Recent studies have shown that the advantages of fiber optic sensors in aircraft flight control are realized at the system level, not in the sensors or components themselves. These advantages derive from a fiber-optic systems approach in which the number and variety of cables and interface circuits are reduced by optical multiplexing. This paper describes a top-down approach to sensor system design which emphasizes selection of a network architecture to maximize system-level criteria prior to specification of sensor types. A key aspect of this design is multiplexing arrays of sensors through a common electro-optical interface. The most desirable multiplexing technique and network architecture would be one which is compatible with all or at least the greatest number of sensors while reducing system size and weight. Similarly those sensor types which are compatible with optical multiplexing are more desirable than those which cannot be easily incorporated into a multiplexed network. Several candidates for multiplexing are compared on the basis of system impact.

There is now a body of in-service flight test experience of fiber optic hardware on vari-ous airframes. A brief summary will be presented plus general observations and conclusions emphasizing those matters that relate to installability, maintainability and in-service reliability of this technology. This experience is used to highlight those more critical areas which need further investigation and technical progress. Priorities are presented for further hardware development and testing which can serve to foster the earlier acceptance of this technology for full-scale production applications.

This paper discusses direct frequency modulation of semiconductor lasers with a linear current ramp and its use in optical sensors. The laser diodes evaluated were the Sharp LT015, Mitsubishi 2901, the Hitachi HL8314 and HLP1400. The maximum attainable freuency deviations ranged between 20 to 50 GHz. Chirp rates ranged from 10 to 10 Hz/sec for modulation amplitudes from 5 to 15 mA and modulation frequencies from 500 Hz to 200 kHz. The upper limit for efficient direct frequency modulation was at 50 KHz. Coherence lengths from less than 1 meter to greater than 5 meters were measured from the devices. Measurements of power level, frequency deviation, and noise predict measurement of distances up to 13 meters with 0.01 cm accuracy, using conventional channel substrate planar AlGaAs lasers.

This paper describes the design and performance of a sensor system based on passive fiber optic sensors utilizing the principle of wavelength division multiplexing. The system is discussed in relation to the requirements of aircraft applications. The requirements on the source, sensor and detection circuits are outlined and a detailed power budget for a 12 bit rotary sensor is given. Measured performance of the various components is presented, along with a discussion of the environmental conditions found in various application areas within the aircraft. The wavelength sensing technique becomes the basis for a common sensor interface, and various techniques are described to provide capability for multiplexing many sensors onto one common interface.

After years of research and development, it appears that extensive use of fiber optics on aircraft is approaching realization. The status of fiber-optic components and systems for aircraft is overviewed, and efforts to develop standards and standardized test procedures are discussed. The accomplishments of the first 2 years of the Fiber Optics Readiness Program at Douglas Aircraft Company is reviewed, and an insight into future efforts is provided.

This paper presents measured performance data for linear fiber optic data bus configurations. Requirements and measurements for the individual data bus components including fiber optic couplers, transmitters, and receivers are given, including environmental performance. Demonstrated performance parameters for several linear data bus configurations with up to 69 nodes and data rates up to 50 megabits per second are presented.

Four high speed optical data bus topologies suitable for avionics applications have been analyzed for system reliability. Counter-rotating rings, redundant parallel rings, and redundant passive and active star networks were modelled by a Monte Carlo simulation in which random failures were assigned to optical links, passive bypasses, and stations according to preselected probabilities. The results of the analysis indicate that of the two ring systems, the counter-rotating ring was less reliable except in the limit of high link reliability and poor station reliability. This suggests that in the case of avionic systems, where connectors often represent a significant failure mode, counter-rotating rings will be less reliable. We also find that techniques for bypassing large numbers of failed stations will not significantly improve ring reliability. Both passive and active stars proved to be more reliable than either ring network, suggesting that a star may be the topology of choice, even in the case of a very large network.

This paper describes an attractive approach for referencing fiber optic intensity sensors in mobile platforms where variations of source, fiber path, or receiver parameters can severely compromise measurement of the desired parameter. The approach, named Time Domain Intensity Normalization (TDIN), operates with a wide variety of intensity-based sensors and also provides a means for sensor multiplexing. It therefore can serve as the basis for a standard fiber optic sensor system interface. Various reference schemes for intensity sensors are compared, followed by discussion of optical and electronic design implementation of TDIN, including system multiplexing. Theoretical analyses of key performance issues and test results (using a position sensor mechanism) are discussed.

