At&t Bell Laboratories

Lucent Technologies Inc.

Bell Telephone Laboratories

At+t Corp.

American Telephone & Telegraph Co., At&t Bell Laboratories

Rogers H Stolen

Richard E Howard

Arthur Ashkin

William Pleibel

Jay R Simpson

Paul F Liao

Chinlon Lin

Ravinder Kumar Jain

Linn F Mollenauer

Ashish Madhukar Vengsarkar

Per Bang Hansen

Robert Meachem Jopson

Theodoor Charlouis Damen

Joseph M Dziedzic

Herman Anton Haus

Michael H Eiselt

Jau-Sheng Wang

An optical transmission system utilizing a nonlinear fiber demultiplexer. A time division multiplexed optical signal is transmitted via a first optical signal path. An optical pump pulse is transmitted via a second optical signal path. The optical pump pulses are synchronized to correspond to the pulses in the multiplexed optical signal for which extraction is desired. The first and second optical signal paths are coupled such that the portions of the multiplexed signals which are synchronized with the optical pump pulses are amplified through Raman gain. The resulting signal is detected and passed through a threshold detector which filters out pulses below an intensity threshold. The desired demultiplexed signal, which was amplified by the pump pulses, passes through the optical threshold detector as an electronic pulse.

Time division demultiplexing using selective Raman amplification

A self-tuning optical waveguide filter for attenuating a lower power light signal at .lambda..sub.1 more than a higher power signal at .lambda..sub.2 comprises a length of single core waveguide and a light injector for applying .lambda..sub.1, .lambda..sub.2 into the waveguide in two propagating modes subject to mode beating. The mode beating produces high intensity regions of .lambda..sub.1 physically displaced from high intensity regions of .lambda..sub.2. A portion of the waveguide is doped with a saturable absorber for disproportionately attenuating wavelengths at lower power levels. Advantageously the waveguide is a single-core fiber having its central core doped with rare-earth saturable absorber. In a preferred embodiment, the fiber is dimensioned to propagate .lambda..sub.1, .lambda..sub.2 in the LP.sub.01 and LP.sub.02 modes, and the saturable absorber is Erbium.

Self-tuning optical waveguide filter

A method for launching a high-power signal into anomalous-dispersion fiber without suffering excess spectral broadening and waveform distortion. A high-power signal is launched as very short optical solitons, typically with a pulse width of approximately 1 to 10 ps. The pulse width of the solitons will broaden adiabatically (or nearly adiabatically) as they propagate down the anomalous-dispersion fiber as the average power of the soliton decreases. At the same time, the optical spectrum will narrow. After some distance of travel, when the width of the pulses have broadened to a suitable duration and the average power has decreased to a point where penalties from nonlinearities are insignificant, the pulses enter a significantly linear propagation regime with first order dispersion near zero. A dispersion-shifted fiber may be used or any additional dispersion can be compensated at the receiver. Consequently, no further significant broadening of the spectrum occurs when the signal is received at the receiver. Additionally, the initial wide spectrum of the solitons will result in a high stimulated Brillouin scattering (SBS) threshold reducing the need for artificial broadening of the spectrum.

Applications of solitons in transmission systems employing high launch

A method and apparatus for non-destructively measuring dispersion-zero wavelengths along an optical fiber makes use of a four-photon-mixing technique to generate mixed, amplified, idler signals at positions or ranges along the fiber. The dispersion zero wavelengths are then calculated using the wavelengths of the generated idler signals after taking into account inaccuracies due to higher order phenomena.

Method and apparatus for measuring dispersion zero along an optical fiber

An optical fiber communications system with Raman amplification of the signal radiation comprises a broadband pump radiation source, or, preferably a multiplicity of pump radiation sources. The sources are selected to result in a pump radiation spectrum such that pump radiation intensity in the fiber core is less than a critical intensity I.sub.c. In particular, the average intensity of pump radiation in a first spectral interval, centered on any wavelength .lambda..sub.p in the pump radiation spectrum and of width equal to the Brillouin line width of the fiber at .lambda..sub.p, is to be less than that average intensity in the first spectral interval that results in conversion of 10% of the radiation in the first spectral interval to stimulated Brillouin radiation. Use of a multiplicity of pump sources not only can reduce pump noise and pump depletion due to stimulated Brillouin scattering, but typically also can result in enhanced system reliability and lower cost. In a preferred embodiment, the invention is a soliton fiber communications system, with pump radiation injected at one or more intermediate fiber locations.

