The development of an optical system for space applications requires that careful attention be given to hardware design and testing. A procedure for developing and qualifying a laser intersatellite communications package is presented along with the derivation of specific levels used in the successful testing of its transmitter assembly. This general approach may also be useful for the development of other high-reliability optical systems.

Very low threshold current density (<50A cm-2, close to the theoretical limit), high quantum efficiency, high power output, low temperature sensitivity, and higher pumping efficiency of 0.98 µm wavelength InGaAs strained quantum well lasers, and very low amplifier noise close to the 3 dB quantum limit have made the 0.98 µm wavelength as the best choice for pumping Er3+-doped fiber amplifiers. Like any other semiconductor laser, these lasers also degrade, but no failure mode specific to these lasers has been observed despite a compressive strain of 1-3 x 10+10 dynes/cm2 in the active QW region. On the contrary, these lasers have immunity to sudden failure and for reasons discussed in the text they show signs of longer lifetimes than their AlGaAs/GaAs counterparts. We expect the 0.98 µm laser reliability to improve in the near future to a level comparable to any other types of semiconductor laser. Narrow far field, high power output in the fundamental transverse mode centered at 0.98 ± 0.005 µm, planarity of the structure for ease of mounting and better heat sinking, and long lifetimes are the major laser structure design considerations.

The mean time to failure (MTTF) for InGaAs planar photodiodes has been predicted to be 1014 hours at room temperature based on lifetests at elevated temperatures of 200, 230 and 250°C (and -12V reverse bias). This improved value is thought to be due to reductions in leakage current which lead to higher reliability. Significant reduction in background doping of the InGaAs absorption layer and mild doping (~2 x 1016cm-3) of the InP cap layer have led to lower leakage currents. The typical room temperature leakage current of a 300 um diameter photodiode is 300 pA @ -5V and a 25% increase in this value constitutes a failure. For InGaAs photodiode arrays, an additional criterion of failure, "popcorn noise" is introduced. Popcorn noise exhibits random charge (current) fluctuations in a p-n junction. The predicted MTTF for a 256-eLement In0.53Ga0.47As array is 108 hours for one diode failure and 3 x 109 hours for five diode failures. Undegraded operation has been observed with a group of In0.8Ga0 2As detectors (which absorb light out to 2.6 um) after 8000 hrs. @ 125oC.

A high temperature (200'C rating) fiber optic cable of fluorocarbon, silica- based glass, and polyimide coating, 100 um core was evaluated for Goddard Space Flight Center (GSFC) applications. Testing was performed to evaluate attenuation characteristics of the cables during environmental stresses and exposure to Co-60 gamma radiation. The cables passed environmental tests, but after irradiation failed the established delta limit of 3 dB at 10 krads for a wavelength of 850 nm and 100 krads for a wavelength of 1300 nm.

Mechanical stress on optical fiber must be low enough to insure that the fiber does not fracture due to static fatigue. In this paper sample data are presented to illustrate the calculation of design stress. The methodology is based on the concepts of linear elastic fracture mechanics, although a strictly empirical treatment of the data would yield essentially the same result. The calculation involves extrapolation of a plot of time to failure versus applied stress. It also requires extrapolation to low failure probability, as well as corrections for the amount of fiber under stress. The temperature and humidity are taken to be constant over the service life, and equal to the worst case field conditions. The calculations require both strength and fatigue data. The example illustrates the relative magnitude of the various terms in the equation for static fatigue lifetime, such as the term for applied stress, the term for failure probability, and the term for amount of fiber under stress. It also shows the sensitivity of the lifetime prediction to uncertainties in the various parameters.

In this paper we describe the development of an optical fiber ac voltage sensor for aircraft and spacecraft applications. Among the most difficult specifications to meet for this application is a temperature stability of ± 1 % from -65 °C to +125 °C. This stability requires a careful selection of materials, components, and optical configuration with further compensation using an optical fiber temperature sensor located near the sensing element. The sensor is a polarimetric design, based on the linear electro-optic effect in bulk bismuth germanate (Bi4Ge3O12). The temperature sensor is also polarimetric, based on the temperature dependence of the birefringence of bulk SiO2. The temperature sensor output is used to automatically adjust the calibration of the instrument.

