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84 PCB007 MAGAZINE I JANUARY 2021 • Well established—A huge body of data was obtained over the last 100 years on polymers including all the popular photoresists • Useful—Unique properties you cannot get anywhere else (such as bend radius, modulators, and index tuning); and unique processing options (such as photolithographic, RIE, direct laser writing, molding, and printing) Polymers also have a number of disadvan- tages: • Unstable—Many have low thermal stability (POF below 80°C) with photodegradation and are sensitive to delamination, moisture and chemicals • Unknown—New materials require new processes, equipment and experience • Useless—Some polymers have losses of POF of 20 dB/km, while optical glass is <0.1 dB/km. The packaging cost of polymers is 80% of the cost in devices Candidate materials are acrylates, haloge- nated acrylates, cyclobutenes, polyimides and polysiloxane. Some of the most popular are listed in Table 1. The optical losses of the poly- mers (dB/cm) are in the lower wavelengths near 840nm. Industrial Optical Waveguide Materials Six materials have emerged in the literature from seven commercial companies: • PDMS (polydimenthylsiloxane) from Wacker • Chamie and Dow Corning- OE4140 • Photodefinable acrylate from Exxelis- Truemode Table 1: Candidate polymers for optical waveguides. (Source: Lucent Technologies and Loughborough University.)