An overview of fiber optic sensors and their practical applications are discussed. Various optical schemes being used for interferometric and non-interferometric sensors are addressed. Transduction coatings along with various applications to sensing elements are also presented. Finally, state-of-the-art sensitivities are given for several sensors, and sensor and component needs are discussed.

A generic class of fiber-optic sensors is evolving rapidly for applications requiring maximum sensitivity. Theoretical and practical performance levels of the Mach-Zehnder types of interferometric sensors will be reviewed. A number of optical and electronic detection/demodulation schemes are becoming available and will be discussed in terms of their various advantages for different sensing applications. Projections for future applications and implementation hardware trends will be highlighted.

High-bandwidth analog applications are a new and very promising area of photonics. Photonics is fast becoming the lead technology in the study of single-shot, rapid-transient phenomena because the photonic equivalent of a conventional diagnostic system offers unsurpassed performance and value.

This paper reviews recent developments in distributed fiber optic sensing systems (DFOSS) employing optical time domain reflectometry (OTDR), polarization optical time domain reflectometry (POTDR), and frequency domain reflectometry (OFDR) techniques. Such systems can time - and/or frequency multiplex a large number of sensors distributed along an optical fiber, and offer unique advantages over conventional multiplexed sensing technology.

Applications of fiber optic sensors in the power generation, chemical process, and steel making industries are discussed. Emphasis is placed on the special needs and requirements in these industries and how optical sensors can uniquely satisfy these needs. Fiber optic sensors are described which make direct measurements of quantities that heretofore could be made only indirectly using conventional sensing methods. Limitations of optical sensors along with their own special application requirements in industry are also discussed. Specific Babcock & Wilcox fiber optic sensors and systems are described which have been developed or are currently under development.

Cost, accuracy and reliability requirements dictate the need to critically examine the fiber optic sensor approaches that are currently being pursued for making absolute measurements. Typical absolute measurements require only moderate sensitivity but high static accuracy over wide environmental conditions. In many applications, in situ calibration is not possible, yet high accuracy must be maintained with tens or hundreds of meters of fiber optic cable and multiple connectors separating the optical sensor head from the associated electronics. For many fiber optic sensor approaches, uncontrollable cable and connector loss variations limit achievable accuracy to a few percent. We present experimental data on cable and connector loss variations and review the resulting accuracy limitations for a variety of generic sensor approaches.

This paper presents the requirements on fibre optic sensors for subsea wellhead monitoring. A possible advantage of fibre optics is increased reliability of the monitoring system. However, to achieve this a substantial amount of development and testing has to be performed. A very important factor in the selection of sensor principles for further development is their possibility for success. New technologies have to solve problems and not increase the probability for failures.

We present here a random and not full digest of optical fibre technology in this country at the end of its first decade, since its birth in 1975. Main items have been moved like: organization of science, industrial background, meeting activities, main topics of interest and chosen organizations active in optical fibre technology. A list of chosen references concerning optical fibre technology and edited in this country closes the digest.

Passive optical "gyros" as well as active optical "gyros" (i.e. ring laser gyros or RLG) are based on the Sagnac effect. The Sagnac effect is the non-reciprocal phase difference experienced by light propagating along opposite directions in a rotating frame. The active technique for measuring the phase difference consists of placing a gain medium within a ring cavity, i.e. a ring laser. In the presence of rotation, the non-reciprocal phase difference that is generated is automatically transformed to a difference in the laser frequencies along the counterpropagating directions in the ring laser. In the passive optical gyros, the non-reciprocal phase shift generated by rotation must be measured using external techniques. There are two types of passive gyros. One type is based on an interferometer approach in which two light beams propagate along opposite directions around a closed path and the phase shift difference generated by rotation is measured. The sensitivity is enhanced considerably by confining the light propagation within a single mode fiber that is wrapped many times around a cylinder. The other type of passive gyro is based on a ring resonator approach in which an external light source is used to measure the difference in the resonance frequency of the cavity along opposite directions. This resonance frequency difference is proportional to the rotation-induced Sagnac phase difference. Optical cavities may be constructed using bulk-optical, fiber-optical or integrated-optical components. At present there is considerable research in progress that is aimed at the development of passive gyros for a variety of applications from precision navigation to robot control. The performance of such gyros at present are very encouraging. The early emphasis on short term noise is now shifting to dynamic range, scale factor stability, light sources, and integrated optic components. In addition, there has been immense progress in the development of low loss fuzed couplers for both the multiturn interferometer gyro and the resonator gyro. The following references will give a good starting point for the interested reader. The references also include the results of recent work mentioned either individually or included in the listed conference proceedings. Futuristic, novel ideas are discussed in references 16 and 17.

