Patent Publication Number: US-11387906-B1

Title: Devices, systems, and methods for underwater laser communications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. application Ser. No. 16/869,540, filed May 7, 2020, which claims the benefit of U.S. Provisional Application No. 62/844,376, filed May 7, 2019, each of which is hereby incorporated by reference in its respective entirety. 
    
    
     FIELD OF THE INVENTION 
     The application relates generally to systems, devices, and methods for underwater communications. In particular, the application relates to utilizing one or more lasers for transmitting and receiving data, including encoded data, underwater. 
     BACKGROUND 
     Underwater communications are used in a variety of industries and for a variety of uses, including, for instance, oil and gas operations, ship operations underwater, diving, submarine operations, autonomous underwater and surface vehicles, seismic monitoring, laying and monitoring communications cables, oceanographic research, military research and operations, and monitoring underwater infrastructure. 
     However, current systems, devices, and methods for underwater communications are complex, hard to scale, and expensive. In addition, they are often unable to effectively communicate and reach their intended targets. 
     Given the foregoing, there exists a significant need for new systems, devices, and methods capable of allowing for effective underwater communications, especially encoded communications. 
     SUMMARY 
     It is to be understood that both the following summary and the detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Neither the summary nor the description that follows is intended to define or limit the scope of the invention to the particular features mentioned in the summary or in the description. 
     In general, embodiments of the present invention are directed to devices, systems, and methods for transmitting information underwater. In particular, the invention in various embodiments comprises an underwater transmitter node that sends information to an underwater receiver node using one or more lasers. The one or more lasers may be focused on to the underwater receiver node using a lens, telescope system, or the like. Additionally, the invention in its various embodiments may be automated such that the one or more lasers can be operated automatically to transmit information in an easy and efficient way without in-depth knowledge of lasers and optics. One of skill in the art will recognize that current systems do not focus energy, but rather attempt a wide-beam approach. Such an approach suffers from numerous drawbacks, including, but not limited to, inability to efficiently and conveniently transmit information. 
     In one or more embodiments of the present invention, the one or more lasers have a wavelength in the blue-green portion of the visible spectrum (400-530 nm), thereby enabling the one or more lasers to transmit effectively through water, including, for instance, ocean water. 
     In some embodiments of the invention, the information transmitted between the underwater transmitter node and the underwater receiver node is an encoded digital transmission. It should be appreciated that two or more different encoding schemes are possible for a given transmission. It should further be appreciated that the communication between the underwater transmitter node and the underwater receiver node may be unidirectional or bidirectional. These encoding schemes are well-known in the art, including, but not limited to, quadrature amplitude modification or on-off keying. 
     At least one embodiment of the invention comprises the use of one or more lasers having wavelengths in the range of 400-530 nm. These one or more lasers optimally transmit through ocean water. One of skill in the art will appreciate that there may be one or more optimal wavelengths for transmission, depending on the exact composition of the water, including, for instance, the number and type of biological and/or plant species present in that water, which impacts the specific wavelengths of light absorption. The optimal wavelength for a given body of water at a given time may be determined experimentally. 
     Purely as a non-limiting example,  FIG. 1  illustrates the result of one laser having a wavelength of 450 nm transmitting through water of various compositions, which is near, or at, the peak transmission point for certain sea water conditions. Although some light from the laser is reduced through the water column, the light is detectable up to a certain range, thereby enabling digital transmission via the laser. Although various embodiments of the invention are described herein with reference to one or more lasers having a wavelength of 450 nm, such disclosure should not be interpreted in a limiting sense. Depending on the conditions and/or composition of the water through which communications are necessary, lasers with more than one wavelength may be used, including, for instance, 475 nm. 
     Some embodiments of the present invention utilize narrow-band lasers in focused, narrow-area transmissions. A skilled artisan will appreciate that wide-area transmissions intrinsically limit both data rate and range, and also increase power requirements of the one or more lasers used. Such a skilled artisan will further appreciate that, in the current state of the art, no devices or systems focus energy from lasers to enable underwater communications. The present invention in its various embodiments enables such communications with, for instance, one or more lasers transmitting in a wavelength of 400-530 nm. 
     At least one embodiment of the invention comprises a system that uses 5-4 encoding and is further capable of using a variant of quad-division multiplexing and multiple wavelengths of one or more lasers in order to increase bandwidth. Such a system may include, for instance, modulated retroreflectors and adaptive optics. APDs may be used rather than PIN diodes. 
