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X(3)

These polymers have excellent potential for use in fabrication of optical switching devices.

1. INTRODUCTION Future telecommunication systems will require all-optical signal processing devices such as ultrafast optical switches and bistable devices. These kind of photonic devices have already attracted considerable attention as key elements for future optical signal processing systems [I]. Highly efficient third-order nonlinear optical (NLO) materials are a key factor for this purpose. For actual device applications, NLO materials should satisfy several requirements as shown in Fig. 1. Low linear loss of less than 1 dB/cm and high processability with the potential for singlemode channel waveguide fabrication are as important as large optical nonlinearity. Polymeric materials are of particular interest because of their potentially fast response time and high damage threshold [2]. Although optical nonlinearity of polymeric NLO materials is limited to 10-9-10-10 esu, channel waveguides must be fabricated for actual device application. To date, the most frequently studied materials have been it-conjugated polymers such as 449 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society

polydiacetylenes and polyacetylene [2]. Although large third-order NLO susceptibilities have been observed in the crystalline states or uniaxially oriented films of these polymers, their high crystallinity results in large light scattering. Furthermore, these polymers are not highly processable because of their infusiblility and insolubility in almost all solvents. Also, they have low transparency because of their light scattering loss. Thus, these factors have precluded their use in optical waveguide devices. The authors have already developed novel highly processable NLO polymers [3]. These new polymers are main-chain polymers in which the nonlinearity generating dyes are actually a part of the polymer backbone. The third-order nonlinear optical properties, X(3), of these polymers have already been investigated. These main chain polymers are one possible candidate for the fabrication of optical waveguides with a large X(3) value because the polymer can contain NLO dyes in high concentrations. There are several papers about main chain X(3) materials such as iTelectron conjugation containing vinyl polymers [4] and aromatic schiff-base structure based X(3) polymers [5]. We have also proposed heteroaromatic polymers as a possible material for the above mentioned purpose [6]. In this paper, we will report on two types of processable NLO polymers, main-chain polymers and heteroaromatic polymers, as possible materials for the purpose. These new polymers are easy to fabricate from solution to amorphous films by conventional spin-coating or casting methods. The z(3) wavelength dependence of these polymers is investigated using thirdharmonic generation (THG) measurements.

(Large optical nonlinearity) Device -application

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The heteroaromatic polymers investigated in this paper are it-conjugated polymers where n-electron e