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spring 1998 logo1998 MRS Spring Meeting & Exhibit

April 13 - 17, 1998 | San Francisco
Meeting Chairs: John A. Emerson, Ronald Gibala, Caroline A. Ross, Leo J. Schowalter

Symposium DD—Reliability of Photonics Materials and Structures


Mitsuo Fukuda 
NTT Opto-electronics Labs 
Kanagawa, 243-01 JAPAN 

Charles Kurkjian
Bell Communications Research
Morristown, NJ 07960

Ephraim Suhir 
Bell Labs, Lucent Technologies 
Rm 1D-443 
Murray Hill, NJ 07974 
Proceedings published as Volume 531 
of the Materials Research Society 
Symposium Proceedings Series.

* Invited paper

Chairs: Mitsuo Fukuda and Ephraim Suhir 
Monday Morning, April 13, 1998 
Salon 14
8:30 AM *DD1.1 RELIABILITY CONSIDERATIONS AND RESULTS FOR WAVEGUIDE COMPONENTS AND PACKAGED DEVICES. Philip J. Anthony, Lucent Technologies, Microelectronics Group, Bell Labs, Breinigsville, PA. 

Advances in optical networking are at last providing a need for more advanced photonic components such as integrated waveguide devices for dense wavelength division multiplexing. The rapid introduction of new technology to commercial systems must not neglect a thorough assessment of the reliability of the base components, any hybrid integration, and the packaging. Three examples will be discussed that involve three separate, non-semiconductor material systems. The diverse nature of the problems encountered will be explored with the intent to extract the common features. The first example will explore a rejuvenated technology, high-speed litium niobate modulators. Advances in materials preparation have made the die-level component extremely stable to environmental changes and to aging. The packaging, however, poses unique challenges, e.g., hermetic assembly using polarization maintaining fiber. The second example with look at present and future extensions of silica-on-silicon waveguide technology, including arrayed waveguide grating routers. The last example will show that advanced materials technology can recast and simplify the packaging considerations for relatively mature technologies such as optical isolators. 

9:00 AM *DD1.2 
CURRENT ADVANCES OF THE DEVELOPMENT OF MATERIALS IN THE FIELD OF WIRING IN JAPAN. Seiji Takagi, Nobuhisa Ishii, Dai Hashimoto, Furukawa Electric, Optotechnology Laboratory, Chiba, JAPAN 

Two of the advances are introduced as new movements in the material developments. One of them is that of the wiring materials used for the new access networks, on which much efforts have been made to achieve economical and reliable networks to subscribers and the other is the plastic optical fiber to be used mainly in the premises as a base of multimedia infrastructure applicable for data and image transmissions. As for the former subject, novel materials and the manufacturing processes are applied to achieve the above problems, including a multi grooved slot for the accommodation of large number of the fibers over the 1000 cores in the cable of small diameter, or foamed fiber jacket which enables easy removing etc. As for the plastic optical fiber cable, a fiber of polycarbonate resin are newly developed by application of partial fluorination technique which enables the transmission of 200 Mbps over 50M what is suitable for the construction of economical and reliable network in the premises or offices. The fiber allows the construction of economical networks by using the LD of 730-820nm, meeting with the wavelength of LD of conventional CD, and features high temperature proof characteristics which enables universal use in the premises or factories. 

9:30 AM *DD1.3 

In this talk we present field data from failures related to materials and devices that are the building blocks of optically amplified dense-wavelength division multiplexed (DWDM) transmission systems. A DWDM transmission system consists of at least three distinct components: an optical multiplexer, one or more optical fiber amplifiers (OFAs), and an optical demultiplexer. A tandem arrangement of these components performs the function of up to 32 independent high speed optical communications channels (about 2 million phone calls) over a single fiber link. Of these components, OFAs are considered the workhorse of this new technology, and, as with any new technology, their reliability is the focus of considerable attention. Commercially available OFAs are erbium-doped silica or fluoride fibers that operate in the 1550 nm optical communication window. Such OFAs consist of an active Er-doped fiber and pump laser(s) that collectively are referred to as the gain module, passive optical components used for routing, and electronic components for monitoring and operational support. We present the result of the failure analysis for each part as well as their role in the failure of the OFA. Using the data from systems deployed in the field, we summarize the history of failures of OFAs and other components and discuss their impact on the reliability of the DWDM system as a whole. From a material, packaging and system integration point of view, we address the reliability merits of different designs that, by and large, perform the same overall function. Finally, we shall outline how network providers that deploy such DWDM systems would benefit from a manufacturing strategy that incorporate reliability in its initial steps starting with the materials and packaging needs. 

