Abstract:
A scanning apparatus adapted to track or other wise communicate with a remote object is provided, comprising a plurality of individually actuatable laser devices, each laser device emitting a laser beam. The scanning apparatus further comprises a moveable lens member disposed adjacent to the output ports such that the laser beams are directed therethrough, the lens member being moveable and cooperable with the laser devices such that each laser beam is directed in a different direction after passing through the lens member. The scanning apparatus is further configured to provide laser beam agility by selectively actuating individual laser devices so as to coarsely track the remote object and to provide laser beam steerability by moving the lens member with respect to an actuated laser device so as to finely track the remote object. An associated method is also provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of optical beam steering and, more particularly, to a scanning apparatus and associated method using vertical-cavity surface-emitting lasers (VCSELs) and a movable lens to provide a steerable agile beam. 
     BACKGROUND OF THE INVENTION 
     Detecting, tracking, and/or communicating with an object moving within a spatial field, also known as a field of search, has many practical and strategic military and commercial applications. Interaction with such a moving object typically involves directing a single detection beam in a raster pattern so as to scan the beam over the field of search. That is, the detection beam is usually guided in a continuous serial pattern such that it is scanned over the search field to cover the entire area thereof If a portion of the detection beam is reflected, an object will likely have been detected by the detection beam during a scan of the search field. However, additional data relating to the object, such as speed and trajectory, may not be determinable until the detection beam has completed the raster scan and returned to the location of the object in the search field. As such, in certain applications, such as military applications, where moving objects may be traveling at a rate of several times the speed of sound, a raster scan detection system may be too slow to be of practical use with modern systems which are continuously increasing in processing speed. Thus, there exists a need for a system capable of scanning, detecting, and/or communicating with a moving object in a faster, more accurate, and more efficient manner than a raster system. 
     In addition, a raster system typically requires complex mechanisms and controls for moving the detection beam in the desired raster pattern. For example, where the search field is a square box, the raster pattern may comprise lateral movement of the beam in an alternating manner across the width of the box, with a longitudinal shift equal to the width of the beam with each lateral reversal of the direction of the beam. Such a scan may start at one corner of the box and end at the opposite diagonal corner, where the beam then reverts back to the initial comer to begin the next scan of the search field. Accordingly, the associated mechanisms and controls may be complex and are usually required to be both accurate and durable in order to maintain precise and optimum operation of the detection system. Thus, there exists a further need for a system capable of scanning, detecting, and/or communicating with a moving object that has a simpler operational mechanism, compared to a raster system, with sufficient accuracy and durability to provide a precise detection system. 
     In certain applications, such scanning, detection, and/or communications systems may be subject to a harsh environment, wherein the system may be exposed to, for example, severe vibrations, g-forces, jarring, and/or impact. Such environmental factors may be detrimental to the performance of a raster-type system. Thus, there exists a further need for a system capable of scanning, detecting, and/or communicating with a moving object that has a simpler and more robust configuration, compared to a raster system, so as to provide a precise and reliable detection system, even in harsh environments. 
     An example of such a scanning, detection, and/or communication system is disclosed by U.S. Pat. No. 5,909,296 to Tsacoyeanes. The &#39;296 patent discloses wide angle beam steering using spherical laser diode arrays. A curved array of lasers causes discrete narrow infrared light beams to be projected within a wide field of view, without requiring mechanical motion of components. However, the Tsacoyeanes device may be difficult to produce due to the precise hemispherical configuration in which the lasers must be placed in order to provide the desired accuracy. In addition, the hemispherical configuration may produce a device having undesirable minimum size constraints as well as a disadvantageous maximum laser density constraint. Further, as disclosed, the Tsacoyeanes device relies upon alignment of individual laser beams with the target in order for the device to function as intended. A gap may therefore exist between adjacent laser elements such that less-than-optimum resolution may be obtained as the device shifts from one laser element to the next. Thus, where an array-type device is used, there exists a need for the system to be capable of transitioning between adjacent laser devices in a “seamless” manner and without a significant loss of resolution. 
