Laser feedback control circuit and method
AssigneeAmoco Corporation
InventorKeith Johnson
Life of this patent
Estimating the term…
Abstract
A feedback circuit, comprising: means for producing from a laser light output a feedback signal which is representative of the noise and frequency dependent output intensity of the laser light output; means for applying a phase shift to the feedback signal; means for converting the feedback signal to a level signal which is representative of the noise in the laser light output; amplifying means for amplifying the phase shifted feedback signal as a function of the level signal to produce a current gain signal; and means for superimposing the current gain signal on the current flowing through the laser diode.
Claims25
In a laser system which, in response to a flow of electrical current through a laser diode, produces a laser light output which is characterized by amplitude noise which is a function of the frequency at which the laser system operates, a feedback circuit comprising:
- a) feedback means, using the laser light output of a laser system which produces light in response to the flow of current through a laser diode, for producing a feedback signal which is representative of the amplitude noise in the laser light output, said feedback means having a gain curve which has a maximum intermediate the ends of predetermined frequency band which includes that portion of said amplitude noise due to the relaxation oscillation frequency of the laser diode;
- b) phase shifting means for applying a phase shift to said feedback signal over said predetermined frequency band while maintaining the gain generally the same;
- c) converting means for converting said feedback signal to a level signal which is a function of the mean of said amplitude noise in the laser light output;
- and
- d) output means, using said phase shifted feedback signal and said level signal, for producing a current gain signal and superimposing said current gain signal on the electrical current flowing through the laser diode to reduce amplitude 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) means for supplying current to said semi-conductor light source to produce laser light which is characterized by amplitude noise which is a function of the said relaxation oscillation frequency;
- c) photo-diode means, which is responsive to said laser light, for producing a feedback signal which is a function of the relative intensity of said noise;
- d) means for producing phase shifted feedback signal from said feedback signal;
- and
- e) output means for applying to said current to said semi-conductor light source a negative feedback output current signal which has a value which is a function of said phase shifted feedback signal and of a variable control signal and which has the effect of substantially reducing said amplitude noise.
An automatic relaxation oscillation noise reduction circuit for a laser system whose output is characterized by relative intensity noise and is a function of the flow of current through laser diode means, comprising:
- a) means for producing an electrical feedback signal which is representative of the optical output of the laser system;
- b) means for shifting the phase of said feedback signal;
- c) means for producing a control signal which is representative of the average noise in said feedback signal;
- and
- d) means for controlling the gain of said phase shifted feedback signal as a function of said control signal to produce a feedback current which is applied to the laser diode means.
A method of automatically reducing relative intensity noise in the output of a laser diode pumped laser system over the life of the laser diode, comprising the steps of:
- a) sensing the output of a laser diode pumped laser system and producing an electrical feedback signal;
- b) amplifying said feedback signal over a frequency band which includes the Relaxation Oscillation Frequency of said laser system, said amplified feedback signal increasing as a function of the frequency of said feedback signal for at least a portion of said frequency band;
- c) shifting the phase of said amplified feedback signal over said frequency band as a function of the frequency of said amplified feedback signal and maintaining the gain of said amplified feedback signal;
- d) producing, from said amplified feedback signal, a control signal which is a function of the noise in said feedback signal;
- and
- e) superimposing onto the current supplied to said laser diode a current signal which is a function of said phase shifted feedback signal and said control signal.
Dependencies are inferred from the claim text.