1 Tbit/s km transmission experiment at 16 Gbit/s using conventional fibre

Describes a single-channel optical transmission experiment that achieved a bit rate-distance product of 1 Tbit/s km over conventional (non-dispersion-shifted) fibre. The transmitter was a directly modulated, 1.3 mu m-wavelength, distributed feedback laser. The receiver employed a semiconductor optical preamplifier and a high-impedance pinHEMT front-end.<>     

Star couplers with gain using multiple erbium-doped fibers pumped with a single laser

An economical method for combining erbium-doped fiber (EDF) amplifiers and star couplers, is presented. It involves simultaneously pumping EDFs placed at the input or output ports of the coupler with a single laser pump source distributed through the coupler itself. In this way, many amplifiers can share the cost of a single pump laser, and the need for individual pump/signal combiners is eliminated.<>     

Solid particle erosion of a plasma spray – physical vapor deposition environmental barrier coating in a combustion environment

Environmental barrier coatings (EBCs) were developed to reduce the susceptibility of SiC-based composites to the rapid volatilization and surface recession that occurs in the presence of water vapor. Extensive research and development has been performed on EBCs, and their corresponding failure mechanisms under different environmental conditions. However, one key failure mechanism, solid particle erosion (SPE), has not been thoroughly investigated. As a result, the present work investigates the SPE behavior of a ytterbium disilicate (Yb₂Si₂O₇) environmental barrier coating (EBC) deposited via plasma spray-physical vapor deposition (PS-PVD). Erosion testing was performed at elevated temperature (1200 °C) in a simulated combustion environment at the NASA Glenn Research Center Erosion Burner Rig Facility. Alumina (Al₂O₃) particles were used as the eroding media. A range of particle kinetic energies and impingement angles were investigated along with the effect of coating surface roughness. The post-erosion damage morphology was characterized using scanning electron microscopy (SEM). The SPE behavior of the PS-PVD EBC was shown to be comparable to other EBC systems reported in the literature.     

Optical fiber index profiling by video analysis of interference fringes

An electronic technique to make fringe displacement measurements on the output field of an interference microscope to 1/1000 of a fringe, not including systematic errors, is described. The method, based upon line-selected video signal analysis, is applied to the evaluation of the refractive index profile of a graded index optical fiber. The index difference at a given point between the core and cladding is determined to better than 1 part in 10(5), implying a precision in the profile parameter alpha of +/-0.005, an order of magnitude better than existing techniques.     

Optical fibre up-taper back-reflector for laser transmitterevaluation

Evaluation of reflection effects on semiconductor laser transmitters is complicated by multipath interference, which causes degradations in bit-error-rate and is independent of laser isolation. The authors have constructed a variable back-reflector utilising optical fibre up-tapers, which eliminates multipath interference effects by reducing spurious reflection levels to below -50 dB. Reflection levels of -50 dB to -16.5 dB into the laser cavity are possible. Results of measurements of reflection effects on several multilongitudinal mode 1.3 μm lasers operating at 1.7 Gbit/s are shown     

Optical fiber tapers at 1.3 µm for self-aligned beam expansion and single-mode hardware

We have experimentally demonstrated the applicability of optical fiber tapers at 1.3 μm as a simple and practical means of achieving beam expansion in a self-aligned unitary structure. These devices have a standard 8.1-μm core at one end which gradually increases in cross section to the order of 100 μm at the other end. Tapers are envisioned as basic building blocks in a multitude of single-mode optical components. Experiments performed on a batch of eight tapers verified, to experimental accuracy, that no significant amount of mode conversion or beam distortion takes places in the taper. The insertion loss of the taper was found to be under 0.1 dB. The sensitivity of the excess loss between two tapers to lateral and axial displacement is greatly reduced as compared to that between two single-mode fibers. For example, the 0.5-dB loss point of taper coupling corresponds to a 10-μm lateral displacement and a 700-μm axial displacement versus respective 1.6-μm and 36.5-μm displacements for fiber coupling. The increased sensitivity to angular displacement is within practical limits.     

Optical fiber up-tapers modeling and performance analysis

An extensive CRAY-computer-based simulator using the propagating beam method for the accurate evaluation of the performance of optical fiber up-tapers is discussed. Up-tapers with and without straight tips and with arbitrary index profiles and tapering functions can be evaluated. Results of the evaluation of various 1.5-cm-long optical up-tapers followed by a straight tip and drawn from special preforms with various index profiles are quite encouraging. They show that beam expansion ratios in the range of 5-10 are feasible with a corresponding insertion loss per taper of less than 0.01-0.025 dB. Tapers shorter than 1.5 cm with insertion loss in the same range are also feasible but have slightly smaller beam expansion ratios     

Optical fiber tapers--A novel approach to self-aligned beam expansion and single-mode hardware

We investigate the performance characteristics of single-mode optical fiber tapers. These devices have a standard single-mode fiber geometry at one end and gradually increase in cross section so that the size of the core at the other end is comparable or greater to that of a multimode fiber. These tapers effectively expand the single-mode spot size and are envisioned as basic building blocks in a multitude of optical components. Analytical and experimental studies, atlambda = 0.63 mum, show that the dominant mode is preserved while traveling through the taper, from either direction. The excess coupling loss between two tapers is less than 0.1 dB. The sensitivity of the excess loss to lateral and axial displacements for two coupled tapered sections is greatly reduced compared to that between two single-mode fibers. The sensitivity to angular displacement is increased but is within practical limits. For example, for an excess loss of 0.5 dB, the maximum allowed lateral displacement is 3.1 μm for taper coupling, while only 0.73 μm is allowed in the case of fiber coupling. An axial displacement of 291 μm for taper coupling produces 0.5 dB loss while a displacement of only 16.5 μm produces a 0.5 dB loss for fiber coupling. For the same loss, angular displacements of 0.42° for the tapers and 1.77° for the fiber are allowed.     

Use of LD-pumped erbium-doped fiber preamplifiers with optimalnoise filtering in a FDMA-FSK 1 Gb/s star network

An erbium-doped fiber amplifier was implemented in a closely spaced FDMA-FSK (frequency-division-multiple-access-frequency-shift-keyed) optical star network with a signaling rate of 1 Gb/s per channel. The fiber preamplifier, which is laser-diode pumped, increases the sensitivity of the direct-detection avalanche photodiode (APD) receiver by 14 dB, allowing for an increased number of network users. This enhanced sensitivity nearly corresponds to all of the available gain of the amplifier. Furthermore, the amplifier noise is optimally filtered by means of a wide band interference filter cascaded with a narrow band fiber Fabry-Perot filter