This paper reports the results from two experimental closed loop gyroscopes using ordinary single mode fiber. Rotation rate bias stability data are presented for both short term (T = 1 sec) and long term (T = 100 sec., NT = 6 hrs). The performance of our systems is displayed in the frequency domain as well as in the time domain. The best performance achieved was a rotation rate noise of .9 °/hr for 1 sec. integration, .30 °/hr for 10 sec. integration and in the long term .08 °/hr for 100 second integration. The extrapolated drift, .2 ° / âœ"hr, was less than an order of magnitude above the shot noise limit. Our second (breadboard) gyroscope has achieved a long term (6 hours) bias stability of 1 °/hr.

This paper is an analysis of temperature and birefringence fluctuation effects on the operation of a Sagnac fiber optic gyroscope. The temperature fluctuations and vibrations cause the optical path length of the light waves within the fiber to fluctuate, and this in turn causes the phase of the optical waves to vary in a random fashion. The random phase variations are a noise source in the gyro and the magnitude of the effect depends upon the demodulation technique used to determine the Sagnac phase shift.

An update of the large area (now 60m2) Passive Resonant Ring Laser Gyro (PRRLG) is given. Some aspects of last year's design have changed; but performance is still predicted to be in the 10-10 earth rate unit (ERU) range. This is of interest for a number of geophysical applications.

Substantial progress has been made in recent years toward the development of producible fiber-optic rotation sensors. An overview is presented of the movement of the fiber-optic gyro into a product at McDonnell Douglas from early developments to a fieldable oil drilling tool. The current state-of-the-art of fiber-optic gyro technology with respect to near term product prospects is assessed.

Progress in developing a fiber-gyroscope integrated-optical chip is reviewed. Two LiNb03 channel-waveguide components are described. Excess insertion loss as low as 5.5 dB has been obtained in a double-Y branch and 40 dB sideband suppression has been achieved in a serrodyne frequency translator.

We present results on a superluminescent diode for the 0.83 μm spectral region with high CW power (12.5 mW), and a bandwidth of q, 160 A. This device is based on the twin channel laser structure on a p-type substrate with current blocking layers.

The worldwide market for precision fiber optic sensors is forecasted, 1984-1994. The forecast is based upon o Analysis of fiber optic sensor and related component current technology, and a forecast of technology advancement o Review and projection of demand for precision sensing, and the penetration which fiber optics will make into this market The analysis and projections are based mainly on interviews conducted worldwide with research teams, government agencies, systems contractors, medical and industrial laboratories, component suppliers and others. The worldwide market for precision (interferometric) fiber optic sensing systems is forecasted to exceed $0.8 billion by 1994. The forecast is segmented by geographical region (Europe, Japan and North America) and by function; o Gyroscope o Sonar o Gradiometer/Magnetometer o Other - Chemical Composition - Atmospheric Acoustic - Temperature - Position - Pressure Requirements for components are reviewed. These include special fiber, emitters and detectors, modulators, couplers, switches, integrated optical circuits and integrated optoelectronics. The advancement in component performance is forecasted. The major driving forces creating fiber optic sensor markets are reviewed. These include fiber optic sensor technical and economic advantages, increasingly stringent operational requirements, and technology evolution. The leading fiber optic sensor and related component development programs are reviewed. Component sources are listed. Funding sources for sensor and component development are outlined, and trends forecasted.

