System, method and device for rapid, high precision, large angle beam steering Number:7,385,768 from the United States Patent and Trademark Office (PTO) owispatent

Title: System, method and device for rapid, high precision, large angle beam steering

Abstract: A system, method and apparatus for rapid, large angle, high-precision steering of one or more beams of light, and in particular, laser beams, using one or more concave reflectors to provide narrow, essentially collimated output beams. The rapid, beam steering device amplifies the angular deflection provided by a small angle steering element by means of one or more concave reflecting surfaces while controlling the divergence of the output beam using a divergence control lens, to produce an essentially collimated output beam in a field of regard that subtends +/-45 degrees on one axis and +/-50 degrees on an orthogonal axis.

Patent Number: 7,385,768 Issued on 06/10/2008 to Wo,   et al.

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Inventors:	Wo; Yei (East Brunswick, NJ), DeChiaro; Steven A. (Freehold, NJ)
Assignee:	D + S Consulting, Inc. (Eatontown, NJ)
Appl. No.:	11/392,854
Filed:	March 29, 2006

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	60738771	Nov., 2005

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Current U.S. Class:	359/727
Field of Search:	359/727,726,728,729,730,731,732,733

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References Cited [Referenced By]

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Other References

Sievenpiper et al., A tunable impedance surface performing as a reconfigurable beam steering reflector, IEEE, Mar. 2002, pp. 384-390, vol. 3, No. 3. cited by other . Ishikawa et al., An integrated micro-optical system for VCSEL-to-fiber active alignment, Sensors and Actuators, 2003, pp. 109-115, A 103, Elsevier. cited by other . Neilson et al., Compact free space crossconnect using individual collimators, Electronic Letters, Jan. 8, 2004, vol., 40 No. 1, IEE. cited by other . Kim et al., Large tilt angle electrostatic force actuated micro-mirror, IEEE Photonics Technology Letters, Nov. 2002, pp. 1569-1571, vol. 14, No. 11. cited by other . Suhonen et al., Scanning micromechanical mirror for fine-pointing units of intersatellite optical links, Smart Mater. Struct. 10 (2001) 1204-1210. Institute of Physical Publis. cited by other . Fan et al., Two-dimensional optical scanner with large angular rotation realized by self-assembled micro-elevator, 1998, pp. 107-108, IEEE. cited by other . Meline et al., Universal beam steering mirror design using the cross blade structure, Acquisition, Tracking, and Pointing VI, 1992, SPIE vol. 1697, pp. 424-442. cited by other . Khan et al., Demonstration of 3-dimensional wide angle laser beam scanner using liquid crystals, Optics Express, Mar. 8, 2004, pp. 868-882, vol. 12, No. 5, Optical Society of America. cited by other . Titus, Beam Steering and Light Deflection, www.lci.kent.edu/boslab/projects/light.sub.13deflection/index.html. cited by other . Carrano, Increasing the effectiveness of steered agile beams, Microsystems Technology Office, 2002. cited by other . Tuantranont et al., MEMS-controllable microlens array for beam steering and precision alignment in optical interconnect systems, University of Colorado, Boulder, CO. cited by other . Baddeley, Laser transformation, Military Information Technology online edition, www.military-information-technology.com/print.sub.13article.cfm?- DocID=597. cited by other . McManamon, Putting on the Shift, Spie's OE Magazine, pp. 15-17, Apr. 2003. cited by other . Hallstig et al., Laser Beam Steering and Tracking using a Liquid Crystal Spatial Light Modulator, Swedish Defense Research Agency (FOI), Linkoping, Sweden. cited by other . Hunwardsen, Optical Phased Array Improves Liquid Crystal Devices Used in Laser Beam Steering Subsystems, www.nasatech.com/Briefs/Mar04/UE10304.html, Rockwell Scientific. cited by other . Gibson et al., Wide angle beam steering for Infrared Countermeasures applications, 2002, pp. 100-111, Proceedings of SPIE vol. 4723. cited by other . Goltsos et al., Agile beam steering using binary optics microlens arrays, Optical Engineering, Nov. 1990, pp. 1392-1397, vol. 29 No. 11, MIT. cited by other . Matkin, Steered agile beams program support for Army requirements, 2002, pp. 1-12, Proceedings of SPIE vol. 4489. cited by other . Leheny, Section II: Reprint of Broad Agency Announcement 99-25 "Steered Agile Beams (STAB)" from the Commerce Business Daily, May 10, 1999, Issue No. PSA-2342. cited by other . Winker, DARPA STAB Kickoff Meeting: Liquid Crystal Agile Beam Steering, Aug. 8, 2000, Rockwell Science Center, Thousand Oaks, CA. cited by other.

Primary Examiner: Thompson; Timothy J.
Attorney, Agent or Firm: Catalina, Jr.; Richard A.

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to, and claims priority from, U.S. Provisional Patent application Ser. No. 60/738,771 filed on Nov. 22, 2005 by Yei Wo and Steven A. DeChiaro titled "High Resolution Large Range Steered Agile Beam Device," the contents of which are hereby incorporated by reference.