Test and measurement of multiple port fiber optic couplers in the production and quality assurance environments raises many concerns in respect to repeatable data, time involved in the setup and alignment of the test equipment, and overall cost of the workstation. Historically, the protocol for the test procedure would involve

This paper will examine the problems and concerns of repairing fiber optic data links on carrier based Navy aircraft and will present the results of fiber optic splice testing that was performed aboard the USS Abraham Lincoln (CVN-72) in January 1991. Mechanical splicing of 50/125 micrometer fiber was performed at the various Navy maintenance levels in order to quantify the ef fects of the aircraft carrier environment on fiber optic splicing. Results, conclusions and recommendations will be given.

A computer simulation model represents the processes of heating a fused silica fiber and drawing it to form a taper. The model is a transient thermal and visco-elastic representation of an axial string of nodes that respond to laser heating and drawing in vacuum chucks. Preliminary sample simulation results are shown.

Since the light propagation property of the currently produced single mode optical fiber couplers has not become clarified, there are various problems with their production method, namely in terms of their operability, stability, reproducibility and durability. The main purpose of this paper is to perform quantitative experiment on the major elements which is thought to influence light propagation of thermally fused biconical taper single mode optical fiber couplers. Furthermore, this paper aims to clarify light propagation property of single mode optical fiber couplers by calculating light output using mode coupled theory, in attempt to improving their production method.

The construction and evaluation of single-mode optical fibre tunable couplers are described with the emphasis on the polarisation maintaining fibre devices. The couplers operate via an evanescent field coupling mechanism and are produced based on the polishing technique. General characteristics including polarisation property, wavelength tunability and limitations are described. Applications of tunable fibre couplers are discussed.

An all-fiber fused WDM for use with erbium doped fiber amplifier (EDFA) is reported. Besides operating on the principle wavelengths of 1480 nm and 1550 nm, it has an additional feature of operating at 1310 nm. This 1310/1480/1550 wavelength division multiplexer (WDM) finds its use with a hybrid optical-electrical amplification system. The three window operation in this device is made possible by using its quasi-sinusoidal coupling ratio (CR) dependence on wavelength. In this paper, we demonstrate a WDM which shows > 15 dB isolation, < 0.5 dB excess loss, and polarization sensitivity of < 1.2% at all the three wavelengths of interest.

The transfer of optical power between a fibre, side polished close to the core, and a multimode waveguide overlay is periodic in terms of variation of the input wavelength as individual high order overlay modes are tuned in and out of resonance with the fibre mode. The development and characterisation of such devices using polished glass, lithium niobate, and vacuum deposited overlays are reported here. It is concluded that this technology is capable of yielding rugged channel selection filters and wavelength division demultiplexers with losses of less than 0.2dB and wavelength selectivity down to a few nanometres.

The fused biconical taper process has been the technology of choice for fabricating a variety of passive fiber optic couplers. These couplers exhibit excellent optical and environmental characteristics. Most recently, this process has been used to fabricate tree and star couplers of various configurations: 1x3, 3x3, 1x4, 4x4 and 1x7 for both local loop and sensing applications. In this paper we report the development of broadband 1x3 and 1x4 couplers for applications requiring simultaneous transmission in both the 1300 and 1550 nm wavelength regions. The wavelength response, insertion loss and optical uniformity of these broadband couplers will be discussed. Their environmental performance will also be presented.

The fabrication of a device which operates beyond the cutoff of the antisymmetric supermode of a coupler is described. The result is a coupler, henceforth referred to as a Superflat™, which holds its coupling ratio to +/- 1% over the wavelength range of 1200 nm to 1600 nm, and yet exhibits losses as low as 0.3 dB. Applications in test and measurement, CATV, and as an all-fiber, fixed attenuator are discussed.

During the past year Gould has developed the means of manufacturing truly fused 1x4 couplers via the fused biconical taper (FBT) process in a reliable and cost effective manner. In this paper various practical aspects of the manufacturing process will be discussed. The optical performance data such as uniformity, insertion loss, polarization sensitivity, and environmental stability data of these components as built in a production environment will also be presented.