A new class of environmental parameter sensors, which operate by the direct interaction between low levels of optical energy and very small coated beams of silicon dioxide, is being developed. The beams are fabricated using well-established silicon micromachining techniques and, in general, have lengths of the order of 100 microns and a cross-section of 5 microns by 1 micron. Optical power levels in the region of microwatts focussed onto the coated surface of these beams can set them into vibration at frequencies of hundreds of kiloHertz with amplitudes of a few nanometres. Such vibrations can easily be detected by optical interferometric techniques, using either a separate optical source as a probe, or even the same source used to initiate the vibrations. If such a beam is interfaced appropriately to an environmentally sensitive element, such as a diaphragm for pressure measurements, or a selectively absorbing film for chemical measurements, its mechanical resonant frequency is correspondingly altered. This frequency change can then be determined by the optical detection system, resulting in an elegant all-optical microsensor.

This paper describes the current status of a passive homodyne demodulator useful for extracting an optical phase signal from a fiber interferometric sensor. An optical demodulator has been developed in conjunction with a sine-cosine electrical demodulator that has a noise floor of a few prad/iffi. This passive homodyne detection has the advantage over other homodyne detection schemes in that it eliminates the need for active feedback phase modulators. The sensitivities achieved are relatively flat over a wide frequency band and temperature range. Comparisons with alternative approaches and discussions of performance data will be presented.

A particle concentration sensor would be useful in many industrial process monitoring applications where in situ measurements are required. These applications include determination of butterfat content of milk, percent insolubles in engine oil, and cell concentration in a bioreactor. A fiber optic probe was designed to measure particle concentration by monitoring the scattered light from the particle-light interaction at the end of a fiber-optic-based probe tip. Linear output was obtained from the sensor over a large range of particle loading for a suspension of 1.7 μm polystyrene microspheres in water and E. coli bacteria in a fermenter.

A fiber array polar nephelometer of advanced design, the FAN I, is capable of in-situ phase function measurements of scattered light from man-made or natural atmospheric particles. The scattered light is measured at 100 different angles throughout 360 degrees, thus potentially providing a measurement of the asymmetry of irregularly shaped particles. Phase functions can be measured at 10 to 100 Hz rates and the range of measurable single particle sizes is from 5gm to as large as 8mm. For particles smaller than 5gm the ensemble average can be measured. The FAN I is microprocessor controlled and the data may be stored on floppy disk or printed out in tabular and/or graphical form. The optical head may be separated from the computer system for operation in field or adverse conditions. Examples of laboratory measured scattering phase functions obtained with the FAN I for spherical and irregular particles are given to illustrate its measurement capabilities.

A noncontact, fiber-optic-based velocity measurement device which has not received much attention in the literature is what could be called a "Retical Image Velocimeter" or RIV. It provides the potential of velocity measurement accuracy comparable to more costly techniques. The chief advantage of the RIV method is that a coherent light source is not required. Instead, an inexpensive light-emitting diode is used in conjunction with fiber optic light guides and a reticle to produce a real fringe image at the point of measurement. Light scattered from particles or surface irregularities moving through this point is modulated by the reticle pattern. Collection, fiber optic transmission, detection, and frequency analysis of this scattered light at a remote location are used to infer the velocity of flow in a transparent media or the speed of a moving surface.

Fiber-optic vibration sensors have the potential to replace conventional technology based on magnetic pick-up coils. Advantages of this technology include immunity to electromagnetic interference, small size and light weight for better coupling, wide bandwidth, large dynamic range, high sensitivity, and potentially low cost. A fiber-optic vibration sensor based on single-mode fiber technology has been built and evaluated for comparison with conventional technology. The device is a grating-based unit designed for quadrature detection. This unit is mounted onto a conventional vibration sensor, and comparisons of the output of the two devices are made.

An analysis is carried out of the variation of photoelastic fiber optic sensor response with optical source spectral linewidth. An analytical expression is derived to predict this variation and incorporated into a computer model based on the properties of a known broadband optical source and silicon photodetector. The model is then compared with experimental results and the possible advantages of the use of broadband optical sources are discussed.

We have developed an analyzer capable of measuring +25 ppm SO2 in a dense slurry spray. The analyzer is based on nondispersive ultraviolet spectroscopy. Absorption is measured over a 10 cm path at the tip of an air-purged fiber optic probe. The analyzer has been used to provide spatially resolved concentration measurements to guide the development of a numerical model of a dry-scrubber process.

