Method and apparatus for optically powering and multiplexing distributed fiber optic sensors

An optical power converting apparatus is provided that may be used with remote sensors. A plurality of remote sensors may be coupled to a backbone optical fiber with each sensor having an optical power converter that receives an optical signal from a head end of that fiber. The optical power converters may store electrical energy derived from that optical signal and use that energy to power the remote sensors. The head end's optical signal may also include a clock signal, and each remote sensor may be set to sense a measurable parameter after a given number of clock cycles have been counted. In a further example, each of the optical sensors may be synchronized before counting these clock signals via a synchronization signal from the optical power converter. The remote sensors may individually and separately uplink their sensed data to the head end on the optical fiber. The apparatus may be implemented in a vehicle health management system, for example.

FIELD OF THE INVENTION

The present invention relates generally to sensors and more particularly to optically-powered sensors.

BACKGROUND OF THE RELATED ART

For years, people have used remote sensors in hostile environments, placing sensors in locations where human or manual data collection is unattainable or too costly. In toxic and environmentally dangerous environments, for example, remote sensors may provide an effective way of measuring data that might otherwise go unmeasured. In space-constrained environments, remote sensors may be useful in reaching otherwise unreachable locations.

Despite the deployment of remote sensors in certain applications, many applications are incompatible with certain types of remote sensors, or remote sensors altogether. Electrically-powered remote sensors, for example, are not used in environments where electrical conduction can lead to sensor damage or environmental damage. In an aircraft, for example, lightning strikes can be dangerous and damage on-board electronics such as those that would be used in and to power electronic sensors. This lightning problem may be exacerbated by the light-weight, less shielding composite structures used with increasing regularity in modern aircraft. In a spacecraft, for example, a lightning strike could harm the electronic sensors used to monitor mission critical launch conditions. In fact, lightning damage has resulted in some infamous losses of spacecraft, including the Atlas G-Centaur AC-67 space mission. Lightning also nearly caused the astronauts to abort the Apollo 12 spacecraft launch, when a lightning strike triggered electrical warning signals and disabled telemetry systems. Moreover, the problem of spiking is not limited to lightning, as other high voltages would be hazardous if combined with electrically powered sensors in certain environments, such as inside fuel tanks where there is the potential for an igniting hazard through short circuits in the electrical wiring.

Not only are electrical field and voltage surges problematic, high-power microwave radiation can also limit the use of certain types of sensors. For example, it is difficult to use electronic sensors to monitor high-power phased array radar systems because of electromagnetic field interference. High voltage isolation is a limiting factor for high-voltage, power-line sensor applications, as well.

Whereas electrically-powered sensors may be incompatible with certain environments, optically-powered sensors may show potential. In aircraft, for example, an optically powered sensor could protect against lightning, electric fields and discharges, and other electronic interference.

Yet, despite the theoretical attractiveness of optically-powered sensors, there are numerous limitations affecting their deployment. One problem is the lack of efficient and effective methods to optically power multiple sensors. Some powering techniques convert an optical energy on a fiber to electrical power at the sensor. However, the techniques are only used to power a single sensor, unless a fiber optic splitter or multiplexing device is used, thereby adding to device cost, weight, and complexity. Furthermore, remote powering techniques can require a minimum of two fibers for each sensor—one fiber to optically power the sensor, another fiber to receive sensor data. Even the commercially-available pie-wedge photonic power converters suggested by some (in addition to being expensive) would require a fiber bundle to receive data from multiple sensors. In short, the present techniques for optically powering remote sensors would require multiple fibers or a large fiber bundle if multiple sensors were to be deployed, and this requirement is undesirable in space- or weight-constrained systems such as an aircraft, or spacecraft.

It is desirable to have a way of optically powering multiple sensors that may be placed remotely from one another, and to do so in a way that remote sensed signals may be communicated to a centralized analyzer via the same fibers used for powering the sensors.

SUMMARY OF THE INVENTION

An embodiment of the invention is an optical power converter comprising: a photodetector for producing an electrical signal; a storage circuit in parallel with the photodetector to store at least a portion of the electrical signal; a first chargeable switch; a second chargeable switch having a different charging time than the first chargeable switch; and a dual transistor switch coupled to the first chargeable switch and the second chargeable switch, wherein the storage circuit is coupled to the dual transistor switch, and wherein during a storing state the photodetector supplies current to the storage circuit and the dual transistor switch is in an off state, and wherein during a driving state, the storage circuit supplies current to switch the dual transistor switch to an on state wherein at least one of the first chargeable switch or the second chargeable switch is in a conducting state.

