Status and perspective for molecular nonlinear optics: from crystals to polymers and fundamentals to applications

Over the past two years, the field of molecular nonlinear optics has benefited from both upstream rejuvenation (the emergence of new molecular engineering guidelines) and downstream application-oriented breakthroughs, helping to bring the field closer to industrial developments. In the fundamentals areas, traditional perspectives based on the paranitroaniline ‘molecular diode’ template are being enlarged to encompass three-dimensional multicharge transfer ‘multipolar’ systems with dipolarless ‘octupoles’, demanding that earlier models and experiments be thoroughly revisited. Furthermore, the relevance of polar structures primarily targeted towards quadratic nonlimear optics has been extended to cubic all-optical processes based on a cascaded sequence of quadratic processes. In the application domain, progress in crystal growth is best illustrated by the demonstration of low threshold pulsed near-IR optical parametric oscillators based on stable organic or organomineral crystals. Functionalized polymers have confirmed their current supremacy as organic optoelectronic device materials with the reports of low voltage electro-optic modulation in integrated waveguide structures and high modulation bandwidth.