Lucent Technologies Inc.

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

At&t Bell Laboratories

Bell Telephone Laboratories

James Power Gordon

Linn F Mollenauer

Robert Meachem Jopson

Herwig Werner Kogelnik

Lynn E Nelson

Pavel V Mamyshev

Mohammed N Islam

Robert E Nahory

Martin Alan Pollack

John M Worlock

Richard L Fork

Janis A Yaldmanis

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

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

Timing jitter problems are effectively eliminated in a soliton transmission system realized in accordance with the principles of the present invention by deploying optical filters whose center frequency intentionally differs from the center frequency of adjacent optical filters. The center frequency of the series of optical filters is translated along the desired length of the system in a predetermined manner such as frequency increasing, frequency decreasing, and combinations of both to create a transmission environment which is substantially opaque to noise while remaining perfectly transparent to solitons.

Soliton transmission system having sliding-frequency guiding filters

A short pulse laser is described which has saturable absorption, saturable gain, group velocity dispersion, and self phase modulation means within a single optical cavity.

Short pulse laser

The propagation speed of optical solitons in single mode optical fiber depends on the wavelength of the solitons. Thus, if solitons of different wavelengths are co-propagating, 'collisions' between pulses can be expected to result. It has been found that collisions between solitons do preserve the soliton character of the colliding pulses, even in the presence of perturbations of the type present in fiber communications systems, e.g., core size variations, distributed or lumped loss, and distributed gain. Thus, a wavelength division multiplexed soliton system is possible, and techniques and formulae for the design of such systems are disclosed. In preferred embodiments, fiber loss is periodically compensated by Raman gain. Typical amplification periods (using currently available silica-based fiber) are 30-50 km, typical pump powers are less than 100 mV, and rate-length products of the order of 3.multidot.10.sup.5 GHz km are possible. Multiplexed soliton systems have several advantages over prior art soliton systems. For instance, they permit attainment of very high transmission rates without the use of very high speed electronics. For instance, an exemplary 3000 km, 24 channel multiplexed soliton system has a total transmission rate of 106 GHz, i.e., 4.5 GHz/channel.

Wavelength division multiplexed soliton optical fiber telecommunication

Devices constructed according to the present invention provide low noise avalanche photodetectors. The devices are comprised of a sequence of at least four layers of semiconductor material of alternating opposed conductivity. In a first embodiment the layers form alternating homojunctions and heterojunctions at the interface between adjacent layers, and the bandgap of the layers on either side of the homojunctions decreases in the direction of the propagating signal. In another embodiment the layers form heterojunctions at the interfaces between adjacent layers; the layers are grouped into a sequence of pairs of layers where the bandgap of the two layers in each pair are substantially equal; and the bandgap of the layers in the sequence of pairs of layers decreases in the direction of the propagating signal. The effect of the structure of the multilayer device is to create traps for one sign of carrier and to prevent the trapped carrier from avalanching through amplification regions of the device.

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Rumson, NJ, United States of America

James Power Gordon