Polarimetry Using Liquid Crystal Variable Retarders

The paper introduces a novel approach to high-precision Stokes polarimetry using liquid crystal variable retarders (LCVRs) instead of mechanical rotating waveplates or intensity-splitting techniques. The commercialized Stokes polarimeter achieves superior accuracy, measuring polarization states with uncertainties under ±2×10⁻³. The system is evaluated against a traditional photodetector, showing discrepancies within ±0.3° for linear polarization angles.

Polarization refers to the orientation of the electric field in a light wave, providing diagnostic insights across fields like remote sensing, spectroscopy, and materials science. The authors describe an LCVR-based polarimeter that offers mechanical simplicity, precision, and dynamic polarization measurement without signal reduction or vibration sensitivity.

Stokes parameters (S0, S1, S2, S3) represent the full polarization state: S0 is total light intensity; S1 indicates horizontal versus vertical linear polarization; S2 represents ±45° linear components; S3 describes right versus left circular polarization. Derived parameters, such as Degree of Polarization (DOP), Degree of Linear Polarization (DOLP), and Degree of Circular Polarization (DOCP), depend on these components.

The liquid crystal polarimeter features two LCVRs that sequentially vary retardance. This setup avoids mechanical rotation, providing low-voltage operation (~10V) compared to Kerr or Pockels cells and enables direct measurement of Stokes components through a time-dependent Mueller matrix model.

Polarimetric measurements involve fitting detected intensity signals to theoretical models using least-squares methods. Calibration requires known polarization inputs (horizontal, vertical, ±45°, circular) to derive optical response functions for accurate Stokes vector determination.

Empirical tests yield mean uncertainty values for Stokes parameters as follows: S0 (5.21×10⁻⁴), S1 (5.95×10⁻⁴), S2 (4.32×10⁻⁴), and S3 (1.65×10⁻³). Error propagation shows minimal sensitivity in DOP calculations but higher variability in azimuthal angle determinations for near-circular states.

The liquid crystal polarimeter’s precision was validated by comparing linear polarization angles with those obtained from a polarizer and photodetector. Agreement within ±0.3° demonstrates its reliability and minimal systematic error.

The liquid crystal-based polarimeter from Meadowlark Optics offers high accuracy, robust calibration, and non-mechanical operation, making it suitable for sensitive optical applications. Future publications will detail theoretical uncertainty derivations. Keywords include polarimeter, polarization, birefringence, liquid crystal variable retarder (LCVR), Stokes vector, Mueller matrix, and photonics instrumentation.