Secure optical communication
First Claim
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1. A method of communicating between a first location and a second location, the method comprising:
- at the first location, generating output signals having an irregular component, and copying the output signals at least in part such that for each output signal, there is a pair of signal copies, the irregular component being common to each of the signal copies of a pair;
transmitting, from the first location, each signal copy of a pair in a common direction over a common communications link;
at the second location, mixing data onto the irregular component of a signal copy for at least some of the pairs of signal copies; and
at the first location, receiving signal copies from the second location and, for pairs of received signal copies, combining the respective irregular components of the signal copies of a pair in order to extract therefrom data mixed at the second location,wherein the data is mixed at the second location such that between periods when data is being mixed, there are quiet intervals during which data is not being mixed.
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Abstract
A secure optical communication scheme uses differential delay D in an unbalanced Mach-Zehender interferometer to provide two copies of the optical source signal at a remote phase modulator separated in time by D. As D is much bigger than the coherence time source, the two copies of the signal are effectively uncorrelated. Both signals are phase-modulated by the remote sender'"'"'s data and returned to the unbalanced interferometer. The phase modulator will be converted into amplitude modulation by the action of the interferometer.
143 Citations
35 Claims
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1. A method of communicating between a first location and a second location, the method comprising:
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at the first location, generating output signals having an irregular component, and copying the output signals at least in part such that for each output signal, there is a pair of signal copies, the irregular component being common to each of the signal copies of a pair; transmitting, from the first location, each signal copy of a pair in a common direction over a common communications link; at the second location, mixing data onto the irregular component of a signal copy for at least some of the pairs of signal copies; and at the first location, receiving signal copies from the second location and, for pairs of received signal copies, combining the respective irregular components of the signal copies of a pair in order to extract therefrom data mixed at the second location, wherein the data is mixed at the second location such that between periods when data is being mixed, there are quiet intervals during which data is not being mixed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method of communicating over a data link, the method comprising:
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generating output signals having an irregular component; copying, at least in part, the output signals such that for each output signal there is a pair of signal copies, the irregular component being common to each of the signal copies of a pair; transmitting at least one signal copy of each pair in a common direction onto a common communications link; receiving, from a remote location, returned signal copies previously transmitted to the remote location, the irregular component of the returned signal copies having data mixed therewith; and combining the received signal copy of a pair with the other signal copy of that pair, such that, in dependence on the combination of the respective irregular components of two signal copies of a pair, a data signal is generated, which data signal is indicative of data mixed remotely with the returned signal copy, wherein the data is remotely mixed such that between periods when data is being mixed, there are quiet intervals during which data is not being mixed. - View Dependent Claims (28)
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29. A method of communicating between a first location and a second location, the method comprising:
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at the first location, copying, at least in part, an output signal received from a source such that for each output signal, there is a pair of signal copies, an irregular component being common to each of the signal copies of a pair; transmitting, from the first location, each signal copy of a pair in a common direction over a common communications link; at the second location, applying data onto the irregular component of a signal copy of at least some of the pairs of signal copies; and at the first location, receiving signal copies from the second location and, for each pair of signal copies, combining the respective irregular components of the signal copies from that pair in order to extract therefrom data mixed at the second location, wherein the data is mixed at the second location such that between periods when data is being mixed, there are quiet intervals during which data is not being mixed.
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30. A communications apparatus comprising:
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a source for generating output signals having an irregular component; a copying stage for copying, at least in part, the output signals from the source such that for each output signal, there is a pair of signal copies, the irregular component being common to each signal copy of a pair; a transmission stage for transmitting the signal copies of a pair in a common direction onto a common communications link; a receiving stage for receiving signal copies returned from a remote location, the irregular component of at least some of the returned signals having data mixed therewith; a combination stage for causing respective irregular components of the returned signals to combine; and data processing means coupled to the combination stage, the data processing means being configured to generate in use a data signal in dependence on a combination of the of the returned signals of a pair, the data signal being representative of data, if any, carried by a returned signal, wherein the data is remotely mixed such that between periods when data is being mixed, there are quiet intervals during which data is not being mixed. - View Dependent Claims (31, 32, 33, 34, 35)
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Specification