Another embodiment of the invention is an optically-powered sensor apparatus comprising: an optical fiber; a head end coupled to the optical fiber to provide optical clock signals on the optical fiber; and at least two sensor modules coupled to the optical fiber and optically powered by the optical clock signals, each sensor module comprising an optical power converter for converting the optical clock signals to electrical clock signals, a timer for counting the electrical clock signals, and a sensor for sensing a measurable parameter, wherein the at least two sensor modules are adapted to sense the measurable parameter after a different number of electrical clock signals have been counted.

A further embodiment of the invention includes a method of time division multiplexing a plurality of sensor modules coupled to an optical fiber, the method comprising: transmitting an optical signal on the optical fiber, the optical signal having a clocking portion wherein optical clock signals are provided and a synchronizing portion; at each of the plurality of sensor modules, receiving the optical signal and converting the optical clock signals of the clocking portion to electrical clock signals; synchronizing each of the plurality of sensor modules; counting the electrical clock signals; and for at least two of the plurality of sensor modules, sensing a measurable parameter after a different number of electrical clock signals have been counted.

Another embodiment of the invention includes an optically-powered sensor apparatus comprising: an optical fiber; a laser source coupled to the optical fiber for providing optical clock signals on the optical fiber; a first sensor module coupled to the optical fiber and optically powered by the laser source, the first sensor module having a sleep mode during which the first sensor module is incapable of sensing a first measurable parameter and an awake mode during which the first sensor module is capable of sensing the first measurable parameter, wherein the first sensor module is adapted to switch from the sleep mode to the awake mode after a first number of optical clock signals have been received at the first sensor module; and a second sensor module coupled to the optical fiber and optically powered by the laser source, the second sensor module having a sleep mode during which the second sensor module is incapable of sensing the second measurable parameter and an awake mode during which the second sensor module is capable of sensing the second measurable parameter, wherein the second sensor module is adapted to switch from the sleep mode to the awake mode after a second number of optical clock signals have been received at the second sensor module, where the second number of optical clock signals is different than the first number of optical clock signals.

Another embodiment of the invention includes a method of diagnosing the state of a vehicle, the method comprising: coupling optical clock signals to the plurality of sensor modules via an optical fiber, each sensor module being disposed at a region of interest and each sensor module having a sleep mode and an awake mode; optically powering the plurality of sensor modules; at each sensor module, counting the number of optical clock signals received during the sleep mode; at each sensor module, in response to the counting of the number of optical clock signals received during the sleep mode, switching the sensor module from the sleep mode to the awake mode, where each sensor module is switched from the sleep mode to the awake mode after a different number of optical clock signals have been counted; at each sensor module, sensing a measurable parameter and producing sensed data; and diagnosing the sensed data from each sensor module.

Some of the embodiments of the invention provide devices and techniques that fiber optically power multiple sensors on an optical fiber. The principle of operation of the optically powered distributed sensors can vary, according to the parameters being sensed, and system designer preference. For example, such sensor nodes can be electronic, magnetic, optical, electro-optic, acoustic/ultrasonic, or combinations thereof. In some of these examples, these sensors may be time division multiplexed to communicate a sensed signal on the same optical fiber used to deliver power to the sensor. The devices and techniques may include synchronizing the multiple sensors and having the multiple sensors communicate their sensed signals on the optical fiber, without interfering with an optical powering signal on that fiber. Of course, the features, functions, and advantages can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments.

DETAILED DESCRIPTION OF AN EXAMPLE

Numerous exemplary devices and techniques are described below, and some are described in relation to rather detailed examples. However, the devices and techniques are not limited to such examples, but rather may be implemented in various applications. For example, although some examples are described as usable in an aircraft, including spacecraft, the devices and techniques may be used in other vehicles or systems. The devices and techniques may be used, more broadly, in any environment in which remote sensing via an optical fiber and a head end, receiver station, or transmitter station may be desired. The devices and techniques may be used in various sensor applications, such as hydrogen sensors applications, oxygen sensing applications, or strain sensor applications, e.g., in shell composite layers. Yet, other applications, e.g., measuring performance along a high-voltage electrical transmission line, will be known to persons of ordinary skill in the art upon reviewing the disclosure herein.

FIG. 1illustrates an example of an optoelectronic sensor system100that may be used to monitor conditions in remote environments, both non-hostile and hostile. Example environments include portions of an aircraft (e.g., an airplane or spacecraft) or other airborne vehicles (e.g., un-manned booster rockets). Further examples include environments where there is potential for exposure to harsh or hazardous conditions, such as oil wells.

