Nonlinear optical polymer applicable for all-optical wavelength converters in communications bands near 1.5 Am Seung Koo Park a, * , Jung Yun Do b , Jung Jin Ju a , Suntak Park a , Min-su Kim a , Myung-Hyun Lee a a Basic Research Laboratory, Electronics and Telecommunications Research Institute, 161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-700, South Korea b Chemistry Education Major Division of Science Education, Pusan National University, 30 Jangjeon-dong, Geumjeong-gu, Busan 609-735, South Korea Received 21 March 2005; accepted 7 April 2005 Available online 25 May 2005 Abstract We prepared acrylic nonlinear optical (NLO) polymers that contained a chromophore with a k-conjugated imine bridge between phenyl and benzothiazole groups, 2-(methyl-{4-[(6-nitro-benzenothiazol-2-ylimino)-methyl]-phenyl}-amino)-ethanol, for all-optical wavelength converters in optical fiber communication. The glass transition temperature (T g ) of the copolymers is between 130 and 143 -C. The molecular weights of the copolymers are comparatively high for obtaining films. An NLO polymer film containing ca. 30 mol% of chromophore shows a high second-order nonlinear optical coefficient (d 33 ) at 1.55 Am, 35 pm/V, as well as a low optical loss at about 0.775 Am, 3.9 dB/cm. The aligned dipole orientation in the film is comparatively thermostable. The deformation difference between the centers of the poled and unpoled regions after periodic poling for quasi-phase matching (QPM) is small, which lessens the light scattering loss. D 2005 Elsevier B.V. All rights reserved. Keywords: All-optical wavelength converter; NLO polymer; Imine; Second-order nonlinear optical coefficient; Optical loss 1. Introduction A wavelength converter is one of the key devices for constructing optical cross connects in wavelength-division multiplexed networks [1]. Difference frequency generation (DFG) is well matched to the wavelength-division multi- plexing architecture because of its properties of multi- channel conversion, low noise, high speed, and good transparency. Several inorganic crystals such as LiNbO 3 and AlGaAs have been employed successfully for this purpose [2,3]. Nonlinear optical (NLO) polymers have been actively developed as substitutes for the inorganic crystals because the properties of these polymers include high nonlinearity, easy waveguide fabrication, and flexible wave- guide design. At the same time, an NLO polymer wave- guide exhibits high optical losses at communication wavelengths because of the intrinsic material absorption caused by the vibration overtones of the polymer main chain and the chromophore [4] and because of the scattering loss caused by poling processes and waveguide fabrications [5]. No results on DFG from a polymeric waveguide have been reported due to these critical disadvantages. Laser frequency doubling at fundamental beam wavelengths of 1.064 and 1.5 Am from NLO polymer waveguides with high losses at wavelengths of second harmonic (SH) beams of the fundamental beams or a low second-order nonlinear optical coefficient (d 33 ) at wavelengths of the fundamental beams has been already reported [5–7]. Quasi-phase matching (QPM) [8], in which light waves are intentionally driven to an interaction with a periodic structure of a nonlinear material, was introduced for obtaining second harmonic generation (SHG) and DFG. Our group has recently reported on SHG from a periodically poled NLO polymer waveguide [9]. This RDAS ((4-{2-[4- (butane-1-sulfonyl)-phenyl]-vinyl}-phenyl)-diethyl-amine) side-chain polymer that we have developed shows com- paratively low optical losses at wavelengths of 1.55 (pumping beam) and 0.775 Am (SH beam of the pumping 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.04.032 * Corresponding author. Tel.: +82 42 860 5162; fax: +82 42 860 6248. E-mail address: skpark@etri.re.kr (S.K. Park). Materials Letters 59 (2005) 2872 – 2875 www.elsevier.com/locate/matlet