Polarization purity and cross-channel intensity correlations.

Area of Science:

• Optics and Photonics
• Remote Sensing
• Polarimetry

Background:

• Measuring polarization purity is essential for optical instruments.
• Existing methods often require phase-sensitive receivers, which are difficult at optical frequencies.
• A prior result related complex field correlation to polarization errors for phase-sensitive receivers.

Purpose of the Study:

• To generalize previous findings on polarization purity monitoring to phase-insensitive measurements.
• To derive a new equation for polarization alignment error using intensity cross-correlation.
• To provide a practical method for assessing polarimeter and depolarizer quality.

Main Methods:

• Derivation of a new equation relating polarization errors (δτ, δε) to the intensity cross-correlation coefficient (ρ(2)).
• Analysis of unpolarized radiation.
• Consideration of specific cases for linearly and circularly polarized bases.

Main Results:

• A new equation for polarization alignment error: cos²(2ϵ)δτ²/2 + δε² ≈ ρ(2).
• Demonstration that only real intensity cross-correlation measurements are needed for unpolarized light.
• Simplified expressions for tilt error (δτ ≈ ρ(2)) in linear polarization and ellipticity error (δϵ ≈ ρ(2)) in circular polarization.

Conclusions:

• The derived method offers a simple and practical way to monitor polarization purity.
• This approach is valuable for evaluating the performance of polarimeters and depolarizers.
• The results are applicable to unpolarized light, overcoming limitations of phase-sensitive techniques.