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POWER OVER OPTICAL FIBER SYSTEM
This disclosure relates to the transmission of electrical power by optical fiber. More particularly, the present disclosure describes a power over optical fiber system that provides electrical power to a remote location.
2. Description of Related Art
Prior art related to the subject matter of the present disclosure may include the following patents:
U.S. Pat. No. 5,469,523, "Composite fiber optic and electrical cable and associated fabrication method," to Blew, et al., dated Nov. 21, 1995; and
U.S. Pat. No. 5,651,081, "Composite fiber optic and electrical cable and associated fabrication method," to Blew, et al, dated Jul. 22, 1997.
Other art related to the subject matter of the present disclosure may include the High Power Optical Data (HiPOD) System from JDS Uniphase of Milpitas, Calif.
This summary is not intended to define the scope of invention or as a list of objects; it is for convenience. An embodiment of the present invention is a power over optical fiber transmission system comprising a transmit unit and a receive unit that are linked by optical fiber. Another embodiment of the present invention comprises a transmit unit that may be used within a power over optical fiber system. Still another embodiment of the present invention comprises a receive unit that may be used within a power over optical fiber system. In further embodiments plural pairs of transmit units and receive units are operated and connected in either parallel or series. In further embodiments each receive unit is equipped to send a feedback signal to its connected transmit unit to indicate that all optical fibers are connected. In that embodiment the transmit unit will first operate at a low power level, sufficient to provide power to operate the processor of the receive unit so that safety and operational checks can be performed. When the checks are performed satisfactorily, the feedback signal will so indicate and then the transmit unit changes to operate at a high power level so as to provide power to the location of the receive unit for use.
The invention will be better understood from the following detailed description, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a power over optical fiber system according to an embodiment of the present invention.
FIG. 2 is a block diagram of a transmit unit for a power over optical fiber system according to an embodiment of the present invention.
FIG. 3 is a block diagram of a receive unit for a power over optical fiber system according to an embodiment of the present invention.
FIG. 4 A is a block diagram of two power over fiber systems connected in a series configuration.
FIG. 4B is a block diagram of two power over fiber systems connected in a parallel configuration.
An embodiment of the present invention is capable of generating up to 30 mA (milliamps) of electricity at 24 volts
for use with remotely deployed electrical equipment. Voltage is created by using light from two high powered lasers that travel down two optical fibers to a receiving unit that has two high power photovoltaic cells that convert the high powered
5 laser light into usable DC voltage. One major advantage of this embodiment is that no electrical connection is required to provide electrical power to remote equipment. Hence, electrical isolation using optical fibers is achieved.
As shown in FIG. 1, this embodiment of a power over fiber
10 system 1000 according to the present invention comprises two devices: a laser transmit unit 100 and a receiver/voltage output unit 200. The two units are linked by optical fibers 300. The laser transmit unit 100 comprises two lasers 110 and an optical receiver 120. The lasers are of the type and specifica
15 tion to transmit their output into multimode fiber. The lasers 110 may comprise diode lasers, such as the 2486-L3 series high-power 2.0 W 830 nm fiber-coupled diode laser from JDS Uniphase of Milpitas, Calif. Power may be supplied to the transmit unit 100 by an external DC power supply 10. Pref
20 erably, the external DC power supply 10 provides a voltage between 24 VDC and 56 VDC. The receive unit 200 comprises two photovoltaic receivers 210 and an optical transmitter 220. The photovoltaic receivers 210 may comprise photovoltaic power converters, such as the PPC-12E 12V
25 photovoltaic power converter from JDS Uniphase of Milpitas, Calif. Power from the receive unit 200 may be supplied to remote equipment 20. Optical fibers 300 linking the two units 100, 200 preferably comprise multimode (62.5 nm/125 nm) optical fiber, where power carrying fibers 310 link the laser
30 110 to the photovoltaic receivers 210 and a feedback fiber 320 links the optical transmitter 220 to the optical receiver 120.