     Thus, there exists a need for a detection/communication system capable of scanning, detecting, and/or communicating with a moving object in a faster, more accurate, and more efficient manner than a raster system. Such a system should also have a simpler operational mechanism with sufficient accuracy and durability to provide a precise detection system and a more robust configuration such that the detection system is reliable, even in harsh environments. In instances where such a system is accomplished by use of an array-type device, the system should be capable of transitioning between adjacent laser devices in a “seamless” manner without a significant loss of resolution. 
     SUMMARY OF THE INVENTION 
     The above and other needs are met by the present invention which, in one embodiment, provides a scanning apparatus for tracking a remote object that is typically moving within a predetermined distance range. A plurality of individually actuatable laser devices are provided, typically in the form of an array, for emitting laser beams. A moveable lens member is disposed proximate to the laser devices such that the laser beams are directed therethrough. The lens member is moveable and cooperable with the laser devices such that each laser beam is directed in a different direction after passing through the lens member. The apparatus is therefore configured to provide laser beam agility by selectively actuating the laser devices and to provide laser beams steerability by moving the lens member with respect to the laser devices. 
     According to one advantageous embodiment of the present invention, the laser devices comprise vertical-cavity surface-emitting lasers (VCSELs), wherein, in some instances, the VCSELs are solder-bumped to a substrate so as to form a fine pitch, solder-bumped VCSEL array. According to some embodiments, the laser devices may be arranged in a substantially planar array. In other instances, a plurality of sub-arrays of VCSELs may be combined to form the array. 
     The lens member is disposed in spaced parallel relation to the array and is moveable within a plane corresponding thereto. The lens member may be moved by at least one actuator in communication therewith, such as a piezoelectric actuator. In this configuration, the laser devices are also individually and selectively actuatable such that sequential actuation of individual laser devices coarsely attunes the laser beams to a corresponding trajectory of the moving object to enable the apparatus to track the moving object. Movement of the lens member with respect to an actuated laser device thereafter finely attunes the corresponding laser beam to the trajectory. As such, the scanning apparatus of the present invention can reliably track moving objects in a rapid manner without using a single laser device to raster scan through the entire area of interest. 
     According to advantageous embodiments, the lens member is configured to cooperate with the laser beams to provide a predetermined magnitude of angular coverage depending on the desired configuration and capabilities of the apparatus. Accordingly, the apparatus is capable of tracking moving objects within a distance range of between about 500 meters and about 2500 meters. In some instances, the apparatus may further comprise a controller capable of individually and selectively actuating the laser devices, wherein sequential actuation of individual laser devices by the controller coarsely attunes the respective laser beams to a corresponding trajectory such that the apparatus is capable of tracking a moving object. The controller may also be configured to direct movement of the lens member with respect to the laser devices so as to finely attune the laser beams to the trajectory. The apparatus may further comprise a detection device for detecting signals from the remote object. In some instances, the controller may be responsive to the detection device so as to actuate the laser devices and move the lens member in order to track the remote object. 
     Another advantageous aspect of the present invention comprises a method of tracking remote objects. First, an array of laser devices capable of emitting laser beams therefrom is provided in spaced relation to a moveable lens member to form a scanning apparatus configured such that the laser beams are directed through the lens member. The lens member is configured so as to direct each laser beam in a different direction. Selected laser devices are thereafter sequentially actuated such that the emitted laser beams directed through the lens member are coarsely attuned to a trajectory of a remote object. The lens member may also be selectively moved with respect to an actuated laser device such that the laser beam emitted thereby is finely attuned to the trajectory of the remote object. 
     In some instances, a solder-bumped array of vertical-cavity surface-emitting lasers (VCSELs) is provided in spaced relation to the moveable lens member. In further instances, the method may include interacting with the remote object by transmitting signals to the remote object and receiving signals from the remote object, wherein the received signals may comprise reflections of the laser beams. In response to the signals received from the remote object, a selected laser device may be actuated and/or the lens member moved so as to facilitate communication with the remote object. 
