Abstract:
The use of spatial light modulators to steer light beams and/or vary a field of view is disclosed. A dual frequency liquid crystal spatial light modulator can be controlled so as to form a blazed phase grating thereon that effects desire deflection of incident light. A dual frequency liquid crystal spatial light modulator can also be controlled so as to communicate light from a desired field of view to an imaging device or the like.

Description:
TECHNICAL FIELD 
   The present invention relates generally to optics and, more particularly, to an apparatus and method for steering a beam of light and/or adjusting a field of view using a spatial light modulator. 
   BACKGROUND 
   Light beams are used in a wide variety of different applications, such as communications, imagery, and weaponry. In such applications it is frequently necessary to steer a beam of light and/or adjust a field of view. In some such applications, beam steering and/or field of view adjustment must be performed rapidly. 
   Beam steering is useful in optical communications, where a modulated light beam originating at a transmitter must be aimed toward a remote receiver. Beam steering is also useful in directed energy weaponry, where a light beam must be aimed toward a distant target. In such instances, it can be desirable to rapidly steer the beam from one receiver or target to another. 
   Field of view adjustment is useful in photography and telescopy, were a desired field of view is imaged and/or viewed. For example, satellite systems for terrestrial monitoring often have simultaneous demands from a plurality of different users. Thus, it is frequently necessary to view several scenes in rapid succession and/or to alternate rapidly between such scenes. 
   Mechanical systems for accomplishing beam steering and/or field of view adjustment are well known. Such mechanical systems include those that utilize movable optical components. For example, a mirror may be aimed so as to effect desired beam steering and/or field of view adjustment. 
   However, as those skilled in the art will appreciate, such mechanical components are subject to wear. Not only can wear contribute to premature failure, but it can also adversely affect the accuracy of a mechanical beam steering/field of view adjustment system prior to failure. 
   Further, such mechanical systems have strict speed limitations. These speed limitations are due, in part, to the inertia of the moving components. Drive motor capacities, current limitations, and structural constraints also contribute to such speed limitations. 
   Further, the mechanical components (mirrors, drive motors, gimbals, and linkages) of such systems have substantial weight and volume. The weight and volume of such mechanical systems makes them unsuitable for some applications. For example, launch vehicle payload weight and volume restrictions may limit the use of mechanical systems in space-based applications. 
   Non-mechanical beam steering/field of view adjustment systems are also known. However, contemporary non-mechanical systems require high voltages and/or expensive technology, thus making them unsuitable for many applications. 
   In view of the shortcomings of such contemporary systems, there is a need for lightweight, small, non-mechanical beam steering and field of view adjustment systems that respond rapidly and do not require high voltages for operation. 
   SUMMARY 
   The use of spatial light modulators, such as duel frequency liquid crystal spatial light modulators, to steer light beams and/or vary a field of view is disclosed. Duel frequency liquid crystal spatial light modulators have rapid response times that make them suitable for use in many time critical applications, such as battlefield communications, real time imaging, and directed energy weaponry. Duel frequency liquid crystal spatial light modulators are substantially lighter in weight as compared to their mechanical counterparts, thus making them particularly desirable for use in space-based applications. 
   According to one aspect of the present invention, a dual frequency liquid crystal spatial light modulator can be controlled so as to form a phase grating thereon that effects desire deflection of incident light. For example, a blazed phase grating can be formed on a dual frequency liquid crystal spatial light modulator. Blazed phase gratings are especially efficient at deflecting light. 
   According to one aspect of the present invention, the deflection of light can be used for beam steering and/or field of view adjustment. Thus, a dual frequency liquid crystal spatial light modulator can used be to direct a beam of light used for communications or weaponry and can also be used to communicate light from a desired field of view to an imaging device or the like. 
   According to one aspect of the present invention, a dual frequency liquid crystal spatial light modulator can be electronically controlled so as to provide the desired deflection of light. Such electronic control is possible because dual frequency liquid crystal spatial light modulators are rapidly programmable and quickly responsive to such programming. That is, a blazed phase grating can be quickly defined and implemented so as to provide the desired degree of light deflection. 
