Abstract:
Disclosed is apparatus and method for establishing and maintaining optical data transfer between a first optical communications device ( 202 ) and a second optical communications device ( 204 ). The devices have a feedback communications link ( 216 ) therebetween. An optical signal ( 214 ), having a predetermined signal profile ( 306 ), is transmitted from a transmission source ( 104 ) within the first optical communications device to an optical receiver ( 112 ) within the second optical communications device. The predetermined signal profile is transmitted from the first device, via the feedback communications link, to the second device. The signal profile ( 408 ) of the optical signal as received by the optical receiver is determined, and compared with the predetermined signal profile to quantify any misalignment or movement of the optical signal with respect to the optical receiver. The transmission of the optical signal is then adjusted by a directing member ( 106 ) responsive to the results of the compared profiles to align and center the optical signal with respect to the optical receiver. Once properly align, the optical signal may be utilized for high speed, high bandwidth data transmission.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates in general to optical wireless communications and, more particularly, to apparatus and methods for establishing and maintaining a reliable optical wireless data link between to transmitting and receiving units.  
         BACKGROUND OF THE INVENTION  
         [0002]    Modern data communications technologies have greatly expanded the ability to communicate large amounts of data over many types of communications facilities. This explosion in communications capability not only permits the communication of large databases, but has also enabled the digital communication of audio and video content. This multimedia communication requires high bandwidth communication, which is now carried out over a variety of facilities, including telephone lines (e.g., fiber optic and twisted pair), coaxial cable (e.g., as supported by cable television service providers), dedicated network cabling within an office or home location, satellite links, and wireless telephony.  
           [0003]    Each of these conventional communications facilities involves certain limitations in their deployment. In the case of communications over the telephone network, high-speed data transmission, such as that provided by digital subscriber line (DSL) services, must be carried out at a specific frequency range to not interfere with voice traffic, and is currently limited in the distance that such high-frequency communications can travel. Of course, communications over “wired” networks, including the telephone network, cable network or dedicated network, requires the running of the physical wires among the locations to be served. This physical installation and maintenance is costly, as well as limiting to the user of the communications network.  
           [0004]    Wireless communication facilities of course overcome the limitation of physical wires and cabling, and provide great flexibility to the user. Conventional wireless technologies involve their own limitations, however. For example, in the case of wireless telephony, the frequencies at which communications may be carried out are regulated and controlled. Furthermore, current wireless telephone communication of large data blocks, such as video, is prohibitively expensive, considering the per-unit-time charges for wireless services. Additionally, wireless telephone communications are subject to interference among the various users within a nearby area. Radio frequency data communication must be carried out within specified frequencies, and is also vulnerable to interference from other transmissions. Satellite transmission is also currently expensive, particularly for bidirectional communications (i.e., beyond the passive reception of television programming).  
           [0005]    Recently, attention has turned to optical wireless networking for data communications. Using this technology, data is transmitted by modulating a light beam, in much the same manner as in the case of fiber optic telephone communications. A photo-receiver receives the modulated light, and demodulates the signal to retrieve the data. As opposed to fiber optic-based optical communications, however, this approach does not use a physical wire for transmission of the light signal. In the case of directed optical communications, a line-of-sight relationship between the transmitter and the receiver permits a modulated light beam, such as that produced by a laser, to travel without the waveguide of a fiber optic cable.  
           [0006]    Hence, optical wireless networks could provide numerous important advantages over other conventional communications systems. First, high frequency light modulation can provide for high bandwidth data communication (e.g., ˜100 Mbps-Gbps). This high bandwidth need not be shared among multiple users, especially when carried out over line-of-sight optical communications between transmitters and receivers. Without other users on the communications link, of course, the bandwidth is not limited by interference from other users, as in the case of wireless telephony. Modulation can also be quite simple, as compared with multiple-user communications that require time or code multiplexing of multiple communications signals. Bi-directional communication can also be readily implemented utilizing this technology. Furthermore, optical frequencies are not currently regulated, and as such no licensing is required for the deployment of extra-premises networks.  
           [0007]    These attributes of optical wireless networks make this technology attractive both for local networks within a building, and also for external networks. Indeed, it is contemplated that optical wireless communications may be useful in data communication within a room, such as for communicating video signals from a computer to a display device, such as a video projector. The costs and effort associated with routing and placing cables in congested, space constrained areas can be eliminated using optical wireless links. If reliable enough, modems using optical wireless links would be especially valuable in mobile product devices such as laptop computers and handheld organizers.  