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Claims

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What is claimed is:

1. A device for rapid, large angle steering of a beam of light emitted by a light source, comprising: a concave reflecting surface having a first focal length; a small angle steering element positioned so as to steer said beam of light towards said concave reflecting surface over a first range of angles such that the reflected beam, reflected from said concave reflecting surface, traverses a second range of angles, and wherein said second range of angles exceeds said first range of angles; and a divergence control lens having a second focal length positioned so as to focus said beam of light to a surface that is essentially said first focal length from said concave reflecting surface, thereby providing a reflected beam that is essentially collimated.

2. The device of claim 1 wherein said concave reflecting surface is a sphere.

3. The device of claim 1 wherein said concave reflecting surface is an aspheric surface.

4. The device of claim 2 wherein said small angle steering element is located at a position that is 1.5 times a radius of said concave reflecting surface from said concave reflecting surface.

5. The device of claim 2 further comprising a collimating lens, a beam expander and a flat mirror, and wherein optical centers of said light source, said collimating lens, said beam expander, said small angle steering element and said flat mirror all lie essentially in a first plane, while an optical center of said concave reflecting surface lies in a second, parallel plane.

6. The device of claim 1 further comprising a second concave reflecting surface having a third focal length and located such that said beam of light steered from said small angle steering element is directed to said first concave reflecting surface via said second concave reflecting surface.

7. The device of claim 6 wherein said second concave reflecting surface is located such that said beam of light steered by said small angle steering element is reflected off said second concave reflecting surface to essentially pass through a point that is the optical axis of said first concave reflecting surface and a distance 1.5 times the radius of said first concave reflecting surface from said first concave reflecting surface.

8. A method of rapid, large angle steering of a beam of light emitted by a light source, comprising: deflecting said beam of light over a first range of angles using a small angle steering element; amplifying said first range of angles to a second range of angles using a concave reflecting surface having a first focal length; and collimating the output beam of said second range of angles using a divergence control lens, said divergence control lens having a second focal length and being positioned so as to focus said beam of light to a surface that is essentially said first focal length from said concave reflecting surface.

9. The method of claim 8 wherein said concave reflecting surface is a sphere.

10. The method of claim 8 wherein said concave reflecting surface is an aspheric surface.

11. The method of claim 9 wherein said small angle steering element is located at a position that is 1.5 times a radius of said concave reflecting surface from said concave reflecting surface.

12. The method of claim 9 further comprising providing a collimating lens, a beam expander and a flat mirror, and wherein said light source, said collimating lens, said beam expander, said small angle steering element and said flat mirror are all located such that their optical centers all lie essentially in a first plane, while said concave reflecting surface is located such that its optical center lies in a second, parallel plane.

13. The method of claim 8 further comprising locating a second concave reflecting surface having a third focal length such that said beam of light steered from said small angle steering element is directed to said first concave reflecting surface via said second concave reflecting surface.

14. The method of claim 13 wherein said second concave reflecting surface is located such that said beam of light steered by said small angle steering element is reflected off said second concave reflecting surface to essentially pass through a point that is the optical axis of said first concave reflecting surface and a distance 1.5 times the radius of said first concave reflecting surface from said first concave reflecting surface.

15. A apparatus for rapid, large angle steering of a beam of light emitted by a laser, comprising: small angle steering means for deflecting said beam of light over a first range of angles; spherical reflecting means for amplifying said first range of angles to a second range of angles, said concave reflecting means having a first focal length; and divergence control lens means for collimating the output beam of said second range of angles, said divergence control lens means having a second focal length and being positioned so as to focus said beam of light to a surface that is essentially said first focal length from said concave reflecting surface.

16. The apparatus of claim 15 wherein said small angle steering means is effectively located at a position that is 1.5 times a radius of said spherical reflecting surface from said spherical reflecting surface, and further comprising a beam expanding means and a flat mirror, and wherein said laser, said collimating lens means, said beam expanding means, said small angle steering means and said flat mirror are all located such that their optical centers all lie essentially in a first plane, while said spherical reflecting means is located such that its optical center lies in a second, parallel plane.

17. The apparatus of claim 15 further comprising locating a second spherical reflecting means having a third focal length such that said beam of light steered from said small angle steering means is directed to said first spherical reflecting means via said second spherical reflecting means.

18. The apparatus of claim 17 wherein said second spherical reflecting means is located such that said beam of light steered by said small angle steering means is reflected off said second spherical reflecting means to essentially pass through a point that is the optical axis of said first spherical reflecting surface and a distance 1.5 times the radius of said first spherical reflecting surface from said first spherical reflecting surface.

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Description

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FIELD OF THE INVENTION

The present invention relates to rapid, wide angle beam steering. More specifically, the present invention relates to a system, method and device for rapid, large angle, high precision steering of one or more beams of light, and particularly, to rapid, large angle steering of laser light beams using concave reflectors. In one preferred embodiment, the present invention is an electronically controlled, rapid and precise, piezo-actuated, large angle beam deflection system, method and device that utilizes reflective optics for amplifying the steering angle of the output beam that results in a field of regard that subtends +/-45 degrees on one axis and +/-50 degrees on an orthogonal axis.

