Page 30: of Marine Technology Magazine (Sep/Oct 2014)

doubles the number of fi bers required in both your cables and the connectors or penetrators you use. The optical circulator offers a way around this.

An optical circulator is a non reciprocal, passive optical device. By non reciprocal, we mean that light traversing the device will travel along a path determined by the direction of propagation. Light propagates through the device from one port to the next, but not in the opposite direction. Typi- cally, these are three port devices. Light that enters through port 1 exits through port 2. Light launched into the circulator through port 2 exits through port 3; not port 1. Any light trying to circulate in the opposite direction is blocked.

The simplest use of optical circulators would be to use a pair of them; one, for example, on an ROV and the other on the support vessel. The umbilical would connect the dry end circulator’s port 2 to the wet end circulator’s port 2. Light launched into port 1 on the dry end would emerge at port 3 on the wet end. Signal returning from the ROV would launch into port 1 on the wet end and be received at port 3 on the dry end.

Thus, we establish two way communication with the ROV over a single fi ber link. The difference is that, unlike the BiDi, this is done within a single wavelength band. The importance

BIRNS Millennium 3F single fi ber cable plugs (CPs) provide high bandwidth in a single optical fi ber and can be expanded from a simplex connection to multi-channel connections using tools such as BiDi modules, optical circulators, or DWDM modules. 30 MTR

September 2014

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