Abstract:
Free-space optics (FSO) is an unlicensed line-of-sight technology that uses modulated optical lasers to transmit information through the atmosphere. By using invisible beams of light, FSO can transmit and receive voice, video, and data information. To date, the primary concentration of FSO research and development has been toward the accurate alignment between two transceivers. The invention (FSO system) provides viable optical beam steering and capturing mechanism to allow fast tracking and accurate pointing between two transceivers of free-space optic (FSO) link that required continuous alignment. This extra ordinary auto-tracking system can reduce the time needed to lock a laser beam between an aircraft and a stationery base station to exchange information in addition to its high accuracy. This invention also provides wider receiving angle compared with the conventional FSO system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
       [0002]    Not Applicable. 
       THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
       [0003]    Not Applicable. 
       REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISC AND AN INCORPORATION-BY-REFERENCE OF THE MATERIAL ON THE COMPACT DISC (SEE § 1.52(E) (5)) 
       [0004]    Not Applicable. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0005]      FIG. 1  is a schematic, diagrammatic view of an exemplary free space optical system constructed in accordance with the present invention having at least two transceivers defining a communication channel. 
           [0006]      FIG. 2  is a schematic, diagrammatic view of the exemplary free space optical system of  FIG. 1  wherein one transceiver is located on an airplane and one transceiver is a ground station. 
           [0007]      FIG. 3  is a schematic block diagram of the exemplary free space optical system of  FIG. 1 . 
           [0008]      FIG. 4  is a perspective view of an exemplary transceiver having a transmitting part and a receiving part for use in the free space optical system of  FIGS. 1 and 2 . 
           [0009]      FIG. 5  is a schematic diagram of a receiving part of the transceiver depicted in accordance with the present invention. 
           [0010]      FIG. 6  is a schematic diagram illustrating a field of view of an exemplary transceiver constructed in accordance with the present invention. 
           [0011]      FIG. 7  is a schematic diagram of an exemplary receiving part of the transceiver having a receiving lens and an array of electromagnetic wave sensors where the position of the focal point on the array of electromagnetic wave sensors changes depending upon the angle of incidence of a electromagnetic wave relative to the receiving lens. 
           [0012]      FIG. 8  is a schematic diagram of another receiving part of a transceiver in accordance with the present invention. 
           [0013]      FIG. 9  is a perspective view of an exemplary steering device for use with the transceiver depicted in  FIG. 1  and constructed in accordance with the present invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0014]    So that the present invention can be understood in detail, a more particular description of the invention may be had by reference to the embodiments thereof that are illustrated in the drawings. It is to be noted, however, that the drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0015]    Referring now to the drawings and in particular to  FIGS. 1 and 2 , shown therein and designated by a reference numeral  10  is a free-space optics (FSO) system  10  constructed in accordance with the present invention. In general, free-space optics (FSO) is an unlicensed line-of-sight technology that uses a modulated electromagnetic wave, such as an optical beam produced by one or more optical lasers, to transmit information (i.e., carried data) through the atmosphere. The system  10  includes at least two spaced apart transceivers  12   a  and  12   b  defining a communication channel  14 . The communication channel  14  is used to transmit and receive multi-media data, such as audio, voice, video, and data information between the transceivers  12   a  and  12   b.    
         [0016]    The free space optics system  10  can be used in a variety of applications, such as a last mile network, a temporary network, disaster recovery and emergency services, cellular connectivity, a virtual Point-to-Multi point network, mobile wireless connectivity, backbone internet connectivity, a satellite uplink connection or outside broadcast applications. The system  10  can also be used to form a part of an air-traffic control system. For example, in the example depicted in  FIG. 2 , the system  10  communicates bi-directionally between an airplane  11  and a ground station  13 . In this example, the transceiver  12   a  is mounted to the airplane  11  and the transceiver  12   b  is mounted to the ground station  13 . Alternatively, the system  10  may communicate bi-directionally between two airplanes having one of each transceiver  12   a  and  12   b  mounted on the airplanes. In another embodiment (not shown), the system  10  communicates bi-directionally between two moving vehicles having one of each transceiver  12   a  and  12   b  mounted on each moving vehicle. 
         [0017]    Transmission of signals using prior art FSO systems generally provide high data rate exchange over a secure network, however, such systems are limited in reception as the goal is to provide accurate alignment between two receivers. See, “Free space optics for laser communications through the air,” D. Killinger, Optics and Photonics News, pp. 36-42, October 2002, the entire contents of which is incorporated by reference in its entirety. By the construction and design of the FSO system  10  as described herein, the FSO system  10  provides at least two advantages over prior art systems: 1) the current FSO system  10  provides a wide receiving angle even when there is no accurate alignment, and 2) the FSO system  10  provides an auto-tracking mechanism to lock both transceivers  12   a  and  12   b  together during mobile FSO communications. This auto-tracking mechanism can be even used with two fast mobile transceivers  12   a  and  12   b . Additionally, the FSO system  10  provides low manufacturing cost, high tracking accuracy, and low weight for each transceiver  12   a  and  12   b , which assist in the installation and use onboard a movable object such as an aircraft. 
