An optical system comprising: at least one cable landing stations ,CLS, coupled to a first trunk path , the first trunk path including at least a first trunk path cable segment (114-3) and a second trunk path cable segment (114-4), each of the first and second trunk path cable segments (114-3, 114-4) comprising an undersea cable having at least one electrical conductor, respectively; and at least one power feed branching unit ,PFBU, (118-3) located in an undersea environment coupled between the first and second trunk path cable segments (114-3, 114-4), the PFBU (118-3) having a DC/DC converter ,DDCM, arrangement (501/518) with a first port (626-1) to electrically couple to the at least one electrical conductor of the first trunk path segment (114-3), a second port (626-2) to electrically couple to the at least one electrical conductor of the second trunk path segment (114-4), and a third port (626-3) to electrically couple to an electrical conductor of a branch path cable segment , characterised in that : the DDCM arrangement is configured to maintain a constant output current level via the second port (626-2) based at least in part on a first input current received via the first port (626-1) coupled to the at least one electrical conductor of the first trunk path segment (114-3) and a second input current received via the third port (626-3) coupled to the electrical conductor of the branch path cable segment . at least one cable landing stations ,CLS, coupled to a first trunk path , the first trunk path including at least a first trunk path cable segment (114-3) and a second trunk path cable segment (114-4), each of the first and second trunk path cable segments (114-3, 114-4) comprising an undersea cable having at least one electrical conductor, respectively; and at least one power feed branching unit ,PFBU, (118-3) located in an undersea environment coupled between the first and second trunk path cable segments (114-3, 114-4), the PFBU (118-3) having a DC/DC converter ,DDCM, arrangement (501/518) with a first port (626-1) to electrically couple to the at least one electrical conductor of the first trunk path segment (114-3), a second port (626-2) to electrically couple to the at least one electrical conductor of the second trunk path segment (114-4), and a third port (626-3) to electrically couple to an electrical conductor of a branch path cable segment , characterised in that : the DDCM arrangement is configured to maintain a constant output current level via the second port (626-2) based at least in part on a first input current received via the first port (626-1) coupled to the at least one electrical conductor of the first trunk path segment (114-3) and a second input current received via the third port (626-3) coupled to the electrical conductor of the branch path cable segment . environment coupled between the first and second trunk path cable segments (114-3, 114-4), the PFBU (118-3) having a DC/DC converter ,DDCM, arrangement (501/518) with a first port (626-1) to electrically couple to the at least one electrical conductor of the first trunk path segment (114-3), a second port (626-2) to electrically couple to the at least one electrical conductor of the second trunk path segment (114-4), and a third port (626-3) to electrically couple to an electrical conductor of a branch path cable segment , characterised in that : the DDCM arrangement is configured to maintain a constant output current level via the second port (626-2) based at least in part on a first input current received via the first port (626-1) coupled to the at least one electrical conductor of the first trunk path segment (114-3) and a second input current received via the third port (626-3) coupled to the electrical conductor of the branch path cable segment . <EOS>