Laser multiple feedback control circuit and method
AssigneeAmoco Corporation
InventorKeith Johnson
Life of this patent
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Abstract
A method and apparatus for reducing the effects of relative intensity noise in a diode laser system by sensing the light output of diode laser system and producing an electrical feedback signal; amplifying the feedback signal over at least two different parts of a frequency band that includes the Relaxation Oscillation Frequency of the laser system; shifting the phase of each of the amplified feedback signals over the frequency band; and superimposing onto the current supplied to the laser diode a current signal that is a function of each of the phase shifted and amplified feedback signals.
Claims20
In a laser system that, in response to a flow of electrical current through a laser diode, produces a laser light output which is characterized by intensity noise that is a function of frequency, a feedback circuit comprising:
- a) conversion means, using the laser light output of a laser system that produces light in response to the flow of current through a laser diode, for producing an electrical input signal that is representative of the intensity noise in the laser light output;
- b) first feedback means for using said electrical input signal and producing a first feedback signal, said first feedback means having a gain curve that has a first maximum located intermediate the ends of a predetermined frequency band, said predetermined frequency band including that portion of said intensity noise due to the relaxation oscillation frequency of the laser diode;
- c) second feedback means for using said electrical input signal and producing a second feedback signal, said second feedback means having a gain curve that has a second maximum located intermediate the ends of said predetermined frequency band and that is separated from said first maximum of said first feedback means;
- and
- d) output means, using said first feedback signal and said second feedback signal, for producing a current gain signal and superimposing said current gain signal on the electrical current flowing through the laser diode to reduce intensity noise generally due to said relaxation oscillation of said laser diode.
A laser system, comprising:
- a) a semi-conductor light source characterized by a relaxation oscillation frequency;
- b) supply means for supplying current to said semi-conductor light source to produce laser light that is characterized by noise that is a function of the said relaxation oscillation frequency;
- c) photo-diode means, that is responsive to said laser light, for producing an input signal that is a function of said noise;
- d) means for producing a plurality of phase shifted feedback signals from said input signal, each of said phase shifted feedback signals being characterized by a gain curve having a maximum located intermediate the ends of a predetermined frequency band and separated from at least one adjacent maximum, said predetermined frequency band including that portion of said amplitude noise due to the relaxation oscillation frequency of the laser diode;
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- e) output means for applying to said supply means a negative feedback output current signal that has a value that is a function of said phase shifted feedback signals and that has the effect of reducing said noise.
An automatic noise reduction circuit for a laser system whose laser light output is characterized by noise and is a function of the flow of electrical current through a semi-conductor component, comprising:
- a) conversion means, responsive to laser light produced in response to the flow of electrical current through a semi-conductor component, for producing an output electrical control signal;
- b) upper bandpass means for receiving said control signal and producing a first electrical feedback signal, said upper bandpass means having a maximum frequency response at a high end of a predetermined frequency band;
- c) middle bandpass means for receiving said control signal and producing a second electrical feedback signal, said middle bandpass means having a maximum frequency response at a location intermediate the ends of said predetermined frequency band;
- d) lower bandpass means for receiving said control signal and producing a third electrical feedback signal, said lower bandpass means having a maximum frequency response at a low end of said predetermined frequency band;
- e) means, using said first feedback signal and said second feedback signal and said third feedback signal, for changing said electrical current flowing through said laser diode means to reduce the noise in said light.
A method of automatically reducing intensity noise in the output of a diode laser system, comprising the steps of:
- a) sensing the output of a diode laser system and producing an electrical feedback signal;
- b) amplifying said feedback signal over at least two different parts of a frequency band that includes the Relaxation Oscillation Frequency of said laser system;
- c) shifting the phase of each of said amplified feedback signals over said frequency band;
- and
- d) superimposing onto the current supplied to said diode laser a current signal that is a function of each of said phase shifted amplified feedback signals.
Dependencies are inferred from the claim text.