10:00 AM DD1.4 
CRITICAL ISSUES IN THE MECHANICAL RELIABLITY OF LIGHTGUIDE FIBERS. C.R. Kurkjian, Fiber Media and Components Group, Bellcore, Morristown, NJ. 

While a great deal of work has been done to understand the mechanical properties of silica-based lightguide fibers, many fundamental questions remain unanswered. In particular there are questions which are critical to our ability to predict fiber lifetimes. Perhaps the most important of these are: 
1. What is the detailed character of the lifetime curve? 
2. Do fatigueand ageing limits exist? 
While these and some closely associated questions, such as the character of the fatigue weakening curve and the value of the inert strength are important, another important question must first be answered. As is well-known, the strength of lightguide fibers is bi-modal, and while the strength of the high strength mode is usually reasonably constant and well-defined; the character and behavior of proof-test level fibers is not all understood. Thus it is important that we first of all characterize the most probable types of proof-test level flaws. Having done this we may then ask the other questions posed above. In this paper we will discuss these problems and suggest techniques to evaluate them. 

10:45 AM *DD1.5 
LONG-TERM RELIABILITY OF OPTICAL FIBER & FIBER DEVICES. Mansoor A. Saifi, Peter R. Stupak, David K. Roland, SpecTran Corporation, Sturbridge, MA. 

World wide nearly 100 million km of optical fiber is deployed for telecommunication networks. The installations include terresrial, buried outdoor and inside building, and transoceanic. The reliability of these installations is assured through a combination of media (fiber and cable) reliability and network architectures. In addition recent explsive growth of high bit rate (tens of gigabit/second) high-density WDM systems utilize fiber based passive and active devices, such as couplers, fiber amplifiers and fiber gratings. This proliferation into active fiber devices, with additional processing steps, requires testing for long-term reliability of both mechanical and optical properties. Relaibility testing of active fiber devices is a new area of research and development. This paper will review material aspects, reliability criteria, and techniques used to measure and assure fiber and fiber based devices long-term reliability. 

11:15 AM *DD1.6 
RELIABILITY PHYSICS IN COMPLEX ASSEMBLIES. G.E. Derkits and F.R. Nash, Lucent Technologies, Bell Labs, Murray Hill, NJ. 

Reliability physics is mainly concerned with the potential for failure of a part or assembly as the result of ``natural lifetime in service'' or as accelerated by external threats such as temperature or humidity. The reliability of aggregates is usually treated as a function of the native reliability of the components. In this talk we discuss reliability physics of complex assemblies in which threats to reliability are generated by the interaction of several parts each of which may perform at an acceptable level under the most stringent testing. We discuss in detail a case involving, metallized diamond parts in hermetic packages which failed due to hydrogenation of thin metallic films by hydrogen exuding from the package material. In this cases, only parts already weakened by fabrication errors failed due to hydrogenation, further complicating the root cause analysis problem. This vžew of reliability may be fruitful or even necessary in the case of complex assemblies manufactured through the interaction of many parts and organizations. While the impact of threats generated internally in an assembly, or generated by the action of one part on another has been considered many times, it is generally looked upon in an ad hoc manner. The assessment of credibility of reliability estimates when a part is assembled from many piece parts made by organizations which have imperfect and incomplete communications is a significant problem in modern manufacturing. By treating reliability as inherently concerned with threats generated by the properties of the assembly itself and its components, we open up the possibility of creating tools which can recognize, calculate and check for the existence of higher order reliability problems in the design. Some partial tools for higher-order reliability checking, such as threat databases and recursive design rule checkers are discussed. 
Chairs: Charles R. Kurkjian and Shin Sumita 
Monday Afternoon, April 13, 1998 
Salon 14

1:30 PM *DD2.1 
FABRICATION OF LARGE SOL GEL BODIES FOR OPTICAL FIBER PREFORMS. D.J. Trevor, D.W. Johnson, Jr., J. B. MacChesney, S. Bhandarkar, M.P. Bohrer, J.W. Fleming, E. M. Monberg, S. Buratto, A. Harris, P. Mitra, and S. Ogawa, Bell Laboratories, Lucent Technologies, Murray Hill, NJ. 