     The present invention in various embodiments further comprises a standard 100Base-FX encoding scheme operating at 31.25 MHz, and transmitting at 100 Mb/s through water for over 30 m. 
     The present invention in at least one embodiment may additionally comprise automated search and track systems employing modulation of laser power level and beam focusing. One such embodiment is depicted herein in  FIGS. 3A-3B , which illustrate a tracking system that has a pressure housing containing the actual laser, a gimbal mirror, a dichroic separator, a beam splitter, an optical receiver, and a quad cell. 
     One of skill in the art will appreciate that the instant invention is therefore useful for underwater communications in a variety of fields and use situations, including, for instance, offshore operations and communications for oil and gas companies, offshore and underwater military communications, telecommunications cable companies and operators, and academic oceanographic research. 
     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, as well as the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate exemplary embodiments and, together with the description, further serve to enable a person skilled in the pertinent art to make and use these embodiments and others that will be apparent to those skilled in the art. 
         FIG. 1  is a graph showing attenuation of light at a wavelength of 450 nm through different water types, which are defined through their respective attenuation coefficients in units of m −1 , according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram illustrating an embodiment of the present invention comprising, in part, a modulating retroreflector and a telescope for receiving the laser-generated transmission. 
         FIGS. 3A-3B  illustrate an automated tracking system according to an embodiment of the present invention. 
         FIG. 4  illustrates an underwater network architecture comprising both sensors and laser nodes, according to an embodiment of the present invention. 
         FIG. 5  illustrates an underwater network architecture for underwater seismic monitoring, according to an embodiment of the present invention. 
         FIG. 6  illustrates an underwater network architecture for monitoring and/or relaying communications, according to an embodiment of the present invention. 
         FIG. 7  illustrates an underwater network architecture for monitoring and/or communicating with underwater vehicles, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is more fully described below with reference to the accompanying figures. The following description is exemplary in that several embodiments are described (e.g., by use of the terms “preferably,” “for example,” or “in one embodiment”); however, such should not be viewed as limiting or as setting forth the only embodiments of the present invention, as the invention encompasses other embodiments not specifically recited in this description, including alternatives, modifications, and equivalents within the spirit and scope of the invention. Further, the use of the terms “invention,” “present invention,” “embodiment,” and similar terms throughout the description are used broadly and not intended to mean that the invention requires, or is limited to, any particular aspect being described or that such description is the only manner in which the invention may be made or used. Additionally, the invention may be described in the context of specific applications; however, the invention may be used in a variety of applications not specifically described. 
     In the several figures, like reference numerals may be used for like elements having like functions even in different drawings. The embodiments described, and their detailed construction and elements, are merely provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the present invention can be carried out in a variety of ways, and does not require any of the specific features described herein. Also, well-known functions or constructions are not described in detail since they would obscure the invention with unnecessary detail. Any signal arrows in the drawings/figures should be considered only as exemplary, and not limiting, unless otherwise specifically noted. Further, the description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. Purely as a non-limiting example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms “a”, “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be noted that, in some alternative implementations, the functions and/or acts noted may occur out of the order as represented in at least one of the several figures. Purely as a non-limiting example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality and/or acts described or depicted. 
     Generally, the present invention is directed to devices, systems, and methods for transmitting information underwater. In particular, the invention in various embodiments comprises an underwater transmitter node that sends information to an underwater receiver node using one or more lasers. The one or more lasers may be focused on to the underwater receiver node using a lens, telescope system, or the like. 
     Some embodiments of the instant invention comprise both unidirectional and bidirectional transmission of data and/or information via one or more lasers. 
     It should be appreciated that data transmitted between the underwater transmitter node and the underwater receiver node may be in the form of an encoded digital transmission. It should further be appreciated that one, or more, different encoding schemes are possible for a given transmission. 
     Accordingly, at least one embodiment of the present invention comprises a system that uses 5-4 encoding and is further capable of using a variant of quad-division multiplexing (e.g., quadrature amplitude modification (QAM) and its sub-variants, which depend on the number of bits per symbol being transmitted) and multiple wavelengths of one or more lasers in order to increase bandwidth. Specifically, multiple lasers are used to increase bandwidth by running them in parallel. Encoding methods such as, for instance, QAM-16, QAM-32, or QAM-64 are used to pack more bits into each transmitted symbol. Such a system may additionally include, for instance, modulated retroreflectors and adaptive optics. All of the above encoding methods are well-known for radio frequency (RF) and laser communications systems. 
