Lucent Technologies Inc.

At&t Bell Laboratories

Bell Telephone Laboratories

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

At+t Corp.

Linn F Mollenauer

Pavel V Mamyshev

Victor Mizrahi

James Power Gordon

Xiang Liu

David M Bloom

Kenneth L Walker

Xing Wei

George T Harvey

Gary Carl Bjorklund

Thomas Andrew Strasser

Calvin M Miller

Neal S Bergano

Richart Elliott Slusher

Walter J Tomlinson, Iii

Jay R Simpson

Rogers H Stolen

Inuk Kang

Colin J McKinstrie

Chunhui Xu

Stephen G Evangelides, Jr

Mohammed N Islam

Jurgen Gripp

William B Gardner

Renen Adar

Jane F Kuhl

Paul A Morton

Eyal Lichtman

Andrew R Grant

Fedor M Mitschke

In one embodiment of the invention a dispersion compensator is provided for use in a dense wavelength division multiplexed optical communication system. The dispersion compensator comprises a periodic-group-delay dispersion compensation module which provides a portion of the dispersion compensation for a dispersion managed span of the optical communication system. A remaining portion of the dispersion compensation for the dispersion managed span is provided by dispersion compensating fiber. The portions of the dispersion compensation provided by each of the periodic-group-delay dispersion compensation module and the dispersion compensating fiber is selected such that the collision-induced timing jitter is reduced.

Dispersion compensation method and apparatus

A new dispersion managed soliton transmission system where the D map period is the same as the amplifier period and the pulse breathing the in the +D sections of the D maps is approximately symmetrical. Pulse breathing symmetry by one or both of two techniques. In one technique a guiding filter is placed at the beginning of the D map period such that the guiding filter reduces the bandwidth of soliton pulses passing through it by a minimum amount. Consequently, pulse breathing symmetry is restored. The path average pulse energy vs.behavior of solitons propagating through the D map is changed such that (1) solitons of modest bandwidths have adequate energy at or near=to provide for error-free transmission over transoceanic distances at or near=0, and (2) such that the path average pulse energy is nearly independent of, at or near=0 for solitons of various pulse widths. The transmission system having this D map is much more tolerant of variations inand pulse width than the prior art. Another technique uses two different types of +D fiber in the +D section so that there is a step change in the ratio of D divided by the cross-sectional area of the fiber, or 'A', as solitons propagate from one type of +D fiber to the other type of +D fiber in the +D section. This step change innullifies the effects of the variation in pulse intensity thereby restoring the pulse breathing symmetry. Furthermore, through the use of intermediate Raman amplification, signal loss in transmission lines having very large amplifier periods, e.g., 80 km or 120 km, is overcome.

Dispersion-managed soliton transmission system with guiding filters

Method and apparatus for synchronizing two different types of modulators in an optical transmission system includes a first modulator generating an optical pulse train, a second modulator encoding data onto the optical pulse train, an optical filter resolving upper and lower modulation sidebands of the optical data and an analyzer measuring the optical power of modulation sidebands and converting the received optical power of the sidebands into a control signal for synchronizing the two modulators. A wedged etalon is the filter element selecting the USB and LSB from the optical data spectrum. The analyzer contains photo-detectors measuring the optical power of the filtered USB and LSB and an electronic differential amplifier producing a control signal based upon photo-detector output. The phase shifter, in response to the control signal, adapts the temporal delay of the first modulator to reduce differences between the power levels of the upper and lower sidebands.

Method and apparatus for synchronizing a pulse carver and a data modulator for optical telecommunication

A nonlinear phase-shift compensation method and apparatus is provided for improving system performance in optical transmission systems. The apparatus includes a phase-shift compensating device that provides a partial compensating phase shift to reduce the nonlinear phase noise resulting from self-phase modulation and amplified spontaneous emissions in an optical transmission system.

Nonlinear phase-shift compensation method and apparatus

A method and apparatus for producing a flat gain over very broad gain bands utilizing backward-pumped Raman amplification. The method allows for dynamic gain control through simple electronic means.

Time-division multiplexed pump wavelengths resulting in ultra broad band, flat, backward pumped Raman gain

Dispersion managed optical transmission line and method for making same

By urging an ordinary single-mode (usually dispersion-shifted) fiber into an external, long period mechanical grating, a highly wavelength-selective coupling between the fiber's guiding mode and a cladding mode is induced. A sequence of such induced gratings, all on the same fiber, can be used to create a many tens of nm wide loss band of arbitrary shape, with resolution of 3 nm or better, whose strength at any wavelength can be continuously adjusted from zero to &minus;17 dB or more. With its simplicity, nearly zero background loss, and especially, with its potential for continual readjustment, the device is ideal for dynamic gain equalization of optical amplifiers.