A colloidal Sol Gel technology has been used to produce large optical fiber preform overcladding tubes. These tubes, which comprise 90% of the glass in single mode optical fiber, form a precise mechanical package around the light guiding core. Fabrication and the rapid drying of large (> 4 kg) extremely weak wet gel bodies without deformation or cracking are challenging aspects of developing this Sol Gel process. We have employed several innovative analytical techniques to develop a quantitative understanding of the drying process. Specifically, we have used MRI (magnetic resonance imaging), NIR (near infrared spectroscopy), pH, elastic modulus and shrinkage and correlated this data with weight loss and chemical formulation. These methods have improved our understanding of the distribution of water, its transport mechanisms and chemical bonding that evolves during drying. This has enabled minimization of drying stress and rapid successful drying without deformation. 

2:00 PM DD2.2 
EVALUATION OF B-VALUES OF TELECOM FIBERS, OBJECTIVES AND METHODS. Torbjoern Svensson, Telia Research, Network Research, Farsta, SWEDEN. 

The lifetime of optical fibers is limited. Most probably the fiber cables will fail due to accident, but attention must be paid to mechanical stresses and ageing of fiber. In the 70s was proposed how to predict lifetime with the use of a ``B-parameter''. At this time the magnitude of B could not be confirmed, and, in the 80s, B was to be abandoned for swiftly tamed equations in which B could be substituted. Occasionally it was argued, that life estimations might be too conservative, and a way ``back to B'' was retrieved. This research has been vivid since, and various sets of instructions for the use of B have been unveiled. Thus, the B-parameter of optical fibers can be used as a convenient tool for estimating the lifetime of fiber used in telecom, but a versatile tool (i.e., the parameter value) which properly fits into equations has proven difficult to achieve. A comparison between various methods indicates that high-speed mechanical testing is the most reliable way to confirm the B-value of coated fibre in environments similar to that of their anticipated network application. Congruent with this, in this paper will be presented experimental techniques currently in use at Telia for evaluation of the B-value of coated silica fibre for telecom applications. Also, a sighted ``dead-end'' due to experimental limitation on speed has been pushed forward by a new technique to be presented. Finally, reasons for, and advantages with testing of abraded fibre are discussed, and some data presented. 

2:45 PM DD2.3 
COMPARISON OF HYPERVELOCITY AND SUBSONIC IMPACT DAMAGE IN FUSED SILICA. J.E. Ritter, K. Jakus, S. Widjaja and R.P. Panat, University of Massachusetts, Department of Mechanical and Industrial Engineering, Amherst, MA. 

The fused silica windows in the Space Shuttle are subjected to hyper velocity impacts by microscopic space debris. On the other hand, fused silica devices and fibers in photonics applications are damaged by subsonic particle impacts, as well as by microscopic contact stresses. In this research both hypervelocity and subsonic impact damage is characterized and compared to that produced by a Vickers indenter. The corresponding fracture strength of both the impacted and indented samples is measured and post-strength factography is carried out to determine the strength controlling defect. An indentation fracture mechanics model is used to explain the subsonic impact results; whereas, a semi-empirical fracture mechanics model is developed for the hypervelocity impact results. 

3:00 PM DD2.4 
THE MECHANICAL BEHAVIOR OF OPTICAL FIBER AS A FUNCTION OF DEW POINT TEMPERATURE. Janet L. Armstrong, John Matthewson, Rutgers Univ, Dept of Ceramics and Materials Engineering, Piscataway, NJ; Charles R. Kurkjian, Bellcore, Morristown, NJ. 