FIG. 2 shows a block diagram of the transmit unit 100 according to an embodiment of the present invention. As shown in FIG. 2, a DC voltage ranging from 24 VDC (volts
35 direct current) to 56 VDC at 2 A (amps) is applied to the DC input 101 of the transmit unit 100 to power the unit locally. This voltage is rectified, filtered and split into 4 voltage sources by a power supply 103 for use by: a microprocessor 150 and accompanying digital circuitry; a laser voltage sup
40 ply (not shown in FIG. 2); a fan voltage supply (not shown in FIG. 2); and a cooler/heater supply (not shown in FIG. 2). The microprocessor 150 may comprise a microcontroller, such as the PIC 16F685 from Microchip Technology, Inc. of Chandler, Ariz.
45 The microprocessor 150 provides for overall control of the transmit unit 100. The microprocessor 150 provides for user interface via indicator light emitting diodes (LEDs) and pushbutton interface 161, and liquid crystal display (LCD) display 163. The microprocessor 150 also receives state information
50 from laser temperature sensors 115 and failsafe interlock 167 and provides control over an alarm contact output 165. The microprocessor 150 also processes feedback information received back from the receive unit 200 via the feedback receiver 120.
55 Initially, the microprocessor 150 checks that the overall stateofthe transmit unitlOO is safe to powerup the lasers 110. The first function of the failsafe interlock 167 and microprocessor 150 is to make sure that the lasers 110 stay off while the transmit unit 100 is powering up. The transmit unit 100 may
60 also have a lockable safety enclosure that limits access to fiber connections for the optical fibers 300. Preferably, the lockable safety enclosure completely covers the fiber connections and contains a switch that couples to the failsafe interlock, where closure of the switch indicates that the enclosure is in
65 place and is locked. The lockable safety enclosure helps prevent users from being radiated with escaping laser energy which could cause eye or skin damage. If the lockable safety
enclosure is present, the failsafe interlock 167 will prevent the lasers 110 from powering up if the enclosure is open or unlocked. Preferably, the microprocessor 150 and the failsafe interlock 167 also operate to shut down the lasers 110 if the safety enclosure is removed or unlocked while the lasers 110 5 are in operation. If the enclosure is open or unlocked, the LCD display 163, which is controlled by the microprocessor 150, preferably displays a message, such as "LOCAL DOOR OPEN, PLEASE CHECK," and the microprocessor 150 prevents the lasers 110 from powering up while the enclosure is 10 open or unlocked. Also, if the enclosure is closed and locked, a "CASE INTERLOCK" LED in the LED indicator display 161 may be lit to indicate successful closure.
If the safety enclosure is closed and locked, the microprocessor 150 preferably checks the operating temperature of 15 both lasers 110. This is done by polling the temperature sensors 115 that are configured to monitor the temperatures of the lasers 110. If the detected temperatures are within the operating range of the lasers (typically 20° C. to 45° C), the microprocessor 150 continues the power-up sequence. If not, 20 the microprocessor 150 turns on a thermoelectric heater/ cooler 111 for the affected laser 110 and heats the laser 110 if too cold, or cools it if too hot until the laser 110 reaches the operating range. Up to this point, no laser 110 has been powered up. Preferably, each laser 110 is not powered up until 25 the tests described above are passed.
If the safety enclosure is closed and the temperature requirements have been met, the microprocessor 150 will then pulse both lasers at low power (about lM the high power setting) in an attempt to receive feedback from the feedback 30 fiber 320 from the receive unit 200. The microprocessor 150 will turn on and pulse the lasers 110 using laser drivers 113 in a low power setting. Preferably, the lasers 110 are pulsed at a rate of 50 uS (microseconds) on and 10 mS (milliseconds) off. This should give the receive unit 200 enough time to gain low 35 power from the photovoltaic receivers 210, start the receiver unit's 200 companion microprocessor (see FIG. 3) and pulse back a status signal. This status signal is received by the transmit unit 100 by the feedback receiver and failsafe control 120 and provided to the transmit unit microprocessor 150. 40 The purpose of this low power setting and short burst rate is to reduce the exposure to harmful infrared laser radiation. The maximum exposure at 10 cm (centimeters) is rated at 10 seconds. Therefore, if the optical fibers are not connected to the outputs of the laser 110, the microprocessor 150 will 45 detect this condition and limit exposure to infrared laser radiation.
