Photonic Polymers for Optical Switching
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ABSTRACT Photonic polymers and devices with improved performances are reported. Optical losses in electro-opic polymers below 0.5 dB/cm at 1.3 and 1.6 pm have been realized. Improvements in thermal stability have led to poled polymers exhibiting a relaxation time of 112 days at 125 0C. The thermo-optic switches reported here are close to the requirements in telecommunications, and electro-optic devices with low switching voltages and high extinction coefficients are described as well.
INTRODUCTION In the near future, photons are likely to take over several tasks currently performed by electrons. The use of optical switching will further increase the accessable bandwidth and functionality of optical networks, and guarantees transparency of the network as well. Both optical routing of high bit rate data streams, and high speed switching can be realized using integrated optical components. Based on newly developed photonic
polymers, we realized thermo-optic routing elements and electro-optic modulators and space switches. This paper presents developments in materials, design and device performance for polymer integrated optics.
POLYMER DEVELOPMENT The basic requirements of polymers for integrated optics applications can be well defined [11, and chemical engineers need to translate these properties into materials characteristics. The most critical issues are: low optical losses in the near-infrared, high nonlinear coefficients and a high thermal stability. Besides these performance characteristics, processability of the materials is of high importance. Since planar waveguides require at least a three-layer polymer system, deposition of second and third layers should be possible without adverse effects on the layers previously deposited. Furthermore, the polymer stack should be insensitive to lithographic processing, metallization etc. Hence, close cooperation between polymer chemists and materials users (clean-room operators) is a must for the development of suitable materials for polymer waveguide devices. 491 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
Low loss
Losses in polymers have two major sources: intrinsic losses due to optical absorption, and extrinsic losses due to scattering at imperfections. The first are dominant in most polymer waveguide systems reported thus far. Two different effects can be distinguished, absorption caused by the long wavelength tail of electronic transitions, and absorption caused by vibrational overtones in the infrared. To reduce the first contribution, nonlinear moieties in electro-optic polymers should have absorption maxima far away from the wavelength for its intended use. Most systems (DANS, diazo-dyes) have a Amax between 350 and 500 nm, which will cause no excess losses in the wavelength region between 1.3 and 1.6 pm. However, the vibrational overtones do cause significant losses in this wavelength region. Especially hydrogen bonds, such as O-H, N-H and C-H, significant absorptions. These can be eliminated by chemical modifications materials. S
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