         [0018]    In general, the transceivers  12   a  and  12   b  are located at each side  16  or  18  of the communication channel  14 . In the example shown in  FIG. 1 , the transceiver  12   a  is located at the side  16  of the communication channel  14 , and the transceiver  12   b  is located at the side  18  of the communication channel  14 . 
         [0019]    Each transceiver  12   a  and  12   b  has a receiving part and a transmitting part. In particular, the transceiver  12   a  has a receiving part  20   a  and a transmitting part  21   a . In the same regard, the transceiver  12   b  has a receiving part  20   b  and a transmitting part  21   b.    
         [0020]    The transmitting part  21   a  of the transceiver  12   a  directs a first electromagnetic wave  22  across the communication channel  14  to the receiving part  20   b  of the transceiver  12   b . Likewise, the transmitting part  21   b  of the transceiver  12   b  directs a second electromagnetic wave  24  across the communication channel  14  to the receiving part  20   a  of the transceiver  12   a . It should be noted that the designation of “first” and “second” does not necessarily imply a temporal relationship between the first electromagnetic wave  22  and the second electromagnetic wave  24  as described herein. 
         [0021]      FIG. 3  is a block diagram of an exemplary transceiver  12   a  of the FSO system  10  constructed in accordance with the present invention. It should be understood that the transceivers  12   a  and  12   b  are similar in construction and function. Thus, only the construction of the transceiver  12   a  will be discussed in detail hereinafter. 
         [0022]    In general, the transceiver  12   a  includes the receiving part  20   a , a controller  28   a , at least one steering device  36   a , and the transmitting part  21   a . In the preferred embodiment, the transceiver  12   a  also includes at least one steering device  36   a . It should be noted, however, that the steering device  36   a  may be a separate component distinguishable from the transceiver  12   a . The receiving part  20   a  of transceiver  12   a  includes an array of electromagnetic wave sensors  32  and a receiving lens  34 . The receiving lens  34  receives the second electromagnetic wave  24  and provides a focused electromagnetic wave  38  to the array of electromagnetic wave sensors  32 . The array of electromagnetic wave sensors  32  receives the focused electromagnetic wave  38  and generates a sensor output signal  40 . The sensor output signal  40  is provided to the controller  28   a  of the transceiver  12   a . The controller  28   a  analyzes the sensor output signal  40  and provides a first control signal  41  to the steering device  36 . The controller  28   a  Analyzes the sensor output signal  40  and provides a first control signal  43  to the steering device  36 . The controller  28   a  may also provide a second control signal  41  to the transmitting part  21   a  to control the optical output power of the electromagnetic wave being transmitted and/or to control an integral electronic steering device (not shown) included within the transmitting part  21   a . The transmitting part  21   a  includes a source of modulated electromagnetic energy  30  that can be implemented in a variety of manners, such as an LED, laser and/or the like. It should be noted that the modulated electromagnetic energy  30  may be transmitted through the receiving lens  34  of the transceiver  12   a . In this regard, the receiving lens  34  would have a dual function of receiving the second electromagnetic wave  24  and transmitting the first electromagnetic wave  22 . 
         [0023]    The receiving part  20   a  and the transmitting part  21   a  of the transceiver  12   a  are preferably mounted next to each other in a way that provides the functionality needed to steer the transmitting beam in addition to steering the receiving part  20   a . As illustrated in  FIG. 4 , the mounting of the receiving part  20   a  and the transmitting part  21   a  may include a housing  50 . Other elements of the transceiver  12   a , such as the controller  28   a  and/or steering device  36 , may also be positioned in or on the housing  50 , or can be separate from or remote from such housing  50 . It should be noted, the transmitting part  21   a  of the transceiver  12   a  and the receiving part  20   a  of the transceiver  12   a  may be separated. 
         [0024]      FIG. 5  is a schematic diagram of one embodiment of the receiving part  20   a  of the transceiver  12   a  including the receiving lens  32  and the array of electromagnetic wave sensors  32 . The receiving lens  34  may be any type of lens able to provide the focused electromagnetic wave  38 . Examples of suitable receiving lens include bi convex, plano-convex, and the like. 