   The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the present invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram illustrating a beam steering system in accordance with an exemplary embodiment of the present invention; and 
       FIG. 2  shows a block diagram illustrating an a field of view adjustment system in accordance with an exemplary embodiment of the present invention. 
   

   Embodiments of the present invention and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
   DETAILED DESCRIPTION 
   At least one embodiment of the present invention comprises a liquid crystal spatial light modulator, such as a dual frequency liquid crystal spatial light modulator, that is configured to facilitate beam steering. Such embodiments of the present invention may find application in optical communications and directed energy weaponry, for example. As those skilled in the art will appreciate, dual frequency liquid crystal spatial light modulators provide enhanced speed and controllability with respect to other types of spatial light modulators. 
   Thus, at least one embodiment of the present invention comprises a non-mechanical way to rapidly change the deflection angle of a light beam, so as to direct the light beam toward a desired target. More particularly, at least one embodiment of the present invention comprises a dual frequency liquid crystal spatial light modulator, electronic means to induce a blazed grating pattern on the dual frequency liquid crystal spatial light modulator, algorithms for varying the blaze period so as to effect beam steering, and algorithms to vary the blaze pitch. 
   Thus, a blazed phase grating can be created within a dual frequency liquid crystal spatial light modulator array. This can be accomplished by sending control signals, e.g., voltage signals of appropriate amplitude, frequency, and duty cycle, to the dual frequency liquid crystal spatial light modulator. The blazed grating deflects incident light by an amount dependent on the period of the grating. The beam deflection angle may be varied in time by varying the control signals. Thus, a beam of light, such as a laser beam, can be rapidly steered from one target to another. 
   The period and blaze angle can be controlled electronically, e.g., by blaze period and pitch control logic Optionally, the beam can be monitored to determine the deflected beam angle and/or wavefront, so as to provide feedback that can be used to control the deflection angle. 
     FIG. 1  shows a beam steering system wherein a dual frequency liquid crystal spatial light modulator  10  receives incident light  11  and provides a steered beam  12 , according to one exemplary embodiment of the present invention. That is, incident light  11  is transmitted through dual frequency liquid crystal spatial light modulator  10  and is affected thereby so as to introduce a deflection angle θ into the steered beam  12 . Incident light  11  can come from a laser, such as a laser that is used to provide light which is modulated for communications or such as a laser that is suitable for use in a directed energy weapon. 
   More particularly, the deflection angle θ is defined by the period of an induced blazed phase grating formed within the dual frequency liquid crystal spatial light modulator  10 . The period of the blazed phase grating can be electronically controlled, so as to provide the desired deflection angle θ. 
   Blaze period and pitch control logic  14  defines the blaze period and pitch required to provide desired deflection angle θ. Blaze period and pitch control logic  14  receives a signal representative of a desired deflection angle and provides a control signal to multiplexed array commands circuit  13 , so as to effect the deflection of light by the desired angle. Multiplexed array commands circuit  13  controls dual frequency liquid crystal spatial light modulator  10 , so as to create the necessary blazed phase grating thereon and thus effect deflection of incident light  11  by the desired deflection angle θ. 
   At least one embodiment of the present invention comprises a dual frequency liquid crystal spatial light modulator configured to facilitate field of view adjustment. Such embodiments of the present invention may find application in imaging, such as in photography (either film or digital) and telescopy, for example. Thus, at least one embodiment of the present invention comprises a non-mechanical way to rapidly change the direction and field of view of a remote imaging system, so as to provide a multiplexed output of targeted scenes. In this manner, a plurality of different scene can be simultaneously viewed substantially in real time. 
   According to one embodiment of the present invention, a liquid crystal spatial light modulator, such as a dual frequency liquid crystal spatial light modulator, is incorporated into an optical system to effect changes in the direction and/or area of the field of view. In addition to the dual frequency liquid crystal spatial light modulator, the optical system can comprise static components, such as refractive and/or reflective elements, e.g., lenses and/or mirrors. The optical system may also comprise optical elements that affect the polarization or wavelength of light. 