BACKGROUND OF THE INVENTION

Precise and controllable delivery of laser beams to a desired location is an important technology with respect to telecommunications, military, and other general industrial applications. Beams of light having a low divergence, such as laser beams, play an important role in military and non-military systems, as they can provide a variety of functions, including, but not limited to, infrared countermeasures ("IRCM"), target designation, and communications, such as free-space optical communications. The most common means of obtaining such delivery is by using large, i.e., macroscopic, mechanically controlled mirrors, lenses and gimbals to steer laser beams. While this technology is mature, it is limited by, among other things, the mechanical nature of mirror movement. Furthermore, inertial properties of mechanically driven mirrors limit the speed with which steering can be changed. In addition, gimbaled or rotating mirrors or reflectors may be vulnerable to vibrations and accelerations.

With regard to military applications, such as infrared countermeasures (IRCM), target tracking and designation, and laser communications, at present, further improvement of these applications is hindered by the lack of small, lightweight, low cost, rapid laser beam steering, pointing, and tracking capabilities. The gimbaled and turret mounted laser systems that are currently available tend to be bulky, heavy, expensive and unsuitable for novel battlefield applications. Military applications would also benefit from an ability to emit multiple independently controlled laser beams and from adaptive optics technology. Each of these functions requires, or can benefit from, the ability to point, steer and track the beam. Current technologies have failed to deliver such abilities in accordance with military and defense requirements.

For example, laser beam or free-space optical communications is a particularly useful application of lasers to battlefield situations. The laser's highly directional beam provides the means for rapidly deployed, enormously high bandwidth, and highly secure point-to-point communications links over tactically significant ranges with good relay capability. These laser beam communications capabilities are, however, limited to communications between relatively large, fixed or slow moving objects, because of the slow speed, relatively large weight and significant power consumption of the current turret mounted, gimbaled laser beam steering systems. Employing current technologies, steered laser beams cannot, for instance, be used to provide communications links between rapidly moving or small vehicles such as, but not limited to, small unmanned flight vehicles, individual foot solders, terrestrial vehicles, or other manned or unmanned aircraft. This presents serious short comings in the era of "smart" battlefield and theater of engagement technologies.

Realizing the untapped, battlefield potential of laser beams, the U.S. Defense Advanced Research Agency ("DARPA") launched the Steered, Agile Beam ("STAB") initiative in 1999, seeking the development of new beam steering technologies. DARPA specified that the new beam steering technologies should be capable of achieving significant reductions in size, weight, power, and cost over conventional methods. The primary objective of the STAB program was to produce a means to rapidly steer a laser beam over a wide three dimensional angular range while maintaining optical alignment with mobile targets at lengthy target ranges. In particular, the list of potentially useful and desired characteristics of the STAB program include the following specifications and objectives: 1) the ability to achieve a steering field of regard of 180.degree. Azimuth and +/-45.degree. Elevation (i.e., the ability to steer or scan a laser beam better than +/-45.degree.), 2) eye safe operation, 3) rapid acquisition of the intended receiver and maintenance of optical alignment with mobile targets at representative target ranges of from 500 m up to 2 or 3 km, 4) correction for atmospheric degradation (if required), 5) covert optical data communications at extremely high bandwidth or throughput, 6) the ability to operate in the presence of strong daylight, 7) side lobe suppression of better than 30 dB, 8) compatibility with current target designation and IRCM infrastructure, and 9) means for covert target designation. The present invention substantially achieves all of these objectives.

As a result of the STAB initiative, numerous new beam-steering applications have been identified; however, current beam-steering technology still does not exist to support the identified applications by the STAB program. Most current optical beam steering systems continue to be mechanically driven systems--in whole or in part--which are complex, bulky, imprecise and expensive, and require high power to produce desired acceleration of the components thereof. The steering of these systems is relatively slow and imprecise, still often requiring mechanical stabilization, and such systems are still sensitive to vibration and acceleration.

Such shortcomings not only fail to meet the basic battlefield objectives established by DARPA, but further permeate other potential applications that would benefit from rapid, wide-angle agile beam steering. For instance, in the near term, new technologies for beam-steering systems with regard to military aircraft must facilitate self-protection (techniques-based infrared countermeasures or IRCM), targeting, passive and active searching and tracking, and free-space optical communications. Moreover, these systems must accommodate, in the longer term, damage-and-degrade-based infrared countermeasures. The new beam steering technologies must also be "conformal" to the outer skin of a vehicle, such as an aircraft, in order to reduce aerodynamic drag, reduce radar cross section, and minimize the obscuration to adjacent electro-optic systems.

In such cases, the optical beam steering system must deflect or steer an optical beam through relatively large angles, and there is a requirement for both a high speed of deflection and a high degree of precision in positioning the beam. A purely mechanical mirrored beam system can cover a large angular field with high resolution, but the speed or agility of the beam is limited by mechanical inertia. Electro-optical, acousto-optical, and low-inertia mechanical beam deflection systems are capable of high speeds of steering, but have a limited number of resolvable angular positions, typically in the magnitude of +/-1.5-3.0 degrees, and constitute, therefore, small angle or "fine" angle beam steering. As such, there is a need for a rapid, high-angle and precise agile beam steering system for numerous military aircraft applications.

