Double frequency conversion apparatus for sourcing radiations having an intrinsically stable wavelength-shift that is quickly tuneable within an extended range, in particular for use in Brillouin analysers

摘要

Apparatus for producing and sourcing two lightwaves having a wavelength-shift known and controllable and suitable to be used as “pump” and “probe” in a stimulated Brillouin analyser in which part of the radiation of frequency f₀ from a primary source (70) is first shifted of a frequency Δf₁ typically from 200 to 1000 MHz lower than the Brillouin shift Δf_B,SNS in the sensor, by a first frequency conversion system comprising a Brillouin ring laser (105) and then is shifted of a frequency Δf₂ in order to fall inside the Brillouin gain band of the sensor through a further tuneable frequency conversion system (105, 106, 107) in which at least one electro-optical modulator generates modulation side bands (117, 119) of frequency (f₀−Δf₁+Δf₂) and (f₀Δf₁−Δf₂), only one of which can fall within a Brillouin gain band of the sensor. The apparatus possibly comprises also a feedback stabilization system that acts on Δf₂ depending on changes in the value of Δf₁ in order to stabilise at least one between |Δf₁+Δf₂| and |Δf₁−Δf₂|. The apparatus solves the following problems of known solutions: wavelength-shift stability and accuracy, wavelength agility, width of the wavelength-shift tuning range, power consumption, tuning speed and industrial cost.