British Telecommunications Public Limited Company

Marco Menchetti

Liam Bussey

Fraser Ashley Burton

Amelia Winterburn

Amelia Lees

Daniel Gilks

Timothy Whitley

This invention provides a method of detecting an electromagnetic field, and a device for 5 performing said method, the method comprising the steps of: transmitting a probe signal at a probe frequency in a first probe signal path and a second probe signal path to an optical receiver, wherein the first probe signal path passes through a transmission medium and the probe frequency is set to excite electrons of the transmission medium from a ground state to a first excited state; transmitting a coupling signal at a coupling frequency in a first coupling signal path, wherein the first coupling signal path overlaps with the first probe signal path in the transmission medium in a first overlapping section, wherein the coupling frequency is set to excite electrons of the transmission medium to a predetermined excited state so as to induce an Electromagnetic Induced Transparency, EIT, effect in the transmission medium such that an incident electromagnetic field at the transmission medium causes a change in refractive index in the transmission medium at the first overlapping section such that there is a change in an optical path length difference between the first probe signal path and the second probe signal path; combining the first path of the probe signal, following its passage of the first overlapping section of the transmission medium, with the second path of the probe signal; and monitoring, at the optical receiver, the intensity of the combined first and second paths of the probe signal so as to detect the incident electromagnetic field at the first overlapping section of the transmission medium as a change in the intensity caused by the change in the optical path length difference between the first probe signal path and the second probe signal path.

Electromagnetic field detector

This invention provides an electromagnetic field detector, a system comprising the electromagnetic field detector, and a method of operating an electromagnetic field detector, the electromagnetic field detector comprising a first optical signal interface configured to receive, from one or more remote optical sources, a first optical signal; an electromagnetic field transmitter configured to transmit a local oscillator electromagnetic field generated from the first optical signal, the electromagnetic field transmitter comprising: a photocurrent generator configured to generate a photocurrent from the first optical signal; and an antenna interface configured to supply the photocurrent to an antenna to transmit the local oscillator electromagnetic field; a second optical signal interface configured to receive, from the one or more remote optical sources, a probe optical signal and a coupling optical signal; and a transmission medium configured to be excited by the probe optical signal and further excited by the coupling optical signal, wherein the probe optical signal has a probe frequency set to excite electrons of the transmission medium to a first excited state and the coupling optical signal has a coupling frequency set to excite electrons of the transmission medium to a predetermined Rydberg state so as to induce an Electromagnetic Induced Transparency, EIT, effect, wherein the transmission medium is further configured to receive a phase-modulated electromagnetic field from a remote transmitter and the local oscillator electromagnetic field such that the combination of the phase-modulated electromagnetic field and the local oscillator electromagnetic field causes a change in the probe optical signal from which a phase state of the phase-modulated electromagnetic field can be detected.

This disclosure provides a method of controlling an electromagnetic field detector by causing a first phase shift to be applied to a second probe signal path so as to cause a variation in a change in intensity of combined first and second paths of a probe signal; obtaining data indicating a second phase shift to be applied to the second probe signal path so as to increase the change in intensity of the combined first and second paths of the probe signal, wherein the second phase shift is determinable from a variation in the change in intensity of the combined first and second paths of the probe signal caused by the first phase shift; and causing the second phase shift to be applied to the second probe signal path.

Controller for an electromagnetic field detector

There is herein disclosed a method of establishing at least a portion of an encryption key, the method including transmitting a first photon along a channel, determining the length of time the first photon takes to propagate along the channel, making a modification to the channel so as to change the length of time it takes a photon to propagate along the channel, transmitting a second photon along the modified channel, determining the length of time the second photon takes to propagate along the modified channel, using the determined lengths of time to determine the at least a portion of an encryption key, and, separately, using the fact that a modification has been made to the channel to determine the at least a portion of an encryption key.

