Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1995-06-07
1997-04-15
Chin, Wellington
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
359181, 359173, 359188, 385 14, H04B 1000
Patent
active
056215606
ABSTRACT:
In external modulation, chirp is reduced by modulating a laser light beam during a modulation period to maintain-light returning to the laser substantially constant. Variations in at least one of the magnitude and phase of light returning to the laser from an external modulator are reduced during the modulation period. An external modulator divides and modulates the light in parallel along separate optical paths. Driving voltages are applied to modulators in each of the optical paths based on first and second parameters. The first driving parameter represents an intensity modulation. The second driving parameter varies depending upon the value of the first driving parameter during modulation to maintain the light returning to the laser substantially constant throughout the modulation period. For example, the second driving parameter can be a function of the first driving parameter during the modulation period to reduce variations in the magnitude and phase of light returning to the laser through the external modulator. According to a second embodiment, the external modulator has a first modulator and a second modulator optically coupled in series between a laser and two complementary output ports. The second modulator is biased during modulation to balance the phase of light passing through first and second output waveguides. With this configuration it is easier to operate the system to reduce variations in the light returning to the laser during modulation. Finally, optical interactions between the modulator and laser which give rise to chirp are further reduced by using two output ports. Accordingly, the modulated laser signal output from the integrated modulator travels greater distances with less pulse spreading over an optical medium.
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Chin Wellington
Lucent Technologies - Inc.
Negash Kinfe-Michael
LandOfFree
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