Multi-channel laser recording system

Claim 2

In a multi-channel laser recording system having a source of coherent energy, means for dividing said energy into a plurality of constituent beams, and means for directing each of said constituent beams onto a surface of a record medium, modulation means for each of said beams, each modulation means including: a first polarizer having a principal axis in alignment with the polarization axis of an input constituent beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axis orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogonal to that of said second polarizer; means for receiving energy transmitted by each of said first and second modulators and for producing in response thereto respective electrical signals representative of the intensity of light transmitted by said respective modulators; and means operative in response to said electrical signals to adjust the bias of said first and second modulators to compensate for the effects of temperature drift therein and maintain a maximum extinction ratio.

Claim 3

The invention according to claim 1 wherein said bias adjusting means includes: means for applying a first calibration signal to each of said first and second modulators to cause energization thereof by drive signals of one polarity; means for applying a second calibration signal to each of said first and second modulators to cause energization thereof by drive signals of opposite polarity; and means operative in response to said respective electrical signals to provide a correction signal for each of said modulators to compensate for the effects of bias drift.

Claim 4

The invention according to claim 1 wherein said bias adjusting means includes first and second bias correction circuits each associated with a respective one of said first and second modulators and each operative sequentially to adjust the bias of a respective modulator.

Claim 5

The invention according to claim 3 wherein each of said first and second bias correction circuits includes: a source of time sequentially related calibration pulses; means for applying a first calibration pulse to the associated modulator to cause energization thereof by drive signals of one polarity; means for applying a second calibration pulse to said associated modulator to cause energization thereof by drive signals of opposite polarity; a first sample and hold circuit enabled by said first calibration pulse and operative to store a potential representative of the magnitude of the electrical signal produceD by said energy receiving means; a differential comparator having one input terminal coupled to the output of said first sample and hold circuit and a second input terminal coupled to said energy receiving means; a second sample and hold circuit enabled by said second calibration pulse and operative to receive an input signal from said differential comparator and to store a potential representative of the difference between the magnitudes of input signals applied to said differential comparator; and means for deriving from the stored potential of said second sample and hold circuit a correction signal for said associated modulator.

Claim 6

The invention according to claim 4 wherein each of said first and second bias correction circuits includes: means for sensing the relative polarity of drive signals applied to said associated modulator and for providing control signals in response to said signal sense determination; and switching means operative in response to said control signals to cause application of drive signals to said associated modulator of a polarity corresponding to the direction of maximum available drive voltage.

Claim 7

The invention according to claim 5 wherein each of said first and second bias correction circuits includes: a limit detector operative to detect when the correction signal from said second sample and hold circuit has reached a predetermined level representative of modulator half wave voltage and to apply a signal to said second sample and hold circuit to adjust the stored potential thereof to a selected value to permit bias correction for multi-cycle drift.

Claim 8

A cascaded electro-optical modulator comprising: a first polarizer having a principal axis in alignment with the polarization axis of an input beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axis orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogonal to that of said second polarizer; means for receiving energy transmitted by each of said first and second modulators and for producing in response thereto respective electrical signals representative of the intensity of light transmitted by said respective modulators; means for applying drive signals of either positive or negative polarity to each of said first and second modulators; means for applying calibration signals to each of said modulators of both positive and negative sense to cause production by said energy receiving means of respective electrical signals representative of the intensity of light transmitted by said respective modulators in response to said calibration signals; and means operative in response to said respective electrical signals ro provide bias correction signals to respective ones of said modulators to compensate for the effects of temperature drift therein.

Claim 9

A cascaded electro-optical modulator comprising: a first polarizer having a principal axis in alignment with the polarization axis of an input beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axis orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogonal to that of said second polarizer; means for receiving energy transmitted by each of said first and second modulators and for producing in response thereto respective electrical signals representative of the intensity of light transmitted by said respective modulators; means for applying drive signals of either positive or negative polarity to each of said first and second modulators; means for applying calibration signals to each of said modulators of both positive and negative sense to cause production by said energy receiving means of respective electrical signals representative of the intensity of light transmitted by said respective modulators in response to said calibration signals; and means operative in response to said respective electrical signals ro provide bias correction signals to respective ones of said modulators to compensate for the effects of temperature drift therein.

