Abstract
We show that, under the right conditions, one can make highly accurate polarization-based measurements without knowing the absolute polarization state of the probing light field. It is shown that light, passed through a randomly varying birefringent material has a well-defined orbit on the Poincar sphere, which we term a generalized polarization state, that is preserved. Changes to the generalized polarization state can then be used in place of the absolute polarization states that make up the generalized state, to measure the change in polarization due to a sample under investigation. We illustrate the usefulness of this analysis approach by demonstrating fiber-based ellipsometry, where the polarization state of the probe light is unknown, and, yet, the ellipsometric angles of the investigated sample (Ψ and Δ) are obtained with an accuracy comparable to that of conventional ellipsometry instruments by measuring changes to the generalized polarization state.
Highlights
Polarization-based measurements are increasingly important, both as a fundamental tool for scientific research [1,2,3,4,5,6,7,8], and as a vital tool for applications in the chemical, food, and pharmaceutical industries
Fiber-based ellipsometry and polarimetry have relied on rather complicated experimental apparatus [20, 21], use a wavelength that is only supported by one polarization mode in a polarization maintaining (PM) fiber [22], or only provide qualitative information [23]
The core discovery that we present in this paper is that, given an input polarization state of light and an optical fiber that is subject to environmentally induced birefringence variations, the output state does not map to every point on the Poincare sphere, but rather, only a discrete set of polarization states are accessible
Summary
Polarization-based measurements are increasingly important, both as a fundamental tool for scientific research [1,2,3,4,5,6,7,8], and as a vital tool for applications in the chemical, food, and pharmaceutical industries. It is generally thought that, in order to make polarization-based measurements, one must know the polarization state of the probing light field throughout the optical train, and, especially, the polarization state of the light incident on the surface of interest. The corollary to this is that the use of optical components that disturb the polarization (e.g., optical fibers) require calibration, and, in the case of optical fibers, where temperature and stress induced birefringence have a large influence on the polarization state, this is not possible in all but the most limited circumstances. Fiber-based ellipsometry and polarimetry have relied on rather complicated experimental apparatus [20, 21], use a wavelength that is only supported by one polarization mode in a PM fiber [22], or only provide qualitative information [23]
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