9634268 Thakur A major objective of this project is to demonstrate picosecond all-optical logic and optical bistability using the large off-resonant nonlinear refractive indices of specific organic single crystal films. The overall project objectives include: i) preparation of single crystal films and device microstructures of organic second and third order optical materials, ii) detailed studies of the off-resonant nonlinearities of the films and, iii) demonstration of devices including phase-matched SHG in waveguides, all-optical and electro-optic switching and logic. The nonlinear optical studies will include polarization dependent SHG and electro-optic effects in second order optical films and time and wavelength resolved nonlinear refractive index measurements for the third order optical films. The mechanisms involved in the off-resonant third order processes will be elucidated and picosecond all-optical logic will be demonstrated using specific organic materials and device geometries. Utilizing organic films of very large second order nonlinearities, electro-optic switching and logic will be demonstrated. Specific conjugated polymers such as polydiacetylenes are known to have extremely large nonlinear refractive indices along with low absorption coefficients in the off-resonant domain. Such large nonlinearities are obtained only if the polymer chains are organized as a single crystal. Specific organic molecular crystals (e.g. NPP, DAST have very large and stable second order nonlinearities which can be utilized in many applications (e.g. SHG for infrared diode lasers, electrooptic switching), if single crystal films and waveguides can be prepared. A method ("shear method" and its modified version) that the principal investigator has established, will be utilized for the preparation of single crystal films of the organic second and third order optical materials. Subsequently specific device microstructures in the Fabry-Perot etalon and waveguide geom etries will be fabricated using the films. The nonlinear optical measurements in the films and waveguides will be performed using established procedures. Recently, we have demonstrated all-optical switching using the off- resonant nonlinearity of a polydiacetylene film, placed in a Fabry-Perot cavity. The measured switching time was limited by the pulse-width (30ps) that was used. Detailed measurements involving all-optical logic and bistability will be performed in this proposed work using ! picosecond and sub-picosecond pulses. Ultrafast all-optical switching and logic in a compact device geometry should have a variety of future applications in photonics. Single crystal films and waveguides of organic materials having very large second order nonlinearities are expected to have near-term applications in frequency conversion and electro-optics. The research as proposed is important for fundamental understanding of these off-resonant nonlinear optical effects and for realizing many practical applications. ***
