A functioning 4-state BB84 DV-QKD System is provided in which components (detectors, modulators, lasers, delay lines, etc) can be exchanged for test purposes. The system uses time-bin phase encoding at time-bin separation of 1ns and a symbol length of 10ns. The wavelength is 1550nm. Modulators can be driven with up to 6V amplitude, lasers and modulators should have PM fiber input/output, in other parts of the system non-polarization maintaining single mode fiber can be used. Decoy states can be implemented, the ratio of decoy and signal amplitude is fixed to 0.5.