Active polarimetric imaging by orthogonality breaking is an alternative polarimetric imaging method developed at the Institut FOTON, Rennes. By illuminating a sample with a dual-frequency dual-polarization (DFDP) beam whose polarizations are orthogonal, it is possible to characterize its diattenuation and the orientation of the anisotropy in a single acquisition. However, this technique is not sensitive to other polarimetric effects such as birefringence or pure depolarization and requires a detection/demodulation chain that introduces non-linearity effects and does not allow results to be obtained quantitatively. In this paper, after a presentation of the orthogonality-break imaging system, we will detail the calibration/correction protocol which is now implemented to take into account the effects of non-linearities. Then, we will show that it is possible, by adding a polarimetric analysis module, to make this method sensitive to the main polarimetric effects. The results obtained on a simulated operational scene will be presented.
We report an in-depth experimental characterization and analysis of an infrared active polarimetric imaging system based on the orthogonality breaking polarization-sensing approach. We first recall the principle of this laser scanning polarimetric imaging technique, based on the illumination of a scene by means of a dual-frequency dual-polarization light source. The experimental design is then described, along with measurements on test scenes with known polarimetric properties used to validate/calibrate the imaging system and to characterize its optical properties (sensitivity and resolution). The noise sources that temporally and spatially affect the quality of the orthogonality breaking data are then investigated. Our results show that the raw temporal signals detected at a given location of the scene are perturbed by Gaussian fluctuations, and the spatial information contained in the images acquired through raster scan of the scene are dominated by speckle noise, which is a common characteristic of active polarimetric imaging systems. Finally, the influence of the source temporal coherence on the images is analyzed experimentally, showing that orthogonality breaking acquisitions can still be performed efficiently with a low-coherence source.
We report the design of a free-space active infrared polarimetric imaging demonstrator operating at 1.55 μm and based
on a non-conventional approach: the orthogonality breaking sensing technique. Relying on the illumination of a scene
with a specific light source, the imager offers an original tradeoff between image acquisition time (~ 1 s) and
polarimetric consistency in comparison to standard polarimetric imagers such as division of time or division of amplitude
systems. We will illustrate the capability of such an imager to enhance the visibility of hidden objects on homemade
A novel technique is proposed to unambiguously determine the magnitude and orientation of linear dichroism. It relies on the use of a dual-frequency dual-polarization coherent source emitting two orthogonal circularly polarized modes at the output. The interaction of such beam with dichroic media is shown to give rise to a beatnote signal in the radiofrequency range. The amplitude and phase of such beatnote makes it possible to fully determine the magnitude and orientation angle of the diattenuation. We also report the application of this method to polarimetric imaging, with promising perspectives in biomedical imaging. Indeed, it provides a direct characterization of dichroic sample orientation, showing uniform estimated dichroism magnitude, whatever the orientation of the sample.