The realization of an ultra-fast source of heralded single photons emitted at the wavelength of 1540 nm is reported. The presented strategy is based on state-of-the-art telecom technology, combined with off-the-shelf fiber components and waveguide non-linear stages pumped by a 10 GHz repetition rate laser. The single photons are heralded at a rate as high as 2.1 MHz with a heralding efficiency of 42%. Single photon character of the source is inferred by measuring the second-order autocorrelation function. For the highest heralding rate, a value as low as 0.023 is found. This not only proves negligible multi-photon contributions but also represents the best measured value reported to date for heralding rates in the MHz regime. These prime performances, associated with a device-like configuration, are key ingredients for both fast and secure quantum communication protocols.The reliable generation of single photon states is crucial for a wide variety of quantum optical technologies, ranging from quantum computation and communication [1,2] to quantum metrology and detector calibration [3,4]. As an example, the use of single photon states is essential in quantum key distribution (QKD) protocols, where the unintended presence of more than one photon per time window can be exploited by an eavesdropper to extract part of the information [5].Ideal sources should be able to emit indistinguishable single photons in a deterministic way, at an arbitrarily high repetition rate and with zero probability of multiphoton emissions [1]. In particular, the request of ultrafast photon sources is mandatory to speed up data exchanges in quantum communication protocols. In anticipation to such optimal cases, a pertinent alternative is represented by heralded single photon sources (HSPS), where the detection of one photon of two simultaneously generated is used to herald the emission time of the second one [1,6]. In such schemes, the produced single photons rate is proportional to the detected heralding photon one, R H , and to the heralding efficiency, P 1 , namely, the probability of observing one heralded photon per heralding event. We note that, in experiments, the value of P 1 is essentially determined by optical losses [6].In the original and most common implementations, pairs of simultaneous photons are generated in nonlinear crystals via spontaneous parametric down conversion (SPDC) of a pump beam [6]. In particular, an accurate choice of the phase matching can lead to the production of photons at telecom wavelength, as required for long distance transmission in optical fibers [7,8]. SPDC being a probabilistic process, a way to obtain high photon rates is to increase the probability of generating the photon pairs as well as the photon transmission after the SPDC crystal. Accordingly, in the last years, many papers have been focusing on the realization of bright SPDC sources [9,10] and much effort has been made towards optimizing paired photon collection, separation and prop- * Corresponding author: virginia.dauria@unice.fr agati...