           [0008]    A common problem with some conventional optical wireless links, however, is that they utilize relatively wide, diffuse optical beams to facilitate the acquisition and maintenance of a light link. The ability to correctly aim a transmitted light beam at a receiver is of importance in optical communications technology. Wider beams can allow for greater tracking tolerance, because exact positioning of a transmitting beam on a receiver is not required to maintain a nominal communication link. The use of wider beams, however, either decreases the intensity (i.e., power) of the beam at the receiver or increases the power required to deliver a high data rate signal, and can result in severe limitations in the usable bandwidth of the data link(s) established, thus decreasing the usefulness of link for many communication applications.  
           [0009]    Some conventional systems attempt to use narrower, more tightly focused optical beams (e.g., laser generated collimated beams) to provide greater communications bandwidth. When utilizing laser-generated collimated beams, which can have quite small spot sizes, the reliability and signal-to-noise ratio of the transmitted signal are degraded if the aim of the transmitting beam strays from an optimum point at the receiver. Considering that many contemplated applications of this technology are in connection with equipment that will not be precisely located, or that may move over time, it is necessary to be able to rapidly and reliably adjust the aim of the light beam.  
           [0010]    Because the integrity of communications does rely on precise optical alignment, conventional solutions can also present problems in circumstances where transceiver units are subject to some vibration or sway (e.g., a building to building link, or a mobile to stationary link). Many conventional systems rely on a low bandwidth direct feedback channel between transceivers, such as a secondary telephone line modem, and some gross mechanical adjustment (e.g., a motorized mechanical assembly housing one or more of the transceivers) to maintain transceiver alignment. Such conventional systems can have problems responding when high frequency vibrations occur, and make it difficult, if not impossible, to successfully track and maintain communications with a moving transceiver. Finally, such conventional systems are often not able to translate changes in signal strength, which is a common method of measuring the integrity of a communications link, into usable positioning information for the mechanical assembly.  
           [0011]    Thus, when either a high degree of transceiver mobility is required, or when transceivers may be subject to high frequency or small scale vibrations, conventional systems are typically incapable of providing reliable, high bandwidth communication.  
         SUMMARY OF THE INVENTION  
         [0012]    Therefore, a versatile system for acquiring and maintaining reliable optical wireless links that provides for simple and cost-effective high performance optical communications, especially where fixed optical units are subject to high frequency vibrations or where optical units are in motion relative to one another, is now needed, providing for efficient and practical utilization of optical wireless communications in mobile products and devices while overcoming the aforementioned limitations of conventional methods.  
           [0013]    The present invention provides a system for implementing an optical communications network. The present invention determines optical beam position information with respect to time at a receiver of an optical wireless link unit. The optical beam is transmitted from a second optical wireless link unit in response to a predetermined beam steering input. The relative motion of the units in relation to one another, and with respect to time, will result yield beam position profiles over time. A beam steering element effectively separates the motion into two components. The first component corresponds directly to the beam steering input, which is predetermined. The second component corresponds to the relative motion, which can be of variable frequency or amplitude. A high bandwidth return channel is provided to relay a high resolution portrait of the beam location profile over time. The present invention processes and utilizes this information to adjust the beam steering element, correcting for the motion or vibrations and maintaining the optical data link between the units. The present invention thus provides robust and efficient optical wireless communications within a given fixed or mobile network or system. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    For a more complete understanding of the present invention, including its features and advantages, reference is made to the following detailed description, taken in conjunction with the accompanying drawings. Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated.  
         [0015]    [0015]FIG. 1 illustrates an optical transceiver in accordance with the present invention;  
         [0016]    [0016]FIG. 2 illustrates one embodiment of an optical communications system in accordance with the present invention;  
         [0017]    [0017]FIG. 3 illustrates one embodiment of a raster pattern in accordance with the present invention;  
         [0018]    [0018]FIG. 4 illustrates the effects of raster movement according to the present invention; and  
         [0019]    [0019]FIG. 5 illustrates a number of raster and detector configurations in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0020]    The present invention defines a system, comprising various structures and methods, implementing an optical communications network. The present invention determines optical beam position information with respect to time at a receiver of an optical wireless link unit. The optical beam is transmitted from a second optical wireless link unit in response to a predetermined beam steering input. The relative motion of the units in relation to one another and with respect to time, will result yield beam position profiles over time. A beam steering element effectively separates the motion into two components. The first component corresponds directly to the beam steering input, which is predetermined. The second component corresponds to the relative motion, which can be of variable frequency or amplitude. A high bandwidth return channel is provided to relay a high resolution portrait of the beam location profile over time. This information is processed and utilized by the present invention to adjust the beam steering element, correcting for the motion or vibrations and maintaining the optical data link between the units. The present invention provides robust and efficient optical wireless communications within a given fixed or mobile network or system.  
