Abstract: One method of determining the signal to noise ratio of an optical signal models the noise floor based on amplified spontaneous emission (ASE) which is accumulated along the link. The ASE wavelength dependence is represented by a known mathematical function with a limited number of parameters. The parameters of this function are derived from measurements of the noise floor at a limited number of points by computational best fit means. A number of fiber grating filters at wavelengths between ITU allocated wavelengths are used to sample the optical noise and reflect the light back. An optical circulator is used to direct the reflected ASE light to an optical switch which allows the detector to select between transmitted and reflected light. The signal transmitted through the switch is monitored by a scanning filter with the appropriate resolution to resolve the signal or noise peaks. A first scan of the transmitted peaks is carried out and the signal is digitized and stored.

Abstract: A bidirectionally amplifying rare earth doped fiber optical amplifier having an equalized gain at multiple wavelengths is disclosed for use in dense wavelength multiplexed bidirectional fiber transmission applications. In a first embodiment, a four port circulator is utilized with two amplifying fibers; one for each direction of propagation and a multiplicity of gratings configured to equalize the gain at the different wavelengths. Different embodiments utilizing three port and four port circulators are utilized. A more general amplifier device with equal gain at multiple wavelengths is disclosed.