A fiber optic fluid level sensor based on transmission attenuation due to bending loss is described. Fibers formed with reverse curvatures of decreasing radii will induce an increasing amount of lower mode light loss to the cladding as the light propagates along the multimode fiber. The sensor is arranged in the fluid in a vertical orientation such that the light travels along the fiber from the bottom or low fluid point to the top or full point. As the fluid covers increasing lengths of the exposed fiber, it strips ever more power from the cladding (assuming the fluid refractive index is greater than the cladding). Data taken with a sensor of this configuration show a monotonic decrease of output intensity as a function of increasing fluid level. As much as a -14dB change occurred over a one-foot fluid level change. Comparison of these results with a mathematical model shows good agreement.

Twin-core and polarimetric fiber optic sensors have been embedded in composite plates and used to measure subsurface flexural and compressive bearing strains. Residual thermal stresses have been observed by measuring the change in the twin-core crosstalk with wave-length near the antisymmetric mode cutoff and subsurface crack initiation and growth has been detected with a subsurface twin-core sensor in a pin-loaded bolt hole fatigue test.

Fiber optics are being effectively utilized in an increasing range of data and information transfer applications. A less mature, but equally challenging, application of fiber optics concerns their use for a host of sensor technologies. Fiber sensors have now been developed for measurement of many physical parameters. These sensor systems frequently exploit several general attributes of fibers, including: cost, an all-dielectric trans-mission medium, freedom from electrical interference, bandwidth, resistance to degradation in severe or adverse environments, light weight, etc. This paper summarizes the use of fiber optics or guided optical systems for radiation sensors. It is limited to passive systems wherein electrical power is not required at the sensor location. However, electrically powered light sources, receivers and/or recorders may still be required for detection and data storage in sensor system operation. This paper emphasizes sensor technologies that permit high bandwidth measurements of transient radiation levels, and will also discuss several low bandwidth applications. In addition to discussion of several specific sensor concepts, an extensive bibliography is included to guide research into these, or other, forms of radiation sensors. The bibliography is subdivided into four major categories. In the bibliography, each paper is listed only once, even though a given paper may include data appropriate to several sections. Furthermore, to avoid long reference lists within the text, only a few of the bibliographical entries are referenced therein. The present conference is not included in the reference list, but includes several related papers. Four other general reviews of related technologies may be of particular benefit.1-4

We have developed and tested a photonic high speed analog data recording system that, when compared with conventional oscilloscope-based systems, offers greater economy, higher bandwidth, electrical isolation, and compactness. The basis of this approach is to record analog photonic signals rather than analog electrical signals. A key component is a prototype High Speed Multi-Channel Data Recorder (HSMCDR). It uses a picosecond streak camera with a digital readout to record multiple fiber-optic data channels, and a dedicated microcomputer to reduce and process that data. To record signals from analog electrical sensors, laser diode transmitters provide an interface to the HSMCDR. Interactive software written for the HSMCDR separates, calibrates, and plots up to 20 waveforms in the customary amplitude versus time format. We describe the HSMCDR, its performance, applications in pulsed power experiments, and its impact in diagnostic technology.

In conjunction with our implementation of photonic diagnostics on pulsed power accelerators at Sandia, we are developing a Photonic Data Recorder (PDR) which sweeps and records photon analog signals directly rather than converting photons to electrons and sweeping the electrons, as in a conventional oscilloscope or streak camera.

Two-dimensional, time-dependent images generated by neutrons, gamma rays, and x-rays incident on fast scintillators are relayed to streak and video cameras over optical fibers. Three dimensions, two spatial and one temporal, have been reduced to two, one in space and time utilizing sampling methods permitting reconstruction of a time-dependent, two-dimensional image subsequent to data recording. The manner in which the sampling is done optimized the ability to reconstruct the image via a maximization of entropy algorithm. This method uses four linear fiber optic arryas typically 30 meters long and up to 35 elements each. A further refinement of this technique collapses the linear array information into four single fibers by wavelength multiplexing. This permits economical transmission of the data over kilometer distances to the recording equipment.

