Abstract:
Systems, devices and methods for transmitting and receiving signals on an optical network are disclosed. In one aspect, a micro device for connecting an electronic device to an optical transmission system is disclosed. The micro device can comprise optical components for receiving optical signals and converting the optical signals to electrical signals, a phase shifter for controlling the phase of the electrical signals, and an attenuator for controlling power level of the electrical signals, wherein the micro device is of a size having low electromagnetic interference susceptibility and emissivity.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to an optical distribution network and, more particularly, to systems, devices and methods for transmitting and receiving signals on an optical network. 
   BACKGROUND 
   Modern vehicles, such as aircraft, have an increasing number of antennas on them. Conventional communications systems utilize a point-to-point system using coaxial cable to connect radio receivers and transmitters to antennas and can be high loss, heavy and high volume systems. Additionally such systems can emit electromagnetic interference (EMI), which can cause reduced data integrity and increased error rates on transmission signals. Conventional communications systems must utilize great care to shield those signals from sources of electromagnetic radiation. 
   Optical communication systems have many advantages over systems that transmit electrical signals. Optical signals are immune to electromagnetic radiation and do not require shielding during transmission. Additionally, electrical signals can be transmitted for only relatively small distances because electrical signals incur losses proportional to the distance. Radio frequency signal losses increase rapidly as frequency increases. Optical signals, on the other hand, can be transmitted for great distances with little or no loss. Further, optical systems can reduce the amount of wiring required and can reduce the weight of the communication system. For these and other reasons, many communication systems incorporate optical signals and utilize optical networks. 
   Wavelength division multiplexing (WDM) can be used in optical networks to transmit many signals simultaneously over a single fiber by encoding them in different wavelengths or channels. An optical network can be bi-directional and permit a plurality of different network topologies. Optical bus interface modules can be used with the optical network that operate as a passive fiber optic coupler, which can be combined with WDM to selectively route optical signals in and out of the optical network at each node. 
   Conventional optical communication systems can be limited in transmitting radio frequency (RF) signals and other analog signals encoded with a high degree of information. Conventional optical communication systems are typically low power systems and the transmission of RF signals through an electronic device, such as an antenna, can require high power. Thus, conventional optical connections to an antenna have typically required a power amplifier at the antenna location on the vehicle, such as an aircraft. This can causes problems due to the heat generated by the power amplifier near the exterior of the aircraft. 
   SUMMARY 
   The invention addresses the problems above by providing systems, methods, and devices for transmitting and receiving signals on an optical network. In one embodiment, a micro device for connecting an electronic device to an optical transmission system is disclosed. The micro device can comprise optical components for receiving optical signals and converting the optical signals to electrical signals, a phase shifter for controlling the phase of the electrical signals, and an attenuator for controlling power level of the electrical signals, wherein the micro device is of a size having low electromagnetic interference susceptibility and emissivity. The electronic device can be an RF antenna and the micro device can also comprise optical components capable of receiving RF electrical signals from the RF antenna and converting the RF electrical signals to optical signals, a limiter for receiving RF electrical signals from the RF antenna, and transmit/receive switches for switching the micro device between a transmit mode and a receive mode 
   These exemplary embodiments are mentioned not to limit or define the invention, but to provide examples of embodiments of the invention to aid understanding thereof. Exemplary embodiments are discussed in the Detailed Description, and further description of the invention is provided there. Advantages offered by the various embodiments of the present invention may be further understood by examining this specification. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention and, together with the description, disclose the principles of the invention. In the drawings: 
       FIG. 1  is a diagram illustrating a portion of an exemplary optical network according to one embodiment of the present invention; 
       FIG. 2  is a diagram illustrating an exemplary micro receiver interface module according to one embodiment of the present invention; 
       FIG. 3  is a diagram illustrating an exemplary micro transmission interface module according to one embodiment of the present invention; 
       FIG. 4  is a diagram illustrating an exemplary micro transceiver interface module according to one embodiment of the present invention; and 
       FIG. 5  is a diagram illustrating a portion of an exemplary optical network according to one embodiment of the present invention; 
   

   DETAILED DESCRIPTION 
   Reference will now be made in detail to preferred embodiments of the invention, non-limiting examples of which are illustrated in the accompanying drawings. 
