Fiber Optics is quickly becoming the preferred media for tele-and data communications, including LANs. The demand generated by the advantages of using glass fiber for information transmission has fueled the rapid development of fiber-optic components for a variety of applications. In particular, there are several types of optical couplers now available in the expanding fiber-optic components market.

The waveguide modes in a linear multimode fiber taper with a step-index profile are analyzed. Formulas and graphical results are presented for the changes in the mode orders of the guided modes with respect to changes in the physical parameters.

Fused biconical tapered (FBT) fiber optic star couplers have been used in a variety of applications at the Nevada Test Site to provide increased signal dynamic range for recording devices. Problems which were observed resulted primarily from the modal selection pro-cesses which occur in FBT couplers. This paper describes the results of work performed to characterize a new type of splitter for the same applications. The new splitters, obtained commercially, were manufactured using reflection techniques rather than the FBT approach. The splitters exhibit virtually none of the modal problems inherent in the FBT couplers.

Three new fiber-optic components are described: an in-line filter, an optical switch, and an in-line attenuator. The in-line filter inserts an optical filter into any fiber line containing a connector while imposing very little cost in additional power loss. The optical switch allows a single output fiber to transmit input from one of two different fibers and permits switching back and forth between the input fibers as needed. The in-line attenuator attenuates signals in fiber lines over a large range of about -30 dB with infinite variability. All three components are rugged, reliable, accurate, and inexpensive. They were developed for the prompt diagnostics used on underground nuclear tests and have successfully performed in this harsh, demanding environment.

The environmental performance of optical couplers, in this case fused biconic taper (FBT) optical couplers, is strongly a function of the packaging technology used to isolate the glass taper region from mechanical stress and contamination. Low thermal expansion metals and glasses have been used successfully as substrates in packaging FBT couplers. The development of a packaging design utilizing injection molding technology provides a low cost alternative to glass or metal packaging designs. A high performance liquid crystal polyester resin, *Vectratm, produced by Celanese Specialty Operations was chosen for this application. Over 100 couplers, utilizing this packaging technology, were environmentally tested under conditions of temperature cycling (-50°C to +85°C), temperature aging (85°C, 1000 hours), humidity (95% @ 65°C) and vibration/shock (2g's, 15g's). The tests were conducted in accordance with MIL-STD 810C. The couplers tested were three port devices using 50/125 micron fiber and a splitting ratio of 1 to 1. The couplers were fabricated at Phalo/DCC, Manchester, NH. The results of the environmental testing indicate that couplers manufactured with this packaging technology are reliable components capable of surviving harsh environmental service conditions.

A 12-channel Littrow-type wavelength division multiplexing coupler has been developed.[1] This coupler exhibits a maximum insertion loss of 10 dB per mux-demux pair per channel. Crosstalk isolation for seven channels is at least 25 dB and on the remaining five channels at least 20 dB. Near end isolation is at least 27 dB. This coupler was tested over the temperature range of 00 C to +40° C with less than 1 nm change in coupler response.

A six-channel Littrow-type wavelength-division-multiplexing (WDM) coupler that uses light-emitting diode (LED) sources has been developed. This coupler is bidirectional and exhibits 19.4 dB insertion loss per mux-demux pair per channel and at least 25 dB crosstalk isolation.

A four channel bidirectional wavelength division multiplexing transmission subsystem, including a single channel fiber optic rotary joint (FORJ), was fabricated and characterized. The performance of all the subsystem components is reported over a range of environmental conditions including temperature, shock, vibration, and humidity. Detailed data describing the optical properties of the multiplexers/demultiplexers is correlated with mathematical models representing theoretical multiplexer/demultiplexer performance. The overall system performance is reported in terms of channel losses, channel isolation, BER, and data rate.

