Active optical measurement device with weak signal amplification

A device for measurement by optical probe comprising at least two light beams of different wavelengths denoted as first beam and second beam, the device illuminating a reference medium by the first beam and receiving a light echo reflected back by the reference medium, and the device comprising:

• an optical coupler receiving, on the one hand, the light echo reflected back by the reference medium and, on the other, the second beam, the optical coupler delivering a resultant wave comprising the second beam and the light echo;
• an optical amplification unit, of bandwidth, receiving the resultant wave and delivering an amplified resultant wave, wherein the frequency of the second beam and the frequency of the light echo are included in the bandwidth of the optical amplification unit;
• a laser unit supplying the first beam for illuminating a separation unit delivering a signal light beam for illuminating an emission/reception optical signal channel, and a reference light beam for illuminating a first input of an optical mixing coupler;
• a laser unit generating the second light beam illuminating a first optical coupler input the optical coupler receiving, at a second input, the light echo originating from the emission/reception optical signal channel, the optical coupler delivering the resultant wave at its output,
• the emission/reception optical signal channel, from the signal light beam, supplying a power optical signal focused into the reference medium, receiving the light echo and transporting it to the optical coupler, where the reference light beam and the power optical signal can be shifted in frequency;
• the optical amplification unit receiving the resultant wave coming from the output of the optical coupler, and generating an amplified resultant wave,
• the optical mixing coupler receiving, at a first input, the reference light beam coming from the separation unit and, at a second input, the amplified resultant wave, and delivering a beat-frequency optical signal comprising the sum of the reference light beam Fr and of the amplified resultant wave;
• a detection unit comprising a photosensitive detector receiving on its sensitive surface the beat-frequency optical signal from the optical mixing coupler and delivering a beat-frequency electrical signal, the frequency of the beat-frequency electrical signal being equal to the difference of the frequency of the reference light beam Fr and of that of the amplified resultant wave.

A device for measurement by optical probe comprising at least two light beams of different wavelengths denoted as first beam and second beam, the device illuminating a reference medium by the first beam and receiving a light echo reflected back by the reference medium, the device comprising:

• an optical coupler receiving the light echo reflected back by the reference medium and the second beam, the optical coupler delivering a resultant wave comprising the second beam and the light echo;
• an optical amplification unit, of bandwidth, receiving the resultant wave and delivering an amplified resultant wave;
• a laser unit supplying the first beam for illuminating a separation unit delivering a secondary beam for illuminating a separation unit and an injection beam for illuminating an optical signal frequency shifting device INJDEF, the separation unit delivering a signal light beam for illuminating an emission/reception optical signal channel, and a reference light beam for illuminating an optical mixing coupler,
• the emission/reception optical signal channel, from the signal light beam, supplying a power optical signal focused into the reference medium, receiving the light echo and transporting it to a first input of the optical coupler, the reference light beam and the power optical signal being shifted in frequency,
• the optical signal frequency shifting device receiving the injection beam and supplying the second beam for illuminating a second input of the optical coupler, the second beam having a wavelength slightly different from that of the injection beam, the optical coupler delivering a resultant wave at its output;
• the optical amplification unit receiving the resultant wave coming from the output of the optical coupler, and generating an amplified resultant wave;
• the optical mixing coupler receiving, at a first input, the reference light beam coming from the separation unit and, at a second input, the amplified resultant wave, and delivering a beat-frequency optical signal comprising the sum of the reference light beam Fr and of the amplified resultant wave;
• and
• a detection unit comprising a photosensitive detector receiving on its sensitive surface the beat-frequency optical signal from the optical mixing coupler and delivering a beat-frequency electrical signal, the frequency of the beat-frequency electrical signal being equal to the difference of the frequency of the reference light beam and of that of the amplified resultant wave.