An arrangement (20, 23, 30) for monitoring an optical fibre, the arrangement comprising: a first node configured to separate an optical monitoring pulse from data signals transmitted along the optical fibre; a photo-sensitive device arranged to produce an electric pulse from the optical pulse separated by the first node; a delay element and a first optical circulator arranged to delay the optical pulse injected at the first node of the optical fibre, wherein the optical pulse is input to a second port of the first optical circulator and output at a third port of the first optical circulator; an optical amplifier arrangement (28, 32) arranged to receive the optical pulse at its input and the produced electric pulse as an operating signal, wherein the delay element is arranged to delay the optical pulse such that the delayed optical pulse is synchronized with the produced electric pulse supplied to the optical amplifier arrangement as an operating signal, for producing an amplified optical pulse; a second optical circulator arranged to receive the amplified optical pulse at a first port and output the amplified optical pulse at a second port; a second node connected to the second port of the second optical circulator, said second node being connected to the first node via a fiber path and configured to combine the amplified optical pulse together with the data signals that were separated at the first node said second optical circulator further being arranged to receive an optical signal reflected back from the optical fibre at the second port and to output the reflected optical signal at a third port via a path bypassing the optical amplifier arrangement to a first port of the first optical circulator, wherein the reflected optical signal is output from the second port of the first circulator to the first node of the optical fibre. a first node configured to separate an optical monitoring pulse from data signals transmitted along the optical fibre; a photo-sensitive device arranged to produce an electric pulse from the optical pulse separated by the first node; a delay element and a first optical circulator arranged to delay the optical pulse injected at the first node of the optical fibre, wherein the optical pulse is input to a second port of the first optical circulator and output at a third port of the first optical circulator; an optical amplifier arrangement (28, 32) arranged to receive the optical pulse at its input and the produced electric pulse as an operating signal, wherein the delay element is arranged to delay the optical pulse such that the delayed optical pulse is synchronized with the produced electric pulse supplied to the optical amplifier arrangement as an operating signal, for producing an amplified optical pulse; a second optical circulator arranged to receive the amplified optical pulse at a first port and output the amplified optical pulse at a second port; a second node connected to the second port of the second optical circulator, said second node being connected to the first node via a fiber path and configured to combine the amplified optical pulse together with the data signals that were separated at the first node said second optical circulator further being arranged to receive an optical signal reflected back from the optical fibre at the second port and to output the reflected optical signal at a third port via a path bypassing the optical amplifier arrangement to a first port of the first optical circulator, wherein the reflected optical signal is output from the second port of the first circulator to the first node of the optical fibre.