Abstract: A compensator for compensating polarisation-mode dispersion, comprises a splitter (30) arranged to split light, according to the light's polarisation, between a first optical path and a second optical path; a combiner (40) arranged to combine light from the first optical path and the second optical path, and a monitor (15) for monitoring the light. An active wavelength-delay device (70) 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 (15).

Abstract: A chromatic-dispersion compensator comprises a plurality of dispersive elements (Q in number. Q?2) each exhibiting a dispersion characteristic D (?) that varies substantially as a polynominal function of wavelength, the polynomial function being of an order (P?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 Dp that is non-zero and does not vary substantially with wavelength an operating bandwidth.

Abstract: A chromatic-dispersion compensator comprises a plurality of dispersive elements (Q in number. Q≧2) each exhibiting a dispersion characteristic D (&lgr;) that varies substantially as a polynominal function of wavelength, the polynominal function being of an order (P−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 DP that is non-zero and does not vary substantially with wavelength over an operating bandwidth.

Abstract: The invention is a circuit and method of limiting the charging voltage applied to an individual cell of a plurality of cells making up a battery being charged in series. It is particularly designed for use with batteries that can be damaged by overcharging, such as Lithium-ion type batteries. In detail, the method includes the following steps: sensing the actual voltage level of the individual cell; comparing the actual voltage level of the individual cell with a specific voltage level and providing an error signal representative thereof; and by-passing the charging current around the individual cell necessary to keep the individual cell voltage level generally equal to the specific voltage level while continuing to charge the remaining cells.

Abstract: 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.