Transcript
Application Note
Photonic Power Solutions for Sensor Applications Introduction Electronic sensors are used in many industrial monitoring and test and measurement situations to record operating parameters or environmental conditions, such as temperature, pressure, humidity, voltage, current and other instrumentation parameters. Many sensors are installed in environments that are hazardous, electrically noisy, inaccessible, or exposed to extreme weather making it difficult for the sensors to be powered over copper cable. Other sensors use batteries as their power source even though the batteries require frequent replacement or recharging. Duplex communications with these devices are often accomplished using standard optical fiber. Using JDSU’s innovative photonic power technology, optical energy delivered via fiber is increasingly used to power remote sensors and associated signal conversion circuitry. Delivering power over fiber optic cable instead of copper wiring or using batteries has several significant benefits: • Immunity to surrounding radio frequency (RF) and magnetic fields, lightning, and high voltage effects • No interfering radiation from the power source • Spark-free operation impervious to RF heating • Operation over longer distances than copper • No need to periodically change batteries or risk failure due to battery degradation
Figure 1. A photonic power module (PPM), including a laser diode, laser driver, photovoltaic power converter (PPC), and fiber interconnect
Figure 1 shows a photonic power module (PPM) where optical power is launched into multimode or singlemode fiber. This optical power illuminates a photovoltaic power converter (PPC) that is colocated with the remote sensors up to several kilometers from the laser source. The PPC is typically a 2-mm x 2 mm gallium arsenide (GaAs) or indium phosphide (InP) chip composed of several p-n junctions that are connected in series such that the voltages from the junctions are additive. The amount of current delivered is proportional to the level of light illuminating the chip. GaAs chips operate in the 780 nm to 980 nm range, and are generally powered by laser diodes launching up to 5 watts of optical power into 62.5 µm or 100 µm multimode fiber. Sensors up to 500 meters from the laser source can be powered in this manner. The optical-to-electrical power conversion efficiency of these GaAs chips is now exceeding 50%. For longer distance sensor applications, up to 10 km, 1300 nm to 1550 nm laser diodes must be used in conjunction with singlemode fiber and InP PPC chips. The
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Application Note: Photonic Power Solutions for Sensor Applications
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Introduction / continued
optical-to-electrical power conversion efficiency of InP chips is approximately 25%. Both types of PPC devices offer conversion efficiencies far greater than typical photovoltaic solar cells. Multi-mode is the preferred fiber for distances of approximately 500 m or less to take advantage of the higher efficiency PPCs operating in the 800 nm to 980 nm wavelength range. However, attenuation is greater in multimode fiber and limits the distance over which the fiber can be deployed. Single-mode fiber is preferred in longer distance applications because of its minimal attenuation. From a power budget standpoint, the reduced attenuation of the fiber more than compensates for the reduced efficiency of the longer wavelength PPC.
Transmitting Power and Data over Fiber The PPM, as previously discussed, serves as the core sub-system for the optically powered data link (OPDL) system, which offers an all-fiber solution for powering and communicating with remote electronic devices. OPDL systems, as shown in Figure 2, are noise-immune turnkey solutions for powering and transmitting data over standard optical fiber. Figure 3 provides a schematic depicting how an OPDL system integrates with a remote sensor. Optical power from a laser diode and driver assembly is launched into the fiber. The optical power is converted into electrical power using a PPC. This converted power drives the sensor and associated analog-to-digital conversion electronics at the remote end. The analog sensor data is converted into a 16-bit digital format and is transmitted into a second fiber using a light emitting diode (LED) in most cases. The data is transmitted to a central processing area where the data is used in its digital format or may be reconverted to analog. Feedback and self-check features monitor all vital functions, including laser output level, data link integrity, recovery and, if necessary, synchronization. This all-fiber approach provides a unique, electrically isolated, lightning-proof power delivery and data transmission system.
