Chiral Liquid-Crystal-Based Concave Holographic Spectrometer on a Curved Substrate.

Chiral liquid crystals (CLCs) self-assemble into a helical structure and can efficiently reflect circularly polarized light with corresponding handedness. Utilizing a curved glass substrate and polymerization of photoaligned CLCs, the operation of focusing and diffraction of incident light can be performed efficiently by a single component. When focusing and diffraction in a planar CLC cell are combined between two glass plates, the imaging suffers from astigmatism in the resulting spectrum. In this work, we demonstrate the operation of a spectrometer with low astigmatism using a polymerized CLC layer on a curved substrate. Two samples are fabricated, and the resulting components are operating in the wavelength range of 500-650 nm. Numerical optical modeling is used to minimize transverse aberrations and obtain a highly linear mapping on a camera sensor. In this way, it is demonstrated that a single reflective thin-film optical CLC component with a thickness of only a few micrometers can be used to realize a compact and efficient spectrometer.