Lucent Technologies Inc.

At&t Bell Laboratories

At+t Corp.

Alcatel Lucent

Nokia Solutions and Networks Oy

Alcatel-lucent USA Inc.

Robert Meachem Jopson

Herwig Werner Kogelnik

Lynn E Nelson

Andrew Roman Chraplyvy

Alan H Gnauck

James Power Gordon

Stojan Radic

Peter Johannes Winzer

Thomas Andrew Strasser

Aref Chowdhury

Julian Stone

James W Sulhoff

Rogers H Stolen

Atul Kumar Srivastava

Yan Sun

Colin J McKinstrie

Thirumala R Halemane

Ren&eacute;-Jean Essiambre

Bartley C Johnson

Joseph Carmine Centanni

Caroline Brisson

Alan H Gnauk

Michael H Eiselt

A bidirectional optical communication system employing one or more spans of hollow-core optical fiber. In at least some embodiments, the hollow-core optical fiber can be used to simultaneously transmit, in opposite directions, optical data signals having substantially the same carrier wavelength. In such embodiments, the spectral efficiency of the bidirectional optical communication system can advantageously be about two times higher than the spectral efficiency of a comparable conventional optical communication system employing only solid-core optical fibers. In some embodiments, the bidirectional optical communication system may have a solid-core optical fiber end-connected between two spans of hollow-core optical fiber. In some embodiments, the bidirectional optical communication system may use a hollow-core optical fiber for transmission of different WDM optical data signals in opposite directions.

Bidirectional optical communication system employing hollow-core fiber

A method of multiple-band switching using a multi-pump fiber parametric switch is demonstrated. The switching architecture combines parametric band amplification, wavelength conversion and selective signal conjugation, enabled by temporal control of at least one pump of the multi-pump parametric device. The switching speed of the present invention is limited by the rise time of the controlled pump(s).

Method and apparatus for multi-band optical switching using multi-pump parametric devices

A scheme is described for mitigating the effects of polarization-mode dispersion (PMD) in a wave-division multiplex (WDM) optical communication system having one or more transmission links with one or more quasi-static waveguide sections coupled by one or more non-static coupling sections. A transmitter is coupled to the transmission link and is adapted to transmit optical signals through the transmission link with wavelength channel spacing of the optical signals greater than about the PMD correlation bandwidth of at least one of the one or more quasi-static waveguide sections, so that the PMD induced outage probability for the system is optimized.

Method and apparatus for PMD mitigation in optical communication systems

A multi-pump phase modulator apparatus and operating method uses only one phase modulator to eliminate SBS without degrading idler(s). The single phase modulator phase modulates multiple pump signals to form multiple phase modulated pump signals using a modulation signal having a modulation period. A delay apparatus delays a first wavelength group by the modulation period relative to other wavelength groups. A combiner combines the delayed first wavelength group with the other wavelength groups to form a combined modulated multiple pump signal. In one embodiment a multi-pump phase parametric apparatus comprises the multi-pump phase modulator apparatus combined with a parametric apparatus to generate an amplified input signal and one or more idlers. Other embodiments of the multi-pump phase conjugator apparatus are used as part of an Optical Switch, Sampler, Tributary Extractor, and Regenerator.

Multiple pump parametric apparatus having no idler broadening

An optical comb generator includes frequency-shifting elements of a particular type that we refer to as a 'frequency mirror.' A frequency mirror mixes input light at a signal frequency and a reference frequency to produce output light at a third frequency that lies in contraposition to the signal frequency relative to the reference frequency. The comb generator includes at least two frequency mirrors, having respective reference frequencies Fand F. At least some of the power of a light beam is shifted by the first frequency mirror from an input frequency to a frequency that lies in contraposition thereto relative to F, and then light at the shifted frequency is shifted to yet a new frequency by the second frequency mirror. The resulting twice-shifted frequency lies in contraposition to the once-shifted frequency, relative to F. The result is that a difference of 2(F&#x2212;F) separates the twice-shifted frequency from the input frequency. This process is repeatable to generate a comb of equally spaced, shifted frequencies. In specific embodiments of the invention, the frequency mirror is a periodically poled lithium niobate (PPLN) device pumped by laser radiation at the pertinent reference frequency.

