Advances in Polarization Engineering

Abstract

Polarization plays an important role in many optical systems and device. This includes devices designed to advantageously use polarization, like liquid crystal displays, and optical systems that measure polarization to obtain information not otherwise available, like instruments found in many modern telescopes. Polarization also needs to be considered in some systems where it is not a primary aspect of the design, like image formation in very high numerical aperture objective lenses. This manuscript discusses three optical engineering projects where accurate polarization analysis or testing was required. Chapter one discusses a case where the need for polarization engineering arises from extreme optical requirements. Exoplanet direct imaging requires extremely high contrast, so any possible phase errors need to be considered. This includes the effects of form birefringence, which had previously not been measured over a large diameter mirror. Chapter one presents the first measurements of form birefringence over a large diameter telescope mirror. Measurements of the 3.75-meter, spherical mirror, coated by vacuum deposition of aluminum, indicate low levels of retardance and diattenuation that vary over the face of the mirror. The retardance and diattenuation had maximum values of about 2x10-3 radians and 0.025% respectively. Initial modeling by Davis J., et al. shows that this level of form birefringence could be impactful in direct imaging systems. The chapter discusses the design of the metrology system used to perform the measurements. The polarization engineering in chapter 2 relates to a remote sensing instrument that detects polarization to provide information in addition to its spectral reflectance measuring capabilities. Chapter two covers the design and testing of the second-generation polarization state generator used for the calibration and testing of Jet Propulsion Laboratory’s (JPL) air-based, multispectral polarimetric imager (AirMSPI). The chapter focuses on the requirements of a polarization standard. The first-generation instrument is analyzed carefully and the lessons learned are applied to improving the second. The updated version has been successfully used for AirMSPI calibration prior to multiple airborne science campaigns. The third chapter discusses the analysis and modification of a nominally non-polarizing optical sub-system that has polarization design requirements. This highlights important polarization issues that occur is systems containing a large number of surfaces. The issues with the systems polarization performance are identified. A method to improve the polarization performance that can be implemented without any additional calculations is demonstrated. The system is then modified to improve the polarization performance while maintaining other important optical properties. Finally, the manufacturability of the modified design is considered.