Claim 10

The invention according to claim 7 wherein said means for applying drive signals includes for each of said first and second modulators: a differential amplifier having positive and negative input terminals and coupled to a power amplifier operative to apply said drive signals to an associated modulator; and wherein said means for applying calibration signals includes for each of said first and second modulators: a source of time sequentially related calibration pulses; means for applying a first calibration pulse to the positive input terminal of said differential amplifier; and means for applying a second calibration pulse to the negaTive input terminal of said differential amplifier; and wherein said bias correction means includes for each of said first and second modulators: means for storing a potential representative of the difference in the intensity of light transmitted by said associated modulator in response to said first and second calibration pulses; and means for applying a correction signal derived from said stored potential to said differential amplifier for bias adjustment of said associated modulator.

Claim 11

The invention according to claim 8 wherein said bias correction means for each of said first and second modulators includes: means for determining the relative sense of drive signals applied to an associated modulator; means operative in response to said sense determination to provide control signals representative of said relative sense; and switching means operative in response to said control signals to cause application of drive signals to said associated modulator of a polarity corresponding to the direction of maximum available drive voltage.

Claim 12

The invention according to claim 8 wherein said bias correction means for each of said first and second modulators includes: means operative to detect when said bias correction signals have reached a predetermined level representative of modulator half wave voltage and to adjust the stored potential of said storage means to a selected value to permit bias correction for multi-cycle drift.

Claim 13

The invention according to claim 10 wherein said potential storing means comprises a sample and hold circuit enabled by one of said calibration signals.

Claim 14

The invention according to claim 7 wherein said means for applying drive signals for each of said first and second modulators includes: a differential amplifier having positive and negative input terminals; a power amplifier coupled to the output of said differential amplifier and operative to apply positive and negative drive signals to an associated modulator; and switching means for selectively applying signals to one of the input terminals of said differential amplifier to thereby cause application of drive signals of predetermined polarity to an associated modulator.

Claim 15

The invention according to claim 12 wherein said switching means includes: first and second switches each operative to receive an input signal and each having an output coupled to a respective input terminal of said differential amplifier; and control means operative to selectively energize one of said first and second switches in accordance with the relative sense of drive signals applied to an associated modulator.

Claim 16

The invention according to claim 13 wherein for each of said first and second modulators said means for applying calibration signals includes: a source of time sequentially related calibration pulses; means for applying a first calibration pulse to the positive input terminal of said differential amplifier; means for applying a second calibration pulse to the negative input terminal of said differential amplifier; and means for applying a third calibration pulse to said control means to enable operation thereof.

Claim 17

A cascaded electro-optical modulator comprising: a first polarizer having a principal axis in alignment with the polarization axis of an input coherent beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axes orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogoNal to that of said second polarizer; photosensor means in light receiving relationship with each of said first and second modulators and for producing in response to received light respective electrical signals representative of the intensity of light transmitted by said respective modulators; means sequentially operative to provide to said modulators calibrated drive signals of both positive and negative polarity to energize respective modulators; means operative in response to said respective electrical signals to determine a difference between the light transmission caused by said calibrated drive signals of positive and negative polarity; means operative in response to said difference to provide a correction signal to said respective modulators to compensate for the effects of temperature drift therein; means for determining the relative sense of drive signals applied to said respective modulators and to provide control signals corresponding to said sense determination; means operative in response to said control signals to cause reversal of the polarity of drive signals applied to said respective modulators when said signal sense determining means detects a reversal of relative sense in said drive signals; and means for determining when said correction signals are of a magnitude equal to a level representative of bias correction for a predetermined bias drift and operative upon such level determination to alter the magnitude of said correction signal to cause bias correction of opposite sense to that of the bias drift.

Claim 18

A cascaded electro-optical modulator comprising: a first polarizer having a principal axis in alignment with the polarization axis of an input coherent beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axes orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogoNal to that of said second polarizer; photosensor means in light receiving relationship with each of said first and second modulators and for producing in response to received light respective electrical signals representative of the intensity of light transmitted by said respective modulators; means sequentially operative to provide to said modulators calibrated drive signals of both positive and negative polarity to energize respective modulators; means operative in response to said respective electrical signals to determine a difference between the light transmission caused by said calibrated drive signals of positive and negative polarity; means operative in response to said difference to provide a correction signal to said respective modulators to compensate for the effects of temperature drift therein; means for determining the relative sense of drive signals applied to said respective modulators and to provide control signals corresponding to said sense determination; means operative in response to said control signals to cause reversal of the polarity of drive signals applied to said respective modulators when said signal sense determining means detects a reversal of relative sense in said drive signals; and means for determining when said correction signals are of a magnitude equal to a level representative of bias correction for a predetermined bias drift and operative upon such level determination to alter the magnitude of said correction signal to cause bias correction of opposite sense to that of the bias drift.

