Coherent light generators – Particular beam control device – Optical output stabilization
Reexamination Certificate
1998-10-01
2001-07-10
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular beam control device
Optical output stabilization
Reexamination Certificate
active
06259712
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method suitable for providing stability of a laser.
INTRODUCTION TO THE INVENTION
The present invention complements our work on optical interferometric measurement apparatus, as particularly articulated in the above referenced U.S. Pat. No. 5,986,759. Accordingly, in this introduction, we turn our attention to disclosing important aspects of the optical interferometric measurement apparatus, to thereby provide a basis for motivation and explication of the complementary present invention, summarized below.
The optical interferometric measurement apparatus subsumes several different aspects. Illustrative first and second aspects comprise the following.
In a first aspect, the measurement apparatus includes:
(1) an optical interferometer with at least two optical outputs, the ratio of whose intensities can vary with a tuning parameter; and
(2) at least one detector, each of which is optically connected to the interferometer, and producing in aggregate at least two linearly-independent signals that depend on the light intensity and the tuning parameter, which are combined to produce a first measurement whose sensitivity to light intensity changes is substantially smaller than that of either of the two linearly-independent signals, and a second measurement whose sensitivity to the tuning parameter is substantially smaller than that of either of the two linearly-independent signals.
In a second aspect, the measurement apparatus includes:
(1) an optical interferometer with at least two optical outputs, the ratio of whose intensities can vary with a tuning parameter; and
(2) at least one detector, each of which is optically connected to the interferometer, and producing in aggregate at least two linearly-independent signals which are combined to produce orthogonal measurements of light intensity and the tuning parameter when light of appropriate wavelength and coherence is input to the optical interferometer.
The measurement apparatus, so defined in two aspects, is informed by the classical Fabry-Perot technique, with a view to overcoming most of its limitations and cited problems, thereby advantageously realizing unusually sensitive and stable optical interferometric measurement capabilities.
SUMMARY OF THE INVENTION
It is intimated above that the present invention can complement the just disclosed optical interferometric measurement apparatus. We have discerned that this complementary action can come about from turning one's attention from its employment as a measurement apparatus, to a disparate activity centering on its employment as a vehicle for providing frequency stabilization of a laser.
This discovery may be manifest in the following ways.
In a first aspect, we disclose a method suitable for providing stability of a laser, the method comprising:
(1) providing a tunable laser capable of outputting a first beam;
(2) providing an apparatus receiving at least a portion of said first beam, the apparatus including:
(i) an optical interferometer with at least two optical outputs each comprising at least one portion derived from said first beam, the ratio of whose intensities can vary with the tuning of the laser; and
(ii) a detector which is optically connected to the interferometer and producing at least two linearly independent signals that depend on the light intensity and the tuning of the laser, which are combined to produce a measurement whose sensitivity to light intensity changes is substantially smaller than that of either of the two linearly independent signals; and
(3) servoing the laser tuning by reference to fluctuations in the measurement.
In this aspect, the servoing of the laser tuning preferably comprises using a deviation of the measurement from a set point as an error signal in a feedback loop controlling the tuning of the laser.
In a second aspect, we disclose a method suitable for providing stability of a laser, the method comprising:
(1) providing a tunable laser capable of outputting a first beam of frequency &ohgr; and power P;
(2) providing an apparatus receiving at least a portion of said first beam, the apparatus including:
(i) a Fabry-Perot interferometer whose input comprises at least one portion derived from said first beam, producing reflected (R) and transmitted (T) beams, the ratio of whose power can vary with &ohgr; the tuning of the laser; and
(ii) a photodetector which is optically connected to the interferometer and producing at least two linearly independent signals corresponding to the optical power in the R and T beams, which are combined to produce a measurement whose sensitivity to changes in P is substantially smaller than that of either of the R and T signals; and
(3) servoing the laser tuning by reference to fluctuations in the measurement.
In this second aspect, the providing of the apparatus may comprise adjusting the gain of at least one of the R and T signals in order to reduce the magnitude of
∂
V
(
R
)
∂
P
-
∂
V
(
T
)
∂
P
when the condition V(R)−V(T)=0 holds, where V(R) and V(T) are the voltages of the R and T signals, respectively.
Alternatively, the providing of the apparatus in this second aspect may comprise attenuating at least one of the R and T beams in order to reduce the magnitude of
∂
V
(
R
)
∂
P
-
∂
V
(
T
)
∂
P
when the condition V(R)−V(T)=0 holds.
The servoing of the laser tuning in this second aspect preferably comprises using a deviation of the first measurement from a set point as an error signal in a feedback loop controlling the tuning of the laser.
REFERENCES:
patent: 5568255 (1996-10-01), Johnson
patent: 5780843 (1998-07-01), Cliche
patent: 5999547 (1999-12-01), Schneider
DeCain Donald Michael
Hobbs Philip C. D.
Pope Keith Randal
Arroyo Teresa M.
International Business Machines - Corporation
Inzirillo Gioacchino
Kaufman, Esq. Stephen C.
McGinn & Gibb PLLC
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