Mechanically induced long period optical fiber gratings

In soliton transmission, third order dispersion of the transmission fibers tends to cause unacceptable variation in the filter strength parameter, .eta. over the wide wavelength bands required for massive wavelength division multiplexing (WDM). The effect of dispersion is substantially eliminated by varying the mirror reflectivities R(.lambda.) of etalon filters with wavelength, such that the strength (.eta.) parameter, in soliton units, essentially remains at the optimal value across the entire WDM transmission band.

Guiding filters for wavelength division multiplexing in soliton

Fiber optic cable waste is avoided by measuring amplitude oscillations of four-wave mixing products in positive-dispersion and negative-dispersion fiber optic cable to determine the lengths of a first, positive-dispersion cable segment and a second, negative-dispersion cable segment that are used to provide a specified length of fiber optic cable having a specified amount of path-average chromatic dispersion. The integrated dispersion of a positive-dispersion fiber optic cable as a function of length is measured to provide a first set of data, and the integrated dispersion of a negative-dispersion fiber optic cable as a function of length is measured to provide a second set of data. A fiber-optic cable is simultaneously fed with two optical signals, a first at wavelength .lambda..sub.1 and a second at wavelength .lambda..sub.2, and the number of sinusoidal oscillations that occur in the four-wave mixing products of the Stokes (or anti-Stokes) sideband as a function of cable length are measured. The second set of data is reflected about a line representing zero length, linearly translated by the specified length along a length axis, and then linearly translated by the specified dispersion along an integrated dispersion axis to provide a transformed second set of data. A point of intersection of the first set of data with the transformed second set of data is calculated. A length coordinate of this point of intersection represents the length of the first cable segment. A length for the second cable segment is calculated by subtracting the length of the first cable segment from the specified length.

Fiber optic cable having a specified path average dispersion

Apparatus for measuring the dispersion and dispersion parameter of an optical fiber as a function of distance (the dispersion map) by the optical-time-domain reflection technique uses a multi-frequency laser with an extra cavity semiconductor optical amplifier switch to generate the short pulses of two wavelengths to displace the four-wave mixing oscillations away from the origin of the complex plane. Additionally laser power is supplied at both ends of the fiber under test to provide pump power to Raman amplify the backscattered signal being measured. Finally a novel Fast Fourier Transform based algorithm is used to calculate the dispersion map fast and accurately.

Dispersion-map measurements of optical fibers

A dispersion-tapered fiber for use in a soliton transmission system having lumped amplifiers to substantially reduce loss associated with pseudo phase matching and to relax the limitations on minimum allowable channel spacing caused by cross-phase modulation. The dispersion tapered fiber has a dispersion tapered either continuously or in steps, in conformity with the fiber loss curve.

Dispersion tapered optical fibers for use in WDM soliton transmission

A system and method in which the chromatic dispersion characteristic, as a function of distance along a section of transmissive fiber, is measured. First and second optical signals are launched into a fiber under test to thereby generate, by a four-wave mixing process in the fiber, a probe signal. Because of a wave-vector phase mismatch, the probe signal power oscillates with a spatial frequency that can be measured as a function of distance in the fiber. The intensity oscillations are measurable as, for example, temporal variations in the Rayleigh backscattered light detected at the input end of the fiber. According to the present invention, the dispersion parameter at one or both of the first and second optical signal wavelengths, as a function of length along the fiber, is derived directly from these intensity oscillation measurements. From this information, it is possible to further derive maps at other wavelengths of interest.

System and method for mapping chromatic dispersion in optical fibers

A clock recovery circuit for following rapid changes in the time phase of a data stream is disclosed. The circuit comprises a low Q resonator coupled to a detection device, such as an electro-optic modulator in a time division demultiplexer or a decision circuit of a receiver. Preferably, a high Q resonator or phase locked oscillator is provided, as well. The present invention is particularly useful in a telecommunications system for transmitting solitons. A method of compensating for changes in time phase of a data stream is also disclosed.

Apparatus and methods for nulling non-random timing jitter in the

An improved optical loop mirror is used in an optical demultiplexer to demultiplex time division multiplexed optical communications channels. High bit-rate optical pulses representing a plurality of time division multiplexed communications channels are input to a 3 dB coupler in an optical loop mirror. The coupler separates the high bit-rate optical pulses into two substantially equal high bit-rate pulse streams propagating in opposite directions around a loop of fiber in the mirror. Lower bit-rate optical switching pulses are injected into the loop so as to substantially coincide with selected pulses in the high bit-rate pulse stream corresponding to a communications channel to be demultiplexed from the plurality of multiplexed communications channels. A gain controlling element, such as an amplifier or a lossy element, in the loop changes the amplitude of one of the two high bit-rate pulse streams flowing in the loop so that the selectivity of the demultiplexer to the desired channel and the rejection of unwanted channels by the demultiplexer is enhanced.

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Colts Neck, NJ, United States of America

Linn F Mollenauer