Donald B. Keck

Pulse broadening in graded-index optical fibers

This paper reports on some theoretical and experimental investigations of the radial refractive index gradient that maximizes the information-carrying capacity of a multimode optical waveguide. The primary difference between this work and previous studies is that the dispersive nature of core and cladding materials is taken into consideration. This leads to a new expression for the index gradient parameter alpha(c) which characterizes the optimal profile. Using the best available refractive index data, it is found that in high-silica waveguides, the dispersive properties of the glasses significantly influence the pulse broadening of near-parabolic fibers, and that the parameter alpha(c) must be altered by 10-20% to compensate for dispersion differences between core and cladding glasses. These predictions are supported by pulse broadening measurements of two graded-index fibers. A comparison is made between the widths and shapes of measured pulses and pulses calculated using the WKB approximation and the near-field measurement of the index profiles. The good agreement found between theory and experiment not only supports the predictions made for the value of alpha(c), but demonstrates an ability to predict pulse broadening in fibers having general index gradients.

Pulse Transmission Through a Dielectric Optical Waveguide

Waveguide propagation of a pulse-modulated carrier wave is formulated to include distortion due to dispersion in both attentuation and phase velocity. An optimum input gaussian pulse width exists for maximum information carrying capacity. Results are applied to a numerical study of several singlemode glass optical waveguides in which mode and dielectric dispersion may total zero at some wavelength. For our low-loss (20 dB/km) guides in kilometer lengths, information rates of at least 3 x 10(10) bits/sec should be attainable.

Spatial and Temporal Power Transfer Measurements on a Low-Loss Optical Waveguide

Experimental measurements of the spatial and temporal transfer of power of a 225-m length of low-loss optical waveguide have been made. In particular, measurement of the angular attenuation showed substantial loss of the high order modes, which reflected itself in an ~8.2 nsec/km decrease in measured dispersion. Additionally there was a reduction of the effective numerical aperture from 0.15 to 0.12. Negligible mode coupling was observed in this particular waveguide, which allowed a phenomenological calculation of temporal output for an assumed uniform excitation of all modes. This agreed well with experimental measurements. Calculation of this output from knowledge of the index profile is presently not in agreement, and some possible reasons are indicated.

Spectral Response of Low-Loss Optical Waveguides

The attainment of 20-dB/km attenuation in experimental single-mode glass optical waveguides has spurred interest in their use for optical communications. The primary wavelength region of interest is in the red or near-infrared region of the spectrum. In this work independent attenuation measurements from 600 nm to 1060 nm have been made on low-loss waveguides and bulk cladding glass, using both laser and scanning-prism monochromator sources. Three bands were observed in the waveguides, at 725 nm, 875 nm, and 950 nm, and identified as due to OH in the glass. Absorptions too small to be precisely measured in the bulk glass measured in them. are seen to be exceedingly important in the waveguides and easily measured in them.

Passive components in the subscriber loop

The status of passive optical components for optical fiber subscriber loop systems is reviewed in the context of the most often discussed architectures. These architectures and the passive component types and functions are described. It is shown how the components are meeting the key functional requirements of interconnection, furcation, and filtration. A logic flow to the evolution of the architecture which is based on the expected development of the passive components is indicated. >

Communications: Single-mode fibers outperform multimode cables: Successful field trials and imminent commercial use stem from high capacity and the need for fewer repeaters

The difference in transmission pattern gives single-mode fibers important advantages which includes a greater information-carrying capacity and the need for fewer repeaters. Some field trials using optical waveguides are discussed. Splicing of the fibers, losses through bending, dispersion, and sources and detectors for single-mode systems are also included.

A future full of light

Thirty years ago an experimental hair-thin glass thread changed the way we communicate, learn, work, and live. It has rapidly transformed todays society and our expectations for the future. The story is not over. Today, the dynamic worldwide communications revolution continues. Where will it end? Researchers have proven that optical fiber can carry 5 Tb of information each second. And over the next ten years fiber-optic technology is expected to increase communications power a million fold, It has been shown that as long as scientists and engineers worldwide continue to invent the technology to send information at a lower cost per bit to one another, creative people will find a reason to send proportionally more bits.

GRIN-V: progress in gradient-index imaging.

The Fifth International Meeting on Gradient-Index Optical Imaging Systems was held in Monterey, California on 19–20 April 1984. Progress in the field is reviewed.

Characteristics Of Optical Fiber Waveguides

The design and performance of optical cables, connector hardware and communication systems are governed by the light transmission and coupling characteristics of waveguide fibers. These characteristics depend upon waveguide design and materials as well as manufacturing tolerances. Measurement methods and limitations are discussed and use and interpretation of waveguide specifications in designing optical links and predicting over-all performance are shown.

Transmission Properties Of Optical Fiber Waveguides

Guided optical communications using glass optical fiber waveguides is a rapidly growing field. In this paper a discussion of the transmission characteristics of the optical fiber will be given. This will include first a description of rays and modes in the waveguide. Attenuation, long the benchmark for judging fibers has its sources broadly grouped into two categories, absorption and scattering. These will be further subdivided into their contributing factors and discussed, giving a summary of the current status of attenuation reduction. The information carrying capacity is potentially limited by two things, differing group velocity for each mode and finite spectral width of the transmitted light. These will be discussed, showing the effect that material properties and the radial index gradient have on information bandwidth. In the multimode waveguide energy may be transferred between modes during transmission. This can be beneficial by causing the information capacity to decrease only as the (fiber length)12 rather than directly as the fiber length as in the case of no mode coupling. It can also be detrimental since there is an additional attenuation associated with mode coupling. This effect will have an impact on fiber parameters as well as on fiber packaging and will be discussed.