An optical and electrical isolating unit for use with a branching unit
located in an undersea optical transmission system is provided. The unit
includes a pressure vessel adapted for use in an undersea environment.
First, second and third ports are located in the pressure vessel for
receiving first, second and third undersea transmission cables,
respectively. The first cable includes an electrical power conductor and
at least one optical fiber. The second cable includes an electrical
conductor, and the third cable, which is electrically unpowered, includes
at least one optical fiber. An electrical power conductor segment is
provided for electrically coupling the conductor in the first cable
received in the first port to the conductor in the second cable received
in the second port. At least one optical fiber segment is located in the
pressure vessel, which segment optically couples the optical fiber of the
first cable to the optical fiber of the third cable.