Method and apparatus for generating a sequence of optical wavelength bands

A method and system for suppressing signal distortions in optical signals associated with nonlinearity in optical fibers includes propagating an optical signal through a transmission medium, the transmission medium comprising a sufficiently low dispersion such that a nonlinear distortion imparted on the propagating optical signal by the transmission medium is imprinted primarily on an optical field phase of the optical signal, and converting the propagated optical signal to an electrical signal such that the optical field phase information of the optical signal is not translated into the electrical domain.

Method and system for suppressing signal distortions associated with nonlinearity in optical fibers

In one method, two light signals, of the same optical frequency, but having orthogonal states of polarization, are transmitted through an optical device and the mean signal delay of each of the light signals is measured. Calculations, based upon disclosed relationships, provide the polarization-independent delay (&tgr; ) through the optical device based upon the mean signal delays (&tgr; and &tgr; ) of each of the light signals. By comparing &tgr; at adjacent wavelengths, the chromatic dispersion of the optical device can be accurately measured even in the presence of PMD. In a second, similar method, four light signals of non-degenerate polarizations states that span Stokes space are utilized. In a modification of the above-described methods based on the measurement of pulse delays, the methods are adapted to the measurement of phase delays of sinusoidally modulated signals.

Chromatic dispersion measurement

Four different light signals, all of the same optical frequency, but, having different states of polarization, are transmitted through an optical device and the mean signal delay of each of the light signals is measured. Calculations, based upon the relationship, &tgr; &equals;&tgr; &minus;&frac12; {right arrow over (&OHgr;)}&middot;{overscore (s)}, describing the polarization dependence of &tgr; (a measured mean signal delay) through the device as a function of &tgr; (a polarization independent delay component of the device), {right arrow over (&OHgr;)} (the PMD vector at the device input) and {overscore (s)} (the input Stokes vector of the light signal), yield the PMD of the device. Also, by comparing data taken at adjacent wavelengths, the chromatic dispersion of the optical device can be accurately measured even in the presence of PMD.

Polarization mode dispersion measurement

Substantially error-free communications is achieved in an optical communication system that includes optical amplifiers by detecting bits transmitted in the amplified optical signal using a detection threshold that is derived as a function of a maximum power level associated with a first bit value, e.g., bit &ldquo;0&rdquo;, and a minimum power level associated with a second bit value, e.g., bit &ldquo;1&rdquo;. Importantly, this detection scheme can be used to accurately detect bit patterns in the amplified signal even in the presence of nonlinear distortions caused by gain variations, such as inter-modal distortion and saturation induced crosstalk. In a wavelength division multiplexed (WDM) system comprising semiconductor optical amplifiers, for example, the detection threshold can be set at a level corresponding to P /2N, where P represents the total power in the WDM signal and N represents the number of optical channels in the WDM signal. According to another aspect of the invention, the effect of gain fluctuations becomes smaller as the number of channels increase. In particular, a smoothing effect is realized for the total effective saturation power as gain variations decrease as a function of an increase in the number of channels. As such, the performance of a semiconductor optical amplifier according to the principles of the invention approaches the linear performance of fiber amplifiers as the number of channels increases.

Lightwave communication systems using semiconductor optical amplifiers

In an optical fiber transmission system, higher order PMD compensation is realized with a sweeper device at the input to the fiber which converts the polarization of the light beam into a frequency dependent polarization whose rate of change is similar to the rate of change of one of the PSPs of the fiber. The frequency dependent polarization of the light beam is then aligned with one of the frequency-dependent PSPs at the input of the fiber. Furthermore, differential group delay dispersion for a given frequency can be reduced by employing a chromatic dispersion compensator prior to the receiver end of the fiber transmission system. Control of the polarization of the light beam can be facilitated by monitoring PMD in the system, or alternatively, monitoring an effect of PMD in the system, such as bit error rates.

Method and apparatus for compensating for higher order PMD in a fiber transmission system

In an optical fiber transmission system, higher order PMD compensation is realized at the output of the transmission fiber. A compensator is placed at the output of the transmission fiber whose PMD vector is equal in magnitude and opposite in direction to the PMD vector at the output of the transmission fiber. The compensator PMD vector sweeps at a rate that matches the frequency sweep rate of the PMD vector at the fiber output. To compensate for second order PMD while avoiding the introduction of higher order PMD effects, a planar sweep is advantageously employed. A polarization pair controller is employed in advance of the compensator to align the PMD vector at the compensator input with the PMD vector at the fiber output so that the two cancel as well as to align the rotational axis of the compensator PMD vector with the rotational axis of the fiber PMD vector. The system may also include a monitoring device to monitor the compensation of fiber PMD, to determine the need for adjustments to the system.

