Method of wavelength multiplexing in fused single-mode fiber couplers

Abstract

An apparatus and method of entering and extracting a discrete wavelength of optical data in a single-mode duplex optical data transmission system relies on a selective evanescent field coupling. A continuous single-mode fiber transmits the two wavelengths in opposite directions with respect to each other. A length of a like single-mode fiber is fused to the continuous single-mode fiber such that the product of the fused length and the coupling coefficient of the fiber pairs equals .pi./2 at one of the optical frequencies to effect one-hundred percent evanescent field coupling to and from the continuous fiber. The product of the coupling coefficient and the fused length equals .pi. at the other optical wavelength to effect a zero percent evanescent field coupling. The other wavelength travels the length of the continuous single-mode fiber uninterrupted while the first wavelength is selectively coupled and decoupled from the fiber as desired.