A diffraction grating etched on the thinned cladding of a single-mode optical fiber offers the convenience of a compact, self-aligned, high-data-rate, wavelength-specific coupler. Various possible arrangements could permit detection or insertion of single- or multi- wavelength signals on a fiber bus. We demonstrated the fabrication of a chirped grating on the cladding of a single-mode fiber by holographic exposure of photoresist followed by argon-ion etching of the fused silica cladding, resulting in grooves with a depth of about 50 nm. This demonstration was done both on the cladding (where coupling to the core would be negligible), and on fibers etched close to the core. Recent work by others has demonstrated the requisite polishing techniques to obtain evanescent-wave coupling of the grating to the fiber core. Our calculations of expected diffraction efficiency generally agree with recently published experiments.

A field installable, low loss single mode fiber optic connector has been developed. A post-assembly cleaving tool and plastic captivator permit assembly of the connector in less than 5 minutes. Floating and ultra precise alignment sleeve and ceramic capillary provide losses less than 1 dB and repeatability less than 0.3 dB.

Over the past three years, GTE Fiber Optic Products has been conducting extensive environmental tests on the Elastomeric Splice to verify its performance in the harsh conditions encountered in the field. These tests include thermal cycling from -40C to +70C, fungus resistance per MIL-STD-810C (Method 508.2), heat/material aging based on activation energies, and blind vs. optimized loss. The results of these tests, which are presented herein, sub-stantiate that the GTE Elastomeric Splice is a proven alternative to fusion and other mechanical splicing systems for both permanent installation as well as emergency repair of multimode and singlemode fiber optic installations.

Numerous technical papers have addressed the design (precision alignment) concepts employed within Fiber Optic connectors. Manufacturers have expounded upon the relationship of lateral, gap and angular misalignment and the resulting coupling loss.¹ These loss mechanisms are within the control (and are the responsibility) of the manufacturer, yet he cannot completely control the optical performance of his product. The total power coupled (between two mated fibers) is also a function of certain fiber parameters.

Loss at any connection between two fibers can be attributed to two distinctly different mechanisms, instantaneous junction loss, and downstream transient loss. This paper discusses the use of short and long measurement conditions to separately identify these losses and the implications for system design with LED sources.

Optical fiber directional couplers fabricated by fused biconical-taper technology have found widespread use in optical communications transmission equipment, in optoelectronic instruments and sensors and in the laboratory proper. Such a broad range of applications is a direct result of the versatility of the biconical-taper approach to the implementation of various types of spitter devices, manifest by the impressive range of high-performance devices that can be made with comparative simplicity using any type of silica fiber, specifically multimode step-or graded-index fiber and monomode polarization-perserving or telecommunications fiber. Devices that have been fabricated from multimode fiber include four-port directional couplers, star couplers with 400 and even more ports and power combiners - the latter using special techniques to ensure the required asymmetric coupling. Notably, combinations of such devices have been successfully incorporated into star-, linear-and hybrid-topology fiber-optic data buses. Four and six-port directional couplers have been made from both monomode polarization-maintaining and standard fiber designed for telecommunications applications. As well, a biconical-taper monomode optical fiber splitter having a continuously variable coupling ratio which can also be operated as a mechanically activated optical by-pass switch for use in fiber optic local area networks has been demonstrated. Recent innovations include a tuned-port low-mode number device that shows very strong asymmetric coupling. In this paper the devices that can be made using fused biconical taper technology will be classified and their operating principles reviewed. Device properties will be discussed, where possible with reference to fundamental optical characteristics of optical bicones, and techniques for tailoring these properties to specific applications, such as wavelength division multiplexing will be explained. Also potential sources of noise arising from the use of monomode and multimode splitters in combination with lasers will be identified. Finally applications of these devices that are either unique or of general interest will be surveyed.

A method of tuning wavelength division multiplexers (WDM) for two arbitrary wavelengths has been developed. The resulting fused single mode WDM's show low insertion loss, <0.5dB, and high isolation, >20dB.