The dew point temperature is defined as the temperature at which condensation forms from a gas containing moisture. This temperature is calculated from the amount of moisture, i.e. humidity, in the gas and its temperature. Dew point temperature is a measure of the water vapor reactivity that encompasses both temperature and concentration effects. The strength of optical fiber has been shown to have a dependence on the humidity and temperature of the test environment and the results of one published study implied that the strength can be expressed as a function of dew point temperature only. While attractive, this idea suggests the strength depends only on the thermodynamics of the water vapor/solid or vapor/liquid equilibrium and does not depend on the kinetics of the reaction between water and silica. In the work that we will describe, the strength has been measured at various humidities and temperatures in order to test the dependence on dew point temperature. The strength and dynamic fatigue data will be interpreted with a stress assisted chemical kinetics model. The degradation reaction order with respect to humidity at different air temperatures will be discussed. 

3:15 PM DD2.5 
MECHANICAL BEHAIVIOR OF OPTICAL MATERIALS BOMBARDED BY HIGH DOSE OF VARIOUS IONS. J.D. Demaree, J.D. Kleinmeyer, U. S. Army Research Laboratory, APG, MD; D. Ila, Center for Irradiation of Materials, Alabama A&M University, Normal, AL; D.B. Poker, D.K. Hensley, Solid State Division, Oak Ridge National Laboratory, Oak Ridge, TN. 

Silica and Sapphire crystals were implanted with keV Cr+, Ti+, Si+ ions as well as MeV Au, Ag, and Cu ions at both room temperature and at elevated temperatures in order to induce strong third order nonlinear optical properties. The implanted metal ions both during the implantation and after post annealing form metallic nano-clusters. We have already studied and reported their linear and nonlinear optical properties. In this paper, we will report the change in the surface compressive stresses and increase the shatter resistance of the material. The implanted materials were examined with Rutherford backscattering spectrometry and ion beam channeling to assess the composition and crystallinity of the implanted material. The effect of implantation on the surface roughness was examined using photon tunneling and atomic force microscopy. Finally, the effects of implantation on the mechanical properties of the material were measured by indentation techniques, including nanoindentation. The effects of both ion implantation and  and post-implantation annealing on the stress state and mechanical durability of the implanted crystals will be discussed. 

3:30 PM *DD2.6 

In order to achieve stable, high return loss in optical connectors, optical continuity is necessary, and this is primarily controlled by the endface geometry of the connector endface. The endface geometry parameters include radius of curvature of the polished ferrule surface, apex offset of the polished surface with respect to the optical axis, and the fiber position relative to the ferrule. Ideally, the cores of the optical fibers in mated connector plugs make and maintain physical contact throughout the temperature range of operation. Whether or not this is actually the case depends on the complex interaction of the connector materials, including the silica fiber, ceramic ferrule (typically zirconia), and the adhesive that fixes the fiber into the ferrule. The dimensional stability of these materials during aging, particularly in high temperature, high humidity environments, affects the ability of the connector plugs to maintain physical contact. Differences in the coefficients of thermal expansion of the different materials result in fiber pistoning relative to the ferrule, and adhesive degradation can result in fiber pushback into the ferrule due to adhesive creep. The degree of pistoning and pushback is strongly related to the glass transition temperature of the adhesive. In addition, zirconia ceramic ferrules sometimes show surface roughening and permanent deformation across the contact region of the mating surfaces. Finally, silica fibers can be attacked and dissolved through exposure to moisture and contaminants at elevated temperatures. This paper will describe how the endface geometry parameters affect optical performance, and how these parameters are in turn affected by the dimensional stability of the connector materials. Recent results on connector material reliability will be presented. 

4:00 PM DD2.7 
SILICONE OPTICAL ATTENUATOR ELEMENTS. William R. Lambert, Robert W. Filas, Bell Laboratories-Lucent Technologies, Murray Hill, NJ; and Wilton W. King, Bell Laboratories-Lucent Technologies, Norcross, GA. 