In addition, the ability to rapidly steer multiple beams from a small, light weight package will allow conformal mounting of IRCM systems across all vulnerable points of a military aircraft. Multiple beam steering will also enable deployment of target illumination and designation systems capable of simultaneous engagement of multiple targets. Current technologies have failed to produce a beam steering system able to scan large angles, rapidly and precisely, and with the capability of accommodating more than one beam.

Recent advances in micro component technologies such as liquid crystals, micro electromechanical systems (MEMS) and optical MEMS, resonant cavity photo detectors, micro-diffractive optics, adaptive optics, micro-cavity quantum well lasers, thin film and photonic bandgap materials, for example, offer new opportunities in the development of "chip-scale" Microsystems for steered laser beam applications. However, such technologies are unable to meet all of the objectives of the STAB program and, in particular, are simply unable to deliver rapid, wide-angle and high precision beam steering capabilities.

Beam steering for IRCM applications, therefore, continue to focus on "macro" approaches to resolving the high angle, high speed, high precision dilemma. As such, size and bulk--undesirable features of current macro approaches--continue to plague current beam steering technology. For example, with regard to IRCM technologies, the prior art includes steering mirrors, pointing gimbals and monochromatic electro-optical, beam steering mechanisms. Steering mirrors require output windows many times the size of the system optical entrance pupil to scan over a large field of regard. Unfortunately, the mirror form factor requirements greatly increases the overall size of the sensor package.

By way of demonstration, a particular gimbaled approach for an IRCM device involves use of an imaging system mounted in a dome that is gimbaled to provide a desired pointing angle. The gimbals must point the entire sensor to scan the field-of-regard. Unfortunately, for aircraft applications, this requires a mirror below the platform line, which necessitates a hole in the platform. In addition, the dome and optical assembly is bulky, typically requires considerable volume, and has a radar cross-section which tends to increases the observe-ability of the vehicle.

Other approaches to an IRCM device have been suggested that would utilize existing technologies, such as a ball-turret recessed into the vehicle body. However, the downside of this approach is that, in order to obtain a full field of regard, a large window is required. This approach is further not feasible because the ball-turret must be deeply recessed and positioned within the body of the vehicle. Such an approach would simply utilize too much space within the aircraft vehicle.

Another approach that has been suggested as a conformal package is to implement a rotating prisms concept, which utilizes two prisms that rotate against each other. However, this approach is not desirable because the system is not entirely reflective, and as a result, there is a pointing error among different colors of the spectrum.

There are many other important applications which call for optical beam steering. One of these applications is free space optical communications, which is important to the telecommunications, cable and satellite television industries, as well as the military, as noted above.

From a military perspective, for example, communications networks that form the backbone of tactical communications are most often bulky, heavy, and time consuming to put into operation. Shortfalls in standard military tactical communications include the following: Frequency allocation is a serious problem. Bandwidth is too narrow for some traffic needs. Radio frequency ("RF") omni-directional emissions allow targeting of defense systems. Very limited use during periods of radio silence. RF traffic more easily intercepted by the enemy. RF signals can be jammed. Time to set up and relocate RF stations (MSE) takes too long. Use of wire as an alternative is costly, time consuming and somewhat inflexible.

Free-space optical communication has a number of advantages over RF communications, not least in the area of security. High performance laser systems have an inherently high level of link transmission security due to the very narrow transmitter beam width. It is necessary to directly interrupt the beam in order to access information, and this is both exceedingly difficult to achieve and easily detectable. For the same reasons, it causes no interference with nearby RF sources. Because lasers operate at a much higher frequency, moreover, they are able to achieve an exponential data throughput improvement. Transferring responsibility for throughput from satellite communication frequencies and into the free-space optical communication world will also free up RF for other military users and for applications that free-space optical communication cannot meet.

Accordingly, there is a need for a beam steering system capable of rapid operation over a wide angular field, and with a high degree of precision. The present invention satisfies this need.

The present invention successfully implements substantially of the aforementioned requirements, including, but not limited to, the DARPA STAB program objectives. The design of the present invention incorporates a high precision small angle steering element or "seeder" utilizing modern technologies such as, but not limited to, electro-optical, acousto-optical, opto-ceramic or piezoelectric actuators and a larger angle steering or amplification feature that is accomplished by spherical reflective devices, e.g., concave mirrors, which amplify the steering angle rendered by the fine-steering element. The novelty of the invention is represented by the amplification of a relative small steering angle, typically less than +/-1.5 degrees to a large steering angle, +/-45 degrees by one or more, but preferably two (2), curved reflectors. Indeed, the present invention can work with most, if not all, of the known small angle "seeder" or steering devices, including such non-mechanical technologies utilizing liquid crystal (LC) or other technologies known to those skilled in the art regarding rapid, small angle, high precision beam steering. The small angle steering can be achieved by any technology with high precision. The invention utilizes the reflection laws of physics and the tremendous speed (3.times.10.sup.8 meters per second) at which the light travels, and solves the problems of many other steering schemes, which usually have less than +/-25 degrees of 2-dimensional steering range. To date, no embodiments of the aforementioned concept have been successfully reduced to practice and the prior art has largely failed to successfully accomplish rapid, high precision, large angle beam steering. The present invention accomplishes precise, large angle beam steering in an eloquent fashion.

