Patent ID: 8295485

Claim:
A measuring unit for determining information from an input signal, the input signal comprising photon pulses, the unit comprising a decoder including an interferometer having first and second optical fiber paths and first and second outputs, said decoder being configured to perform a measurement on an input signal photon pulse using a first operator configured to distinguish between two orthogonal states of said input signal and a second operator selected from an inverting operator configured to invert the result of the measurement by the first operator by inverting the outputs of the decoder and a null operator configured to have a null effect on the result of the measurement by the first operator; an inversion controller configured to select for each photon pulse whether the inverting operator or the null operator is used as the second operator; at least one photon detector configured to detect the first and second outputs of said decoder; and a detection processor connected to the inversion controller and configured to selectively invert a detected output of said at least one photon detector depending on the selected second operator.