The 125 Mbaud FDDI LAN standard is being incorporated by major manufacturers into their structural wiring strategies. At floor level with wiring strategy must include direct 125 Mbaud links over distances typically in the range 50 - 100 m. Plastic optical fiber links could offer an attractive solution for such links, but have not been considered due to their predicted low bandwidth. The work discussed in this paper demonstrates practically that the speed and Bit Error Rate (BER) requirements of the Fiber Distributed Data Interface (ANSI FDDI) links can be met by plastic fiber for link lengths up to 90 m using low cost robust technology.
Optical time domain reflectometry (OTDR) measurements have been performed to characterize the minimum reflection signature from PMMA plastic fiber splices. The dominant splice reflection sources due to inexact index matching and fiber core misalignment were carefully examined. A clearly detectable intrinsic OTDR reflection signature was observed with all tested fibers. The measured reflectivities varied from -54 to -27 dB. The characteristics of this signature were mapped out vs. experimental variables such as fiber surface roughness, polishing procedure, fiber-fiber alignment, and index matching characteristics.
The majority of production applications using plastic optical fiber (POF) have been for illumination applications. These applications continue to be refined and new illumination applications continue to be introduced. Point-to-point data communication applications of POF are beginning to appear in production vehicles. New developments in connection systems and networking components are occurring rapidly. This paper discusses recently developed components for illumination and data communications. The illumination components were designed for three different applications: lamp monitoring, keyhole illumination, and PRNDL indication (gear shift). Components for data communications include two connection systems and two passive stars designed for networking. The two connections systems are a 16 electrical/1 optical system for point-to-point links and a 5 electrical/2 optical for two-way optical communications. The two stars are a 16 node star and 7 node star. Performance characteristics and design advantages are described for all components.
A new optical time-domain reflectometer has been developed to investigate standard plastic optical fibers with PMMA as core material. The reflectometer allows to locate reflections and to obtain the fiber attenuation characteristics by analyzing the time dependence of the detected Rayleigh backscattered light. The measurement setup is working with 660 nm wavelength typical for transmission systems with PMMA fibers. Oversampling and digital signal processing including convolution and deconvolution decrease noise floor and increase the measurement resolution to the range of ten centimeters.
For system-optimizations beyond the coupling-length of plastic optical fibers, the excitation conditions become very important, because the coupling between light source and fiber influences the attenuation and bandwidth of the system. A modified measurement technique for mode selection in plastic optical fibers with step-index profiles is introduced. For testing and characterization of these fibers, low and high order meridional rays are used, excited by changing the excitation angle of the incoming light beam, which is either a focussed laser beam or an endface of an excitation fiber. Measurement results are presented, including the separation of the measured high excess losses into two components.
Pulse broadening in large core step-index optical fibers is dominated by multimode dispersion. The bandwidth of PMMA core polymer optical fiber depends on launch conditions, being substantially greater for collimated input than for mode-filled launching. The dispersion behavior is significantly affected by both mode dependent attenuation and by power coupling between modes. The results of time-domain dispersion measurements performed at 650 nm are presented and examined. The effects of launching conditions and fiber numerical aperture on bandwidth are discussed. Mode conversion is studied by examining far-field output patterns under various launch conditions. Disturbances caused by sharp bends, splices, and couplers can modify the distribution of energy among modes and thus effect the dispersion. Because only the propagation after the disturbance is effected, a given fiber optic link can have different effective bandwidths in the two counter propagating directions. Finally, a method of realizing higher effective bandwidth over a given fiber by mode-selective detection is presented.
Transition of optical components from laboratory concept demonstrations to flight-worthy production-ready devices is of great interest to both system integrators and potential component manufacturers. Technology limitations have been one barrier to success, though limited communication between air-frame system engineers and optical developers appears to be as significant. The current presentation will address some of the detailed requirement characteristics for application in military rotorcraft, with emphasis on performance, redundancy, size, weight, and environmental conditions.
