SUBMARINE CABLE BRANCHING UNITS WITH FIBER PAIR SWITCHING
FIG4 is a functional block diagram of another one example of a fiber pair switching branching unit consistent with the present disclosure 
FIG4 illustrates another example of a FPS-BU 130c consistent with the present disclosure. In general, in the FPS-BU 130c optical couplers are used to tap each input trunk fiber to obtain a copy of the inbound optical spectrum and connect it to the optical filtering devices, e.g. WSSs. The inbound spectra on each on trunk fiber is filtered and combined to form the output spectrum on each drop fiber of the branch cable. The outbound spectrum on each add fiber of the branch cable is filtered and combined with the trunk traffic on each trunk output fiber of the trunk cable to form the output spectrum on each trunk output fiber. A system consistent with the present disclosure is not limited to the examples described herein and can be provided in a variety of configurations. For example, the embodiment shown in FIG4 may be described as a "broadcast and select" configuration. However, the positions of the couplers, NxM drop WSS, the WSSs and the NxM splitter could be reversed to provide a "filter and combine" architecture consistent with the present disclosure. Also, the selectively controllable RORD, WSSs, N x M drop WSS and/the NxM add splitter can be implemented as single units, or may be implemented with a combination of lower port count optical filter devices. A system consistent with the present disclosure could be implemented with single-instance or with redundant reconfigurable optical filtering units on each path.
block diagram
420
splitter
412
drop fiber
422
drop WSS
402
branch cable fiber pair
162
branch cable branch cables
112
cable
406
drop fiber
404
branch cable fiber pair side branch cable fiber
410
add fiber
408
add fiber
['1. An optical communication system comprising: a trunk terminal configured to provide trunk signals on a plurality of fiber pairs of a trunk cable; a branch terminal configured to provide a branch add signal on a branch cable; and a fiber pair switching branching unit coupled to the trunk cable and the branch cable for receiving the trunk signals and the branch add signal, the branching unit comprising: at least a first optical routing device coupled to the trunk cable and configured to receive the trunk signals from each of the plurality of fiber pairs, the first optical routing device being controllable to couple signals from selected one of the plurality of fiber pairs to a drop fiber of the branch cable; and at least a second optical routing device coupled to the branch cable and configured to receive the branch add signal from the branch cable, the second optical routing device being controllable to couple the branch add signal to a fiber of one of the plurality of fiber pairs.', '3. The optical communication system of claim 1, wherein the second optical routing device is coupled to the branch cable through an associated optical splitter, wherein the optical splitter has an input port coupled to the branch cable to receive the branch add signal and a plurality of output ports, one of the plurality of output ports being coupled to the second optical routing device; wherein a second one of the output ports is coupled to a third optical routing device, the third wavelength device being controllable to couple the branch add signal to separate fiber of one of the plurality of fiber pairs.']