Precise control of the center wavelength and bandwidth of wavelength-selective single-mode fiber couplers

Low-loss asymmetrical single-mode fiber wavelength-selective directional couplers are fabricated at low cost. Proper control of the remaining cladding thickness and the interaction length of the half-couplers produces exactly the required bandwidth and center wavelength of the filter. Increasing the interaction length reduces the bandwidth and the sidelobes. Calculated values show good agreement with the experimental results.