A self-consistent computer analysis of beam propagation in a twin-ridge waveguide coupler with distributed gain is presented. The structure is assumed to be fabricated in double heterostructure material which is electrically pumped to provide the gain. Non-linear coupling between the ridge-guides occurs because of the effects of lateral carrier diffusion and stimulated recombination on the lateral complex refractive index profile of the structure. The paper uses the beam propagation method to examine the longitudinal development of the optical field distribution in the coupler for a range of injection current densities.

The evanescent field coupling between an optical fibre, side polished close to the core, and a high index multimode waveguide overlay is periodic in terms of the overlay index as individual high order modes are tuned in and out of resonance with the fibre mode. By biasing close to a resonance such a response is suitable for the implementation of an electro-optic modulation function for in line encoding. In this paper the demonstration and characterisation of an in line optical fibre modulator using lithium niobate in the role of the overlay is reported. Such devices do not require interruption of the fibre for component insertion and are thus mechanically robust.

It has been demonstrated that power (>95%) can be switched between an optical fibre, side polished close to the core, and a high index multimode waveguide overlay. Using lithium niobate sandwiched between optically transparent indium-tin-oxide electrodes in the role of the overlay, electro-optic switching has been observed. By applying a second polished fibre block to the top surface of the overlay, power may be switched between two fibres. This paper addresses such issues as insertion loss, switching voltage and on off ratios in these devices.

The characteristics and applications of an optical switch are described, which uses a thermo-optic effect in a Mach-Zehnder interferometer type waveguide device. One possible application is automatic loop 1 or loop C testing of OCUs or DSUs on an optical line for changes in applied electrical power, whose tests can be conducted including optical line loss.

Using the point-matching method a comparative study has been made of the propagation characteristics of a triangular-cored glass fiber waveguide which is loaded on one or two sides with a highly conducting substance, the remaining side/sides being adjacent to a dielectric material of lower refractive index than that of the core.

A theoretical analysis is performed of the frequency noise, relative intensity moise and frequency chirp of tunable two-section and three-section DBR lasers (LDs), taking into account the nonlinear gain compression effect. For a two-section DBR LD the frequency and intensity noise is shown to depend significantly on the tuning current, particularly at low frequencies (below the GHz range) and for low and moderate values of the grating coupling coefficient. For high values of this coefficient the tuning dependence is generally negligible when the tuning is performed only through the DBR section, but it becomes significant when using the phase control current in a three-section device. Except in the vicinity of a mode jump, the frequency chirp of a DBR LD is shown to have a little dependence on the tuning current. The possibility to measure the effective linewidth enhancement factor from the high-frequency behaviour of the chirp is suggested.

The waveguide characteristics of metal-clad ridge-waveguide (MCRW) lasers are analyzed by the equivalent current theory associated with the effective index method. The enhanced lateral mode confinement, and increased mode loss are calculated for different metals. All these results are in analytic form, which has not been published before and makes us easy to get the waveguide characteristics calculation. The optimum design of MCRW lasers is discussed by using these analytic formulas.

GalnAsSb/GaAlAsSb SAM APDs were fabricated and investigated. The GaAlAsSb solid solution of the "resonant" composition (x=0.04, Eg = ?0 ) was used in the multiplication region of the devices. Large ionization rate ratio (?/? =60) and low excess noise factor ( F=Mf f=0.2) was experimentally observed.

The high power and broad spectral output of superluminescent diodes (SLDs) are desirable for fiber optic gyroscopes, optical sensors and short to medium haul communications. Certain applications are sensitive to spectral modulation on the subnanometer wavelength scale where coherent interference can be a source of noise. We present a simple SLD design which eliminates the optical feedback within the chip normally responsible for spectral modulation. Although the design can be applied to conventional SLD wavelengths, initial device demonstration at 960 nm has been chosen to illustrate SLD operation in a materials system in which spectral modulation is particularly difficult to suppress. Ridge waveguide based SLDs suitable for coupling to single mode fiber have been fabricated. Typical output is 10 mW cw at 140 mA with a spectral width of 30 nm and less than 5% spectral modulation over a wide range of operating conditions.

The use of optical absorption to detect methane requires a suitable rugged source. An edge emitting LED suitable for use with single mode fiber systems, emitting at 1640nm is described. A coupled power of 130?W at 25°C has been demonstrated.

