| 摘要 |
An optical line system comprises: (i) an optical fibre that includes a plurality of reflectors, for example Bragg gratings, located at different positions along the optical fibre; and (ii) a monitoring arrangement located in the region of one end of the optical fibre for monitoring the system by an optical reflectometry method in which light is reflected by the reflectors. The system is characterised in that at least two of the reflectors have reflectivities that differ from one another, the reflector that is more distant from the monitoring arrangement having a higher reflectivity than the Bragg grating that is nearer to the monitoring arrangement. Preferably the reflectivities of the reflectors increases as the distance from the monitoring arrangement increase, the reflectivities preferably having the relationship (I) Rn-1=(2T<2>Rn+1)-(1+4T<2>Rn)<1/2>/2T<2>Rn where: Rn is the reflectivity of the n th reflector from the monitoring arrangement, Rn-1 is the reflectivity of the (n-1)th reflector from the monitoring arrangement, and T is the transmission coefficient of any branch that may be present between the (n-1)th and the n th reflector (and is unity if no such branch exists). Such a system has the advantage that the signal-to-noise ratio of the most distant reflectors is increased by the greatest extent so that differences in the signal-to-noise ratio of different reflectors is reduced.
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