         [0021]    It should be understood that the principles and applications disclosed herein can be applied to a wide range of optical communications systems utilizing a variety of optical transmission and reception technologies. For purposes of explanation and illustration, the present invention is hereafter described in reference to several specific embodiments of high performance optical communication systems. The present invention, however, is equally applicable in any number of communication networks that might enjoy the benefits and advantages provided by the present invention.  
         [0022]    The present invention is now described beginning in reference to FIG. 1, which illustrates an optical transceiver  100  according to the present invention. Transceiver  100  comprises a housing  102 , light source  104  disposed within housing  102 , beam directing member  106  disposed within housing  102 , transmit aperture  108 , receive aperture  110 , optical detector  112  disposed within housing  102 , and a processor member  114 . Housing  102  may comprise any application appropriate structure that will house the necessary elements, such as a molded plastic enclosure or even a semiconductor substrate. Source  104  may comprise a number of appropriate devices and systems, but for purposes of explanation and illustration, will be depicted and treated as a collimated beam generating laser. Source  104  will operate responsive to processor  114 , or some other processor means, to transmit high speed data communications via the light that it sources. Generally, member  106  will be interposed, either directly or indirectly, between source  104  and aperture  108  such that a transmitted light path  116  from source  104  is directed to member  106  and then out of housing  102  through aperture  108  to a receiving unit. Aperture  108  may comprise any desired structure, from a simple opening in housing  102  to any number of optical filters or lenses.  
         [0023]    Beam directing member  106  is responsively coupled via link  118  to processor  114 , and comprises an optical element or elements that provide the ability to manipulate and redirect light path  116  at very high speed and with very fine resolution. While there are a number of possible configurations and apparatus (e.g., series of optical lenses and filters) that would suffice, one embodiment of element  106  comprises an analog, 2-axis micro mirror. As those skilled in the art should be aware, such a micromicron provides for electromagnetic control responsive to processor  114 , providing very fast light deflection in very fine increments. Other elements have similar responsiveness may be utilized according to the present invention.  
         [0024]    Detector  112  may comprise any suitable photo detection device, or array of devices, disposed within housing  102  in proximity to aperture  110  to receive an incoming light path  120 . Alternatively, detector  112  could be disposed directly within aperture  110  or directly upon an outer surface of housing  102 . Detector  112  is coupled to processor  114  via link  122 . Processor  114  may be disposed within, or as part of, housing  102 , or alternatively, may be remotely located apart from housing  102 . In the latter case, links  118  and  122  may comprise appropriate physical (e.g., wiring) or wireless (e.g., RF) signal paths between housing  102  and processor  114 . Processor  114  may comprise any appropriate processor device (e.g., DSP) or processing capacity (e.g., personal computer) providing the ability to process data and algorithms in accordance with this invention. Finally, source  104  may be responsively coupled to processor  114  via link  124 , or alternatively, may be activated responsive to some other desired external stimulus (e.g., another separate processor). In operation, source  104  initiates data communications via light path  116  responsive to some stimulus (e.g., a signal from processor  114 ). Light path  116  proceeds to member  106  where the direction of path  116  may be altered in varying degrees as it is directed onto and out of aperture  108  towards a desired target. Processor  114  can signal member  106  to alter, in varying degrees, the direction of path  116 . Incoming light path  120  is received through aperture  110  by detector  112 , and desired data is delivered to processor  114  via link  122 .  