Preferably, a front panel laser status "TRANSMIT" LED, that is part of the LED indicator display 161, flashes during this time to indicate laser activity of low power pulsing to the 50 receive unit 200. Also, the LCD display will display the message "NO FEEDBACK LOOP, CHECK ALL FIBERS" if no feedback signal is received from the receive unit 200. As indicated above, if there is no closed loop, the lasers 110 will never go to a higher power. Once the microprocessor 150 55 determines that both power carrying fibers 310 and feedback fiber 320 are connected correctly; feedback is received by the failsafe control 120; and the safety enclosure is shut, the microprocessor 150 determines that both lasers 110 are properly connected and are ready for powering up to full power. 60
Preferably, the temperatures of the lasers 110 are monitored before powering the lasers 110 to full power to determine that the operating temperatures of the lasers 110 are within nominal ranges. These laser temperatures are also preferably monitored during full power operation of the lasers 65 110. These temperatures are constantly monitored by the microprocessor 150 and temperature sensors 115. If the tern
peratures are detected as being outside of a preferred operating range (for example, +20° C. to +35° C), the thermoelectric cooler/heaters 111 activate to return the temperatures to within the preferred range. If after some set time (e.g., one minute) the temperatures do not return to the preferred range, either because of failures of the thermoelectric cooler/heaters 111 or if the surrounding temperature has caused the lasers 110 to be outside their normal operating range, the microprocessor 150 will command the lasers 110 to turn off and generate either the message "EXCESSIVE HEAT, PLEASE CHECK" or "EXCESSIVE COLD, PLEASE CHECK" on the LCD display 163 (depending on the fault condition). Further, the microprocessor 150 may also cause a "HEATER" LED or "COOLER" LED on the LED indicator display 161 to flash to indicate the cause of laser power interruption. Once the laser temperatures have returned to within the preferred range, the microprocessor 150 will restart the power-up process and determine if: (1) the enclosure is open or unlocked; (2) the fibers are connected and (3) the laser temperatures are acceptable. If all three tests pass, then the microprocessor 150 will command the lasers 110 to full power again.
When the full power mode is engaged, the feedback from the receive unit 200 is constantly tested by the failsafe control 120 to see if loss of signal has occurred. Loss of signal can occur if one or more of the fibers 300 has been disconnected or has become damaged. If this condition occurs, the lasers 110 are shut down quickly before any damage can occur. Preferably, the lasers 110 shut down within 300 u.S of loss of signal. Once feedback is detected by the failsafe control 120, a "RCV FEEDBACK" LED in the LED indicator display 161 may be lit to indicate successful feedback is in progress. Also, when the lasers 110 have achieved full power, the "TRANSMIT" LEDs will stay lit (instead of flashing) to show steady state operation. If any errors occur such as: safety enclosure open; feedback not found, normal temperature not achieved before operating; or if the receiver is in a test mode, an "ALARM" LED will be lit in the LED indicator display 161 to indicate the presence of one of these errors. The LCD display 163 may also display details on the error condition and report to the user where the error exists.
While the lasers 110 are operating in full power, their temperatures may vary because of operating heat. The thermoelectric cooler/heater 111 will maintain laser temperatures. When the thermoelectric cooler 111 is on to cool the lasers 110, a "COOLER" LED in the LED Display 163 may indicate that the cooler 111 is in operation. When the thermoelectric heater 111 is on to heat the lasers 110, a "HEATER" LED in the LED Display 163 may indicate that the heater 111 is in operation. When the laser temperatures reach normal, the cooler/heater 111 and associated LEDs will turn off. Further, to help the temperature of the lasers stay within normal range, a fan may be used to cool the lasers 110 and other circuitry. Preferably, this fan would stay in constant operation no matter what the operational mode of the transmit unit 100.
The LCD display 163 may also have an associated "DISPLAY MODE" pushbutton on the indicator display to allow polling of various conditions of the transmitter unit 100. Pushing the pushbutton repeatedly will scroll through various displays. For example, at any time, the temperature of both lasers 110 could be displayed by selecting this mode, in either Fahrenheit or Celsius based on user selection. Further, the microprocessor 150 may be programmed to store maximum and/or minimum temperature excursions for the lasers 110 during the operation of the transmit unit 100. The user could then select the display of these maximum and minimum temperatures on the LCD display 163, or reset the stored temperatures to have the microprocessor 150 to again store the