Abstract: A method of determining an optical transform imparted by a multimode optical fibre (300) is disclosed. The wherein the multimode fibre (300) comprises a proximal end, a distal end, and at least one modified region (260) between the proximal end and distal end. The modified region (260) is configured to transmit light toward the proximal end in response to light propagating through the multimode optical fibre (300) from the proximal end to the distal end. The method comprises coupling (101) forward propagating light into the proximal end of the multimode optical fibre; detecting (102), at the proximal end, backward propagating light transmitted from the at least one modified region in response to the forward propagating light; and determining (103) an optical transform from the detected backward propagating light.

Abstract: Method of laser modifying an optical fibre to form a modified region at a target location within the fibre, comprising positioning at least a portion of an optical fibre in a laser system for modification by a laser, applying a correction to an active optical element of the laser system to modify wavefront properties of the laser to counteract an effect of aberration on laser focus, and laser modifying the optical fibre at the target location using the laser with the corrected wavefront properties to produce the modified region.

Abstract: Method of laser modifying an optical fibre to form a modified region at a target location within the fibre, comprising positioning at least a portion of an optical fibre in a laser system for modification by a laser, applying a correction to an active optical element of the laser system to modify wavefront properties of the laser to counteract an effect of aberration on laser focus, and laser modifying the optical fibre at the target location using the laser with the corrected wavefront properties to produce the modified region.

Abstract: A device for modulation of light (16) having a wavelength, comprising: a first substrate (10) with a first face (81) and a second opposite face (82), and comprising a first electrode (11); a second substrate (20) adjacent to the second face (82) and defining a gap between the first and second substrate (10, 20), the second substrate (20) comprising a second electrode (21); a responsive liquid crystal layer (15) disposed in the gap, wherein the responsive liquid crystal layer (15) has a flexoelectro-optic chiral nematic phase, and is birefringent with an optic axis that tilts in response to an applied electric field between the first and second electrode (11, 21); and a mirror adjacent to the second substrate (20), the mirror configured to reflect incident circular polarised light while preserving its handedness.

Abstract: A device for modulation of light (16) having a wavelength, comprising: a first substrate (10) with a first face (81) and a second opposite face (82), and comprising a first electrode (11); a second substrate (20) adjacent to the second face (82) and defining a gap between the first and second substrate (10, 20), the second substrate (20) comprising a second electrode (21); a responsive liquid crystal layer (15) disposed in the gap, wherein the responsive liquid crystal layer (15) has a flexoelectro-optic chiral nematic phase, and is birefringent with an optic axis that tilts in response to an applied electric field between the first and second electrode (11, 21); and a minor adjacent to the second substrate (20), the minor configured to reflect incident circular polarised light while preserving its handedness.

Abstract: The information marked on one electronic content is compared to that marked on another electronic content in order to determine if either are unauthorised. There are a number of ways of comparing the information in order to make this determination. One way is to detect if two electronic content accessed by the same device have information associated with different users. Another way is to detect if two electronic content accessed by different devices have information associated with a single user. A further way is to use the time or sequence of access in conjunction with the information. Other ways of determining unauthorised content are disclosed.

Abstract: The information marked on one electronic content is compared to that marked on another electronic content in order to determine if either are unauthorised. There are a number of ways of comparing the information in order to make this determination. One way is to detect if two electronic content accessed by the same device have information associated with different users. Another way is to detect if two electronic content accessed by different devices have information associated with a single user. A further way is to use the time or sequence of access in conjunction with the information. Other ways of determining unauthorised content are disclosed.

Abstract: Method of laser modifying an optical fibre to form a modified region at a target location within the fibre, comprising positioning at least a portion of an optical fibre in a laser system for modification by a laser, applying a correction to an active optical element of the laser system to modify wavefront properties of the laser to counteract an effect of aberration on laser focus, and laser modifying the optical fibre at the target location using the laser with the corrected wavefront properties to produce the modified region.

Abstract: Systems and methods for interrogating sensing systems utilising bursts of samples. Bursts of samples correspond to optical pulses returning from optical sensors, where pulses are spaced at a period significantly longer than the pulse width, giving irregular sample spacing. The interrogation system and method processes the irregular busts of samples to recover phase information from received signals.

Abstract: Systems and methods for interrogating sensing systems utilising bursts of samples. Bursts of samples correspond to optical pulses returning from optical sensors, where pulses are spaced at a period significantly longer than the pulse width, giving irregular sample spacing. The interrogation system and method processes the irregular busts of samples to recover phase information from received signals.

Abstract: The information marked on one electronic content is compared to that marked on another electronic content in order to determine if either are unauthorised. There are a number of ways of comparing the information in order to make this determination. One way is to detect if two electronic content accessed by the same device have information associated with different users. Another way is to detect if two electronic content accessed by different devices have information associated with a single user. A further way is to use the time or sequence of access in conjunction with the information. Other ways of determining unauthorised content are disclosed.

