H.M. Presby

A wavelength-division multiplexed passive optical network with cost-shared components

We demonstrate a passive optical network (PON), based on a wavelength-division multiplexing router, with modulators (instead of lasers) at the subscriber terminals. A single, cost-shared, tunable laser is time-division multiplexed to provide bidirectional switched WDM services for N subscribers with independent formats and bit-rates for each. Simultaneous support of telephony and compressed digital video are presented in which RF subcarrier multiplexing is used to provide service segregation and resolve upstream packet contention.<<ETX>>

Ideal microlenses for laser to fiber coupling

The design and fabrication of ideal microlenses for semiconductor laser to fiber coupling are reported. Properly coated for reflections, lenses of the new design can theoretically collect 100% of the radiated energy of a modal-symmetric laser source. The crucial feature is its hyperbolic shape. Microlenses fabricated directly on the end of the fiber by laser micromachining have demonstrated up to 90% coupling efficiency. This performance represents a major advance in microlens technology when compared to currently fabricated hemispherical microlenses which are at best 55% efficient. A theoretical comparison of the two lens shapes illuminates the advantages of the hyperbolic profile. The ability to couple all of the light from a semiconductor laser into a fiber has far-reaching implications for all optical communication systems. >

LARnet, a local access router network

A novel local access network, LARNet, is proposed and demonstrated. A multifrequency laser, whose wavelength COMB94 is matched to that of a passive waveguide router in the remote node, is used as a downstream signal source. A 1.3-/spl mu/m commercially available LED provides the upstream signal. LARNet solves a major problem of WDM networks, the spectral alignment between the optical wavelengths of different channels. Furthermore. The expensive components are shared among all subscribers. Our measurements indicate that aggregate rates of 2 Gbps downstream and 155 Mbps upstream are feasible.<<ETX>>

A new technique for the preparation of low-loss and graded-index optical fibers

The lowest loss optical waveguides to date are those of high silica composition prepared by vapor deposition. The present article describes a method for producing waveguides having a GeO 2 -SiO 2 core and SiO 2 cladding. These combine low loss with relatively large index differences between core and cladding, Large index differences create problems in optical communication systems because of dispersion effects. Means of index grading so as to decrease dispersion are also described.

A 16*1 wavelength division multiplexer with integrated distributed Bragg reflector lasers and electroabsorption modulators

The integrated operation of a 16*1 wavelength-division-multiplexed (WDM) source with distributed Bragg reflector (DBR) lasers and electroabsorption modulators has been demonstrated. By using repeated holographic exposures and wet chemical etching, 16 different wavelengths from 1.544 to 1.553 mu m with an average channel spacing of 6 AA are obtained. A high-performance combiner is used to obtain a very uniform coupling into the single-output waveguide, and with the integration of an optical amplifier an average optical power of -8 dBm per channel is coupled into a single-mode fiber.<<ETX>>

Binary silica optical fibers: refractive index and profile dispersion measurements.

The variation of the core-cladding refractive index difference Deltan(lambda) is determined as a function of wavelength for GeO(2)-SiO(2), B(2)O(3)-SiO(2), TiO(2)-SiO(2), P(2)O(5)-SiO(2), Al(2)O(3)-SiO(2), and Cs(2)O-SiO(2) optical fibers. The measurements are obtained by electronically processing the output of an interference microscope illuminated by a monochromatic light source variable over the 0.5-1.1-microm range. The Deltan(lambda) results are utilized to calculate the precise grading of the refractive index profile characterized by an exponent alpha(lambda) required to achieve a minimum modal dispersion. The material dispersion for these compositions is also calculated with the aid of available n(lambda) data for SiO(2).

An 18-channel multifrequency laser

A multifrequency laser (MFL) is demonstrated that runs simultaneously CW on 18 channels spaced by 103 GHz. The laser emits -14.6-dBm power per wavelength channel into single-mode fiber. Each wavelength channel can be modulated at 1.24 Gb/s. The MFL exhibits a stable and reproducible optical channel spacing owing to the reproducibility of the waveguide grating router that serves as the intracavity filter element.

Dynamic gain compensation in saturated erbium-doped fiber amplifiers

Dynamic compensation of low-frequency gain fluctuations in saturated erbium-doped fiber amplifiers is demonstrated. This compensation, based on a simple feedback-loop scheme makes it possible to reduce transient gain fluctuations efficiently across the whole amplifier bandwidth using only a low-power optical feedback signal. Such an, automatic gain control technique could be applied to suppress data packet interference due to traffic bursts in multiple-access networks, as well as in the implementation of long-haul fiber systems using erbium fiber amplifiers.<<ETX>>

Laser micromachining of efficient fiber microlenses

We present results of the use of a CO(2) waveguide laser for the reproducible fabrication of efficient microlenses on single-mode optical fibers. Short intense laser pulses are used both to melt microlens tips to specific radii and to micromachine microlenses by ablative removal of small (~1-mum(2)) areas of glass from the fiber surface. CO(2) laser heating of fiber tips results in more consistent lens curvature than the electric arc commonly used in microlens fabrication. The microlenses formed using a laser microlathe, in which spinning fibers are shaped by simultaneous cutting and heating in the pulsed CO(2) laser beam, show excellent laser-fiber coupling with losses in the 1.5-3-dB range, an improvement of more than 2 dB over coupling with standard microlenses made by the etch and melt technique.

Refractive index and diameter measurements of unclad optical fibers

A new method is presented to determine the refractive index and the diameter of unclad optical fibers. The technique is based on an analysis of the back-scattered light when a beam from a cw laser impinges upon the fiber. A geometrical-optics analysis shows that the position of a sharp cutoff in the radiation pattern determines the refractive index, whereas the distance between certain successive minima gives the diameter. The theory is compared to experimental observations, with excellent agreement.