Abstract: A system for checking the correct operation of a wavelength filter comprising a wavelength filter comprising a first selectively reflective element (SRE) for reflecting a first signal of a first wavelength and a second SRE for reflecting a second signal of a different wavelength. The system also detects the second signal reflected by the second selectively reflective element.

Abstract: A system for individually controlling the chromatic dispersion of one or more wavelength division multiplexed (WDM) optical signals, chromatic dispersion is compensated a plurality if individually controllable differential optical delay elements. An example of a suitable differential optical delay element is a tunable fiber Bragg grating filter whose spectral response varies along the length of the grating, i.e. is chirped in a non-linear fashion. The system may, in addition, comprise one or more second individually controllable optical delay elements arranged so as to compensate for any unwanted delays across the wavelength band of a signal introduced by a first delay element. Optical circulators may be used to route signals into and between the pluralities of differential optical delay elements. This system has the advantage of providing a compact multi-channel selective differential delay suitable for compensating for chromatic dispersion in a WDM optical communications network.

Abstract: An optical switching arrangement, e.g. an add-drop multiplexer or switch, for receiving an input signal comprising a plurality of input wavelength encoded optical channels. The arrangement includes a selector for selecting from the plurality of input optical channels for forming a plurality of output signals comprising selected ones of the plurality of input optical channels. A combination of input optical channels in any one of the plurality of output signals is different from a combination of input optical channels in the input signal. The selector comprises a plurality of selective reflectors for selectively reflecting optical channels selected from the plurality of input optical channels. The plurality of selective reflectors are arranged to selectively reflect each of the input optical channels selected for forming the plurality of output signals.

Abstract: An optical communications system for communication of a plurality of wavelength multiplexed channels. The communications system comprises a node. The node comprises a plurality of add-drop multiplexers (ADM), one per channel. Each ADM comprises a tributary. The ADMs are interconnected by the tributaries.

Abstract: A method for upgrading an-optical communications system in which the system comprises a plurality of nodes linked by one or more optical paths. Each path for the communication of traffic includes a single optical channel. Each node comprises add/drop multiplexers (ADM) for adding and dropping signals in electrical form, and conversion circuitry for converting between electrical and optical form signals output by the ADM for transmission via a first one of the optical paths, and for converting signals received via a second one of the optical paths for input to the ADM.

Abstract: A system for individually controlling the power levels of a plurality of wavelength division multiplexed (WDM) optical signals in a single optical guide comprising a first plurality of individually controllable optical attenuators. An example of a suitable optical attenuator is a tunable fiber Bragg grating filter whose reflectivity characteristic varies with wavelength over an active region thereof. By tuning the filter, it is possible to control the reflectivity at a particular wavelength in the active region. The system may, in addition, comprise a second plurality of optical attenuators arranged so as to compensate for any power level distortion introduced by the first plurality. Optical circulators may be used to route signals into and between the pluralities of optical attenuators.

Abstract: A photonics system comprising an optical circulator, comprising a plurality of ports; a first port arranged to receive a plurality of spatially separate optical signals each comprising a plurality of wavelengths; the optical circulator arranged to pass the plurality of optical signals to a second port so as to produce them as spatially separate signals; a plurality of optical wavelength filters arranged at the second port, in which each of the plurality of optical wavelength filters is arranged to align with a different one of the plurality of optical signals at the second port, each of the plurality of optical wavelength filters for selectively reflecting a selection of the plurality of wavelengths comprised in the respective optical signal and selectively passing others of the plurality of wavelengths.