To provide remote sensing within a system, such as an aircraft, the system100has a head end102, or base station, that communicates with a plurality of sensor modules104, via an optical fiber backbone106. The head end102, for example, may have a laser source and may send an optical signal on the fiber106to the sensor modules104. As described in further detail below, that optical signal may provide timing information to the sensor modules104and may also optically power them. Based on the timing information, the sensor modules104may provide sensed data back to the head end102.

Although the modules104may be placed in traditionally difficult-to-reach locations, the head end102typically is stored in a non-hostile location accessible to personnel or analysis equipment. However, this need not be the case.

In the illustrated example, the backbone fiber106extends along a series of monitoring regions108each representing an area monitored by the modules104, such as different areas within an aircraft. The sizes of the regions108may depend on the type of sensors deployed, and thus, are only generally shown. The apparatuses and methods described herein are not limited to a particular type of sensor.

The backbone fiber106may be formed of any number of suitable optical fibers. However, as certain remote environments may benefit from more rugged fibers, a hard clad silica (HCS) trunk fiber, such as a 200 μm core, multimode fiber may be used. By way of example, not limitation, a fiber rated at 40 pounds or higher tensile strength may be used. An example HCS fiber is available from OFS Specialty Photonics of Avon, Conn. Further, the fiber106may be coated with a plastic coating that prevents moisture from producing embrittlement within the fiber core, which would reduce fiber strength. However, despite these examples, the present disclosure is not limited to a particular fiber, size, composition, or fabrication technique.

Each sensor module104may be coupled to the fiber106via a coupler110, and each sensor module104may have at least one sensor112coupled to that coupler110. The coupler110may represent two couplings, one a coupling of the module104to the fiber106for receiving optical power, the other a coupling of the sensor module104to the fiber106for transmitting a sensed signal on the fiber106. The couplings may be achieved through a variety of techniques, such as hard clad silica tapping techniques. For example, to receive optical power, a photodiode may be directly adhered to the fiber106to absorb the optical power from the fiber106. In this case, the efficiency of coupling the optical power to the photodiode may be enhanced by removing part of the fiber cladding. Removing the cladding at an angle, to create a slanted surface can reflect light more efficiently onto the photodiode attached to the side of the fiber. For improved efficiency, the surface of the slant can be metallized, for example, by metal evaporation. An example coupling technique is shown inFIG. 2Bdiscussed below. To transmit a sensed signal, a tap optical fiber (e.g., optical fiber tap204, inFIG. 2A) may be coupled to the fiber106. If the sensor112includes a vertical cavity surface emitting laser (VCSEL), for example, the tap fiber at the sensor112may be positioned at the focal point of a lens that collects the output from that VCSEL. A VCSEL produces an emission cone that is typically quite small, and, thus, a small tap may be used, one that is not susceptible to detrimental power leakage into the VCSEL from the optical power on the fiber106. In another example, the sensed signal may be coupled directly from the VCSEL into the fiber106, without use of a tap fiber or waveguide, in a similar way as discussed for the photodetector. In another example, the coupler110may include a single tap fiber in combination with a splitter/combiner for coupling received and transmitted light.

The couplings of coupler110may be designed to occur at a radial bend of the fiber106, where the bend will naturally facilitate light leakage into or out of the fiber. The cladding of the fiber106at the bend may be partially or fully removed by an etching or ablation technique to enhance coupling efficiently.

FIG. 2Aillustrates a more detailed example of the sensing module104and, thus, shares like reference numerous withFIG. 1. A photodetector200, or solar cell, is coupled directly to the fiber106to receive optical power signals. The photodetector200is also connected to a power converter202, for optically powering the sensor112, as explained in further detail below.

In the illustrated example, an optical fiber tap204is coupled directly to the sensor112to couple optical energy from the sensor112into the fiber106, for example to upload a sensed output signal to the head end102. Each of the sensor modules104ofFIG. 1may be identical to that detailed inFIG. 2A, or some or all of the modules104may be different.

FIG. 2Billustrates an example of direct coupling of a photodetector200to the side of the optical fiber106, thus extracting some light leaking through the fiber cladding at the location of the contact, which may use an adhesive216. Light extraction efficiency into the photodetector200can be significantly increased using, for example, a small notch210at the side of the fiber. The intersection of the angled surfaces212and214, which constitute notch210need to be rounded and not at a sharp line, so the notch does not weaken the fiber106significantly. Fiber106may be glued down locally near the location of the notch to a small support plate218, to additionally strengthen the fiber106, near the location of the notch. Notch210may be created by, for example, gently running a file with triangular cross section against the side of the fiber. A small fraction of the light traveling in fiber106exits the approximately vertical surface212, and reflects from the slanted surface214onto the photodetector200. The surface214can be made more reflective by deposition of a thin metal film, for example, by angled deposition, such that the surface212is not metallized.

