Wavelength-selective directional coupler made of nonidentical single-mode fibers

Low-loss asymmetrical single-mode fiber directional couplers applicable to WDM between transmission channels at 1300 and 1500 nm have been constructed. The crossover wavelength of these couplers can be tuned by a suitable intermediate layer. Theoretical calculations show that fiber multiplexers with channel spacings less than 20 nm Can be fabricated.