Abstract: An optical sensing system, comprising a plurality of optical sensors (206 . . . 209), first (203 . . . 205) and second (215, 216) input trees, and first (210 . . . 212) and second (219, 220) output trees. The first and second input trees are configured to direct respective optical signals from a first (202) and a second (214) input to each of the sensors, and the first and second output trees are configured to direct optical signals from each of the sensors (206 . . . 209) to a first (213) and a second (221) optical output. The first and second input and/or output trees are configured to direct signals of particular wavelengths (A1 . . . D-1, A2 . . . D2) from particular sensors to the first and second input and/or output, respectively. A redundant connection system thus provided allows continued operation in the event of a fibre or cable break (300).

Abstract: Optical impairments such as dispersion and fibre nonlinearity are compensated by generating a pre-distorted electrical signal at the transmitter. This signal is modulated onto a carrier signal, so that it is upconverted in frequency. This up converted signal is then used to modulate an optical source. Generally the optical signal will have two sidebands, one of which has the correctly pre-distorted information and the other which is unwanted. Information in the unwanted optical sideband is either filtered optically or electrically. In the preferred embodiments, the transmitter uses a tunable semiconductor laser with an integrated electroabsorption modulator to modulate the light. The preferred receiver is a coherent receiver with a tunable local oscillator laser. The receiver uses an electrical filter to remove the information in the unwanted sideband.

Abstract: A method and system for mitigating effects of dispersion in an optical link. A pair of digital sample streams are synthesized representing a target optical E-field having a spectrum selected such that the convolution of the spectrum with itself yields a signal having beat terms that contain phase information of the target optical E-field. A complex optical modulator is driven in accordance with the computed orthogonal sample values.

Abstract: Optical impairments such as dispersion and fibre nonlinearity are compensated by generating a pre-distorted electrical signal at the transmitter. This signal is modulated onto a carrier signal, so that it is upconverted in frequency. This up converted signal is then used to modulate an optical source. Generally the optical signal will have two sidebands, one of which has the correctly pre-distorted information and the other which is unwanted. Information in the unwanted optical sideband is either filtered optically or electrically. In the preferred embodiments, the transmitter uses a tunable semiconductor laser with an integrated electroabsorption modulator to modulate the light. The preferred receiver is a coherent receiver with a tunable local oscillator laser. The receiver uses an electrical filter to remove the information in the unwanted sideband.

Abstract: A method and system for mitigating effects of dispersion in an optical link. A pair of digital sample streams are synthesized representing a target optical E-field having a spectrum selected such that the convolution of the spectrum with itself yields a signal having beat terms that contain phase information of the target optical E-field. A complex optical modulator is driven in accordance with the computed orthogonal sample values.

Abstract: A polarization mode dispersion (PMD) compensation arrangement receives an optical input data signal which has been subjected to PMD. The arrangement comprises an adaptive chromatic dispersion compensator (24) and a first-order PMD compensator (20,22) in series, wherein the adaptive chromatic dispersion compensator is controlled to provide compensation for both chromatic dispersion and second order PMD. The compensation arrangement is used in a node of an optical network.

Abstract: An optical dispersion compensation device includes a first optical compensation unit that applies non-linear dispersion compensation across a signal band, the first optical compensation unit being coupled to a second optical compensation unit that applies a degree of linear dispersion compensation across the signal band. The approach taken is to provide broadband dispersion compensation by applying dispersion slope compensation across the signal band to equalise residual dispersion slope and by applying a degree of linear compensation separately to affect the required linear dispersion compensation. Using these two degrees of freedom it is possible to set the desired dispersion slope and linear dispersion (whether positive or negative) to affect broadband dispersion compensation without needing to demultiplex the optical signal.

Abstract: An optical transmission system comprises a transmitter 1 having an optical source 2 adapted to emit light, a modulator 4 operable to modulate the light to produce a modulated optical signal and a dispersion element 8 adapted to apply dispersion to the modulated optical signal. The optical signal being modulated by the application of predetermined chirp thereto and the modulated optical signal having predetermined dispersion applied thereto, such that the signal is discernible at a point, along either a positive or negative dispersion fibre 16, in a range between a minimum and a maximum distance relative to the transmitter 1.

Abstract: An optical transmission system comprises a transmitter 1 having an optical source 2 adapted to emit light, a modulator 4 operable to modulate the light to produce a modulated optical signal and a dispersion element 8 adapted to apply dispersion to the modulated optical signal The optical signal being modulated by the application of predetermined chirp thereto and the modulated optical signal having predetermined dispersion applied thereto, such that the signal is discernible at a point, along either a positive or negative dispersion fibre 16, in a range between a minimum and a maximum distance relative to the transmitter 1.