A detailed example of the head end102is shown inFIGS. 3A and 3B. The head end102may include two sections, a coupler300and a laser module302, where the fiber106is connected to the coupler300via a pigtail connection304, in the illustrated example.

The coupler300provides spatial filtering to transmit optical power signals from laser314part of the head end102into the fiber backbone106to the sensor modules104, and to transmit sensed optical signals from the sensor modules104to a head end photodetector (e.g., photodetector320) for receiving sensor data. The coupler300includes an optical plate306having a slit308(see, FIG.3C). The plate306may be coated with reflective material, such as aluminum, silver, chrome or gold, or made of such reflective materials. An example plate306is the NT38-559 precision air slit available from Edmund Industrial Optics of Barrington, N.J. The plate306is positioned a distance from an input lens310, positioned a focal distance from the pigtail304. The optical plate306is also positioned a distance from a lens312coupled to a laser source314for producing the optical power signals. The laser source314may be one that emits output energy over a strip width, for example, over a 5 μm×50 μm output window. The slit308may be sized and positioned such that the output from the laser source314may be coupled directly through the slit308and into the fiber106, through lenses310and312, as shown.

The optical plate306is also positioned to communicate with a lens316, which receives optical signals from the remote sensors via the fiber106, after energy from the fiber106is reflected by the plate306onto an optional mirror318. That is, for light coming out of the fiber106, the end of the fiber106is imaged onto the slit308. But if the fiber106is circular in cross-section at its end, and if the image of that core is large enough, then much of the light signal imaged on the plate306, and centered on the slit308will fall outside the area of the slit308, and reflect off the plate306, and imaged by the lens316onto a photodetector320.

In an alternative example to spatial filtering, a dichroic beam splitter or color filtering may be used in the coupler300, whereby the spatial filter306is replaced by a filter that transmits the wavelength of laser314at the head end102, but reflects the wavelengths of all of the VCSELs or other light sources such as light emitting diodes at sensor modules104. Alternatively, a prism or other polarization-dependent reflector may be used to transmit the power laser314light and reflect light returning from the sensor modules104.

The head end102also includes the module302that includes the power laser section and sensor data receiver section(s). The module302includes the laser source314and the photodetector320, as well as a microcontroller322that controls operation of the laser source314through a digital-to-analog converter (DAC)323. The laser source314may be any type of laser source, including an edge emitting laser, VCSEL, or diode laser. Alternatively, the laser source314may be a chemical or gas laser, or may represent an optical amplifier, such as a fiber amplifier or optical parametric amplifier.

In operation, the head end102may provide an optical signal having both a high state and a low state. Therefore, a modulator324is positioned to modulate the output from the laser314. The optical signal, for example, may include an optical clock signal. That is, the laser module302may produce optical clock signals of any given repetition rate, for example, a 50% duty cycle optical clock signal having a 1 to 10 kilohertz repetition rate. In the illustrated example, the modulator324receives a clock control signal from a clock circuit326coupled to the microcontroller322. Alternatively, the modulator324may be part of the laser314.

Contrastingly, to receive optical energy from the fiber106, the output of the photodetector320is provided to an amplifier328, such as a transimpedance amplifier. The amplifier328is coupled to an analog-to-digital converter (ADC)330coupled to the microcontroller322. Module302containing the laser and sensor data receiver sections may be powered by a power supply332.

In an example operation of the system100, the head end102produces an optical signal (e.g., one having clock signals over at least a portion) on the fiber106that propagates to each of the sensor modules104. The power converters202at each module104may receive this optical signal at substantially the same time, to power the sensor modules104. The clock signal portion of the optical signal may provide a timing signal through which these modules104may be instructed to turn on and begin sensing. For example, each distinct module104may be set to sense a measurable parameter after receipt of different numbers of these timing signals. The modules104may then use the fiber106to uplink a sensed output signal or other signal to the head end102, e.g., after their respective number of timing signals has been received and during a time period the head end is not providing an optical signal thus avoiding interference. As such, the system100may provide a time division multiplexed set of remote sensors that are optically powered by a signal on the same fiber that is used to transmit (uplink) sensed signals from the remote sensors.

