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Abstract

Bar code readers using laser diodes conserve electrical power and limit output laser radiation to levels required by governmental regulation (1 milliwatt average power) by utilizing a laser diode having a output optical power vs laser current characteristic which has a slope efficiency (the ratio of the change in power to the change in current, .DELTA.P/.DELTA.I, which is less than 1 in the region where stimulated (laser) emission occurs. The laser is operated with current pulses having a duty cycle less than 100%, and preferably in the range from 50% to 20% in the stimulated emission region of its characteristic, such that the average output laser power does not exceed the level required by government regulations (1 mw) while the laser output during the pulses is greater than 1 mw. Upon detection after reflection or scattering (return of light) from the bar code, the optical signal is photodetected to provide an electrical signal which is envelope detected and components of the signal at the repetition rate of the current pulses are removed, as by filtering. The filtered signal is digitized to provide a digital signal from which the bar code may be decoded.

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First Claim