Experiments on long wavelength (1550 nm) "plug and play" quantum cryptography systems

Summary form only given. Quantum cryptography is a technique for establishing a fundamentally secure cryptographic key, using the encoding of the key on single photon pulses. In the recent years here has been a remarkable progress in experimental implementations at 1300 nm wavelength. However, for 1550 nm wavelength, there are few results, as the performance of single photon detectors for 1550 nm has been considered insufficient. We report on the implementation of a 1550 nm stable plug-and-play interferometric scheme for quantum cryptography, and for simplicity, we have only implemented a two-state encoding.