FIG. 4illustrates an example power converter circuit400that may be used as the power converter200. A photodetector402receives an optical clock signal and converts that signal to electrical energy that is stored in an electrical storage device404, in parallel with the detector402. An output from the detector402is also coupled to a first chargeable switch406and a second chargeable switch408. The first chargeable switch406is connected to a first output line410, which may be a clock signal line. The second chargeable switch408may be coupled to a second line412, which may be a synchronization (sync) signal line. Both chargeable switches406and408are coupled to a switch414coupled to ground. In an alternative example, two switches may be used, one for each of the elements406and408, and both switches may be coupled to receive an output from the detector402, which may be a photo-responsive device, such as a photodiode or solar cell. Example photodetectors include PIN photodiodes and pie-wedge-type photodetectors, such as the PPC-6E available from Photonic Power Systems of Cupertino, Calif. Additional examples are provided herein, for example in connection withFIG. 5.

The chargeable switches406and408may be separately chargeable, such that when charged the switch414can put the charged switches406and408into a conducting state. If either of the switches406and408is uncharged, then the switch414would not place that switch into a conducting state. The switch414has an on state and off state and may be any electrically controllable switch, including a bipolar transistor, integrated gate bipolar transistor, field effect transistor including JFETs or MOSFETs (which may be either enhancement or depletion mode devices), uni-junction or programmable uni-junction transistor, an SCR, Schottky diode, or any combination of these, which may be both discrete or integrated in form, and may or may not be matched in the sense that this term is applied within the field of differential amplifiers.

The electrical energy from the detector402is partially stored in the electrical storage device404and is partially used to assist in saturating the chargeable switches406and408. The detector402may provide an electrical signal during a high cycle of a clocking portion of the optical signal on fiber106, i.e., when photons are received at the detector402, at which time the storage device404is in a storing state. During the low cycle of a clocking portion of the optical signal, no electrical energy is produced by the detector402, but instead, the electrical storage device404enters a driving state and powers the switch414to turn on the chargeable switches406and408. The switch414may turn on one or both of these switches406and408, depending upon the desired operation and upon whether the switches406and408are already charged. For example, during normal clock signal operation, the switch414may turn on only the chargeable switch406, to ensure that a clock signal is communicated on the line410. This could create an electronic clock signal every optical clock cycle, for example. The switch414may turn on the chargeable switch406less frequently, for example, to communicate a less-frequent sync signal on the line412. A determination as to when to turn on either of the switches406or408may be made by switch414or via the information in the optical signal.

FIG. 5illustrates a detailed circuit500that represents an example implementation of the power converter202. The circuit500includes a solar cell502(as the detector402) for receiving an optical clock signal from a coupler connected to a backbone optical fiber, such as the fiber106. The solar cell502is coupled across an inductor (X2)504and a capacitor (C2)506that form the storage device404. These elements are coupled to a power output line507and a common node508. The node508is also coupled to a first, low resistance resistor (R2)510and a first, higher resistance resistor (R3)512. The node508is also coupled to a second, low resistance resistor (R4)514and a second, higher resistance resistor (R1)516. Resistors510and512are coupled across a capacitor (C1)518, and resistors514and516are coupled across a capacitor (C3)520. Capacitor518is coupled to a clock signal output line522and to the collector of a transistor524at node526. Capacitor520is coupled to a synchronization signal output line528and to the collector of a transistor530at node532.

The transistors524and530are each coupled to ground at their emitters and share a base node534. In this configuration, the transistors524and530form a dual transistor switch536with a base node534coupled to the bypass capacitor506. The dual transistor switch536may be a XN5553 transistor, available from Matsushita Corporation of Japan. The solar cell502may have a p-type/insulator/n-type (PIN) layer configuration, as these configurations have lower capacitance translating into a lower power level threshold. Various solar cell devices for optical powering may be used, including pie-wedge solar cells. By way of example, not limitation, solar cells may be formed of a gallium arsenide (GaAs), gallium indium phosphide, aluminum gallium arsenide, indium gallium arsenide, silicon, germanium or a combination of these. Multi-layer solar cell structures formed on a single wafer, such as a GaAs wafer, may be used. Further, the solar cell502may or may not have an anti-reflection coating, or other measures to improve efficiency.

In operation, the solar cell502forces current to flow through the inductor504during the high cycle of the optical signal.

During the low cycle, no current is produced by the solar cell502, but rather the solar cell502is reverse biased, which blocks current flow compared to the direction of current flow during the high cycle. In an example implementation, the optical signal may include an optical clock signal having a 50% duty cycle and a repetition rate from about 1 to 10 kHz, resulting in high and low cycle times of between 0.05 to 0.5 milliseconds.