   Referring now to the drawings in which like numerals indicate like elements throughout the several figures,  FIG. 1  is a diagram illustrating a portion of an exemplary optical communication system or network  100  according to one embodiment of the present invention. The optical communication network  100  can utilize WDM and can be a bi-directional optical transport system that permits a plurality of different network topologies. U.S. Pat. No. 5,898,801, which is hereby incorporated in its entirety by this reference, discloses such a system. The optical network  100  can be designed to permit communication to and from electronic devices, such as electronic circuits and antennas. In one embodiment, an array of low power antennas is utilized. The optical network  100  includes an optical bus  102  and a series of optical bus interface modules (OBIMs)  104  coupled to the optical bus  102 . Each OBIM is capable of inserting, extracting, and transmitting light bi-directionally over one, two or a plurality of fiber optic transmission lines carrying one, two or a plurality of analog, digital, or discrete signals that are encoded using one, two, or a plurality of encoding techniques. The OBIMs  104  used with the optical network  100  can be configured like the OBIMs disclosed in U.S. Pat. No. 5,901,260, which is hereby incorporated in its entirety by this reference. 
   Each electronic device  106 , such as an electronic circuit or antenna is connected to a micro photonics interface module  108 , shown in  FIG. 1 , for example, as a micro RF photonics interface module. The RF photonics interface module  108  is coupled to the optical bus  102  via an OBIM  104 . The optical network  100  also includes a controller  110  for controlling the electronic devices  106  and processing the signals received by the electronic devices  106 . In an embodiment where an array of antennas is utilized, the individual antennas  106  can be controlled by the controller  110  to form desired beam patterns and to steer the beam patterns. The beam patterns can be steered by controlling the phase of the signals applied to each of the antennas  106 . By introducing phase delays in the signals applied to the different antennas  106 , the beams formed by the antenna array can be selectively steered in a given direction. 
   The micro RF photonics interface module  108  can convert an RF electrical signal to an optical signal or an optical signal to an RF electrical signal. The interface module  108  is of a size small enough that is has low electromagnetic interference susceptibility and emissivity. For example, the interface module  108  can comprise electronic components sized on the order of microns. In one embodiment, the interface module  108  is a one-millimeter by one-millimeter by three-millimeters module and is suitable for mounting in a miniature RF antenna connector or in the skin or structure of a vehicle or other apparatus or structure. The interface module  108  can have electronics leads to conduct electronics signals and fiber optics leads to conduct optical signals and receive photonics power. In one embodiment, the fiber optics leads are suitable for single mode wavelength division multiplex (WDM) signal transmission and for photonics power. In one embodiment, the single mode signal is transmitted at one or more wavelengths in the 1550 nanometer band and the (multimode) photonics power is transmitted in the 850 nanometer band. The photonics power can be generated by an off board laser and provided to the interface module  108  for conversion to electronics power. The interface module can be configured as a receiver module, as a transmission module, or as a transceiver module that is switchable to transmit or receive. 
   In an alternative embodiment (not shown), an antenna can connect to a micro RF photonics interface module and the interface module can connect to an electro-optical interface via optical fiber. The electro-optical interface can connect to the controller. 
     FIG. 2  is a diagram illustrating an exemplary micro receiver interface module  200 , such as an RF receiver module, according to one embodiment of the present invention. The RF receiver module  200  receives an electrical signal  20 , such as an RF electrical signal, via an electronic device, such as an antenna element  22 , and outputs a photonics output signal  10 . The received RF electrical signal  20  is received by the RF receiver module  200  in a limiter  202 . The limiter  202  can control unexpectedly strong signals and reduce such signals in order to protect the electronics in the RF receiver module  200 . The RF electrical signal next can be received by a low noise amplifier  204  where the RF electrical signal is amplified to distinguish it from noise received along with the RF electrical signal. The RF electrical signal can next pass through an attenuator  206 . The attenuator  206  allows for the weighting of the RF electrical signal, if necessary. The RF electrical signal can next pass through a phase shifter  208 . The phase shifter  208  allows for the control of the phase. The RF electrical signal next passes through drive amplifier  210 . The drive amplifier  210  boosts the RF electrical signal to make up for the losses in the RF electrical signal due to the phase shifter  208  and the attenuator  206  or expected or potential losses in a laser modulator. The RF electrical signal is then received by a laser modulator  224  in the optical components  212  where it is converted from a RF electrical signal to a photonic output signal  10  and sent to an optical switch  228 . The optical switch in transmit mode outputs the photonic signal on an optical fiber cable. 
