ACCURATE TUNING OF MISMATCHED TWIN-CORE FIBER FILTERS

We have demonstrated a reproducible and accurate way of tuning the cou pling wavelength of a mismatched twin-core filter. This method allows high quality all-fiber filters to be implemented with low loss at any desired wavelength over a range of few hundred nanometers from the sam e fiber. An similar to 500-nm tuning range is demonstrated, limited on ly by the measurement setup and not by the technique itself. Highly ac curate control of the filtering wavelength in combination with control of filtering strength by adjustment of the length of the twin-core fi bers allows complex filter profiles to be implemented by cascading of several different filters. These filters are also very stable to a cha nge in temperature (similar to 0.26 nm/100 degrees C at 1.55 mu m) and strain (less than 0.3 nm/mstrain at 1.55 mu m), permitting easy packa ging. (C) 1998 Optical Society of America.