The practices needed to transfer the techniques to fabricate state-of-the-art optical sensor devices for aircraft applications from a laboratory environment to a production environmental have been analyzed. The experience gained from the development of several types of technologies as applied to sensors has been used as a baseline to generate procedural guidelines to begin the transfer of technology. Views on the design methods required during the development phase, in view of an inevitable production phase are presented.
A ladar fiber optic sensor (LFOS) for aircraft applications is described. Chirped intensity- modulated ranging is used to estimate linear position. LFOS technology offers several advantages over other fiber optic sensor techniques proposed for aircraft position sensing applications, including small and robust transducer heads, inherent multiplexing capability, and inherent fault isolation capability. LFOS sensors have been integrated inside a flight control surface hydraulic actuator and inside a pilot's sidestick controller. Closed loop operation of the actuator using the LFOS sensor for position feedback was successfully demonstrated in the laboratory. The LFOS sensors in the sidestick controller were used as inputs to fly a flight simulator. The current LFOS interface electronics is contained on two VME circuit cards, with the capability to service four multiplexed sensors. Excellent performance has been achieved. Deviation from linearity over a 7-in. stroke is better than 0.05% of full scale. The RMS measurement noise is less than 15 microns for a 1 millisecond measurement interval.
During the past five years, fiber optic position sensing for aerospace applications based on high bandwidth chirped modulation of laser diode sources has been explored by a number of organizations. These investigations can be classified into two primary approaches: chirped Frequency Modulated/Carrier Wave (FM/CW) and chirped Amplitude Modulated/Carrier Wave (AM/CW). In this paper, the results of a system level analysis, which compares these two approaches in light of aerospace position sensing requirements, is presented. Key strengths and weaknesses of each approach are reviewed and conclusions are drawn concerning the applicability of each approach to aerospace position sensing. The primary conclusion is that the Doppler frequency shift imposed upon the optical carrier by the dynamic aerospace environment, is a major obstacle to the deployment of sensors based on the chirped FM/CW approach. While, in contrast, the performance of the chirped AM/CW approach is relatively insensitive to Doppler frequency shifts.
A fiber optic sensing system with an intensity sensor and an RF modulated source has been shown to have sensitivity and resolution much higher than a comparable system employing low modulating frequencies or DC mode of operation. Also the RF modulation with an appropriate configuration of the sensing system provides compensation for the unwanted intensity losses. This paper describes the basic principles and applications of a fiber optic sensing system employing an RF modulated source. In addition the paper discusses various configurations of the system itself, its components, and modulation and detection schemes. Experimental data are also presented.
About fifteen years ago, it became pretty clear that a combination of fiber optic and photonic technologies offered an opportunity to use light to perform almost any of the functions traditionally performed with wire and electronics--as well as to gain a number of unique advantages in the process. Sensors were quickly recognized as prime candidates for conversion to optics because the new technologies promised to eliminate noise susceptibility, a problem that has always plagued instrumentation engineers. As a bonus, the new technology also appeared to make the long-sought true digital sensors a practical reality. The benefits appeared so attractive that nearly all major suppliers and users of sensors began some kind of program to get on the bandwagon. The ensuing worldwide explosion of activity resulted in literally thousands of technical papers and patents, but a discouragingly small number of practical off- the-shelf devices. This paper will review the field of fiber optic position sensors, will categorize the various types, will discuss their relative advantages and disadvantages, and will outline the problem areas which still remain to be solved before the technology is likely to find the predicted widespread use.
Optical temperature compensation schemes for the ratiometric interrogation of spectral modulation sensors for source temperature robustness are presented. We have obtained better than 50 - 100X decrease of the temperature coefficient of the sensitivity using these types of compensation. We have also developed a spectrographic interrogation scheme that provides increased source temperature robustness; this affords a significantly improved accuracy over FADEC temperature ranges as well as temperature coefficient of the sensitivity that is substantially and further reduced. This latter compensation scheme can be integrated in a small E/O package including the detection, analog and digital signal processing. We find that these interrogation schemes can be used within a detector spatially multiplexed architecture.
