Coherent lidar system with improved signal-to-noise ratio

A coherent lidar imaging system comprising:

• a laser source (SL) configured so as to emit laser radiation (L) with a temporally modulated optical frequency (F L),
• a detection device (Det) comprising a matrix array of pixels (P), a pixel (Pij) comprising a photodetector component (PD(i,j)),
• a first optical device, called splitter (DS), designed to spatially split the laser radiation (L) into a beam, called reference beam (Lref), and into a beam, called object beam (Lo), that is directed towards a scene to be observed (Obj),
• an optical imaging system (Im) having an optical axis (AO) and producing an image of the scene by imaging an object beam reflected by the scene (Lo,r) on the pixels of the detection device, a fraction of the object beam reflected by said scene and illuminating a pixel being called pixel image beam (Lo,r/pix),
• a second optical device (D2) designed to route a fraction of the reference beam, called pixel reference beam (Lref/pix), to each photodetector,
• the second optical device (D2) and the optical imaging system (Im) furthermore being configured so as to superimpose, at the photodetector component of a pixel and in a substantially identical propagation direction, the pixel reference beam (Lref/pix) and the pixel image beam (Lo,r/pix), forming a pixel recombined beam (Lrec/pix),
• the photodetector component of a pixel being configured so as to generate a pixel detected signal (Spix) from the pixel recombined beam, the pixel detected signal having an intensity, called pixel total intensity (Itot/pix), the pixel total intensity comprising a modulated intensity (IAC/pix) and a constant intensity (IDC/pix), the splitter having a variable first transmittance (T1) that is identical for all of the pixels and modulable,
• the second optical device furthermore comprising at least one intensity modulator (IM, IMIij) designed to modulate an intensity of each pixel reference beam by applying a modulable pixel transmittance (xij),
• the coherent lidar imaging system furthermore comprising a processing unit (UT) configured so as to apply a first transmittance value (T1) and, for each pixel, a pixel transmittance value (xij), said values being determined via a control loop and using an optimization criterion, the optimization criterion comprising obtaining, for each pixel, a pixel total intensity less than a threshold intensity (Is), and obtaining an improved signal-to-noise ratio (SNR),
• the coherent lidar imaging system furthermore being configured so as to determine, for each pixel, a beat frequency (F(i,j)) of the recombined beam.