Monocrystalline blue-phase liquid crystals for optical wave mixing and prospective applications in passive optical limiting and image processing

Recent advances in the synthesis of large areal size monocrystalline 3-D chiral photonic crystals based on blue-phase liquid crystals (BPLC) are briefly reviewed. Unlike their usual polycrystal counterparts formed by self-assembly, monocrystalline BPLC’s ensure crystal/optical-phase uniformity, leading to significant improvement in the overall image/signal quality and resolution as well as process efficiency in optical wave-mixing based real time holography and image processing. In general, optical nonlinearity (characterized by the intensity dependent index coefficient n₂ in cm²/Watt) of a transparent material is in inverse relationship to the response speed τ, i.e., n₂/τ is roughly a constant. Noteworthily, pristine and transparent BPLC’s having the same organic constituents as their 1-D cholesteric counterpart, possess effective optical nonlinearities near the band-edges that can be as high as 10^-11 to 10^-10cm²/Watt with a sub-picosecond [10^-13s or less] response time, i.e. n₂/τ~10² to 10³. This is two to three orders of magnitude larger than all other known transparent nonlinear optical materials. Special fabrication techniques of large areal size BPLC will be presented, along with their prospective use in ultrafast laser pulse modulation and polarization switching, wave mixing, passive optical limiting, free-space optical wave front conjugation and neural network-like image processing operation.