SUMMARY OF THE INVENTION

The present invention relates to rapid, wide angle beam steering. More specifically, the present invention relates to a system, method and device for rapid, large angle, high precision steering of one or more beams of light, and particularly, to rapid, large angle steering of laser light beams using concave reflectors. In one preferred embodiment, the present invention is an electronically controlled, rapid and precise, piezo-actuated, large angle beam amplification system, method and device that utilize reflective optics for amplifying the steering angle of the output beam that results in a field of regard that subtends +/-45 degrees on one axis and +/-50 degrees on an orthogonal axis.

In a preferred embodiment, the rapid beam steering device or system includes a small angle steering element positioned to steer a beam of laser light over a first range of angles towards a concave reflecting surface such as a spherical mirror. The focal length, size and position of the spherical mirror are chosen such that the reflected beam traverses a significantly wider range of angles, i.e., the concave reflecting surface effectively amplifies the angular steering of the small angle steering element. In addition, the rapid beam steering device includes a divergence control lens. In a preferred embodiment of the invention, the focal length and position of the divergence control lens are selected so as to focus the laser beam to a surface that is essentially the focal length of the concave reflecting surface short of the concave reflecting surface. This arrangement of elements results in a reflected beam that is essentially collimated.

In further embodiments of the invention, the rapid beam steering system or device may include a second mirror. This may be a flat mirror utilized to fold the design to make it more compact or the second mirror may be another concave reflecting surface used to further increase the angular amplification of the small angle steering element. In addition, the optical components, particularly the concave mirrors, may be used in off-axis configurations to allow the output beam to sweep over a large solid angle without obstruction.

These and other features of the invention will be more fully understood by references to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing a spherical reflecting surface amplifying a beam steering angle.

FIG. 1A is a drawing of a perspective view of the device illustrated in FIG. 1, showing a spherical reflecting surface amplifying a beam steering angle.

FIG. 2 is a schematic drawing showing a beam steering apparatus having a spherical reflecting surface and a reasonably collimated output beam.

FIG. 3 is a schematic drawing showing a beam steering apparatus having a spherical reflecting surface and a well-collimated output beam.

FIG. 3A is drawing of a perspective view of the invention illustrated in FIG. 3, showing a beam steering apparatus having a spherical reflecting surface and a well-collimated output beam.

FIG. 4 is a schematic drawing showing a beam steering apparatus having two spherical mirrors and a well-collimated output beam.

FIG. 5 is a schematic drawing showing a further embodiment of a beam steering apparatus having two spherical mirrors and a well-collimated output beam.

FIG. 5A is a drawing of a perspective view of the invention illustrated in FIG. 5, showing a further embodiment of a beam steering apparatus having two spherical mirrors and a well-collimated output beam.

FIG. 5B is drawing of a further perspective view of the invention illustrated in FIG. 5, showing a further embodiment of a beam steering apparatus having two spherical mirrors and a well-collimated output beam.

FIG. 6 is a schematic drawing showing a beam steering apparatus having two off-axis spherical mirrors and a reasonably collimated output beam.

FIG. 6A is drawing of a perspective view of the invention illustrated in FIG. 6, showing a beam steering apparatus having two off-axis spherical mirrors and a reasonably collimated output beam.

FIG. 6B is a drawing of a further perspective view of the invention illustrated in FIG. 6, showing a beam steering apparatus having two off-axis spherical mirrors and a reasonably collimated output beam.

FIG. 7 is a schematic drawing showing an embodiment of a beam steering apparatus having a flat mirror and a spherical mirror.

FIG. 8 is a further view of the invention illustrated in FIG. 7.

FIG. 9 is a further illustration of a beam steering apparatus having two spherical mirrors and a reasonably collimated output beam.

FIG. 9A is a further illustration of a beam steering apparatus having two spherical mirrors and a reasonably collimated output beam, showing a plurality of beam steering angles.

FIG. 10 is a polar iso-candela plot showing the output of the invention as embodied in the apparatus of FIG. 9.

FIG. 11 is an illustration of magnification of an input angle using a spherical reflector.

FIG. 12 is a schematic drawing showing an embodiment of a beam steering apparatus having a fiber collimator, a first, second and third lens, and a tuning mirror.

DETAILED DESCRIPTION

The present invention relates to rapid, wide angle beam steering. More specifically, the present invention relates to a system, method and device for rapid, large angle, high precision steering of one or more beams of light, and particularly, to rapid, large angle steering of laser light beams using concave reflectors.

Small angle laser beam steering technologies are well known. For instance, there are multiple technologies that can provide laser beam steering over ranges of the order of +/-1.5 degrees or other similar small angular ranges. These devices typically use electrically controlled actuators and other devices and may include, but are not limited to, liquid crystal (LC) technologies (e.g., liquid crystal light modulators, liquid crystal digital light deflectors, liquid crystal phase shifters, zero-twist nematic liquid crystal spatial light modulators, liquid crystal optical phased arrays (such as that developed by Rockwell Scientific Co.), among many such liquid crystal based devices), micro electromechanical systems (MEMS) and optical MEMS, resonant cavity photo detectors, micro-diffractive optics, adaptive optics, thin film, photonic bandgap materials, electro-optical, acousto-optical, opto-ceramic and piezo-electric actuators. These small angle beam steering technologies have some of the characteristics that the U.S. Defense Advanced Research Agency (DARPA) is seeking in its STAB initiative, such as rapid and accurate direction control using equipment that is small, light and relatively low cost. These small angle beam steering technologies do not, however, incorporate or embody the most important required characteristic, which is the ability to steer the beam over large angles, preferably of the order of +/-45 degrees, in a rapid and precise manner.

