Raman amplification in distributed optical fiber sensing systems

An optical fiber sensing system for providing Raman amplification, comprising:

• a sensing optical fiber deployable in a sensing environment;
• a first optical source operable to generate probe pulses of light at a probe wavelength;
• a second optical source operable to generate pump light at a pump wavelength shorter than the probe wavelength;
• means operable to modulate the pump light generated by the second optical source to produce a time-varying intensity profile;
• and
• an optical coupling device arranged to receive the probe pulses from the first optical source and modulated pump light from the modulation means and to launch the probe pulses and the pump light into the sensing fiber for propagation along the sensing fiber to achieve Raman amplification of backscattered light produced by the probe pulses as they propagate, such that the intensity of the launched pump light during launch of the probe pulses is different from the intensity at one or more other times.