An optical transmitter is described which uses a commercial LED coupled to an external modulator to achieve a 1.25 Gb/s data rate. Both a Mach-Zehnder modulator and a reverse ?? directional coupler were evaluated for modulation of the optical signal. Analytical expressions are derived for the extinction ratio in each device as a function of spectral width of the source. Experimentally, both devices produced an extinction ratio > 20 dB with peak output powers of —20.1 and —23.9 dBm respectively. We estimate that by minimising losses in the system, peak output powers of —12.5 and —15.1 dBm respectively can be achieved with the two devices using the available LED. We also discuss design improvements which can reduce the wavelength sensitivity of the ?? switch and describe a drive circuit capable of extending the upper frequency limit of the current switch from 200 to 1250 MHz.

In a modern lightwave communication system, it is preferable to have a low dispersion penalty, long fiber span and a very high bit rate. There are many practical restrictions to achieve these targeted features. Consequently different approaches are available to optimise the operating conditions of the system. One of these limitations is the effect of the transit time in the photodiode on the performance of the whole receiver end that operates in multi-gigabit regime. Here in this paper we explore an approach to model the transit time within an optical receiver. This model used to formulate a moment generating function (mgf) which is later coupled within a Chernoff Upper Bound (CB) of the probability of error. Conditions are derived for reducing the effect of transit time, in the sense of minimising a CB for a Poisson channel. Firstly, a brief review of the role of the transit time on the speed of response of a photodiode is presented.

In this paper a method for determining the attenuation parameters of optical components is introduced. Measurements of insertion loss and return loss are performed by using an RF network analyzer with an appropriate optical test set. System performances and accuracy are evaluated in the time domain at ?= 1300 and 1550 nm wavelength. Measurements of various optical connectors are also provided.

This work presents the description of a very compact optical connector for coupling high-power laser radiation (Nd:YAG) to optical fibers. GRIN-rod lenses have been used because they have several characteristics (such as small dimensions, plane and parallel faces with focus near the exit face) which make them suitable for fiber components. A special coupling unit to connect the microlens with the fiber has been designed, thus obtaining a very compact and stable element. Furthermore, the insertion of a conventional prefocusing lens at the laser exit has been provided, in order to obtain better coupling efficiency and to increase misalignment tolerances of the GRIN rod-fiber component A theoretical analysis by means of an optical design program, together with the description of the experimental characterization of the coupling system, are reported.

A technology is described which allows singlemode and multimode optical fibers to be bent in radii less than 1mm without significant increase in loss or long term reliability. This technology is particularly suitable for the development of high-performance low-cost right- angle connectors for high-density patch panels and interconnects.

The increasing industry requirements for reduced back-reflection (also called return loss) from fiber optic connectors has required the connectorization and cable assembly manufacturers to develop advanced end finishes for singlemode connectors. Since most telecommunications systems use components from a variety of manufactures, the intermateability of the connectors from different vendors is a major concern. This paper presents the results of a study to measure this intermateability for singlemode FC style connectors

The developed underwater mateable fibreoptic connector prevents contamination of the optical coupling endfaces, withstands the hydrostatic pressure and provide optical alignment with a repeatability of 0,1 micron. Optical interfaces and high precision parts are protected by silicone grease, both in a mated and demated position. The measured transmission loss using single mode fibre is below 0,5 dB after ten matings in a mixture of water and 1% drilling mud. Hydrostatic pressure of 200 bars did not have any influence on connector performance.

Requirements to transmit electrical power and data across rotary joints have existed for many years. Traditionally, such functions were accomlished with electromechanical sliding contact slip rings. As technologies requiring the use of slip ring apparatus progressed,the inherent characteristics of electromechanical slip rings began to impose increasingly severe limitations on system performance.

Couplers will play an important role in the deployment of fiber-in-the-loop (FITL) systems. Corning is currently using a planar integrated optics technology to manufacture couplers that are well-suited for FITL applications.

