At+t Corp.

At&t Bell Laboratories

Amoco Corporation

British Telecommunications Corporation

Richard G Smart

John L Zyskind

James W Sulhoff

David John DiGiovanni

Jonathan A Nagel

David Colin Hanna

Neal S Bergano

Bruce M Nyman

Joseph D Evankow

Anne C Tropper

Jeremy N Carter

Anne Christine Tropper

Jennifer Aspell

Praseodymium doped waveguide lasers

High output power, high gain, and low noise are achieved in a two-stage optical amplifier, suitable for use as a repeater for a long haul lightwave communication system, in accordance with the principles of the invention, by employing a first amplifying stage having a signal gain sufficiently small to prevent self-saturation by amplified stimulated emission (ASE) that uses counter-propagating pump light to cause maximum inversion of the first stage amplifying medium. In an illustrative embodiment of the invention, EDFAs are used in each of two amplifying stages. The length of the EDFA in the first stage is short enough to ensure nearly complete inversion of the EDFA from pump light that counter-propagates with the signal. The counter-propagating pump light allows the invention to advantageously avoid the significant noise figure penalty from the input loss associated with co-propagating pump light. And, noise figure is improved because complete inversion is achieved throughout the EDFA, and, at the input where the noise figure is most sensitive to inversion. The short length also eliminates self-saturation of the EDFA from ASE which degrades the noise figure. However, the length, and hence the gain, of the EDFA in the first stage is long enough to provide sufficient gain so that the noise figure of the two-stage amplifier, as a whole, is determined primarily by that of the first stage. A second EDFA in the second stage of the amplifier may then be configured using co-propagating or counter-propagating pump light for additional signal amplification to provide the required output power and gain for long haul lightwave systems. Other aspects of illustrative embodiments of the invention include the use of passive optical elements including filters, isolators, and attenuators.

High power, high gain, low noise, two-stage optical amplifier

The present invention relates to a method of mitigating gain peaking in a chain of fiber amplifiers by pumping the amplifiers at a predetermined wavelength to produce gain over a specified wavelength range.

Method of mitigating gain peaking using a chain of fiber amplifiers

An optical fibre amplifier comprises a thulium-doped optical fibre pumped at 790 nm by a semi-conductor diode laser coupled to the fibre via optical fibre coupler. The amplifier is optically coupled in series to a pair of systems fibres to provide amplification to optical signals.

Optical fibre amplifier and laser

In an embodiment for obtaining accurate noise figure measurements for any degree of saturation of an optical amplifier, a polarizer is located at the output of the optical amplifier. The amplified spontaneous noise (ASE) produced by an optical amplifier is not polarized, whereas the amplified signal has a well defined state of polarization which is preferably linear. If the amplified signal is not linearly polarized, it can be rendered linearly polarized in one direction by means of a polarization controller located downstream of the polarizer. By setting the polarizer to have its state of polarization orthogonal to that of the linearly polarized amplified signal, the spectral density of the ASE from the polarizer can be measured without associated distortion due to the signal. By sequentially adjusting the polarization controller to minimize and then maximize the signal which it passes, sequential measurements of the ASE spectral density and gain of the optical amplifier can be obtained. Continuous measurements of the ASE can be obtained by placing a splitter such as a 3dB coupler between the polarizer and the optical amplifier and setting the state of polarization of the polarizer to be continuously orthogonal to the state of polarization of the amplified signal from one leg of the splitter. At the same time, a signal from the other leg of the splitter which consists of ASE noise plus the amplified signal can be used to obtain the gain of the optical amplifier. From the measurements of the ASE with and without the amplified signal, the noise figure of the optical amplifier can be calculated.

Measurement of an optical amplifier parameter with polarization

Growing community of inventors

Naperville, IL, United States of America

Richard G Smart