| 摘要 |
The present invention proposes a method and a device to add and drop optical channels in an optical transmission system (1) in which a multi-channel optical signal is transmitted into an optical fiber line (300). The OADM (Optical Add/Drop Multiplexer) device (695; 695') includes an optical splitter (673) receiving an input signal which includes at least one sub-group of the whole channels. Optical splitter (673) has an unbalanced power splitting ratio-in the range 60:40 to 90:10-for feeding a main power fraction (60% to 90%) of said input signal to a first output port and a secondary power fraction (40% to 10%) of said input signal to a second output port. The secondary power fraction defines a drop signal and is received by a demultiplexer (680; 682) where drop channels are extracted. The main power fraction defines a pass-through signal which is conveyed from the optical splitter (673) to an optical coupler (674) where the pass-through signal is coupled with an add signal, coming from a multiplexer (681). Optical coupler (674) has an unbalanced coupling ratio-in the range 60:40 to 90:10-so that it generates an output signal prevalently constituted by the pass-through signal. Cascaded Bragg gratings (678), positioned between the optical splitter (673) and the optical coupler (674), selectively retro-reflect the drop channels from the pass-through signal, and an optical isolator (679), positioned before the optical splitter (673), suppresses the retro-reflected drop channels.
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