In this paper we describe an in-line single-mode fiber optic wavelength division multiplexer/demultiplexer designed to operate at 1.32 um and 1.55 um. This device was fabricated using evanescent wave coupler technology and consequently exhibits an insertion loss on the order of 0.05 db and a high degree of stability with regard to changes in temperature and input polarization. As a demultiplexer, the device provides wavelength isolation of 16 db at 1.32 um and 18 db at 1.55 um, both of which can be increased to greater than 40 db with the addition of simple edge filters.

Single-mode fiber couplers commonly are used in single-mode systems and fiber sensors to distribute and recombine optical signals. A widely used method for making single-mode fiber couplers is the fused-tapered technique.1'2" The equations that describe the coupling between tapered fibers require numerical evaluation. This requirement makes it difficult to predict the coupler response for different fiber parameters and taper geometries. The simple equation derived in this paper describes the coupling of power between two fibers and easily relates coupled power to the fiber parameters and taper geometry.

Fused, polarisation maintaining, evanescent-wave couplers have been fabricated from D-fibre. Coupling is controlled by a core diffusion technique which we call "diffusion tuning". Losses lower than 0.1 di! and polarisation extinction ratios as high as 30.6 dB have been observed. The couplers are highly stable, intrinsically robust and have the potential of being made very small in size.

Advanced single mode fiber sensors have been the subject of continued research over the past few years. Of particular importance has been the trend toward the use of highly bi-refringent single mode fibers. High birefringence fiber, while simplifying sensor design, complicates the design of system components such as couplers. In this paper the development of single mode polarization maintaining couplers is presented.

Until recently, single mode couplers were laboratory curiosities. Now, however, several companies offer high quality couplers as commercial products. Improvements in coupler manufacturing have been made, on a regular basis, to the point where 50% couplers with less than 0.5 dB loss are routinely available. Generally, these couplers are fabricated by hand, a, process which is inefficient, in terms of the consistency of the couplers fabricated and extremely labor intensive, thereby limiting total output. In this paper, we discuss an automated single mode coupler facility. This assembly system has the advantages of high yield, reproducible coupling ratio and loss values, and high volume output.

An automatable mass production system capable of manufacturing low loss (less than 0.1 dB) fused single mode fiber optic couplers at a rate in excess of 30,000 pieces per work station year has been developed. The design requirements and limitations observed in the initial development of a manual version of this system are discussed. Integration of users optical and mechanical requirements, optical fiber design, and coupler manufacturing tooling is an important goal in the effort to reduce costs to large volume users.

When the end of a single-mode fiber is polished and placed in an index-matching liquid, a reflection will occur. Its amplitude depends on two factors: (1) the difference between the liquid's refractive index and that of the fiber and (2) the polishing procedure used. By proper choice of both, the end-reflection can be reduced to below -60 dB. When two well-polished fiber ends are joined together with a small, liquid-filled gap between them, the resulting reflection will be the coherent addition of the two individual end-reflections. By adjusting the gap, this reflection can be made either greater than or less than the indi-vidual end-reflections.

A new single-mode optical fiber splicer using a direct core observation has been developed. This splicer can both align the core axes of optical fibers and estimate splice losses by means of image processing. Thus, with this new splicer, only one work site is required for splicing in the field.

That low loss demountable multimode connectors can be produced using multiple ball fibre centering and biconical plug alignment is well established. These principles have been applied in the development of a connector for use with single mode fibre with good results. This paper describes the design and development process and presents results showing that high performance has been achieved without sacrificing strength, practicability, producibility or reliability.

A new plastic connector was developed for a 200/250 micron multimode fiber that does not use epoxy, nor needs polishing to complete the assembly, hence termed epoxyless and polishless connector. The insertion loss for a mated pair had a mean value of 0.93 dB and the time required to assemble this connector to a cable was less than two minutes. When subjected to environmental testing the connector did not exhibit any deterioration in perform-ance.