Intensity modulation induced by macrobending in multimode optical fibers is presented as a transduction mechanism for analog position sensing in harsh aerospace environments. The macrobend sensor described herein is most suitable for short stroke applications (1 to 10 mm) where an intrinsic sensor is desired and only moderate linearity is required (< ± 1 %). Macrobend sensors are built and tested with intensity referencing and modal conditioning. The latter allow for sensor replacement without in-situ calibration. The theory, design tradeoffs, and test results of generic intrinsic macrobend position sensors are presented.

This paper reports on the development of a high performance, ruggedized multimode star coupler intended for use in fiber optic data transmission networks aboard naval surface ships. The coupler was designed to exhibit superior optical performance, both in terms of low loss and highly uniform coupling. It was also designed to survive a range of severe environmental and mechanical tests, including impact from a 400 lb hammer dropped from a 5 foot height, and a temperature range of -62 to 125°C. The coupler sizes produced ranged from 8 x 8 to 64 x 64 port devices. Essential features of the design along with sample performance data are presented.

The evolutionary incorporation of fiber optic technology in the remote operation of motor control systems is described in this paper. The program is proposed for naval application. The research and development was sponsored and funded by Ingalls Independent Research and Development (IRAD) funds. Shipboard installation was sponsored by the Naval Sea Systems Command (NAVSEA) PMS-400C. It represents the first significant effort to employ light in the remote operation of motor control functions found aboard a naval vessel. Although focused on one ship class, the program's achievements apply to most naval and commercial ships as well as many nonseagoing systems. The operational requirements of the local and remote station transceivers employed in motor control systems are presented in this paper. These include the network topology and electro-optic control, switching, and indicator circuits of several fiber optic motor control system design evolutions. The designs were all driven by operational requirements. Engineering options and design conclusions are presented. Resulting conclusions are that the use of fiber optic technology in the remote operation of naval shipboard motor control systems is both feasible and practical. It provides significant weight, EMI, and safety advantages over existing systems yet its installation, operation, and maintenance can be performed by existing personnel with little additional training.

The recent development of a unique optical fiber tapping system has extended the advantages of noise-free communications and sensing to passive bus networks. This new tapping technique will be described and discussed in the context of short distance networks suitable for a variety of platforms and vehicles. These linear networks may be implemented with either prefabricated, multidrop harnesses or post-installation tapping. Networks based on this technique may be "head-end" driven, 1 x N topologies or totally passive, launch/drop bidirectional architectures. The range of achievable tap ratios, environmental considerations and device selection are analyzed with emphasis on system budget modelling. Actual examples of both types of networks will be discussed in detail with particular emphasis on an 80 node (160 tap) launch/drop optical bus achieved on a single unbroken fiber.

A personal-computer based simulator has been developed to analyze different wavelength division multiplexed (WDM) configurations in optical fiber sensing and communication systems. Trade-offs are investigated in order to optimize system performance. Power budgets, channel widths and cross talk calculations are carried out for a system completely specified by the user. When exact loss variations with wavelength are not available, simplifying assumptions are incorporated in the model. The simulator uses a transfer function approach and is modular in nature.

While the benefits of fiber optics have been known for over a decade, the implementation of fiber optics into the U.S. Navy has only begun to accelerate in the last few years. Reason dictates that this must be a carefully planned and controlled process. Standardization of fiber optic components, in type and performance, is the first and most important step in fiber optic system development. There is no doubt that fiber optics will have a great impact on shipboard data communications systems. The coincident evolution of fiber optic technology and distributed data transfer architectures (Local Area Networks) will enable ship designers to dramatically improve shipboard combat system performance and survivability. Data transfer architectures such as the Survivable Adaptable Fiber Optic Embedded Network (SAFENET) are currently being developed for implementation into the U.S. fleet before the end of the century. This paper will address the physical media portion of the SAFENET network architecture currently being developed by the Navy laboratories and industry. Additionally, it will highlight the supporting development of fiber optic component standards.

