Revisiting organic optical nonlinearity leads to a new class of materials

In the late 1980s and 1990s, researchers in industry and academia became captivated by so-called organic nonlinear optical (ONLO) materials, as is evident from SPIE Proceedings of that period. The ultrafast response of the π-electrons of ONLO materials to time-dependent electric fields—which translates into active control of light—clearly afforded a unique opportunity vis-à-vis ultrahigh (terahertz) bandwidth devices for information processing, computing, and sensing. The secondand third-order nonlinearities of ONLOmaterials also promised radically enhanced performance. But the quantum and statistical mechanical theoretical methods needed to realize these advantages still had to be worked out.1, 2 Also, auxiliary material issues, including optical loss, thermal stability, and photostability, were neglected. Moreover, the processing advantages of ONLO materials, e.g., amenability to low-temperature techniques such as nanoimprint lithography3 and compatibility with a wide range of disparate other materials and device architectures,4–6 have only just begun to be explored and demonstrated. As a result, application of ONLO materials never moved past the prototype stage, and most companies abandoned their research and development efforts in the area. Lockheed Martin appears to be the noticeable exception: since 2000 the company’s researchers have made substantial progress in understanding optical loss.7, 8 Now, greater understanding of electro-optic activity and auxiliary issues, together with improved performance, has led to renewed attention to ONLO materials. This interest is heightened by their amplified response in devices with nanoscopic dimensions (e.g., slotted silicon photonic devices such as ring microresonators4). Electro-optic coefficients in the range of Figure 1. The exceptional linear and nonlinear optical properties of BCOGs. (Left) The variation of normalized electro-optic activity (r33/Epol , where r33 is the principal element of the electro-optic tensor and Epol is the applied electrical poling field) with number density is shown for doping of the YL124 chromophore into different host materials. These are, respectively, a DR1-co-PMMA polymer (structure shown at the bottom right) and a multi-chromophore-containing dendrimer denoted as PAS41.1, 2 The doping leads to dramatic enhancement of electro-optic activity. (Right) BCOGs are also characterized by the absence of spectral line broadening and solvatochromic shifts, as shown in the graph. Abs: Absorption.