Dynamic power control for an external cavity stabilized laser diode in a holographic scanner

Claim 2

In a raster output scanner, the combination of: (a) a laser diode with an internal lasing cavity having front and rear facets as the source of a high intensity scanning beam; (b) an optical system for scanning and focusing said beam on a recording member including a rotatable holographic scanning element; (c) converting means for converting the laser diode internal lasing cavity to an external lasing cavity to inhibit diode mode hopping, said converting means including (1) an anti-reflective covering on the front facet to convert the laser diode internal cavity to a gain medium, (2) means for collimating the light output of said diode into parallel light beams, (3) transmissive wavelength selecting means for dispersing said light beams in accordance with the wavelength of the individual light beams, and (4) means to reflect a predetermined one of the light beams back on itself and against the laser diode internal cavity rear facet whereby the laser diode is forced to operate in a single mode corresponding to the wavelength of the predetermined light beam; and (d) means for correcting for diode power variations resulting from conversion of said laser diode internal cavity to said external cavity by said converting means including (1) means to sampling the power output of said laser diode following conversion of said laser diode internal cavity to said external cavity to provide a signal representing diode power output; (2) means for comparing said signal with a predetermined reference signal to provide a control signal; and (3) means for adjusting the power input to said laser diode in response to said control signal to maintain substantially constant laser diode power while inhibiting laser diode mode hopping.

Claim 3

The scanner according to claim 1 in which said sampling means samples light emitted from said laser diode rear facet.

Claim 4

The scanner according to claim 1 in which said sampling means samples the zero order beam passing through said transmission wavelength selecting means.

Claim 5

The scanner according to claim 1 in which said sampling means samples the light output of said laser diode at the output of said external cavity.

Claim 6

The scanner according to claim 1 in which said scanning element comprises a transmissive holographic disc having successive grating facets about the periphery thereof, said sampling means sampling the zero order component of said scanning beam undiffracted by said holographic disc grating facets.

Claim 7

The scanner according to claim 1 in which said sampling means includes: (a) a light detector for converting light impinging thereon to said signal, and (b) lens means for focusing said light from said laser diode on said light detector.

Claim 8

In a raster output scanner the combination of: (a) a laser diode with an internal lasing cavity with front and rear facets as the source of a high intensity scanning beam, (b) an optical system for scanning and focusing the beam on a recording member including a rotatable holographic scanning element, (c) converting means for converting the laser diode internal lasing cavity to an external lasing cavity to inhibit diode mode hopping, said converting means including (1) an anti-reflective covering on the front facet to convert the laser diode internal cavity to a gain medium, (2) means for collimating the light output of said diode into parallel light beams, (3) transmissive wavelength selecting means for dispersing said light beams in accordance with the wavelength of the individual light beams, and (4) means to reflect a predetermined one of the light beams back on itself and against the laser diode internal cavity rear facet whereby the laser diode is forced to operate in a single mode corresponding to the wavelength of the predetermined light beam; and (d) means for correcting for diode power variations resulting from conversion of said laser diode internal cavity to said external cavity by said converting means, said correcting means including (1) comparator means, (2) photosensitive means for monitoring the intensity of the beam output by said laser diode, said photosensitive means generating a first potential representative of the instantaneous intensity of the beam output of said laser diode to one input of said comparator means; (3) means providing a preset second potential representative of desired laser diode beam intensity to a second input of said comparator means; said comparator means comparing said first and second potentials to provide an intensity control signal; (4) first control means responsive to an image signal to provide maximum sink current through said laser diode to actuate said laser diode whereby said laser diode generates a beam of maximum intensity; and (5) second control means adapted when said beam reaches a predetermined intensity to reduce said sink current through said laser diode to reduce the intensity of said laser diode beam in response to said intensity control signal whereby the intensity of the laser diode beam is adjusted to provide said desired beam intensity.

Claim 9

In a raster output scanner the combination of: (a) a laser diode with an internal lasing cavity with front and rear facets as the source of a high intensity scanning beam, (b) an optical system for scanning and focusing the beam on a recording member including a rotatable holographic scanning element, (c) converting means for converting the laser diode internal lasing cavity to an external lasing cavity to inhibit diode mode hopping, said converting means including (1) an anti-reflective covering on the front facet to convert the laser diode internal cavity to a gain medium, (2) means for collimating the light output of said diode into parallel light beams, (3) transmissive wavelength selecting means for dispersing said light beams in accordance with the wavelength of the individual light beams, and (4) means to reflect a predetermined one of the light beams back on itself and against the laser diode internal cavity rear facet whereby the laser diode is forced to operate in a single mode corresponding to the wavelength of the predetermined light beam; and (d) means for correcting for diode power variations resulting from conversion of said laser diode internal cavity to said external cavity by said converting means, said correcting means including (1) comparator means, (2) photosensitive means for monitoring the intensity of the beam output by said laser diode, said photosensitive means generating a first potential representative of the instantaneous intensity of the beam output of said laser diode to one input of said comparator means; (3) means providing a preset second potential representative of desired laser diode beam intensity to a second input of said comparator means; said comparator means comparing said first and second potentials to provide an intensity control signal; (4) first control means responsive to an image signal to provide maximum sink current through said laser diode to actuate said laser diode whereby said laser diode generates a beam of maximum intensity; and (5) second control means adapted when said beam reaches a predetermined intensity to reduce said sink current through said laser diode to reduce the intensity of said laser diode beam in response to said intensity control signal whereby the intensity of the laser diode beam is adjusted to provide said desired beam intensity.

Claim 10

The scanner according to claim 7 in which said first control means terminates said sink current in the absence of said image signal whereby said laser diode is inoperative.

Claim 11

The scanner according to claim 7 in which said photosensitive means monitors said laser beam intensity through said laser diode rear facet.

Claim 12

The scanner according to claim 7 in which said photosensitive means monitors the intensity of the zero order beam passing through said transmissive wavelength selecting means.

Claim 13

The scanner according to claim 7 in which said photosensitive means monitors the intensity of the laser diode beam at the output of said external cavity.

Claim 14

The scanner according to claim 7 in which said scanning element comprises a transmissive holographic disc having a plurality of grating facets, said photosensitive means monitoring the zero order component of said scanning beam at said grating facets.