Patent ID: 6901087

Claim:
A broadband laser source comprising: a resonant cavity containing a medium which emits optical energy in a continuum of wavelengths in response to application of pump energy to the medium; a source of pump energy for producing said optical energy; a frequency shifter within the resonant cavity; and a tuneable spectral filter within the resonant cavity; the resonant cavity being a ring structure which contains a rare-earth doped single-mode optical fibre, an optical isolator, an input fibre coupler for coupling the pump energy into the resonant cavity, and an output fibre coupler through which broadband laser light exits the resonant cavity; and the apparatus being such that in use the tuneable spectral filter has a peak wavelength which is repeatedly swept in a substantially resonant fashion over a wavelength range equal to, or a fraction of, a linewidth of the broadband source such that the rate of change of the peak wavelength of the tuneable spectral filter is substantially equal to the rate of change of the frequency of the optical energy as it is frequency shifted within the resonant cavity by the frequency shifter.