To quantum key distribution

This invention provides a method of detecting a photon in a first frequency range, the method comprising the steps of: exciting a first transmission medium by a first probe signal at a first probe frequency, wherein the first probe signal excites electrons of the first transmission medium from a ground state of the first transmission medium to a first excited state of the first transmission medium; exciting the first transmission medium by a first coupling signal at a first coupling frequency, wherein the first coupling signal overlaps with the first probe signal in the first transmission medium and excites electrons of the first transmission medium to a predetermined excited state of the first transmission medium such that a first photon in the first frequency range and having a first polarisation incident upon the first transmission medium excites an electron in the predetermined excited state of the first transmission medium to a further excited state of the first transmission medium, wherein a first photon in a second frequency range is emitted as part of a subsequent deexcitation of the electron from the further excited state of the first transmission medium; detecting the first photon in the first frequency range and having the first polarisation by detecting the first photon in the second frequency range; exciting a second transmission medium by a second probe signal at a second probe frequency, wherein the second probe signal excites electrons of the second transmission medium from a ground state of the second transmission medium to a first excited state of the second transmission medium; exciting the second transmission medium by a second coupling signal at a second coupling frequency, wherein the second coupling signal overlaps with the second probe signal in the second transmission medium and excites electrons of the second transmission medium to a predetermined excited state of the second transmission medium such that a second photon in the first frequency range incident upon the second transmission medium and having a second polarisation excites an electron in the predetermined excited state of the second transmission medium to a further excited state of the second transmission medium, wherein a second photon in the second frequency range is emitted as part of a subsequent deexcitation of the electron in the further excited state of the second transmission medium; and detecting the second photon in the first frequency range having the second polarisation by detecting the second photon in the second frequency range. This invention also provides a detector and system for implementing said method.

This disclosure provides an electromagnetic field detector, and a method of operating the electromagnetic field detector in a wireless telecommunications network, the electromagnetic field detector including a first optical transmitter, a second optical transmitter, and a transmission medium, wherein the first optical transmitter is configured to transmit a probe signal at a probe frequency and the second optical transmitter is configured to transmit a coupling signal at a coupling frequency, wherein the probe frequency is set to excite electrons of the transmission medium from a ground state to a first excited state and the coupling frequency is set to excite electrons of the transmission medium to a predetermined excited state so as to induce an Electromagnetic Induced Transparency (EIT) effect such that an incident electromagnetic field at the transmission medium causes a detectable change in the probe signal.

Electromagnetic field receiver

This disclosure provides a method of receiving a plurality of data streams at an electromagnetic field receiver in a wireless telecommunications network, the method including obtaining data indicating detection of a first electromagnetic field incident at a transmission medium during a timeslot of a first subset of a plurality of timeslots; associating the detected first electromagnetic field with a first data stream of a plurality of data streams; obtaining data indicating detection of a second electromagnetic field incident at the transmission medium during a timeslot of a second subset of the plurality of timeslots; and associating the detected second electromagnetic field with a second data stream of the plurality of data streams.

This disclosure provides an optical network, and a method in an optical network, wherein: each reference optical transmitter is configured to transmit a reference optical signal on an associated second optical fiber of a plurality of second optical fibers, each reference error signal generator is configured to generate a reference error signal based on a reflection of the reference optical signal on the associated second optical fiber of the plurality of second optical fibers, and each reference phase shifter is configured to apply a phase shift to the first optical signal based on the reference error signal.

Optical network

This disclosure relates to an optical limiter for limiting the radiant flux of an optical source beam, including an optical control port for illumination by an optical control beam originating from the source beam; an optical input port for illumination by an optical transmission beam originating from the source beam; an optical output port for illumination by the transmission beam; and a thermally driven light mill; wherein the light mill is arranged with respect to the input port, the control port and the output port such that: illumination of the control port by the control beam drives the light mill to rotate only when the control beam has a radiant flux equal to or in excess of a predetermined radiant flux threshold; and rotation of the light mill causes an area of the output port illuminated by the transmission beam to change.

Optical limiter and method for limiting radiant flux

An optical switch is proposed, for routing an optical transmission signal according to an optical control signal, including one or more optical control ports; three or more optical transmission ports; a light director; and a thermally driven light mill; where the light mill and the light director are arranged with respect to each other, to the one or more control ports and to the three or more transmission ports such that: illumination of a respective one of the one or more control ports by a control beam carrying the control signal drives the light mill to rotate towards a respective position in which the light director is arranged so as to direct a transmission beam carrying the transmission signal, entering the switch via a respective one of the transmission ports, to exit the switch via a respective other of the transmission ports.

Growing community of inventors

London, United Kingdom

Marco Menchetti