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DYNAMIC LASER POWER AND TEMPERATURE CONTROL EMPLOYING A SINGLE PHOTO-DIODE SENSOR

IP.com Disclosure Number: IPCOM000026597D
Original Publication Date: 1992-Dec-31
Included in the Prior Art Database: 2004-Apr-06
Document File: 6 page(s) / 268K

Publishing Venue

Xerox Disclosure Journal

Abstract

Combining a laser diode with a holographic scanning system presents a major problem associated with the phenomenon of laser diodes to mode hop due to the diode's inherent frequency instability. This operational occurrence with laser diodes is rooted in the very broad gain characteristic of the device and its tendency to shift frequencies with changes in temperature. As a result, laser diodes, even those laser diodes normally operating as single longitude mode lasers, do shift from one longitudinal mode to another as a result of temperature or power level change.

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Page 1 of 6

XEROX DISCLOSURE IOU RNAL

DYNAMIC LASER POWER AND TEMPERATURE CONTROL U.S. C1.346/108 EMPLOYING A SINGLE PHOTO-
DIODE SENSOR
Robert A. Lonis

Proposed Classification Int. C1. GOlD 09/42

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XEROX DISCLOSURE JOURNAL Vol. 17 No 6 NovembedDecember 1992 421

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DYNAMIC LASER POWER AND TEMPERATURE CONTROL EMPLOYING A SINGLE PHOTODIODE SENSOR(Cont'd)

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422 XEROX DISCLOSURE JOURNAL Vol17 No 6 November/December 1992

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Page 3 of 6

DYNAMIC LASER POWER AND TEMPERATURE CONTROL EMPLOYING A SINGLE PHOTODIODE SENSOR(Cont'd)

Combining a laser diode with a holographic scanning system presents a major problem associated with the phenomenon of laser diodes to mode hop due to the diode's inherent frequency instability. This operational occurrence with laser diodes is rooted in the very broad gain characteristic of the device and its tendency to shift frequencies with changes in temperature. As a result, laser diodes, even those laser diodes normally operating as single longitude mode lasers, do shift from one longitudinal mode to another as a result of temperature or power level change.

Disclosed herein is a method for real time power correction of the light produced by a laser diode used in a holographic scanner and a corresponding temperature control for the same laser diode by means of a single sensor, namely a silicon photodiode. The specific feature of the invention is to eliminate print quality defects produced by variations in light power and the discontinuous variations of wavelength at the laser output that are due to temperature changes. Until now, each scheme has been envisioned separately, requiring different light power and temperature sensors. For example, U.S.

Patent 4,699,446 issued October 13,1987 to Martin E. Banton et al. (assigned to the Xerox Corporation) discloses the use of a monitor photodiode as the feedback element enabling control of the real time light output of a laser diode. Xerox Corporation U.S. Patent 4,733,253 issued March 22, 1988 to Joseph J.
Daniele and Xerox Corporation U.S. Patent 4,737,798 issued April 12,1988 to Robert A.Lonis et al., disclose the control of the temperature of the laser diode case in such a manner as to place the laser diode in a temperature range that would eliminate mode hopping.

The nature of a silicon photodiode is such that in a photovolt- aic/photoconductive application it will give an indication of the quantity of photons impinging on its surface area thus enabling its use as a real time feedback element for laser light power output. But, when the photodiode is forward biased as a signal or switching diode, it will exhibit the well known temperature dependence of forward voltage which is approximately -2 mV...