Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1994-08-22
1996-03-26
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
359187, 372 31, H04B 1004
Patent
active
055022987
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for controlling an output of a laser diode over temperature so as to control and optimally maintain constant its extinction ratio, and a method for initially setting HIGH and LOW outputs of the laser diode so as to have a desired extinction ratio.
Various control circuits have been proposed in the prior art for maintaining an output of a laser diode. FIG. 1 illustrates various characteristic curves for a laser diode whereby current I versus power P is graphed, the three curves illustrating data for a laser diode at three distinct temperatures. As is evident and known, a pedestal bias current 4 of the laser diode increases with temperature. One method of controlling an output of a laser diode is to incorporate a thermoelectric cooler into a laser package so as to keep the diode at a constant temperature so that its pedestal bias current remains constant. Accordingly, an extinction ratio of the laser diode, defined as the ratio between its HIGH power output divided by its LOW power output can easily be maintained constant. A disadvantage of such proposals is that thermoelectric cooler designs tend to increase the laser cost, and decreases reliability of the laser diode since any failure in the thermoelectric cooler device or its circuitry will result in the applied bias current being inappropriate as the temperature of the laser diode varies.
Circuits have also been proposed whereby a LOW pedestal power is monitored successively over time for the laser diode and incrementally increased or decreased in response to comparison to a preset dynamic threshold. One such circuit is described by Geller, U.S. Pat. No. 5,036,189, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. Though the Geller circuit readily establishes and maintains an appropriate LOW pedestal bias current, it does not control the HIGH power output of the laser. Referring back to FIG. 1, since a slope of the current versus power output of a laser changes over temperature, for a constant modulation current I.sub.M, the laser extinction ratio (the ratio between the laser HIGH power divided by the laser LOW power) will change over time. If the extinction ratio becomes too small, increased noise results at an optical receiver detecting an output of the laser which results in undesirable bit errors.
It has also been proposed to utilize circuitry which maintains the average laser modulation power constant over time. Such circuits also suffer from a disadvantage that the laser output extinction ratio will change with temperature. Specifically, referring to FIG. 1, curve 3 illustrates how such circuitry works on an output of the laser and illustrates that noise detected by the receiver when the laser emits a LOW output is undesirably high, i.e. greater than the power output at the laser threshold pedestal.
SUMMARY OF THE INVENTION WITH OBJECTS
It is an object of the present invention to eliminate the above noted drawbacks in laser design and provide an apparatus whereby an extinction ratio of a laser output is maintained constant over various temperatures.
It is a further object of the invention to provide a laser whereby its LOW bias power is monitored and adjusted over time to maintain the laser at a predetermined pedestal bias output threshold value, and independently monitor the HIGH output level of the laser and keep that output at another predetermined value, periodically over time, so as to achieve stability over temperature.
These and other objects of the invention are achieved by a circuit for controlling an extinction ratio of an output of a laser which is not maintained at a constant temperature, comprising: a magnitude of an intensity of optical radiation emitted by a light source while the light source is transmitting a continuous logical 1, the logical 1 being transmitted sufficiently long to achieve a stabilized constant value for the first voltage magnitude which is detected; of a magnitude of an inten
REFERENCES:
patent: 4369525 (1983-01-01), Breton et al.
patent: 4471494 (1984-09-01), Keil et al.
patent: 4580044 (1986-04-01), Hongo et al.
patent: 4689795 (1987-08-01), Yoshimoto et al.
patent: 4709416 (1987-11-01), Patterson
patent: 4718118 (1988-01-01), Viola
patent: 4853934 (1989-08-01), Sakurai
patent: 4985896 (1991-01-01), Kimizuka et al.
patent: 4995045 (1991-02-01), Burley et al.
patent: 4995105 (1991-02-01), Wechsler
patent: 5027362 (1991-06-01), Hokanson et al.
patent: 5036189 (1991-07-01), Geller
patent: 5065456 (1991-11-01), Nakayama
patent: 5091797 (1992-02-01), Proebster
patent: 5311005 (1994-05-01), Visocchi
patent: 5394416 (1995-02-01), Ries
Japanese Patent Abstract, Publication No. 63 280 482 (NEC Corp).
Japanese Patent Abstract, Publication No. 59 063 787 (Fujitsu KK).
Japanese Patent Abstract, Publication No. 61 052 042 (Hitachi Ltd).
Lee John R.
Raynet Ericsson
Westin Edward P.
LandOfFree
Apparatus and method for controlling an extinction ratio of a la does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for controlling an extinction ratio of a la, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for controlling an extinction ratio of a la will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-917624