     Thus, a scanning apparatus and method according to embodiments of the present invention provides a detection/communication system and method capable of scanning, detecting, and/or communicating with a remote object in a faster, more accurate, and more efficient manner than a raster system since the plurality of laser devices allows a multiplexed approach to examining the area of interest. Embodiments of a scanning apparatus according to the present invention also provide a simpler operational mechanism, as a result of selective actuation of individual laser devices having at least a reduced amount of moving parts compared to a raster system, with increased accuracy and lower scanning and detection times, while being durable and robust so as to provide a precise detection system that is reliable, even in a harsh environment. Both the coarse and fine attunement provisions provide more accurate tracking and allow for transitions between adjacent laser devices in a relatively seamless manner, without a significant loss of resolution. Therefore, embodiments of a scanning apparatus and method according to the present invention provide advantages over conventional detection/communication systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Some of the advantages of the present invention having been stated, others will appear as the description proceeds, when considered in conjunction with the accompanying drawings, which are not necessarily drawn to scale, in which: 
     FIGS. 1A and 1B are schematic representations of a scanning apparatus according to one embodiment of the present invention. 
     FIG. 2 is a schematic representation of a scanning apparatus according to one embodiment of the present invention illustrating the effect of the lens member on laser beams emitted from laser devices within the array. 
     FIG. 3 is a block diagram representation of a scanning apparatus according to one embodiment of the present invention. 
     FIG. 4A is a schematic representation of a conventional raster scan process. 
     FIG. 4B is a schematic representation of a multiplexed scan process used by a scanning apparatus according to one embodiment of the present invention. 
     FIG. 5 is a schematic representation of a scanning apparatus according to one embodiment of the present invention illustrating a range of coverage of the array of laser devices and the capability of tracking a moving object within that range. 
     FIG. 6A is a schematic representation of a scanning apparatus according to one embodiment of the present invention illustrating a laser beam coinciding with a target. 
     FIG. 6B is a schematic representation of a scanning apparatus according to one embodiment of the present invention illustrating a laser beam being steered to coincide with a target, by moving the lens member, after the target has shifted such that the target no longer coincides with the laser beam. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. 
     FIGS. 1A and 1B schematically illustrate one embodiment of a scanning apparatus, indicated generally by the numeral  100 , which includes the features of the present invention. The scanning device  100  comprises a plurality of individually actuatable laser devices  200  wherein, according to one embodiment, the laser devices  200  are arranged in an array  300 . Disposed adjacent to the array  300  is a moveable lens member  400 , wherein laser beams produced by each laser device  200  are directed to pass through the lens member  400 . Still further, according to one embodiment of the present invention, the lens member  400  may be moveable within a reference frame  500  via one or more actuators  600  operably engaged therebetween, as indicated by FIG.  1 B. 
     According to one advantageous aspect of the present invention, the laser devices  200  comprise vertical-cavity surface-emitting lasers (VCSELs), wherein each VCSEL may, for example, comprise a monolithic growth on an indium phosphide (InP) substrate. The VCSEL may include, for instance, InGaAs or strain-compensated InGaAs quantum wells surrounded by high bandgap InAlGaAs cladding layers. One advantageous VCSEL is made by Picolight, Inc. of Boulder, Colo., USA and is commercially available under the name “Gigabit Per Second Vertical Cavity Surface Emitting Laser.” VCSEL devices are known to those skilled in the art and will not be further detailed herein. In some instances, the VCSEL operates on a 1550 nm wavelength and is optimized for eye-safe single-mode emission in order to provide a single beam with a narrow divergence angle. 
     In order to form the array  300 , a plurality of VCSELs  200  are mounted on a substrate  250 , such as a silicon or sapphire substrate with any necessary interconnects and, in some instances, active drive circuitry, wherein the VCSELSs  200  are mounted using, for example, a solder-bump process. Such a solder-bump process is known to those skilled in the art and is the subject of U.S. Pat. Nos. 4,950,623, 4,921,157, 5,289,631, 5,615,825, 5,162,257, 5,237,434, 5,407,121, 5,767,010, 5,892,179, 5,902,686, and 5,793,116, all assigned to the Microelectronics Center of North Carolina (also known as “MCNC”), the assignee of the present invention. According to one advantageous aspect of the present invention, the array  300  may be formed in a batch wafer fabrication process to provide, for example, an array of 400(20×20) VCSEL elements  200  solder bumped to a substrate  250  to form an array with a fine pitch of approximately 100 micrometers, thereby providing an overall array size of about 2-3 mm by 2-3 mm. The array  300  is thereby fabricated to be substantially planar and, in some instances, may be configured such that the laser beams are emitted from a substantially planar surface. 