     The invention in its various embodiments may further comprise a standard 100Base-FX encoding scheme operating at between 31.25 MHz and 62.5 MHz, and transmitting at 100 Mb/s through water for over 30 m. Although such an encoding scheme is generally well-known in the art, it should be appreciated that currently-available devices and systems are unable to use this or other encoding schemes for laser-based communications through water, and especially not in an autonomous or semi-autonomous fashion. For example, currently-existing free space air communication systems require careful manual alignment, while the present invention in its various embodiments removes the need for such manual alignment while maintaining tight beam functionality. 
     Further embodiments may additionally comprise automated search and track systems employing modulation of laser power level and beam focusing. 
     One of skill in the art will recognize that the one or more lasers in the present invention may have a wavelength in the blue-green portion of the visible spectrum, thereby enabling the one or more lasers to transmit effectively through water, including, for instance, ocean water. 
     A non-limiting example of a laser transmitting light at a wavelength of 450 nm through different water types is shown in  FIG. 1 . Each of these water types on the graph is defined via its respective attenuation coefficient, in units of m −1 . The lines represent different types of sea water conditions. 
     As can be seen in  FIG. 1 , the ability of a given laser operating at 450 nm to transmit light through water is dependent on the specific type of water through which that light is transmitted. One of skill in the art will appreciate that such dependency is not limited to a laser operating at 450 nm. Detection down to 0.1% (10 −3 ) transmission or lower is possible, depending on the sensitivity of the detectors used. 
     It should additionally be appreciated that different bodies of water, as well as different portions of water columns within the same body of water, may have different impacts on the transmission ability of a given laser. Such differential impacts may depend on, for instance, the exact composition of the water, as well as the number and type of biological and/or plant species present in that water. These differences produce different types of water that can be classified according to the Jerlov classification scheme. The optical properties of different Jerlov water types are known to those of skill in the art. 
     Transmission of a message via one or more lasers may either unidirectional or bidirectional. Purely as a non-limiting example, an underwater transmitting node, which may comprise one or more lasers, may transmit data to an underwater receiving node in a unidirectional way. At minimum, however, only one laser is needed to transmit unidirectionally. There are at least two methods for transmitting data in a bidirectional way. First, one or more lasers can be present on both the transmitting end and the receiving end. Second, a laser may be located at one location such as, for example, the transmitting location, and a modulating retroreflector may be located at another location such as, for instance, the receiving location. The modulating retroreflector changes the signal sent by the laser as it returns that signal to the original transmitting location. A photodiode may also tap part of the signal from the retroreflector in order to receive transmissions from the laser. 
     A non-limiting example of a two-way communication system with a modulating retroreflector is shown in further detail in  FIG. 2 . The two-way communication system comprises a transmission subsystem  202  that is underwater, a surface cable  204  that connects the transmission subsystem to the surface of the water, and one or more modulating retroreflectors  206 . 
     The transmission subsystem  202  itself comprises a laser  208  that emits a beam to one or more steerable mirrors  210 . The beam transmits data and/or information that may be encoded. The steerable mirrors  210  then direct the beam to the one or more modulating retroreflectors  206 , which may be 10 m or more from the transmission subsystem  202 . A photo-diode (not shown) may be in complex with the one or more modulating retroreflectors in order to tap the beam sent by the laser  208  (i.e. read the signal from the laser at the retro-reflector location). 
     The one or more modulating retroreflectors receive the beam from the laser  208  and then redirect the beam back to the transmission subsystem. A telescope  212  in the transmission subsystem receives the beam that is redirected back from the one or more modulating retroreflectors, thereby enabling the transmission subsystem to also receive data in addition to transmitting data. An APD (avalanche photodiode)  214  may be complexed with the telescope. Such an APD is a tunable sensitivity photodetector capable of applying multiplicative gain to an incoming optical signal. Using such an APD over a standard photodiode results in an increase in the maximum range of the system and/or the maximum attenuation the system can tolerate. 
     The transmission subsystem may also comprise communication electronics  216 . These communication electronics convert incoming optical signals into copper network traffic, as well as handle intersystem communication (i.e., communication between components of the system). The communication electronics  216  further control the network stack and ensure that all data on the network arrives at its intended location. 
     A skilled artisan will appreciate that the one or more modulating retroreflectors  206  may be replaced by a second transmission subsystem (not shown) that is identical to the transmission subsystem  202 . As a result, this second transmission subsystem comprises, in part, a second laser. The second laser operates at either the same wavelength as the laser  208 , or a different wavelength to reduce the effects of backscatter from the laser  208 . Non-limiting examples of these different wavelengths include 450, 475, 487, and 515 nm. It should be appreciated that the laser  208  and/or the second laser may be gated to reduce the backscatter effect(s), a principle well-known in the art as “range gating”. It should further be appreciated that the laser  208  would not transmit data at the same time as the second laser. 