Optical communications system comprising Raman amplification means

A Fresnel lens is fabricated by depositing concentric layers of first and second materials in alternation on a substrate surface. The substrate and deposited layers are then drawn down to provide a predetermined Fresnel lens zone structure.

Fresnel lens fabrication

The invention provides a method for making an optical fiber with a uniformly thin section of cladding. A preform having a core and at least one cladding layer is first made. The preform is prepared by cutting the preform so that the core is close to the surface of the preform. An optical fiber is pulled from the cut preform so the core is close to the surface of the optical fiber. The fiber may have cladding further removed by etching. A material selective etch may be used to make a protruding core fiber. Etching may be done on the preform before pulling the fiber.

Exposed core optical fibers, and method of making same

A device using a birefringent optical fiber having periodic integral perturbations with the period equal to the birefringence beat length being useful as, for example, a polarization rotator and an optical filter.

Optical fiber having in-line polarization filter

Selected portions of the interior surface of a substrate tube, or of the cladding or core layers deposited on the interior surface of the substrate tube, are treated by one or more process steps such as shaping, diffusing, leaching, or depositing. Patterning processes such as photolithography and lift-off are employed to define the selected portions. The resulting core and/or cladding layers of the fiber can be made to have a variety of geometric shapes and composition profiles useful, for example, in realizing birefringent fibers and multiple-core fibers. Also described is the similar treating of metal layers and the incorporation of such layers into the fiber.

Optical fiber with embedded metal layer

An inline single-mode fiber attenuator (10) is disclosed which may be formed by a tandem combination of a birefringent polarization-preserving fiber (12) and a single polarization fiber (14). The birefringent fiber functions as a variable wave plate and the single polarization fiber functions as a fiber polarizer. By continuously changing the local birefringence of the birefringent fiber with, for example, tension, pressure, or temperature, the phase difference between the two polarization components of light traveling through the birefringent fiber is continuously modified. The difference in phase causes suppression of one of the polarization components as it enters the fiber polarizer and, therefore, the output of the fiber polarizer, the sum of the two polarizations, is attenuated. The attenuator may be tuned by changing the local birefringence of the birefringent fiber. An inline optical fiber bandpass filter may be formed by cascading a plurality of appropriately arranged inline fiber attenuators formed in accordance with the present invention.

Inline optical fiber attentuator

The present invention relates to a technique for producing polarization-preserving and single polarization optical fibers. As disclosed, high birefringence is introduced into the preform by deforming the fiber preform such that a cladding layer becomes flat and highly conformable, while the core remains hard and substantially round. In particular, a cladding layer with a relatively low melting point is utilized such that when the preform is heated the cladding becomes liquified while the core remains solid. The preform may then be deformed so that the cladding layer is substantially flattened. Standard drawing techniques may then be utilized to form polarization-preserving fibers and single polarization fibers from the preform.

Method of fabricating high birefringence fibers

The present invention relates to a single-mode single-polarization optical fiber which is capable of functioning as an in-line fiber polarizer which allows only one polarization of the fundamental mode to propagate along the fiber. In structure, the fiber comprises a central core region (10) and a cladding region (12) which is substantially in contact with the central core region. The various regions are formed such that the refractive index of an outer cladding region is greater than the refractive index of an inner cladding region but less than that of the core region. The arrangement of the present invention produces stress-birefringence between the cladding regions and the central core region sufficient to split the two orthogonal polarizations (n.sub..parallel. and n.sub..perp.) of the fundamental mode such that the desired polarization propagates freely and the undesired polarization is attenuated by tunneling through the cladding layers.

Single-mode single-polarization optical fiber

A method of making a polarization-preserving optical fiber is disclosed having a first step of fabricating a substrate tube to have a wall of nonuniform thickness, the nonuniformity in thickness being arranged about the wall of the substrate tube so that maxima and minima in wall thickness lie in planes which are substantially orthogonal. This first step is followed by deposition of cladding layers and a core layer within the substrate tube. The substrate is then collapsed and the fiber drawn therefrom. The nonuniform wall thickness of the substrate tube operates together with differential thermal contraction of the layers to produce stress-induced birefringence in the fiber, which birefringence provides a polarization-preserving optical fiber.

Polarization-preserving optical fiber

A tunable radiation source employing the stimulated Raman-scattering process is disclosed. The source generates several orders of Stokes radiation in an optical-fiber oscillator cavity, which Stokes radiation may be independently tuned by incorporating separate tuning elements for the several Stokes orders. Several different arrangements of fiber and tuning elements are disclosed.

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Rumson, NJ, United States of America

Rogers H Stolen