         [0025]    Referring now to FIG. 2, a simple communication system  200  according to the present invention is illustrated. System  200  comprises a first optical transceiver  202  and a second optical transceiver  204  of the type described in reference to FIG. 1. Although particular configuration may be varied depending upon system requirements, actual materials used, and desired performance, for ease of reference FIG. 2 depicts the transmit aperture  206  of transceiver  202  aligned with the receive aperture  208  of transceiver  204 . Similarly, the receive aperture  210  of transceiver  202  is aligned with the transmit aperture  212  of transceiver  204 . Generally, these initial alignments can be made manually to within a few degrees accuracy. Assuming that transceiver  202  is initiating communications, it will direct a transmit communications beam  214  at transceiver  204 . System  200  will have a feedback path established between transceivers  202  and  204 . This feedback path may take the form of a separate physical or wireless communications link  216  between the transceivers, or may comprise communication via a communications beam  218  from transceiver  204  to transceiver  202 . In general, this feedback path will be used to communicate a variety of information between the transceivers to successfully target beam  214  and, once successfully targeted, to keep the high speed data transfer occurring through beam  214  locked on. A separate link  216  may be used as a temporary feedback path only to initiate communications, at which point feedback operation may be switched to a direct optical link  218  between the two transceivers. Alternatively, a diffuse optical beam link between the two transceivers may be used as the initial feedback link, until the high speed direct optical communications can be established. A number of such possibilities, depending upon particular design and performance requirements, will be apparent upon reference to this specification to those skilled in the art.  
         [0026]    The present invention communicates a variety of information between the optical communication units. Utilizing the present invention, a transmit beam  214  may be initiated with a known signal strength, and rastered in a predetermined pattern. This information is communicated to the receiving unit  204  via the feedback path. Unit  204  then compares, via the appropriate processor algorithms, the signal strength and profile as measured at its detector with the predetermined signal information. Any deviation or difference data is analyzed and communicated back, via the feedback path to transmitting unit  202 , which may then use that data to adjust, via its beam directing member, the direction of beam  214 . This process is described in greater detail with reference now to FIGS. 3 and 4.  
         [0027]    [0027]FIG. 3 a  depicts an illustrative raster pattern scheme  300 . A transmitted light beam is traced in a pattern  302  around detector  304 . Although not completely symmetrical, pattern  302  is effectively centered on detector  304 . FIG. 3 b  depicts a plot  306  illustrating the characteristics of the signal received at detector  304  at various points t 0 , t 1 , t 2 , and t 3  along pattern  302 . Plot  306  provides a profile of specific signal intensity and duration data that can be algorithmically compared and analyzed to determine whether the raster pattern  302  is centered on detector  304  or not. FIG. 4 provides an illustration of effects on signal profile if the transmitted raster pattern is moved or moving off center. FIG. 4 depicts four instances  400 ,  402 ,  404 , and  406  of raster pattern  302  as it is gradually moved off center to the side of detector  304 . Plot  408  depicts the signal profile data as measured over four t 3  intervals corresponding to the four instances  400 - 406  of raster pattern  302 .  
         [0028]    As illustrated, plot  408  deviates measurably from the predetermined pattern in plot  306 . The profile information for the transmitted beam raster pattern is communicated, via the feedback path, to the receiving unit. The processor of the receiving unit utilizes this information to determine any deviation in the raster pattern it actually receives at its detector. This deviation is analyzed, and associated with either the static variance from center, or movement away from center, of pattern  302 . Once the variance or movement is analyzed, this information may be communicated back to the transmitting unit so that it makes appropriate adjustments, via its processor and beam steering member, to center the transmitted beam, effectively locking it on. This process is iterated continuously to maintain stable high speed optical communication between the two transceivers.  
         [0029]    As illustrated in FIG. 5, a large number of raster and detector array patterns are possible. Depending upon particular design and application constraints, raster patterns and detector configurations may be optimized. Symmetrical raster patterns, although useful, are not absolutely necessary; only patterns in which some variance in the regularity of the pattern and its resulting signal profile may be readily identified. As an alternative to, or in addition to, rastering the transmit beam, one embodiment includes a primary signal detector, which would be utilized for actual data communications, arrayed with a number of positional detectors, which would be utilized only to analyze the relative positional intensity of the transmitted beam. In this embodiment, the additional detectors provide a positional distribution, increasing accuracy of the signal profile and tracking process. Such an embodiment could detect relative movement faster (i.e., without completing an entire raster cycle), and thus increase the speed and efficiency of the tracking process. In addition, certain applications may incorporate the use of light pipes or other light directing devices to better analyze varying beam widths and intensities; enhancing detector responsiveness and profile characteristics. All such variations are comprehended by the present invention.  
         [0030]    Thus, utilizing the present invention, designers can provide a high speed, high bandwidth communications utilizing optical wireless technology. Data communications will be reliable and cost effective, providing the ability to implement optical wireless technology in a number of applications where such technology was impossible or impractical to use.  
         [0031]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Upon reference to the description, it will be apparent to persons skilled in the art that various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention can be made without departing from the spirit and scope of the invention. It is therefore intended that the appended claims encompass any such modifications or embodiments.