At&t Bell Laboratories

Emmanuel Desurvire

Clinton R Giles

John L Zyskind

Jay R Simpson

Matthew S Whalen

Randy C Giles

In a transmission system having concatenated optical amplifiers, gain saturation of the optical amplifiers at any stage is caused by the extraction of power from the amplifier by the ASE and amplification of the signal and of the ASE from previous stages. Three methods of operating transmission systems are classsified as free-running, constant-total power and constant-signal power. Differences in performance of the three systems arise from the propagation of signal power and the buildup of the ASE. It is now disclosed that the buildup of ASE noise in a system of either lumped or distributed concatenated optical amplifers can be limited by operating at least a plurality of the optical amplifers to provide unsaturated gain which is greater than the loss of the system and/or each optical amplifier is operated in its saturated state.

Method of operating concatenated optical amplifiers

This invention relates to an Erbium doped fiber amplifier having improved operating characteristics. Parameters which determine the operating characteristics of an erbium doped fiber amplifier are the concentration of erbium in the core of a fiber; the ratio of the radius of the core of the fiber doped with erbium relative to the radius of the core of the fiber, and, the length of the fiber. It is now recognized that improved fiber amplifier performance can be obtained by varying the core-cladding refractive index difference of the fiber. The various parameters are here defined for providing an erbium doped fiber amplifier having optimum gain characteristics.

Erbium-doped fiber amplifier

This invention is a rare earth doped optical amplifier with increased gain and lowered pump thresholds. The amplifying scheme is based on a 3 level lasing system rather than the more prevalent 4 level lasing system. Additionally, the transmission mode of the optical fiber at the pump wavelength has a radius which is substantially equal to or greater than the radius of the distribution profile of the rare earth ions in the fiber amplifier core. With the inventive amplifier, a gain of 37 dB and a saturation power of 11.3 dBm has been obtained with only 54 mW of launch power at .lambda.=1.49 .mu.m.

This invention is directed toward reducing substantially the loss incurred when two optical fibers of different mode diameters are coupled together. In this invention, the coupling of one fiber to that of another where the fibers are of different mode diameters is not with a tapered fusion, core-to-core splice, but with an evanescent field fiber coupler. Briefly, to achieve amplification of a weak optical signal, an amplifying fiber is inserted into the system at one or a plurality of locations. More specifically, at a desired location, the transmission fiber is severed to provide two sections and the severed sections are transversely coupled to the amplifying fiber. The weak signal from the first section of the transmission fiber is coupled into the amplifying fiber via a first evanescent field type of fiber coupler; and the amplified signal is coupled from the amplifying fiber to the second section of the transmission fiber via a second evanescent field type of fiber coupler. The first evanescent field type of fiber coupler is designed to couple substantially all of the signal energy from the first section of the transmission fiber to the amplifying fiber and to couple substantially none of the laser diode pump signal or energy from the amplifying fiber to the transmission fiber. The second evanescent field type of fiber coupler is designed to couple substantially all of the signal energy in the amplifying fiber to the transmitting fiber and substantially no laser diode pump energy is transferred from the amplifying fiber to the transmission fiber. Either or both cut ends of the transmission fiber can be coupled to monitor devices to detect and determine the value of the signal being coupled into and/or out of the amplifying fiber to control, for example, the gain of the amplifying fiber.

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Middletown, NJ, United States of America

Emmanuel Desurvire