Abstract:
Systems and methods for a reconfigurable, long-range, underwater data-communication network are described. The network provides a low cost, low power, lightweight, and easy to deploy underwater communication system capable of being operated at long distances. The network may include a cabled ocean observatory, which may be deployed underwater and connected to a surface buoy. The cabled ocean observatory may be connected to one or more removable underwater sensors via fiber optic cables. The underwater sensors may be disposed at underwater locations at long distances from the cabled ocean observatory. Fiber optic extension modules may be permanently connected to each end of the fiber optic cables. Each fiber optic extension module may include an optical transceiver, a power supply, and an inductive element for removably coupling an underwater sensor or the cabled ocean observatory to the fiber optic cable.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/223,876, filed Jul. 8, 2009 and entitled “Fiber Optic Observatory Link For Medium Bandwidth Data Communication”, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    There is an increasing need for long term observation of large portions of the earth-ocean system. In particular, scientists wish to monitor oceanic processes as well as improve predictive modeling of complex natural phenomena that vary over distance and time. Ocean observatories are being deployed at the seafloor and connected by cable or buoy to surface networks to help scientists study these oceanic processes. These observatories are really large computer and power networks having scientific equipment such as spectrometers or seismometers. These seafloor observatories may be located many hundreds of kilometers off the coast of the nearest shore station and may be positioned at depths of over 5000 meters. Typically, the observatory has one or more network connections to shore stations through which data collected from the seafloor observatory can be passed onto the Internet and which can serve seafloor instruments with power and control commands. Although existing and proposed observatory systems promise high electrical power and real-time communications, they have severe limitations with regard to the distance that instrumentation can be deployed from the observatory (either coastal, regional, or buoys) due to power, communications, and cost constraints. In addition these devices are large, heavy, and deployment is cumbersome and costly, often requiring an ROV. 
         [0003]    Accordingly, there is a need for a low cost, low power, lightweight, and easy to deploy underwater communication system capable of being operated at long distances. 
       SUMMARY OF THE INVENTION 
       [0004]    The systems and methods described herein provide a reconfigurable, long-range, underwater data-communication network. In particular, the network provides a low cost, low power, lightweight, and easy to deploy underwater communication system capable of being operated at long distances. 
         [0005]    In one aspect, a reconfigurable, long-range, underwater data-communication network may include a cabled ocean observatory, which may be deployed underwater and connected to a surface buoy. The cabled ocean observatory may be connected to one or more removable underwater sensors via fiber optic cables. The underwater sensors may be disposed at underwater locations at long distances from the cabled ocean observatory. Fiber optic extension modules may be permanently connected to each end of the fiber optic cables. Each fiber optic extension module may include an optical transceiver, a power supply, and an inductive element for removably coupling an underwater sensor or the cabled ocean observatory to the fiber optic cable. 
         [0006]    In some embodiments, each fiber optic extension module may include a first inductive element and each removable underwater sensor may include a second inductive element. The first inductive element may be coupled with the second inductive element. In some embodiments, each fiber optic extension module may include a first inductive element and the cabled observatory may include a third inductive element. The first inductive element may be coupled with the third inductive element. In some embodiments, parasitic power generated at the underwater sensor may be inductively transferred to the fiber optic extension module via the inductive coupling. In some embodiments, underwater sensors may be connected together in a daisy-chain configuration such that each connection includes additional fiber optic cable and an additional fiber optic extension module at each end of the additional cable. 
         [0007]    In some embodiments, the optical transceiver of the fiber optic extension module may include a laser configured to operate such that the module has a total power consumption of less than about 1 W when transmitting data at distances of over 100 km at about 9600 baud. In some embodiments, the laser may be configured to transmit data using an on-off keying protocol. In some embodiments, the optical transceiver may minimize power consumption by operating only when a detector receives optical signals. In some embodiments, the fiber optic extension module may be enclosed in a waterproof housing. In some embodiments, the fiber optic extension module may include one or more LiH batteries as power supplies. In some embodiments, the fiber optic extension module may weigh less than about 20 kg. In some embodiments, the fiber optic extension modules may be arranged in a mesh architecture, a bus architecture, a ring architecture, or a star architecture. 
         [0008]    In some embodiments, the fiber optic cable may be configured with separate data channels carrying data packets, and control and time channels for carrying control and time signals. The control and time signals may transmitted separate from the data packets. In some embodiments, the fiber optic extension module may include an out-of-band communication module for detecting the control and time signals. The out-of-band communication module may be coupled to the fiber optic cable. It may further provide distribution of in-band data packets and out-of-band control and time signals among the network. 
         [0009]    In some embodiments, the network may include means for measuring transmission latency among the plurality of fiber optic extension modules. In some embodiments, the fiber optic extension module may include a control module for regulating flow of the control and time signals across the control and time channels in the fiber optic cable. In some embodiments, the control module may include an interface controller for selectively allowing data channels internal to the fiber optic extension module to access control and time channels carrying control and time signals among the different fiber optic extension modules in the network. 
         [0010]    In another aspect, an underwater communication network may include a cabled ocean observatory, one or more removable underwater sensor, and one or more fiber optic cables having a fiber optic extension module at each end. The removable underwater sensor may be disposed at an underwater location at a long distance from the cabled ocean observatory. The fiber optic extension module may be inductively coupled to the cabled ocean observatory and the removable sensor. The sensor may send serial data across an inductive coupling to the fiber optic extension module. An optical transceiver in the fiber optic extension module may modulate based on the received data. The modulation may be accomplished by operating a laser in the optical transceiver using an on-off keying protocol. The fiber optic extension module may send the modulated optical signals across the fiber optic cable to another fiber optic extension module. The other fiber optic extension module may receive and convert the modulated optical signal to serial data. The other fiber optic extension module may send the received serial data across an inductive coupling to the cabled observatory. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further descriptions thereof, with reference to the accompanying drawings wherein, 
           [0012]      FIG. 1  depicts a long range subsea sensor and communication network, according to an illustrative embodiment of the invention. 
           [0013]      FIG. 2  depicts a fiber optic extension module, according to an illustrative embodiment of the invention. 
           [0014]      FIG. 3  depicts a driver circuit for a laser source in a fiber optic extension module, according to an illustrative embodiment of the invention. 
           [0015]      FIG. 4  depicts an inductive coupling system and a signaling system for a subsea inductive modem, according to an illustrative embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The systems and methods described herein will now be described with reference to certain illustrative embodiments. However, the invention is not to be limited to these illustrated embodiments which are provided merely for the purpose of describing the systems and methods of the invention and are not to be understood as limiting in anyway. 
         [0017]      FIG. 1  depicts a long range subsea sensor and communication network  100 , according to an illustrative embodiment of the invention. System  100  includes a cabled ocean observatory  104  submerged under a water body  122  at a desired depth. A cabled ocean observatory may be designed around either a surface buoy containing an autonomous power source and wireless (e.g., satellite) communications link or a submarine fiber optic/power cable connecting one or more seafloor science nodes to the terrestrial power grid and communications backhaul. A cabled ocean observatory may provide unprecedented amounts of power and two-way bandwidth to access and control instrument networks and platforms in the ocean. The cabled ocean observatory  104  is attached to a surface buoy  102 . The surface buoy  102  may remain floating on the surface of the water. A high capability buoy may contain diesel generators that deliver up to 1 kW of power. A cable  108  extending from the buoy is attached to submerged platform  106 . 
         [0018]    During operation, the observatory  104  may be disposed on the submerged platform  106  and lowered to a desired depth. The system  100  includes a plurality of underwater sensors  118   a - 118   d  disposed or scattered at various locations underwater. The underwater sensors may include a temperature sensor, a pressure sensor, a motion sensor, a light sensor, a video camera, or any other suitable type of sensor. The underwater sensors  118   a - 118   d  are connected to the cabled ocean observatory  104  by fiber optic cable  116 . Fiber optic cable may be advantageous over, for example, copper cable, since signals travel along them with less loss and are immune to electromagnetic interference. Fiber optic cable may be easier to deploy underwater due to lighter weight. However, the fiber optic cable may require protective covering capable of guarding against corrosion and damage from, e.g., fish bites. The fiber optic cable may be surrounded by a protective jacket layer made of, for example, plastic. The fiber optic cable  116  may extend for distances greater than 50 km. In certain embodiments, the fiber optic cable  116  may extend for distances greater than 100 km. The fiber optic cable  116  may extend for distances greater than 200 km. The fiber optic cable  116  may include a bundle of a plurality fiber optic wires. 
         [0019]    System  100  includes a plurality of fiber optic extension modules  112 . Generally, the fiber optic module  112  interfaces the fiber optic cable  116  with one or more observatories, sensors, devices or vehicles. In the illustrated embodiment, module  112  connects the observatory  104  to the fiber optic cable  116 . Particularly, the observatory  104  may include one or more electrical cables  114  extending in one or more different directions. The electrical cables  114  may interface with the electronics housed in the observatory  104 . The electrical cables  114  may interface with the fiber optic cable through module  112 . The module  112  will be described in more detail with reference to  FIG. 2 . The electrical cables  114  may also interface with electronics and other equipment located on the surface of the water. For example, the electrical cables  114  may be connected to the surface buoy  102  through the wire  110  that connects the buoy  102  and the observatory  104 . In some embodiments, one or more of the plurality of underwater sensors may be removable. One or more of the underwater sensors  118   a - 118   d  may be inductively coupled with ocean observatory  104  via inductive elements in modules  112 , requiring no connectors. The inductive coupling system will be described in more detail with reference to  FIG. 4 . 
         [0020]    The module  112  may also connect the fiber optic cable  116  to the underwater sensors  118   a - 118   d.  As depicted, underwater sensor  118   a  includes an electrical cable  120   a  that interfaces with the module  112  and fiber optic cable  116  to allow the underwater sensor  118   a  to communicate over long distances with the observatory  104 . Similarly, sensor  118   b  connects via electrical cable  120   b,  modules  112  and fiber optic cable  116  to the observatory  104 . In certain embodiments, underwater sensors  118   a  and  118   b  may be located on opposite sides of the cabled ocean observatory and may be separated by a distance from about 100 km to about 400 km. In certain embodiments, underwater sensors  118   a  and  118   b  may be separated by a distance of less than 100 km. The underwater sensors  118   a - 118   d  may be separated by even greater distances by daisy-chaining a plurality of sensors to extend their range. For example, sensor  118   d  may be connected to sensor  118   c,  which in turn may be connected to observatory  104 . Fiber optic cable  116  may connect sensor  118   d  with sensor  118   c  via modules  112 . The modules  112  may be arranged in a mesh architecture, a bus architecture, a ring architecture, a star architecture, or any other suitable type of architecture. 
         [0021]      FIG. 2  depicts a fiber optic extension module  112 , according to an illustrative embodiment of the invention. In particular, module  112  connects an electrical cable  204  from a sensor, observatory or other device to a fiber optic cable  116 . In some embodiments, the fiber optic cable  116  is permanently connected to the fiber optic extension module  112 . The permanent connection may be made using, for example, epoxy or some other adhesive. The connection may be designed with the intention of infrequent disconnection of the fiber optic cable  116  from the fiber optic extension module  112 . The module  112  may includes electrical wiring  206  and an inductively coupled modem  208  having inductive coils  210  and  212 . The module  112  includes an optical transceiver and other electronics  214 , and one or more power supply units  216 . In some embodiments, power supply units  216  may include LiH batteries. The optical transceiver  214  is configured for transmitting and receiving data as optical signals over an optic channel. The optical transceiver  214  may be configured as an out-of-band communications module for coupling to the fiber optic cable  116 . In particular, the optical transceiver  214  may be configured for transmitting and receiving control and time signals out of band and separately from data packets that may be transmitted or received in-band. The optical transceiver  214  may allow for accessing principle in-band data communication modules and power modules in a distributed network of devices, independent of the proper function of those principle modules. 
         [0022]    Generally, the fiber optic extension module  112  allows for accessing the sensors  118  in the network via their primitive, typically low data rate, access methods and protocols and employ a minimal suite of simple equipment for the out-of-band system. Additionally and optionally, the fiber optic extension module  112  may provide for low power consumption permitting operation on auxiliary power such as a battery during malfunction of the power system. For example, module  112  may include a wake-up circuit (or detector) for causing the device to enter into an active state in response to an incoming signal. The module  112  may be configured to switch into a state of low or zero power consumption according to a timed prearrangement or by lack of incoming signals, unless an optical signal is detected. A suitable out-of-band communication module for use with the extension module  112  and optical transceiver  214  is, for example, described in commonly-owned U.S. patent application Ser. No. 11/702,851, entitled “Communication/Power Network Having Out-Of-Band Time and Control Signaling,” the entire contents of which are incorporated herein by reference. 
         [0023]    In some embodiments, system  100  may include means for measuring transmission latency among the plurality of fiber optic extension modules. System  100  may further include a time distribution system for synchronizing clocks within the modules  112  in response to a timing pulse transmitted over the optical channel. Modules  112  may include a clock sync update logic board capable of adjusting the clock sync signal to take into consideration the latency that arises from the transfer of the sync signal across the multiple meters that make up the out-of-band communication fiber length. In some embodiments, module  112  may include a control module for regulating flow of the control and time signals across the control and time channels in the fiber optic cable  116 . In some embodiments, the control module may include an interface controller for selectively allowing data channels internal to module  112  to access control and time channels carrying control and time signals among modules  112 . 
         [0024]    In some embodiments, a fiber optic extension module is connected to a 10 km link provided by a fiber optic cable operating at 9600 baud to 56 kbps. The module is independently powered by Lithium cells, and utilizes a low power sleep/wakeup circuit. The module includes 3 mW lasers with reliable transmission over 100 km. Data connections to the module are made via inductive coupling through an inductive modem. The module weighs 20 kg requiring only a small boat or a scuba diver for deployment. 
         [0025]      FIG. 3  depicts a driver circuit for a laser source in a fiber optic extension module, according to an illustrative embodiment of the invention. In some embodiments, the optical transceiver  214  may include a laser source (e.g., a laser diode) configured to operate such that module  112  has a total power consumption of less than about 1 W when transmitting data at distances of over 100 km at about 9600 baud. In some embodiments, the laser diode may consume less than about 3 mW of power while transmitting reliability over 100 km. In some embodiments, the laser diode may be configured to transmit data using an on-off keying protocol. The on-off keying of the laser diode allows for omitting a constant carrier on the laser source. By removing this constant carrier, the amount of power consumed by the laser diode may be substantially reduced. This may reduce the available bandwidth of the laser. In some embodiments, the available bandwidth may be limited to about 1 Mbps. However, by removing the constant carrier, the feedback mechanism normally employed for laser power regulation may be removed. To address this, a configuration of an op-amp in the circuit may be established. The depicted circuit allows power regulation without a constant carrier. Laser power may be regulated through feedback control, allowing for power regulation for the depicted system that does not employ a constant carrier. 
         [0026]      FIG. 4  depicts an inductive coupling system and a signaling system for a subsea inductive modem, according to an illustrative embodiment of the invention. A fiber optic extension module may include an inductively coupled modem having one or more inductive coils or elements. The underwater sensors and the cabled ocean observatory may include one or more inductive coils to be coupled with the fiber optic extension module. The underwater sensors or the cabled ocean observatory may be connected to the fiber optic extension modules via an inductive modem to allow for easy removal of the sensor by a diver when required. Inductive modems inherently provide data transfer without physically contact, thus avoiding the need for expensive underwater pluggable electrical/optical connectors. Using a conventional underwater connector may require a shutdown in order to reconfigure the module. However, the non-contact inductive method may further permit efficient reconfiguration of the module without shutting it down. In some embodiments, the inductive coils or elements may be configured to recharge the system  100 . The inductive modem may transfer parasitic power generated at the underwater sensor to the fiber optic extension module. Power may be transferred while allowing the inductive modem to simultaneously operate in communications mode. The parasitic power may used to charge batteries in the fiber optic extension module, allowing for long-term use without battery replacement. 
         [0027]    Although, described with reference to underwater sensors  118   a - 118   d,  it should be noted that system  100  may be used in conjunction with any and all types of sensors, underwater vehicles such as ROVs and AUVs, cabled or tethered observatories, devices buried under the sea bed, tools and logging devices used under water and under the surface of the seabed such as ROTs. Examples of suitable sensors, ROVs, and AUVs may be found in commonly-owned U.S. patent applications Ser. No. 11/796,874, entitled “Systems And Methods For Analyzing Underwater, Subsurface And Atmospheric Environments”, Ser. No. 11/348,726, entitled “Systems And Methods For Underwater Optical Communication”, and Ser. No. 12/148,226, entitled “Systems And Methods For Tethering Underwater Vehicles”, the entire contents of which are incorporated herein by reference. 
         [0028]    Those skilled in the art will know or be able to ascertain using no more than routine experimentation, many equivalents to the embodiments and practices described herein. Accordingly, it will be understood that the invention is not to be limited to the embodiments disclosed herein, but is to be understood from the following claims, which are to be interpreted as broadly as allowed under the law.