A system has been developed to transmit analog signals through 1-km-long fiber-optic cables having bandwidths up to 1.5 GHz. Semiconductor injection laser-diode transmitters operating at a wavelength of about 815 nm are directly modulated by electrical signals from radiation detectors. Graded-index optical fibers transmit the optical signals to a remote facility, where they are recorded on a single streak camera.

Optical fibers using pure quartz or quartz doped with rare earth elements have been used as magnetic field sensors [1]. In these sensors Faraday rotation of the optical polarization direction is used as the basis for measuring magnetic field strength. The angle of polarization rotation in the fiber is 0=BUL, where B is magnetic field strength, V is the Verdet constant, and L is the propagation path length. Typically an analyzer is used after the fiber to convert polarization rotation into intensity modulation.

We have developed a calibrated optical fiber Faraday rotation current sensor. A strong magnetic field in an optical fiber introduces circular birefringence, causing the plane of polarization of light to rotate by an amount proportional to the magnetic field. Faraday loops used in the past were nonlinear due to the stress-induced linear birefringence caused by bending the loop. This linear birefringence interfered with the Faraday rotation, yielding a complicated relationship between the current and detected light signal. We have found a way to overcome the effects of the unwanted linear birefringence and produce a calibrated current waveform. The calibration is limited only by the accurate knowledge of the Verdet constant of the optical fiber. Results of recent experiments as well as planned measurements will be presented.

We have demonstrated phase modulation of rotating linearly polarized light by current-induced Faraday rotation in a single mode optical fiber and used the technique to measure the current in ZT-40M, a Reversed-Field Pinch. We have also demonstrated the practicality of using twisted sensing fiber to overcome the problems associated with linear birefringence.

A method for multiplexing interferometric optical sensors is reviewed, and theoretical results are presented which predict the phase sensitivity of sensors multiplexed using this method. The multiplexing technique--"coherence multiplexing' is based on the use of a source whose coherence length is short compared to most system optical path length differences. The use of a single-mode semiconductor laser diode source typically leads to a min-imum detectable phase on the order of a milliradian per VHz. Small improvements result from the use of a noise-canceling balanced detection scheme. Sensitivity in the microradian per VHz regime might be achieved through the use of a shorter coherence length source such as a superluminescent diode.

Plastic scintillators can be coupled to light fibers to make small, simple, and inexpensive x-ray detectors. These detectors have been developed for use at the Nevada Test Site (NTS) for the remote detection of x-rays. Light produced in the scintillator can be transmitted by the fiber for several hundred meters to a photodetector, which is usually a streak camera or a photomultiplier tube. The use of a streak camera allows many channels to be recorded simultaneously. A parameter study has been done to measure the sensitivity of these detectors as a function of scintillator geometry, type of scintillator, coupling geometry, and x-ray energy. The results can be qualitatively explained by a simple geometric theory. A recent use of these detectors at NTS was the measurement of an x-ray spectrum. System performance for this measurement will be reviewed.

We have developed a highly accurate, non-perturbing, non-invasive voltage monitor for multi-megavolt measurements in water using the electro-optic Kerr effect. The strong electric field causes the normally isotropic water to become linearly birefringent, with the birefringence axis aligned along the field. A beam polarized at 45° with respect to the electric field will experience a phase difference in the parallel and perpendicular components by an amount proportional to the square of the electric field. Measuring the phase change gives an accurate and precise value of the electric field.

We have successfully demonstrated a photonic free space microwave frequency sensor at the Sandia High Power Microwave facility. This sensor, which uses the Pockels effect, is a miniature dielectric device that we constructed from electro-optic and fiber-optic components. In this sensor, an incident pulsed microwave electric field modulates a carrier laser beam at the microwave frequency. The depth of modulation is proportional to the field strength. Since the bandwidth of the detected signal exceeds that of conventional transient signal digitizers, we use a prototype High Speed Multichannel Data Recorder that we have developed. This instrument employs a high bandwidth streak camera to record the sensor signal in real time, without the need for downmixing. Because it is small and dielectric, the sensor is non-perturbing. Its input and output leads are fiber-optic and therefore immune to electromagnetic interference. Because the sensor is broadband, we can Fourier transform the pulse and obtain a power spectrum. We discuss the construction and use of this sensor and present data showing the direct recording of a 3 GHz microwave pulse on the High Speed Multichannel Data Recorder. We also discuss the use of multigigahertz analog laser diode transmitters in extending the bandwidth of conventional pulsed microwave diagnostics.

