Advances in vectorial polarization-resolved imaging are bringing new capabilities to applications ranging from fundamental physics through to clinical diagnosis. Imaging polarimetry requires determination of the Mueller matrix (MM) at every point, providing a complete description of an object’s vectorial properties. Despite forming a comprehensive representation, the MM does not usually provide easily interpretable information about the object’s internal structure. Certain simpler vectorial metrics are derived from subsets of the MM elements. These metrics permit extraction of signatures that provide direct indicators of hidden optical properties of complex systems, while featuring an intriguing asymmetry about what information can or cannot be inferred via these metrics. We harness such characteristics to reveal the spin Hall effect of light, infer microscopic structure within laser-written photonic waveguides, and conduct rapid pathological diagnosis through analysis of healthy and cancerous tissue. This provides new insight for the broader usage of such asymmetric inferred vectorial information.
Graded index (GRIN) lenses focus light through a radially symmetric refractive index profile. It is not widely appreciated that the ion-exchange process that creates the index profile also causes a radially symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here we show that this birefringence can be harnessed as a basis of a versatile and expandable vectorial state manipulator. Using standard GRIN lenses in cascade with other optical components, we generate various states, including full Poincaré beams that also contain orbital angular momentum. The combination of highly-symmetrical graded refractive index and corresponding birefringence – which benefit from the mature technology of the ion-exchange process – permit precise, simultaneous, phase and polarization modulation, which – when combined in a cascade structure with other elements – forms the basis for several applications. The non-pixelated nature of the birefringence of the lens, optical efficiency of the lens, and complex geometric phase inside the lens may also benefit future applications such as precision beam generation and quantum manipulation. All of these complex vectorial beam manipulations are achieved using off-the-shelf, inexpensive, passive optical components.
Intraoperative feedback on tissue function, such as blood volume and oxygenation would be useful to the surgeon in
cases where current clinical practice relies on subjective measures, such as identification of ischaemic bowel or tissue
viability during anastomosis formation. Also, tissue surface profiling may be used to detect and identify certain
pathologies, as well as diagnosing aspects of tissue health such as gut motility. In this paper a dual modality laparoscopic
system is presented that combines multispectral reflectance and 3D surface imaging. White light illumination from a
xenon source is detected by a laparoscope-mounted fast filter wheel camera to assemble a multispectral image (MSI)
cube. Surface shape is then calculated using a spectrally-encoded structured light (SL) pattern detected by the same
camera and triangulated using an active stereo technique. Images of porcine small bowel were acquired during open
surgery. Tissue reflectance spectra were acquired and blood volume was calculated at each spatial pixel across the bowel
wall and mesentery. SL features were segmented and identified using a ‘normalised cut’ algoritm and the colour vector
of each spot. Using the 3D geometry defined by the camera coordinate system the multispectral data could be overlaid
onto the surface mesh. Dual MSI and SL imaging has the potential to provide augmented views to the surgeon supplying
diagnostic information related to blood supply health and organ function. Future work on this system will include filter
optimisation to reduce noise in tissue optical property measurement, and minimise spot identification errors in the SL
pattern.
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