Abstract: 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 photo

Abstract: 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 photo

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: There is herein provided a method of controlling the frequency of operation of a component of a telecommunications network, the method including combining a first signal and a second signal to form a heterodyne signal, transmitting the heterodyne signal from a first node of the telecommunications network, detecting the transmitted heterodyne signal at a second node of the telecommunications network, and controlling a frequency of operation of a component of the telecommunications network using a frequency of the detected heterodyne signal.

Abstract: 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.

Abstract: 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

Abstract: 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.

Abstract: This disclosure provides a method of receiving a plurality of data streams at an electromagnetic field receiver in a wireless telecommunications network, 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.

Abstract: This disclosure provides a method of operating a central node in a telecommunications network, the telecommunications network including an optical network and a plurality of distributed nodes each configured to use a first optical signal at a first wavelength, the method including producing a first optical signal at a second wavelength; directing the first optical signal into a first path for the first optical signal and a second path for the first optical signal, wherein the first path for the first optical signal is connected to a first optical stabilizer to stabilize the first optical signal produced by the central node, and the second path for the first optical signal provides the first optical signal to the optical network for distribution to each of the plurality of distributed nodes, wherein the second wavelength has a lower transmission loss than the first wavelength.

Abstract: 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.

Abstract: 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.

Abstract: An aspect relates to an optical limiter (200) for limiting the radiant flux of an optical source beam, comprising: an optical control port (221) for illumination by an optical control beam originating from the source beam; an optical input port (221) for illumination by an optical transmission beam originating from the source beam; an optical output port (225) for illumination by the transmission beam; and a thermally driven light mill (211, 212); 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.

Abstract: 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.

Abstract: 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.