Speckle noise reducing for laser based barcode readers
AssigneeSymbol Technologies, Inc.
InventorsMiklos STERN, Vladimir Gurevich, Dmitry Yavid
Life of this patent
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Abstract
A method and apparatus for reducing speckle noise in laser based barcode readers. The apparatus includes a semiconductor laser diode for producing a laser beam. The apparatus also includes electronic circuitry operative to alternate the current passing through the semiconductor laser diode between a current above the threshold current and a current below the threshold current. The current passing through the semiconductor laser diode is alternated with a sufficiently high transition rate for reducing the coherence length of the laser beam.
Claims19
A device for scanning a symbol comprising:
- a semiconductor laser diode for producing a laser beam, wherein the semiconductor laser diode has a threshold current;
- a scan mirror for scanning the laser beam across the symbol;
- a photodetector for detecting the light reflected from the symbol;
- and
- electronic circuitry operative to alternate the current passing through the semiconductor laser diode between a current above the threshold current and a current below the threshold current, wherein the current passing through the semiconductor laser diode is alternated with a transition rate sufficiently high such that the average coherence length of the laser beam generated thereby is at least 10% smaller than the coherence length of an equivalent laser beam when the semiconductor laser diode is operating with a continuous DC current that has the same average current value as the current being alternated.
A device for scanning a symbol comprising:
- a semiconductor laser diode for producing a laser beam, wherein the semiconductor laser diode has a threshold current;
- a scan mirror for scanning the laser beam across the symbol;
- a photodetector for detecting the light reflected from the symbol;
- and
- electronic circuitry operative to alternate the current passing through the semiconductor laser diode between a current above the threshold current and a current below the threshold current, wherein the current passing through the semiconductor laser diode is alternated at a transition rate of at least 40,000,000 times per second.
A method of reading a symbol, comprising the steps of:
- presenting a device that outputs a laser beam from a semiconductor laser diode, wherein the semiconductor laser diode has a threshold current;
- presenting an object with the symbol to the device;
- aligning the symbol with the device so that the laser beam is incident on the symbol;
- scanning the laser beam across the symbol with a scan mirror;
- detecting the light reflected from the symbol with a photodetector;
- and
- alternating the current passing through the semiconductor laser diode between a current above the threshold current and a current below the threshold current, wherein the current passing through the semiconductor laser diode is alternated with a transition rate sufficiently high such that the average coherence length of the laser beam generated thereby is at least 10% smaller than the coherence length of an equivalent laser beam when the semiconductor laser diode is operating with a continuous DC current that has the same average current value as the current being alternated.
A method of reading a symbol, comprising the steps of:
- presenting a device that outputs a laser beam from a semiconductor laser diode, wherein the semiconductor laser diode has a threshold current;
- presenting an object with the symbol to the device;
- aligning the symbol with the device so that the laser beam is incident on the symbol;
- scanning the laser beam across the symbol with a scan mirror;
- detecting the light reflected from the symbol with a photodetector;
- and
- alternating the current passing through the semiconductor laser diode between a current above the threshold current and a current below the threshold current at a transition rate of at least 40,000,000 times per second.
Dependencies are inferred from the claim text.