There is provided an integrated-optic transmitter for transmitting light pulses to a further optical apparatus for generating a quantum cryptographic key according to at least one quantum cryptography technique. There is also provided an integrated-optic receiver for generating a quantum cryptographic key from light pulses received from a further optical apparatus. The transmitter apparatus splits incoming light into two paths to temporally separate the split light pulses and controls the output intensity of each split pulse as well as the phase of at least one of the split pulses. The receiver apparatus receives first and second light pulses and controls the output intensity of each said pulse between a first and a second optical detector. The light input into the second detector passes through an integrated element that controls the amount of light output into two paths that recombine before at least a portion is output to the second detector.