A new method of pigtailing lasers produces an over-filled launch for bandwidth measurements without the use of a conventional mode-scrambler. Improvements are made over a conventional mode-scrambler system in both power coupled to the launch and improved reliability of the launched distribution. This technique utilizes a large-core/high-numerical aperture step-index multimode fiber to act on the high divergence angle of a laser diode. Within a few meters of the laser, mode power is uniformly distributed over more than 95% of the core diameter and fills 90% of the numerical aperture. This distribution then is transported, unchanged, to the fiber under test at the bandwidth launch. The fiber can be selected such that it efficiently over-fills the fiber under test, while not wasting power by launching into the cladding.

In this paper, fused biconical taper (FBT) hard clad silica (HCSR) couplers of varying port configurations will be characterized with respect to the parameters most important to system designers. Port insertion loss, uniformity, back reflection, launch conditions and the effects of environmental conditions will be addressed.

Singlemode, fiber optic wavelength division multiplexer configurations have been devised to provide low insertion loss over a wide optical bandpass with excellent near and far end crosstalk performance. This paper describes a compact high isolation device and examines the effects of high isolation WDMs in high data rate transmission system applications. The optical performance of these devices is discussed, as well as the results of environmental testing.

Experience with the optical fibre video-communications networks in France has highlighted the signifiance of optical fibre jointing techniques which require :

The temperature sensitivities of three common types of commercially available high- birefringent PM fibers (bow-tie, PANDA and elliptical core fiber) have been measured by a dynamic polarimetric method. The phase retardation of two eigen polarizations in these fibers have been obtained and compared, with the temperature changing from -10 °C to 100 °C. An oil bath was used to heat the fibers and dry ice to produce low temperatures. The results show that within the above temperature range, the phase retardation of these three fibers increase almost linearly with temperature. The temperature sensitivities of the bow-tie, PANDA and elliptical core fibers are 7.35, 7.57 and 1.1 rad/m °C, respectively.

A fiber—embeded optical isolator with in-line fiber polarizer is proposed and fabricated. The optical isolator consists of the in-line fiber polarizers, the crystal Faraday roator, and the fiber GRIN—rod coupling system. In the coupling system, the both conventional and polarization maintaining single—mode fiber have been utilized. Isolation and insertion losses at I. 5pm are 25dB and 4. 5dB, respectively.

Fundamental mode lasers with broad spectral emission will play an important role in laser projection techniques. The use of conventional single—mode fibers for such applications is limited by the wavelength dependence of their characteristics, i.e. mode radius, angle of divergence, and attenuation. Single—mode fibers with achromatic properties are thus required and we will describe two types, where either the mode radius or the angle of divergence is independent of the wavelength.

The testing and design considerations for direct detector fiber optic receivers of high sensitivity, can have a significant effect on the reliability and performance of these sub-systems. This paper includes a discussion of receiver state-of-the-art performance, component and design criteria, testing procedures and testing results of recently demonstrated, high sensitivity receivers.

The buffer coating of an optical fibre has long been regarded as a purely mechanical part of the fibre, with no part to play in the optical properties of the fibre or fibre systems, other than as a cladding mode stripper. It is therefore generally assumed that once light enters the buffer coating it is lost from the system. For example, most theories concerning bend loss from optical fibres make the equivalent assumption that the cladding has infinite extent

This paper is an update of one published with the same title and by the same authors in a special issue of “Optical Engineering” on optical fiber reliability in June 1991. It points out some recent major advances in two areas of importance to fiber strength and reliability. These are (1) the measurement and prediction of small crack velocities and thus long failure times, and (2) a consideration of the minimum fatigue rate possible in an hermetically-coated fiber.

An engineering methodology for estimating the mechanical reliability of optical fiber is being developed within a fracture mechanics framework. The model, one of several currently under development, expresses allowable inservice stresses as a fraction of fiber strength in a fatigue environment for a range of n values and fiber types. Of particular importance is the need for obtaining strength data on fiber lengths appropriate for the application.

A computer program is described that can analyze optical fiber fatigue data from a variety of fatigue experiments and for a variety of crack growth kinetics models and can then predict long term static fatigue behavior. The key feature of the program is its’ ability to analyze the statistical uncertainty in the predictions due to scatter in the data to which the models are fitted. It is shown that uncertainty in the lifetime predictions is often dominated by the uncertainty in the choice of the appropriate crack growth model. It is therefore concluded that a range of models should be considered when making lifetime predictions.

