Lucent Technologies Inc.

Mintera Corporation

At+t Corp.

Oclaro (north America Inc.)

Pavel V Mamyshev

Linn F Mollenauer

Benny P Mikkelsen

Fenghai Liu

Christian J Rasmussen

Thomas Andrew Strasser

Myles Kimmitt

Yuval Shohet

James Power Gordon

Joel R Edinberg

Tina Fjelde

John E Kaufmann

Andrew R Grant

Kent Springer

Optical communications networks rely on optical receivers to demodulate optical signals and convert the demodulated optical signal into an electrical signal. Optical receivers may be associated with one or more characteristics which can be made to vary during a transmission of an optical signal in order to improve the quality of the received signal. The present invention may determine a value for the characteristics based on an amount of optical filtering on a communications link which transmits the signal. The value for the characteristics of the receiver may be determined by observing a characteristic of a detector associated with the receiver, such as a ratio of the average photocurrents of the constructive and destructive ports of the detector. The observed characteristic of the detector may be mapped to a predetermined value for the characteristic of the receiver in a lookup table, which may be queried during operation of the receiver.

Self-adaptive receivers not requiring FEC feedback

An optical communication device such as a transmitter or receiver has a control loop for controlling relative phase of two related optical signals based on signal peak intensity. An optical transmitter measures the signal peak intensity of a combined optical signal representing two data channels to adjust relative phase as desired. An optical receiver measures the signal peak intensity of combined electrical signals, single electrical signals or single optical signals to adjust relative phase as desired. Signal peak intensity is minimized or maximized by adjusting the relative phase, depending upon the modulation configuration used. The feedback control provides a consistent and robust control to stabilize the optical communication device in the presence of variables such as temperature changes, aging and manufacturing tolerances.

Method and apparatus for control of DPSK and DQPSK receivers and transmitters

An optical receiver includes a demodulator having a delay interferometer comprising an optical input that receives a phase modulated optical signal from a bandwidth limited transmission system. The delay interferometer has a free spectral range that is larger than a symbol rate of the phase modulated optical signal by an amount that improves receiver performance. The receiver also includes a differential detector having a first and a second photodetector. The first photodetector is optically coupled to the constructive optical output of the delay interferometer. The second photodetector is optically coupled to the destructive optical output of the delay interferometer. The differential detector combines a first electrical detection signal generated by the first photodetector and a second electrical detection signal generated by the second photodetector to generate an electrical reception signal.

Partial DPSK (PDPSK) transmission systems

In an optical transmitter, continuous wave light from a laser passes through a data modulator (DM) for non-return-to-zero (NRZ) encoding of a data stream and through a pulse modulator to add return-to-zero encoding to the modulated optical signal. A modulator controller monitors the output optical signal power, optimizes the bias setting for the DM and the PM, and optimizes the phase relationship between the pulse and data components of the modulated optical signal. For each optimization, a low amplitude and low frequency dither signal is injected at appropriate points in the modulator. A single photo detector and electrical receiver are used in a multiplexed fashion to monitor the optical output signal and derive separate feedback signals. Remaining control circuitry forces a null in a respective residual dither component in the optical output signal to maintain the desired bias level or phase alignment.

Control of an optical modulator for desired biasing of data and pulse modulators

Different techniques for generating spectrally efficient carrier-suppressed modulated optical signals, also known as 'phase-shaped binary transmission' (PSBT) signals, employ electrical components that generate only 2-level or binary signals, in contrast to techniques that require 3-level electrical drivers. The PSBT modulators can be used with return-to-zero (RZ) modulators for generating RZ-PSBT signals, which have the characteristic of even greater spectral efficiency than NRZ PSBT signals. The technique is generalized to RZ signals with an arbitrary phase difference between pulses. These signals can be generated by shifting the central (carrier) frequency of an RZ modulated optical signal, which can be done using a certain phase modulation or using spectral filtering with a passband offset from the center (carrier) frequency of the modulated optical signal, and the signals can also be generated by phase modulation at a frequency lower than the signaling rate of the modulated signal.

Methods and apparatus for spectrally efficient optical modulation

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

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

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

The specification relates to a method and apparatus for all-optical regeneration of return-to-zero (RZ) data streams. The effect of self-phase modulation (SPM) of a data signal passing through a nonlinear medium (NLM) creates spectral broadening in individual data pulses which are then subsequently filtered to pass a selected bandwidth centered at a frequency, .omega..sub.f, which is shifted with respect to the input data carrier frequency, .omega..sub.0. Since the degree of broadening of a pulse passing through the NLM is a function of the initial intensity of the pulse, noise in data 'zeros' (null values) possess insufficient intensity (providing incidental distortion pulse intensity attributable to accumulated process noise is less than a critical value) to cause the requisite amount of spectral broadening to encompass the selected filter bandwidth centered around .omega..sub.f, and the noise is subsequently suppressed. Conversely, noise (amplitude fluctuations) in data 'ones' (set values) possess sufficient intensity (providing input pulse intensity, including incidental distortion pulse intensity, is greater than a critical value) to cause the requisite amount of spectral broadening to encompass the selected filter bandwidth centered around .omega..sub.f, and that portion of the spectrally broadened pulse contained within the bandwidth centered around .omega..sub.f is subsequently passed.

Method and apparatus for all-optical data regeneration

Apparatus and method for generating a return-to-zero (RZ) optical data stream. A laser or other continuous wave (CW) optical source generates an optical carrier signal which is applied to a phase modulator. A return-to-zero data generator multiplies a non-return-to-zero (NRZ) electrical data stream and a sinusoidal electrical signal to generate an RZ electrical data stream. The phase modulator modulates the RZ electrical data stream onto the optical carrier signal to generate a phase-modulated optical signal. A Stokes portion or an anti-Stokes portion of the phase-modulated optical signal spectrum is then spectrally separated in an optical filter to provide a corresponding output RZ optical data stream. The spectral separation may be provided using a discrete filter coupled to the output of the phase modulator, or using transmission line filtering in a soliton transmission system. The use of the phase modulator to perform data encoding operations avoids the modulation bias drift problems inherent in amplitude modulators.

Phase modulator-based generation of high-quality high bit rate

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

Method and apparatus of soliton transmission using a non-soliton source are described. The soliton transmission is generally in the form of an optical pulse sequence, Intensity and phase modulation of a continuous wave optical signal generates a pair of optical pulse sequences related to Stokes and anti-Stokes components of the doubly modulated optical signal. By proper alignment of the optical frequency of the cw optical signal with the passband of a filtered transmission line, it is possible to have the filtered transmission line comprising sliding frequency-guiding filters permit only one of the pulse sequences to be selected and thereby form a soliton pulse sequence.

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Middletown, NJ, United States of America

Pavel V Mamyshev