Properties of a Variable-delay Polarization Modulator

TL;DR

This paper studies the polarization modulation properties of a variable-delay polarization modulator (VPM), analyzing its behavior across different wavelengths and providing test results and electromagnetic simulations.

Contribution

It offers a comprehensive characterization of VPM response, including the effects of grid geometry and wavelength, supported by experimental data and circuit modeling.

Findings

Phase delay accurately describes VPM at long wavelengths.

Additional grid parameters are needed for shorter wavelengths.

Electromagnetic simulations match experimental results.

Abstract

We investigate the polarization modulation properties of a variable-delay polarization modulator (VPM). The VPM modulates polarization via a variable separation between a polarizing grid and a parallel mirror. We find that in the limit where the wavelength is much larger than the diameter of the metal wires that comprise the grid, the phase delay derived from the geometric separation between the mirror and the grid is sufficient to characterize the device. However, outside of this range, additional parameters describing the polarizing grid geometry must be included to fully characterize the modulator response. In this paper, we report test results of a VPM at wavelengths of 350 microns and 3 mm. Electromagnetic simulations of wire grid polarizers were performed and are summarized using a simple circuit model that incorporates the loss and polarization properties of the device.