Fujitsu Corporation

Hewlett-packard Company

British Telecommunications Public Limited Company

Stuart Douglas Walker

Michael Charles Parker

Makiko Hisatomi

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.

Method and apparatus relating to secure communication

A compensator for compensating polarisation-mode dispersion, comprises a splitter () arranged to split light, according to the light's polarisation, between a first optical path and a second optical path; a combiner () arranged to combine light from the first optical path and the second optical path, and a monitor () for monitoring the light. An active wavelength-delay device () is provided in the first optical path and arranged such that components of the light travelling in the first optical path and having different wavelengths are subjected to different delays, the delays being selected according to an output from the monitor ().

Compensator for polarization-mode dispersion compensation

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.

Fresnel zoned microstructured fibre and lens

A chromatic-dispersion compensator comprises a plurality of dispersive elements (Q in number. Q&#x2267;2) each exhibiting a dispersion characteristic D (&#x3bb;) that varies substantially as a polynominal function of wavelength, the polynomial function being of an order (P&#x2212;2) greater than 0, the dispersion characteristics being displaced in wavelength relative to each other such that the compensator has a net Pth-order dispersion characteristic Dthat is non-zero and does not vary substantially with wavelength an operating bandwidth.

Compensator for compensation of higher-order chromatic dispersion

Laser drive circuit

Bias controller and method

The present invention provides techniques for analyzing sub-carrier multiplexed (SCM) networks in which a pseudo-random binary sequence (PRBS) test signal is applied to a component or components of the network and the resulting signal is analyzed. A phase locked loop circuit extracts the PRBS and provides a signal which removes from the test signal the frequency component corresponding to the channel under investigation. The spectral properties of the PRBS enable broadband analysis of an SCM network to be carried out.

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Colchester, United Kingdom

Stuart Douglas Walker