A stable wavelength-tunable triggered source of single photons and cascaded photon pairs at the telecom C-band - Zeuner, K D; Paul, M; Lettner, T; Hedlund, C Reuterskiöld Reuterskiöld; Schweickert, L; Steinhauer, S; Yang, L; Zichi, J; Hammar, M; Jöns, Klaus D.; Zwiller, V