During the low cycle of the optical signal, the inductor504reverse biases the solar cell502, and voltage across the inductor504continues to rise in an inductive kick until the inductor504changes from a storing state to a driving state and forces current to flow through the capacitor506and into emitter-base junctions538of the transistor switch536. The emitter-base junctions538act as a rectifier for the circuit500. Using a XN5553 circuit as the switch536, the switch536is well matched and is reverse biased on the emitter-base voltage by the bypass capacitor506. Thus, the dual transistor536has relatively low leakage current. The dual transistor may also have a high voltage rating on the reverse emitter-base voltage, in an example, 15 volts.

When base current flows from the inductor504into the transistor switch536, both transistors524and530turn on, pulling the collectors a bit below ground, because the emitters go below ground by a diode drop, and the transistors524and530saturate. The saturation pulls nodes526and532on capacitors518and520low, respectively. If these capacitors518and520have had sufficient time to charge, through resistors512and516, then the clock and sync output lines522and528, respectively, will pull low, as well.

The capacitance and resistance values for the circuit500may be set such that only the clock line522pulls low every clock cycle, however. The RC time constant of the resistors514,516and capacitor520may be long enough to prevent a sync pulse from being sent on line528simply from the high/low transistors of the optical clock portion of the optical signal. That is, the charging time during the optical clock cycle will not be sufficient to charge this RC constant, with only a few milliseconds of charging from the solar cell502. Instead, as explained in further detail below, the head end may skip a number of optical clock cycles, within the optical signal, every few seconds. If the skipped number of optical clock cycles is long enough, the capacitor520will saturate and a sync signal will be provided on line528at the start of the next optical power pulse. By way of example, every 1 to 3 seconds, approximately 15 optical clock cycles in a row may be skipped on the optical signal from the head end, resulting in about 15 milliseconds of no signal. This may leave enough time to charge the capacitor520through resistor516.

Example values for various capacitors and resistors of the circuit500are provided in Table 1. These values are by way of example only, as is the structure of the circuit500. The circuit elements illustrated may be replaced or eliminated. The inductor504may be replaced with another storage device, such as a transformer, for example.

The sync and clock lines528and522are coupled to a microcontroller600of a sensor apparatus602(shown inFIG. 6). An example of a microcontroller that may be used as the microcontroller600is the PIC microcontroller, available from Microchip Technology of Chandler, Ariz., which is capable of counting a signal (e.g., a clock signal) during a sleep mode. Sleep-mode counting has the advantage of reduced power consumption, as the microcontroller only periodically awakes, for example, after a given counter number has been reached.

As shown, the clock line522is coupled from the power converter500to a timer circuit604within the microcontroller600. As the capacitor518saturates every optical clock cycle, the power converter500provides an electrical clock signal to the timer circuit604every optical clock cycle, which the timer604counts, in an example. The sync line528is coupled to an interrupt circuit606of the microcontroller600, which may be used to synchronize the sensor602with other sensors on the backbone fiber, so that each sensor module will begin counting clock signals at substantially the same synchronized time. The microcontroller600also includes a reset circuit608coupled to a voltage detector610that receives a power level voltage from power line507of the circuit500. The voltage detector610, for example, may maintain the microcontroller in an off state until the voltage across capacitor506reaches a certain amount. The reset circuit608may be used to set the maximum counter value for the timer circuit604to adjust the number of electrical clock signals that are counted before the microcontroller awakes.

The power converter500and sensor602may form part of one sensor module, where a backbone fiber would have a plurality of such sensor modules. Each module would receive the same optical clock signal via the optical signal from the head end. The sync pulses on line528for each sensor module serves as the timing starting point that synchronizes all these sensor modules to each other, and to the head end sending the optical clock signal. Each sensor modules' microcontroller600is reset by the sync pulses received at the interrupt circuit606. Each timer circuit604then counts the number of clock signals received after that sync pulse, which the microcontroller600can do in a sleep mode. Each sensor modules' microcontroller600may be programmed, in firmware, to count a different number of clock pulses before waking the microcontroller600, via a timer overflow interrupt. In this way, the sensor modules are time-division-multiplexed to turn on at different times. The head end may be programmed to identify which sensing module is awake at a particular time based on the number of clock pulses countered therein, based on the order in which the sensor module is awakened in relation to the other sensor modules on the backbone fiber, or based on the number of clock signals provided by the head end. In any event, the head end is able to identify which of the sensor modules on the backbone fiber is transmitting its sensed output signal at a given time.

