Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1998-12-21
2001-04-17
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S247000, C347S236000, C347S237000
Reexamination Certificate
active
06219083
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to laser imaging systems and relates more particularly to a circuit for correcting mode hop in the laser used in a laser printer.
BACKGROUND OF THE INVENTION
The Mode Hop Fix circuit corrects for the exposure errors that occur due to laser mode hops. Mode hopping is a characteristic of semiconductor lasers where the output emission wavelength can jump suddenly as the operating condition of the laser changes. Mode hops can be caused by changes in the laser's temperature and optical feedback. Mode hops cause exposure changes in two ways. First, the emission efficiency of the laser generally changes when the mode hops resulting in an obvious change in exposure. Second, the emission wavelength changes when a mode hop occurs. If the media's response curve isn't sufficiently flat it is possible that noticeable exposure changes will occur.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a solution to the problems of the prior art.
According to a feature of the present invention, there is provided a laser imaging system comprising: a diode laser for producing a laser beam; a beamsplitter for splitting the laser beam into a laser writing portion and a feedback portion; a photodetector for detecting the feedback portion; a photodetector amplifier for amplifying the output of the photodetector; a sample and hold coupled to the photodetector amplifier; an integrator adder; an integrator for integrating the outputs of the photodetector amplifier and the sample and hold processed by the integrator adder; and a laser input circuit including a laser amplifier, a linear power signal provider, a threshold power signal provider, and a laser input adder for adding the laser power signal, the linear power signal, and the output of the integrator.
ADVANTAGEOUS EFFECT OF THE INVENTION
The Mode Hop Fix circuit corrects for the exposure errors that occur due to laser mode hops.
REFERENCES:
patent: 5107275 (1992-04-01), Tsuruoka et al.
patent: 5309461 (1994-05-01), Call et al.
patent: 5557469 (1996-09-01), Markle et al.
Dhurjaty Sreeram
Rhoda Brian K.
Seim Douglas
Eastman Kodak Company
Le N.
Noval William F.
Pham Hai C.
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