Abstract: A routing and wavelength assignment method for use in an optical fiber system, comprising: (i) identifying a plurality of paths between a source node and a destination node, (ii) selecting one of the plurality of identified paths, (iii) defining within the spectrum band of the selected path one or more blocks of spectral resource, in which each block comprises either: one or more unused wavelength channels, or one or more wavelength channels having the same spectral width, (iv) obtaining an entropy value of the selected path defining the spectrum fragmentation across its spectrum band, based on a logarithm of the ratio of the number of wavelength channels in each of the one or more blocks, to the total number of wavelength channels across the spectrum band, (v) iterating (ii) to (v) until the entropy value of each of the plurality of identified paths has been determined, and (vi) choosing from the plurality of identified paths a path having the lowest entropy value.

Abstract: A routing and wavelength assignment method for use in an optical fiber network includes (i) identifying a path between each node pair in the network, (ii) identifying a block of spectral resource within the spectrum band of the identified path of a selected node pair, (iii) calculating a spectrum entropy value of the identified path of the selected node pair based on a logarithm of the ratio of the number of wavelength channels in each of the one or more blocks, to the total number of wavelength channels across the spectrum band, (iv) iterating (ii) and (iii) in respect of each of the paths between each other node pair in the network, until a spectrum entropy value of all the paths between all the node pairs has been calculated, (v) summing the spectrum entropy value of all of the paths between all of the node pairs to obtain a network spectrum entropy value in respect of a network configuration based on the paths between the node pairs, and (vi) determining from the network spectrum entropy value whether a s

Abstract: A routing and wavelength assignment method for use in an optical fiber network includes (i) identifying a path between each node pair in the network, (ii) identifying a block of spectral resource within the spectrum band of the identified path of a selected node pair, (iii) calculating a spectrum entropy value of the identified path of the selected node pair based on a logarithm of the ratio of the number of wavelength channels in each of the one or more blocks, to the total number of wavelength channels across the spectrum band, (iv) iterating (ii) and (iii) in respect of each of the paths between each other node pair in the network, until a spectrum entropy value of all the paths between all the node pairs has been calculated, (v) summing the spectrum entropy value of all of the paths between all of the node pairs to obtain a network spectrum entropy value in respect of a network configuration based on the paths between the node pairs, and (vi) determining from the network spectrum entropy value whether a s

Abstract: A routing and wavelength assignment method for use in an optical fiber system, comprising; (i) identifying a plurality of paths between a source node and a destination node, (ii) selecting one of the plurality of identified paths, (iii) defining within the spectrum band of the selected path one or more blocks of spectral resource, in which each block comprises either: one or more unused wavelength channels, or one or more wavelength channels having the same spectral width, (iv) obtaining an entropy value of the selected path defining the spectrum fragmentation across its spectrum band, based on a logarithm of the ratio of the number of wavelength channels in each of the one or more blocks, to the total number of wavelength channels across the spectrum band, (v) iterating (ii) to (v) until the entropy value of each of the plurality of identified paths has been determined, and (vi) choosing from the plurality of identified paths a path having the lowest entropy value.

Abstract: Data is encrypted onto an electromagnetic beam by providing an electromagnetic beam having a signal component having a modal state, wherein the signal component is susceptible to accumulation of a geometric phase, and a reference component, transmitted along a path over at least part of which the signal component accumulates a geometric phase by transformation of its modal state from a first to a second modal state, from the second to at least one further modal state, and then back to the first modal state; and modulating with the data the geometric phase so accumulated, by modulating the modal state transformations. Data is decrypted from a received electromagnetic beam by corresponding processing of the received electromagnetic beam and by comparing an overall phase of the signal component with an overall phase of the reference component so as to retrieve the modulation.

Abstract: An apparatus and method for providing a delay to an optical signal including a Latin router having a plurality of input ports, including at least one signal-input port, and a plurality of output ports, including at least one signal-output port, and a plurality of optical waveguides, each connecting one of the input ports to one of the output ports that is not a signal-output port, in which the plurality of waveguides are connected between the input ports and the output ports in an arrangement such that a first signal entering the device and mapped to any one of the output ports experiences a delay that is different from a delay that is experienced by a second signal entering the device and mapped to a different one of the output ports.