   Wave Division Multiplexing (WDM) control signals can also be received by the optical components  212  of the module  200 . The WDM signals can be received on the same fiber optic cable as the photonic output signals or can be received from a different cable. In one embodiment, the WDM signals are received by the optical switch  228 , which in receive mode passes the signals to a filter  220 . The filter  220  can filter the photonics signals into separate signals based on wavelength. For example, signals on wavelengths λ 1  to λ N  can be separated into distinct signals and can each be converted to electric signals by a photonics detector D, such as a photo diode. The optical components  212  can also contain additional components to convert electrical signals to photonic signals, such as a laser and an optical modulator. 
   The signals on wavelengths λ 1  to λ N  can be control signals used to control various aspects of the operation of the module  200 . The signals on wavelengths λ 1  to λ N  can also be Health Monitoring (HM) signals such as, for example, Built-In Test (BIT), Optical Time Domain Reflectometer (OTDR), and blanking signals from other modules, that can be used to verify that the module is operating appropriately and that all components within the module are operating appropriately. The HM signals can be used with a coupler  230  to send and receive test signals through the module  200  and various components of the module  200 . While  FIG. 2  illustrates one coupler  230  at the input of module  200 , one skilled in the art would understand that the module  200  can have many couplers located throughout the module  200  to identify and isolate any problems with the components of the module  200  or input signals to the module  200 . One skilled in the art would also understand that the HM signals can be simple or complex signals. 
   Photonics power for the module  200  can be supplied by input photonics signals on the same cable as the photonics output signal or, alternatively, the photonics power can be supplied by a separate cable. The photonics power signal P can be converted to an electrical signal by a photonics detector D and transmitted to a power supply  226 . The power supply  226  can power the module  200 . In an alternative embodiment, the power supply can receive an electrical power signal, such as an AC power signal. In one embodiment, the electrical power signal can result from harvested energy, such as vibration or temperature harvested energy. 
     FIG. 3  is a diagram illustrating an exemplary micro transmission interface module  300 , such as an RF transmission module according to one embodiment of the present invention. The transmission module  300  receives an input photonics signal  10  and transmits a electrical signal  20 , such as an RF electrical signal, to an electronic device, as shown in  FIG. 3 , an antenna element  22 . The photonics signal  10  can comprise multiple WDM signals, including the transmission signal and control signals. The WDM signals are received by a filter  301  in the optical components  302  of the module  300 . The filter  301  can filter the photonics signals into separate signals based on wavelength. For example, signals on wavelengths λ 1  to λ N  are separated from the transmission signal. All of the input signals, including the transmission signal, can be converted to electrical signals by a photonics detector D, such as a photo diode. The optical components  302  can also contain additional components to convert an electrical signal to a photonic signal, such as a laser and an optical modulator. 
   The signals on wavelengths λ 1  to λ N  can be control signals used to control various aspects of the operation of the module  300 . The signals on wavelengths λ 1  to λ N  can also be Health Monitoring (HM) signals such as, for example, Built-In Test (BIT), Optical Time Domain Reflectometer (OTDR), and blanking signals from other modules, that can be used to verify that the module is operating appropriately and that all components within the module are operating appropriately. The HM signals can be used with couplers  312  A,B to send test and receive signals through the module  300  and various components of the module  300 . While  FIG. 3  illustrates two couplers  312  A,B, one skilled in the art would understand that the module  300  can have many couplers located throughout the module  300  to identify and isolate any problems with the components of the module  300  or input signals to the module  300 . One skilled in the art would also understand that the HM signals can be simple or complex signals. 