     The lens member  400  is disposed adjacent to the array  300  and, in some instances, in spaced parallel relation as shown in FIG.  2 . The lens member  400  may be, for example, derived from a positive (converging) lens and is positioned at distance equal to its focal length from the array  300 . In one embodiment, the lens member  400  has a focal length of and is disposed about 15 mm away from the array  300 . Each laser beam emitted from a corresponding VCSEL  200  through the lens member  400  will therefore be directed in a different direction after passing through the lens member  400 . According to one advantageous aspect of the present invention, several sub-arrays may be grouped together to form the array  300  and combined with an appropriate lens member  400  such that each individual VCSEL  200  produces a laser beam which covers an area of, for example, less than a square degree, after the laser beam passes through the lens member  400  and reaches the desired range. In some instances, the range may be between, for example, about 500 meters and about 2500 meters, although the scanning apparatus  100  can be readily configured for other ranges, if desired. The lens member  400  is further configured such that both microdiffractive and macroscopic refractive optics correct for beam divergence and reduce side lobe emissions so as to increase the usable range of the VCSEL  200  for targeting and communication, while reducing the possibility of the laser beam being intercepted. Thus, it is understood that the lens member  400  may have many different configuration depending on the particular characteristics required, wherein the lens members may comprise, for example, multiple lens elements such as singlet, doublet, triplet, and aspheric lens elements as well as diffractive elements. 
     According to one embodiment of the present invention, the lens member  400  is arranged within a framework  500  which may, for example, serve as both a support for the lens member  400  as well providing a positional reference between the array  300  and the lens member  400 . Supporting the lens member  400  within the framework  500  are one or more actuators  600  operably engaged therebetween. Such actuators  600  serve to render the lens member  400  moveable within the framework  500  and with respect to the underlying array  300 . The actuator  600  may comprise, for example, parallel and series bimorphs, unimorphs, and high-displacement bender-type actuators. According to one embodiment, edge-mounted piezoelectric bender-type actuators are used in order to provide a large planar displacement for moving and controlling the position of the lens member  400 . The piezoelectric actuators  600  may provide, for example, 200 micrometers or more of travel distance for the lens member  400 . Piezoelectric actuators are commercially available from several sources, including Piezo Systems, Inc. of Cambridge, Mass. 
     As depicted in FIG. 3, the scanning apparatus  100  also preferably includes a controller  150 , such as a microcontroller or a PC/104 type computer. Among other capabilities, the controller  150  actuates the laser devices  200  to emit laser signals, typically using high voltage drivers, such as high voltage operational amplifiers (not shown), and selectively energizes the actuators  600  to controllably position the lens member  400 . 
     The scanning apparatus  100 , according to embodiments of the present invention, may be used for several different purposes. For example, the individual VCSELs  200  may be simultaneously actuated so as to provide a multiplexed approach to scanning a particular field. FIG. 4A shows a field  800  being scanned in a conventional raster pattern by a single beam (beginning in the upper left comer of the field and moving toward the upper right hand comer thereof), wherein the single beam must cover the entire field  800  in a serial pattern in order to scan the entire area thereof. In contrast, FIG. 4B shows a multiplexed scanning approach according to embodiments of the present invention, wherein simultaneous actuation of the VCSELs  200  within the array  300  provides a fast and complete scan of the field  800  since each VCSEL  200  simultaneously scans only a small area (schematically indicated by the separate black lines) of the entire field  800 . In such instances, the use of a multiplexed scanning process increases the speed of the scanning apparatus  100  by several orders of magnitude, for example, 1000 times, over a comparable conventional raster scanning system. 
