| 摘要 |
A first- and second-order polarisation-mode dispersion (PMD) compensator comprises a polarisation controller 20 to polarise incoming light along two orthogonal axes, a splitter 30 arranged to split light according to the light's polarisation between first and second optical paths, a combiner 40 arranged to combine light from the two optical paths and a monitor 65 for monitoring the light output. An active wavelength-delay device 70 which may be an arrayed waveguide grating (fig. 2) is provided in one of the paths to delay different wavelengths by different amounts, thereby compensating for chromatic dispersion due to second-order PMD. The AWG also has an active group delay element (110, fig. 2) for compensating differential group delay (DGD) or first-order PMD. The delays are selected in accordance with the monitored output. Various arrangements are disclosed. For example, the single AWG unit may be replaced by two separate elements in the same path (280, 290 fig. 6) or in different paths (280, 290 fig. 7).
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