A common electro-optic interface (EO) has been designed and tested with a new optic sensor decoding architecture. The new EO module converts Wavelength Division Multiplexed (WDM) position, temperature and pressure signals using the same circuitry. This module uses the combination of Digital Signal Processing (DSP) technology along with a new temperature and pressure sensing technology. This approach results in common circuitry for processing three dissimilar inputs. The new architecture was made possible by advancements in two major areas, DSP and growth of advanced materials with tailored optic properties. This paper will discuss both the top level architecture of sensors and EO module and the performance advantages.
Several advantages may be realized when implementing fiber optic technology in flight controls. However, the system designer must consider maximum multiplexing of fiber optic sensors while maintaining system reliability in the flight control architecture to fully exploit the technology. Analysis of fiber optic technology conducted at less than the system level may not reveal the full advantages.
Time division multiplexing of spectral modulation fiber optic sensors for aircraft engine control is presented. The paper addresses the architectural properties, the accuracy, the benefits and problems of different type of sources, the spectral stability and update times using these sources, the size, weight, and power issues, and finally the technology needs regarding FADEC mountability. The fiber optic sensors include temperature, pressure, and position spectral modulation sensors.
In its purest conceptual form, Fly-by-light (FBL) utilizes optical signals for communications, sensor interrogations and for both the control and powering of actuation stages. Unfortunately, the current level of technology does not allow for a realization of this concept in its original form. Optical control by definition requires optical logic operation, but an optical computer does not exist. The optical powering of actuation stages is also difficult to accomplish because efficient mechanisms for conversion of optical to mechanical energy are not currently known.
A fiber optic temperature sensor (FOTS) system consisting of an optical probe, a flexible fiber optic cable, and an electro-optic signal processor was fabricated to measure the gas temperature in a turbine engine. The optical probe contained an emissive source embedded in a sapphire lightguide coupled to a fiber-optic jumper cable and was retrofitted into an existing thermocouple probe housing. The flexible fiber optic cable was constructed with 200 micron core, polyimide-coated fiber and was ruggedized for an aircraft environment. The electro- optic signal processing unit was used to ratio the intensities of two wavelength intervals and provided an analog output value of the indicated temperature. Subsequently, this optical sensors system was installed on a NASA Dryden F-15 Highly Integrated Digital Electronic Control (HIDEC) Aircraft Engine and several flight tests were conducted. Over the course of flight testing, the FOTS system's response was proportional to the average of the existing thermocouples sensing the changes in turbine engine thermal conditions.
A novel intensity-based liquid level sensor which operates up to 300 degree(s)C is described in this paper. Liquid level measurements for different liquids with refractive index ranging from 1.33 to 1.635 have been obtained with extinction ratios between 20 dB and 39 dB. Measurement hysteresis for measurement of lubricate oil was 0.175 mm.
Digital or ladar fiber optic position sensors may be a promising alternative to electrical LVDT or RVDT for aeronautics. They are rugged devices, they do not need some form of referencing to avoid any error arising from random in-line loss, and they give absolute measurement results. Besides they are to date, the sensors which are the most advanced in tests for aeronautical applications. In this paper we present new concepts for these sensors which make them easier to implement on an aircraft. One of these ideas consists in referencing the optical fiber length from the emitter/receiver to the ladar sensing head, thus making the sensor acquisition independent of the optical fiber length. The other principles which are discussed in this paper concern digital fiber optic sensors. The second concept consists in adding a checksum to each position encoding word in order to test if the measure is valid or not. At last we propose a specific quantization law.
This paper describes a newly developed compact high reliability fiber coupled laser diode which is capable of providing enhanced performance under extreme environmental conditions including a very wide operating temperature range. Careful choice of package materials to minimize thermal and mechanical stress, used with proven manufacturing methods, has resulted in highly stable coupling of the optical fiber pigtail to a high performance MOCVD- grown Multi-Quantum Well laser chip. Electro-optical characteristics over temperature are described together with a demonstration of device stability over a range of environmental conditions. Real time device lifetime data is also presented.
