News Column

Patent Issued for Optical Fiber Amplifier with Improved Transient Performance

September 10, 2014

By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventor Rapp, Lutz (Deisenhofen, DE), filed on September 7, 2009, was published online on August 26, 2014.

The assignee for this patent, patent number 8817366, is Xieon Networks S.a.r.l. (Luxembourg, LU).

Reporters obtained the following quote from the background information supplied by the inventors: "Optical fiber amplifiers are widely used for signal amplification in optical data transmitting networks based on wavelength-division multiplexing (WDM). Changes in network configuration, component failures, fiber breaks or protection switching can cause abrupt changes of optical input power. These changes cause fast changes of amplifier output power which can be transferred to other wavelengths due to nonlinear fiber effects and the non-ideal dynamic properties of erbium-doped fiber amplifiers (EDFAs). These changes can propagate to other sites leading to optical power fluctuations across the whole network and possibly to oscillations. Thus, even channels that are not directly affected by the switching operations or failures can suffer from some performance degradation at the receivers.

"Furthermore, gain variations can also accumulate in a cascade of amplifiers. Thus, even small gain variations can result in significant power changes at the receivers. Therefore, efficient amplifier control techniques are required that allow to keep the inversion and as a consequence the gain profile of an amplifier or an amplifier stage relatively constant even if the input power changes.

"Fast electronic control architectures are currently the most economical solution to stabilize the gain of EDFAs. Commonly, feedback architectures are used since they allow to adjust the gain or output power to given target values and to compensate for control errors. However, purely feedback based controllers cannot meet the transient performance requirements for dynamically reconfigured networks. Fortunately, feedback controllers can be complemented by a feedforward controller. The combination of the two types of controllers provides quick response to any changes with the feedback system cleaning up for any error in the predetermined adjustment made by the feedforward control.

"On the other hand, cost reduction has become a continuing task. Therefore pump power splitting has become a widely used technique to reduce amplifier cost. If pump power splitting is applied to amplifier stages that are separated by a component afflicted with delay such as a dispersion compensating fiber (DCF) unacceptable poor transient performance is gained. Therefore, pump splitting is typically applied only to stages that are all before the DCF or all after the DCF."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventor's summary information for this patent: "Therefore it is an object of the present invention to provide a fiber amplifier at reasonable costs with improved transient performance.

"The invention refers to an optical amplifier with a first amplifier stage receiving an input signal (WS1) and a second amplifier stage connected in series and outputting an output signal; an optical delay element inserted between said amplifier stages; a common pump source generating a pump signal; a power splitter, which input is connected to the common pump source and which outputs are connected to the first amplifier stage and the second amplifier stage respectively; a control unit determining the power of the pump signal, said control unit receiving a feedforward control signal derived from an optical input signal and delaying the reaction of the feedforward control by a feedforward delay time, which is less than a delay time of said optical delay element, thereby reducing the gain variation of an output signal.

"The maximum gain variation of the output signal is minimized by setting the right delay of the feedforward control.

"Dispersion of the transmission fiber is advantageously compensated if the optical delay element is a dispersion compensating fiber.

"For higher technical requirements it is necessary that the control unit is in addition extended by feedback control of amplifier gain and/or output power.

"It is advantageously that the pump signal splitter is a variable splitter.

"This allows performance adaptation to noise and transient requirements.

"A possible control unit comprises a second delay element for delaying the feedforward control signal and an adder connected to an output of the second delay element and receiving a feedforward control signal and a feedback control circuit for receiving an electrical measuring input signal derived from the optical input signal and receiving an electrical measuring output signal derived from the optical output signal and generating a feedback control signal, which is combined with the feedforward control signal.

"More flexible is a control unit implemented as programmable processor receiving the electrical measuring signals derived from the input signal and output signal respectively.

"This allows simple adaptation of the amplifier performance according to network requirements.

"The amplifier performance is optimized by choosing the delay of the second delay element and the splitting factor according to network requirements.

"The amplifier performance using a processor solution is optimized by programming a delay of the pump signal related to the feedforward control signal while the splitting factor of the splitter is chosen according to network requirements.

"For a more flexible solution it is necessary that the delay of the feedforward control and the splitting factor are adjustable by adapting control parameters of the control unit.

"The transient performance can be further improved if the second amplifier stage is pumped via a pump signal delay element.

"This allows a smaller delay between the power drop and the reduction of the first pump signal pumping the first amplifier stage."

For more information, see this patent: Rapp, Lutz. Optical Fiber Amplifier with Improved Transient Performance. U.S. Patent Number 8817366, filed September 7, 2009, and published online on August 26, 2014. Patent URL:

Keywords for this news article include: Xieon Networks S.a.r.l.

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Source: Journal of Engineering

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