Leslie A. Reith

Powering the fiber loop optically-a cost analysis

Recent successes in transporting optical power near the 1-W level via optical fiber suggest that it may be possible to operate conventional telephone station sets using electricity derived photovoltaically from light in a fiber. The authors investigate the constraints on optical powering in fiber-in-the-loop (FITL) applications and assess its applicability in terms of end-to-end efficiency, loop length, and system cost. To make this assessment, they look at several different optical-powering system architectures and components vis-a-vis their cost-versus-delivered-power capability. Related issues such as safety and reliability are discussed. >

Relaxed-tolerance optoelectronic device packaging

The authors present an approach to single-mode fiber coupling which results in relaxed alignment tolerances during the package assembly process. The authors use a ball lens to couple from the optical device either directly to single-mode fiber (SMF), or indirectly to SMF through a fiber lens. The ball lens is aligned and mounted in the first assembly stage. The lens is aligned and fixed either mechanically or semiactively. In the second stage of assembly, the SMF is aligned so as to compensate for any small misalignments of the ball lens. The authors have achieved coupling efficiencies of 33-40 % with this coupling scheme. It has been used for coupling to standard laser diodes and to near-traveling wave optical amplifiers. Fiber-to-fiber gains of 8.5-10 dB have been achieved with packaged devices. The approach provides some versatility with respect to the placement of passive optical components inside the package. >

Demonstration of a photonic space switch utilizing acousto-optic elements

A multicasting photonic space switch is proposed and demonstrated utilizing acousto-optic Bragg cells in a free-space active splitting, passive combining optical architecture. A 4 x 4 switch is demonstrated at optical wavelength X = 0.83pm using Te02 Bragg cells. Fiber-to-fiber insertion loss of 15 dB, crosstalk of -20 dB, extinction ratio of >30 dB, and polarization sensitivity of 0.8 dB has been measured. Feasibility of switch operation at 1.3 m is also shown for Te02. Although this design was fabricated as a 4x4, expansion to 14x 14 can be accommodated with modifications to the optical element design. Calculations indicate that a maximum switch size of 20 x 20 and an insertion loss of 11 dB is possible, with crosstalk and extinction ratios greater than 30 dB.

Theory of LED coupling to single-mode fibers

A theory is developed to estimate the coupling efficiency and sensitivity of an LED coupled to a single-mode fiber. Our analysis is found to be in good agreement with experimental results.

Issues relating to the performance of optical connectors and splices

The performance of an optical splice or connector is defined by its insertion loss and reflectance. Insertion loss is well understood and primarily depends on the precision of the alignment of the two fiber cores. Reflectance performance is more complex; it depends strongly on the fiber separation and the refractive index of the media between the fiber endfaces, as well as the preparation of the endfaces. This paper describes the principle sources of loss and reflectance for both mechanical splices and connectors. The connectors considered are those with cylindrical-ferrule, physical-contact design and the mechanical splices considered are those which use either index-matching gels or adhesives at the fiber-fiber interface. The paper shows data illustrating typical performance parameters. Finally, some specific concerns that exist regarding reliability and intermateability issues are considered. These include the issue of fiber motion in connectors and particulate occlusion (e.g., voids, contaminants, droplets) in splices.

Coupling sensitivity of an edge-emitting LED to single-mode fiber

An edge-emitting LED coupled to a single-mode fiber shows increased coupling sensitivity to fiber displacement compared with multimode fiber. Sensitivity to lateral misalignment in the direction perpendicular to the junction plane of the LED increases by at least a factor of three, regardless of the coupling scheme used. A reciprocal relationship between peak coupling efficiency and sensitivity to misalignment is observed. We show that a previous theory for laser coupling can be extended to include edge-emitting LEDs, and that it predicts this relationship. The results for different coupling schemes are discussed with respect to LED packaging.

Materials issues in the development and use of lightguide fibers, cables, and components

Lightguide technology is now considered to be mature. Indeed, improvements in all aspects of this technology over the years have been most impressive - multimode to singlemode fiber, electronic to optical amplification and the newest and perhaps the most important: the use of WDM and DWDM technologies. In spite of these striking advances, the very nature of the silica lightguide material poses reliability issues which have not yet been fully resolved or in some cases even confronted. These issues by and large have to do with the intrinsic brittle nature of the glass material. In order to assure reliable performance of these lightguide fibers in telecommunications service environments, coating and cabling technologies developed over the past two decades have evolved to give robust fiber optic cables, devices and components. In this presentation, we review key materials issues in the development and use of lightguide technology in telecommunications. Furthermore, we analyze current trends and discuss major materials reliability issues that need to be resolved for further developments in future applications of optical fibers, fiber optic cables and fiber-based components.

Mechanical reliability of fiber optic splices

Todays feeder applications and future distribution applications call for shorter-length, higher fiber count cables, more splices per kilometer, and increased connectorization. Whapham estimates that five to eight splices per subscriber will be required for a branched distribution and loop network. In addition, splices and connectors in the loop will experience harsher environments than the controlled environment of a telephone central office or typical remote site. In the distribution portion, between the remote site and the optical network unit (ONU), the splices can be subjected to a wide range of temperature and humidity extremes, as can the ONU itself. The increased handling and the harsher environments in the local loop place significant new demands on the performance of optical splices.

Utilization of electroplating to lock fibers for use in optical device packaging

An electroplating technique for permanently fixing single-mode fibers into position in optical device packages is described. In this technique, the fiber is mounted in a metal tube and aligned to an optical device mounted on a metal substrate. The fiber is in close proximity to the substrate and a flexible conductive gel is used to connect the two electrically. The fiber, gel, and substrate thus form the plating cathode. When immersed in a plating bath with an anode inserted, metal can be deposited across the gel, forming a strong metal bridge between the fiber and substrate, locking the fiber into position. Under appropriate conditions, misalignments within +or-1 mu m during the plating process have been observed. This technique was used to package a laser diode transmitter, which locked the laser-to-fiber alignment to within 0.7 mu m, or 0.1 dB of the optimum coupled power. >

Broadband 1.5-µm InGaAsP traveling-wave laser amplifier with angled facets

Current traveling-wave laser amplifiers rely on good antireflection coatings on both facets to prohibit the Fabry-Perot resonance. It requires extremely tight control on the refractive index and thickness of dielectric layers.1,2 A simpler way to suppress the Fabry-Perot resonance is to slant the waveguide (gain region) from the cleavage plane so that the internal light reflected by the cleaved facets does not couple back into the waveguide and is, therefore, lost [Fig. 1(a)]. The reflectivity for the lowest-order TE mode decreases exponentially with the slant angle θI.3 High-power GaAs superluminescent diodes have been made with 5° inclination.4,5 Here we report a broadband 1.5-μm InGaAsP traveling-wave laser amplifier (TWA) with angled facets.