     Embodiments of the present invention further include automated search and track systems employing modulation of laser power level and beam focusing.  FIG. 3A  depicts a non-limiting example of such a track system  300 . The system  300  has a pressure housing  302  containing various components, including the actual laser  304  used for underwater communications (which may, in at least some embodiments, comprise multiple lasers transmitting and/or receiving at different wavelengths), a gimbal mirror  306 , a dichroic separator  308 , a beam splitter  310 , an optical receiver  312 , and a quad cell  314 . 
     The gimbal mirror  306  is used to control the pitch and yaw of the system  300 . The dichroic separator  308  can be used to separate different lasers based on their color; that is, separation of lasers that are transmitting and/or receiving at different wavelengths. The beam splitter  310  reflects a portion (e.g., half) of received energy (e.g., from another laser transmitting information from another system) into a position detector, which can be the quad cell  314  or a lateral effect or other type of position-sensing detector, and transmits another portion (e.g., the other half) of the received energy to the optical receiver  312  that generates the communication signals. The quad cell, or other type of position-sensing detector, provides pointing feedback to the gimbal mirror to maintain linkage between the system  300  and other remote system(s). 
       FIG. 3B  depicts a further non-limiting example of a track system in the context of an underwater laser communications system according to at least one embodiment of the present invention. A first underwater laser communications module  302  comprises a first laser  304  that sends laser-based information, via its beam, through a first gimbal mirror  306 , and then through a second gimbal mirror  306  located in a second underwater laser communications module  307 . The beam from first laser  304  then passes through a beam splitter  310  in this second module, and is received by both the quad cell  314  in the second module. 
     This second module  307  also comprises a second laser  304  that can send laser-based information, via its beam, back to the first module  302 . This second laser  304  passes a beam through the first and second gimbal mirrors  306 . The beam then passes through the first beam splitter in the first module and reaches the quad cell  314  in the first module and a receiver  316  in the first module. 
     The present invention in various embodiments comprises a system for transmitting and receiving underwater laser-mediated communications, which may be referred to herein as “ULTRA.” 
     Turning now to  FIG. 4 , a non-limiting example of ULTRA is shown. ULTRA may comprise one or more communications nodes  402 , one or more laser hubs  404 , one or more communications buoys  406 , and optionally an AUV/ROV (Autonomous Underwater Vehicle/Remote Operated Vehicle) to transmit data from ULTRA to the surface. 
     Each communication node  402  comprises, in part, a modulating retroreflector. Each laser hub  404  comprises, in part, one or more lasers that are connected by cables to an above-water and/or surface network. A given laser hub may further comprise one or more acoustic modems as secondary communications devices. 
     The one or more communications buoys  406  chain the laser hubs together underwater with cables (for example fiber optic cables and power umbilicals). The communications buoy is itself connected to an above-water and/or surface platform  408 , thereby connecting all of the components of the ULTRA system together. As a non-limiting example, the buoy could be connected to the platform  408  via cable and/or radio link. Additionally, the communications buoy may be located a customizable distance from the platform. It should be appreciated that, although communications buoys currently exist that can be tethered, via, for instance, fiber-optic cables, to underwater infrastructure, the ULTRA system enables connection of these buoys to more components and/or devices than what is currently possible. 
     One of skill in the art will appreciate that any number of communication nodes and/or laser hubs can be connected to a given communication buoy, and any number of communications buoys can be connected to a given platform. In such a fashion, the ULTRA system is scalable to larger networks. 
       FIG. 5  illustrates a non-limiting use example of an ULTRA system, according to an embodiment of the present invention. The ULTRA system may be used for continuous 4D seismic field monitoring. In this example, the communication nodes are 4D sensor nodes  502  that can collect real-time seismic data and relay it to the central hub  504  which can transmit it over the umbilical uplink to the surface infrastructure  506 . Each 4D sensor node  502  shown may represent a series of 4D nodes linked together through multiple ULTRA relays. The ULTRA system shown can collect data on four channels at 24 bits, and up to 2000 Hz, with two acquisition channels at 24 bits, and up to 500 Hz. The total data collection rate is 270 Kbps per node. An AUV/ROV  508  is also part of this ULTRA system, and can be used to visit nodes  502  or talk to the laser hub  504 . The communication nodes  502  are queried by the laser hub  504  at regular intervals and send back their collected data using their retro-reflectors. 