Presently, the only available means of obtaining delivery of large angle beam steering is with the use of large, i.e., macroscopic, mechanically controlled mirrors, lenses and gimbals to steer laser beams. Most current optical beam steering systems continue to be mechanically driven systems that are complex, bulky, imprecise and expensive, and require high power to produce desired acceleration of the components thereof. While this technology is mature, it is limited by, among other things, the mechanical nature of mirror movement. Furthermore, inertial properties of mechanically driven mirrors limit the speed with which steering can be changed. The steering of these systems is relatively slow and imprecise, still often requiring mechanical stabilization, and such systems are sensitive to vibration and acceleration

In a preferred embodiment of the current invention, the short comings of the small angle laser beam steering (fine steering) technologies and the macro-mechanical, large angle beam steering technologies are overcome by amplifying the angular steering of small angle laser beam steering technologies using a novel arrangement of low cost, conventional reflection and refraction optics that also control the beam divergence, resulting not only in precise and rapid steering range amplification on the order of +/-45 degrees, but also steering speed acceleration amplification due to the fact that light travels at enormous speeds. Thus, according to a preferred embodiment of the present invention, rapid, large angle and precise steering of one or more beams of light is achieved, thereby overcoming the shortcomings of present day small angle and large angle technologies.

Significantly, preferred embodiments of the present invention are able to scan a beam, preferably a laser beam, from one angle representing an extreme final output angle in a field of regard of +45 degrees to an opposite, extreme final output angle in the field of regard of -45 degrees (thereby steering the laser beam a total of approximately 90 degrees within the field of regard of +/-45 degrees), and are able to employ a random accessibility of a beam within the field of regard of +/-45 degrees, all in the order of several nanoseconds to slightly less than 1 millisecond (<1 ms), depending on the speed of the small angle seeder or steering technology utilized, which may be an all electronic and non-mechanical small angle seeder or steering element, or which may be an electronic small angle seeder or steering element with slight mechanical properties, such as an electronically controllable small angle steered planar mirror controlled by piezo-electric controllers or actuators. Virtually any small angle seeder or steering technology, device or system may be incorporated into the present invention. For example, where higher speed and enhanced performance are desired, a small angle steering element such as a seeder utilizing MEMS technology may be used in the present invention, thereby achieving a full field of regard scan (approximately 90 degrees or +/-45 degrees) at extremely high speed. One of ordinary skill in the art will realize that the invention disclosed within is not restricted to any specific small angle seeder or steering element or device, and that speed and performance of the invention may be adjusted by utilizing faster and more enhanced performance seeders or small angle steering elements at an increased cost. The utilization of various small angle seeders or steering elements in accordance with the present invention in its various embodiments shall be readily known to those skilled in the art. As such, the present invention is not limited to the present small angle seeder or steering technology and as that technology develops in the future, it may be readily adapted to the present invention and its range amplification properties as demonstrated herein.

In order to better understand the present invention, it is useful to first consider some simpler embodiments of the invention and the limitations of those embodiments before considering the preferred embodiments. These will be discussed with reference to the accompanying drawings in which, as far as possible, like numbers and other references refer to like elements.

Although every reasonable attempt is made in the accompanying drawings to represent the various elements of the embodiments in relative scale, it is not always possible to do so with the limitations of two-dimensional paper. Accordingly, in order to properly represent the relationships of various features among each other in the depicted embodiments and to properly demonstrate the invention in a reasonably simplified fashion, it is necessary at times to deviate from absolute scale in the attached drawings. However, one of ordinary skill in the art would fully appreciate and acknowledge any such scale deviations as not limiting the enablement of the disclosed embodiments.

FIG. 1 is a schematic drawing showing a spherical reflecting surface amplifying a beam steering angle.

In particular, FIG. 1 shows how a concave reflecting surface having at least one focal point may be used to amplify the angle through which a beam is steered. For simplicity, a sphere having an optical axis along the line c-u is chosen as the concave reflecting surface 12. A narrow beam of light from a reasonably collimated light source is directed towards the concave reflecting surface 12 via the point u. For simplicity, only the two beams representing the extremes of beam steering in one plane are shown in FIG. 1. At the one extreme of the steering range, the beam 14 passes through or originates from the point u at an angle .alpha. radians to the optical axis c-u. The beam 14 is reflected off the reflecting surface 12 as beam 16 passing through the point v on the optical axis, making an angle .beta. radians with respect to the optical axis. The distances c-v and c-u may be calculated from the focusing properties of a concave spherical mirror for paraxial rays. This may take the form of the equation 1/v+1/u=1/f=2/r (and thus, f=r/2 in this configuration), where f is the focal length c-f and r is the radius of curvature of the sphere.