The one-dimensional nature of the optical fibre offers the possibility for its use in a range of distributed measurement sensors. Thus, in addition to all the accepted advantages offered by optical fibres in the sensing function, one has the advantage of a knowledge of the spatial distribution of the measurand. Methods so far explored for implementation of both intrinsic and extrinsic distributed systems are discussed, and prospects for the future are reviewed.

Optical fiber waveguide imbedded between plys of graphite-epoxy composite materials is used to determine the dynamic three-dimensional strain within the materials by OTDR and subsequent signal processing. This paper describes methods used for imbedding optical fiber within composites, results of the fiber measurements of internal strain location, and inherent limitations on the spatial, temporal, and strain amplitude domain resolutions of the technique.

A novel optical time domain reflectometry technique is described which uses the Raman Spectrum of backscattered light to give the temperature distribution along a conventional optical fibre. Temperatures from 77K to 800K can be measured. Spatial resolution is better than 3m, with sensor lengths of up to lkm.

A sensor system where a number of Fabry-Perot interferometer sensors are placed in series on a single-mode fiber is discussed. Each Fabry-Perot sensor is resonant within a unique bandpass of optical wavelengths and transmits with small attenuation at all other wavelengths. Fiber Fabry-Perot interferometers with narrow-band resonances are formed by placing a matched pair of bandpass reflectors on the fiber. The sensor system has three major subsystems: a swept frequency laser, frequency selective Fabry-Perot sensors, and demodulation hardware. A grating formed by holographic process is placed in the evanescent field to produce a frequency selective reflector. Individual sensors are polled by a frequency swept laser. As the laser wavelength is scanned over the resonance bandpass of the first sensor, Fabry-Perot fringes from the first sensor are read out. As the laser continues to sweep its optical frequency, the first sensor's gratings no longer act as reflectors; the sensor becomes transparent to the optical probe. After a sufficient optical wavelength guard band, the resonance band of the second sensor is reached and fringes from the second sensor are read out. Fabry-Perot phase and fringe order information are recovered by a combination of optical and electronic signal processing. The optical processor is a second Fabry-Perot interferometer which is used as an analyzer to aid recovery of the phase information.

Optical frequency domain reflectometry (OFDR) shows promise as a diagnostic tool for high resolution ranging in fiber optic networks/integrated optic devices, and for high resolution distributed fiber optic sensing. Chirped semiconductor lasers may be employed to obtain submillimeter spatial resolutions. This paper discusses applications, some signal processing aspects of this technology, the potential, and actual performance of some experimental laboratory OFDR systems.

A review of present status and some future trends in single-mode and multimode-multicore optical fibres (MOFs) for sensors, buses and instrumentation applications is presented, Among the fibres, components, systems and problems to be aisc.Assed are: three and four core quasi monomode fibres, some characteristics of interaction of MOFs with external physical fields, a new kind of t2,tnomission called Core Division Multiplexing (CDM) and sensitivity of MOF based optical fibre interferometers, Performance characteristics of the different MOF based devices are summarized and compared.System requirements and some future trends are also presented and debated.

An optical magnetometer, which is capable of measuring static as well as dynamic magnetic fields, is presented. An all-fiber Marc-Zender interferometer, powered by a laser diode, was used to measure the strain of a metallic glass strip. Using a magnetic feedback technique and an AC-magnetic bias field, a minimum de-tectable field of 5pGauss in 1 Hz equivalent noise bandwidth was achieved. The magnetometer responds linearly from 0 Hz to a 3 dB bandwidth of 253 Hz and has a dynamic range of more than 100 dB.

The directional properties of a metallic glass sensing element have been investigated using an all fib pr Mach-Zender interferometer. A magnetic field sensitivity, at low frequency, of 2x10-te in the direction of the element was obtained with cross-sensitivities in the orthogonal directions being in the 0.1 Oe range.

