Hyung-jae Lee

Low‐loss passive polymer waveguides by using chlorofluorinated polyimides

Chlorofluorinated polyimides were prepared from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 2,2′-dichloro-4,4′-diaminobiphenyl (DCB) for optical waveguide applications. The resulting optical polymers exhibited good thermal stability, controllable refractive index, and low optical loss in the optical communication wavelengths of 1.3 and 1.55 µm. The control of refractive indices of the polymers was achieved by copolymerization of 6FDA/PFMB and 6FDA/DCB. As the amount of DCB was increased, the refractive indices of polymer were increased. The effect of addition of chlorine on optical properties of polymers such as absorption loss in the near-IR region were also investigated. Rib-type optical waveguides were fabricated using these chlorofluorinated polyimides. These waveguides exhibited low loss of less than 0.4 dB/cm for both TE and TM polarizations.

Evaluation of fluorinated polyimide etching processes for optical waveguide fabrication

Fluorinated polyimides have attracted much attention as potential materials for optical waveguide fabrication due to their high thermal stability, humidity resistance, as well as low optical loss in the wavelength region of optical communications. For the fabrication of optical waveguide structures, reactive ion etching (RIE) has been widely used. According to our study, the highest etch rate obtained with vertical profile for RIE of fluorinated polyimides with O 2 plasma was 300 nm/min. Inductively coupled plasma (ICP) etching of Ultradel® 9020D fluorinated polyimide has been conducted to obtain waveguide channels with higher etch rate and more vertical profile than is possible with RIE. The etch rate and the etch profile have been investigated as a function of ICP power, r.f. chuck power, O 2 flow rate, and chamber pressure. Etch rates of 1700 nm/min to 2200 nm/min with vertical profile and smooth sidewall were obtained by ICP etching at an ICP power of 500 W, r.f. chuck power of 150 W to 350 W, chamber pressure of 5 mTorr and O 2 flow rate of 40 sccm. Under these conditions there was no appreciable change in the etch rate with chamber pressure in the range 5-20 mTorr.