Properties of a variable-delay polarization modulator

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 µm 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.

Note: Vector reflectometry in a beam waveguide

“…The deviation of this point from d/λ ∼ 0.75 is expected due to the phase shift of the grid circuit. 16 The null is measured at a depth of −50 dB which is higher than predicted by the simple model that is limited only by ohmic losses in the grid-mirror structure. We find a 0.1 • misalignment in angle of the grid relative to the axis of the OMT is sufficient to explain the measured effect.…”

The Balloon Experimental Twin Telescope for infrared interferometry (BETTII): first flight

“…The CDL was designed using heritage from other Goddard-developed mechanisms 13,14 , and was successfully tested both in the lab and in flight. During normal operation, the CDL carries out a scan every 3 seconds.…”

Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

“…To capture details of the VPM operation beyond the ideal model, we implement a transmission-line model for the VPM based on Chuss et al (2012). The two main manifestations of the improved fidelity of the transmission-line model over the ideal model are: (1) a small modification of the distance/phase relation in Equation (3); and (2) precise treatments of the polarization isolation and finite absorptance of the VPM's components.…”

“…We have implemented the transmission line model described by Chuss et al (2012) using a grid having 50 μm diameter wires on a 110 μm center-to-center wire spacing. The surface of the wire is copper with a conductivity of´-6 10 S m 7 1 · .…”