The microcontroller600may be coupled to an input/output stage612coupled to a sensor614that is positioned to sense a measurable parameter or property in the sensed region around the sensor module. The microcontroller600may power any type of sensor desired for sensing, including both optical and non-optical sensors and those of low or even high power, if operated only for short periods. In an example, the microcontroller600may be coupled to a tin oxide (SnO2) hydrogen sensor for monitoring hydrogen content in environments on an aircraft. Alternatively, a solid-state hydrogen sensor using palladium films may be used. In any event, the examples are not limited to a particularly type of sensor. The sensor614may include a light source and a photodiode, for example. In alternative examples, such as measuring operating conditions on a power line at remote locations, a current or voltage sensor/detector may be used.

In the illustrated example, the signal from the sensor614is coupled to an amplifier616that may include an optional shutdown pin coupled to input/output interface612of the microcontroller600to save power. The signal is then coupled to an analog-to-digital converter (ADC)618and back into the microcontroller600, at serial port or bus619, which then processes the signal and uses it to control and power a laser driver620for driving a laser622. The laser driver620, for example, may be a modulator and the laser622a VCSEL. An output624(e.g., a sensed output signal) of the laser622is coupled to the backbone fiber via a coupler, such as the coupler110or other couples described above with reference toFIGS. 1,2A and2B.

In the illustrated configuration, power for the devices may be turned off except for the voltage detector. For example, by using an operation at amplifier with a shut down pin, as the amp616, the microcontroller600may turn off the amp616when it is not needed. In fact, the sensor614, ADC618, laser device620, and laser622may be turned off when the microcontroller600is asleep, leaving only the voltage detector610on. This ability to operate in sleep mode may substantially reduce power consumption. Additionally, operating the ADC618and laser driver620on the same serial port or bus619provides power advantage, as the microcontroller600uses less clock cycles and as the elements619and620may be kept off longer.

The sensor602is shown by way of example. The sensor602may include additional or fewer elements. The sensor602may include additional sensors as well, such as voltage or temperature sensors that can be used to monitor and communicate sensor performance data to the head end.

To illustrate an example operation of the power converter and the sensor602,FIG. 7illustrates an example optical signal702that may be sent from the head end106. The clock signal702includes a clocking portion707, where the clock cycles occur, and a synchronization (dropout) portion708where a number of clock cycles have been skipped by the head end106, and the optical signal702is in a continuous low state. The clock signal portion707has a 50% duty cycle comprising a high cycle state704and a low cycle state706on every clock cycle.

Line710represents the electrical clock signal line522from the power converter200to the sensor602. The clock signal710is maintained high through the first high cycle704. However, after the high cycle704, the power converter500is triggered to supply a negative clock signal712to the sensor602. The sensor602may count the received clock signals712via the timer circuit604. The sensor602may be separately programmed to output a sensed signal after a determined number of these clock signals712have been counted. Line714illustrates the sync output line528for the power converter500.

The power converter500has an output to provide a sync signal to the microcontroller600. By way of example, not limitation, a sync signal716is sent from the power converter500to the microcontroller600following the end of the first clock cycle after the dropout in the clocking708. In the illustrated example, the sync pulse716occurs just after the dropout in the clocking portion708has ended in accordance with activation of the switch414or530due to the inductive kick element of504. Each sensor module on the backbone fiber would receive this sync pulse716simultaneously, which may be used to synchronize each of the sensor modules.

A first output signal from a first sensor module is illustrated at line718and includes sensed data720. The sensor module producing the output signal718has been programmed to provide its sensed data720after counting a single clock pulse712′, after the sync signal716. The sensed data720is only sent during a low cycle706′ of the clock signal702to avoid interference with the high cycle704, as both clock signal and sensed signals are sent on the same optical fiber106. Alternatively the sensed data720may be sent during a high cycle when, for example, the sensor laser source operates at a different wavelength than that of the signal from the head end. A second sensor module may count a different number of clock signals after the sync signal716and produce an output722. In this example, the sensor module has been programmed to count two clock pulses (712′ and712″) after the sync data716, before for uplinking its sensed data724during another low cycle726.

The illustrated output718and722represent signals produced by the laser622and are by way of example. The temporal separation between sensed output signals from different sensor modules may be better resolved in a time division multiplexed configuration if each sensor module is programmed to provide an output after numerous clock signals. By way of example,FIG. 8illustrates a sync line802with three identical clocking portions804,806, and808, each representing 50 clock cycles. After the first temporal region804, a first remote sensor produces an output signal810. After the second temporal distance806, a second remote sensor produces an output812. After the third temporal region808, a third remote sensor produces the output814.