Using a loop antenna in series with a semiconductor laser, am optically coupled electromagnetic field probe has demonstrates sensitivities better than 3 iiV/(m.Hz1/2). The probes outside dimensiOns are equal to 5.7 X 5.7 X 1.3 cm j. It can be used to measure fields with frequencies as high as 2 GHz. The dynamic range is estimated to exceed 6 orders of magnitude for incident microwave powers.

A new fiber-optic temperature sesnor using a polarization maintaining fiber and a transverse Zeeman laser based on heterodyne interferometry has been developed. The temperature variation is detected by coupling two orthogonal linear polirization components of a laser beam, each differently phase-modulated during transmitting a birefringent single-mode polarization maintaining fiber. A transverse He-Ne Zeeman laser was developed to achieve heterodyning demodulation of the phase-shift caused by the temperature of the fiber. Experimental result demonstrates that this sensor has the temperature resolution of 0.0032°C with a very wide dynamic range. Besides, this fiber sensor has the advantages of simple construction and ruggedness against pressure turbulence.

A requirement to measure' temperature' in 1.2 Tesla magnetic fields by a. reliable, low resolution, permanently calibrated instrument. has led to the development of an all-dielectric sensor'. It is composed. of fiber optic communication line, gradient index lenses and a temperature sensitve narrow band-pass, interference filter. The spectral location of the filter passband is temperature dependent and was observed, as a large modulation of transmitted laser power on the filter edge. The resolution of a. sensor based on the spectral mean of transmitted light was better than 5 degrees celsius from 20 to 150 degrees celsius. A. line source in a. wavelength region away from the filter resonance is used for continuous spectrometer calibration. The multiplexing of sensors, is described.

Some glasses and other materials are optically active only in the presence of a magnetic field where the plane of polarized light is rotated. This property is called the Faraday effect. The rotation angle/unit of magnetic field and optical path length is called the Verdet constant (V). The rotation angle 8F defined as @F = V iHdL where H = magnetic flux and L = fiber length.

The standard fibre optic reflectometer appears to have been overlooked as a means of making a fibre optic temperature sensor in favor of other more complex arrangements. The present sensor uses temperature induced variations of the refractive index of a captive volume of liquid at the end of an optical communications grade multimode fibre. The geometry of the sensing fibre tip is as simple as it is possible to imagine i.e. a flat, cleaved face, normal to the fibre axis. A short theoretical basis of the physics of the sensor will be presented. Systems constructed in both the 840 nm and 1300 nm wavelength regions are discussed. The linearity, noise characteristics, sensitivity, time response, temperature range and stability of these sensors have been examined.

The standard fibre optic reflectometer has been reexamined. Reflectometers have been configured to measure various physical parameters but the fundamental parameter that is sensed is refractive index. This study has focussed on the basic characteristics of this simple sensor, its linearity, its sensitivity and its potential problem areas when applied in real world situations.

In this work a fibre optic temperature sensor, tested in the range 20-130°C, using the change in the absorption characteristics of a doped glass with temperature is reported. A novel referencing technique using fluorescence of neodymium in glass to allow for variations in the input light level is incorporated in the device and its applicability discussed.

The integration and standardization of optoelectronic components seem to lead to the next stage:3 of optical fibre technology development. Both processes concern components of normalized optical and electrical inputs/ outputs - as far as dimensions and signal formats are concerned - with very strictly stated mutual dependencies between two different levels of the signal /taking also internal hybrid feed-backs into account/. The work attempts to introduce into broad problems covered by mentioned two processes and is composed of three parts: a digest of the topic, presentation of main groups of hybrid optoelectronic components for optical fibre transmission and instrumentation systems and debate of experimental results. We have presented general assumptions and main directions of hybrid and then monolithic integration of optoelectronic components for optical fibre technology. Certain aspects of mentioned two levels of integration have been compared. An arbitrary classification of main groups of hybrid optoelectronic components /HOCs/ and devices has been performed, from the point of View of own laboratory experiments. The following groups have been distinguished among HOCs: multisegmental, multiple and hybrid photoemitters, hybrid photodetectors with with complex optical fibre cone or loop couplers and filters, photoemitter/photodetector coupled pair type of HOCs, and also integrated transmitters, receivers and transceivers for optical fibre transmission and instrumentation systems.