Function content in automobiles has been projected to increase throughout the '90s. Accordingly, electromagnetic compatibility will become increasingly difficult to attain with all-conductor-based data transmission. The need for alternatives such as fiber optics is assumed. This paper discusses the issues to be addressed when using fiber optics in automotive data transmission applications. Connectors, packaging and data transmission subsystem impact are covered.

This paper describes the development of a plastic optical fiber doped with organic fluorescent materials, the fiber consists of a polycarbonate core with a glass transition temperature of 150°C and a cladding made of a new polymer. The minimum optical attenuation is 1.0 dB/m at a 765 nm wavelength in the near infrared region. The fiber has excellent characteristics for use with a 1 mW light source with a spot size of 0.5 to 2 mm. The fiber is thermally stable up to 125 T and is very flexible. Furthermore, light can be transmitted through the fiber with the incident optical beam perpendicular to the fiber as well as at parallel to it. With these characteristics, the fiber should be useful for transmitting several wavelengths.

This paper describes the development of a fibre-optic in-cylinder pressure transducer for internal combustion engines. The device is intended as a lower cost alternative to conventional piezo-electric pressure sensors which are widely used in engine development work. The current application identified is for a device with a full scale deflection of 150 bar for use in the development of advanced diesel engine control systems for cars and light vans. By suitable choice of materials the sensor has potential applications in the aerospace and industrial fields, for example the instrumentation of jet engines.

Within the next 5 to 10 years optical fibers are expected to be used in automobile local area networks. For this application, both glass and plastic fibers have the potential to play a significant role. Under the hood, where the operating temperatures tend to be too high for plastic fibers, glass based fibers are likely to be used. Glass based fibers are also intended for use in fiber optic sensors, for example, in engine control systems. However, in general, the preferred fiber material is plastic due to economic considerations. In the case of optical fibers for a network within the passenger compartment, plastic optical fibers are adequate and several prototype systems have already been built and demonstrated. The principal reasons for considering the use of optical fibers are discussed in several papers (1-3). A key component in an optical fiber network is a star coupler. This paper will deal with the fabrication and test results of a prototype 7x7 transmissive star coupler developed at Battelle. The optical fiber diameter chosen for the development of the star coupler is a 1 mm diameter fiber manufactured by Mitsubishi (ESKA-40). Currently both 750 and 1000 micron diameter fibers are under consideration for the automobile but the technology reported here is capable of accommodating either fiber. The final choice of the fiber type will depend on several economic factors which are yet unknown.

A multiplexed optical transmission system for automobiles utilizing newly developed polymer fiber has been proposed. The system is composed with a star-shaped optical network, in which the ootical signals can be transmitted bi-directionally through polymer optical fiber and optical branches with the central and local controllers. The polymer fiber has been developed for this purpose in order to overcome the conventional problems which prevented its wide use for a long time. The new polymer fiber is fabricated with a thereto-setting resin for core which is pushed out from heating furnace after the process of polymerization. The fiber shows the desirable characteristics for this application, that is, the heat resistance is as high as 200°C, and the transmission loss is as low as 0.5003/m at 660 nm wavelength.

Fiber optic tethers can be used with many types of vehicles to bring back TV and other sensor information from the vehicle and to transmit command signals to the vehicle. Their use enables a vehicle under human control to penetrate into areas that are too dangerous, confined or in otherwise not suitable for manned vehicles to go. The vehicle is fearless, and does not have to provide space and support equipment for a man. We will discuss some of the general types of vehicles for which tethered fiber optic links have been demonstrated.

This paper describes a design concept for a distributed system that is modular and provides a means of transferring analog signals, synchronous or asynchronous digital data (either bit serial or byte serial), and discrete status/control information in any mix. Maximum flexibility is a key feature. The system will accommodate a broad spectrum of operators and communication assets (both audio and digital), data acquisition/control system (analog or digital), and interconnection between multiple processors and peripheral devices. The architecture and protocol will accommodate both cable or optical fiber. Connectivities are established without using a central controller or switch. Analog signals can be distributed from one user to any number of other analog users without reduction in signal quality. Also, data can be distributed from any data terminal device to any other data terminal device. The flexible design allows for a wide variety of functional and operator interface capabilities with minimum impact to the hardware.

