Optical: systems and elements – Lens – With support
Reexamination Certificate
2002-08-12
2004-06-22
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
C359S822000, C359S831000
Reexamination Certificate
active
06754013
ABSTRACT:
FIELD OF INVENTION
This invention relates to a device for mechanically adjusting an optical element, and more specifically to a device for adjusting the tilt angle of a lens or mirror and locking the position in a manner that is stable over temperature, time and environmental stresses.
BACKGROUND
An optical mount is a device that points a laser beam by controlling the orientation of an optic. In a laser system, a laser beam strikes an optic and is directed to a further point on the optical pathway by the interaction between the beam and the optic. The optical mount can be used to redirect the laser beam to another point by repositioning the optic.
There is a requirement in laser systems for very high thermal and mechanical stability in order to maintain beam quality, output power, beam divergence and mechanical boresight. Lasers are used in precision applications, such as surveying and military targeting, and in demanding environments, such as the environments in which military laser systems typically operate, have such very high stability requirements.
Ideally, enhanced stability laser systems would be designed and built with no adjustable components. With everything immovably fixed, alignment and boresight stability would depend solely on the quality of the basic design. There would be less tendency for misalignment in the field. Unfortunately, this option would lead to lasers with relatively broad tolerances and relatively poor performance. Over the years, the laser system industry has developed adjustment systems for lasers and the optical components with which they operate that result in very good laser alignment and stability—albeit at the cost of additional system complexity, increased manufacturing time for alignment of the laser system, and increased labor costs. For laser systems having high stability requirements, such as military laser systems, the additional complexity, time and alignment labor costs are significantly higher.
The use of adjustable mounting apparatus for supporting optical components in a laser system such as optical fibers, mirrors, beam splitters, lenses, gratings, and the like, is known. For example, it is frequently necessary to position a first optical element, such as a mirror, optical fiber, or waveguide relative to a second optical element, such as another mirror, optical fiber, waveguide, or beam expander microscope objective lens. Frequently, the relative positioning of such optical components must be very precise, often requiring accuracies on the order of wavelength dimensions. Even smaller allowable tolerances are anticipated in the future.
One approach to the design of precision laser system alignment mounts has been based on kinematic mounting, where three directional constraints determine the alignment. Typically, this might be accomplished with two plates, one mounted on the other at three points, the first point being a ball in socket in each of the plates, the second point being a ball in v-grooves in each plate aligned radially with the sockets, and the third point being a screw threaded through one plate and resting on the surface of the second plate on a radial line from the sockets. The plates can be held together with springs attached to their outer edges. This mechanism has a hinge point formed by the two balls. When the screw is adjusted, one plate will tilt with respect to the other and, if one plate is fixed, the edge of the second plate will be translated perpendicular to the radial line from the hinge to the adjustment screw. The difficulty with this semi-kinematic mounting mechanism is that, as additional adjustments are needed along other axes, additional alignment assemblies must be stacked, thereby increasing the size and complexity of the laser system.
Typical alignment fixtures use a pair of screws to set the alignment in one direction. One screw is used to push the alignment fixture while the other is used to pull the alignment fixture (opposing screws). When the correct alignment of the laser system has been achieved, both screws are “tightened” to prevent any additional movement of the alignment fixture when the system is exposed to shock and vibration environments. Tightening the adjustment screws, however, will change the system alignment just performed unless it is exactly balanced, and detracts from the ability to make very fine alignment adjustments. Stability of such a locking system is also questionable because the stress induced in the mechanism by the screws is along the direction of adjustment. When the stress changes due to changed environmental conditions, the adjustments change as well. Achieving the exact adjustment balance is very tedious and time consuming, resulting in increased cost and time for manufacturing the laser system.
An alternative approach to locking a laser system's alignment has been to use a single screw pushing against a stiff spring. To lock the alignment fixture after the laser system has been aligned, a nut on the single screw is tightened against the fixture. This is a variant of the two screw approach described in the paragraph above. Both of these locking schemes suffer the same problem of potentially changing the just-performed alignment setting when the locking nut tension is increased, again causing additional time and effort to be spent aligning the laser system, along with the added attendant cost. Both schemes also suffer from the same stability problem because of their reliance on the stress conditions of the interface between the adjustment screw and the mount along the direction of travel.
A variety of optical elements can be selected for use as a laser beam relay, depending upon it purpose and application. Laser system design involves a continuing struggle to balance laser performance requirements against the various operational and environmental stability requirements in which the system will operate, and to balance the ease of manufacture and alignment of the laser system against its requirements for long and short term stability in the environment where the delivered laser system will be used. The task of optically aligning the output of a laser beam is alleviated to some extent by the systems disclosed in the prior art.
In addition, U.S. Pat. No. 4,869,583 discloses a laser relay mounting assembly which receives and conducts a laser beam wherein the laser relay mounting assembly adjusts the laser output coincident with a desired axis which further describes a locking screw. U.S. Pat. No. 6,198,580 describes a gimbaled optical mount using a bearing element as a pivot point. There is an optical mount with a locking fastener disclosed in U.S. Pat. No. 6,016,230.
However, the state of the art implementations have yet to satisfy the commercial applications for an optical mounting and there is considerable room for improvement. Thus, there is a need for improved apparatus for easy alignment of optical components that provides low cross talk and enhanced locking strength. In particular, there needs to be an improved locking mechanism that does not impart forces in the angular direction. There is also a need for improved apparatus that permits fine alignment of optical components and a means for quickly locking the adjusted position of the optical element. Also, there is a need for improved apparatus that will permit aligned optical components to retain their alignment under very adverse and demanding operational and environmental conditions, such as the environments in which military laser systems operate. The locking mechanism should be strong to overcome adverse environmental conditions.
SUMMARY OF THE INVENTION
The invention is devised in the light of the problems of the prior art described herein. Accordingly it is a general object of the present invention to provide a novel and useful apparatus and technique that can solve the problems described herein. The foregoing needs are satisfied by the apparatus disclosed herein for easy mounting and alignment of optical components in such a manner that permits aligned optical components to retain their alignment
BAE Systems Information and Electronic Systems Integration Inc.
Maine & Asmus
Thomas Brandi
LandOfFree
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