Low-loss Tunable Optical Filters
In this project we create a polarization independent tunable optical filter with potential for low cost and compact implementation for applications including compactspectroscopy and hyperspectral imaging. The basic approach involves the use of tunable Polarization Gratings (PGs) in a stacked configuration analogous to Lyot or Solc Filters. The PGs are tuned by electrical control of their birefringence to create a passband filter without the use of polarizers, thereby allowing very high overall transmittance (~100%).
Motivation and Approach
The basic design involves layering at least three PGs of varying thicknesses and then collecting the zero-order transmittance. The overall transmittance of the stack can be described as a multiplication of the zero-th order efficiencies of each individual component. When properly tuned to a given design wavelength, this filter stack can produce a narrow pass band with very high transmittance. The key aspect of this approach is that we do not use any polarizers within the system.
This tunable optical filter will be completely independent of input polarization, which significantly improves maximum peak transmittance as compared to polarizer-based filters. We also show a potential for highly compact implementation for a variety of applications including compact spectrometry and imaging spectroscopy.