Highly efficient and stable nonlinear optical polymers via chemical cross-linking under electric field

Abstract

Extending the novel method of Eich et al. [J. Appl. Phys. 66, 3241 (1989)] to prepare highly stable second-order nonlinear optical (NLO) polymers via chemical cross-linking under electric field, we have obtained a new polymer exhibiting large and stable second-order optical nonlinearities after relaxation at 80 °C. This was achieved by forming a network polymer from two NLO-active monomers, bifunctional N,N-(diglycidyl)-4-nitroaniline and trifunctional N-(2-aminophenyl)-4-nitroaniline. Here, every NLO moiety is connected to the network by a single covalent bond. After full cure under corona poling at 120 °C, the sample exhibited at ambient conditions d33≂50 pm/V and d31≂16 pm/V at 1064 nm fundamental wavelength, as estimated from the Maker fringe data. Upon heating to 80 °C, the nonlinearities decreased somewhat initially, but leveled off and remained stable at 80 °C. This stable sample gave d33≂42 pm/V and d31≂14 pm/V at ambient conditions. Furthermore, the linear electro-optical coefficient of this sample, measured with a Mach–Zehnder interferometer, was r13≂6.5 pm/V at 530.9 nm. From this r13 coefficient one estimates d31≂11 pm/V at 1064 nm, in good agreement with the Maker fringe value.

Thickness dependence of second-harmonic generation in thin films fabricated from ionically self-assembled monolayers

“…As a result of the ionic attraction between successive layers, the ISAM (2) films self-assemble into a noncentrosymmetric structure that has exhibited no measurable decay of (2) at room temperature over a period of more than one year. The second-harmonic intensity of the films exhibits the expected quadratic dependence on film thickness up to at least 100 bilayers, corresponding to a film thickness of 120 nm.…”

“…As a result of the multitude of potential frequency conversion, optical modulation, and optical switching applications that stem from the (2) second-order susceptibility, several novel methods for creating noncentrosymmetric materials incorporating organic molecules with large ␤ molecular susceptibilities have been developed over the past decade. These include electric-field poled polymers, [1][2][3] Langmuir-Blodgett films, [4][5][6] and covalent selfassembled monolayer structures. [7][8][9] We report here detailed studies of a ionically self-assembled monolayer technique for the creation of noncentrosymmetric organic thin films with substantial (2) values.…”

“…The ISAM method involves the alternate dipping of a charged substrate into an aqueous solution of a cation followed by dipping in an aqueous solution of an anion at room temperature. Using commercial ionic polymer dyes, the ISAM technique has been used to produce a noncentrosymmetric arrangement of nonlinear optical ͑NLO͒ chromophores to yield thin films with (2) values comparable to that of quartz. Importantly, the second-harmonic intensity generated by the films exhibits the expected quadratic dependence on film thickness for films as thick as 100 bilayers.…”

“…͑Received 29 June 1998; accepted for publication 17 November 1998͒ An ionically self-assembled monolayer ͑ISAM͒ technique for thin-film deposition has been employed to fabricate materials possessing the noncentrosymmetry that is requisite for a second-order, (2) , nonlinear optical response. As a result of the ionic attraction between successive layers, the ISAM (2) films self-assemble into a noncentrosymmetric structure that has exhibited no measurable decay of (2) at room temperature over a period of more than one year.…”

“…These include electric-field poled polymers, [1][2][3] Langmuir-Blodgett films, [4][5][6] and covalent selfassembled monolayer structures. [7][8][9] We report here detailed studies of a ionically self-assembled monolayer technique for the creation of noncentrosymmetric organic thin films with substantial (2) values. The advantages of this technique include simple, rapid, inexpensive production, and long-term stability of the induced (2) without the need for additional processing such as electric-field poling or chemical reactions.…”