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Method and system for first-order RF amplitude and bias control of a modulator
| Details |
Inventors: Sikora, John K.;
Assignee: Alcatel (Paris, FR)
Primary Examiner: Hgo; Hung N.
Assistant Examiner:
Attorney, Agent or Firm: Smith; Jessica W., Sewell; V. Lawrence
A method and system are disclosed for robustly (using first order effects) controlling the bias point and radio frequency (RF) amplitude level of a modulator for an optical transmitter. The method comprises the steps of extracting an output dither signal component of a digital optical output signal from the optical transmitter to drive a feedback loop; measuring the output dither signal component in the feedback loop for comparison to an input dither signal to the modulator; comparing the output dither signal to the input dither signal to determine their difference; and, based on the difference between them, maintaining the bias point and the RF amplitude level at an optimum value by varying an input voltage to the modulator via the feedback loop. One embodiment of the system of this invention comprises a laser for providing an input light, a modulator to modulate the input light and generate a digital optical output signal, a radio frequency (RF) feedback loop to control an RF input voltage to the modulator, a bias feedback loop to control a bias input voltage to the modulator, an RF amplitude dither circuit to provide an RF input dither signal to the RF voltage input, and a bias dither circuit to provide a bias input dither signal to the bias voltage input. The modulator can be a Mach-Zehnder modulator. |
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DETAILED DESCRIPTION Therefore, a need exists for a method and system for controlling the RF amplitude and bias value of a modulator using first-order linear effects.
A further need exists for a method and system for first-order RF amplitude and bias control of a modulator that uses a feedback loop to control RF amplitude, so that RF amplitude can track changes in the modulator and in the RF train, over temperature and time.
Still further, a need exists for first-order RF amplitude and bias control of a modulator having a high signal-to-noise ratio and comprising a robust circuit high bandwidth feedback loops.
The present invention provides a method and system for first-order RF amplitude and bias control of a modulator that substantially eliminates or reduces disadvantages and problems associated with previously developed methods and systems for RF amplitude and bias control of a modulator within a digital lightwave communications system.
In particular, the present invention provides a method and system for robustly (using first order effects) controlling the bias point and radio frequency (RF) amplitude level of a modulator for an optical transmitter.
The method comprises the steps of extracting an output dither signal component of a digital optical output signal from the optical transmitter to drive a feedback loop; measuring the output dither signal component in the feedback loop for comparison to an input dither signal to the modulator; comparing the output dither signal to the input dither signal to determine their difference; and, based on the difference between them, maintaining the bias point and the RF amplitude level at an optimum value by varying an input voltage to the modulator via the feedback loop.
One embodiment of the system of this invention comprises a laser for providing an input light, a modulator to modulate the input light and generate a digital optical output signal, a radio frequency (RF) feedback loop to control an RF input voltage to the modulator, a bias feedback loop to control a bias input voltage to the modulator, an RF amplitude dither circuit to provide an RF input dither signal to the RF voltage input, and a bias dither circuit to provide a bias input dither signal to the bias voltage input
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TV Signal 
