A tapered optical fiber coupler includes a first fiber with a core (11) and a cladding (12) and a second fiber with a core (21), an inner cladding (22) and an outer cladding (23). In the stretched, coupling regions of the device, the coupling regions (44, 50) of the fibers form of coupling region waveguides with dispersion curves crossing one another at a preselected operating wavelength. The one or more claddings of each fiber has a monotonic decreasing refractive index distribution, and the refractive index distributions of the claddings (12, 22, 23) are different from one another. Coupling of light from one another occurs only in the narrow band of wavelengths surrounding the operating wavelengths. The outside diameters and core diameters of the fibers may be identical to one another and identical to those of standard optical fibers. Thus, the device can be connected in an optical system.