At the other extreme of the steering range, the beam 15 passing through or originating from the point u is reflected as the beam 17 also passing through the point v on the optical axis. In this way, a beam steered through or originating from u over a range of solid angle of 2.alpha. steradians has the range of angles of steering amplified to 2.beta. steradians by reflecting surface 12. This phenomenon is illustrated in FIG. 1 for the case when the concave reflecting surface is a sphere, and the range of angles is small enough for the paraxial ray approximation to be a valid approximation.

A significant shortcoming of the simple beam amplification scheme of FIG. 1 is that the beam 16 having an amplified steering angle is a diverging beam, as shown by the divergence angle .gamma. of beam 16. This beam divergence is a result of the focusing effect of the reflecting surface 12 on the rays of light making up beam 14 when reflected to become reflected beam 16. Having a diverging beam 16 limits the useful range of the reflected beam 16.

FIG. 1A is a perspective drawing of the device illustrated in FIG. 1, showing a spherical reflecting surface amplifying a beam steering angle.

In particular, FIG. 1A shows how a concave reflecting surface having at least one focal point may be used to amplify the angle through which a beam is steered. For simplicity, a sphere having an optical axis along the line c-u is chosen as the concave reflecting surface 12. A narrow beam of light from a reasonably collimated light source 18 is directed towards the concave reflecting surface 12 via the point u. Again, for simplicity, only two beams representing the extremes of beam steering in only one two-dimensional plane 11 (out of an infinite number of possible planes) passing through the optical axis are shown in FIG. 1A. At the one extreme of the steering range, the beam 14 passes through or originates from the point u at an angle .alpha. radians to the optical axis. In FIG. 1A, the beam 14 originates at point u from a light beam source 18, such as, but not limited to, a laser light source. The beam 14 is reflected off the reflecting surface 12 as beam 16 passing through the point v on the optical axis, making an angle .beta. radians with respect to the optical axis. The distances c-v and c-u may be calculated from the focusing properties of a concave spherical mirror for paraxial rays. Again, this may take the form of the equation 1/v+1/u=1/f=2/r (and thus, f=r/2 in this configuration), where f is the focal length c-f and r is the radius of curvature of the sphere.

At the other extreme of the steering range plane in FIG. 1A, the beam 15 passing through or originating from the point u is reflected off of the concave reflecting surface 12 as the beam 17 passing through the point v on the optical axis. In this way, a beam steered through or originating from u over a range of solid angle of 2.alpha. steradians has the range of angles of steering amplified to 2.beta. steradians by reflecting surface 12. This phenomenon is illustrated in FIG. 1 and FIG. 1A for the case when the concave reflecting surface is a sphere, and the range of angles is small enough for the paraxial ray approximation to be a valid approximation.

The three dimensional cone 13 emanating from point v on the optical axis represents a theoretical field of regard for beams reflected from surface 12 in this configuration, initially originating or passing through point u, and depending on the precise shape of the concave reflecting surface 12 and the precise location of points c and u. Output beams 16 and 17, being extremes of beam steering in only one two-dimensional plane 11 (out of an infinite number of possible planes) are oriented 180.degree. from each other with respect to the optical axis.

Again, a significant shortcoming of the simple beam amplification scheme of FIG. 1A is that the beam 16 having an amplified steering angle is a diverging beam, as shown by the divergence angle .gamma. of beam 16. This beam divergence is a result of the focusing effect of the reflecting surface 12 on the rays of light making up beam 14 when reflected to become reflected beam 16. Having a diverging beam 16 limits the useful range of the reflected beam 16.

In the above embodiments and examples, and in the embodiments and examples to follow, it should be noted that the concave reflective surface 12 is not limited to only a concave reflecting surface that is a sphere or is spherical, but is meant to further include, without limitation, concave reflecting surfaces that are aspherical, cylindrical, paraboloidal, ellipsoidal, hyperboloidal, or any other suitable curved three-dimensional shape, with the appropriate modification(s) to the respective embodiment utilizing a non-spherical concave reflecting surface based on the particular focal properties and behavior of such non-spherical reflecting surface, as would be appreciated by one skilled in the art. However, as shown in the embodiment in FIGS. 1 and 1A, the concave reflecting surface 12 is a spherical reflector, and the principles and methodology set forth regarding this embodiment are based on and calculated from the focusing properties of a concave spherical mirror for paraxial rays.

FIG. 2 is a schematic drawing showing a beam steering apparatus having a spherical reflecting surface and a reasonably collimated output beam, i.e. having an acceptable divergence of about 1/2 micro-radian.

Although the concave reflecting surface 12 in the apparatus illustrated in FIG. 2 is a sphere or is spherical in shape, it should be noted that this embodiment is not limited to only a concave reflecting surface that is a sphere or is spherical, but is meant to further include, without limitation, concave reflecting surfaces that are aspherical, cylindrical, paraboloidal, ellipsoidal, hyperboloidal, or any other suitable curved three-dimensional shape, with the appropriate modification(s) to an embodiment utilizing a non-spherical concave reflecting surface based on the particular focal properties and behavior of such non-spherical reflecting surface, as would be appreciated by one skilled in the art. However, as shown in the embodiment in FIG. 2, the concave reflecting surface 12 is a spherical reflector, and the principles and methodology set forth regarding this embodiment are based on and calculated from the focusing properties of a concave spherical mirror for paraxial rays.