Several techniques to enhance the coherence.characteristics of semiconductor lasers are reviewed. Applications of these laser sources to optical fiber sensors, that is, a fiber-optic laser Doppler velocimeter (FLDV), an optical passive ring-resonator gyroscope (OPRG), and a fiber-optic time domain ref lectmeter (OTDR), are described.

Measurement of optical attenuance over long path-lengths and at relatively specific wavelengths, is facilitated by recent developments in laser-diode technology, compared to previous instrumentation methods. Substantial optical power may be coupled into low divergence optical beams and at higher power efficiency compared to other sources. Unfortunately, well-known characteristics of solid-state laser diodes predicate use of complicated bias and modulation stabilization methods to avoid both facet damage and operation below threshold over temperature extremes. Although temperature control of the laser emitter is possible to eliminate these problems and provide mode stabilization, system power efficiency is compromised. The accuracy of the aforementioned feedback methods is discussed relative to temperature effects within the optical and electronic portions of the system. Angular emission changes and wavelength/temperature coefficients of detectors used for feedback limit the accuracy attainable. Examples are given for a specific laser diode operating near 800 nm. Additional correction methods are discussed which result in improved stability without adversely affecting system power efficiency. Experimental verification and overall system accuracy are reported.

The overall gain Gz and frequency bandwidth aVy, of Fabry-Perot type semiconductor laser amplifier have been measured. From the equations of this type laser amplifier q= and 41)4 are calculated. The comparison of measured data and calculated values are discussed.

We describe a fast (35 ps or less), spectrally broad (at least 600 nm) light source for use in characterizing and calibrating photonics equipment. The spectral output of the source is described, and examples of its use are given.

Light polarising effects in "bow-tie" birefringent fibre are reviewed. This has led to the development of compact robust polariser devices as well as low-loss fibres which polarise the transmitted light c-Ter long distances. These components find immediate application in fibre sensors such as cn,, fibre gyroscope, where up to 62dB of polarisation extinction with less than 1dB insertion loss is typical for a fibre polariser.

High birefringence, polarization retaining single-mode optical waveguides have been developed for applications requiring stable performance when the fiber is coiled. Recent designs employing high-expansion aluminum-doped stress rods have demonstrated polarization holding parameters better than 6.0 x 10-6m-1 with little degradation of h-parameter or attenuation down to 2 cm diameter coil configurations.

A new analytical technique for analyzing microbending losses of step-index, single-mode fibers is reported. The technique is applicable to fibers with arbitrary N.A., large deformation periods and radiation escaping at arbitrary angles to fiber axis. Two dimensional fiber deformations can be studied and information on radiation loss, propagation directions and polarization content of scattered radiation can be obtained. The effect of fiber radius on radiation loss and the distribution of radiation power between different space harmonics is investigated. It is found that radiation loss depends strongly on fiber radius and that the maximum loss for different space harmonics occurs at the same radius. At the fiber radius resulting in maximum loss, the radiated power is sharply peaked around optimum period lengths for both fundamental and higher-order space harmonics. It is shown that the fraction of radiated power in a higher-order space harmonic can be larger than that in the fundamental space harmonic at large deformation periods. The results indicate that microbending sensors do not necessarily have to operate at the fundamental harmonic of deformation spectrum.

A new in-line single mode fiber optic polarizer based on the cut off properties of a waveguide is presented. Unlike previous evanescent field polarizers, the new device radiates the unwanted polarization directly from the core. Design features, testing and performance are briefly discussed.

Elliptical polarization maintaining single mode fibers were fabricated with both round and conformal elliptical coating configurations in order to externally identify the fiber axes. These fibers were then level wound onto various diameter coils and tested for polarization holding ability (h parameter). The test results are reported and an analysis is made of the effect of coating configuration and axial alignment on the state of polarization (SOP).

While applications for optical fiber multiply, the importance of factors affecting the reliability of the optical systems also increases. This paper reviews some of the significant cause and effect relationships that exist in this area.