       FIG. 6  illustrates another non-limiting use example of an ULTRA system, according to an embodiment of the present invention. This example depicts a use scenario in which a full-time residency network is set up on well hardware using thermoelectric energy as a power source. One of skill in the art will recognize that such a setup is not feasible with current optical communications technologies. In other words, the ULTRA system depicted is powered by a thermoelectric generator  602  that uses thermoelectric power from thermal power harvesting, which utilizes an existing temperature differential (e.g., between a hot oil pipe and the cold sea floor) to generate electricity using a semiconductor sandwich. In this use scenario, the ULTRA system again comprises one or more communications nodes  604  that can collect data and transmit such data to a laser hub  606 , which is in turn connected to, and can relay the data to, surface infrastructure  608 . The ULTRA system shown may be used for subsea system monitoring, with one or more communications nodes that enable real-time monitoring of underwater and/or subsea conditions. The communications hubs transmit their monitoring data to the laser hub via their retro-reflectors. 
       FIG. 7  illustrates a further non-limiting use example of an ULTRA system, according to an embodiment of the present invention. This example depicts a use scenario for tetherless operation of AUV/ROV assets at a well site. As shown, the ULTRA system may be used for autonomous vehicle communications, with one or more communications nodes  702  located on the autonomous vehicle  704 . The vehicle can then conduct video surveillance of, for instance, the ocean or sea floor, which is then communicated to the laser hub  706 , which is linked to an above-water and/or surface platform  708 . Such a system enables augmented navigation of the vehicle as well as streaming video analytics. A skilled artisan will further recognize that such a system is advantageous over current state-of-the-art systems because it eliminates the need for a tether/umbilical for the AUV/ROV  704 , preventing potentially dangerous and costly umbilical snags on environmental obstacles. In the illustrated use example, sonar may be required for localization, in which case each of the one or more communications nodes  702  would be fitted with an acoustic receiver. 
     As an additional non-limiting example, an ULTRA system according to an embodiment of the present invention may comprise, for instance, one or more lasers having a wavelength of 450 nm, up to 80 mW of transmitted power, a 100Base-FX standard encoding which is 4B5B (reference: https://en.wikipedia.org/wiki/4B5B), modulation at 31.25 MHz, and an effective transmission at 100 Mbits/second. The ULTRA system may further comprise a PIN diode as a receiver at each communications node, which is connected to a standard amplifier and demodulator. The amplifier and demodulator modify existing 100Base-FX media transceivers. Each communications node may have multiple sets of transmitters and receivers. One of skill in the art will recognize that the one or more lasers transmitting data looks like a fiber optic cable to the electronics, with the laser driver modified to level-shift the laser-modulating signal to match the required input of the laser diode. In other words, current telecommunications equipment can be adapted by appropriate translation electronics to operate underwater in embodiments of the present invention. 
     It should be appreciated that more potential use examples than those described herein are possible. For instance, the present invention in its various embodiments may be custom modulated to better cope with underwater physics, such as, for example, backscatter, objects falling or moving in the laser beam(s), and the like. An avalanche photodiode may also be utilized to receive fainter signals. Additionally, adaptive optics may be utilized to improve both transmission of the laser signal as well as reception of the laser signal. Active targeting and/or acquisition may also be used to automatically align the transmitter of the signal and the receiver. Further, machine vision may be utilized to aid in locating adjacent nodes during the automatic alignment process. 
     The various components of the present invention described herein may be coated with non-toxic, anti-biofouling coatings in order to improve function and lifespan. Additionally, the invention in its various embodiments can perform wide-area searches using broadened transmit beams and retroreflectors to find the receivers, then narrow down the one or more laser beams for high speed operations underwater. To find such receivers, a coarse search mode is utilized in order to find a nearby receiver with a wide field of regard. Once the receiver is found, the field of regard is narrowed until one or more laser beams is directed at the found receiver. 
     These and other objectives and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification. 
     The invention is not limited to the particular embodiments illustrated in the drawings and described above in detail. Those skilled in the art will recognize that other arrangements could be devised. The invention encompasses every possible combination of the various features of each embodiment disclosed. One or more of the elements described herein with respect to various embodiments can be implemented in a more separated or integrated manner than explicitly described, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. While the invention has been described with reference to specific illustrative embodiments, modifications and variations of the invention may be constructed without departing from the spirit and scope of the invention as set forth in the following claims.