Polarization to phase converter
View Patent ↗The invention provides an apparatus and method for time delaying different polarization components of a signal relative to one another, comprising a polarization signal splitter which splits first and second polarization components of an input signal into a first component signal and a second component signal such that said first component signal propagates along a first path and the second component signal propagates along a second path, wherein said first component signal reaches a location relative to when said second component reaches said location at times differing by a delayed time, and use of the apparatus in a communication system. The apparatus may be used for quantum cryptography, to convert a sender's polarization-qubit signal into a signal appropriate for channels and receivers based on phase-encoded schemes.
1. A quantum cryptography system comprising:
a sending unit adapted to generate polarization-encoded qubits;
a polarization-to-phase converter operatively coupled to the sending unit and adapted to receive the polarization-encoded qubits and transform them to phase-encoded qubits; and
a receiving unit operatively coupled to the polarization-to-phase converter and adapted to:
a) receive the phase-encoded qubits from the polarization-to-phase converter;
b) split each phase-encoded qubit into a pair of first and second phase-encoded qubits;
c) randomly phase-modulate one of the phase-encoded qubits in the pair with one of a limited number of select phase modulations;
d) combine the first and second phase-encoded qubits so that they interfere; and
e) detect the interfered first and second phase-encoded qubits.
2. The system of claim 1 , further including:
a first optical fiber linking the sending unit to the polarization-to-phase converter; and
a second optical fiber linking the polarization-to-phase converter to the receiving unit.
3. The system of claim 1 , wherein the polarization-to-phase converter includes first and second polarization-dependent paths having different path lengths.
4. A method of converting polarization-encoded qubits to phase-encoded qubits, comprising:
generating the polarization-encoded qubits at a sending unit and transmitting the polarization-encoded qubits to a polarization-to-phase converter;
receiving the polarization-encoded qubits at the polarization-to-phase converter;
converting the polarization-encoded qubits to the phase-encoded qubits at the polarization-to-phase converter; and
receiving the phase-encoded qubits from the polarization-to-phase converter at a receiving unit, and further including performing the following acts at the receiving unit:
a) splitting each phase-encoded qubit into a pair of first and second phase-encoded qubits;
b) randomly phase-modulating one of the first and second qubits with one of a limited number of select phase modulations;
c) interfering the first and second phase-encoded qubits; and
d) detecting the result of said interfering.
5. The method of claim 4 , wherein converting the polarization-encoded qubits to phase-encoded qubits includes:
splitting each polarization-encoded qubit into first and second polarization components;
directing the first and second polarization components over respective polarization-dependent paths having different path lengths; and
recombining the first and second polarization components.