A theoretical approach is developed to evaluate pressure detection sensitivity and its temperature dependence for diaphragm-type fiber optic combustion pressure sensors. Temperature-induced mechanical response variations and diaphragm optical reflectivity degradation, particularly at high temperatures, are identified as the two major factors that produce errors in sensitivity, and hence in pressure measurement. Experimental results using hermetically sealed sensor construction prove the feasibility of maintaining diaphragm optical reflectivity under high temperatures. This analysis predicts that simple temperature compensation could reduce temperature-induced errors in sensor output, and obtain desired pressure measurement accuracies. Engine tests performed with the present fiber optic sensors demonstrate good signal-to-noise performance and temperature stability.
We describe the development of a fiber based video distribution for aircraft entertainment. The fiber system delivers live satellite video to every seat in the aircraft and can be interface to the interactive services presently being deployed on commercial aircraft.
Fiber optic communication networks have been implemented in the commercial building and campus arena as well as in numemus strategic and ttical military applications for more than five years. Similarly, experimental prototype systems for avionic applications have been developedand demonstrated foranumberofyears. With therecentadveinofa widely acceptedindustry fiber optic LAN standard, FDDI, as well as advances in technology, implementation ofa high speed fiber optic communication network in an airplane is now readily achievable with relatively low risk.
Advancements in distributed avionics processing imposes significant data communications requirements on next-generation aircraft. Higher performance, improved fault tolerance, and increased connectivity are needed to support such applications as the Electronic Library System, Onboard Maintenance System, and Cabin Management System. In response, the Onboard Local Area Network (OLAN) project was initiated in the ARINC Databus Subcommittee. OLAN is a networking profile based on the International Standards Organization Fiber Distributed Data Interface LAN standard. OLAN characteristics specify a subset of capabilities, and exclude any options not appropriate for use in aircraft. In this paper, the history of OLAN work is traced, the OLAN architecture is introduced, and specific OLAN protocol profiles are summarized. Finally, challenges confronting the OLAN are examined.
Command and control (C2) aircraft are host to an array of communications, information processing, and electronic control systems. The previous method of interconnecting this equipment involves point-to-point wiring harnesses between devices. A fiber optic broadband bus can be used to improve this situation by consolidating equipment connections on a shared medium. This network, known as the Onboard Connectivity Network (OCN), is being prototypes for application on the U.S. Government's Special Air Mission aircraft. Significant weight reduction and simplified future systems integration are the primary benefits of the OCN. The OCN design integrates voice, data, control, and video communications on a 3GHZ single mode fiber backbone. Communications within the aircraft use 500 MHz coaxial cable subnetworks connected to the backbone. The entire network is a dual redundant system for enhanced reliability. Node topologies are based on VMEbus to encourage use of commercial products and facilitate future evolution of the backbone topology. Network encryption technologies are being developed for OCN communications security. Automated workstations will be implemented to control and switch communications assets and to provide a technical control, test, and monitoring function.
A new POF fiber/cable will be discussed based on both calculation and measurements, attenuation, intermodal dispersion and material dispersion. Improvements in POF fiber/cable mechanical properties have been achieved without compromising optical transmission characteristics. After forty thousand repeated bending cycles the cable jacked with PVCl, for flame resistance, maintain the original level of optical transmission. The feasibility of 10 Mbps POF data links with visible LEDs and 125 Mbps data links with LDs are evaluated. The color filtering effects of POF, LED/LD thermal drift, and intermodal dispersion will be considered.
In spite of Plastic Optical Fibers' (POFs) assets, their attenuation still remains too high (usually near 200 dB.km-1 at 650 nm) and far from the theoretical one. The transmittance could be improved by optimizing the interface between the cladding and the core. Thus a process of a new ORMOSIL (ORganically MOdified SILicate) cladding which is obtained by sol-gel technology is proposed for PMMA fibers. Coupling agents are able to assure the adhesion of the core fibers by chemical links with the coating.