The beam steering apparatus of FIG. 2 includes a reasonably collimated light source 18 that emits a beam of light 20 such as, but not limited to, a laser light source. This beam of light is directed via an opening in the concave reflecting surface 12 to a small angle steering element 24 located at the point u. The small angle steering element 24 may be, but is not limited to, an electronically controllable small angle steered planar mirror controlled by piezoelectric controllers such as the S-330 piezo tip/tilt platforms supplied by Physik Instrumente (PI) GmbH & Co. KG of Karlsruhe, Germany. These devices have a tip/tilt range of 2 mrad and provide 4 mrad optical beam deflection with sub-.mu.rad resolution and are designed for mirrors up to 50 mm in diameter. In addition, these devices are capable of steering the beam, within the parameters of the instrument, to a fixed point or fixed angle, stopping and holding the steered beam at said fixed point or fixed angle for any period of time as may be desired, as opposed to beam steering devices that perform constant resonance scanning. This allows full scale deflection to be scanned in about or slightly less than 1 millisecond (<1 ms). The small angle steering element of FIG. 2 may also be, but is not limited to, an acousto-optical deflector, a micro-electro-mechanical systems (MEMS) micro-mirror, a Strontium Barium Niobate (SBN) electro-optical crystal or an opto-ceramic system, or any other suitable small angle beam steering device, preferably a reflective small angle steering device.

As previously noted, the present invention as demonstrated in FIG. 2 is not limited to any particular small angle seeder or steering device. Essentially any small angle seeder or steering device as known to those skilled in the art may be used as small angle steering element 24 in this embodiment. One of ordinary skill in the art will realize that the invention disclosed within is not restricted to any specific small angle seeder or steering element or device, and that speed and performance of the invention can be adjusted by utilizing faster and more enhanced performance seeders or small angle steering elements at an increased cost. The utilization of various small angle seeders or steering elements in accordance with the invention disclosed in FIG. 2 and its various embodiments shall be readily known to those skilled in the art. As such, the present invention is not limited to the present small angle seeder or steering technology and as that technology develops in the future, it may readily be adapted to the present invention and its range amplification properties as demonstrated herein.

After passing through a divergence control focusing lens 22, the focused light 23 is directed via an opening in the concave reflecting surface 12 to a small angle steering element 24. The small angle steering element 24 is positioned at point u and steers the beam 23 as a reflected beam onto the concave reflecting surface 12. For simplicity, only two beams representing the extremes of the steering range in one plane are shown in FIG. 2. At one end of the range, the beam 23 is deflected as beam 14 to the concave reflecting surface 12 from where it is reflected as beam 16. At the other end of the range, the beam is deflected as beam 15 to concave reflecting surface 12 from where it is reflected as beam 17. In the system of FIG. 2, the divergence control lens 22 focuses the beam 20, as beam 23, emitted by light source 18 to a surface 28, above the concave reflecting surface 12. Surface 26 represents a second such surface passing through focal point f and being parallel to concave reflecting surface 12. The surfaces 26 and 28 coincide or intersect at the point that beams 14 and 15 pass through them, represented by points f' and f'' respectively. This means that beam 14, in this configuration, is focused at surface 26, being that surface 28 and surface 26 coincide at point f'. Since surface 26 is parallel to concave reflecting surface 12, but separated from it by a distance equal to the focal length f of the reflecting surface 12, the result is that, within the approximations of paraxial rays, the final reflected output beam 16 is a collimated beam.

A shortcoming of the beam steering apparatus of FIG. 2 is that although surfaces 26 and 28 are coincident for beams 14 and 15 (at points f' and f'', respectively), in general, the surfaces do not coincide as a whole. As such, although the divergence is reduced throughout the steering range, there is nonetheless some residual divergence at beam steering angles other than the extreme angle of the range as demonstrated in this drawing by beams 14 and 15.

FIG. 3 is a schematic drawing showing a beam steering apparatus having a spherical reflecting surface and a well-collimated output beam, which may have a beam divergence of 1/2 micro-radian or less.

Although the concave reflecting surface 12 in the apparatus illustrated in FIG. 3 is a sphere or is spherical in shape, it should be noted that this embodiment is not limited only to a concave reflecting surface that is a sphere or is spherical, but is meant to further include, without limitation, concave reflecting surfaces that are aspherical, cylindrical, paraboloidal, ellipsoidal, hyperboloidal, or any other suitable curved three-dimensional shape, with the appropriate modification(s) to an embodiment utilizing a non-spherical concave reflecting surface based on the particular focal properties and behavior of such non-spherical reflecting surface, as would be appreciated by one skilled in the art. However, as shown in the embodiment in FIG. 3, the concave reflecting surface 12 is a spherical reflector, and the principles and methodology set forth regarding this embodiment are based on and calculated from the focusing properties of a concave spherical mirror for paraxial rays.

The beam steering apparatus of FIG. 3 includes a reasonably collimated light source 18 that emits a beam of light 20 such as, but not limited to, a laser light beam. In the system of FIG. 3, there is also a divergence control