Precision of retardance autocalibration in full-Stokes division-of-focal-plane imaging polarimeters.

We investigate the validity domain and precision of retardance autocalibration in full-Stokes imaging polarimeters based on a linear division-of-focal-plane polarization camera. We demonstrate that the level of precision of autocalibration in these systems gets worse as the degree of linear polarization of input Stokes vector approaches zero. Autocalibration is impossible when the input is purely circular or totally unpolarized. In all other cases, reaching a given level of precision requires a higher signal-to-noise ratio as the input gets closer to circular or unpolarized.

Precision of retardance autocalibration in full-Stokes division-of-focal-plane imaging polarimeters: publisher's note.

This publisher's note contains corrections to Opt. Lett.44, 5410 (2019)OPLEDP0146-959210.1364/OL.44.005410.

Optimal tradeoff between precision and sampling rate in DoFP imaging polarimeters.

A linear division-of-focal-plane camera combined with a controllable polarization modulator constitutes a versatile full-Stokes imager with four possible sampling rate modes, depending on the number of acquisitions. Considering several polarization modulator architectures, we determine the parameter settings that minimize estimation variance in each sampling rate mode, so that precision, sampling rate, and acquisition time can be optimally and dynamically balanced to implement the imaging solution best adapted to a given application.

Polarimetric precision of micropolarizer grid-based camera in the presence of additive and Poisson shot noise.

Polarimetric cameras based on micropolarizer grids make it possible to design division of focal plane (DoFP) polarimeters. However, the polarimetric estimation precision reached by these devices depends on their realization quality, which is estimated by calibration. We derive the theoretical expressions of the estimation variance of such polarimetric parameters as an angle of linear polarization and degree of linear polarization as a function of the calibrated micropolarizer characteristics. These values can be compared with the variances that would be obtained with ideal micropolarizers in order to quantitatively assess the effect of manufacturing defects on polarimetric performance. These results are validated by experimental measurements on a real-world camera.

Optimal configuration of static Mueller imagers for target detection.

We investigate the target detection performance of static Mueller imagers that implement a fixed number of illumination and analysis polarization states. Using a maximin approach, we demonstrate that the optimal sets of measurement vectors consist in regular tetrahedra on the Poincaré sphere and that, in this case, the obtained target/background contrast has a very simple expression. We then derive a universal lower bound on the contrast ratio between the best channel of a static imager and a fully adaptive one, and in a special case of practical interest, we demonstrate that this ratio is bounded and always larger than 1/9. This is very important in practice since static imagers are much easier to build and operate. Our results show that they constitute a good alternative where ultimate contrast improvement is not necessary.

In vivo imaging of uterine cervix with a Mueller polarimetric colposcope.

Mueller polarimetric imaging enables the detection and quantification of modifications of the collagen fibers in the uterine cervix due to the development of a precancerous lesion. This information is not accessible through the use of the classic colposcope, a low magnification microscope used in current practice for cervical cancer screening. However, the in vivo application of Mueller polarimetric imaging poses an instrumental challenge: the device should be sufficiently compact, while still being able to perform fast and accurate acquisition of Mueller matrices in real-world conditions. In this study, the first wide field Mueller Polarimetric Colposcope (MPC) for the in vivo analysis of uterine cervix is presented. The MPC has been fabricated by grafting a miniaturized Mueller polarimetric imager on a classic colposcope. This new imaging tool performs the fast acquisition of Mueller polarimetric images, thus eliminating any blurring effects due to patient movements. It can be easily used by a practitioner with little change to their existing practice. Finally, the MPC was tested in vivo on a number of patients in the field.

Polarized light imaging specifies the anisotropy of light scattering in the superficial layer of a tissue.

This report describes how optical images acquired using linearly polarized light can specify the anisotropy of scattering (g) and the ratio of reduced scattering [µs'=µs(1−g)] to absorption (µa), i.e., N'=µs'/µa. A camera acquired copolarized (HH) and crosspolarized (HV) reflectance images of a tissue (skin), which yielded images based on the intensity (I=HH+HV) and difference (Q=HH−HV) of reflectance images. Monte Carlo simulations generated an analysis grid (or lookup table), which mapped Q and I into a grid of g versus N', i.e., g(Q,I) and N'(Q,I). The anisotropy g is interesting because it is sensitive to the submicrometer structure of biological tissues. Hence, polarized light imaging can monitor shifts in the submicrometer (50 to 1000 nm) structure of tissues. The Q values for forearm skin on two subjects (one Caucasian, one pigmented) were in the range of 0.046±0.007 (24), which is the mean±SD for 24 measurements on 8 skin sites×3 visible wavelengths, 470, 524, and 625 nm, which indicated g values of 0.67±0.07 (24).