Abstract: An optical sensing system uses light scattered from a sensing fibre to sense conditions along the fibre, and has a receiver with a frequency to amplitude converter to obtain a frequency of a Brillouin component of the received scattered light, to deduce the conditions. This converter can avoid time consuming scanning of frequencies to obtain the Brillouin frequency spectrum, and avoids the heavy processing load of deducing a peak or average frequency from the spectrum. The converter can be implemented in the optical domain using a grating or interferometer, or in the electrical domain using a diplexer or electrical interferometer. It can generate complementary signals, having opposite signs, a ratio of these signals representing the frequency. This can avoid sensitivity to amplitude changes in the received scattered signals and provide common mode rejection of noise.

Abstract: A polarization mode dispersion (PMD) compensation arrangement receives an optical input data signal which has been subjected to PMD. The arrangement comprises an adaptive chromatic dispersion compensator (24) and a first-order PMD compensator (20,22) in series, wherein the adaptive chromatic dispersion compensator is controlled to provide compensation for both chromatic dispersion and second order PMD. The compensation arrangement is used in a node of an optical network.

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: An apparatus and a method for compensating for polarisation mode dispersion in an optical signal. The apparatus includes a chirped Bragg reflector extending longitudinally along an optical waveguide, the waveguide being susceptible to stress birefringence; and at least one tuning element located at a position along the length of the waveguide. The tuning element is operable to, in use, apply a stress to the waveguide so as to alter the magnitude and the orientation of the birefringence of the waveguide for compensation of the polarisation mode dispersion of the optical signal. Higher order PMD compensation can be achieved by providing two such tuning elements along the waveguide.

Abstract: The present specification describes strain applicators, incorporating two actuators having different actuation characteristics acting in cooperation, and their use in adjustable optical filters and adjustable dispersion devices (such as compensators) to controllably strain fiber Bragg gratings to alter their reflectance characteristics. Preferred examples of the strain applicators are hybrids of a fast response actuator with a slower device, and provide a wide overall range of adjustment with fast response tuning within that range.

Abstract: A PMD (polarisation mode dispersion) emulator which provides at least first and second order emulation of PMD effects observed in fiber installed in the field consists of a small number of concatenated lengths of high birefringence fiber having an appropriate distribution of relative DGDs (differential group delays), and connected with random relative orientation. Varying some parameter, such as temperature distribution, allows the emulator to provide accelerated exploration of random fluctuations in PMD which, in the field, may require many weeks, or longer, to observe.