The strength degradation of three commercially available telecommunications fibers was evaluated after stress-free aging in 85°C liquid water, 85°C at 94% r.h., 85°C at 85% r.h., and 85°C at 60% r.h. Interim results show that the three fibers show different aging resistances, depending on the environment. Strength loss of up to 50% after 45 days in 85°C water was observed. Atomic Force Microscopy was used to image the cladding surface, and estimate the strength determining flaw size. The data show qualitative correlation between strength loss and flaw size. While the mechanisms underlying stress-free crack growth are not well understood, strength degradation must be predicted, nonetheless, in order to ensure acceptable reliability for fiber-based systems in the outside plant.

An overview is given of what fiber optic standards are and where they are generated. Fiber optic reliability is particularly important because of traffic density and migration closer to the subscriber. Fatigue testing may be used to estimate long-term fiber reliability either in the form of a probabilistic lifetime for a known applied stress, or as a safe stress for a lifetime goal.

The long-term mechanical reliability of optical fiber in connectors and splices will be determined by the magnitude of the stress on the fiber, the operating environment, and the size and geometry of the flaws in the fiber. Examples which demonstrate the generation of fiber damage when using conventional fiber termination tools, techniques and components are given, and the effects of interaction between the extrinsic flaws generated and fiber failure are shown. Problems associated with making realistic, lifetime/reliability predictions are reviewed.

The reliability of passive optical branching devices continues to be studied within the optical communications industry. This paper will discuss a methodology for characterization of device reliability from multiple facets.

A rugged simplex hermaphroditic connector has been developed for use in tactical fiber-optic applications such as radar and radio remoting, and various robotic systems. The single-terminus connector is intended for use wherever bi-directional transmission is required. It was designed to operate while meeting severe environmental and mechanical conditions experienced in the field. Both multimode and single-mode designs of the connector have been developed. Connectors have insertion loss of less than 1 dB when installed on either 50/125 pm multimode fiber or single-mode fiber. In addition to low loss and ruggedness, connector design features include cable retention hardware which requires neither special tools nor adhesives, waterproofing seals, and ease of cleaning without special kits. The connector was designed to accommodate existing tactical cables whose diameters range from 2.5 to 4.0 mm, and is capable of withstanding tensile loads up to 1335 newtons. Operating temperature range is from -46°C to 71°C; storage temperature extremes are -57°C and 85°C. The new connector is small, being only 1.4 cm in diameter and 8.6 cm long, including bend limiter. It weights less than 30 gm. A complementary bulkhead receptacle is equally rugged and may be mounted on panels up to 6.4 mm thick. EMI shielding has been incorporated in the unit.

A new method based on the fiber microdeformation theory and image processing techniques has been developed to estimate splice losses of single-mode fibers for fusion splicers. The method is to be found more accurate than the conventional butt-joint approximation, especially when the core deformation is relatively large near the splice point. More than 2000 splice tests have been made. Correlations between the estimations and the measurements under different conditions are illustrated.

Engineers are commonly tasked with doing qualification and quality assurance testing on large numbers of fiber components simultaneously, such as in long term environmental tests. The use of seperate, discrete tests sets for each component is neither economical nor sufficiently accurate. An automated approach using large Multi-Channel 1xN Switches with integrated GPIB software is described.

A major factor that determines the reliability of silica optical fibers in high temperature environments is the nature of the coating material and process. We have demonstrated coating silica fibers using dc planar magnetron sputter deposition. A unique feature of this method is the ability to hermetically coat fiber with high temperature metals that are impossible to deposit by conventional fiber coating processes. Such coatings are deposited uniformly in thickness with relatively high efficiencies. The results obtained with adherent, pinhole-free copper coatings indicate that the process is suitable for on-line coating of optical fibers as they are drawn.

High reliability and low maintenance are critical attributes of optical cable. Considering the service environment, we can predict some of the possible failure modes in optical cables and develop performance requirements and testing programs for them. However, it is unrealistic to expect that all modes of failure can be anticipated and understood quantitatively. Sometimes the cause of failure is obvious, but at other times the cause of the failure is poorly understood and is worthy of further investigation. By conducting several post-mortem analyses, we have gained an improved understanding of potential failure modes.