Diffractive Filters with Liquid Crystals for Spectral and Polarization Engineering

Liquid crystal displays (LCDs) demonstrate several basic features of liquid crystal filters – high contrast, electrically tunable in a wide spectral and dynamic range with high spatial resolution, and the capability of aperture sizes comparable to the Hubble Space Telescope at the price of an average 1” bandpass filter found in a common industrial optics catalogue. LCDs, in essence, are electrically tunable half-wave retardation plates sandwiched between polarizers. No polarizers are needed, however, for controlling transmission spectra when the LC alignment is modulated across the panel, thereby modulating the phase of circularly polarized components of light propagating through it.

The combination of electrical tunability, large aperture scalability and programmable spectral and polarization control make these LC-based filters particularly attractive for emerging biophotonic imaging platforms, where rapid wavelength selection, compact form factors, and high optical efficiency are increasingly important.

Such diffractive waveplates represent a new generation of optical elements wherein near-unity diffraction efficiency can be achieved in micrometer-thick films that could be combined, just like conventional waveplates, to produce desired polarization distribution, hence, the diffraction spectra of light. LC polymers are best adapted for obtaining complex polarization and spectral filtering functions. Those functions can be combined with other optical functions while maintaining high efficiency and a compact form factor. Thus, thin planar structures have been demonstrated that deflect one wavelength band without affecting another, and lenses that focus only red, green or blue have been developed for multispectral imaging.

Self-organizing monolithic LC diffractive bandgap structures allow overcoming some of the manufacturing challenges of multilayer dielectric coatings wherein dozens of layers need to be deposited with nanometer precision and even small errors in thickness or refractive index variations accumulate, degrading performance. Such LC structures also mitigate the adverse effects of thermal expansion between dielectric layers and intrinsic film stresses while providing adhesion to all types of substrates.

Tabiryan will present and discuss technology opportunities for both transmissive and reflective LC filters, emphasizing their applicability from the UV to the MWIR spectral regions, enhanced radiation tolerance due to their non-absorptive nature, environmental robustness enabled by their monolithic structure, and rapid customization for controlling polarization, spectrum, and topological charge.

About the presenter
Nelson Tabiryan, Ph.D., is the CEO of Beam Engineering for Advanced Measurements Corporation (BEAM Co.) co-founded with Dr. Boris Zeldovich in 1996. The company pioneered and is leading the development of the Fourth Generation Optics technology having demonstrated the first large aperture and electrically switchable geometrical phase planar lenses and related breakthrough optics and photonics components and devices for augmented reality glasses, non-mechanical beam steering systems for auto-navigation, free-space optical communication, high energy laser beam control systems, and for other emerging applications.

Tabiryan earned a doctorate in physics and mathematics, is OSA Fellow, NIAC Fellow, recipient of the Frederiks Medal, and the American Chemical Society’s Cooperative Research Award (with T.J. Bunning and T.J. White). He is the chairman/co-chairman, program committee member, keynote, plenary and invited speaker in numerous conferences with over 300 published papers and 50 issued patents covering all key aspects of liquid crystal geometrical phase optics.