The ability of nonlinear optical materials to transmit, process and store information forms the basis of emerging optoelectronic and photonic technologies. Organic chromophore-containing polymers, in which the refractive index can be controlled by light or an electric field, are expected to play an important role.

Design and synthesis of chromophores and polymers for electro-optic and photorefractive applications

The current state of materials development in nonlinear optics is summarized, and the promise of these materials is critically evaluated. Properties and important materials constants of current commercial materials and of new, promising, inorganic and organic molecular and polymeric materials with potential in second- and third-order nonlinear optical applications are presented.

https://science.sciencemag.org/content/sci/253/5017/281.full.pdf

Nonlinear optical materials.

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

A simple reflection technique for measuring the electro‐optic coefficient of nonlinear optical polymeric films is described. The technique is based on the polarization rotation of a laser beam due to the electro‐optic effect. It requires no waveguiding and can be used to measure polymeric films during, as well as after, the electrical poling process. The results are in excellent agreement with those obtained from the more conventional but much more time consuming waveguiding method.

Simple reflection technique for measuring the electro‐optic coefficient of poled polymers

A two-state, four-orbital, independent electron analysis of the first optical molecular hyperpolarizability, β, leads to the prediction that |β| maximizes at a combination of donor and acceptor strengths for a given conjugated bridge. Molecular design strategies that focus on the energetic manipulations of the bridge states are proposed for the optimization of β. The limitations of molecular classes based on common bridge structures are highlighted and more promising candidates are described. Experimental results supporting the validity of this approach are presented.

https://science.sciencemag.org/content/sci/252/5002/103.full.pdf

Approaches for Optimizing the First Electronic Hyperpolarizability of Conjugated Organic Molecules

We report the observation of second harmonic generation in a new class of organic polymeric materials, namely, electric field poled polymer glasses. Both the observed second harmonic coefficient (d33=6.0±1.3×10−9 esu, at 1.58 μm wavelength) and the poling process are described by a thermodynamic model that we have developed. The ability to form thin films from these materials may qualify them for integrated optics applications.

Second harmonic generation in poled polymer films

Electro‐optic phase modulation was measured along with optical second‐harmonic generation in thin films of a new copolymer containing a dicyanovinyl‐terminated azo dye side chain Orientational order was imparted to these films by poling with a corona discharge Details of the electro‐optic measurement technique, in which the real part of the electro‐optic coefficient can be determined directly, are presented Taking advantage of the increased orientation imparted by corona poling and the hindered motion of the nonlinear optical moiety in the side chain of the polymer leads to substantial improvements in both the magnitude and stability of nonlinear optical susceptibilities compared to guest‐host polymer systems ordered by electrode poling

Electro-optic phase modulation and optical second-harmonic generation in corona-poled polymer films

An electrooptic or optical parametric device comprises a noncrystalline second order optically nonlinear element and means for providing an optical input to and an optical output from said element wherein said element comprises an organic molecule having second order optical susceptibility incorporated in a directionally oriented manner in an optically clear glassy polymer. When said device is employed in an electrooptic mode it includes means for applying an electric field and/or optical input to said element for altering an optical property thereof.

Nonlinear optical materials and devices

A new class of organic quinoid systems possessing intrinsically large, nonlinear second‐order optical susceptibilities has been developed based on theoretical calculations and dc‐induced second‐harmonic generation measurements of the molecular second‐order optical susceptibilities β. For one example, 2‐(4‐dicyanomethylenecyclohexa‐2, 5‐dienylidine)‐imidazolidine (DCNQI), βx = −240±60×10−30 cm5/esu. The unusually large magnitude and sign originate from certain charge‐correlated features in the quinoid ground and excited states.

S. J. Lalama

Papers

Second harmonic generation in poled polymer films

Electro-optic phase modulation and optical second-harmonic generation in corona-poled polymer films

Nonlinear optical materials and devices

Exceptional second-order nonlinear optical susceptibilities of quinoid systems

First single-crystal polymers exhibiting phase-matched second-harmonic generation (A)