Method and apparatus for compensating for higher order paid PMD in a fiber transmission system at the fiber output

The present invention consists of a method and apparatus for measuring first and higher order PMD vectors in optical fibers. For each first-order PMD vector determination, two distinct polarization states are sequentially injected into an optical device under test for each of a pair of frequencies &ohgr; and &ohgr;&plus;&Dgr;&ohgr; . A Stokes vector s representing the first polarization state must not be parallel or anti-parallel to a Stokes vector s representing the second polarization state, but the relative angle between s and s need not be known. The frequency interval &Dgr;&ohgr; is large to obtain a high signal-to-noise ratio. Thus, four light beams are injected, the first at frequency &ohgr; and polarization s , the second at frequency &ohgr; and polarization s , the third at frequency &ohgr;&plus;&Dgr;&ohgr; and polarization s , and the fourth light at frequency &ohgr;&plus;&Dgr;&ohgr; and polarization s . The output polarizations of these beams are measured and four corresponding output Stokes vectors are determined. A first-order PMD vector is then calculated from the four input Stokes vectors and four output Stokes vectors. Each subsequent PMD vector determination is then made using a pair of frequencies which differs from the previous pair of frequencies by a frequency interval &Dgr;&ohgr; which is small compared to &Dgr;&ohgr; . Since &Dgr;&ohgr; can be small, high spectral resolution of the PMD vector can be obtained, while still maintaining good signal-to-noise ratio provided by using a large &Dgr;&ohgr; . The good signal-to-noise ratio and high spectral resolution of the PMD vector allow the accurate determination of second- and higher-order PMD vectors.

Method for measurement of first-and second-order polarization mode dispersion vectors in optical fibers

Resonances in cross-phase-modulation (CPM) impairment occur in wavelength-division-multiplexed (WDM) transmission systems, having multiple equal dispersion-length amplifier spans, when channels have an integral number of bit walk-throughs per amplifier span. The CPM resonances are reduced by mis-matching the amplifier span lengths (and/or dispersion in each span) so an integral number of bit walk-throughs do not occur in successive amplifier spans. The CPM resonances are reduced by adding different lengths of dispersion-compensating fiber to each span, using different modulation bit rates and/or clock phase delay for each channel, and using different wavelength-selective clock phase delays for each channel.

Wavelength division multiplexed system having reduced cross-phase modulation

An apparatus and method for simultaneously taking measurements that are used for determining PMD vectors. This reduces the time interval over which all measurements are taken and reduces inaccuracy caused by PMD variation during the time measurement interval. The apparatus and method may be used in conjunction with any technique for calculating PMD, such as the Poincare Sphere Technique or Jones Matrix Eigenanalysis. The apparatus simultaneously produces multiple light beams. To distinguish each light beam from the others, each beam is given a distinct modulation. All the beams are then combined and passed through the optical device under test. A polarization measuring device then measures the output polarization of the combined beam and outputs one or more composite electrical signals that describe the Stokes components of the output polarization of the combined beam and that have the same modulations present in the original combined beam. Using modulation filters having the same modulations as given to each original light beam, electrical signals may be extracted from the composite electrical signals that describe the Stokes components of the output polarization corresponding to each original light beam. Also, measurement and control of the frequency difference between light beams used for determining PMD vectors is improved by receiving light beams of two distinct frequencies using a detector that then outputs a signal having a frequency equal to the difference in frequencies of the light beams. In addition, a feedback loop is used to better control the frequency difference between two light sources. Also, a frequency shifter is used to generate two light beams separated by a specific frequency interval.

Apparatus and method for improving the accuracy of polarization mode

A time delay device for an optical signal wherein an optical frequency comb is generated by a comb generation device. The optical frequency comb consists of a plurality of discrete and temporally spaced optical channels or carriers. The separation of the channels is dictated by the shifting frequency applied to the comb generation device and the temporal spacing is defined by the length of fiber used so that a time delay is created for each traverse of the fiber loop by the optical frequency comb. A filter connected to the comb generation device is used for tuning to a particular frequency or channel in the optical comb to obtain an optical signal having a desired time delay.

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Rumson, NJ, United States of America

Robert Meachem Jopson