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 to1000MHz 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 (f₀- Δf₁- 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.