fig. 4. Interference fringes of Gaussian mode and generated OAM modes of l ranging between −10 and +10 under different incident wavelengths. Each OAM mode could be decomposed to an LHCP part and an RHCP part corresponding to two rows of interference patterns. The conversion efficiency of different OAM modes is also shown at the bottom.

Fig. 5. Relation between the topological charges and the electrically driving power (red marks), together with the corresponding driving voltage (blue marks), while the incident wavelength is fixed at 1554.56 nm. The insets are the interference fringes corresponding to each OAM mode of the LHCP state.

Fig. 6. Mode purities of azimuthally polarized OAM modes with l ranging between −10 and +10.

Fig. 7. (a) Typical coincidence counts of heralded single photons with an OAM mode of l=5; coincidence counts and CAR of heralded single photons with OAM modes of l=3–7.