Lucent Technologies manufactures and markets a family of SC and ST singlemode attenuator products which are low cost and easy to use. The attenuator elements are available in the attenuation range of 3 to 20 dB and are housed in buildout barrels which snap into companion buildout blocks to form complete optical oouplings. The attenuator element is a 0.086-inch diameter thermoplastic material which, depending upon the attenuation, has a thickness from 0.006 to 0.065 inches. In order to meet the full range of customer performance requirements, the attenuators are fabricated using three different thermoplastic materials which provide a range of reflection and mechanical stability. An ideal attenuator element should not creep at tempertures up to 80ºC and would exhibit a reflection of less than -60 dB at optical telecommunication wavelengths. Commercially available thermoplastic materials cannot meet these requirements. We have demonstrated the feasibility of using silicone material as an optical attenuator element which offers improved reflectance, and being elastomeric does not permanently creep under load. The attenuation and reflection of thermoplastic and silicone attenuator elements during repeated mating/demating cycles were measured and compared. Similar measurements were also performed on attenuator elements which had been exposed to thermal aging at 85ºC for 1,200 hours. Thermoplastic creep during mating produced an indentation of the surface of the element which subsequently compromised the reproducibility of reflection in repeated matings of conventional products. Silicone attenuation elements exhibit recoverable deformation and hence the reflection during repeated matings was highly reproducible. An optical attenuator product employing a silicone element will provide reflection of from -55 dB to -65 dB, throughout the full temperature range of -40ºC to +80C characterstic of the most demanding telecommunications equipment environments. 

Chairs: Philip J. Anthony and Seiji Takagi 
Tuesday Morning, April 14, 1998 
Salon 14
8:30 AM *DD3.1 
CREEP-RESISTANT SOLDERS FOR PACKAGING IN OPTICAL COMMUNICATION DEVICES. S. Jin and H. Mavoori, Bell Laboratories, Lucent Technologies, Murray Hill, NJ. 

Packaging of optical communication devices involving the alignment of optical fibers or laser devices requires solder joints with strict dimensional stability under long-term service conditions. Because of their relatively low melting points and microstructural instability, many solder alloys are susceptible to creep deformation even at or near room temperature. In this work, we report on the structure and properties of new solder alloys with significantly improved creep resistance. These solders, e.g., based on Pb-Sn, Bi-Sn, Sn-Ag, and Au-Sn, contain extremely fine dispersoid particles, the presence of which restricts the microstructural changes and reduces the extent of creep deformation of the solders by as much as two orders of magnitude. Solder alloy fabrication, microstructural evolution and mechanical properties will be discussed. 

9:00 AM DD3.2 
MECHANISM OF MOTION OF AN OPTICAL FIBER ALIGNED BY A SOLDER DROPLET. Adam Powell, James Warren, National Institute of Standards and Technology, Metallurgy Division, Gaithersburg, MD; Christopher Bailey, University of Greenwich, Dept. Computing and Mathematical Sciences, London, UNITED KINGDOM. 

Solder is often used as an adhesive to attach optical fibers to a circuit board. In this talk we will discuss efforts to model the motion of an optical fiber during the wetting and solidification of the solder droplet. The extent of motion is determined by several competing forces, during three stages of solder joint formation. First, capillary forces of the liquid phase control the fiber position. Second, during solidification, the presence of the liquid-solid-vapor triple line as well as a reduced liquid solder volume leads to a change in the net capillary force on the optical fiber. Finally, the solidification front itself can make contact with the the fiber. Finite element models are used to calculate the time-dependent position of the solidification front and shape of the free surface. 

9:15 AM DD3.3 
THE RELIABILITY OF PLASTIC PACKAGING OF OPTOELECTRONIC DEVICES FOR TELECOM USE. Mitsuo Fukuda and Kuniharu Kato*, NTT Opto-electronics Laboratories, Atsugi-shi, Kanagawa, JAPAN *Nakagunn, Ibaraki, JAPAN. 

