Abstract: A first signal is generated having a first frequency spectrum comprising one or more stopbands in which components of the first signal exhibit attenuated energy relative to an average energy of the first signal. A second signal is generated having a second frequency spectrum comprising non-zero energy at frequencies within the one or more stopbands. A third signal is generated by a crosstalk-inducing subsystem from a combination of the first signal and the second signal. The third signal is detected at a receiver device and an estimate of crosstalk induced by the crosstalk-inducing subsystem is calculated using a measurement of the third signal at the frequencies within the one or more stopbands. According to some examples, the second frequency spectrum comprises a tone within at least one of the stopbands.

Abstract: A ganged optical switch comprising at least one wavelength selective ganged optical switching element, first and second sets of input ports, and first and second sets of output ports. Optical signals entering one of the first set of input ports can be routed, in a first routing, via the at least one ganged optical switching element to one of the second set of output ports, and optical signals entering one of the first set of input ports can be routed, in a second routing, via the at least one ganged optical switching element to one of the second set of output ports. The ganged optical switching element ensures that the first and second routings are interdependent. In one embodiment, some of the output ports are shared between the first and second sets of output ports. ROADMs and protection switching applications of the ganged optical switches of the invention are also disclosed.

Abstract: An optical roundabout comprising optical switching elements arranged in a ring, the routing of the inputs of each internal optical switch to its outputs being ganged, each internal optical switching element having add and drop ports, and connected to its next optical switching element around the ring by an optical waveguide.

Abstract: A method of compensating the polarisation mode dispersion (PMD) of an optical transmission path carrying clocked digital data traffic involves modulating the state of polarisation (SOP) of the light launched into the transmission path, and employing consequential frequency components in an electrical signal detected at the far end of the transmission path to regulate the birefringence of a polarisation state controller portion of a birefringent element inserted between the transmission path and the receiver's photodetector. The SOP modulation, when represented on a Poincaré sphere, has an oscillatory rotational component at a frequency f1 about a first axis of the sphere and an oscillatory rotational component at a frequency f2 about a second axis of the sphere that is orthogonal to said first axis, and where f1≠f2, f1≠2f2, and f2≠2f1.

Abstract: A method of measuring the polarization mode dispersion (PMD) of an optical transmission path carrying clocked digital data traffic involves modulating the state of polarization (SOP) of the light launched into the transmission path, and detecting consequential frequency components in an electrical signal detected at the far end of the transmission path. The SOP modulation, when represented on a Poincaré sphere, has an oscillatory rotational component at a frequency f1 about a first axis of the sphere and an oscillatory rotational component at a frequency f2 about a second axis of the sphere that is orthogonal to said first axis, and where f1≠f2, f1≠2f2, and f2≠2f1.