         [0025]    The array of electromagnetic wave sensors  32  is mounted at the focal plane of the receiving lens  34  to receive the incident focused electromagnetic wave  38 . Generally, the array of electromagnetic wave sensors  32  defines a receiving surface  52 . Preferably, the array of electromagnetic wave sensors  32  is mounted at a distance substantially equal to the focal length (f) of the receiving lens  34  as illustrated in  FIG. 5 . As described herein, the focal length (f) is the distance from the surface of the receiving lens  34  to its focal point  39 . Mounting of the electromagnetic wave sensors  32  at a distance substantially equal to the focal length (f) provides for the convergence of the focused electromagnetic waves  38  at the focal point  39 . Alternatively, the array of electromagnetic wave sensors  32  is mounted at a pre-determined distance (d) and the position of the focused electromagnetic waves  38  can be algorithmically determined. 
         [0026]    The array of electromagnetic wave sensors  32  receives the focused electromagnetic wave  38  and converts the focused electromagnetic wave  38  into a format capable of being measured, such as, for example, an electric format. Examples of suitable electromagnetic wave sensors for use in the array  32  include photosensors, such as photodiodes, phototransistors, charge-coupled devices, a position sensing photodiode, and/or the like. In the preferred embodiment, at least a portion of the array of electromagnetic wave sensors  32  is composed of PSDs. As described herein, a PSD is a photodetector that provides measurements indicative of a variety of factors, such as position, power, spot size and spot shape of an incident optical beam or spot image. 
         [0027]    The electromagnetic wave sensors  32  detect a variety of factors indicative of the focused electromagnetic wave  38 , such as optical power and position. The electromagnetic wave sensors  32  can measure the optical power at any location within its receiving surface  52 . By using the array of electromagnetic wave sensors  32 , the receiving surface  52  has an area greater than a portion of the receiving surface  52  formed by any single photodetector in the array. Reading the optical power at any location at the focal plane (or away from the focal plane) allows the receiving lens  34  the ability to receive the electromagnetic waves  22  from any direction. This ability increases the receiving range of the transceiver  12   a  as illustrated in  FIG. 6 . 
         [0028]    As illustrated in the schematic diagram of  FIG. 7 , the focal point  39  on the array of electromagnetic wave sensors  32  changes depending upon the angle of incidence of the electromagnetic wave  22  relative to the receiving lens  34 . For example, when electromagnetic wave  22  is perpendicularly incident to the receiving lens  34 , the focal point  39  will be desirably located at the center of the receiving surface  52  of the array of electromagnetic wave sensors  32 . Alternatively, when the electromagnetic wave  22  is incident on the receiving lens  34  with an angle from the off-axis of the receiving lens  34 , the focused electromagnetic wave  38  will be positioned at a different location from the center according to the value of the receiving angle. As such, the receiving lens  34  will typically concentrate the optical power at the receiving surface  52  of the array of electromagnetic wave sensors  32  at a location specified by the value of the incident angle from the off-axis of the receiving lens  34 . The position readings of this focal point  39  can be used by the controller  28   a  to generate control signal  43  to the steering device  26  in order to realign the receiving lens  34  such that the focal point  39  is located at the center of the receiving surface  52 . 
         [0029]      FIG. 8  illustrates another embodiment of the receiving part  20   a  having multiple receiving lenses  34  in a spherical arrangement. The array of electromagnetic wave sensors  32  are mounted at the focal plane of each corresponding receiving lens  34  to receive the incident focused electromagnetic waves  38 . The array of electromagnetic wave sensors  32  also defines a spherical receiving surface  52   a.    
         [0030]    The sensor output signals  40  produced by the electromagnetic wave sensors  32  are then passed to one or more controllers  28   a  (or associated device(s) or system(s)). The sensor output signals  40  can be passed to the controller  28   a  from the electromagnetic wave sensors  32  utilizing any suitable communication link, such as a wired communication link, a wireless communication link, or combinations thereof. 
         [0031]    The controller  28   a  analyzes the signals to demodulate and extract the carried data from the received electromagnetic wave (i.e., the electromagnetic wave  24 ). The controller  28   a  reads the measured optical power and demodulates the signal according to the modulation scheme used in the FSO system  10 . For example, the modulation can be on-off keying modulation or any other type of modulation. 
         [0032]    The controller  28   a  of the free space optical system  10  can also be used to generate one or more control signal  43  according to its position readings to control the steering device  36  of the receiving part  20   a . The controller  28   a  communicates the control signal  43  to the steering device  36  using any suitable communication system, such as a wired or wireless communication system. In generating the control signals  41  and/or  43 , the controller  28   a  analyzes the measurement of position of the focal point  39 . For example, if position readings obtained by the controller  28   a  are (x, y)=(1, 0), the generated control signal  41  would direct the steering device  36  to move in the x-direction 1 degree and remain fixed in the y-direction. 