Figure 2. A typical OPDL system consisting of a laser power module and a remote power conversion and data transmission module
Application Note: Photonic Power Solutions for Sensor Applications
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Transmitting Power and Data over Fiber / continued
Remote Module Power Power
Remote Analog Sensor
Analog to Digital Converter
PPC (2-12 VDC)
Optical Fiber (1 m to 2 km of multimode or singlemode fiber)
LED Signal Transmitter LED Driver
Network Control
Laser Diode and Driver Signal Receiver
OPDL System
Digital to Analog Converter
Local Module
Figure 3. A schematic diagram of an optically powered data link (OPDL) system
Optically Powering Remote Sensors OPDL technology offers an all-fiber solution for powering and communicating with sensors for a wide range of applications, including test and measurement; sensing in industrial, medical, aerospace, and homeland security applications; video surveillance; and electric power current monitoring. The following electronic measurement devices can benefit from this all-fiber solution: 1. Electromagnetic compatibility instrumentation 2. Fuel gauges and sensors on aircraft 3. Underground exploration, mapping, and seismic monitors 4. Location tracking equipment in underground mining operations 5. Video surveillance cameras 6. Medical monitoring devices 7. Current transducers in electric power transmission grids The key advantage in most of the applications listed above is immunity to the surrounding environment, permitting operation in high radiation fields, potentially explosive environments, and hazardous environmental conditions such as high temperatures or pressures. In addition, the use of optical fiber fully isolates the electronics from lightning and high voltage effects and eliminates the possibility of RF induced heating. All of these factors translate into increased personnel safety, improved equipment reliability, and reduced maintenance costs.
Application Note: Photonic Power Solutions for Sensor Applications
Optically Powered Sensors for Electromagnetic Interference Testing The test and measurement industry is increasingly using OPDL technology to perform electromagnetic emissions measurement of many different types of commercial products, including cell phones and other wireless devices, computers, televisions, and automotive equipment. Electrical circuits produce electric and magnetic fields that radiate RF energy, increasing the possibility of the electronics exceeding government-regulated electromagnetic interference (EMI) limits. Various forms of instrumentation are used to quantify emission levels and help identify EMI sources. Typically, batteries have been used as the power source for this instrumentation. Frequently, the testing must be halted in order to recharge or replace the batteries. This downtime limits the number of measurements that can be performed in a 24-hour period. As shown in Figure 4, OPDL technology can continuously power the instrumentation while generating sampling data at high rates, facilitating performance measurement. The OPDL serves as an isolated power supply to drive instrumentation, offering a very pure power source that contributes no extraneous interference and eliminates the need for batteries. Testing can be completed more efficiently and more cost effectively. The small size of the photovoltaic power converter makes it compatible for use with compact instrumentation in confined test areas.
Fiber Optic Power Cable
OPDL
Data Collection or DataUnit Control
Collection or Control Unit
Fiber Optic Data Cable
Instrumentation Instrumentation or Remote or Remote Electronics Electronics
Standard USB Cable
Laser Source and Optical Data Link
Fiber Optic Fiber Power Optic Cable
Data Cable
Standard Standard USB Cable USB Cable Power Powerand andData Data Conversion ConversionModule Module
Figure 4. Isolated power and data transmission for enhanced electromagnetic interference measurements
Summary Photonic power harnesses the power of light to offer a totally new method of driving sensors. This technology offers particular advantages in high voltage, RF, EMI, and magnetic fields or where spark-free or lightning-proof operation is required. It is increasingly used in a wide range of applications, including test and measurement; sensing in industrial, medical, aerospace, and homeland security applications; video surveillance; and electric power current monitoring. OPDL systems combine photonic power with duplex digital communication to offer an all-fiber solution for power and data transmission.
All statements, technical information and recommendations related to the products herein are based upon information believed to be reliable or accurate. However, the accuracy or completeness thereof is not guaranteed, and no responsibility is assumed for any inaccuracies. The user assumes all risks and liability whatsoever in connection with the use of a product or its application. JDSU reserves the right to change at any time without notice the design, specifications, function, fit or form of its products described herein, including withdrawal at any time of a product offered for sale herein. JDSU makes no representations that the products herein are free from any intellectual property claims of others. Please contact JDSU for more information. JDSU and the JDSU logo are trademarks of JDS Uniphase Corporation. Other trademarks are the property of their respective holders. ©2006 JDS Uniphase Corporation. All rights reserved. 10143191 Rev. 001 08/06 PPSSA.AN.PP.AE
NORTH AMERICA : 800 498-JDSU (5378)
WORLDWIDE : +800 5378-JDSU
WEBSITE : www.jdsu.com
Reviewed December 2006
