Patent ID: 8005323

Claim:
A sensing system for sending electromagnetic signals along a waveguide and sensing conditions at one or more sensing locations along the waveguide, the system comprising a transmitting means and a receiving means, wherein the transmitting means is arranged to generate two or more streams of pulses having spatially separate paths, the pulses of one of the streams having a suitable shape to cause a controlled conversion of the pulses to a different wavelength, before combining the streams to form a combined stream and sending the combined stream along the waveguide, and the receiving means is arranged to receive signals returned from the one or more sensing locations, by detecting an up shifted component returned from one of the pulses at a first wavelength, and a down shifted component returned from one of the pulses transmitted at a higher wavelength, down shifted to the first wavelength and the receiving means is adapted to compensate for different losses along the waveguide at different wavelengths and determine the conditions based on the received signals.