Abstract: Techniques for driving a directly modulated laser whilst correcting non-linearities an optical output waveform, based on generating a modulating current waveform that approximates an ideal modulating current that produces a linear optical output waveform. The techniques enable useful, practical approximations to the ideal modulating current to be determined.

Abstract: Systems for, and methods of, detecting an attack on an optical communication channel are presented. The techniques can include sending, from a sender to a receiver, and over the optical communication channel, an optical signal, where the optical signal includes a classical optical signal representing first information and a quantum optical signal representing second information. The techniques can include detecting, by the receiver, third information from at least a portion of the quantum optical signal and sending, by the receiver to the sender, the third information. The techniques can include determining, by the sender, an indication of an attack on the optical communication channel based on at least a portion of the second information and the third information. The techniques can include triggering an alarm based on the determining.

Abstract: An RFID system comprises an array of antennas each configured to emit a plurality of beams in different directions. The beams of each pair of adjacent antennas are directed towards one another and overlap. A pair of adjacent antennas transmits simultaneously and the overlapping beams interfere to create an interference pattern. An RFID reader controls the relative phase and/or frequency of the beams to move the interference pattern to read an RFID tag within the moving pattern. As the chance of a RFID tag responding to an emitted beam generally increases with signal strength of the reader beam an area of constructive interference means that RFID tags in that region are more likely to respond to the signal. The system can cover a large proportion of the area below ceiling-mounted antennas, where cover generally means that RFID tags in that area will be successfully read.

Abstract: An RFID system comprises an array of antennas each configured to emit a plurality of beams in different directions. The beams of each pair of adjacent antennas are directed towards one another and overlap. A pair of adjacent antennas transmits simultaneously and the overlapping beams interfere to create an interference pattern. An RFID reader controls the relative phase and/or frequency of the beams to move the interference pattern to read an RFID tag within the moving pattern. As the chance of a RFID tag responding to an emitted beam generally increases with signal strength of the reader beam an area of constructive interference means that RFID tags in that region are more likely to respond to the signal. The system can cover a large proportion of the area below ceiling-mounted antennas, where cover generally means that RFID tags in that area will be successfully read.

Abstract: A method and an apparatus are provided for launching light into an entrance facet of a MMF of an optical MMF link in a way that excites one or more targeted higher-order mode groups in the MMF. The light is launched into the entrance facet of the MMF as a line of phase-modulated spots, referred to herein as a “line launch”. The line launch causes one or more targeted higher-order mode groups to be excited in the MMF. The use of the line launch to excite one or more higher-order mode groups in the MMF increases the bandwidth of the link and allows overall link lengths to be increased. In addition, the use of the line launch is reliable and robust despite defects in the MMF and despite connector offsets. Thus, the use of the line launch ensures that a sufficient increase in link bandwidth will be achieved despite the existence of defects in the MMF and even if there is some amount of optical misalignment due to the connector being offset relative to the corresponding receptacle.

Abstract: Optical radiation is applied to a multimode optical fibre, either from another fibre or from a laser, in such a way as to control the mode distribution in the multimode optical fibre. The mode distribution is selected in such a way as to improve performance, for example to avoid transmission nulls or to reduce noise due to reflections back to a laser.

Abstract: A method of transmission of radio signals over all types of graded-index multimode fibre is provided. The method comprises launching optical radiation into the core of the multimode fibre with a specified restricted launch to allow multiple trans-verse mode lasers transmitters to be used in low cost radio over fibre links. The launch technique allows a reduction in modal dispersion and modal interference, thus greatly improving the transmission performance of radio over fibre signals over multimode fibre as well as reducing system impairments such as outages and link failures.

Abstract: A vertical cavity surface emitting laser device (10) has a discontinuity (11) formed within the body of the device. When the device is in use, the direction of polarization of light emitted from the device is substantially aligned with a boundary of the discontinuity.