The degradation modes and reliability of laser diode and photodiode plastic modules are clarified for telecom use. Two kinds of plastic modules, rectangular and coaxial types, were developed and examined. The rectangular type is a plastic module consisting of a 1300 nm spot-size converted laser diode, a waveguide type photodiode, and a planar lightwave circuit (PLC). These devices were encapsulated with transparent silicone resin and then covered with black epoxy resin. The coaxial type is a pig-tail type laser module in which the laser is encapsulated on a TO-18 stem with transparent silicone resin or epoxy resin after the optical fiber is inserted into the fiber guide formed on the heat sink. These plastic modules were subjected to various kinds of environmental tests and long-term endurance tests. Under high temperature-high humidity tests (85C and 85%RH), the main long-term degradation mode for the devices was introduced by humidity, and the degradation rate tended to be high as the electrical bias on the laser diodes and photodiodes was intensified. The degradation rate of the photodiode was, for example, proportional to the square root of the magnitude of electrical bias. The final long-term stability was determined less by the device lives than by the optical connectors. Under temperature cycling tests (-40C to 85C), most of the modules operated stably for over 2000 cycles. During long-term operation, all of the modules operated stably without any rapid degradation. For the coaxial-type laser diode modules, stable operation was observed for more than 10000 hours even under conditions of 70C and 5 mW light output. Based on the clarification of the degradation mode and the reliability tests, the feasibility of the application of plastic packaging to optoelectronic devices for telecom use is clearly demonstrated. 

9:30 AM *DD3.4 
RELIABILITY OF GRADED-INDEX POLYMER OPTICAL FIBERS. Lee L. Blyler, Jr., Todd Salamon, Christine Ronaghan, Bell Laboratories, Lucent Technologies, Murray Hill, NJ. 

Opportunities exist for the application of newly emerging, low loss, graded-index polymer optical fibers (GI-POF) as high bandwidth media for data transmission in local area networks and for interconnection of large telcom switches and computer systems. These fibers are fabricated by distributing refractive index-raising dopants to form a core profile in a transparent glassy polymer fiber. The long term reliability of the GI-POF depends on the degree to which the dopant remains immobilized in the polymer glass in service environments. This paper presents a methodology for assessing the diffusion kinetics of dopants in polymer optical fibers and for relating these measurements to GI-POF reliability. 

10:30 AM *DD3.5 
LIFETIME AND RELIABILITY EVALUATION FOR POLYMERIC STRUCTURAL COMPONENTS. A. Chudnovsky* and R.S. Li**; *The University of Illinois at Chicago, Chicago, IL; **Automotive and Industrial Electronics Packaging, Motorola Inc., Northbrook, IL. 

Polymeric materials have been used in both rigid printed circuit board (PCB) and flexible PCBs in electronic packaging. They serve as load bearing and protective elements of the packaging structures. The industry faces various problems due to the loss of structural integrity associated with delamination, crazing, shear banding and cracking of the packaging. Reliability and life prediction of electronic products require fundamental understanding of material properties, manufacturing, service condition and theoretical modeling. Valuable experience in this area has been accumulated over the course of polymeric material applications and engineering structures. In this paper, we review more traditional, i.e., empirical methods as well as more advanced theoretical models for lifetime and reliability predictions. We are going to address the major fracture mechanisms in context of material morphology; structural dimensions environmental and loading conditions. An example of fatigue-crack-initiation mechanisms map illustrates a strong scale dependence of fracture phenomena. Thus the difficulties to translate experience accumulated in large-scale structure to small scale electronic packaging is also addressed. Special attention is drawn to the problems of multi-layer (laminated) structure fracture associated with interfacial crack as well as crack perpendicular to the interface. 

11:00 AM DD3.6 
RELIABILITY ASSURANCE FOR POLYMER-BASED THERMO-OPTIC PHOTONIC SPACE SWITCHES. Peter DeDobbelaere, Paul van der Wel, Ben Hendriksen and Rien Flipse, Akzo Nobel Photonics, Arnhem, NETHERLANDS; John Thackara, Ning Zhu, Janelle Freeman, Akzo Nobel Electronic Products Inc., Sunnyvale, CA. 

The operation of BeamBox solid state optical space switches is based on the thermo-optic effect in polymers. Their advantages include low driving power, digital switching, operation at both 1300 and 1550 nm windows, polarization independence, compact size no moving parts and fast switching (< 2 ms). The combination of these advantages makes those switches ideally suited for telecommunication applications such as optical cross-connects, wavelength add-drop multiplexers and network protection. High reliability is an important requirement for applicabillty of photonic space switches. The reliability target for BeamBox switches is a failure rate of a few hundred FITS for a lifetime of 20 years. To reach this target, an extensive reliability assurance plan has been implernented.