Directional couplers using fluorinated polyimide waveguides

Optical properties of directional couplers using a fluorinated polyimide waveguide were demonstrated. At a wavelength of 1.3 mu m, directional couplers with the,refractive index difference of 0.3% between the core and cladding have a maximum power coupling ratio of more than 97 and 96% for TE and TM polarizations, respectively. The excess loss for a 3-dB coupler was as low as 0.3 dB. Moreover, the change in the coupling ratio of the 3-dB couplers remained within 0.5% between 25 and 100 degrees C.