         [0033]    The steering device  36  directs the electromagnetic wave  24  to the electromagnetic wave sensors  32  through the receiving lens  34 . The steering device  36  can move the receiving lens  34  and/or the electromagnetic wave sensors  32 , or can steer the electromagnetic wave  22  or combinations thereof. Additionally, more than one steering device  36  may be used in the receiving part  20   a  to direct the electromagnetic wave  24  to the array of electromagnetic sensors  32 . Further, it should be understood that the steering devices  36  can have different effects on the incident beam, or the receiving lens  34 . For example, one of the steering devices  36  can be adapted and/or utilized for a coarse adjustment, and another one of the steering devices  36  can be adapted and/or utilized for a fine adjustment. 
         [0034]    The steering device  36  can be implemented in a variety of manners, such as a motor (stepper, AC or DC) a solenoid, a steering mirror or the like. For example, the receiving part  20   a  can be provided with two stepper or DC motors installed beneath transceiver  12   a  (or at any suitable location) to control the direction of where the transceiver  12   a  is pointing. The steering device  36  should be installed in a way that provide capabilities of receiving the control signal  43  and directing the transceiver  12   a  toward any location in the three dimensional space. For example, the use of a gimbal within the steering device  36  can allow for the free rotation of the transceiver  12   a  to tilt freely in any direction. 
         [0035]      FIG. 9  illustrates one embodiment of the transceiver  12   a  in which the steering device  36  includes the use of a gimbal  70  allowing for movement of the receiving part  20   a  and the transmitting part  21   a  in the x and y directions. The gimbal  70  can be implemented in a variety of manners. For example, the gimbal  70  can be a pan and tilt gimbal, such as a Model 20 Servo, manufactured by Sagebrush Technology, Inc. of Albuquerque, N. Mex. A copy of a specification document for the Model 20 Servo manufactured by Sagebrush Technology is included in an information disclosure statement filed contemporaneously herewith and is incorporated by reference in its entirety. 
         [0036]    The controller  28   a  of the free space optical system  10  can also be used to generate control signals according to its position readings to control a second steering device  36   b  within the transmitting part  21   a . The controller  28   a  communicates with the transmitting part  21   a  using any suitable communication system, such as a wired or wireless communication system. For example, in one preferred embodiment, the controller  28   a  communicates the control signals to the transmitting part  28   a  utilizing a transmitter of the receiver part  20   a  utilizing an out of band modulated laser beam. 
         [0037]    Alternatively, the controller  28   a  of the free space optical system  10  can be used to generate controls signals  41  and  43  to both the receiving and transmitting parts  20   a  and  21   a  separately. Repositioning the receiving and transmitting parts  20   a  and  21   a  separately can be effective when using one of several available steering technologies, for example, Micro-electro-mechanical (MEMS)-microlens arrays, galvanometric scanners, optical phased arrays, acousto-optic scanners, and optical phased prism arrays and the like. 
         [0038]    It should be understood that the controller  28   a  can be implemented as any device suitable for performing the functions described above. For example, the controller  28   a  can be implemented as a computer system running software adapted to perform the functions described above, and the software and carried data can be stored on one or more computer readable mediums. Examples of a computer readable medium include an optical storage device, a magnetic storage device, an electronic storage device, or the like. The term “Computer System” as used herein means a system or systems that are able to embody and/or execute the logic of the processes described herein. The logic embodied in the form of software instructions or firmware may be executed on any appropriate hardware which may be a dedicated system or systems, or a general purpose computer system, or distributed processing computer system, all of which are well understood in the art, and a detailed description of how to make or use such computers is not deemed necessary herein. When the computer system is used to execute the logic of the processes described herein, such computer(s) and/or execution can be conducted at a same geographic location or multiple different geographic locations. Furthermore, the execution of the logic can be conducted continuously or at multiple discrete times. 
         [0039]    Contemplated herein is a method of using an FSO system  10 . This method generally includes the step of initially determining the location of each transceiver  12   a  and  12   b . The locations of each transceiver  12   a  and  12   b  may be determined using any suitable method such as, for example, through a global positioning system. Upon determining the location of each transceiver  12   a  and  12   b , the transceivers  12   a  and  12   b  are directed towards each other to form the communication channel  14 . Once the communication channel  14  is formed, the FSO system  10  adjusts the positions of the transmitting and receiving parts of both transceivers  12   a  and  12   b  without having to provide updated location information of each transceiver  12   a  and/or  12   b . Adjustment of the transceivers  12   a  and  12   b  maintains the communication channel  14  between the transceivers  12   a  and  12   b  such that electromagnetic waves  22  and  24  are able to be transmitted and received to the transceivers  12   a  and  12   b.    
         [0040]    This description is intended for purposes of illustration only and should not be construed in a limiting sense. The scope of this invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. “A,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.