| 摘要 |
A monitor for monitoring the optical signal parameters in an optical fibre comprises an optical fibre 1 having an access region 9 of reduced cladding thickness sufficient to allow access to the evanescent field of the optical fibre, and an optical element mounted adjacent to the access region to enable use to be made of data therein. The system can establish whether there is light in the fibre and monitor its properties, including its polarisation state, wavelength, power or the information it carries. Preferably the optical element comprises a photodetector 11. A lens 15 and, additionally or alternatively, a polariser or wavelength filter may be interposed between the access region and the photodetector. Alternatively the optical element may comprise a second optical fibre (see figure 12). Also described is an arrangement for controlling the power in a optical fibre comprising an optical attenuator upstream of a monitor as described above (see figure 14). |
