Nonlinear optical properties of chromophore-functionalized polymeric materials

Abstract

ABSTRACT Nonlinear optical (NLO) properties of chromophore-functionalized polymeric materials (dye-attached sid echain polymers and dye-introduced main chain polymers) are discussed. These polymers show promise for use in NLO devices because of their processability, transparency and thermal stability. A dicyanovinyl-terminated methyl-substituted diazo dye-attached methacrylate copolymer (3RDCVXY), which is newly synthesized by the authors, is investigated for its second and third-order NLO properties. The βμ g (β: second-order nonlinear optical molecular susceptibility, μg:dipole moment) value of 3RDCVXY is greater than that of a previously reported nitro-substituted diazo dye (3RNO 2 ) and a monoazo dye (2RNO 2 ) from 1-06 to 1-70 μm wavelengths. The methyl-substitution is effective for increasing the dye content in the copolymer and as a result the content of the 3RDCVXY dye is nearly 2 times larger than that of the 3RNO 2 dye. The second-order nonlinear optical coefficient (χ (2) ) measurement of the polymers as a function of fundamental wavelength reveals that the maximum χ (2) of 3RDCVXY reaches 1.0 × 10 −6 esu, which is larger than those of 3RNO 2 and LiNbO 3 by 3 and 7 times, respectively. A thermal aging test shows that the χ (2) of 3RDCVXY is stable even at 80°C for more than 6 months. 3RDCVXY can, therefore be, used as a material for optical devices. A traveling wave phase modulator is fabricated using 3RDCVXY. To date a half wave voltage of 5V has been obtained for a 15 mm channel waveguide with an r 33 of 40 pm/V at 633 nm, which is larger than that of a LiNbO 3 . From the χ (2) value, a half voltage of less than 2V is possible by refining the modulator fabrication process. An application as a highly sensitive electric field sensor for internal electrical signal measurement in ICs is also discussed. The third-order nonlinear optical coefficient (χ (3) ) of 3RDCVXY reaches 5 × 10 −11 esu at the near resonant region. This value is almost the same as that of 3RNO 2 . With polymers where the dye molecules are introduced into the polymer backbone (a main chain polymer), a χ (3) larger than 10 −11 esu is obtained even in a monoazo dye introduced polymer. From this point of view, main chain polymers are promising for the development of large χ (3) processable material.