Vectorial properties of light beams and illuminated objects have long been a subject of scientific exploration, exploited in a wide range of techno­logical appli­cations from bio­medical optics to multiphoton lithography. Such properties can be described using either a Jones matrix or a Mueller matrix (MM). While the Jones matrix is typically used for dealing with fully polarized light interference, the MM contains 16 elements that can compre­hensively represent the polari­zation charac­teristics or vectorial properties of a given object.

Although the MM provides abundant information, the elements are not well-defined. They must be unpacked or decomposed to extract the specific polarization parameters. Current research directions in MM decom­position aim to extract meaningful metrics that can provide useful vectorial information for related applications, such as exotic material charac­terization or precise cancer boundary detection. An inter­national team of researchers recently collaborated to develop a new framework for describing a class of vectorial metrics that can be extracted from the MM. The newly demons­trated framework establishes a universal metric, derived from subsets of the MM elements. This is used to calculate different vectorial metrics that represent different physical properties of the sampled target object.

Intuitively speaking, the framework is like a cabinet with drawers, where each drawer offers a different metric, available to benefit a variety of applications. All the elements inside all the drawers are all the different combinations of Mueller matrix elements. Through the framework, the metrics become available to serve a variety of functions. For instance, they can 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.

Aside from those applications in which the metrics mainly reveal information about the target, the new framework also intro­duces other possible roles for the metrics. Chao He from Oxford University’s Department of Engi­neering Science offers an example of a new role: “By optimizing the value of a specific metric, passive polari­zation aberration compen­sation can be achieved. In our demonstration, we use the vectorial metric value as an indicator to model a compen­sation in optical design that can eliminate the polari­zation distortion created by the intrinsic birefringence of the GRIN lens.” In addition to potential roles for the formal symmetry/­asymmetry metrics, He and his colleagues suggest prospects for exploring new metrics. This work provides intriguing insights into different uses of vectorial metrics. Vec­torial metrics and their roles present a vast research area to be explored, with a broad horizon of potential future applications. (Source: SPIE)

Reference: C. He et al.: Revealing complex optical phenomena through vectorial metrics, Adv. Phot. 4, 026001 (2022); DOI: 10.1117/1.AP.4.2.026001

Link: Dynamic Optics and Photonics, Dept. of Engineering Science, Oxford University, Oxford, UK