Abstract: Data is encrypted onto an electromagnetic beam by providing an electromagnetic beam having a signal component having a modal state, wherein the signal component is susceptible to accumulation of a geometric phase, and a reference component, transmitted along a path over at least part of which the signal component accumulates a geometric phase by transformation of its modal state from a first to a second modal state, from the second to at least one further modal state, and then back to the first modal state; and modulating with the data the geometric phase so accumulated, by modulating the modal state transformations. Data is decrypted from a received electromagnetic beam by corresponding processing of the received electromagnetic beam and by comparing an overall phase of the signal component with an overall phase of the reference component so as to retrieve the modulation.

Abstract: An optical waveguide comprises a core and is characterised in that the core has a refractive index that includes a radial discontinuity and varies, with increasing azimuthal angle ?, from a first value n2 at a first side of the discontinuity to a second value n1 at a second side of the discontinuity.

Abstract: The invention relates to the field of grating structures. The invention provides a longitudinal grating having an aperiodic structure, wherein the grating has a selected response characteristic and any repeated unit cell in the structure is significantly longer than a characteristic length associated with the selected response characteristic.

Abstract: A fresenel zoned microstructured optical fiber is described. The fiber is constructed of concentric zones, each zone being defined by discontinuities in the refractive index. The refractive index within each zone may either be constant or may vary, for example each zone being a section of a parabola or hyperbola. The fiber may be used as a lens, for example for coupling light between fibers with different core sizes.

Abstract: A method for producing aperiodic gratings and waveguides with aperiodic gratings uses a simulated annealing process that starts with a random configuration of grating elements and iteratively computes a spectral response from a Fourier transform of the configuration of grating elements obtained in successive iterations. A cost function is computed as a convergence criterion. The aperiodic grating can be used, for example, as a filter in WDM applications.

Abstract: A method for producing aperiodic gratings and waveguides with aperiodic gratings uses a simulated annealing process that starts with a random configuration of grating elements and iteratively computes a spectral response from a Fourier transform of the configuration of grating elements obtained in successive iterations. A cost function is computed as a convergence criterion. The aperiodic grating can be used, for example, as a filter in WDM applications.

Abstract: A chromatic-dispersion compensator comprises: an input (3) for light of a plurality of wavelengths &lgr;i; an output for output of the light; a plurality of chromalically dispersive elements (1, 2) situated between the input (3) and the output and each exhibiting a dispersion characteristic that varies approximately periodically with wavelength, the variation having a maximum ripple amplitude Ai, each dispersive element (1, 2) exhibiting a dispersion characteristic of generally the same form as that of each other dispersive element (1, 2) but displaced in wavelength &lgr; so that, over the operating bandwidth, the compensator exhibits a overall dispersion characteristic that has a variation with wavelength having a maximum ripple amplitude that is less than the sum of the respective maximum amplitudes Ai.

Abstract: A holographic filter for an optical communication system is configurable to provide signal power equalisation for a number of optical signals or signal channels in a wavelength division multiplexed system.

Abstract: A holographic filter for an optical communication system is configurable to provide signal power equalisation for a number of optical signals or signal channels in a wavelength division multiplexed system.

Abstract: An arrayed wavelength grating device has a series of waveguiding channels (3) interconnecting two free space regions (2,4) across which light inputting and outputting the device passes. There are differences in optical path length between any two of said channels (3) lying adjacent to one other in said series, which differences are defined by respective optical path length increments. The optical path length progression across said channels (3) is non-linear, not being defined by any one value of the path length increments, nor by a plural number of values of the path length increments each defining a linear optical path length progression of a subset of at least three of said channels (3).

Abstract: An arrayed wavelength grating device has a series of waveguiding channels (3) interconnecting two free space regions (2,4) across which light inputting and outputting the device passes. There are differences in optical path length between any two of said channels (3) lying adjacent to one other in said series, which differences are defined by respective optical path length increments. The optical path length progression across said channels (3) is non-linear, not being defined by any one value of the path length increments, nor by a plural number of values of the path length increments each defining a linear optical path length progression of a subset of at least three of said channels (3).

Abstract: A tunable optical wavelength selective filter is constituted by a dynamic holographic diffraction element (3) in combination with a fixed diffraction grating or hologram (2). The dynamic diffraction element (3) is preferably implemented as an electronically controlled image displayed on a pixelated spatial light modulator and in particular a spatial light modulating using photo-electronic integrated circuits fabricated using silicon VLSI technology and integrated with ferro-electric liquid crystals. Amongst other uses the filter can be implemented to form a digitally tunable laser.