Avionics for the advanced aerospace systems is becoming increasingly more sophisticated to meet the demands of on-board automated real time control, diagnostics and health monitoring. This requires a large number of sensors and processors distributed throughout the vehicle. A large amount of data and control/command signals have to be handled by the network onboard. The weight, noise immunity, high bandwidth and power consumption are some of the advantages offered by FO-LAN's (Fiberoptic Local Area networks). These features serve the avionic network needs very well. Designing a FO-LAN's is generally done on an individual basis and every new FO-LAN has to be designed from scratch. Recent advances in Al and CIM (Computer Integrated Manufacturing) have helped develop powerful techniques for creating design environments where components and networks can be designed (and simulated, if desired) directly from system specifications. We are using such techniques to develop a design environment for avionics FO-LAN's.

As fiber optic systems are integrated into missile and space platforms, a growing need emerges for fiber optic switches capable of withstanding and operating in severe environments. Present commercial devices do not meet the stringent requirements for missile or space environments, nor are they always available in the required configuration. This paper explores some of the design considerations for a single-mode fiber optic crossbar switch for harsh environments. Some possible implementations of switching elements are described, and the design features of the chosen switch implementation are also described. Loss mechanisms for the switch are discussed, and test results are given for the sleeted design.

The Fiberoptic Guided Missile (FOG-M) was developed in the U.S. Army's Research, Development, and Engineering Center (RDEC) as a demonstration system for killing armor in an infantry application. The RDEC design uses a television sensor in the nose of the missile for in-flight target acquisition, bringing the video signal down a fiberoptic link that pays out behind the missile as it flies, to a gunner securely hidden in a defiladed launch vehicle. The gunner is able to select the target on a video screen and lock on an autotracker or alternately manually track the target to impact. The system design would use a common warhead for either armor or helicopter targets. The system is currently mounted on the High Mobility, Multipurpose Wheeled Vehicle (HMMWV), containing the gunner's station, launcher, and flight missiles. The gunner's station includes the capability for detailed mission planning, digital map display based on the Defense Mapping Agency's digital map databases, and display of the air battle situation for the gunner. Automatic targeting, control of multiple missiles in the air simultaneously, navigation using a digital correlator, and autotracking of moving targets in cluttered backgrounds with gunner selectable offset tracking capability are also available. The system has a capability to train the gunner using a perspective view scene generator that mimics the video scene he would be presented during missile flight. The scene generator uses the same hardware that displays the digital map, while a simulation of the missile runs in one of the system's computer processors to accurately move the seeker presentation around the scene. All of the other hardware used in embedded training is the same as the actual firing hardware. The system concept has been chosen by the Army as the non-line-of-sight (NLOS) component of the Forward Area Air Defense System (FAADS). The initial design is being upgraded for the MIL SPEC environment to allow early operational evaluation by the user. The lessons learned by these tests will be used to aid the full scale development program beginning in FY88. This paper describes aspects of the system designed by the Army's RDEC, with special emphasis on the mechanics of fiberoptic datalink winding and payout concerns.

The majority of the fiber optic effort for the Space Station is contained in the Data Management System and the Communications and Tracking System. This paper describes the functional requirements and architecture for each fiber optic system. Design and environmental concerns unique to the Space Station will be emphasized. Finally, possible uses for fiber optic sensors are discussed.

Simulation and analysis results are described for a wideband fiber optic intermediate frequency distribution channel for a frequency division multiple access (FDMA) system where antenna equipment is remotely located from the signal processing equipment. The fiber optic distribution channel accommodates multiple signals received from a single antenna with differing power levels. Performance parameters addressed are intermodulation degradations, laser noise, and adjacent channel interference, as they impact the over all system design. Simulation results showed that the laser diode modulation level can be allowed to reach 100% without considerable degradation. The laser noise must be controlled as to provide a noise floor of less than -90 dBW/Hz. The fiber optic link increases the degradation due to power imbalance yet diminishes the effects of the transmit amplifier nonlinearity. Overall, optimal operation conditions can be found to yield a degradation level of about .1 dB caused by the fiber optic link.

Conventional data buses, telemetry links, and sensors using wire harnesses as the transmission media suffer from numerous shortcomings, especially when utilized in spacecraft. This paper describes fiber optic networks which could be implemented in launch vehicles in the near-term. Special emphasis will be placed on the increase in reliability which fiber optics affords over conventional cable/wire approaches.