Diffractive Optics in the Infrared (DiOptIR) LDRD 67109 final report.

Abstract

This diffractive optical element (DOE) LDRD is divided into two tasks. In Task 1, we develop two new DOE technologies: 1) a broad wavelength band effective anti-reflection (AR) structure and 2) a design tool to encode dispersion and polarization information into a unique diffraction pattern. In Task 2, we model, design, and fabricate a subwavelength polarization splitter.The first technology is an anti-reflective (AR) layer that may be etched into the DOE surface. For many wavelengths of interest, transmissive silicon DOEs are ideal. However, a significant portion of light (30% from each surface) is lost due to Fresnel reflection. To address this issue, we investigate a subwavelength, surface relief structure that acts as an effective AR coating.The second DOE component technology in Task 1 is a design tool to determine the optimal DOE surface relief structure that can encode the light's degree of dispersion and polarization into a unique spatial pattern. Many signals of interest have unique spatial, temporal, spectral, and polarization signatures. The ability to disperse the signal into a unique diffraction pattern would result in improved signal detection sensitivity with a simultaneous reduction in false alarm.Task 2 of this LDRD project is to investigate the modeling, design, and fabrication of subwavelength birefringent devices for polarimetric spectral sensing and imaging applications. Polarimetric spectral sensing measures the spectrum of the light and polarization state of light at each wavelength simultaneously. The capability to obtain both polarization and spectral information can help develop target/object signature and identify the target/object for several applications in NP&MC and national security.