Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-01-05
2001-05-22
Mack, Ricky (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S846000, C359S872000
Reexamination Certificate
active
06236490
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to optical systems and methods and, more particularly, to the field of deformable mirrors used in adaptive optical systems for compensating a wavefront for errors induced by atmospheric and other disturbances.
BACKGROUND OF THE INVENTION
In a number of optical systems, including those used for high energy laser applications, a beam control system is required to correct a wavefront for wavefront errors generated internally by the system, as well as for external disturbances. The wavefront errors can be large in magnitude and can exhibit a varying spatial and temporal frequency content.
As an example, in airborne laser applications the large magnitude/low frequency errors can be attributed to a boundary layer near the conformal window, while the small magnitude/high frequency (spatial and temporal) error can be attributed to atmospheric turbulence.
As another example, in a wide field of view (WFOV) application the large magnitude/lower frequency wavefront error can originate in a field-dependent WFOV beam expander, while the smaller magnitude/higher frequency wavefront error may originate in the laser and beam control system.
Referring to
FIG. 1
, a conventional technique to compensate for these wavefront errors employs two deformable mirrors
1
and
2
. Mirror
1
is used to compensate for the large magnitude/low frequency error (low bandwidth (BW)), while mirror
2
is used to compensate for the smaller magnitude/higher frequency error (high BW). Deformable mirror
1
includes a base plate or backup structure
3
that supports a plurality of first actuators
5
, which in turn support a facesheet
4
having a reflective surface
4
A. Deformable mirror
2
is similarly constructed to include a backup structure
6
that supports a plurality of second actuators
8
, which in turn support a facesheet
7
having a reflective surface
7
A.
In general, the first actuators
5
will provide a larger range of linear motion (wider dynamic range), but with longer response time (lower BW), than the second actuators
8
. A beam
9
to be wavefront corrected must therefore be directed so as to impinge on both surfaces
4
A and
7
A, with the large magnitude/lower frequency wavefront error being corrected by the low BW mirror
1
, while the smaller magnitude/higher frequency wavefront error is corrected by the high BW mirror
2
.
It can be seen that this approach to wavefront correction increases the complexity, mass, volume and cost of the system by requiring two mirror structures, with additional transfer optics (not shown) for directing the beam between the two mirror structures.
OBJECTS AND ADVANTAGES OF THE INVENTION
It is a first object and advantage of this invention to provide an improved deformable mirror system that overcomes the foregoing and other problems.
It is a further object and advantage of this invention to provide a dual stage deformable mirror structure that requires only one backup structure, and only one reflective surface, for simultaneously compensating a wavefront of interest for both the large magnitude/lower frequency wavefront errors and the smaller magnitude/higher frequency wavefront errors.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects and advantages are realized by methods and apparatus in accordance with embodiments of this invention.
A multistage deformable mirror structure is constructed and operated so as to simultaneously compensate an incident wavefront for both large and small magnitude and low and high temporal and spatial frequency wavefront errors with a dual stage device. In accordance with this invention a mirror facesheet is provided that is supported by and deformed with a set of high bandwidth actuators that are closely spaced together. The set of high bandwidth, closely spaced actuators are supported by an intermediate deformable structure which, in turn, is supported by and deformed with a set of larger dynamic range actuators. The set of larger dynamic range actuators operate with a lower bandwidth, and are spaced at wider intervals than the set of high bandwidth actuators. As the intermediate structure is deformed, the deformed shape is transmitted through the closely spaced, high bandwidth actuators and deforms the mirror facesheet so as to correct for the large magnitude/lower frequency wavefront errors. Simultaneously, the set of high bandwidth, closely spaced actuators are selectively operated to compensate an incident wavefront for the smaller magnitude/higher frequency wavefront errors. The single mirror facesheet is thus simultaneously deformed and given a shape suitable for compensating the incident wavefront for the large and small magnitude and low and high temporal and spatial frequency wavefront errors.
A multistage deformable mirror structure, in accordance with the teachings of this invention, includes a backup structure having a support surface; a mirror facesheet having an optical surface; and, interposed between the support surface and the optical surface, at least one intermediate deformable structure that is coupled at a first surface to the support surface through a first set of linear actuators for being deformed by the set first set of actuators. The at least one intermediate deformable structure is also coupled at an opposing second surface to the optical surface through a second set of linear actuators for deforming the optical surface. The optical surface assumes a shape that is a combination of the deformation imparted to the at least one intermediate deformable structure by the first set of linear actuators, and the deformation imparted to it by the second set of linear actuators.
The first set of linear actuators have a wider dynamic range than the second set of linear actuators, and the optical surface is deformed so as to simultaneously compensate an incident wavefront for both large and small magnitude and low and high temporal and spatial frequency wavefront errors. The first set of linear actuators operate with a lower bandwidth, and are spaced at wider intervals, than the second set of linear actuators.
Also disclosed is a method for simultaneously compensating a wavefront for large magnitude/low frequency error and small magnitude/high frequency error. This method includes steps of: (a) directing the wavefront to an optical surface of a facesheet of a deformable mirror structure; and (b) simultaneously deforming the optical surface with a first set of actuators, applied through an intermediate deformable structure, and with a second set of actuators that are mounted on the intermediate deformable structure.
The step of simultaneously deforming includes a step of varying the linear extension of individual ones of the second set of actuators at a higher rate than the linear extension of the first set of actuators is varied. In this manner the second set of actuators are operated to deform the optical surface for correcting for the small magnitude/high frequency error, while the first set of actuators are operated to simultaneously deform the optical surface for correcting for the larger magnitude/lower frequency error.
REFERENCES:
patent: 5274479 (1993-12-01), Zmek et al.
patent: 5864215 (1999-01-01), Shen et al.
Mack Ricky
The B. F. Goodrich Company
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