   Command are issued by a data processing and control system, which in turn are translated into voltage signals that are communicated to the elements of the dual frequency liquid crystal spatial light modulator, so as to effect desired control thereof. The control signals effect a varying refractive index across the dual frequency liquid crystal spatial light modulator. Thus, the dual frequency liquid crystal spatial light modulator can function substantially like a programmable lens, whose optical properties can be rapidly changed. 
   The dual frequency liquid crystal spatial light modulator is used to vary the tilt and focus of incoming light. It may also be used (in combination with other optical elements) to vary a zoom or magnification incoming light. In combination with the static elements of the optical system, these changes effect the direction and field of view of an imaging system. 
   The changes can be made synchronously with respect to the acquisition frame rate of the monitoring system. By this means, successive image frames can be dedicated to multiple scenes. The frames from each scene are segregated electronically, so that they can be displayed and/or recorded independently. 
     FIG. 2  shows a non-mechanical method and system for adjusting the field of view of a camera, according to one exemplary embodiment of the present invention. A dual frequency liquid crystal spatial light modulator  20  receives light  22  representing a field of view and provides light  21  processed thereby to an imaging system  27 , such as that of a camera. 
   Optionally, static optical elements  23  and/or  24  are interposed within the optical path. For example, input side static optical elements  24  can receive light  26  that defines a field of view and can provide light  22  to dual frequency liquid crystal spatial light modulator  20 . Input side static optical elements  24  can provide desired focus, zoom, polarization and/or filtering, for example. 
   Also, light  21  from dual frequency liquid crystal spatial light modulator  20  can be provided to output side static optical element  23 , which in turn provide light  25  to imaging system  27 . Output side static optical elements  23  can provide desired focus, zoom, polarization and/or filtering, for example. 
   Imaging system  27  can provide an electronic signal representative of an image of the field of view to a signal processing/control system  28 , which in turn provides a control signal to dual frequency liquid crystal spatial light modulator  20 , so as to effect viewing of the desired field of view. The control signal provided by signal processing/control system  28  can also determine the focus, zoom, or other desired optical parameters of the viewed image. 
   Commanded field of view circuit  29  provides a signal to signal processing/control system  28  that is representative of a desired field of view. That is, this control signal determines what field of view dual frequency liquid crystal spatial light modulator  20  is configured to provide. The desired field of field commanded by commanded field of view circuit  29  can be defined by either a human operator or an automated system. 
   Although the description herein refers to a dual frequency liquid crystal spatial light modulator, those skilled in the art will appreciate the other types of devices, e.g., other types of spatial light modulators, are likewise suitable, at least for some applications. Thus, discussion of the present invention as comprising a dual frequency liquid crystal spatial light modulator is by way of example only, and not by way of limitation. 
   Further, although the use of a single dual frequency liquid crystal spatial light modulator is discussed herein, those skilled in the art will appreciate that a plurality of dual frequency liquid crystal spatial light modulators or the like may alternatively be used, such as in tandem so as to provide a lensing effect that facilitates both focus and zoom. 
   According to one embodiment of the present invention, beam steering and field of view adjustment systems can be dedicated to a single particular function. That is, a beam steering system can perform beam steering without performing field of view adjustment and vice-versa. However, according to another embodiment of the present invention, a single system can perform both beam steering and field of view adjustment. This may be accomplished using at least some common components for these two functions. For example, a single dual frequency liquid crystal spatial light modulator can be used for both beam steering and field of view adjustment. 
   Thus, according to at least one embodiment of the present invention, a method and system for rapidly steering a light beam, such as for use in communications or weaponry, is provided. According to at least one embodiment of the present invention, a method and system is provided for changing a camera&#39;s field of view according to a multiplexing strategy is provided. Further, one or more embodiments of the present invention provide lightweight, small, non-mechanical beam steering and/or field of view adjustment systems that respond rapidly and do not require high voltages for operation. 
   Embodiments described above illustrate but do not limit the invention. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the present invention. Accordingly, the scope of the invention is defined only by the following claims.