Claim 19

A multi-channel laser recording system comprising: a source of laser energy; means for dividing said energy into a plurality of constituent beams; means for directing each of said constituent beams onto a surface of a record medium; means for modulating each of said beams, each modulation means including: a first polarizer having a principal axis in alignment with the polarization axis of an input coherent beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axes orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogonal to that of said second polarizer; photosensor means in light receiving relationship with each of said first and second modulators and for producing in response to received light respective electrical signals representative of the intensity of light transmitted by said respective modulators; means sequentially operative to provide to said modulators calibrated drive signals of both positive and negative polarity to energize respective modulators; means operative in response to said respective electrical signals to determine a difference between the light transmission caused by said calibrated drive signals of positive and negative polarity; means operative in response to said difference to provide a correction signal to said respective modulators to compensate for the effects of temperature drift therein; means for determining the relative sense of drive signals applied to said respective modulators and to provide control signals corresponding to said sense determination; means operative in response to said control signals to cause reversal of the polarity of drive signals applied to said respective modulators when said signal sense determining means detects a reversal of relative sense in said drive signals; and means for determining when said correction signals are of a magnitude equal to a level representative oF bias correction for a predetermined bias drift and operative upon such level determination to alter the magnitude of said correction signal to cause bias correction of opposite sense to that of the bias drift.

Claim 20

A multi-channel laser recording system comprising: a source of laser energy; means for dividing said energy into a plurality of constituent beams; means for directing each of said constituent beams onto a surface of a record medium; means for modulating each of said beams, each modulation means including: a first polarizer having a principal axis in alignment with the polarization axis of an input coherent beam; a first electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said first polarizer; a second polarizer in light transmitting relationship at the output end of said first modulator and having its principal axes orthogonal to that of said first polarizer; a second electro-optical modulator having its principal axes symmetrically aligned on respective opposite sides of the principal axis of said second polarizer; a third polarizer in light transmitting relationship at the output end of said second modulator and having its principal axis orthogonal to that of said second polarizer; photosensor means in light receiving relationship with each of said first and second modulators and for producing in response to received light respective electrical signals representative of the intensity of light transmitted by said respective modulators; means sequentially operative to provide to said modulators calibrated drive signals of both positive and negative polarity to energize respective modulators; means operative in response to said respective electrical signals to determine a difference between the light transmission caused by said calibrated drive signals of positive and negative polarity; means operative in response to said difference to provide a correction signal to said respective modulators to compensate for the effects of temperature drift therein; means for determining the relative sense of drive signals applied to said respective modulators and to provide control signals corresponding to said sense determination; means operative in response to said control signals to cause reversal of the polarity of drive signals applied to said respective modulators when said signal sense determining means detects a reversal of relative sense in said drive signals; and means for determining when said correction signals are of a magnitude equal to a level representative oF bias correction for a predetermined bias drift and operative upon such level determination to alter the magnitude of said correction signal to cause bias correction of opposite sense to that of the bias drift.

Claim 21

In a coherent energy modulation system having at least one electro-optical modulator adapted to transmit energy therethrough in accordance with applied drive signals, a method for dynamically maintaining an optimum extinction ratio and comprising the steps of: applying a calibration signal of one polarity to said modulator; applying a calibration signal of opposite polarity to that of said first calibration signal to said modulator; deriving electrical output signals representative of the magnitudes of energy transmitted by said modulator in response to said first and second calibration signals; determining the difference between the magnitudes of said electrical output signals; storing a representation of said magnitude difference; deriving from said stored representation a bias correction signal for compensation of the effects of temperature drift in said modulator; determining the relative sense of drive signals applied to said modulator; deriving control signals in response to said relative sense determination; and causing the inversion of said drive signals applied to said modulator upon polarity reversal of said drive signals.

Claim 22

In a coherent energy modulation system having at least one electro-optical modulator adapted to transmit energy therethrough in accordance with applied drive signals, a method for dynamically maintaining an optimum extinction ratio and comprising the steps of: applying a calibration signal of one polarity to said modulator; applying a calibration signal of opposite polarity to that of said first calibration signal to said modulator; deriving electrical output signals representative of the magnitudes of energy transmitted by said modulator in response to said first and second calibration signals; determining the difference between the magnitudes of said electrical output signals; storing a representation of said magnitude difference; deriving from said stored representation a bias correction signal for compensation of the effects of temperature drift in said modulator; determining the relative sense of drive signals applied to said modulator; deriving control signals in response to said relative sense determination; and causing the inversion of said drive signals applied to said modulator upon polarity reversal of said drive signals.

Claim 23

The invention according to claim 17 wherein said electro-optical modulator is a cascaded modulator and said method is sequentially performed for each modulator of the cascaded assembly.