Microheater control of wavelength-flattened fiber coupler properties

A novel process is proposed for fusing and tapering a fiber coupler with a microheater, and the conditions for fabricating wavelength-flattened fiber couplers with this method are established. This microheater could be used to obtain fiber-processing temperatures near 1700 °C in air. Fibers with cladding diameters of 125 and 107 µm were used. The peak coupling ratio was controlled quantitatively and increased exponentially with increases in fusing time at each temperature. The average excess loss at 1.55 µm was 0.05 dB, and the average coupling ratio deviation for a change in the incident light polarization angle was 0.48%, with an average coupling ratio of 13.7% (n = 14). These properties were obtained with an accurately controlled fusing temperature and a wide and stable microheater heat region for tapering.