Numerous alternatives exist. Techniques and apparatuses for providing an optical system of time division multiplexed remotely located sensor modules are described. And, while it is contemplated that each of the sensor modules could transmit a signal to a head end after a different number of electrical clock signals have been counted, alternatively one or more of the distributed sensor modules may communicate a sensed signal at the same time. The head end may be able to resolve such signals based on differences in frequency, amplitude, or phase, for example. Furthermore, although in some examples it is useful to provide a sensed signal during a low state of the optical signal from the head end, some or all of the sensed signals may be transmitted during a high state. In further alternatives, data other than sensed data may be provided by the remote sensor module. The sensor modules, in particular their microcontrollers, may be programmed to provide operational data on the sensor module, for example, data indicating whether the sensor module is operating or the present voltage level out of the power converter.

The sensed output signal includes data representing a measured parameter, such as temperature. The data may be conveyed by the strength of the sensed signal sent, or via frequency modulation, phase modulation, binary 1's and 0's, or other information imparting techniques. The output signal from the sensor module could instead represent an actual counter value stored in a timer. This counter value could be used by the head end to determine if any of the remote sensor modules lag behind others. In such examples, the head end may send a reset or other instructional data signal to the remote sensor modules. Or at least the head end may identify to a user which sensor modules may be malfunctioning. In any of these examples, multiple data types may be uplinked to the head end during a sync portion.

Numerous applications may be achieved with systems in which a head end is capable of optically powering remote sensors on a fiber, where those remote sensors are able to communicate a sensed signal or other parameter back to the head end on that fiber. For example, a head end can operate at higher power levels, but then reduce output power upon sensing a break in the fiber. The head end may detect where one or more of the nodes are unresponsive. The head end may then either turn off the optical power signal, or reduce the optical power down to a lower, safer level. Additionally, the head end may cause the sensor modules to run at lower duty cycles, using less power, by running longer intervals between synchronization pulses.

It is also possible to send commands from the head end to the sensor modules by, for example, altering the number of clock cycles between dropouts, as a means of encoding transmitted data/commands. It is possible to do such encoding, without interfering with the ability to alter the number of clock cycles between dropouts for optimization of power usage within the sensor modules.

Diagnostic systems may now be implemented with reduced requirements for manual inspections and reduced system downtime. In a vehicle health management system, for example, an optical sensor system may deploy multiple distributed sensors that provide in-flight diagnostic data. In such applications, a diagnostic system may monitor flight or vehicle conditions and generate a responsive maintenance program or protocol in response thereto. The diagnostic system, for example, may have a head end that collects the sensor data from various locations in a vehicle and commutes that data to a management system for algorithm-based or other decision making. The management system may be internal or external to the vehicle, and communication may be wired or wireless, e.g., via a satellite link between a spacecraft, orbital satellite and an earth-based management system with transceiver. The management system may be a computer system, such as personal computer or computer network capable of executing code or algorithms associated with diagnostic assessments of the sensed information.

By way of example, not limitation,FIG. 9illustrates an optical sensor system900used in an aircraft902that has a plurality of locations904,906,908to be sensed. The locations904,906,908may represent areas within the aircraft monitored for environmental conditions or other performance metrics, including flight critical data. In the illustrated example, the system900includes a head end910coupled to three sensors912,914and916via an optical fiber918for optical powering and data communication. The head end910may perform data acquisition, receiving photonic signals from the sensors912,914and916and processes the received signals. The head910may perform full diagnostic analysis on the signals received from the remote sensors912,914and916or may communicate signals to a management system920, such as a computer or computer network. In the illustrated example, the management system920is external to the aircraft902and in communication with the aircraft communications system or head end directly via a transceiver922. By way of example, not limitation, the management system920may execute coded algorithms to perform data analysis such as filtering, data comparison, data compression/decrompression, Fourier transforms, power spectral density calculations, and diagnosis of sensed structural component fatigue, usage, overload conditions, and/or environment exposures, depending on the sensors deployed. In some examples, the management system920may perform or be part of a predictive system that executes prognostic algorithms based on diagnostic data. Such algorithms may be useful in predicting crack growth, strain life, corrosion damage, or other residual strength and life metrics based on diagnostic data and vehicle data (e.g., payload, usage, and environmental exposure). Example systems are described in U.S. Pat. No. 6,691,007, entitled “Vehical Condition Monitoring System,” which is expressly incorporated herein by reference.