Data signals can be transmitted via the same optical fibers that are used to transmit power from base stations to remote stations containing sensors and associated circuitry. [A prototype system based on fiber-optic transmission of data and power is described in "General-Purpose Optically Powered Sensor and Control System" (NPO-19604), which is the first of two articles preceding this one.] The implementation of the present data-transmission/power-transmission concept involves the choice of one of several possible modulation schemes (see figure); the choice of a scheme for a specific system depends, in part, on whether the power-supply optical signal is steady or is modulated as described in the immediately preceding article, "Transmitting Power to Sensor Circuitry via Modulated Light" (NPO-19603).
In the case of a nominally steady power-supply optical signal, the data modulation can consist of brief interruptions of this signal; the modulation can be picked off by a simple amplifier circuit added to the power-conversion circuit in the remote station. In an experiment, data were transmitted at rates as high as 9.6 kb/s. The power-conversion circuit can be designed with sufficient reserve capacity and with a capacitor, or other energy-storage device to supply power to the other circuits in the remote station during the interruptions.
If the power-supply optical signal is nominally a steady pulse train in which the light is on half the time and off half the time, then the pulse train can be modified for transmission of data by the differential Manchester code. In the absence of data, the pulse train continues undisturbed; when data are present, some of the "on" pulses are changed to "off" pulses, and an equal number of "off" pulses are changed to "on" pulses. Because the total numbers of "on" and "off" pulses remain the same, the time-averaged transmitted power does not change.
In principle, it should also be possible to transmit data from the remote station back to the base station along the power-supply optical fiber. A microprocessor-controlled data-transmission optoelectronic circuit in the remote station would be synchronized with the Manchester-code pulses; during the "off" periods of the Manchester code, this circuit would transmit trains of relatively high-frequency data pulses.
NPO-19605
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Transmitting Data Signals via Fiber-Optic Power Lines
(reference NPO-19605) is currently available for download from the TSP library.
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Overview
The document discusses a novel method developed by Shannon P. Jackson and Harold Kirkham at NASA's Jet Propulsion Laboratory for transmitting data signals via fiber-optic power lines. This innovative approach allows for the simultaneous transmission of power and data over a single optical fiber, significantly reducing costs, especially in sensor networks where multiple fibers would otherwise be required.
The system operates by modulating optical power from a base station to remote electronic sensors. It can utilize either continuous light or alternating, chopped light to convey information. The modulation of the optical power enables the transmission of data as well as power, addressing the challenges of providing a reliable power source for remote electronic measurement systems. Traditional methods often require separate fibers for power and data, which increases complexity and costs.
The document outlines two primary modulation schemes for data transmission. In the case of a steady power-supply optical signal, data can be transmitted through brief interruptions of this signal. This method allows for data to be picked off by a simple amplifier circuit added to the power-conversion circuit at the remote station. In experiments, data rates of up to 9.6 kb/s have been achieved. Alternatively, if the power-supply signal is a pulse train, the differential Manchester code can be employed, where the presence of data modifies the pulse train without changing the overall power levels.
The technology is particularly beneficial for applications requiring long-term deployment of sensors, such as structural monitoring or high-voltage measurements, where traditional power sources like batteries are impractical. The document emphasizes that the system has been successfully demonstrated, with data being transmitted to a microprocessor-based control system powered optically.
Overall, this advancement in fiber-optic technology not only enhances the efficiency of data transmission in remote sensing applications but also simplifies the infrastructure needed for such systems. By integrating power and data transmission into a single fiber, the method presents a cost-effective solution for future sensor networks, paving the way for more sophisticated and reliable remote monitoring systems.