     FIG. 5 shows another application of the scanning apparatus  100 , wherein the apparatus  100  is used to track a remote target or object  700  that is typically moving. As shown, the scanning apparatus  100  is capable of covering a wide angular area due to the directing of the laser beams by the lens member  400 . Such an area of coverage may include, for example, a 45° field for an apparatus configured to cover a wide field of view or a 1° field where a precision angular alignment is required. Note that the angular fields described herein are merely examples and it will be understood that the apparatus  100  may be configured in many different manners to produce angular fields of coverage that are wider or more minute and precise as necessary in accordance with the spirit and scope of the present invention. Where the scanning apparatus  100  locks onto the target  700 , the target  700  may be coarsely tracked by sequentially actuating appropriate VCSELs  200  that correspond to the track of the target  700 . The actuated VCSELs  200  may be, for instance, adjacent VCSELs  200  in the array  300  where the target  700  is moving in a slow trajectory at a large range with respect to the scanning apparatus  100 . Where the target  700  is closer in range to the apparatus, 100  or moving at a faster rate, the appropriate VCSELs  200  may be more widely spaced about the array  300 . While the target  700  passes through the small area of the field covered by a respective laser device  200 , the laser device  200  can lock onto the target  700  and be fine-tuned to closely follow the target  700  by controllably moving the lens member  400  as described below. 
     As shown in FIG. 6A, once an individual VCSEL  200  is actuated, the laser beam passes through the lens member  400  and is directed in a known direction to engage a mobile target  700 . As described above, the structure of the scanning apparatus  100  designates each VCSEL  200  to serve a certain area which, in some instances, comprises less than a square degree within the specified range of the apparatus  100  of between about 500 meters and about 2500 meters. Thus, each VCSEL  200  serves a predetermined angular cell of travel for the target  700 . However, as the target  700  moves within that cell, the focus of the laser beam may vary, thereby leading to a less than optimum signal strength in some portions of the cell. The loss of signal strength is detected with a detector  650 , such as, for example, a p-i-n detector, wherein at least a portion of one such detector  650  is typically associated with each laser device  200 . The detector  650  is typically mounted on the substrate  250  and detects signals, such as signals reflected from the target  700 . The controller  150  preferably monitors the output of the detector  650  as shown in FIG. 3 so as to determine any change in the signal strength. 
     In instances where the target  700  remains within the designated cell, but the signal strength has decreased, the actuator  600  is actuated as shown in FIG. 6B such that the lens member  400  is moved with respect to the actuated VCSEL  200 . Controlled movement of the lens member  400  with respect to the actuated VCSEL  200  steers the laser beam in the direction of the target  700  so as to provide higher or optimum beam quality on the target  700 , as determined by greater signal strength at the detector  650 . In some instances, the piezoelectric actuator  600  is capable of fine tuning the angular position of the laser beam within a millisecond. Thus, the sequential actuation of different VCSELs  200  provides a coarse tracking mechanism for tracking the target  700  from one cell to another as shown in FIG. 5, while optical beam steering using the change in the position of the lens member  400  with respect to the actuator  600  provides fine tracking of the target  700  within a particular angular cell. Where the laser beams are locked onto a target  700 , the scanning apparatus  100  may also be used to transmit data or other signals therebetween at a data transmission rate of, for example, 1 Gb/s. In order to accomplish interaction between the apparatus  100  and the target  700 , the detector  650  may also serve to receive and/or detect the signals transmitted by the target  700 . 
     A scanning apparatus  100  according to embodiments of the present invention may have many different configurations and be used for a variety of other purposes. For example, the array  300  may be part of a larger module which comprises a plurality of similar arrays. The lens member  400  may also be configured as, for example, an array of lens members with each lens member in the array corresponding to a particular VCSEL  200 . In further instances, the actuator  600  may be operably engaged with the lens member  400  to move the lens member  400  in different manners within, for example, a plane substantially parallel to the array  300  or in a plane disposed perpendicularly thereto. As for other applications, the scanning apparatus  100  may be used in the multiplexed scanning approach to, for example, track a plurality of moving targets  700 . 
     Thus, a scanning apparatus  100  according to embodiments of the present invention provides a detection/communication system capable of scanning, detecting, and/or communicating with a moving object in a faster, more accurate, and more efficient manner than a raster system. Such a scanning apparatus  100  also provides a simpler operational mechanism that is accurate and durable and provides a robust configuration, wherein the resulting system is precise and reliable, even in harsh environments. Embodiments of the present invention also provide an array-type device that provides both a coarse tracking mechanism as well as a fine tracking mechanism and therefore allows tracking of a target in a “seamless” manner while maintaining optimum resolution during the tracking process. 
     Many modifications and other embodiments of the invention will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.