   Photonics power for the module  300  can be supplied by input photonics signals on the same cable as the photonics output signal or, alternatively, the photonics power can be supplied by a separate cable. The photonics power signal P can be converted to an electrical signal by a photonics detector D and transmitted to a power supply  305 . The power supply  305  can power the module  300 . In an alternative embodiment, the power supply can receive an electrical power signal, such as an AC power signal. In one embodiment, the electrical power signal can result from harvested energy, such as vibration or temperature harvested energy. 
   The electrical transmission signal, such as an RF electrical signal, can be received by a drive amplifier  304 . The drive amplifier  304  can be necessary due to the relatively low power converted photonic signal to bring the RF electrical signal up in power so that it can be controlled, if necessary. The amplified RF electrical signal can then be phase shifted by a phase shifter  306 . The phase shifter  306  allows for control of the phase of the RF electrical signal. A variable resister/attenuator  308  can receive the RF electrical signal and can allow for the power level of the RF electrical signal to be controlled. The RF electrical signal can then be received by a power amplifier  310 , which amplifies the RF electrical signal. The power amplifier  310  can be a single stage amplifier or can be a two or more stage power amplifier. The RF electrical signal is then received and broadcast by the antenna element  22 . 
     FIG. 4  is a diagram illustrating an exemplary micro transceiver interface module  400 , such as an RF transceiver module, according to one embodiment of the present invention. The RF transceiver module  400  can both receive a photonic input signal  10  and transmit an electrical signal  20 , such as an RF electrical signal, and can receive an electrical signal  20 , such as an RF electrical signal, and transmit a photonic output signal  10 . In transmit mode, the photonic signal  10  is received by optical components  402  converted into an RF electrical signal. The photonics signal  10  can comprise multiple WDM signals, including the transmission signal and control signals. The WDM signals are received by an optical switch and then sent to a filter  401 . The filter  401  can filter the photonics signals into separate signals based on wavelength. For example, signals on wavelengths λ 1  to λ N  are separated from the transmission signal. All of the input signals, including the transmission signal, can be converted to electrical signals by a photonics detector D, such as a photo diode. 
   The signals on wavelengths λ 1  to λ N  can be control signals used to control various aspects of the operation of the module  400 . The signals on wavelengths λ 1  to λ N  can also be Health Monitoring (HM) signals such as, for example, Built-In Test (BIT), Optical Time Domain Reflectometer (OTDR), and blanking signals from other modules, that can be used to verify that the module is operating appropriately and that all components within the module are operating appropriately. The HM signals can be used with couplers  426  A,B to send test and receive signals through the module  400  and various components of the module  400 . While  FIG. 4  illustrates two couplers  412  A,B, one skilled in the art would understand that the module  400  can have many couplers located throughout the module  400  to identify and isolate any problems with the components of the module  400  or input signals to the module  400 . One skilled in the art would also understand that the HM signals can be simple or complex signals. 
   The converted RF transmission electrical signal can then be sent to the transmit-receive switch  404 . In transmit mode, the transmit-receive switch  404  is open and allows the RF electrical signal to pass to a drive amplifier  406 . From the drive amplifier  406 , the RF electrical signal can pass through a phase shifter  408 , and attenuator  410 . If necessary, the RF electrical signal can also pass through a second drive amplifier  412 . The RF electrical signal is then received at the second transmit-receive switch  414 , which in transmit mode is open and allows the RF electrical signal to pass through to a power amplifier  416  where the RF electrical signal is amplified. The RF electrical signal is then received by a third transmit-receive switch  418 . In transmit mode, the third transmit-receive switch  418  is open and allows the RF electrical signal  20  to be transmitted to the antenna element  22 . The antenna element  22  can then broadcast the signal. 
