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Voltage-controlled optical phase shifter is key. Optical phase shifter stabilizes propagation delay of fiber-optic transmission line by compensating for temperature and pressure effects. Applicable to phased array antenna systems and very-long-baseline interferometer distribution systems.
The present investigation is concerned with the development of single-mode optical fiber distribution systems. It is pointed out that single-mode fibers represent potentially a superior medium for the distribution of frequency and timing reference signals and wideband (400 MHz) IF signals. In this connection, single-mode fibers have the potential to improve the capability and precision of NASA's Deep Space Network (DSN). Attention is given to problems related to precise time synchronization throughout the DSN, questions regarding the selection of a transmission medium, and the function of the distribution systems, taking into account specific improvements possible by an employment of single-mode fibers.
Method of splicing single-mode optical fibers results in very low transmission losses through joined fiber ends. Coupling losses between joined optical-fiber ends only 0.1 dB. Method needs no special operator training.
Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described.
A 100-MHz reference frequency from a hydrogen maser frequency standard has been transmitted via optical fiber over a 14-km distance with a measured stability of 1.5 X 10 to the-15 power for 1000 seconds averaging time. This capability was demonstrated in a frequency distribution experiment performed in April, 1986. The reference frequency was transmitted over a single-mode fiber-optic link from Deep Space Station (DSS) 13 to DSS 12 and back. The background leading up to the experiment and the significance of stable reference frequency distribution in the Deep Space Network (DSN) is discussed. Also described are the experiment, including the fiber-optic link, the measurement method and equipment, and finally the results of the experiment.
A high-isolation single-mode fiber optic isolator assembly was designed and fabricated. The measured forward loss is 2.6 dB and the reverse loss (isolation) is greater than 70 dB. This is a 30-dB higher isolation than the isolation of the best fiber optic isolator previously reported. This isolator provides isolation between the semiconductor laser diode and the optical fiber in a precise reference frequency transmission system. The isolation of the laser greatly reduces the system's sensitivity to microphonics.
Assembly of commercially available components acts as single-mode fiber-optic isolator with lower forward-transmission loss and higher attenuation of reverse transmission than previously achieved in single unit. New design reduces cost and improves performance of optical gyroscopes, precise time- and frequency-signal-distribution systems, and other systems that include fiber optics and isolators.
A low-loss, high-isolation, fiber-optic isolator for use in single-mode fiber systems utilizes a Faraday rotator and two polarizers, one at each end angularly oriented from each other at the angle of rotation for isolation, and two aspheric lens connectors to couple optical fibers to the Faraday isolator to reduce forward loss to about 2.5 dB and improve isolation to greater than 70 dB.
A low loss optical isolator suitable for fiber-optic uses has been assembled from commercial components. The isolator exhibits reverse isolation of greater than 70 dB, with a forward loss of less than 1.3dB. This system provides an effective approach for reducing instabilities encountered in the output signal of semiconductor lasers in certain applications of fiber-optic systems. The paper presents a phenomenological explanation for the superior performance of the isolator system.
A number of recently developed fiber-optic components that hold the promise of unprecedented stability for passively stabilized frequency distribution links are characterized. These components include a fiber-optic transmitter, an optical isolator, and a new type of fiber-optic cable. A novel laser transmitter exhibits extremely low sensitivity to intensity and polarization changes of reflected light due to cable flexure. This virtually eliminates one of the shortcomings in previous laser transmitters. A high-isolation, low-loss optical isolator has been developed which also virtually eliminates laser sensitivity to changes in intensity and polarization of reflected light. A newly developed fiber has been tested. This fiber has a thermal coefficient of delay of less than 0.5 parts per million per deg C, nearly 20 times lower than the best coaxial hardline cable and 10 times lower than any previous fiber-optic cable. These components are highly suitable for distribution systems with short extent, such as within a Deep Space Communications Complex. Here, these new components are described and the test results presented.
A technique for stabilizing reference frequencies transmitted over fiber-optic cable in a frequency distribution system is discussed. The distribution system utilizes fiber-optic cable as the transmission medium to distribute precise reference signals from a frequency standard to remote users. The stability goal of the distribution system is to transmit a 100-MHz signal over a 22-km fiber-optic cable and maintain a stability of 1 part in 10(17) for 1000-second averaging times. Active stabilization of the link is required to reduce phase variations produced by environmental effects, and is achieved by transmitting the reference signal from the frequency standard to the remote unit and then reflecting back to the reference unit over the same optical fiber. By comparing the phase of the transmitted and reflected signals at the reference unit, phase variations of the remote signal can be measured. An error voltage derived from the phase difference between the two signals is used to add correction phase.
System for distribution of 100-MHz reference signal features transmission through optical fiber to station 22 km away and stabilization of frequency by radio frequency phase-conjugation method. Compensates for variations in phase (caused mostly by changes in temperature along optical fiber) of signal arriving at remote station. Involves measurement and control of phases of transmitted and reflected signals at reference station to obtain reference phase at remote station.
The effect of the linewidth of a single longitude-mode laser on the frequency stability of a frequency reference transmitted over a single-mode optical fiber is analyzed. The interaction of the random laser frequency deviations with the dispersion of the optical fiber is considered to determine theoretically the effect on the Allan deviation (square root of the Allan variance) of the transmitted frequency reference. It is shown that the magnitude of this effect may determine the limit of the ultimate stability possible for frequency reference transmission on optical fiber, but is not a serious limitation to present system performance.
Data are presented on the thermal coefficient of delay for various coaxial and fiber optic cables, as measured by the Frequency and Timing Systems Engineering Group and the Time and Frequency Systems Research Group. The measured pressure coefficient of delay is also given for the air-dielectric coaxial cables. A description of the measurement method and a description of each of the cables and its use at JPL and in the DSN are included. An improvement in frequency and phase stability by a factor of ten is possible with the use of fiber optics.
A novel fiber-optic system with dynamic range of up to 150 dB-Hz for transmission of microwave analog signals is described. The design, analysis, and laboratory evaluations of this system are reported, and potential applications in the NASA/JPL Deep Space Network are discussed.
Diplex fiber-optic link part of Goldstone Deep Space Communications complex. Relatively inexpensive equipment delivers signals of high quality. At central station, signal combiner adds 5-MHz reference-frequency signal and 36-bit time-code signal, forming composite signal, which modulates light transmitted along optical fiber. At remote station, fiber-optic receiver detects composite signal and provides input to diplexer, which separates frequency reference signal from time-code signal. Signals then amplified to desired levels.
The principal considerations in the design of fiber-optic transmitters for highly phase-stable radio frequency and microwave analog transmission are discussed. Criteria for a fiber-optic transmitter design with improved amplitude and phase-noise performance are developed through consideration of factors affecting the phase noise, including low-frequency laser-bias supply noise, the magnitude and proximity of external reflections into the laser, and temperature excursions of the laser-transmitter package.
A fieldable trapped ion frequency standard based on Hg-199(+) ions confined in a hybrid rf/dc linear ion trap is developed. This trap permits storage of large numbers of ions with reduced susceptibility to the second-order Doppler effect caused by the rf confining fields. In preliminary measurements a stability of 2 to 3 x 10(exp -15) was obtained for 10000 second averaging times. These measurements were carried out with a 120 mHz wide atomic resonance line for the 40.5 GHz clock transition with a second order Doppler shift from the rf trapping field of 6 x 10(exp -13).