   In receive mode, the RF transceiver module  400  receives an electrical signal  20 , such as an RF electrical signal, via an electronic device, such as the antenna element  22 . The RF electrical signal is then received by the transmit-receive switch  418 . The transmit-receive switch  418  in receive mode causes the RF electrical signal to pass through to a limiter  420  and a low noise amplifier  422 . From there, the RF electrical signal goes to the transmit-receive switch  404  which in receive mode causes the RF electrical signal to pass through the drive amplifier  406 , the phase shifter  408 , the attenuator  410 , and a second drive amplifier  412 . From there, the RF electrical signal is received by the transmit-receive switch  414 , which in receive mode causes the RF electrical signal to go to the optical components  402 . The optical components  402  can convert the RF electrical signal to a photonic signal using a laser modulator and transmit the photonic signal  10  through the optical switch over optical fiber. 
   Photonics power for the module  400  can be supplied by input photonics signals on the same cable as the photonics output signal or, alternatively, the photonics power can be supplied by a separate cable. The photonics power signal P can be converted to an electrical signal by a photonics detector D and transmitted to a power supply  424 . The power supply  424  can power the module  400 . In an alternative embodiment, the power supply can receive an electrical power signal, such as a platform power signal. In one embodiment, the electrical power signal can result from harvested energy, such as vibration or temperature harvested energy. 
     FIG. 5  is a diagram illustrating a portion of an exemplary optical network  500  according to another embodiment of the present invention. In this embodiment, an electrical subsystem  502 , such as a radio transmit/receive subsystem, utilizes point to point connections to connect to electronic devices,  504 , such as an antenna. In another embodiment, the optical network  500  can be used to connect two electrical subsystems. In the embodiment shown in  FIG. 5 , interface modules  506 ,  507 ,  508 ,  509  can be used to convert from electrical signals to photonics signals and photonics signals to electrical signals. For example, cables  510  and  512  are fiber optic cables and can carry photonics signals to and from the interface modules  506 ,  507 ,  508 ,  509 . In one embodiment, cables  514 ,  516 ,  518 ,  522  are electrical pigtails and can carry electrical signals to and from the interface modules  506 ,  507 ,  508 ,  509 . The pigtails can be connected to a pin in an RF connector or can be connected directly to an electronic circuit, which may include an antenna feed point. In one embodiment, pigtails  516  and  518  connect to a bulkhead connector pin, such as used on an aircraft. In one embodiment, the fiber optic cables  510  and  512  can have a length of several meters and the pigtails  514 ,  516 ,  518 ,  522  can have a length of one millimeter long. 
   Interface module  506 , for example, can receive electrical signals from subsystem  502  via pigtail  514 , convert the signals to photonic signals, and output the photonic signals to optical cable  510 . Interface module can also receive photonic signals from interface module  507  via optic cable  510 , convert the signals to electrical signals, and output the electrical signals to pigtail  514 . The other interface modules  507 ,  508 ,  509  can operate in a similar manner. For example, the subsystem can transmit signals through the interface modules, pigtails and optic cables to antenna  504 . While an antenna  504  is illustrated in  FIG. 5 , one skilled in the art would understand that this could be another subsystem or bulkhead. 
   In one embodiment, the interface modules  506 ,  507 ,  508 ,  509  can receive photonics power P. The photonics power can be supplied to the interface modules  506 ,  507 ,  508 ,  509  from the fiber optic cables  510 ,  512  or can be supplied by separate fiber optic cables. In another embodiment, the interface modules  506 ,  507 ,  508 ,  509  can receive electrical power signals, such as a platform power signal. In one embodiment, the electrical power signal can result from harvested energy, such as vibration or temperature harvested energy. In one embodiment, the interface modules can receive WDM photonics control signals. These WDM photonics control signals can be received on the fiber optic cables  510 ,  512  or can be received on separate fiber optic cables. In the embodiment shown in  FIG. 5 , the interface modules are used so that electrical coaxial cable typically used to connect electronic devices can be replaced with fiber optics cable, which can dramatically reduce the weight of the system. Moreover, the network  500  makes use of optical cables without the use of optical connectors, which are difficult to cleans and subject to damage. 
   The foregoing description of the preferred embodiments of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated.